7 files changed, 32 insertions, 13 deletions

diff --git a/lib/dump.lua b/lib/dump.lua
index 41feff44..00f59977 100644
--- a/lib/dump.lua
+++ b/lib/dump.lua
@@ -397,6 +397,8 @@ local function dump_ir(tr, dumpsnap, dumpreg)
             local litn = litname[op]
             if litn and litn[op2] then
               out:write("  ", litn[op2])
+            elseif op == "UREFO " or op == "UREFC " then
+              out:write(format("  #%-3d", shr(op2, 8)))
             else
               out:write(format("  #%-3d", op2))
             end
diff --git a/src/lj_asm.c b/src/lj_asm.c
index 50f877e7..20d26278 100644
--- a/src/lj_asm.c
+++ b/src/lj_asm.c
@@ -1105,7 +1105,7 @@ static void asm_fuseahuref(ASMState *as, IRRef ref, RegSet allow)
     case IR_UREFC:
       if (irref_isk(ir->op1)) {
         GCfunc *fn = ir_kfunc(IR(ir->op1));
-        GCupval *uv = &gcref(fn->l.uvptr[ir->op2])->uv;
+        GCupval *uv = &gcref(fn->l.uvptr[(ir->op2 >> 8)])->uv;
         as->mrm.ofs = ptr2addr(&uv->tv);
         as->mrm.base = as->mrm.idx = RID_NONE;
         return;
@@ -1702,7 +1702,7 @@ static void asm_uref(ASMState *as, IRIns *ir)
     Reg dest = ra_dest(as, ir, RSET_GPR);
     if (irref_isk(ir->op1)) {
       GCfunc *fn = ir_kfunc(IR(ir->op1));
-      MRef *v = &gcref(fn->l.uvptr[ir->op2])->uv.v;
+      MRef *v = &gcref(fn->l.uvptr[(ir->op2 >> 8)])->uv.v;
       emit_rma(as, XO_MOV, dest, v);
     } else {
       Reg uv = ra_scratch(as, RSET_GPR);
@@ -1716,7 +1716,7 @@ static void asm_uref(ASMState *as, IRIns *ir)
         emit_rmro(as, XO_MOV, dest, uv, offsetof(GCupval, v));
       }
       emit_rmro(as, XO_MOV, uv, func,
-                (int32_t)offsetof(GCfuncL, uvptr) + 4*(int32_t)ir->op2);
+                (int32_t)offsetof(GCfuncL, uvptr) + 4*(int32_t)(ir->op2 >> 8));
     }
   }
 }
diff --git a/src/lj_func.c b/src/lj_func.c
index 231701db..078ced92 100644
--- a/src/lj_func.c
+++ b/src/lj_func.c
@@ -169,10 +169,11 @@ GCfunc *lj_func_newL_gc(lua_State *L, GCproto *pt, GCfuncL *parent)
   nuv = fn->l.nupvalues;
   base = L->base;
   for (i = 0; i < nuv; i++) {
-    ptrdiff_t v = pt->uv[i];
+    uint32_t v = pt->uv[i];
     GCupval *uv;
     if ((v & 0x8000)) {
       uv = func_finduv(L, base + (v & 0xff));
+      uv->dhash = (uint32_t)(uintptr_t)gcref(parent->pt) ^ (v << 24);
     } else {
       uv = &gcref(puv[v])->uv;
     }
diff --git a/src/lj_obj.h b/src/lj_obj.h
index 85d904f3..ecce03ed 100644
--- a/src/lj_obj.h
+++ b/src/lj_obj.h
@@ -397,7 +397,7 @@ typedef struct GCupval {
     };
   };
   MRef v;               /* Points to stack slot (open) or above (closed). */
-  int32_t unusedv;      /* For consistent alignment. */
+  uint32_t dhash;       /* Disambiguation hash: dh1 != dh2 => cannot alias. */
 } GCupval;
 
 #define uvprev(uv_)     (&gcref((uv_)->prev)->uv)
diff --git a/src/lj_opt_fold.c b/src/lj_opt_fold.c
index 41c87e2f..a8550e1f 100644
--- a/src/lj_opt_fold.c
+++ b/src/lj_opt_fold.c
@@ -1146,12 +1146,12 @@ LJFOLDF(cse_uref)
   if (LJ_LIKELY(J->flags & JIT_F_OPT_CSE)) {
     IRRef ref = J->chain[fins->o];
     GCfunc *fn = ir_kfunc(fleft);
-    GCupval *uv = gco2uv(gcref(fn->l.uvptr[fins->op2]));
+    GCupval *uv = gco2uv(gcref(fn->l.uvptr[(fins->op2 >> 8)]));
     while (ref > 0) {
       IRIns *ir = IR(ref);
       if (irref_isk(ir->op1)) {
         GCfunc *fn2 = ir_kfunc(IR(ir->op1));
-        if (gco2uv(gcref(fn2->l.uvptr[ir->op2])) == uv) {
+        if (gco2uv(gcref(fn2->l.uvptr[(ir->op2 >> 8)])) == uv) {
           if (fins->o == IR_UREFO && gcstep_barrier(J, ref))
             break;
           return ref;
diff --git a/src/lj_opt_mem.c b/src/lj_opt_mem.c
index 521c8590..57948311 100644
--- a/src/lj_opt_mem.c
+++ b/src/lj_opt_mem.c
@@ -277,12 +277,17 @@ static AliasRet aa_uref(IRIns *refa, IRIns *refb)
 {
   if (refa->o != refb->o)
     return ALIAS_NO;  /* Different UREFx type. */
-  if (refa->op1 != refb->op1)
-    return ALIAS_MAY;  /* Different function. */
-  else if (refa->op2 == refb->op2)
-    return ALIAS_MUST;  /* Same function, same upvalue idx. */
-  else
-    return ALIAS_NO;  /* Same function, different upvalue idx. */
+  if (refa->op1 == refb->op1) {  /* Same function. */
+    if (refa->op2 == refb->op2)
+      return ALIAS_MUST;  /* Same function, same upvalue idx. */
+    else
+      return ALIAS_NO;  /* Same function, different upvalue idx. */
+  } else {  /* Different functions, check disambiguation hash values. */
+    if (((refa->op2 ^ refb->op2) & 0xff))
+      return ALIAS_NO;  /* Upvalues with different hash values cannot alias. */
+    else
+      return ALIAS_MAY;  /* No conclusion can be drawn for same hash value. */
+  }
 }
 
 /* ULOAD forwarding. */
diff --git a/src/lj_record.c b/src/lj_record.c
index 0dfd1f73..b998c020 100644
--- a/src/lj_record.c
+++ b/src/lj_record.c
@@ -781,6 +781,15 @@ static TRef rec_idx(jit_State *J, RecordIndex *ix)
 
 /* -- Upvalue access ------------------------------------------------------ */
 
+/* Shrink disambiguation hash into an 8 bit value. */
+static uint32_t shrink_dhash(uint32_t lo, uint32_t hi)
+{
+  lo ^= hi; hi = lj_rol(hi, 14);
+  lo -= hi; hi = lj_rol(hi, 5);
+  hi ^= lo; hi -= lj_rol(lo, 27);
+  return (hi & 0xff);
+}
+
 /* Record upvalue load/store. */
 static TRef rec_upvalue(jit_State *J, uint32_t uv, TRef val)
 {
@@ -788,6 +797,8 @@ static TRef rec_upvalue(jit_State *J, uint32_t uv, TRef val)
   TRef fn = getcurrf(J);
   IRRef uref;
   int needbarrier = 0;
+  /* Note: this effectively limits LJ_MAX_UPVAL to 127. */
+  uv = (uv << 8) | shrink_dhash(uvp->dhash, uvp->dhash-0x04c11db7);
   if (!uvp->closed) {
     /* In current stack? */
     if (uvval(uvp) >= J->L->stack && uvval(uvp) < J->L->maxstack) {