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/Statistic.h"
31 #include "llvm/ADT/STLExtras.h"
36 static Statistic NumSpills("spiller", "Number of register spills");
37 static Statistic NumStores("spiller", "Number of stores added");
38 static Statistic NumLoads ("spiller", "Number of loads added");
39 static Statistic NumReused("spiller", "Number of values reused");
40 static Statistic NumDSE ("spiller", "Number of dead stores elided");
41 static Statistic NumDCE ("spiller", "Number of copies elided");
43 enum SpillerName { simple, local };
45 static cl::opt<SpillerName>
47 cl::desc("Spiller to use: (default: local)"),
49 cl::values(clEnumVal(simple, " simple spiller"),
50 clEnumVal(local, " local spiller"),
55 //===----------------------------------------------------------------------===//
56 // VirtRegMap implementation
57 //===----------------------------------------------------------------------===//
59 VirtRegMap::VirtRegMap(MachineFunction &mf)
60 : TII(*mf.getTarget().getInstrInfo()), MF(mf),
61 Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT) {
65 void VirtRegMap::grow() {
66 Virt2PhysMap.grow(MF.getSSARegMap()->getLastVirtReg());
67 Virt2StackSlotMap.grow(MF.getSSARegMap()->getLastVirtReg());
70 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) {
71 assert(MRegisterInfo::isVirtualRegister(virtReg));
72 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
73 "attempt to assign stack slot to already spilled register");
74 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg);
75 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(),
77 Virt2StackSlotMap[virtReg] = frameIndex;
82 void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) {
83 assert(MRegisterInfo::isVirtualRegister(virtReg));
84 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
85 "attempt to assign stack slot to already spilled register");
86 Virt2StackSlotMap[virtReg] = frameIndex;
89 void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI,
90 unsigned OpNo, MachineInstr *NewMI) {
91 // Move previous memory references folded to new instruction.
92 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI);
93 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI),
94 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) {
95 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second));
96 MI2VirtMap.erase(I++);
100 const TargetInstrDescriptor *TID = OldMI->getInstrDescriptor();
101 if (TID->getOperandConstraint(OpNo, TOI::TIED_TO) != -1 ||
102 TID->findTiedToSrcOperand(OpNo) != -1) {
103 // Folded a two-address operand.
105 } else if (OldMI->getOperand(OpNo).isDef()) {
111 // add new memory reference
112 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo)));
115 void VirtRegMap::print(std::ostream &OS) const {
120 void VirtRegMap::print(OStream &OS) const {
121 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo();
123 OS << "********** REGISTER MAP **********\n";
124 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
125 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) {
126 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG)
127 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n";
131 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
132 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i)
133 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT)
134 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n";
138 void VirtRegMap::dump() const {
144 //===----------------------------------------------------------------------===//
145 // Simple Spiller Implementation
146 //===----------------------------------------------------------------------===//
148 Spiller::~Spiller() {}
151 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller {
152 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM);
156 bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
157 DOUT << "********** REWRITE MACHINE CODE **********\n";
158 DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';
159 const TargetMachine &TM = MF.getTarget();
160 const MRegisterInfo &MRI = *TM.getRegisterInfo();
161 bool *PhysRegsUsed = MF.getUsedPhysregs();
163 // LoadedRegs - Keep track of which vregs are loaded, so that we only load
164 // each vreg once (in the case where a spilled vreg is used by multiple
165 // operands). This is always smaller than the number of operands to the
166 // current machine instr, so it should be small.
167 std::vector<unsigned> LoadedRegs;
169 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
171 DOUT << MBBI->getBasicBlock()->getName() << ":\n";
172 MachineBasicBlock &MBB = *MBBI;
173 for (MachineBasicBlock::iterator MII = MBB.begin(),
174 E = MBB.end(); MII != E; ++MII) {
175 MachineInstr &MI = *MII;
176 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
177 MachineOperand &MO = MI.getOperand(i);
178 if (MO.isRegister() && MO.getReg())
179 if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
180 unsigned VirtReg = MO.getReg();
181 unsigned PhysReg = VRM.getPhys(VirtReg);
182 if (VRM.hasStackSlot(VirtReg)) {
183 int StackSlot = VRM.getStackSlot(VirtReg);
184 const TargetRegisterClass* RC =
185 MF.getSSARegMap()->getRegClass(VirtReg);
188 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg)
189 == LoadedRegs.end()) {
190 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
191 LoadedRegs.push_back(VirtReg);
193 DOUT << '\t' << *prior(MII);
197 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
201 PhysRegsUsed[PhysReg] = true;
202 MI.getOperand(i).setReg(PhysReg);
204 PhysRegsUsed[MO.getReg()] = true;
215 //===----------------------------------------------------------------------===//
216 // Local Spiller Implementation
217 //===----------------------------------------------------------------------===//
220 /// LocalSpiller - This spiller does a simple pass over the machine basic
221 /// block to attempt to keep spills in registers as much as possible for
222 /// blocks that have low register pressure (the vreg may be spilled due to
223 /// register pressure in other blocks).
224 class VISIBILITY_HIDDEN LocalSpiller : public Spiller {
225 const MRegisterInfo *MRI;
226 const TargetInstrInfo *TII;
228 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
229 MRI = MF.getTarget().getRegisterInfo();
230 TII = MF.getTarget().getInstrInfo();
231 DOUT << "\n**** Local spiller rewriting function '"
232 << MF.getFunction()->getName() << "':\n";
234 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
236 RewriteMBB(*MBB, VRM);
240 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM);
241 void ClobberPhysReg(unsigned PR, std::map<int, unsigned> &SpillSlots,
242 std::multimap<unsigned, int> &PhysRegs);
243 void ClobberPhysRegOnly(unsigned PR, std::map<int, unsigned> &SpillSlots,
244 std::multimap<unsigned, int> &PhysRegs);
245 void ModifyStackSlot(int Slot, std::map<int, unsigned> &SpillSlots,
246 std::multimap<unsigned, int> &PhysRegs);
250 /// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
251 /// top down, keep track of which spills slots are available in each register.
253 /// Note that not all physregs are created equal here. In particular, some
254 /// physregs are reloads that we are allowed to clobber or ignore at any time.
255 /// Other physregs are values that the register allocated program is using that
256 /// we cannot CHANGE, but we can read if we like. We keep track of this on a
257 /// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable
258 /// entries. The predicate 'canClobberPhysReg()' checks this bit and
259 /// addAvailable sets it if.
261 class VISIBILITY_HIDDEN AvailableSpills {
262 const MRegisterInfo *MRI;
263 const TargetInstrInfo *TII;
265 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual
266 // register values that are still available, due to being loaded or stored to,
267 // but not invalidated yet.
268 std::map<int, unsigned> SpillSlotsAvailable;
270 // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating
271 // which stack slot values are currently held by a physreg. This is used to
272 // invalidate entries in SpillSlotsAvailable when a physreg is modified.
273 std::multimap<unsigned, int> PhysRegsAvailable;
275 void disallowClobberPhysRegOnly(unsigned PhysReg);
277 void ClobberPhysRegOnly(unsigned PhysReg);
279 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii)
280 : MRI(mri), TII(tii) {
283 /// getSpillSlotPhysReg - If the specified stack slot is available in a
284 /// physical register, return that PhysReg, otherwise return 0.
285 unsigned getSpillSlotPhysReg(int Slot) const {
286 std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot);
287 if (I != SpillSlotsAvailable.end())
288 return I->second >> 1; // Remove the CanClobber bit.
292 const MRegisterInfo *getRegInfo() const { return MRI; }
294 /// addAvailable - Mark that the specified stack slot is available in the
295 /// specified physreg. If CanClobber is true, the physreg can be modified at
296 /// any time without changing the semantics of the program.
297 void addAvailable(int Slot, unsigned Reg, bool CanClobber = true) {
298 // If this stack slot is thought to be available in some other physreg,
299 // remove its record.
300 ModifyStackSlot(Slot);
302 PhysRegsAvailable.insert(std::make_pair(Reg, Slot));
303 SpillSlotsAvailable[Slot] = (Reg << 1) | (unsigned)CanClobber;
305 DOUT << "Remembering SS#" << Slot << " in physreg "
306 << MRI->getName(Reg) << "\n";
309 /// canClobberPhysReg - Return true if the spiller is allowed to change the
310 /// value of the specified stackslot register if it desires. The specified
311 /// stack slot must be available in a physreg for this query to make sense.
312 bool canClobberPhysReg(int Slot) const {
313 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!");
314 return SpillSlotsAvailable.find(Slot)->second & 1;
317 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
318 /// stackslot register. The register is still available but is no longer
319 /// allowed to be modifed.
320 void disallowClobberPhysReg(unsigned PhysReg);
322 /// ClobberPhysReg - This is called when the specified physreg changes
323 /// value. We use this to invalidate any info about stuff we thing lives in
324 /// it and any of its aliases.
325 void ClobberPhysReg(unsigned PhysReg);
327 /// ModifyStackSlot - This method is called when the value in a stack slot
328 /// changes. This removes information about which register the previous value
329 /// for this slot lives in (as the previous value is dead now).
330 void ModifyStackSlot(int Slot);
334 /// disallowClobberPhysRegOnly - Unset the CanClobber bit of the specified
335 /// stackslot register. The register is still available but is no longer
336 /// allowed to be modifed.
337 void AvailableSpills::disallowClobberPhysRegOnly(unsigned PhysReg) {
338 std::multimap<unsigned, int>::iterator I =
339 PhysRegsAvailable.lower_bound(PhysReg);
340 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
341 int Slot = I->second;
343 assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg &&
344 "Bidirectional map mismatch!");
345 SpillSlotsAvailable[Slot] &= ~1;
346 DOUT << "PhysReg " << MRI->getName(PhysReg)
347 << " copied, it is available for use but can no longer be modified\n";
351 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
352 /// stackslot register and its aliases. The register and its aliases may
353 /// still available but is no longer allowed to be modifed.
354 void AvailableSpills::disallowClobberPhysReg(unsigned PhysReg) {
355 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
356 disallowClobberPhysRegOnly(*AS);
357 disallowClobberPhysRegOnly(PhysReg);
360 /// ClobberPhysRegOnly - This is called when the specified physreg changes
361 /// value. We use this to invalidate any info about stuff we thing lives in it.
362 void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
363 std::multimap<unsigned, int>::iterator I =
364 PhysRegsAvailable.lower_bound(PhysReg);
365 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
366 int Slot = I->second;
367 PhysRegsAvailable.erase(I++);
368 assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg &&
369 "Bidirectional map mismatch!");
370 SpillSlotsAvailable.erase(Slot);
371 DOUT << "PhysReg " << MRI->getName(PhysReg)
372 << " clobbered, invalidating SS#" << Slot << "\n";
376 /// ClobberPhysReg - This is called when the specified physreg changes
377 /// value. We use this to invalidate any info about stuff we thing lives in
378 /// it and any of its aliases.
379 void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
380 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
381 ClobberPhysRegOnly(*AS);
382 ClobberPhysRegOnly(PhysReg);
385 /// ModifyStackSlot - This method is called when the value in a stack slot
386 /// changes. This removes information about which register the previous value
387 /// for this slot lives in (as the previous value is dead now).
388 void AvailableSpills::ModifyStackSlot(int Slot) {
389 std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot);
390 if (It == SpillSlotsAvailable.end()) return;
391 unsigned Reg = It->second >> 1;
392 SpillSlotsAvailable.erase(It);
394 // This register may hold the value of multiple stack slots, only remove this
395 // stack slot from the set of values the register contains.
396 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
398 assert(I != PhysRegsAvailable.end() && I->first == Reg &&
399 "Map inverse broken!");
400 if (I->second == Slot) break;
402 PhysRegsAvailable.erase(I);
407 // ReusedOp - For each reused operand, we keep track of a bit of information, in
408 // case we need to rollback upon processing a new operand. See comments below.
411 // The MachineInstr operand that reused an available value.
414 // StackSlot - The spill slot of the value being reused.
417 // PhysRegReused - The physical register the value was available in.
418 unsigned PhysRegReused;
420 // AssignedPhysReg - The physreg that was assigned for use by the reload.
421 unsigned AssignedPhysReg;
423 // VirtReg - The virtual register itself.
426 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
428 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr),
432 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
433 /// is reused instead of reloaded.
434 class VISIBILITY_HIDDEN ReuseInfo {
436 std::vector<ReusedOp> Reuses;
437 bool *PhysRegsClobbered;
439 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) {
440 PhysRegsClobbered = new bool[mri->getNumRegs()];
441 std::fill(PhysRegsClobbered, PhysRegsClobbered+mri->getNumRegs(), false);
444 delete[] PhysRegsClobbered;
447 bool hasReuses() const {
448 return !Reuses.empty();
451 /// addReuse - If we choose to reuse a virtual register that is already
452 /// available instead of reloading it, remember that we did so.
453 void addReuse(unsigned OpNo, unsigned StackSlot,
454 unsigned PhysRegReused, unsigned AssignedPhysReg,
456 // If the reload is to the assigned register anyway, no undo will be
458 if (PhysRegReused == AssignedPhysReg) return;
460 // Otherwise, remember this.
461 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused,
462 AssignedPhysReg, VirtReg));
465 void markClobbered(unsigned PhysReg) {
466 PhysRegsClobbered[PhysReg] = true;
469 bool isClobbered(unsigned PhysReg) const {
470 return PhysRegsClobbered[PhysReg];
473 /// GetRegForReload - We are about to emit a reload into PhysReg. If there
474 /// is some other operand that is using the specified register, either pick
475 /// a new register to use, or evict the previous reload and use this reg.
476 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
477 AvailableSpills &Spills,
478 std::map<int, MachineInstr*> &MaybeDeadStores) {
479 if (Reuses.empty()) return PhysReg; // This is most often empty.
481 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
482 ReusedOp &Op = Reuses[ro];
483 // If we find some other reuse that was supposed to use this register
484 // exactly for its reload, we can change this reload to use ITS reload
486 if (Op.PhysRegReused == PhysReg) {
487 // Yup, use the reload register that we didn't use before.
488 unsigned NewReg = Op.AssignedPhysReg;
489 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores);
491 // Otherwise, we might also have a problem if a previously reused
492 // value aliases the new register. If so, codegen the previous reload
494 unsigned PRRU = Op.PhysRegReused;
495 const MRegisterInfo *MRI = Spills.getRegInfo();
496 if (MRI->areAliases(PRRU, PhysReg)) {
497 // Okay, we found out that an alias of a reused register
498 // was used. This isn't good because it means we have
499 // to undo a previous reuse.
500 MachineBasicBlock *MBB = MI->getParent();
501 const TargetRegisterClass *AliasRC =
502 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg);
504 // Copy Op out of the vector and remove it, we're going to insert an
505 // explicit load for it.
507 Reuses.erase(Reuses.begin()+ro);
509 // Ok, we're going to try to reload the assigned physreg into the
510 // slot that we were supposed to in the first place. However, that
511 // register could hold a reuse. Check to see if it conflicts or
512 // would prefer us to use a different register.
513 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg,
514 MI, Spills, MaybeDeadStores);
516 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg,
517 NewOp.StackSlot, AliasRC);
518 Spills.ClobberPhysReg(NewPhysReg);
519 Spills.ClobberPhysReg(NewOp.PhysRegReused);
521 // Any stores to this stack slot are not dead anymore.
522 MaybeDeadStores.erase(NewOp.StackSlot);
524 MI->getOperand(NewOp.Operand).setReg(NewPhysReg);
526 Spills.addAvailable(NewOp.StackSlot, NewPhysReg);
528 DEBUG(MachineBasicBlock::iterator MII = MI;
529 DOUT << '\t' << *prior(MII));
531 DOUT << "Reuse undone!\n";
534 // Finally, PhysReg is now available, go ahead and use it.
545 /// rewriteMBB - Keep track of which spills are available even after the
546 /// register allocator is done with them. If possible, avoid reloading vregs.
547 void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
549 DOUT << MBB.getBasicBlock()->getName() << ":\n";
551 // Spills - Keep track of which spilled values are available in physregs so
552 // that we can choose to reuse the physregs instead of emitting reloads.
553 AvailableSpills Spills(MRI, TII);
555 // MaybeDeadStores - When we need to write a value back into a stack slot,
556 // keep track of the inserted store. If the stack slot value is never read
557 // (because the value was used from some available register, for example), and
558 // subsequently stored to, the original store is dead. This map keeps track
559 // of inserted stores that are not used. If we see a subsequent store to the
560 // same stack slot, the original store is deleted.
561 std::map<int, MachineInstr*> MaybeDeadStores;
563 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs();
565 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
567 MachineInstr &MI = *MII;
568 MachineBasicBlock::iterator NextMII = MII; ++NextMII;
570 /// ReusedOperands - Keep track of operand reuse in case we need to undo
572 ReuseInfo ReusedOperands(MI, MRI);
574 // Loop over all of the implicit defs, clearing them from our available
576 const TargetInstrDescriptor *TID = MI.getInstrDescriptor();
577 const unsigned *ImpDef = TID->ImplicitDefs;
579 for ( ; *ImpDef; ++ImpDef) {
580 PhysRegsUsed[*ImpDef] = true;
581 ReusedOperands.markClobbered(*ImpDef);
582 Spills.ClobberPhysReg(*ImpDef);
586 // Process all of the spilled uses and all non spilled reg references.
587 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
588 MachineOperand &MO = MI.getOperand(i);
589 if (!MO.isRegister() || MO.getReg() == 0)
590 continue; // Ignore non-register operands.
592 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) {
593 // Ignore physregs for spilling, but remember that it is used by this
595 PhysRegsUsed[MO.getReg()] = true;
596 ReusedOperands.markClobbered(MO.getReg());
600 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) &&
601 "Not a virtual or a physical register?");
603 unsigned VirtReg = MO.getReg();
604 if (!VRM.hasStackSlot(VirtReg)) {
605 // This virtual register was assigned a physreg!
606 unsigned Phys = VRM.getPhys(VirtReg);
607 PhysRegsUsed[Phys] = true;
609 ReusedOperands.markClobbered(Phys);
610 MI.getOperand(i).setReg(Phys);
614 // This virtual register is now known to be a spilled value.
616 continue; // Handle defs in the loop below (handle use&def here though)
618 int StackSlot = VRM.getStackSlot(VirtReg);
621 // Check to see if this stack slot is available.
622 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) {
624 // This spilled operand might be part of a two-address operand. If this
625 // is the case, then changing it will necessarily require changing the
626 // def part of the instruction as well. However, in some cases, we
627 // aren't allowed to modify the reused register. If none of these cases
629 bool CanReuse = true;
630 int ti = TID->getOperandConstraint(i, TOI::TIED_TO);
632 MI.getOperand(ti).isReg() &&
633 MI.getOperand(ti).getReg() == VirtReg) {
634 // Okay, we have a two address operand. We can reuse this physreg as
635 // long as we are allowed to clobber the value and there is an earlier
636 // def that has already clobbered the physreg.
637 CanReuse = Spills.canClobberPhysReg(StackSlot) &&
638 !ReusedOperands.isClobbered(PhysReg);
642 // If this stack slot value is already available, reuse it!
643 DOUT << "Reusing SS#" << StackSlot << " from physreg "
644 << MRI->getName(PhysReg) << " for vreg"
645 << VirtReg <<" instead of reloading into physreg "
646 << MRI->getName(VRM.getPhys(VirtReg)) << "\n";
647 MI.getOperand(i).setReg(PhysReg);
649 // The only technical detail we have is that we don't know that
650 // PhysReg won't be clobbered by a reloaded stack slot that occurs
651 // later in the instruction. In particular, consider 'op V1, V2'.
652 // If V1 is available in physreg R0, we would choose to reuse it
653 // here, instead of reloading it into the register the allocator
654 // indicated (say R1). However, V2 might have to be reloaded
655 // later, and it might indicate that it needs to live in R0. When
656 // this occurs, we need to have information available that
657 // indicates it is safe to use R1 for the reload instead of R0.
659 // To further complicate matters, we might conflict with an alias,
660 // or R0 and R1 might not be compatible with each other. In this
661 // case, we actually insert a reload for V1 in R1, ensuring that
662 // we can get at R0 or its alias.
663 ReusedOperands.addReuse(i, StackSlot, PhysReg,
664 VRM.getPhys(VirtReg), VirtReg);
666 // Only mark it clobbered if this is a use&def operand.
667 ReusedOperands.markClobbered(PhysReg);
672 // Otherwise we have a situation where we have a two-address instruction
673 // whose mod/ref operand needs to be reloaded. This reload is already
674 // available in some register "PhysReg", but if we used PhysReg as the
675 // operand to our 2-addr instruction, the instruction would modify
676 // PhysReg. This isn't cool if something later uses PhysReg and expects
677 // to get its initial value.
679 // To avoid this problem, and to avoid doing a load right after a store,
680 // we emit a copy from PhysReg into the designated register for this
682 unsigned DesignatedReg = VRM.getPhys(VirtReg);
683 assert(DesignatedReg && "Must map virtreg to physreg!");
685 // Note that, if we reused a register for a previous operand, the
686 // register we want to reload into might not actually be
687 // available. If this occurs, use the register indicated by the
689 if (ReusedOperands.hasReuses())
690 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI,
691 Spills, MaybeDeadStores);
693 // If the mapped designated register is actually the physreg we have
694 // incoming, we don't need to inserted a dead copy.
695 if (DesignatedReg == PhysReg) {
696 // If this stack slot value is already available, reuse it!
697 DOUT << "Reusing SS#" << StackSlot << " from physreg "
698 << MRI->getName(PhysReg) << " for vreg"
700 << " instead of reloading into same physreg.\n";
701 MI.getOperand(i).setReg(PhysReg);
702 ReusedOperands.markClobbered(PhysReg);
707 const TargetRegisterClass* RC =
708 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
710 PhysRegsUsed[DesignatedReg] = true;
711 ReusedOperands.markClobbered(DesignatedReg);
712 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC);
714 // This invalidates DesignatedReg.
715 Spills.ClobberPhysReg(DesignatedReg);
717 Spills.addAvailable(StackSlot, DesignatedReg);
718 MI.getOperand(i).setReg(DesignatedReg);
719 DOUT << '\t' << *prior(MII);
724 // Otherwise, reload it and remember that we have it.
725 PhysReg = VRM.getPhys(VirtReg);
726 assert(PhysReg && "Must map virtreg to physreg!");
727 const TargetRegisterClass* RC =
728 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
730 // Note that, if we reused a register for a previous operand, the
731 // register we want to reload into might not actually be
732 // available. If this occurs, use the register indicated by the
734 if (ReusedOperands.hasReuses())
735 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
736 Spills, MaybeDeadStores);
738 PhysRegsUsed[PhysReg] = true;
739 ReusedOperands.markClobbered(PhysReg);
740 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
741 // This invalidates PhysReg.
742 Spills.ClobberPhysReg(PhysReg);
744 // Any stores to this stack slot are not dead anymore.
745 MaybeDeadStores.erase(StackSlot);
746 Spills.addAvailable(StackSlot, PhysReg);
748 MI.getOperand(i).setReg(PhysReg);
749 DOUT << '\t' << *prior(MII);
754 // If we have folded references to memory operands, make sure we clear all
755 // physical registers that may contain the value of the spilled virtual
757 VirtRegMap::MI2VirtMapTy::const_iterator I, End;
758 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
759 DOUT << "Folded vreg: " << I->second.first << " MR: "
761 unsigned VirtReg = I->second.first;
762 VirtRegMap::ModRef MR = I->second.second;
763 if (!VRM.hasStackSlot(VirtReg)) {
764 DOUT << ": No stack slot!\n";
767 int SS = VRM.getStackSlot(VirtReg);
768 DOUT << " - StackSlot: " << SS << "\n";
770 // If this folded instruction is just a use, check to see if it's a
771 // straight load from the virt reg slot.
772 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
774 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
775 if (FrameIdx == SS) {
776 // If this spill slot is available, turn it into a copy (or nothing)
777 // instead of leaving it as a load!
778 if (unsigned InReg = Spills.getSpillSlotPhysReg(SS)) {
779 DOUT << "Promoted Load To Copy: " << MI;
780 MachineFunction &MF = *MBB.getParent();
781 if (DestReg != InReg) {
782 MRI->copyRegToReg(MBB, &MI, DestReg, InReg,
783 MF.getSSARegMap()->getRegClass(VirtReg));
784 // Revisit the copy so we make sure to notice the effects of the
785 // operation on the destreg (either needing to RA it if it's
786 // virtual or needing to clobber any values if it's physical).
788 --NextMII; // backtrack to the copy.
790 VRM.RemoveFromFoldedVirtMap(&MI);
792 goto ProcessNextInst;
798 // If this reference is not a use, any previous store is now dead.
799 // Otherwise, the store to this stack slot is not dead anymore.
800 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS);
801 if (MDSI != MaybeDeadStores.end()) {
802 if (MR & VirtRegMap::isRef) // Previous store is not dead.
803 MaybeDeadStores.erase(MDSI);
805 // If we get here, the store is dead, nuke it now.
806 assert(VirtRegMap::isMod && "Can't be modref!");
807 DOUT << "Removed dead store:\t" << *MDSI->second;
808 MBB.erase(MDSI->second);
809 VRM.RemoveFromFoldedVirtMap(MDSI->second);
810 MaybeDeadStores.erase(MDSI);
815 // If the spill slot value is available, and this is a new definition of
816 // the value, the value is not available anymore.
817 if (MR & VirtRegMap::isMod) {
818 // Notice that the value in this stack slot has been modified.
819 Spills.ModifyStackSlot(SS);
821 // If this is *just* a mod of the value, check to see if this is just a
822 // store to the spill slot (i.e. the spill got merged into the copy). If
823 // so, realize that the vreg is available now, and add the store to the
824 // MaybeDeadStore info.
826 if (!(MR & VirtRegMap::isRef)) {
827 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
828 assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
829 "Src hasn't been allocated yet?");
830 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark
831 // this as a potentially dead store in case there is a subsequent
832 // store into the stack slot without a read from it.
833 MaybeDeadStores[StackSlot] = &MI;
835 // If the stack slot value was previously available in some other
836 // register, change it now. Otherwise, make the register available,
838 Spills.addAvailable(StackSlot, SrcReg, false /*don't clobber*/);
844 // Process all of the spilled defs.
845 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
846 MachineOperand &MO = MI.getOperand(i);
847 if (MO.isRegister() && MO.getReg() && MO.isDef()) {
848 unsigned VirtReg = MO.getReg();
850 if (!MRegisterInfo::isVirtualRegister(VirtReg)) {
851 // Check to see if this is a noop copy. If so, eliminate the
852 // instruction before considering the dest reg to be changed.
854 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
856 DOUT << "Removing now-noop copy: " << MI;
858 VRM.RemoveFromFoldedVirtMap(&MI);
859 Spills.disallowClobberPhysReg(VirtReg);
860 goto ProcessNextInst;
863 // If it's not a no-op copy, it clobbers the value in the destreg.
864 Spills.ClobberPhysReg(VirtReg);
865 ReusedOperands.markClobbered(VirtReg);
867 // Check to see if this instruction is a load from a stack slot into
868 // a register. If so, this provides the stack slot value in the reg.
870 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
871 assert(DestReg == VirtReg && "Unknown load situation!");
873 // Otherwise, if it wasn't available, remember that it is now!
874 Spills.addAvailable(FrameIdx, DestReg);
875 goto ProcessNextInst;
881 // The only vregs left are stack slot definitions.
882 int StackSlot = VRM.getStackSlot(VirtReg);
883 const TargetRegisterClass *RC =
884 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
886 // If this def is part of a two-address operand, make sure to execute
887 // the store from the correct physical register.
889 int TiedOp = MI.getInstrDescriptor()->findTiedToSrcOperand(i);
891 PhysReg = MI.getOperand(TiedOp).getReg();
893 PhysReg = VRM.getPhys(VirtReg);
894 if (ReusedOperands.isClobbered(PhysReg)) {
895 // Another def has taken the assigned physreg. It must have been a
896 // use&def which got it due to reuse. Undo the reuse!
897 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
898 Spills, MaybeDeadStores);
902 PhysRegsUsed[PhysReg] = true;
903 ReusedOperands.markClobbered(PhysReg);
904 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
905 DOUT << "Store:\t" << *next(MII);
906 MI.getOperand(i).setReg(PhysReg);
908 // Check to see if this is a noop copy. If so, eliminate the
909 // instruction before considering the dest reg to be changed.
912 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
914 DOUT << "Removing now-noop copy: " << MI;
916 VRM.RemoveFromFoldedVirtMap(&MI);
917 goto ProcessNextInst;
921 // If there is a dead store to this stack slot, nuke it now.
922 MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
924 DOUT << "Removed dead store:\t" << *LastStore;
926 MBB.erase(LastStore);
927 VRM.RemoveFromFoldedVirtMap(LastStore);
929 LastStore = next(MII);
931 // If the stack slot value was previously available in some other
932 // register, change it now. Otherwise, make the register available,
934 Spills.ModifyStackSlot(StackSlot);
935 Spills.ClobberPhysReg(PhysReg);
936 Spills.addAvailable(StackSlot, PhysReg);
947 llvm::Spiller* llvm::createSpiller() {
948 switch (SpillerOpt) {
949 default: assert(0 && "Unreachable!");
951 return new LocalSpiller();
953 return new SimpleSpiller();