From: kaz@kylheku.com   
      
   On 2011-11-02, George Neuner  wrote:   
   > Yes.  But the compiler can't count on register renaming ... it can see   
   > only the architectural named registers.  If the code in question had   
   > copied Rx-> Ry then renaming would have been possible, but instead the   
   > code performed a constant load to each register.  No possibility of   
   > rename sharing there.   
      
   If the register holds a value that is used, but not clobbered, then renaming is   
   moot. The two blocks of code both depend on rx being zero, and so nothing is   
   achieved by splitting the instruction set register into two physical registers.   
      
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