424 lines
12 KiB
C++
424 lines
12 KiB
C++
//===-------------- MIRCanonicalizer.cpp - MIR Canonicalizer --------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// The purpose of this pass is to employ a canonical code transformation so
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// that code compiled with slightly different IR passes can be diffed more
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// effectively than otherwise. This is done by renaming vregs in a given
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// LiveRange in a canonical way. This pass also does a pseudo-scheduling to
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// move defs closer to their use inorder to reduce diffs caused by slightly
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// different schedules.
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//
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// Basic Usage:
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//
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// llc -o - -run-pass mir-canonicalizer example.mir
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//
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// Reorders instructions canonically.
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// Renames virtual register operands canonically.
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// Strips certain MIR artifacts (optionally).
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//
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//===----------------------------------------------------------------------===//
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#include "MIRVRegNamerUtils.h"
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#include "llvm/ADT/PostOrderIterator.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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#define DEBUG_TYPE "mir-canonicalizer"
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static cl::opt<unsigned>
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CanonicalizeFunctionNumber("canon-nth-function", cl::Hidden, cl::init(~0u),
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cl::value_desc("N"),
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cl::desc("Function number to canonicalize."));
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namespace {
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class MIRCanonicalizer : public MachineFunctionPass {
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public:
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static char ID;
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MIRCanonicalizer() : MachineFunctionPass(ID) {}
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StringRef getPassName() const override {
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return "Rename register operands in a canonical ordering.";
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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bool runOnMachineFunction(MachineFunction &MF) override;
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};
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} // end anonymous namespace
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char MIRCanonicalizer::ID;
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char &llvm::MIRCanonicalizerID = MIRCanonicalizer::ID;
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INITIALIZE_PASS_BEGIN(MIRCanonicalizer, "mir-canonicalizer",
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"Rename Register Operands Canonically", false, false)
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INITIALIZE_PASS_END(MIRCanonicalizer, "mir-canonicalizer",
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"Rename Register Operands Canonically", false, false)
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static std::vector<MachineBasicBlock *> GetRPOList(MachineFunction &MF) {
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if (MF.empty())
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return {};
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ReversePostOrderTraversal<MachineBasicBlock *> RPOT(&*MF.begin());
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std::vector<MachineBasicBlock *> RPOList;
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append_range(RPOList, RPOT);
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return RPOList;
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}
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static bool
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rescheduleLexographically(std::vector<MachineInstr *> instructions,
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MachineBasicBlock *MBB,
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std::function<MachineBasicBlock::iterator()> getPos) {
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bool Changed = false;
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using StringInstrPair = std::pair<std::string, MachineInstr *>;
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std::vector<StringInstrPair> StringInstrMap;
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for (auto *II : instructions) {
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std::string S;
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raw_string_ostream OS(S);
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II->print(OS);
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OS.flush();
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// Trim the assignment, or start from the beginning in the case of a store.
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const size_t i = S.find('=');
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StringInstrMap.push_back({(i == std::string::npos) ? S : S.substr(i), II});
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}
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llvm::sort(StringInstrMap, llvm::less_first());
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for (auto &II : StringInstrMap) {
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LLVM_DEBUG({
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dbgs() << "Splicing ";
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II.second->dump();
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dbgs() << " right before: ";
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getPos()->dump();
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});
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Changed = true;
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MBB->splice(getPos(), MBB, II.second);
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}
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return Changed;
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}
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static bool rescheduleCanonically(unsigned &PseudoIdempotentInstCount,
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MachineBasicBlock *MBB) {
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bool Changed = false;
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// Calculates the distance of MI from the beginning of its parent BB.
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auto getInstrIdx = [](const MachineInstr &MI) {
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unsigned i = 0;
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for (auto &CurMI : *MI.getParent()) {
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if (&CurMI == &MI)
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return i;
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i++;
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}
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return ~0U;
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};
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// Pre-Populate vector of instructions to reschedule so that we don't
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// clobber the iterator.
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std::vector<MachineInstr *> Instructions;
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for (auto &MI : *MBB) {
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Instructions.push_back(&MI);
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}
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std::map<MachineInstr *, std::vector<MachineInstr *>> MultiUsers;
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std::map<unsigned, MachineInstr *> MultiUserLookup;
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unsigned UseToBringDefCloserToCount = 0;
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std::vector<MachineInstr *> PseudoIdempotentInstructions;
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std::vector<unsigned> PhysRegDefs;
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for (auto *II : Instructions) {
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for (unsigned i = 1; i < II->getNumOperands(); i++) {
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MachineOperand &MO = II->getOperand(i);
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if (!MO.isReg())
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continue;
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if (Register::isVirtualRegister(MO.getReg()))
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continue;
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if (!MO.isDef())
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continue;
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PhysRegDefs.push_back(MO.getReg());
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}
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}
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for (auto *II : Instructions) {
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if (II->getNumOperands() == 0)
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continue;
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if (II->mayLoadOrStore())
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continue;
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MachineOperand &MO = II->getOperand(0);
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if (!MO.isReg() || !Register::isVirtualRegister(MO.getReg()))
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continue;
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if (!MO.isDef())
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continue;
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bool IsPseudoIdempotent = true;
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for (unsigned i = 1; i < II->getNumOperands(); i++) {
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if (II->getOperand(i).isImm()) {
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continue;
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}
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if (II->getOperand(i).isReg()) {
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if (!Register::isVirtualRegister(II->getOperand(i).getReg()))
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if (!llvm::is_contained(PhysRegDefs, II->getOperand(i).getReg())) {
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continue;
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}
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}
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IsPseudoIdempotent = false;
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break;
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}
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if (IsPseudoIdempotent) {
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PseudoIdempotentInstructions.push_back(II);
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continue;
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}
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LLVM_DEBUG(dbgs() << "Operand " << 0 << " of "; II->dump(); MO.dump(););
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MachineInstr *Def = II;
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unsigned Distance = ~0U;
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MachineInstr *UseToBringDefCloserTo = nullptr;
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MachineRegisterInfo *MRI = &MBB->getParent()->getRegInfo();
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for (auto &UO : MRI->use_nodbg_operands(MO.getReg())) {
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MachineInstr *UseInst = UO.getParent();
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const unsigned DefLoc = getInstrIdx(*Def);
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const unsigned UseLoc = getInstrIdx(*UseInst);
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const unsigned Delta = (UseLoc - DefLoc);
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if (UseInst->getParent() != Def->getParent())
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continue;
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if (DefLoc >= UseLoc)
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continue;
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if (Delta < Distance) {
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Distance = Delta;
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UseToBringDefCloserTo = UseInst;
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MultiUserLookup[UseToBringDefCloserToCount++] = UseToBringDefCloserTo;
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}
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}
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const auto BBE = MBB->instr_end();
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MachineBasicBlock::iterator DefI = BBE;
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MachineBasicBlock::iterator UseI = BBE;
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for (auto BBI = MBB->instr_begin(); BBI != BBE; ++BBI) {
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if (DefI != BBE && UseI != BBE)
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break;
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if (&*BBI == Def) {
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DefI = BBI;
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continue;
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}
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if (&*BBI == UseToBringDefCloserTo) {
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UseI = BBI;
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continue;
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}
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}
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if (DefI == BBE || UseI == BBE)
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continue;
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LLVM_DEBUG({
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dbgs() << "Splicing ";
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DefI->dump();
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dbgs() << " right before: ";
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UseI->dump();
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});
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MultiUsers[UseToBringDefCloserTo].push_back(Def);
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Changed = true;
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MBB->splice(UseI, MBB, DefI);
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}
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// Sort the defs for users of multiple defs lexographically.
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for (const auto &E : MultiUserLookup) {
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auto UseI = llvm::find_if(MBB->instrs(), [&](MachineInstr &MI) -> bool {
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return &MI == E.second;
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});
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if (UseI == MBB->instr_end())
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continue;
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LLVM_DEBUG(
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dbgs() << "Rescheduling Multi-Use Instructions Lexographically.";);
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Changed |= rescheduleLexographically(
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MultiUsers[E.second], MBB,
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[&]() -> MachineBasicBlock::iterator { return UseI; });
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}
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PseudoIdempotentInstCount = PseudoIdempotentInstructions.size();
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LLVM_DEBUG(
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dbgs() << "Rescheduling Idempotent Instructions Lexographically.";);
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Changed |= rescheduleLexographically(
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PseudoIdempotentInstructions, MBB,
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[&]() -> MachineBasicBlock::iterator { return MBB->begin(); });
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return Changed;
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}
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static bool propagateLocalCopies(MachineBasicBlock *MBB) {
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bool Changed = false;
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MachineRegisterInfo &MRI = MBB->getParent()->getRegInfo();
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std::vector<MachineInstr *> Copies;
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for (MachineInstr &MI : MBB->instrs()) {
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if (MI.isCopy())
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Copies.push_back(&MI);
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}
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for (MachineInstr *MI : Copies) {
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if (!MI->getOperand(0).isReg())
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continue;
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if (!MI->getOperand(1).isReg())
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continue;
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const Register Dst = MI->getOperand(0).getReg();
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const Register Src = MI->getOperand(1).getReg();
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if (!Register::isVirtualRegister(Dst))
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continue;
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if (!Register::isVirtualRegister(Src))
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continue;
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// Not folding COPY instructions if regbankselect has not set the RCs.
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// Why are we only considering Register Classes? Because the verifier
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// sometimes gets upset if the register classes don't match even if the
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// types do. A future patch might add COPY folding for matching types in
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// pre-registerbankselect code.
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if (!MRI.getRegClassOrNull(Dst))
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continue;
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if (MRI.getRegClass(Dst) != MRI.getRegClass(Src))
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continue;
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std::vector<MachineOperand *> Uses;
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for (MachineOperand &MO : MRI.use_operands(Dst))
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Uses.push_back(&MO);
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for (auto *MO : Uses)
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MO->setReg(Src);
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Changed = true;
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MI->eraseFromParent();
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}
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return Changed;
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}
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static bool doDefKillClear(MachineBasicBlock *MBB) {
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bool Changed = false;
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for (auto &MI : *MBB) {
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for (auto &MO : MI.operands()) {
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if (!MO.isReg())
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continue;
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if (!MO.isDef() && MO.isKill()) {
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Changed = true;
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MO.setIsKill(false);
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}
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if (MO.isDef() && MO.isDead()) {
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Changed = true;
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MO.setIsDead(false);
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}
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}
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}
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return Changed;
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}
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static bool runOnBasicBlock(MachineBasicBlock *MBB,
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unsigned BasicBlockNum, VRegRenamer &Renamer) {
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LLVM_DEBUG({
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dbgs() << "\n\n NEW BASIC BLOCK: " << MBB->getName() << " \n\n";
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dbgs() << "\n\n================================================\n\n";
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});
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bool Changed = false;
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LLVM_DEBUG(dbgs() << "\n\n NEW BASIC BLOCK: " << MBB->getName() << "\n\n";);
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LLVM_DEBUG(dbgs() << "MBB Before Canonical Copy Propagation:\n";
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MBB->dump(););
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Changed |= propagateLocalCopies(MBB);
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LLVM_DEBUG(dbgs() << "MBB After Canonical Copy Propagation:\n"; MBB->dump(););
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LLVM_DEBUG(dbgs() << "MBB Before Scheduling:\n"; MBB->dump(););
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unsigned IdempotentInstCount = 0;
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Changed |= rescheduleCanonically(IdempotentInstCount, MBB);
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LLVM_DEBUG(dbgs() << "MBB After Scheduling:\n"; MBB->dump(););
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Changed |= Renamer.renameVRegs(MBB, BasicBlockNum);
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// TODO: Consider dropping this. Dropping kill defs is probably not
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// semantically sound.
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Changed |= doDefKillClear(MBB);
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LLVM_DEBUG(dbgs() << "Updated MachineBasicBlock:\n"; MBB->dump();
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dbgs() << "\n";);
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LLVM_DEBUG(
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dbgs() << "\n\n================================================\n\n");
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return Changed;
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}
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bool MIRCanonicalizer::runOnMachineFunction(MachineFunction &MF) {
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static unsigned functionNum = 0;
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if (CanonicalizeFunctionNumber != ~0U) {
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if (CanonicalizeFunctionNumber != functionNum++)
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return false;
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LLVM_DEBUG(dbgs() << "\n Canonicalizing Function " << MF.getName()
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<< "\n";);
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}
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// we need a valid vreg to create a vreg type for skipping all those
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// stray vreg numbers so reach alignment/canonical vreg values.
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std::vector<MachineBasicBlock *> RPOList = GetRPOList(MF);
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LLVM_DEBUG(
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dbgs() << "\n\n NEW MACHINE FUNCTION: " << MF.getName() << " \n\n";
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dbgs() << "\n\n================================================\n\n";
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dbgs() << "Total Basic Blocks: " << RPOList.size() << "\n";
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for (auto MBB
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: RPOList) { dbgs() << MBB->getName() << "\n"; } dbgs()
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<< "\n\n================================================\n\n";);
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unsigned BBNum = 0;
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bool Changed = false;
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MachineRegisterInfo &MRI = MF.getRegInfo();
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VRegRenamer Renamer(MRI);
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for (auto MBB : RPOList)
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Changed |= runOnBasicBlock(MBB, BBNum++, Renamer);
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return Changed;
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}
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