llvm/llvm/lib/Target/AArch64/AArch64CondBrTuning.cpp

//===-- AArch64CondBrTuning.cpp --- Conditional branch tuning for AArch64 -===//
//
// 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 a pass that transforms CBZ/CBNZ/TBZ/TBNZ instructions
/// into a conditional branch (B.cond), when the NZCV flags can be set for
/// "free".  This is preferred on targets that have more flexibility when
/// scheduling B.cond instructions as compared to CBZ/CBNZ/TBZ/TBNZ (assuming
/// all other variables are equal).  This can also reduce register pressure.
///
/// A few examples:
///
/// 1) add w8, w0, w1  -> cmn w0, w1             ; CMN is an alias of ADDS.
///    cbz w8, .LBB_2  -> b.eq .LBB0_2
///
/// 2) add w8, w0, w1  -> adds w8, w0, w1        ; w8 has multiple uses.
///    cbz w8, .LBB1_2 -> b.eq .LBB1_2
///
/// 3) sub w8, w0, w1       -> subs w8, w0, w1   ; w8 has multiple uses.
///    tbz w8, #31, .LBB6_2 -> b.pl .LBB6_2
///
//===----------------------------------------------------------------------===//

#include "AArch64.h"
#include "AArch64Subtarget.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"

usingnamespacellvm;

#define DEBUG_TYPE …
#define AARCH64_CONDBR_TUNING_NAME …

namespace {
class AArch64CondBrTuning : public MachineFunctionPass { … };
} // end anonymous namespace

char AArch64CondBrTuning::ID = …;

INITIALIZE_PASS(…)

void AArch64CondBrTuning::getAnalysisUsage(AnalysisUsage &AU) const { … }

MachineInstr *AArch64CondBrTuning::getOperandDef(const MachineOperand &MO) { … }

MachineInstr *AArch64CondBrTuning::convertToFlagSetting(MachineInstr &MI,
                                                        bool IsFlagSetting,
                                                        bool Is64Bit) { … }

MachineInstr *AArch64CondBrTuning::convertToCondBr(MachineInstr &MI) { … }

bool AArch64CondBrTuning::tryToTuneBranch(MachineInstr &MI,
                                          MachineInstr &DefMI) { … }

bool AArch64CondBrTuning::runOnMachineFunction(MachineFunction &MF) { … }

FunctionPass *llvm::createAArch64CondBrTuning() { … }