VirtRegMap.cpp revision b870100f2a2be0e7de99f7710db01a3e1f9d305b
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> 33#include <iostream> 34using namespace llvm; 35 36namespace { 37 static Statistic<> NumSpills("spiller", "Number of register spills"); 38 static Statistic<> NumStores("spiller", "Number of stores added"); 39 static Statistic<> NumLoads ("spiller", "Number of loads added"); 40 static Statistic<> NumReused("spiller", "Number of values reused"); 41 static Statistic<> NumDSE ("spiller", "Number of dead stores elided"); 42 static Statistic<> NumDCE ("spiller", "Number of copies elided"); 43 44 enum SpillerName { simple, local }; 45 46 static cl::opt<SpillerName> 47 SpillerOpt("spiller", 48 cl::desc("Spiller to use: (default: local)"), 49 cl::Prefix, 50 cl::values(clEnumVal(simple, " simple spiller"), 51 clEnumVal(local, " local spiller"), 52 clEnumValEnd), 53 cl::init(local)); 54} 55 56//===----------------------------------------------------------------------===// 57// VirtRegMap implementation 58//===----------------------------------------------------------------------===// 59 60VirtRegMap::VirtRegMap(MachineFunction &mf) 61 : TII(*mf.getTarget().getInstrInfo()), MF(mf), 62 Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT) { 63 grow(); 64} 65 66void VirtRegMap::grow() { 67 Virt2PhysMap.grow(MF.getSSARegMap()->getLastVirtReg()); 68 Virt2StackSlotMap.grow(MF.getSSARegMap()->getLastVirtReg()); 69} 70 71int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) { 72 assert(MRegisterInfo::isVirtualRegister(virtReg)); 73 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && 74 "attempt to assign stack slot to already spilled register"); 75 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg); 76 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(), 77 RC->getAlignment()); 78 Virt2StackSlotMap[virtReg] = frameIndex; 79 ++NumSpills; 80 return frameIndex; 81} 82 83void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) { 84 assert(MRegisterInfo::isVirtualRegister(virtReg)); 85 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && 86 "attempt to assign stack slot to already spilled register"); 87 Virt2StackSlotMap[virtReg] = frameIndex; 88} 89 90void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI, 91 unsigned OpNo, MachineInstr *NewMI) { 92 // Move previous memory references folded to new instruction. 93 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI); 94 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI), 95 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) { 96 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second)); 97 MI2VirtMap.erase(I++); 98 } 99 100 ModRef MRInfo; 101 if (OpNo < 2 && TII.isTwoAddrInstr(OldMI->getOpcode())) { 102 // Folded a two-address operand. 103 MRInfo = isModRef; 104 } else if (OldMI->getOperand(OpNo).isDef()) { 105 MRInfo = isMod; 106 } else { 107 MRInfo = isRef; 108 } 109 110 // add new memory reference 111 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo))); 112} 113 114void VirtRegMap::print(std::ostream &OS) const { 115 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo(); 116 117 OS << "********** REGISTER MAP **********\n"; 118 for (unsigned i = MRegisterInfo::FirstVirtualRegister, 119 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) { 120 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG) 121 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n"; 122 123 } 124 125 for (unsigned i = MRegisterInfo::FirstVirtualRegister, 126 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) 127 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT) 128 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n"; 129 OS << '\n'; 130} 131 132void VirtRegMap::dump() const { print(std::cerr); } 133 134 135//===----------------------------------------------------------------------===// 136// Simple Spiller Implementation 137//===----------------------------------------------------------------------===// 138 139Spiller::~Spiller() {} 140 141namespace { 142 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller { 143 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM); 144 }; 145} 146 147bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) { 148 DEBUG(std::cerr << "********** REWRITE MACHINE CODE **********\n"); 149 DEBUG(std::cerr << "********** Function: " 150 << MF.getFunction()->getName() << '\n'); 151 const TargetMachine &TM = MF.getTarget(); 152 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 153 bool *PhysRegsUsed = MF.getUsedPhysregs(); 154 155 // LoadedRegs - Keep track of which vregs are loaded, so that we only load 156 // each vreg once (in the case where a spilled vreg is used by multiple 157 // operands). This is always smaller than the number of operands to the 158 // current machine instr, so it should be small. 159 std::vector<unsigned> LoadedRegs; 160 161 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end(); 162 MBBI != E; ++MBBI) { 163 DEBUG(std::cerr << MBBI->getBasicBlock()->getName() << ":\n"); 164 MachineBasicBlock &MBB = *MBBI; 165 for (MachineBasicBlock::iterator MII = MBB.begin(), 166 E = MBB.end(); MII != E; ++MII) { 167 MachineInstr &MI = *MII; 168 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 169 MachineOperand &MO = MI.getOperand(i); 170 if (MO.isRegister() && MO.getReg()) 171 if (MRegisterInfo::isVirtualRegister(MO.getReg())) { 172 unsigned VirtReg = MO.getReg(); 173 unsigned PhysReg = VRM.getPhys(VirtReg); 174 if (VRM.hasStackSlot(VirtReg)) { 175 int StackSlot = VRM.getStackSlot(VirtReg); 176 const TargetRegisterClass* RC = 177 MF.getSSARegMap()->getRegClass(VirtReg); 178 179 if (MO.isUse() && 180 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg) 181 == LoadedRegs.end()) { 182 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC); 183 LoadedRegs.push_back(VirtReg); 184 ++NumLoads; 185 DEBUG(std::cerr << '\t' << *prior(MII)); 186 } 187 188 if (MO.isDef()) { 189 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC); 190 ++NumStores; 191 } 192 } 193 PhysRegsUsed[PhysReg] = true; 194 MI.getOperand(i).setReg(PhysReg); 195 } else { 196 PhysRegsUsed[MO.getReg()] = true; 197 } 198 } 199 200 DEBUG(std::cerr << '\t' << MI); 201 LoadedRegs.clear(); 202 } 203 } 204 return true; 205} 206 207//===----------------------------------------------------------------------===// 208// Local Spiller Implementation 209//===----------------------------------------------------------------------===// 210 211namespace { 212 /// LocalSpiller - This spiller does a simple pass over the machine basic 213 /// block to attempt to keep spills in registers as much as possible for 214 /// blocks that have low register pressure (the vreg may be spilled due to 215 /// register pressure in other blocks). 216 class VISIBILITY_HIDDEN LocalSpiller : public Spiller { 217 const MRegisterInfo *MRI; 218 const TargetInstrInfo *TII; 219 public: 220 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) { 221 MRI = MF.getTarget().getRegisterInfo(); 222 TII = MF.getTarget().getInstrInfo(); 223 DEBUG(std::cerr << "\n**** Local spiller rewriting function '" 224 << MF.getFunction()->getName() << "':\n"); 225 226 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end(); 227 MBB != E; ++MBB) 228 RewriteMBB(*MBB, VRM); 229 return true; 230 } 231 private: 232 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM); 233 void ClobberPhysReg(unsigned PR, std::map<int, unsigned> &SpillSlots, 234 std::multimap<unsigned, int> &PhysRegs); 235 void ClobberPhysRegOnly(unsigned PR, std::map<int, unsigned> &SpillSlots, 236 std::multimap<unsigned, int> &PhysRegs); 237 void ModifyStackSlot(int Slot, std::map<int, unsigned> &SpillSlots, 238 std::multimap<unsigned, int> &PhysRegs); 239 }; 240} 241 242/// AvailableSpills - As the local spiller is scanning and rewriting an MBB from 243/// top down, keep track of which spills slots are available in each register. 244/// 245/// Note that not all physregs are created equal here. In particular, some 246/// physregs are reloads that we are allowed to clobber or ignore at any time. 247/// Other physregs are values that the register allocated program is using that 248/// we cannot CHANGE, but we can read if we like. We keep track of this on a 249/// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable 250/// entries. The predicate 'canClobberPhysReg()' checks this bit and 251/// addAvailable sets it if. 252namespace { 253class VISIBILITY_HIDDEN AvailableSpills { 254 const MRegisterInfo *MRI; 255 const TargetInstrInfo *TII; 256 257 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual 258 // register values that are still available, due to being loaded or stored to, 259 // but not invalidated yet. 260 std::map<int, unsigned> SpillSlotsAvailable; 261 262 // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating 263 // which stack slot values are currently held by a physreg. This is used to 264 // invalidate entries in SpillSlotsAvailable when a physreg is modified. 265 std::multimap<unsigned, int> PhysRegsAvailable; 266 267 void ClobberPhysRegOnly(unsigned PhysReg); 268public: 269 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii) 270 : MRI(mri), TII(tii) { 271 } 272 273 /// getSpillSlotPhysReg - If the specified stack slot is available in a 274 /// physical register, return that PhysReg, otherwise return 0. 275 unsigned getSpillSlotPhysReg(int Slot) const { 276 std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot); 277 if (I != SpillSlotsAvailable.end()) 278 return I->second >> 1; // Remove the CanClobber bit. 279 return 0; 280 } 281 282 const MRegisterInfo *getRegInfo() const { return MRI; } 283 284 /// addAvailable - Mark that the specified stack slot is available in the 285 /// specified physreg. If CanClobber is true, the physreg can be modified at 286 /// any time without changing the semantics of the program. 287 void addAvailable(int Slot, unsigned Reg, bool CanClobber = true) { 288 // If this stack slot is thought to be available in some other physreg, 289 // remove its record. 290 ModifyStackSlot(Slot); 291 292 PhysRegsAvailable.insert(std::make_pair(Reg, Slot)); 293 SpillSlotsAvailable[Slot] = (Reg << 1) | (unsigned)CanClobber; 294 295 DEBUG(std::cerr << "Remembering SS#" << Slot << " in physreg " 296 << MRI->getName(Reg) << "\n"); 297 } 298 299 /// canClobberPhysReg - Return true if the spiller is allowed to change the 300 /// value of the specified stackslot register if it desires. The specified 301 /// stack slot must be available in a physreg for this query to make sense. 302 bool canClobberPhysReg(int Slot) const { 303 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!"); 304 return SpillSlotsAvailable.find(Slot)->second & 1; 305 } 306 307 /// ClobberPhysReg - This is called when the specified physreg changes 308 /// value. We use this to invalidate any info about stuff we thing lives in 309 /// it and any of its aliases. 310 void ClobberPhysReg(unsigned PhysReg); 311 312 /// ModifyStackSlot - This method is called when the value in a stack slot 313 /// changes. This removes information about which register the previous value 314 /// for this slot lives in (as the previous value is dead now). 315 void ModifyStackSlot(int Slot); 316}; 317} 318 319/// ClobberPhysRegOnly - This is called when the specified physreg changes 320/// value. We use this to invalidate any info about stuff we thing lives in it. 321void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) { 322 std::multimap<unsigned, int>::iterator I = 323 PhysRegsAvailable.lower_bound(PhysReg); 324 while (I != PhysRegsAvailable.end() && I->first == PhysReg) { 325 int Slot = I->second; 326 PhysRegsAvailable.erase(I++); 327 assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg && 328 "Bidirectional map mismatch!"); 329 SpillSlotsAvailable.erase(Slot); 330 DEBUG(std::cerr << "PhysReg " << MRI->getName(PhysReg) 331 << " clobbered, invalidating SS#" << Slot << "\n"); 332 } 333} 334 335/// ClobberPhysReg - This is called when the specified physreg changes 336/// value. We use this to invalidate any info about stuff we thing lives in 337/// it and any of its aliases. 338void AvailableSpills::ClobberPhysReg(unsigned PhysReg) { 339 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS) 340 ClobberPhysRegOnly(*AS); 341 ClobberPhysRegOnly(PhysReg); 342} 343 344/// ModifyStackSlot - This method is called when the value in a stack slot 345/// changes. This removes information about which register the previous value 346/// for this slot lives in (as the previous value is dead now). 347void AvailableSpills::ModifyStackSlot(int Slot) { 348 std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot); 349 if (It == SpillSlotsAvailable.end()) return; 350 unsigned Reg = It->second >> 1; 351 SpillSlotsAvailable.erase(It); 352 353 // This register may hold the value of multiple stack slots, only remove this 354 // stack slot from the set of values the register contains. 355 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg); 356 for (; ; ++I) { 357 assert(I != PhysRegsAvailable.end() && I->first == Reg && 358 "Map inverse broken!"); 359 if (I->second == Slot) break; 360 } 361 PhysRegsAvailable.erase(I); 362} 363 364 365 366// ReusedOp - For each reused operand, we keep track of a bit of information, in 367// case we need to rollback upon processing a new operand. See comments below. 368namespace { 369 struct ReusedOp { 370 // The MachineInstr operand that reused an available value. 371 unsigned Operand; 372 373 // StackSlot - The spill slot of the value being reused. 374 unsigned StackSlot; 375 376 // PhysRegReused - The physical register the value was available in. 377 unsigned PhysRegReused; 378 379 // AssignedPhysReg - The physreg that was assigned for use by the reload. 380 unsigned AssignedPhysReg; 381 382 // VirtReg - The virtual register itself. 383 unsigned VirtReg; 384 385 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr, 386 unsigned vreg) 387 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr), 388 VirtReg(vreg) {} 389 }; 390 391 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that 392 /// is reused instead of reloaded. 393 class VISIBILITY_HIDDEN ReuseInfo { 394 MachineInstr &MI; 395 std::vector<ReusedOp> Reuses; 396 public: 397 ReuseInfo(MachineInstr &mi) : MI(mi) {} 398 399 bool hasReuses() const { 400 return !Reuses.empty(); 401 } 402 403 /// addReuse - If we choose to reuse a virtual register that is already 404 /// available instead of reloading it, remember that we did so. 405 void addReuse(unsigned OpNo, unsigned StackSlot, 406 unsigned PhysRegReused, unsigned AssignedPhysReg, 407 unsigned VirtReg) { 408 // If the reload is to the assigned register anyway, no undo will be 409 // required. 410 if (PhysRegReused == AssignedPhysReg) return; 411 412 // Otherwise, remember this. 413 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused, 414 AssignedPhysReg, VirtReg)); 415 } 416 417 /// GetRegForReload - We are about to emit a reload into PhysReg. If there 418 /// is some other operand that is using the specified register, either pick 419 /// a new register to use, or evict the previous reload and use this reg. 420 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI, 421 AvailableSpills &Spills, 422 std::map<int, MachineInstr*> &MaybeDeadStores) { 423 if (Reuses.empty()) return PhysReg; // This is most often empty. 424 425 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) { 426 ReusedOp &Op = Reuses[ro]; 427 // If we find some other reuse that was supposed to use this register 428 // exactly for its reload, we can change this reload to use ITS reload 429 // register. 430 if (Op.PhysRegReused == PhysReg) { 431 // Yup, use the reload register that we didn't use before. 432 unsigned NewReg = Op.AssignedPhysReg; 433 434 // Remove the record for the previous reuse. We know it can never be 435 // invalidated now. 436 Reuses.erase(Reuses.begin()+ro); 437 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores); 438 } else { 439 // Otherwise, we might also have a problem if a previously reused 440 // value aliases the new register. If so, codegen the previous reload 441 // and use this one. 442 unsigned PRRU = Op.PhysRegReused; 443 const MRegisterInfo *MRI = Spills.getRegInfo(); 444 if (MRI->areAliases(PRRU, PhysReg)) { 445 // Okay, we found out that an alias of a reused register 446 // was used. This isn't good because it means we have 447 // to undo a previous reuse. 448 MachineBasicBlock *MBB = MI->getParent(); 449 const TargetRegisterClass *AliasRC = 450 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg); 451 452 // Copy Op out of the vector and remove it, we're going to insert an 453 // explicit load for it. 454 ReusedOp NewOp = Op; 455 Reuses.erase(Reuses.begin()+ro); 456 457 // Ok, we're going to try to reload the assigned physreg into the 458 // slot that we were supposed to in the first place. However, that 459 // register could hold a reuse. Check to see if it conflicts or 460 // would prefer us to use a different register. 461 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg, 462 MI, Spills, MaybeDeadStores); 463 464 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg, 465 NewOp.StackSlot, AliasRC); 466 Spills.ClobberPhysReg(NewPhysReg); 467 Spills.ClobberPhysReg(NewOp.PhysRegReused); 468 469 // Any stores to this stack slot are not dead anymore. 470 MaybeDeadStores.erase(NewOp.StackSlot); 471 472 MI->getOperand(NewOp.Operand).setReg(NewPhysReg); 473 474 Spills.addAvailable(NewOp.StackSlot, NewPhysReg); 475 ++NumLoads; 476 DEBUG(MachineBasicBlock::iterator MII = MI; 477 std::cerr << '\t' << *prior(MII)); 478 479 DEBUG(std::cerr << "Reuse undone!\n"); 480 --NumReused; 481 482 // Finally, PhysReg is now available, go ahead and use it. 483 return PhysReg; 484 } 485 } 486 } 487 return PhysReg; 488 } 489 }; 490} 491 492 493/// rewriteMBB - Keep track of which spills are available even after the 494/// register allocator is done with them. If possible, avoid reloading vregs. 495void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) { 496 497 DEBUG(std::cerr << MBB.getBasicBlock()->getName() << ":\n"); 498 499 // Spills - Keep track of which spilled values are available in physregs so 500 // that we can choose to reuse the physregs instead of emitting reloads. 501 AvailableSpills Spills(MRI, TII); 502 503 // MaybeDeadStores - When we need to write a value back into a stack slot, 504 // keep track of the inserted store. If the stack slot value is never read 505 // (because the value was used from some available register, for example), and 506 // subsequently stored to, the original store is dead. This map keeps track 507 // of inserted stores that are not used. If we see a subsequent store to the 508 // same stack slot, the original store is deleted. 509 std::map<int, MachineInstr*> MaybeDeadStores; 510 511 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs(); 512 513 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end(); 514 MII != E; ) { 515 MachineInstr &MI = *MII; 516 MachineBasicBlock::iterator NextMII = MII; ++NextMII; 517 518 /// ReusedOperands - Keep track of operand reuse in case we need to undo 519 /// reuse. 520 ReuseInfo ReusedOperands(MI); 521 522 // Process all of the spilled uses and all non spilled reg references. 523 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 524 MachineOperand &MO = MI.getOperand(i); 525 if (!MO.isRegister() || MO.getReg() == 0) 526 continue; // Ignore non-register operands. 527 528 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) { 529 // Ignore physregs for spilling, but remember that it is used by this 530 // function. 531 PhysRegsUsed[MO.getReg()] = true; 532 continue; 533 } 534 535 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) && 536 "Not a virtual or a physical register?"); 537 538 unsigned VirtReg = MO.getReg(); 539 if (!VRM.hasStackSlot(VirtReg)) { 540 // This virtual register was assigned a physreg! 541 unsigned Phys = VRM.getPhys(VirtReg); 542 PhysRegsUsed[Phys] = true; 543 MI.getOperand(i).setReg(Phys); 544 continue; 545 } 546 547 // This virtual register is now known to be a spilled value. 548 if (!MO.isUse()) 549 continue; // Handle defs in the loop below (handle use&def here though) 550 551 int StackSlot = VRM.getStackSlot(VirtReg); 552 unsigned PhysReg; 553 554 // Check to see if this stack slot is available. 555 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) { 556 557 // This spilled operand might be part of a two-address operand. If this 558 // is the case, then changing it will necessarily require changing the 559 // def part of the instruction as well. However, in some cases, we 560 // aren't allowed to modify the reused register. If none of these cases 561 // apply, reuse it. 562 bool CanReuse = true; 563 if (i == 1 && MI.getOperand(0).isReg() && 564 MI.getOperand(0).getReg() == VirtReg && 565 TII->isTwoAddrInstr(MI.getOpcode())) { 566 // Okay, we have a two address operand. We can reuse this physreg as 567 // long as we are allowed to clobber the value. 568 CanReuse = Spills.canClobberPhysReg(StackSlot); 569 } 570 571 if (CanReuse) { 572 // If this stack slot value is already available, reuse it! 573 DEBUG(std::cerr << "Reusing SS#" << StackSlot << " from physreg " 574 << MRI->getName(PhysReg) << " for vreg" 575 << VirtReg <<" instead of reloading into physreg " 576 << MRI->getName(VRM.getPhys(VirtReg)) << "\n"); 577 MI.getOperand(i).setReg(PhysReg); 578 579 // The only technical detail we have is that we don't know that 580 // PhysReg won't be clobbered by a reloaded stack slot that occurs 581 // later in the instruction. In particular, consider 'op V1, V2'. 582 // If V1 is available in physreg R0, we would choose to reuse it 583 // here, instead of reloading it into the register the allocator 584 // indicated (say R1). However, V2 might have to be reloaded 585 // later, and it might indicate that it needs to live in R0. When 586 // this occurs, we need to have information available that 587 // indicates it is safe to use R1 for the reload instead of R0. 588 // 589 // To further complicate matters, we might conflict with an alias, 590 // or R0 and R1 might not be compatible with each other. In this 591 // case, we actually insert a reload for V1 in R1, ensuring that 592 // we can get at R0 or its alias. 593 ReusedOperands.addReuse(i, StackSlot, PhysReg, 594 VRM.getPhys(VirtReg), VirtReg); 595 ++NumReused; 596 continue; 597 } 598 599 // Otherwise we have a situation where we have a two-address instruction 600 // whose mod/ref operand needs to be reloaded. This reload is already 601 // available in some register "PhysReg", but if we used PhysReg as the 602 // operand to our 2-addr instruction, the instruction would modify 603 // PhysReg. This isn't cool if something later uses PhysReg and expects 604 // to get its initial value. 605 // 606 // To avoid this problem, and to avoid doing a load right after a store, 607 // we emit a copy from PhysReg into the designated register for this 608 // operand. 609 unsigned DesignatedReg = VRM.getPhys(VirtReg); 610 assert(DesignatedReg && "Must map virtreg to physreg!"); 611 612 // Note that, if we reused a register for a previous operand, the 613 // register we want to reload into might not actually be 614 // available. If this occurs, use the register indicated by the 615 // reuser. 616 if (ReusedOperands.hasReuses()) 617 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI, 618 Spills, MaybeDeadStores); 619 620 // If the mapped designated register is actually the physreg we have 621 // incoming, we don't need to inserted a dead copy. 622 if (DesignatedReg == PhysReg) { 623 // If this stack slot value is already available, reuse it! 624 DEBUG(std::cerr << "Reusing SS#" << StackSlot << " from physreg " 625 << MRI->getName(PhysReg) << " for vreg" 626 << VirtReg 627 << " instead of reloading into same physreg.\n"); 628 MI.getOperand(i).setReg(PhysReg); 629 ++NumReused; 630 continue; 631 } 632 633 const TargetRegisterClass* RC = 634 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 635 636 PhysRegsUsed[DesignatedReg] = true; 637 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC); 638 639 // This invalidates DesignatedReg. 640 Spills.ClobberPhysReg(DesignatedReg); 641 642 Spills.addAvailable(StackSlot, DesignatedReg); 643 MI.getOperand(i).setReg(DesignatedReg); 644 DEBUG(std::cerr << '\t' << *prior(MII)); 645 ++NumReused; 646 continue; 647 } 648 649 // Otherwise, reload it and remember that we have it. 650 PhysReg = VRM.getPhys(VirtReg); 651 assert(PhysReg && "Must map virtreg to physreg!"); 652 const TargetRegisterClass* RC = 653 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 654 655 // Note that, if we reused a register for a previous operand, the 656 // register we want to reload into might not actually be 657 // available. If this occurs, use the register indicated by the 658 // reuser. 659 if (ReusedOperands.hasReuses()) 660 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI, 661 Spills, MaybeDeadStores); 662 663 PhysRegsUsed[PhysReg] = true; 664 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC); 665 // This invalidates PhysReg. 666 Spills.ClobberPhysReg(PhysReg); 667 668 // Any stores to this stack slot are not dead anymore. 669 MaybeDeadStores.erase(StackSlot); 670 Spills.addAvailable(StackSlot, PhysReg); 671 ++NumLoads; 672 MI.getOperand(i).setReg(PhysReg); 673 DEBUG(std::cerr << '\t' << *prior(MII)); 674 } 675 676 // Loop over all of the implicit defs, clearing them from our available 677 // sets. 678 const unsigned *ImpDef = TII->getImplicitDefs(MI.getOpcode()); 679 if (ImpDef) { 680 for ( ; *ImpDef; ++ImpDef) { 681 PhysRegsUsed[*ImpDef] = true; 682 Spills.ClobberPhysReg(*ImpDef); 683 } 684 } 685 686 DEBUG(std::cerr << '\t' << MI); 687 688 // If we have folded references to memory operands, make sure we clear all 689 // physical registers that may contain the value of the spilled virtual 690 // register 691 VirtRegMap::MI2VirtMapTy::const_iterator I, End; 692 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) { 693 DEBUG(std::cerr << "Folded vreg: " << I->second.first << " MR: " 694 << I->second.second); 695 unsigned VirtReg = I->second.first; 696 VirtRegMap::ModRef MR = I->second.second; 697 if (!VRM.hasStackSlot(VirtReg)) { 698 DEBUG(std::cerr << ": No stack slot!\n"); 699 continue; 700 } 701 int SS = VRM.getStackSlot(VirtReg); 702 DEBUG(std::cerr << " - StackSlot: " << SS << "\n"); 703 704 // If this folded instruction is just a use, check to see if it's a 705 // straight load from the virt reg slot. 706 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) { 707 int FrameIdx; 708 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) { 709 // If this spill slot is available, turn it into a copy (or nothing) 710 // instead of leaving it as a load! 711 unsigned InReg; 712 if (FrameIdx == SS && (InReg = Spills.getSpillSlotPhysReg(SS))) { 713 DEBUG(std::cerr << "Promoted Load To Copy: " << MI); 714 MachineFunction &MF = *MBB.getParent(); 715 if (DestReg != InReg) { 716 MRI->copyRegToReg(MBB, &MI, DestReg, InReg, 717 MF.getSSARegMap()->getRegClass(VirtReg)); 718 // Revisit the copy so we make sure to notice the effects of the 719 // operation on the destreg (either needing to RA it if it's 720 // virtual or needing to clobber any values if it's physical). 721 NextMII = &MI; 722 --NextMII; // backtrack to the copy. 723 } 724 VRM.RemoveFromFoldedVirtMap(&MI); 725 MBB.erase(&MI); 726 goto ProcessNextInst; 727 } 728 } 729 } 730 731 // If this reference is not a use, any previous store is now dead. 732 // Otherwise, the store to this stack slot is not dead anymore. 733 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS); 734 if (MDSI != MaybeDeadStores.end()) { 735 if (MR & VirtRegMap::isRef) // Previous store is not dead. 736 MaybeDeadStores.erase(MDSI); 737 else { 738 // If we get here, the store is dead, nuke it now. 739 assert(VirtRegMap::isMod && "Can't be modref!"); 740 DEBUG(std::cerr << "Removed dead store:\t" << *MDSI->second); 741 MBB.erase(MDSI->second); 742 VRM.RemoveFromFoldedVirtMap(MDSI->second); 743 MaybeDeadStores.erase(MDSI); 744 ++NumDSE; 745 } 746 } 747 748 // If the spill slot value is available, and this is a new definition of 749 // the value, the value is not available anymore. 750 if (MR & VirtRegMap::isMod) { 751 // Notice that the value in this stack slot has been modified. 752 Spills.ModifyStackSlot(SS); 753 754 // If this is *just* a mod of the value, check to see if this is just a 755 // store to the spill slot (i.e. the spill got merged into the copy). If 756 // so, realize that the vreg is available now, and add the store to the 757 // MaybeDeadStore info. 758 int StackSlot; 759 if (!(MR & VirtRegMap::isRef)) { 760 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) { 761 assert(MRegisterInfo::isPhysicalRegister(SrcReg) && 762 "Src hasn't been allocated yet?"); 763 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark 764 // this as a potentially dead store in case there is a subsequent 765 // store into the stack slot without a read from it. 766 MaybeDeadStores[StackSlot] = &MI; 767 768 // If the stack slot value was previously available in some other 769 // register, change it now. Otherwise, make the register available, 770 // in PhysReg. 771 Spills.addAvailable(StackSlot, SrcReg, false /*don't clobber*/); 772 } 773 } 774 } 775 } 776 777 // Process all of the spilled defs. 778 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { 779 MachineOperand &MO = MI.getOperand(i); 780 if (MO.isRegister() && MO.getReg() && MO.isDef()) { 781 unsigned VirtReg = MO.getReg(); 782 783 if (!MRegisterInfo::isVirtualRegister(VirtReg)) { 784 // Check to see if this is a noop copy. If so, eliminate the 785 // instruction before considering the dest reg to be changed. 786 unsigned Src, Dst; 787 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) { 788 ++NumDCE; 789 DEBUG(std::cerr << "Removing now-noop copy: " << MI); 790 MBB.erase(&MI); 791 VRM.RemoveFromFoldedVirtMap(&MI); 792 goto ProcessNextInst; 793 } 794 Spills.ClobberPhysReg(VirtReg); 795 continue; 796 } 797 798 // The only vregs left are stack slot definitions. 799 int StackSlot = VRM.getStackSlot(VirtReg); 800 const TargetRegisterClass *RC = 801 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); 802 803 // If this def is part of a two-address operand, make sure to execute 804 // the store from the correct physical register. 805 unsigned PhysReg; 806 if (i == 0 && TII->isTwoAddrInstr(MI.getOpcode())) 807 PhysReg = MI.getOperand(1).getReg(); 808 else 809 PhysReg = VRM.getPhys(VirtReg); 810 811 PhysRegsUsed[PhysReg] = true; 812 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC); 813 DEBUG(std::cerr << "Store:\t" << *next(MII)); 814 MI.getOperand(i).setReg(PhysReg); 815 816 // Check to see if this is a noop copy. If so, eliminate the 817 // instruction before considering the dest reg to be changed. 818 { 819 unsigned Src, Dst; 820 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) { 821 ++NumDCE; 822 DEBUG(std::cerr << "Removing now-noop copy: " << MI); 823 MBB.erase(&MI); 824 VRM.RemoveFromFoldedVirtMap(&MI); 825 goto ProcessNextInst; 826 } 827 } 828 829 // If there is a dead store to this stack slot, nuke it now. 830 MachineInstr *&LastStore = MaybeDeadStores[StackSlot]; 831 if (LastStore) { 832 DEBUG(std::cerr << "Removed dead store:\t" << *LastStore); 833 ++NumDSE; 834 MBB.erase(LastStore); 835 VRM.RemoveFromFoldedVirtMap(LastStore); 836 } 837 LastStore = next(MII); 838 839 // If the stack slot value was previously available in some other 840 // register, change it now. Otherwise, make the register available, 841 // in PhysReg. 842 Spills.ModifyStackSlot(StackSlot); 843 Spills.ClobberPhysReg(PhysReg); 844 Spills.addAvailable(StackSlot, PhysReg); 845 ++NumStores; 846 } 847 } 848 ProcessNextInst: 849 MII = NextMII; 850 } 851} 852 853 854 855llvm::Spiller* llvm::createSpiller() { 856 switch (SpillerOpt) { 857 default: assert(0 && "Unreachable!"); 858 case local: 859 return new LocalSpiller(); 860 case simple: 861 return new SimpleSpiller(); 862 } 863} 864