VirtRegMap.cpp revision addc55af6c7f8b71eedd68d48f6a93ceecff2840
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/ADT/Statistic.h" 30#include "llvm/ADT/STLExtras.h" 31#include <algorithm> 32#include <iostream> 33using namespace llvm; 34 35namespace { 36 Statistic<> NumSpills("spiller", "Number of register spills"); 37 Statistic<> NumStores("spiller", "Number of stores added"); 38 Statistic<> NumLoads ("spiller", "Number of loads added"); 39 Statistic<> NumReused("spiller", "Number of values reused"); 40 Statistic<> NumDSE ("spiller", "Number of dead stores elided"); 41 Statistic<> NumDCE ("spiller", "Number of copies elided"); 42 43 enum SpillerName { simple, local }; 44 45 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 59void VirtRegMap::grow() { 60 Virt2PhysMap.grow(MF.getSSARegMap()->getLastVirtReg()); 61 Virt2StackSlotMap.grow(MF.getSSARegMap()->getLastVirtReg()); 62} 63 64int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) { 65 assert(MRegisterInfo::isVirtualRegister(virtReg)); 66 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && 67 "attempt to assign stack slot to already spilled register"); 68 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg); 69 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(), 70 RC->getAlignment()); 71 Virt2StackSlotMap[virtReg] = frameIndex; 72 ++NumSpills; 73 return frameIndex; 74} 75 76void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) { 77 assert(MRegisterInfo::isVirtualRegister(virtReg)); 78 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && 79 "attempt to assign stack slot to already spilled register"); 80 Virt2StackSlotMap[virtReg] = frameIndex; 81} 82 83void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI, 84 unsigned OpNo, MachineInstr *NewMI) { 85 // Move previous memory references folded to new instruction. 86 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI); 87 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI), 88 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) { 89 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second)); 90 MI2VirtMap.erase(I++); 91 } 92 93 ModRef MRInfo; 94 if (!OldMI->getOperand(OpNo).isDef()) { 95 assert(OldMI->getOperand(OpNo).isUse() && "Operand is not use or def?"); 96 MRInfo = isRef; 97 } else { 98 MRInfo = OldMI->getOperand(OpNo).isUse() ? isModRef : isMod; 99 } 100 101 // add new memory reference 102 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo))); 103} 104 105void VirtRegMap::print(std::ostream &OS) const { 106 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo(); 107 108 OS << "********** REGISTER MAP **********\n"; 109 for (unsigned i = MRegisterInfo::FirstVirtualRegister, 110 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) { 111 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG) 112 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n"; 113 114 } 115 116 for (unsigned i = MRegisterInfo::FirstVirtualRegister, 117 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) 118 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT) 119 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n"; 120 OS << '\n'; 121} 122 123void VirtRegMap::dump() const { print(std::cerr); } 124 125 126//===----------------------------------------------------------------------===// 127// Simple Spiller Implementation 128//===----------------------------------------------------------------------===// 129 130Spiller::~Spiller() {} 131 132namespace { 133 struct SimpleSpiller : public Spiller { 134 bool runOnMachineFunction(MachineFunction& mf, const VirtRegMap &VRM); 135 }; 136} 137 138bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, 139 const VirtRegMap &VRM) { 140 DEBUG(std::cerr << "********** REWRITE MACHINE CODE **********\n"); 141 DEBUG(std::cerr << "********** Function: " 142 << MF.getFunction()->getName() << '\n'); 143 const TargetMachine &TM = MF.getTarget(); 144 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 145 bool *PhysRegsUsed = MF.getUsedPhysregs(); 146 147 // LoadedRegs - Keep track of which vregs are loaded, so that we only load 148 // each vreg once (in the case where a spilled vreg is used by multiple 149 // operands). This is always smaller than the number of operands to the 150 // current machine instr, so it should be small. 151 std::vector<unsigned> LoadedRegs; 152 153 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end(); 154 MBBI != E; ++MBBI) { 155 DEBUG(std::cerr << MBBI->getBasicBlock()->getName() << ":\n"); 156 MachineBasicBlock &MBB = *MBBI; 157 for (MachineBasicBlock::iterator MII = MBB.begin(), 158 E = MBB.end(); MII != E; ++MII) { 159 MachineInstr &MI = *MII; 160 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 161 MachineOperand &MO = MI.getOperand(i); 162 if (MO.isRegister() && MO.getReg()) 163 if (MRegisterInfo::isVirtualRegister(MO.getReg())) { 164 unsigned VirtReg = MO.getReg(); 165 unsigned PhysReg = VRM.getPhys(VirtReg); 166 if (VRM.hasStackSlot(VirtReg)) { 167 int StackSlot = VRM.getStackSlot(VirtReg); 168 const TargetRegisterClass* RC = 169 MF.getSSARegMap()->getRegClass(VirtReg); 170 171 if (MO.isUse() && 172 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg) 173 == LoadedRegs.end()) { 174 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC); 175 LoadedRegs.push_back(VirtReg); 176 ++NumLoads; 177 DEBUG(std::cerr << '\t' << *prior(MII)); 178 } 179 180 if (MO.isDef()) { 181 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC); 182 ++NumStores; 183 } 184 } 185 PhysRegsUsed[PhysReg] = true; 186 MI.SetMachineOperandReg(i, PhysReg); 187 } else { 188 PhysRegsUsed[MO.getReg()] = true; 189 } 190 } 191 192 DEBUG(std::cerr << '\t' << MI); 193 LoadedRegs.clear(); 194 } 195 } 196 return true; 197} 198 199//===----------------------------------------------------------------------===// 200// Local Spiller Implementation 201//===----------------------------------------------------------------------===// 202 203namespace { 204 /// LocalSpiller - This spiller does a simple pass over the machine basic 205 /// block to attempt to keep spills in registers as much as possible for 206 /// blocks that have low register pressure (the vreg may be spilled due to 207 /// register pressure in other blocks). 208 class LocalSpiller : public Spiller { 209 const MRegisterInfo *MRI; 210 const TargetInstrInfo *TII; 211 public: 212 bool runOnMachineFunction(MachineFunction &MF, const VirtRegMap &VRM) { 213 MRI = MF.getTarget().getRegisterInfo(); 214 TII = MF.getTarget().getInstrInfo(); 215 DEBUG(std::cerr << "\n**** Local spiller rewriting function '" 216 << MF.getFunction()->getName() << "':\n"); 217 218 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end(); 219 MBB != E; ++MBB) 220 RewriteMBB(*MBB, VRM); 221 return true; 222 } 223 private: 224 void RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM); 225 void ClobberPhysReg(unsigned PR, std::map<int, unsigned> &SpillSlots, 226 std::multimap<unsigned, int> &PhysRegs); 227 void ClobberPhysRegOnly(unsigned PR, std::map<int, unsigned> &SpillSlots, 228 std::multimap<unsigned, int> &PhysRegs); 229 void ModifyStackSlot(int Slot, std::map<int, unsigned> &SpillSlots, 230 std::multimap<unsigned, int> &PhysRegs); 231 }; 232} 233 234/// AvailableSpills - As the local spiller is scanning and rewriting an MBB from 235/// top down, keep track of which spills slots are available in each register. 236/// 237/// Note that not all physregs are created equal here. In particular, some 238/// physregs are reloads that we are allowed to clobber or ignore at any time. 239/// Other physregs are values that the register allocated program is using that 240/// we cannot CHANGE, but we can read if we like. We keep track of this on a 241/// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable 242/// entries. The predicate 'canClobberPhysReg()' checks this bit and 243/// addAvailable sets it if. 244class AvailableSpills { 245 const MRegisterInfo *MRI; 246 const TargetInstrInfo *TII; 247 248 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual 249 // register values that are still available, due to being loaded or stored to, 250 // but not invalidated yet. 251 std::map<int, unsigned> SpillSlotsAvailable; 252 253 // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating 254 // which stack slot values are currently held by a physreg. This is used to 255 // invalidate entries in SpillSlotsAvailable when a physreg is modified. 256 std::multimap<unsigned, int> PhysRegsAvailable; 257 258 void ClobberPhysRegOnly(unsigned PhysReg); 259public: 260 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii) 261 : MRI(mri), TII(tii) { 262 } 263 264 /// getSpillSlotPhysReg - If the specified stack slot is available in a 265 /// physical register, return that PhysReg, otherwise return 0. 266 unsigned getSpillSlotPhysReg(int Slot) const { 267 std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot); 268 if (I != SpillSlotsAvailable.end()) 269 return I->second >> 1; // Remove the CanClobber bit. 270 return 0; 271 } 272 273 const MRegisterInfo *getRegInfo() const { return MRI; } 274 275 /// addAvailable - Mark that the specified stack slot is available in the 276 /// specified physreg. If CanClobber is true, the physreg can be modified at 277 /// any time without changing the semantics of the program. 278 void addAvailable(int Slot, unsigned Reg, bool CanClobber = true) { 279 // If this stack slot is thought to be available in some other physreg, 280 // remove its record. 281 ModifyStackSlot(Slot); 282 283 PhysRegsAvailable.insert(std::make_pair(Reg, Slot)); 284 SpillSlotsAvailable[Slot] = (Reg << 1) | (unsigned)CanClobber; 285 286 DEBUG(std::cerr << "Remembering SS#" << Slot << " in physreg " 287 << MRI->getName(Reg) << "\n"); 288 } 289 290 /// canClobberPhysReg - Return true if the spiller is allowed to change the 291 /// value of the specified stackslot register if it desires. The specified 292 /// stack slot must be available in a physreg for this query to make sense. 293 bool canClobberPhysReg(int Slot) const { 294 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!"); 295 return SpillSlotsAvailable.find(Slot)->second & 1; 296 } 297 298 /// ClobberPhysReg - This is called when the specified physreg changes 299 /// value. We use this to invalidate any info about stuff we thing lives in 300 /// it and any of its aliases. 301 void ClobberPhysReg(unsigned PhysReg); 302 303 /// ModifyStackSlot - This method is called when the value in a stack slot 304 /// changes. This removes information about which register the previous value 305 /// for this slot lives in (as the previous value is dead now). 306 void ModifyStackSlot(int Slot); 307}; 308 309/// ClobberPhysRegOnly - This is called when the specified physreg changes 310/// value. We use this to invalidate any info about stuff we thing lives in it. 311void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) { 312 std::multimap<unsigned, int>::iterator I = 313 PhysRegsAvailable.lower_bound(PhysReg); 314 while (I != PhysRegsAvailable.end() && I->first == PhysReg) { 315 int Slot = I->second; 316 PhysRegsAvailable.erase(I++); 317 assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg && 318 "Bidirectional map mismatch!"); 319 SpillSlotsAvailable.erase(Slot); 320 DEBUG(std::cerr << "PhysReg " << MRI->getName(PhysReg) 321 << " clobbered, invalidating SS#" << Slot << "\n"); 322 } 323} 324 325/// ClobberPhysReg - This is called when the specified physreg changes 326/// value. We use this to invalidate any info about stuff we thing lives in 327/// it and any of its aliases. 328void AvailableSpills::ClobberPhysReg(unsigned PhysReg) { 329 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS) 330 ClobberPhysRegOnly(*AS); 331 ClobberPhysRegOnly(PhysReg); 332} 333 334/// ModifyStackSlot - This method is called when the value in a stack slot 335/// changes. This removes information about which register the previous value 336/// for this slot lives in (as the previous value is dead now). 337void AvailableSpills::ModifyStackSlot(int Slot) { 338 std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot); 339 if (It == SpillSlotsAvailable.end()) return; 340 unsigned Reg = It->second >> 1; 341 SpillSlotsAvailable.erase(It); 342 343 // This register may hold the value of multiple stack slots, only remove this 344 // stack slot from the set of values the register contains. 345 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg); 346 for (; ; ++I) { 347 assert(I != PhysRegsAvailable.end() && I->first == Reg && 348 "Map inverse broken!"); 349 if (I->second == Slot) break; 350 } 351 PhysRegsAvailable.erase(I); 352} 353 354 355 356// ReusedOp - For each reused operand, we keep track of a bit of information, in 357// case we need to rollback upon processing a new operand. See comments below. 358namespace { 359 struct ReusedOp { 360 // The MachineInstr operand that reused an available value. 361 unsigned Operand; 362 363 // StackSlot - The spill slot of the value being reused. 364 unsigned StackSlot; 365 366 // PhysRegReused - The physical register the value was available in. 367 unsigned PhysRegReused; 368 369 // AssignedPhysReg - The physreg that was assigned for use by the reload. 370 unsigned AssignedPhysReg; 371 372 // VirtReg - The virtual register itself. 373 unsigned VirtReg; 374 375 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr, 376 unsigned vreg) 377 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr), 378 VirtReg(vreg) {} 379 }; 380 381 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that 382 /// is reused instead of reloaded. 383 class ReuseInfo { 384 MachineInstr &MI; 385 std::vector<ReusedOp> Reuses; 386 public: 387 ReuseInfo(MachineInstr &mi) : MI(mi) {} 388 389 bool hasReuses() const { 390 return !Reuses.empty(); 391 } 392 393 /// addReuse - If we choose to reuse a virtual register that is already 394 /// available instead of reloading it, remember that we did so. 395 void addReuse(unsigned OpNo, unsigned StackSlot, 396 unsigned PhysRegReused, unsigned AssignedPhysReg, 397 unsigned VirtReg) { 398 // If the reload is to the assigned register anyway, no undo will be 399 // required. 400 if (PhysRegReused == AssignedPhysReg) return; 401 402 // Otherwise, remember this. 403 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused, 404 AssignedPhysReg, VirtReg)); 405 } 406 407 /// GetRegForReload - We are about to emit a reload into PhysReg. If there 408 /// is some other operand that is using the specified register, either pick 409 /// a new register to use, or evict the previous reload and use this reg. 410 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI, 411 AvailableSpills &Spills, 412 std::map<int, MachineInstr*> &MaybeDeadStores) { 413 if (Reuses.empty()) return PhysReg; // This is most often empty. 414 415 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) { 416 ReusedOp &Op = Reuses[ro]; 417 // If we find some other reuse that was supposed to use this register 418 // exactly for its reload, we can change this reload to use ITS reload 419 // register. 420 if (Op.PhysRegReused == PhysReg) { 421 // Yup, use the reload register that we didn't use before. 422 unsigned NewReg = Op.AssignedPhysReg; 423 424 // Remove the record for the previous reuse. We know it can never be 425 // invalidated now. 426 Reuses.erase(Reuses.begin()+ro); 427 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores); 428 } else { 429 // Otherwise, we might also have a problem if a previously reused 430 // value aliases the new register. If so, codegen the previous reload 431 // and use this one. 432 unsigned PRRU = Op.PhysRegReused; 433 const MRegisterInfo *MRI = Spills.getRegInfo(); 434 if (MRI->areAliases(PRRU, PhysReg)) { 435 // Okay, we found out that an alias of a reused register 436 // was used. This isn't good because it means we have 437 // to undo a previous reuse. 438 MachineBasicBlock *MBB = MI->getParent(); 439 const TargetRegisterClass *AliasRC = 440 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg); 441 442 // Copy Op out of the vector and remove it, we're going to insert an 443 // explicit load for it. 444 ReusedOp NewOp = Op; 445 Reuses.erase(Reuses.begin()+ro); 446 447 // Ok, we're going to try to reload the assigned physreg into the 448 // slot that we were supposed to in the first place. However, that 449 // register could hold a reuse. Check to see if it conflicts or 450 // would prefer us to use a different register. 451 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg, 452 MI, Spills, MaybeDeadStores); 453 454 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg, 455 NewOp.StackSlot, AliasRC); 456 Spills.ClobberPhysReg(NewPhysReg); 457 Spills.ClobberPhysReg(NewOp.PhysRegReused); 458 459 // Any stores to this stack slot are not dead anymore. 460 MaybeDeadStores.erase(NewOp.StackSlot); 461 462 MI->SetMachineOperandReg(NewOp.Operand, NewPhysReg); 463 464 Spills.addAvailable(NewOp.StackSlot, NewPhysReg); 465 ++NumLoads; 466 DEBUG(MachineBasicBlock::iterator MII = MI; 467 std::cerr << '\t' << *prior(MII)); 468 469 DEBUG(std::cerr << "Reuse undone!\n"); 470 --NumReused; 471 472 // Finally, PhysReg is now available, go ahead and use it. 473 return PhysReg; 474 } 475 } 476 } 477 return PhysReg; 478 } 479 }; 480} 481 482 483/// rewriteMBB - Keep track of which spills are available even after the 484/// register allocator is done with them. If possible, avoid reloading vregs. 485void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, const VirtRegMap &VRM) { 486 487 DEBUG(std::cerr << MBB.getBasicBlock()->getName() << ":\n"); 488 489 // Spills - Keep track of which spilled values are available in physregs so 490 // that we can choose to reuse the physregs instead of emitting reloads. 491 AvailableSpills Spills(MRI, TII); 492 493 // DefAndUseVReg - When we see a def&use operand that is spilled, keep track 494 // of it. ".first" is the machine operand index (should always be 0 for now), 495 // and ".second" is the virtual register that is spilled. 496 std::vector<std::pair<unsigned, unsigned> > DefAndUseVReg; 497 498 // MaybeDeadStores - When we need to write a value back into a stack slot, 499 // keep track of the inserted store. If the stack slot value is never read 500 // (because the value was used from some available register, for example), and 501 // subsequently stored to, the original store is dead. This map keeps track 502 // of inserted stores that are not used. If we see a subsequent store to the 503 // same stack slot, the original store is deleted. 504 std::map<int, MachineInstr*> MaybeDeadStores; 505 506 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs(); 507 508 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end(); 509 MII != E; ) { 510 MachineInstr &MI = *MII; 511 MachineBasicBlock::iterator NextMII = MII; ++NextMII; 512 513 /// ReusedOperands - Keep track of operand reuse in case we need to undo 514 /// reuse. 515 ReuseInfo ReusedOperands(MI); 516 517 DefAndUseVReg.clear(); 518 519 // Process all of the spilled uses and all non spilled reg references. 520 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 521 MachineOperand &MO = MI.getOperand(i); 522 if (!MO.isRegister() || MO.getReg() == 0) 523 continue; // Ignore non-register operands. 524 525 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) { 526 // Ignore physregs for spilling, but remember that it is used by this 527 // function. 528 PhysRegsUsed[MO.getReg()] = true; 529 continue; 530 } 531 532 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) && 533 "Not a virtual or a physical register?"); 534 535 unsigned VirtReg = MO.getReg(); 536 if (!VRM.hasStackSlot(VirtReg)) { 537 // This virtual register was assigned a physreg! 538 unsigned Phys = VRM.getPhys(VirtReg); 539 PhysRegsUsed[Phys] = true; 540 MI.SetMachineOperandReg(i, Phys); 541 continue; 542 } 543 544 // This virtual register is now known to be a spilled value. 545 if (!MO.isUse()) 546 continue; // Handle defs in the loop below (handle use&def here though) 547 548 // If this is both a def and a use, we need to emit a store to the 549 // stack slot after the instruction. Keep track of D&U operands 550 // because we are about to change it to a physreg here. 551 if (MO.isDef()) { 552 // Remember that this was a def-and-use operand, and that the 553 // stack slot is live after this instruction executes. 554 DefAndUseVReg.push_back(std::make_pair(i, VirtReg)); 555 } 556 557 int StackSlot = VRM.getStackSlot(VirtReg); 558 unsigned PhysReg; 559 560 // Check to see if this stack slot is available. 561 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) { 562 563 // Don't reuse it for a def&use operand if we aren't allowed to change 564 // the physreg! 565 if (!MO.isDef() || Spills.canClobberPhysReg(StackSlot)) { 566 // If this stack slot value is already available, reuse it! 567 DEBUG(std::cerr << "Reusing SS#" << StackSlot << " from physreg " 568 << MRI->getName(PhysReg) << " for vreg" 569 << VirtReg <<" instead of reloading into physreg " 570 << MRI->getName(VRM.getPhys(VirtReg)) << "\n"); 571 MI.SetMachineOperandReg(i, PhysReg); 572 573 // The only technical detail we have is that we don't know that 574 // PhysReg won't be clobbered by a reloaded stack slot that occurs 575 // later in the instruction. In particular, consider 'op V1, V2'. 576 // If V1 is available in physreg R0, we would choose to reuse it 577 // here, instead of reloading it into the register the allocator 578 // indicated (say R1). However, V2 might have to be reloaded 579 // later, and it might indicate that it needs to live in R0. When 580 // this occurs, we need to have information available that 581 // indicates it is safe to use R1 for the reload instead of R0. 582 // 583 // To further complicate matters, we might conflict with an alias, 584 // or R0 and R1 might not be compatible with each other. In this 585 // case, we actually insert a reload for V1 in R1, ensuring that 586 // we can get at R0 or its alias. 587 ReusedOperands.addReuse(i, StackSlot, PhysReg, 588 VRM.getPhys(VirtReg), VirtReg); 589 ++NumReused; 590 continue; 591 } 592 593 // Otherwise we have a situation where we have a two-address instruction 594 // whose mod/ref operand needs to be reloaded. This reload is already 595 // available in some register "PhysReg", but if we used PhysReg as the 596 // operand to our 2-addr instruction, the instruction would modify 597 // PhysReg. This isn't cool if something later uses PhysReg and expects 598 // to get its initial value. 599 // 600 // To avoid this problem, and to avoid doing a load right after a store, 601 // we emit a copy from PhysReg into the designated register for this 602 // operand. 603 unsigned DesignatedReg = VRM.getPhys(VirtReg); 604 assert(DesignatedReg && "Must map virtreg to physreg!"); 605 606 // Note that, if we reused a register for a previous operand, the 607 // register we want to reload into might not actually be 608 // available. If this occurs, use the register indicated by the 609 // reuser. 610 if (ReusedOperands.hasReuses()) 611 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI, 612 Spills, MaybeDeadStores); 613 614 const TargetRegisterClass* RC = 615 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 616 617 PhysRegsUsed[DesignatedReg] = true; 618 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC); 619 620 // This invalidates DesignatedReg. 621 Spills.ClobberPhysReg(DesignatedReg); 622 623 Spills.addAvailable(StackSlot, DesignatedReg); 624 MI.SetMachineOperandReg(i, DesignatedReg); 625 DEBUG(std::cerr << '\t' << *prior(MII)); 626 ++NumReused; 627 continue; 628 } 629 630 // Otherwise, reload it and remember that we have it. 631 PhysReg = VRM.getPhys(VirtReg); 632 assert(PhysReg && "Must map virtreg to physreg!"); 633 const TargetRegisterClass* RC = 634 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 635 636 // Note that, if we reused a register for a previous operand, the 637 // register we want to reload into might not actually be 638 // available. If this occurs, use the register indicated by the 639 // reuser. 640 if (ReusedOperands.hasReuses()) 641 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI, 642 Spills, MaybeDeadStores); 643 644 PhysRegsUsed[PhysReg] = true; 645 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC); 646 // This invalidates PhysReg. 647 Spills.ClobberPhysReg(PhysReg); 648 649 // Any stores to this stack slot are not dead anymore. 650 MaybeDeadStores.erase(StackSlot); 651 Spills.addAvailable(StackSlot, PhysReg); 652 ++NumLoads; 653 MI.SetMachineOperandReg(i, PhysReg); 654 DEBUG(std::cerr << '\t' << *prior(MII)); 655 } 656 657 // Loop over all of the implicit defs, clearing them from our available 658 // sets. 659 for (const unsigned *ImpDef = TII->getImplicitDefs(MI.getOpcode()); 660 *ImpDef; ++ImpDef) { 661 PhysRegsUsed[*ImpDef] = true; 662 Spills.ClobberPhysReg(*ImpDef); 663 } 664 665 DEBUG(std::cerr << '\t' << MI); 666 667 // If we have folded references to memory operands, make sure we clear all 668 // physical registers that may contain the value of the spilled virtual 669 // register 670 VirtRegMap::MI2VirtMapTy::const_iterator I, End; 671 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) { 672 DEBUG(std::cerr << "Folded vreg: " << I->second.first << " MR: " 673 << I->second.second); 674 unsigned VirtReg = I->second.first; 675 VirtRegMap::ModRef MR = I->second.second; 676 if (!VRM.hasStackSlot(VirtReg)) { 677 DEBUG(std::cerr << ": No stack slot!\n"); 678 continue; 679 } 680 int SS = VRM.getStackSlot(VirtReg); 681 DEBUG(std::cerr << " - StackSlot: " << SS << "\n"); 682 683 // If this folded instruction is just a use, check to see if it's a 684 // straight load from the virt reg slot. 685 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) { 686 int FrameIdx; 687 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) { 688 // If this spill slot is available, turn it into a copy (or nothing) 689 // instead of leaving it as a load! 690 unsigned InReg; 691 if (FrameIdx == SS && (InReg = Spills.getSpillSlotPhysReg(SS))) { 692 DEBUG(std::cerr << "Promoted Load To Copy: " << MI); 693 MachineFunction &MF = *MBB.getParent(); 694 if (DestReg != InReg) { 695 MRI->copyRegToReg(MBB, &MI, DestReg, InReg, 696 MF.getSSARegMap()->getRegClass(VirtReg)); 697 // Revisit the copy so we make sure to notice the effects of the 698 // operation on the destreg (either needing to RA it if it's 699 // virtual or needing to clobber any values if it's physical). 700 NextMII = &MI; 701 --NextMII; // backtrack to the copy. 702 } 703 MBB.erase(&MI); 704 goto ProcessNextInst; 705 } 706 } 707 } 708 709 // If this reference is not a use, any previous store is now dead. 710 // Otherwise, the store to this stack slot is not dead anymore. 711 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS); 712 if (MDSI != MaybeDeadStores.end()) { 713 if (MR & VirtRegMap::isRef) // Previous store is not dead. 714 MaybeDeadStores.erase(MDSI); 715 else { 716 // If we get here, the store is dead, nuke it now. 717 assert(MR == VirtRegMap::isMod && "Can't be modref!"); 718 MBB.erase(MDSI->second); 719 MaybeDeadStores.erase(MDSI); 720 ++NumDSE; 721 } 722 } 723 724 // If the spill slot value is available, and this is a new definition of 725 // the value, the value is not available anymore. 726 if (MR & VirtRegMap::isMod) { 727 // Notice that the value in this stack slot has been modified. 728 Spills.ModifyStackSlot(SS); 729 730 // If this is *just* a mod of the value, check to see if this is just a 731 // store to the spill slot (i.e. the spill got merged into the copy). If 732 // so, realize that the vreg is available now, and add the store to the 733 // MaybeDeadStore info. 734 int StackSlot; 735 if (!(MR & VirtRegMap::isRef)) { 736 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) { 737 assert(MRegisterInfo::isPhysicalRegister(SrcReg) && 738 "Src hasn't been allocated yet?"); 739 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark 740 // this as a potentially dead store in case there is a subsequent 741 // store into the stack slot without a read from it. 742 MaybeDeadStores[StackSlot] = &MI; 743 744 // If the stack slot value was previously available in some other 745 // register, change it now. Otherwise, make the register available, 746 // in PhysReg. 747 Spills.addAvailable(StackSlot, SrcReg, false /*don't clobber*/); 748 } 749 } 750 } 751 } 752 753 // Process all of the spilled defs. 754 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 755 MachineOperand &MO = MI.getOperand(i); 756 if (MO.isRegister() && MO.getReg() && MO.isDef()) { 757 unsigned VirtReg = MO.getReg(); 758 759 if (!MRegisterInfo::isVirtualRegister(VirtReg)) { 760 // Check to see if this is a def-and-use vreg operand that we do need 761 // to insert a store for. 762 bool OpTakenCareOf = false; 763 if (MO.isUse() && !DefAndUseVReg.empty()) { 764 for (unsigned dau = 0, e = DefAndUseVReg.size(); dau != e; ++dau) 765 if (DefAndUseVReg[dau].first == i) { 766 VirtReg = DefAndUseVReg[dau].second; 767 OpTakenCareOf = true; 768 break; 769 } 770 } 771 772 if (!OpTakenCareOf) { 773 // Check to see if this is a noop copy. If so, eliminate the 774 // instruction before considering the dest reg to be changed. 775 unsigned Src, Dst; 776 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) { 777 ++NumDCE; 778 DEBUG(std::cerr << "Removing now-noop copy: " << MI); 779 MBB.erase(&MI); 780 goto ProcessNextInst; 781 } 782 Spills.ClobberPhysReg(VirtReg); 783 continue; 784 } 785 } 786 787 // The only vregs left are stack slot definitions. 788 int StackSlot = VRM.getStackSlot(VirtReg); 789 const TargetRegisterClass *RC = 790 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 791 unsigned PhysReg; 792 793 // If this is a def&use operand, and we used a different physreg for 794 // it than the one assigned, make sure to execute the store from the 795 // correct physical register. 796 if (MO.getReg() == VirtReg) 797 PhysReg = VRM.getPhys(VirtReg); 798 else 799 PhysReg = MO.getReg(); 800 801 PhysRegsUsed[PhysReg] = true; 802 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC); 803 DEBUG(std::cerr << "Store:\t" << *next(MII)); 804 MI.SetMachineOperandReg(i, PhysReg); 805 806 // Check to see if this is a noop copy. If so, eliminate the 807 // instruction before considering the dest reg to be changed. 808 { 809 unsigned Src, Dst; 810 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) { 811 ++NumDCE; 812 DEBUG(std::cerr << "Removing now-noop copy: " << MI); 813 MBB.erase(&MI); 814 goto ProcessNextInst; 815 } 816 } 817 818 // If there is a dead store to this stack slot, nuke it now. 819 MachineInstr *&LastStore = MaybeDeadStores[StackSlot]; 820 if (LastStore) { 821 DEBUG(std::cerr << " Killed store:\t" << *LastStore); 822 ++NumDSE; 823 MBB.erase(LastStore); 824 } 825 LastStore = next(MII); 826 827 // If the stack slot value was previously available in some other 828 // register, change it now. Otherwise, make the register available, 829 // in PhysReg. 830 Spills.ModifyStackSlot(StackSlot); 831 Spills.ClobberPhysReg(PhysReg); 832 Spills.addAvailable(StackSlot, PhysReg); 833 ++NumStores; 834 } 835 } 836 ProcessNextInst: 837 MII = NextMII; 838 } 839} 840 841 842 843llvm::Spiller* llvm::createSpiller() { 844 switch (SpillerOpt) { 845 default: assert(0 && "Unreachable!"); 846 case local: 847 return new LocalSpiller(); 848 case simple: 849 return new SimpleSpiller(); 850 } 851} 852