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[InstCombine] Avoid infinite loop in foldSelectValueEquivalence #142754

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Merged
dtcxzyw merged 1 commit into from
Jun 4, 2025
Merged

[InstCombine] Avoid infinite loop in foldSelectValueEquivalence #142754

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6 changes: 5 additions & 1 deletion llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1312,7 +1312,11 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,

// If NewOp is a constant and OldOp is not replace iff NewOp doesn't
// contain and undef elements.
if (match(NewOp, m_ImmConstant()) || NewOp == V) {
// Make sure that V is always simpler than TrueVal, otherwise we might
// end up in an infinite loop.
if (match(NewOp, m_ImmConstant()) ||
(isa<Instruction>(TrueVal) &&
is_contained(cast<Instruction>(TrueVal)->operands(), V))) {
if (isGuaranteedNotToBeUndef(NewOp, SQ.AC, &Sel, &DT))
return replaceOperand(Sel, Swapped ? 2 : 1, V);
return nullptr;
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20 changes: 20 additions & 0 deletions llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll
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Expand Up @@ -182,3 +182,23 @@ define i8 @replace_with_y_for_simple_binop_fail(i8 %x, i8 noundef %y, i8 %z, i8
%sel = select i1 %cmp, i8 %mul, i8 %z
ret i8 %sel
}

; Make sure we don't run into an infinite loop.
define i32 @pr142405(i32 noundef %x) {
; CHECK-LABEL: @pr142405(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SMAX:%.*]] = call i32 @llvm.smax.i32(i32 [[X:%.*]], i32 0)
; CHECK-NEXT: [[MASKED:%.*]] = and i32 [[SMAX]], 65535
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[X]], [[MASKED]]
; CHECK-NEXT: [[TMP0:%.*]] = and i32 [[SMAX]], 1
; CHECK-NEXT: [[AND:%.*]] = select i1 [[CMP]], i32 [[TMP0]], i32 0
; CHECK-NEXT: ret i32 [[AND]]
;
entry:
%smax = call i32 @llvm.smax.i32(i32 %x, i32 0)
%masked = and i32 %smax, 65535
%cmp = icmp eq i32 %x, %masked
%sel = select i1 %cmp, i32 %smax, i32 0
%and = and i32 %sel, 1
ret i32 %and
}
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