MergeFunctions.cpp revision d489332549f226701825de990a2f5869dad96ace
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. If both functions are 21// overridable, we move the functionality into a new internal function and 22// leave two overridable thunks to it. 23// 24//===----------------------------------------------------------------------===// 25// 26// Future work: 27// 28// * virtual functions. 29// 30// Many functions have their address taken by the virtual function table for 31// the object they belong to. However, as long as it's only used for a lookup 32// and call, this is irrelevant, and we'd like to fold such functions. 33// 34// * switch from n^2 pair-wise comparisons to an n-way comparison for each 35// bucket. 36// 37// * be smarter about bitcasts. 38// 39// In order to fold functions, we will sometimes add either bitcast instructions 40// or bitcast constant expressions. Unfortunately, this can confound further 41// analysis since the two functions differ where one has a bitcast and the 42// other doesn't. We should learn to look through bitcasts. 43// 44//===----------------------------------------------------------------------===// 45 46#define DEBUG_TYPE "mergefunc" 47#include "llvm/Transforms/IPO.h" 48#include "llvm/ADT/DenseSet.h" 49#include "llvm/ADT/FoldingSet.h" 50#include "llvm/ADT/SmallSet.h" 51#include "llvm/ADT/Statistic.h" 52#include "llvm/ADT/STLExtras.h" 53#include "llvm/Constants.h" 54#include "llvm/InlineAsm.h" 55#include "llvm/Instructions.h" 56#include "llvm/LLVMContext.h" 57#include "llvm/Module.h" 58#include "llvm/Pass.h" 59#include "llvm/Support/CallSite.h" 60#include "llvm/Support/Debug.h" 61#include "llvm/Support/ErrorHandling.h" 62#include "llvm/Support/IRBuilder.h" 63#include "llvm/Support/ValueHandle.h" 64#include "llvm/Support/raw_ostream.h" 65#include "llvm/Target/TargetData.h" 66#include <vector> 67using namespace llvm; 68 69STATISTIC(NumFunctionsMerged, "Number of functions merged"); 70STATISTIC(NumThunksWritten, "Number of thunks generated"); 71STATISTIC(NumAliasesWritten, "Number of aliases generated"); 72STATISTIC(NumDoubleWeak, "Number of new functions created"); 73 74/// Creates a hash-code for the function which is the same for any two 75/// functions that will compare equal, without looking at the instructions 76/// inside the function. 77static unsigned profileFunction(const Function *F) { 78 const FunctionType *FTy = F->getFunctionType(); 79 80 FoldingSetNodeID ID; 81 ID.AddInteger(F->size()); 82 ID.AddInteger(F->getCallingConv()); 83 ID.AddBoolean(F->hasGC()); 84 ID.AddBoolean(FTy->isVarArg()); 85 ID.AddInteger(FTy->getReturnType()->getTypeID()); 86 for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i) 87 ID.AddInteger(FTy->getParamType(i)->getTypeID()); 88 return ID.ComputeHash(); 89} 90 91namespace { 92 93/// ComparableFunction - A struct that pairs together functions with a 94/// TargetData so that we can keep them together as elements in the DenseSet. 95class ComparableFunction { 96public: 97 static const ComparableFunction EmptyKey; 98 static const ComparableFunction TombstoneKey; 99 100 ComparableFunction(Function *Func, TargetData *TD) 101 : Func(Func), Hash(profileFunction(Func)), TD(TD) {} 102 103 Function *getFunc() const { return Func; } 104 unsigned getHash() const { return Hash; } 105 TargetData *getTD() const { return TD; } 106 107 // Drops AssertingVH reference to the function. Outside of debug mode, this 108 // does nothing. 109 void release() { 110 assert(Func && 111 "Attempted to release function twice, or release empty/tombstone!"); 112 Func = NULL; 113 } 114 115private: 116 explicit ComparableFunction(unsigned Hash) 117 : Func(NULL), Hash(Hash), TD(NULL) {} 118 119 AssertingVH<Function> Func; 120 unsigned Hash; 121 TargetData *TD; 122}; 123 124const ComparableFunction ComparableFunction::EmptyKey = ComparableFunction(0); 125const ComparableFunction ComparableFunction::TombstoneKey = 126 ComparableFunction(1); 127 128} 129 130namespace llvm { 131 template <> 132 struct DenseMapInfo<ComparableFunction> { 133 static ComparableFunction getEmptyKey() { 134 return ComparableFunction::EmptyKey; 135 } 136 static ComparableFunction getTombstoneKey() { 137 return ComparableFunction::TombstoneKey; 138 } 139 static unsigned getHashValue(const ComparableFunction &CF) { 140 return CF.getHash(); 141 } 142 static bool isEqual(const ComparableFunction &LHS, 143 const ComparableFunction &RHS); 144 }; 145} 146 147namespace { 148 149/// FunctionComparator - Compares two functions to determine whether or not 150/// they will generate machine code with the same behaviour. TargetData is 151/// used if available. The comparator always fails conservatively (erring on the 152/// side of claiming that two functions are different). 153class FunctionComparator { 154public: 155 FunctionComparator(const TargetData *TD, const Function *F1, 156 const Function *F2) 157 : F1(F1), F2(F2), TD(TD), IDMap1Count(0), IDMap2Count(0) {} 158 159 /// Test whether the two functions have equivalent behaviour. 160 bool compare(); 161 162private: 163 /// Test whether two basic blocks have equivalent behaviour. 164 bool compare(const BasicBlock *BB1, const BasicBlock *BB2); 165 166 /// Assign or look up previously assigned numbers for the two values, and 167 /// return whether the numbers are equal. Numbers are assigned in the order 168 /// visited. 169 bool enumerate(const Value *V1, const Value *V2); 170 171 /// Compare two Instructions for equivalence, similar to 172 /// Instruction::isSameOperationAs but with modifications to the type 173 /// comparison. 174 bool isEquivalentOperation(const Instruction *I1, 175 const Instruction *I2) const; 176 177 /// Compare two GEPs for equivalent pointer arithmetic. 178 bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2); 179 bool isEquivalentGEP(const GetElementPtrInst *GEP1, 180 const GetElementPtrInst *GEP2) { 181 return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2)); 182 } 183 184 /// Compare two Types, treating all pointer types as equal. 185 bool isEquivalentType(const Type *Ty1, const Type *Ty2) const; 186 187 // The two functions undergoing comparison. 188 const Function *F1, *F2; 189 190 const TargetData *TD; 191 192 typedef DenseMap<const Value *, unsigned long> IDMap; 193 IDMap Map1, Map2; 194 unsigned long IDMap1Count, IDMap2Count; 195}; 196 197} 198 199// Any two pointers in the same address space are equivalent, intptr_t and 200// pointers are equivalent. Otherwise, standard type equivalence rules apply. 201bool FunctionComparator::isEquivalentType(const Type *Ty1, 202 const Type *Ty2) const { 203 if (Ty1 == Ty2) 204 return true; 205 if (Ty1->getTypeID() != Ty2->getTypeID()) { 206 if (TD) { 207 LLVMContext &Ctx = Ty1->getContext(); 208 if (isa<PointerType>(Ty1) && Ty2 == TD->getIntPtrType(Ctx)) return true; 209 if (isa<PointerType>(Ty2) && Ty1 == TD->getIntPtrType(Ctx)) return true; 210 } 211 return false; 212 } 213 214 switch(Ty1->getTypeID()) { 215 default: 216 llvm_unreachable("Unknown type!"); 217 // Fall through in Release mode. 218 case Type::IntegerTyID: 219 case Type::OpaqueTyID: 220 case Type::VectorTyID: 221 // Ty1 == Ty2 would have returned true earlier. 222 return false; 223 224 case Type::VoidTyID: 225 case Type::FloatTyID: 226 case Type::DoubleTyID: 227 case Type::X86_FP80TyID: 228 case Type::FP128TyID: 229 case Type::PPC_FP128TyID: 230 case Type::LabelTyID: 231 case Type::MetadataTyID: 232 return true; 233 234 case Type::PointerTyID: { 235 const PointerType *PTy1 = cast<PointerType>(Ty1); 236 const PointerType *PTy2 = cast<PointerType>(Ty2); 237 return PTy1->getAddressSpace() == PTy2->getAddressSpace(); 238 } 239 240 case Type::StructTyID: { 241 const StructType *STy1 = cast<StructType>(Ty1); 242 const StructType *STy2 = cast<StructType>(Ty2); 243 if (STy1->getNumElements() != STy2->getNumElements()) 244 return false; 245 246 if (STy1->isPacked() != STy2->isPacked()) 247 return false; 248 249 for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) { 250 if (!isEquivalentType(STy1->getElementType(i), STy2->getElementType(i))) 251 return false; 252 } 253 return true; 254 } 255 256 case Type::FunctionTyID: { 257 const FunctionType *FTy1 = cast<FunctionType>(Ty1); 258 const FunctionType *FTy2 = cast<FunctionType>(Ty2); 259 if (FTy1->getNumParams() != FTy2->getNumParams() || 260 FTy1->isVarArg() != FTy2->isVarArg()) 261 return false; 262 263 if (!isEquivalentType(FTy1->getReturnType(), FTy2->getReturnType())) 264 return false; 265 266 for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) { 267 if (!isEquivalentType(FTy1->getParamType(i), FTy2->getParamType(i))) 268 return false; 269 } 270 return true; 271 } 272 273 case Type::ArrayTyID: { 274 const ArrayType *ATy1 = cast<ArrayType>(Ty1); 275 const ArrayType *ATy2 = cast<ArrayType>(Ty2); 276 return ATy1->getNumElements() == ATy2->getNumElements() && 277 isEquivalentType(ATy1->getElementType(), ATy2->getElementType()); 278 } 279 } 280} 281 282// Determine whether the two operations are the same except that pointer-to-A 283// and pointer-to-B are equivalent. This should be kept in sync with 284// Instruction::isSameOperationAs. 285bool FunctionComparator::isEquivalentOperation(const Instruction *I1, 286 const Instruction *I2) const { 287 if (I1->getOpcode() != I2->getOpcode() || 288 I1->getNumOperands() != I2->getNumOperands() || 289 !isEquivalentType(I1->getType(), I2->getType()) || 290 !I1->hasSameSubclassOptionalData(I2)) 291 return false; 292 293 // We have two instructions of identical opcode and #operands. Check to see 294 // if all operands are the same type 295 for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i) 296 if (!isEquivalentType(I1->getOperand(i)->getType(), 297 I2->getOperand(i)->getType())) 298 return false; 299 300 // Check special state that is a part of some instructions. 301 if (const LoadInst *LI = dyn_cast<LoadInst>(I1)) 302 return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() && 303 LI->getAlignment() == cast<LoadInst>(I2)->getAlignment(); 304 if (const StoreInst *SI = dyn_cast<StoreInst>(I1)) 305 return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() && 306 SI->getAlignment() == cast<StoreInst>(I2)->getAlignment(); 307 if (const CmpInst *CI = dyn_cast<CmpInst>(I1)) 308 return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate(); 309 if (const CallInst *CI = dyn_cast<CallInst>(I1)) 310 return CI->isTailCall() == cast<CallInst>(I2)->isTailCall() && 311 CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() && 312 CI->getAttributes() == cast<CallInst>(I2)->getAttributes(); 313 if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1)) 314 return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() && 315 CI->getAttributes() == cast<InvokeInst>(I2)->getAttributes(); 316 if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) { 317 if (IVI->getNumIndices() != cast<InsertValueInst>(I2)->getNumIndices()) 318 return false; 319 for (unsigned i = 0, e = IVI->getNumIndices(); i != e; ++i) 320 if (IVI->idx_begin()[i] != cast<InsertValueInst>(I2)->idx_begin()[i]) 321 return false; 322 return true; 323 } 324 if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) { 325 if (EVI->getNumIndices() != cast<ExtractValueInst>(I2)->getNumIndices()) 326 return false; 327 for (unsigned i = 0, e = EVI->getNumIndices(); i != e; ++i) 328 if (EVI->idx_begin()[i] != cast<ExtractValueInst>(I2)->idx_begin()[i]) 329 return false; 330 return true; 331 } 332 333 return true; 334} 335 336// Determine whether two GEP operations perform the same underlying arithmetic. 337bool FunctionComparator::isEquivalentGEP(const GEPOperator *GEP1, 338 const GEPOperator *GEP2) { 339 // When we have target data, we can reduce the GEP down to the value in bytes 340 // added to the address. 341 if (TD && GEP1->hasAllConstantIndices() && GEP2->hasAllConstantIndices()) { 342 SmallVector<Value *, 8> Indices1(GEP1->idx_begin(), GEP1->idx_end()); 343 SmallVector<Value *, 8> Indices2(GEP2->idx_begin(), GEP2->idx_end()); 344 uint64_t Offset1 = TD->getIndexedOffset(GEP1->getPointerOperandType(), 345 Indices1.data(), Indices1.size()); 346 uint64_t Offset2 = TD->getIndexedOffset(GEP2->getPointerOperandType(), 347 Indices2.data(), Indices2.size()); 348 return Offset1 == Offset2; 349 } 350 351 if (GEP1->getPointerOperand()->getType() != 352 GEP2->getPointerOperand()->getType()) 353 return false; 354 355 if (GEP1->getNumOperands() != GEP2->getNumOperands()) 356 return false; 357 358 for (unsigned i = 0, e = GEP1->getNumOperands(); i != e; ++i) { 359 if (!enumerate(GEP1->getOperand(i), GEP2->getOperand(i))) 360 return false; 361 } 362 363 return true; 364} 365 366// Compare two values used by the two functions under pair-wise comparison. If 367// this is the first time the values are seen, they're added to the mapping so 368// that we will detect mismatches on next use. 369bool FunctionComparator::enumerate(const Value *V1, const Value *V2) { 370 // Check for function @f1 referring to itself and function @f2 referring to 371 // itself, or referring to each other, or both referring to either of them. 372 // They're all equivalent if the two functions are otherwise equivalent. 373 if (V1 == F1 && V2 == F2) 374 return true; 375 if (V1 == F2 && V2 == F1) 376 return true; 377 378 if (const Constant *C1 = dyn_cast<Constant>(V1)) { 379 if (V1 == V2) return true; 380 const Constant *C2 = dyn_cast<Constant>(V2); 381 if (!C2) return false; 382 // TODO: constant expressions with GEP or references to F1 or F2. 383 if (C1->isNullValue() && C2->isNullValue() && 384 isEquivalentType(C1->getType(), C2->getType())) 385 return true; 386 // Try bitcasting C2 to C1's type. If the bitcast is legal and returns C1 387 // then they must have equal bit patterns. 388 return C1->getType()->canLosslesslyBitCastTo(C2->getType()) && 389 C1 == ConstantExpr::getBitCast(const_cast<Constant*>(C2), C1->getType()); 390 } 391 392 if (isa<InlineAsm>(V1) || isa<InlineAsm>(V2)) 393 return V1 == V2; 394 395 unsigned long &ID1 = Map1[V1]; 396 if (!ID1) 397 ID1 = ++IDMap1Count; 398 399 unsigned long &ID2 = Map2[V2]; 400 if (!ID2) 401 ID2 = ++IDMap2Count; 402 403 return ID1 == ID2; 404} 405 406// Test whether two basic blocks have equivalent behaviour. 407bool FunctionComparator::compare(const BasicBlock *BB1, const BasicBlock *BB2) { 408 BasicBlock::const_iterator F1I = BB1->begin(), F1E = BB1->end(); 409 BasicBlock::const_iterator F2I = BB2->begin(), F2E = BB2->end(); 410 411 do { 412 if (!enumerate(F1I, F2I)) 413 return false; 414 415 if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(F1I)) { 416 const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(F2I); 417 if (!GEP2) 418 return false; 419 420 if (!enumerate(GEP1->getPointerOperand(), GEP2->getPointerOperand())) 421 return false; 422 423 if (!isEquivalentGEP(GEP1, GEP2)) 424 return false; 425 } else { 426 if (!isEquivalentOperation(F1I, F2I)) 427 return false; 428 429 assert(F1I->getNumOperands() == F2I->getNumOperands()); 430 for (unsigned i = 0, e = F1I->getNumOperands(); i != e; ++i) { 431 Value *OpF1 = F1I->getOperand(i); 432 Value *OpF2 = F2I->getOperand(i); 433 434 if (!enumerate(OpF1, OpF2)) 435 return false; 436 437 if (OpF1->getValueID() != OpF2->getValueID() || 438 !isEquivalentType(OpF1->getType(), OpF2->getType())) 439 return false; 440 } 441 } 442 443 ++F1I, ++F2I; 444 } while (F1I != F1E && F2I != F2E); 445 446 return F1I == F1E && F2I == F2E; 447} 448 449// Test whether the two functions have equivalent behaviour. 450bool FunctionComparator::compare() { 451 // We need to recheck everything, but check the things that weren't included 452 // in the hash first. 453 454 if (F1->getAttributes() != F2->getAttributes()) 455 return false; 456 457 if (F1->hasGC() != F2->hasGC()) 458 return false; 459 460 if (F1->hasGC() && F1->getGC() != F2->getGC()) 461 return false; 462 463 if (F1->hasSection() != F2->hasSection()) 464 return false; 465 466 if (F1->hasSection() && F1->getSection() != F2->getSection()) 467 return false; 468 469 if (F1->isVarArg() != F2->isVarArg()) 470 return false; 471 472 // TODO: if it's internal and only used in direct calls, we could handle this 473 // case too. 474 if (F1->getCallingConv() != F2->getCallingConv()) 475 return false; 476 477 if (!isEquivalentType(F1->getFunctionType(), F2->getFunctionType())) 478 return false; 479 480 assert(F1->arg_size() == F2->arg_size() && 481 "Identically typed functions have different numbers of args!"); 482 483 // Visit the arguments so that they get enumerated in the order they're 484 // passed in. 485 for (Function::const_arg_iterator f1i = F1->arg_begin(), 486 f2i = F2->arg_begin(), f1e = F1->arg_end(); f1i != f1e; ++f1i, ++f2i) { 487 if (!enumerate(f1i, f2i)) 488 llvm_unreachable("Arguments repeat!"); 489 } 490 491 // We do a CFG-ordered walk since the actual ordering of the blocks in the 492 // linked list is immaterial. Our walk starts at the entry block for both 493 // functions, then takes each block from each terminator in order. As an 494 // artifact, this also means that unreachable blocks are ignored. 495 SmallVector<const BasicBlock *, 8> F1BBs, F2BBs; 496 SmallSet<const BasicBlock *, 128> VisitedBBs; // in terms of F1. 497 498 F1BBs.push_back(&F1->getEntryBlock()); 499 F2BBs.push_back(&F2->getEntryBlock()); 500 501 VisitedBBs.insert(F1BBs[0]); 502 while (!F1BBs.empty()) { 503 const BasicBlock *F1BB = F1BBs.pop_back_val(); 504 const BasicBlock *F2BB = F2BBs.pop_back_val(); 505 506 if (!enumerate(F1BB, F2BB) || !compare(F1BB, F2BB)) 507 return false; 508 509 const TerminatorInst *F1TI = F1BB->getTerminator(); 510 const TerminatorInst *F2TI = F2BB->getTerminator(); 511 512 assert(F1TI->getNumSuccessors() == F2TI->getNumSuccessors()); 513 for (unsigned i = 0, e = F1TI->getNumSuccessors(); i != e; ++i) { 514 if (!VisitedBBs.insert(F1TI->getSuccessor(i))) 515 continue; 516 517 F1BBs.push_back(F1TI->getSuccessor(i)); 518 F2BBs.push_back(F2TI->getSuccessor(i)); 519 } 520 } 521 return true; 522} 523 524namespace { 525 526/// MergeFunctions finds functions which will generate identical machine code, 527/// by considering all pointer types to be equivalent. Once identified, 528/// MergeFunctions will fold them by replacing a call to one to a call to a 529/// bitcast of the other. 530/// 531class MergeFunctions : public ModulePass { 532public: 533 static char ID; 534 MergeFunctions() 535 : ModulePass(ID), HasGlobalAliases(false) { 536 initializeMergeFunctionsPass(*PassRegistry::getPassRegistry()); 537 } 538 539 bool runOnModule(Module &M); 540 541private: 542 typedef DenseSet<ComparableFunction> FnSetType; 543 544 /// A work queue of functions that may have been modified and should be 545 /// analyzed again. 546 std::vector<WeakVH> Deferred; 547 548 /// Insert a ComparableFunction into the FnSet, or merge it away if it's 549 /// equal to one that's already present. 550 bool insert(ComparableFunction &NewF); 551 552 /// Remove a Function from the FnSet and queue it up for a second sweep of 553 /// analysis. 554 void remove(Function *F); 555 556 /// Find the functions that use this Value and remove them from FnSet and 557 /// queue the functions. 558 void removeUsers(Value *V); 559 560 /// Replace all direct calls of Old with calls of New. Will bitcast New if 561 /// necessary to make types match. 562 void replaceDirectCallers(Function *Old, Function *New); 563 564 /// Merge two equivalent functions. Upon completion, G may be deleted, or may 565 /// be converted into a thunk. In either case, it should never be visited 566 /// again. 567 void mergeTwoFunctions(Function *F, Function *G); 568 569 /// Replace G with a thunk or an alias to F. Deletes G. 570 void writeThunkOrAlias(Function *F, Function *G); 571 572 /// Replace G with a simple tail call to bitcast(F). Also replace direct uses 573 /// of G with bitcast(F). Deletes G. 574 void writeThunk(Function *F, Function *G); 575 576 /// Replace G with an alias to F. Deletes G. 577 void writeAlias(Function *F, Function *G); 578 579 /// The set of all distinct functions. Use the insert() and remove() methods 580 /// to modify it. 581 FnSetType FnSet; 582 583 /// TargetData for more accurate GEP comparisons. May be NULL. 584 TargetData *TD; 585 586 /// Whether or not the target supports global aliases. 587 bool HasGlobalAliases; 588}; 589 590} // end anonymous namespace 591 592char MergeFunctions::ID = 0; 593INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false) 594 595ModulePass *llvm::createMergeFunctionsPass() { 596 return new MergeFunctions(); 597} 598 599bool MergeFunctions::runOnModule(Module &M) { 600 bool Changed = false; 601 TD = getAnalysisIfAvailable<TargetData>(); 602 603 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) { 604 if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) 605 Deferred.push_back(WeakVH(I)); 606 } 607 FnSet.resize(Deferred.size()); 608 609 do { 610 std::vector<WeakVH> Worklist; 611 Deferred.swap(Worklist); 612 613 DEBUG(dbgs() << "size of module: " << M.size() << '\n'); 614 DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n'); 615 616 // Insert only strong functions and merge them. Strong function merging 617 // always deletes one of them. 618 for (std::vector<WeakVH>::iterator I = Worklist.begin(), 619 E = Worklist.end(); I != E; ++I) { 620 if (!*I) continue; 621 Function *F = cast<Function>(*I); 622 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() && 623 !F->mayBeOverridden()) { 624 ComparableFunction CF = ComparableFunction(F, TD); 625 Changed |= insert(CF); 626 } 627 } 628 629 // Insert only weak functions and merge them. By doing these second we 630 // create thunks to the strong function when possible. When two weak 631 // functions are identical, we create a new strong function with two weak 632 // weak thunks to it which are identical but not mergable. 633 for (std::vector<WeakVH>::iterator I = Worklist.begin(), 634 E = Worklist.end(); I != E; ++I) { 635 if (!*I) continue; 636 Function *F = cast<Function>(*I); 637 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() && 638 F->mayBeOverridden()) { 639 ComparableFunction CF = ComparableFunction(F, TD); 640 Changed |= insert(CF); 641 } 642 } 643 DEBUG(dbgs() << "size of FnSet: " << FnSet.size() << '\n'); 644 } while (!Deferred.empty()); 645 646 FnSet.clear(); 647 648 return Changed; 649} 650 651bool DenseMapInfo<ComparableFunction>::isEqual(const ComparableFunction &LHS, 652 const ComparableFunction &RHS) { 653 if (LHS.getFunc() == RHS.getFunc() && 654 LHS.getHash() == RHS.getHash()) 655 return true; 656 if (!LHS.getFunc() || !RHS.getFunc()) 657 return false; 658 assert(LHS.getTD() == RHS.getTD() && 659 "Comparing functions for different targets"); 660 661 return FunctionComparator(LHS.getTD(), LHS.getFunc(), 662 RHS.getFunc()).compare(); 663} 664 665// Replace direct callers of Old with New. 666void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) { 667 Constant *BitcastNew = ConstantExpr::getBitCast(New, Old->getType()); 668 for (Value::use_iterator UI = Old->use_begin(), UE = Old->use_end(); 669 UI != UE;) { 670 Value::use_iterator TheIter = UI; 671 ++UI; 672 CallSite CS(*TheIter); 673 if (CS && CS.isCallee(TheIter)) { 674 remove(CS.getInstruction()->getParent()->getParent()); 675 TheIter.getUse().set(BitcastNew); 676 } 677 } 678} 679 680// Replace G with an alias to F if possible, or else a thunk to F. Deletes G. 681void MergeFunctions::writeThunkOrAlias(Function *F, Function *G) { 682 if (HasGlobalAliases && G->hasUnnamedAddr()) { 683 if (G->hasExternalLinkage() || G->hasLocalLinkage() || 684 G->hasWeakLinkage()) { 685 writeAlias(F, G); 686 return; 687 } 688 } 689 690 writeThunk(F, G); 691} 692 693// Replace G with a simple tail call to bitcast(F). Also replace direct uses 694// of G with bitcast(F). Deletes G. 695void MergeFunctions::writeThunk(Function *F, Function *G) { 696 if (!G->mayBeOverridden()) { 697 // Redirect direct callers of G to F. 698 replaceDirectCallers(G, F); 699 } 700 701 // If G was internal then we may have replaced all uses of G with F. If so, 702 // stop here and delete G. There's no need for a thunk. 703 if (G->hasLocalLinkage() && G->use_empty()) { 704 G->eraseFromParent(); 705 return; 706 } 707 708 Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "", 709 G->getParent()); 710 BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG); 711 IRBuilder<false> Builder(BB); 712 713 SmallVector<Value *, 16> Args; 714 unsigned i = 0; 715 const FunctionType *FFTy = F->getFunctionType(); 716 for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end(); 717 AI != AE; ++AI) { 718 Args.push_back(Builder.CreateBitCast(AI, FFTy->getParamType(i))); 719 ++i; 720 } 721 722 CallInst *CI = Builder.CreateCall(F, Args.begin(), Args.end()); 723 CI->setTailCall(); 724 CI->setCallingConv(F->getCallingConv()); 725 if (NewG->getReturnType()->isVoidTy()) { 726 Builder.CreateRetVoid(); 727 } else { 728 Builder.CreateRet(Builder.CreateBitCast(CI, NewG->getReturnType())); 729 } 730 731 NewG->copyAttributesFrom(G); 732 NewG->takeName(G); 733 removeUsers(G); 734 G->replaceAllUsesWith(NewG); 735 G->eraseFromParent(); 736 737 DEBUG(dbgs() << "writeThunk: " << NewG->getName() << '\n'); 738 ++NumThunksWritten; 739} 740 741// Replace G with an alias to F and delete G. 742void MergeFunctions::writeAlias(Function *F, Function *G) { 743 Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType()); 744 GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "", 745 BitcastF, G->getParent()); 746 F->setAlignment(std::max(F->getAlignment(), G->getAlignment())); 747 GA->takeName(G); 748 GA->setVisibility(G->getVisibility()); 749 removeUsers(G); 750 G->replaceAllUsesWith(GA); 751 G->eraseFromParent(); 752 753 DEBUG(dbgs() << "writeAlias: " << GA->getName() << '\n'); 754 ++NumAliasesWritten; 755} 756 757// Merge two equivalent functions. Upon completion, Function G is deleted. 758void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) { 759 if (F->mayBeOverridden()) { 760 assert(G->mayBeOverridden()); 761 762 if (HasGlobalAliases) { 763 // Make them both thunks to the same internal function. 764 Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "", 765 F->getParent()); 766 H->copyAttributesFrom(F); 767 H->takeName(F); 768 removeUsers(F); 769 F->replaceAllUsesWith(H); 770 771 unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment()); 772 773 writeAlias(F, G); 774 writeAlias(F, H); 775 776 F->setAlignment(MaxAlignment); 777 F->setLinkage(GlobalValue::PrivateLinkage); 778 } else { 779 // We can't merge them. Instead, pick one and update all direct callers 780 // to call it and hope that we improve the instruction cache hit rate. 781 replaceDirectCallers(G, F); 782 } 783 784 ++NumDoubleWeak; 785 } else { 786 writeThunkOrAlias(F, G); 787 } 788 789 ++NumFunctionsMerged; 790} 791 792// Insert a ComparableFunction into the FnSet, or merge it away if equal to one 793// that was already inserted. 794bool MergeFunctions::insert(ComparableFunction &NewF) { 795 std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF); 796 if (Result.second) 797 return false; 798 799 const ComparableFunction &OldF = *Result.first; 800 801 // Never thunk a strong function to a weak function. 802 assert(!OldF.getFunc()->mayBeOverridden() || 803 NewF.getFunc()->mayBeOverridden()); 804 805 DEBUG(dbgs() << " " << OldF.getFunc()->getName() << " == " 806 << NewF.getFunc()->getName() << '\n'); 807 808 Function *DeleteF = NewF.getFunc(); 809 NewF.release(); 810 mergeTwoFunctions(OldF.getFunc(), DeleteF); 811 return true; 812} 813 814// Remove a function from FnSet. If it was already in FnSet, add it to Deferred 815// so that we'll look at it in the next round. 816void MergeFunctions::remove(Function *F) { 817 ComparableFunction CF = ComparableFunction(F, TD); 818 if (FnSet.erase(CF)) { 819 Deferred.push_back(F); 820 } 821} 822 823// For each instruction used by the value, remove() the function that contains 824// the instruction. This should happen right before a call to RAUW. 825void MergeFunctions::removeUsers(Value *V) { 826 std::vector<Value *> Worklist; 827 Worklist.push_back(V); 828 while (!Worklist.empty()) { 829 Value *V = Worklist.back(); 830 Worklist.pop_back(); 831 832 for (Value::use_iterator UI = V->use_begin(), UE = V->use_end(); 833 UI != UE; ++UI) { 834 Use &U = UI.getUse(); 835 if (Instruction *I = dyn_cast<Instruction>(U.getUser())) { 836 remove(I->getParent()->getParent()); 837 } else if (isa<GlobalValue>(U.getUser())) { 838 // do nothing 839 } else if (Constant *C = dyn_cast<Constant>(U.getUser())) { 840 for (Value::use_iterator CUI = C->use_begin(), CUE = C->use_end(); 841 CUI != CUE; ++CUI) 842 Worklist.push_back(*CUI); 843 } 844 } 845 } 846} 847