RegAllocPBQP.cpp revision bdd8f3b69a2b988e8986456908be2fe36133a99b
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// Author: Lang Hames 31// Email: lhames@gmail.com 32// 33//===----------------------------------------------------------------------===// 34 35// TODO: 36// 37// * Use of std::set in constructPBQPProblem destroys allocation order preference. 38// Switch to an order preserving container. 39// 40// * Coalescing support. 41 42#define DEBUG_TYPE "regalloc" 43 44#include "PBQP.h" 45#include "VirtRegMap.h" 46#include "llvm/CodeGen/MachineFunctionPass.h" 47#include "llvm/CodeGen/RegAllocRegistry.h" 48#include "llvm/CodeGen/LiveIntervalAnalysis.h" 49#include "llvm/CodeGen/MachineRegisterInfo.h" 50#include "llvm/CodeGen/MachineLoopInfo.h" 51#include "llvm/Target/TargetMachine.h" 52#include "llvm/Target/TargetInstrInfo.h" 53#include "llvm/Support/Debug.h" 54#include <memory> 55#include <map> 56#include <set> 57#include <vector> 58#include <limits> 59 60using namespace llvm; 61 62static RegisterRegAlloc 63registerPBQPRepAlloc("pbqp", " PBQP register allocator", 64 createPBQPRegisterAllocator); 65 66 67namespace { 68 69 //! 70 //! PBQP based allocators solve the register allocation problem by mapping 71 //! register allocation problems to Partitioned Boolean Quadratic 72 //! Programming problems. 73 class VISIBILITY_HIDDEN PBQPRegAlloc : public MachineFunctionPass { 74 public: 75 76 static char ID; 77 78 //! Construct a PBQP register allocator. 79 PBQPRegAlloc() : MachineFunctionPass((intptr_t)&ID) {} 80 81 //! Return the pass name. 82 virtual const char* getPassName() const throw() { 83 return "PBQP Register Allocator"; 84 } 85 86 //! PBQP analysis usage. 87 virtual void getAnalysisUsage(AnalysisUsage &au) const { 88 au.addRequired<LiveIntervals>(); 89 au.addRequired<MachineLoopInfo>(); 90 MachineFunctionPass::getAnalysisUsage(au); 91 } 92 93 //! Perform register allocation 94 virtual bool runOnMachineFunction(MachineFunction &MF); 95 96 private: 97 typedef std::map<const LiveInterval*, unsigned> LI2NodeMap; 98 typedef std::vector<const LiveInterval*> Node2LIMap; 99 typedef std::vector<unsigned> AllowedSet; 100 typedef std::vector<AllowedSet> AllowedSetMap; 101 typedef std::set<unsigned> IgnoreSet; 102 103 MachineFunction *mf; 104 const TargetMachine *tm; 105 const TargetRegisterInfo *tri; 106 const TargetInstrInfo *tii; 107 const MachineLoopInfo *loopInfo; 108 MachineRegisterInfo *mri; 109 110 LiveIntervals *li; 111 VirtRegMap *vrm; 112 113 LI2NodeMap li2Node; 114 Node2LIMap node2LI; 115 AllowedSetMap allowedSets; 116 IgnoreSet ignoreSet; 117 118 //! Builds a PBQP cost vector. 119 template <typename Container> 120 PBQPVector* buildCostVector(const Container &allowed, 121 PBQPNum spillCost) const; 122 123 //! \brief Builds a PBQP interference matrix. 124 //! 125 //! @return Either a pointer to a non-zero PBQP matrix representing the 126 //! allocation option costs, or a null pointer for a zero matrix. 127 //! 128 //! Expects allowed sets for two interfering LiveIntervals. These allowed 129 //! sets should contain only allocable registers from the LiveInterval's 130 //! register class, with any interfering pre-colored registers removed. 131 template <typename Container> 132 PBQPMatrix* buildInterferenceMatrix(const Container &allowed1, 133 const Container &allowed2) const; 134 135 //! 136 //! Expects allowed sets for two potentially coalescable LiveIntervals, 137 //! and an estimated benefit due to coalescing. The allowed sets should 138 //! contain only allocable registers from the LiveInterval's register 139 //! classes, with any interfering pre-colored registers removed. 140 template <typename Container> 141 PBQPMatrix* buildCoalescingMatrix(const Container &allowed1, 142 const Container &allowed2, 143 PBQPNum cBenefit) const; 144 145 //! \brief Helper function for constructInitialPBQPProblem(). 146 //! 147 //! This function iterates over the Function we are about to allocate for 148 //! and computes spill costs. 149 void calcSpillCosts(); 150 151 //! \brief Scans the MachineFunction being allocated to find coalescing 152 // opportunities. 153 void findCoalescingOpportunities(); 154 155 //! \brief Constructs a PBQP problem representation of the register 156 //! allocation problem for this function. 157 //! 158 //! @return a PBQP solver object for the register allocation problem. 159 pbqp* constructPBQPProblem(); 160 161 //! \brief Given a solved PBQP problem maps this solution back to a register 162 //! assignment. 163 bool mapPBQPToRegAlloc(pbqp *problem); 164 165 }; 166 167 char PBQPRegAlloc::ID = 0; 168} 169 170 171template <typename Container> 172PBQPVector* PBQPRegAlloc::buildCostVector(const Container &allowed, 173 PBQPNum spillCost) const { 174 175 // Allocate vector. Additional element (0th) used for spill option 176 PBQPVector *v = new PBQPVector(allowed.size() + 1); 177 178 (*v)[0] = spillCost; 179 180 return v; 181} 182 183template <typename Container> 184PBQPMatrix* PBQPRegAlloc::buildInterferenceMatrix( 185 const Container &allowed1, const Container &allowed2) const { 186 187 typedef typename Container::const_iterator ContainerIterator; 188 189 // Construct a PBQP matrix representing the cost of allocation options. The 190 // rows and columns correspond to the allocation options for the two live 191 // intervals. Elements will be infinite where corresponding registers alias, 192 // since we cannot allocate aliasing registers to interfering live intervals. 193 // All other elements (non-aliasing combinations) will have zero cost. Note 194 // that the spill option (element 0,0) has zero cost, since we can allocate 195 // both intervals to memory safely (the cost for each individual allocation 196 // to memory is accounted for by the cost vectors for each live interval). 197 PBQPMatrix *m = new PBQPMatrix(allowed1.size() + 1, allowed2.size() + 1); 198 199 // Assume this is a zero matrix until proven otherwise. Zero matrices occur 200 // between interfering live ranges with non-overlapping register sets (e.g. 201 // non-overlapping reg classes, or disjoint sets of allowed regs within the 202 // same class). The term "overlapping" is used advisedly: sets which do not 203 // intersect, but contain registers which alias, will have non-zero matrices. 204 // We optimize zero matrices away to improve solver speed. 205 bool isZeroMatrix = true; 206 207 208 // Row index. Starts at 1, since the 0th row is for the spill option, which 209 // is always zero. 210 unsigned ri = 1; 211 212 // Iterate over allowed sets, insert infinities where required. 213 for (ContainerIterator a1Itr = allowed1.begin(), a1End = allowed1.end(); 214 a1Itr != a1End; ++a1Itr) { 215 216 // Column index, starts at 1 as for row index. 217 unsigned ci = 1; 218 unsigned reg1 = *a1Itr; 219 220 for (ContainerIterator a2Itr = allowed2.begin(), a2End = allowed2.end(); 221 a2Itr != a2End; ++a2Itr) { 222 223 unsigned reg2 = *a2Itr; 224 225 // If the row/column regs are identical or alias insert an infinity. 226 if ((reg1 == reg2) || tri->areAliases(reg1, reg2)) { 227 (*m)[ri][ci] = std::numeric_limits<PBQPNum>::infinity(); 228 isZeroMatrix = false; 229 } 230 231 ++ci; 232 } 233 234 ++ri; 235 } 236 237 // If this turns out to be a zero matrix... 238 if (isZeroMatrix) { 239 // free it and return null. 240 delete m; 241 return 0; 242 } 243 244 // ...otherwise return the cost matrix. 245 return m; 246} 247 248void PBQPRegAlloc::calcSpillCosts() { 249 250 // Calculate the spill cost for each live interval by iterating over the 251 // function counting loads and stores, with loop depth taken into account. 252 for (MachineFunction::const_iterator bbItr = mf->begin(), bbEnd = mf->end(); 253 bbItr != bbEnd; ++bbItr) { 254 255 const MachineBasicBlock *mbb = &*bbItr; 256 float loopDepth = loopInfo->getLoopDepth(mbb); 257 258 for (MachineBasicBlock::const_iterator 259 iItr = mbb->begin(), iEnd = mbb->end(); iItr != iEnd; ++iItr) { 260 261 const MachineInstr *instr = &*iItr; 262 263 for (unsigned opNo = 0; opNo < instr->getNumOperands(); ++opNo) { 264 265 const MachineOperand &mo = instr->getOperand(opNo); 266 267 // We're not interested in non-registers... 268 if (!mo.isReg()) 269 continue; 270 271 unsigned moReg = mo.getReg(); 272 273 // ...Or invalid registers... 274 if (moReg == 0) 275 continue; 276 277 // ...Or physical registers... 278 if (TargetRegisterInfo::isPhysicalRegister(moReg)) 279 continue; 280 281 assert ((mo.isUse() || mo.isDef()) && 282 "Not a use, not a def, what is it?"); 283 284 //... Just the virtual registers. We treat loads and stores as equal. 285 li->getInterval(moReg).weight += powf(10.0f, loopDepth); 286 } 287 288 } 289 290 } 291 292} 293 294pbqp* PBQPRegAlloc::constructPBQPProblem() { 295 296 typedef std::vector<const LiveInterval*> LIVector; 297 typedef std::set<unsigned> RegSet; 298 299 // These will store the physical & virtual intervals, respectively. 300 LIVector physIntervals, virtIntervals; 301 302 // Start by clearing the old node <-> live interval mappings & allowed sets 303 li2Node.clear(); 304 node2LI.clear(); 305 allowedSets.clear(); 306 307 // Iterate over intervals classifying them as physical or virtual, and 308 // constructing live interval <-> node number mappings. 309 for (LiveIntervals::iterator itr = li->begin(), end = li->end(); 310 itr != end; ++itr) { 311 312 if (itr->second->getNumValNums() != 0) { 313 DOUT << "Live range has " << itr->second->getNumValNums() << ": " << itr->second << "\n"; 314 } 315 316 if (TargetRegisterInfo::isPhysicalRegister(itr->first)) { 317 physIntervals.push_back(itr->second); 318 mri->setPhysRegUsed(itr->second->reg); 319 } 320 else { 321 322 // If we've allocated this virtual register interval a stack slot on a 323 // previous round then it's not an allocation candidate 324 if (ignoreSet.find(itr->first) != ignoreSet.end()) 325 continue; 326 327 li2Node[itr->second] = node2LI.size(); 328 node2LI.push_back(itr->second); 329 virtIntervals.push_back(itr->second); 330 } 331 } 332 333 // Early out if there's no regs to allocate for. 334 if (virtIntervals.empty()) 335 return 0; 336 337 // Construct a PBQP solver for this problem 338 pbqp *solver = alloc_pbqp(virtIntervals.size()); 339 340 // Resize allowedSets container appropriately. 341 allowedSets.resize(virtIntervals.size()); 342 343 // Iterate over virtual register intervals to compute allowed sets... 344 for (unsigned node = 0; node < node2LI.size(); ++node) { 345 346 // Grab pointers to the interval and its register class. 347 const LiveInterval *li = node2LI[node]; 348 const TargetRegisterClass *liRC = mri->getRegClass(li->reg); 349 350 // Start by assuming all allocable registers in the class are allowed... 351 RegSet liAllowed(liRC->allocation_order_begin(*mf), 352 liRC->allocation_order_end(*mf)); 353 354 // If this range is non-empty then eliminate the physical registers which 355 // overlap with this range, along with all their aliases. 356 if (!li->empty()) { 357 for (LIVector::iterator pItr = physIntervals.begin(), 358 pEnd = physIntervals.end(); pItr != pEnd; ++pItr) { 359 360 if (li->overlaps(**pItr)) { 361 362 unsigned pReg = (*pItr)->reg; 363 364 // Remove the overlapping reg... 365 liAllowed.erase(pReg); 366 367 const unsigned *aliasItr = tri->getAliasSet(pReg); 368 369 if (aliasItr != 0) { 370 // ...and its aliases. 371 for (; *aliasItr != 0; ++aliasItr) { 372 liAllowed.erase(*aliasItr); 373 } 374 375 } 376 377 } 378 379 } 380 381 } 382 383 // Copy the allowed set into a member vector for use when constructing cost 384 // vectors & matrices, and mapping PBQP solutions back to assignments. 385 allowedSets[node] = AllowedSet(liAllowed.begin(), liAllowed.end()); 386 387 // Set the spill cost to the interval weight, or epsilon if the 388 // interval weight is zero 389 PBQPNum spillCost = (li->weight != 0.0) ? 390 li->weight : std::numeric_limits<PBQPNum>::min(); 391 392 // Build a cost vector for this interval. 393 add_pbqp_nodecosts(solver, node, 394 buildCostVector(allowedSets[node], spillCost)); 395 396 } 397 398 // Now add the cost matrices... 399 for (unsigned node1 = 0; node1 < node2LI.size(); ++node1) { 400 401 const LiveInterval *li = node2LI[node1]; 402 403 if (li->empty()) 404 continue; 405 406 // Test for live range overlaps and insert interference matrices. 407 for (unsigned node2 = node1 + 1; node2 < node2LI.size(); ++node2) { 408 const LiveInterval *li2 = node2LI[node2]; 409 410 if (li2->empty()) 411 continue; 412 413 if (li->overlaps(*li2)) { 414 PBQPMatrix *m = 415 buildInterferenceMatrix(allowedSets[node1], allowedSets[node2]); 416 417 if (m != 0) { 418 add_pbqp_edgecosts(solver, node1, node2, m); 419 delete m; 420 } 421 } 422 } 423 } 424 425 // We're done, PBQP problem constructed - return it. 426 return solver; 427} 428 429bool PBQPRegAlloc::mapPBQPToRegAlloc(pbqp *problem) { 430 431 // Set to true if we have any spills 432 bool anotherRoundNeeded = false; 433 434 // Clear the existing allocation. 435 vrm->clearAllVirt(); 436 437 // Iterate over the nodes mapping the PBQP solution to a register assignment. 438 for (unsigned node = 0; node < node2LI.size(); ++node) { 439 unsigned symReg = node2LI[node]->reg, 440 allocSelection = get_pbqp_solution(problem, node); 441 442 // If the PBQP solution is non-zero it's a physical register... 443 if (allocSelection != 0) { 444 // Get the physical reg, subtracting 1 to account for the spill option. 445 unsigned physReg = allowedSets[node][allocSelection - 1]; 446 447 // Add to the virt reg map and update the used phys regs. 448 vrm->assignVirt2Phys(symReg, physReg); 449 mri->setPhysRegUsed(physReg); 450 } 451 // ...Otherwise it's a spill. 452 else { 453 454 // Make sure we ignore this virtual reg on the next round 455 // of allocation 456 ignoreSet.insert(node2LI[node]->reg); 457 458 float SSWeight; 459 460 // Insert spill ranges for this live range 461 SmallVector<LiveInterval*, 8> spillIs; 462 std::vector<LiveInterval*> newSpills = 463 li->addIntervalsForSpills(*node2LI[node], spillIs, loopInfo, *vrm, 464 SSWeight); 465 466 // We need another round if spill intervals were added. 467 anotherRoundNeeded |= !newSpills.empty(); 468 } 469 } 470 471 return !anotherRoundNeeded; 472} 473 474bool PBQPRegAlloc::runOnMachineFunction(MachineFunction &MF) { 475 476 mf = &MF; 477 tm = &mf->getTarget(); 478 tri = tm->getRegisterInfo(); 479 mri = &mf->getRegInfo(); 480 481 li = &getAnalysis<LiveIntervals>(); 482 loopInfo = &getAnalysis<MachineLoopInfo>(); 483 484 std::auto_ptr<VirtRegMap> vrmAutoPtr(new VirtRegMap(*mf)); 485 vrm = vrmAutoPtr.get(); 486 487 // Allocator main loop: 488 // 489 // * Map current regalloc problem to a PBQP problem 490 // * Solve the PBQP problem 491 // * Map the solution back to a register allocation 492 // * Spill if necessary 493 // 494 // This process is continued till no more spills are generated. 495 496 bool regallocComplete = false; 497 498 // Calculate spill costs for intervals 499 calcSpillCosts(); 500 501 while (!regallocComplete) { 502 pbqp *problem = constructPBQPProblem(); 503 504 // Fast out if there's no problem to solve. 505 if (problem == 0) 506 return true; 507 508 solve_pbqp(problem); 509 510 regallocComplete = mapPBQPToRegAlloc(problem); 511 512 free_pbqp(problem); 513 } 514 515 ignoreSet.clear(); 516 517 std::auto_ptr<Spiller> spiller(createSpiller()); 518 519 spiller->runOnMachineFunction(*mf, *vrm); 520 521 return true; 522} 523 524FunctionPass* llvm::createPBQPRegisterAllocator() { 525 return new PBQPRegAlloc(); 526} 527 528 529#undef DEBUG_TYPE 530