Use a root array register for constant loads and stack guards on x64....

src/x64/virtual-frame-x64.cc

 // Copyright 2009 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 187 matching lines @@
 
 
 void VirtualFrame::EmitPush(Handle<Object> value) {
   ASSERT(stack_pointer_ == element_count() - 1);
   elements_.Add(FrameElement::MemoryElement());
   stack_pointer_++;
   __ Push(value);
 }
 
 
+void VirtualFrame::EmitPush(Heap::RootListIndex index) {
+  ASSERT(stack_pointer_ == element_count() - 1);
+  elements_.Add(FrameElement::MemoryElement());
+  stack_pointer_++;
+  __ PushRoot(index);
+}
+
+
 void VirtualFrame::Drop(int count) {
   ASSERT(count >= 0);
   ASSERT(height() >= count);
   int num_virtual_elements = (element_count() - 1) - stack_pointer_;
 
   // Emit code to lower the stack pointer if necessary.
   if (num_virtual_elements < count) {
     int num_dropped = count - num_virtual_elements;
     stack_pointer_ -= num_dropped;
     __ addq(rsp, Immediate(num_dropped * kPointerSize));
@@ skipping 826 matching lines @@
   // Grow the expression stack by handler size less one (the return
   // address is already pushed by a call instruction).
   Adjust(kHandlerSize - 1);
   __ PushTryHandler(IN_JAVASCRIPT, type);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal