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 ReMatId(MAX_STACK_SLOT+1) {
69 void VirtRegMap::grow() {
70 Virt2PhysMap.grow(MF.getSSARegMap()->getLastVirtReg());
71 Virt2StackSlotMap.grow(MF.getSSARegMap()->getLastVirtReg());
74 int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) {
75 assert(MRegisterInfo::isVirtualRegister(virtReg));
76 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
77 "attempt to assign stack slot to already spilled register");
78 const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg);
79 int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(),
81 Virt2StackSlotMap[virtReg] = frameIndex;
86 void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) {
87 assert(MRegisterInfo::isVirtualRegister(virtReg));
88 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
89 "attempt to assign stack slot to already spilled register");
90 Virt2StackSlotMap[virtReg] = frameIndex;
93 int VirtRegMap::assignVirtReMatId(unsigned virtReg) {
94 assert(MRegisterInfo::isVirtualRegister(virtReg));
95 assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT &&
96 "attempt to assign re-mat id to already spilled register");
97 Virt2StackSlotMap[virtReg] = ReMatId;
102 void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI,
103 unsigned OpNo, MachineInstr *NewMI) {
104 // Move previous memory references folded to new instruction.
105 MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI);
106 for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI),
107 E = MI2VirtMap.end(); I != E && I->first == OldMI; ) {
108 MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second));
109 MI2VirtMap.erase(I++);
113 const TargetInstrDescriptor *TID = OldMI->getInstrDescriptor();
114 if (TID->getOperandConstraint(OpNo, TOI::TIED_TO) != -1 ||
115 TID->findTiedToSrcOperand(OpNo) != -1) {
116 // Folded a two-address operand.
118 } else if (OldMI->getOperand(OpNo).isDef()) {
124 // add new memory reference
125 MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo)));
128 void VirtRegMap::print(std::ostream &OS) const {
129 const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo();
131 OS << "********** REGISTER MAP **********\n";
132 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
133 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) {
134 if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG)
135 OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n";
139 for (unsigned i = MRegisterInfo::FirstVirtualRegister,
140 e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i)
141 if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT)
142 OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n";
146 void VirtRegMap::dump() const {
151 //===----------------------------------------------------------------------===//
152 // Simple Spiller Implementation
153 //===----------------------------------------------------------------------===//
155 Spiller::~Spiller() {}
158 struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller {
159 bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM);
163 bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
164 DOUT << "********** REWRITE MACHINE CODE **********\n";
165 DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';
166 const TargetMachine &TM = MF.getTarget();
167 const MRegisterInfo &MRI = *TM.getRegisterInfo();
168 bool *PhysRegsUsed = MF.getUsedPhysregs();
170 // LoadedRegs - Keep track of which vregs are loaded, so that we only load
171 // each vreg once (in the case where a spilled vreg is used by multiple
172 // operands). This is always smaller than the number of operands to the
173 // current machine instr, so it should be small.
174 std::vector<unsigned> LoadedRegs;
176 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
178 DOUT << MBBI->getBasicBlock()->getName() << ":\n";
179 MachineBasicBlock &MBB = *MBBI;
180 for (MachineBasicBlock::iterator MII = MBB.begin(),
181 E = MBB.end(); MII != E; ++MII) {
182 MachineInstr &MI = *MII;
183 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
184 MachineOperand &MO = MI.getOperand(i);
185 if (MO.isRegister() && MO.getReg())
186 if (MRegisterInfo::isVirtualRegister(MO.getReg())) {
187 unsigned VirtReg = MO.getReg();
188 unsigned PhysReg = VRM.getPhys(VirtReg);
189 if (VRM.hasStackSlot(VirtReg)) {
190 int StackSlot = VRM.getStackSlot(VirtReg);
191 const TargetRegisterClass* RC =
192 MF.getSSARegMap()->getRegClass(VirtReg);
195 std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg)
196 == LoadedRegs.end()) {
197 MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
198 LoadedRegs.push_back(VirtReg);
200 DOUT << '\t' << *prior(MII);
204 MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
208 PhysRegsUsed[PhysReg] = true;
209 MI.getOperand(i).setReg(PhysReg);
211 PhysRegsUsed[MO.getReg()] = true;
222 //===----------------------------------------------------------------------===//
223 // Local Spiller Implementation
224 //===----------------------------------------------------------------------===//
227 /// LocalSpiller - This spiller does a simple pass over the machine basic
228 /// block to attempt to keep spills in registers as much as possible for
229 /// blocks that have low register pressure (the vreg may be spilled due to
230 /// register pressure in other blocks).
231 class VISIBILITY_HIDDEN LocalSpiller : public Spiller {
232 const MRegisterInfo *MRI;
233 const TargetInstrInfo *TII;
235 bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
236 MRI = MF.getTarget().getRegisterInfo();
237 TII = MF.getTarget().getInstrInfo();
238 DOUT << "\n**** Local spiller rewriting function '"
239 << MF.getFunction()->getName() << "':\n";
241 std::vector<MachineInstr *> ReMatedMIs;
242 for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
244 RewriteMBB(*MBB, VRM, ReMatedMIs);
245 for (unsigned i = 0, e = ReMatedMIs.size(); i != e; ++i)
246 delete ReMatedMIs[i];
250 void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM,
251 std::vector<MachineInstr*> &ReMatedMIs);
255 /// AvailableSpills - As the local spiller is scanning and rewriting an MBB from
256 /// top down, keep track of which spills slots are available in each register.
258 /// Note that not all physregs are created equal here. In particular, some
259 /// physregs are reloads that we are allowed to clobber or ignore at any time.
260 /// Other physregs are values that the register allocated program is using that
261 /// we cannot CHANGE, but we can read if we like. We keep track of this on a
262 /// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable
263 /// entries. The predicate 'canClobberPhysReg()' checks this bit and
264 /// addAvailable sets it if.
266 class VISIBILITY_HIDDEN AvailableSpills {
267 const MRegisterInfo *MRI;
268 const TargetInstrInfo *TII;
270 // SpillSlotsAvailable - This map keeps track of all of the spilled virtual
271 // register values that are still available, due to being loaded or stored to,
272 // but not invalidated yet. It also tracks the instructions that defined
273 // or used the register.
274 typedef std::pair<unsigned, std::vector<MachineInstr*> > SSInfo;
275 std::map<int, SSInfo> SpillSlotsAvailable;
277 // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating
278 // which stack slot values are currently held by a physreg. This is used to
279 // invalidate entries in SpillSlotsAvailable when a physreg is modified.
280 std::multimap<unsigned, int> PhysRegsAvailable;
282 void disallowClobberPhysRegOnly(unsigned PhysReg);
284 void ClobberPhysRegOnly(unsigned PhysReg);
286 AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii)
287 : MRI(mri), TII(tii) {
290 const MRegisterInfo *getRegInfo() const { return MRI; }
292 /// getSpillSlotPhysReg - If the specified stack slot is available in a
293 /// physical register, return that PhysReg, otherwise return 0. It also
294 /// returns by reference the instruction that either defines or last uses
296 unsigned getSpillSlotPhysReg(int Slot, MachineInstr *&SSMI) const {
297 std::map<int, SSInfo>::const_iterator I = SpillSlotsAvailable.find(Slot);
298 if (I != SpillSlotsAvailable.end()) {
299 if (!I->second.second.empty())
300 SSMI = I->second.second.back();
301 return I->second.first >> 1; // Remove the CanClobber bit.
306 /// addLastUse - Add the last use information of all stack slots whose
307 /// values are available in the specific register.
308 void addLastUse(unsigned PhysReg, MachineInstr *Use) {
309 std::multimap<unsigned, int>::iterator I =
310 PhysRegsAvailable.lower_bound(PhysReg);
311 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
312 int Slot = I->second;
315 std::map<int, SSInfo>::iterator II = SpillSlotsAvailable.find(Slot);
316 assert(II != SpillSlotsAvailable.end() && "Slot not available!");
317 unsigned Val = II->second.first;
318 assert((Val >> 1) == PhysReg && "Bidirectional map mismatch!");
319 // This can be true if there are multiple uses of the same register.
320 if (II->second.second.back() != Use)
321 II->second.second.push_back(Use);
325 /// removeLastUse - Remove the last use information of all stack slots whose
326 /// values are available in the specific register.
327 void removeLastUse(unsigned PhysReg, MachineInstr *Use) {
328 std::multimap<unsigned, int>::iterator I =
329 PhysRegsAvailable.lower_bound(PhysReg);
330 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
331 int Slot = I->second;
334 std::map<int, SSInfo>::iterator II = SpillSlotsAvailable.find(Slot);
335 assert(II != SpillSlotsAvailable.end() && "Slot not available!");
336 unsigned Val = II->second.first;
337 assert((Val >> 1) == PhysReg && "Bidirectional map mismatch!");
338 if (II->second.second.back() == Use)
339 II->second.second.pop_back();
343 /// addAvailable - Mark that the specified stack slot is available in the
344 /// specified physreg. If CanClobber is true, the physreg can be modified at
345 /// any time without changing the semantics of the program.
346 void addAvailable(int Slot, MachineInstr *MI, unsigned Reg,
347 bool CanClobber = true) {
348 // If this stack slot is thought to be available in some other physreg,
349 // remove its record.
350 ModifyStackSlot(Slot);
352 PhysRegsAvailable.insert(std::make_pair(Reg, Slot));
353 std::vector<MachineInstr*> DefUses;
354 DefUses.push_back(MI);
355 SpillSlotsAvailable[Slot] =
356 std::make_pair((Reg << 1) | (unsigned)CanClobber, DefUses);
358 if (Slot > VirtRegMap::MAX_STACK_SLOT)
359 DOUT << "Remembering RM#" << Slot-VirtRegMap::MAX_STACK_SLOT-1;
361 DOUT << "Remembering SS#" << Slot;
362 DOUT << " in physreg " << MRI->getName(Reg) << "\n";
365 /// canClobberPhysReg - Return true if the spiller is allowed to change the
366 /// value of the specified stackslot register if it desires. The specified
367 /// stack slot must be available in a physreg for this query to make sense.
368 bool canClobberPhysReg(int Slot) const {
369 assert(SpillSlotsAvailable.count(Slot) && "Slot not available!");
370 return SpillSlotsAvailable.find(Slot)->second.first & 1;
373 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
374 /// stackslot register. The register is still available but is no longer
375 /// allowed to be modifed.
376 void disallowClobberPhysReg(unsigned PhysReg);
378 /// ClobberPhysReg - This is called when the specified physreg changes
379 /// value. We use this to invalidate any info about stuff we thing lives in
380 /// it and any of its aliases.
381 void ClobberPhysReg(unsigned PhysReg);
383 /// ModifyStackSlot - This method is called when the value in a stack slot
384 /// changes. This removes information about which register the previous value
385 /// for this slot lives in (as the previous value is dead now).
386 void ModifyStackSlot(int Slot);
390 /// disallowClobberPhysRegOnly - Unset the CanClobber bit of the specified
391 /// stackslot register. The register is still available but is no longer
392 /// allowed to be modifed.
393 void AvailableSpills::disallowClobberPhysRegOnly(unsigned PhysReg) {
394 std::multimap<unsigned, int>::iterator I =
395 PhysRegsAvailable.lower_bound(PhysReg);
396 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
397 int Slot = I->second;
399 assert((SpillSlotsAvailable[Slot].first >> 1) == PhysReg &&
400 "Bidirectional map mismatch!");
401 SpillSlotsAvailable[Slot].first &= ~1;
402 DOUT << "PhysReg " << MRI->getName(PhysReg)
403 << " copied, it is available for use but can no longer be modified\n";
407 /// disallowClobberPhysReg - Unset the CanClobber bit of the specified
408 /// stackslot register and its aliases. The register and its aliases may
409 /// still available but is no longer allowed to be modifed.
410 void AvailableSpills::disallowClobberPhysReg(unsigned PhysReg) {
411 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
412 disallowClobberPhysRegOnly(*AS);
413 disallowClobberPhysRegOnly(PhysReg);
416 /// ClobberPhysRegOnly - This is called when the specified physreg changes
417 /// value. We use this to invalidate any info about stuff we thing lives in it.
418 void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) {
419 std::multimap<unsigned, int>::iterator I =
420 PhysRegsAvailable.lower_bound(PhysReg);
421 while (I != PhysRegsAvailable.end() && I->first == PhysReg) {
422 int Slot = I->second;
423 PhysRegsAvailable.erase(I++);
424 assert((SpillSlotsAvailable[Slot].first >> 1) == PhysReg &&
425 "Bidirectional map mismatch!");
426 SpillSlotsAvailable.erase(Slot);
427 DOUT << "PhysReg " << MRI->getName(PhysReg)
428 << " clobbered, invalidating ";
429 if (Slot > VirtRegMap::MAX_STACK_SLOT)
430 DOUT << "RM#" << Slot-VirtRegMap::MAX_STACK_SLOT-1 << "\n";
432 DOUT << "SS#" << Slot << "\n";
436 /// ClobberPhysReg - This is called when the specified physreg changes
437 /// value. We use this to invalidate any info about stuff we thing lives in
438 /// it and any of its aliases.
439 void AvailableSpills::ClobberPhysReg(unsigned PhysReg) {
440 for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS)
441 ClobberPhysRegOnly(*AS);
442 ClobberPhysRegOnly(PhysReg);
445 /// ModifyStackSlot - This method is called when the value in a stack slot
446 /// changes. This removes information about which register the previous value
447 /// for this slot lives in (as the previous value is dead now).
448 void AvailableSpills::ModifyStackSlot(int Slot) {
449 std::map<int, SSInfo>::iterator It = SpillSlotsAvailable.find(Slot);
450 if (It == SpillSlotsAvailable.end()) return;
451 unsigned Reg = It->second.first >> 1;
452 SpillSlotsAvailable.erase(It);
454 // This register may hold the value of multiple stack slots, only remove this
455 // stack slot from the set of values the register contains.
456 std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg);
458 assert(I != PhysRegsAvailable.end() && I->first == Reg &&
459 "Map inverse broken!");
460 if (I->second == Slot) break;
462 PhysRegsAvailable.erase(I);
467 // ReusedOp - For each reused operand, we keep track of a bit of information, in
468 // case we need to rollback upon processing a new operand. See comments below.
471 // The MachineInstr operand that reused an available value.
474 // StackSlot - The spill slot of the value being reused.
477 // PhysRegReused - The physical register the value was available in.
478 unsigned PhysRegReused;
480 // AssignedPhysReg - The physreg that was assigned for use by the reload.
481 unsigned AssignedPhysReg;
483 // VirtReg - The virtual register itself.
486 ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr,
488 : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr),
492 /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that
493 /// is reused instead of reloaded.
494 class VISIBILITY_HIDDEN ReuseInfo {
496 std::vector<ReusedOp> Reuses;
497 BitVector PhysRegsClobbered;
499 ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) {
500 PhysRegsClobbered.resize(mri->getNumRegs());
503 bool hasReuses() const {
504 return !Reuses.empty();
507 /// addReuse - If we choose to reuse a virtual register that is already
508 /// available instead of reloading it, remember that we did so.
509 void addReuse(unsigned OpNo, unsigned StackSlot,
510 unsigned PhysRegReused, unsigned AssignedPhysReg,
512 // If the reload is to the assigned register anyway, no undo will be
514 if (PhysRegReused == AssignedPhysReg) return;
516 // Otherwise, remember this.
517 Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused,
518 AssignedPhysReg, VirtReg));
521 void markClobbered(unsigned PhysReg) {
522 PhysRegsClobbered.set(PhysReg);
525 bool isClobbered(unsigned PhysReg) const {
526 return PhysRegsClobbered.test(PhysReg);
529 /// GetRegForReload - We are about to emit a reload into PhysReg. If there
530 /// is some other operand that is using the specified register, either pick
531 /// a new register to use, or evict the previous reload and use this reg.
532 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
533 AvailableSpills &Spills,
534 std::map<int, MachineInstr*> &MaybeDeadStores,
535 SmallSet<unsigned, 8> &Rejected) {
536 if (Reuses.empty()) return PhysReg; // This is most often empty.
538 for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) {
539 ReusedOp &Op = Reuses[ro];
540 // If we find some other reuse that was supposed to use this register
541 // exactly for its reload, we can change this reload to use ITS reload
542 // register. That is, unless its reload register has already been
543 // considered and subsequently rejected because it has also been reused
544 // by another operand.
545 if (Op.PhysRegReused == PhysReg &&
546 Rejected.count(Op.AssignedPhysReg) == 0) {
547 // Yup, use the reload register that we didn't use before.
548 unsigned NewReg = Op.AssignedPhysReg;
549 Rejected.insert(PhysReg);
550 return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores, Rejected);
552 // Otherwise, we might also have a problem if a previously reused
553 // value aliases the new register. If so, codegen the previous reload
555 unsigned PRRU = Op.PhysRegReused;
556 const MRegisterInfo *MRI = Spills.getRegInfo();
557 if (MRI->areAliases(PRRU, PhysReg)) {
558 // Okay, we found out that an alias of a reused register
559 // was used. This isn't good because it means we have
560 // to undo a previous reuse.
561 MachineBasicBlock *MBB = MI->getParent();
562 const TargetRegisterClass *AliasRC =
563 MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg);
565 // Copy Op out of the vector and remove it, we're going to insert an
566 // explicit load for it.
568 Reuses.erase(Reuses.begin()+ro);
570 // Ok, we're going to try to reload the assigned physreg into the
571 // slot that we were supposed to in the first place. However, that
572 // register could hold a reuse. Check to see if it conflicts or
573 // would prefer us to use a different register.
574 unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg,
575 MI, Spills, MaybeDeadStores, Rejected);
577 MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg,
578 NewOp.StackSlot, AliasRC);
579 Spills.ClobberPhysReg(NewPhysReg);
580 Spills.ClobberPhysReg(NewOp.PhysRegReused);
582 // Any stores to this stack slot are not dead anymore.
583 MaybeDeadStores.erase(NewOp.StackSlot);
585 MI->getOperand(NewOp.Operand).setReg(NewPhysReg);
587 Spills.addAvailable(NewOp.StackSlot, MI, NewPhysReg);
589 DEBUG(MachineBasicBlock::iterator MII = MI;
590 DOUT << '\t' << *prior(MII));
592 DOUT << "Reuse undone!\n";
595 // Finally, PhysReg is now available, go ahead and use it.
603 /// GetRegForReload - Helper for the above GetRegForReload(). Add a
604 /// 'Rejected' set to remember which registers have been considered and
605 /// rejected for the reload. This avoids infinite looping in case like
608 /// t2 <- assigned r0 for use by the reload but ended up reuse r1
609 /// t3 <- assigned r1 for use by the reload but ended up reuse r0
611 /// sees r1 is taken by t2, tries t2's reload register r0
612 /// sees r0 is taken by t3, tries t3's reload register r1
613 /// sees r1 is taken by t2, tries t2's reload register r0 ...
614 unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI,
615 AvailableSpills &Spills,
616 std::map<int, MachineInstr*> &MaybeDeadStores) {
617 SmallSet<unsigned, 8> Rejected;
618 return GetRegForReload(PhysReg, MI, Spills, MaybeDeadStores, Rejected);
624 /// rewriteMBB - Keep track of which spills are available even after the
625 /// register allocator is done with them. If possible, avoid reloading vregs.
626 void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM,
627 std::vector<MachineInstr*> &ReMatedMIs) {
629 DOUT << MBB.getBasicBlock()->getName() << ":\n";
631 // Spills - Keep track of which spilled values are available in physregs so
632 // that we can choose to reuse the physregs instead of emitting reloads.
633 AvailableSpills Spills(MRI, TII);
635 // MaybeDeadStores - When we need to write a value back into a stack slot,
636 // keep track of the inserted store. If the stack slot value is never read
637 // (because the value was used from some available register, for example), and
638 // subsequently stored to, the original store is dead. This map keeps track
639 // of inserted stores that are not used. If we see a subsequent store to the
640 // same stack slot, the original store is deleted.
641 std::map<int, MachineInstr*> MaybeDeadStores;
643 bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs();
645 for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
647 MachineInstr &MI = *MII;
648 MachineBasicBlock::iterator NextMII = MII; ++NextMII;
650 /// ReusedOperands - Keep track of operand reuse in case we need to undo
652 ReuseInfo ReusedOperands(MI, MRI);
654 // Loop over all of the implicit defs, clearing them from our available
656 const TargetInstrDescriptor *TID = MI.getInstrDescriptor();
658 // If this instruction is being rematerialized, just remove it!
659 if (TID->Flags & M_REMATERIALIZIBLE) {
661 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
662 MachineOperand &MO = MI.getOperand(i);
663 if (!MO.isRegister() || MO.getReg() == 0)
664 continue; // Ignore non-register operands.
665 if (MO.isDef() && !VRM.isReMaterialized(MO.getReg())) {
671 VRM.RemoveFromFoldedVirtMap(&MI);
672 ReMatedMIs.push_back(MI.removeFromParent());
678 const unsigned *ImpDef = TID->ImplicitDefs;
680 for ( ; *ImpDef; ++ImpDef) {
681 PhysRegsUsed[*ImpDef] = true;
682 ReusedOperands.markClobbered(*ImpDef);
683 Spills.ClobberPhysReg(*ImpDef);
687 // Process all of the spilled uses and all non spilled reg references.
688 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
689 MachineOperand &MO = MI.getOperand(i);
690 if (!MO.isRegister() || MO.getReg() == 0)
691 continue; // Ignore non-register operands.
693 if (MRegisterInfo::isPhysicalRegister(MO.getReg())) {
694 // Ignore physregs for spilling, but remember that it is used by this
696 PhysRegsUsed[MO.getReg()] = true;
697 ReusedOperands.markClobbered(MO.getReg());
701 assert(MRegisterInfo::isVirtualRegister(MO.getReg()) &&
702 "Not a virtual or a physical register?");
704 unsigned VirtReg = MO.getReg();
705 if (!VRM.hasStackSlot(VirtReg)) {
706 // This virtual register was assigned a physreg!
707 unsigned Phys = VRM.getPhys(VirtReg);
708 PhysRegsUsed[Phys] = true;
710 ReusedOperands.markClobbered(Phys);
711 MI.getOperand(i).setReg(Phys);
715 // This virtual register is now known to be a spilled value.
717 continue; // Handle defs in the loop below (handle use&def here though)
719 bool doReMat = VRM.isReMaterialized(VirtReg);
720 int StackSlot = VRM.getStackSlot(VirtReg);
723 // Check to see if this stack slot is available.
724 MachineInstr *SSMI = NULL;
725 if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot, SSMI))) {
726 // This spilled operand might be part of a two-address operand. If this
727 // is the case, then changing it will necessarily require changing the
728 // def part of the instruction as well. However, in some cases, we
729 // aren't allowed to modify the reused register. If none of these cases
731 bool CanReuse = true;
732 int ti = TID->getOperandConstraint(i, TOI::TIED_TO);
734 MI.getOperand(ti).isReg() &&
735 MI.getOperand(ti).getReg() == VirtReg) {
736 // Okay, we have a two address operand. We can reuse this physreg as
737 // long as we are allowed to clobber the value and there isn't an
738 // earlier def that has already clobbered the physreg.
739 CanReuse = Spills.canClobberPhysReg(StackSlot) &&
740 !ReusedOperands.isClobbered(PhysReg);
744 // If this stack slot value is already available, reuse it!
745 if (StackSlot > VirtRegMap::MAX_STACK_SLOT)
746 DOUT << "Reusing RM#" << StackSlot-VirtRegMap::MAX_STACK_SLOT-1;
748 DOUT << "Reusing SS#" << StackSlot;
749 DOUT << " from physreg "
750 << MRI->getName(PhysReg) << " for vreg"
751 << VirtReg <<" instead of reloading into physreg "
752 << MRI->getName(VRM.getPhys(VirtReg)) << "\n";
753 MI.getOperand(i).setReg(PhysReg);
755 // Extend the live range of the MI that last kill the register if
757 bool WasKill = false;
759 int UIdx = SSMI->findRegisterUseOperand(PhysReg, true);
761 MachineOperand &MOK = SSMI->getOperand(UIdx);
762 WasKill = MOK.isKill();
767 // Unless it's the use of a two-address code, transfer the kill
768 // of the reused register to this use.
770 MI.getOperand(i).setIsKill();
771 Spills.addLastUse(PhysReg, &MI);
774 // The only technical detail we have is that we don't know that
775 // PhysReg won't be clobbered by a reloaded stack slot that occurs
776 // later in the instruction. In particular, consider 'op V1, V2'.
777 // If V1 is available in physreg R0, we would choose to reuse it
778 // here, instead of reloading it into the register the allocator
779 // indicated (say R1). However, V2 might have to be reloaded
780 // later, and it might indicate that it needs to live in R0. When
781 // this occurs, we need to have information available that
782 // indicates it is safe to use R1 for the reload instead of R0.
784 // To further complicate matters, we might conflict with an alias,
785 // or R0 and R1 might not be compatible with each other. In this
786 // case, we actually insert a reload for V1 in R1, ensuring that
787 // we can get at R0 or its alias.
788 ReusedOperands.addReuse(i, StackSlot, PhysReg,
789 VRM.getPhys(VirtReg), VirtReg);
791 // Only mark it clobbered if this is a use&def operand.
792 ReusedOperands.markClobbered(PhysReg);
797 // Otherwise we have a situation where we have a two-address instruction
798 // whose mod/ref operand needs to be reloaded. This reload is already
799 // available in some register "PhysReg", but if we used PhysReg as the
800 // operand to our 2-addr instruction, the instruction would modify
801 // PhysReg. This isn't cool if something later uses PhysReg and expects
802 // to get its initial value.
804 // To avoid this problem, and to avoid doing a load right after a store,
805 // we emit a copy from PhysReg into the designated register for this
807 unsigned DesignatedReg = VRM.getPhys(VirtReg);
808 assert(DesignatedReg && "Must map virtreg to physreg!");
810 // Note that, if we reused a register for a previous operand, the
811 // register we want to reload into might not actually be
812 // available. If this occurs, use the register indicated by the
814 if (ReusedOperands.hasReuses())
815 DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI,
816 Spills, MaybeDeadStores);
818 // If the mapped designated register is actually the physreg we have
819 // incoming, we don't need to inserted a dead copy.
820 if (DesignatedReg == PhysReg) {
821 // If this stack slot value is already available, reuse it!
822 if (StackSlot > VirtRegMap::MAX_STACK_SLOT)
823 DOUT << "Reusing RM#" << StackSlot-VirtRegMap::MAX_STACK_SLOT-1;
825 DOUT << "Reusing SS#" << StackSlot;
826 DOUT << " from physreg " << MRI->getName(PhysReg) << " for vreg"
828 << " instead of reloading into same physreg.\n";
829 MI.getOperand(i).setReg(PhysReg);
830 ReusedOperands.markClobbered(PhysReg);
835 const TargetRegisterClass* RC =
836 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
838 PhysRegsUsed[DesignatedReg] = true;
839 ReusedOperands.markClobbered(DesignatedReg);
840 MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC);
842 // Extend the live range of the MI that last kill the register if
844 bool WasKill = false;
846 int UIdx = SSMI->findRegisterUseOperand(PhysReg, true);
848 MachineOperand &MOK = SSMI->getOperand(UIdx);
849 WasKill = MOK.isKill();
853 MachineInstr *CopyMI = prior(MII);
855 // Transfer kill to the next use.
856 int UIdx = CopyMI->findRegisterUseOperand(PhysReg);
858 MachineOperand &MOU = CopyMI->getOperand(UIdx);
861 Spills.addLastUse(PhysReg, CopyMI);
863 // This invalidates DesignatedReg.
864 Spills.ClobberPhysReg(DesignatedReg);
866 Spills.addAvailable(StackSlot, &MI, DesignatedReg);
867 MI.getOperand(i).setReg(DesignatedReg);
868 DOUT << '\t' << *prior(MII);
873 // Otherwise, reload it and remember that we have it.
874 PhysReg = VRM.getPhys(VirtReg);
875 assert(PhysReg && "Must map virtreg to physreg!");
876 const TargetRegisterClass* RC =
877 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
879 // Note that, if we reused a register for a previous operand, the
880 // register we want to reload into might not actually be
881 // available. If this occurs, use the register indicated by the
883 if (ReusedOperands.hasReuses())
884 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
885 Spills, MaybeDeadStores);
887 PhysRegsUsed[PhysReg] = true;
888 ReusedOperands.markClobbered(PhysReg);
890 MRI->reMaterialize(MBB, &MI, PhysReg, VRM.getReMaterializedMI(VirtReg));
892 MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
893 // This invalidates PhysReg.
894 Spills.ClobberPhysReg(PhysReg);
896 // Any stores to this stack slot are not dead anymore.
898 MaybeDeadStores.erase(StackSlot);
899 Spills.addAvailable(StackSlot, &MI, PhysReg);
900 // Assumes this is the last use. IsKill will be unset if reg is reused
901 // unless it's a two-address operand.
902 if (TID->getOperandConstraint(i, TOI::TIED_TO) == -1)
903 MI.getOperand(i).setIsKill();
905 MI.getOperand(i).setReg(PhysReg);
906 DOUT << '\t' << *prior(MII);
911 // If we have folded references to memory operands, make sure we clear all
912 // physical registers that may contain the value of the spilled virtual
914 VirtRegMap::MI2VirtMapTy::const_iterator I, End;
915 for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) {
916 DOUT << "Folded vreg: " << I->second.first << " MR: "
918 unsigned VirtReg = I->second.first;
919 VirtRegMap::ModRef MR = I->second.second;
920 if (!VRM.hasStackSlot(VirtReg)) {
921 DOUT << ": No stack slot!\n";
924 int SS = VRM.getStackSlot(VirtReg);
925 DOUT << " - StackSlot: " << SS << "\n";
927 // If this folded instruction is just a use, check to see if it's a
928 // straight load from the virt reg slot.
929 if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) {
931 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
932 if (FrameIdx == SS) {
933 // If this spill slot is available, turn it into a copy (or nothing)
934 // instead of leaving it as a load!
935 MachineInstr *SSMI = NULL;
936 if (unsigned InReg = Spills.getSpillSlotPhysReg(SS, SSMI)) {
937 DOUT << "Promoted Load To Copy: " << MI;
938 MachineFunction &MF = *MBB.getParent();
939 if (DestReg != InReg) {
940 MRI->copyRegToReg(MBB, &MI, DestReg, InReg,
941 MF.getSSARegMap()->getRegClass(VirtReg));
942 // Revisit the copy so we make sure to notice the effects of the
943 // operation on the destreg (either needing to RA it if it's
944 // virtual or needing to clobber any values if it's physical).
946 --NextMII; // backtrack to the copy.
948 DOUT << "Removing now-noop copy: " << MI;
950 // Either way, the live range of the last kill of InReg has been
951 // extended. Remove its kill.
952 bool WasKill = false;
954 int UIdx = SSMI->findRegisterUseOperand(InReg, true);
956 MachineOperand &MOK = SSMI->getOperand(UIdx);
957 WasKill = MOK.isKill();
961 if (NextMII != MBB.end()) {
962 // If NextMII uses InReg and the use is not a two address
963 // operand, mark it killed.
964 int UIdx = NextMII->findRegisterUseOperand(InReg);
966 MachineOperand &MOU = NextMII->getOperand(UIdx);
968 const TargetInstrDescriptor *NTID =
969 NextMII->getInstrDescriptor();
970 if (UIdx >= NTID->numOperands ||
971 NTID->getOperandConstraint(UIdx, TOI::TIED_TO) == -1)
974 Spills.addLastUse(InReg, &(*NextMII));
978 VRM.RemoveFromFoldedVirtMap(&MI);
980 goto ProcessNextInst;
986 // If this reference is not a use, any previous store is now dead.
987 // Otherwise, the store to this stack slot is not dead anymore.
988 std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS);
989 if (MDSI != MaybeDeadStores.end()) {
990 if (MR & VirtRegMap::isRef) // Previous store is not dead.
991 MaybeDeadStores.erase(MDSI);
993 // If we get here, the store is dead, nuke it now.
994 assert(VirtRegMap::isMod && "Can't be modref!");
995 DOUT << "Removed dead store:\t" << *MDSI->second;
996 MBB.erase(MDSI->second);
997 VRM.RemoveFromFoldedVirtMap(MDSI->second);
998 MaybeDeadStores.erase(MDSI);
1003 // If the spill slot value is available, and this is a new definition of
1004 // the value, the value is not available anymore.
1005 if (MR & VirtRegMap::isMod) {
1006 // Notice that the value in this stack slot has been modified.
1007 Spills.ModifyStackSlot(SS);
1009 // If this is *just* a mod of the value, check to see if this is just a
1010 // store to the spill slot (i.e. the spill got merged into the copy). If
1011 // so, realize that the vreg is available now, and add the store to the
1012 // MaybeDeadStore info.
1014 if (!(MR & VirtRegMap::isRef)) {
1015 if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) {
1016 assert(MRegisterInfo::isPhysicalRegister(SrcReg) &&
1017 "Src hasn't been allocated yet?");
1018 // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark
1019 // this as a potentially dead store in case there is a subsequent
1020 // store into the stack slot without a read from it.
1021 MaybeDeadStores[StackSlot] = &MI;
1023 // If the stack slot value was previously available in some other
1024 // register, change it now. Otherwise, make the register available,
1026 Spills.addAvailable(StackSlot, &MI, SrcReg, false/*don't clobber*/);
1032 // Process all of the spilled defs.
1033 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
1034 MachineOperand &MO = MI.getOperand(i);
1035 if (MO.isRegister() && MO.getReg() && MO.isDef()) {
1036 unsigned VirtReg = MO.getReg();
1038 if (!MRegisterInfo::isVirtualRegister(VirtReg)) {
1039 // Check to see if this is a noop copy. If so, eliminate the
1040 // instruction before considering the dest reg to be changed.
1042 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
1044 DOUT << "Removing now-noop copy: " << MI;
1045 Spills.removeLastUse(Src, &MI);
1047 VRM.RemoveFromFoldedVirtMap(&MI);
1048 Spills.disallowClobberPhysReg(VirtReg);
1049 goto ProcessNextInst;
1052 // If it's not a no-op copy, it clobbers the value in the destreg.
1053 Spills.ClobberPhysReg(VirtReg);
1054 ReusedOperands.markClobbered(VirtReg);
1056 // Check to see if this instruction is a load from a stack slot into
1057 // a register. If so, this provides the stack slot value in the reg.
1059 if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) {
1060 assert(DestReg == VirtReg && "Unknown load situation!");
1062 // Otherwise, if it wasn't available, remember that it is now!
1063 Spills.addAvailable(FrameIdx, &MI, DestReg);
1064 goto ProcessNextInst;
1070 // The only vregs left are stack slot definitions.
1071 int StackSlot = VRM.getStackSlot(VirtReg);
1072 const TargetRegisterClass *RC =
1073 MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);
1075 // If this def is part of a two-address operand, make sure to execute
1076 // the store from the correct physical register.
1078 int TiedOp = MI.getInstrDescriptor()->findTiedToSrcOperand(i);
1080 PhysReg = MI.getOperand(TiedOp).getReg();
1082 PhysReg = VRM.getPhys(VirtReg);
1083 if (ReusedOperands.isClobbered(PhysReg)) {
1084 // Another def has taken the assigned physreg. It must have been a
1085 // use&def which got it due to reuse. Undo the reuse!
1086 PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI,
1087 Spills, MaybeDeadStores);
1091 PhysRegsUsed[PhysReg] = true;
1092 ReusedOperands.markClobbered(PhysReg);
1093 MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC);
1094 DOUT << "Store:\t" << *next(MII);
1095 MI.getOperand(i).setReg(PhysReg);
1097 // If there is a dead store to this stack slot, nuke it now.
1098 MachineInstr *&LastStore = MaybeDeadStores[StackSlot];
1100 DOUT << "Removed dead store:\t" << *LastStore;
1102 MBB.erase(LastStore);
1103 VRM.RemoveFromFoldedVirtMap(LastStore);
1105 LastStore = next(MII);
1107 // If the stack slot value was previously available in some other
1108 // register, change it now. Otherwise, make the register available,
1110 Spills.ModifyStackSlot(StackSlot);
1111 Spills.ClobberPhysReg(PhysReg);
1112 Spills.addAvailable(StackSlot, LastStore, PhysReg);
1115 // Check to see if this is a noop copy. If so, eliminate the
1116 // instruction before considering the dest reg to be changed.
1119 if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) {
1121 DOUT << "Removing now-noop copy: " << MI;
1122 Spills.removeLastUse(Src, &MI);
1124 VRM.RemoveFromFoldedVirtMap(&MI);
1125 goto ProcessNextInst;
1137 llvm::Spiller* llvm::createSpiller() {
1138 switch (SpillerOpt) {
1139 default: assert(0 && "Unreachable!");
1141 return new LocalSpiller();
1143 return new SimpleSpiller();