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[LAA] Clean up APInt-overflow related code #140048

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Merged
merged 2 commits into from
Jun 30, 2025
Merged

[LAA] Clean up APInt-overflow related code #140048

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[LAA] Clean up APInt-overflow related code
artagnon May 15, 2025
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[LAA] Add comment
artagnon Jun 30, 2025
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31 changes: 14 additions & 17 deletions llvm/lib/Analysis/LoopAccessAnalysis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -949,18 +949,12 @@ getStrideFromAddRec(const SCEVAddRecExpr *AR, const Loop *Lp, Type *AccessTy,
int64_t Size = AllocSize.getFixedValue();

// Huge step value - give up.
if (APStepVal->getBitWidth() > 64)
std::optional<int64_t> StepVal = APStepVal->trySExtValue();
if (!StepVal)
return std::nullopt;

int64_t StepVal = APStepVal->getSExtValue();

// Strided access.
int64_t Stride = StepVal / Size;
int64_t Rem = StepVal % Size;
if (Rem)
return std::nullopt;

return Stride;
return *StepVal % Size ? std::nullopt : std::make_optional(*StepVal / Size);
}

/// Check whether \p AR is a non-wrapping AddRec. If \p Ptr is not nullptr, use
Expand Down Expand Up @@ -2135,15 +2129,18 @@ MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
DL, SE, *(PSE.getSymbolicMaxBackedgeTakenCount()), *Dist, MaxStride))
return Dependence::NoDep;

// Attempt to prove strided accesses independent.
const APInt *ConstDist = nullptr;
if (match(Dist, m_scev_APInt(ConstDist))) {
uint64_t Distance = ConstDist->abs().getZExtValue();
// The rest of this function relies on ConstDist being at most 64-bits, which
// is checked earlier. Will assert if the calling code changes.
const APInt *APDist = nullptr;
uint64_t ConstDist =
match(Dist, m_scev_APInt(APDist)) ? APDist->abs().getZExtValue() : 0;

// Attempt to prove strided accesses independent.
if (APDist) {
// If the distance between accesses and their strides are known constants,
// check whether the accesses interlace each other.
if (Distance > 0 && CommonStride && CommonStride > 1 && HasSameSize &&
areStridedAccessesIndependent(Distance, *CommonStride, TypeByteSize)) {
if (ConstDist > 0 && CommonStride && CommonStride > 1 && HasSameSize &&
areStridedAccessesIndependent(ConstDist, *CommonStride, TypeByteSize)) {
LLVM_DEBUG(dbgs() << "LAA: Strided accesses are independent\n");
return Dependence::NoDep;
}
Expand Down Expand Up @@ -2184,8 +2181,8 @@ MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
FoundNonConstantDistanceDependence |= ShouldRetryWithRuntimeCheck;
return Dependence::Unknown;
}
if (!HasSameSize || couldPreventStoreLoadForward(
ConstDist->abs().getZExtValue(), TypeByteSize)) {
if (!HasSameSize ||
couldPreventStoreLoadForward(ConstDist, TypeByteSize)) {
LLVM_DEBUG(
dbgs() << "LAA: Forward but may prevent st->ld forwarding\n");
return Dependence::ForwardButPreventsForwarding;
Expand Down
14 changes: 6 additions & 8 deletions llvm/test/Analysis/LoopAccessAnalysis/dependences-i128-inductions.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -10,9 +10,9 @@ define void @backward_i128(ptr %A, i128 %n) {
; CHECK-LABEL: 'backward_i128'
; CHECK-NEXT: loop:
; CHECK-NEXT: Report: unsafe dependent memory operations in loop. Use #pragma clang loop distribute(enable) to allow loop distribution to attempt to isolate the offending operations into a separate loop
; CHECK-NEXT: Unsafe indirect dependence.
; CHECK-NEXT: Backward loop carried data dependence.
; CHECK-NEXT: Dependences:
; CHECK-NEXT: IndirectUnsafe:
; CHECK-NEXT: Backward:
; CHECK-NEXT: %l = load i32, ptr %gep.A, align 4 ->
; CHECK-NEXT: store i32 %l, ptr %gep.A.1, align 4
; CHECK-EMPTY:
Expand Down Expand Up @@ -45,10 +45,9 @@ exit:
define void @forward_i128(ptr %A, i128 %n) {
; CHECK-LABEL: 'forward_i128'
; CHECK-NEXT: loop:
; CHECK-NEXT: Report: unsafe dependent memory operations in loop. Use #pragma clang loop distribute(enable) to allow loop distribution to attempt to isolate the offending operations into a separate loop
; CHECK-NEXT: Unsafe indirect dependence.
; CHECK-NEXT: Memory dependences are safe
; CHECK-NEXT: Dependences:
; CHECK-NEXT: IndirectUnsafe:
; CHECK-NEXT: Forward:
; CHECK-NEXT: %l = load i32, ptr %gep.A.1, align 4 ->
; CHECK-NEXT: store i32 %l, ptr %gep.A, align 4
; CHECK-EMPTY:
Expand Down Expand Up @@ -81,10 +80,9 @@ exit:
define void @forward_negative_step(ptr %A, i128 %n) {
; CHECK-LABEL: 'forward_negative_step'
; CHECK-NEXT: loop:
; CHECK-NEXT: Report: unsafe dependent memory operations in loop. Use #pragma clang loop distribute(enable) to allow loop distribution to attempt to isolate the offending operations into a separate loop
; CHECK-NEXT: Unsafe indirect dependence.
; CHECK-NEXT: Memory dependences are safe
; CHECK-NEXT: Dependences:
; CHECK-NEXT: IndirectUnsafe:
; CHECK-NEXT: Forward:
; CHECK-NEXT: %l = load i32, ptr %gep.A, align 4 ->
; CHECK-NEXT: store i32 %l, ptr %gep.A.1, align 4
; CHECK-EMPTY:
Expand Down
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