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[CodeGen] Fix FoldConstantVectorArithmetic for scalable vectors 

For now I have changed FoldConstantVectorArithmetic to return early
if we encounter a scalable vector, since the subsequent code assumes
you can perform lane-wise constant folds. However, in future work we
should be able to extend this to look at splats of a constant value
and fold those if possible. I have also added the same code to
FoldConstantArithmetic, since that deals with vectors too.

The warnings I fixed in this patch were being generated by this
existing test:

  CodeGen/AArch64/sve-int-arith.ll

Differential Revision: https://reviews.llvm.org/D79421
This commit is contained in:
David Sherwood 2020-05-06 08:03:15 +01:00
parent 8c24f33158
commit fb1c55b57d
1 changed files with 15 additions and 2 deletions
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17
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -4915,8 +4915,14 @@ SDValue SelectionDAG::FoldConstantArithmetic(unsigned Opcode, const SDLoc &DL,
if (GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(N2))
return FoldSymbolOffset(Opcode, VT, GA, N1);
// For vectors, extract each constant element and fold them individually.
// Either input may be an undef value.
// TODO: All the folds below are performed lane-by-lane and assume a fixed
// vector width, however we should be able to do constant folds involving
// splat vector nodes too.
if (VT.isScalableVector())
return SDValue();
// For fixed width vectors, extract each constant element and fold them
// individually. Either input may be an undef value.
auto *BV1 = dyn_cast<BuildVectorSDNode>(N1);
if (!BV1 && !N1->isUndef())
return SDValue();
@ -4992,6 +4998,13 @@ SDValue SelectionDAG::FoldConstantVectorArithmetic(unsigned Opcode,
if (!VT.isVector())
return SDValue();
// TODO: All the folds below are performed lane-by-lane and assume a fixed
// vector width, however we should be able to do constant folds involving
// splat vector nodes too.
if (VT.isScalableVector())
return SDValue();
// From this point onwards all vectors are assumed to be fixed width.
unsigned NumElts = VT.getVectorNumElements();
auto IsScalarOrSameVectorSize = [&](const SDValue &Op) {