1 //===-- llvm/CodeGen/VirtRegMap.cpp - Virtual Register Map ----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the VirtRegMap class.
12 // It also contains implementations of the the Spiller interface, which, given a
13 // virtual register map and a machine function, eliminates all virtual
14 // references by replacing them with physical register references - adding spill
17 //===----------------------------------------------------------------------===//
19 #define DEBUG_TYPE "spiller"
20 #include "VirtRegMap.h"
21 #include "llvm/Function.h"
22 #include "llvm/CodeGen/MachineFrameInfo.h"
23 #include "llvm/CodeGen/MachineFunction.h"
24 #include "llvm/CodeGen/SSARegMap.h"
25 #include "llvm/Target/TargetMachine.h"
26 #include "llvm/Target/TargetInstrInfo.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/Compiler.h"
30 #include "llvm/ADT/Statistic.h"
31 #include "llvm/ADT/STLExtras.h"
36 static Statistic NumSpills("spiller", "Number of register spills");
37 static Statistic NumStores("spiller", "Number of stores added");
38 static Statistic NumLoads ("spiller", "Number of loads added");
39 static Statistic NumReused("spiller", "Number of values reused");
40 static Statistic NumDSE ("spiller", "Number of dead stores elided");
41 static Statistic NumDCE ("spiller", "Number of copies elided");
43 enum SpillerName { simple, local };
45 static cl::opt<SpillerName>
47 cl::desc("Spiller to use: (default: local)"),
49 cl::values(clEnumVal(simple, " simple spiller"),
50 clEnumVal(local, " local spiller"),
55 //===----------------------------------------------------------------------===//
56 // VirtRegMap implementation
57 //===----------------------------------------------------------------------===//
59 VirtRegMap::VirtRegMap(MachineFunction &mf)
60 : TII(*mf.getTarget().getInstrInfo()), MF(mf),
61 Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT) {
65 void VirtRegMap::grow() {
66 Virt2PhysMap.grow(MF.getSSARegMap()->getLastVirtReg());
67 Virt2StackSlotMap.grow(MF.getSSARegMap()->getLastVirtReg());
70 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) {
71 assert(MRegisterInfo::isVirtualRegister(virtReg));
72 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
73 "attempt to assign stack slot to already spilled register");
74 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg);
75 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(),
77 Virt2StackSlotMap[virtReg] = frameIndex;
82 void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) {
83 assert(MRegisterInfo::isVirtualRegister(virtReg));
84 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
85 "attempt to assign stack slot to already spilled register");
86 Virt2StackSlotMap[virtReg] = frameIndex;
89 void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI,
90 unsigned OpNo, MachineInstr *NewMI) {
91 // Move previous memory references folded to new instruction.
92 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI);
93 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI),
94 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) {
95 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second));
96 MI2VirtMap.erase(I++);
100 const TargetInstrDescriptor *TID = OldMI->getInstrDescriptor();
101 if (TID->getOperandConstraint(OpNo, TOI::TIED_TO) != -1 ||
102 TID->findTiedToSrcOperand(OpNo) != -1) {
103 // Folded a two-address operand.
105 } else if (OldMI->getOperand(OpNo).isDef()) {
111 // add new memory reference
112 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo)));
115 void VirtRegMap::print(std::ostream &OS) const {
120 void VirtRegMap::print(OStream &OS) const {
121 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo();
123 OS << "********** REGISTER MAP **********\n";
124 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
125 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) {
126 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG)
127 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n";
131 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
132 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i)
133 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT)
134 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n";
138 void VirtRegMap::dump() const {
144 //===----------------------------------------------------------------------===//
145 // Simple Spiller Implementation
146 //===----------------------------------------------------------------------===//
148 Spiller::~Spiller() {}
151 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller {
152 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM);
156 bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
157 DOUT << "********** REWRITE MACHINE CODE **********\n";
158 DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';
159 const TargetMachine &TM = MF.getTarget();
160 const MRegisterInfo &MRI = *TM.getRegisterInfo();
161 bool *PhysRegsUsed = MF.getUsedPhysregs();
163 // LoadedRegs - Keep track of which vregs are loaded, so that we only load
164 // each vreg once (in the case where a spilled vreg is used by multiple
165 // operands). This is always smaller than the number of operands to the
166 // current machine instr, so it should be small.
167 std::vector<unsigned> LoadedRegs;
169 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
171 DOUT << MBBI->getBasicBlock()->getName() << ":\n";
172 MachineBasicBlock &MBB = *MBBI;
173 for (MachineBasicBlock::iterator MII = MBB.begin(),
174 E = MBB.end(); MII != E; ++MII) {
175 MachineInstr &MI = *MII;
176 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
177 MachineOperand &MO = MI.getOperand(i);
178 if (MO.isRegister() && MO.getReg())
179 if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
180 unsigned VirtReg = MO.getReg();
181 unsigned PhysReg = VRM.getPhys(VirtReg);
182 if (VRM.hasStackSlot(VirtReg)) {
183 int StackSlot = VRM.getStackSlot(VirtReg);
184 const TargetRegisterClass* RC =
185 MF.getSSARegMap()->getRegClass(VirtReg);
188 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg)
189 == LoadedRegs.end()) {
190 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
191 LoadedRegs.push_back(VirtReg);
193 DOUT << '\t' << *prior(MII);
197 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
201 PhysRegsUsed[PhysReg] = true;
202 MI.getOperand(i).setReg(PhysReg);
204 PhysRegsUsed[MO.getReg()] = true;
215 //===----------------------------------------------------------------------===//
216 // Local Spiller Implementation
217 //===----------------------------------------------------------------------===//
220 /// LocalSpiller - This spiller does a simple pass over the machine basic
221 /// block to attempt to keep spills in registers as much as possible for
222 /// blocks that have low register pressure (the vreg may be spilled due to
223 /// register pressure in other blocks).
224 class VISIBILITY_HIDDEN LocalSpiller : public Spiller {
225 const MRegisterInfo *MRI;
226 const TargetInstrInfo *TII;
228 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
229 MRI = MF.getTarget().getRegisterInfo();
230 TII = MF.getTarget().getInstrInfo();
231 DOUT << "\n**** Local spiller rewriting function '"
232 << MF.getFunction()->getName() << "':\n";
234 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
236 RewriteMBB(*MBB, VRM);
240 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM);
241 void ClobberPhysReg(unsigned PR, std::map<int, unsigned> &SpillSlots,
242 std::multimap<unsigned, int> &PhysRegs);
243 void ClobberPhysRegOnly(unsigned PR, std::map<int, unsigned> &SpillSlots,
244 std::multimap<unsigned, int> &PhysRegs);
245 void ModifyStackSlot(int Slot, std::map<int, unsigned> &SpillSlots,
246 std::multimap<unsigned, int> &PhysRegs);
250 /// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
251 /// top down, keep track of which spills slots are available in each register.
253 /// Note that not all physregs are created equal here. In particular, some
254 /// physregs are reloads that we are allowed to clobber or ignore at any time.
255 /// Other physregs are values that the register allocated program is using that
256 /// we cannot CHANGE, but we can read if we like. We keep track of this on a
257 /// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable
258 /// entries. The predicate 'canClobberPhysReg()' checks this bit and
259 /// addAvailable sets it if.
261 class VISIBILITY_HIDDEN AvailableSpills {
262 const MRegisterInfo *MRI;
263 const TargetInstrInfo *TII;
265 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual
266 // register values that are still available, due to being loaded or stored to,
267 // but not invalidated yet.
268 std::map<int, unsigned> SpillSlotsAvailable;
270 // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating
271 // which stack slot values are currently held by a physreg. This is used to
272 // invalidate entries in SpillSlotsAvailable when a physreg is modified.
273 std::multimap<unsigned, int> PhysRegsAvailable;
275 void ClobberPhysRegOnly(unsigned PhysReg);
277 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii)
278 : MRI(mri), TII(tii) {
281 /// getSpillSlotPhysReg - If the specified stack slot is available in a
282 /// physical register, return that PhysReg, otherwise return 0.
283 unsigned getSpillSlotPhysReg(int Slot) const {
284 std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot);
285 if (I != SpillSlotsAvailable.end())
286 return I->second >> 1; // Remove the CanClobber bit.
290 const MRegisterInfo *getRegInfo() const { return MRI; }
292 /// addAvailable - Mark that the specified stack slot is available in the
293 /// specified physreg. If CanClobber is true, the physreg can be modified at
294 /// any time without changing the semantics of the program.
295 void addAvailable(int Slot, unsigned Reg, bool CanClobber = true) {
296 // If this stack slot is thought to be available in some other physreg,
297 // remove its record.
298 ModifyStackSlot(Slot);
300 PhysRegsAvailable.insert(std::make_pair(Reg, Slot));
301 SpillSlotsAvailable[Slot] = (Reg << 1) | (unsigned)CanClobber;
303 DOUT << "Remembering SS#" << Slot << " in physreg "
304 << MRI->getName(Reg) << "\n";
307 /// canClobberPhysReg - Return true if the spiller is allowed to change the
308 /// value of the specified stackslot register if it desires. The specified
309 /// stack slot must be available in a physreg for this query to make sense.
310 bool canClobberPhysReg(int Slot) const {
311 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!");
312 return SpillSlotsAvailable.find(Slot)->second & 1;
315 /// ClobberPhysReg - This is called when the specified physreg changes
316 /// value. We use this to invalidate any info about stuff we thing lives in
317 /// it and any of its aliases.
318 void ClobberPhysReg(unsigned PhysReg);
320 /// ModifyStackSlot - This method is called when the value in a stack slot
321 /// changes. This removes information about which register the previous value
322 /// for this slot lives in (as the previous value is dead now).
323 void ModifyStackSlot(int Slot);
327 /// ClobberPhysRegOnly - This is called when the specified physreg changes
328 /// value. We use this to invalidate any info about stuff we thing lives in it.
329 void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
330 std::multimap<unsigned, int>::iterator I =
331 PhysRegsAvailable.lower_bound(PhysReg);
332 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
333 int Slot = I->second;
334 PhysRegsAvailable.erase(I++);
335 assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg &&
336 "Bidirectional map mismatch!");
337 SpillSlotsAvailable.erase(Slot);
338 DOUT << "PhysReg " << MRI->getName(PhysReg)
339 << " clobbered, invalidating SS#" << Slot << "\n";
343 /// ClobberPhysReg - This is called when the specified physreg changes
344 /// value. We use this to invalidate any info about stuff we thing lives in
345 /// it and any of its aliases.
346 void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
347 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
348 ClobberPhysRegOnly(*AS);
349 ClobberPhysRegOnly(PhysReg);
352 /// ModifyStackSlot - This method is called when the value in a stack slot
353 /// changes. This removes information about which register the previous value
354 /// for this slot lives in (as the previous value is dead now).
355 void AvailableSpills::ModifyStackSlot(int Slot) {
356 std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot);
357 if (It == SpillSlotsAvailable.end()) return;
358 unsigned Reg = It->second >> 1;
359 SpillSlotsAvailable.erase(It);
361 // This register may hold the value of multiple stack slots, only remove this
362 // stack slot from the set of values the register contains.
363 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
365 assert(I != PhysRegsAvailable.end() && I->first == Reg &&
366 "Map inverse broken!");
367 if (I->second == Slot) break;
369 PhysRegsAvailable.erase(I);
374 // ReusedOp - For each reused operand, we keep track of a bit of information, in
375 // case we need to rollback upon processing a new operand. See comments below.
378 // The MachineInstr operand that reused an available value.
381 // StackSlot - The spill slot of the value being reused.
384 // PhysRegReused - The physical register the value was available in.
385 unsigned PhysRegReused;
387 // AssignedPhysReg - The physreg that was assigned for use by the reload.
388 unsigned AssignedPhysReg;
390 // VirtReg - The virtual register itself.
393 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
395 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr),
399 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
400 /// is reused instead of reloaded.
401 class VISIBILITY_HIDDEN ReuseInfo {
403 std::vector<ReusedOp> Reuses;
404 bool *PhysRegsClobbered;
406 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) {
407 PhysRegsClobbered = new bool[mri->getNumRegs()];
408 std::fill(PhysRegsClobbered, PhysRegsClobbered+mri->getNumRegs(), false);
411 delete[] PhysRegsClobbered;
414 bool hasReuses() const {
415 return !Reuses.empty();
418 /// addReuse - If we choose to reuse a virtual register that is already
419 /// available instead of reloading it, remember that we did so.
420 void addReuse(unsigned OpNo, unsigned StackSlot,
421 unsigned PhysRegReused, unsigned AssignedPhysReg,
423 // If the reload is to the assigned register anyway, no undo will be
425 if (PhysRegReused == AssignedPhysReg) return;
427 // Otherwise, remember this.
428 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused,
429 AssignedPhysReg, VirtReg));
432 void markClobbered(unsigned PhysReg) {
433 PhysRegsClobbered[PhysReg] = true;
436 bool isClobbered(unsigned PhysReg) const {
437 return PhysRegsClobbered[PhysReg];
440 /// GetRegForReload - We are about to emit a reload into PhysReg. If there
441 /// is some other operand that is using the specified register, either pick
442 /// a new register to use, or evict the previous reload and use this reg.
443 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
444 AvailableSpills &Spills,
445 std::map<int, MachineInstr*> &MaybeDeadStores) {
446 if (Reuses.empty()) return PhysReg; // This is most often empty.
448 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
449 ReusedOp &Op = Reuses[ro];
450 // If we find some other reuse that was supposed to use this register
451 // exactly for its reload, we can change this reload to use ITS reload
453 if (Op.PhysRegReused == PhysReg) {
454 // Yup, use the reload register that we didn't use before.
455 unsigned NewReg = Op.AssignedPhysReg;
456 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores);
458 // Otherwise, we might also have a problem if a previously reused
459 // value aliases the new register. If so, codegen the previous reload
461 unsigned PRRU = Op.PhysRegReused;
462 const MRegisterInfo *MRI = Spills.getRegInfo();
463 if (MRI->areAliases(PRRU, PhysReg)) {
464 // Okay, we found out that an alias of a reused register
465 // was used. This isn't good because it means we have
466 // to undo a previous reuse.
467 MachineBasicBlock *MBB = MI->getParent();
468 const TargetRegisterClass *AliasRC =
469 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg);
471 // Copy Op out of the vector and remove it, we're going to insert an
472 // explicit load for it.
474 Reuses.erase(Reuses.begin()+ro);
476 // Ok, we're going to try to reload the assigned physreg into the
477 // slot that we were supposed to in the first place. However, that
478 // register could hold a reuse. Check to see if it conflicts or
479 // would prefer us to use a different register.
480 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg,
481 MI, Spills, MaybeDeadStores);
483 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg,
484 NewOp.StackSlot, AliasRC);
485 Spills.ClobberPhysReg(NewPhysReg);
486 Spills.ClobberPhysReg(NewOp.PhysRegReused);
488 // Any stores to this stack slot are not dead anymore.
489 MaybeDeadStores.erase(NewOp.StackSlot);
491 MI->getOperand(NewOp.Operand).setReg(NewPhysReg);
493 Spills.addAvailable(NewOp.StackSlot, NewPhysReg);
495 DEBUG(MachineBasicBlock::iterator MII = MI;
496 DOUT << '\t' << *prior(MII));
498 DOUT << "Reuse undone!\n";
501 // Finally, PhysReg is now available, go ahead and use it.
512 /// rewriteMBB - Keep track of which spills are available even after the
513 /// register allocator is done with them. If possible, avoid reloading vregs.
514 void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
516 DOUT << MBB.getBasicBlock()->getName() << ":\n";
518 // Spills - Keep track of which spilled values are available in physregs so
519 // that we can choose to reuse the physregs instead of emitting reloads.
520 AvailableSpills Spills(MRI, TII);
522 // MaybeDeadStores - When we need to write a value back into a stack slot,
523 // keep track of the inserted store. If the stack slot value is never read
524 // (because the value was used from some available register, for example), and
525 // subsequently stored to, the original store is dead. This map keeps track
526 // of inserted stores that are not used. If we see a subsequent store to the
527 // same stack slot, the original store is deleted.
528 std::map<int, MachineInstr*> MaybeDeadStores;
530 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs();
532 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
534 MachineInstr &MI = *MII;
535 MachineBasicBlock::iterator NextMII = MII; ++NextMII;
537 /// ReusedOperands - Keep track of operand reuse in case we need to undo
539 ReuseInfo ReusedOperands(MI, MRI);
541 // Loop over all of the implicit defs, clearing them from our available
543 const unsigned *ImpDef = TII->getImplicitDefs(MI.getOpcode());
545 for ( ; *ImpDef; ++ImpDef) {
546 PhysRegsUsed[*ImpDef] = true;
547 ReusedOperands.markClobbered(*ImpDef);
548 Spills.ClobberPhysReg(*ImpDef);
552 // Process all of the spilled uses and all non spilled reg references.
553 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
554 MachineOperand &MO = MI.getOperand(i);
555 if (!MO.isRegister() || MO.getReg() == 0)
556 continue; // Ignore non-register operands.
558 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) {
559 // Ignore physregs for spilling, but remember that it is used by this
561 PhysRegsUsed[MO.getReg()] = true;
562 ReusedOperands.markClobbered(MO.getReg());
566 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) &&
567 "Not a virtual or a physical register?");
569 unsigned VirtReg = MO.getReg();
570 if (!VRM.hasStackSlot(VirtReg)) {
571 // This virtual register was assigned a physreg!
572 unsigned Phys = VRM.getPhys(VirtReg);
573 PhysRegsUsed[Phys] = true;
575 ReusedOperands.markClobbered(Phys);
576 MI.getOperand(i).setReg(Phys);
580 // This virtual register is now known to be a spilled value.
582 continue; // Handle defs in the loop below (handle use&def here though)
584 int StackSlot = VRM.getStackSlot(VirtReg);
587 // Check to see if this stack slot is available.
588 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) {
590 // This spilled operand might be part of a two-address operand. If this
591 // is the case, then changing it will necessarily require changing the
592 // def part of the instruction as well. However, in some cases, we
593 // aren't allowed to modify the reused register. If none of these cases
595 bool CanReuse = true;
596 int ti = MI.getInstrDescriptor()->getOperandConstraint(i, TOI::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 = MI.getInstrDescriptor()->findTiedToSrcOperand(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();