//===- X86MacroFusion.cpp - X86 Macro Fusion ------------------------------===//

//

// 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 contains the X86 implementation of the DAG scheduling

/// mutation to pair instructions back to back.

//

//===----------------------------------------------------------------------===//

#include "X86MacroFusion.h"

#include "MCTargetDesc/X86BaseInfo.h"

#include "X86Subtarget.h"

#include "llvm/CodeGen/MacroFusion.h"

#include "llvm/CodeGen/ScheduleDAGMutation.h"

#include "llvm/CodeGen/TargetInstrInfo.h"

using namespace llvm;

static X86::FirstMacroFusionInstKind classifyFirst(const MachineInstr &MI) {

  return X86::classifyFirstOpcodeInMacroFusion(MI.getOpcode());

}

static X86::SecondMacroFusionInstKind classifySecond(const MachineInstr &MI) {

  X86::CondCode CC = X86::getCondFromBranch(MI);

  return X86::classifySecondCondCodeInMacroFusion(CC);

}

/// Check if the instr pair, FirstMI and SecondMI, should be fused

/// together. Given SecondMI, when FirstMI is unspecified, then check if

/// SecondMI may be part of a fused pair at all.

static bool shouldScheduleAdjacent(const TargetInstrInfo &TII,

                                   const TargetSubtargetInfo &TSI,

                                   const MachineInstr *FirstMI,

                                   const MachineInstr &SecondMI) {

  const X86Subtarget &ST = static_cast<const X86Subtarget &>(TSI);

  // Check if this processor supports any kind of fusion.

  if (!(ST.hasBranchFusion() || ST.hasMacroFusion()))

    return false;

  const X86::SecondMacroFusionInstKind BranchKind = classifySecond(SecondMI);

  if (BranchKind == X86::SecondMacroFusionInstKind::Invalid)

    return false; // Second cannot be fused with anything.

  if (FirstMI == nullptr)

    return true; // We're only checking whether Second can be fused at all.

  const X86::FirstMacroFusionInstKind TestKind = classifyFirst(*FirstMI);

  if (ST.hasBranchFusion()) {

    // Branch fusion can merge CMP and TEST with all conditional jumps.

    return (TestKind == X86::FirstMacroFusionInstKind::Cmp ||

            TestKind == X86::FirstMacroFusionInstKind::Test);

  }

  if (ST.hasMacroFusion()) {

    return X86::isMacroFused(TestKind, BranchKind);

  }

  llvm_unreachable("unknown fusion type");

}

namespace llvm {

std::unique_ptr<ScheduleDAGMutation> createX86MacroFusionDAGMutation() {

  return createMacroFusionDAGMutation(shouldScheduleAdjacent,

                                      /*BranchOnly=*/true);

}

} // end namespace llvm