71 files changed, 1363 insertions, 927 deletions

diff --git a/src/Makefile b/src/Makefile
index 82a57032..a96c1997 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -484,7 +484,7 @@ LJLIB_O= lib_base.o lib_math.o lib_bit.o lib_string.o lib_table.o \
          lib_io.o lib_os.o lib_package.o lib_debug.o lib_jit.o lib_ffi.o
 LJLIB_C= $(LJLIB_O:.o=.c)
 
-LJCORE_O= lj_gc.o lj_err.o lj_char.o lj_bc.o lj_obj.o lj_buf.o \
+LJCORE_O= lj_assert.o lj_gc.o lj_err.o lj_char.o lj_bc.o lj_obj.o lj_buf.o \
           lj_str.o lj_tab.o lj_func.o lj_udata.o lj_meta.o lj_debug.o \
           lj_state.o lj_dispatch.o lj_vmevent.o lj_vmmath.o lj_strscan.o \
           lj_strfmt.o lj_strfmt_num.o lj_api.o lj_profile.o \
diff --git a/src/Makefile.dep b/src/Makefile.dep
index 2b1cb5ef..03dba96b 100644
--- a/src/Makefile.dep
+++ b/src/Makefile.dep
@@ -51,6 +51,7 @@ lj_asm.o: lj_asm.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h lj_gc.h \
  lj_ircall.h lj_iropt.h lj_mcode.h lj_trace.h lj_dispatch.h lj_traceerr.h \
  lj_snap.h lj_asm.h lj_vm.h lj_target.h lj_target_*.h lj_emit_*.h \
  lj_asm_*.h
+lj_assert.o: lj_assert.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h
 lj_bc.o: lj_bc.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h lj_bc.h \
  lj_bcdef.h
 lj_bcread.o: lj_bcread.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
@@ -155,7 +156,7 @@ lj_opt_loop.o: lj_opt_loop.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
  lj_iropt.h lj_trace.h lj_dispatch.h lj_bc.h lj_traceerr.h lj_snap.h \
  lj_vm.h
 lj_opt_mem.o: lj_opt_mem.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
- lj_tab.h lj_ir.h lj_jit.h lj_iropt.h lj_ircall.h
+ lj_tab.h lj_ir.h lj_jit.h lj_iropt.h lj_ircall.h lj_dispatch.h lj_bc.h
 lj_opt_narrow.o: lj_opt_narrow.c lj_obj.h lua.h luaconf.h lj_def.h \
  lj_arch.h lj_bc.h lj_ir.h lj_jit.h lj_iropt.h lj_trace.h lj_dispatch.h \
  lj_traceerr.h lj_vm.h lj_strscan.h
@@ -206,13 +207,13 @@ lj_vmevent.o: lj_vmevent.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
  lj_vm.h lj_vmevent.h
 lj_vmmath.o: lj_vmmath.c lj_obj.h lua.h luaconf.h lj_def.h lj_arch.h \
  lj_ir.h lj_vm.h
-ljamalg.o: ljamalg.c lua.h luaconf.h lauxlib.h lj_gc.c lj_obj.h lj_def.h \
- lj_arch.h lj_gc.h lj_err.h lj_errmsg.h lj_buf.h lj_str.h lj_tab.h \
- lj_func.h lj_udata.h lj_meta.h lj_state.h lj_frame.h lj_bc.h lj_ctype.h \
- lj_cdata.h lj_trace.h lj_jit.h lj_ir.h lj_dispatch.h lj_traceerr.h \
- lj_vm.h lj_err.c lj_debug.h lj_ff.h lj_ffdef.h lj_strfmt.h lj_char.c \
- lj_char.h lj_bc.c lj_bcdef.h lj_obj.c lj_buf.c lj_str.c lj_tab.c \
- lj_func.c lj_udata.c lj_meta.c lj_strscan.h lj_lib.h lj_debug.c \
+ljamalg.o: ljamalg.c lua.h luaconf.h lauxlib.h lj_assert.c lj_obj.h \
+ lj_def.h lj_arch.h lj_gc.c lj_gc.h lj_err.h lj_errmsg.h lj_buf.h \
+ lj_str.h lj_tab.h lj_func.h lj_udata.h lj_meta.h lj_state.h lj_frame.h \
+ lj_bc.h lj_ctype.h lj_cdata.h lj_trace.h lj_jit.h lj_ir.h lj_dispatch.h \
+ lj_traceerr.h lj_vm.h lj_err.c lj_debug.h lj_ff.h lj_ffdef.h lj_strfmt.h \
+ lj_char.c lj_char.h lj_bc.c lj_bcdef.h lj_obj.c lj_buf.c lj_str.c \
+ lj_tab.c lj_func.c lj_udata.c lj_meta.c lj_strscan.h lj_lib.h lj_debug.c \
  lj_state.c lj_lex.h lj_alloc.h luajit.h lj_dispatch.c lj_ccallback.h \
  lj_profile.h lj_vmevent.c lj_vmevent.h lj_vmmath.c lj_strscan.c \
  lj_strfmt.c lj_strfmt_num.c lj_api.c lj_profile.c lj_lex.c lualib.h \
diff --git a/src/lib_io.c b/src/lib_io.c
index 5e9d0d66..c7d1bb31 100644
--- a/src/lib_io.c
+++ b/src/lib_io.c
@@ -101,9 +101,6 @@ static int io_file_close(lua_State *L, IOFileUD *iof)
     stat = pclose(iof->fp);
 #elif LJ_TARGET_WINDOWS && !LJ_TARGET_XBOXONE && !LJ_TARGET_UWP
     stat = _pclose(iof->fp);
-#else
-    lua_assert(0);
-    return 0;
 #endif
 #if LJ_52
     iof->fp = NULL;
@@ -112,7 +109,8 @@ static int io_file_close(lua_State *L, IOFileUD *iof)
     ok = (stat != -1);
 #endif
   } else {
-    lua_assert((iof->type & IOFILE_TYPE_MASK) == IOFILE_TYPE_STDF);
+    lj_assertL((iof->type & IOFILE_TYPE_MASK) == IOFILE_TYPE_STDF,
+               "close of unknown FILE* type");
     setnilV(L->top++);
     lua_pushliteral(L, "cannot close standard file");
     return 2;
diff --git a/src/lib_jit.c b/src/lib_jit.c
index acd6c293..7348ef21 100644
--- a/src/lib_jit.c
+++ b/src/lib_jit.c
@@ -227,7 +227,7 @@ LJLIB_CF(jit_util_funcbc)
   if (pc < pt->sizebc) {
     BCIns ins = proto_bc(pt)[pc];
     BCOp op = bc_op(ins);
-    lua_assert(op < BC__MAX);
+    lj_assertL(op < BC__MAX, "bad bytecode op %d", op);
     setintV(L->top, ins);
     setintV(L->top+1, lj_bc_mode[op]);
     L->top += 2;
@@ -491,7 +491,7 @@ static int jitopt_param(jit_State *J, const char *str)
   int i;
   for (i = 0; i < JIT_P__MAX; i++) {
     size_t len = *(const uint8_t *)lst;
-    lua_assert(len != 0);
+    lj_assertJ(len != 0, "bad JIT_P_STRING");
     if (strncmp(str, lst+1, len) == 0 && str[len] == '=') {
       int32_t n = 0;
       const char *p = &str[len+1];
diff --git a/src/lib_string.c b/src/lib_string.c
index 6b88ee9b..0d9290bc 100644
--- a/src/lib_string.c
+++ b/src/lib_string.c
@@ -136,7 +136,7 @@ LJLIB_CF(string_dump)
 /* ------------------------------------------------------------------------ */
 
 /* macro to `unsign' a character */
-#define uchar(c)        ((unsigned char)(c))
+#define uchar(c)        ((unsigned char)(c))
 
 #define CAP_UNFINISHED  (-1)
 #define CAP_POSITION    (-2)
@@ -645,7 +645,7 @@ static GCstr *string_fmt_tostring(lua_State *L, int arg, int retry)
 {
   TValue *o = L->base+arg-1;
   cTValue *mo;
-  lua_assert(o < L->top);  /* Caller already checks for existence. */
+  lj_assertL(o < L->top, "bad usage");  /* Caller already checks for existence. */
   if (LJ_LIKELY(tvisstr(o)))
     return strV(o);
   if (retry != 2 && !tvisnil(mo = lj_meta_lookup(L, o, MM_tostring))) {
@@ -717,7 +717,7 @@ again:
         lj_strfmt_putptr(sb, lj_obj_ptr(L->base+arg-1));
         break;
       default:
-        lua_assert(0);
+        lj_assertL(0, "bad string format type");
         break;
       }
     }
diff --git a/src/lj_api.c b/src/lj_api.c
index 24ae6611..f1cfebbc 100644
--- a/src/lj_api.c
+++ b/src/lj_api.c
@@ -28,8 +28,8 @@
 
 /* -- Common helper functions --------------------------------------------- */
 
-#define api_checknelems(L, n)           api_check(L, (n) <= (L->top - L->base))
-#define api_checkvalidindex(L, i)       api_check(L, (i) != niltv(L))
+#define lj_checkapi_slot(idx) \
+  lj_checkapi((idx) <= (L->top - L->base), "stack slot %d out of range", (idx))
 
 static TValue *index2adr(lua_State *L, int idx)
 {
@@ -37,7 +37,8 @@ static TValue *index2adr(lua_State *L, int idx)
     TValue *o = L->base + (idx - 1);
     return o < L->top ? o : niltv(L);
   } else if (idx > LUA_REGISTRYINDEX) {
-    api_check(L, idx != 0 && -idx <= L->top - L->base);
+    lj_checkapi(idx != 0 && -idx <= L->top - L->base,
+                "bad stack slot %d", idx);
     return L->top + idx;
   } else if (idx == LUA_GLOBALSINDEX) {
     TValue *o = &G(L)->tmptv;
@@ -47,7 +48,8 @@ static TValue *index2adr(lua_State *L, int idx)
     return registry(L);
   } else {
     GCfunc *fn = curr_func(L);
-    api_check(L, fn->c.gct == ~LJ_TFUNC && !isluafunc(fn));
+    lj_checkapi(fn->c.gct == ~LJ_TFUNC && !isluafunc(fn),
+                "calling frame is not a C function");
     if (idx == LUA_ENVIRONINDEX) {
       TValue *o = &G(L)->tmptv;
       settabV(L, o, tabref(fn->c.env));
@@ -59,13 +61,27 @@ static TValue *index2adr(lua_State *L, int idx)
   }
 }
 
-static TValue *stkindex2adr(lua_State *L, int idx)
+static LJ_AINLINE TValue *index2adr_check(lua_State *L, int idx)
+{
+  TValue *o = index2adr(L, idx);
+  lj_checkapi(o != niltv(L), "invalid stack slot %d", idx);
+  return o;
+}
+
+static TValue *index2adr_stack(lua_State *L, int idx)
 {
   if (idx > 0) {
     TValue *o = L->base + (idx - 1);
+    if (o < L->top) {
+      return o;
+    } else {
+      lj_checkapi(0, "invalid stack slot %d", idx);
+      return niltv(L);
+    }
     return o < L->top ? o : niltv(L);
   } else {
-    api_check(L, idx != 0 && -idx <= L->top - L->base);
+    lj_checkapi(idx != 0 && -idx <= L->top - L->base,
+                "invalid stack slot %d", idx);
     return L->top + idx;
   }
 }
@@ -99,17 +115,17 @@ LUALIB_API void luaL_checkstack(lua_State *L, int size, const char *msg)
     lj_err_callerv(L, LJ_ERR_STKOVM, msg);
 }
 
-LUA_API void lua_xmove(lua_State *from, lua_State *to, int n)
+LUA_API void lua_xmove(lua_State *L, lua_State *to, int n)
 {
   TValue *f, *t;
-  if (from == to) return;
-  api_checknelems(from, n);
-  api_check(from, G(from) == G(to));
+  if (L == to) return;
+  lj_checkapi_slot(n);
+  lj_checkapi(G(L) == G(to), "move across global states");
   lj_state_checkstack(to, (MSize)n);
-  f = from->top;
+  f = L->top;
   t = to->top = to->top + n;
   while (--n >= 0) copyTV(to, --t, --f);
-  from->top = f;
+  L->top = f;
 }
 
 LUA_API const lua_Number *lua_version(lua_State *L)
@@ -129,7 +145,7 @@ LUA_API int lua_gettop(lua_State *L)
 LUA_API void lua_settop(lua_State *L, int idx)
 {
   if (idx >= 0) {
-    api_check(L, idx <= tvref(L->maxstack) - L->base);
+    lj_checkapi(idx <= tvref(L->maxstack) - L->base, "bad stack slot %d", idx);
     if (L->base + idx > L->top) {
       if (L->base + idx >= tvref(L->maxstack))
         lj_state_growstack(L, (MSize)idx - (MSize)(L->top - L->base));
@@ -138,23 +154,21 @@ LUA_API void lua_settop(lua_State *L, int idx)
       L->top = L->base + idx;
     }
   } else {
-    api_check(L, -(idx+1) <= (L->top - L->base));
+    lj_checkapi(-(idx+1) <= (L->top - L->base), "bad stack slot %d", idx);
     L->top += idx+1;  /* Shrinks top (idx < 0). */
   }
 }
 
 LUA_API void lua_remove(lua_State *L, int idx)
 {
-  TValue *p = stkindex2adr(L, idx);
-  api_checkvalidindex(L, p);
+  TValue *p = index2adr_stack(L, idx);
   while (++p < L->top) copyTV(L, p-1, p);
   L->top--;
 }
 
 LUA_API void lua_insert(lua_State *L, int idx)
 {
-  TValue *q, *p = stkindex2adr(L, idx);
-  api_checkvalidindex(L, p);
+  TValue *q, *p = index2adr_stack(L, idx);
   for (q = L->top; q > p; q--) copyTV(L, q, q-1);
   copyTV(L, p, L->top);
 }
@@ -162,19 +176,18 @@ LUA_API void lua_insert(lua_State *L, int idx)
 static void copy_slot(lua_State *L, TValue *f, int idx)
 {
   if (idx == LUA_GLOBALSINDEX) {
-    api_check(L, tvistab(f));
+    lj_checkapi(tvistab(f), "stack slot %d is not a table", idx);
     /* NOBARRIER: A thread (i.e. L) is never black. */
     setgcref(L->env, obj2gco(tabV(f)));
   } else if (idx == LUA_ENVIRONINDEX) {
     GCfunc *fn = curr_func(L);
     if (fn->c.gct != ~LJ_TFUNC)
       lj_err_msg(L, LJ_ERR_NOENV);
-    api_check(L, tvistab(f));
+    lj_checkapi(tvistab(f), "stack slot %d is not a table", idx);
     setgcref(fn->c.env, obj2gco(tabV(f)));
     lj_gc_barrier(L, fn, f);
   } else {
-    TValue *o = index2adr(L, idx);
-    api_checkvalidindex(L, o);
+    TValue *o = index2adr_check(L, idx);
     copyTV(L, o, f);
     if (idx < LUA_GLOBALSINDEX)  /* Need a barrier for upvalues. */
       lj_gc_barrier(L, curr_func(L), f);
@@ -183,7 +196,7 @@ static void copy_slot(lua_State *L, TValue *f, int idx)
 
 LUA_API void lua_replace(lua_State *L, int idx)
 {
-  api_checknelems(L, 1);
+  lj_checkapi_slot(1);
   copy_slot(L, L->top - 1, idx);
   L->top--;
 }
@@ -219,7 +232,7 @@ LUA_API int lua_type(lua_State *L, int idx)
 #else
     int tt = (int)(((t < 8 ? 0x98042110u : 0x75a06u) >> 4*(t&7)) & 15u);
 #endif
-    lua_assert(tt != LUA_TNIL || tvisnil(o));
+    lj_assertL(tt != LUA_TNIL || tvisnil(o), "bad tag conversion");
     return tt;
   }
 }
@@ -677,14 +690,14 @@ LUA_API void lua_pushcclosure(lua_State *L, lua_CFunction f, int n)
 {
   GCfunc *fn;
   lj_gc_check(L);
-  api_checknelems(L, n);
+  lj_checkapi_slot(n);
   fn = lj_func_newC(L, (MSize)n, getcurrenv(L));
   fn->c.f = f;
   L->top -= n;
   while (n--)
     copyTV(L, &fn->c.upvalue[n], L->top+n);
   setfuncV(L, L->top, fn);
-  lua_assert(iswhite(obj2gco(fn)));
+  lj_assertL(iswhite(obj2gco(fn)), "new GC object is not white");
   incr_top(L);
 }
 
@@ -754,7 +767,7 @@ LUA_API void *lua_newuserdata(lua_State *L, size_t size)
 
 LUA_API void lua_concat(lua_State *L, int n)
 {
-  api_checknelems(L, n);
+  lj_checkapi_slot(n);
   if (n >= 2) {
     n--;
     do {
@@ -780,9 +793,8 @@ LUA_API void lua_concat(lua_State *L, int n)
 
 LUA_API void lua_gettable(lua_State *L, int idx)
 {
-  cTValue *v, *t = index2adr(L, idx);
-  api_checkvalidindex(L, t);
-  v = lj_meta_tget(L, t, L->top-1);
+  cTValue *t = index2adr_check(L, idx);
+  cTValue *v = lj_meta_tget(L, t, L->top-1);
   if (v == NULL) {
     L->top += 2;
     lj_vm_call(L, L->top-2, 1+1);
@@ -794,9 +806,8 @@ LUA_API void lua_gettable(lua_State *L, int idx)
 
 LUA_API void lua_getfield(lua_State *L, int idx, const char *k)
 {
-  cTValue *v, *t = index2adr(L, idx);
+  cTValue *v, *t = index2adr_check(L, idx);
   TValue key;
-  api_checkvalidindex(L, t);
   setstrV(L, &key, lj_str_newz(L, k));
   v = lj_meta_tget(L, t, &key);
   if (v == NULL) {
@@ -812,14 +823,14 @@ LUA_API void lua_getfield(lua_State *L, int idx, const char *k)
 LUA_API void lua_rawget(lua_State *L, int idx)
 {
   cTValue *t = index2adr(L, idx);
-  api_check(L, tvistab(t));
+  lj_checkapi(tvistab(t), "stack slot %d is not a table", idx);
   copyTV(L, L->top-1, lj_tab_get(L, tabV(t), L->top-1));
 }
 
 LUA_API void lua_rawgeti(lua_State *L, int idx, int n)
 {
   cTValue *v, *t = index2adr(L, idx);
-  api_check(L, tvistab(t));
+  lj_checkapi(tvistab(t), "stack slot %d is not a table", idx);
   v = lj_tab_getint(tabV(t), n);
   if (v) {
     copyTV(L, L->top, v);
@@ -861,8 +872,7 @@ LUALIB_API int luaL_getmetafield(lua_State *L, int idx, const char *field)
 
 LUA_API void lua_getfenv(lua_State *L, int idx)
 {
-  cTValue *o = index2adr(L, idx);
-  api_checkvalidindex(L, o);
+  cTValue *o = index2adr_check(L, idx);
   if (tvisfunc(o)) {
     settabV(L, L->top, tabref(funcV(o)->c.env));
   } else if (tvisudata(o)) {
@@ -879,7 +889,7 @@ LUA_API int lua_next(lua_State *L, int idx)
 {
   cTValue *t = index2adr(L, idx);
   int more;
-  api_check(L, tvistab(t));
+  lj_checkapi(tvistab(t), "stack slot %d is not a table", idx);
   more = lj_tab_next(L, tabV(t), L->top-1);
   if (more) {
     incr_top(L);  /* Return new key and value slot. */
@@ -905,7 +915,7 @@ LUA_API void *lua_upvalueid(lua_State *L, int idx, int n)
 {
   GCfunc *fn = funcV(index2adr(L, idx));
   n--;
-  api_check(L, (uint32_t)n < fn->l.nupvalues);
+  lj_checkapi((uint32_t)n < fn->l.nupvalues, "bad upvalue %d", n);
   return isluafunc(fn) ? (void *)gcref(fn->l.uvptr[n]) :
                          (void *)&fn->c.upvalue[n];
 }
@@ -915,8 +925,10 @@ LUA_API void lua_upvaluejoin(lua_State *L, int idx1, int n1, int idx2, int n2)
   GCfunc *fn1 = funcV(index2adr(L, idx1));
   GCfunc *fn2 = funcV(index2adr(L, idx2));
   n1--; n2--;
-  api_check(L, isluafunc(fn1) && (uint32_t)n1 < fn1->l.nupvalues);
-  api_check(L, isluafunc(fn2) && (uint32_t)n2 < fn2->l.nupvalues);
+  lj_checkapi(isluafunc(fn1), "stack slot %d is not a Lua function", idx1);
+  lj_checkapi(isluafunc(fn2), "stack slot %d is not a Lua function", idx2);
+  lj_checkapi((uint32_t)n1 < fn1->l.nupvalues, "bad upvalue %d", n1+1);
+  lj_checkapi((uint32_t)n2 < fn2->l.nupvalues, "bad upvalue %d", n2+1);
   setgcrefr(fn1->l.uvptr[n1], fn2->l.uvptr[n2]);
   lj_gc_objbarrier(L, fn1, gcref(fn1->l.uvptr[n1]));
 }
@@ -945,9 +957,8 @@ LUALIB_API void *luaL_checkudata(lua_State *L, int idx, const char *tname)
 LUA_API void lua_settable(lua_State *L, int idx)
 {
   TValue *o;
-  cTValue *t = index2adr(L, idx);
-  api_checknelems(L, 2);
-  api_checkvalidindex(L, t);
+  cTValue *t = index2adr_check(L, idx);
+  lj_checkapi_slot(2);
   o = lj_meta_tset(L, t, L->top-2);
   if (o) {
     /* NOBARRIER: lj_meta_tset ensures the table is not black. */
@@ -966,9 +977,8 @@ LUA_API void lua_setfield(lua_State *L, int idx, const char *k)
 {
   TValue *o;
   TValue key;
-  cTValue *t = index2adr(L, idx);
-  api_checknelems(L, 1);
-  api_checkvalidindex(L, t);
+  cTValue *t = index2adr_check(L, idx);
+  lj_checkapi_slot(1);
   setstrV(L, &key, lj_str_newz(L, k));
   o = lj_meta_tset(L, t, &key);
   if (o) {
@@ -987,7 +997,7 @@ LUA_API void lua_rawset(lua_State *L, int idx)
 {
   GCtab *t = tabV(index2adr(L, idx));
   TValue *dst, *key;
-  api_checknelems(L, 2);
+  lj_checkapi_slot(2);
   key = L->top-2;
   dst = lj_tab_set(L, t, key);
   copyTV(L, dst, key+1);
@@ -999,7 +1009,7 @@ LUA_API void lua_rawseti(lua_State *L, int idx, int n)
 {
   GCtab *t = tabV(index2adr(L, idx));
   TValue *dst, *src;
-  api_checknelems(L, 1);
+  lj_checkapi_slot(1);
   dst = lj_tab_setint(L, t, n);
   src = L->top-1;
   copyTV(L, dst, src);
@@ -1011,13 +1021,12 @@ LUA_API int lua_setmetatable(lua_State *L, int idx)
 {
   global_State *g;
   GCtab *mt;
-  cTValue *o = index2adr(L, idx);
-  api_checknelems(L, 1);
-  api_checkvalidindex(L, o);
+  cTValue *o = index2adr_check(L, idx);
+  lj_checkapi_slot(1);
   if (tvisnil(L->top-1)) {
     mt = NULL;
   } else {
-    api_check(L, tvistab(L->top-1));
+    lj_checkapi(tvistab(L->top-1), "top stack slot is not a table");
     mt = tabV(L->top-1);
   }
   g = G(L);
@@ -1054,11 +1063,10 @@ LUALIB_API void luaL_setmetatable(lua_State *L, const char *tname)
 
 LUA_API int lua_setfenv(lua_State *L, int idx)
 {
-  cTValue *o = index2adr(L, idx);
+  cTValue *o = index2adr_check(L, idx);
   GCtab *t;
-  api_checknelems(L, 1);
-  api_checkvalidindex(L, o);
-  api_check(L, tvistab(L->top-1));
+  lj_checkapi_slot(1);
+  lj_checkapi(tvistab(L->top-1), "top stack slot is not a table");
   t = tabV(L->top-1);
   if (tvisfunc(o)) {
     setgcref(funcV(o)->c.env, obj2gco(t));
@@ -1081,7 +1089,7 @@ LUA_API const char *lua_setupvalue(lua_State *L, int idx, int n)
   TValue *val;
   GCobj *o;
   const char *name;
-  api_checknelems(L, 1);
+  lj_checkapi_slot(1);
   name = lj_debug_uvnamev(f, (uint32_t)(n-1), &val, &o);
   if (name) {
     L->top--;
@@ -1108,8 +1116,9 @@ static TValue *api_call_base(lua_State *L, int nargs)
 
 LUA_API void lua_call(lua_State *L, int nargs, int nresults)
 {
-  api_check(L, L->status == LUA_OK || L->status == LUA_ERRERR);
-  api_checknelems(L, nargs+1);
+  lj_checkapi(L->status == LUA_OK || L->status == LUA_ERRERR,
+              "thread called in wrong state %d", L->status);
+  lj_checkapi_slot(nargs+1);
   lj_vm_call(L, api_call_base(L, nargs), nresults+1);
 }
 
@@ -1119,13 +1128,13 @@ LUA_API int lua_pcall(lua_State *L, int nargs, int nresults, int errfunc)
   uint8_t oldh = hook_save(g);
   ptrdiff_t ef;
   int status;
-  api_check(L, L->status == LUA_OK || L->status == LUA_ERRERR);
-  api_checknelems(L, nargs+1);
+  lj_checkapi(L->status == LUA_OK || L->status == LUA_ERRERR,
+              "thread called in wrong state %d", L->status);
+  lj_checkapi_slot(nargs+1);
   if (errfunc == 0) {
     ef = 0;
   } else {
-    cTValue *o = stkindex2adr(L, errfunc);
-    api_checkvalidindex(L, o);
+    cTValue *o = index2adr_stack(L, errfunc);
     ef = savestack(L, o);
   }
   status = lj_vm_pcall(L, api_call_base(L, nargs), nresults+1, ef);
@@ -1151,7 +1160,8 @@ LUA_API int lua_cpcall(lua_State *L, lua_CFunction func, void *ud)
   global_State *g = G(L);
   uint8_t oldh = hook_save(g);
   int status;
-  api_check(L, L->status == LUA_OK || L->status == LUA_ERRERR);
+  lj_checkapi(L->status == LUA_OK || L->status == LUA_ERRERR,
+              "thread called in wrong state %d", L->status);
   status = lj_vm_cpcall(L, func, ud, cpcall);
   if (status) hook_restore(g, oldh);
   return status;
diff --git a/src/lj_asm.c b/src/lj_asm.c
index 90373f27..2659c8a2 100644
--- a/src/lj_asm.c
+++ b/src/lj_asm.c
@@ -96,6 +96,12 @@ typedef struct ASMState {
   uint16_t parentmap[LJ_MAX_JSLOTS];  /* Parent instruction to RegSP map. */
 } ASMState;
 
+#ifdef LUA_USE_ASSERT
+#define lj_assertA(c, ...)      lj_assertG_(J2G(as->J), (c), __VA_ARGS__)
+#else
+#define lj_assertA(c, ...)      ((void)as)
+#endif
+
 #define IR(ref)                 (&as->ir[(ref)])
 
 #define ASMREF_TMP1             REF_TRUE        /* Temp. register. */
@@ -127,9 +133,8 @@ static LJ_AINLINE void checkmclim(ASMState *as)
 #ifdef LUA_USE_ASSERT
   if (as->mcp + MCLIM_REDZONE < as->mcp_prev) {
     IRIns *ir = IR(as->curins+1);
-    fprintf(stderr, "RED ZONE OVERFLOW: %p IR %04d  %02d %04d %04d\n", as->mcp,
-            as->curins+1-REF_BIAS, ir->o, ir->op1-REF_BIAS, ir->op2-REF_BIAS);
-    lua_assert(0);
+    lj_assertA(0, "red zone overflow: %p IR %04d  %02d %04d %04d\n", as->mcp,
+      as->curins+1-REF_BIAS, ir->o, ir->op1-REF_BIAS, ir->op2-REF_BIAS);
   }
 #endif
   if (LJ_UNLIKELY(as->mcp < as->mclim)) asm_mclimit(as);
@@ -243,7 +248,7 @@ static void ra_dprintf(ASMState *as, const char *fmt, ...)
           *p++ = *q >= 'A' && *q <= 'Z' ? *q + 0x20 : *q;
       } else {
         *p++ = '?';
-        lua_assert(0);
+        lj_assertA(0, "bad register %d for debug format \"%s\"", r, fmt);
       }
     } else if (e[1] == 'f' || e[1] == 'i') {
       IRRef ref;
@@ -261,7 +266,7 @@ static void ra_dprintf(ASMState *as, const char *fmt, ...)
     } else if (e[1] == 'x') {
       p += sprintf(p, "%08x", va_arg(argp, int32_t));
     } else {
-      lua_assert(0);
+      lj_assertA(0, "bad debug format code");
     }
     fmt = e+2;
   }
@@ -320,7 +325,7 @@ static Reg ra_rematk(ASMState *as, IRRef ref)
   Reg r;
   if (ra_iskref(ref)) {
     r = ra_krefreg(ref);
-    lua_assert(!rset_test(as->freeset, r));
+    lj_assertA(!rset_test(as->freeset, r), "rematk of free reg %d", r);
     ra_free(as, r);
     ra_modified(as, r);
 #if LJ_64
@@ -332,7 +337,9 @@ static Reg ra_rematk(ASMState *as, IRRef ref)
   }
   ir = IR(ref);
   r = ir->r;
-  lua_assert(ra_hasreg(r) && !ra_hasspill(ir->s));
+  lj_assertA(ra_hasreg(r), "rematk of K%03d has no reg", REF_BIAS - ref);
+  lj_assertA(!ra_hasspill(ir->s),
+             "rematk of K%03d has spill slot [%x]", REF_BIAS - ref, ir->s);
   ra_free(as, r);
   ra_modified(as, r);
   ir->r = RID_INIT;  /* Do not keep any hint. */
@@ -346,7 +353,8 @@ static Reg ra_rematk(ASMState *as, IRRef ref)
     ra_sethint(ir->r, RID_BASE);  /* Restore BASE register hint. */
     emit_getgl(as, r, jit_base);
   } else if (emit_canremat(ASMREF_L) && ir->o == IR_KPRI) {
-    lua_assert(irt_isnil(ir->t));  /* REF_NIL stores ASMREF_L register. */
+    /* REF_NIL stores ASMREF_L register. */
+    lj_assertA(irt_isnil(ir->t), "rematk of bad ASMREF_L");
     emit_getgl(as, r, cur_L);
 #if LJ_64
   } else if (ir->o == IR_KINT64) {
@@ -359,8 +367,9 @@ static Reg ra_rematk(ASMState *as, IRRef ref)
 #endif
 #endif
   } else {
-    lua_assert(ir->o == IR_KINT || ir->o == IR_KGC ||
-               ir->o == IR_KPTR || ir->o == IR_KKPTR || ir->o == IR_KNULL);
+    lj_assertA(ir->o == IR_KINT || ir->o == IR_KGC ||
+               ir->o == IR_KPTR || ir->o == IR_KKPTR || ir->o == IR_KNULL,
+               "rematk of bad IR op %d", ir->o);
     emit_loadi(as, r, ir->i);
   }
   return r;
@@ -370,7 +379,8 @@ static Reg ra_rematk(ASMState *as, IRRef ref)
 static int32_t ra_spill(ASMState *as, IRIns *ir)
 {
   int32_t slot = ir->s;
-  lua_assert(ir >= as->ir + REF_TRUE);
+  lj_assertA(ir >= as->ir + REF_TRUE,
+             "spill of K%03d", REF_BIAS - (int)(ir - as->ir));
   if (!ra_hasspill(slot)) {
     if (irt_is64(ir->t)) {
       slot = as->evenspill;
@@ -395,7 +405,9 @@ static Reg ra_releasetmp(ASMState *as, IRRef ref)
 {
   IRIns *ir = IR(ref);
   Reg r = ir->r;
-  lua_assert(ra_hasreg(r) && !ra_hasspill(ir->s));
+  lj_assertA(ra_hasreg(r), "release of TMP%d has no reg", ref-ASMREF_TMP1+1);
+  lj_assertA(!ra_hasspill(ir->s),
+             "release of TMP%d has spill slot [%x]", ref-ASMREF_TMP1+1, ir->s);
   ra_free(as, r);
   ra_modified(as, r);
   ir->r = RID_INIT;
@@ -411,7 +423,7 @@ static Reg ra_restore(ASMState *as, IRRef ref)
     IRIns *ir = IR(ref);
     int32_t ofs = ra_spill(as, ir);  /* Force a spill slot. */
     Reg r = ir->r;
-    lua_assert(ra_hasreg(r));
+    lj_assertA(ra_hasreg(r), "restore of IR %04d has no reg", ref - REF_BIAS);
     ra_sethint(ir->r, r);  /* Keep hint. */
     ra_free(as, r);
     if (!rset_test(as->weakset, r)) {  /* Only restore non-weak references. */
@@ -440,14 +452,15 @@ static Reg ra_evict(ASMState *as, RegSet allow)
 {
   IRRef ref;
   RegCost cost = ~(RegCost)0;
-  lua_assert(allow != RSET_EMPTY);
+  lj_assertA(allow != RSET_EMPTY, "evict from empty set");
   if (RID_NUM_FPR == 0 || allow < RID2RSET(RID_MAX_GPR)) {
     GPRDEF(MINCOST)
   } else {
     FPRDEF(MINCOST)
   }
   ref = regcost_ref(cost);
-  lua_assert(ra_iskref(ref) || (ref >= as->T->nk && ref < as->T->nins));
+  lj_assertA(ra_iskref(ref) || (ref >= as->T->nk && ref < as->T->nins),
+             "evict of out-of-range IR %04d", ref - REF_BIAS);
   /* Preferably pick any weak ref instead of a non-weak, non-const ref. */
   if (!irref_isk(ref) && (as->weakset & allow)) {
     IRIns *ir = IR(ref);
@@ -605,7 +618,8 @@ static Reg ra_allocref(ASMState *as, IRRef ref, RegSet allow)
   IRIns *ir = IR(ref);
   RegSet pick = as->freeset & allow;
   Reg r;
-  lua_assert(ra_noreg(ir->r));
+  lj_assertA(ra_noreg(ir->r),
+             "IR %04d already has reg %d", ref - REF_BIAS, ir->r);
   if (pick) {
     /* First check register hint from propagation or PHI. */
     if (ra_hashint(ir->r)) {
@@ -669,8 +683,10 @@ static void ra_rename(ASMState *as, Reg down, Reg up)
   IRIns *ir = IR(ref);
   ir->r = (uint8_t)up;
   as->cost[down] = 0;
-  lua_assert((down < RID_MAX_GPR) == (up < RID_MAX_GPR));
-  lua_assert(!rset_test(as->freeset, down) && rset_test(as->freeset, up));
+  lj_assertA((down < RID_MAX_GPR) == (up < RID_MAX_GPR),
+             "rename between GPR/FPR %d and %d", down, up);
+  lj_assertA(!rset_test(as->freeset, down), "rename from free reg %d", down);
+  lj_assertA(rset_test(as->freeset, up), "rename to non-free reg %d", up);
   ra_free(as, down);  /* 'down' is free ... */
   ra_modified(as, down);
   rset_clear(as->freeset, up);  /* ... and 'up' is now allocated. */
@@ -711,7 +727,7 @@ static void ra_destreg(ASMState *as, IRIns *ir, Reg r)
 {
   Reg dest = ra_dest(as, ir, RID2RSET(r));
   if (dest != r) {
-    lua_assert(rset_test(as->freeset, r));
+    lj_assertA(rset_test(as->freeset, r), "dest reg %d is not free", r);
     ra_modified(as, r);
     emit_movrr(as, ir, dest, r);
   }
@@ -744,8 +760,9 @@ static void ra_left(ASMState *as, Reg dest, IRRef lref)
 #endif
 #endif
       } else if (ir->o != IR_KPRI) {
-        lua_assert(ir->o == IR_KINT || ir->o == IR_KGC ||
-                   ir->o == IR_KPTR || ir->o == IR_KKPTR || ir->o == IR_KNULL);
+        lj_assertA(ir->o == IR_KINT || ir->o == IR_KGC ||
+                   ir->o == IR_KPTR || ir->o == IR_KKPTR || ir->o == IR_KNULL,
+                   "K%03d has bad IR op %d", REF_BIAS - lref, ir->o);
         emit_loadi(as, dest, ir->i);
         return;
       }
@@ -887,11 +904,14 @@ static void asm_snap_alloc1(ASMState *as, IRRef ref)
 #endif
       {  /* Allocate stored values for TNEW, TDUP and CNEW. */
         IRIns *irs;
-        lua_assert(ir->o == IR_TNEW || ir->o == IR_TDUP || ir->o == IR_CNEW);
+        lj_assertA(ir->o == IR_TNEW || ir->o == IR_TDUP || ir->o == IR_CNEW,
+                   "sink of IR %04d has bad op %d", ref - REF_BIAS, ir->o);
         for (irs = IR(as->snapref-1); irs > ir; irs--)
           if (irs->r == RID_SINK && asm_sunk_store(as, ir, irs)) {
-            lua_assert(irs->o == IR_ASTORE || irs->o == IR_HSTORE ||
-                       irs->o == IR_FSTORE || irs->o == IR_XSTORE);
+            lj_assertA(irs->o == IR_ASTORE || irs->o == IR_HSTORE ||
+                       irs->o == IR_FSTORE || irs->o == IR_XSTORE,
+                       "sunk store IR %04d has bad op %d",
+                       (int)(irs - as->ir) - REF_BIAS, irs->o);
             asm_snap_alloc1(as, irs->op2);
             if (LJ_32 && (irs+1)->o == IR_HIOP)
               asm_snap_alloc1(as, (irs+1)->op2);
@@ -938,7 +958,9 @@ static void asm_snap_alloc(ASMState *as)
     if (!irref_isk(ref)) {
       asm_snap_alloc1(as, ref);
       if (LJ_SOFTFP && (sn & SNAP_SOFTFPNUM)) {
-        lua_assert(irt_type(IR(ref+1)->t) == IRT_SOFTFP);
+        lj_assertA(irt_type(IR(ref+1)->t) == IRT_SOFTFP,
+                   "snap %d[%d] points to bad SOFTFP IR %04d",
+                   as->snapno, n, ref - REF_BIAS);
         asm_snap_alloc1(as, ref+1);
       }
     }
@@ -1002,19 +1024,20 @@ static int32_t asm_stack_adjust(ASMState *as)
 }
 
 /* Must match with hash*() in lj_tab.c. */
-static uint32_t ir_khash(IRIns *ir)
+static uint32_t ir_khash(ASMState *as, IRIns *ir)
 {
   uint32_t lo, hi;
+  UNUSED(as);
   if (irt_isstr(ir->t)) {
     return ir_kstr(ir)->hash;
   } else if (irt_isnum(ir->t)) {
     lo = ir_knum(ir)->u32.lo;
     hi = ir_knum(ir)->u32.hi << 1;
   } else if (irt_ispri(ir->t)) {
-    lua_assert(!irt_isnil(ir->t));
+    lj_assertA(!irt_isnil(ir->t), "hash of nil key");
     return irt_type(ir->t)-IRT_FALSE;
   } else {
-    lua_assert(irt_isgcv(ir->t));
+    lj_assertA(irt_isgcv(ir->t), "hash of bad IR type %d", irt_type(ir->t));
     lo = u32ptr(ir_kgc(ir));
 #if LJ_GC64
     hi = (uint32_t)(u64ptr(ir_kgc(ir)) >> 32) | (irt_toitype(ir->t) << 15);
@@ -1122,7 +1145,8 @@ static void asm_bufput(ASMState *as, IRIns *ir)
   args[0] = ir->op1;  /* SBuf * */
   args[1] = ir->op2;  /* GCstr * */
   irs = IR(ir->op2);
-  lua_assert(irt_isstr(irs->t));
+  lj_assertA(irt_isstr(irs->t),
+             "BUFPUT of non-string IR %04d", ir->op2 - REF_BIAS);
   if (irs->o == IR_KGC) {
     GCstr *s = ir_kstr(irs);
     if (s->len == 1) {  /* Optimize put of single-char string constant. */
@@ -1136,7 +1160,8 @@ static void asm_bufput(ASMState *as, IRIns *ir)
         args[1] = ASMREF_TMP1;  /* TValue * */
         ci = &lj_ir_callinfo[IRCALL_lj_strfmt_putnum];
       } else {
-        lua_assert(irt_isinteger(IR(irs->op1)->t));
+        lj_assertA(irt_isinteger(IR(irs->op1)->t),
+                   "TOSTR of non-numeric IR %04d", irs->op1);
         args[1] = irs->op1;  /* int */
         if (irs->op2 == IRTOSTR_INT)
           ci = &lj_ir_callinfo[IRCALL_lj_strfmt_putint];
@@ -1201,7 +1226,8 @@ static void asm_conv64(ASMState *as, IRIns *ir)
   IRType dt = (((ir-1)->op2 & IRCONV_DSTMASK) >> IRCONV_DSH);
   IRCallID id;
   IRRef args[2];
-  lua_assert((ir-1)->o == IR_CONV && ir->o == IR_HIOP);
+  lj_assertA((ir-1)->o == IR_CONV && ir->o == IR_HIOP,
+             "not a CONV/HIOP pair at IR %04d", (int)(ir - as->ir) - REF_BIAS);
   args[LJ_BE] = (ir-1)->op1;
   args[LJ_LE] = ir->op1;
   if (st == IRT_NUM || st == IRT_FLOAT) {
@@ -1256,15 +1282,16 @@ static void asm_collectargs(ASMState *as, IRIns *ir,
                             const CCallInfo *ci, IRRef *args)
 {
   uint32_t n = CCI_XNARGS(ci);
-  lua_assert(n <= CCI_NARGS_MAX*2);  /* Account for split args. */
+  /* Account for split args. */
+  lj_assertA(n <= CCI_NARGS_MAX*2, "too many args %d to collect", n);
   if ((ci->flags & CCI_L)) { *args++ = ASMREF_L; n--; }
   while (n-- > 1) {
     ir = IR(ir->op1);
-    lua_assert(ir->o == IR_CARG);
+    lj_assertA(ir->o == IR_CARG, "malformed CALL arg tree");
     args[n] = ir->op2 == REF_NIL ? 0 : ir->op2;
   }
   args[0] = ir->op1 == REF_NIL ? 0 : ir->op1;
-  lua_assert(IR(ir->op1)->o != IR_CARG);
+  lj_assertA(IR(ir->op1)->o != IR_CARG, "malformed CALL arg tree");
 }
 
 /* Reconstruct CCallInfo flags for CALLX*. */
@@ -1648,7 +1675,10 @@ static void asm_ir(ASMState *as, IRIns *ir)
   switch ((IROp)ir->o) {
   /* Miscellaneous ops. */
   case IR_LOOP: asm_loop(as); break;
-  case IR_NOP: case IR_XBAR: lua_assert(!ra_used(ir)); break;
+  case IR_NOP: case IR_XBAR:
+    lj_assertA(!ra_used(ir),
+               "IR %04d not unused", (int)(ir - as->ir) - REF_BIAS);
+    break;
   case IR_USE:
     ra_alloc1(as, ir->op1, irt_isfp(ir->t) ? RSET_FPR : RSET_GPR); break;
   case IR_PHI: asm_phi(as, ir); break;
@@ -1687,7 +1717,9 @@ static void asm_ir(ASMState *as, IRIns *ir)
 #if LJ_SOFTFP32
   case IR_DIV: case IR_POW: case IR_ABS:
   case IR_LDEXP: case IR_FPMATH: case IR_TOBIT:
-    lua_assert(0);  /* Unused for LJ_SOFTFP32. */
+    /* Unused for LJ_SOFTFP32. */
+    lj_assertA(0, "IR %04d with unused op %d",
+                  (int)(ir - as->ir) - REF_BIAS, ir->o);
     break;
 #else
   case IR_DIV: asm_div(as, ir); break;
@@ -1736,7 +1768,8 @@ static void asm_ir(ASMState *as, IRIns *ir)
 #if LJ_HASFFI
     asm_cnew(as, ir);
 #else
-    lua_assert(0);
+    lj_assertA(0, "IR %04d with unused op %d",
+                  (int)(ir - as->ir) - REF_BIAS, ir->o);
 #endif
     break;
 
@@ -1814,8 +1847,10 @@ static void asm_head_side(ASMState *as)
   for (i = as->stopins; i > REF_BASE; i--) {
     IRIns *ir = IR(i);
     RegSP rs;
-    lua_assert((ir->o == IR_SLOAD && (ir->op2 & IRSLOAD_PARENT)) ||
-               (LJ_SOFTFP && ir->o == IR_HIOP) || ir->o == IR_PVAL);
+    lj_assertA((ir->o == IR_SLOAD && (ir->op2 & IRSLOAD_PARENT)) ||
+               (LJ_SOFTFP && ir->o == IR_HIOP) || ir->o == IR_PVAL,
+               "IR %04d has bad parent op %d",
+               (int)(ir - as->ir) - REF_BIAS, ir->o);
     rs = as->parentmap[i - REF_FIRST];
     if (ra_hasreg(ir->r)) {
       rset_clear(allow, ir->r);
@@ -2074,7 +2109,7 @@ static void asm_setup_regsp(ASMState *as)
   ir = IR(REF_FIRST);
   if (as->parent) {
     uint16_t *p;
-    lastir = lj_snap_regspmap(as->parent, as->J->exitno, ir);
+    lastir = lj_snap_regspmap(as->J, as->parent, as->J->exitno, ir);
     if (lastir - ir > LJ_MAX_JSLOTS)
       lj_trace_err(as->J, LJ_TRERR_NYICOAL);
     as->stopins = (IRRef)((lastir-1) - as->ir);
@@ -2378,7 +2413,10 @@ void lj_asm_trace(jit_State *J, GCtrace *T)
     /* Assemble a trace in linear backwards order. */
     for (as->curins--; as->curins > as->stopins; as->curins--) {
       IRIns *ir = IR(as->curins);
-      lua_assert(!(LJ_32 && irt_isint64(ir->t)));  /* Handled by SPLIT. */
+      /* 64 bit types handled by SPLIT for 32 bit archs. */
+      lj_assertA(!(LJ_32 && irt_isint64(ir->t)),
+                 "IR %04d has unsplit 64 bit type",
+                 (int)(ir - as->ir) - REF_BIAS);
       if (!ra_used(ir) && !ir_sideeff(ir) && (as->flags & JIT_F_OPT_DCE))
         continue;  /* Dead-code elimination can be soooo easy. */
       if (irt_isguard(ir->t))
@@ -2408,7 +2446,7 @@ void lj_asm_trace(jit_State *J, GCtrace *T)
     asm_phi_fixup(as);
 
     if (J->curfinal->nins >= T->nins) {  /* IR didn't grow? */
-      lua_assert(J->curfinal->nk == T->nk);
+      lj_assertA(J->curfinal->nk == T->nk, "unexpected IR constant growth");
       memcpy(J->curfinal->ir + as->orignins, T->ir + as->orignins,
              (T->nins - as->orignins) * sizeof(IRIns));  /* Copy RENAMEs. */
       T->nins = J->curfinal->nins;
diff --git a/src/lj_asm_arm.h b/src/lj_asm_arm.h
index f922ed0f..56ce4a07 100644
--- a/src/lj_asm_arm.h
+++ b/src/lj_asm_arm.h
@@ -41,7 +41,7 @@ static Reg ra_scratchpair(ASMState *as, RegSet allow)
       }
     }
   }
-  lua_assert(rset_test(RSET_GPREVEN, r));
+  lj_assertA(rset_test(RSET_GPREVEN, r), "odd reg %d", r);
   ra_modified(as, r);
   ra_modified(as, r+1);
   RA_DBGX((as, "scratchpair    $r $r", r, r+1));
@@ -269,7 +269,7 @@ static void asm_fusexref(ASMState *as, ARMIns ai, Reg rd, IRRef ref,
         return;
       }
     } else if (ir->o == IR_STRREF && !(!LJ_SOFTFP && (ai & 0x08000000))) {
-      lua_assert(ofs == 0);
+      lj_assertA(ofs == 0, "bad usage");
       ofs = (int32_t)sizeof(GCstr);
       if (irref_isk(ir->op2)) {
         ofs += IR(ir->op2)->i;
@@ -389,9 +389,11 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
       as->freeset |= (of & RSET_RANGE(REGARG_FIRSTGPR, REGARG_LASTGPR+1));
       if (irt_isnum(ir->t)) gpr = (gpr+1) & ~1u;
       if (gpr <= REGARG_LASTGPR) {
-        lua_assert(rset_test(as->freeset, gpr));  /* Must have been evicted. */
+        lj_assertA(rset_test(as->freeset, gpr),
+                   "reg %d not free", gpr);  /* Must have been evicted. */
         if (irt_isnum(ir->t)) {
-          lua_assert(rset_test(as->freeset, gpr+1));  /* Ditto. */
+          lj_assertA(rset_test(as->freeset, gpr+1),
+                     "reg %d not free", gpr+1);  /* Ditto. */
           emit_dnm(as, ARMI_VMOV_RR_D, gpr, gpr+1, (src & 15));
           gpr += 2;
         } else {
@@ -408,7 +410,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 #endif
     {
       if (gpr <= REGARG_LASTGPR) {
-        lua_assert(rset_test(as->freeset, gpr));  /* Must have been evicted. */
+        lj_assertA(rset_test(as->freeset, gpr),
+                   "reg %d not free", gpr);  /* Must have been evicted. */
         if (ref) ra_leftov(as, gpr, ref);
         gpr++;
       } else {
@@ -433,7 +436,7 @@ static void asm_setupresult(ASMState *as, IRIns *ir, const CCallInfo *ci)
     rset_clear(drop, (ir+1)->r);  /* Dest reg handled below. */
   ra_evictset(as, drop);  /* Evictions must be performed first. */
   if (ra_used(ir)) {
-    lua_assert(!irt_ispri(ir->t));
+    lj_assertA(!irt_ispri(ir->t), "PRI dest");
     if (!LJ_SOFTFP && irt_isfp(ir->t)) {
       if (LJ_ABI_SOFTFP || (ci->flags & (CCI_CASTU64|CCI_VARARG))) {
         Reg dest = (ra_dest(as, ir, RSET_FPR) & 15);
@@ -530,13 +533,17 @@ static void asm_conv(ASMState *as, IRIns *ir)
 #endif
   IRRef lref = ir->op1;
   /* 64 bit integer conversions are handled by SPLIT. */
-  lua_assert(!irt_isint64(ir->t) && !(st == IRT_I64 || st == IRT_U64));
+  lj_assertA(!irt_isint64(ir->t) && !(st == IRT_I64 || st == IRT_U64),
+             "IR %04d has unsplit 64 bit type",
+             (int)(ir - as->ir) - REF_BIAS);
 #if LJ_SOFTFP
   /* FP conversions are handled by SPLIT. */
-  lua_assert(!irt_isfp(ir->t) && !(st == IRT_NUM || st == IRT_FLOAT));
+  lj_assertA(!irt_isfp(ir->t) && !(st == IRT_NUM || st == IRT_FLOAT),
+             "IR %04d has FP type",
+             (int)(ir - as->ir) - REF_BIAS);
   /* Can't check for same types: SPLIT uses CONV int.int + BXOR for sfp NEG. */
 #else
-  lua_assert(irt_type(ir->t) != st);
+  lj_assertA(irt_type(ir->t) != st, "inconsistent types for CONV");
   if (irt_isfp(ir->t)) {
     Reg dest = ra_dest(as, ir, RSET_FPR);
     if (stfp) {  /* FP to FP conversion. */
@@ -553,7 +560,8 @@ static void asm_conv(ASMState *as, IRIns *ir)
   } else if (stfp) {  /* FP to integer conversion. */
     if (irt_isguard(ir->t)) {
       /* Checked conversions are only supported from number to int. */
-      lua_assert(irt_isint(ir->t) && st == IRT_NUM);
+      lj_assertA(irt_isint(ir->t) && st == IRT_NUM,
+                 "bad type for checked CONV");
       asm_tointg(as, ir, ra_alloc1(as, lref, RSET_FPR));
     } else {
       Reg left = ra_alloc1(as, lref, RSET_FPR);
@@ -572,7 +580,7 @@ static void asm_conv(ASMState *as, IRIns *ir)
     Reg dest = ra_dest(as, ir, RSET_GPR);
     if (st >= IRT_I8 && st <= IRT_U16) {  /* Extend to 32 bit integer. */
       Reg left = ra_alloc1(as, lref, RSET_GPR);
-      lua_assert(irt_isint(ir->t) || irt_isu32(ir->t));
+      lj_assertA(irt_isint(ir->t) || irt_isu32(ir->t), "bad type for CONV EXT");
       if ((as->flags & JIT_F_ARMV6)) {
         ARMIns ai = st == IRT_I8 ? ARMI_SXTB :
                     st == IRT_U8 ? ARMI_UXTB :
@@ -667,7 +675,7 @@ static void asm_tvptr(ASMState *as, Reg dest, IRRef ref)
       ra_allockreg(as, i32ptr(ir_knum(ir)), dest);
     } else {
 #if LJ_SOFTFP
-      lua_assert(0);
+      lj_assertA(0, "unsplit FP op");
 #else
       /* Otherwise force a spill and use the spill slot. */
       emit_opk(as, ARMI_ADD, dest, RID_SP, ra_spill(as, ir), RSET_GPR);
@@ -811,7 +819,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
   *l_loop = ARMF_CC(ARMI_B, CC_NE) | ((as->mcp-l_loop-2) & 0x00ffffffu);
 
   /* Load main position relative to tab->node into dest. */
-  khash = irref_isk(refkey) ? ir_khash(irkey) : 1;
+  khash = irref_isk(refkey) ? ir_khash(as, irkey) : 1;
   if (khash == 0) {
     emit_lso(as, ARMI_LDR, dest, tab, (int32_t)offsetof(GCtab, node));
   } else {
@@ -867,7 +875,7 @@ static void asm_hrefk(ASMState *as, IRIns *ir)
   Reg node = ra_alloc1(as, ir->op1, RSET_GPR);
   Reg key = RID_NONE, type = RID_TMP, idx = node;
   RegSet allow = rset_exclude(RSET_GPR, node);
-  lua_assert(ofs % sizeof(Node) == 0);
+  lj_assertA(ofs % sizeof(Node) == 0, "unaligned HREFK slot");
   if (ofs > 4095) {
     idx = dest;
     rset_clear(allow, dest);
@@ -934,7 +942,7 @@ static void asm_uref(ASMState *as, IRIns *ir)
 static void asm_fref(ASMState *as, IRIns *ir)
 {
   UNUSED(as); UNUSED(ir);
-  lua_assert(!ra_used(ir));
+  lj_assertA(!ra_used(ir), "unfused FREF");
 }
 
 static void asm_strref(ASMState *as, IRIns *ir)
@@ -971,25 +979,27 @@ static void asm_strref(ASMState *as, IRIns *ir)
 
 /* -- Loads and stores ---------------------------------------------------- */
 
-static ARMIns asm_fxloadins(IRIns *ir)
+static ARMIns asm_fxloadins(ASMState *as, IRIns *ir)
 {
+  UNUSED(as);
   switch (irt_type(ir->t)) {
   case IRT_I8: return ARMI_LDRSB;
   case IRT_U8: return ARMI_LDRB;
   case IRT_I16: return ARMI_LDRSH;
   case IRT_U16: return ARMI_LDRH;
-  case IRT_NUM: lua_assert(!LJ_SOFTFP); return ARMI_VLDR_D;
+  case IRT_NUM: lj_assertA(!LJ_SOFTFP, "unsplit FP op"); return ARMI_VLDR_D;
   case IRT_FLOAT: if (!LJ_SOFTFP) return ARMI_VLDR_S;  /* fallthrough */
   default: return ARMI_LDR;
   }
 }
 
-static ARMIns asm_fxstoreins(IRIns *ir)
+static ARMIns asm_fxstoreins(ASMState *as, IRIns *ir)
 {
+  UNUSED(as);
   switch (irt_type(ir->t)) {
   case IRT_I8: case IRT_U8: return ARMI_STRB;
   case IRT_I16: case IRT_U16: return ARMI_STRH;
-  case IRT_NUM: lua_assert(!LJ_SOFTFP); return ARMI_VSTR_D;
+  case IRT_NUM: lj_assertA(!LJ_SOFTFP, "unsplit FP op"); return ARMI_VSTR_D;
   case IRT_FLOAT: if (!LJ_SOFTFP) return ARMI_VSTR_S;  /* fallthrough */
   default: return ARMI_STR;
   }
@@ -997,12 +1007,13 @@ static ARMIns asm_fxstoreins(IRIns *ir)
 
 static void asm_fload(ASMState *as, IRIns *ir)
 {
-  if (ir->op1 == REF_NIL) {
-    lua_assert(!ra_used(ir));  /* We can end up here if DCE is turned off. */
+  if (ir->op1 == REF_NIL) {  /* FLOAD from GG_State with offset. */
+    /* We can end up here if DCE is turned off. */
+    lj_assertA(!ra_used(ir), "NYI FLOAD GG_State");
   } else {
     Reg dest = ra_dest(as, ir, RSET_GPR);
     Reg idx = ra_alloc1(as, ir->op1, RSET_GPR);
-    ARMIns ai = asm_fxloadins(ir);
+    ARMIns ai = asm_fxloadins(as, ir);
     int32_t ofs;
     if (ir->op2 == IRFL_TAB_ARRAY) {
       ofs = asm_fuseabase(as, ir->op1);
@@ -1026,7 +1037,7 @@ static void asm_fstore(ASMState *as, IRIns *ir)
     IRIns *irf = IR(ir->op1);
     Reg idx = ra_alloc1(as, irf->op1, rset_exclude(RSET_GPR, src));
     int32_t ofs = field_ofs[irf->op2];
-    ARMIns ai = asm_fxstoreins(ir);
+    ARMIns ai = asm_fxstoreins(as, ir);
     if ((ai & 0x04000000))
       emit_lso(as, ai, src, idx, ofs);
     else
@@ -1038,8 +1049,8 @@ static void asm_xload(ASMState *as, IRIns *ir)
 {
   Reg dest = ra_dest(as, ir,
                      (!LJ_SOFTFP && irt_isfp(ir->t)) ? RSET_FPR : RSET_GPR);
-  lua_assert(!(ir->op2 & IRXLOAD_UNALIGNED));
-  asm_fusexref(as, asm_fxloadins(ir), dest, ir->op1, RSET_GPR, 0);
+  lj_assertA(!(ir->op2 & IRXLOAD_UNALIGNED), "unaligned XLOAD");
+  asm_fusexref(as, asm_fxloadins(as, ir), dest, ir->op1, RSET_GPR, 0);
 }
 
 static void asm_xstore_(ASMState *as, IRIns *ir, int32_t ofs)
@@ -1047,7 +1058,7 @@ static void asm_xstore_(ASMState *as, IRIns *ir, int32_t ofs)
   if (ir->r != RID_SINK) {
     Reg src = ra_alloc1(as, ir->op2,
                         (!LJ_SOFTFP && irt_isfp(ir->t)) ? RSET_FPR : RSET_GPR);
-    asm_fusexref(as, asm_fxstoreins(ir), src, ir->op1,
+    asm_fusexref(as, asm_fxstoreins(as, ir), src, ir->op1,
                  rset_exclude(RSET_GPR, src), ofs);
   }
 }
@@ -1066,8 +1077,9 @@ static void asm_ahuvload(ASMState *as, IRIns *ir)
     rset_clear(allow, type);
   }
   if (ra_used(ir)) {
-    lua_assert((LJ_SOFTFP ? 0 : irt_isnum(ir->t)) ||
-               irt_isint(ir->t) || irt_isaddr(ir->t));
+    lj_assertA((LJ_SOFTFP ? 0 : irt_isnum(ir->t)) ||
+               irt_isint(ir->t) || irt_isaddr(ir->t),
+               "bad load type %d", irt_type(ir->t));
     dest = ra_dest(as, ir, (!LJ_SOFTFP && t == IRT_NUM) ? RSET_FPR : allow);
     rset_clear(allow, dest);
   }
@@ -1133,10 +1145,13 @@ static void asm_sload(ASMState *as, IRIns *ir)
   IRType t = hiop ? IRT_NUM : irt_type(ir->t);
   Reg dest = RID_NONE, type = RID_NONE, base;
   RegSet allow = RSET_GPR;
-  lua_assert(!(ir->op2 & IRSLOAD_PARENT));  /* Handled by asm_head_side(). */
-  lua_assert(irt_isguard(ir->t) || !(ir->op2 & IRSLOAD_TYPECHECK));
+  lj_assertA(!(ir->op2 & IRSLOAD_PARENT),
+             "bad parent SLOAD");  /* Handled by asm_head_side(). */
+  lj_assertA(irt_isguard(ir->t) || !(ir->op2 & IRSLOAD_TYPECHECK),
+             "inconsistent SLOAD variant");
 #if LJ_SOFTFP
-  lua_assert(!(ir->op2 & IRSLOAD_CONVERT));  /* Handled by LJ_SOFTFP SPLIT. */
+  lj_assertA(!(ir->op2 & IRSLOAD_CONVERT),
+             "unsplit SLOAD convert");  /* Handled by LJ_SOFTFP SPLIT. */
   if (hiop && ra_used(ir+1)) {
     type = ra_dest(as, ir+1, allow);
     rset_clear(allow, type);
@@ -1152,8 +1167,9 @@ static void asm_sload(ASMState *as, IRIns *ir)
     Reg tmp = RID_NONE;
     if ((ir->op2 & IRSLOAD_CONVERT))
       tmp = ra_scratch(as, t == IRT_INT ? RSET_FPR : RSET_GPR);
-    lua_assert((LJ_SOFTFP ? 0 : irt_isnum(ir->t)) ||
-               irt_isint(ir->t) || irt_isaddr(ir->t));
+    lj_assertA((LJ_SOFTFP ? 0 : irt_isnum(ir->t)) ||
+               irt_isint(ir->t) || irt_isaddr(ir->t),
+               "bad SLOAD type %d", irt_type(ir->t));
     dest = ra_dest(as, ir, (!LJ_SOFTFP && t == IRT_NUM) ? RSET_FPR : allow);
     rset_clear(allow, dest);
     base = ra_alloc1(as, REF_BASE, allow);
@@ -1218,7 +1234,8 @@ static void asm_cnew(ASMState *as, IRIns *ir)
   IRRef args[4];
   RegSet allow = (RSET_GPR & ~RSET_SCRATCH);
   RegSet drop = RSET_SCRATCH;
-  lua_assert(sz != CTSIZE_INVALID || (ir->o == IR_CNEW && ir->op2 != REF_NIL));
+  lj_assertA(sz != CTSIZE_INVALID || (ir->o == IR_CNEW && ir->op2 != REF_NIL),
+             "bad CNEW/CNEWI operands");
 
   as->gcsteps++;
   if (ra_hasreg(ir->r))
@@ -1230,10 +1247,10 @@ static void asm_cnew(ASMState *as, IRIns *ir)
   /* Initialize immutable cdata object. */
   if (ir->o == IR_CNEWI) {
     int32_t ofs = sizeof(GCcdata);
-    lua_assert(sz == 4 || sz == 8);
+    lj_assertA(sz == 4 || sz == 8, "bad CNEWI size %d", sz);
     if (sz == 8) {
       ofs += 4; ir++;
-      lua_assert(ir->o == IR_HIOP);
+      lj_assertA(ir->o == IR_HIOP, "expected HIOP for CNEWI");
     }
     for (;;) {
       Reg r = ra_alloc1(as, ir->op2, allow);
@@ -1299,7 +1316,7 @@ static void asm_obar(ASMState *as, IRIns *ir)
   MCLabel l_end;
   Reg obj, val, tmp;
   /* No need for other object barriers (yet). */
-  lua_assert(IR(ir->op1)->o == IR_UREFC);
+  lj_assertA(IR(ir->op1)->o == IR_UREFC, "bad OBAR type");
   ra_evictset(as, RSET_SCRATCH);
   l_end = emit_label(as);
   args[0] = ASMREF_TMP1;  /* global_State *g */
@@ -1575,7 +1592,7 @@ static void asm_bitshift(ASMState *as, IRIns *ir, ARMShift sh)
 #define asm_bshr(as, ir)        asm_bitshift(as, ir, ARMSH_LSR)
 #define asm_bsar(as, ir)        asm_bitshift(as, ir, ARMSH_ASR)
 #define asm_bror(as, ir)        asm_bitshift(as, ir, ARMSH_ROR)
-#define asm_brol(as, ir)        lua_assert(0)
+#define asm_brol(as, ir)        lj_assertA(0, "unexpected BROL")
 
 static void asm_intmin_max(ASMState *as, IRIns *ir, int cc)
 {
@@ -1726,7 +1743,8 @@ static void asm_intcomp(ASMState *as, IRIns *ir)
   Reg left;
   uint32_t m;
   int cmpprev0 = 0;
-  lua_assert(irt_isint(ir->t) || irt_isu32(ir->t) || irt_isaddr(ir->t));
+  lj_assertA(irt_isint(ir->t) || irt_isu32(ir->t) || irt_isaddr(ir->t),
+             "bad comparison data type %d", irt_type(ir->t));
   if (asm_swapops(as, lref, rref)) {
     Reg tmp = lref; lref = rref; rref = tmp;
     if (cc >= CC_GE) cc ^= 7;  /* LT <-> GT, LE <-> GE */
@@ -1895,10 +1913,11 @@ static void asm_hiop(ASMState *as, IRIns *ir)
   case IR_CNEWI:
     /* Nothing to do here. Handled by lo op itself. */
     break;
-  default: lua_assert(0); break;
+  default: lj_assertA(0, "bad HIOP for op %d", (ir-1)->o); break;
   }
 #else
-  UNUSED(as); UNUSED(ir); lua_assert(0);
+  /* Unused without SOFTFP or FFI. */
+  UNUSED(as); UNUSED(ir); lj_assertA(0, "unexpected HIOP");
 #endif
 }
 
@@ -1923,7 +1942,7 @@ static void asm_stack_check(ASMState *as, BCReg topslot,
   if (irp) {
     if (!ra_hasspill(irp->s)) {
       pbase = irp->r;
-      lua_assert(ra_hasreg(pbase));
+      lj_assertA(ra_hasreg(pbase), "base reg lost");
     } else if (allow) {
       pbase = rset_pickbot(allow);
     } else {
@@ -1935,7 +1954,7 @@ static void asm_stack_check(ASMState *as, BCReg topslot,
   }
   emit_branch(as, ARMF_CC(ARMI_BL, CC_LS), exitstub_addr(as->J, exitno));
   k = emit_isk12(0, (int32_t)(8*topslot));
-  lua_assert(k);
+  lj_assertA(k, "slot offset %d does not fit in K12", 8*topslot);
   emit_n(as, ARMI_CMP^k, RID_TMP);
   emit_dnm(as, ARMI_SUB, RID_TMP, RID_TMP, pbase);
   emit_lso(as, ARMI_LDR, RID_TMP, RID_TMP,
@@ -1972,7 +1991,8 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
 #if LJ_SOFTFP
       RegSet odd = rset_exclude(RSET_GPRODD, RID_BASE);
       Reg tmp;
-      lua_assert(irref_isk(ref));  /* LJ_SOFTFP: must be a number constant. */
+      /* LJ_SOFTFP: must be a number constant. */
+      lj_assertA(irref_isk(ref), "unsplit FP op");
       tmp = ra_allock(as, (int32_t)ir_knum(ir)->u32.lo,
                       rset_exclude(RSET_GPREVEN, RID_BASE));
       emit_lso(as, ARMI_STR, tmp, RID_BASE, ofs);
@@ -1986,7 +2006,8 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
     } else {
       RegSet odd = rset_exclude(RSET_GPRODD, RID_BASE);
       Reg type;
-      lua_assert(irt_ispri(ir->t) || irt_isaddr(ir->t) || irt_isinteger(ir->t));
+      lj_assertA(irt_ispri(ir->t) || irt_isaddr(ir->t) || irt_isinteger(ir->t),
+                 "restore of IR type %d", irt_type(ir->t));
       if (!irt_ispri(ir->t)) {
         Reg src = ra_alloc1(as, ref, rset_exclude(RSET_GPREVEN, RID_BASE));
         emit_lso(as, ARMI_STR, src, RID_BASE, ofs);
@@ -2006,7 +2027,7 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
     }
     checkmclim(as);
   }
-  lua_assert(map + nent == flinks);
+  lj_assertA(map + nent == flinks, "inconsistent frames in snapshot");
 }
 
 /* -- GC handling --------------------------------------------------------- */
@@ -2092,7 +2113,7 @@ static RegSet asm_head_side_base(ASMState *as, IRIns *irp, RegSet allow)
     rset_clear(allow, ra_dest(as, ir, allow));
   } else {
     Reg r = irp->r;
-    lua_assert(ra_hasreg(r));
+    lj_assertA(ra_hasreg(r), "base reg lost");
     rset_clear(allow, r);
     if (r != ir->r && !rset_test(as->freeset, r))
       ra_restore(as, regcost_ref(as->cost[r]));
@@ -2114,7 +2135,7 @@ static void asm_tail_fixup(ASMState *as, TraceNo lnk)
   } else {
     /* Patch stack adjustment. */
     uint32_t k = emit_isk12(ARMI_ADD, spadj);
-    lua_assert(k);
+    lj_assertA(k, "stack adjustment %d does not fit in K12", spadj);
     p[-2] = (ARMI_ADD^k) | ARMF_D(RID_SP) | ARMF_N(RID_SP);
   }
   /* Patch exit branch. */
@@ -2196,7 +2217,7 @@ void lj_asm_patchexit(jit_State *J, GCtrace *T, ExitNo exitno, MCode *target)
       if (!cstart) cstart = p;
     }
   }
-  lua_assert(cstart != NULL);
+  lj_assertJ(cstart != NULL, "exit stub %d not found", exitno);
   lj_mcode_sync(cstart, cend);
   lj_mcode_patch(J, mcarea, 1);
 }
diff --git a/src/lj_asm_arm64.h b/src/lj_asm_arm64.h
index a3502223..0729a3a5 100644
--- a/src/lj_asm_arm64.h
+++ b/src/lj_asm_arm64.h
@@ -213,7 +213,7 @@ static uint32_t asm_fuseopm(ASMState *as, A64Ins ai, IRRef ref, RegSet allow)
     return A64F_M(ir->r);
   } else if (irref_isk(ref)) {
     uint32_t m;
-    int64_t k = get_k64val(ir);
+    int64_t k = get_k64val(as, ref);
     if ((ai & 0x1f000000) == 0x0a000000)
       m = emit_isk13(k, irt_is64(ir->t));
     else
@@ -354,9 +354,9 @@ static int asm_fusemadd(ASMState *as, IRIns *ir, A64Ins ai, A64Ins air)
 static int asm_fuseandshift(ASMState *as, IRIns *ir)
 {
   IRIns *irl = IR(ir->op1);
-  lua_assert(ir->o == IR_BAND);
+  lj_assertA(ir->o == IR_BAND, "bad usage");
   if (canfuse(as, irl) && irref_isk(ir->op2)) {
-    uint64_t mask = get_k64val(IR(ir->op2));
+    uint64_t mask = get_k64val(as, ir->op2);
     if (irref_isk(irl->op2) && (irl->o == IR_BSHR || irl->o == IR_BSHL)) {
       int32_t shmask = irt_is64(irl->t) ? 63 : 31;
       int32_t shift = (IR(irl->op2)->i & shmask);
@@ -384,7 +384,7 @@ static int asm_fuseandshift(ASMState *as, IRIns *ir)
 static int asm_fuseorshift(ASMState *as, IRIns *ir)
 {
   IRIns *irl = IR(ir->op1), *irr = IR(ir->op2);
-  lua_assert(ir->o == IR_BOR);
+  lj_assertA(ir->o == IR_BOR, "bad usage");
   if (canfuse(as, irl) && canfuse(as, irr) &&
       ((irl->o == IR_BSHR && irr->o == IR_BSHL) ||
        (irl->o == IR_BSHL && irr->o == IR_BSHR))) {
@@ -428,7 +428,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
     if (ref) {
       if (irt_isfp(ir->t)) {
         if (fpr <= REGARG_LASTFPR) {
-          lua_assert(rset_test(as->freeset, fpr)); /* Must have been evicted. */
+          lj_assertA(rset_test(as->freeset, fpr),
+                     "reg %d not free", fpr);  /* Must have been evicted. */
           ra_leftov(as, fpr, ref);
           fpr++;
         } else {
@@ -438,7 +439,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
         }
       } else {
         if (gpr <= REGARG_LASTGPR) {
-          lua_assert(rset_test(as->freeset, gpr)); /* Must have been evicted. */
+          lj_assertA(rset_test(as->freeset, gpr),
+                     "reg %d not free", gpr);  /* Must have been evicted. */
           ra_leftov(as, gpr, ref);
           gpr++;
         } else {
@@ -459,7 +461,7 @@ static void asm_setupresult(ASMState *as, IRIns *ir, const CCallInfo *ci)
     rset_clear(drop, ir->r); /* Dest reg handled below. */
   ra_evictset(as, drop); /* Evictions must be performed first. */
   if (ra_used(ir)) {
-    lua_assert(!irt_ispri(ir->t));
+    lj_assertA(!irt_ispri(ir->t), "PRI dest");
     if (irt_isfp(ir->t)) {
       if (ci->flags & CCI_CASTU64) {
         Reg dest = ra_dest(as, ir, RSET_FPR) & 31;
@@ -546,7 +548,7 @@ static void asm_conv(ASMState *as, IRIns *ir)
   int st64 = (st == IRT_I64 || st == IRT_U64 || st == IRT_P64);
   int stfp = (st == IRT_NUM || st == IRT_FLOAT);
   IRRef lref = ir->op1;
-  lua_assert(irt_type(ir->t) != st);
+  lj_assertA(irt_type(ir->t) != st, "inconsistent types for CONV");
   if (irt_isfp(ir->t)) {
     Reg dest = ra_dest(as, ir, RSET_FPR);
     if (stfp) {  /* FP to FP conversion. */
@@ -566,7 +568,8 @@ static void asm_conv(ASMState *as, IRIns *ir)
   } else if (stfp) {  /* FP to integer conversion. */
     if (irt_isguard(ir->t)) {
       /* Checked conversions are only supported from number to int. */
-      lua_assert(irt_isint(ir->t) && st == IRT_NUM);
+      lj_assertA(irt_isint(ir->t) && st == IRT_NUM,
+                 "bad type for checked CONV");
       asm_tointg(as, ir, ra_alloc1(as, lref, RSET_FPR));
     } else {
       Reg left = ra_alloc1(as, lref, RSET_FPR);
@@ -586,7 +589,7 @@ static void asm_conv(ASMState *as, IRIns *ir)
     A64Ins ai = st == IRT_I8 ? A64I_SXTBw :
                 st == IRT_U8 ? A64I_UXTBw :
                 st == IRT_I16 ? A64I_SXTHw : A64I_UXTHw;
-    lua_assert(irt_isint(ir->t) || irt_isu32(ir->t));
+    lj_assertA(irt_isint(ir->t) || irt_isu32(ir->t), "bad type for CONV EXT");
     emit_dn(as, ai, dest, left);
   } else {
     Reg dest = ra_dest(as, ir, RSET_GPR);
@@ -650,7 +653,8 @@ static void asm_tvstore64(ASMState *as, Reg base, int32_t ofs, IRRef ref)
 {
   RegSet allow = rset_exclude(RSET_GPR, base);
   IRIns *ir = IR(ref);
-  lua_assert(irt_ispri(ir->t) || irt_isaddr(ir->t) || irt_isinteger(ir->t));
+  lj_assertA(irt_ispri(ir->t) || irt_isaddr(ir->t) || irt_isinteger(ir->t),
+             "store of IR type %d", irt_type(ir->t));
   if (irref_isk(ref)) {
     TValue k;
     lj_ir_kvalue(as->J->L, &k, ir);
@@ -770,7 +774,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
     }
     rset_clear(allow, scr);
   } else {
-    lua_assert(irt_ispri(kt) && !irt_isnil(kt));
+    lj_assertA(irt_ispri(kt) && !irt_isnil(kt), "bad HREF key type");
     type = ra_allock(as, ~((int64_t)~irt_toitype(ir->t) << 47), allow);
     scr = ra_scratch(as, rset_clear(allow, type));
     rset_clear(allow, scr);
@@ -831,7 +835,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
     rset_clear(allow, type);
   }
   /* Load main position relative to tab->node into dest. */
-  khash = isk ? ir_khash(irkey) : 1;
+  khash = isk ? ir_khash(as, irkey) : 1;
   if (khash == 0) {
     emit_lso(as, A64I_LDRx, dest, tab, offsetof(GCtab, node));
   } else {
@@ -886,7 +890,7 @@ static void asm_hrefk(ASMState *as, IRIns *ir)
   Reg key, idx = node;
   RegSet allow = rset_exclude(RSET_GPR, node);
   uint64_t k;
-  lua_assert(ofs % sizeof(Node) == 0);
+  lj_assertA(ofs % sizeof(Node) == 0, "unaligned HREFK slot");
   if (bigofs) {
     idx = dest;
     rset_clear(allow, dest);
@@ -936,7 +940,7 @@ static void asm_uref(ASMState *as, IRIns *ir)
 static void asm_fref(ASMState *as, IRIns *ir)
 {
   UNUSED(as); UNUSED(ir);
-  lua_assert(!ra_used(ir));
+  lj_assertA(!ra_used(ir), "unfused FREF");
 }
 
 static void asm_strref(ASMState *as, IRIns *ir)
@@ -988,7 +992,7 @@ static void asm_fload(ASMState *as, IRIns *ir)
   Reg idx;
   A64Ins ai = asm_fxloadins(ir);
   int32_t ofs;
-  if (ir->op1 == REF_NIL) {
+  if (ir->op1 == REF_NIL) {  /* FLOAD from GG_State with offset. */
     idx = RID_GL;
     ofs = (ir->op2 << 2) - GG_OFS(g);
   } else {
@@ -1019,7 +1023,7 @@ static void asm_fstore(ASMState *as, IRIns *ir)
 static void asm_xload(ASMState *as, IRIns *ir)
 {
   Reg dest = ra_dest(as, ir, irt_isfp(ir->t) ? RSET_FPR : RSET_GPR);
-  lua_assert(!(ir->op2 & IRXLOAD_UNALIGNED));
+  lj_assertA(!(ir->op2 & IRXLOAD_UNALIGNED), "unaligned XLOAD");
   asm_fusexref(as, asm_fxloadins(ir), dest, ir->op1, RSET_GPR);
 }
 
@@ -1037,8 +1041,9 @@ static void asm_ahuvload(ASMState *as, IRIns *ir)
   Reg idx, tmp, type;
   int32_t ofs = 0;
   RegSet gpr = RSET_GPR, allow = irt_isnum(ir->t) ? RSET_FPR : RSET_GPR;
-  lua_assert(irt_isnum(ir->t) || irt_ispri(ir->t) || irt_isaddr(ir->t) ||
-             irt_isint(ir->t));
+  lj_assertA(irt_isnum(ir->t) || irt_ispri(ir->t) || irt_isaddr(ir->t) ||
+             irt_isint(ir->t),
+             "bad load type %d", irt_type(ir->t));
   if (ra_used(ir)) {
     Reg dest = ra_dest(as, ir, allow);
     tmp = irt_isnum(ir->t) ? ra_scratch(as, rset_clear(gpr, dest)) : dest;
@@ -1057,7 +1062,8 @@ static void asm_ahuvload(ASMState *as, IRIns *ir)
   /* Always do the type check, even if the load result is unused. */
   asm_guardcc(as, irt_isnum(ir->t) ? CC_LS : CC_NE);
   if (irt_type(ir->t) >= IRT_NUM) {
-    lua_assert(irt_isinteger(ir->t) || irt_isnum(ir->t));
+    lj_assertA(irt_isinteger(ir->t) || irt_isnum(ir->t),
+               "bad load type %d", irt_type(ir->t));
     emit_nm(as, A64I_CMPx | A64F_SH(A64SH_LSR, 32),
             ra_allock(as, LJ_TISNUM << 15, rset_exclude(gpr, idx)), tmp);
   } else if (irt_isaddr(ir->t)) {
@@ -1122,8 +1128,10 @@ static void asm_sload(ASMState *as, IRIns *ir)
   IRType1 t = ir->t;
   Reg dest = RID_NONE, base;
   RegSet allow = RSET_GPR;
-  lua_assert(!(ir->op2 & IRSLOAD_PARENT));  /* Handled by asm_head_side(). */
-  lua_assert(irt_isguard(t) || !(ir->op2 & IRSLOAD_TYPECHECK));
+  lj_assertA(!(ir->op2 & IRSLOAD_PARENT),
+             "bad parent SLOAD");  /* Handled by asm_head_side(). */
+  lj_assertA(irt_isguard(t) || !(ir->op2 & IRSLOAD_TYPECHECK),
+             "inconsistent SLOAD variant");
   if ((ir->op2 & IRSLOAD_CONVERT) && irt_isguard(t) && irt_isint(t)) {
     dest = ra_scratch(as, RSET_FPR);
     asm_tointg(as, ir, dest);
@@ -1132,7 +1140,8 @@ static void asm_sload(ASMState *as, IRIns *ir)
     Reg tmp = RID_NONE;
     if ((ir->op2 & IRSLOAD_CONVERT))
       tmp = ra_scratch(as, irt_isint(t) ? RSET_FPR : RSET_GPR);
-    lua_assert((irt_isnum(t)) || irt_isint(t) || irt_isaddr(t));
+    lj_assertA((irt_isnum(t)) || irt_isint(t) || irt_isaddr(t),
+               "bad SLOAD type %d", irt_type(t));
     dest = ra_dest(as, ir, irt_isnum(t) ? RSET_FPR : allow);
     base = ra_alloc1(as, REF_BASE, rset_clear(allow, dest));
     if (irt_isaddr(t)) {
@@ -1172,7 +1181,8 @@ dotypecheck:
     /* Need type check, even if the load result is unused. */
     asm_guardcc(as, irt_isnum(t) ? CC_LS : CC_NE);
     if (irt_type(t) >= IRT_NUM) {
-      lua_assert(irt_isinteger(t) || irt_isnum(t));
+      lj_assertA(irt_isinteger(t) || irt_isnum(t),
+                 "bad SLOAD type %d", irt_type(t));
       emit_nm(as, A64I_CMPx | A64F_SH(A64SH_LSR, 32),
               ra_allock(as, LJ_TISNUM << 15, allow), tmp);
     } else if (irt_isnil(t)) {
@@ -1207,7 +1217,8 @@ static void asm_cnew(ASMState *as, IRIns *ir)
   const CCallInfo *ci = &lj_ir_callinfo[IRCALL_lj_mem_newgco];
   IRRef args[4];
   RegSet allow = (RSET_GPR & ~RSET_SCRATCH);
-  lua_assert(sz != CTSIZE_INVALID || (ir->o == IR_CNEW && ir->op2 != REF_NIL));
+  lj_assertA(sz != CTSIZE_INVALID || (ir->o == IR_CNEW && ir->op2 != REF_NIL),
+             "bad CNEW/CNEWI operands");
 
   as->gcsteps++;
   asm_setupresult(as, ir, ci);  /* GCcdata * */
@@ -1215,7 +1226,7 @@ static void asm_cnew(ASMState *as, IRIns *ir)
   if (ir->o == IR_CNEWI) {
     int32_t ofs = sizeof(GCcdata);
     Reg r = ra_alloc1(as, ir->op2, allow);
-    lua_assert(sz == 4 || sz == 8);
+    lj_assertA(sz == 4 || sz == 8, "bad CNEWI size %d", sz);
     emit_lso(as, sz == 8 ? A64I_STRx : A64I_STRw, r, RID_RET, ofs);
   } else if (ir->op2 != REF_NIL) {  /* Create VLA/VLS/aligned cdata. */
     ci = &lj_ir_callinfo[IRCALL_lj_cdata_newv];
@@ -1274,7 +1285,7 @@ static void asm_obar(ASMState *as, IRIns *ir)
   RegSet allow = RSET_GPR;
   Reg obj, val, tmp;
   /* No need for other object barriers (yet). */
-  lua_assert(IR(ir->op1)->o == IR_UREFC);
+  lj_assertA(IR(ir->op1)->o == IR_UREFC, "bad OBAR type");
   ra_evictset(as, RSET_SCRATCH);
   l_end = emit_label(as);
   args[0] = ASMREF_TMP1;  /* global_State *g */
@@ -1544,7 +1555,7 @@ static void asm_bitshift(ASMState *as, IRIns *ir, A64Ins ai, A64Shift sh)
 #define asm_bshr(as, ir)        asm_bitshift(as, ir, A64I_UBFMw, A64SH_LSR)
 #define asm_bsar(as, ir)        asm_bitshift(as, ir, A64I_SBFMw, A64SH_ASR)
 #define asm_bror(as, ir)        asm_bitshift(as, ir, A64I_EXTRw, A64SH_ROR)
-#define asm_brol(as, ir)        lua_assert(0)
+#define asm_brol(as, ir)        lj_assertA(0, "unexpected BROL")
 
 static void asm_intmin_max(ASMState *as, IRIns *ir, A64CC cc)
 {
@@ -1625,15 +1636,16 @@ static void asm_intcomp(ASMState *as, IRIns *ir)
   Reg left;
   uint32_t m;
   int cmpprev0 = 0;
-  lua_assert(irt_is64(ir->t) || irt_isint(ir->t) ||
-             irt_isu32(ir->t) || irt_isaddr(ir->t) || irt_isu8(ir->t));
+  lj_assertA(irt_is64(ir->t) || irt_isint(ir->t) ||
+             irt_isu32(ir->t) || irt_isaddr(ir->t) || irt_isu8(ir->t),
+             "bad comparison data type %d", irt_type(ir->t));
   if (asm_swapops(as, lref, rref)) {
     IRRef tmp = lref; lref = rref; rref = tmp;
     if (cc >= CC_GE) cc ^= 7;  /* LT <-> GT, LE <-> GE */
     else if (cc > CC_NE) cc ^= 11;  /* LO <-> HI, LS <-> HS */
   }
   oldcc = cc;
-  if (irref_isk(rref) && get_k64val(IR(rref)) == 0) {
+  if (irref_isk(rref) && get_k64val(as, rref) == 0) {
     IRIns *irl = IR(lref);
     if (cc == CC_GE) cc = CC_PL;
     else if (cc == CC_LT) cc = CC_MI;
@@ -1648,7 +1660,7 @@ static void asm_intcomp(ASMState *as, IRIns *ir)
         Reg tmp = blref; blref = brref; brref = tmp;
       }
       if (irref_isk(brref)) {
-        uint64_t k = get_k64val(IR(brref));
+        uint64_t k = get_k64val(as, brref);
         if (k && !(k & (k-1)) && (cc == CC_EQ || cc == CC_NE)) {
           asm_guardtnb(as, cc == CC_EQ ? A64I_TBZ : A64I_TBNZ,
                        ra_alloc1(as, blref, RSET_GPR), emit_ctz64(k));
@@ -1697,7 +1709,8 @@ static void asm_comp(ASMState *as, IRIns *ir)
 /* Hiword op of a split 64 bit op. Previous op must be the loword op. */
 static void asm_hiop(ASMState *as, IRIns *ir)
 {
-  UNUSED(as); UNUSED(ir); lua_assert(0);  /* Unused on 64 bit. */
+  UNUSED(as); UNUSED(ir);
+  lj_assertA(0, "unexpected HIOP");  /* Unused on 64 bit. */
 }
 
 /* -- Profiling ----------------------------------------------------------- */
@@ -1705,7 +1718,7 @@ static void asm_hiop(ASMState *as, IRIns *ir)
 static void asm_prof(ASMState *as, IRIns *ir)
 {
   uint32_t k = emit_isk13(HOOK_PROFILE, 0);
-  lua_assert(k != 0);
+  lj_assertA(k != 0, "HOOK_PROFILE does not fit in K13");
   UNUSED(ir);
   asm_guardcc(as, CC_NE);
   emit_n(as, A64I_TSTw^k, RID_TMP);
@@ -1723,7 +1736,7 @@ static void asm_stack_check(ASMState *as, BCReg topslot,
   if (irp) {
     if (!ra_hasspill(irp->s)) {
       pbase = irp->r;
-      lua_assert(ra_hasreg(pbase));
+      lj_assertA(ra_hasreg(pbase), "base reg lost");
     } else if (allow) {
       pbase = rset_pickbot(allow);
     } else {
@@ -1735,7 +1748,7 @@ static void asm_stack_check(ASMState *as, BCReg topslot,
   }
   emit_cond_branch(as, CC_LS, asm_exitstub_addr(as, exitno));
   k = emit_isk12((8*topslot));
-  lua_assert(k);
+  lj_assertA(k, "slot offset %d does not fit in K12", 8*topslot);
   emit_n(as, A64I_CMPx^k, RID_TMP);
   emit_dnm(as, A64I_SUBx, RID_TMP, RID_TMP, pbase);
   emit_lso(as, A64I_LDRx, RID_TMP, RID_TMP,
@@ -1776,7 +1789,7 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
     }
     checkmclim(as);
   }
-  lua_assert(map + nent == flinks);
+  lj_assertA(map + nent == flinks, "inconsistent frames in snapshot");
 }
 
 /* -- GC handling --------------------------------------------------------- */
@@ -1864,7 +1877,7 @@ static RegSet asm_head_side_base(ASMState *as, IRIns *irp, RegSet allow)
     rset_clear(allow, ra_dest(as, ir, allow));
   } else {
     Reg r = irp->r;
-    lua_assert(ra_hasreg(r));
+    lj_assertA(ra_hasreg(r), "base reg lost");
     rset_clear(allow, r);
     if (r != ir->r && !rset_test(as->freeset, r))
       ra_restore(as, regcost_ref(as->cost[r]));
@@ -1888,7 +1901,7 @@ static void asm_tail_fixup(ASMState *as, TraceNo lnk)
   } else {
     /* Patch stack adjustment. */
     uint32_t k = emit_isk12(spadj);
-    lua_assert(k);
+    lj_assertA(k, "stack adjustment %d does not fit in K12", spadj);
     p[-2] = (A64I_ADDx^k) | A64F_D(RID_SP) | A64F_N(RID_SP);
   }
   /* Patch exit branch. */
@@ -1974,7 +1987,7 @@ void lj_asm_patchexit(jit_State *J, GCtrace *T, ExitNo exitno, MCode *target)
     } else if ((ins & 0xfc000000u) == 0x14000000u &&
                ((ins ^ (px-p)) & 0x03ffffffu) == 0) {
       /* Patch b. */
-      lua_assert(A64F_S_OK(delta, 26));
+      lj_assertJ(A64F_S_OK(delta, 26), "branch target out of range");
       *p = A64I_LE((ins & 0xfc000000u) | A64F_S26(delta));
       if (!cstart) cstart = p;
     } else if ((ins & 0x7e000000u) == 0x34000000u &&
@@ -1995,7 +2008,7 @@ void lj_asm_patchexit(jit_State *J, GCtrace *T, ExitNo exitno, MCode *target)
   }
   {  /* Always patch long-range branch in exit stub itself. */
     ptrdiff_t delta = target - px;
-    lua_assert(A64F_S_OK(delta, 26));
+    lj_assertJ(A64F_S_OK(delta, 26), "branch target out of range");
     *px = A64I_B | A64F_S26(delta);
     if (!cstart) cstart = px;
   }
diff --git a/src/lj_asm_mips.h b/src/lj_asm_mips.h
index 6d898c5f..a2b8d8e0 100644
--- a/src/lj_asm_mips.h
+++ b/src/lj_asm_mips.h
@@ -23,7 +23,7 @@ static Reg ra_alloc1z(ASMState *as, IRRef ref, RegSet allow)
 {
   Reg r = IR(ref)->r;
   if (ra_noreg(r)) {
-    if (!(allow & RSET_FPR) && irref_isk(ref) && get_kval(IR(ref)) == 0)
+    if (!(allow & RSET_FPR) && irref_isk(ref) && get_kval(as, ref) == 0)
       return RID_ZERO;
     r = ra_allocref(as, ref, allow);
   } else {
@@ -66,10 +66,10 @@ static void asm_sparejump_setup(ASMState *as)
 {
   MCode *mxp = as->mcbot;
   if (((uintptr_t)mxp & (LJ_PAGESIZE-1)) == sizeof(MCLink)) {
-    lua_assert(MIPSI_NOP == 0);
+    lj_assertA(MIPSI_NOP == 0, "bad NOP");
     memset(mxp, 0, MIPS_SPAREJUMP*2*sizeof(MCode));
     mxp += MIPS_SPAREJUMP*2;
-    lua_assert(mxp < as->mctop);
+    lj_assertA(mxp < as->mctop, "MIPS_SPAREJUMP too big");
     lj_mcode_sync(as->mcbot, mxp);
     lj_mcode_commitbot(as->J, mxp);
     as->mcbot = mxp;
@@ -84,7 +84,8 @@ static void asm_exitstub_setup(ASMState *as)
   /* sw TMP, 0(sp); j ->vm_exit_handler; li TMP, traceno */
   *--mxp = MIPSI_LI|MIPSF_T(RID_TMP)|as->T->traceno;
   *--mxp = MIPSI_J|((((uintptr_t)(void *)lj_vm_exit_handler)>>2)&0x03ffffffu);
-  lua_assert(((uintptr_t)mxp ^ (uintptr_t)(void *)lj_vm_exit_handler)>>28 == 0);
+  lj_assertA(((uintptr_t)mxp ^ (uintptr_t)(void *)lj_vm_exit_handler)>>28 == 0,
+             "branch target out of range");
   *--mxp = MIPSI_SW|MIPSF_T(RID_TMP)|MIPSF_S(RID_SP)|0;
   as->mctop = mxp;
 }
@@ -195,20 +196,20 @@ static void asm_fusexref(ASMState *as, MIPSIns mi, Reg rt, IRRef ref,
   if (ra_noreg(ir->r) && canfuse(as, ir)) {
     if (ir->o == IR_ADD) {
       intptr_t ofs2;
-      if (irref_isk(ir->op2) && (ofs2 = ofs + get_kval(IR(ir->op2)),
+      if (irref_isk(ir->op2) && (ofs2 = ofs + get_kval(as, ir->op2),
                                  checki16(ofs2))) {
         ref = ir->op1;
         ofs = (int32_t)ofs2;
       }
     } else if (ir->o == IR_STRREF) {
       intptr_t ofs2 = 65536;
-      lua_assert(ofs == 0);
+      lj_assertA(ofs == 0, "bad usage");
       ofs = (int32_t)sizeof(GCstr);
       if (irref_isk(ir->op2)) {
-        ofs2 = ofs + get_kval(IR(ir->op2));
+        ofs2 = ofs + get_kval(as, ir->op2);
         ref = ir->op1;
       } else if (irref_isk(ir->op1)) {
-        ofs2 = ofs + get_kval(IR(ir->op1));
+        ofs2 = ofs + get_kval(as, ir->op1);
         ref = ir->op2;
       }
       if (!checki16(ofs2)) {
@@ -252,7 +253,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 #if !LJ_SOFTFP
       if (irt_isfp(ir->t) && fpr <= REGARG_LASTFPR &&
           !(ci->flags & CCI_VARARG)) {
-        lua_assert(rset_test(as->freeset, fpr));  /* Already evicted. */
+        lj_assertA(rset_test(as->freeset, fpr),
+                   "reg %d not free", fpr);  /* Already evicted. */
         ra_leftov(as, fpr, ref);
         fpr += LJ_32 ? 2 : 1;
         gpr += (LJ_32 && irt_isnum(ir->t)) ? 2 : 1;
@@ -264,7 +266,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 #endif
         if (LJ_32 && irt_isnum(ir->t)) gpr = (gpr+1) & ~1;
         if (gpr <= REGARG_LASTGPR) {
-          lua_assert(rset_test(as->freeset, gpr));  /* Already evicted. */
+          lj_assertA(rset_test(as->freeset, gpr),
+                     "reg %d not free", gpr);  /* Already evicted. */
 #if !LJ_SOFTFP
           if (irt_isfp(ir->t)) {
             RegSet of = as->freeset;
@@ -277,7 +280,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 #if LJ_32
               emit_tg(as, MIPSI_MFC1, gpr+(LJ_BE?0:1), r+1);
               emit_tg(as, MIPSI_MFC1, gpr+(LJ_BE?1:0), r);
-              lua_assert(rset_test(as->freeset, gpr+1));  /* Already evicted. */
+              lj_assertA(rset_test(as->freeset, gpr+1),
+                         "reg %d not free", gpr+1);  /* Already evicted. */
               gpr += 2;
 #else
               emit_tg(as, MIPSI_DMFC1, gpr, r);
@@ -347,7 +351,7 @@ static void asm_setupresult(ASMState *as, IRIns *ir, const CCallInfo *ci)
 #endif
   ra_evictset(as, drop);  /* Evictions must be performed first. */
   if (ra_used(ir)) {
-    lua_assert(!irt_ispri(ir->t));
+    lj_assertA(!irt_ispri(ir->t), "PRI dest");
     if (!LJ_SOFTFP && irt_isfp(ir->t)) {
       if ((ci->flags & CCI_CASTU64)) {
         int32_t ofs = sps_scale(ir->s);
@@ -395,7 +399,7 @@ static void asm_callx(ASMState *as, IRIns *ir)
   func = ir->op2; irf = IR(func);
   if (irf->o == IR_CARG) { func = irf->op1; irf = IR(func); }
   if (irref_isk(func)) {  /* Call to constant address. */
-    ci.func = (ASMFunction)(void *)get_kval(irf);
+    ci.func = (ASMFunction)(void *)get_kval(as, func);
   } else {  /* Need specific register for indirect calls. */
     Reg r = ra_alloc1(as, func, RID2RSET(RID_CFUNCADDR));
     MCode *p = as->mcp;
@@ -512,15 +516,19 @@ static void asm_conv(ASMState *as, IRIns *ir)
 #endif
   IRRef lref = ir->op1;
 #if LJ_32
-  lua_assert(!(irt_isint64(ir->t) ||
-               (st == IRT_I64 || st == IRT_U64))); /* Handled by SPLIT. */
+  /* 64 bit integer conversions are handled by SPLIT. */
+  lj_assertA(!(irt_isint64(ir->t) || (st == IRT_I64 || st == IRT_U64)),
+             "IR %04d has unsplit 64 bit type",
+             (int)(ir - as->ir) - REF_BIAS);
 #endif
 #if LJ_SOFTFP32
   /* FP conversions are handled by SPLIT. */
-  lua_assert(!irt_isfp(ir->t) && !(st == IRT_NUM || st == IRT_FLOAT));
+  lj_assertA(!irt_isfp(ir->t) && !(st == IRT_NUM || st == IRT_FLOAT),
+             "IR %04d has FP type",
+             (int)(ir - as->ir) - REF_BIAS);
   /* Can't check for same types: SPLIT uses CONV int.int + BXOR for sfp NEG. */
 #else
-  lua_assert(irt_type(ir->t) != st);
+  lj_assertA(irt_type(ir->t) != st, "inconsistent types for CONV");
 #if !LJ_SOFTFP
   if (irt_isfp(ir->t)) {
     Reg dest = ra_dest(as, ir, RSET_FPR);
@@ -579,7 +587,8 @@ static void asm_conv(ASMState *as, IRIns *ir)
   } else if (stfp) {  /* FP to integer conversion. */
     if (irt_isguard(ir->t)) {
       /* Checked conversions are only supported from number to int. */
-      lua_assert(irt_isint(ir->t) && st == IRT_NUM);
+      lj_assertA(irt_isint(ir->t) && st == IRT_NUM,
+                 "bad type for checked CONV");
       asm_tointg(as, ir, ra_alloc1(as, lref, RSET_FPR));
     } else {
       Reg dest = ra_dest(as, ir, RSET_GPR);
@@ -679,7 +688,8 @@ static void asm_conv(ASMState *as, IRIns *ir)
   } else if (stfp) {  /* FP to integer conversion. */
     if (irt_isguard(ir->t)) {
       /* Checked conversions are only supported from number to int. */
-      lua_assert(irt_isint(ir->t) && st == IRT_NUM);
+      lj_assertA(irt_isint(ir->t) && st == IRT_NUM,
+                 "bad type for checked CONV");
       asm_tointg(as, ir, RID_NONE);
     } else {
       IRCallID cid = irt_is64(ir->t) ?
@@ -698,7 +708,7 @@ static void asm_conv(ASMState *as, IRIns *ir)
     Reg dest = ra_dest(as, ir, RSET_GPR);
     if (st >= IRT_I8 && st <= IRT_U16) {  /* Extend to 32 bit integer. */
       Reg left = ra_alloc1(as, ir->op1, RSET_GPR);
-      lua_assert(irt_isint(ir->t) || irt_isu32(ir->t));
+      lj_assertA(irt_isint(ir->t) || irt_isu32(ir->t), "bad type for CONV EXT");
       if ((ir->op2 & IRCONV_SEXT)) {
         if (LJ_64 || (as->flags & JIT_F_MIPSXXR2)) {
           emit_dst(as, st == IRT_I8 ? MIPSI_SEB : MIPSI_SEH, dest, 0, left);
@@ -795,7 +805,8 @@ static void asm_tvstore64(ASMState *as, Reg base, int32_t ofs, IRRef ref)
 {
   RegSet allow = rset_exclude(RSET_GPR, base);
   IRIns *ir = IR(ref);
-  lua_assert(irt_ispri(ir->t) || irt_isaddr(ir->t) || irt_isinteger(ir->t));
+  lj_assertA(irt_ispri(ir->t) || irt_isaddr(ir->t) || irt_isinteger(ir->t),
+             "store of IR type %d", irt_type(ir->t));
   if (irref_isk(ref)) {
     TValue k;
     lj_ir_kvalue(as->J->L, &k, ir);
@@ -944,7 +955,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
       if (isk && irt_isaddr(kt)) {
         k = ((int64_t)irt_toitype(irkey->t) << 47) | irkey[1].tv.u64;
       } else {
-        lua_assert(irt_ispri(kt) && !irt_isnil(kt));
+        lj_assertA(irt_ispri(kt) && !irt_isnil(kt), "bad HREF key type");
         k = ~((int64_t)~irt_toitype(ir->t) << 47);
       }
       cmp64 = ra_allock(as, k, allow);
@@ -1012,7 +1023,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
 #endif
 
   /* Load main position relative to tab->node into dest. */
-  khash = isk ? ir_khash(irkey) : 1;
+  khash = isk ? ir_khash(as, irkey) : 1;
   if (khash == 0) {
     emit_tsi(as, MIPSI_AL, dest, tab, (int32_t)offsetof(GCtab, node));
   } else {
@@ -1020,7 +1031,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
     if (isk)
       tmphash = ra_allock(as, khash, allow);
     emit_dst(as, MIPSI_AADDU, dest, dest, tmp1);
-    lua_assert(sizeof(Node) == 24);
+    lj_assertA(sizeof(Node) == 24, "bad Node size");
     emit_dst(as, MIPSI_SUBU, tmp1, tmp2, tmp1);
     emit_dta(as, MIPSI_SLL, tmp1, tmp1, 3);
     emit_dta(as, MIPSI_SLL, tmp2, tmp1, 5);
@@ -1098,7 +1109,7 @@ static void asm_hrefk(ASMState *as, IRIns *ir)
   Reg key = ra_scratch(as, allow);
   int64_t k;
 #endif
-  lua_assert(ofs % sizeof(Node) == 0);
+  lj_assertA(ofs % sizeof(Node) == 0, "unaligned HREFK slot");
   if (ofs > 32736) {
     idx = dest;
     rset_clear(allow, dest);
@@ -1127,7 +1138,7 @@ nolo:
   emit_tsi(as, MIPSI_LW, type, idx, kofs+(LJ_BE?0:4));
 #else
   if (irt_ispri(irkey->t)) {
-    lua_assert(!irt_isnil(irkey->t));
+    lj_assertA(!irt_isnil(irkey->t), "bad HREFK key type");
     k = ~((int64_t)~irt_toitype(irkey->t) << 47);
   } else if (irt_isnum(irkey->t)) {
     k = (int64_t)ir_knum(irkey)->u64;
@@ -1166,7 +1177,7 @@ static void asm_uref(ASMState *as, IRIns *ir)
 static void asm_fref(ASMState *as, IRIns *ir)
 {
   UNUSED(as); UNUSED(ir);
-  lua_assert(!ra_used(ir));
+  lj_assertA(!ra_used(ir), "unfused FREF");
 }
 
 static void asm_strref(ASMState *as, IRIns *ir)
@@ -1221,14 +1232,17 @@ static void asm_strref(ASMState *as, IRIns *ir)
 
 /* -- Loads and stores ---------------------------------------------------- */
 
-static MIPSIns asm_fxloadins(IRIns *ir)
+static MIPSIns asm_fxloadins(ASMState *as, IRIns *ir)
 {
+  UNUSED(as);
   switch (irt_type(ir->t)) {
   case IRT_I8: return MIPSI_LB;
   case IRT_U8: return MIPSI_LBU;
   case IRT_I16: return MIPSI_LH;
   case IRT_U16: return MIPSI_LHU;
-  case IRT_NUM: lua_assert(!LJ_SOFTFP32); if (!LJ_SOFTFP) return MIPSI_LDC1;
+  case IRT_NUM:
+    lj_assertA(!LJ_SOFTFP32, "unsplit FP op");
+    if (!LJ_SOFTFP) return MIPSI_LDC1;
   /* fallthrough */
   case IRT_FLOAT: if (!LJ_SOFTFP) return MIPSI_LWC1;
   /* fallthrough */
@@ -1236,12 +1250,15 @@ static MIPSIns asm_fxloadins(IRIns *ir)
   }
 }
 
-static MIPSIns asm_fxstoreins(IRIns *ir)
+static MIPSIns asm_fxstoreins(ASMState *as, IRIns *ir)
 {
+  UNUSED(as);
   switch (irt_type(ir->t)) {
   case IRT_I8: case IRT_U8: return MIPSI_SB;
   case IRT_I16: case IRT_U16: return MIPSI_SH;
-  case IRT_NUM: lua_assert(!LJ_SOFTFP32); if (!LJ_SOFTFP) return MIPSI_SDC1;
+  case IRT_NUM:
+    lj_assertA(!LJ_SOFTFP32, "unsplit FP op");
+    if (!LJ_SOFTFP) return MIPSI_SDC1;
   /* fallthrough */
   case IRT_FLOAT: if (!LJ_SOFTFP) return MIPSI_SWC1;
   /* fallthrough */
@@ -1252,10 +1269,10 @@ static MIPSIns asm_fxstoreins(IRIns *ir)
 static void asm_fload(ASMState *as, IRIns *ir)
 {
   Reg dest = ra_dest(as, ir, RSET_GPR);
-  MIPSIns mi = asm_fxloadins(ir);
+  MIPSIns mi = asm_fxloadins(as, ir);
   Reg idx;
   int32_t ofs;
-  if (ir->op1 == REF_NIL) {
+  if (ir->op1 == REF_NIL) {  /* FLOAD from GG_State with offset. */
     idx = RID_JGL;
     ofs = (ir->op2 << 2) - 32768 - GG_OFS(g);
   } else {
@@ -1269,7 +1286,7 @@ static void asm_fload(ASMState *as, IRIns *ir)
     }
     ofs = field_ofs[ir->op2];
   }
-  lua_assert(!irt_isfp(ir->t));
+  lj_assertA(!irt_isfp(ir->t), "bad FP FLOAD");
   emit_tsi(as, mi, dest, idx, ofs);
 }
 
@@ -1280,8 +1297,8 @@ static void asm_fstore(ASMState *as, IRIns *ir)
     IRIns *irf = IR(ir->op1);
     Reg idx = ra_alloc1(as, irf->op1, rset_exclude(RSET_GPR, src));
     int32_t ofs = field_ofs[irf->op2];
-    MIPSIns mi = asm_fxstoreins(ir);
-    lua_assert(!irt_isfp(ir->t));
+    MIPSIns mi = asm_fxstoreins(as, ir);
+    lj_assertA(!irt_isfp(ir->t), "bad FP FSTORE");
     emit_tsi(as, mi, src, idx, ofs);
   }
 }
@@ -1290,8 +1307,9 @@ static void asm_xload(ASMState *as, IRIns *ir)
 {
   Reg dest = ra_dest(as, ir,
     (!LJ_SOFTFP && irt_isfp(ir->t)) ? RSET_FPR : RSET_GPR);
-  lua_assert(LJ_TARGET_UNALIGNED || !(ir->op2 & IRXLOAD_UNALIGNED));
-  asm_fusexref(as, asm_fxloadins(ir), dest, ir->op1, RSET_GPR, 0);
+  lj_assertA(LJ_TARGET_UNALIGNED || !(ir->op2 & IRXLOAD_UNALIGNED),
+             "unaligned XLOAD");
+  asm_fusexref(as, asm_fxloadins(as, ir), dest, ir->op1, RSET_GPR, 0);
 }
 
 static void asm_xstore_(ASMState *as, IRIns *ir, int32_t ofs)
@@ -1299,7 +1317,7 @@ static void asm_xstore_(ASMState *as, IRIns *ir, int32_t ofs)
   if (ir->r != RID_SINK) {
     Reg src = ra_alloc1z(as, ir->op2,
       (!LJ_SOFTFP && irt_isfp(ir->t)) ? RSET_FPR : RSET_GPR);
-    asm_fusexref(as, asm_fxstoreins(ir), src, ir->op1,
+    asm_fusexref(as, asm_fxstoreins(as, ir), src, ir->op1,
                  rset_exclude(RSET_GPR, src), ofs);
   }
 }
@@ -1321,8 +1339,9 @@ static void asm_ahuvload(ASMState *as, IRIns *ir)
     }
   }
   if (ra_used(ir)) {
-    lua_assert((LJ_SOFTFP32 ? 0 : irt_isnum(ir->t)) ||
-               irt_isint(ir->t) || irt_isaddr(ir->t));
+    lj_assertA((LJ_SOFTFP32 ? 0 : irt_isnum(ir->t)) ||
+               irt_isint(ir->t) || irt_isaddr(ir->t),
+               "bad load type %d", irt_type(ir->t));
     dest = ra_dest(as, ir, (!LJ_SOFTFP && irt_isnum(t)) ? RSET_FPR : allow);
     rset_clear(allow, dest);
 #if LJ_64
@@ -1427,10 +1446,13 @@ static void asm_sload(ASMState *as, IRIns *ir)
 #else
   int32_t ofs = 8*((int32_t)ir->op1-2);
 #endif
-  lua_assert(!(ir->op2 & IRSLOAD_PARENT));  /* Handled by asm_head_side(). */
-  lua_assert(irt_isguard(ir->t) || !(ir->op2 & IRSLOAD_TYPECHECK));
+  lj_assertA(!(ir->op2 & IRSLOAD_PARENT),
+             "bad parent SLOAD");  /* Handled by asm_head_side(). */
+  lj_assertA(irt_isguard(ir->t) || !(ir->op2 & IRSLOAD_TYPECHECK),
+             "inconsistent SLOAD variant");
 #if LJ_SOFTFP32
-  lua_assert(!(ir->op2 & IRSLOAD_CONVERT));  /* Handled by LJ_SOFTFP SPLIT. */
+  lj_assertA(!(ir->op2 & IRSLOAD_CONVERT),
+             "unsplit SLOAD convert");  /* Handled by LJ_SOFTFP SPLIT. */
   if (hiop && ra_used(ir+1)) {
     type = ra_dest(as, ir+1, allow);
     rset_clear(allow, type);
@@ -1443,8 +1465,9 @@ static void asm_sload(ASMState *as, IRIns *ir)
   } else
 #endif
   if (ra_used(ir)) {
-    lua_assert((LJ_SOFTFP32 ? 0 : irt_isnum(ir->t)) ||
-               irt_isint(ir->t) || irt_isaddr(ir->t));
+    lj_assertA((LJ_SOFTFP32 ? 0 : irt_isnum(ir->t)) ||
+               irt_isint(ir->t) || irt_isaddr(ir->t),
+               "bad SLOAD type %d", irt_type(ir->t));
     dest = ra_dest(as, ir, (!LJ_SOFTFP && irt_isnum(t)) ? RSET_FPR : allow);
     rset_clear(allow, dest);
     base = ra_alloc1(as, REF_BASE, allow);
@@ -1554,7 +1577,8 @@ static void asm_cnew(ASMState *as, IRIns *ir)
   const CCallInfo *ci = &lj_ir_callinfo[IRCALL_lj_mem_newgco];
   IRRef args[4];
   RegSet drop = RSET_SCRATCH;
-  lua_assert(sz != CTSIZE_INVALID || (ir->o == IR_CNEW && ir->op2 != REF_NIL));
+  lj_assertA(sz != CTSIZE_INVALID || (ir->o == IR_CNEW && ir->op2 != REF_NIL),
+             "bad CNEW/CNEWI operands");
 
   as->gcsteps++;
   if (ra_hasreg(ir->r))
@@ -1570,7 +1594,7 @@ static void asm_cnew(ASMState *as, IRIns *ir)
     int32_t ofs = sizeof(GCcdata);
     if (sz == 8) {
       ofs += 4;
-      lua_assert((ir+1)->o == IR_HIOP);
+      lj_assertA((ir+1)->o == IR_HIOP, "expected HIOP for CNEWI");
       if (LJ_LE) ir++;
     }
     for (;;) {
@@ -1584,7 +1608,7 @@ static void asm_cnew(ASMState *as, IRIns *ir)
     emit_tsi(as, sz == 8 ? MIPSI_SD : MIPSI_SW, ra_alloc1(as, ir->op2, allow),
              RID_RET, sizeof(GCcdata));
 #endif
-    lua_assert(sz == 4 || sz == 8);
+    lj_assertA(sz == 4 || sz == 8, "bad CNEWI size %d", sz);
   } else if (ir->op2 != REF_NIL) {  /* Create VLA/VLS/aligned cdata. */
     ci = &lj_ir_callinfo[IRCALL_lj_cdata_newv];
     args[0] = ASMREF_L;     /* lua_State *L */
@@ -1634,7 +1658,7 @@ static void asm_obar(ASMState *as, IRIns *ir)
   MCLabel l_end;
   Reg obj, val, tmp;
   /* No need for other object barriers (yet). */
-  lua_assert(IR(ir->op1)->o == IR_UREFC);
+  lj_assertA(IR(ir->op1)->o == IR_UREFC, "bad OBAR type");
   ra_evictset(as, RSET_SCRATCH);
   l_end = emit_label(as);
   args[0] = ASMREF_TMP1;  /* global_State *g */
@@ -1709,7 +1733,7 @@ static void asm_add(ASMState *as, IRIns *ir)
     Reg dest = ra_dest(as, ir, RSET_GPR);
     Reg right, left = ra_hintalloc(as, ir->op1, dest, RSET_GPR);
     if (irref_isk(ir->op2)) {
-      intptr_t k = get_kval(IR(ir->op2));
+      intptr_t k = get_kval(as, ir->op2);
       if (checki16(k)) {
         emit_tsi(as, (LJ_64 && irt_is64(t)) ? MIPSI_DADDIU : MIPSI_ADDIU, dest,
                  left, k);
@@ -1810,7 +1834,7 @@ static void asm_arithov(ASMState *as, IRIns *ir)
 {
   /* TODO MIPSR6: bovc/bnvc. Caveat: no delay slot to load RID_TMP. */
   Reg right, left, tmp, dest = ra_dest(as, ir, RSET_GPR);
-  lua_assert(!irt_is64(ir->t));
+  lj_assertA(!irt_is64(ir->t), "bad usage");
   if (irref_isk(ir->op2)) {
     int k = IR(ir->op2)->i;
     if (ir->o == IR_SUBOV) k = -k;
@@ -1997,7 +2021,7 @@ static void asm_bitop(ASMState *as, IRIns *ir, MIPSIns mi, MIPSIns mik)
   Reg dest = ra_dest(as, ir, RSET_GPR);
   Reg right, left = ra_hintalloc(as, ir->op1, dest, RSET_GPR);
   if (irref_isk(ir->op2)) {
-    intptr_t k = get_kval(IR(ir->op2));
+    intptr_t k = get_kval(as, ir->op2);
     if (checku16(k)) {
       emit_tsi(as, mik, dest, left, k);
       return;
@@ -2030,7 +2054,7 @@ static void asm_bitshift(ASMState *as, IRIns *ir, MIPSIns mi, MIPSIns mik)
 #define asm_bshl(as, ir)        asm_bitshift(as, ir, MIPSI_SLLV, MIPSI_SLL)
 #define asm_bshr(as, ir)        asm_bitshift(as, ir, MIPSI_SRLV, MIPSI_SRL)
 #define asm_bsar(as, ir)        asm_bitshift(as, ir, MIPSI_SRAV, MIPSI_SRA)
-#define asm_brol(as, ir)        lua_assert(0)
+#define asm_brol(as, ir)        lj_assertA(0, "unexpected BROL")
 
 static void asm_bror(ASMState *as, IRIns *ir)
 {
@@ -2222,13 +2246,13 @@ static void asm_comp(ASMState *as, IRIns *ir)
   } else {
     Reg right, left = ra_alloc1(as, ir->op1, RSET_GPR);
     if (op == IR_ABC) op = IR_UGT;
-    if ((op&4) == 0 && irref_isk(ir->op2) && get_kval(IR(ir->op2)) == 0) {
+    if ((op&4) == 0 && irref_isk(ir->op2) && get_kval(as, ir->op2) == 0) {
       MIPSIns mi = (op&2) ? ((op&1) ? MIPSI_BLEZ : MIPSI_BGTZ) :
                             ((op&1) ? MIPSI_BLTZ : MIPSI_BGEZ);
       asm_guard(as, mi, left, 0);
     } else {
       if (irref_isk(ir->op2)) {
-        intptr_t k = get_kval(IR(ir->op2));
+        intptr_t k = get_kval(as, ir->op2);
         if ((op&2)) k++;
         if (checki16(k)) {
           asm_guard(as, (op&1) ? MIPSI_BNE : MIPSI_BEQ, RID_TMP, RID_ZERO);
@@ -2384,10 +2408,11 @@ static void asm_hiop(ASMState *as, IRIns *ir)
   case IR_CNEWI:
     /* Nothing to do here. Handled by lo op itself. */
     break;
-  default: lua_assert(0); break;
+  default: lj_assertA(0, "bad HIOP for op %d", (ir-1)->o); break;
   }
 #else
-  UNUSED(as); UNUSED(ir); lua_assert(0);  /* Unused without FFI. */
+  /* Unused on MIPS64 or without SOFTFP or FFI. */
+  UNUSED(as); UNUSED(ir); lj_assertA(0, "unexpected HIOP");
 #endif
 }
 
@@ -2456,7 +2481,8 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
 #if LJ_SOFTFP32
       Reg tmp;
       RegSet allow = rset_exclude(RSET_GPR, RID_BASE);
-      lua_assert(irref_isk(ref));  /* LJ_SOFTFP: must be a number constant. */
+      /* LJ_SOFTFP: must be a number constant. */
+      lj_assertA(irref_isk(ref), "unsplit FP op");
       tmp = ra_allock(as, (int32_t)ir_knum(ir)->u32.lo, allow);
       emit_tsi(as, MIPSI_SW, tmp, RID_BASE, ofs+(LJ_BE?4:0));
       if (rset_test(as->freeset, tmp+1)) allow = RID2RSET(tmp+1);
@@ -2473,7 +2499,8 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
 #if LJ_32
       RegSet allow = rset_exclude(RSET_GPR, RID_BASE);
       Reg type;
-      lua_assert(irt_ispri(ir->t) || irt_isaddr(ir->t) || irt_isinteger(ir->t));
+      lj_assertA(irt_ispri(ir->t) || irt_isaddr(ir->t) || irt_isinteger(ir->t),
+                 "restore of IR type %d", irt_type(ir->t));
       if (!irt_ispri(ir->t)) {
         Reg src = ra_alloc1(as, ref, allow);
         rset_clear(allow, src);
@@ -2496,7 +2523,7 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
     }
     checkmclim(as);
   }
-  lua_assert(map + nent == flinks);
+  lj_assertA(map + nent == flinks, "inconsistent frames in snapshot");
 }
 
 /* -- GC handling --------------------------------------------------------- */
@@ -2694,7 +2721,7 @@ void lj_asm_patchexit(jit_State *J, GCtrace *T, ExitNo exitno, MCode *target)
         }
       } else if (p+1 == pe) {
         /* Patch NOP after code for inverted loop branch. Use of J is ok. */
-        lua_assert(p[1] == MIPSI_NOP);
+        lj_assertJ(p[1] == MIPSI_NOP, "expected NOP");
         p[1] = tjump;
         *p = MIPSI_NOP;  /* Replace the load of the exit number. */
         cstop = p+2;
diff --git a/src/lj_asm_ppc.h b/src/lj_asm_ppc.h
index c15b89fe..498fdac3 100644
--- a/src/lj_asm_ppc.h
+++ b/src/lj_asm_ppc.h
@@ -181,7 +181,7 @@ static void asm_fusexref(ASMState *as, PPCIns pi, Reg rt, IRRef ref,
         return;
       }
     } else if (ir->o == IR_STRREF) {
-      lua_assert(ofs == 0);
+      lj_assertA(ofs == 0, "bad usage");
       ofs = (int32_t)sizeof(GCstr);
       if (irref_isk(ir->op2)) {
         ofs += IR(ir->op2)->i;
@@ -268,7 +268,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 #if !LJ_SOFTFP
       if (irt_isfp(ir->t)) {
         if (fpr <= REGARG_LASTFPR) {
-          lua_assert(rset_test(as->freeset, fpr));  /* Already evicted. */
+          lj_assertA(rset_test(as->freeset, fpr),
+                     "reg %d not free", fpr);  /* Already evicted. */
           ra_leftov(as, fpr, ref);
           fpr++;
         } else {
@@ -281,7 +282,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 #endif
       {
         if (gpr <= REGARG_LASTGPR) {
-          lua_assert(rset_test(as->freeset, gpr));  /* Already evicted. */
+          lj_assertA(rset_test(as->freeset, gpr),
+                     "reg %d not free", gpr);  /* Already evicted. */
           ra_leftov(as, gpr, ref);
           gpr++;
         } else {
@@ -319,7 +321,7 @@ static void asm_setupresult(ASMState *as, IRIns *ir, const CCallInfo *ci)
     rset_clear(drop, (ir+1)->r);  /* Dest reg handled below. */
   ra_evictset(as, drop);  /* Evictions must be performed first. */
   if (ra_used(ir)) {
-    lua_assert(!irt_ispri(ir->t));
+    lj_assertA(!irt_ispri(ir->t), "PRI dest");
     if (!LJ_SOFTFP && irt_isfp(ir->t)) {
       if ((ci->flags & CCI_CASTU64)) {
         /* Use spill slot or temp slots. */
@@ -431,14 +433,18 @@ static void asm_conv(ASMState *as, IRIns *ir)
   int stfp = (st == IRT_NUM || st == IRT_FLOAT);
 #endif
   IRRef lref = ir->op1;
-  lua_assert(!(irt_isint64(ir->t) ||
-               (st == IRT_I64 || st == IRT_U64))); /* Handled by SPLIT. */
+  /* 64 bit integer conversions are handled by SPLIT. */
+  lj_assertA(!(irt_isint64(ir->t) || (st == IRT_I64 || st == IRT_U64)),
+             "IR %04d has unsplit 64 bit type",
+             (int)(ir - as->ir) - REF_BIAS);
 #if LJ_SOFTFP
   /* FP conversions are handled by SPLIT. */
-  lua_assert(!irt_isfp(ir->t) && !(st == IRT_NUM || st == IRT_FLOAT));
+  lj_assertA(!irt_isfp(ir->t) && !(st == IRT_NUM || st == IRT_FLOAT),
+             "IR %04d has FP type",
+             (int)(ir - as->ir) - REF_BIAS);
   /* Can't check for same types: SPLIT uses CONV int.int + BXOR for sfp NEG. */
 #else
-  lua_assert(irt_type(ir->t) != st);
+  lj_assertA(irt_type(ir->t) != st, "inconsistent types for CONV");
   if (irt_isfp(ir->t)) {
     Reg dest = ra_dest(as, ir, RSET_FPR);
     if (stfp) {  /* FP to FP conversion. */
@@ -467,7 +473,8 @@ static void asm_conv(ASMState *as, IRIns *ir)
   } else if (stfp) {  /* FP to integer conversion. */
     if (irt_isguard(ir->t)) {
       /* Checked conversions are only supported from number to int. */
-      lua_assert(irt_isint(ir->t) && st == IRT_NUM);
+      lj_assertA(irt_isint(ir->t) && st == IRT_NUM,
+                 "bad type for checked CONV");
       asm_tointg(as, ir, ra_alloc1(as, lref, RSET_FPR));
     } else {
       Reg dest = ra_dest(as, ir, RSET_GPR);
@@ -503,7 +510,7 @@ static void asm_conv(ASMState *as, IRIns *ir)
     Reg dest = ra_dest(as, ir, RSET_GPR);
     if (st >= IRT_I8 && st <= IRT_U16) {  /* Extend to 32 bit integer. */
       Reg left = ra_alloc1(as, ir->op1, RSET_GPR);
-      lua_assert(irt_isint(ir->t) || irt_isu32(ir->t));
+      lj_assertA(irt_isint(ir->t) || irt_isu32(ir->t), "bad type for CONV EXT");
       if ((ir->op2 & IRCONV_SEXT))
         emit_as(as, st == IRT_I8 ? PPCI_EXTSB : PPCI_EXTSH, dest, left);
       else
@@ -699,7 +706,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
             (((char *)as->mcp-(char *)l_loop) & 0xffffu);
 
   /* Load main position relative to tab->node into dest. */
-  khash = isk ? ir_khash(irkey) : 1;
+  khash = isk ? ir_khash(as, irkey) : 1;
   if (khash == 0) {
     emit_tai(as, PPCI_LWZ, dest, tab, (int32_t)offsetof(GCtab, node));
   } else {
@@ -754,7 +761,7 @@ static void asm_hrefk(ASMState *as, IRIns *ir)
   Reg node = ra_alloc1(as, ir->op1, RSET_GPR);
   Reg key = RID_NONE, type = RID_TMP, idx = node;
   RegSet allow = rset_exclude(RSET_GPR, node);
-  lua_assert(ofs % sizeof(Node) == 0);
+  lj_assertA(ofs % sizeof(Node) == 0, "unaligned HREFK slot");
   if (ofs > 32736) {
     idx = dest;
     rset_clear(allow, dest);
@@ -813,7 +820,7 @@ static void asm_uref(ASMState *as, IRIns *ir)
 static void asm_fref(ASMState *as, IRIns *ir)
 {
   UNUSED(as); UNUSED(ir);
-  lua_assert(!ra_used(ir));
+  lj_assertA(!ra_used(ir), "unfused FREF");
 }
 
 static void asm_strref(ASMState *as, IRIns *ir)
@@ -853,25 +860,27 @@ static void asm_strref(ASMState *as, IRIns *ir)
 
 /* -- Loads and stores ---------------------------------------------------- */
 
-static PPCIns asm_fxloadins(IRIns *ir)
+static PPCIns asm_fxloadins(ASMState *as, IRIns *ir)
 {
+  UNUSED(as);
   switch (irt_type(ir->t)) {
   case IRT_I8: return PPCI_LBZ;  /* Needs sign-extension. */
   case IRT_U8: return PPCI_LBZ;
   case IRT_I16: return PPCI_LHA;
   case IRT_U16: return PPCI_LHZ;
-  case IRT_NUM: lua_assert(!LJ_SOFTFP); return PPCI_LFD;
+  case IRT_NUM: lj_assertA(!LJ_SOFTFP, "unsplit FP op"); return PPCI_LFD;
   case IRT_FLOAT: if (!LJ_SOFTFP) return PPCI_LFS;
   default: return PPCI_LWZ;
   }
 }
 
-static PPCIns asm_fxstoreins(IRIns *ir)
+static PPCIns asm_fxstoreins(ASMState *as, IRIns *ir)
 {
+  UNUSED(as);
   switch (irt_type(ir->t)) {
   case IRT_I8: case IRT_U8: return PPCI_STB;
   case IRT_I16: case IRT_U16: return PPCI_STH;
-  case IRT_NUM: lua_assert(!LJ_SOFTFP); return PPCI_STFD;
+  case IRT_NUM: lj_assertA(!LJ_SOFTFP, "unsplit FP op"); return PPCI_STFD;
   case IRT_FLOAT: if (!LJ_SOFTFP) return PPCI_STFS;
   default: return PPCI_STW;
   }
@@ -880,10 +889,10 @@ static PPCIns asm_fxstoreins(IRIns *ir)
 static void asm_fload(ASMState *as, IRIns *ir)
 {
   Reg dest = ra_dest(as, ir, RSET_GPR);
-  PPCIns pi = asm_fxloadins(ir);
+  PPCIns pi = asm_fxloadins(as, ir);
   Reg idx;
   int32_t ofs;
-  if (ir->op1 == REF_NIL) {
+  if (ir->op1 == REF_NIL) {  /* FLOAD from GG_State with offset. */
     idx = RID_JGL;
     ofs = (ir->op2 << 2) - 32768;
   } else {
@@ -897,7 +906,7 @@ static void asm_fload(ASMState *as, IRIns *ir)
     }
     ofs = field_ofs[ir->op2];
   }
-  lua_assert(!irt_isi8(ir->t));
+  lj_assertA(!irt_isi8(ir->t), "unsupported FLOAD I8");
   emit_tai(as, pi, dest, idx, ofs);
 }
 
@@ -908,7 +917,7 @@ static void asm_fstore(ASMState *as, IRIns *ir)
     IRIns *irf = IR(ir->op1);
     Reg idx = ra_alloc1(as, irf->op1, rset_exclude(RSET_GPR, src));
     int32_t ofs = field_ofs[irf->op2];
-    PPCIns pi = asm_fxstoreins(ir);
+    PPCIns pi = asm_fxstoreins(as, ir);
     emit_tai(as, pi, src, idx, ofs);
   }
 }
@@ -917,10 +926,10 @@ static void asm_xload(ASMState *as, IRIns *ir)
 {
   Reg dest = ra_dest(as, ir,
     (!LJ_SOFTFP && irt_isfp(ir->t)) ? RSET_FPR : RSET_GPR);
-  lua_assert(!(ir->op2 & IRXLOAD_UNALIGNED));
+  lj_assertA(!(ir->op2 & IRXLOAD_UNALIGNED), "unaligned XLOAD");
   if (irt_isi8(ir->t))
     emit_as(as, PPCI_EXTSB, dest, dest);
-  asm_fusexref(as, asm_fxloadins(ir), dest, ir->op1, RSET_GPR, 0);
+  asm_fusexref(as, asm_fxloadins(as, ir), dest, ir->op1, RSET_GPR, 0);
 }
 
 static void asm_xstore_(ASMState *as, IRIns *ir, int32_t ofs)
@@ -936,7 +945,7 @@ static void asm_xstore_(ASMState *as, IRIns *ir, int32_t ofs)
   } else {
     Reg src = ra_alloc1(as, ir->op2,
       (!LJ_SOFTFP && irt_isfp(ir->t)) ? RSET_FPR : RSET_GPR);
-    asm_fusexref(as, asm_fxstoreins(ir), src, ir->op1,
+    asm_fusexref(as, asm_fxstoreins(as, ir), src, ir->op1,
                  rset_exclude(RSET_GPR, src), ofs);
   }
 }
@@ -958,8 +967,9 @@ static void asm_ahuvload(ASMState *as, IRIns *ir)
     ofs = 0;
   }
   if (ra_used(ir)) {
-    lua_assert((LJ_SOFTFP ? 0 : irt_isnum(ir->t)) ||
-               irt_isint(ir->t) || irt_isaddr(ir->t));
+    lj_assertA((LJ_SOFTFP ? 0 : irt_isnum(ir->t)) ||
+               irt_isint(ir->t) || irt_isaddr(ir->t),
+               "bad load type %d", irt_type(ir->t));
     if (LJ_SOFTFP || !irt_isnum(t)) ofs = 0;
     dest = ra_dest(as, ir, (!LJ_SOFTFP && irt_isnum(t)) ? RSET_FPR : allow);
     rset_clear(allow, dest);
@@ -1042,12 +1052,16 @@ static void asm_sload(ASMState *as, IRIns *ir)
   int hiop = (LJ_SOFTFP && (ir+1)->o == IR_HIOP);
   if (hiop)
     t.irt = IRT_NUM;
-  lua_assert(!(ir->op2 & IRSLOAD_PARENT));  /* Handled by asm_head_side(). */
-  lua_assert(irt_isguard(ir->t) || !(ir->op2 & IRSLOAD_TYPECHECK));
-  lua_assert(LJ_DUALNUM ||
-             !irt_isint(t) || (ir->op2 & (IRSLOAD_CONVERT|IRSLOAD_FRAME)));
+  lj_assertA(!(ir->op2 & IRSLOAD_PARENT),
+             "bad parent SLOAD");  /* Handled by asm_head_side(). */
+  lj_assertA(irt_isguard(ir->t) || !(ir->op2 & IRSLOAD_TYPECHECK),
+             "inconsistent SLOAD variant");
+  lj_assertA(LJ_DUALNUM ||
+             !irt_isint(t) || (ir->op2 & (IRSLOAD_CONVERT|IRSLOAD_FRAME)),
+             "bad SLOAD type");
 #if LJ_SOFTFP
-  lua_assert(!(ir->op2 & IRSLOAD_CONVERT));  /* Handled by LJ_SOFTFP SPLIT. */
+  lj_assertA(!(ir->op2 & IRSLOAD_CONVERT),
+             "unsplit SLOAD convert");  /* Handled by LJ_SOFTFP SPLIT. */
   if (hiop && ra_used(ir+1)) {
     type = ra_dest(as, ir+1, allow);
     rset_clear(allow, type);
@@ -1060,7 +1074,8 @@ static void asm_sload(ASMState *as, IRIns *ir)
   } else
 #endif
   if (ra_used(ir)) {
-    lua_assert(irt_isnum(t) || irt_isint(t) || irt_isaddr(t));
+    lj_assertA(irt_isnum(t) || irt_isint(t) || irt_isaddr(t),
+               "bad SLOAD type %d", irt_type(ir->t));
     dest = ra_dest(as, ir, (!LJ_SOFTFP && irt_isnum(t)) ? RSET_FPR : allow);
     rset_clear(allow, dest);
     base = ra_alloc1(as, REF_BASE, allow);
@@ -1127,7 +1142,8 @@ static void asm_cnew(ASMState *as, IRIns *ir)
   const CCallInfo *ci = &lj_ir_callinfo[IRCALL_lj_mem_newgco];
   IRRef args[4];
   RegSet drop = RSET_SCRATCH;
-  lua_assert(sz != CTSIZE_INVALID || (ir->o == IR_CNEW && ir->op2 != REF_NIL));
+  lj_assertA(sz != CTSIZE_INVALID || (ir->o == IR_CNEW && ir->op2 != REF_NIL),
+             "bad CNEW/CNEWI operands");
 
   as->gcsteps++;
   if (ra_hasreg(ir->r))
@@ -1140,10 +1156,10 @@ static void asm_cnew(ASMState *as, IRIns *ir)
   if (ir->o == IR_CNEWI) {
     RegSet allow = (RSET_GPR & ~RSET_SCRATCH);
     int32_t ofs = sizeof(GCcdata);
-    lua_assert(sz == 4 || sz == 8);
+    lj_assertA(sz == 4 || sz == 8, "bad CNEWI size %d", sz);
     if (sz == 8) {
       ofs += 4;
-      lua_assert((ir+1)->o == IR_HIOP);
+      lj_assertA((ir+1)->o == IR_HIOP, "expected HIOP for CNEWI");
     }
     for (;;) {
       Reg r = ra_alloc1(as, ir->op2, allow);
@@ -1187,7 +1203,7 @@ static void asm_tbar(ASMState *as, IRIns *ir)
   emit_tai(as, PPCI_STW, link, tab, (int32_t)offsetof(GCtab, gclist));
   emit_tai(as, PPCI_STB, mark, tab, (int32_t)offsetof(GCtab, marked));
   emit_setgl(as, tab, gc.grayagain);
-  lua_assert(LJ_GC_BLACK == 0x04);
+  lj_assertA(LJ_GC_BLACK == 0x04, "bad LJ_GC_BLACK");
   emit_rot(as, PPCI_RLWINM, mark, mark, 0, 30, 28);  /* Clear black bit. */
   emit_getgl(as, link, gc.grayagain);
   emit_condbranch(as, PPCI_BC|PPCF_Y, CC_EQ, l_end);
@@ -1202,7 +1218,7 @@ static void asm_obar(ASMState *as, IRIns *ir)
   MCLabel l_end;
   Reg obj, val, tmp;
   /* No need for other object barriers (yet). */
-  lua_assert(IR(ir->op1)->o == IR_UREFC);
+  lj_assertA(IR(ir->op1)->o == IR_UREFC, "bad OBAR type");
   ra_evictset(as, RSET_SCRATCH);
   l_end = emit_label(as);
   args[0] = ASMREF_TMP1;  /* global_State *g */
@@ -1673,7 +1689,7 @@ static void asm_bitshift(ASMState *as, IRIns *ir, PPCIns pi, PPCIns pik)
 #define asm_brol(as, ir) \
   asm_bitshift(as, ir, PPCI_RLWNM|PPCF_MB(0)|PPCF_ME(31), \
                        PPCI_RLWINM|PPCF_MB(0)|PPCF_ME(31))
-#define asm_bror(as, ir)        lua_assert(0)
+#define asm_bror(as, ir)        lj_assertA(0, "unexpected BROR")
 
 #if LJ_SOFTFP
 static void asm_sfpmin_max(ASMState *as, IRIns *ir)
@@ -1947,10 +1963,11 @@ static void asm_hiop(ASMState *as, IRIns *ir)
   case IR_CNEWI:
     /* Nothing to do here. Handled by lo op itself. */
     break;
-  default: lua_assert(0); break;
+  default: lj_assertA(0, "bad HIOP for op %d", (ir-1)->o); break;
   }
 #else
-  UNUSED(as); UNUSED(ir); lua_assert(0);  /* Unused without FFI. */
+  /* Unused without SOFTFP or FFI. */
+  UNUSED(as); UNUSED(ir); lj_assertA(0, "unexpected HIOP");
 #endif
 }
 
@@ -2010,7 +2027,8 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
 #if LJ_SOFTFP
       Reg tmp;
       RegSet allow = rset_exclude(RSET_GPR, RID_BASE);
-      lua_assert(irref_isk(ref));  /* LJ_SOFTFP: must be a number constant. */
+      /* LJ_SOFTFP: must be a number constant. */
+      lj_assertA(irref_isk(ref), "unsplit FP op");
       tmp = ra_allock(as, (int32_t)ir_knum(ir)->u32.lo, allow);
       emit_tai(as, PPCI_STW, tmp, RID_BASE, ofs+(LJ_BE?4:0));
       if (rset_test(as->freeset, tmp+1)) allow = RID2RSET(tmp+1);
@@ -2023,7 +2041,8 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
     } else {
       Reg type;
       RegSet allow = rset_exclude(RSET_GPR, RID_BASE);
-      lua_assert(irt_ispri(ir->t) || irt_isaddr(ir->t) || irt_isinteger(ir->t));
+      lj_assertA(irt_ispri(ir->t) || irt_isaddr(ir->t) || irt_isinteger(ir->t),
+                 "restore of IR type %d", irt_type(ir->t));
       if (!irt_ispri(ir->t)) {
         Reg src = ra_alloc1(as, ref, allow);
         rset_clear(allow, src);
@@ -2043,7 +2062,7 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
     }
     checkmclim(as);
   }
-  lua_assert(map + nent == flinks);
+  lj_assertA(map + nent == flinks, "inconsistent frames in snapshot");
 }
 
 /* -- GC handling --------------------------------------------------------- */
@@ -2141,7 +2160,7 @@ static void asm_tail_fixup(ASMState *as, TraceNo lnk)
     as->mctop = p;
   } else {
     /* Patch stack adjustment. */
-    lua_assert(checki16(CFRAME_SIZE+spadj));
+    lj_assertA(checki16(CFRAME_SIZE+spadj), "stack adjustment out of range");
     p[-3] = PPCI_ADDI | PPCF_T(RID_TMP) | PPCF_A(RID_SP) | (CFRAME_SIZE+spadj);
     p[-2] = PPCI_STWU | PPCF_T(RID_TMP) | PPCF_A(RID_SP) | spadj;
   }
@@ -2218,14 +2237,16 @@ void lj_asm_patchexit(jit_State *J, GCtrace *T, ExitNo exitno, MCode *target)
     } else if ((ins & 0xfc000000u) == PPCI_B &&
                ((ins ^ ((char *)px-(char *)p)) & 0x03ffffffu) == 0) {
       ptrdiff_t delta = (char *)target - (char *)p;
-      lua_assert(((delta + 0x02000000) >> 26) == 0);
+      lj_assertJ(((delta + 0x02000000) >> 26) == 0,
+                 "branch target out of range");
       *p = PPCI_B | ((uint32_t)delta & 0x03ffffffu);
       if (!cstart) cstart = p;
     }
   }
   {  /* Always patch long-range branch in exit stub itself. */
     ptrdiff_t delta = (char *)target - (char *)px - clearso;
-    lua_assert(((delta + 0x02000000) >> 26) == 0);
+    lj_assertJ(((delta + 0x02000000) >> 26) == 0,
+               "branch target out of range");
     *px = PPCI_B | ((uint32_t)delta & 0x03ffffffu);
   }
   if (!cstart) cstart = px;
diff --git a/src/lj_asm_x86.h b/src/lj_asm_x86.h
index 7356a5f0..a3adee14 100644
--- a/src/lj_asm_x86.h
+++ b/src/lj_asm_x86.h
@@ -31,7 +31,7 @@ static MCode *asm_exitstub_gen(ASMState *as, ExitNo group)
 #endif
   /* Jump to exit handler which fills in the ExitState. */
   *mxp++ = XI_JMP; mxp += 4;
-  *((int32_t *)(mxp-4)) = jmprel(mxp, (MCode *)(void *)lj_vm_exit_handler);
+  *((int32_t *)(mxp-4)) = jmprel(as->J, mxp, (MCode *)(void *)lj_vm_exit_handler);
   /* Commit the code for this group (even if assembly fails later on). */
   lj_mcode_commitbot(as->J, mxp);
   as->mcbot = mxp;
@@ -60,7 +60,7 @@ static void asm_guardcc(ASMState *as, int cc)
   MCode *p = as->mcp;
   if (LJ_UNLIKELY(p == as->invmcp)) {
     as->loopinv = 1;
-    *(int32_t *)(p+1) = jmprel(p+5, target);
+    *(int32_t *)(p+1) = jmprel(as->J, p+5, target);
     target = p;
     cc ^= 1;
     if (as->realign) {
@@ -131,7 +131,7 @@ static IRRef asm_fuseabase(ASMState *as, IRRef ref)
   as->mrm.ofs = 0;
   if (irb->o == IR_FLOAD) {
     IRIns *ira = IR(irb->op1);
-    lua_assert(irb->op2 == IRFL_TAB_ARRAY);
+    lj_assertA(irb->op2 == IRFL_TAB_ARRAY, "expected FLOAD TAB_ARRAY");
     /* We can avoid the FLOAD of t->array for colocated arrays. */
     if (ira->o == IR_TNEW && ira->op1 <= LJ_MAX_COLOSIZE &&
         !neverfuse(as) && noconflict(as, irb->op1, IR_NEWREF, 1)) {
@@ -150,7 +150,7 @@ static IRRef asm_fuseabase(ASMState *as, IRRef ref)
 static void asm_fusearef(ASMState *as, IRIns *ir, RegSet allow)
 {
   IRIns *irx;
-  lua_assert(ir->o == IR_AREF);
+  lj_assertA(ir->o == IR_AREF, "expected AREF");
   as->mrm.base = (uint8_t)ra_alloc1(as, asm_fuseabase(as, ir->op1), allow);
   irx = IR(ir->op2);
   if (irref_isk(ir->op2)) {
@@ -217,8 +217,9 @@ static void asm_fuseahuref(ASMState *as, IRRef ref, RegSet allow)
       }
       break;
     default:
-      lua_assert(ir->o == IR_HREF || ir->o == IR_NEWREF || ir->o == IR_UREFO ||
-                 ir->o == IR_KKPTR);
+      lj_assertA(ir->o == IR_HREF || ir->o == IR_NEWREF || ir->o == IR_UREFO ||
+                 ir->o == IR_KKPTR,
+                 "bad IR op %d", ir->o);
       break;
     }
   }
@@ -230,9 +231,10 @@ static void asm_fuseahuref(ASMState *as, IRRef ref, RegSet allow)
 /* Fuse FLOAD/FREF reference into memory operand. */
 static void asm_fusefref(ASMState *as, IRIns *ir, RegSet allow)
 {
-  lua_assert(ir->o == IR_FLOAD || ir->o == IR_FREF);
+  lj_assertA(ir->o == IR_FLOAD || ir->o == IR_FREF,
+             "bad IR op %d", ir->o);
   as->mrm.idx = RID_NONE;
-  if (ir->op1 == REF_NIL) {
+  if (ir->op1 == REF_NIL) {  /* FLOAD from GG_State with offset. */
 #if LJ_GC64
     as->mrm.ofs = (int32_t)(ir->op2 << 2) - GG_OFS(dispatch);
     as->mrm.base = RID_DISPATCH;
@@ -271,7 +273,7 @@ static void asm_fusefref(ASMState *as, IRIns *ir, RegSet allow)
 static void asm_fusestrref(ASMState *as, IRIns *ir, RegSet allow)
 {
   IRIns *irr;
-  lua_assert(ir->o == IR_STRREF);
+  lj_assertA(ir->o == IR_STRREF, "bad IR op %d", ir->o);
   as->mrm.base = as->mrm.idx = RID_NONE;
   as->mrm.scale = XM_SCALE1;
   as->mrm.ofs = sizeof(GCstr);
@@ -378,9 +380,10 @@ static Reg asm_fuseloadk64(ASMState *as, IRIns *ir)
              checki32(mctopofs(as, k)) && checki32(mctopofs(as, k+1))) {
     as->mrm.ofs = (int32_t)mcpofs(as, k);
     as->mrm.base = RID_RIP;
-  } else {
+  } else {  /* Intern 64 bit constant at bottom of mcode. */
     if (ir->i) {
-      lua_assert(*k == *(uint64_t*)(as->mctop - ir->i));
+      lj_assertA(*k == *(uint64_t*)(as->mctop - ir->i),
+                 "bad interned 64 bit constant");
     } else {
       while ((uintptr_t)as->mcbot & 7) *as->mcbot++ = XI_INT3;
       *(uint64_t*)as->mcbot = *k;
@@ -420,12 +423,12 @@ static Reg asm_fuseload(ASMState *as, IRRef ref, RegSet allow)
   }
   if (ir->o == IR_KNUM) {
     RegSet avail = as->freeset & ~as->modset & RSET_FPR;
-    lua_assert(allow != RSET_EMPTY);
+    lj_assertA(allow != RSET_EMPTY, "no register allowed");
     if (!(avail & (avail-1)))  /* Fuse if less than two regs available. */
       return asm_fuseloadk64(as, ir);
   } else if (ref == REF_BASE || ir->o == IR_KINT64) {
     RegSet avail = as->freeset & ~as->modset & RSET_GPR;
-    lua_assert(allow != RSET_EMPTY);
+    lj_assertA(allow != RSET_EMPTY, "no register allowed");
     if (!(avail & (avail-1))) {  /* Fuse if less than two regs available. */
       if (ref == REF_BASE) {
 #if LJ_GC64
@@ -606,7 +609,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
 #endif
           emit_loadi(as, r, ir->i);
       } else {
-        lua_assert(rset_test(as->freeset, r));  /* Must have been evicted. */
+        /* Must have been evicted. */
+        lj_assertA(rset_test(as->freeset, r), "reg %d not free", r);
         if (ra_hasreg(ir->r)) {
           ra_noweak(as, ir->r);
           emit_movrr(as, ir, r, ir->r);
@@ -615,7 +619,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
         }
       }
     } else if (irt_isfp(ir->t)) {  /* FP argument is on stack. */
-      lua_assert(!(irt_isfloat(ir->t) && irref_isk(ref)));  /* No float k. */
+      lj_assertA(!(irt_isfloat(ir->t) && irref_isk(ref)),
+                 "unexpected float constant");
       if (LJ_32 && (ofs & 4) && irref_isk(ref)) {
         /* Split stores for unaligned FP consts. */
         emit_movmroi(as, RID_ESP, ofs, (int32_t)ir_knum(ir)->u32.lo);
@@ -691,7 +696,7 @@ static void asm_setupresult(ASMState *as, IRIns *ir, const CCallInfo *ci)
       ra_destpair(as, ir);
 #endif
     } else {
-      lua_assert(!irt_ispri(ir->t));
+      lj_assertA(!irt_ispri(ir->t), "PRI dest");
       ra_destreg(as, ir, RID_RET);
     }
   } else if (LJ_32 && irt_isfp(ir->t) && !(ci->flags & CCI_CASTU64)) {
@@ -810,8 +815,10 @@ static void asm_conv(ASMState *as, IRIns *ir)
   int st64 = (st == IRT_I64 || st == IRT_U64 || (LJ_64 && st == IRT_P64));
   int stfp = (st == IRT_NUM || st == IRT_FLOAT);
   IRRef lref = ir->op1;
-  lua_assert(irt_type(ir->t) != st);
-  lua_assert(!(LJ_32 && (irt_isint64(ir->t) || st64)));  /* Handled by SPLIT. */
+  lj_assertA(irt_type(ir->t) != st, "inconsistent types for CONV");
+  lj_assertA(!(LJ_32 && (irt_isint64(ir->t) || st64)),
+             "IR %04d has unsplit 64 bit type",
+             (int)(ir - as->ir) - REF_BIAS);
   if (irt_isfp(ir->t)) {
     Reg dest = ra_dest(as, ir, RSET_FPR);
     if (stfp) {  /* FP to FP conversion. */
@@ -847,7 +854,8 @@ static void asm_conv(ASMState *as, IRIns *ir)
   } else if (stfp) {  /* FP to integer conversion. */
     if (irt_isguard(ir->t)) {
       /* Checked conversions are only supported from number to int. */
-      lua_assert(irt_isint(ir->t) && st == IRT_NUM);
+      lj_assertA(irt_isint(ir->t) && st == IRT_NUM,
+                 "bad type for checked CONV");
       asm_tointg(as, ir, ra_alloc1(as, lref, RSET_FPR));
     } else {
       Reg dest = ra_dest(as, ir, RSET_GPR);
@@ -882,7 +890,7 @@ static void asm_conv(ASMState *as, IRIns *ir)
     Reg left, dest = ra_dest(as, ir, RSET_GPR);
     RegSet allow = RSET_GPR;
     x86Op op;
-    lua_assert(irt_isint(ir->t) || irt_isu32(ir->t));
+    lj_assertA(irt_isint(ir->t) || irt_isu32(ir->t), "bad type for CONV EXT");
     if (st == IRT_I8) {
       op = XO_MOVSXb; allow = RSET_GPR8; dest |= FORCE_REX;
     } else if (st == IRT_U8) {
@@ -953,7 +961,7 @@ static void asm_conv_fp_int64(ASMState *as, IRIns *ir)
     emit_sjcc(as, CC_NS, l_end);
     emit_rr(as, XO_TEST, hi, hi);  /* Check if u64 >= 2^63. */
   } else {
-    lua_assert(((ir-1)->op2 & IRCONV_SRCMASK) == IRT_I64);
+    lj_assertA(((ir-1)->op2 & IRCONV_SRCMASK) == IRT_I64, "bad type for CONV");
   }
   emit_rmro(as, XO_FILDq, XOg_FILDq, RID_ESP, 0);
   /* NYI: Avoid narrow-to-wide store-to-load forwarding stall. */
@@ -967,8 +975,8 @@ static void asm_conv_int64_fp(ASMState *as, IRIns *ir)
   IRType st = (IRType)((ir-1)->op2 & IRCONV_SRCMASK);
   IRType dt = (((ir-1)->op2 & IRCONV_DSTMASK) >> IRCONV_DSH);
   Reg lo, hi;
-  lua_assert(st == IRT_NUM || st == IRT_FLOAT);
-  lua_assert(dt == IRT_I64 || dt == IRT_U64);
+  lj_assertA(st == IRT_NUM || st == IRT_FLOAT, "bad type for CONV");
+  lj_assertA(dt == IRT_I64 || dt == IRT_U64, "bad type for CONV");
   hi = ra_dest(as, ir, RSET_GPR);
   lo = ra_dest(as, ir-1, rset_exclude(RSET_GPR, hi));
   if (ra_used(ir-1)) emit_rmro(as, XO_MOV, lo, RID_ESP, 0);
@@ -1180,13 +1188,13 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
       emit_rmro(as, XO_CMP, tmp|REX_64, dest, offsetof(Node, key.u64));
     }
   } else {
-    lua_assert(irt_ispri(kt) && !irt_isnil(kt));
+    lj_assertA(irt_ispri(kt) && !irt_isnil(kt), "bad HREF key type");
     emit_u32(as, (irt_toitype(kt)<<15)|0x7fff);
     emit_rmro(as, XO_ARITHi, XOg_CMP, dest, offsetof(Node, key.it));
 #else
   } else {
     if (!irt_ispri(kt)) {
-      lua_assert(irt_isaddr(kt));
+      lj_assertA(irt_isaddr(kt), "bad HREF key type");
       if (isk)
         emit_gmroi(as, XG_ARITHi(XOg_CMP), dest, offsetof(Node, key.gcr),
                    ptr2addr(ir_kgc(irkey)));
@@ -1194,7 +1202,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
         emit_rmro(as, XO_CMP, key, dest, offsetof(Node, key.gcr));
       emit_sjcc(as, CC_NE, l_next);
     }
-    lua_assert(!irt_isnil(kt));
+    lj_assertA(!irt_isnil(kt), "bad HREF key type");
     emit_i8(as, irt_toitype(kt));
     emit_rmro(as, XO_ARITHi8, XOg_CMP, dest, offsetof(Node, key.it));
 #endif
@@ -1209,7 +1217,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
 #endif
 
   /* Load main position relative to tab->node into dest. */
-  khash = isk ? ir_khash(irkey) : 1;
+  khash = isk ? ir_khash(as, irkey) : 1;
   if (khash == 0) {
     emit_rmro(as, XO_MOV, dest|REX_GC64, tab, offsetof(GCtab, node));
   } else {
@@ -1271,7 +1279,7 @@ static void asm_hrefk(ASMState *as, IRIns *ir)
 #if !LJ_64
   MCLabel l_exit;
 #endif
-  lua_assert(ofs % sizeof(Node) == 0);
+  lj_assertA(ofs % sizeof(Node) == 0, "unaligned HREFK slot");
   if (ra_hasreg(dest)) {
     if (ofs != 0) {
       if (dest == node)
@@ -1288,7 +1296,8 @@ static void asm_hrefk(ASMState *as, IRIns *ir)
     Reg key = ra_scratch(as, rset_exclude(RSET_GPR, node));
     emit_rmro(as, XO_CMP, key|REX_64, node,
                ofs + (int32_t)offsetof(Node, key.u64));
-    lua_assert(irt_isnum(irkey->t) || irt_isgcv(irkey->t));
+    lj_assertA(irt_isnum(irkey->t) || irt_isgcv(irkey->t),
+               "bad HREFK key type");
     /* Assumes -0.0 is already canonicalized to +0.0. */
     emit_loadu64(as, key, irt_isnum(irkey->t) ? ir_knum(irkey)->u64 :
 #if LJ_GC64
@@ -1299,7 +1308,7 @@ static void asm_hrefk(ASMState *as, IRIns *ir)
                           (uint64_t)(uint32_t)ptr2addr(ir_kgc(irkey)));
 #endif
   } else {
-    lua_assert(!irt_isnil(irkey->t));
+    lj_assertA(!irt_isnil(irkey->t), "bad HREFK key type");
 #if LJ_GC64
     emit_i32(as, (irt_toitype(irkey->t)<<15)|0x7fff);
     emit_rmro(as, XO_ARITHi, XOg_CMP, node,
@@ -1323,13 +1332,13 @@ static void asm_hrefk(ASMState *as, IRIns *ir)
                (int32_t)ir_knum(irkey)->u32.hi);
   } else {
     if (!irt_ispri(irkey->t)) {
-      lua_assert(irt_isgcv(irkey->t));
+      lj_assertA(irt_isgcv(irkey->t), "bad HREFK key type");
       emit_gmroi(as, XG_ARITHi(XOg_CMP), node,
                  ofs + (int32_t)offsetof(Node, key.gcr),
                  ptr2addr(ir_kgc(irkey)));
       emit_sjcc(as, CC_NE, l_exit);
     }
-    lua_assert(!irt_isnil(irkey->t));
+    lj_assertA(!irt_isnil(irkey->t), "bad HREFK key type");
     emit_i8(as, irt_toitype(irkey->t));
     emit_rmro(as, XO_ARITHi8, XOg_CMP, node,
               ofs + (int32_t)offsetof(Node, key.it));
@@ -1402,7 +1411,8 @@ static void asm_fxload(ASMState *as, IRIns *ir)
     if (LJ_64 && irt_is64(ir->t))
       dest |= REX_64;
     else
-      lua_assert(irt_isint(ir->t) || irt_isu32(ir->t) || irt_isaddr(ir->t));
+      lj_assertA(irt_isint(ir->t) || irt_isu32(ir->t) || irt_isaddr(ir->t),
+                 "unsplit 64 bit load");
     xo = XO_MOV;
     break;
   }
@@ -1447,13 +1457,16 @@ static void asm_fxstore(ASMState *as, IRIns *ir)
     case IRT_NUM: xo = XO_MOVSDto; break;
     case IRT_FLOAT: xo = XO_MOVSSto; break;
 #if LJ_64 && !LJ_GC64
-    case IRT_LIGHTUD: lua_assert(0);  /* NYI: mask 64 bit lightuserdata. */
+    case IRT_LIGHTUD:
+      /* NYI: mask 64 bit lightuserdata. */
+      lj_assertA(0, "store of lightuserdata");
 #endif
     default:
       if (LJ_64 && irt_is64(ir->t))
         src |= REX_64;
       else
-        lua_assert(irt_isint(ir->t) || irt_isu32(ir->t) || irt_isaddr(ir->t));
+        lj_assertA(irt_isint(ir->t) || irt_isu32(ir->t) || irt_isaddr(ir->t),
+                   "unsplit 64 bit store");
       xo = XO_MOVto;
       break;
     }
@@ -1467,8 +1480,8 @@ static void asm_fxstore(ASMState *as, IRIns *ir)
       emit_i8(as, k);
       emit_mrm(as, XO_MOVmib, 0, RID_MRM);
     } else {
-      lua_assert(irt_is64(ir->t) || irt_isint(ir->t) || irt_isu32(ir->t) ||
-                 irt_isaddr(ir->t));
+      lj_assertA(irt_is64(ir->t) || irt_isint(ir->t) || irt_isu32(ir->t) ||
+                 irt_isaddr(ir->t), "bad store type");
       emit_i32(as, k);
       emit_mrm(as, XO_MOVmi, REX_64IR(ir, 0), RID_MRM);
     }
@@ -1503,8 +1516,9 @@ static void asm_ahuvload(ASMState *as, IRIns *ir)
 #if LJ_GC64
   Reg tmp = RID_NONE;
 #endif
-  lua_assert(irt_isnum(ir->t) || irt_ispri(ir->t) || irt_isaddr(ir->t) ||
-             (LJ_DUALNUM && irt_isint(ir->t)));
+  lj_assertA(irt_isnum(ir->t) || irt_ispri(ir->t) || irt_isaddr(ir->t) ||
+             (LJ_DUALNUM && irt_isint(ir->t)),
+             "bad load type %d", irt_type(ir->t));
 #if LJ_64 && !LJ_GC64
   if (irt_islightud(ir->t)) {
     Reg dest = asm_load_lightud64(as, ir, 1);
@@ -1551,7 +1565,8 @@ static void asm_ahuvload(ASMState *as, IRIns *ir)
   as->mrm.ofs += 4;
   asm_guardcc(as, irt_isnum(ir->t) ? CC_AE : CC_NE);
   if (LJ_64 && irt_type(ir->t) >= IRT_NUM) {
-    lua_assert(irt_isinteger(ir->t) || irt_isnum(ir->t));
+    lj_assertA(irt_isinteger(ir->t) || irt_isnum(ir->t),
+               "bad load type %d", irt_type(ir->t));
 #if LJ_GC64
     emit_u32(as, LJ_TISNUM << 15);
 #else
@@ -1633,13 +1648,14 @@ static void asm_ahustore(ASMState *as, IRIns *ir)
 #endif
       emit_mrm(as, XO_MOVto, src, RID_MRM);
     } else if (!irt_ispri(irr->t)) {
-      lua_assert(irt_isaddr(ir->t) || (LJ_DUALNUM && irt_isinteger(ir->t)));
+      lj_assertA(irt_isaddr(ir->t) || (LJ_DUALNUM && irt_isinteger(ir->t)),
+                 "bad store type");
       emit_i32(as, irr->i);
       emit_mrm(as, XO_MOVmi, 0, RID_MRM);
     }
     as->mrm.ofs += 4;
 #if LJ_GC64
-    lua_assert(LJ_DUALNUM && irt_isinteger(ir->t));
+    lj_assertA(LJ_DUALNUM && irt_isinteger(ir->t), "bad store type");
     emit_i32(as, LJ_TNUMX << 15);
 #else
     emit_i32(as, (int32_t)irt_toitype(ir->t));
@@ -1654,10 +1670,13 @@ static void asm_sload(ASMState *as, IRIns *ir)
                 (!LJ_FR2 && (ir->op2 & IRSLOAD_FRAME) ? 4 : 0);
   IRType1 t = ir->t;
   Reg base;
-  lua_assert(!(ir->op2 & IRSLOAD_PARENT));  /* Handled by asm_head_side(). */
-  lua_assert(irt_isguard(t) || !(ir->op2 & IRSLOAD_TYPECHECK));
-  lua_assert(LJ_DUALNUM ||
-             !irt_isint(t) || (ir->op2 & (IRSLOAD_CONVERT|IRSLOAD_FRAME)));
+  lj_assertA(!(ir->op2 & IRSLOAD_PARENT),
+             "bad parent SLOAD"); /* Handled by asm_head_side(). */
+  lj_assertA(irt_isguard(t) || !(ir->op2 & IRSLOAD_TYPECHECK),
+             "inconsistent SLOAD variant");
+  lj_assertA(LJ_DUALNUM ||
+             !irt_isint(t) || (ir->op2 & (IRSLOAD_CONVERT|IRSLOAD_FRAME)),
+             "bad SLOAD type");
   if ((ir->op2 & IRSLOAD_CONVERT) && irt_isguard(t) && irt_isint(t)) {
     Reg left = ra_scratch(as, RSET_FPR);
     asm_tointg(as, ir, left);  /* Frees dest reg. Do this before base alloc. */
@@ -1677,7 +1696,8 @@ static void asm_sload(ASMState *as, IRIns *ir)
     RegSet allow = irt_isnum(t) ? RSET_FPR : RSET_GPR;
     Reg dest = ra_dest(as, ir, allow);
     base = ra_alloc1(as, REF_BASE, RSET_GPR);
-    lua_assert(irt_isnum(t) || irt_isint(t) || irt_isaddr(t));
+    lj_assertA(irt_isnum(t) || irt_isint(t) || irt_isaddr(t),
+               "bad SLOAD type %d", irt_type(t));
     if ((ir->op2 & IRSLOAD_CONVERT)) {
       t.irt = irt_isint(t) ? IRT_NUM : IRT_INT;  /* Check for original type. */
       emit_rmro(as, irt_isint(t) ? XO_CVTSI2SD : XO_CVTTSD2SI, dest, base, ofs);
@@ -1723,7 +1743,8 @@ static void asm_sload(ASMState *as, IRIns *ir)
     /* Need type check, even if the load result is unused. */
     asm_guardcc(as, irt_isnum(t) ? CC_AE : CC_NE);
     if (LJ_64 && irt_type(t) >= IRT_NUM) {
-      lua_assert(irt_isinteger(t) || irt_isnum(t));
+      lj_assertA(irt_isinteger(t) || irt_isnum(t),
+                 "bad SLOAD type %d", irt_type(t));
 #if LJ_GC64
       emit_u32(as, LJ_TISNUM << 15);
 #else
@@ -1775,7 +1796,8 @@ static void asm_cnew(ASMState *as, IRIns *ir)
   CTInfo info = lj_ctype_info(cts, id, &sz);
   const CCallInfo *ci = &lj_ir_callinfo[IRCALL_lj_mem_newgco];
   IRRef args[4];
-  lua_assert(sz != CTSIZE_INVALID || (ir->o == IR_CNEW && ir->op2 != REF_NIL));
+  lj_assertA(sz != CTSIZE_INVALID || (ir->o == IR_CNEW && ir->op2 != REF_NIL),
+             "bad CNEW/CNEWI operands");
 
   as->gcsteps++;
   asm_setupresult(as, ir, ci);  /* GCcdata * */
@@ -1805,7 +1827,7 @@ static void asm_cnew(ASMState *as, IRIns *ir)
     int32_t ofs = sizeof(GCcdata);
     if (sz == 8) {
       ofs += 4; ir++;
-      lua_assert(ir->o == IR_HIOP);
+      lj_assertA(ir->o == IR_HIOP, "missing CNEWI HIOP");
     }
     do {
       if (irref_isk(ir->op2)) {
@@ -1819,7 +1841,7 @@ static void asm_cnew(ASMState *as, IRIns *ir)
       ofs -= 4; ir--;
     } while (1);
 #endif
-    lua_assert(sz == 4 || sz == 8);
+    lj_assertA(sz == 4 || sz == 8, "bad CNEWI size %d", sz);
   } else if (ir->op2 != REF_NIL) {  /* Create VLA/VLS/aligned cdata. */
     ci = &lj_ir_callinfo[IRCALL_lj_cdata_newv];
     args[0] = ASMREF_L;     /* lua_State *L */
@@ -1869,7 +1891,7 @@ static void asm_obar(ASMState *as, IRIns *ir)
   MCLabel l_end;
   Reg obj;
   /* No need for other object barriers (yet). */
-  lua_assert(IR(ir->op1)->o == IR_UREFC);
+  lj_assertA(IR(ir->op1)->o == IR_UREFC, "bad OBAR type");
   ra_evictset(as, RSET_SCRATCH);
   l_end = emit_label(as);
   args[0] = ASMREF_TMP1;  /* global_State *g */
@@ -1986,7 +2008,7 @@ static int asm_swapops(ASMState *as, IRIns *ir)
 {
   IRIns *irl = IR(ir->op1);
   IRIns *irr = IR(ir->op2);
-  lua_assert(ra_noreg(irr->r));
+  lj_assertA(ra_noreg(irr->r), "bad usage");
   if (!irm_iscomm(lj_ir_mode[ir->o]))
     return 0;  /* Can't swap non-commutative operations. */
   if (irref_isk(ir->op2))
@@ -2376,8 +2398,9 @@ static void asm_comp(ASMState *as, IRIns *ir)
     IROp leftop = (IROp)(IR(lref)->o);
     Reg r64 = REX_64IR(ir, 0);
     int32_t imm = 0;
-    lua_assert(irt_is64(ir->t) || irt_isint(ir->t) ||
-               irt_isu32(ir->t) || irt_isaddr(ir->t) || irt_isu8(ir->t));
+    lj_assertA(irt_is64(ir->t) || irt_isint(ir->t) ||
+               irt_isu32(ir->t) || irt_isaddr(ir->t) || irt_isu8(ir->t),
+               "bad comparison data type %d", irt_type(ir->t));
     /* Swap constants (only for ABC) and fusable loads to the right. */
     if (irref_isk(lref) || (!irref_isk(rref) && opisfusableload(leftop))) {
       if ((cc & 0xc) == 0xc) cc ^= 0x53;  /* L <-> G, LE <-> GE */
@@ -2459,7 +2482,7 @@ static void asm_comp(ASMState *as, IRIns *ir)
           /* Use test r,r instead of cmp r,0. */
           x86Op xo = XO_TEST;
           if (irt_isu8(ir->t)) {
-            lua_assert(ir->o == IR_EQ || ir->o == IR_NE);
+            lj_assertA(ir->o == IR_EQ || ir->o == IR_NE, "bad usage");
             xo = XO_TESTb;
             if (!rset_test(RSET_RANGE(RID_EAX, RID_EBX+1), left)) {
               if (LJ_64) {
@@ -2615,10 +2638,11 @@ static void asm_hiop(ASMState *as, IRIns *ir)
   case IR_CNEWI:
     /* Nothing to do here. Handled by CNEWI itself. */
     break;
-  default: lua_assert(0); break;
+  default: lj_assertA(0, "bad HIOP for op %d", (ir-1)->o); break;
   }
 #else
-  UNUSED(as); UNUSED(ir); lua_assert(0);  /* Unused on x64 or without FFI. */
+  /* Unused on x64 or without FFI. */
+  UNUSED(as); UNUSED(ir); lj_assertA(0, "unexpected HIOP");
 #endif
 }
 
@@ -2684,8 +2708,9 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
       Reg src = ra_alloc1(as, ref, RSET_FPR);
       emit_rmro(as, XO_MOVSDto, src, RID_BASE, ofs);
     } else {
-      lua_assert(irt_ispri(ir->t) || irt_isaddr(ir->t) ||
-                 (LJ_DUALNUM && irt_isinteger(ir->t)));
+      lj_assertA(irt_ispri(ir->t) || irt_isaddr(ir->t) ||
+                 (LJ_DUALNUM && irt_isinteger(ir->t)),
+                 "restore of IR type %d", irt_type(ir->t));
       if (!irref_isk(ref)) {
         Reg src = ra_alloc1(as, ref, rset_exclude(RSET_GPR, RID_BASE));
 #if LJ_GC64
@@ -2730,7 +2755,7 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
     }
     checkmclim(as);
   }
-  lua_assert(map + nent == flinks);
+  lj_assertA(map + nent == flinks, "inconsistent frames in snapshot");
 }
 
 /* -- GC handling --------------------------------------------------------- */
@@ -2774,16 +2799,16 @@ static void asm_loop_fixup(ASMState *as)
   MCode *target = as->mcp;
   if (as->realign) {  /* Realigned loops use short jumps. */
     as->realign = NULL;  /* Stop another retry. */
-    lua_assert(((intptr_t)target & 15) == 0);
+    lj_assertA(((intptr_t)target & 15) == 0, "loop realign failed");
     if (as->loopinv) {  /* Inverted loop branch? */
       p -= 5;
       p[0] = XI_JMP;
-      lua_assert(target - p >= -128);
+      lj_assertA(target - p >= -128, "loop realign failed");
       p[-1] = (MCode)(target - p);  /* Patch sjcc. */
       if (as->loopinv == 2)
         p[-3] = (MCode)(target - p + 2);  /* Patch opt. short jp. */
     } else {
-      lua_assert(target - p >= -128);
+      lj_assertA(target - p >= -128, "loop realign failed");
       p[-1] = (MCode)(int8_t)(target - p);  /* Patch short jmp. */
       p[-2] = XI_JMPs;
     }
@@ -2880,7 +2905,7 @@ static void asm_tail_fixup(ASMState *as, TraceNo lnk)
   }
   /* Patch exit branch. */
   target = lnk ? traceref(as->J, lnk)->mcode : (MCode *)lj_vm_exit_interp;
-  *(int32_t *)(p-4) = jmprel(p, target);
+  *(int32_t *)(p-4) = jmprel(as->J, p, target);
   p[-5] = XI_JMP;
   /* Drop unused mcode tail. Fill with NOPs to make the prefetcher happy. */
   for (q = as->mctop-1; q >= p; q--)
@@ -3053,17 +3078,17 @@ void lj_asm_patchexit(jit_State *J, GCtrace *T, ExitNo exitno, MCode *target)
   uint32_t statei = u32ptr(&J2G(J)->vmstate);
 #endif
   if (len > 5 && p[len-5] == XI_JMP && p+len-6 + *(int32_t *)(p+len-4) == px)
-    *(int32_t *)(p+len-4) = jmprel(p+len, target);
+    *(int32_t *)(p+len-4) = jmprel(J, p+len, target);
   /* Do not patch parent exit for a stack check. Skip beyond vmstate update. */
   for (; p < pe; p += asm_x86_inslen(p)) {
     intptr_t ofs = LJ_GC64 ? (p[0] & 0xf0) == 0x40 : LJ_64;
     if (*(uint32_t *)(p+2+ofs) == statei && p[ofs+LJ_GC64-LJ_64] == XI_MOVmi)
       break;
   }
-  lua_assert(p < pe);
+  lj_assertJ(p < pe, "instruction length decoder failed");
   for (; p < pe; p += asm_x86_inslen(p))
     if ((*(uint16_t *)p & 0xf0ff) == 0x800f && p + *(int32_t *)(p+2) == px)
-      *(int32_t *)(p+2) = jmprel(p+6, target);
+      *(int32_t *)(p+2) = jmprel(J, p+6, target);
   lj_mcode_sync(T->mcode, T->mcode + T->szmcode);
   lj_mcode_patch(J, mcarea, 1);
 }
diff --git a/src/lj_assert.c b/src/lj_assert.c
new file mode 100644
index 00000000..7989dbe6
--- /dev/null
+++ b/src/lj_assert.c
@@ -0,0 +1,28 @@
+/*
+** Internal assertions.
+** Copyright (C) 2005-2020 Mike Pall. See Copyright Notice in luajit.h
+*/
+
+#define lj_assert_c
+#define LUA_CORE
+
+#if defined(LUA_USE_ASSERT) || defined(LUA_USE_APICHECK)
+
+#include <stdio.h>
+
+#include "lj_obj.h"
+
+void lj_assert_fail(global_State *g, const char *file, int line,
+                    const char *func, const char *fmt, ...)
+{
+  va_list argp;
+  va_start(argp, fmt);
+  fprintf(stderr, "LuaJIT ASSERT %s:%d: %s: ", file, line, func);
+  vfprintf(stderr, fmt, argp);
+  fputc('\n', stderr);
+  va_end(argp);
+  UNUSED(g);  /* May be NULL. TODO: optionally dump state. */
+  abort();
+}
+
+#endif
diff --git a/src/lj_bcread.c b/src/lj_bcread.c
index 1585272f..1d9547be 100644
--- a/src/lj_bcread.c
+++ b/src/lj_bcread.c
@@ -47,7 +47,7 @@ static LJ_NOINLINE void bcread_error(LexState *ls, ErrMsg em)
 /* Refill buffer. */
 static LJ_NOINLINE void bcread_fill(LexState *ls, MSize len, int need)
 {
-  lua_assert(len != 0);
+  lj_assertLS(len != 0, "empty refill");
   if (len > LJ_MAX_BUF || ls->c < 0)
     bcread_error(ls, LJ_ERR_BCBAD);
   do {
@@ -57,7 +57,7 @@ static LJ_NOINLINE void bcread_fill(LexState *ls, MSize len, int need)
     MSize n = (MSize)(ls->pe - ls->p);
     if (n) {  /* Copy remainder to buffer. */
       if (sbuflen(&ls->sb)) {  /* Move down in buffer. */
-        lua_assert(ls->pe == sbufP(&ls->sb));
+        lj_assertLS(ls->pe == sbufP(&ls->sb), "bad buffer pointer");
         if (ls->p != p) memmove(p, ls->p, n);
       } else {  /* Copy from buffer provided by reader. */
         p = lj_buf_need(&ls->sb, len);
@@ -107,7 +107,7 @@ static LJ_AINLINE uint8_t *bcread_mem(LexState *ls, MSize len)
 {
   uint8_t *p = (uint8_t *)ls->p;
   ls->p += len;
-  lua_assert(ls->p <= ls->pe);
+  lj_assertLS(ls->p <= ls->pe, "buffer read overflow");
   return p;
 }
 
@@ -120,7 +120,7 @@ static void bcread_block(LexState *ls, void *q, MSize len)
 /* Read byte from buffer. */
 static LJ_AINLINE uint32_t bcread_byte(LexState *ls)
 {
-  lua_assert(ls->p < ls->pe);
+  lj_assertLS(ls->p < ls->pe, "buffer read overflow");
   return (uint32_t)(uint8_t)*ls->p++;
 }
 
@@ -128,7 +128,7 @@ static LJ_AINLINE uint32_t bcread_byte(LexState *ls)
 static LJ_AINLINE uint32_t bcread_uleb128(LexState *ls)
 {
   uint32_t v = lj_buf_ruleb128(&ls->p);
-  lua_assert(ls->p <= ls->pe);
+  lj_assertLS(ls->p <= ls->pe, "buffer read overflow");
   return v;
 }
 
@@ -145,7 +145,7 @@ static uint32_t bcread_uleb128_33(LexState *ls)
    } while (*p++ >= 0x80);
   }
   ls->p = (char *)p;
-  lua_assert(ls->p <= ls->pe);
+  lj_assertLS(ls->p <= ls->pe, "buffer read overflow");
   return v;
 }
 
@@ -192,7 +192,7 @@ static void bcread_ktabk(LexState *ls, TValue *o)
     o->u32.lo = bcread_uleb128(ls);
     o->u32.hi = bcread_uleb128(ls);
   } else {
-    lua_assert(tp <= BCDUMP_KTAB_TRUE);
+    lj_assertLS(tp <= BCDUMP_KTAB_TRUE, "bad constant type %d", tp);
     setpriV(o, ~tp);
   }
 }
@@ -214,7 +214,7 @@ static GCtab *bcread_ktab(LexState *ls)
     for (i = 0; i < nhash; i++) {
       TValue key;
       bcread_ktabk(ls, &key);
-      lua_assert(!tvisnil(&key));
+      lj_assertLS(!tvisnil(&key), "nil key");
       bcread_ktabk(ls, lj_tab_set(ls->L, t, &key));
     }
   }
@@ -251,7 +251,7 @@ static void bcread_kgc(LexState *ls, GCproto *pt, MSize sizekgc)
 #endif
     } else {
       lua_State *L = ls->L;
-      lua_assert(tp == BCDUMP_KGC_CHILD);
+      lj_assertLS(tp == BCDUMP_KGC_CHILD, "bad constant type %d", tp);
       if (L->top <= bcread_oldtop(L, ls))  /* Stack underflow? */
         bcread_error(ls, LJ_ERR_BCBAD);
       L->top--;
@@ -422,7 +422,7 @@ static int bcread_header(LexState *ls)
 GCproto *lj_bcread(LexState *ls)
 {
   lua_State *L = ls->L;
-  lua_assert(ls->c == BCDUMP_HEAD1);
+  lj_assertLS(ls->c == BCDUMP_HEAD1, "bad bytecode header");
   bcread_savetop(L, ls, L->top);
   lj_buf_reset(&ls->sb);
   /* Check for a valid bytecode dump header. */
diff --git a/src/lj_bcwrite.c b/src/lj_bcwrite.c
index dd38289e..a8c310b8 100644
--- a/src/lj_bcwrite.c
+++ b/src/lj_bcwrite.c
@@ -29,8 +29,17 @@ typedef struct BCWriteCtx {
   void *wdata;                  /* Writer callback data. */
   int strip;                    /* Strip debug info. */
   int status;                   /* Status from writer callback. */
+#ifdef LUA_USE_ASSERT
+  global_State *g;
+#endif
 } BCWriteCtx;
 
+#ifdef LUA_USE_ASSERT
+#define lj_assertBCW(c, ...)    lj_assertG_(ctx->g, (c), __VA_ARGS__)
+#else
+#define lj_assertBCW(c, ...)    ((void)ctx)
+#endif
+
 /* -- Bytecode writer ----------------------------------------------------- */
 
 /* Write a single constant key/value of a template table. */
@@ -61,7 +70,7 @@ static void bcwrite_ktabk(BCWriteCtx *ctx, cTValue *o, int narrow)
     p = lj_strfmt_wuleb128(p, o->u32.lo);
     p = lj_strfmt_wuleb128(p, o->u32.hi);
   } else {
-    lua_assert(tvispri(o));
+    lj_assertBCW(tvispri(o), "unhandled type %d", itype(o));
     *p++ = BCDUMP_KTAB_NIL+~itype(o);
   }
   setsbufP(&ctx->sb, p);
@@ -121,7 +130,7 @@ static void bcwrite_kgc(BCWriteCtx *ctx, GCproto *pt)
       tp = BCDUMP_KGC_STR + gco2str(o)->len;
       need = 5+gco2str(o)->len;
     } else if (o->gch.gct == ~LJ_TPROTO) {
-      lua_assert((pt->flags & PROTO_CHILD));
+      lj_assertBCW((pt->flags & PROTO_CHILD), "prototype has unexpected child");
       tp = BCDUMP_KGC_CHILD;
 #if LJ_HASFFI
     } else if (o->gch.gct == ~LJ_TCDATA) {
@@ -132,12 +141,14 @@ static void bcwrite_kgc(BCWriteCtx *ctx, GCproto *pt)
       } else if (id == CTID_UINT64) {
         tp = BCDUMP_KGC_U64;
       } else {
-        lua_assert(id == CTID_COMPLEX_DOUBLE);
+        lj_assertBCW(id == CTID_COMPLEX_DOUBLE,
+                     "bad cdata constant CTID %d", id);
         tp = BCDUMP_KGC_COMPLEX;
       }
 #endif
     } else {
-      lua_assert(o->gch.gct == ~LJ_TTAB);
+      lj_assertBCW(o->gch.gct == ~LJ_TTAB,
+                   "bad constant GC type %d", o->gch.gct);
       tp = BCDUMP_KGC_TAB;
       need = 1+2*5;
     }
@@ -289,7 +300,7 @@ static void bcwrite_proto(BCWriteCtx *ctx, GCproto *pt)
     MSize nn = (lj_fls(n)+8)*9 >> 6;
     char *q = sbufB(&ctx->sb) + (5 - nn);
     p = lj_strfmt_wuleb128(q, n);  /* Fill in final size. */
-    lua_assert(p == sbufB(&ctx->sb) + 5);
+    lj_assertBCW(p == sbufB(&ctx->sb) + 5, "bad ULEB128 write");
     ctx->status = ctx->wfunc(sbufL(&ctx->sb), q, nn+n, ctx->wdata);
   }
 }
@@ -349,6 +360,9 @@ int lj_bcwrite(lua_State *L, GCproto *pt, lua_Writer writer, void *data,
   ctx.wdata = data;
   ctx.strip = strip;
   ctx.status = 0;
+#ifdef LUA_USE_ASSERT
+  ctx.g = G(L);
+#endif
   lj_buf_init(L, &ctx.sb);
   status = lj_vm_cpcall(L, NULL, &ctx, cpwriter);
   if (status == 0) status = ctx.status;
diff --git a/src/lj_buf.c b/src/lj_buf.c
index c8778016..935ae488 100644
--- a/src/lj_buf.c
+++ b/src/lj_buf.c
@@ -30,7 +30,7 @@ static void buf_grow(SBuf *sb, MSize sz)
 
 LJ_NOINLINE char *LJ_FASTCALL lj_buf_need2(SBuf *sb, MSize sz)
 {
-  lua_assert(sz > sbufsz(sb));
+  lj_assertG_(G(sbufL(sb)), sz > sbufsz(sb), "SBuf overflow");
   if (LJ_UNLIKELY(sz > LJ_MAX_BUF))
     lj_err_mem(sbufL(sb));
   buf_grow(sb, sz);
@@ -40,7 +40,7 @@ LJ_NOINLINE char *LJ_FASTCALL lj_buf_need2(SBuf *sb, MSize sz)
 LJ_NOINLINE char *LJ_FASTCALL lj_buf_more2(SBuf *sb, MSize sz)
 {
   MSize len = sbuflen(sb);
-  lua_assert(sz > sbufleft(sb));
+  lj_assertG_(G(sbufL(sb)), sz > sbufleft(sb), "SBuf overflow");
   if (LJ_UNLIKELY(sz > LJ_MAX_BUF || len + sz > LJ_MAX_BUF))
     lj_err_mem(sbufL(sb));
   buf_grow(sb, len + sz);
diff --git a/src/lj_carith.c b/src/lj_carith.c
index cf71aaf5..65ad2c10 100644
--- a/src/lj_carith.c
+++ b/src/lj_carith.c
@@ -122,7 +122,7 @@ static int carith_ptr(lua_State *L, CTState *cts, CDArith *ca, MMS mm)
         setboolV(L->top-1, ((uintptr_t)pp < (uintptr_t)pp2));
         return 1;
       } else {
-        lua_assert(mm == MM_le);
+        lj_assertL(mm == MM_le, "bad metamethod %d", mm);
         setboolV(L->top-1, ((uintptr_t)pp <= (uintptr_t)pp2));
         return 1;
       }
@@ -208,7 +208,9 @@ static int carith_int64(lua_State *L, CTState *cts, CDArith *ca, MMS mm)
         *up = lj_carith_powu64(u0, u1);
       break;
     case MM_unm: *up = (uint64_t)-(int64_t)u0; break;
-    default: lua_assert(0); break;
+    default:
+      lj_assertL(0, "bad metamethod %d", mm);
+      break;
     }
     lj_gc_check(L);
     return 1;
@@ -301,7 +303,9 @@ uint64_t lj_carith_shift64(uint64_t x, int32_t sh, int op)
   case IR_BSAR-IR_BSHL: x = lj_carith_sar64(x, sh); break;
   case IR_BROL-IR_BSHL: x = lj_carith_rol64(x, sh); break;
   case IR_BROR-IR_BSHL: x = lj_carith_ror64(x, sh); break;
-  default: lua_assert(0); break;
+  default:
+    lj_assertX(0, "bad shift op %d", op);
+    break;
   }
   return x;
 }
diff --git a/src/lj_ccall.c b/src/lj_ccall.c
index 499a01d8..5ac1b4da 100644
--- a/src/lj_ccall.c
+++ b/src/lj_ccall.c
@@ -391,7 +391,8 @@
 #define CCALL_HANDLE_GPR \
   /* Try to pass argument in GPRs. */ \
   if (n > 1) { \
-    lua_assert(n == 2 || n == 4);  /* int64_t or complex (float). */ \
+    /* int64_t or complex (float). */ \
+    lj_assertL(n == 2 || n == 4, "bad GPR size %d", n); \
     if (ctype_isinteger(d->info) || ctype_isfp(d->info)) \
       ngpr = (ngpr + 1u) & ~1u;  /* Align int64_t to regpair. */ \
     else if (ngpr + n > maxgpr) \
@@ -642,7 +643,8 @@ static void ccall_classify_ct(CTState *cts, CType *ct, int *rcl, CTSize ofs)
     ccall_classify_struct(cts, ct, rcl, ofs);
   } else {
     int cl = ctype_isfp(ct->info) ? CCALL_RCL_SSE : CCALL_RCL_INT;
-    lua_assert(ctype_hassize(ct->info));
+    lj_assertCTS(ctype_hassize(ct->info),
+                 "classify ctype %08x without size", ct->info);
     if ((ofs & (ct->size-1))) cl = CCALL_RCL_MEM;  /* Unaligned. */
     rcl[(ofs >= 8)] |= cl;
   }
@@ -667,12 +669,13 @@ static int ccall_classify_struct(CTState *cts, CType *ct, int *rcl, CTSize ofs)
 }
 
 /* Try to split up a small struct into registers. */
-static int ccall_struct_reg(CCallState *cc, GPRArg *dp, int *rcl)
+static int ccall_struct_reg(CCallState *cc, CTState *cts, GPRArg *dp, int *rcl)
 {
   MSize ngpr = cc->ngpr, nfpr = cc->nfpr;
   uint32_t i;
+  UNUSED(cts);
   for (i = 0; i < 2; i++) {
-    lua_assert(!(rcl[i] & CCALL_RCL_MEM));
+    lj_assertCTS(!(rcl[i] & CCALL_RCL_MEM), "pass mem struct in reg");
     if ((rcl[i] & CCALL_RCL_INT)) {  /* Integer class takes precedence. */
       if (ngpr >= CCALL_NARG_GPR) return 1;  /* Register overflow. */
       cc->gpr[ngpr++] = dp[i];
@@ -693,7 +696,8 @@ static int ccall_struct_arg(CCallState *cc, CTState *cts, CType *d, int *rcl,
   dp[0] = dp[1] = 0;
   /* Convert to temp. struct. */
   lj_cconv_ct_tv(cts, d, (uint8_t *)dp, o, CCF_ARG(narg));
-  if (ccall_struct_reg(cc, dp, rcl)) {  /* Register overflow? Pass on stack. */
+  if (ccall_struct_reg(cc, cts, dp, rcl)) {
+    /* Register overflow? Pass on stack. */
     MSize nsp = cc->nsp, n = rcl[1] ? 2 : 1;
     if (nsp + n > CCALL_MAXSTACK) return 1;  /* Too many arguments. */
     cc->nsp = nsp + n;
@@ -990,7 +994,7 @@ static int ccall_set_args(lua_State *L, CTState *cts, CType *ct,
     if (fid) {  /* Get argument type from field. */
       CType *ctf = ctype_get(cts, fid);
       fid = ctf->sib;
-      lua_assert(ctype_isfield(ctf->info));
+      lj_assertL(ctype_isfield(ctf->info), "field expected");
       did = ctype_cid(ctf->info);
     } else {
       if (!(ct->info & CTF_VARARG))
@@ -1138,7 +1142,8 @@ static int ccall_get_results(lua_State *L, CTState *cts, CType *ct,
   CCALL_HANDLE_RET
 #endif
   /* No reference types end up here, so there's no need for the CTypeID. */
-  lua_assert(!(ctype_isrefarray(ctr->info) || ctype_isstruct(ctr->info)));
+  lj_assertL(!(ctype_isrefarray(ctr->info) || ctype_isstruct(ctr->info)),
+             "unexpected reference ctype");
   return lj_cconv_tv_ct(cts, ctr, 0, L->top-1, sp);
 }
 
diff --git a/src/lj_ccallback.c b/src/lj_ccallback.c
index 4edd8a35..49775d2b 100644
--- a/src/lj_ccallback.c
+++ b/src/lj_ccallback.c
@@ -107,9 +107,9 @@ MSize lj_ccallback_ptr2slot(CTState *cts, void *p)
 /* Initialize machine code for callback function pointers. */
 #if LJ_OS_NOJIT
 /* Disabled callback support. */
-#define callback_mcode_init(g, p)       UNUSED(p)
+#define callback_mcode_init(g, p)       (p)
 #elif LJ_TARGET_X86ORX64
-static void callback_mcode_init(global_State *g, uint8_t *page)
+static void *callback_mcode_init(global_State *g, uint8_t *page)
 {
   uint8_t *p = page;
   uint8_t *target = (uint8_t *)(void *)lj_vm_ffi_callback;
@@ -143,10 +143,10 @@ static void callback_mcode_init(global_State *g, uint8_t *page)
       *p++ = XI_JMPs; *p++ = (uint8_t)((2+2)*(31-(slot&31)) - 2);
     }
   }
-  lua_assert(p - page <= CALLBACK_MCODE_SIZE);
+  return p;
 }
 #elif LJ_TARGET_ARM
-static void callback_mcode_init(global_State *g, uint32_t *page)
+static void *callback_mcode_init(global_State *g, uint32_t *page)
 {
   uint32_t *p = page;
   void *target = (void *)lj_vm_ffi_callback;
@@ -165,10 +165,10 @@ static void callback_mcode_init(global_State *g, uint32_t *page)
     *p = ARMI_B | ((page-p-2) & 0x00ffffffu);
     p++;
   }
-  lua_assert(p - page <= CALLBACK_MCODE_SIZE);
+  return p;
 }
 #elif LJ_TARGET_ARM64
-static void callback_mcode_init(global_State *g, uint32_t *page)
+static void *callback_mcode_init(global_State *g, uint32_t *page)
 {
   uint32_t *p = page;
   void *target = (void *)lj_vm_ffi_callback;
@@ -185,10 +185,10 @@ static void callback_mcode_init(global_State *g, uint32_t *page)
     *p = A64I_LE(A64I_B | A64F_S26((page-p) & 0x03ffffffu));
     p++;
   }
-  lua_assert(p - page <= CALLBACK_MCODE_SIZE);
+  return p;
 }
 #elif LJ_TARGET_PPC
-static void callback_mcode_init(global_State *g, uint32_t *page)
+static void *callback_mcode_init(global_State *g, uint32_t *page)
 {
   uint32_t *p = page;
   void *target = (void *)lj_vm_ffi_callback;
@@ -204,10 +204,10 @@ static void callback_mcode_init(global_State *g, uint32_t *page)
     *p = PPCI_B | (((page-p) & 0x00ffffffu) << 2);
     p++;
   }
-  lua_assert(p - page <= CALLBACK_MCODE_SIZE);
+  return p;
 }
 #elif LJ_TARGET_MIPS
-static void callback_mcode_init(global_State *g, uint32_t *page)
+static void *callback_mcode_init(global_State *g, uint32_t *page)
 {
   uint32_t *p = page;
   uintptr_t target = (uintptr_t)(void *)lj_vm_ffi_callback;
@@ -236,11 +236,11 @@ static void callback_mcode_init(global_State *g, uint32_t *page)
     p++;
     *p++ = MIPSI_LI | MIPSF_T(RID_R1) | slot;
   }
-  lua_assert(p - page <= CALLBACK_MCODE_SIZE);
+  return p;
 }
 #else
 /* Missing support for this architecture. */
-#define callback_mcode_init(g, p)       UNUSED(p)
+#define callback_mcode_init(g, p)       (p)
 #endif
 
 /* -- Machine code management --------------------------------------------- */
@@ -263,7 +263,7 @@ static void callback_mcode_init(global_State *g, uint32_t *page)
 static void callback_mcode_new(CTState *cts)
 {
   size_t sz = (size_t)CALLBACK_MCODE_SIZE;
-  void *p;
+  void *p, *pe;
   if (CALLBACK_MAX_SLOT == 0)
     lj_err_caller(cts->L, LJ_ERR_FFI_CBACKOV);
 #if LJ_TARGET_WINDOWS
@@ -280,7 +280,10 @@ static void callback_mcode_new(CTState *cts)
   p = lj_mem_new(cts->L, sz);
 #endif
   cts->cb.mcode = p;
-  callback_mcode_init(cts->g, p);
+  pe = callback_mcode_init(cts->g, p);
+  UNUSED(pe);
+  lj_assertCTS((size_t)((char *)pe - (char *)p) <= sz,
+               "miscalculated CALLBACK_MAX_SLOT");
   lj_mcode_sync(p, (char *)p + sz);
 #if LJ_TARGET_WINDOWS
   {
@@ -421,8 +424,9 @@ void lj_ccallback_mcode_free(CTState *cts)
 
 #define CALLBACK_HANDLE_GPR \
   if (n > 1) { \
-    lua_assert(((LJ_ABI_SOFTFP && ctype_isnum(cta->info)) ||  /* double. */ \
-                ctype_isinteger(cta->info)) && n == 2);  /* int64_t. */ \
+    lj_assertCTS(((LJ_ABI_SOFTFP && ctype_isnum(cta->info)) ||  /* double. */ \
+                 ctype_isinteger(cta->info)) && n == 2,  /* int64_t. */ \
+                 "bad GPR type"); \
     ngpr = (ngpr + 1u) & ~1u;  /* Align int64_t to regpair. */ \
   } \
   if (ngpr + n <= maxgpr) { \
@@ -579,7 +583,7 @@ static void callback_conv_args(CTState *cts, lua_State *L)
       CTSize sz;
       int isfp;
       MSize n;
-      lua_assert(ctype_isfield(ctf->info));
+      lj_assertCTS(ctype_isfield(ctf->info), "field expected");
       cta = ctype_rawchild(cts, ctf);
       isfp = ctype_isfp(cta->info);
       sz = (cta->size + CTSIZE_PTR-1) & ~(CTSIZE_PTR-1);
@@ -671,7 +675,7 @@ lua_State * LJ_FASTCALL lj_ccallback_enter(CTState *cts, void *cf)
 {
   lua_State *L = cts->L;
   global_State *g = cts->g;
-  lua_assert(L != NULL);
+  lj_assertG(L != NULL, "uninitialized cts->L in callback");
   if (tvref(g->jit_base)) {
     setstrV(L, L->top++, lj_err_str(L, LJ_ERR_FFI_BADCBACK));
     if (g->panic) g->panic(L);
@@ -756,7 +760,7 @@ static CType *callback_checkfunc(CTState *cts, CType *ct)
       CType *ctf = ctype_get(cts, fid);
       if (!ctype_isattrib(ctf->info)) {
         CType *cta;
-        lua_assert(ctype_isfield(ctf->info));
+        lj_assertCTS(ctype_isfield(ctf->info), "field expected");
         cta = ctype_rawchild(cts, ctf);
         if (!(ctype_isenum(cta->info) || ctype_isptr(cta->info) ||
               (ctype_isnum(cta->info) && cta->size <= 8)) ||
diff --git a/src/lj_cconv.c b/src/lj_cconv.c
index 03ed0ce2..400c2ae6 100644
--- a/src/lj_cconv.c
+++ b/src/lj_cconv.c
@@ -122,19 +122,25 @@ void lj_cconv_ct_ct(CTState *cts, CType *d, CType *s,
   CTInfo dinfo = d->info, sinfo = s->info;
   void *tmpptr;
 
-  lua_assert(!ctype_isenum(dinfo) && !ctype_isenum(sinfo));
-  lua_assert(!ctype_isattrib(dinfo) && !ctype_isattrib(sinfo));
+  lj_assertCTS(!ctype_isenum(dinfo) && !ctype_isenum(sinfo),
+               "unresolved enum");
+  lj_assertCTS(!ctype_isattrib(dinfo) && !ctype_isattrib(sinfo),
+               "unstripped attribute");
 
   if (ctype_type(dinfo) > CT_MAYCONVERT || ctype_type(sinfo) > CT_MAYCONVERT)
     goto err_conv;
 
   /* Some basic sanity checks. */
-  lua_assert(!ctype_isnum(dinfo) || dsize > 0);
-  lua_assert(!ctype_isnum(sinfo) || ssize > 0);
-  lua_assert(!ctype_isbool(dinfo) || dsize == 1 || dsize == 4);
-  lua_assert(!ctype_isbool(sinfo) || ssize == 1 || ssize == 4);
-  lua_assert(!ctype_isinteger(dinfo) || (1u<<lj_fls(dsize)) == dsize);
-  lua_assert(!ctype_isinteger(sinfo) || (1u<<lj_fls(ssize)) == ssize);
+  lj_assertCTS(!ctype_isnum(dinfo) || dsize > 0, "bad size for number type");
+  lj_assertCTS(!ctype_isnum(sinfo) || ssize > 0, "bad size for number type");
+  lj_assertCTS(!ctype_isbool(dinfo) || dsize == 1 || dsize == 4,
+               "bad size for bool type");
+  lj_assertCTS(!ctype_isbool(sinfo) || ssize == 1 || ssize == 4,
+               "bad size for bool type");
+  lj_assertCTS(!ctype_isinteger(dinfo) || (1u<<lj_fls(dsize)) == dsize,
+               "bad size for integer type");
+  lj_assertCTS(!ctype_isinteger(sinfo) || (1u<<lj_fls(ssize)) == ssize,
+               "bad size for integer type");
 
   switch (cconv_idx2(dinfo, sinfo)) {
   /* Destination is a bool. */
@@ -357,7 +363,7 @@ void lj_cconv_ct_ct(CTState *cts, CType *d, CType *s,
     if ((flags & CCF_CAST) || (d->info & CTF_VLA) || d != s)
       goto err_conv;  /* Must be exact same type. */
 copyval:  /* Copy value. */
-    lua_assert(dsize == ssize);
+    lj_assertCTS(dsize == ssize, "value copy with different sizes");
     memcpy(dp, sp, dsize);
     break;
 
@@ -389,7 +395,7 @@ int lj_cconv_tv_ct(CTState *cts, CType *s, CTypeID sid,
         lj_cconv_ct_ct(cts, ctype_get(cts, CTID_DOUBLE), s,
                        (uint8_t *)&o->n, sp, 0);
         /* Numbers are NOT canonicalized here! Beware of uninitialized data. */
-        lua_assert(tvisnum(o));
+        lj_assertCTS(tvisnum(o), "non-canonical NaN passed");
       }
     } else {
       uint32_t b = s->size == 1 ? (*sp != 0) : (*(int *)sp != 0);
@@ -406,7 +412,7 @@ int lj_cconv_tv_ct(CTState *cts, CType *s, CTypeID sid,
     CTSize sz;
   copyval:  /* Copy value. */
     sz = s->size;
-    lua_assert(sz != CTSIZE_INVALID);
+    lj_assertCTS(sz != CTSIZE_INVALID, "value copy with invalid size");
     /* Attributes are stripped, qualifiers are kept (but mostly ignored). */
     cd = lj_cdata_new(cts, ctype_typeid(cts, s), sz);
     setcdataV(cts->L, o, cd);
@@ -421,19 +427,22 @@ int lj_cconv_tv_bf(CTState *cts, CType *s, TValue *o, uint8_t *sp)
   CTInfo info = s->info;
   CTSize pos, bsz;
   uint32_t val;
-  lua_assert(ctype_isbitfield(info));
+  lj_assertCTS(ctype_isbitfield(info), "bitfield expected");
   /* NYI: packed bitfields may cause misaligned reads. */
   switch (ctype_bitcsz(info)) {
   case 4: val = *(uint32_t *)sp; break;
   case 2: val = *(uint16_t *)sp; break;
   case 1: val = *(uint8_t *)sp; break;
-  default: lua_assert(0); val = 0; break;
+  default:
+    lj_assertCTS(0, "bad bitfield container size %d", ctype_bitcsz(info));
+    val = 0;
+    break;
   }
   /* Check if a packed bitfield crosses a container boundary. */
   pos = ctype_bitpos(info);
   bsz = ctype_bitbsz(info);
-  lua_assert(pos < 8*ctype_bitcsz(info));
-  lua_assert(bsz > 0 && bsz <= 8*ctype_bitcsz(info));
+  lj_assertCTS(pos < 8*ctype_bitcsz(info), "bad bitfield position");
+  lj_assertCTS(bsz > 0 && bsz <= 8*ctype_bitcsz(info), "bad bitfield size");
   if (pos + bsz > 8*ctype_bitcsz(info))
     lj_err_caller(cts->L, LJ_ERR_FFI_NYIPACKBIT);
   if (!(info & CTF_BOOL)) {
@@ -449,7 +458,7 @@ int lj_cconv_tv_bf(CTState *cts, CType *s, TValue *o, uint8_t *sp)
     }
   } else {
     uint32_t b = (val >> pos) & 1;
-    lua_assert(bsz == 1);
+    lj_assertCTS(bsz == 1, "bad bool bitfield size");
     setboolV(o, b);
     setboolV(&cts->g->tmptv2, b);  /* Remember for trace recorder. */
   }
@@ -553,7 +562,7 @@ void lj_cconv_ct_tv(CTState *cts, CType *d,
     sid = cdataV(o)->ctypeid;
     s = ctype_get(cts, sid);
     if (ctype_isref(s->info)) {  /* Resolve reference for value. */
-      lua_assert(s->size == CTSIZE_PTR);
+      lj_assertCTS(s->size == CTSIZE_PTR, "ref is not pointer-sized");
       sp = *(void **)sp;
       sid = ctype_cid(s->info);
     }
@@ -571,7 +580,7 @@ void lj_cconv_ct_tv(CTState *cts, CType *d,
       CType *cct = lj_ctype_getfield(cts, d, str, &ofs);
       if (!cct || !ctype_isconstval(cct->info))
         goto err_conv;
-      lua_assert(d->size == 4);
+      lj_assertCTS(d->size == 4, "only 32 bit enum supported");  /* NYI */
       sp = (uint8_t *)&cct->size;
       sid = ctype_cid(cct->info);
     } else if (ctype_isrefarray(d->info)) {  /* Copy string to array. */
@@ -635,10 +644,10 @@ void lj_cconv_bf_tv(CTState *cts, CType *d, uint8_t *dp, TValue *o)
   CTInfo info = d->info;
   CTSize pos, bsz;
   uint32_t val, mask;
-  lua_assert(ctype_isbitfield(info));
+  lj_assertCTS(ctype_isbitfield(info), "bitfield expected");
   if ((info & CTF_BOOL)) {
     uint8_t tmpbool;
-    lua_assert(ctype_bitbsz(info) == 1);
+    lj_assertCTS(ctype_bitbsz(info) == 1, "bad bool bitfield size");
     lj_cconv_ct_tv(cts, ctype_get(cts, CTID_BOOL), &tmpbool, o, 0);
     val = tmpbool;
   } else {
@@ -647,8 +656,8 @@ void lj_cconv_bf_tv(CTState *cts, CType *d, uint8_t *dp, TValue *o)
   }
   pos = ctype_bitpos(info);
   bsz = ctype_bitbsz(info);
-  lua_assert(pos < 8*ctype_bitcsz(info));
-  lua_assert(bsz > 0 && bsz <= 8*ctype_bitcsz(info));
+  lj_assertCTS(pos < 8*ctype_bitcsz(info), "bad bitfield position");
+  lj_assertCTS(bsz > 0 && bsz <= 8*ctype_bitcsz(info), "bad bitfield size");
   /* Check if a packed bitfield crosses a container boundary. */
   if (pos + bsz > 8*ctype_bitcsz(info))
     lj_err_caller(cts->L, LJ_ERR_FFI_NYIPACKBIT);
@@ -659,7 +668,9 @@ void lj_cconv_bf_tv(CTState *cts, CType *d, uint8_t *dp, TValue *o)
   case 4: *(uint32_t *)dp = (*(uint32_t *)dp & ~mask) | (uint32_t)val; break;
   case 2: *(uint16_t *)dp = (*(uint16_t *)dp & ~mask) | (uint16_t)val; break;
   case 1: *(uint8_t *)dp = (*(uint8_t *)dp & ~mask) | (uint8_t)val; break;
-  default: lua_assert(0); break;
+  default:
+    lj_assertCTS(0, "bad bitfield container size %d", ctype_bitcsz(info));
+    break;
   }
 }
 
diff --git a/src/lj_cconv.h b/src/lj_cconv.h
index 2fd5a71c..1f716d2a 100644
--- a/src/lj_cconv.h
+++ b/src/lj_cconv.h
@@ -27,13 +27,14 @@ enum {
 static LJ_AINLINE uint32_t cconv_idx(CTInfo info)
 {
   uint32_t idx = ((info >> 26) & 15u);  /* Dispatch bits. */
-  lua_assert(ctype_type(info) <= CT_MAYCONVERT);
+  lj_assertX(ctype_type(info) <= CT_MAYCONVERT,
+             "cannot convert ctype %08x", info);
 #if LJ_64
   idx = ((uint32_t)(U64x(f436fff5,fff7f021) >> 4*idx) & 15u);
 #else
   idx = (((idx < 8 ? 0xfff7f021u : 0xf436fff5) >> 4*(idx & 7u)) & 15u);
 #endif
-  lua_assert(idx < 8);
+  lj_assertX(idx < 8, "cannot convert ctype %08x", info);
   return idx;
 }
 
diff --git a/src/lj_cdata.c b/src/lj_cdata.c
index 10d9423d..a827d1ec 100644
--- a/src/lj_cdata.c
+++ b/src/lj_cdata.c
@@ -35,7 +35,7 @@ GCcdata *lj_cdata_newv(lua_State *L, CTypeID id, CTSize sz, CTSize align)
   uintptr_t adata = (uintptr_t)p + sizeof(GCcdataVar) + sizeof(GCcdata);
   uintptr_t almask = (1u << align) - 1u;
   GCcdata *cd = (GCcdata *)(((adata + almask) & ~almask) - sizeof(GCcdata));
-  lua_assert((char *)cd - p < 65536);
+  lj_assertL((char *)cd - p < 65536, "excessive cdata alignment");
   cdatav(cd)->offset = (uint16_t)((char *)cd - p);
   cdatav(cd)->extra = extra;
   cdatav(cd)->len = sz;
@@ -76,8 +76,8 @@ void LJ_FASTCALL lj_cdata_free(global_State *g, GCcdata *cd)
   } else if (LJ_LIKELY(!cdataisv(cd))) {
     CType *ct = ctype_raw(ctype_ctsG(g), cd->ctypeid);
     CTSize sz = ctype_hassize(ct->info) ? ct->size : CTSIZE_PTR;
-    lua_assert(ctype_hassize(ct->info) || ctype_isfunc(ct->info) ||
-               ctype_isextern(ct->info));
+    lj_assertG(ctype_hassize(ct->info) || ctype_isfunc(ct->info) ||
+               ctype_isextern(ct->info), "free of ctype without a size");
     lj_mem_free(g, cd, sizeof(GCcdata) + sz);
   } else {
     lj_mem_free(g, memcdatav(cd), sizecdatav(cd));
@@ -115,7 +115,7 @@ CType *lj_cdata_index(CTState *cts, GCcdata *cd, cTValue *key, uint8_t **pp,
 
   /* Resolve reference for cdata object. */
   if (ctype_isref(ct->info)) {
-    lua_assert(ct->size == CTSIZE_PTR);
+    lj_assertCTS(ct->size == CTSIZE_PTR, "ref is not pointer-sized");
     p = *(uint8_t **)p;
     ct = ctype_child(cts, ct);
   }
@@ -126,7 +126,8 @@ collect_attrib:
     if (ctype_attrib(ct->info) == CTA_QUAL) *qual |= ct->size;
     ct = ctype_child(cts, ct);
   }
-  lua_assert(!ctype_isref(ct->info));  /* Interning rejects refs to refs. */
+  /* Interning rejects refs to refs. */
+  lj_assertCTS(!ctype_isref(ct->info), "bad ref of ref");
 
   if (tvisint(key)) {
     idx = (ptrdiff_t)intV(key);
@@ -212,7 +213,8 @@ collect_attrib:
 static void cdata_getconst(CTState *cts, TValue *o, CType *ct)
 {
   CType *ctt = ctype_child(cts, ct);
-  lua_assert(ctype_isinteger(ctt->info) && ctt->size <= 4);
+  lj_assertCTS(ctype_isinteger(ctt->info) && ctt->size <= 4,
+               "only 32 bit const supported");  /* NYI */
   /* Constants are already zero-extended/sign-extended to 32 bits. */
   if ((ctt->info & CTF_UNSIGNED) && (int32_t)ct->size < 0)
     setnumV(o, (lua_Number)(uint32_t)ct->size);
@@ -233,13 +235,14 @@ int lj_cdata_get(CTState *cts, CType *s, TValue *o, uint8_t *sp)
   }
 
   /* Get child type of pointer/array/field. */
-  lua_assert(ctype_ispointer(s->info) || ctype_isfield(s->info));
+  lj_assertCTS(ctype_ispointer(s->info) || ctype_isfield(s->info),
+               "pointer or field expected");
   sid = ctype_cid(s->info);
   s = ctype_get(cts, sid);
 
   /* Resolve reference for field. */
   if (ctype_isref(s->info)) {
-    lua_assert(s->size == CTSIZE_PTR);
+    lj_assertCTS(s->size == CTSIZE_PTR, "ref is not pointer-sized");
     sp = *(uint8_t **)sp;
     sid = ctype_cid(s->info);
     s = ctype_get(cts, sid);
@@ -266,12 +269,13 @@ void lj_cdata_set(CTState *cts, CType *d, uint8_t *dp, TValue *o, CTInfo qual)
   }
 
   /* Get child type of pointer/array/field. */
-  lua_assert(ctype_ispointer(d->info) || ctype_isfield(d->info));
+  lj_assertCTS(ctype_ispointer(d->info) || ctype_isfield(d->info),
+               "pointer or field expected");
   d = ctype_child(cts, d);
 
   /* Resolve reference for field. */
   if (ctype_isref(d->info)) {
-    lua_assert(d->size == CTSIZE_PTR);
+    lj_assertCTS(d->size == CTSIZE_PTR, "ref is not pointer-sized");
     dp = *(uint8_t **)dp;
     d = ctype_child(cts, d);
   }
@@ -286,7 +290,8 @@ void lj_cdata_set(CTState *cts, CType *d, uint8_t *dp, TValue *o, CTInfo qual)
     d = ctype_child(cts, d);
   }
 
-  lua_assert(ctype_hassize(d->info) && !ctype_isvoid(d->info));
+  lj_assertCTS(ctype_hassize(d->info), "store to ctype without size");
+  lj_assertCTS(!ctype_isvoid(d->info), "store to void type");
 
   if (((d->info|qual) & CTF_CONST)) {
   err_const:
diff --git a/src/lj_cdata.h b/src/lj_cdata.h
index c1089e64..c3df8ba0 100644
--- a/src/lj_cdata.h
+++ b/src/lj_cdata.h
@@ -18,7 +18,7 @@ static LJ_AINLINE void *cdata_getptr(void *p, CTSize sz)
   if (LJ_64 && sz == 4) {  /* Support 32 bit pointers on 64 bit targets. */
     return ((void *)(uintptr_t)*(uint32_t *)p);
   } else {
-    lua_assert(sz == CTSIZE_PTR);
+    lj_assertX(sz == CTSIZE_PTR, "bad pointer size %d", sz);
     return *(void **)p;
   }
 }
@@ -29,7 +29,7 @@ static LJ_AINLINE void cdata_setptr(void *p, CTSize sz, const void *v)
   if (LJ_64 && sz == 4) {  /* Support 32 bit pointers on 64 bit targets. */
     *(uint32_t *)p = (uint32_t)(uintptr_t)v;
   } else {
-    lua_assert(sz == CTSIZE_PTR);
+    lj_assertX(sz == CTSIZE_PTR, "bad pointer size %d", sz);
     *(void **)p = (void *)v;
   }
 }
@@ -40,7 +40,8 @@ static LJ_AINLINE GCcdata *lj_cdata_new(CTState *cts, CTypeID id, CTSize sz)
   GCcdata *cd;
 #ifdef LUA_USE_ASSERT
   CType *ct = ctype_raw(cts, id);
-  lua_assert((ctype_hassize(ct->info) ? ct->size : CTSIZE_PTR) == sz);
+  lj_assertCTS((ctype_hassize(ct->info) ? ct->size : CTSIZE_PTR) == sz,
+               "inconsistent size of fixed-size cdata alloc");
 #endif
   cd = (GCcdata *)lj_mem_newgco(cts->L, sizeof(GCcdata) + sz);
   cd->gct = ~LJ_TCDATA;
diff --git a/src/lj_clib.c b/src/lj_clib.c
index 2ea6ff45..8da41a83 100644
--- a/src/lj_clib.c
+++ b/src/lj_clib.c
@@ -350,7 +350,8 @@ TValue *lj_clib_index(lua_State *L, CLibrary *cl, GCstr *name)
       lj_err_callerv(L, LJ_ERR_FFI_NODECL, strdata(name));
     if (ctype_isconstval(ct->info)) {
       CType *ctt = ctype_child(cts, ct);
-      lua_assert(ctype_isinteger(ctt->info) && ctt->size <= 4);
+      lj_assertCTS(ctype_isinteger(ctt->info) && ctt->size <= 4,
+                   "only 32 bit const supported");  /* NYI */
       if ((ctt->info & CTF_UNSIGNED) && (int32_t)ct->size < 0)
         setnumV(tv, (lua_Number)(uint32_t)ct->size);
       else
@@ -362,7 +363,8 @@ TValue *lj_clib_index(lua_State *L, CLibrary *cl, GCstr *name)
 #endif
       void *p = clib_getsym(cl, sym);
       GCcdata *cd;
-      lua_assert(ctype_isfunc(ct->info) || ctype_isextern(ct->info));
+      lj_assertCTS(ctype_isfunc(ct->info) || ctype_isextern(ct->info),
+                   "unexpected ctype %08x in clib", ct->info);
 #if LJ_TARGET_X86 && LJ_ABI_WIN
       /* Retry with decorated name for fastcall/stdcall functions. */
       if (!p && ctype_isfunc(ct->info)) {
diff --git a/src/lj_cparse.c b/src/lj_cparse.c
index a393965e..78628bba 100644
--- a/src/lj_cparse.c
+++ b/src/lj_cparse.c
@@ -28,6 +28,12 @@
 ** If in doubt, please check the input against your favorite C compiler.
 */
 
+#ifdef LUA_USE_ASSERT
+#define lj_assertCP(c, ...)     (lj_assertG_(G(cp->L), (c), __VA_ARGS__))
+#else
+#define lj_assertCP(c, ...)     ((void)cp)
+#endif
+
 /* -- Miscellaneous ------------------------------------------------------- */
 
 /* Match string against a C literal. */
@@ -61,7 +67,7 @@ LJ_NORET static void cp_err(CPState *cp, ErrMsg em);
 
 static const char *cp_tok2str(CPState *cp, CPToken tok)
 {
-  lua_assert(tok < CTOK_FIRSTDECL);
+  lj_assertCP(tok < CTOK_FIRSTDECL, "bad CPToken %d", tok);
   if (tok > CTOK_OFS)
     return ctoknames[tok-CTOK_OFS-1];
   else if (!lj_char_iscntrl(tok))
@@ -392,7 +398,7 @@ static void cp_init(CPState *cp)
   cp->curpack = 0;
   cp->packstack[0] = 255;
   lj_buf_init(cp->L, &cp->sb);
-  lua_assert(cp->p != NULL);
+  lj_assertCP(cp->p != NULL, "uninitialized cp->p");
   cp_get(cp);  /* Read-ahead first char. */
   cp->tok = 0;
   cp->tmask = CPNS_DEFAULT;
@@ -853,12 +859,13 @@ static CTypeID cp_decl_intern(CPState *cp, CPDecl *decl)
     /* The cid is already part of info for copies of pointers/functions. */
     idx = ct->next;
     if (ctype_istypedef(info)) {
-      lua_assert(id == 0);
+      lj_assertCP(id == 0, "typedef not at toplevel");
       id = ctype_cid(info);
       /* Always refetch info/size, since struct/enum may have been completed. */
       cinfo = ctype_get(cp->cts, id)->info;
       csize = ctype_get(cp->cts, id)->size;
-      lua_assert(ctype_isstruct(cinfo) || ctype_isenum(cinfo));
+      lj_assertCP(ctype_isstruct(cinfo) || ctype_isenum(cinfo),
+                  "typedef of bad type");
     } else if (ctype_isfunc(info)) {  /* Intern function. */
       CType *fct;
       CTypeID fid;
@@ -891,7 +898,7 @@ static CTypeID cp_decl_intern(CPState *cp, CPDecl *decl)
       /* Inherit csize/cinfo from original type. */
     } else {
       if (ctype_isnum(info)) {  /* Handle mode/vector-size attributes. */
-        lua_assert(id == 0);
+        lj_assertCP(id == 0, "number not at toplevel");
         if (!(info & CTF_BOOL)) {
           CTSize msize = ctype_msizeP(decl->attr);
           CTSize vsize = ctype_vsizeP(decl->attr);
@@ -946,7 +953,7 @@ static CTypeID cp_decl_intern(CPState *cp, CPDecl *decl)
           info = (info & ~CTF_ALIGN) | (cinfo & CTF_ALIGN);
         info |= (cinfo & CTF_QUAL);  /* Inherit qual. */
       } else {
-        lua_assert(ctype_isvoid(info));
+        lj_assertCP(ctype_isvoid(info), "bad ctype %08x", info);
       }
       csize = size;
       cinfo = info+id;
@@ -1585,7 +1592,7 @@ end_decl:
         cp_errmsg(cp, cp->tok, LJ_ERR_FFI_DECLSPEC);
       sz = sizeof(int);
     }
-    lua_assert(sz != 0);
+    lj_assertCP(sz != 0, "basic ctype with zero size");
     info += CTALIGN(lj_fls(sz));  /* Use natural alignment. */
     info += (decl->attr & CTF_QUAL);  /* Merge qualifiers. */
     cp_push(decl, info, sz);
@@ -1845,7 +1852,7 @@ static void cp_decl_multi(CPState *cp)
           /* Treat both static and extern function declarations as extern. */
           ct = ctype_get(cp->cts, ctypeid);
           /* We always get new anonymous functions (typedefs are copied). */
-          lua_assert(gcref(ct->name) == NULL);
+          lj_assertCP(gcref(ct->name) == NULL, "unexpected named function");
           id = ctypeid;  /* Just name it. */
         } else if ((scl & CDF_STATIC)) {  /* Accept static constants. */
           id = cp_decl_constinit(cp, &ct, ctypeid);
@@ -1902,7 +1909,7 @@ static TValue *cpcparser(lua_State *L, lua_CFunction dummy, void *ud)
     cp_decl_single(cp);
   if (cp->param && cp->param != cp->L->top)
     cp_err(cp, LJ_ERR_FFI_NUMPARAM);
-  lua_assert(cp->depth == 0);
+  lj_assertCP(cp->depth == 0, "unbalanced cparser declaration depth");
   return NULL;
 }
 
diff --git a/src/lj_crecord.c b/src/lj_crecord.c
index e50fdbf7..7ae1479e 100644
--- a/src/lj_crecord.c
+++ b/src/lj_crecord.c
@@ -61,7 +61,8 @@ static GCcdata *argv2cdata(jit_State *J, TRef tr, cTValue *o)
 static CTypeID crec_constructor(jit_State *J, GCcdata *cd, TRef tr)
 {
   CTypeID id;
-  lua_assert(tref_iscdata(tr) && cd->ctypeid == CTID_CTYPEID);
+  lj_assertJ(tref_iscdata(tr) && cd->ctypeid == CTID_CTYPEID,
+             "expected CTypeID cdata");
   id = *(CTypeID *)cdataptr(cd);
   tr = emitir(IRT(IR_FLOAD, IRT_INT), tr, IRFL_CDATA_INT);
   emitir(IRTG(IR_EQ, IRT_INT), tr, lj_ir_kint(J, (int32_t)id));
@@ -237,13 +238,14 @@ static void crec_copy(jit_State *J, TRef trdst, TRef trsrc, TRef trlen,
     if (len > CREC_COPY_MAXLEN) goto fallback;
     if (ct) {
       CTState *cts = ctype_ctsG(J2G(J));
-      lua_assert(ctype_isarray(ct->info) || ctype_isstruct(ct->info));
+      lj_assertJ(ctype_isarray(ct->info) || ctype_isstruct(ct->info),
+                 "copy of non-aggregate");
       if (ctype_isarray(ct->info)) {
         CType *cct = ctype_rawchild(cts, ct);
         tp = crec_ct2irt(cts, cct);
         if (tp == IRT_CDATA) goto rawcopy;
         step = lj_ir_type_size[tp];
-        lua_assert((len & (step-1)) == 0);
+        lj_assertJ((len & (step-1)) == 0, "copy of fractional size");
       } else if ((ct->info & CTF_UNION)) {
         step = (1u << ctype_align(ct->info));
         goto rawcopy;
@@ -629,7 +631,8 @@ static TRef crec_ct_tv(jit_State *J, CType *d, TRef dp, TRef sp, cTValue *sval)
       /* Specialize to the name of the enum constant. */
       emitir(IRTG(IR_EQ, IRT_STR), sp, lj_ir_kstr(J, str));
       if (cct && ctype_isconstval(cct->info)) {
-        lua_assert(ctype_child(cts, cct)->size == 4);
+        lj_assertJ(ctype_child(cts, cct)->size == 4,
+                   "only 32 bit const supported");  /* NYI */
         svisnz = (void *)(intptr_t)(ofs != 0);
         sp = lj_ir_kint(J, (int32_t)ofs);
         sid = ctype_cid(cct->info);
@@ -757,7 +760,7 @@ static void crec_index_bf(jit_State *J, RecordFFData *rd, TRef ptr, CTInfo info)
   IRType t = IRT_I8 + 2*lj_fls(ctype_bitcsz(info)) + ((info&CTF_UNSIGNED)?1:0);
   TRef tr = emitir(IRT(IR_XLOAD, t), ptr, 0);
   CTSize pos = ctype_bitpos(info), bsz = ctype_bitbsz(info), shift = 32 - bsz;
-  lua_assert(t <= IRT_U32);  /* NYI: 64 bit bitfields. */
+  lj_assertJ(t <= IRT_U32, "only 32 bit bitfields supported");  /* NYI */
   if (rd->data == 0) {  /* __index metamethod. */
     if ((info & CTF_BOOL)) {
       tr = emitir(IRTI(IR_BAND), tr, lj_ir_kint(J, (int32_t)((1u << pos))));
@@ -769,7 +772,7 @@ static void crec_index_bf(jit_State *J, RecordFFData *rd, TRef ptr, CTInfo info)
       tr = emitir(IRTI(IR_BSHL), tr, lj_ir_kint(J, shift - pos));
       tr = emitir(IRTI(IR_BSAR), tr, lj_ir_kint(J, shift));
     } else {
-      lua_assert(bsz < 32);  /* Full-size fields cannot end up here. */
+      lj_assertJ(bsz < 32, "unexpected full bitfield index");
       tr = emitir(IRTI(IR_BSHR), tr, lj_ir_kint(J, pos));
       tr = emitir(IRTI(IR_BAND), tr, lj_ir_kint(J, (int32_t)((1u << bsz)-1)));
       /* We can omit the U32 to NUM conversion, since bsz < 32. */
@@ -884,7 +887,7 @@ again:
           crec_index_bf(J, rd, ptr, fct->info);
           return;
         } else {
-          lua_assert(ctype_isfield(fct->info));
+          lj_assertJ(ctype_isfield(fct->info), "field expected");
           sid = ctype_cid(fct->info);
         }
       }
@@ -1111,7 +1114,7 @@ static TRef crec_call_args(jit_State *J, RecordFFData *rd,
     if (fid) {  /* Get argument type from field. */
       CType *ctf = ctype_get(cts, fid);
       fid = ctf->sib;
-      lua_assert(ctype_isfield(ctf->info));
+      lj_assertJ(ctype_isfield(ctf->info), "field expected");
       did = ctype_cid(ctf->info);
     } else {
       if (!(ct->info & CTF_VARARG))
diff --git a/src/lj_ctype.c b/src/lj_ctype.c
index 7e96e1bc..0e3f8855 100644
--- a/src/lj_ctype.c
+++ b/src/lj_ctype.c
@@ -153,7 +153,7 @@ CTypeID lj_ctype_new(CTState *cts, CType **ctp)
 {
   CTypeID id = cts->top;
   CType *ct;
-  lua_assert(cts->L);
+  lj_assertCTS(cts->L, "uninitialized cts->L");
   if (LJ_UNLIKELY(id >= cts->sizetab)) {
     if (id >= CTID_MAX) lj_err_msg(cts->L, LJ_ERR_TABOV);
 #ifdef LUAJIT_CTYPE_CHECK_ANCHOR
@@ -182,7 +182,7 @@ CTypeID lj_ctype_intern(CTState *cts, CTInfo info, CTSize size)
 {
   uint32_t h = ct_hashtype(info, size);
   CTypeID id = cts->hash[h];
-  lua_assert(cts->L);
+  lj_assertCTS(cts->L, "uninitialized cts->L");
   while (id) {
     CType *ct = ctype_get(cts, id);
     if (ct->info == info && ct->size == size)
@@ -298,9 +298,9 @@ CTSize lj_ctype_vlsize(CTState *cts, CType *ct, CTSize nelem)
     }
     ct = ctype_raw(cts, arrid);
   }
-  lua_assert(ctype_isvlarray(ct->info));  /* Must be a VLA. */
+  lj_assertCTS(ctype_isvlarray(ct->info), "VLA expected");
   ct = ctype_rawchild(cts, ct);  /* Get array element. */
-  lua_assert(ctype_hassize(ct->info));
+  lj_assertCTS(ctype_hassize(ct->info), "bad VLA without size");
   /* Calculate actual size of VLA and check for overflow. */
   xsz += (uint64_t)ct->size * nelem;
   return xsz < 0x80000000u ? (CTSize)xsz : CTSIZE_INVALID;
@@ -323,7 +323,8 @@ CTInfo lj_ctype_info(CTState *cts, CTypeID id, CTSize *szp)
     } else {
       if (!(qual & CTFP_ALIGNED)) qual |= (info & CTF_ALIGN);
       qual |= (info & ~(CTF_ALIGN|CTMASK_CID));
-      lua_assert(ctype_hassize(info) || ctype_isfunc(info));
+      lj_assertCTS(ctype_hassize(info) || ctype_isfunc(info),
+                   "ctype without size");
       *szp = ctype_isfunc(info) ? CTSIZE_INVALID : ct->size;
       break;
     }
@@ -528,7 +529,7 @@ static void ctype_repr(CTRepr *ctr, CTypeID id)
       ctype_appc(ctr, ')');
       break;
     default:
-      lua_assert(0);
+      lj_assertG_(ctr->cts->g, 0, "bad ctype %08x", info);
       break;
     }
     ct = ctype_get(ctr->cts, ctype_cid(info));
diff --git a/src/lj_ctype.h b/src/lj_ctype.h
index 73cefef8..8c8fc790 100644
--- a/src/lj_ctype.h
+++ b/src/lj_ctype.h
@@ -260,6 +260,12 @@ typedef struct CTState {
 
 #define CT_MEMALIGN     3       /* Alignment guaranteed by memory allocator. */
 
+#ifdef LUA_USE_ASSERT
+#define lj_assertCTS(c, ...)    (lj_assertG_(cts->g, (c), __VA_ARGS__))
+#else
+#define lj_assertCTS(c, ...)    ((void)cts)
+#endif
+
 /* -- Predefined types ---------------------------------------------------- */
 
 /* Target-dependent types. */
@@ -392,7 +398,8 @@ static LJ_AINLINE CTState *ctype_cts(lua_State *L)
 /* Check C type ID for validity when assertions are enabled. */
 static LJ_AINLINE CTypeID ctype_check(CTState *cts, CTypeID id)
 {
-  lua_assert(id > 0 && id < cts->top); UNUSED(cts);
+  UNUSED(cts);
+  lj_assertCTS(id > 0 && id < cts->top, "bad CTID %d", id);
   return id;
 }
 
@@ -408,8 +415,9 @@ static LJ_AINLINE CType *ctype_get(CTState *cts, CTypeID id)
 /* Get child C type. */
 static LJ_AINLINE CType *ctype_child(CTState *cts, CType *ct)
 {
-  lua_assert(!(ctype_isvoid(ct->info) || ctype_isstruct(ct->info) ||
-             ctype_isbitfield(ct->info)));  /* These don't have children. */
+  lj_assertCTS(!(ctype_isvoid(ct->info) || ctype_isstruct(ct->info) ||
+               ctype_isbitfield(ct->info)),
+               "ctype %08x has no children", ct->info);
   return ctype_get(cts, ctype_cid(ct->info));
 }
 
diff --git a/src/lj_debug.c b/src/lj_debug.c
index 2f2ea9f0..c1f0f314 100644
--- a/src/lj_debug.c
+++ b/src/lj_debug.c
@@ -55,7 +55,8 @@ static BCPos debug_framepc(lua_State *L, GCfunc *fn, cTValue *nextframe)
   const BCIns *ins;
   GCproto *pt;
   BCPos pos;
-  lua_assert(fn->c.gct == ~LJ_TFUNC || fn->c.gct == ~LJ_TTHREAD);
+  lj_assertL(fn->c.gct == ~LJ_TFUNC || fn->c.gct == ~LJ_TTHREAD,
+             "function or frame expected");
   if (!isluafunc(fn)) {  /* Cannot derive a PC for non-Lua functions. */
     return NO_BCPOS;
   } else if (nextframe == NULL) {  /* Lua function on top. */
@@ -100,7 +101,7 @@ static BCPos debug_framepc(lua_State *L, GCfunc *fn, cTValue *nextframe)
 #if LJ_HASJIT
   if (pos > pt->sizebc) {  /* Undo the effects of lj_trace_exit for JLOOP. */
     GCtrace *T = (GCtrace *)((char *)(ins-1) - offsetof(GCtrace, startins));
-    lua_assert(bc_isret(bc_op(ins[-1])));
+    lj_assertL(bc_isret(bc_op(ins[-1])), "return bytecode expected");
     pos = proto_bcpos(pt, mref(T->startpc, const BCIns));
   }
 #endif
@@ -133,7 +134,7 @@ static BCLine debug_frameline(lua_State *L, GCfunc *fn, cTValue *nextframe)
   BCPos pc = debug_framepc(L, fn, nextframe);
   if (pc != NO_BCPOS) {
     GCproto *pt = funcproto(fn);
-    lua_assert(pc <= pt->sizebc);
+    lj_assertL(pc <= pt->sizebc, "PC out of range");
     return lj_debug_line(pt, pc);
   }
   return -1;
@@ -214,7 +215,7 @@ static TValue *debug_localname(lua_State *L, const lua_Debug *ar,
 const char *lj_debug_uvname(GCproto *pt, uint32_t idx)
 {
   const uint8_t *p = proto_uvinfo(pt);
-  lua_assert(idx < pt->sizeuv);
+  lj_assertX(idx < pt->sizeuv, "bad upvalue index");
   if (!p) return "";
   if (idx) while (*p++ || --idx) ;
   return (const char *)p;
@@ -439,13 +440,14 @@ int lj_debug_getinfo(lua_State *L, const char *what, lj_Debug *ar, int ext)
   } else {
     uint32_t offset = (uint32_t)ar->i_ci & 0xffff;
     uint32_t size = (uint32_t)ar->i_ci >> 16;
-    lua_assert(offset != 0);
+    lj_assertL(offset != 0, "bad frame offset");
     frame = tvref(L->stack) + offset;
     if (size) nextframe = frame + size;
-    lua_assert(frame <= tvref(L->maxstack) &&
-               (!nextframe || nextframe <= tvref(L->maxstack)));
+    lj_assertL(frame <= tvref(L->maxstack) &&
+               (!nextframe || nextframe <= tvref(L->maxstack)),
+               "broken frame chain");
     fn = frame_func(frame);
-    lua_assert(fn->c.gct == ~LJ_TFUNC);
+    lj_assertL(fn->c.gct == ~LJ_TFUNC, "bad frame function");
   }
   for (; *what; what++) {
     if (*what == 'S') {
diff --git a/src/lj_def.h b/src/lj_def.h
index 75aaeb79..af0687c4 100644
--- a/src/lj_def.h
+++ b/src/lj_def.h
@@ -337,14 +337,28 @@ static LJ_AINLINE uint32_t lj_getu32(const void *v)
 #define LJ_FUNCA_NORET  LJ_FUNCA LJ_NORET
 #define LJ_ASMF_NORET   LJ_ASMF LJ_NORET
 
-/* Runtime assertions. */
-#ifdef lua_assert
-#define check_exp(c, e)         (lua_assert(c), (e))
-#define api_check(l, e)         lua_assert(e)
+/* Internal assertions. */
+#if defined(LUA_USE_ASSERT) || defined(LUA_USE_APICHECK)
+#define lj_assert_check(g, c, ...) \
+  ((c) ? (void)0 : \
+   (lj_assert_fail((g), __FILE__, __LINE__, __func__, __VA_ARGS__), 0))
+#define lj_checkapi(c, ...)     lj_assert_check(G(L), (c), __VA_ARGS__)
 #else
-#define lua_assert(c)           ((void)0)
+#define lj_checkapi(c, ...)     ((void)L)
+#endif
+
+#ifdef LUA_USE_ASSERT
+#define lj_assertG_(g, c, ...)  lj_assert_check((g), (c), __VA_ARGS__)
+#define lj_assertG(c, ...)      lj_assert_check(g, (c), __VA_ARGS__)
+#define lj_assertL(c, ...)      lj_assert_check(G(L), (c), __VA_ARGS__)
+#define lj_assertX(c, ...)      lj_assert_check(NULL, (c), __VA_ARGS__)
+#define check_exp(c, e)         (lj_assertX((c), #c), (e))
+#else
+#define lj_assertG_(g, c, ...)  ((void)0)
+#define lj_assertG(c, ...)      ((void)g)
+#define lj_assertL(c, ...)      ((void)L)
+#define lj_assertX(c, ...)      ((void)0)
 #define check_exp(c, e)         (e)
-#define api_check               luai_apicheck
 #endif
 
 /* Static assertions. */
diff --git a/src/lj_dispatch.c b/src/lj_dispatch.c
index 39416d00..c608e223 100644
--- a/src/lj_dispatch.c
+++ b/src/lj_dispatch.c
@@ -367,7 +367,7 @@ static void callhook(lua_State *L, int event, BCLine line)
     hook_enter(g);
 #endif
     hookf(L, &ar);
-    lua_assert(hook_active(g));
+    lj_assertG(hook_active(g), "active hook flag removed");
     setgcref(g->cur_L, obj2gco(L));
 #if LJ_HASPROFILE && !LJ_PROFILE_SIGPROF
     lj_profile_hook_leave(g);
@@ -415,7 +415,8 @@ void LJ_FASTCALL lj_dispatch_ins(lua_State *L, const BCIns *pc)
 #endif
       J->L = L;
       lj_trace_ins(J, pc-1);  /* The interpreter bytecode PC is offset by 1. */
-      lua_assert(L->top - L->base == delta);
+      lj_assertG(L->top - L->base == delta,
+                 "unbalanced stack after tracing of instruction");
     }
   }
 #endif
@@ -475,7 +476,8 @@ ASMFunction LJ_FASTCALL lj_dispatch_call(lua_State *L, const BCIns *pc)
 #endif
     pc = (const BCIns *)((uintptr_t)pc & ~(uintptr_t)1);
     lj_trace_hot(J, pc);
-    lua_assert(L->top - L->base == delta);
+    lj_assertG(L->top - L->base == delta,
+               "unbalanced stack after hot call");
     goto out;
   } else if (J->state != LJ_TRACE_IDLE &&
              !(g->hookmask & (HOOK_GC|HOOK_VMEVENT))) {
@@ -484,7 +486,8 @@ ASMFunction LJ_FASTCALL lj_dispatch_call(lua_State *L, const BCIns *pc)
 #endif
     /* Record the FUNC* bytecodes, too. */
     lj_trace_ins(J, pc-1);  /* The interpreter bytecode PC is offset by 1. */
-    lua_assert(L->top - L->base == delta);
+    lj_assertG(L->top - L->base == delta,
+               "unbalanced stack after hot instruction");
   }
 #endif
   if ((g->hookmask & LUA_MASKCALL)) {
diff --git a/src/lj_emit_arm.h b/src/lj_emit_arm.h
index 25561549..165d546d 100644
--- a/src/lj_emit_arm.h
+++ b/src/lj_emit_arm.h
@@ -81,7 +81,8 @@ static void emit_m(ASMState *as, ARMIns ai, Reg rm)
 
 static void emit_lsox(ASMState *as, ARMIns ai, Reg rd, Reg rn, int32_t ofs)
 {
-  lua_assert(ofs >= -255 && ofs <= 255);
+  lj_assertA(ofs >= -255 && ofs <= 255,
+             "load/store offset %d out of range", ofs);
   if (ofs < 0) ofs = -ofs; else ai |= ARMI_LS_U;
   *--as->mcp = ai | ARMI_LS_P | ARMI_LSX_I | ARMF_D(rd) | ARMF_N(rn) |
                ((ofs & 0xf0) << 4) | (ofs & 0x0f);
@@ -89,7 +90,8 @@ static void emit_lsox(ASMState *as, ARMIns ai, Reg rd, Reg rn, int32_t ofs)
 
 static void emit_lso(ASMState *as, ARMIns ai, Reg rd, Reg rn, int32_t ofs)
 {
-  lua_assert(ofs >= -4095 && ofs <= 4095);
+  lj_assertA(ofs >= -4095 && ofs <= 4095,
+             "load/store offset %d out of range", ofs);
   /* Combine LDR/STR pairs to LDRD/STRD. */
   if (*as->mcp == (ai|ARMI_LS_P|ARMI_LS_U|ARMF_D(rd^1)|ARMF_N(rn)|(ofs^4)) &&
       (ai & ~(ARMI_LDR^ARMI_STR)) == ARMI_STR && rd != rn &&
@@ -106,7 +108,8 @@ static void emit_lso(ASMState *as, ARMIns ai, Reg rd, Reg rn, int32_t ofs)
 #if !LJ_SOFTFP
 static void emit_vlso(ASMState *as, ARMIns ai, Reg rd, Reg rn, int32_t ofs)
 {
-  lua_assert(ofs >= -1020 && ofs <= 1020 && (ofs&3) == 0);
+  lj_assertA(ofs >= -1020 && ofs <= 1020 && (ofs&3) == 0,
+             "load/store offset %d out of range", ofs);
   if (ofs < 0) ofs = -ofs; else ai |= ARMI_LS_U;
   *--as->mcp = ai | ARMI_LS_P | ARMF_D(rd & 15) | ARMF_N(rn) | (ofs >> 2);
 }
@@ -124,7 +127,7 @@ static int emit_kdelta1(ASMState *as, Reg d, int32_t i)
   while (work) {
     Reg r = rset_picktop(work);
     IRRef ref = regcost_ref(as->cost[r]);
-    lua_assert(r != d);
+    lj_assertA(r != d, "dest reg not free");
     if (emit_canremat(ref)) {
       int32_t delta = i - (ra_iskref(ref) ? ra_krefk(as, ref) : IR(ref)->i);
       uint32_t k = emit_isk12(ARMI_ADD, delta);
@@ -142,13 +145,13 @@ static int emit_kdelta1(ASMState *as, Reg d, int32_t i)
 }
 
 /* Try to find a two step delta relative to another constant. */
-static int emit_kdelta2(ASMState *as, Reg d, int32_t i)
+static int emit_kdelta2(ASMState *as, Reg rd, int32_t i)
 {
   RegSet work = ~as->freeset & RSET_GPR;
   while (work) {
     Reg r = rset_picktop(work);
     IRRef ref = regcost_ref(as->cost[r]);
-    lua_assert(r != d);
+    lj_assertA(r != rd, "dest reg %d not free", rd);
     if (emit_canremat(ref)) {
       int32_t other = ra_iskref(ref) ? ra_krefk(as, ref) : IR(ref)->i;
       if (other) {
@@ -159,8 +162,8 @@ static int emit_kdelta2(ASMState *as, Reg d, int32_t i)
         k2 = emit_isk12(0, delta & (255 << sh));
         k = emit_isk12(0, delta & ~(255 << sh));
         if (k) {
-          emit_dn(as, ARMI_ADD^k2^inv, d, d);
-          emit_dn(as, ARMI_ADD^k^inv, d, r);
+          emit_dn(as, ARMI_ADD^k2^inv, rd, rd);
+          emit_dn(as, ARMI_ADD^k^inv, rd, r);
           return 1;
         }
       }
@@ -171,23 +174,24 @@ static int emit_kdelta2(ASMState *as, Reg d, int32_t i)
 }
 
 /* Load a 32 bit constant into a GPR. */
-static void emit_loadi(ASMState *as, Reg r, int32_t i)
+static void emit_loadi(ASMState *as, Reg rd, int32_t i)
 {
   uint32_t k = emit_isk12(ARMI_MOV, i);
-  lua_assert(rset_test(as->freeset, r) || r == RID_TMP);
+  lj_assertA(rset_test(as->freeset, rd) || rd == RID_TMP,
+             "dest reg %d not free", rd);
   if (k) {
     /* Standard K12 constant. */
-    emit_d(as, ARMI_MOV^k, r);
+    emit_d(as, ARMI_MOV^k, rd);
   } else if ((as->flags & JIT_F_ARMV6T2) && (uint32_t)i < 0x00010000u) {
     /* 16 bit loword constant for ARMv6T2. */
-    emit_d(as, ARMI_MOVW|(i & 0x0fff)|((i & 0xf000)<<4), r);
-  } else if (emit_kdelta1(as, r, i)) {
+    emit_d(as, ARMI_MOVW|(i & 0x0fff)|((i & 0xf000)<<4), rd);
+  } else if (emit_kdelta1(as, rd, i)) {
     /* One step delta relative to another constant. */
   } else if ((as->flags & JIT_F_ARMV6T2)) {
     /* 32 bit hiword/loword constant for ARMv6T2. */
-    emit_d(as, ARMI_MOVT|((i>>16) & 0x0fff)|(((i>>16) & 0xf000)<<4), r);
-    emit_d(as, ARMI_MOVW|(i & 0x0fff)|((i & 0xf000)<<4), r);
-  } else if (emit_kdelta2(as, r, i)) {
+    emit_d(as, ARMI_MOVT|((i>>16) & 0x0fff)|(((i>>16) & 0xf000)<<4), rd);
+    emit_d(as, ARMI_MOVW|(i & 0x0fff)|((i & 0xf000)<<4), rd);
+  } else if (emit_kdelta2(as, rd, i)) {
     /* Two step delta relative to another constant. */
   } else {
     /* Otherwise construct the constant with up to 4 instructions. */
@@ -197,15 +201,15 @@ static void emit_loadi(ASMState *as, Reg r, int32_t i)
       int32_t m = i & (255 << sh);
       i &= ~(255 << sh);
       if (i == 0) {
-        emit_d(as, ARMI_MOV ^ emit_isk12(0, m), r);
+        emit_d(as, ARMI_MOV ^ emit_isk12(0, m), rd);
         break;
       }
-      emit_dn(as, ARMI_ORR ^ emit_isk12(0, m), r, r);
+      emit_dn(as, ARMI_ORR ^ emit_isk12(0, m), rd, rd);
     }
   }
 }
 
-#define emit_loada(as, r, addr)         emit_loadi(as, (r), i32ptr((addr)))
+#define emit_loada(as, rd, addr)        emit_loadi(as, (rd), i32ptr((addr)))
 
 static Reg ra_allock(ASMState *as, intptr_t k, RegSet allow);
 
@@ -261,7 +265,7 @@ static void emit_branch(ASMState *as, ARMIns ai, MCode *target)
 {
   MCode *p = as->mcp;
   ptrdiff_t delta = (target - p) - 1;
-  lua_assert(((delta + 0x00800000) >> 24) == 0);
+  lj_assertA(((delta + 0x00800000) >> 24) == 0, "branch target out of range");
   *--p = ai | ((uint32_t)delta & 0x00ffffffu);
   as->mcp = p;
 }
@@ -289,7 +293,7 @@ static void emit_call(ASMState *as, void *target)
 static void emit_movrr(ASMState *as, IRIns *ir, Reg dst, Reg src)
 {
 #if LJ_SOFTFP
-  lua_assert(!irt_isnum(ir->t)); UNUSED(ir);
+  lj_assertA(!irt_isnum(ir->t), "unexpected FP op"); UNUSED(ir);
 #else
   if (dst >= RID_MAX_GPR) {
     emit_dm(as, irt_isnum(ir->t) ? ARMI_VMOV_D : ARMI_VMOV_S,
@@ -313,7 +317,7 @@ static void emit_movrr(ASMState *as, IRIns *ir, Reg dst, Reg src)
 static void emit_loadofs(ASMState *as, IRIns *ir, Reg r, Reg base, int32_t ofs)
 {
 #if LJ_SOFTFP
-  lua_assert(!irt_isnum(ir->t)); UNUSED(ir);
+  lj_assertA(!irt_isnum(ir->t), "unexpected FP op"); UNUSED(ir);
 #else
   if (r >= RID_MAX_GPR)
     emit_vlso(as, irt_isnum(ir->t) ? ARMI_VLDR_D : ARMI_VLDR_S, r, base, ofs);
@@ -326,7 +330,7 @@ static void emit_loadofs(ASMState *as, IRIns *ir, Reg r, Reg base, int32_t ofs)
 static void emit_storeofs(ASMState *as, IRIns *ir, Reg r, Reg base, int32_t ofs)
 {
 #if LJ_SOFTFP
-  lua_assert(!irt_isnum(ir->t)); UNUSED(ir);
+  lj_assertA(!irt_isnum(ir->t), "unexpected FP op"); UNUSED(ir);
 #else
   if (r >= RID_MAX_GPR)
     emit_vlso(as, irt_isnum(ir->t) ? ARMI_VSTR_D : ARMI_VSTR_S, r, base, ofs);
diff --git a/src/lj_emit_arm64.h b/src/lj_emit_arm64.h
index f09c0f3a..61a2df82 100644
--- a/src/lj_emit_arm64.h
+++ b/src/lj_emit_arm64.h
@@ -8,8 +8,9 @@
 
 /* -- Constant encoding --------------------------------------------------- */
 
-static uint64_t get_k64val(IRIns *ir)
+static uint64_t get_k64val(ASMState *as, IRRef ref)
 {
+  IRIns *ir = IR(ref);
   if (ir->o == IR_KINT64) {
     return ir_kint64(ir)->u64;
   } else if (ir->o == IR_KGC) {
@@ -17,7 +18,8 @@ static uint64_t get_k64val(IRIns *ir)
   } else if (ir->o == IR_KPTR || ir->o == IR_KKPTR) {
     return (uint64_t)ir_kptr(ir);
   } else {
-    lua_assert(ir->o == IR_KINT || ir->o == IR_KNULL);
+    lj_assertA(ir->o == IR_KINT || ir->o == IR_KNULL,
+               "bad 64 bit const IR op %d", ir->o);
     return ir->i;  /* Sign-extended. */
   }
 }
@@ -122,7 +124,7 @@ static int emit_checkofs(A64Ins ai, int64_t ofs)
 static void emit_lso(ASMState *as, A64Ins ai, Reg rd, Reg rn, int64_t ofs)
 {
   int ot = emit_checkofs(ai, ofs), sc = (ai >> 30) & 3;
-  lua_assert(ot);
+  lj_assertA(ot, "load/store offset %d out of range", ofs);
   /* Combine LDR/STR pairs to LDP/STP. */
   if ((sc == 2 || sc == 3) &&
       (!(ai & 0x400000) || rd != rn) &&
@@ -166,10 +168,10 @@ static int emit_kdelta(ASMState *as, Reg rd, uint64_t k, int lim)
   while (work) {
     Reg r = rset_picktop(work);
     IRRef ref = regcost_ref(as->cost[r]);
-    lua_assert(r != rd);
+    lj_assertA(r != rd, "dest reg %d not free", rd);
     if (ref < REF_TRUE) {
       uint64_t kx = ra_iskref(ref) ? (uint64_t)ra_krefk(as, ref) :
-                                     get_k64val(IR(ref));
+                                     get_k64val(as, ref);
       int64_t delta = (int64_t)(k - kx);
       if (delta == 0) {
         emit_dm(as, A64I_MOVx, rd, r);
@@ -312,7 +314,7 @@ static void emit_cond_branch(ASMState *as, A64CC cond, MCode *target)
 {
   MCode *p = --as->mcp;
   ptrdiff_t delta = target - p;
-  lua_assert(A64F_S_OK(delta, 19));
+  lj_assertA(A64F_S_OK(delta, 19), "branch target out of range");
   *p = A64I_BCC | A64F_S19(delta) | cond;
 }
 
@@ -320,7 +322,7 @@ static void emit_branch(ASMState *as, A64Ins ai, MCode *target)
 {
   MCode *p = --as->mcp;
   ptrdiff_t delta = target - p;
-  lua_assert(A64F_S_OK(delta, 26));
+  lj_assertA(A64F_S_OK(delta, 26), "branch target out of range");
   *p = ai | A64F_S26(delta);
 }
 
@@ -328,7 +330,8 @@ static void emit_tnb(ASMState *as, A64Ins ai, Reg r, uint32_t bit, MCode *target
 {
   MCode *p = --as->mcp;
   ptrdiff_t delta = target - p;
-  lua_assert(bit < 63 && A64F_S_OK(delta, 14));
+  lj_assertA(bit < 63, "bit number out of range");
+  lj_assertA(A64F_S_OK(delta, 14), "branch target out of range");
   if (bit > 31) ai |= A64I_X;
   *p = ai | A64F_BIT(bit & 31) | A64F_S14(delta) | r;
 }
@@ -337,7 +340,7 @@ static void emit_cnb(ASMState *as, A64Ins ai, Reg r, MCode *target)
 {
   MCode *p = --as->mcp;
   ptrdiff_t delta = target - p;
-  lua_assert(A64F_S_OK(delta, 19));
+  lj_assertA(A64F_S_OK(delta, 19), "branch target out of range");
   *p = ai | A64F_S19(delta) | r;
 }
 
diff --git a/src/lj_emit_mips.h b/src/lj_emit_mips.h
index bdabcf16..3de5ff18 100644
--- a/src/lj_emit_mips.h
+++ b/src/lj_emit_mips.h
@@ -4,8 +4,9 @@
 */
 
 #if LJ_64
-static intptr_t get_k64val(IRIns *ir)
+static intptr_t get_k64val(ASMState *as, IRRef ref)
 {
+  IRIns *ir = IR(ref);
   if (ir->o == IR_KINT64) {
     return (intptr_t)ir_kint64(ir)->u64;
   } else if (ir->o == IR_KGC) {
@@ -15,16 +16,17 @@ static intptr_t get_k64val(IRIns *ir)
   } else if (LJ_SOFTFP && ir->o == IR_KNUM) {
     return (intptr_t)ir_knum(ir)->u64;
   } else {
-    lua_assert(ir->o == IR_KINT || ir->o == IR_KNULL);
+    lj_assertA(ir->o == IR_KINT || ir->o == IR_KNULL,
+               "bad 64 bit const IR op %d", ir->o);
     return ir->i;  /* Sign-extended. */
   }
 }
 #endif
 
 #if LJ_64
-#define get_kval(ir)            get_k64val(ir)
+#define get_kval(as, ref)       get_k64val(as, ref)
 #else
-#define get_kval(ir)            ((ir)->i)
+#define get_kval(as, ref)       (IR((ref))->i)
 #endif
 
 /* -- Emit basic instructions --------------------------------------------- */
@@ -82,18 +84,18 @@ static void emit_tsml(ASMState *as, MIPSIns mi, Reg rt, Reg rs, uint32_t msb,
 #define emit_canremat(ref)      ((ref) <= REF_BASE)
 
 /* Try to find a one step delta relative to another constant. */
-static int emit_kdelta1(ASMState *as, Reg t, intptr_t i)
+static int emit_kdelta1(ASMState *as, Reg rd, intptr_t i)
 {
   RegSet work = ~as->freeset & RSET_GPR;
   while (work) {
     Reg r = rset_picktop(work);
     IRRef ref = regcost_ref(as->cost[r]);
-    lua_assert(r != t);
+    lj_assertA(r != rd, "dest reg %d not free", rd);
     if (ref < ASMREF_L) {
       intptr_t delta = (intptr_t)((uintptr_t)i -
-        (uintptr_t)(ra_iskref(ref) ? ra_krefk(as, ref) : get_kval(IR(ref))));
+        (uintptr_t)(ra_iskref(ref) ? ra_krefk(as, ref) : get_kval(as, ref)));
       if (checki16(delta)) {
-        emit_tsi(as, MIPSI_AADDIU, t, r, delta);
+        emit_tsi(as, MIPSI_AADDIU, rd, r, delta);
         return 1;
       }
     }
@@ -223,7 +225,7 @@ static void emit_branch(ASMState *as, MIPSIns mi, Reg rs, Reg rt, MCode *target)
 {
   MCode *p = as->mcp;
   ptrdiff_t delta = target - p;
-  lua_assert(((delta + 0x8000) >> 16) == 0);
+  lj_assertA(((delta + 0x8000) >> 16) == 0, "branch target out of range");
   *--p = mi | MIPSF_S(rs) | MIPSF_T(rt) | ((uint32_t)delta & 0xffffu);
   as->mcp = p;
 }
@@ -299,7 +301,7 @@ static void emit_storeofs(ASMState *as, IRIns *ir, Reg r, Reg base, int32_t ofs)
 static void emit_addptr(ASMState *as, Reg r, int32_t ofs)
 {
   if (ofs) {
-    lua_assert(checki16(ofs));
+    lj_assertA(checki16(ofs), "offset %d out of range", ofs);
     emit_tsi(as, MIPSI_AADDIU, r, r, ofs);
   }
 }
diff --git a/src/lj_emit_ppc.h b/src/lj_emit_ppc.h
index 69765528..6bc74c04 100644
--- a/src/lj_emit_ppc.h
+++ b/src/lj_emit_ppc.h
@@ -41,13 +41,13 @@ static void emit_rot(ASMState *as, PPCIns pi, Reg ra, Reg rs,
 
 static void emit_slwi(ASMState *as, Reg ra, Reg rs, int32_t n)
 {
-  lua_assert(n >= 0 && n < 32);
+  lj_assertA(n >= 0 && n < 32, "shift out or range");
   emit_rot(as, PPCI_RLWINM, ra, rs, n, 0, 31-n);
 }
 
 static void emit_rotlwi(ASMState *as, Reg ra, Reg rs, int32_t n)
 {
-  lua_assert(n >= 0 && n < 32);
+  lj_assertA(n >= 0 && n < 32, "shift out or range");
   emit_rot(as, PPCI_RLWINM, ra, rs, n, 0, 31);
 }
 
@@ -57,17 +57,17 @@ static void emit_rotlwi(ASMState *as, Reg ra, Reg rs, int32_t n)
 #define emit_canremat(ref)      ((ref) <= REF_BASE)
 
 /* Try to find a one step delta relative to another constant. */
-static int emit_kdelta1(ASMState *as, Reg t, int32_t i)
+static int emit_kdelta1(ASMState *as, Reg rd, int32_t i)
 {
   RegSet work = ~as->freeset & RSET_GPR;
   while (work) {
     Reg r = rset_picktop(work);
     IRRef ref = regcost_ref(as->cost[r]);
-    lua_assert(r != t);
+    lj_assertA(r != rd, "dest reg %d not free", rd);
     if (ref < ASMREF_L) {
       int32_t delta = i - (ra_iskref(ref) ? ra_krefk(as, ref) : IR(ref)->i);
       if (checki16(delta)) {
-        emit_tai(as, PPCI_ADDI, t, r, delta);
+        emit_tai(as, PPCI_ADDI, rd, r, delta);
         return 1;
       }
     }
@@ -144,7 +144,7 @@ static void emit_condbranch(ASMState *as, PPCIns pi, PPCCC cc, MCode *target)
 {
   MCode *p = --as->mcp;
   ptrdiff_t delta = (char *)target - (char *)p;
-  lua_assert(((delta + 0x8000) >> 16) == 0);
+  lj_assertA(((delta + 0x8000) >> 16) == 0, "branch target out of range");
   pi ^= (delta & 0x8000) * (PPCF_Y/0x8000);
   *p = pi | PPCF_CC(cc) | ((uint32_t)delta & 0xffffu);
 }
diff --git a/src/lj_emit_x86.h b/src/lj_emit_x86.h
index b17e28a5..66750a96 100644
--- a/src/lj_emit_x86.h
+++ b/src/lj_emit_x86.h
@@ -92,7 +92,7 @@ static void emit_rr(ASMState *as, x86Op xo, Reg r1, Reg r2)
 /* [addr] is sign-extended in x64 and must be in lower 2G (not 4G). */
 static int32_t ptr2addr(const void *p)
 {
-  lua_assert((uintptr_t)p < (uintptr_t)0x80000000);
+  lj_assertX((uintptr_t)p < (uintptr_t)0x80000000, "pointer outside 2G range");
   return i32ptr(p);
 }
 #else
@@ -208,7 +208,7 @@ static void emit_mrm(ASMState *as, x86Op xo, Reg rr, Reg rb)
       rb = RID_ESP;
 #endif
     } else if (LJ_GC64 && rb == RID_RIP) {
-      lua_assert(as->mrm.idx == RID_NONE);
+      lj_assertA(as->mrm.idx == RID_NONE, "RIP-rel mrm cannot have index");
       mode = XM_OFS0;
       p -= 4;
       *(int32_t *)p = as->mrm.ofs;
@@ -401,7 +401,8 @@ static void emit_loadk64(ASMState *as, Reg r, IRIns *ir)
     emit_rma(as, xo, r64, k);
   } else {
     if (ir->i) {
-      lua_assert(*k == *(uint64_t*)(as->mctop - ir->i));
+      lj_assertA(*k == *(uint64_t*)(as->mctop - ir->i),
+                 "bad interned 64 bit constant");
     } else if (as->curins <= as->stopins && rset_test(RSET_GPR, r)) {
       emit_loadu64(as, r, *k);
       return;
@@ -433,7 +434,7 @@ static void emit_sjmp(ASMState *as, MCLabel target)
 {
   MCode *p = as->mcp;
   ptrdiff_t delta = target - p;
-  lua_assert(delta == (int8_t)delta);
+  lj_assertA(delta == (int8_t)delta, "short jump target out of range");
   p[-1] = (MCode)(int8_t)delta;
   p[-2] = XI_JMPs;
   as->mcp = p - 2;
@@ -445,7 +446,7 @@ static void emit_sjcc(ASMState *as, int cc, MCLabel target)
 {
   MCode *p = as->mcp;
   ptrdiff_t delta = target - p;
-  lua_assert(delta == (int8_t)delta);
+  lj_assertA(delta == (int8_t)delta, "short jump target out of range");
   p[-1] = (MCode)(int8_t)delta;
   p[-2] = (MCode)(XI_JCCs+(cc&15));
   as->mcp = p - 2;
@@ -471,10 +472,11 @@ static void emit_sfixup(ASMState *as, MCLabel source)
 #define emit_label(as)          ((as)->mcp)
 
 /* Compute relative 32 bit offset for jump and call instructions. */
-static LJ_AINLINE int32_t jmprel(MCode *p, MCode *target)
+static LJ_AINLINE int32_t jmprel(jit_State *J, MCode *p, MCode *target)
 {
   ptrdiff_t delta = target - p;
-  lua_assert(delta == (int32_t)delta);
+  UNUSED(J);
+  lj_assertJ(delta == (int32_t)delta, "jump target out of range");
   return (int32_t)delta;
 }
 
@@ -482,7 +484,7 @@ static LJ_AINLINE int32_t jmprel(MCode *p, MCode *target)
 static void emit_jcc(ASMState *as, int cc, MCode *target)
 {
   MCode *p = as->mcp;
-  *(int32_t *)(p-4) = jmprel(p, target);
+  *(int32_t *)(p-4) = jmprel(as->J, p, target);
   p[-5] = (MCode)(XI_JCCn+(cc&15));
   p[-6] = 0x0f;
   as->mcp = p - 6;
@@ -492,7 +494,7 @@ static void emit_jcc(ASMState *as, int cc, MCode *target)
 static void emit_jmp(ASMState *as, MCode *target)
 {
   MCode *p = as->mcp;
-  *(int32_t *)(p-4) = jmprel(p, target);
+  *(int32_t *)(p-4) = jmprel(as->J, p, target);
   p[-5] = XI_JMP;
   as->mcp = p - 5;
 }
@@ -509,7 +511,7 @@ static void emit_call_(ASMState *as, MCode *target)
     return;
   }
 #endif
-  *(int32_t *)(p-4) = jmprel(p, target);
+  *(int32_t *)(p-4) = jmprel(as->J, p, target);
   p[-5] = XI_CALL;
   as->mcp = p - 5;
 }
diff --git a/src/lj_err.c b/src/lj_err.c
index 52498932..41fbf5c7 100644
--- a/src/lj_err.c
+++ b/src/lj_err.c
@@ -589,7 +589,7 @@ static ptrdiff_t finderrfunc(lua_State *L)
         return savestack(L, frame_prevd(frame)+1);  /* xpcall's errorfunc. */
       return 0;
     default:
-      lua_assert(0);
+      lj_assertL(0, "bad frame type");
       return 0;
     }
   }
diff --git a/src/lj_func.c b/src/lj_func.c
index 9afdb638..fb267885 100644
--- a/src/lj_func.c
+++ b/src/lj_func.c
@@ -24,9 +24,11 @@ void LJ_FASTCALL lj_func_freeproto(global_State *g, GCproto *pt)
 
 /* -- Upvalues ------------------------------------------------------------ */
 
-static void unlinkuv(GCupval *uv)
+static void unlinkuv(global_State *g, GCupval *uv)
 {
-  lua_assert(uvprev(uvnext(uv)) == uv && uvnext(uvprev(uv)) == uv);
+  UNUSED(g);
+  lj_assertG(uvprev(uvnext(uv)) == uv && uvnext(uvprev(uv)) == uv,
+             "broken upvalue chain");
   setgcrefr(uvnext(uv)->prev, uv->prev);
   setgcrefr(uvprev(uv)->next, uv->next);
 }
@@ -40,7 +42,7 @@ static GCupval *func_finduv(lua_State *L, TValue *slot)
   GCupval *uv;
   /* Search the sorted list of open upvalues. */
   while (gcref(*pp) != NULL && uvval((p = gco2uv(gcref(*pp)))) >= slot) {
-    lua_assert(!p->closed && uvval(p) != &p->tv);
+    lj_assertG(!p->closed && uvval(p) != &p->tv, "closed upvalue in chain");
     if (uvval(p) == slot) {  /* Found open upvalue pointing to same slot? */
       if (isdead(g, obj2gco(p)))  /* Resurrect it, if it's dead. */
         flipwhite(obj2gco(p));
@@ -61,7 +63,8 @@ static GCupval *func_finduv(lua_State *L, TValue *slot)
   setgcrefr(uv->next, g->uvhead.next);
   setgcref(uvnext(uv)->prev, obj2gco(uv));
   setgcref(g->uvhead.next, obj2gco(uv));
-  lua_assert(uvprev(uvnext(uv)) == uv && uvnext(uvprev(uv)) == uv);
+  lj_assertG(uvprev(uvnext(uv)) == uv && uvnext(uvprev(uv)) == uv,
+             "broken upvalue chain");
   return uv;
 }
 
@@ -84,12 +87,13 @@ void LJ_FASTCALL lj_func_closeuv(lua_State *L, TValue *level)
   while (gcref(L->openupval) != NULL &&
          uvval((uv = gco2uv(gcref(L->openupval)))) >= level) {
     GCobj *o = obj2gco(uv);
-    lua_assert(!isblack(o) && !uv->closed && uvval(uv) != &uv->tv);
+    lj_assertG(!isblack(o), "bad black upvalue");
+    lj_assertG(!uv->closed && uvval(uv) != &uv->tv, "closed upvalue in chain");
     setgcrefr(L->openupval, uv->nextgc);  /* No longer in open list. */
     if (isdead(g, o)) {
       lj_func_freeuv(g, uv);
     } else {
-      unlinkuv(uv);
+      unlinkuv(g, uv);
       lj_gc_closeuv(g, uv);
     }
   }
@@ -98,7 +102,7 @@ void LJ_FASTCALL lj_func_closeuv(lua_State *L, TValue *level)
 void LJ_FASTCALL lj_func_freeuv(global_State *g, GCupval *uv)
 {
   if (!uv->closed)
-    unlinkuv(uv);
+    unlinkuv(g, uv);
   lj_mem_freet(g, uv);
 }
 
diff --git a/src/lj_gc.c b/src/lj_gc.c
index 81439aab..671b5983 100644
--- a/src/lj_gc.c
+++ b/src/lj_gc.c
@@ -42,7 +42,8 @@
 
 /* Mark a TValue (if needed). */
 #define gc_marktv(g, tv) \
-  { lua_assert(!tvisgcv(tv) || (~itype(tv) == gcval(tv)->gch.gct)); \
+  { lj_assertG(!tvisgcv(tv) || (~itype(tv) == gcval(tv)->gch.gct), \
+               "TValue and GC type mismatch"); \
     if (tviswhite(tv)) gc_mark(g, gcV(tv)); }
 
 /* Mark a GCobj (if needed). */
@@ -56,7 +57,8 @@
 static void gc_mark(global_State *g, GCobj *o)
 {
   int gct = o->gch.gct;
-  lua_assert(iswhite(o) && !isdead(g, o));
+  lj_assertG(iswhite(o), "mark of non-white object");
+  lj_assertG(!isdead(g, o), "mark of dead object");
   white2gray(o);
   if (LJ_UNLIKELY(gct == ~LJ_TUDATA)) {
     GCtab *mt = tabref(gco2ud(o)->metatable);
@@ -69,8 +71,9 @@ static void gc_mark(global_State *g, GCobj *o)
     if (uv->closed)
       gray2black(o);  /* Closed upvalues are never gray. */
   } else if (gct != ~LJ_TSTR && gct != ~LJ_TCDATA) {
-    lua_assert(gct == ~LJ_TFUNC || gct == ~LJ_TTAB ||
-               gct == ~LJ_TTHREAD || gct == ~LJ_TPROTO || gct == ~LJ_TTRACE);
+    lj_assertG(gct == ~LJ_TFUNC || gct == ~LJ_TTAB ||
+               gct == ~LJ_TTHREAD || gct == ~LJ_TPROTO || gct == ~LJ_TTRACE,
+               "bad GC type %d", gct);
     setgcrefr(o->gch.gclist, g->gc.gray);
     setgcref(g->gc.gray, o);
   }
@@ -103,7 +106,8 @@ static void gc_mark_uv(global_State *g)
 {
   GCupval *uv;
   for (uv = uvnext(&g->uvhead); uv != &g->uvhead; uv = uvnext(uv)) {
-    lua_assert(uvprev(uvnext(uv)) == uv && uvnext(uvprev(uv)) == uv);
+    lj_assertG(uvprev(uvnext(uv)) == uv && uvnext(uvprev(uv)) == uv,
+               "broken upvalue chain");
     if (isgray(obj2gco(uv)))
       gc_marktv(g, uvval(uv));
   }
@@ -198,7 +202,7 @@ static int gc_traverse_tab(global_State *g, GCtab *t)
     for (i = 0; i <= hmask; i++) {
       Node *n = &node[i];
       if (!tvisnil(&n->val)) {  /* Mark non-empty slot. */
-        lua_assert(!tvisnil(&n->key));
+        lj_assertG(!tvisnil(&n->key), "mark of nil key in non-empty slot");
         if (!(weak & LJ_GC_WEAKKEY)) gc_marktv(g, &n->key);
         if (!(weak & LJ_GC_WEAKVAL)) gc_marktv(g, &n->val);
       }
@@ -213,7 +217,8 @@ static void gc_traverse_func(global_State *g, GCfunc *fn)
   gc_markobj(g, tabref(fn->c.env));
   if (isluafunc(fn)) {
     uint32_t i;
-    lua_assert(fn->l.nupvalues <= funcproto(fn)->sizeuv);
+    lj_assertG(fn->l.nupvalues <= funcproto(fn)->sizeuv,
+               "function upvalues out of range");
     gc_markobj(g, funcproto(fn));
     for (i = 0; i < fn->l.nupvalues; i++)  /* Mark Lua function upvalues. */
       gc_markobj(g, &gcref(fn->l.uvptr[i])->uv);
@@ -229,7 +234,7 @@ static void gc_traverse_func(global_State *g, GCfunc *fn)
 static void gc_marktrace(global_State *g, TraceNo traceno)
 {
   GCobj *o = obj2gco(traceref(G2J(g), traceno));
-  lua_assert(traceno != G2J(g)->cur.traceno);
+  lj_assertG(traceno != G2J(g)->cur.traceno, "active trace escaped");
   if (iswhite(o)) {
     white2gray(o);
     setgcrefr(o->gch.gclist, g->gc.gray);
@@ -310,7 +315,7 @@ static size_t propagatemark(global_State *g)
 {
   GCobj *o = gcref(g->gc.gray);
   int gct = o->gch.gct;
-  lua_assert(isgray(o));
+  lj_assertG(isgray(o), "propagation of non-gray object");
   gray2black(o);
   setgcrefr(g->gc.gray, o->gch.gclist);  /* Remove from gray list. */
   if (LJ_LIKELY(gct == ~LJ_TTAB)) {
@@ -342,7 +347,7 @@ static size_t propagatemark(global_State *g)
     return ((sizeof(GCtrace)+7)&~7) + (T->nins-T->nk)*sizeof(IRIns) +
            T->nsnap*sizeof(SnapShot) + T->nsnapmap*sizeof(SnapEntry);
 #else
-    lua_assert(0);
+    lj_assertG(0, "bad GC type %d", gct);
     return 0;
 #endif
   }
@@ -396,11 +401,13 @@ static GCRef *gc_sweep(global_State *g, GCRef *p, uint32_t lim)
     if (o->gch.gct == ~LJ_TTHREAD)  /* Need to sweep open upvalues, too. */
       gc_fullsweep(g, &gco2th(o)->openupval);
     if (((o->gch.marked ^ LJ_GC_WHITES) & ow)) {  /* Black or current white? */
-      lua_assert(!isdead(g, o) || (o->gch.marked & LJ_GC_FIXED));
+      lj_assertG(!isdead(g, o) || (o->gch.marked & LJ_GC_FIXED),
+                 "sweep of undead object");
       makewhite(g, o);  /* Value is alive, change to the current white. */
       p = &o->gch.nextgc;
     } else {  /* Otherwise value is dead, free it. */
-      lua_assert(isdead(g, o) || ow == LJ_GC_SFIXED);
+      lj_assertG(isdead(g, o) || ow == LJ_GC_SFIXED,
+                 "sweep of unlive object");
       setgcrefr(*p, o->gch.nextgc);
       if (o == gcref(g->gc.root))
         setgcrefr(g->gc.root, o->gch.nextgc);  /* Adjust list anchor. */
@@ -427,11 +434,12 @@ static int gc_mayclear(cTValue *o, int val)
 }
 
 /* Clear collected entries from weak tables. */
-static void gc_clearweak(GCobj *o)
+static void gc_clearweak(global_State *g, GCobj *o)
 {
+  UNUSED(g);
   while (o) {
     GCtab *t = gco2tab(o);
-    lua_assert((t->marked & LJ_GC_WEAK));
+    lj_assertG((t->marked & LJ_GC_WEAK), "clear of non-weak table");
     if ((t->marked & LJ_GC_WEAKVAL)) {
       MSize i, asize = t->asize;
       for (i = 0; i < asize; i++) {
@@ -488,7 +496,7 @@ static void gc_finalize(lua_State *L)
   global_State *g = G(L);
   GCobj *o = gcnext(gcref(g->gc.mmudata));
   cTValue *mo;
-  lua_assert(tvref(g->jit_base) == NULL);  /* Must not be called on trace. */
+  lj_assertG(tvref(g->jit_base) == NULL, "finalizer called on trace");
   /* Unchain from list of userdata to be finalized. */
   if (o == gcref(g->gc.mmudata))
     setgcrefnull(g->gc.mmudata);
@@ -580,7 +588,7 @@ static void atomic(global_State *g, lua_State *L)
 
   setgcrefr(g->gc.gray, g->gc.weak);  /* Empty the list of weak tables. */
   setgcrefnull(g->gc.weak);
-  lua_assert(!iswhite(obj2gco(mainthread(g))));
+  lj_assertG(!iswhite(obj2gco(mainthread(g))), "main thread turned white");
   gc_markobj(g, L);  /* Mark running thread. */
   gc_traverse_curtrace(g);  /* Traverse current trace. */
   gc_mark_gcroot(g);  /* Mark GC roots (again). */
@@ -595,7 +603,7 @@ static void atomic(global_State *g, lua_State *L)
   udsize += gc_propagate_gray(g);  /* And propagate the marks. */
 
   /* All marking done, clear weak tables. */
-  gc_clearweak(gcref(g->gc.weak));
+  gc_clearweak(g, gcref(g->gc.weak));
 
   lj_buf_shrink(L, &g->tmpbuf);  /* Shrink temp buffer. */
 
@@ -631,14 +639,14 @@ static size_t gc_onestep(lua_State *L)
     gc_fullsweep(g, &g->strhash[g->gc.sweepstr++]);  /* Sweep one chain. */
     if (g->gc.sweepstr > g->strmask)
       g->gc.state = GCSsweep;  /* All string hash chains sweeped. */
-    lua_assert(old >= g->gc.total);
+    lj_assertG(old >= g->gc.total, "sweep increased memory");
     g->gc.estimate -= old - g->gc.total;
     return GCSWEEPCOST;
     }
   case GCSsweep: {
     GCSize old = g->gc.total;
     setmref(g->gc.sweep, gc_sweep(g, mref(g->gc.sweep, GCRef), GCSWEEPMAX));
-    lua_assert(old >= g->gc.total);
+    lj_assertG(old >= g->gc.total, "sweep increased memory");
     g->gc.estimate -= old - g->gc.total;
     if (gcref(*mref(g->gc.sweep, GCRef)) == NULL) {
       if (g->strnum <= (g->strmask >> 2) && g->strmask > LJ_MIN_STRTAB*2-1)
@@ -671,7 +679,7 @@ static size_t gc_onestep(lua_State *L)
     g->gc.debt = 0;
     return 0;
   default:
-    lua_assert(0);
+    lj_assertG(0, "bad GC state");
     return 0;
   }
 }
@@ -745,7 +753,8 @@ void lj_gc_fullgc(lua_State *L)
   }
   while (g->gc.state == GCSsweepstring || g->gc.state == GCSsweep)
     gc_onestep(L);  /* Finish sweep. */
-  lua_assert(g->gc.state == GCSfinalize || g->gc.state == GCSpause);
+  lj_assertG(g->gc.state == GCSfinalize || g->gc.state == GCSpause,
+             "bad GC state");
   /* Now perform a full GC. */
   g->gc.state = GCSpause;
   do { gc_onestep(L); } while (g->gc.state != GCSpause);
@@ -758,9 +767,11 @@ void lj_gc_fullgc(lua_State *L)
 /* Move the GC propagation frontier forward. */
 void lj_gc_barrierf(global_State *g, GCobj *o, GCobj *v)
 {
-  lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
-  lua_assert(g->gc.state != GCSfinalize && g->gc.state != GCSpause);
-  lua_assert(o->gch.gct != ~LJ_TTAB);
+  lj_assertG(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o),
+             "bad object states for forward barrier");
+  lj_assertG(g->gc.state != GCSfinalize && g->gc.state != GCSpause,
+             "bad GC state");
+  lj_assertG(o->gch.gct != ~LJ_TTAB, "barrier object is not a table");
   /* Preserve invariant during propagation. Otherwise it doesn't matter. */
   if (g->gc.state == GCSpropagate || g->gc.state == GCSatomic)
     gc_mark(g, v);  /* Move frontier forward. */
@@ -797,7 +808,8 @@ void lj_gc_closeuv(global_State *g, GCupval *uv)
         lj_gc_barrierf(g, o, gcV(&uv->tv));
     } else {
       makewhite(g, o);  /* Make it white, i.e. sweep the upvalue. */
-      lua_assert(g->gc.state != GCSfinalize && g->gc.state != GCSpause);
+      lj_assertG(g->gc.state != GCSfinalize && g->gc.state != GCSpause,
+                 "bad GC state");
     }
   }
 }
@@ -817,12 +829,13 @@ void lj_gc_barriertrace(global_State *g, uint32_t traceno)
 void *lj_mem_realloc(lua_State *L, void *p, GCSize osz, GCSize nsz)
 {
   global_State *g = G(L);
-  lua_assert((osz == 0) == (p == NULL));
+  lj_assertG((osz == 0) == (p == NULL), "realloc API violation");
   p = g->allocf(g->allocd, p, osz, nsz);
   if (p == NULL && nsz > 0)
     lj_err_mem(L);
-  lua_assert((nsz == 0) == (p == NULL));
-  lua_assert(checkptrGC(p));
+  lj_assertG((nsz == 0) == (p == NULL), "allocf API violation");
+  lj_assertG(checkptrGC(p),
+             "allocated memory address %p outside required range", p);
   g->gc.total = (g->gc.total - osz) + nsz;
   return p;
 }
@@ -834,7 +847,8 @@ void * LJ_FASTCALL lj_mem_newgco(lua_State *L, GCSize size)
   GCobj *o = (GCobj *)g->allocf(g->allocd, NULL, 0, size);
   if (o == NULL)
     lj_err_mem(L);
-  lua_assert(checkptrGC(o));
+  lj_assertG(checkptrGC(o),
+             "allocated memory address %p outside required range", o);
   g->gc.total += size;
   setgcrefr(o->gch.nextgc, g->gc.root);
   setgcref(g->gc.root, o);
diff --git a/src/lj_gc.h b/src/lj_gc.h
index 1725c639..6fc88cf9 100644
--- a/src/lj_gc.h
+++ b/src/lj_gc.h
@@ -81,8 +81,10 @@ LJ_FUNC void lj_gc_barriertrace(global_State *g, uint32_t traceno);
 static LJ_AINLINE void lj_gc_barrierback(global_State *g, GCtab *t)
 {
   GCobj *o = obj2gco(t);
-  lua_assert(isblack(o) && !isdead(g, o));
-  lua_assert(g->gc.state != GCSfinalize && g->gc.state != GCSpause);
+  lj_assertG(isblack(o) && !isdead(g, o),
+             "bad object states for backward barrier");
+  lj_assertG(g->gc.state != GCSfinalize && g->gc.state != GCSpause,
+             "bad GC state");
   black2gray(o);
   setgcrefr(t->gclist, g->gc.grayagain);
   setgcref(g->gc.grayagain, o);
diff --git a/src/lj_gdbjit.c b/src/lj_gdbjit.c
index a20d9ae2..69585e51 100644
--- a/src/lj_gdbjit.c
+++ b/src/lj_gdbjit.c
@@ -724,7 +724,7 @@ static void gdbjit_buildobj(GDBJITctx *ctx)
   SECTALIGN(ctx->p, sizeof(uintptr_t));
   gdbjit_initsect(ctx, GDBJIT_SECT_eh_frame, gdbjit_ehframe);
   ctx->objsize = (size_t)((char *)ctx->p - (char *)obj);
-  lua_assert(ctx->objsize < sizeof(GDBJITobj));
+  lj_assertX(ctx->objsize < sizeof(GDBJITobj), "GDBJITobj overflow");
 }
 
 #undef SECTALIGN
@@ -782,7 +782,8 @@ void lj_gdbjit_addtrace(jit_State *J, GCtrace *T)
   ctx.spadjp = CFRAME_SIZE_JIT +
                (MSize)(parent ? traceref(J, parent)->spadjust : 0);
   ctx.spadj = CFRAME_SIZE_JIT + T->spadjust;
-  lua_assert(startpc >= proto_bc(pt) && startpc < proto_bc(pt) + pt->sizebc);
+  lj_assertJ(startpc >= proto_bc(pt) && startpc < proto_bc(pt) + pt->sizebc,
+             "start PC out of range");
   ctx.lineno = lj_debug_line(pt, proto_bcpos(pt, startpc));
   ctx.filename = proto_chunknamestr(pt);
   if (*ctx.filename == '@' || *ctx.filename == '=')
diff --git a/src/lj_ir.c b/src/lj_ir.c
index 1dd25f23..600e432c 100644
--- a/src/lj_ir.c
+++ b/src/lj_ir.c
@@ -38,7 +38,7 @@
 #define fins                    (&J->fold.ins)
 
 /* Pass IR on to next optimization in chain (FOLD). */
-#define emitir(ot, a, b)        (lj_ir_set(J, (ot), (a), (b)), lj_opt_fold(J))
+#define emitir(ot, a, b)        (lj_ir_set(J, (ot), (a), (b)), lj_opt_fold(J))
 
 /* -- IR tables ----------------------------------------------------------- */
 
@@ -90,8 +90,9 @@ static void lj_ir_growbot(jit_State *J)
 {
   IRIns *baseir = J->irbuf + J->irbotlim;
   MSize szins = J->irtoplim - J->irbotlim;
-  lua_assert(szins != 0);
-  lua_assert(J->cur.nk == J->irbotlim || J->cur.nk-1 == J->irbotlim);
+  lj_assertJ(szins != 0, "zero IR size");
+  lj_assertJ(J->cur.nk == J->irbotlim || J->cur.nk-1 == J->irbotlim,
+             "unexpected IR growth");
   if (J->cur.nins + (szins >> 1) < J->irtoplim) {
     /* More than half of the buffer is free on top: shift up by a quarter. */
     MSize ofs = szins >> 2;
@@ -148,9 +149,10 @@ TRef lj_ir_call(jit_State *J, IRCallID id, ...)
 /* Load field of type t from GG_State + offset. Must be 32 bit aligned. */
 LJ_FUNC TRef lj_ir_ggfload(jit_State *J, IRType t, uintptr_t ofs)
 {
-  lua_assert((ofs & 3) == 0);
+  lj_assertJ((ofs & 3) == 0, "unaligned GG_State field offset");
   ofs >>= 2;
-  lua_assert(ofs >= IRFL__MAX && ofs <= 0x3ff);  /* 10 bit FOLD key limit. */
+  lj_assertJ(ofs >= IRFL__MAX && ofs <= 0x3ff,
+             "GG_State field offset breaks 10 bit FOLD key limit");
   lj_ir_set(J, IRT(IR_FLOAD, t), REF_NIL, ofs);
   return lj_opt_fold(J);
 }
@@ -181,7 +183,7 @@ static LJ_AINLINE IRRef ir_nextk(jit_State *J)
 static LJ_AINLINE IRRef ir_nextk64(jit_State *J)
 {
   IRRef ref = J->cur.nk - 2;
-  lua_assert(J->state != LJ_TRACE_ASM);
+  lj_assertJ(J->state != LJ_TRACE_ASM, "bad JIT state");
   if (LJ_UNLIKELY(ref < J->irbotlim)) lj_ir_growbot(J);
   J->cur.nk = ref;
   return ref;
@@ -277,7 +279,7 @@ TRef lj_ir_kgc(jit_State *J, GCobj *o, IRType t)
 {
   IRIns *ir, *cir = J->cur.ir;
   IRRef ref;
-  lua_assert(!isdead(J2G(J), o));
+  lj_assertJ(!isdead(J2G(J), o), "interning of dead GC object");
   for (ref = J->chain[IR_KGC]; ref; ref = cir[ref].prev)
     if (ir_kgc(&cir[ref]) == o)
       goto found;
@@ -299,7 +301,7 @@ TRef lj_ir_ktrace(jit_State *J)
 {
   IRRef ref = ir_nextkgc(J);
   IRIns *ir = IR(ref);
-  lua_assert(irt_toitype_(IRT_P64) == LJ_TTRACE);
+  lj_assertJ(irt_toitype_(IRT_P64) == LJ_TTRACE, "mismatched type mapping");
   ir->t.irt = IRT_P64;
   ir->o = LJ_GC64 ? IR_KNUM : IR_KNULL;  /* Not IR_KGC yet, but same size. */
   ir->op12 = 0;
@@ -313,7 +315,7 @@ TRef lj_ir_kptr_(jit_State *J, IROp op, void *ptr)
   IRIns *ir, *cir = J->cur.ir;
   IRRef ref;
 #if LJ_64 && !LJ_GC64
-  lua_assert((void *)(uintptr_t)u32ptr(ptr) == ptr);
+  lj_assertJ((void *)(uintptr_t)u32ptr(ptr) == ptr, "out-of-range GC pointer");
 #endif
   for (ref = J->chain[op]; ref; ref = cir[ref].prev)
     if (ir_kptr(&cir[ref]) == ptr)
@@ -360,7 +362,8 @@ TRef lj_ir_kslot(jit_State *J, TRef key, IRRef slot)
   IRRef2 op12 = IRREF2((IRRef1)key, (IRRef1)slot);
   IRRef ref;
   /* Const part is not touched by CSE/DCE, so 0-65535 is ok for IRMlit here. */
-  lua_assert(tref_isk(key) && slot == (IRRef)(IRRef1)slot);
+  lj_assertJ(tref_isk(key) && slot == (IRRef)(IRRef1)slot,
+             "out-of-range key/slot");
   for (ref = J->chain[IR_KSLOT]; ref; ref = cir[ref].prev)
     if (cir[ref].op12 == op12)
       goto found;
@@ -381,7 +384,7 @@ found:
 void lj_ir_kvalue(lua_State *L, TValue *tv, const IRIns *ir)
 {
   UNUSED(L);
-  lua_assert(ir->o != IR_KSLOT);  /* Common mistake. */
+  lj_assertL(ir->o != IR_KSLOT, "unexpected KSLOT");  /* Common mistake. */
   switch (ir->o) {
   case IR_KPRI: setpriV(tv, irt_toitype(ir->t)); break;
   case IR_KINT: setintV(tv, ir->i); break;
@@ -397,7 +400,7 @@ void lj_ir_kvalue(lua_State *L, TValue *tv, const IRIns *ir)
     break;
     }
 #endif
-  default: lua_assert(0); break;
+  default: lj_assertL(0, "bad IR constant op %d", ir->o); break;
   }
 }
 
@@ -457,7 +460,7 @@ int lj_ir_numcmp(lua_Number a, lua_Number b, IROp op)
   case IR_UGE: return !(a < b);
   case IR_ULE: return !(a > b);
   case IR_UGT: return !(a <= b);
-  default: lua_assert(0); return 0;
+  default: lj_assertX(0, "bad IR op %d", op); return 0;
   }
 }
 
@@ -470,7 +473,7 @@ int lj_ir_strcmp(GCstr *a, GCstr *b, IROp op)
   case IR_GE: return (res >= 0);
   case IR_LE: return (res <= 0);
   case IR_GT: return (res > 0);
-  default: lua_assert(0); return 0;
+  default: lj_assertX(0, "bad IR op %d", op); return 0;
   }
 }
 
diff --git a/src/lj_ir.h b/src/lj_ir.h
index a801d5d0..6116f7e5 100644
--- a/src/lj_ir.h
+++ b/src/lj_ir.h
@@ -413,11 +413,12 @@ static LJ_AINLINE IRType itype2irt(const TValue *tv)
 
 static LJ_AINLINE uint32_t irt_toitype_(IRType t)
 {
-  lua_assert(!LJ_64 || LJ_GC64 || t != IRT_LIGHTUD);
+  lj_assertX(!LJ_64 || LJ_GC64 || t != IRT_LIGHTUD,
+             "no plain type tag for lightuserdata");
   if (LJ_DUALNUM && t > IRT_NUM) {
     return LJ_TISNUM;
   } else {
-    lua_assert(t <= IRT_NUM);
+    lj_assertX(t <= IRT_NUM, "no plain type tag for IR type %d", t);
     return ~(uint32_t)t;
   }
 }
diff --git a/src/lj_jit.h b/src/lj_jit.h
index a9c602f0..fa754b64 100644
--- a/src/lj_jit.h
+++ b/src/lj_jit.h
@@ -510,6 +510,12 @@ LJ_ALIGN(16)		/* For DISPATCH-relative addresses in assembler part. */
 #endif
 jit_State;
 
+#ifdef LUA_USE_ASSERT
+#define lj_assertJ(c, ...)      lj_assertG_(J2G(J), (c), __VA_ARGS__)
+#else
+#define lj_assertJ(c, ...)      ((void)J)
+#endif
+
 /* Trivial PRNG e.g. used for penalty randomization. */
 static LJ_AINLINE uint32_t LJ_PRNG_BITS(jit_State *J, int bits)
 {
diff --git a/src/lj_lex.c b/src/lj_lex.c
index ada0876e..61c7ff43 100644
--- a/src/lj_lex.c
+++ b/src/lj_lex.c
@@ -82,7 +82,7 @@ static LJ_AINLINE LexChar lex_savenext(LexState *ls)
 static void lex_newline(LexState *ls)
 {
   LexChar old = ls->c;
-  lua_assert(lex_iseol(ls));
+  lj_assertLS(lex_iseol(ls), "bad usage");
   lex_next(ls);  /* Skip "\n" or "\r". */
   if (lex_iseol(ls) && ls->c != old) lex_next(ls);  /* Skip "\n\r" or "\r\n". */
   if (++ls->linenumber >= LJ_MAX_LINE)
@@ -96,7 +96,7 @@ static void lex_number(LexState *ls, TValue *tv)
 {
   StrScanFmt fmt;
   LexChar c, xp = 'e';
-  lua_assert(lj_char_isdigit(ls->c));
+  lj_assertLS(lj_char_isdigit(ls->c), "bad usage");
   if ((c = ls->c) == '0' && (lex_savenext(ls) | 0x20) == 'x')
     xp = 'p';
   while (lj_char_isident(ls->c) || ls->c == '.' ||
@@ -116,7 +116,8 @@ static void lex_number(LexState *ls, TValue *tv)
   } else if (fmt != STRSCAN_ERROR) {
     lua_State *L = ls->L;
     GCcdata *cd;
-    lua_assert(fmt == STRSCAN_I64 || fmt == STRSCAN_U64 || fmt == STRSCAN_IMAG);
+    lj_assertLS(fmt == STRSCAN_I64 || fmt == STRSCAN_U64 || fmt == STRSCAN_IMAG,
+                "unexpected number format %d", fmt);
     if (!ctype_ctsG(G(L))) {
       ptrdiff_t oldtop = savestack(L, L->top);
       luaopen_ffi(L);  /* Load FFI library on-demand. */
@@ -133,7 +134,8 @@ static void lex_number(LexState *ls, TValue *tv)
     lj_parse_keepcdata(ls, tv, cd);
 #endif
   } else {
-    lua_assert(fmt == STRSCAN_ERROR);
+    lj_assertLS(fmt == STRSCAN_ERROR,
+                "unexpected number format %d", fmt);
     lj_lex_error(ls, TK_number, LJ_ERR_XNUMBER);
   }
 }
@@ -143,7 +145,7 @@ static int lex_skipeq(LexState *ls)
 {
   int count = 0;
   LexChar s = ls->c;
-  lua_assert(s == '[' || s == ']');
+  lj_assertLS(s == '[' || s == ']', "bad usage");
   while (lex_savenext(ls) == '=' && count < 0x20000000)
     count++;
   return (ls->c == s) ? count : (-count) - 1;
@@ -469,7 +471,7 @@ void lj_lex_next(LexState *ls)
 /* Look ahead for the next token. */
 LexToken lj_lex_lookahead(LexState *ls)
 {
-  lua_assert(ls->lookahead == TK_eof);
+  lj_assertLS(ls->lookahead == TK_eof, "double lookahead");
   ls->lookahead = lex_scan(ls, &ls->lookaheadval);
   return ls->lookahead;
 }
diff --git a/src/lj_lex.h b/src/lj_lex.h
index 8665aa2a..e1b5610b 100644
--- a/src/lj_lex.h
+++ b/src/lj_lex.h
@@ -84,4 +84,10 @@ LJ_FUNC const char *lj_lex_token2str(LexState *ls, LexToken tok);
 LJ_FUNC_NORET void lj_lex_error(LexState *ls, LexToken tok, ErrMsg em, ...);
 LJ_FUNC void lj_lex_init(lua_State *L);
 
+#ifdef LUA_USE_ASSERT
+#define lj_assertLS(c, ...)     (lj_assertG_(G(ls->L), (c), __VA_ARGS__))
+#else
+#define lj_assertLS(c, ...)     ((void)ls)
+#endif
+
 #endif
diff --git a/src/lj_load.c b/src/lj_load.c
index 746bf428..e5918c04 100644
--- a/src/lj_load.c
+++ b/src/lj_load.c
@@ -159,7 +159,7 @@ LUALIB_API int luaL_loadstring(lua_State *L, const char *s)
 LUA_API int lua_dump(lua_State *L, lua_Writer writer, void *data)
 {
   cTValue *o = L->top-1;
-  api_check(L, L->top > L->base);
+  lj_checkapi(L->top > L->base, "top slot empty");
   if (tvisfunc(o) && isluafunc(funcV(o)))
     return lj_bcwrite(L, funcproto(funcV(o)), writer, data, 0);
   else
diff --git a/src/lj_mcode.c b/src/lj_mcode.c
index bc3e922f..e64c5878 100644
--- a/src/lj_mcode.c
+++ b/src/lj_mcode.c
@@ -351,7 +351,7 @@ MCode *lj_mcode_patch(jit_State *J, MCode *ptr, int finish)
     /* Otherwise search through the list of MCode areas. */
     for (;;) {
       mc = ((MCLink *)mc)->next;
-      lua_assert(mc != NULL);
+      lj_assertJ(mc != NULL, "broken MCode area chain");
       if (ptr >= mc && ptr < (MCode *)((char *)mc + ((MCLink *)mc)->size)) {
         if (LJ_UNLIKELY(mcode_setprot(mc, ((MCLink *)mc)->size, MCPROT_GEN)))
           mcode_protfail(J);
diff --git a/src/lj_meta.c b/src/lj_meta.c
index 7391ff00..2cdb6a0f 100644
--- a/src/lj_meta.c
+++ b/src/lj_meta.c
@@ -47,7 +47,7 @@ void lj_meta_init(lua_State *L)
 cTValue *lj_meta_cache(GCtab *mt, MMS mm, GCstr *name)
 {
   cTValue *mo = lj_tab_getstr(mt, name);
-  lua_assert(mm <= MM_FAST);
+  lj_assertX(mm <= MM_FAST, "bad metamethod %d", mm);
   if (!mo || tvisnil(mo)) {  /* No metamethod? */
     mt->nomm |= (uint8_t)(1u<<mm);  /* Set negative cache flag. */
     return NULL;
@@ -363,7 +363,7 @@ TValue * LJ_FASTCALL lj_meta_equal_cd(lua_State *L, BCIns ins)
   } else if (op == BC_ISEQN) {
     o2 = &mref(curr_proto(L)->k, cTValue)[bc_d(ins)];
   } else {
-    lua_assert(op == BC_ISEQP);
+    lj_assertL(op == BC_ISEQP, "bad bytecode op %d", op);
     setpriV(&tv, ~bc_d(ins));
     o2 = &tv;
   }
@@ -426,7 +426,7 @@ void lj_meta_istype(lua_State *L, BCReg ra, BCReg tp)
 {
   L->top = curr_topL(L);
   ra++; tp--;
-  lua_assert(LJ_DUALNUM || tp != ~LJ_TNUMX);  /* ISTYPE -> ISNUM broken. */
+  lj_assertL(LJ_DUALNUM || tp != ~LJ_TNUMX, "bad type for ISTYPE");
   if (LJ_DUALNUM && tp == ~LJ_TNUMX) lj_lib_checkint(L, ra);
   else if (tp == ~LJ_TNUMX+1) lj_lib_checknum(L, ra);
   else if (tp == ~LJ_TSTR) lj_lib_checkstr(L, ra);
diff --git a/src/lj_obj.h b/src/lj_obj.h
index 7d582949..c0ae6892 100644
--- a/src/lj_obj.h
+++ b/src/lj_obj.h
@@ -679,6 +679,11 @@ struct lua_State {
 #define curr_topL(L)            (L->base + curr_proto(L)->framesize)
 #define curr_top(L)             (curr_funcisL(L) ? curr_topL(L) : L->top)
 
+#if defined(LUA_USE_ASSERT) || defined(LUA_USE_APICHECK)
+LJ_FUNC_NORET void lj_assert_fail(global_State *g, const char *file, int line,
+                                  const char *func, const char *fmt, ...);
+#endif
+
 /* -- GC object definition and conversions -------------------------------- */
 
 /* GC header for generic access to common fields of GC objects. */
@@ -732,10 +737,6 @@ typedef union GCobj {
 
 /* -- TValue getters/setters ---------------------------------------------- */
 
-#ifdef LUA_USE_ASSERT
-#include "lj_gc.h"
-#endif
-
 /* Macros to test types. */
 #if LJ_GC64
 #define itype(o)        ((uint32_t)((o)->it64 >> 47))
@@ -856,9 +857,19 @@ static LJ_AINLINE void setlightudV(TValue *o, void *p)
 #define setcont(o, f)           setlightudV((o), contptr(f))
 #endif
 
-#define tvchecklive(L, o) \
-  UNUSED(L), lua_assert(!tvisgcv(o) || \
-  ((~itype(o) == gcval(o)->gch.gct) && !isdead(G(L), gcval(o))))
+static LJ_AINLINE void checklivetv(lua_State *L, TValue *o, const char *msg)
+{
+  UNUSED(L); UNUSED(o); UNUSED(msg);
+#if LUA_USE_ASSERT
+  if (tvisgcv(o)) {
+    lj_assertL(~itype(o) == gcval(o)->gch.gct,
+               "mismatch of TValue type %d vs GC type %d",
+               ~itype(o), gcval(o)->gch.gct);
+    /* Copy of isdead check from lj_gc.h to avoid circular include. */
+    lj_assertL(!(gcval(o)->gch.marked & (G(L)->gc.currentwhite ^ 3) & 3), msg);
+  }
+#endif
+}
 
 static LJ_AINLINE void setgcVraw(TValue *o, GCobj *v, uint32_t itype)
 {
@@ -871,7 +882,8 @@ static LJ_AINLINE void setgcVraw(TValue *o, GCobj *v, uint32_t itype)
 
 static LJ_AINLINE void setgcV(lua_State *L, TValue *o, GCobj *v, uint32_t it)
 {
-  setgcVraw(o, v, it); tvchecklive(L, o);
+  setgcVraw(o, v, it);
+  checklivetv(L, o, "store to dead GC object");
 }
 
 #define define_setV(name, type, tag) \
@@ -918,7 +930,8 @@ static LJ_AINLINE void setint64V(TValue *o, int64_t i)
 /* Copy tagged values. */
 static LJ_AINLINE void copyTV(lua_State *L, TValue *o1, const TValue *o2)
 {
-  *o1 = *o2; tvchecklive(L, o1);
+  *o1 = *o2;
+  checklivetv(L, o1, "copy of dead GC object");
 }
 
 /* -- Number to integer conversion ---------------------------------------- */
diff --git a/src/lj_opt_fold.c b/src/lj_opt_fold.c
index 42c57c9b..96f272b8 100644
--- a/src/lj_opt_fold.c
+++ b/src/lj_opt_fold.c
@@ -282,7 +282,7 @@ static int32_t kfold_intop(int32_t k1, int32_t k2, IROp op)
   case IR_BROR: k1 = (int32_t)lj_ror((uint32_t)k1, (k2 & 31)); break;
   case IR_MIN: k1 = k1 < k2 ? k1 : k2; break;
   case IR_MAX: k1 = k1 > k2 ? k1 : k2; break;
-  default: lua_assert(0); break;
+  default: lj_assertX(0, "bad IR op %d", op); break;
   }
   return k1;
 }
@@ -354,7 +354,7 @@ LJFOLDF(kfold_intcomp)
   case IR_ULE: return CONDFOLD((uint32_t)a <= (uint32_t)b);
   case IR_ABC:
   case IR_UGT: return CONDFOLD((uint32_t)a > (uint32_t)b);
-  default: lua_assert(0); return FAILFOLD;
+  default: lj_assertJ(0, "bad IR op %d", fins->o); return FAILFOLD;
   }
 }
 
@@ -368,10 +368,12 @@ LJFOLDF(kfold_intcomp0)
 
 /* -- Constant folding for 64 bit integers -------------------------------- */
 
-static uint64_t kfold_int64arith(uint64_t k1, uint64_t k2, IROp op)
+static uint64_t kfold_int64arith(jit_State *J, uint64_t k1, uint64_t k2,
+                                 IROp op)
 {
-  switch (op) {
+  UNUSED(J);
 #if LJ_HASFFI
+  switch (op) {
   case IR_ADD: k1 += k2; break;
   case IR_SUB: k1 -= k2; break;
   case IR_MUL: k1 *= k2; break;
@@ -383,9 +385,12 @@ static uint64_t kfold_int64arith(uint64_t k1, uint64_t k2, IROp op)
   case IR_BSAR: k1 >>= (k2 & 63); break;
   case IR_BROL: k1 = (int32_t)lj_rol((uint32_t)k1, (k2 & 63)); break;
   case IR_BROR: k1 = (int32_t)lj_ror((uint32_t)k1, (k2 & 63)); break;
-#endif
-  default: UNUSED(k2); lua_assert(0); break;
+  default: lj_assertJ(0, "bad IR op %d", op); break;
   }
+#else
+  UNUSED(k2); UNUSED(op);
+  lj_assertJ(0, "FFI IR op without FFI");
+#endif
   return k1;
 }
 
@@ -397,7 +402,7 @@ LJFOLD(BOR KINT64 KINT64)
 LJFOLD(BXOR KINT64 KINT64)
 LJFOLDF(kfold_int64arith)
 {
-  return INT64FOLD(kfold_int64arith(ir_k64(fleft)->u64,
+  return INT64FOLD(kfold_int64arith(J, ir_k64(fleft)->u64,
                                     ir_k64(fright)->u64, (IROp)fins->o));
 }
 
@@ -419,7 +424,7 @@ LJFOLDF(kfold_int64arith2)
   }
   return INT64FOLD(k1);
 #else
-  UNUSED(J); lua_assert(0); return FAILFOLD;
+  UNUSED(J); lj_assertJ(0, "FFI IR op without FFI"); return FAILFOLD;
 #endif
 }
 
@@ -435,7 +440,7 @@ LJFOLDF(kfold_int64shift)
   int32_t sh = (fright->i & 63);
   return INT64FOLD(lj_carith_shift64(k, sh, fins->o - IR_BSHL));
 #else
-  UNUSED(J); lua_assert(0); return FAILFOLD;
+  UNUSED(J); lj_assertJ(0, "FFI IR op without FFI"); return FAILFOLD;
 #endif
 }
 
@@ -445,7 +450,7 @@ LJFOLDF(kfold_bnot64)
 #if LJ_HASFFI
   return INT64FOLD(~ir_k64(fleft)->u64);
 #else
-  UNUSED(J); lua_assert(0); return FAILFOLD;
+  UNUSED(J); lj_assertJ(0, "FFI IR op without FFI"); return FAILFOLD;
 #endif
 }
 
@@ -455,7 +460,7 @@ LJFOLDF(kfold_bswap64)
 #if LJ_HASFFI
   return INT64FOLD(lj_bswap64(ir_k64(fleft)->u64));
 #else
-  UNUSED(J); lua_assert(0); return FAILFOLD;
+  UNUSED(J); lj_assertJ(0, "FFI IR op without FFI"); return FAILFOLD;
 #endif
 }
 
@@ -480,10 +485,10 @@ LJFOLDF(kfold_int64comp)
   case IR_UGE: return CONDFOLD(a >= b);
   case IR_ULE: return CONDFOLD(a <= b);
   case IR_UGT: return CONDFOLD(a > b);
-  default: lua_assert(0); return FAILFOLD;
+  default: lj_assertJ(0, "bad IR op %d", fins->o); return FAILFOLD;
   }
 #else
-  UNUSED(J); lua_assert(0); return FAILFOLD;
+  UNUSED(J); lj_assertJ(0, "FFI IR op without FFI"); return FAILFOLD;
 #endif
 }
 
@@ -495,7 +500,7 @@ LJFOLDF(kfold_int64comp0)
     return DROPFOLD;
   return NEXTFOLD;
 #else
-  UNUSED(J); lua_assert(0); return FAILFOLD;
+  UNUSED(J); lj_assertJ(0, "FFI IR op without FFI"); return FAILFOLD;
 #endif
 }
 
@@ -520,7 +525,7 @@ LJFOLD(STRREF KGC KINT)
 LJFOLDF(kfold_strref)
 {
   GCstr *str = ir_kstr(fleft);
-  lua_assert((MSize)fright->i <= str->len);
+  lj_assertJ((MSize)fright->i <= str->len, "bad string ref");
   return lj_ir_kkptr(J, (char *)strdata(str) + fright->i);
 }
 
@@ -616,8 +621,9 @@ LJFOLDF(bufput_kgc)
 LJFOLD(BUFSTR any any)
 LJFOLDF(bufstr_kfold_cse)
 {
-  lua_assert(fleft->o == IR_BUFHDR || fleft->o == IR_BUFPUT ||
-             fleft->o == IR_CALLL);
+  lj_assertJ(fleft->o == IR_BUFHDR || fleft->o == IR_BUFPUT ||
+             fleft->o == IR_CALLL,
+             "bad buffer constructor IR op %d", fleft->o);
   if (LJ_LIKELY(J->flags & JIT_F_OPT_FOLD)) {
     if (fleft->o == IR_BUFHDR) {  /* No put operations? */
       if (!(fleft->op2 & IRBUFHDR_APPEND))  /* Empty buffer? */
@@ -637,8 +643,9 @@ LJFOLDF(bufstr_kfold_cse)
     while (ref) {
       IRIns *irs = IR(ref), *ira = fleft, *irb = IR(irs->op1);
       while (ira->o == irb->o && ira->op2 == irb->op2) {
-        lua_assert(ira->o == IR_BUFHDR || ira->o == IR_BUFPUT ||
-                   ira->o == IR_CALLL || ira->o == IR_CARG);
+        lj_assertJ(ira->o == IR_BUFHDR || ira->o == IR_BUFPUT ||
+                   ira->o == IR_CALLL || ira->o == IR_CARG,
+                   "bad buffer constructor IR op %d", ira->o);
         if (ira->o == IR_BUFHDR && !(ira->op2 & IRBUFHDR_APPEND))
           return ref;  /* CSE succeeded. */
         if (ira->o == IR_CALLL && ira->op2 == IRCALL_lj_buf_puttab)
@@ -697,7 +704,7 @@ LJFOLD(CALLL CARG IRCALL_lj_strfmt_putfchar)
 LJFOLDF(bufput_kfold_fmt)
 {
   IRIns *irc = IR(fleft->op1);
-  lua_assert(irref_isk(irc->op2));  /* SFormat must be const. */
+  lj_assertJ(irref_isk(irc->op2), "SFormat must be const");
   if (irref_isk(fleft->op2)) {
     SFormat sf = (SFormat)IR(irc->op2)->i;
     IRIns *ira = IR(fleft->op2);
@@ -1216,10 +1223,10 @@ LJFOLDF(simplify_tobit_conv)
 {
   /* Fold even across PHI to avoid expensive num->int conversions in loop. */
   if ((fleft->op2 & IRCONV_SRCMASK) == IRT_INT) {
-    lua_assert(irt_isnum(fleft->t));
+    lj_assertJ(irt_isnum(fleft->t), "expected TOBIT number arg");
     return fleft->op1;
   } else if ((fleft->op2 & IRCONV_SRCMASK) == IRT_U32) {
-    lua_assert(irt_isnum(fleft->t));
+    lj_assertJ(irt_isnum(fleft->t), "expected TOBIT number arg");
     fins->o = IR_CONV;
     fins->op1 = fleft->op1;
     fins->op2 = (IRT_INT<<5)|IRT_U32;
@@ -1259,7 +1266,7 @@ LJFOLDF(simplify_conv_sext)
   /* Use scalar evolution analysis results to strength-reduce sign-extension. */
   if (ref == J->scev.idx) {
     IRRef lo = J->scev.dir ? J->scev.start : J->scev.stop;
-    lua_assert(irt_isint(J->scev.t));
+    lj_assertJ(irt_isint(J->scev.t), "only int SCEV supported");
     if (lo && IR(lo)->o == IR_KINT && IR(lo)->i + ofs >= 0) {
     ok_reduce:
 #if LJ_TARGET_X64
@@ -1335,7 +1342,8 @@ LJFOLDF(narrow_convert)
   /* Narrowing ignores PHIs and repeating it inside the loop is not useful. */
   if (J->chain[IR_LOOP])
     return NEXTFOLD;
-  lua_assert(fins->o != IR_CONV || (fins->op2&IRCONV_CONVMASK) != IRCONV_TOBIT);
+  lj_assertJ(fins->o != IR_CONV || (fins->op2&IRCONV_CONVMASK) != IRCONV_TOBIT,
+             "unexpected CONV TOBIT");
   return lj_opt_narrow_convert(J);
 }
 
@@ -1441,7 +1449,7 @@ LJFOLDF(simplify_intmul_k64)
     return simplify_intmul_k(J, (int32_t)ir_kint64(fright)->u64);
   return NEXTFOLD;
 #else
-  UNUSED(J); lua_assert(0); return FAILFOLD;
+  UNUSED(J); lj_assertJ(0, "FFI IR op without FFI"); return FAILFOLD;
 #endif
 }
 
@@ -1449,7 +1457,7 @@ LJFOLD(MOD any KINT)
 LJFOLDF(simplify_intmod_k)
 {
   int32_t k = fright->i;
-  lua_assert(k != 0);
+  lj_assertJ(k != 0, "integer mod 0");
   if (k > 0 && (k & (k-1)) == 0) {  /* i % (2^k) ==> i & (2^k-1) */
     fins->o = IR_BAND;
     fins->op2 = lj_ir_kint(J, k-1);
@@ -1699,7 +1707,8 @@ LJFOLDF(simplify_shiftk_andk)
     fins->ot = IRTI(IR_BAND);
     return RETRYFOLD;
   } else if (irk->o == IR_KINT64) {
-    uint64_t k = kfold_int64arith(ir_k64(irk)->u64, fright->i, (IROp)fins->o);
+    uint64_t k = kfold_int64arith(J, ir_k64(irk)->u64, fright->i,
+                                  (IROp)fins->o);
     IROpT ot = fleft->ot;
     fins->op1 = fleft->op1;
     fins->op1 = (IRRef1)lj_opt_fold(J);
@@ -1747,8 +1756,8 @@ LJFOLDF(simplify_andor_k64)
   IRIns *irk = IR(fleft->op2);
   PHIBARRIER(fleft);
   if (irk->o == IR_KINT64) {
-    uint64_t k = kfold_int64arith(ir_k64(irk)->u64,
-                                  ir_k64(fright)->u64, (IROp)fins->o);
+    uint64_t k = kfold_int64arith(J, ir_k64(irk)->u64, ir_k64(fright)->u64,
+                                  (IROp)fins->o);
     /* (i | k1) & k2 ==> i & k2, if (k1 & k2) == 0. */
     /* (i & k1) | k2 ==> i | k2, if (k1 | k2) == -1. */
     if (k == (fins->o == IR_BAND ? (uint64_t)0 : ~(uint64_t)0)) {
@@ -1758,7 +1767,7 @@ LJFOLDF(simplify_andor_k64)
   }
   return NEXTFOLD;
 #else
-  UNUSED(J); lua_assert(0); return FAILFOLD;
+  UNUSED(J); lj_assertJ(0, "FFI IR op without FFI"); return FAILFOLD;
 #endif
 }
 
@@ -1794,8 +1803,8 @@ LJFOLDF(reassoc_intarith_k64)
 #if LJ_HASFFI
   IRIns *irk = IR(fleft->op2);
   if (irk->o == IR_KINT64) {
-    uint64_t k = kfold_int64arith(ir_k64(irk)->u64,
-                                  ir_k64(fright)->u64, (IROp)fins->o);
+    uint64_t k = kfold_int64arith(J, ir_k64(irk)->u64, ir_k64(fright)->u64,
+                                  (IROp)fins->o);
     PHIBARRIER(fleft);
     fins->op1 = fleft->op1;
     fins->op2 = (IRRef1)lj_ir_kint64(J, k);
@@ -1803,7 +1812,7 @@ LJFOLDF(reassoc_intarith_k64)
   }
   return NEXTFOLD;
 #else
-  UNUSED(J); lua_assert(0); return FAILFOLD;
+  UNUSED(J); lj_assertJ(0, "FFI IR op without FFI"); return FAILFOLD;
 #endif
 }
 
@@ -2058,7 +2067,7 @@ LJFOLDF(merge_eqne_snew_kgc)
 {
   GCstr *kstr = ir_kstr(fright);
   int32_t len = (int32_t)kstr->len;
-  lua_assert(irt_isstr(fins->t));
+  lj_assertJ(irt_isstr(fins->t), "bad equality IR type");
 
 #if LJ_TARGET_UNALIGNED
 #define FOLD_SNEW_MAX_LEN       4  /* Handle string lengths 0, 1, 2, 3, 4. */
@@ -2122,7 +2131,7 @@ LJFOLD(HLOAD KKPTR)
 LJFOLDF(kfold_hload_kkptr)
 {
   UNUSED(J);
-  lua_assert(ir_kptr(fleft) == niltvg(J2G(J)));
+  lj_assertJ(ir_kptr(fleft) == niltvg(J2G(J)), "expected niltv");
   return TREF_NIL;
 }
 
@@ -2333,7 +2342,7 @@ LJFOLDF(fwd_sload)
     TRef tr = lj_opt_cse(J);
     return tref_ref(tr) < J->chain[IR_RETF] ? EMITFOLD : tr;
   } else {
-    lua_assert(J->slot[fins->op1] != 0);
+    lj_assertJ(J->slot[fins->op1] != 0, "uninitialized slot accessed");
     return J->slot[fins->op1];
   }
 }
@@ -2448,8 +2457,9 @@ TRef LJ_FASTCALL lj_opt_fold(jit_State *J)
   IRRef ref;
 
   if (LJ_UNLIKELY((J->flags & JIT_F_OPT_MASK) != JIT_F_OPT_DEFAULT)) {
-    lua_assert(((JIT_F_OPT_FOLD|JIT_F_OPT_FWD|JIT_F_OPT_CSE|JIT_F_OPT_DSE) |
-                JIT_F_OPT_DEFAULT) == JIT_F_OPT_DEFAULT);
+    lj_assertJ(((JIT_F_OPT_FOLD|JIT_F_OPT_FWD|JIT_F_OPT_CSE|JIT_F_OPT_DSE) |
+                JIT_F_OPT_DEFAULT) == JIT_F_OPT_DEFAULT,
+               "bad JIT_F_OPT_DEFAULT");
     /* Folding disabled? Chain to CSE, but not for loads/stores/allocs. */
     if (!(J->flags & JIT_F_OPT_FOLD) && irm_kind(lj_ir_mode[fins->o]) == IRM_N)
       return lj_opt_cse(J);
@@ -2511,7 +2521,7 @@ retry:
     return lj_ir_kint(J, fins->i);
   if (ref == FAILFOLD)
     lj_trace_err(J, LJ_TRERR_GFAIL);
-  lua_assert(ref == DROPFOLD);
+  lj_assertJ(ref == DROPFOLD, "bad fold result");
   return REF_DROP;
 }
 
diff --git a/src/lj_opt_loop.c b/src/lj_opt_loop.c
index 2eacb7d7..0e5189cd 100644
--- a/src/lj_opt_loop.c
+++ b/src/lj_opt_loop.c
@@ -299,7 +299,8 @@ static void loop_unroll(LoopState *lps)
   loopmap = &J->cur.snapmap[loopsnap->mapofs];
   /* The PC of snapshot #0 and the loop snapshot must match. */
   psentinel = &loopmap[loopsnap->nent];
-  lua_assert(*psentinel == J->cur.snapmap[J->cur.snap[0].nent]);
+  lj_assertJ(*psentinel == J->cur.snapmap[J->cur.snap[0].nent],
+             "mismatched PC for loop snapshot");
   *psentinel = SNAP(255, 0, 0);  /* Replace PC with temporary sentinel. */
 
   /* Start substitution with snapshot #1 (#0 is empty for root traces). */
@@ -372,7 +373,7 @@ static void loop_unroll(LoopState *lps)
   }
   if (!irt_isguard(J->guardemit))  /* Drop redundant snapshot. */
     J->cur.nsnapmap = (uint32_t)J->cur.snap[--J->cur.nsnap].mapofs;
-  lua_assert(J->cur.nsnapmap <= J->sizesnapmap);
+  lj_assertJ(J->cur.nsnapmap <= J->sizesnapmap, "bad snapshot map index");
   *psentinel = J->cur.snapmap[J->cur.snap[0].nent];  /* Restore PC. */
 
   loop_emit_phi(J, subst, phi, nphi, onsnap);
diff --git a/src/lj_opt_mem.c b/src/lj_opt_mem.c
index 4c2c05fe..80517f16 100644
--- a/src/lj_opt_mem.c
+++ b/src/lj_opt_mem.c
@@ -18,6 +18,7 @@
 #include "lj_jit.h"
 #include "lj_iropt.h"
 #include "lj_ircall.h"
+#include "lj_dispatch.h"
 
 /* Some local macros to save typing. Undef'd at the end. */
 #define IR(ref)         (&J->cur.ir[(ref)])
@@ -56,8 +57,8 @@ static AliasRet aa_table(jit_State *J, IRRef ta, IRRef tb)
 {
   IRIns *taba = IR(ta), *tabb = IR(tb);
   int newa, newb;
-  lua_assert(ta != tb);
-  lua_assert(irt_istab(taba->t) && irt_istab(tabb->t));
+  lj_assertJ(ta != tb, "bad usage");
+  lj_assertJ(irt_istab(taba->t) && irt_istab(tabb->t), "bad usage");
   /* Disambiguate new allocations. */
   newa = (taba->o == IR_TNEW || taba->o == IR_TDUP);
   newb = (tabb->o == IR_TNEW || tabb->o == IR_TDUP);
@@ -99,7 +100,7 @@ static AliasRet aa_ahref(jit_State *J, IRIns *refa, IRIns *refb)
     /* Disambiguate array references based on index arithmetic. */
     int32_t ofsa = 0, ofsb = 0;
     IRRef basea = ka, baseb = kb;
-    lua_assert(refb->o == IR_AREF);
+    lj_assertJ(refb->o == IR_AREF, "expected AREF");
     /* Gather base and offset from t[base] or t[base+-ofs]. */
     if (keya->o == IR_ADD && irref_isk(keya->op2)) {
       basea = keya->op1;
@@ -117,8 +118,9 @@ static AliasRet aa_ahref(jit_State *J, IRIns *refa, IRIns *refb)
       return ALIAS_NO;  /* t[base+-o1] vs. t[base+-o2] and o1 != o2. */
   } else {
     /* Disambiguate hash references based on the type of their keys. */
-    lua_assert((refa->o==IR_HREF || refa->o==IR_HREFK || refa->o==IR_NEWREF) &&
-               (refb->o==IR_HREF || refb->o==IR_HREFK || refb->o==IR_NEWREF));
+    lj_assertJ((refa->o==IR_HREF || refa->o==IR_HREFK || refa->o==IR_NEWREF) &&
+               (refb->o==IR_HREF || refb->o==IR_HREFK || refb->o==IR_NEWREF),
+               "bad xREF IR op %d or %d", refa->o, refb->o);
     if (!irt_sametype(keya->t, keyb->t))
       return ALIAS_NO;  /* Different key types. */
   }
@@ -192,7 +194,8 @@ static TRef fwd_ahload(jit_State *J, IRRef xref)
         if (key->o == IR_KSLOT) key = IR(key->op1);
         lj_ir_kvalue(J->L, &keyv, key);
         tv = lj_tab_get(J->L, ir_ktab(IR(ir->op1)), &keyv);
-        lua_assert(itype2irt(tv) == irt_type(fins->t));
+        lj_assertJ(itype2irt(tv) == irt_type(fins->t),
+                   "mismatched type in constant table");
         if (irt_isnum(fins->t))
           return lj_ir_knum_u64(J, tv->u64);
         else if (LJ_DUALNUM && irt_isint(fins->t))
diff --git a/src/lj_opt_narrow.c b/src/lj_opt_narrow.c
index 94cce582..a381d8d8 100644
--- a/src/lj_opt_narrow.c
+++ b/src/lj_opt_narrow.c
@@ -372,17 +372,17 @@ static IRRef narrow_conv_emit(jit_State *J, NarrowConv *nc)
     } else if (op == NARROW_CONV) {
       *sp++ = emitir_raw(convot, ref, convop2);  /* Raw emit avoids a loop. */
     } else if (op == NARROW_SEXT) {
-      lua_assert(sp >= nc->stack+1);
+      lj_assertJ(sp >= nc->stack+1, "stack underflow");
       sp[-1] = emitir(IRT(IR_CONV, IRT_I64), sp[-1],
                       (IRT_I64<<5)|IRT_INT|IRCONV_SEXT);
     } else if (op == NARROW_INT) {
-      lua_assert(next < last);
+      lj_assertJ(next < last, "missing arg to NARROW_INT");
       *sp++ = nc->t == IRT_I64 ?
               lj_ir_kint64(J, (int64_t)(int32_t)*next++) :
               lj_ir_kint(J, *next++);
     } else {  /* Regular IROpT. Pops two operands and pushes one result. */
       IRRef mode = nc->mode;
-      lua_assert(sp >= nc->stack+2);
+      lj_assertJ(sp >= nc->stack+2, "stack underflow");
       sp--;
       /* Omit some overflow checks for array indexing. See comments above. */
       if ((mode & IRCONV_CONVMASK) == IRCONV_INDEX) {
@@ -398,7 +398,7 @@ static IRRef narrow_conv_emit(jit_State *J, NarrowConv *nc)
         narrow_bpc_set(J, narrow_ref(ref), narrow_ref(sp[-1]), mode);
     }
   }
-  lua_assert(sp == nc->stack+1);
+  lj_assertJ(sp == nc->stack+1, "stack misalignment");
   return nc->stack[0];
 }
 
@@ -452,7 +452,7 @@ static TRef narrow_stripov(jit_State *J, TRef tr, int lastop, IRRef mode)
 TRef LJ_FASTCALL lj_opt_narrow_index(jit_State *J, TRef tr)
 {
   IRIns *ir;
-  lua_assert(tref_isnumber(tr));
+  lj_assertJ(tref_isnumber(tr), "expected number type");
   if (tref_isnum(tr))  /* Conversion may be narrowed, too. See above. */
     return emitir(IRTGI(IR_CONV), tr, IRCONV_INT_NUM|IRCONV_INDEX);
   /* Omit some overflow checks for array indexing. See comments above. */
@@ -499,7 +499,7 @@ TRef LJ_FASTCALL lj_opt_narrow_tobit(jit_State *J, TRef tr)
 /* Narrow C array index (overflow undefined). */
 TRef LJ_FASTCALL lj_opt_narrow_cindex(jit_State *J, TRef tr)
 {
-  lua_assert(tref_isnumber(tr));
+  lj_assertJ(tref_isnumber(tr), "expected number type");
   if (tref_isnum(tr))
     return emitir(IRT(IR_CONV, IRT_INTP), tr, (IRT_INTP<<5)|IRT_NUM|IRCONV_ANY);
   /* Undefined overflow semantics allow stripping of ADDOV, SUBOV and MULOV. */
@@ -627,9 +627,10 @@ static int narrow_forl(jit_State *J, cTValue *o)
 /* Narrow the FORL index type by looking at the runtime values. */
 IRType lj_opt_narrow_forl(jit_State *J, cTValue *tv)
 {
-  lua_assert(tvisnumber(&tv[FORL_IDX]) &&
+  lj_assertJ(tvisnumber(&tv[FORL_IDX]) &&
              tvisnumber(&tv[FORL_STOP]) &&
-             tvisnumber(&tv[FORL_STEP]));
+             tvisnumber(&tv[FORL_STEP]),
+             "expected number types");
   /* Narrow only if the runtime values of start/stop/step are all integers. */
   if (narrow_forl(J, &tv[FORL_IDX]) &&
       narrow_forl(J, &tv[FORL_STOP]) &&
diff --git a/src/lj_opt_split.c b/src/lj_opt_split.c
index 7925cfa5..798a02cc 100644
--- a/src/lj_opt_split.c
+++ b/src/lj_opt_split.c
@@ -235,7 +235,7 @@ static IRRef split_bitshift(jit_State *J, IRRef1 *hisubst,
         return split_emit(J, IRTI(IR_BOR), t1, t2);
       } else {
         IRRef t1 = ir->prev, t2;
-        lua_assert(op == IR_BSHR || op == IR_BSAR);
+        lj_assertJ(op == IR_BSHR || op == IR_BSAR, "bad usage");
         nir->o = IR_BSHR;
         t2 = split_emit(J, IRTI(IR_BSHL), hi, lj_ir_kint(J, (-k&31)));
         ir->prev = split_emit(J, IRTI(IR_BOR), t1, t2);
@@ -250,7 +250,7 @@ static IRRef split_bitshift(jit_State *J, IRRef1 *hisubst,
         ir->prev = lj_ir_kint(J, 0);
         return lo;
       } else {
-        lua_assert(op == IR_BSHR || op == IR_BSAR);
+        lj_assertJ(op == IR_BSHR || op == IR_BSAR, "bad usage");
         if (k == 32) {
           J->cur.nins--;
           ir->prev = hi;
@@ -429,7 +429,7 @@ static void split_ir(jit_State *J)
         hi = split_emit(J, IRT(IR_HIOP, IRT_SOFTFP), nref, nref);
         break;
       case IR_FLOAD:
-        lua_assert(ir->op1 == REF_NIL);
+        lj_assertJ(ir->op1 == REF_NIL, "expected FLOAD from GG_State");
         hi = lj_ir_kint(J, *(int32_t*)((char*)J2GG(J) + ir->op2 + LJ_LE*4));
         nir->op2 += LJ_BE*4;
         break;
@@ -465,8 +465,9 @@ static void split_ir(jit_State *J)
           break;
         }
 #endif
-        lua_assert(st == IRT_INT ||
-                   (LJ_32 && LJ_HASFFI && (st == IRT_U32 || st == IRT_FLOAT)));
+        lj_assertJ(st == IRT_INT ||
+                   (LJ_32 && LJ_HASFFI && (st == IRT_U32 || st == IRT_FLOAT)),
+                   "bad source type for CONV");
         nir->o = IR_CALLN;
 #if LJ_32 && LJ_HASFFI
         nir->op2 = st == IRT_INT ? IRCALL_softfp_i2d :
@@ -496,7 +497,8 @@ static void split_ir(jit_State *J)
         hi = nir->op2;
         break;
       default:
-        lua_assert(ir->o <= IR_NE || ir->o == IR_MIN || ir->o == IR_MAX);
+        lj_assertJ(ir->o <= IR_NE || ir->o == IR_MIN || ir->o == IR_MAX,
+                   "bad IR op %d", ir->o);
         hi = split_emit(J, IRTG(IR_HIOP, IRT_SOFTFP),
                         hisubst[ir->op1], hisubst[ir->op2]);
         break;
@@ -553,7 +555,7 @@ static void split_ir(jit_State *J)
         hi = split_bitshift(J, hisubst, oir, nir, ir);
         break;
       case IR_FLOAD:
-        lua_assert(ir->op2 == IRFL_CDATA_INT64);
+        lj_assertJ(ir->op2 == IRFL_CDATA_INT64, "only INT64 supported");
         hi = split_emit(J, IRTI(IR_FLOAD), nir->op1, IRFL_CDATA_INT64_4);
 #if LJ_BE
         ir->prev = hi; hi = nref;
@@ -619,7 +621,7 @@ static void split_ir(jit_State *J)
         hi = nir->op2;
         break;
       default:
-        lua_assert(ir->o <= IR_NE);  /* Comparisons. */
+        lj_assertJ(ir->o <= IR_NE, "bad IR op %d", ir->o);  /* Comparisons. */
         split_emit(J, IRTGI(IR_HIOP), hiref, hisubst[ir->op2]);
         break;
       }
@@ -697,7 +699,7 @@ static void split_ir(jit_State *J)
 #if LJ_SOFTFP
       if (st == IRT_NUM || (LJ_32 && LJ_HASFFI && st == IRT_FLOAT)) {
         if (irt_isguard(ir->t)) {
-          lua_assert(st == IRT_NUM && irt_isint(ir->t));
+          lj_assertJ(st == IRT_NUM && irt_isint(ir->t), "bad CONV types");
           J->cur.nins--;
           ir->prev = split_num2int(J, nir->op1, hisubst[ir->op1], 1);
         } else {
@@ -828,7 +830,7 @@ void lj_opt_split(jit_State *J)
   if (!J->needsplit)
     J->needsplit = split_needsplit(J);
 #else
-  lua_assert(J->needsplit >= split_needsplit(J));  /* Verify flag. */
+  lj_assertJ(J->needsplit >= split_needsplit(J), "bad SPLIT state");
 #endif
   if (J->needsplit) {
     int errcode = lj_vm_cpcall(J->L, NULL, J, cpsplit);
diff --git a/src/lj_parse.c b/src/lj_parse.c
index 33955ab8..3ae05446 100644
--- a/src/lj_parse.c
+++ b/src/lj_parse.c
@@ -163,6 +163,12 @@ LJ_STATIC_ASSERT((int)BC_MULVV-(int)BC_ADDVV == (int)OPR_MUL-(int)OPR_ADD);
 LJ_STATIC_ASSERT((int)BC_DIVVV-(int)BC_ADDVV == (int)OPR_DIV-(int)OPR_ADD);
 LJ_STATIC_ASSERT((int)BC_MODVV-(int)BC_ADDVV == (int)OPR_MOD-(int)OPR_ADD);
 
+#ifdef LUA_USE_ASSERT
+#define lj_assertFS(c, ...)     (lj_assertG_(G(fs->L), (c), __VA_ARGS__))
+#else
+#define lj_assertFS(c, ...)     ((void)fs)
+#endif
+
 /* -- Error handling ------------------------------------------------------ */
 
 LJ_NORET LJ_NOINLINE static void err_syntax(LexState *ls, ErrMsg em)
@@ -200,7 +206,7 @@ static BCReg const_num(FuncState *fs, ExpDesc *e)
 {
   lua_State *L = fs->L;
   TValue *o;
-  lua_assert(expr_isnumk(e));
+  lj_assertFS(expr_isnumk(e), "bad usage");
   o = lj_tab_set(L, fs->kt, &e->u.nval);
   if (tvhaskslot(o))
     return tvkslot(o);
@@ -225,7 +231,7 @@ static BCReg const_gc(FuncState *fs, GCobj *gc, uint32_t itype)
 /* Add a string constant. */
 static BCReg const_str(FuncState *fs, ExpDesc *e)
 {
-  lua_assert(expr_isstrk(e) || e->k == VGLOBAL);
+  lj_assertFS(expr_isstrk(e) || e->k == VGLOBAL, "bad usage");
   return const_gc(fs, obj2gco(e->u.sval), LJ_TSTR);
 }
 
@@ -313,7 +319,7 @@ static void jmp_patchins(FuncState *fs, BCPos pc, BCPos dest)
 {
   BCIns *jmp = &fs->bcbase[pc].ins;
   BCPos offset = dest-(pc+1)+BCBIAS_J;
-  lua_assert(dest != NO_JMP);
+  lj_assertFS(dest != NO_JMP, "uninitialized jump target");
   if (offset > BCMAX_D)
     err_syntax(fs->ls, LJ_ERR_XJUMP);
   setbc_d(jmp, offset);
@@ -362,7 +368,7 @@ static void jmp_patch(FuncState *fs, BCPos list, BCPos target)
   if (target == fs->pc) {
     jmp_tohere(fs, list);
   } else {
-    lua_assert(target < fs->pc);
+    lj_assertFS(target < fs->pc, "bad jump target");
     jmp_patchval(fs, list, target, NO_REG, target);
   }
 }
@@ -392,7 +398,7 @@ static void bcreg_free(FuncState *fs, BCReg reg)
 {
   if (reg >= fs->nactvar) {
     fs->freereg--;
-    lua_assert(reg == fs->freereg);
+    lj_assertFS(reg == fs->freereg, "bad regfree");
   }
 }
 
@@ -542,7 +548,7 @@ static void expr_toreg_nobranch(FuncState *fs, ExpDesc *e, BCReg reg)
   } else if (e->k <= VKTRUE) {
     ins = BCINS_AD(BC_KPRI, reg, const_pri(e));
   } else {
-    lua_assert(e->k == VVOID || e->k == VJMP);
+    lj_assertFS(e->k == VVOID || e->k == VJMP, "bad expr type %d", e->k);
     return;
   }
   bcemit_INS(fs, ins);
@@ -637,7 +643,7 @@ static void bcemit_store(FuncState *fs, ExpDesc *var, ExpDesc *e)
     ins = BCINS_AD(BC_GSET, ra, const_str(fs, var));
   } else {
     BCReg ra, rc;
-    lua_assert(var->k == VINDEXED);
+    lj_assertFS(var->k == VINDEXED, "bad expr type %d", var->k);
     ra = expr_toanyreg(fs, e);
     rc = var->u.s.aux;
     if ((int32_t)rc < 0) {
@@ -645,10 +651,12 @@ static void bcemit_store(FuncState *fs, ExpDesc *var, ExpDesc *e)
     } else if (rc > BCMAX_C) {
       ins = BCINS_ABC(BC_TSETB, ra, var->u.s.info, rc-(BCMAX_C+1));
     } else {
+#ifdef LUA_USE_ASSERT
       /* Free late alloced key reg to avoid assert on free of value reg. */
       /* This can only happen when called from expr_table(). */
-      lua_assert(e->k != VNONRELOC || ra < fs->nactvar ||
-                 rc < ra || (bcreg_free(fs, rc),1));
+      if (e->k == VNONRELOC && ra >= fs->nactvar && rc >= ra)
+        bcreg_free(fs, rc);
+#endif
       ins = BCINS_ABC(BC_TSETV, ra, var->u.s.info, rc);
     }
   }
@@ -663,7 +671,7 @@ static void bcemit_method(FuncState *fs, ExpDesc *e, ExpDesc *key)
   expr_free(fs, e);
   func = fs->freereg;
   bcemit_AD(fs, BC_MOV, func+1+LJ_FR2, obj);  /* Copy object to 1st argument. */
-  lua_assert(expr_isstrk(key));
+  lj_assertFS(expr_isstrk(key), "bad usage");
   idx = const_str(fs, key);
   if (idx <= BCMAX_C) {
     bcreg_reserve(fs, 2+LJ_FR2);
@@ -803,7 +811,8 @@ static void bcemit_arith(FuncState *fs, BinOpr opr, ExpDesc *e1, ExpDesc *e2)
     else
       rc = expr_toanyreg(fs, e2);
     /* 1st operand discharged by bcemit_binop_left, but need KNUM/KSHORT. */
-    lua_assert(expr_isnumk(e1) || e1->k == VNONRELOC);
+    lj_assertFS(expr_isnumk(e1) || e1->k == VNONRELOC,
+                "bad expr type %d", e1->k);
     expr_toval(fs, e1);
     /* Avoid two consts to satisfy bytecode constraints. */
     if (expr_isnumk(e1) && !expr_isnumk(e2) &&
@@ -891,19 +900,20 @@ static void bcemit_binop(FuncState *fs, BinOpr op, ExpDesc *e1, ExpDesc *e2)
   if (op <= OPR_POW) {
     bcemit_arith(fs, op, e1, e2);
   } else if (op == OPR_AND) {
-    lua_assert(e1->t == NO_JMP);  /* List must be closed. */
+    lj_assertFS(e1->t == NO_JMP, "jump list not closed");
     expr_discharge(fs, e2);
     jmp_append(fs, &e2->f, e1->f);
     *e1 = *e2;
   } else if (op == OPR_OR) {
-    lua_assert(e1->f == NO_JMP);  /* List must be closed. */
+    lj_assertFS(e1->f == NO_JMP, "jump list not closed");
     expr_discharge(fs, e2);
     jmp_append(fs, &e2->t, e1->t);
     *e1 = *e2;
   } else if (op == OPR_CONCAT) {
     expr_toval(fs, e2);
     if (e2->k == VRELOCABLE && bc_op(*bcptr(fs, e2)) == BC_CAT) {
-      lua_assert(e1->u.s.info == bc_b(*bcptr(fs, e2))-1);
+      lj_assertFS(e1->u.s.info == bc_b(*bcptr(fs, e2))-1,
+                  "bad CAT stack layout");
       expr_free(fs, e1);
       setbc_b(bcptr(fs, e2), e1->u.s.info);
       e1->u.s.info = e2->u.s.info;
@@ -915,8 +925,9 @@ static void bcemit_binop(FuncState *fs, BinOpr op, ExpDesc *e1, ExpDesc *e2)
     }
     e1->k = VRELOCABLE;
   } else {
-    lua_assert(op == OPR_NE || op == OPR_EQ ||
-               op == OPR_LT || op == OPR_GE || op == OPR_LE || op == OPR_GT);
+    lj_assertFS(op == OPR_NE || op == OPR_EQ ||
+               op == OPR_LT || op == OPR_GE || op == OPR_LE || op == OPR_GT,
+               "bad binop %d", op);
     bcemit_comp(fs, op, e1, e2);
   }
 }
@@ -945,10 +956,10 @@ static void bcemit_unop(FuncState *fs, BCOp op, ExpDesc *e)
       e->u.s.info = fs->freereg-1;
       e->k = VNONRELOC;
     } else {
-      lua_assert(e->k == VNONRELOC);
+      lj_assertFS(e->k == VNONRELOC, "bad expr type %d", e->k);
     }
   } else {
-    lua_assert(op == BC_UNM || op == BC_LEN);
+    lj_assertFS(op == BC_UNM || op == BC_LEN, "bad unop %d", op);
     if (op == BC_UNM && !expr_hasjump(e)) {  /* Constant-fold negations. */
 #if LJ_HASFFI
       if (e->k == VKCDATA) {  /* Fold in-place since cdata is not interned. */
@@ -1043,8 +1054,9 @@ static void var_new(LexState *ls, BCReg n, GCstr *name)
       lj_lex_error(ls, 0, LJ_ERR_XLIMC, LJ_MAX_VSTACK);
     lj_mem_growvec(ls->L, ls->vstack, ls->sizevstack, LJ_MAX_VSTACK, VarInfo);
   }
-  lua_assert((uintptr_t)name < VARNAME__MAX ||
-             lj_tab_getstr(fs->kt, name) != NULL);
+  lj_assertFS((uintptr_t)name < VARNAME__MAX ||
+              lj_tab_getstr(fs->kt, name) != NULL,
+              "unanchored variable name");
   /* NOBARRIER: name is anchored in fs->kt and ls->vstack is not a GCobj. */
   setgcref(ls->vstack[vtop].name, obj2gco(name));
   fs->varmap[fs->nactvar+n] = (uint16_t)vtop;
@@ -1099,7 +1111,7 @@ static MSize var_lookup_uv(FuncState *fs, MSize vidx, ExpDesc *e)
       return i;  /* Already exists. */
   /* Otherwise create a new one. */
   checklimit(fs, fs->nuv, LJ_MAX_UPVAL, "upvalues");
-  lua_assert(e->k == VLOCAL || e->k == VUPVAL);
+  lj_assertFS(e->k == VLOCAL || e->k == VUPVAL, "bad expr type %d", e->k);
   fs->uvmap[n] = (uint16_t)vidx;
   fs->uvtmp[n] = (uint16_t)(e->k == VLOCAL ? vidx : LJ_MAX_VSTACK+e->u.s.info);
   fs->nuv = n+1;
@@ -1150,7 +1162,8 @@ static MSize gola_new(LexState *ls, GCstr *name, uint8_t info, BCPos pc)
       lj_lex_error(ls, 0, LJ_ERR_XLIMC, LJ_MAX_VSTACK);
     lj_mem_growvec(ls->L, ls->vstack, ls->sizevstack, LJ_MAX_VSTACK, VarInfo);
   }
-  lua_assert(name == NAME_BREAK || lj_tab_getstr(fs->kt, name) != NULL);
+  lj_assertFS(name == NAME_BREAK || lj_tab_getstr(fs->kt, name) != NULL,
+              "unanchored label name");
   /* NOBARRIER: name is anchored in fs->kt and ls->vstack is not a GCobj. */
   setgcref(ls->vstack[vtop].name, obj2gco(name));
   ls->vstack[vtop].startpc = pc;
@@ -1180,8 +1193,9 @@ static void gola_close(LexState *ls, VarInfo *vg)
   FuncState *fs = ls->fs;
   BCPos pc = vg->startpc;
   BCIns *ip = &fs->bcbase[pc].ins;
-  lua_assert(gola_isgoto(vg));
-  lua_assert(bc_op(*ip) == BC_JMP || bc_op(*ip) == BC_UCLO);
+  lj_assertFS(gola_isgoto(vg), "expected goto");
+  lj_assertFS(bc_op(*ip) == BC_JMP || bc_op(*ip) == BC_UCLO,
+              "bad bytecode op %d", bc_op(*ip));
   setbc_a(ip, vg->slot);
   if (bc_op(*ip) == BC_JMP) {
     BCPos next = jmp_next(fs, pc);
@@ -1200,9 +1214,9 @@ static void gola_resolve(LexState *ls, FuncScope *bl, MSize idx)
     if (gcrefeq(vg->name, vl->name) && gola_isgoto(vg)) {
       if (vg->slot < vl->slot) {
         GCstr *name = strref(var_get(ls, ls->fs, vg->slot).name);
-        lua_assert((uintptr_t)name >= VARNAME__MAX);
+        lj_assertLS((uintptr_t)name >= VARNAME__MAX, "expected goto name");
         ls->linenumber = ls->fs->bcbase[vg->startpc].line;
-        lua_assert(strref(vg->name) != NAME_BREAK);
+        lj_assertLS(strref(vg->name) != NAME_BREAK, "unexpected break");
         lj_lex_error(ls, 0, LJ_ERR_XGSCOPE,
                      strdata(strref(vg->name)), strdata(name));
       }
@@ -1266,7 +1280,7 @@ static void fscope_begin(FuncState *fs, FuncScope *bl, int flags)
   bl->vstart = fs->ls->vtop;
   bl->prev = fs->bl;
   fs->bl = bl;
-  lua_assert(fs->freereg == fs->nactvar);
+  lj_assertFS(fs->freereg == fs->nactvar, "bad regalloc");
 }
 
 /* End a scope. */
@@ -1277,7 +1291,7 @@ static void fscope_end(FuncState *fs)
   fs->bl = bl->prev;
   var_remove(ls, bl->nactvar);
   fs->freereg = fs->nactvar;
-  lua_assert(bl->nactvar == fs->nactvar);
+  lj_assertFS(bl->nactvar == fs->nactvar, "bad regalloc");
   if ((bl->flags & (FSCOPE_UPVAL|FSCOPE_NOCLOSE)) == FSCOPE_UPVAL)
     bcemit_AJ(fs, BC_UCLO, bl->nactvar, 0);
   if ((bl->flags & FSCOPE_BREAK)) {
@@ -1364,13 +1378,13 @@ static void fs_fixup_k(FuncState *fs, GCproto *pt, void *kptr)
     Node *n = &node[i];
     if (tvhaskslot(&n->val)) {
       ptrdiff_t kidx = (ptrdiff_t)tvkslot(&n->val);
-      lua_assert(!tvisint(&n->key));
+      lj_assertFS(!tvisint(&n->key), "unexpected integer key");
       if (tvisnum(&n->key)) {
         TValue *tv = &((TValue *)kptr)[kidx];
         if (LJ_DUALNUM) {
           lua_Number nn = numV(&n->key);
           int32_t k = lj_num2int(nn);
-          lua_assert(!tvismzero(&n->key));
+          lj_assertFS(!tvismzero(&n->key), "unexpected -0 key");
           if ((lua_Number)k == nn)
             setintV(tv, k);
           else
@@ -1418,21 +1432,21 @@ static void fs_fixup_line(FuncState *fs, GCproto *pt,
     uint8_t *li = (uint8_t *)lineinfo;
     do {
       BCLine delta = base[i].line - first;
-      lua_assert(delta >= 0 && delta < 256);
+      lj_assertFS(delta >= 0 && delta < 256, "bad line delta");
       li[i] = (uint8_t)delta;
     } while (++i < n);
   } else if (LJ_LIKELY(numline < 65536)) {
     uint16_t *li = (uint16_t *)lineinfo;
     do {
       BCLine delta = base[i].line - first;
-      lua_assert(delta >= 0 && delta < 65536);
+      lj_assertFS(delta >= 0 && delta < 65536, "bad line delta");
       li[i] = (uint16_t)delta;
     } while (++i < n);
   } else {
     uint32_t *li = (uint32_t *)lineinfo;
     do {
       BCLine delta = base[i].line - first;
-      lua_assert(delta >= 0);
+      lj_assertFS(delta >= 0, "bad line delta");
       li[i] = (uint32_t)delta;
     } while (++i < n);
   }
@@ -1522,7 +1536,7 @@ static void fs_fixup_ret(FuncState *fs)
   }
   fs->bl->flags |= FSCOPE_NOCLOSE;  /* Handled above. */
   fscope_end(fs);
-  lua_assert(fs->bl == NULL);
+  lj_assertFS(fs->bl == NULL, "bad scope nesting");
   /* May need to fixup returns encoded before first function was created. */
   if (fs->flags & PROTO_FIXUP_RETURN) {
     BCPos pc;
@@ -1594,7 +1608,7 @@ static GCproto *fs_finish(LexState *ls, BCLine line)
   L->top--;  /* Pop table of constants. */
   ls->vtop = fs->vbase;  /* Reset variable stack. */
   ls->fs = fs->prev;
-  lua_assert(ls->fs != NULL || ls->tok == TK_eof);
+  lj_assertL(ls->fs != NULL || ls->tok == TK_eof, "bad parser state");
   return pt;
 }
 
@@ -1688,14 +1702,15 @@ static void expr_bracket(LexState *ls, ExpDesc *v)
 }
 
 /* Get value of constant expression. */
-static void expr_kvalue(TValue *v, ExpDesc *e)
+static void expr_kvalue(FuncState *fs, TValue *v, ExpDesc *e)
 {
+  UNUSED(fs);
   if (e->k <= VKTRUE) {
     setpriV(v, ~(uint32_t)e->k);
   } else if (e->k == VKSTR) {
     setgcVraw(v, obj2gco(e->u.sval), LJ_TSTR);
   } else {
-    lua_assert(tvisnumber(expr_numtv(e)));
+    lj_assertFS(tvisnumber(expr_numtv(e)), "bad number constant");
     *v = *expr_numtv(e);
   }
 }
@@ -1745,11 +1760,11 @@ static void expr_table(LexState *ls, ExpDesc *e)
         fs->bcbase[pc].ins = BCINS_AD(BC_TDUP, freg-1, kidx);
       }
       vcall = 0;
-      expr_kvalue(&k, &key);
+      expr_kvalue(fs, &k, &key);
       v = lj_tab_set(fs->L, t, &k);
       lj_gc_anybarriert(fs->L, t);
       if (expr_isk_nojump(&val)) {  /* Add const key/value to template table. */
-        expr_kvalue(v, &val);
+        expr_kvalue(fs, v, &val);
       } else {  /* Otherwise create dummy string key (avoids lj_tab_newkey). */
         settabV(fs->L, v, t);  /* Preserve key with table itself as value. */
         fixt = 1;   /* Fix this later, after all resizes. */
@@ -1768,8 +1783,9 @@ static void expr_table(LexState *ls, ExpDesc *e)
   if (vcall) {
     BCInsLine *ilp = &fs->bcbase[fs->pc-1];
     ExpDesc en;
-    lua_assert(bc_a(ilp->ins) == freg &&
-               bc_op(ilp->ins) == (narr > 256 ? BC_TSETV : BC_TSETB));
+    lj_assertFS(bc_a(ilp->ins) == freg &&
+                bc_op(ilp->ins) == (narr > 256 ? BC_TSETV : BC_TSETB),
+                "bad CALL code generation");
     expr_init(&en, VKNUM, 0);
     en.u.nval.u32.lo = narr-1;
     en.u.nval.u32.hi = 0x43300000;  /* Biased integer to avoid denormals. */
@@ -1799,7 +1815,7 @@ static void expr_table(LexState *ls, ExpDesc *e)
       for (i = 0; i <= hmask; i++) {
         Node *n = &node[i];
         if (tvistab(&n->val)) {
-          lua_assert(tabV(&n->val) == t);
+          lj_assertFS(tabV(&n->val) == t, "bad dummy key in template table");
           setnilV(&n->val);  /* Turn value into nil. */
         }
       }
@@ -1830,7 +1846,7 @@ static BCReg parse_params(LexState *ls, int needself)
     } while (lex_opt(ls, ','));
   }
   var_add(ls, nparams);
-  lua_assert(fs->nactvar == nparams);
+  lj_assertFS(fs->nactvar == nparams, "bad regalloc");
   bcreg_reserve(fs, nparams);
   lex_check(ls, ')');
   return nparams;
@@ -1917,7 +1933,7 @@ static void parse_args(LexState *ls, ExpDesc *e)
     err_syntax(ls, LJ_ERR_XFUNARG);
     return;  /* Silence compiler. */
   }
-  lua_assert(e->k == VNONRELOC);
+  lj_assertFS(e->k == VNONRELOC, "bad expr type %d", e->k);
   base = e->u.s.info;  /* Base register for call. */
   if (args.k == VCALL) {
     ins = BCINS_ABC(BC_CALLM, base, 2, args.u.s.aux - base - 1 - LJ_FR2);
@@ -2687,8 +2703,9 @@ static void parse_chunk(LexState *ls)
   while (!islast && !parse_isend(ls->tok)) {
     islast = parse_stmt(ls);
     lex_opt(ls, ';');
-    lua_assert(ls->fs->framesize >= ls->fs->freereg &&
-               ls->fs->freereg >= ls->fs->nactvar);
+    lj_assertLS(ls->fs->framesize >= ls->fs->freereg &&
+                ls->fs->freereg >= ls->fs->nactvar,
+                "bad regalloc");
     ls->fs->freereg = ls->fs->nactvar;  /* Free registers after each stmt. */
   }
   synlevel_end(ls);
@@ -2723,9 +2740,8 @@ GCproto *lj_parse(LexState *ls)
     err_token(ls, TK_eof);
   pt = fs_finish(ls, ls->linenumber);
   L->top--;  /* Drop chunkname. */
-  lua_assert(fs.prev == NULL);
-  lua_assert(ls->fs == NULL);
-  lua_assert(pt->sizeuv == 0);
+  lj_assertL(fs.prev == NULL && ls->fs == NULL, "mismatched frame nesting");
+  lj_assertL(pt->sizeuv == 0, "toplevel proto has upvalues");
   return pt;
 }
 
diff --git a/src/lj_record.c b/src/lj_record.c
index 4fc22742..2a4a766e 100644
--- a/src/lj_record.c
+++ b/src/lj_record.c
@@ -50,34 +50,52 @@
 static void rec_check_ir(jit_State *J)
 {
   IRRef i, nins = J->cur.nins, nk = J->cur.nk;
-  lua_assert(nk <= REF_BIAS && nins >= REF_BIAS && nins < 65536);
+  lj_assertJ(nk <= REF_BIAS && nins >= REF_BIAS && nins < 65536,
+             "inconsistent IR layout");
   for (i = nk; i < nins; i++) {
     IRIns *ir = IR(i);
     uint32_t mode = lj_ir_mode[ir->o];
     IRRef op1 = ir->op1;
     IRRef op2 = ir->op2;
+    const char *err = NULL;
     switch (irm_op1(mode)) {
-    case IRMnone: lua_assert(op1 == 0); break;
-    case IRMref: lua_assert(op1 >= nk);
-      lua_assert(i >= REF_BIAS ? op1 < i : op1 > i); break;
+    case IRMnone:
+      if (op1 != 0) err = "IRMnone op1 used";
+      break;
+    case IRMref:
+      if (op1 < nk || (i >= REF_BIAS ? op1 >= i : op1 <= i))
+        err = "IRMref op1 out of range";
+      break;
     case IRMlit: break;
-    case IRMcst: lua_assert(i < REF_BIAS);
+    case IRMcst:
+      if (i >= REF_BIAS) { err = "constant in IR range"; break; }
       if (irt_is64(ir->t) && ir->o != IR_KNULL)
         i++;
       continue;
     }
     switch (irm_op2(mode)) {
-    case IRMnone: lua_assert(op2 == 0); break;
-    case IRMref: lua_assert(op2 >= nk);
-      lua_assert(i >= REF_BIAS ? op2 < i : op2 > i); break;
+    case IRMnone:
+      if (op2) err = "IRMnone op2 used";
+      break;
+    case IRMref:
+      if (op2 < nk || (i >= REF_BIAS ? op2 >= i : op2 <= i))
+        err = "IRMref op2 out of range";
+      break;
     case IRMlit: break;
-    case IRMcst: lua_assert(0); break;
+    case IRMcst: err = "IRMcst op2"; break;
     }
-    if (ir->prev) {
-      lua_assert(ir->prev >= nk);
-      lua_assert(i >= REF_BIAS ? ir->prev < i : ir->prev > i);
-      lua_assert(ir->o == IR_NOP || IR(ir->prev)->o == ir->o);
+    if (!err && ir->prev) {
+      if (ir->prev < nk || (i >= REF_BIAS ? ir->prev >= i : ir->prev <= i))
+        err = "chain out of range";
+      else if (ir->o != IR_NOP && IR(ir->prev)->o != ir->o)
+        err = "chain to different op";
     }
+    lj_assertJ(!err, "bad IR %04d op %d(%04d,%04d): %s",
+               i-REF_BIAS,
+               ir->o,
+               irm_op1(mode) == IRMref ? op1-REF_BIAS : op1,
+               irm_op2(mode) == IRMref ? op2-REF_BIAS : op2,
+               err);
   }
 }
 
@@ -87,9 +105,10 @@ static void rec_check_slots(jit_State *J)
   BCReg s, nslots = J->baseslot + J->maxslot;
   int32_t depth = 0;
   cTValue *base = J->L->base - J->baseslot;
-  lua_assert(J->baseslot >= 1+LJ_FR2);
-  lua_assert(J->baseslot == 1+LJ_FR2 || (J->slot[J->baseslot-1] & TREF_FRAME));
-  lua_assert(nslots <= LJ_MAX_JSLOTS);
+  lj_assertJ(J->baseslot >= 1+LJ_FR2, "bad baseslot");
+  lj_assertJ(J->baseslot == 1+LJ_FR2 || (J->slot[J->baseslot-1] & TREF_FRAME),
+             "baseslot does not point to frame");
+  lj_assertJ(nslots <= LJ_MAX_JSLOTS, "slot overflow");
   for (s = 0; s < nslots; s++) {
     TRef tr = J->slot[s];
     if (tr) {
@@ -97,56 +116,65 @@ static void rec_check_slots(jit_State *J)
       IRRef ref = tref_ref(tr);
       IRIns *ir = NULL;  /* Silence compiler. */
       if (!LJ_FR2 || ref || !(tr & (TREF_FRAME | TREF_CONT))) {
-        lua_assert(ref >= J->cur.nk && ref < J->cur.nins);
+        lj_assertJ(ref >= J->cur.nk && ref < J->cur.nins,
+                   "slot %d ref %04d out of range", s, ref - REF_BIAS);
         ir = IR(ref);
-        lua_assert(irt_t(ir->t) == tref_t(tr));
+        lj_assertJ(irt_t(ir->t) == tref_t(tr), "slot %d IR type mismatch", s);
       }
       if (s == 0) {
-        lua_assert(tref_isfunc(tr));
+        lj_assertJ(tref_isfunc(tr), "frame slot 0 is not a function");
 #if LJ_FR2
       } else if (s == 1) {
-        lua_assert((tr & ~TREF_FRAME) == 0);
+        lj_assertJ((tr & ~TREF_FRAME) == 0, "bad frame slot 1");
 #endif
       } else if ((tr & TREF_FRAME)) {
         GCfunc *fn = gco2func(frame_gc(tv));
         BCReg delta = (BCReg)(tv - frame_prev(tv));
 #if LJ_FR2
-        if (ref)
-          lua_assert(ir_knum(ir)->u64 == tv->u64);
+        lj_assertJ(!ref || ir_knum(ir)->u64 == tv->u64,
+                   "frame slot %d PC mismatch", s);
         tr = J->slot[s-1];
         ir = IR(tref_ref(tr));
 #endif
-        lua_assert(tref_isfunc(tr));
-        if (tref_isk(tr)) lua_assert(fn == ir_kfunc(ir));
-        lua_assert(s > delta + LJ_FR2 ? (J->slot[s-delta] & TREF_FRAME)
-                                      : (s == delta + LJ_FR2));
+        lj_assertJ(tref_isfunc(tr),
+                   "frame slot %d is not a function", s-LJ_FR2);
+        lj_assertJ(!tref_isk(tr) || fn == ir_kfunc(ir),
+                   "frame slot %d function mismatch", s-LJ_FR2);
+        lj_assertJ(s > delta + LJ_FR2 ? (J->slot[s-delta] & TREF_FRAME)
+                                      : (s == delta + LJ_FR2),
+                   "frame slot %d broken chain", s-LJ_FR2);
         depth++;
       } else if ((tr & TREF_CONT)) {
 #if LJ_FR2
-        if (ref)
-          lua_assert(ir_knum(ir)->u64 == tv->u64);
+        lj_assertJ(!ref || ir_knum(ir)->u64 == tv->u64,
+                   "cont slot %d continuation mismatch", s);
 #else
-        lua_assert(ir_kptr(ir) == gcrefp(tv->gcr, void));
+        lj_assertJ(ir_kptr(ir) == gcrefp(tv->gcr, void),
+                   "cont slot %d continuation mismatch", s);
 #endif
-        lua_assert((J->slot[s+1+LJ_FR2] & TREF_FRAME));
+        lj_assertJ((J->slot[s+1+LJ_FR2] & TREF_FRAME),
+                   "cont slot %d not followed by frame", s);
         depth++;
       } else {
-        if (tvisnumber(tv))
-          lua_assert(tref_isnumber(tr));  /* Could be IRT_INT etc., too. */
-        else
-          lua_assert(itype2irt(tv) == tref_type(tr));
+        /* Number repr. may differ, but other types must be the same. */
+        lj_assertJ(tvisnumber(tv) ? tref_isnumber(tr) :
+                                    itype2irt(tv) == tref_type(tr),
+                   "slot %d type mismatch: stack type %d vs IR type %d",
+                   s, itypemap(tv), tref_type(tr));
         if (tref_isk(tr)) {  /* Compare constants. */
           TValue tvk;
           lj_ir_kvalue(J->L, &tvk, ir);
-          if (!(tvisnum(&tvk) && tvisnan(&tvk)))
-            lua_assert(lj_obj_equal(tv, &tvk));
-          else
-            lua_assert(tvisnum(tv) && tvisnan(tv));
+          lj_assertJ((tvisnum(&tvk) && tvisnan(&tvk)) ?
+                     (tvisnum(tv) && tvisnan(tv)) :
+                     lj_obj_equal(tv, &tvk),
+                     "slot %d const mismatch: stack %016llx vs IR %016llx",
+                     s, tv->u64, tvk.u64);
         }
       }
     }
   }
-  lua_assert(J->framedepth == depth);
+  lj_assertJ(J->framedepth == depth,
+             "frame depth mismatch %d vs %d", J->framedepth, depth);
 }
 #endif
 
@@ -182,7 +210,7 @@ static TRef getcurrf(jit_State *J)
 {
   if (J->base[-1-LJ_FR2])
     return J->base[-1-LJ_FR2];
-  lua_assert(J->baseslot == 1+LJ_FR2);
+  lj_assertJ(J->baseslot == 1+LJ_FR2, "bad baseslot");
   return sloadt(J, -1-LJ_FR2, IRT_FUNC, IRSLOAD_READONLY);
 }
 
@@ -427,7 +455,8 @@ static void rec_for_loop(jit_State *J, const BCIns *fori, ScEvEntry *scev,
   TRef stop = fori_arg(J, fori, ra+FORL_STOP, t, mode);
   TRef step = fori_arg(J, fori, ra+FORL_STEP, t, mode);
   int tc, dir = rec_for_direction(&tv[FORL_STEP]);
-  lua_assert(bc_op(*fori) == BC_FORI || bc_op(*fori) == BC_JFORI);
+  lj_assertJ(bc_op(*fori) == BC_FORI || bc_op(*fori) == BC_JFORI,
+             "bad bytecode %d instead of FORI/JFORI", bc_op(*fori));
   scev->t.irt = t;
   scev->dir = dir;
   scev->stop = tref_ref(stop);
@@ -483,7 +512,7 @@ static LoopEvent rec_for(jit_State *J, const BCIns *fori, int isforl)
                                                    IRT_NUM;
     for (i = FORL_IDX; i <= FORL_STEP; i++) {
       if (!tr[i]) sload(J, ra+i);
-      lua_assert(tref_isnumber_str(tr[i]));
+      lj_assertJ(tref_isnumber_str(tr[i]), "bad FORI argument type");
       if (tref_isstr(tr[i]))
         tr[i] = emitir(IRTG(IR_STRTO, IRT_NUM), tr[i], 0);
       if (t == IRT_INT) {
@@ -615,7 +644,8 @@ static void rec_loop_jit(jit_State *J, TraceNo lnk, LoopEvent ev)
 static int rec_profile_need(jit_State *J, GCproto *pt, const BCIns *pc)
 {
   GCproto *ppt;
-  lua_assert(J->prof_mode == 'f' || J->prof_mode == 'l');
+  lj_assertJ(J->prof_mode == 'f' || J->prof_mode == 'l',
+             "bad profiler mode %c", J->prof_mode);
   if (!pt)
     return 0;
   ppt = J->prev_pt;
@@ -793,7 +823,7 @@ void lj_record_ret(jit_State *J, BCReg rbase, ptrdiff_t gotresults)
     BCReg cbase = (BCReg)frame_delta(frame);
     if (--J->framedepth <= 0)
       lj_trace_err(J, LJ_TRERR_NYIRETL);
-    lua_assert(J->baseslot > 1+LJ_FR2);
+    lj_assertJ(J->baseslot > 1+LJ_FR2, "bad baseslot for return");
     gotresults++;
     rbase += cbase;
     J->baseslot -= (BCReg)cbase;
@@ -817,7 +847,7 @@ void lj_record_ret(jit_State *J, BCReg rbase, ptrdiff_t gotresults)
     BCReg cbase = (BCReg)frame_delta(frame);
     if (--J->framedepth < 0)  /* NYI: return of vararg func to lower frame. */
       lj_trace_err(J, LJ_TRERR_NYIRETL);
-    lua_assert(J->baseslot > 1+LJ_FR2);
+    lj_assertJ(J->baseslot > 1+LJ_FR2, "bad baseslot for return");
     rbase += cbase;
     J->baseslot -= (BCReg)cbase;
     J->base -= cbase;
@@ -844,7 +874,7 @@ void lj_record_ret(jit_State *J, BCReg rbase, ptrdiff_t gotresults)
     J->maxslot = cbase+(BCReg)nresults;
     if (J->framedepth > 0) {  /* Return to a frame that is part of the trace. */
       J->framedepth--;
-      lua_assert(J->baseslot > cbase+1+LJ_FR2);
+      lj_assertJ(J->baseslot > cbase+1+LJ_FR2, "bad baseslot for return");
       J->baseslot -= cbase+1+LJ_FR2;
       J->base -= cbase+1+LJ_FR2;
     } else if (J->parent == 0 && J->exitno == 0 &&
@@ -859,7 +889,7 @@ void lj_record_ret(jit_State *J, BCReg rbase, ptrdiff_t gotresults)
       emitir(IRTG(IR_RETF, IRT_PGC), trpt, trpc);
       J->retdepth++;
       J->needsnap = 1;
-      lua_assert(J->baseslot == 1+LJ_FR2);
+      lj_assertJ(J->baseslot == 1+LJ_FR2, "bad baseslot for return");
       /* Shift result slots up and clear the slots of the new frame below. */
       memmove(J->base + cbase, J->base-1-LJ_FR2, sizeof(TRef)*nresults);
       memset(J->base-1-LJ_FR2, 0, sizeof(TRef)*(cbase+1+LJ_FR2));
@@ -907,12 +937,13 @@ void lj_record_ret(jit_State *J, BCReg rbase, ptrdiff_t gotresults)
       }  /* Otherwise continue with another __concat call. */
     } else {
       /* Result type already specialized. */
-      lua_assert(cont == lj_cont_condf || cont == lj_cont_condt);
+      lj_assertJ(cont == lj_cont_condf || cont == lj_cont_condt,
+                 "bad continuation type");
     }
   } else {
     lj_trace_err(J, LJ_TRERR_NYIRETL);  /* NYI: handle return to C frame. */
   }
-  lua_assert(J->baseslot >= 1+LJ_FR2);
+  lj_assertJ(J->baseslot >= 1+LJ_FR2, "bad baseslot for return");
 }
 
 /* -- Metamethod handling ------------------------------------------------- */
@@ -1167,7 +1198,7 @@ static void rec_mm_comp_cdata(jit_State *J, RecordIndex *ix, int op, MMS mm)
     ix->tab = ix->val;
     copyTV(J->L, &ix->tabv, &ix->valv);
   } else {
-    lua_assert(tref_iscdata(ix->key));
+    lj_assertJ(tref_iscdata(ix->key), "cdata expected");
     ix->tab = ix->key;
     copyTV(J->L, &ix->tabv, &ix->keyv);
   }
@@ -1264,7 +1295,8 @@ static void rec_idx_abc(jit_State *J, TRef asizeref, TRef ikey, uint32_t asize)
     /* Got scalar evolution analysis results for this reference? */
     if (ref == J->scev.idx) {
       int32_t stop;
-      lua_assert(irt_isint(J->scev.t) && ir->o == IR_SLOAD);
+      lj_assertJ(irt_isint(J->scev.t) && ir->o == IR_SLOAD,
+                 "only int SCEV supported");
       stop = numberVint(&(J->L->base - J->baseslot)[ir->op1 + FORL_STOP]);
       /* Runtime value for stop of loop is within bounds? */
       if ((uint64_t)stop + ofs < (uint64_t)asize) {
@@ -1382,7 +1414,7 @@ TRef lj_record_idx(jit_State *J, RecordIndex *ix)
 
   while (!tref_istab(ix->tab)) { /* Handle non-table lookup. */
     /* Never call raw lj_record_idx() on non-table. */
-    lua_assert(ix->idxchain != 0);
+    lj_assertJ(ix->idxchain != 0, "bad usage");
     if (!lj_record_mm_lookup(J, ix, ix->val ? MM_newindex : MM_index))
       lj_trace_err(J, LJ_TRERR_NOMM);
   handlemm:
@@ -1466,10 +1498,10 @@ TRef lj_record_idx(jit_State *J, RecordIndex *ix)
         emitir(IRTG(oldv == niltvg(J2G(J)) ? IR_EQ : IR_NE, IRT_PGC),
                xref, lj_ir_kkptr(J, niltvg(J2G(J))));
       if (ix->idxchain && lj_record_mm_lookup(J, ix, MM_newindex)) {
-        lua_assert(hasmm);
+        lj_assertJ(hasmm, "inconsistent metamethod handling");
         goto handlemm;
       }
-      lua_assert(!hasmm);
+      lj_assertJ(!hasmm, "inconsistent metamethod handling");
       if (oldv == niltvg(J2G(J))) {  /* Need to insert a new key. */
         TRef key = ix->key;
         if (tref_isinteger(key))  /* NEWREF needs a TValue as a key. */
@@ -1575,7 +1607,7 @@ static TRef rec_upvalue(jit_State *J, uint32_t uv, TRef val)
   int needbarrier = 0;
   if (rec_upvalue_constify(J, uvp)) {  /* Try to constify immutable upvalue. */
     TRef tr, kfunc;
-    lua_assert(val == 0);
+    lj_assertJ(val == 0, "bad usage");
     if (!tref_isk(fn)) {  /* Late specialization of current function. */
       if (J->pt->flags >= PROTO_CLC_POLY)
         goto noconstify;
@@ -1697,7 +1729,7 @@ static void rec_func_vararg(jit_State *J)
 {
   GCproto *pt = J->pt;
   BCReg s, fixargs, vframe = J->maxslot+1+LJ_FR2;
-  lua_assert((pt->flags & PROTO_VARARG));
+  lj_assertJ((pt->flags & PROTO_VARARG), "FUNCV in non-vararg function");
   if (J->baseslot + vframe + pt->framesize >= LJ_MAX_JSLOTS)
     lj_trace_err(J, LJ_TRERR_STACKOV);
   J->base[vframe-1-LJ_FR2] = J->base[-1-LJ_FR2];  /* Copy function up. */
@@ -1766,7 +1798,7 @@ static void rec_varg(jit_State *J, BCReg dst, ptrdiff_t nresults)
 {
   int32_t numparams = J->pt->numparams;
   ptrdiff_t nvararg = frame_delta(J->L->base-1) - numparams - 1 - LJ_FR2;
-  lua_assert(frame_isvarg(J->L->base-1));
+  lj_assertJ(frame_isvarg(J->L->base-1), "VARG in non-vararg frame");
   if (LJ_FR2 && dst > J->maxslot)
     J->base[dst-1] = 0;  /* Prevent resurrection of unrelated slot. */
   if (J->framedepth > 0) {  /* Simple case: varargs defined on-trace. */
@@ -1889,7 +1921,7 @@ static TRef rec_cat(jit_State *J, BCReg baseslot, BCReg topslot)
   TValue savetv[5];
   BCReg s;
   RecordIndex ix;
-  lua_assert(baseslot < topslot);
+  lj_assertJ(baseslot < topslot, "bad CAT arg");
   for (s = baseslot; s <= topslot; s++)
     (void)getslot(J, s);  /* Ensure all arguments have a reference. */
   if (tref_isnumber_str(top[0]) && tref_isnumber_str(top[-1])) {
@@ -2013,7 +2045,7 @@ void lj_record_ins(jit_State *J)
       if (bc_op(*J->pc) >= BC__MAX)
         return;
       break;
-    default: lua_assert(0); break;
+    default: lj_assertJ(0, "bad post-processing mode"); break;
     }
     J->postproc = LJ_POST_NONE;
   }
@@ -2381,7 +2413,8 @@ void lj_record_ins(jit_State *J)
       J->loopref = J->cur.nins;
     break;
   case BC_JFORI:
-    lua_assert(bc_op(pc[(ptrdiff_t)rc-BCBIAS_J]) == BC_JFORL);
+    lj_assertJ(bc_op(pc[(ptrdiff_t)rc-BCBIAS_J]) == BC_JFORL,
+               "JFORI does not point to JFORL");
     if (rec_for(J, pc, 0) != LOOPEV_LEAVE)  /* Link to existing loop. */
       lj_record_stop(J, LJ_TRLINK_ROOT, bc_d(pc[(ptrdiff_t)rc-BCBIAS_J]));
     /* Continue tracing if the loop is not entered. */
@@ -2434,7 +2467,8 @@ void lj_record_ins(jit_State *J)
     rec_func_lua(J);
     break;
   case BC_JFUNCV:
-    lua_assert(0);  /* Cannot happen. No hotcall counting for varag funcs. */
+    /* Cannot happen. No hotcall counting for varag funcs. */
+    lj_assertJ(0, "unsupported vararg hotcall");
     break;
 
   case BC_FUNCC:
@@ -2494,11 +2528,11 @@ static const BCIns *rec_setup_root(jit_State *J)
     J->bc_min = pc;
     break;
   case BC_ITERL:
-    lua_assert(bc_op(pc[-1]) == BC_ITERC);
+    lj_assertJ(bc_op(pc[-1]) == BC_ITERC, "no ITERC before ITERL");
     J->maxslot = ra + bc_b(pc[-1]) - 1;
     J->bc_extent = (MSize)(-bc_j(ins))*sizeof(BCIns);
     pc += 1+bc_j(ins);
-    lua_assert(bc_op(pc[-1]) == BC_JMP);
+    lj_assertJ(bc_op(pc[-1]) == BC_JMP, "ITERL does not point to JMP+1");
     J->bc_min = pc;
     break;
   case BC_LOOP:
@@ -2530,7 +2564,7 @@ static const BCIns *rec_setup_root(jit_State *J)
     pc++;
     break;
   default:
-    lua_assert(0);
+    lj_assertJ(0, "bad root trace start bytecode %d", bc_op(ins));
     break;
   }
   return pc;
diff --git a/src/lj_snap.c b/src/lj_snap.c
index a47c0e3e..a21894f6 100644
--- a/src/lj_snap.c
+++ b/src/lj_snap.c
@@ -110,7 +110,7 @@ static MSize snapshot_framelinks(jit_State *J, SnapEntry *map, uint8_t *topslot)
   cTValue *ftop = isluafunc(fn) ? (frame+funcproto(fn)->framesize) : J->L->top;
 #if LJ_FR2
   uint64_t pcbase = (u64ptr(J->pc) << 8) | (J->baseslot - 2);
-  lua_assert(2 <= J->baseslot && J->baseslot <= 257);
+  lj_assertJ(2 <= J->baseslot && J->baseslot <= 257, "bad baseslot");
   memcpy(map, &pcbase, sizeof(uint64_t));
 #else
   MSize f = 0;
@@ -129,7 +129,7 @@ static MSize snapshot_framelinks(jit_State *J, SnapEntry *map, uint8_t *topslot)
 #endif
       frame = frame_prevd(frame);
     } else {
-      lua_assert(!frame_isc(frame));
+      lj_assertJ(!frame_isc(frame), "broken frame chain");
 #if !LJ_FR2
       map[f++] = SNAP_MKFTSZ(frame_ftsz(frame));
 #endif
@@ -141,10 +141,10 @@ static MSize snapshot_framelinks(jit_State *J, SnapEntry *map, uint8_t *topslot)
   }
   *topslot = (uint8_t)(ftop - lim);
 #if LJ_FR2
-  lua_assert(sizeof(SnapEntry) * 2 == sizeof(uint64_t));
+  lj_assertJ(sizeof(SnapEntry) * 2 == sizeof(uint64_t), "bad SnapEntry def");
   return 2;
 #else
-  lua_assert(f == (MSize)(1 + J->framedepth));
+  lj_assertJ(f == (MSize)(1 + J->framedepth), "miscalculated snapshot size");
   return f;
 #endif
 }
@@ -222,7 +222,8 @@ static BCReg snap_usedef(jit_State *J, uint8_t *udf,
 #define DEF_SLOT(s)             udf[(s)] *= 3
 
   /* Scan through following bytecode and check for uses/defs. */
-  lua_assert(pc >= proto_bc(J->pt) && pc < proto_bc(J->pt) + J->pt->sizebc);
+  lj_assertJ(pc >= proto_bc(J->pt) && pc < proto_bc(J->pt) + J->pt->sizebc,
+             "snapshot PC out of range");
   for (;;) {
     BCIns ins = *pc++;
     BCOp op = bc_op(ins);
@@ -233,7 +234,7 @@ static BCReg snap_usedef(jit_State *J, uint8_t *udf,
     switch (bcmode_c(op)) {
     case BCMvar: USE_SLOT(bc_c(ins)); break;
     case BCMrbase:
-      lua_assert(op == BC_CAT);
+      lj_assertJ(op == BC_CAT, "unhandled op %d with RC rbase", op);
       for (s = bc_b(ins); s <= bc_c(ins); s++) USE_SLOT(s);
       for (; s < maxslot; s++) DEF_SLOT(s);
       break;
@@ -285,7 +286,8 @@ static BCReg snap_usedef(jit_State *J, uint8_t *udf,
       break;
     default: break;
     }
-    lua_assert(pc >= proto_bc(J->pt) && pc < proto_bc(J->pt) + J->pt->sizebc);
+    lj_assertJ(pc >= proto_bc(J->pt) && pc < proto_bc(J->pt) + J->pt->sizebc,
+               "use/def analysis PC out of range");
   }
 
 #undef USE_SLOT
@@ -356,19 +358,20 @@ static RegSP snap_renameref(GCtrace *T, SnapNo lim, IRRef ref, RegSP rs)
 }
 
 /* Copy RegSP from parent snapshot to the parent links of the IR. */
-IRIns *lj_snap_regspmap(GCtrace *T, SnapNo snapno, IRIns *ir)
+IRIns *lj_snap_regspmap(jit_State *J, GCtrace *T, SnapNo snapno, IRIns *ir)
 {
   SnapShot *snap = &T->snap[snapno];
   SnapEntry *map = &T->snapmap[snap->mapofs];
   BloomFilter rfilt = snap_renamefilter(T, snapno);
   MSize n = 0;
   IRRef ref = 0;
+  UNUSED(J);
   for ( ; ; ir++) {
     uint32_t rs;
     if (ir->o == IR_SLOAD) {
       if (!(ir->op2 & IRSLOAD_PARENT)) break;
       for ( ; ; n++) {
-        lua_assert(n < snap->nent);
+        lj_assertJ(n < snap->nent, "slot %d not found in snapshot", ir->op1);
         if (snap_slot(map[n]) == ir->op1) {
           ref = snap_ref(map[n++]);
           break;
@@ -385,7 +388,7 @@ IRIns *lj_snap_regspmap(GCtrace *T, SnapNo snapno, IRIns *ir)
     if (bloomtest(rfilt, ref))
       rs = snap_renameref(T, snapno, ref, rs);
     ir->prev = (uint16_t)rs;
-    lua_assert(regsp_used(rs));
+    lj_assertJ(regsp_used(rs), "unused IR %04d in snapshot", ref - REF_BIAS);
   }
   return ir;
 }
@@ -403,7 +406,7 @@ static TRef snap_replay_const(jit_State *J, IRIns *ir)
   case IR_KNUM: case IR_KINT64:
     return lj_ir_k64(J, (IROp)ir->o, ir_k64(ir)->u64);
   case IR_KPTR: return lj_ir_kptr(J, ir_kptr(ir));  /* Continuation. */
-  default: lua_assert(0); return TREF_NIL; break;
+  default: lj_assertJ(0, "bad IR constant op %d", ir->o); return TREF_NIL;
   }
 }
 
@@ -481,7 +484,7 @@ void lj_snap_replay(jit_State *J, GCtrace *T)
         tr = snap_replay_const(J, ir);
     } else if (!regsp_used(ir->prev)) {
       pass23 = 1;
-      lua_assert(s != 0);
+      lj_assertJ(s != 0, "unused slot 0 in snapshot");
       tr = s;
     } else {
       IRType t = irt_type(ir->t);
@@ -507,8 +510,9 @@ void lj_snap_replay(jit_State *J, GCtrace *T)
       if (regsp_reg(ir->r) == RID_SUNK) {
         if (J->slot[snap_slot(sn)] != snap_slot(sn)) continue;
         pass23 = 1;
-        lua_assert(ir->o == IR_TNEW || ir->o == IR_TDUP ||
-                   ir->o == IR_CNEW || ir->o == IR_CNEWI);
+        lj_assertJ(ir->o == IR_TNEW || ir->o == IR_TDUP ||
+                   ir->o == IR_CNEW || ir->o == IR_CNEWI,
+                   "sunk parent IR %04d has bad op %d", refp - REF_BIAS, ir->o);
         if (ir->op1 >= T->nk) snap_pref(J, T, map, nent, seen, ir->op1);
         if (ir->op2 >= T->nk) snap_pref(J, T, map, nent, seen, ir->op2);
         if (LJ_HASFFI && ir->o == IR_CNEWI) {
@@ -526,7 +530,8 @@ void lj_snap_replay(jit_State *J, GCtrace *T)
             }
         }
       } else if (!irref_isk(refp) && !regsp_used(ir->prev)) {
-        lua_assert(ir->o == IR_CONV && ir->op2 == IRCONV_NUM_INT);
+        lj_assertJ(ir->o == IR_CONV && ir->op2 == IRCONV_NUM_INT,
+                   "sunk parent IR %04d has bad op %d", refp - REF_BIAS, ir->o);
         J->slot[snap_slot(sn)] = snap_pref(J, T, map, nent, seen, ir->op1);
       }
     }
@@ -576,7 +581,9 @@ void lj_snap_replay(jit_State *J, GCtrace *T)
               val = snap_pref(J, T, map, nent, seen, irs->op2);
               if (val == 0) {
                 IRIns *irc = &T->ir[irs->op2];
-                lua_assert(irc->o == IR_CONV && irc->op2 == IRCONV_NUM_INT);
+                lj_assertJ(irc->o == IR_CONV && irc->op2 == IRCONV_NUM_INT,
+                           "sunk store for parent IR %04d with bad op %d",
+                           refp - REF_BIAS, irc->o);
                 val = snap_pref(J, T, map, nent, seen, irc->op1);
                 val = emitir(IRTN(IR_CONV), val, IRCONV_NUM_INT);
               } else if ((LJ_SOFTFP32 || (LJ_32 && LJ_HASFFI)) &&
@@ -645,13 +652,14 @@ static void snap_restoreval(jit_State *J, GCtrace *T, ExitState *ex,
       o->u64 = *(uint64_t *)sps;
 #endif
     } else {
-      lua_assert(!irt_ispri(t));  /* PRI refs never have a spill slot. */
+      lj_assertJ(!irt_ispri(t), "PRI ref with spill slot");
       setgcV(J->L, o, (GCobj *)(uintptr_t)*(GCSize *)sps, irt_toitype(t));
     }
   } else {  /* Restore from register. */
     Reg r = regsp_reg(rs);
     if (ra_noreg(r)) {
-      lua_assert(ir->o == IR_CONV && ir->op2 == IRCONV_NUM_INT);
+      lj_assertJ(ir->o == IR_CONV && ir->op2 == IRCONV_NUM_INT,
+                 "restore from IR %04d has no reg", ref - REF_BIAS);
       snap_restoreval(J, T, ex, snapno, rfilt, ir->op1, o);
       if (LJ_DUALNUM) setnumV(o, (lua_Number)intV(o));
       return;
@@ -679,7 +687,7 @@ static void snap_restoreval(jit_State *J, GCtrace *T, ExitState *ex,
 
 #if LJ_HASFFI
 /* Restore raw data from the trace exit state. */
-static void snap_restoredata(GCtrace *T, ExitState *ex,
+static void snap_restoredata(jit_State *J, GCtrace *T, ExitState *ex,
                              SnapNo snapno, BloomFilter rfilt,
                              IRRef ref, void *dst, CTSize sz)
 {
@@ -687,6 +695,7 @@ static void snap_restoredata(GCtrace *T, ExitState *ex,
   RegSP rs = ir->prev;
   int32_t *src;
   uint64_t tmp;
+  UNUSED(J);
   if (irref_isk(ref)) {
     if (ir_isk64(ir)) {
       src = (int32_t *)&ir[1];
@@ -709,8 +718,9 @@ static void snap_restoredata(GCtrace *T, ExitState *ex,
       Reg r = regsp_reg(rs);
       if (ra_noreg(r)) {
         /* Note: this assumes CNEWI is never used for SOFTFP split numbers. */
-        lua_assert(sz == 8 && ir->o == IR_CONV && ir->op2 == IRCONV_NUM_INT);
-        snap_restoredata(T, ex, snapno, rfilt, ir->op1, dst, 4);
+        lj_assertJ(sz == 8 && ir->o == IR_CONV && ir->op2 == IRCONV_NUM_INT,
+                   "restore from IR %04d has no reg", ref - REF_BIAS);
+        snap_restoredata(J, T, ex, snapno, rfilt, ir->op1, dst, 4);
         *(lua_Number *)dst = (lua_Number)*(int32_t *)dst;
         return;
       }
@@ -731,7 +741,8 @@ static void snap_restoredata(GCtrace *T, ExitState *ex,
       if (LJ_64 && LJ_BE && sz == 4) src++;
     }
   }
-  lua_assert(sz == 1 || sz == 2 || sz == 4 || sz == 8);
+  lj_assertJ(sz == 1 || sz == 2 || sz == 4 || sz == 8,
+             "restore from IR %04d with bad size %d", ref - REF_BIAS, sz);
   if (sz == 4) *(int32_t *)dst = *src;
   else if (sz == 8) *(int64_t *)dst = *(int64_t *)src;
   else if (sz == 1) *(int8_t *)dst = (int8_t)*src;
@@ -744,8 +755,9 @@ static void snap_unsink(jit_State *J, GCtrace *T, ExitState *ex,
                         SnapNo snapno, BloomFilter rfilt,
                         IRIns *ir, TValue *o)
 {
-  lua_assert(ir->o == IR_TNEW || ir->o == IR_TDUP ||
-             ir->o == IR_CNEW || ir->o == IR_CNEWI);
+  lj_assertJ(ir->o == IR_TNEW || ir->o == IR_TDUP ||
+             ir->o == IR_CNEW || ir->o == IR_CNEWI,
+             "sunk allocation with bad op %d", ir->o);
 #if LJ_HASFFI
   if (ir->o == IR_CNEW || ir->o == IR_CNEWI) {
     CTState *cts = ctype_cts(J->L);
@@ -756,13 +768,14 @@ static void snap_unsink(jit_State *J, GCtrace *T, ExitState *ex,
     setcdataV(J->L, o, cd);
     if (ir->o == IR_CNEWI) {
       uint8_t *p = (uint8_t *)cdataptr(cd);
-      lua_assert(sz == 4 || sz == 8);
+      lj_assertJ(sz == 4 || sz == 8, "sunk cdata with bad size %d", sz);
       if (LJ_32 && sz == 8 && ir+1 < T->ir + T->nins && (ir+1)->o == IR_HIOP) {
-        snap_restoredata(T, ex, snapno, rfilt, (ir+1)->op2, LJ_LE?p+4:p, 4);
+        snap_restoredata(J, T, ex, snapno, rfilt, (ir+1)->op2,
+                         LJ_LE ? p+4 : p, 4);
         if (LJ_BE) p += 4;
         sz = 4;
       }
-      snap_restoredata(T, ex, snapno, rfilt, ir->op2, p, sz);
+      snap_restoredata(J, T, ex, snapno, rfilt, ir->op2, p, sz);
     } else {
       IRIns *irs, *irlast = &T->ir[T->snap[snapno].ref];
       for (irs = ir+1; irs < irlast; irs++)
@@ -770,8 +783,11 @@ static void snap_unsink(jit_State *J, GCtrace *T, ExitState *ex,
           IRIns *iro = &T->ir[T->ir[irs->op1].op2];
           uint8_t *p = (uint8_t *)cd;
           CTSize szs;
-          lua_assert(irs->o == IR_XSTORE && T->ir[irs->op1].o == IR_ADD);
-          lua_assert(iro->o == IR_KINT || iro->o == IR_KINT64);
+          lj_assertJ(irs->o == IR_XSTORE, "sunk store with bad op %d", irs->o);
+          lj_assertJ(T->ir[irs->op1].o == IR_ADD,
+                     "sunk store with bad add op %d", T->ir[irs->op1].o);
+          lj_assertJ(iro->o == IR_KINT || iro->o == IR_KINT64,
+                     "sunk store with bad const offset op %d", iro->o);
           if (irt_is64(irs->t)) szs = 8;
           else if (irt_isi8(irs->t) || irt_isu8(irs->t)) szs = 1;
           else if (irt_isi16(irs->t) || irt_isu16(irs->t)) szs = 2;
@@ -780,14 +796,16 @@ static void snap_unsink(jit_State *J, GCtrace *T, ExitState *ex,
             p += (int64_t)ir_k64(iro)->u64;
           else
             p += iro->i;
-          lua_assert(p >= (uint8_t *)cdataptr(cd) &&
-                     p + szs <= (uint8_t *)cdataptr(cd) + sz);
+          lj_assertJ(p >= (uint8_t *)cdataptr(cd) &&
+                     p + szs <= (uint8_t *)cdataptr(cd) + sz,
+                     "sunk store with offset out of range");
           if (LJ_32 && irs+1 < T->ir + T->nins && (irs+1)->o == IR_HIOP) {
-            lua_assert(szs == 4);
-            snap_restoredata(T, ex, snapno, rfilt, (irs+1)->op2, LJ_LE?p+4:p,4);
+            lj_assertJ(szs == 4, "sunk store with bad size %d", szs);
+            snap_restoredata(J, T, ex, snapno, rfilt, (irs+1)->op2,
+                             LJ_LE ? p+4 : p, 4);
             if (LJ_BE) p += 4;
           }
-          snap_restoredata(T, ex, snapno, rfilt, irs->op2, p, szs);
+          snap_restoredata(J, T, ex, snapno, rfilt, irs->op2, p, szs);
         }
     }
   } else
@@ -802,10 +820,12 @@ static void snap_unsink(jit_State *J, GCtrace *T, ExitState *ex,
       if (irs->r == RID_SINK && snap_sunk_store(T, ir, irs)) {
         IRIns *irk = &T->ir[irs->op1];
         TValue tmp, *val;
-        lua_assert(irs->o == IR_ASTORE || irs->o == IR_HSTORE ||
-                   irs->o == IR_FSTORE);
+        lj_assertJ(irs->o == IR_ASTORE || irs->o == IR_HSTORE ||
+                   irs->o == IR_FSTORE,
+                   "sunk store with bad op %d", irs->o);
         if (irk->o == IR_FREF) {
-          lua_assert(irk->op2 == IRFL_TAB_META);
+          lj_assertJ(irk->op2 == IRFL_TAB_META,
+                     "sunk store with bad field %d", irk->op2);
           snap_restoreval(J, T, ex, snapno, rfilt, irs->op2, &tmp);
           /* NOBARRIER: The table is new (marked white). */
           setgcref(t->metatable, obj2gco(tabV(&tmp)));
@@ -893,7 +913,7 @@ const BCIns *lj_snap_restore(jit_State *J, void *exptr)
 #if LJ_FR2
   L->base += (map[nent+LJ_BE] & 0xff);
 #endif
-  lua_assert(map + nent == flinks);
+  lj_assertJ(map + nent == flinks, "inconsistent frames in snapshot");
 
   /* Compute current stack top. */
   switch (bc_op(*pc)) {
diff --git a/src/lj_snap.h b/src/lj_snap.h
index 816a9b79..f1760b05 100644
--- a/src/lj_snap.h
+++ b/src/lj_snap.h
@@ -13,7 +13,8 @@
 LJ_FUNC void lj_snap_add(jit_State *J);
 LJ_FUNC void lj_snap_purge(jit_State *J);
 LJ_FUNC void lj_snap_shrink(jit_State *J);
-LJ_FUNC IRIns *lj_snap_regspmap(GCtrace *T, SnapNo snapno, IRIns *ir);
+LJ_FUNC IRIns *lj_snap_regspmap(jit_State *J, GCtrace *T, SnapNo snapno,
+                                IRIns *ir);
 LJ_FUNC void lj_snap_replay(jit_State *J, GCtrace *T);
 LJ_FUNC const BCIns *lj_snap_restore(jit_State *J, void *exptr);
 LJ_FUNC void lj_snap_grow_buf_(jit_State *J, MSize need);
diff --git a/src/lj_state.c b/src/lj_state.c
index dc82e260..7081a474 100644
--- a/src/lj_state.c
+++ b/src/lj_state.c
@@ -60,7 +60,8 @@ static void resizestack(lua_State *L, MSize n)
   MSize oldsize = L->stacksize;
   MSize realsize = n + 1 + LJ_STACK_EXTRA;
   GCobj *up;
-  lua_assert((MSize)(tvref(L->maxstack)-oldst)==L->stacksize-LJ_STACK_EXTRA-1);
+  lj_assertL((MSize)(tvref(L->maxstack)-oldst) == L->stacksize-LJ_STACK_EXTRA-1,
+             "inconsistent stack size");
   st = (TValue *)lj_mem_realloc(L, tvref(L->stack),
                                 (MSize)(oldsize*sizeof(TValue)),
                                 (MSize)(realsize*sizeof(TValue)));
@@ -162,8 +163,9 @@ static void close_state(lua_State *L)
   global_State *g = G(L);
   lj_func_closeuv(L, tvref(L->stack));
   lj_gc_freeall(g);
-  lua_assert(gcref(g->gc.root) == obj2gco(L));
-  lua_assert(g->strnum == 0);
+  lj_assertG(gcref(g->gc.root) == obj2gco(L),
+             "main thread is not first GC object");
+  lj_assertG(g->strnum == 0, "leaked %d strings", g->strnum);
   lj_trace_freestate(g);
 #if LJ_HASFFI
   lj_ctype_freestate(g);
@@ -171,7 +173,9 @@ static void close_state(lua_State *L)
   lj_mem_freevec(g, g->strhash, g->strmask+1, GCRef);
   lj_buf_free(g, &g->tmpbuf);
   lj_mem_freevec(g, tvref(L->stack), L->stacksize, TValue);
-  lua_assert(g->gc.total == sizeof(GG_State));
+  lj_assertG(g->gc.total == sizeof(GG_State),
+             "memory leak of %lld bytes",
+             (long long)(g->gc.total - sizeof(GG_State)));
 #ifndef LUAJIT_USE_SYSMALLOC
   if (g->allocf == lj_alloc_f)
     lj_alloc_destroy(g->allocd);
@@ -283,17 +287,17 @@ lua_State *lj_state_new(lua_State *L)
   setmrefr(L1->glref, L->glref);
   setgcrefr(L1->env, L->env);
   stack_init(L1, L);  /* init stack */
-  lua_assert(iswhite(obj2gco(L1)));
+  lj_assertL(iswhite(obj2gco(L1)), "new thread object is not white");
   return L1;
 }
 
 void LJ_FASTCALL lj_state_free(global_State *g, lua_State *L)
 {
-  lua_assert(L != mainthread(g));
+  lj_assertG(L != mainthread(g), "free of main thread");
   if (obj2gco(L) == gcref(g->cur_L))
     setgcrefnull(g->cur_L);
   lj_func_closeuv(L, tvref(L->stack));
-  lua_assert(gcref(L->openupval) == NULL);
+  lj_assertG(gcref(L->openupval) == NULL, "stale open upvalues");
   lj_mem_freevec(g, tvref(L->stack), L->stacksize, TValue);
   lj_mem_freet(g, L);
 }
diff --git a/src/lj_str.c b/src/lj_str.c
index ec74afa5..0253c15e 100644
--- a/src/lj_str.c
+++ b/src/lj_str.c
@@ -41,8 +41,9 @@ int32_t LJ_FASTCALL lj_str_cmp(GCstr *a, GCstr *b)
 static LJ_AINLINE int str_fastcmp(const char *a, const char *b, MSize len)
 {
   MSize i = 0;
-  lua_assert(len > 0);
-  lua_assert((((uintptr_t)a+len-1) & (LJ_PAGESIZE-1)) <= LJ_PAGESIZE-4);
+  lj_assertX(len > 0, "fast string compare with zero length");
+  lj_assertX((((uintptr_t)a+len-1) & (LJ_PAGESIZE-1)) <= LJ_PAGESIZE-4,
+             "fast string compare crossing page boundary");
   do {  /* Note: innocuous access up to end of string + 3. */
     uint32_t v = lj_getu32(a+i) ^ *(const uint32_t *)(b+i);
     if (v) {
diff --git a/src/lj_strfmt.c b/src/lj_strfmt.c
index 8f968d32..331d9474 100644
--- a/src/lj_strfmt.c
+++ b/src/lj_strfmt.c
@@ -320,7 +320,7 @@ SBuf *lj_strfmt_putfxint(SBuf *sb, SFormat sf, uint64_t k)
   if ((sf & STRFMT_F_LEFT))
     while (width-- > pprec) *p++ = ' ';
 
-  lua_assert(need == (MSize)(p - ps));
+  lj_assertX(need == (MSize)(p - ps), "miscalculated format size");
   setsbufP(sb, p);
   return sb;
 }
@@ -449,7 +449,7 @@ const char *lj_strfmt_pushvf(lua_State *L, const char *fmt, va_list argp)
     case STRFMT_ERR:
     default:
       lj_buf_putb(sb, '?');
-      lua_assert(0);
+      lj_assertL(0, "bad string format near offset %d", fs.len);
       break;
     }
   }
diff --git a/src/lj_strfmt.h b/src/lj_strfmt.h
index 339f8e15..b4fbbb94 100644
--- a/src/lj_strfmt.h
+++ b/src/lj_strfmt.h
@@ -79,7 +79,8 @@ static LJ_AINLINE void lj_strfmt_init(FormatState *fs, const char *p, MSize len)
 {
   fs->p = (const uint8_t *)p;
   fs->e = (const uint8_t *)p + len;
-  lua_assert(*fs->e == 0);  /* Must be NUL-terminated (may have NULs inside). */
+  /* Must be NUL-terminated. May have NULs inside, too. */
+  lj_assertX(*fs->e == 0, "format not NUL-terminated");
 }
 
 /* Raw conversions. */
diff --git a/src/lj_strfmt_num.c b/src/lj_strfmt_num.c
index 36b11dc0..8cb5d47f 100644
--- a/src/lj_strfmt_num.c
+++ b/src/lj_strfmt_num.c
@@ -257,7 +257,7 @@ static int nd_similar(uint32_t* nd, uint32_t ndhi, uint32_t* ref, MSize hilen,
   } else {
     prec -= hilen - 9;
   }
-  lua_assert(prec < 9);
+  lj_assertX(prec < 9, "bad precision %d", prec);
   lj_strfmt_wuint9(nd9, nd[ndhi]);
   lj_strfmt_wuint9(ref9, *ref);
   return !memcmp(nd9, ref9, prec) && (nd9[prec] < '5') == (ref9[prec] < '5');
@@ -414,14 +414,14 @@ static char *lj_strfmt_wfnum(SBuf *sb, SFormat sf, lua_Number n, char *p)
         ** Rescaling was performed, but this introduced some error, and might
         ** have pushed us across a rounding boundary. We check whether this
         ** error affected the result by introducing even more error (2ulp in
-        ** either direction), and seeing whether a roundary boundary was
+        ** either direction), and seeing whether a rounding boundary was
         ** crossed. Having already converted the -2ulp case, we save off its
         ** most significant digits, convert the +2ulp case, and compare them.
         */
         int32_t eidx = e + 70 + (ND_MUL2K_MAX_SHIFT < 29)
                          + (t.u32.lo >= 0xfffffffe && !(~t.u32.hi << 12));
         const int8_t *m_e = four_ulp_m_e + eidx * 2;
-        lua_assert(0 <= eidx && eidx < 128);
+        lj_assertG_(G(sbufL(sb)), 0 <= eidx && eidx < 128, "bad eidx %d", eidx);
         nd[33] = nd[ndhi];
         nd[32] = nd[(ndhi - 1) & 0x3f];
         nd[31] = nd[(ndhi - 2) & 0x3f];
diff --git a/src/lj_strscan.c b/src/lj_strscan.c
index 433b33a3..0e37a4f6 100644
--- a/src/lj_strscan.c
+++ b/src/lj_strscan.c
@@ -93,7 +93,7 @@ static void strscan_double(uint64_t x, TValue *o, int32_t ex2, int32_t neg)
   }
 
   /* Convert to double using a signed int64_t conversion, then rescale. */
-  lua_assert((int64_t)x >= 0);
+  lj_assertX((int64_t)x >= 0, "bad double conversion");
   n = (double)(int64_t)x;
   if (neg) n = -n;
   if (ex2) n = ldexp(n, ex2);
@@ -262,7 +262,7 @@ static StrScanFmt strscan_dec(const uint8_t *p, TValue *o,
     uint32_t hi = 0, lo = (uint32_t)(xip-xi);
     int32_t ex2 = 0, idig = (int32_t)lo + (ex10 >> 1);
 
-    lua_assert(lo > 0 && (ex10 & 1) == 0);
+    lj_assertX(lo > 0 && (ex10 & 1) == 0, "bad lo %d ex10 %d", lo, ex10);
 
     /* Handle simple overflow/underflow. */
     if (idig > 310/2) { if (neg) setminfV(o); else setpinfV(o); return fmt; }
@@ -528,7 +528,7 @@ int LJ_FASTCALL lj_strscan_num(GCstr *str, TValue *o)
 {
   StrScanFmt fmt = lj_strscan_scan((const uint8_t *)strdata(str), str->len, o,
                                    STRSCAN_OPT_TONUM);
-  lua_assert(fmt == STRSCAN_ERROR || fmt == STRSCAN_NUM);
+  lj_assertX(fmt == STRSCAN_ERROR || fmt == STRSCAN_NUM, "bad scan format");
   return (fmt != STRSCAN_ERROR);
 }
 
@@ -537,7 +537,8 @@ int LJ_FASTCALL lj_strscan_number(GCstr *str, TValue *o)
 {
   StrScanFmt fmt = lj_strscan_scan((const uint8_t *)strdata(str), str->len, o,
                                    STRSCAN_OPT_TOINT);
-  lua_assert(fmt == STRSCAN_ERROR || fmt == STRSCAN_NUM || fmt == STRSCAN_INT);
+  lj_assertX(fmt == STRSCAN_ERROR || fmt == STRSCAN_NUM || fmt == STRSCAN_INT,
+             "bad scan format");
   if (fmt == STRSCAN_INT) setitype(o, LJ_TISNUM);
   return (fmt != STRSCAN_ERROR);
 }
diff --git a/src/lj_tab.c b/src/lj_tab.c
index eb9ef4af..efc423cb 100644
--- a/src/lj_tab.c
+++ b/src/lj_tab.c
@@ -38,7 +38,7 @@ static LJ_AINLINE Node *hashmask(const GCtab *t, uint32_t hash)
 /* Hash an arbitrary key and return its anchor position in the hash table. */
 static Node *hashkey(const GCtab *t, cTValue *key)
 {
-  lua_assert(!tvisint(key));
+  lj_assertX(!tvisint(key), "attempt to hash integer");
   if (tvisstr(key))
     return hashstr(t, strV(key));
   else if (tvisnum(key))
@@ -57,7 +57,7 @@ static LJ_AINLINE void newhpart(lua_State *L, GCtab *t, uint32_t hbits)
 {
   uint32_t hsize;
   Node *node;
-  lua_assert(hbits != 0);
+  lj_assertL(hbits != 0, "zero hash size");
   if (hbits > LJ_MAX_HBITS)
     lj_err_msg(L, LJ_ERR_TABOV);
   hsize = 1u << hbits;
@@ -78,7 +78,7 @@ static LJ_AINLINE void clearhpart(GCtab *t)
 {
   uint32_t i, hmask = t->hmask;
   Node *node = noderef(t->node);
-  lua_assert(t->hmask != 0);
+  lj_assertX(t->hmask != 0, "empty hash part");
   for (i = 0; i <= hmask; i++) {
     Node *n = &node[i];
     setmref(n->next, NULL);
@@ -103,7 +103,7 @@ static GCtab *newtab(lua_State *L, uint32_t asize, uint32_t hbits)
   /* First try to colocate the array part. */
   if (LJ_MAX_COLOSIZE != 0 && asize > 0 && asize <= LJ_MAX_COLOSIZE) {
     Node *nilnode;
-    lua_assert((sizeof(GCtab) & 7) == 0);
+    lj_assertL((sizeof(GCtab) & 7) == 0, "bad GCtab size");
     t = (GCtab *)lj_mem_newgco(L, sizetabcolo(asize));
     t->gct = ~LJ_TTAB;
     t->nomm = (uint8_t)~0;
@@ -185,7 +185,8 @@ GCtab * LJ_FASTCALL lj_tab_dup(lua_State *L, const GCtab *kt)
   GCtab *t;
   uint32_t asize, hmask;
   t = newtab(L, kt->asize, kt->hmask > 0 ? lj_fls(kt->hmask)+1 : 0);
-  lua_assert(kt->asize == t->asize && kt->hmask == t->hmask);
+  lj_assertL(kt->asize == t->asize && kt->hmask == t->hmask,
+             "mismatched size of table and template");
   t->nomm = 0;  /* Keys with metamethod names may be present. */
   asize = kt->asize;
   if (asize > 0) {
@@ -310,7 +311,7 @@ void lj_tab_resize(lua_State *L, GCtab *t, uint32_t asize, uint32_t hbits)
 
 static uint32_t countint(cTValue *key, uint32_t *bins)
 {
-  lua_assert(!tvisint(key));
+  lj_assertX(!tvisint(key), "bad integer key");
   if (tvisnum(key)) {
     lua_Number nk = numV(key);
     int32_t k = lj_num2int(nk);
@@ -463,7 +464,8 @@ TValue *lj_tab_newkey(lua_State *L, GCtab *t, cTValue *key)
   if (!tvisnil(&n->val) || t->hmask == 0) {
     Node *nodebase = noderef(t->node);
     Node *collide, *freenode = getfreetop(t, nodebase);
-    lua_assert(freenode >= nodebase && freenode <= nodebase+t->hmask+1);
+    lj_assertL(freenode >= nodebase && freenode <= nodebase+t->hmask+1,
+               "bad freenode");
     do {
       if (freenode == nodebase) {  /* No free node found? */
         rehashtab(L, t, key);  /* Rehash table. */
@@ -471,7 +473,7 @@ TValue *lj_tab_newkey(lua_State *L, GCtab *t, cTValue *key)
       }
     } while (!tvisnil(&(--freenode)->key));
     setfreetop(t, nodebase, freenode);
-    lua_assert(freenode != &G(L)->nilnode);
+    lj_assertL(freenode != &G(L)->nilnode, "store to fallback hash");
     collide = hashkey(t, &n->key);
     if (collide != n) {  /* Colliding node not the main node? */
       while (noderef(collide->next) != n)  /* Find predecessor. */
@@ -527,7 +529,7 @@ TValue *lj_tab_newkey(lua_State *L, GCtab *t, cTValue *key)
   if (LJ_UNLIKELY(tvismzero(&n->key)))
     n->key.u64 = 0;
   lj_gc_anybarriert(L, t);
-  lua_assert(tvisnil(&n->val));
+  lj_assertL(tvisnil(&n->val), "new hash slot is not empty");
   return &n->val;
 }
 
diff --git a/src/lj_target.h b/src/lj_target.h
index 47c960bc..ce67d000 100644
--- a/src/lj_target.h
+++ b/src/lj_target.h
@@ -152,7 +152,8 @@ typedef uint32_t RegCost;
 /* Return the address of an exit stub. */
 static LJ_AINLINE char *exitstub_addr_(char **group, uint32_t exitno)
 {
-  lua_assert(group[exitno / EXITSTUBS_PER_GROUP] != NULL);
+  lj_assertX(group[exitno / EXITSTUBS_PER_GROUP] != NULL,
+             "exit stub group for exit %d uninitialized", exitno);
   return (char *)group[exitno / EXITSTUBS_PER_GROUP] +
          EXITSTUB_SPACING*(exitno % EXITSTUBS_PER_GROUP);
 }
diff --git a/src/lj_trace.c b/src/lj_trace.c
index a43c8c4e..c4e728c6 100644
--- a/src/lj_trace.c
+++ b/src/lj_trace.c
@@ -104,7 +104,8 @@ static void perftools_addtrace(GCtrace *T)
     name++;
   else
     name = "(string)";
-  lua_assert(startpc >= proto_bc(pt) && startpc < proto_bc(pt) + pt->sizebc);
+  lj_assertX(startpc >= proto_bc(pt) && startpc < proto_bc(pt) + pt->sizebc,
+             "trace PC out of range");
   lineno = lj_debug_line(pt, proto_bcpos(pt, startpc));
   if (!fp) {
     char fname[40];
@@ -183,7 +184,7 @@ void lj_trace_reenableproto(GCproto *pt)
 {
   if ((pt->flags & PROTO_ILOOP)) {
     BCIns *bc = proto_bc(pt);
-    BCPos i, sizebc = pt->sizebc;;
+    BCPos i, sizebc = pt->sizebc;
     pt->flags &= ~PROTO_ILOOP;
     if (bc_op(bc[0]) == BC_IFUNCF)
       setbc_op(&bc[0], BC_FUNCF);
@@ -205,27 +206,28 @@ static void trace_unpatch(jit_State *J, GCtrace *T)
     return;  /* No need to unpatch branches in parent traces (yet). */
   switch (bc_op(*pc)) {
   case BC_JFORL:
-    lua_assert(traceref(J, bc_d(*pc)) == T);
+    lj_assertJ(traceref(J, bc_d(*pc)) == T, "JFORL references other trace");
     *pc = T->startins;
     pc += bc_j(T->startins);
-    lua_assert(bc_op(*pc) == BC_JFORI);
+    lj_assertJ(bc_op(*pc) == BC_JFORI, "FORL does not point to JFORI");
     setbc_op(pc, BC_FORI);
     break;
   case BC_JITERL:
   case BC_JLOOP:
-    lua_assert(op == BC_ITERL || op == BC_LOOP || bc_isret(op));
+    lj_assertJ(op == BC_ITERL || op == BC_LOOP || bc_isret(op),
+               "bad original bytecode %d", op);
     *pc = T->startins;
     break;
   case BC_JMP:
-    lua_assert(op == BC_ITERL);
+    lj_assertJ(op == BC_ITERL, "bad original bytecode %d", op);
     pc += bc_j(*pc)+2;
     if (bc_op(*pc) == BC_JITERL) {
-      lua_assert(traceref(J, bc_d(*pc)) == T);
+      lj_assertJ(traceref(J, bc_d(*pc)) == T, "JITERL references other trace");
       *pc = T->startins;
     }
     break;
   case BC_JFUNCF:
-    lua_assert(op == BC_FUNCF);
+    lj_assertJ(op == BC_FUNCF, "bad original bytecode %d", op);
     *pc = T->startins;
     break;
   default:  /* Already unpatched. */
@@ -237,7 +239,8 @@ static void trace_unpatch(jit_State *J, GCtrace *T)
 static void trace_flushroot(jit_State *J, GCtrace *T)
 {
   GCproto *pt = &gcref(T->startpt)->pt;
-  lua_assert(T->root == 0 && pt != NULL);
+  lj_assertJ(T->root == 0, "not a root trace");
+  lj_assertJ(pt != NULL, "trace has no prototype");
   /* First unpatch any modified bytecode. */
   trace_unpatch(J, T);
   /* Unlink root trace from chain anchored in prototype. */
@@ -353,7 +356,8 @@ void lj_trace_freestate(global_State *g)
   {  /* This assumes all traces have already been freed. */
     ptrdiff_t i;
     for (i = 1; i < (ptrdiff_t)J->sizetrace; i++)
-      lua_assert(i == (ptrdiff_t)J->cur.traceno || traceref(J, i) == NULL);
+      lj_assertG(i == (ptrdiff_t)J->cur.traceno || traceref(J, i) == NULL,
+                 "trace still allocated");
   }
 #endif
   lj_mcode_free(J);
@@ -408,8 +412,9 @@ static void trace_start(jit_State *J)
   if ((J->pt->flags & PROTO_NOJIT)) {  /* JIT disabled for this proto? */
     if (J->parent == 0 && J->exitno == 0) {
       /* Lazy bytecode patching to disable hotcount events. */
-      lua_assert(bc_op(*J->pc) == BC_FORL || bc_op(*J->pc) == BC_ITERL ||
-                 bc_op(*J->pc) == BC_LOOP || bc_op(*J->pc) == BC_FUNCF);
+      lj_assertJ(bc_op(*J->pc) == BC_FORL || bc_op(*J->pc) == BC_ITERL ||
+                 bc_op(*J->pc) == BC_LOOP || bc_op(*J->pc) == BC_FUNCF,
+                 "bad hot bytecode %d", bc_op(*J->pc));
       setbc_op(J->pc, (int)bc_op(*J->pc)+(int)BC_ILOOP-(int)BC_LOOP);
       J->pt->flags |= PROTO_ILOOP;
     }
@@ -420,7 +425,8 @@ static void trace_start(jit_State *J)
   /* Get a new trace number. */
   traceno = trace_findfree(J);
   if (LJ_UNLIKELY(traceno == 0)) {  /* No free trace? */
-    lua_assert((J2G(J)->hookmask & HOOK_GC) == 0);
+    lj_assertJ((J2G(J)->hookmask & HOOK_GC) == 0,
+               "recorder called from GC hook");
     lj_trace_flushall(J->L);
     J->state = LJ_TRACE_IDLE;  /* Silently ignored. */
     return;
@@ -496,7 +502,7 @@ static void trace_stop(jit_State *J)
     goto addroot;
   case BC_JMP:
     /* Patch exit branch in parent to side trace entry. */
-    lua_assert(J->parent != 0 && J->cur.root != 0);
+    lj_assertJ(J->parent != 0 && J->cur.root != 0, "not a side trace");
     lj_asm_patchexit(J, traceref(J, J->parent), J->exitno, J->cur.mcode);
     /* Avoid compiling a side trace twice (stack resizing uses parent exit). */
     traceref(J, J->parent)->snap[J->exitno].count = SNAPCOUNT_DONE;
@@ -515,7 +521,7 @@ static void trace_stop(jit_State *J)
     traceref(J, J->exitno)->link = traceno;
     break;
   default:
-    lua_assert(0);
+    lj_assertJ(0, "bad stop bytecode %d", op);
     break;
   }
 
@@ -536,8 +542,8 @@ static void trace_stop(jit_State *J)
 static int trace_downrec(jit_State *J)
 {
   /* Restart recording at the return instruction. */
-  lua_assert(J->pt != NULL);
-  lua_assert(bc_isret(bc_op(*J->pc)));
+  lj_assertJ(J->pt != NULL, "no active prototype");
+  lj_assertJ(bc_isret(bc_op(*J->pc)), "not at a return bytecode");
   if (bc_op(*J->pc) == BC_RETM)
     return 0;  /* NYI: down-recursion with RETM. */
   J->parent = 0;
@@ -750,7 +756,7 @@ static void trace_hotside(jit_State *J, const BCIns *pc)
       isluafunc(curr_func(J->L)) &&
       snap->count != SNAPCOUNT_DONE &&
       ++snap->count >= J->param[JIT_P_hotexit]) {
-    lua_assert(J->state == LJ_TRACE_IDLE);
+    lj_assertJ(J->state == LJ_TRACE_IDLE, "hot side exit while recording");
     /* J->parent is non-zero for a side trace. */
     J->state = LJ_TRACE_START;
     lj_trace_ins(J, pc);
@@ -822,7 +828,7 @@ static TraceNo trace_exit_find(jit_State *J, MCode *pc)
     if (T && pc >= T->mcode && pc < (MCode *)((char *)T->mcode + T->szmcode))
       return traceno;
   }
-  lua_assert(0);
+  lj_assertJ(0, "bad exit pc");
   return 0;
 }
 #endif
@@ -844,13 +850,13 @@ int LJ_FASTCALL lj_trace_exit(jit_State *J, void *exptr)
   T = traceref(J, J->parent); UNUSED(T);
 #ifdef EXITSTATE_CHECKEXIT
   if (J->exitno == T->nsnap) {  /* Treat stack check like a parent exit. */
-    lua_assert(T->root != 0);
+    lj_assertJ(T->root != 0, "stack check in root trace");
     J->exitno = T->ir[REF_BASE].op2;
     J->parent = T->ir[REF_BASE].op1;
     T = traceref(J, J->parent);
   }
 #endif
-  lua_assert(T != NULL && J->exitno < T->nsnap);
+  lj_assertJ(T != NULL && J->exitno < T->nsnap, "bad trace or exit number");
   exd.J = J;
   exd.exptr = exptr;
   errcode = lj_vm_cpcall(L, NULL, &exd, trace_exit_cp);
diff --git a/src/lj_vmmath.c b/src/lj_vmmath.c
index 623a686d..9ed37bf2 100644
--- a/src/lj_vmmath.c
+++ b/src/lj_vmmath.c
@@ -60,7 +60,8 @@ double lj_vm_foldarith(double x, double y, int op)
 int32_t LJ_FASTCALL lj_vm_modi(int32_t a, int32_t b)
 {
   uint32_t y, ua, ub;
-  lua_assert(b != 0);  /* This must be checked before using this function. */
+  /* This must be checked before using this function. */
+  lj_assertX(b != 0, "modulo with zero divisor");
   ua = a < 0 ? (uint32_t)-a : (uint32_t)a;
   ub = b < 0 ? (uint32_t)-b : (uint32_t)b;
   y = ua % ub;
@@ -84,7 +85,7 @@ double lj_vm_log2(double a)
 static double lj_vm_powui(double x, uint32_t k)
 {
   double y;
-  lua_assert(k != 0);
+  lj_assertX(k != 0, "pow with zero exponent");
   for (; (k & 1) == 0; k >>= 1) x *= x;
   y = x;
   if ((k >>= 1) != 0) {
@@ -123,7 +124,7 @@ double lj_vm_foldfpm(double x, int fpm)
   case IRFPM_SQRT: return sqrt(x);
   case IRFPM_LOG: return log(x);
   case IRFPM_LOG2: return lj_vm_log2(x);
-  default: lua_assert(0);
+  default: lj_assertX(0, "bad fpm %d", fpm);
   }
   return 0;
 }
diff --git a/src/ljamalg.c b/src/ljamalg.c
index 6712d435..19980241 100644
--- a/src/ljamalg.c
+++ b/src/ljamalg.c
@@ -18,6 +18,7 @@
 #include "lua.h"
 #include "lauxlib.h"
 
+#include "lj_assert.c"
 #include "lj_gc.c"
 #include "lj_err.c"
 #include "lj_char.c"
diff --git a/src/luaconf.h b/src/luaconf.h
index d422827a..18fb961d 100644
--- a/src/luaconf.h
+++ b/src/luaconf.h
@@ -136,7 +136,7 @@
 
 #define LUALIB_API      LUA_API
 
-/* Support for internal assertions. */
+/* Compatibility support for assertions. */
 #if defined(LUA_USE_ASSERT) || defined(LUA_USE_APICHECK)
 #include <assert.h>
 #endif