llvm/llvm/lib/CodeGen/MIRCanonicalizerPass.cpp

//===-------------- MIRCanonicalizer.cpp - MIR Canonicalizer --------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// The purpose of this pass is to employ a canonical code transformation so
// that code compiled with slightly different IR passes can be diffed more
// effectively than otherwise. This is done by renaming vregs in a given
// LiveRange in a canonical way. This pass also does a pseudo-scheduling to
// move defs closer to their use inorder to reduce diffs caused by slightly
// different schedules.
//
// Basic Usage:
//
// llc -o - -run-pass mir-canonicalizer example.mir
//
// Reorders instructions canonically.
// Renames virtual register operands canonically.
// Strips certain MIR artifacts (optionally).
//
//===----------------------------------------------------------------------===//

#include "MIRVRegNamerUtils.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"

usingnamespacellvm;

#define DEBUG_TYPE …

static cl::opt<unsigned>
    CanonicalizeFunctionNumber("canon-nth-function", cl::Hidden, cl::init(~0u),
                               cl::value_desc("N"),
                               cl::desc("Function number to canonicalize."));

namespace {

class MIRCanonicalizer : public MachineFunctionPass { … };

} // end anonymous namespace

char MIRCanonicalizer::ID;

char &llvm::MIRCanonicalizerID = …;

INITIALIZE_PASS_BEGIN(MIRCanonicalizer, "mir-canonicalizer",
                      "Rename Register Operands Canonically", false, false)

INITIALIZE_PASS_END(MIRCanonicalizer, "mir-canonicalizer",
                    "Rename Register Operands Canonically", false, false)

static std::vector<MachineBasicBlock *> GetRPOList(MachineFunction &MF) { … }

static bool
rescheduleLexographically(std::vector<MachineInstr *> instructions,
                          MachineBasicBlock *MBB,
                          std::function<MachineBasicBlock::iterator()> getPos) { … }

static bool rescheduleCanonically(unsigned &PseudoIdempotentInstCount,
                                  MachineBasicBlock *MBB) { … }

static bool propagateLocalCopies(MachineBasicBlock *MBB) { … }

static bool doDefKillClear(MachineBasicBlock *MBB) { … }

static bool runOnBasicBlock(MachineBasicBlock *MBB,
                            unsigned BasicBlockNum, VRegRenamer &Renamer) { … }

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