aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/clang16/lib/Analysis/LiveVariables.cpp
blob: 6d03dd05ca3d27704c9d90c13691c26ff97efb1a (plain) (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
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
//=- LiveVariables.cpp - Live Variable Analysis for Source CFGs ----------*-==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements Live Variables analysis for source-level CFGs.
//
//===----------------------------------------------------------------------===//

#include "clang/Analysis/Analyses/LiveVariables.h"
#include "clang/AST/Stmt.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/Analysis/AnalysisDeclContext.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/FlowSensitive/DataflowWorklist.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <optional>
#include <vector>

using namespace clang;

namespace {
class LiveVariablesImpl {
public:
  AnalysisDeclContext &analysisContext;
  llvm::ImmutableSet<const Expr *>::Factory ESetFact;
  llvm::ImmutableSet<const VarDecl *>::Factory DSetFact;
  llvm::ImmutableSet<const BindingDecl *>::Factory BSetFact;
  llvm::DenseMap<const CFGBlock *, LiveVariables::LivenessValues> blocksEndToLiveness;
  llvm::DenseMap<const CFGBlock *, LiveVariables::LivenessValues> blocksBeginToLiveness;
  llvm::DenseMap<const Stmt *, LiveVariables::LivenessValues> stmtsToLiveness;
  llvm::DenseMap<const DeclRefExpr *, unsigned> inAssignment;
  const bool killAtAssign;

  LiveVariables::LivenessValues
  merge(LiveVariables::LivenessValues valsA,
        LiveVariables::LivenessValues valsB);

  LiveVariables::LivenessValues
  runOnBlock(const CFGBlock *block, LiveVariables::LivenessValues val,
             LiveVariables::Observer *obs = nullptr);

  void dumpBlockLiveness(const SourceManager& M);
  void dumpExprLiveness(const SourceManager& M);

  LiveVariablesImpl(AnalysisDeclContext &ac, bool KillAtAssign)
      : analysisContext(ac),
        ESetFact(false), // Do not canonicalize ImmutableSets by default.
        DSetFact(false), // This is a *major* performance win.
        BSetFact(false), killAtAssign(KillAtAssign) {}
};
} // namespace

static LiveVariablesImpl &getImpl(void *x) {
  return *((LiveVariablesImpl *) x);
}

//===----------------------------------------------------------------------===//
// Operations and queries on LivenessValues.
//===----------------------------------------------------------------------===//

bool LiveVariables::LivenessValues::isLive(const Expr *E) const {
  return liveExprs.contains(E);
}

bool LiveVariables::LivenessValues::isLive(const VarDecl *D) const {
  if (const auto *DD = dyn_cast<DecompositionDecl>(D)) {
    bool alive = false;
    for (const BindingDecl *BD : DD->bindings())
      alive |= liveBindings.contains(BD);

    // Note: the only known case this condition is necessary, is when a bindig
    // to a tuple-like structure is created. The HoldingVar initializers have a
    // DeclRefExpr to the DecompositionDecl.
    alive |= liveDecls.contains(DD);
    return alive;
  }
  return liveDecls.contains(D);
}

namespace {
  template <typename SET>
  SET mergeSets(SET A, SET B) {
    if (A.isEmpty())
      return B;

    for (typename SET::iterator it = B.begin(), ei = B.end(); it != ei; ++it) {
      A = A.add(*it);
    }
    return A;
  }
} // namespace

void LiveVariables::Observer::anchor() { }

LiveVariables::LivenessValues
LiveVariablesImpl::merge(LiveVariables::LivenessValues valsA,
                         LiveVariables::LivenessValues valsB) {

  llvm::ImmutableSetRef<const Expr *> SSetRefA(
      valsA.liveExprs.getRootWithoutRetain(), ESetFact.getTreeFactory()),
      SSetRefB(valsB.liveExprs.getRootWithoutRetain(),
               ESetFact.getTreeFactory());

  llvm::ImmutableSetRef<const VarDecl *>
    DSetRefA(valsA.liveDecls.getRootWithoutRetain(), DSetFact.getTreeFactory()),
    DSetRefB(valsB.liveDecls.getRootWithoutRetain(), DSetFact.getTreeFactory());

  llvm::ImmutableSetRef<const BindingDecl *>
    BSetRefA(valsA.liveBindings.getRootWithoutRetain(), BSetFact.getTreeFactory()),
    BSetRefB(valsB.liveBindings.getRootWithoutRetain(), BSetFact.getTreeFactory());

  SSetRefA = mergeSets(SSetRefA, SSetRefB);
  DSetRefA = mergeSets(DSetRefA, DSetRefB);
  BSetRefA = mergeSets(BSetRefA, BSetRefB);

  // asImmutableSet() canonicalizes the tree, allowing us to do an easy
  // comparison afterwards.
  return LiveVariables::LivenessValues(SSetRefA.asImmutableSet(),
                                       DSetRefA.asImmutableSet(),
                                       BSetRefA.asImmutableSet());
}

bool LiveVariables::LivenessValues::equals(const LivenessValues &V) const {
  return liveExprs == V.liveExprs && liveDecls == V.liveDecls;
}

//===----------------------------------------------------------------------===//
// Query methods.
//===----------------------------------------------------------------------===//

static bool isAlwaysAlive(const VarDecl *D) {
  return D->hasGlobalStorage();
}

bool LiveVariables::isLive(const CFGBlock *B, const VarDecl *D) {
  return isAlwaysAlive(D) || getImpl(impl).blocksEndToLiveness[B].isLive(D);
}

bool LiveVariables::isLive(const Stmt *S, const VarDecl *D) {
  return isAlwaysAlive(D) || getImpl(impl).stmtsToLiveness[S].isLive(D);
}

bool LiveVariables::isLive(const Stmt *Loc, const Expr *Val) {
  return getImpl(impl).stmtsToLiveness[Loc].isLive(Val);
}

//===----------------------------------------------------------------------===//
// Dataflow computation.
//===----------------------------------------------------------------------===//

namespace {
class TransferFunctions : public StmtVisitor<TransferFunctions> {
  LiveVariablesImpl &LV;
  LiveVariables::LivenessValues &val;
  LiveVariables::Observer *observer;
  const CFGBlock *currentBlock;
public:
  TransferFunctions(LiveVariablesImpl &im,
                    LiveVariables::LivenessValues &Val,
                    LiveVariables::Observer *Observer,
                    const CFGBlock *CurrentBlock)
  : LV(im), val(Val), observer(Observer), currentBlock(CurrentBlock) {}

  void VisitBinaryOperator(BinaryOperator *BO);
  void VisitBlockExpr(BlockExpr *BE);
  void VisitDeclRefExpr(DeclRefExpr *DR);
  void VisitDeclStmt(DeclStmt *DS);
  void VisitObjCForCollectionStmt(ObjCForCollectionStmt *OS);
  void VisitUnaryExprOrTypeTraitExpr(UnaryExprOrTypeTraitExpr *UE);
  void VisitUnaryOperator(UnaryOperator *UO);
  void Visit(Stmt *S);
};
} // namespace

static const VariableArrayType *FindVA(QualType Ty) {
  const Type *ty = Ty.getTypePtr();
  while (const ArrayType *VT = dyn_cast<ArrayType>(ty)) {
    if (const VariableArrayType *VAT = dyn_cast<VariableArrayType>(VT))
      if (VAT->getSizeExpr())
        return VAT;

    ty = VT->getElementType().getTypePtr();
  }

  return nullptr;
}

static const Expr *LookThroughExpr(const Expr *E) {
  while (E) {
    if (const Expr *Ex = dyn_cast<Expr>(E))
      E = Ex->IgnoreParens();
    if (const FullExpr *FE = dyn_cast<FullExpr>(E)) {
      E = FE->getSubExpr();
      continue;
    }
    if (const OpaqueValueExpr *OVE = dyn_cast<OpaqueValueExpr>(E)) {
      E = OVE->getSourceExpr();
      continue;
    }
    break;
  }
  return E;
}

static void AddLiveExpr(llvm::ImmutableSet<const Expr *> &Set,
                        llvm::ImmutableSet<const Expr *>::Factory &F,
                        const Expr *E) {
  Set = F.add(Set, LookThroughExpr(E));
}

void TransferFunctions::Visit(Stmt *S) {
  if (observer)
    observer->observeStmt(S, currentBlock, val);

  StmtVisitor<TransferFunctions>::Visit(S);

  if (const auto *E = dyn_cast<Expr>(S)) {
    val.liveExprs = LV.ESetFact.remove(val.liveExprs, E);
  }

  // Mark all children expressions live.

  switch (S->getStmtClass()) {
    default:
      break;
    case Stmt::StmtExprClass: {
      // For statement expressions, look through the compound statement.
      S = cast<StmtExpr>(S)->getSubStmt();
      break;
    }
    case Stmt::CXXMemberCallExprClass: {
      // Include the implicit "this" pointer as being live.
      CXXMemberCallExpr *CE = cast<CXXMemberCallExpr>(S);
      if (Expr *ImplicitObj = CE->getImplicitObjectArgument()) {
        AddLiveExpr(val.liveExprs, LV.ESetFact, ImplicitObj);
      }
      break;
    }
    case Stmt::ObjCMessageExprClass: {
      // In calls to super, include the implicit "self" pointer as being live.
      ObjCMessageExpr *CE = cast<ObjCMessageExpr>(S);
      if (CE->getReceiverKind() == ObjCMessageExpr::SuperInstance)
        val.liveDecls = LV.DSetFact.add(val.liveDecls,
                                        LV.analysisContext.getSelfDecl());
      break;
    }
    case Stmt::DeclStmtClass: {
      const DeclStmt *DS = cast<DeclStmt>(S);
      if (const VarDecl *VD = dyn_cast<VarDecl>(DS->getSingleDecl())) {
        for (const VariableArrayType* VA = FindVA(VD->getType());
             VA != nullptr; VA = FindVA(VA->getElementType())) {
          AddLiveExpr(val.liveExprs, LV.ESetFact, VA->getSizeExpr());
        }
      }
      break;
    }
    case Stmt::PseudoObjectExprClass: {
      // A pseudo-object operation only directly consumes its result
      // expression.
      Expr *child = cast<PseudoObjectExpr>(S)->getResultExpr();
      if (!child) return;
      if (OpaqueValueExpr *OV = dyn_cast<OpaqueValueExpr>(child))
        child = OV->getSourceExpr();
      child = child->IgnoreParens();
      val.liveExprs = LV.ESetFact.add(val.liveExprs, child);
      return;
    }

    // FIXME: These cases eventually shouldn't be needed.
    case Stmt::ExprWithCleanupsClass: {
      S = cast<ExprWithCleanups>(S)->getSubExpr();
      break;
    }
    case Stmt::CXXBindTemporaryExprClass: {
      S = cast<CXXBindTemporaryExpr>(S)->getSubExpr();
      break;
    }
    case Stmt::UnaryExprOrTypeTraitExprClass: {
      // No need to unconditionally visit subexpressions.
      return;
    }
    case Stmt::IfStmtClass: {
      // If one of the branches is an expression rather than a compound
      // statement, it will be bad if we mark it as live at the terminator
      // of the if-statement (i.e., immediately after the condition expression).
      AddLiveExpr(val.liveExprs, LV.ESetFact, cast<IfStmt>(S)->getCond());
      return;
    }
    case Stmt::WhileStmtClass: {
      // If the loop body is an expression rather than a compound statement,
      // it will be bad if we mark it as live at the terminator of the loop
      // (i.e., immediately after the condition expression).
      AddLiveExpr(val.liveExprs, LV.ESetFact, cast<WhileStmt>(S)->getCond());
      return;
    }
    case Stmt::DoStmtClass: {
      // If the loop body is an expression rather than a compound statement,
      // it will be bad if we mark it as live at the terminator of the loop
      // (i.e., immediately after the condition expression).
      AddLiveExpr(val.liveExprs, LV.ESetFact, cast<DoStmt>(S)->getCond());
      return;
    }
    case Stmt::ForStmtClass: {
      // If the loop body is an expression rather than a compound statement,
      // it will be bad if we mark it as live at the terminator of the loop
      // (i.e., immediately after the condition expression).
      AddLiveExpr(val.liveExprs, LV.ESetFact, cast<ForStmt>(S)->getCond());
      return;
    }

  }

  // HACK + FIXME: What is this? One could only guess that this is an attempt to
  // fish for live values, for example, arguments from a call expression.
  // Maybe we could take inspiration from UninitializedVariable analysis?
  for (Stmt *Child : S->children()) {
    if (const auto *E = dyn_cast_or_null<Expr>(Child))
      AddLiveExpr(val.liveExprs, LV.ESetFact, E);
  }
}

static bool writeShouldKill(const VarDecl *VD) {
  return VD && !VD->getType()->isReferenceType() &&
    !isAlwaysAlive(VD);
}

void TransferFunctions::VisitBinaryOperator(BinaryOperator *B) {
  if (LV.killAtAssign && B->getOpcode() == BO_Assign) {
    if (const auto *DR = dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParens())) {
      LV.inAssignment[DR] = 1;
    }
  }
  if (B->isAssignmentOp()) {
    if (!LV.killAtAssign)
      return;

    // Assigning to a variable?
    Expr *LHS = B->getLHS()->IgnoreParens();

    if (DeclRefExpr *DR = dyn_cast<DeclRefExpr>(LHS)) {
      const Decl* D = DR->getDecl();
      bool Killed = false;

      if (const BindingDecl* BD = dyn_cast<BindingDecl>(D)) {
        Killed = !BD->getType()->isReferenceType();
        if (Killed) {
          if (const auto *HV = BD->getHoldingVar())
            val.liveDecls = LV.DSetFact.remove(val.liveDecls, HV);

          val.liveBindings = LV.BSetFact.remove(val.liveBindings, BD);
        }
      } else if (const auto *VD = dyn_cast<VarDecl>(D)) {
        Killed = writeShouldKill(VD);
        if (Killed)
          val.liveDecls = LV.DSetFact.remove(val.liveDecls, VD);

      }

      if (Killed && observer)
        observer->observerKill(DR);
    }
  }
}

void TransferFunctions::VisitBlockExpr(BlockExpr *BE) {
  for (const VarDecl *VD :
       LV.analysisContext.getReferencedBlockVars(BE->getBlockDecl())) {
    if (isAlwaysAlive(VD))
      continue;
    val.liveDecls = LV.DSetFact.add(val.liveDecls, VD);
  }
}

void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *DR) {
  const Decl* D = DR->getDecl();
  bool InAssignment = LV.inAssignment[DR];
  if (const auto *BD = dyn_cast<BindingDecl>(D)) {
    if (!InAssignment) {
      if (const auto *HV = BD->getHoldingVar())
        val.liveDecls = LV.DSetFact.add(val.liveDecls, HV);

      val.liveBindings = LV.BSetFact.add(val.liveBindings, BD);
    }
  } else if (const auto *VD = dyn_cast<VarDecl>(D)) {
    if (!InAssignment && !isAlwaysAlive(VD))
      val.liveDecls = LV.DSetFact.add(val.liveDecls, VD);
  }
}

void TransferFunctions::VisitDeclStmt(DeclStmt *DS) {
  for (const auto *DI : DS->decls()) {
    if (const auto *DD = dyn_cast<DecompositionDecl>(DI)) {
      for (const auto *BD : DD->bindings()) {
        if (const auto *HV = BD->getHoldingVar())
          val.liveDecls = LV.DSetFact.remove(val.liveDecls, HV);

        val.liveBindings = LV.BSetFact.remove(val.liveBindings, BD);
      }

      // When a bindig to a tuple-like structure is created, the HoldingVar
      // initializers have a DeclRefExpr to the DecompositionDecl.
      val.liveDecls = LV.DSetFact.remove(val.liveDecls, DD);
    } else if (const auto *VD = dyn_cast<VarDecl>(DI)) {
      if (!isAlwaysAlive(VD))
        val.liveDecls = LV.DSetFact.remove(val.liveDecls, VD);
    }
  }
}

void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *OS) {
  // Kill the iteration variable.
  DeclRefExpr *DR = nullptr;
  const VarDecl *VD = nullptr;

  Stmt *element = OS->getElement();
  if (DeclStmt *DS = dyn_cast<DeclStmt>(element)) {
    VD = cast<VarDecl>(DS->getSingleDecl());
  }
  else if ((DR = dyn_cast<DeclRefExpr>(cast<Expr>(element)->IgnoreParens()))) {
    VD = cast<VarDecl>(DR->getDecl());
  }

  if (VD) {
    val.liveDecls = LV.DSetFact.remove(val.liveDecls, VD);
    if (observer && DR)
      observer->observerKill(DR);
  }
}

void TransferFunctions::
VisitUnaryExprOrTypeTraitExpr(UnaryExprOrTypeTraitExpr *UE)
{
  // While sizeof(var) doesn't technically extend the liveness of 'var', it
  // does extent the liveness of metadata if 'var' is a VariableArrayType.
  // We handle that special case here.
  if (UE->getKind() != UETT_SizeOf || UE->isArgumentType())
    return;

  const Expr *subEx = UE->getArgumentExpr();
  if (subEx->getType()->isVariableArrayType()) {
    assert(subEx->isLValue());
    val.liveExprs = LV.ESetFact.add(val.liveExprs, subEx->IgnoreParens());
  }
}

void TransferFunctions::VisitUnaryOperator(UnaryOperator *UO) {
  // Treat ++/-- as a kill.
  // Note we don't actually have to do anything if we don't have an observer,
  // since a ++/-- acts as both a kill and a "use".
  if (!observer)
    return;

  switch (UO->getOpcode()) {
  default:
    return;
  case UO_PostInc:
  case UO_PostDec:
  case UO_PreInc:
  case UO_PreDec:
    break;
  }

  if (auto *DR = dyn_cast<DeclRefExpr>(UO->getSubExpr()->IgnoreParens())) {
    const Decl *D = DR->getDecl();
    if (isa<VarDecl>(D) || isa<BindingDecl>(D)) {
      // Treat ++/-- as a kill.
      observer->observerKill(DR);
    }
  }
}

LiveVariables::LivenessValues
LiveVariablesImpl::runOnBlock(const CFGBlock *block,
                              LiveVariables::LivenessValues val,
                              LiveVariables::Observer *obs) {

  TransferFunctions TF(*this, val, obs, block);

  // Visit the terminator (if any).
  if (const Stmt *term = block->getTerminatorStmt())
    TF.Visit(const_cast<Stmt*>(term));

  // Apply the transfer function for all Stmts in the block.
  for (CFGBlock::const_reverse_iterator it = block->rbegin(),
       ei = block->rend(); it != ei; ++it) {
    const CFGElement &elem = *it;

    if (std::optional<CFGAutomaticObjDtor> Dtor =
            elem.getAs<CFGAutomaticObjDtor>()) {
      val.liveDecls = DSetFact.add(val.liveDecls, Dtor->getVarDecl());
      continue;
    }

    if (!elem.getAs<CFGStmt>())
      continue;

    const Stmt *S = elem.castAs<CFGStmt>().getStmt();
    TF.Visit(const_cast<Stmt*>(S));
    stmtsToLiveness[S] = val;
  }
  return val;
}

void LiveVariables::runOnAllBlocks(LiveVariables::Observer &obs) {
  const CFG *cfg = getImpl(impl).analysisContext.getCFG();
  for (CFG::const_iterator it = cfg->begin(), ei = cfg->end(); it != ei; ++it)
    getImpl(impl).runOnBlock(*it, getImpl(impl).blocksEndToLiveness[*it], &obs);
}

LiveVariables::LiveVariables(void *im) : impl(im) {}

LiveVariables::~LiveVariables() {
  delete (LiveVariablesImpl*) impl;
}

std::unique_ptr<LiveVariables>
LiveVariables::computeLiveness(AnalysisDeclContext &AC, bool killAtAssign) {

  // No CFG?  Bail out.
  CFG *cfg = AC.getCFG();
  if (!cfg)
    return nullptr;

  // The analysis currently has scalability issues for very large CFGs.
  // Bail out if it looks too large.
  if (cfg->getNumBlockIDs() > 300000)
    return nullptr;

  LiveVariablesImpl *LV = new LiveVariablesImpl(AC, killAtAssign);

  // Construct the dataflow worklist.  Enqueue the exit block as the
  // start of the analysis.
  BackwardDataflowWorklist worklist(*cfg, AC);
  llvm::BitVector everAnalyzedBlock(cfg->getNumBlockIDs());

  // FIXME: we should enqueue using post order.
  for (const CFGBlock *B : cfg->nodes()) {
    worklist.enqueueBlock(B);
  }

  while (const CFGBlock *block = worklist.dequeue()) {
    // Determine if the block's end value has changed.  If not, we
    // have nothing left to do for this block.
    LivenessValues &prevVal = LV->blocksEndToLiveness[block];

    // Merge the values of all successor blocks.
    LivenessValues val;
    for (CFGBlock::const_succ_iterator it = block->succ_begin(),
                                       ei = block->succ_end(); it != ei; ++it) {
      if (const CFGBlock *succ = *it) {
        val = LV->merge(val, LV->blocksBeginToLiveness[succ]);
      }
    }

    if (!everAnalyzedBlock[block->getBlockID()])
      everAnalyzedBlock[block->getBlockID()] = true;
    else if (prevVal.equals(val))
      continue;

    prevVal = val;

    // Update the dataflow value for the start of this block.
    LV->blocksBeginToLiveness[block] = LV->runOnBlock(block, val);

    // Enqueue the value to the predecessors.
    worklist.enqueuePredecessors(block);
  }

  return std::unique_ptr<LiveVariables>(new LiveVariables(LV));
}

void LiveVariables::dumpBlockLiveness(const SourceManager &M) {
  getImpl(impl).dumpBlockLiveness(M);
}

void LiveVariablesImpl::dumpBlockLiveness(const SourceManager &M) {
  std::vector<const CFGBlock *> vec;
  for (llvm::DenseMap<const CFGBlock *, LiveVariables::LivenessValues>::iterator
       it = blocksEndToLiveness.begin(), ei = blocksEndToLiveness.end();
       it != ei; ++it) {
    vec.push_back(it->first);
  }
  llvm::sort(vec, [](const CFGBlock *A, const CFGBlock *B) {
    return A->getBlockID() < B->getBlockID();
  });

  std::vector<const VarDecl*> declVec;

  for (std::vector<const CFGBlock *>::iterator
        it = vec.begin(), ei = vec.end(); it != ei; ++it) {
    llvm::errs() << "\n[ B" << (*it)->getBlockID()
                 << " (live variables at block exit) ]\n";

    LiveVariables::LivenessValues vals = blocksEndToLiveness[*it];
    declVec.clear();

    for (llvm::ImmutableSet<const VarDecl *>::iterator si =
          vals.liveDecls.begin(),
          se = vals.liveDecls.end(); si != se; ++si) {
      declVec.push_back(*si);
    }

    llvm::sort(declVec, [](const Decl *A, const Decl *B) {
      return A->getBeginLoc() < B->getBeginLoc();
    });

    for (std::vector<const VarDecl*>::iterator di = declVec.begin(),
         de = declVec.end(); di != de; ++di) {
      llvm::errs() << " " << (*di)->getDeclName().getAsString()
                   << " <";
      (*di)->getLocation().print(llvm::errs(), M);
      llvm::errs() << ">\n";
    }
  }
  llvm::errs() << "\n";
}

void LiveVariables::dumpExprLiveness(const SourceManager &M) {
  getImpl(impl).dumpExprLiveness(M);
}

void LiveVariablesImpl::dumpExprLiveness(const SourceManager &M) {
  // Don't iterate over blockEndsToLiveness directly because it's not sorted.
  for (const CFGBlock *B : *analysisContext.getCFG()) {

    llvm::errs() << "\n[ B" << B->getBlockID()
                 << " (live expressions at block exit) ]\n";
    for (const Expr *E : blocksEndToLiveness[B].liveExprs) {
      llvm::errs() << "\n";
      E->dump();
    }
    llvm::errs() << "\n";
  }
}

const void *LiveVariables::getTag() { static int x; return &x; }
const void *RelaxedLiveVariables::getTag() { static int x; return &x; }