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/BitVector.h"
31 #include "llvm/ADT/Statistic.h"
32 #include "llvm/ADT/STLExtras.h"
33 #include "llvm/ADT/SmallSet.h"
37 STATISTIC(NumSpills, "Number of register spills");
38 STATISTIC(NumReMats, "Number of re-materialization");
39 STATISTIC(NumDRM , "Number of re-materializable defs elided");
40 STATISTIC(NumStores, "Number of stores added");
41 STATISTIC(NumLoads , "Number of loads added");
42 STATISTIC(NumReused, "Number of values reused");
43 STATISTIC(NumDSE , "Number of dead stores elided");
44 STATISTIC(NumDCE , "Number of copies elided");
47 enum SpillerName { simple, local };
49 static cl::opt<SpillerName>
51 cl::desc("Spiller to use: (default: local)"),
53 cl::values(clEnumVal(simple, " simple spiller"),
54 clEnumVal(local, " local spiller"),
59 //===----------------------------------------------------------------------===//
60 // VirtRegMap implementation
61 //===----------------------------------------------------------------------===//
63 VirtRegMap::VirtRegMap(MachineFunction &mf)
64 : TII(*mf.getTarget().getInstrInfo()), MF(mf),
65 Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT),
66 Virt2ReMatIdMap(NO_STACK_SLOT), ReMatMap(NULL),
67 ReMatId(MAX_STACK_SLOT+1) {
71 void VirtRegMap::grow() {
72 unsigned LastVirtReg = MF.getSSARegMap()->getLastVirtReg();
73 Virt2PhysMap.grow(LastVirtReg);
74 Virt2StackSlotMap.grow(LastVirtReg);
75 Virt2ReMatIdMap.grow(LastVirtReg);
76 ReMatMap.grow(LastVirtReg);
79 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) {
80 assert(MRegisterInfo::isVirtualRegister(virtReg));
81 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
82 "attempt to assign stack slot to already spilled register");
83 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg);
84 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(),
86 Virt2StackSlotMap[virtReg] = frameIndex;
91 void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) {
92 assert(MRegisterInfo::isVirtualRegister(virtReg));
93 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
94 "attempt to assign stack slot to already spilled register");
95 assert((frameIndex >= 0 ||
96 (frameIndex >= MF.getFrameInfo()->getObjectIndexBegin())) &&
97 "illegal fixed frame index");
98 Virt2StackSlotMap[virtReg] = frameIndex;
101 int VirtRegMap::assignVirtReMatId(unsigned virtReg) {
102 assert(MRegisterInfo::isVirtualRegister(virtReg));
103 assert(Virt2ReMatIdMap[virtReg] == NO_STACK_SLOT &&
104 "attempt to assign re-mat id to already spilled register");
105 Virt2ReMatIdMap[virtReg] = ReMatId;
109 void VirtRegMap::assignVirtReMatId(unsigned virtReg, int id) {
110 assert(MRegisterInfo::isVirtualRegister(virtReg));
111 assert(Virt2ReMatIdMap[virtReg] == NO_STACK_SLOT &&
112 "attempt to assign re-mat id to already spilled register");
113 Virt2ReMatIdMap[virtReg] = id;
116 void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI,
117 unsigned OpNo, MachineInstr *NewMI) {
118 // Move previous memory references folded to new instruction.
119 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI);
120 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI),
121 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) {
122 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second));
123 MI2VirtMap.erase(I++);
127 const TargetInstrDescriptor *TID = OldMI->getInstrDescriptor();
128 if (TID->getOperandConstraint(OpNo, TOI::TIED_TO) != -1 ||
129 TID->findTiedToSrcOperand(OpNo) != -1) {
130 // Folded a two-address operand.
132 } else if (OldMI->getOperand(OpNo).isDef()) {
138 // add new memory reference
139 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo)));
142 void VirtRegMap::print(std::ostream &OS) const {
143 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo();
145 OS << "********** REGISTER MAP **********\n";
146 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
147 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) {
148 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG)
149 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n";
153 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
154 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i)
155 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT)
156 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n";
160 void VirtRegMap::dump() const {
165 //===----------------------------------------------------------------------===//
166 // Simple Spiller Implementation
167 //===----------------------------------------------------------------------===//
169 Spiller::~Spiller() {}
172 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller {
173 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM);
177 bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
178 DOUT << "********** REWRITE MACHINE CODE **********\n";
179 DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';
180 const TargetMachine &TM = MF.getTarget();
181 const MRegisterInfo &MRI = *TM.getRegisterInfo();
183 // LoadedRegs - Keep track of which vregs are loaded, so that we only load
184 // each vreg once (in the case where a spilled vreg is used by multiple
185 // operands). This is always smaller than the number of operands to the
186 // current machine instr, so it should be small.
187 std::vector<unsigned> LoadedRegs;
189 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
191 DOUT << MBBI->getBasicBlock()->getName() << ":\n";
192 MachineBasicBlock &MBB = *MBBI;
193 for (MachineBasicBlock::iterator MII = MBB.begin(),
194 E = MBB.end(); MII != E; ++MII) {
195 MachineInstr &MI = *MII;
196 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
197 MachineOperand &MO = MI.getOperand(i);
198 if (MO.isRegister() && MO.getReg())
199 if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
200 unsigned VirtReg = MO.getReg();
201 unsigned PhysReg = VRM.getPhys(VirtReg);
202 if (!VRM.isAssignedReg(VirtReg)) {
203 int StackSlot = VRM.getStackSlot(VirtReg);
204 const TargetRegisterClass* RC =
205 MF.getSSARegMap()->getRegClass(VirtReg);
208 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg)
209 == LoadedRegs.end()) {
210 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
211 LoadedRegs.push_back(VirtReg);
213 DOUT << '\t' << *prior(MII);
217 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
221 MF.setPhysRegUsed(PhysReg);
222 MI.getOperand(i).setReg(PhysReg);
224 MF.setPhysRegUsed(MO.getReg());
235 //===----------------------------------------------------------------------===//
236 // Local Spiller Implementation
237 //===----------------------------------------------------------------------===//
240 /// LocalSpiller - This spiller does a simple pass over the machine basic
241 /// block to attempt to keep spills in registers as much as possible for
242 /// blocks that have low register pressure (the vreg may be spilled due to
243 /// register pressure in other blocks).
244 class VISIBILITY_HIDDEN LocalSpiller : public Spiller {
245 const MRegisterInfo *MRI;
246 const TargetInstrInfo *TII;
248 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
249 MRI = MF.getTarget().getRegisterInfo();
250 TII = MF.getTarget().getInstrInfo();
251 DOUT << "\n**** Local spiller rewriting function '"
252 << MF.getFunction()->getName() << "':\n";
254 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
256 RewriteMBB(*MBB, VRM);
260 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM);
264 /// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
265 /// top down, keep track of which spills slots or remat are available in each
268 /// Note that not all physregs are created equal here. In particular, some
269 /// physregs are reloads that we are allowed to clobber or ignore at any time.
270 /// Other physregs are values that the register allocated program is using that
271 /// we cannot CHANGE, but we can read if we like. We keep track of this on a
272 /// per-stack-slot / remat id basis as the low bit in the value of the
273 /// SpillSlotsAvailable entries. The predicate 'canClobberPhysReg()' checks
274 /// this bit and addAvailable sets it if.
276 class VISIBILITY_HIDDEN AvailableSpills {
277 const MRegisterInfo *MRI;
278 const TargetInstrInfo *TII;
280 // SpillSlotsOrReMatsAvailable - This map keeps track of all of the spilled
281 // or remat'ed virtual register values that are still available, due to being
282 // loaded or stored to, but not invalidated yet.
283 std::map<int, unsigned> SpillSlotsOrReMatsAvailable;
285 // PhysRegsAvailable - This is the inverse of SpillSlotsOrReMatsAvailable,
286 // indicating which stack slot values are currently held by a physreg. This
287 // is used to invalidate entries in SpillSlotsOrReMatsAvailable when a
288 // physreg is modified.
289 std::multimap<unsigned, int> PhysRegsAvailable;
291 void disallowClobberPhysRegOnly(unsigned PhysReg);
293 void ClobberPhysRegOnly(unsigned PhysReg);
295 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii)
296 : MRI(mri), TII(tii) {
299 const MRegisterInfo *getRegInfo() const { return MRI; }
301 /// getSpillSlotOrReMatPhysReg - If the specified stack slot or remat is
302 /// available in a physical register, return that PhysReg, otherwise
304 unsigned getSpillSlotOrReMatPhysReg(int Slot) const {
305 std::map<int, unsigned>::const_iterator I =
306 SpillSlotsOrReMatsAvailable.find(Slot);
307 if (I != SpillSlotsOrReMatsAvailable.end()) {
308 return I->second >> 1; // Remove the CanClobber bit.
313 /// addAvailable - Mark that the specified stack slot / remat is available in
314 /// the specified physreg. If CanClobber is true, the physreg can be modified
315 /// at any time without changing the semantics of the program.
316 void addAvailable(int SlotOrReMat, MachineInstr *MI, unsigned Reg,
317 bool CanClobber = true) {
318 // If this stack slot is thought to be available in some other physreg,
319 // remove its record.
320 ModifyStackSlotOrReMat(SlotOrReMat);
322 PhysRegsAvailable.insert(std::make_pair(Reg, SlotOrReMat));
323 SpillSlotsOrReMatsAvailable[SlotOrReMat]= (Reg << 1) | (unsigned)CanClobber;
325 if (SlotOrReMat > VirtRegMap::MAX_STACK_SLOT)
326 DOUT << "Remembering RM#" << SlotOrReMat-VirtRegMap::MAX_STACK_SLOT-1;
328 DOUT << "Remembering SS#" << SlotOrReMat;
329 DOUT << " in physreg " << MRI->getName(Reg) << "\n";
332 /// canClobberPhysReg - Return true if the spiller is allowed to change the
333 /// value of the specified stackslot register if it desires. The specified
334 /// stack slot must be available in a physreg for this query to make sense.
335 bool canClobberPhysReg(int SlotOrReMat) const {
336 assert(SpillSlotsOrReMatsAvailable.count(SlotOrReMat) &&
337 "Value not available!");
338 return SpillSlotsOrReMatsAvailable.find(SlotOrReMat)->second & 1;
341 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
342 /// stackslot register. The register is still available but is no longer
343 /// allowed to be modifed.
344 void disallowClobberPhysReg(unsigned PhysReg);
346 /// ClobberPhysReg - This is called when the specified physreg changes
347 /// value. We use this to invalidate any info about stuff we thing lives in
348 /// it and any of its aliases.
349 void ClobberPhysReg(unsigned PhysReg);
351 /// ModifyStackSlotOrReMat - This method is called when the value in a stack
352 /// slot changes. This removes information about which register the previous
353 /// value for this slot lives in (as the previous value is dead now).
354 void ModifyStackSlotOrReMat(int SlotOrReMat);
358 /// disallowClobberPhysRegOnly - Unset the CanClobber bit of the specified
359 /// stackslot register. The register is still available but is no longer
360 /// allowed to be modifed.
361 void AvailableSpills::disallowClobberPhysRegOnly(unsigned PhysReg) {
362 std::multimap<unsigned, int>::iterator I =
363 PhysRegsAvailable.lower_bound(PhysReg);
364 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
365 int SlotOrReMat = I->second;
367 assert((SpillSlotsOrReMatsAvailable[SlotOrReMat] >> 1) == PhysReg &&
368 "Bidirectional map mismatch!");
369 SpillSlotsOrReMatsAvailable[SlotOrReMat] &= ~1;
370 DOUT << "PhysReg " << MRI->getName(PhysReg)
371 << " copied, it is available for use but can no longer be modified\n";
375 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
376 /// stackslot register and its aliases. The register and its aliases may
377 /// still available but is no longer allowed to be modifed.
378 void AvailableSpills::disallowClobberPhysReg(unsigned PhysReg) {
379 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
380 disallowClobberPhysRegOnly(*AS);
381 disallowClobberPhysRegOnly(PhysReg);
384 /// ClobberPhysRegOnly - This is called when the specified physreg changes
385 /// value. We use this to invalidate any info about stuff we thing lives in it.
386 void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
387 std::multimap<unsigned, int>::iterator I =
388 PhysRegsAvailable.lower_bound(PhysReg);
389 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
390 int SlotOrReMat = I->second;
391 PhysRegsAvailable.erase(I++);
392 assert((SpillSlotsOrReMatsAvailable[SlotOrReMat] >> 1) == PhysReg &&
393 "Bidirectional map mismatch!");
394 SpillSlotsOrReMatsAvailable.erase(SlotOrReMat);
395 DOUT << "PhysReg " << MRI->getName(PhysReg)
396 << " clobbered, invalidating ";
397 if (SlotOrReMat > VirtRegMap::MAX_STACK_SLOT)
398 DOUT << "RM#" << SlotOrReMat-VirtRegMap::MAX_STACK_SLOT-1 << "\n";
400 DOUT << "SS#" << SlotOrReMat << "\n";
404 /// ClobberPhysReg - This is called when the specified physreg changes
405 /// value. We use this to invalidate any info about stuff we thing lives in
406 /// it and any of its aliases.
407 void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
408 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
409 ClobberPhysRegOnly(*AS);
410 ClobberPhysRegOnly(PhysReg);
413 /// ModifyStackSlotOrReMat - This method is called when the value in a stack
414 /// slot changes. This removes information about which register the previous
415 /// value for this slot lives in (as the previous value is dead now).
416 void AvailableSpills::ModifyStackSlotOrReMat(int SlotOrReMat) {
417 std::map<int, unsigned>::iterator It =
418 SpillSlotsOrReMatsAvailable.find(SlotOrReMat);
419 if (It == SpillSlotsOrReMatsAvailable.end()) return;
420 unsigned Reg = It->second >> 1;
421 SpillSlotsOrReMatsAvailable.erase(It);
423 // This register may hold the value of multiple stack slots, only remove this
424 // stack slot from the set of values the register contains.
425 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
427 assert(I != PhysRegsAvailable.end() && I->first == Reg &&
428 "Map inverse broken!");
429 if (I->second == SlotOrReMat) break;
431 PhysRegsAvailable.erase(I);
436 /// InvalidateKills - MI is going to be deleted. If any of its operands are
437 /// marked kill, then invalidate the information.
438 static void InvalidateKills(MachineInstr &MI, BitVector &RegKills,
439 std::vector<MachineOperand*> &KillOps,
440 SmallVector<unsigned, 1> *KillRegs = NULL) {
441 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
442 MachineOperand &MO = MI.getOperand(i);
443 if (!MO.isReg() || !MO.isUse() || !MO.isKill())
445 unsigned Reg = MO.getReg();
447 KillRegs->push_back(Reg);
448 if (KillOps[Reg] == &MO) {
455 /// InvalidateRegDef - If the def operand of the specified def MI is now dead
456 /// (since it's spill instruction is removed), mark it isDead. Also checks if
457 /// the def MI has other definition operands that are not dead. Returns it by
459 static bool InvalidateRegDef(MachineBasicBlock::iterator I,
460 MachineInstr &NewDef, unsigned Reg,
462 // Due to remat, it's possible this reg isn't being reused. That is,
463 // the def of this reg (by prev MI) is now dead.
464 MachineInstr *DefMI = I;
465 MachineOperand *DefOp = NULL;
466 for (unsigned i = 0, e = DefMI->getNumOperands(); i != e; ++i) {
467 MachineOperand &MO = DefMI->getOperand(i);
468 if (MO.isReg() && MO.isDef()) {
469 if (MO.getReg() == Reg)
471 else if (!MO.isDead())
478 bool FoundUse = false, Done = false;
479 MachineBasicBlock::iterator E = NewDef;
481 for (; !Done && I != E; ++I) {
482 MachineInstr *NMI = I;
483 for (unsigned j = 0, ee = NMI->getNumOperands(); j != ee; ++j) {
484 MachineOperand &MO = NMI->getOperand(j);
485 if (!MO.isReg() || MO.getReg() != Reg)
489 Done = true; // Stop after scanning all the operands of this MI.
500 /// UpdateKills - Track and update kill info. If a MI reads a register that is
501 /// marked kill, then it must be due to register reuse. Transfer the kill info
503 static void UpdateKills(MachineInstr &MI, BitVector &RegKills,
504 std::vector<MachineOperand*> &KillOps) {
505 const TargetInstrDescriptor *TID = MI.getInstrDescriptor();
506 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
507 MachineOperand &MO = MI.getOperand(i);
508 if (!MO.isReg() || !MO.isUse())
510 unsigned Reg = MO.getReg();
515 // That can't be right. Register is killed but not re-defined and it's
516 // being reused. Let's fix that.
517 KillOps[Reg]->unsetIsKill();
518 if (i < TID->numOperands &&
519 TID->getOperandConstraint(i, TOI::TIED_TO) == -1)
520 // Unless it's a two-address operand, this is the new kill.
530 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
531 const MachineOperand &MO = MI.getOperand(i);
532 if (!MO.isReg() || !MO.isDef())
534 unsigned Reg = MO.getReg();
541 // ReusedOp - For each reused operand, we keep track of a bit of information, in
542 // case we need to rollback upon processing a new operand. See comments below.
545 // The MachineInstr operand that reused an available value.
548 // StackSlotOrReMat - The spill slot or remat id of the value being reused.
549 unsigned StackSlotOrReMat;
551 // PhysRegReused - The physical register the value was available in.
552 unsigned PhysRegReused;
554 // AssignedPhysReg - The physreg that was assigned for use by the reload.
555 unsigned AssignedPhysReg;
557 // VirtReg - The virtual register itself.
560 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
562 : Operand(o), StackSlotOrReMat(ss), PhysRegReused(prr),
563 AssignedPhysReg(apr), VirtReg(vreg) {}
566 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
567 /// is reused instead of reloaded.
568 class VISIBILITY_HIDDEN ReuseInfo {
570 std::vector<ReusedOp> Reuses;
571 BitVector PhysRegsClobbered;
573 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) {
574 PhysRegsClobbered.resize(mri->getNumRegs());
577 bool hasReuses() const {
578 return !Reuses.empty();
581 /// addReuse - If we choose to reuse a virtual register that is already
582 /// available instead of reloading it, remember that we did so.
583 void addReuse(unsigned OpNo, unsigned StackSlotOrReMat,
584 unsigned PhysRegReused, unsigned AssignedPhysReg,
586 // If the reload is to the assigned register anyway, no undo will be
588 if (PhysRegReused == AssignedPhysReg) return;
590 // Otherwise, remember this.
591 Reuses.push_back(ReusedOp(OpNo, StackSlotOrReMat, PhysRegReused,
592 AssignedPhysReg, VirtReg));
595 void markClobbered(unsigned PhysReg) {
596 PhysRegsClobbered.set(PhysReg);
599 bool isClobbered(unsigned PhysReg) const {
600 return PhysRegsClobbered.test(PhysReg);
603 /// GetRegForReload - We are about to emit a reload into PhysReg. If there
604 /// is some other operand that is using the specified register, either pick
605 /// a new register to use, or evict the previous reload and use this reg.
606 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
607 AvailableSpills &Spills,
608 std::vector<MachineInstr*> &MaybeDeadStores,
609 SmallSet<unsigned, 8> &Rejected,
611 std::vector<MachineOperand*> &KillOps,
613 if (Reuses.empty()) return PhysReg; // This is most often empty.
615 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
616 ReusedOp &Op = Reuses[ro];
617 // If we find some other reuse that was supposed to use this register
618 // exactly for its reload, we can change this reload to use ITS reload
619 // register. That is, unless its reload register has already been
620 // considered and subsequently rejected because it has also been reused
621 // by another operand.
622 if (Op.PhysRegReused == PhysReg &&
623 Rejected.count(Op.AssignedPhysReg) == 0) {
624 // Yup, use the reload register that we didn't use before.
625 unsigned NewReg = Op.AssignedPhysReg;
626 Rejected.insert(PhysReg);
627 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores, Rejected,
628 RegKills, KillOps, VRM);
630 // Otherwise, we might also have a problem if a previously reused
631 // value aliases the new register. If so, codegen the previous reload
633 unsigned PRRU = Op.PhysRegReused;
634 const MRegisterInfo *MRI = Spills.getRegInfo();
635 if (MRI->areAliases(PRRU, PhysReg)) {
636 // Okay, we found out that an alias of a reused register
637 // was used. This isn't good because it means we have
638 // to undo a previous reuse.
639 MachineBasicBlock *MBB = MI->getParent();
640 const TargetRegisterClass *AliasRC =
641 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg);
643 // Copy Op out of the vector and remove it, we're going to insert an
644 // explicit load for it.
646 Reuses.erase(Reuses.begin()+ro);
648 // Ok, we're going to try to reload the assigned physreg into the
649 // slot that we were supposed to in the first place. However, that
650 // register could hold a reuse. Check to see if it conflicts or
651 // would prefer us to use a different register.
652 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg,
653 MI, Spills, MaybeDeadStores,
654 Rejected, RegKills, KillOps, VRM);
656 if (NewOp.StackSlotOrReMat > VirtRegMap::MAX_STACK_SLOT) {
657 MRI->reMaterialize(*MBB, MI, NewPhysReg,
658 VRM.getReMaterializedMI(NewOp.VirtReg));
661 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg,
662 NewOp.StackSlotOrReMat, AliasRC);
663 // Any stores to this stack slot are not dead anymore.
664 MaybeDeadStores[NewOp.StackSlotOrReMat] = NULL;
667 Spills.ClobberPhysReg(NewPhysReg);
668 Spills.ClobberPhysReg(NewOp.PhysRegReused);
670 MI->getOperand(NewOp.Operand).setReg(NewPhysReg);
672 Spills.addAvailable(NewOp.StackSlotOrReMat, MI, NewPhysReg);
673 MachineBasicBlock::iterator MII = MI;
675 UpdateKills(*MII, RegKills, KillOps);
676 DOUT << '\t' << *MII;
678 DOUT << "Reuse undone!\n";
681 // Finally, PhysReg is now available, go ahead and use it.
689 /// GetRegForReload - Helper for the above GetRegForReload(). Add a
690 /// 'Rejected' set to remember which registers have been considered and
691 /// rejected for the reload. This avoids infinite looping in case like
694 /// t2 <- assigned r0 for use by the reload but ended up reuse r1
695 /// t3 <- assigned r1 for use by the reload but ended up reuse r0
697 /// sees r1 is taken by t2, tries t2's reload register r0
698 /// sees r0 is taken by t3, tries t3's reload register r1
699 /// sees r1 is taken by t2, tries t2's reload register r0 ...
700 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
701 AvailableSpills &Spills,
702 std::vector<MachineInstr*> &MaybeDeadStores,
704 std::vector<MachineOperand*> &KillOps,
706 SmallSet<unsigned, 8> Rejected;
707 return GetRegForReload(PhysReg, MI, Spills, MaybeDeadStores, Rejected,
708 RegKills, KillOps, VRM);
714 /// rewriteMBB - Keep track of which spills are available even after the
715 /// register allocator is done with them. If possible, avoid reloading vregs.
716 void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
717 DOUT << MBB.getBasicBlock()->getName() << ":\n";
719 MachineFunction &MF = *MBB.getParent();
721 // Spills - Keep track of which spilled values are available in physregs so
722 // that we can choose to reuse the physregs instead of emitting reloads.
723 AvailableSpills Spills(MRI, TII);
725 // MaybeDeadStores - When we need to write a value back into a stack slot,
726 // keep track of the inserted store. If the stack slot value is never read
727 // (because the value was used from some available register, for example), and
728 // subsequently stored to, the original store is dead. This map keeps track
729 // of inserted stores that are not used. If we see a subsequent store to the
730 // same stack slot, the original store is deleted.
731 std::vector<MachineInstr*> MaybeDeadStores;
732 MaybeDeadStores.resize(MF.getFrameInfo()->getObjectIndexEnd(), NULL);
734 // ReMatDefs - These are rematerializable def MIs which are not deleted.
735 SmallSet<MachineInstr*, 4> ReMatDefs;
737 // Keep track of kill information.
738 BitVector RegKills(MRI->getNumRegs());
739 std::vector<MachineOperand*> KillOps;
740 KillOps.resize(MRI->getNumRegs(), NULL);
742 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
744 MachineInstr &MI = *MII;
745 MachineBasicBlock::iterator NextMII = MII; ++NextMII;
746 VirtRegMap::MI2VirtMapTy::const_iterator I, End;
749 bool BackTracked = false;
751 /// ReusedOperands - Keep track of operand reuse in case we need to undo
753 ReuseInfo ReusedOperands(MI, MRI);
755 // Loop over all of the implicit defs, clearing them from our available
757 const TargetInstrDescriptor *TID = MI.getInstrDescriptor();
758 if (TID->ImplicitDefs) {
759 const unsigned *ImpDef = TID->ImplicitDefs;
760 for ( ; *ImpDef; ++ImpDef) {
761 MF.setPhysRegUsed(*ImpDef);
762 ReusedOperands.markClobbered(*ImpDef);
763 Spills.ClobberPhysReg(*ImpDef);
767 // Process all of the spilled uses and all non spilled reg references.
768 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
769 MachineOperand &MO = MI.getOperand(i);
770 if (!MO.isRegister() || MO.getReg() == 0)
771 continue; // Ignore non-register operands.
773 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) {
774 // Ignore physregs for spilling, but remember that it is used by this
776 MF.setPhysRegUsed(MO.getReg());
777 ReusedOperands.markClobbered(MO.getReg());
781 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) &&
782 "Not a virtual or a physical register?");
784 unsigned VirtReg = MO.getReg();
785 if (VRM.isAssignedReg(VirtReg)) {
786 // This virtual register was assigned a physreg!
787 unsigned Phys = VRM.getPhys(VirtReg);
788 MF.setPhysRegUsed(Phys);
790 ReusedOperands.markClobbered(Phys);
791 MI.getOperand(i).setReg(Phys);
795 // This virtual register is now known to be a spilled value.
797 continue; // Handle defs in the loop below (handle use&def here though)
799 bool DoReMat = VRM.isReMaterialized(VirtReg);
800 int SSorRMId = DoReMat
801 ? VRM.getReMatId(VirtReg) : VRM.getStackSlot(VirtReg);
802 int ReuseSlot = SSorRMId;
804 // Check to see if this stack slot is available.
805 unsigned PhysReg = Spills.getSpillSlotOrReMatPhysReg(SSorRMId);
806 if (!PhysReg && DoReMat) {
807 // This use is rematerializable. But perhaps the value is available in
808 // stack if the definition is not deleted. If so, check if we can
810 ReuseSlot = VRM.getStackSlot(VirtReg);
811 if (ReuseSlot != VirtRegMap::NO_STACK_SLOT)
812 PhysReg = Spills.getSpillSlotOrReMatPhysReg(ReuseSlot);
815 // This spilled operand might be part of a two-address operand. If this
816 // is the case, then changing it will necessarily require changing the
817 // def part of the instruction as well. However, in some cases, we
818 // aren't allowed to modify the reused register. If none of these cases
820 bool CanReuse = true;
821 int ti = TID->getOperandConstraint(i, TOI::TIED_TO);
823 MI.getOperand(ti).isReg() &&
824 MI.getOperand(ti).getReg() == VirtReg) {
825 // Okay, we have a two address operand. We can reuse this physreg as
826 // long as we are allowed to clobber the value and there isn't an
827 // earlier def that has already clobbered the physreg.
828 CanReuse = Spills.canClobberPhysReg(ReuseSlot) &&
829 !ReusedOperands.isClobbered(PhysReg);
833 // If this stack slot value is already available, reuse it!
834 if (ReuseSlot > VirtRegMap::MAX_STACK_SLOT)
835 DOUT << "Reusing RM#" << ReuseSlot-VirtRegMap::MAX_STACK_SLOT-1;
837 DOUT << "Reusing SS#" << ReuseSlot;
838 DOUT << " from physreg "
839 << MRI->getName(PhysReg) << " for vreg"
840 << VirtReg <<" instead of reloading into physreg "
841 << MRI->getName(VRM.getPhys(VirtReg)) << "\n";
842 MI.getOperand(i).setReg(PhysReg);
844 // The only technical detail we have is that we don't know that
845 // PhysReg won't be clobbered by a reloaded stack slot that occurs
846 // later in the instruction. In particular, consider 'op V1, V2'.
847 // If V1 is available in physreg R0, we would choose to reuse it
848 // here, instead of reloading it into the register the allocator
849 // indicated (say R1). However, V2 might have to be reloaded
850 // later, and it might indicate that it needs to live in R0. When
851 // this occurs, we need to have information available that
852 // indicates it is safe to use R1 for the reload instead of R0.
854 // To further complicate matters, we might conflict with an alias,
855 // or R0 and R1 might not be compatible with each other. In this
856 // case, we actually insert a reload for V1 in R1, ensuring that
857 // we can get at R0 or its alias.
858 ReusedOperands.addReuse(i, ReuseSlot, PhysReg,
859 VRM.getPhys(VirtReg), VirtReg);
861 // Only mark it clobbered if this is a use&def operand.
862 ReusedOperands.markClobbered(PhysReg);
865 if (MI.getOperand(i).isKill() &&
866 ReuseSlot <= VirtRegMap::MAX_STACK_SLOT) {
867 // This was the last use and the spilled value is still available
868 // for reuse. That means the spill was unnecessary!
869 MachineInstr* DeadStore = MaybeDeadStores[ReuseSlot];
871 DOUT << "Removed dead store:\t" << *DeadStore;
872 InvalidateKills(*DeadStore, RegKills, KillOps);
873 MBB.erase(DeadStore);
874 VRM.RemoveFromFoldedVirtMap(DeadStore);
875 MaybeDeadStores[ReuseSlot] = NULL;
882 // Otherwise we have a situation where we have a two-address instruction
883 // whose mod/ref operand needs to be reloaded. This reload is already
884 // available in some register "PhysReg", but if we used PhysReg as the
885 // operand to our 2-addr instruction, the instruction would modify
886 // PhysReg. This isn't cool if something later uses PhysReg and expects
887 // to get its initial value.
889 // To avoid this problem, and to avoid doing a load right after a store,
890 // we emit a copy from PhysReg into the designated register for this
892 unsigned DesignatedReg = VRM.getPhys(VirtReg);
893 assert(DesignatedReg && "Must map virtreg to physreg!");
895 // Note that, if we reused a register for a previous operand, the
896 // register we want to reload into might not actually be
897 // available. If this occurs, use the register indicated by the
899 if (ReusedOperands.hasReuses())
900 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI,
901 Spills, MaybeDeadStores, RegKills, KillOps, VRM);
903 // If the mapped designated register is actually the physreg we have
904 // incoming, we don't need to inserted a dead copy.
905 if (DesignatedReg == PhysReg) {
906 // If this stack slot value is already available, reuse it!
907 if (ReuseSlot > VirtRegMap::MAX_STACK_SLOT)
908 DOUT << "Reusing RM#" << ReuseSlot-VirtRegMap::MAX_STACK_SLOT-1;
910 DOUT << "Reusing SS#" << ReuseSlot;
911 DOUT << " from physreg " << MRI->getName(PhysReg) << " for vreg"
913 << " instead of reloading into same physreg.\n";
914 MI.getOperand(i).setReg(PhysReg);
915 ReusedOperands.markClobbered(PhysReg);
920 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(VirtReg);
921 MF.setPhysRegUsed(DesignatedReg);
922 ReusedOperands.markClobbered(DesignatedReg);
923 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC);
925 MachineInstr *CopyMI = prior(MII);
926 UpdateKills(*CopyMI, RegKills, KillOps);
928 // This invalidates DesignatedReg.
929 Spills.ClobberPhysReg(DesignatedReg);
931 Spills.addAvailable(ReuseSlot, &MI, DesignatedReg);
932 MI.getOperand(i).setReg(DesignatedReg);
933 DOUT << '\t' << *prior(MII);
938 // Otherwise, reload it and remember that we have it.
939 PhysReg = VRM.getPhys(VirtReg);
940 assert(PhysReg && "Must map virtreg to physreg!");
941 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(VirtReg);
943 // Note that, if we reused a register for a previous operand, the
944 // register we want to reload into might not actually be
945 // available. If this occurs, use the register indicated by the
947 if (ReusedOperands.hasReuses())
948 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
949 Spills, MaybeDeadStores, RegKills, KillOps, VRM);
951 MF.setPhysRegUsed(PhysReg);
952 ReusedOperands.markClobbered(PhysReg);
954 MRI->reMaterialize(MBB, &MI, PhysReg, VRM.getReMaterializedMI(VirtReg));
957 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, SSorRMId, RC);
960 // This invalidates PhysReg.
961 Spills.ClobberPhysReg(PhysReg);
963 // Any stores to this stack slot are not dead anymore.
965 MaybeDeadStores[SSorRMId] = NULL;
966 Spills.addAvailable(SSorRMId, &MI, PhysReg);
967 // Assumes this is the last use. IsKill will be unset if reg is reused
968 // unless it's a two-address operand.
969 if (TID->getOperandConstraint(i, TOI::TIED_TO) == -1)
970 MI.getOperand(i).setIsKill();
971 MI.getOperand(i).setReg(PhysReg);
972 UpdateKills(*prior(MII), RegKills, KillOps);
973 DOUT << '\t' << *prior(MII);
978 // If we have folded references to memory operands, make sure we clear all
979 // physical registers that may contain the value of the spilled virtual
981 SmallSet<int, 1> FoldedSS;
982 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
983 DOUT << "Folded vreg: " << I->second.first << " MR: "
985 unsigned VirtReg = I->second.first;
986 VirtRegMap::ModRef MR = I->second.second;
987 if (VRM.isAssignedReg(VirtReg)) {
988 DOUT << ": No stack slot!\n";
991 int SS = VRM.getStackSlot(VirtReg);
993 DOUT << " - StackSlot: " << SS << "\n";
995 // If this folded instruction is just a use, check to see if it's a
996 // straight load from the virt reg slot.
997 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
999 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
1000 if (FrameIdx == SS) {
1001 // If this spill slot is available, turn it into a copy (or nothing)
1002 // instead of leaving it as a load!
1003 if (unsigned InReg = Spills.getSpillSlotOrReMatPhysReg(SS)) {
1004 DOUT << "Promoted Load To Copy: " << MI;
1005 if (DestReg != InReg) {
1006 MRI->copyRegToReg(MBB, &MI, DestReg, InReg,
1007 MF.getSSARegMap()->getRegClass(VirtReg));
1008 // Revisit the copy so we make sure to notice the effects of the
1009 // operation on the destreg (either needing to RA it if it's
1010 // virtual or needing to clobber any values if it's physical).
1012 --NextMII; // backtrack to the copy.
1015 DOUT << "Removing now-noop copy: " << MI;
1017 VRM.RemoveFromFoldedVirtMap(&MI);
1020 goto ProcessNextInst;
1026 // If this reference is not a use, any previous store is now dead.
1027 // Otherwise, the store to this stack slot is not dead anymore.
1028 MachineInstr* DeadStore = MaybeDeadStores[SS];
1030 if (!(MR & VirtRegMap::isRef)) { // Previous store is dead.
1031 // If we get here, the store is dead, nuke it now.
1032 assert(VirtRegMap::isMod && "Can't be modref!");
1033 DOUT << "Removed dead store:\t" << *DeadStore;
1034 InvalidateKills(*DeadStore, RegKills, KillOps);
1035 MBB.erase(DeadStore);
1036 VRM.RemoveFromFoldedVirtMap(DeadStore);
1039 MaybeDeadStores[SS] = NULL;
1042 // If the spill slot value is available, and this is a new definition of
1043 // the value, the value is not available anymore.
1044 if (MR & VirtRegMap::isMod) {
1045 // Notice that the value in this stack slot has been modified.
1046 Spills.ModifyStackSlotOrReMat(SS);
1048 // If this is *just* a mod of the value, check to see if this is just a
1049 // store to the spill slot (i.e. the spill got merged into the copy). If
1050 // so, realize that the vreg is available now, and add the store to the
1051 // MaybeDeadStore info.
1053 if (!(MR & VirtRegMap::isRef)) {
1054 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
1055 assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
1056 "Src hasn't been allocated yet?");
1057 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark
1058 // this as a potentially dead store in case there is a subsequent
1059 // store into the stack slot without a read from it.
1060 MaybeDeadStores[StackSlot] = &MI;
1062 // If the stack slot value was previously available in some other
1063 // register, change it now. Otherwise, make the register available,
1065 Spills.addAvailable(StackSlot, &MI, SrcReg, false/*don't clobber*/);
1071 // Process all of the spilled defs.
1072 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
1073 MachineOperand &MO = MI.getOperand(i);
1074 if (MO.isRegister() && MO.getReg() && MO.isDef()) {
1075 unsigned VirtReg = MO.getReg();
1077 if (!MRegisterInfo::isVirtualRegister(VirtReg)) {
1078 // Check to see if this is a noop copy. If so, eliminate the
1079 // instruction before considering the dest reg to be changed.
1081 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
1083 DOUT << "Removing now-noop copy: " << MI;
1086 VRM.RemoveFromFoldedVirtMap(&MI);
1087 Spills.disallowClobberPhysReg(VirtReg);
1088 goto ProcessNextInst;
1091 // If it's not a no-op copy, it clobbers the value in the destreg.
1092 Spills.ClobberPhysReg(VirtReg);
1093 ReusedOperands.markClobbered(VirtReg);
1095 // Check to see if this instruction is a load from a stack slot into
1096 // a register. If so, this provides the stack slot value in the reg.
1098 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
1099 assert(DestReg == VirtReg && "Unknown load situation!");
1101 // If it is a folded reference, then it's not safe to clobber.
1102 bool Folded = FoldedSS.count(FrameIdx);
1103 // Otherwise, if it wasn't available, remember that it is now!
1104 Spills.addAvailable(FrameIdx, &MI, DestReg, !Folded);
1105 goto ProcessNextInst;
1111 bool DoReMat = VRM.isReMaterialized(VirtReg);
1113 ReMatDefs.insert(&MI);
1115 // The only vregs left are stack slot definitions.
1116 int StackSlot = VRM.getStackSlot(VirtReg);
1117 const TargetRegisterClass *RC = MF.getSSARegMap()->getRegClass(VirtReg);
1119 // If this def is part of a two-address operand, make sure to execute
1120 // the store from the correct physical register.
1122 int TiedOp = MI.getInstrDescriptor()->findTiedToSrcOperand(i);
1124 PhysReg = MI.getOperand(TiedOp).getReg();
1126 PhysReg = VRM.getPhys(VirtReg);
1127 if (ReusedOperands.isClobbered(PhysReg)) {
1128 // Another def has taken the assigned physreg. It must have been a
1129 // use&def which got it due to reuse. Undo the reuse!
1130 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
1131 Spills, MaybeDeadStores, RegKills, KillOps, VRM);
1135 MF.setPhysRegUsed(PhysReg);
1136 ReusedOperands.markClobbered(PhysReg);
1137 MI.getOperand(i).setReg(PhysReg);
1139 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
1140 DOUT << "Store:\t" << *next(MII);
1142 // If there is a dead store to this stack slot, nuke it now.
1143 MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
1145 DOUT << "Removed dead store:\t" << *LastStore;
1147 SmallVector<unsigned, 1> KillRegs;
1148 InvalidateKills(*LastStore, RegKills, KillOps, &KillRegs);
1149 MachineBasicBlock::iterator PrevMII = LastStore;
1150 bool CheckDef = PrevMII != MBB.begin();
1153 MBB.erase(LastStore);
1154 VRM.RemoveFromFoldedVirtMap(LastStore);
1156 // Look at defs of killed registers on the store. Mark the defs
1157 // as dead since the store has been deleted and they aren't
1159 for (unsigned j = 0, ee = KillRegs.size(); j != ee; ++j) {
1160 bool HasOtherDef = false;
1161 if (InvalidateRegDef(PrevMII, MI, KillRegs[j], HasOtherDef)) {
1162 MachineInstr *DeadDef = PrevMII;
1163 if (ReMatDefs.count(DeadDef) && !HasOtherDef) {
1164 // FIXME: This assumes a remat def does not have side
1167 VRM.RemoveFromFoldedVirtMap(DeadDef);
1174 LastStore = next(MII);
1176 // If the stack slot value was previously available in some other
1177 // register, change it now. Otherwise, make the register available,
1179 Spills.ModifyStackSlotOrReMat(StackSlot);
1180 Spills.ClobberPhysReg(PhysReg);
1181 Spills.addAvailable(StackSlot, LastStore, PhysReg);
1184 // Check to see if this is a noop copy. If so, eliminate the
1185 // instruction before considering the dest reg to be changed.
1188 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
1190 DOUT << "Removing now-noop copy: " << MI;
1193 VRM.RemoveFromFoldedVirtMap(&MI);
1194 UpdateKills(*LastStore, RegKills, KillOps);
1195 goto ProcessNextInst;
1202 if (!Erased && !BackTracked)
1203 for (MachineBasicBlock::iterator II = MI; II != NextMII; ++II)
1204 UpdateKills(*II, RegKills, KillOps);
1210 llvm::Spiller* llvm::createSpiller() {
1211 switch (SpillerOpt) {
1212 default: assert(0 && "Unreachable!");
1214 return new LocalSpiller();
1216 return new SimpleSpiller();