diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp --- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp +++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp @@ -8264,10 +8264,32 @@ } static SDValue performSUBCombine(SDNode *N, SelectionDAG &DAG) { - // fold (sub x, (select lhs, rhs, cc, 0, y)) -> - // (select lhs, rhs, cc, x, (sub x, y)) SDValue N0 = N->getOperand(0); SDValue N1 = N->getOperand(1); + + // Prefer to make this 'add 0/1' rather than 'sub 0/1' + // sub constant(!0), 0/1 -> add constant - 1, 1/0 + // NODE: constant == 0, No redundant instructions are generated. + // (sub constant, (setcc x, y, eq/neq)) -> + // (add (setcc x, y, neq/eq), constant - 1) + auto *Nnz0 = dyn_cast(N0); + if (Nnz0 && N1.getOpcode() == ISD::SETCC && N1.hasOneUse()) { + const auto *CC = cast(N1->getOperand(2)); + ISD::CondCode CCVal = CC->get(); + if (!Nnz0->isZero() && isIntEqualitySetCC(CCVal)) { + EVT VT = N->getValueType(0); + const APInt &ImmVal = Nnz0->getAPIntValue(); + SDValue CCInverse = + DAG.getCondCode(ISD::getSetCCInverse(CCVal, N0.getValueType())); + SDValue NewN0 = DAG.getNode(ISD::SETCC, SDLoc(N), VT, N1->getOperand(0), + N1->getOperand(1), CCInverse); + SDValue NewN1 = DAG.getConstant(ImmVal - 1, SDLoc(N), VT); + return DAG.getNode(ISD::ADD, SDLoc(N), VT, NewN0, NewN1); + } + } + + // fold (sub x, (select lhs, rhs, cc, 0, y)) -> + // (select lhs, rhs, cc, x, (sub x, y)) return combineSelectAndUse(N, N1, N0, DAG, /*AllOnes*/ false); } diff --git a/llvm/test/CodeGen/RISCV/setcc-logic.ll b/llvm/test/CodeGen/RISCV/setcc-logic.ll --- a/llvm/test/CodeGen/RISCV/setcc-logic.ll +++ b/llvm/test/CodeGen/RISCV/setcc-logic.ll @@ -118,3 +118,24 @@ %r = and i1 %a, %b ret i1 %r } + +define i32 @bar(i32 %n) { +; RV32I-LABEL: bar: +; RV32I: # %bb.0: # %entry +; RV32I-NEXT: addi a0, a0, -9 +; RV32I-NEXT: snez a0, a0 +; RV32I-NEXT: addi a0, a0, 1 +; RV32I-NEXT: ret +; +; RV64I-LABEL: bar: +; RV64I: # %bb.0: # %entry +; RV64I-NEXT: sext.w a0, a0 +; RV64I-NEXT: addi a0, a0, -9 +; RV64I-NEXT: snez a0, a0 +; RV64I-NEXT: addi a0, a0, 1 +; RV64I-NEXT: ret +entry: + %cmp = icmp eq i32 %n, 9 + %a = select i1 %cmp, i32 1, i32 2 + ret i32 %a +}