GVN.cpp revision f2aa160b357c98d8c37b69ea9775aa3e097d1319 
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/CommandLine.h"
36#include "llvm/Support/Compiler.h"
37#include "llvm/Support/Debug.h"
38#include "llvm/Transforms/Utils/BasicBlockUtils.h"
39using namespace llvm;
40
41STATISTIC(NumGVNInstr, "Number of instructions deleted");
42STATISTIC(NumGVNLoad, "Number of loads deleted");
43STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
44
45static cl::opt<bool> EnablePRE("enable-pre",
46                               cl::init(false), cl::Hidden);
47
48//===----------------------------------------------------------------------===//
49//                         ValueTable Class
50//===----------------------------------------------------------------------===//
51
52/// This class holds the mapping between values and value numbers.  It is used
53/// as an efficient mechanism to determine the expression-wise equivalence of
54/// two values.
55namespace {
56  struct VISIBILITY_HIDDEN Expression {
57    enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
58                            FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
59                            ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
60                            ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
61                            FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
62                            FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
63                            FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
64                            SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
65                            FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
66                            PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
67                            EMPTY, TOMBSTONE };
68
69    ExpressionOpcode opcode;
70    const Type* type;
71    uint32_t firstVN;
72    uint32_t secondVN;
73    uint32_t thirdVN;
74    SmallVector<uint32_t, 4> varargs;
75    Value* function;
76
77    Expression() { }
78    Expression(ExpressionOpcode o) : opcode(o) { }
79
80    bool operator==(const Expression &other) const {
81      if (opcode != other.opcode)
82        return false;
83      else if (opcode == EMPTY || opcode == TOMBSTONE)
84        return true;
85      else if (type != other.type)
86        return false;
87      else if (function != other.function)
88        return false;
89      else if (firstVN != other.firstVN)
90        return false;
91      else if (secondVN != other.secondVN)
92        return false;
93      else if (thirdVN != other.thirdVN)
94        return false;
95      else {
96        if (varargs.size() != other.varargs.size())
97          return false;
98
99        for (size_t i = 0; i < varargs.size(); ++i)
100          if (varargs[i] != other.varargs[i])
101            return false;
102
103        return true;
104      }
105    }
106
107    bool operator!=(const Expression &other) const {
108      if (opcode != other.opcode)
109        return true;
110      else if (opcode == EMPTY || opcode == TOMBSTONE)
111        return false;
112      else if (type != other.type)
113        return true;
114      else if (function != other.function)
115        return true;
116      else if (firstVN != other.firstVN)
117        return true;
118      else if (secondVN != other.secondVN)
119        return true;
120      else if (thirdVN != other.thirdVN)
121        return true;
122      else {
123        if (varargs.size() != other.varargs.size())
124          return true;
125
126        for (size_t i = 0; i < varargs.size(); ++i)
127          if (varargs[i] != other.varargs[i])
128            return true;
129
130          return false;
131      }
132    }
133  };
134
135  class VISIBILITY_HIDDEN ValueTable {
136    private:
137      DenseMap<Value*, uint32_t> valueNumbering;
138      DenseMap<Expression, uint32_t> expressionNumbering;
139      AliasAnalysis* AA;
140      MemoryDependenceAnalysis* MD;
141      DominatorTree* DT;
142
143      uint32_t nextValueNumber;
144
145      Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
146      Expression::ExpressionOpcode getOpcode(CmpInst* C);
147      Expression::ExpressionOpcode getOpcode(CastInst* C);
148      Expression create_expression(BinaryOperator* BO);
149      Expression create_expression(CmpInst* C);
150      Expression create_expression(ShuffleVectorInst* V);
151      Expression create_expression(ExtractElementInst* C);
152      Expression create_expression(InsertElementInst* V);
153      Expression create_expression(SelectInst* V);
154      Expression create_expression(CastInst* C);
155      Expression create_expression(GetElementPtrInst* G);
156      Expression create_expression(CallInst* C);
157      Expression create_expression(Constant* C);
158    public:
159      ValueTable() : nextValueNumber(1) { }
160      uint32_t lookup_or_add(Value* V);
161      uint32_t lookup(Value* V) const;
162      void add(Value* V, uint32_t num);
163      void clear();
164      void erase(Value* v);
165      unsigned size();
166      void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
167      void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
168      void setDomTree(DominatorTree* D) { DT = D; }
169  };
170}
171
172namespace llvm {
173template <> struct DenseMapInfo<Expression> {
174  static inline Expression getEmptyKey() {
175    return Expression(Expression::EMPTY);
176  }
177
178  static inline Expression getTombstoneKey() {
179    return Expression(Expression::TOMBSTONE);
180  }
181
182  static unsigned getHashValue(const Expression e) {
183    unsigned hash = e.opcode;
184
185    hash = e.firstVN + hash * 37;
186    hash = e.secondVN + hash * 37;
187    hash = e.thirdVN + hash * 37;
188
189    hash = ((unsigned)((uintptr_t)e.type >> 4) ^
190            (unsigned)((uintptr_t)e.type >> 9)) +
191           hash * 37;
192
193    for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
194         E = e.varargs.end(); I != E; ++I)
195      hash = *I + hash * 37;
196
197    hash = ((unsigned)((uintptr_t)e.function >> 4) ^
198            (unsigned)((uintptr_t)e.function >> 9)) +
199           hash * 37;
200
201    return hash;
202  }
203  static bool isEqual(const Expression &LHS, const Expression &RHS) {
204    return LHS == RHS;
205  }
206  static bool isPod() { return true; }
207};
208}
209
210//===----------------------------------------------------------------------===//
211//                     ValueTable Internal Functions
212//===----------------------------------------------------------------------===//
213Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
214  switch(BO->getOpcode()) {
215  default: // THIS SHOULD NEVER HAPPEN
216    assert(0 && "Binary operator with unknown opcode?");
217  case Instruction::Add:  return Expression::ADD;
218  case Instruction::Sub:  return Expression::SUB;
219  case Instruction::Mul:  return Expression::MUL;
220  case Instruction::UDiv: return Expression::UDIV;
221  case Instruction::SDiv: return Expression::SDIV;
222  case Instruction::FDiv: return Expression::FDIV;
223  case Instruction::URem: return Expression::UREM;
224  case Instruction::SRem: return Expression::SREM;
225  case Instruction::FRem: return Expression::FREM;
226  case Instruction::Shl:  return Expression::SHL;
227  case Instruction::LShr: return Expression::LSHR;
228  case Instruction::AShr: return Expression::ASHR;
229  case Instruction::And:  return Expression::AND;
230  case Instruction::Or:   return Expression::OR;
231  case Instruction::Xor:  return Expression::XOR;
232  }
233}
234
235Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
236  if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) {
237    switch (C->getPredicate()) {
238    default:  // THIS SHOULD NEVER HAPPEN
239      assert(0 && "Comparison with unknown predicate?");
240    case ICmpInst::ICMP_EQ:  return Expression::ICMPEQ;
241    case ICmpInst::ICMP_NE:  return Expression::ICMPNE;
242    case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
243    case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
244    case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
245    case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
246    case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
247    case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
248    case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
249    case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
250    }
251  }
252  assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare");
253  switch (C->getPredicate()) {
254  default: // THIS SHOULD NEVER HAPPEN
255    assert(0 && "Comparison with unknown predicate?");
256  case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
257  case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
258  case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
259  case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
260  case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
261  case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
262  case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
263  case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
264  case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
265  case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
266  case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
267  case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
268  case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
269  case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
270  }
271}
272
273Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
274  switch(C->getOpcode()) {
275  default: // THIS SHOULD NEVER HAPPEN
276    assert(0 && "Cast operator with unknown opcode?");
277  case Instruction::Trunc:    return Expression::TRUNC;
278  case Instruction::ZExt:     return Expression::ZEXT;
279  case Instruction::SExt:     return Expression::SEXT;
280  case Instruction::FPToUI:   return Expression::FPTOUI;
281  case Instruction::FPToSI:   return Expression::FPTOSI;
282  case Instruction::UIToFP:   return Expression::UITOFP;
283  case Instruction::SIToFP:   return Expression::SITOFP;
284  case Instruction::FPTrunc:  return Expression::FPTRUNC;
285  case Instruction::FPExt:    return Expression::FPEXT;
286  case Instruction::PtrToInt: return Expression::PTRTOINT;
287  case Instruction::IntToPtr: return Expression::INTTOPTR;
288  case Instruction::BitCast:  return Expression::BITCAST;
289  }
290}
291
292Expression ValueTable::create_expression(CallInst* C) {
293  Expression e;
294
295  e.type = C->getType();
296  e.firstVN = 0;
297  e.secondVN = 0;
298  e.thirdVN = 0;
299  e.function = C->getCalledFunction();
300  e.opcode = Expression::CALL;
301
302  for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
303       I != E; ++I)
304    e.varargs.push_back(lookup_or_add(*I));
305
306  return e;
307}
308
309Expression ValueTable::create_expression(BinaryOperator* BO) {
310  Expression e;
311
312  e.firstVN = lookup_or_add(BO->getOperand(0));
313  e.secondVN = lookup_or_add(BO->getOperand(1));
314  e.thirdVN = 0;
315  e.function = 0;
316  e.type = BO->getType();
317  e.opcode = getOpcode(BO);
318
319  return e;
320}
321
322Expression ValueTable::create_expression(CmpInst* C) {
323  Expression e;
324
325  e.firstVN = lookup_or_add(C->getOperand(0));
326  e.secondVN = lookup_or_add(C->getOperand(1));
327  e.thirdVN = 0;
328  e.function = 0;
329  e.type = C->getType();
330  e.opcode = getOpcode(C);
331
332  return e;
333}
334
335Expression ValueTable::create_expression(CastInst* C) {
336  Expression e;
337
338  e.firstVN = lookup_or_add(C->getOperand(0));
339  e.secondVN = 0;
340  e.thirdVN = 0;
341  e.function = 0;
342  e.type = C->getType();
343  e.opcode = getOpcode(C);
344
345  return e;
346}
347
348Expression ValueTable::create_expression(ShuffleVectorInst* S) {
349  Expression e;
350
351  e.firstVN = lookup_or_add(S->getOperand(0));
352  e.secondVN = lookup_or_add(S->getOperand(1));
353  e.thirdVN = lookup_or_add(S->getOperand(2));
354  e.function = 0;
355  e.type = S->getType();
356  e.opcode = Expression::SHUFFLE;
357
358  return e;
359}
360
361Expression ValueTable::create_expression(ExtractElementInst* E) {
362  Expression e;
363
364  e.firstVN = lookup_or_add(E->getOperand(0));
365  e.secondVN = lookup_or_add(E->getOperand(1));
366  e.thirdVN = 0;
367  e.function = 0;
368  e.type = E->getType();
369  e.opcode = Expression::EXTRACT;
370
371  return e;
372}
373
374Expression ValueTable::create_expression(InsertElementInst* I) {
375  Expression e;
376
377  e.firstVN = lookup_or_add(I->getOperand(0));
378  e.secondVN = lookup_or_add(I->getOperand(1));
379  e.thirdVN = lookup_or_add(I->getOperand(2));
380  e.function = 0;
381  e.type = I->getType();
382  e.opcode = Expression::INSERT;
383
384  return e;
385}
386
387Expression ValueTable::create_expression(SelectInst* I) {
388  Expression e;
389
390  e.firstVN = lookup_or_add(I->getCondition());
391  e.secondVN = lookup_or_add(I->getTrueValue());
392  e.thirdVN = lookup_or_add(I->getFalseValue());
393  e.function = 0;
394  e.type = I->getType();
395  e.opcode = Expression::SELECT;
396
397  return e;
398}
399
400Expression ValueTable::create_expression(GetElementPtrInst* G) {
401  Expression e;
402
403  e.firstVN = lookup_or_add(G->getPointerOperand());
404  e.secondVN = 0;
405  e.thirdVN = 0;
406  e.function = 0;
407  e.type = G->getType();
408  e.opcode = Expression::GEP;
409
410  for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
411       I != E; ++I)
412    e.varargs.push_back(lookup_or_add(*I));
413
414  return e;
415}
416
417//===----------------------------------------------------------------------===//
418//                     ValueTable External Functions
419//===----------------------------------------------------------------------===//
420
421/// add - Insert a value into the table with a specified value number.
422void ValueTable::add(Value* V, uint32_t num) {
423  valueNumbering.insert(std::make_pair(V, num));
424}
425
426/// lookup_or_add - Returns the value number for the specified value, assigning
427/// it a new number if it did not have one before.
428uint32_t ValueTable::lookup_or_add(Value* V) {
429  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
430  if (VI != valueNumbering.end())
431    return VI->second;
432
433  if (CallInst* C = dyn_cast<CallInst>(V)) {
434    if (AA->doesNotAccessMemory(C)) {
435      Expression e = create_expression(C);
436
437      DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
438      if (EI != expressionNumbering.end()) {
439        valueNumbering.insert(std::make_pair(V, EI->second));
440        return EI->second;
441      } else {
442        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
443        valueNumbering.insert(std::make_pair(V, nextValueNumber));
444
445        return nextValueNumber++;
446      }
447    } else if (AA->onlyReadsMemory(C)) {
448      Expression e = create_expression(C);
449
450      if (expressionNumbering.find(e) == expressionNumbering.end()) {
451        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
452        valueNumbering.insert(std::make_pair(V, nextValueNumber));
453        return nextValueNumber++;
454      }
455
456      Instruction* local_dep = MD->getDependency(C);
457
458      if (local_dep == MemoryDependenceAnalysis::None) {
459        valueNumbering.insert(std::make_pair(V, nextValueNumber));
460        return nextValueNumber++;
461      } else if (local_dep != MemoryDependenceAnalysis::NonLocal) {
462        if (!isa<CallInst>(local_dep)) {
463          valueNumbering.insert(std::make_pair(V, nextValueNumber));
464          return nextValueNumber++;
465        }
466
467        CallInst* local_cdep = cast<CallInst>(local_dep);
468
469        if (local_cdep->getCalledFunction() != C->getCalledFunction() ||
470            local_cdep->getNumOperands() != C->getNumOperands()) {
471          valueNumbering.insert(std::make_pair(V, nextValueNumber));
472          return nextValueNumber++;
473        } else if (!C->getCalledFunction()) {
474          valueNumbering.insert(std::make_pair(V, nextValueNumber));
475          return nextValueNumber++;
476        } else {
477          for (unsigned i = 1; i < C->getNumOperands(); ++i) {
478            uint32_t c_vn = lookup_or_add(C->getOperand(i));
479            uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
480            if (c_vn != cd_vn) {
481              valueNumbering.insert(std::make_pair(V, nextValueNumber));
482              return nextValueNumber++;
483            }
484          }
485
486          uint32_t v = lookup_or_add(local_cdep);
487          valueNumbering.insert(std::make_pair(V, v));
488          return v;
489        }
490      }
491
492
493      DenseMap<BasicBlock*, Value*> deps;
494      MD->getNonLocalDependency(C, deps);
495      CallInst* cdep = 0;
496
497      for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(),
498           E = deps.end(); I != E; ++I) {
499        if (I->second == MemoryDependenceAnalysis::None) {
500          valueNumbering.insert(std::make_pair(V, nextValueNumber));
501
502          return nextValueNumber++;
503        } else if (I->second != MemoryDependenceAnalysis::NonLocal) {
504          if (DT->properlyDominates(I->first, C->getParent())) {
505            if (CallInst* CD = dyn_cast<CallInst>(I->second))
506              cdep = CD;
507            else {
508              valueNumbering.insert(std::make_pair(V, nextValueNumber));
509              return nextValueNumber++;
510            }
511          } else {
512            valueNumbering.insert(std::make_pair(V, nextValueNumber));
513            return nextValueNumber++;
514          }
515        }
516      }
517
518      if (!cdep) {
519        valueNumbering.insert(std::make_pair(V, nextValueNumber));
520        return nextValueNumber++;
521      }
522
523      if (cdep->getCalledFunction() != C->getCalledFunction() ||
524          cdep->getNumOperands() != C->getNumOperands()) {
525        valueNumbering.insert(std::make_pair(V, nextValueNumber));
526        return nextValueNumber++;
527      } else if (!C->getCalledFunction()) {
528        valueNumbering.insert(std::make_pair(V, nextValueNumber));
529        return nextValueNumber++;
530      } else {
531        for (unsigned i = 1; i < C->getNumOperands(); ++i) {
532          uint32_t c_vn = lookup_or_add(C->getOperand(i));
533          uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
534          if (c_vn != cd_vn) {
535            valueNumbering.insert(std::make_pair(V, nextValueNumber));
536            return nextValueNumber++;
537          }
538        }
539
540        uint32_t v = lookup_or_add(cdep);
541        valueNumbering.insert(std::make_pair(V, v));
542        return v;
543      }
544
545    } else {
546      valueNumbering.insert(std::make_pair(V, nextValueNumber));
547      return nextValueNumber++;
548    }
549  } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
550    Expression e = create_expression(BO);
551
552    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
553    if (EI != expressionNumbering.end()) {
554      valueNumbering.insert(std::make_pair(V, EI->second));
555      return EI->second;
556    } else {
557      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
558      valueNumbering.insert(std::make_pair(V, nextValueNumber));
559
560      return nextValueNumber++;
561    }
562  } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
563    Expression e = create_expression(C);
564
565    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
566    if (EI != expressionNumbering.end()) {
567      valueNumbering.insert(std::make_pair(V, EI->second));
568      return EI->second;
569    } else {
570      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
571      valueNumbering.insert(std::make_pair(V, nextValueNumber));
572
573      return nextValueNumber++;
574    }
575  } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
576    Expression e = create_expression(U);
577
578    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
579    if (EI != expressionNumbering.end()) {
580      valueNumbering.insert(std::make_pair(V, EI->second));
581      return EI->second;
582    } else {
583      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
584      valueNumbering.insert(std::make_pair(V, nextValueNumber));
585
586      return nextValueNumber++;
587    }
588  } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
589    Expression e = create_expression(U);
590
591    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
592    if (EI != expressionNumbering.end()) {
593      valueNumbering.insert(std::make_pair(V, EI->second));
594      return EI->second;
595    } else {
596      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
597      valueNumbering.insert(std::make_pair(V, nextValueNumber));
598
599      return nextValueNumber++;
600    }
601  } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
602    Expression e = create_expression(U);
603
604    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
605    if (EI != expressionNumbering.end()) {
606      valueNumbering.insert(std::make_pair(V, EI->second));
607      return EI->second;
608    } else {
609      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
610      valueNumbering.insert(std::make_pair(V, nextValueNumber));
611
612      return nextValueNumber++;
613    }
614  } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
615    Expression e = create_expression(U);
616
617    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
618    if (EI != expressionNumbering.end()) {
619      valueNumbering.insert(std::make_pair(V, EI->second));
620      return EI->second;
621    } else {
622      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
623      valueNumbering.insert(std::make_pair(V, nextValueNumber));
624
625      return nextValueNumber++;
626    }
627  } else if (CastInst* U = dyn_cast<CastInst>(V)) {
628    Expression e = create_expression(U);
629
630    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
631    if (EI != expressionNumbering.end()) {
632      valueNumbering.insert(std::make_pair(V, EI->second));
633      return EI->second;
634    } else {
635      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
636      valueNumbering.insert(std::make_pair(V, nextValueNumber));
637
638      return nextValueNumber++;
639    }
640  } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
641    Expression e = create_expression(U);
642
643    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
644    if (EI != expressionNumbering.end()) {
645      valueNumbering.insert(std::make_pair(V, EI->second));
646      return EI->second;
647    } else {
648      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
649      valueNumbering.insert(std::make_pair(V, nextValueNumber));
650
651      return nextValueNumber++;
652    }
653  } else {
654    valueNumbering.insert(std::make_pair(V, nextValueNumber));
655    return nextValueNumber++;
656  }
657}
658
659/// lookup - Returns the value number of the specified value. Fails if
660/// the value has not yet been numbered.
661uint32_t ValueTable::lookup(Value* V) const {
662  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
663  assert(VI != valueNumbering.end() && "Value not numbered?");
664  return VI->second;
665}
666
667/// clear - Remove all entries from the ValueTable
668void ValueTable::clear() {
669  valueNumbering.clear();
670  expressionNumbering.clear();
671  nextValueNumber = 1;
672}
673
674/// erase - Remove a value from the value numbering
675void ValueTable::erase(Value* V) {
676  valueNumbering.erase(V);
677}
678
679//===----------------------------------------------------------------------===//
680//                         GVN Pass
681//===----------------------------------------------------------------------===//
682
683namespace llvm {
684  template<> struct DenseMapInfo<uint32_t> {
685    static inline uint32_t getEmptyKey() { return ~0; }
686    static inline uint32_t getTombstoneKey() { return ~0 - 1; }
687    static unsigned getHashValue(const uint32_t& Val) { return Val * 37; }
688    static bool isPod() { return true; }
689    static bool isEqual(const uint32_t& LHS, const uint32_t& RHS) {
690      return LHS == RHS;
691    }
692  };
693}
694
695namespace {
696  struct VISIBILITY_HIDDEN ValueNumberScope {
697    ValueNumberScope* parent;
698    DenseMap<uint32_t, Value*> table;
699
700    ValueNumberScope(ValueNumberScope* p) : parent(p) { }
701  };
702}
703
704namespace {
705
706  class VISIBILITY_HIDDEN GVN : public FunctionPass {
707    bool runOnFunction(Function &F);
708  public:
709    static char ID; // Pass identification, replacement for typeid
710    GVN() : FunctionPass((intptr_t)&ID) { }
711
712  private:
713    ValueTable VN;
714    DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
715
716    typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
717    PhiMapType phiMap;
718
719
720    // This transformation requires dominator postdominator info
721    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
722      AU.addRequired<DominatorTree>();
723      AU.addRequired<MemoryDependenceAnalysis>();
724      AU.addRequired<AliasAnalysis>();
725
726      AU.addPreserved<DominatorTree>();
727      AU.addPreserved<AliasAnalysis>();
728      AU.addPreserved<MemoryDependenceAnalysis>();
729    }
730
731    // Helper fuctions
732    // FIXME: eliminate or document these better
733    bool processLoad(LoadInst* L,
734                     DenseMap<Value*, LoadInst*> &lastLoad,
735                     SmallVectorImpl<Instruction*> &toErase);
736    bool processInstruction(Instruction* I,
737                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
738                            SmallVectorImpl<Instruction*> &toErase);
739    bool processNonLocalLoad(LoadInst* L,
740                             SmallVectorImpl<Instruction*> &toErase);
741    bool processBlock(DomTreeNode* DTN);
742    Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
743                            DenseMap<BasicBlock*, Value*> &Phis,
744                            bool top_level = false);
745    void dump(DenseMap<uint32_t, Value*>& d);
746    bool iterateOnFunction(Function &F);
747    Value* CollapsePhi(PHINode* p);
748    bool isSafeReplacement(PHINode* p, Instruction* inst);
749    bool performPRE(Function& F);
750    Value* lookupNumber(BasicBlock* BB, uint32_t num);
751  };
752
753  char GVN::ID = 0;
754}
755
756// createGVNPass - The public interface to this file...
757FunctionPass *llvm::createGVNPass() { return new GVN(); }
758
759static RegisterPass<GVN> X("gvn",
760                           "Global Value Numbering");
761
762void GVN::dump(DenseMap<uint32_t, Value*>& d) {
763  printf("{\n");
764  for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
765       E = d.end(); I != E; ++I) {
766      printf("%d\n", I->first);
767      I->second->dump();
768  }
769  printf("}\n");
770}
771
772Value* GVN::CollapsePhi(PHINode* p) {
773  DominatorTree &DT = getAnalysis<DominatorTree>();
774  Value* constVal = p->hasConstantValue();
775
776  if (!constVal) return 0;
777
778  Instruction* inst = dyn_cast<Instruction>(constVal);
779  if (!inst)
780    return constVal;
781
782  if (DT.dominates(inst, p))
783    if (isSafeReplacement(p, inst))
784      return inst;
785  return 0;
786}
787
788bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
789  if (!isa<PHINode>(inst))
790    return true;
791
792  for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
793       UI != E; ++UI)
794    if (PHINode* use_phi = dyn_cast<PHINode>(UI))
795      if (use_phi->getParent() == inst->getParent())
796        return false;
797
798  return true;
799}
800
801/// GetValueForBlock - Get the value to use within the specified basic block.
802/// available values are in Phis.
803Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
804                             DenseMap<BasicBlock*, Value*> &Phis,
805                             bool top_level) {
806
807  // If we have already computed this value, return the previously computed val.
808  DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
809  if (V != Phis.end() && !top_level) return V->second;
810
811  if (!getAnalysis<DominatorTree>().isReachableFromEntry(BB)) {
812    Phis[BB] = UndefValue::get(orig->getType());
813    return UndefValue::get(orig->getType());
814  }
815
816  BasicBlock* singlePred = BB->getSinglePredecessor();
817  if (singlePred) {
818    Value *ret = GetValueForBlock(singlePred, orig, Phis);
819    Phis[BB] = ret;
820    return ret;
821  }
822
823  // Otherwise, the idom is the loop, so we need to insert a PHI node.  Do so
824  // now, then get values to fill in the incoming values for the PHI.
825  PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
826                                BB->begin());
827  PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
828
829  if (Phis.count(BB) == 0)
830    Phis.insert(std::make_pair(BB, PN));
831
832  // Fill in the incoming values for the block.
833  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
834    Value* val = GetValueForBlock(*PI, orig, Phis);
835    PN->addIncoming(val, *PI);
836  }
837
838  AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
839  AA.copyValue(orig, PN);
840
841  // Attempt to collapse PHI nodes that are trivially redundant
842  Value* v = CollapsePhi(PN);
843  if (!v) {
844    // Cache our phi construction results
845    phiMap[orig->getPointerOperand()].insert(PN);
846    return PN;
847  }
848
849  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
850
851  MD.removeInstruction(PN);
852  PN->replaceAllUsesWith(v);
853
854  for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
855       E = Phis.end(); I != E; ++I)
856    if (I->second == PN)
857      I->second = v;
858
859  PN->eraseFromParent();
860
861  Phis[BB] = v;
862  return v;
863}
864
865/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
866/// non-local by performing PHI construction.
867bool GVN::processNonLocalLoad(LoadInst* L,
868                              SmallVectorImpl<Instruction*> &toErase) {
869  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
870
871  // Find the non-local dependencies of the load
872  DenseMap<BasicBlock*, Value*> deps;
873  MD.getNonLocalDependency(L, deps);
874
875  DenseMap<BasicBlock*, Value*> repl;
876
877  // Filter out useless results (non-locals, etc)
878  for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
879       I != E; ++I) {
880    if (I->second == MemoryDependenceAnalysis::None)
881      return false;
882
883    if (I->second == MemoryDependenceAnalysis::NonLocal)
884      continue;
885
886    if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
887      if (S->getPointerOperand() != L->getPointerOperand())
888        return false;
889      repl[I->first] = S->getOperand(0);
890    } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
891      if (LD->getPointerOperand() != L->getPointerOperand())
892        return false;
893      repl[I->first] = LD;
894    } else {
895      return false;
896    }
897  }
898
899  // Use cached PHI construction information from previous runs
900  SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
901  for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
902       I != E; ++I) {
903    if ((*I)->getParent() == L->getParent()) {
904      MD.removeInstruction(L);
905      L->replaceAllUsesWith(*I);
906      toErase.push_back(L);
907      NumGVNLoad++;
908      return true;
909    }
910
911    repl.insert(std::make_pair((*I)->getParent(), *I));
912  }
913
914  // Perform PHI construction
915  SmallPtrSet<BasicBlock*, 4> visited;
916  Value* v = GetValueForBlock(L->getParent(), L, repl, true);
917
918  MD.removeInstruction(L);
919  L->replaceAllUsesWith(v);
920  toErase.push_back(L);
921  NumGVNLoad++;
922
923  return true;
924}
925
926/// processLoad - Attempt to eliminate a load, first by eliminating it
927/// locally, and then attempting non-local elimination if that fails.
928bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad,
929                      SmallVectorImpl<Instruction*> &toErase) {
930  if (L->isVolatile()) {
931    lastLoad[L->getPointerOperand()] = L;
932    return false;
933  }
934
935  Value* pointer = L->getPointerOperand();
936  LoadInst*& last = lastLoad[pointer];
937
938  // ... to a pointer that has been loaded from before...
939  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
940  bool removedNonLocal = false;
941  Instruction* dep = MD.getDependency(L);
942  if (dep == MemoryDependenceAnalysis::NonLocal &&
943      L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
944    removedNonLocal = processNonLocalLoad(L, toErase);
945
946    if (!removedNonLocal)
947      last = L;
948
949    return removedNonLocal;
950  }
951
952
953  bool deletedLoad = false;
954
955  // Walk up the dependency chain until we either find
956  // a dependency we can use, or we can't walk any further
957  while (dep != MemoryDependenceAnalysis::None &&
958         dep != MemoryDependenceAnalysis::NonLocal &&
959         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
960    // ... that depends on a store ...
961    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
962      if (S->getPointerOperand() == pointer) {
963        // Remove it!
964        MD.removeInstruction(L);
965
966        L->replaceAllUsesWith(S->getOperand(0));
967        toErase.push_back(L);
968        deletedLoad = true;
969        NumGVNLoad++;
970      }
971
972      // Whether we removed it or not, we can't
973      // go any further
974      break;
975    } else if (!last) {
976      // If we don't depend on a store, and we haven't
977      // been loaded before, bail.
978      break;
979    } else if (dep == last) {
980      // Remove it!
981      MD.removeInstruction(L);
982
983      L->replaceAllUsesWith(last);
984      toErase.push_back(L);
985      deletedLoad = true;
986      NumGVNLoad++;
987
988      break;
989    } else {
990      dep = MD.getDependency(L, dep);
991    }
992  }
993
994  if (dep != MemoryDependenceAnalysis::None &&
995      dep != MemoryDependenceAnalysis::NonLocal &&
996      isa<AllocationInst>(dep)) {
997    // Check that this load is actually from the
998    // allocation we found
999    Value* v = L->getOperand(0);
1000    while (true) {
1001      if (BitCastInst *BC = dyn_cast<BitCastInst>(v))
1002        v = BC->getOperand(0);
1003      else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v))
1004        v = GEP->getOperand(0);
1005      else
1006        break;
1007    }
1008    if (v == dep) {
1009      // If this load depends directly on an allocation, there isn't
1010      // anything stored there; therefore, we can optimize this load
1011      // to undef.
1012      MD.removeInstruction(L);
1013
1014      L->replaceAllUsesWith(UndefValue::get(L->getType()));
1015      toErase.push_back(L);
1016      deletedLoad = true;
1017      NumGVNLoad++;
1018    }
1019  }
1020
1021  if (!deletedLoad)
1022    last = L;
1023
1024  return deletedLoad;
1025}
1026
1027Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
1028  DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1029  if (I == localAvail.end())
1030    return 0;
1031
1032  ValueNumberScope* locals = I->second;
1033
1034  while (locals) {
1035    DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num);
1036    if (I != locals->table.end())
1037      return I->second;
1038    else
1039      locals = locals->parent;
1040  }
1041
1042  return 0;
1043}
1044
1045/// processInstruction - When calculating availability, handle an instruction
1046/// by inserting it into the appropriate sets
1047bool GVN::processInstruction(Instruction *I,
1048                             DenseMap<Value*, LoadInst*> &lastSeenLoad,
1049                             SmallVectorImpl<Instruction*> &toErase) {
1050  if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1051    bool changed = processLoad(L, lastSeenLoad, toErase);
1052
1053    if (!changed) {
1054      unsigned num = VN.lookup_or_add(L);
1055      localAvail[I->getParent()]->table.insert(std::make_pair(num, L));
1056    }
1057
1058    return changed;
1059  }
1060
1061  unsigned num = VN.lookup_or_add(I);
1062
1063  // Allocations are always uniquely numbered, so we can save time and memory
1064  // by fast failing them.
1065  if (isa<AllocationInst>(I)) {
1066    localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1067    return false;
1068  }
1069
1070  // Collapse PHI nodes
1071  if (PHINode* p = dyn_cast<PHINode>(I)) {
1072    Value* constVal = CollapsePhi(p);
1073
1074    if (constVal) {
1075      for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1076           PI != PE; ++PI)
1077        if (PI->second.count(p))
1078          PI->second.erase(p);
1079
1080      p->replaceAllUsesWith(constVal);
1081      toErase.push_back(p);
1082    } else {
1083      localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1084    }
1085  // Perform value-number based elimination
1086  } else if (Value* repl = lookupNumber(I->getParent(), num)) {
1087    // Remove it!
1088    MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1089    MD.removeInstruction(I);
1090
1091    VN.erase(I);
1092    I->replaceAllUsesWith(repl);
1093    toErase.push_back(I);
1094    return true;
1095  } else if (!I->isTerminator()) {
1096    localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1097  }
1098
1099  return false;
1100}
1101
1102// GVN::runOnFunction - This is the main transformation entry point for a
1103// function.
1104//
1105bool GVN::runOnFunction(Function& F) {
1106  VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1107  VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>());
1108  VN.setDomTree(&getAnalysis<DominatorTree>());
1109
1110  bool changed = false;
1111  bool shouldContinue = true;
1112
1113  while (shouldContinue) {
1114    shouldContinue = iterateOnFunction(F);
1115    changed |= shouldContinue;
1116  }
1117
1118  return changed;
1119}
1120
1121
1122bool GVN::processBlock(DomTreeNode* DTN) {
1123  BasicBlock* BB = DTN->getBlock();
1124
1125  SmallVector<Instruction*, 8> toErase;
1126  DenseMap<Value*, LoadInst*> lastSeenLoad;
1127  bool changed_function = false;
1128
1129  if (DTN->getIDom())
1130    localAvail[BB] =
1131                  new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]);
1132  else
1133    localAvail[BB] = new ValueNumberScope(0);
1134
1135  for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1136       BI != BE;) {
1137    changed_function |= processInstruction(BI, lastSeenLoad, toErase);
1138    if (toErase.empty()) {
1139      ++BI;
1140      continue;
1141    }
1142
1143    // If we need some instructions deleted, do it now.
1144    NumGVNInstr += toErase.size();
1145
1146    // Avoid iterator invalidation.
1147    bool AtStart = BI == BB->begin();
1148    if (!AtStart)
1149      --BI;
1150
1151    for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1152         E = toErase.end(); I != E; ++I)
1153      (*I)->eraseFromParent();
1154
1155    if (AtStart)
1156      BI = BB->begin();
1157    else
1158      ++BI;
1159
1160    toErase.clear();
1161  }
1162
1163  return changed_function;
1164}
1165
1166/// performPRE - Perform a purely local form of PRE that looks for diamond
1167/// control flow patterns and attempts to perform simple PRE at the join point.
1168bool GVN::performPRE(Function& F) {
1169  bool changed = false;
1170  SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
1171  for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
1172       DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
1173    BasicBlock* CurrentBlock = *DI;
1174
1175    // Nothing to PRE in the entry block.
1176    if (CurrentBlock == &F.getEntryBlock()) continue;
1177
1178    for (BasicBlock::iterator BI = CurrentBlock->begin(),
1179         BE = CurrentBlock->end(); BI != BE; ) {
1180      if (isa<AllocationInst>(BI) || isa<TerminatorInst>(BI) ||
1181          isa<PHINode>(BI) || BI->mayReadFromMemory() ||
1182          BI->mayWriteToMemory()) {
1183        BI++;
1184        continue;
1185      }
1186
1187      uint32_t valno = VN.lookup(BI);
1188
1189      // Look for the predecessors for PRE opportunities.  We're
1190      // only trying to solve the basic diamond case, where
1191      // a value is computed in the successor and one predecessor,
1192      // but not the other.  We also explicitly disallow cases
1193      // where the successor is its own predecessor, because they're
1194      // more complicated to get right.
1195      unsigned numWith = 0;
1196      unsigned numWithout = 0;
1197      BasicBlock* PREPred = 0;
1198      DenseMap<BasicBlock*, Value*> predMap;
1199      for (pred_iterator PI = pred_begin(CurrentBlock),
1200           PE = pred_end(CurrentBlock); PI != PE; ++PI) {
1201        // We're not interested in PRE where the block is its
1202        // own predecessor, on in blocks with predecessors
1203        // that are not reachable.
1204        if (*PI == CurrentBlock) {
1205          numWithout = 2;
1206          break;
1207        } else if (!localAvail.count(*PI))  {
1208          numWithout = 2;
1209          break;
1210        }
1211
1212        DenseMap<uint32_t, Value*>::iterator predV =
1213                                            localAvail[*PI]->table.find(valno);
1214        if (predV == localAvail[*PI]->table.end()) {
1215          PREPred = *PI;
1216          numWithout++;
1217        } else if (predV->second == BI) {
1218          numWithout = 2;
1219        } else {
1220          predMap[*PI] = predV->second;
1221          numWith++;
1222        }
1223      }
1224
1225      // Don't do PRE when it might increase code size, i.e. when
1226      // we would need to insert instructions in more than one pred.
1227      if (numWithout != 1 || numWith == 0) {
1228        BI++;
1229        continue;
1230      }
1231
1232      // We can't do PRE safely on a critical edge, so instead we schedule
1233      // the edge to be split and perform the PRE the next time we iterate
1234      // on the function.
1235      unsigned succNum = 0;
1236      for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
1237           i != e; ++i)
1238        if (PREPred->getTerminator()->getSuccessor(i) == PREPred) {
1239          succNum = i;
1240          break;
1241        }
1242
1243      if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
1244        toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
1245        changed = true;
1246        BI++;
1247        continue;
1248      }
1249
1250      // Instantiate the expression the in predecessor that lacked it.
1251      // Because we are going top-down through the block, all value numbers
1252      // will be available in the predecessor by the time we need them.  Any
1253      // that weren't original present will have been instantiated earlier
1254      // in this loop.
1255      Instruction* PREInstr = BI->clone();
1256      bool success = true;
1257      for (unsigned i = 0; i < BI->getNumOperands(); ++i) {
1258        Value* op = BI->getOperand(i);
1259        if (isa<Argument>(op) || isa<Constant>(op) || isa<GlobalValue>(op))
1260          PREInstr->setOperand(i, op);
1261        else if (!lookupNumber(PREPred, VN.lookup(op))) {
1262          success = false;
1263          break;
1264        } else
1265          PREInstr->setOperand(i, lookupNumber(PREPred, VN.lookup(op)));
1266      }
1267
1268      // Fail out if we encounter an operand that is not available in
1269      // the PRE predecessor.  This is typically because of loads which
1270      // are not value numbered precisely.
1271      if (!success) {
1272        delete PREInstr;
1273        BI++;
1274        continue;
1275      }
1276
1277      PREInstr->insertBefore(PREPred->getTerminator());
1278      PREInstr->setName(BI->getName() + ".pre");
1279      predMap[PREPred] = PREInstr;
1280      VN.add(PREInstr, valno);
1281      NumGVNPRE++;
1282
1283      // Update the availability map to include the new instruction.
1284      localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr));
1285
1286      // Create a PHI to make the value available in this block.
1287      PHINode* Phi = PHINode::Create(BI->getType(),
1288                                     BI->getName() + ".pre-phi",
1289                                     CurrentBlock->begin());
1290      for (pred_iterator PI = pred_begin(CurrentBlock),
1291           PE = pred_end(CurrentBlock); PI != PE; ++PI)
1292        Phi->addIncoming(predMap[*PI], *PI);
1293
1294      VN.add(Phi, valno);
1295      localAvail[CurrentBlock]->table[valno] = Phi;
1296
1297      BI->replaceAllUsesWith(Phi);
1298      VN.erase(BI);
1299
1300      Instruction* erase = BI;
1301      BI++;
1302      erase->eraseFromParent();
1303
1304      changed = true;
1305    }
1306  }
1307
1308  for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
1309       I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
1310    SplitCriticalEdge(I->first, I->second, this);
1311
1312  return changed;
1313}
1314
1315// GVN::iterateOnFunction - Executes one iteration of GVN
1316bool GVN::iterateOnFunction(Function &F) {
1317  // Clean out global sets from any previous functions
1318  VN.clear();
1319  phiMap.clear();
1320
1321  for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1322       I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
1323    delete I->second;
1324  localAvail.clear();
1325
1326  DominatorTree &DT = getAnalysis<DominatorTree>();
1327
1328  // Top-down walk of the dominator tree
1329  bool changed = false;
1330  for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
1331       DE = df_end(DT.getRootNode()); DI != DE; ++DI)
1332    changed |= processBlock(*DI);
1333
1334  if (EnablePRE)
1335    changed |= performPRE(F);
1336
1337  return changed;
1338}
1339