LoadUint32() doesn't need a scratch register.

src/ia32/lithium-ia32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "v8.h"
 
 #if V8_TARGET_ARCH_IA32
 
 #include "lithium-allocator-inl.h"
 #include "ia32/lithium-ia32.h"
@@ skipping 1923 matching lines @@
       LOperand* value = needs_temp ? UseTempRegister(val) : UseRegister(val);
       LOperand* temp = needs_temp ? TempRegister() : NULL;
       LInstruction* result =
           DefineAsRegister(new(zone()) LDoubleToI(value, temp));
       if (!truncating) result = AssignEnvironment(result);
       return result;
     }
   } else if (from.IsInteger32()) {
     info()->MarkAsDeferredCalling();
     if (to.IsTagged()) {
+      LOperand* value = UseRegister(val);
       if (!instr->CheckFlag(HValue::kCanOverflow)) {
-        LOperand* value = UseRegister(val);
         return DefineSameAsFirst(new(zone()) LSmiTag(value));
       } else if (val->CheckFlag(HInstruction::kUint32)) {
-        LOperand* value = UseRegister(val);
-        LOperand* temp1 = TempRegister();
-        LOperand* temp2 = FixedTemp(xmm1);
-        LNumberTagU* result = new(zone()) LNumberTagU(value, temp1, temp2);
+        LOperand* temp = TempRegister();
+        LNumberTagU* result = new(zone()) LNumberTagU(value, temp);
         return AssignPointerMap(DefineSameAsFirst(result));
       } else {
-        LOperand* value = UseRegister(val);
         LOperand* temp = TempRegister();
         LNumberTagI* result = new(zone()) LNumberTagI(value, temp);
         return AssignPointerMap(DefineSameAsFirst(result));
       }
     } else if (to.IsSmi()) {
       LOperand* value = UseRegister(val);
       LInstruction* result = DefineSameAsFirst(new(zone()) LSmiTag(value));
       if (instr->CheckFlag(HValue::kCanOverflow)) {
         result = AssignEnvironment(result);
       }
       return result;
     } else {
       ASSERT(to.IsDouble());
       if (val->CheckFlag(HInstruction::kUint32)) {
-        LOperand* temp = FixedTemp(xmm1);
-        return DefineAsRegister(
-            new(zone()) LUint32ToDouble(UseRegister(val), temp));
+        return DefineAsRegister(new(zone()) LUint32ToDouble(UseRegister(val)));
       } else {
         return DefineAsRegister(new(zone()) LInteger32ToDouble(Use(val)));
       }
     }
   }
   UNREACHABLE();
   return NULL;
 }
 
 
@@ skipping 696 matching lines @@
   LOperand* index = UseTempRegister(instr->index());
   LLoadFieldByIndex* load = new(zone()) LLoadFieldByIndex(object, index);
   LInstruction* result = DefineSameAsFirst(load);
   return AssignPointerMap(result);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32