MIPS: Eliminate Smi check when changing from Smi to Integer32

src/mips/lithium-mips.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 1810 matching lines @@
       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());
       LOperand* value = NULL;
       LInstruction* res = NULL;
-      if (instr->value()->type().IsSmi()) {
-        value = UseRegisterAtStart(instr->value());
+      HValue* val = instr->value();
+      if (val->type().IsSmi() || val->representation().IsSmi()) {
+        value = UseRegisterAtStart(val);
         res = DefineAsRegister(new(zone()) LSmiUntag(value, false));
       } else {
-        value = UseRegister(instr->value());
+        value = UseRegister(val);
         LOperand* temp1 = TempRegister();
         LOperand* temp2 = instr->CanTruncateToInt32() ? TempRegister()
                                                       : NULL;
         LOperand* temp3 = FixedTemp(f22);
         res = DefineSameAsFirst(new(zone()) LTaggedToI(value,
                                                        temp1,
                                                        temp2,
                                                        temp3));
         res = AssignEnvironment(res);
       }
@@ skipping 653 matching lines @@
 
 
 LInstruction* LChunkBuilder::DoLoadFieldByIndex(HLoadFieldByIndex* instr) {
   LOperand* object = UseRegister(instr->object());
   LOperand* index = UseRegister(instr->index());
   return DefineAsRegister(new(zone()) LLoadFieldByIndex(object, index));
 }
 
 
 } }  // namespace v8::internal