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[DA] Add overflow check in ExactSIV #157086

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Merged
merged 3 commits into from
Sep 19, 2025
Merged

[DA] Add overflow check in ExactSIV #157086

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38b8bdd
[DA] Add overflow check in ExactSIV
kasuga-fj Sep 5, 2025
a4f0f1f
fix comment
kasuga-fj Sep 16, 2025
146b38e
Revert "fix comment"
kasuga-fj Sep 19, 2025
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14 changes: 13 additions & 1 deletion llvm/lib/Analysis/DependenceAnalysis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1170,6 +1170,15 @@ const SCEVConstant *DependenceInfo::collectConstantUpperBound(const Loop *L,
return nullptr;
}

/// Returns \p A - \p B if it guaranteed not to signed wrap. Otherwise returns
/// nullptr. \p A and \p B must have the same integer type.
static const SCEV *minusSCEVNoSignedOverflow(const SCEV *A, const SCEV *B,
ScalarEvolution &SE) {
if (SE.willNotOverflow(Instruction::Sub, /*Signed=*/true, A, B))
return SE.getMinusSCEV(A, B);
return nullptr;
}

// testZIV -
// When we have a pair of subscripts of the form [c1] and [c2],
// where c1 and c2 are both loop invariant, we attack it using
Expand Down Expand Up @@ -1626,7 +1635,9 @@ bool DependenceInfo::exactSIVtest(const SCEV *SrcCoeff, const SCEV *DstCoeff,
assert(0 < Level && Level <= CommonLevels && "Level out of range");
Level--;
Result.Consistent = false;
const SCEV *Delta = SE->getMinusSCEV(DstConst, SrcConst);
const SCEV *Delta = minusSCEVNoSignedOverflow(DstConst, SrcConst, *SE);
if (!Delta)
return false;
LLVM_DEBUG(dbgs() << "\t Delta = " << *Delta << "\n");
NewConstraint.setLine(SrcCoeff, SE->getNegativeSCEV(DstCoeff), Delta,
CurLoop);
Expand Down Expand Up @@ -1716,6 +1727,7 @@ bool DependenceInfo::exactSIVtest(const SCEV *SrcCoeff, const SCEV *DstCoeff,
// explore directions
unsigned NewDirection = Dependence::DVEntry::NONE;
APInt LowerDistance, UpperDistance;
// TODO: Overflow check may be needed.
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I suspect this part could cause overflows, but not entirely sure...

if (TA.sgt(TB)) {
LowerDistance = (TY - TX) + (TA - TB) * TL;
UpperDistance = (TY - TX) + (TA - TB) * TU;
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Analysis/DependenceAnalysis/ExactSIV.ll
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Expand Up @@ -841,7 +841,7 @@ define void @exact14(ptr %A) {
; CHECK-SIV-ONLY-NEXT: Src: store i8 0, ptr %idx.0, align 1 --> Dst: store i8 0, ptr %idx.0, align 1
; CHECK-SIV-ONLY-NEXT: da analyze - none!
; CHECK-SIV-ONLY-NEXT: Src: store i8 0, ptr %idx.0, align 1 --> Dst: store i8 1, ptr %idx.1, align 1
; CHECK-SIV-ONLY-NEXT: da analyze - none!
; CHECK-SIV-ONLY-NEXT: da analyze - output [*|<]!
; CHECK-SIV-ONLY-NEXT: Src: store i8 1, ptr %idx.1, align 1 --> Dst: store i8 1, ptr %idx.1, align 1
; CHECK-SIV-ONLY-NEXT: da analyze - none!
;
Expand Down