Relax register constraints for LMathSqrt.

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 9bc33833166c4951c1aa32913794cb80b2c689c7..e15d4a69875fcbe108a369927a7a496ffd36b9e1 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1182,9 +1182,8 @@ LInstruction* LChunkBuilder::DoMathExp(HUnaryMathOperation* instr) {
 
 
 LInstruction* LChunkBuilder::DoMathSqrt(HUnaryMathOperation* instr) {
-  LOperand* input = UseRegisterAtStart(instr->value());
-  LMathSqrt* result = new(zone()) LMathSqrt(input);
-  return DefineSameAsFirst(result);
+  LOperand* input = UseAtStart(instr->value());
+  return DefineAsRegister(new(zone()) LMathSqrt(input));
 }