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 "llvm/CodeGen/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("liveintervals", "Number of intervals");
45 Statistic<> numJoined ("liveintervals", "Number of joined intervals");
46 Statistic<> numPeep ("liveintervals", "Number of identity moves "
47 "eliminated after coalescing");
48 Statistic<> numFolded ("liveintervals", "Number of register operands "
51 join("join-liveintervals",
52 cl::desc("Join compatible live intervals"),
56 void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const
58 AU.addPreserved<LiveVariables>();
59 AU.addRequired<LiveVariables>();
60 AU.addPreservedID(PHIEliminationID);
61 AU.addRequiredID(PHIEliminationID);
62 AU.addRequiredID(TwoAddressInstructionPassID);
63 AU.addRequired<LoopInfo>();
64 MachineFunctionPass::getAnalysisUsage(AU);
67 void LiveIntervals::releaseMemory()
78 /// runOnMachineFunction - Register allocate the whole function
80 bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
82 tm_ = &fn.getTarget();
83 mri_ = tm_->getRegisterInfo();
84 lv_ = &getAnalysis<LiveVariables>();
86 // number MachineInstrs
88 for (MachineFunction::iterator mbb = mf_->begin(), mbbEnd = mf_->end();
89 mbb != mbbEnd; ++mbb) {
90 const std::pair<MachineBasicBlock*, unsigned>& entry =
91 lv_->getMachineBasicBlockInfo(mbb);
92 bool inserted = mbbi2mbbMap_.insert(std::make_pair(entry.second,
94 assert(inserted && "multiple index -> MachineBasicBlock");
96 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
98 inserted = mi2iMap_.insert(std::make_pair(mi, miIndex)).second;
99 assert(inserted && "multiple MachineInstr -> index mappings");
100 i2miMap_.push_back(mi);
101 miIndex += InstrSlots::NUM;
107 numIntervals += intervals_.size();
109 // join intervals if requested
110 if (join) joinIntervals();
112 // perform a final pass over the instructions and compute spill
113 // weights, coalesce virtual registers and remove identity moves
114 const LoopInfo& loopInfo = getAnalysis<LoopInfo>();
115 const TargetInstrInfo& tii = tm_->getInstrInfo();
117 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
118 mbbi != mbbe; ++mbbi) {
119 MachineBasicBlock* mbb = mbbi;
120 unsigned loopDepth = loopInfo.getLoopDepth(mbb->getBasicBlock());
122 for (MachineBasicBlock::iterator mii = mbb->begin(), mie = mbb->end();
124 for (unsigned i = 0; i < mii->getNumOperands(); ++i) {
125 const MachineOperand& mop = mii->getOperand(i);
126 if (mop.isRegister()) {
127 // replace register with representative register
128 unsigned reg = rep(mop.getReg());
129 mii->SetMachineOperandReg(i, reg);
131 if (MRegisterInfo::isVirtualRegister(reg)) {
132 Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
133 assert(r2iit != r2iMap_.end());
134 r2iit->second->weight += pow(10.0F, loopDepth);
139 // if the move is now an identity move delete it
140 unsigned srcReg, dstReg;
141 if (tii.isMoveInstr(*mii, srcReg, dstReg) && srcReg == dstReg) {
142 // remove index -> MachineInstr and
143 // MachineInstr -> index mappings
144 Mi2IndexMap::iterator mi2i = mi2iMap_.find(mii);
145 if (mi2i != mi2iMap_.end()) {
146 i2miMap_[mi2i->second/InstrSlots::NUM] = 0;
147 mi2iMap_.erase(mi2i);
149 mii = mbbi->erase(mii);
157 intervals_.sort(StartPointComp());
158 DEBUG(std::cerr << "********** INTERVALS **********\n");
159 DEBUG(std::copy(intervals_.begin(), intervals_.end(),
160 std::ostream_iterator<Interval>(std::cerr, "\n")));
161 DEBUG(std::cerr << "********** MACHINEINSTRS **********\n");
163 for (unsigned i = 0; i != i2miMap_.size(); ++i) {
164 if (const MachineInstr* mi = i2miMap_[i]) {
165 std:: cerr << i * InstrSlots::NUM << '\t';
166 mi->print(std::cerr, *tm_);
173 void LiveIntervals::updateSpilledInterval(Interval& li, int slot)
175 assert(li.weight != std::numeric_limits<float>::infinity() &&
176 "attempt to spill already spilled interval!");
177 Interval::Ranges oldRanges;
178 swap(oldRanges, li.ranges);
180 DEBUG(std::cerr << "\t\t\t\tupdating interval: " << li);
182 for (Interval::Ranges::iterator i = oldRanges.begin(), e = oldRanges.end();
184 unsigned index = getBaseIndex(i->first);
185 unsigned end = getBaseIndex(i->second-1) + InstrSlots::NUM;
186 for (; index < end; index += InstrSlots::NUM) {
187 // skip deleted instructions
188 while (!getInstructionFromIndex(index)) index += InstrSlots::NUM;
189 MachineBasicBlock::iterator mi = getInstructionFromIndex(index);
191 for (unsigned i = 0; i < mi->getNumOperands(); ++i) {
192 MachineOperand& mop = mi->getOperand(i);
193 if (mop.isRegister() && mop.getReg() == li.reg) {
194 // This is tricky. We need to add information in
195 // the interval about the spill code so we have to
196 // use our extra load/store slots.
198 // If we have a use we are going to have a load so
199 // we start the interval from the load slot
200 // onwards. Otherwise we start from the def slot.
201 unsigned start = (mop.isUse() ?
202 getLoadIndex(index) :
204 // If we have a def we are going to have a store
205 // right after it so we end the interval after the
206 // use of the next instruction. Otherwise we end
207 // after the use of this instruction.
208 unsigned end = 1 + (mop.isDef() ?
209 getUseIndex(index+InstrSlots::NUM) :
211 li.addRange(start, end);
216 // the new spill weight is now infinity as it cannot be spilled again
217 li.weight = std::numeric_limits<float>::infinity();
218 DEBUG(std::cerr << '\n');
221 void LiveIntervals::printRegName(unsigned reg) const
223 if (MRegisterInfo::isPhysicalRegister(reg))
224 std::cerr << mri_->getName(reg);
226 std::cerr << "%reg" << reg;
229 void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
230 MachineBasicBlock::iterator mi,
233 DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
234 LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
236 Interval* interval = 0;
237 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
238 if (r2iit == r2iMap_.end() || r2iit->first != reg) {
240 intervals_.push_back(Interval(reg));
241 // update interval index for this register
242 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
243 interval = &intervals_.back();
245 // iterate over all of the blocks that the variable is
246 // completely live in, adding them to the live
247 // interval. obviously we only need to do this once.
248 for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
249 if (vi.AliveBlocks[i]) {
250 MachineBasicBlock* mbb = lv_->getIndexMachineBasicBlock(i);
253 getInstructionIndex(&mbb->front()),
254 getInstructionIndex(&mbb->back()) + InstrSlots::NUM);
260 interval = &*r2iit->second;
263 unsigned baseIndex = getInstructionIndex(mi);
265 bool killedInDefiningBasicBlock = false;
266 for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
267 MachineBasicBlock* killerBlock = vi.Kills[i].first;
268 MachineInstr* killerInstr = vi.Kills[i].second;
269 unsigned start = (mbb == killerBlock ?
270 getDefIndex(baseIndex) :
271 getInstructionIndex(&killerBlock->front()));
272 unsigned end = (killerInstr == mi ?
276 getUseIndex(getInstructionIndex(killerInstr))+1);
277 // we do not want to add invalid ranges. these can happen when
278 // a variable has its latest use and is redefined later on in
279 // the same basic block (common with variables introduced by
282 killedInDefiningBasicBlock |= mbb == killerBlock;
283 interval->addRange(start, end);
287 if (!killedInDefiningBasicBlock) {
288 unsigned end = getInstructionIndex(&mbb->back()) + InstrSlots::NUM;
289 interval->addRange(getDefIndex(baseIndex), end);
291 DEBUG(std::cerr << '\n');
294 void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
295 MachineBasicBlock::iterator mi,
298 DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
299 typedef LiveVariables::killed_iterator KillIter;
301 MachineBasicBlock::iterator e = mbb->end();
302 unsigned baseIndex = getInstructionIndex(mi);
303 unsigned start = getDefIndex(baseIndex);
304 unsigned end = start;
306 // a variable can be dead by the instruction defining it
307 for (KillIter ki = lv_->dead_begin(mi), ke = lv_->dead_end(mi);
309 if (reg == ki->second) {
310 DEBUG(std::cerr << " dead");
311 end = getDefIndex(start) + 1;
316 // a variable can only be killed by subsequent instructions
319 baseIndex += InstrSlots::NUM;
320 for (KillIter ki = lv_->killed_begin(mi), ke = lv_->killed_end(mi);
322 if (reg == ki->second) {
323 DEBUG(std::cerr << " killed");
324 end = getUseIndex(baseIndex) + 1;
331 assert(start < end && "did not find end of interval?");
333 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
334 if (r2iit != r2iMap_.end() && r2iit->first == reg) {
335 r2iit->second->addRange(start, end);
338 intervals_.push_back(Interval(reg));
339 // update interval index for this register
340 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
341 intervals_.back().addRange(start, end);
343 DEBUG(std::cerr << '\n');
346 void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
347 MachineBasicBlock::iterator mi,
350 if (MRegisterInfo::isPhysicalRegister(reg)) {
351 if (lv_->getAllocatablePhysicalRegisters()[reg]) {
352 handlePhysicalRegisterDef(mbb, mi, reg);
353 for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
354 handlePhysicalRegisterDef(mbb, mi, *as);
358 handleVirtualRegisterDef(mbb, mi, reg);
362 unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
364 Mi2IndexMap::const_iterator it = mi2iMap_.find(instr);
365 return (it == mi2iMap_.end() ?
366 std::numeric_limits<unsigned>::max() :
370 MachineInstr* LiveIntervals::getInstructionFromIndex(unsigned index) const
372 index /= InstrSlots::NUM; // convert index to vector index
373 assert(index < i2miMap_.size() &&
374 "index does not correspond to an instruction");
375 return i2miMap_[index];
378 /// computeIntervals - computes the live intervals for virtual
379 /// registers. for some ordering of the machine instructions [1,N] a
380 /// live interval is an interval [i, j) where 1 <= i <= j < N for
381 /// which a variable is live
382 void LiveIntervals::computeIntervals()
384 DEBUG(std::cerr << "********** COMPUTING LIVE INTERVALS **********\n");
385 DEBUG(std::cerr << "********** Function: "
386 << mf_->getFunction()->getName() << '\n');
388 for (MbbIndex2MbbMap::iterator
389 it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
391 MachineBasicBlock* mbb = it->second;
392 DEBUG(std::cerr << mbb->getBasicBlock()->getName() << ":\n");
394 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
396 const TargetInstrDescriptor& tid =
397 tm_->getInstrInfo().get(mi->getOpcode());
398 DEBUG(std::cerr << getInstructionIndex(mi) << "\t";
399 mi->print(std::cerr, *tm_));
401 // handle implicit defs
402 for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
403 handleRegisterDef(mbb, mi, *id);
405 // handle explicit defs
406 for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
407 MachineOperand& mop = mi->getOperand(i);
408 // handle register defs - build intervals
409 if (mop.isRegister() && mop.isDef())
410 handleRegisterDef(mbb, mi, mop.getReg());
416 unsigned LiveIntervals::rep(unsigned reg)
418 Reg2RegMap::iterator it = r2rMap_.find(reg);
419 if (it != r2rMap_.end())
420 return it->second = rep(it->second);
424 void LiveIntervals::joinIntervals()
426 DEBUG(std::cerr << "********** JOINING INTERVALS ***********\n");
428 const TargetInstrInfo& tii = tm_->getInstrInfo();
430 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
431 mbbi != mbbe; ++mbbi) {
432 MachineBasicBlock* mbb = mbbi;
433 DEBUG(std::cerr << mbb->getBasicBlock()->getName() << ":\n");
435 for (MachineBasicBlock::iterator mi = mbb->begin(), mie = mbb->end();
437 const TargetInstrDescriptor& tid =
438 tm_->getInstrInfo().get(mi->getOpcode());
439 DEBUG(std::cerr << getInstructionIndex(mi) << '\t';
440 mi->print(std::cerr, *tm_););
442 // we only join virtual registers with allocatable
443 // physical registers since we do not have liveness information
444 // on not allocatable physical registers
446 if (tii.isMoveInstr(*mi, regA, regB) &&
447 (MRegisterInfo::isVirtualRegister(regA) ||
448 lv_->getAllocatablePhysicalRegisters()[regA]) &&
449 (MRegisterInfo::isVirtualRegister(regB) ||
450 lv_->getAllocatablePhysicalRegisters()[regB])) {
452 // get representative registers
456 // if they are already joined we continue
460 Reg2IntervalMap::iterator r2iA = r2iMap_.find(regA);
461 assert(r2iA != r2iMap_.end());
462 Reg2IntervalMap::iterator r2iB = r2iMap_.find(regB);
463 assert(r2iB != r2iMap_.end());
465 Intervals::iterator intA = r2iA->second;
466 Intervals::iterator intB = r2iB->second;
468 // both A and B are virtual registers
469 if (MRegisterInfo::isVirtualRegister(intA->reg) &&
470 MRegisterInfo::isVirtualRegister(intB->reg)) {
472 const TargetRegisterClass *rcA, *rcB;
473 rcA = mf_->getSSARegMap()->getRegClass(intA->reg);
474 rcB = mf_->getSSARegMap()->getRegClass(intB->reg);
475 assert(rcA == rcB && "registers must be of the same class");
477 // if their intervals do not overlap we join them
478 if (!intB->overlaps(*intA)) {
480 r2iB->second = r2iA->second;
481 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
482 intervals_.erase(intB);
486 else if (MRegisterInfo::isPhysicalRegister(intA->reg) ^
487 MRegisterInfo::isPhysicalRegister(intB->reg)) {
488 if (MRegisterInfo::isPhysicalRegister(intB->reg)) {
489 std::swap(regA, regB);
490 std::swap(intA, intB);
491 std::swap(r2iA, r2iB);
494 assert(MRegisterInfo::isPhysicalRegister(intA->reg) &&
495 MRegisterInfo::isVirtualRegister(intB->reg) &&
496 "A must be physical and B must be virtual");
498 if (!intA->overlaps(*intB) &&
499 !overlapsAliases(*intA, *intB)) {
501 r2iB->second = r2iA->second;
502 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
503 intervals_.erase(intB);
512 bool LiveIntervals::overlapsAliases(const Interval& lhs,
513 const Interval& rhs) const
515 assert(MRegisterInfo::isPhysicalRegister(lhs.reg) &&
516 "first interval must describe a physical register");
518 for (const unsigned* as = mri_->getAliasSet(lhs.reg); *as; ++as) {
519 Reg2IntervalMap::const_iterator r2i = r2iMap_.find(*as);
520 assert(r2i != r2iMap_.end() && "alias does not have interval?");
521 if (rhs.overlaps(*r2i->second))
528 LiveIntervals::Interval::Interval(unsigned r)
530 weight((MRegisterInfo::isPhysicalRegister(r) ?
531 std::numeric_limits<float>::infinity() : 0.0F))
536 bool LiveIntervals::Interval::spilled() const
538 return (weight == std::numeric_limits<float>::infinity() &&
539 MRegisterInfo::isVirtualRegister(reg));
542 // An example for liveAt():
544 // this = [1,4), liveAt(0) will return false. The instruction defining
545 // this spans slots [0,3]. The interval belongs to an spilled
546 // definition of the variable it represents. This is because slot 1 is
547 // used (def slot) and spans up to slot 3 (store slot).
549 bool LiveIntervals::Interval::liveAt(unsigned index) const
551 Range dummy(index, index+1);
552 Ranges::const_iterator r = std::upper_bound(ranges.begin(),
555 if (r == ranges.begin())
559 return index >= r->first && index < r->second;
562 // An example for overlaps():
566 // 8: C = A + B ;; last use of A
568 // The live intervals should look like:
574 // A->overlaps(C) should return false since we want to be able to join
576 bool LiveIntervals::Interval::overlaps(const Interval& other) const
578 Ranges::const_iterator i = ranges.begin();
579 Ranges::const_iterator ie = ranges.end();
580 Ranges::const_iterator j = other.ranges.begin();
581 Ranges::const_iterator je = other.ranges.end();
582 if (i->first < j->first) {
583 i = std::upper_bound(i, ie, *j);
584 if (i != ranges.begin()) --i;
586 else if (j->first < i->first) {
587 j = std::upper_bound(j, je, *i);
588 if (j != other.ranges.begin()) --j;
591 while (i != ie && j != je) {
592 if (i->first == j->first) {
596 if (i->first > j->first) {
600 assert(i->first < j->first);
602 if (i->second > j->first) {
614 void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
616 assert(start < end && "Invalid range to add!");
617 DEBUG(std::cerr << " +[" << start << ',' << end << ")");
618 //assert(start < end && "invalid range?");
619 Range range = std::make_pair(start, end);
620 Ranges::iterator it =
621 ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
624 it = mergeRangesForward(it);
625 it = mergeRangesBackward(it);
628 void LiveIntervals::Interval::join(const LiveIntervals::Interval& other)
630 DEBUG(std::cerr << "\t\tjoining " << *this << " with " << other << '\n');
631 Ranges::iterator cur = ranges.begin();
633 for (Ranges::const_iterator i = other.ranges.begin(),
634 e = other.ranges.end(); i != e; ++i) {
635 cur = ranges.insert(std::upper_bound(cur, ranges.end(), *i), *i);
636 cur = mergeRangesForward(cur);
637 cur = mergeRangesBackward(cur);
639 if (MRegisterInfo::isVirtualRegister(reg))
640 weight += other.weight;
643 LiveIntervals::Interval::Ranges::iterator
644 LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
646 for (Ranges::iterator n = next(it);
647 n != ranges.end() && ((it->second & 1) + it->second) >= n->first; ) {
648 it->second = std::max(it->second, n->second);
654 LiveIntervals::Interval::Ranges::iterator
655 LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
657 while (it != ranges.begin()) {
658 Ranges::iterator p = prior(it);
659 if (it->first > ((p->second & 1) + p->second)) break;
661 it->first = std::min(it->first, p->first);
662 it->second = std::max(it->second, p->second);
663 it = ranges.erase(p);
669 std::ostream& llvm::operator<<(std::ostream& os,
670 const LiveIntervals::Interval& li)
672 os << "%reg" << li.reg << ',' << li.weight << " = ";
674 return os << "EMPTY";
675 for (LiveIntervals::Interval::Ranges::const_iterator
676 i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
677 os << "[" << i->first << "," << i->second << ")";