1 //===-- llvm/CodeGen/VirtRegMap.cpp - Virtual Register Map ----------------===//
3 // The LLVM Compiler Infrastructure
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.
8 //===----------------------------------------------------------------------===//
10 // This file implements the VirtRegMap class.
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
17 //===----------------------------------------------------------------------===//
19 #define DEBUG_TYPE "spiller"
20 #include "VirtRegMap.h"
21 #include "llvm/Function.h"
22 #include "llvm/CodeGen/MachineFrameInfo.h"
23 #include "llvm/CodeGen/MachineFunction.h"
24 #include "llvm/CodeGen/SSARegMap.h"
25 #include "llvm/Target/TargetMachine.h"
26 #include "llvm/Target/TargetInstrInfo.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/Compiler.h"
30 #include "llvm/ADT/BitVector.h"
31 #include "llvm/ADT/Statistic.h"
32 #include "llvm/ADT/STLExtras.h"
33 #include "llvm/ADT/SmallSet.h"
37 STATISTIC(NumSpills, "Number of register spills");
38 STATISTIC(NumStores, "Number of stores added");
39 STATISTIC(NumLoads , "Number of loads added");
40 STATISTIC(NumReused, "Number of values reused");
41 STATISTIC(NumDSE , "Number of dead stores elided");
42 STATISTIC(NumDCE , "Number of copies elided");
45 enum SpillerName { simple, local };
47 static cl::opt<SpillerName>
49 cl::desc("Spiller to use: (default: local)"),
51 cl::values(clEnumVal(simple, " simple spiller"),
52 clEnumVal(local, " local spiller"),
57 //===----------------------------------------------------------------------===//
58 // VirtRegMap implementation
59 //===----------------------------------------------------------------------===//
61 VirtRegMap::VirtRegMap(MachineFunction &mf)
62 : TII(*mf.getTarget().getInstrInfo()), MF(mf),
63 Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT) {
67 void VirtRegMap::grow() {
68 Virt2PhysMap.grow(MF.getSSARegMap()->getLastVirtReg());
69 Virt2StackSlotMap.grow(MF.getSSARegMap()->getLastVirtReg());
72 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) {
73 assert(MRegisterInfo::isVirtualRegister(virtReg));
74 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
75 "attempt to assign stack slot to already spilled register");
76 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg);
77 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(),
79 Virt2StackSlotMap[virtReg] = frameIndex;
84 void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) {
85 assert(MRegisterInfo::isVirtualRegister(virtReg));
86 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
87 "attempt to assign stack slot to already spilled register");
88 Virt2StackSlotMap[virtReg] = frameIndex;
91 void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI,
92 unsigned OpNo, MachineInstr *NewMI) {
93 // Move previous memory references folded to new instruction.
94 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI);
95 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI),
96 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) {
97 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second));
98 MI2VirtMap.erase(I++);
102 const TargetInstrDescriptor *TID = OldMI->getInstrDescriptor();
103 if (TID->getOperandConstraint(OpNo, TOI::TIED_TO) != -1 ||
104 TID->findTiedToSrcOperand(OpNo) != -1) {
105 // Folded a two-address operand.
107 } else if (OldMI->getOperand(OpNo).isDef()) {
113 // add new memory reference
114 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo)));
117 void VirtRegMap::print(std::ostream &OS) const {
118 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo();
120 OS << "********** REGISTER MAP **********\n";
121 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
122 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) {
123 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG)
124 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n";
128 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
129 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i)
130 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT)
131 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n";
135 void VirtRegMap::dump() const {
140 //===----------------------------------------------------------------------===//
141 // Simple Spiller Implementation
142 //===----------------------------------------------------------------------===//
144 Spiller::~Spiller() {}
147 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller {
148 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM);
152 bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
153 DOUT << "********** REWRITE MACHINE CODE **********\n";
154 DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';
155 const TargetMachine &TM = MF.getTarget();
156 const MRegisterInfo &MRI = *TM.getRegisterInfo();
157 bool *PhysRegsUsed = MF.getUsedPhysregs();
159 // LoadedRegs - Keep track of which vregs are loaded, so that we only load
160 // each vreg once (in the case where a spilled vreg is used by multiple
161 // operands). This is always smaller than the number of operands to the
162 // current machine instr, so it should be small.
163 std::vector<unsigned> LoadedRegs;
165 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
167 DOUT << MBBI->getBasicBlock()->getName() << ":\n";
168 MachineBasicBlock &MBB = *MBBI;
169 for (MachineBasicBlock::iterator MII = MBB.begin(),
170 E = MBB.end(); MII != E; ++MII) {
171 MachineInstr &MI = *MII;
172 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
173 MachineOperand &MO = MI.getOperand(i);
174 if (MO.isRegister() && MO.getReg())
175 if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
176 unsigned VirtReg = MO.getReg();
177 unsigned PhysReg = VRM.getPhys(VirtReg);
178 if (VRM.hasStackSlot(VirtReg)) {
179 int StackSlot = VRM.getStackSlot(VirtReg);
180 const TargetRegisterClass* RC =
181 MF.getSSARegMap()->getRegClass(VirtReg);
184 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg)
185 == LoadedRegs.end()) {
186 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
187 LoadedRegs.push_back(VirtReg);
189 DOUT << '\t' << *prior(MII);
193 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
197 PhysRegsUsed[PhysReg] = true;
198 MI.getOperand(i).setReg(PhysReg);
200 PhysRegsUsed[MO.getReg()] = true;
211 //===----------------------------------------------------------------------===//
212 // Local Spiller Implementation
213 //===----------------------------------------------------------------------===//
216 /// LocalSpiller - This spiller does a simple pass over the machine basic
217 /// block to attempt to keep spills in registers as much as possible for
218 /// blocks that have low register pressure (the vreg may be spilled due to
219 /// register pressure in other blocks).
220 class VISIBILITY_HIDDEN LocalSpiller : public Spiller {
221 const MRegisterInfo *MRI;
222 const TargetInstrInfo *TII;
224 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
225 MRI = MF.getTarget().getRegisterInfo();
226 TII = MF.getTarget().getInstrInfo();
227 DOUT << "\n**** Local spiller rewriting function '"
228 << MF.getFunction()->getName() << "':\n";
230 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
232 RewriteMBB(*MBB, VRM);
236 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM);
240 /// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
241 /// top down, keep track of which spills slots are available in each register.
243 /// Note that not all physregs are created equal here. In particular, some
244 /// physregs are reloads that we are allowed to clobber or ignore at any time.
245 /// Other physregs are values that the register allocated program is using that
246 /// we cannot CHANGE, but we can read if we like. We keep track of this on a
247 /// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable
248 /// entries. The predicate 'canClobberPhysReg()' checks this bit and
249 /// addAvailable sets it if.
251 class VISIBILITY_HIDDEN AvailableSpills {
252 const MRegisterInfo *MRI;
253 const TargetInstrInfo *TII;
255 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual
256 // register values that are still available, due to being loaded or stored to,
257 // but not invalidated yet. It also tracks the instructions that defined
258 // or used the register.
259 typedef std::pair<unsigned, std::vector<MachineInstr*> > SSInfo;
260 std::map<int, SSInfo> SpillSlotsAvailable;
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;
267 void disallowClobberPhysRegOnly(unsigned PhysReg);
269 void ClobberPhysRegOnly(unsigned PhysReg);
271 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii)
272 : MRI(mri), TII(tii) {
275 const MRegisterInfo *getRegInfo() const { return MRI; }
277 /// getSpillSlotPhysReg - If the specified stack slot is available in a
278 /// physical register, return that PhysReg, otherwise return 0. It also
279 /// returns by reference the instruction that either defines or last uses
281 unsigned getSpillSlotPhysReg(int Slot, MachineInstr *&SSMI) const {
282 std::map<int, SSInfo>::const_iterator I = SpillSlotsAvailable.find(Slot);
283 if (I != SpillSlotsAvailable.end()) {
284 if (!I->second.second.empty())
285 SSMI = I->second.second.back();
286 return I->second.first >> 1; // Remove the CanClobber bit.
291 /// addLastUse - Add the last use information of all stack slots whose
292 /// values are available in the specific register.
293 void addLastUse(unsigned PhysReg, MachineInstr *Use) {
294 std::multimap<unsigned, int>::iterator I =
295 PhysRegsAvailable.lower_bound(PhysReg);
296 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
297 int Slot = I->second;
300 std::map<int, SSInfo>::iterator II = SpillSlotsAvailable.find(Slot);
301 assert(II != SpillSlotsAvailable.end() && "Slot not available!");
302 unsigned Val = II->second.first;
303 assert((Val >> 1) == PhysReg && "Bidirectional map mismatch!");
304 II->second.second.push_back(Use);
308 /// removeLastUse - Remove the last use information of all stack slots whose
309 /// values are available in the specific register.
310 void removeLastUse(unsigned PhysReg, MachineInstr *Use) {
311 std::multimap<unsigned, int>::iterator I =
312 PhysRegsAvailable.lower_bound(PhysReg);
313 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
314 int Slot = I->second;
317 std::map<int, SSInfo>::iterator II = SpillSlotsAvailable.find(Slot);
318 assert(II != SpillSlotsAvailable.end() && "Slot not available!");
319 unsigned Val = II->second.first;
320 assert((Val >> 1) == PhysReg && "Bidirectional map mismatch!");
321 if (II->second.second.back() == Use)
322 II->second.second.pop_back();
326 /// addAvailable - Mark that the specified stack slot is available in the
327 /// specified physreg. If CanClobber is true, the physreg can be modified at
328 /// any time without changing the semantics of the program.
329 void addAvailable(int Slot, MachineInstr *MI, unsigned Reg,
330 bool CanClobber = true) {
331 // If this stack slot is thought to be available in some other physreg,
332 // remove its record.
333 ModifyStackSlot(Slot);
335 PhysRegsAvailable.insert(std::make_pair(Reg, Slot));
336 std::vector<MachineInstr*> DefUses;
337 DefUses.push_back(MI);
338 SpillSlotsAvailable[Slot] =
339 std::make_pair((Reg << 1) | (unsigned)CanClobber, DefUses);
341 DOUT << "Remembering SS#" << Slot << " in physreg "
342 << MRI->getName(Reg) << "\n";
345 /// canClobberPhysReg - Return true if the spiller is allowed to change the
346 /// value of the specified stackslot register if it desires. The specified
347 /// stack slot must be available in a physreg for this query to make sense.
348 bool canClobberPhysReg(int Slot) const {
349 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!");
350 return SpillSlotsAvailable.find(Slot)->second.first & 1;
353 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
354 /// stackslot register. The register is still available but is no longer
355 /// allowed to be modifed.
356 void disallowClobberPhysReg(unsigned PhysReg);
358 /// ClobberPhysReg - This is called when the specified physreg changes
359 /// value. We use this to invalidate any info about stuff we thing lives in
360 /// it and any of its aliases.
361 void ClobberPhysReg(unsigned PhysReg);
363 /// ModifyStackSlot - This method is called when the value in a stack slot
364 /// changes. This removes information about which register the previous value
365 /// for this slot lives in (as the previous value is dead now).
366 void ModifyStackSlot(int Slot);
370 /// disallowClobberPhysRegOnly - Unset the CanClobber bit of the specified
371 /// stackslot register. The register is still available but is no longer
372 /// allowed to be modifed.
373 void AvailableSpills::disallowClobberPhysRegOnly(unsigned PhysReg) {
374 std::multimap<unsigned, int>::iterator I =
375 PhysRegsAvailable.lower_bound(PhysReg);
376 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
377 int Slot = I->second;
379 assert((SpillSlotsAvailable[Slot].first >> 1) == PhysReg &&
380 "Bidirectional map mismatch!");
381 SpillSlotsAvailable[Slot].first &= ~1;
382 DOUT << "PhysReg " << MRI->getName(PhysReg)
383 << " copied, it is available for use but can no longer be modified\n";
387 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
388 /// stackslot register and its aliases. The register and its aliases may
389 /// still available but is no longer allowed to be modifed.
390 void AvailableSpills::disallowClobberPhysReg(unsigned PhysReg) {
391 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
392 disallowClobberPhysRegOnly(*AS);
393 disallowClobberPhysRegOnly(PhysReg);
396 /// ClobberPhysRegOnly - This is called when the specified physreg changes
397 /// value. We use this to invalidate any info about stuff we thing lives in it.
398 void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
399 std::multimap<unsigned, int>::iterator I =
400 PhysRegsAvailable.lower_bound(PhysReg);
401 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
402 int Slot = I->second;
403 PhysRegsAvailable.erase(I++);
404 assert((SpillSlotsAvailable[Slot].first >> 1) == PhysReg &&
405 "Bidirectional map mismatch!");
406 SpillSlotsAvailable.erase(Slot);
407 DOUT << "PhysReg " << MRI->getName(PhysReg)
408 << " clobbered, invalidating SS#" << Slot << "\n";
412 /// ClobberPhysReg - This is called when the specified physreg changes
413 /// value. We use this to invalidate any info about stuff we thing lives in
414 /// it and any of its aliases.
415 void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
416 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
417 ClobberPhysRegOnly(*AS);
418 ClobberPhysRegOnly(PhysReg);
421 /// ModifyStackSlot - This method is called when the value in a stack slot
422 /// changes. This removes information about which register the previous value
423 /// for this slot lives in (as the previous value is dead now).
424 void AvailableSpills::ModifyStackSlot(int Slot) {
425 std::map<int, SSInfo>::iterator It = SpillSlotsAvailable.find(Slot);
426 if (It == SpillSlotsAvailable.end()) return;
427 unsigned Reg = It->second.first >> 1;
428 SpillSlotsAvailable.erase(It);
430 // This register may hold the value of multiple stack slots, only remove this
431 // stack slot from the set of values the register contains.
432 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
434 assert(I != PhysRegsAvailable.end() && I->first == Reg &&
435 "Map inverse broken!");
436 if (I->second == Slot) break;
438 PhysRegsAvailable.erase(I);
443 // ReusedOp - For each reused operand, we keep track of a bit of information, in
444 // case we need to rollback upon processing a new operand. See comments below.
447 // The MachineInstr operand that reused an available value.
450 // StackSlot - The spill slot of the value being reused.
453 // PhysRegReused - The physical register the value was available in.
454 unsigned PhysRegReused;
456 // AssignedPhysReg - The physreg that was assigned for use by the reload.
457 unsigned AssignedPhysReg;
459 // VirtReg - The virtual register itself.
462 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
464 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr),
468 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
469 /// is reused instead of reloaded.
470 class VISIBILITY_HIDDEN ReuseInfo {
472 std::vector<ReusedOp> Reuses;
473 BitVector PhysRegsClobbered;
475 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) {
476 PhysRegsClobbered.resize(mri->getNumRegs());
479 bool hasReuses() const {
480 return !Reuses.empty();
483 /// addReuse - If we choose to reuse a virtual register that is already
484 /// available instead of reloading it, remember that we did so.
485 void addReuse(unsigned OpNo, unsigned StackSlot,
486 unsigned PhysRegReused, unsigned AssignedPhysReg,
488 // If the reload is to the assigned register anyway, no undo will be
490 if (PhysRegReused == AssignedPhysReg) return;
492 // Otherwise, remember this.
493 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused,
494 AssignedPhysReg, VirtReg));
497 void markClobbered(unsigned PhysReg) {
498 PhysRegsClobbered.set(PhysReg);
501 bool isClobbered(unsigned PhysReg) const {
502 return PhysRegsClobbered.test(PhysReg);
505 /// GetRegForReload - We are about to emit a reload into PhysReg. If there
506 /// is some other operand that is using the specified register, either pick
507 /// a new register to use, or evict the previous reload and use this reg.
508 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
509 AvailableSpills &Spills,
510 std::map<int, MachineInstr*> &MaybeDeadStores,
511 SmallSet<unsigned, 8> &Rejected) {
512 if (Reuses.empty()) return PhysReg; // This is most often empty.
514 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
515 ReusedOp &Op = Reuses[ro];
516 // If we find some other reuse that was supposed to use this register
517 // exactly for its reload, we can change this reload to use ITS reload
518 // register. That is, unless its reload register has already been
519 // considered and subsequently rejected because it has also been reused
520 // by another operand.
521 if (Op.PhysRegReused == PhysReg &&
522 Rejected.count(Op.AssignedPhysReg) == 0) {
523 // Yup, use the reload register that we didn't use before.
524 unsigned NewReg = Op.AssignedPhysReg;
525 Rejected.insert(PhysReg);
526 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores, Rejected);
528 // Otherwise, we might also have a problem if a previously reused
529 // value aliases the new register. If so, codegen the previous reload
531 unsigned PRRU = Op.PhysRegReused;
532 const MRegisterInfo *MRI = Spills.getRegInfo();
533 if (MRI->areAliases(PRRU, PhysReg)) {
534 // Okay, we found out that an alias of a reused register
535 // was used. This isn't good because it means we have
536 // to undo a previous reuse.
537 MachineBasicBlock *MBB = MI->getParent();
538 const TargetRegisterClass *AliasRC =
539 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg);
541 // Copy Op out of the vector and remove it, we're going to insert an
542 // explicit load for it.
544 Reuses.erase(Reuses.begin()+ro);
546 // Ok, we're going to try to reload the assigned physreg into the
547 // slot that we were supposed to in the first place. However, that
548 // register could hold a reuse. Check to see if it conflicts or
549 // would prefer us to use a different register.
550 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg,
551 MI, Spills, MaybeDeadStores, Rejected);
553 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg,
554 NewOp.StackSlot, AliasRC);
555 Spills.ClobberPhysReg(NewPhysReg);
556 Spills.ClobberPhysReg(NewOp.PhysRegReused);
558 // Any stores to this stack slot are not dead anymore.
559 MaybeDeadStores.erase(NewOp.StackSlot);
561 MI->getOperand(NewOp.Operand).setReg(NewPhysReg);
563 Spills.addAvailable(NewOp.StackSlot, MI, NewPhysReg);
565 DEBUG(MachineBasicBlock::iterator MII = MI;
566 DOUT << '\t' << *prior(MII));
568 DOUT << "Reuse undone!\n";
571 // Finally, PhysReg is now available, go ahead and use it.
579 /// GetRegForReload - Helper for the above GetRegForReload(). Add a
580 /// 'Rejected' set to remember which registers have been considered and
581 /// rejected for the reload. This avoids infinite looping in case like
584 /// t2 <- assigned r0 for use by the reload but ended up reuse r1
585 /// t3 <- assigned r1 for use by the reload but ended up reuse r0
587 /// sees r1 is taken by t2, tries t2's reload register r0
588 /// sees r0 is taken by t3, tries t3's reload register r1
589 /// sees r1 is taken by t2, tries t2's reload register r0 ...
590 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
591 AvailableSpills &Spills,
592 std::map<int, MachineInstr*> &MaybeDeadStores) {
593 SmallSet<unsigned, 8> Rejected;
594 return GetRegForReload(PhysReg, MI, Spills, MaybeDeadStores, Rejected);
600 /// rewriteMBB - Keep track of which spills are available even after the
601 /// register allocator is done with them. If possible, avoid reloading vregs.
602 void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
604 DOUT << MBB.getBasicBlock()->getName() << ":\n";
606 // Spills - Keep track of which spilled values are available in physregs so
607 // that we can choose to reuse the physregs instead of emitting reloads.
608 AvailableSpills Spills(MRI, TII);
610 // MaybeDeadStores - When we need to write a value back into a stack slot,
611 // keep track of the inserted store. If the stack slot value is never read
612 // (because the value was used from some available register, for example), and
613 // subsequently stored to, the original store is dead. This map keeps track
614 // of inserted stores that are not used. If we see a subsequent store to the
615 // same stack slot, the original store is deleted.
616 std::map<int, MachineInstr*> MaybeDeadStores;
618 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs();
620 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
622 MachineInstr &MI = *MII;
623 MachineBasicBlock::iterator NextMII = MII; ++NextMII;
625 /// ReusedOperands - Keep track of operand reuse in case we need to undo
627 ReuseInfo ReusedOperands(MI, MRI);
629 // Loop over all of the implicit defs, clearing them from our available
631 const TargetInstrDescriptor *TID = MI.getInstrDescriptor();
632 const unsigned *ImpDef = TID->ImplicitDefs;
634 for ( ; *ImpDef; ++ImpDef) {
635 PhysRegsUsed[*ImpDef] = true;
636 ReusedOperands.markClobbered(*ImpDef);
637 Spills.ClobberPhysReg(*ImpDef);
641 // Process all of the spilled uses and all non spilled reg references.
642 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
643 MachineOperand &MO = MI.getOperand(i);
644 if (!MO.isRegister() || MO.getReg() == 0)
645 continue; // Ignore non-register operands.
647 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) {
648 // Ignore physregs for spilling, but remember that it is used by this
650 PhysRegsUsed[MO.getReg()] = true;
651 ReusedOperands.markClobbered(MO.getReg());
655 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) &&
656 "Not a virtual or a physical register?");
658 unsigned VirtReg = MO.getReg();
659 if (!VRM.hasStackSlot(VirtReg)) {
660 // This virtual register was assigned a physreg!
661 unsigned Phys = VRM.getPhys(VirtReg);
662 PhysRegsUsed[Phys] = true;
664 ReusedOperands.markClobbered(Phys);
665 MI.getOperand(i).setReg(Phys);
669 // This virtual register is now known to be a spilled value.
671 continue; // Handle defs in the loop below (handle use&def here though)
673 int StackSlot = VRM.getStackSlot(VirtReg);
676 // Check to see if this stack slot is available.
677 MachineInstr *SSMI = NULL;
678 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot, SSMI))) {
679 // This spilled operand might be part of a two-address operand. If this
680 // is the case, then changing it will necessarily require changing the
681 // def part of the instruction as well. However, in some cases, we
682 // aren't allowed to modify the reused register. If none of these cases
684 bool CanReuse = true;
685 int ti = TID->getOperandConstraint(i, TOI::TIED_TO);
687 MI.getOperand(ti).isReg() &&
688 MI.getOperand(ti).getReg() == VirtReg) {
689 // Okay, we have a two address operand. We can reuse this physreg as
690 // long as we are allowed to clobber the value and there isn't an
691 // earlier def that has already clobbered the physreg.
692 CanReuse = Spills.canClobberPhysReg(StackSlot) &&
693 !ReusedOperands.isClobbered(PhysReg);
697 // If this stack slot value is already available, reuse it!
698 DOUT << "Reusing SS#" << StackSlot << " from physreg "
699 << MRI->getName(PhysReg) << " for vreg"
700 << VirtReg <<" instead of reloading into physreg "
701 << MRI->getName(VRM.getPhys(VirtReg)) << "\n";
702 MI.getOperand(i).setReg(PhysReg);
704 // Extend the live range of the MI that last kill the register if
707 MachineOperand *MOK = SSMI->findRegisterUseOperand(PhysReg, true);
712 // Unless it's the use of a two-address code, transfer the kill
713 // of the reused register to this use.
714 MI.getOperand(i).setIsKill();
715 Spills.addLastUse(PhysReg, &MI);
718 // The only technical detail we have is that we don't know that
719 // PhysReg won't be clobbered by a reloaded stack slot that occurs
720 // later in the instruction. In particular, consider 'op V1, V2'.
721 // If V1 is available in physreg R0, we would choose to reuse it
722 // here, instead of reloading it into the register the allocator
723 // indicated (say R1). However, V2 might have to be reloaded
724 // later, and it might indicate that it needs to live in R0. When
725 // this occurs, we need to have information available that
726 // indicates it is safe to use R1 for the reload instead of R0.
728 // To further complicate matters, we might conflict with an alias,
729 // or R0 and R1 might not be compatible with each other. In this
730 // case, we actually insert a reload for V1 in R1, ensuring that
731 // we can get at R0 or its alias.
732 ReusedOperands.addReuse(i, StackSlot, PhysReg,
733 VRM.getPhys(VirtReg), VirtReg);
735 // Only mark it clobbered if this is a use&def operand.
736 ReusedOperands.markClobbered(PhysReg);
741 // Otherwise we have a situation where we have a two-address instruction
742 // whose mod/ref operand needs to be reloaded. This reload is already
743 // available in some register "PhysReg", but if we used PhysReg as the
744 // operand to our 2-addr instruction, the instruction would modify
745 // PhysReg. This isn't cool if something later uses PhysReg and expects
746 // to get its initial value.
748 // To avoid this problem, and to avoid doing a load right after a store,
749 // we emit a copy from PhysReg into the designated register for this
751 unsigned DesignatedReg = VRM.getPhys(VirtReg);
752 assert(DesignatedReg && "Must map virtreg to physreg!");
754 // Note that, if we reused a register for a previous operand, the
755 // register we want to reload into might not actually be
756 // available. If this occurs, use the register indicated by the
758 if (ReusedOperands.hasReuses())
759 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI,
760 Spills, MaybeDeadStores);
762 // If the mapped designated register is actually the physreg we have
763 // incoming, we don't need to inserted a dead copy.
764 if (DesignatedReg == PhysReg) {
765 // If this stack slot value is already available, reuse it!
766 DOUT << "Reusing SS#" << StackSlot << " from physreg "
767 << MRI->getName(PhysReg) << " for vreg"
769 << " instead of reloading into same physreg.\n";
770 MI.getOperand(i).setReg(PhysReg);
771 ReusedOperands.markClobbered(PhysReg);
776 const TargetRegisterClass* RC =
777 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
779 PhysRegsUsed[DesignatedReg] = true;
780 ReusedOperands.markClobbered(DesignatedReg);
781 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC);
783 // Extend the live range of the MI that last kill the register if
786 MachineOperand *MOK = SSMI->findRegisterUseOperand(PhysReg, true);
790 MachineInstr *CopyMI = prior(MII);
791 MachineOperand *MOU = CopyMI->findRegisterUseOperand(PhysReg);
793 Spills.addLastUse(PhysReg, &MI);
795 // This invalidates DesignatedReg.
796 Spills.ClobberPhysReg(DesignatedReg);
798 Spills.addAvailable(StackSlot, &MI, DesignatedReg);
799 MI.getOperand(i).setReg(DesignatedReg);
800 DOUT << '\t' << *prior(MII);
805 // Otherwise, reload it and remember that we have it.
806 PhysReg = VRM.getPhys(VirtReg);
807 assert(PhysReg && "Must map virtreg to physreg!");
808 const TargetRegisterClass* RC =
809 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
811 // Note that, if we reused a register for a previous operand, the
812 // register we want to reload into might not actually be
813 // available. If this occurs, use the register indicated by the
815 if (ReusedOperands.hasReuses())
816 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
817 Spills, MaybeDeadStores);
819 PhysRegsUsed[PhysReg] = true;
820 ReusedOperands.markClobbered(PhysReg);
821 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
822 // This invalidates PhysReg.
823 Spills.ClobberPhysReg(PhysReg);
825 // Any stores to this stack slot are not dead anymore.
826 MaybeDeadStores.erase(StackSlot);
827 Spills.addAvailable(StackSlot, &MI, PhysReg);
828 // Assumes this is the last use. IsKill will be unset if reg is reused
829 // unless it's a two-address operand.
830 if (TID->getOperandConstraint(i, TOI::TIED_TO) == -1)
831 MI.getOperand(i).setIsKill();
833 MI.getOperand(i).setReg(PhysReg);
834 DOUT << '\t' << *prior(MII);
839 // If we have folded references to memory operands, make sure we clear all
840 // physical registers that may contain the value of the spilled virtual
842 VirtRegMap::MI2VirtMapTy::const_iterator I, End;
843 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
844 DOUT << "Folded vreg: " << I->second.first << " MR: "
846 unsigned VirtReg = I->second.first;
847 VirtRegMap::ModRef MR = I->second.second;
848 if (!VRM.hasStackSlot(VirtReg)) {
849 DOUT << ": No stack slot!\n";
852 int SS = VRM.getStackSlot(VirtReg);
853 DOUT << " - StackSlot: " << SS << "\n";
855 // If this folded instruction is just a use, check to see if it's a
856 // straight load from the virt reg slot.
857 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
859 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
860 if (FrameIdx == SS) {
861 // If this spill slot is available, turn it into a copy (or nothing)
862 // instead of leaving it as a load!
863 MachineInstr *SSMI = NULL;
864 if (unsigned InReg = Spills.getSpillSlotPhysReg(SS, SSMI)) {
865 DOUT << "Promoted Load To Copy: " << MI;
866 MachineFunction &MF = *MBB.getParent();
867 if (DestReg != InReg) {
868 MRI->copyRegToReg(MBB, &MI, DestReg, InReg,
869 MF.getSSARegMap()->getRegClass(VirtReg));
870 // Revisit the copy so we make sure to notice the effects of the
871 // operation on the destreg (either needing to RA it if it's
872 // virtual or needing to clobber any values if it's physical).
874 --NextMII; // backtrack to the copy.
876 DOUT << "Removing now-noop copy: " << MI;
878 // Either way, the live range of the last kill of InReg has been
879 // extended. Remove its kill.
881 MachineOperand *MOK = SSMI->findRegisterUseOperand(InReg, true);
885 if (NextMII != MBB.end()) {
886 // If NextMII uses InReg (must be the copy?), mark it killed.
887 MachineOperand *MOU = NextMII->findRegisterUseOperand(InReg);
890 Spills.addLastUse(InReg, &(*NextMII));
894 VRM.RemoveFromFoldedVirtMap(&MI);
896 goto ProcessNextInst;
902 // If this reference is not a use, any previous store is now dead.
903 // Otherwise, the store to this stack slot is not dead anymore.
904 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS);
905 if (MDSI != MaybeDeadStores.end()) {
906 if (MR & VirtRegMap::isRef) // Previous store is not dead.
907 MaybeDeadStores.erase(MDSI);
909 // If we get here, the store is dead, nuke it now.
910 assert(VirtRegMap::isMod && "Can't be modref!");
911 DOUT << "Removed dead store:\t" << *MDSI->second;
912 MBB.erase(MDSI->second);
913 VRM.RemoveFromFoldedVirtMap(MDSI->second);
914 MaybeDeadStores.erase(MDSI);
919 // If the spill slot value is available, and this is a new definition of
920 // the value, the value is not available anymore.
921 if (MR & VirtRegMap::isMod) {
922 // Notice that the value in this stack slot has been modified.
923 Spills.ModifyStackSlot(SS);
925 // If this is *just* a mod of the value, check to see if this is just a
926 // store to the spill slot (i.e. the spill got merged into the copy). If
927 // so, realize that the vreg is available now, and add the store to the
928 // MaybeDeadStore info.
930 if (!(MR & VirtRegMap::isRef)) {
931 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
932 assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
933 "Src hasn't been allocated yet?");
934 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark
935 // this as a potentially dead store in case there is a subsequent
936 // store into the stack slot without a read from it.
937 MaybeDeadStores[StackSlot] = &MI;
939 // If the stack slot value was previously available in some other
940 // register, change it now. Otherwise, make the register available,
942 Spills.addAvailable(StackSlot, &MI, SrcReg, false/*don't clobber*/);
948 // Process all of the spilled defs.
949 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
950 MachineOperand &MO = MI.getOperand(i);
951 if (MO.isRegister() && MO.getReg() && MO.isDef()) {
952 unsigned VirtReg = MO.getReg();
954 if (!MRegisterInfo::isVirtualRegister(VirtReg)) {
955 // Check to see if this is a noop copy. If so, eliminate the
956 // instruction before considering the dest reg to be changed.
958 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
960 DOUT << "Removing now-noop copy: " << MI;
961 Spills.removeLastUse(Src, &MI);
963 VRM.RemoveFromFoldedVirtMap(&MI);
964 Spills.disallowClobberPhysReg(VirtReg);
965 goto ProcessNextInst;
968 // If it's not a no-op copy, it clobbers the value in the destreg.
969 Spills.ClobberPhysReg(VirtReg);
970 ReusedOperands.markClobbered(VirtReg);
972 // Check to see if this instruction is a load from a stack slot into
973 // a register. If so, this provides the stack slot value in the reg.
975 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
976 assert(DestReg == VirtReg && "Unknown load situation!");
978 // Otherwise, if it wasn't available, remember that it is now!
979 Spills.addAvailable(FrameIdx, &MI, DestReg);
980 goto ProcessNextInst;
986 // The only vregs left are stack slot definitions.
987 int StackSlot = VRM.getStackSlot(VirtReg);
988 const TargetRegisterClass *RC =
989 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
991 // If this def is part of a two-address operand, make sure to execute
992 // the store from the correct physical register.
994 int TiedOp = MI.getInstrDescriptor()->findTiedToSrcOperand(i);
996 PhysReg = MI.getOperand(TiedOp).getReg();
998 PhysReg = VRM.getPhys(VirtReg);
999 if (ReusedOperands.isClobbered(PhysReg)) {
1000 // Another def has taken the assigned physreg. It must have been a
1001 // use&def which got it due to reuse. Undo the reuse!
1002 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
1003 Spills, MaybeDeadStores);
1007 PhysRegsUsed[PhysReg] = true;
1008 ReusedOperands.markClobbered(PhysReg);
1009 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
1010 DOUT << "Store:\t" << *next(MII);
1011 MI.getOperand(i).setReg(PhysReg);
1013 // If there is a dead store to this stack slot, nuke it now.
1014 MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
1016 DOUT << "Removed dead store:\t" << *LastStore;
1018 MBB.erase(LastStore);
1019 VRM.RemoveFromFoldedVirtMap(LastStore);
1021 LastStore = next(MII);
1023 // If the stack slot value was previously available in some other
1024 // register, change it now. Otherwise, make the register available,
1026 Spills.ModifyStackSlot(StackSlot);
1027 Spills.ClobberPhysReg(PhysReg);
1028 Spills.addAvailable(StackSlot, LastStore, PhysReg);
1031 // Check to see if this is a noop copy. If so, eliminate the
1032 // instruction before considering the dest reg to be changed.
1035 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
1037 DOUT << "Removing now-noop copy: " << MI;
1039 VRM.RemoveFromFoldedVirtMap(&MI);
1040 goto ProcessNextInst;
1052 llvm::Spiller* llvm::createSpiller() {
1053 switch (SpillerOpt) {
1054 default: assert(0 && "Unreachable!");
1056 return new LocalSpiller();
1058 return new SimpleSpiller();