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//===-------------- 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/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <queue>
using namespace llvm;
namespace llvm {
extern char &MIRCanonicalizerID;
} // namespace llvm
#define DEBUG_TYPE "mir-canonicalizer"
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 {
public:
static char ID;
MIRCanonicalizer() : MachineFunctionPass(ID) {}
StringRef getPassName() const override {
return "Rename register operands in a canonical ordering.";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
bool runOnMachineFunction(MachineFunction &MF) override;
};
} // end anonymous namespace
char MIRCanonicalizer::ID;
char &llvm::MIRCanonicalizerID = MIRCanonicalizer::ID;
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) {
if (MF.empty())
return {};
ReversePostOrderTraversal<MachineBasicBlock *> RPOT(&*MF.begin());
std::vector<MachineBasicBlock *> RPOList;
for (auto MBB : RPOT) {
RPOList.push_back(MBB);
}
return RPOList;
}
static bool
rescheduleLexographically(std::vector<MachineInstr *> instructions,
MachineBasicBlock *MBB,
std::function<MachineBasicBlock::iterator()> getPos) {
bool Changed = false;
using StringInstrPair = std::pair<std::string, MachineInstr *>;
std::vector<StringInstrPair> StringInstrMap;
for (auto *II : instructions) {
std::string S;
raw_string_ostream OS(S);
II->print(OS);
OS.flush();
// Trim the assignment, or start from the begining in the case of a store.
const size_t i = S.find("=");
StringInstrMap.push_back({(i == std::string::npos) ? S : S.substr(i), II});
}
llvm::sort(StringInstrMap,
[](const StringInstrPair &a, const StringInstrPair &b) -> bool {
return (a.first < b.first);
});
for (auto &II : StringInstrMap) {
LLVM_DEBUG({
dbgs() << "Splicing ";
II.second->dump();
dbgs() << " right before: ";
getPos()->dump();
});
Changed = true;
MBB->splice(getPos(), MBB, II.second);
}
return Changed;
}
static bool rescheduleCanonically(unsigned &PseudoIdempotentInstCount,
MachineBasicBlock *MBB) {
bool Changed = false;
// Calculates the distance of MI from the begining of its parent BB.
auto getInstrIdx = [](const MachineInstr &MI) {
unsigned i = 0;
for (auto &CurMI : *MI.getParent()) {
if (&CurMI == &MI)
return i;
i++;
}
return ~0U;
};
// Pre-Populate vector of instructions to reschedule so that we don't
// clobber the iterator.
std::vector<MachineInstr *> Instructions;
for (auto &MI : *MBB) {
Instructions.push_back(&MI);
}
std::map<MachineInstr *, std::vector<MachineInstr *>> MultiUsers;
std::map<unsigned, MachineInstr *> MultiUserLookup;
unsigned UseToBringDefCloserToCount = 0;
std::vector<MachineInstr *> PseudoIdempotentInstructions;
std::vector<unsigned> PhysRegDefs;
for (auto *II : Instructions) {
for (unsigned i = 1; i < II->getNumOperands(); i++) {
MachineOperand &MO = II->getOperand(i);
if (!MO.isReg())
continue;
if (Register::isVirtualRegister(MO.getReg()))
continue;
if (!MO.isDef())
continue;
PhysRegDefs.push_back(MO.getReg());
}
}
for (auto *II : Instructions) {
if (II->getNumOperands() == 0)
continue;
if (II->mayLoadOrStore())
continue;
MachineOperand &MO = II->getOperand(0);
if (!MO.isReg() || !Register::isVirtualRegister(MO.getReg()))
continue;
if (!MO.isDef())
continue;
bool IsPseudoIdempotent = true;
for (unsigned i = 1; i < II->getNumOperands(); i++) {
if (II->getOperand(i).isImm()) {
continue;
}
if (II->getOperand(i).isReg()) {
if (!Register::isVirtualRegister(II->getOperand(i).getReg()))
if (llvm::find(PhysRegDefs, II->getOperand(i).getReg()) ==
PhysRegDefs.end()) {
continue;
}
}
IsPseudoIdempotent = false;
break;
}
if (IsPseudoIdempotent) {
PseudoIdempotentInstructions.push_back(II);
continue;
}
LLVM_DEBUG(dbgs() << "Operand " << 0 << " of "; II->dump(); MO.dump(););
MachineInstr *Def = II;
unsigned Distance = ~0U;
MachineInstr *UseToBringDefCloserTo = nullptr;
MachineRegisterInfo *MRI = &MBB->getParent()->getRegInfo();
for (auto &UO : MRI->use_nodbg_operands(MO.getReg())) {
MachineInstr *UseInst = UO.getParent();
const unsigned DefLoc = getInstrIdx(*Def);
const unsigned UseLoc = getInstrIdx(*UseInst);
const unsigned Delta = (UseLoc - DefLoc);
if (UseInst->getParent() != Def->getParent())
continue;
if (DefLoc >= UseLoc)
continue;
if (Delta < Distance) {
Distance = Delta;
UseToBringDefCloserTo = UseInst;
MultiUserLookup[UseToBringDefCloserToCount++] = UseToBringDefCloserTo;
}
}
const auto BBE = MBB->instr_end();
MachineBasicBlock::iterator DefI = BBE;
MachineBasicBlock::iterator UseI = BBE;
for (auto BBI = MBB->instr_begin(); BBI != BBE; ++BBI) {
if (DefI != BBE && UseI != BBE)
break;
if (&*BBI == Def) {
DefI = BBI;
continue;
}
if (&*BBI == UseToBringDefCloserTo) {
UseI = BBI;
continue;
}
}
if (DefI == BBE || UseI == BBE)
continue;
LLVM_DEBUG({
dbgs() << "Splicing ";
DefI->dump();
dbgs() << " right before: ";
UseI->dump();
});
MultiUsers[UseToBringDefCloserTo].push_back(Def);
Changed = true;
MBB->splice(UseI, MBB, DefI);
}
// Sort the defs for users of multiple defs lexographically.
for (const auto &E : MultiUserLookup) {
auto UseI =
std::find_if(MBB->instr_begin(), MBB->instr_end(),
[&](MachineInstr &MI) -> bool { return &MI == E.second; });
if (UseI == MBB->instr_end())
continue;
LLVM_DEBUG(
dbgs() << "Rescheduling Multi-Use Instructions Lexographically.";);
Changed |= rescheduleLexographically(
MultiUsers[E.second], MBB,
[&]() -> MachineBasicBlock::iterator { return UseI; });
}
PseudoIdempotentInstCount = PseudoIdempotentInstructions.size();
LLVM_DEBUG(
dbgs() << "Rescheduling Idempotent Instructions Lexographically.";);
Changed |= rescheduleLexographically(
PseudoIdempotentInstructions, MBB,
[&]() -> MachineBasicBlock::iterator { return MBB->begin(); });
return Changed;
}
static bool propagateLocalCopies(MachineBasicBlock *MBB) {
bool Changed = false;
MachineRegisterInfo &MRI = MBB->getParent()->getRegInfo();
std::vector<MachineInstr *> Copies;
for (MachineInstr &MI : MBB->instrs()) {
if (MI.isCopy())
Copies.push_back(&MI);
}
for (MachineInstr *MI : Copies) {
if (!MI->getOperand(0).isReg())
continue;
if (!MI->getOperand(1).isReg())
continue;
const Register Dst = MI->getOperand(0).getReg();
const Register Src = MI->getOperand(1).getReg();
if (!Register::isVirtualRegister(Dst))
continue;
if (!Register::isVirtualRegister(Src))
continue;
// Not folding COPY instructions if regbankselect has not set the RCs.
// Why are we only considering Register Classes? Because the verifier
// sometimes gets upset if the register classes don't match even if the
// types do. A future patch might add COPY folding for matching types in
// pre-registerbankselect code.
if (!MRI.getRegClassOrNull(Dst))
continue;
if (MRI.getRegClass(Dst) != MRI.getRegClass(Src))
continue;
std::vector<MachineOperand *> Uses;
for (auto UI = MRI.use_begin(Dst); UI != MRI.use_end(); ++UI)
Uses.push_back(&*UI);
for (auto *MO : Uses)
MO->setReg(Src);
Changed = true;
MI->eraseFromParent();
}
return Changed;
}
static bool doDefKillClear(MachineBasicBlock *MBB) {
bool Changed = false;
for (auto &MI : *MBB) {
for (auto &MO : MI.operands()) {
if (!MO.isReg())
continue;
if (!MO.isDef() && MO.isKill()) {
Changed = true;
MO.setIsKill(false);
}
if (MO.isDef() && MO.isDead()) {
Changed = true;
MO.setIsDead(false);
}
}
}
return Changed;
}
static bool runOnBasicBlock(MachineBasicBlock *MBB,
unsigned BasicBlockNum, VRegRenamer &Renamer) {
LLVM_DEBUG({
dbgs() << "\n\n NEW BASIC BLOCK: " << MBB->getName() << " \n\n";
dbgs() << "\n\n================================================\n\n";
});
bool Changed = false;
LLVM_DEBUG(dbgs() << "\n\n NEW BASIC BLOCK: " << MBB->getName() << "\n\n";);
LLVM_DEBUG(dbgs() << "MBB Before Canonical Copy Propagation:\n";
MBB->dump(););
Changed |= propagateLocalCopies(MBB);
LLVM_DEBUG(dbgs() << "MBB After Canonical Copy Propagation:\n"; MBB->dump(););
LLVM_DEBUG(dbgs() << "MBB Before Scheduling:\n"; MBB->dump(););
unsigned IdempotentInstCount = 0;
Changed |= rescheduleCanonically(IdempotentInstCount, MBB);
LLVM_DEBUG(dbgs() << "MBB After Scheduling:\n"; MBB->dump(););
Changed |= Renamer.renameVRegs(MBB, BasicBlockNum);
// TODO: Consider dropping this. Dropping kill defs is probably not
// semantically sound.
Changed |= doDefKillClear(MBB);
LLVM_DEBUG(dbgs() << "Updated MachineBasicBlock:\n"; MBB->dump();
dbgs() << "\n";);
LLVM_DEBUG(
dbgs() << "\n\n================================================\n\n");
return Changed;
}
bool MIRCanonicalizer::runOnMachineFunction(MachineFunction &MF) {
static unsigned functionNum = 0;
if (CanonicalizeFunctionNumber != ~0U) {
if (CanonicalizeFunctionNumber != functionNum++)
return false;
LLVM_DEBUG(dbgs() << "\n Canonicalizing Function " << MF.getName()
<< "\n";);
}
// we need a valid vreg to create a vreg type for skipping all those
// stray vreg numbers so reach alignment/canonical vreg values.
std::vector<MachineBasicBlock *> RPOList = GetRPOList(MF);
LLVM_DEBUG(
dbgs() << "\n\n NEW MACHINE FUNCTION: " << MF.getName() << " \n\n";
dbgs() << "\n\n================================================\n\n";
dbgs() << "Total Basic Blocks: " << RPOList.size() << "\n";
for (auto MBB
: RPOList) { dbgs() << MBB->getName() << "\n"; } dbgs()
<< "\n\n================================================\n\n";);
unsigned BBNum = 0;
bool Changed = false;
MachineRegisterInfo &MRI = MF.getRegInfo();
VRegRenamer Renamer(MRI);
for (auto MBB : RPOList)
Changed |= runOnBasicBlock(MBB, BBNum++, Renamer);
return Changed;
}