GVN.cpp revision 5fc4abac3db46b6e6b3824163c0f1252c1ab0ebb 
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/ADT/BitVector.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/Statistic.h"
30#include "llvm/Analysis/Dominators.h"
31#include "llvm/Analysis/AliasAnalysis.h"
32#include "llvm/Analysis/MemoryDependenceAnalysis.h"
33#include "llvm/Support/CFG.h"
34#include "llvm/Support/Compiler.h"
35using namespace llvm;
36
37//===----------------------------------------------------------------------===//
38//                         ValueTable Class
39//===----------------------------------------------------------------------===//
40
41/// This class holds the mapping between values and value numbers.  It is used
42/// as an efficient mechanism to determine the expression-wise equivalence of
43/// two values.
44namespace {
45  struct VISIBILITY_HIDDEN Expression {
46    enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
47                            FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
48                            ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
49                            ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
50                            FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
51                            FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
52                            FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
53                            SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
54                            FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
55                            PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, EMPTY,
56                            TOMBSTONE };
57
58    ExpressionOpcode opcode;
59    const Type* type;
60    uint32_t firstVN;
61    uint32_t secondVN;
62    uint32_t thirdVN;
63    SmallVector<uint32_t, 4> varargs;
64    Value* function;
65
66    Expression() { }
67    Expression(ExpressionOpcode o) : opcode(o) { }
68
69    bool operator==(const Expression &other) const {
70      if (opcode != other.opcode)
71        return false;
72      else if (opcode == EMPTY || opcode == TOMBSTONE)
73        return true;
74      else if (type != other.type)
75        return false;
76      else if (function != other.function)
77        return false;
78      else if (firstVN != other.firstVN)
79        return false;
80      else if (secondVN != other.secondVN)
81        return false;
82      else if (thirdVN != other.thirdVN)
83        return false;
84      else {
85        if (varargs.size() != other.varargs.size())
86          return false;
87
88        for (size_t i = 0; i < varargs.size(); ++i)
89          if (varargs[i] != other.varargs[i])
90            return false;
91
92        return true;
93      }
94    }
95
96    bool operator!=(const Expression &other) const {
97      if (opcode != other.opcode)
98        return true;
99      else if (opcode == EMPTY || opcode == TOMBSTONE)
100        return false;
101      else if (type != other.type)
102        return true;
103      else if (function != other.function)
104        return true;
105      else if (firstVN != other.firstVN)
106        return true;
107      else if (secondVN != other.secondVN)
108        return true;
109      else if (thirdVN != other.thirdVN)
110        return true;
111      else {
112        if (varargs.size() != other.varargs.size())
113          return true;
114
115        for (size_t i = 0; i < varargs.size(); ++i)
116          if (varargs[i] != other.varargs[i])
117            return true;
118
119          return false;
120      }
121    }
122  };
123
124  class VISIBILITY_HIDDEN ValueTable {
125    private:
126      DenseMap<Value*, uint32_t> valueNumbering;
127      DenseMap<Expression, uint32_t> expressionNumbering;
128      AliasAnalysis* AA;
129
130      uint32_t nextValueNumber;
131
132      Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
133      Expression::ExpressionOpcode getOpcode(CmpInst* C);
134      Expression::ExpressionOpcode getOpcode(CastInst* C);
135      Expression create_expression(BinaryOperator* BO);
136      Expression create_expression(CmpInst* C);
137      Expression create_expression(ShuffleVectorInst* V);
138      Expression create_expression(ExtractElementInst* C);
139      Expression create_expression(InsertElementInst* V);
140      Expression create_expression(SelectInst* V);
141      Expression create_expression(CastInst* C);
142      Expression create_expression(GetElementPtrInst* G);
143      Expression create_expression(CallInst* C);
144    public:
145      ValueTable() : nextValueNumber(1) { }
146      uint32_t lookup_or_add(Value* V);
147      uint32_t lookup(Value* V) const;
148      void add(Value* V, uint32_t num);
149      void clear();
150      void erase(Value* v);
151      unsigned size();
152      void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
153      uint32_t hash_operand(Value* v);
154  };
155}
156
157namespace llvm {
158template <> struct DenseMapInfo<Expression> {
159  static inline Expression getEmptyKey() {
160    return Expression(Expression::EMPTY);
161  }
162
163  static inline Expression getTombstoneKey() {
164    return Expression(Expression::TOMBSTONE);
165  }
166
167  static unsigned getHashValue(const Expression e) {
168    unsigned hash = e.opcode;
169
170    hash = e.firstVN + hash * 37;
171    hash = e.secondVN + hash * 37;
172    hash = e.thirdVN + hash * 37;
173
174    hash = (unsigned)((uintptr_t)e.type >> 4) ^
175            (unsigned)((uintptr_t)e.type >> 9) +
176            hash * 37;
177
178    for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
179         E = e.varargs.end(); I != E; ++I)
180      hash = *I + hash * 37;
181
182    hash = (unsigned)((uintptr_t)e.function >> 4) ^
183            (unsigned)((uintptr_t)e.function >> 9) +
184            hash * 37;
185
186    return hash;
187  }
188  static bool isEqual(const Expression &LHS, const Expression &RHS) {
189    return LHS == RHS;
190  }
191  static bool isPod() { return true; }
192};
193}
194
195//===----------------------------------------------------------------------===//
196//                     ValueTable Internal Functions
197//===----------------------------------------------------------------------===//
198Expression::ExpressionOpcode
199                             ValueTable::getOpcode(BinaryOperator* BO) {
200  switch(BO->getOpcode()) {
201    case Instruction::Add:
202      return Expression::ADD;
203    case Instruction::Sub:
204      return Expression::SUB;
205    case Instruction::Mul:
206      return Expression::MUL;
207    case Instruction::UDiv:
208      return Expression::UDIV;
209    case Instruction::SDiv:
210      return Expression::SDIV;
211    case Instruction::FDiv:
212      return Expression::FDIV;
213    case Instruction::URem:
214      return Expression::UREM;
215    case Instruction::SRem:
216      return Expression::SREM;
217    case Instruction::FRem:
218      return Expression::FREM;
219    case Instruction::Shl:
220      return Expression::SHL;
221    case Instruction::LShr:
222      return Expression::LSHR;
223    case Instruction::AShr:
224      return Expression::ASHR;
225    case Instruction::And:
226      return Expression::AND;
227    case Instruction::Or:
228      return Expression::OR;
229    case Instruction::Xor:
230      return Expression::XOR;
231
232    // THIS SHOULD NEVER HAPPEN
233    default:
234      assert(0 && "Binary operator with unknown opcode?");
235      return Expression::ADD;
236  }
237}
238
239Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
240  if (C->getOpcode() == Instruction::ICmp) {
241    switch (C->getPredicate()) {
242      case ICmpInst::ICMP_EQ:
243        return Expression::ICMPEQ;
244      case ICmpInst::ICMP_NE:
245        return Expression::ICMPNE;
246      case ICmpInst::ICMP_UGT:
247        return Expression::ICMPUGT;
248      case ICmpInst::ICMP_UGE:
249        return Expression::ICMPUGE;
250      case ICmpInst::ICMP_ULT:
251        return Expression::ICMPULT;
252      case ICmpInst::ICMP_ULE:
253        return Expression::ICMPULE;
254      case ICmpInst::ICMP_SGT:
255        return Expression::ICMPSGT;
256      case ICmpInst::ICMP_SGE:
257        return Expression::ICMPSGE;
258      case ICmpInst::ICMP_SLT:
259        return Expression::ICMPSLT;
260      case ICmpInst::ICMP_SLE:
261        return Expression::ICMPSLE;
262
263      // THIS SHOULD NEVER HAPPEN
264      default:
265        assert(0 && "Comparison with unknown predicate?");
266        return Expression::ICMPEQ;
267    }
268  } else {
269    switch (C->getPredicate()) {
270      case FCmpInst::FCMP_OEQ:
271        return Expression::FCMPOEQ;
272      case FCmpInst::FCMP_OGT:
273        return Expression::FCMPOGT;
274      case FCmpInst::FCMP_OGE:
275        return Expression::FCMPOGE;
276      case FCmpInst::FCMP_OLT:
277        return Expression::FCMPOLT;
278      case FCmpInst::FCMP_OLE:
279        return Expression::FCMPOLE;
280      case FCmpInst::FCMP_ONE:
281        return Expression::FCMPONE;
282      case FCmpInst::FCMP_ORD:
283        return Expression::FCMPORD;
284      case FCmpInst::FCMP_UNO:
285        return Expression::FCMPUNO;
286      case FCmpInst::FCMP_UEQ:
287        return Expression::FCMPUEQ;
288      case FCmpInst::FCMP_UGT:
289        return Expression::FCMPUGT;
290      case FCmpInst::FCMP_UGE:
291        return Expression::FCMPUGE;
292      case FCmpInst::FCMP_ULT:
293        return Expression::FCMPULT;
294      case FCmpInst::FCMP_ULE:
295        return Expression::FCMPULE;
296      case FCmpInst::FCMP_UNE:
297        return Expression::FCMPUNE;
298
299      // THIS SHOULD NEVER HAPPEN
300      default:
301        assert(0 && "Comparison with unknown predicate?");
302        return Expression::FCMPOEQ;
303    }
304  }
305}
306
307Expression::ExpressionOpcode
308                             ValueTable::getOpcode(CastInst* C) {
309  switch(C->getOpcode()) {
310    case Instruction::Trunc:
311      return Expression::TRUNC;
312    case Instruction::ZExt:
313      return Expression::ZEXT;
314    case Instruction::SExt:
315      return Expression::SEXT;
316    case Instruction::FPToUI:
317      return Expression::FPTOUI;
318    case Instruction::FPToSI:
319      return Expression::FPTOSI;
320    case Instruction::UIToFP:
321      return Expression::UITOFP;
322    case Instruction::SIToFP:
323      return Expression::SITOFP;
324    case Instruction::FPTrunc:
325      return Expression::FPTRUNC;
326    case Instruction::FPExt:
327      return Expression::FPEXT;
328    case Instruction::PtrToInt:
329      return Expression::PTRTOINT;
330    case Instruction::IntToPtr:
331      return Expression::INTTOPTR;
332    case Instruction::BitCast:
333      return Expression::BITCAST;
334
335    // THIS SHOULD NEVER HAPPEN
336    default:
337      assert(0 && "Cast operator with unknown opcode?");
338      return Expression::BITCAST;
339  }
340}
341
342uint32_t ValueTable::hash_operand(Value* v) {
343  if (CallInst* CI = dyn_cast<CallInst>(v))
344    if (!AA->doesNotAccessMemory(CI))
345      return nextValueNumber++;
346
347  return lookup_or_add(v);
348}
349
350Expression ValueTable::create_expression(CallInst* C) {
351  Expression e;
352
353  e.type = C->getType();
354  e.firstVN = 0;
355  e.secondVN = 0;
356  e.thirdVN = 0;
357  e.function = C->getCalledFunction();
358  e.opcode = Expression::CALL;
359
360  for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
361       I != E; ++I)
362    e.varargs.push_back(hash_operand(*I));
363
364  return e;
365}
366
367Expression ValueTable::create_expression(BinaryOperator* BO) {
368  Expression e;
369
370  e.firstVN = hash_operand(BO->getOperand(0));
371  e.secondVN = hash_operand(BO->getOperand(1));
372  e.thirdVN = 0;
373  e.function = 0;
374  e.type = BO->getType();
375  e.opcode = getOpcode(BO);
376
377  return e;
378}
379
380Expression ValueTable::create_expression(CmpInst* C) {
381  Expression e;
382
383  e.firstVN = hash_operand(C->getOperand(0));
384  e.secondVN = hash_operand(C->getOperand(1));
385  e.thirdVN = 0;
386  e.function = 0;
387  e.type = C->getType();
388  e.opcode = getOpcode(C);
389
390  return e;
391}
392
393Expression ValueTable::create_expression(CastInst* C) {
394  Expression e;
395
396  e.firstVN = hash_operand(C->getOperand(0));
397  e.secondVN = 0;
398  e.thirdVN = 0;
399  e.function = 0;
400  e.type = C->getType();
401  e.opcode = getOpcode(C);
402
403  return e;
404}
405
406Expression ValueTable::create_expression(ShuffleVectorInst* S) {
407  Expression e;
408
409  e.firstVN = hash_operand(S->getOperand(0));
410  e.secondVN = hash_operand(S->getOperand(1));
411  e.thirdVN = hash_operand(S->getOperand(2));
412  e.function = 0;
413  e.type = S->getType();
414  e.opcode = Expression::SHUFFLE;
415
416  return e;
417}
418
419Expression ValueTable::create_expression(ExtractElementInst* E) {
420  Expression e;
421
422  e.firstVN = hash_operand(E->getOperand(0));
423  e.secondVN = hash_operand(E->getOperand(1));
424  e.thirdVN = 0;
425  e.function = 0;
426  e.type = E->getType();
427  e.opcode = Expression::EXTRACT;
428
429  return e;
430}
431
432Expression ValueTable::create_expression(InsertElementInst* I) {
433  Expression e;
434
435  e.firstVN = hash_operand(I->getOperand(0));
436  e.secondVN = hash_operand(I->getOperand(1));
437  e.thirdVN = hash_operand(I->getOperand(2));
438  e.function = 0;
439  e.type = I->getType();
440  e.opcode = Expression::INSERT;
441
442  return e;
443}
444
445Expression ValueTable::create_expression(SelectInst* I) {
446  Expression e;
447
448  e.firstVN = hash_operand(I->getCondition());
449  e.secondVN = hash_operand(I->getTrueValue());
450  e.thirdVN = hash_operand(I->getFalseValue());
451  e.function = 0;
452  e.type = I->getType();
453  e.opcode = Expression::SELECT;
454
455  return e;
456}
457
458Expression ValueTable::create_expression(GetElementPtrInst* G) {
459  Expression e;
460
461  e.firstVN = hash_operand(G->getPointerOperand());
462  e.secondVN = 0;
463  e.thirdVN = 0;
464  e.function = 0;
465  e.type = G->getType();
466  e.opcode = Expression::GEP;
467
468  for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
469       I != E; ++I)
470    e.varargs.push_back(hash_operand(*I));
471
472  return e;
473}
474
475//===----------------------------------------------------------------------===//
476//                     ValueTable External Functions
477//===----------------------------------------------------------------------===//
478
479/// lookup_or_add - Returns the value number for the specified value, assigning
480/// it a new number if it did not have one before.
481uint32_t ValueTable::lookup_or_add(Value* V) {
482  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
483  if (VI != valueNumbering.end())
484    return VI->second;
485
486  if (CallInst* C = dyn_cast<CallInst>(V)) {
487    if (AA->onlyReadsMemory(C)) { // includes doesNotAccessMemory
488      Expression e = create_expression(C);
489
490      DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
491      if (EI != expressionNumbering.end()) {
492        valueNumbering.insert(std::make_pair(V, EI->second));
493        return EI->second;
494      } else {
495        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
496        valueNumbering.insert(std::make_pair(V, nextValueNumber));
497
498        return nextValueNumber++;
499      }
500    } else {
501      valueNumbering.insert(std::make_pair(V, nextValueNumber));
502      return nextValueNumber++;
503    }
504  } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
505    Expression e = create_expression(BO);
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 (CmpInst* C = dyn_cast<CmpInst>(V)) {
518    Expression e = create_expression(C);
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 (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(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 if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
544    Expression e = create_expression(U);
545
546    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
547    if (EI != expressionNumbering.end()) {
548      valueNumbering.insert(std::make_pair(V, EI->second));
549      return EI->second;
550    } else {
551      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
552      valueNumbering.insert(std::make_pair(V, nextValueNumber));
553
554      return nextValueNumber++;
555    }
556  } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
557    Expression e = create_expression(U);
558
559    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
560    if (EI != expressionNumbering.end()) {
561      valueNumbering.insert(std::make_pair(V, EI->second));
562      return EI->second;
563    } else {
564      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
565      valueNumbering.insert(std::make_pair(V, nextValueNumber));
566
567      return nextValueNumber++;
568    }
569  } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
570    Expression e = create_expression(U);
571
572    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
573    if (EI != expressionNumbering.end()) {
574      valueNumbering.insert(std::make_pair(V, EI->second));
575      return EI->second;
576    } else {
577      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
578      valueNumbering.insert(std::make_pair(V, nextValueNumber));
579
580      return nextValueNumber++;
581    }
582  } else if (CastInst* U = dyn_cast<CastInst>(V)) {
583    Expression e = create_expression(U);
584
585    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
586    if (EI != expressionNumbering.end()) {
587      valueNumbering.insert(std::make_pair(V, EI->second));
588      return EI->second;
589    } else {
590      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
591      valueNumbering.insert(std::make_pair(V, nextValueNumber));
592
593      return nextValueNumber++;
594    }
595  } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
596    Expression e = create_expression(U);
597
598    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
599    if (EI != expressionNumbering.end()) {
600      valueNumbering.insert(std::make_pair(V, EI->second));
601      return EI->second;
602    } else {
603      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
604      valueNumbering.insert(std::make_pair(V, nextValueNumber));
605
606      return nextValueNumber++;
607    }
608  } else {
609    valueNumbering.insert(std::make_pair(V, nextValueNumber));
610    return nextValueNumber++;
611  }
612}
613
614/// lookup - Returns the value number of the specified value. Fails if
615/// the value has not yet been numbered.
616uint32_t ValueTable::lookup(Value* V) const {
617  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
618  if (VI != valueNumbering.end())
619    return VI->second;
620  else
621    assert(0 && "Value not numbered?");
622
623  return 0;
624}
625
626/// clear - Remove all entries from the ValueTable
627void ValueTable::clear() {
628  valueNumbering.clear();
629  expressionNumbering.clear();
630  nextValueNumber = 1;
631}
632
633/// erase - Remove a value from the value numbering
634void ValueTable::erase(Value* V) {
635  valueNumbering.erase(V);
636}
637
638//===----------------------------------------------------------------------===//
639//                       ValueNumberedSet Class
640//===----------------------------------------------------------------------===//
641namespace {
642class ValueNumberedSet {
643  private:
644    SmallPtrSet<Value*, 8> contents;
645    BitVector numbers;
646  public:
647    ValueNumberedSet() { numbers.resize(1); }
648    ValueNumberedSet(const ValueNumberedSet& other) {
649      numbers = other.numbers;
650      contents = other.contents;
651    }
652
653    typedef SmallPtrSet<Value*, 8>::iterator iterator;
654
655    iterator begin() { return contents.begin(); }
656    iterator end() { return contents.end(); }
657
658    bool insert(Value* v) { return contents.insert(v); }
659    void insert(iterator I, iterator E) { contents.insert(I, E); }
660    void erase(Value* v) { contents.erase(v); }
661    unsigned count(Value* v) { return contents.count(v); }
662    size_t size() { return contents.size(); }
663
664    void set(unsigned i)  {
665      if (i >= numbers.size())
666        numbers.resize(i+1);
667
668      numbers.set(i);
669    }
670
671    void operator=(const ValueNumberedSet& other) {
672      contents = other.contents;
673      numbers = other.numbers;
674    }
675
676    void reset(unsigned i)  {
677      if (i < numbers.size())
678        numbers.reset(i);
679    }
680
681    bool test(unsigned i)  {
682      if (i >= numbers.size())
683        return false;
684
685      return numbers.test(i);
686    }
687
688    void clear() {
689      contents.clear();
690      numbers.clear();
691    }
692};
693}
694
695//===----------------------------------------------------------------------===//
696//                         GVN Pass
697//===----------------------------------------------------------------------===//
698
699namespace {
700
701  class VISIBILITY_HIDDEN GVN : public FunctionPass {
702    bool runOnFunction(Function &F);
703  public:
704    static char ID; // Pass identification, replacement for typeid
705    GVN() : FunctionPass((intptr_t)&ID) { }
706
707  private:
708    ValueTable VN;
709
710    DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
711
712    typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
713    PhiMapType phiMap;
714
715
716    // This transformation requires dominator postdominator info
717    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
718      AU.setPreservesCFG();
719      AU.addRequired<DominatorTree>();
720      AU.addRequired<MemoryDependenceAnalysis>();
721      AU.addRequired<AliasAnalysis>();
722      AU.addPreserved<AliasAnalysis>();
723      AU.addPreserved<MemoryDependenceAnalysis>();
724    }
725
726    // Helper fuctions
727    // FIXME: eliminate or document these better
728    Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
729    void val_insert(ValueNumberedSet& s, Value* v);
730    bool processLoad(LoadInst* L,
731                     DenseMap<Value*, LoadInst*>& lastLoad,
732                     SmallVector<Instruction*, 4>& toErase);
733    bool processInstruction(Instruction* I,
734                            ValueNumberedSet& currAvail,
735                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
736                            SmallVector<Instruction*, 4>& toErase);
737    bool processNonLocalLoad(LoadInst* L,
738                             SmallVector<Instruction*, 4>& toErase);
739    Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
740                            DenseMap<BasicBlock*, Value*> &Phis,
741                            bool top_level = false);
742    void dump(DenseMap<BasicBlock*, Value*>& d);
743    bool iterateOnFunction(Function &F);
744    Value* CollapsePhi(PHINode* p);
745    bool isSafeReplacement(PHINode* p, Instruction* inst);
746  };
747
748  char GVN::ID = 0;
749
750}
751
752// createGVNPass - The public interface to this file...
753FunctionPass *llvm::createGVNPass() { return new GVN(); }
754
755static RegisterPass<GVN> X("gvn",
756                           "Global Value Numbering");
757
758STATISTIC(NumGVNInstr, "Number of instructions deleted");
759STATISTIC(NumGVNLoad, "Number of loads deleted");
760
761/// find_leader - Given a set and a value number, return the first
762/// element of the set with that value number, or 0 if no such element
763/// is present
764Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
765  if (!vals.test(v))
766    return 0;
767
768  for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
769       I != E; ++I)
770    if (v == VN.lookup(*I))
771      return *I;
772
773  assert(0 && "No leader found, but present bit is set?");
774  return 0;
775}
776
777/// val_insert - Insert a value into a set only if there is not a value
778/// with the same value number already in the set
779void GVN::val_insert(ValueNumberedSet& s, Value* v) {
780  uint32_t num = VN.lookup(v);
781  if (!s.test(num))
782    s.insert(v);
783}
784
785void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
786  printf("{\n");
787  for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
788       E = d.end(); I != E; ++I) {
789    if (I->second == MemoryDependenceAnalysis::None)
790      printf("None\n");
791    else
792      I->second->dump();
793  }
794  printf("}\n");
795}
796
797Value* GVN::CollapsePhi(PHINode* p) {
798  DominatorTree &DT = getAnalysis<DominatorTree>();
799  Value* constVal = p->hasConstantValue();
800
801  if (constVal) {
802    if (Instruction* inst = dyn_cast<Instruction>(constVal)) {
803      if (DT.dominates(inst, p))
804        if (isSafeReplacement(p, inst))
805          return inst;
806    } else {
807      return constVal;
808    }
809  }
810
811  return 0;
812}
813
814bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
815  if (!isa<PHINode>(inst))
816    return true;
817
818  for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
819       UI != E; ++UI)
820    if (PHINode* use_phi = dyn_cast<PHINode>(UI))
821      if (use_phi->getParent() == inst->getParent())
822        return false;
823
824  return true;
825}
826
827/// GetValueForBlock - Get the value to use within the specified basic block.
828/// available values are in Phis.
829Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
830                               DenseMap<BasicBlock*, Value*> &Phis,
831                               bool top_level) {
832
833  // If we have already computed this value, return the previously computed val.
834  DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
835  if (V != Phis.end() && !top_level) return V->second;
836
837  BasicBlock* singlePred = BB->getSinglePredecessor();
838  if (singlePred) {
839    Value *ret = GetValueForBlock(singlePred, orig, Phis);
840    Phis[BB] = ret;
841    return ret;
842  }
843  // Otherwise, the idom is the loop, so we need to insert a PHI node.  Do so
844  // now, then get values to fill in the incoming values for the PHI.
845  PHINode *PN = new PHINode(orig->getType(), orig->getName()+".rle",
846                            BB->begin());
847  PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
848
849  if (Phis.count(BB) == 0)
850    Phis.insert(std::make_pair(BB, PN));
851
852  // Fill in the incoming values for the block.
853  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
854    Value* val = GetValueForBlock(*PI, orig, Phis);
855
856    PN->addIncoming(val, *PI);
857  }
858
859  // Attempt to collapse PHI nodes that are trivially redundant
860  Value* v = CollapsePhi(PN);
861  if (v) {
862    MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
863
864    MD.removeInstruction(PN);
865    PN->replaceAllUsesWith(v);
866
867    for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
868         E = Phis.end(); I != E; ++I)
869      if (I->second == PN)
870        I->second = v;
871
872    PN->eraseFromParent();
873
874    Phis[BB] = v;
875
876    return v;
877  }
878
879  // Cache our phi construction results
880  phiMap[orig->getPointerOperand()].insert(PN);
881  return PN;
882}
883
884/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
885/// non-local by performing PHI construction.
886bool GVN::processNonLocalLoad(LoadInst* L,
887                              SmallVector<Instruction*, 4>& toErase) {
888  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
889
890  // Find the non-local dependencies of the load
891  DenseMap<BasicBlock*, Value*> deps;
892  MD.getNonLocalDependency(L, deps);
893
894  DenseMap<BasicBlock*, Value*> repl;
895
896  // Filter out useless results (non-locals, etc)
897  for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
898       I != E; ++I)
899    if (I->second == MemoryDependenceAnalysis::None) {
900      return false;
901    } else if (I->second == MemoryDependenceAnalysis::NonLocal) {
902      continue;
903    } else if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
904      if (S->getPointerOperand() == L->getPointerOperand())
905        repl[I->first] = S->getOperand(0);
906      else
907        return false;
908    } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
909      if (LD->getPointerOperand() == L->getPointerOperand())
910        repl[I->first] = LD;
911      else
912        return false;
913    } else {
914      return false;
915    }
916
917  // Use cached PHI construction information from previous runs
918  SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
919  for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
920       I != E; ++I) {
921    if ((*I)->getParent() == L->getParent()) {
922      MD.removeInstruction(L);
923      L->replaceAllUsesWith(*I);
924      toErase.push_back(L);
925      NumGVNLoad++;
926
927      return true;
928    } else {
929      repl.insert(std::make_pair((*I)->getParent(), *I));
930    }
931  }
932
933  // Perform PHI construction
934  SmallPtrSet<BasicBlock*, 4> visited;
935  Value* v = GetValueForBlock(L->getParent(), L, repl, true);
936
937  MD.removeInstruction(L);
938  L->replaceAllUsesWith(v);
939  toErase.push_back(L);
940  NumGVNLoad++;
941
942  return true;
943}
944
945/// processLoad - Attempt to eliminate a load, first by eliminating it
946/// locally, and then attempting non-local elimination if that fails.
947bool GVN::processLoad(LoadInst* L,
948                         DenseMap<Value*, LoadInst*>& lastLoad,
949                         SmallVector<Instruction*, 4>& toErase) {
950  if (L->isVolatile()) {
951    lastLoad[L->getPointerOperand()] = L;
952    return false;
953  }
954
955  Value* pointer = L->getPointerOperand();
956  LoadInst*& last = lastLoad[pointer];
957
958  // ... to a pointer that has been loaded from before...
959  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
960  bool removedNonLocal = false;
961  Instruction* dep = MD.getDependency(L);
962  if (dep == MemoryDependenceAnalysis::NonLocal &&
963      L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
964    removedNonLocal = processNonLocalLoad(L, toErase);
965
966    if (!removedNonLocal)
967      last = L;
968
969    return removedNonLocal;
970  }
971
972
973  bool deletedLoad = false;
974
975  // Walk up the dependency chain until we either find
976  // a dependency we can use, or we can't walk any further
977  while (dep != MemoryDependenceAnalysis::None &&
978         dep != MemoryDependenceAnalysis::NonLocal &&
979         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
980    // ... that depends on a store ...
981    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
982      if (S->getPointerOperand() == pointer) {
983        // Remove it!
984        MD.removeInstruction(L);
985
986        L->replaceAllUsesWith(S->getOperand(0));
987        toErase.push_back(L);
988        deletedLoad = true;
989        NumGVNLoad++;
990      }
991
992      // Whether we removed it or not, we can't
993      // go any further
994      break;
995    } else if (!last) {
996      // If we don't depend on a store, and we haven't
997      // been loaded before, bail.
998      break;
999    } else if (dep == last) {
1000      // Remove it!
1001      MD.removeInstruction(L);
1002
1003      L->replaceAllUsesWith(last);
1004      toErase.push_back(L);
1005      deletedLoad = true;
1006      NumGVNLoad++;
1007
1008      break;
1009    } else {
1010      dep = MD.getDependency(L, dep);
1011    }
1012  }
1013
1014  if (!deletedLoad)
1015    last = L;
1016
1017  return deletedLoad;
1018}
1019
1020/// processInstruction - When calculating availability, handle an instruction
1021/// by inserting it into the appropriate sets
1022bool GVN::processInstruction(Instruction* I,
1023                                ValueNumberedSet& currAvail,
1024                                DenseMap<Value*, LoadInst*>& lastSeenLoad,
1025                                SmallVector<Instruction*, 4>& toErase) {
1026  if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1027    return processLoad(L, lastSeenLoad, toErase);
1028  }
1029
1030  unsigned num = VN.lookup_or_add(I);
1031
1032  // Collapse PHI nodes
1033  if (PHINode* p = dyn_cast<PHINode>(I)) {
1034    Value* constVal = CollapsePhi(p);
1035
1036    if (constVal) {
1037      for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1038           PI != PE; ++PI)
1039        if (PI->second.count(p))
1040          PI->second.erase(p);
1041
1042      p->replaceAllUsesWith(constVal);
1043      toErase.push_back(p);
1044    }
1045  // Perform value-number based elimination
1046  } else if (currAvail.test(num)) {
1047    Value* repl = find_leader(currAvail, num);
1048
1049    if (CallInst* CI = dyn_cast<CallInst>(I)) {
1050      AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
1051      if (!AA.doesNotAccessMemory(CI)) {
1052        MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1053        if (cast<Instruction>(repl)->getParent() != CI->getParent() ||
1054            MD.getDependency(CI) != MD.getDependency(cast<CallInst>(repl))) {
1055          // There must be an intervening may-alias store, so nothing from
1056          // this point on will be able to be replaced with the preceding call
1057          currAvail.erase(repl);
1058          currAvail.insert(I);
1059
1060          return false;
1061        }
1062      }
1063    }
1064
1065    // Remove it!
1066    MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1067    MD.removeInstruction(I);
1068
1069    VN.erase(I);
1070    I->replaceAllUsesWith(repl);
1071    toErase.push_back(I);
1072    return true;
1073  } else if (!I->isTerminator()) {
1074    currAvail.set(num);
1075    currAvail.insert(I);
1076  }
1077
1078  return false;
1079}
1080
1081// GVN::runOnFunction - This is the main transformation entry point for a
1082// function.
1083//
1084bool GVN::runOnFunction(Function& F) {
1085  VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1086
1087  bool changed = false;
1088  bool shouldContinue = true;
1089
1090  while (shouldContinue) {
1091    shouldContinue = iterateOnFunction(F);
1092    changed |= shouldContinue;
1093  }
1094
1095  return changed;
1096}
1097
1098
1099// GVN::iterateOnFunction - Executes one iteration of GVN
1100bool GVN::iterateOnFunction(Function &F) {
1101  // Clean out global sets from any previous functions
1102  VN.clear();
1103  availableOut.clear();
1104  phiMap.clear();
1105
1106  bool changed_function = false;
1107
1108  DominatorTree &DT = getAnalysis<DominatorTree>();
1109
1110  SmallVector<Instruction*, 4> toErase;
1111
1112  // Top-down walk of the dominator tree
1113  for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
1114         E = df_end(DT.getRootNode()); DI != E; ++DI) {
1115
1116    // Get the set to update for this block
1117    ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
1118    DenseMap<Value*, LoadInst*> lastSeenLoad;
1119
1120    BasicBlock* BB = DI->getBlock();
1121
1122    // A block inherits AVAIL_OUT from its dominator
1123    if (DI->getIDom() != 0)
1124      currAvail = availableOut[DI->getIDom()->getBlock()];
1125
1126    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1127         BI != BE; ) {
1128      changed_function |= processInstruction(BI, currAvail,
1129                                             lastSeenLoad, toErase);
1130
1131      NumGVNInstr += toErase.size();
1132
1133      // Avoid iterator invalidation
1134      ++BI;
1135
1136      for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1137           E = toErase.end(); I != E; ++I)
1138        (*I)->eraseFromParent();
1139
1140      toErase.clear();
1141    }
1142  }
1143
1144  return changed_function;
1145}
1146