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[BasicAA] Make use of nusw+nuw -> nneg implication #102141

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Merged
merged 1 commit into from
Aug 7, 2024
Merged

[BasicAA] Make use of nusw+nuw -> nneg implication #102141

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10 changes: 8 additions & 2 deletions llvm/lib/Analysis/BasicAliasAnalysis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -337,6 +337,10 @@ struct CastedValue {
assert(N.getBitWidth() == V->getType()->getPrimitiveSizeInBits() &&
"Incompatible bit width");
if (TruncBits) N = N.truncate(N.getBitWidth() - TruncBits);
if (IsNonNegative && !N.isAllNonNegative())
N = N.intersectWith(
ConstantRange(APInt::getZero(N.getBitWidth()),
APInt::getSignedMinValue(N.getBitWidth())));
if (SExtBits) N = N.signExtend(N.getBitWidth() + SExtBits);
if (ZExtBits) N = N.zeroExtend(N.getBitWidth() + ZExtBits);
return N;
Expand Down Expand Up @@ -693,15 +697,17 @@ BasicAAResult::DecomposeGEPExpression(const Value *V, const DataLayout &DL,

// If the integer type is smaller than the index size, it is implicitly
// sign extended or truncated to index size.
bool NUSW = GEPOp->hasNoUnsignedSignedWrap();
bool NonNeg = NUSW && GEPOp->hasNoUnsignedWrap();
unsigned Width = Index->getType()->getIntegerBitWidth();
unsigned SExtBits = IndexSize > Width ? IndexSize - Width : 0;
unsigned TruncBits = IndexSize < Width ? Width - IndexSize : 0;
LinearExpression LE = GetLinearExpression(
CastedValue(Index, 0, SExtBits, TruncBits, false), DL, 0, AC, DT);
CastedValue(Index, 0, SExtBits, TruncBits, NonNeg), DL, 0, AC, DT);

// Scale by the type size.
unsigned TypeSize = AllocTypeSize.getFixedValue();
LE = LE.mul(APInt(IndexSize, TypeSize), GEPOp->hasNoUnsignedSignedWrap());
LE = LE.mul(APInt(IndexSize, TypeSize), NUSW);
Decomposed.Offset += LE.Offset.sext(MaxIndexSize);
APInt Scale = LE.Scale.sext(MaxIndexSize);

Expand Down
20 changes: 20 additions & 0 deletions llvm/test/Analysis/BasicAA/nusw_nuw_nonneg.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
; RUN: opt < %s -passes=aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s

; CHECK-LABEL: test
; CHECK: NoAlias: i8* %p.minus.2, i8* %p.plus.2
; CHECK: MayAlias: i8* %p.idx.maybeneg, i8* %p.minus.2
; CHECK: MayAlias: i8* %p.idx.maybeneg, i8* %p.plus.2
; CHECK: NoAlias: i8* %p.idx.nneg, i8* %p.minus.2
; CHECK: MayAlias: i8* %p.idx.nneg, i8* %p.plus.2
; CHECK: MustAlias: i8* %p.idx.maybeneg, i8* %p.idx.nneg
define void @test(ptr %p, i64 %idx) {
%p.minus.2 = getelementptr i8, ptr %p, i64 -2
%p.plus.2 = getelementptr i8, ptr %p, i64 2
%p.idx.maybeneg = getelementptr inbounds i8, ptr %p, i64 %idx
%p.idx.nneg = getelementptr nuw nusw i8, ptr %p, i64 %idx
load i8, ptr %p.minus.2
load i8, ptr %p.plus.2
load i8, ptr %p.idx.maybeneg
load i8, ptr %p.idx.nneg
ret void
}
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