diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp --- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp @@ -2853,15 +2853,17 @@ // (C && A) || (!C && B) --> sel C, A, B // (A && C) || (!C && B) --> sel C, A, B // (C && A) || (B && !C) --> sel C, A, B - // (A && C) || (B && !C) --> sel C, A, B (only with real 'and' ops) + // (A && C) || (B && !C) --> sel C, A, B (may require freeze) if (match(FalseVal, m_c_LogicalAnd(m_Not(m_Value(C)), m_Value(B))) && match(CondVal, m_c_LogicalAnd(m_Specific(C), m_Value(A)))) { auto *SelCond = dyn_cast(CondVal); auto *SelFVal = dyn_cast(FalseVal); - if (!SelCond || !SelFVal || - !match(SelFVal->getTrueValue(), - m_Not(m_Specific(SelCond->getTrueValue())))) - return SelectInst::Create(C, A, B); + bool MayNeedFreeze = SelCond && SelFVal && + match(SelFVal->getTrueValue(), + m_Not(m_Specific(SelCond->getTrueValue()))); + if (MayNeedFreeze) + C = Builder.CreateFreeze(C); + return SelectInst::Create(C, A, B); } // (!C && A) || (C && B) --> sel C, B, A diff --git a/llvm/test/Transforms/InstCombine/select-safe-transforms.ll b/llvm/test/Transforms/InstCombine/select-safe-transforms.ll --- a/llvm/test/Transforms/InstCombine/select-safe-transforms.ll +++ b/llvm/test/Transforms/InstCombine/select-safe-transforms.ll @@ -529,14 +529,12 @@ ret i1 %or } -; This is not safe to transform if 'c' could be poison. +; Freeze 'c' to prevent poison from leaking. define i1 @bools2_logical_commute3(i1 %a, i1 %b, i1 %c) { ; CHECK-LABEL: @bools2_logical_commute3( -; CHECK-NEXT: [[NOT:%.*]] = xor i1 [[C:%.*]], true -; CHECK-NEXT: [[AND1:%.*]] = select i1 [[A:%.*]], i1 [[C]], i1 false -; CHECK-NEXT: [[AND2:%.*]] = select i1 [[B:%.*]], i1 [[NOT]], i1 false -; CHECK-NEXT: [[OR:%.*]] = select i1 [[AND1]], i1 true, i1 [[AND2]] +; CHECK-NEXT: [[TMP1:%.*]] = freeze i1 [[C:%.*]] +; CHECK-NEXT: [[OR:%.*]] = select i1 [[TMP1]], i1 [[A:%.*]], i1 [[B:%.*]] ; CHECK-NEXT: ret i1 [[OR]] ; %not = xor i1 %c, -1 @@ -546,6 +544,9 @@ ret i1 %or } +; No freeze needed when 'c' is guaranteed not be poison. +; Intermediate logic folds may already reduce this. + define i1 @bools2_logical_commute3_nopoison(i1 %a, i1 %b, i1 noundef %c) { ; CHECK-LABEL: @bools2_logical_commute3_nopoison( ; CHECK-NEXT: [[OR:%.*]] = select i1 [[C:%.*]], i1 [[A:%.*]], i1 [[B:%.*]]