GVN.cpp revision 45537917eec15e5c3ef75c0ee2bf8963b02f3a54 
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
17#include "llvm/Transforms/Scalar.h"
18#include "llvm/BasicBlock.h"
19#include "llvm/Constants.h"
20#include "llvm/DerivedTypes.h"
21#include "llvm/Function.h"
22#include "llvm/Instructions.h"
23#include "llvm/Value.h"
24#include "llvm/Analysis/Dominators.h"
25#include "llvm/ADT/BitVector.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/MemoryDependenceAnalysis.h"
32#include "llvm/Support/CFG.h"
33#include "llvm/Support/Compiler.h"
34using namespace llvm;
35
36//===----------------------------------------------------------------------===//
37//                         ValueTable Class
38//===----------------------------------------------------------------------===//
39
40/// This class holds the mapping between values and value numbers.  It is used
41/// as an efficient mechanism to determine the expression-wise equivalence of
42/// two values.
43namespace {
44  struct VISIBILITY_HIDDEN Expression {
45    enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
46                            FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
47                            ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
48                            ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
49                            FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
50                            FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
51                            FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
52                            SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
53                            FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
54                            PTRTOINT, INTTOPTR, BITCAST, GEP, EMPTY,
55                            TOMBSTONE };
56
57    ExpressionOpcode opcode;
58    const Type* type;
59    uint32_t firstVN;
60    uint32_t secondVN;
61    uint32_t thirdVN;
62    SmallVector<uint32_t, 4> varargs;
63
64    Expression() { }
65    Expression(ExpressionOpcode o) : opcode(o) { }
66
67    bool operator==(const Expression &other) const {
68      if (opcode != other.opcode)
69        return false;
70      else if (opcode == EMPTY || opcode == TOMBSTONE)
71        return true;
72      else if (type != other.type)
73        return false;
74      else if (firstVN != other.firstVN)
75        return false;
76      else if (secondVN != other.secondVN)
77        return false;
78      else if (thirdVN != other.thirdVN)
79        return false;
80      else {
81        if (varargs.size() != other.varargs.size())
82          return false;
83
84        for (size_t i = 0; i < varargs.size(); ++i)
85          if (varargs[i] != other.varargs[i])
86            return false;
87
88        return true;
89      }
90    }
91
92    bool operator!=(const Expression &other) const {
93      if (opcode != other.opcode)
94        return true;
95      else if (opcode == EMPTY || opcode == TOMBSTONE)
96        return false;
97      else if (type != other.type)
98        return true;
99      else if (firstVN != other.firstVN)
100        return true;
101      else if (secondVN != other.secondVN)
102        return true;
103      else if (thirdVN != other.thirdVN)
104        return true;
105      else {
106        if (varargs.size() != other.varargs.size())
107          return true;
108
109        for (size_t i = 0; i < varargs.size(); ++i)
110          if (varargs[i] != other.varargs[i])
111            return true;
112
113          return false;
114      }
115    }
116  };
117
118  class VISIBILITY_HIDDEN ValueTable {
119    private:
120      DenseMap<Value*, uint32_t> valueNumbering;
121      DenseMap<Expression, uint32_t> expressionNumbering;
122
123      uint32_t nextValueNumber;
124
125      Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
126      Expression::ExpressionOpcode getOpcode(CmpInst* C);
127      Expression::ExpressionOpcode getOpcode(CastInst* C);
128      Expression create_expression(BinaryOperator* BO);
129      Expression create_expression(CmpInst* C);
130      Expression create_expression(ShuffleVectorInst* V);
131      Expression create_expression(ExtractElementInst* C);
132      Expression create_expression(InsertElementInst* V);
133      Expression create_expression(SelectInst* V);
134      Expression create_expression(CastInst* C);
135      Expression create_expression(GetElementPtrInst* G);
136    public:
137      ValueTable() { nextValueNumber = 1; }
138      uint32_t lookup_or_add(Value* V);
139      uint32_t lookup(Value* V) const;
140      void add(Value* V, uint32_t num);
141      void clear();
142      void erase(Value* v);
143      unsigned size();
144  };
145}
146
147namespace llvm {
148template <> struct DenseMapKeyInfo<Expression> {
149  static inline Expression getEmptyKey() { return Expression(Expression::EMPTY); }
150  static inline Expression getTombstoneKey() { return Expression(Expression::TOMBSTONE); }
151
152  static unsigned getHashValue(const Expression e) {
153    unsigned hash = e.opcode;
154
155    hash = e.firstVN + hash * 37;
156    hash = e.secondVN + hash * 37;
157    hash = e.thirdVN + hash * 37;
158
159    hash = (unsigned)((uintptr_t)e.type >> 4) ^
160            (unsigned)((uintptr_t)e.type >> 9) +
161            hash * 37;
162
163    for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), E = e.varargs.end();
164         I != E; ++I)
165      hash = *I + hash * 37;
166
167    return hash;
168  }
169  static bool isPod() { return true; }
170};
171}
172
173//===----------------------------------------------------------------------===//
174//                     ValueTable Internal Functions
175//===----------------------------------------------------------------------===//
176Expression::ExpressionOpcode
177                             ValueTable::getOpcode(BinaryOperator* BO) {
178  switch(BO->getOpcode()) {
179    case Instruction::Add:
180      return Expression::ADD;
181    case Instruction::Sub:
182      return Expression::SUB;
183    case Instruction::Mul:
184      return Expression::MUL;
185    case Instruction::UDiv:
186      return Expression::UDIV;
187    case Instruction::SDiv:
188      return Expression::SDIV;
189    case Instruction::FDiv:
190      return Expression::FDIV;
191    case Instruction::URem:
192      return Expression::UREM;
193    case Instruction::SRem:
194      return Expression::SREM;
195    case Instruction::FRem:
196      return Expression::FREM;
197    case Instruction::Shl:
198      return Expression::SHL;
199    case Instruction::LShr:
200      return Expression::LSHR;
201    case Instruction::AShr:
202      return Expression::ASHR;
203    case Instruction::And:
204      return Expression::AND;
205    case Instruction::Or:
206      return Expression::OR;
207    case Instruction::Xor:
208      return Expression::XOR;
209
210    // THIS SHOULD NEVER HAPPEN
211    default:
212      assert(0 && "Binary operator with unknown opcode?");
213      return Expression::ADD;
214  }
215}
216
217Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
218  if (C->getOpcode() == Instruction::ICmp) {
219    switch (C->getPredicate()) {
220      case ICmpInst::ICMP_EQ:
221        return Expression::ICMPEQ;
222      case ICmpInst::ICMP_NE:
223        return Expression::ICMPNE;
224      case ICmpInst::ICMP_UGT:
225        return Expression::ICMPUGT;
226      case ICmpInst::ICMP_UGE:
227        return Expression::ICMPUGE;
228      case ICmpInst::ICMP_ULT:
229        return Expression::ICMPULT;
230      case ICmpInst::ICMP_ULE:
231        return Expression::ICMPULE;
232      case ICmpInst::ICMP_SGT:
233        return Expression::ICMPSGT;
234      case ICmpInst::ICMP_SGE:
235        return Expression::ICMPSGE;
236      case ICmpInst::ICMP_SLT:
237        return Expression::ICMPSLT;
238      case ICmpInst::ICMP_SLE:
239        return Expression::ICMPSLE;
240
241      // THIS SHOULD NEVER HAPPEN
242      default:
243        assert(0 && "Comparison with unknown predicate?");
244        return Expression::ICMPEQ;
245    }
246  } else {
247    switch (C->getPredicate()) {
248      case FCmpInst::FCMP_OEQ:
249        return Expression::FCMPOEQ;
250      case FCmpInst::FCMP_OGT:
251        return Expression::FCMPOGT;
252      case FCmpInst::FCMP_OGE:
253        return Expression::FCMPOGE;
254      case FCmpInst::FCMP_OLT:
255        return Expression::FCMPOLT;
256      case FCmpInst::FCMP_OLE:
257        return Expression::FCMPOLE;
258      case FCmpInst::FCMP_ONE:
259        return Expression::FCMPONE;
260      case FCmpInst::FCMP_ORD:
261        return Expression::FCMPORD;
262      case FCmpInst::FCMP_UNO:
263        return Expression::FCMPUNO;
264      case FCmpInst::FCMP_UEQ:
265        return Expression::FCMPUEQ;
266      case FCmpInst::FCMP_UGT:
267        return Expression::FCMPUGT;
268      case FCmpInst::FCMP_UGE:
269        return Expression::FCMPUGE;
270      case FCmpInst::FCMP_ULT:
271        return Expression::FCMPULT;
272      case FCmpInst::FCMP_ULE:
273        return Expression::FCMPULE;
274      case FCmpInst::FCMP_UNE:
275        return Expression::FCMPUNE;
276
277      // THIS SHOULD NEVER HAPPEN
278      default:
279        assert(0 && "Comparison with unknown predicate?");
280        return Expression::FCMPOEQ;
281    }
282  }
283}
284
285Expression::ExpressionOpcode
286                             ValueTable::getOpcode(CastInst* C) {
287  switch(C->getOpcode()) {
288    case Instruction::Trunc:
289      return Expression::TRUNC;
290    case Instruction::ZExt:
291      return Expression::ZEXT;
292    case Instruction::SExt:
293      return Expression::SEXT;
294    case Instruction::FPToUI:
295      return Expression::FPTOUI;
296    case Instruction::FPToSI:
297      return Expression::FPTOSI;
298    case Instruction::UIToFP:
299      return Expression::UITOFP;
300    case Instruction::SIToFP:
301      return Expression::SITOFP;
302    case Instruction::FPTrunc:
303      return Expression::FPTRUNC;
304    case Instruction::FPExt:
305      return Expression::FPEXT;
306    case Instruction::PtrToInt:
307      return Expression::PTRTOINT;
308    case Instruction::IntToPtr:
309      return Expression::INTTOPTR;
310    case Instruction::BitCast:
311      return Expression::BITCAST;
312
313    // THIS SHOULD NEVER HAPPEN
314    default:
315      assert(0 && "Cast operator with unknown opcode?");
316      return Expression::BITCAST;
317  }
318}
319
320Expression ValueTable::create_expression(BinaryOperator* BO) {
321  Expression e;
322
323  e.firstVN = lookup_or_add(BO->getOperand(0));
324  e.secondVN = lookup_or_add(BO->getOperand(1));
325  e.thirdVN = 0;
326  e.type = BO->getType();
327  e.opcode = getOpcode(BO);
328
329  return e;
330}
331
332Expression ValueTable::create_expression(CmpInst* C) {
333  Expression e;
334
335  e.firstVN = lookup_or_add(C->getOperand(0));
336  e.secondVN = lookup_or_add(C->getOperand(1));
337  e.thirdVN = 0;
338  e.type = C->getType();
339  e.opcode = getOpcode(C);
340
341  return e;
342}
343
344Expression ValueTable::create_expression(CastInst* C) {
345  Expression e;
346
347  e.firstVN = lookup_or_add(C->getOperand(0));
348  e.secondVN = 0;
349  e.thirdVN = 0;
350  e.type = C->getType();
351  e.opcode = getOpcode(C);
352
353  return e;
354}
355
356Expression ValueTable::create_expression(ShuffleVectorInst* S) {
357  Expression e;
358
359  e.firstVN = lookup_or_add(S->getOperand(0));
360  e.secondVN = lookup_or_add(S->getOperand(1));
361  e.thirdVN = lookup_or_add(S->getOperand(2));
362  e.type = S->getType();
363  e.opcode = Expression::SHUFFLE;
364
365  return e;
366}
367
368Expression ValueTable::create_expression(ExtractElementInst* E) {
369  Expression e;
370
371  e.firstVN = lookup_or_add(E->getOperand(0));
372  e.secondVN = lookup_or_add(E->getOperand(1));
373  e.thirdVN = 0;
374  e.type = E->getType();
375  e.opcode = Expression::EXTRACT;
376
377  return e;
378}
379
380Expression ValueTable::create_expression(InsertElementInst* I) {
381  Expression e;
382
383  e.firstVN = lookup_or_add(I->getOperand(0));
384  e.secondVN = lookup_or_add(I->getOperand(1));
385  e.thirdVN = lookup_or_add(I->getOperand(2));
386  e.type = I->getType();
387  e.opcode = Expression::INSERT;
388
389  return e;
390}
391
392Expression ValueTable::create_expression(SelectInst* I) {
393  Expression e;
394
395  e.firstVN = lookup_or_add(I->getCondition());
396  e.secondVN = lookup_or_add(I->getTrueValue());
397  e.thirdVN = lookup_or_add(I->getFalseValue());
398  e.type = I->getType();
399  e.opcode = Expression::SELECT;
400
401  return e;
402}
403
404Expression ValueTable::create_expression(GetElementPtrInst* G) {
405  Expression e;
406
407  e.firstVN = lookup_or_add(G->getPointerOperand());
408  e.secondVN = 0;
409  e.thirdVN = 0;
410  e.type = G->getType();
411  e.opcode = Expression::GEP;
412
413  for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
414       I != E; ++I)
415    e.varargs.push_back(lookup_or_add(*I));
416
417  return e;
418}
419
420//===----------------------------------------------------------------------===//
421//                     ValueTable External Functions
422//===----------------------------------------------------------------------===//
423
424/// lookup_or_add - Returns the value number for the specified value, assigning
425/// it a new number if it did not have one before.
426uint32_t ValueTable::lookup_or_add(Value* V) {
427  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
428  if (VI != valueNumbering.end())
429    return VI->second;
430
431
432  if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
433    Expression e = create_expression(BO);
434
435    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
436    if (EI != expressionNumbering.end()) {
437      valueNumbering.insert(std::make_pair(V, EI->second));
438      return EI->second;
439    } else {
440      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
441      valueNumbering.insert(std::make_pair(V, nextValueNumber));
442
443      return nextValueNumber++;
444    }
445  } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
446    Expression e = create_expression(C);
447
448    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
449    if (EI != expressionNumbering.end()) {
450      valueNumbering.insert(std::make_pair(V, EI->second));
451      return EI->second;
452    } else {
453      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
454      valueNumbering.insert(std::make_pair(V, nextValueNumber));
455
456      return nextValueNumber++;
457    }
458  } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
459    Expression e = create_expression(U);
460
461    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
462    if (EI != expressionNumbering.end()) {
463      valueNumbering.insert(std::make_pair(V, EI->second));
464      return EI->second;
465    } else {
466      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
467      valueNumbering.insert(std::make_pair(V, nextValueNumber));
468
469      return nextValueNumber++;
470    }
471  } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
472    Expression e = create_expression(U);
473
474    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
475    if (EI != expressionNumbering.end()) {
476      valueNumbering.insert(std::make_pair(V, EI->second));
477      return EI->second;
478    } else {
479      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
480      valueNumbering.insert(std::make_pair(V, nextValueNumber));
481
482      return nextValueNumber++;
483    }
484  } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
485    Expression e = create_expression(U);
486
487    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
488    if (EI != expressionNumbering.end()) {
489      valueNumbering.insert(std::make_pair(V, EI->second));
490      return EI->second;
491    } else {
492      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
493      valueNumbering.insert(std::make_pair(V, nextValueNumber));
494
495      return nextValueNumber++;
496    }
497  } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
498    Expression e = create_expression(U);
499
500    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
501    if (EI != expressionNumbering.end()) {
502      valueNumbering.insert(std::make_pair(V, EI->second));
503      return EI->second;
504    } else {
505      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
506      valueNumbering.insert(std::make_pair(V, nextValueNumber));
507
508      return nextValueNumber++;
509    }
510  } else if (CastInst* U = dyn_cast<CastInst>(V)) {
511    Expression e = create_expression(U);
512
513    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
514    if (EI != expressionNumbering.end()) {
515      valueNumbering.insert(std::make_pair(V, EI->second));
516      return EI->second;
517    } else {
518      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
519      valueNumbering.insert(std::make_pair(V, nextValueNumber));
520
521      return nextValueNumber++;
522    }
523  } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
524    Expression e = create_expression(U);
525
526    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
527    if (EI != expressionNumbering.end()) {
528      valueNumbering.insert(std::make_pair(V, EI->second));
529      return EI->second;
530    } else {
531      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
532      valueNumbering.insert(std::make_pair(V, nextValueNumber));
533
534      return nextValueNumber++;
535    }
536  } else {
537    valueNumbering.insert(std::make_pair(V, nextValueNumber));
538    return nextValueNumber++;
539  }
540}
541
542/// lookup - Returns the value number of the specified value. Fails if
543/// the value has not yet been numbered.
544uint32_t ValueTable::lookup(Value* V) const {
545  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
546  if (VI != valueNumbering.end())
547    return VI->second;
548  else
549    assert(0 && "Value not numbered?");
550
551  return 0;
552}
553
554/// clear - Remove all entries from the ValueTable
555void ValueTable::clear() {
556  valueNumbering.clear();
557  expressionNumbering.clear();
558  nextValueNumber = 1;
559}
560
561//===----------------------------------------------------------------------===//
562//                       ValueNumberedSet Class
563//===----------------------------------------------------------------------===//
564namespace {
565class ValueNumberedSet {
566  private:
567    SmallPtrSet<Value*, 8> contents;
568    BitVector numbers;
569  public:
570    ValueNumberedSet() { numbers.resize(1); }
571    ValueNumberedSet(const ValueNumberedSet& other) {
572      numbers = other.numbers;
573      contents = other.contents;
574    }
575
576    typedef SmallPtrSet<Value*, 8>::iterator iterator;
577
578    iterator begin() { return contents.begin(); }
579    iterator end() { return contents.end(); }
580
581    bool insert(Value* v) { return contents.insert(v); }
582    void insert(iterator I, iterator E) { contents.insert(I, E); }
583    void erase(Value* v) { contents.erase(v); }
584    unsigned count(Value* v) { return contents.count(v); }
585    size_t size() { return contents.size(); }
586
587    void set(unsigned i)  {
588      if (i >= numbers.size())
589        numbers.resize(i+1);
590
591      numbers.set(i);
592    }
593
594    void operator=(const ValueNumberedSet& other) {
595      contents = other.contents;
596      numbers = other.numbers;
597    }
598
599    void reset(unsigned i)  {
600      if (i < numbers.size())
601        numbers.reset(i);
602    }
603
604    bool test(unsigned i)  {
605      if (i >= numbers.size())
606        return false;
607
608      return numbers.test(i);
609    }
610
611    void clear() {
612      contents.clear();
613      numbers.clear();
614    }
615};
616}
617
618//===----------------------------------------------------------------------===//
619//                         GVN Pass
620//===----------------------------------------------------------------------===//
621
622namespace {
623
624  class VISIBILITY_HIDDEN GVN : public FunctionPass {
625    bool runOnFunction(Function &F);
626  public:
627    static char ID; // Pass identification, replacement for typeid
628    GVN() : FunctionPass((intptr_t)&ID) { }
629
630  private:
631    ValueTable VN;
632
633    DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
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.addPreserved<MemoryDependenceAnalysis>();
641    }
642
643    // Helper fuctions
644    // FIXME: eliminate or document these better
645    Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
646    void val_insert(ValueNumberedSet& s, Value* v);
647    bool processLoad(LoadInst* L,
648                     DenseMap<Value*, LoadInst*>& lastLoad,
649                     SmallVector<Instruction*, 4>& toErase);
650    bool processInstruction(Instruction* I,
651                            ValueNumberedSet& currAvail,
652                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
653                            SmallVector<Instruction*, 4>& toErase);
654    bool processNonLocalLoad(LoadInst* L, SmallVector<Instruction*, 4>& toErase);
655    Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
656                                  DenseMap<BasicBlock*, Value*> &Phis);
657    void dump(DenseMap<BasicBlock*, Value*>& d);
658  };
659
660  char GVN::ID = 0;
661
662}
663
664// createGVNPass - The public interface to this file...
665FunctionPass *llvm::createGVNPass() { return new GVN(); }
666
667static RegisterPass<GVN> X("gvn",
668                           "Global Value Numbering");
669
670STATISTIC(NumGVNInstr, "Number of instructions deleted");
671STATISTIC(NumGVNLoad, "Number of loads deleted");
672
673/// find_leader - Given a set and a value number, return the first
674/// element of the set with that value number, or 0 if no such element
675/// is present
676Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
677  if (!vals.test(v))
678    return 0;
679
680  for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
681       I != E; ++I)
682    if (v == VN.lookup(*I))
683      return *I;
684
685  assert(0 && "No leader found, but present bit is set?");
686  return 0;
687}
688
689/// val_insert - Insert a value into a set only if there is not a value
690/// with the same value number already in the set
691void GVN::val_insert(ValueNumberedSet& s, Value* v) {
692  uint32_t num = VN.lookup(v);
693  if (!s.test(num))
694    s.insert(v);
695}
696
697void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
698  printf("{\n");
699  for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
700       E = d.end(); I != E; ++I) {
701    if (I->second == MemoryDependenceAnalysis::None)
702      printf("None\n");
703    else
704      I->second->dump();
705  }
706  printf("}\n");
707}
708
709
710/// GetValueForBlock - Get the value to use within the specified basic block.
711/// available values are in Phis.
712Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
713                               DenseMap<BasicBlock*, Value*> &Phis) {
714  DominatorTree &DT = getAnalysis<DominatorTree>();
715
716  // If we have already computed this value, return the previously computed val.
717  Value *&V = Phis[BB];
718  if (V) return V;
719
720  DomTreeNode *IDom = DT.getNode(BB)->getIDom();
721
722  if (IDom && Phis.count(IDom->getBlock())) {
723    return V = GetValueForBlock(IDom->getBlock(), orig, Phis);
724  }
725
726
727
728  // Otherwise, the idom is the loop, so we need to insert a PHI node.  Do so
729  // now, then get values to fill in the incoming values for the PHI.
730  PHINode *PN = new PHINode(orig->getType(), orig->getName()+".rle",
731                            BB->begin());
732  PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
733  V = PN;
734
735  // Fill in the incoming values for the block.
736  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
737    PN->addIncoming(GetValueForBlock(DT.getNode(*PI)->getBlock(), orig, Phis), *PI);
738  return PN;
739}
740
741bool GVN::processNonLocalLoad(LoadInst* L, SmallVector<Instruction*, 4>& toErase) {
742  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
743
744  DenseMap<BasicBlock*, Value*> deps;
745  bool ret = MD.getNonLocalDependency(L, deps);
746  if (!ret)
747    return false;
748
749  DenseMap<BasicBlock*, Value*> repl;
750  for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
751       I != E; ++I)
752    if (I->second == MemoryDependenceAnalysis::None) {
753      return false;
754    } else if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
755      if (S->getPointerOperand() == L->getPointerOperand())
756        repl.insert(std::make_pair(I->first, S->getOperand(0)));
757      else
758        return false;
759    } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
760      if (LD->getPointerOperand() == L->getPointerOperand())
761        repl.insert(std::make_pair(I->first, LD));
762      else
763        return false;
764    } else {
765      return false;
766    }
767
768  SmallPtrSet<BasicBlock*, 4> visited;
769  Value* v = GetValueForBlock(L->getParent(), L, repl);
770
771  MD.removeInstruction(L);
772  L->replaceAllUsesWith(v);
773  toErase.push_back(L);
774
775  return true;
776}
777
778bool GVN::processLoad(LoadInst* L,
779                         DenseMap<Value*, LoadInst*>& lastLoad,
780                         SmallVector<Instruction*, 4>& toErase) {
781  if (L->isVolatile()) {
782    lastLoad[L->getPointerOperand()] = L;
783    return false;
784  }
785
786  Value* pointer = L->getPointerOperand();
787  LoadInst*& last = lastLoad[pointer];
788
789  // ... to a pointer that has been loaded from before...
790  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
791  Instruction* dep = MD.getDependency(L);
792  if (dep == MemoryDependenceAnalysis::NonLocal &&
793      L->getParent() != &L->getParent()->getParent()->getEntryBlock())
794    processNonLocalLoad(L, toErase);
795  bool deletedLoad = false;
796
797  while (dep != MemoryDependenceAnalysis::None &&
798         dep != MemoryDependenceAnalysis::NonLocal &&
799         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
800    // ... that depends on a store ...
801    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
802      if (S->getPointerOperand() == pointer) {
803        // Remove it!
804        MD.removeInstruction(L);
805
806        L->replaceAllUsesWith(S->getOperand(0));
807        toErase.push_back(L);
808        deletedLoad = true;
809        NumGVNLoad++;
810      }
811
812      // Whether we removed it or not, we can't
813      // go any further
814      break;
815    } else if (!last) {
816      // If we don't depend on a store, and we haven't
817      // been loaded before, bail.
818      break;
819    } else if (dep == last) {
820      // Remove it!
821      MD.removeInstruction(L);
822
823      L->replaceAllUsesWith(last);
824      toErase.push_back(L);
825      deletedLoad = true;
826      NumGVNLoad++;
827
828      break;
829    } else {
830      dep = MD.getDependency(L, dep);
831    }
832  }
833
834  if (!deletedLoad)
835    last = L;
836
837  return deletedLoad;
838}
839
840/// buildsets_availout - When calculating availability, handle an instruction
841/// by inserting it into the appropriate sets
842bool GVN::processInstruction(Instruction* I,
843                                ValueNumberedSet& currAvail,
844                                DenseMap<Value*, LoadInst*>& lastSeenLoad,
845                                SmallVector<Instruction*, 4>& toErase) {
846  if (LoadInst* L = dyn_cast<LoadInst>(I)) {
847    return processLoad(L, lastSeenLoad, toErase);
848  }
849
850  unsigned num = VN.lookup_or_add(I);
851
852  if (currAvail.test(num)) {
853    Value* repl = find_leader(currAvail, num);
854
855    I->replaceAllUsesWith(repl);
856    toErase.push_back(I);
857    return true;
858  } else if (!I->isTerminator()) {
859    currAvail.set(num);
860    currAvail.insert(I);
861  }
862
863  return false;
864}
865
866// GVN::runOnFunction - This is the main transformation entry point for a
867// function.
868//
869bool GVN::runOnFunction(Function &F) {
870  // Clean out global sets from any previous functions
871  VN.clear();
872  availableOut.clear();
873
874  bool changed_function = false;
875
876  DominatorTree &DT = getAnalysis<DominatorTree>();
877
878  SmallVector<Instruction*, 4> toErase;
879
880  // Top-down walk of the dominator tree
881  for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
882         E = df_end(DT.getRootNode()); DI != E; ++DI) {
883
884    // Get the set to update for this block
885    ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
886    DenseMap<Value*, LoadInst*> lastSeenLoad;
887
888    BasicBlock* BB = DI->getBlock();
889
890    // A block inherits AVAIL_OUT from its dominator
891    if (DI->getIDom() != 0)
892      currAvail = availableOut[DI->getIDom()->getBlock()];
893
894    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
895         BI != BE; ++BI) {
896      changed_function |= processInstruction(BI, currAvail, lastSeenLoad, toErase);
897
898      NumGVNInstr += toErase.size();
899
900      for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
901           E = toErase.end(); I != E; ++I)
902        (*I)->eraseFromParent();
903
904      toErase.clear();
905    }
906  }
907
908  return changed_function;
909}
910