lib/Transforms/IPO/MergeFunctions.cpp

   1 //===- MergeFunctions.cpp - Merge identical functions ---------------------===//
   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 looks for equivalent functions that are mergable and folds them.
  11 //
  12 // A hash is computed from the function, based on its type and number of
  13 // basic blocks.
  14 //
  15 // Once all hashes are computed, we perform an expensive equality comparison
  16 // on each function pair. This takes n^2/2 comparisons per bucket, so it's
  17 // important that the hash function be high quality. The equality comparison
  18 // iterates through each instruction in each basic block.
  19 //
  20 // When a match is found, the functions are folded. We can only fold two
  21 // functions when we know that the definition of one of them is not
  22 // overridable.
  23 //
  24 //===----------------------------------------------------------------------===//
  25 //
  26 // Future work:
  27 //
  28 // * fold vector<T*>::push_back and vector<S*>::push_back.
  29 //
  30 // These two functions have different types, but in a way that doesn't matter
  31 // to us. As long as we never see an S or T itself, using S* and S** is the
  32 // same as using a T* and T**.
  33 //
  34 // * virtual functions.
  35 //
  36 // Many functions have their address taken by the virtual function table for
  37 // the object they belong to. However, as long as it's only used for a lookup
  38 // and call, this is irrelevant, and we'd like to fold such implementations.
  39 //
  40 //===----------------------------------------------------------------------===//
  41
  42 #define DEBUG_TYPE "mergefunc"
  43 #include "llvm/Transforms/IPO.h"
  44 #include "llvm/ADT/DenseMap.h"
  45 #include "llvm/ADT/FoldingSet.h"
  46 #include "llvm/ADT/Statistic.h"
  47 #include "llvm/Constants.h"
  48 #include "llvm/InlineAsm.h"
  49 #include "llvm/Instructions.h"
  50 #include "llvm/LLVMContext.h"
  51 #include "llvm/Module.h"
  52 #include "llvm/Pass.h"
  53 #include "llvm/Support/CallSite.h"
  54 #include "llvm/Support/Debug.h"
  55 #include "llvm/Support/ErrorHandling.h"
  56 #include "llvm/Support/raw_ostream.h"
  57 #include <map>
  58 #include <vector>
  59 using namespace llvm;
  60
  61 STATISTIC(NumFunctionsMerged, "Number of functions merged");
  62
  63 namespace {
  64   struct MergeFunctions : public ModulePass {
  65     static char ID; // Pass identification, replacement for typeid
  66     MergeFunctions() : ModulePass(&ID) {}
  67
  68     bool runOnModule(Module &M);
  69   };
  70 }
  71
  72 char MergeFunctions::ID = 0;
  73 static RegisterPass<MergeFunctions>
  74 X("mergefunc", "Merge Functions");
  75
  76 ModulePass *llvm::createMergeFunctionsPass() {
  77   return new MergeFunctions();
  78 }
  79
  80 // ===----------------------------------------------------------------------===
  81 // Comparison of functions
  82 // ===----------------------------------------------------------------------===
  83
  84 static unsigned long hash(const Function *F) {
  85   const FunctionType *FTy = F->getFunctionType();
  86
  87   FoldingSetNodeID ID;
  88   ID.AddInteger(F->size());
  89   ID.AddInteger(F->getCallingConv());
  90   ID.AddBoolean(F->hasGC());
  91   ID.AddBoolean(FTy->isVarArg());
  92   ID.AddInteger(FTy->getReturnType()->getTypeID());
  93   for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
  94     ID.AddInteger(FTy->getParamType(i)->getTypeID());
  95   return ID.ComputeHash();
  96 }
  97
  98 /// IgnoreBitcasts - given a bitcast, returns the first non-bitcast found by
  99 /// walking the chain of cast operands. Otherwise, returns the argument.
 100 static Value* IgnoreBitcasts(Value *V) {
 101   while (BitCastInst *BC = dyn_cast<BitCastInst>(V))
 102     V = BC->getOperand(0);
 103
 104   return V;
 105 }
 106
 107 /// isEquivalentType - any two pointers are equivalent. Otherwise, standard
 108 /// type equivalence rules apply.
 109 static bool isEquivalentType(const Type *Ty1, const Type *Ty2) {
 110   if (Ty1 == Ty2)
 111     return true;
 112   if (Ty1->getTypeID() != Ty2->getTypeID())
 113     return false;
 114
 115   switch(Ty1->getTypeID()) {
 116   case Type::VoidTyID:
 117   case Type::FloatTyID:
 118   case Type::DoubleTyID:
 119   case Type::X86_FP80TyID:
 120   case Type::FP128TyID:
 121   case Type::PPC_FP128TyID:
 122   case Type::LabelTyID:
 123   case Type::MetadataTyID:
 124     return true;
 125
 126   case Type::IntegerTyID:
 127   case Type::OpaqueTyID:
 128     // Ty1 == Ty2 would have returned true earlier.
 129     return false;
 130
 131   default:
 132     llvm_unreachable("Unknown type!");
 133     return false;
 134
 135   case Type::PointerTyID: {
 136     const PointerType *PTy1 = cast<PointerType>(Ty1);
 137     const PointerType *PTy2 = cast<PointerType>(Ty2);
 138     return PTy1->getAddressSpace() == PTy2->getAddressSpace();
 139   }
 140
 141   case Type::StructTyID: {
 142     const StructType *STy1 = cast<StructType>(Ty1);
 143     const StructType *STy2 = cast<StructType>(Ty2);
 144     if (STy1->getNumElements() != STy2->getNumElements())
 145       return false;
 146
 147     if (STy1->isPacked() != STy2->isPacked())
 148       return false;
 149
 150     for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) {
 151       if (!isEquivalentType(STy1->getElementType(i), STy2->getElementType(i)))
 152         return false;
 153     }
 154     return true;
 155   }
 156
 157   case Type::FunctionTyID: {
 158     const FunctionType *FTy1 = cast<FunctionType>(Ty1);
 159     const FunctionType *FTy2 = cast<FunctionType>(Ty2);
 160     if (FTy1->getNumParams() != FTy2->getNumParams() ||
 161         FTy1->isVarArg() != FTy2->isVarArg())
 162       return false;
 163
 164     if (!isEquivalentType(FTy1->getReturnType(), FTy2->getReturnType()))
 165       return false;
 166
 167     for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) {
 168       if (!isEquivalentType(FTy1->getParamType(i), FTy2->getParamType(i)))
 169         return false;
 170     }
 171     return true;
 172   }
 173
 174   case Type::ArrayTyID:
 175   case Type::VectorTyID: {
 176     const SequentialType *STy1 = cast<SequentialType>(Ty1);
 177     const SequentialType *STy2 = cast<SequentialType>(Ty2);
 178     return isEquivalentType(STy1->getElementType(), STy2->getElementType());
 179   }
 180   }
 181 }
 182
 183 /// isEquivalentOperation - determine whether the two operations are the same
 184 /// except that pointer-to-A and pointer-to-B are equivalent. This should be
 185 /// kept in sync with Instruction::isSameOperationAs.
 186 static bool
 187 isEquivalentOperation(const Instruction *I1, const Instruction *I2) {
 188   if (I1->getOpcode() != I2->getOpcode() ||
 189       I1->getNumOperands() != I2->getNumOperands() ||
 190       !isEquivalentType(I1->getType(), I2->getType()) ||
 191       !I1->hasSameSubclassOptionalData(I2))
 192     return false;
 193
 194   // We have two instructions of identical opcode and #operands.  Check to see
 195   // if all operands are the same type
 196   for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i)
 197     if (!isEquivalentType(I1->getOperand(i)->getType(),
 198                           I2->getOperand(i)->getType()))
 199       return false;
 200
 201   // Check special state that is a part of some instructions.
 202   if (const LoadInst *LI = dyn_cast<LoadInst>(I1))
 203     return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() &&
 204            LI->getAlignment() == cast<LoadInst>(I2)->getAlignment();
 205   if (const StoreInst *SI = dyn_cast<StoreInst>(I1))
 206     return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() &&
 207            SI->getAlignment() == cast<StoreInst>(I2)->getAlignment();
 208   if (const CmpInst *CI = dyn_cast<CmpInst>(I1))
 209     return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate();
 210   if (const CallInst *CI = dyn_cast<CallInst>(I1))
 211     return CI->isTailCall() == cast<CallInst>(I2)->isTailCall() &&
 212            CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() &&
 213            CI->getAttributes().getRawPointer() ==
 214              cast<CallInst>(I2)->getAttributes().getRawPointer();
 215   if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1))
 216     return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() &&
 217            CI->getAttributes().getRawPointer() ==
 218              cast<InvokeInst>(I2)->getAttributes().getRawPointer();
 219   if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) {
 220     if (IVI->getNumIndices() != cast<InsertValueInst>(I2)->getNumIndices())
 221       return false;
 222     for (unsigned i = 0, e = IVI->getNumIndices(); i != e; ++i)
 223       if (IVI->idx_begin()[i] != cast<InsertValueInst>(I2)->idx_begin()[i])
 224         return false;
 225     return true;
 226   }
 227   if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) {
 228     if (EVI->getNumIndices() != cast<ExtractValueInst>(I2)->getNumIndices())
 229       return false;
 230     for (unsigned i = 0, e = EVI->getNumIndices(); i != e; ++i)
 231       if (EVI->idx_begin()[i] != cast<ExtractValueInst>(I2)->idx_begin()[i])
 232         return false;
 233     return true;
 234   }
 235
 236   return true;
 237 }
 238
 239 static bool compare(const Value *V, const Value *U) {
 240   assert(!isa<BasicBlock>(V) && !isa<BasicBlock>(U) &&
 241          "Must not compare basic blocks.");
 242
 243   assert(isEquivalentType(V->getType(), U->getType()) &&
 244         "Two of the same operation have operands of different type.");
 245
 246   // TODO: If the constant is an expression of F, we should accept that it's
 247   // equal to the same expression in terms of G.
 248   if (isa<Constant>(V))
 249     return V == U;
 250
 251   // The caller has ensured that ValueMap[V] != U. Since Arguments are
 252   // pre-loaded into the ValueMap, and Instructions are added as we go, we know
 253   // that this can only be a mis-match.
 254   if (isa<Instruction>(V) || isa<Argument>(V))
 255     return false;
 256
 257   if (isa<InlineAsm>(V) && isa<InlineAsm>(U)) {
 258     const InlineAsm *IAF = cast<InlineAsm>(V);
 259     const InlineAsm *IAG = cast<InlineAsm>(U);
 260     return IAF->getAsmString() == IAG->getAsmString() &&
 261            IAF->getConstraintString() == IAG->getConstraintString();
 262   }
 263
 264   return false;
 265 }
 266
 267 static bool equals(const BasicBlock *BB1, const BasicBlock *BB2,
 268                    DenseMap<const Value *, const Value *> &ValueMap,
 269                    DenseMap<const Value *, const Value *> &SpeculationMap) {
 270   // Speculatively add it anyways. If it's false, we'll notice a difference
 271   // later, and this won't matter.
 272   ValueMap[BB1] = BB2;
 273
 274   BasicBlock::const_iterator FI = BB1->begin(), FE = BB1->end();
 275   BasicBlock::const_iterator GI = BB2->begin(), GE = BB2->end();
 276
 277   do {
 278     if (isa<BitCastInst>(FI)) {
 279       ++FI;
 280       continue;
 281     }
 282     if (isa<BitCastInst>(GI)) {
 283       ++GI;
 284       continue;
 285     }
 286
 287     if (!isEquivalentOperation(FI, GI))
 288       return false;
 289
 290     if (isa<GetElementPtrInst>(FI)) {
 291       const GetElementPtrInst *GEPF = cast<GetElementPtrInst>(FI);
 292       const GetElementPtrInst *GEPG = cast<GetElementPtrInst>(GI);
 293       if (GEPF->hasAllZeroIndices() && GEPG->hasAllZeroIndices()) {
 294         // It's effectively a bitcast.
 295         ++FI, ++GI;
 296         continue;
 297       }
 298
 299       // TODO: we only really care about the elements before the index
 300       if (FI->getOperand(0)->getType() != GI->getOperand(0)->getType())
 301         return false;
 302     }
 303
 304     if (ValueMap[FI] == GI) {
 305       ++FI, ++GI;
 306       continue;
 307     }
 308
 309     if (ValueMap[FI] != NULL)
 310       return false;
 311
 312     for (unsigned i = 0, e = FI->getNumOperands(); i != e; ++i) {
 313       Value *OpF = IgnoreBitcasts(FI->getOperand(i));
 314       Value *OpG = IgnoreBitcasts(GI->getOperand(i));
 315
 316       if (ValueMap[OpF] == OpG)
 317         continue;
 318
 319       if (ValueMap[OpF] != NULL)
 320         return false;
 321
 322       if (OpF->getValueID() != OpG->getValueID() ||
 323           !isEquivalentType(OpF->getType(), OpG->getType()))
 324         return false;
 325
 326       if (isa<PHINode>(FI)) {
 327         if (SpeculationMap[OpF] == NULL)
 328           SpeculationMap[OpF] = OpG;
 329         else if (SpeculationMap[OpF] != OpG)
 330           return false;
 331         continue;
 332       } else if (isa<BasicBlock>(OpF)) {
 333         assert(isa<TerminatorInst>(FI) &&
 334                "BasicBlock referenced by non-Terminator non-PHI");
 335         // This call changes the ValueMap, hence we can't use
 336         // Value *& = ValueMap[...]
 337         if (!equals(cast<BasicBlock>(OpF), cast<BasicBlock>(OpG), ValueMap,
 338                     SpeculationMap))
 339           return false;
 340       } else {
 341         if (!compare(OpF, OpG))
 342           return false;
 343       }
 344
 345       ValueMap[OpF] = OpG;
 346     }
 347
 348     ValueMap[FI] = GI;
 349     ++FI, ++GI;
 350   } while (FI != FE && GI != GE);
 351
 352   return FI == FE && GI == GE;
 353 }
 354
 355 static bool equals(const Function *F, const Function *G) {
 356   // We need to recheck everything, but check the things that weren't included
 357   // in the hash first.
 358
 359   if (F->getAttributes() != G->getAttributes())
 360     return false;
 361
 362   if (F->hasGC() != G->hasGC())
 363     return false;
 364
 365   if (F->hasGC() && F->getGC() != G->getGC())
 366     return false;
 367
 368   if (F->hasSection() != G->hasSection())
 369     return false;
 370
 371   if (F->hasSection() && F->getSection() != G->getSection())
 372     return false;
 373
 374   if (F->isVarArg() != G->isVarArg())
 375     return false;
 376
 377   // TODO: if it's internal and only used in direct calls, we could handle this
 378   // case too.
 379   if (F->getCallingConv() != G->getCallingConv())
 380     return false;
 381
 382   if (!isEquivalentType(F->getFunctionType(), G->getFunctionType()))
 383     return false;
 384
 385   DenseMap<const Value *, const Value *> ValueMap;
 386   DenseMap<const Value *, const Value *> SpeculationMap;
 387   ValueMap[F] = G;
 388
 389   assert(F->arg_size() == G->arg_size() &&
 390          "Identical functions have a different number of args.");
 391
 392   for (Function::const_arg_iterator fi = F->arg_begin(), gi = G->arg_begin(),
 393          fe = F->arg_end(); fi != fe; ++fi, ++gi)
 394     ValueMap[fi] = gi;
 395
 396   if (!equals(&F->getEntryBlock(), &G->getEntryBlock(), ValueMap,
 397               SpeculationMap))
 398     return false;
 399
 400   for (DenseMap<const Value *, const Value *>::iterator
 401          I = SpeculationMap.begin(), E = SpeculationMap.end(); I != E; ++I) {
 402     if (ValueMap[I->first] != I->second)
 403       return false;
 404   }
 405
 406   return true;
 407 }
 408
 409 // ===----------------------------------------------------------------------===
 410 // Folding of functions
 411 // ===----------------------------------------------------------------------===
 412
 413 // Cases:
 414 // * F is external strong, G is external strong:
 415 //   turn G into a thunk to F    (1)
 416 // * F is external strong, G is external weak:
 417 //   turn G into a thunk to F    (1)
 418 // * F is external weak, G is external weak:
 419 //   unfoldable
 420 // * F is external strong, G is internal:
 421 //   address of G taken:
 422 //     turn G into a thunk to F  (1)
 423 //   address of G not taken:
 424 //     make G an alias to F      (2)
 425 // * F is internal, G is external weak
 426 //   address of F is taken:
 427 //     turn G into a thunk to F  (1)
 428 //   address of F is not taken:
 429 //     make G an alias of F      (2)
 430 // * F is internal, G is internal:
 431 //   address of F and G are taken:
 432 //     turn G into a thunk to F  (1)
 433 //   address of G is not taken:
 434 //     make G an alias to F      (2)
 435 //
 436 // alias requires linkage == (external,local,weak) fallback to creating a thunk
 437 // external means 'externally visible' linkage != (internal,private)
 438 // internal means linkage == (internal,private)
 439 // weak means linkage mayBeOverridable
 440 // being external implies that the address is taken
 441 //
 442 // 1. turn G into a thunk to F
 443 // 2. make G an alias to F
 444
 445 enum LinkageCategory {
 446   ExternalStrong,
 447   ExternalWeak,
 448   Internal
 449 };
 450
 451 static LinkageCategory categorize(const Function *F) {
 452   switch (F->getLinkage()) {
 453   case GlobalValue::InternalLinkage:
 454   case GlobalValue::PrivateLinkage:
 455   case GlobalValue::LinkerPrivateLinkage:
 456     return Internal;
 457
 458   case GlobalValue::WeakAnyLinkage:
 459   case GlobalValue::WeakODRLinkage:
 460   case GlobalValue::ExternalWeakLinkage:
 461     return ExternalWeak;
 462
 463   case GlobalValue::ExternalLinkage:
 464   case GlobalValue::AvailableExternallyLinkage:
 465   case GlobalValue::LinkOnceAnyLinkage:
 466   case GlobalValue::LinkOnceODRLinkage:
 467   case GlobalValue::AppendingLinkage:
 468   case GlobalValue::DLLImportLinkage:
 469   case GlobalValue::DLLExportLinkage:
 470   case GlobalValue::CommonLinkage:
 471     return ExternalStrong;
 472   }
 473
 474   llvm_unreachable("Unknown LinkageType.");
 475   return ExternalWeak;
 476 }
 477
 478 static void ThunkGToF(Function *F, Function *G) {
 479   Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "",
 480                                     G->getParent());
 481   BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG);
 482
 483   std::vector<Value *> Args;
 484   unsigned i = 0;
 485   const FunctionType *FFTy = F->getFunctionType();
 486   for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end();
 487        AI != AE; ++AI) {
 488     if (FFTy->getParamType(i) == AI->getType())
 489       Args.push_back(AI);
 490     else {
 491       Value *BCI = new BitCastInst(AI, FFTy->getParamType(i), "", BB);
 492       Args.push_back(BCI);
 493     }
 494     ++i;
 495   }
 496
 497   CallInst *CI = CallInst::Create(F, Args.begin(), Args.end(), "", BB);
 498   CI->setTailCall();
 499   CI->setCallingConv(F->getCallingConv());
 500   if (NewG->getReturnType()->isVoidTy()) {
 501     ReturnInst::Create(F->getContext(), BB);
 502   } else if (CI->getType() != NewG->getReturnType()) {
 503     Value *BCI = new BitCastInst(CI, NewG->getReturnType(), "", BB);
 504     ReturnInst::Create(F->getContext(), BCI, BB);
 505   } else {
 506     ReturnInst::Create(F->getContext(), CI, BB);
 507   }
 508
 509   NewG->copyAttributesFrom(G);
 510   NewG->takeName(G);
 511   G->replaceAllUsesWith(NewG);
 512   G->eraseFromParent();
 513
 514   // TODO: look at direct callers to G and make them all direct callers to F.
 515 }
 516
 517 static void AliasGToF(Function *F, Function *G) {
 518   if (!G->hasExternalLinkage() && !G->hasLocalLinkage() && !G->hasWeakLinkage())
 519     return ThunkGToF(F, G);
 520
 521   GlobalAlias *GA = new GlobalAlias(
 522     G->getType(), G->getLinkage(), "",
 523     ConstantExpr::getBitCast(F, G->getType()), G->getParent());
 524   F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
 525   GA->takeName(G);
 526   GA->setVisibility(G->getVisibility());
 527   G->replaceAllUsesWith(GA);
 528   G->eraseFromParent();
 529 }
 530
 531 static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) {
 532   Function *F = FnVec[i];
 533   Function *G = FnVec[j];
 534
 535   LinkageCategory catF = categorize(F);
 536   LinkageCategory catG = categorize(G);
 537
 538   if (catF == ExternalWeak || (catF == Internal && catG == ExternalStrong)) {
 539     std::swap(FnVec[i], FnVec[j]);
 540     std::swap(F, G);
 541     std::swap(catF, catG);
 542   }
 543
 544   switch (catF) {
 545     case ExternalStrong:
 546       switch (catG) {
 547         case ExternalStrong:
 548         case ExternalWeak:
 549           ThunkGToF(F, G);
 550           break;
 551         case Internal:
 552           if (G->hasAddressTaken())
 553             ThunkGToF(F, G);
 554           else
 555             AliasGToF(F, G);
 556           break;
 557       }
 558       break;
 559
 560     case ExternalWeak: {
 561       assert(catG == ExternalWeak);
 562
 563       // Make them both thunks to the same internal function.
 564       F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
 565       Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "",
 566                                      F->getParent());
 567       H->copyAttributesFrom(F);
 568       H->takeName(F);
 569       F->replaceAllUsesWith(H);
 570
 571       ThunkGToF(F, G);
 572       ThunkGToF(F, H);
 573
 574       F->setLinkage(GlobalValue::InternalLinkage);
 575     } break;
 576
 577     case Internal:
 578       switch (catG) {
 579         case ExternalStrong:
 580           llvm_unreachable(0);
 581           // fall-through
 582         case ExternalWeak:
 583           if (F->hasAddressTaken())
 584             ThunkGToF(F, G);
 585           else
 586             AliasGToF(F, G);
 587           break;
 588         case Internal: {
 589           bool addrTakenF = F->hasAddressTaken();
 590           bool addrTakenG = G->hasAddressTaken();
 591           if (!addrTakenF && addrTakenG) {
 592             std::swap(FnVec[i], FnVec[j]);
 593             std::swap(F, G);
 594             std::swap(addrTakenF, addrTakenG);
 595           }
 596
 597           if (addrTakenF && addrTakenG) {
 598             ThunkGToF(F, G);
 599           } else {
 600             assert(!addrTakenG);
 601             AliasGToF(F, G);
 602           }
 603         } break;
 604       }
 605       break;
 606   }
 607
 608   ++NumFunctionsMerged;
 609   return true;
 610 }
 611
 612 // ===----------------------------------------------------------------------===
 613 // Pass definition
 614 // ===----------------------------------------------------------------------===
 615
 616 bool MergeFunctions::runOnModule(Module &M) {
 617   bool Changed = false;
 618
 619   std::map<unsigned long, std::vector<Function *> > FnMap;
 620
 621   for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
 622     if (F->isDeclaration() || F->isIntrinsic())
 623       continue;
 624
 625     FnMap[hash(F)].push_back(F);
 626   }
 627
 628   // TODO: instead of running in a loop, we could also fold functions in
 629   // callgraph order. Constructing the CFG probably isn't cheaper than just
 630   // running in a loop, unless it happened to already be available.
 631
 632   bool LocalChanged;
 633   do {
 634     LocalChanged = false;
 635     DEBUG(dbgs() << "size: " << FnMap.size() << "\n");
 636     for (std::map<unsigned long, std::vector<Function *> >::iterator
 637          I = FnMap.begin(), E = FnMap.end(); I != E; ++I) {
 638       std::vector<Function *> &FnVec = I->second;
 639       DEBUG(dbgs() << "hash (" << I->first << "): " << FnVec.size() << "\n");
 640
 641       for (int i = 0, e = FnVec.size(); i != e; ++i) {
 642         for (int j = i + 1; j != e; ++j) {
 643           bool isEqual = equals(FnVec[i], FnVec[j]);
 644
 645           DEBUG(dbgs() << "  " << FnVec[i]->getName()
 646                 << (isEqual ? " == " : " != ")
 647                 << FnVec[j]->getName() << "\n");
 648
 649           if (isEqual) {
 650             if (fold(FnVec, i, j)) {
 651               LocalChanged = true;
 652               FnVec.erase(FnVec.begin() + j);
 653               --j, --e;
 654             }
 655           }
 656         }
 657       }
 658
 659     }
 660     Changed |= LocalChanged;
 661   } while (LocalChanged);
 662
 663   return Changed;
 664 }