1 //===-- RegAllocFast.cpp - A fast register allocator for debug code -------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This register allocator allocates registers to a basic block at a time,
11 // attempting to keep values in registers and reusing registers as appropriate.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "regalloc"
16 #include "RegisterClassInfo.h"
17 #include "llvm/BasicBlock.h"
18 #include "llvm/CodeGen/MachineFunctionPass.h"
19 #include "llvm/CodeGen/MachineInstr.h"
20 #include "llvm/CodeGen/MachineInstrBuilder.h"
21 #include "llvm/CodeGen/MachineFrameInfo.h"
22 #include "llvm/CodeGen/MachineRegisterInfo.h"
23 #include "llvm/CodeGen/Passes.h"
24 #include "llvm/CodeGen/RegAllocRegistry.h"
25 #include "llvm/Target/TargetInstrInfo.h"
26 #include "llvm/Target/TargetMachine.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/ADT/DenseMap.h"
32 #include "llvm/ADT/IndexedMap.h"
33 #include "llvm/ADT/SmallSet.h"
34 #include "llvm/ADT/SmallVector.h"
35 #include "llvm/ADT/SparseSet.h"
36 #include "llvm/ADT/Statistic.h"
37 #include "llvm/ADT/STLExtras.h"
41 STATISTIC(NumStores, "Number of stores added");
42 STATISTIC(NumLoads , "Number of loads added");
43 STATISTIC(NumCopies, "Number of copies coalesced");
45 static RegisterRegAlloc
46 fastRegAlloc("fast", "fast register allocator", createFastRegisterAllocator);
49 class RAFast : public MachineFunctionPass {
52 RAFast() : MachineFunctionPass(ID), StackSlotForVirtReg(-1),
53 isBulkSpilling(false) {}
55 const TargetMachine *TM;
57 MachineRegisterInfo *MRI;
58 const TargetRegisterInfo *TRI;
59 const TargetInstrInfo *TII;
60 RegisterClassInfo RegClassInfo;
62 // Basic block currently being allocated.
63 MachineBasicBlock *MBB;
65 // StackSlotForVirtReg - Maps virtual regs to the frame index where these
66 // values are spilled.
67 IndexedMap<int, VirtReg2IndexFunctor> StackSlotForVirtReg;
69 // Everything we know about a live virtual register.
71 MachineInstr *LastUse; // Last instr to use reg.
72 unsigned VirtReg; // Virtual register number.
73 unsigned PhysReg; // Currently held here.
74 unsigned short LastOpNum; // OpNum on LastUse.
75 bool Dirty; // Register needs spill.
77 explicit LiveReg(unsigned v)
78 : LastUse(0), VirtReg(v), PhysReg(0), LastOpNum(0), Dirty(false) {}
80 unsigned getSparseSetIndex() const {
81 return TargetRegisterInfo::virtReg2Index(VirtReg);
85 typedef SparseSet<LiveReg> LiveRegMap;
87 // LiveVirtRegs - This map contains entries for each virtual register
88 // that is currently available in a physical register.
89 LiveRegMap LiveVirtRegs;
91 DenseMap<unsigned, SmallVector<MachineInstr *, 4> > LiveDbgValueMap;
93 // RegState - Track the state of a physical register.
95 // A disabled register is not available for allocation, but an alias may
96 // be in use. A register can only be moved out of the disabled state if
97 // all aliases are disabled.
100 // A free register is not currently in use and can be allocated
101 // immediately without checking aliases.
104 // A reserved register has been assigned explicitly (e.g., setting up a
105 // call parameter), and it remains reserved until it is used.
108 // A register state may also be a virtual register number, indication that
109 // the physical register is currently allocated to a virtual register. In
110 // that case, LiveVirtRegs contains the inverse mapping.
113 // PhysRegState - One of the RegState enums, or a virtreg.
114 std::vector<unsigned> PhysRegState;
116 // UsedInInstr - BitVector of physregs that are used in the current
117 // instruction, and so cannot be allocated.
118 BitVector UsedInInstr;
120 // SkippedInstrs - Descriptors of instructions whose clobber list was
121 // ignored because all registers were spilled. It is still necessary to
122 // mark all the clobbered registers as used by the function.
123 SmallPtrSet<const MCInstrDesc*, 4> SkippedInstrs;
125 // isBulkSpilling - This flag is set when LiveRegMap will be cleared
126 // completely after spilling all live registers. LiveRegMap entries should
133 spillImpossible = ~0u
136 virtual const char *getPassName() const {
137 return "Fast Register Allocator";
140 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
141 AU.setPreservesCFG();
142 MachineFunctionPass::getAnalysisUsage(AU);
146 bool runOnMachineFunction(MachineFunction &Fn);
147 void AllocateBasicBlock();
148 void handleThroughOperands(MachineInstr *MI,
149 SmallVectorImpl<unsigned> &VirtDead);
150 int getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC);
151 bool isLastUseOfLocalReg(MachineOperand&);
153 void addKillFlag(const LiveReg&);
154 void killVirtReg(LiveRegMap::iterator);
155 void killVirtReg(unsigned VirtReg);
156 void spillVirtReg(MachineBasicBlock::iterator MI, LiveRegMap::iterator);
157 void spillVirtReg(MachineBasicBlock::iterator MI, unsigned VirtReg);
159 void usePhysReg(MachineOperand&);
160 void definePhysReg(MachineInstr *MI, unsigned PhysReg, RegState NewState);
161 unsigned calcSpillCost(unsigned PhysReg) const;
162 void assignVirtToPhysReg(LiveReg&, unsigned PhysReg);
163 LiveRegMap::iterator findLiveVirtReg(unsigned VirtReg) {
164 return LiveVirtRegs.find(TargetRegisterInfo::virtReg2Index(VirtReg));
166 LiveRegMap::const_iterator findLiveVirtReg(unsigned VirtReg) const {
167 return LiveVirtRegs.find(TargetRegisterInfo::virtReg2Index(VirtReg));
169 LiveRegMap::iterator assignVirtToPhysReg(unsigned VReg, unsigned PhysReg);
170 LiveRegMap::iterator allocVirtReg(MachineInstr *MI, LiveRegMap::iterator,
172 LiveRegMap::iterator defineVirtReg(MachineInstr *MI, unsigned OpNum,
173 unsigned VirtReg, unsigned Hint);
174 LiveRegMap::iterator reloadVirtReg(MachineInstr *MI, unsigned OpNum,
175 unsigned VirtReg, unsigned Hint);
176 void spillAll(MachineInstr *MI);
177 bool setPhysReg(MachineInstr *MI, unsigned OpNum, unsigned PhysReg);
178 void addRetOperands(MachineBasicBlock *MBB);
183 /// getStackSpaceFor - This allocates space for the specified virtual register
184 /// to be held on the stack.
185 int RAFast::getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC) {
186 // Find the location Reg would belong...
187 int SS = StackSlotForVirtReg[VirtReg];
189 return SS; // Already has space allocated?
191 // Allocate a new stack object for this spill location...
192 int FrameIdx = MF->getFrameInfo()->CreateSpillStackObject(RC->getSize(),
196 StackSlotForVirtReg[VirtReg] = FrameIdx;
200 /// isLastUseOfLocalReg - Return true if MO is the only remaining reference to
201 /// its virtual register, and it is guaranteed to be a block-local register.
203 bool RAFast::isLastUseOfLocalReg(MachineOperand &MO) {
204 // Check for non-debug uses or defs following MO.
205 // This is the most likely way to fail - fast path it.
206 MachineOperand *Next = &MO;
207 while ((Next = Next->getNextOperandForReg()))
208 if (!Next->isDebug())
211 // If the register has ever been spilled or reloaded, we conservatively assume
212 // it is a global register used in multiple blocks.
213 if (StackSlotForVirtReg[MO.getReg()] != -1)
216 // Check that the use/def chain has exactly one operand - MO.
217 return &MRI->reg_nodbg_begin(MO.getReg()).getOperand() == &MO;
220 /// addKillFlag - Set kill flags on last use of a virtual register.
221 void RAFast::addKillFlag(const LiveReg &LR) {
222 if (!LR.LastUse) return;
223 MachineOperand &MO = LR.LastUse->getOperand(LR.LastOpNum);
224 if (MO.isUse() && !LR.LastUse->isRegTiedToDefOperand(LR.LastOpNum)) {
225 if (MO.getReg() == LR.PhysReg)
228 LR.LastUse->addRegisterKilled(LR.PhysReg, TRI, true);
232 /// killVirtReg - Mark virtreg as no longer available.
233 void RAFast::killVirtReg(LiveRegMap::iterator LRI) {
235 assert(PhysRegState[LRI->PhysReg] == LRI->VirtReg &&
236 "Broken RegState mapping");
237 PhysRegState[LRI->PhysReg] = regFree;
238 // Erase from LiveVirtRegs unless we're spilling in bulk.
240 LiveVirtRegs.erase(LRI);
243 /// killVirtReg - Mark virtreg as no longer available.
244 void RAFast::killVirtReg(unsigned VirtReg) {
245 assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
246 "killVirtReg needs a virtual register");
247 LiveRegMap::iterator LRI = findLiveVirtReg(VirtReg);
248 if (LRI != LiveVirtRegs.end())
252 /// spillVirtReg - This method spills the value specified by VirtReg into the
253 /// corresponding stack slot if needed.
254 void RAFast::spillVirtReg(MachineBasicBlock::iterator MI, unsigned VirtReg) {
255 assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
256 "Spilling a physical register is illegal!");
257 LiveRegMap::iterator LRI = findLiveVirtReg(VirtReg);
258 assert(LRI != LiveVirtRegs.end() && "Spilling unmapped virtual register");
259 spillVirtReg(MI, LRI);
262 /// spillVirtReg - Do the actual work of spilling.
263 void RAFast::spillVirtReg(MachineBasicBlock::iterator MI,
264 LiveRegMap::iterator LRI) {
266 assert(PhysRegState[LR.PhysReg] == LRI->VirtReg && "Broken RegState mapping");
269 // If this physreg is used by the instruction, we want to kill it on the
270 // instruction, not on the spill.
271 bool SpillKill = LR.LastUse != MI;
273 DEBUG(dbgs() << "Spilling " << PrintReg(LRI->VirtReg, TRI)
274 << " in " << PrintReg(LR.PhysReg, TRI));
275 const TargetRegisterClass *RC = MRI->getRegClass(LRI->VirtReg);
276 int FI = getStackSpaceFor(LRI->VirtReg, RC);
277 DEBUG(dbgs() << " to stack slot #" << FI << "\n");
278 TII->storeRegToStackSlot(*MBB, MI, LR.PhysReg, SpillKill, FI, RC, TRI);
279 ++NumStores; // Update statistics
281 // If this register is used by DBG_VALUE then insert new DBG_VALUE to
282 // identify spilled location as the place to find corresponding variable's
284 SmallVector<MachineInstr *, 4> &LRIDbgValues =
285 LiveDbgValueMap[LRI->VirtReg];
286 for (unsigned li = 0, le = LRIDbgValues.size(); li != le; ++li) {
287 MachineInstr *DBG = LRIDbgValues[li];
288 const MDNode *MDPtr =
289 DBG->getOperand(DBG->getNumOperands()-1).getMetadata();
291 if (DBG->getOperand(1).isImm())
292 Offset = DBG->getOperand(1).getImm();
294 if (MI == MBB->end()) {
295 // If MI is at basic block end then use last instruction's location.
296 MachineBasicBlock::iterator EI = MI;
297 DL = (--EI)->getDebugLoc();
300 DL = MI->getDebugLoc();
301 if (MachineInstr *NewDV =
302 TII->emitFrameIndexDebugValue(*MF, FI, Offset, MDPtr, DL)) {
303 MachineBasicBlock *MBB = DBG->getParent();
304 MBB->insert(MI, NewDV);
305 DEBUG(dbgs() << "Inserting debug info due to spill:" << "\n" << *NewDV);
308 // Now this register is spilled there is should not be any DBG_VALUE
309 // pointing to this register because they are all pointing to spilled value
311 LRIDbgValues.clear();
313 LR.LastUse = 0; // Don't kill register again
318 /// spillAll - Spill all dirty virtregs without killing them.
319 void RAFast::spillAll(MachineInstr *MI) {
320 if (LiveVirtRegs.empty()) return;
321 isBulkSpilling = true;
322 // The LiveRegMap is keyed by an unsigned (the virtreg number), so the order
323 // of spilling here is deterministic, if arbitrary.
324 for (LiveRegMap::iterator i = LiveVirtRegs.begin(), e = LiveVirtRegs.end();
327 LiveVirtRegs.clear();
328 isBulkSpilling = false;
331 /// usePhysReg - Handle the direct use of a physical register.
332 /// Check that the register is not used by a virtreg.
333 /// Kill the physreg, marking it free.
334 /// This may add implicit kills to MO->getParent() and invalidate MO.
335 void RAFast::usePhysReg(MachineOperand &MO) {
336 unsigned PhysReg = MO.getReg();
337 assert(TargetRegisterInfo::isPhysicalRegister(PhysReg) &&
338 "Bad usePhysReg operand");
340 switch (PhysRegState[PhysReg]) {
344 PhysRegState[PhysReg] = regFree;
347 UsedInInstr.set(PhysReg);
351 // The physreg was allocated to a virtual register. That means the value we
352 // wanted has been clobbered.
353 llvm_unreachable("Instruction uses an allocated register");
356 // Maybe a superregister is reserved?
357 for (const uint16_t *AS = TRI->getAliasSet(PhysReg);
358 unsigned Alias = *AS; ++AS) {
359 switch (PhysRegState[Alias]) {
363 assert(TRI->isSuperRegister(PhysReg, Alias) &&
364 "Instruction is not using a subregister of a reserved register");
365 // Leave the superregister in the working set.
366 PhysRegState[Alias] = regFree;
367 UsedInInstr.set(Alias);
368 MO.getParent()->addRegisterKilled(Alias, TRI, true);
371 if (TRI->isSuperRegister(PhysReg, Alias)) {
372 // Leave the superregister in the working set.
373 UsedInInstr.set(Alias);
374 MO.getParent()->addRegisterKilled(Alias, TRI, true);
377 // Some other alias was in the working set - clear it.
378 PhysRegState[Alias] = regDisabled;
381 llvm_unreachable("Instruction uses an alias of an allocated register");
385 // All aliases are disabled, bring register into working set.
386 PhysRegState[PhysReg] = regFree;
387 UsedInInstr.set(PhysReg);
391 /// definePhysReg - Mark PhysReg as reserved or free after spilling any
392 /// virtregs. This is very similar to defineVirtReg except the physreg is
393 /// reserved instead of allocated.
394 void RAFast::definePhysReg(MachineInstr *MI, unsigned PhysReg,
396 UsedInInstr.set(PhysReg);
397 switch (unsigned VirtReg = PhysRegState[PhysReg]) {
401 spillVirtReg(MI, VirtReg);
405 PhysRegState[PhysReg] = NewState;
409 // This is a disabled register, disable all aliases.
410 PhysRegState[PhysReg] = NewState;
411 for (const uint16_t *AS = TRI->getAliasSet(PhysReg);
412 unsigned Alias = *AS; ++AS) {
413 switch (unsigned VirtReg = PhysRegState[Alias]) {
417 spillVirtReg(MI, VirtReg);
421 PhysRegState[Alias] = regDisabled;
422 if (TRI->isSuperRegister(PhysReg, Alias))
430 // calcSpillCost - Return the cost of spilling clearing out PhysReg and
431 // aliases so it is free for allocation.
432 // Returns 0 when PhysReg is free or disabled with all aliases disabled - it
433 // can be allocated directly.
434 // Returns spillImpossible when PhysReg or an alias can't be spilled.
435 unsigned RAFast::calcSpillCost(unsigned PhysReg) const {
436 if (UsedInInstr.test(PhysReg)) {
437 DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " is already used in instr.\n");
438 return spillImpossible;
440 switch (unsigned VirtReg = PhysRegState[PhysReg]) {
446 DEBUG(dbgs() << PrintReg(VirtReg, TRI) << " corresponding "
447 << PrintReg(PhysReg, TRI) << " is reserved already.\n");
448 return spillImpossible;
450 LiveRegMap::const_iterator I = findLiveVirtReg(VirtReg);
451 assert(I != LiveVirtRegs.end() && "Missing VirtReg entry");
452 return I->Dirty ? spillDirty : spillClean;
456 // This is a disabled register, add up cost of aliases.
457 DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " is disabled.\n");
459 for (const uint16_t *AS = TRI->getAliasSet(PhysReg);
460 unsigned Alias = *AS; ++AS) {
461 if (UsedInInstr.test(Alias))
462 return spillImpossible;
463 switch (unsigned VirtReg = PhysRegState[Alias]) {
470 return spillImpossible;
472 LiveRegMap::const_iterator I = findLiveVirtReg(VirtReg);
473 assert(I != LiveVirtRegs.end() && "Missing VirtReg entry");
474 Cost += I->Dirty ? spillDirty : spillClean;
483 /// assignVirtToPhysReg - This method updates local state so that we know
484 /// that PhysReg is the proper container for VirtReg now. The physical
485 /// register must not be used for anything else when this is called.
487 void RAFast::assignVirtToPhysReg(LiveReg &LR, unsigned PhysReg) {
488 DEBUG(dbgs() << "Assigning " << PrintReg(LR.VirtReg, TRI) << " to "
489 << PrintReg(PhysReg, TRI) << "\n");
490 PhysRegState[PhysReg] = LR.VirtReg;
491 assert(!LR.PhysReg && "Already assigned a physreg");
492 LR.PhysReg = PhysReg;
495 RAFast::LiveRegMap::iterator
496 RAFast::assignVirtToPhysReg(unsigned VirtReg, unsigned PhysReg) {
497 LiveRegMap::iterator LRI = findLiveVirtReg(VirtReg);
498 assert(LRI != LiveVirtRegs.end() && "VirtReg disappeared");
499 assignVirtToPhysReg(*LRI, PhysReg);
503 /// allocVirtReg - Allocate a physical register for VirtReg.
504 RAFast::LiveRegMap::iterator RAFast::allocVirtReg(MachineInstr *MI,
505 LiveRegMap::iterator LRI,
507 const unsigned VirtReg = LRI->VirtReg;
509 assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
510 "Can only allocate virtual registers");
512 const TargetRegisterClass *RC = MRI->getRegClass(VirtReg);
514 // Ignore invalid hints.
515 if (Hint && (!TargetRegisterInfo::isPhysicalRegister(Hint) ||
516 !RC->contains(Hint) || !RegClassInfo.isAllocatable(Hint)))
519 // Take hint when possible.
521 // Ignore the hint if we would have to spill a dirty register.
522 unsigned Cost = calcSpillCost(Hint);
523 if (Cost < spillDirty) {
525 definePhysReg(MI, Hint, regFree);
526 // definePhysReg may kill virtual registers and modify LiveVirtRegs.
527 // That invalidates LRI, so run a new lookup for VirtReg.
528 return assignVirtToPhysReg(VirtReg, Hint);
532 ArrayRef<unsigned> AO = RegClassInfo.getOrder(RC);
534 // First try to find a completely free register.
535 for (ArrayRef<unsigned>::iterator I = AO.begin(), E = AO.end(); I != E; ++I) {
536 unsigned PhysReg = *I;
537 if (PhysRegState[PhysReg] == regFree && !UsedInInstr.test(PhysReg)) {
538 assignVirtToPhysReg(*LRI, PhysReg);
543 DEBUG(dbgs() << "Allocating " << PrintReg(VirtReg) << " from "
544 << RC->getName() << "\n");
546 unsigned BestReg = 0, BestCost = spillImpossible;
547 for (ArrayRef<unsigned>::iterator I = AO.begin(), E = AO.end(); I != E; ++I) {
548 unsigned Cost = calcSpillCost(*I);
549 DEBUG(dbgs() << "\tRegister: " << PrintReg(*I, TRI) << "\n");
550 DEBUG(dbgs() << "\tCost: " << Cost << "\n");
551 DEBUG(dbgs() << "\tBestCost: " << BestCost << "\n");
552 // Cost is 0 when all aliases are already disabled.
554 assignVirtToPhysReg(*LRI, *I);
558 BestReg = *I, BestCost = Cost;
562 definePhysReg(MI, BestReg, regFree);
563 // definePhysReg may kill virtual registers and modify LiveVirtRegs.
564 // That invalidates LRI, so run a new lookup for VirtReg.
565 return assignVirtToPhysReg(VirtReg, BestReg);
568 // Nothing we can do. Report an error and keep going with a bad allocation.
569 MI->emitError("ran out of registers during register allocation");
570 definePhysReg(MI, *AO.begin(), regFree);
571 return assignVirtToPhysReg(VirtReg, *AO.begin());
574 /// defineVirtReg - Allocate a register for VirtReg and mark it as dirty.
575 RAFast::LiveRegMap::iterator
576 RAFast::defineVirtReg(MachineInstr *MI, unsigned OpNum,
577 unsigned VirtReg, unsigned Hint) {
578 assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
579 "Not a virtual register");
580 LiveRegMap::iterator LRI;
582 tie(LRI, New) = LiveVirtRegs.insert(LiveReg(VirtReg));
584 // If there is no hint, peek at the only use of this register.
585 if ((!Hint || !TargetRegisterInfo::isPhysicalRegister(Hint)) &&
586 MRI->hasOneNonDBGUse(VirtReg)) {
587 const MachineInstr &UseMI = *MRI->use_nodbg_begin(VirtReg);
588 // It's a copy, use the destination register as a hint.
589 if (UseMI.isCopyLike())
590 Hint = UseMI.getOperand(0).getReg();
592 LRI = allocVirtReg(MI, LRI, Hint);
593 } else if (LRI->LastUse) {
594 // Redefining a live register - kill at the last use, unless it is this
595 // instruction defining VirtReg multiple times.
596 if (LRI->LastUse != MI || LRI->LastUse->getOperand(LRI->LastOpNum).isUse())
599 assert(LRI->PhysReg && "Register not assigned");
601 LRI->LastOpNum = OpNum;
603 UsedInInstr.set(LRI->PhysReg);
607 /// reloadVirtReg - Make sure VirtReg is available in a physreg and return it.
608 RAFast::LiveRegMap::iterator
609 RAFast::reloadVirtReg(MachineInstr *MI, unsigned OpNum,
610 unsigned VirtReg, unsigned Hint) {
611 assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
612 "Not a virtual register");
613 LiveRegMap::iterator LRI;
615 tie(LRI, New) = LiveVirtRegs.insert(LiveReg(VirtReg));
616 MachineOperand &MO = MI->getOperand(OpNum);
618 LRI = allocVirtReg(MI, LRI, Hint);
619 const TargetRegisterClass *RC = MRI->getRegClass(VirtReg);
620 int FrameIndex = getStackSpaceFor(VirtReg, RC);
621 DEBUG(dbgs() << "Reloading " << PrintReg(VirtReg, TRI) << " into "
622 << PrintReg(LRI->PhysReg, TRI) << "\n");
623 TII->loadRegFromStackSlot(*MBB, MI, LRI->PhysReg, FrameIndex, RC, TRI);
625 } else if (LRI->Dirty) {
626 if (isLastUseOfLocalReg(MO)) {
627 DEBUG(dbgs() << "Killing last use: " << MO << "\n");
632 } else if (MO.isKill()) {
633 DEBUG(dbgs() << "Clearing dubious kill: " << MO << "\n");
635 } else if (MO.isDead()) {
636 DEBUG(dbgs() << "Clearing dubious dead: " << MO << "\n");
639 } else if (MO.isKill()) {
640 // We must remove kill flags from uses of reloaded registers because the
641 // register would be killed immediately, and there might be a second use:
642 // %foo = OR %x<kill>, %x
643 // This would cause a second reload of %x into a different register.
644 DEBUG(dbgs() << "Clearing clean kill: " << MO << "\n");
646 } else if (MO.isDead()) {
647 DEBUG(dbgs() << "Clearing clean dead: " << MO << "\n");
650 assert(LRI->PhysReg && "Register not assigned");
652 LRI->LastOpNum = OpNum;
653 UsedInInstr.set(LRI->PhysReg);
657 // setPhysReg - Change operand OpNum in MI the refer the PhysReg, considering
658 // subregs. This may invalidate any operand pointers.
659 // Return true if the operand kills its register.
660 bool RAFast::setPhysReg(MachineInstr *MI, unsigned OpNum, unsigned PhysReg) {
661 MachineOperand &MO = MI->getOperand(OpNum);
662 bool Dead = MO.isDead();
663 if (!MO.getSubReg()) {
665 return MO.isKill() || Dead;
668 // Handle subregister index.
669 MO.setReg(PhysReg ? TRI->getSubReg(PhysReg, MO.getSubReg()) : 0);
672 // A kill flag implies killing the full register. Add corresponding super
675 MI->addRegisterKilled(PhysReg, TRI, true);
679 // A <def,read-undef> of a sub-register requires an implicit def of the full
681 if (MO.isDef() && MO.isUndef())
682 MI->addRegisterDefined(PhysReg, TRI);
687 // Handle special instruction operand like early clobbers and tied ops when
688 // there are additional physreg defines.
689 void RAFast::handleThroughOperands(MachineInstr *MI,
690 SmallVectorImpl<unsigned> &VirtDead) {
691 DEBUG(dbgs() << "Scanning for through registers:");
692 SmallSet<unsigned, 8> ThroughRegs;
693 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
694 MachineOperand &MO = MI->getOperand(i);
695 if (!MO.isReg()) continue;
696 unsigned Reg = MO.getReg();
697 if (!TargetRegisterInfo::isVirtualRegister(Reg))
699 if (MO.isEarlyClobber() || MI->isRegTiedToDefOperand(i) ||
700 (MO.getSubReg() && MI->readsVirtualRegister(Reg))) {
701 if (ThroughRegs.insert(Reg))
702 DEBUG(dbgs() << ' ' << PrintReg(Reg));
706 // If any physreg defines collide with preallocated through registers,
707 // we must spill and reallocate.
708 DEBUG(dbgs() << "\nChecking for physdef collisions.\n");
709 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
710 MachineOperand &MO = MI->getOperand(i);
711 if (!MO.isReg() || !MO.isDef()) continue;
712 unsigned Reg = MO.getReg();
713 if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
714 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
715 UsedInInstr.set(*AI);
716 if (ThroughRegs.count(PhysRegState[*AI]))
717 definePhysReg(MI, *AI, regFree);
721 SmallVector<unsigned, 8> PartialDefs;
722 DEBUG(dbgs() << "Allocating tied uses.\n");
723 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
724 MachineOperand &MO = MI->getOperand(i);
725 if (!MO.isReg()) continue;
726 unsigned Reg = MO.getReg();
727 if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
730 if (!MI->isRegTiedToDefOperand(i, &DefIdx)) continue;
731 DEBUG(dbgs() << "Operand " << i << "("<< MO << ") is tied to operand "
733 LiveRegMap::iterator LRI = reloadVirtReg(MI, i, Reg, 0);
734 unsigned PhysReg = LRI->PhysReg;
735 setPhysReg(MI, i, PhysReg);
736 // Note: we don't update the def operand yet. That would cause the normal
737 // def-scan to attempt spilling.
738 } else if (MO.getSubReg() && MI->readsVirtualRegister(Reg)) {
739 DEBUG(dbgs() << "Partial redefine: " << MO << "\n");
740 // Reload the register, but don't assign to the operand just yet.
741 // That would confuse the later phys-def processing pass.
742 LiveRegMap::iterator LRI = reloadVirtReg(MI, i, Reg, 0);
743 PartialDefs.push_back(LRI->PhysReg);
747 DEBUG(dbgs() << "Allocating early clobbers.\n");
748 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
749 MachineOperand &MO = MI->getOperand(i);
750 if (!MO.isReg()) continue;
751 unsigned Reg = MO.getReg();
752 if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
753 if (!MO.isEarlyClobber())
755 // Note: defineVirtReg may invalidate MO.
756 LiveRegMap::iterator LRI = defineVirtReg(MI, i, Reg, 0);
757 unsigned PhysReg = LRI->PhysReg;
758 if (setPhysReg(MI, i, PhysReg))
759 VirtDead.push_back(Reg);
762 // Restore UsedInInstr to a state usable for allocating normal virtual uses.
764 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
765 MachineOperand &MO = MI->getOperand(i);
766 if (!MO.isReg() || (MO.isDef() && !MO.isEarlyClobber())) continue;
767 unsigned Reg = MO.getReg();
768 if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
769 DEBUG(dbgs() << "\tSetting " << PrintReg(Reg, TRI)
770 << " as used in instr\n");
771 UsedInInstr.set(Reg);
774 // Also mark PartialDefs as used to avoid reallocation.
775 for (unsigned i = 0, e = PartialDefs.size(); i != e; ++i)
776 UsedInInstr.set(PartialDefs[i]);
779 /// addRetOperand - ensure that a return instruction has an operand for each
780 /// value live out of the function.
782 /// Things marked both call and return are tail calls; do not do this for them.
783 /// The tail callee need not take the same registers as input that it produces
784 /// as output, and there are dependencies for its input registers elsewhere.
786 /// FIXME: This should be done as part of instruction selection, and this helper
787 /// should be deleted. Until then, we use custom logic here to create the proper
788 /// operand under all circumstances. We can't use addRegisterKilled because that
789 /// doesn't make sense for undefined values. We can't simply avoid calling it
790 /// for undefined values, because we must ensure that the operand always exists.
791 void RAFast::addRetOperands(MachineBasicBlock *MBB) {
792 if (MBB->empty() || !MBB->back().isReturn() || MBB->back().isCall())
795 MachineInstr *MI = &MBB->back();
797 for (MachineRegisterInfo::liveout_iterator
798 I = MBB->getParent()->getRegInfo().liveout_begin(),
799 E = MBB->getParent()->getRegInfo().liveout_end(); I != E; ++I) {
801 assert(TargetRegisterInfo::isPhysicalRegister(Reg) &&
802 "Cannot have a live-out virtual register.");
804 bool hasDef = PhysRegState[Reg] == regReserved;
806 // Check if this register already has an operand.
808 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
809 MachineOperand &MO = MI->getOperand(i);
810 if (!MO.isReg() || !MO.isUse())
813 unsigned OperReg = MO.getReg();
814 if (!TargetRegisterInfo::isPhysicalRegister(OperReg))
817 if (OperReg == Reg || TRI->isSuperRegister(OperReg, Reg)) {
818 // If the ret already has an operand for this physreg or a superset,
819 // don't duplicate it. Set the kill flag if the value is defined.
820 if (hasDef && !MO.isKill())
827 MI->addOperand(MachineOperand::CreateReg(Reg,
834 void RAFast::AllocateBasicBlock() {
835 DEBUG(dbgs() << "\nAllocating " << *MBB);
837 PhysRegState.assign(TRI->getNumRegs(), regDisabled);
838 assert(LiveVirtRegs.empty() && "Mapping not cleared from last block?");
840 MachineBasicBlock::iterator MII = MBB->begin();
842 // Add live-in registers as live.
843 for (MachineBasicBlock::livein_iterator I = MBB->livein_begin(),
844 E = MBB->livein_end(); I != E; ++I)
845 if (RegClassInfo.isAllocatable(*I))
846 definePhysReg(MII, *I, regReserved);
848 SmallVector<unsigned, 8> VirtDead;
849 SmallVector<MachineInstr*, 32> Coalesced;
851 // Otherwise, sequentially allocate each instruction in the MBB.
852 while (MII != MBB->end()) {
853 MachineInstr *MI = MII++;
854 const MCInstrDesc &MCID = MI->getDesc();
856 dbgs() << "\n>> " << *MI << "Regs:";
857 for (unsigned Reg = 1, E = TRI->getNumRegs(); Reg != E; ++Reg) {
858 if (PhysRegState[Reg] == regDisabled) continue;
859 dbgs() << " " << TRI->getName(Reg);
860 switch(PhysRegState[Reg]) {
867 dbgs() << '=' << PrintReg(PhysRegState[Reg]);
868 LiveRegMap::iterator I = findLiveVirtReg(PhysRegState[Reg]);
869 assert(I != LiveVirtRegs.end() && "Missing VirtReg entry");
872 assert(I->PhysReg == Reg && "Bad inverse map");
878 // Check that LiveVirtRegs is the inverse.
879 for (LiveRegMap::iterator i = LiveVirtRegs.begin(),
880 e = LiveVirtRegs.end(); i != e; ++i) {
881 assert(TargetRegisterInfo::isVirtualRegister(i->VirtReg) &&
883 assert(TargetRegisterInfo::isPhysicalRegister(i->PhysReg) &&
885 assert(PhysRegState[i->PhysReg] == i->VirtReg && "Bad inverse map");
889 // Debug values are not allowed to change codegen in any way.
890 if (MI->isDebugValue()) {
891 bool ScanDbgValue = true;
892 while (ScanDbgValue) {
893 ScanDbgValue = false;
894 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
895 MachineOperand &MO = MI->getOperand(i);
896 if (!MO.isReg()) continue;
897 unsigned Reg = MO.getReg();
898 if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
899 LiveRegMap::iterator LRI = findLiveVirtReg(Reg);
900 if (LRI != LiveVirtRegs.end())
901 setPhysReg(MI, i, LRI->PhysReg);
903 int SS = StackSlotForVirtReg[Reg];
905 // We can't allocate a physreg for a DebugValue, sorry!
906 DEBUG(dbgs() << "Unable to allocate vreg used by DBG_VALUE");
910 // Modify DBG_VALUE now that the value is in a spill slot.
911 int64_t Offset = MI->getOperand(1).getImm();
912 const MDNode *MDPtr =
913 MI->getOperand(MI->getNumOperands()-1).getMetadata();
914 DebugLoc DL = MI->getDebugLoc();
915 if (MachineInstr *NewDV =
916 TII->emitFrameIndexDebugValue(*MF, SS, Offset, MDPtr, DL)) {
917 DEBUG(dbgs() << "Modifying debug info due to spill:" <<
919 MachineBasicBlock *MBB = MI->getParent();
920 MBB->insert(MBB->erase(MI), NewDV);
921 // Scan NewDV operands from the beginning.
926 // We can't allocate a physreg for a DebugValue; sorry!
927 DEBUG(dbgs() << "Unable to allocate vreg used by DBG_VALUE");
932 LiveDbgValueMap[Reg].push_back(MI);
939 // If this is a copy, we may be able to coalesce.
940 unsigned CopySrc = 0, CopyDst = 0, CopySrcSub = 0, CopyDstSub = 0;
942 CopyDst = MI->getOperand(0).getReg();
943 CopySrc = MI->getOperand(1).getReg();
944 CopyDstSub = MI->getOperand(0).getSubReg();
945 CopySrcSub = MI->getOperand(1).getSubReg();
948 // Track registers used by instruction.
952 // Mark physreg uses and early clobbers as used.
953 // Find the end of the virtreg operands
954 unsigned VirtOpEnd = 0;
955 bool hasTiedOps = false;
956 bool hasEarlyClobbers = false;
957 bool hasPartialRedefs = false;
958 bool hasPhysDefs = false;
959 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
960 MachineOperand &MO = MI->getOperand(i);
961 if (!MO.isReg()) continue;
962 unsigned Reg = MO.getReg();
964 if (TargetRegisterInfo::isVirtualRegister(Reg)) {
967 hasTiedOps = hasTiedOps ||
968 MCID.getOperandConstraint(i, MCOI::TIED_TO) != -1;
970 if (MO.isEarlyClobber())
971 hasEarlyClobbers = true;
972 if (MO.getSubReg() && MI->readsVirtualRegister(Reg))
973 hasPartialRedefs = true;
977 if (!RegClassInfo.isAllocatable(Reg)) continue;
980 } else if (MO.isEarlyClobber()) {
981 definePhysReg(MI, Reg, (MO.isImplicit() || MO.isDead()) ?
982 regFree : regReserved);
983 hasEarlyClobbers = true;
988 // The instruction may have virtual register operands that must be allocated
989 // the same register at use-time and def-time: early clobbers and tied
990 // operands. If there are also physical defs, these registers must avoid
991 // both physical defs and uses, making them more constrained than normal
993 // Similarly, if there are multiple defs and tied operands, we must make
994 // sure the same register is allocated to uses and defs.
995 // We didn't detect inline asm tied operands above, so just make this extra
996 // pass for all inline asm.
997 if (MI->isInlineAsm() || hasEarlyClobbers || hasPartialRedefs ||
998 (hasTiedOps && (hasPhysDefs || MCID.getNumDefs() > 1))) {
999 handleThroughOperands(MI, VirtDead);
1000 // Don't attempt coalescing when we have funny stuff going on.
1002 // Pretend we have early clobbers so the use operands get marked below.
1003 // This is not necessary for the common case of a single tied use.
1004 hasEarlyClobbers = true;
1008 // Allocate virtreg uses.
1009 for (unsigned i = 0; i != VirtOpEnd; ++i) {
1010 MachineOperand &MO = MI->getOperand(i);
1011 if (!MO.isReg()) continue;
1012 unsigned Reg = MO.getReg();
1013 if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
1015 LiveRegMap::iterator LRI = reloadVirtReg(MI, i, Reg, CopyDst);
1016 unsigned PhysReg = LRI->PhysReg;
1017 CopySrc = (CopySrc == Reg || CopySrc == PhysReg) ? PhysReg : 0;
1018 if (setPhysReg(MI, i, PhysReg))
1023 MRI->addPhysRegsUsed(UsedInInstr);
1025 // Track registers defined by instruction - early clobbers and tied uses at
1027 UsedInInstr.reset();
1028 if (hasEarlyClobbers) {
1029 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
1030 MachineOperand &MO = MI->getOperand(i);
1031 if (!MO.isReg()) continue;
1032 unsigned Reg = MO.getReg();
1033 if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
1034 // Look for physreg defs and tied uses.
1035 if (!MO.isDef() && !MI->isRegTiedToDefOperand(i)) continue;
1036 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
1037 UsedInInstr.set(*AI);
1041 unsigned DefOpEnd = MI->getNumOperands();
1043 // Spill all virtregs before a call. This serves two purposes: 1. If an
1044 // exception is thrown, the landing pad is going to expect to find
1045 // registers in their spill slots, and 2. we don't have to wade through
1046 // all the <imp-def> operands on the call instruction.
1047 DefOpEnd = VirtOpEnd;
1048 DEBUG(dbgs() << " Spilling remaining registers before call.\n");
1051 // The imp-defs are skipped below, but we still need to mark those
1052 // registers as used by the function.
1053 SkippedInstrs.insert(&MCID);
1057 // Allocate defs and collect dead defs.
1058 for (unsigned i = 0; i != DefOpEnd; ++i) {
1059 MachineOperand &MO = MI->getOperand(i);
1060 if (!MO.isReg() || !MO.isDef() || !MO.getReg() || MO.isEarlyClobber())
1062 unsigned Reg = MO.getReg();
1064 if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
1065 if (!RegClassInfo.isAllocatable(Reg)) continue;
1066 definePhysReg(MI, Reg, (MO.isImplicit() || MO.isDead()) ?
1067 regFree : regReserved);
1070 LiveRegMap::iterator LRI = defineVirtReg(MI, i, Reg, CopySrc);
1071 unsigned PhysReg = LRI->PhysReg;
1072 if (setPhysReg(MI, i, PhysReg)) {
1073 VirtDead.push_back(Reg);
1074 CopyDst = 0; // cancel coalescing;
1076 CopyDst = (CopyDst == Reg || CopyDst == PhysReg) ? PhysReg : 0;
1079 // Kill dead defs after the scan to ensure that multiple defs of the same
1080 // register are allocated identically. We didn't need to do this for uses
1081 // because we are crerating our own kill flags, and they are always at the
1083 for (unsigned i = 0, e = VirtDead.size(); i != e; ++i)
1084 killVirtReg(VirtDead[i]);
1087 MRI->addPhysRegsUsed(UsedInInstr);
1089 if (CopyDst && CopyDst == CopySrc && CopyDstSub == CopySrcSub) {
1090 DEBUG(dbgs() << "-- coalescing: " << *MI);
1091 Coalesced.push_back(MI);
1093 DEBUG(dbgs() << "<< " << *MI);
1097 // Spill all physical registers holding virtual registers now.
1098 DEBUG(dbgs() << "Spilling live registers at end of block.\n");
1099 spillAll(MBB->getFirstTerminator());
1101 // Erase all the coalesced copies. We are delaying it until now because
1102 // LiveVirtRegs might refer to the instrs.
1103 for (unsigned i = 0, e = Coalesced.size(); i != e; ++i)
1104 MBB->erase(Coalesced[i]);
1105 NumCopies += Coalesced.size();
1107 // addRetOperands must run after we've seen all defs in this block.
1108 addRetOperands(MBB);
1113 /// runOnMachineFunction - Register allocate the whole function
1115 bool RAFast::runOnMachineFunction(MachineFunction &Fn) {
1116 DEBUG(dbgs() << "********** FAST REGISTER ALLOCATION **********\n"
1117 << "********** Function: "
1118 << ((Value*)Fn.getFunction())->getName() << '\n');
1120 MRI = &MF->getRegInfo();
1121 TM = &Fn.getTarget();
1122 TRI = TM->getRegisterInfo();
1123 TII = TM->getInstrInfo();
1124 MRI->freezeReservedRegs(Fn);
1125 RegClassInfo.runOnMachineFunction(Fn);
1126 UsedInInstr.resize(TRI->getNumRegs());
1128 assert(!MRI->isSSA() && "regalloc requires leaving SSA");
1130 // initialize the virtual->physical register map to have a 'null'
1131 // mapping for all virtual registers
1132 StackSlotForVirtReg.resize(MRI->getNumVirtRegs());
1133 LiveVirtRegs.setUniverse(MRI->getNumVirtRegs());
1135 // Loop over all of the basic blocks, eliminating virtual register references
1136 for (MachineFunction::iterator MBBi = Fn.begin(), MBBe = Fn.end();
1137 MBBi != MBBe; ++MBBi) {
1139 AllocateBasicBlock();
1142 // Add the clobber lists for all the instructions we skipped earlier.
1143 for (SmallPtrSet<const MCInstrDesc*, 4>::const_iterator
1144 I = SkippedInstrs.begin(), E = SkippedInstrs.end(); I != E; ++I)
1145 if (const uint16_t *Defs = (*I)->getImplicitDefs())
1147 MRI->setPhysRegUsed(*Defs++);
1149 // All machine operands and other references to virtual registers have been
1150 // replaced. Remove the virtual registers.
1151 MRI->clearVirtRegs();
1153 SkippedInstrs.clear();
1154 StackSlotForVirtReg.clear();
1155 LiveDbgValueMap.clear();
1159 FunctionPass *llvm::createFastRegisterAllocator() {
1160 return new RAFast();