Eliminate redundant smi checks

src/x64/lithium-x64.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 1626 matching lines @@
   Representation from = instr->from();
   Representation to = instr->to();
   if (from.IsTagged()) {
     if (to.IsDouble()) {
       LOperand* value = UseRegister(instr->value());
       LNumberUntagD* res = new(zone()) LNumberUntagD(value);
       return AssignEnvironment(DefineAsRegister(res));
     } else {
       ASSERT(to.IsInteger32());
       LOperand* value = UseRegister(instr->value());
-      bool needs_check = !instr->value()->type().IsSmi();
-      if (needs_check) {
+      if (instr->value()->IsValueTaggedSmi()) {
+        return DefineSameAsFirst(new(zone()) LSmiUntag(value, false));
+      } else {
         bool truncating = instr->CanTruncateToInt32();
         LOperand* xmm_temp = truncating ? NULL : FixedTemp(xmm1);
         LTaggedToI* res = new(zone()) LTaggedToI(value, xmm_temp);
         return AssignEnvironment(DefineSameAsFirst(res));
-      } else {
-        return DefineSameAsFirst(new(zone()) LSmiUntag(value, needs_check));
       }
     }
   } else if (from.IsDouble()) {
     if (to.IsTagged()) {
       LOperand* value = UseRegister(instr->value());
       LOperand* temp = TempRegister();
 
       // Make sure that temp and result_temp are different registers.
       LUnallocated* result_temp = TempRegister();
       LNumberTagD* result = new(zone()) LNumberTagD(value, temp);
@@ skipping 662 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_X64