MergeFunctions.cpp revision 8eb3e54592ae7d7b43454fcd08d0da7a51ecd4d8
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 const InlineAsm *IA1 = cast<InlineAsm>(V1); 394 const InlineAsm *IA2 = cast<InlineAsm>(V2); 395 return IA1->getAsmString() == IA2->getAsmString() && 396 IA1->getConstraintString() == IA2->getConstraintString(); 397 } 398 399 unsigned long &ID1 = Map1[V1]; 400 if (!ID1) 401 ID1 = ++IDMap1Count; 402 403 unsigned long &ID2 = Map2[V2]; 404 if (!ID2) 405 ID2 = ++IDMap2Count; 406 407 return ID1 == ID2; 408} 409 410// Test whether two basic blocks have equivalent behaviour. 411bool FunctionComparator::compare(const BasicBlock *BB1, const BasicBlock *BB2) { 412 BasicBlock::const_iterator F1I = BB1->begin(), F1E = BB1->end(); 413 BasicBlock::const_iterator F2I = BB2->begin(), F2E = BB2->end(); 414 415 do { 416 if (!enumerate(F1I, F2I)) 417 return false; 418 419 if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(F1I)) { 420 const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(F2I); 421 if (!GEP2) 422 return false; 423 424 if (!enumerate(GEP1->getPointerOperand(), GEP2->getPointerOperand())) 425 return false; 426 427 if (!isEquivalentGEP(GEP1, GEP2)) 428 return false; 429 } else { 430 if (!isEquivalentOperation(F1I, F2I)) 431 return false; 432 433 assert(F1I->getNumOperands() == F2I->getNumOperands()); 434 for (unsigned i = 0, e = F1I->getNumOperands(); i != e; ++i) { 435 Value *OpF1 = F1I->getOperand(i); 436 Value *OpF2 = F2I->getOperand(i); 437 438 if (!enumerate(OpF1, OpF2)) 439 return false; 440 441 if (OpF1->getValueID() != OpF2->getValueID() || 442 !isEquivalentType(OpF1->getType(), OpF2->getType())) 443 return false; 444 } 445 } 446 447 ++F1I, ++F2I; 448 } while (F1I != F1E && F2I != F2E); 449 450 return F1I == F1E && F2I == F2E; 451} 452 453// Test whether the two functions have equivalent behaviour. 454bool FunctionComparator::compare() { 455 // We need to recheck everything, but check the things that weren't included 456 // in the hash first. 457 458 if (F1->getAttributes() != F2->getAttributes()) 459 return false; 460 461 if (F1->hasGC() != F2->hasGC()) 462 return false; 463 464 if (F1->hasGC() && F1->getGC() != F2->getGC()) 465 return false; 466 467 if (F1->hasSection() != F2->hasSection()) 468 return false; 469 470 if (F1->hasSection() && F1->getSection() != F2->getSection()) 471 return false; 472 473 if (F1->isVarArg() != F2->isVarArg()) 474 return false; 475 476 // TODO: if it's internal and only used in direct calls, we could handle this 477 // case too. 478 if (F1->getCallingConv() != F2->getCallingConv()) 479 return false; 480 481 if (!isEquivalentType(F1->getFunctionType(), F2->getFunctionType())) 482 return false; 483 484 assert(F1->arg_size() == F2->arg_size() && 485 "Identically typed functions have different numbers of args!"); 486 487 // Visit the arguments so that they get enumerated in the order they're 488 // passed in. 489 for (Function::const_arg_iterator f1i = F1->arg_begin(), 490 f2i = F2->arg_begin(), f1e = F1->arg_end(); f1i != f1e; ++f1i, ++f2i) { 491 if (!enumerate(f1i, f2i)) 492 llvm_unreachable("Arguments repeat!"); 493 } 494 495 // We do a CFG-ordered walk since the actual ordering of the blocks in the 496 // linked list is immaterial. Our walk starts at the entry block for both 497 // functions, then takes each block from each terminator in order. As an 498 // artifact, this also means that unreachable blocks are ignored. 499 SmallVector<const BasicBlock *, 8> F1BBs, F2BBs; 500 SmallSet<const BasicBlock *, 128> VisitedBBs; // in terms of F1. 501 502 F1BBs.push_back(&F1->getEntryBlock()); 503 F2BBs.push_back(&F2->getEntryBlock()); 504 505 VisitedBBs.insert(F1BBs[0]); 506 while (!F1BBs.empty()) { 507 const BasicBlock *F1BB = F1BBs.pop_back_val(); 508 const BasicBlock *F2BB = F2BBs.pop_back_val(); 509 510 if (!enumerate(F1BB, F2BB) || !compare(F1BB, F2BB)) 511 return false; 512 513 const TerminatorInst *F1TI = F1BB->getTerminator(); 514 const TerminatorInst *F2TI = F2BB->getTerminator(); 515 516 assert(F1TI->getNumSuccessors() == F2TI->getNumSuccessors()); 517 for (unsigned i = 0, e = F1TI->getNumSuccessors(); i != e; ++i) { 518 if (!VisitedBBs.insert(F1TI->getSuccessor(i))) 519 continue; 520 521 F1BBs.push_back(F1TI->getSuccessor(i)); 522 F2BBs.push_back(F2TI->getSuccessor(i)); 523 } 524 } 525 return true; 526} 527 528namespace { 529 530/// MergeFunctions finds functions which will generate identical machine code, 531/// by considering all pointer types to be equivalent. Once identified, 532/// MergeFunctions will fold them by replacing a call to one to a call to a 533/// bitcast of the other. 534/// 535class MergeFunctions : public ModulePass { 536public: 537 static char ID; 538 MergeFunctions() 539 : ModulePass(ID), HasGlobalAliases(false) { 540 initializeMergeFunctionsPass(*PassRegistry::getPassRegistry()); 541 } 542 543 bool runOnModule(Module &M); 544 545private: 546 typedef DenseSet<ComparableFunction> FnSetType; 547 548 /// A work queue of functions that may have been modified and should be 549 /// analyzed again. 550 std::vector<WeakVH> Deferred; 551 552 /// Insert a ComparableFunction into the FnSet, or merge it away if it's 553 /// equal to one that's already present. 554 bool insert(ComparableFunction &NewF); 555 556 /// Remove a Function from the FnSet and queue it up for a second sweep of 557 /// analysis. 558 void remove(Function *F); 559 560 /// Find the functions that use this Value and remove them from FnSet and 561 /// queue the functions. 562 void removeUsers(Value *V); 563 564 /// Replace all direct calls of Old with calls of New. Will bitcast New if 565 /// necessary to make types match. 566 void replaceDirectCallers(Function *Old, Function *New); 567 568 /// Merge two equivalent functions. Upon completion, G may be deleted, or may 569 /// be converted into a thunk. In either case, it should never be visited 570 /// again. 571 void mergeTwoFunctions(Function *F, Function *G); 572 573 /// Replace G with a thunk or an alias to F. Deletes G. 574 void writeThunkOrAlias(Function *F, Function *G); 575 576 /// Replace G with a simple tail call to bitcast(F). Also replace direct uses 577 /// of G with bitcast(F). Deletes G. 578 void writeThunk(Function *F, Function *G); 579 580 /// Replace G with an alias to F. Deletes G. 581 void writeAlias(Function *F, Function *G); 582 583 /// The set of all distinct functions. Use the insert() and remove() methods 584 /// to modify it. 585 FnSetType FnSet; 586 587 /// TargetData for more accurate GEP comparisons. May be NULL. 588 TargetData *TD; 589 590 /// Whether or not the target supports global aliases. 591 bool HasGlobalAliases; 592}; 593 594} // end anonymous namespace 595 596char MergeFunctions::ID = 0; 597INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false) 598 599ModulePass *llvm::createMergeFunctionsPass() { 600 return new MergeFunctions(); 601} 602 603bool MergeFunctions::runOnModule(Module &M) { 604 bool Changed = false; 605 TD = getAnalysisIfAvailable<TargetData>(); 606 607 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) { 608 if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) 609 Deferred.push_back(WeakVH(I)); 610 } 611 FnSet.resize(Deferred.size()); 612 613 do { 614 std::vector<WeakVH> Worklist; 615 Deferred.swap(Worklist); 616 617 DEBUG(dbgs() << "size of module: " << M.size() << '\n'); 618 DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n'); 619 620 // Insert only strong functions and merge them. Strong function merging 621 // always deletes one of them. 622 for (std::vector<WeakVH>::iterator I = Worklist.begin(), 623 E = Worklist.end(); I != E; ++I) { 624 if (!*I) continue; 625 Function *F = cast<Function>(*I); 626 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() && 627 !F->mayBeOverridden()) { 628 ComparableFunction CF = ComparableFunction(F, TD); 629 Changed |= insert(CF); 630 } 631 } 632 633 // Insert only weak functions and merge them. By doing these second we 634 // create thunks to the strong function when possible. When two weak 635 // functions are identical, we create a new strong function with two weak 636 // weak thunks to it which are identical but not mergable. 637 for (std::vector<WeakVH>::iterator I = Worklist.begin(), 638 E = Worklist.end(); I != E; ++I) { 639 if (!*I) continue; 640 Function *F = cast<Function>(*I); 641 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() && 642 F->mayBeOverridden()) { 643 ComparableFunction CF = ComparableFunction(F, TD); 644 Changed |= insert(CF); 645 } 646 } 647 DEBUG(dbgs() << "size of FnSet: " << FnSet.size() << '\n'); 648 } while (!Deferred.empty()); 649 650 FnSet.clear(); 651 652 return Changed; 653} 654 655bool DenseMapInfo<ComparableFunction>::isEqual(const ComparableFunction &LHS, 656 const ComparableFunction &RHS) { 657 if (LHS.getFunc() == RHS.getFunc() && 658 LHS.getHash() == RHS.getHash()) 659 return true; 660 if (!LHS.getFunc() || !RHS.getFunc()) 661 return false; 662 assert(LHS.getTD() == RHS.getTD() && 663 "Comparing functions for different targets"); 664 665 return FunctionComparator(LHS.getTD(), LHS.getFunc(), 666 RHS.getFunc()).compare(); 667} 668 669// Replace direct callers of Old with New. 670void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) { 671 Constant *BitcastNew = ConstantExpr::getBitCast(New, Old->getType()); 672 for (Value::use_iterator UI = Old->use_begin(), UE = Old->use_end(); 673 UI != UE;) { 674 Value::use_iterator TheIter = UI; 675 ++UI; 676 CallSite CS(*TheIter); 677 if (CS && CS.isCallee(TheIter)) { 678 remove(CS.getInstruction()->getParent()->getParent()); 679 TheIter.getUse().set(BitcastNew); 680 } 681 } 682} 683 684// Replace G with an alias to F if possible, or else a thunk to F. Deletes G. 685void MergeFunctions::writeThunkOrAlias(Function *F, Function *G) { 686 if (HasGlobalAliases && G->hasUnnamedAddr()) { 687 if (G->hasExternalLinkage() || G->hasLocalLinkage() || 688 G->hasWeakLinkage()) { 689 writeAlias(F, G); 690 return; 691 } 692 } 693 694 writeThunk(F, G); 695} 696 697// Replace G with a simple tail call to bitcast(F). Also replace direct uses 698// of G with bitcast(F). Deletes G. 699void MergeFunctions::writeThunk(Function *F, Function *G) { 700 if (!G->mayBeOverridden()) { 701 // Redirect direct callers of G to F. 702 replaceDirectCallers(G, F); 703 } 704 705 // If G was internal then we may have replaced all uses of G with F. If so, 706 // stop here and delete G. There's no need for a thunk. 707 if (G->hasLocalLinkage() && G->use_empty()) { 708 G->eraseFromParent(); 709 return; 710 } 711 712 Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "", 713 G->getParent()); 714 BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG); 715 IRBuilder<false> Builder(BB); 716 717 SmallVector<Value *, 16> Args; 718 unsigned i = 0; 719 const FunctionType *FFTy = F->getFunctionType(); 720 for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end(); 721 AI != AE; ++AI) { 722 Args.push_back(Builder.CreateBitCast(AI, FFTy->getParamType(i))); 723 ++i; 724 } 725 726 CallInst *CI = Builder.CreateCall(F, Args.begin(), Args.end()); 727 CI->setTailCall(); 728 CI->setCallingConv(F->getCallingConv()); 729 if (NewG->getReturnType()->isVoidTy()) { 730 Builder.CreateRetVoid(); 731 } else { 732 Builder.CreateRet(Builder.CreateBitCast(CI, NewG->getReturnType())); 733 } 734 735 NewG->copyAttributesFrom(G); 736 NewG->takeName(G); 737 removeUsers(G); 738 G->replaceAllUsesWith(NewG); 739 G->eraseFromParent(); 740 741 DEBUG(dbgs() << "writeThunk: " << NewG->getName() << '\n'); 742 ++NumThunksWritten; 743} 744 745// Replace G with an alias to F and delete G. 746void MergeFunctions::writeAlias(Function *F, Function *G) { 747 Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType()); 748 GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "", 749 BitcastF, G->getParent()); 750 F->setAlignment(std::max(F->getAlignment(), G->getAlignment())); 751 GA->takeName(G); 752 GA->setVisibility(G->getVisibility()); 753 removeUsers(G); 754 G->replaceAllUsesWith(GA); 755 G->eraseFromParent(); 756 757 DEBUG(dbgs() << "writeAlias: " << GA->getName() << '\n'); 758 ++NumAliasesWritten; 759} 760 761// Merge two equivalent functions. Upon completion, Function G is deleted. 762void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) { 763 if (F->mayBeOverridden()) { 764 assert(G->mayBeOverridden()); 765 766 if (HasGlobalAliases) { 767 // Make them both thunks to the same internal function. 768 Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "", 769 F->getParent()); 770 H->copyAttributesFrom(F); 771 H->takeName(F); 772 removeUsers(F); 773 F->replaceAllUsesWith(H); 774 775 unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment()); 776 777 writeAlias(F, G); 778 writeAlias(F, H); 779 780 F->setAlignment(MaxAlignment); 781 F->setLinkage(GlobalValue::PrivateLinkage); 782 } else { 783 // We can't merge them. Instead, pick one and update all direct callers 784 // to call it and hope that we improve the instruction cache hit rate. 785 replaceDirectCallers(G, F); 786 } 787 788 ++NumDoubleWeak; 789 } else { 790 writeThunkOrAlias(F, G); 791 } 792 793 ++NumFunctionsMerged; 794} 795 796// Insert a ComparableFunction into the FnSet, or merge it away if equal to one 797// that was already inserted. 798bool MergeFunctions::insert(ComparableFunction &NewF) { 799 std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF); 800 if (Result.second) 801 return false; 802 803 const ComparableFunction &OldF = *Result.first; 804 805 // Never thunk a strong function to a weak function. 806 assert(!OldF.getFunc()->mayBeOverridden() || 807 NewF.getFunc()->mayBeOverridden()); 808 809 DEBUG(dbgs() << " " << OldF.getFunc()->getName() << " == " 810 << NewF.getFunc()->getName() << '\n'); 811 812 Function *DeleteF = NewF.getFunc(); 813 NewF.release(); 814 mergeTwoFunctions(OldF.getFunc(), DeleteF); 815 return true; 816} 817 818// Remove a function from FnSet. If it was already in FnSet, add it to Deferred 819// so that we'll look at it in the next round. 820void MergeFunctions::remove(Function *F) { 821 ComparableFunction CF = ComparableFunction(F, TD); 822 if (FnSet.erase(CF)) { 823 Deferred.push_back(F); 824 } 825} 826 827// For each instruction used by the value, remove() the function that contains 828// the instruction. This should happen right before a call to RAUW. 829void MergeFunctions::removeUsers(Value *V) { 830 std::vector<Value *> Worklist; 831 Worklist.push_back(V); 832 while (!Worklist.empty()) { 833 Value *V = Worklist.back(); 834 Worklist.pop_back(); 835 836 for (Value::use_iterator UI = V->use_begin(), UE = V->use_end(); 837 UI != UE; ++UI) { 838 Use &U = UI.getUse(); 839 if (Instruction *I = dyn_cast<Instruction>(U.getUser())) { 840 remove(I->getParent()->getParent()); 841 } else if (isa<GlobalValue>(U.getUser())) { 842 // do nothing 843 } else if (Constant *C = dyn_cast<Constant>(U.getUser())) { 844 for (Value::use_iterator CUI = C->use_begin(), CUE = C->use_end(); 845 CUI != CUE; ++CUI) 846 Worklist.push_back(*CUI); 847 } 848 } 849 } 850} 851