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 if (TII.getOperandConstraint(OldMI->getOpcode(), OpNo, TOI::TIED_TO) != -1) {
101 // Folded a two-address operand.
103 } else if (OldMI->getOperand(OpNo).isDef()) {
109 // add new memory reference
110 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo)));
113 void VirtRegMap::print(std::ostream &OS) const {
114 llvm_ostream LOS(OS);
118 void VirtRegMap::print(llvm_ostream &OS) const {
119 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo();
121 OS << "********** REGISTER MAP **********\n";
122 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
123 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) {
124 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG)
125 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n";
129 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
130 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i)
131 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT)
132 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n";
136 void VirtRegMap::dump() const {
137 llvm_ostream OS = DOUT;
142 //===----------------------------------------------------------------------===//
143 // Simple Spiller Implementation
144 //===----------------------------------------------------------------------===//
146 Spiller::~Spiller() {}
149 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller {
150 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM);
154 bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
155 DOUT << "********** REWRITE MACHINE CODE **********\n";
156 DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';
157 const TargetMachine &TM = MF.getTarget();
158 const MRegisterInfo &MRI = *TM.getRegisterInfo();
159 bool *PhysRegsUsed = MF.getUsedPhysregs();
161 // LoadedRegs - Keep track of which vregs are loaded, so that we only load
162 // each vreg once (in the case where a spilled vreg is used by multiple
163 // operands). This is always smaller than the number of operands to the
164 // current machine instr, so it should be small.
165 std::vector<unsigned> LoadedRegs;
167 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
169 DOUT << MBBI->getBasicBlock()->getName() << ":\n";
170 MachineBasicBlock &MBB = *MBBI;
171 for (MachineBasicBlock::iterator MII = MBB.begin(),
172 E = MBB.end(); MII != E; ++MII) {
173 MachineInstr &MI = *MII;
174 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
175 MachineOperand &MO = MI.getOperand(i);
176 if (MO.isRegister() && MO.getReg())
177 if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
178 unsigned VirtReg = MO.getReg();
179 unsigned PhysReg = VRM.getPhys(VirtReg);
180 if (VRM.hasStackSlot(VirtReg)) {
181 int StackSlot = VRM.getStackSlot(VirtReg);
182 const TargetRegisterClass* RC =
183 MF.getSSARegMap()->getRegClass(VirtReg);
186 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg)
187 == LoadedRegs.end()) {
188 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
189 LoadedRegs.push_back(VirtReg);
191 DOUT << '\t' << *prior(MII);
195 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
199 PhysRegsUsed[PhysReg] = true;
200 MI.getOperand(i).setReg(PhysReg);
202 PhysRegsUsed[MO.getReg()] = true;
213 //===----------------------------------------------------------------------===//
214 // Local Spiller Implementation
215 //===----------------------------------------------------------------------===//
218 /// LocalSpiller - This spiller does a simple pass over the machine basic
219 /// block to attempt to keep spills in registers as much as possible for
220 /// blocks that have low register pressure (the vreg may be spilled due to
221 /// register pressure in other blocks).
222 class VISIBILITY_HIDDEN LocalSpiller : public Spiller {
223 const MRegisterInfo *MRI;
224 const TargetInstrInfo *TII;
226 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
227 MRI = MF.getTarget().getRegisterInfo();
228 TII = MF.getTarget().getInstrInfo();
229 DOUT << "\n**** Local spiller rewriting function '"
230 << MF.getFunction()->getName() << "':\n";
232 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
234 RewriteMBB(*MBB, VRM);
238 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM);
239 void ClobberPhysReg(unsigned PR, std::map<int, unsigned> &SpillSlots,
240 std::multimap<unsigned, int> &PhysRegs);
241 void ClobberPhysRegOnly(unsigned PR, std::map<int, unsigned> &SpillSlots,
242 std::multimap<unsigned, int> &PhysRegs);
243 void ModifyStackSlot(int Slot, std::map<int, unsigned> &SpillSlots,
244 std::multimap<unsigned, int> &PhysRegs);
248 /// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
249 /// top down, keep track of which spills slots are available in each register.
251 /// Note that not all physregs are created equal here. In particular, some
252 /// physregs are reloads that we are allowed to clobber or ignore at any time.
253 /// Other physregs are values that the register allocated program is using that
254 /// we cannot CHANGE, but we can read if we like. We keep track of this on a
255 /// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable
256 /// entries. The predicate 'canClobberPhysReg()' checks this bit and
257 /// addAvailable sets it if.
259 class VISIBILITY_HIDDEN AvailableSpills {
260 const MRegisterInfo *MRI;
261 const TargetInstrInfo *TII;
263 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual
264 // register values that are still available, due to being loaded or stored to,
265 // but not invalidated yet.
266 std::map<int, unsigned> SpillSlotsAvailable;
268 // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating
269 // which stack slot values are currently held by a physreg. This is used to
270 // invalidate entries in SpillSlotsAvailable when a physreg is modified.
271 std::multimap<unsigned, int> PhysRegsAvailable;
273 void ClobberPhysRegOnly(unsigned PhysReg);
275 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii)
276 : MRI(mri), TII(tii) {
279 /// getSpillSlotPhysReg - If the specified stack slot is available in a
280 /// physical register, return that PhysReg, otherwise return 0.
281 unsigned getSpillSlotPhysReg(int Slot) const {
282 std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot);
283 if (I != SpillSlotsAvailable.end())
284 return I->second >> 1; // Remove the CanClobber bit.
288 const MRegisterInfo *getRegInfo() const { return MRI; }
290 /// addAvailable - Mark that the specified stack slot is available in the
291 /// specified physreg. If CanClobber is true, the physreg can be modified at
292 /// any time without changing the semantics of the program.
293 void addAvailable(int Slot, unsigned Reg, bool CanClobber = true) {
294 // If this stack slot is thought to be available in some other physreg,
295 // remove its record.
296 ModifyStackSlot(Slot);
298 PhysRegsAvailable.insert(std::make_pair(Reg, Slot));
299 SpillSlotsAvailable[Slot] = (Reg << 1) | (unsigned)CanClobber;
301 DOUT << "Remembering SS#" << Slot << " in physreg "
302 << MRI->getName(Reg) << "\n";
305 /// canClobberPhysReg - Return true if the spiller is allowed to change the
306 /// value of the specified stackslot register if it desires. The specified
307 /// stack slot must be available in a physreg for this query to make sense.
308 bool canClobberPhysReg(int Slot) const {
309 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!");
310 return SpillSlotsAvailable.find(Slot)->second & 1;
313 /// ClobberPhysReg - This is called when the specified physreg changes
314 /// value. We use this to invalidate any info about stuff we thing lives in
315 /// it and any of its aliases.
316 void ClobberPhysReg(unsigned PhysReg);
318 /// ModifyStackSlot - This method is called when the value in a stack slot
319 /// changes. This removes information about which register the previous value
320 /// for this slot lives in (as the previous value is dead now).
321 void ModifyStackSlot(int Slot);
325 /// ClobberPhysRegOnly - This is called when the specified physreg changes
326 /// value. We use this to invalidate any info about stuff we thing lives in it.
327 void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
328 std::multimap<unsigned, int>::iterator I =
329 PhysRegsAvailable.lower_bound(PhysReg);
330 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
331 int Slot = I->second;
332 PhysRegsAvailable.erase(I++);
333 assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg &&
334 "Bidirectional map mismatch!");
335 SpillSlotsAvailable.erase(Slot);
336 DOUT << "PhysReg " << MRI->getName(PhysReg)
337 << " clobbered, invalidating SS#" << Slot << "\n";
341 /// ClobberPhysReg - This is called when the specified physreg changes
342 /// value. We use this to invalidate any info about stuff we thing lives in
343 /// it and any of its aliases.
344 void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
345 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
346 ClobberPhysRegOnly(*AS);
347 ClobberPhysRegOnly(PhysReg);
350 /// ModifyStackSlot - This method is called when the value in a stack slot
351 /// changes. This removes information about which register the previous value
352 /// for this slot lives in (as the previous value is dead now).
353 void AvailableSpills::ModifyStackSlot(int Slot) {
354 std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot);
355 if (It == SpillSlotsAvailable.end()) return;
356 unsigned Reg = It->second >> 1;
357 SpillSlotsAvailable.erase(It);
359 // This register may hold the value of multiple stack slots, only remove this
360 // stack slot from the set of values the register contains.
361 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
363 assert(I != PhysRegsAvailable.end() && I->first == Reg &&
364 "Map inverse broken!");
365 if (I->second == Slot) break;
367 PhysRegsAvailable.erase(I);
372 // ReusedOp - For each reused operand, we keep track of a bit of information, in
373 // case we need to rollback upon processing a new operand. See comments below.
376 // The MachineInstr operand that reused an available value.
379 // StackSlot - The spill slot of the value being reused.
382 // PhysRegReused - The physical register the value was available in.
383 unsigned PhysRegReused;
385 // AssignedPhysReg - The physreg that was assigned for use by the reload.
386 unsigned AssignedPhysReg;
388 // VirtReg - The virtual register itself.
391 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
393 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr),
397 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
398 /// is reused instead of reloaded.
399 class VISIBILITY_HIDDEN ReuseInfo {
401 std::vector<ReusedOp> Reuses;
402 bool *PhysRegsClobbered;
404 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) {
405 PhysRegsClobbered = new bool[mri->getNumRegs()];
406 std::fill(PhysRegsClobbered, PhysRegsClobbered+mri->getNumRegs(), false);
409 delete[] PhysRegsClobbered;
412 bool hasReuses() const {
413 return !Reuses.empty();
416 /// addReuse - If we choose to reuse a virtual register that is already
417 /// available instead of reloading it, remember that we did so.
418 void addReuse(unsigned OpNo, unsigned StackSlot,
419 unsigned PhysRegReused, unsigned AssignedPhysReg,
421 // If the reload is to the assigned register anyway, no undo will be
423 if (PhysRegReused == AssignedPhysReg) return;
425 // Otherwise, remember this.
426 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused,
427 AssignedPhysReg, VirtReg));
430 void markClobbered(unsigned PhysReg) {
431 PhysRegsClobbered[PhysReg] = true;
434 bool isClobbered(unsigned PhysReg) const {
435 return PhysRegsClobbered[PhysReg];
438 /// GetRegForReload - We are about to emit a reload into PhysReg. If there
439 /// is some other operand that is using the specified register, either pick
440 /// a new register to use, or evict the previous reload and use this reg.
441 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
442 AvailableSpills &Spills,
443 std::map<int, MachineInstr*> &MaybeDeadStores) {
444 if (Reuses.empty()) return PhysReg; // This is most often empty.
446 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
447 ReusedOp &Op = Reuses[ro];
448 // If we find some other reuse that was supposed to use this register
449 // exactly for its reload, we can change this reload to use ITS reload
451 if (Op.PhysRegReused == PhysReg) {
452 // Yup, use the reload register that we didn't use before.
453 unsigned NewReg = Op.AssignedPhysReg;
454 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores);
456 // Otherwise, we might also have a problem if a previously reused
457 // value aliases the new register. If so, codegen the previous reload
459 unsigned PRRU = Op.PhysRegReused;
460 const MRegisterInfo *MRI = Spills.getRegInfo();
461 if (MRI->areAliases(PRRU, PhysReg)) {
462 // Okay, we found out that an alias of a reused register
463 // was used. This isn't good because it means we have
464 // to undo a previous reuse.
465 MachineBasicBlock *MBB = MI->getParent();
466 const TargetRegisterClass *AliasRC =
467 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg);
469 // Copy Op out of the vector and remove it, we're going to insert an
470 // explicit load for it.
472 Reuses.erase(Reuses.begin()+ro);
474 // Ok, we're going to try to reload the assigned physreg into the
475 // slot that we were supposed to in the first place. However, that
476 // register could hold a reuse. Check to see if it conflicts or
477 // would prefer us to use a different register.
478 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg,
479 MI, Spills, MaybeDeadStores);
481 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg,
482 NewOp.StackSlot, AliasRC);
483 Spills.ClobberPhysReg(NewPhysReg);
484 Spills.ClobberPhysReg(NewOp.PhysRegReused);
486 // Any stores to this stack slot are not dead anymore.
487 MaybeDeadStores.erase(NewOp.StackSlot);
489 MI->getOperand(NewOp.Operand).setReg(NewPhysReg);
491 Spills.addAvailable(NewOp.StackSlot, NewPhysReg);
493 DEBUG(MachineBasicBlock::iterator MII = MI;
494 DOUT << '\t' << *prior(MII));
496 DOUT << "Reuse undone!\n";
499 // Finally, PhysReg is now available, go ahead and use it.
510 /// rewriteMBB - Keep track of which spills are available even after the
511 /// register allocator is done with them. If possible, avoid reloading vregs.
512 void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
514 DOUT << MBB.getBasicBlock()->getName() << ":\n";
516 // Spills - Keep track of which spilled values are available in physregs so
517 // that we can choose to reuse the physregs instead of emitting reloads.
518 AvailableSpills Spills(MRI, TII);
520 // MaybeDeadStores - When we need to write a value back into a stack slot,
521 // keep track of the inserted store. If the stack slot value is never read
522 // (because the value was used from some available register, for example), and
523 // subsequently stored to, the original store is dead. This map keeps track
524 // of inserted stores that are not used. If we see a subsequent store to the
525 // same stack slot, the original store is deleted.
526 std::map<int, MachineInstr*> MaybeDeadStores;
528 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs();
530 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
532 MachineInstr &MI = *MII;
533 MachineBasicBlock::iterator NextMII = MII; ++NextMII;
535 /// ReusedOperands - Keep track of operand reuse in case we need to undo
537 ReuseInfo ReusedOperands(MI, MRI);
539 // Loop over all of the implicit defs, clearing them from our available
541 const unsigned *ImpDef = TII->getImplicitDefs(MI.getOpcode());
543 for ( ; *ImpDef; ++ImpDef) {
544 PhysRegsUsed[*ImpDef] = true;
545 ReusedOperands.markClobbered(*ImpDef);
546 Spills.ClobberPhysReg(*ImpDef);
550 // Process all of the spilled uses and all non spilled reg references.
551 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
552 MachineOperand &MO = MI.getOperand(i);
553 if (!MO.isRegister() || MO.getReg() == 0)
554 continue; // Ignore non-register operands.
556 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) {
557 // Ignore physregs for spilling, but remember that it is used by this
559 PhysRegsUsed[MO.getReg()] = true;
560 ReusedOperands.markClobbered(MO.getReg());
564 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) &&
565 "Not a virtual or a physical register?");
567 unsigned VirtReg = MO.getReg();
568 if (!VRM.hasStackSlot(VirtReg)) {
569 // This virtual register was assigned a physreg!
570 unsigned Phys = VRM.getPhys(VirtReg);
571 PhysRegsUsed[Phys] = true;
573 ReusedOperands.markClobbered(Phys);
574 MI.getOperand(i).setReg(Phys);
578 // This virtual register is now known to be a spilled value.
580 continue; // Handle defs in the loop below (handle use&def here though)
582 int StackSlot = VRM.getStackSlot(VirtReg);
585 // Check to see if this stack slot is available.
586 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) {
588 // This spilled operand might be part of a two-address operand. If this
589 // is the case, then changing it will necessarily require changing the
590 // def part of the instruction as well. However, in some cases, we
591 // aren't allowed to modify the reused register. If none of these cases
593 bool CanReuse = true;
594 int ti = TII->getOperandConstraint(MI.getOpcode(), i, TOI::TIED_TO);
596 MI.getOperand(ti).isReg() &&
597 MI.getOperand(ti).getReg() == VirtReg) {
598 // Okay, we have a two address operand. We can reuse this physreg as
599 // long as we are allowed to clobber the value and there is an earlier
600 // def that has already clobbered the physreg.
601 CanReuse = Spills.canClobberPhysReg(StackSlot) &&
602 !ReusedOperands.isClobbered(PhysReg);
606 // If this stack slot value is already available, reuse it!
607 DOUT << "Reusing SS#" << StackSlot << " from physreg "
608 << MRI->getName(PhysReg) << " for vreg"
609 << VirtReg <<" instead of reloading into physreg "
610 << MRI->getName(VRM.getPhys(VirtReg)) << "\n";
611 MI.getOperand(i).setReg(PhysReg);
613 // The only technical detail we have is that we don't know that
614 // PhysReg won't be clobbered by a reloaded stack slot that occurs
615 // later in the instruction. In particular, consider 'op V1, V2'.
616 // If V1 is available in physreg R0, we would choose to reuse it
617 // here, instead of reloading it into the register the allocator
618 // indicated (say R1). However, V2 might have to be reloaded
619 // later, and it might indicate that it needs to live in R0. When
620 // this occurs, we need to have information available that
621 // indicates it is safe to use R1 for the reload instead of R0.
623 // To further complicate matters, we might conflict with an alias,
624 // or R0 and R1 might not be compatible with each other. In this
625 // case, we actually insert a reload for V1 in R1, ensuring that
626 // we can get at R0 or its alias.
627 ReusedOperands.addReuse(i, StackSlot, PhysReg,
628 VRM.getPhys(VirtReg), VirtReg);
630 // Only mark it clobbered if this is a use&def operand.
631 ReusedOperands.markClobbered(PhysReg);
636 // Otherwise we have a situation where we have a two-address instruction
637 // whose mod/ref operand needs to be reloaded. This reload is already
638 // available in some register "PhysReg", but if we used PhysReg as the
639 // operand to our 2-addr instruction, the instruction would modify
640 // PhysReg. This isn't cool if something later uses PhysReg and expects
641 // to get its initial value.
643 // To avoid this problem, and to avoid doing a load right after a store,
644 // we emit a copy from PhysReg into the designated register for this
646 unsigned DesignatedReg = VRM.getPhys(VirtReg);
647 assert(DesignatedReg && "Must map virtreg to physreg!");
649 // Note that, if we reused a register for a previous operand, the
650 // register we want to reload into might not actually be
651 // available. If this occurs, use the register indicated by the
653 if (ReusedOperands.hasReuses())
654 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI,
655 Spills, MaybeDeadStores);
657 // If the mapped designated register is actually the physreg we have
658 // incoming, we don't need to inserted a dead copy.
659 if (DesignatedReg == PhysReg) {
660 // If this stack slot value is already available, reuse it!
661 DOUT << "Reusing SS#" << StackSlot << " from physreg "
662 << MRI->getName(PhysReg) << " for vreg"
664 << " instead of reloading into same physreg.\n";
665 MI.getOperand(i).setReg(PhysReg);
666 ReusedOperands.markClobbered(PhysReg);
671 const TargetRegisterClass* RC =
672 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
674 PhysRegsUsed[DesignatedReg] = true;
675 ReusedOperands.markClobbered(DesignatedReg);
676 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC);
678 // This invalidates DesignatedReg.
679 Spills.ClobberPhysReg(DesignatedReg);
681 Spills.addAvailable(StackSlot, DesignatedReg);
682 MI.getOperand(i).setReg(DesignatedReg);
683 DOUT << '\t' << *prior(MII);
688 // Otherwise, reload it and remember that we have it.
689 PhysReg = VRM.getPhys(VirtReg);
690 assert(PhysReg && "Must map virtreg to physreg!");
691 const TargetRegisterClass* RC =
692 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
694 // Note that, if we reused a register for a previous operand, the
695 // register we want to reload into might not actually be
696 // available. If this occurs, use the register indicated by the
698 if (ReusedOperands.hasReuses())
699 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
700 Spills, MaybeDeadStores);
702 PhysRegsUsed[PhysReg] = true;
703 ReusedOperands.markClobbered(PhysReg);
704 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
705 // This invalidates PhysReg.
706 Spills.ClobberPhysReg(PhysReg);
708 // Any stores to this stack slot are not dead anymore.
709 MaybeDeadStores.erase(StackSlot);
710 Spills.addAvailable(StackSlot, PhysReg);
712 MI.getOperand(i).setReg(PhysReg);
713 DOUT << '\t' << *prior(MII);
718 // If we have folded references to memory operands, make sure we clear all
719 // physical registers that may contain the value of the spilled virtual
721 VirtRegMap::MI2VirtMapTy::const_iterator I, End;
722 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
723 DOUT << "Folded vreg: " << I->second.first << " MR: "
725 unsigned VirtReg = I->second.first;
726 VirtRegMap::ModRef MR = I->second.second;
727 if (!VRM.hasStackSlot(VirtReg)) {
728 DOUT << ": No stack slot!\n";
731 int SS = VRM.getStackSlot(VirtReg);
732 DOUT << " - StackSlot: " << SS << "\n";
734 // If this folded instruction is just a use, check to see if it's a
735 // straight load from the virt reg slot.
736 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
738 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
739 if (FrameIdx == SS) {
740 // If this spill slot is available, turn it into a copy (or nothing)
741 // instead of leaving it as a load!
742 if (unsigned InReg = Spills.getSpillSlotPhysReg(SS)) {
743 DOUT << "Promoted Load To Copy: " << MI;
744 MachineFunction &MF = *MBB.getParent();
745 if (DestReg != InReg) {
746 MRI->copyRegToReg(MBB, &MI, DestReg, InReg,
747 MF.getSSARegMap()->getRegClass(VirtReg));
748 // Revisit the copy so we make sure to notice the effects of the
749 // operation on the destreg (either needing to RA it if it's
750 // virtual or needing to clobber any values if it's physical).
752 --NextMII; // backtrack to the copy.
754 VRM.RemoveFromFoldedVirtMap(&MI);
756 goto ProcessNextInst;
762 // If this reference is not a use, any previous store is now dead.
763 // Otherwise, the store to this stack slot is not dead anymore.
764 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS);
765 if (MDSI != MaybeDeadStores.end()) {
766 if (MR & VirtRegMap::isRef) // Previous store is not dead.
767 MaybeDeadStores.erase(MDSI);
769 // If we get here, the store is dead, nuke it now.
770 assert(VirtRegMap::isMod && "Can't be modref!");
771 DOUT << "Removed dead store:\t" << *MDSI->second;
772 MBB.erase(MDSI->second);
773 VRM.RemoveFromFoldedVirtMap(MDSI->second);
774 MaybeDeadStores.erase(MDSI);
779 // If the spill slot value is available, and this is a new definition of
780 // the value, the value is not available anymore.
781 if (MR & VirtRegMap::isMod) {
782 // Notice that the value in this stack slot has been modified.
783 Spills.ModifyStackSlot(SS);
785 // If this is *just* a mod of the value, check to see if this is just a
786 // store to the spill slot (i.e. the spill got merged into the copy). If
787 // so, realize that the vreg is available now, and add the store to the
788 // MaybeDeadStore info.
790 if (!(MR & VirtRegMap::isRef)) {
791 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
792 assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
793 "Src hasn't been allocated yet?");
794 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark
795 // this as a potentially dead store in case there is a subsequent
796 // store into the stack slot without a read from it.
797 MaybeDeadStores[StackSlot] = &MI;
799 // If the stack slot value was previously available in some other
800 // register, change it now. Otherwise, make the register available,
802 Spills.addAvailable(StackSlot, SrcReg, false /*don't clobber*/);
808 // Process all of the spilled defs.
809 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
810 MachineOperand &MO = MI.getOperand(i);
811 if (MO.isRegister() && MO.getReg() && MO.isDef()) {
812 unsigned VirtReg = MO.getReg();
814 if (!MRegisterInfo::isVirtualRegister(VirtReg)) {
815 // Check to see if this is a noop copy. If so, eliminate the
816 // instruction before considering the dest reg to be changed.
818 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
820 DOUT << "Removing now-noop copy: " << MI;
822 VRM.RemoveFromFoldedVirtMap(&MI);
823 goto ProcessNextInst;
826 // If it's not a no-op copy, it clobbers the value in the destreg.
827 Spills.ClobberPhysReg(VirtReg);
828 ReusedOperands.markClobbered(VirtReg);
830 // Check to see if this instruction is a load from a stack slot into
831 // a register. If so, this provides the stack slot value in the reg.
833 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
834 assert(DestReg == VirtReg && "Unknown load situation!");
836 // Otherwise, if it wasn't available, remember that it is now!
837 Spills.addAvailable(FrameIdx, DestReg);
838 goto ProcessNextInst;
844 // The only vregs left are stack slot definitions.
845 int StackSlot = VRM.getStackSlot(VirtReg);
846 const TargetRegisterClass *RC =
847 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
849 // If this def is part of a two-address operand, make sure to execute
850 // the store from the correct physical register.
852 int TiedOp = TII->findTiedToSrcOperand(MI.getOpcode(), i);
854 PhysReg = MI.getOperand(TiedOp).getReg();
856 PhysReg = VRM.getPhys(VirtReg);
857 if (ReusedOperands.isClobbered(PhysReg)) {
858 // Another def has taken the assigned physreg. It must have been a
859 // use&def which got it due to reuse. Undo the reuse!
860 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
861 Spills, MaybeDeadStores);
865 PhysRegsUsed[PhysReg] = true;
866 ReusedOperands.markClobbered(PhysReg);
867 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
868 DOUT << "Store:\t" << *next(MII);
869 MI.getOperand(i).setReg(PhysReg);
871 // Check to see if this is a noop copy. If so, eliminate the
872 // instruction before considering the dest reg to be changed.
875 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
877 DOUT << "Removing now-noop copy: " << MI;
879 VRM.RemoveFromFoldedVirtMap(&MI);
880 goto ProcessNextInst;
884 // If there is a dead store to this stack slot, nuke it now.
885 MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
887 DOUT << "Removed dead store:\t" << *LastStore;
889 MBB.erase(LastStore);
890 VRM.RemoveFromFoldedVirtMap(LastStore);
892 LastStore = next(MII);
894 // If the stack slot value was previously available in some other
895 // register, change it now. Otherwise, make the register available,
897 Spills.ModifyStackSlot(StackSlot);
898 Spills.ClobberPhysReg(PhysReg);
899 Spills.addAvailable(StackSlot, PhysReg);
910 llvm::Spiller* llvm::createSpiller() {
911 switch (SpillerOpt) {
912 default: assert(0 && "Unreachable!");
914 return new LocalSpiller();
916 return new SimpleSpiller();