MergeFunctions.cpp revision aa76e9e2cf50af190de90bc778b7f7e42ef9ceff
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/Constants.h" 49#include "llvm/IRBuilder.h" 50#include "llvm/InlineAsm.h" 51#include "llvm/Instructions.h" 52#include "llvm/LLVMContext.h" 53#include "llvm/Module.h" 54#include "llvm/Operator.h" 55#include "llvm/Pass.h" 56#include "llvm/ADT/DenseSet.h" 57#include "llvm/ADT/FoldingSet.h" 58#include "llvm/ADT/STLExtras.h" 59#include "llvm/ADT/SmallSet.h" 60#include "llvm/ADT/Statistic.h" 61#include "llvm/Support/CallSite.h" 62#include "llvm/Support/Debug.h" 63#include "llvm/Support/ErrorHandling.h" 64#include "llvm/Support/ValueHandle.h" 65#include "llvm/Support/raw_ostream.h" 66#include "llvm/DataLayout.h" 67#include <vector> 68using namespace llvm; 69 70STATISTIC(NumFunctionsMerged, "Number of functions merged"); 71STATISTIC(NumThunksWritten, "Number of thunks generated"); 72STATISTIC(NumAliasesWritten, "Number of aliases generated"); 73STATISTIC(NumDoubleWeak, "Number of new functions created"); 74 75/// Creates a hash-code for the function which is the same for any two 76/// functions that will compare equal, without looking at the instructions 77/// inside the function. 78static unsigned profileFunction(const Function *F) { 79 FunctionType *FTy = F->getFunctionType(); 80 81 FoldingSetNodeID ID; 82 ID.AddInteger(F->size()); 83 ID.AddInteger(F->getCallingConv()); 84 ID.AddBoolean(F->hasGC()); 85 ID.AddBoolean(FTy->isVarArg()); 86 ID.AddInteger(FTy->getReturnType()->getTypeID()); 87 for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i) 88 ID.AddInteger(FTy->getParamType(i)->getTypeID()); 89 return ID.ComputeHash(); 90} 91 92namespace { 93 94/// ComparableFunction - A struct that pairs together functions with a 95/// DataLayout so that we can keep them together as elements in the DenseSet. 96class ComparableFunction { 97public: 98 static const ComparableFunction EmptyKey; 99 static const ComparableFunction TombstoneKey; 100 static DataLayout * const LookupOnly; 101 102 ComparableFunction(Function *Func, DataLayout *TD) 103 : Func(Func), Hash(profileFunction(Func)), TD(TD) {} 104 105 Function *getFunc() const { return Func; } 106 unsigned getHash() const { return Hash; } 107 DataLayout *getTD() const { return TD; } 108 109 // Drops AssertingVH reference to the function. Outside of debug mode, this 110 // does nothing. 111 void release() { 112 assert(Func && 113 "Attempted to release function twice, or release empty/tombstone!"); 114 Func = NULL; 115 } 116 117private: 118 explicit ComparableFunction(unsigned Hash) 119 : Func(NULL), Hash(Hash), TD(NULL) {} 120 121 AssertingVH<Function> Func; 122 unsigned Hash; 123 DataLayout *TD; 124}; 125 126const ComparableFunction ComparableFunction::EmptyKey = ComparableFunction(0); 127const ComparableFunction ComparableFunction::TombstoneKey = 128 ComparableFunction(1); 129DataLayout *const ComparableFunction::LookupOnly = (DataLayout*)(-1); 130 131} 132 133namespace llvm { 134 template <> 135 struct DenseMapInfo<ComparableFunction> { 136 static ComparableFunction getEmptyKey() { 137 return ComparableFunction::EmptyKey; 138 } 139 static ComparableFunction getTombstoneKey() { 140 return ComparableFunction::TombstoneKey; 141 } 142 static unsigned getHashValue(const ComparableFunction &CF) { 143 return CF.getHash(); 144 } 145 static bool isEqual(const ComparableFunction &LHS, 146 const ComparableFunction &RHS); 147 }; 148} 149 150namespace { 151 152/// FunctionComparator - Compares two functions to determine whether or not 153/// they will generate machine code with the same behaviour. DataLayout is 154/// used if available. The comparator always fails conservatively (erring on the 155/// side of claiming that two functions are different). 156class FunctionComparator { 157public: 158 FunctionComparator(const DataLayout *TD, const Function *F1, 159 const Function *F2) 160 : F1(F1), F2(F2), TD(TD) {} 161 162 /// Test whether the two functions have equivalent behaviour. 163 bool compare(); 164 165private: 166 /// Test whether two basic blocks have equivalent behaviour. 167 bool compare(const BasicBlock *BB1, const BasicBlock *BB2); 168 169 /// Assign or look up previously assigned numbers for the two values, and 170 /// return whether the numbers are equal. Numbers are assigned in the order 171 /// visited. 172 bool enumerate(const Value *V1, const Value *V2); 173 174 /// Compare two Instructions for equivalence, similar to 175 /// Instruction::isSameOperationAs but with modifications to the type 176 /// comparison. 177 bool isEquivalentOperation(const Instruction *I1, 178 const Instruction *I2) const; 179 180 /// Compare two GEPs for equivalent pointer arithmetic. 181 bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2); 182 bool isEquivalentGEP(const GetElementPtrInst *GEP1, 183 const GetElementPtrInst *GEP2) { 184 return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2)); 185 } 186 187 /// Compare two Types, treating all pointer types as equal. 188 bool isEquivalentType(Type *Ty1, Type *Ty2) const; 189 190 // The two functions undergoing comparison. 191 const Function *F1, *F2; 192 193 const DataLayout *TD; 194 195 DenseMap<const Value *, const Value *> id_map; 196 DenseSet<const Value *> seen_values; 197}; 198 199} 200 201// Any two pointers in the same address space are equivalent, intptr_t and 202// pointers are equivalent. Otherwise, standard type equivalence rules apply. 203bool FunctionComparator::isEquivalentType(Type *Ty1, 204 Type *Ty2) const { 205 if (Ty1 == Ty2) 206 return true; 207 if (Ty1->getTypeID() != Ty2->getTypeID()) { 208 if (TD) { 209 if (isa<PointerType>(Ty1) && Ty2 == TD->getIntPtrType(Ty1)) return true; 210 if (isa<PointerType>(Ty2) && Ty1 == TD->getIntPtrType(Ty2)) return true; 211 } 212 return false; 213 } 214 215 switch (Ty1->getTypeID()) { 216 default: 217 llvm_unreachable("Unknown type!"); 218 // Fall through in Release mode. 219 case Type::IntegerTyID: 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 PointerType *PTy1 = cast<PointerType>(Ty1); 236 PointerType *PTy2 = cast<PointerType>(Ty2); 237 return PTy1->getAddressSpace() == PTy2->getAddressSpace(); 238 } 239 240 case Type::StructTyID: { 241 StructType *STy1 = cast<StructType>(Ty1); 242 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 FunctionType *FTy1 = cast<FunctionType>(Ty1); 258 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 ArrayType *ATy1 = cast<ArrayType>(Ty1); 275 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 // Differences from Instruction::isSameOperationAs: 288 // * replace type comparison with calls to isEquivalentType. 289 // * we test for I->hasSameSubclassOptionalData (nuw/nsw/tail) at the top 290 // * because of the above, we don't test for the tail bit on calls later on 291 if (I1->getOpcode() != I2->getOpcode() || 292 I1->getNumOperands() != I2->getNumOperands() || 293 !isEquivalentType(I1->getType(), I2->getType()) || 294 !I1->hasSameSubclassOptionalData(I2)) 295 return false; 296 297 // We have two instructions of identical opcode and #operands. Check to see 298 // if all operands are the same type 299 for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i) 300 if (!isEquivalentType(I1->getOperand(i)->getType(), 301 I2->getOperand(i)->getType())) 302 return false; 303 304 // Check special state that is a part of some instructions. 305 if (const LoadInst *LI = dyn_cast<LoadInst>(I1)) 306 return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() && 307 LI->getAlignment() == cast<LoadInst>(I2)->getAlignment() && 308 LI->getOrdering() == cast<LoadInst>(I2)->getOrdering() && 309 LI->getSynchScope() == cast<LoadInst>(I2)->getSynchScope(); 310 if (const StoreInst *SI = dyn_cast<StoreInst>(I1)) 311 return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() && 312 SI->getAlignment() == cast<StoreInst>(I2)->getAlignment() && 313 SI->getOrdering() == cast<StoreInst>(I2)->getOrdering() && 314 SI->getSynchScope() == cast<StoreInst>(I2)->getSynchScope(); 315 if (const CmpInst *CI = dyn_cast<CmpInst>(I1)) 316 return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate(); 317 if (const CallInst *CI = dyn_cast<CallInst>(I1)) 318 return CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() && 319 CI->getAttributes() == cast<CallInst>(I2)->getAttributes(); 320 if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1)) 321 return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() && 322 CI->getAttributes() == cast<InvokeInst>(I2)->getAttributes(); 323 if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) 324 return IVI->getIndices() == cast<InsertValueInst>(I2)->getIndices(); 325 if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) 326 return EVI->getIndices() == cast<ExtractValueInst>(I2)->getIndices(); 327 if (const FenceInst *FI = dyn_cast<FenceInst>(I1)) 328 return FI->getOrdering() == cast<FenceInst>(I2)->getOrdering() && 329 FI->getSynchScope() == cast<FenceInst>(I2)->getSynchScope(); 330 if (const AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(I1)) 331 return CXI->isVolatile() == cast<AtomicCmpXchgInst>(I2)->isVolatile() && 332 CXI->getOrdering() == cast<AtomicCmpXchgInst>(I2)->getOrdering() && 333 CXI->getSynchScope() == cast<AtomicCmpXchgInst>(I2)->getSynchScope(); 334 if (const AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(I1)) 335 return RMWI->getOperation() == cast<AtomicRMWInst>(I2)->getOperation() && 336 RMWI->isVolatile() == cast<AtomicRMWInst>(I2)->isVolatile() && 337 RMWI->getOrdering() == cast<AtomicRMWInst>(I2)->getOrdering() && 338 RMWI->getSynchScope() == cast<AtomicRMWInst>(I2)->getSynchScope(); 339 340 return true; 341} 342 343// Determine whether two GEP operations perform the same underlying arithmetic. 344bool FunctionComparator::isEquivalentGEP(const GEPOperator *GEP1, 345 const GEPOperator *GEP2) { 346 // When we have target data, we can reduce the GEP down to the value in bytes 347 // added to the address. 348 if (TD && GEP1->hasAllConstantIndices() && GEP2->hasAllConstantIndices()) { 349 SmallVector<Value *, 8> Indices1(GEP1->idx_begin(), GEP1->idx_end()); 350 SmallVector<Value *, 8> Indices2(GEP2->idx_begin(), GEP2->idx_end()); 351 uint64_t Offset1 = TD->getIndexedOffset(GEP1->getPointerOperandType(), 352 Indices1); 353 uint64_t Offset2 = TD->getIndexedOffset(GEP2->getPointerOperandType(), 354 Indices2); 355 return Offset1 == Offset2; 356 } 357 358 if (GEP1->getPointerOperand()->getType() != 359 GEP2->getPointerOperand()->getType()) 360 return false; 361 362 if (GEP1->getNumOperands() != GEP2->getNumOperands()) 363 return false; 364 365 for (unsigned i = 0, e = GEP1->getNumOperands(); i != e; ++i) { 366 if (!enumerate(GEP1->getOperand(i), GEP2->getOperand(i))) 367 return false; 368 } 369 370 return true; 371} 372 373// Compare two values used by the two functions under pair-wise comparison. If 374// this is the first time the values are seen, they're added to the mapping so 375// that we will detect mismatches on next use. 376bool FunctionComparator::enumerate(const Value *V1, const Value *V2) { 377 // Check for function @f1 referring to itself and function @f2 referring to 378 // itself, or referring to each other, or both referring to either of them. 379 // They're all equivalent if the two functions are otherwise equivalent. 380 if (V1 == F1 && V2 == F2) 381 return true; 382 if (V1 == F2 && V2 == F1) 383 return true; 384 385 if (const Constant *C1 = dyn_cast<Constant>(V1)) { 386 if (V1 == V2) return true; 387 const Constant *C2 = dyn_cast<Constant>(V2); 388 if (!C2) return false; 389 // TODO: constant expressions with GEP or references to F1 or F2. 390 if (C1->isNullValue() && C2->isNullValue() && 391 isEquivalentType(C1->getType(), C2->getType())) 392 return true; 393 // Try bitcasting C2 to C1's type. If the bitcast is legal and returns C1 394 // then they must have equal bit patterns. 395 return C1->getType()->canLosslesslyBitCastTo(C2->getType()) && 396 C1 == ConstantExpr::getBitCast(const_cast<Constant*>(C2), C1->getType()); 397 } 398 399 if (isa<InlineAsm>(V1) || isa<InlineAsm>(V2)) 400 return V1 == V2; 401 402 // Check that V1 maps to V2. If we find a value that V1 maps to then we simply 403 // check whether it's equal to V2. When there is no mapping then we need to 404 // ensure that V2 isn't already equivalent to something else. For this 405 // purpose, we track the V2 values in a set. 406 407 const Value *&map_elem = id_map[V1]; 408 if (map_elem) 409 return map_elem == V2; 410 if (!seen_values.insert(V2).second) 411 return false; 412 map_elem = V2; 413 return true; 414} 415 416// Test whether two basic blocks have equivalent behaviour. 417bool FunctionComparator::compare(const BasicBlock *BB1, const BasicBlock *BB2) { 418 BasicBlock::const_iterator F1I = BB1->begin(), F1E = BB1->end(); 419 BasicBlock::const_iterator F2I = BB2->begin(), F2E = BB2->end(); 420 421 do { 422 if (!enumerate(F1I, F2I)) 423 return false; 424 425 if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(F1I)) { 426 const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(F2I); 427 if (!GEP2) 428 return false; 429 430 if (!enumerate(GEP1->getPointerOperand(), GEP2->getPointerOperand())) 431 return false; 432 433 if (!isEquivalentGEP(GEP1, GEP2)) 434 return false; 435 } else { 436 if (!isEquivalentOperation(F1I, F2I)) 437 return false; 438 439 assert(F1I->getNumOperands() == F2I->getNumOperands()); 440 for (unsigned i = 0, e = F1I->getNumOperands(); i != e; ++i) { 441 Value *OpF1 = F1I->getOperand(i); 442 Value *OpF2 = F2I->getOperand(i); 443 444 if (!enumerate(OpF1, OpF2)) 445 return false; 446 447 if (OpF1->getValueID() != OpF2->getValueID() || 448 !isEquivalentType(OpF1->getType(), OpF2->getType())) 449 return false; 450 } 451 } 452 453 ++F1I, ++F2I; 454 } while (F1I != F1E && F2I != F2E); 455 456 return F1I == F1E && F2I == F2E; 457} 458 459// Test whether the two functions have equivalent behaviour. 460bool FunctionComparator::compare() { 461 // We need to recheck everything, but check the things that weren't included 462 // in the hash first. 463 464 if (F1->getAttributes() != F2->getAttributes()) 465 return false; 466 467 if (F1->hasGC() != F2->hasGC()) 468 return false; 469 470 if (F1->hasGC() && F1->getGC() != F2->getGC()) 471 return false; 472 473 if (F1->hasSection() != F2->hasSection()) 474 return false; 475 476 if (F1->hasSection() && F1->getSection() != F2->getSection()) 477 return false; 478 479 if (F1->isVarArg() != F2->isVarArg()) 480 return false; 481 482 // TODO: if it's internal and only used in direct calls, we could handle this 483 // case too. 484 if (F1->getCallingConv() != F2->getCallingConv()) 485 return false; 486 487 if (!isEquivalentType(F1->getFunctionType(), F2->getFunctionType())) 488 return false; 489 490 assert(F1->arg_size() == F2->arg_size() && 491 "Identically typed functions have different numbers of args!"); 492 493 // Visit the arguments so that they get enumerated in the order they're 494 // passed in. 495 for (Function::const_arg_iterator f1i = F1->arg_begin(), 496 f2i = F2->arg_begin(), f1e = F1->arg_end(); f1i != f1e; ++f1i, ++f2i) { 497 if (!enumerate(f1i, f2i)) 498 llvm_unreachable("Arguments repeat!"); 499 } 500 501 // We do a CFG-ordered walk since the actual ordering of the blocks in the 502 // linked list is immaterial. Our walk starts at the entry block for both 503 // functions, then takes each block from each terminator in order. As an 504 // artifact, this also means that unreachable blocks are ignored. 505 SmallVector<const BasicBlock *, 8> F1BBs, F2BBs; 506 SmallSet<const BasicBlock *, 128> VisitedBBs; // in terms of F1. 507 508 F1BBs.push_back(&F1->getEntryBlock()); 509 F2BBs.push_back(&F2->getEntryBlock()); 510 511 VisitedBBs.insert(F1BBs[0]); 512 while (!F1BBs.empty()) { 513 const BasicBlock *F1BB = F1BBs.pop_back_val(); 514 const BasicBlock *F2BB = F2BBs.pop_back_val(); 515 516 if (!enumerate(F1BB, F2BB) || !compare(F1BB, F2BB)) 517 return false; 518 519 const TerminatorInst *F1TI = F1BB->getTerminator(); 520 const TerminatorInst *F2TI = F2BB->getTerminator(); 521 522 assert(F1TI->getNumSuccessors() == F2TI->getNumSuccessors()); 523 for (unsigned i = 0, e = F1TI->getNumSuccessors(); i != e; ++i) { 524 if (!VisitedBBs.insert(F1TI->getSuccessor(i))) 525 continue; 526 527 F1BBs.push_back(F1TI->getSuccessor(i)); 528 F2BBs.push_back(F2TI->getSuccessor(i)); 529 } 530 } 531 return true; 532} 533 534namespace { 535 536/// MergeFunctions finds functions which will generate identical machine code, 537/// by considering all pointer types to be equivalent. Once identified, 538/// MergeFunctions will fold them by replacing a call to one to a call to a 539/// bitcast of the other. 540/// 541class MergeFunctions : public ModulePass { 542public: 543 static char ID; 544 MergeFunctions() 545 : ModulePass(ID), HasGlobalAliases(false) { 546 initializeMergeFunctionsPass(*PassRegistry::getPassRegistry()); 547 } 548 549 bool runOnModule(Module &M); 550 551private: 552 typedef DenseSet<ComparableFunction> FnSetType; 553 554 /// A work queue of functions that may have been modified and should be 555 /// analyzed again. 556 std::vector<WeakVH> Deferred; 557 558 /// Insert a ComparableFunction into the FnSet, or merge it away if it's 559 /// equal to one that's already present. 560 bool insert(ComparableFunction &NewF); 561 562 /// Remove a Function from the FnSet and queue it up for a second sweep of 563 /// analysis. 564 void remove(Function *F); 565 566 /// Find the functions that use this Value and remove them from FnSet and 567 /// queue the functions. 568 void removeUsers(Value *V); 569 570 /// Replace all direct calls of Old with calls of New. Will bitcast New if 571 /// necessary to make types match. 572 void replaceDirectCallers(Function *Old, Function *New); 573 574 /// Merge two equivalent functions. Upon completion, G may be deleted, or may 575 /// be converted into a thunk. In either case, it should never be visited 576 /// again. 577 void mergeTwoFunctions(Function *F, Function *G); 578 579 /// Replace G with a thunk or an alias to F. Deletes G. 580 void writeThunkOrAlias(Function *F, Function *G); 581 582 /// Replace G with a simple tail call to bitcast(F). Also replace direct uses 583 /// of G with bitcast(F). Deletes G. 584 void writeThunk(Function *F, Function *G); 585 586 /// Replace G with an alias to F. Deletes G. 587 void writeAlias(Function *F, Function *G); 588 589 /// The set of all distinct functions. Use the insert() and remove() methods 590 /// to modify it. 591 FnSetType FnSet; 592 593 /// DataLayout for more accurate GEP comparisons. May be NULL. 594 DataLayout *TD; 595 596 /// Whether or not the target supports global aliases. 597 bool HasGlobalAliases; 598}; 599 600} // end anonymous namespace 601 602char MergeFunctions::ID = 0; 603INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false) 604 605ModulePass *llvm::createMergeFunctionsPass() { 606 return new MergeFunctions(); 607} 608 609bool MergeFunctions::runOnModule(Module &M) { 610 bool Changed = false; 611 TD = getAnalysisIfAvailable<DataLayout>(); 612 613 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) { 614 if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) 615 Deferred.push_back(WeakVH(I)); 616 } 617 FnSet.resize(Deferred.size()); 618 619 do { 620 std::vector<WeakVH> Worklist; 621 Deferred.swap(Worklist); 622 623 DEBUG(dbgs() << "size of module: " << M.size() << '\n'); 624 DEBUG(dbgs() << "size of worklist: " << Worklist.size() << '\n'); 625 626 // Insert only strong functions and merge them. Strong function merging 627 // always deletes one of them. 628 for (std::vector<WeakVH>::iterator I = Worklist.begin(), 629 E = Worklist.end(); I != E; ++I) { 630 if (!*I) continue; 631 Function *F = cast<Function>(*I); 632 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() && 633 !F->mayBeOverridden()) { 634 ComparableFunction CF = ComparableFunction(F, TD); 635 Changed |= insert(CF); 636 } 637 } 638 639 // Insert only weak functions and merge them. By doing these second we 640 // create thunks to the strong function when possible. When two weak 641 // functions are identical, we create a new strong function with two weak 642 // weak thunks to it which are identical but not mergable. 643 for (std::vector<WeakVH>::iterator I = Worklist.begin(), 644 E = Worklist.end(); I != E; ++I) { 645 if (!*I) continue; 646 Function *F = cast<Function>(*I); 647 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() && 648 F->mayBeOverridden()) { 649 ComparableFunction CF = ComparableFunction(F, TD); 650 Changed |= insert(CF); 651 } 652 } 653 DEBUG(dbgs() << "size of FnSet: " << FnSet.size() << '\n'); 654 } while (!Deferred.empty()); 655 656 FnSet.clear(); 657 658 return Changed; 659} 660 661bool DenseMapInfo<ComparableFunction>::isEqual(const ComparableFunction &LHS, 662 const ComparableFunction &RHS) { 663 if (LHS.getFunc() == RHS.getFunc() && 664 LHS.getHash() == RHS.getHash()) 665 return true; 666 if (!LHS.getFunc() || !RHS.getFunc()) 667 return false; 668 669 // One of these is a special "underlying pointer comparison only" object. 670 if (LHS.getTD() == ComparableFunction::LookupOnly || 671 RHS.getTD() == ComparableFunction::LookupOnly) 672 return false; 673 674 assert(LHS.getTD() == RHS.getTD() && 675 "Comparing functions for different targets"); 676 677 return FunctionComparator(LHS.getTD(), LHS.getFunc(), 678 RHS.getFunc()).compare(); 679} 680 681// Replace direct callers of Old with New. 682void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) { 683 Constant *BitcastNew = ConstantExpr::getBitCast(New, Old->getType()); 684 for (Value::use_iterator UI = Old->use_begin(), UE = Old->use_end(); 685 UI != UE;) { 686 Value::use_iterator TheIter = UI; 687 ++UI; 688 CallSite CS(*TheIter); 689 if (CS && CS.isCallee(TheIter)) { 690 remove(CS.getInstruction()->getParent()->getParent()); 691 TheIter.getUse().set(BitcastNew); 692 } 693 } 694} 695 696// Replace G with an alias to F if possible, or else a thunk to F. Deletes G. 697void MergeFunctions::writeThunkOrAlias(Function *F, Function *G) { 698 if (HasGlobalAliases && G->hasUnnamedAddr()) { 699 if (G->hasExternalLinkage() || G->hasLocalLinkage() || 700 G->hasWeakLinkage()) { 701 writeAlias(F, G); 702 return; 703 } 704 } 705 706 writeThunk(F, G); 707} 708 709// Replace G with a simple tail call to bitcast(F). Also replace direct uses 710// of G with bitcast(F). Deletes G. 711void MergeFunctions::writeThunk(Function *F, Function *G) { 712 if (!G->mayBeOverridden()) { 713 // Redirect direct callers of G to F. 714 replaceDirectCallers(G, F); 715 } 716 717 // If G was internal then we may have replaced all uses of G with F. If so, 718 // stop here and delete G. There's no need for a thunk. 719 if (G->hasLocalLinkage() && G->use_empty()) { 720 G->eraseFromParent(); 721 return; 722 } 723 724 Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "", 725 G->getParent()); 726 BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG); 727 IRBuilder<false> Builder(BB); 728 729 SmallVector<Value *, 16> Args; 730 unsigned i = 0; 731 FunctionType *FFTy = F->getFunctionType(); 732 for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end(); 733 AI != AE; ++AI) { 734 Args.push_back(Builder.CreateBitCast(AI, FFTy->getParamType(i))); 735 ++i; 736 } 737 738 CallInst *CI = Builder.CreateCall(F, Args); 739 CI->setTailCall(); 740 CI->setCallingConv(F->getCallingConv()); 741 if (NewG->getReturnType()->isVoidTy()) { 742 Builder.CreateRetVoid(); 743 } else { 744 Builder.CreateRet(Builder.CreateBitCast(CI, NewG->getReturnType())); 745 } 746 747 NewG->copyAttributesFrom(G); 748 NewG->takeName(G); 749 removeUsers(G); 750 G->replaceAllUsesWith(NewG); 751 G->eraseFromParent(); 752 753 DEBUG(dbgs() << "writeThunk: " << NewG->getName() << '\n'); 754 ++NumThunksWritten; 755} 756 757// Replace G with an alias to F and delete G. 758void MergeFunctions::writeAlias(Function *F, Function *G) { 759 Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType()); 760 GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "", 761 BitcastF, G->getParent()); 762 F->setAlignment(std::max(F->getAlignment(), G->getAlignment())); 763 GA->takeName(G); 764 GA->setVisibility(G->getVisibility()); 765 removeUsers(G); 766 G->replaceAllUsesWith(GA); 767 G->eraseFromParent(); 768 769 DEBUG(dbgs() << "writeAlias: " << GA->getName() << '\n'); 770 ++NumAliasesWritten; 771} 772 773// Merge two equivalent functions. Upon completion, Function G is deleted. 774void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) { 775 if (F->mayBeOverridden()) { 776 assert(G->mayBeOverridden()); 777 778 if (HasGlobalAliases) { 779 // Make them both thunks to the same internal function. 780 Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "", 781 F->getParent()); 782 H->copyAttributesFrom(F); 783 H->takeName(F); 784 removeUsers(F); 785 F->replaceAllUsesWith(H); 786 787 unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment()); 788 789 writeAlias(F, G); 790 writeAlias(F, H); 791 792 F->setAlignment(MaxAlignment); 793 F->setLinkage(GlobalValue::PrivateLinkage); 794 } else { 795 // We can't merge them. Instead, pick one and update all direct callers 796 // to call it and hope that we improve the instruction cache hit rate. 797 replaceDirectCallers(G, F); 798 } 799 800 ++NumDoubleWeak; 801 } else { 802 writeThunkOrAlias(F, G); 803 } 804 805 ++NumFunctionsMerged; 806} 807 808// Insert a ComparableFunction into the FnSet, or merge it away if equal to one 809// that was already inserted. 810bool MergeFunctions::insert(ComparableFunction &NewF) { 811 std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF); 812 if (Result.second) { 813 DEBUG(dbgs() << "Inserting as unique: " << NewF.getFunc()->getName() << '\n'); 814 return false; 815 } 816 817 const ComparableFunction &OldF = *Result.first; 818 819 // Never thunk a strong function to a weak function. 820 assert(!OldF.getFunc()->mayBeOverridden() || 821 NewF.getFunc()->mayBeOverridden()); 822 823 DEBUG(dbgs() << " " << OldF.getFunc()->getName() << " == " 824 << NewF.getFunc()->getName() << '\n'); 825 826 Function *DeleteF = NewF.getFunc(); 827 NewF.release(); 828 mergeTwoFunctions(OldF.getFunc(), DeleteF); 829 return true; 830} 831 832// Remove a function from FnSet. If it was already in FnSet, add it to Deferred 833// so that we'll look at it in the next round. 834void MergeFunctions::remove(Function *F) { 835 // We need to make sure we remove F, not a function "equal" to F per the 836 // function equality comparator. 837 // 838 // The special "lookup only" ComparableFunction bypasses the expensive 839 // function comparison in favour of a pointer comparison on the underlying 840 // Function*'s. 841 ComparableFunction CF = ComparableFunction(F, ComparableFunction::LookupOnly); 842 if (FnSet.erase(CF)) { 843 DEBUG(dbgs() << "Removed " << F->getName() << " from set and deferred it.\n"); 844 Deferred.push_back(F); 845 } 846} 847 848// For each instruction used by the value, remove() the function that contains 849// the instruction. This should happen right before a call to RAUW. 850void MergeFunctions::removeUsers(Value *V) { 851 std::vector<Value *> Worklist; 852 Worklist.push_back(V); 853 while (!Worklist.empty()) { 854 Value *V = Worklist.back(); 855 Worklist.pop_back(); 856 857 for (Value::use_iterator UI = V->use_begin(), UE = V->use_end(); 858 UI != UE; ++UI) { 859 Use &U = UI.getUse(); 860 if (Instruction *I = dyn_cast<Instruction>(U.getUser())) { 861 remove(I->getParent()->getParent()); 862 } else if (isa<GlobalValue>(U.getUser())) { 863 // do nothing 864 } else if (Constant *C = dyn_cast<Constant>(U.getUser())) { 865 for (Value::use_iterator CUI = C->use_begin(), CUE = C->use_end(); 866 CUI != CUE; ++CUI) 867 Worklist.push_back(*CUI); 868 } 869 } 870 } 871} 872