llvm/llvm/lib/CodeGen/BreakFalseDeps.cpp

//==- llvm/CodeGen/BreakFalseDeps.cpp - Break False Dependency Fix -*- 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 Break False Dependency pass.
///
/// Some instructions have false dependencies which cause unnecessary stalls.
/// For example, instructions may write part of a register and implicitly
/// need to read the other parts of the register. This may cause unwanted
/// stalls preventing otherwise unrelated instructions from executing in
/// parallel in an out-of-order CPU.
/// This pass is aimed at identifying and avoiding these dependencies.
//
//===----------------------------------------------------------------------===//

#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/CodeGen/LivePhysRegs.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/ReachingDefAnalysis.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/InitializePasses.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/MC/MCRegister.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Support/Debug.h"

usingnamespacellvm;

namespace llvm {

class BreakFalseDeps : public MachineFunctionPass { … };

} // namespace llvm

#define DEBUG_TYPE …

char BreakFalseDeps::ID = …;
INITIALIZE_PASS_BEGIN(BreakFalseDeps, DEBUG_TYPE, "BreakFalseDeps", false, false)
INITIALIZE_PASS_DEPENDENCY(ReachingDefAnalysis)
INITIALIZE_PASS_END(BreakFalseDeps, DEBUG_TYPE, "BreakFalseDeps", false, false)

FunctionPass *llvm::createBreakFalseDeps() { … }

bool BreakFalseDeps::pickBestRegisterForUndef(MachineInstr *MI, unsigned OpIdx,
  unsigned Pref) { … }

bool BreakFalseDeps::shouldBreakDependence(MachineInstr *MI, unsigned OpIdx,
                                           unsigned Pref) { … }

void BreakFalseDeps::processDefs(MachineInstr *MI) { … }

void BreakFalseDeps::processUndefReads(MachineBasicBlock *MBB) { … }

void BreakFalseDeps::processBasicBlock(MachineBasicBlock *MBB) { … }

bool BreakFalseDeps::runOnMachineFunction(MachineFunction &mf) { … }