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 instruction that last defined
258 // or used the register.
259 typedef std::pair<unsigned, 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 SSMI = I->second.second;
285 return I->second.first >> 1; // Remove the CanClobber bit.
290 /// UpdateLastUses - Update the last use information of all stack slots whose
291 /// values are available in the specific register.
292 void UpdateLastUse(unsigned PhysReg, MachineInstr *Use) {
293 std::multimap<unsigned, int>::iterator I =
294 PhysRegsAvailable.lower_bound(PhysReg);
295 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
296 int Slot = I->second;
299 std::map<int, SSInfo>::iterator II = SpillSlotsAvailable.find(Slot);
300 assert(II != SpillSlotsAvailable.end() && "Slot not available!");
301 unsigned Val = II->second.first;
302 assert((Val >> 1) == PhysReg && "Bidirectional map mismatch!");
303 SpillSlotsAvailable.erase(Slot);
304 SpillSlotsAvailable[Slot] = std::make_pair(Val, Use);
308 /// addAvailable - Mark that the specified stack slot is available in the
309 /// specified physreg. If CanClobber is true, the physreg can be modified at
310 /// any time without changing the semantics of the program.
311 void addAvailable(int Slot, MachineInstr *MI, unsigned Reg,
312 bool CanClobber = true) {
313 // If this stack slot is thought to be available in some other physreg,
314 // remove its record.
315 ModifyStackSlot(Slot);
317 PhysRegsAvailable.insert(std::make_pair(Reg, Slot));
318 SpillSlotsAvailable[Slot] =
319 std::make_pair((Reg << 1) | (unsigned)CanClobber, MI);
321 DOUT << "Remembering SS#" << Slot << " in physreg "
322 << MRI->getName(Reg) << "\n";
325 /// canClobberPhysReg - Return true if the spiller is allowed to change the
326 /// value of the specified stackslot register if it desires. The specified
327 /// stack slot must be available in a physreg for this query to make sense.
328 bool canClobberPhysReg(int Slot) const {
329 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!");
330 return SpillSlotsAvailable.find(Slot)->second.first & 1;
333 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
334 /// stackslot register. The register is still available but is no longer
335 /// allowed to be modifed.
336 void disallowClobberPhysReg(unsigned PhysReg);
338 /// ClobberPhysReg - This is called when the specified physreg changes
339 /// value. We use this to invalidate any info about stuff we thing lives in
340 /// it and any of its aliases.
341 void ClobberPhysReg(unsigned PhysReg);
343 /// ModifyStackSlot - This method is called when the value in a stack slot
344 /// changes. This removes information about which register the previous value
345 /// for this slot lives in (as the previous value is dead now).
346 void ModifyStackSlot(int Slot);
350 /// disallowClobberPhysRegOnly - Unset the CanClobber bit of the specified
351 /// stackslot register. The register is still available but is no longer
352 /// allowed to be modifed.
353 void AvailableSpills::disallowClobberPhysRegOnly(unsigned PhysReg) {
354 std::multimap<unsigned, int>::iterator I =
355 PhysRegsAvailable.lower_bound(PhysReg);
356 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
357 int Slot = I->second;
359 assert((SpillSlotsAvailable[Slot].first >> 1) == PhysReg &&
360 "Bidirectional map mismatch!");
361 SpillSlotsAvailable[Slot].first &= ~1;
362 DOUT << "PhysReg " << MRI->getName(PhysReg)
363 << " copied, it is available for use but can no longer be modified\n";
367 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
368 /// stackslot register and its aliases. The register and its aliases may
369 /// still available but is no longer allowed to be modifed.
370 void AvailableSpills::disallowClobberPhysReg(unsigned PhysReg) {
371 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
372 disallowClobberPhysRegOnly(*AS);
373 disallowClobberPhysRegOnly(PhysReg);
376 /// ClobberPhysRegOnly - This is called when the specified physreg changes
377 /// value. We use this to invalidate any info about stuff we thing lives in it.
378 void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
379 std::multimap<unsigned, int>::iterator I =
380 PhysRegsAvailable.lower_bound(PhysReg);
381 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
382 int Slot = I->second;
383 PhysRegsAvailable.erase(I++);
384 assert((SpillSlotsAvailable[Slot].first >> 1) == PhysReg &&
385 "Bidirectional map mismatch!");
386 SpillSlotsAvailable.erase(Slot);
387 DOUT << "PhysReg " << MRI->getName(PhysReg)
388 << " clobbered, invalidating SS#" << Slot << "\n";
392 /// ClobberPhysReg - This is called when the specified physreg changes
393 /// value. We use this to invalidate any info about stuff we thing lives in
394 /// it and any of its aliases.
395 void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
396 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
397 ClobberPhysRegOnly(*AS);
398 ClobberPhysRegOnly(PhysReg);
401 /// ModifyStackSlot - This method is called when the value in a stack slot
402 /// changes. This removes information about which register the previous value
403 /// for this slot lives in (as the previous value is dead now).
404 void AvailableSpills::ModifyStackSlot(int Slot) {
405 std::map<int, SSInfo>::iterator It = SpillSlotsAvailable.find(Slot);
406 if (It == SpillSlotsAvailable.end()) return;
407 unsigned Reg = It->second.first >> 1;
408 SpillSlotsAvailable.erase(It);
410 // This register may hold the value of multiple stack slots, only remove this
411 // stack slot from the set of values the register contains.
412 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
414 assert(I != PhysRegsAvailable.end() && I->first == Reg &&
415 "Map inverse broken!");
416 if (I->second == Slot) break;
418 PhysRegsAvailable.erase(I);
423 // ReusedOp - For each reused operand, we keep track of a bit of information, in
424 // case we need to rollback upon processing a new operand. See comments below.
427 // The MachineInstr operand that reused an available value.
430 // StackSlot - The spill slot of the value being reused.
433 // PhysRegReused - The physical register the value was available in.
434 unsigned PhysRegReused;
436 // AssignedPhysReg - The physreg that was assigned for use by the reload.
437 unsigned AssignedPhysReg;
439 // VirtReg - The virtual register itself.
442 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
444 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr),
448 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
449 /// is reused instead of reloaded.
450 class VISIBILITY_HIDDEN ReuseInfo {
452 std::vector<ReusedOp> Reuses;
453 BitVector PhysRegsClobbered;
455 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) {
456 PhysRegsClobbered.resize(mri->getNumRegs());
459 bool hasReuses() const {
460 return !Reuses.empty();
463 /// addReuse - If we choose to reuse a virtual register that is already
464 /// available instead of reloading it, remember that we did so.
465 void addReuse(unsigned OpNo, unsigned StackSlot,
466 unsigned PhysRegReused, unsigned AssignedPhysReg,
468 // If the reload is to the assigned register anyway, no undo will be
470 if (PhysRegReused == AssignedPhysReg) return;
472 // Otherwise, remember this.
473 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused,
474 AssignedPhysReg, VirtReg));
477 void markClobbered(unsigned PhysReg) {
478 PhysRegsClobbered.set(PhysReg);
481 bool isClobbered(unsigned PhysReg) const {
482 return PhysRegsClobbered.test(PhysReg);
485 /// GetRegForReload - We are about to emit a reload into PhysReg. If there
486 /// is some other operand that is using the specified register, either pick
487 /// a new register to use, or evict the previous reload and use this reg.
488 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
489 AvailableSpills &Spills,
490 std::map<int, MachineInstr*> &MaybeDeadStores,
491 SmallSet<unsigned, 8> &Rejected) {
492 if (Reuses.empty()) return PhysReg; // This is most often empty.
494 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
495 ReusedOp &Op = Reuses[ro];
496 // If we find some other reuse that was supposed to use this register
497 // exactly for its reload, we can change this reload to use ITS reload
498 // register. That is, unless its reload register has already been
499 // considered and subsequently rejected because it has also been reused
500 // by another operand.
501 if (Op.PhysRegReused == PhysReg &&
502 Rejected.count(Op.AssignedPhysReg) == 0) {
503 // Yup, use the reload register that we didn't use before.
504 unsigned NewReg = Op.AssignedPhysReg;
505 Rejected.insert(PhysReg);
506 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores, Rejected);
508 // Otherwise, we might also have a problem if a previously reused
509 // value aliases the new register. If so, codegen the previous reload
511 unsigned PRRU = Op.PhysRegReused;
512 const MRegisterInfo *MRI = Spills.getRegInfo();
513 if (MRI->areAliases(PRRU, PhysReg)) {
514 // Okay, we found out that an alias of a reused register
515 // was used. This isn't good because it means we have
516 // to undo a previous reuse.
517 MachineBasicBlock *MBB = MI->getParent();
518 const TargetRegisterClass *AliasRC =
519 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg);
521 // Copy Op out of the vector and remove it, we're going to insert an
522 // explicit load for it.
524 Reuses.erase(Reuses.begin()+ro);
526 // Ok, we're going to try to reload the assigned physreg into the
527 // slot that we were supposed to in the first place. However, that
528 // register could hold a reuse. Check to see if it conflicts or
529 // would prefer us to use a different register.
530 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg,
531 MI, Spills, MaybeDeadStores, Rejected);
533 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg,
534 NewOp.StackSlot, AliasRC);
535 Spills.ClobberPhysReg(NewPhysReg);
536 Spills.ClobberPhysReg(NewOp.PhysRegReused);
538 // Any stores to this stack slot are not dead anymore.
539 MaybeDeadStores.erase(NewOp.StackSlot);
541 MI->getOperand(NewOp.Operand).setReg(NewPhysReg);
543 Spills.addAvailable(NewOp.StackSlot, MI, NewPhysReg);
545 DEBUG(MachineBasicBlock::iterator MII = MI;
546 DOUT << '\t' << *prior(MII));
548 DOUT << "Reuse undone!\n";
551 // Finally, PhysReg is now available, go ahead and use it.
559 /// GetRegForReload - Helper for the above GetRegForReload(). Add a
560 /// 'Rejected' set to remember which registers have been considered and
561 /// rejected for the reload. This avoids infinite looping in case like
564 /// t2 <- assigned r0 for use by the reload but ended up reuse r1
565 /// t3 <- assigned r1 for use by the reload but ended up reuse r0
567 /// sees r1 is taken by t2, tries t2's reload register r0
568 /// sees r0 is taken by t3, tries t3's reload register r1
569 /// sees r1 is taken by t2, tries t2's reload register r0 ...
570 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
571 AvailableSpills &Spills,
572 std::map<int, MachineInstr*> &MaybeDeadStores) {
573 SmallSet<unsigned, 8> Rejected;
574 return GetRegForReload(PhysReg, MI, Spills, MaybeDeadStores, Rejected);
580 /// rewriteMBB - Keep track of which spills are available even after the
581 /// register allocator is done with them. If possible, avoid reloading vregs.
582 void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
584 DOUT << MBB.getBasicBlock()->getName() << ":\n";
586 // Spills - Keep track of which spilled values are available in physregs so
587 // that we can choose to reuse the physregs instead of emitting reloads.
588 AvailableSpills Spills(MRI, TII);
590 // MaybeDeadStores - When we need to write a value back into a stack slot,
591 // keep track of the inserted store. If the stack slot value is never read
592 // (because the value was used from some available register, for example), and
593 // subsequently stored to, the original store is dead. This map keeps track
594 // of inserted stores that are not used. If we see a subsequent store to the
595 // same stack slot, the original store is deleted.
596 std::map<int, MachineInstr*> MaybeDeadStores;
598 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs();
600 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
602 MachineInstr &MI = *MII;
603 MachineBasicBlock::iterator NextMII = MII; ++NextMII;
605 /// ReusedOperands - Keep track of operand reuse in case we need to undo
607 ReuseInfo ReusedOperands(MI, MRI);
609 // Loop over all of the implicit defs, clearing them from our available
611 const TargetInstrDescriptor *TID = MI.getInstrDescriptor();
612 const unsigned *ImpDef = TID->ImplicitDefs;
614 for ( ; *ImpDef; ++ImpDef) {
615 PhysRegsUsed[*ImpDef] = true;
616 ReusedOperands.markClobbered(*ImpDef);
617 Spills.ClobberPhysReg(*ImpDef);
621 // Process all of the spilled uses and all non spilled reg references.
622 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
623 MachineOperand &MO = MI.getOperand(i);
624 if (!MO.isRegister() || MO.getReg() == 0)
625 continue; // Ignore non-register operands.
627 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) {
628 // Ignore physregs for spilling, but remember that it is used by this
630 PhysRegsUsed[MO.getReg()] = true;
631 ReusedOperands.markClobbered(MO.getReg());
635 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) &&
636 "Not a virtual or a physical register?");
638 unsigned VirtReg = MO.getReg();
639 if (!VRM.hasStackSlot(VirtReg)) {
640 // This virtual register was assigned a physreg!
641 unsigned Phys = VRM.getPhys(VirtReg);
642 PhysRegsUsed[Phys] = true;
644 ReusedOperands.markClobbered(Phys);
645 MI.getOperand(i).setReg(Phys);
649 // This virtual register is now known to be a spilled value.
651 continue; // Handle defs in the loop below (handle use&def here though)
653 int StackSlot = VRM.getStackSlot(VirtReg);
656 // Check to see if this stack slot is available.
657 MachineInstr *SSMI = NULL;
658 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot, SSMI))) {
659 // This spilled operand might be part of a two-address operand. If this
660 // is the case, then changing it will necessarily require changing the
661 // def part of the instruction as well. However, in some cases, we
662 // aren't allowed to modify the reused register. If none of these cases
664 bool CanReuse = true;
665 int ti = TID->getOperandConstraint(i, TOI::TIED_TO);
667 MI.getOperand(ti).isReg() &&
668 MI.getOperand(ti).getReg() == VirtReg) {
669 // Okay, we have a two address operand. We can reuse this physreg as
670 // long as we are allowed to clobber the value and there isn't an
671 // earlier def that has already clobbered the physreg.
672 CanReuse = Spills.canClobberPhysReg(StackSlot) &&
673 !ReusedOperands.isClobbered(PhysReg);
677 // If this stack slot value is already available, reuse it!
678 DOUT << "Reusing SS#" << StackSlot << " from physreg "
679 << MRI->getName(PhysReg) << " for vreg"
680 << VirtReg <<" instead of reloading into physreg "
681 << MRI->getName(VRM.getPhys(VirtReg)) << "\n";
682 MI.getOperand(i).setReg(PhysReg);
684 // Extend the live range of the MI that last kill the register if
686 MachineOperand *MOK = SSMI->findRegisterUseOperand(PhysReg, true);
690 // Unless it's the use of a two-address code, transfer the kill
691 // of the reused register to this use.
692 MI.getOperand(i).setIsKill();
693 Spills.UpdateLastUse(PhysReg, &MI);
697 // The only technical detail we have is that we don't know that
698 // PhysReg won't be clobbered by a reloaded stack slot that occurs
699 // later in the instruction. In particular, consider 'op V1, V2'.
700 // If V1 is available in physreg R0, we would choose to reuse it
701 // here, instead of reloading it into the register the allocator
702 // indicated (say R1). However, V2 might have to be reloaded
703 // later, and it might indicate that it needs to live in R0. When
704 // this occurs, we need to have information available that
705 // indicates it is safe to use R1 for the reload instead of R0.
707 // To further complicate matters, we might conflict with an alias,
708 // or R0 and R1 might not be compatible with each other. In this
709 // case, we actually insert a reload for V1 in R1, ensuring that
710 // we can get at R0 or its alias.
711 ReusedOperands.addReuse(i, StackSlot, PhysReg,
712 VRM.getPhys(VirtReg), VirtReg);
714 // Only mark it clobbered if this is a use&def operand.
715 ReusedOperands.markClobbered(PhysReg);
720 // Otherwise we have a situation where we have a two-address instruction
721 // whose mod/ref operand needs to be reloaded. This reload is already
722 // available in some register "PhysReg", but if we used PhysReg as the
723 // operand to our 2-addr instruction, the instruction would modify
724 // PhysReg. This isn't cool if something later uses PhysReg and expects
725 // to get its initial value.
727 // To avoid this problem, and to avoid doing a load right after a store,
728 // we emit a copy from PhysReg into the designated register for this
730 unsigned DesignatedReg = VRM.getPhys(VirtReg);
731 assert(DesignatedReg && "Must map virtreg to physreg!");
733 // Note that, if we reused a register for a previous operand, the
734 // register we want to reload into might not actually be
735 // available. If this occurs, use the register indicated by the
737 if (ReusedOperands.hasReuses())
738 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI,
739 Spills, MaybeDeadStores);
741 // If the mapped designated register is actually the physreg we have
742 // incoming, we don't need to inserted a dead copy.
743 if (DesignatedReg == PhysReg) {
744 // If this stack slot value is already available, reuse it!
745 DOUT << "Reusing SS#" << StackSlot << " from physreg "
746 << MRI->getName(PhysReg) << " for vreg"
748 << " instead of reloading into same physreg.\n";
749 MI.getOperand(i).setReg(PhysReg);
750 ReusedOperands.markClobbered(PhysReg);
755 const TargetRegisterClass* RC =
756 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
758 PhysRegsUsed[DesignatedReg] = true;
759 ReusedOperands.markClobbered(DesignatedReg);
760 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC);
762 // Extend the live range of the MI that last kill the register if
765 MachineOperand *MOK = SSMI->findRegisterUseOperand(PhysReg, true);
767 MachineInstr *CopyMI = prior(MII);
768 MachineOperand *MOU = CopyMI->findRegisterUseOperand(PhysReg);
771 Spills.UpdateLastUse(PhysReg, &MI);
775 // This invalidates DesignatedReg.
776 Spills.ClobberPhysReg(DesignatedReg);
778 Spills.addAvailable(StackSlot, &MI, DesignatedReg);
779 MI.getOperand(i).setReg(DesignatedReg);
780 DOUT << '\t' << *prior(MII);
785 // Otherwise, reload it and remember that we have it.
786 PhysReg = VRM.getPhys(VirtReg);
787 assert(PhysReg && "Must map virtreg to physreg!");
788 const TargetRegisterClass* RC =
789 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
791 // Note that, if we reused a register for a previous operand, the
792 // register we want to reload into might not actually be
793 // available. If this occurs, use the register indicated by the
795 if (ReusedOperands.hasReuses())
796 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
797 Spills, MaybeDeadStores);
799 PhysRegsUsed[PhysReg] = true;
800 ReusedOperands.markClobbered(PhysReg);
801 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
802 // This invalidates PhysReg.
803 Spills.ClobberPhysReg(PhysReg);
805 // Any stores to this stack slot are not dead anymore.
806 MaybeDeadStores.erase(StackSlot);
807 Spills.addAvailable(StackSlot, &MI, PhysReg);
808 // Assumes this is the last use. IsKill will be unset if reg is reused
809 // unless it's a two-address operand.
810 if (TID->getOperandConstraint(i, TOI::TIED_TO) == -1)
811 MI.getOperand(i).setIsKill();
813 MI.getOperand(i).setReg(PhysReg);
814 DOUT << '\t' << *prior(MII);
819 // If we have folded references to memory operands, make sure we clear all
820 // physical registers that may contain the value of the spilled virtual
822 VirtRegMap::MI2VirtMapTy::const_iterator I, End;
823 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
824 DOUT << "Folded vreg: " << I->second.first << " MR: "
826 unsigned VirtReg = I->second.first;
827 VirtRegMap::ModRef MR = I->second.second;
828 if (!VRM.hasStackSlot(VirtReg)) {
829 DOUT << ": No stack slot!\n";
832 int SS = VRM.getStackSlot(VirtReg);
833 DOUT << " - StackSlot: " << SS << "\n";
835 // If this folded instruction is just a use, check to see if it's a
836 // straight load from the virt reg slot.
837 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
839 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
840 if (FrameIdx == SS) {
841 // If this spill slot is available, turn it into a copy (or nothing)
842 // instead of leaving it as a load!
843 MachineInstr *SSMI = NULL;
844 if (unsigned InReg = Spills.getSpillSlotPhysReg(SS, SSMI)) {
845 DOUT << "Promoted Load To Copy: " << MI;
846 MachineFunction &MF = *MBB.getParent();
847 if (DestReg != InReg) {
848 MRI->copyRegToReg(MBB, &MI, DestReg, InReg,
849 MF.getSSARegMap()->getRegClass(VirtReg));
850 // Revisit the copy so we make sure to notice the effects of the
851 // operation on the destreg (either needing to RA it if it's
852 // virtual or needing to clobber any values if it's physical).
854 --NextMII; // backtrack to the copy.
856 DOUT << "Removing now-noop copy: " << MI;
858 // Either way, the live range of the last kill of InReg has been
859 // extended. Remove its kill.
860 MachineOperand *MOK = SSMI->findRegisterUseOperand(InReg, true);
861 if (MOK && NextMII != MBB.end()) {
863 // If NextMII uses InReg (must be the copy?), mark it killed.
864 MachineOperand *MOU = NextMII->findRegisterUseOperand(InReg);
867 Spills.UpdateLastUse(InReg, &(*NextMII));
871 VRM.RemoveFromFoldedVirtMap(&MI);
873 goto ProcessNextInst;
879 // If this reference is not a use, any previous store is now dead.
880 // Otherwise, the store to this stack slot is not dead anymore.
881 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS);
882 if (MDSI != MaybeDeadStores.end()) {
883 if (MR & VirtRegMap::isRef) // Previous store is not dead.
884 MaybeDeadStores.erase(MDSI);
886 // If we get here, the store is dead, nuke it now.
887 assert(VirtRegMap::isMod && "Can't be modref!");
888 DOUT << "Removed dead store:\t" << *MDSI->second;
889 MBB.erase(MDSI->second);
890 VRM.RemoveFromFoldedVirtMap(MDSI->second);
891 MaybeDeadStores.erase(MDSI);
896 // If the spill slot value is available, and this is a new definition of
897 // the value, the value is not available anymore.
898 if (MR & VirtRegMap::isMod) {
899 // Notice that the value in this stack slot has been modified.
900 Spills.ModifyStackSlot(SS);
902 // If this is *just* a mod of the value, check to see if this is just a
903 // store to the spill slot (i.e. the spill got merged into the copy). If
904 // so, realize that the vreg is available now, and add the store to the
905 // MaybeDeadStore info.
907 if (!(MR & VirtRegMap::isRef)) {
908 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
909 assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
910 "Src hasn't been allocated yet?");
911 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark
912 // this as a potentially dead store in case there is a subsequent
913 // store into the stack slot without a read from it.
914 MaybeDeadStores[StackSlot] = &MI;
916 // If the stack slot value was previously available in some other
917 // register, change it now. Otherwise, make the register available,
919 Spills.addAvailable(StackSlot, &MI, SrcReg, false/*don't clobber*/);
925 // Process all of the spilled defs.
926 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
927 MachineOperand &MO = MI.getOperand(i);
928 if (MO.isRegister() && MO.getReg() && MO.isDef()) {
929 unsigned VirtReg = MO.getReg();
931 if (!MRegisterInfo::isVirtualRegister(VirtReg)) {
932 // Check to see if this is a noop copy. If so, eliminate the
933 // instruction before considering the dest reg to be changed.
935 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
937 DOUT << "Removing now-noop copy: " << MI;
939 VRM.RemoveFromFoldedVirtMap(&MI);
940 Spills.UpdateLastUse(Src, NULL);
941 Spills.disallowClobberPhysReg(VirtReg);
942 goto ProcessNextInst;
945 // If it's not a no-op copy, it clobbers the value in the destreg.
946 Spills.ClobberPhysReg(VirtReg);
947 ReusedOperands.markClobbered(VirtReg);
949 // Check to see if this instruction is a load from a stack slot into
950 // a register. If so, this provides the stack slot value in the reg.
952 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
953 assert(DestReg == VirtReg && "Unknown load situation!");
955 // Otherwise, if it wasn't available, remember that it is now!
956 Spills.addAvailable(FrameIdx, &MI, DestReg);
957 goto ProcessNextInst;
963 // The only vregs left are stack slot definitions.
964 int StackSlot = VRM.getStackSlot(VirtReg);
965 const TargetRegisterClass *RC =
966 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
968 // If this def is part of a two-address operand, make sure to execute
969 // the store from the correct physical register.
971 int TiedOp = MI.getInstrDescriptor()->findTiedToSrcOperand(i);
973 PhysReg = MI.getOperand(TiedOp).getReg();
975 PhysReg = VRM.getPhys(VirtReg);
976 if (ReusedOperands.isClobbered(PhysReg)) {
977 // Another def has taken the assigned physreg. It must have been a
978 // use&def which got it due to reuse. Undo the reuse!
979 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
980 Spills, MaybeDeadStores);
984 PhysRegsUsed[PhysReg] = true;
985 ReusedOperands.markClobbered(PhysReg);
986 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
987 DOUT << "Store:\t" << *next(MII);
988 MI.getOperand(i).setReg(PhysReg);
990 // If there is a dead store to this stack slot, nuke it now.
991 MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
993 DOUT << "Removed dead store:\t" << *LastStore;
995 MBB.erase(LastStore);
996 VRM.RemoveFromFoldedVirtMap(LastStore);
998 LastStore = next(MII);
1000 // If the stack slot value was previously available in some other
1001 // register, change it now. Otherwise, make the register available,
1003 Spills.ModifyStackSlot(StackSlot);
1004 Spills.ClobberPhysReg(PhysReg);
1005 Spills.addAvailable(StackSlot, LastStore, PhysReg);
1008 // Check to see if this is a noop copy. If so, eliminate the
1009 // instruction before considering the dest reg to be changed.
1012 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
1014 DOUT << "Removing now-noop copy: " << MI;
1016 VRM.RemoveFromFoldedVirtMap(&MI);
1017 goto ProcessNextInst;
1029 llvm::Spiller* llvm::createSpiller() {
1030 switch (SpillerOpt) {
1031 default: assert(0 && "Unreachable!");
1033 return new LocalSpiller();
1035 return new SimpleSpiller();