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"
40 RegisterAnalysis<LiveIntervals> X("liveintervals",
41 "Live Interval Analysis");
43 Statistic<> numIntervals("liveintervals", "Number of intervals");
44 Statistic<> numJoined ("liveintervals", "Number of joined intervals");
47 join("join-liveintervals",
48 cl::desc("Join compatible live intervals"),
52 void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const
54 AU.addPreserved<LiveVariables>();
55 AU.addRequired<LiveVariables>();
56 AU.addPreservedID(PHIEliminationID);
57 AU.addRequiredID(PHIEliminationID);
58 AU.addRequiredID(TwoAddressInstructionPassID);
59 AU.addRequired<LoopInfo>();
60 MachineFunctionPass::getAnalysisUsage(AU);
63 void LiveIntervals::releaseMemory()
74 /// runOnMachineFunction - Register allocate the whole function
76 bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
77 DEBUG(std::cerr << "Machine Function\n");
79 tm_ = &fn.getTarget();
80 mri_ = tm_->getRegisterInfo();
81 lv_ = &getAnalysis<LiveVariables>();
83 // number MachineInstrs
85 for (MachineFunction::iterator mbb = mf_->begin(), mbbEnd = mf_->end();
86 mbb != mbbEnd; ++mbb) {
87 const std::pair<MachineBasicBlock*, unsigned>& entry =
88 lv_->getMachineBasicBlockInfo(mbb);
89 bool inserted = mbbi2mbbMap_.insert(std::make_pair(entry.second,
91 assert(inserted && "multiple index -> MachineBasicBlock");
93 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
95 inserted = mi2iMap_.insert(std::make_pair(*mi, miIndex)).second;
96 assert(inserted && "multiple MachineInstr -> index mappings");
103 // compute spill weights
104 const LoopInfo& loopInfo = getAnalysis<LoopInfo>();
105 const TargetInstrInfo& tii = tm_->getInstrInfo();
107 for (MachineFunction::const_iterator mbbi = mf_->begin(),
108 mbbe = mf_->end(); mbbi != mbbe; ++mbbi) {
109 const MachineBasicBlock* mbb = mbbi;
110 unsigned loopDepth = loopInfo.getLoopDepth(mbb->getBasicBlock());
112 for (MachineBasicBlock::const_iterator mii = mbb->begin(),
113 mie = mbb->end(); mii != mie; ++mii) {
114 MachineInstr* mi = *mii;
116 for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
117 MachineOperand& mop = mi->getOperand(i);
118 if (mop.isRegister() &&
119 MRegisterInfo::isVirtualRegister(mop.getReg())) {
120 unsigned reg = mop.getAllocatedRegNum();
121 Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
122 assert(r2iit != r2iMap_.end());
123 r2iit->second->weight += pow(10.0F, loopDepth);
129 // join intervals if requested
130 if (join) joinIntervals();
132 numIntervals += intervals_.size();
134 intervals_.sort(StartPointComp());
135 DEBUG(std::copy(intervals_.begin(), intervals_.end(),
136 std::ostream_iterator<Interval>(std::cerr, "\n")));
140 void LiveIntervals::printRegName(unsigned reg) const
142 if (MRegisterInfo::isPhysicalRegister(reg))
143 std::cerr << mri_->getName(reg);
145 std::cerr << '%' << reg;
148 void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
149 MachineBasicBlock::iterator mi,
152 DEBUG(std::cerr << "\t\tregister: ";printRegName(reg); std::cerr << '\n');
154 LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
156 Interval* interval = 0;
157 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
158 if (r2iit == r2iMap_.end() || r2iit->first != reg) {
160 intervals_.push_back(Interval(reg));
161 // update interval index for this register
162 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
163 interval = &intervals_.back();
165 // iterate over all of the blocks that the variable is
166 // completely live in, adding them to the live
167 // interval. obviously we only need to do this once.
168 for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
169 if (vi.AliveBlocks[i]) {
170 MachineBasicBlock* mbb = lv_->getIndexMachineBasicBlock(i);
172 interval->addRange(getInstructionIndex(mbb->front()),
173 getInstructionIndex(mbb->back()) + 1);
179 interval = &*r2iit->second;
182 // we consider defs to happen at the second time slot of the
184 unsigned instrIndex = getInstructionIndex(*mi) + 1;
186 bool killedInDefiningBasicBlock = false;
187 for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
188 MachineBasicBlock* killerBlock = vi.Kills[i].first;
189 MachineInstr* killerInstr = vi.Kills[i].second;
190 unsigned start = (mbb == killerBlock ?
192 getInstructionIndex(killerBlock->front()));
193 unsigned end = (killerInstr == *mi ?
194 instrIndex + 1 : // dead
195 getInstructionIndex(killerInstr) + 1); // killed
196 // we do not want to add invalid ranges. these can happen when
197 // a variable has its latest use and is redefined later on in
198 // the same basic block (common with variables introduced by
201 killedInDefiningBasicBlock |= mbb == killerBlock;
202 interval->addRange(start, end);
206 if (!killedInDefiningBasicBlock) {
207 unsigned end = getInstructionIndex(mbb->back()) + 1;
208 interval->addRange(instrIndex, end);
212 void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
213 MachineBasicBlock::iterator mi,
216 typedef LiveVariables::killed_iterator KillIter;
218 DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
220 MachineBasicBlock::iterator e = mbb->end();
221 // we consider defs to happen at the second time slot of the
224 start = end = getInstructionIndex(*mi) + 1;
226 // a variable can be dead by the instruction defining it
227 for (KillIter ki = lv_->dead_begin(*mi), ke = lv_->dead_end(*mi);
229 if (reg == ki->second) {
230 DEBUG(std::cerr << " dead\n");
236 // a variable can only be killed by subsequent instructions
240 for (KillIter ki = lv_->killed_begin(*mi), ke = lv_->killed_end(*mi);
242 if (reg == ki->second) {
243 DEBUG(std::cerr << " killed\n");
250 assert(start < end && "did not find end of interval?");
252 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
253 if (r2iit != r2iMap_.end() && r2iit->first == reg) {
254 r2iit->second->addRange(start, end);
257 intervals_.push_back(Interval(reg));
258 // update interval index for this register
259 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
260 intervals_.back().addRange(start, end);
264 void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
265 MachineBasicBlock::iterator mi,
268 if (MRegisterInfo::isPhysicalRegister(reg)) {
269 if (lv_->getAllocatablePhysicalRegisters()[reg]) {
270 handlePhysicalRegisterDef(mbb, mi, reg);
271 for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
272 handlePhysicalRegisterDef(mbb, mi, *as);
276 handleVirtualRegisterDef(mbb, mi, reg);
280 unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
282 assert(mi2iMap_.find(instr) != mi2iMap_.end() &&
283 "instruction not assigned a number");
284 return mi2iMap_.find(instr)->second;
287 /// computeIntervals - computes the live intervals for virtual
288 /// registers. for some ordering of the machine instructions [1,N] a
289 /// live interval is an interval [i, j) where 1 <= i <= j < N for
290 /// which a variable is live
291 void LiveIntervals::computeIntervals()
293 DEBUG(std::cerr << "computing live intervals:\n");
295 for (MbbIndex2MbbMap::iterator
296 it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
298 MachineBasicBlock* mbb = it->second;
299 DEBUG(std::cerr << "machine basic block: "
300 << mbb->getBasicBlock()->getName() << "\n");
302 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
304 MachineInstr* instr = *mi;
305 const TargetInstrDescriptor& tid =
306 tm_->getInstrInfo().get(instr->getOpcode());
307 DEBUG(std::cerr << "\t[" << getInstructionIndex(instr) << "] ";
308 instr->print(std::cerr, *tm_););
310 // handle implicit defs
311 for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
312 handleRegisterDef(mbb, mi, *id);
314 // handle explicit defs
315 for (int i = instr->getNumOperands() - 1; i >= 0; --i) {
316 MachineOperand& mop = instr->getOperand(i);
317 // handle register defs - build intervals
318 if (mop.isRegister() && mop.isDef())
319 handleRegisterDef(mbb, mi, mop.getAllocatedRegNum());
325 unsigned LiveIntervals::rep(unsigned reg)
327 Reg2RegMap::iterator it = r2rMap_.find(reg);
328 if (it != r2rMap_.end())
329 return it->second = rep(it->second);
333 void LiveIntervals::joinIntervals()
335 DEBUG(std::cerr << "joining compatible intervals:\n");
337 const TargetInstrInfo& tii = tm_->getInstrInfo();
339 for (MachineFunction::const_iterator mbbi = mf_->begin(),
340 mbbe = mf_->end(); mbbi != mbbe; ++mbbi) {
341 const MachineBasicBlock* mbb = mbbi;
342 DEBUG(std::cerr << "machine basic block: "
343 << mbb->getBasicBlock()->getName() << "\n");
345 for (MachineBasicBlock::const_iterator mii = mbb->begin(),
346 mie = mbb->end(); mii != mie; ++mii) {
347 MachineInstr* mi = *mii;
348 const TargetInstrDescriptor& tid =
349 tm_->getInstrInfo().get(mi->getOpcode());
350 DEBUG(std::cerr << "\t\tinstruction["
351 << getInstructionIndex(mi) << "]: ";
352 mi->print(std::cerr, *tm_););
354 // we only join virtual registers with allocatable
355 // physical registers since we do not have liveness information
356 // on not allocatable physical registers
358 if (tii.isMoveInstr(*mi, regA, regB) &&
359 (MRegisterInfo::isVirtualRegister(regA) ||
360 lv_->getAllocatablePhysicalRegisters()[regA]) &&
361 (MRegisterInfo::isVirtualRegister(regB) ||
362 lv_->getAllocatablePhysicalRegisters()[regB])) {
364 // get representative registers
368 // if they are already joined we continue
372 Reg2IntervalMap::iterator r2iA = r2iMap_.find(regA);
373 assert(r2iA != r2iMap_.end());
374 Reg2IntervalMap::iterator r2iB = r2iMap_.find(regB);
375 assert(r2iB != r2iMap_.end());
377 Intervals::iterator intA = r2iA->second;
378 Intervals::iterator intB = r2iB->second;
380 // both A and B are virtual registers
381 if (MRegisterInfo::isVirtualRegister(intA->reg) &&
382 MRegisterInfo::isVirtualRegister(intB->reg)) {
384 const TargetRegisterClass *rcA, *rcB;
385 rcA = mf_->getSSARegMap()->getRegClass(intA->reg);
386 rcB = mf_->getSSARegMap()->getRegClass(intB->reg);
387 assert(rcA == rcB && "registers must be of the same class");
389 // if their intervals do not overlap we join them
390 if (!intB->overlaps(*intA)) {
392 r2iB->second = r2iA->second;
393 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
394 intervals_.erase(intB);
398 else if (MRegisterInfo::isPhysicalRegister(intA->reg) ^
399 MRegisterInfo::isPhysicalRegister(intB->reg)) {
400 if (MRegisterInfo::isPhysicalRegister(intB->reg)) {
401 std::swap(regA, regB);
402 std::swap(intA, intB);
403 std::swap(r2iA, r2iB);
406 assert(MRegisterInfo::isPhysicalRegister(intA->reg) &&
407 MRegisterInfo::isVirtualRegister(intB->reg) &&
408 "A must be physical and B must be virtual");
410 if (!intA->overlaps(*intB) &&
411 !overlapsAliases(*intA, *intB)) {
413 r2iB->second = r2iA->second;
414 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
415 intervals_.erase(intB);
424 bool LiveIntervals::overlapsAliases(const Interval& lhs,
425 const Interval& rhs) const
427 assert(MRegisterInfo::isPhysicalRegister(lhs.reg) &&
428 "first interval must describe a physical register");
430 for (const unsigned* as = mri_->getAliasSet(lhs.reg); *as; ++as) {
431 Reg2IntervalMap::const_iterator r2i = r2iMap_.find(*as);
432 assert(r2i != r2iMap_.end() && "alias does not have interval?");
433 if (rhs.overlaps(*r2i->second))
440 LiveIntervals::Interval::Interval(unsigned r)
442 weight((MRegisterInfo::isPhysicalRegister(r) ?
443 std::numeric_limits<float>::max() : 0.0F))
448 // An example for liveAt():
450 // this = [1,2), liveAt(0) will return false. The instruction defining
451 // this spans slots [0,1]. Since it is a definition we say that it is
452 // live in the second slot onwards. By ending the lifetime of this
453 // interval at 2 it means that it is not used at all. liveAt(1)
454 // returns true which means that this clobbers a register at
457 // this = [1,4), liveAt(0) will return false and liveAt(2) will return
458 // true. The variable is defined at instruction 0 and last used at 2.
459 bool LiveIntervals::Interval::liveAt(unsigned index) const
461 Range dummy(index, index+1);
462 Ranges::const_iterator r = std::upper_bound(ranges.begin(),
465 if (r == ranges.begin())
469 return index >= r->first && index < r->second;
472 // An example for overlaps():
476 // 4: C = A + B ;; last use of A
478 // The live intervals should look like:
484 // A->overlaps(C) should return false since we want to be able to join
486 bool LiveIntervals::Interval::overlaps(const Interval& other) const
488 Ranges::const_iterator i = ranges.begin();
489 Ranges::const_iterator ie = ranges.end();
490 Ranges::const_iterator j = other.ranges.begin();
491 Ranges::const_iterator je = other.ranges.end();
492 if (i->first < j->first) {
493 i = std::upper_bound(i, ie, *j);
494 if (i != ranges.begin()) --i;
496 else if (j->first < i->first) {
497 j = std::upper_bound(j, je, *i);
498 if (j != other.ranges.begin()) --j;
501 while (i != ie && j != je) {
502 if (i->first == j->first) {
506 if (i->first > j->first) {
510 assert(i->first < j->first);
512 if (i->second > j->first) {
524 void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
526 assert(start < end && "Invalid range to add!");
527 DEBUG(std::cerr << "\t\t\tadding range: [" << start <<','<< end << ") -> ");
528 //assert(start < end && "invalid range?");
529 Range range = std::make_pair(start, end);
530 Ranges::iterator it =
531 ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
534 it = mergeRangesForward(it);
535 it = mergeRangesBackward(it);
536 DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
539 void LiveIntervals::Interval::join(const LiveIntervals::Interval& other)
541 DEBUG(std::cerr << "\t\t\t\tjoining intervals: "
542 << other << " and " << *this << '\n');
543 Ranges::iterator cur = ranges.begin();
545 for (Ranges::const_iterator i = other.ranges.begin(),
546 e = other.ranges.end(); i != e; ++i) {
547 cur = ranges.insert(std::upper_bound(cur, ranges.end(), *i), *i);
548 cur = mergeRangesForward(cur);
549 cur = mergeRangesBackward(cur);
551 if (MRegisterInfo::isVirtualRegister(reg))
552 weight += other.weight;
554 DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
557 LiveIntervals::Interval::Ranges::iterator
558 LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
560 for (Ranges::iterator next = it + 1;
561 next != ranges.end() && it->second >= next->first; ) {
562 it->second = std::max(it->second, next->second);
563 next = ranges.erase(next);
568 LiveIntervals::Interval::Ranges::iterator
569 LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
571 while (it != ranges.begin()) {
572 Ranges::iterator prev = it - 1;
573 if (it->first > prev->second) break;
575 it->first = std::min(it->first, prev->first);
576 it->second = std::max(it->second, prev->second);
577 it = ranges.erase(prev);
583 std::ostream& llvm::operator<<(std::ostream& os,
584 const LiveIntervals::Interval& li)
586 os << "%reg" << li.reg << ',' << li.weight << " = ";
587 for (LiveIntervals::Interval::Ranges::const_iterator
588 i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
589 os << "[" << i->first << "," << i->second << ")";