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

[Andrea Di Biagio]

I changed those comments at revision 225080.

On Fri, Jan 2, 2015 at 10:41 AM, Andrea Di Biagio
<andrea.dibiagio at gmail.com> wrote:
> 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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