[PATCH][X86] Lower unsigned vsetcc to psubus in certain cases

[Adam Nemet]

On Feb 25, 2014, at 5:07 PM, Quentin Colombet <qcolombet at apple.com> wrote:

> Hi Adam,
> 
> This LGTM with two comments:

Hi Quentin,

Thanks very  much for the review.

> 
> 1. Could you add a comment on why this is not useful for AVX?
>  +      if (Subtarget->hasAVX())
>  +        break;

Done.

> 
> 2. As it is your CHECK-LABEL lines may cause failure on pecoff target, see r201931 on how to fix that.

Added colon after the label name and -mtriple to the command line.

New version is attached including the check-in message.  Please apply it for me, thank you.

Adam


> 
> Thanks,
> -Quentin
> 
> On Feb 24, 2014, at 2:36 PM, Adam Nemet <anemet at apple.com> wrote:
> 
>> This is another improvement for SingleSource/Benchmarks/Misc/lowercase.c.
>> 
>> The current approach to lower a vsetult is to flip the sign bit of the operands, swap the operands and then use a (signed) pcmpgt.  psubus (unsigned saturating subtract) can be used to emulate a vsetult more efficiently:
>> 
>> +    case ISD::SETULT: {
>> +      // If the comparison is against a constant we can turn this into a
>> +      // setule.  With psubus, setule does not require a swap.  This is
>> +      // beneficial because the constant in the register is no longer
>> +      // destructed as the destination so it can be hoisted out of a loop.
>> 
>> I also enable lowering via psubus in a few other cases where it’s clearly beneficial: setule and setuge if minu/maxu cannot be used.  You can see the improvements in the diff to the existing test vec_setcc.ll.
>> 
>> I am leaving the other case alone for now because it’s harder to reason about profitability in those cases.
>> 
>> Tested on x86_64-apple-darwin.
>> 
>> Please apply if it looks good.
>> 
>> Adam
>> 
>> <rdar://problem/14338765>
>> 
>> <vsetcc-psubus-v1.patch>_______________________________________________
>> llvm-commits mailing list
>> llvm-commits at cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> 

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