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"
39 Statistic<double> efficiency
40 ("regalloc", "Ratio of intervals processed over total intervals");
41 Statistic<> NumBacktracks("regalloc", "Number of times we had to backtrack");
43 static unsigned numIterations = 0;
44 static unsigned numIntervals = 0;
46 struct RA : public MachineFunctionPass {
47 typedef std::pair<LiveInterval*, LiveInterval::iterator> IntervalPtr;
48 typedef std::vector<IntervalPtr> IntervalPtrs;
50 /// RelatedRegClasses - This structure is built the first time a function is
51 /// compiled, and keeps track of which register classes have registers that
52 /// belong to multiple classes or have aliases that are in other classes.
53 EquivalenceClasses<const TargetRegisterClass*> RelatedRegClasses;
54 std::map<unsigned, const TargetRegisterClass*> OneClassForEachPhysReg;
57 const TargetMachine* tm_;
58 const MRegisterInfo* mri_;
62 /// handled_ - Intervals are added to the handled_ set in the order of their
63 /// start value. This is uses for backtracking.
64 std::vector<LiveInterval*> handled_;
66 /// fixed_ - Intervals that correspond to machine registers.
70 /// active_ - Intervals that are currently being processed, and which have a
71 /// live range active for the current point.
74 /// inactive_ - Intervals that are currently being processed, but which have
75 /// a hold at the current point.
76 IntervalPtrs inactive_;
78 typedef std::priority_queue<LiveInterval*,
79 std::vector<LiveInterval*>,
80 greater_ptr<LiveInterval> > IntervalHeap;
81 IntervalHeap unhandled_;
82 std::auto_ptr<PhysRegTracker> prt_;
83 std::auto_ptr<VirtRegMap> vrm_;
84 std::auto_ptr<Spiller> spiller_;
87 virtual const char* getPassName() const {
88 return "Linear Scan Register Allocator";
91 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
92 AU.addRequired<LiveIntervals>();
93 MachineFunctionPass::getAnalysisUsage(AU);
96 /// runOnMachineFunction - register allocate the whole function
97 bool runOnMachineFunction(MachineFunction&);
100 /// linearScan - the linear scan algorithm
103 /// initIntervalSets - initialize the interval sets.
105 void initIntervalSets();
107 /// processActiveIntervals - expire old intervals and move non-overlapping
108 /// ones to the inactive list.
109 void processActiveIntervals(unsigned CurPoint);
111 /// processInactiveIntervals - expire old intervals and move overlapping
112 /// ones to the active list.
113 void processInactiveIntervals(unsigned CurPoint);
115 /// assignRegOrStackSlotAtInterval - assign a register if one
116 /// is available, or spill.
117 void assignRegOrStackSlotAtInterval(LiveInterval* cur);
120 /// register handling helpers
123 /// getFreePhysReg - return a free physical register for this virtual
124 /// register interval if we have one, otherwise return 0.
125 unsigned getFreePhysReg(LiveInterval* cur);
127 /// assignVirt2StackSlot - assigns this virtual register to a
128 /// stack slot. returns the stack slot
129 int assignVirt2StackSlot(unsigned virtReg);
131 void ComputeRelatedRegClasses();
133 template <typename ItTy>
134 void printIntervals(const char* const str, ItTy i, ItTy e) const {
135 if (str) std::cerr << str << " intervals:\n";
136 for (; i != e; ++i) {
137 std::cerr << "\t" << *i->first << " -> ";
138 unsigned reg = i->first->reg;
139 if (MRegisterInfo::isVirtualRegister(reg)) {
140 reg = vrm_->getPhys(reg);
142 std::cerr << mri_->getName(reg) << '\n';
148 void RA::ComputeRelatedRegClasses() {
149 const MRegisterInfo &MRI = *mri_;
151 // First pass, add all reg classes to the union, and determine at least one
152 // reg class that each register is in.
153 bool HasAliases = false;
154 for (MRegisterInfo::regclass_iterator RCI = MRI.regclass_begin(),
155 E = MRI.regclass_end(); RCI != E; ++RCI) {
156 RelatedRegClasses.insert(*RCI);
157 for (TargetRegisterClass::iterator I = (*RCI)->begin(), E = (*RCI)->end();
159 HasAliases = HasAliases || *MRI.getAliasSet(*I) != 0;
161 const TargetRegisterClass *&PRC = OneClassForEachPhysReg[*I];
163 // Already processed this register. Just make sure we know that
164 // multiple register classes share a register.
165 RelatedRegClasses.unionSets(PRC, *RCI);
172 // Second pass, now that we know conservatively what register classes each reg
173 // belongs to, add info about aliases. We don't need to do this for targets
174 // without register aliases.
176 for (std::map<unsigned, const TargetRegisterClass*>::iterator
177 I = OneClassForEachPhysReg.begin(), E = OneClassForEachPhysReg.end();
179 for (const unsigned *AS = MRI.getAliasSet(I->first); *AS; ++AS)
180 RelatedRegClasses.unionSets(I->second, OneClassForEachPhysReg[*AS]);
183 bool RA::runOnMachineFunction(MachineFunction &fn) {
185 tm_ = &fn.getTarget();
186 mri_ = tm_->getRegisterInfo();
187 li_ = &getAnalysis<LiveIntervals>();
189 // If this is the first function compiled, compute the related reg classes.
190 if (RelatedRegClasses.empty())
191 ComputeRelatedRegClasses();
193 PhysRegsUsed = new bool[mri_->getNumRegs()];
194 std::fill(PhysRegsUsed, PhysRegsUsed+mri_->getNumRegs(), false);
195 fn.setUsedPhysRegs(PhysRegsUsed);
197 if (!prt_.get()) prt_.reset(new PhysRegTracker(*mri_));
198 vrm_.reset(new VirtRegMap(*mf_));
199 if (!spiller_.get()) spiller_.reset(createSpiller());
205 // Rewrite spill code and update the PhysRegsUsed set.
206 spiller_->runOnMachineFunction(*mf_, *vrm_);
208 vrm_.reset(); // Free the VirtRegMap
211 while (!unhandled_.empty()) unhandled_.pop();
220 /// initIntervalSets - initialize the interval sets.
222 void RA::initIntervalSets()
224 assert(unhandled_.empty() && fixed_.empty() &&
225 active_.empty() && inactive_.empty() &&
226 "interval sets should be empty on initialization");
228 for (LiveIntervals::iterator i = li_->begin(), e = li_->end(); i != e; ++i) {
229 if (MRegisterInfo::isPhysicalRegister(i->second.reg)) {
230 PhysRegsUsed[i->second.reg] = true;
231 fixed_.push_back(std::make_pair(&i->second, i->second.begin()));
233 unhandled_.push(&i->second);
237 void RA::linearScan()
239 // linear scan algorithm
240 DEBUG(std::cerr << "********** LINEAR SCAN **********\n");
241 DEBUG(std::cerr << "********** Function: "
242 << mf_->getFunction()->getName() << '\n');
244 // DEBUG(printIntervals("unhandled", unhandled_.begin(), unhandled_.end()));
245 DEBUG(printIntervals("fixed", fixed_.begin(), fixed_.end()));
246 DEBUG(printIntervals("active", active_.begin(), active_.end()));
247 DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
249 while (!unhandled_.empty()) {
250 // pick the interval with the earliest start point
251 LiveInterval* cur = unhandled_.top();
254 DEBUG(std::cerr << "\n*** CURRENT ***: " << *cur << '\n');
256 processActiveIntervals(cur->beginNumber());
257 processInactiveIntervals(cur->beginNumber());
259 assert(MRegisterInfo::isVirtualRegister(cur->reg) &&
260 "Can only allocate virtual registers!");
262 // Allocating a virtual register. try to find a free
263 // physical register or spill an interval (possibly this one) in order to
265 assignRegOrStackSlotAtInterval(cur);
267 DEBUG(printIntervals("active", active_.begin(), active_.end()));
268 DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
270 numIntervals += li_->getNumIntervals();
271 efficiency = double(numIterations) / double(numIntervals);
273 // expire any remaining active intervals
274 for (IntervalPtrs::reverse_iterator
275 i = active_.rbegin(); i != active_.rend(); ) {
276 unsigned reg = i->first->reg;
277 DEBUG(std::cerr << "\tinterval " << *i->first << " expired\n");
278 assert(MRegisterInfo::isVirtualRegister(reg) &&
279 "Can only allocate virtual registers!");
280 reg = vrm_->getPhys(reg);
281 prt_->delRegUse(reg);
282 i = IntervalPtrs::reverse_iterator(active_.erase(i.base()-1));
285 // expire any remaining inactive intervals
286 for (IntervalPtrs::reverse_iterator
287 i = inactive_.rbegin(); i != inactive_.rend(); ) {
288 DEBUG(std::cerr << "\tinterval " << *i->first << " expired\n");
289 i = IntervalPtrs::reverse_iterator(inactive_.erase(i.base()-1));
292 DEBUG(std::cerr << *vrm_);
295 /// processActiveIntervals - expire old intervals and move non-overlapping ones
296 /// to the inactive list.
297 void RA::processActiveIntervals(unsigned CurPoint)
299 DEBUG(std::cerr << "\tprocessing active intervals:\n");
301 for (unsigned i = 0, e = active_.size(); i != e; ++i) {
302 LiveInterval *Interval = active_[i].first;
303 LiveInterval::iterator IntervalPos = active_[i].second;
304 unsigned reg = Interval->reg;
306 IntervalPos = Interval->advanceTo(IntervalPos, CurPoint);
308 if (IntervalPos == Interval->end()) { // Remove expired intervals.
309 DEBUG(std::cerr << "\t\tinterval " << *Interval << " expired\n");
310 assert(MRegisterInfo::isVirtualRegister(reg) &&
311 "Can only allocate virtual registers!");
312 reg = vrm_->getPhys(reg);
313 prt_->delRegUse(reg);
315 // Pop off the end of the list.
316 active_[i] = active_.back();
320 } else if (IntervalPos->start > CurPoint) {
321 // Move inactive intervals to inactive list.
322 DEBUG(std::cerr << "\t\tinterval " << *Interval << " inactive\n");
323 assert(MRegisterInfo::isVirtualRegister(reg) &&
324 "Can only allocate virtual registers!");
325 reg = vrm_->getPhys(reg);
326 prt_->delRegUse(reg);
328 inactive_.push_back(std::make_pair(Interval, IntervalPos));
330 // Pop off the end of the list.
331 active_[i] = active_.back();
335 // Otherwise, just update the iterator position.
336 active_[i].second = IntervalPos;
341 /// processInactiveIntervals - expire old intervals and move overlapping
342 /// ones to the active list.
343 void RA::processInactiveIntervals(unsigned CurPoint)
345 DEBUG(std::cerr << "\tprocessing inactive intervals:\n");
347 for (unsigned i = 0, e = inactive_.size(); i != e; ++i) {
348 LiveInterval *Interval = inactive_[i].first;
349 LiveInterval::iterator IntervalPos = inactive_[i].second;
350 unsigned reg = Interval->reg;
352 IntervalPos = Interval->advanceTo(IntervalPos, CurPoint);
354 if (IntervalPos == Interval->end()) { // remove expired intervals.
355 DEBUG(std::cerr << "\t\tinterval " << *Interval << " expired\n");
357 // Pop off the end of the list.
358 inactive_[i] = inactive_.back();
359 inactive_.pop_back();
361 } else if (IntervalPos->start <= CurPoint) {
362 // move re-activated intervals in active list
363 DEBUG(std::cerr << "\t\tinterval " << *Interval << " active\n");
364 assert(MRegisterInfo::isVirtualRegister(reg) &&
365 "Can only allocate virtual registers!");
366 reg = vrm_->getPhys(reg);
367 prt_->addRegUse(reg);
369 active_.push_back(std::make_pair(Interval, IntervalPos));
371 // Pop off the end of the list.
372 inactive_[i] = inactive_.back();
373 inactive_.pop_back();
376 // Otherwise, just update the iterator position.
377 inactive_[i].second = IntervalPos;
382 /// updateSpillWeights - updates the spill weights of the specifed physical
383 /// register and its weight.
384 static void updateSpillWeights(std::vector<float> &Weights,
385 unsigned reg, float weight,
386 const MRegisterInfo *MRI) {
387 Weights[reg] += weight;
388 for (const unsigned* as = MRI->getAliasSet(reg); *as; ++as)
389 Weights[*as] += weight;
392 static RA::IntervalPtrs::iterator FindIntervalInVector(RA::IntervalPtrs &IP,
394 for (RA::IntervalPtrs::iterator I = IP.begin(), E = IP.end(); I != E; ++I)
395 if (I->first == LI) return I;
399 static void RevertVectorIteratorsTo(RA::IntervalPtrs &V, unsigned Point) {
400 for (unsigned i = 0, e = V.size(); i != e; ++i) {
401 RA::IntervalPtr &IP = V[i];
402 LiveInterval::iterator I = std::upper_bound(IP.first->begin(),
404 if (I != IP.first->begin()) --I;
410 /// assignRegOrStackSlotAtInterval - assign a register if one is available, or
412 void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
414 DEBUG(std::cerr << "\tallocating current interval: ");
416 PhysRegTracker backupPrt = *prt_;
418 std::vector<std::pair<unsigned, float> > SpillWeightsToAdd;
419 unsigned StartPosition = cur->beginNumber();
420 const TargetRegisterClass *RC = mf_->getSSARegMap()->getRegClass(cur->reg);
421 const TargetRegisterClass *RCLeader = RelatedRegClasses.getLeaderValue(RC);
423 // for every interval in inactive we overlap with, mark the
424 // register as not free and update spill weights.
425 for (IntervalPtrs::const_iterator i = inactive_.begin(),
426 e = inactive_.end(); i != e; ++i) {
427 unsigned Reg = i->first->reg;
428 assert(MRegisterInfo::isVirtualRegister(Reg) &&
429 "Can only allocate virtual registers!");
430 const TargetRegisterClass *RegRC = mf_->getSSARegMap()->getRegClass(Reg);
431 // If this is not in a related reg class to the register we're allocating,
433 if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader &&
434 cur->overlapsFrom(*i->first, i->second-1)) {
435 Reg = vrm_->getPhys(Reg);
436 prt_->addRegUse(Reg);
437 SpillWeightsToAdd.push_back(std::make_pair(Reg, i->first->weight));
441 // Speculatively check to see if we can get a register right now. If not,
442 // we know we won't be able to by adding more constraints. If so, we can
443 // check to see if it is valid. Doing an exhaustive search of the fixed_ list
444 // is very bad (it contains all callee clobbered registers for any functions
445 // with a call), so we want to avoid doing that if possible.
446 unsigned physReg = getFreePhysReg(cur);
448 // We got a register. However, if it's in the fixed_ list, we might
449 // conflict with it. Check to see if we conflict with it or any of its
451 std::set<unsigned> RegAliases;
452 for (const unsigned *AS = mri_->getAliasSet(physReg); *AS; ++AS)
453 RegAliases.insert(*AS);
455 bool ConflictsWithFixed = false;
456 for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
457 if (physReg == fixed_[i].first->reg ||
458 RegAliases.count(fixed_[i].first->reg)) {
459 // Okay, this reg is on the fixed list. Check to see if we actually
461 IntervalPtr &IP = fixed_[i];
462 LiveInterval *I = IP.first;
463 if (I->endNumber() > StartPosition) {
464 LiveInterval::iterator II = I->advanceTo(IP.second, StartPosition);
466 if (II != I->begin() && II->start > StartPosition)
468 if (cur->overlapsFrom(*I, II)) {
469 ConflictsWithFixed = true;
476 // Okay, the register picked by our speculative getFreePhysReg call turned
477 // out to be in use. Actually add all of the conflicting fixed registers to
478 // prt so we can do an accurate query.
479 if (ConflictsWithFixed) {
480 // For every interval in fixed we overlap with, mark the register as not
481 // free and update spill weights.
482 for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
483 IntervalPtr &IP = fixed_[i];
484 LiveInterval *I = IP.first;
486 const TargetRegisterClass *RegRC = OneClassForEachPhysReg[I->reg];
487 if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader &&
488 I->endNumber() > StartPosition) {
489 LiveInterval::iterator II = I->advanceTo(IP.second, StartPosition);
491 if (II != I->begin() && II->start > StartPosition)
493 if (cur->overlapsFrom(*I, II)) {
494 unsigned reg = I->reg;
495 prt_->addRegUse(reg);
496 SpillWeightsToAdd.push_back(std::make_pair(reg, I->weight));
501 // Using the newly updated prt_ object, which includes conflicts in the
502 // future, see if there are any registers available.
503 physReg = getFreePhysReg(cur);
507 // Restore the physical register tracker, removing information about the
511 // if we find a free register, we are done: assign this virtual to
512 // the free physical register and add this interval to the active
515 DEBUG(std::cerr << mri_->getName(physReg) << '\n');
516 vrm_->assignVirt2Phys(cur->reg, physReg);
517 prt_->addRegUse(physReg);
518 active_.push_back(std::make_pair(cur, cur->begin()));
519 handled_.push_back(cur);
522 DEBUG(std::cerr << "no free registers\n");
524 // Compile the spill weights into an array that is better for scanning.
525 std::vector<float> SpillWeights(mri_->getNumRegs(), 0.0);
526 for (std::vector<std::pair<unsigned, float> >::iterator
527 I = SpillWeightsToAdd.begin(), E = SpillWeightsToAdd.end(); I != E; ++I)
528 updateSpillWeights(SpillWeights, I->first, I->second, mri_);
530 // for each interval in active, update spill weights.
531 for (IntervalPtrs::const_iterator i = active_.begin(), e = active_.end();
533 unsigned reg = i->first->reg;
534 assert(MRegisterInfo::isVirtualRegister(reg) &&
535 "Can only allocate virtual registers!");
536 reg = vrm_->getPhys(reg);
537 updateSpillWeights(SpillWeights, reg, i->first->weight, mri_);
540 DEBUG(std::cerr << "\tassigning stack slot at interval "<< *cur << ":\n");
542 // Find a register to spill.
543 float minWeight = float(HUGE_VAL);
545 for (TargetRegisterClass::iterator i = RC->allocation_order_begin(*mf_),
546 e = RC->allocation_order_end(*mf_); i != e; ++i) {
548 if (minWeight > SpillWeights[reg]) {
549 minWeight = SpillWeights[reg];
554 // If we didn't find a register that is spillable, try aliases?
556 // FIXME: assert(minReg && "Didn't find any reg!");
557 DEBUG(std::cerr << "\t\tregister with min weight: "
558 << mri_->getName(minReg) << " (" << minWeight << ")\n");
560 // if the current has the minimum weight, we need to spill it and
561 // add any added intervals back to unhandled, and restart
563 if (cur->weight <= minWeight) {
564 DEBUG(std::cerr << "\t\t\tspilling(c): " << *cur << '\n';);
565 int slot = vrm_->assignVirt2StackSlot(cur->reg);
566 std::vector<LiveInterval*> added =
567 li_->addIntervalsForSpills(*cur, *vrm_, slot);
569 return; // Early exit if all spills were folded.
571 // Merge added with unhandled. Note that we know that
572 // addIntervalsForSpills returns intervals sorted by their starting
574 for (unsigned i = 0, e = added.size(); i != e; ++i)
575 unhandled_.push(added[i]);
581 // push the current interval back to unhandled since we are going
582 // to re-run at least this iteration. Since we didn't modify it it
583 // should go back right in the front of the list
584 unhandled_.push(cur);
586 // otherwise we spill all intervals aliasing the register with
587 // minimum weight, rollback to the interval with the earliest
588 // start point and let the linear scan algorithm run again
589 std::vector<LiveInterval*> added;
590 assert(MRegisterInfo::isPhysicalRegister(minReg) &&
591 "did not choose a register to spill?");
592 std::vector<bool> toSpill(mri_->getNumRegs(), false);
594 // We are going to spill minReg and all its aliases.
595 toSpill[minReg] = true;
596 for (const unsigned* as = mri_->getAliasSet(minReg); *as; ++as)
599 // the earliest start of a spilled interval indicates up to where
600 // in handled we need to roll back
601 unsigned earliestStart = cur->beginNumber();
603 // set of spilled vregs (used later to rollback properly)
604 std::set<unsigned> spilled;
606 // spill live intervals of virtual regs mapped to the physical register we
607 // want to clear (and its aliases). We only spill those that overlap with the
608 // current interval as the rest do not affect its allocation. we also keep
609 // track of the earliest start of all spilled live intervals since this will
610 // mark our rollback point.
611 for (IntervalPtrs::iterator i = active_.begin(); i != active_.end(); ++i) {
612 unsigned reg = i->first->reg;
613 if (//MRegisterInfo::isVirtualRegister(reg) &&
614 toSpill[vrm_->getPhys(reg)] &&
615 cur->overlapsFrom(*i->first, i->second)) {
616 DEBUG(std::cerr << "\t\t\tspilling(a): " << *i->first << '\n');
617 earliestStart = std::min(earliestStart, i->first->beginNumber());
618 int slot = vrm_->assignVirt2StackSlot(i->first->reg);
619 std::vector<LiveInterval*> newIs =
620 li_->addIntervalsForSpills(*i->first, *vrm_, slot);
621 std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
625 for (IntervalPtrs::iterator i = inactive_.begin(); i != inactive_.end(); ++i){
626 unsigned reg = i->first->reg;
627 if (//MRegisterInfo::isVirtualRegister(reg) &&
628 toSpill[vrm_->getPhys(reg)] &&
629 cur->overlapsFrom(*i->first, i->second-1)) {
630 DEBUG(std::cerr << "\t\t\tspilling(i): " << *i->first << '\n');
631 earliestStart = std::min(earliestStart, i->first->beginNumber());
632 int slot = vrm_->assignVirt2StackSlot(reg);
633 std::vector<LiveInterval*> newIs =
634 li_->addIntervalsForSpills(*i->first, *vrm_, slot);
635 std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
640 DEBUG(std::cerr << "\t\trolling back to: " << earliestStart << '\n');
642 // Scan handled in reverse order up to the earliest start of a
643 // spilled live interval and undo each one, restoring the state of
645 while (!handled_.empty()) {
646 LiveInterval* i = handled_.back();
647 // If this interval starts before t we are done.
648 if (i->beginNumber() < earliestStart)
650 DEBUG(std::cerr << "\t\t\tundo changes for: " << *i << '\n');
653 // When undoing a live interval allocation we must know if it is active or
654 // inactive to properly update the PhysRegTracker and the VirtRegMap.
655 IntervalPtrs::iterator it;
656 if ((it = FindIntervalInVector(active_, i)) != active_.end()) {
658 assert(!MRegisterInfo::isPhysicalRegister(i->reg));
659 if (!spilled.count(i->reg))
661 prt_->delRegUse(vrm_->getPhys(i->reg));
662 vrm_->clearVirt(i->reg);
663 } else if ((it = FindIntervalInVector(inactive_, i)) != inactive_.end()) {
665 assert(!MRegisterInfo::isPhysicalRegister(i->reg));
666 if (!spilled.count(i->reg))
668 vrm_->clearVirt(i->reg);
670 assert(MRegisterInfo::isVirtualRegister(i->reg) &&
671 "Can only allocate virtual registers!");
672 vrm_->clearVirt(i->reg);
677 // Rewind the iterators in the active, inactive, and fixed lists back to the
678 // point we reverted to.
679 RevertVectorIteratorsTo(active_, earliestStart);
680 RevertVectorIteratorsTo(inactive_, earliestStart);
681 RevertVectorIteratorsTo(fixed_, earliestStart);
683 // scan the rest and undo each interval that expired after t and
684 // insert it in active (the next iteration of the algorithm will
685 // put it in inactive if required)
686 for (unsigned i = 0, e = handled_.size(); i != e; ++i) {
687 LiveInterval *HI = handled_[i];
688 if (!HI->expiredAt(earliestStart) &&
689 HI->expiredAt(cur->beginNumber())) {
690 DEBUG(std::cerr << "\t\t\tundo changes for: " << *HI << '\n');
691 active_.push_back(std::make_pair(HI, HI->begin()));
692 assert(!MRegisterInfo::isPhysicalRegister(HI->reg));
693 prt_->addRegUse(vrm_->getPhys(HI->reg));
697 // merge added with unhandled
698 for (unsigned i = 0, e = added.size(); i != e; ++i)
699 unhandled_.push(added[i]);
702 /// getFreePhysReg - return a free physical register for this virtual register
703 /// interval if we have one, otherwise return 0.
704 unsigned RA::getFreePhysReg(LiveInterval *cur) {
705 std::vector<unsigned> inactiveCounts(mri_->getNumRegs(), 0);
706 unsigned MaxInactiveCount = 0;
708 const TargetRegisterClass *RC = mf_->getSSARegMap()->getRegClass(cur->reg);
709 const TargetRegisterClass *RCLeader = RelatedRegClasses.getLeaderValue(RC);
711 for (IntervalPtrs::iterator i = inactive_.begin(), e = inactive_.end();
713 unsigned reg = i->first->reg;
714 assert(MRegisterInfo::isVirtualRegister(reg) &&
715 "Can only allocate virtual registers!");
717 // If this is not in a related reg class to the register we're allocating,
719 const TargetRegisterClass *RegRC = mf_->getSSARegMap()->getRegClass(reg);
720 if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader) {
721 reg = vrm_->getPhys(reg);
722 ++inactiveCounts[reg];
723 MaxInactiveCount = std::max(MaxInactiveCount, inactiveCounts[reg]);
727 const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
729 unsigned FreeReg = 0;
730 unsigned FreeRegInactiveCount = 0;
732 // Scan for the first available register.
733 TargetRegisterClass::iterator I = rc->allocation_order_begin(*mf_);
734 TargetRegisterClass::iterator E = rc->allocation_order_end(*mf_);
736 if (prt_->isRegAvail(*I)) {
738 FreeRegInactiveCount = inactiveCounts[FreeReg];
742 // If there are no free regs, or if this reg has the max inactive count,
743 // return this register.
744 if (FreeReg == 0 || FreeRegInactiveCount == MaxInactiveCount) return FreeReg;
746 // Continue scanning the registers, looking for the one with the highest
747 // inactive count. Alkis found that this reduced register pressure very
748 // slightly on X86 (in rev 1.94 of this file), though this should probably be
750 for (; I != E; ++I) {
752 if (prt_->isRegAvail(Reg) && FreeRegInactiveCount < inactiveCounts[Reg]) {
754 FreeRegInactiveCount = inactiveCounts[Reg];
755 if (FreeRegInactiveCount == MaxInactiveCount)
756 break; // We found the one with the max inactive count.
763 FunctionPass* llvm::createLinearScanRegisterAllocator() {