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[ConstraintElim] Bail out on non-canonical GEPs #156688

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Merged
dtcxzyw merged 1 commit into from
Sep 3, 2025
Merged

[ConstraintElim] Bail out on non-canonical GEPs #156688

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8 changes: 6 additions & 2 deletions llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1125,6 +1125,12 @@ static bool getConstraintFromMemoryAccess(GetElementPtrInst &GEP,
if (Offset.VariableOffsets.size() != 1)
return false;

uint64_t BitWidth = Offset.ConstantOffset.getBitWidth();
auto &[Index, Scale] = Offset.VariableOffsets.front();
// Bail out on non-canonical GEPs.
if (Index->getType()->getScalarSizeInBits() != BitWidth)
return false;

ObjectSizeOpts Opts;
// Workaround for gep inbounds, ptr null, idx.
Opts.NullIsUnknownSize = true;
Expand All @@ -1140,8 +1146,6 @@ static bool getConstraintFromMemoryAccess(GetElementPtrInst &GEP,
// With nuw flag, we know that the index addition doesn't have unsigned wrap.
// If (AllocSize - (ConstOffset + AccessSize)) wraps around, there is no valid
// value for Index.
uint64_t BitWidth = Offset.ConstantOffset.getBitWidth();
auto &[Index, Scale] = Offset.VariableOffsets.front();
APInt MaxIndex = (APInt(BitWidth, Size->getFixedValue() - AccessSize,
/*isSigned=*/false, /*implicitTrunc=*/true) -
Offset.ConstantOffset)
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18 changes: 18 additions & 0 deletions llvm/test/Transforms/ConstraintElimination/implied-by-bounded-memory-access.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -371,3 +371,21 @@ define i8 @load_from_null(i64 %idx) {
%add = add i8 %load, %zext
ret i8 %add
}

define i8 @load_global_non_canonical_gep(i32 %idx) {
; CHECK-LABEL: define i8 @load_global_non_canonical_gep(
; CHECK-SAME: i32 [[IDX:%.*]]) {
; CHECK-NEXT: [[GEP:%.*]] = getelementptr nuw i8, ptr @g, i32 [[IDX]]
; CHECK-NEXT: [[LOAD:%.*]] = load i8, ptr [[GEP]], align 1
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[IDX]], 5
; CHECK-NEXT: [[ZEXT:%.*]] = zext i1 [[CMP]] to i8
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[LOAD]], [[ZEXT]]
; CHECK-NEXT: ret i8 [[ADD]]
;
%gep = getelementptr nuw i8, ptr @g, i32 %idx
%load = load i8, ptr %gep
%cmp = icmp ult i32 %idx, 5
%zext = zext i1 %cmp to i8
%add = add i8 %load, %zext
ret i8 %add
}