Index: lib/Transforms/Scalar/NaryReassociate.cpp =================================================================== --- lib/Transforms/Scalar/NaryReassociate.cpp +++ lib/Transforms/Scalar/NaryReassociate.cpp @@ -463,6 +463,12 @@ Instruction *NaryReassociatePass::tryReassociatedBinaryOp(const SCEV *LHSExpr, Value *RHS, BinaryOperator *I) { + // Need to avoid special case (C1*v)*(C2*v) = 0 because of overflow and + // there is Instruction "mul x, 0", as it leads to infinite loop + if (I->getOpcode() == Instruction::Mul && LHSExpr->isZero() && + SE->getSCEV(RHS)->isZero()) + return nullptr; + // Look for the closest dominator LHS of I that computes LHSExpr, and replace // I with LHS op RHS. auto *LHS = findClosestMatchingDominator(LHSExpr, I); Index: test/Transforms/NaryReassociate/pr35710.ll =================================================================== --- test/Transforms/NaryReassociate/pr35710.ll +++ test/Transforms/NaryReassociate/pr35710.ll @@ -0,0 +1,19 @@ +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py +; RUN: opt < %s -nary-reassociate -S | FileCheck %s + +; The test check that compilation does not fall into infinite loop. + +define i8 @foo(i8 %v) local_unnamed_addr #0 { +; CHECK-LABEL: @foo( +; CHECK-NEXT: region.0: +; CHECK-NEXT: [[TMP0:%.*]] = mul nsw i8 16, [[V:%.*]] +; CHECK-NEXT: [[TMP1:%.*]] = mul nsw i8 0, [[TMP0]] +; CHECK-NEXT: [[TMP2:%.*]] = mul i8 [[TMP1]], [[TMP0]] +; CHECK-NEXT: ret i8 [[TMP2]] +; +region.0: + %0 = mul nsw i8 16, %v + %1 = mul nsw i8 0, %0 + %2 = mul nsw i8 1, %1 + ret i8 %2 +}