1 //===------ RegAllocPBQP.cpp ---- PBQP Register Allocator -------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file contains a Partitioned Boolean Quadratic Programming (PBQP) based
11 // register allocator for LLVM. This allocator works by constructing a PBQP
12 // problem representing the register allocation problem under consideration,
13 // solving this using a PBQP solver, and mapping the solution back to a
14 // register assignment. If any variables are selected for spilling then spill
15 // code is inserted and the process repeated.
16 //
17 // The PBQP solver (pbqp.c) provided for this allocator uses a heuristic tuned
18 // for register allocation. For more information on PBQP for register
19 // allocation, see the following papers:
20 //
21 //   (1) Hames, L. and Scholz, B. 2006. Nearly optimal register allocation with
22 //   PBQP. In Proceedings of the 7th Joint Modular Languages Conference
23 //   (JMLC'06). LNCS, vol. 4228. Springer, New York, NY, USA. 346-361.
24 //
25 //   (2) Scholz, B., Eckstein, E. 2002. Register allocation for irregular
26 //   architectures. In Proceedings of the Joint Conference on Languages,
27 //   Compilers and Tools for Embedded Systems (LCTES'02), ACM Press, New York,
28 //   NY, USA, 139-148.
29 //
30 //===----------------------------------------------------------------------===//
31 
32 #include "llvm/CodeGen/RegAllocPBQP.h"
33 #include "RegisterCoalescer.h"
34 #include "Spiller.h"
35 #include "llvm/Analysis/AliasAnalysis.h"
36 #include "llvm/CodeGen/CalcSpillWeights.h"
37 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
38 #include "llvm/CodeGen/LiveRangeEdit.h"
39 #include "llvm/CodeGen/LiveStackAnalysis.h"
40 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
41 #include "llvm/CodeGen/MachineDominators.h"
42 #include "llvm/CodeGen/MachineFunctionPass.h"
43 #include "llvm/CodeGen/MachineLoopInfo.h"
44 #include "llvm/CodeGen/MachineRegisterInfo.h"
45 #include "llvm/CodeGen/RegAllocRegistry.h"
46 #include "llvm/CodeGen/VirtRegMap.h"
47 #include "llvm/IR/Module.h"
48 #include "llvm/Support/Debug.h"
49 #include "llvm/Support/FileSystem.h"
50 #include "llvm/Support/raw_ostream.h"
51 #include "llvm/Target/TargetInstrInfo.h"
52 #include "llvm/Target/TargetMachine.h"
53 #include "llvm/Target/TargetSubtargetInfo.h"
54 #include <limits>
55 #include <memory>
56 #include <set>
57 #include <sstream>
58 #include <vector>
59 
60 using namespace llvm;
61 
62 #define DEBUG_TYPE "regalloc"
63 
64 static RegisterRegAlloc
65 registerPBQPRepAlloc("pbqp", "PBQP register allocator",
66                        createDefaultPBQPRegisterAllocator);
67 
68 static cl::opt<bool>
69 pbqpCoalescing("pbqp-coalescing",
70                 cl::desc("Attempt coalescing during PBQP register allocation."),
71                 cl::init(false), cl::Hidden);
72 
73 #ifndef NDEBUG
74 static cl::opt<bool>
75 pbqpDumpGraphs("pbqp-dump-graphs",
76                cl::desc("Dump graphs for each function/round in the compilation unit."),
77                cl::init(false), cl::Hidden);
78 #endif
79 
80 namespace {
81 
82 ///
83 /// PBQP based allocators solve the register allocation problem by mapping
84 /// register allocation problems to Partitioned Boolean Quadratic
85 /// Programming problems.
86 class RegAllocPBQP : public MachineFunctionPass {
87 public:
88 
89   static char ID;
90 
91   /// Construct a PBQP register allocator.
92   RegAllocPBQP(std::unique_ptr<PBQPBuilder> b, char *cPassID = nullptr)
93       : MachineFunctionPass(ID), builder(std::move(b)), customPassID(cPassID) {
94     initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
95     initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
96     initializeLiveStacksPass(*PassRegistry::getPassRegistry());
97     initializeVirtRegMapPass(*PassRegistry::getPassRegistry());
98   }
99 
100   /// Return the pass name.
101   const char* getPassName() const override {
102     return "PBQP Register Allocator";
103   }
104 
105   /// PBQP analysis usage.
106   void getAnalysisUsage(AnalysisUsage &au) const override;
107 
108   /// Perform register allocation
109   bool runOnMachineFunction(MachineFunction &MF) override;
110 
111 private:
112 
113   typedef std::map<const LiveInterval*, unsigned> LI2NodeMap;
114   typedef std::vector<const LiveInterval*> Node2LIMap;
115   typedef std::vector<unsigned> AllowedSet;
116   typedef std::vector<AllowedSet> AllowedSetMap;
117   typedef std::pair<unsigned, unsigned> RegPair;
118   typedef std::map<RegPair, PBQP::PBQPNum> CoalesceMap;
119   typedef std::set<unsigned> RegSet;
120 
121   std::unique_ptr<PBQPBuilder> builder;
122 
123   char *customPassID;
124 
125   MachineFunction *mf;
126   const TargetMachine *tm;
127   const TargetRegisterInfo *tri;
128   const TargetInstrInfo *tii;
129   MachineRegisterInfo *mri;
130   const MachineBlockFrequencyInfo *mbfi;
131 
132   std::unique_ptr<Spiller> spiller;
133   LiveIntervals *lis;
134   LiveStacks *lss;
135   VirtRegMap *vrm;
136 
137   RegSet vregsToAlloc, emptyIntervalVRegs;
138 
139   /// \brief Finds the initial set of vreg intervals to allocate.
140   void findVRegIntervalsToAlloc();
141 
142   /// \brief Given a solved PBQP problem maps this solution back to a register
143   /// assignment.
144   bool mapPBQPToRegAlloc(const PBQPRAProblem &problem,
145                          const PBQP::Solution &solution);
146 
147   /// \brief Postprocessing before final spilling. Sets basic block "live in"
148   /// variables.
149   void finalizeAlloc() const;
150 
151 };
152 
153 char RegAllocPBQP::ID = 0;
154 
155 } // End anonymous namespace.
156 
157 unsigned PBQPRAProblem::getVRegForNode(PBQPRAGraph::NodeId node) const {
158   Node2VReg::const_iterator vregItr = node2VReg.find(node);
159   assert(vregItr != node2VReg.end() && "No vreg for node.");
160   return vregItr->second;
161 }
162 
163 PBQPRAGraph::NodeId PBQPRAProblem::getNodeForVReg(unsigned vreg) const {
164   VReg2Node::const_iterator nodeItr = vreg2Node.find(vreg);
165   assert(nodeItr != vreg2Node.end() && "No node for vreg.");
166   return nodeItr->second;
167 
168 }
169 
170 const PBQPRAProblem::AllowedSet&
171   PBQPRAProblem::getAllowedSet(unsigned vreg) const {
172   AllowedSetMap::const_iterator allowedSetItr = allowedSets.find(vreg);
173   assert(allowedSetItr != allowedSets.end() && "No pregs for vreg.");
174   const AllowedSet &allowedSet = allowedSetItr->second;
175   return allowedSet;
176 }
177 
178 unsigned PBQPRAProblem::getPRegForOption(unsigned vreg, unsigned option) const {
179   assert(isPRegOption(vreg, option) && "Not a preg option.");
180 
181   const AllowedSet& allowedSet = getAllowedSet(vreg);
182   assert(option <= allowedSet.size() && "Option outside allowed set.");
183   return allowedSet[option - 1];
184 }
185 
186 PBQPRAProblem *PBQPBuilder::build(MachineFunction *mf, const LiveIntervals *lis,
187                                   const MachineBlockFrequencyInfo *mbfi,
188                                   const RegSet &vregs) {
189 
190   LiveIntervals *LIS = const_cast<LiveIntervals*>(lis);
191   MachineRegisterInfo *mri = &mf->getRegInfo();
192   const TargetRegisterInfo *tri = mf->getSubtarget().getRegisterInfo();
193 
194   std::unique_ptr<PBQPRAProblem> p(new PBQPRAProblem());
195   PBQPRAGraph &g = p->getGraph();
196   RegSet pregs;
197 
198   // Collect the set of preg intervals, record that they're used in the MF.
199   for (unsigned Reg = 1, e = tri->getNumRegs(); Reg != e; ++Reg) {
200     if (mri->def_empty(Reg))
201       continue;
202     pregs.insert(Reg);
203     mri->setPhysRegUsed(Reg);
204   }
205 
206   // Iterate over vregs.
207   for (RegSet::const_iterator vregItr = vregs.begin(), vregEnd = vregs.end();
208        vregItr != vregEnd; ++vregItr) {
209     unsigned vreg = *vregItr;
210     const TargetRegisterClass *trc = mri->getRegClass(vreg);
211     LiveInterval *vregLI = &LIS->getInterval(vreg);
212 
213     // Record any overlaps with regmask operands.
214     BitVector regMaskOverlaps;
215     LIS->checkRegMaskInterference(*vregLI, regMaskOverlaps);
216 
217     // Compute an initial allowed set for the current vreg.
218     typedef std::vector<unsigned> VRAllowed;
219     VRAllowed vrAllowed;
220     ArrayRef<MCPhysReg> rawOrder = trc->getRawAllocationOrder(*mf);
221     for (unsigned i = 0; i != rawOrder.size(); ++i) {
222       unsigned preg = rawOrder[i];
223       if (mri->isReserved(preg))
224         continue;
225 
226       // vregLI crosses a regmask operand that clobbers preg.
227       if (!regMaskOverlaps.empty() && !regMaskOverlaps.test(preg))
228         continue;
229 
230       // vregLI overlaps fixed regunit interference.
231       bool Interference = false;
232       for (MCRegUnitIterator Units(preg, tri); Units.isValid(); ++Units) {
233         if (vregLI->overlaps(LIS->getRegUnit(*Units))) {
234           Interference = true;
235           break;
236         }
237       }
238       if (Interference)
239         continue;
240 
241       // preg is usable for this virtual register.
242       vrAllowed.push_back(preg);
243     }
244 
245     PBQP::Vector nodeCosts(vrAllowed.size() + 1, 0);
246 
247     PBQP::PBQPNum spillCost = (vregLI->weight != 0.0) ?
248         vregLI->weight : std::numeric_limits<PBQP::PBQPNum>::min();
249 
250     addSpillCosts(nodeCosts, spillCost);
251 
252     // Construct the node.
253     PBQPRAGraph::NodeId nId = g.addNode(std::move(nodeCosts));
254 
255     // Record the mapping and allowed set in the problem.
256     p->recordVReg(vreg, nId, vrAllowed.begin(), vrAllowed.end());
257 
258   }
259 
260   for (RegSet::const_iterator vr1Itr = vregs.begin(), vrEnd = vregs.end();
261          vr1Itr != vrEnd; ++vr1Itr) {
262     unsigned vr1 = *vr1Itr;
263     const LiveInterval &l1 = lis->getInterval(vr1);
264     const PBQPRAProblem::AllowedSet &vr1Allowed = p->getAllowedSet(vr1);
265 
266     for (RegSet::const_iterator vr2Itr = std::next(vr1Itr); vr2Itr != vrEnd;
267          ++vr2Itr) {
268       unsigned vr2 = *vr2Itr;
269       const LiveInterval &l2 = lis->getInterval(vr2);
270       const PBQPRAProblem::AllowedSet &vr2Allowed = p->getAllowedSet(vr2);
271 
272       assert(!l2.empty() && "Empty interval in vreg set?");
273       if (l1.overlaps(l2)) {
274         PBQP::Matrix edgeCosts(vr1Allowed.size()+1, vr2Allowed.size()+1, 0);
275         addInterferenceCosts(edgeCosts, vr1Allowed, vr2Allowed, tri);
276 
277         g.addEdge(p->getNodeForVReg(vr1), p->getNodeForVReg(vr2),
278                   std::move(edgeCosts));
279       }
280     }
281   }
282 
283   return p.release();
284 }
285 
286 void PBQPBuilder::addSpillCosts(PBQP::Vector &costVec,
287                                 PBQP::PBQPNum spillCost) {
288   costVec[0] = spillCost;
289 }
290 
291 void PBQPBuilder::addInterferenceCosts(
292                                     PBQP::Matrix &costMat,
293                                     const PBQPRAProblem::AllowedSet &vr1Allowed,
294                                     const PBQPRAProblem::AllowedSet &vr2Allowed,
295                                     const TargetRegisterInfo *tri) {
296   assert(costMat.getRows() == vr1Allowed.size() + 1 && "Matrix height mismatch.");
297   assert(costMat.getCols() == vr2Allowed.size() + 1 && "Matrix width mismatch.");
298 
299   for (unsigned i = 0; i != vr1Allowed.size(); ++i) {
300     unsigned preg1 = vr1Allowed[i];
301 
302     for (unsigned j = 0; j != vr2Allowed.size(); ++j) {
303       unsigned preg2 = vr2Allowed[j];
304 
305       if (tri->regsOverlap(preg1, preg2)) {
306         costMat[i + 1][j + 1] = std::numeric_limits<PBQP::PBQPNum>::infinity();
307       }
308     }
309   }
310 }
311 
312 PBQPRAProblem *PBQPBuilderWithCoalescing::build(MachineFunction *mf,
313                                                 const LiveIntervals *lis,
314                                                 const MachineBlockFrequencyInfo *mbfi,
315                                                 const RegSet &vregs) {
316 
317   std::unique_ptr<PBQPRAProblem> p(PBQPBuilder::build(mf, lis, mbfi, vregs));
318   PBQPRAGraph &g = p->getGraph();
319 
320   const TargetMachine &tm = mf->getTarget();
321   CoalescerPair cp(*tm.getSubtargetImpl()->getRegisterInfo());
322 
323   // Scan the machine function and add a coalescing cost whenever CoalescerPair
324   // gives the Ok.
325   for (const auto &mbb : *mf) {
326     for (const auto &mi : mbb) {
327       if (!cp.setRegisters(&mi)) {
328         continue; // Not coalescable.
329       }
330 
331       if (cp.getSrcReg() == cp.getDstReg()) {
332         continue; // Already coalesced.
333       }
334 
335       unsigned dst = cp.getDstReg(),
336                src = cp.getSrcReg();
337 
338       const float copyFactor = 0.5; // Cost of copy relative to load. Current
339       // value plucked randomly out of the air.
340 
341       PBQP::PBQPNum cBenefit =
342         copyFactor * LiveIntervals::getSpillWeight(false, true, mbfi, &mi);
343 
344       if (cp.isPhys()) {
345         if (!mf->getRegInfo().isAllocatable(dst)) {
346           continue;
347         }
348 
349         const PBQPRAProblem::AllowedSet &allowed = p->getAllowedSet(src);
350         unsigned pregOpt = 0;
351         while (pregOpt < allowed.size() && allowed[pregOpt] != dst) {
352           ++pregOpt;
353         }
354         if (pregOpt < allowed.size()) {
355           ++pregOpt; // +1 to account for spill option.
356           PBQPRAGraph::NodeId node = p->getNodeForVReg(src);
357           llvm::dbgs() << "Reading node costs for node " << node << "\n";
358           llvm::dbgs() << "Source node: " << &g.getNodeCosts(node) << "\n";
359           PBQP::Vector newCosts(g.getNodeCosts(node));
360           addPhysRegCoalesce(newCosts, pregOpt, cBenefit);
361           g.setNodeCosts(node, newCosts);
362         }
363       } else {
364         const PBQPRAProblem::AllowedSet *allowed1 = &p->getAllowedSet(dst);
365         const PBQPRAProblem::AllowedSet *allowed2 = &p->getAllowedSet(src);
366         PBQPRAGraph::NodeId node1 = p->getNodeForVReg(dst);
367         PBQPRAGraph::NodeId node2 = p->getNodeForVReg(src);
368         PBQPRAGraph::EdgeId edge = g.findEdge(node1, node2);
369         if (edge == g.invalidEdgeId()) {
370           PBQP::Matrix costs(allowed1->size() + 1, allowed2->size() + 1, 0);
371           addVirtRegCoalesce(costs, *allowed1, *allowed2, cBenefit);
372           g.addEdge(node1, node2, costs);
373         } else {
374           if (g.getEdgeNode1Id(edge) == node2) {
375             std::swap(node1, node2);
376             std::swap(allowed1, allowed2);
377           }
378           PBQP::Matrix costs(g.getEdgeCosts(edge));
379           addVirtRegCoalesce(costs, *allowed1, *allowed2, cBenefit);
380           g.setEdgeCosts(edge, costs);
381         }
382       }
383     }
384   }
385 
386   return p.release();
387 }
388 
389 void PBQPBuilderWithCoalescing::addPhysRegCoalesce(PBQP::Vector &costVec,
390                                                    unsigned pregOption,
391                                                    PBQP::PBQPNum benefit) {
392   costVec[pregOption] += -benefit;
393 }
394 
395 void PBQPBuilderWithCoalescing::addVirtRegCoalesce(
396                                     PBQP::Matrix &costMat,
397                                     const PBQPRAProblem::AllowedSet &vr1Allowed,
398                                     const PBQPRAProblem::AllowedSet &vr2Allowed,
399                                     PBQP::PBQPNum benefit) {
400 
401   assert(costMat.getRows() == vr1Allowed.size() + 1 && "Size mismatch.");
402   assert(costMat.getCols() == vr2Allowed.size() + 1 && "Size mismatch.");
403 
404   for (unsigned i = 0; i != vr1Allowed.size(); ++i) {
405     unsigned preg1 = vr1Allowed[i];
406     for (unsigned j = 0; j != vr2Allowed.size(); ++j) {
407       unsigned preg2 = vr2Allowed[j];
408 
409       if (preg1 == preg2) {
410         costMat[i + 1][j + 1] += -benefit;
411       }
412     }
413   }
414 }
415 
416 
417 void RegAllocPBQP::getAnalysisUsage(AnalysisUsage &au) const {
418   au.setPreservesCFG();
419   au.addRequired<AliasAnalysis>();
420   au.addPreserved<AliasAnalysis>();
421   au.addRequired<SlotIndexes>();
422   au.addPreserved<SlotIndexes>();
423   au.addRequired<LiveIntervals>();
424   au.addPreserved<LiveIntervals>();
425   //au.addRequiredID(SplitCriticalEdgesID);
426   if (customPassID)
427     au.addRequiredID(*customPassID);
428   au.addRequired<LiveStacks>();
429   au.addPreserved<LiveStacks>();
430   au.addRequired<MachineBlockFrequencyInfo>();
431   au.addPreserved<MachineBlockFrequencyInfo>();
432   au.addRequired<MachineLoopInfo>();
433   au.addPreserved<MachineLoopInfo>();
434   au.addRequired<MachineDominatorTree>();
435   au.addPreserved<MachineDominatorTree>();
436   au.addRequired<VirtRegMap>();
437   au.addPreserved<VirtRegMap>();
438   MachineFunctionPass::getAnalysisUsage(au);
439 }
440 
441 void RegAllocPBQP::findVRegIntervalsToAlloc() {
442 
443   // Iterate over all live ranges.
444   for (unsigned i = 0, e = mri->getNumVirtRegs(); i != e; ++i) {
445     unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
446     if (mri->reg_nodbg_empty(Reg))
447       continue;
448     LiveInterval *li = &lis->getInterval(Reg);
449 
450     // If this live interval is non-empty we will use pbqp to allocate it.
451     // Empty intervals we allocate in a simple post-processing stage in
452     // finalizeAlloc.
453     if (!li->empty()) {
454       vregsToAlloc.insert(li->reg);
455     } else {
456       emptyIntervalVRegs.insert(li->reg);
457     }
458   }
459 }
460 
461 bool RegAllocPBQP::mapPBQPToRegAlloc(const PBQPRAProblem &problem,
462                                      const PBQP::Solution &solution) {
463   // Set to true if we have any spills
464   bool anotherRoundNeeded = false;
465 
466   // Clear the existing allocation.
467   vrm->clearAllVirt();
468 
469   const PBQPRAGraph &g = problem.getGraph();
470   // Iterate over the nodes mapping the PBQP solution to a register
471   // assignment.
472   for (auto NId : g.nodeIds()) {
473     unsigned vreg = problem.getVRegForNode(NId);
474     unsigned alloc = solution.getSelection(NId);
475 
476     if (problem.isPRegOption(vreg, alloc)) {
477       unsigned preg = problem.getPRegForOption(vreg, alloc);
478       DEBUG(dbgs() << "VREG " << PrintReg(vreg, tri) << " -> "
479             << tri->getName(preg) << "\n");
480       assert(preg != 0 && "Invalid preg selected.");
481       vrm->assignVirt2Phys(vreg, preg);
482     } else if (problem.isSpillOption(vreg, alloc)) {
483       vregsToAlloc.erase(vreg);
484       SmallVector<unsigned, 8> newSpills;
485       LiveRangeEdit LRE(&lis->getInterval(vreg), newSpills, *mf, *lis, vrm);
486       spiller->spill(LRE);
487 
488       DEBUG(dbgs() << "VREG " << PrintReg(vreg, tri) << " -> SPILLED (Cost: "
489                    << LRE.getParent().weight << ", New vregs: ");
490 
491       // Copy any newly inserted live intervals into the list of regs to
492       // allocate.
493       for (LiveRangeEdit::iterator itr = LRE.begin(), end = LRE.end();
494            itr != end; ++itr) {
495         LiveInterval &li = lis->getInterval(*itr);
496         assert(!li.empty() && "Empty spill range.");
497         DEBUG(dbgs() << PrintReg(li.reg, tri) << " ");
498         vregsToAlloc.insert(li.reg);
499       }
500 
501       DEBUG(dbgs() << ")\n");
502 
503       // We need another round if spill intervals were added.
504       anotherRoundNeeded |= !LRE.empty();
505     } else {
506       llvm_unreachable("Unknown allocation option.");
507     }
508   }
509 
510   return !anotherRoundNeeded;
511 }
512 
513 
514 void RegAllocPBQP::finalizeAlloc() const {
515   // First allocate registers for the empty intervals.
516   for (RegSet::const_iterator
517          itr = emptyIntervalVRegs.begin(), end = emptyIntervalVRegs.end();
518          itr != end; ++itr) {
519     LiveInterval *li = &lis->getInterval(*itr);
520 
521     unsigned physReg = mri->getSimpleHint(li->reg);
522 
523     if (physReg == 0) {
524       const TargetRegisterClass *liRC = mri->getRegClass(li->reg);
525       physReg = liRC->getRawAllocationOrder(*mf).front();
526     }
527 
528     vrm->assignVirt2Phys(li->reg, physReg);
529   }
530 }
531 
532 bool RegAllocPBQP::runOnMachineFunction(MachineFunction &MF) {
533 
534   mf = &MF;
535   tm = &mf->getTarget();
536   tri = tm->getSubtargetImpl()->getRegisterInfo();
537   tii = tm->getSubtargetImpl()->getInstrInfo();
538   mri = &mf->getRegInfo();
539 
540   lis = &getAnalysis<LiveIntervals>();
541   lss = &getAnalysis<LiveStacks>();
542   mbfi = &getAnalysis<MachineBlockFrequencyInfo>();
543 
544   calculateSpillWeightsAndHints(*lis, MF, getAnalysis<MachineLoopInfo>(),
545                                 *mbfi);
546 
547   vrm = &getAnalysis<VirtRegMap>();
548   spiller.reset(createInlineSpiller(*this, MF, *vrm));
549 
550   mri->freezeReservedRegs(MF);
551 
552   DEBUG(dbgs() << "PBQP Register Allocating for " << mf->getName() << "\n");
553 
554   // Allocator main loop:
555   //
556   // * Map current regalloc problem to a PBQP problem
557   // * Solve the PBQP problem
558   // * Map the solution back to a register allocation
559   // * Spill if necessary
560   //
561   // This process is continued till no more spills are generated.
562 
563   // Find the vreg intervals in need of allocation.
564   findVRegIntervalsToAlloc();
565 
566 #ifndef NDEBUG
567   const Function* func = mf->getFunction();
568   std::string fqn =
569     func->getParent()->getModuleIdentifier() + "." +
570     func->getName().str();
571 #endif
572 
573   // If there are non-empty intervals allocate them using pbqp.
574   if (!vregsToAlloc.empty()) {
575 
576     bool pbqpAllocComplete = false;
577     unsigned round = 0;
578 
579     while (!pbqpAllocComplete) {
580       DEBUG(dbgs() << "  PBQP Regalloc round " << round << ":\n");
581 
582       std::unique_ptr<PBQPRAProblem> problem(
583           builder->build(mf, lis, mbfi, vregsToAlloc));
584 
585 #ifndef NDEBUG
586       if (pbqpDumpGraphs) {
587         std::ostringstream rs;
588         rs << round;
589         std::string graphFileName(fqn + "." + rs.str() + ".pbqpgraph");
590         std::string tmp;
591         raw_fd_ostream os(graphFileName.c_str(), tmp, sys::fs::F_Text);
592         DEBUG(dbgs() << "Dumping graph for round " << round << " to \""
593               << graphFileName << "\"\n");
594         problem->getGraph().dump(os);
595       }
596 #endif
597 
598       PBQP::Solution solution =
599         PBQP::RegAlloc::solve(problem->getGraph());
600 
601       pbqpAllocComplete = mapPBQPToRegAlloc(*problem, solution);
602 
603       ++round;
604     }
605   }
606 
607   // Finalise allocation, allocate empty ranges.
608   finalizeAlloc();
609   vregsToAlloc.clear();
610   emptyIntervalVRegs.clear();
611 
612   DEBUG(dbgs() << "Post alloc VirtRegMap:\n" << *vrm << "\n");
613 
614   return true;
615 }
616 
617 FunctionPass *
618 llvm::createPBQPRegisterAllocator(std::unique_ptr<PBQPBuilder> builder,
619                                   char *customPassID) {
620   return new RegAllocPBQP(std::move(builder), customPassID);
621 }
622 
623 FunctionPass* llvm::createDefaultPBQPRegisterAllocator() {
624   std::unique_ptr<PBQPBuilder> Builder;
625   if (pbqpCoalescing)
626     Builder = llvm::make_unique<PBQPBuilderWithCoalescing>();
627   else
628     Builder = llvm::make_unique<PBQPBuilder>();
629   return createPBQPRegisterAllocator(std::move(Builder));
630 }
631 
632 #undef DEBUG_TYPE
633