GVN.cpp revision 0cd320362e91852c8f7f2c8c4841498aab7f92fa 
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/BasicBlock.h"
19#include "llvm/Instructions.h"
20#include "llvm/Function.h"
21#include "llvm/DerivedTypes.h"
22#include "llvm/Analysis/Dominators.h"
23#include "llvm/ADT/BitVector.h"
24#include "llvm/ADT/DenseMap.h"
25#include "llvm/ADT/DepthFirstIterator.h"
26#include "llvm/ADT/SmallPtrSet.h"
27#include "llvm/ADT/SmallVector.h"
28#include "llvm/ADT/Statistic.h"
29#include "llvm/Analysis/MemoryDependenceAnalysis.h"
30#include "llvm/Support/CFG.h"
31#include "llvm/Support/Compiler.h"
32using namespace llvm;
33
34//===----------------------------------------------------------------------===//
35//                         ValueTable Class
36//===----------------------------------------------------------------------===//
37
38/// This class holds the mapping between values and value numbers.  It is used
39/// as an efficient mechanism to determine the expression-wise equivalence of
40/// two values.
41namespace {
42  struct VISIBILITY_HIDDEN Expression {
43    enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
44                            FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
45                            ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
46                            ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
47                            FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
48                            FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
49                            FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
50                            SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
51                            FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
52                            PTRTOINT, INTTOPTR, BITCAST, GEP, EMPTY,
53                            TOMBSTONE };
54
55    ExpressionOpcode opcode;
56    const Type* type;
57    uint32_t firstVN;
58    uint32_t secondVN;
59    uint32_t thirdVN;
60    SmallVector<uint32_t, 4> varargs;
61
62    Expression() { }
63    Expression(ExpressionOpcode o) : opcode(o) { }
64
65    bool operator==(const Expression &other) const {
66      if (opcode != other.opcode)
67        return false;
68      else if (opcode == EMPTY || opcode == TOMBSTONE)
69        return true;
70      else if (type != other.type)
71        return false;
72      else if (firstVN != other.firstVN)
73        return false;
74      else if (secondVN != other.secondVN)
75        return false;
76      else if (thirdVN != other.thirdVN)
77        return false;
78      else {
79        if (varargs.size() != other.varargs.size())
80          return false;
81
82        for (size_t i = 0; i < varargs.size(); ++i)
83          if (varargs[i] != other.varargs[i])
84            return false;
85
86        return true;
87      }
88    }
89
90    bool operator!=(const Expression &other) const {
91      if (opcode != other.opcode)
92        return true;
93      else if (opcode == EMPTY || opcode == TOMBSTONE)
94        return false;
95      else if (type != other.type)
96        return true;
97      else if (firstVN != other.firstVN)
98        return true;
99      else if (secondVN != other.secondVN)
100        return true;
101      else if (thirdVN != other.thirdVN)
102        return true;
103      else {
104        if (varargs.size() != other.varargs.size())
105          return true;
106
107        for (size_t i = 0; i < varargs.size(); ++i)
108          if (varargs[i] != other.varargs[i])
109            return true;
110
111          return false;
112      }
113    }
114  };
115
116  class VISIBILITY_HIDDEN ValueTable {
117    private:
118      DenseMap<Value*, uint32_t> valueNumbering;
119      DenseMap<Expression, uint32_t> expressionNumbering;
120
121      uint32_t nextValueNumber;
122
123      Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
124      Expression::ExpressionOpcode getOpcode(CmpInst* C);
125      Expression::ExpressionOpcode getOpcode(CastInst* C);
126      Expression create_expression(BinaryOperator* BO);
127      Expression create_expression(CmpInst* C);
128      Expression create_expression(ShuffleVectorInst* V);
129      Expression create_expression(ExtractElementInst* C);
130      Expression create_expression(InsertElementInst* V);
131      Expression create_expression(SelectInst* V);
132      Expression create_expression(CastInst* C);
133      Expression create_expression(GetElementPtrInst* G);
134    public:
135      ValueTable() { nextValueNumber = 1; }
136      uint32_t lookup_or_add(Value* V);
137      uint32_t lookup(Value* V) const;
138      void add(Value* V, uint32_t num);
139      void clear();
140      void erase(Value* v);
141      unsigned size();
142  };
143}
144
145namespace llvm {
146template <> struct DenseMapKeyInfo<Expression> {
147  static inline Expression getEmptyKey() { return Expression(Expression::EMPTY); }
148  static inline Expression getTombstoneKey() { return Expression(Expression::TOMBSTONE); }
149
150  static unsigned getHashValue(const Expression e) {
151    unsigned hash = e.opcode;
152
153    hash = e.firstVN + hash * 37;
154    hash = e.secondVN + hash * 37;
155    hash = e.thirdVN + hash * 37;
156
157    hash = (unsigned)((uintptr_t)e.type >> 4) ^
158            (unsigned)((uintptr_t)e.type >> 9) +
159            hash * 37;
160
161    for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), E = e.varargs.end();
162         I != E; ++I)
163      hash = *I + hash * 37;
164
165    return hash;
166  }
167  static bool isPod() { return true; }
168};
169}
170
171//===----------------------------------------------------------------------===//
172//                     ValueTable Internal Functions
173//===----------------------------------------------------------------------===//
174Expression::ExpressionOpcode
175                             ValueTable::getOpcode(BinaryOperator* BO) {
176  switch(BO->getOpcode()) {
177    case Instruction::Add:
178      return Expression::ADD;
179    case Instruction::Sub:
180      return Expression::SUB;
181    case Instruction::Mul:
182      return Expression::MUL;
183    case Instruction::UDiv:
184      return Expression::UDIV;
185    case Instruction::SDiv:
186      return Expression::SDIV;
187    case Instruction::FDiv:
188      return Expression::FDIV;
189    case Instruction::URem:
190      return Expression::UREM;
191    case Instruction::SRem:
192      return Expression::SREM;
193    case Instruction::FRem:
194      return Expression::FREM;
195    case Instruction::Shl:
196      return Expression::SHL;
197    case Instruction::LShr:
198      return Expression::LSHR;
199    case Instruction::AShr:
200      return Expression::ASHR;
201    case Instruction::And:
202      return Expression::AND;
203    case Instruction::Or:
204      return Expression::OR;
205    case Instruction::Xor:
206      return Expression::XOR;
207
208    // THIS SHOULD NEVER HAPPEN
209    default:
210      assert(0 && "Binary operator with unknown opcode?");
211      return Expression::ADD;
212  }
213}
214
215Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
216  if (C->getOpcode() == Instruction::ICmp) {
217    switch (C->getPredicate()) {
218      case ICmpInst::ICMP_EQ:
219        return Expression::ICMPEQ;
220      case ICmpInst::ICMP_NE:
221        return Expression::ICMPNE;
222      case ICmpInst::ICMP_UGT:
223        return Expression::ICMPUGT;
224      case ICmpInst::ICMP_UGE:
225        return Expression::ICMPUGE;
226      case ICmpInst::ICMP_ULT:
227        return Expression::ICMPULT;
228      case ICmpInst::ICMP_ULE:
229        return Expression::ICMPULE;
230      case ICmpInst::ICMP_SGT:
231        return Expression::ICMPSGT;
232      case ICmpInst::ICMP_SGE:
233        return Expression::ICMPSGE;
234      case ICmpInst::ICMP_SLT:
235        return Expression::ICMPSLT;
236      case ICmpInst::ICMP_SLE:
237        return Expression::ICMPSLE;
238
239      // THIS SHOULD NEVER HAPPEN
240      default:
241        assert(0 && "Comparison with unknown predicate?");
242        return Expression::ICMPEQ;
243    }
244  } else {
245    switch (C->getPredicate()) {
246      case FCmpInst::FCMP_OEQ:
247        return Expression::FCMPOEQ;
248      case FCmpInst::FCMP_OGT:
249        return Expression::FCMPOGT;
250      case FCmpInst::FCMP_OGE:
251        return Expression::FCMPOGE;
252      case FCmpInst::FCMP_OLT:
253        return Expression::FCMPOLT;
254      case FCmpInst::FCMP_OLE:
255        return Expression::FCMPOLE;
256      case FCmpInst::FCMP_ONE:
257        return Expression::FCMPONE;
258      case FCmpInst::FCMP_ORD:
259        return Expression::FCMPORD;
260      case FCmpInst::FCMP_UNO:
261        return Expression::FCMPUNO;
262      case FCmpInst::FCMP_UEQ:
263        return Expression::FCMPUEQ;
264      case FCmpInst::FCMP_UGT:
265        return Expression::FCMPUGT;
266      case FCmpInst::FCMP_UGE:
267        return Expression::FCMPUGE;
268      case FCmpInst::FCMP_ULT:
269        return Expression::FCMPULT;
270      case FCmpInst::FCMP_ULE:
271        return Expression::FCMPULE;
272      case FCmpInst::FCMP_UNE:
273        return Expression::FCMPUNE;
274
275      // THIS SHOULD NEVER HAPPEN
276      default:
277        assert(0 && "Comparison with unknown predicate?");
278        return Expression::FCMPOEQ;
279    }
280  }
281}
282
283Expression::ExpressionOpcode
284                             ValueTable::getOpcode(CastInst* C) {
285  switch(C->getOpcode()) {
286    case Instruction::Trunc:
287      return Expression::TRUNC;
288    case Instruction::ZExt:
289      return Expression::ZEXT;
290    case Instruction::SExt:
291      return Expression::SEXT;
292    case Instruction::FPToUI:
293      return Expression::FPTOUI;
294    case Instruction::FPToSI:
295      return Expression::FPTOSI;
296    case Instruction::UIToFP:
297      return Expression::UITOFP;
298    case Instruction::SIToFP:
299      return Expression::SITOFP;
300    case Instruction::FPTrunc:
301      return Expression::FPTRUNC;
302    case Instruction::FPExt:
303      return Expression::FPEXT;
304    case Instruction::PtrToInt:
305      return Expression::PTRTOINT;
306    case Instruction::IntToPtr:
307      return Expression::INTTOPTR;
308    case Instruction::BitCast:
309      return Expression::BITCAST;
310
311    // THIS SHOULD NEVER HAPPEN
312    default:
313      assert(0 && "Cast operator with unknown opcode?");
314      return Expression::BITCAST;
315  }
316}
317
318Expression ValueTable::create_expression(BinaryOperator* BO) {
319  Expression e;
320
321  e.firstVN = lookup_or_add(BO->getOperand(0));
322  e.secondVN = lookup_or_add(BO->getOperand(1));
323  e.thirdVN = 0;
324  e.type = BO->getType();
325  e.opcode = getOpcode(BO);
326
327  return e;
328}
329
330Expression ValueTable::create_expression(CmpInst* C) {
331  Expression e;
332
333  e.firstVN = lookup_or_add(C->getOperand(0));
334  e.secondVN = lookup_or_add(C->getOperand(1));
335  e.thirdVN = 0;
336  e.type = C->getType();
337  e.opcode = getOpcode(C);
338
339  return e;
340}
341
342Expression ValueTable::create_expression(CastInst* C) {
343  Expression e;
344
345  e.firstVN = lookup_or_add(C->getOperand(0));
346  e.secondVN = 0;
347  e.thirdVN = 0;
348  e.type = C->getType();
349  e.opcode = getOpcode(C);
350
351  return e;
352}
353
354Expression ValueTable::create_expression(ShuffleVectorInst* S) {
355  Expression e;
356
357  e.firstVN = lookup_or_add(S->getOperand(0));
358  e.secondVN = lookup_or_add(S->getOperand(1));
359  e.thirdVN = lookup_or_add(S->getOperand(2));
360  e.type = S->getType();
361  e.opcode = Expression::SHUFFLE;
362
363  return e;
364}
365
366Expression ValueTable::create_expression(ExtractElementInst* E) {
367  Expression e;
368
369  e.firstVN = lookup_or_add(E->getOperand(0));
370  e.secondVN = lookup_or_add(E->getOperand(1));
371  e.thirdVN = 0;
372  e.type = E->getType();
373  e.opcode = Expression::EXTRACT;
374
375  return e;
376}
377
378Expression ValueTable::create_expression(InsertElementInst* I) {
379  Expression e;
380
381  e.firstVN = lookup_or_add(I->getOperand(0));
382  e.secondVN = lookup_or_add(I->getOperand(1));
383  e.thirdVN = lookup_or_add(I->getOperand(2));
384  e.type = I->getType();
385  e.opcode = Expression::INSERT;
386
387  return e;
388}
389
390Expression ValueTable::create_expression(SelectInst* I) {
391  Expression e;
392
393  e.firstVN = lookup_or_add(I->getCondition());
394  e.secondVN = lookup_or_add(I->getTrueValue());
395  e.thirdVN = lookup_or_add(I->getFalseValue());
396  e.type = I->getType();
397  e.opcode = Expression::SELECT;
398
399  return e;
400}
401
402Expression ValueTable::create_expression(GetElementPtrInst* G) {
403  Expression e;
404
405  e.firstVN = lookup_or_add(G->getPointerOperand());
406  e.secondVN = 0;
407  e.thirdVN = 0;
408  e.type = G->getType();
409  e.opcode = Expression::GEP;
410
411  for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
412       I != E; ++I)
413    e.varargs.push_back(lookup_or_add(*I));
414
415  return e;
416}
417
418//===----------------------------------------------------------------------===//
419//                     ValueTable External Functions
420//===----------------------------------------------------------------------===//
421
422/// lookup_or_add - Returns the value number for the specified value, assigning
423/// it a new number if it did not have one before.
424uint32_t ValueTable::lookup_or_add(Value* V) {
425  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
426  if (VI != valueNumbering.end())
427    return VI->second;
428
429
430  if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
431    Expression e = create_expression(BO);
432
433    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
434    if (EI != expressionNumbering.end()) {
435      valueNumbering.insert(std::make_pair(V, EI->second));
436      return EI->second;
437    } else {
438      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
439      valueNumbering.insert(std::make_pair(V, nextValueNumber));
440
441      return nextValueNumber++;
442    }
443  } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
444    Expression e = create_expression(C);
445
446    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
447    if (EI != expressionNumbering.end()) {
448      valueNumbering.insert(std::make_pair(V, EI->second));
449      return EI->second;
450    } else {
451      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
452      valueNumbering.insert(std::make_pair(V, nextValueNumber));
453
454      return nextValueNumber++;
455    }
456  } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
457    Expression e = create_expression(U);
458
459    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
460    if (EI != expressionNumbering.end()) {
461      valueNumbering.insert(std::make_pair(V, EI->second));
462      return EI->second;
463    } else {
464      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
465      valueNumbering.insert(std::make_pair(V, nextValueNumber));
466
467      return nextValueNumber++;
468    }
469  } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
470    Expression e = create_expression(U);
471
472    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
473    if (EI != expressionNumbering.end()) {
474      valueNumbering.insert(std::make_pair(V, EI->second));
475      return EI->second;
476    } else {
477      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
478      valueNumbering.insert(std::make_pair(V, nextValueNumber));
479
480      return nextValueNumber++;
481    }
482  } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
483    Expression e = create_expression(U);
484
485    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
486    if (EI != expressionNumbering.end()) {
487      valueNumbering.insert(std::make_pair(V, EI->second));
488      return EI->second;
489    } else {
490      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
491      valueNumbering.insert(std::make_pair(V, nextValueNumber));
492
493      return nextValueNumber++;
494    }
495  } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
496    Expression e = create_expression(U);
497
498    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
499    if (EI != expressionNumbering.end()) {
500      valueNumbering.insert(std::make_pair(V, EI->second));
501      return EI->second;
502    } else {
503      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
504      valueNumbering.insert(std::make_pair(V, nextValueNumber));
505
506      return nextValueNumber++;
507    }
508  } else if (CastInst* U = dyn_cast<CastInst>(V)) {
509    Expression e = create_expression(U);
510
511    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
512    if (EI != expressionNumbering.end()) {
513      valueNumbering.insert(std::make_pair(V, EI->second));
514      return EI->second;
515    } else {
516      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
517      valueNumbering.insert(std::make_pair(V, nextValueNumber));
518
519      return nextValueNumber++;
520    }
521  } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
522    Expression e = create_expression(U);
523
524    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
525    if (EI != expressionNumbering.end()) {
526      valueNumbering.insert(std::make_pair(V, EI->second));
527      return EI->second;
528    } else {
529      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
530      valueNumbering.insert(std::make_pair(V, nextValueNumber));
531
532      return nextValueNumber++;
533    }
534  } else {
535    valueNumbering.insert(std::make_pair(V, nextValueNumber));
536    return nextValueNumber++;
537  }
538}
539
540/// lookup - Returns the value number of the specified value. Fails if
541/// the value has not yet been numbered.
542uint32_t ValueTable::lookup(Value* V) const {
543  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
544  if (VI != valueNumbering.end())
545    return VI->second;
546  else
547    assert(0 && "Value not numbered?");
548
549  return 0;
550}
551
552/// clear - Remove all entries from the ValueTable
553void ValueTable::clear() {
554  valueNumbering.clear();
555  expressionNumbering.clear();
556  nextValueNumber = 1;
557}
558
559//===----------------------------------------------------------------------===//
560//                       ValueNumberedSet Class
561//===----------------------------------------------------------------------===//
562namespace {
563class ValueNumberedSet {
564  private:
565    SmallPtrSet<Value*, 8> contents;
566    BitVector numbers;
567  public:
568    ValueNumberedSet() { numbers.resize(1); }
569    ValueNumberedSet(const ValueNumberedSet& other) {
570      numbers = other.numbers;
571      contents = other.contents;
572    }
573
574    typedef SmallPtrSet<Value*, 8>::iterator iterator;
575
576    iterator begin() { return contents.begin(); }
577    iterator end() { return contents.end(); }
578
579    bool insert(Value* v) { return contents.insert(v); }
580    void insert(iterator I, iterator E) { contents.insert(I, E); }
581    void erase(Value* v) { contents.erase(v); }
582    unsigned count(Value* v) { return contents.count(v); }
583    size_t size() { return contents.size(); }
584
585    void set(unsigned i)  {
586      if (i >= numbers.size())
587        numbers.resize(i+1);
588
589      numbers.set(i);
590    }
591
592    void operator=(const ValueNumberedSet& other) {
593      contents = other.contents;
594      numbers = other.numbers;
595    }
596
597    void reset(unsigned i)  {
598      if (i < numbers.size())
599        numbers.reset(i);
600    }
601
602    bool test(unsigned i)  {
603      if (i >= numbers.size())
604        return false;
605
606      return numbers.test(i);
607    }
608
609    void clear() {
610      contents.clear();
611      numbers.clear();
612    }
613};
614}
615
616//===----------------------------------------------------------------------===//
617//                         GVN Pass
618//===----------------------------------------------------------------------===//
619
620namespace {
621
622  class VISIBILITY_HIDDEN GVN : public FunctionPass {
623    bool runOnFunction(Function &F);
624  public:
625    static char ID; // Pass identification, replacement for typeid
626    GVN() : FunctionPass((intptr_t)&ID) { }
627
628  private:
629    ValueTable VN;
630
631    DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
632
633    // This transformation requires dominator postdominator info
634    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
635      AU.setPreservesCFG();
636      AU.addRequired<DominatorTree>();
637      AU.addRequired<MemoryDependenceAnalysis>();
638      AU.addPreserved<MemoryDependenceAnalysis>();
639    }
640
641    // Helper fuctions
642    // FIXME: eliminate or document these better
643    Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
644    void val_insert(ValueNumberedSet& s, Value* v);
645    bool processLoad(LoadInst* L,
646                     DenseMap<Value*, LoadInst*>& lastLoad,
647                     SmallVector<Instruction*, 4>& toErase);
648    bool processInstruction(Instruction* I,
649                            ValueNumberedSet& currAvail,
650                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
651                            SmallVector<Instruction*, 4>& toErase);
652    bool processNonLocalLoad(LoadInst* L, SmallVector<Instruction*, 4>& toErase);
653    Value *performPHIConstruction(BasicBlock *BB, LoadInst* orig,
654                                  DenseMap<BasicBlock*, Value*> &Phis);
655    void dump(DenseMap<BasicBlock*, Value*>& d);
656  };
657
658  char GVN::ID = 0;
659
660}
661
662// createGVNPass - The public interface to this file...
663FunctionPass *llvm::createGVNPass() { return new GVN(); }
664
665static RegisterPass<GVN> X("gvn",
666                           "Global Value Numbering");
667
668STATISTIC(NumGVNInstr, "Number of instructions deleted");
669STATISTIC(NumGVNLoad, "Number of loads deleted");
670
671/// find_leader - Given a set and a value number, return the first
672/// element of the set with that value number, or 0 if no such element
673/// is present
674Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
675  if (!vals.test(v))
676    return 0;
677
678  for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
679       I != E; ++I)
680    if (v == VN.lookup(*I))
681      return *I;
682
683  assert(0 && "No leader found, but present bit is set?");
684  return 0;
685}
686
687/// val_insert - Insert a value into a set only if there is not a value
688/// with the same value number already in the set
689void GVN::val_insert(ValueNumberedSet& s, Value* v) {
690  uint32_t num = VN.lookup(v);
691  if (!s.test(num))
692    s.insert(v);
693}
694
695void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
696  printf("{\n");
697  for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
698       E = d.end(); I != E; ++I) {
699    if (I->second == MemoryDependenceAnalysis::None)
700      printf("None\n");
701    else
702      I->second->dump();
703  }
704  printf("}\n");
705}
706
707
708Value *GVN::performPHIConstruction(BasicBlock *BB, LoadInst* orig,
709                                   DenseMap<BasicBlock*, Value*> &Phis) {
710  DenseMap<BasicBlock*, Value*>::iterator DI = Phis.find(BB);
711  if (DI != Phis.end())
712    return DI->second;
713
714  unsigned numPreds = std::distance(pred_begin(BB), pred_end(BB));
715
716  if (numPreds == 1) {
717    Phis[BB] = Phis[*pred_begin(BB)];
718    return Phis[BB];
719  } else {
720    PHINode *PN = new PHINode(orig->getType(), orig->getName()+".rle", BB->begin());
721    PN->reserveOperandSpace(numPreds);
722
723    // Fill in the incoming values for the block.
724    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
725      PN->addIncoming(performPHIConstruction(*PI, orig, Phis), *PI);
726
727    bool all_same = PN->getNumIncomingValues() != 1;
728    Value* first = PN->getIncomingValue(0);
729    for (unsigned i = 1; i < PN->getNumIncomingValues(); ++i)
730      all_same &= (PN->getIncomingValue(i) == first);
731
732    if (all_same) {
733      PN->eraseFromParent();
734      return first;
735    } else {
736      return PN;
737    }
738  }
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  Value* v = performPHIConstruction(L->getParent(), L, repl);
769
770  MD.removeInstruction(L);
771  L->replaceAllUsesWith(v);
772  toErase.push_back(L);
773
774  return true;
775}
776
777bool GVN::processLoad(LoadInst* L,
778                         DenseMap<Value*, LoadInst*>& lastLoad,
779                         SmallVector<Instruction*, 4>& toErase) {
780  if (L->isVolatile()) {
781    lastLoad[L->getPointerOperand()] = L;
782    return false;
783  }
784
785  Value* pointer = L->getPointerOperand();
786  LoadInst*& last = lastLoad[pointer];
787
788  // ... to a pointer that has been loaded from before...
789  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
790  Instruction* dep = MD.getDependency(L);
791  if (dep == MemoryDependenceAnalysis::NonLocal &&
792      L->getParent() != &L->getParent()->getParent()->getEntryBlock())
793    processNonLocalLoad(L, toErase);
794  bool deletedLoad = false;
795
796  while (dep != MemoryDependenceAnalysis::None &&
797         dep != MemoryDependenceAnalysis::NonLocal &&
798         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
799    // ... that depends on a store ...
800    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
801      if (S->getPointerOperand() == pointer) {
802        // Remove it!
803        MD.removeInstruction(L);
804
805        L->replaceAllUsesWith(S->getOperand(0));
806        toErase.push_back(L);
807        deletedLoad = true;
808        NumGVNLoad++;
809      }
810
811      // Whether we removed it or not, we can't
812      // go any further
813      break;
814    } else if (!last) {
815      // If we don't depend on a store, and we haven't
816      // been loaded before, bail.
817      break;
818    } else if (dep == last) {
819      // Remove it!
820      MD.removeInstruction(L);
821
822      L->replaceAllUsesWith(last);
823      toErase.push_back(L);
824      deletedLoad = true;
825      NumGVNLoad++;
826
827      break;
828    } else {
829      dep = MD.getDependency(L, dep);
830    }
831  }
832
833  if (!deletedLoad)
834    last = L;
835
836  return deletedLoad;
837}
838
839/// buildsets_availout - When calculating availability, handle an instruction
840/// by inserting it into the appropriate sets
841bool GVN::processInstruction(Instruction* I,
842                                ValueNumberedSet& currAvail,
843                                DenseMap<Value*, LoadInst*>& lastSeenLoad,
844                                SmallVector<Instruction*, 4>& toErase) {
845  if (LoadInst* L = dyn_cast<LoadInst>(I)) {
846    return processLoad(L, lastSeenLoad, toErase);
847  }
848
849  unsigned num = VN.lookup_or_add(I);
850
851  if (currAvail.test(num)) {
852    Value* repl = find_leader(currAvail, num);
853
854    I->replaceAllUsesWith(repl);
855    toErase.push_back(I);
856    return true;
857  } else if (!I->isTerminator()) {
858    currAvail.set(num);
859    currAvail.insert(I);
860  }
861
862  return false;
863}
864
865// GVN::runOnFunction - This is the main transformation entry point for a
866// function.
867//
868bool GVN::runOnFunction(Function &F) {
869  // Clean out global sets from any previous functions
870  VN.clear();
871  availableOut.clear();
872
873  bool changed_function = false;
874
875  DominatorTree &DT = getAnalysis<DominatorTree>();
876
877  SmallVector<Instruction*, 4> toErase;
878
879  // Top-down walk of the dominator tree
880  for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
881         E = df_end(DT.getRootNode()); DI != E; ++DI) {
882
883    // Get the set to update for this block
884    ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
885    DenseMap<Value*, LoadInst*> lastSeenLoad;
886
887    BasicBlock* BB = DI->getBlock();
888
889    // A block inherits AVAIL_OUT from its dominator
890    if (DI->getIDom() != 0)
891      currAvail = availableOut[DI->getIDom()->getBlock()];
892
893    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
894         BI != BE; ++BI) {
895      changed_function |= processInstruction(BI, currAvail, lastSeenLoad, toErase);
896
897      NumGVNInstr += toErase.size();
898
899      for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
900           E = toErase.end(); I != E; ++I)
901        (*I)->eraseFromParent();
902
903      toErase.clear();
904    }
905  }
906
907  return changed_function;
908}
909