[llvm] r277959 - [X86] lowerVectorShuffle - ensure that undefined mask elements only use SM_SentinelUndef
Simon Pilgrim via llvm-commits
llvm-commits at lists.llvm.org
Sun Aug 7 13:49:06 PDT 2016
Sure, I’ll make the change tomorrow. Simon.
> On 7 Aug 2016, at 20:10, Craig Topper <craig.topper at gmail.com> wrote:
>
> Can we instead add an assertion here and in getVectorShuffle and fix any code that breaks the rule?
>
> On Sunday, August 7, 2016, Simon Pilgrim <llvm-dev at redking.me.uk <mailto:llvm-dev at redking.me.uk>> wrote:
> No, but we don’t seem to have a hard rule that VECTOR_SHUFFLE can only use (-1) to define undefined mask elements - AFAICT it can be any negative value. This is preventing us from sharing a number of chunks of x86 shuffle matching code that current use Mask[i] < 0 to match all undefineds.
>
> Simon.
>
>> On 7 Aug 2016, at 16:56, Craig Topper <craig.topper at gmail.com <javascript:_e(%7B%7D,'cvml','craig.topper at gmail.com');>> wrote:
>>
>> I don't quite understand this. Does combining come through lowerVectorShuffle? Or when would a VECTOR_SHUFFLE come through where this wasn't true?
>>
>> On Sunday, August 7, 2016, Simon Pilgrim via llvm-commits <llvm-commits at lists.llvm.org <javascript:_e(%7B%7D,'cvml','llvm-commits at lists.llvm.org');>> wrote:
>> Author: rksimon
>> Date: Sun Aug 7 10:29:12 2016
>> New Revision: 277959
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=277959&view=rev <http://llvm.org/viewvc/llvm-project?rev=277959&view=rev>
>> Log:
>> [X86] lowerVectorShuffle - ensure that undefined mask elements only use SM_SentinelUndef
>>
>> Help lowering and combining (which can specify SM_SentinelZero mask elements) share more shuffle matching code.
>>
>> 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/X86/X86ISelLowering.cpp?rev=277959&r1=277958&r2=277959&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=277959&r1=277958&r2=277959&view=diff>
>> ==============================================================================
>> --- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
>> +++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Sun Aug 7 10:29:12 2016
>> @@ -12281,6 +12281,15 @@ static SDValue lowerVectorShuffle(SDValu
>> return DAG.getVectorShuffle(VT, DL, V1, V2, NewMask);
>> }
>>
>> + // Ensure that undefined mask elements only use SM_SentinelUndef.
>> + if (llvm::any_of(Mask, [](int M) { return M < SM_SentinelUndef; })) {
>> + SmallVector<int, 8> NewMask(Mask.begin(), Mask.end());
>> + for (int &M : NewMask)
>> + if (M < SM_SentinelUndef)
>> + M = SM_SentinelUndef;
>> + return DAG.getVectorShuffle(VT, DL, V1, V2, NewMask);
>> + }
>> +
>> // We actually see shuffles that are entirely re-arrangements of a set of
>> // zero inputs. This mostly happens while decomposing complex shuffles into
>> // simple ones. Directly lower these as a buildvector of zeros.
>>
>>
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>>
>>
>> --
>> ~Craig
>
>
>
> --
> ~Craig
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