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[VPlan] Add legal checks in VPWidenMemoryRecipe::computeCost(). NFC #110445

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[VPlan] Add legal checks in VPWidenMemoryRecipe::computeCost(). NFC #110445

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5 changes: 5 additions & 0 deletions llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2237,6 +2237,11 @@ InstructionCost VPWidenMemoryRecipe::computeCost(ElementCount VF,
const Value *Ptr = getLoadStorePointerOperand(&Ingredient);
assert(!Reverse &&
"Inconsecutive memory access should not have the order.");
if ((isa<LoadInst>(Ingredient) &&
!Ctx.TTI.isLegalMaskedGather(Ty, Alignment)) ||
(isa<StoreInst>(Ingredient) &&
!Ctx.TTI.isLegalMaskedScatter(Ty, Alignment)))
return InstructionCost::getInvalid();
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@fhahn fhahn Oct 3, 2024

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shouldn't getGatherScatterOpCost return Invalid in those cases as we pass IsMasked ?

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@ElvisWang123 ElvisWang123 Oct 3, 2024

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I am not sure who has the responsibility to do the legal check transformations or TTI.
In RISCV, getGatherScatterOpCost will do the legal check and return invalid cost when it fail.
In the default target, getGatherScatterOpCost just return the constant cost no matter it is legal or not.

I found the legacy cost model explicit check if the gather/scatter is legal in LoopVectorizationCostModel::setCostBasedWideningDecision().

So adding this check can prevent misaligned between legacy cost model and the vplan-based cost model when a target isLegalMaskedGather() = false && getGatherScatterOpCost() is valid .

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@fhahn fhahn Oct 4, 2024

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I see. I think the difference is that while the legacy cost model needs to consider all options for the input, no masked VPWidenMemoryRecipe should be created , if masked mem-ops aren't legal I think

return Ctx.TTI.getAddressComputationCost(Ty) +
Ctx.TTI.getGatherScatterOpCost(Ingredient.getOpcode(), Ty, Ptr,
IsMasked, Alignment, CostKind,
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