GVN.cpp revision 1fb136464deda4feb6724c9874d17eb4867633c0 
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 (CI->getCalledFunction() &&
345        !AA->doesNotAccessMemory(CI->getCalledFunction()))
346      return nextValueNumber++;
347
348  return lookup_or_add(v);
349}
350
351Expression ValueTable::create_expression(CallInst* C) {
352  Expression e;
353
354  e.type = C->getType();
355  e.firstVN = 0;
356  e.secondVN = 0;
357  e.thirdVN = 0;
358  e.function = C->getCalledFunction();
359  e.opcode = Expression::CALL;
360
361  for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
362       I != E; ++I)
363    e.varargs.push_back(hash_operand(*I));
364
365  return e;
366}
367
368Expression ValueTable::create_expression(BinaryOperator* BO) {
369  Expression e;
370
371  e.firstVN = hash_operand(BO->getOperand(0));
372  e.secondVN = hash_operand(BO->getOperand(1));
373  e.thirdVN = 0;
374  e.function = 0;
375  e.type = BO->getType();
376  e.opcode = getOpcode(BO);
377
378  return e;
379}
380
381Expression ValueTable::create_expression(CmpInst* C) {
382  Expression e;
383
384  e.firstVN = hash_operand(C->getOperand(0));
385  e.secondVN = hash_operand(C->getOperand(1));
386  e.thirdVN = 0;
387  e.function = 0;
388  e.type = C->getType();
389  e.opcode = getOpcode(C);
390
391  return e;
392}
393
394Expression ValueTable::create_expression(CastInst* C) {
395  Expression e;
396
397  e.firstVN = hash_operand(C->getOperand(0));
398  e.secondVN = 0;
399  e.thirdVN = 0;
400  e.function = 0;
401  e.type = C->getType();
402  e.opcode = getOpcode(C);
403
404  return e;
405}
406
407Expression ValueTable::create_expression(ShuffleVectorInst* S) {
408  Expression e;
409
410  e.firstVN = hash_operand(S->getOperand(0));
411  e.secondVN = hash_operand(S->getOperand(1));
412  e.thirdVN = hash_operand(S->getOperand(2));
413  e.function = 0;
414  e.type = S->getType();
415  e.opcode = Expression::SHUFFLE;
416
417  return e;
418}
419
420Expression ValueTable::create_expression(ExtractElementInst* E) {
421  Expression e;
422
423  e.firstVN = hash_operand(E->getOperand(0));
424  e.secondVN = hash_operand(E->getOperand(1));
425  e.thirdVN = 0;
426  e.function = 0;
427  e.type = E->getType();
428  e.opcode = Expression::EXTRACT;
429
430  return e;
431}
432
433Expression ValueTable::create_expression(InsertElementInst* I) {
434  Expression e;
435
436  e.firstVN = hash_operand(I->getOperand(0));
437  e.secondVN = hash_operand(I->getOperand(1));
438  e.thirdVN = hash_operand(I->getOperand(2));
439  e.function = 0;
440  e.type = I->getType();
441  e.opcode = Expression::INSERT;
442
443  return e;
444}
445
446Expression ValueTable::create_expression(SelectInst* I) {
447  Expression e;
448
449  e.firstVN = hash_operand(I->getCondition());
450  e.secondVN = hash_operand(I->getTrueValue());
451  e.thirdVN = hash_operand(I->getFalseValue());
452  e.function = 0;
453  e.type = I->getType();
454  e.opcode = Expression::SELECT;
455
456  return e;
457}
458
459Expression ValueTable::create_expression(GetElementPtrInst* G) {
460  Expression e;
461
462  e.firstVN = hash_operand(G->getPointerOperand());
463  e.secondVN = 0;
464  e.thirdVN = 0;
465  e.function = 0;
466  e.type = G->getType();
467  e.opcode = Expression::GEP;
468
469  for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
470       I != E; ++I)
471    e.varargs.push_back(hash_operand(*I));
472
473  return e;
474}
475
476//===----------------------------------------------------------------------===//
477//                     ValueTable External Functions
478//===----------------------------------------------------------------------===//
479
480/// lookup_or_add - Returns the value number for the specified value, assigning
481/// it a new number if it did not have one before.
482uint32_t ValueTable::lookup_or_add(Value* V) {
483  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
484  if (VI != valueNumbering.end())
485    return VI->second;
486
487  if (CallInst* C = dyn_cast<CallInst>(V)) {
488    if (C->getCalledFunction() &&
489        (AA->doesNotAccessMemory(C->getCalledFunction()) ||
490         AA->onlyReadsMemory(C->getCalledFunction()))) {
491      Expression e = create_expression(C);
492
493      DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
494      if (EI != expressionNumbering.end()) {
495        valueNumbering.insert(std::make_pair(V, EI->second));
496        return EI->second;
497      } else {
498        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
499        valueNumbering.insert(std::make_pair(V, nextValueNumber));
500
501        return nextValueNumber++;
502      }
503    } else {
504      valueNumbering.insert(std::make_pair(V, nextValueNumber));
505      return nextValueNumber++;
506    }
507  } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
508    Expression e = create_expression(BO);
509
510    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
511    if (EI != expressionNumbering.end()) {
512      valueNumbering.insert(std::make_pair(V, EI->second));
513      return EI->second;
514    } else {
515      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
516      valueNumbering.insert(std::make_pair(V, nextValueNumber));
517
518      return nextValueNumber++;
519    }
520  } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
521    Expression e = create_expression(C);
522
523    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
524    if (EI != expressionNumbering.end()) {
525      valueNumbering.insert(std::make_pair(V, EI->second));
526      return EI->second;
527    } else {
528      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
529      valueNumbering.insert(std::make_pair(V, nextValueNumber));
530
531      return nextValueNumber++;
532    }
533  } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
534    Expression e = create_expression(U);
535
536    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
537    if (EI != expressionNumbering.end()) {
538      valueNumbering.insert(std::make_pair(V, EI->second));
539      return EI->second;
540    } else {
541      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
542      valueNumbering.insert(std::make_pair(V, nextValueNumber));
543
544      return nextValueNumber++;
545    }
546  } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
547    Expression e = create_expression(U);
548
549    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
550    if (EI != expressionNumbering.end()) {
551      valueNumbering.insert(std::make_pair(V, EI->second));
552      return EI->second;
553    } else {
554      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
555      valueNumbering.insert(std::make_pair(V, nextValueNumber));
556
557      return nextValueNumber++;
558    }
559  } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
560    Expression e = create_expression(U);
561
562    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
563    if (EI != expressionNumbering.end()) {
564      valueNumbering.insert(std::make_pair(V, EI->second));
565      return EI->second;
566    } else {
567      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
568      valueNumbering.insert(std::make_pair(V, nextValueNumber));
569
570      return nextValueNumber++;
571    }
572  } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
573    Expression e = create_expression(U);
574
575    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
576    if (EI != expressionNumbering.end()) {
577      valueNumbering.insert(std::make_pair(V, EI->second));
578      return EI->second;
579    } else {
580      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
581      valueNumbering.insert(std::make_pair(V, nextValueNumber));
582
583      return nextValueNumber++;
584    }
585  } else if (CastInst* U = dyn_cast<CastInst>(V)) {
586    Expression e = create_expression(U);
587
588    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
589    if (EI != expressionNumbering.end()) {
590      valueNumbering.insert(std::make_pair(V, EI->second));
591      return EI->second;
592    } else {
593      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
594      valueNumbering.insert(std::make_pair(V, nextValueNumber));
595
596      return nextValueNumber++;
597    }
598  } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
599    Expression e = create_expression(U);
600
601    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
602    if (EI != expressionNumbering.end()) {
603      valueNumbering.insert(std::make_pair(V, EI->second));
604      return EI->second;
605    } else {
606      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
607      valueNumbering.insert(std::make_pair(V, nextValueNumber));
608
609      return nextValueNumber++;
610    }
611  } else {
612    valueNumbering.insert(std::make_pair(V, nextValueNumber));
613    return nextValueNumber++;
614  }
615}
616
617/// lookup - Returns the value number of the specified value. Fails if
618/// the value has not yet been numbered.
619uint32_t ValueTable::lookup(Value* V) const {
620  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
621  if (VI != valueNumbering.end())
622    return VI->second;
623  else
624    assert(0 && "Value not numbered?");
625
626  return 0;
627}
628
629/// clear - Remove all entries from the ValueTable
630void ValueTable::clear() {
631  valueNumbering.clear();
632  expressionNumbering.clear();
633  nextValueNumber = 1;
634}
635
636/// erase - Remove a value from the value numbering
637void ValueTable::erase(Value* V) {
638  valueNumbering.erase(V);
639}
640
641//===----------------------------------------------------------------------===//
642//                       ValueNumberedSet Class
643//===----------------------------------------------------------------------===//
644namespace {
645class ValueNumberedSet {
646  private:
647    SmallPtrSet<Value*, 8> contents;
648    BitVector numbers;
649  public:
650    ValueNumberedSet() { numbers.resize(1); }
651    ValueNumberedSet(const ValueNumberedSet& other) {
652      numbers = other.numbers;
653      contents = other.contents;
654    }
655
656    typedef SmallPtrSet<Value*, 8>::iterator iterator;
657
658    iterator begin() { return contents.begin(); }
659    iterator end() { return contents.end(); }
660
661    bool insert(Value* v) { return contents.insert(v); }
662    void insert(iterator I, iterator E) { contents.insert(I, E); }
663    void erase(Value* v) { contents.erase(v); }
664    unsigned count(Value* v) { return contents.count(v); }
665    size_t size() { return contents.size(); }
666
667    void set(unsigned i)  {
668      if (i >= numbers.size())
669        numbers.resize(i+1);
670
671      numbers.set(i);
672    }
673
674    void operator=(const ValueNumberedSet& other) {
675      contents = other.contents;
676      numbers = other.numbers;
677    }
678
679    void reset(unsigned i)  {
680      if (i < numbers.size())
681        numbers.reset(i);
682    }
683
684    bool test(unsigned i)  {
685      if (i >= numbers.size())
686        return false;
687
688      return numbers.test(i);
689    }
690
691    void clear() {
692      contents.clear();
693      numbers.clear();
694    }
695};
696}
697
698//===----------------------------------------------------------------------===//
699//                         GVN Pass
700//===----------------------------------------------------------------------===//
701
702namespace {
703
704  class VISIBILITY_HIDDEN GVN : public FunctionPass {
705    bool runOnFunction(Function &F);
706  public:
707    static char ID; // Pass identification, replacement for typeid
708    GVN() : FunctionPass((intptr_t)&ID) { }
709
710  private:
711    ValueTable VN;
712
713    DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
714
715    typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
716    PhiMapType phiMap;
717
718
719    // This transformation requires dominator postdominator info
720    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
721      AU.setPreservesCFG();
722      AU.addRequired<DominatorTree>();
723      AU.addRequired<MemoryDependenceAnalysis>();
724      AU.addRequired<AliasAnalysis>();
725      AU.addPreserved<AliasAnalysis>();
726      AU.addPreserved<MemoryDependenceAnalysis>();
727    }
728
729    // Helper fuctions
730    // FIXME: eliminate or document these better
731    Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
732    void val_insert(ValueNumberedSet& s, Value* v);
733    bool processLoad(LoadInst* L,
734                     DenseMap<Value*, LoadInst*>& lastLoad,
735                     SmallVector<Instruction*, 4>& toErase);
736    bool processInstruction(Instruction* I,
737                            ValueNumberedSet& currAvail,
738                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
739                            SmallVector<Instruction*, 4>& toErase);
740    bool processNonLocalLoad(LoadInst* L,
741                             SmallVector<Instruction*, 4>& toErase);
742    Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
743                            DenseMap<BasicBlock*, Value*> &Phis,
744                            bool top_level = false);
745    void dump(DenseMap<BasicBlock*, Value*>& d);
746    bool iterateOnFunction(Function &F);
747    Value* CollapsePhi(PHINode* p);
748    bool isSafeReplacement(PHINode* p, Instruction* inst);
749  };
750
751  char GVN::ID = 0;
752
753}
754
755// createGVNPass - The public interface to this file...
756FunctionPass *llvm::createGVNPass() { return new GVN(); }
757
758static RegisterPass<GVN> X("gvn",
759                           "Global Value Numbering");
760
761STATISTIC(NumGVNInstr, "Number of instructions deleted");
762STATISTIC(NumGVNLoad, "Number of loads deleted");
763
764/// find_leader - Given a set and a value number, return the first
765/// element of the set with that value number, or 0 if no such element
766/// is present
767Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
768  if (!vals.test(v))
769    return 0;
770
771  for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
772       I != E; ++I)
773    if (v == VN.lookup(*I))
774      return *I;
775
776  assert(0 && "No leader found, but present bit is set?");
777  return 0;
778}
779
780/// val_insert - Insert a value into a set only if there is not a value
781/// with the same value number already in the set
782void GVN::val_insert(ValueNumberedSet& s, Value* v) {
783  uint32_t num = VN.lookup(v);
784  if (!s.test(num))
785    s.insert(v);
786}
787
788void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
789  printf("{\n");
790  for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
791       E = d.end(); I != E; ++I) {
792    if (I->second == MemoryDependenceAnalysis::None)
793      printf("None\n");
794    else
795      I->second->dump();
796  }
797  printf("}\n");
798}
799
800Value* GVN::CollapsePhi(PHINode* p) {
801  DominatorTree &DT = getAnalysis<DominatorTree>();
802  Value* constVal = p->hasConstantValue();
803
804  if (constVal) {
805    if (Instruction* inst = dyn_cast<Instruction>(constVal)) {
806      if (DT.dominates(inst, p))
807        if (isSafeReplacement(p, inst))
808          return inst;
809    } else {
810      return constVal;
811    }
812  }
813
814  return 0;
815}
816
817bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
818  if (!isa<PHINode>(inst))
819    return true;
820
821  for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
822       UI != E; ++UI)
823    if (PHINode* use_phi = dyn_cast<PHINode>(UI))
824      if (use_phi->getParent() == inst->getParent())
825        return false;
826
827  return true;
828}
829
830/// GetValueForBlock - Get the value to use within the specified basic block.
831/// available values are in Phis.
832Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
833                               DenseMap<BasicBlock*, Value*> &Phis,
834                               bool top_level) {
835
836  // If we have already computed this value, return the previously computed val.
837  DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
838  if (V != Phis.end() && !top_level) return V->second;
839
840  BasicBlock* singlePred = BB->getSinglePredecessor();
841  if (singlePred) {
842    Value *ret = GetValueForBlock(singlePred, orig, Phis);
843    Phis[BB] = ret;
844    return ret;
845  }
846  // Otherwise, the idom is the loop, so we need to insert a PHI node.  Do so
847  // now, then get values to fill in the incoming values for the PHI.
848  PHINode *PN = new PHINode(orig->getType(), orig->getName()+".rle",
849                            BB->begin());
850  PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
851
852  if (Phis.count(BB) == 0)
853    Phis.insert(std::make_pair(BB, PN));
854
855  // Fill in the incoming values for the block.
856  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
857    Value* val = GetValueForBlock(*PI, orig, Phis);
858
859    PN->addIncoming(val, *PI);
860  }
861
862  // Attempt to collapse PHI nodes that are trivially redundant
863  Value* v = CollapsePhi(PN);
864  if (v) {
865    MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
866
867    MD.removeInstruction(PN);
868    PN->replaceAllUsesWith(v);
869
870    for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
871         E = Phis.end(); I != E; ++I)
872      if (I->second == PN)
873        I->second = v;
874
875    PN->eraseFromParent();
876
877    Phis[BB] = v;
878
879    return v;
880  }
881
882  // Cache our phi construction results
883  phiMap[orig->getPointerOperand()].insert(PN);
884  return PN;
885}
886
887/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
888/// non-local by performing PHI construction.
889bool GVN::processNonLocalLoad(LoadInst* L,
890                              SmallVector<Instruction*, 4>& toErase) {
891  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
892
893  // Find the non-local dependencies of the load
894  DenseMap<BasicBlock*, Value*> deps;
895  MD.getNonLocalDependency(L, deps);
896
897  DenseMap<BasicBlock*, Value*> repl;
898
899  // Filter out useless results (non-locals, etc)
900  for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
901       I != E; ++I)
902    if (I->second == MemoryDependenceAnalysis::None) {
903      return false;
904    } else if (I->second == MemoryDependenceAnalysis::NonLocal) {
905      continue;
906    } else if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
907      if (S->getPointerOperand() == L->getPointerOperand())
908        repl[I->first] = S->getOperand(0);
909      else
910        return false;
911    } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
912      if (LD->getPointerOperand() == L->getPointerOperand())
913        repl[I->first] = LD;
914      else
915        return false;
916    } else {
917      return false;
918    }
919
920  // Use cached PHI construction information from previous runs
921  SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
922  for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
923       I != E; ++I) {
924    if ((*I)->getParent() == L->getParent()) {
925      MD.removeInstruction(L);
926      L->replaceAllUsesWith(*I);
927      toErase.push_back(L);
928      NumGVNLoad++;
929
930      return true;
931    } else {
932      repl.insert(std::make_pair((*I)->getParent(), *I));
933    }
934  }
935
936  // Perform PHI construction
937  SmallPtrSet<BasicBlock*, 4> visited;
938  Value* v = GetValueForBlock(L->getParent(), L, repl, true);
939
940  MD.removeInstruction(L);
941  L->replaceAllUsesWith(v);
942  toErase.push_back(L);
943  NumGVNLoad++;
944
945  return true;
946}
947
948/// processLoad - Attempt to eliminate a load, first by eliminating it
949/// locally, and then attempting non-local elimination if that fails.
950bool GVN::processLoad(LoadInst* L,
951                         DenseMap<Value*, LoadInst*>& lastLoad,
952                         SmallVector<Instruction*, 4>& toErase) {
953  if (L->isVolatile()) {
954    lastLoad[L->getPointerOperand()] = L;
955    return false;
956  }
957
958  Value* pointer = L->getPointerOperand();
959  LoadInst*& last = lastLoad[pointer];
960
961  // ... to a pointer that has been loaded from before...
962  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
963  bool removedNonLocal = false;
964  Instruction* dep = MD.getDependency(L);
965  if (dep == MemoryDependenceAnalysis::NonLocal &&
966      L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
967    removedNonLocal = processNonLocalLoad(L, toErase);
968
969    if (!removedNonLocal)
970      last = L;
971
972    return removedNonLocal;
973  }
974
975
976  bool deletedLoad = false;
977
978  // Walk up the dependency chain until we either find
979  // a dependency we can use, or we can't walk any further
980  while (dep != MemoryDependenceAnalysis::None &&
981         dep != MemoryDependenceAnalysis::NonLocal &&
982         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
983    // ... that depends on a store ...
984    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
985      if (S->getPointerOperand() == pointer) {
986        // Remove it!
987        MD.removeInstruction(L);
988
989        L->replaceAllUsesWith(S->getOperand(0));
990        toErase.push_back(L);
991        deletedLoad = true;
992        NumGVNLoad++;
993      }
994
995      // Whether we removed it or not, we can't
996      // go any further
997      break;
998    } else if (!last) {
999      // If we don't depend on a store, and we haven't
1000      // been loaded before, bail.
1001      break;
1002    } else if (dep == last) {
1003      // Remove it!
1004      MD.removeInstruction(L);
1005
1006      L->replaceAllUsesWith(last);
1007      toErase.push_back(L);
1008      deletedLoad = true;
1009      NumGVNLoad++;
1010
1011      break;
1012    } else {
1013      dep = MD.getDependency(L, dep);
1014    }
1015  }
1016
1017  if (!deletedLoad)
1018    last = L;
1019
1020  return deletedLoad;
1021}
1022
1023/// processInstruction - When calculating availability, handle an instruction
1024/// by inserting it into the appropriate sets
1025bool GVN::processInstruction(Instruction* I,
1026                                ValueNumberedSet& currAvail,
1027                                DenseMap<Value*, LoadInst*>& lastSeenLoad,
1028                                SmallVector<Instruction*, 4>& toErase) {
1029  if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1030    return processLoad(L, lastSeenLoad, toErase);
1031  }
1032
1033  unsigned num = VN.lookup_or_add(I);
1034
1035  // Collapse PHI nodes
1036  if (PHINode* p = dyn_cast<PHINode>(I)) {
1037    Value* constVal = CollapsePhi(p);
1038
1039    if (constVal) {
1040      for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1041           PI != PE; ++PI)
1042        if (PI->second.count(p))
1043          PI->second.erase(p);
1044
1045      p->replaceAllUsesWith(constVal);
1046      toErase.push_back(p);
1047    }
1048  // Perform value-number based elimination
1049  } else if (currAvail.test(num)) {
1050    Value* repl = find_leader(currAvail, num);
1051
1052    if (CallInst* CI = dyn_cast<CallInst>(I)) {
1053      AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
1054      if (CI->getCalledFunction() &&
1055          !AA.doesNotAccessMemory(CI->getCalledFunction())) {
1056        MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1057        if (cast<Instruction>(repl)->getParent() != CI->getParent() ||
1058            MD.getDependency(CI) != MD.getDependency(cast<CallInst>(repl))) {
1059          // There must be an intervening may-alias store, so nothing from
1060          // this point on will be able to be replaced with the preceding call
1061          currAvail.erase(repl);
1062          currAvail.insert(I);
1063
1064          return false;
1065        }
1066      }
1067    }
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