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+//===-------------- MIRCanonicalizer.cpp - MIR Canonicalizer --------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// 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 "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/CodeGen/TargetInstrInfo.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."));
+
+static cl::opt<unsigned>
+CanonicalizeBasicBlockNumber("canon-nth-basicblock", cl::Hidden, cl::init(~0u),
+ cl::value_desc("N"),
+ cl::desc("BasicBlock 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
+
+enum VRType { RSE_Reg = 0, RSE_FrameIndex, RSE_NewCandidate };
+class TypedVReg {
+ VRType type;
+ unsigned reg;
+
+public:
+ TypedVReg(unsigned reg) : type(RSE_Reg), reg(reg) {}
+ TypedVReg(VRType type) : type(type), reg(~0U) {
+ assert(type != RSE_Reg && "Expected a non-register type.");
+ }
+
+ bool isReg() const { return type == RSE_Reg; }
+ bool isFrameIndex() const { return type == RSE_FrameIndex; }
+ bool isCandidate() const { return type == RSE_NewCandidate; }
+
+ VRType getType() const { return type; }
+ unsigned getReg() const {
+ assert(this->isReg() && "Expected a virtual or physical register.");
+ return reg;
+ }
+};
+
+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) {
+ ReversePostOrderTraversal<MachineBasicBlock *> RPOT(&*MF.begin());
+ std::vector<MachineBasicBlock *> RPOList;
+ for (auto MBB : RPOT) {
+ RPOList.push_back(MBB);
+ }
+
+ return RPOList;
+}
+
+// Set a dummy vreg. We use this vregs register class to generate throw-away
+// vregs that are used to skip vreg numbers so that vreg numbers line up.
+static unsigned GetDummyVReg(const MachineFunction &MF) {
+ for (auto &MBB : MF) {
+ for (auto &MI : MBB) {
+ for (auto &MO : MI.operands()) {
+ if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
+ continue;
+ return MO.getReg();
+ }
+ }
+ }
+
+ return ~0U;
+}
+
+static bool rescheduleCanonically(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);
+ }
+
+ for (auto *II : Instructions) {
+ if (II->getNumOperands() == 0)
+ continue;
+
+ MachineOperand &MO = II->getOperand(0);
+ if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
+ continue;
+
+ 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;
+ }
+ }
+
+ 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) && (&*BBI != UseToBringDefCloserTo))
+ continue;
+
+ if (&*BBI == Def) {
+ DefI = BBI;
+ continue;
+ }
+
+ if (&*BBI == UseToBringDefCloserTo) {
+ UseI = BBI;
+ continue;
+ }
+ }
+
+ if (DefI == BBE || UseI == BBE)
+ continue;
+
+ DEBUG({
+ dbgs() << "Splicing ";
+ DefI->dump();
+ dbgs() << " right before: ";
+ UseI->dump();
+ });
+
+ Changed = true;
+ MBB->splice(UseI, MBB, DefI);
+ }
+
+ return Changed;
+}
+
+/// Here we find our candidates. What makes an interesting candidate?
+/// An candidate for a canonicalization tree root is normally any kind of
+/// instruction that causes side effects such as a store to memory or a copy to
+/// a physical register or a return instruction. We use these as an expression
+/// tree root that we walk inorder to build a canonical walk which should result
+/// in canoncal vreg renaming.
+static std::vector<MachineInstr *> populateCandidates(MachineBasicBlock *MBB) {
+ std::vector<MachineInstr *> Candidates;
+ MachineRegisterInfo &MRI = MBB->getParent()->getRegInfo();
+
+ for (auto II = MBB->begin(), IE = MBB->end(); II != IE; ++II) {
+ MachineInstr *MI = &*II;
+
+ bool DoesMISideEffect = false;
+
+ if (MI->getNumOperands() > 0 && MI->getOperand(0).isReg()) {
+ const unsigned Dst = MI->getOperand(0).getReg();
+ DoesMISideEffect |= !TargetRegisterInfo::isVirtualRegister(Dst);
+
+ for (auto UI = MRI.use_begin(Dst); UI != MRI.use_end(); ++UI) {
+ if (DoesMISideEffect) break;
+ DoesMISideEffect |= (UI->getParent()->getParent() != MI->getParent());
+ }
+ }
+
+ if (!MI->mayStore() && !MI->isBranch() && !DoesMISideEffect)
+ continue;
+
+ DEBUG(dbgs() << "Found Candidate: "; MI->dump(););
+ Candidates.push_back(MI);
+ }
+
+ return Candidates;
+}
+
+void doCandidateWalk(std::vector<TypedVReg> &VRegs,
+ std::queue <TypedVReg> &RegQueue,
+ std::vector<MachineInstr *> &VisitedMIs,
+ const MachineBasicBlock *MBB) {
+
+ const MachineFunction &MF = *MBB->getParent();
+ const MachineRegisterInfo &MRI = MF.getRegInfo();
+
+ while (!RegQueue.empty()) {
+
+ auto TReg = RegQueue.front();
+ RegQueue.pop();
+
+ if (TReg.isFrameIndex()) {
+ DEBUG(dbgs() << "Popping frame index.\n";);
+ VRegs.push_back(TypedVReg(RSE_FrameIndex));
+ continue;
+ }
+
+ assert(TReg.isReg() && "Expected vreg or physreg.");
+ unsigned Reg = TReg.getReg();
+
+ if (TargetRegisterInfo::isVirtualRegister(Reg)) {
+ DEBUG({
+ dbgs() << "Popping vreg ";
+ MRI.def_begin(Reg)->dump();
+ dbgs() << "\n";
+ });
+
+ if (!llvm::any_of(VRegs, [&](const TypedVReg &TR) {
+ return TR.isReg() && TR.getReg() == Reg;
+ })) {
+ VRegs.push_back(TypedVReg(Reg));
+ }
+ } else {
+ DEBUG(dbgs() << "Popping physreg.\n";);
+ VRegs.push_back(TypedVReg(Reg));
+ continue;
+ }
+
+ for (auto RI = MRI.def_begin(Reg), RE = MRI.def_end(); RI != RE; ++RI) {
+ MachineInstr *Def = RI->getParent();
+
+ if (Def->getParent() != MBB)
+ continue;
+
+ if (llvm::any_of(VisitedMIs,
+ [&](const MachineInstr *VMI) { return Def == VMI; })) {
+ break;
+ }
+
+ DEBUG({
+ dbgs() << "\n========================\n";
+ dbgs() << "Visited MI: ";
+ Def->dump();
+ dbgs() << "BB Name: " << Def->getParent()->getName() << "\n";
+ dbgs() << "\n========================\n";
+ });
+ VisitedMIs.push_back(Def);
+ for (unsigned I = 1, E = Def->getNumOperands(); I != E; ++I) {
+
+ MachineOperand &MO = Def->getOperand(I);
+ if (MO.isFI()) {
+ DEBUG(dbgs() << "Pushing frame index.\n";);
+ RegQueue.push(TypedVReg(RSE_FrameIndex));
+ }
+
+ if (!MO.isReg())
+ continue;
+ RegQueue.push(TypedVReg(MO.getReg()));
+ }
+ }
+ }
+}
+
+// TODO: Work to remove this in the future. One day when we have named vregs
+// we should be able to form the canonical name based on some characteristic
+// we see in that point of the expression tree (like if we were to name based
+// on some sort of value numbering scheme).
+static void SkipVRegs(unsigned &VRegGapIndex, MachineRegisterInfo &MRI,
+ const TargetRegisterClass *RC) {
+ const unsigned VR_GAP = (++VRegGapIndex * 1000);
+
+ DEBUG({
+ dbgs() << "Adjusting per-BB VR_GAP for BB" << VRegGapIndex << " to "
+ << VR_GAP << "\n";
+ });
+
+ unsigned I = MRI.createVirtualRegister(RC);
+ const unsigned E = (((I + VR_GAP) / VR_GAP) + 1) * VR_GAP;
+ while (I != E) {
+ I = MRI.createVirtualRegister(RC);
+ }
+}
+
+static std::map<unsigned, unsigned>
+GetVRegRenameMap(const std::vector<TypedVReg> &VRegs,
+ const std::vector<unsigned> &renamedInOtherBB,
+ MachineRegisterInfo &MRI,
+ const TargetRegisterClass *RC) {
+ std::map<unsigned, unsigned> VRegRenameMap;
+ unsigned LastRenameReg = MRI.createVirtualRegister(RC);
+ bool FirstCandidate = true;
+
+ for (auto &vreg : VRegs) {
+ if (vreg.isFrameIndex()) {
+ // We skip one vreg for any frame index because there is a good chance
+ // (especially when comparing SelectionDAG to GlobalISel generated MIR)
+ // that in the other file we are just getting an incoming vreg that comes
+ // from a copy from a frame index. So it's safe to skip by one.
+ LastRenameReg = MRI.createVirtualRegister(RC);
+ DEBUG(dbgs() << "Skipping rename for FI " << LastRenameReg << "\n";);
+ continue;
+ } else if (vreg.isCandidate()) {
+
+ // After the first candidate, for every subsequent candidate, we skip mod
+ // 10 registers so that the candidates are more likely to start at the
+ // same vreg number making it more likely that the canonical walk from the
+ // candidate insruction. We don't need to skip from the first candidate of
+ // the BasicBlock because we already skip ahead several vregs for each BB.
+ while (LastRenameReg % 10) {
+ if (!FirstCandidate) break;
+ LastRenameReg = MRI.createVirtualRegister(RC);
+
+ DEBUG({
+ dbgs() << "Skipping rename for new candidate " << LastRenameReg
+ << "\n";
+ });
+ }
+ FirstCandidate = false;
+ continue;
+ } else if (!TargetRegisterInfo::isVirtualRegister(vreg.getReg())) {
+ LastRenameReg = MRI.createVirtualRegister(RC);
+ DEBUG({
+ dbgs() << "Skipping rename for Phys Reg " << LastRenameReg << "\n";
+ });
+ continue;
+ }
+
+ auto Reg = vreg.getReg();
+ if (llvm::find(renamedInOtherBB, Reg) != renamedInOtherBB.end()) {
+ DEBUG(dbgs() << "Vreg " << Reg << " already renamed in other BB.\n";);
+ continue;
+ }
+
+ auto Rename = MRI.createVirtualRegister(MRI.getRegClass(Reg));
+ LastRenameReg = Rename;
+
+ if (VRegRenameMap.find(Reg) == VRegRenameMap.end()) {
+ DEBUG(dbgs() << "Mapping vreg ";);
+ if (MRI.reg_begin(Reg) != MRI.reg_end()) {
+ DEBUG(auto foo = &*MRI.reg_begin(Reg); foo->dump(););
+ } else {
+ DEBUG(dbgs() << Reg;);
+ }
+ DEBUG(dbgs() << " to ";);
+ if (MRI.reg_begin(Rename) != MRI.reg_end()) {
+ DEBUG(auto foo = &*MRI.reg_begin(Rename); foo->dump(););
+ } else {
+ DEBUG(dbgs() << Rename;);
+ }
+ DEBUG(dbgs() << "\n";);
+
+ VRegRenameMap.insert(std::pair<unsigned, unsigned>(Reg, Rename));
+ }
+ }
+
+ return VRegRenameMap;
+}
+
+static bool doVRegRenaming(std::vector<unsigned> &RenamedInOtherBB,
+ const std::map<unsigned, unsigned> &VRegRenameMap,
+ MachineRegisterInfo &MRI) {
+ bool Changed = false;
+ for (auto I = VRegRenameMap.begin(), E = VRegRenameMap.end(); I != E; ++I) {
+
+ auto VReg = I->first;
+ auto Rename = I->second;
+
+ RenamedInOtherBB.push_back(Rename);
+
+ std::vector<MachineOperand *> RenameMOs;
+ for (auto &MO : MRI.reg_operands(VReg)) {
+ RenameMOs.push_back(&MO);
+ }
+
+ for (auto *MO : RenameMOs) {
+ Changed = true;
+ MO->setReg(Rename);
+
+ if (!MO->isDef())
+ MO->setIsKill(false);
+ }
+ }
+
+ 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,
+ std::vector<StringRef> &bbNames,
+ std::vector<unsigned> &renamedInOtherBB,
+ unsigned &basicBlockNum, unsigned &VRegGapIndex) {
+
+ if (CanonicalizeBasicBlockNumber != ~0U) {
+ if (CanonicalizeBasicBlockNumber != basicBlockNum++)
+ return false;
+ DEBUG(dbgs() << "\n Canonicalizing BasicBlock " << MBB->getName() << "\n";);
+ }
+
+ if (llvm::find(bbNames, MBB->getName()) != bbNames.end()) {
+ DEBUG({
+ dbgs() << "Found potentially duplicate BasicBlocks: " << MBB->getName()
+ << "\n";
+ });
+ return false;
+ }
+
+ DEBUG({
+ dbgs() << "\n\n NEW BASIC BLOCK: " << MBB->getName() << " \n\n";
+ dbgs() << "\n\n================================================\n\n";
+ });
+
+ bool Changed = false;
+ MachineFunction &MF = *MBB->getParent();
+ MachineRegisterInfo &MRI = MF.getRegInfo();
+
+ const unsigned DummyVReg = GetDummyVReg(MF);
+ const TargetRegisterClass *DummyRC =
+ (DummyVReg == ~0U) ? nullptr : MRI.getRegClass(DummyVReg);
+ if (!DummyRC) return false;
+
+ bbNames.push_back(MBB->getName());
+ DEBUG(dbgs() << "\n\n NEW BASIC BLOCK: " << MBB->getName() << "\n\n";);
+
+ DEBUG(dbgs() << "MBB Before Scheduling:\n"; MBB->dump(););
+ Changed |= rescheduleCanonically(MBB);
+ DEBUG(dbgs() << "MBB After Scheduling:\n"; MBB->dump(););
+
+ std::vector<MachineInstr *> Candidates = populateCandidates(MBB);
+ std::vector<MachineInstr *> VisitedMIs;
+ std::copy(Candidates.begin(), Candidates.end(),
+ std::back_inserter(VisitedMIs));
+
+ std::vector<TypedVReg> VRegs;
+ for (auto candidate : Candidates) {
+ VRegs.push_back(TypedVReg(RSE_NewCandidate));
+
+ std::queue<TypedVReg> RegQueue;
+
+ // Here we walk the vreg operands of a non-root node along our walk.
+ // The root nodes are the original candidates (stores normally).
+ // These are normally not the root nodes (except for the case of copies to
+ // physical registers).
+ for (unsigned i = 1; i < candidate->getNumOperands(); i++) {
+ if (candidate->mayStore() || candidate->isBranch())
+ break;
+
+ MachineOperand &MO = candidate->getOperand(i);
+ if (!(MO.isReg() && TargetRegisterInfo::isVirtualRegister(MO.getReg())))
+ continue;
+
+ DEBUG(dbgs() << "Enqueue register"; MO.dump(); dbgs() << "\n";);
+ RegQueue.push(TypedVReg(MO.getReg()));
+ }
+
+ // Here we walk the root candidates. We start from the 0th operand because
+ // the root is normally a store to a vreg.
+ for (unsigned i = 0; i < candidate->getNumOperands(); i++) {
+
+ if (!candidate->mayStore() && !candidate->isBranch())
+ break;
+
+ MachineOperand &MO = candidate->getOperand(i);
+
+ // TODO: Do we want to only add vregs here?
+ if (!MO.isReg() && !MO.isFI())
+ continue;
+
+ DEBUG(dbgs() << "Enqueue Reg/FI"; MO.dump(); dbgs() << "\n";);
+
+ RegQueue.push(MO.isReg() ? TypedVReg(MO.getReg()) :
+ TypedVReg(RSE_FrameIndex));
+ }
+
+ doCandidateWalk(VRegs, RegQueue, VisitedMIs, MBB);
+ }
+
+ // If we have populated no vregs to rename then bail.
+ // The rest of this function does the vreg remaping.
+ if (VRegs.size() == 0)
+ return Changed;
+
+ // Skip some vregs, so we can recon where we'll land next.
+ SkipVRegs(VRegGapIndex, MRI, DummyRC);
+
+ auto VRegRenameMap = GetVRegRenameMap(VRegs, renamedInOtherBB, MRI, DummyRC);
+ Changed |= doVRegRenaming(renamedInOtherBB, VRegRenameMap, MRI);
+ Changed |= doDefKillClear(MBB);
+
+ DEBUG(dbgs() << "Updated MachineBasicBlock:\n"; MBB->dump(); dbgs() << "\n";);
+ 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;
+ 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);
+
+ 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";
+ );
+
+ std::vector<StringRef> BBNames;
+ std::vector<unsigned> RenamedInOtherBB;
+
+ unsigned GapIdx = 0;
+ unsigned BBNum = 0;
+
+ bool Changed = false;
+
+ for (auto MBB : RPOList)
+ Changed |= runOnBasicBlock(MBB, BBNames, RenamedInOtherBB, BBNum, GapIdx);
+
+ return Changed;
+}
+
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