llvm/lib/Target/X86/MCA/X86CustomBehaviour.cpp

//===------------------- X86CustomBehaviour.cpp -----------------*-C++ -* -===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
///
/// This file implements methods from the X86CustomBehaviour class.
///
//===----------------------------------------------------------------------===//

#include "X86CustomBehaviour.h"
#include "MCTargetDesc/X86BaseInfo.h"
#include "TargetInfo/X86TargetInfo.h"
#include "llvm-c/Visibility.h"
#include "llvm/MC/TargetRegistry.h"

namespace llvm {
namespace mca {

void X86InstrPostProcess::setMemBarriers(Instruction &Inst, const MCInst &MCI) {
  switch (MCI.getOpcode()) {
  case X86::MFENCE:
    Inst.setLoadBarrier(true);
    Inst.setStoreBarrier(true);
    break;
  case X86::LFENCE:
    Inst.setLoadBarrier(true);
    break;
  case X86::SFENCE:
    Inst.setStoreBarrier(true);
    break;
  }
}

void X86InstrPostProcess::useStackEngine(Instruction &Inst, const MCInst &MCI) {
  // TODO(boomanaiden154): We currently do not handle PUSHF/POPF because we
  // have not done the necessary benchmarking to see if they are also
  // optimized by the stack engine.
  // TODO: We currently just remove all RSP writes from stack operations. This
  // is not fully correct because we do not model sync uops which will
  // delay subsequent rsp using non-stack instructions.
  if (X86::isPOP(MCI.getOpcode()) || X86::isPUSH(MCI.getOpcode())) {
    auto *StackRegisterDef =
        llvm::find_if(Inst.getDefs(), [](const WriteState &State) {
          return State.getRegisterID() == X86::RSP;
        });
    assert(
        StackRegisterDef != Inst.getDefs().end() &&
        "Expected push instruction to implicitly use stack pointer register.");
    Inst.getDefs().erase(StackRegisterDef);
  }
}

void X86InstrPostProcess::postProcessInstruction(Instruction &Inst,
                                                 const MCInst &MCI) {
  // Set IsALoadBarrier and IsAStoreBarrier flags.
  setMemBarriers(Inst, MCI);
  useStackEngine(Inst, MCI);
}

} // namespace mca
} // namespace llvm

using namespace llvm;
using namespace mca;

static InstrPostProcess *createX86InstrPostProcess(const MCSubtargetInfo &STI,
                                                   const MCInstrInfo &MCII) {
  return new X86InstrPostProcess(STI, MCII);
}

/// Extern function to initialize the targets for the X86 backend

extern "C" LLVM_C_ABI void LLVMInitializeX86TargetMCA() {
  TargetRegistry::RegisterInstrPostProcess(getTheX86_32Target(),
                                           createX86InstrPostProcess);
  TargetRegistry::RegisterInstrPostProcess(getTheX86_64Target(),
                                           createX86InstrPostProcess);
}