1 //===-- llvm/CodeGen/VirtRegMap.cpp - Virtual Register Map ----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the VirtRegMap class.
12 // It also contains implementations of the Spiller interface, which, given a
13 // virtual register map and a machine function, eliminates all virtual
14 // references by replacing them with physical register references - adding spill
17 //===----------------------------------------------------------------------===//
19 #include "llvm/CodeGen/VirtRegMap.h"
20 #include "LiveDebugVariables.h"
21 #include "llvm/ADT/STLExtras.h"
22 #include "llvm/ADT/Statistic.h"
23 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
24 #include "llvm/CodeGen/LiveStackAnalysis.h"
25 #include "llvm/CodeGen/MachineFrameInfo.h"
26 #include "llvm/CodeGen/MachineFunction.h"
27 #include "llvm/CodeGen/MachineInstrBuilder.h"
28 #include "llvm/CodeGen/MachineRegisterInfo.h"
29 #include "llvm/CodeGen/Passes.h"
30 #include "llvm/IR/Function.h"
31 #include "llvm/Support/Compiler.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/raw_ostream.h"
34 #include "llvm/Target/TargetInstrInfo.h"
35 #include "llvm/Target/TargetMachine.h"
36 #include "llvm/Target/TargetRegisterInfo.h"
37 #include "llvm/Target/TargetSubtargetInfo.h"
41 #define DEBUG_TYPE "regalloc"
43 STATISTIC(NumSpillSlots, "Number of spill slots allocated");
44 STATISTIC(NumIdCopies, "Number of identity moves eliminated after rewriting");
46 //===----------------------------------------------------------------------===//
47 // VirtRegMap implementation
48 //===----------------------------------------------------------------------===//
50 char VirtRegMap::ID = 0;
52 INITIALIZE_PASS(VirtRegMap, "virtregmap", "Virtual Register Map", false, false)
54 bool VirtRegMap::runOnMachineFunction(MachineFunction &mf) {
55 MRI = &mf.getRegInfo();
56 TII = mf.getSubtarget().getInstrInfo();
57 TRI = mf.getSubtarget().getRegisterInfo();
61 Virt2StackSlotMap.clear();
62 Virt2SplitMap.clear();
68 void VirtRegMap::grow() {
69 unsigned NumRegs = MF->getRegInfo().getNumVirtRegs();
70 Virt2PhysMap.resize(NumRegs);
71 Virt2StackSlotMap.resize(NumRegs);
72 Virt2SplitMap.resize(NumRegs);
75 void VirtRegMap::assignVirt2Phys(unsigned virtReg, MCPhysReg physReg) {
76 assert(TargetRegisterInfo::isVirtualRegister(virtReg) &&
77 TargetRegisterInfo::isPhysicalRegister(physReg));
78 assert(Virt2PhysMap[virtReg] == NO_PHYS_REG &&
79 "attempt to assign physical register to already mapped "
81 assert(!getRegInfo().isReserved(physReg) &&
82 "Attempt to map virtReg to a reserved physReg");
83 Virt2PhysMap[virtReg] = physReg;
86 unsigned VirtRegMap::createSpillSlot(const TargetRegisterClass *RC) {
87 unsigned Size = TRI->getSpillSize(*RC);
88 unsigned Align = TRI->getSpillAlignment(*RC);
89 int SS = MF->getFrameInfo().CreateSpillStackObject(Size, Align);
94 bool VirtRegMap::hasPreferredPhys(unsigned VirtReg) {
95 unsigned Hint = MRI->getSimpleHint(VirtReg);
98 if (TargetRegisterInfo::isVirtualRegister(Hint))
100 return getPhys(VirtReg) == Hint;
103 bool VirtRegMap::hasKnownPreference(unsigned VirtReg) {
104 std::pair<unsigned, unsigned> Hint = MRI->getRegAllocationHint(VirtReg);
105 if (TargetRegisterInfo::isPhysicalRegister(Hint.second))
107 if (TargetRegisterInfo::isVirtualRegister(Hint.second))
108 return hasPhys(Hint.second);
112 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) {
113 assert(TargetRegisterInfo::isVirtualRegister(virtReg));
114 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
115 "attempt to assign stack slot to already spilled register");
116 const TargetRegisterClass* RC = MF->getRegInfo().getRegClass(virtReg);
117 return Virt2StackSlotMap[virtReg] = createSpillSlot(RC);
120 void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int SS) {
121 assert(TargetRegisterInfo::isVirtualRegister(virtReg));
122 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
123 "attempt to assign stack slot to already spilled register");
125 (SS >= MF->getFrameInfo().getObjectIndexBegin())) &&
126 "illegal fixed frame index");
127 Virt2StackSlotMap[virtReg] = SS;
130 void VirtRegMap::print(raw_ostream &OS, const Module*) const {
131 OS << "********** REGISTER MAP **********\n";
132 for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
133 unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
134 if (Virt2PhysMap[Reg] != (unsigned)VirtRegMap::NO_PHYS_REG) {
135 OS << '[' << PrintReg(Reg, TRI) << " -> "
136 << PrintReg(Virt2PhysMap[Reg], TRI) << "] "
137 << TRI->getRegClassName(MRI->getRegClass(Reg)) << "\n";
141 for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
142 unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
143 if (Virt2StackSlotMap[Reg] != VirtRegMap::NO_STACK_SLOT) {
144 OS << '[' << PrintReg(Reg, TRI) << " -> fi#" << Virt2StackSlotMap[Reg]
145 << "] " << TRI->getRegClassName(MRI->getRegClass(Reg)) << "\n";
151 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
152 LLVM_DUMP_METHOD void VirtRegMap::dump() const {
157 //===----------------------------------------------------------------------===//
159 //===----------------------------------------------------------------------===//
161 // The VirtRegRewriter is the last of the register allocator passes.
162 // It rewrites virtual registers to physical registers as specified in the
163 // VirtRegMap analysis. It also updates live-in information on basic blocks
164 // according to LiveIntervals.
167 class VirtRegRewriter : public MachineFunctionPass {
169 const TargetMachine *TM;
170 const TargetRegisterInfo *TRI;
171 const TargetInstrInfo *TII;
172 MachineRegisterInfo *MRI;
173 SlotIndexes *Indexes;
178 void addMBBLiveIns();
179 bool readsUndefSubreg(const MachineOperand &MO) const;
180 void addLiveInsForSubRanges(const LiveInterval &LI, unsigned PhysReg) const;
181 void handleIdentityCopy(MachineInstr &MI) const;
182 void expandCopyBundle(MachineInstr &MI) const;
186 VirtRegRewriter() : MachineFunctionPass(ID) {}
188 void getAnalysisUsage(AnalysisUsage &AU) const override;
190 bool runOnMachineFunction(MachineFunction&) override;
191 MachineFunctionProperties getSetProperties() const override {
192 return MachineFunctionProperties().set(
193 MachineFunctionProperties::Property::NoVRegs);
196 } // end anonymous namespace
198 char &llvm::VirtRegRewriterID = VirtRegRewriter::ID;
200 INITIALIZE_PASS_BEGIN(VirtRegRewriter, "virtregrewriter",
201 "Virtual Register Rewriter", false, false)
202 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
203 INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
204 INITIALIZE_PASS_DEPENDENCY(LiveDebugVariables)
205 INITIALIZE_PASS_DEPENDENCY(LiveStacks)
206 INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
207 INITIALIZE_PASS_END(VirtRegRewriter, "virtregrewriter",
208 "Virtual Register Rewriter", false, false)
210 char VirtRegRewriter::ID = 0;
212 void VirtRegRewriter::getAnalysisUsage(AnalysisUsage &AU) const {
213 AU.setPreservesCFG();
214 AU.addRequired<LiveIntervals>();
215 AU.addRequired<SlotIndexes>();
216 AU.addPreserved<SlotIndexes>();
217 AU.addRequired<LiveDebugVariables>();
218 AU.addRequired<LiveStacks>();
219 AU.addPreserved<LiveStacks>();
220 AU.addRequired<VirtRegMap>();
221 MachineFunctionPass::getAnalysisUsage(AU);
224 bool VirtRegRewriter::runOnMachineFunction(MachineFunction &fn) {
226 TM = &MF->getTarget();
227 TRI = MF->getSubtarget().getRegisterInfo();
228 TII = MF->getSubtarget().getInstrInfo();
229 MRI = &MF->getRegInfo();
230 Indexes = &getAnalysis<SlotIndexes>();
231 LIS = &getAnalysis<LiveIntervals>();
232 VRM = &getAnalysis<VirtRegMap>();
233 DEBUG(dbgs() << "********** REWRITE VIRTUAL REGISTERS **********\n"
234 << "********** Function: "
235 << MF->getName() << '\n');
238 // Add kill flags while we still have virtual registers.
239 LIS->addKillFlags(VRM);
241 // Live-in lists on basic blocks are required for physregs.
244 // Rewrite virtual registers.
247 // Write out new DBG_VALUE instructions.
248 getAnalysis<LiveDebugVariables>().emitDebugValues(VRM);
250 // All machine operands and other references to virtual registers have been
251 // replaced. Remove the virtual registers and release all the transient data.
253 MRI->clearVirtRegs();
257 void VirtRegRewriter::addLiveInsForSubRanges(const LiveInterval &LI,
258 unsigned PhysReg) const {
260 assert(LI.hasSubRanges());
262 typedef std::pair<const LiveInterval::SubRange *,
263 LiveInterval::const_iterator> SubRangeIteratorPair;
264 SmallVector<SubRangeIteratorPair, 4> SubRanges;
267 for (const LiveInterval::SubRange &SR : LI.subranges()) {
268 SubRanges.push_back(std::make_pair(&SR, SR.begin()));
269 if (!First.isValid() || SR.segments.front().start < First)
270 First = SR.segments.front().start;
271 if (!Last.isValid() || SR.segments.back().end > Last)
272 Last = SR.segments.back().end;
275 // Check all mbb start positions between First and Last while
276 // simulatenously advancing an iterator for each subrange.
277 for (SlotIndexes::MBBIndexIterator MBBI = Indexes->findMBBIndex(First);
278 MBBI != Indexes->MBBIndexEnd() && MBBI->first <= Last; ++MBBI) {
279 SlotIndex MBBBegin = MBBI->first;
280 // Advance all subrange iterators so that their end position is just
281 // behind MBBBegin (or the iterator is at the end).
282 LaneBitmask LaneMask;
283 for (auto &RangeIterPair : SubRanges) {
284 const LiveInterval::SubRange *SR = RangeIterPair.first;
285 LiveInterval::const_iterator &SRI = RangeIterPair.second;
286 while (SRI != SR->end() && SRI->end <= MBBBegin)
288 if (SRI == SR->end())
290 if (SRI->start <= MBBBegin)
291 LaneMask |= SR->LaneMask;
295 MachineBasicBlock *MBB = MBBI->second;
296 MBB->addLiveIn(PhysReg, LaneMask);
300 // Compute MBB live-in lists from virtual register live ranges and their
302 void VirtRegRewriter::addMBBLiveIns() {
303 for (unsigned Idx = 0, IdxE = MRI->getNumVirtRegs(); Idx != IdxE; ++Idx) {
304 unsigned VirtReg = TargetRegisterInfo::index2VirtReg(Idx);
305 if (MRI->reg_nodbg_empty(VirtReg))
307 LiveInterval &LI = LIS->getInterval(VirtReg);
308 if (LI.empty() || LIS->intervalIsInOneMBB(LI))
310 // This is a virtual register that is live across basic blocks. Its
311 // assigned PhysReg must be marked as live-in to those blocks.
312 unsigned PhysReg = VRM->getPhys(VirtReg);
313 assert(PhysReg != VirtRegMap::NO_PHYS_REG && "Unmapped virtual register.");
315 if (LI.hasSubRanges()) {
316 addLiveInsForSubRanges(LI, PhysReg);
318 // Go over MBB begin positions and see if we have segments covering them.
319 // The following works because segments and the MBBIndex list are both
320 // sorted by slot indexes.
321 SlotIndexes::MBBIndexIterator I = Indexes->MBBIndexBegin();
322 for (const auto &Seg : LI) {
323 I = Indexes->advanceMBBIndex(I, Seg.start);
324 for (; I != Indexes->MBBIndexEnd() && I->first < Seg.end; ++I) {
325 MachineBasicBlock *MBB = I->second;
326 MBB->addLiveIn(PhysReg);
332 // Sort and unique MBB LiveIns as we've not checked if SubReg/PhysReg were in
333 // each MBB's LiveIns set before calling addLiveIn on them.
334 for (MachineBasicBlock &MBB : *MF)
335 MBB.sortUniqueLiveIns();
338 /// Returns true if the given machine operand \p MO only reads undefined lanes.
339 /// The function only works for use operands with a subregister set.
340 bool VirtRegRewriter::readsUndefSubreg(const MachineOperand &MO) const {
341 // Shortcut if the operand is already marked undef.
345 unsigned Reg = MO.getReg();
346 const LiveInterval &LI = LIS->getInterval(Reg);
347 const MachineInstr &MI = *MO.getParent();
348 SlotIndex BaseIndex = LIS->getInstructionIndex(MI);
349 // This code is only meant to handle reading undefined subregisters which
350 // we couldn't properly detect before.
351 assert(LI.liveAt(BaseIndex) &&
352 "Reads of completely dead register should be marked undef already");
353 unsigned SubRegIdx = MO.getSubReg();
354 assert(SubRegIdx != 0 && LI.hasSubRanges());
355 LaneBitmask UseMask = TRI->getSubRegIndexLaneMask(SubRegIdx);
356 // See if any of the relevant subregister liveranges is defined at this point.
357 for (const LiveInterval::SubRange &SR : LI.subranges()) {
358 if ((SR.LaneMask & UseMask).any() && SR.liveAt(BaseIndex))
364 void VirtRegRewriter::handleIdentityCopy(MachineInstr &MI) const {
365 if (!MI.isIdentityCopy())
367 DEBUG(dbgs() << "Identity copy: " << MI);
371 // %R0 = COPY %R0<undef>
372 // %AL = COPY %AL, %EAX<imp-def>
373 // give us additional liveness information: The target (super-)register
374 // must not be valid before this point. Replace the COPY with a KILL
375 // instruction to maintain this information.
376 if (MI.getOperand(0).isUndef() || MI.getNumOperands() > 2) {
377 MI.setDesc(TII->get(TargetOpcode::KILL));
378 DEBUG(dbgs() << " replace by: " << MI);
383 Indexes->removeSingleMachineInstrFromMaps(MI);
384 MI.eraseFromBundle();
385 DEBUG(dbgs() << " deleted.\n");
388 /// The liverange splitting logic sometimes produces bundles of copies when
389 /// subregisters are involved. Expand these into a sequence of copy instructions
390 /// after processing the last in the bundle. Does not update LiveIntervals
391 /// which we shouldn't need for this instruction anymore.
392 void VirtRegRewriter::expandCopyBundle(MachineInstr &MI) const {
396 if (MI.isBundledWithPred() && !MI.isBundledWithSucc()) {
397 // Only do this when the complete bundle is made out of COPYs.
398 MachineBasicBlock &MBB = *MI.getParent();
399 for (MachineBasicBlock::reverse_instr_iterator I =
400 std::next(MI.getReverseIterator()), E = MBB.instr_rend();
401 I != E && I->isBundledWithSucc(); ++I) {
406 for (MachineBasicBlock::reverse_instr_iterator I = MI.getReverseIterator();
407 I->isBundledWithPred(); ) {
408 MachineInstr &MI = *I;
411 MI.unbundleFromPred();
413 Indexes->insertMachineInstrInMaps(MI);
418 void VirtRegRewriter::rewrite() {
419 bool NoSubRegLiveness = !MRI->subRegLivenessEnabled();
420 SmallVector<unsigned, 8> SuperDeads;
421 SmallVector<unsigned, 8> SuperDefs;
422 SmallVector<unsigned, 8> SuperKills;
424 for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
425 MBBI != MBBE; ++MBBI) {
426 DEBUG(MBBI->print(dbgs(), Indexes));
427 for (MachineBasicBlock::instr_iterator
428 MII = MBBI->instr_begin(), MIE = MBBI->instr_end(); MII != MIE;) {
429 MachineInstr *MI = &*MII;
432 for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
433 MOE = MI->operands_end(); MOI != MOE; ++MOI) {
434 MachineOperand &MO = *MOI;
436 // Make sure MRI knows about registers clobbered by regmasks.
438 MRI->addPhysRegsUsedFromRegMask(MO.getRegMask());
440 if (!MO.isReg() || !TargetRegisterInfo::isVirtualRegister(MO.getReg()))
442 unsigned VirtReg = MO.getReg();
443 unsigned PhysReg = VRM->getPhys(VirtReg);
444 assert(PhysReg != VirtRegMap::NO_PHYS_REG &&
445 "Instruction uses unmapped VirtReg");
446 assert(!MRI->isReserved(PhysReg) && "Reserved register assignment");
448 // Preserve semantics of sub-register operands.
449 unsigned SubReg = MO.getSubReg();
451 if (NoSubRegLiveness) {
452 // A virtual register kill refers to the whole register, so we may
453 // have to add <imp-use,kill> operands for the super-register. A
454 // partial redef always kills and redefines the super-register.
455 if (MO.readsReg() && (MO.isDef() || MO.isKill()))
456 SuperKills.push_back(PhysReg);
459 // Also add implicit defs for the super-register.
461 SuperDeads.push_back(PhysReg);
463 SuperDefs.push_back(PhysReg);
467 if (readsUndefSubreg(MO))
468 // We need to add an <undef> flag if the subregister is
469 // completely undefined (and we are not adding super-register
472 } else if (!MO.isDead()) {
477 // The <def,undef> and <def,internal> flags only make sense for
478 // sub-register defs, and we are substituting a full physreg. An
479 // <imp-use,kill> operand from the SuperKills list will represent the
480 // partial read of the super-register.
482 MO.setIsUndef(false);
483 MO.setIsInternalRead(false);
486 // PhysReg operands cannot have subregister indexes.
487 PhysReg = TRI->getSubReg(PhysReg, SubReg);
488 assert(PhysReg && "Invalid SubReg for physical register");
491 // Rewrite. Note we could have used MachineOperand::substPhysReg(), but
492 // we need the inlining here.
496 // Add any missing super-register kills after rewriting the whole
498 while (!SuperKills.empty())
499 MI->addRegisterKilled(SuperKills.pop_back_val(), TRI, true);
501 while (!SuperDeads.empty())
502 MI->addRegisterDead(SuperDeads.pop_back_val(), TRI, true);
504 while (!SuperDefs.empty())
505 MI->addRegisterDefined(SuperDefs.pop_back_val(), TRI);
507 DEBUG(dbgs() << "> " << *MI);
509 expandCopyBundle(*MI);
511 // We can remove identity copies right now.
512 handleIdentityCopy(*MI);