MergeFunctions.cpp revision a279bc3da55691784064cb47200a1c584408b8ab
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/Compiler.h" 55#include "llvm/Support/Debug.h" 56#include "llvm/Support/ErrorHandling.h" 57#include "llvm/Support/raw_ostream.h" 58#include <map> 59#include <vector> 60using namespace llvm; 61 62STATISTIC(NumFunctionsMerged, "Number of functions merged"); 63 64namespace { 65 struct VISIBILITY_HIDDEN MergeFunctions : public ModulePass { 66 static char ID; // Pass identification, replacement for typeid 67 MergeFunctions() : ModulePass(&ID) {} 68 69 bool runOnModule(Module &M); 70 }; 71} 72 73char MergeFunctions::ID = 0; 74static RegisterPass<MergeFunctions> 75X("mergefunc", "Merge Functions"); 76 77ModulePass *llvm::createMergeFunctionsPass() { 78 return new MergeFunctions(); 79} 80 81// ===----------------------------------------------------------------------=== 82// Comparison of functions 83// ===----------------------------------------------------------------------=== 84 85static unsigned long hash(const Function *F) { 86 const FunctionType *FTy = F->getFunctionType(); 87 88 FoldingSetNodeID ID; 89 ID.AddInteger(F->size()); 90 ID.AddInteger(F->getCallingConv()); 91 ID.AddBoolean(F->hasGC()); 92 ID.AddBoolean(FTy->isVarArg()); 93 ID.AddInteger(FTy->getReturnType()->getTypeID()); 94 for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i) 95 ID.AddInteger(FTy->getParamType(i)->getTypeID()); 96 return ID.ComputeHash(); 97} 98 99/// IgnoreBitcasts - given a bitcast, returns the first non-bitcast found by 100/// walking the chain of cast operands. Otherwise, returns the argument. 101static Value* IgnoreBitcasts(Value *V) { 102 while (BitCastInst *BC = dyn_cast<BitCastInst>(V)) 103 V = BC->getOperand(0); 104 105 return V; 106} 107 108/// isEquivalentType - any two pointers are equivalent. Otherwise, standard 109/// type equivalence rules apply. 110static bool isEquivalentType(const Type *Ty1, const Type *Ty2) { 111 if (Ty1 == Ty2) 112 return true; 113 if (Ty1->getTypeID() != Ty2->getTypeID()) 114 return false; 115 116 switch(Ty1->getTypeID()) { 117 case Type::VoidTyID: 118 case Type::FloatTyID: 119 case Type::DoubleTyID: 120 case Type::X86_FP80TyID: 121 case Type::FP128TyID: 122 case Type::PPC_FP128TyID: 123 case Type::LabelTyID: 124 case Type::MetadataTyID: 125 return true; 126 127 case Type::IntegerTyID: 128 case Type::OpaqueTyID: 129 // Ty1 == Ty2 would have returned true earlier. 130 return false; 131 132 default: 133 llvm_unreachable("Unknown type!"); 134 return false; 135 136 case Type::PointerTyID: { 137 const PointerType *PTy1 = cast<PointerType>(Ty1); 138 const PointerType *PTy2 = cast<PointerType>(Ty2); 139 return PTy1->getAddressSpace() == PTy2->getAddressSpace(); 140 } 141 142 case Type::StructTyID: { 143 const StructType *STy1 = cast<StructType>(Ty1); 144 const StructType *STy2 = cast<StructType>(Ty2); 145 if (STy1->getNumElements() != STy2->getNumElements()) 146 return false; 147 148 if (STy1->isPacked() != STy2->isPacked()) 149 return false; 150 151 for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) { 152 if (!isEquivalentType(STy1->getElementType(i), STy2->getElementType(i))) 153 return false; 154 } 155 return true; 156 } 157 158 case Type::FunctionTyID: { 159 const FunctionType *FTy1 = cast<FunctionType>(Ty1); 160 const FunctionType *FTy2 = cast<FunctionType>(Ty2); 161 if (FTy1->getNumParams() != FTy2->getNumParams() || 162 FTy1->isVarArg() != FTy2->isVarArg()) 163 return false; 164 165 if (!isEquivalentType(FTy1->getReturnType(), FTy2->getReturnType())) 166 return false; 167 168 for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) { 169 if (!isEquivalentType(FTy1->getParamType(i), FTy2->getParamType(i))) 170 return false; 171 } 172 return true; 173 } 174 175 case Type::ArrayTyID: 176 case Type::VectorTyID: { 177 const SequentialType *STy1 = cast<SequentialType>(Ty1); 178 const SequentialType *STy2 = cast<SequentialType>(Ty2); 179 return isEquivalentType(STy1->getElementType(), STy2->getElementType()); 180 } 181 } 182} 183 184/// isEquivalentOperation - determine whether the two operations are the same 185/// except that pointer-to-A and pointer-to-B are equivalent. This should be 186/// kept in sync with Instruction::isSameOperationAs. 187static bool 188isEquivalentOperation(const Instruction *I1, const Instruction *I2) { 189 if (I1->getOpcode() != I2->getOpcode() || 190 I1->getNumOperands() != I2->getNumOperands() || 191 !isEquivalentType(I1->getType(), I2->getType()) || 192 !I1->hasSameSubclassOptionalData(I2)) 193 return false; 194 195 // We have two instructions of identical opcode and #operands. Check to see 196 // if all operands are the same type 197 for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i) 198 if (!isEquivalentType(I1->getOperand(i)->getType(), 199 I2->getOperand(i)->getType())) 200 return false; 201 202 // Check special state that is a part of some instructions. 203 if (const LoadInst *LI = dyn_cast<LoadInst>(I1)) 204 return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() && 205 LI->getAlignment() == cast<LoadInst>(I2)->getAlignment(); 206 if (const StoreInst *SI = dyn_cast<StoreInst>(I1)) 207 return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() && 208 SI->getAlignment() == cast<StoreInst>(I2)->getAlignment(); 209 if (const CmpInst *CI = dyn_cast<CmpInst>(I1)) 210 return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate(); 211 if (const CallInst *CI = dyn_cast<CallInst>(I1)) 212 return CI->isTailCall() == cast<CallInst>(I2)->isTailCall() && 213 CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() && 214 CI->getAttributes().getRawPointer() == 215 cast<CallInst>(I2)->getAttributes().getRawPointer(); 216 if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1)) 217 return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() && 218 CI->getAttributes().getRawPointer() == 219 cast<InvokeInst>(I2)->getAttributes().getRawPointer(); 220 if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) { 221 if (IVI->getNumIndices() != cast<InsertValueInst>(I2)->getNumIndices()) 222 return false; 223 for (unsigned i = 0, e = IVI->getNumIndices(); i != e; ++i) 224 if (IVI->idx_begin()[i] != cast<InsertValueInst>(I2)->idx_begin()[i]) 225 return false; 226 return true; 227 } 228 if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) { 229 if (EVI->getNumIndices() != cast<ExtractValueInst>(I2)->getNumIndices()) 230 return false; 231 for (unsigned i = 0, e = EVI->getNumIndices(); i != e; ++i) 232 if (EVI->idx_begin()[i] != cast<ExtractValueInst>(I2)->idx_begin()[i]) 233 return false; 234 return true; 235 } 236 237 return true; 238} 239 240static bool compare(const Value *V, const Value *U) { 241 assert(!isa<BasicBlock>(V) && !isa<BasicBlock>(U) && 242 "Must not compare basic blocks."); 243 244 assert(isEquivalentType(V->getType(), U->getType()) && 245 "Two of the same operation have operands of different type."); 246 247 // TODO: If the constant is an expression of F, we should accept that it's 248 // equal to the same expression in terms of G. 249 if (isa<Constant>(V)) 250 return V == U; 251 252 // The caller has ensured that ValueMap[V] != U. Since Arguments are 253 // pre-loaded into the ValueMap, and Instructions are added as we go, we know 254 // that this can only be a mis-match. 255 if (isa<Instruction>(V) || isa<Argument>(V)) 256 return false; 257 258 if (isa<InlineAsm>(V) && isa<InlineAsm>(U)) { 259 const InlineAsm *IAF = cast<InlineAsm>(V); 260 const InlineAsm *IAG = cast<InlineAsm>(U); 261 return IAF->getAsmString() == IAG->getAsmString() && 262 IAF->getConstraintString() == IAG->getConstraintString(); 263 } 264 265 return false; 266} 267 268static bool equals(const BasicBlock *BB1, const BasicBlock *BB2, 269 DenseMap<const Value *, const Value *> &ValueMap, 270 DenseMap<const Value *, const Value *> &SpeculationMap) { 271 // Speculatively add it anyways. If it's false, we'll notice a difference 272 // later, and this won't matter. 273 ValueMap[BB1] = BB2; 274 275 BasicBlock::const_iterator FI = BB1->begin(), FE = BB1->end(); 276 BasicBlock::const_iterator GI = BB2->begin(), GE = BB2->end(); 277 278 do { 279 if (isa<BitCastInst>(FI)) { 280 ++FI; 281 continue; 282 } 283 if (isa<BitCastInst>(GI)) { 284 ++GI; 285 continue; 286 } 287 288 if (!isEquivalentOperation(FI, GI)) 289 return false; 290 291 if (isa<GetElementPtrInst>(FI)) { 292 const GetElementPtrInst *GEPF = cast<GetElementPtrInst>(FI); 293 const GetElementPtrInst *GEPG = cast<GetElementPtrInst>(GI); 294 if (GEPF->hasAllZeroIndices() && GEPG->hasAllZeroIndices()) { 295 // It's effectively a bitcast. 296 ++FI, ++GI; 297 continue; 298 } 299 300 // TODO: we only really care about the elements before the index 301 if (FI->getOperand(0)->getType() != GI->getOperand(0)->getType()) 302 return false; 303 } 304 305 if (ValueMap[FI] == GI) { 306 ++FI, ++GI; 307 continue; 308 } 309 310 if (ValueMap[FI] != NULL) 311 return false; 312 313 for (unsigned i = 0, e = FI->getNumOperands(); i != e; ++i) { 314 Value *OpF = IgnoreBitcasts(FI->getOperand(i)); 315 Value *OpG = IgnoreBitcasts(GI->getOperand(i)); 316 317 if (ValueMap[OpF] == OpG) 318 continue; 319 320 if (ValueMap[OpF] != NULL) 321 return false; 322 323 if (OpF->getValueID() != OpG->getValueID() || 324 !isEquivalentType(OpF->getType(), OpG->getType())) 325 return false; 326 327 if (isa<PHINode>(FI)) { 328 if (SpeculationMap[OpF] == NULL) 329 SpeculationMap[OpF] = OpG; 330 else if (SpeculationMap[OpF] != OpG) 331 return false; 332 continue; 333 } else if (isa<BasicBlock>(OpF)) { 334 assert(isa<TerminatorInst>(FI) && 335 "BasicBlock referenced by non-Terminator non-PHI"); 336 // This call changes the ValueMap, hence we can't use 337 // Value *& = ValueMap[...] 338 if (!equals(cast<BasicBlock>(OpF), cast<BasicBlock>(OpG), ValueMap, 339 SpeculationMap)) 340 return false; 341 } else { 342 if (!compare(OpF, OpG)) 343 return false; 344 } 345 346 ValueMap[OpF] = OpG; 347 } 348 349 ValueMap[FI] = GI; 350 ++FI, ++GI; 351 } while (FI != FE && GI != GE); 352 353 return FI == FE && GI == GE; 354} 355 356static bool equals(const Function *F, const Function *G) { 357 // We need to recheck everything, but check the things that weren't included 358 // in the hash first. 359 360 if (F->getAttributes() != G->getAttributes()) 361 return false; 362 363 if (F->hasGC() != G->hasGC()) 364 return false; 365 366 if (F->hasGC() && F->getGC() != G->getGC()) 367 return false; 368 369 if (F->hasSection() != G->hasSection()) 370 return false; 371 372 if (F->hasSection() && F->getSection() != G->getSection()) 373 return false; 374 375 if (F->isVarArg() != G->isVarArg()) 376 return false; 377 378 // TODO: if it's internal and only used in direct calls, we could handle this 379 // case too. 380 if (F->getCallingConv() != G->getCallingConv()) 381 return false; 382 383 if (!isEquivalentType(F->getFunctionType(), G->getFunctionType())) 384 return false; 385 386 DenseMap<const Value *, const Value *> ValueMap; 387 DenseMap<const Value *, const Value *> SpeculationMap; 388 ValueMap[F] = G; 389 390 assert(F->arg_size() == G->arg_size() && 391 "Identical functions have a different number of args."); 392 393 for (Function::const_arg_iterator fi = F->arg_begin(), gi = G->arg_begin(), 394 fe = F->arg_end(); fi != fe; ++fi, ++gi) 395 ValueMap[fi] = gi; 396 397 if (!equals(&F->getEntryBlock(), &G->getEntryBlock(), ValueMap, 398 SpeculationMap)) 399 return false; 400 401 for (DenseMap<const Value *, const Value *>::iterator 402 I = SpeculationMap.begin(), E = SpeculationMap.end(); I != E; ++I) { 403 if (ValueMap[I->first] != I->second) 404 return false; 405 } 406 407 return true; 408} 409 410// ===----------------------------------------------------------------------=== 411// Folding of functions 412// ===----------------------------------------------------------------------=== 413 414// Cases: 415// * F is external strong, G is external strong: 416// turn G into a thunk to F (1) 417// * F is external strong, G is external weak: 418// turn G into a thunk to F (1) 419// * F is external weak, G is external weak: 420// unfoldable 421// * F is external strong, G is internal: 422// address of G taken: 423// turn G into a thunk to F (1) 424// address of G not taken: 425// make G an alias to F (2) 426// * F is internal, G is external weak 427// address of F is taken: 428// turn G into a thunk to F (1) 429// address of F is not taken: 430// make G an alias of F (2) 431// * F is internal, G is internal: 432// address of F and G are taken: 433// turn G into a thunk to F (1) 434// address of G is not taken: 435// make G an alias to F (2) 436// 437// alias requires linkage == (external,local,weak) fallback to creating a thunk 438// external means 'externally visible' linkage != (internal,private) 439// internal means linkage == (internal,private) 440// weak means linkage mayBeOverridable 441// being external implies that the address is taken 442// 443// 1. turn G into a thunk to F 444// 2. make G an alias to F 445 446enum LinkageCategory { 447 ExternalStrong, 448 ExternalWeak, 449 Internal 450}; 451 452static LinkageCategory categorize(const Function *F) { 453 switch (F->getLinkage()) { 454 case GlobalValue::InternalLinkage: 455 case GlobalValue::PrivateLinkage: 456 case GlobalValue::LinkerPrivateLinkage: 457 return Internal; 458 459 case GlobalValue::WeakAnyLinkage: 460 case GlobalValue::WeakODRLinkage: 461 case GlobalValue::ExternalWeakLinkage: 462 return ExternalWeak; 463 464 case GlobalValue::ExternalLinkage: 465 case GlobalValue::AvailableExternallyLinkage: 466 case GlobalValue::LinkOnceAnyLinkage: 467 case GlobalValue::LinkOnceODRLinkage: 468 case GlobalValue::AppendingLinkage: 469 case GlobalValue::DLLImportLinkage: 470 case GlobalValue::DLLExportLinkage: 471 case GlobalValue::GhostLinkage: 472 case GlobalValue::CommonLinkage: 473 return ExternalStrong; 474 } 475 476 llvm_unreachable("Unknown LinkageType."); 477 return ExternalWeak; 478} 479 480static void ThunkGToF(Function *F, Function *G) { 481 Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "", 482 G->getParent()); 483 BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG); 484 485 std::vector<Value *> Args; 486 unsigned i = 0; 487 const FunctionType *FFTy = F->getFunctionType(); 488 for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end(); 489 AI != AE; ++AI) { 490 if (FFTy->getParamType(i) == AI->getType()) 491 Args.push_back(AI); 492 else { 493 Value *BCI = new BitCastInst(AI, FFTy->getParamType(i), "", BB); 494 Args.push_back(BCI); 495 } 496 ++i; 497 } 498 499 CallInst *CI = CallInst::Create(F, Args.begin(), Args.end(), "", BB); 500 CI->setTailCall(); 501 CI->setCallingConv(F->getCallingConv()); 502 if (NewG->getReturnType() == Type::getVoidTy(F->getContext())) { 503 ReturnInst::Create(F->getContext(), BB); 504 } else if (CI->getType() != NewG->getReturnType()) { 505 Value *BCI = new BitCastInst(CI, NewG->getReturnType(), "", BB); 506 ReturnInst::Create(F->getContext(), BCI, BB); 507 } else { 508 ReturnInst::Create(F->getContext(), CI, BB); 509 } 510 511 NewG->copyAttributesFrom(G); 512 NewG->takeName(G); 513 G->replaceAllUsesWith(NewG); 514 G->eraseFromParent(); 515 516 // TODO: look at direct callers to G and make them all direct callers to F. 517} 518 519static void AliasGToF(Function *F, Function *G) { 520 if (!G->hasExternalLinkage() && !G->hasLocalLinkage() && !G->hasWeakLinkage()) 521 return ThunkGToF(F, G); 522 523 GlobalAlias *GA = new GlobalAlias( 524 G->getType(), G->getLinkage(), "", 525 ConstantExpr::getBitCast(F, G->getType()), G->getParent()); 526 F->setAlignment(std::max(F->getAlignment(), G->getAlignment())); 527 GA->takeName(G); 528 GA->setVisibility(G->getVisibility()); 529 G->replaceAllUsesWith(GA); 530 G->eraseFromParent(); 531} 532 533static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) { 534 Function *F = FnVec[i]; 535 Function *G = FnVec[j]; 536 537 LinkageCategory catF = categorize(F); 538 LinkageCategory catG = categorize(G); 539 540 if (catF == ExternalWeak || (catF == Internal && catG == ExternalStrong)) { 541 std::swap(FnVec[i], FnVec[j]); 542 std::swap(F, G); 543 std::swap(catF, catG); 544 } 545 546 switch (catF) { 547 case ExternalStrong: 548 switch (catG) { 549 case ExternalStrong: 550 case ExternalWeak: 551 ThunkGToF(F, G); 552 break; 553 case Internal: 554 if (G->hasAddressTaken()) 555 ThunkGToF(F, G); 556 else 557 AliasGToF(F, G); 558 break; 559 } 560 break; 561 562 case ExternalWeak: { 563 assert(catG == ExternalWeak); 564 565 // Make them both thunks to the same internal function. 566 F->setAlignment(std::max(F->getAlignment(), G->getAlignment())); 567 Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "", 568 F->getParent()); 569 H->copyAttributesFrom(F); 570 H->takeName(F); 571 F->replaceAllUsesWith(H); 572 573 ThunkGToF(F, G); 574 ThunkGToF(F, H); 575 576 F->setLinkage(GlobalValue::InternalLinkage); 577 } break; 578 579 case Internal: 580 switch (catG) { 581 case ExternalStrong: 582 llvm_unreachable(0); 583 // fall-through 584 case ExternalWeak: 585 if (F->hasAddressTaken()) 586 ThunkGToF(F, G); 587 else 588 AliasGToF(F, G); 589 break; 590 case Internal: { 591 bool addrTakenF = F->hasAddressTaken(); 592 bool addrTakenG = G->hasAddressTaken(); 593 if (!addrTakenF && addrTakenG) { 594 std::swap(FnVec[i], FnVec[j]); 595 std::swap(F, G); 596 std::swap(addrTakenF, addrTakenG); 597 } 598 599 if (addrTakenF && addrTakenG) { 600 ThunkGToF(F, G); 601 } else { 602 assert(!addrTakenG); 603 AliasGToF(F, G); 604 } 605 } break; 606 } 607 break; 608 } 609 610 ++NumFunctionsMerged; 611 return true; 612} 613 614// ===----------------------------------------------------------------------=== 615// Pass definition 616// ===----------------------------------------------------------------------=== 617 618bool MergeFunctions::runOnModule(Module &M) { 619 bool Changed = false; 620 621 std::map<unsigned long, std::vector<Function *> > FnMap; 622 623 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) { 624 if (F->isDeclaration() || F->isIntrinsic()) 625 continue; 626 627 FnMap[hash(F)].push_back(F); 628 } 629 630 // TODO: instead of running in a loop, we could also fold functions in 631 // callgraph order. Constructing the CFG probably isn't cheaper than just 632 // running in a loop, unless it happened to already be available. 633 634 bool LocalChanged; 635 do { 636 LocalChanged = false; 637 DEBUG(errs() << "size: " << FnMap.size() << "\n"); 638 for (std::map<unsigned long, std::vector<Function *> >::iterator 639 I = FnMap.begin(), E = FnMap.end(); I != E; ++I) { 640 std::vector<Function *> &FnVec = I->second; 641 DEBUG(errs() << "hash (" << I->first << "): " << FnVec.size() << "\n"); 642 643 for (int i = 0, e = FnVec.size(); i != e; ++i) { 644 for (int j = i + 1; j != e; ++j) { 645 bool isEqual = equals(FnVec[i], FnVec[j]); 646 647 DEBUG(errs() << " " << FnVec[i]->getName() 648 << (isEqual ? " == " : " != ") 649 << FnVec[j]->getName() << "\n"); 650 651 if (isEqual) { 652 if (fold(FnVec, i, j)) { 653 LocalChanged = true; 654 FnVec.erase(FnVec.begin() + j); 655 --j, --e; 656 } 657 } 658 } 659 } 660 661 } 662 Changed |= LocalChanged; 663 } while (LocalChanged); 664 665 return Changed; 666} 667