[LLVMdev] What happened to XCHG_rr?

[Chris Lattner]

On Jul 20, 2008, at 12:54 PM, Fernando Magno Quintao Pereira wrote:

>
> I was using them to do SSA-elimination after register allocation. I  
> can
> implement swaps using three XOR's, but then the code becomes a little
> bigger and slower. I think even for the sake of completeness, the X86
> back-end should offer the possibility of swapping two registers with  
> one
> single instruction. Do you guys think there is any possibility that  
> those
> instructions could come back to the main trunk of LLVM?

Until mainline has code that can generate them, it isn't useful to  
have them.  Why not just include them in your local changes?  If those  
changes ever get committed to mainline, they'd naturally come in with  
them.

-Chris