[PATCH] D117210: [CodeGen] Support folds of not(cmp(cc, ...)) -> cmp(!cc, ...) for scalable vectors

[David Sherwood via Phabricator via llvm-commits]

david-arm added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:3160
   APInt CVal;
   if (auto *CN = dyn_cast<ConstantSDNode>(N)) {
     CVal = CN->getAPIntValue();
----------------
sdesmalen wrote:
> Instead of checking for SPLAT_VECTOR explicitly, how about:
> 
>   if (auto *CN = dyn_cast<ConstantSDNode>(N)) {
>     CVal = CN->getAPIntValue();
>   } else if (isConstantSplatVector(N, CVal)) {
>     unsigned EltWidth = N->getValueType(0).getScalarSizeInBits();
>     if (EltWidth < CVal.getBitwidth())
>       CVal = CVal.trunc(EltWidth);
>   } else
>     return false;
> 
Sadly this doesn't work because `isConstantSplatVector` demands the element width of the result be the same as the element width in the BuildVectorSDNode, which means we end up with lots of failing tests. It's just a minor point, but `isConstantSplatVector` also permits FP splats, so we'd have to restrict it to integer too.


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  https://reviews.llvm.org/D117210/new/

https://reviews.llvm.org/D117210