GVN.cpp revision 5c274eebc6b5444db123028f29b7491763c08585 
1//===- GVN.cpp - Eliminate redundant values and loads ------------===//
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 pass performs global value numbering to eliminate fully redundant
11// instructions.  It also performs simple dead load elimination.
12//
13// Note that this pass does the value numbering itself, it does not use the
14// ValueNumbering analysis passes.
15//
16//===----------------------------------------------------------------------===//
17
18#define DEBUG_TYPE "gvn"
19#include "llvm/Transforms/Scalar.h"
20#include "llvm/BasicBlock.h"
21#include "llvm/Constants.h"
22#include "llvm/DerivedTypes.h"
23#include "llvm/Function.h"
24#include "llvm/Instructions.h"
25#include "llvm/Value.h"
26#include "llvm/ADT/DenseMap.h"
27#include "llvm/ADT/DepthFirstIterator.h"
28#include "llvm/ADT/SmallPtrSet.h"
29#include "llvm/ADT/SmallVector.h"
30#include "llvm/ADT/Statistic.h"
31#include "llvm/Analysis/Dominators.h"
32#include "llvm/Analysis/AliasAnalysis.h"
33#include "llvm/Analysis/MemoryDependenceAnalysis.h"
34#include "llvm/Support/CFG.h"
35#include "llvm/Support/Compiler.h"
36#include "llvm/Support/Debug.h"
37#include "llvm/Transforms/Utils/BasicBlockUtils.h"
38using namespace llvm;
39
40STATISTIC(NumGVNInstr, "Number of instructions deleted");
41STATISTIC(NumGVNLoad, "Number of loads deleted");
42STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
43
44//===----------------------------------------------------------------------===//
45//                         ValueTable Class
46//===----------------------------------------------------------------------===//
47
48/// This class holds the mapping between values and value numbers.  It is used
49/// as an efficient mechanism to determine the expression-wise equivalence of
50/// two values.
51namespace {
52  struct VISIBILITY_HIDDEN Expression {
53    enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
54                            FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
55                            ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
56                            ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
57                            FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
58                            FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
59                            FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
60                            SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
61                            FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
62                            PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
63                            EMPTY, TOMBSTONE };
64
65    ExpressionOpcode opcode;
66    const Type* type;
67    uint32_t firstVN;
68    uint32_t secondVN;
69    uint32_t thirdVN;
70    SmallVector<uint32_t, 4> varargs;
71    Value* function;
72
73    Expression() { }
74    Expression(ExpressionOpcode o) : opcode(o) { }
75
76    bool operator==(const Expression &other) const {
77      if (opcode != other.opcode)
78        return false;
79      else if (opcode == EMPTY || opcode == TOMBSTONE)
80        return true;
81      else if (type != other.type)
82        return false;
83      else if (function != other.function)
84        return false;
85      else if (firstVN != other.firstVN)
86        return false;
87      else if (secondVN != other.secondVN)
88        return false;
89      else if (thirdVN != other.thirdVN)
90        return false;
91      else {
92        if (varargs.size() != other.varargs.size())
93          return false;
94
95        for (size_t i = 0; i < varargs.size(); ++i)
96          if (varargs[i] != other.varargs[i])
97            return false;
98
99        return true;
100      }
101    }
102
103    bool operator!=(const Expression &other) const {
104      if (opcode != other.opcode)
105        return true;
106      else if (opcode == EMPTY || opcode == TOMBSTONE)
107        return false;
108      else if (type != other.type)
109        return true;
110      else if (function != other.function)
111        return true;
112      else if (firstVN != other.firstVN)
113        return true;
114      else if (secondVN != other.secondVN)
115        return true;
116      else if (thirdVN != other.thirdVN)
117        return true;
118      else {
119        if (varargs.size() != other.varargs.size())
120          return true;
121
122        for (size_t i = 0; i < varargs.size(); ++i)
123          if (varargs[i] != other.varargs[i])
124            return true;
125
126          return false;
127      }
128    }
129  };
130
131  class VISIBILITY_HIDDEN ValueTable {
132    private:
133      DenseMap<Value*, uint32_t> valueNumbering;
134      DenseMap<Expression, uint32_t> expressionNumbering;
135      AliasAnalysis* AA;
136      MemoryDependenceAnalysis* MD;
137      DominatorTree* DT;
138
139      uint32_t nextValueNumber;
140
141      Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
142      Expression::ExpressionOpcode getOpcode(CmpInst* C);
143      Expression::ExpressionOpcode getOpcode(CastInst* C);
144      Expression create_expression(BinaryOperator* BO);
145      Expression create_expression(CmpInst* C);
146      Expression create_expression(ShuffleVectorInst* V);
147      Expression create_expression(ExtractElementInst* C);
148      Expression create_expression(InsertElementInst* V);
149      Expression create_expression(SelectInst* V);
150      Expression create_expression(CastInst* C);
151      Expression create_expression(GetElementPtrInst* G);
152      Expression create_expression(CallInst* C);
153      Expression create_expression(Constant* C);
154    public:
155      ValueTable() : nextValueNumber(1) { }
156      uint32_t lookup_or_add(Value* V);
157      uint32_t lookup(Value* V) const;
158      void add(Value* V, uint32_t num);
159      void clear();
160      void erase(Value* v);
161      unsigned size();
162      void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
163      void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
164      void setDomTree(DominatorTree* D) { DT = D; }
165  };
166}
167
168namespace llvm {
169template <> struct DenseMapInfo<Expression> {
170  static inline Expression getEmptyKey() {
171    return Expression(Expression::EMPTY);
172  }
173
174  static inline Expression getTombstoneKey() {
175    return Expression(Expression::TOMBSTONE);
176  }
177
178  static unsigned getHashValue(const Expression e) {
179    unsigned hash = e.opcode;
180
181    hash = e.firstVN + hash * 37;
182    hash = e.secondVN + hash * 37;
183    hash = e.thirdVN + hash * 37;
184
185    hash = ((unsigned)((uintptr_t)e.type >> 4) ^
186            (unsigned)((uintptr_t)e.type >> 9)) +
187           hash * 37;
188
189    for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
190         E = e.varargs.end(); I != E; ++I)
191      hash = *I + hash * 37;
192
193    hash = ((unsigned)((uintptr_t)e.function >> 4) ^
194            (unsigned)((uintptr_t)e.function >> 9)) +
195           hash * 37;
196
197    return hash;
198  }
199  static bool isEqual(const Expression &LHS, const Expression &RHS) {
200    return LHS == RHS;
201  }
202  static bool isPod() { return true; }
203};
204}
205
206//===----------------------------------------------------------------------===//
207//                     ValueTable Internal Functions
208//===----------------------------------------------------------------------===//
209Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
210  switch(BO->getOpcode()) {
211  default: // THIS SHOULD NEVER HAPPEN
212    assert(0 && "Binary operator with unknown opcode?");
213  case Instruction::Add:  return Expression::ADD;
214  case Instruction::Sub:  return Expression::SUB;
215  case Instruction::Mul:  return Expression::MUL;
216  case Instruction::UDiv: return Expression::UDIV;
217  case Instruction::SDiv: return Expression::SDIV;
218  case Instruction::FDiv: return Expression::FDIV;
219  case Instruction::URem: return Expression::UREM;
220  case Instruction::SRem: return Expression::SREM;
221  case Instruction::FRem: return Expression::FREM;
222  case Instruction::Shl:  return Expression::SHL;
223  case Instruction::LShr: return Expression::LSHR;
224  case Instruction::AShr: return Expression::ASHR;
225  case Instruction::And:  return Expression::AND;
226  case Instruction::Or:   return Expression::OR;
227  case Instruction::Xor:  return Expression::XOR;
228  }
229}
230
231Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
232  if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) {
233    switch (C->getPredicate()) {
234    default:  // THIS SHOULD NEVER HAPPEN
235      assert(0 && "Comparison with unknown predicate?");
236    case ICmpInst::ICMP_EQ:  return Expression::ICMPEQ;
237    case ICmpInst::ICMP_NE:  return Expression::ICMPNE;
238    case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
239    case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
240    case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
241    case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
242    case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
243    case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
244    case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
245    case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
246    }
247  }
248  assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare");
249  switch (C->getPredicate()) {
250  default: // THIS SHOULD NEVER HAPPEN
251    assert(0 && "Comparison with unknown predicate?");
252  case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
253  case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
254  case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
255  case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
256  case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
257  case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
258  case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
259  case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
260  case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
261  case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
262  case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
263  case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
264  case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
265  case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
266  }
267}
268
269Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
270  switch(C->getOpcode()) {
271  default: // THIS SHOULD NEVER HAPPEN
272    assert(0 && "Cast operator with unknown opcode?");
273  case Instruction::Trunc:    return Expression::TRUNC;
274  case Instruction::ZExt:     return Expression::ZEXT;
275  case Instruction::SExt:     return Expression::SEXT;
276  case Instruction::FPToUI:   return Expression::FPTOUI;
277  case Instruction::FPToSI:   return Expression::FPTOSI;
278  case Instruction::UIToFP:   return Expression::UITOFP;
279  case Instruction::SIToFP:   return Expression::SITOFP;
280  case Instruction::FPTrunc:  return Expression::FPTRUNC;
281  case Instruction::FPExt:    return Expression::FPEXT;
282  case Instruction::PtrToInt: return Expression::PTRTOINT;
283  case Instruction::IntToPtr: return Expression::INTTOPTR;
284  case Instruction::BitCast:  return Expression::BITCAST;
285  }
286}
287
288Expression ValueTable::create_expression(CallInst* C) {
289  Expression e;
290
291  e.type = C->getType();
292  e.firstVN = 0;
293  e.secondVN = 0;
294  e.thirdVN = 0;
295  e.function = C->getCalledFunction();
296  e.opcode = Expression::CALL;
297
298  for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
299       I != E; ++I)
300    e.varargs.push_back(lookup_or_add(*I));
301
302  return e;
303}
304
305Expression ValueTable::create_expression(BinaryOperator* BO) {
306  Expression e;
307
308  e.firstVN = lookup_or_add(BO->getOperand(0));
309  e.secondVN = lookup_or_add(BO->getOperand(1));
310  e.thirdVN = 0;
311  e.function = 0;
312  e.type = BO->getType();
313  e.opcode = getOpcode(BO);
314
315  return e;
316}
317
318Expression ValueTable::create_expression(CmpInst* C) {
319  Expression e;
320
321  e.firstVN = lookup_or_add(C->getOperand(0));
322  e.secondVN = lookup_or_add(C->getOperand(1));
323  e.thirdVN = 0;
324  e.function = 0;
325  e.type = C->getType();
326  e.opcode = getOpcode(C);
327
328  return e;
329}
330
331Expression ValueTable::create_expression(CastInst* C) {
332  Expression e;
333
334  e.firstVN = lookup_or_add(C->getOperand(0));
335  e.secondVN = 0;
336  e.thirdVN = 0;
337  e.function = 0;
338  e.type = C->getType();
339  e.opcode = getOpcode(C);
340
341  return e;
342}
343
344Expression ValueTable::create_expression(ShuffleVectorInst* S) {
345  Expression e;
346
347  e.firstVN = lookup_or_add(S->getOperand(0));
348  e.secondVN = lookup_or_add(S->getOperand(1));
349  e.thirdVN = lookup_or_add(S->getOperand(2));
350  e.function = 0;
351  e.type = S->getType();
352  e.opcode = Expression::SHUFFLE;
353
354  return e;
355}
356
357Expression ValueTable::create_expression(ExtractElementInst* E) {
358  Expression e;
359
360  e.firstVN = lookup_or_add(E->getOperand(0));
361  e.secondVN = lookup_or_add(E->getOperand(1));
362  e.thirdVN = 0;
363  e.function = 0;
364  e.type = E->getType();
365  e.opcode = Expression::EXTRACT;
366
367  return e;
368}
369
370Expression ValueTable::create_expression(InsertElementInst* I) {
371  Expression e;
372
373  e.firstVN = lookup_or_add(I->getOperand(0));
374  e.secondVN = lookup_or_add(I->getOperand(1));
375  e.thirdVN = lookup_or_add(I->getOperand(2));
376  e.function = 0;
377  e.type = I->getType();
378  e.opcode = Expression::INSERT;
379
380  return e;
381}
382
383Expression ValueTable::create_expression(SelectInst* I) {
384  Expression e;
385
386  e.firstVN = lookup_or_add(I->getCondition());
387  e.secondVN = lookup_or_add(I->getTrueValue());
388  e.thirdVN = lookup_or_add(I->getFalseValue());
389  e.function = 0;
390  e.type = I->getType();
391  e.opcode = Expression::SELECT;
392
393  return e;
394}
395
396Expression ValueTable::create_expression(GetElementPtrInst* G) {
397  Expression e;
398
399  e.firstVN = lookup_or_add(G->getPointerOperand());
400  e.secondVN = 0;
401  e.thirdVN = 0;
402  e.function = 0;
403  e.type = G->getType();
404  e.opcode = Expression::GEP;
405
406  for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
407       I != E; ++I)
408    e.varargs.push_back(lookup_or_add(*I));
409
410  return e;
411}
412
413//===----------------------------------------------------------------------===//
414//                     ValueTable External Functions
415//===----------------------------------------------------------------------===//
416
417/// add - Insert a value into the table with a specified value number.
418void ValueTable::add(Value* V, uint32_t num) {
419  valueNumbering.insert(std::make_pair(V, num));
420}
421
422/// lookup_or_add - Returns the value number for the specified value, assigning
423/// it a new number if it did not have one before.
424uint32_t ValueTable::lookup_or_add(Value* V) {
425  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
426  if (VI != valueNumbering.end())
427    return VI->second;
428
429  if (CallInst* C = dyn_cast<CallInst>(V)) {
430    if (AA->doesNotAccessMemory(C)) {
431      Expression e = create_expression(C);
432
433      DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
434      if (EI != expressionNumbering.end()) {
435        valueNumbering.insert(std::make_pair(V, EI->second));
436        return EI->second;
437      } else {
438        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
439        valueNumbering.insert(std::make_pair(V, nextValueNumber));
440
441        return nextValueNumber++;
442      }
443    } else if (AA->onlyReadsMemory(C)) {
444      Expression e = create_expression(C);
445
446      if (expressionNumbering.find(e) == expressionNumbering.end()) {
447        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
448        valueNumbering.insert(std::make_pair(V, nextValueNumber));
449        return nextValueNumber++;
450      }
451
452      Instruction* local_dep = MD->getDependency(C);
453
454      if (local_dep == MemoryDependenceAnalysis::None) {
455        valueNumbering.insert(std::make_pair(V, nextValueNumber));
456        return nextValueNumber++;
457      } else if (local_dep != MemoryDependenceAnalysis::NonLocal) {
458        if (!isa<CallInst>(local_dep)) {
459          valueNumbering.insert(std::make_pair(V, nextValueNumber));
460          return nextValueNumber++;
461        }
462
463        CallInst* local_cdep = cast<CallInst>(local_dep);
464
465        if (local_cdep->getCalledFunction() != C->getCalledFunction() ||
466            local_cdep->getNumOperands() != C->getNumOperands()) {
467          valueNumbering.insert(std::make_pair(V, nextValueNumber));
468          return nextValueNumber++;
469        } else if (!C->getCalledFunction()) {
470          valueNumbering.insert(std::make_pair(V, nextValueNumber));
471          return nextValueNumber++;
472        } else {
473          for (unsigned i = 1; i < C->getNumOperands(); ++i) {
474            uint32_t c_vn = lookup_or_add(C->getOperand(i));
475            uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
476            if (c_vn != cd_vn) {
477              valueNumbering.insert(std::make_pair(V, nextValueNumber));
478              return nextValueNumber++;
479            }
480          }
481
482          uint32_t v = lookup_or_add(local_cdep);
483          valueNumbering.insert(std::make_pair(V, v));
484          return v;
485        }
486      }
487
488
489      DenseMap<BasicBlock*, Value*> deps;
490      MD->getNonLocalDependency(C, deps);
491      CallInst* cdep = 0;
492
493      for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(),
494           E = deps.end(); I != E; ++I) {
495        if (I->second == MemoryDependenceAnalysis::None) {
496          valueNumbering.insert(std::make_pair(V, nextValueNumber));
497
498          return nextValueNumber++;
499        } else if (I->second != MemoryDependenceAnalysis::NonLocal) {
500          if (DT->properlyDominates(I->first, C->getParent())) {
501            if (CallInst* CD = dyn_cast<CallInst>(I->second))
502              cdep = CD;
503            else {
504              valueNumbering.insert(std::make_pair(V, nextValueNumber));
505              return nextValueNumber++;
506            }
507          } else {
508            valueNumbering.insert(std::make_pair(V, nextValueNumber));
509            return nextValueNumber++;
510          }
511        }
512      }
513
514      if (!cdep) {
515        valueNumbering.insert(std::make_pair(V, nextValueNumber));
516        return nextValueNumber++;
517      }
518
519      if (cdep->getCalledFunction() != C->getCalledFunction() ||
520          cdep->getNumOperands() != C->getNumOperands()) {
521        valueNumbering.insert(std::make_pair(V, nextValueNumber));
522        return nextValueNumber++;
523      } else if (!C->getCalledFunction()) {
524        valueNumbering.insert(std::make_pair(V, nextValueNumber));
525        return nextValueNumber++;
526      } else {
527        for (unsigned i = 1; i < C->getNumOperands(); ++i) {
528          uint32_t c_vn = lookup_or_add(C->getOperand(i));
529          uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
530          if (c_vn != cd_vn) {
531            valueNumbering.insert(std::make_pair(V, nextValueNumber));
532            return nextValueNumber++;
533          }
534        }
535
536        uint32_t v = lookup_or_add(cdep);
537        valueNumbering.insert(std::make_pair(V, v));
538        return v;
539      }
540
541    } else {
542      valueNumbering.insert(std::make_pair(V, nextValueNumber));
543      return nextValueNumber++;
544    }
545  } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
546    Expression e = create_expression(BO);
547
548    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
549    if (EI != expressionNumbering.end()) {
550      valueNumbering.insert(std::make_pair(V, EI->second));
551      return EI->second;
552    } else {
553      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
554      valueNumbering.insert(std::make_pair(V, nextValueNumber));
555
556      return nextValueNumber++;
557    }
558  } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
559    Expression e = create_expression(C);
560
561    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
562    if (EI != expressionNumbering.end()) {
563      valueNumbering.insert(std::make_pair(V, EI->second));
564      return EI->second;
565    } else {
566      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
567      valueNumbering.insert(std::make_pair(V, nextValueNumber));
568
569      return nextValueNumber++;
570    }
571  } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
572    Expression e = create_expression(U);
573
574    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
575    if (EI != expressionNumbering.end()) {
576      valueNumbering.insert(std::make_pair(V, EI->second));
577      return EI->second;
578    } else {
579      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
580      valueNumbering.insert(std::make_pair(V, nextValueNumber));
581
582      return nextValueNumber++;
583    }
584  } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
585    Expression e = create_expression(U);
586
587    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
588    if (EI != expressionNumbering.end()) {
589      valueNumbering.insert(std::make_pair(V, EI->second));
590      return EI->second;
591    } else {
592      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
593      valueNumbering.insert(std::make_pair(V, nextValueNumber));
594
595      return nextValueNumber++;
596    }
597  } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
598    Expression e = create_expression(U);
599
600    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
601    if (EI != expressionNumbering.end()) {
602      valueNumbering.insert(std::make_pair(V, EI->second));
603      return EI->second;
604    } else {
605      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
606      valueNumbering.insert(std::make_pair(V, nextValueNumber));
607
608      return nextValueNumber++;
609    }
610  } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
611    Expression e = create_expression(U);
612
613    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
614    if (EI != expressionNumbering.end()) {
615      valueNumbering.insert(std::make_pair(V, EI->second));
616      return EI->second;
617    } else {
618      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
619      valueNumbering.insert(std::make_pair(V, nextValueNumber));
620
621      return nextValueNumber++;
622    }
623  } else if (CastInst* U = dyn_cast<CastInst>(V)) {
624    Expression e = create_expression(U);
625
626    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
627    if (EI != expressionNumbering.end()) {
628      valueNumbering.insert(std::make_pair(V, EI->second));
629      return EI->second;
630    } else {
631      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
632      valueNumbering.insert(std::make_pair(V, nextValueNumber));
633
634      return nextValueNumber++;
635    }
636  } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
637    Expression e = create_expression(U);
638
639    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
640    if (EI != expressionNumbering.end()) {
641      valueNumbering.insert(std::make_pair(V, EI->second));
642      return EI->second;
643    } else {
644      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
645      valueNumbering.insert(std::make_pair(V, nextValueNumber));
646
647      return nextValueNumber++;
648    }
649  } else {
650    valueNumbering.insert(std::make_pair(V, nextValueNumber));
651    return nextValueNumber++;
652  }
653}
654
655/// lookup - Returns the value number of the specified value. Fails if
656/// the value has not yet been numbered.
657uint32_t ValueTable::lookup(Value* V) const {
658  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
659  assert(VI != valueNumbering.end() && "Value not numbered?");
660  return VI->second;
661}
662
663/// clear - Remove all entries from the ValueTable
664void ValueTable::clear() {
665  valueNumbering.clear();
666  expressionNumbering.clear();
667  nextValueNumber = 1;
668}
669
670/// erase - Remove a value from the value numbering
671void ValueTable::erase(Value* V) {
672  valueNumbering.erase(V);
673}
674
675//===----------------------------------------------------------------------===//
676//                         GVN Pass
677//===----------------------------------------------------------------------===//
678
679namespace llvm {
680  template<> struct DenseMapInfo<uint32_t> {
681    static inline uint32_t getEmptyKey() { return ~0; }
682    static inline uint32_t getTombstoneKey() { return ~0 - 1; }
683    static unsigned getHashValue(const uint32_t& Val) { return Val * 37; }
684    static bool isPod() { return true; }
685    static bool isEqual(const uint32_t& LHS, const uint32_t& RHS) {
686      return LHS == RHS;
687    }
688  };
689}
690
691namespace {
692
693  class VISIBILITY_HIDDEN GVN : public FunctionPass {
694    bool runOnFunction(Function &F);
695  public:
696    static char ID; // Pass identification, replacement for typeid
697    GVN() : FunctionPass((intptr_t)&ID) { }
698
699  private:
700    ValueTable VN;
701    DenseMap<BasicBlock*, DenseMap<uint32_t, Value*> > localAvail;
702
703    typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
704    PhiMapType phiMap;
705
706
707    // This transformation requires dominator postdominator info
708    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
709      AU.setPreservesCFG();
710      AU.addRequired<DominatorTree>();
711      AU.addRequired<MemoryDependenceAnalysis>();
712      AU.addRequired<AliasAnalysis>();
713      AU.addPreserved<AliasAnalysis>();
714      AU.addPreserved<MemoryDependenceAnalysis>();
715    }
716
717    // Helper fuctions
718    // FIXME: eliminate or document these better
719    bool processLoad(LoadInst* L,
720                     DenseMap<Value*, LoadInst*> &lastLoad,
721                     SmallVectorImpl<Instruction*> &toErase);
722    bool processInstruction(Instruction* I,
723                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
724                            SmallVectorImpl<Instruction*> &toErase);
725    bool processNonLocalLoad(LoadInst* L,
726                             SmallVectorImpl<Instruction*> &toErase);
727    bool processBlock(DomTreeNode* DTN);
728    Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
729                            DenseMap<BasicBlock*, Value*> &Phis,
730                            bool top_level = false);
731    void dump(DenseMap<uint32_t, Value*>& d);
732    bool iterateOnFunction(Function &F);
733    Value* CollapsePhi(PHINode* p);
734    bool isSafeReplacement(PHINode* p, Instruction* inst);
735    bool performPRE(Function& F);
736  };
737
738  char GVN::ID = 0;
739}
740
741// createGVNPass - The public interface to this file...
742FunctionPass *llvm::createGVNPass() { return new GVN(); }
743
744static RegisterPass<GVN> X("gvn",
745                           "Global Value Numbering");
746
747void GVN::dump(DenseMap<uint32_t, Value*>& d) {
748  printf("{\n");
749  for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
750       E = d.end(); I != E; ++I) {
751      printf("%d\n", I->first);
752      I->second->dump();
753  }
754  printf("}\n");
755}
756
757Value* GVN::CollapsePhi(PHINode* p) {
758  DominatorTree &DT = getAnalysis<DominatorTree>();
759  Value* constVal = p->hasConstantValue();
760
761  if (!constVal) return 0;
762
763  Instruction* inst = dyn_cast<Instruction>(constVal);
764  if (!inst)
765    return constVal;
766
767  if (DT.dominates(inst, p))
768    if (isSafeReplacement(p, inst))
769      return inst;
770  return 0;
771}
772
773bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
774  if (!isa<PHINode>(inst))
775    return true;
776
777  for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
778       UI != E; ++UI)
779    if (PHINode* use_phi = dyn_cast<PHINode>(UI))
780      if (use_phi->getParent() == inst->getParent())
781        return false;
782
783  return true;
784}
785
786/// GetValueForBlock - Get the value to use within the specified basic block.
787/// available values are in Phis.
788Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
789                             DenseMap<BasicBlock*, Value*> &Phis,
790                             bool top_level) {
791
792  // If we have already computed this value, return the previously computed val.
793  DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
794  if (V != Phis.end() && !top_level) return V->second;
795
796  BasicBlock* singlePred = BB->getSinglePredecessor();
797  if (singlePred) {
798    Value *ret = GetValueForBlock(singlePred, orig, Phis);
799    Phis[BB] = ret;
800    return ret;
801  }
802
803  // Otherwise, the idom is the loop, so we need to insert a PHI node.  Do so
804  // now, then get values to fill in the incoming values for the PHI.
805  PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
806                                BB->begin());
807  PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
808
809  if (Phis.count(BB) == 0)
810    Phis.insert(std::make_pair(BB, PN));
811
812  // Fill in the incoming values for the block.
813  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
814    Value* val = GetValueForBlock(*PI, orig, Phis);
815    PN->addIncoming(val, *PI);
816  }
817
818  AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
819  AA.copyValue(orig, PN);
820
821  // Attempt to collapse PHI nodes that are trivially redundant
822  Value* v = CollapsePhi(PN);
823  if (!v) {
824    // Cache our phi construction results
825    phiMap[orig->getPointerOperand()].insert(PN);
826    return PN;
827  }
828
829  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
830
831  MD.removeInstruction(PN);
832  PN->replaceAllUsesWith(v);
833
834  for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
835       E = Phis.end(); I != E; ++I)
836    if (I->second == PN)
837      I->second = v;
838
839  PN->eraseFromParent();
840
841  Phis[BB] = v;
842  return v;
843}
844
845/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
846/// non-local by performing PHI construction.
847bool GVN::processNonLocalLoad(LoadInst* L,
848                              SmallVectorImpl<Instruction*> &toErase) {
849  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
850
851  // Find the non-local dependencies of the load
852  DenseMap<BasicBlock*, Value*> deps;
853  MD.getNonLocalDependency(L, deps);
854
855  DenseMap<BasicBlock*, Value*> repl;
856
857  // Filter out useless results (non-locals, etc)
858  for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
859       I != E; ++I) {
860    if (I->second == MemoryDependenceAnalysis::None)
861      return false;
862
863    if (I->second == MemoryDependenceAnalysis::NonLocal)
864      continue;
865
866    if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
867      if (S->getPointerOperand() != L->getPointerOperand())
868        return false;
869      repl[I->first] = S->getOperand(0);
870    } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
871      if (LD->getPointerOperand() != L->getPointerOperand())
872        return false;
873      repl[I->first] = LD;
874    } else {
875      return false;
876    }
877  }
878
879  // Use cached PHI construction information from previous runs
880  SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
881  for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
882       I != E; ++I) {
883    if ((*I)->getParent() == L->getParent()) {
884      MD.removeInstruction(L);
885      L->replaceAllUsesWith(*I);
886      toErase.push_back(L);
887      NumGVNLoad++;
888      return true;
889    }
890
891    repl.insert(std::make_pair((*I)->getParent(), *I));
892  }
893
894  // Perform PHI construction
895  SmallPtrSet<BasicBlock*, 4> visited;
896  Value* v = GetValueForBlock(L->getParent(), L, repl, true);
897
898  MD.removeInstruction(L);
899  L->replaceAllUsesWith(v);
900  toErase.push_back(L);
901  NumGVNLoad++;
902
903  return true;
904}
905
906/// processLoad - Attempt to eliminate a load, first by eliminating it
907/// locally, and then attempting non-local elimination if that fails.
908bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad,
909                      SmallVectorImpl<Instruction*> &toErase) {
910  if (L->isVolatile()) {
911    lastLoad[L->getPointerOperand()] = L;
912    return false;
913  }
914
915  Value* pointer = L->getPointerOperand();
916  LoadInst*& last = lastLoad[pointer];
917
918  // ... to a pointer that has been loaded from before...
919  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
920  bool removedNonLocal = false;
921  Instruction* dep = MD.getDependency(L);
922  if (dep == MemoryDependenceAnalysis::NonLocal &&
923      L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
924    removedNonLocal = processNonLocalLoad(L, toErase);
925
926    if (!removedNonLocal)
927      last = L;
928
929    return removedNonLocal;
930  }
931
932
933  bool deletedLoad = false;
934
935  // Walk up the dependency chain until we either find
936  // a dependency we can use, or we can't walk any further
937  while (dep != MemoryDependenceAnalysis::None &&
938         dep != MemoryDependenceAnalysis::NonLocal &&
939         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
940    // ... that depends on a store ...
941    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
942      if (S->getPointerOperand() == pointer) {
943        // Remove it!
944        MD.removeInstruction(L);
945
946        L->replaceAllUsesWith(S->getOperand(0));
947        toErase.push_back(L);
948        deletedLoad = true;
949        NumGVNLoad++;
950      }
951
952      // Whether we removed it or not, we can't
953      // go any further
954      break;
955    } else if (!last) {
956      // If we don't depend on a store, and we haven't
957      // been loaded before, bail.
958      break;
959    } else if (dep == last) {
960      // Remove it!
961      MD.removeInstruction(L);
962
963      L->replaceAllUsesWith(last);
964      toErase.push_back(L);
965      deletedLoad = true;
966      NumGVNLoad++;
967
968      break;
969    } else {
970      dep = MD.getDependency(L, dep);
971    }
972  }
973
974  if (dep != MemoryDependenceAnalysis::None &&
975      dep != MemoryDependenceAnalysis::NonLocal &&
976      isa<AllocationInst>(dep)) {
977    // Check that this load is actually from the
978    // allocation we found
979    Value* v = L->getOperand(0);
980    while (true) {
981      if (BitCastInst *BC = dyn_cast<BitCastInst>(v))
982        v = BC->getOperand(0);
983      else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v))
984        v = GEP->getOperand(0);
985      else
986        break;
987    }
988    if (v == dep) {
989      // If this load depends directly on an allocation, there isn't
990      // anything stored there; therefore, we can optimize this load
991      // to undef.
992      MD.removeInstruction(L);
993
994      L->replaceAllUsesWith(UndefValue::get(L->getType()));
995      toErase.push_back(L);
996      deletedLoad = true;
997      NumGVNLoad++;
998    }
999  }
1000
1001  if (!deletedLoad)
1002    last = L;
1003
1004  return deletedLoad;
1005}
1006
1007/// processInstruction - When calculating availability, handle an instruction
1008/// by inserting it into the appropriate sets
1009bool GVN::processInstruction(Instruction *I,
1010                             DenseMap<Value*, LoadInst*> &lastSeenLoad,
1011                             SmallVectorImpl<Instruction*> &toErase) {
1012  if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1013    bool changed = processLoad(L, lastSeenLoad, toErase);
1014
1015    if (!changed) {
1016      unsigned num = VN.lookup_or_add(L);
1017      localAvail[I->getParent()].insert(std::make_pair(num, L));
1018    }
1019
1020    return changed;
1021  }
1022
1023  unsigned num = VN.lookup_or_add(I);
1024
1025  // Allocations are always uniquely numbered, so we can save time and memory
1026  // by fast failing them.
1027  if (isa<AllocationInst>(I)) {
1028    localAvail[I->getParent()].insert(std::make_pair(num, I));
1029    return false;
1030  }
1031
1032  // Collapse PHI nodes
1033  if (PHINode* p = dyn_cast<PHINode>(I)) {
1034    Value* constVal = CollapsePhi(p);
1035
1036    if (constVal) {
1037      for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1038           PI != PE; ++PI)
1039        if (PI->second.count(p))
1040          PI->second.erase(p);
1041
1042      p->replaceAllUsesWith(constVal);
1043      toErase.push_back(p);
1044    } else {
1045      localAvail[I->getParent()].insert(std::make_pair(num, I));
1046    }
1047  // Perform value-number based elimination
1048  } else if (localAvail[I->getParent()].count(num)) {
1049    Value* repl = localAvail[I->getParent()][num];
1050
1051    // Remove it!
1052    MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1053    MD.removeInstruction(I);
1054
1055    VN.erase(I);
1056    I->replaceAllUsesWith(repl);
1057    toErase.push_back(I);
1058    return true;
1059  } else if (!I->isTerminator()) {
1060    localAvail[I->getParent()].insert(std::make_pair(num, I));
1061  }
1062
1063  return false;
1064}
1065
1066// GVN::runOnFunction - This is the main transformation entry point for a
1067// function.
1068//
1069bool GVN::runOnFunction(Function& F) {
1070  VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1071  VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>());
1072  VN.setDomTree(&getAnalysis<DominatorTree>());
1073
1074  bool changed = false;
1075  bool shouldContinue = true;
1076
1077  while (shouldContinue) {
1078    shouldContinue = iterateOnFunction(F);
1079    changed |= shouldContinue;
1080  }
1081
1082  return changed;
1083}
1084
1085
1086bool GVN::processBlock(DomTreeNode* DTN) {
1087  BasicBlock* BB = DTN->getBlock();
1088
1089  SmallVector<Instruction*, 8> toErase;
1090  DenseMap<Value*, LoadInst*> lastSeenLoad;
1091  bool changed_function = false;
1092
1093  if (DTN->getIDom())
1094    localAvail.insert(std::make_pair(BB,
1095                      localAvail[DTN->getIDom()->getBlock()]));
1096
1097  for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1098       BI != BE;) {
1099    changed_function |= processInstruction(BI, lastSeenLoad, toErase);
1100    if (toErase.empty()) {
1101      ++BI;
1102      continue;
1103    }
1104
1105    // If we need some instructions deleted, do it now.
1106    NumGVNInstr += toErase.size();
1107
1108    // Avoid iterator invalidation.
1109    bool AtStart = BI == BB->begin();
1110    if (!AtStart)
1111      --BI;
1112
1113    for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1114         E = toErase.end(); I != E; ++I)
1115      (*I)->eraseFromParent();
1116
1117    if (AtStart)
1118      BI = BB->begin();
1119    else
1120      ++BI;
1121
1122    toErase.clear();
1123  }
1124
1125  return changed_function;
1126}
1127
1128/// performPRE - Perform a purely local form of PRE that looks for diamond
1129/// control flow patterns and attempts to perform simple PRE at the join point.
1130bool GVN::performPRE(Function& F) {
1131  bool changed = false;
1132  SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
1133  for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
1134       DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
1135    BasicBlock* CurrentBlock = *DI;
1136
1137    // Nothing to PRE in the entry block.
1138    if (CurrentBlock == &F.getEntryBlock()) continue;
1139
1140    for (BasicBlock::iterator BI = CurrentBlock->begin(),
1141         BE = CurrentBlock->end(); BI != BE; ) {
1142      if (isa<AllocaInst>(BI) || isa<TerminatorInst>(BI) ||
1143          isa<LoadInst>(BI) || isa<StoreInst>(BI) ||
1144          isa<CallInst>(BI) || isa<PHINode>(BI)) {
1145        BI++;
1146        continue;
1147      }
1148
1149      uint32_t valno = VN.lookup(BI);
1150
1151      // Look for the predecessors for PRE opportunities.  We're
1152      // only trying to solve the basic diamond case, where
1153      // a value is computed in the successor and one predecessor,
1154      // but not the other.  We also explicitly disallow cases
1155      // where the successor is its own predecessor, because they're
1156      // more complicated to get right.
1157      unsigned numWith = 0;
1158      unsigned numWithout = 0;
1159      BasicBlock* PREPred = 0;
1160      for (pred_iterator PI = pred_begin(CurrentBlock),
1161           PE = pred_end(CurrentBlock); PI != PE; ++PI) {
1162        // We're not interested in PRE where the block is its
1163        // own predecessor.
1164        if (*PI == CurrentBlock)
1165          numWithout = 2;
1166
1167        if (!localAvail[*PI].count(valno)) {
1168          PREPred = *PI;
1169          numWithout++;
1170        } else if (localAvail[*PI][valno] == BI) {
1171          numWithout = 2;
1172        } else {
1173          numWith++;
1174        }
1175      }
1176
1177      // Don't do PRE when it might increase code size, i.e. when
1178      // we would need to insert instructions in more than one pred.
1179      if (numWithout != 1 || numWith == 0) {
1180        BI++;
1181        continue;
1182      }
1183
1184      // We can't do PRE safely on a critical edge, so instead we schedule
1185      // the edge to be split and perform the PRE the next time we iterate
1186      // on the function.
1187      unsigned succNum = 0;
1188      for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
1189           i != e; ++i)
1190        if (PREPred->getTerminator()->getSuccessor(i) == PREPred) {
1191          succNum = i;
1192          break;
1193        }
1194
1195      if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
1196        toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
1197        changed = true;
1198        BI++;
1199        continue;
1200      }
1201
1202      // Instantiate the expression the in predecessor that lacked it.
1203      // Because we are going top-down through the block, all value numbers
1204      // will be available in the predecessor by the time we need them.  Any
1205      // that weren't original present will have been instantiated earlier
1206      // in this loop.
1207      Instruction* PREInstr = BI->clone();
1208      bool success = true;
1209      for (unsigned i = 0; i < BI->getNumOperands(); ++i) {
1210        Value* op = BI->getOperand(i);
1211        if (isa<Argument>(op) || isa<Constant>(op) || isa<GlobalValue>(op))
1212          PREInstr->setOperand(i, op);
1213        else if (!localAvail[PREPred].count(VN.lookup(op))) {
1214          success = false;
1215          break;
1216        } else
1217          PREInstr->setOperand(i, localAvail[PREPred][VN.lookup(op)]);
1218      }
1219
1220      // Fail out if we encounter an operand that is not available in
1221      // the PRE predecessor.  This is typically because of loads which
1222      // are not value numbered precisely.
1223      if (!success) {
1224        delete PREInstr;
1225        BI++;
1226        continue;
1227      }
1228
1229      PREInstr->insertBefore(PREPred->getTerminator());
1230      PREInstr->setName(BI->getName() + ".pre");
1231      VN.add(PREInstr, valno);
1232      NumGVNPRE++;
1233
1234      // Update the availability map to include the new instruction.
1235      localAvail[PREPred].insert(std::make_pair(valno, PREInstr));
1236
1237      // Create a PHI to make the value available in this block.
1238      PHINode* Phi = PHINode::Create(BI->getType(),
1239                                     BI->getName() + ".pre-phi",
1240                                     CurrentBlock->begin());
1241      for (pred_iterator PI = pred_begin(CurrentBlock),
1242           PE = pred_end(CurrentBlock); PI != PE; ++PI)
1243        Phi->addIncoming(localAvail[*PI][valno], *PI);
1244
1245      VN.add(Phi, valno);
1246
1247      // The newly created PHI completely replaces the old instruction,
1248      // so we need to update the maps to reflect this.
1249      for (DenseMap<BasicBlock*, DenseMap<uint32_t, Value*> >::iterator
1250           UI = localAvail.begin(), UE = localAvail.end(); UI != UE; ++UI)
1251        for (DenseMap<uint32_t, Value*>::iterator UUI = UI->second.begin(),
1252             UUE = UI->second.end(); UUI != UUE; ++UUI)
1253            if (UUI->second == BI)
1254              UUI->second = Phi;
1255
1256      BI->replaceAllUsesWith(Phi);
1257      VN.erase(BI);
1258
1259      Instruction* erase = BI;
1260      BI++;
1261      erase->eraseFromParent();
1262
1263      changed = true;
1264    }
1265  }
1266
1267  for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
1268       I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
1269    SplitCriticalEdge(I->first, I->second, this);
1270
1271  return changed;
1272}
1273
1274// GVN::iterateOnFunction - Executes one iteration of GVN
1275bool GVN::iterateOnFunction(Function &F) {
1276  // Clean out global sets from any previous functions
1277  VN.clear();
1278  localAvail.clear();
1279  phiMap.clear();
1280
1281  DominatorTree &DT = getAnalysis<DominatorTree>();
1282
1283  // Top-down walk of the dominator tree
1284  bool changed = false;
1285  for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
1286       DE = df_end(DT.getRootNode()); DI != DE; ++DI)
1287    changed |= processBlock(*DI);
1288
1289  changed |= performPRE(F);
1290  return changed;
1291}
1292