RegAllocFast.cpp revision 27ce3b96e51887995f94d8c78a6c7e79bf7cdcdd 
1//===-- RegAllocFast.cpp - A fast register allocator for debug code -------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
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.
12//
13//===----------------------------------------------------------------------===//
14
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/Statistic.h"
36#include "llvm/ADT/STLExtras.h"
37#include <algorithm>
38using namespace llvm;
39
40STATISTIC(NumStores, "Number of stores added");
41STATISTIC(NumLoads , "Number of loads added");
42STATISTIC(NumCopies, "Number of copies coalesced");
43
44static RegisterRegAlloc
45  fastRegAlloc("fast", "fast register allocator", createFastRegisterAllocator);
46
47namespace {
48  class RAFast : public MachineFunctionPass {
49  public:
50    static char ID;
51    RAFast() : MachineFunctionPass(ID), StackSlotForVirtReg(-1),
52               isBulkSpilling(false) {
53      initializePHIEliminationPass(*PassRegistry::getPassRegistry());
54      initializeTwoAddressInstructionPassPass(*PassRegistry::getPassRegistry());
55    }
56  private:
57    const TargetMachine *TM;
58    MachineFunction *MF;
59    MachineRegisterInfo *MRI;
60    const TargetRegisterInfo *TRI;
61    const TargetInstrInfo *TII;
62    RegisterClassInfo RegClassInfo;
63
64    // Basic block currently being allocated.
65    MachineBasicBlock *MBB;
66
67    // StackSlotForVirtReg - Maps virtual regs to the frame index where these
68    // values are spilled.
69    IndexedMap<int, VirtReg2IndexFunctor> StackSlotForVirtReg;
70
71    // Everything we know about a live virtual register.
72    struct LiveReg {
73      MachineInstr *LastUse;    // Last instr to use reg.
74      unsigned PhysReg;         // Currently held here.
75      unsigned short LastOpNum; // OpNum on LastUse.
76      bool Dirty;               // Register needs spill.
77
78      LiveReg(unsigned p=0) : LastUse(0), PhysReg(p), LastOpNum(0),
79                              Dirty(false) {}
80    };
81
82    typedef DenseMap<unsigned, LiveReg> LiveRegMap;
83    typedef LiveRegMap::value_type LiveRegEntry;
84
85    // LiveVirtRegs - This map contains entries for each virtual register
86    // that is currently available in a physical register.
87    LiveRegMap LiveVirtRegs;
88
89    DenseMap<unsigned, SmallVector<MachineInstr *, 4> > LiveDbgValueMap;
90
91    // RegState - Track the state of a physical register.
92    enum RegState {
93      // A disabled register is not available for allocation, but an alias may
94      // be in use. A register can only be moved out of the disabled state if
95      // all aliases are disabled.
96      regDisabled,
97
98      // A free register is not currently in use and can be allocated
99      // immediately without checking aliases.
100      regFree,
101
102      // A reserved register has been assigned explicitly (e.g., setting up a
103      // call parameter), and it remains reserved until it is used.
104      regReserved
105
106      // A register state may also be a virtual register number, indication that
107      // the physical register is currently allocated to a virtual register. In
108      // that case, LiveVirtRegs contains the inverse mapping.
109    };
110
111    // PhysRegState - One of the RegState enums, or a virtreg.
112    std::vector<unsigned> PhysRegState;
113
114    // UsedInInstr - BitVector of physregs that are used in the current
115    // instruction, and so cannot be allocated.
116    BitVector UsedInInstr;
117
118    // SkippedInstrs - Descriptors of instructions whose clobber list was
119    // ignored because all registers were spilled. It is still necessary to
120    // mark all the clobbered registers as used by the function.
121    SmallPtrSet<const TargetInstrDesc*, 4> SkippedInstrs;
122
123    // isBulkSpilling - This flag is set when LiveRegMap will be cleared
124    // completely after spilling all live registers. LiveRegMap entries should
125    // not be erased.
126    bool isBulkSpilling;
127
128    enum {
129      spillClean = 1,
130      spillDirty = 100,
131      spillImpossible = ~0u
132    };
133  public:
134    virtual const char *getPassName() const {
135      return "Fast Register Allocator";
136    }
137
138    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
139      AU.setPreservesCFG();
140      AU.addRequiredID(PHIEliminationID);
141      AU.addRequiredID(TwoAddressInstructionPassID);
142      MachineFunctionPass::getAnalysisUsage(AU);
143    }
144
145  private:
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&);
152
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);
158
159    void usePhysReg(MachineOperand&);
160    void definePhysReg(MachineInstr *MI, unsigned PhysReg, RegState NewState);
161    unsigned calcSpillCost(unsigned PhysReg) const;
162    void assignVirtToPhysReg(LiveRegEntry &LRE, unsigned PhysReg);
163    void allocVirtReg(MachineInstr *MI, LiveRegEntry &LRE, unsigned Hint);
164    LiveRegMap::iterator defineVirtReg(MachineInstr *MI, unsigned OpNum,
165                                       unsigned VirtReg, unsigned Hint);
166    LiveRegMap::iterator reloadVirtReg(MachineInstr *MI, unsigned OpNum,
167                                       unsigned VirtReg, unsigned Hint);
168    void spillAll(MachineInstr *MI);
169    bool setPhysReg(MachineInstr *MI, unsigned OpNum, unsigned PhysReg);
170  };
171  char RAFast::ID = 0;
172}
173
174/// getStackSpaceFor - This allocates space for the specified virtual register
175/// to be held on the stack.
176int RAFast::getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC) {
177  // Find the location Reg would belong...
178  int SS = StackSlotForVirtReg[VirtReg];
179  if (SS != -1)
180    return SS;          // Already has space allocated?
181
182  // Allocate a new stack object for this spill location...
183  int FrameIdx = MF->getFrameInfo()->CreateSpillStackObject(RC->getSize(),
184                                                            RC->getAlignment());
185
186  // Assign the slot.
187  StackSlotForVirtReg[VirtReg] = FrameIdx;
188  return FrameIdx;
189}
190
191/// isLastUseOfLocalReg - Return true if MO is the only remaining reference to
192/// its virtual register, and it is guaranteed to be a block-local register.
193///
194bool RAFast::isLastUseOfLocalReg(MachineOperand &MO) {
195  // Check for non-debug uses or defs following MO.
196  // This is the most likely way to fail - fast path it.
197  MachineOperand *Next = &MO;
198  while ((Next = Next->getNextOperandForReg()))
199    if (!Next->isDebug())
200      return false;
201
202  // If the register has ever been spilled or reloaded, we conservatively assume
203  // it is a global register used in multiple blocks.
204  if (StackSlotForVirtReg[MO.getReg()] != -1)
205    return false;
206
207  // Check that the use/def chain has exactly one operand - MO.
208  return &MRI->reg_nodbg_begin(MO.getReg()).getOperand() == &MO;
209}
210
211/// addKillFlag - Set kill flags on last use of a virtual register.
212void RAFast::addKillFlag(const LiveReg &LR) {
213  if (!LR.LastUse) return;
214  MachineOperand &MO = LR.LastUse->getOperand(LR.LastOpNum);
215  if (MO.isUse() && !LR.LastUse->isRegTiedToDefOperand(LR.LastOpNum)) {
216    if (MO.getReg() == LR.PhysReg)
217      MO.setIsKill();
218    else
219      LR.LastUse->addRegisterKilled(LR.PhysReg, TRI, true);
220  }
221}
222
223/// killVirtReg - Mark virtreg as no longer available.
224void RAFast::killVirtReg(LiveRegMap::iterator LRI) {
225  addKillFlag(LRI->second);
226  const LiveReg &LR = LRI->second;
227  assert(PhysRegState[LR.PhysReg] == LRI->first && "Broken RegState mapping");
228  PhysRegState[LR.PhysReg] = regFree;
229  // Erase from LiveVirtRegs unless we're spilling in bulk.
230  if (!isBulkSpilling)
231    LiveVirtRegs.erase(LRI);
232}
233
234/// killVirtReg - Mark virtreg as no longer available.
235void RAFast::killVirtReg(unsigned VirtReg) {
236  assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
237         "killVirtReg needs a virtual register");
238  LiveRegMap::iterator LRI = LiveVirtRegs.find(VirtReg);
239  if (LRI != LiveVirtRegs.end())
240    killVirtReg(LRI);
241}
242
243/// spillVirtReg - This method spills the value specified by VirtReg into the
244/// corresponding stack slot if needed.
245void RAFast::spillVirtReg(MachineBasicBlock::iterator MI, unsigned VirtReg) {
246  assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
247         "Spilling a physical register is illegal!");
248  LiveRegMap::iterator LRI = LiveVirtRegs.find(VirtReg);
249  assert(LRI != LiveVirtRegs.end() && "Spilling unmapped virtual register");
250  spillVirtReg(MI, LRI);
251}
252
253/// spillVirtReg - Do the actual work of spilling.
254void RAFast::spillVirtReg(MachineBasicBlock::iterator MI,
255                          LiveRegMap::iterator LRI) {
256  LiveReg &LR = LRI->second;
257  assert(PhysRegState[LR.PhysReg] == LRI->first && "Broken RegState mapping");
258
259  if (LR.Dirty) {
260    // If this physreg is used by the instruction, we want to kill it on the
261    // instruction, not on the spill.
262    bool SpillKill = LR.LastUse != MI;
263    LR.Dirty = false;
264    DEBUG(dbgs() << "Spilling " << PrintReg(LRI->first, TRI)
265                 << " in " << PrintReg(LR.PhysReg, TRI));
266    const TargetRegisterClass *RC = MRI->getRegClass(LRI->first);
267    int FI = getStackSpaceFor(LRI->first, RC);
268    DEBUG(dbgs() << " to stack slot #" << FI << "\n");
269    TII->storeRegToStackSlot(*MBB, MI, LR.PhysReg, SpillKill, FI, RC, TRI);
270    ++NumStores;   // Update statistics
271
272    // If this register is used by DBG_VALUE then insert new DBG_VALUE to
273    // identify spilled location as the place to find corresponding variable's
274    // value.
275    SmallVector<MachineInstr *, 4> &LRIDbgValues = LiveDbgValueMap[LRI->first];
276    for (unsigned li = 0, le = LRIDbgValues.size(); li != le; ++li) {
277      MachineInstr *DBG = LRIDbgValues[li];
278      const MDNode *MDPtr =
279        DBG->getOperand(DBG->getNumOperands()-1).getMetadata();
280      int64_t Offset = 0;
281      if (DBG->getOperand(1).isImm())
282        Offset = DBG->getOperand(1).getImm();
283      DebugLoc DL;
284      if (MI == MBB->end()) {
285        // If MI is at basic block end then use last instruction's location.
286        MachineBasicBlock::iterator EI = MI;
287        DL = (--EI)->getDebugLoc();
288      }
289      else
290        DL = MI->getDebugLoc();
291      if (MachineInstr *NewDV =
292          TII->emitFrameIndexDebugValue(*MF, FI, Offset, MDPtr, DL)) {
293        MachineBasicBlock *MBB = DBG->getParent();
294        MBB->insert(MI, NewDV);
295        DEBUG(dbgs() << "Inserting debug info due to spill:" << "\n" << *NewDV);
296      }
297    }
298    // Now this register is spilled there is should not be any DBG_VALUE pointing
299    // to this register because they are all pointing to spilled value now.
300    LRIDbgValues.clear();
301    if (SpillKill)
302      LR.LastUse = 0; // Don't kill register again
303  }
304  killVirtReg(LRI);
305}
306
307/// spillAll - Spill all dirty virtregs without killing them.
308void RAFast::spillAll(MachineInstr *MI) {
309  if (LiveVirtRegs.empty()) return;
310  isBulkSpilling = true;
311  // The LiveRegMap is keyed by an unsigned (the virtreg number), so the order
312  // of spilling here is deterministic, if arbitrary.
313  for (LiveRegMap::iterator i = LiveVirtRegs.begin(), e = LiveVirtRegs.end();
314       i != e; ++i)
315    spillVirtReg(MI, i);
316  LiveVirtRegs.clear();
317  isBulkSpilling = false;
318}
319
320/// usePhysReg - Handle the direct use of a physical register.
321/// Check that the register is not used by a virtreg.
322/// Kill the physreg, marking it free.
323/// This may add implicit kills to MO->getParent() and invalidate MO.
324void RAFast::usePhysReg(MachineOperand &MO) {
325  unsigned PhysReg = MO.getReg();
326  assert(TargetRegisterInfo::isPhysicalRegister(PhysReg) &&
327         "Bad usePhysReg operand");
328
329  switch (PhysRegState[PhysReg]) {
330  case regDisabled:
331    break;
332  case regReserved:
333    PhysRegState[PhysReg] = regFree;
334    // Fall through
335  case regFree:
336    UsedInInstr.set(PhysReg);
337    MO.setIsKill();
338    return;
339  default:
340    // The physreg was allocated to a virtual register. That means the value we
341    // wanted has been clobbered.
342    llvm_unreachable("Instruction uses an allocated register");
343  }
344
345  // Maybe a superregister is reserved?
346  for (const unsigned *AS = TRI->getAliasSet(PhysReg);
347       unsigned Alias = *AS; ++AS) {
348    switch (PhysRegState[Alias]) {
349    case regDisabled:
350      break;
351    case regReserved:
352      assert(TRI->isSuperRegister(PhysReg, Alias) &&
353             "Instruction is not using a subregister of a reserved register");
354      // Leave the superregister in the working set.
355      PhysRegState[Alias] = regFree;
356      UsedInInstr.set(Alias);
357      MO.getParent()->addRegisterKilled(Alias, TRI, true);
358      return;
359    case regFree:
360      if (TRI->isSuperRegister(PhysReg, Alias)) {
361        // Leave the superregister in the working set.
362        UsedInInstr.set(Alias);
363        MO.getParent()->addRegisterKilled(Alias, TRI, true);
364        return;
365      }
366      // Some other alias was in the working set - clear it.
367      PhysRegState[Alias] = regDisabled;
368      break;
369    default:
370      llvm_unreachable("Instruction uses an alias of an allocated register");
371    }
372  }
373
374  // All aliases are disabled, bring register into working set.
375  PhysRegState[PhysReg] = regFree;
376  UsedInInstr.set(PhysReg);
377  MO.setIsKill();
378}
379
380/// definePhysReg - Mark PhysReg as reserved or free after spilling any
381/// virtregs. This is very similar to defineVirtReg except the physreg is
382/// reserved instead of allocated.
383void RAFast::definePhysReg(MachineInstr *MI, unsigned PhysReg,
384                           RegState NewState) {
385  UsedInInstr.set(PhysReg);
386  switch (unsigned VirtReg = PhysRegState[PhysReg]) {
387  case regDisabled:
388    break;
389  default:
390    spillVirtReg(MI, VirtReg);
391    // Fall through.
392  case regFree:
393  case regReserved:
394    PhysRegState[PhysReg] = NewState;
395    return;
396  }
397
398  // This is a disabled register, disable all aliases.
399  PhysRegState[PhysReg] = NewState;
400  for (const unsigned *AS = TRI->getAliasSet(PhysReg);
401       unsigned Alias = *AS; ++AS) {
402    switch (unsigned VirtReg = PhysRegState[Alias]) {
403    case regDisabled:
404      break;
405    default:
406      spillVirtReg(MI, VirtReg);
407      // Fall through.
408    case regFree:
409    case regReserved:
410      PhysRegState[Alias] = regDisabled;
411      if (TRI->isSuperRegister(PhysReg, Alias))
412        return;
413      break;
414    }
415  }
416}
417
418
419// calcSpillCost - Return the cost of spilling clearing out PhysReg and
420// aliases so it is free for allocation.
421// Returns 0 when PhysReg is free or disabled with all aliases disabled - it
422// can be allocated directly.
423// Returns spillImpossible when PhysReg or an alias can't be spilled.
424unsigned RAFast::calcSpillCost(unsigned PhysReg) const {
425  if (UsedInInstr.test(PhysReg)) {
426    DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " is already used in instr.\n");
427    return spillImpossible;
428  }
429  switch (unsigned VirtReg = PhysRegState[PhysReg]) {
430  case regDisabled:
431    break;
432  case regFree:
433    return 0;
434  case regReserved:
435    DEBUG(dbgs() << PrintReg(VirtReg, TRI) << " corresponding "
436                 << PrintReg(PhysReg, TRI) << " is reserved already.\n");
437    return spillImpossible;
438  default:
439    return LiveVirtRegs.lookup(VirtReg).Dirty ? spillDirty : spillClean;
440  }
441
442  // This is a disabled register, add up cost of aliases.
443  DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " is disabled.\n");
444  unsigned Cost = 0;
445  for (const unsigned *AS = TRI->getAliasSet(PhysReg);
446       unsigned Alias = *AS; ++AS) {
447    if (UsedInInstr.test(Alias))
448      return spillImpossible;
449    switch (unsigned VirtReg = PhysRegState[Alias]) {
450    case regDisabled:
451      break;
452    case regFree:
453      ++Cost;
454      break;
455    case regReserved:
456      return spillImpossible;
457    default:
458      Cost += LiveVirtRegs.lookup(VirtReg).Dirty ? spillDirty : spillClean;
459      break;
460    }
461  }
462  return Cost;
463}
464
465
466/// assignVirtToPhysReg - This method updates local state so that we know
467/// that PhysReg is the proper container for VirtReg now.  The physical
468/// register must not be used for anything else when this is called.
469///
470void RAFast::assignVirtToPhysReg(LiveRegEntry &LRE, unsigned PhysReg) {
471  DEBUG(dbgs() << "Assigning " << PrintReg(LRE.first, TRI) << " to "
472               << PrintReg(PhysReg, TRI) << "\n");
473  PhysRegState[PhysReg] = LRE.first;
474  assert(!LRE.second.PhysReg && "Already assigned a physreg");
475  LRE.second.PhysReg = PhysReg;
476}
477
478/// allocVirtReg - Allocate a physical register for VirtReg.
479void RAFast::allocVirtReg(MachineInstr *MI, LiveRegEntry &LRE, unsigned Hint) {
480  const unsigned VirtReg = LRE.first;
481
482  assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
483         "Can only allocate virtual registers");
484
485  const TargetRegisterClass *RC = MRI->getRegClass(VirtReg);
486
487  // Ignore invalid hints.
488  if (Hint && (!TargetRegisterInfo::isPhysicalRegister(Hint) ||
489               !RC->contains(Hint) || !RegClassInfo.isAllocatable(Hint)))
490    Hint = 0;
491
492  // Take hint when possible.
493  if (Hint) {
494    // Ignore the hint if we would have to spill a dirty register.
495    unsigned Cost = calcSpillCost(Hint);
496    if (Cost < spillDirty) {
497      if (Cost)
498        definePhysReg(MI, Hint, regFree);
499      return assignVirtToPhysReg(LRE, Hint);
500    }
501  }
502
503  ArrayRef<unsigned> AO = RegClassInfo.getOrder(RC);
504
505  // First try to find a completely free register.
506  for (ArrayRef<unsigned>::iterator I = AO.begin(), E = AO.end(); I != E; ++I) {
507    unsigned PhysReg = *I;
508    if (PhysRegState[PhysReg] == regFree && !UsedInInstr.test(PhysReg))
509      return assignVirtToPhysReg(LRE, PhysReg);
510  }
511
512  DEBUG(dbgs() << "Allocating " << PrintReg(VirtReg) << " from "
513               << RC->getName() << "\n");
514
515  unsigned BestReg = 0, BestCost = spillImpossible;
516  for (ArrayRef<unsigned>::iterator I = AO.begin(), E = AO.end(); I != E; ++I) {
517    unsigned Cost = calcSpillCost(*I);
518    DEBUG(dbgs() << "\tRegister: " << PrintReg(*I, TRI) << "\n");
519    DEBUG(dbgs() << "\tCost: " << Cost << "\n");
520    DEBUG(dbgs() << "\tBestCost: " << BestCost << "\n");
521    // Cost is 0 when all aliases are already disabled.
522    if (Cost == 0)
523      return assignVirtToPhysReg(LRE, *I);
524    if (Cost < BestCost)
525      BestReg = *I, BestCost = Cost;
526  }
527
528  if (BestReg) {
529    definePhysReg(MI, BestReg, regFree);
530    return assignVirtToPhysReg(LRE, BestReg);
531  }
532
533  // Nothing we can do.
534  std::string msg;
535  raw_string_ostream Msg(msg);
536  Msg << "Ran out of registers during register allocation!";
537  if (MI->isInlineAsm()) {
538    Msg << "\nPlease check your inline asm statement for "
539        << "invalid constraints:\n";
540    MI->print(Msg, TM);
541  }
542  report_fatal_error(Msg.str());
543}
544
545/// defineVirtReg - Allocate a register for VirtReg and mark it as dirty.
546RAFast::LiveRegMap::iterator
547RAFast::defineVirtReg(MachineInstr *MI, unsigned OpNum,
548                      unsigned VirtReg, unsigned Hint) {
549  assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
550         "Not a virtual register");
551  LiveRegMap::iterator LRI;
552  bool New;
553  tie(LRI, New) = LiveVirtRegs.insert(std::make_pair(VirtReg, LiveReg()));
554  LiveReg &LR = LRI->second;
555  if (New) {
556    // If there is no hint, peek at the only use of this register.
557    if ((!Hint || !TargetRegisterInfo::isPhysicalRegister(Hint)) &&
558        MRI->hasOneNonDBGUse(VirtReg)) {
559      const MachineInstr &UseMI = *MRI->use_nodbg_begin(VirtReg);
560      // It's a copy, use the destination register as a hint.
561      if (UseMI.isCopyLike())
562        Hint = UseMI.getOperand(0).getReg();
563    }
564    allocVirtReg(MI, *LRI, Hint);
565  } else if (LR.LastUse) {
566    // Redefining a live register - kill at the last use, unless it is this
567    // instruction defining VirtReg multiple times.
568    if (LR.LastUse != MI || LR.LastUse->getOperand(LR.LastOpNum).isUse())
569      addKillFlag(LR);
570  }
571  assert(LR.PhysReg && "Register not assigned");
572  LR.LastUse = MI;
573  LR.LastOpNum = OpNum;
574  LR.Dirty = true;
575  UsedInInstr.set(LR.PhysReg);
576  return LRI;
577}
578
579/// reloadVirtReg - Make sure VirtReg is available in a physreg and return it.
580RAFast::LiveRegMap::iterator
581RAFast::reloadVirtReg(MachineInstr *MI, unsigned OpNum,
582                      unsigned VirtReg, unsigned Hint) {
583  assert(TargetRegisterInfo::isVirtualRegister(VirtReg) &&
584         "Not a virtual register");
585  LiveRegMap::iterator LRI;
586  bool New;
587  tie(LRI, New) = LiveVirtRegs.insert(std::make_pair(VirtReg, LiveReg()));
588  LiveReg &LR = LRI->second;
589  MachineOperand &MO = MI->getOperand(OpNum);
590  if (New) {
591    allocVirtReg(MI, *LRI, Hint);
592    const TargetRegisterClass *RC = MRI->getRegClass(VirtReg);
593    int FrameIndex = getStackSpaceFor(VirtReg, RC);
594    DEBUG(dbgs() << "Reloading " << PrintReg(VirtReg, TRI) << " into "
595                 << PrintReg(LR.PhysReg, TRI) << "\n");
596    TII->loadRegFromStackSlot(*MBB, MI, LR.PhysReg, FrameIndex, RC, TRI);
597    ++NumLoads;
598  } else if (LR.Dirty) {
599    if (isLastUseOfLocalReg(MO)) {
600      DEBUG(dbgs() << "Killing last use: " << MO << "\n");
601      if (MO.isUse())
602        MO.setIsKill();
603      else
604        MO.setIsDead();
605    } else if (MO.isKill()) {
606      DEBUG(dbgs() << "Clearing dubious kill: " << MO << "\n");
607      MO.setIsKill(false);
608    } else if (MO.isDead()) {
609      DEBUG(dbgs() << "Clearing dubious dead: " << MO << "\n");
610      MO.setIsDead(false);
611    }
612  } else if (MO.isKill()) {
613    // We must remove kill flags from uses of reloaded registers because the
614    // register would be killed immediately, and there might be a second use:
615    //   %foo = OR %x<kill>, %x
616    // This would cause a second reload of %x into a different register.
617    DEBUG(dbgs() << "Clearing clean kill: " << MO << "\n");
618    MO.setIsKill(false);
619  } else if (MO.isDead()) {
620    DEBUG(dbgs() << "Clearing clean dead: " << MO << "\n");
621    MO.setIsDead(false);
622  }
623  assert(LR.PhysReg && "Register not assigned");
624  LR.LastUse = MI;
625  LR.LastOpNum = OpNum;
626  UsedInInstr.set(LR.PhysReg);
627  return LRI;
628}
629
630// setPhysReg - Change operand OpNum in MI the refer the PhysReg, considering
631// subregs. This may invalidate any operand pointers.
632// Return true if the operand kills its register.
633bool RAFast::setPhysReg(MachineInstr *MI, unsigned OpNum, unsigned PhysReg) {
634  MachineOperand &MO = MI->getOperand(OpNum);
635  if (!MO.getSubReg()) {
636    MO.setReg(PhysReg);
637    return MO.isKill() || MO.isDead();
638  }
639
640  // Handle subregister index.
641  MO.setReg(PhysReg ? TRI->getSubReg(PhysReg, MO.getSubReg()) : 0);
642  MO.setSubReg(0);
643
644  // A kill flag implies killing the full register. Add corresponding super
645  // register kill.
646  if (MO.isKill()) {
647    MI->addRegisterKilled(PhysReg, TRI, true);
648    return true;
649  }
650  return MO.isDead();
651}
652
653// Handle special instruction operand like early clobbers and tied ops when
654// there are additional physreg defines.
655void RAFast::handleThroughOperands(MachineInstr *MI,
656                                   SmallVectorImpl<unsigned> &VirtDead) {
657  DEBUG(dbgs() << "Scanning for through registers:");
658  SmallSet<unsigned, 8> ThroughRegs;
659  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
660    MachineOperand &MO = MI->getOperand(i);
661    if (!MO.isReg()) continue;
662    unsigned Reg = MO.getReg();
663    if (!TargetRegisterInfo::isVirtualRegister(Reg))
664      continue;
665    if (MO.isEarlyClobber() || MI->isRegTiedToDefOperand(i) ||
666        (MO.getSubReg() && MI->readsVirtualRegister(Reg))) {
667      if (ThroughRegs.insert(Reg))
668        DEBUG(dbgs() << ' ' << PrintReg(Reg));
669    }
670  }
671
672  // If any physreg defines collide with preallocated through registers,
673  // we must spill and reallocate.
674  DEBUG(dbgs() << "\nChecking for physdef collisions.\n");
675  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
676    MachineOperand &MO = MI->getOperand(i);
677    if (!MO.isReg() || !MO.isDef()) continue;
678    unsigned Reg = MO.getReg();
679    if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
680    UsedInInstr.set(Reg);
681    if (ThroughRegs.count(PhysRegState[Reg]))
682      definePhysReg(MI, Reg, regFree);
683    for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
684      UsedInInstr.set(*AS);
685      if (ThroughRegs.count(PhysRegState[*AS]))
686        definePhysReg(MI, *AS, regFree);
687    }
688  }
689
690  SmallVector<unsigned, 8> PartialDefs;
691  DEBUG(dbgs() << "Allocating tied uses and early clobbers.\n");
692  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
693    MachineOperand &MO = MI->getOperand(i);
694    if (!MO.isReg()) continue;
695    unsigned Reg = MO.getReg();
696    if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
697    if (MO.isUse()) {
698      unsigned DefIdx = 0;
699      if (!MI->isRegTiedToDefOperand(i, &DefIdx)) continue;
700      DEBUG(dbgs() << "Operand " << i << "("<< MO << ") is tied to operand "
701        << DefIdx << ".\n");
702      LiveRegMap::iterator LRI = reloadVirtReg(MI, i, Reg, 0);
703      unsigned PhysReg = LRI->second.PhysReg;
704      setPhysReg(MI, i, PhysReg);
705      // Note: we don't update the def operand yet. That would cause the normal
706      // def-scan to attempt spilling.
707    } else if (MO.getSubReg() && MI->readsVirtualRegister(Reg)) {
708      DEBUG(dbgs() << "Partial redefine: " << MO << "\n");
709      // Reload the register, but don't assign to the operand just yet.
710      // That would confuse the later phys-def processing pass.
711      LiveRegMap::iterator LRI = reloadVirtReg(MI, i, Reg, 0);
712      PartialDefs.push_back(LRI->second.PhysReg);
713    } else if (MO.isEarlyClobber()) {
714      // Note: defineVirtReg may invalidate MO.
715      LiveRegMap::iterator LRI = defineVirtReg(MI, i, Reg, 0);
716      unsigned PhysReg = LRI->second.PhysReg;
717      if (setPhysReg(MI, i, PhysReg))
718        VirtDead.push_back(Reg);
719    }
720  }
721
722  // Restore UsedInInstr to a state usable for allocating normal virtual uses.
723  UsedInInstr.reset();
724  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
725    MachineOperand &MO = MI->getOperand(i);
726    if (!MO.isReg() || (MO.isDef() && !MO.isEarlyClobber())) continue;
727    unsigned Reg = MO.getReg();
728    if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
729    DEBUG(dbgs() << "\tSetting " << PrintReg(Reg, TRI)
730                 << " as used in instr\n");
731    UsedInInstr.set(Reg);
732  }
733
734  // Also mark PartialDefs as used to avoid reallocation.
735  for (unsigned i = 0, e = PartialDefs.size(); i != e; ++i)
736    UsedInInstr.set(PartialDefs[i]);
737}
738
739void RAFast::AllocateBasicBlock() {
740  DEBUG(dbgs() << "\nAllocating " << *MBB);
741
742  // FIXME: This should probably be added by instruction selection instead?
743  // If the last instruction in the block is a return, make sure to mark it as
744  // using all of the live-out values in the function.  Things marked both call
745  // and return are tail calls; do not do this for them.  The tail callee need
746  // not take the same registers as input that it produces as output, and there
747  // are dependencies for its input registers elsewhere.
748  if (!MBB->empty() && MBB->back().getDesc().isReturn() &&
749      !MBB->back().getDesc().isCall()) {
750    MachineInstr *Ret = &MBB->back();
751
752    for (MachineRegisterInfo::liveout_iterator
753         I = MF->getRegInfo().liveout_begin(),
754         E = MF->getRegInfo().liveout_end(); I != E; ++I) {
755      assert(TargetRegisterInfo::isPhysicalRegister(*I) &&
756             "Cannot have a live-out virtual register.");
757
758      // Add live-out registers as implicit uses.
759      Ret->addRegisterKilled(*I, TRI, true);
760    }
761  }
762
763  PhysRegState.assign(TRI->getNumRegs(), regDisabled);
764  assert(LiveVirtRegs.empty() && "Mapping not cleared form last block?");
765
766  MachineBasicBlock::iterator MII = MBB->begin();
767
768  // Add live-in registers as live.
769  for (MachineBasicBlock::livein_iterator I = MBB->livein_begin(),
770         E = MBB->livein_end(); I != E; ++I)
771    if (RegClassInfo.isAllocatable(*I))
772      definePhysReg(MII, *I, regReserved);
773
774  SmallVector<unsigned, 8> VirtDead;
775  SmallVector<MachineInstr*, 32> Coalesced;
776
777  // Otherwise, sequentially allocate each instruction in the MBB.
778  while (MII != MBB->end()) {
779    MachineInstr *MI = MII++;
780    const TargetInstrDesc &TID = MI->getDesc();
781    DEBUG({
782        dbgs() << "\n>> " << *MI << "Regs:";
783        for (unsigned Reg = 1, E = TRI->getNumRegs(); Reg != E; ++Reg) {
784          if (PhysRegState[Reg] == regDisabled) continue;
785          dbgs() << " " << TRI->getName(Reg);
786          switch(PhysRegState[Reg]) {
787          case regFree:
788            break;
789          case regReserved:
790            dbgs() << "*";
791            break;
792          default:
793            dbgs() << '=' << PrintReg(PhysRegState[Reg]);
794            if (LiveVirtRegs[PhysRegState[Reg]].Dirty)
795              dbgs() << "*";
796            assert(LiveVirtRegs[PhysRegState[Reg]].PhysReg == Reg &&
797                   "Bad inverse map");
798            break;
799          }
800        }
801        dbgs() << '\n';
802        // Check that LiveVirtRegs is the inverse.
803        for (LiveRegMap::iterator i = LiveVirtRegs.begin(),
804             e = LiveVirtRegs.end(); i != e; ++i) {
805           assert(TargetRegisterInfo::isVirtualRegister(i->first) &&
806                  "Bad map key");
807           assert(TargetRegisterInfo::isPhysicalRegister(i->second.PhysReg) &&
808                  "Bad map value");
809           assert(PhysRegState[i->second.PhysReg] == i->first &&
810                  "Bad inverse map");
811        }
812      });
813
814    // Debug values are not allowed to change codegen in any way.
815    if (MI->isDebugValue()) {
816      bool ScanDbgValue = true;
817      while (ScanDbgValue) {
818        ScanDbgValue = false;
819        for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
820          MachineOperand &MO = MI->getOperand(i);
821          if (!MO.isReg()) continue;
822          unsigned Reg = MO.getReg();
823          if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
824          LiveDbgValueMap[Reg].push_back(MI);
825          LiveRegMap::iterator LRI = LiveVirtRegs.find(Reg);
826          if (LRI != LiveVirtRegs.end())
827            setPhysReg(MI, i, LRI->second.PhysReg);
828          else {
829            int SS = StackSlotForVirtReg[Reg];
830            if (SS == -1) {
831              // We can't allocate a physreg for a DebugValue, sorry!
832              DEBUG(dbgs() << "Unable to allocate vreg used by DBG_VALUE");
833              MO.setReg(0);
834            }
835            else {
836              // Modify DBG_VALUE now that the value is in a spill slot.
837              int64_t Offset = MI->getOperand(1).getImm();
838              const MDNode *MDPtr =
839                MI->getOperand(MI->getNumOperands()-1).getMetadata();
840              DebugLoc DL = MI->getDebugLoc();
841              if (MachineInstr *NewDV =
842                  TII->emitFrameIndexDebugValue(*MF, SS, Offset, MDPtr, DL)) {
843                DEBUG(dbgs() << "Modifying debug info due to spill:" <<
844                      "\t" << *MI);
845                MachineBasicBlock *MBB = MI->getParent();
846                MBB->insert(MBB->erase(MI), NewDV);
847                // Scan NewDV operands from the beginning.
848                MI = NewDV;
849                ScanDbgValue = true;
850                break;
851              } else {
852                // We can't allocate a physreg for a DebugValue; sorry!
853                DEBUG(dbgs() << "Unable to allocate vreg used by DBG_VALUE");
854                MO.setReg(0);
855              }
856            }
857          }
858        }
859      }
860      // Next instruction.
861      continue;
862    }
863
864    // If this is a copy, we may be able to coalesce.
865    unsigned CopySrc = 0, CopyDst = 0, CopySrcSub = 0, CopyDstSub = 0;
866    if (MI->isCopy()) {
867      CopyDst = MI->getOperand(0).getReg();
868      CopySrc = MI->getOperand(1).getReg();
869      CopyDstSub = MI->getOperand(0).getSubReg();
870      CopySrcSub = MI->getOperand(1).getSubReg();
871    }
872
873    // Track registers used by instruction.
874    UsedInInstr.reset();
875
876    // First scan.
877    // Mark physreg uses and early clobbers as used.
878    // Find the end of the virtreg operands
879    unsigned VirtOpEnd = 0;
880    bool hasTiedOps = false;
881    bool hasEarlyClobbers = false;
882    bool hasPartialRedefs = false;
883    bool hasPhysDefs = false;
884    for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
885      MachineOperand &MO = MI->getOperand(i);
886      if (!MO.isReg()) continue;
887      unsigned Reg = MO.getReg();
888      if (!Reg) continue;
889      if (TargetRegisterInfo::isVirtualRegister(Reg)) {
890        VirtOpEnd = i+1;
891        if (MO.isUse()) {
892          hasTiedOps = hasTiedOps ||
893                                TID.getOperandConstraint(i, TOI::TIED_TO) != -1;
894        } else {
895          if (MO.isEarlyClobber())
896            hasEarlyClobbers = true;
897          if (MO.getSubReg() && MI->readsVirtualRegister(Reg))
898            hasPartialRedefs = true;
899        }
900        continue;
901      }
902      if (!RegClassInfo.isAllocatable(Reg)) continue;
903      if (MO.isUse()) {
904        usePhysReg(MO);
905      } else if (MO.isEarlyClobber()) {
906        definePhysReg(MI, Reg, (MO.isImplicit() || MO.isDead()) ?
907                               regFree : regReserved);
908        hasEarlyClobbers = true;
909      } else
910        hasPhysDefs = true;
911    }
912
913    // The instruction may have virtual register operands that must be allocated
914    // the same register at use-time and def-time: early clobbers and tied
915    // operands. If there are also physical defs, these registers must avoid
916    // both physical defs and uses, making them more constrained than normal
917    // operands.
918    // Similarly, if there are multiple defs and tied operands, we must make
919    // sure the same register is allocated to uses and defs.
920    // We didn't detect inline asm tied operands above, so just make this extra
921    // pass for all inline asm.
922    if (MI->isInlineAsm() || hasEarlyClobbers || hasPartialRedefs ||
923        (hasTiedOps && (hasPhysDefs || TID.getNumDefs() > 1))) {
924      handleThroughOperands(MI, VirtDead);
925      // Don't attempt coalescing when we have funny stuff going on.
926      CopyDst = 0;
927      // Pretend we have early clobbers so the use operands get marked below.
928      // This is not necessary for the common case of a single tied use.
929      hasEarlyClobbers = true;
930    }
931
932    // Second scan.
933    // Allocate virtreg uses.
934    for (unsigned i = 0; i != VirtOpEnd; ++i) {
935      MachineOperand &MO = MI->getOperand(i);
936      if (!MO.isReg()) continue;
937      unsigned Reg = MO.getReg();
938      if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue;
939      if (MO.isUse()) {
940        LiveRegMap::iterator LRI = reloadVirtReg(MI, i, Reg, CopyDst);
941        unsigned PhysReg = LRI->second.PhysReg;
942        CopySrc = (CopySrc == Reg || CopySrc == PhysReg) ? PhysReg : 0;
943        if (setPhysReg(MI, i, PhysReg))
944          killVirtReg(LRI);
945      }
946    }
947
948    MRI->addPhysRegsUsed(UsedInInstr);
949
950    // Track registers defined by instruction - early clobbers and tied uses at
951    // this point.
952    UsedInInstr.reset();
953    if (hasEarlyClobbers) {
954      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
955        MachineOperand &MO = MI->getOperand(i);
956        if (!MO.isReg()) continue;
957        unsigned Reg = MO.getReg();
958        if (!Reg || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
959        // Look for physreg defs and tied uses.
960        if (!MO.isDef() && !MI->isRegTiedToDefOperand(i)) continue;
961        UsedInInstr.set(Reg);
962        for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
963          UsedInInstr.set(*AS);
964      }
965    }
966
967    unsigned DefOpEnd = MI->getNumOperands();
968    if (TID.isCall()) {
969      // Spill all virtregs before a call. This serves two purposes: 1. If an
970      // exception is thrown, the landing pad is going to expect to find
971      // registers in their spill slots, and 2. we don't have to wade through
972      // all the <imp-def> operands on the call instruction.
973      DefOpEnd = VirtOpEnd;
974      DEBUG(dbgs() << "  Spilling remaining registers before call.\n");
975      spillAll(MI);
976
977      // The imp-defs are skipped below, but we still need to mark those
978      // registers as used by the function.
979      SkippedInstrs.insert(&TID);
980    }
981
982    // Third scan.
983    // Allocate defs and collect dead defs.
984    for (unsigned i = 0; i != DefOpEnd; ++i) {
985      MachineOperand &MO = MI->getOperand(i);
986      if (!MO.isReg() || !MO.isDef() || !MO.getReg() || MO.isEarlyClobber())
987        continue;
988      unsigned Reg = MO.getReg();
989
990      if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
991        if (!RegClassInfo.isAllocatable(Reg)) continue;
992        definePhysReg(MI, Reg, (MO.isImplicit() || MO.isDead()) ?
993                               regFree : regReserved);
994        continue;
995      }
996      LiveRegMap::iterator LRI = defineVirtReg(MI, i, Reg, CopySrc);
997      unsigned PhysReg = LRI->second.PhysReg;
998      if (setPhysReg(MI, i, PhysReg)) {
999        VirtDead.push_back(Reg);
1000        CopyDst = 0; // cancel coalescing;
1001      } else
1002        CopyDst = (CopyDst == Reg || CopyDst == PhysReg) ? PhysReg : 0;
1003    }
1004
1005    // Kill dead defs after the scan to ensure that multiple defs of the same
1006    // register are allocated identically. We didn't need to do this for uses
1007    // because we are crerating our own kill flags, and they are always at the
1008    // last use.
1009    for (unsigned i = 0, e = VirtDead.size(); i != e; ++i)
1010      killVirtReg(VirtDead[i]);
1011    VirtDead.clear();
1012
1013    MRI->addPhysRegsUsed(UsedInInstr);
1014
1015    if (CopyDst && CopyDst == CopySrc && CopyDstSub == CopySrcSub) {
1016      DEBUG(dbgs() << "-- coalescing: " << *MI);
1017      Coalesced.push_back(MI);
1018    } else {
1019      DEBUG(dbgs() << "<< " << *MI);
1020    }
1021  }
1022
1023  // Spill all physical registers holding virtual registers now.
1024  DEBUG(dbgs() << "Spilling live registers at end of block.\n");
1025  spillAll(MBB->getFirstTerminator());
1026
1027  // Erase all the coalesced copies. We are delaying it until now because
1028  // LiveVirtRegs might refer to the instrs.
1029  for (unsigned i = 0, e = Coalesced.size(); i != e; ++i)
1030    MBB->erase(Coalesced[i]);
1031  NumCopies += Coalesced.size();
1032
1033  DEBUG(MBB->dump());
1034}
1035
1036/// runOnMachineFunction - Register allocate the whole function
1037///
1038bool RAFast::runOnMachineFunction(MachineFunction &Fn) {
1039  DEBUG(dbgs() << "********** FAST REGISTER ALLOCATION **********\n"
1040               << "********** Function: "
1041               << ((Value*)Fn.getFunction())->getName() << '\n');
1042  MF = &Fn;
1043  MRI = &MF->getRegInfo();
1044  TM = &Fn.getTarget();
1045  TRI = TM->getRegisterInfo();
1046  TII = TM->getInstrInfo();
1047  RegClassInfo.runOnMachineFunction(Fn);
1048  UsedInInstr.resize(TRI->getNumRegs());
1049
1050  // initialize the virtual->physical register map to have a 'null'
1051  // mapping for all virtual registers
1052  StackSlotForVirtReg.resize(MRI->getNumVirtRegs());
1053
1054  // Loop over all of the basic blocks, eliminating virtual register references
1055  for (MachineFunction::iterator MBBi = Fn.begin(), MBBe = Fn.end();
1056       MBBi != MBBe; ++MBBi) {
1057    MBB = &*MBBi;
1058    AllocateBasicBlock();
1059  }
1060
1061  // Make sure the set of used physregs is closed under subreg operations.
1062  MRI->closePhysRegsUsed(*TRI);
1063
1064  // Add the clobber lists for all the instructions we skipped earlier.
1065  for (SmallPtrSet<const TargetInstrDesc*, 4>::const_iterator
1066       I = SkippedInstrs.begin(), E = SkippedInstrs.end(); I != E; ++I)
1067    if (const unsigned *Defs = (*I)->getImplicitDefs())
1068      while (*Defs)
1069        MRI->setPhysRegUsed(*Defs++);
1070
1071  SkippedInstrs.clear();
1072  StackSlotForVirtReg.clear();
1073  LiveDbgValueMap.clear();
1074  return true;
1075}
1076
1077FunctionPass *llvm::createFastRegisterAllocator() {
1078  return new RAFast();
1079}
1080