LLVM  10.0.0svn
LiveVariables.cpp
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1 //===-- LiveVariables.cpp - Live Variable Analysis for Machine Code -------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the LiveVariable analysis pass. For each machine
10 // instruction in the function, this pass calculates the set of registers that
11 // are immediately dead after the instruction (i.e., the instruction calculates
12 // the value, but it is never used) and the set of registers that are used by
13 // the instruction, but are never used after the instruction (i.e., they are
14 // killed).
15 //
16 // This class computes live variables using a sparse implementation based on
17 // the machine code SSA form. This class computes live variable information for
18 // each virtual and _register allocatable_ physical register in a function. It
19 // uses the dominance properties of SSA form to efficiently compute live
20 // variables for virtual registers, and assumes that physical registers are only
21 // live within a single basic block (allowing it to do a single local analysis
22 // to resolve physical register lifetimes in each basic block). If a physical
23 // register is not register allocatable, it is not tracked. This is useful for
24 // things like the stack pointer and condition codes.
25 //
26 //===----------------------------------------------------------------------===//
27 
30 #include "llvm/ADT/STLExtras.h"
31 #include "llvm/ADT/SmallPtrSet.h"
32 #include "llvm/ADT/SmallSet.h"
35 #include "llvm/CodeGen/Passes.h"
36 #include "llvm/Config/llvm-config.h"
37 #include "llvm/Support/Debug.h"
40 #include <algorithm>
41 using namespace llvm;
42 
43 char LiveVariables::ID = 0;
46  "Live Variable Analysis", false, false)
47 INITIALIZE_PASS_DEPENDENCY(UnreachableMachineBlockElim)
49  "Live Variable Analysis", false, false)
50 
51 
52 void LiveVariables::getAnalysisUsage(AnalysisUsage &AU) const {
53  AU.addRequiredID(UnreachableMachineBlockElimID);
54  AU.setPreservesAll();
56 }
57 
60  for (unsigned i = 0, e = Kills.size(); i != e; ++i)
61  if (Kills[i]->getParent() == MBB)
62  return Kills[i];
63  return nullptr;
64 }
65 
66 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
68  dbgs() << " Alive in blocks: ";
70  E = AliveBlocks.end(); I != E; ++I)
71  dbgs() << *I << ", ";
72  dbgs() << "\n Killed by:";
73  if (Kills.empty())
74  dbgs() << " No instructions.\n";
75  else {
76  for (unsigned i = 0, e = Kills.size(); i != e; ++i)
77  dbgs() << "\n #" << i << ": " << *Kills[i];
78  dbgs() << "\n";
79  }
80 }
81 #endif
82 
83 /// getVarInfo - Get (possibly creating) a VarInfo object for the given vreg.
86  "getVarInfo: not a virtual register!");
87  VirtRegInfo.grow(RegIdx);
88  return VirtRegInfo[RegIdx];
89 }
90 
92  MachineBasicBlock *DefBlock,
93  MachineBasicBlock *MBB,
94  std::vector<MachineBasicBlock*> &WorkList) {
95  unsigned BBNum = MBB->getNumber();
96 
97  // Check to see if this basic block is one of the killing blocks. If so,
98  // remove it.
99  for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i)
100  if (VRInfo.Kills[i]->getParent() == MBB) {
101  VRInfo.Kills.erase(VRInfo.Kills.begin()+i); // Erase entry
102  break;
103  }
104 
105  if (MBB == DefBlock) return; // Terminate recursion
106 
107  if (VRInfo.AliveBlocks.test(BBNum))
108  return; // We already know the block is live
109 
110  // Mark the variable known alive in this bb
111  VRInfo.AliveBlocks.set(BBNum);
112 
113  assert(MBB != &MF->front() && "Can't find reaching def for virtreg");
114  WorkList.insert(WorkList.end(), MBB->pred_rbegin(), MBB->pred_rend());
115 }
116 
118  MachineBasicBlock *DefBlock,
119  MachineBasicBlock *MBB) {
120  std::vector<MachineBasicBlock*> WorkList;
121  MarkVirtRegAliveInBlock(VRInfo, DefBlock, MBB, WorkList);
122 
123  while (!WorkList.empty()) {
124  MachineBasicBlock *Pred = WorkList.back();
125  WorkList.pop_back();
126  MarkVirtRegAliveInBlock(VRInfo, DefBlock, Pred, WorkList);
127  }
128 }
129 
131  MachineInstr &MI) {
132  assert(MRI->getVRegDef(reg) && "Register use before def!");
133 
134  unsigned BBNum = MBB->getNumber();
135 
136  VarInfo& VRInfo = getVarInfo(reg);
137 
138  // Check to see if this basic block is already a kill block.
139  if (!VRInfo.Kills.empty() && VRInfo.Kills.back()->getParent() == MBB) {
140  // Yes, this register is killed in this basic block already. Increase the
141  // live range by updating the kill instruction.
142  VRInfo.Kills.back() = &MI;
143  return;
144  }
145 
146 #ifndef NDEBUG
147  for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i)
148  assert(VRInfo.Kills[i]->getParent() != MBB && "entry should be at end!");
149 #endif
150 
151  // This situation can occur:
152  //
153  // ,------.
154  // | |
155  // | v
156  // | t2 = phi ... t1 ...
157  // | |
158  // | v
159  // | t1 = ...
160  // | ... = ... t1 ...
161  // | |
162  // `------'
163  //
164  // where there is a use in a PHI node that's a predecessor to the defining
165  // block. We don't want to mark all predecessors as having the value "alive"
166  // in this case.
167  if (MBB == MRI->getVRegDef(reg)->getParent()) return;
168 
169  // Add a new kill entry for this basic block. If this virtual register is
170  // already marked as alive in this basic block, that means it is alive in at
171  // least one of the successor blocks, it's not a kill.
172  if (!VRInfo.AliveBlocks.test(BBNum))
173  VRInfo.Kills.push_back(&MI);
174 
175  // Update all dominating blocks to mark them as "known live".
177  E = MBB->pred_end(); PI != E; ++PI)
178  MarkVirtRegAliveInBlock(VRInfo, MRI->getVRegDef(reg)->getParent(), *PI);
179 }
180 
182  VarInfo &VRInfo = getVarInfo(Reg);
183 
184  if (VRInfo.AliveBlocks.empty())
185  // If vr is not alive in any block, then defaults to dead.
186  VRInfo.Kills.push_back(&MI);
187 }
188 
189 /// FindLastPartialDef - Return the last partial def of the specified register.
190 /// Also returns the sub-registers that're defined by the instruction.
191 MachineInstr *LiveVariables::FindLastPartialDef(unsigned Reg,
192  SmallSet<unsigned,4> &PartDefRegs) {
193  unsigned LastDefReg = 0;
194  unsigned LastDefDist = 0;
195  MachineInstr *LastDef = nullptr;
196  for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
197  unsigned SubReg = *SubRegs;
198  MachineInstr *Def = PhysRegDef[SubReg];
199  if (!Def)
200  continue;
201  unsigned Dist = DistanceMap[Def];
202  if (Dist > LastDefDist) {
203  LastDefReg = SubReg;
204  LastDef = Def;
205  LastDefDist = Dist;
206  }
207  }
208 
209  if (!LastDef)
210  return nullptr;
211 
212  PartDefRegs.insert(LastDefReg);
213  for (unsigned i = 0, e = LastDef->getNumOperands(); i != e; ++i) {
214  MachineOperand &MO = LastDef->getOperand(i);
215  if (!MO.isReg() || !MO.isDef() || MO.getReg() == 0)
216  continue;
217  Register DefReg = MO.getReg();
218  if (TRI->isSubRegister(Reg, DefReg)) {
219  for (MCSubRegIterator SubRegs(DefReg, TRI, /*IncludeSelf=*/true);
220  SubRegs.isValid(); ++SubRegs)
221  PartDefRegs.insert(*SubRegs);
222  }
223  }
224  return LastDef;
225 }
226 
227 /// HandlePhysRegUse - Turn previous partial def's into read/mod/writes. Add
228 /// implicit defs to a machine instruction if there was an earlier def of its
229 /// super-register.
230 void LiveVariables::HandlePhysRegUse(unsigned Reg, MachineInstr &MI) {
231  MachineInstr *LastDef = PhysRegDef[Reg];
232  // If there was a previous use or a "full" def all is well.
233  if (!LastDef && !PhysRegUse[Reg]) {
234  // Otherwise, the last sub-register def implicitly defines this register.
235  // e.g.
236  // AH =
237  // AL = ... implicit-def EAX, implicit killed AH
238  // = AH
239  // ...
240  // = EAX
241  // All of the sub-registers must have been defined before the use of Reg!
242  SmallSet<unsigned, 4> PartDefRegs;
243  MachineInstr *LastPartialDef = FindLastPartialDef(Reg, PartDefRegs);
244  // If LastPartialDef is NULL, it must be using a livein register.
245  if (LastPartialDef) {
246  LastPartialDef->addOperand(MachineOperand::CreateReg(Reg, true/*IsDef*/,
247  true/*IsImp*/));
248  PhysRegDef[Reg] = LastPartialDef;
249  SmallSet<unsigned, 8> Processed;
250  for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
251  unsigned SubReg = *SubRegs;
252  if (Processed.count(SubReg))
253  continue;
254  if (PartDefRegs.count(SubReg))
255  continue;
256  // This part of Reg was defined before the last partial def. It's killed
257  // here.
258  LastPartialDef->addOperand(MachineOperand::CreateReg(SubReg,
259  false/*IsDef*/,
260  true/*IsImp*/));
261  PhysRegDef[SubReg] = LastPartialDef;
262  for (MCSubRegIterator SS(SubReg, TRI); SS.isValid(); ++SS)
263  Processed.insert(*SS);
264  }
265  }
266  } else if (LastDef && !PhysRegUse[Reg] &&
267  !LastDef->findRegisterDefOperand(Reg))
268  // Last def defines the super register, add an implicit def of reg.
269  LastDef->addOperand(MachineOperand::CreateReg(Reg, true/*IsDef*/,
270  true/*IsImp*/));
271 
272  // Remember this use.
273  for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
274  SubRegs.isValid(); ++SubRegs)
275  PhysRegUse[*SubRegs] = &MI;
276 }
277 
278 /// FindLastRefOrPartRef - Return the last reference or partial reference of
279 /// the specified register.
280 MachineInstr *LiveVariables::FindLastRefOrPartRef(unsigned Reg) {
281  MachineInstr *LastDef = PhysRegDef[Reg];
282  MachineInstr *LastUse = PhysRegUse[Reg];
283  if (!LastDef && !LastUse)
284  return nullptr;
285 
286  MachineInstr *LastRefOrPartRef = LastUse ? LastUse : LastDef;
287  unsigned LastRefOrPartRefDist = DistanceMap[LastRefOrPartRef];
288  unsigned LastPartDefDist = 0;
289  for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
290  unsigned SubReg = *SubRegs;
291  MachineInstr *Def = PhysRegDef[SubReg];
292  if (Def && Def != LastDef) {
293  // There was a def of this sub-register in between. This is a partial
294  // def, keep track of the last one.
295  unsigned Dist = DistanceMap[Def];
296  if (Dist > LastPartDefDist)
297  LastPartDefDist = Dist;
298  } else if (MachineInstr *Use = PhysRegUse[SubReg]) {
299  unsigned Dist = DistanceMap[Use];
300  if (Dist > LastRefOrPartRefDist) {
301  LastRefOrPartRefDist = Dist;
302  LastRefOrPartRef = Use;
303  }
304  }
305  }
306 
307  return LastRefOrPartRef;
308 }
309 
310 bool LiveVariables::HandlePhysRegKill(unsigned Reg, MachineInstr *MI) {
311  MachineInstr *LastDef = PhysRegDef[Reg];
312  MachineInstr *LastUse = PhysRegUse[Reg];
313  if (!LastDef && !LastUse)
314  return false;
315 
316  MachineInstr *LastRefOrPartRef = LastUse ? LastUse : LastDef;
317  unsigned LastRefOrPartRefDist = DistanceMap[LastRefOrPartRef];
318  // The whole register is used.
319  // AL =
320  // AH =
321  //
322  // = AX
323  // = AL, implicit killed AX
324  // AX =
325  //
326  // Or whole register is defined, but not used at all.
327  // dead AX =
328  // ...
329  // AX =
330  //
331  // Or whole register is defined, but only partly used.
332  // dead AX = implicit-def AL
333  // = killed AL
334  // AX =
335  MachineInstr *LastPartDef = nullptr;
336  unsigned LastPartDefDist = 0;
337  SmallSet<unsigned, 8> PartUses;
338  for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
339  unsigned SubReg = *SubRegs;
340  MachineInstr *Def = PhysRegDef[SubReg];
341  if (Def && Def != LastDef) {
342  // There was a def of this sub-register in between. This is a partial
343  // def, keep track of the last one.
344  unsigned Dist = DistanceMap[Def];
345  if (Dist > LastPartDefDist) {
346  LastPartDefDist = Dist;
347  LastPartDef = Def;
348  }
349  continue;
350  }
351  if (MachineInstr *Use = PhysRegUse[SubReg]) {
352  for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true); SS.isValid();
353  ++SS)
354  PartUses.insert(*SS);
355  unsigned Dist = DistanceMap[Use];
356  if (Dist > LastRefOrPartRefDist) {
357  LastRefOrPartRefDist = Dist;
358  LastRefOrPartRef = Use;
359  }
360  }
361  }
362 
363  if (!PhysRegUse[Reg]) {
364  // Partial uses. Mark register def dead and add implicit def of
365  // sub-registers which are used.
366  // dead EAX = op implicit-def AL
367  // That is, EAX def is dead but AL def extends pass it.
368  PhysRegDef[Reg]->addRegisterDead(Reg, TRI, true);
369  for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
370  unsigned SubReg = *SubRegs;
371  if (!PartUses.count(SubReg))
372  continue;
373  bool NeedDef = true;
374  if (PhysRegDef[Reg] == PhysRegDef[SubReg]) {
375  MachineOperand *MO = PhysRegDef[Reg]->findRegisterDefOperand(SubReg);
376  if (MO) {
377  NeedDef = false;
378  assert(!MO->isDead());
379  }
380  }
381  if (NeedDef)
382  PhysRegDef[Reg]->addOperand(MachineOperand::CreateReg(SubReg,
383  true/*IsDef*/, true/*IsImp*/));
384  MachineInstr *LastSubRef = FindLastRefOrPartRef(SubReg);
385  if (LastSubRef)
386  LastSubRef->addRegisterKilled(SubReg, TRI, true);
387  else {
388  LastRefOrPartRef->addRegisterKilled(SubReg, TRI, true);
389  for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true);
390  SS.isValid(); ++SS)
391  PhysRegUse[*SS] = LastRefOrPartRef;
392  }
393  for (MCSubRegIterator SS(SubReg, TRI); SS.isValid(); ++SS)
394  PartUses.erase(*SS);
395  }
396  } else if (LastRefOrPartRef == PhysRegDef[Reg] && LastRefOrPartRef != MI) {
397  if (LastPartDef)
398  // The last partial def kills the register.
399  LastPartDef->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
400  true/*IsImp*/, true/*IsKill*/));
401  else {
402  MachineOperand *MO =
403  LastRefOrPartRef->findRegisterDefOperand(Reg, false, false, TRI);
404  bool NeedEC = MO->isEarlyClobber() && MO->getReg() != Reg;
405  // If the last reference is the last def, then it's not used at all.
406  // That is, unless we are currently processing the last reference itself.
407  LastRefOrPartRef->addRegisterDead(Reg, TRI, true);
408  if (NeedEC) {
409  // If we are adding a subreg def and the superreg def is marked early
410  // clobber, add an early clobber marker to the subreg def.
411  MO = LastRefOrPartRef->findRegisterDefOperand(Reg);
412  if (MO)
413  MO->setIsEarlyClobber();
414  }
415  }
416  } else
417  LastRefOrPartRef->addRegisterKilled(Reg, TRI, true);
418  return true;
419 }
420 
421 void LiveVariables::HandleRegMask(const MachineOperand &MO) {
422  // Call HandlePhysRegKill() for all live registers clobbered by Mask.
423  // Clobbered registers are always dead, sp there is no need to use
424  // HandlePhysRegDef().
425  for (unsigned Reg = 1, NumRegs = TRI->getNumRegs(); Reg != NumRegs; ++Reg) {
426  // Skip dead regs.
427  if (!PhysRegDef[Reg] && !PhysRegUse[Reg])
428  continue;
429  // Skip mask-preserved regs.
430  if (!MO.clobbersPhysReg(Reg))
431  continue;
432  // Kill the largest clobbered super-register.
433  // This avoids needless implicit operands.
434  unsigned Super = Reg;
435  for (MCSuperRegIterator SR(Reg, TRI); SR.isValid(); ++SR)
436  if ((PhysRegDef[*SR] || PhysRegUse[*SR]) && MO.clobbersPhysReg(*SR))
437  Super = *SR;
438  HandlePhysRegKill(Super, nullptr);
439  }
440 }
441 
442 void LiveVariables::HandlePhysRegDef(unsigned Reg, MachineInstr *MI,
444  // What parts of the register are previously defined?
446  if (PhysRegDef[Reg] || PhysRegUse[Reg]) {
447  for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
448  SubRegs.isValid(); ++SubRegs)
449  Live.insert(*SubRegs);
450  } else {
451  for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
452  unsigned SubReg = *SubRegs;
453  // If a register isn't itself defined, but all parts that make up of it
454  // are defined, then consider it also defined.
455  // e.g.
456  // AL =
457  // AH =
458  // = AX
459  if (Live.count(SubReg))
460  continue;
461  if (PhysRegDef[SubReg] || PhysRegUse[SubReg]) {
462  for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true);
463  SS.isValid(); ++SS)
464  Live.insert(*SS);
465  }
466  }
467  }
468 
469  // Start from the largest piece, find the last time any part of the register
470  // is referenced.
471  HandlePhysRegKill(Reg, MI);
472  // Only some of the sub-registers are used.
473  for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
474  unsigned SubReg = *SubRegs;
475  if (!Live.count(SubReg))
476  // Skip if this sub-register isn't defined.
477  continue;
478  HandlePhysRegKill(SubReg, MI);
479  }
480 
481  if (MI)
482  Defs.push_back(Reg); // Remember this def.
483 }
484 
485 void LiveVariables::UpdatePhysRegDefs(MachineInstr &MI,
487  while (!Defs.empty()) {
488  unsigned Reg = Defs.back();
489  Defs.pop_back();
490  for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
491  SubRegs.isValid(); ++SubRegs) {
492  unsigned SubReg = *SubRegs;
493  PhysRegDef[SubReg] = &MI;
494  PhysRegUse[SubReg] = nullptr;
495  }
496  }
497 }
498 
499 void LiveVariables::runOnInstr(MachineInstr &MI,
501  assert(!MI.isDebugInstr());
502  // Process all of the operands of the instruction...
503  unsigned NumOperandsToProcess = MI.getNumOperands();
504 
505  // Unless it is a PHI node. In this case, ONLY process the DEF, not any
506  // of the uses. They will be handled in other basic blocks.
507  if (MI.isPHI())
508  NumOperandsToProcess = 1;
509 
510  // Clear kill and dead markers. LV will recompute them.
511  SmallVector<unsigned, 4> UseRegs;
512  SmallVector<unsigned, 4> DefRegs;
513  SmallVector<unsigned, 1> RegMasks;
514  for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
515  MachineOperand &MO = MI.getOperand(i);
516  if (MO.isRegMask()) {
517  RegMasks.push_back(i);
518  continue;
519  }
520  if (!MO.isReg() || MO.getReg() == 0)
521  continue;
522  Register MOReg = MO.getReg();
523  if (MO.isUse()) {
524  if (!(Register::isPhysicalRegister(MOReg) && MRI->isReserved(MOReg)))
525  MO.setIsKill(false);
526  if (MO.readsReg())
527  UseRegs.push_back(MOReg);
528  } else {
529  assert(MO.isDef());
530  // FIXME: We should not remove any dead flags. However the MIPS RDDSP
531  // instruction needs it at the moment: http://llvm.org/PR27116.
532  if (Register::isPhysicalRegister(MOReg) && !MRI->isReserved(MOReg))
533  MO.setIsDead(false);
534  DefRegs.push_back(MOReg);
535  }
536  }
537 
538  MachineBasicBlock *MBB = MI.getParent();
539  // Process all uses.
540  for (unsigned i = 0, e = UseRegs.size(); i != e; ++i) {
541  unsigned MOReg = UseRegs[i];
542  if (Register::isVirtualRegister(MOReg))
543  HandleVirtRegUse(MOReg, MBB, MI);
544  else if (!MRI->isReserved(MOReg))
545  HandlePhysRegUse(MOReg, MI);
546  }
547 
548  // Process all masked registers. (Call clobbers).
549  for (unsigned i = 0, e = RegMasks.size(); i != e; ++i)
550  HandleRegMask(MI.getOperand(RegMasks[i]));
551 
552  // Process all defs.
553  for (unsigned i = 0, e = DefRegs.size(); i != e; ++i) {
554  unsigned MOReg = DefRegs[i];
555  if (Register::isVirtualRegister(MOReg))
556  HandleVirtRegDef(MOReg, MI);
557  else if (!MRI->isReserved(MOReg))
558  HandlePhysRegDef(MOReg, &MI, Defs);
559  }
560  UpdatePhysRegDefs(MI, Defs);
561 }
562 
563 void LiveVariables::runOnBlock(MachineBasicBlock *MBB, const unsigned NumRegs) {
564  // Mark live-in registers as live-in.
566  for (const auto &LI : MBB->liveins()) {
567  assert(Register::isPhysicalRegister(LI.PhysReg) &&
568  "Cannot have a live-in virtual register!");
569  HandlePhysRegDef(LI.PhysReg, nullptr, Defs);
570  }
571 
572  // Loop over all of the instructions, processing them.
573  DistanceMap.clear();
574  unsigned Dist = 0;
575  for (MachineInstr &MI : *MBB) {
576  if (MI.isDebugInstr())
577  continue;
578  DistanceMap.insert(std::make_pair(&MI, Dist++));
579 
580  runOnInstr(MI, Defs);
581  }
582 
583  // Handle any virtual assignments from PHI nodes which might be at the
584  // bottom of this basic block. We check all of our successor blocks to see
585  // if they have PHI nodes, and if so, we simulate an assignment at the end
586  // of the current block.
587  if (!PHIVarInfo[MBB->getNumber()].empty()) {
588  SmallVectorImpl<unsigned> &VarInfoVec = PHIVarInfo[MBB->getNumber()];
589 
590  for (SmallVectorImpl<unsigned>::iterator I = VarInfoVec.begin(),
591  E = VarInfoVec.end(); I != E; ++I)
592  // Mark it alive only in the block we are representing.
593  MarkVirtRegAliveInBlock(getVarInfo(*I),MRI->getVRegDef(*I)->getParent(),
594  MBB);
595  }
596 
597  // MachineCSE may CSE instructions which write to non-allocatable physical
598  // registers across MBBs. Remember if any reserved register is liveout.
599  SmallSet<unsigned, 4> LiveOuts;
600  for (MachineBasicBlock::const_succ_iterator SI = MBB->succ_begin(),
601  SE = MBB->succ_end(); SI != SE; ++SI) {
602  MachineBasicBlock *SuccMBB = *SI;
603  if (SuccMBB->isEHPad())
604  continue;
605  for (const auto &LI : SuccMBB->liveins()) {
606  if (!TRI->isInAllocatableClass(LI.PhysReg))
607  // Ignore other live-ins, e.g. those that are live into landing pads.
608  LiveOuts.insert(LI.PhysReg);
609  }
610  }
611 
612  // Loop over PhysRegDef / PhysRegUse, killing any registers that are
613  // available at the end of the basic block.
614  for (unsigned i = 0; i != NumRegs; ++i)
615  if ((PhysRegDef[i] || PhysRegUse[i]) && !LiveOuts.count(i))
616  HandlePhysRegDef(i, nullptr, Defs);
617 }
618 
620  MF = &mf;
621  MRI = &mf.getRegInfo();
622  TRI = MF->getSubtarget().getRegisterInfo();
623 
624  const unsigned NumRegs = TRI->getNumRegs();
625  PhysRegDef.assign(NumRegs, nullptr);
626  PhysRegUse.assign(NumRegs, nullptr);
627  PHIVarInfo.resize(MF->getNumBlockIDs());
628  PHIJoins.clear();
629 
630  // FIXME: LiveIntervals will be updated to remove its dependence on
631  // LiveVariables to improve compilation time and eliminate bizarre pass
632  // dependencies. Until then, we can't change much in -O0.
633  if (!MRI->isSSA())
634  report_fatal_error("regalloc=... not currently supported with -O0");
635 
636  analyzePHINodes(mf);
637 
638  // Calculate live variable information in depth first order on the CFG of the
639  // function. This guarantees that we will see the definition of a virtual
640  // register before its uses due to dominance properties of SSA (except for PHI
641  // nodes, which are treated as a special case).
642  MachineBasicBlock *Entry = &MF->front();
644 
645  for (MachineBasicBlock *MBB : depth_first_ext(Entry, Visited)) {
646  runOnBlock(MBB, NumRegs);
647 
648  PhysRegDef.assign(NumRegs, nullptr);
649  PhysRegUse.assign(NumRegs, nullptr);
650  }
651 
652  // Convert and transfer the dead / killed information we have gathered into
653  // VirtRegInfo onto MI's.
654  for (unsigned i = 0, e1 = VirtRegInfo.size(); i != e1; ++i) {
655  const unsigned Reg = Register::index2VirtReg(i);
656  for (unsigned j = 0, e2 = VirtRegInfo[Reg].Kills.size(); j != e2; ++j)
657  if (VirtRegInfo[Reg].Kills[j] == MRI->getVRegDef(Reg))
658  VirtRegInfo[Reg].Kills[j]->addRegisterDead(Reg, TRI);
659  else
660  VirtRegInfo[Reg].Kills[j]->addRegisterKilled(Reg, TRI);
661  }
662 
663  // Check to make sure there are no unreachable blocks in the MC CFG for the
664  // function. If so, it is due to a bug in the instruction selector or some
665  // other part of the code generator if this happens.
666 #ifndef NDEBUG
667  for(MachineFunction::iterator i = MF->begin(), e = MF->end(); i != e; ++i)
668  assert(Visited.count(&*i) != 0 && "unreachable basic block found");
669 #endif
670 
671  PhysRegDef.clear();
672  PhysRegUse.clear();
673  PHIVarInfo.clear();
674 
675  return false;
676 }
677 
678 /// replaceKillInstruction - Update register kill info by replacing a kill
679 /// instruction with a new one.
681  MachineInstr &NewMI) {
682  VarInfo &VI = getVarInfo(Reg);
683  std::replace(VI.Kills.begin(), VI.Kills.end(), &OldMI, &NewMI);
684 }
685 
686 /// removeVirtualRegistersKilled - Remove all killed info for the specified
687 /// instruction.
689  for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
690  MachineOperand &MO = MI.getOperand(i);
691  if (MO.isReg() && MO.isKill()) {
692  MO.setIsKill(false);
693  Register Reg = MO.getReg();
694  if (Register::isVirtualRegister(Reg)) {
695  bool removed = getVarInfo(Reg).removeKill(MI);
696  assert(removed && "kill not in register's VarInfo?");
697  (void)removed;
698  }
699  }
700  }
701 }
702 
703 /// analyzePHINodes - Gather information about the PHI nodes in here. In
704 /// particular, we want to map the variable information of a virtual register
705 /// which is used in a PHI node. We map that to the BB the vreg is coming from.
706 ///
707 void LiveVariables::analyzePHINodes(const MachineFunction& Fn) {
708  for (const auto &MBB : Fn)
709  for (const auto &BBI : MBB) {
710  if (!BBI.isPHI())
711  break;
712  for (unsigned i = 1, e = BBI.getNumOperands(); i != e; i += 2)
713  if (BBI.getOperand(i).readsReg())
714  PHIVarInfo[BBI.getOperand(i + 1).getMBB()->getNumber()]
715  .push_back(BBI.getOperand(i).getReg());
716  }
717 }
718 
720  unsigned Reg,
721  MachineRegisterInfo &MRI) {
722  unsigned Num = MBB.getNumber();
723 
724  // Reg is live-through.
725  if (AliveBlocks.test(Num))
726  return true;
727 
728  // Registers defined in MBB cannot be live in.
729  const MachineInstr *Def = MRI.getVRegDef(Reg);
730  if (Def && Def->getParent() == &MBB)
731  return false;
732 
733  // Reg was not defined in MBB, was it killed here?
734  return findKill(&MBB);
735 }
736 
737 bool LiveVariables::isLiveOut(unsigned Reg, const MachineBasicBlock &MBB) {
739 
741  for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i)
742  Kills.insert(VI.Kills[i]->getParent());
743 
744  // Loop over all of the successors of the basic block, checking to see if
745  // the value is either live in the block, or if it is killed in the block.
746  for (const MachineBasicBlock *SuccMBB : MBB.successors()) {
747  // Is it alive in this successor?
748  unsigned SuccIdx = SuccMBB->getNumber();
749  if (VI.AliveBlocks.test(SuccIdx))
750  return true;
751  // Or is it live because there is a use in a successor that kills it?
752  if (Kills.count(SuccMBB))
753  return true;
754  }
755 
756  return false;
757 }
758 
759 /// addNewBlock - Add a new basic block BB as an empty succcessor to DomBB. All
760 /// variables that are live out of DomBB will be marked as passing live through
761 /// BB.
763  MachineBasicBlock *DomBB,
764  MachineBasicBlock *SuccBB) {
765  const unsigned NumNew = BB->getNumber();
766 
768 
769  MachineBasicBlock::iterator BBI = SuccBB->begin(), BBE = SuccBB->end();
770  for (; BBI != BBE && BBI->isPHI(); ++BBI) {
771  // Record the def of the PHI node.
772  Defs.insert(BBI->getOperand(0).getReg());
773 
774  // All registers used by PHI nodes in SuccBB must be live through BB.
775  for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
776  if (BBI->getOperand(i+1).getMBB() == BB)
777  getVarInfo(BBI->getOperand(i).getReg()).AliveBlocks.set(NumNew);
778  }
779 
780  // Record all vreg defs and kills of all instructions in SuccBB.
781  for (; BBI != BBE; ++BBI) {
782  for (MachineInstr::mop_iterator I = BBI->operands_begin(),
783  E = BBI->operands_end(); I != E; ++I) {
784  if (I->isReg() && Register::isVirtualRegister(I->getReg())) {
785  if (I->isDef())
786  Defs.insert(I->getReg());
787  else if (I->isKill())
788  Kills.insert(I->getReg());
789  }
790  }
791  }
792 
793  // Update info for all live variables
794  for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
795  unsigned Reg = Register::index2VirtReg(i);
796 
797  // If the Defs is defined in the successor it can't be live in BB.
798  if (Defs.count(Reg))
799  continue;
800 
801  // If the register is either killed in or live through SuccBB it's also live
802  // through BB.
803  VarInfo &VI = getVarInfo(Reg);
804  if (Kills.count(Reg) || VI.AliveBlocks.test(SuccBB->getNumber()))
805  VI.AliveBlocks.set(NumNew);
806  }
807 }
bool isRegMask() const
isRegMask - Tests if this is a MO_RegisterMask operand.
iterator end() const
pred_reverse_iterator pred_rbegin()
pred_reverse_iterator pred_rend()
LLVM_ATTRIBUTE_NORETURN void report_fatal_error(Error Err, bool gen_crash_diag=true)
Report a serious error, calling any installed error handler.
Definition: Error.cpp:139
This class represents lattice values for constants.
Definition: AllocatorList.h:23
#define LLVM_DUMP_METHOD
Mark debug helper function definitions like dump() that should not be stripped from debug builds...
Definition: Compiler.h:484
void set(unsigned Idx)
void push_back(const T &Elt)
Definition: SmallVector.h:211
bool runOnMachineFunction(MachineFunction &MF) override
runOnMachineFunction - This method must be overloaded to perform the desired machine code transformat...
static bool isPhysicalRegister(unsigned Reg)
Return true if the specified register number is in the physical register namespace.
Definition: Register.h:63
bool isLiveOut(unsigned Reg, const MachineBasicBlock &MBB)
isLiveOut - Determine if Reg is live out from MBB, when not considering PHI nodes.
unsigned Reg
bool addRegisterDead(Register Reg, const TargetRegisterInfo *RegInfo, bool AddIfNotFound=false)
We have determined MI defined a register without a use.
void HandleVirtRegUse(unsigned reg, MachineBasicBlock *MBB, MachineInstr &MI)
VarInfo - This represents the regions where a virtual register is live in the program.
Definition: LiveVariables.h:78
unsigned const TargetRegisterInfo * TRI
void setIsDead(bool Val=true)
static unsigned index2VirtReg(unsigned Index)
Convert a 0-based index to a virtual register number.
Definition: Register.h:83
MachineInstr * findKill(const MachineBasicBlock *MBB) const
findKill - Find a kill instruction in MBB. Return NULL if none is found.
std::vector< MachineBasicBlock * >::const_iterator const_pred_iterator
bool isPHI() const
bool erase(const T &V)
Definition: SmallSet.h:207
iterator_range< succ_iterator > successors()
iterator begin() const
bool removeKill(MachineInstr &MI)
removeKill - Delete a kill corresponding to the specified machine instruction.
Definition: LiveVariables.h:93
bool isEarlyClobber() const
bool test(unsigned Idx) const
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:50
MCSuperRegIterator enumerates all super-registers of Reg.
unsigned getNumOperands() const
Retuns the total number of operands.
Definition: MachineInstr.h:414
A Use represents the edge between a Value definition and its users.
Definition: Use.h:55
unsigned SubReg
SparseBitVector AliveBlocks
AliveBlocks - Set of blocks in which this value is alive completely through.
Definition: LiveVariables.h:83
MachineInstr * getVRegDef(unsigned Reg) const
getVRegDef - Return the machine instr that defines the specified virtual register or null if none is ...
char & UnreachableMachineBlockElimID
UnreachableMachineBlockElimination - This pass removes unreachable machine basic blocks.
void setIsEarlyClobber(bool Val=true)
bool readsReg() const
readsReg - Returns true if this operand reads the previous value of its register. ...
bool addRegisterKilled(Register IncomingReg, const TargetRegisterInfo *RegInfo, bool AddIfNotFound=false)
We have determined MI kills a register.
int getNumber() const
MachineBasicBlocks are uniquely numbered at the function level, unless they&#39;re not in a MachineFuncti...
char & LiveVariablesID
LiveVariables pass - This pass computes the set of blocks in which each variable is life and sets mac...
unsigned const MachineRegisterInfo * MRI
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
SmallSet - This maintains a set of unique values, optimizing for the case when the set is small (less...
Definition: SmallSet.h:134
std::pair< iterator, bool > insert(const ValueT &V)
Definition: DenseSet.h:187
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:370
iterator_range< df_ext_iterator< T, SetTy > > depth_first_ext(const T &G, SetTy &S)
Represent the analysis usage information of a pass.
constexpr double e
Definition: MathExtras.h:57
static void replace(Module &M, GlobalVariable *Old, GlobalVariable *New)
livevars
std::vector< MachineBasicBlock * >::const_iterator const_succ_iterator
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:381
std::pair< NoneType, bool > insert(const T &V)
insert - Insert an element into the set if it isn&#39;t already there.
Definition: SmallSet.h:180
static MachineOperand CreateReg(Register Reg, bool isDef, bool isImp=false, bool isKill=false, bool isDead=false, bool isUndef=false, bool isEarlyClobber=false, unsigned SubReg=0, bool isDebug=false, bool isInternalRead=false, bool isRenamable=false)
VarInfo & getVarInfo(unsigned RegIdx)
getVarInfo - Return the VarInfo structure for the specified VIRTUAL register.
MCSubRegIterator enumerates all sub-registers of Reg.
size_t size() const
Definition: SmallVector.h:52
bool isDebugInstr() const
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE, "Assign register bank of generic virtual registers", false, false) RegBankSelect
void MarkVirtRegAliveInBlock(VarInfo &VRInfo, MachineBasicBlock *DefBlock, MachineBasicBlock *BB)
MachineOperand * findRegisterDefOperand(Register Reg, bool isDead=false, bool Overlap=false, const TargetRegisterInfo *TRI=nullptr)
Wrapper for findRegisterDefOperandIdx, it returns a pointer to the MachineOperand rather than an inde...
void setIsKill(bool Val=true)
void addNewBlock(MachineBasicBlock *BB, MachineBasicBlock *DomBB, MachineBasicBlock *SuccBB)
addNewBlock - Add a new basic block BB between DomBB and SuccBB.
std::vector< MachineInstr * > Kills
Kills - List of MachineInstruction&#39;s which are the last use of this virtual register (kill it) in the...
Definition: LiveVariables.h:88
Iterator for intrusive lists based on ilist_node.
void replaceKillInstruction(unsigned Reg, MachineInstr &OldMI, MachineInstr &NewMI)
replaceKillInstruction - Update register kill info by replacing a kill instruction with a new one...
void HandleVirtRegDef(unsigned reg, MachineInstr &MI)
void addOperand(MachineFunction &MF, const MachineOperand &Op)
Add the specified operand to the instruction.
bool isLiveIn(const MachineBasicBlock &MBB, unsigned Reg, MachineRegisterInfo &MRI)
isLiveIn - Is Reg live in to MBB? This means that Reg is live through MBB, or it is killed in MBB...
MachineOperand class - Representation of each machine instruction operand.
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
static bool clobbersPhysReg(const uint32_t *RegMask, unsigned PhysReg)
clobbersPhysReg - Returns true if this RegMask clobbers PhysReg.
void removeVirtualRegistersKilled(MachineInstr &MI)
removeVirtualRegistersKilled - Remove all killed info for the specified instruction.
bool isValid() const
isValid - returns true if this iterator is not yet at the end.
const MachineBasicBlock * getParent() const
Definition: MachineInstr.h:256
MachineRegisterInfo - Keep track of information for virtual and physical registers, including vreg register classes, use/def chains for registers, etc.
Representation of each machine instruction.
Definition: MachineInstr.h:64
MachineRegisterInfo & getRegInfo()
getRegInfo - Return information about the registers currently in use.
bool isEHPad() const
Returns true if the block is a landing pad.
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:55
#define I(x, y, z)
Definition: MD5.cpp:58
size_type count(const_arg_type_t< ValueT > V) const
Return 1 if the specified key is in the set, 0 otherwise.
Definition: DenseSet.h:91
iterator_range< livein_iterator > liveins() const
bool isReg() const
isReg - Tests if this is a MO_Register operand.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
SparseBitVectorIterator iterator
static bool isVirtualRegister(unsigned Reg)
Return true if the specified register number is in the virtual register namespace.
Definition: Register.h:69
static const Function * getParent(const Value *V)
IRTranslator LLVM IR MI
INITIALIZE_PASS_BEGIN(LiveVariables, "livevars", "Live Variable Analysis", false, false) INITIALIZE_PASS_END(LiveVariables
Register getReg() const
getReg - Returns the register number.
const MachineOperand & getOperand(unsigned i) const
Definition: MachineInstr.h:416
Wrapper class representing virtual and physical registers.
Definition: Register.h:19
size_type count(const T &V) const
count - Return 1 if the element is in the set, 0 otherwise.
Definition: SmallSet.h:164