MergeFunctions.cpp revision b0104e1bb56cde925d91a5b2432a18f87214484a
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"); 70 71namespace { 72 73static unsigned ProfileFunction(const Function *F) { 74 const FunctionType *FTy = F->getFunctionType(); 75 76 FoldingSetNodeID ID; 77 ID.AddInteger(F->size()); 78 ID.AddInteger(F->getCallingConv()); 79 ID.AddBoolean(F->hasGC()); 80 ID.AddBoolean(FTy->isVarArg()); 81 ID.AddInteger(FTy->getReturnType()->getTypeID()); 82 for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i) 83 ID.AddInteger(FTy->getParamType(i)->getTypeID()); 84 return ID.ComputeHash(); 85} 86 87class ComparableFunction { 88public: 89 ComparableFunction(Function *Func, TargetData *TD) 90 : Func(Func), Hash(ProfileFunction(Func)), TD(TD) {} 91 92 AssertingVH<Function> const Func; 93 const unsigned Hash; 94 TargetData * const TD; 95}; 96 97struct MergeFunctionsEqualityInfo { 98 static ComparableFunction *getEmptyKey() { 99 return reinterpret_cast<ComparableFunction*>(0); 100 } 101 static ComparableFunction *getTombstoneKey() { 102 return reinterpret_cast<ComparableFunction*>(-1); 103 } 104 static unsigned getHashValue(const ComparableFunction *CF) { 105 return CF->Hash; 106 } 107 static bool isEqual(const ComparableFunction *LHS, 108 const ComparableFunction *RHS); 109}; 110 111/// MergeFunctions finds functions which will generate identical machine code, 112/// by considering all pointer types to be equivalent. Once identified, 113/// MergeFunctions will fold them by replacing a call to one to a call to a 114/// bitcast of the other. 115/// 116class MergeFunctions : public ModulePass { 117public: 118 static char ID; 119 MergeFunctions() : ModulePass(ID) {} 120 121 bool runOnModule(Module &M); 122 123private: 124 typedef DenseSet<ComparableFunction *, MergeFunctionsEqualityInfo> FnSetType; 125 126 127 /// Insert a ComparableFunction into the FnSet, or merge it away if it's 128 /// equal to one that's already present. 129 bool Insert(FnSetType &FnSet, ComparableFunction *NewF); 130 131 /// MergeTwoFunctions - Merge two equivalent functions. Upon completion, G 132 /// may be deleted, or may be converted into a thunk. In either case, it 133 /// should never be visited again. 134 void MergeTwoFunctions(Function *F, Function *G) const; 135 136 /// WriteThunk - Replace G with a simple tail call to bitcast(F). Also 137 /// replace direct uses of G with bitcast(F). Deletes G. 138 void WriteThunk(Function *F, Function *G) const; 139 140 TargetData *TD; 141}; 142 143} // end anonymous namespace 144 145char MergeFunctions::ID = 0; 146INITIALIZE_PASS(MergeFunctions, "mergefunc", "Merge Functions", false, false); 147 148ModulePass *llvm::createMergeFunctionsPass() { 149 return new MergeFunctions(); 150} 151 152namespace { 153/// FunctionComparator - Compares two functions to determine whether or not 154/// they will generate machine code with the same behaviour. TargetData is 155/// used if available. The comparator always fails conservatively (erring on the 156/// side of claiming that two functions are different). 157class FunctionComparator { 158public: 159 FunctionComparator(const TargetData *TD, const Function *F1, 160 const Function *F2) 161 : F1(F1), F2(F2), TD(TD), IDMap1Count(0), IDMap2Count(0) {} 162 163 /// Compare - test whether the two functions have equivalent behaviour. 164 bool Compare(); 165 166private: 167 /// Compare - test whether two basic blocks have equivalent behaviour. 168 bool Compare(const BasicBlock *BB1, const BasicBlock *BB2); 169 170 /// Enumerate - Assign or look up previously assigned numbers for the two 171 /// values, and return whether the numbers are equal. Numbers are assigned in 172 /// the order visited. 173 bool Enumerate(const Value *V1, const Value *V2); 174 175 /// isEquivalentOperation - Compare two Instructions for equivalence, similar 176 /// to Instruction::isSameOperationAs but with modifications to the type 177 /// comparison. 178 bool isEquivalentOperation(const Instruction *I1, 179 const Instruction *I2) const; 180 181 /// isEquivalentGEP - Compare two GEPs for equivalent pointer arithmetic. 182 bool isEquivalentGEP(const GEPOperator *GEP1, const GEPOperator *GEP2); 183 bool isEquivalentGEP(const GetElementPtrInst *GEP1, 184 const GetElementPtrInst *GEP2) { 185 return isEquivalentGEP(cast<GEPOperator>(GEP1), cast<GEPOperator>(GEP2)); 186 } 187 188 /// isEquivalentType - Compare two Types, treating all pointer types as equal. 189 bool isEquivalentType(const Type *Ty1, const Type *Ty2) const; 190 191 // The two functions undergoing comparison. 192 const Function *F1, *F2; 193 194 const TargetData *TD; 195 196 typedef DenseMap<const Value *, unsigned long> IDMap; 197 IDMap Map1, Map2; 198 unsigned long IDMap1Count, IDMap2Count; 199}; 200} 201 202/// isEquivalentType - any two pointers in the same address space are 203/// equivalent. Otherwise, standard type equivalence rules apply. 204bool FunctionComparator::isEquivalentType(const Type *Ty1, 205 const Type *Ty2) const { 206 if (Ty1 == Ty2) 207 return true; 208 if (Ty1->getTypeID() != Ty2->getTypeID()) 209 return false; 210 211 switch(Ty1->getTypeID()) { 212 default: 213 llvm_unreachable("Unknown type!"); 214 // Fall through in Release mode. 215 case Type::IntegerTyID: 216 case Type::OpaqueTyID: 217 // Ty1 == Ty2 would have returned true earlier. 218 return false; 219 220 case Type::VoidTyID: 221 case Type::FloatTyID: 222 case Type::DoubleTyID: 223 case Type::X86_FP80TyID: 224 case Type::FP128TyID: 225 case Type::PPC_FP128TyID: 226 case Type::LabelTyID: 227 case Type::MetadataTyID: 228 return true; 229 230 case Type::PointerTyID: { 231 const PointerType *PTy1 = cast<PointerType>(Ty1); 232 const PointerType *PTy2 = cast<PointerType>(Ty2); 233 return PTy1->getAddressSpace() == PTy2->getAddressSpace(); 234 } 235 236 case Type::StructTyID: { 237 const StructType *STy1 = cast<StructType>(Ty1); 238 const StructType *STy2 = cast<StructType>(Ty2); 239 if (STy1->getNumElements() != STy2->getNumElements()) 240 return false; 241 242 if (STy1->isPacked() != STy2->isPacked()) 243 return false; 244 245 for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) { 246 if (!isEquivalentType(STy1->getElementType(i), STy2->getElementType(i))) 247 return false; 248 } 249 return true; 250 } 251 252 case Type::FunctionTyID: { 253 const FunctionType *FTy1 = cast<FunctionType>(Ty1); 254 const FunctionType *FTy2 = cast<FunctionType>(Ty2); 255 if (FTy1->getNumParams() != FTy2->getNumParams() || 256 FTy1->isVarArg() != FTy2->isVarArg()) 257 return false; 258 259 if (!isEquivalentType(FTy1->getReturnType(), FTy2->getReturnType())) 260 return false; 261 262 for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) { 263 if (!isEquivalentType(FTy1->getParamType(i), FTy2->getParamType(i))) 264 return false; 265 } 266 return true; 267 } 268 269 case Type::ArrayTyID: { 270 const ArrayType *ATy1 = cast<ArrayType>(Ty1); 271 const ArrayType *ATy2 = cast<ArrayType>(Ty2); 272 return ATy1->getNumElements() == ATy2->getNumElements() && 273 isEquivalentType(ATy1->getElementType(), ATy2->getElementType()); 274 } 275 276 case Type::VectorTyID: { 277 const VectorType *VTy1 = cast<VectorType>(Ty1); 278 const VectorType *VTy2 = cast<VectorType>(Ty2); 279 return VTy1->getNumElements() == VTy2->getNumElements() && 280 isEquivalentType(VTy1->getElementType(), VTy2->getElementType()); 281 } 282 } 283} 284 285/// isEquivalentOperation - determine whether the two operations are the same 286/// except that pointer-to-A and pointer-to-B are equivalent. This should be 287/// kept in sync with Instruction::isSameOperationAs. 288bool FunctionComparator::isEquivalentOperation(const Instruction *I1, 289 const Instruction *I2) const { 290 if (I1->getOpcode() != I2->getOpcode() || 291 I1->getNumOperands() != I2->getNumOperands() || 292 !isEquivalentType(I1->getType(), I2->getType()) || 293 !I1->hasSameSubclassOptionalData(I2)) 294 return false; 295 296 // We have two instructions of identical opcode and #operands. Check to see 297 // if all operands are the same type 298 for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i) 299 if (!isEquivalentType(I1->getOperand(i)->getType(), 300 I2->getOperand(i)->getType())) 301 return false; 302 303 // Check special state that is a part of some instructions. 304 if (const LoadInst *LI = dyn_cast<LoadInst>(I1)) 305 return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() && 306 LI->getAlignment() == cast<LoadInst>(I2)->getAlignment(); 307 if (const StoreInst *SI = dyn_cast<StoreInst>(I1)) 308 return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() && 309 SI->getAlignment() == cast<StoreInst>(I2)->getAlignment(); 310 if (const CmpInst *CI = dyn_cast<CmpInst>(I1)) 311 return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate(); 312 if (const CallInst *CI = dyn_cast<CallInst>(I1)) 313 return CI->isTailCall() == cast<CallInst>(I2)->isTailCall() && 314 CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() && 315 CI->getAttributes().getRawPointer() == 316 cast<CallInst>(I2)->getAttributes().getRawPointer(); 317 if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1)) 318 return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() && 319 CI->getAttributes().getRawPointer() == 320 cast<InvokeInst>(I2)->getAttributes().getRawPointer(); 321 if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) { 322 if (IVI->getNumIndices() != cast<InsertValueInst>(I2)->getNumIndices()) 323 return false; 324 for (unsigned i = 0, e = IVI->getNumIndices(); i != e; ++i) 325 if (IVI->idx_begin()[i] != cast<InsertValueInst>(I2)->idx_begin()[i]) 326 return false; 327 return true; 328 } 329 if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) { 330 if (EVI->getNumIndices() != cast<ExtractValueInst>(I2)->getNumIndices()) 331 return false; 332 for (unsigned i = 0, e = EVI->getNumIndices(); i != e; ++i) 333 if (EVI->idx_begin()[i] != cast<ExtractValueInst>(I2)->idx_begin()[i]) 334 return false; 335 return true; 336 } 337 338 return true; 339} 340 341/// isEquivalentGEP - determine whether two GEP operations perform the same 342/// underlying arithmetic. 343bool FunctionComparator::isEquivalentGEP(const GEPOperator *GEP1, 344 const GEPOperator *GEP2) { 345 // When we have target data, we can reduce the GEP down to the value in bytes 346 // added to the address. 347 if (TD && GEP1->hasAllConstantIndices() && GEP2->hasAllConstantIndices()) { 348 SmallVector<Value *, 8> Indices1(GEP1->idx_begin(), GEP1->idx_end()); 349 SmallVector<Value *, 8> Indices2(GEP2->idx_begin(), GEP2->idx_end()); 350 uint64_t Offset1 = TD->getIndexedOffset(GEP1->getPointerOperandType(), 351 Indices1.data(), Indices1.size()); 352 uint64_t Offset2 = TD->getIndexedOffset(GEP2->getPointerOperandType(), 353 Indices2.data(), Indices2.size()); 354 return Offset1 == Offset2; 355 } 356 357 if (GEP1->getPointerOperand()->getType() != 358 GEP2->getPointerOperand()->getType()) 359 return false; 360 361 if (GEP1->getNumOperands() != GEP2->getNumOperands()) 362 return false; 363 364 for (unsigned i = 0, e = GEP1->getNumOperands(); i != e; ++i) { 365 if (!Enumerate(GEP1->getOperand(i), GEP2->getOperand(i))) 366 return false; 367 } 368 369 return true; 370} 371 372/// Enumerate - Compare two values used by the two functions under pair-wise 373/// comparison. If this is the first time the values are seen, they're added to 374/// the mapping so that we will detect mismatches on next use. 375bool FunctionComparator::Enumerate(const Value *V1, const Value *V2) { 376 // Check for function @f1 referring to itself and function @f2 referring to 377 // itself, or referring to each other, or both referring to either of them. 378 // They're all equivalent if the two functions are otherwise equivalent. 379 if (V1 == F1 && V2 == F2) 380 return true; 381 if (V1 == F2 && V2 == F1) 382 return true; 383 384 // TODO: constant expressions with GEP or references to F1 or F2. 385 if (isa<Constant>(V1)) 386 return V1 == V2; 387 388 if (isa<InlineAsm>(V1) && isa<InlineAsm>(V2)) { 389 const InlineAsm *IA1 = cast<InlineAsm>(V1); 390 const InlineAsm *IA2 = cast<InlineAsm>(V2); 391 return IA1->getAsmString() == IA2->getAsmString() && 392 IA1->getConstraintString() == IA2->getConstraintString(); 393 } 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/// Compare - 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/// Compare - 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 "Identical functions have a different number 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} 523 524/// WriteThunk - Replace G with a simple tail call to bitcast(F). Also replace 525/// direct uses of G with bitcast(F). Deletes G. 526void MergeFunctions::WriteThunk(Function *F, Function *G) const { 527 if (!G->mayBeOverridden()) { 528 // Redirect direct callers of G to F. 529 Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType()); 530 for (Value::use_iterator UI = G->use_begin(), UE = G->use_end(); 531 UI != UE;) { 532 Value::use_iterator TheIter = UI; 533 ++UI; 534 CallSite CS(*TheIter); 535 if (CS && CS.isCallee(TheIter)) 536 TheIter.getUse().set(BitcastF); 537 } 538 } 539 540 // If G was internal then we may have replaced all uses if G with F. If so, 541 // stop here and delete G. There's no need for a thunk. 542 if (G->hasLocalLinkage() && G->use_empty()) { 543 G->eraseFromParent(); 544 return; 545 } 546 547 Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(), "", 548 G->getParent()); 549 BasicBlock *BB = BasicBlock::Create(F->getContext(), "", NewG); 550 IRBuilder<false> Builder(BB); 551 552 SmallVector<Value *, 16> Args; 553 unsigned i = 0; 554 const FunctionType *FFTy = F->getFunctionType(); 555 for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end(); 556 AI != AE; ++AI) { 557 Args.push_back(Builder.CreateBitCast(AI, FFTy->getParamType(i))); 558 ++i; 559 } 560 561 CallInst *CI = Builder.CreateCall(F, Args.begin(), Args.end()); 562 CI->setTailCall(); 563 CI->setCallingConv(F->getCallingConv()); 564 if (NewG->getReturnType()->isVoidTy()) { 565 Builder.CreateRetVoid(); 566 } else { 567 Builder.CreateRet(Builder.CreateBitCast(CI, NewG->getReturnType())); 568 } 569 570 NewG->copyAttributesFrom(G); 571 NewG->takeName(G); 572 G->replaceAllUsesWith(NewG); 573 G->eraseFromParent(); 574} 575 576/// MergeTwoFunctions - Merge two equivalent functions. Upon completion, 577/// Function G is deleted. 578void MergeFunctions::MergeTwoFunctions(Function *F, Function *G) const { 579 if (F->isWeakForLinker()) { 580 assert(G->isWeakForLinker()); 581 582 // Make them both thunks to the same internal function. 583 Function *H = Function::Create(F->getFunctionType(), F->getLinkage(), "", 584 F->getParent()); 585 H->copyAttributesFrom(F); 586 H->takeName(F); 587 F->replaceAllUsesWith(H); 588 589 unsigned MaxAlignment = std::max(G->getAlignment(), H->getAlignment()); 590 591 WriteThunk(F, G); 592 WriteThunk(F, H); 593 594 F->setAlignment(MaxAlignment); 595 F->setLinkage(GlobalValue::InternalLinkage); 596 } else { 597 WriteThunk(F, G); 598 } 599 600 ++NumFunctionsMerged; 601} 602 603// Insert - Insert a ComparableFunction into the FnSet, or merge it away if 604// equal to one that's already inserted. 605bool MergeFunctions::Insert(FnSetType &FnSet, ComparableFunction *NewF) { 606 std::pair<FnSetType::iterator, bool> Result = FnSet.insert(NewF); 607 if (Result.second) 608 return false; 609 610 ComparableFunction *OldF = *Result.first; 611 assert(OldF && "Expected a hash collision"); 612 613 // Never thunk a strong function to a weak function. 614 assert(!OldF->Func->isWeakForLinker() || NewF->Func->isWeakForLinker()); 615 616 DEBUG(dbgs() << " " << OldF->Func->getName() << " == " 617 << NewF->Func->getName() << '\n'); 618 619 Function *DeleteF = NewF->Func; 620 delete NewF; 621 MergeTwoFunctions(OldF->Func, DeleteF); 622 return true; 623} 624 625// IsThunk - This method determines whether or not a given Function is a thunk\// like the ones emitted by this pass and therefore not subject to further 626// merging. 627static bool IsThunk(const Function *F) { 628 // The safe direction to fail is to return true. In that case, the function 629 // will be removed from merging analysis. If we failed to including functions 630 // then we may try to merge unmergable thing (ie., identical weak functions) 631 // which will push us into an infinite loop. 632 633 if (F->size() != 1) 634 return false; 635 636 const BasicBlock *BB = &F->front(); 637 // A thunk is: 638 // bitcast-inst* 639 // optional-reg tail call @thunkee(args...*) 640 // ret void|optional-reg 641 // where the args are in the same order as the arguments. 642 643 // Verify that the sequence of bitcast-inst's are all casts of arguments and 644 // that there aren't any extras (ie. no repeated casts). 645 int LastArgNo = -1; 646 BasicBlock::const_iterator I = BB->begin(); 647 while (const BitCastInst *BCI = dyn_cast<BitCastInst>(I)) { 648 const Argument *A = dyn_cast<Argument>(BCI->getOperand(0)); 649 if (!A) return false; 650 if ((int)A->getArgNo() >= LastArgNo) return false; 651 LastArgNo = A->getArgNo(); 652 ++I; 653 } 654 655 // Verify that the call instruction has the same arguments as this function 656 // and that they're all either the incoming argument or a cast of the right 657 // argument. 658 const CallInst *CI = dyn_cast<CallInst>(I++); 659 if (!CI || !CI->isTailCall() || 660 CI->getNumArgOperands() != F->arg_size()) return false; 661 662 for (unsigned i = 0, e = CI->getNumArgOperands(); i != e; ++i) { 663 const Value *V = CI->getArgOperand(i); 664 const Argument *A = dyn_cast<Argument>(V); 665 if (!A) { 666 const BitCastInst *BCI = dyn_cast<BitCastInst>(V); 667 if (!BCI) return false; 668 A = cast<Argument>(BCI->getOperand(0)); 669 } 670 if (A->getArgNo() != i) return false; 671 } 672 673 // Verify that the terminator is a ret void (if we're void) or a ret of the 674 // call's return, or a ret of a bitcast of the call's return. 675 const Value *RetOp = CI; 676 if (const BitCastInst *BCI = dyn_cast<BitCastInst>(I)) { 677 ++I; 678 if (BCI->getOperand(0) != CI) return false; 679 RetOp = BCI; 680 } 681 const ReturnInst *RI = dyn_cast<ReturnInst>(I); 682 if (!RI) return false; 683 if (RI->getNumOperands() == 0) 684 return CI->getType()->isVoidTy(); 685 return RI->getReturnValue() == CI; 686} 687 688bool MergeFunctions::runOnModule(Module &M) { 689 bool Changed = false; 690 TD = getAnalysisIfAvailable<TargetData>(); 691 692 bool LocalChanged; 693 do { 694 DEBUG(dbgs() << "size: " << M.size() << '\n'); 695 LocalChanged = false; 696 FnSetType FnSet; 697 698 // Insert only strong functions and merge them. Strong function merging 699 // always deletes one of them. 700 for (Module::iterator I = M.begin(), E = M.end(); I != E;) { 701 Function *F = I++; 702 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() && 703 !F->isWeakForLinker() && !IsThunk(F)) { 704 ComparableFunction *CF = new ComparableFunction(F, TD); 705 LocalChanged |= Insert(FnSet, CF); 706 } 707 } 708 709 // Insert only weak functions and merge them. By doing these second we 710 // create thunks to the strong function when possible. When two weak 711 // functions are identical, we create a new strong function with two weak 712 // weak thunks to it which are identical but not mergable. 713 for (Module::iterator I = M.begin(), E = M.end(); I != E;) { 714 Function *F = I++; 715 if (!F->isDeclaration() && !F->hasAvailableExternallyLinkage() && 716 F->isWeakForLinker() && !IsThunk(F)) { 717 ComparableFunction *CF = new ComparableFunction(F, TD); 718 LocalChanged |= Insert(FnSet, CF); 719 } 720 } 721 DeleteContainerPointers(FnSet); 722 Changed |= LocalChanged; 723 } while (LocalChanged); 724 725 return Changed; 726} 727 728bool MergeFunctionsEqualityInfo::isEqual(const ComparableFunction *LHS, 729 const ComparableFunction *RHS) { 730 if (LHS == RHS) 731 return true; 732 if (LHS == getEmptyKey() || LHS == getTombstoneKey() || 733 RHS == getEmptyKey() || RHS == getTombstoneKey()) 734 return false; 735 assert(LHS->TD == RHS->TD && "Comparing functions for different targets"); 736 return FunctionComparator(LHS->TD, LHS->Func, RHS->Func).Compare(); 737} 738