1 //===-- RegAllocLinearScan.cpp - Linear Scan register allocator -----------===//
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 a linear scan register allocator.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "regalloc"
15 #include "llvm/Function.h"
16 #include "llvm/CodeGen/MachineFunctionPass.h"
17 #include "llvm/CodeGen/MachineInstr.h"
18 #include "llvm/CodeGen/Passes.h"
19 #include "llvm/CodeGen/SSARegMap.h"
20 #include "llvm/Target/MRegisterInfo.h"
21 #include "llvm/Target/TargetMachine.h"
22 #include "Support/Debug.h"
23 #include "Support/Statistic.h"
24 #include "Support/STLExtras.h"
25 #include "LiveIntervalAnalysis.h"
26 #include "PhysRegTracker.h"
27 #include "VirtRegMap.h"
37 Statistic<double> efficiency
38 ("regalloc", "Ratio of intervals processed over total intervals");
40 static unsigned numIterations = 0;
41 static unsigned numIntervals = 0;
43 class RA : public MachineFunctionPass {
46 const TargetMachine* tm_;
47 const MRegisterInfo* mri_;
49 typedef std::vector<LiveInterval*> IntervalPtrs;
50 IntervalPtrs handled_, fixed_, active_, inactive_;
51 typedef std::priority_queue<LiveInterval*,
53 greater_ptr<LiveInterval> > IntervalHeap;
54 IntervalHeap unhandled_;
55 std::auto_ptr<PhysRegTracker> prt_;
56 std::auto_ptr<VirtRegMap> vrm_;
57 std::auto_ptr<Spiller> spiller_;
59 typedef std::vector<float> SpillWeights;
60 SpillWeights spillWeights_;
63 virtual const char* getPassName() const {
64 return "Linear Scan Register Allocator";
67 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
68 AU.addRequired<LiveIntervals>();
69 MachineFunctionPass::getAnalysisUsage(AU);
72 /// runOnMachineFunction - register allocate the whole function
73 bool runOnMachineFunction(MachineFunction&);
78 /// linearScan - the linear scan algorithm
81 /// initIntervalSets - initializa the four interval sets:
82 /// unhandled, fixed, active and inactive
83 void initIntervalSets();
85 /// processActiveIntervals - expire old intervals and move
86 /// non-overlapping ones to the incative list
87 void processActiveIntervals(LiveInterval* cur);
89 /// processInactiveIntervals - expire old intervals and move
90 /// overlapping ones to the active list
91 void processInactiveIntervals(LiveInterval* cur);
93 /// updateSpillWeights - updates the spill weights of the
94 /// specifed physical register and its weight
95 void updateSpillWeights(unsigned reg, SpillWeights::value_type weight);
97 /// assignRegOrStackSlotAtInterval - assign a register if one
98 /// is available, or spill.
99 void assignRegOrStackSlotAtInterval(LiveInterval* cur);
102 /// register handling helpers
105 /// getFreePhysReg - return a free physical register for this
106 /// virtual register interval if we have one, otherwise return
108 unsigned getFreePhysReg(LiveInterval* cur);
110 /// assignVirt2StackSlot - assigns this virtual register to a
111 /// stack slot. returns the stack slot
112 int assignVirt2StackSlot(unsigned virtReg);
114 template <typename ItTy>
115 void printIntervals(const char* const str, ItTy i, ItTy e) const {
116 if (str) std::cerr << str << " intervals:\n";
117 for (; i != e; ++i) {
118 std::cerr << "\t" << **i << " -> ";
119 unsigned reg = (*i)->reg;
120 if (MRegisterInfo::isVirtualRegister(reg)) {
121 reg = vrm_->getPhys(reg);
123 std::cerr << mri_->getName(reg) << '\n';
129 void RA::releaseMemory()
131 while (!unhandled_.empty()) unhandled_.pop();
138 bool RA::runOnMachineFunction(MachineFunction &fn) {
140 tm_ = &fn.getTarget();
141 mri_ = tm_->getRegisterInfo();
142 li_ = &getAnalysis<LiveIntervals>();
143 if (!prt_.get()) prt_.reset(new PhysRegTracker(*mri_));
144 vrm_.reset(new VirtRegMap(*mf_));
145 if (!spiller_.get()) spiller_.reset(createSpiller());
151 spiller_->runOnMachineFunction(*mf_, *vrm_);
156 void RA::linearScan()
158 // linear scan algorithm
159 DEBUG(std::cerr << "********** LINEAR SCAN **********\n");
160 DEBUG(std::cerr << "********** Function: "
161 << mf_->getFunction()->getName() << '\n');
163 // DEBUG(printIntervals("unhandled", unhandled_.begin(), unhandled_.end()));
164 DEBUG(printIntervals("fixed", fixed_.begin(), fixed_.end()));
165 DEBUG(printIntervals("active", active_.begin(), active_.end()));
166 DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
168 while (!unhandled_.empty()) {
169 // pick the interval with the earliest start point
170 LiveInterval* cur = unhandled_.top();
173 DEBUG(std::cerr << "\n*** CURRENT ***: " << *cur << '\n');
175 processActiveIntervals(cur);
176 processInactiveIntervals(cur);
178 // if this register is fixed we are done
179 if (MRegisterInfo::isPhysicalRegister(cur->reg)) {
180 prt_->addRegUse(cur->reg);
181 active_.push_back(cur);
182 handled_.push_back(cur);
184 // otherwise we are allocating a virtual register. try to find
185 // a free physical register or spill an interval in order to
186 // assign it one (we could spill the current though).
188 assignRegOrStackSlotAtInterval(cur);
191 DEBUG(printIntervals("active", active_.begin(), active_.end()));
192 DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
194 numIntervals += li_->getNumIntervals();
195 efficiency = double(numIterations) / double(numIntervals);
197 // expire any remaining active intervals
198 for (IntervalPtrs::reverse_iterator
199 i = active_.rbegin(); i != active_.rend(); ) {
200 unsigned reg = (*i)->reg;
201 DEBUG(std::cerr << "\tinterval " << **i << " expired\n");
202 if (MRegisterInfo::isVirtualRegister(reg))
203 reg = vrm_->getPhys(reg);
204 prt_->delRegUse(reg);
205 i = IntervalPtrs::reverse_iterator(active_.erase(i.base()-1));
208 // expire any remaining inactive intervals
209 for (IntervalPtrs::reverse_iterator
210 i = inactive_.rbegin(); i != inactive_.rend(); ) {
211 DEBUG(std::cerr << "\tinterval " << **i << " expired\n");
212 i = IntervalPtrs::reverse_iterator(inactive_.erase(i.base()-1));
215 DEBUG(std::cerr << *vrm_);
218 void RA::initIntervalSets()
220 assert(unhandled_.empty() && fixed_.empty() &&
221 active_.empty() && inactive_.empty() &&
222 "interval sets should be empty on initialization");
224 for (LiveIntervals::iterator i = li_->begin(), e = li_->end(); i != e; ++i){
225 unhandled_.push(&i->second);
226 if (MRegisterInfo::isPhysicalRegister(i->second.reg))
227 fixed_.push_back(&i->second);
231 void RA::processActiveIntervals(IntervalPtrs::value_type cur)
233 DEBUG(std::cerr << "\tprocessing active intervals:\n");
234 for (IntervalPtrs::reverse_iterator
235 i = active_.rbegin(); i != active_.rend();) {
236 unsigned reg = (*i)->reg;
237 // remove expired intervals
238 if ((*i)->expiredAt(cur->start())) {
239 DEBUG(std::cerr << "\t\tinterval " << **i << " expired\n");
240 if (MRegisterInfo::isVirtualRegister(reg))
241 reg = vrm_->getPhys(reg);
242 prt_->delRegUse(reg);
243 // remove from active
244 i = IntervalPtrs::reverse_iterator(active_.erase(i.base()-1));
246 // move inactive intervals to inactive list
247 else if (!(*i)->liveAt(cur->start())) {
248 DEBUG(std::cerr << "\t\tinterval " << **i << " inactive\n");
249 if (MRegisterInfo::isVirtualRegister(reg))
250 reg = vrm_->getPhys(reg);
251 prt_->delRegUse(reg);
253 inactive_.push_back(*i);
254 // remove from active
255 i = IntervalPtrs::reverse_iterator(active_.erase(i.base()-1));
263 void RA::processInactiveIntervals(IntervalPtrs::value_type cur)
265 DEBUG(std::cerr << "\tprocessing inactive intervals:\n");
266 for (IntervalPtrs::reverse_iterator
267 i = inactive_.rbegin(); i != inactive_.rend();) {
268 unsigned reg = (*i)->reg;
270 // remove expired intervals
271 if ((*i)->expiredAt(cur->start())) {
272 DEBUG(std::cerr << "\t\tinterval " << **i << " expired\n");
273 // remove from inactive
274 i = IntervalPtrs::reverse_iterator(inactive_.erase(i.base()-1));
276 // move re-activated intervals in active list
277 else if ((*i)->liveAt(cur->start())) {
278 DEBUG(std::cerr << "\t\tinterval " << **i << " active\n");
279 if (MRegisterInfo::isVirtualRegister(reg))
280 reg = vrm_->getPhys(reg);
281 prt_->addRegUse(reg);
283 active_.push_back(*i);
284 // remove from inactive
285 i = IntervalPtrs::reverse_iterator(inactive_.erase(i.base()-1));
293 void RA::updateSpillWeights(unsigned reg, SpillWeights::value_type weight)
295 spillWeights_[reg] += weight;
296 for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
297 spillWeights_[*as] += weight;
300 void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
302 DEBUG(std::cerr << "\tallocating current interval: ");
304 PhysRegTracker backupPrt = *prt_;
306 spillWeights_.assign(mri_->getNumRegs(), 0.0);
308 // for each interval in active update spill weights
309 for (IntervalPtrs::const_iterator i = active_.begin(), e = active_.end();
311 unsigned reg = (*i)->reg;
312 if (MRegisterInfo::isVirtualRegister(reg))
313 reg = vrm_->getPhys(reg);
314 updateSpillWeights(reg, (*i)->weight);
317 // for every interval in inactive we overlap with, mark the
318 // register as not free and update spill weights
319 for (IntervalPtrs::const_iterator i = inactive_.begin(),
320 e = inactive_.end(); i != e; ++i) {
321 if (cur->overlaps(**i)) {
322 unsigned reg = (*i)->reg;
323 if (MRegisterInfo::isVirtualRegister(reg))
324 reg = vrm_->getPhys(reg);
325 prt_->addRegUse(reg);
326 updateSpillWeights(reg, (*i)->weight);
330 // for every interval in fixed we overlap with,
331 // mark the register as not free and update spill weights
332 for (IntervalPtrs::const_iterator i = fixed_.begin(),
333 e = fixed_.end(); i != e; ++i) {
334 if (cur->overlaps(**i)) {
335 unsigned reg = (*i)->reg;
336 prt_->addRegUse(reg);
337 updateSpillWeights(reg, (*i)->weight);
341 unsigned physReg = getFreePhysReg(cur);
342 // restore the physical register tracker
344 // if we find a free register, we are done: assign this virtual to
345 // the free physical register and add this interval to the active
348 DEBUG(std::cerr << mri_->getName(physReg) << '\n');
349 vrm_->assignVirt2Phys(cur->reg, physReg);
350 prt_->addRegUse(physReg);
351 active_.push_back(cur);
352 handled_.push_back(cur);
355 DEBUG(std::cerr << "no free registers\n");
357 DEBUG(std::cerr << "\tassigning stack slot at interval "<< *cur << ":\n");
359 float minWeight = HUGE_VAL;
361 const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
362 for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_);
363 i != rc->allocation_order_end(*mf_); ++i) {
365 if (minWeight > spillWeights_[reg]) {
366 minWeight = spillWeights_[reg];
370 DEBUG(std::cerr << "\t\tregister with min weight: "
371 << mri_->getName(minReg) << " (" << minWeight << ")\n");
373 // if the current has the minimum weight, we need to spill it and
374 // add any added intervals back to unhandled, and restart
376 if (cur->weight <= minWeight) {
377 DEBUG(std::cerr << "\t\t\tspilling(c): " << *cur << '\n';);
378 int slot = vrm_->assignVirt2StackSlot(cur->reg);
379 std::vector<LiveInterval*> added =
380 li_->addIntervalsForSpills(*cur, *vrm_, slot);
382 return; // Early exit if all spills were folded.
384 // Merge added with unhandled. Note that we know that
385 // addIntervalsForSpills returns intervals sorted by their starting
387 for (unsigned i = 0, e = added.size(); i != e; ++i)
388 unhandled_.push(added[i]);
392 // push the current interval back to unhandled since we are going
393 // to re-run at least this iteration. Since we didn't modify it it
394 // should go back right in the front of the list
395 unhandled_.push(cur);
397 // otherwise we spill all intervals aliasing the register with
398 // minimum weight, rollback to the interval with the earliest
399 // start point and let the linear scan algorithm run again
400 std::vector<LiveInterval*> added;
401 assert(MRegisterInfo::isPhysicalRegister(minReg) &&
402 "did not choose a register to spill?");
403 std::vector<bool> toSpill(mri_->getNumRegs(), false);
404 // we are going to spill minReg and all its aliases
405 toSpill[minReg] = true;
406 for (const unsigned* as = mri_->getAliasSet(minReg); *as; ++as)
409 // the earliest start of a spilled interval indicates up to where
410 // in handled we need to roll back
411 unsigned earliestStart = cur->start();
413 // set of spilled vregs (used later to rollback properly)
414 std::set<unsigned> spilled;
416 // spill live intervals of virtual regs mapped to the physical
417 // register we want to clear (and its aliases). we only spill
418 // those that overlap with the current interval as the rest do not
419 // affect its allocation. we also keep track of the earliest start
420 // of all spilled live intervals since this will mark our rollback
422 for (IntervalPtrs::iterator
423 i = active_.begin(); i != active_.end(); ++i) {
424 unsigned reg = (*i)->reg;
425 if (MRegisterInfo::isVirtualRegister(reg) &&
426 toSpill[vrm_->getPhys(reg)] &&
427 cur->overlaps(**i)) {
428 DEBUG(std::cerr << "\t\t\tspilling(a): " << **i << '\n');
429 earliestStart = std::min(earliestStart, (*i)->start());
430 int slot = vrm_->assignVirt2StackSlot((*i)->reg);
431 std::vector<LiveInterval*> newIs =
432 li_->addIntervalsForSpills(**i, *vrm_, slot);
433 std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
437 for (IntervalPtrs::iterator
438 i = inactive_.begin(); i != inactive_.end(); ++i) {
439 unsigned reg = (*i)->reg;
440 if (MRegisterInfo::isVirtualRegister(reg) &&
441 toSpill[vrm_->getPhys(reg)] &&
442 cur->overlaps(**i)) {
443 DEBUG(std::cerr << "\t\t\tspilling(i): " << **i << '\n');
444 earliestStart = std::min(earliestStart, (*i)->start());
445 int slot = vrm_->assignVirt2StackSlot((*i)->reg);
446 std::vector<LiveInterval*> newIs =
447 li_->addIntervalsForSpills(**i, *vrm_, slot);
448 std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
453 DEBUG(std::cerr << "\t\trolling back to: " << earliestStart << '\n');
454 // scan handled in reverse order up to the earliaset start of a
455 // spilled live interval and undo each one, restoring the state of
457 while (!handled_.empty()) {
458 LiveInterval* i = handled_.back();
459 // if this interval starts before t we are done
460 if (i->start() < earliestStart)
462 DEBUG(std::cerr << "\t\t\tundo changes for: " << *i << '\n');
464 // when undoing a live interval allocation we must know if it
465 // is active or inactive to properly update the PhysRegTracker
466 // and the VirtRegMap
467 IntervalPtrs::iterator it;
468 if ((it = find(active_.begin(), active_.end(), i)) != active_.end()) {
470 if (MRegisterInfo::isPhysicalRegister(i->reg)) {
471 prt_->delRegUse(i->reg);
475 if (!spilled.count(i->reg))
477 prt_->delRegUse(vrm_->getPhys(i->reg));
478 vrm_->clearVirt(i->reg);
481 else if ((it = find(inactive_.begin(), inactive_.end(), i)) != inactive_.end()) {
483 if (MRegisterInfo::isPhysicalRegister(i->reg))
486 if (!spilled.count(i->reg))
488 vrm_->clearVirt(i->reg);
492 if (MRegisterInfo::isVirtualRegister(i->reg))
493 vrm_->clearVirt(i->reg);
498 // scan the rest and undo each interval that expired after t and
499 // insert it in active (the next iteration of the algorithm will
500 // put it in inactive if required)
501 IntervalPtrs::iterator i = handled_.begin(), e = handled_.end();
502 for (; i != e; ++i) {
503 if (!(*i)->expiredAt(earliestStart) && (*i)->expiredAt(cur->start())) {
504 DEBUG(std::cerr << "\t\t\tundo changes for: " << **i << '\n');
505 active_.push_back(*i);
506 if (MRegisterInfo::isPhysicalRegister((*i)->reg))
507 prt_->addRegUse((*i)->reg);
509 prt_->addRegUse(vrm_->getPhys((*i)->reg));
513 std::sort(added.begin(), added.end(), less_ptr<LiveInterval>());
514 // merge added with unhandled
515 for (unsigned i = 0, e = added.size(); i != e; ++i)
516 unhandled_.push(added[i]);
519 unsigned RA::getFreePhysReg(LiveInterval* cur)
521 const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
523 for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_);
524 i != rc->allocation_order_end(*mf_); ++i) {
526 if (prt_->isRegAvail(reg))
532 FunctionPass* llvm::createLinearScanRegisterAllocator() {