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");
50 join("join-liveintervals",
51 cl::desc("Join compatible live intervals"),
55 void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const
57 AU.addPreserved<LiveVariables>();
58 AU.addRequired<LiveVariables>();
59 AU.addPreservedID(PHIEliminationID);
60 AU.addRequiredID(PHIEliminationID);
61 AU.addRequiredID(TwoAddressInstructionPassID);
62 AU.addRequired<LoopInfo>();
63 MachineFunctionPass::getAnalysisUsage(AU);
66 void LiveIntervals::releaseMemory()
77 /// runOnMachineFunction - Register allocate the whole function
79 bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
80 DEBUG(std::cerr << "MACHINE FUNCTION: "; fn.print(std::cerr));
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);
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/2] = 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*2 << '\t';
166 mi->print(std::cerr, *tm_);
173 void LiveIntervals::updateSpilledInterval(Interval& li)
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 for (Interval::Ranges::iterator i = oldRanges.begin(), e = oldRanges.end();
182 unsigned index = i->first & ~1;
183 unsigned end = i->second;
185 for (; index < end; index += 2) {
186 // skip deleted instructions
187 while (!getInstructionFromIndex(index)) index += 2;
188 MachineInstr* mi = getInstructionFromIndex(index);
189 for (unsigned i = 0; i < mi->getNumOperands(); ++i) {
190 MachineOperand& mop = mi->getOperand(i);
191 if (mop.isRegister()) {
192 unsigned reg = mop.getReg();
193 if (rep(reg) == li.reg) {
195 li.addRange(index, index+2);
197 li.addRange(index+1, index+2);
203 // the new spill weight is now infinity as it cannot be spilled again
204 li.weight = std::numeric_limits<float>::infinity();
207 void LiveIntervals::printRegName(unsigned reg) const
209 if (MRegisterInfo::isPhysicalRegister(reg))
210 std::cerr << mri_->getName(reg);
212 std::cerr << '%' << reg;
215 void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
216 MachineBasicBlock::iterator mi,
219 DEBUG(std::cerr << "\t\tregister: ";printRegName(reg); std::cerr << '\n');
221 LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
223 Interval* interval = 0;
224 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
225 if (r2iit == r2iMap_.end() || r2iit->first != reg) {
227 intervals_.push_back(Interval(reg));
228 // update interval index for this register
229 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
230 interval = &intervals_.back();
232 // iterate over all of the blocks that the variable is
233 // completely live in, adding them to the live
234 // interval. obviously we only need to do this once.
235 for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
236 if (vi.AliveBlocks[i]) {
237 MachineBasicBlock* mbb = lv_->getIndexMachineBasicBlock(i);
239 interval->addRange(getInstructionIndex(&mbb->front()),
240 getInstructionIndex(&mbb->back()) + 1);
246 interval = &*r2iit->second;
249 // we consider defs to happen at the second time slot of the
251 unsigned instrIndex = getInstructionIndex(mi) + 1;
253 bool killedInDefiningBasicBlock = false;
254 for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
255 MachineBasicBlock* killerBlock = vi.Kills[i].first;
256 MachineInstr* killerInstr = vi.Kills[i].second;
257 unsigned start = (mbb == killerBlock ?
259 getInstructionIndex(&killerBlock->front()));
260 unsigned end = (killerInstr == mi ?
261 instrIndex + 1 : // dead
262 getInstructionIndex(killerInstr) + 1); // killed
263 // we do not want to add invalid ranges. these can happen when
264 // a variable has its latest use and is redefined later on in
265 // the same basic block (common with variables introduced by
268 killedInDefiningBasicBlock |= mbb == killerBlock;
269 interval->addRange(start, end);
273 if (!killedInDefiningBasicBlock) {
274 unsigned end = getInstructionIndex(&mbb->back()) + 1;
275 interval->addRange(instrIndex, end);
279 void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
280 MachineBasicBlock::iterator mi,
283 typedef LiveVariables::killed_iterator KillIter;
285 DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
287 MachineBasicBlock::iterator e = mbb->end();
288 // we consider defs to happen at the second time slot of the
291 start = end = getInstructionIndex(mi) + 1;
293 // a variable can be dead by the instruction defining it
294 for (KillIter ki = lv_->dead_begin(mi), ke = lv_->dead_end(mi);
296 if (reg == ki->second) {
297 DEBUG(std::cerr << " dead\n");
303 // a variable can only be killed by subsequent instructions
307 for (KillIter ki = lv_->killed_begin(mi), ke = lv_->killed_end(mi);
309 if (reg == ki->second) {
310 DEBUG(std::cerr << " killed\n");
317 assert(start < end && "did not find end of interval?");
319 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
320 if (r2iit != r2iMap_.end() && r2iit->first == reg) {
321 r2iit->second->addRange(start, end);
324 intervals_.push_back(Interval(reg));
325 // update interval index for this register
326 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
327 intervals_.back().addRange(start, end);
331 void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
332 MachineBasicBlock::iterator mi,
335 if (MRegisterInfo::isPhysicalRegister(reg)) {
336 if (lv_->getAllocatablePhysicalRegisters()[reg]) {
337 handlePhysicalRegisterDef(mbb, mi, reg);
338 for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
339 handlePhysicalRegisterDef(mbb, mi, *as);
343 handleVirtualRegisterDef(mbb, mi, reg);
347 unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
349 Mi2IndexMap::const_iterator it = mi2iMap_.find(instr);
350 return it == mi2iMap_.end() ? std::numeric_limits<unsigned>::max() : it->second;
353 MachineInstr* LiveIntervals::getInstructionFromIndex(unsigned index) const
355 index /= 2; // convert index to vector index
356 assert(index < i2miMap_.size() &&
357 "index does not correspond to an instruction");
358 return i2miMap_[index];
361 /// computeIntervals - computes the live intervals for virtual
362 /// registers. for some ordering of the machine instructions [1,N] a
363 /// live interval is an interval [i, j) where 1 <= i <= j < N for
364 /// which a variable is live
365 void LiveIntervals::computeIntervals()
367 DEBUG(std::cerr << "*** COMPUTING LIVE INTERVALS ***\n");
369 for (MbbIndex2MbbMap::iterator
370 it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
372 MachineBasicBlock* mbb = it->second;
373 DEBUG(std::cerr << mbb->getBasicBlock()->getName() << ":\n");
375 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
377 const TargetInstrDescriptor& tid =
378 tm_->getInstrInfo().get(mi->getOpcode());
379 DEBUG(std::cerr << "[" << getInstructionIndex(mi) << "]\t";
380 mi->print(std::cerr, *tm_););
382 // handle implicit defs
383 for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
384 handleRegisterDef(mbb, mi, *id);
386 // handle explicit defs
387 for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
388 MachineOperand& mop = mi->getOperand(i);
389 // handle register defs - build intervals
390 if (mop.isRegister() && mop.isDef())
391 handleRegisterDef(mbb, mi, mop.getReg());
397 unsigned LiveIntervals::rep(unsigned reg)
399 Reg2RegMap::iterator it = r2rMap_.find(reg);
400 if (it != r2rMap_.end())
401 return it->second = rep(it->second);
405 void LiveIntervals::joinIntervals()
407 DEBUG(std::cerr << "** JOINING INTERVALS ***\n");
409 const TargetInstrInfo& tii = tm_->getInstrInfo();
411 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
412 mbbi != mbbe; ++mbbi) {
413 MachineBasicBlock* mbb = mbbi;
414 DEBUG(std::cerr << mbb->getBasicBlock()->getName() << ":\n");
416 for (MachineBasicBlock::iterator mi = mbb->begin(), mie = mbb->end();
418 const TargetInstrDescriptor& tid =
419 tm_->getInstrInfo().get(mi->getOpcode());
420 DEBUG(std::cerr << "[" << getInstructionIndex(mi) << "]\t";
421 mi->print(std::cerr, *tm_););
423 // we only join virtual registers with allocatable
424 // physical registers since we do not have liveness information
425 // on not allocatable physical registers
427 if (tii.isMoveInstr(*mi, regA, regB) &&
428 (MRegisterInfo::isVirtualRegister(regA) ||
429 lv_->getAllocatablePhysicalRegisters()[regA]) &&
430 (MRegisterInfo::isVirtualRegister(regB) ||
431 lv_->getAllocatablePhysicalRegisters()[regB])) {
433 // get representative registers
437 // if they are already joined we continue
441 Reg2IntervalMap::iterator r2iA = r2iMap_.find(regA);
442 assert(r2iA != r2iMap_.end());
443 Reg2IntervalMap::iterator r2iB = r2iMap_.find(regB);
444 assert(r2iB != r2iMap_.end());
446 Intervals::iterator intA = r2iA->second;
447 Intervals::iterator intB = r2iB->second;
449 // both A and B are virtual registers
450 if (MRegisterInfo::isVirtualRegister(intA->reg) &&
451 MRegisterInfo::isVirtualRegister(intB->reg)) {
453 const TargetRegisterClass *rcA, *rcB;
454 rcA = mf_->getSSARegMap()->getRegClass(intA->reg);
455 rcB = mf_->getSSARegMap()->getRegClass(intB->reg);
456 assert(rcA == rcB && "registers must be of the same class");
458 // if their intervals do not overlap we join them
459 if (!intB->overlaps(*intA)) {
461 r2iB->second = r2iA->second;
462 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
463 intervals_.erase(intB);
467 else if (MRegisterInfo::isPhysicalRegister(intA->reg) ^
468 MRegisterInfo::isPhysicalRegister(intB->reg)) {
469 if (MRegisterInfo::isPhysicalRegister(intB->reg)) {
470 std::swap(regA, regB);
471 std::swap(intA, intB);
472 std::swap(r2iA, r2iB);
475 assert(MRegisterInfo::isPhysicalRegister(intA->reg) &&
476 MRegisterInfo::isVirtualRegister(intB->reg) &&
477 "A must be physical and B must be virtual");
479 if (!intA->overlaps(*intB) &&
480 !overlapsAliases(*intA, *intB)) {
482 r2iB->second = r2iA->second;
483 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
484 intervals_.erase(intB);
493 bool LiveIntervals::overlapsAliases(const Interval& lhs,
494 const Interval& rhs) const
496 assert(MRegisterInfo::isPhysicalRegister(lhs.reg) &&
497 "first interval must describe a physical register");
499 for (const unsigned* as = mri_->getAliasSet(lhs.reg); *as; ++as) {
500 Reg2IntervalMap::const_iterator r2i = r2iMap_.find(*as);
501 assert(r2i != r2iMap_.end() && "alias does not have interval?");
502 if (rhs.overlaps(*r2i->second))
509 LiveIntervals::Interval::Interval(unsigned r)
511 weight((MRegisterInfo::isPhysicalRegister(r) ?
512 std::numeric_limits<float>::infinity() : 0.0F))
517 // An example for liveAt():
519 // this = [1,2), liveAt(0) will return false. The instruction defining
520 // this spans slots [0,1]. Since it is a definition we say that it is
521 // live in the second slot onwards. By ending the lifetime of this
522 // interval at 2 it means that it is not used at all. liveAt(1)
523 // returns true which means that this clobbers a register at
526 // this = [1,4), liveAt(0) will return false and liveAt(2) will return
527 // true. The variable is defined at instruction 0 and last used at 2.
528 bool LiveIntervals::Interval::liveAt(unsigned index) const
530 Range dummy(index, index+1);
531 Ranges::const_iterator r = std::upper_bound(ranges.begin(),
534 if (r == ranges.begin())
538 return index >= r->first && index < r->second;
541 // An example for overlaps():
545 // 4: C = A + B ;; last use of A
547 // The live intervals should look like:
553 // A->overlaps(C) should return false since we want to be able to join
555 bool LiveIntervals::Interval::overlaps(const Interval& other) const
557 Ranges::const_iterator i = ranges.begin();
558 Ranges::const_iterator ie = ranges.end();
559 Ranges::const_iterator j = other.ranges.begin();
560 Ranges::const_iterator je = other.ranges.end();
561 if (i->first < j->first) {
562 i = std::upper_bound(i, ie, *j);
563 if (i != ranges.begin()) --i;
565 else if (j->first < i->first) {
566 j = std::upper_bound(j, je, *i);
567 if (j != other.ranges.begin()) --j;
570 while (i != ie && j != je) {
571 if (i->first == j->first) {
575 if (i->first > j->first) {
579 assert(i->first < j->first);
581 if (i->second > j->first) {
593 void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
595 assert(start < end && "Invalid range to add!");
596 DEBUG(std::cerr << "\t\t\tadding range: [" << start <<','<< end << ") -> ");
597 //assert(start < end && "invalid range?");
598 Range range = std::make_pair(start, end);
599 Ranges::iterator it =
600 ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
603 it = mergeRangesForward(it);
604 it = mergeRangesBackward(it);
605 DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
608 void LiveIntervals::Interval::join(const LiveIntervals::Interval& other)
610 DEBUG(std::cerr << "\t\t\t\tjoining intervals: "
611 << other << " and " << *this << '\n');
612 Ranges::iterator cur = ranges.begin();
614 for (Ranges::const_iterator i = other.ranges.begin(),
615 e = other.ranges.end(); i != e; ++i) {
616 cur = ranges.insert(std::upper_bound(cur, ranges.end(), *i), *i);
617 cur = mergeRangesForward(cur);
618 cur = mergeRangesBackward(cur);
620 if (MRegisterInfo::isVirtualRegister(reg))
621 weight += other.weight;
623 DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
626 LiveIntervals::Interval::Ranges::iterator
627 LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
629 for (Ranges::iterator next = it + 1;
630 next != ranges.end() && it->second >= next->first; ) {
631 it->second = std::max(it->second, next->second);
632 next = ranges.erase(next);
637 LiveIntervals::Interval::Ranges::iterator
638 LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
640 while (it != ranges.begin()) {
641 Ranges::iterator prev = it - 1;
642 if (it->first > prev->second) break;
644 it->first = std::min(it->first, prev->first);
645 it->second = std::max(it->second, prev->second);
646 it = ranges.erase(prev);
652 std::ostream& llvm::operator<<(std::ostream& os,
653 const LiveIntervals::Interval& li)
655 os << "%reg" << li.reg << ',' << li.weight << " = ";
656 for (LiveIntervals::Interval::Ranges::const_iterator
657 i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
658 os << "[" << i->first << "," << i->second << ")";