llvm/llvm/lib/CodeGen/OptimizePHIs.cpp

//===- OptimizePHIs.cpp - Optimize machine instruction PHIs ---------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This pass optimizes machine instruction PHIs to take advantage of
// opportunities created during DAG legalization.
//
//===----------------------------------------------------------------------===//

#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include <cassert>

usingnamespacellvm;

#define DEBUG_TYPE …

STATISTIC(NumPHICycles, "Number of PHI cycles replaced");
STATISTIC(NumDeadPHICycles, "Number of dead PHI cycles");

namespace {

  class OptimizePHIs : public MachineFunctionPass { … };

} // end anonymous namespace

char OptimizePHIs::ID = …;

char &llvm::OptimizePHIsID = …;

INITIALIZE_PASS(…)

bool OptimizePHIs::runOnMachineFunction(MachineFunction &Fn) { … }

/// IsSingleValuePHICycle - Check if MI is a PHI where all the source operands
/// are copies of SingleValReg, possibly via copies through other PHIs. If
/// SingleValReg is zero on entry, it is set to the register with the single
/// non-copy value. PHIsInCycle is a set used to keep track of the PHIs that
/// have been scanned. PHIs may be grouped by cycle, several cycles or chains.
bool OptimizePHIs::IsSingleValuePHICycle(MachineInstr *MI,
                                         unsigned &SingleValReg,
                                         InstrSet &PHIsInCycle) { … }

/// IsDeadPHICycle - Check if the register defined by a PHI is only used by
/// other PHIs in a cycle.
bool OptimizePHIs::IsDeadPHICycle(MachineInstr *MI, InstrSet &PHIsInCycle) { … }

/// OptimizeBB - Remove dead PHI cycles and PHI cycles that can be replaced by
/// a single value.
bool OptimizePHIs::OptimizeBB(MachineBasicBlock &MBB) { … }