Two small fixes for the Math.sin and Math.cos optimizations.

src/ia32/codegen-ia32.cc

 // Copyright 2006-2009 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 4977 matching lines @@
   FloatingPointHelper::AllocateHeapNumber(masm_,
                                           call_runtime.entry_label(),
                                           scratch1.reg(),
                                           scratch2.reg(),
                                           heap_number.reg());
   scratch1.Unuse();
   scratch2.Unuse();
 
   // Store the result in the allocated heap number.
   __ fstp_d(FieldOperand(heap_number.reg(), HeapNumber::kValueOffset));
-  // Pop the extra copy of the argument.
-  frame_->Pop();
-  // Push the result on the frame.
-  frame_->Push(&heap_number);
-  heap_number.Unuse();
+  // Replace the extra copy of the argument with the result.
+  frame_->SetElementAt(0, &heap_number);
   done.Jump();
 
   call_runtime.Bind();
   // Free ST(0) which was not popped before calling into the runtime.
   __ ffree(0);
   Result answer;
   switch (op) {
     case SIN:
       answer = frame_->CallRuntime(Runtime::kMath_sin, 1);
       break;
@@ skipping 2585 matching lines @@
 
   // Slow-case: Go through the JavaScript implementation.
   __ bind(&slow);
   __ InvokeBuiltin(Builtins::INSTANCE_OF, JUMP_FUNCTION);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal