[InstCombine] Convert logical and/or with trunc nuw to i1 into bitwise ops#198178
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…e ops iff trunc nuw to i1 can not be poison.
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@llvm/pr-subscribers-llvm-transforms Author: Andreas Jonson (andjo403) Changesif it is know that regression seen in dtcxzyw/llvm-opt-benchmark#3528 (comment) from #184182 proof https://alive2.llvm.org/ce/z/xQ2Sj- Full diff: https://github.com/llvm/llvm-project/pull/198178.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index a064aa1016399..4a47a2a06809b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -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;
@@ -3678,6 +3678,16 @@ 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));
+ unsigned BitWidth = A->getType()->getScalarSizeInBits();
+ return ConstantRange(APInt::getZero(BitWidth), APInt(BitWidth, 2))
+ .contains(computeConstantRangeIncludingKnownBits(
+ A, false,
+ SQ.getWithInstruction(cast<Instruction>(ValAssumedPoison))));
+ }
return false;
}
@@ -3703,13 +3713,13 @@ 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)) {
@@ -3749,13 +3759,13 @@ 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)) {
diff --git a/llvm/test/Transforms/InstCombine/logical-select.ll b/llvm/test/Transforms/InstCombine/logical-select.ll
index e6de063969a6a..85e8c98455c91 100644
--- a/llvm/test/Transforms/InstCombine/logical-select.ll
+++ b/llvm/test/Transforms/InstCombine/logical-select.ll
@@ -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
+}
|
nikic
reviewed
May 17, 2026
| assert(ValAssumedPoison->getType()->isIntOrIntVectorTy(1)); | ||
| unsigned BitWidth = A->getType()->getScalarSizeInBits(); | ||
| return ConstantRange(APInt::getZero(BitWidth), APInt(BitWidth, 2)) | ||
| .contains(computeConstantRangeIncludingKnownBits( |
Contributor
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Can you use just computeKnownBits here? I don't think computeConstantRange() adds any precision here, as it's a power of 2 range.
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no changes in local run of llvm-opt-benchmark with the change so fix pushed
MaxGraey
reviewed
May 17, 2026
pedroMVicente
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that referenced
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May 19, 2026
…e ops (llvm#198178) if it is know that `trunc nuw to i1 ` can not be poison logical and/or can be folded to bitwise ops. proof https://alive2.llvm.org/ce/z/xQ2Sj-
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if it is know that
trunc nuw to i1can not be poison logical and/or can be folded to bitwise ops.regression seen in dtcxzyw/llvm-opt-benchmark#3528 (comment) from #184182
proof https://alive2.llvm.org/ce/z/xQ2Sj-