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[LICM] Use OverflowTracking to preserve NUW/NSW when reassociating. #140404

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Merged
merged 1 commit into from
May 20, 2025
+13 −10
Merged

[LICM] Use OverflowTracking to preserve NUW/NSW when reassociating. #140404

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19 changes: 11 additions & 8 deletions llvm/lib/Transforms/Scalar/LICM.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2864,14 +2864,7 @@ static bool hoistBOAssociation(Instruction &I, Loop &L,
auto *NewBO = BinaryOperator::Create(
Opcode, LV, Inv, BO->getName() + ".reass", BO->getIterator());

// Copy NUW for ADDs if both instructions have it.
if (Opcode == Instruction::Add && BO->hasNoUnsignedWrap() &&
BO0->hasNoUnsignedWrap()) {
// If `Inv` was not constant-folded, a new Instruction has been created.
if (auto *I = dyn_cast<Instruction>(Inv))
I->setHasNoUnsignedWrap(true);
NewBO->setHasNoUnsignedWrap(true);
} else if (Opcode == Instruction::FAdd || Opcode == Instruction::FMul) {
if (Opcode == Instruction::FAdd || Opcode == Instruction::FMul) {
// Intersect FMF flags for FADD and FMUL.
FastMathFlags Intersect = BO->getFastMathFlags() & BO0->getFastMathFlags();
if (auto *I = dyn_cast<Instruction>(Inv))
Expand All @@ -2884,6 +2877,16 @@ static bool hoistBOAssociation(Instruction &I, Loop &L,
if (auto *I = dyn_cast<PossiblyDisjointInst>(Inv))
I->setIsDisjoint(Disjoint);
cast<PossiblyDisjointInst>(NewBO)->setIsDisjoint(Disjoint);
} else {
OverflowTracking Flags;
Flags.AllKnownNonNegative = false;
Flags.AllKnownNonZero = false;
Flags.mergeFlags(*BO);
Flags.mergeFlags(*BO0);
// If `Inv` was not constant-folded, a new Instruction has been created.
if (auto *I = dyn_cast<Instruction>(Inv))
Flags.applyFlags(*I);
Flags.applyFlags(*NewBO);
}

BO->replaceAllUsesWith(NewBO);
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4 changes: 2 additions & 2 deletions llvm/test/Transforms/LICM/hoist-binop.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -371,13 +371,13 @@ loop:
define void @add_nuw_nsw(i64 %c1, i64 %c2) {
; CHECK-LABEL: @add_nuw_nsw(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[INVARIANT_OP:%.*]] = add nuw i64 [[C1:%.*]], [[C2:%.*]]
; CHECK-NEXT: [[INVARIANT_OP:%.*]] = add nuw nsw i64 [[C1:%.*]], [[C2:%.*]]
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INDEX_NEXT_REASS:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[STEP_ADD:%.*]] = add nuw nsw i64 [[INDEX]], [[C1]]
; CHECK-NEXT: call void @use(i64 [[STEP_ADD]])
; CHECK-NEXT: [[INDEX_NEXT_REASS]] = add nuw i64 [[INDEX]], [[INVARIANT_OP]]
; CHECK-NEXT: [[INDEX_NEXT_REASS]] = add nuw nsw i64 [[INDEX]], [[INVARIANT_OP]]
; CHECK-NEXT: br label [[LOOP]]
;
entry:
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