GVN.cpp revision 845f524c25de18917f72e8847d7e138d65e4ef08 
1//===- GVN.cpp - Eliminate redundant values and loads ------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This pass performs global value numbering to eliminate fully redundant
11// instructions.  It also performs simple dead load elimination.
12//
13// Note that this pass does the value numbering itself, it does not use the
14// ValueNumbering analysis passes.
15//
16//===----------------------------------------------------------------------===//
17
18#define DEBUG_TYPE "gvn"
19#include "llvm/Transforms/Scalar.h"
20#include "llvm/BasicBlock.h"
21#include "llvm/Constants.h"
22#include "llvm/DerivedTypes.h"
23#include "llvm/Function.h"
24#include "llvm/Instructions.h"
25#include "llvm/Value.h"
26#include "llvm/ADT/DenseMap.h"
27#include "llvm/ADT/DepthFirstIterator.h"
28#include "llvm/ADT/SmallPtrSet.h"
29#include "llvm/ADT/SmallVector.h"
30#include "llvm/ADT/SparseBitVector.h"
31#include "llvm/ADT/Statistic.h"
32#include "llvm/Analysis/Dominators.h"
33#include "llvm/Analysis/AliasAnalysis.h"
34#include "llvm/Analysis/MemoryDependenceAnalysis.h"
35#include "llvm/Support/CFG.h"
36#include "llvm/Support/Compiler.h"
37#include "llvm/Support/Debug.h"
38using namespace llvm;
39
40STATISTIC(NumGVNInstr, "Number of instructions deleted");
41STATISTIC(NumGVNLoad, "Number of loads deleted");
42
43//===----------------------------------------------------------------------===//
44//                         ValueTable Class
45//===----------------------------------------------------------------------===//
46
47/// This class holds the mapping between values and value numbers.  It is used
48/// as an efficient mechanism to determine the expression-wise equivalence of
49/// two values.
50namespace {
51  struct VISIBILITY_HIDDEN Expression {
52    enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
53                            FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
54                            ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
55                            ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
56                            FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
57                            FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
58                            FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
59                            SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
60                            FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
61                            PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
62                            EMPTY, TOMBSTONE };
63
64    ExpressionOpcode opcode;
65    const Type* type;
66    uint32_t firstVN;
67    uint32_t secondVN;
68    uint32_t thirdVN;
69    SmallVector<uint32_t, 4> varargs;
70    Value* function;
71
72    Expression() { }
73    Expression(ExpressionOpcode o) : opcode(o) { }
74
75    bool operator==(const Expression &other) const {
76      if (opcode != other.opcode)
77        return false;
78      else if (opcode == EMPTY || opcode == TOMBSTONE)
79        return true;
80      else if (type != other.type)
81        return false;
82      else if (function != other.function)
83        return false;
84      else if (firstVN != other.firstVN)
85        return false;
86      else if (secondVN != other.secondVN)
87        return false;
88      else if (thirdVN != other.thirdVN)
89        return false;
90      else {
91        if (varargs.size() != other.varargs.size())
92          return false;
93
94        for (size_t i = 0; i < varargs.size(); ++i)
95          if (varargs[i] != other.varargs[i])
96            return false;
97
98        return true;
99      }
100    }
101
102    bool operator!=(const Expression &other) const {
103      if (opcode != other.opcode)
104        return true;
105      else if (opcode == EMPTY || opcode == TOMBSTONE)
106        return false;
107      else if (type != other.type)
108        return true;
109      else if (function != other.function)
110        return true;
111      else if (firstVN != other.firstVN)
112        return true;
113      else if (secondVN != other.secondVN)
114        return true;
115      else if (thirdVN != other.thirdVN)
116        return true;
117      else {
118        if (varargs.size() != other.varargs.size())
119          return true;
120
121        for (size_t i = 0; i < varargs.size(); ++i)
122          if (varargs[i] != other.varargs[i])
123            return true;
124
125          return false;
126      }
127    }
128  };
129
130  class VISIBILITY_HIDDEN ValueTable {
131    private:
132      DenseMap<Value*, uint32_t> valueNumbering;
133      DenseMap<Expression, uint32_t> expressionNumbering;
134      AliasAnalysis* AA;
135      MemoryDependenceAnalysis* MD;
136      DominatorTree* DT;
137
138      uint32_t nextValueNumber;
139
140      Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
141      Expression::ExpressionOpcode getOpcode(CmpInst* C);
142      Expression::ExpressionOpcode getOpcode(CastInst* C);
143      Expression create_expression(BinaryOperator* BO);
144      Expression create_expression(CmpInst* C);
145      Expression create_expression(ShuffleVectorInst* V);
146      Expression create_expression(ExtractElementInst* C);
147      Expression create_expression(InsertElementInst* V);
148      Expression create_expression(SelectInst* V);
149      Expression create_expression(CastInst* C);
150      Expression create_expression(GetElementPtrInst* G);
151      Expression create_expression(CallInst* C);
152      Expression create_expression(Constant* C);
153    public:
154      ValueTable() : nextValueNumber(1) { }
155      uint32_t lookup_or_add(Value* V);
156      uint32_t lookup(Value* V) const;
157      void add(Value* V, uint32_t num);
158      void clear();
159      void erase(Value* v);
160      unsigned size();
161      void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
162      void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
163      void setDomTree(DominatorTree* D) { DT = D; }
164  };
165}
166
167namespace llvm {
168template <> struct DenseMapInfo<Expression> {
169  static inline Expression getEmptyKey() {
170    return Expression(Expression::EMPTY);
171  }
172
173  static inline Expression getTombstoneKey() {
174    return Expression(Expression::TOMBSTONE);
175  }
176
177  static unsigned getHashValue(const Expression e) {
178    unsigned hash = e.opcode;
179
180    hash = e.firstVN + hash * 37;
181    hash = e.secondVN + hash * 37;
182    hash = e.thirdVN + hash * 37;
183
184    hash = ((unsigned)((uintptr_t)e.type >> 4) ^
185            (unsigned)((uintptr_t)e.type >> 9)) +
186           hash * 37;
187
188    for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
189         E = e.varargs.end(); I != E; ++I)
190      hash = *I + hash * 37;
191
192    hash = ((unsigned)((uintptr_t)e.function >> 4) ^
193            (unsigned)((uintptr_t)e.function >> 9)) +
194           hash * 37;
195
196    return hash;
197  }
198  static bool isEqual(const Expression &LHS, const Expression &RHS) {
199    return LHS == RHS;
200  }
201  static bool isPod() { return true; }
202};
203}
204
205//===----------------------------------------------------------------------===//
206//                     ValueTable Internal Functions
207//===----------------------------------------------------------------------===//
208Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
209  switch(BO->getOpcode()) {
210  default: // THIS SHOULD NEVER HAPPEN
211    assert(0 && "Binary operator with unknown opcode?");
212  case Instruction::Add:  return Expression::ADD;
213  case Instruction::Sub:  return Expression::SUB;
214  case Instruction::Mul:  return Expression::MUL;
215  case Instruction::UDiv: return Expression::UDIV;
216  case Instruction::SDiv: return Expression::SDIV;
217  case Instruction::FDiv: return Expression::FDIV;
218  case Instruction::URem: return Expression::UREM;
219  case Instruction::SRem: return Expression::SREM;
220  case Instruction::FRem: return Expression::FREM;
221  case Instruction::Shl:  return Expression::SHL;
222  case Instruction::LShr: return Expression::LSHR;
223  case Instruction::AShr: return Expression::ASHR;
224  case Instruction::And:  return Expression::AND;
225  case Instruction::Or:   return Expression::OR;
226  case Instruction::Xor:  return Expression::XOR;
227  }
228}
229
230Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
231  if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) {
232    switch (C->getPredicate()) {
233    default:  // THIS SHOULD NEVER HAPPEN
234      assert(0 && "Comparison with unknown predicate?");
235    case ICmpInst::ICMP_EQ:  return Expression::ICMPEQ;
236    case ICmpInst::ICMP_NE:  return Expression::ICMPNE;
237    case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
238    case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
239    case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
240    case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
241    case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
242    case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
243    case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
244    case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
245    }
246  }
247  assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare");
248  switch (C->getPredicate()) {
249  default: // THIS SHOULD NEVER HAPPEN
250    assert(0 && "Comparison with unknown predicate?");
251  case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
252  case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
253  case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
254  case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
255  case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
256  case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
257  case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
258  case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
259  case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
260  case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
261  case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
262  case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
263  case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
264  case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
265  }
266}
267
268Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
269  switch(C->getOpcode()) {
270  default: // THIS SHOULD NEVER HAPPEN
271    assert(0 && "Cast operator with unknown opcode?");
272  case Instruction::Trunc:    return Expression::TRUNC;
273  case Instruction::ZExt:     return Expression::ZEXT;
274  case Instruction::SExt:     return Expression::SEXT;
275  case Instruction::FPToUI:   return Expression::FPTOUI;
276  case Instruction::FPToSI:   return Expression::FPTOSI;
277  case Instruction::UIToFP:   return Expression::UITOFP;
278  case Instruction::SIToFP:   return Expression::SITOFP;
279  case Instruction::FPTrunc:  return Expression::FPTRUNC;
280  case Instruction::FPExt:    return Expression::FPEXT;
281  case Instruction::PtrToInt: return Expression::PTRTOINT;
282  case Instruction::IntToPtr: return Expression::INTTOPTR;
283  case Instruction::BitCast:  return Expression::BITCAST;
284  }
285}
286
287Expression ValueTable::create_expression(CallInst* C) {
288  Expression e;
289
290  e.type = C->getType();
291  e.firstVN = 0;
292  e.secondVN = 0;
293  e.thirdVN = 0;
294  e.function = C->getCalledFunction();
295  e.opcode = Expression::CALL;
296
297  for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
298       I != E; ++I)
299    e.varargs.push_back(lookup_or_add(*I));
300
301  return e;
302}
303
304Expression ValueTable::create_expression(BinaryOperator* BO) {
305  Expression e;
306
307  e.firstVN = lookup_or_add(BO->getOperand(0));
308  e.secondVN = lookup_or_add(BO->getOperand(1));
309  e.thirdVN = 0;
310  e.function = 0;
311  e.type = BO->getType();
312  e.opcode = getOpcode(BO);
313
314  return e;
315}
316
317Expression ValueTable::create_expression(CmpInst* C) {
318  Expression e;
319
320  e.firstVN = lookup_or_add(C->getOperand(0));
321  e.secondVN = lookup_or_add(C->getOperand(1));
322  e.thirdVN = 0;
323  e.function = 0;
324  e.type = C->getType();
325  e.opcode = getOpcode(C);
326
327  return e;
328}
329
330Expression ValueTable::create_expression(CastInst* C) {
331  Expression e;
332
333  e.firstVN = lookup_or_add(C->getOperand(0));
334  e.secondVN = 0;
335  e.thirdVN = 0;
336  e.function = 0;
337  e.type = C->getType();
338  e.opcode = getOpcode(C);
339
340  return e;
341}
342
343Expression ValueTable::create_expression(ShuffleVectorInst* S) {
344  Expression e;
345
346  e.firstVN = lookup_or_add(S->getOperand(0));
347  e.secondVN = lookup_or_add(S->getOperand(1));
348  e.thirdVN = lookup_or_add(S->getOperand(2));
349  e.function = 0;
350  e.type = S->getType();
351  e.opcode = Expression::SHUFFLE;
352
353  return e;
354}
355
356Expression ValueTable::create_expression(ExtractElementInst* E) {
357  Expression e;
358
359  e.firstVN = lookup_or_add(E->getOperand(0));
360  e.secondVN = lookup_or_add(E->getOperand(1));
361  e.thirdVN = 0;
362  e.function = 0;
363  e.type = E->getType();
364  e.opcode = Expression::EXTRACT;
365
366  return e;
367}
368
369Expression ValueTable::create_expression(InsertElementInst* I) {
370  Expression e;
371
372  e.firstVN = lookup_or_add(I->getOperand(0));
373  e.secondVN = lookup_or_add(I->getOperand(1));
374  e.thirdVN = lookup_or_add(I->getOperand(2));
375  e.function = 0;
376  e.type = I->getType();
377  e.opcode = Expression::INSERT;
378
379  return e;
380}
381
382Expression ValueTable::create_expression(SelectInst* I) {
383  Expression e;
384
385  e.firstVN = lookup_or_add(I->getCondition());
386  e.secondVN = lookup_or_add(I->getTrueValue());
387  e.thirdVN = lookup_or_add(I->getFalseValue());
388  e.function = 0;
389  e.type = I->getType();
390  e.opcode = Expression::SELECT;
391
392  return e;
393}
394
395Expression ValueTable::create_expression(GetElementPtrInst* G) {
396  Expression e;
397
398  e.firstVN = lookup_or_add(G->getPointerOperand());
399  e.secondVN = 0;
400  e.thirdVN = 0;
401  e.function = 0;
402  e.type = G->getType();
403  e.opcode = Expression::GEP;
404
405  for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
406       I != E; ++I)
407    e.varargs.push_back(lookup_or_add(*I));
408
409  return e;
410}
411
412//===----------------------------------------------------------------------===//
413//                     ValueTable External Functions
414//===----------------------------------------------------------------------===//
415
416/// lookup_or_add - Returns the value number for the specified value, assigning
417/// it a new number if it did not have one before.
418uint32_t ValueTable::lookup_or_add(Value* V) {
419  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
420  if (VI != valueNumbering.end())
421    return VI->second;
422
423  if (CallInst* C = dyn_cast<CallInst>(V)) {
424    if (AA->doesNotAccessMemory(C)) {
425      Expression e = create_expression(C);
426
427      DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
428      if (EI != expressionNumbering.end()) {
429        valueNumbering.insert(std::make_pair(V, EI->second));
430        return EI->second;
431      } else {
432        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
433        valueNumbering.insert(std::make_pair(V, nextValueNumber));
434
435        return nextValueNumber++;
436      }
437    } else if (AA->onlyReadsMemory(C)) {
438      Expression e = create_expression(C);
439
440      if (expressionNumbering.find(e) == expressionNumbering.end()) {
441        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
442        valueNumbering.insert(std::make_pair(V, nextValueNumber));
443        return nextValueNumber++;
444      }
445
446      Instruction* local_dep = MD->getDependency(C);
447
448      if (local_dep == MemoryDependenceAnalysis::None) {
449        valueNumbering.insert(std::make_pair(V, nextValueNumber));
450        return nextValueNumber++;
451      } else if (local_dep != MemoryDependenceAnalysis::NonLocal) {
452        if (!isa<CallInst>(local_dep)) {
453          valueNumbering.insert(std::make_pair(V, nextValueNumber));
454          return nextValueNumber++;
455        }
456
457        CallInst* local_cdep = cast<CallInst>(local_dep);
458
459        if (local_cdep->getCalledFunction() != C->getCalledFunction() ||
460            local_cdep->getNumOperands() != C->getNumOperands()) {
461          valueNumbering.insert(std::make_pair(V, nextValueNumber));
462          return nextValueNumber++;
463        } else if (!C->getCalledFunction()) {
464          valueNumbering.insert(std::make_pair(V, nextValueNumber));
465          return nextValueNumber++;
466        } else {
467          for (unsigned i = 1; i < C->getNumOperands(); ++i) {
468            uint32_t c_vn = lookup_or_add(C->getOperand(i));
469            uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
470            if (c_vn != cd_vn) {
471              valueNumbering.insert(std::make_pair(V, nextValueNumber));
472              return nextValueNumber++;
473            }
474          }
475
476          uint32_t v = lookup_or_add(local_cdep);
477          valueNumbering.insert(std::make_pair(V, v));
478          return v;
479        }
480      }
481
482
483      DenseMap<BasicBlock*, Value*> deps;
484      MD->getNonLocalDependency(C, deps);
485      CallInst* cdep = 0;
486
487      for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(),
488           E = deps.end(); I != E; ++I) {
489        if (I->second == MemoryDependenceAnalysis::None) {
490          valueNumbering.insert(std::make_pair(V, nextValueNumber));
491
492          return nextValueNumber++;
493        } else if (I->second != MemoryDependenceAnalysis::NonLocal) {
494          if (DT->dominates(I->first, C->getParent())) {
495            if (CallInst* CD = dyn_cast<CallInst>(I->second))
496              cdep = CD;
497            else {
498              valueNumbering.insert(std::make_pair(V, nextValueNumber));
499              return nextValueNumber++;
500            }
501          } else {
502            valueNumbering.insert(std::make_pair(V, nextValueNumber));
503            return nextValueNumber++;
504          }
505        }
506      }
507
508      if (!cdep) {
509        valueNumbering.insert(std::make_pair(V, nextValueNumber));
510        return nextValueNumber++;
511      }
512
513      if (cdep->getCalledFunction() != C->getCalledFunction() ||
514          cdep->getNumOperands() != C->getNumOperands()) {
515        valueNumbering.insert(std::make_pair(V, nextValueNumber));
516        return nextValueNumber++;
517      } else if (!C->getCalledFunction()) {
518        valueNumbering.insert(std::make_pair(V, nextValueNumber));
519        return nextValueNumber++;
520      } else {
521        for (unsigned i = 1; i < C->getNumOperands(); ++i) {
522          uint32_t c_vn = lookup_or_add(C->getOperand(i));
523          uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
524          if (c_vn != cd_vn) {
525            valueNumbering.insert(std::make_pair(V, nextValueNumber));
526            return nextValueNumber++;
527          }
528        }
529
530        uint32_t v = lookup_or_add(cdep);
531        valueNumbering.insert(std::make_pair(V, v));
532        return v;
533      }
534
535    } else {
536      valueNumbering.insert(std::make_pair(V, nextValueNumber));
537      return nextValueNumber++;
538    }
539  } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
540    Expression e = create_expression(BO);
541
542    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
543    if (EI != expressionNumbering.end()) {
544      valueNumbering.insert(std::make_pair(V, EI->second));
545      return EI->second;
546    } else {
547      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
548      valueNumbering.insert(std::make_pair(V, nextValueNumber));
549
550      return nextValueNumber++;
551    }
552  } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
553    Expression e = create_expression(C);
554
555    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
556    if (EI != expressionNumbering.end()) {
557      valueNumbering.insert(std::make_pair(V, EI->second));
558      return EI->second;
559    } else {
560      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
561      valueNumbering.insert(std::make_pair(V, nextValueNumber));
562
563      return nextValueNumber++;
564    }
565  } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
566    Expression e = create_expression(U);
567
568    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
569    if (EI != expressionNumbering.end()) {
570      valueNumbering.insert(std::make_pair(V, EI->second));
571      return EI->second;
572    } else {
573      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
574      valueNumbering.insert(std::make_pair(V, nextValueNumber));
575
576      return nextValueNumber++;
577    }
578  } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
579    Expression e = create_expression(U);
580
581    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
582    if (EI != expressionNumbering.end()) {
583      valueNumbering.insert(std::make_pair(V, EI->second));
584      return EI->second;
585    } else {
586      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
587      valueNumbering.insert(std::make_pair(V, nextValueNumber));
588
589      return nextValueNumber++;
590    }
591  } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
592    Expression e = create_expression(U);
593
594    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
595    if (EI != expressionNumbering.end()) {
596      valueNumbering.insert(std::make_pair(V, EI->second));
597      return EI->second;
598    } else {
599      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
600      valueNumbering.insert(std::make_pair(V, nextValueNumber));
601
602      return nextValueNumber++;
603    }
604  } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
605    Expression e = create_expression(U);
606
607    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
608    if (EI != expressionNumbering.end()) {
609      valueNumbering.insert(std::make_pair(V, EI->second));
610      return EI->second;
611    } else {
612      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
613      valueNumbering.insert(std::make_pair(V, nextValueNumber));
614
615      return nextValueNumber++;
616    }
617  } else if (CastInst* U = dyn_cast<CastInst>(V)) {
618    Expression e = create_expression(U);
619
620    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
621    if (EI != expressionNumbering.end()) {
622      valueNumbering.insert(std::make_pair(V, EI->second));
623      return EI->second;
624    } else {
625      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
626      valueNumbering.insert(std::make_pair(V, nextValueNumber));
627
628      return nextValueNumber++;
629    }
630  } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
631    Expression e = create_expression(U);
632
633    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
634    if (EI != expressionNumbering.end()) {
635      valueNumbering.insert(std::make_pair(V, EI->second));
636      return EI->second;
637    } else {
638      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
639      valueNumbering.insert(std::make_pair(V, nextValueNumber));
640
641      return nextValueNumber++;
642    }
643  } else {
644    valueNumbering.insert(std::make_pair(V, nextValueNumber));
645    return nextValueNumber++;
646  }
647}
648
649/// lookup - Returns the value number of the specified value. Fails if
650/// the value has not yet been numbered.
651uint32_t ValueTable::lookup(Value* V) const {
652  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
653  assert(VI != valueNumbering.end() && "Value not numbered?");
654  return VI->second;
655}
656
657/// clear - Remove all entries from the ValueTable
658void ValueTable::clear() {
659  valueNumbering.clear();
660  expressionNumbering.clear();
661  nextValueNumber = 1;
662}
663
664/// erase - Remove a value from the value numbering
665void ValueTable::erase(Value* V) {
666  valueNumbering.erase(V);
667}
668
669//===----------------------------------------------------------------------===//
670//                       ValueNumberedSet Class
671//===----------------------------------------------------------------------===//
672namespace {
673class VISIBILITY_HIDDEN ValueNumberedSet {
674  private:
675    SmallPtrSet<Value*, 8> contents;
676    SparseBitVector<64> numbers;
677  public:
678    ValueNumberedSet() { }
679    ValueNumberedSet(const ValueNumberedSet& other) {
680      numbers = other.numbers;
681      contents = other.contents;
682    }
683
684    typedef SmallPtrSet<Value*, 8>::iterator iterator;
685
686    iterator begin() { return contents.begin(); }
687    iterator end() { return contents.end(); }
688
689    bool insert(Value* v) { return contents.insert(v); }
690    void insert(iterator I, iterator E) { contents.insert(I, E); }
691    void erase(Value* v) { contents.erase(v); }
692    unsigned count(Value* v) { return contents.count(v); }
693    size_t size() { return contents.size(); }
694
695    void set(unsigned i)  {
696      numbers.set(i);
697    }
698
699    void operator=(const ValueNumberedSet& other) {
700      contents = other.contents;
701      numbers = other.numbers;
702    }
703
704    void reset(unsigned i)  {
705      numbers.reset(i);
706    }
707
708    bool test(unsigned i)  {
709      return numbers.test(i);
710    }
711};
712}
713
714//===----------------------------------------------------------------------===//
715//                         GVN Pass
716//===----------------------------------------------------------------------===//
717
718namespace {
719
720  class VISIBILITY_HIDDEN GVN : public FunctionPass {
721    bool runOnFunction(Function &F);
722  public:
723    static char ID; // Pass identification, replacement for typeid
724    GVN() : FunctionPass((intptr_t)&ID) { }
725
726  private:
727    ValueTable VN;
728
729    DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
730
731    typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
732    PhiMapType phiMap;
733
734
735    // This transformation requires dominator postdominator info
736    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
737      AU.setPreservesCFG();
738      AU.addRequired<DominatorTree>();
739      AU.addRequired<MemoryDependenceAnalysis>();
740      AU.addRequired<AliasAnalysis>();
741      AU.addPreserved<AliasAnalysis>();
742      AU.addPreserved<MemoryDependenceAnalysis>();
743    }
744
745    // Helper fuctions
746    // FIXME: eliminate or document these better
747    Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
748    void val_insert(ValueNumberedSet& s, Value* v);
749    bool processLoad(LoadInst* L,
750                     DenseMap<Value*, LoadInst*> &lastLoad,
751                     SmallVectorImpl<Instruction*> &toErase);
752    bool processInstruction(Instruction* I,
753                            ValueNumberedSet& currAvail,
754                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
755                            SmallVectorImpl<Instruction*> &toErase);
756    bool processNonLocalLoad(LoadInst* L,
757                             SmallVectorImpl<Instruction*> &toErase);
758    Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
759                            DenseMap<BasicBlock*, Value*> &Phis,
760                            bool top_level = false);
761    void dump(DenseMap<BasicBlock*, Value*>& d);
762    bool iterateOnFunction(Function &F);
763    Value* CollapsePhi(PHINode* p);
764    bool isSafeReplacement(PHINode* p, Instruction* inst);
765  };
766
767  char GVN::ID = 0;
768}
769
770// createGVNPass - The public interface to this file...
771FunctionPass *llvm::createGVNPass() { return new GVN(); }
772
773static RegisterPass<GVN> X("gvn",
774                           "Global Value Numbering");
775
776/// find_leader - Given a set and a value number, return the first
777/// element of the set with that value number, or 0 if no such element
778/// is present
779Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
780  if (!vals.test(v))
781    return 0;
782
783  for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
784       I != E; ++I)
785    if (v == VN.lookup(*I))
786      return *I;
787
788  assert(0 && "No leader found, but present bit is set?");
789  return 0;
790}
791
792/// val_insert - Insert a value into a set only if there is not a value
793/// with the same value number already in the set
794void GVN::val_insert(ValueNumberedSet& s, Value* v) {
795  uint32_t num = VN.lookup(v);
796  if (!s.test(num))
797    s.insert(v);
798}
799
800void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
801  printf("{\n");
802  for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
803       E = d.end(); I != E; ++I) {
804    if (I->second == MemoryDependenceAnalysis::None)
805      printf("None\n");
806    else
807      I->second->dump();
808  }
809  printf("}\n");
810}
811
812Value* GVN::CollapsePhi(PHINode* p) {
813  DominatorTree &DT = getAnalysis<DominatorTree>();
814  Value* constVal = p->hasConstantValue();
815
816  if (!constVal) return 0;
817
818  Instruction* inst = dyn_cast<Instruction>(constVal);
819  if (!inst)
820    return constVal;
821
822  if (DT.dominates(inst, p))
823    if (isSafeReplacement(p, inst))
824      return inst;
825  return 0;
826}
827
828bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
829  if (!isa<PHINode>(inst))
830    return true;
831
832  for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
833       UI != E; ++UI)
834    if (PHINode* use_phi = dyn_cast<PHINode>(UI))
835      if (use_phi->getParent() == inst->getParent())
836        return false;
837
838  return true;
839}
840
841/// GetValueForBlock - Get the value to use within the specified basic block.
842/// available values are in Phis.
843Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
844                             DenseMap<BasicBlock*, Value*> &Phis,
845                             bool top_level) {
846
847  // If we have already computed this value, return the previously computed val.
848  DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
849  if (V != Phis.end() && !top_level) return V->second;
850
851  BasicBlock* singlePred = BB->getSinglePredecessor();
852  if (singlePred) {
853    Value *ret = GetValueForBlock(singlePred, orig, Phis);
854    Phis[BB] = ret;
855    return ret;
856  }
857
858  // Otherwise, the idom is the loop, so we need to insert a PHI node.  Do so
859  // now, then get values to fill in the incoming values for the PHI.
860  PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
861                                BB->begin());
862  PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
863
864  if (Phis.count(BB) == 0)
865    Phis.insert(std::make_pair(BB, PN));
866
867  // Fill in the incoming values for the block.
868  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
869    Value* val = GetValueForBlock(*PI, orig, Phis);
870    PN->addIncoming(val, *PI);
871  }
872
873  AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
874  AA.copyValue(orig, PN);
875
876  // Attempt to collapse PHI nodes that are trivially redundant
877  Value* v = CollapsePhi(PN);
878  if (!v) {
879    // Cache our phi construction results
880    phiMap[orig->getPointerOperand()].insert(PN);
881    return PN;
882  }
883
884  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
885
886  MD.removeInstruction(PN);
887  PN->replaceAllUsesWith(v);
888
889  for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
890       E = Phis.end(); I != E; ++I)
891    if (I->second == PN)
892      I->second = v;
893
894  PN->eraseFromParent();
895
896  Phis[BB] = v;
897  return v;
898}
899
900/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
901/// non-local by performing PHI construction.
902bool GVN::processNonLocalLoad(LoadInst* L,
903                              SmallVectorImpl<Instruction*> &toErase) {
904  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
905
906  // Find the non-local dependencies of the load
907  DenseMap<BasicBlock*, Value*> deps;
908  MD.getNonLocalDependency(L, deps);
909
910  DenseMap<BasicBlock*, Value*> repl;
911
912  // Filter out useless results (non-locals, etc)
913  for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
914       I != E; ++I) {
915    if (I->second == MemoryDependenceAnalysis::None)
916      return false;
917
918    if (I->second == MemoryDependenceAnalysis::NonLocal)
919      continue;
920
921    if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
922      if (S->getPointerOperand() != L->getPointerOperand())
923        return false;
924      repl[I->first] = S->getOperand(0);
925    } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
926      if (LD->getPointerOperand() != L->getPointerOperand())
927        return false;
928      repl[I->first] = LD;
929    } else {
930      return false;
931    }
932  }
933
934  // Use cached PHI construction information from previous runs
935  SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
936  for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
937       I != E; ++I) {
938    if ((*I)->getParent() == L->getParent()) {
939      MD.removeInstruction(L);
940      L->replaceAllUsesWith(*I);
941      toErase.push_back(L);
942      NumGVNLoad++;
943      return true;
944    }
945
946    repl.insert(std::make_pair((*I)->getParent(), *I));
947  }
948
949  // Perform PHI construction
950  SmallPtrSet<BasicBlock*, 4> visited;
951  Value* v = GetValueForBlock(L->getParent(), L, repl, true);
952
953  MD.removeInstruction(L);
954  L->replaceAllUsesWith(v);
955  toErase.push_back(L);
956  NumGVNLoad++;
957
958  return true;
959}
960
961/// processLoad - Attempt to eliminate a load, first by eliminating it
962/// locally, and then attempting non-local elimination if that fails.
963bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad,
964                      SmallVectorImpl<Instruction*> &toErase) {
965  if (L->isVolatile()) {
966    lastLoad[L->getPointerOperand()] = L;
967    return false;
968  }
969
970  Value* pointer = L->getPointerOperand();
971  LoadInst*& last = lastLoad[pointer];
972
973  // ... to a pointer that has been loaded from before...
974  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
975  bool removedNonLocal = false;
976  Instruction* dep = MD.getDependency(L);
977  if (dep == MemoryDependenceAnalysis::NonLocal &&
978      L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
979    removedNonLocal = processNonLocalLoad(L, toErase);
980
981    if (!removedNonLocal)
982      last = L;
983
984    return removedNonLocal;
985  }
986
987
988  bool deletedLoad = false;
989
990  // Walk up the dependency chain until we either find
991  // a dependency we can use, or we can't walk any further
992  while (dep != MemoryDependenceAnalysis::None &&
993         dep != MemoryDependenceAnalysis::NonLocal &&
994         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
995    // ... that depends on a store ...
996    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
997      if (S->getPointerOperand() == pointer) {
998        // Remove it!
999        MD.removeInstruction(L);
1000
1001        L->replaceAllUsesWith(S->getOperand(0));
1002        toErase.push_back(L);
1003        deletedLoad = true;
1004        NumGVNLoad++;
1005      }
1006
1007      // Whether we removed it or not, we can't
1008      // go any further
1009      break;
1010    } else if (!last) {
1011      // If we don't depend on a store, and we haven't
1012      // been loaded before, bail.
1013      break;
1014    } else if (dep == last) {
1015      // Remove it!
1016      MD.removeInstruction(L);
1017
1018      L->replaceAllUsesWith(last);
1019      toErase.push_back(L);
1020      deletedLoad = true;
1021      NumGVNLoad++;
1022
1023      break;
1024    } else {
1025      dep = MD.getDependency(L, dep);
1026    }
1027  }
1028
1029  if (dep != MemoryDependenceAnalysis::None &&
1030      dep != MemoryDependenceAnalysis::NonLocal &&
1031      isa<AllocationInst>(dep)) {
1032    // Check that this load is actually from the
1033    // allocation we found
1034    Value* v = L->getOperand(0);
1035    while (true) {
1036      if (BitCastInst *BC = dyn_cast<BitCastInst>(v))
1037        v = BC->getOperand(0);
1038      else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v))
1039        v = GEP->getOperand(0);
1040      else
1041        break;
1042    }
1043    if (v == dep) {
1044      // If this load depends directly on an allocation, there isn't
1045      // anything stored there; therefore, we can optimize this load
1046      // to undef.
1047      MD.removeInstruction(L);
1048
1049      L->replaceAllUsesWith(UndefValue::get(L->getType()));
1050      toErase.push_back(L);
1051      deletedLoad = true;
1052      NumGVNLoad++;
1053    }
1054  }
1055
1056  if (!deletedLoad)
1057    last = L;
1058
1059  return deletedLoad;
1060}
1061
1062/// processInstruction - When calculating availability, handle an instruction
1063/// by inserting it into the appropriate sets
1064bool GVN::processInstruction(Instruction *I, ValueNumberedSet &currAvail,
1065                             DenseMap<Value*, LoadInst*> &lastSeenLoad,
1066                             SmallVectorImpl<Instruction*> &toErase) {
1067  if (LoadInst* L = dyn_cast<LoadInst>(I))
1068    return processLoad(L, lastSeenLoad, toErase);
1069
1070  // Allocations are always uniquely numbered, so we can save time and memory
1071  // by fast failing them.
1072  if (isa<AllocationInst>(I))
1073    return false;
1074
1075  unsigned num = VN.lookup_or_add(I);
1076
1077  // Collapse PHI nodes
1078  if (PHINode* p = dyn_cast<PHINode>(I)) {
1079    Value* constVal = CollapsePhi(p);
1080
1081    if (constVal) {
1082      for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1083           PI != PE; ++PI)
1084        if (PI->second.count(p))
1085          PI->second.erase(p);
1086
1087      p->replaceAllUsesWith(constVal);
1088      toErase.push_back(p);
1089    }
1090  // Perform value-number based elimination
1091  } else if (currAvail.test(num)) {
1092    Value* repl = find_leader(currAvail, num);
1093
1094    // Remove it!
1095    MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1096    MD.removeInstruction(I);
1097
1098    VN.erase(I);
1099    I->replaceAllUsesWith(repl);
1100    toErase.push_back(I);
1101    return true;
1102  } else if (!I->isTerminator()) {
1103    currAvail.set(num);
1104    currAvail.insert(I);
1105  }
1106
1107  return false;
1108}
1109
1110// GVN::runOnFunction - This is the main transformation entry point for a
1111// function.
1112//
1113bool GVN::runOnFunction(Function& F) {
1114  VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1115  VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>());
1116  VN.setDomTree(&getAnalysis<DominatorTree>());
1117
1118  bool changed = false;
1119  bool shouldContinue = true;
1120
1121  while (shouldContinue) {
1122    shouldContinue = iterateOnFunction(F);
1123    changed |= shouldContinue;
1124  }
1125
1126  return changed;
1127}
1128
1129
1130// GVN::iterateOnFunction - Executes one iteration of GVN
1131bool GVN::iterateOnFunction(Function &F) {
1132  // Clean out global sets from any previous functions
1133  VN.clear();
1134  availableOut.clear();
1135  phiMap.clear();
1136
1137  bool changed_function = false;
1138
1139  DominatorTree &DT = getAnalysis<DominatorTree>();
1140
1141  SmallVector<Instruction*, 8> toErase;
1142  DenseMap<Value*, LoadInst*> lastSeenLoad;
1143  DenseMap<DomTreeNode*, size_t> numChildrenVisited;
1144
1145  // Top-down walk of the dominator tree
1146  for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
1147         E = df_end(DT.getRootNode()); DI != E; ++DI) {
1148
1149    // Get the set to update for this block
1150    ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
1151    lastSeenLoad.clear();
1152
1153    BasicBlock* BB = DI->getBlock();
1154
1155    // A block inherits AVAIL_OUT from its dominator
1156    if (DI->getIDom() != 0) {
1157      currAvail = availableOut[DI->getIDom()->getBlock()];
1158
1159      numChildrenVisited[DI->getIDom()]++;
1160
1161      if (numChildrenVisited[DI->getIDom()] == DI->getIDom()->getNumChildren()) {
1162        availableOut.erase(DI->getIDom()->getBlock());
1163        numChildrenVisited.erase(DI->getIDom());
1164      }
1165    }
1166
1167    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1168         BI != BE;) {
1169      changed_function |= processInstruction(BI, currAvail,
1170                                             lastSeenLoad, toErase);
1171      if (toErase.empty()) {
1172        ++BI;
1173        continue;
1174      }
1175
1176      // If we need some instructions deleted, do it now.
1177      NumGVNInstr += toErase.size();
1178
1179      // Avoid iterator invalidation.
1180      bool AtStart = BI == BB->begin();
1181      if (!AtStart)
1182        --BI;
1183
1184      for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1185           E = toErase.end(); I != E; ++I)
1186        (*I)->eraseFromParent();
1187
1188      if (AtStart)
1189        BI = BB->begin();
1190      else
1191        ++BI;
1192
1193      toErase.clear();
1194    }
1195  }
1196
1197  return changed_function;
1198}
1199