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[InstCombine] Convert logical and/or with trunc nuw to i1 into bitwise ops #198178

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Merged
andjo403 merged 3 commits into from
May 17, 2026
Merged

[InstCombine] Convert logical and/or with trunc nuw to i1 into bitwise ops #198178

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1ad1640
[InstCombine] Pre commit test (NFC)
andjo403 May 17, 2026
c11b572
[InstCombine] Convert logical and/or with trunc nuw to i1 into bitwis…
andjo403 May 17, 2026
9ea6879
fixup! [InstCombine] Convert logical and/or with trunc nuw to i1 into…
andjo403 May 17, 2026
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18 changes: 13 additions & 5 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3653,7 +3653,7 @@ static Instruction *foldNestedSelects(SelectInst &OuterSelVal,
/// already poison. For example, if ValAssumedPoison is `icmp samesign X, 10`
/// and V is `icmp ne X, 5`, impliesPoisonOrCond returns true.
static bool impliesPoisonOrCond(const Value *ValAssumedPoison, const Value *V,
bool Expected) {
bool Expected, const SimplifyQuery &SQ) {
if (impliesPoison(ValAssumedPoison, V))
return true;

Expand All @@ -3678,6 +3678,14 @@ static bool impliesPoisonOrCond(const Value *ValAssumedPoison, const Value *V,
*RHSC2);
}
}
Value *A;
if (match(ValAssumedPoison, m_NUWTrunc(m_Value(A))) &&
isGuaranteedNotToBePoison(A)) {
assert(ValAssumedPoison->getType()->isIntOrIntVectorTy(1));
return computeKnownBits(
A, SQ.getWithInstruction(cast<Instruction>(ValAssumedPoison)))
.getMaxValue() == 1;
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}

return false;
}
Expand All @@ -3703,13 +3711,13 @@ Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) {
// checks whether folding it does not convert a well-defined value into
// poison.
if (match(TrueVal, m_One())) {
if (impliesPoisonOrCond(FalseVal, CondVal, /*Expected=*/false)) {
if (impliesPoisonOrCond(FalseVal, CondVal, /*Expected=*/false, SQ)) {
// Change: A = select B, true, C --> A = or B, C
return BinaryOperator::CreateOr(CondVal, FalseVal);
}

if (match(CondVal, m_OneUse(m_Select(m_Value(A), m_One(), m_Value(B)))) &&
impliesPoisonOrCond(FalseVal, B, /*Expected=*/false)) {
impliesPoisonOrCond(FalseVal, B, /*Expected=*/false, SQ)) {
// (A || B) || C --> A || (B | C)
Value *LOr = Builder.CreateLogicalOr(A, Builder.CreateOr(B, FalseVal));
if (auto *I = dyn_cast<Instruction>(LOr)) {
Expand Down Expand Up @@ -3749,13 +3757,13 @@ Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) {
}

if (match(FalseVal, m_Zero())) {
if (impliesPoisonOrCond(TrueVal, CondVal, /*Expected=*/true)) {
if (impliesPoisonOrCond(TrueVal, CondVal, /*Expected=*/true, SQ)) {
// Change: A = select B, C, false --> A = and B, C
return BinaryOperator::CreateAnd(CondVal, TrueVal);
}

if (match(CondVal, m_OneUse(m_Select(m_Value(A), m_Value(B), m_Zero()))) &&
impliesPoisonOrCond(TrueVal, B, /*Expected=*/true)) {
impliesPoisonOrCond(TrueVal, B, /*Expected=*/true, SQ)) {
// (A && B) && C --> A && (B & C)
Value *LAnd = Builder.CreateLogicalAnd(A, Builder.CreateAnd(B, TrueVal));
if (auto *I = dyn_cast<Instruction>(LAnd)) {
Expand Down
55 changes: 55 additions & 0 deletions llvm/test/Transforms/InstCombine/logical-select.ll
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Expand Up @@ -1637,3 +1637,58 @@ define <2 x i1> @test_logical_and_icmp_samesign_vec_with_poison_tv(<2 x i8> %x)
%and = select <2 x i1> %cmp1, <2 x i1> %cmp2, <2 x i1> zeroinitializer
ret <2 x i1> %and
}

define i1 @test_logical_and_trunc_nuw(i1 %c, i8 noundef range(i8 0,2) %x) {
; CHECK-LABEL: @test_logical_and_trunc_nuw(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[X:%.*]] to i1
; CHECK-NEXT: [[AND:%.*]] = and i1 [[C:%.*]], [[TRUNC]]
; CHECK-NEXT: ret i1 [[AND]]
;
%trunc = trunc nuw i8 %x to i1
%and = select i1 %c, i1 %trunc, i1 false
ret i1 %and
}

define i1 @test_logical_or_trunc_nuw(i1 %c, i8 noundef range(i8 0,2) %x) {
; CHECK-LABEL: @test_logical_or_trunc_nuw(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[X:%.*]] to i1
; CHECK-NEXT: [[OR:%.*]] = or i1 [[C:%.*]], [[TRUNC]]
; CHECK-NEXT: ret i1 [[OR]]
;
%trunc = trunc nuw i8 %x to i1
%or = select i1 %c, i1 true, i1 %trunc
ret i1 %or
}

define <2 x i1> @test_logical_and_trunc_nuw_vec(<2 x i1> %c, <2 x i8> noundef range(i8 0,2) %x) {
; CHECK-LABEL: @test_logical_and_trunc_nuw_vec(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw <2 x i8> [[X:%.*]] to <2 x i1>
; CHECK-NEXT: [[AND:%.*]] = and <2 x i1> [[C:%.*]], [[TRUNC]]
; CHECK-NEXT: ret <2 x i1> [[AND]]
;
%trunc = trunc nuw <2 x i8> %x to <2 x i1>
%and = select <2 x i1> %c, <2 x i1> %trunc, <2 x i1> zeroinitializer
ret <2 x i1> %and
}

define i1 @neg_test_logical_and_trunc_nuw_no_range(i1 %c, i8 noundef %x) {
; CHECK-LABEL: @neg_test_logical_and_trunc_nuw_no_range(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[X:%.*]] to i1
; CHECK-NEXT: [[AND:%.*]] = select i1 [[C:%.*]], i1 [[TRUNC]], i1 false
; CHECK-NEXT: ret i1 [[AND]]
;
%trunc = trunc nuw i8 %x to i1
%and = select i1 %c, i1 %trunc, i1 false
ret i1 %and
}

define i1 @neg_test_logical_and_trunc_nuw_no_noundef(i1 %c, i8 range(i8 0,2) %x) {
; CHECK-LABEL: @neg_test_logical_and_trunc_nuw_no_noundef(
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[X:%.*]] to i1
; CHECK-NEXT: [[AND:%.*]] = select i1 [[C:%.*]], i1 [[TRUNC]], i1 false
; CHECK-NEXT: ret i1 [[AND]]
;
%trunc = trunc nuw i8 %x to i1
%and = select i1 %c, i1 %trunc, i1 false
ret i1 %and
}