MergeFunctions.cpp revision 3867f09c00d3df76d6e87b112d46154ba909a757
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/Module.h" 51#include "llvm/Pass.h" 52#include "llvm/Support/CallSite.h" 53#include "llvm/Support/Compiler.h" 54#include "llvm/Support/Debug.h" 55#include <map> 56#include <vector> 57using namespace llvm; 58 59STATISTIC(NumFunctionsMerged, "Number of functions merged"); 60 61namespace { 62 struct VISIBILITY_HIDDEN MergeFunctions : public ModulePass { 63 static char ID; // Pass identification, replacement for typeid 64 MergeFunctions() : ModulePass((intptr_t)&ID) {} 65 66 bool runOnModule(Module &M); 67 }; 68} 69 70char MergeFunctions::ID = 0; 71static RegisterPass<MergeFunctions> 72X("mergefunc", "Merge Functions"); 73 74ModulePass *llvm::createMergeFunctionsPass() { 75 return new MergeFunctions(); 76} 77 78// ===----------------------------------------------------------------------=== 79// Comparison of functions 80// ===----------------------------------------------------------------------=== 81 82static unsigned long hash(const Function *F) { 83 const FunctionType *FTy = F->getFunctionType(); 84 85 FoldingSetNodeID ID; 86 ID.AddInteger(F->size()); 87 ID.AddInteger(F->getCallingConv()); 88 ID.AddBoolean(F->hasGC()); 89 ID.AddBoolean(FTy->isVarArg()); 90 ID.AddInteger(FTy->getReturnType()->getTypeID()); 91 for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i) 92 ID.AddInteger(FTy->getParamType(i)->getTypeID()); 93 return ID.ComputeHash(); 94} 95 96/// IgnoreBitcasts - given a bitcast, returns the first non-bitcast found by 97/// walking the chain of cast operands. Otherwise, returns the argument. 98static Value* IgnoreBitcasts(Value *V) { 99 while (BitCastInst *BC = dyn_cast<BitCastInst>(V)) 100 V = BC->getOperand(0); 101 102 return V; 103} 104 105/// isEquivalentType - any two pointers are equivalent. Otherwise, standard 106/// type equivalence rules apply. 107static bool isEquivalentType(const Type *Ty1, const Type *Ty2) { 108 if (Ty1 == Ty2) 109 return true; 110 if (Ty1->getTypeID() != Ty2->getTypeID()) 111 return false; 112 113 switch(Ty1->getTypeID()) { 114 case Type::VoidTyID: 115 case Type::FloatTyID: 116 case Type::DoubleTyID: 117 case Type::X86_FP80TyID: 118 case Type::FP128TyID: 119 case Type::PPC_FP128TyID: 120 case Type::LabelTyID: 121 case Type::MetadataTyID: 122 return true; 123 124 case Type::IntegerTyID: 125 case Type::OpaqueTyID: 126 // Ty1 == Ty2 would have returned true earlier. 127 return false; 128 129 default: 130 assert(0 && "Unknown type!"); 131 return false; 132 133 case Type::PointerTyID: { 134 const PointerType *PTy1 = cast<PointerType>(Ty1); 135 const PointerType *PTy2 = cast<PointerType>(Ty2); 136 return PTy1->getAddressSpace() == PTy2->getAddressSpace(); 137 } 138 139 case Type::StructTyID: { 140 const StructType *STy1 = cast<StructType>(Ty1); 141 const StructType *STy2 = cast<StructType>(Ty2); 142 if (STy1->getNumElements() != STy2->getNumElements()) 143 return false; 144 145 if (STy1->isPacked() != STy2->isPacked()) 146 return false; 147 148 for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) { 149 if (!isEquivalentType(STy1->getElementType(i), STy2->getElementType(i))) 150 return false; 151 } 152 return true; 153 } 154 155 case Type::FunctionTyID: { 156 const FunctionType *FTy1 = cast<FunctionType>(Ty1); 157 const FunctionType *FTy2 = cast<FunctionType>(Ty2); 158 if (FTy1->getNumParams() != FTy2->getNumParams() || 159 FTy1->isVarArg() != FTy2->isVarArg()) 160 return false; 161 162 if (!isEquivalentType(FTy1->getReturnType(), FTy2->getReturnType())) 163 return false; 164 165 for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) { 166 if (!isEquivalentType(FTy1->getParamType(i), FTy2->getParamType(i))) 167 return false; 168 } 169 return true; 170 } 171 172 case Type::ArrayTyID: 173 case Type::VectorTyID: { 174 const SequentialType *STy1 = cast<SequentialType>(Ty1); 175 const SequentialType *STy2 = cast<SequentialType>(Ty2); 176 return isEquivalentType(STy1->getElementType(), STy2->getElementType()); 177 } 178 } 179} 180 181/// isEquivalentOperation - determine whether the two operations are the same 182/// except that pointer-to-A and pointer-to-B are equivalent. This should be 183/// kept in sync with Instruction::isSameOperandAs. 184static bool isEquivalentOperation(const Instruction *I1, const Instruction *I2) { 185 if (I1->getOpcode() != I2->getOpcode() || 186 I1->getNumOperands() != I2->getNumOperands() || 187 !isEquivalentType(I1->getType(), I2->getType())) 188 return false; 189 190 // We have two instructions of identical opcode and #operands. Check to see 191 // if all operands are the same type 192 for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i) 193 if (!isEquivalentType(I1->getOperand(i)->getType(), 194 I2->getOperand(i)->getType())) 195 return false; 196 197 // Check special state that is a part of some instructions. 198 if (const LoadInst *LI = dyn_cast<LoadInst>(I1)) 199 return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() && 200 LI->getAlignment() == cast<LoadInst>(I2)->getAlignment(); 201 if (const StoreInst *SI = dyn_cast<StoreInst>(I1)) 202 return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() && 203 SI->getAlignment() == cast<StoreInst>(I2)->getAlignment(); 204 if (const CmpInst *CI = dyn_cast<CmpInst>(I1)) 205 return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate(); 206 if (const CallInst *CI = dyn_cast<CallInst>(I1)) 207 return CI->isTailCall() == cast<CallInst>(I2)->isTailCall() && 208 CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() && 209 CI->getAttributes().getRawPointer() == 210 cast<CallInst>(I2)->getAttributes().getRawPointer(); 211 if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1)) 212 return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() && 213 CI->getAttributes().getRawPointer() == 214 cast<InvokeInst>(I2)->getAttributes().getRawPointer(); 215 if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) { 216 if (IVI->getNumIndices() != cast<InsertValueInst>(I2)->getNumIndices()) 217 return false; 218 for (unsigned i = 0, e = IVI->getNumIndices(); i != e; ++i) 219 if (IVI->idx_begin()[i] != cast<InsertValueInst>(I2)->idx_begin()[i]) 220 return false; 221 return true; 222 } 223 if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) { 224 if (EVI->getNumIndices() != cast<ExtractValueInst>(I2)->getNumIndices()) 225 return false; 226 for (unsigned i = 0, e = EVI->getNumIndices(); i != e; ++i) 227 if (EVI->idx_begin()[i] != cast<ExtractValueInst>(I2)->idx_begin()[i]) 228 return false; 229 return true; 230 } 231 232 return true; 233} 234 235static bool compare(const Value *V, const Value *U) { 236 assert(!isa<BasicBlock>(V) && !isa<BasicBlock>(U) && 237 "Must not compare basic blocks."); 238 239 assert(isEquivalentType(V->getType(), U->getType()) && 240 "Two of the same operation have operands of different type."); 241 242 // TODO: If the constant is an expression of F, we should accept that it's 243 // equal to the same expression in terms of G. 244 if (isa<Constant>(V)) 245 return V == U; 246 247 // The caller has ensured that ValueMap[V] != U. Since Arguments are 248 // pre-loaded into the ValueMap, and Instructions are added as we go, we know 249 // that this can only be a mis-match. 250 if (isa<Instruction>(V) || isa<Argument>(V)) 251 return false; 252 253 if (isa<InlineAsm>(V) && isa<InlineAsm>(U)) { 254 const InlineAsm *IAF = cast<InlineAsm>(V); 255 const InlineAsm *IAG = cast<InlineAsm>(U); 256 return IAF->getAsmString() == IAG->getAsmString() && 257 IAF->getConstraintString() == IAG->getConstraintString(); 258 } 259 260 return false; 261} 262 263static bool equals(const BasicBlock *BB1, const BasicBlock *BB2, 264 DenseMap<const Value *, const Value *> &ValueMap, 265 DenseMap<const Value *, const Value *> &SpeculationMap) { 266 // Speculatively add it anyways. If it's false, we'll notice a difference 267 // later, and this won't matter. 268 ValueMap[BB1] = BB2; 269 270 BasicBlock::const_iterator FI = BB1->begin(), FE = BB1->end(); 271 BasicBlock::const_iterator GI = BB2->begin(), GE = BB2->end(); 272 273 do { 274 if (isa<BitCastInst>(FI)) { 275 ++FI; 276 continue; 277 } 278 if (isa<BitCastInst>(GI)) { 279 ++GI; 280 continue; 281 } 282 283 if (!isEquivalentOperation(FI, GI)) 284 return false; 285 286 if (ValueMap[FI] == GI) { 287 ++FI, ++GI; 288 continue; 289 } 290 291 if (ValueMap[FI] != NULL) 292 return false; 293 294 for (unsigned i = 0, e = FI->getNumOperands(); i != e; ++i) { 295 Value *OpF = IgnoreBitcasts(FI->getOperand(i)); 296 Value *OpG = IgnoreBitcasts(GI->getOperand(i)); 297 298 if (ValueMap[OpF] == OpG) 299 continue; 300 301 if (ValueMap[OpF] != NULL) 302 return false; 303 304 if (OpF->getValueID() != OpG->getValueID() || 305 !isEquivalentType(OpF->getType(), OpG->getType())) 306 return false; 307 308 if (isa<PHINode>(FI)) { 309 if (SpeculationMap[OpF] == NULL) 310 SpeculationMap[OpF] = OpG; 311 else if (SpeculationMap[OpF] != OpG) 312 return false; 313 continue; 314 } else if (isa<BasicBlock>(OpF)) { 315 assert(isa<TerminatorInst>(FI) && 316 "BasicBlock referenced by non-Terminator non-PHI"); 317 // This call changes the ValueMap, hence we can't use 318 // Value *& = ValueMap[...] 319 if (!equals(cast<BasicBlock>(OpF), cast<BasicBlock>(OpG), ValueMap, 320 SpeculationMap)) 321 return false; 322 } else { 323 if (!compare(OpF, OpG)) 324 return false; 325 } 326 327 ValueMap[OpF] = OpG; 328 } 329 330 ValueMap[FI] = GI; 331 ++FI, ++GI; 332 } while (FI != FE && GI != GE); 333 334 return FI == FE && GI == GE; 335} 336 337static bool equals(const Function *F, const Function *G) { 338 // We need to recheck everything, but check the things that weren't included 339 // in the hash first. 340 341 if (F->getAttributes() != G->getAttributes()) 342 return false; 343 344 if (F->hasGC() != G->hasGC()) 345 return false; 346 347 if (F->hasGC() && F->getGC() != G->getGC()) 348 return false; 349 350 if (F->hasSection() != G->hasSection()) 351 return false; 352 353 if (F->hasSection() && F->getSection() != G->getSection()) 354 return false; 355 356 if (F->isVarArg() != G->isVarArg()) 357 return false; 358 359 // TODO: if it's internal and only used in direct calls, we could handle this 360 // case too. 361 if (F->getCallingConv() != G->getCallingConv()) 362 return false; 363 364 if (!isEquivalentType(F->getFunctionType(), G->getFunctionType())) 365 return false; 366 367 DenseMap<const Value *, const Value *> ValueMap; 368 DenseMap<const Value *, const Value *> SpeculationMap; 369 ValueMap[F] = G; 370 371 assert(F->arg_size() == G->arg_size() && 372 "Identical functions have a different number of args."); 373 374 for (Function::const_arg_iterator fi = F->arg_begin(), gi = G->arg_begin(), 375 fe = F->arg_end(); fi != fe; ++fi, ++gi) 376 ValueMap[fi] = gi; 377 378 if (!equals(&F->getEntryBlock(), &G->getEntryBlock(), ValueMap, 379 SpeculationMap)) 380 return false; 381 382 for (DenseMap<const Value *, const Value *>::iterator 383 I = SpeculationMap.begin(), E = SpeculationMap.end(); I != E; ++I) { 384 if (ValueMap[I->first] != I->second) 385 return false; 386 } 387 388 return true; 389} 390 391// ===----------------------------------------------------------------------=== 392// Folding of functions 393// ===----------------------------------------------------------------------=== 394 395// Cases: 396// * F is external strong, G is external strong: 397// turn G into a thunk to F (1) 398// * F is external strong, G is external weak: 399// turn G into a thunk to F (1) 400// * F is external weak, G is external weak: 401// unfoldable 402// * F is external strong, G is internal: 403// address of G taken: 404// turn G into a thunk to F (1) 405// address of G not taken: 406// make G an alias to F (2) 407// * F is internal, G is external weak 408// address of F is taken: 409// turn G into a thunk to F (1) 410// address of F is not taken: 411// make G an alias of F (2) 412// * F is internal, G is internal: 413// address of F and G are taken: 414// turn G into a thunk to F (1) 415// address of G is not taken: 416// make G an alias to F (2) 417// 418// alias requires linkage == (external,local,weak) fallback to creating a thunk 419// external means 'externally visible' linkage != (internal,private) 420// internal means linkage == (internal,private) 421// weak means linkage mayBeOverridable 422// being external implies that the address is taken 423// 424// 1. turn G into a thunk to F 425// 2. make G an alias to F 426 427enum LinkageCategory { 428 ExternalStrong, 429 ExternalWeak, 430 Internal 431}; 432 433static LinkageCategory categorize(const Function *F) { 434 switch (F->getLinkage()) { 435 case GlobalValue::InternalLinkage: 436 case GlobalValue::PrivateLinkage: 437 return Internal; 438 439 case GlobalValue::WeakAnyLinkage: 440 case GlobalValue::WeakODRLinkage: 441 case GlobalValue::ExternalWeakLinkage: 442 return ExternalWeak; 443 444 case GlobalValue::ExternalLinkage: 445 case GlobalValue::AvailableExternallyLinkage: 446 case GlobalValue::LinkOnceAnyLinkage: 447 case GlobalValue::LinkOnceODRLinkage: 448 case GlobalValue::AppendingLinkage: 449 case GlobalValue::DLLImportLinkage: 450 case GlobalValue::DLLExportLinkage: 451 case GlobalValue::GhostLinkage: 452 case GlobalValue::CommonLinkage: 453 return ExternalStrong; 454 } 455 456 assert(0 && "Unknown LinkageType."); 457 return ExternalWeak; 458} 459 460static void ThunkGToF(Function *F, Function *G) { 461 Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "", 462 G->getParent()); 463 BasicBlock *BB = BasicBlock::Create("", NewG); 464 465 std::vector<Value *> Args; 466 unsigned i = 0; 467 const FunctionType *FFTy = F->getFunctionType(); 468 for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end(); 469 AI != AE; ++AI) { 470 if (FFTy->getParamType(i) == AI->getType()) 471 Args.push_back(AI); 472 else { 473 Value *BCI = new BitCastInst(AI, FFTy->getParamType(i), "", BB); 474 Args.push_back(BCI); 475 } 476 ++i; 477 } 478 479 CallInst *CI = CallInst::Create(F, Args.begin(), Args.end(), "", BB); 480 CI->setTailCall(); 481 CI->setCallingConv(F->getCallingConv()); 482 if (NewG->getReturnType() == Type::VoidTy) { 483 ReturnInst::Create(BB); 484 } else if (CI->getType() != NewG->getReturnType()) { 485 Value *BCI = new BitCastInst(CI, NewG->getReturnType(), "", BB); 486 ReturnInst::Create(BCI, BB); 487 } else { 488 ReturnInst::Create(CI, BB); 489 } 490 491 NewG->copyAttributesFrom(G); 492 NewG->takeName(G); 493 G->replaceAllUsesWith(NewG); 494 G->eraseFromParent(); 495 496 // TODO: look at direct callers to G and make them all direct callers to F. 497} 498 499static void AliasGToF(Function *F, Function *G) { 500 if (!G->hasExternalLinkage() && !G->hasLocalLinkage() && !G->hasWeakLinkage()) 501 return ThunkGToF(F, G); 502 503 GlobalAlias *GA = new GlobalAlias( 504 G->getType(), G->getLinkage(), "", 505 ConstantExpr::getBitCast(F, G->getType()), G->getParent()); 506 F->setAlignment(std::max(F->getAlignment(), G->getAlignment())); 507 GA->takeName(G); 508 GA->setVisibility(G->getVisibility()); 509 G->replaceAllUsesWith(GA); 510 G->eraseFromParent(); 511} 512 513static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) { 514 Function *F = FnVec[i]; 515 Function *G = FnVec[j]; 516 517 LinkageCategory catF = categorize(F); 518 LinkageCategory catG = categorize(G); 519 520 if (catF == ExternalWeak || (catF == Internal && catG == ExternalStrong)) { 521 std::swap(FnVec[i], FnVec[j]); 522 std::swap(F, G); 523 std::swap(catF, catG); 524 } 525 526 switch (catF) { 527 case ExternalStrong: 528 switch (catG) { 529 case ExternalStrong: 530 case ExternalWeak: 531 ThunkGToF(F, G); 532 break; 533 case Internal: 534 if (G->hasAddressTaken()) 535 ThunkGToF(F, G); 536 else 537 AliasGToF(F, G); 538 break; 539 } 540 break; 541 542 case ExternalWeak: { 543 assert(catG == ExternalWeak); 544 545 // Make them both thunks to the same internal function. 546 F->setAlignment(std::max(F->getAlignment(), G->getAlignment())); 547 Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "", 548 F->getParent()); 549 H->copyAttributesFrom(F); 550 H->takeName(F); 551 F->replaceAllUsesWith(H); 552 553 ThunkGToF(F, G); 554 ThunkGToF(F, H); 555 556 F->setLinkage(GlobalValue::InternalLinkage); 557 } break; 558 559 case Internal: 560 switch (catG) { 561 case ExternalStrong: 562 assert(0); 563 // fall-through 564 case ExternalWeak: 565 if (F->hasAddressTaken()) 566 ThunkGToF(F, G); 567 else 568 AliasGToF(F, G); 569 break; 570 case Internal: { 571 bool addrTakenF = F->hasAddressTaken(); 572 bool addrTakenG = G->hasAddressTaken(); 573 if (!addrTakenF && addrTakenG) { 574 std::swap(FnVec[i], FnVec[j]); 575 std::swap(F, G); 576 std::swap(addrTakenF, addrTakenG); 577 } 578 579 if (addrTakenF && addrTakenG) { 580 ThunkGToF(F, G); 581 } else { 582 assert(!addrTakenG); 583 AliasGToF(F, G); 584 } 585 } break; 586 } 587 break; 588 } 589 590 ++NumFunctionsMerged; 591 return true; 592} 593 594// ===----------------------------------------------------------------------=== 595// Pass definition 596// ===----------------------------------------------------------------------=== 597 598bool MergeFunctions::runOnModule(Module &M) { 599 bool Changed = false; 600 601 std::map<unsigned long, std::vector<Function *> > FnMap; 602 603 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) { 604 if (F->isDeclaration() || F->isIntrinsic()) 605 continue; 606 607 FnMap[hash(F)].push_back(F); 608 } 609 610 // TODO: instead of running in a loop, we could also fold functions in 611 // callgraph order. Constructing the CFG probably isn't cheaper than just 612 // running in a loop, unless it happened to already be available. 613 614 bool LocalChanged; 615 do { 616 LocalChanged = false; 617 DOUT << "size: " << FnMap.size() << "\n"; 618 for (std::map<unsigned long, std::vector<Function *> >::iterator 619 I = FnMap.begin(), E = FnMap.end(); I != E; ++I) { 620 std::vector<Function *> &FnVec = I->second; 621 DOUT << "hash (" << I->first << "): " << FnVec.size() << "\n"; 622 623 for (int i = 0, e = FnVec.size(); i != e; ++i) { 624 for (int j = i + 1; j != e; ++j) { 625 bool isEqual = equals(FnVec[i], FnVec[j]); 626 627 DOUT << " " << FnVec[i]->getName() 628 << (isEqual ? " == " : " != ") 629 << FnVec[j]->getName() << "\n"; 630 631 if (isEqual) { 632 if (fold(FnVec, i, j)) { 633 LocalChanged = true; 634 FnVec.erase(FnVec.begin() + j); 635 --j, --e; 636 } 637 } 638 } 639 } 640 641 } 642 Changed |= LocalChanged; 643 } while (LocalChanged); 644 645 return Changed; 646} 647