Index: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp =================================================================== --- llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp +++ llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp @@ -1013,6 +1013,12 @@ Cmp.getPredicate() == CanonicalPred) return nullptr; + // Bail out on unsimplified X-0 operand (due to some worklist management bug), + // as this may cause an infinite combine loop. Let the sub be folded first. + if (match(LHS, m_Sub(m_Value(), m_Zero())) || + match(RHS, m_Sub(m_Value(), m_Zero()))) + return nullptr; + // Create the canonical compare and plug it into the select. Sel.setCondition(Builder.CreateICmp(CanonicalPred, LHS, RHS)); Index: llvm/test/Transforms/InstCombine/pr44541.ll =================================================================== --- /dev/null +++ llvm/test/Transforms/InstCombine/pr44541.ll @@ -0,0 +1,25 @@ +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py +; RUN: opt -S -instcombine -expensive-combines=0 -instcombine-infinite-loop-threshold=3 < %s | FileCheck %s + +; This test used to cause an infinite combine loop. + +define i16 @passthru(i16 returned %x) { +; CHECK-LABEL: @passthru( +; CHECK-NEXT: ret i16 [[X:%.*]] +; + ret i16 %x +} + +define i16 @test(i16 %arg) { +; CHECK-LABEL: @test( +; CHECK-NEXT: [[ZERO:%.*]] = call i16 @passthru(i16 0) +; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i16 [[ARG:%.*]], 0 +; CHECK-NEXT: [[RET:%.*]] = select i1 [[TMP1]], i16 [[ARG]], i16 0 +; CHECK-NEXT: ret i16 [[RET]] +; + %zero = call i16 @passthru(i16 0) + %sub = sub nuw nsw i16 %arg, %zero + %cmp = icmp slt i16 %sub, 0 + %ret = select i1 %cmp, i16 0, i16 %sub + ret i16 %ret +}