Lazily save double registers for HCallRuntime instructions within Hydrogen code stubs.

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
diff --git a/src/x64/lithium-x64.h b/src/x64/lithium-x64.h
index f827ef6badc9ddaa84354d3c2f8ef5f0fe83441b..1cd186da5c627aec9e031475d722150be7d37553 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -272,7 +272,7 @@ class LInstruction : public ZoneObject {
   // Interface to the register allocator and iterators.
   bool ClobbersTemps() const { return IsCall(); }
   bool ClobbersRegisters() const { return IsCall(); }
-  bool ClobbersDoubleRegisters() const { return IsCall(); }
+  virtual bool ClobbersDoubleRegisters() const { return IsCall(); }
 
   virtual void SetDeferredLazyDeoptimizationEnvironment(LEnvironment* env) { }
 
@@ -1919,8 +1919,13 @@ class LCallRuntime V8_FINAL : public LTemplateInstruction<1, 0, 0> {
   DECLARE_CONCRETE_INSTRUCTION(CallRuntime, "call-runtime")
   DECLARE_HYDROGEN_ACCESSOR(CallRuntime)
 
+  virtual bool ClobbersDoubleRegisters() const V8_OVERRIDE {
+    return save_doubles() == kDontSaveFPRegs;
+  }
+
   const Runtime::Function* function() const { return hydrogen()->function(); }
   int arity() const { return hydrogen()->argument_count(); }
+  SaveFPRegsMode save_doubles() const { return hydrogen()->save_doubles(); }
 };