[InstCombine] Don't handle non-canonical index type in icmp of load fold #151346
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We should just bail out and wait for it to be canonicalized. The current implementation could emit a trunc without actually performing the transform.
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@llvm/pr-subscribers-llvm-transforms Author: Nikita Popov (nikic) ChangesWe should just bail out and wait for it to be canonicalized. The current implementation could emit a trunc without actually performing the transform. Full diff: https://github.com/llvm/llvm-project/pull/151346.diff 1 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index da9b12686a8f1..b268fea85ab07 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -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.
@@ -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);
- }
// 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.
|
dtcxzyw
approved these changes
Jul 30, 2025
| 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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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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We should just bail out and wait for it to be canonicalized. The current implementation could emit a trunc without actually performing the transform.