diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp index 188c045a0dee..796b4021d273 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp @@ -54,38 +54,34 @@ static Value *createMinMax(InstCombiner::BuilderTy &Builder, return Builder.CreateSelect(Builder.CreateICmp(Pred, A, B), A, B); } -/// Replace a select operand based on an equality comparison with the identity -/// constant of a binop. +/// Fold +/// %A = icmp eq/ne i8 %x, 0 +/// %B = op i8 %x, %z +/// %C = select i1 %A, i8 %B, i8 %y +/// To +/// %C = select i1 %A, i8 %z, i8 %y +/// OP: binop with an identity constant +/// TODO: support for non-commutative and FP opcodes static Instruction *foldSelectBinOpIdentity(SelectInst &Sel) { - // The select condition must be an equality compare with a constant operand. - // TODO: Support FP compares. - Value *X; + + Value *Cond = Sel.getCondition(); + Value *X, *Z; Constant *C; CmpInst::Predicate Pred; - if (!match(Sel.getCondition(), m_ICmp(Pred, m_Value(X), m_Constant(C))) || + if (!match(Cond, m_ICmp(Pred, m_Value(X), m_Constant(C))) || !ICmpInst::isEquality(Pred)) return nullptr; - // A select operand must be a binop, and the compare constant must be the - // identity constant for that binop. - // TODO: Support non-commutative binops. bool IsEq = Pred == ICmpInst::ICMP_EQ; - BinaryOperator *BO; - if (!match(Sel.getOperand(IsEq ? 1 : 2), m_BinOp(BO)) || - ConstantExpr::getBinOpIdentity(BO->getOpcode(), X->getType(), false) != C) - return nullptr; - - // Last, match the compare variable operand with a binop operand. - Value *Y; - if (!match(BO, m_c_BinOp(m_Value(Y), m_Specific(X)))) - return nullptr; - - // BO = binop Y, X - // S = { select (cmp eq X, C), BO, ? } or { select (cmp ne X, C), ?, BO } - // => - // S = { select (cmp eq X, C), Y, ? } or { select (cmp ne X, C), ?, Y } - Sel.setOperand(IsEq ? 1 : 2, Y); - return &Sel; + auto *BO = + dyn_cast(IsEq ? Sel.getTrueValue() : Sel.getFalseValue()); + // TODO: support for undefs + if (BO && match(BO, m_c_BinOp(m_Specific(X), m_Value(Z))) && + ConstantExpr::getBinOpIdentity(BO->getOpcode(), X->getType()) == C) { + Sel.setOperand(IsEq ? 1 : 2, Z); + return &Sel; + } + return nullptr; } /// This folds: