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(NumStores, "Number of stores added");
40 STATISTIC(NumLoads , "Number of loads added");
41 STATISTIC(NumReused, "Number of values reused");
42 STATISTIC(NumDSE , "Number of dead stores elided");
43 STATISTIC(NumDCE , "Number of copies elided");
46 enum SpillerName { simple, local };
48 static cl::opt<SpillerName>
50 cl::desc("Spiller to use: (default: local)"),
52 cl::values(clEnumVal(simple, " simple spiller"),
53 clEnumVal(local, " local spiller"),
58 //===----------------------------------------------------------------------===//
59 // VirtRegMap implementation
60 //===----------------------------------------------------------------------===//
62 VirtRegMap::VirtRegMap(MachineFunction &mf)
63 : TII(*mf.getTarget().getInstrInfo()), MF(mf),
64 Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT),
65 Virt2ReMatIdMap(NO_STACK_SLOT), ReMatMap(NULL),
66 ReMatId(MAX_STACK_SLOT+1) {
70 void VirtRegMap::grow() {
71 unsigned LastVirtReg = MF.getSSARegMap()->getLastVirtReg();
72 Virt2PhysMap.grow(LastVirtReg);
73 Virt2StackSlotMap.grow(LastVirtReg);
74 Virt2ReMatIdMap.grow(LastVirtReg);
75 ReMatMap.grow(LastVirtReg);
78 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) {
79 assert(MRegisterInfo::isVirtualRegister(virtReg));
80 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
81 "attempt to assign stack slot to already spilled register");
82 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg);
83 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(),
85 Virt2StackSlotMap[virtReg] = frameIndex;
90 void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) {
91 assert(MRegisterInfo::isVirtualRegister(virtReg));
92 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
93 "attempt to assign stack slot to already spilled register");
94 assert((frameIndex >= 0 ||
95 (frameIndex >= MF.getFrameInfo()->getObjectIndexBegin())) &&
96 "illegal fixed frame index");
97 Virt2StackSlotMap[virtReg] = frameIndex;
100 int VirtRegMap::assignVirtReMatId(unsigned virtReg) {
101 assert(MRegisterInfo::isVirtualRegister(virtReg));
102 assert(Virt2ReMatIdMap[virtReg] == NO_STACK_SLOT &&
103 "attempt to assign re-mat id to already spilled register");
104 Virt2ReMatIdMap[virtReg] = ReMatId;
108 void VirtRegMap::assignVirtReMatId(unsigned virtReg, int id) {
109 assert(MRegisterInfo::isVirtualRegister(virtReg));
110 assert(Virt2ReMatIdMap[virtReg] == NO_STACK_SLOT &&
111 "attempt to assign re-mat id to already spilled register");
112 Virt2ReMatIdMap[virtReg] = id;
115 void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI,
116 unsigned OpNo, MachineInstr *NewMI) {
117 // Move previous memory references folded to new instruction.
118 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI);
119 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI),
120 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) {
121 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second));
122 MI2VirtMap.erase(I++);
126 const TargetInstrDescriptor *TID = OldMI->getInstrDescriptor();
127 if (TID->getOperandConstraint(OpNo, TOI::TIED_TO) != -1 ||
128 TID->findTiedToSrcOperand(OpNo) != -1) {
129 // Folded a two-address operand.
131 } else if (OldMI->getOperand(OpNo).isDef()) {
137 // add new memory reference
138 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo)));
141 void VirtRegMap::print(std::ostream &OS) const {
142 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo();
144 OS << "********** REGISTER MAP **********\n";
145 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
146 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) {
147 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG)
148 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n";
152 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
153 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i)
154 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT)
155 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n";
159 void VirtRegMap::dump() const {
164 //===----------------------------------------------------------------------===//
165 // Simple Spiller Implementation
166 //===----------------------------------------------------------------------===//
168 Spiller::~Spiller() {}
171 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller {
172 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM);
176 bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
177 DOUT << "********** REWRITE MACHINE CODE **********\n";
178 DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';
179 const TargetMachine &TM = MF.getTarget();
180 const MRegisterInfo &MRI = *TM.getRegisterInfo();
182 // LoadedRegs - Keep track of which vregs are loaded, so that we only load
183 // each vreg once (in the case where a spilled vreg is used by multiple
184 // operands). This is always smaller than the number of operands to the
185 // current machine instr, so it should be small.
186 std::vector<unsigned> LoadedRegs;
188 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
190 DOUT << MBBI->getBasicBlock()->getName() << ":\n";
191 MachineBasicBlock &MBB = *MBBI;
192 for (MachineBasicBlock::iterator MII = MBB.begin(),
193 E = MBB.end(); MII != E; ++MII) {
194 MachineInstr &MI = *MII;
195 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
196 MachineOperand &MO = MI.getOperand(i);
197 if (MO.isRegister() && MO.getReg())
198 if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
199 unsigned VirtReg = MO.getReg();
200 unsigned PhysReg = VRM.getPhys(VirtReg);
201 if (!VRM.isAssignedReg(VirtReg)) {
202 int StackSlot = VRM.getStackSlot(VirtReg);
203 const TargetRegisterClass* RC =
204 MF.getSSARegMap()->getRegClass(VirtReg);
207 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg)
208 == LoadedRegs.end()) {
209 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
210 LoadedRegs.push_back(VirtReg);
212 DOUT << '\t' << *prior(MII);
216 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
220 MF.setPhysRegUsed(PhysReg);
221 MI.getOperand(i).setReg(PhysReg);
223 MF.setPhysRegUsed(MO.getReg());
234 //===----------------------------------------------------------------------===//
235 // Local Spiller Implementation
236 //===----------------------------------------------------------------------===//
239 /// LocalSpiller - This spiller does a simple pass over the machine basic
240 /// block to attempt to keep spills in registers as much as possible for
241 /// blocks that have low register pressure (the vreg may be spilled due to
242 /// register pressure in other blocks).
243 class VISIBILITY_HIDDEN LocalSpiller : public Spiller {
244 const MRegisterInfo *MRI;
245 const TargetInstrInfo *TII;
247 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
248 MRI = MF.getTarget().getRegisterInfo();
249 TII = MF.getTarget().getInstrInfo();
250 DOUT << "\n**** Local spiller rewriting function '"
251 << MF.getFunction()->getName() << "':\n";
253 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
255 RewriteMBB(*MBB, VRM);
259 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM);
263 /// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
264 /// top down, keep track of which spills slots or remat are available in each
267 /// Note that not all physregs are created equal here. In particular, some
268 /// physregs are reloads that we are allowed to clobber or ignore at any time.
269 /// Other physregs are values that the register allocated program is using that
270 /// we cannot CHANGE, but we can read if we like. We keep track of this on a
271 /// per-stack-slot / remat id basis as the low bit in the value of the
272 /// SpillSlotsAvailable entries. The predicate 'canClobberPhysReg()' checks
273 /// this bit and addAvailable sets it if.
275 class VISIBILITY_HIDDEN AvailableSpills {
276 const MRegisterInfo *MRI;
277 const TargetInstrInfo *TII;
279 // SpillSlotsOrReMatsAvailable - This map keeps track of all of the spilled
280 // or remat'ed virtual register values that are still available, due to being
281 // loaded or stored to, but not invalidated yet.
282 std::map<int, unsigned> SpillSlotsOrReMatsAvailable;
284 // PhysRegsAvailable - This is the inverse of SpillSlotsOrReMatsAvailable,
285 // indicating which stack slot values are currently held by a physreg. This
286 // is used to invalidate entries in SpillSlotsOrReMatsAvailable when a
287 // physreg is modified.
288 std::multimap<unsigned, int> PhysRegsAvailable;
290 void disallowClobberPhysRegOnly(unsigned PhysReg);
292 void ClobberPhysRegOnly(unsigned PhysReg);
294 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii)
295 : MRI(mri), TII(tii) {
298 const MRegisterInfo *getRegInfo() const { return MRI; }
300 /// getSpillSlotOrReMatPhysReg - If the specified stack slot or remat is
301 /// available in a physical register, return that PhysReg, otherwise
303 unsigned getSpillSlotOrReMatPhysReg(int Slot) const {
304 std::map<int, unsigned>::const_iterator I =
305 SpillSlotsOrReMatsAvailable.find(Slot);
306 if (I != SpillSlotsOrReMatsAvailable.end()) {
307 return I->second >> 1; // Remove the CanClobber bit.
312 /// addAvailable - Mark that the specified stack slot / remat is available in
313 /// the specified physreg. If CanClobber is true, the physreg can be modified
314 /// at any time without changing the semantics of the program.
315 void addAvailable(int SlotOrReMat, MachineInstr *MI, unsigned Reg,
316 bool CanClobber = true) {
317 // If this stack slot is thought to be available in some other physreg,
318 // remove its record.
319 ModifyStackSlotOrReMat(SlotOrReMat);
321 PhysRegsAvailable.insert(std::make_pair(Reg, SlotOrReMat));
322 SpillSlotsOrReMatsAvailable[SlotOrReMat] = (Reg << 1) | (unsigned)CanClobber;
324 if (SlotOrReMat > VirtRegMap::MAX_STACK_SLOT)
325 DOUT << "Remembering RM#" << SlotOrReMat-VirtRegMap::MAX_STACK_SLOT-1;
327 DOUT << "Remembering SS#" << SlotOrReMat;
328 DOUT << " in physreg " << MRI->getName(Reg) << "\n";
331 /// canClobberPhysReg - Return true if the spiller is allowed to change the
332 /// value of the specified stackslot register if it desires. The specified
333 /// stack slot must be available in a physreg for this query to make sense.
334 bool canClobberPhysReg(int SlotOrReMat) const {
335 assert(SpillSlotsOrReMatsAvailable.count(SlotOrReMat) && "Value not available!");
336 return SpillSlotsOrReMatsAvailable.find(SlotOrReMat)->second & 1;
339 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
340 /// stackslot register. The register is still available but is no longer
341 /// allowed to be modifed.
342 void disallowClobberPhysReg(unsigned PhysReg);
344 /// ClobberPhysReg - This is called when the specified physreg changes
345 /// value. We use this to invalidate any info about stuff we thing lives in
346 /// it and any of its aliases.
347 void ClobberPhysReg(unsigned PhysReg);
349 /// ModifyStackSlotOrReMat - This method is called when the value in a stack slot
350 /// changes. This removes information about which register the previous value
351 /// for this slot lives in (as the previous value is dead now).
352 void ModifyStackSlotOrReMat(int SlotOrReMat);
356 /// disallowClobberPhysRegOnly - Unset the CanClobber bit of the specified
357 /// stackslot register. The register is still available but is no longer
358 /// allowed to be modifed.
359 void AvailableSpills::disallowClobberPhysRegOnly(unsigned PhysReg) {
360 std::multimap<unsigned, int>::iterator I =
361 PhysRegsAvailable.lower_bound(PhysReg);
362 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
363 int SlotOrReMat = I->second;
365 assert((SpillSlotsOrReMatsAvailable[SlotOrReMat] >> 1) == PhysReg &&
366 "Bidirectional map mismatch!");
367 SpillSlotsOrReMatsAvailable[SlotOrReMat] &= ~1;
368 DOUT << "PhysReg " << MRI->getName(PhysReg)
369 << " copied, it is available for use but can no longer be modified\n";
373 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
374 /// stackslot register and its aliases. The register and its aliases may
375 /// still available but is no longer allowed to be modifed.
376 void AvailableSpills::disallowClobberPhysReg(unsigned PhysReg) {
377 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
378 disallowClobberPhysRegOnly(*AS);
379 disallowClobberPhysRegOnly(PhysReg);
382 /// ClobberPhysRegOnly - This is called when the specified physreg changes
383 /// value. We use this to invalidate any info about stuff we thing lives in it.
384 void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
385 std::multimap<unsigned, int>::iterator I =
386 PhysRegsAvailable.lower_bound(PhysReg);
387 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
388 int SlotOrReMat = I->second;
389 PhysRegsAvailable.erase(I++);
390 assert((SpillSlotsOrReMatsAvailable[SlotOrReMat] >> 1) == PhysReg &&
391 "Bidirectional map mismatch!");
392 SpillSlotsOrReMatsAvailable.erase(SlotOrReMat);
393 DOUT << "PhysReg " << MRI->getName(PhysReg)
394 << " clobbered, invalidating ";
395 if (SlotOrReMat > VirtRegMap::MAX_STACK_SLOT)
396 DOUT << "RM#" << SlotOrReMat-VirtRegMap::MAX_STACK_SLOT-1 << "\n";
398 DOUT << "SS#" << SlotOrReMat << "\n";
402 /// ClobberPhysReg - This is called when the specified physreg changes
403 /// value. We use this to invalidate any info about stuff we thing lives in
404 /// it and any of its aliases.
405 void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
406 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
407 ClobberPhysRegOnly(*AS);
408 ClobberPhysRegOnly(PhysReg);
411 /// ModifyStackSlotOrReMat - This method is called when the value in a stack slot
412 /// changes. This removes information about which register the previous value
413 /// for this slot lives in (as the previous value is dead now).
414 void AvailableSpills::ModifyStackSlotOrReMat(int SlotOrReMat) {
415 std::map<int, unsigned>::iterator It = SpillSlotsOrReMatsAvailable.find(SlotOrReMat);
416 if (It == SpillSlotsOrReMatsAvailable.end()) return;
417 unsigned Reg = It->second >> 1;
418 SpillSlotsOrReMatsAvailable.erase(It);
420 // This register may hold the value of multiple stack slots, only remove this
421 // stack slot from the set of values the register contains.
422 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
424 assert(I != PhysRegsAvailable.end() && I->first == Reg &&
425 "Map inverse broken!");
426 if (I->second == SlotOrReMat) break;
428 PhysRegsAvailable.erase(I);
433 /// InvalidateKills - MI is going to be deleted. If any of its operands are
434 /// marked kill, then invalidate the information.
435 static void InvalidateKills(MachineInstr &MI, BitVector &RegKills,
436 std::vector<MachineOperand*> &KillOps,
437 MachineInstr *NewDef = NULL) {
438 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
439 MachineOperand &MO = MI.getOperand(i);
440 if (!MO.isReg() || !MO.isUse() || !MO.isKill())
442 unsigned Reg = MO.getReg();
444 // Due to remat, it's possible this reg isn't being reused. That is,
445 // the def of this reg (by prev MI) is now dead.
446 bool FoundUse = false, Done = false;
447 MachineBasicBlock::iterator I = MI, E = NewDef;
449 for (; !Done && I != E; ++I) {
450 MachineInstr *NMI = I;
451 for (unsigned j = 0, ee = NMI->getNumOperands(); j != ee; ++j) {
452 MachineOperand &MO = NMI->getOperand(j);
453 if (!MO.isReg() || MO.getReg() != Reg)
457 Done = true; // Stop after scanning all the operands of this MI.
462 MachineBasicBlock::iterator MII = MI;
463 MachineInstr *DefMI = prior(MII);
464 MachineOperand *DefOp = DefMI->findRegisterDefOperand(Reg);
465 assert(DefOp && "Missing def?");
469 if (KillOps[Reg] == &MO) {
476 /// UpdateKills - Track and update kill info. If a MI reads a register that is
477 /// marked kill, then it must be due to register reuse. Transfer the kill info
479 static void UpdateKills(MachineInstr &MI, BitVector &RegKills,
480 std::vector<MachineOperand*> &KillOps) {
481 const TargetInstrDescriptor *TID = MI.getInstrDescriptor();
482 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
483 MachineOperand &MO = MI.getOperand(i);
484 if (!MO.isReg() || !MO.isUse())
486 unsigned Reg = MO.getReg();
491 // That can't be right. Register is killed but not re-defined and it's
492 // being reused. Let's fix that.
493 KillOps[Reg]->unsetIsKill();
494 if (i < TID->numOperands &&
495 TID->getOperandConstraint(i, TOI::TIED_TO) == -1)
496 // Unless it's a two-address operand, this is the new kill.
506 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
507 const MachineOperand &MO = MI.getOperand(i);
508 if (!MO.isReg() || !MO.isDef())
510 unsigned Reg = MO.getReg();
517 // ReusedOp - For each reused operand, we keep track of a bit of information, in
518 // case we need to rollback upon processing a new operand. See comments below.
521 // The MachineInstr operand that reused an available value.
524 // StackSlotOrReMat - The spill slot or remat id of the value being reused.
525 unsigned StackSlotOrReMat;
527 // PhysRegReused - The physical register the value was available in.
528 unsigned PhysRegReused;
530 // AssignedPhysReg - The physreg that was assigned for use by the reload.
531 unsigned AssignedPhysReg;
533 // VirtReg - The virtual register itself.
536 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
538 : Operand(o), StackSlotOrReMat(ss), PhysRegReused(prr), AssignedPhysReg(apr),
542 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
543 /// is reused instead of reloaded.
544 class VISIBILITY_HIDDEN ReuseInfo {
546 std::vector<ReusedOp> Reuses;
547 BitVector PhysRegsClobbered;
549 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) {
550 PhysRegsClobbered.resize(mri->getNumRegs());
553 bool hasReuses() const {
554 return !Reuses.empty();
557 /// addReuse - If we choose to reuse a virtual register that is already
558 /// available instead of reloading it, remember that we did so.
559 void addReuse(unsigned OpNo, unsigned StackSlotOrReMat,
560 unsigned PhysRegReused, unsigned AssignedPhysReg,
562 // If the reload is to the assigned register anyway, no undo will be
564 if (PhysRegReused == AssignedPhysReg) return;
566 // Otherwise, remember this.
567 Reuses.push_back(ReusedOp(OpNo, StackSlotOrReMat, PhysRegReused,
568 AssignedPhysReg, VirtReg));
571 void markClobbered(unsigned PhysReg) {
572 PhysRegsClobbered.set(PhysReg);
575 bool isClobbered(unsigned PhysReg) const {
576 return PhysRegsClobbered.test(PhysReg);
579 /// GetRegForReload - We are about to emit a reload into PhysReg. If there
580 /// is some other operand that is using the specified register, either pick
581 /// a new register to use, or evict the previous reload and use this reg.
582 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
583 AvailableSpills &Spills,
584 std::vector<MachineInstr*> &MaybeDeadStores,
585 SmallSet<unsigned, 8> &Rejected,
587 std::vector<MachineOperand*> &KillOps,
589 if (Reuses.empty()) return PhysReg; // This is most often empty.
591 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
592 ReusedOp &Op = Reuses[ro];
593 // If we find some other reuse that was supposed to use this register
594 // exactly for its reload, we can change this reload to use ITS reload
595 // register. That is, unless its reload register has already been
596 // considered and subsequently rejected because it has also been reused
597 // by another operand.
598 if (Op.PhysRegReused == PhysReg &&
599 Rejected.count(Op.AssignedPhysReg) == 0) {
600 // Yup, use the reload register that we didn't use before.
601 unsigned NewReg = Op.AssignedPhysReg;
602 Rejected.insert(PhysReg);
603 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores, Rejected,
604 RegKills, KillOps, VRM);
606 // Otherwise, we might also have a problem if a previously reused
607 // value aliases the new register. If so, codegen the previous reload
609 unsigned PRRU = Op.PhysRegReused;
610 const MRegisterInfo *MRI = Spills.getRegInfo();
611 if (MRI->areAliases(PRRU, PhysReg)) {
612 // Okay, we found out that an alias of a reused register
613 // was used. This isn't good because it means we have
614 // to undo a previous reuse.
615 MachineBasicBlock *MBB = MI->getParent();
616 const TargetRegisterClass *AliasRC =
617 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg);
619 // Copy Op out of the vector and remove it, we're going to insert an
620 // explicit load for it.
622 Reuses.erase(Reuses.begin()+ro);
624 // Ok, we're going to try to reload the assigned physreg into the
625 // slot that we were supposed to in the first place. However, that
626 // register could hold a reuse. Check to see if it conflicts or
627 // would prefer us to use a different register.
628 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg,
629 MI, Spills, MaybeDeadStores,
630 Rejected, RegKills, KillOps, VRM);
632 if (NewOp.StackSlotOrReMat > VirtRegMap::MAX_STACK_SLOT) {
633 MRI->reMaterialize(*MBB, MI, NewPhysReg,
634 VRM.getReMaterializedMI(NewOp.VirtReg));
637 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg,
638 NewOp.StackSlotOrReMat, AliasRC);
639 // Any stores to this stack slot are not dead anymore.
640 MaybeDeadStores[NewOp.StackSlotOrReMat] = NULL;
643 Spills.ClobberPhysReg(NewPhysReg);
644 Spills.ClobberPhysReg(NewOp.PhysRegReused);
646 MI->getOperand(NewOp.Operand).setReg(NewPhysReg);
648 Spills.addAvailable(NewOp.StackSlotOrReMat, MI, NewPhysReg);
649 MachineBasicBlock::iterator MII = MI;
651 UpdateKills(*MII, RegKills, KillOps);
652 DOUT << '\t' << *MII;
654 DOUT << "Reuse undone!\n";
657 // Finally, PhysReg is now available, go ahead and use it.
665 /// GetRegForReload - Helper for the above GetRegForReload(). Add a
666 /// 'Rejected' set to remember which registers have been considered and
667 /// rejected for the reload. This avoids infinite looping in case like
670 /// t2 <- assigned r0 for use by the reload but ended up reuse r1
671 /// t3 <- assigned r1 for use by the reload but ended up reuse r0
673 /// sees r1 is taken by t2, tries t2's reload register r0
674 /// sees r0 is taken by t3, tries t3's reload register r1
675 /// sees r1 is taken by t2, tries t2's reload register r0 ...
676 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
677 AvailableSpills &Spills,
678 std::vector<MachineInstr*> &MaybeDeadStores,
680 std::vector<MachineOperand*> &KillOps,
682 SmallSet<unsigned, 8> Rejected;
683 return GetRegForReload(PhysReg, MI, Spills, MaybeDeadStores, Rejected,
684 RegKills, KillOps, VRM);
690 /// rewriteMBB - Keep track of which spills are available even after the
691 /// register allocator is done with them. If possible, avoid reloading vregs.
692 void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM) {
693 DOUT << MBB.getBasicBlock()->getName() << ":\n";
695 MachineFunction &MF = *MBB.getParent();
697 // Spills - Keep track of which spilled values are available in physregs so
698 // that we can choose to reuse the physregs instead of emitting reloads.
699 AvailableSpills Spills(MRI, TII);
701 // MaybeDeadStores - When we need to write a value back into a stack slot,
702 // keep track of the inserted store. If the stack slot value is never read
703 // (because the value was used from some available register, for example), and
704 // subsequently stored to, the original store is dead. This map keeps track
705 // of inserted stores that are not used. If we see a subsequent store to the
706 // same stack slot, the original store is deleted.
707 std::vector<MachineInstr*> MaybeDeadStores;
708 MaybeDeadStores.resize(MF.getFrameInfo()->getObjectIndexEnd(), NULL);
710 // Keep track of kill information.
711 BitVector RegKills(MRI->getNumRegs());
712 std::vector<MachineOperand*> KillOps;
713 KillOps.resize(MRI->getNumRegs(), NULL);
715 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
717 MachineInstr &MI = *MII;
718 MachineBasicBlock::iterator NextMII = MII; ++NextMII;
719 VirtRegMap::MI2VirtMapTy::const_iterator I, End;
722 bool BackTracked = false;
724 /// ReusedOperands - Keep track of operand reuse in case we need to undo
726 ReuseInfo ReusedOperands(MI, MRI);
728 // Loop over all of the implicit defs, clearing them from our available
730 const TargetInstrDescriptor *TID = MI.getInstrDescriptor();
731 if (TID->ImplicitDefs) {
732 const unsigned *ImpDef = TID->ImplicitDefs;
733 for ( ; *ImpDef; ++ImpDef) {
734 MF.setPhysRegUsed(*ImpDef);
735 ReusedOperands.markClobbered(*ImpDef);
736 Spills.ClobberPhysReg(*ImpDef);
740 // Process all of the spilled uses and all non spilled reg references.
741 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
742 MachineOperand &MO = MI.getOperand(i);
743 if (!MO.isRegister() || MO.getReg() == 0)
744 continue; // Ignore non-register operands.
746 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) {
747 // Ignore physregs for spilling, but remember that it is used by this
749 MF.setPhysRegUsed(MO.getReg());
750 ReusedOperands.markClobbered(MO.getReg());
754 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) &&
755 "Not a virtual or a physical register?");
757 unsigned VirtReg = MO.getReg();
758 if (VRM.isAssignedReg(VirtReg)) {
759 // This virtual register was assigned a physreg!
760 unsigned Phys = VRM.getPhys(VirtReg);
761 MF.setPhysRegUsed(Phys);
763 ReusedOperands.markClobbered(Phys);
764 MI.getOperand(i).setReg(Phys);
768 // This virtual register is now known to be a spilled value.
770 continue; // Handle defs in the loop below (handle use&def here though)
772 bool DoReMat = VRM.isReMaterialized(VirtReg);
773 int SSorRMId = DoReMat
774 ? VRM.getReMatId(VirtReg) : VRM.getStackSlot(VirtReg);
775 int ReuseSlot = SSorRMId;
777 // Check to see if this stack slot is available.
778 unsigned PhysReg = Spills.getSpillSlotOrReMatPhysReg(SSorRMId);
779 if (!PhysReg && DoReMat) {
780 // This use is rematerializable. But perhaps the value is available in
781 // stack if the definition is not deleted. If so, check if we can
783 ReuseSlot = VRM.getStackSlot(VirtReg);
784 if (ReuseSlot != VirtRegMap::NO_STACK_SLOT)
785 PhysReg = Spills.getSpillSlotOrReMatPhysReg(ReuseSlot);
788 // This spilled operand might be part of a two-address operand. If this
789 // is the case, then changing it will necessarily require changing the
790 // def part of the instruction as well. However, in some cases, we
791 // aren't allowed to modify the reused register. If none of these cases
793 bool CanReuse = true;
794 int ti = TID->getOperandConstraint(i, TOI::TIED_TO);
796 MI.getOperand(ti).isReg() &&
797 MI.getOperand(ti).getReg() == VirtReg) {
798 // Okay, we have a two address operand. We can reuse this physreg as
799 // long as we are allowed to clobber the value and there isn't an
800 // earlier def that has already clobbered the physreg.
801 CanReuse = Spills.canClobberPhysReg(ReuseSlot) &&
802 !ReusedOperands.isClobbered(PhysReg);
806 // If this stack slot value is already available, reuse it!
807 if (ReuseSlot > VirtRegMap::MAX_STACK_SLOT)
808 DOUT << "Reusing RM#" << ReuseSlot-VirtRegMap::MAX_STACK_SLOT-1;
810 DOUT << "Reusing SS#" << ReuseSlot;
811 DOUT << " from physreg "
812 << MRI->getName(PhysReg) << " for vreg"
813 << VirtReg <<" instead of reloading into physreg "
814 << MRI->getName(VRM.getPhys(VirtReg)) << "\n";
815 MI.getOperand(i).setReg(PhysReg);
817 // The only technical detail we have is that we don't know that
818 // PhysReg won't be clobbered by a reloaded stack slot that occurs
819 // later in the instruction. In particular, consider 'op V1, V2'.
820 // If V1 is available in physreg R0, we would choose to reuse it
821 // here, instead of reloading it into the register the allocator
822 // indicated (say R1). However, V2 might have to be reloaded
823 // later, and it might indicate that it needs to live in R0. When
824 // this occurs, we need to have information available that
825 // indicates it is safe to use R1 for the reload instead of R0.
827 // To further complicate matters, we might conflict with an alias,
828 // or R0 and R1 might not be compatible with each other. In this
829 // case, we actually insert a reload for V1 in R1, ensuring that
830 // we can get at R0 or its alias.
831 ReusedOperands.addReuse(i, ReuseSlot, PhysReg,
832 VRM.getPhys(VirtReg), VirtReg);
834 // Only mark it clobbered if this is a use&def operand.
835 ReusedOperands.markClobbered(PhysReg);
838 if (MI.getOperand(i).isKill() &&
839 ReuseSlot <= VirtRegMap::MAX_STACK_SLOT) {
840 // This was the last use and the spilled value is still available
841 // for reuse. That means the spill was unnecessary!
842 MachineInstr* DeadStore = MaybeDeadStores[ReuseSlot];
844 DOUT << "Removed dead store:\t" << *DeadStore;
845 InvalidateKills(*DeadStore, RegKills, KillOps);
846 MBB.erase(DeadStore);
847 VRM.RemoveFromFoldedVirtMap(DeadStore);
848 MaybeDeadStores[ReuseSlot] = NULL;
855 // Otherwise we have a situation where we have a two-address instruction
856 // whose mod/ref operand needs to be reloaded. This reload is already
857 // available in some register "PhysReg", but if we used PhysReg as the
858 // operand to our 2-addr instruction, the instruction would modify
859 // PhysReg. This isn't cool if something later uses PhysReg and expects
860 // to get its initial value.
862 // To avoid this problem, and to avoid doing a load right after a store,
863 // we emit a copy from PhysReg into the designated register for this
865 unsigned DesignatedReg = VRM.getPhys(VirtReg);
866 assert(DesignatedReg && "Must map virtreg to physreg!");
868 // Note that, if we reused a register for a previous operand, the
869 // register we want to reload into might not actually be
870 // available. If this occurs, use the register indicated by the
872 if (ReusedOperands.hasReuses())
873 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI,
874 Spills, MaybeDeadStores, RegKills, KillOps, VRM);
876 // If the mapped designated register is actually the physreg we have
877 // incoming, we don't need to inserted a dead copy.
878 if (DesignatedReg == PhysReg) {
879 // If this stack slot value is already available, reuse it!
880 if (ReuseSlot > VirtRegMap::MAX_STACK_SLOT)
881 DOUT << "Reusing RM#" << ReuseSlot-VirtRegMap::MAX_STACK_SLOT-1;
883 DOUT << "Reusing SS#" << ReuseSlot;
884 DOUT << " from physreg " << MRI->getName(PhysReg) << " for vreg"
886 << " instead of reloading into same physreg.\n";
887 MI.getOperand(i).setReg(PhysReg);
888 ReusedOperands.markClobbered(PhysReg);
893 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(VirtReg);
894 MF.setPhysRegUsed(DesignatedReg);
895 ReusedOperands.markClobbered(DesignatedReg);
896 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC);
898 MachineInstr *CopyMI = prior(MII);
899 UpdateKills(*CopyMI, RegKills, KillOps);
901 // This invalidates DesignatedReg.
902 Spills.ClobberPhysReg(DesignatedReg);
904 Spills.addAvailable(ReuseSlot, &MI, DesignatedReg);
905 MI.getOperand(i).setReg(DesignatedReg);
906 DOUT << '\t' << *prior(MII);
911 // Otherwise, reload it and remember that we have it.
912 PhysReg = VRM.getPhys(VirtReg);
913 assert(PhysReg && "Must map virtreg to physreg!");
914 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(VirtReg);
916 // Note that, if we reused a register for a previous operand, the
917 // register we want to reload into might not actually be
918 // available. If this occurs, use the register indicated by the
920 if (ReusedOperands.hasReuses())
921 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
922 Spills, MaybeDeadStores, RegKills, KillOps, VRM);
924 MF.setPhysRegUsed(PhysReg);
925 ReusedOperands.markClobbered(PhysReg);
927 MRI->reMaterialize(MBB, &MI, PhysReg, VRM.getReMaterializedMI(VirtReg));
930 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, SSorRMId, RC);
933 // This invalidates PhysReg.
934 Spills.ClobberPhysReg(PhysReg);
936 // Any stores to this stack slot are not dead anymore.
938 MaybeDeadStores[SSorRMId] = NULL;
939 Spills.addAvailable(SSorRMId, &MI, PhysReg);
940 // Assumes this is the last use. IsKill will be unset if reg is reused
941 // unless it's a two-address operand.
942 if (TID->getOperandConstraint(i, TOI::TIED_TO) == -1)
943 MI.getOperand(i).setIsKill();
944 MI.getOperand(i).setReg(PhysReg);
945 UpdateKills(*prior(MII), RegKills, KillOps);
946 DOUT << '\t' << *prior(MII);
951 // If we have folded references to memory operands, make sure we clear all
952 // physical registers that may contain the value of the spilled virtual
954 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
955 DOUT << "Folded vreg: " << I->second.first << " MR: "
957 unsigned VirtReg = I->second.first;
958 VirtRegMap::ModRef MR = I->second.second;
959 if (VRM.isAssignedReg(VirtReg)) {
960 DOUT << ": No stack slot!\n";
963 int SS = VRM.getStackSlot(VirtReg);
964 DOUT << " - StackSlot: " << SS << "\n";
966 // If this folded instruction is just a use, check to see if it's a
967 // straight load from the virt reg slot.
968 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
970 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
971 if (FrameIdx == SS) {
972 // If this spill slot is available, turn it into a copy (or nothing)
973 // instead of leaving it as a load!
974 if (unsigned InReg = Spills.getSpillSlotOrReMatPhysReg(SS)) {
975 DOUT << "Promoted Load To Copy: " << MI;
976 if (DestReg != InReg) {
977 MRI->copyRegToReg(MBB, &MI, DestReg, InReg,
978 MF.getSSARegMap()->getRegClass(VirtReg));
979 // Revisit the copy so we make sure to notice the effects of the
980 // operation on the destreg (either needing to RA it if it's
981 // virtual or needing to clobber any values if it's physical).
983 --NextMII; // backtrack to the copy.
986 DOUT << "Removing now-noop copy: " << MI;
988 VRM.RemoveFromFoldedVirtMap(&MI);
991 goto ProcessNextInst;
997 // If this reference is not a use, any previous store is now dead.
998 // Otherwise, the store to this stack slot is not dead anymore.
999 MachineInstr* DeadStore = MaybeDeadStores[SS];
1001 if (!(MR & VirtRegMap::isRef)) { // Previous store is dead.
1002 // If we get here, the store is dead, nuke it now.
1003 assert(VirtRegMap::isMod && "Can't be modref!");
1004 DOUT << "Removed dead store:\t" << *DeadStore;
1005 InvalidateKills(*DeadStore, RegKills, KillOps);
1006 MBB.erase(DeadStore);
1007 VRM.RemoveFromFoldedVirtMap(DeadStore);
1010 MaybeDeadStores[SS] = NULL;
1013 // If the spill slot value is available, and this is a new definition of
1014 // the value, the value is not available anymore.
1015 if (MR & VirtRegMap::isMod) {
1016 // Notice that the value in this stack slot has been modified.
1017 Spills.ModifyStackSlotOrReMat(SS);
1019 // If this is *just* a mod of the value, check to see if this is just a
1020 // store to the spill slot (i.e. the spill got merged into the copy). If
1021 // so, realize that the vreg is available now, and add the store to the
1022 // MaybeDeadStore info.
1024 if (!(MR & VirtRegMap::isRef)) {
1025 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
1026 assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
1027 "Src hasn't been allocated yet?");
1028 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark
1029 // this as a potentially dead store in case there is a subsequent
1030 // store into the stack slot without a read from it.
1031 MaybeDeadStores[StackSlot] = &MI;
1033 // If the stack slot value was previously available in some other
1034 // register, change it now. Otherwise, make the register available,
1036 Spills.addAvailable(StackSlot, &MI, SrcReg, false/*don't clobber*/);
1042 // Process all of the spilled defs.
1043 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
1044 MachineOperand &MO = MI.getOperand(i);
1045 if (MO.isRegister() && MO.getReg() && MO.isDef()) {
1046 unsigned VirtReg = MO.getReg();
1048 if (!MRegisterInfo::isVirtualRegister(VirtReg)) {
1049 // Check to see if this is a noop copy. If so, eliminate the
1050 // instruction before considering the dest reg to be changed.
1052 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
1054 DOUT << "Removing now-noop copy: " << MI;
1057 VRM.RemoveFromFoldedVirtMap(&MI);
1058 Spills.disallowClobberPhysReg(VirtReg);
1059 goto ProcessNextInst;
1062 // If it's not a no-op copy, it clobbers the value in the destreg.
1063 Spills.ClobberPhysReg(VirtReg);
1064 ReusedOperands.markClobbered(VirtReg);
1066 // Check to see if this instruction is a load from a stack slot into
1067 // a register. If so, this provides the stack slot value in the reg.
1069 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
1070 assert(DestReg == VirtReg && "Unknown load situation!");
1072 // Otherwise, if it wasn't available, remember that it is now!
1073 Spills.addAvailable(FrameIdx, &MI, DestReg);
1074 goto ProcessNextInst;
1080 // The only vregs left are stack slot definitions.
1081 int StackSlot = VRM.getStackSlot(VirtReg);
1082 const TargetRegisterClass *RC = MF.getSSARegMap()->getRegClass(VirtReg);
1084 // If this def is part of a two-address operand, make sure to execute
1085 // the store from the correct physical register.
1087 int TiedOp = MI.getInstrDescriptor()->findTiedToSrcOperand(i);
1089 PhysReg = MI.getOperand(TiedOp).getReg();
1091 PhysReg = VRM.getPhys(VirtReg);
1092 if (ReusedOperands.isClobbered(PhysReg)) {
1093 // Another def has taken the assigned physreg. It must have been a
1094 // use&def which got it due to reuse. Undo the reuse!
1095 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
1096 Spills, MaybeDeadStores, RegKills, KillOps, VRM);
1100 MF.setPhysRegUsed(PhysReg);
1101 ReusedOperands.markClobbered(PhysReg);
1102 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
1103 DOUT << "Store:\t" << *next(MII);
1104 MI.getOperand(i).setReg(PhysReg);
1106 // If there is a dead store to this stack slot, nuke it now.
1107 MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
1109 DOUT << "Removed dead store:\t" << *LastStore;
1111 InvalidateKills(*LastStore, RegKills, KillOps, &MI);
1112 MBB.erase(LastStore);
1113 VRM.RemoveFromFoldedVirtMap(LastStore);
1115 LastStore = next(MII);
1117 // If the stack slot value was previously available in some other
1118 // register, change it now. Otherwise, make the register available,
1120 Spills.ModifyStackSlotOrReMat(StackSlot);
1121 Spills.ClobberPhysReg(PhysReg);
1122 Spills.addAvailable(StackSlot, LastStore, PhysReg);
1125 // Check to see if this is a noop copy. If so, eliminate the
1126 // instruction before considering the dest reg to be changed.
1129 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
1131 DOUT << "Removing now-noop copy: " << MI;
1134 VRM.RemoveFromFoldedVirtMap(&MI);
1135 UpdateKills(*LastStore, RegKills, KillOps);
1136 goto ProcessNextInst;
1142 if (!Erased && !BackTracked)
1143 for (MachineBasicBlock::iterator II = MI; II != NextMII; ++II)
1144 UpdateKills(*II, RegKills, KillOps);
1150 llvm::Spiller* llvm::createSpiller() {
1151 switch (SpillerOpt) {
1152 default: assert(0 && "Unreachable!");
1154 return new LocalSpiller();
1156 return new SimpleSpiller();