diff --git a/llvm/lib/Target/M68k/M68kISelDAGToDAG.cpp b/llvm/lib/Target/M68k/M68kISelDAGToDAG.cpp --- a/llvm/lib/Target/M68k/M68kISelDAGToDAG.cpp +++ b/llvm/lib/Target/M68k/M68kISelDAGToDAG.cpp @@ -181,6 +181,7 @@ } bool runOnMachineFunction(MachineFunction &MF) override; + bool IsProfitableToFold(SDValue N, SDNode *U, SDNode *Root) const override; private: /// Keep a pointer to the M68kSubtarget around so that we can @@ -311,6 +312,33 @@ }; } // namespace +bool M68kDAGToDAGISel::IsProfitableToFold(SDValue N, SDNode *U, + SDNode *Root) const { + if (OptLevel == CodeGenOpt::None) + return false; + + if (U == Root) { + switch (U->getOpcode()) { + default: + return true; + case M68kISD::SUB: + case ISD::SUB: + // Prefer NEG instruction when zero subtracts a value. + // e.g. + // move.l #0, %d0 + // sub.l (4,%sp), %d0 + // vs. + // move.l (4,%sp), %d0 + // neg.l %d0 + if (llvm::isNullConstant(U->getOperand(0))) + return false; + break; + } + } + + return true; +} + bool M68kDAGToDAGISel::runOnMachineFunction(MachineFunction &MF) { Subtarget = &MF.getSubtarget(); return SelectionDAGISel::runOnMachineFunction(MF); diff --git a/llvm/test/CodeGen/M68k/Arith/imul-neg.ll b/llvm/test/CodeGen/M68k/Arith/imul-neg.ll --- a/llvm/test/CodeGen/M68k/Arith/imul-neg.ll +++ b/llvm/test/CodeGen/M68k/Arith/imul-neg.ll @@ -1,14 +1,34 @@ ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py ; RUN: llc < %s -mtriple=m68k-linux | FileCheck %s -; FIXME: When using SelectionDAGISel, the following cases use -; `sub` rather than the expected `neg` + +define i8 @mul255_8(i8 %A) { +; CHECK-LABEL: mul255_8: +; CHECK: .cfi_startproc +; CHECK-NEXT: ; %bb.0: +; CHECK-NEXT: move.b (7,%sp), %d0 +; CHECK-NEXT: neg.b %d0 +; CHECK-NEXT: rts + %mul = mul i8 %A, 255 + ret i8 %mul +} + +define i16 @mul65535_16(i16 %A) { +; CHECK-LABEL: mul65535_16: +; CHECK: .cfi_startproc +; CHECK-NEXT: ; %bb.0: +; CHECK-NEXT: move.w (6,%sp), %d0 +; CHECK-NEXT: neg.w %d0 +; CHECK-NEXT: rts + %mul = mul i16 %A, 65535 + ret i16 %mul +} define i32 @mul4294967295_32(i32 %A) { ; CHECK-LABEL: mul4294967295_32: ; CHECK: .cfi_startproc ; CHECK-NEXT: ; %bb.0: -; CHECK-NEXT: move.l #0, %d0 -; CHECK-NEXT: sub.l (4,%sp), %d0 +; CHECK-NEXT: move.l (4,%sp), %d0 +; CHECK-NEXT: neg.l %d0 ; CHECK-NEXT: rts %mul = mul i32 %A, 4294967295 ret i32 %mul @@ -19,10 +39,10 @@ ; CHECK-LABEL: mul18446744073709551615_64: ; CHECK: .cfi_startproc ; CHECK-NEXT: ; %bb.0: -; CHECK-NEXT: move.l (4,%sp), %d0 -; CHECK-NEXT: move.l #0, %d1 -; CHECK-NEXT: sub.l (8,%sp), %d1 -; CHECK-NEXT: negx.l %d0 +; CHECK-NEXT: move.l (4,%sp), %d0 +; CHECK-NEXT: move.l (8,%sp), %d1 +; CHECK-NEXT: neg.l %d1 +; CHECK-NEXT: negx.l %d0 ; CHECK-NEXT: rts %mul = mul i64 %A, 18446744073709551615 ret i64 %mul