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[RISCV][GISel] Don't custom legalize load/store of vector of pointers if ELEN < XLEN. #101565

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Aug 13, 2024
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[RISCV][GISel] Don't custom legalize load/store of vector of pointers if ELEN < XLEN. #101565

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8 changes: 5 additions & 3 deletions llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -330,9 +330,11 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)

// we will take the custom lowering logic if we have scalable vector types
// with non-standard alignments
LoadStoreActions.customIf(
LegalityPredicates::any(typeIsLegalIntOrFPVec(0, IntOrFPVecTys, ST),
typeIsLegalPtrVec(0, PtrVecTys, ST)));
LoadStoreActions.customIf(typeIsLegalIntOrFPVec(0, IntOrFPVecTys, ST));

// Pointers require that XLen sized elements are legal.
if (XLen <= ST.getELen())
LoadStoreActions.customIf(typeIsLegalPtrVec(0, PtrVecTys, ST));
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// Pointers require that XLen sized elements are legal.

Do we need to mark as legal in the ELEN < XLEN case? with a call to legalIf?

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We don't seem to have marked any pointer vectors with legalIf. I think they just go to the custom handler and get treated as legal if they pass the alignment check.

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Should we be marking pointer types legal with legalIf? The only case they need to go through custom is when they have special alignment.

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Maybe. It would make the custom handler simpler, we wouldn't need to call allowsMemoryAccessForAlignment since we wouldn't get to the custom handler if we had already check the alignment with legalIf.

On the other hand calling allowsMemoryAccessForAlignment allows us to handle FeatureUnalignedVectorMem correctly. So maybe that's a vote for removing the legalIf and just letting the custom handle always handle it?

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On the other hand calling allowsMemoryAccessForAlignment allows us to handle FeatureUnalignedVectorMem correctly. So maybe that's a vote for removing the legalIf and just letting the custom handle always handle it?

Do we care about FeatureUnalignedVectorMem in the aligned cases? If we were to move the legalIf, it could probably be done in another patch because it doesn't have to do with pointers.

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Do we care about FeatureUnalignedVectorMem in the aligned cases? If we were to move the legalIf, it could probably be done in another patch because it doesn't have to do with pointers.

No. But by listing the aligned cases explicitly with legalIf we're effectively hardcoding what allowsMemoryAccessForAlignment is already capable of checking. Is there an advantage to having both a legalIf and a customIf when the customIf can already handle the legal case?

}

LoadStoreActions.widenScalarToNextPow2(0, /* MinSize = */ 8)
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