GVN.cpp revision 16db1f70b780db099972b05ec6418a3f82d46d91 
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//===----------------------------------------------------------------------===//
14
15#define DEBUG_TYPE "gvn"
16#include "llvm/Transforms/Scalar.h"
17#include "llvm/BasicBlock.h"
18#include "llvm/Constants.h"
19#include "llvm/DerivedTypes.h"
20#include "llvm/Function.h"
21#include "llvm/Instructions.h"
22#include "llvm/Value.h"
23#include "llvm/ADT/DenseMap.h"
24#include "llvm/ADT/DepthFirstIterator.h"
25#include "llvm/ADT/SmallPtrSet.h"
26#include "llvm/ADT/SmallVector.h"
27#include "llvm/ADT/SparseBitVector.h"
28#include "llvm/ADT/Statistic.h"
29#include "llvm/Analysis/Dominators.h"
30#include "llvm/Analysis/AliasAnalysis.h"
31#include "llvm/Analysis/MemoryDependenceAnalysis.h"
32#include "llvm/Support/CFG.h"
33#include "llvm/Support/Compiler.h"
34#include "llvm/Support/Debug.h"
35#include <list>
36using namespace llvm;
37
38STATISTIC(NumGVNInstr, "Number of instructions deleted");
39STATISTIC(NumGVNLoad, "Number of loads deleted");
40
41//===----------------------------------------------------------------------===//
42//                         ValueTable Class
43//===----------------------------------------------------------------------===//
44
45/// This class holds the mapping between values and value numbers.  It is used
46/// as an efficient mechanism to determine the expression-wise equivalence of
47/// two values.
48namespace {
49  struct VISIBILITY_HIDDEN Expression {
50    enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
51                            FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
52                            ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
53                            ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
54                            FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
55                            FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
56                            FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
57                            SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
58                            FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
59                            PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
60                            EMPTY, TOMBSTONE };
61
62    ExpressionOpcode opcode;
63    const Type* type;
64    uint32_t firstVN;
65    uint32_t secondVN;
66    uint32_t thirdVN;
67    SmallVector<uint32_t, 4> varargs;
68    Value* function;
69
70    Expression() { }
71    Expression(ExpressionOpcode o) : opcode(o) { }
72
73    bool operator==(const Expression &other) const {
74      if (opcode != other.opcode)
75        return false;
76      else if (opcode == EMPTY || opcode == TOMBSTONE)
77        return true;
78      else if (type != other.type)
79        return false;
80      else if (function != other.function)
81        return false;
82      else if (firstVN != other.firstVN)
83        return false;
84      else if (secondVN != other.secondVN)
85        return false;
86      else if (thirdVN != other.thirdVN)
87        return false;
88      else {
89        if (varargs.size() != other.varargs.size())
90          return false;
91
92        for (size_t i = 0; i < varargs.size(); ++i)
93          if (varargs[i] != other.varargs[i])
94            return false;
95
96        return true;
97      }
98    }
99
100    bool operator!=(const Expression &other) const {
101      if (opcode != other.opcode)
102        return true;
103      else if (opcode == EMPTY || opcode == TOMBSTONE)
104        return false;
105      else if (type != other.type)
106        return true;
107      else if (function != other.function)
108        return true;
109      else if (firstVN != other.firstVN)
110        return true;
111      else if (secondVN != other.secondVN)
112        return true;
113      else if (thirdVN != other.thirdVN)
114        return true;
115      else {
116        if (varargs.size() != other.varargs.size())
117          return true;
118
119        for (size_t i = 0; i < varargs.size(); ++i)
120          if (varargs[i] != other.varargs[i])
121            return true;
122
123          return false;
124      }
125    }
126  };
127
128  class VISIBILITY_HIDDEN ValueTable {
129    private:
130      DenseMap<Value*, uint32_t> valueNumbering;
131      DenseMap<Expression, uint32_t> expressionNumbering;
132      AliasAnalysis* AA;
133      MemoryDependenceAnalysis* MD;
134      DominatorTree* DT;
135
136      uint32_t nextValueNumber;
137
138      Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
139      Expression::ExpressionOpcode getOpcode(CmpInst* C);
140      Expression::ExpressionOpcode getOpcode(CastInst* C);
141      Expression create_expression(BinaryOperator* BO);
142      Expression create_expression(CmpInst* C);
143      Expression create_expression(ShuffleVectorInst* V);
144      Expression create_expression(ExtractElementInst* C);
145      Expression create_expression(InsertElementInst* V);
146      Expression create_expression(SelectInst* V);
147      Expression create_expression(CastInst* C);
148      Expression create_expression(GetElementPtrInst* G);
149      Expression create_expression(CallInst* C);
150      Expression create_expression(Constant* C);
151    public:
152      ValueTable() : nextValueNumber(1) { }
153      uint32_t lookup_or_add(Value* V);
154      uint32_t lookup(Value* V) const;
155      void add(Value* V, uint32_t num);
156      void clear();
157      void erase(Value* v);
158      unsigned size();
159      void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
160      void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
161      void setDomTree(DominatorTree* D) { DT = D; }
162  };
163}
164
165namespace llvm {
166template <> struct DenseMapInfo<Expression> {
167  static inline Expression getEmptyKey() {
168    return Expression(Expression::EMPTY);
169  }
170
171  static inline Expression getTombstoneKey() {
172    return Expression(Expression::TOMBSTONE);
173  }
174
175  static unsigned getHashValue(const Expression e) {
176    unsigned hash = e.opcode;
177
178    hash = e.firstVN + hash * 37;
179    hash = e.secondVN + hash * 37;
180    hash = e.thirdVN + hash * 37;
181
182    hash = ((unsigned)((uintptr_t)e.type >> 4) ^
183            (unsigned)((uintptr_t)e.type >> 9)) +
184           hash * 37;
185
186    for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
187         E = e.varargs.end(); I != E; ++I)
188      hash = *I + hash * 37;
189
190    hash = ((unsigned)((uintptr_t)e.function >> 4) ^
191            (unsigned)((uintptr_t)e.function >> 9)) +
192           hash * 37;
193
194    return hash;
195  }
196  static bool isEqual(const Expression &LHS, const Expression &RHS) {
197    return LHS == RHS;
198  }
199  static bool isPod() { return true; }
200};
201}
202
203//===----------------------------------------------------------------------===//
204//                     ValueTable Internal Functions
205//===----------------------------------------------------------------------===//
206Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
207  switch(BO->getOpcode()) {
208  default: // THIS SHOULD NEVER HAPPEN
209    assert(0 && "Binary operator with unknown opcode?");
210  case Instruction::Add:  return Expression::ADD;
211  case Instruction::Sub:  return Expression::SUB;
212  case Instruction::Mul:  return Expression::MUL;
213  case Instruction::UDiv: return Expression::UDIV;
214  case Instruction::SDiv: return Expression::SDIV;
215  case Instruction::FDiv: return Expression::FDIV;
216  case Instruction::URem: return Expression::UREM;
217  case Instruction::SRem: return Expression::SREM;
218  case Instruction::FRem: return Expression::FREM;
219  case Instruction::Shl:  return Expression::SHL;
220  case Instruction::LShr: return Expression::LSHR;
221  case Instruction::AShr: return Expression::ASHR;
222  case Instruction::And:  return Expression::AND;
223  case Instruction::Or:   return Expression::OR;
224  case Instruction::Xor:  return Expression::XOR;
225  }
226}
227
228Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
229  if (isa<ICmpInst>(C)) {
230    switch (C->getPredicate()) {
231    default:  // THIS SHOULD NEVER HAPPEN
232      assert(0 && "Comparison with unknown predicate?");
233    case ICmpInst::ICMP_EQ:  return Expression::ICMPEQ;
234    case ICmpInst::ICMP_NE:  return Expression::ICMPNE;
235    case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
236    case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
237    case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
238    case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
239    case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
240    case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
241    case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
242    case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
243    }
244  }
245  assert(isa<FCmpInst>(C) && "Unknown compare");
246  switch (C->getPredicate()) {
247  default: // THIS SHOULD NEVER HAPPEN
248    assert(0 && "Comparison with unknown predicate?");
249  case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
250  case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
251  case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
252  case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
253  case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
254  case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
255  case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
256  case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
257  case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
258  case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
259  case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
260  case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
261  case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
262  case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
263  }
264}
265
266Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
267  switch(C->getOpcode()) {
268  default: // THIS SHOULD NEVER HAPPEN
269    assert(0 && "Cast operator with unknown opcode?");
270  case Instruction::Trunc:    return Expression::TRUNC;
271  case Instruction::ZExt:     return Expression::ZEXT;
272  case Instruction::SExt:     return Expression::SEXT;
273  case Instruction::FPToUI:   return Expression::FPTOUI;
274  case Instruction::FPToSI:   return Expression::FPTOSI;
275  case Instruction::UIToFP:   return Expression::UITOFP;
276  case Instruction::SIToFP:   return Expression::SITOFP;
277  case Instruction::FPTrunc:  return Expression::FPTRUNC;
278  case Instruction::FPExt:    return Expression::FPEXT;
279  case Instruction::PtrToInt: return Expression::PTRTOINT;
280  case Instruction::IntToPtr: return Expression::INTTOPTR;
281  case Instruction::BitCast:  return Expression::BITCAST;
282  }
283}
284
285Expression ValueTable::create_expression(CallInst* C) {
286  Expression e;
287
288  e.type = C->getType();
289  e.firstVN = 0;
290  e.secondVN = 0;
291  e.thirdVN = 0;
292  e.function = C->getCalledFunction();
293  e.opcode = Expression::CALL;
294
295  for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
296       I != E; ++I)
297    e.varargs.push_back(lookup_or_add(*I));
298
299  return e;
300}
301
302Expression ValueTable::create_expression(BinaryOperator* BO) {
303  Expression e;
304
305  e.firstVN = lookup_or_add(BO->getOperand(0));
306  e.secondVN = lookup_or_add(BO->getOperand(1));
307  e.thirdVN = 0;
308  e.function = 0;
309  e.type = BO->getType();
310  e.opcode = getOpcode(BO);
311
312  return e;
313}
314
315Expression ValueTable::create_expression(CmpInst* C) {
316  Expression e;
317
318  e.firstVN = lookup_or_add(C->getOperand(0));
319  e.secondVN = lookup_or_add(C->getOperand(1));
320  e.thirdVN = 0;
321  e.function = 0;
322  e.type = C->getType();
323  e.opcode = getOpcode(C);
324
325  return e;
326}
327
328Expression ValueTable::create_expression(CastInst* C) {
329  Expression e;
330
331  e.firstVN = lookup_or_add(C->getOperand(0));
332  e.secondVN = 0;
333  e.thirdVN = 0;
334  e.function = 0;
335  e.type = C->getType();
336  e.opcode = getOpcode(C);
337
338  return e;
339}
340
341Expression ValueTable::create_expression(ShuffleVectorInst* S) {
342  Expression e;
343
344  e.firstVN = lookup_or_add(S->getOperand(0));
345  e.secondVN = lookup_or_add(S->getOperand(1));
346  e.thirdVN = lookup_or_add(S->getOperand(2));
347  e.function = 0;
348  e.type = S->getType();
349  e.opcode = Expression::SHUFFLE;
350
351  return e;
352}
353
354Expression ValueTable::create_expression(ExtractElementInst* E) {
355  Expression e;
356
357  e.firstVN = lookup_or_add(E->getOperand(0));
358  e.secondVN = lookup_or_add(E->getOperand(1));
359  e.thirdVN = 0;
360  e.function = 0;
361  e.type = E->getType();
362  e.opcode = Expression::EXTRACT;
363
364  return e;
365}
366
367Expression ValueTable::create_expression(InsertElementInst* I) {
368  Expression e;
369
370  e.firstVN = lookup_or_add(I->getOperand(0));
371  e.secondVN = lookup_or_add(I->getOperand(1));
372  e.thirdVN = lookup_or_add(I->getOperand(2));
373  e.function = 0;
374  e.type = I->getType();
375  e.opcode = Expression::INSERT;
376
377  return e;
378}
379
380Expression ValueTable::create_expression(SelectInst* I) {
381  Expression e;
382
383  e.firstVN = lookup_or_add(I->getCondition());
384  e.secondVN = lookup_or_add(I->getTrueValue());
385  e.thirdVN = lookup_or_add(I->getFalseValue());
386  e.function = 0;
387  e.type = I->getType();
388  e.opcode = Expression::SELECT;
389
390  return e;
391}
392
393Expression ValueTable::create_expression(GetElementPtrInst* G) {
394  Expression e;
395
396  e.firstVN = lookup_or_add(G->getPointerOperand());
397  e.secondVN = 0;
398  e.thirdVN = 0;
399  e.function = 0;
400  e.type = G->getType();
401  e.opcode = Expression::GEP;
402
403  for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
404       I != E; ++I)
405    e.varargs.push_back(lookup_or_add(*I));
406
407  return e;
408}
409
410//===----------------------------------------------------------------------===//
411//                     ValueTable External Functions
412//===----------------------------------------------------------------------===//
413
414/// lookup_or_add - Returns the value number for the specified value, assigning
415/// it a new number if it did not have one before.
416uint32_t ValueTable::lookup_or_add(Value* V) {
417  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
418  if (VI != valueNumbering.end())
419    return VI->second;
420
421  if (CallInst* C = dyn_cast<CallInst>(V)) {
422    if (AA->doesNotAccessMemory(C)) {
423      Expression e = create_expression(C);
424
425      DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
426      if (EI != expressionNumbering.end()) {
427        valueNumbering.insert(std::make_pair(V, EI->second));
428        return EI->second;
429      } else {
430        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
431        valueNumbering.insert(std::make_pair(V, nextValueNumber));
432
433        return nextValueNumber++;
434      }
435    } else if (AA->onlyReadsMemory(C)) {
436      Expression e = create_expression(C);
437
438      if (expressionNumbering.find(e) == expressionNumbering.end()) {
439        expressionNumbering.insert(std::make_pair(e, nextValueNumber));
440        valueNumbering.insert(std::make_pair(V, nextValueNumber));
441        return nextValueNumber++;
442      }
443
444      DenseMap<BasicBlock*, Value*> deps;
445      MD->getNonLocalDependency(C, deps);
446      CallInst* cdep = 0;
447
448      for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(),
449           E = deps.end(); I != E; ++I) {
450        if (I->second == MemoryDependenceAnalysis::None) {
451          valueNumbering.insert(std::make_pair(V, nextValueNumber));
452
453          return nextValueNumber++;
454        } else if (I->second != MemoryDependenceAnalysis::NonLocal) {
455          if (DT->dominates(I->first, C->getParent())) {
456            if (CallInst* CD = dyn_cast<CallInst>(I->second))
457              cdep = CD;
458            else {
459              valueNumbering.insert(std::make_pair(V, nextValueNumber));
460              return nextValueNumber++;
461            }
462          } else {
463            valueNumbering.insert(std::make_pair(V, nextValueNumber));
464            return nextValueNumber++;
465          }
466        }
467      }
468
469      if (!cdep) {
470        valueNumbering.insert(std::make_pair(V, nextValueNumber));
471        return nextValueNumber++;
472      }
473
474      if (cdep->getCalledFunction() != C->getCalledFunction() ||
475          cdep->getNumOperands() != C->getNumOperands()) {
476        valueNumbering.insert(std::make_pair(V, nextValueNumber));
477        return nextValueNumber++;
478      } else if (!C->getCalledFunction()) {
479        valueNumbering.insert(std::make_pair(V, nextValueNumber));
480        return nextValueNumber++;
481      } else {
482        for (unsigned i = 1; i < C->getNumOperands(); ++i) {
483          uint32_t c_vn = lookup_or_add(C->getOperand(i));
484          uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
485          if (c_vn != cd_vn) {
486            valueNumbering.insert(std::make_pair(V, nextValueNumber));
487            return nextValueNumber++;
488          }
489        }
490
491        uint32_t v = valueNumbering[cdep];
492        valueNumbering.insert(std::make_pair(V, v));
493        return v;
494      }
495
496    } else {
497      valueNumbering.insert(std::make_pair(V, nextValueNumber));
498      return nextValueNumber++;
499    }
500  } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
501    Expression e = create_expression(BO);
502
503    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
504    if (EI != expressionNumbering.end()) {
505      valueNumbering.insert(std::make_pair(V, EI->second));
506      return EI->second;
507    } else {
508      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
509      valueNumbering.insert(std::make_pair(V, nextValueNumber));
510
511      return nextValueNumber++;
512    }
513  } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
514    Expression e = create_expression(C);
515
516    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
517    if (EI != expressionNumbering.end()) {
518      valueNumbering.insert(std::make_pair(V, EI->second));
519      return EI->second;
520    } else {
521      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
522      valueNumbering.insert(std::make_pair(V, nextValueNumber));
523
524      return nextValueNumber++;
525    }
526  } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
527    Expression e = create_expression(U);
528
529    DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
530    if (EI != expressionNumbering.end()) {
531      valueNumbering.insert(std::make_pair(V, EI->second));
532      return EI->second;
533    } else {
534      expressionNumbering.insert(std::make_pair(e, nextValueNumber));
535      valueNumbering.insert(std::make_pair(V, nextValueNumber));
536
537      return nextValueNumber++;
538    }
539  } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
540    Expression e = create_expression(U);
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 (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
553    Expression e = create_expression(U);
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 (SelectInst* U = dyn_cast<SelectInst>(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 (CastInst* U = dyn_cast<CastInst>(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 (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(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 {
605    valueNumbering.insert(std::make_pair(V, nextValueNumber));
606    return nextValueNumber++;
607  }
608}
609
610/// lookup - Returns the value number of the specified value. Fails if
611/// the value has not yet been numbered.
612uint32_t ValueTable::lookup(Value* V) const {
613  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
614  assert(VI != valueNumbering.end() && "Value not numbered?");
615  return VI->second;
616}
617
618/// clear - Remove all entries from the ValueTable
619void ValueTable::clear() {
620  valueNumbering.clear();
621  expressionNumbering.clear();
622  nextValueNumber = 1;
623}
624
625/// erase - Remove a value from the value numbering
626void ValueTable::erase(Value* V) {
627  valueNumbering.erase(V);
628}
629
630//===----------------------------------------------------------------------===//
631//                       ValueNumberedSet Class
632//===----------------------------------------------------------------------===//
633namespace {
634class VISIBILITY_HIDDEN ValueNumberedSet {
635  private:
636    SmallPtrSet<Value*, 8> contents;
637    SparseBitVector<64> numbers;
638  public:
639    ValueNumberedSet() { }
640    ValueNumberedSet(const ValueNumberedSet& other) {
641      numbers = other.numbers;
642      contents = other.contents;
643    }
644
645    typedef SmallPtrSet<Value*, 8>::iterator iterator;
646
647    iterator begin() { return contents.begin(); }
648    iterator end() { return contents.end(); }
649
650    bool insert(Value* v) { return contents.insert(v); }
651    void insert(iterator I, iterator E) { contents.insert(I, E); }
652    void erase(Value* v) { contents.erase(v); }
653    unsigned count(Value* v) { return contents.count(v); }
654    size_t size() { return contents.size(); }
655
656    void set(unsigned i)  {
657      numbers.set(i);
658    }
659
660    void operator=(const ValueNumberedSet& other) {
661      contents = other.contents;
662      numbers = other.numbers;
663    }
664
665    void reset(unsigned i)  {
666      numbers.reset(i);
667    }
668
669    bool test(unsigned i)  {
670      return numbers.test(i);
671    }
672};
673}
674
675//===----------------------------------------------------------------------===//
676//                         GVN Pass
677//===----------------------------------------------------------------------===//
678
679namespace {
680
681  class VISIBILITY_HIDDEN GVN : public FunctionPass {
682    bool runOnFunction(Function &F);
683  public:
684    static char ID; // Pass identification, replacement for typeid
685    GVN() : FunctionPass((intptr_t)&ID) { }
686
687  private:
688    ValueTable VN;
689
690    DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
691
692    typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
693    PhiMapType phiMap;
694
695
696    // This transformation requires dominator postdominator info
697    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
698      AU.setPreservesCFG();
699      AU.addRequired<DominatorTree>();
700      AU.addRequired<MemoryDependenceAnalysis>();
701      AU.addRequired<AliasAnalysis>();
702      AU.addPreserved<AliasAnalysis>();
703      AU.addPreserved<MemoryDependenceAnalysis>();
704    }
705
706    // Helper fuctions
707    // FIXME: eliminate or document these better
708    Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
709    void val_insert(ValueNumberedSet& s, Value* v);
710    bool processLoad(LoadInst* L,
711                     DenseMap<Value*, LoadInst*> &lastLoad,
712                     SmallVectorImpl<Instruction*> &toErase);
713    bool processInstruction(Instruction* I,
714                            ValueNumberedSet& currAvail,
715                            DenseMap<Value*, LoadInst*>& lastSeenLoad,
716                            SmallVectorImpl<Instruction*> &toErase);
717    bool processNonLocalLoad(LoadInst* L,
718                             SmallVectorImpl<Instruction*> &toErase);
719    Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
720                            DenseMap<BasicBlock*, Value*> &Phis,
721                            bool top_level = false);
722    void dump(DenseMap<BasicBlock*, Value*>& d);
723    bool iterateOnFunction(Function &F);
724    Value* CollapsePhi(PHINode* p);
725    bool isSafeReplacement(PHINode* p, Instruction* inst);
726  };
727
728  char GVN::ID = 0;
729}
730
731// createGVNPass - The public interface to this file...
732FunctionPass *llvm::createGVNPass() { return new GVN(); }
733
734static RegisterPass<GVN> X("gvn",
735                           "Global Value Numbering");
736
737/// find_leader - Given a set and a value number, return the first
738/// element of the set with that value number, or 0 if no such element
739/// is present
740Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
741  if (!vals.test(v))
742    return 0;
743
744  for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
745       I != E; ++I)
746    if (v == VN.lookup(*I))
747      return *I;
748
749  assert(0 && "No leader found, but present bit is set?");
750  return 0;
751}
752
753/// val_insert - Insert a value into a set only if there is not a value
754/// with the same value number already in the set
755void GVN::val_insert(ValueNumberedSet& s, Value* v) {
756  uint32_t num = VN.lookup(v);
757  if (!s.test(num))
758    s.insert(v);
759}
760
761void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
762  printf("{\n");
763  for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
764       E = d.end(); I != E; ++I) {
765    if (I->second == MemoryDependenceAnalysis::None)
766      printf("None\n");
767    else
768      I->second->dump();
769  }
770  printf("}\n");
771}
772
773Value* GVN::CollapsePhi(PHINode* p) {
774  DominatorTree &DT = getAnalysis<DominatorTree>();
775  Value* constVal = p->hasConstantValue();
776
777  if (!constVal) return 0;
778
779  Instruction* inst = dyn_cast<Instruction>(constVal);
780  if (!inst)
781    return constVal;
782
783  if (DT.dominates(inst, p))
784    if (isSafeReplacement(p, inst))
785      return inst;
786  return 0;
787}
788
789bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
790  if (!isa<PHINode>(inst))
791    return true;
792
793  for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
794       UI != E; ++UI)
795    if (PHINode* use_phi = dyn_cast<PHINode>(UI))
796      if (use_phi->getParent() == inst->getParent())
797        return false;
798
799  return true;
800}
801
802/// GetValueForBlock - Get the value to use within the specified basic block.
803/// available values are in Phis.
804Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
805                             DenseMap<BasicBlock*, Value*> &Phis,
806                             bool top_level) {
807
808  // If we have already computed this value, return the previously computed val.
809  DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
810  if (V != Phis.end() && !top_level) return V->second;
811
812  BasicBlock* singlePred = BB->getSinglePredecessor();
813  if (singlePred) {
814    Value *ret = GetValueForBlock(singlePred, orig, Phis);
815    Phis[BB] = ret;
816    return ret;
817  }
818
819  // Otherwise, the idom is the loop, so we need to insert a PHI node.  Do so
820  // now, then get values to fill in the incoming values for the PHI.
821  PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
822                                BB->begin());
823  PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
824
825  if (Phis.count(BB) == 0)
826    Phis.insert(std::make_pair(BB, PN));
827
828  // Fill in the incoming values for the block.
829  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
830    Value* val = GetValueForBlock(*PI, orig, Phis);
831    PN->addIncoming(val, *PI);
832  }
833
834  AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
835  AA.copyValue(orig, PN);
836
837  // Attempt to collapse PHI nodes that are trivially redundant
838  Value* v = CollapsePhi(PN);
839  if (!v) {
840    // Cache our phi construction results
841    phiMap[orig->getPointerOperand()].insert(PN);
842    return PN;
843  }
844
845  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
846
847  MD.removeInstruction(PN);
848  PN->replaceAllUsesWith(v);
849
850  for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
851       E = Phis.end(); I != E; ++I)
852    if (I->second == PN)
853      I->second = v;
854
855  PN->eraseFromParent();
856
857  Phis[BB] = v;
858  return v;
859}
860
861/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
862/// non-local by performing PHI construction.
863bool GVN::processNonLocalLoad(LoadInst* L,
864                              SmallVectorImpl<Instruction*> &toErase) {
865  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
866
867  // Find the non-local dependencies of the load
868  DenseMap<BasicBlock*, Value*> deps;
869  MD.getNonLocalDependency(L, deps);
870
871  DenseMap<BasicBlock*, Value*> repl;
872
873  // Filter out useless results (non-locals, etc)
874  for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
875       I != E; ++I) {
876    if (I->second == MemoryDependenceAnalysis::None)
877      return false;
878
879    if (I->second == MemoryDependenceAnalysis::NonLocal)
880      continue;
881
882    if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
883      if (S->getPointerOperand() != L->getPointerOperand())
884        return false;
885      repl[I->first] = S->getOperand(0);
886    } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
887      if (LD->getPointerOperand() != L->getPointerOperand())
888        return false;
889      repl[I->first] = LD;
890    } else {
891      return false;
892    }
893  }
894
895  // Use cached PHI construction information from previous runs
896  SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
897  for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
898       I != E; ++I) {
899    if ((*I)->getParent() == L->getParent()) {
900      MD.removeInstruction(L);
901      L->replaceAllUsesWith(*I);
902      toErase.push_back(L);
903      NumGVNLoad++;
904      return true;
905    }
906
907    repl.insert(std::make_pair((*I)->getParent(), *I));
908  }
909
910  // Perform PHI construction
911  SmallPtrSet<BasicBlock*, 4> visited;
912  Value* v = GetValueForBlock(L->getParent(), L, repl, true);
913
914  MD.removeInstruction(L);
915  L->replaceAllUsesWith(v);
916  toErase.push_back(L);
917  NumGVNLoad++;
918
919  return true;
920}
921
922/// processLoad - Attempt to eliminate a load, first by eliminating it
923/// locally, and then attempting non-local elimination if that fails.
924bool GVN::processLoad(LoadInst *L, DenseMap<Value*, LoadInst*> &lastLoad,
925                      SmallVectorImpl<Instruction*> &toErase) {
926  if (L->isVolatile()) {
927    lastLoad[L->getPointerOperand()] = L;
928    return false;
929  }
930
931  Value* pointer = L->getPointerOperand();
932  LoadInst*& last = lastLoad[pointer];
933
934  // ... to a pointer that has been loaded from before...
935  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
936  bool removedNonLocal = false;
937  Instruction* dep = MD.getDependency(L);
938  if (dep == MemoryDependenceAnalysis::NonLocal &&
939      L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
940    removedNonLocal = processNonLocalLoad(L, toErase);
941
942    if (!removedNonLocal)
943      last = L;
944
945    return removedNonLocal;
946  }
947
948
949  bool deletedLoad = false;
950
951  // Walk up the dependency chain until we either find
952  // a dependency we can use, or we can't walk any further
953  while (dep != MemoryDependenceAnalysis::None &&
954         dep != MemoryDependenceAnalysis::NonLocal &&
955         (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
956    // ... that depends on a store ...
957    if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
958      if (S->getPointerOperand() == pointer) {
959        // Remove it!
960        MD.removeInstruction(L);
961
962        L->replaceAllUsesWith(S->getOperand(0));
963        toErase.push_back(L);
964        deletedLoad = true;
965        NumGVNLoad++;
966      }
967
968      // Whether we removed it or not, we can't
969      // go any further
970      break;
971    } else if (!last) {
972      // If we don't depend on a store, and we haven't
973      // been loaded before, bail.
974      break;
975    } else if (dep == last) {
976      // Remove it!
977      MD.removeInstruction(L);
978
979      L->replaceAllUsesWith(last);
980      toErase.push_back(L);
981      deletedLoad = true;
982      NumGVNLoad++;
983
984      break;
985    } else {
986      dep = MD.getDependency(L, dep);
987    }
988  }
989
990  if (dep != MemoryDependenceAnalysis::None &&
991      dep != MemoryDependenceAnalysis::NonLocal &&
992      isa<AllocationInst>(dep)) {
993    // Check that this load is actually from the
994    // allocation we found
995    Value* v = L->getOperand(0);
996    while (true) {
997      if (BitCastInst *BC = dyn_cast<BitCastInst>(v))
998        v = BC->getOperand(0);
999      else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v))
1000        v = GEP->getOperand(0);
1001      else
1002        break;
1003    }
1004    if (v == dep) {
1005      // If this load depends directly on an allocation, there isn't
1006      // anything stored there; therefore, we can optimize this load
1007      // to undef.
1008      MD.removeInstruction(L);
1009
1010      L->replaceAllUsesWith(UndefValue::get(L->getType()));
1011      toErase.push_back(L);
1012      deletedLoad = true;
1013      NumGVNLoad++;
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, ValueNumberedSet &currAvail,
1026                             DenseMap<Value*, LoadInst*> &lastSeenLoad,
1027                             SmallVectorImpl<Instruction*> &toErase) {
1028  if (LoadInst* L = dyn_cast<LoadInst>(I))
1029    return processLoad(L, lastSeenLoad, toErase);
1030
1031  // Allocations are always uniquely numbered, so we can save time and memory
1032  // by fast failing them.
1033  if (isa<AllocationInst>(I))
1034    return false;
1035
1036  unsigned num = VN.lookup_or_add(I);
1037
1038  // Collapse PHI nodes
1039  if (PHINode* p = dyn_cast<PHINode>(I)) {
1040    Value* constVal = CollapsePhi(p);
1041
1042    if (constVal) {
1043      for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1044           PI != PE; ++PI)
1045        if (PI->second.count(p))
1046          PI->second.erase(p);
1047
1048      p->replaceAllUsesWith(constVal);
1049      toErase.push_back(p);
1050    }
1051  // Perform value-number based elimination
1052  } else if (currAvail.test(num)) {
1053    Value* repl = find_leader(currAvail, num);
1054
1055    // Remove it!
1056    MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1057    MD.removeInstruction(I);
1058
1059    VN.erase(I);
1060    I->replaceAllUsesWith(repl);
1061    toErase.push_back(I);
1062    return true;
1063  } else if (!I->isTerminator()) {
1064    currAvail.set(num);
1065    currAvail.insert(I);
1066  }
1067
1068  return false;
1069}
1070
1071// GVN::runOnFunction - This is the main transformation entry point for a
1072// function.
1073//
1074bool GVN::runOnFunction(Function& F) {
1075  VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1076  VN.setMemDep(&getAnalysis<MemoryDependenceAnalysis>());
1077  VN.setDomTree(&getAnalysis<DominatorTree>());
1078
1079  bool changed = false;
1080  bool shouldContinue = true;
1081
1082  while (shouldContinue) {
1083    shouldContinue = iterateOnFunction(F);
1084    changed |= shouldContinue;
1085  }
1086
1087  return changed;
1088}
1089
1090
1091// GVN::iterateOnFunction - Executes one iteration of GVN
1092bool GVN::iterateOnFunction(Function &F) {
1093  // Clean out global sets from any previous functions
1094  VN.clear();
1095  availableOut.clear();
1096  phiMap.clear();
1097
1098  bool changed_function = false;
1099
1100  DominatorTree &DT = getAnalysis<DominatorTree>();
1101
1102  SmallVector<Instruction*, 8> toErase;
1103  DenseMap<Value*, LoadInst*> lastSeenLoad;
1104  DenseMap<DomTreeNode*, size_t> numChildrenVisited;
1105
1106  // Top-down walk of the dominator tree
1107  for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
1108         E = df_end(DT.getRootNode()); DI != E; ++DI) {
1109
1110    // Get the set to update for this block
1111    ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
1112    lastSeenLoad.clear();
1113
1114    BasicBlock* BB = DI->getBlock();
1115
1116    // A block inherits AVAIL_OUT from its dominator
1117    if (DI->getIDom() != 0) {
1118      currAvail = availableOut[DI->getIDom()->getBlock()];
1119
1120      numChildrenVisited[DI->getIDom()]++;
1121
1122      if (numChildrenVisited[DI->getIDom()] == DI->getIDom()->getNumChildren()) {
1123        availableOut.erase(DI->getIDom()->getBlock());
1124        numChildrenVisited.erase(DI->getIDom());
1125      }
1126    }
1127
1128    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1129         BI != BE;) {
1130      changed_function |= processInstruction(BI, currAvail,
1131                                             lastSeenLoad, toErase);
1132      if (toErase.empty()) {
1133        ++BI;
1134        continue;
1135      }
1136
1137      // If we need some instructions deleted, do it now.
1138      NumGVNInstr += toErase.size();
1139
1140      // Avoid iterator invalidation.
1141      bool AtStart = BI == BB->begin();
1142      if (!AtStart)
1143        --BI;
1144
1145      for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1146           E = toErase.end(); I != E; ++I)
1147        (*I)->eraseFromParent();
1148
1149      if (AtStart)
1150        BI = BB->begin();
1151      else
1152        ++BI;
1153
1154      toErase.clear();
1155    }
1156  }
1157
1158  return changed_function;
1159}
1160