1 //===-- LiveIntervals.cpp - Live Interval Analysis ------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the LiveInterval analysis pass which is used
11 // by the Linear Scan Register allocator. This pass linearizes the
12 // basic blocks of the function in DFS order and uses the
13 // LiveVariables pass to conservatively compute live intervals for
14 // each virtual and physical register.
16 //===----------------------------------------------------------------------===//
18 #define DEBUG_TYPE "liveintervals"
19 #include "LiveIntervals.h"
20 #include "llvm/Value.h"
21 #include "llvm/Analysis/LoopInfo.h"
22 #include "llvm/CodeGen/LiveVariables.h"
23 #include "llvm/CodeGen/MachineFrameInfo.h"
24 #include "llvm/CodeGen/MachineInstr.h"
25 #include "llvm/CodeGen/Passes.h"
26 #include "llvm/CodeGen/SSARegMap.h"
27 #include "llvm/Target/MRegisterInfo.h"
28 #include "llvm/Target/TargetInstrInfo.h"
29 #include "llvm/Target/TargetMachine.h"
30 #include "Support/CommandLine.h"
31 #include "Support/Debug.h"
32 #include "Support/Statistic.h"
33 #include "Support/STLExtras.h"
34 #include "VirtRegMap.h"
41 RegisterAnalysis<LiveIntervals> X("liveintervals",
42 "Live Interval Analysis");
44 Statistic<> numIntervals
45 ("liveintervals", "Number of original intervals");
47 Statistic<> numIntervalsAfter
48 ("liveintervals", "Number of intervals after coalescing");
51 ("liveintervals", "Number of interval joins performed");
54 ("liveintervals", "Number of identity moves eliminated after coalescing");
57 ("liveintervals", "Number of loads/stores folded into instructions");
60 join("join-liveintervals",
61 cl::desc("Join compatible live intervals"),
65 void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const
67 AU.addPreserved<LiveVariables>();
68 AU.addRequired<LiveVariables>();
69 AU.addPreservedID(PHIEliminationID);
70 AU.addRequiredID(PHIEliminationID);
71 AU.addRequiredID(TwoAddressInstructionPassID);
72 AU.addRequired<LoopInfo>();
73 MachineFunctionPass::getAnalysisUsage(AU);
76 void LiveIntervals::releaseMemory()
87 /// runOnMachineFunction - Register allocate the whole function
89 bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
91 tm_ = &fn.getTarget();
92 mri_ = tm_->getRegisterInfo();
93 lv_ = &getAnalysis<LiveVariables>();
95 // number MachineInstrs
97 for (MachineFunction::iterator mbb = mf_->begin(), mbbEnd = mf_->end();
98 mbb != mbbEnd; ++mbb) {
99 unsigned mbbIdx = lv_->getMachineBasicBlockIndex(mbb);
100 bool inserted = mbbi2mbbMap_.insert(std::make_pair(mbbIdx,
102 assert(inserted && "multiple index -> MachineBasicBlock");
104 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
106 inserted = mi2iMap_.insert(std::make_pair(mi, miIndex)).second;
107 assert(inserted && "multiple MachineInstr -> index mappings");
108 i2miMap_.push_back(mi);
109 miIndex += InstrSlots::NUM;
115 numIntervals += intervals_.size();
117 // join intervals if requested
118 if (join) joinIntervals();
120 numIntervalsAfter += intervals_.size();
122 // perform a final pass over the instructions and compute spill
123 // weights, coalesce virtual registers and remove identity moves
124 const LoopInfo& loopInfo = getAnalysis<LoopInfo>();
125 const TargetInstrInfo& tii = tm_->getInstrInfo();
127 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
128 mbbi != mbbe; ++mbbi) {
129 MachineBasicBlock* mbb = mbbi;
130 unsigned loopDepth = loopInfo.getLoopDepth(mbb->getBasicBlock());
132 for (MachineBasicBlock::iterator mii = mbb->begin(), mie = mbb->end();
134 // if the move will be an identity move delete it
135 unsigned srcReg, dstReg;
136 if (tii.isMoveInstr(*mii, srcReg, dstReg) &&
137 rep(srcReg) == rep(dstReg)) {
138 // remove from def list
139 Interval& interval = getOrCreateInterval(rep(dstReg));
140 // remove index -> MachineInstr and
141 // MachineInstr -> index mappings
142 Mi2IndexMap::iterator mi2i = mi2iMap_.find(mii);
143 if (mi2i != mi2iMap_.end()) {
144 i2miMap_[mi2i->second/InstrSlots::NUM] = 0;
145 mi2iMap_.erase(mi2i);
147 mii = mbbi->erase(mii);
151 for (unsigned i = 0; i < mii->getNumOperands(); ++i) {
152 const MachineOperand& mop = mii->getOperand(i);
153 if (mop.isRegister() && mop.getReg() &&
154 MRegisterInfo::isVirtualRegister(mop.getReg())) {
155 // replace register with representative register
156 unsigned reg = rep(mop.getReg());
157 mii->SetMachineOperandReg(i, reg);
159 Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
160 assert(r2iit != r2iMap_.end());
161 r2iit->second->weight +=
162 (mop.isUse() + mop.isDef()) * pow(10.0F, loopDepth);
171 DEBUG(std::cerr << "********** INTERVALS **********\n");
172 DEBUG(std::copy(intervals_.begin(), intervals_.end(),
173 std::ostream_iterator<Interval>(std::cerr, "\n")));
174 DEBUG(std::cerr << "********** MACHINEINSTRS **********\n");
176 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
177 mbbi != mbbe; ++mbbi) {
178 std::cerr << ((Value*)mbbi->getBasicBlock())->getName() << ":\n";
179 for (MachineBasicBlock::iterator mii = mbbi->begin(),
180 mie = mbbi->end(); mii != mie; ++mii) {
181 std::cerr << getInstructionIndex(mii) << '\t';
182 mii->print(std::cerr, *tm_);
189 std::vector<Interval*> LiveIntervals::addIntervalsForSpills(const Interval& li,
193 std::vector<Interval*> added;
195 assert(li.weight != HUGE_VAL &&
196 "attempt to spill already spilled interval!");
198 DEBUG(std::cerr << "\t\t\t\tadding intervals for spills for interval: "
201 const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(li.reg);
203 for (Interval::Ranges::const_iterator
204 i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
205 unsigned index = getBaseIndex(i->first);
206 unsigned end = getBaseIndex(i->second-1) + InstrSlots::NUM;
207 for (; index < end; index += InstrSlots::NUM) {
208 // skip deleted instructions
209 while (!getInstructionFromIndex(index)) index += InstrSlots::NUM;
210 MachineBasicBlock::iterator mi = getInstructionFromIndex(index);
213 for (unsigned i = 0; i < mi->getNumOperands(); ++i) {
214 MachineOperand& mop = mi->getOperand(i);
215 if (mop.isRegister() && mop.getReg() == li.reg) {
216 if (MachineInstr* fmi =
217 mri_->foldMemoryOperand(mi, i, slot)) {
218 lv_->instructionChanged(mi, fmi);
219 vrm.virtFolded(li.reg, mi, fmi);
221 i2miMap_[index/InstrSlots::NUM] = fmi;
222 mi2iMap_[fmi] = index;
223 MachineBasicBlock& mbb = *mi->getParent();
224 mi = mbb.insert(mbb.erase(mi), fmi);
229 // This is tricky. We need to add information in
230 // the interval about the spill code so we have to
231 // use our extra load/store slots.
233 // If we have a use we are going to have a load so
234 // we start the interval from the load slot
235 // onwards. Otherwise we start from the def slot.
236 unsigned start = (mop.isUse() ?
237 getLoadIndex(index) :
239 // If we have a def we are going to have a store
240 // right after it so we end the interval after the
241 // use of the next instruction. Otherwise we end
242 // after the use of this instruction.
243 unsigned end = 1 + (mop.isDef() ?
244 getUseIndex(index+InstrSlots::NUM) :
247 // create a new register for this spill
249 mf_->getSSARegMap()->createVirtualRegister(rc);
250 mi->SetMachineOperandReg(i, nReg);
252 vrm.assignVirt2StackSlot(nReg, slot);
253 Interval& nI = getOrCreateInterval(nReg);
255 // the spill weight is now infinity as it
256 // cannot be spilled again
257 nI.weight = HUGE_VAL;
258 nI.addRange(start, end);
259 added.push_back(&nI);
260 // update live variables
261 lv_->addVirtualRegisterKilled(nReg, mi->getParent(),mi);
262 DEBUG(std::cerr << "\t\t\t\tadded new interval: "
273 void LiveIntervals::printRegName(unsigned reg) const
275 if (MRegisterInfo::isPhysicalRegister(reg))
276 std::cerr << mri_->getName(reg);
278 std::cerr << "%reg" << reg;
281 void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
282 MachineBasicBlock::iterator mi,
285 DEBUG(std::cerr << "\t\tregister: "; printRegName(interval.reg));
286 LiveVariables::VarInfo& vi = lv_->getVarInfo(interval.reg);
288 // iterate over all of the blocks that the variable is completely
289 // live in, adding them to the live interval. obviously we only
290 // need to do this once.
291 if (interval.empty()) {
292 for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
293 if (vi.AliveBlocks[i]) {
294 MachineBasicBlock* mbb = lv_->getIndexMachineBasicBlock(i);
297 getInstructionIndex(&mbb->front()),
298 getInstructionIndex(&mbb->back()) + InstrSlots::NUM);
304 unsigned baseIndex = getInstructionIndex(mi);
306 bool killedInDefiningBasicBlock = false;
307 for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
308 MachineBasicBlock* killerBlock = vi.Kills[i].first;
309 MachineInstr* killerInstr = vi.Kills[i].second;
310 unsigned start = (mbb == killerBlock ?
311 getDefIndex(baseIndex) :
312 getInstructionIndex(&killerBlock->front()));
313 unsigned end = (killerInstr == mi ?
317 getUseIndex(getInstructionIndex(killerInstr))+1);
318 // we do not want to add invalid ranges. these can happen when
319 // a variable has its latest use and is redefined later on in
320 // the same basic block (common with variables introduced by
323 killedInDefiningBasicBlock |= mbb == killerBlock;
324 interval.addRange(start, end);
328 if (!killedInDefiningBasicBlock) {
329 unsigned end = getInstructionIndex(&mbb->back()) + InstrSlots::NUM;
330 interval.addRange(getDefIndex(baseIndex), end);
332 DEBUG(std::cerr << '\n');
335 void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
336 MachineBasicBlock::iterator mi,
339 DEBUG(std::cerr << "\t\tregister: "; printRegName(interval.reg));
340 typedef LiveVariables::killed_iterator KillIter;
342 MachineBasicBlock::iterator e = mbb->end();
343 unsigned baseIndex = getInstructionIndex(mi);
344 unsigned start = getDefIndex(baseIndex);
345 unsigned end = start;
347 // a variable can be dead by the instruction defining it
348 for (KillIter ki = lv_->dead_begin(mi), ke = lv_->dead_end(mi);
350 if (interval.reg == ki->second) {
351 DEBUG(std::cerr << " dead");
352 end = getDefIndex(start) + 1;
357 // a variable can only be killed by subsequent instructions
360 baseIndex += InstrSlots::NUM;
361 for (KillIter ki = lv_->killed_begin(mi), ke = lv_->killed_end(mi);
363 if (interval.reg == ki->second) {
364 DEBUG(std::cerr << " killed");
365 end = getUseIndex(baseIndex) + 1;
372 assert(start < end && "did not find end of interval?");
373 interval.addRange(start, end);
374 DEBUG(std::cerr << '\n');
377 void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
378 MachineBasicBlock::iterator mi,
381 if (MRegisterInfo::isPhysicalRegister(reg)) {
382 if (lv_->getAllocatablePhysicalRegisters()[reg]) {
383 handlePhysicalRegisterDef(mbb, mi, getOrCreateInterval(reg));
384 for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
385 handlePhysicalRegisterDef(mbb, mi, getOrCreateInterval(*as));
389 handleVirtualRegisterDef(mbb, mi, getOrCreateInterval(reg));
392 unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
394 Mi2IndexMap::const_iterator it = mi2iMap_.find(instr);
395 return (it == mi2iMap_.end() ?
396 std::numeric_limits<unsigned>::max() :
400 MachineInstr* LiveIntervals::getInstructionFromIndex(unsigned index) const
402 index /= InstrSlots::NUM; // convert index to vector index
403 assert(index < i2miMap_.size() &&
404 "index does not correspond to an instruction");
405 return i2miMap_[index];
408 /// computeIntervals - computes the live intervals for virtual
409 /// registers. for some ordering of the machine instructions [1,N] a
410 /// live interval is an interval [i, j) where 1 <= i <= j < N for
411 /// which a variable is live
412 void LiveIntervals::computeIntervals()
414 DEBUG(std::cerr << "********** COMPUTING LIVE INTERVALS **********\n");
415 DEBUG(std::cerr << "********** Function: "
416 << ((Value*)mf_->getFunction())->getName() << '\n');
418 for (MbbIndex2MbbMap::iterator
419 it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
421 MachineBasicBlock* mbb = it->second;
422 DEBUG(std::cerr << ((Value*)mbb->getBasicBlock())->getName() << ":\n");
424 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
426 const TargetInstrDescriptor& tid =
427 tm_->getInstrInfo().get(mi->getOpcode());
428 DEBUG(std::cerr << getInstructionIndex(mi) << "\t";
429 mi->print(std::cerr, *tm_));
431 // handle implicit defs
432 for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
433 handleRegisterDef(mbb, mi, *id);
435 // handle explicit defs
436 for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
437 MachineOperand& mop = mi->getOperand(i);
438 // handle register defs - build intervals
439 if (mop.isRegister() && mop.getReg() && mop.isDef())
440 handleRegisterDef(mbb, mi, mop.getReg());
446 unsigned LiveIntervals::rep(unsigned reg)
448 Reg2RegMap::iterator it = r2rMap_.find(reg);
449 if (it != r2rMap_.end())
450 return it->second = rep(it->second);
454 void LiveIntervals::joinIntervals()
456 DEBUG(std::cerr << "********** JOINING INTERVALS ***********\n");
458 const TargetInstrInfo& tii = tm_->getInstrInfo();
460 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
461 mbbi != mbbe; ++mbbi) {
462 MachineBasicBlock* mbb = mbbi;
463 DEBUG(std::cerr << ((Value*)mbb->getBasicBlock())->getName() << ":\n");
465 for (MachineBasicBlock::iterator mi = mbb->begin(), mie = mbb->end();
467 const TargetInstrDescriptor& tid =
468 tm_->getInstrInfo().get(mi->getOpcode());
469 DEBUG(std::cerr << getInstructionIndex(mi) << '\t';
470 mi->print(std::cerr, *tm_););
472 // we only join virtual registers with allocatable
473 // physical registers since we do not have liveness information
474 // on not allocatable physical registers
476 if (tii.isMoveInstr(*mi, regA, regB) &&
477 (MRegisterInfo::isVirtualRegister(regA) ||
478 lv_->getAllocatablePhysicalRegisters()[regA]) &&
479 (MRegisterInfo::isVirtualRegister(regB) ||
480 lv_->getAllocatablePhysicalRegisters()[regB])) {
482 // get representative registers
486 // if they are already joined we continue
490 Reg2IntervalMap::iterator r2iA = r2iMap_.find(regA);
491 assert(r2iA != r2iMap_.end());
492 Reg2IntervalMap::iterator r2iB = r2iMap_.find(regB);
493 assert(r2iB != r2iMap_.end());
495 Intervals::iterator intA = r2iA->second;
496 Intervals::iterator intB = r2iB->second;
498 // both A and B are virtual registers
499 if (MRegisterInfo::isVirtualRegister(intA->reg) &&
500 MRegisterInfo::isVirtualRegister(intB->reg)) {
502 const TargetRegisterClass *rcA, *rcB;
503 rcA = mf_->getSSARegMap()->getRegClass(intA->reg);
504 rcB = mf_->getSSARegMap()->getRegClass(intB->reg);
505 assert(rcA == rcB && "registers must be of the same class");
507 // if their intervals do not overlap we join them
508 if (!intB->overlaps(*intA)) {
510 r2iB->second = r2iA->second;
511 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
512 intervals_.erase(intB);
515 else if (MRegisterInfo::isPhysicalRegister(intA->reg) ^
516 MRegisterInfo::isPhysicalRegister(intB->reg)) {
517 if (MRegisterInfo::isPhysicalRegister(intB->reg)) {
518 std::swap(regA, regB);
519 std::swap(intA, intB);
520 std::swap(r2iA, r2iB);
523 assert(MRegisterInfo::isPhysicalRegister(intA->reg) &&
524 MRegisterInfo::isVirtualRegister(intB->reg) &&
525 "A must be physical and B must be virtual");
527 if (!intA->overlaps(*intB) &&
528 !overlapsAliases(*intA, *intB)) {
530 r2iB->second = r2iA->second;
531 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
532 intervals_.erase(intB);
540 bool LiveIntervals::overlapsAliases(const Interval& lhs,
541 const Interval& rhs) const
543 assert(MRegisterInfo::isPhysicalRegister(lhs.reg) &&
544 "first interval must describe a physical register");
546 for (const unsigned* as = mri_->getAliasSet(lhs.reg); *as; ++as) {
547 Reg2IntervalMap::const_iterator r2i = r2iMap_.find(*as);
548 assert(r2i != r2iMap_.end() && "alias does not have interval?");
549 if (rhs.overlaps(*r2i->second))
556 Interval& LiveIntervals::getOrCreateInterval(unsigned reg)
558 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
559 if (r2iit == r2iMap_.end() || r2iit->first != reg) {
560 intervals_.push_back(Interval(reg));
561 r2iit = r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
564 return *r2iit->second;
567 Interval::Interval(unsigned r)
569 weight((MRegisterInfo::isPhysicalRegister(r) ? HUGE_VAL : 0.0F))
573 bool Interval::spilled() const
575 return (weight == HUGE_VAL &&
576 MRegisterInfo::isVirtualRegister(reg));
579 // An example for liveAt():
581 // this = [1,4), liveAt(0) will return false. The instruction defining
582 // this spans slots [0,3]. The interval belongs to an spilled
583 // definition of the variable it represents. This is because slot 1 is
584 // used (def slot) and spans up to slot 3 (store slot).
586 bool Interval::liveAt(unsigned index) const
588 Range dummy(index, index+1);
589 Ranges::const_iterator r = std::upper_bound(ranges.begin(),
592 if (r == ranges.begin())
596 return index >= r->first && index < r->second;
599 // An example for overlaps():
603 // 8: C = A + B ;; last use of A
605 // The live intervals should look like:
611 // A->overlaps(C) should return false since we want to be able to join
613 bool Interval::overlaps(const Interval& other) const
615 Ranges::const_iterator i = ranges.begin();
616 Ranges::const_iterator ie = ranges.end();
617 Ranges::const_iterator j = other.ranges.begin();
618 Ranges::const_iterator je = other.ranges.end();
619 if (i->first < j->first) {
620 i = std::upper_bound(i, ie, *j);
621 if (i != ranges.begin()) --i;
623 else if (j->first < i->first) {
624 j = std::upper_bound(j, je, *i);
625 if (j != other.ranges.begin()) --j;
628 while (i != ie && j != je) {
629 if (i->first == j->first) {
633 if (i->first > j->first) {
637 assert(i->first < j->first);
639 if (i->second > j->first) {
651 void Interval::addRange(unsigned start, unsigned end)
653 assert(start < end && "Invalid range to add!");
654 DEBUG(std::cerr << " +[" << start << ',' << end << ")");
655 //assert(start < end && "invalid range?");
656 Range range = std::make_pair(start, end);
657 Ranges::iterator it =
658 ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
661 it = mergeRangesForward(it);
662 it = mergeRangesBackward(it);
665 void Interval::join(const Interval& other)
667 DEBUG(std::cerr << "\t\tjoining " << *this << " with " << other << '\n');
668 Ranges::iterator cur = ranges.begin();
670 for (Ranges::const_iterator i = other.ranges.begin(),
671 e = other.ranges.end(); i != e; ++i) {
672 cur = ranges.insert(std::upper_bound(cur, ranges.end(), *i), *i);
673 cur = mergeRangesForward(cur);
674 cur = mergeRangesBackward(cur);
676 weight += other.weight;
680 Interval::Ranges::iterator Interval::mergeRangesForward(Ranges::iterator it)
683 while ((n = next(it)) != ranges.end()) {
684 if (n->first > it->second)
686 it->second = std::max(it->second, n->second);
692 Interval::Ranges::iterator Interval::mergeRangesBackward(Ranges::iterator it)
694 while (it != ranges.begin()) {
695 Ranges::iterator p = prior(it);
696 if (it->first > p->second)
699 it->first = std::min(it->first, p->first);
700 it->second = std::max(it->second, p->second);
701 it = ranges.erase(p);
707 std::ostream& llvm::operator<<(std::ostream& os, const Interval& li)
709 os << "%reg" << li.reg << ',' << li.weight;
711 return os << "EMPTY";
714 for (Interval::Ranges::const_iterator
715 i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
716 os << "[" << i->first << "," << i->second << ")";