Index: llvm/lib/Target/AArch64/AArch64ISelLowering.cpp =================================================================== --- llvm/lib/Target/AArch64/AArch64ISelLowering.cpp +++ llvm/lib/Target/AArch64/AArch64ISelLowering.cpp @@ -16854,6 +16854,30 @@ return SDValue(); } +// ((X >> C) - Y) + Z --> (Z - Y) + (X >> C) +static SDValue performAddCombineSubShift(SDNode *N, SDValue SUB, SDValue Z, + SelectionDAG &DAG) { + if (isa(Z)) + return SDValue(); + + if (SUB.getOpcode() != ISD::SUB || !SUB.hasOneUse()) + return SDValue(); + + SDValue SHL = SUB.getOperand(0); + if (SHL.getOpcode() != ISD::SHL || !SHL.hasOneUse()) + return SDValue(); + + if (!isa(SHL.getOperand(1))) + return SDValue(); + + SDLoc DL(N); + EVT VT = N->getValueType(0); + + SDValue Y = SUB.getOperand(1); + SDValue NewSub = DAG.getNode(ISD::SUB, DL, VT, Z, Y); + return DAG.getNode(ISD::ADD, DL, VT, NewSub, SHL); +} + static SDValue performAddCombineForShiftedOperands(SDNode *N, SelectionDAG &DAG) { // NOTE: Swapping LHS and RHS is not done for SUB, since SUB is not @@ -16871,6 +16895,11 @@ SDValue LHS = N->getOperand(0); SDValue RHS = N->getOperand(1); + if (SDValue Val = performAddCombineSubShift(N, LHS, RHS, DAG)) + return Val; + if (SDValue Val = performAddCombineSubShift(N, RHS, LHS, DAG)) + return Val; + uint64_t LHSImm = 0, RHSImm = 0; // If both operand are shifted by imm and shift amount is not greater than 4 // for one operand, swap LHS and RHS to put operand with smaller shift amount Index: llvm/test/CodeGen/AArch64/addsub.ll =================================================================== --- llvm/test/CodeGen/AArch64/addsub.ll +++ llvm/test/CodeGen/AArch64/addsub.ll @@ -697,9 +697,8 @@ define i32 @commute_subop0(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: commute_subop0: ; CHECK: // %bb.0: -; CHECK-NEXT: lsl w8, w0, #3 -; CHECK-NEXT: sub w8, w8, w1 -; CHECK-NEXT: add w0, w8, w2 +; CHECK-NEXT: sub w8, w2, w1 +; CHECK-NEXT: add w0, w8, w0, lsl #3 ; CHECK-NEXT: ret %shl = shl i32 %x, 3 %sub = sub i32 %shl, %y @@ -710,9 +709,8 @@ define i32 @commute_subop0_cadd(i32 %x, i32 %y, i32 %z) { ; CHECK-LABEL: commute_subop0_cadd: ; CHECK: // %bb.0: -; CHECK-NEXT: lsl w8, w0, #3 -; CHECK-NEXT: sub w8, w8, w1 -; CHECK-NEXT: add w0, w2, w8 +; CHECK-NEXT: sub w8, w2, w1 +; CHECK-NEXT: add w0, w8, w0, lsl #3 ; CHECK-NEXT: ret %shl = shl i32 %x, 3 %sub = sub i32 %shl, %y @@ -723,9 +721,8 @@ define i32 @commute_subop0_mul(i32 %x, i32 %y) { ; CHECK-LABEL: commute_subop0_mul: ; CHECK: // %bb.0: -; CHECK-NEXT: lsl w8, w0, #3 -; CHECK-NEXT: sub w8, w8, w0 -; CHECK-NEXT: add w0, w8, w1 +; CHECK-NEXT: sub w8, w1, w0 +; CHECK-NEXT: add w0, w8, w0, lsl #3 ; CHECK-NEXT: ret %mul = mul i32 %x, 7 %add = add i32 %mul, %y