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/CodeGen/LiveIntervalAnalysis.h"
16 #include "PhysRegTracker.h"
17 #include "VirtRegMap.h"
18 #include "llvm/Function.h"
19 #include "llvm/CodeGen/MachineFunctionPass.h"
20 #include "llvm/CodeGen/MachineInstr.h"
21 #include "llvm/CodeGen/Passes.h"
22 #include "llvm/CodeGen/SSARegMap.h"
23 #include "llvm/Target/MRegisterInfo.h"
24 #include "llvm/Target/TargetMachine.h"
25 #include "llvm/ADT/EquivalenceClasses.h"
26 #include "llvm/ADT/Statistic.h"
27 #include "llvm/ADT/STLExtras.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/Visibility.h"
40 static Statistic<double> efficiency
41 ("regalloc", "Ratio of intervals processed over total intervals");
42 static Statistic<> NumBacktracks
43 ("regalloc", "Number of times we had to backtrack");
45 static unsigned numIterations = 0;
46 static unsigned numIntervals = 0;
48 struct VISIBILITY_HIDDEN RA : public MachineFunctionPass {
49 typedef std::pair<LiveInterval*, LiveInterval::iterator> IntervalPtr;
50 typedef std::vector<IntervalPtr> IntervalPtrs;
52 /// RelatedRegClasses - This structure is built the first time a function is
53 /// compiled, and keeps track of which register classes have registers that
54 /// belong to multiple classes or have aliases that are in other classes.
55 EquivalenceClasses<const TargetRegisterClass*> RelatedRegClasses;
56 std::map<unsigned, const TargetRegisterClass*> OneClassForEachPhysReg;
59 const TargetMachine* tm_;
60 const MRegisterInfo* mri_;
64 /// handled_ - Intervals are added to the handled_ set in the order of their
65 /// start value. This is uses for backtracking.
66 std::vector<LiveInterval*> handled_;
68 /// fixed_ - Intervals that correspond to machine registers.
72 /// active_ - Intervals that are currently being processed, and which have a
73 /// live range active for the current point.
76 /// inactive_ - Intervals that are currently being processed, but which have
77 /// a hold at the current point.
78 IntervalPtrs inactive_;
80 typedef std::priority_queue<LiveInterval*,
81 std::vector<LiveInterval*>,
82 greater_ptr<LiveInterval> > IntervalHeap;
83 IntervalHeap unhandled_;
84 std::auto_ptr<PhysRegTracker> prt_;
85 std::auto_ptr<VirtRegMap> vrm_;
86 std::auto_ptr<Spiller> spiller_;
89 virtual const char* getPassName() const {
90 return "Linear Scan Register Allocator";
93 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
94 AU.addRequired<LiveIntervals>();
95 MachineFunctionPass::getAnalysisUsage(AU);
98 /// runOnMachineFunction - register allocate the whole function
99 bool runOnMachineFunction(MachineFunction&);
102 /// linearScan - the linear scan algorithm
105 /// initIntervalSets - initialize the interval sets.
107 void initIntervalSets();
109 /// processActiveIntervals - expire old intervals and move non-overlapping
110 /// ones to the inactive list.
111 void processActiveIntervals(unsigned CurPoint);
113 /// processInactiveIntervals - expire old intervals and move overlapping
114 /// ones to the active list.
115 void processInactiveIntervals(unsigned CurPoint);
117 /// assignRegOrStackSlotAtInterval - assign a register if one
118 /// is available, or spill.
119 void assignRegOrStackSlotAtInterval(LiveInterval* cur);
122 /// register handling helpers
125 /// getFreePhysReg - return a free physical register for this virtual
126 /// register interval if we have one, otherwise return 0.
127 unsigned getFreePhysReg(LiveInterval* cur);
129 /// assignVirt2StackSlot - assigns this virtual register to a
130 /// stack slot. returns the stack slot
131 int assignVirt2StackSlot(unsigned virtReg);
133 void ComputeRelatedRegClasses();
135 template <typename ItTy>
136 void printIntervals(const char* const str, ItTy i, ItTy e) const {
137 if (str) std::cerr << str << " intervals:\n";
138 for (; i != e; ++i) {
139 std::cerr << "\t" << *i->first << " -> ";
140 unsigned reg = i->first->reg;
141 if (MRegisterInfo::isVirtualRegister(reg)) {
142 reg = vrm_->getPhys(reg);
144 std::cerr << mri_->getName(reg) << '\n';
150 void RA::ComputeRelatedRegClasses() {
151 const MRegisterInfo &MRI = *mri_;
153 // First pass, add all reg classes to the union, and determine at least one
154 // reg class that each register is in.
155 bool HasAliases = false;
156 for (MRegisterInfo::regclass_iterator RCI = MRI.regclass_begin(),
157 E = MRI.regclass_end(); RCI != E; ++RCI) {
158 RelatedRegClasses.insert(*RCI);
159 for (TargetRegisterClass::iterator I = (*RCI)->begin(), E = (*RCI)->end();
161 HasAliases = HasAliases || *MRI.getAliasSet(*I) != 0;
163 const TargetRegisterClass *&PRC = OneClassForEachPhysReg[*I];
165 // Already processed this register. Just make sure we know that
166 // multiple register classes share a register.
167 RelatedRegClasses.unionSets(PRC, *RCI);
174 // Second pass, now that we know conservatively what register classes each reg
175 // belongs to, add info about aliases. We don't need to do this for targets
176 // without register aliases.
178 for (std::map<unsigned, const TargetRegisterClass*>::iterator
179 I = OneClassForEachPhysReg.begin(), E = OneClassForEachPhysReg.end();
181 for (const unsigned *AS = MRI.getAliasSet(I->first); *AS; ++AS)
182 RelatedRegClasses.unionSets(I->second, OneClassForEachPhysReg[*AS]);
185 bool RA::runOnMachineFunction(MachineFunction &fn) {
187 tm_ = &fn.getTarget();
188 mri_ = tm_->getRegisterInfo();
189 li_ = &getAnalysis<LiveIntervals>();
191 // If this is the first function compiled, compute the related reg classes.
192 if (RelatedRegClasses.empty())
193 ComputeRelatedRegClasses();
195 PhysRegsUsed = new bool[mri_->getNumRegs()];
196 std::fill(PhysRegsUsed, PhysRegsUsed+mri_->getNumRegs(), false);
197 fn.setUsedPhysRegs(PhysRegsUsed);
199 if (!prt_.get()) prt_.reset(new PhysRegTracker(*mri_));
200 vrm_.reset(new VirtRegMap(*mf_));
201 if (!spiller_.get()) spiller_.reset(createSpiller());
207 // Rewrite spill code and update the PhysRegsUsed set.
208 spiller_->runOnMachineFunction(*mf_, *vrm_);
210 vrm_.reset(); // Free the VirtRegMap
213 while (!unhandled_.empty()) unhandled_.pop();
222 /// initIntervalSets - initialize the interval sets.
224 void RA::initIntervalSets()
226 assert(unhandled_.empty() && fixed_.empty() &&
227 active_.empty() && inactive_.empty() &&
228 "interval sets should be empty on initialization");
230 for (LiveIntervals::iterator i = li_->begin(), e = li_->end(); i != e; ++i) {
231 if (MRegisterInfo::isPhysicalRegister(i->second.reg)) {
232 PhysRegsUsed[i->second.reg] = true;
233 fixed_.push_back(std::make_pair(&i->second, i->second.begin()));
235 unhandled_.push(&i->second);
239 void RA::linearScan()
241 // linear scan algorithm
242 DEBUG(std::cerr << "********** LINEAR SCAN **********\n");
243 DEBUG(std::cerr << "********** Function: "
244 << mf_->getFunction()->getName() << '\n');
246 // DEBUG(printIntervals("unhandled", unhandled_.begin(), unhandled_.end()));
247 DEBUG(printIntervals("fixed", fixed_.begin(), fixed_.end()));
248 DEBUG(printIntervals("active", active_.begin(), active_.end()));
249 DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
251 while (!unhandled_.empty()) {
252 // pick the interval with the earliest start point
253 LiveInterval* cur = unhandled_.top();
256 DEBUG(std::cerr << "\n*** CURRENT ***: " << *cur << '\n');
258 processActiveIntervals(cur->beginNumber());
259 processInactiveIntervals(cur->beginNumber());
261 assert(MRegisterInfo::isVirtualRegister(cur->reg) &&
262 "Can only allocate virtual registers!");
264 // Allocating a virtual register. try to find a free
265 // physical register or spill an interval (possibly this one) in order to
267 assignRegOrStackSlotAtInterval(cur);
269 DEBUG(printIntervals("active", active_.begin(), active_.end()));
270 DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
272 numIntervals += li_->getNumIntervals();
273 efficiency = double(numIterations) / double(numIntervals);
275 // expire any remaining active intervals
276 for (IntervalPtrs::reverse_iterator
277 i = active_.rbegin(); i != active_.rend(); ) {
278 unsigned reg = i->first->reg;
279 DEBUG(std::cerr << "\tinterval " << *i->first << " expired\n");
280 assert(MRegisterInfo::isVirtualRegister(reg) &&
281 "Can only allocate virtual registers!");
282 reg = vrm_->getPhys(reg);
283 prt_->delRegUse(reg);
284 i = IntervalPtrs::reverse_iterator(active_.erase(i.base()-1));
287 // expire any remaining inactive intervals
288 for (IntervalPtrs::reverse_iterator
289 i = inactive_.rbegin(); i != inactive_.rend(); ) {
290 DEBUG(std::cerr << "\tinterval " << *i->first << " expired\n");
291 i = IntervalPtrs::reverse_iterator(inactive_.erase(i.base()-1));
294 DEBUG(std::cerr << *vrm_);
297 /// processActiveIntervals - expire old intervals and move non-overlapping ones
298 /// to the inactive list.
299 void RA::processActiveIntervals(unsigned CurPoint)
301 DEBUG(std::cerr << "\tprocessing active intervals:\n");
303 for (unsigned i = 0, e = active_.size(); i != e; ++i) {
304 LiveInterval *Interval = active_[i].first;
305 LiveInterval::iterator IntervalPos = active_[i].second;
306 unsigned reg = Interval->reg;
308 IntervalPos = Interval->advanceTo(IntervalPos, CurPoint);
310 if (IntervalPos == Interval->end()) { // Remove expired intervals.
311 DEBUG(std::cerr << "\t\tinterval " << *Interval << " expired\n");
312 assert(MRegisterInfo::isVirtualRegister(reg) &&
313 "Can only allocate virtual registers!");
314 reg = vrm_->getPhys(reg);
315 prt_->delRegUse(reg);
317 // Pop off the end of the list.
318 active_[i] = active_.back();
322 } else if (IntervalPos->start > CurPoint) {
323 // Move inactive intervals to inactive list.
324 DEBUG(std::cerr << "\t\tinterval " << *Interval << " inactive\n");
325 assert(MRegisterInfo::isVirtualRegister(reg) &&
326 "Can only allocate virtual registers!");
327 reg = vrm_->getPhys(reg);
328 prt_->delRegUse(reg);
330 inactive_.push_back(std::make_pair(Interval, IntervalPos));
332 // Pop off the end of the list.
333 active_[i] = active_.back();
337 // Otherwise, just update the iterator position.
338 active_[i].second = IntervalPos;
343 /// processInactiveIntervals - expire old intervals and move overlapping
344 /// ones to the active list.
345 void RA::processInactiveIntervals(unsigned CurPoint)
347 DEBUG(std::cerr << "\tprocessing inactive intervals:\n");
349 for (unsigned i = 0, e = inactive_.size(); i != e; ++i) {
350 LiveInterval *Interval = inactive_[i].first;
351 LiveInterval::iterator IntervalPos = inactive_[i].second;
352 unsigned reg = Interval->reg;
354 IntervalPos = Interval->advanceTo(IntervalPos, CurPoint);
356 if (IntervalPos == Interval->end()) { // remove expired intervals.
357 DEBUG(std::cerr << "\t\tinterval " << *Interval << " expired\n");
359 // Pop off the end of the list.
360 inactive_[i] = inactive_.back();
361 inactive_.pop_back();
363 } else if (IntervalPos->start <= CurPoint) {
364 // move re-activated intervals in active list
365 DEBUG(std::cerr << "\t\tinterval " << *Interval << " active\n");
366 assert(MRegisterInfo::isVirtualRegister(reg) &&
367 "Can only allocate virtual registers!");
368 reg = vrm_->getPhys(reg);
369 prt_->addRegUse(reg);
371 active_.push_back(std::make_pair(Interval, IntervalPos));
373 // Pop off the end of the list.
374 inactive_[i] = inactive_.back();
375 inactive_.pop_back();
378 // Otherwise, just update the iterator position.
379 inactive_[i].second = IntervalPos;
384 /// updateSpillWeights - updates the spill weights of the specifed physical
385 /// register and its weight.
386 static void updateSpillWeights(std::vector<float> &Weights,
387 unsigned reg, float weight,
388 const MRegisterInfo *MRI) {
389 Weights[reg] += weight;
390 for (const unsigned* as = MRI->getAliasSet(reg); *as; ++as)
391 Weights[*as] += weight;
394 static RA::IntervalPtrs::iterator FindIntervalInVector(RA::IntervalPtrs &IP,
396 for (RA::IntervalPtrs::iterator I = IP.begin(), E = IP.end(); I != E; ++I)
397 if (I->first == LI) return I;
401 static void RevertVectorIteratorsTo(RA::IntervalPtrs &V, unsigned Point) {
402 for (unsigned i = 0, e = V.size(); i != e; ++i) {
403 RA::IntervalPtr &IP = V[i];
404 LiveInterval::iterator I = std::upper_bound(IP.first->begin(),
406 if (I != IP.first->begin()) --I;
411 /// assignRegOrStackSlotAtInterval - assign a register if one is available, or
413 void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
415 DEBUG(std::cerr << "\tallocating current interval: ");
417 PhysRegTracker backupPrt = *prt_;
419 std::vector<std::pair<unsigned, float> > SpillWeightsToAdd;
420 unsigned StartPosition = cur->beginNumber();
421 const TargetRegisterClass *RC = mf_->getSSARegMap()->getRegClass(cur->reg);
422 const TargetRegisterClass *RCLeader = RelatedRegClasses.getLeaderValue(RC);
424 // for every interval in inactive we overlap with, mark the
425 // register as not free and update spill weights.
426 for (IntervalPtrs::const_iterator i = inactive_.begin(),
427 e = inactive_.end(); i != e; ++i) {
428 unsigned Reg = i->first->reg;
429 assert(MRegisterInfo::isVirtualRegister(Reg) &&
430 "Can only allocate virtual registers!");
431 const TargetRegisterClass *RegRC = mf_->getSSARegMap()->getRegClass(Reg);
432 // If this is not in a related reg class to the register we're allocating,
434 if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader &&
435 cur->overlapsFrom(*i->first, i->second-1)) {
436 Reg = vrm_->getPhys(Reg);
437 prt_->addRegUse(Reg);
438 SpillWeightsToAdd.push_back(std::make_pair(Reg, i->first->weight));
442 // Speculatively check to see if we can get a register right now. If not,
443 // we know we won't be able to by adding more constraints. If so, we can
444 // check to see if it is valid. Doing an exhaustive search of the fixed_ list
445 // is very bad (it contains all callee clobbered registers for any functions
446 // with a call), so we want to avoid doing that if possible.
447 unsigned physReg = getFreePhysReg(cur);
449 // We got a register. However, if it's in the fixed_ list, we might
450 // conflict with it. Check to see if we conflict with it or any of its
452 std::set<unsigned> RegAliases;
453 for (const unsigned *AS = mri_->getAliasSet(physReg); *AS; ++AS)
454 RegAliases.insert(*AS);
456 bool ConflictsWithFixed = false;
457 for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
458 if (physReg == fixed_[i].first->reg ||
459 RegAliases.count(fixed_[i].first->reg)) {
460 // Okay, this reg is on the fixed list. Check to see if we actually
462 IntervalPtr &IP = fixed_[i];
463 LiveInterval *I = IP.first;
464 if (I->endNumber() > StartPosition) {
465 LiveInterval::iterator II = I->advanceTo(IP.second, StartPosition);
467 if (II != I->begin() && II->start > StartPosition)
469 if (cur->overlapsFrom(*I, II)) {
470 ConflictsWithFixed = true;
477 // Okay, the register picked by our speculative getFreePhysReg call turned
478 // out to be in use. Actually add all of the conflicting fixed registers to
479 // prt so we can do an accurate query.
480 if (ConflictsWithFixed) {
481 // For every interval in fixed we overlap with, mark the register as not
482 // free and update spill weights.
483 for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
484 IntervalPtr &IP = fixed_[i];
485 LiveInterval *I = IP.first;
487 const TargetRegisterClass *RegRC = OneClassForEachPhysReg[I->reg];
488 if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader &&
489 I->endNumber() > StartPosition) {
490 LiveInterval::iterator II = I->advanceTo(IP.second, StartPosition);
492 if (II != I->begin() && II->start > StartPosition)
494 if (cur->overlapsFrom(*I, II)) {
495 unsigned reg = I->reg;
496 prt_->addRegUse(reg);
497 SpillWeightsToAdd.push_back(std::make_pair(reg, I->weight));
502 // Using the newly updated prt_ object, which includes conflicts in the
503 // future, see if there are any registers available.
504 physReg = getFreePhysReg(cur);
508 // Restore the physical register tracker, removing information about the
512 // if we find a free register, we are done: assign this virtual to
513 // the free physical register and add this interval to the active
516 DEBUG(std::cerr << mri_->getName(physReg) << '\n');
517 vrm_->assignVirt2Phys(cur->reg, physReg);
518 prt_->addRegUse(physReg);
519 active_.push_back(std::make_pair(cur, cur->begin()));
520 handled_.push_back(cur);
523 DEBUG(std::cerr << "no free registers\n");
525 // Compile the spill weights into an array that is better for scanning.
526 std::vector<float> SpillWeights(mri_->getNumRegs(), 0.0);
527 for (std::vector<std::pair<unsigned, float> >::iterator
528 I = SpillWeightsToAdd.begin(), E = SpillWeightsToAdd.end(); I != E; ++I)
529 updateSpillWeights(SpillWeights, I->first, I->second, mri_);
531 // for each interval in active, update spill weights.
532 for (IntervalPtrs::const_iterator i = active_.begin(), e = active_.end();
534 unsigned reg = i->first->reg;
535 assert(MRegisterInfo::isVirtualRegister(reg) &&
536 "Can only allocate virtual registers!");
537 reg = vrm_->getPhys(reg);
538 updateSpillWeights(SpillWeights, reg, i->first->weight, mri_);
541 DEBUG(std::cerr << "\tassigning stack slot at interval "<< *cur << ":\n");
543 // Find a register to spill.
544 float minWeight = float(HUGE_VAL);
546 for (TargetRegisterClass::iterator i = RC->allocation_order_begin(*mf_),
547 e = RC->allocation_order_end(*mf_); i != e; ++i) {
549 if (minWeight > SpillWeights[reg]) {
550 minWeight = SpillWeights[reg];
555 // If we didn't find a register that is spillable, try aliases?
557 for (TargetRegisterClass::iterator i = RC->allocation_order_begin(*mf_),
558 e = RC->allocation_order_end(*mf_); i != e; ++i) {
560 // No need to worry about if the alias register size < regsize of RC.
561 // We are going to spill all registers that alias it anyway.
562 for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as) {
563 if (minWeight > SpillWeights[*as]) {
564 minWeight = SpillWeights[*as];
570 // All registers must have inf weight. Just grab one!
572 minReg = *RC->allocation_order_begin(*mf_);
575 DEBUG(std::cerr << "\t\tregister with min weight: "
576 << mri_->getName(minReg) << " (" << minWeight << ")\n");
578 // if the current has the minimum weight, we need to spill it and
579 // add any added intervals back to unhandled, and restart
581 if (cur->weight != float(HUGE_VAL) && cur->weight <= minWeight) {
582 DEBUG(std::cerr << "\t\t\tspilling(c): " << *cur << '\n';);
583 int slot = vrm_->assignVirt2StackSlot(cur->reg);
584 std::vector<LiveInterval*> added =
585 li_->addIntervalsForSpills(*cur, *vrm_, slot);
587 return; // Early exit if all spills were folded.
589 // Merge added with unhandled. Note that we know that
590 // addIntervalsForSpills returns intervals sorted by their starting
592 for (unsigned i = 0, e = added.size(); i != e; ++i)
593 unhandled_.push(added[i]);
599 // push the current interval back to unhandled since we are going
600 // to re-run at least this iteration. Since we didn't modify it it
601 // should go back right in the front of the list
602 unhandled_.push(cur);
604 // otherwise we spill all intervals aliasing the register with
605 // minimum weight, rollback to the interval with the earliest
606 // start point and let the linear scan algorithm run again
607 std::vector<LiveInterval*> added;
608 assert(MRegisterInfo::isPhysicalRegister(minReg) &&
609 "did not choose a register to spill?");
610 std::vector<bool> toSpill(mri_->getNumRegs(), false);
612 // We are going to spill minReg and all its aliases.
613 toSpill[minReg] = true;
614 for (const unsigned* as = mri_->getAliasSet(minReg); *as; ++as)
617 // the earliest start of a spilled interval indicates up to where
618 // in handled we need to roll back
619 unsigned earliestStart = cur->beginNumber();
621 // set of spilled vregs (used later to rollback properly)
622 std::set<unsigned> spilled;
624 // spill live intervals of virtual regs mapped to the physical register we
625 // want to clear (and its aliases). We only spill those that overlap with the
626 // current interval as the rest do not affect its allocation. we also keep
627 // track of the earliest start of all spilled live intervals since this will
628 // mark our rollback point.
629 for (IntervalPtrs::iterator i = active_.begin(); i != active_.end(); ++i) {
630 unsigned reg = i->first->reg;
631 if (//MRegisterInfo::isVirtualRegister(reg) &&
632 toSpill[vrm_->getPhys(reg)] &&
633 cur->overlapsFrom(*i->first, i->second)) {
634 DEBUG(std::cerr << "\t\t\tspilling(a): " << *i->first << '\n');
635 earliestStart = std::min(earliestStart, i->first->beginNumber());
636 int slot = vrm_->assignVirt2StackSlot(i->first->reg);
637 std::vector<LiveInterval*> newIs =
638 li_->addIntervalsForSpills(*i->first, *vrm_, slot);
639 std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
643 for (IntervalPtrs::iterator i = inactive_.begin(); i != inactive_.end(); ++i){
644 unsigned reg = i->first->reg;
645 if (//MRegisterInfo::isVirtualRegister(reg) &&
646 toSpill[vrm_->getPhys(reg)] &&
647 cur->overlapsFrom(*i->first, i->second-1)) {
648 DEBUG(std::cerr << "\t\t\tspilling(i): " << *i->first << '\n');
649 earliestStart = std::min(earliestStart, i->first->beginNumber());
650 int slot = vrm_->assignVirt2StackSlot(reg);
651 std::vector<LiveInterval*> newIs =
652 li_->addIntervalsForSpills(*i->first, *vrm_, slot);
653 std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
658 DEBUG(std::cerr << "\t\trolling back to: " << earliestStart << '\n');
660 // Scan handled in reverse order up to the earliest start of a
661 // spilled live interval and undo each one, restoring the state of
663 while (!handled_.empty()) {
664 LiveInterval* i = handled_.back();
665 // If this interval starts before t we are done.
666 if (i->beginNumber() < earliestStart)
668 DEBUG(std::cerr << "\t\t\tundo changes for: " << *i << '\n');
671 // When undoing a live interval allocation we must know if it is active or
672 // inactive to properly update the PhysRegTracker and the VirtRegMap.
673 IntervalPtrs::iterator it;
674 if ((it = FindIntervalInVector(active_, i)) != active_.end()) {
676 assert(!MRegisterInfo::isPhysicalRegister(i->reg));
677 if (!spilled.count(i->reg))
679 prt_->delRegUse(vrm_->getPhys(i->reg));
680 vrm_->clearVirt(i->reg);
681 } else if ((it = FindIntervalInVector(inactive_, i)) != inactive_.end()) {
683 assert(!MRegisterInfo::isPhysicalRegister(i->reg));
684 if (!spilled.count(i->reg))
686 vrm_->clearVirt(i->reg);
688 assert(MRegisterInfo::isVirtualRegister(i->reg) &&
689 "Can only allocate virtual registers!");
690 vrm_->clearVirt(i->reg);
695 // Rewind the iterators in the active, inactive, and fixed lists back to the
696 // point we reverted to.
697 RevertVectorIteratorsTo(active_, earliestStart);
698 RevertVectorIteratorsTo(inactive_, earliestStart);
699 RevertVectorIteratorsTo(fixed_, earliestStart);
701 // scan the rest and undo each interval that expired after t and
702 // insert it in active (the next iteration of the algorithm will
703 // put it in inactive if required)
704 for (unsigned i = 0, e = handled_.size(); i != e; ++i) {
705 LiveInterval *HI = handled_[i];
706 if (!HI->expiredAt(earliestStart) &&
707 HI->expiredAt(cur->beginNumber())) {
708 DEBUG(std::cerr << "\t\t\tundo changes for: " << *HI << '\n');
709 active_.push_back(std::make_pair(HI, HI->begin()));
710 assert(!MRegisterInfo::isPhysicalRegister(HI->reg));
711 prt_->addRegUse(vrm_->getPhys(HI->reg));
715 // merge added with unhandled
716 for (unsigned i = 0, e = added.size(); i != e; ++i)
717 unhandled_.push(added[i]);
720 /// getFreePhysReg - return a free physical register for this virtual register
721 /// interval if we have one, otherwise return 0.
722 unsigned RA::getFreePhysReg(LiveInterval *cur) {
723 std::vector<unsigned> inactiveCounts(mri_->getNumRegs(), 0);
724 unsigned MaxInactiveCount = 0;
726 const TargetRegisterClass *RC = mf_->getSSARegMap()->getRegClass(cur->reg);
727 const TargetRegisterClass *RCLeader = RelatedRegClasses.getLeaderValue(RC);
729 for (IntervalPtrs::iterator i = inactive_.begin(), e = inactive_.end();
731 unsigned reg = i->first->reg;
732 assert(MRegisterInfo::isVirtualRegister(reg) &&
733 "Can only allocate virtual registers!");
735 // If this is not in a related reg class to the register we're allocating,
737 const TargetRegisterClass *RegRC = mf_->getSSARegMap()->getRegClass(reg);
738 if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader) {
739 reg = vrm_->getPhys(reg);
740 ++inactiveCounts[reg];
741 MaxInactiveCount = std::max(MaxInactiveCount, inactiveCounts[reg]);
745 const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
747 unsigned FreeReg = 0;
748 unsigned FreeRegInactiveCount = 0;
750 // Scan for the first available register.
751 TargetRegisterClass::iterator I = rc->allocation_order_begin(*mf_);
752 TargetRegisterClass::iterator E = rc->allocation_order_end(*mf_);
754 if (prt_->isRegAvail(*I)) {
756 FreeRegInactiveCount = inactiveCounts[FreeReg];
760 // If there are no free regs, or if this reg has the max inactive count,
761 // return this register.
762 if (FreeReg == 0 || FreeRegInactiveCount == MaxInactiveCount) return FreeReg;
764 // Continue scanning the registers, looking for the one with the highest
765 // inactive count. Alkis found that this reduced register pressure very
766 // slightly on X86 (in rev 1.94 of this file), though this should probably be
768 for (; I != E; ++I) {
770 if (prt_->isRegAvail(Reg) && FreeRegInactiveCount < inactiveCounts[Reg]) {
772 FreeRegInactiveCount = inactiveCounts[Reg];
773 if (FreeRegInactiveCount == MaxInactiveCount)
774 break; // We found the one with the max inactive count.
781 FunctionPass* llvm::createLinearScanRegisterAllocator() {