Eliminate Smi check when changing from Smi to Integer32

src/ia32/lithium-ia32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1886 matching lines @@
   // representation change phase of Hydrogen.
   UNREACHABLE();
   return NULL;
 }
 
 
 LInstruction* LChunkBuilder::DoChange(HChange* instr) {
   Representation from = instr->from();
   Representation to = instr->to();
   if (from.IsSmi()) {
-    if (to.IsTagged()) {
+    if (to.IsSmiOrTagged()) {

[Toon Verwaest, 2013/08/12 14:53:42]

Smi -> Smi doesn't happen, so this is superfluous.

[weiliang.lin2, 2013/08/13 02:36:57]

Done.

       LOperand* value = UseRegister(instr->value());
       return DefineSameAsFirst(new(zone()) LDummyUse(value));
     }
+    if (to.IsInteger32()) {
+      LOperand* value = UseRegister(instr->value());
+      return DefineSameAsFirst(new(zone()) LSmiUntag(value, false));
+    }
     from = Representation::Tagged();
   }
   // Only mark conversions that might need to allocate as calling rather than
   // all changes. This makes simple, non-allocating conversion not have to force
   // building a stack frame.
   if (from.IsTagged()) {
     if (to.IsDouble()) {
       info()->MarkAsDeferredCalling();
       LOperand* value = UseRegister(instr->value());
       // Temp register only necessary for minus zero check.
       LOperand* temp = instr->deoptimize_on_minus_zero()
                        ? TempRegister()
                        : NULL;
       LNumberUntagD* res = new(zone()) LNumberUntagD(value, temp);

[Toon Verwaest, 2013/08/12 14:53:42]

We should probably check the value representation in NumberUntagD as well?

[weiliang.lin2, 2013/08/13 02:36:57]

Done.

I found that NumberUntagD has already check the value representation. Could you
please have a double check?

       return AssignEnvironment(DefineAsRegister(res));
     } else if (to.IsSmi()) {
       HValue* val = instr->value();
       LOperand* value = UseRegister(val);
       if (val->type().IsSmi()) {
         return DefineSameAsFirst(new(zone()) LDummyUse(value));
       }
       return AssignEnvironment(DefineSameAsFirst(new(zone()) LCheckSmi(value)));
     } else {
       ASSERT(to.IsInteger32());
       if (instr->value()->type().IsSmi()) {

[Toon Verwaest, 2013/08/12 14:53:42]

What about val->type().IsSmi() || val->representation().IsSmi() instead of
duplicating code above?

[weiliang.lin2, 2013/08/13 02:36:57]

Yes, that is another way to fix
Done.

         LOperand* value = UseRegister(instr->value());
         return DefineSameAsFirst(new(zone()) LSmiUntag(value, false));
       } else {
         bool truncating = instr->CanTruncateToInt32();
         if (CpuFeatures::IsSafeForSnapshot(SSE2)) {
           LOperand* value = UseRegister(instr->value());
           LOperand* xmm_temp =
               (truncating && CpuFeatures::IsSupported(SSE3))
               ? NULL
               : FixedTemp(xmm1);
@@ skipping 780 matching lines @@
 LInstruction* LChunkBuilder::DoLoadFieldByIndex(HLoadFieldByIndex* instr) {
   LOperand* object = UseRegister(instr->object());
   LOperand* index = UseTempRegister(instr->index());
   return DefineSameAsFirst(new(zone()) LLoadFieldByIndex(object, index));
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32