lib/Transforms/Scalar/GVN.cpp

   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/IntrinsicInst.h"
  25 #include "llvm/Value.h"
  26 #include "llvm/ADT/DenseMap.h"
  27 #include "llvm/ADT/DepthFirstIterator.h"
  28 #include "llvm/ADT/PostOrderIterator.h"
  29 #include "llvm/ADT/SmallPtrSet.h"
  30 #include "llvm/ADT/SmallVector.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/CommandLine.h"
  37 #include "llvm/Support/Compiler.h"
  38 #include "llvm/Support/Debug.h"
  39 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  40 #include <cstdio>
  41 using namespace llvm;
  42
  43 STATISTIC(NumGVNInstr,  "Number of instructions deleted");
  44 STATISTIC(NumGVNLoad,   "Number of loads deleted");
  45 STATISTIC(NumGVNPRE,    "Number of instructions PRE'd");
  46 STATISTIC(NumGVNBlocks, "Number of blocks merged");
  47 STATISTIC(NumPRELoad,   "Number of loads PRE'd");
  48
  49 static cl::opt<bool> EnablePRE("enable-pre",
  50                                cl::init(true), cl::Hidden);
  51 cl::opt<bool> EnableLoadPRE("enable-load-pre"/*, cl::init(true)*/);
  52
  53 //===----------------------------------------------------------------------===//
  54 //                         ValueTable Class
  55 //===----------------------------------------------------------------------===//
  56
  57 /// This class holds the mapping between values and value numbers.  It is used
  58 /// as an efficient mechanism to determine the expression-wise equivalence of
  59 /// two values.
  60 namespace {
  61   struct VISIBILITY_HIDDEN Expression {
  62     enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
  63                             FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
  64                             ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
  65                             ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
  66                             FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
  67                             FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
  68                             FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
  69                             SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
  70                             FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
  71                             PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
  72                             EMPTY, TOMBSTONE };
  73
  74     ExpressionOpcode opcode;
  75     const Type* type;
  76     uint32_t firstVN;
  77     uint32_t secondVN;
  78     uint32_t thirdVN;
  79     SmallVector<uint32_t, 4> varargs;
  80     Value* function;
  81
  82     Expression() { }
  83     Expression(ExpressionOpcode o) : opcode(o) { }
  84
  85     bool operator==(const Expression &other) const {
  86       if (opcode != other.opcode)
  87         return false;
  88       else if (opcode == EMPTY || opcode == TOMBSTONE)
  89         return true;
  90       else if (type != other.type)
  91         return false;
  92       else if (function != other.function)
  93         return false;
  94       else if (firstVN != other.firstVN)
  95         return false;
  96       else if (secondVN != other.secondVN)
  97         return false;
  98       else if (thirdVN != other.thirdVN)
  99         return false;
 100       else {
 101         if (varargs.size() != other.varargs.size())
 102           return false;
 103
 104         for (size_t i = 0; i < varargs.size(); ++i)
 105           if (varargs[i] != other.varargs[i])
 106             return false;
 107
 108         return true;
 109       }
 110     }
 111
 112     bool operator!=(const Expression &other) const {
 113       return !(*this == other);
 114     }
 115   };
 116
 117   class VISIBILITY_HIDDEN ValueTable {
 118     private:
 119       DenseMap<Value*, uint32_t> valueNumbering;
 120       DenseMap<Expression, uint32_t> expressionNumbering;
 121       AliasAnalysis* AA;
 122       MemoryDependenceAnalysis* MD;
 123       DominatorTree* DT;
 124
 125       uint32_t nextValueNumber;
 126
 127       Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
 128       Expression::ExpressionOpcode getOpcode(CmpInst* C);
 129       Expression::ExpressionOpcode getOpcode(CastInst* C);
 130       Expression create_expression(BinaryOperator* BO);
 131       Expression create_expression(CmpInst* C);
 132       Expression create_expression(ShuffleVectorInst* V);
 133       Expression create_expression(ExtractElementInst* C);
 134       Expression create_expression(InsertElementInst* V);
 135       Expression create_expression(SelectInst* V);
 136       Expression create_expression(CastInst* C);
 137       Expression create_expression(GetElementPtrInst* G);
 138       Expression create_expression(CallInst* C);
 139       Expression create_expression(Constant* C);
 140     public:
 141       ValueTable() : nextValueNumber(1) { }
 142       uint32_t lookup_or_add(Value* V);
 143       uint32_t lookup(Value* V) const;
 144       void add(Value* V, uint32_t num);
 145       void clear();
 146       void erase(Value* v);
 147       unsigned size();
 148       void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
 149       AliasAnalysis *getAliasAnalysis() const { return AA; }
 150       void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
 151       void setDomTree(DominatorTree* D) { DT = D; }
 152       uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
 153       void verifyRemoved(const Value *) const;
 154   };
 155 }
 156
 157 namespace llvm {
 158 template <> 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 //===----------------------------------------------------------------------===//
 198 Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
 199   switch(BO->getOpcode()) {
 200   default: // THIS SHOULD NEVER HAPPEN
 201     assert(0 && "Binary operator with unknown opcode?");
 202   case Instruction::Add:  return Expression::ADD;
 203   case Instruction::Sub:  return Expression::SUB;
 204   case Instruction::Mul:  return Expression::MUL;
 205   case Instruction::UDiv: return Expression::UDIV;
 206   case Instruction::SDiv: return Expression::SDIV;
 207   case Instruction::FDiv: return Expression::FDIV;
 208   case Instruction::URem: return Expression::UREM;
 209   case Instruction::SRem: return Expression::SREM;
 210   case Instruction::FRem: return Expression::FREM;
 211   case Instruction::Shl:  return Expression::SHL;
 212   case Instruction::LShr: return Expression::LSHR;
 213   case Instruction::AShr: return Expression::ASHR;
 214   case Instruction::And:  return Expression::AND;
 215   case Instruction::Or:   return Expression::OR;
 216   case Instruction::Xor:  return Expression::XOR;
 217   }
 218 }
 219
 220 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
 221   if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) {
 222     switch (C->getPredicate()) {
 223     default:  // THIS SHOULD NEVER HAPPEN
 224       assert(0 && "Comparison with unknown predicate?");
 225     case ICmpInst::ICMP_EQ:  return Expression::ICMPEQ;
 226     case ICmpInst::ICMP_NE:  return Expression::ICMPNE;
 227     case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
 228     case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
 229     case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
 230     case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
 231     case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
 232     case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
 233     case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
 234     case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
 235     }
 236   }
 237   assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare");
 238   switch (C->getPredicate()) {
 239   default: // THIS SHOULD NEVER HAPPEN
 240     assert(0 && "Comparison with unknown predicate?");
 241   case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
 242   case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
 243   case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
 244   case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
 245   case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
 246   case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
 247   case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
 248   case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
 249   case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
 250   case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
 251   case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
 252   case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
 253   case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
 254   case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
 255   }
 256 }
 257
 258 Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
 259   switch(C->getOpcode()) {
 260   default: // THIS SHOULD NEVER HAPPEN
 261     assert(0 && "Cast operator with unknown opcode?");
 262   case Instruction::Trunc:    return Expression::TRUNC;
 263   case Instruction::ZExt:     return Expression::ZEXT;
 264   case Instruction::SExt:     return Expression::SEXT;
 265   case Instruction::FPToUI:   return Expression::FPTOUI;
 266   case Instruction::FPToSI:   return Expression::FPTOSI;
 267   case Instruction::UIToFP:   return Expression::UITOFP;
 268   case Instruction::SIToFP:   return Expression::SITOFP;
 269   case Instruction::FPTrunc:  return Expression::FPTRUNC;
 270   case Instruction::FPExt:    return Expression::FPEXT;
 271   case Instruction::PtrToInt: return Expression::PTRTOINT;
 272   case Instruction::IntToPtr: return Expression::INTTOPTR;
 273   case Instruction::BitCast:  return Expression::BITCAST;
 274   }
 275 }
 276
 277 Expression ValueTable::create_expression(CallInst* C) {
 278   Expression e;
 279
 280   e.type = C->getType();
 281   e.firstVN = 0;
 282   e.secondVN = 0;
 283   e.thirdVN = 0;
 284   e.function = C->getCalledFunction();
 285   e.opcode = Expression::CALL;
 286
 287   for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
 288        I != E; ++I)
 289     e.varargs.push_back(lookup_or_add(*I));
 290
 291   return e;
 292 }
 293
 294 Expression ValueTable::create_expression(BinaryOperator* BO) {
 295   Expression e;
 296
 297   e.firstVN = lookup_or_add(BO->getOperand(0));
 298   e.secondVN = lookup_or_add(BO->getOperand(1));
 299   e.thirdVN = 0;
 300   e.function = 0;
 301   e.type = BO->getType();
 302   e.opcode = getOpcode(BO);
 303
 304   return e;
 305 }
 306
 307 Expression ValueTable::create_expression(CmpInst* C) {
 308   Expression e;
 309
 310   e.firstVN = lookup_or_add(C->getOperand(0));
 311   e.secondVN = lookup_or_add(C->getOperand(1));
 312   e.thirdVN = 0;
 313   e.function = 0;
 314   e.type = C->getType();
 315   e.opcode = getOpcode(C);
 316
 317   return e;
 318 }
 319
 320 Expression ValueTable::create_expression(CastInst* C) {
 321   Expression e;
 322
 323   e.firstVN = lookup_or_add(C->getOperand(0));
 324   e.secondVN = 0;
 325   e.thirdVN = 0;
 326   e.function = 0;
 327   e.type = C->getType();
 328   e.opcode = getOpcode(C);
 329
 330   return e;
 331 }
 332
 333 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
 334   Expression e;
 335
 336   e.firstVN = lookup_or_add(S->getOperand(0));
 337   e.secondVN = lookup_or_add(S->getOperand(1));
 338   e.thirdVN = lookup_or_add(S->getOperand(2));
 339   e.function = 0;
 340   e.type = S->getType();
 341   e.opcode = Expression::SHUFFLE;
 342
 343   return e;
 344 }
 345
 346 Expression ValueTable::create_expression(ExtractElementInst* E) {
 347   Expression e;
 348
 349   e.firstVN = lookup_or_add(E->getOperand(0));
 350   e.secondVN = lookup_or_add(E->getOperand(1));
 351   e.thirdVN = 0;
 352   e.function = 0;
 353   e.type = E->getType();
 354   e.opcode = Expression::EXTRACT;
 355
 356   return e;
 357 }
 358
 359 Expression ValueTable::create_expression(InsertElementInst* I) {
 360   Expression e;
 361
 362   e.firstVN = lookup_or_add(I->getOperand(0));
 363   e.secondVN = lookup_or_add(I->getOperand(1));
 364   e.thirdVN = lookup_or_add(I->getOperand(2));
 365   e.function = 0;
 366   e.type = I->getType();
 367   e.opcode = Expression::INSERT;
 368
 369   return e;
 370 }
 371
 372 Expression ValueTable::create_expression(SelectInst* I) {
 373   Expression e;
 374
 375   e.firstVN = lookup_or_add(I->getCondition());
 376   e.secondVN = lookup_or_add(I->getTrueValue());
 377   e.thirdVN = lookup_or_add(I->getFalseValue());
 378   e.function = 0;
 379   e.type = I->getType();
 380   e.opcode = Expression::SELECT;
 381
 382   return e;
 383 }
 384
 385 Expression ValueTable::create_expression(GetElementPtrInst* G) {
 386   Expression e;
 387
 388   e.firstVN = lookup_or_add(G->getPointerOperand());
 389   e.secondVN = 0;
 390   e.thirdVN = 0;
 391   e.function = 0;
 392   e.type = G->getType();
 393   e.opcode = Expression::GEP;
 394
 395   for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
 396        I != E; ++I)
 397     e.varargs.push_back(lookup_or_add(*I));
 398
 399   return e;
 400 }
 401
 402 //===----------------------------------------------------------------------===//
 403 //                     ValueTable External Functions
 404 //===----------------------------------------------------------------------===//
 405
 406 /// add - Insert a value into the table with a specified value number.
 407 void ValueTable::add(Value* V, uint32_t num) {
 408   valueNumbering.insert(std::make_pair(V, num));
 409 }
 410
 411 /// lookup_or_add - Returns the value number for the specified value, assigning
 412 /// it a new number if it did not have one before.
 413 uint32_t ValueTable::lookup_or_add(Value* V) {
 414   DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
 415   if (VI != valueNumbering.end())
 416     return VI->second;
 417
 418   if (CallInst* C = dyn_cast<CallInst>(V)) {
 419     if (AA->doesNotAccessMemory(C)) {
 420       Expression e = create_expression(C);
 421
 422       DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
 423       if (EI != expressionNumbering.end()) {
 424         valueNumbering.insert(std::make_pair(V, EI->second));
 425         return EI->second;
 426       } else {
 427         expressionNumbering.insert(std::make_pair(e, nextValueNumber));
 428         valueNumbering.insert(std::make_pair(V, nextValueNumber));
 429
 430         return nextValueNumber++;
 431       }
 432     } else if (AA->onlyReadsMemory(C)) {
 433       Expression e = create_expression(C);
 434
 435       if (expressionNumbering.find(e) == expressionNumbering.end()) {
 436         expressionNumbering.insert(std::make_pair(e, nextValueNumber));
 437         valueNumbering.insert(std::make_pair(V, nextValueNumber));
 438         return nextValueNumber++;
 439       }
 440
 441       MemDepResult local_dep = MD->getDependency(C);
 442
 443       if (!local_dep.isDef() && !local_dep.isNonLocal()) {
 444         valueNumbering.insert(std::make_pair(V, nextValueNumber));
 445         return nextValueNumber++;
 446       }
 447
 448       if (local_dep.isDef()) {
 449         CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
 450
 451         if (local_cdep->getNumOperands() != C->getNumOperands()) {
 452           valueNumbering.insert(std::make_pair(V, nextValueNumber));
 453           return nextValueNumber++;
 454         }
 455
 456         for (unsigned i = 1; i < C->getNumOperands(); ++i) {
 457           uint32_t c_vn = lookup_or_add(C->getOperand(i));
 458           uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
 459           if (c_vn != cd_vn) {
 460             valueNumbering.insert(std::make_pair(V, nextValueNumber));
 461             return nextValueNumber++;
 462           }
 463         }
 464
 465         uint32_t v = lookup_or_add(local_cdep);
 466         valueNumbering.insert(std::make_pair(V, v));
 467         return v;
 468       }
 469
 470       // Non-local case.
 471       const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
 472         MD->getNonLocalCallDependency(CallSite(C));
 473       // FIXME: call/call dependencies for readonly calls should return def, not
 474       // clobber!  Move the checking logic to MemDep!
 475       CallInst* cdep = 0;
 476
 477       // Check to see if we have a single dominating call instruction that is
 478       // identical to C.
 479       for (unsigned i = 0, e = deps.size(); i != e; ++i) {
 480         const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
 481         // Ignore non-local dependencies.
 482         if (I->second.isNonLocal())
 483           continue;
 484
 485         // We don't handle non-depedencies.  If we already have a call, reject
 486         // instruction dependencies.
 487         if (I->second.isClobber() || cdep != 0) {
 488           cdep = 0;
 489           break;
 490         }
 491
 492         CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
 493         // FIXME: All duplicated with non-local case.
 494         if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){
 495           cdep = NonLocalDepCall;
 496           continue;
 497         }
 498
 499         cdep = 0;
 500         break;
 501       }
 502
 503       if (!cdep) {
 504         valueNumbering.insert(std::make_pair(V, nextValueNumber));
 505         return nextValueNumber++;
 506       }
 507
 508       if (cdep->getNumOperands() != C->getNumOperands()) {
 509         valueNumbering.insert(std::make_pair(V, nextValueNumber));
 510         return nextValueNumber++;
 511       }
 512       for (unsigned i = 1; i < C->getNumOperands(); ++i) {
 513         uint32_t c_vn = lookup_or_add(C->getOperand(i));
 514         uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
 515         if (c_vn != cd_vn) {
 516           valueNumbering.insert(std::make_pair(V, nextValueNumber));
 517           return nextValueNumber++;
 518         }
 519       }
 520
 521       uint32_t v = lookup_or_add(cdep);
 522       valueNumbering.insert(std::make_pair(V, v));
 523       return v;
 524
 525     } else {
 526       valueNumbering.insert(std::make_pair(V, nextValueNumber));
 527       return nextValueNumber++;
 528     }
 529   } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
 530     Expression e = create_expression(BO);
 531
 532     DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
 533     if (EI != expressionNumbering.end()) {
 534       valueNumbering.insert(std::make_pair(V, EI->second));
 535       return EI->second;
 536     } else {
 537       expressionNumbering.insert(std::make_pair(e, nextValueNumber));
 538       valueNumbering.insert(std::make_pair(V, nextValueNumber));
 539
 540       return nextValueNumber++;
 541     }
 542   } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
 543     Expression e = create_expression(C);
 544
 545     DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
 546     if (EI != expressionNumbering.end()) {
 547       valueNumbering.insert(std::make_pair(V, EI->second));
 548       return EI->second;
 549     } else {
 550       expressionNumbering.insert(std::make_pair(e, nextValueNumber));
 551       valueNumbering.insert(std::make_pair(V, nextValueNumber));
 552
 553       return nextValueNumber++;
 554     }
 555   } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
 556     Expression e = create_expression(U);
 557
 558     DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
 559     if (EI != expressionNumbering.end()) {
 560       valueNumbering.insert(std::make_pair(V, EI->second));
 561       return EI->second;
 562     } else {
 563       expressionNumbering.insert(std::make_pair(e, nextValueNumber));
 564       valueNumbering.insert(std::make_pair(V, nextValueNumber));
 565
 566       return nextValueNumber++;
 567     }
 568   } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
 569     Expression e = create_expression(U);
 570
 571     DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
 572     if (EI != expressionNumbering.end()) {
 573       valueNumbering.insert(std::make_pair(V, EI->second));
 574       return EI->second;
 575     } else {
 576       expressionNumbering.insert(std::make_pair(e, nextValueNumber));
 577       valueNumbering.insert(std::make_pair(V, nextValueNumber));
 578
 579       return nextValueNumber++;
 580     }
 581   } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
 582     Expression e = create_expression(U);
 583
 584     DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
 585     if (EI != expressionNumbering.end()) {
 586       valueNumbering.insert(std::make_pair(V, EI->second));
 587       return EI->second;
 588     } else {
 589       expressionNumbering.insert(std::make_pair(e, nextValueNumber));
 590       valueNumbering.insert(std::make_pair(V, nextValueNumber));
 591
 592       return nextValueNumber++;
 593     }
 594   } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
 595     Expression e = create_expression(U);
 596
 597     DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
 598     if (EI != expressionNumbering.end()) {
 599       valueNumbering.insert(std::make_pair(V, EI->second));
 600       return EI->second;
 601     } else {
 602       expressionNumbering.insert(std::make_pair(e, nextValueNumber));
 603       valueNumbering.insert(std::make_pair(V, nextValueNumber));
 604
 605       return nextValueNumber++;
 606     }
 607   } else if (CastInst* U = dyn_cast<CastInst>(V)) {
 608     Expression e = create_expression(U);
 609
 610     DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
 611     if (EI != expressionNumbering.end()) {
 612       valueNumbering.insert(std::make_pair(V, EI->second));
 613       return EI->second;
 614     } else {
 615       expressionNumbering.insert(std::make_pair(e, nextValueNumber));
 616       valueNumbering.insert(std::make_pair(V, nextValueNumber));
 617
 618       return nextValueNumber++;
 619     }
 620   } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
 621     Expression e = create_expression(U);
 622
 623     DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
 624     if (EI != expressionNumbering.end()) {
 625       valueNumbering.insert(std::make_pair(V, EI->second));
 626       return EI->second;
 627     } else {
 628       expressionNumbering.insert(std::make_pair(e, nextValueNumber));
 629       valueNumbering.insert(std::make_pair(V, nextValueNumber));
 630
 631       return nextValueNumber++;
 632     }
 633   } else {
 634     valueNumbering.insert(std::make_pair(V, nextValueNumber));
 635     return nextValueNumber++;
 636   }
 637 }
 638
 639 /// lookup - Returns the value number of the specified value. Fails if
 640 /// the value has not yet been numbered.
 641 uint32_t ValueTable::lookup(Value* V) const {
 642   DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
 643   assert(VI != valueNumbering.end() && "Value not numbered?");
 644   return VI->second;
 645 }
 646
 647 /// clear - Remove all entries from the ValueTable
 648 void ValueTable::clear() {
 649   valueNumbering.clear();
 650   expressionNumbering.clear();
 651   nextValueNumber = 1;
 652 }
 653
 654 /// erase - Remove a value from the value numbering
 655 void ValueTable::erase(Value* V) {
 656   valueNumbering.erase(V);
 657 }
 658
 659 /// verifyRemoved - Verify that the value is removed from all internal data
 660 /// structures.
 661 void ValueTable::verifyRemoved(const Value *V) const {
 662   for (DenseMap<Value*, uint32_t>::iterator
 663          I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
 664     assert(I->first != V && "Inst still occurs in value numbering map!");
 665   }
 666 }
 667
 668 //===----------------------------------------------------------------------===//
 669 //                                GVN Pass
 670 //===----------------------------------------------------------------------===//
 671
 672 namespace {
 673   struct VISIBILITY_HIDDEN ValueNumberScope {
 674     ValueNumberScope* parent;
 675     DenseMap<uint32_t, Value*> table;
 676
 677     ValueNumberScope(ValueNumberScope* p) : parent(p) { }
 678   };
 679 }
 680
 681 namespace {
 682
 683   class VISIBILITY_HIDDEN GVN : public FunctionPass {
 684     bool runOnFunction(Function &F);
 685   public:
 686     static char ID; // Pass identification, replacement for typeid
 687     GVN() : FunctionPass(&ID) { }
 688
 689   private:
 690     MemoryDependenceAnalysis *MD;
 691     DominatorTree *DT;
 692
 693     ValueTable VN;
 694     DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
 695
 696     typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
 697     PhiMapType phiMap;
 698
 699
 700     // This transformation requires dominator postdominator info
 701     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
 702       AU.addRequired<DominatorTree>();
 703       AU.addRequired<MemoryDependenceAnalysis>();
 704       AU.addRequired<AliasAnalysis>();
 705
 706       AU.addPreserved<DominatorTree>();
 707       AU.addPreserved<AliasAnalysis>();
 708     }
 709
 710     // Helper fuctions
 711     // FIXME: eliminate or document these better
 712     bool processLoad(LoadInst* L,
 713                      SmallVectorImpl<Instruction*> &toErase);
 714     bool processInstruction(Instruction* I,
 715                             SmallVectorImpl<Instruction*> &toErase);
 716     bool processNonLocalLoad(LoadInst* L,
 717                              SmallVectorImpl<Instruction*> &toErase);
 718     bool processBlock(BasicBlock* BB);
 719     Value *GetValueForBlock(BasicBlock *BB, Instruction* orig,
 720                             DenseMap<BasicBlock*, Value*> &Phis,
 721                             bool top_level = false);
 722     void dump(DenseMap<uint32_t, Value*>& d);
 723     bool iterateOnFunction(Function &F);
 724     Value* CollapsePhi(PHINode* p);
 725     bool isSafeReplacement(PHINode* p, Instruction* inst);
 726     bool performPRE(Function& F);
 727     Value* lookupNumber(BasicBlock* BB, uint32_t num);
 728     bool mergeBlockIntoPredecessor(BasicBlock* BB);
 729     Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno);
 730     void cleanupGlobalSets();
 731     void verifyRemoved(const Instruction *I) const;
 732   };
 733
 734   char GVN::ID = 0;
 735 }
 736
 737 // createGVNPass - The public interface to this file...
 738 FunctionPass *llvm::createGVNPass() { return new GVN(); }
 739
 740 static RegisterPass<GVN> X("gvn",
 741                            "Global Value Numbering");
 742
 743 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
 744   printf("{\n");
 745   for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
 746        E = d.end(); I != E; ++I) {
 747       printf("%d\n", I->first);
 748       I->second->dump();
 749   }
 750   printf("}\n");
 751 }
 752
 753 Value* GVN::CollapsePhi(PHINode* p) {
 754   Value* constVal = p->hasConstantValue();
 755   if (!constVal) return 0;
 756
 757   Instruction* inst = dyn_cast<Instruction>(constVal);
 758   if (!inst)
 759     return constVal;
 760
 761   if (DT->dominates(inst, p))
 762     if (isSafeReplacement(p, inst))
 763       return inst;
 764   return 0;
 765 }
 766
 767 bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
 768   if (!isa<PHINode>(inst))
 769     return true;
 770
 771   for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
 772        UI != E; ++UI)
 773     if (PHINode* use_phi = dyn_cast<PHINode>(UI))
 774       if (use_phi->getParent() == inst->getParent())
 775         return false;
 776
 777   return true;
 778 }
 779
 780 /// GetValueForBlock - Get the value to use within the specified basic block.
 781 /// available values are in Phis.
 782 Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig,
 783                              DenseMap<BasicBlock*, Value*> &Phis,
 784                              bool top_level) {
 785
 786   // If we have already computed this value, return the previously computed val.
 787   DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
 788   if (V != Phis.end() && !top_level) return V->second;
 789
 790   // If the block is unreachable, just return undef, since this path
 791   // can't actually occur at runtime.
 792   if (!DT->isReachableFromEntry(BB))
 793     return Phis[BB] = UndefValue::get(orig->getType());
 794
 795   if (BasicBlock *Pred = BB->getSinglePredecessor()) {
 796     Value *ret = GetValueForBlock(Pred, orig, Phis);
 797     Phis[BB] = ret;
 798     return ret;
 799   }
 800
 801   // Get the number of predecessors of this block so we can reserve space later.
 802   // If there is already a PHI in it, use the #preds from it, otherwise count.
 803   // Getting it from the PHI is constant time.
 804   unsigned NumPreds;
 805   if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin()))
 806     NumPreds = ExistingPN->getNumIncomingValues();
 807   else
 808     NumPreds = std::distance(pred_begin(BB), pred_end(BB));
 809
 810   // Otherwise, the idom is the loop, so we need to insert a PHI node.  Do so
 811   // now, then get values to fill in the incoming values for the PHI.
 812   PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
 813                                 BB->begin());
 814   PN->reserveOperandSpace(NumPreds);
 815
 816   Phis.insert(std::make_pair(BB, PN));
 817
 818   // Fill in the incoming values for the block.
 819   for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
 820     Value* val = GetValueForBlock(*PI, orig, Phis);
 821     PN->addIncoming(val, *PI);
 822   }
 823
 824   VN.getAliasAnalysis()->copyValue(orig, PN);
 825
 826   // Attempt to collapse PHI nodes that are trivially redundant
 827   Value* v = CollapsePhi(PN);
 828   if (!v) {
 829     // Cache our phi construction results
 830     if (LoadInst* L = dyn_cast<LoadInst>(orig))
 831       phiMap[L->getPointerOperand()].insert(PN);
 832     else
 833       phiMap[orig].insert(PN);
 834
 835     return PN;
 836   }
 837
 838   PN->replaceAllUsesWith(v);
 839   if (isa<PointerType>(v->getType()))
 840     MD->invalidateCachedPointerInfo(v);
 841
 842   for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
 843        E = Phis.end(); I != E; ++I)
 844     if (I->second == PN)
 845       I->second = v;
 846
 847   DEBUG(cerr << "GVN removed: " << *PN);
 848   MD->removeInstruction(PN);
 849   PN->eraseFromParent();
 850   DEBUG(verifyRemoved(PN));
 851
 852   Phis[BB] = v;
 853   return v;
 854 }
 855
 856 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
 857 /// we're analyzing is fully available in the specified block.  As we go, keep
 858 /// track of which blocks we know are fully alive in FullyAvailableBlocks.  This
 859 /// map is actually a tri-state map with the following values:
 860 ///   0) we know the block *is not* fully available.
 861 ///   1) we know the block *is* fully available.
 862 ///   2) we do not know whether the block is fully available or not, but we are
 863 ///      currently speculating that it will be.
 864 ///   3) we are speculating for this block and have used that to speculate for
 865 ///      other blocks.
 866 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
 867                             DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
 868   // Optimistically assume that the block is fully available and check to see
 869   // if we already know about this block in one lookup.
 870   std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
 871     FullyAvailableBlocks.insert(std::make_pair(BB, 2));
 872
 873   // If the entry already existed for this block, return the precomputed value.
 874   if (!IV.second) {
 875     // If this is a speculative "available" value, mark it as being used for
 876     // speculation of other blocks.
 877     if (IV.first->second == 2)
 878       IV.first->second = 3;
 879     return IV.first->second != 0;
 880   }
 881
 882   // Otherwise, see if it is fully available in all predecessors.
 883   pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
 884
 885   // If this block has no predecessors, it isn't live-in here.
 886   if (PI == PE)
 887     goto SpeculationFailure;
 888
 889   for (; PI != PE; ++PI)
 890     // If the value isn't fully available in one of our predecessors, then it
 891     // isn't fully available in this block either.  Undo our previous
 892     // optimistic assumption and bail out.
 893     if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
 894       goto SpeculationFailure;
 895
 896   return true;
 897
 898 // SpeculationFailure - If we get here, we found out that this is not, after
 899 // all, a fully-available block.  We have a problem if we speculated on this and
 900 // used the speculation to mark other blocks as available.
 901 SpeculationFailure:
 902   char &BBVal = FullyAvailableBlocks[BB];
 903
 904   // If we didn't speculate on this, just return with it set to false.
 905   if (BBVal == 2) {
 906     BBVal = 0;
 907     return false;
 908   }
 909
 910   // If we did speculate on this value, we could have blocks set to 1 that are
 911   // incorrect.  Walk the (transitive) successors of this block and mark them as
 912   // 0 if set to one.
 913   SmallVector<BasicBlock*, 32> BBWorklist;
 914   BBWorklist.push_back(BB);
 915
 916   while (!BBWorklist.empty()) {
 917     BasicBlock *Entry = BBWorklist.pop_back_val();
 918     // Note that this sets blocks to 0 (unavailable) if they happen to not
 919     // already be in FullyAvailableBlocks.  This is safe.
 920     char &EntryVal = FullyAvailableBlocks[Entry];
 921     if (EntryVal == 0) continue;  // Already unavailable.
 922
 923     // Mark as unavailable.
 924     EntryVal = 0;
 925
 926     for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
 927       BBWorklist.push_back(*I);
 928   }
 929
 930   return false;
 931 }
 932
 933 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
 934 /// non-local by performing PHI construction.
 935 bool GVN::processNonLocalLoad(LoadInst *LI,
 936                               SmallVectorImpl<Instruction*> &toErase) {
 937   // Find the non-local dependencies of the load.
 938   SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps;
 939   MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
 940                                    Deps);
 941   //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI);
 942
 943   // If we had to process more than one hundred blocks to find the
 944   // dependencies, this load isn't worth worrying about.  Optimizing
 945   // it will be too expensive.
 946   if (Deps.size() > 100)
 947     return false;
 948
 949   // If we had a phi translation failure, we'll have a single entry which is a
 950   // clobber in the current block.  Reject this early.
 951   if (Deps.size() == 1 && Deps[0].second.isClobber())
 952     return false;
 953
 954   // Filter out useless results (non-locals, etc).  Keep track of the blocks
 955   // where we have a value available in repl, also keep track of whether we see
 956   // dependencies that produce an unknown value for the load (such as a call
 957   // that could potentially clobber the load).
 958   SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock;
 959   SmallVector<BasicBlock*, 16> UnavailableBlocks;
 960
 961   for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
 962     BasicBlock *DepBB = Deps[i].first;
 963     MemDepResult DepInfo = Deps[i].second;
 964
 965     if (DepInfo.isClobber()) {
 966       UnavailableBlocks.push_back(DepBB);
 967       continue;
 968     }
 969
 970     Instruction *DepInst = DepInfo.getInst();
 971
 972     // Loading the allocation -> undef.
 973     if (isa<AllocationInst>(DepInst)) {
 974       ValuesPerBlock.push_back(std::make_pair(DepBB,
 975                                               UndefValue::get(LI->getType())));
 976       continue;
 977     }
 978
 979     if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
 980       // Reject loads and stores that are to the same address but are of
 981       // different types.
 982       // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because
 983       // of bitfield access, it would be interesting to optimize for it at some
 984       // point.
 985       if (S->getOperand(0)->getType() != LI->getType()) {
 986         UnavailableBlocks.push_back(DepBB);
 987         continue;
 988       }
 989
 990       ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
 991
 992     } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) {
 993       if (LD->getType() != LI->getType()) {
 994         UnavailableBlocks.push_back(DepBB);
 995         continue;
 996       }
 997       ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
 998     } else {
 999       UnavailableBlocks.push_back(DepBB);
1000       continue;
1001     }
1002   }
1003
1004   // If we have no predecessors that produce a known value for this load, exit
1005   // early.
1006   if (ValuesPerBlock.empty()) return false;
1007
1008   // If all of the instructions we depend on produce a known value for this
1009   // load, then it is fully redundant and we can use PHI insertion to compute
1010   // its value.  Insert PHIs and remove the fully redundant value now.
1011   if (UnavailableBlocks.empty()) {
1012     // Use cached PHI construction information from previous runs
1013     SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1014     // FIXME: What does phiMap do? Are we positive it isn't getting invalidated?
1015     for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1016          I != E; ++I) {
1017       if ((*I)->getParent() == LI->getParent()) {
1018         DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI);
1019         LI->replaceAllUsesWith(*I);
1020         if (isa<PointerType>((*I)->getType()))
1021           MD->invalidateCachedPointerInfo(*I);
1022         toErase.push_back(LI);
1023         NumGVNLoad++;
1024         return true;
1025       }
1026
1027       ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1028     }
1029
1030     DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI);
1031
1032     DenseMap<BasicBlock*, Value*> BlockReplValues;
1033     BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1034     // Perform PHI construction.
1035     Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1036     LI->replaceAllUsesWith(v);
1037
1038     if (isa<PHINode>(v))
1039       v->takeName(LI);
1040     if (isa<PointerType>(v->getType()))
1041       MD->invalidateCachedPointerInfo(v);
1042     toErase.push_back(LI);
1043     NumGVNLoad++;
1044     return true;
1045   }
1046
1047   if (!EnablePRE || !EnableLoadPRE)
1048     return false;
1049
1050   // Okay, we have *some* definitions of the value.  This means that the value
1051   // is available in some of our (transitive) predecessors.  Lets think about
1052   // doing PRE of this load.  This will involve inserting a new load into the
1053   // predecessor when it's not available.  We could do this in general, but
1054   // prefer to not increase code size.  As such, we only do this when we know
1055   // that we only have to insert *one* load (which means we're basically moving
1056   // the load, not inserting a new one).
1057
1058   // Everything we do here is based on local predecessors of LI's block.  If it
1059   // only has one predecessor, bail now.
1060   BasicBlock *LoadBB = LI->getParent();
1061   if (LoadBB->getSinglePredecessor())
1062     return false;
1063
1064   // If we have a repl set with LI itself in it, this means we have a loop where
1065   // at least one of the values is LI.  Since this means that we won't be able
1066   // to eliminate LI even if we insert uses in the other predecessors, we will
1067   // end up increasing code size.  Reject this by scanning for LI.
1068   for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1069     if (ValuesPerBlock[i].second == LI)
1070       return false;
1071
1072   // Okay, we have some hope :).  Check to see if the loaded value is fully
1073   // available in all but one predecessor.
1074   // FIXME: If we could restructure the CFG, we could make a common pred with
1075   // all the preds that don't have an available LI and insert a new load into
1076   // that one block.
1077   BasicBlock *UnavailablePred = 0;
1078
1079   DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1080   for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1081     FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
1082   for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1083     FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1084
1085   for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1086        PI != E; ++PI) {
1087     if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1088       continue;
1089
1090     // If this load is not available in multiple predecessors, reject it.
1091     if (UnavailablePred && UnavailablePred != *PI)
1092       return false;
1093     UnavailablePred = *PI;
1094   }
1095
1096   assert(UnavailablePred != 0 &&
1097          "Fully available value should be eliminated above!");
1098
1099   // If the loaded pointer is PHI node defined in this block, do PHI translation
1100   // to get its value in the predecessor.
1101   Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred);
1102
1103   // Make sure the value is live in the predecessor.  If it was defined by a
1104   // non-PHI instruction in this block, we don't know how to recompute it above.
1105   if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr))
1106     if (!DT->dominates(LPInst->getParent(), UnavailablePred)) {
1107       DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: "
1108                  << *LPInst << *LI << "\n");
1109       return false;
1110     }
1111
1112   // We don't currently handle critical edges :(
1113   if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1114     DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1115                 << UnavailablePred->getName() << "': " << *LI);
1116     return false;
1117   }
1118
1119   // Okay, we can eliminate this load by inserting a reload in the predecessor
1120   // and using PHI construction to get the value in the other predecessors, do
1121   // it.
1122   DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI);
1123
1124   Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1125                                 LI->getAlignment(),
1126                                 UnavailablePred->getTerminator());
1127
1128   DenseMap<BasicBlock*, Value*> BlockReplValues;
1129   BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1130   BlockReplValues[UnavailablePred] = NewLoad;
1131
1132   // Perform PHI construction.
1133   Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1134   LI->replaceAllUsesWith(v);
1135   if (isa<PHINode>(v))
1136     v->takeName(LI);
1137   if (isa<PointerType>(v->getType()))
1138     MD->invalidateCachedPointerInfo(v);
1139   toErase.push_back(LI);
1140   NumPRELoad++;
1141   return true;
1142 }
1143
1144 /// processLoad - Attempt to eliminate a load, first by eliminating it
1145 /// locally, and then attempting non-local elimination if that fails.
1146 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1147   if (L->isVolatile())
1148     return false;
1149
1150   Value* pointer = L->getPointerOperand();
1151
1152   // ... to a pointer that has been loaded from before...
1153   MemDepResult dep = MD->getDependency(L);
1154
1155   // If the value isn't available, don't do anything!
1156   if (dep.isClobber())
1157     return false;
1158
1159   // If it is defined in another block, try harder.
1160   if (dep.isNonLocal())
1161     return processNonLocalLoad(L, toErase);
1162
1163   Instruction *DepInst = dep.getInst();
1164   if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1165     // Only forward substitute stores to loads of the same type.
1166     // FIXME: Could do better!
1167     if (DepSI->getPointerOperand()->getType() != pointer->getType())
1168       return false;
1169
1170     // Remove it!
1171     L->replaceAllUsesWith(DepSI->getOperand(0));
1172     if (isa<PointerType>(DepSI->getOperand(0)->getType()))
1173       MD->invalidateCachedPointerInfo(DepSI->getOperand(0));
1174     toErase.push_back(L);
1175     NumGVNLoad++;
1176     return true;
1177   }
1178
1179   if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1180     // Only forward substitute stores to loads of the same type.
1181     // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
1182     if (DepLI->getType() != L->getType())
1183       return false;
1184
1185     // Remove it!
1186     L->replaceAllUsesWith(DepLI);
1187     if (isa<PointerType>(DepLI->getType()))
1188       MD->invalidateCachedPointerInfo(DepLI);
1189     toErase.push_back(L);
1190     NumGVNLoad++;
1191     return true;
1192   }
1193
1194   // If this load really doesn't depend on anything, then we must be loading an
1195   // undef value.  This can happen when loading for a fresh allocation with no
1196   // intervening stores, for example.
1197   if (isa<AllocationInst>(DepInst)) {
1198     L->replaceAllUsesWith(UndefValue::get(L->getType()));
1199     toErase.push_back(L);
1200     NumGVNLoad++;
1201     return true;
1202   }
1203
1204   return false;
1205 }
1206
1207 Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
1208   DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1209   if (I == localAvail.end())
1210     return 0;
1211
1212   ValueNumberScope* locals = I->second;
1213
1214   while (locals) {
1215     DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num);
1216     if (I != locals->table.end())
1217       return I->second;
1218     else
1219       locals = locals->parent;
1220   }
1221
1222   return 0;
1223 }
1224
1225 /// AttemptRedundancyElimination - If the "fast path" of redundancy elimination
1226 /// by inheritance from the dominator fails, see if we can perform phi
1227 /// construction to eliminate the redundancy.
1228 Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) {
1229   BasicBlock* BaseBlock = orig->getParent();
1230
1231   SmallPtrSet<BasicBlock*, 4> Visited;
1232   SmallVector<BasicBlock*, 8> Stack;
1233   Stack.push_back(BaseBlock);
1234
1235   DenseMap<BasicBlock*, Value*> Results;
1236
1237   // Walk backwards through our predecessors, looking for instances of the
1238   // value number we're looking for.  Instances are recorded in the Results
1239   // map, which is then used to perform phi construction.
1240   while (!Stack.empty()) {
1241     BasicBlock* Current = Stack.back();
1242     Stack.pop_back();
1243
1244     // If we've walked all the way to a proper dominator, then give up. Cases
1245     // where the instance is in the dominator will have been caught by the fast
1246     // path, and any cases that require phi construction further than this are
1247     // probably not worth it anyways.  Note that this is a SIGNIFICANT compile
1248     // time improvement.
1249     if (DT->properlyDominates(Current, orig->getParent())) return 0;
1250
1251     DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA =
1252                                                        localAvail.find(Current);
1253     if (LA == localAvail.end()) return 0;
1254     DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno);
1255
1256     if (V != LA->second->table.end()) {
1257       // Found an instance, record it.
1258       Results.insert(std::make_pair(Current, V->second));
1259       continue;
1260     }
1261
1262     // If we reach the beginning of the function, then give up.
1263     if (pred_begin(Current) == pred_end(Current))
1264       return 0;
1265
1266     for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current);
1267          PI != PE; ++PI)
1268       if (Visited.insert(*PI))
1269         Stack.push_back(*PI);
1270   }
1271
1272   // If we didn't find instances, give up.  Otherwise, perform phi construction.
1273   if (Results.size() == 0)
1274     return 0;
1275   else
1276     return GetValueForBlock(BaseBlock, orig, Results, true);
1277 }
1278
1279 /// processInstruction - When calculating availability, handle an instruction
1280 /// by inserting it into the appropriate sets
1281 bool GVN::processInstruction(Instruction *I,
1282                              SmallVectorImpl<Instruction*> &toErase) {
1283   if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1284     bool changed = processLoad(L, toErase);
1285
1286     if (!changed) {
1287       unsigned num = VN.lookup_or_add(L);
1288       localAvail[I->getParent()]->table.insert(std::make_pair(num, L));
1289     }
1290
1291     return changed;
1292   }
1293
1294   uint32_t nextNum = VN.getNextUnusedValueNumber();
1295   unsigned num = VN.lookup_or_add(I);
1296
1297   if (BranchInst* BI = dyn_cast<BranchInst>(I)) {
1298     localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1299
1300     if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1301       return false;
1302
1303     Value* branchCond = BI->getCondition();
1304     uint32_t condVN = VN.lookup_or_add(branchCond);
1305
1306     BasicBlock* trueSucc = BI->getSuccessor(0);
1307     BasicBlock* falseSucc = BI->getSuccessor(1);
1308
1309     if (trueSucc->getSinglePredecessor())
1310       localAvail[trueSucc]->table[condVN] = ConstantInt::getTrue();
1311     if (falseSucc->getSinglePredecessor())
1312       localAvail[falseSucc]->table[condVN] = ConstantInt::getFalse();
1313
1314     return false;
1315
1316   // Allocations are always uniquely numbered, so we can save time and memory
1317   // by fast failing them.
1318   } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
1319     localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1320     return false;
1321   }
1322
1323   // Collapse PHI nodes
1324   if (PHINode* p = dyn_cast<PHINode>(I)) {
1325     Value* constVal = CollapsePhi(p);
1326
1327     if (constVal) {
1328       for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1329            PI != PE; ++PI)
1330         PI->second.erase(p);
1331
1332       p->replaceAllUsesWith(constVal);
1333       if (isa<PointerType>(constVal->getType()))
1334         MD->invalidateCachedPointerInfo(constVal);
1335       VN.erase(p);
1336
1337       toErase.push_back(p);
1338     } else {
1339       localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1340     }
1341
1342   // If the number we were assigned was a brand new VN, then we don't
1343   // need to do a lookup to see if the number already exists
1344   // somewhere in the domtree: it can't!
1345   } else if (num == nextNum) {
1346     localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1347
1348   // Perform fast-path value-number based elimination of values inherited from
1349   // dominators.
1350   } else if (Value* repl = lookupNumber(I->getParent(), num)) {
1351     // Remove it!
1352     VN.erase(I);
1353     I->replaceAllUsesWith(repl);
1354     if (isa<PointerType>(repl->getType()))
1355       MD->invalidateCachedPointerInfo(repl);
1356     toErase.push_back(I);
1357     return true;
1358
1359 #if 0
1360   // Perform slow-pathvalue-number based elimination with phi construction.
1361   } else if (Value* repl = AttemptRedundancyElimination(I, num)) {
1362     // Remove it!
1363     VN.erase(I);
1364     I->replaceAllUsesWith(repl);
1365     if (isa<PointerType>(repl->getType()))
1366       MD->invalidateCachedPointerInfo(repl);
1367     toErase.push_back(I);
1368     return true;
1369 #endif
1370   } else {
1371     localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1372   }
1373
1374   return false;
1375 }
1376
1377 /// runOnFunction - This is the main transformation entry point for a function.
1378 bool GVN::runOnFunction(Function& F) {
1379   MD = &getAnalysis<MemoryDependenceAnalysis>();
1380   DT = &getAnalysis<DominatorTree>();
1381   VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1382   VN.setMemDep(MD);
1383   VN.setDomTree(DT);
1384
1385   bool changed = false;
1386   bool shouldContinue = true;
1387
1388   // Merge unconditional branches, allowing PRE to catch more
1389   // optimization opportunities.
1390   for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1391     BasicBlock* BB = FI;
1392     ++FI;
1393     bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1394     if (removedBlock) NumGVNBlocks++;
1395
1396     changed |= removedBlock;
1397   }
1398
1399   unsigned Iteration = 0;
1400
1401   while (shouldContinue) {
1402     DEBUG(cerr << "GVN iteration: " << Iteration << "\n");
1403     shouldContinue = iterateOnFunction(F);
1404     changed |= shouldContinue;
1405     ++Iteration;
1406   }
1407
1408   if (EnablePRE) {
1409     bool PREChanged = true;
1410     while (PREChanged) {
1411       PREChanged = performPRE(F);
1412       changed |= PREChanged;
1413     }
1414   }
1415   // FIXME: Should perform GVN again after PRE does something.  PRE can move
1416   // computations into blocks where they become fully redundant.  Note that
1417   // we can't do this until PRE's critical edge splitting updates memdep.
1418   // Actually, when this happens, we should just fully integrate PRE into GVN.
1419
1420   cleanupGlobalSets();
1421
1422   return changed;
1423 }
1424
1425
1426 bool GVN::processBlock(BasicBlock* BB) {
1427   // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
1428   // incrementing BI before processing an instruction).
1429   SmallVector<Instruction*, 8> toErase;
1430   bool changed_function = false;
1431
1432   for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1433        BI != BE;) {
1434     changed_function |= processInstruction(BI, toErase);
1435     if (toErase.empty()) {
1436       ++BI;
1437       continue;
1438     }
1439
1440     // If we need some instructions deleted, do it now.
1441     NumGVNInstr += toErase.size();
1442
1443     // Avoid iterator invalidation.
1444     bool AtStart = BI == BB->begin();
1445     if (!AtStart)
1446       --BI;
1447
1448     for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1449          E = toErase.end(); I != E; ++I) {
1450       DEBUG(cerr << "GVN removed: " << **I);
1451       MD->removeInstruction(*I);
1452       (*I)->eraseFromParent();
1453       DEBUG(verifyRemoved(*I));
1454     }
1455     toErase.clear();
1456
1457     if (AtStart)
1458       BI = BB->begin();
1459     else
1460       ++BI;
1461   }
1462
1463   return changed_function;
1464 }
1465
1466 /// performPRE - Perform a purely local form of PRE that looks for diamond
1467 /// control flow patterns and attempts to perform simple PRE at the join point.
1468 bool GVN::performPRE(Function& F) {
1469   bool Changed = false;
1470   SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
1471   DenseMap<BasicBlock*, Value*> predMap;
1472   for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
1473        DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
1474     BasicBlock* CurrentBlock = *DI;
1475
1476     // Nothing to PRE in the entry block.
1477     if (CurrentBlock == &F.getEntryBlock()) continue;
1478
1479     for (BasicBlock::iterator BI = CurrentBlock->begin(),
1480          BE = CurrentBlock->end(); BI != BE; ) {
1481       Instruction *CurInst = BI++;
1482
1483       if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
1484           isa<PHINode>(CurInst) || (CurInst->getType() == Type::VoidTy) ||
1485           CurInst->mayReadFromMemory() || CurInst->mayWriteToMemory() ||
1486           isa<DbgInfoIntrinsic>(CurInst))
1487         continue;
1488
1489       uint32_t valno = VN.lookup(CurInst);
1490
1491       // Look for the predecessors for PRE opportunities.  We're
1492       // only trying to solve the basic diamond case, where
1493       // a value is computed in the successor and one predecessor,
1494       // but not the other.  We also explicitly disallow cases
1495       // where the successor is its own predecessor, because they're
1496       // more complicated to get right.
1497       unsigned numWith = 0;
1498       unsigned numWithout = 0;
1499       BasicBlock* PREPred = 0;
1500       predMap.clear();
1501
1502       for (pred_iterator PI = pred_begin(CurrentBlock),
1503            PE = pred_end(CurrentBlock); PI != PE; ++PI) {
1504         // We're not interested in PRE where the block is its
1505         // own predecessor, on in blocks with predecessors
1506         // that are not reachable.
1507         if (*PI == CurrentBlock) {
1508           numWithout = 2;
1509           break;
1510         } else if (!localAvail.count(*PI))  {
1511           numWithout = 2;
1512           break;
1513         }
1514
1515         DenseMap<uint32_t, Value*>::iterator predV =
1516                                             localAvail[*PI]->table.find(valno);
1517         if (predV == localAvail[*PI]->table.end()) {
1518           PREPred = *PI;
1519           numWithout++;
1520         } else if (predV->second == CurInst) {
1521           numWithout = 2;
1522         } else {
1523           predMap[*PI] = predV->second;
1524           numWith++;
1525         }
1526       }
1527
1528       // Don't do PRE when it might increase code size, i.e. when
1529       // we would need to insert instructions in more than one pred.
1530       if (numWithout != 1 || numWith == 0)
1531         continue;
1532
1533       // We can't do PRE safely on a critical edge, so instead we schedule
1534       // the edge to be split and perform the PRE the next time we iterate
1535       // on the function.
1536       unsigned succNum = 0;
1537       for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
1538            i != e; ++i)
1539         if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
1540           succNum = i;
1541           break;
1542         }
1543
1544       if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
1545         toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
1546         continue;
1547       }
1548
1549       // Instantiate the expression the in predecessor that lacked it.
1550       // Because we are going top-down through the block, all value numbers
1551       // will be available in the predecessor by the time we need them.  Any
1552       // that weren't original present will have been instantiated earlier
1553       // in this loop.
1554       Instruction* PREInstr = CurInst->clone();
1555       bool success = true;
1556       for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
1557         Value *Op = PREInstr->getOperand(i);
1558         if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
1559           continue;
1560
1561         if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
1562           PREInstr->setOperand(i, V);
1563         } else {
1564           success = false;
1565           break;
1566         }
1567       }
1568
1569       // Fail out if we encounter an operand that is not available in
1570       // the PRE predecessor.  This is typically because of loads which
1571       // are not value numbered precisely.
1572       if (!success) {
1573         delete PREInstr;
1574         DEBUG(verifyRemoved(PREInstr));
1575         continue;
1576       }
1577
1578       PREInstr->insertBefore(PREPred->getTerminator());
1579       PREInstr->setName(CurInst->getName() + ".pre");
1580       predMap[PREPred] = PREInstr;
1581       VN.add(PREInstr, valno);
1582       NumGVNPRE++;
1583
1584       // Update the availability map to include the new instruction.
1585       localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr));
1586
1587       // Create a PHI to make the value available in this block.
1588       PHINode* Phi = PHINode::Create(CurInst->getType(),
1589                                      CurInst->getName() + ".pre-phi",
1590                                      CurrentBlock->begin());
1591       for (pred_iterator PI = pred_begin(CurrentBlock),
1592            PE = pred_end(CurrentBlock); PI != PE; ++PI)
1593         Phi->addIncoming(predMap[*PI], *PI);
1594
1595       VN.add(Phi, valno);
1596       localAvail[CurrentBlock]->table[valno] = Phi;
1597
1598       CurInst->replaceAllUsesWith(Phi);
1599       if (isa<PointerType>(Phi->getType()))
1600         MD->invalidateCachedPointerInfo(Phi);
1601       VN.erase(CurInst);
1602
1603       DEBUG(cerr << "GVN PRE removed: " << *CurInst);
1604       MD->removeInstruction(CurInst);
1605       CurInst->eraseFromParent();
1606       DEBUG(verifyRemoved(CurInst));
1607       Changed = true;
1608     }
1609   }
1610
1611   for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
1612        I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
1613     SplitCriticalEdge(I->first, I->second, this);
1614
1615   return Changed || toSplit.size();
1616 }
1617
1618 /// iterateOnFunction - Executes one iteration of GVN
1619 bool GVN::iterateOnFunction(Function &F) {
1620   cleanupGlobalSets();
1621
1622   for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1623        DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
1624     if (DI->getIDom())
1625       localAvail[DI->getBlock()] =
1626                    new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
1627     else
1628       localAvail[DI->getBlock()] = new ValueNumberScope(0);
1629   }
1630
1631   // Top-down walk of the dominator tree
1632   bool changed = false;
1633 #if 0
1634   // Needed for value numbering with phi construction to work.
1635   ReversePostOrderTraversal<Function*> RPOT(&F);
1636   for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
1637        RE = RPOT.end(); RI != RE; ++RI)
1638     changed |= processBlock(*RI);
1639 #else
1640   for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1641        DE = df_end(DT->getRootNode()); DI != DE; ++DI)
1642     changed |= processBlock(DI->getBlock());
1643 #endif
1644
1645   return changed;
1646 }
1647
1648 void GVN::cleanupGlobalSets() {
1649   VN.clear();
1650   phiMap.clear();
1651
1652   for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1653        I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
1654     delete I->second;
1655   localAvail.clear();
1656 }
1657
1658 /// verifyRemoved - Verify that the specified instruction does not occur in our
1659 /// internal data structures.
1660 void GVN::verifyRemoved(const Instruction *Inst) const {
1661   VN.verifyRemoved(Inst);
1662
1663   // Walk through the PHI map to make sure the instruction isn't hiding in there
1664   // somewhere.
1665   for (PhiMapType::iterator
1666          I = phiMap.begin(), E = phiMap.end(); I != E; ++I) {
1667     assert(I->first != Inst && "Inst is still a key in PHI map!");
1668
1669     for (SmallPtrSet<Instruction*, 4>::iterator
1670            II = I->second.begin(), IE = I->second.end(); II != IE; ++II) {
1671       assert(*II != Inst && "Inst is still a value in PHI map!");
1672     }
1673   }
1674
1675   // Walk through the value number scope to make sure the instruction isn't
1676   // ferreted away in it.
1677   for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1678          I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
1679     const ValueNumberScope *VNS = I->second;
1680
1681     while (VNS) {
1682       for (DenseMap<uint32_t, Value*>::iterator
1683              II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
1684         assert(II->second != Inst && "Inst still in value numbering scope!");
1685       }
1686
1687       VNS = VNS->parent;
1688     }
1689   }
1690 }