Tweak register allocation for Math.round and do not use roundsd.

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 1066 matching lines @@
     return MarkAsCall(DefineFixedDouble(result, xmm1), instr);
   } else if (op == kMathExp) {
     ASSERT(instr->representation().IsDouble());
     ASSERT(instr->value()->representation().IsDouble());
     LOperand* value = UseTempRegister(instr->value());
     LOperand* temp1 = TempRegister();
     LOperand* temp2 = TempRegister();
     LMathExp* result = new(zone()) LMathExp(value, temp1, temp2);
     return DefineAsRegister(result);
   } else {
-    LOperand* input;
-    if (op == kMathRound &&
-        (!CpuFeatures::IsSupported(SSE4_1) ||
-         instr->CheckFlag(HValue::kBailoutOnMinusZero))) {
-      // Math.round implemented without roundsd.  Input may be overwritten.
-      ASSERT(instr->value()->representation().IsDouble());
-      input = UseTempRegister(instr->value());
-    } else {
-      input = UseRegisterAtStart(instr->value());
-    }
+    LOperand* input = UseRegisterAtStart(instr->value());
     LUnaryMathOperation* result = new(zone()) LUnaryMathOperation(input);
     switch (op) {
       case kMathAbs:
         return AssignEnvironment(AssignPointerMap(DefineSameAsFirst(result)));
       case kMathFloor:
         return AssignEnvironment(DefineAsRegister(result));
       case kMathRound:
         return AssignEnvironment(DefineAsRegister(result));
       case kMathSqrt:
         return DefineSameAsFirst(result);
@@ skipping 1310 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