[LLVMdev] Register allocation in LLVM

Nate Begeman natebegeman at mac.com
Mon May 1 13:12:34 PDT 2006

On May 1, 2006, at 12:28 PM, Patrick Meredith wrote:

> On Apr 30, 2006, at 10:42 PM, Chris Lattner wrote:
> Such an instruction can happen in rename, which makes it about the  
> least resource intensive instruction besides nop.

It can, but in the case of x86, it is not implemented that way.  The  
xchg instruction carries a lot of architectural baggage around with  
it, and on most implementations is at least twice as expensive as a  
reg to reg move.


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