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 mi = mbb->begin(),
113 mie = mbb->end(); mi != mie; ++mi) {
114 for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
115 const MachineOperand& mop = mi->getOperand(i);
116 if (mop.isRegister() &&
117 MRegisterInfo::isVirtualRegister(mop.getReg())) {
118 unsigned reg = mop.getAllocatedRegNum();
119 Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
120 assert(r2iit != r2iMap_.end());
121 r2iit->second->weight += pow(10.0F, loopDepth);
127 // join intervals if requested
128 if (join) joinIntervals();
130 numIntervals += intervals_.size();
132 intervals_.sort(StartPointComp());
133 DEBUG(std::copy(intervals_.begin(), intervals_.end(),
134 std::ostream_iterator<Interval>(std::cerr, "\n")));
138 void LiveIntervals::printRegName(unsigned reg) const
140 if (MRegisterInfo::isPhysicalRegister(reg))
141 std::cerr << mri_->getName(reg);
143 std::cerr << '%' << reg;
146 void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
147 MachineBasicBlock::iterator mi,
150 DEBUG(std::cerr << "\t\tregister: ";printRegName(reg); std::cerr << '\n');
152 LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
154 Interval* interval = 0;
155 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
156 if (r2iit == r2iMap_.end() || r2iit->first != reg) {
158 intervals_.push_back(Interval(reg));
159 // update interval index for this register
160 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
161 interval = &intervals_.back();
163 // iterate over all of the blocks that the variable is
164 // completely live in, adding them to the live
165 // interval. obviously we only need to do this once.
166 for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
167 if (vi.AliveBlocks[i]) {
168 MachineBasicBlock* mbb = lv_->getIndexMachineBasicBlock(i);
170 interval->addRange(getInstructionIndex(&mbb->front()),
171 getInstructionIndex(&mbb->back()) + 1);
177 interval = &*r2iit->second;
180 // we consider defs to happen at the second time slot of the
182 unsigned instrIndex = getInstructionIndex(mi) + 1;
184 bool killedInDefiningBasicBlock = false;
185 for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
186 MachineBasicBlock* killerBlock = vi.Kills[i].first;
187 MachineInstr* killerInstr = vi.Kills[i].second;
188 unsigned start = (mbb == killerBlock ?
190 getInstructionIndex(&killerBlock->front()));
191 unsigned end = (killerInstr == mi ?
192 instrIndex + 1 : // dead
193 getInstructionIndex(killerInstr) + 1); // killed
194 // we do not want to add invalid ranges. these can happen when
195 // a variable has its latest use and is redefined later on in
196 // the same basic block (common with variables introduced by
199 killedInDefiningBasicBlock |= mbb == killerBlock;
200 interval->addRange(start, end);
204 if (!killedInDefiningBasicBlock) {
205 unsigned end = getInstructionIndex(&mbb->back()) + 1;
206 interval->addRange(instrIndex, end);
210 void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
211 MachineBasicBlock::iterator mi,
214 typedef LiveVariables::killed_iterator KillIter;
216 DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
218 MachineBasicBlock::iterator e = mbb->end();
219 // we consider defs to happen at the second time slot of the
222 start = end = getInstructionIndex(mi) + 1;
224 // a variable can be dead by the instruction defining it
225 for (KillIter ki = lv_->dead_begin(mi), ke = lv_->dead_end(mi);
227 if (reg == ki->second) {
228 DEBUG(std::cerr << " dead\n");
234 // a variable can only be killed by subsequent instructions
238 for (KillIter ki = lv_->killed_begin(mi), ke = lv_->killed_end(mi);
240 if (reg == ki->second) {
241 DEBUG(std::cerr << " killed\n");
248 assert(start < end && "did not find end of interval?");
250 Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
251 if (r2iit != r2iMap_.end() && r2iit->first == reg) {
252 r2iit->second->addRange(start, end);
255 intervals_.push_back(Interval(reg));
256 // update interval index for this register
257 r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
258 intervals_.back().addRange(start, end);
262 void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
263 MachineBasicBlock::iterator mi,
266 if (MRegisterInfo::isPhysicalRegister(reg)) {
267 if (lv_->getAllocatablePhysicalRegisters()[reg]) {
268 handlePhysicalRegisterDef(mbb, mi, reg);
269 for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
270 handlePhysicalRegisterDef(mbb, mi, *as);
274 handleVirtualRegisterDef(mbb, mi, reg);
278 unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
280 assert(mi2iMap_.find(instr) != mi2iMap_.end() &&
281 "instruction not assigned a number");
282 return mi2iMap_.find(instr)->second;
285 /// computeIntervals - computes the live intervals for virtual
286 /// registers. for some ordering of the machine instructions [1,N] a
287 /// live interval is an interval [i, j) where 1 <= i <= j < N for
288 /// which a variable is live
289 void LiveIntervals::computeIntervals()
291 DEBUG(std::cerr << "computing live intervals:\n");
293 for (MbbIndex2MbbMap::iterator
294 it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
296 MachineBasicBlock* mbb = it->second;
297 DEBUG(std::cerr << "machine basic block: "
298 << mbb->getBasicBlock()->getName() << "\n");
300 for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
302 const TargetInstrDescriptor& tid =
303 tm_->getInstrInfo().get(mi->getOpcode());
304 DEBUG(std::cerr << "\t[" << getInstructionIndex(mi) << "] ";
305 mi->print(std::cerr, *tm_););
307 // handle implicit defs
308 for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
309 handleRegisterDef(mbb, mi, *id);
311 // handle explicit defs
312 for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
313 MachineOperand& mop = mi->getOperand(i);
314 // handle register defs - build intervals
315 if (mop.isRegister() && mop.isDef())
316 handleRegisterDef(mbb, mi, mop.getAllocatedRegNum());
322 unsigned LiveIntervals::rep(unsigned reg)
324 Reg2RegMap::iterator it = r2rMap_.find(reg);
325 if (it != r2rMap_.end())
326 return it->second = rep(it->second);
330 void LiveIntervals::joinIntervals()
332 DEBUG(std::cerr << "joining compatible intervals:\n");
334 const TargetInstrInfo& tii = tm_->getInstrInfo();
336 for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
337 mbbi != mbbe; ++mbbi) {
338 MachineBasicBlock* mbb = mbbi;
339 DEBUG(std::cerr << "machine basic block: "
340 << mbb->getBasicBlock()->getName() << "\n");
342 for (MachineBasicBlock::iterator mi = mbb->begin(), mie = mbb->end();
344 const TargetInstrDescriptor& tid =
345 tm_->getInstrInfo().get(mi->getOpcode());
346 DEBUG(std::cerr << "\t\tinstruction["
347 << getInstructionIndex(mi) << "]: ";
348 mi->print(std::cerr, *tm_););
350 // we only join virtual registers with allocatable
351 // physical registers since we do not have liveness information
352 // on not allocatable physical registers
354 if (tii.isMoveInstr(*mi, regA, regB) &&
355 (MRegisterInfo::isVirtualRegister(regA) ||
356 lv_->getAllocatablePhysicalRegisters()[regA]) &&
357 (MRegisterInfo::isVirtualRegister(regB) ||
358 lv_->getAllocatablePhysicalRegisters()[regB])) {
360 // get representative registers
364 // if they are already joined we continue
368 Reg2IntervalMap::iterator r2iA = r2iMap_.find(regA);
369 assert(r2iA != r2iMap_.end());
370 Reg2IntervalMap::iterator r2iB = r2iMap_.find(regB);
371 assert(r2iB != r2iMap_.end());
373 Intervals::iterator intA = r2iA->second;
374 Intervals::iterator intB = r2iB->second;
376 // both A and B are virtual registers
377 if (MRegisterInfo::isVirtualRegister(intA->reg) &&
378 MRegisterInfo::isVirtualRegister(intB->reg)) {
380 const TargetRegisterClass *rcA, *rcB;
381 rcA = mf_->getSSARegMap()->getRegClass(intA->reg);
382 rcB = mf_->getSSARegMap()->getRegClass(intB->reg);
383 assert(rcA == rcB && "registers must be of the same class");
385 // if their intervals do not overlap we join them
386 if (!intB->overlaps(*intA)) {
388 r2iB->second = r2iA->second;
389 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
390 intervals_.erase(intB);
394 else if (MRegisterInfo::isPhysicalRegister(intA->reg) ^
395 MRegisterInfo::isPhysicalRegister(intB->reg)) {
396 if (MRegisterInfo::isPhysicalRegister(intB->reg)) {
397 std::swap(regA, regB);
398 std::swap(intA, intB);
399 std::swap(r2iA, r2iB);
402 assert(MRegisterInfo::isPhysicalRegister(intA->reg) &&
403 MRegisterInfo::isVirtualRegister(intB->reg) &&
404 "A must be physical and B must be virtual");
406 if (!intA->overlaps(*intB) &&
407 !overlapsAliases(*intA, *intB)) {
409 r2iB->second = r2iA->second;
410 r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
411 intervals_.erase(intB);
420 bool LiveIntervals::overlapsAliases(const Interval& lhs,
421 const Interval& rhs) const
423 assert(MRegisterInfo::isPhysicalRegister(lhs.reg) &&
424 "first interval must describe a physical register");
426 for (const unsigned* as = mri_->getAliasSet(lhs.reg); *as; ++as) {
427 Reg2IntervalMap::const_iterator r2i = r2iMap_.find(*as);
428 assert(r2i != r2iMap_.end() && "alias does not have interval?");
429 if (rhs.overlaps(*r2i->second))
436 LiveIntervals::Interval::Interval(unsigned r)
438 weight((MRegisterInfo::isPhysicalRegister(r) ?
439 std::numeric_limits<float>::max() : 0.0F))
444 // An example for liveAt():
446 // this = [1,2), liveAt(0) will return false. The instruction defining
447 // this spans slots [0,1]. Since it is a definition we say that it is
448 // live in the second slot onwards. By ending the lifetime of this
449 // interval at 2 it means that it is not used at all. liveAt(1)
450 // returns true which means that this clobbers a register at
453 // this = [1,4), liveAt(0) will return false and liveAt(2) will return
454 // true. The variable is defined at instruction 0 and last used at 2.
455 bool LiveIntervals::Interval::liveAt(unsigned index) const
457 Range dummy(index, index+1);
458 Ranges::const_iterator r = std::upper_bound(ranges.begin(),
461 if (r == ranges.begin())
465 return index >= r->first && index < r->second;
468 // An example for overlaps():
472 // 4: C = A + B ;; last use of A
474 // The live intervals should look like:
480 // A->overlaps(C) should return false since we want to be able to join
482 bool LiveIntervals::Interval::overlaps(const Interval& other) const
484 Ranges::const_iterator i = ranges.begin();
485 Ranges::const_iterator ie = ranges.end();
486 Ranges::const_iterator j = other.ranges.begin();
487 Ranges::const_iterator je = other.ranges.end();
488 if (i->first < j->first) {
489 i = std::upper_bound(i, ie, *j);
490 if (i != ranges.begin()) --i;
492 else if (j->first < i->first) {
493 j = std::upper_bound(j, je, *i);
494 if (j != other.ranges.begin()) --j;
497 while (i != ie && j != je) {
498 if (i->first == j->first) {
502 if (i->first > j->first) {
506 assert(i->first < j->first);
508 if (i->second > j->first) {
520 void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
522 assert(start < end && "Invalid range to add!");
523 DEBUG(std::cerr << "\t\t\tadding range: [" << start <<','<< end << ") -> ");
524 //assert(start < end && "invalid range?");
525 Range range = std::make_pair(start, end);
526 Ranges::iterator it =
527 ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
530 it = mergeRangesForward(it);
531 it = mergeRangesBackward(it);
532 DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
535 void LiveIntervals::Interval::join(const LiveIntervals::Interval& other)
537 DEBUG(std::cerr << "\t\t\t\tjoining intervals: "
538 << other << " and " << *this << '\n');
539 Ranges::iterator cur = ranges.begin();
541 for (Ranges::const_iterator i = other.ranges.begin(),
542 e = other.ranges.end(); i != e; ++i) {
543 cur = ranges.insert(std::upper_bound(cur, ranges.end(), *i), *i);
544 cur = mergeRangesForward(cur);
545 cur = mergeRangesBackward(cur);
547 if (MRegisterInfo::isVirtualRegister(reg))
548 weight += other.weight;
550 DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
553 LiveIntervals::Interval::Ranges::iterator
554 LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
556 for (Ranges::iterator next = it + 1;
557 next != ranges.end() && it->second >= next->first; ) {
558 it->second = std::max(it->second, next->second);
559 next = ranges.erase(next);
564 LiveIntervals::Interval::Ranges::iterator
565 LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
567 while (it != ranges.begin()) {
568 Ranges::iterator prev = it - 1;
569 if (it->first > prev->second) break;
571 it->first = std::min(it->first, prev->first);
572 it->second = std::max(it->second, prev->second);
573 it = ranges.erase(prev);
579 std::ostream& llvm::operator<<(std::ostream& os,
580 const LiveIntervals::Interval& li)
582 os << "%reg" << li.reg << ',' << li.weight << " = ";
583 for (LiveIntervals::Interval::Ranges::const_iterator
584 i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
585 os << "[" << i->first << "," << i->second << ")";