Copy of changelist from issue 16450. Converts compare operation...

src/virtual-frame-ia32.cc

 // Copyright 2008 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 114 matching lines @@
 }
 
 
 void VirtualFrame::Unuse(Register reg) {
   frame_registers_.Unuse(reg);
   cgen_->allocator()->Unuse(reg);
 }
 
 
 void VirtualFrame::Spill(Register target) {
+  if (!frame_registers_.is_used(target)) return;
   for (int i = 0; i < elements_.length(); i++) {
     if (elements_[i].is_register() && elements_[i].reg().is(target)) {
       SpillElementAt(i);
     }
   }
 }
 
 
 // Spill any register if possible, making its external reference count zero.
 Register VirtualFrame::SpillAnyRegister() {
@@ skipping 816 matching lines @@
       return false;
     }
   }
   return true;
 }
 #endif
 
 #undef __
 
 } }  // namespace v8::internal