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,
101 TargetInstrInfo::TIED_TO)) {
102 // Folded a two-address operand.
104 } else if (OldMI->getOperand(OpNo).isDef()) {
110 // add new memory reference
111 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo)));
114 void VirtRegMap::print(std::ostream &OS) const {
115 llvm_ostream LOS(OS);
119 void VirtRegMap::print(llvm_ostream &OS) const {
120 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo();
122 OS << "********** REGISTER MAP **********\n";
123 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
124 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) {
125 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG)
126 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n";
130 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
131 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i)
132 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT)
133 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n";
137 void VirtRegMap::dump() const {
138 llvm_ostream OS = DOUT;
143 //===----------------------------------------------------------------------===//
144 // Simple Spiller Implementation
145 //===----------------------------------------------------------------------===//
147 Spiller::~Spiller() {}
150 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller {
151 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM);
155 bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
156 DOUT << "********** REWRITE MACHINE CODE **********\n";
157 DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';
158 const TargetMachine &TM = MF.getTarget();
159 const MRegisterInfo &MRI = *TM.getRegisterInfo();
160 bool *PhysRegsUsed = MF.getUsedPhysregs();
162 // LoadedRegs - Keep track of which vregs are loaded, so that we only load
163 // each vreg once (in the case where a spilled vreg is used by multiple
164 // operands). This is always smaller than the number of operands to the
165 // current machine instr, so it should be small.
166 std::vector<unsigned> LoadedRegs;
168 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
170 DOUT << MBBI->getBasicBlock()->getName() << ":\n";
171 MachineBasicBlock &MBB = *MBBI;
172 for (MachineBasicBlock::iterator MII = MBB.begin(),
173 E = MBB.end(); MII != E; ++MII) {
174 MachineInstr &MI = *MII;
175 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
176 MachineOperand &MO = MI.getOperand(i);
177 if (MO.isRegister() && MO.getReg())
178 if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
179 unsigned VirtReg = MO.getReg();
180 unsigned PhysReg = VRM.getPhys(VirtReg);
181 if (VRM.hasStackSlot(VirtReg)) {
182 int StackSlot = VRM.getStackSlot(VirtReg);
183 const TargetRegisterClass* RC =
184 MF.getSSARegMap()->getRegClass(VirtReg);
187 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg)
188 == LoadedRegs.end()) {
189 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
190 LoadedRegs.push_back(VirtReg);
192 DOUT << '\t' << *prior(MII);
196 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
200 PhysRegsUsed[PhysReg] = true;
201 MI.getOperand(i).setReg(PhysReg);
203 PhysRegsUsed[MO.getReg()] = true;
214 //===----------------------------------------------------------------------===//
215 // Local Spiller Implementation
216 //===----------------------------------------------------------------------===//
219 /// LocalSpiller - This spiller does a simple pass over the machine basic
220 /// block to attempt to keep spills in registers as much as possible for
221 /// blocks that have low register pressure (the vreg may be spilled due to
222 /// register pressure in other blocks).
223 class VISIBILITY_HIDDEN LocalSpiller : public Spiller {
224 const MRegisterInfo *MRI;
225 const TargetInstrInfo *TII;
227 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
228 MRI = MF.getTarget().getRegisterInfo();
229 TII = MF.getTarget().getInstrInfo();
230 DOUT << "\n**** Local spiller rewriting function '"
231 << MF.getFunction()->getName() << "':\n";
233 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
235 RewriteMBB(*MBB, VRM);
239 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM);
240 void ClobberPhysReg(unsigned PR, std::map<int, unsigned> &SpillSlots,
241 std::multimap<unsigned, int> &PhysRegs);
242 void ClobberPhysRegOnly(unsigned PR, std::map<int, unsigned> &SpillSlots,
243 std::multimap<unsigned, int> &PhysRegs);
244 void ModifyStackSlot(int Slot, std::map<int, unsigned> &SpillSlots,
245 std::multimap<unsigned, int> &PhysRegs);
249 /// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
250 /// top down, keep track of which spills slots are available in each register.
252 /// Note that not all physregs are created equal here. In particular, some
253 /// physregs are reloads that we are allowed to clobber or ignore at any time.
254 /// Other physregs are values that the register allocated program is using that
255 /// we cannot CHANGE, but we can read if we like. We keep track of this on a
256 /// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable
257 /// entries. The predicate 'canClobberPhysReg()' checks this bit and
258 /// addAvailable sets it if.
260 class VISIBILITY_HIDDEN AvailableSpills {
261 const MRegisterInfo *MRI;
262 const TargetInstrInfo *TII;
264 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual
265 // register values that are still available, due to being loaded or stored to,
266 // but not invalidated yet.
267 std::map<int, unsigned> SpillSlotsAvailable;
269 // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating
270 // which stack slot values are currently held by a physreg. This is used to
271 // invalidate entries in SpillSlotsAvailable when a physreg is modified.
272 std::multimap<unsigned, int> PhysRegsAvailable;
274 void ClobberPhysRegOnly(unsigned PhysReg);
276 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii)
277 : MRI(mri), TII(tii) {
280 /// getSpillSlotPhysReg - If the specified stack slot is available in a
281 /// physical register, return that PhysReg, otherwise return 0.
282 unsigned getSpillSlotPhysReg(int Slot) const {
283 std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot);
284 if (I != SpillSlotsAvailable.end())
285 return I->second >> 1; // Remove the CanClobber bit.
289 const MRegisterInfo *getRegInfo() const { return MRI; }
291 /// addAvailable - Mark that the specified stack slot is available in the
292 /// specified physreg. If CanClobber is true, the physreg can be modified at
293 /// any time without changing the semantics of the program.
294 void addAvailable(int Slot, unsigned Reg, bool CanClobber = true) {
295 // If this stack slot is thought to be available in some other physreg,
296 // remove its record.
297 ModifyStackSlot(Slot);
299 PhysRegsAvailable.insert(std::make_pair(Reg, Slot));
300 SpillSlotsAvailable[Slot] = (Reg << 1) | (unsigned)CanClobber;
302 DOUT << "Remembering SS#" << Slot << " in physreg "
303 << MRI->getName(Reg) << "\n";
306 /// canClobberPhysReg - Return true if the spiller is allowed to change the
307 /// value of the specified stackslot register if it desires. The specified
308 /// stack slot must be available in a physreg for this query to make sense.
309 bool canClobberPhysReg(int Slot) const {
310 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!");
311 return SpillSlotsAvailable.find(Slot)->second & 1;
314 /// ClobberPhysReg - This is called when the specified physreg changes
315 /// value. We use this to invalidate any info about stuff we thing lives in
316 /// it and any of its aliases.
317 void ClobberPhysReg(unsigned PhysReg);
319 /// ModifyStackSlot - This method is called when the value in a stack slot
320 /// changes. This removes information about which register the previous value
321 /// for this slot lives in (as the previous value is dead now).
322 void ModifyStackSlot(int Slot);
326 /// ClobberPhysRegOnly - This is called when the specified physreg changes
327 /// value. We use this to invalidate any info about stuff we thing lives in it.
328 void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
329 std::multimap<unsigned, int>::iterator I =
330 PhysRegsAvailable.lower_bound(PhysReg);
331 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
332 int Slot = I->second;
333 PhysRegsAvailable.erase(I++);
334 assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg &&
335 "Bidirectional map mismatch!");
336 SpillSlotsAvailable.erase(Slot);
337 DOUT << "PhysReg " << MRI->getName(PhysReg)
338 << " clobbered, invalidating SS#" << Slot << "\n";
342 /// ClobberPhysReg - This is called when the specified physreg changes
343 /// value. We use this to invalidate any info about stuff we thing lives in
344 /// it and any of its aliases.
345 void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
346 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
347 ClobberPhysRegOnly(*AS);
348 ClobberPhysRegOnly(PhysReg);
351 /// ModifyStackSlot - This method is called when the value in a stack slot
352 /// changes. This removes information about which register the previous value
353 /// for this slot lives in (as the previous value is dead now).
354 void AvailableSpills::ModifyStackSlot(int Slot) {
355 std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot);
356 if (It == SpillSlotsAvailable.end()) return;
357 unsigned Reg = It->second >> 1;
358 SpillSlotsAvailable.erase(It);
360 // This register may hold the value of multiple stack slots, only remove this
361 // stack slot from the set of values the register contains.
362 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
364 assert(I != PhysRegsAvailable.end() && I->first == Reg &&
365 "Map inverse broken!");
366 if (I->second == Slot) break;
368 PhysRegsAvailable.erase(I);
373 // ReusedOp - For each reused operand, we keep track of a bit of information, in
374 // case we need to rollback upon processing a new operand. See comments below.
377 // The MachineInstr operand that reused an available value.
380 // StackSlot - The spill slot of the value being reused.
383 // PhysRegReused - The physical register the value was available in.
384 unsigned PhysRegReused;
386 // AssignedPhysReg - The physreg that was assigned for use by the reload.
387 unsigned AssignedPhysReg;
389 // VirtReg - The virtual register itself.
392 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
394 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr),
398 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
399 /// is reused instead of reloaded.
400 class VISIBILITY_HIDDEN ReuseInfo {
402 std::vector<ReusedOp> Reuses;
403 bool *PhysRegsClobbered;
405 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) {
406 PhysRegsClobbered = new bool[mri->getNumRegs()];
407 std::fill(PhysRegsClobbered, PhysRegsClobbered+mri->getNumRegs(), false);
410 delete[] PhysRegsClobbered;
413 bool hasReuses() const {
414 return !Reuses.empty();
417 /// addReuse - If we choose to reuse a virtual register that is already
418 /// available instead of reloading it, remember that we did so.
419 void addReuse(unsigned OpNo, unsigned StackSlot,
420 unsigned PhysRegReused, unsigned AssignedPhysReg,
422 // If the reload is to the assigned register anyway, no undo will be
424 if (PhysRegReused == AssignedPhysReg) return;
426 // Otherwise, remember this.
427 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused,
428 AssignedPhysReg, VirtReg));
431 void markClobbered(unsigned PhysReg) {
432 PhysRegsClobbered[PhysReg] = true;
435 bool isClobbered(unsigned PhysReg) const {
436 return PhysRegsClobbered[PhysReg];
439 /// GetRegForReload - We are about to emit a reload into PhysReg. If there
440 /// is some other operand that is using the specified register, either pick
441 /// a new register to use, or evict the previous reload and use this reg.
442 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
443 AvailableSpills &Spills,
444 std::map<int, MachineInstr*> &MaybeDeadStores) {
445 if (Reuses.empty()) return PhysReg; // This is most often empty.
447 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
448 ReusedOp &Op = Reuses[ro];
449 // If we find some other reuse that was supposed to use this register
450 // exactly for its reload, we can change this reload to use ITS reload
452 if (Op.PhysRegReused == PhysReg) {
453 // Yup, use the reload register that we didn't use before.
454 unsigned NewReg = Op.AssignedPhysReg;
455 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores);
457 // Otherwise, we might also have a problem if a previously reused
458 // value aliases the new register. If so, codegen the previous reload
460 unsigned PRRU = Op.PhysRegReused;
461 const MRegisterInfo *MRI = Spills.getRegInfo();
462 if (MRI->areAliases(PRRU, PhysReg)) {
463 // Okay, we found out that an alias of a reused register
464 // was used. This isn't good because it means we have
465 // to undo a previous reuse.
466 MachineBasicBlock *MBB = MI->getParent();
467 const TargetRegisterClass *AliasRC =
468 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg);
470 // Copy Op out of the vector and remove it, we're going to insert an
471 // explicit load for it.
473 Reuses.erase(Reuses.begin()+ro);
475 // Ok, we're going to try to reload the assigned physreg into the
476 // slot that we were supposed to in the first place. However, that
477 // register could hold a reuse. Check to see if it conflicts or
478 // would prefer us to use a different register.
479 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg,
480 MI, Spills, MaybeDeadStores);
482 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg,
483 NewOp.StackSlot, AliasRC);
484 Spills.ClobberPhysReg(NewPhysReg);
485 Spills.ClobberPhysReg(NewOp.PhysRegReused);
487 // Any stores to this stack slot are not dead anymore.
488 MaybeDeadStores.erase(NewOp.StackSlot);
490 MI->getOperand(NewOp.Operand).setReg(NewPhysReg);
492 Spills.addAvailable(NewOp.StackSlot, NewPhysReg);
494 DEBUG(MachineBasicBlock::iterator MII = MI;
495 DOUT << '\t' << *prior(MII));
497 DOUT << "Reuse undone!\n";
500 // Finally, PhysReg is now available, go ahead and use it.
511 /// rewriteMBB - Keep track of which spills are available even after the
512 /// register allocator is done with them. If possible, avoid reloading vregs.
513 void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
515 DOUT << MBB.getBasicBlock()->getName() << ":\n";
517 // Spills - Keep track of which spilled values are available in physregs so
518 // that we can choose to reuse the physregs instead of emitting reloads.
519 AvailableSpills Spills(MRI, TII);
521 // MaybeDeadStores - When we need to write a value back into a stack slot,
522 // keep track of the inserted store. If the stack slot value is never read
523 // (because the value was used from some available register, for example), and
524 // subsequently stored to, the original store is dead. This map keeps track
525 // of inserted stores that are not used. If we see a subsequent store to the
526 // same stack slot, the original store is deleted.
527 std::map<int, MachineInstr*> MaybeDeadStores;
529 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs();
531 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
533 MachineInstr &MI = *MII;
534 MachineBasicBlock::iterator NextMII = MII; ++NextMII;
536 /// ReusedOperands - Keep track of operand reuse in case we need to undo
538 ReuseInfo ReusedOperands(MI, MRI);
540 // Loop over all of the implicit defs, clearing them from our available
542 const unsigned *ImpDef = TII->getImplicitDefs(MI.getOpcode());
544 for ( ; *ImpDef; ++ImpDef) {
545 PhysRegsUsed[*ImpDef] = true;
546 ReusedOperands.markClobbered(*ImpDef);
547 Spills.ClobberPhysReg(*ImpDef);
551 // Process all of the spilled uses and all non spilled reg references.
552 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
553 MachineOperand &MO = MI.getOperand(i);
554 if (!MO.isRegister() || MO.getReg() == 0)
555 continue; // Ignore non-register operands.
557 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) {
558 // Ignore physregs for spilling, but remember that it is used by this
560 PhysRegsUsed[MO.getReg()] = true;
561 ReusedOperands.markClobbered(MO.getReg());
565 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) &&
566 "Not a virtual or a physical register?");
568 unsigned VirtReg = MO.getReg();
569 if (!VRM.hasStackSlot(VirtReg)) {
570 // This virtual register was assigned a physreg!
571 unsigned Phys = VRM.getPhys(VirtReg);
572 PhysRegsUsed[Phys] = true;
574 ReusedOperands.markClobbered(Phys);
575 MI.getOperand(i).setReg(Phys);
579 // This virtual register is now known to be a spilled value.
581 continue; // Handle defs in the loop below (handle use&def here though)
583 int StackSlot = VRM.getStackSlot(VirtReg);
586 // Check to see if this stack slot is available.
587 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) {
589 // This spilled operand might be part of a two-address operand. If this
590 // is the case, then changing it will necessarily require changing the
591 // def part of the instruction as well. However, in some cases, we
592 // aren't allowed to modify the reused register. If none of these cases
594 bool CanReuse = true;
595 int ti = TII->getOperandConstraint(MI.getOpcode(), i,
596 TargetInstrInfo::TIED_TO);
598 MI.getOperand(ti).isReg() &&
599 MI.getOperand(ti).getReg() == VirtReg) {
600 // Okay, we have a two address operand. We can reuse this physreg as
601 // long as we are allowed to clobber the value and there is an earlier
602 // def that has already clobbered the physreg.
603 CanReuse = Spills.canClobberPhysReg(StackSlot) &&
604 !ReusedOperands.isClobbered(PhysReg);
608 // If this stack slot value is already available, reuse it!
609 DOUT << "Reusing SS#" << StackSlot << " from physreg "
610 << MRI->getName(PhysReg) << " for vreg"
611 << VirtReg <<" instead of reloading into physreg "
612 << MRI->getName(VRM.getPhys(VirtReg)) << "\n";
613 MI.getOperand(i).setReg(PhysReg);
615 // The only technical detail we have is that we don't know that
616 // PhysReg won't be clobbered by a reloaded stack slot that occurs
617 // later in the instruction. In particular, consider 'op V1, V2'.
618 // If V1 is available in physreg R0, we would choose to reuse it
619 // here, instead of reloading it into the register the allocator
620 // indicated (say R1). However, V2 might have to be reloaded
621 // later, and it might indicate that it needs to live in R0. When
622 // this occurs, we need to have information available that
623 // indicates it is safe to use R1 for the reload instead of R0.
625 // To further complicate matters, we might conflict with an alias,
626 // or R0 and R1 might not be compatible with each other. In this
627 // case, we actually insert a reload for V1 in R1, ensuring that
628 // we can get at R0 or its alias.
629 ReusedOperands.addReuse(i, StackSlot, PhysReg,
630 VRM.getPhys(VirtReg), VirtReg);
632 // Only mark it clobbered if this is a use&def operand.
633 ReusedOperands.markClobbered(PhysReg);
638 // Otherwise we have a situation where we have a two-address instruction
639 // whose mod/ref operand needs to be reloaded. This reload is already
640 // available in some register "PhysReg", but if we used PhysReg as the
641 // operand to our 2-addr instruction, the instruction would modify
642 // PhysReg. This isn't cool if something later uses PhysReg and expects
643 // to get its initial value.
645 // To avoid this problem, and to avoid doing a load right after a store,
646 // we emit a copy from PhysReg into the designated register for this
648 unsigned DesignatedReg = VRM.getPhys(VirtReg);
649 assert(DesignatedReg && "Must map virtreg to physreg!");
651 // Note that, if we reused a register for a previous operand, the
652 // register we want to reload into might not actually be
653 // available. If this occurs, use the register indicated by the
655 if (ReusedOperands.hasReuses())
656 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI,
657 Spills, MaybeDeadStores);
659 // If the mapped designated register is actually the physreg we have
660 // incoming, we don't need to inserted a dead copy.
661 if (DesignatedReg == PhysReg) {
662 // If this stack slot value is already available, reuse it!
663 DOUT << "Reusing SS#" << StackSlot << " from physreg "
664 << MRI->getName(PhysReg) << " for vreg"
666 << " instead of reloading into same physreg.\n";
667 MI.getOperand(i).setReg(PhysReg);
668 ReusedOperands.markClobbered(PhysReg);
673 const TargetRegisterClass* RC =
674 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
676 PhysRegsUsed[DesignatedReg] = true;
677 ReusedOperands.markClobbered(DesignatedReg);
678 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC);
680 // This invalidates DesignatedReg.
681 Spills.ClobberPhysReg(DesignatedReg);
683 Spills.addAvailable(StackSlot, DesignatedReg);
684 MI.getOperand(i).setReg(DesignatedReg);
685 DOUT << '\t' << *prior(MII);
690 // Otherwise, reload it and remember that we have it.
691 PhysReg = VRM.getPhys(VirtReg);
692 assert(PhysReg && "Must map virtreg to physreg!");
693 const TargetRegisterClass* RC =
694 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
696 // Note that, if we reused a register for a previous operand, the
697 // register we want to reload into might not actually be
698 // available. If this occurs, use the register indicated by the
700 if (ReusedOperands.hasReuses())
701 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
702 Spills, MaybeDeadStores);
704 PhysRegsUsed[PhysReg] = true;
705 ReusedOperands.markClobbered(PhysReg);
706 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
707 // This invalidates PhysReg.
708 Spills.ClobberPhysReg(PhysReg);
710 // Any stores to this stack slot are not dead anymore.
711 MaybeDeadStores.erase(StackSlot);
712 Spills.addAvailable(StackSlot, PhysReg);
714 MI.getOperand(i).setReg(PhysReg);
715 DOUT << '\t' << *prior(MII);
720 // If we have folded references to memory operands, make sure we clear all
721 // physical registers that may contain the value of the spilled virtual
723 VirtRegMap::MI2VirtMapTy::const_iterator I, End;
724 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
725 DOUT << "Folded vreg: " << I->second.first << " MR: "
727 unsigned VirtReg = I->second.first;
728 VirtRegMap::ModRef MR = I->second.second;
729 if (!VRM.hasStackSlot(VirtReg)) {
730 DOUT << ": No stack slot!\n";
733 int SS = VRM.getStackSlot(VirtReg);
734 DOUT << " - StackSlot: " << SS << "\n";
736 // If this folded instruction is just a use, check to see if it's a
737 // straight load from the virt reg slot.
738 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
740 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
741 if (FrameIdx == SS) {
742 // If this spill slot is available, turn it into a copy (or nothing)
743 // instead of leaving it as a load!
744 if (unsigned InReg = Spills.getSpillSlotPhysReg(SS)) {
745 DOUT << "Promoted Load To Copy: " << MI;
746 MachineFunction &MF = *MBB.getParent();
747 if (DestReg != InReg) {
748 MRI->copyRegToReg(MBB, &MI, DestReg, InReg,
749 MF.getSSARegMap()->getRegClass(VirtReg));
750 // Revisit the copy so we make sure to notice the effects of the
751 // operation on the destreg (either needing to RA it if it's
752 // virtual or needing to clobber any values if it's physical).
754 --NextMII; // backtrack to the copy.
756 VRM.RemoveFromFoldedVirtMap(&MI);
758 goto ProcessNextInst;
764 // If this reference is not a use, any previous store is now dead.
765 // Otherwise, the store to this stack slot is not dead anymore.
766 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS);
767 if (MDSI != MaybeDeadStores.end()) {
768 if (MR & VirtRegMap::isRef) // Previous store is not dead.
769 MaybeDeadStores.erase(MDSI);
771 // If we get here, the store is dead, nuke it now.
772 assert(VirtRegMap::isMod && "Can't be modref!");
773 DOUT << "Removed dead store:\t" << *MDSI->second;
774 MBB.erase(MDSI->second);
775 VRM.RemoveFromFoldedVirtMap(MDSI->second);
776 MaybeDeadStores.erase(MDSI);
781 // If the spill slot value is available, and this is a new definition of
782 // the value, the value is not available anymore.
783 if (MR & VirtRegMap::isMod) {
784 // Notice that the value in this stack slot has been modified.
785 Spills.ModifyStackSlot(SS);
787 // If this is *just* a mod of the value, check to see if this is just a
788 // store to the spill slot (i.e. the spill got merged into the copy). If
789 // so, realize that the vreg is available now, and add the store to the
790 // MaybeDeadStore info.
792 if (!(MR & VirtRegMap::isRef)) {
793 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
794 assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
795 "Src hasn't been allocated yet?");
796 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark
797 // this as a potentially dead store in case there is a subsequent
798 // store into the stack slot without a read from it.
799 MaybeDeadStores[StackSlot] = &MI;
801 // If the stack slot value was previously available in some other
802 // register, change it now. Otherwise, make the register available,
804 Spills.addAvailable(StackSlot, SrcReg, false /*don't clobber*/);
810 // Process all of the spilled defs.
811 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
812 MachineOperand &MO = MI.getOperand(i);
813 if (MO.isRegister() && MO.getReg() && MO.isDef()) {
814 unsigned VirtReg = MO.getReg();
816 if (!MRegisterInfo::isVirtualRegister(VirtReg)) {
817 // Check to see if this is a noop copy. If so, eliminate the
818 // instruction before considering the dest reg to be changed.
820 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
822 DOUT << "Removing now-noop copy: " << MI;
824 VRM.RemoveFromFoldedVirtMap(&MI);
825 goto ProcessNextInst;
828 // If it's not a no-op copy, it clobbers the value in the destreg.
829 Spills.ClobberPhysReg(VirtReg);
830 ReusedOperands.markClobbered(VirtReg);
832 // Check to see if this instruction is a load from a stack slot into
833 // a register. If so, this provides the stack slot value in the reg.
835 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
836 assert(DestReg == VirtReg && "Unknown load situation!");
838 // Otherwise, if it wasn't available, remember that it is now!
839 Spills.addAvailable(FrameIdx, DestReg);
840 goto ProcessNextInst;
846 // The only vregs left are stack slot definitions.
847 int StackSlot = VRM.getStackSlot(VirtReg);
848 const TargetRegisterClass *RC =
849 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
851 // If this def is part of a two-address operand, make sure to execute
852 // the store from the correct physical register.
854 int TiedOp = TII->findTiedToSrcOperand(MI.getOpcode(), i);
856 PhysReg = MI.getOperand(TiedOp).getReg();
858 PhysReg = VRM.getPhys(VirtReg);
859 if (ReusedOperands.isClobbered(PhysReg)) {
860 // Another def has taken the assigned physreg. It must have been a
861 // use&def which got it due to reuse. Undo the reuse!
862 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
863 Spills, MaybeDeadStores);
867 PhysRegsUsed[PhysReg] = true;
868 ReusedOperands.markClobbered(PhysReg);
869 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
870 DOUT << "Store:\t" << *next(MII);
871 MI.getOperand(i).setReg(PhysReg);
873 // Check to see if this is a noop copy. If so, eliminate the
874 // instruction before considering the dest reg to be changed.
877 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
879 DOUT << "Removing now-noop copy: " << MI;
881 VRM.RemoveFromFoldedVirtMap(&MI);
882 goto ProcessNextInst;
886 // If there is a dead store to this stack slot, nuke it now.
887 MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
889 DOUT << "Removed dead store:\t" << *LastStore;
891 MBB.erase(LastStore);
892 VRM.RemoveFromFoldedVirtMap(LastStore);
894 LastStore = next(MII);
896 // If the stack slot value was previously available in some other
897 // register, change it now. Otherwise, make the register available,
899 Spills.ModifyStackSlot(StackSlot);
900 Spills.ClobberPhysReg(PhysReg);
901 Spills.addAvailable(StackSlot, PhysReg);
912 llvm::Spiller* llvm::createSpiller() {
913 switch (SpillerOpt) {
914 default: assert(0 && "Unreachable!");
916 return new LocalSpiller();
918 return new SimpleSpiller();