[PATCH] [SimplifyCFG] Teach when it is profitable to speculate calls to @llvm.cttz/ctlz.

[Quentin Colombet]

Hi Andrea,

> My idea is to do the following (if you agree):

> 

> - move this logic into CodeGenPrepare;

> - guard the code against a check on the subtarget (something like 'isCheapToSpeculateCttzCtlz').

> - On X86 that method would return true if we have TZCNT/LZCNT or if we have feature CMOV.


Sounds good to me.

Thanks,
-Quentin


http://reviews.llvm.org/D6679

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