[llvm] [ValueTracking] Support trunc nuw condition in isImpliedCondition (PR #141528)
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llvm-commits at lists.llvm.org
Mon May 26 13:40:24 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-analysis
Author: Andreas Jonson (andjo403)
<details>
<summary>Changes</summary>
Many trunc nuw conditions is implied/implies icmp instructions.
Proof: https://alive2.llvm.org/ce/z/oqQyxC
cc https://github.com/llvm/llvm-project/issues/134093
---
Full diff: https://github.com/llvm/llvm-project/pull/141528.diff
2 Files Affected:
- (modified) llvm/lib/Analysis/ValueTracking.cpp (+23-10)
- (modified) llvm/test/Transforms/InstCombine/select-safe-impliedcond-transforms.ll (+82)
``````````diff
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 5b9338b500ecc..b7084cf3619f3 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -9165,15 +9165,13 @@ isImpliedCondCommonOperandWithCR(CmpPredicate LPred, const ConstantRange &LCR,
/// is true. Return false if LHS implies RHS is false. Otherwise, return
/// std::nullopt if we can't infer anything.
static std::optional<bool>
-isImpliedCondICmps(const ICmpInst *LHS, CmpPredicate RPred, const Value *R0,
- const Value *R1, const DataLayout &DL, bool LHSIsTrue) {
- Value *L0 = LHS->getOperand(0);
- Value *L1 = LHS->getOperand(1);
-
+isImpliedCondICmps(CmpPredicate LPred, const Value *L0, const Value *L1,
+ CmpPredicate RPred, const Value *R0, const Value *R1,
+ const DataLayout &DL, bool LHSIsTrue) {
// The rest of the logic assumes the LHS condition is true. If that's not the
// case, invert the predicate to make it so.
- CmpPredicate LPred =
- LHSIsTrue ? LHS->getCmpPredicate() : LHS->getInverseCmpPredicate();
+ if (!LHSIsTrue)
+ LPred = ICmpInst::getInverseCmpPredicate(LPred);
// We can have non-canonical operands, so try to normalize any common operand
// to L0/R0.
@@ -9314,9 +9312,15 @@ llvm::isImpliedCondition(const Value *LHS, CmpPredicate RHSPred,
LHSIsTrue = !LHSIsTrue;
// Both LHS and RHS are icmps.
- const ICmpInst *LHSCmp = dyn_cast<ICmpInst>(LHS);
- if (LHSCmp)
- return isImpliedCondICmps(LHSCmp, RHSPred, RHSOp0, RHSOp1, DL, LHSIsTrue);
+ if (const auto *LHSCmp = dyn_cast<ICmpInst>(LHS))
+ return isImpliedCondICmps(LHSCmp->getCmpPredicate(), LHSCmp->getOperand(0),
+ LHSCmp->getOperand(1), RHSPred, RHSOp0, RHSOp1,
+ DL, LHSIsTrue);
+ const Value *V;
+ if (match(LHS, m_NUWTrunc(m_Value(V))))
+ return isImpliedCondICmps(CmpInst::ICMP_NE, V,
+ ConstantInt::get(V->getType(), 0), RHSPred,
+ RHSOp0, RHSOp1, DL, LHSIsTrue);
/// The LHS should be an 'or', 'and', or a 'select' instruction. We expect
/// the RHS to be an icmp.
@@ -9354,6 +9358,15 @@ std::optional<bool> llvm::isImpliedCondition(const Value *LHS, const Value *RHS,
return std::nullopt;
}
+ const Value *V;
+ if (match(RHS, m_NUWTrunc(m_Value(V)))) {
+ if (auto Implied = isImpliedCondition(LHS, CmpInst::ICMP_NE, V,
+ ConstantInt::get(V->getType(), 0), DL,
+ LHSIsTrue, Depth))
+ return InvertRHS ? !*Implied : *Implied;
+ return std::nullopt;
+ }
+
if (Depth == MaxAnalysisRecursionDepth)
return std::nullopt;
diff --git a/llvm/test/Transforms/InstCombine/select-safe-impliedcond-transforms.ll b/llvm/test/Transforms/InstCombine/select-safe-impliedcond-transforms.ll
index 4b66b71773683..ba34930dc14c1 100644
--- a/llvm/test/Transforms/InstCombine/select-safe-impliedcond-transforms.ll
+++ b/llvm/test/Transforms/InstCombine/select-safe-impliedcond-transforms.ll
@@ -176,3 +176,85 @@ define i1 @a_false_implies_b_false2_comm(i8 %z, i1 %X, i1 %Y) {
%res = or i1 %sel, %a
ret i1 %res
}
+
+define i1 @trunc_nuw_implies_icmp_eq(i8 %x, i1 %c) {
+; CHECK-LABEL: @trunc_nuw_implies_icmp_eq(
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i8 [[X:%.*]] to i1
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[TRUNC]], i1 true, i1 [[C:%.*]]
+; CHECK-NEXT: ret i1 [[SEL2]]
+;
+ %trunc = trunc nuw i8 %x to i1
+ %cmp = icmp eq i8 %x, 0
+ %sel1 = select i1 %cmp, i1 %c, i1 false
+ %sel2 = select i1 %trunc, i1 true, i1 %sel1
+ ret i1 %sel2
+}
+
+define i1 @icmp_eq_implies_trunc_nuw(i8 %x, i1 %c) {
+; CHECK-LABEL: @icmp_eq_implies_trunc_nuw(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP]], i1 true, i1 [[C:%.*]]
+; CHECK-NEXT: ret i1 [[SEL2]]
+;
+ %trunc = trunc nuw i8 %x to i1
+ %cmp = icmp eq i8 %x, 0
+ %sel1 = select i1 %trunc, i1 %c, i1 false
+ %sel2 = select i1 %cmp, i1 true, i1 %sel1
+ ret i1 %sel2
+}
+
+define <2 x i1> @trunc_nuw_implies_icmp_eq_vec(<2 x i8> %x, <2 x i1> %c) {
+; CHECK-LABEL: @trunc_nuw_implies_icmp_eq_vec(
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw <2 x i8> [[X:%.*]] to <2 x i1>
+; CHECK-NEXT: [[SEL2:%.*]] = select <2 x i1> [[TRUNC]], <2 x i1> splat (i1 true), <2 x i1> [[C:%.*]]
+; CHECK-NEXT: ret <2 x i1> [[SEL2]]
+;
+ %trunc = trunc nuw <2 x i8> %x to <2 x i1>
+ %cmp = icmp eq <2 x i8> %x, splat (i8 0)
+ %sel1 = select <2 x i1> %cmp, <2 x i1> %c, <2 x i1> splat (i1 false)
+ %sel2 = select <2 x i1> %trunc, <2 x i1> splat (i1 true), <2 x i1> %sel1
+ ret <2 x i1> %sel2
+}
+
+define <2 x i1> @icmp_eq_implies_trunc_nuw_vec(<2 x i8> %x, <2 x i1> %c) {
+; CHECK-LABEL: @icmp_eq_implies_trunc_nuw_vec(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i8> [[X:%.*]], zeroinitializer
+; CHECK-NEXT: [[SEL2:%.*]] = select <2 x i1> [[CMP]], <2 x i1> splat (i1 true), <2 x i1> [[C:%.*]]
+; CHECK-NEXT: ret <2 x i1> [[SEL2]]
+;
+ %trunc = trunc nuw <2 x i8> %x to <2 x i1>
+ %cmp = icmp eq <2 x i8> %x, splat (i8 0)
+ %sel1 = select <2 x i1> %trunc, <2 x i1> %c, <2 x i1> splat (i1 false)
+ %sel2 = select <2 x i1> %cmp, <2 x i1> splat (i1 true), <2 x i1> %sel1
+ ret <2 x i1> %sel2
+}
+
+define i1 @neg_trunc_implies_icmp_eq(i8 %x, i1 %c) {
+; CHECK-LABEL: @neg_trunc_implies_icmp_eq(
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[X:%.*]] to i1
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], 0
+; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP]], i1 [[C:%.*]], i1 false
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[TRUNC]], i1 true, i1 [[SEL1]]
+; CHECK-NEXT: ret i1 [[SEL2]]
+;
+ %trunc = trunc i8 %x to i1
+ %cmp = icmp eq i8 %x, 0
+ %sel1 = select i1 %cmp, i1 %c, i1 false
+ %sel2 = select i1 %trunc, i1 true, i1 %sel1
+ ret i1 %sel2
+}
+
+define i1 @neg_icmp_eq_implies_trunc(i8 %x, i1 %c) {
+; CHECK-LABEL: @neg_icmp_eq_implies_trunc(
+; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[X:%.*]] to i1
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], 0
+; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[TRUNC]], i1 [[C:%.*]], i1 false
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP]], i1 true, i1 [[SEL1]]
+; CHECK-NEXT: ret i1 [[SEL2]]
+;
+ %trunc = trunc i8 %x to i1
+ %cmp = icmp eq i8 %x, 0
+ %sel1 = select i1 %trunc, i1 %c, i1 false
+ %sel2 = select i1 %cmp, i1 true, i1 %sel1
+ ret i1 %sel2
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/141528
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