X64: Made simpler version of fast-smi-loop code.

src/x64/virtual-frame-x64.h

 // 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 370 matching lines @@
   // emit code to affect the physical frame.  Does not clobber any registers
   // excepting possibly the stack pointer.
   void Drop(int count);
 
   // Drop one element.
   void Drop() { Drop(1); }
 
   // Duplicate the top element of the frame.
   void Dup() { PushFrameSlotAt(element_count() - 1); }
 
+  // Duplicate the n'th element from the top of the frame.
+  // Dup(1) is equivalent to Dup().
+  void Dup(int n) {
+    ASSERT(n > 0);
+    PushFrameSlotAt(element_count() - n);
+  }
+
   // Pop an element from the top of the expression stack.  Returns a
   // Result, which may be a constant or a register.
   Result Pop();
 
   // Pop and save an element from the top of the expression stack and
   // emit a corresponding pop instruction.
   void EmitPop(Register reg);
   void EmitPop(const Operand& operand);
 
   // Push an element on top of the expression stack and emit a
@@ skipping 192 matching lines @@
 
   // Classes that need raw access to the elements_ array.
   friend class FrameRegisterState;
   friend class JumpTarget;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_VIRTUAL_FRAME_X64_H_