llvm.org GIT mirror llvm / release_31 lib / Transforms / Utils / SSAUpdater.cpp
release_31

Tree @release_31 (Download .tar.gz)

SSAUpdater.cpp @release_31raw · history · blame

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
//===- SSAUpdater.cpp - Unstructured SSA Update Tool ----------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the SSAUpdater class.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "ssaupdater"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Support/AlignOf.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"

using namespace llvm;

typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
static AvailableValsTy &getAvailableVals(void *AV) {
  return *static_cast<AvailableValsTy*>(AV);
}

SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
  : AV(0), ProtoType(0), ProtoName(), InsertedPHIs(NewPHI) {}

SSAUpdater::~SSAUpdater() {
  delete &getAvailableVals(AV);
}

/// Initialize - Reset this object to get ready for a new set of SSA
/// updates with type 'Ty'.  PHI nodes get a name based on 'Name'.
void SSAUpdater::Initialize(Type *Ty, StringRef Name) {
  if (AV == 0)
    AV = new AvailableValsTy();
  else
    getAvailableVals(AV).clear();
  ProtoType = Ty;
  ProtoName = Name;
}

/// HasValueForBlock - Return true if the SSAUpdater already has a value for
/// the specified block.
bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
  return getAvailableVals(AV).count(BB);
}

/// AddAvailableValue - Indicate that a rewritten value is available in the
/// specified block with the specified value.
void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
  assert(ProtoType != 0 && "Need to initialize SSAUpdater");
  assert(ProtoType == V->getType() &&
         "All rewritten values must have the same type");
  getAvailableVals(AV)[BB] = V;
}

/// IsEquivalentPHI - Check if PHI has the same incoming value as specified
/// in ValueMapping for each predecessor block.
static bool IsEquivalentPHI(PHINode *PHI,
                            DenseMap<BasicBlock*, Value*> &ValueMapping) {
  unsigned PHINumValues = PHI->getNumIncomingValues();
  if (PHINumValues != ValueMapping.size())
    return false;

  // Scan the phi to see if it matches.
  for (unsigned i = 0, e = PHINumValues; i != e; ++i)
    if (ValueMapping[PHI->getIncomingBlock(i)] !=
        PHI->getIncomingValue(i)) {
      return false;
    }

  return true;
}

/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
/// live at the end of the specified block.
Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
  Value *Res = GetValueAtEndOfBlockInternal(BB);
  return Res;
}

/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
/// is live in the middle of the specified block.
///
/// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
/// important case: if there is a definition of the rewritten value after the
/// 'use' in BB.  Consider code like this:
///
///      X1 = ...
///   SomeBB:
///      use(X)
///      X2 = ...
///      br Cond, SomeBB, OutBB
///
/// In this case, there are two values (X1 and X2) added to the AvailableVals
/// set by the client of the rewriter, and those values are both live out of
/// their respective blocks.  However, the use of X happens in the *middle* of
/// a block.  Because of this, we need to insert a new PHI node in SomeBB to
/// merge the appropriate values, and this value isn't live out of the block.
///
Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
  // If there is no definition of the renamed variable in this block, just use
  // GetValueAtEndOfBlock to do our work.
  if (!HasValueForBlock(BB))
    return GetValueAtEndOfBlock(BB);

  // Otherwise, we have the hard case.  Get the live-in values for each
  // predecessor.
  SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
  Value *SingularValue = 0;

  // We can get our predecessor info by walking the pred_iterator list, but it
  // is relatively slow.  If we already have PHI nodes in this block, walk one
  // of them to get the predecessor list instead.
  if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
    for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
      BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
      Value *PredVal = GetValueAtEndOfBlock(PredBB);
      PredValues.push_back(std::make_pair(PredBB, PredVal));

      // Compute SingularValue.
      if (i == 0)
        SingularValue = PredVal;
      else if (PredVal != SingularValue)
        SingularValue = 0;
    }
  } else {
    bool isFirstPred = true;
    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
      BasicBlock *PredBB = *PI;
      Value *PredVal = GetValueAtEndOfBlock(PredBB);
      PredValues.push_back(std::make_pair(PredBB, PredVal));

      // Compute SingularValue.
      if (isFirstPred) {
        SingularValue = PredVal;
        isFirstPred = false;
      } else if (PredVal != SingularValue)
        SingularValue = 0;
    }
  }

  // If there are no predecessors, just return undef.
  if (PredValues.empty())
    return UndefValue::get(ProtoType);

  // Otherwise, if all the merged values are the same, just use it.
  if (SingularValue != 0)
    return SingularValue;

  // Otherwise, we do need a PHI: check to see if we already have one available
  // in this block that produces the right value.
  if (isa<PHINode>(BB->begin())) {
    DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(),
                                               PredValues.end());
    PHINode *SomePHI;
    for (BasicBlock::iterator It = BB->begin();
         (SomePHI = dyn_cast<PHINode>(It)); ++It) {
      if (IsEquivalentPHI(SomePHI, ValueMapping))
        return SomePHI;
    }
  }

  // Ok, we have no way out, insert a new one now.
  PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
                                         ProtoName, &BB->front());

  // Fill in all the predecessors of the PHI.
  for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
    InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);

  // See if the PHI node can be merged to a single value.  This can happen in
  // loop cases when we get a PHI of itself and one other value.
  if (Value *V = SimplifyInstruction(InsertedPHI)) {
    InsertedPHI->eraseFromParent();
    return V;
  }

  // Set DebugLoc.
  InsertedPHI->setDebugLoc(GetFirstDebugLocInBasicBlock(BB));

  // If the client wants to know about all new instructions, tell it.
  if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);

  DEBUG(dbgs() << "  Inserted PHI: " << *InsertedPHI << "\n");
  return InsertedPHI;
}

/// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
/// which use their value in the corresponding predecessor.
void SSAUpdater::RewriteUse(Use &U) {
  Instruction *User = cast<Instruction>(U.getUser());

  Value *V;
  if (PHINode *UserPN = dyn_cast<PHINode>(User))
    V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
  else
    V = GetValueInMiddleOfBlock(User->getParent());

  U.set(V);
}

/// RewriteUseAfterInsertions - Rewrite a use, just like RewriteUse.  However,
/// this version of the method can rewrite uses in the same block as a
/// definition, because it assumes that all uses of a value are below any
/// inserted values.
void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
  Instruction *User = cast<Instruction>(U.getUser());
  
  Value *V;
  if (PHINode *UserPN = dyn_cast<PHINode>(User))
    V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
  else
    V = GetValueAtEndOfBlock(User->getParent());
  
  U.set(V);
}

/// PHIiter - Iterator for PHI operands.  This is used for the PHI_iterator
/// in the SSAUpdaterImpl template.
namespace {
  class PHIiter {
  private:
    PHINode *PHI;
    unsigned idx;

  public:
    explicit PHIiter(PHINode *P) // begin iterator
      : PHI(P), idx(0) {}
    PHIiter(PHINode *P, bool) // end iterator
      : PHI(P), idx(PHI->getNumIncomingValues()) {}

    PHIiter &operator++() { ++idx; return *this; } 
    bool operator==(const PHIiter& x) const { return idx == x.idx; }
    bool operator!=(const PHIiter& x) const { return !operator==(x); }
    Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
    BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
  };
}

/// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template,
/// specialized for SSAUpdater.
namespace llvm {
template<>
class SSAUpdaterTraits<SSAUpdater> {
public:
  typedef BasicBlock BlkT;
  typedef Value *ValT;
  typedef PHINode PhiT;

  typedef succ_iterator BlkSucc_iterator;
  static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
  static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }

  typedef PHIiter PHI_iterator;
  static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
  static inline PHI_iterator PHI_end(PhiT *PHI) {
    return PHI_iterator(PHI, true);
  }

  /// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
  /// vector, set Info->NumPreds, and allocate space in Info->Preds.
  static void FindPredecessorBlocks(BasicBlock *BB,
                                    SmallVectorImpl<BasicBlock*> *Preds) {
    // We can get our predecessor info by walking the pred_iterator list,
    // but it is relatively slow.  If we already have PHI nodes in this
    // block, walk one of them to get the predecessor list instead.
    if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
      for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
        Preds->push_back(SomePhi->getIncomingBlock(PI));
    } else {
      for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
        Preds->push_back(*PI);
    }
  }

  /// GetUndefVal - Get an undefined value of the same type as the value
  /// being handled.
  static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
    return UndefValue::get(Updater->ProtoType);
  }

  /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
  /// Reserve space for the operands but do not fill them in yet.
  static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
                               SSAUpdater *Updater) {
    PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
                                   Updater->ProtoName, &BB->front());
    return PHI;
  }

  /// AddPHIOperand - Add the specified value as an operand of the PHI for
  /// the specified predecessor block.
  static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
    PHI->addIncoming(Val, Pred);
  }

  /// InstrIsPHI - Check if an instruction is a PHI.
  ///
  static PHINode *InstrIsPHI(Instruction *I) {
    return dyn_cast<PHINode>(I);
  }

  /// ValueIsPHI - Check if a value is a PHI.
  ///
  static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
    return dyn_cast<PHINode>(Val);
  }

  /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
  /// operands, i.e., it was just added.
  static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
    PHINode *PHI = ValueIsPHI(Val, Updater);
    if (PHI && PHI->getNumIncomingValues() == 0)
      return PHI;
    return 0;
  }

  /// GetPHIValue - For the specified PHI instruction, return the value
  /// that it defines.
  static Value *GetPHIValue(PHINode *PHI) {
    return PHI;
  }
};

} // End llvm namespace

/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
/// for the specified BB and if so, return it.  If not, construct SSA form by
/// first calculating the required placement of PHIs and then inserting new
/// PHIs where needed.
Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
  AvailableValsTy &AvailableVals = getAvailableVals(AV);
  if (Value *V = AvailableVals[BB])
    return V;

  SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
  return Impl.GetValue(BB);
}

//===----------------------------------------------------------------------===//
// LoadAndStorePromoter Implementation
//===----------------------------------------------------------------------===//

LoadAndStorePromoter::
LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
                     SSAUpdater &S, StringRef BaseName) : SSA(S) {
  if (Insts.empty()) return;
  
  Value *SomeVal;
  if (LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
    SomeVal = LI;
  else
    SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);

  if (BaseName.empty())
    BaseName = SomeVal->getName();
  SSA.Initialize(SomeVal->getType(), BaseName);
}


void LoadAndStorePromoter::
run(const SmallVectorImpl<Instruction*> &Insts) const {
  
  // First step: bucket up uses of the alloca by the block they occur in.
  // This is important because we have to handle multiple defs/uses in a block
  // ourselves: SSAUpdater is purely for cross-block references.
  DenseMap<BasicBlock*, TinyPtrVector<Instruction*> > UsesByBlock;
  
  for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
    Instruction *User = Insts[i];
    UsesByBlock[User->getParent()].push_back(User);
  }
  
  // Okay, now we can iterate over all the blocks in the function with uses,
  // processing them.  Keep track of which loads are loading a live-in value.
  // Walk the uses in the use-list order to be determinstic.
  SmallVector<LoadInst*, 32> LiveInLoads;
  DenseMap<Value*, Value*> ReplacedLoads;
  
  for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
    Instruction *User = Insts[i];
    BasicBlock *BB = User->getParent();
    TinyPtrVector<Instruction*> &BlockUses = UsesByBlock[BB];
    
    // If this block has already been processed, ignore this repeat use.
    if (BlockUses.empty()) continue;
    
    // Okay, this is the first use in the block.  If this block just has a
    // single user in it, we can rewrite it trivially.
    if (BlockUses.size() == 1) {
      // If it is a store, it is a trivial def of the value in the block.
      if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
        updateDebugInfo(SI);
        SSA.AddAvailableValue(BB, SI->getOperand(0));
      } else 
        // Otherwise it is a load, queue it to rewrite as a live-in load.
        LiveInLoads.push_back(cast<LoadInst>(User));
      BlockUses.clear();
      continue;
    }
    
    // Otherwise, check to see if this block is all loads.
    bool HasStore = false;
    for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
      if (isa<StoreInst>(BlockUses[i])) {
        HasStore = true;
        break;
      }
    }
    
    // If so, we can queue them all as live in loads.  We don't have an
    // efficient way to tell which on is first in the block and don't want to
    // scan large blocks, so just add all loads as live ins.
    if (!HasStore) {
      for (unsigned i = 0, e = BlockUses.size(); i != e; ++i)
        LiveInLoads.push_back(cast<LoadInst>(BlockUses[i]));
      BlockUses.clear();
      continue;
    }
    
    // Otherwise, we have mixed loads and stores (or just a bunch of stores).
    // Since SSAUpdater is purely for cross-block values, we need to determine
    // the order of these instructions in the block.  If the first use in the
    // block is a load, then it uses the live in value.  The last store defines
    // the live out value.  We handle this by doing a linear scan of the block.
    Value *StoredValue = 0;
    for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
      if (LoadInst *L = dyn_cast<LoadInst>(II)) {
        // If this is a load from an unrelated pointer, ignore it.
        if (!isInstInList(L, Insts)) continue;
        
        // If we haven't seen a store yet, this is a live in use, otherwise
        // use the stored value.
        if (StoredValue) {
          replaceLoadWithValue(L, StoredValue);
          L->replaceAllUsesWith(StoredValue);
          ReplacedLoads[L] = StoredValue;
        } else {
          LiveInLoads.push_back(L);
        }
        continue;
      }
      
      if (StoreInst *SI = dyn_cast<StoreInst>(II)) {
        // If this is a store to an unrelated pointer, ignore it.
        if (!isInstInList(SI, Insts)) continue;
        updateDebugInfo(SI);

        // Remember that this is the active value in the block.
        StoredValue = SI->getOperand(0);
      }
    }
    
    // The last stored value that happened is the live-out for the block.
    assert(StoredValue && "Already checked that there is a store in block");
    SSA.AddAvailableValue(BB, StoredValue);
    BlockUses.clear();
  }
  
  // Okay, now we rewrite all loads that use live-in values in the loop,
  // inserting PHI nodes as necessary.
  for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) {
    LoadInst *ALoad = LiveInLoads[i];
    Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
    replaceLoadWithValue(ALoad, NewVal);

    // Avoid assertions in unreachable code.
    if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
    ALoad->replaceAllUsesWith(NewVal);
    ReplacedLoads[ALoad] = NewVal;
  }
  
  // Allow the client to do stuff before we start nuking things.
  doExtraRewritesBeforeFinalDeletion();
  
  // Now that everything is rewritten, delete the old instructions from the
  // function.  They should all be dead now.
  for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
    Instruction *User = Insts[i];
    
    // If this is a load that still has uses, then the load must have been added
    // as a live value in the SSAUpdate data structure for a block (e.g. because
    // the loaded value was stored later).  In this case, we need to recursively
    // propagate the updates until we get to the real value.
    if (!User->use_empty()) {
      Value *NewVal = ReplacedLoads[User];
      assert(NewVal && "not a replaced load?");
      
      // Propagate down to the ultimate replacee.  The intermediately loads
      // could theoretically already have been deleted, so we don't want to
      // dereference the Value*'s.
      DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
      while (RLI != ReplacedLoads.end()) {
        NewVal = RLI->second;
        RLI = ReplacedLoads.find(NewVal);
      }
      
      replaceLoadWithValue(cast<LoadInst>(User), NewVal);
      User->replaceAllUsesWith(NewVal);
    }
    
    instructionDeleted(User);
    User->eraseFromParent();
  }
}

bool
LoadAndStorePromoter::isInstInList(Instruction *I,
                                   const SmallVectorImpl<Instruction*> &Insts)
                                   const {
  return std::find(Insts.begin(), Insts.end(), I) != Insts.end();
}