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[InstCombine] Don't handle non-canonical index type in icmp of load fold #151346

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Merged
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Jul 30, 2025
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[InstCombine] Don't handle non-canonical index type in icmp of load fold #151346

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16 changes: 5 additions & 11 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -163,6 +163,11 @@ Instruction *InstCombinerImpl::foldCmpLoadFromIndexedGlobal(
LaterIndices.push_back(IdxVal);
}

Value *Idx = GEP->getOperand(2);
// If the index type is non-canonical, wait for it to be canonicalized.
if (Idx->getType() != DL.getIndexType(GEP->getType()))
return nullptr;

enum { Overdefined = -3, Undefined = -2 };

// Variables for our state machines.
Expand Down Expand Up @@ -290,17 +295,6 @@ Instruction *InstCombinerImpl::foldCmpLoadFromIndexedGlobal(

// Now that we've scanned the entire array, emit our new comparison(s). We
// order the state machines in complexity of the generated code.
Value *Idx = GEP->getOperand(2);

// If the index is larger than the pointer offset size of the target, truncate
// the index down like the GEP would do implicitly. We don't have to do this
// for an inbounds GEP because the index can't be out of range.
if (!GEP->isInBounds()) {
Type *PtrIdxTy = DL.getIndexType(GEP->getType());
unsigned OffsetSize = PtrIdxTy->getIntegerBitWidth();
if (Idx->getType()->getPrimitiveSizeInBits().getFixedValue() > OffsetSize)
Idx = Builder.CreateTrunc(Idx, PtrIdxTy);
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@dtcxzyw dtcxzyw Jul 30, 2025

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It reminds me that we can add nsw/nuw to the trunc when canonicalizing the index type: https://alive2.llvm.org/ce/z/niXbox

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@nikic nikic Jul 31, 2025

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#151516

}

// If inbounds keyword is not present, Idx * ElementSize can overflow.
// Let's assume that ElementSize is 2 and the wanted value is at offset 0.
Expand Down