[llvm] r277959 - [X86] lowerVectorShuffle - ensure that undefined mask elements only use SM_SentinelUndef

[Simon Pilgrim via llvm-commits]

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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