[LLVMdev] LLVM 2.8 and MMX

Nicolas Capens
Tue, 07 Sep 2010 14:45:58 -0000

Hi all,



I've tested a recent revision and noticed that using 64-bit vectors became
very slow. It looks like they are expanded to non-MMX instructions to avoid
breaking code which does not clear the MMX state using emms?



For my project I'm already manually inserting emms instructions in the right
places, so I'd really like 64-bit vector operations to be lowered to MMX
instructions for best performance. So is there some way to get that behavior
back? I tried making IsVerbotenVectorType return false but that didn't
appear to help.



I would be very grateful if someone would add a switch to disable the
expanding before the 2.8 release is finalized.



Cheers,



Nicolas

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