x64/LJ_GC64: Add missing backend support and enable JIT compilation.

Contributed by Peter Cawley.

10 files changed, 517 insertions, 90 deletions

diff --git a/src/lj_arch.h b/src/lj_arch.h
index 72622a21..3c3c98b1 100644
--- a/src/lj_arch.h
+++ b/src/lj_arch.h
@@ -453,7 +453,7 @@
 #endif
 
 /* Disable or enable the JIT compiler. */
-#if defined(LUAJIT_DISABLE_JIT) || defined(LJ_ARCH_NOJIT) || defined(LJ_OS_NOJIT) || LJ_GC64
+#if defined(LUAJIT_DISABLE_JIT) || defined(LJ_ARCH_NOJIT) || defined(LJ_OS_NOJIT)
 #define LJ_HASJIT               0
 #else
 #define LJ_HASJIT               1
diff --git a/src/lj_asm.c b/src/lj_asm.c
index 5dd7ca3a..dba5c178 100644
--- a/src/lj_asm.c
+++ b/src/lj_asm.c
@@ -346,6 +346,12 @@ static Reg ra_rematk(ASMState *as, IRRef ref)
 #if LJ_64
   } else if (ir->o == IR_KINT64) {
     emit_loadu64(as, r, ir_kint64(ir)->u64);
+#if LJ_GC64
+  } else if (ir->o == IR_KGC) {
+    emit_loadu64(as, r, (uintptr_t)ir_kgc(ir));
+  } else if (ir->o == IR_KPTR || ir->o == IR_KKPTR) {
+    emit_loadu64(as, r, (uintptr_t)ir_kptr(ir));
+#endif
 #endif
   } else {
     lua_assert(ir->o == IR_KINT || ir->o == IR_KGC ||
@@ -1920,8 +1926,12 @@ static void asm_tail_link(ASMState *as)
       if (bc_isret(bc_op(*retpc)))
         pc = retpc;
     }
+#if LJ_GC64
+    emit_loadu64(as, RID_LPC, u64ptr(pc));
+#else
     ra_allockreg(as, i32ptr(J2GG(as->J)->dispatch), RID_DISPATCH);
     ra_allockreg(as, i32ptr(pc), RID_LPC);
+#endif
     mres = (int32_t)(snap->nslots - baseslot - LJ_FR2);
     switch (bc_op(*pc)) {
     case BC_CALLM: case BC_CALLMT:
@@ -2314,6 +2324,7 @@ void lj_asm_trace(jit_State *J, GCtrace *T)
       as->curins = as->T->snap[0].ref;
       asm_snap_prep(as);  /* The GC check is a guard. */
       asm_gc_check(as);
+      as->curins = as->stopins;
     }
     ra_evictk(as);
     if (as->parent)
diff --git a/src/lj_asm_x86.h b/src/lj_asm_x86.h
index 83fe22b2..7d07336a 100644
--- a/src/lj_asm_x86.h
+++ b/src/lj_asm_x86.h
@@ -21,12 +21,14 @@ static MCode *asm_exitstub_gen(ASMState *as, ExitNo group)
   }
   /* Push the high byte of the exitno for each exit stub group. */
   *mxp++ = XI_PUSHi8; *mxp++ = (MCode)((group*EXITSTUBS_PER_GROUP)>>8);
+#if !LJ_GC64
   /* Store DISPATCH at original stack slot 0. Account for the two push ops. */
   *mxp++ = XI_MOVmi;
   *mxp++ = MODRM(XM_OFS8, 0, RID_ESP);
   *mxp++ = MODRM(XM_SCALE1, RID_ESP, RID_ESP);
   *mxp++ = 2*sizeof(void *);
   *(int32_t *)mxp = ptr2addr(J2GG(as->J)->dispatch); mxp += 4;
+#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);
@@ -62,10 +64,14 @@ static void asm_guardcc(ASMState *as, int cc)
     target = p;
     cc ^= 1;
     if (as->realign) {
+      if (LJ_GC64 && LJ_UNLIKELY(as->mrm.base == RID_RIP))
+        as->mrm.ofs += 2;  /* Fixup RIP offset for pending fused load. */
       emit_sjcc(as, cc, target);
       return;
     }
   }
+  if (LJ_GC64 && LJ_UNLIKELY(as->mrm.base == RID_RIP))
+    as->mrm.ofs += 6;  /* Fixup RIP offset for pending fused load. */
   emit_jcc(as, cc, target);
 }
 
@@ -79,6 +85,15 @@ static int asm_isk32(ASMState *as, IRRef ref, int32_t *k)
 {
   if (irref_isk(ref)) {
     IRIns *ir = IR(ref);
+#if LJ_GC64
+    if (ir->o == IR_KNULL || !irt_is64(ir->t)) {
+      *k = ir->i;
+      return 1;
+    } else if (checki32((int64_t)ir_k64(ir)->u64)) {
+      *k = (int32_t)ir_k64(ir)->u64;
+      return 1;
+    }
+#else
     if (ir->o != IR_KINT64) {
       *k = ir->i;
       return 1;
@@ -86,6 +101,7 @@ static int asm_isk32(ASMState *as, IRRef ref, int32_t *k)
       *k = (int32_t)ir_kint64(ir)->u64;
       return 1;
     }
+#endif
   }
   return 0;
 }
@@ -185,9 +201,19 @@ static void asm_fuseahuref(ASMState *as, IRRef ref, RegSet allow)
       if (irref_isk(ir->op1)) {
         GCfunc *fn = ir_kfunc(IR(ir->op1));
         GCupval *uv = &gcref(fn->l.uvptr[(ir->op2 >> 8)])->uv;
+#if LJ_GC64
+        int64_t ofs = dispofs(as, &uv->tv);
+        if (checki32(ofs) && checki32(ofs+4)) {
+          as->mrm.ofs = (int32_t)ofs;
+          as->mrm.base = RID_DISPATCH;
+          as->mrm.idx = RID_NONE;
+          return;
+        }
+#else
         as->mrm.ofs = ptr2addr(&uv->tv);
         as->mrm.base = as->mrm.idx = RID_NONE;
         return;
+#endif
       }
       break;
     default:
@@ -207,17 +233,38 @@ static void asm_fusefref(ASMState *as, IRIns *ir, RegSet allow)
   lua_assert(ir->o == IR_FLOAD || ir->o == IR_FREF);
   as->mrm.idx = RID_NONE;
   if (ir->op1 == REF_NIL) {
+#if LJ_GC64
+    as->mrm.ofs = (int32_t)ir->op2 - GG_OFS(dispatch);
+    as->mrm.base = RID_DISPATCH;
+#else
     as->mrm.ofs = (int32_t)ir->op2 + ptr2addr(J2GG(as->J));
     as->mrm.base = RID_NONE;
+#endif
     return;
   }
   as->mrm.ofs = field_ofs[ir->op2];
   if (irref_isk(ir->op1)) {
-    as->mrm.ofs += IR(ir->op1)->i;
+    IRIns *op1 = IR(ir->op1);
+#if LJ_GC64
+    if (ir->op1 == REF_NIL) {
+      as->mrm.ofs -= GG_OFS(dispatch);
+      as->mrm.base = RID_DISPATCH;
+      return;
+    } else if (op1->o == IR_KPTR || op1->o == IR_KKPTR) {
+      intptr_t ofs = dispofs(as, ir_kptr(op1));
+      if (checki32(as->mrm.ofs + ofs)) {
+        as->mrm.ofs += (int32_t)ofs;
+        as->mrm.base = RID_DISPATCH;
+        return;
+      }
+    }
+#else
+    as->mrm.ofs += op1->i;
     as->mrm.base = RID_NONE;
-  } else {
-    as->mrm.base = (uint8_t)ra_alloc1(as, ir->op1, allow);
+    return;
+#endif
   }
+  as->mrm.base = (uint8_t)ra_alloc1(as, ir->op1, allow);
 }
 
 /* Fuse string reference into memory operand. */
@@ -228,7 +275,7 @@ static void asm_fusestrref(ASMState *as, IRIns *ir, RegSet allow)
   as->mrm.base = as->mrm.idx = RID_NONE;
   as->mrm.scale = XM_SCALE1;
   as->mrm.ofs = sizeof(GCstr);
-  if (irref_isk(ir->op1)) {
+  if (!LJ_GC64 && irref_isk(ir->op1)) {
     as->mrm.ofs += IR(ir->op1)->i;
   } else {
     Reg r = ra_alloc1(as, ir->op1, allow);
@@ -260,10 +307,20 @@ static void asm_fusexref(ASMState *as, IRRef ref, RegSet allow)
   IRIns *ir = IR(ref);
   as->mrm.idx = RID_NONE;
   if (ir->o == IR_KPTR || ir->o == IR_KKPTR) {
+#if LJ_GC64
+    intptr_t ofs = dispofs(as, ir_kptr(ir));
+    if (checki32(ofs)) {
+      as->mrm.ofs = (int32_t)ofs;
+      as->mrm.base = RID_DISPATCH;
+      return;
+    }
+  } if (0) {
+#else
     as->mrm.ofs = ir->i;
     as->mrm.base = RID_NONE;
   } else if (ir->o == IR_STRREF) {
     asm_fusestrref(as, ir, allow);
+#endif
   } else {
     as->mrm.ofs = 0;
     if (canfuse(as, ir) && ir->o == IR_ADD && ra_noreg(ir->r)) {
@@ -310,13 +367,41 @@ static void asm_fusexref(ASMState *as, IRRef ref, RegSet allow)
 static Reg asm_fuseloadk64(ASMState *as, IRIns *ir)
 {
   const uint64_t *k = &ir_k64(ir)->u64;
-  as->mrm.ofs = ptr2addr(k);
-  as->mrm.base = RID_NONE;
+  if (!LJ_GC64 || checki32((intptr_t)k)) {
+    as->mrm.ofs = ptr2addr(k);
+    as->mrm.base = RID_NONE;
+#if LJ_GC64
+  } else if (checki32(dispofs(as, k))) {
+    as->mrm.ofs = (int32_t)dispofs(as, k);
+    as->mrm.base = RID_DISPATCH;
+  } else if (checki32(mcpofs(as, k)) && checki32(mcpofs(as, k+1)) &&
+             checki32(mctopofs(as, k)) && checki32(mctopofs(as, k+1))) {
+    as->mrm.ofs = (int32_t)mcpofs(as, k);
+    as->mrm.base = RID_RIP;
+  } else {
+    if (ir->i) {
+      lua_assert(*k == *(uint64_t*)(as->mctop - ir->i));
+    } else {
+      while ((uintptr_t)as->mcbot & 7) *as->mcbot++ = XI_INT3;
+      *(uint64_t*)as->mcbot = *k;
+      ir->i = (int32_t)(as->mctop - as->mcbot);
+      as->mcbot += 8;
+      as->mclim = as->mcbot + MCLIM_REDZONE;
+    }
+    as->mrm.ofs = (int32_t)mcpofs(as, as->mctop - ir->i);
+    as->mrm.base = RID_RIP;
+#endif
+  }
   as->mrm.idx = RID_NONE;
   return RID_MRM;
 }
 
-/* Fuse load into memory operand. */
+/* Fuse load into memory operand.
+**
+** Important caveat: this may emit RIP-relative loads! So don't place any
+** code emitters between this function and the use of its result.
+** The only permitted exception is asm_guardcc().
+*/
 static Reg asm_fuseload(ASMState *as, IRRef ref, RegSet allow)
 {
   IRIns *ir = IR(ref);
@@ -346,7 +431,8 @@ static Reg asm_fuseload(ASMState *as, IRRef ref, RegSet allow)
     RegSet xallow = (allow & RSET_GPR) ? allow : RSET_GPR;
     if (ir->o == IR_SLOAD) {
       if (!(ir->op2 & (IRSLOAD_PARENT|IRSLOAD_CONVERT)) &&
-          noconflict(as, ref, IR_RETF, 0)) {
+          noconflict(as, ref, IR_RETF, 0) &&
+          !(LJ_GC64 && irt_isaddr(ir->t))) {
         as->mrm.base = (uint8_t)ra_alloc1(as, REF_BASE, xallow);
         as->mrm.ofs = 8*((int32_t)ir->op1-1-LJ_FR2) +
                       (!LJ_FR2 && (ir->op2 & IRSLOAD_FRAME) ? 4 : 0);
@@ -361,7 +447,8 @@ static Reg asm_fuseload(ASMState *as, IRRef ref, RegSet allow)
         return RID_MRM;
       }
     } else if (ir->o == IR_ALOAD || ir->o == IR_HLOAD || ir->o == IR_ULOAD) {
-      if (noconflict(as, ref, ir->o + IRDELTA_L2S, 0)) {
+      if (noconflict(as, ref, ir->o + IRDELTA_L2S, 0) &&
+          !(LJ_GC64 && irt_isaddr(ir->t))) {
         asm_fuseahuref(as, ir->op1, xallow);
         return RID_MRM;
       }
@@ -374,7 +461,7 @@ static Reg asm_fuseload(ASMState *as, IRRef ref, RegSet allow)
         asm_fusexref(as, ir->op1, xallow);
         return RID_MRM;
       }
-    } else if (ir->o == IR_VLOAD) {
+    } else if (ir->o == IR_VLOAD && !(LJ_GC64 && irt_isaddr(ir->t))) {
       asm_fuseahuref(as, ir->op1, xallow);
       return RID_MRM;
     }
@@ -499,8 +586,8 @@ static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args)
     if (r) {  /* Argument is in a register. */
       if (r < RID_MAX_GPR && ref < ASMREF_TMP1) {
 #if LJ_64
-        if (ir->o == IR_KINT64)
-          emit_loadu64(as, r, ir_kint64(ir)->u64);
+        if (LJ_GC64 ? ir->o != IR_KINT : ir->o == IR_KINT64)
+          emit_loadu64(as, r, ir_k64(ir)->u64);
         else
 #endif
           emit_loadi(as, r, ir->i);
@@ -668,7 +755,7 @@ static void asm_retf(ASMState *as, IRIns *ir)
   emit_addptr(as, base, -8*delta);
   asm_guardcc(as, CC_NE);
 #if LJ_FR2
-  emit_rmro(as, XO_CMP, rpc, base, -8);
+  emit_rmro(as, XO_CMP, rpc|REX_GC64, base, -8);
   emit_loadu64(as, rpc, u64ptr(pc));
 #else
   emit_gmroi(as, XG_ARITHi(XOg_CMP), base, -4, ptr2addr(pc));
@@ -696,8 +783,9 @@ static void asm_tobit(ASMState *as, IRIns *ir)
   Reg tmp = ra_noreg(IR(ir->op1)->r) ?
               ra_alloc1(as, ir->op1, RSET_FPR) :
               ra_scratch(as, RSET_FPR);
-  Reg right = asm_fuseload(as, ir->op2, rset_exclude(RSET_FPR, tmp));
+  Reg right;
   emit_rr(as, XO_MOVDto, tmp, dest);
+  right = asm_fuseload(as, ir->op2, rset_exclude(RSET_FPR, tmp));
   emit_mrm(as, XO_ADDSD, tmp, right);
   ra_left(as, tmp, ir->op1);
 }
@@ -768,13 +856,12 @@ static void asm_conv(ASMState *as, IRIns *ir)
         emit_rr(as, op, dest|REX_64, tmp);
         ra_left(as, tmp, lref);
       } else {
-        Reg left = asm_fuseload(as, lref, RSET_FPR);
         if (LJ_64 && irt_isu32(ir->t))
           emit_rr(as, XO_MOV, dest, dest);  /* Zero hiword. */
         emit_mrm(as, op,
                  dest|((LJ_64 &&
                         (irt_is64(ir->t) || irt_isu32(ir->t))) ? REX_64 : 0),
-                 left);
+                 asm_fuseload(as, lref, RSET_FPR));
       }
     }
   } else if (st >= IRT_I8 && st <= IRT_U16) {  /* Extend to 32 bit integer. */
@@ -952,6 +1039,24 @@ static void asm_tvptr(ASMState *as, Reg dest, IRRef ref)
       emit_rmro(as, XO_LEA, dest|REX_64, RID_ESP, ra_spill(as, ir));
   } else {
     /* Otherwise use g->tmptv to hold the TValue. */
+#if LJ_GC64
+    if (irref_isk(ref)) {
+      TValue k;
+      lj_ir_kvalue(as->J->L, &k, ir);
+      emit_movmroi(as, dest, 4, k.u32.hi);
+      emit_movmroi(as, dest, 0, k.u32.lo);
+    } else {
+      /* TODO: 64 bit store + 32 bit load-modify-store is suboptimal. */
+      Reg src = ra_alloc1(as, ref, rset_exclude(RSET_GPR, dest));
+      if (irt_is64(ir->t)) {
+        emit_u32(as, irt_toitype(ir->t) << 15);
+        emit_rmro(as, XO_ARITHi, XOg_OR, dest, 4);
+      } else {
+        emit_movmroi(as, dest, 4, (irt_toitype(ir->t) << 15) | 0x7fff);
+      }
+      emit_movtomro(as, REX_64IR(ir, src), dest, 0);
+    }
+#else
     if (!irref_isk(ref)) {
       Reg src = ra_alloc1(as, ref, rset_exclude(RSET_GPR, dest));
       emit_movtomro(as, REX_64IR(ir, src), dest, 0);
@@ -960,6 +1065,7 @@ static void asm_tvptr(ASMState *as, Reg dest, IRRef ref)
     }
     if (!(LJ_64 && irt_islightud(ir->t)))
       emit_movmroi(as, dest, 4, irt_toitype(ir->t));
+#endif
     emit_loada(as, dest, &J2G(as->J)->tmptv);
   }
 }
@@ -969,9 +1075,9 @@ static void asm_aref(ASMState *as, IRIns *ir)
   Reg dest = ra_dest(as, ir, RSET_GPR);
   asm_fusearef(as, ir, RSET_GPR);
   if (!(as->mrm.idx == RID_NONE && as->mrm.ofs == 0))
-    emit_mrm(as, XO_LEA, dest, RID_MRM);
+    emit_mrm(as, XO_LEA, dest|REX_GC64, RID_MRM);
   else if (as->mrm.base != dest)
-    emit_rr(as, XO_MOV, dest, as->mrm.base);
+    emit_rr(as, XO_MOV, dest|REX_GC64, as->mrm.base);
 }
 
 /* Inlined hash lookup. Specialized for key type and for const keys.
@@ -998,7 +1104,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
   if (!isk) {
     rset_clear(allow, tab);
     key = ra_alloc1(as, ir->op2, irt_isnum(kt) ? RSET_FPR : allow);
-    if (!irt_isstr(kt))
+    if (LJ_GC64 || !irt_isstr(kt))
       tmp = ra_scratch(as, rset_exclude(allow, key));
   }
 
@@ -1011,8 +1117,8 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
 
   /* Follow hash chain until the end. */
   l_loop = emit_sjcc_label(as, CC_NZ);
-  emit_rr(as, XO_TEST, dest, dest);
-  emit_rmro(as, XO_MOV, dest, dest, offsetof(Node, next));
+  emit_rr(as, XO_TEST, dest|REX_GC64, dest);
+  emit_rmro(as, XO_MOV, dest|REX_GC64, dest, offsetof(Node, next));
   l_next = emit_label(as);
 
   /* Type and value comparison. */
@@ -1033,7 +1139,7 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
       emit_rmro(as, XO_UCOMISD, key, dest, offsetof(Node, key.n));
       emit_sjcc(as, CC_AE, l_next);
       /* The type check avoids NaN penalties and complaints from Valgrind. */
-#if LJ_64
+#if LJ_64 && !LJ_GC64
       emit_u32(as, LJ_TISNUM);
       emit_rmro(as, XO_ARITHi, XOg_CMP, dest, offsetof(Node, key.it));
 #else
@@ -1041,10 +1147,27 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
       emit_rmro(as, XO_ARITHi8, XOg_CMP, dest, offsetof(Node, key.it));
 #endif
     }
-#if LJ_64
+#if LJ_64 && !LJ_GC64
   } else if (irt_islightud(kt)) {
     emit_rmro(as, XO_CMP, key|REX_64, dest, offsetof(Node, key.u64));
-#endif
+#elif LJ_GC64
+  } else if (irt_isaddr(kt)) {
+    if (isk) {
+      TValue k;
+      k.u64 = ((uint64_t)irt_toitype(irkey->t) << 47) | irkey[1].tv.u64;
+      emit_gmroi(as, XG_ARITHi(XOg_CMP), dest, offsetof(Node, key.u32.lo),
+                 k.u32.lo);
+      emit_sjcc(as, CC_NE, l_next);
+      emit_gmroi(as, XG_ARITHi(XOg_CMP), dest, offsetof(Node, key.u32.hi),
+                 k.u32.hi);
+    } else {
+      emit_rmro(as, XO_CMP, tmp|REX_64, dest, offsetof(Node, key.u64));
+    }
+  } else {
+    lua_assert(irt_ispri(kt) && !irt_isnil(kt));
+    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));
@@ -1058,16 +1181,23 @@ static void asm_href(ASMState *as, IRIns *ir, IROp merge)
     lua_assert(!irt_isnil(kt));
     emit_i8(as, irt_toitype(kt));
     emit_rmro(as, XO_ARITHi8, XOg_CMP, dest, offsetof(Node, key.it));
+#endif
   }
   emit_sfixup(as, l_loop);
   checkmclim(as);
+#if LJ_GC64
+  if (!isk && irt_isaddr(kt)) {
+    emit_rr(as, XO_OR, tmp|REX_64, key);
+    emit_loadu64(as, tmp, (uint64_t)irt_toitype(kt) << 47);
+  }
+#endif
 
   /* Load main position relative to tab->node into dest. */
   khash = isk ? ir_khash(irkey) : 1;
   if (khash == 0) {
-    emit_rmro(as, XO_MOV, dest, tab, offsetof(GCtab, node));
+    emit_rmro(as, XO_MOV, dest|REX_GC64, tab, offsetof(GCtab, node));
   } else {
-    emit_rmro(as, XO_ARITH(XOg_ADD), dest, tab, offsetof(GCtab, node));
+    emit_rmro(as, XO_ARITH(XOg_ADD), dest|REX_GC64, tab, offsetof(GCtab,node));
     if ((as->flags & JIT_F_PREFER_IMUL)) {
       emit_i8(as, sizeof(Node));
       emit_rr(as, XO_IMULi8, dest, dest);
@@ -1122,11 +1252,11 @@ static void asm_hrefk(ASMState *as, IRIns *ir)
   if (ra_hasreg(dest)) {
     if (ofs != 0) {
       if (dest == node && !(as->flags & JIT_F_LEA_AGU))
-        emit_gri(as, XG_ARITHi(XOg_ADD), dest, ofs);
+        emit_gri(as, XG_ARITHi(XOg_ADD), dest|REX_GC64, ofs);
       else
-        emit_rmro(as, XO_LEA, dest, node, ofs);
+        emit_rmro(as, XO_LEA, dest|REX_GC64, node, ofs);
     } else if (dest != node) {
-      emit_rr(as, XO_MOV, dest, node);
+      emit_rr(as, XO_MOV, dest|REX_GC64, node);
     }
   }
   asm_guardcc(as, CC_NE);
@@ -1138,13 +1268,24 @@ static void asm_hrefk(ASMState *as, IRIns *ir)
     lua_assert(irt_isnum(irkey->t) || irt_isgcv(irkey->t));
     /* Assumes -0.0 is already canonicalized to +0.0. */
     emit_loadu64(as, key, irt_isnum(irkey->t) ? ir_knum(irkey)->u64 :
+#if LJ_GC64
+                          ((uint64_t)irt_toitype(irkey->t) << 47) |
+                          (uint64_t)ir_kgc(irkey));
+#else
                           ((uint64_t)irt_toitype(irkey->t) << 32) |
                           (uint64_t)(uint32_t)ptr2addr(ir_kgc(irkey)));
+#endif
   } else {
     lua_assert(!irt_isnil(irkey->t));
+#if LJ_GC64
+    emit_i32(as, (irt_toitype(irkey->t)<<15)|0x7fff);
+    emit_rmro(as, XO_ARITHi, XOg_CMP, node,
+              ofs + (int32_t)offsetof(Node, key.it));
+#else
     emit_i8(as, irt_toitype(irkey->t));
     emit_rmro(as, XO_ARITHi8, XOg_CMP, node,
               ofs + (int32_t)offsetof(Node, key.it));
+#endif
   }
 #else
   l_exit = emit_label(as);
@@ -1179,20 +1320,21 @@ static void asm_uref(ASMState *as, IRIns *ir)
   if (irref_isk(ir->op1)) {
     GCfunc *fn = ir_kfunc(IR(ir->op1));
     MRef *v = &gcref(fn->l.uvptr[(ir->op2 >> 8)])->uv.v;
-    emit_rma(as, XO_MOV, dest, v);
+    emit_rma(as, XO_MOV, dest|REX_GC64, v);
   } else {
     Reg uv = ra_scratch(as, RSET_GPR);
     Reg func = ra_alloc1(as, ir->op1, RSET_GPR);
     if (ir->o == IR_UREFC) {
-      emit_rmro(as, XO_LEA, dest, uv, offsetof(GCupval, tv));
+      emit_rmro(as, XO_LEA, dest|REX_GC64, uv, offsetof(GCupval, tv));
       asm_guardcc(as, CC_NE);
       emit_i8(as, 1);
       emit_rmro(as, XO_ARITHib, XOg_CMP, uv, offsetof(GCupval, closed));
     } else {
-      emit_rmro(as, XO_MOV, dest, uv, offsetof(GCupval, v));
+      emit_rmro(as, XO_MOV, dest|REX_GC64, uv, offsetof(GCupval, v));
     }
-    emit_rmro(as, XO_MOV, uv, func,
-              (int32_t)offsetof(GCfuncL, uvptr) + 4*(int32_t)(ir->op2 >> 8));
+    emit_rmro(as, XO_MOV, uv|REX_GC64, func,
+              (int32_t)offsetof(GCfuncL, uvptr) +
+              (int32_t)sizeof(MRef) * (int32_t)(ir->op2 >> 8));
   }
 }
 
@@ -1210,9 +1352,9 @@ static void asm_strref(ASMState *as, IRIns *ir)
   if (as->mrm.base == RID_NONE)
     emit_loadi(as, dest, as->mrm.ofs);
   else if (as->mrm.base == dest && as->mrm.idx == RID_NONE)
-    emit_gri(as, XG_ARITHi(XOg_ADD), dest, as->mrm.ofs);
+    emit_gri(as, XG_ARITHi(XOg_ADD), dest|REX_GC64, as->mrm.ofs);
   else
-    emit_mrm(as, XO_LEA, dest, RID_MRM);
+    emit_mrm(as, XO_LEA, dest|REX_GC64, RID_MRM);
 }
 
 /* -- Loads and stores ---------------------------------------------------- */
@@ -1281,7 +1423,7 @@ static void asm_fxstore(ASMState *as, IRIns *ir)
     case IRT_I16: case IRT_U16: xo = XO_MOVtow; break;
     case IRT_NUM: xo = XO_MOVSDto; break;
     case IRT_FLOAT: xo = XO_MOVSSto; break;
-#if LJ_64
+#if LJ_64 && !LJ_GC64
     case IRT_LIGHTUD: lua_assert(0);  /* NYI: mask 64 bit lightuserdata. */
 #endif
     default:
@@ -1313,7 +1455,7 @@ static void asm_fxstore(ASMState *as, IRIns *ir)
 #define asm_fstore(as, ir)      asm_fxstore(as, ir)
 #define asm_xstore(as, ir)      asm_fxstore(as, ir)
 
-#if LJ_64
+#if LJ_64 && !LJ_GC64
 static Reg asm_load_lightud64(ASMState *as, IRIns *ir, int typecheck)
 {
   if (ra_used(ir) || typecheck) {
@@ -1335,9 +1477,12 @@ static Reg asm_load_lightud64(ASMState *as, IRIns *ir, int typecheck)
 
 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)));
-#if LJ_64
+#if LJ_64 && !LJ_GC64
   if (irt_islightud(ir->t)) {
     Reg dest = asm_load_lightud64(as, ir, 1);
     if (ra_hasreg(dest)) {
@@ -1351,20 +1496,64 @@ static void asm_ahuvload(ASMState *as, IRIns *ir)
     RegSet allow = irt_isnum(ir->t) ? RSET_FPR : RSET_GPR;
     Reg dest = ra_dest(as, ir, allow);
     asm_fuseahuref(as, ir->op1, RSET_GPR);
+#if LJ_GC64
+    if (irt_isaddr(ir->t)) {
+      emit_shifti(as, XOg_SHR|REX_64, dest, 17);
+      asm_guardcc(as, CC_NE);
+      emit_i8(as, irt_toitype(ir->t));
+      emit_rr(as, XO_ARITHi8, XOg_CMP, dest);
+      emit_i8(as, XI_O16);
+      if ((as->flags & JIT_F_BMI2)) {
+        emit_i8(as, 47);
+        emit_mrm(as, XV_RORX|VEX_64, dest, RID_MRM);
+      } else {
+        emit_shifti(as, XOg_ROR|REX_64, dest, 47);
+        emit_mrm(as, XO_MOV, dest|REX_64, RID_MRM);
+      }
+      return;
+    } else
+#endif
     emit_mrm(as, dest < RID_MAX_GPR ? XO_MOV : XO_MOVSD, dest, RID_MRM);
   } else {
-    asm_fuseahuref(as, ir->op1, RSET_GPR);
+    RegSet gpr = RSET_GPR;
+#if LJ_GC64
+    if (irt_isaddr(ir->t)) {
+      tmp = ra_scratch(as, RSET_GPR);
+      gpr = rset_exclude(gpr, tmp);
+    }
+#endif
+    asm_fuseahuref(as, ir->op1, gpr);
   }
   /* Always do the type check, even if the load result is unused. */
   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));
+#if LJ_GC64
+    emit_u32(as, LJ_TISNUM << 15);
+#else
     emit_u32(as, LJ_TISNUM);
+#endif
+    emit_mrm(as, XO_ARITHi, XOg_CMP, RID_MRM);
+#if LJ_GC64
+  } else if (irt_isaddr(ir->t)) {
+    as->mrm.ofs -= 4;
+    emit_i8(as, irt_toitype(ir->t));
+    emit_mrm(as, XO_ARITHi8, XOg_CMP, tmp);
+    emit_shifti(as, XOg_SAR|REX_64, tmp, 47);
+    emit_mrm(as, XO_MOV, tmp|REX_64, RID_MRM);
+  } else if (irt_isnil(ir->t)) {
+    as->mrm.ofs -= 4;
+    emit_i8(as, -1);
+    emit_mrm(as, XO_ARITHi8, XOg_CMP|REX_64, RID_MRM);
+  } else {
+    emit_u32(as, (irt_toitype(ir->t) << 15) | 0x7fff);
     emit_mrm(as, XO_ARITHi, XOg_CMP, RID_MRM);
+#else
   } else {
     emit_i8(as, irt_toitype(ir->t));
     emit_mrm(as, XO_ARITHi8, XOg_CMP, RID_MRM);
+#endif
   }
 }
 
@@ -1376,12 +1565,28 @@ static void asm_ahustore(ASMState *as, IRIns *ir)
     Reg src = ra_alloc1(as, ir->op2, RSET_FPR);
     asm_fuseahuref(as, ir->op1, RSET_GPR);
     emit_mrm(as, XO_MOVSDto, src, RID_MRM);
-#if LJ_64
+#if LJ_64 && !LJ_GC64
   } else if (irt_islightud(ir->t)) {
     Reg src = ra_alloc1(as, ir->op2, RSET_GPR);
     asm_fuseahuref(as, ir->op1, rset_exclude(RSET_GPR, src));
     emit_mrm(as, XO_MOVto, src|REX_64, RID_MRM);
 #endif
+#if LJ_GC64
+  } else if (irref_isk(ir->op2)) {
+    TValue k;
+    lj_ir_kvalue(as->J->L, &k, IR(ir->op2));
+    asm_fuseahuref(as, ir->op1, RSET_GPR);
+    if (tvisnil(&k)) {
+      emit_i32(as, -1);
+      emit_mrm(as, XO_MOVmi, REX_64, RID_MRM);
+    } else {
+      emit_u32(as, k.u32.lo);
+      emit_mrm(as, XO_MOVmi, 0, RID_MRM);
+      as->mrm.ofs += 4;
+      emit_u32(as, k.u32.hi);
+      emit_mrm(as, XO_MOVmi, 0, RID_MRM);
+    }
+#endif
   } else {
     IRIns *irr = IR(ir->op2);
     RegSet allow = RSET_GPR;
@@ -1392,6 +1597,17 @@ static void asm_ahustore(ASMState *as, IRIns *ir)
     }
     asm_fuseahuref(as, ir->op1, allow);
     if (ra_hasreg(src)) {
+#if LJ_GC64
+      if (!(LJ_DUALNUM && irt_isinteger(ir->t))) {
+        /* TODO: 64 bit store + 32 bit load-modify-store is suboptimal. */
+        as->mrm.ofs += 4;
+        emit_u32(as, irt_toitype(ir->t) << 15);
+        emit_mrm(as, XO_ARITHi, XOg_OR, RID_MRM);
+        as->mrm.ofs -= 4;
+        emit_mrm(as, XO_MOVto, src|REX_64, RID_MRM);
+        return;
+      }
+#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)));
@@ -1399,7 +1615,12 @@ static void asm_ahustore(ASMState *as, IRIns *ir)
       emit_mrm(as, XO_MOVmi, 0, RID_MRM);
     }
     as->mrm.ofs += 4;
+#if LJ_GC64
+    lua_assert(LJ_DUALNUM && irt_isinteger(ir->t));
+    emit_i32(as, LJ_TNUMX << 15);
+#else
     emit_i32(as, (int32_t)irt_toitype(ir->t));
+#endif
     emit_mrm(as, XO_MOVmi, 0, RID_MRM);
   }
 }
@@ -1420,7 +1641,7 @@ static void asm_sload(ASMState *as, IRIns *ir)
     base = ra_alloc1(as, REF_BASE, RSET_GPR);
     emit_rmro(as, XO_MOVSD, left, base, ofs);
     t.irt = IRT_NUM;  /* Continue with a regular number type check. */
-#if LJ_64
+#if LJ_64 && !LJ_GC64
   } else if (irt_islightud(t)) {
     Reg dest = asm_load_lightud64(as, ir, (ir->op2 & IRSLOAD_TYPECHECK));
     if (ra_hasreg(dest)) {
@@ -1438,6 +1659,36 @@ static void asm_sload(ASMState *as, IRIns *ir)
       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);
     } else {
+#if LJ_GC64
+      if (irt_isaddr(t)) {
+        /* LJ_GC64 type check + tag removal without BMI2 and with BMI2:
+        **
+        **  mov r64, [addr]    rorx r64, [addr], 47
+        **  ror r64, 47
+        **  cmp r16, itype     cmp r16, itype
+        **  jne ->exit         jne ->exit
+        **  shr r64, 16        shr r64, 16
+        */
+        emit_shifti(as, XOg_SHR|REX_64, dest, 17);
+        if ((ir->op2 & IRSLOAD_TYPECHECK)) {
+          asm_guardcc(as, CC_NE);
+          emit_i8(as, irt_toitype(t));
+          emit_rr(as, XO_ARITHi8, XOg_CMP, dest);
+          emit_i8(as, XI_O16);
+        }
+        if ((as->flags & JIT_F_BMI2)) {
+          emit_i8(as, 47);
+          emit_rmro(as, XV_RORX|VEX_64, dest, base, ofs);
+        } else {
+          if ((ir->op2 & IRSLOAD_TYPECHECK))
+            emit_shifti(as, XOg_ROR|REX_64, dest, 47);
+          else
+            emit_shifti(as, XOg_SHL|REX_64, dest, 17);
+          emit_rmro(as, XO_MOV, dest|REX_64, base, ofs);
+        }
+        return;
+      } else
+#endif
       emit_rmro(as, irt_isnum(t) ? XO_MOVSD : XO_MOV, dest, base, ofs);
     }
   } else {
@@ -1450,11 +1701,42 @@ static void asm_sload(ASMState *as, IRIns *ir)
     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));
+#if LJ_GC64
+      emit_u32(as, LJ_TISNUM << 15);
+#else
       emit_u32(as, LJ_TISNUM);
+#endif
       emit_rmro(as, XO_ARITHi, XOg_CMP, base, ofs+4);
+#if LJ_GC64
+    } else if (irt_isnil(t)) {
+      /* LJ_GC64 type check for nil:
+      **
+      **   cmp qword [addr], -1
+      **   jne ->exit
+      */
+      emit_i8(as, -1);
+      emit_rmro(as, XO_ARITHi8, XOg_CMP|REX_64, base, ofs);
+    } else if (irt_ispri(t)) {
+      emit_u32(as, (irt_toitype(t) << 15) | 0x7fff);
+      emit_rmro(as, XO_ARITHi, XOg_CMP, base, ofs+4);
+    } else {
+      /* LJ_GC64 type check only:
+      **
+      **   mov r64, [addr]
+      **   sar r64, 47
+      **   cmp r32, itype
+      **   jne ->exit
+      */
+      Reg tmp = ra_scratch(as, rset_exclude(RSET_GPR, base));
+      emit_i8(as, irt_toitype(t));
+      emit_rr(as, XO_ARITHi8, XOg_CMP, tmp);
+      emit_shifti(as, XOg_SAR|REX_64, tmp, 47);
+      emit_rmro(as, XO_MOV, tmp|REX_64, base, ofs+4);
+#else
     } else {
       emit_i8(as, irt_toitype(t));
       emit_rmro(as, XO_ARITHi8, XOg_CMP, base, ofs+4);
+#endif
     }
   }
 }
@@ -1548,7 +1830,7 @@ static void asm_tbar(ASMState *as, IRIns *ir)
   Reg tab = ra_alloc1(as, ir->op1, RSET_GPR);
   Reg tmp = ra_scratch(as, rset_exclude(RSET_GPR, tab));
   MCLabel l_end = emit_label(as);
-  emit_movtomro(as, tmp, tab, offsetof(GCtab, gclist));
+  emit_movtomro(as, tmp|REX_GC64, tab, offsetof(GCtab, gclist));
   emit_setgl(as, tab, gc.grayagain);
   emit_getgl(as, tmp, gc.grayagain);
   emit_i8(as, ~LJ_GC_BLACK);
@@ -2084,7 +2366,6 @@ static void asm_comp(ASMState *as, IRIns *ir)
       cc ^= (VCC_PS|(5<<4));  /* A <-> B, AE <-> BE, PS <-> none */
     }
     left = ra_alloc1(as, lref, RSET_FPR);
-    right = asm_fuseload(as, rref, rset_exclude(RSET_FPR, left));
     l_around = emit_label(as);
     asm_guardcc(as, cc >> 4);
     if (cc & VCC_P) {  /* Extra CC_P branch required? */
@@ -2101,6 +2382,7 @@ static void asm_comp(ASMState *as, IRIns *ir)
           emit_jcc(as, CC_P, as->mcp);
       }
     }
+    right = asm_fuseload(as, rref, rset_exclude(RSET_FPR, left));
     emit_mrm(as, XO_UCOMISD, left, right);
   } else {
     IRRef lref = ir->op1, rref = ir->op2;
@@ -2377,13 +2659,18 @@ static void asm_stack_check(ASMState *as, BCReg topslot,
     emit_rmro(as, XO_MOV, r|REX_64, RID_ESP, 0);
   else
     ra_modified(as, r);
-  emit_gri(as, XG_ARITHi(XOg_CMP), r, (int32_t)(8*topslot));
+  emit_gri(as, XG_ARITHi(XOg_CMP), r|REX_GC64, (int32_t)(8*topslot));
   if (ra_hasreg(pbase) && pbase != r)
-    emit_rr(as, XO_ARITH(XOg_SUB), r, pbase);
+    emit_rr(as, XO_ARITH(XOg_SUB), r|REX_GC64, pbase);
   else
+#if LJ_GC64
+    emit_rmro(as, XO_ARITH(XOg_SUB), r|REX_64, RID_DISPATCH,
+              (int32_t)dispofs(as, &J2G(as->J)->jit_base));
+#else
     emit_rmro(as, XO_ARITH(XOg_SUB), r, RID_NONE,
               ptr2addr(&J2G(as->J)->jit_base));
-  emit_rmro(as, XO_MOV, r, r, offsetof(lua_State, maxstack));
+#endif
+  emit_rmro(as, XO_MOV, r|REX_GC64, r, offsetof(lua_State, maxstack));
   emit_getgl(as, r, cur_L);
   if (allow == RSET_EMPTY)  /* Spill temp. register. */
     emit_rmro(as, XO_MOVto, r|REX_64, RID_ESP, 0);
@@ -2414,18 +2701,44 @@ static void asm_stack_restore(ASMState *as, SnapShot *snap)
                  (LJ_DUALNUM && irt_isinteger(ir->t)));
       if (!irref_isk(ref)) {
         Reg src = ra_alloc1(as, ref, rset_exclude(RSET_GPR, RID_BASE));
+#if LJ_GC64
+        if (irt_is64(ir->t)) {
+          /* TODO: 64 bit store + 32 bit load-modify-store is suboptimal. */
+          emit_u32(as, irt_toitype(ir->t) << 15);
+          emit_rmro(as, XO_ARITHi, XOg_OR, RID_BASE, ofs+4);
+        } else if (LJ_DUALNUM && irt_isinteger(ir->t)) {
+          emit_movmroi(as, RID_BASE, ofs+4, LJ_TISNUM << 15);
+        } else {
+          emit_movmroi(as, RID_BASE, ofs+4, (irt_toitype(ir->t)<<15)|0x7fff);
+        }
+#endif
         emit_movtomro(as, REX_64IR(ir, src), RID_BASE, ofs);
+#if LJ_GC64
+      } else {
+        TValue k;
+        lj_ir_kvalue(as->J->L, &k, ir);
+        if (tvisnil(&k)) {
+          emit_i32(as, -1);
+          emit_rmro(as, XO_MOVmi, REX_64, RID_BASE, ofs);
+        } else {
+          emit_movmroi(as, RID_BASE, ofs+4, k.u32.hi);
+          emit_movmroi(as, RID_BASE, ofs, k.u32.lo);
+        }
+#else
       } else if (!irt_ispri(ir->t)) {
         emit_movmroi(as, RID_BASE, ofs, ir->i);
+#endif
       }
       if ((sn & (SNAP_CONT|SNAP_FRAME))) {
 #if !LJ_FR2
         if (s != 0)  /* Do not overwrite link to previous frame. */
           emit_movmroi(as, RID_BASE, ofs+4, (int32_t)(*flinks--));
 #endif
+#if !LJ_GC64
       } else {
         if (!(LJ_64 && irt_islightud(ir->t)))
           emit_movmroi(as, RID_BASE, ofs+4, irt_toitype(ir->t));
+#endif
       }
     }
     checkmclim(as);
@@ -2451,11 +2764,15 @@ static void asm_gc_check(ASMState *as)
   args[1] = ASMREF_TMP2;  /* MSize steps     */
   asm_gencall(as, ci, args);
   tmp = ra_releasetmp(as, ASMREF_TMP1);
+#if LJ_GC64
+  emit_rmro(as, XO_LEA, tmp|REX_64, RID_DISPATCH, GG_DISP2G);
+#else
   emit_loada(as, tmp, J2G(as->J));
+#endif
   emit_loadi(as, ra_releasetmp(as, ASMREF_TMP2), as->gcsteps);
   /* Jump around GC step if GC total < GC threshold. */
   emit_sjcc(as, CC_B, l_end);
-  emit_opgl(as, XO_ARITH(XOg_CMP), tmp, gc.threshold);
+  emit_opgl(as, XO_ARITH(XOg_CMP), tmp|REX_GC64, gc.threshold);
   emit_getgl(as, tmp, gc.total);
   as->gcsteps = 0;
   checkmclim(as);
@@ -2520,7 +2837,7 @@ static void asm_head_root_base(ASMState *as)
     if (rset_test(as->modset, r) || irt_ismarked(ir->t))
       ir->r = RID_INIT;  /* No inheritance for modified BASE register. */
     if (r != RID_BASE)
-      emit_rr(as, XO_MOV, r, RID_BASE);
+      emit_rr(as, XO_MOV, r|REX_GC64, RID_BASE);
   }
 }
 
@@ -2536,8 +2853,9 @@ static RegSet asm_head_side_base(ASMState *as, IRIns *irp, RegSet allow)
     if (irp->r == r) {
       rset_clear(allow, r);  /* Mark same BASE register as coalesced. */
     } else if (ra_hasreg(irp->r) && rset_test(as->freeset, irp->r)) {
+      /* Move from coalesced parent reg. */
       rset_clear(allow, irp->r);
-      emit_rr(as, XO_MOV, r, irp->r);  /* Move from coalesced parent reg. */
+      emit_rr(as, XO_MOV, r|REX_GC64, irp->r);
     } else {
       emit_getgl(as, r, jit_base);  /* Otherwise reload BASE. */
     }
@@ -2750,13 +3068,19 @@ void lj_asm_patchexit(jit_State *J, GCtrace *T, ExitNo exitno, MCode *target)
   MSize len = T->szmcode;
   MCode *px = exitstub_addr(J, exitno) - 6;
   MCode *pe = p+len-6;
-  uint32_t stateaddr = u32ptr(&J2G(J)->vmstate);
+#if LJ_GC64
+  uint32_t statei = (uint32_t)(GG_OFS(g.vmstate) - GG_OFS(dispatch));
+#else
+  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);
   /* Do not patch parent exit for a stack check. Skip beyond vmstate update. */
-  for (; p < pe; p += asm_x86_inslen(p))
-    if (*(uint32_t *)(p+(LJ_64 ? 3 : 2)) == stateaddr && p[0] == XI_MOVmi)
+  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);
   for (; p < pe; p += asm_x86_inslen(p))
     if ((*(uint16_t *)p & 0xf0ff) == 0x800f && p + *(int32_t *)(p+2) == px)
diff --git a/src/lj_emit_x86.h b/src/lj_emit_x86.h
index 3d6f13f4..f0bca938 100644
--- a/src/lj_emit_x86.h
+++ b/src/lj_emit_x86.h
@@ -20,6 +20,11 @@
 #define REX_64                  0
 #define VEX_64                  0
 #endif
+#if LJ_GC64
+#define REX_GC64                REX_64
+#else
+#define REX_GC64                0
+#endif
 
 #define emit_i8(as, i)          (*--as->mcp = (MCode)(i))
 #define emit_i32(as, i)         (*(int32_t *)(as->mcp-4) = (i), as->mcp -= 4)
@@ -94,26 +99,17 @@ static int32_t ptr2addr(const void *p)
 #define ptr2addr(p)     (i32ptr((p)))
 #endif
 
-/* op r, [addr] */
-static void emit_rma(ASMState *as, x86Op xo, Reg rr, const void *addr)
-{
-  MCode *p = as->mcp;
-  *(int32_t *)(p-4) = ptr2addr(addr);
-#if LJ_64
-  p[-5] = MODRM(XM_SCALE1, RID_ESP, RID_EBP);
-  as->mcp = emit_opm(xo, XM_OFS0, rr, RID_ESP, p, -5);
-#else
-  as->mcp = emit_opm(xo, XM_OFS0, rr, RID_EBP, p, -4);
-#endif
-}
-
 /* op r, [base+ofs] */
 static void emit_rmro(ASMState *as, x86Op xo, Reg rr, Reg rb, int32_t ofs)
 {
   MCode *p = as->mcp;
   x86Mode mode;
   if (ra_hasreg(rb)) {
-    if (ofs == 0 && (rb&7) != RID_EBP) {
+    if (LJ_GC64 && rb == RID_RIP) {
+      mode = XM_OFS0;
+      p -= 4;
+      *(int32_t *)p = ofs;
+    } else if (ofs == 0 && (rb&7) != RID_EBP) {
       mode = XM_OFS0;
     } else if (checki8(ofs)) {
       *--p = (MCode)ofs;
@@ -211,6 +207,11 @@ static void emit_mrm(ASMState *as, x86Op xo, Reg rr, Reg rb)
       *--p = MODRM(XM_SCALE1, RID_ESP, RID_EBP);
       rb = RID_ESP;
 #endif
+    } else if (LJ_GC64 && rb == RID_RIP) {
+      lua_assert(as->mrm.idx == RID_NONE);
+      mode = XM_OFS0;
+      p -= 4;
+      *(int32_t *)p = as->mrm.ofs;
     } else {
       if (as->mrm.ofs == 0 && (rb&7) != RID_EBP) {
         mode = XM_OFS0;
@@ -264,8 +265,8 @@ static void emit_movmroi(ASMState *as, Reg base, int32_t ofs, int32_t i)
 /* Get/set global_State fields. */
 #define emit_opgl(as, xo, r, field) \
   emit_rma(as, (xo), (r), (void *)&J2G(as->J)->field)
-#define emit_getgl(as, r, field)        emit_opgl(as, XO_MOV, (r), field)
-#define emit_setgl(as, r, field)        emit_opgl(as, XO_MOVto, (r), field)
+#define emit_getgl(as, r, field) emit_opgl(as, XO_MOV, (r)|REX_GC64, field)
+#define emit_setgl(as, r, field) emit_opgl(as, XO_MOVto, (r)|REX_GC64, field)
 
 #define emit_setvmstate(as, i) \
   (emit_i32(as, i), emit_opgl(as, XO_MOVmi, 0, vmstate))
@@ -288,9 +289,21 @@ static void emit_loadi(ASMState *as, Reg r, int32_t i)
   }
 }
 
+#if LJ_GC64
+#define dispofs(as, k) \
+  ((intptr_t)((uintptr_t)(k) - (uintptr_t)J2GG(as->J)->dispatch))
+#define mcpofs(as, k) \
+  ((intptr_t)((uintptr_t)(k) - (uintptr_t)as->mcp))
+#define mctopofs(as, k) \
+  ((intptr_t)((uintptr_t)(k) - (uintptr_t)as->mctop))
+/* mov r, addr */
+#define emit_loada(as, r, addr) \
+  emit_loadu64(as, (r), (uintptr_t)(addr))
+#else
 /* mov r, addr */
 #define emit_loada(as, r, addr) \
   emit_loadi(as, (r), ptr2addr((addr)))
+#endif
 
 #if LJ_64
 /* mov r, imm64 or shorter 32 bit extended load. */
@@ -302,6 +315,15 @@ static void emit_loadu64(ASMState *as, Reg r, uint64_t u64)
     MCode *p = as->mcp;
     *(int32_t *)(p-4) = (int32_t)u64;
     as->mcp = emit_opm(XO_MOVmi, XM_REG, REX_64, r, p, -4);
+#if LJ_GC64
+  } else if (checki32(dispofs(as, u64))) {
+    emit_rmro(as, XO_LEA, r|REX_64, RID_DISPATCH, (int32_t)dispofs(as, u64));
+  } else if (checki32(mcpofs(as, u64)) && checki32(mctopofs(as, u64))) {
+    /* Since as->realign assumes the code size doesn't change, check
+    ** RIP-relative addressing reachability for both as->mcp and as->mctop.
+    */
+    emit_rmro(as, XO_LEA, r|REX_64, RID_RIP, (int32_t)mcpofs(as, u64));
+#endif
   } else {  /* Full-size 64 bit load. */
     MCode *p = as->mcp;
     *(uint64_t *)(p-8) = u64;
@@ -313,22 +335,69 @@ static void emit_loadu64(ASMState *as, Reg r, uint64_t u64)
 }
 #endif
 
+/* op r, [addr] */
+static void emit_rma(ASMState *as, x86Op xo, Reg rr, const void *addr)
+{
+#if LJ_GC64
+  if (checki32(dispofs(as, addr))) {
+    emit_rmro(as, xo, rr, RID_DISPATCH, (int32_t)dispofs(as, addr));
+  } else if (checki32(mcpofs(as, addr)) && checki32(mctopofs(as, addr))) {
+    emit_rmro(as, xo, rr, RID_RIP, (int32_t)mcpofs(as, addr));
+  } else if (!checki32((intptr_t)addr) && (xo == XO_MOV || xo == XO_MOVSD)) {
+    emit_rmro(as, xo, rr, rr, 0);
+    emit_loadu64(as, rr, (uintptr_t)addr);
+  } else
+#endif
+  {
+    MCode *p = as->mcp;
+    *(int32_t *)(p-4) = ptr2addr(addr);
+#if LJ_64
+    p[-5] = MODRM(XM_SCALE1, RID_ESP, RID_EBP);
+    as->mcp = emit_opm(xo, XM_OFS0, rr, RID_ESP, p, -5);
+#else
+    as->mcp = emit_opm(xo, XM_OFS0, rr, RID_EBP, p, -4);
+#endif
+  }
+}
+
 /* Load 64 bit IR constant into register. */
 static void emit_loadk64(ASMState *as, Reg r, IRIns *ir)
 {
+  Reg r64;
+  x86Op xo;
   const uint64_t *k = &ir_k64(ir)->u64;
   if (rset_test(RSET_FPR, r)) {
-    if (*k == 0) {
-      emit_rr(as, XO_XORPS, r, r);
-    } else {
-      emit_rma(as, XO_MOVSD, r, k);
-    }
+    r64 = r;
+    xo = XO_MOVSD;
   } else {
-    if (*k == 0) {
-      emit_rr(as, XO_ARITH(XOg_XOR), r, r);
+    r64 = r | REX_64;
+    xo = XO_MOV;
+  }
+  if (*k == 0) {
+    emit_rr(as, rset_test(RSET_FPR, r) ? XO_XORPS : XO_ARITH(XOg_XOR), r, r);
+#if LJ_GC64
+  } else if (checki32((intptr_t)k) || checki32(dispofs(as, k)) ||
+             (checki32(mcpofs(as, k)) && checki32(mctopofs(as, k)))) {
+    emit_rma(as, xo, r64, k);
+  } else {
+    if (ir->i) {
+      lua_assert(*k == *(uint64_t*)(as->mctop - ir->i));
+    } else if (as->curins <= as->stopins && rset_test(RSET_GPR, r)) {
+      emit_loadu64(as, r, *k);
+      return;
     } else {
-      emit_rma(as, XO_MOV, r | REX_64, k);
+      /* If all else fails, add the FP constant at the MCode area bottom. */
+      while ((uintptr_t)as->mcbot & 7) *as->mcbot++ = XI_INT3;
+      *(uint64_t *)as->mcbot = *k;
+      ir->i = (int32_t)(as->mctop - as->mcbot);
+      as->mcbot += 8;
+      as->mclim = as->mcbot + MCLIM_REDZONE;
     }
+    emit_rmro(as, xo, r64, RID_RIP, (int32_t)mcpofs(as, as->mctop - ir->i));
+#else
+  } else {
+    emit_rma(as, xo, r64, k);
+#endif
   }
 }
 
@@ -470,9 +539,9 @@ static void emit_addptr(ASMState *as, Reg r, int32_t ofs)
 {
   if (ofs) {
     if ((as->flags & JIT_F_LEA_AGU))
-      emit_rmro(as, XO_LEA, r, r, ofs);
+      emit_rmro(as, XO_LEA, r|REX_GC64, r, ofs);
     else
-      emit_gri(as, XG_ARITHi(XOg_ADD), r, ofs);
+      emit_gri(as, XG_ARITHi(XOg_ADD), r|REX_GC64, ofs);
   }
 }
 
diff --git a/src/lj_ffrecord.c b/src/lj_ffrecord.c
index 64a9a65d..6d141a20 100644
--- a/src/lj_ffrecord.c
+++ b/src/lj_ffrecord.c
@@ -1114,8 +1114,13 @@ static TRef recff_io_fp(jit_State *J, TRef *udp, int32_t id)
 {
   TRef tr, ud, fp;
   if (id) {  /* io.func() */
+#if LJ_GC64
+    /* TODO: fix ARM32 asm_fload(), so we can use this for all archs. */
+    ud = lj_ir_ggfload(J, IRT_UDATA, GG_OFS(g.gcroot[id]));
+#else
     tr = lj_ir_kptr(J, &J2G(J)->gcroot[id]);
     ud = emitir(IRT(IR_XLOAD, IRT_UDATA), tr, 0);
+#endif
   } else {  /* fp:method() */
     ud = J->base[0];
     if (!tref_isudata(ud))
diff --git a/src/lj_ir.h b/src/lj_ir.h
index 4e9c85c7..e77f7b99 100644
--- a/src/lj_ir.h
+++ b/src/lj_ir.h
@@ -412,7 +412,7 @@ static LJ_AINLINE IRType itype2irt(const TValue *tv)
 
 static LJ_AINLINE uint32_t irt_toitype_(IRType t)
 {
-  lua_assert(!LJ_64 || t != IRT_LIGHTUD);
+  lua_assert(!LJ_64 || LJ_GC64 || t != IRT_LIGHTUD);
   if (LJ_DUALNUM && t > IRT_NUM) {
     return LJ_TISNUM;
   } else {
@@ -568,7 +568,11 @@ typedef union IRIns {
 #define ir_knum(ir)     check_exp((ir)->o == IR_KNUM, &(ir)[1].tv)
 #define ir_kint64(ir)   check_exp((ir)->o == IR_KINT64, &(ir)[1].tv)
 #define ir_k64(ir) \
-  check_exp((ir)->o == IR_KNUM || (ir)->o == IR_KINT64, &(ir)[1].tv)
+  check_exp((ir)->o == IR_KNUM || (ir)->o == IR_KINT64 || \
+            (LJ_GC64 && \
+             ((ir)->o == IR_KGC || \
+              (ir)->o == IR_KPTR || (ir)->o == IR_KKPTR)), \
+            &(ir)[1].tv)
 #define ir_kptr(ir) \
   check_exp((ir)->o == IR_KPTR || (ir)->o == IR_KKPTR, \
     mref((ir)[LJ_GC64].ptr, void))
diff --git a/src/lj_record.c b/src/lj_record.c
index f0481050..3c67e1a0 100644
--- a/src/lj_record.c
+++ b/src/lj_record.c
@@ -976,7 +976,13 @@ int lj_record_mm_lookup(jit_State *J, RecordIndex *ix, MMS mm)
     }
     /* The cdata metatable is treated as immutable. */
     if (LJ_HASFFI && tref_iscdata(ix->tab)) goto immutable_mt;
+#if LJ_GC64
+    /* TODO: fix ARM32 asm_fload(), so we can use this for all archs. */
+    ix->mt = mix.tab = lj_ir_ggfload(J, IRT_TAB,
+      GG_OFS(g.gcroot[GCROOT_BASEMT+itypemap(&ix->tabv)]));
+#else
     ix->mt = mix.tab = lj_ir_ktab(J, mt);
+#endif
     goto nocheck;
   }
   ix->mt = mt ? mix.tab : TREF_NIL;
diff --git a/src/lj_snap.c b/src/lj_snap.c
index 33c058be..0a08d4d4 100644
--- a/src/lj_snap.c
+++ b/src/lj_snap.c
@@ -623,7 +623,6 @@ static void snap_restoreval(jit_State *J, GCtrace *T, ExitState *ex,
   }
   if (LJ_UNLIKELY(bloomtest(rfilt, ref)))
     rs = snap_renameref(T, snapno, ref, rs);
-  lua_assert(!LJ_GC64);  /* TODO_GC64: handle 64 bit references. */
   if (ra_hasspill(regsp_spill(rs))) {  /* Restore from spill slot. */
     int32_t *sps = &ex->spill[regsp_spill(rs)];
     if (irt_isinteger(t)) {
@@ -632,9 +631,11 @@ static void snap_restoreval(jit_State *J, GCtrace *T, ExitState *ex,
     } else if (irt_isnum(t)) {
       o->u64 = *(uint64_t *)sps;
 #endif
-    } else if (LJ_64 && irt_islightud(t)) {
+#if LJ_64 && !LJ_GC64
+    } else if (irt_islightud(t)) {
       /* 64 bit lightuserdata which may escape already has the tag bits. */
       o->u64 = *(uint64_t *)sps;
+#endif
     } else {
       lua_assert(!irt_ispri(t));  /* PRI refs never have a spill slot. */
       setgcV(J->L, o, (GCobj *)(uintptr_t)*(GCSize *)sps, irt_toitype(t));
@@ -652,9 +653,11 @@ static void snap_restoreval(jit_State *J, GCtrace *T, ExitState *ex,
     } else if (irt_isnum(t)) {
       setnumV(o, ex->fpr[r-RID_MIN_FPR]);
 #endif
-    } else if (LJ_64 && irt_is64(t)) {
+#if LJ_64 && !LJ_GC64
+    } else if (irt_is64(t)) {
       /* 64 bit values that already have the tag bits. */
       o->u64 = ex->gpr[r-RID_MIN_GPR];
+#endif
     } else if (irt_ispri(t)) {
       setpriV(o, irt_toitype(t));
     } else {
diff --git a/src/lj_target_x86.h b/src/lj_target_x86.h
index e29f4748..d5429597 100644
--- a/src/lj_target_x86.h
+++ b/src/lj_target_x86.h
@@ -22,7 +22,7 @@
   _(XMM0) _(XMM1) _(XMM2) _(XMM3) _(XMM4) _(XMM5) _(XMM6) _(XMM7)
 #endif
 #define VRIDDEF(_) \
-  _(MRM)
+  _(MRM) _(RIP)
 
 #define RIDENUM(name)   RID_##name,
 
@@ -31,6 +31,7 @@ enum {
   FPRDEF(RIDENUM)               /* Floating-point registers (FPRs). */
   RID_MAX,
   RID_MRM = RID_MAX,            /* Pseudo-id for ModRM operand. */
+  RID_RIP = RID_MAX+1,          /* Pseudo-id for RIP (x64 only). */
 
   /* Calling conventions. */
   RID_SP = RID_ESP,
@@ -63,8 +64,10 @@ enum {
 
 /* -- Register sets ------------------------------------------------------- */
 
-/* Make use of all registers, except the stack pointer. */
-#define RSET_GPR        (RSET_RANGE(RID_MIN_GPR, RID_MAX_GPR)-RID2RSET(RID_ESP))
+/* Make use of all registers, except the stack pointer (and maybe DISPATCH). */
+#define RSET_GPR        (RSET_RANGE(RID_MIN_GPR, RID_MAX_GPR) \
+                         - RID2RSET(RID_ESP) \
+                         - LJ_GC64*RID2RSET(RID_DISPATCH))
 #define RSET_FPR        (RSET_RANGE(RID_MIN_FPR, RID_MAX_FPR))
 #define RSET_ALL        (RSET_GPR|RSET_FPR)
 #define RSET_INIT       RSET_ALL
@@ -200,6 +203,7 @@ typedef struct {
 */
 typedef enum {
   /* Fixed length opcodes. XI_* prefix. */
+  XI_O16 =      0x66,
   XI_NOP =      0x90,
   XI_XCHGa =    0x90,
   XI_CALL =     0xe8,
@@ -217,6 +221,7 @@ typedef enum {
   XI_PUSHi8 =   0x6a,
   XI_TESTb =    0x84,
   XI_TEST =     0x85,
+  XI_INT3 =     0xcc,
   XI_MOVmi =    0xc7,
   XI_GROUP5 =   0xff,
 
@@ -243,6 +248,7 @@ typedef enum {
   XV_SHRX =     XV_f20f38(f7),
 
   /* Variable-length opcodes. XO_* prefix. */
+  XO_OR =       XO_(0b),
   XO_MOV =      XO_(8b),
   XO_MOVto =    XO_(89),
   XO_MOVtow =   XO_66(89),
diff --git a/src/vm_x64.dasc b/src/vm_x64.dasc
index 759e30ec..d38ac907 100644
--- a/src/vm_x64.dasc
+++ b/src/vm_x64.dasc
@@ -2401,8 +2401,7 @@ static void build_subroutines(BuildCtx *ctx)
   |  movzx RCd, byte [rbp-8]            // Reconstruct exit number.
   |  mov RCH, byte [rbp-16]
   |  mov [rbp-8], r15; mov [rbp-16], r14
-  |  // Caveat: DISPATCH is rbx.
-  |  mov DISPATCH, [ebp]
+  |  // DISPATCH is preserved on-trace in LJ_GC64 mode.
   |  mov RAd, [DISPATCH+DISPATCH_GL(vmstate)]   // Get trace number.
   |  set_vmstate EXIT
   |  mov [DISPATCH+DISPATCH_J(exitno)], RCd