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) {
194 unsigned start = mop.isUse() ? index : index+1;
195 unsigned end = mop.isDef() ? index+2 : index+1;
196 li.addRange(start, end);
202 // the new spill weight is now infinity as it cannot be spilled again
203 li.weight = std::numeric_limits<float>::infinity();
206 void LiveIntervals::printRegName(unsigned reg) const
208 if (MRegisterInfo::isPhysicalRegister(reg))
209 std::cerr << mri_->getName(reg);
211 std::cerr << '%' << reg;
214 void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
215 MachineBasicBlock::iterator mi,
218 DEBUG(std::cerr << "\t\tregister: ";printRegName(reg); std::cerr << '\n');
220 LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
222 Interval* interval = 0;
223 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
224 if (r2iit == r2iMap_.end() || r2iit->first != reg) {
226 intervals_.push_back(Interval(reg));
227 // update interval index for this register
228 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
229 interval = &intervals_.back();
231 // iterate over all of the blocks that the variable is
232 // completely live in, adding them to the live
233 // interval. obviously we only need to do this once.
234 for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
235 if (vi.AliveBlocks[i]) {
236 MachineBasicBlock* mbb = lv_->getIndexMachineBasicBlock(i);
238 interval->addRange(getInstructionIndex(&mbb->front()),
239 getInstructionIndex(&mbb->back()) + 1);
245 interval = &*r2iit->second;
248 // we consider defs to happen at the second time slot of the
250 unsigned instrIndex = getInstructionIndex(mi) + 1;
252 bool killedInDefiningBasicBlock = false;
253 for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
254 MachineBasicBlock* killerBlock = vi.Kills[i].first;
255 MachineInstr* killerInstr = vi.Kills[i].second;
256 unsigned start = (mbb == killerBlock ?
258 getInstructionIndex(&killerBlock->front()));
259 unsigned end = (killerInstr == mi ?
260 instrIndex + 1 : // dead
261 getInstructionIndex(killerInstr) + 1); // killed
262 // we do not want to add invalid ranges. these can happen when
263 // a variable has its latest use and is redefined later on in
264 // the same basic block (common with variables introduced by
267 killedInDefiningBasicBlock |= mbb == killerBlock;
268 interval->addRange(start, end);
272 if (!killedInDefiningBasicBlock) {
273 unsigned end = getInstructionIndex(&mbb->back()) + 1;
274 interval->addRange(instrIndex, end);
278 void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
279 MachineBasicBlock::iterator mi,
282 typedef LiveVariables::killed_iterator KillIter;
284 DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
286 MachineBasicBlock::iterator e = mbb->end();
287 // we consider defs to happen at the second time slot of the
290 start = end = getInstructionIndex(mi) + 1;
292 // a variable can be dead by the instruction defining it
293 for (KillIter ki = lv_->dead_begin(mi), ke = lv_->dead_end(mi);
295 if (reg == ki->second) {
296 DEBUG(std::cerr << " dead\n");
302 // a variable can only be killed by subsequent instructions
306 for (KillIter ki = lv_->killed_begin(mi), ke = lv_->killed_end(mi);
308 if (reg == ki->second) {
309 DEBUG(std::cerr << " killed\n");
316 assert(start < end && "did not find end of interval?");
318 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
319 if (r2iit != r2iMap_.end() && r2iit->first == reg) {
320 r2iit->second->addRange(start, end);
323 intervals_.push_back(Interval(reg));
324 // update interval index for this register
325 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
326 intervals_.back().addRange(start, end);
330 void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
331 MachineBasicBlock::iterator mi,
334 if (MRegisterInfo::isPhysicalRegister(reg)) {
335 if (lv_->getAllocatablePhysicalRegisters()[reg]) {
336 handlePhysicalRegisterDef(mbb, mi, reg);
337 for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
338 handlePhysicalRegisterDef(mbb, mi, *as);
342 handleVirtualRegisterDef(mbb, mi, reg);
346 unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
348 Mi2IndexMap::const_iterator it = mi2iMap_.find(instr);
349 return it == mi2iMap_.end() ? std::numeric_limits<unsigned>::max() : it->second;
352 MachineInstr* LiveIntervals::getInstructionFromIndex(unsigned index) const
354 index /= 2; // convert index to vector index
355 assert(index < i2miMap_.size() &&
356 "index does not correspond to an instruction");
357 return i2miMap_[index];
360 /// computeIntervals - computes the live intervals for virtual
361 /// registers. for some ordering of the machine instructions [1,N] a
362 /// live interval is an interval [i, j) where 1 <= i <= j < N for
363 /// which a variable is live
364 void LiveIntervals::computeIntervals()
366 DEBUG(std::cerr << "*** COMPUTING LIVE INTERVALS ***\n");
368 for (MbbIndex2MbbMap::iterator
369 it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
371 MachineBasicBlock* mbb = it->second;
372 DEBUG(std::cerr << mbb->getBasicBlock()->getName() << ":\n");
374 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
376 const TargetInstrDescriptor& tid =
377 tm_->getInstrInfo().get(mi->getOpcode());
378 DEBUG(std::cerr << "[" << getInstructionIndex(mi) << "]\t";
379 mi->print(std::cerr, *tm_););
381 // handle implicit defs
382 for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
383 handleRegisterDef(mbb, mi, *id);
385 // handle explicit defs
386 for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
387 MachineOperand& mop = mi->getOperand(i);
388 // handle register defs - build intervals
389 if (mop.isRegister() && mop.isDef())
390 handleRegisterDef(mbb, mi, mop.getReg());
396 unsigned LiveIntervals::rep(unsigned reg)
398 Reg2RegMap::iterator it = r2rMap_.find(reg);
399 if (it != r2rMap_.end())
400 return it->second = rep(it->second);
404 void LiveIntervals::joinIntervals()
406 DEBUG(std::cerr << "** JOINING INTERVALS ***\n");
408 const TargetInstrInfo& tii = tm_->getInstrInfo();
410 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
411 mbbi != mbbe; ++mbbi) {
412 MachineBasicBlock* mbb = mbbi;
413 DEBUG(std::cerr << mbb->getBasicBlock()->getName() << ":\n");
415 for (MachineBasicBlock::iterator mi = mbb->begin(), mie = mbb->end();
417 const TargetInstrDescriptor& tid =
418 tm_->getInstrInfo().get(mi->getOpcode());
419 DEBUG(std::cerr << "[" << getInstructionIndex(mi) << "]\t";
420 mi->print(std::cerr, *tm_););
422 // we only join virtual registers with allocatable
423 // physical registers since we do not have liveness information
424 // on not allocatable physical registers
426 if (tii.isMoveInstr(*mi, regA, regB) &&
427 (MRegisterInfo::isVirtualRegister(regA) ||
428 lv_->getAllocatablePhysicalRegisters()[regA]) &&
429 (MRegisterInfo::isVirtualRegister(regB) ||
430 lv_->getAllocatablePhysicalRegisters()[regB])) {
432 // get representative registers
436 // if they are already joined we continue
440 Reg2IntervalMap::iterator r2iA = r2iMap_.find(regA);
441 assert(r2iA != r2iMap_.end());
442 Reg2IntervalMap::iterator r2iB = r2iMap_.find(regB);
443 assert(r2iB != r2iMap_.end());
445 Intervals::iterator intA = r2iA->second;
446 Intervals::iterator intB = r2iB->second;
448 // both A and B are virtual registers
449 if (MRegisterInfo::isVirtualRegister(intA->reg) &&
450 MRegisterInfo::isVirtualRegister(intB->reg)) {
452 const TargetRegisterClass *rcA, *rcB;
453 rcA = mf_->getSSARegMap()->getRegClass(intA->reg);
454 rcB = mf_->getSSARegMap()->getRegClass(intB->reg);
455 assert(rcA == rcB && "registers must be of the same class");
457 // if their intervals do not overlap we join them
458 if (!intB->overlaps(*intA)) {
460 r2iB->second = r2iA->second;
461 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
462 intervals_.erase(intB);
466 else if (MRegisterInfo::isPhysicalRegister(intA->reg) ^
467 MRegisterInfo::isPhysicalRegister(intB->reg)) {
468 if (MRegisterInfo::isPhysicalRegister(intB->reg)) {
469 std::swap(regA, regB);
470 std::swap(intA, intB);
471 std::swap(r2iA, r2iB);
474 assert(MRegisterInfo::isPhysicalRegister(intA->reg) &&
475 MRegisterInfo::isVirtualRegister(intB->reg) &&
476 "A must be physical and B must be virtual");
478 if (!intA->overlaps(*intB) &&
479 !overlapsAliases(*intA, *intB)) {
481 r2iB->second = r2iA->second;
482 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
483 intervals_.erase(intB);
492 bool LiveIntervals::overlapsAliases(const Interval& lhs,
493 const Interval& rhs) const
495 assert(MRegisterInfo::isPhysicalRegister(lhs.reg) &&
496 "first interval must describe a physical register");
498 for (const unsigned* as = mri_->getAliasSet(lhs.reg); *as; ++as) {
499 Reg2IntervalMap::const_iterator r2i = r2iMap_.find(*as);
500 assert(r2i != r2iMap_.end() && "alias does not have interval?");
501 if (rhs.overlaps(*r2i->second))
508 LiveIntervals::Interval::Interval(unsigned r)
510 weight((MRegisterInfo::isPhysicalRegister(r) ?
511 std::numeric_limits<float>::infinity() : 0.0F))
516 // An example for liveAt():
518 // this = [1,2), liveAt(0) will return false. The instruction defining
519 // this spans slots [0,1]. Since it is a definition we say that it is
520 // live in the second slot onwards. By ending the lifetime of this
521 // interval at 2 it means that it is not used at all. liveAt(1)
522 // returns true which means that this clobbers a register at
525 // this = [1,4), liveAt(0) will return false and liveAt(2) will return
526 // true. The variable is defined at instruction 0 and last used at 2.
527 bool LiveIntervals::Interval::liveAt(unsigned index) const
529 Range dummy(index, index+1);
530 Ranges::const_iterator r = std::upper_bound(ranges.begin(),
533 if (r == ranges.begin())
537 return index >= r->first && index < r->second;
540 // An example for overlaps():
544 // 4: C = A + B ;; last use of A
546 // The live intervals should look like:
552 // A->overlaps(C) should return false since we want to be able to join
554 bool LiveIntervals::Interval::overlaps(const Interval& other) const
556 Ranges::const_iterator i = ranges.begin();
557 Ranges::const_iterator ie = ranges.end();
558 Ranges::const_iterator j = other.ranges.begin();
559 Ranges::const_iterator je = other.ranges.end();
560 if (i->first < j->first) {
561 i = std::upper_bound(i, ie, *j);
562 if (i != ranges.begin()) --i;
564 else if (j->first < i->first) {
565 j = std::upper_bound(j, je, *i);
566 if (j != other.ranges.begin()) --j;
569 while (i != ie && j != je) {
570 if (i->first == j->first) {
574 if (i->first > j->first) {
578 assert(i->first < j->first);
580 if (i->second > j->first) {
592 void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
594 assert(start < end && "Invalid range to add!");
595 DEBUG(std::cerr << "\t\t\tadding range: [" << start <<','<< end << ") -> ");
596 //assert(start < end && "invalid range?");
597 Range range = std::make_pair(start, end);
598 Ranges::iterator it =
599 ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
602 it = mergeRangesForward(it);
603 it = mergeRangesBackward(it);
604 DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
607 void LiveIntervals::Interval::join(const LiveIntervals::Interval& other)
609 DEBUG(std::cerr << "\t\t\t\tjoining intervals: "
610 << other << " and " << *this << '\n');
611 Ranges::iterator cur = ranges.begin();
613 for (Ranges::const_iterator i = other.ranges.begin(),
614 e = other.ranges.end(); i != e; ++i) {
615 cur = ranges.insert(std::upper_bound(cur, ranges.end(), *i), *i);
616 cur = mergeRangesForward(cur);
617 cur = mergeRangesBackward(cur);
619 if (MRegisterInfo::isVirtualRegister(reg))
620 weight += other.weight;
622 DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
625 LiveIntervals::Interval::Ranges::iterator
626 LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
628 for (Ranges::iterator n = next(it);
629 n != ranges.end() && ((it->second & 1) + it->second) >= n->first; ) {
630 it->second = std::max(it->second, n->second);
636 LiveIntervals::Interval::Ranges::iterator
637 LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
639 while (it != ranges.begin()) {
640 Ranges::iterator p = prior(it);
641 if (it->first > ((p->second & 1) + p->second)) break;
643 it->first = std::min(it->first, p->first);
644 it->second = std::max(it->second, p->second);
645 it = ranges.erase(p);
651 std::ostream& llvm::operator<<(std::ostream& os,
652 const LiveIntervals::Interval& li)
654 os << "%reg" << li.reg << ',' << li.weight << " = ";
655 for (LiveIntervals::Interval::Ranges::const_iterator
656 i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
657 os << "[" << i->first << "," << i->second << ")";