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"
37 static Statistic<> NumSpills("spiller", "Number of register spills");
38 static Statistic<> NumStores("spiller", "Number of stores added");
39 static Statistic<> NumLoads ("spiller", "Number of loads added");
40 static Statistic<> NumReused("spiller", "Number of values reused");
41 static Statistic<> NumDSE ("spiller", "Number of dead stores elided");
42 static Statistic<> NumDCE ("spiller", "Number of copies elided");
44 enum SpillerName { simple, local };
46 static cl::opt<SpillerName>
48 cl::desc("Spiller to use: (default: local)"),
50 cl::values(clEnumVal(simple, " simple spiller"),
51 clEnumVal(local, " local spiller"),
56 //===----------------------------------------------------------------------===//
57 // VirtRegMap implementation
58 //===----------------------------------------------------------------------===//
60 VirtRegMap::VirtRegMap(MachineFunction &mf)
61 : TII(*mf.getTarget().getInstrInfo()), MF(mf),
62 Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT) {
66 void VirtRegMap::grow() {
67 Virt2PhysMap.grow(MF.getSSARegMap()->getLastVirtReg());
68 Virt2StackSlotMap.grow(MF.getSSARegMap()->getLastVirtReg());
71 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) {
72 assert(MRegisterInfo::isVirtualRegister(virtReg));
73 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
74 "attempt to assign stack slot to already spilled register");
75 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg);
76 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(),
78 Virt2StackSlotMap[virtReg] = frameIndex;
83 void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) {
84 assert(MRegisterInfo::isVirtualRegister(virtReg));
85 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
86 "attempt to assign stack slot to already spilled register");
87 Virt2StackSlotMap[virtReg] = frameIndex;
90 void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI,
91 unsigned OpNo, MachineInstr *NewMI) {
92 // Move previous memory references folded to new instruction.
93 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI);
94 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI),
95 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) {
96 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second));
97 MI2VirtMap.erase(I++);
101 if (TII.getOperandConstraint(OldMI->getOpcode(), OpNo,
102 TargetInstrInfo::TIED_TO)) {
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 {
116 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo();
118 OS << "********** REGISTER MAP **********\n";
119 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
120 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) {
121 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG)
122 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n";
126 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
127 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i)
128 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT)
129 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n";
133 void VirtRegMap::dump() const { print(std::cerr); }
136 //===----------------------------------------------------------------------===//
137 // Simple Spiller Implementation
138 //===----------------------------------------------------------------------===//
140 Spiller::~Spiller() {}
143 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller {
144 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM);
148 bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
149 DEBUG(std::cerr << "********** REWRITE MACHINE CODE **********\n");
150 DEBUG(std::cerr << "********** Function: "
151 << MF.getFunction()->getName() << '\n');
152 const TargetMachine &TM = MF.getTarget();
153 const MRegisterInfo &MRI = *TM.getRegisterInfo();
154 bool *PhysRegsUsed = MF.getUsedPhysregs();
156 // LoadedRegs - Keep track of which vregs are loaded, so that we only load
157 // each vreg once (in the case where a spilled vreg is used by multiple
158 // operands). This is always smaller than the number of operands to the
159 // current machine instr, so it should be small.
160 std::vector<unsigned> LoadedRegs;
162 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
164 DEBUG(std::cerr << MBBI->getBasicBlock()->getName() << ":\n");
165 MachineBasicBlock &MBB = *MBBI;
166 for (MachineBasicBlock::iterator MII = MBB.begin(),
167 E = MBB.end(); MII != E; ++MII) {
168 MachineInstr &MI = *MII;
169 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
170 MachineOperand &MO = MI.getOperand(i);
171 if (MO.isRegister() && MO.getReg())
172 if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
173 unsigned VirtReg = MO.getReg();
174 unsigned PhysReg = VRM.getPhys(VirtReg);
175 if (VRM.hasStackSlot(VirtReg)) {
176 int StackSlot = VRM.getStackSlot(VirtReg);
177 const TargetRegisterClass* RC =
178 MF.getSSARegMap()->getRegClass(VirtReg);
181 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg)
182 == LoadedRegs.end()) {
183 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
184 LoadedRegs.push_back(VirtReg);
186 DEBUG(std::cerr << '\t' << *prior(MII));
190 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
194 PhysRegsUsed[PhysReg] = true;
195 MI.getOperand(i).setReg(PhysReg);
197 PhysRegsUsed[MO.getReg()] = true;
201 DEBUG(std::cerr << '\t' << MI);
208 //===----------------------------------------------------------------------===//
209 // Local Spiller Implementation
210 //===----------------------------------------------------------------------===//
213 /// LocalSpiller - This spiller does a simple pass over the machine basic
214 /// block to attempt to keep spills in registers as much as possible for
215 /// blocks that have low register pressure (the vreg may be spilled due to
216 /// register pressure in other blocks).
217 class VISIBILITY_HIDDEN LocalSpiller : public Spiller {
218 const MRegisterInfo *MRI;
219 const TargetInstrInfo *TII;
221 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
222 MRI = MF.getTarget().getRegisterInfo();
223 TII = MF.getTarget().getInstrInfo();
224 DEBUG(std::cerr << "\n**** Local spiller rewriting function '"
225 << MF.getFunction()->getName() << "':\n");
227 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
229 RewriteMBB(*MBB, VRM);
233 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM);
234 void ClobberPhysReg(unsigned PR, std::map<int, unsigned> &SpillSlots,
235 std::multimap<unsigned, int> &PhysRegs);
236 void ClobberPhysRegOnly(unsigned PR, std::map<int, unsigned> &SpillSlots,
237 std::multimap<unsigned, int> &PhysRegs);
238 void ModifyStackSlot(int Slot, std::map<int, unsigned> &SpillSlots,
239 std::multimap<unsigned, int> &PhysRegs);
243 /// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
244 /// top down, keep track of which spills slots are available in each register.
246 /// Note that not all physregs are created equal here. In particular, some
247 /// physregs are reloads that we are allowed to clobber or ignore at any time.
248 /// Other physregs are values that the register allocated program is using that
249 /// we cannot CHANGE, but we can read if we like. We keep track of this on a
250 /// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable
251 /// entries. The predicate 'canClobberPhysReg()' checks this bit and
252 /// addAvailable sets it if.
254 class VISIBILITY_HIDDEN AvailableSpills {
255 const MRegisterInfo *MRI;
256 const TargetInstrInfo *TII;
258 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual
259 // register values that are still available, due to being loaded or stored to,
260 // but not invalidated yet.
261 std::map<int, unsigned> SpillSlotsAvailable;
263 // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating
264 // which stack slot values are currently held by a physreg. This is used to
265 // invalidate entries in SpillSlotsAvailable when a physreg is modified.
266 std::multimap<unsigned, int> PhysRegsAvailable;
268 void ClobberPhysRegOnly(unsigned PhysReg);
270 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii)
271 : MRI(mri), TII(tii) {
274 /// getSpillSlotPhysReg - If the specified stack slot is available in a
275 /// physical register, return that PhysReg, otherwise return 0.
276 unsigned getSpillSlotPhysReg(int Slot) const {
277 std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot);
278 if (I != SpillSlotsAvailable.end())
279 return I->second >> 1; // Remove the CanClobber bit.
283 const MRegisterInfo *getRegInfo() const { return MRI; }
285 /// addAvailable - Mark that the specified stack slot is available in the
286 /// specified physreg. If CanClobber is true, the physreg can be modified at
287 /// any time without changing the semantics of the program.
288 void addAvailable(int Slot, unsigned Reg, bool CanClobber = true) {
289 // If this stack slot is thought to be available in some other physreg,
290 // remove its record.
291 ModifyStackSlot(Slot);
293 PhysRegsAvailable.insert(std::make_pair(Reg, Slot));
294 SpillSlotsAvailable[Slot] = (Reg << 1) | (unsigned)CanClobber;
296 DEBUG(std::cerr << "Remembering SS#" << Slot << " in physreg "
297 << MRI->getName(Reg) << "\n");
300 /// canClobberPhysReg - Return true if the spiller is allowed to change the
301 /// value of the specified stackslot register if it desires. The specified
302 /// stack slot must be available in a physreg for this query to make sense.
303 bool canClobberPhysReg(int Slot) const {
304 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!");
305 return SpillSlotsAvailable.find(Slot)->second & 1;
308 /// ClobberPhysReg - This is called when the specified physreg changes
309 /// value. We use this to invalidate any info about stuff we thing lives in
310 /// it and any of its aliases.
311 void ClobberPhysReg(unsigned PhysReg);
313 /// ModifyStackSlot - This method is called when the value in a stack slot
314 /// changes. This removes information about which register the previous value
315 /// for this slot lives in (as the previous value is dead now).
316 void ModifyStackSlot(int Slot);
320 /// ClobberPhysRegOnly - This is called when the specified physreg changes
321 /// value. We use this to invalidate any info about stuff we thing lives in it.
322 void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
323 std::multimap<unsigned, int>::iterator I =
324 PhysRegsAvailable.lower_bound(PhysReg);
325 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
326 int Slot = I->second;
327 PhysRegsAvailable.erase(I++);
328 assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg &&
329 "Bidirectional map mismatch!");
330 SpillSlotsAvailable.erase(Slot);
331 DEBUG(std::cerr << "PhysReg " << MRI->getName(PhysReg)
332 << " clobbered, invalidating SS#" << Slot << "\n");
336 /// ClobberPhysReg - This is called when the specified physreg changes
337 /// value. We use this to invalidate any info about stuff we thing lives in
338 /// it and any of its aliases.
339 void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
340 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
341 ClobberPhysRegOnly(*AS);
342 ClobberPhysRegOnly(PhysReg);
345 /// ModifyStackSlot - This method is called when the value in a stack slot
346 /// changes. This removes information about which register the previous value
347 /// for this slot lives in (as the previous value is dead now).
348 void AvailableSpills::ModifyStackSlot(int Slot) {
349 std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot);
350 if (It == SpillSlotsAvailable.end()) return;
351 unsigned Reg = It->second >> 1;
352 SpillSlotsAvailable.erase(It);
354 // This register may hold the value of multiple stack slots, only remove this
355 // stack slot from the set of values the register contains.
356 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
358 assert(I != PhysRegsAvailable.end() && I->first == Reg &&
359 "Map inverse broken!");
360 if (I->second == Slot) break;
362 PhysRegsAvailable.erase(I);
367 // ReusedOp - For each reused operand, we keep track of a bit of information, in
368 // case we need to rollback upon processing a new operand. See comments below.
371 // The MachineInstr operand that reused an available value.
374 // StackSlot - The spill slot of the value being reused.
377 // PhysRegReused - The physical register the value was available in.
378 unsigned PhysRegReused;
380 // AssignedPhysReg - The physreg that was assigned for use by the reload.
381 unsigned AssignedPhysReg;
383 // VirtReg - The virtual register itself.
386 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
388 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr),
392 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
393 /// is reused instead of reloaded.
394 class VISIBILITY_HIDDEN ReuseInfo {
396 std::vector<ReusedOp> Reuses;
397 bool *PhysRegsClobbered;
399 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) {
400 PhysRegsClobbered = new bool[mri->getNumRegs()];
401 std::fill(PhysRegsClobbered, PhysRegsClobbered+mri->getNumRegs(), false);
404 delete[] PhysRegsClobbered;
407 bool hasReuses() const {
408 return !Reuses.empty();
411 /// addReuse - If we choose to reuse a virtual register that is already
412 /// available instead of reloading it, remember that we did so.
413 void addReuse(unsigned OpNo, unsigned StackSlot,
414 unsigned PhysRegReused, unsigned AssignedPhysReg,
416 // If the reload is to the assigned register anyway, no undo will be
418 if (PhysRegReused == AssignedPhysReg) return;
420 // Otherwise, remember this.
421 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused,
422 AssignedPhysReg, VirtReg));
425 void markClobbered(unsigned PhysReg) {
426 PhysRegsClobbered[PhysReg] = true;
429 bool isClobbered(unsigned PhysReg) const {
430 return PhysRegsClobbered[PhysReg];
433 /// GetRegForReload - We are about to emit a reload into PhysReg. If there
434 /// is some other operand that is using the specified register, either pick
435 /// a new register to use, or evict the previous reload and use this reg.
436 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
437 AvailableSpills &Spills,
438 std::map<int, MachineInstr*> &MaybeDeadStores) {
439 if (Reuses.empty()) return PhysReg; // This is most often empty.
441 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
442 ReusedOp &Op = Reuses[ro];
443 // If we find some other reuse that was supposed to use this register
444 // exactly for its reload, we can change this reload to use ITS reload
446 if (Op.PhysRegReused == PhysReg) {
447 // Yup, use the reload register that we didn't use before.
448 unsigned NewReg = Op.AssignedPhysReg;
449 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores);
451 // Otherwise, we might also have a problem if a previously reused
452 // value aliases the new register. If so, codegen the previous reload
454 unsigned PRRU = Op.PhysRegReused;
455 const MRegisterInfo *MRI = Spills.getRegInfo();
456 if (MRI->areAliases(PRRU, PhysReg)) {
457 // Okay, we found out that an alias of a reused register
458 // was used. This isn't good because it means we have
459 // to undo a previous reuse.
460 MachineBasicBlock *MBB = MI->getParent();
461 const TargetRegisterClass *AliasRC =
462 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg);
464 // Copy Op out of the vector and remove it, we're going to insert an
465 // explicit load for it.
467 Reuses.erase(Reuses.begin()+ro);
469 // Ok, we're going to try to reload the assigned physreg into the
470 // slot that we were supposed to in the first place. However, that
471 // register could hold a reuse. Check to see if it conflicts or
472 // would prefer us to use a different register.
473 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg,
474 MI, Spills, MaybeDeadStores);
476 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg,
477 NewOp.StackSlot, AliasRC);
478 Spills.ClobberPhysReg(NewPhysReg);
479 Spills.ClobberPhysReg(NewOp.PhysRegReused);
481 // Any stores to this stack slot are not dead anymore.
482 MaybeDeadStores.erase(NewOp.StackSlot);
484 MI->getOperand(NewOp.Operand).setReg(NewPhysReg);
486 Spills.addAvailable(NewOp.StackSlot, NewPhysReg);
488 DEBUG(MachineBasicBlock::iterator MII = MI;
489 std::cerr << '\t' << *prior(MII));
491 DEBUG(std::cerr << "Reuse undone!\n");
494 // Finally, PhysReg is now available, go ahead and use it.
505 /// rewriteMBB - Keep track of which spills are available even after the
506 /// register allocator is done with them. If possible, avoid reloading vregs.
507 void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
509 DEBUG(std::cerr << MBB.getBasicBlock()->getName() << ":\n");
511 // Spills - Keep track of which spilled values are available in physregs so
512 // that we can choose to reuse the physregs instead of emitting reloads.
513 AvailableSpills Spills(MRI, TII);
515 // MaybeDeadStores - When we need to write a value back into a stack slot,
516 // keep track of the inserted store. If the stack slot value is never read
517 // (because the value was used from some available register, for example), and
518 // subsequently stored to, the original store is dead. This map keeps track
519 // of inserted stores that are not used. If we see a subsequent store to the
520 // same stack slot, the original store is deleted.
521 std::map<int, MachineInstr*> MaybeDeadStores;
523 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs();
525 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
527 MachineInstr &MI = *MII;
528 MachineBasicBlock::iterator NextMII = MII; ++NextMII;
530 /// ReusedOperands - Keep track of operand reuse in case we need to undo
532 ReuseInfo ReusedOperands(MI, MRI);
534 // Loop over all of the implicit defs, clearing them from our available
536 const unsigned *ImpDef = TII->getImplicitDefs(MI.getOpcode());
538 for ( ; *ImpDef; ++ImpDef) {
539 PhysRegsUsed[*ImpDef] = true;
540 ReusedOperands.markClobbered(*ImpDef);
541 Spills.ClobberPhysReg(*ImpDef);
545 // Process all of the spilled uses and all non spilled reg references.
546 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
547 MachineOperand &MO = MI.getOperand(i);
548 if (!MO.isRegister() || MO.getReg() == 0)
549 continue; // Ignore non-register operands.
551 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) {
552 // Ignore physregs for spilling, but remember that it is used by this
554 PhysRegsUsed[MO.getReg()] = true;
555 ReusedOperands.markClobbered(MO.getReg());
559 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) &&
560 "Not a virtual or a physical register?");
562 unsigned VirtReg = MO.getReg();
563 if (!VRM.hasStackSlot(VirtReg)) {
564 // This virtual register was assigned a physreg!
565 unsigned Phys = VRM.getPhys(VirtReg);
566 PhysRegsUsed[Phys] = true;
568 ReusedOperands.markClobbered(Phys);
569 MI.getOperand(i).setReg(Phys);
573 // This virtual register is now known to be a spilled value.
575 continue; // Handle defs in the loop below (handle use&def here though)
577 int StackSlot = VRM.getStackSlot(VirtReg);
580 // Check to see if this stack slot is available.
581 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) {
583 // This spilled operand might be part of a two-address operand. If this
584 // is the case, then changing it will necessarily require changing the
585 // def part of the instruction as well. However, in some cases, we
586 // aren't allowed to modify the reused register. If none of these cases
588 bool CanReuse = true;
589 int ti = TII->getOperandConstraint(MI.getOpcode(), i,
590 TargetInstrInfo::TIED_TO);
592 MI.getOperand(ti).isReg() &&
593 MI.getOperand(ti).getReg() == VirtReg) {
594 // Okay, we have a two address operand. We can reuse this physreg as
595 // long as we are allowed to clobber the value and there is an earlier
596 // def that has already clobbered the physreg.
597 CanReuse = Spills.canClobberPhysReg(StackSlot) &&
598 !ReusedOperands.isClobbered(PhysReg);
602 // If this stack slot value is already available, reuse it!
603 DEBUG(std::cerr << "Reusing SS#" << StackSlot << " from physreg "
604 << MRI->getName(PhysReg) << " for vreg"
605 << VirtReg <<" instead of reloading into physreg "
606 << MRI->getName(VRM.getPhys(VirtReg)) << "\n");
607 MI.getOperand(i).setReg(PhysReg);
609 // The only technical detail we have is that we don't know that
610 // PhysReg won't be clobbered by a reloaded stack slot that occurs
611 // later in the instruction. In particular, consider 'op V1, V2'.
612 // If V1 is available in physreg R0, we would choose to reuse it
613 // here, instead of reloading it into the register the allocator
614 // indicated (say R1). However, V2 might have to be reloaded
615 // later, and it might indicate that it needs to live in R0. When
616 // this occurs, we need to have information available that
617 // indicates it is safe to use R1 for the reload instead of R0.
619 // To further complicate matters, we might conflict with an alias,
620 // or R0 and R1 might not be compatible with each other. In this
621 // case, we actually insert a reload for V1 in R1, ensuring that
622 // we can get at R0 or its alias.
623 ReusedOperands.addReuse(i, StackSlot, PhysReg,
624 VRM.getPhys(VirtReg), VirtReg);
626 // Only mark it clobbered if this is a use&def operand.
627 ReusedOperands.markClobbered(PhysReg);
632 // Otherwise we have a situation where we have a two-address instruction
633 // whose mod/ref operand needs to be reloaded. This reload is already
634 // available in some register "PhysReg", but if we used PhysReg as the
635 // operand to our 2-addr instruction, the instruction would modify
636 // PhysReg. This isn't cool if something later uses PhysReg and expects
637 // to get its initial value.
639 // To avoid this problem, and to avoid doing a load right after a store,
640 // we emit a copy from PhysReg into the designated register for this
642 unsigned DesignatedReg = VRM.getPhys(VirtReg);
643 assert(DesignatedReg && "Must map virtreg to physreg!");
645 // Note that, if we reused a register for a previous operand, the
646 // register we want to reload into might not actually be
647 // available. If this occurs, use the register indicated by the
649 if (ReusedOperands.hasReuses())
650 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI,
651 Spills, MaybeDeadStores);
653 // If the mapped designated register is actually the physreg we have
654 // incoming, we don't need to inserted a dead copy.
655 if (DesignatedReg == PhysReg) {
656 // If this stack slot value is already available, reuse it!
657 DEBUG(std::cerr << "Reusing SS#" << StackSlot << " from physreg "
658 << MRI->getName(PhysReg) << " for vreg"
660 << " instead of reloading into same physreg.\n");
661 MI.getOperand(i).setReg(PhysReg);
662 ReusedOperands.markClobbered(PhysReg);
667 const TargetRegisterClass* RC =
668 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
670 PhysRegsUsed[DesignatedReg] = true;
671 ReusedOperands.markClobbered(DesignatedReg);
672 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC);
674 // This invalidates DesignatedReg.
675 Spills.ClobberPhysReg(DesignatedReg);
677 Spills.addAvailable(StackSlot, DesignatedReg);
678 MI.getOperand(i).setReg(DesignatedReg);
679 DEBUG(std::cerr << '\t' << *prior(MII));
684 // Otherwise, reload it and remember that we have it.
685 PhysReg = VRM.getPhys(VirtReg);
686 assert(PhysReg && "Must map virtreg to physreg!");
687 const TargetRegisterClass* RC =
688 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
690 // Note that, if we reused a register for a previous operand, the
691 // register we want to reload into might not actually be
692 // available. If this occurs, use the register indicated by the
694 if (ReusedOperands.hasReuses())
695 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
696 Spills, MaybeDeadStores);
698 PhysRegsUsed[PhysReg] = true;
699 ReusedOperands.markClobbered(PhysReg);
700 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
701 // This invalidates PhysReg.
702 Spills.ClobberPhysReg(PhysReg);
704 // Any stores to this stack slot are not dead anymore.
705 MaybeDeadStores.erase(StackSlot);
706 Spills.addAvailable(StackSlot, PhysReg);
708 MI.getOperand(i).setReg(PhysReg);
709 DEBUG(std::cerr << '\t' << *prior(MII));
712 DEBUG(std::cerr << '\t' << MI);
714 // If we have folded references to memory operands, make sure we clear all
715 // physical registers that may contain the value of the spilled virtual
717 VirtRegMap::MI2VirtMapTy::const_iterator I, End;
718 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
719 DEBUG(std::cerr << "Folded vreg: " << I->second.first << " MR: "
720 << I->second.second);
721 unsigned VirtReg = I->second.first;
722 VirtRegMap::ModRef MR = I->second.second;
723 if (!VRM.hasStackSlot(VirtReg)) {
724 DEBUG(std::cerr << ": No stack slot!\n");
727 int SS = VRM.getStackSlot(VirtReg);
728 DEBUG(std::cerr << " - StackSlot: " << SS << "\n");
730 // If this folded instruction is just a use, check to see if it's a
731 // straight load from the virt reg slot.
732 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
734 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
735 if (FrameIdx == SS) {
736 // If this spill slot is available, turn it into a copy (or nothing)
737 // instead of leaving it as a load!
738 if (unsigned InReg = Spills.getSpillSlotPhysReg(SS)) {
739 DEBUG(std::cerr << "Promoted Load To Copy: " << MI);
740 MachineFunction &MF = *MBB.getParent();
741 if (DestReg != InReg) {
742 MRI->copyRegToReg(MBB, &MI, DestReg, InReg,
743 MF.getSSARegMap()->getRegClass(VirtReg));
744 // Revisit the copy so we make sure to notice the effects of the
745 // operation on the destreg (either needing to RA it if it's
746 // virtual or needing to clobber any values if it's physical).
748 --NextMII; // backtrack to the copy.
750 VRM.RemoveFromFoldedVirtMap(&MI);
752 goto ProcessNextInst;
758 // If this reference is not a use, any previous store is now dead.
759 // Otherwise, the store to this stack slot is not dead anymore.
760 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS);
761 if (MDSI != MaybeDeadStores.end()) {
762 if (MR & VirtRegMap::isRef) // Previous store is not dead.
763 MaybeDeadStores.erase(MDSI);
765 // If we get here, the store is dead, nuke it now.
766 assert(VirtRegMap::isMod && "Can't be modref!");
767 DEBUG(std::cerr << "Removed dead store:\t" << *MDSI->second);
768 MBB.erase(MDSI->second);
769 VRM.RemoveFromFoldedVirtMap(MDSI->second);
770 MaybeDeadStores.erase(MDSI);
775 // If the spill slot value is available, and this is a new definition of
776 // the value, the value is not available anymore.
777 if (MR & VirtRegMap::isMod) {
778 // Notice that the value in this stack slot has been modified.
779 Spills.ModifyStackSlot(SS);
781 // If this is *just* a mod of the value, check to see if this is just a
782 // store to the spill slot (i.e. the spill got merged into the copy). If
783 // so, realize that the vreg is available now, and add the store to the
784 // MaybeDeadStore info.
786 if (!(MR & VirtRegMap::isRef)) {
787 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
788 assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
789 "Src hasn't been allocated yet?");
790 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark
791 // this as a potentially dead store in case there is a subsequent
792 // store into the stack slot without a read from it.
793 MaybeDeadStores[StackSlot] = &MI;
795 // If the stack slot value was previously available in some other
796 // register, change it now. Otherwise, make the register available,
798 Spills.addAvailable(StackSlot, SrcReg, false /*don't clobber*/);
804 // Process all of the spilled defs.
805 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
806 MachineOperand &MO = MI.getOperand(i);
807 if (MO.isRegister() && MO.getReg() && MO.isDef()) {
808 unsigned VirtReg = MO.getReg();
810 if (!MRegisterInfo::isVirtualRegister(VirtReg)) {
811 // Check to see if this is a noop copy. If so, eliminate the
812 // instruction before considering the dest reg to be changed.
814 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
816 DEBUG(std::cerr << "Removing now-noop copy: " << MI);
818 VRM.RemoveFromFoldedVirtMap(&MI);
819 goto ProcessNextInst;
822 // If it's not a no-op copy, it clobbers the value in the destreg.
823 Spills.ClobberPhysReg(VirtReg);
824 ReusedOperands.markClobbered(VirtReg);
826 // Check to see if this instruction is a load from a stack slot into
827 // a register. If so, this provides the stack slot value in the reg.
829 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
830 assert(DestReg == VirtReg && "Unknown load situation!");
832 // Otherwise, if it wasn't available, remember that it is now!
833 Spills.addAvailable(FrameIdx, DestReg);
834 goto ProcessNextInst;
840 // The only vregs left are stack slot definitions.
841 int StackSlot = VRM.getStackSlot(VirtReg);
842 const TargetRegisterClass *RC =
843 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
845 // If this def is part of a two-address operand, make sure to execute
846 // the store from the correct physical register.
848 int TiedOp = TII->findTiedToSrcOperand(MI.getOpcode(), i);
850 PhysReg = MI.getOperand(TiedOp).getReg();
852 PhysReg = VRM.getPhys(VirtReg);
853 if (ReusedOperands.isClobbered(PhysReg)) {
854 // Another def has taken the assigned physreg. It must have been a
855 // use&def which got it due to reuse. Undo the reuse!
856 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
857 Spills, MaybeDeadStores);
861 PhysRegsUsed[PhysReg] = true;
862 ReusedOperands.markClobbered(PhysReg);
863 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
864 DEBUG(std::cerr << "Store:\t" << *next(MII));
865 MI.getOperand(i).setReg(PhysReg);
867 // Check to see if this is a noop copy. If so, eliminate the
868 // instruction before considering the dest reg to be changed.
871 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
873 DEBUG(std::cerr << "Removing now-noop copy: " << MI);
875 VRM.RemoveFromFoldedVirtMap(&MI);
876 goto ProcessNextInst;
880 // If there is a dead store to this stack slot, nuke it now.
881 MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
883 DEBUG(std::cerr << "Removed dead store:\t" << *LastStore);
885 MBB.erase(LastStore);
886 VRM.RemoveFromFoldedVirtMap(LastStore);
888 LastStore = next(MII);
890 // If the stack slot value was previously available in some other
891 // register, change it now. Otherwise, make the register available,
893 Spills.ModifyStackSlot(StackSlot);
894 Spills.ClobberPhysReg(PhysReg);
895 Spills.addAvailable(StackSlot, PhysReg);
906 llvm::Spiller* llvm::createSpiller() {
907 switch (SpillerOpt) {
908 default: assert(0 && "Unreachable!");
910 return new LocalSpiller();
912 return new SimpleSpiller();