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[SCEVExpander] Do not reuse disjoint or #80281

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Merged
merged 1 commit into from
Feb 2, 2024
Merged

[SCEVExpander] Do not reuse disjoint or #80281

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7 changes: 7 additions & 0 deletions llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1398,6 +1398,13 @@ canReuseInstruction(ScalarEvolution &SE, const SCEV *S, Instruction *I,
if (!I)
return false;

// Disjoint or instructions are interpreted as adds by SCEV. However, we
// can't replace an arbitrary add with disjoint or, even if we drop the
// flag. We would need to convert the or into an add.
if (auto *PDI = dyn_cast<PossiblyDisjointInst>(I))
if (PDI->isDisjoint())
return false;

// FIXME: Ignore vscale, even though it technically could be poison. Do this
// because SCEV currently assumes it can't be poison. Remove this special
// case once we proper model when vscale can be poison.
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5 changes: 3 additions & 2 deletions llvm/test/Transforms/IndVarSimplify/pr79861.ll
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Expand Up @@ -75,14 +75,15 @@ define void @expander_or_disjoint(i64 %n) {
; CHECK-LABEL: define void @expander_or_disjoint(
; CHECK-SAME: i64 [[N:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[OR:%.*]] = or i64 [[N]], 1
; CHECK-NEXT: [[OR:%.*]] = or disjoint i64 [[N]], 1
; CHECK-NEXT: [[TMP0:%.*]] = add i64 [[N]], 1
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_INC:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[IV_INC]] = add i64 [[IV]], 1
; CHECK-NEXT: [[ADD:%.*]] = add i64 [[IV]], [[OR]]
; CHECK-NEXT: call void @use(i64 [[ADD]])
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i64 [[IV_INC]], [[OR]]
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i64 [[IV_INC]], [[TMP0]]
; CHECK-NEXT: br i1 [[EXITCOND]], label [[LOOP]], label [[EXIT:%.*]]
; CHECK: exit:
; CHECK-NEXT: ret void
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