Fix a performance bug in the register contraints for polymorphic loads.

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 1917 matching lines @@
 LInstruction* LChunkBuilder::DoLoadNamedField(HLoadNamedField* instr) {
   ASSERT(instr->representation().IsTagged());
   LOperand* obj = UseRegisterAtStart(instr->object());
   return DefineAsRegister(new(zone()) LLoadNamedField(obj));
 }
 
 
 LInstruction* LChunkBuilder::DoLoadNamedFieldPolymorphic(
     HLoadNamedFieldPolymorphic* instr) {
   ASSERT(instr->representation().IsTagged());
-  LOperand* context = UseFixed(instr->context(), esi);
   if (instr->need_generic()) {
+    LOperand* context = UseFixed(instr->context(), esi);
     LOperand* obj = UseFixed(instr->object(), eax);
     LLoadNamedFieldPolymorphic* result =
         new(zone()) LLoadNamedFieldPolymorphic(context, obj);
     return MarkAsCall(DefineFixed(result, eax), instr);
   } else {
+    LOperand* context = UseAny(instr->context());  // Not actually used.
     LOperand* obj = UseRegisterAtStart(instr->object());
     LLoadNamedFieldPolymorphic* result =
         new(zone()) LLoadNamedFieldPolymorphic(context, obj);
     return AssignEnvironment(DefineAsRegister(result));
   }
 }
 
 
 LInstruction* LChunkBuilder::DoLoadNamedGeneric(HLoadNamedGeneric* instr) {
   LOperand* context = UseFixed(instr->context(), esi);
@@ skipping 478 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