GVN.cpp revision 8f46c78fcc96dd748fe3568ada91c18de7d9e68e 
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//===----------------------------------------------------------------------===//
14
15#define DEBUG_TYPE "gvn"
16#include "llvm/Transforms/Scalar.h"
17#include "llvm/BasicBlock.h"
18#include "llvm/Constants.h"
19#include "llvm/DerivedTypes.h"
20#include "llvm/Function.h"
21#include "llvm/IntrinsicInst.h"
22#include "llvm/Instructions.h"
23#include "llvm/ParameterAttributes.h"
24#include "llvm/Value.h"
25#include "llvm/ADT/DenseMap.h"
26#include "llvm/ADT/DepthFirstIterator.h"
27#include "llvm/ADT/SmallPtrSet.h"
28#include "llvm/ADT/SmallVector.h"
29#include "llvm/ADT/SparseBitVector.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/Support/GetElementPtrTypeIterator.h"
39#include "llvm/Target/TargetData.h"
40#include <list>
41using namespace llvm;
42
43STATISTIC(NumGVNInstr, "Number of instructions deleted");
44STATISTIC(NumGVNLoad, "Number of loads deleted");
45
46//===----------------------------------------------------------------------===//
47//                         ValueTable Class
48//===----------------------------------------------------------------------===//
49
50/// This class holds the mapping between values and value numbers.  It is used
51/// as an efficient mechanism to determine the expression-wise equivalence of
52/// two values.
53namespace {
54  struct VISIBILITY_HIDDEN Expression {
55    enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
56                            FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
57                            ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
58                            ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
59                            FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
60                            FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
61                            FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
62                            SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
63                            FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
64                            PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, EMPTY,
65                            TOMBSTONE };
66
67    ExpressionOpcode opcode;
68    const Type* type;
69    uint32_t firstVN;
70    uint32_t secondVN;
71    uint32_t thirdVN;
72    SmallVector<uint32_t, 4> varargs;
73    Value* function;
74
75    Expression() { }
76    Expression(ExpressionOpcode o) : opcode(o) { }
77
78    bool operator==(const Expression &other) const {
79      if (opcode != other.opcode)
80        return false;
81      else if (opcode == EMPTY || opcode == TOMBSTONE)
82        return true;
83      else if (type != other.type)
84        return false;
85      else if (function != other.function)
86        return false;
87      else if (firstVN != other.firstVN)
88        return false;
89      else if (secondVN != other.secondVN)
90        return false;
91      else if (thirdVN != other.thirdVN)
92        return false;
93      else {
94        if (varargs.size() != other.varargs.size())
95          return false;
96
97        for (size_t i = 0; i < varargs.size(); ++i)
98          if (varargs[i] != other.varargs[i])
99            return false;
100
101        return true;
102      }
103    }
104
105    bool operator!=(const Expression &other) const {
106      if (opcode != other.opcode)
107        return true;
108      else if (opcode == EMPTY || opcode == TOMBSTONE)
109        return false;
110      else if (type != other.type)
111        return true;
112      else if (function != other.function)
113        return true;
114      else if (firstVN != other.firstVN)
115        return true;
116      else if (secondVN != other.secondVN)
117        return true;
118      else if (thirdVN != other.thirdVN)
119        return true;
120      else {
121        if (varargs.size() != other.varargs.size())
122          return true;
123
124        for (size_t i = 0; i < varargs.size(); ++i)
125          if (varargs[i] != other.varargs[i])
126            return true;
127
128          return false;
129      }
130    }
131  };
132
133  class VISIBILITY_HIDDEN ValueTable {
134    private:
135      DenseMap<Value*, uint32_t> valueNumbering;
136      DenseMap<Expression, uint32_t> expressionNumbering;
137      AliasAnalysis* AA;
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    public:
154      ValueTable() : nextValueNumber(1) { }
155      uint32_t lookup_or_add(Value* V);
156      uint32_t lookup(Value* V) const;
157      void add(Value* V, uint32_t num);
158      void clear();
159      void erase(Value* v);
160      unsigned size();
161      void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
162  };
163}
164
165namespace llvm {
166template <> struct DenseMapInfo<Expression> {
167  static inline Expression getEmptyKey() {
168    return Expression(Expression::EMPTY);
169  }
170
171  static inline Expression getTombstoneKey() {
172    return Expression(Expression::TOMBSTONE);
173  }
174
175  static unsigned getHashValue(const Expression e) {
176    unsigned hash = e.opcode;
177
178    hash = e.firstVN + hash * 37;
179    hash = e.secondVN + hash * 37;
180    hash = e.thirdVN + hash * 37;
181
182    hash = ((unsigned)((uintptr_t)e.type >> 4) ^
183            (unsigned)((uintptr_t)e.type >> 9)) +
184           hash * 37;
185
186    for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
187         E = e.varargs.end(); I != E; ++I)
188      hash = *I + hash * 37;
189
190    hash = ((unsigned)((uintptr_t)e.function >> 4) ^
191            (unsigned)((uintptr_t)e.function >> 9)) +
192           hash * 37;
193
194    return hash;
195  }
196  static bool isEqual(const Expression &LHS, const Expression &RHS) {
197    return LHS == RHS;
198  }
199  static bool isPod() { return true; }
200};
201}
202
203//===----------------------------------------------------------------------===//
204//                     ValueTable Internal Functions
205//===----------------------------------------------------------------------===//
206Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
207  switch(BO->getOpcode()) {
208  default: // THIS SHOULD NEVER HAPPEN
209    assert(0 && "Binary operator with unknown opcode?");
210  case Instruction::Add:  return Expression::ADD;
211  case Instruction::Sub:  return Expression::SUB;
212  case Instruction::Mul:  return Expression::MUL;
213  case Instruction::UDiv: return Expression::UDIV;
214  case Instruction::SDiv: return Expression::SDIV;
215  case Instruction::FDiv: return Expression::FDIV;
216  case Instruction::URem: return Expression::UREM;
217  case Instruction::SRem: return Expression::SREM;
218  case Instruction::FRem: return Expression::FREM;
219  case Instruction::Shl:  return Expression::SHL;
220  case Instruction::LShr: return Expression::LSHR;
221  case Instruction::AShr: return Expression::ASHR;
222  case Instruction::And:  return Expression::AND;
223  case Instruction::Or:   return Expression::OR;
224  case Instruction::Xor:  return Expression::XOR;
225  }
226}
227
228Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
229  if (isa<ICmpInst>(C)) {
230    switch (C->getPredicate()) {
231    default:  // THIS SHOULD NEVER HAPPEN
232      assert(0 && "Comparison with unknown predicate?");
233    case ICmpInst::ICMP_EQ:  return Expression::ICMPEQ;
234    case ICmpInst::ICMP_NE:  return Expression::ICMPNE;
235    case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
236    case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
237    case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
238    case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
239    case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
240    case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
241    case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
242    case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
243    }
244  }
245  assert(isa<FCmpInst>(C) && "Unknown compare");
246  switch (C->getPredicate()) {
247  default: // THIS SHOULD NEVER HAPPEN
248    assert(0 && "Comparison with unknown predicate?");
249  case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
250  case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
251  case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
252  case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
253  case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
254  case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
255  case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
256  case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
257  case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
258  case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
259  case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
260  case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
261  case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
262  case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
263  }
264}
265
266Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
267  switch(C->getOpcode()) {
268  default: // THIS SHOULD NEVER HAPPEN
269    assert(0 && "Cast operator with unknown opcode?");
270  case Instruction::Trunc:    return Expression::TRUNC;
271  case Instruction::ZExt:     return Expression::ZEXT;
272  case Instruction::SExt:     return Expression::SEXT;
273  case Instruction::FPToUI:   return Expression::FPTOUI;
274  case Instruction::FPToSI:   return Expression::FPTOSI;
275  case Instruction::UIToFP:   return Expression::UITOFP;
276  case Instruction::SIToFP:   return Expression::SITOFP;
277  case Instruction::FPTrunc:  return Expression::FPTRUNC;
278  case Instruction::FPExt:    return Expression::FPEXT;
279  case Instruction::PtrToInt: return Expression::PTRTOINT;
280  case Instruction::IntToPtr: return Expression::INTTOPTR;
281  case Instruction::BitCast:  return Expression::BITCAST;
282  }
283}
284
285Expression ValueTable::create_expression(CallInst* C) {
286  Expression e;
287
288  e.type = C->getType();
289  e.firstVN = 0;
290  e.secondVN = 0;
291  e.thirdVN = 0;
292  e.function = C->getCalledFunction();
293  e.opcode = Expression::CALL;
294
295  for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
296       I != E; ++I)
297    e.varargs.push_back(lookup_or_add(*I));
298
299  return e;
300}
301
302Expression ValueTable::create_expression(BinaryOperator* BO) {
303  Expression e;
304
305  e.firstVN = lookup_or_add(BO->getOperand(0));
306  e.secondVN = lookup_or_add(BO->getOperand(1));
307  e.thirdVN = 0;
308  e.function = 0;
309  e.type = BO->getType();
310  e.opcode = getOpcode(BO);
311
312  return e;
313}
314
315Expression ValueTable::create_expression(CmpInst* C) {
316  Expression e;
317
318  e.firstVN = lookup_or_add(C->getOperand(0));
319  e.secondVN = lookup_or_add(C->getOperand(1));
320  e.thirdVN = 0;
321  e.function = 0;
322  e.type = C->getType();
323  e.opcode = getOpcode(C);
324
325  return e;
326}
327
328Expression ValueTable::create_expression(CastInst* C) {
329  Expression e;
330
331  e.firstVN = lookup_or_add(C->getOperand(0));
332  e.secondVN = 0;
333  e.thirdVN = 0;
334  e.function = 0;
335  e.type = C->getType();
336  e.opcode = getOpcode(C);
337
338  return e;
339}
340
341Expression ValueTable::create_expression(ShuffleVectorInst* S) {
342  Expression e;
343
344  e.firstVN = lookup_or_add(S->getOperand(0));
345  e.secondVN = lookup_or_add(S->getOperand(1));
346  e.thirdVN = lookup_or_add(S->getOperand(2));
347  e.function = 0;
348  e.type = S->getType();
349  e.opcode = Expression::SHUFFLE;
350
351  return e;
352}
353
354Expression ValueTable::create_expression(ExtractElementInst* E) {
355  Expression e;
356
357  e.firstVN = lookup_or_add(E->getOperand(0));
358  e.secondVN = lookup_or_add(E->getOperand(1));
359  e.thirdVN = 0;
360  e.function = 0;
361  e.type = E->getType();
362  e.opcode = Expression::EXTRACT;
363
364  return e;
365}
366
367Expression ValueTable::create_expression(InsertElementInst* I) {
368  Expression e;
369
370  e.firstVN = lookup_or_add(I->getOperand(0));
371  e.secondVN = lookup_or_add(I->getOperand(1));
372  e.thirdVN = lookup_or_add(I->getOperand(2));
373  e.function = 0;
374  e.type = I->getType();
375  e.opcode = Expression::INSERT;
376
377  return e;
378}
379
380Expression ValueTable::create_expression(SelectInst* I) {
381  Expression e;
382
383  e.firstVN = lookup_or_add(I->getCondition());
384  e.secondVN = lookup_or_add(I->getTrueValue());
385  e.thirdVN = lookup_or_add(I->getFalseValue());
386  e.function = 0;
387  e.type = I->getType();
388  e.opcode = Expression::SELECT;
389
390  return e;
391}
392
393Expression ValueTable::create_expression(GetElementPtrInst* G) {
394  Expression e;
395
396  e.firstVN = lookup_or_add(G->getPointerOperand());
397  e.secondVN = 0;
398  e.thirdVN = 0;
399  e.function = 0;
400  e.type = G->getType();
401  e.opcode = Expression::GEP;
402
403  for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
404       I != E; ++I)
405    e.varargs.push_back(lookup_or_add(*I));
406
407  return e;
408}
409
410//===----------------------------------------------------------------------===//
411//                     ValueTable External Functions
412//===----------------------------------------------------------------------===//
413
414/// lookup_or_add - Returns the value number for the specified value, assigning
415/// it a new number if it did not have one before.
416uint32_t ValueTable::lookup_or_add(Value* V) {
417  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
418  if (VI != valueNumbering.end())
419    return VI->second;
420
421  if (CallInst* C = dyn_cast<CallInst>(V)) {
422    if (AA->doesNotAccessMemory(C)) {
423      Expression e = create_expression(C);
424
425      DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
426      if (EI != expressionNumbering.end()) {
427        valueNumbering.insert(std::make_pair(V, EI->second));
428        return EI->second;
429      } else {
430        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
431        valueNumbering.insert(std::make_pair(V, nextValueNumber));
432
433        return nextValueNumber++;
434      }
435    } else {
436      valueNumbering.insert(std::make_pair(V, nextValueNumber));
437      return nextValueNumber++;
438    }
439  } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
440    Expression e = create_expression(BO);
441
442    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
443    if (EI != expressionNumbering.end()) {
444      valueNumbering.insert(std::make_pair(V, EI->second));
445      return EI->second;
446    } else {
447      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
448      valueNumbering.insert(std::make_pair(V, nextValueNumber));
449
450      return nextValueNumber++;
451    }
452  } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
453    Expression e = create_expression(C);
454
455    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
456    if (EI != expressionNumbering.end()) {
457      valueNumbering.insert(std::make_pair(V, EI->second));
458      return EI->second;
459    } else {
460      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
461      valueNumbering.insert(std::make_pair(V, nextValueNumber));
462
463      return nextValueNumber++;
464    }
465  } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
466    Expression e = create_expression(U);
467
468    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
469    if (EI != expressionNumbering.end()) {
470      valueNumbering.insert(std::make_pair(V, EI->second));
471      return EI->second;
472    } else {
473      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
474      valueNumbering.insert(std::make_pair(V, nextValueNumber));
475
476      return nextValueNumber++;
477    }
478  } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
479    Expression e = create_expression(U);
480
481    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
482    if (EI != expressionNumbering.end()) {
483      valueNumbering.insert(std::make_pair(V, EI->second));
484      return EI->second;
485    } else {
486      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
487      valueNumbering.insert(std::make_pair(V, nextValueNumber));
488
489      return nextValueNumber++;
490    }
491  } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
492    Expression e = create_expression(U);
493
494    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
495    if (EI != expressionNumbering.end()) {
496      valueNumbering.insert(std::make_pair(V, EI->second));
497      return EI->second;
498    } else {
499      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
500      valueNumbering.insert(std::make_pair(V, nextValueNumber));
501
502      return nextValueNumber++;
503    }
504  } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
505    Expression e = create_expression(U);
506
507    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
508    if (EI != expressionNumbering.end()) {
509      valueNumbering.insert(std::make_pair(V, EI->second));
510      return EI->second;
511    } else {
512      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
513      valueNumbering.insert(std::make_pair(V, nextValueNumber));
514
515      return nextValueNumber++;
516    }
517  } else if (CastInst* U = dyn_cast<CastInst>(V)) {
518    Expression e = create_expression(U);
519
520    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
521    if (EI != expressionNumbering.end()) {
522      valueNumbering.insert(std::make_pair(V, EI->second));
523      return EI->second;
524    } else {
525      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
526      valueNumbering.insert(std::make_pair(V, nextValueNumber));
527
528      return nextValueNumber++;
529    }
530  } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
531    Expression e = create_expression(U);
532
533    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
534    if (EI != expressionNumbering.end()) {
535      valueNumbering.insert(std::make_pair(V, EI->second));
536      return EI->second;
537    } else {
538      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
539      valueNumbering.insert(std::make_pair(V, nextValueNumber));
540
541      return nextValueNumber++;
542    }
543  } else {
544    valueNumbering.insert(std::make_pair(V, nextValueNumber));
545    return nextValueNumber++;
546  }
547}
548
549/// lookup - Returns the value number of the specified value. Fails if
550/// the value has not yet been numbered.
551uint32_t ValueTable::lookup(Value* V) const {
552  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
553  assert(VI != valueNumbering.end() && "Value not numbered?");
554  return VI->second;
555}
556
557/// clear - Remove all entries from the ValueTable
558void ValueTable::clear() {
559  valueNumbering.clear();
560  expressionNumbering.clear();
561  nextValueNumber = 1;
562}
563
564/// erase - Remove a value from the value numbering
565void ValueTable::erase(Value* V) {
566  valueNumbering.erase(V);
567}
568
569//===----------------------------------------------------------------------===//
570//                       ValueNumberedSet Class
571//===----------------------------------------------------------------------===//
572namespace {
573class VISIBILITY_HIDDEN ValueNumberedSet {
574  private:
575    SmallPtrSet<Value*, 8> contents;
576    SparseBitVector<64> numbers;
577  public:
578    ValueNumberedSet() { }
579    ValueNumberedSet(const ValueNumberedSet& other) {
580      numbers = other.numbers;
581      contents = other.contents;
582    }
583
584    typedef SmallPtrSet<Value*, 8>::iterator iterator;
585
586    iterator begin() { return contents.begin(); }
587    iterator end() { return contents.end(); }
588
589    bool insert(Value* v) { return contents.insert(v); }
590    void insert(iterator I, iterator E) { contents.insert(I, E); }
591    void erase(Value* v) { contents.erase(v); }
592    unsigned count(Value* v) { return contents.count(v); }
593    size_t size() { return contents.size(); }
594
595    void set(unsigned i)  {
596      numbers.set(i);
597    }
598
599    void operator=(const ValueNumberedSet& other) {
600      contents = other.contents;
601      numbers = other.numbers;
602    }
603
604    void reset(unsigned i)  {
605      numbers.reset(i);
606    }
607
608    bool test(unsigned i)  {
609      return numbers.test(i);
610    }
611};
612}
613
614//===----------------------------------------------------------------------===//
615//                         GVN Pass
616//===----------------------------------------------------------------------===//
617
618namespace {
619
620  class VISIBILITY_HIDDEN GVN : public FunctionPass {
621    bool runOnFunction(Function &F);
622  public:
623    static char ID; // Pass identification, replacement for typeid
624    GVN() : FunctionPass((intptr_t)&ID) { }
625
626  private:
627    ValueTable VN;
628
629    DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
630
631    typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
632    PhiMapType phiMap;
633
634
635    // This transformation requires dominator postdominator info
636    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
637      AU.setPreservesCFG();
638      AU.addRequired<DominatorTree>();
639      AU.addRequired<MemoryDependenceAnalysis>();
640      AU.addRequired<AliasAnalysis>();
641      AU.addRequired<TargetData>();
642      AU.addPreserved<AliasAnalysis>();
643      AU.addPreserved<MemoryDependenceAnalysis>();
644      AU.addPreserved<TargetData>();
645    }
646
647    // Helper fuctions
648    // FIXME: eliminate or document these better
649    Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
650    void val_insert(ValueNumberedSet& s, Value* v);
651    bool processLoad(LoadInst* L,
652                     DenseMap<Value*, LoadInst*> &lastLoad,
653                     SmallVectorImpl<Instruction*> &toErase);
654    bool processInstruction(Instruction* I,
655                            ValueNumberedSet& currAvail,
656                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
657                            SmallVectorImpl<Instruction*> &toErase);
658    bool processNonLocalLoad(LoadInst* L,
659                             SmallVectorImpl<Instruction*> &toErase);
660    Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
661                            DenseMap<BasicBlock*, Value*> &Phis,
662                            bool top_level = false);
663    void dump(DenseMap<BasicBlock*, Value*>& d);
664    bool iterateOnFunction(Function &F);
665    Value* CollapsePhi(PHINode* p);
666    bool isSafeReplacement(PHINode* p, Instruction* inst);
667  };
668
669  char GVN::ID = 0;
670}
671
672// createGVNPass - The public interface to this file...
673FunctionPass *llvm::createGVNPass() { return new GVN(); }
674
675static RegisterPass<GVN> X("gvn",
676                           "Global Value Numbering");
677
678/// find_leader - Given a set and a value number, return the first
679/// element of the set with that value number, or 0 if no such element
680/// is present
681Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
682  if (!vals.test(v))
683    return 0;
684
685  for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
686       I != E; ++I)
687    if (v == VN.lookup(*I))
688      return *I;
689
690  assert(0 && "No leader found, but present bit is set?");
691  return 0;
692}
693
694/// val_insert - Insert a value into a set only if there is not a value
695/// with the same value number already in the set
696void GVN::val_insert(ValueNumberedSet& s, Value* v) {
697  uint32_t num = VN.lookup(v);
698  if (!s.test(num))
699    s.insert(v);
700}
701
702void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
703  printf("{\n");
704  for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
705       E = d.end(); I != E; ++I) {
706    if (I->second == MemoryDependenceAnalysis::None)
707      printf("None\n");
708    else
709      I->second->dump();
710  }
711  printf("}\n");
712}
713
714Value* GVN::CollapsePhi(PHINode* p) {
715  DominatorTree &DT = getAnalysis<DominatorTree>();
716  Value* constVal = p->hasConstantValue();
717
718  if (!constVal) return 0;
719
720  Instruction* inst = dyn_cast<Instruction>(constVal);
721  if (!inst)
722    return constVal;
723
724  if (DT.dominates(inst, p))
725    if (isSafeReplacement(p, inst))
726      return inst;
727  return 0;
728}
729
730bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
731  if (!isa<PHINode>(inst))
732    return true;
733
734  for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
735       UI != E; ++UI)
736    if (PHINode* use_phi = dyn_cast<PHINode>(UI))
737      if (use_phi->getParent() == inst->getParent())
738        return false;
739
740  return true;
741}
742
743/// GetValueForBlock - Get the value to use within the specified basic block.
744/// available values are in Phis.
745Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
746                             DenseMap<BasicBlock*, Value*> &Phis,
747                             bool top_level) {
748
749  // If we have already computed this value, return the previously computed val.
750  DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
751  if (V != Phis.end() && !top_level) return V->second;
752
753  BasicBlock* singlePred = BB->getSinglePredecessor();
754  if (singlePred) {
755    Value *ret = GetValueForBlock(singlePred, orig, Phis);
756    Phis[BB] = ret;
757    return ret;
758  }
759
760  // Otherwise, the idom is the loop, so we need to insert a PHI node.  Do so
761  // now, then get values to fill in the incoming values for the PHI.
762  PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
763                                BB->begin());
764  PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
765
766  if (Phis.count(BB) == 0)
767    Phis.insert(std::make_pair(BB, PN));
768
769  // Fill in the incoming values for the block.
770  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
771    Value* val = GetValueForBlock(*PI, orig, Phis);
772    PN->addIncoming(val, *PI);
773  }
774
775  AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
776  AA.copyValue(orig, PN);
777
778  // Attempt to collapse PHI nodes that are trivially redundant
779  Value* v = CollapsePhi(PN);
780  if (!v) {
781    // Cache our phi construction results
782    phiMap[orig->getPointerOperand()].insert(PN);
783    return PN;
784  }
785
786  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
787
788  MD.removeInstruction(PN);
789  PN->replaceAllUsesWith(v);
790
791  for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
792       E = Phis.end(); I != E; ++I)
793    if (I->second == PN)
794      I->second = v;
795
796  PN->eraseFromParent();
797
798  Phis[BB] = v;
799  return v;
800}
801
802/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
803/// non-local by performing PHI construction.
804bool GVN::processNonLocalLoad(LoadInst* L,
805                              SmallVectorImpl<Instruction*> &toErase) {
806  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
807
808  // Find the non-local dependencies of the load
809  DenseMap<BasicBlock*, Value*> deps;
810  MD.getNonLocalDependency(L, deps);
811
812  DenseMap<BasicBlock*, Value*> repl;
813
814  // Filter out useless results (non-locals, etc)
815  for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
816       I != E; ++I) {
817    if (I->second == MemoryDependenceAnalysis::None)
818      return false;
819
820    if (I->second == MemoryDependenceAnalysis::NonLocal)
821      continue;
822
823    if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
824      if (S->getPointerOperand() != L->getPointerOperand())
825        return false;
826      repl[I->first] = S->getOperand(0);
827    } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
828      if (LD->getPointerOperand() != L->getPointerOperand())
829        return false;
830      repl[I->first] = LD;
831    } else {
832      return false;
833    }
834  }
835
836  // Use cached PHI construction information from previous runs
837  SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
838  for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
839       I != E; ++I) {
840    if ((*I)->getParent() == L->getParent()) {
841      MD.removeInstruction(L);
842      L->replaceAllUsesWith(*I);
843      toErase.push_back(L);
844      NumGVNLoad++;
845      return true;
846    }
847
848    repl.insert(std::make_pair((*I)->getParent(), *I));
849  }
850
851  // Perform PHI construction
852  SmallPtrSet<BasicBlock*, 4> visited;
853  Value* v = GetValueForBlock(L->getParent(), L, repl, true);
854
855  MD.removeInstruction(L);
856  L->replaceAllUsesWith(v);
857  toErase.push_back(L);
858  NumGVNLoad++;
859
860  return true;
861}
862
863/// processLoad - Attempt to eliminate a load, first by eliminating it
864/// locally, and then attempting non-local elimination if that fails.
865bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad,
866                      SmallVectorImpl<Instruction*> &toErase) {
867  if (L->isVolatile()) {
868    lastLoad[L->getPointerOperand()] = L;
869    return false;
870  }
871
872  Value* pointer = L->getPointerOperand();
873  LoadInst*& last = lastLoad[pointer];
874
875  // ... to a pointer that has been loaded from before...
876  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
877  bool removedNonLocal = false;
878  Instruction* dep = MD.getDependency(L);
879  if (dep == MemoryDependenceAnalysis::NonLocal &&
880      L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
881    removedNonLocal = processNonLocalLoad(L, toErase);
882
883    if (!removedNonLocal)
884      last = L;
885
886    return removedNonLocal;
887  }
888
889
890  bool deletedLoad = false;
891
892  // Walk up the dependency chain until we either find
893  // a dependency we can use, or we can't walk any further
894  while (dep != MemoryDependenceAnalysis::None &&
895         dep != MemoryDependenceAnalysis::NonLocal &&
896         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
897    // ... that depends on a store ...
898    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
899      if (S->getPointerOperand() == pointer) {
900        // Remove it!
901        MD.removeInstruction(L);
902
903        L->replaceAllUsesWith(S->getOperand(0));
904        toErase.push_back(L);
905        deletedLoad = true;
906        NumGVNLoad++;
907      }
908
909      // Whether we removed it or not, we can't
910      // go any further
911      break;
912    } else if (!last) {
913      // If we don't depend on a store, and we haven't
914      // been loaded before, bail.
915      break;
916    } else if (dep == last) {
917      // Remove it!
918      MD.removeInstruction(L);
919
920      L->replaceAllUsesWith(last);
921      toErase.push_back(L);
922      deletedLoad = true;
923      NumGVNLoad++;
924
925      break;
926    } else {
927      dep = MD.getDependency(L, dep);
928    }
929  }
930
931  if (dep != MemoryDependenceAnalysis::None &&
932      dep != MemoryDependenceAnalysis::NonLocal &&
933      isa<AllocationInst>(dep)) {
934    // Check that this load is actually from the
935    // allocation we found
936    Value* v = L->getOperand(0);
937    while (true) {
938      if (BitCastInst *BC = dyn_cast<BitCastInst>(v))
939        v = BC->getOperand(0);
940      else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v))
941        v = GEP->getOperand(0);
942      else
943        break;
944    }
945    if (v == dep) {
946      // If this load depends directly on an allocation, there isn't
947      // anything stored there; therefore, we can optimize this load
948      // to undef.
949      MD.removeInstruction(L);
950
951      L->replaceAllUsesWith(UndefValue::get(L->getType()));
952      toErase.push_back(L);
953      deletedLoad = true;
954      NumGVNLoad++;
955    }
956  }
957
958  if (!deletedLoad)
959    last = L;
960
961  return deletedLoad;
962}
963
964/// processInstruction - When calculating availability, handle an instruction
965/// by inserting it into the appropriate sets
966bool GVN::processInstruction(Instruction *I, ValueNumberedSet &currAvail,
967                             DenseMap<Value*, LoadInst*> &lastSeenLoad,
968                             SmallVectorImpl<Instruction*> &toErase) {
969  if (LoadInst* L = dyn_cast<LoadInst>(I))
970    return processLoad(L, lastSeenLoad, toErase);
971
972  // Allocations are always uniquely numbered, so we can save time and memory
973  // by fast failing them.
974  if (isa<AllocationInst>(I))
975    return false;
976
977  unsigned num = VN.lookup_or_add(I);
978
979  // Collapse PHI nodes
980  if (PHINode* p = dyn_cast<PHINode>(I)) {
981    Value* constVal = CollapsePhi(p);
982
983    if (constVal) {
984      for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
985           PI != PE; ++PI)
986        if (PI->second.count(p))
987          PI->second.erase(p);
988
989      p->replaceAllUsesWith(constVal);
990      toErase.push_back(p);
991    }
992  // Perform value-number based elimination
993  } else if (currAvail.test(num)) {
994    Value* repl = find_leader(currAvail, num);
995
996    if (CallInst* CI = dyn_cast<CallInst>(I)) {
997      AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
998      if (!AA.doesNotAccessMemory(CI)) {
999        MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1000        if (cast<Instruction>(repl)->getParent() != CI->getParent() ||
1001            MD.getDependency(CI) != MD.getDependency(cast<CallInst>(repl))) {
1002          // There must be an intervening may-alias store, so nothing from
1003          // this point on will be able to be replaced with the preceding call
1004          currAvail.erase(repl);
1005          currAvail.insert(I);
1006
1007          return false;
1008        }
1009      }
1010    }
1011
1012    // Remove it!
1013    MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1014    MD.removeInstruction(I);
1015
1016    VN.erase(I);
1017    I->replaceAllUsesWith(repl);
1018    toErase.push_back(I);
1019    return true;
1020  } else if (!I->isTerminator()) {
1021    currAvail.set(num);
1022    currAvail.insert(I);
1023  }
1024
1025  return false;
1026}
1027
1028// GVN::runOnFunction - This is the main transformation entry point for a
1029// function.
1030//
1031bool GVN::runOnFunction(Function& F) {
1032  VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1033
1034  bool changed = false;
1035  bool shouldContinue = true;
1036
1037  while (shouldContinue) {
1038    shouldContinue = iterateOnFunction(F);
1039    changed |= shouldContinue;
1040  }
1041
1042  return changed;
1043}
1044
1045
1046// GVN::iterateOnFunction - Executes one iteration of GVN
1047bool GVN::iterateOnFunction(Function &F) {
1048  // Clean out global sets from any previous functions
1049  VN.clear();
1050  availableOut.clear();
1051  phiMap.clear();
1052
1053  bool changed_function = false;
1054
1055  DominatorTree &DT = getAnalysis<DominatorTree>();
1056
1057  SmallVector<Instruction*, 8> toErase;
1058  DenseMap<Value*, LoadInst*> lastSeenLoad;
1059  DenseMap<DomTreeNode*, size_t> numChildrenVisited;
1060
1061  // Top-down walk of the dominator tree
1062  for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
1063         E = df_end(DT.getRootNode()); DI != E; ++DI) {
1064
1065    // Get the set to update for this block
1066    ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
1067    lastSeenLoad.clear();
1068
1069    BasicBlock* BB = DI->getBlock();
1070
1071    // A block inherits AVAIL_OUT from its dominator
1072    if (DI->getIDom() != 0) {
1073      currAvail = availableOut[DI->getIDom()->getBlock()];
1074
1075      numChildrenVisited[DI->getIDom()]++;
1076
1077      if (numChildrenVisited[DI->getIDom()] == DI->getIDom()->getNumChildren()) {
1078        availableOut.erase(DI->getIDom()->getBlock());
1079        numChildrenVisited.erase(DI->getIDom());
1080      }
1081    }
1082
1083    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1084         BI != BE;) {
1085      changed_function |= processInstruction(BI, currAvail,
1086                                             lastSeenLoad, toErase);
1087      if (toErase.empty()) {
1088        ++BI;
1089        continue;
1090      }
1091
1092      // If we need some instructions deleted, do it now.
1093      NumGVNInstr += toErase.size();
1094
1095      // Avoid iterator invalidation.
1096      bool AtStart = BI == BB->begin();
1097      if (!AtStart)
1098        --BI;
1099
1100      for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1101           E = toErase.end(); I != E; ++I)
1102        (*I)->eraseFromParent();
1103
1104      if (AtStart)
1105        BI = BB->begin();
1106      else
1107        ++BI;
1108
1109      toErase.clear();
1110    }
1111  }
1112
1113  return changed_function;
1114}
1115