VirtRegMap.cpp revision cc22a7a2adfea3fc318a6d8ca0c692a8e892105b
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/Statistic.h" 31#include "llvm/ADT/STLExtras.h" 32#include <algorithm> 33using namespace llvm; 34 35namespace { 36 static Statistic NumSpills("spiller", "Number of register spills"); 37 static Statistic NumStores("spiller", "Number of stores added"); 38 static Statistic NumLoads ("spiller", "Number of loads added"); 39 static Statistic NumReused("spiller", "Number of values reused"); 40 static Statistic NumDSE ("spiller", "Number of dead stores elided"); 41 static Statistic NumDCE ("spiller", "Number of copies elided"); 42 43 enum SpillerName { simple, local }; 44 45 static cl::opt<SpillerName> 46 SpillerOpt("spiller", 47 cl::desc("Spiller to use: (default: local)"), 48 cl::Prefix, 49 cl::values(clEnumVal(simple, " simple spiller"), 50 clEnumVal(local, " local spiller"), 51 clEnumValEnd), 52 cl::init(local)); 53} 54 55//===----------------------------------------------------------------------===// 56// VirtRegMap implementation 57//===----------------------------------------------------------------------===// 58 59VirtRegMap::VirtRegMap(MachineFunction &mf) 60 : TII(*mf.getTarget().getInstrInfo()), MF(mf), 61 Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT) { 62 grow(); 63} 64 65void VirtRegMap::grow() { 66 Virt2PhysMap.grow(MF.getSSARegMap()->getLastVirtReg()); 67 Virt2StackSlotMap.grow(MF.getSSARegMap()->getLastVirtReg()); 68} 69 70int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) { 71 assert(MRegisterInfo::isVirtualRegister(virtReg)); 72 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && 73 "attempt to assign stack slot to already spilled register"); 74 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg); 75 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(), 76 RC->getAlignment()); 77 Virt2StackSlotMap[virtReg] = frameIndex; 78 ++NumSpills; 79 return frameIndex; 80} 81 82void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) { 83 assert(MRegisterInfo::isVirtualRegister(virtReg)); 84 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && 85 "attempt to assign stack slot to already spilled register"); 86 Virt2StackSlotMap[virtReg] = frameIndex; 87} 88 89void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI, 90 unsigned OpNo, MachineInstr *NewMI) { 91 // Move previous memory references folded to new instruction. 92 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI); 93 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI), 94 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) { 95 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second)); 96 MI2VirtMap.erase(I++); 97 } 98 99 ModRef MRInfo; 100 const TargetInstrDescriptor *TID = OldMI->getInstrDescriptor(); 101 if (TID->getOperandConstraint(OpNo, TOI::TIED_TO) != -1 || 102 TID->findTiedToSrcOperand(OpNo) != -1) { 103 // Folded a two-address operand. 104 MRInfo = isModRef; 105 } else if (OldMI->getOperand(OpNo).isDef()) { 106 MRInfo = isMod; 107 } else { 108 MRInfo = isRef; 109 } 110 111 // add new memory reference 112 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo))); 113} 114 115void VirtRegMap::print(std::ostream &OS) const { 116 OStream LOS(OS); 117 print(LOS); 118} 119 120void VirtRegMap::print(OStream &OS) const { 121 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo(); 122 123 OS << "********** REGISTER MAP **********\n"; 124 for (unsigned i = MRegisterInfo::FirstVirtualRegister, 125 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) { 126 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG) 127 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n"; 128 129 } 130 131 for (unsigned i = MRegisterInfo::FirstVirtualRegister, 132 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) 133 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT) 134 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n"; 135 OS << '\n'; 136} 137 138void VirtRegMap::dump() const { 139 OStream OS = DOUT; 140 print(OS); 141} 142 143 144//===----------------------------------------------------------------------===// 145// Simple Spiller Implementation 146//===----------------------------------------------------------------------===// 147 148Spiller::~Spiller() {} 149 150namespace { 151 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller { 152 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM); 153 }; 154} 155 156bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) { 157 DOUT << "********** REWRITE MACHINE CODE **********\n"; 158 DOUT << "********** Function: " << MF.getFunction()->getName() << '\n'; 159 const TargetMachine &TM = MF.getTarget(); 160 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 161 bool *PhysRegsUsed = MF.getUsedPhysregs(); 162 163 // LoadedRegs - Keep track of which vregs are loaded, so that we only load 164 // each vreg once (in the case where a spilled vreg is used by multiple 165 // operands). This is always smaller than the number of operands to the 166 // current machine instr, so it should be small. 167 std::vector<unsigned> LoadedRegs; 168 169 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end(); 170 MBBI != E; ++MBBI) { 171 DOUT << MBBI->getBasicBlock()->getName() << ":\n"; 172 MachineBasicBlock &MBB = *MBBI; 173 for (MachineBasicBlock::iterator MII = MBB.begin(), 174 E = MBB.end(); MII != E; ++MII) { 175 MachineInstr &MI = *MII; 176 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 177 MachineOperand &MO = MI.getOperand(i); 178 if (MO.isRegister() && MO.getReg()) 179 if (MRegisterInfo::isVirtualRegister(MO.getReg())) { 180 unsigned VirtReg = MO.getReg(); 181 unsigned PhysReg = VRM.getPhys(VirtReg); 182 if (VRM.hasStackSlot(VirtReg)) { 183 int StackSlot = VRM.getStackSlot(VirtReg); 184 const TargetRegisterClass* RC = 185 MF.getSSARegMap()->getRegClass(VirtReg); 186 187 if (MO.isUse() && 188 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg) 189 == LoadedRegs.end()) { 190 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC); 191 LoadedRegs.push_back(VirtReg); 192 ++NumLoads; 193 DOUT << '\t' << *prior(MII); 194 } 195 196 if (MO.isDef()) { 197 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC); 198 ++NumStores; 199 } 200 } 201 PhysRegsUsed[PhysReg] = true; 202 MI.getOperand(i).setReg(PhysReg); 203 } else { 204 PhysRegsUsed[MO.getReg()] = true; 205 } 206 } 207 208 DOUT << '\t' << MI; 209 LoadedRegs.clear(); 210 } 211 } 212 return true; 213} 214 215//===----------------------------------------------------------------------===// 216// Local Spiller Implementation 217//===----------------------------------------------------------------------===// 218 219namespace { 220 /// LocalSpiller - This spiller does a simple pass over the machine basic 221 /// block to attempt to keep spills in registers as much as possible for 222 /// blocks that have low register pressure (the vreg may be spilled due to 223 /// register pressure in other blocks). 224 class VISIBILITY_HIDDEN LocalSpiller : public Spiller { 225 const MRegisterInfo *MRI; 226 const TargetInstrInfo *TII; 227 public: 228 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) { 229 MRI = MF.getTarget().getRegisterInfo(); 230 TII = MF.getTarget().getInstrInfo(); 231 DOUT << "\n**** Local spiller rewriting function '" 232 << MF.getFunction()->getName() << "':\n"; 233 234 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end(); 235 MBB != E; ++MBB) 236 RewriteMBB(*MBB, VRM); 237 return true; 238 } 239 private: 240 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM); 241 void ClobberPhysReg(unsigned PR, std::map<int, unsigned> &SpillSlots, 242 std::multimap<unsigned, int> &PhysRegs); 243 void ClobberPhysRegOnly(unsigned PR, std::map<int, unsigned> &SpillSlots, 244 std::multimap<unsigned, int> &PhysRegs); 245 void ModifyStackSlot(int Slot, std::map<int, unsigned> &SpillSlots, 246 std::multimap<unsigned, int> &PhysRegs); 247 }; 248} 249 250/// AvailableSpills - As the local spiller is scanning and rewriting an MBB from 251/// top down, keep track of which spills slots are available in each register. 252/// 253/// Note that not all physregs are created equal here. In particular, some 254/// physregs are reloads that we are allowed to clobber or ignore at any time. 255/// Other physregs are values that the register allocated program is using that 256/// we cannot CHANGE, but we can read if we like. We keep track of this on a 257/// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable 258/// entries. The predicate 'canClobberPhysReg()' checks this bit and 259/// addAvailable sets it if. 260namespace { 261class VISIBILITY_HIDDEN AvailableSpills { 262 const MRegisterInfo *MRI; 263 const TargetInstrInfo *TII; 264 265 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual 266 // register values that are still available, due to being loaded or stored to, 267 // but not invalidated yet. 268 std::map<int, unsigned> SpillSlotsAvailable; 269 270 // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating 271 // which stack slot values are currently held by a physreg. This is used to 272 // invalidate entries in SpillSlotsAvailable when a physreg is modified. 273 std::multimap<unsigned, int> PhysRegsAvailable; 274 275 void ClobberPhysRegOnly(unsigned PhysReg); 276public: 277 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii) 278 : MRI(mri), TII(tii) { 279 } 280 281 /// getSpillSlotPhysReg - If the specified stack slot is available in a 282 /// physical register, return that PhysReg, otherwise return 0. 283 unsigned getSpillSlotPhysReg(int Slot) const { 284 std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot); 285 if (I != SpillSlotsAvailable.end()) 286 return I->second >> 1; // Remove the CanClobber bit. 287 return 0; 288 } 289 290 const MRegisterInfo *getRegInfo() const { return MRI; } 291 292 /// addAvailable - Mark that the specified stack slot is available in the 293 /// specified physreg. If CanClobber is true, the physreg can be modified at 294 /// any time without changing the semantics of the program. 295 void addAvailable(int Slot, unsigned Reg, bool CanClobber = true) { 296 // If this stack slot is thought to be available in some other physreg, 297 // remove its record. 298 ModifyStackSlot(Slot); 299 300 PhysRegsAvailable.insert(std::make_pair(Reg, Slot)); 301 SpillSlotsAvailable[Slot] = (Reg << 1) | (unsigned)CanClobber; 302 303 DOUT << "Remembering SS#" << Slot << " in physreg " 304 << MRI->getName(Reg) << "\n"; 305 } 306 307 /// canClobberPhysReg - Return true if the spiller is allowed to change the 308 /// value of the specified stackslot register if it desires. The specified 309 /// stack slot must be available in a physreg for this query to make sense. 310 bool canClobberPhysReg(int Slot) const { 311 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!"); 312 return SpillSlotsAvailable.find(Slot)->second & 1; 313 } 314 315 /// ClobberPhysReg - This is called when the specified physreg changes 316 /// value. We use this to invalidate any info about stuff we thing lives in 317 /// it and any of its aliases. 318 void ClobberPhysReg(unsigned PhysReg); 319 320 /// ModifyStackSlot - This method is called when the value in a stack slot 321 /// changes. This removes information about which register the previous value 322 /// for this slot lives in (as the previous value is dead now). 323 void ModifyStackSlot(int Slot); 324}; 325} 326 327/// ClobberPhysRegOnly - This is called when the specified physreg changes 328/// value. We use this to invalidate any info about stuff we thing lives in it. 329void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) { 330 std::multimap<unsigned, int>::iterator I = 331 PhysRegsAvailable.lower_bound(PhysReg); 332 while (I != PhysRegsAvailable.end() && I->first == PhysReg) { 333 int Slot = I->second; 334 PhysRegsAvailable.erase(I++); 335 assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg && 336 "Bidirectional map mismatch!"); 337 SpillSlotsAvailable.erase(Slot); 338 DOUT << "PhysReg " << MRI->getName(PhysReg) 339 << " clobbered, invalidating SS#" << Slot << "\n"; 340 } 341} 342 343/// ClobberPhysReg - This is called when the specified physreg changes 344/// value. We use this to invalidate any info about stuff we thing lives in 345/// it and any of its aliases. 346void AvailableSpills::ClobberPhysReg(unsigned PhysReg) { 347 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS) 348 ClobberPhysRegOnly(*AS); 349 ClobberPhysRegOnly(PhysReg); 350} 351 352/// ModifyStackSlot - This method is called when the value in a stack slot 353/// changes. This removes information about which register the previous value 354/// for this slot lives in (as the previous value is dead now). 355void AvailableSpills::ModifyStackSlot(int Slot) { 356 std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot); 357 if (It == SpillSlotsAvailable.end()) return; 358 unsigned Reg = It->second >> 1; 359 SpillSlotsAvailable.erase(It); 360 361 // This register may hold the value of multiple stack slots, only remove this 362 // stack slot from the set of values the register contains. 363 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg); 364 for (; ; ++I) { 365 assert(I != PhysRegsAvailable.end() && I->first == Reg && 366 "Map inverse broken!"); 367 if (I->second == Slot) break; 368 } 369 PhysRegsAvailable.erase(I); 370} 371 372 373 374// ReusedOp - For each reused operand, we keep track of a bit of information, in 375// case we need to rollback upon processing a new operand. See comments below. 376namespace { 377 struct ReusedOp { 378 // The MachineInstr operand that reused an available value. 379 unsigned Operand; 380 381 // StackSlot - The spill slot of the value being reused. 382 unsigned StackSlot; 383 384 // PhysRegReused - The physical register the value was available in. 385 unsigned PhysRegReused; 386 387 // AssignedPhysReg - The physreg that was assigned for use by the reload. 388 unsigned AssignedPhysReg; 389 390 // VirtReg - The virtual register itself. 391 unsigned VirtReg; 392 393 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr, 394 unsigned vreg) 395 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr), 396 VirtReg(vreg) {} 397 }; 398 399 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that 400 /// is reused instead of reloaded. 401 class VISIBILITY_HIDDEN ReuseInfo { 402 MachineInstr &MI; 403 std::vector<ReusedOp> Reuses; 404 bool *PhysRegsClobbered; 405 public: 406 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) { 407 PhysRegsClobbered = new bool[mri->getNumRegs()]; 408 std::fill(PhysRegsClobbered, PhysRegsClobbered+mri->getNumRegs(), false); 409 } 410 ~ReuseInfo() { 411 delete[] PhysRegsClobbered; 412 } 413 414 bool hasReuses() const { 415 return !Reuses.empty(); 416 } 417 418 /// addReuse - If we choose to reuse a virtual register that is already 419 /// available instead of reloading it, remember that we did so. 420 void addReuse(unsigned OpNo, unsigned StackSlot, 421 unsigned PhysRegReused, unsigned AssignedPhysReg, 422 unsigned VirtReg) { 423 // If the reload is to the assigned register anyway, no undo will be 424 // required. 425 if (PhysRegReused == AssignedPhysReg) return; 426 427 // Otherwise, remember this. 428 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused, 429 AssignedPhysReg, VirtReg)); 430 } 431 432 void markClobbered(unsigned PhysReg) { 433 PhysRegsClobbered[PhysReg] = true; 434 } 435 436 bool isClobbered(unsigned PhysReg) const { 437 return PhysRegsClobbered[PhysReg]; 438 } 439 440 /// GetRegForReload - We are about to emit a reload into PhysReg. If there 441 /// is some other operand that is using the specified register, either pick 442 /// a new register to use, or evict the previous reload and use this reg. 443 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI, 444 AvailableSpills &Spills, 445 std::map<int, MachineInstr*> &MaybeDeadStores) { 446 if (Reuses.empty()) return PhysReg; // This is most often empty. 447 448 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) { 449 ReusedOp &Op = Reuses[ro]; 450 // If we find some other reuse that was supposed to use this register 451 // exactly for its reload, we can change this reload to use ITS reload 452 // register. 453 if (Op.PhysRegReused == PhysReg) { 454 // Yup, use the reload register that we didn't use before. 455 unsigned NewReg = Op.AssignedPhysReg; 456 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores); 457 } else { 458 // Otherwise, we might also have a problem if a previously reused 459 // value aliases the new register. If so, codegen the previous reload 460 // and use this one. 461 unsigned PRRU = Op.PhysRegReused; 462 const MRegisterInfo *MRI = Spills.getRegInfo(); 463 if (MRI->areAliases(PRRU, PhysReg)) { 464 // Okay, we found out that an alias of a reused register 465 // was used. This isn't good because it means we have 466 // to undo a previous reuse. 467 MachineBasicBlock *MBB = MI->getParent(); 468 const TargetRegisterClass *AliasRC = 469 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg); 470 471 // Copy Op out of the vector and remove it, we're going to insert an 472 // explicit load for it. 473 ReusedOp NewOp = Op; 474 Reuses.erase(Reuses.begin()+ro); 475 476 // Ok, we're going to try to reload the assigned physreg into the 477 // slot that we were supposed to in the first place. However, that 478 // register could hold a reuse. Check to see if it conflicts or 479 // would prefer us to use a different register. 480 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg, 481 MI, Spills, MaybeDeadStores); 482 483 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg, 484 NewOp.StackSlot, AliasRC); 485 Spills.ClobberPhysReg(NewPhysReg); 486 Spills.ClobberPhysReg(NewOp.PhysRegReused); 487 488 // Any stores to this stack slot are not dead anymore. 489 MaybeDeadStores.erase(NewOp.StackSlot); 490 491 MI->getOperand(NewOp.Operand).setReg(NewPhysReg); 492 493 Spills.addAvailable(NewOp.StackSlot, NewPhysReg); 494 ++NumLoads; 495 DEBUG(MachineBasicBlock::iterator MII = MI; 496 DOUT << '\t' << *prior(MII)); 497 498 DOUT << "Reuse undone!\n"; 499 --NumReused; 500 501 // Finally, PhysReg is now available, go ahead and use it. 502 return PhysReg; 503 } 504 } 505 } 506 return PhysReg; 507 } 508 }; 509} 510 511 512/// rewriteMBB - Keep track of which spills are available even after the 513/// register allocator is done with them. If possible, avoid reloading vregs. 514void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) { 515 516 DOUT << MBB.getBasicBlock()->getName() << ":\n"; 517 518 // Spills - Keep track of which spilled values are available in physregs so 519 // that we can choose to reuse the physregs instead of emitting reloads. 520 AvailableSpills Spills(MRI, TII); 521 522 // MaybeDeadStores - When we need to write a value back into a stack slot, 523 // keep track of the inserted store. If the stack slot value is never read 524 // (because the value was used from some available register, for example), and 525 // subsequently stored to, the original store is dead. This map keeps track 526 // of inserted stores that are not used. If we see a subsequent store to the 527 // same stack slot, the original store is deleted. 528 std::map<int, MachineInstr*> MaybeDeadStores; 529 530 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs(); 531 532 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end(); 533 MII != E; ) { 534 MachineInstr &MI = *MII; 535 MachineBasicBlock::iterator NextMII = MII; ++NextMII; 536 537 /// ReusedOperands - Keep track of operand reuse in case we need to undo 538 /// reuse. 539 ReuseInfo ReusedOperands(MI, MRI); 540 541 // Loop over all of the implicit defs, clearing them from our available 542 // sets. 543 const unsigned *ImpDef = TII->getImplicitDefs(MI.getOpcode()); 544 if (ImpDef) { 545 for ( ; *ImpDef; ++ImpDef) { 546 PhysRegsUsed[*ImpDef] = true; 547 ReusedOperands.markClobbered(*ImpDef); 548 Spills.ClobberPhysReg(*ImpDef); 549 } 550 } 551 552 // Process all of the spilled uses and all non spilled reg references. 553 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 554 MachineOperand &MO = MI.getOperand(i); 555 if (!MO.isRegister() || MO.getReg() == 0) 556 continue; // Ignore non-register operands. 557 558 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) { 559 // Ignore physregs for spilling, but remember that it is used by this 560 // function. 561 PhysRegsUsed[MO.getReg()] = true; 562 ReusedOperands.markClobbered(MO.getReg()); 563 continue; 564 } 565 566 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) && 567 "Not a virtual or a physical register?"); 568 569 unsigned VirtReg = MO.getReg(); 570 if (!VRM.hasStackSlot(VirtReg)) { 571 // This virtual register was assigned a physreg! 572 unsigned Phys = VRM.getPhys(VirtReg); 573 PhysRegsUsed[Phys] = true; 574 if (MO.isDef()) 575 ReusedOperands.markClobbered(Phys); 576 MI.getOperand(i).setReg(Phys); 577 continue; 578 } 579 580 // This virtual register is now known to be a spilled value. 581 if (!MO.isUse()) 582 continue; // Handle defs in the loop below (handle use&def here though) 583 584 int StackSlot = VRM.getStackSlot(VirtReg); 585 unsigned PhysReg; 586 587 // Check to see if this stack slot is available. 588 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) { 589 590 // This spilled operand might be part of a two-address operand. If this 591 // is the case, then changing it will necessarily require changing the 592 // def part of the instruction as well. However, in some cases, we 593 // aren't allowed to modify the reused register. If none of these cases 594 // apply, reuse it. 595 bool CanReuse = true; 596 int ti = MI.getInstrDescriptor()->getOperandConstraint(i, TOI::TIED_TO); 597 if (ti != -1 && 598 MI.getOperand(ti).isReg() && 599 MI.getOperand(ti).getReg() == VirtReg) { 600 // Okay, we have a two address operand. We can reuse this physreg as 601 // long as we are allowed to clobber the value and there is an earlier 602 // def that has already clobbered the physreg. 603 CanReuse = Spills.canClobberPhysReg(StackSlot) && 604 !ReusedOperands.isClobbered(PhysReg); 605 } 606 607 if (CanReuse) { 608 // If this stack slot value is already available, reuse it! 609 DOUT << "Reusing SS#" << StackSlot << " from physreg " 610 << MRI->getName(PhysReg) << " for vreg" 611 << VirtReg <<" instead of reloading into physreg " 612 << MRI->getName(VRM.getPhys(VirtReg)) << "\n"; 613 MI.getOperand(i).setReg(PhysReg); 614 615 // The only technical detail we have is that we don't know that 616 // PhysReg won't be clobbered by a reloaded stack slot that occurs 617 // later in the instruction. In particular, consider 'op V1, V2'. 618 // If V1 is available in physreg R0, we would choose to reuse it 619 // here, instead of reloading it into the register the allocator 620 // indicated (say R1). However, V2 might have to be reloaded 621 // later, and it might indicate that it needs to live in R0. When 622 // this occurs, we need to have information available that 623 // indicates it is safe to use R1 for the reload instead of R0. 624 // 625 // To further complicate matters, we might conflict with an alias, 626 // or R0 and R1 might not be compatible with each other. In this 627 // case, we actually insert a reload for V1 in R1, ensuring that 628 // we can get at R0 or its alias. 629 ReusedOperands.addReuse(i, StackSlot, PhysReg, 630 VRM.getPhys(VirtReg), VirtReg); 631 if (ti != -1) 632 // Only mark it clobbered if this is a use&def operand. 633 ReusedOperands.markClobbered(PhysReg); 634 ++NumReused; 635 continue; 636 } 637 638 // Otherwise we have a situation where we have a two-address instruction 639 // whose mod/ref operand needs to be reloaded. This reload is already 640 // available in some register "PhysReg", but if we used PhysReg as the 641 // operand to our 2-addr instruction, the instruction would modify 642 // PhysReg. This isn't cool if something later uses PhysReg and expects 643 // to get its initial value. 644 // 645 // To avoid this problem, and to avoid doing a load right after a store, 646 // we emit a copy from PhysReg into the designated register for this 647 // operand. 648 unsigned DesignatedReg = VRM.getPhys(VirtReg); 649 assert(DesignatedReg && "Must map virtreg to physreg!"); 650 651 // Note that, if we reused a register for a previous operand, the 652 // register we want to reload into might not actually be 653 // available. If this occurs, use the register indicated by the 654 // reuser. 655 if (ReusedOperands.hasReuses()) 656 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI, 657 Spills, MaybeDeadStores); 658 659 // If the mapped designated register is actually the physreg we have 660 // incoming, we don't need to inserted a dead copy. 661 if (DesignatedReg == PhysReg) { 662 // If this stack slot value is already available, reuse it! 663 DOUT << "Reusing SS#" << StackSlot << " from physreg " 664 << MRI->getName(PhysReg) << " for vreg" 665 << VirtReg 666 << " instead of reloading into same physreg.\n"; 667 MI.getOperand(i).setReg(PhysReg); 668 ReusedOperands.markClobbered(PhysReg); 669 ++NumReused; 670 continue; 671 } 672 673 const TargetRegisterClass* RC = 674 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 675 676 PhysRegsUsed[DesignatedReg] = true; 677 ReusedOperands.markClobbered(DesignatedReg); 678 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC); 679 680 // This invalidates DesignatedReg. 681 Spills.ClobberPhysReg(DesignatedReg); 682 683 Spills.addAvailable(StackSlot, DesignatedReg); 684 MI.getOperand(i).setReg(DesignatedReg); 685 DOUT << '\t' << *prior(MII); 686 ++NumReused; 687 continue; 688 } 689 690 // Otherwise, reload it and remember that we have it. 691 PhysReg = VRM.getPhys(VirtReg); 692 assert(PhysReg && "Must map virtreg to physreg!"); 693 const TargetRegisterClass* RC = 694 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 695 696 // Note that, if we reused a register for a previous operand, the 697 // register we want to reload into might not actually be 698 // available. If this occurs, use the register indicated by the 699 // reuser. 700 if (ReusedOperands.hasReuses()) 701 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI, 702 Spills, MaybeDeadStores); 703 704 PhysRegsUsed[PhysReg] = true; 705 ReusedOperands.markClobbered(PhysReg); 706 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC); 707 // This invalidates PhysReg. 708 Spills.ClobberPhysReg(PhysReg); 709 710 // Any stores to this stack slot are not dead anymore. 711 MaybeDeadStores.erase(StackSlot); 712 Spills.addAvailable(StackSlot, PhysReg); 713 ++NumLoads; 714 MI.getOperand(i).setReg(PhysReg); 715 DOUT << '\t' << *prior(MII); 716 } 717 718 DOUT << '\t' << MI; 719 720 // If we have folded references to memory operands, make sure we clear all 721 // physical registers that may contain the value of the spilled virtual 722 // register 723 VirtRegMap::MI2VirtMapTy::const_iterator I, End; 724 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) { 725 DOUT << "Folded vreg: " << I->second.first << " MR: " 726 << I->second.second; 727 unsigned VirtReg = I->second.first; 728 VirtRegMap::ModRef MR = I->second.second; 729 if (!VRM.hasStackSlot(VirtReg)) { 730 DOUT << ": No stack slot!\n"; 731 continue; 732 } 733 int SS = VRM.getStackSlot(VirtReg); 734 DOUT << " - StackSlot: " << SS << "\n"; 735 736 // If this folded instruction is just a use, check to see if it's a 737 // straight load from the virt reg slot. 738 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) { 739 int FrameIdx; 740 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) { 741 if (FrameIdx == SS) { 742 // If this spill slot is available, turn it into a copy (or nothing) 743 // instead of leaving it as a load! 744 if (unsigned InReg = Spills.getSpillSlotPhysReg(SS)) { 745 DOUT << "Promoted Load To Copy: " << MI; 746 MachineFunction &MF = *MBB.getParent(); 747 if (DestReg != InReg) { 748 MRI->copyRegToReg(MBB, &MI, DestReg, InReg, 749 MF.getSSARegMap()->getRegClass(VirtReg)); 750 // Revisit the copy so we make sure to notice the effects of the 751 // operation on the destreg (either needing to RA it if it's 752 // virtual or needing to clobber any values if it's physical). 753 NextMII = &MI; 754 --NextMII; // backtrack to the copy. 755 } 756 VRM.RemoveFromFoldedVirtMap(&MI); 757 MBB.erase(&MI); 758 goto ProcessNextInst; 759 } 760 } 761 } 762 } 763 764 // If this reference is not a use, any previous store is now dead. 765 // Otherwise, the store to this stack slot is not dead anymore. 766 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS); 767 if (MDSI != MaybeDeadStores.end()) { 768 if (MR & VirtRegMap::isRef) // Previous store is not dead. 769 MaybeDeadStores.erase(MDSI); 770 else { 771 // If we get here, the store is dead, nuke it now. 772 assert(VirtRegMap::isMod && "Can't be modref!"); 773 DOUT << "Removed dead store:\t" << *MDSI->second; 774 MBB.erase(MDSI->second); 775 VRM.RemoveFromFoldedVirtMap(MDSI->second); 776 MaybeDeadStores.erase(MDSI); 777 ++NumDSE; 778 } 779 } 780 781 // If the spill slot value is available, and this is a new definition of 782 // the value, the value is not available anymore. 783 if (MR & VirtRegMap::isMod) { 784 // Notice that the value in this stack slot has been modified. 785 Spills.ModifyStackSlot(SS); 786 787 // If this is *just* a mod of the value, check to see if this is just a 788 // store to the spill slot (i.e. the spill got merged into the copy). If 789 // so, realize that the vreg is available now, and add the store to the 790 // MaybeDeadStore info. 791 int StackSlot; 792 if (!(MR & VirtRegMap::isRef)) { 793 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) { 794 assert(MRegisterInfo::isPhysicalRegister(SrcReg) && 795 "Src hasn't been allocated yet?"); 796 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark 797 // this as a potentially dead store in case there is a subsequent 798 // store into the stack slot without a read from it. 799 MaybeDeadStores[StackSlot] = &MI; 800 801 // If the stack slot value was previously available in some other 802 // register, change it now. Otherwise, make the register available, 803 // in PhysReg. 804 Spills.addAvailable(StackSlot, SrcReg, false /*don't clobber*/); 805 } 806 } 807 } 808 } 809 810 // Process all of the spilled defs. 811 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 812 MachineOperand &MO = MI.getOperand(i); 813 if (MO.isRegister() && MO.getReg() && MO.isDef()) { 814 unsigned VirtReg = MO.getReg(); 815 816 if (!MRegisterInfo::isVirtualRegister(VirtReg)) { 817 // Check to see if this is a noop copy. If so, eliminate the 818 // instruction before considering the dest reg to be changed. 819 unsigned Src, Dst; 820 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) { 821 ++NumDCE; 822 DOUT << "Removing now-noop copy: " << MI; 823 MBB.erase(&MI); 824 VRM.RemoveFromFoldedVirtMap(&MI); 825 goto ProcessNextInst; 826 } 827 828 // If it's not a no-op copy, it clobbers the value in the destreg. 829 Spills.ClobberPhysReg(VirtReg); 830 ReusedOperands.markClobbered(VirtReg); 831 832 // Check to see if this instruction is a load from a stack slot into 833 // a register. If so, this provides the stack slot value in the reg. 834 int FrameIdx; 835 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) { 836 assert(DestReg == VirtReg && "Unknown load situation!"); 837 838 // Otherwise, if it wasn't available, remember that it is now! 839 Spills.addAvailable(FrameIdx, DestReg); 840 goto ProcessNextInst; 841 } 842 843 continue; 844 } 845 846 // The only vregs left are stack slot definitions. 847 int StackSlot = VRM.getStackSlot(VirtReg); 848 const TargetRegisterClass *RC = 849 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 850 851 // If this def is part of a two-address operand, make sure to execute 852 // the store from the correct physical register. 853 unsigned PhysReg; 854 int TiedOp = MI.getInstrDescriptor()->findTiedToSrcOperand(i); 855 if (TiedOp != -1) 856 PhysReg = MI.getOperand(TiedOp).getReg(); 857 else { 858 PhysReg = VRM.getPhys(VirtReg); 859 if (ReusedOperands.isClobbered(PhysReg)) { 860 // Another def has taken the assigned physreg. It must have been a 861 // use&def which got it due to reuse. Undo the reuse! 862 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI, 863 Spills, MaybeDeadStores); 864 } 865 } 866 867 PhysRegsUsed[PhysReg] = true; 868 ReusedOperands.markClobbered(PhysReg); 869 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC); 870 DOUT << "Store:\t" << *next(MII); 871 MI.getOperand(i).setReg(PhysReg); 872 873 // Check to see if this is a noop copy. If so, eliminate the 874 // instruction before considering the dest reg to be changed. 875 { 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 goto ProcessNextInst; 883 } 884 } 885 886 // If there is a dead store to this stack slot, nuke it now. 887 MachineInstr *&LastStore = MaybeDeadStores[StackSlot]; 888 if (LastStore) { 889 DOUT << "Removed dead store:\t" << *LastStore; 890 ++NumDSE; 891 MBB.erase(LastStore); 892 VRM.RemoveFromFoldedVirtMap(LastStore); 893 } 894 LastStore = next(MII); 895 896 // If the stack slot value was previously available in some other 897 // register, change it now. Otherwise, make the register available, 898 // in PhysReg. 899 Spills.ModifyStackSlot(StackSlot); 900 Spills.ClobberPhysReg(PhysReg); 901 Spills.addAvailable(StackSlot, PhysReg); 902 ++NumStores; 903 } 904 } 905 ProcessNextInst: 906 MII = NextMII; 907 } 908} 909 910 911 912llvm::Spiller* llvm::createSpiller() { 913 switch (SpillerOpt) { 914 default: assert(0 && "Unreachable!"); 915 case local: 916 return new LocalSpiller(); 917 case simple: 918 return new SimpleSpiller(); 919 } 920} 921