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/Analysis/LoopInfo.h"
21 #include "llvm/CodeGen/LiveVariables.h"
22 #include "llvm/CodeGen/MachineFrameInfo.h"
23 #include "llvm/CodeGen/MachineInstr.h"
24 #include "llvm/CodeGen/Passes.h"
25 #include "llvm/CodeGen/SSARegMap.h"
26 #include "llvm/Target/MRegisterInfo.h"
27 #include "llvm/Target/TargetInstrInfo.h"
28 #include "llvm/Target/TargetMachine.h"
29 #include "llvm/Support/CFG.h"
30 #include "Support/CommandLine.h"
31 #include "Support/Debug.h"
32 #include "Support/Statistic.h"
33 #include "Support/STLExtras.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 const std::pair<MachineBasicBlock*, unsigned>& entry =
100 lv_->getMachineBasicBlockInfo(mbb);
101 bool inserted = mbbi2mbbMap_.insert(std::make_pair(entry.second,
102 entry.first)).second;
103 assert(inserted && "multiple index -> MachineBasicBlock");
105 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
107 inserted = mi2iMap_.insert(std::make_pair(mi, miIndex)).second;
108 assert(inserted && "multiple MachineInstr -> index mappings");
109 i2miMap_.push_back(mi);
110 miIndex += InstrSlots::NUM;
116 numIntervals += intervals_.size();
118 // join intervals if requested
119 if (join) joinIntervals();
121 numIntervalsAfter += intervals_.size();
123 // perform a final pass over the instructions and compute spill
124 // weights, coalesce virtual registers and remove identity moves
125 const LoopInfo& loopInfo = getAnalysis<LoopInfo>();
126 const TargetInstrInfo& tii = tm_->getInstrInfo();
128 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
129 mbbi != mbbe; ++mbbi) {
130 MachineBasicBlock* mbb = mbbi;
131 unsigned loopDepth = loopInfo.getLoopDepth(mbb->getBasicBlock());
133 for (MachineBasicBlock::iterator mii = mbb->begin(), mie = mbb->end();
135 for (unsigned i = 0; i < mii->getNumOperands(); ++i) {
136 const MachineOperand& mop = mii->getOperand(i);
137 if (mop.isRegister() && mop.getReg()) {
138 // replace register with representative register
139 unsigned reg = rep(mop.getReg());
140 mii->SetMachineOperandReg(i, reg);
142 if (MRegisterInfo::isVirtualRegister(reg)) {
143 Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
144 assert(r2iit != r2iMap_.end());
145 r2iit->second->weight += pow(10.0F, loopDepth);
150 // if the move is now an identity move delete it
151 unsigned srcReg, dstReg;
152 if (tii.isMoveInstr(*mii, srcReg, dstReg) && srcReg == dstReg) {
153 // remove index -> MachineInstr and
154 // MachineInstr -> index mappings
155 Mi2IndexMap::iterator mi2i = mi2iMap_.find(mii);
156 if (mi2i != mi2iMap_.end()) {
157 i2miMap_[mi2i->second/InstrSlots::NUM] = 0;
158 mi2iMap_.erase(mi2i);
160 mii = mbbi->erase(mii);
168 intervals_.sort(StartPointComp());
169 DEBUG(std::cerr << "********** INTERVALS **********\n");
170 DEBUG(std::copy(intervals_.begin(), intervals_.end(),
171 std::ostream_iterator<Interval>(std::cerr, "\n")));
172 DEBUG(std::cerr << "********** MACHINEINSTRS **********\n");
174 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
175 mbbi != mbbe; ++mbbi) {
176 std::cerr << mbbi->getBasicBlock()->getName() << ":\n";
177 for (MachineBasicBlock::iterator mii = mbbi->begin(),
178 mie = mbbi->end(); mii != mie; ++mii) {
179 std::cerr << getInstructionIndex(mii) << '\t';
180 mii->print(std::cerr, *tm_);
187 void LiveIntervals::updateSpilledInterval(Interval& li, int slot)
189 assert(li.weight != std::numeric_limits<float>::infinity() &&
190 "attempt to spill already spilled interval!");
191 Interval::Ranges oldRanges;
192 swap(oldRanges, li.ranges);
194 DEBUG(std::cerr << "\t\t\t\tupdating interval: " << li);
196 for (Interval::Ranges::iterator i = oldRanges.begin(), e = oldRanges.end();
198 unsigned index = getBaseIndex(i->first);
199 unsigned end = getBaseIndex(i->second-1) + InstrSlots::NUM;
200 for (; index < end; index += InstrSlots::NUM) {
201 // skip deleted instructions
202 while (!getInstructionFromIndex(index)) index += InstrSlots::NUM;
203 MachineBasicBlock::iterator mi = getInstructionFromIndex(index);
205 for (unsigned i = 0; i < mi->getNumOperands(); ++i) {
206 MachineOperand& mop = mi->getOperand(i);
207 if (mop.isRegister() && mop.getReg() == li.reg) {
208 // This is tricky. We need to add information in
209 // the interval about the spill code so we have to
210 // use our extra load/store slots.
212 // If we have a use we are going to have a load so
213 // we start the interval from the load slot
214 // onwards. Otherwise we start from the def slot.
215 unsigned start = (mop.isUse() ?
216 getLoadIndex(index) :
218 // If we have a def we are going to have a store
219 // right after it so we end the interval after the
220 // use of the next instruction. Otherwise we end
221 // after the use of this instruction.
222 unsigned end = 1 + (mop.isDef() ?
223 getUseIndex(index+InstrSlots::NUM) :
225 li.addRange(start, end);
230 // the new spill weight is now infinity as it cannot be spilled again
231 li.weight = std::numeric_limits<float>::infinity();
232 DEBUG(std::cerr << '\n');
233 DEBUG(std::cerr << "\t\t\t\tupdated interval: " << li << '\n');
236 void LiveIntervals::printRegName(unsigned reg) const
238 if (MRegisterInfo::isPhysicalRegister(reg))
239 std::cerr << mri_->getName(reg);
241 std::cerr << "%reg" << reg;
244 void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
245 MachineBasicBlock::iterator mi,
248 DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
249 LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
251 Interval* interval = 0;
252 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
253 if (r2iit == r2iMap_.end() || r2iit->first != reg) {
255 intervals_.push_back(Interval(reg));
256 // update interval index for this register
257 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
258 interval = &intervals_.back();
260 // iterate over all of the blocks that the variable is
261 // completely live in, adding them to the live
262 // interval. obviously we only need to do this once.
263 for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
264 if (vi.AliveBlocks[i]) {
265 MachineBasicBlock* mbb = lv_->getIndexMachineBasicBlock(i);
268 getInstructionIndex(&mbb->front()),
269 getInstructionIndex(&mbb->back()) + InstrSlots::NUM);
275 interval = &*r2iit->second;
278 unsigned baseIndex = getInstructionIndex(mi);
280 bool killedInDefiningBasicBlock = false;
281 for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
282 MachineBasicBlock* killerBlock = vi.Kills[i].first;
283 MachineInstr* killerInstr = vi.Kills[i].second;
284 unsigned start = (mbb == killerBlock ?
285 getDefIndex(baseIndex) :
286 getInstructionIndex(&killerBlock->front()));
287 unsigned end = (killerInstr == mi ?
291 getUseIndex(getInstructionIndex(killerInstr))+1);
292 // we do not want to add invalid ranges. these can happen when
293 // a variable has its latest use and is redefined later on in
294 // the same basic block (common with variables introduced by
297 killedInDefiningBasicBlock |= mbb == killerBlock;
298 interval->addRange(start, end);
302 if (!killedInDefiningBasicBlock) {
303 unsigned end = getInstructionIndex(&mbb->back()) + InstrSlots::NUM;
304 interval->addRange(getDefIndex(baseIndex), end);
306 DEBUG(std::cerr << '\n');
309 void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
310 MachineBasicBlock::iterator mi,
313 DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
314 typedef LiveVariables::killed_iterator KillIter;
316 MachineBasicBlock::iterator e = mbb->end();
317 unsigned baseIndex = getInstructionIndex(mi);
318 unsigned start = getDefIndex(baseIndex);
319 unsigned end = start;
321 // a variable can be dead by the instruction defining it
322 for (KillIter ki = lv_->dead_begin(mi), ke = lv_->dead_end(mi);
324 if (reg == ki->second) {
325 DEBUG(std::cerr << " dead");
326 end = getDefIndex(start) + 1;
331 // a variable can only be killed by subsequent instructions
334 baseIndex += InstrSlots::NUM;
335 for (KillIter ki = lv_->killed_begin(mi), ke = lv_->killed_end(mi);
337 if (reg == ki->second) {
338 DEBUG(std::cerr << " killed");
339 end = getUseIndex(baseIndex) + 1;
346 assert(start < end && "did not find end of interval?");
348 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
349 if (r2iit != r2iMap_.end() && r2iit->first == reg) {
350 r2iit->second->addRange(start, end);
353 intervals_.push_back(Interval(reg));
354 // update interval index for this register
355 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
356 intervals_.back().addRange(start, end);
358 DEBUG(std::cerr << '\n');
361 void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
362 MachineBasicBlock::iterator mi,
365 if (MRegisterInfo::isPhysicalRegister(reg)) {
366 if (lv_->getAllocatablePhysicalRegisters()[reg]) {
367 handlePhysicalRegisterDef(mbb, mi, reg);
368 for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
369 handlePhysicalRegisterDef(mbb, mi, *as);
373 handleVirtualRegisterDef(mbb, mi, reg);
377 unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
379 Mi2IndexMap::const_iterator it = mi2iMap_.find(instr);
380 return (it == mi2iMap_.end() ?
381 std::numeric_limits<unsigned>::max() :
385 MachineInstr* LiveIntervals::getInstructionFromIndex(unsigned index) const
387 index /= InstrSlots::NUM; // convert index to vector index
388 assert(index < i2miMap_.size() &&
389 "index does not correspond to an instruction");
390 return i2miMap_[index];
393 /// computeIntervals - computes the live intervals for virtual
394 /// registers. for some ordering of the machine instructions [1,N] a
395 /// live interval is an interval [i, j) where 1 <= i <= j < N for
396 /// which a variable is live
397 void LiveIntervals::computeIntervals()
399 DEBUG(std::cerr << "********** COMPUTING LIVE INTERVALS **********\n");
400 DEBUG(std::cerr << "********** Function: "
401 << mf_->getFunction()->getName() << '\n');
403 for (MbbIndex2MbbMap::iterator
404 it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
406 MachineBasicBlock* mbb = it->second;
407 DEBUG(std::cerr << mbb->getBasicBlock()->getName() << ":\n");
409 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
411 const TargetInstrDescriptor& tid =
412 tm_->getInstrInfo().get(mi->getOpcode());
413 DEBUG(std::cerr << getInstructionIndex(mi) << "\t";
414 mi->print(std::cerr, *tm_));
416 // handle implicit defs
417 for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
418 handleRegisterDef(mbb, mi, *id);
420 // handle explicit defs
421 for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
422 MachineOperand& mop = mi->getOperand(i);
423 // handle register defs - build intervals
424 if (mop.isRegister() && mop.getReg() && mop.isDef())
425 handleRegisterDef(mbb, mi, mop.getReg());
431 unsigned LiveIntervals::rep(unsigned reg)
433 Reg2RegMap::iterator it = r2rMap_.find(reg);
434 if (it != r2rMap_.end())
435 return it->second = rep(it->second);
439 void LiveIntervals::joinIntervals()
441 DEBUG(std::cerr << "********** JOINING INTERVALS ***********\n");
443 const TargetInstrInfo& tii = tm_->getInstrInfo();
445 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
446 mbbi != mbbe; ++mbbi) {
447 MachineBasicBlock* mbb = mbbi;
448 DEBUG(std::cerr << mbb->getBasicBlock()->getName() << ":\n");
450 for (MachineBasicBlock::iterator mi = mbb->begin(), mie = mbb->end();
452 const TargetInstrDescriptor& tid =
453 tm_->getInstrInfo().get(mi->getOpcode());
454 DEBUG(std::cerr << getInstructionIndex(mi) << '\t';
455 mi->print(std::cerr, *tm_););
457 // we only join virtual registers with allocatable
458 // physical registers since we do not have liveness information
459 // on not allocatable physical registers
461 if (tii.isMoveInstr(*mi, regA, regB) &&
462 (MRegisterInfo::isVirtualRegister(regA) ||
463 lv_->getAllocatablePhysicalRegisters()[regA]) &&
464 (MRegisterInfo::isVirtualRegister(regB) ||
465 lv_->getAllocatablePhysicalRegisters()[regB])) {
467 // get representative registers
471 // if they are already joined we continue
475 Reg2IntervalMap::iterator r2iA = r2iMap_.find(regA);
476 assert(r2iA != r2iMap_.end());
477 Reg2IntervalMap::iterator r2iB = r2iMap_.find(regB);
478 assert(r2iB != r2iMap_.end());
480 Intervals::iterator intA = r2iA->second;
481 Intervals::iterator intB = r2iB->second;
483 // both A and B are virtual registers
484 if (MRegisterInfo::isVirtualRegister(intA->reg) &&
485 MRegisterInfo::isVirtualRegister(intB->reg)) {
487 const TargetRegisterClass *rcA, *rcB;
488 rcA = mf_->getSSARegMap()->getRegClass(intA->reg);
489 rcB = mf_->getSSARegMap()->getRegClass(intB->reg);
490 assert(rcA == rcB && "registers must be of the same class");
492 // if their intervals do not overlap we join them
493 if (!intB->overlaps(*intA)) {
495 r2iB->second = r2iA->second;
496 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
497 intervals_.erase(intB);
500 else if (MRegisterInfo::isPhysicalRegister(intA->reg) ^
501 MRegisterInfo::isPhysicalRegister(intB->reg)) {
502 if (MRegisterInfo::isPhysicalRegister(intB->reg)) {
503 std::swap(regA, regB);
504 std::swap(intA, intB);
505 std::swap(r2iA, r2iB);
508 assert(MRegisterInfo::isPhysicalRegister(intA->reg) &&
509 MRegisterInfo::isVirtualRegister(intB->reg) &&
510 "A must be physical and B must be virtual");
512 if (!intA->overlaps(*intB) &&
513 !overlapsAliases(*intA, *intB)) {
515 r2iB->second = r2iA->second;
516 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
517 intervals_.erase(intB);
525 bool LiveIntervals::overlapsAliases(const Interval& lhs,
526 const Interval& rhs) const
528 assert(MRegisterInfo::isPhysicalRegister(lhs.reg) &&
529 "first interval must describe a physical register");
531 for (const unsigned* as = mri_->getAliasSet(lhs.reg); *as; ++as) {
532 Reg2IntervalMap::const_iterator r2i = r2iMap_.find(*as);
533 assert(r2i != r2iMap_.end() && "alias does not have interval?");
534 if (rhs.overlaps(*r2i->second))
541 LiveIntervals::Interval::Interval(unsigned r)
543 weight((MRegisterInfo::isPhysicalRegister(r) ?
544 std::numeric_limits<float>::infinity() : 0.0F))
549 bool LiveIntervals::Interval::spilled() const
551 return (weight == std::numeric_limits<float>::infinity() &&
552 MRegisterInfo::isVirtualRegister(reg));
555 // An example for liveAt():
557 // this = [1,4), liveAt(0) will return false. The instruction defining
558 // this spans slots [0,3]. The interval belongs to an spilled
559 // definition of the variable it represents. This is because slot 1 is
560 // used (def slot) and spans up to slot 3 (store slot).
562 bool LiveIntervals::Interval::liveAt(unsigned index) const
564 Range dummy(index, index+1);
565 Ranges::const_iterator r = std::upper_bound(ranges.begin(),
568 if (r == ranges.begin())
572 return index >= r->first && index < r->second;
575 // An example for overlaps():
579 // 8: C = A + B ;; last use of A
581 // The live intervals should look like:
587 // A->overlaps(C) should return false since we want to be able to join
589 bool LiveIntervals::Interval::overlaps(const Interval& other) const
591 Ranges::const_iterator i = ranges.begin();
592 Ranges::const_iterator ie = ranges.end();
593 Ranges::const_iterator j = other.ranges.begin();
594 Ranges::const_iterator je = other.ranges.end();
595 if (i->first < j->first) {
596 i = std::upper_bound(i, ie, *j);
597 if (i != ranges.begin()) --i;
599 else if (j->first < i->first) {
600 j = std::upper_bound(j, je, *i);
601 if (j != other.ranges.begin()) --j;
604 while (i != ie && j != je) {
605 if (i->first == j->first) {
609 if (i->first > j->first) {
613 assert(i->first < j->first);
615 if (i->second > j->first) {
627 void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
629 assert(start < end && "Invalid range to add!");
630 DEBUG(std::cerr << " +[" << start << ',' << end << ")");
631 //assert(start < end && "invalid range?");
632 Range range = std::make_pair(start, end);
633 Ranges::iterator it =
634 ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
637 it = mergeRangesForward(it);
638 it = mergeRangesBackward(it);
641 void LiveIntervals::Interval::join(const LiveIntervals::Interval& other)
643 DEBUG(std::cerr << "\t\tjoining " << *this << " with " << other << '\n');
644 Ranges::iterator cur = ranges.begin();
646 for (Ranges::const_iterator i = other.ranges.begin(),
647 e = other.ranges.end(); i != e; ++i) {
648 cur = ranges.insert(std::upper_bound(cur, ranges.end(), *i), *i);
649 cur = mergeRangesForward(cur);
650 cur = mergeRangesBackward(cur);
652 weight += other.weight;
656 LiveIntervals::Interval::Ranges::iterator
657 LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
660 while ((n = next(it)) != ranges.end()) {
661 if (n->first > it->second)
663 it->second = std::max(it->second, n->second);
669 LiveIntervals::Interval::Ranges::iterator
670 LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
672 while (it != ranges.begin()) {
673 Ranges::iterator p = prior(it);
674 if (it->first > p->second)
677 it->first = std::min(it->first, p->first);
678 it->second = std::max(it->second, p->second);
679 it = ranges.erase(p);
685 std::ostream& llvm::operator<<(std::ostream& os,
686 const LiveIntervals::Interval& li)
688 os << "%reg" << li.reg << ',' << li.weight << " = ";
690 return os << "EMPTY";
691 for (LiveIntervals::Interval::Ranges::const_iterator
692 i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
693 os << "[" << i->first << "," << i->second << ")";