[llvm] r224899 - [CodeGenPrepare] Teach when it is profitable to speculate calls to @llvm.cttz/ctlz.

[Andrea Di Biagio]

Thanks for the feedback Paul.
I will fix the comments.

Cheers,
Andrea

On Thu, Jan 1, 2015 at 10:04 PM, Robinson, Paul
<Paul_Robinson at playstation.sony.com> wrote:
> Hi Andrea, one comment comment...
>
>> +bool X86TargetLowering::isCheapToSpeculateCttz() const {
>> +  // Don't try to speculate cttz if we can't directly use TZCNT.
>> +  return Subtarget->hasBMI();
>> +}
>> +
>> +bool X86TargetLowering::isCheapToSpeculateCtlz() const {
>> +  // Don't try to speculate ctlz if we can't directly use LZCNT.
>> +  return Subtarget->hasLZCNT();
>
> These predicates default to "don't speculate" so the point here is
> what conditions should override the default; and phrasing those as
> positive statements would be easier to read than double-negatives.
> Maybe something like:
> // Speculate cttz only if we can directly use TZCNT.
> and similar for ctlz.
>
> Thanks,
> --paulr
>
>
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