VirtRegMap.cpp revision 91e2390818080ae2b059e3ff850a9455858e4f7b
1//===-- llvm/CodeGen/VirtRegMap.cpp - Virtual Register Map ----------------===// 2// 3// The LLVM Compiler Infrastructure 4// 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. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements the VirtRegMap class. 11// 12// It also contains implementations of the the Spiller interface, which, given a 13// virtual register map and a machine function, eliminates all virtual 14// references by replacing them with physical register references - adding spill 15// code as necessary. 16// 17//===----------------------------------------------------------------------===// 18 19#define DEBUG_TYPE "spiller" 20#include "VirtRegMap.h" 21#include "llvm/Function.h" 22#include "llvm/CodeGen/MachineFrameInfo.h" 23#include "llvm/CodeGen/MachineFunction.h" 24#include "llvm/CodeGen/SSARegMap.h" 25#include "llvm/Target/TargetMachine.h" 26#include "llvm/Target/TargetInstrInfo.h" 27#include "llvm/Support/CommandLine.h" 28#include "llvm/Support/Debug.h" 29#include "llvm/Support/Compiler.h" 30#include "llvm/ADT/BitVector.h" 31#include "llvm/ADT/Statistic.h" 32#include "llvm/ADT/STLExtras.h" 33#include "llvm/ADT/SmallSet.h" 34#include <algorithm> 35using namespace llvm; 36 37STATISTIC(NumSpills, "Number of register spills"); 38STATISTIC(NumStores, "Number of stores added"); 39STATISTIC(NumLoads , "Number of loads added"); 40STATISTIC(NumReused, "Number of values reused"); 41STATISTIC(NumDSE , "Number of dead stores elided"); 42STATISTIC(NumDCE , "Number of copies elided"); 43 44namespace { 45 enum SpillerName { simple, local }; 46 47 static cl::opt<SpillerName> 48 SpillerOpt("spiller", 49 cl::desc("Spiller to use: (default: local)"), 50 cl::Prefix, 51 cl::values(clEnumVal(simple, " simple spiller"), 52 clEnumVal(local, " local spiller"), 53 clEnumValEnd), 54 cl::init(local)); 55} 56 57//===----------------------------------------------------------------------===// 58// VirtRegMap implementation 59//===----------------------------------------------------------------------===// 60 61VirtRegMap::VirtRegMap(MachineFunction &mf) 62 : TII(*mf.getTarget().getInstrInfo()), MF(mf), 63 Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT) { 64 grow(); 65} 66 67void VirtRegMap::grow() { 68 Virt2PhysMap.grow(MF.getSSARegMap()->getLastVirtReg()); 69 Virt2StackSlotMap.grow(MF.getSSARegMap()->getLastVirtReg()); 70} 71 72int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) { 73 assert(MRegisterInfo::isVirtualRegister(virtReg)); 74 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && 75 "attempt to assign stack slot to already spilled register"); 76 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg); 77 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(), 78 RC->getAlignment()); 79 Virt2StackSlotMap[virtReg] = frameIndex; 80 ++NumSpills; 81 return frameIndex; 82} 83 84void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) { 85 assert(MRegisterInfo::isVirtualRegister(virtReg)); 86 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && 87 "attempt to assign stack slot to already spilled register"); 88 Virt2StackSlotMap[virtReg] = frameIndex; 89} 90 91void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI, 92 unsigned OpNo, MachineInstr *NewMI) { 93 // Move previous memory references folded to new instruction. 94 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI); 95 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI), 96 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) { 97 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second)); 98 MI2VirtMap.erase(I++); 99 } 100 101 ModRef MRInfo; 102 const TargetInstrDescriptor *TID = OldMI->getInstrDescriptor(); 103 if (TID->getOperandConstraint(OpNo, TOI::TIED_TO) != -1 || 104 TID->findTiedToSrcOperand(OpNo) != -1) { 105 // Folded a two-address operand. 106 MRInfo = isModRef; 107 } else if (OldMI->getOperand(OpNo).isDef()) { 108 MRInfo = isMod; 109 } else { 110 MRInfo = isRef; 111 } 112 113 // add new memory reference 114 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo))); 115} 116 117void VirtRegMap::print(std::ostream &OS) const { 118 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo(); 119 120 OS << "********** REGISTER MAP **********\n"; 121 for (unsigned i = MRegisterInfo::FirstVirtualRegister, 122 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) { 123 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG) 124 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n"; 125 126 } 127 128 for (unsigned i = MRegisterInfo::FirstVirtualRegister, 129 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) 130 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT) 131 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n"; 132 OS << '\n'; 133} 134 135void VirtRegMap::dump() const { 136 print(DOUT); 137} 138 139 140//===----------------------------------------------------------------------===// 141// Simple Spiller Implementation 142//===----------------------------------------------------------------------===// 143 144Spiller::~Spiller() {} 145 146namespace { 147 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller { 148 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM); 149 }; 150} 151 152bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) { 153 DOUT << "********** REWRITE MACHINE CODE **********\n"; 154 DOUT << "********** Function: " << MF.getFunction()->getName() << '\n'; 155 const TargetMachine &TM = MF.getTarget(); 156 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 157 bool *PhysRegsUsed = MF.getUsedPhysregs(); 158 159 // LoadedRegs - Keep track of which vregs are loaded, so that we only load 160 // each vreg once (in the case where a spilled vreg is used by multiple 161 // operands). This is always smaller than the number of operands to the 162 // current machine instr, so it should be small. 163 std::vector<unsigned> LoadedRegs; 164 165 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end(); 166 MBBI != E; ++MBBI) { 167 DOUT << MBBI->getBasicBlock()->getName() << ":\n"; 168 MachineBasicBlock &MBB = *MBBI; 169 for (MachineBasicBlock::iterator MII = MBB.begin(), 170 E = MBB.end(); MII != E; ++MII) { 171 MachineInstr &MI = *MII; 172 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 173 MachineOperand &MO = MI.getOperand(i); 174 if (MO.isRegister() && MO.getReg()) 175 if (MRegisterInfo::isVirtualRegister(MO.getReg())) { 176 unsigned VirtReg = MO.getReg(); 177 unsigned PhysReg = VRM.getPhys(VirtReg); 178 if (VRM.hasStackSlot(VirtReg)) { 179 int StackSlot = VRM.getStackSlot(VirtReg); 180 const TargetRegisterClass* RC = 181 MF.getSSARegMap()->getRegClass(VirtReg); 182 183 if (MO.isUse() && 184 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg) 185 == LoadedRegs.end()) { 186 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC); 187 LoadedRegs.push_back(VirtReg); 188 ++NumLoads; 189 DOUT << '\t' << *prior(MII); 190 } 191 192 if (MO.isDef()) { 193 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC); 194 ++NumStores; 195 } 196 } 197 PhysRegsUsed[PhysReg] = true; 198 MI.getOperand(i).setReg(PhysReg); 199 } else { 200 PhysRegsUsed[MO.getReg()] = true; 201 } 202 } 203 204 DOUT << '\t' << MI; 205 LoadedRegs.clear(); 206 } 207 } 208 return true; 209} 210 211//===----------------------------------------------------------------------===// 212// Local Spiller Implementation 213//===----------------------------------------------------------------------===// 214 215namespace { 216 /// LocalSpiller - This spiller does a simple pass over the machine basic 217 /// block to attempt to keep spills in registers as much as possible for 218 /// blocks that have low register pressure (the vreg may be spilled due to 219 /// register pressure in other blocks). 220 class VISIBILITY_HIDDEN LocalSpiller : public Spiller { 221 const MRegisterInfo *MRI; 222 const TargetInstrInfo *TII; 223 public: 224 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) { 225 MRI = MF.getTarget().getRegisterInfo(); 226 TII = MF.getTarget().getInstrInfo(); 227 DOUT << "\n**** Local spiller rewriting function '" 228 << MF.getFunction()->getName() << "':\n"; 229 230 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end(); 231 MBB != E; ++MBB) 232 RewriteMBB(*MBB, VRM); 233 return true; 234 } 235 private: 236 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM); 237 }; 238} 239 240/// AvailableSpills - As the local spiller is scanning and rewriting an MBB from 241/// top down, keep track of which spills slots are available in each register. 242/// 243/// Note that not all physregs are created equal here. In particular, some 244/// physregs are reloads that we are allowed to clobber or ignore at any time. 245/// Other physregs are values that the register allocated program is using that 246/// we cannot CHANGE, but we can read if we like. We keep track of this on a 247/// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable 248/// entries. The predicate 'canClobberPhysReg()' checks this bit and 249/// addAvailable sets it if. 250namespace { 251class VISIBILITY_HIDDEN AvailableSpills { 252 const MRegisterInfo *MRI; 253 const TargetInstrInfo *TII; 254 255 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual 256 // register values that are still available, due to being loaded or stored to, 257 // but not invalidated yet. 258 typedef std::pair<unsigned, MachineInstr*> SSInfo; 259 std::map<int, SSInfo> SpillSlotsAvailable; 260 261 // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating 262 // which stack slot values are currently held by a physreg. This is used to 263 // invalidate entries in SpillSlotsAvailable when a physreg is modified. 264 std::multimap<unsigned, int> PhysRegsAvailable; 265 266 void disallowClobberPhysRegOnly(unsigned PhysReg); 267 268 void ClobberPhysRegOnly(unsigned PhysReg); 269public: 270 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii) 271 : MRI(mri), TII(tii) { 272 } 273 274 const MRegisterInfo *getRegInfo() const { return MRI; } 275 276 /// getSpillSlotPhysReg - If the specified stack slot is available in a 277 /// physical register, return that PhysReg, otherwise return 0. It also 278 /// returns by reference the instruction that either defines or last uses 279 /// the register. 280 unsigned getSpillSlotPhysReg(int Slot, MachineInstr *&SSMI) const { 281 std::map<int, SSInfo>::const_iterator I = SpillSlotsAvailable.find(Slot); 282 if (I != SpillSlotsAvailable.end()) { 283 SSMI = I->second.second; 284 return I->second.first >> 1; // Remove the CanClobber bit. 285 } 286 return 0; 287 } 288 289 /// addAvailable - Mark that the specified stack slot is available in the 290 /// specified physreg. If CanClobber is true, the physreg can be modified at 291 /// any time without changing the semantics of the program. 292 void addAvailable(int Slot, MachineInstr *MI, unsigned Reg, 293 bool CanClobber = true) { 294 // If this stack slot is thought to be available in some other physreg, 295 // remove its record. 296 ModifyStackSlot(Slot); 297 298 PhysRegsAvailable.insert(std::make_pair(Reg, Slot)); 299 SpillSlotsAvailable[Slot] = 300 std::make_pair((Reg << 1) | (unsigned)CanClobber, MI); 301 302 DOUT << "Remembering SS#" << Slot << " in physreg " 303 << MRI->getName(Reg) << "\n"; 304 } 305 306 /// canClobberPhysReg - Return true if the spiller is allowed to change the 307 /// value of the specified stackslot register if it desires. The specified 308 /// stack slot must be available in a physreg for this query to make sense. 309 bool canClobberPhysReg(int Slot) const { 310 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!"); 311 return SpillSlotsAvailable.find(Slot)->second.first & 1; 312 } 313 314 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified 315 /// stackslot register. The register is still available but is no longer 316 /// allowed to be modifed. 317 void disallowClobberPhysReg(unsigned PhysReg); 318 319 /// ClobberPhysReg - This is called when the specified physreg changes 320 /// value. We use this to invalidate any info about stuff we thing lives in 321 /// it and any of its aliases. 322 void ClobberPhysReg(unsigned PhysReg); 323 324 /// ModifyStackSlot - This method is called when the value in a stack slot 325 /// changes. This removes information about which register the previous value 326 /// for this slot lives in (as the previous value is dead now). 327 void ModifyStackSlot(int Slot); 328}; 329} 330 331/// disallowClobberPhysRegOnly - Unset the CanClobber bit of the specified 332/// stackslot register. The register is still available but is no longer 333/// allowed to be modifed. 334void AvailableSpills::disallowClobberPhysRegOnly(unsigned PhysReg) { 335 std::multimap<unsigned, int>::iterator I = 336 PhysRegsAvailable.lower_bound(PhysReg); 337 while (I != PhysRegsAvailable.end() && I->first == PhysReg) { 338 int Slot = I->second; 339 I++; 340 assert((SpillSlotsAvailable[Slot].first >> 1) == PhysReg && 341 "Bidirectional map mismatch!"); 342 SpillSlotsAvailable[Slot].first &= ~1; 343 DOUT << "PhysReg " << MRI->getName(PhysReg) 344 << " copied, it is available for use but can no longer be modified\n"; 345 } 346} 347 348/// disallowClobberPhysReg - Unset the CanClobber bit of the specified 349/// stackslot register and its aliases. The register and its aliases may 350/// still available but is no longer allowed to be modifed. 351void AvailableSpills::disallowClobberPhysReg(unsigned PhysReg) { 352 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS) 353 disallowClobberPhysRegOnly(*AS); 354 disallowClobberPhysRegOnly(PhysReg); 355} 356 357/// ClobberPhysRegOnly - This is called when the specified physreg changes 358/// value. We use this to invalidate any info about stuff we thing lives in it. 359void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) { 360 std::multimap<unsigned, int>::iterator I = 361 PhysRegsAvailable.lower_bound(PhysReg); 362 while (I != PhysRegsAvailable.end() && I->first == PhysReg) { 363 int Slot = I->second; 364 PhysRegsAvailable.erase(I++); 365 assert((SpillSlotsAvailable[Slot].first >> 1) == PhysReg && 366 "Bidirectional map mismatch!"); 367 SpillSlotsAvailable.erase(Slot); 368 DOUT << "PhysReg " << MRI->getName(PhysReg) 369 << " clobbered, invalidating SS#" << Slot << "\n"; 370 } 371} 372 373/// ClobberPhysReg - This is called when the specified physreg changes 374/// value. We use this to invalidate any info about stuff we thing lives in 375/// it and any of its aliases. 376void AvailableSpills::ClobberPhysReg(unsigned PhysReg) { 377 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS) 378 ClobberPhysRegOnly(*AS); 379 ClobberPhysRegOnly(PhysReg); 380} 381 382/// ModifyStackSlot - This method is called when the value in a stack slot 383/// changes. This removes information about which register the previous value 384/// for this slot lives in (as the previous value is dead now). 385void AvailableSpills::ModifyStackSlot(int Slot) { 386 std::map<int, SSInfo>::iterator It = SpillSlotsAvailable.find(Slot); 387 if (It == SpillSlotsAvailable.end()) return; 388 unsigned Reg = It->second.first >> 1; 389 SpillSlotsAvailable.erase(It); 390 391 // This register may hold the value of multiple stack slots, only remove this 392 // stack slot from the set of values the register contains. 393 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg); 394 for (; ; ++I) { 395 assert(I != PhysRegsAvailable.end() && I->first == Reg && 396 "Map inverse broken!"); 397 if (I->second == Slot) break; 398 } 399 PhysRegsAvailable.erase(I); 400} 401 402 403 404// ReusedOp - For each reused operand, we keep track of a bit of information, in 405// case we need to rollback upon processing a new operand. See comments below. 406namespace { 407 struct ReusedOp { 408 // The MachineInstr operand that reused an available value. 409 unsigned Operand; 410 411 // StackSlot - The spill slot of the value being reused. 412 unsigned StackSlot; 413 414 // PhysRegReused - The physical register the value was available in. 415 unsigned PhysRegReused; 416 417 // AssignedPhysReg - The physreg that was assigned for use by the reload. 418 unsigned AssignedPhysReg; 419 420 // VirtReg - The virtual register itself. 421 unsigned VirtReg; 422 423 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr, 424 unsigned vreg) 425 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr), 426 VirtReg(vreg) {} 427 }; 428 429 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that 430 /// is reused instead of reloaded. 431 class VISIBILITY_HIDDEN ReuseInfo { 432 MachineInstr &MI; 433 std::vector<ReusedOp> Reuses; 434 BitVector PhysRegsClobbered; 435 public: 436 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) { 437 PhysRegsClobbered.resize(mri->getNumRegs()); 438 } 439 440 bool hasReuses() const { 441 return !Reuses.empty(); 442 } 443 444 /// addReuse - If we choose to reuse a virtual register that is already 445 /// available instead of reloading it, remember that we did so. 446 void addReuse(unsigned OpNo, unsigned StackSlot, 447 unsigned PhysRegReused, unsigned AssignedPhysReg, 448 unsigned VirtReg) { 449 // If the reload is to the assigned register anyway, no undo will be 450 // required. 451 if (PhysRegReused == AssignedPhysReg) return; 452 453 // Otherwise, remember this. 454 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused, 455 AssignedPhysReg, VirtReg)); 456 } 457 458 void markClobbered(unsigned PhysReg) { 459 PhysRegsClobbered.set(PhysReg); 460 } 461 462 bool isClobbered(unsigned PhysReg) const { 463 return PhysRegsClobbered.test(PhysReg); 464 } 465 466 /// GetRegForReload - We are about to emit a reload into PhysReg. If there 467 /// is some other operand that is using the specified register, either pick 468 /// a new register to use, or evict the previous reload and use this reg. 469 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI, 470 AvailableSpills &Spills, 471 std::map<int, MachineInstr*> &MaybeDeadStores, 472 SmallSet<unsigned, 8> &Rejected) { 473 if (Reuses.empty()) return PhysReg; // This is most often empty. 474 475 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) { 476 ReusedOp &Op = Reuses[ro]; 477 // If we find some other reuse that was supposed to use this register 478 // exactly for its reload, we can change this reload to use ITS reload 479 // register. That is, unless its reload register has already been 480 // considered and subsequently rejected because it has also been reused 481 // by another operand. 482 if (Op.PhysRegReused == PhysReg && 483 Rejected.count(Op.AssignedPhysReg) == 0) { 484 // Yup, use the reload register that we didn't use before. 485 unsigned NewReg = Op.AssignedPhysReg; 486 Rejected.insert(PhysReg); 487 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores, Rejected); 488 } else { 489 // Otherwise, we might also have a problem if a previously reused 490 // value aliases the new register. If so, codegen the previous reload 491 // and use this one. 492 unsigned PRRU = Op.PhysRegReused; 493 const MRegisterInfo *MRI = Spills.getRegInfo(); 494 if (MRI->areAliases(PRRU, PhysReg)) { 495 // Okay, we found out that an alias of a reused register 496 // was used. This isn't good because it means we have 497 // to undo a previous reuse. 498 MachineBasicBlock *MBB = MI->getParent(); 499 const TargetRegisterClass *AliasRC = 500 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg); 501 502 // Copy Op out of the vector and remove it, we're going to insert an 503 // explicit load for it. 504 ReusedOp NewOp = Op; 505 Reuses.erase(Reuses.begin()+ro); 506 507 // Ok, we're going to try to reload the assigned physreg into the 508 // slot that we were supposed to in the first place. However, that 509 // register could hold a reuse. Check to see if it conflicts or 510 // would prefer us to use a different register. 511 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg, 512 MI, Spills, MaybeDeadStores, Rejected); 513 514 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg, 515 NewOp.StackSlot, AliasRC); 516 Spills.ClobberPhysReg(NewPhysReg); 517 Spills.ClobberPhysReg(NewOp.PhysRegReused); 518 519 // Any stores to this stack slot are not dead anymore. 520 MaybeDeadStores.erase(NewOp.StackSlot); 521 522 MI->getOperand(NewOp.Operand).setReg(NewPhysReg); 523 524 Spills.addAvailable(NewOp.StackSlot, MI, NewPhysReg); 525 ++NumLoads; 526 DEBUG(MachineBasicBlock::iterator MII = MI; 527 DOUT << '\t' << *prior(MII)); 528 529 DOUT << "Reuse undone!\n"; 530 --NumReused; 531 532 // Finally, PhysReg is now available, go ahead and use it. 533 return PhysReg; 534 } 535 } 536 } 537 return PhysReg; 538 } 539 540 /// GetRegForReload - Helper for the above GetRegForReload(). Add a 541 /// 'Rejected' set to remember which registers have been considered and 542 /// rejected for the reload. This avoids infinite looping in case like 543 /// this: 544 /// t1 := op t2, t3 545 /// t2 <- assigned r0 for use by the reload but ended up reuse r1 546 /// t3 <- assigned r1 for use by the reload but ended up reuse r0 547 /// t1 <- desires r1 548 /// sees r1 is taken by t2, tries t2's reload register r0 549 /// sees r0 is taken by t3, tries t3's reload register r1 550 /// sees r1 is taken by t2, tries t2's reload register r0 ... 551 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI, 552 AvailableSpills &Spills, 553 std::map<int, MachineInstr*> &MaybeDeadStores) { 554 SmallSet<unsigned, 8> Rejected; 555 return GetRegForReload(PhysReg, MI, Spills, MaybeDeadStores, Rejected); 556 } 557 }; 558} 559 560 561/// rewriteMBB - Keep track of which spills are available even after the 562/// register allocator is done with them. If possible, avoid reloading vregs. 563void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) { 564 565 DOUT << MBB.getBasicBlock()->getName() << ":\n"; 566 567 // Spills - Keep track of which spilled values are available in physregs so 568 // that we can choose to reuse the physregs instead of emitting reloads. 569 AvailableSpills Spills(MRI, TII); 570 571 // MaybeDeadStores - When we need to write a value back into a stack slot, 572 // keep track of the inserted store. If the stack slot value is never read 573 // (because the value was used from some available register, for example), and 574 // subsequently stored to, the original store is dead. This map keeps track 575 // of inserted stores that are not used. If we see a subsequent store to the 576 // same stack slot, the original store is deleted. 577 std::map<int, MachineInstr*> MaybeDeadStores; 578 579 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs(); 580 581 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end(); 582 MII != E; ) { 583 MachineInstr &MI = *MII; 584 MachineBasicBlock::iterator NextMII = MII; ++NextMII; 585 586 /// ReusedOperands - Keep track of operand reuse in case we need to undo 587 /// reuse. 588 ReuseInfo ReusedOperands(MI, MRI); 589 590 // Loop over all of the implicit defs, clearing them from our available 591 // sets. 592 const TargetInstrDescriptor *TID = MI.getInstrDescriptor(); 593 const unsigned *ImpDef = TID->ImplicitDefs; 594 if (ImpDef) { 595 for ( ; *ImpDef; ++ImpDef) { 596 PhysRegsUsed[*ImpDef] = true; 597 ReusedOperands.markClobbered(*ImpDef); 598 Spills.ClobberPhysReg(*ImpDef); 599 } 600 } 601 602 // Process all of the spilled uses and all non spilled reg references. 603 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 604 MachineOperand &MO = MI.getOperand(i); 605 if (!MO.isRegister() || MO.getReg() == 0) 606 continue; // Ignore non-register operands. 607 608 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) { 609 // Ignore physregs for spilling, but remember that it is used by this 610 // function. 611 PhysRegsUsed[MO.getReg()] = true; 612 ReusedOperands.markClobbered(MO.getReg()); 613 continue; 614 } 615 616 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) && 617 "Not a virtual or a physical register?"); 618 619 unsigned VirtReg = MO.getReg(); 620 if (!VRM.hasStackSlot(VirtReg)) { 621 // This virtual register was assigned a physreg! 622 unsigned Phys = VRM.getPhys(VirtReg); 623 PhysRegsUsed[Phys] = true; 624 if (MO.isDef()) 625 ReusedOperands.markClobbered(Phys); 626 MI.getOperand(i).setReg(Phys); 627 continue; 628 } 629 630 // This virtual register is now known to be a spilled value. 631 if (!MO.isUse()) 632 continue; // Handle defs in the loop below (handle use&def here though) 633 634 int StackSlot = VRM.getStackSlot(VirtReg); 635 unsigned PhysReg; 636 637 // Check to see if this stack slot is available. 638 MachineInstr *SSMI = NULL; 639 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot, SSMI))) { 640 // This spilled operand might be part of a two-address operand. If this 641 // is the case, then changing it will necessarily require changing the 642 // def part of the instruction as well. However, in some cases, we 643 // aren't allowed to modify the reused register. If none of these cases 644 // apply, reuse it. 645 bool CanReuse = true; 646 int ti = TID->getOperandConstraint(i, TOI::TIED_TO); 647 if (ti != -1 && 648 MI.getOperand(ti).isReg() && 649 MI.getOperand(ti).getReg() == VirtReg) { 650 // Okay, we have a two address operand. We can reuse this physreg as 651 // long as we are allowed to clobber the value and there isn't an 652 // earlier def that has already clobbered the physreg. 653 CanReuse = Spills.canClobberPhysReg(StackSlot) && 654 !ReusedOperands.isClobbered(PhysReg); 655 } 656 657 if (CanReuse) { 658 // If this stack slot value is already available, reuse it! 659 DOUT << "Reusing SS#" << StackSlot << " from physreg " 660 << MRI->getName(PhysReg) << " for vreg" 661 << VirtReg <<" instead of reloading into physreg " 662 << MRI->getName(VRM.getPhys(VirtReg)) << "\n"; 663 MI.getOperand(i).setReg(PhysReg); 664 665 // Extend the live range of the MI that last kill the register if 666 // necessary. 667 MachineOperand *MOK = SSMI->findRegisterUseOperand(PhysReg, true); 668 if (MOK) 669 MOK->unsetIsKill(); 670 671 // The only technical detail we have is that we don't know that 672 // PhysReg won't be clobbered by a reloaded stack slot that occurs 673 // later in the instruction. In particular, consider 'op V1, V2'. 674 // If V1 is available in physreg R0, we would choose to reuse it 675 // here, instead of reloading it into the register the allocator 676 // indicated (say R1). However, V2 might have to be reloaded 677 // later, and it might indicate that it needs to live in R0. When 678 // this occurs, we need to have information available that 679 // indicates it is safe to use R1 for the reload instead of R0. 680 // 681 // To further complicate matters, we might conflict with an alias, 682 // or R0 and R1 might not be compatible with each other. In this 683 // case, we actually insert a reload for V1 in R1, ensuring that 684 // we can get at R0 or its alias. 685 ReusedOperands.addReuse(i, StackSlot, PhysReg, 686 VRM.getPhys(VirtReg), VirtReg); 687 if (ti != -1) 688 // Only mark it clobbered if this is a use&def operand. 689 ReusedOperands.markClobbered(PhysReg); 690 ++NumReused; 691 continue; 692 } 693 694 // Otherwise we have a situation where we have a two-address instruction 695 // whose mod/ref operand needs to be reloaded. This reload is already 696 // available in some register "PhysReg", but if we used PhysReg as the 697 // operand to our 2-addr instruction, the instruction would modify 698 // PhysReg. This isn't cool if something later uses PhysReg and expects 699 // to get its initial value. 700 // 701 // To avoid this problem, and to avoid doing a load right after a store, 702 // we emit a copy from PhysReg into the designated register for this 703 // operand. 704 unsigned DesignatedReg = VRM.getPhys(VirtReg); 705 assert(DesignatedReg && "Must map virtreg to physreg!"); 706 707 // Note that, if we reused a register for a previous operand, the 708 // register we want to reload into might not actually be 709 // available. If this occurs, use the register indicated by the 710 // reuser. 711 if (ReusedOperands.hasReuses()) 712 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI, 713 Spills, MaybeDeadStores); 714 715 // If the mapped designated register is actually the physreg we have 716 // incoming, we don't need to inserted a dead copy. 717 if (DesignatedReg == PhysReg) { 718 // If this stack slot value is already available, reuse it! 719 DOUT << "Reusing SS#" << StackSlot << " from physreg " 720 << MRI->getName(PhysReg) << " for vreg" 721 << VirtReg 722 << " instead of reloading into same physreg.\n"; 723 MI.getOperand(i).setReg(PhysReg); 724 ReusedOperands.markClobbered(PhysReg); 725 ++NumReused; 726 continue; 727 } 728 729 const TargetRegisterClass* RC = 730 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 731 732 PhysRegsUsed[DesignatedReg] = true; 733 ReusedOperands.markClobbered(DesignatedReg); 734 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC); 735 736 // This invalidates DesignatedReg. 737 Spills.ClobberPhysReg(DesignatedReg); 738 739 Spills.addAvailable(StackSlot, &MI, DesignatedReg); 740 MI.getOperand(i).setReg(DesignatedReg); 741 DOUT << '\t' << *prior(MII); 742 ++NumReused; 743 continue; 744 } 745 746 // Otherwise, reload it and remember that we have it. 747 PhysReg = VRM.getPhys(VirtReg); 748 assert(PhysReg && "Must map virtreg to physreg!"); 749 const TargetRegisterClass* RC = 750 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 751 752 // Note that, if we reused a register for a previous operand, the 753 // register we want to reload into might not actually be 754 // available. If this occurs, use the register indicated by the 755 // reuser. 756 if (ReusedOperands.hasReuses()) 757 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI, 758 Spills, MaybeDeadStores); 759 760 PhysRegsUsed[PhysReg] = true; 761 ReusedOperands.markClobbered(PhysReg); 762 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC); 763 // This invalidates PhysReg. 764 Spills.ClobberPhysReg(PhysReg); 765 766 // Any stores to this stack slot are not dead anymore. 767 MaybeDeadStores.erase(StackSlot); 768 Spills.addAvailable(StackSlot, &MI, PhysReg); 769 ++NumLoads; 770 MI.getOperand(i).setReg(PhysReg); 771 DOUT << '\t' << *prior(MII); 772 } 773 774 DOUT << '\t' << MI; 775 776 // If we have folded references to memory operands, make sure we clear all 777 // physical registers that may contain the value of the spilled virtual 778 // register 779 VirtRegMap::MI2VirtMapTy::const_iterator I, End; 780 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) { 781 DOUT << "Folded vreg: " << I->second.first << " MR: " 782 << I->second.second; 783 unsigned VirtReg = I->second.first; 784 VirtRegMap::ModRef MR = I->second.second; 785 if (!VRM.hasStackSlot(VirtReg)) { 786 DOUT << ": No stack slot!\n"; 787 continue; 788 } 789 int SS = VRM.getStackSlot(VirtReg); 790 DOUT << " - StackSlot: " << SS << "\n"; 791 792 // If this folded instruction is just a use, check to see if it's a 793 // straight load from the virt reg slot. 794 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) { 795 int FrameIdx; 796 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) { 797 if (FrameIdx == SS) { 798 // If this spill slot is available, turn it into a copy (or nothing) 799 // instead of leaving it as a load! 800 MachineInstr *Dummy = NULL; 801 if (unsigned InReg = Spills.getSpillSlotPhysReg(SS, Dummy)) { 802 DOUT << "Promoted Load To Copy: " << MI; 803 MachineFunction &MF = *MBB.getParent(); 804 if (DestReg != InReg) { 805 MRI->copyRegToReg(MBB, &MI, DestReg, InReg, 806 MF.getSSARegMap()->getRegClass(VirtReg)); 807 // Revisit the copy so we make sure to notice the effects of the 808 // operation on the destreg (either needing to RA it if it's 809 // virtual or needing to clobber any values if it's physical). 810 NextMII = &MI; 811 --NextMII; // backtrack to the copy. 812 } 813 VRM.RemoveFromFoldedVirtMap(&MI); 814 MBB.erase(&MI); 815 goto ProcessNextInst; 816 } 817 } 818 } 819 } 820 821 // If this reference is not a use, any previous store is now dead. 822 // Otherwise, the store to this stack slot is not dead anymore. 823 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS); 824 if (MDSI != MaybeDeadStores.end()) { 825 if (MR & VirtRegMap::isRef) // Previous store is not dead. 826 MaybeDeadStores.erase(MDSI); 827 else { 828 // If we get here, the store is dead, nuke it now. 829 assert(VirtRegMap::isMod && "Can't be modref!"); 830 DOUT << "Removed dead store:\t" << *MDSI->second; 831 MBB.erase(MDSI->second); 832 VRM.RemoveFromFoldedVirtMap(MDSI->second); 833 MaybeDeadStores.erase(MDSI); 834 ++NumDSE; 835 } 836 } 837 838 // If the spill slot value is available, and this is a new definition of 839 // the value, the value is not available anymore. 840 if (MR & VirtRegMap::isMod) { 841 // Notice that the value in this stack slot has been modified. 842 Spills.ModifyStackSlot(SS); 843 844 // If this is *just* a mod of the value, check to see if this is just a 845 // store to the spill slot (i.e. the spill got merged into the copy). If 846 // so, realize that the vreg is available now, and add the store to the 847 // MaybeDeadStore info. 848 int StackSlot; 849 if (!(MR & VirtRegMap::isRef)) { 850 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) { 851 assert(MRegisterInfo::isPhysicalRegister(SrcReg) && 852 "Src hasn't been allocated yet?"); 853 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark 854 // this as a potentially dead store in case there is a subsequent 855 // store into the stack slot without a read from it. 856 MaybeDeadStores[StackSlot] = &MI; 857 858 // If the stack slot value was previously available in some other 859 // register, change it now. Otherwise, make the register available, 860 // in PhysReg. 861 Spills.addAvailable(StackSlot, &MI, SrcReg, false/*don't clobber*/); 862 } 863 } 864 } 865 } 866 867 // Process all of the spilled defs. 868 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 869 MachineOperand &MO = MI.getOperand(i); 870 if (MO.isRegister() && MO.getReg() && MO.isDef()) { 871 unsigned VirtReg = MO.getReg(); 872 873 if (!MRegisterInfo::isVirtualRegister(VirtReg)) { 874 // Check to see if this is a noop copy. If so, eliminate the 875 // instruction before considering the dest reg to be changed. 876 unsigned Src, Dst; 877 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) { 878 ++NumDCE; 879 DOUT << "Removing now-noop copy: " << MI; 880 MBB.erase(&MI); 881 VRM.RemoveFromFoldedVirtMap(&MI); 882 Spills.disallowClobberPhysReg(VirtReg); 883 goto ProcessNextInst; 884 } 885 886 // If it's not a no-op copy, it clobbers the value in the destreg. 887 Spills.ClobberPhysReg(VirtReg); 888 ReusedOperands.markClobbered(VirtReg); 889 890 // Check to see if this instruction is a load from a stack slot into 891 // a register. If so, this provides the stack slot value in the reg. 892 int FrameIdx; 893 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) { 894 assert(DestReg == VirtReg && "Unknown load situation!"); 895 896 // Otherwise, if it wasn't available, remember that it is now! 897 Spills.addAvailable(FrameIdx, &MI, DestReg); 898 goto ProcessNextInst; 899 } 900 901 continue; 902 } 903 904 // The only vregs left are stack slot definitions. 905 int StackSlot = VRM.getStackSlot(VirtReg); 906 const TargetRegisterClass *RC = 907 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 908 909 // If this def is part of a two-address operand, make sure to execute 910 // the store from the correct physical register. 911 unsigned PhysReg; 912 int TiedOp = MI.getInstrDescriptor()->findTiedToSrcOperand(i); 913 if (TiedOp != -1) 914 PhysReg = MI.getOperand(TiedOp).getReg(); 915 else { 916 PhysReg = VRM.getPhys(VirtReg); 917 if (ReusedOperands.isClobbered(PhysReg)) { 918 // Another def has taken the assigned physreg. It must have been a 919 // use&def which got it due to reuse. Undo the reuse! 920 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI, 921 Spills, MaybeDeadStores); 922 } 923 } 924 925 PhysRegsUsed[PhysReg] = true; 926 ReusedOperands.markClobbered(PhysReg); 927 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC); 928 DOUT << "Store:\t" << *next(MII); 929 MI.getOperand(i).setReg(PhysReg); 930 931 // If there is a dead store to this stack slot, nuke it now. 932 MachineInstr *&LastStore = MaybeDeadStores[StackSlot]; 933 if (LastStore) { 934 DOUT << "Removed dead store:\t" << *LastStore; 935 ++NumDSE; 936 MBB.erase(LastStore); 937 VRM.RemoveFromFoldedVirtMap(LastStore); 938 } 939 LastStore = next(MII); 940 941 // If the stack slot value was previously available in some other 942 // register, change it now. Otherwise, make the register available, 943 // in PhysReg. 944 Spills.ModifyStackSlot(StackSlot); 945 Spills.ClobberPhysReg(PhysReg); 946 Spills.addAvailable(StackSlot, LastStore, PhysReg); 947 ++NumStores; 948 949 // Check to see if this is a noop copy. If so, eliminate the 950 // instruction before considering the dest reg to be changed. 951 { 952 unsigned Src, Dst; 953 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) { 954 ++NumDCE; 955 DOUT << "Removing now-noop copy: " << MI; 956 MBB.erase(&MI); 957 VRM.RemoveFromFoldedVirtMap(&MI); 958 goto ProcessNextInst; 959 } 960 } 961 } 962 } 963 ProcessNextInst: 964 MII = NextMII; 965 } 966} 967 968 969 970llvm::Spiller* llvm::createSpiller() { 971 switch (SpillerOpt) { 972 default: assert(0 && "Unreachable!"); 973 case local: 974 return new LocalSpiller(); 975 case simple: 976 return new SimpleSpiller(); 977 } 978} 979