GVN.cpp revision 1ad2cb75553a30bcec9fdc15733a20df6bc50431 
1//===- GVN.cpp - Eliminate redundant values and loads ------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by the Owen Anderson and is distributed under
6// the University of Illinois Open Source 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//===----------------------------------------------------------------------===//
14
15#define DEBUG_TYPE "gvn"
16#include "llvm/Value.h"
17#include "llvm/Transforms/Scalar.h"
18#include "llvm/Instructions.h"
19#include "llvm/Function.h"
20#include "llvm/DerivedTypes.h"
21#include "llvm/Analysis/Dominators.h"
22#include "llvm/ADT/BitVector.h"
23#include "llvm/ADT/DenseMap.h"
24#include "llvm/ADT/DepthFirstIterator.h"
25#include "llvm/ADT/SmallPtrSet.h"
26#include "llvm/ADT/SmallVector.h"
27#include "llvm/ADT/Statistic.h"
28#include "llvm/Analysis/MemoryDependenceAnalysis.h"
29#include "llvm/Support/CFG.h"
30#include "llvm/Support/Compiler.h"
31using namespace llvm;
32
33//===----------------------------------------------------------------------===//
34//                         ValueTable Class
35//===----------------------------------------------------------------------===//
36
37/// This class holds the mapping between values and value numbers.  It is used
38/// as an efficient mechanism to determine the expression-wise equivalence of
39/// two values.
40namespace {
41  struct VISIBILITY_HIDDEN Expression {
42    enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
43                            FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
44                            ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
45                            ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
46                            FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
47                            FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
48                            FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
49                            SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
50                            FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
51                            PTRTOINT, INTTOPTR, BITCAST, GEP, EMPTY,
52                            TOMBSTONE };
53
54    ExpressionOpcode opcode;
55    const Type* type;
56    uint32_t firstVN;
57    uint32_t secondVN;
58    uint32_t thirdVN;
59    SmallVector<uint32_t, 4> varargs;
60
61    Expression() { }
62    Expression(ExpressionOpcode o) : opcode(o) { }
63
64    bool operator==(const Expression &other) const {
65      if (opcode != other.opcode)
66        return false;
67      else if (opcode == EMPTY || opcode == TOMBSTONE)
68        return true;
69      else if (type != other.type)
70        return false;
71      else if (firstVN != other.firstVN)
72        return false;
73      else if (secondVN != other.secondVN)
74        return false;
75      else if (thirdVN != other.thirdVN)
76        return false;
77      else {
78        if (varargs.size() != other.varargs.size())
79          return false;
80
81        for (size_t i = 0; i < varargs.size(); ++i)
82          if (varargs[i] != other.varargs[i])
83            return false;
84
85        return true;
86      }
87    }
88
89    bool operator!=(const Expression &other) const {
90      if (opcode != other.opcode)
91        return true;
92      else if (opcode == EMPTY || opcode == TOMBSTONE)
93        return false;
94      else if (type != other.type)
95        return true;
96      else if (firstVN != other.firstVN)
97        return true;
98      else if (secondVN != other.secondVN)
99        return true;
100      else if (thirdVN != other.thirdVN)
101        return true;
102      else {
103        if (varargs.size() != other.varargs.size())
104          return true;
105
106        for (size_t i = 0; i < varargs.size(); ++i)
107          if (varargs[i] != other.varargs[i])
108            return true;
109
110          return false;
111      }
112    }
113  };
114
115  class VISIBILITY_HIDDEN ValueTable {
116    private:
117      DenseMap<Value*, uint32_t> valueNumbering;
118      DenseMap<Expression, uint32_t> expressionNumbering;
119
120      uint32_t nextValueNumber;
121
122      Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
123      Expression::ExpressionOpcode getOpcode(CmpInst* C);
124      Expression::ExpressionOpcode getOpcode(CastInst* C);
125      Expression create_expression(BinaryOperator* BO);
126      Expression create_expression(CmpInst* C);
127      Expression create_expression(ShuffleVectorInst* V);
128      Expression create_expression(ExtractElementInst* C);
129      Expression create_expression(InsertElementInst* V);
130      Expression create_expression(SelectInst* V);
131      Expression create_expression(CastInst* C);
132      Expression create_expression(GetElementPtrInst* G);
133    public:
134      ValueTable() { nextValueNumber = 1; }
135      uint32_t lookup_or_add(Value* V);
136      uint32_t lookup(Value* V) const;
137      void add(Value* V, uint32_t num);
138      void clear();
139      void erase(Value* v);
140      unsigned size();
141  };
142}
143
144namespace llvm {
145template <> struct DenseMapKeyInfo<Expression> {
146  static inline Expression getEmptyKey() { return Expression(Expression::EMPTY); }
147  static inline Expression getTombstoneKey() { return Expression(Expression::TOMBSTONE); }
148
149  static unsigned getHashValue(const Expression e) {
150    unsigned hash = e.opcode;
151
152    hash = e.firstVN + hash * 37;
153    hash = e.secondVN + hash * 37;
154    hash = e.thirdVN + hash * 37;
155
156    hash = (unsigned)((uintptr_t)e.type >> 4) ^
157            (unsigned)((uintptr_t)e.type >> 9) +
158            hash * 37;
159
160    for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), E = e.varargs.end();
161         I != E; ++I)
162      hash = *I + hash * 37;
163
164    return hash;
165  }
166  static bool isPod() { return true; }
167};
168}
169
170//===----------------------------------------------------------------------===//
171//                     ValueTable Internal Functions
172//===----------------------------------------------------------------------===//
173Expression::ExpressionOpcode
174                             ValueTable::getOpcode(BinaryOperator* BO) {
175  switch(BO->getOpcode()) {
176    case Instruction::Add:
177      return Expression::ADD;
178    case Instruction::Sub:
179      return Expression::SUB;
180    case Instruction::Mul:
181      return Expression::MUL;
182    case Instruction::UDiv:
183      return Expression::UDIV;
184    case Instruction::SDiv:
185      return Expression::SDIV;
186    case Instruction::FDiv:
187      return Expression::FDIV;
188    case Instruction::URem:
189      return Expression::UREM;
190    case Instruction::SRem:
191      return Expression::SREM;
192    case Instruction::FRem:
193      return Expression::FREM;
194    case Instruction::Shl:
195      return Expression::SHL;
196    case Instruction::LShr:
197      return Expression::LSHR;
198    case Instruction::AShr:
199      return Expression::ASHR;
200    case Instruction::And:
201      return Expression::AND;
202    case Instruction::Or:
203      return Expression::OR;
204    case Instruction::Xor:
205      return Expression::XOR;
206
207    // THIS SHOULD NEVER HAPPEN
208    default:
209      assert(0 && "Binary operator with unknown opcode?");
210      return Expression::ADD;
211  }
212}
213
214Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
215  if (C->getOpcode() == Instruction::ICmp) {
216    switch (C->getPredicate()) {
217      case ICmpInst::ICMP_EQ:
218        return Expression::ICMPEQ;
219      case ICmpInst::ICMP_NE:
220        return Expression::ICMPNE;
221      case ICmpInst::ICMP_UGT:
222        return Expression::ICMPUGT;
223      case ICmpInst::ICMP_UGE:
224        return Expression::ICMPUGE;
225      case ICmpInst::ICMP_ULT:
226        return Expression::ICMPULT;
227      case ICmpInst::ICMP_ULE:
228        return Expression::ICMPULE;
229      case ICmpInst::ICMP_SGT:
230        return Expression::ICMPSGT;
231      case ICmpInst::ICMP_SGE:
232        return Expression::ICMPSGE;
233      case ICmpInst::ICMP_SLT:
234        return Expression::ICMPSLT;
235      case ICmpInst::ICMP_SLE:
236        return Expression::ICMPSLE;
237
238      // THIS SHOULD NEVER HAPPEN
239      default:
240        assert(0 && "Comparison with unknown predicate?");
241        return Expression::ICMPEQ;
242    }
243  } else {
244    switch (C->getPredicate()) {
245      case FCmpInst::FCMP_OEQ:
246        return Expression::FCMPOEQ;
247      case FCmpInst::FCMP_OGT:
248        return Expression::FCMPOGT;
249      case FCmpInst::FCMP_OGE:
250        return Expression::FCMPOGE;
251      case FCmpInst::FCMP_OLT:
252        return Expression::FCMPOLT;
253      case FCmpInst::FCMP_OLE:
254        return Expression::FCMPOLE;
255      case FCmpInst::FCMP_ONE:
256        return Expression::FCMPONE;
257      case FCmpInst::FCMP_ORD:
258        return Expression::FCMPORD;
259      case FCmpInst::FCMP_UNO:
260        return Expression::FCMPUNO;
261      case FCmpInst::FCMP_UEQ:
262        return Expression::FCMPUEQ;
263      case FCmpInst::FCMP_UGT:
264        return Expression::FCMPUGT;
265      case FCmpInst::FCMP_UGE:
266        return Expression::FCMPUGE;
267      case FCmpInst::FCMP_ULT:
268        return Expression::FCMPULT;
269      case FCmpInst::FCMP_ULE:
270        return Expression::FCMPULE;
271      case FCmpInst::FCMP_UNE:
272        return Expression::FCMPUNE;
273
274      // THIS SHOULD NEVER HAPPEN
275      default:
276        assert(0 && "Comparison with unknown predicate?");
277        return Expression::FCMPOEQ;
278    }
279  }
280}
281
282Expression::ExpressionOpcode
283                             ValueTable::getOpcode(CastInst* C) {
284  switch(C->getOpcode()) {
285    case Instruction::Trunc:
286      return Expression::TRUNC;
287    case Instruction::ZExt:
288      return Expression::ZEXT;
289    case Instruction::SExt:
290      return Expression::SEXT;
291    case Instruction::FPToUI:
292      return Expression::FPTOUI;
293    case Instruction::FPToSI:
294      return Expression::FPTOSI;
295    case Instruction::UIToFP:
296      return Expression::UITOFP;
297    case Instruction::SIToFP:
298      return Expression::SITOFP;
299    case Instruction::FPTrunc:
300      return Expression::FPTRUNC;
301    case Instruction::FPExt:
302      return Expression::FPEXT;
303    case Instruction::PtrToInt:
304      return Expression::PTRTOINT;
305    case Instruction::IntToPtr:
306      return Expression::INTTOPTR;
307    case Instruction::BitCast:
308      return Expression::BITCAST;
309
310    // THIS SHOULD NEVER HAPPEN
311    default:
312      assert(0 && "Cast operator with unknown opcode?");
313      return Expression::BITCAST;
314  }
315}
316
317Expression ValueTable::create_expression(BinaryOperator* BO) {
318  Expression e;
319
320  e.firstVN = lookup_or_add(BO->getOperand(0));
321  e.secondVN = lookup_or_add(BO->getOperand(1));
322  e.thirdVN = 0;
323  e.type = BO->getType();
324  e.opcode = getOpcode(BO);
325
326  return e;
327}
328
329Expression ValueTable::create_expression(CmpInst* C) {
330  Expression e;
331
332  e.firstVN = lookup_or_add(C->getOperand(0));
333  e.secondVN = lookup_or_add(C->getOperand(1));
334  e.thirdVN = 0;
335  e.type = C->getType();
336  e.opcode = getOpcode(C);
337
338  return e;
339}
340
341Expression ValueTable::create_expression(CastInst* C) {
342  Expression e;
343
344  e.firstVN = lookup_or_add(C->getOperand(0));
345  e.secondVN = 0;
346  e.thirdVN = 0;
347  e.type = C->getType();
348  e.opcode = getOpcode(C);
349
350  return e;
351}
352
353Expression ValueTable::create_expression(ShuffleVectorInst* S) {
354  Expression e;
355
356  e.firstVN = lookup_or_add(S->getOperand(0));
357  e.secondVN = lookup_or_add(S->getOperand(1));
358  e.thirdVN = lookup_or_add(S->getOperand(2));
359  e.type = S->getType();
360  e.opcode = Expression::SHUFFLE;
361
362  return e;
363}
364
365Expression ValueTable::create_expression(ExtractElementInst* E) {
366  Expression e;
367
368  e.firstVN = lookup_or_add(E->getOperand(0));
369  e.secondVN = lookup_or_add(E->getOperand(1));
370  e.thirdVN = 0;
371  e.type = E->getType();
372  e.opcode = Expression::EXTRACT;
373
374  return e;
375}
376
377Expression ValueTable::create_expression(InsertElementInst* I) {
378  Expression e;
379
380  e.firstVN = lookup_or_add(I->getOperand(0));
381  e.secondVN = lookup_or_add(I->getOperand(1));
382  e.thirdVN = lookup_or_add(I->getOperand(2));
383  e.type = I->getType();
384  e.opcode = Expression::INSERT;
385
386  return e;
387}
388
389Expression ValueTable::create_expression(SelectInst* I) {
390  Expression e;
391
392  e.firstVN = lookup_or_add(I->getCondition());
393  e.secondVN = lookup_or_add(I->getTrueValue());
394  e.thirdVN = lookup_or_add(I->getFalseValue());
395  e.type = I->getType();
396  e.opcode = Expression::SELECT;
397
398  return e;
399}
400
401Expression ValueTable::create_expression(GetElementPtrInst* G) {
402  Expression e;
403
404  e.firstVN = lookup_or_add(G->getPointerOperand());
405  e.secondVN = 0;
406  e.thirdVN = 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/// lookup_or_add - Returns the value number for the specified value, assigning
422/// it a new number if it did not have one before.
423uint32_t ValueTable::lookup_or_add(Value* V) {
424  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
425  if (VI != valueNumbering.end())
426    return VI->second;
427
428
429  if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
430    Expression e = create_expression(BO);
431
432    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
433    if (EI != expressionNumbering.end()) {
434      valueNumbering.insert(std::make_pair(V, EI->second));
435      return EI->second;
436    } else {
437      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
438      valueNumbering.insert(std::make_pair(V, nextValueNumber));
439
440      return nextValueNumber++;
441    }
442  } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
443    Expression e = create_expression(C);
444
445    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
446    if (EI != expressionNumbering.end()) {
447      valueNumbering.insert(std::make_pair(V, EI->second));
448      return EI->second;
449    } else {
450      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
451      valueNumbering.insert(std::make_pair(V, nextValueNumber));
452
453      return nextValueNumber++;
454    }
455  } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
456    Expression e = create_expression(U);
457
458    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
459    if (EI != expressionNumbering.end()) {
460      valueNumbering.insert(std::make_pair(V, EI->second));
461      return EI->second;
462    } else {
463      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
464      valueNumbering.insert(std::make_pair(V, nextValueNumber));
465
466      return nextValueNumber++;
467    }
468  } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
469    Expression e = create_expression(U);
470
471    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
472    if (EI != expressionNumbering.end()) {
473      valueNumbering.insert(std::make_pair(V, EI->second));
474      return EI->second;
475    } else {
476      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
477      valueNumbering.insert(std::make_pair(V, nextValueNumber));
478
479      return nextValueNumber++;
480    }
481  } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
482    Expression e = create_expression(U);
483
484    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
485    if (EI != expressionNumbering.end()) {
486      valueNumbering.insert(std::make_pair(V, EI->second));
487      return EI->second;
488    } else {
489      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
490      valueNumbering.insert(std::make_pair(V, nextValueNumber));
491
492      return nextValueNumber++;
493    }
494  } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
495    Expression e = create_expression(U);
496
497    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
498    if (EI != expressionNumbering.end()) {
499      valueNumbering.insert(std::make_pair(V, EI->second));
500      return EI->second;
501    } else {
502      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
503      valueNumbering.insert(std::make_pair(V, nextValueNumber));
504
505      return nextValueNumber++;
506    }
507  } else if (CastInst* U = dyn_cast<CastInst>(V)) {
508    Expression e = create_expression(U);
509
510    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
511    if (EI != expressionNumbering.end()) {
512      valueNumbering.insert(std::make_pair(V, EI->second));
513      return EI->second;
514    } else {
515      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
516      valueNumbering.insert(std::make_pair(V, nextValueNumber));
517
518      return nextValueNumber++;
519    }
520  } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
521    Expression e = create_expression(U);
522
523    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
524    if (EI != expressionNumbering.end()) {
525      valueNumbering.insert(std::make_pair(V, EI->second));
526      return EI->second;
527    } else {
528      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
529      valueNumbering.insert(std::make_pair(V, nextValueNumber));
530
531      return nextValueNumber++;
532    }
533  } else {
534    valueNumbering.insert(std::make_pair(V, nextValueNumber));
535    return nextValueNumber++;
536  }
537}
538
539/// lookup - Returns the value number of the specified value. Fails if
540/// the value has not yet been numbered.
541uint32_t ValueTable::lookup(Value* V) const {
542  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
543  if (VI != valueNumbering.end())
544    return VI->second;
545  else
546    assert(0 && "Value not numbered?");
547
548  return 0;
549}
550
551/// clear - Remove all entries from the ValueTable
552void ValueTable::clear() {
553  valueNumbering.clear();
554  expressionNumbering.clear();
555  nextValueNumber = 1;
556}
557
558//===----------------------------------------------------------------------===//
559//                       ValueNumberedSet Class
560//===----------------------------------------------------------------------===//
561namespace {
562class ValueNumberedSet {
563  private:
564    SmallPtrSet<Value*, 8> contents;
565    BitVector numbers;
566  public:
567    ValueNumberedSet() { numbers.resize(1); }
568    ValueNumberedSet(const ValueNumberedSet& other) {
569      numbers = other.numbers;
570      contents = other.contents;
571    }
572
573    typedef SmallPtrSet<Value*, 8>::iterator iterator;
574
575    iterator begin() { return contents.begin(); }
576    iterator end() { return contents.end(); }
577
578    bool insert(Value* v) { return contents.insert(v); }
579    void insert(iterator I, iterator E) { contents.insert(I, E); }
580    void erase(Value* v) { contents.erase(v); }
581    unsigned count(Value* v) { return contents.count(v); }
582    size_t size() { return contents.size(); }
583
584    void set(unsigned i)  {
585      if (i >= numbers.size())
586        numbers.resize(i+1);
587
588      numbers.set(i);
589    }
590
591    void operator=(const ValueNumberedSet& other) {
592      contents = other.contents;
593      numbers = other.numbers;
594    }
595
596    void reset(unsigned i)  {
597      if (i < numbers.size())
598        numbers.reset(i);
599    }
600
601    bool test(unsigned i)  {
602      if (i >= numbers.size())
603        return false;
604
605      return numbers.test(i);
606    }
607
608    void clear() {
609      contents.clear();
610      numbers.clear();
611    }
612};
613}
614
615//===----------------------------------------------------------------------===//
616//                         GVN Pass
617//===----------------------------------------------------------------------===//
618
619namespace {
620
621  class VISIBILITY_HIDDEN GVN : public FunctionPass {
622    bool runOnFunction(Function &F);
623  public:
624    static char ID; // Pass identification, replacement for typeid
625    GVN() : FunctionPass((intptr_t)&ID) { }
626
627  private:
628    ValueTable VN;
629
630    DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
631
632    // This transformation requires dominator postdominator info
633    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
634      AU.setPreservesCFG();
635      AU.addRequired<DominatorTree>();
636      AU.addRequired<MemoryDependenceAnalysis>();
637      AU.addPreserved<MemoryDependenceAnalysis>();
638    }
639
640    // Helper fuctions
641    // FIXME: eliminate or document these better
642    Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
643    void val_insert(ValueNumberedSet& s, Value* v);
644    bool processLoad(LoadInst* L,
645                     DenseMap<Value*, LoadInst*>& lastLoad,
646                     SmallVector<Instruction*, 4>& toErase);
647    bool processInstruction(Instruction* I,
648                            ValueNumberedSet& currAvail,
649                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
650                            SmallVector<Instruction*, 4>& toErase);
651  };
652
653  char GVN::ID = 0;
654
655}
656
657// createGVNPass - The public interface to this file...
658FunctionPass *llvm::createGVNPass() { return new GVN(); }
659
660static RegisterPass<GVN> X("gvn",
661                           "Global Value Numbering");
662
663STATISTIC(NumGVNInstr, "Number of instructions deleted");
664STATISTIC(NumGVNLoad, "Number of loads deleted");
665
666/// find_leader - Given a set and a value number, return the first
667/// element of the set with that value number, or 0 if no such element
668/// is present
669Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
670  if (!vals.test(v))
671    return 0;
672
673  for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
674       I != E; ++I)
675    if (v == VN.lookup(*I))
676      return *I;
677
678  assert(0 && "No leader found, but present bit is set?");
679  return 0;
680}
681
682/// val_insert - Insert a value into a set only if there is not a value
683/// with the same value number already in the set
684void GVN::val_insert(ValueNumberedSet& s, Value* v) {
685  uint32_t num = VN.lookup(v);
686  if (!s.test(num))
687    s.insert(v);
688}
689
690bool GVN::processLoad(LoadInst* L,
691                         DenseMap<Value*, LoadInst*>& lastLoad,
692                         SmallVector<Instruction*, 4>& toErase) {
693  if (L->isVolatile()) {
694    lastLoad[L->getPointerOperand()] = L;
695    return false;
696  }
697
698  Value* pointer = L->getPointerOperand();
699  LoadInst*& last = lastLoad[pointer];
700
701  // ... to a pointer that has been loaded from before...
702  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
703  Instruction* dep = MD.getDependency(L);
704  bool deletedLoad = false;
705
706  while (dep != MemoryDependenceAnalysis::None &&
707         dep != MemoryDependenceAnalysis::NonLocal &&
708         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
709    // ... that depends on a store ...
710    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
711      if (S->getPointerOperand() == pointer) {
712        // Remove it!
713        MD.removeInstruction(L);
714
715        L->replaceAllUsesWith(S->getOperand(0));
716        toErase.push_back(L);
717        deletedLoad = true;
718        NumGVNLoad++;
719      }
720
721      // Whether we removed it or not, we can't
722      // go any further
723      break;
724    } else if (!last) {
725      // If we don't depend on a store, and we haven't
726      // been loaded before, bail.
727      break;
728    } else if (dep == last) {
729      // Remove it!
730      MD.removeInstruction(L);
731
732      L->replaceAllUsesWith(last);
733      toErase.push_back(L);
734      deletedLoad = true;
735      NumGVNLoad++;
736
737      break;
738    } else {
739      dep = MD.getDependency(L, dep);
740    }
741  }
742
743  if (!deletedLoad)
744    last = L;
745
746  return deletedLoad;
747}
748
749/// buildsets_availout - When calculating availability, handle an instruction
750/// by inserting it into the appropriate sets
751bool GVN::processInstruction(Instruction* I,
752                                ValueNumberedSet& currAvail,
753                                DenseMap<Value*, LoadInst*>& lastSeenLoad,
754                                SmallVector<Instruction*, 4>& toErase) {
755  if (LoadInst* L = dyn_cast<LoadInst>(I)) {
756    return processLoad(L, lastSeenLoad, toErase);
757  }
758
759  unsigned num = VN.lookup_or_add(I);
760
761  if (currAvail.test(num)) {
762    Value* repl = find_leader(currAvail, num);
763
764    I->replaceAllUsesWith(repl);
765    toErase.push_back(I);
766    return true;
767  } else if (!I->isTerminator()) {
768    currAvail.set(num);
769    currAvail.insert(I);
770  }
771
772  return false;
773}
774
775// GVN::runOnFunction - This is the main transformation entry point for a
776// function.
777//
778bool GVN::runOnFunction(Function &F) {
779  // Clean out global sets from any previous functions
780  VN.clear();
781  availableOut.clear();
782
783  bool changed_function = false;
784
785  DominatorTree &DT = getAnalysis<DominatorTree>();
786
787  SmallVector<Instruction*, 4> toErase;
788
789  // Top-down walk of the dominator tree
790  for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
791         E = df_end(DT.getRootNode()); DI != E; ++DI) {
792
793    // Get the set to update for this block
794    ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
795    DenseMap<Value*, LoadInst*> lastSeenLoad;
796
797    BasicBlock* BB = DI->getBlock();
798
799    // A block inherits AVAIL_OUT from its dominator
800    if (DI->getIDom() != 0)
801      currAvail = availableOut[DI->getIDom()->getBlock()];
802
803    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
804         BI != BE; ++BI) {
805      processInstruction(BI, currAvail, lastSeenLoad, toErase);
806    }
807  }
808
809  NumGVNInstr = toErase.size();
810
811  for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
812       E = toErase.end(); I != E; ++I)
813    (*I)->eraseFromParent();
814
815  return changed_function;
816}
817