[llvm] r310794 - [AVX512] Correct isExtractSubvectorCheap so that it will return the correct answers for extracting 128-bits from a 512-bit vector and for mask registers.

[Craig Topper via llvm-commits]

Yes that was supposed to be Index == 0. I'll fix. Why doesn't clang have
that warning?

~Craig

On Sun, Aug 13, 2017 at 1:11 PM, Sean Silva via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

>
>
> On Sun, Aug 13, 2017 at 10:40 AM, Craig Topper via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: ctopper
>> Date: Sun Aug 13 10:40:02 2017
>> New Revision: 310794
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=310794&view=rev
>> Log:
>> [AVX512] Correct isExtractSubvectorCheap so that it will return the
>> correct answers for extracting 128-bits from a 512-bit vector and for mask
>> registers.
>>
>> Previously it would not return true for extracting either of the upper
>> quarters of a 512-bit registers.
>>
>> For mask registers we support extracting anything from index 0. And
>> otherwise we only support extracting the upper half of a register.
>>
>> Differential Revision: https://reviews.llvm.org/D36638
>>
>> Modified:
>>     llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
>>
>> Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X8
>> 6/X86ISelLowering.cpp?rev=310794&r1=310793&r2=310794&view=diff
>> ============================================================
>> ==================
>> --- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
>> +++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Sun Aug 13 10:40:02
>> 2017
>> @@ -4579,7 +4579,13 @@ bool X86TargetLowering::isExtractSubvect
>>    if (!isOperationLegalOrCustom(ISD::EXTRACT_SUBVECTOR, ResVT))
>>      return false;
>>
>> -  return (Index == 0 || Index == ResVT.getVectorNumElements());
>> +  // Mask vectors support all subregister combinations and operations
>> that
>> +  // extract half of vector.
>> +  if (ResVT.getVectorElementType() == MVT::i1)
>> +    return Index = 0 || ((ResVT.getSizeInBits() == SrcVT.getSizeInBits()
>> * 2) &&
>> +                         (Index == ResVT.getVectorNumElements()));
>>
>
>
> Is this supposed to be `Index == 0`?
>
> I'm getting this warning (`gcc version 5.4.0 20160609 (Ubuntu
> 5.4.0-6ubuntu1~16.04.4) `):
>
> /home/sean/pg/llvm/llvm/lib/Target/X86/X86ISelLowering.cpp: In member
> function ‘virtual bool llvm::X86TargetLowering::
> isExtractSubvectorCheap(llvm::EVT, llvm::EVT, unsigned int) const’:
> /home/sean/pg/llvm/llvm/lib/Target/X86/X86ISelLowering.cpp:4586:65:
> warning: suggest parentheses around assignment used as truth value
> [-Wparentheses]
>                           (Index == ResVT.getVectorNumElements()));
>                                                                  ^
>
>
> -- Sean Silva
>
>
>> +
>> +  return (Index % ResVT.getVectorNumElements()) == 0;
>>  }
>>
>>  bool X86TargetLowering::isCheapToSpeculateCttz() const {
>>
>>
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