MergeFunctions.cpp revision a142c9302b690cda799737d78ec29414e3b47fc8
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::isSameOperationAs. 184static bool 185isEquivalentOperation(const Instruction *I1, const Instruction *I2) { 186 if (I1->getOpcode() != I2->getOpcode() || 187 I1->getNumOperands() != I2->getNumOperands() || 188 !isEquivalentType(I1->getType(), I2->getType())) 189 return false; 190 191 // We have two instructions of identical opcode and #operands. Check to see 192 // if all operands are the same type 193 for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i) 194 if (!isEquivalentType(I1->getOperand(i)->getType(), 195 I2->getOperand(i)->getType())) 196 return false; 197 198 // Check special state that is a part of some instructions. 199 if (const LoadInst *LI = dyn_cast<LoadInst>(I1)) 200 return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() && 201 LI->getAlignment() == cast<LoadInst>(I2)->getAlignment(); 202 if (const StoreInst *SI = dyn_cast<StoreInst>(I1)) 203 return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() && 204 SI->getAlignment() == cast<StoreInst>(I2)->getAlignment(); 205 if (const CmpInst *CI = dyn_cast<CmpInst>(I1)) 206 return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate(); 207 if (const CallInst *CI = dyn_cast<CallInst>(I1)) 208 return CI->isTailCall() == cast<CallInst>(I2)->isTailCall() && 209 CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() && 210 CI->getAttributes().getRawPointer() == 211 cast<CallInst>(I2)->getAttributes().getRawPointer(); 212 if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1)) 213 return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() && 214 CI->getAttributes().getRawPointer() == 215 cast<InvokeInst>(I2)->getAttributes().getRawPointer(); 216 if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) { 217 if (IVI->getNumIndices() != cast<InsertValueInst>(I2)->getNumIndices()) 218 return false; 219 for (unsigned i = 0, e = IVI->getNumIndices(); i != e; ++i) 220 if (IVI->idx_begin()[i] != cast<InsertValueInst>(I2)->idx_begin()[i]) 221 return false; 222 return true; 223 } 224 if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) { 225 if (EVI->getNumIndices() != cast<ExtractValueInst>(I2)->getNumIndices()) 226 return false; 227 for (unsigned i = 0, e = EVI->getNumIndices(); i != e; ++i) 228 if (EVI->idx_begin()[i] != cast<ExtractValueInst>(I2)->idx_begin()[i]) 229 return false; 230 return true; 231 } 232 233 return true; 234} 235 236static bool compare(const Value *V, const Value *U) { 237 assert(!isa<BasicBlock>(V) && !isa<BasicBlock>(U) && 238 "Must not compare basic blocks."); 239 240 assert(isEquivalentType(V->getType(), U->getType()) && 241 "Two of the same operation have operands of different type."); 242 243 // TODO: If the constant is an expression of F, we should accept that it's 244 // equal to the same expression in terms of G. 245 if (isa<Constant>(V)) 246 return V == U; 247 248 // The caller has ensured that ValueMap[V] != U. Since Arguments are 249 // pre-loaded into the ValueMap, and Instructions are added as we go, we know 250 // that this can only be a mis-match. 251 if (isa<Instruction>(V) || isa<Argument>(V)) 252 return false; 253 254 if (isa<InlineAsm>(V) && isa<InlineAsm>(U)) { 255 const InlineAsm *IAF = cast<InlineAsm>(V); 256 const InlineAsm *IAG = cast<InlineAsm>(U); 257 return IAF->getAsmString() == IAG->getAsmString() && 258 IAF->getConstraintString() == IAG->getConstraintString(); 259 } 260 261 return false; 262} 263 264static bool equals(const BasicBlock *BB1, const BasicBlock *BB2, 265 DenseMap<const Value *, const Value *> &ValueMap, 266 DenseMap<const Value *, const Value *> &SpeculationMap) { 267 // Speculatively add it anyways. If it's false, we'll notice a difference 268 // later, and this won't matter. 269 ValueMap[BB1] = BB2; 270 271 BasicBlock::const_iterator FI = BB1->begin(), FE = BB1->end(); 272 BasicBlock::const_iterator GI = BB2->begin(), GE = BB2->end(); 273 274 do { 275 if (isa<BitCastInst>(FI)) { 276 ++FI; 277 continue; 278 } 279 if (isa<BitCastInst>(GI)) { 280 ++GI; 281 continue; 282 } 283 284 if (!isEquivalentOperation(FI, GI)) 285 return false; 286 287 if (isa<GetElementPtrInst>(FI)) { 288 const GetElementPtrInst *GEPF = cast<GetElementPtrInst>(FI); 289 const GetElementPtrInst *GEPG = cast<GetElementPtrInst>(GI); 290 if (GEPF->hasAllZeroIndices() && GEPG->hasAllZeroIndices()) { 291 // It's effectively a bitcast. 292 ++FI, ++GI; 293 continue; 294 } 295 296 // TODO: we only really care about the elements before the index 297 if (FI->getOperand(0)->getType() != GI->getOperand(0)->getType()) 298 return false; 299 } 300 301 if (ValueMap[FI] == GI) { 302 ++FI, ++GI; 303 continue; 304 } 305 306 if (ValueMap[FI] != NULL) 307 return false; 308 309 for (unsigned i = 0, e = FI->getNumOperands(); i != e; ++i) { 310 Value *OpF = IgnoreBitcasts(FI->getOperand(i)); 311 Value *OpG = IgnoreBitcasts(GI->getOperand(i)); 312 313 if (ValueMap[OpF] == OpG) 314 continue; 315 316 if (ValueMap[OpF] != NULL) 317 return false; 318 319 if (OpF->getValueID() != OpG->getValueID() || 320 !isEquivalentType(OpF->getType(), OpG->getType())) 321 return false; 322 323 if (isa<PHINode>(FI)) { 324 if (SpeculationMap[OpF] == NULL) 325 SpeculationMap[OpF] = OpG; 326 else if (SpeculationMap[OpF] != OpG) 327 return false; 328 continue; 329 } else if (isa<BasicBlock>(OpF)) { 330 assert(isa<TerminatorInst>(FI) && 331 "BasicBlock referenced by non-Terminator non-PHI"); 332 // This call changes the ValueMap, hence we can't use 333 // Value *& = ValueMap[...] 334 if (!equals(cast<BasicBlock>(OpF), cast<BasicBlock>(OpG), ValueMap, 335 SpeculationMap)) 336 return false; 337 } else { 338 if (!compare(OpF, OpG)) 339 return false; 340 } 341 342 ValueMap[OpF] = OpG; 343 } 344 345 ValueMap[FI] = GI; 346 ++FI, ++GI; 347 } while (FI != FE && GI != GE); 348 349 return FI == FE && GI == GE; 350} 351 352static bool equals(const Function *F, const Function *G) { 353 // We need to recheck everything, but check the things that weren't included 354 // in the hash first. 355 356 if (F->getAttributes() != G->getAttributes()) 357 return false; 358 359 if (F->hasGC() != G->hasGC()) 360 return false; 361 362 if (F->hasGC() && F->getGC() != G->getGC()) 363 return false; 364 365 if (F->hasSection() != G->hasSection()) 366 return false; 367 368 if (F->hasSection() && F->getSection() != G->getSection()) 369 return false; 370 371 if (F->isVarArg() != G->isVarArg()) 372 return false; 373 374 // TODO: if it's internal and only used in direct calls, we could handle this 375 // case too. 376 if (F->getCallingConv() != G->getCallingConv()) 377 return false; 378 379 if (!isEquivalentType(F->getFunctionType(), G->getFunctionType())) 380 return false; 381 382 DenseMap<const Value *, const Value *> ValueMap; 383 DenseMap<const Value *, const Value *> SpeculationMap; 384 ValueMap[F] = G; 385 386 assert(F->arg_size() == G->arg_size() && 387 "Identical functions have a different number of args."); 388 389 for (Function::const_arg_iterator fi = F->arg_begin(), gi = G->arg_begin(), 390 fe = F->arg_end(); fi != fe; ++fi, ++gi) 391 ValueMap[fi] = gi; 392 393 if (!equals(&F->getEntryBlock(), &G->getEntryBlock(), ValueMap, 394 SpeculationMap)) 395 return false; 396 397 for (DenseMap<const Value *, const Value *>::iterator 398 I = SpeculationMap.begin(), E = SpeculationMap.end(); I != E; ++I) { 399 if (ValueMap[I->first] != I->second) 400 return false; 401 } 402 403 return true; 404} 405 406// ===----------------------------------------------------------------------=== 407// Folding of functions 408// ===----------------------------------------------------------------------=== 409 410// Cases: 411// * F is external strong, G is external strong: 412// turn G into a thunk to F (1) 413// * F is external strong, G is external weak: 414// turn G into a thunk to F (1) 415// * F is external weak, G is external weak: 416// unfoldable 417// * F is external strong, G is internal: 418// address of G taken: 419// turn G into a thunk to F (1) 420// address of G not taken: 421// make G an alias to F (2) 422// * F is internal, G is external weak 423// address of F is taken: 424// turn G into a thunk to F (1) 425// address of F is not taken: 426// make G an alias of F (2) 427// * F is internal, G is internal: 428// address of F and G are taken: 429// turn G into a thunk to F (1) 430// address of G is not taken: 431// make G an alias to F (2) 432// 433// alias requires linkage == (external,local,weak) fallback to creating a thunk 434// external means 'externally visible' linkage != (internal,private) 435// internal means linkage == (internal,private) 436// weak means linkage mayBeOverridable 437// being external implies that the address is taken 438// 439// 1. turn G into a thunk to F 440// 2. make G an alias to F 441 442enum LinkageCategory { 443 ExternalStrong, 444 ExternalWeak, 445 Internal 446}; 447 448static LinkageCategory categorize(const Function *F) { 449 switch (F->getLinkage()) { 450 case GlobalValue::InternalLinkage: 451 case GlobalValue::PrivateLinkage: 452 return Internal; 453 454 case GlobalValue::WeakAnyLinkage: 455 case GlobalValue::WeakODRLinkage: 456 case GlobalValue::ExternalWeakLinkage: 457 return ExternalWeak; 458 459 case GlobalValue::ExternalLinkage: 460 case GlobalValue::AvailableExternallyLinkage: 461 case GlobalValue::LinkOnceAnyLinkage: 462 case GlobalValue::LinkOnceODRLinkage: 463 case GlobalValue::AppendingLinkage: 464 case GlobalValue::DLLImportLinkage: 465 case GlobalValue::DLLExportLinkage: 466 case GlobalValue::GhostLinkage: 467 case GlobalValue::CommonLinkage: 468 return ExternalStrong; 469 } 470 471 assert(0 && "Unknown LinkageType."); 472 return ExternalWeak; 473} 474 475static void ThunkGToF(Function *F, Function *G) { 476 Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "", 477 G->getParent()); 478 BasicBlock *BB = BasicBlock::Create("", NewG); 479 480 std::vector<Value *> Args; 481 unsigned i = 0; 482 const FunctionType *FFTy = F->getFunctionType(); 483 for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end(); 484 AI != AE; ++AI) { 485 if (FFTy->getParamType(i) == AI->getType()) 486 Args.push_back(AI); 487 else { 488 Value *BCI = new BitCastInst(AI, FFTy->getParamType(i), "", BB); 489 Args.push_back(BCI); 490 } 491 ++i; 492 } 493 494 CallInst *CI = CallInst::Create(F, Args.begin(), Args.end(), "", BB); 495 CI->setTailCall(); 496 CI->setCallingConv(F->getCallingConv()); 497 if (NewG->getReturnType() == Type::VoidTy) { 498 ReturnInst::Create(BB); 499 } else if (CI->getType() != NewG->getReturnType()) { 500 Value *BCI = new BitCastInst(CI, NewG->getReturnType(), "", BB); 501 ReturnInst::Create(BCI, BB); 502 } else { 503 ReturnInst::Create(CI, BB); 504 } 505 506 NewG->copyAttributesFrom(G); 507 NewG->takeName(G); 508 G->replaceAllUsesWith(NewG); 509 G->eraseFromParent(); 510 511 // TODO: look at direct callers to G and make them all direct callers to F. 512} 513 514static void AliasGToF(Function *F, Function *G) { 515 if (!G->hasExternalLinkage() && !G->hasLocalLinkage() && !G->hasWeakLinkage()) 516 return ThunkGToF(F, G); 517 518 GlobalAlias *GA = new GlobalAlias( 519 G->getType(), G->getLinkage(), "", 520 ConstantExpr::getBitCast(F, G->getType()), G->getParent()); 521 F->setAlignment(std::max(F->getAlignment(), G->getAlignment())); 522 GA->takeName(G); 523 GA->setVisibility(G->getVisibility()); 524 G->replaceAllUsesWith(GA); 525 G->eraseFromParent(); 526} 527 528static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) { 529 Function *F = FnVec[i]; 530 Function *G = FnVec[j]; 531 532 LinkageCategory catF = categorize(F); 533 LinkageCategory catG = categorize(G); 534 535 if (catF == ExternalWeak || (catF == Internal && catG == ExternalStrong)) { 536 std::swap(FnVec[i], FnVec[j]); 537 std::swap(F, G); 538 std::swap(catF, catG); 539 } 540 541 switch (catF) { 542 case ExternalStrong: 543 switch (catG) { 544 case ExternalStrong: 545 case ExternalWeak: 546 ThunkGToF(F, G); 547 break; 548 case Internal: 549 if (G->hasAddressTaken()) 550 ThunkGToF(F, G); 551 else 552 AliasGToF(F, G); 553 break; 554 } 555 break; 556 557 case ExternalWeak: { 558 assert(catG == ExternalWeak); 559 560 // Make them both thunks to the same internal function. 561 F->setAlignment(std::max(F->getAlignment(), G->getAlignment())); 562 Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "", 563 F->getParent()); 564 H->copyAttributesFrom(F); 565 H->takeName(F); 566 F->replaceAllUsesWith(H); 567 568 ThunkGToF(F, G); 569 ThunkGToF(F, H); 570 571 F->setLinkage(GlobalValue::InternalLinkage); 572 } break; 573 574 case Internal: 575 switch (catG) { 576 case ExternalStrong: 577 assert(0); 578 // fall-through 579 case ExternalWeak: 580 if (F->hasAddressTaken()) 581 ThunkGToF(F, G); 582 else 583 AliasGToF(F, G); 584 break; 585 case Internal: { 586 bool addrTakenF = F->hasAddressTaken(); 587 bool addrTakenG = G->hasAddressTaken(); 588 if (!addrTakenF && addrTakenG) { 589 std::swap(FnVec[i], FnVec[j]); 590 std::swap(F, G); 591 std::swap(addrTakenF, addrTakenG); 592 } 593 594 if (addrTakenF && addrTakenG) { 595 ThunkGToF(F, G); 596 } else { 597 assert(!addrTakenG); 598 AliasGToF(F, G); 599 } 600 } break; 601 } 602 break; 603 } 604 605 ++NumFunctionsMerged; 606 return true; 607} 608 609// ===----------------------------------------------------------------------=== 610// Pass definition 611// ===----------------------------------------------------------------------=== 612 613bool MergeFunctions::runOnModule(Module &M) { 614 bool Changed = false; 615 616 std::map<unsigned long, std::vector<Function *> > FnMap; 617 618 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) { 619 if (F->isDeclaration() || F->isIntrinsic()) 620 continue; 621 622 FnMap[hash(F)].push_back(F); 623 } 624 625 // TODO: instead of running in a loop, we could also fold functions in 626 // callgraph order. Constructing the CFG probably isn't cheaper than just 627 // running in a loop, unless it happened to already be available. 628 629 bool LocalChanged; 630 do { 631 LocalChanged = false; 632 DOUT << "size: " << FnMap.size() << "\n"; 633 for (std::map<unsigned long, std::vector<Function *> >::iterator 634 I = FnMap.begin(), E = FnMap.end(); I != E; ++I) { 635 std::vector<Function *> &FnVec = I->second; 636 DOUT << "hash (" << I->first << "): " << FnVec.size() << "\n"; 637 638 for (int i = 0, e = FnVec.size(); i != e; ++i) { 639 for (int j = i + 1; j != e; ++j) { 640 bool isEqual = equals(FnVec[i], FnVec[j]); 641 642 DOUT << " " << FnVec[i]->getName() 643 << (isEqual ? " == " : " != ") 644 << FnVec[j]->getName() << "\n"; 645 646 if (isEqual) { 647 if (fold(FnVec, i, j)) { 648 LocalChanged = true; 649 FnVec.erase(FnVec.begin() + j); 650 --j, --e; 651 } 652 } 653 } 654 } 655 656 } 657 Changed |= LocalChanged; 658 } while (LocalChanged); 659 660 return Changed; 661} 662