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

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 7d680ae1d227683076373c9f5d2da33f62305005..1075b2ed0ea52f255ea3cd01873db76f12c74fb3 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1084,16 +1084,7 @@ LInstruction* LChunkBuilder::DoUnaryMathOperation(HUnaryMathOperation* instr) {
     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: