GlobalOpt.cpp revision a9390a4d5f5d568059a80970d22194b165d097a7
1//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===// 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 transforms simple global variables that never have their address 11// taken. If obviously true, it marks read/write globals as constant, deletes 12// variables only stored to, etc. 13// 14//===----------------------------------------------------------------------===// 15 16#define DEBUG_TYPE "globalopt" 17#include "llvm/Transforms/IPO.h" 18#include "llvm/CallingConv.h" 19#include "llvm/Constants.h" 20#include "llvm/DerivedTypes.h" 21#include "llvm/Instructions.h" 22#include "llvm/IntrinsicInst.h" 23#include "llvm/Module.h" 24#include "llvm/Operator.h" 25#include "llvm/Pass.h" 26#include "llvm/Analysis/ConstantFolding.h" 27#include "llvm/Analysis/MemoryBuiltins.h" 28#include "llvm/Target/TargetData.h" 29#include "llvm/Support/CallSite.h" 30#include "llvm/Support/Debug.h" 31#include "llvm/Support/ErrorHandling.h" 32#include "llvm/Support/GetElementPtrTypeIterator.h" 33#include "llvm/Support/MathExtras.h" 34#include "llvm/Support/raw_ostream.h" 35#include "llvm/ADT/DenseMap.h" 36#include "llvm/ADT/SmallPtrSet.h" 37#include "llvm/ADT/SmallVector.h" 38#include "llvm/ADT/Statistic.h" 39#include "llvm/ADT/STLExtras.h" 40#include <algorithm> 41using namespace llvm; 42 43STATISTIC(NumMarked , "Number of globals marked constant"); 44STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr"); 45STATISTIC(NumSRA , "Number of aggregate globals broken into scalars"); 46STATISTIC(NumHeapSRA , "Number of heap objects SRA'd"); 47STATISTIC(NumSubstitute,"Number of globals with initializers stored into them"); 48STATISTIC(NumDeleted , "Number of globals deleted"); 49STATISTIC(NumFnDeleted , "Number of functions deleted"); 50STATISTIC(NumGlobUses , "Number of global uses devirtualized"); 51STATISTIC(NumLocalized , "Number of globals localized"); 52STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans"); 53STATISTIC(NumFastCallFns , "Number of functions converted to fastcc"); 54STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated"); 55STATISTIC(NumNestRemoved , "Number of nest attributes removed"); 56STATISTIC(NumAliasesResolved, "Number of global aliases resolved"); 57STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated"); 58STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed"); 59 60namespace { 61 struct GlobalStatus; 62 struct GlobalOpt : public ModulePass { 63 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 64 } 65 static char ID; // Pass identification, replacement for typeid 66 GlobalOpt() : ModulePass(ID) { 67 initializeGlobalOptPass(*PassRegistry::getPassRegistry()); 68 } 69 70 bool runOnModule(Module &M); 71 72 private: 73 GlobalVariable *FindGlobalCtors(Module &M); 74 bool OptimizeFunctions(Module &M); 75 bool OptimizeGlobalVars(Module &M); 76 bool OptimizeGlobalAliases(Module &M); 77 bool OptimizeGlobalCtorsList(GlobalVariable *&GCL); 78 bool ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI); 79 bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI, 80 const SmallPtrSet<const PHINode*, 16> &PHIUsers, 81 const GlobalStatus &GS); 82 bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn); 83 }; 84} 85 86char GlobalOpt::ID = 0; 87INITIALIZE_PASS(GlobalOpt, "globalopt", 88 "Global Variable Optimizer", false, false) 89 90ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); } 91 92namespace { 93 94/// GlobalStatus - As we analyze each global, keep track of some information 95/// about it. If we find out that the address of the global is taken, none of 96/// this info will be accurate. 97struct GlobalStatus { 98 /// isCompared - True if the global's address is used in a comparison. 99 bool isCompared; 100 101 /// isLoaded - True if the global is ever loaded. If the global isn't ever 102 /// loaded it can be deleted. 103 bool isLoaded; 104 105 /// StoredType - Keep track of what stores to the global look like. 106 /// 107 enum StoredType { 108 /// NotStored - There is no store to this global. It can thus be marked 109 /// constant. 110 NotStored, 111 112 /// isInitializerStored - This global is stored to, but the only thing 113 /// stored is the constant it was initialized with. This is only tracked 114 /// for scalar globals. 115 isInitializerStored, 116 117 /// isStoredOnce - This global is stored to, but only its initializer and 118 /// one other value is ever stored to it. If this global isStoredOnce, we 119 /// track the value stored to it in StoredOnceValue below. This is only 120 /// tracked for scalar globals. 121 isStoredOnce, 122 123 /// isStored - This global is stored to by multiple values or something else 124 /// that we cannot track. 125 isStored 126 } StoredType; 127 128 /// StoredOnceValue - If only one value (besides the initializer constant) is 129 /// ever stored to this global, keep track of what value it is. 130 Value *StoredOnceValue; 131 132 /// AccessingFunction/HasMultipleAccessingFunctions - These start out 133 /// null/false. When the first accessing function is noticed, it is recorded. 134 /// When a second different accessing function is noticed, 135 /// HasMultipleAccessingFunctions is set to true. 136 const Function *AccessingFunction; 137 bool HasMultipleAccessingFunctions; 138 139 /// HasNonInstructionUser - Set to true if this global has a user that is not 140 /// an instruction (e.g. a constant expr or GV initializer). 141 bool HasNonInstructionUser; 142 143 /// HasPHIUser - Set to true if this global has a user that is a PHI node. 144 bool HasPHIUser; 145 146 GlobalStatus() : isCompared(false), isLoaded(false), StoredType(NotStored), 147 StoredOnceValue(0), AccessingFunction(0), 148 HasMultipleAccessingFunctions(false), HasNonInstructionUser(false), 149 HasPHIUser(false) {} 150}; 151 152} 153 154// SafeToDestroyConstant - It is safe to destroy a constant iff it is only used 155// by constants itself. Note that constants cannot be cyclic, so this test is 156// pretty easy to implement recursively. 157// 158static bool SafeToDestroyConstant(const Constant *C) { 159 if (isa<GlobalValue>(C)) return false; 160 161 for (Value::const_use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; 162 ++UI) 163 if (const Constant *CU = dyn_cast<Constant>(*UI)) { 164 if (!SafeToDestroyConstant(CU)) return false; 165 } else 166 return false; 167 return true; 168} 169 170 171/// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus 172/// structure. If the global has its address taken, return true to indicate we 173/// can't do anything with it. 174/// 175static bool AnalyzeGlobal(const Value *V, GlobalStatus &GS, 176 SmallPtrSet<const PHINode*, 16> &PHIUsers) { 177 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; 178 ++UI) { 179 const User *U = *UI; 180 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { 181 GS.HasNonInstructionUser = true; 182 183 // If the result of the constantexpr isn't pointer type, then we won't 184 // know to expect it in various places. Just reject early. 185 if (!isa<PointerType>(CE->getType())) return true; 186 187 if (AnalyzeGlobal(CE, GS, PHIUsers)) return true; 188 } else if (const Instruction *I = dyn_cast<Instruction>(U)) { 189 if (!GS.HasMultipleAccessingFunctions) { 190 const Function *F = I->getParent()->getParent(); 191 if (GS.AccessingFunction == 0) 192 GS.AccessingFunction = F; 193 else if (GS.AccessingFunction != F) 194 GS.HasMultipleAccessingFunctions = true; 195 } 196 if (const LoadInst *LI = dyn_cast<LoadInst>(I)) { 197 GS.isLoaded = true; 198 // Don't hack on volatile/atomic loads. 199 if (!LI->isSimple()) return true; 200 } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) { 201 // Don't allow a store OF the address, only stores TO the address. 202 if (SI->getOperand(0) == V) return true; 203 204 // Don't hack on volatile/atomic stores. 205 if (!SI->isSimple()) return true; 206 207 // If this is a direct store to the global (i.e., the global is a scalar 208 // value, not an aggregate), keep more specific information about 209 // stores. 210 if (GS.StoredType != GlobalStatus::isStored) { 211 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>( 212 SI->getOperand(1))) { 213 Value *StoredVal = SI->getOperand(0); 214 if (StoredVal == GV->getInitializer()) { 215 if (GS.StoredType < GlobalStatus::isInitializerStored) 216 GS.StoredType = GlobalStatus::isInitializerStored; 217 } else if (isa<LoadInst>(StoredVal) && 218 cast<LoadInst>(StoredVal)->getOperand(0) == GV) { 219 if (GS.StoredType < GlobalStatus::isInitializerStored) 220 GS.StoredType = GlobalStatus::isInitializerStored; 221 } else if (GS.StoredType < GlobalStatus::isStoredOnce) { 222 GS.StoredType = GlobalStatus::isStoredOnce; 223 GS.StoredOnceValue = StoredVal; 224 } else if (GS.StoredType == GlobalStatus::isStoredOnce && 225 GS.StoredOnceValue == StoredVal) { 226 // noop. 227 } else { 228 GS.StoredType = GlobalStatus::isStored; 229 } 230 } else { 231 GS.StoredType = GlobalStatus::isStored; 232 } 233 } 234 } else if (isa<GetElementPtrInst>(I)) { 235 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 236 } else if (isa<SelectInst>(I)) { 237 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 238 } else if (const PHINode *PN = dyn_cast<PHINode>(I)) { 239 // PHI nodes we can check just like select or GEP instructions, but we 240 // have to be careful about infinite recursion. 241 if (PHIUsers.insert(PN)) // Not already visited. 242 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 243 GS.HasPHIUser = true; 244 } else if (isa<CmpInst>(I)) { 245 GS.isCompared = true; 246 } else if (const MemTransferInst *MTI = dyn_cast<MemTransferInst>(I)) { 247 if (MTI->isVolatile()) return true; 248 if (MTI->getArgOperand(0) == V) 249 GS.StoredType = GlobalStatus::isStored; 250 if (MTI->getArgOperand(1) == V) 251 GS.isLoaded = true; 252 } else if (const MemSetInst *MSI = dyn_cast<MemSetInst>(I)) { 253 assert(MSI->getArgOperand(0) == V && "Memset only takes one pointer!"); 254 if (MSI->isVolatile()) return true; 255 GS.StoredType = GlobalStatus::isStored; 256 } else { 257 return true; // Any other non-load instruction might take address! 258 } 259 } else if (const Constant *C = dyn_cast<Constant>(U)) { 260 GS.HasNonInstructionUser = true; 261 // We might have a dead and dangling constant hanging off of here. 262 if (!SafeToDestroyConstant(C)) 263 return true; 264 } else { 265 GS.HasNonInstructionUser = true; 266 // Otherwise must be some other user. 267 return true; 268 } 269 } 270 271 return false; 272} 273 274static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx) { 275 ConstantInt *CI = dyn_cast<ConstantInt>(Idx); 276 if (!CI) return 0; 277 unsigned IdxV = CI->getZExtValue(); 278 279 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) { 280 if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV); 281 } else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) { 282 if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV); 283 } else if (ConstantVector *CP = dyn_cast<ConstantVector>(Agg)) { 284 if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV); 285 } else if (isa<ConstantAggregateZero>(Agg)) { 286 if (StructType *STy = dyn_cast<StructType>(Agg->getType())) { 287 if (IdxV < STy->getNumElements()) 288 return Constant::getNullValue(STy->getElementType(IdxV)); 289 } else if (SequentialType *STy = 290 dyn_cast<SequentialType>(Agg->getType())) { 291 return Constant::getNullValue(STy->getElementType()); 292 } 293 } else if (isa<UndefValue>(Agg)) { 294 if (StructType *STy = dyn_cast<StructType>(Agg->getType())) { 295 if (IdxV < STy->getNumElements()) 296 return UndefValue::get(STy->getElementType(IdxV)); 297 } else if (SequentialType *STy = 298 dyn_cast<SequentialType>(Agg->getType())) { 299 return UndefValue::get(STy->getElementType()); 300 } 301 } 302 return 0; 303} 304 305 306/// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all 307/// users of the global, cleaning up the obvious ones. This is largely just a 308/// quick scan over the use list to clean up the easy and obvious cruft. This 309/// returns true if it made a change. 310static bool CleanupConstantGlobalUsers(Value *V, Constant *Init) { 311 bool Changed = false; 312 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) { 313 User *U = *UI++; 314 315 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 316 if (Init) { 317 // Replace the load with the initializer. 318 LI->replaceAllUsesWith(Init); 319 LI->eraseFromParent(); 320 Changed = true; 321 } 322 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 323 // Store must be unreachable or storing Init into the global. 324 SI->eraseFromParent(); 325 Changed = true; 326 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { 327 if (CE->getOpcode() == Instruction::GetElementPtr) { 328 Constant *SubInit = 0; 329 if (Init) 330 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); 331 Changed |= CleanupConstantGlobalUsers(CE, SubInit); 332 } else if (CE->getOpcode() == Instruction::BitCast && 333 CE->getType()->isPointerTy()) { 334 // Pointer cast, delete any stores and memsets to the global. 335 Changed |= CleanupConstantGlobalUsers(CE, 0); 336 } 337 338 if (CE->use_empty()) { 339 CE->destroyConstant(); 340 Changed = true; 341 } 342 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 343 // Do not transform "gepinst (gep constexpr (GV))" here, because forming 344 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold 345 // and will invalidate our notion of what Init is. 346 Constant *SubInit = 0; 347 if (!isa<ConstantExpr>(GEP->getOperand(0))) { 348 ConstantExpr *CE = 349 dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP)); 350 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr) 351 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); 352 } 353 Changed |= CleanupConstantGlobalUsers(GEP, SubInit); 354 355 if (GEP->use_empty()) { 356 GEP->eraseFromParent(); 357 Changed = true; 358 } 359 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv 360 if (MI->getRawDest() == V) { 361 MI->eraseFromParent(); 362 Changed = true; 363 } 364 365 } else if (Constant *C = dyn_cast<Constant>(U)) { 366 // If we have a chain of dead constantexprs or other things dangling from 367 // us, and if they are all dead, nuke them without remorse. 368 if (SafeToDestroyConstant(C)) { 369 C->destroyConstant(); 370 // This could have invalidated UI, start over from scratch. 371 CleanupConstantGlobalUsers(V, Init); 372 return true; 373 } 374 } 375 } 376 return Changed; 377} 378 379/// isSafeSROAElementUse - Return true if the specified instruction is a safe 380/// user of a derived expression from a global that we want to SROA. 381static bool isSafeSROAElementUse(Value *V) { 382 // We might have a dead and dangling constant hanging off of here. 383 if (Constant *C = dyn_cast<Constant>(V)) 384 return SafeToDestroyConstant(C); 385 386 Instruction *I = dyn_cast<Instruction>(V); 387 if (!I) return false; 388 389 // Loads are ok. 390 if (isa<LoadInst>(I)) return true; 391 392 // Stores *to* the pointer are ok. 393 if (StoreInst *SI = dyn_cast<StoreInst>(I)) 394 return SI->getOperand(0) != V; 395 396 // Otherwise, it must be a GEP. 397 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I); 398 if (GEPI == 0) return false; 399 400 if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) || 401 !cast<Constant>(GEPI->getOperand(1))->isNullValue()) 402 return false; 403 404 for (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end(); 405 I != E; ++I) 406 if (!isSafeSROAElementUse(*I)) 407 return false; 408 return true; 409} 410 411 412/// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value. 413/// Look at it and its uses and decide whether it is safe to SROA this global. 414/// 415static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) { 416 // The user of the global must be a GEP Inst or a ConstantExpr GEP. 417 if (!isa<GetElementPtrInst>(U) && 418 (!isa<ConstantExpr>(U) || 419 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr)) 420 return false; 421 422 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we 423 // don't like < 3 operand CE's, and we don't like non-constant integer 424 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some 425 // value of C. 426 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) || 427 !cast<Constant>(U->getOperand(1))->isNullValue() || 428 !isa<ConstantInt>(U->getOperand(2))) 429 return false; 430 431 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U); 432 ++GEPI; // Skip over the pointer index. 433 434 // If this is a use of an array allocation, do a bit more checking for sanity. 435 if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) { 436 uint64_t NumElements = AT->getNumElements(); 437 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2)); 438 439 // Check to make sure that index falls within the array. If not, 440 // something funny is going on, so we won't do the optimization. 441 // 442 if (Idx->getZExtValue() >= NumElements) 443 return false; 444 445 // We cannot scalar repl this level of the array unless any array 446 // sub-indices are in-range constants. In particular, consider: 447 // A[0][i]. We cannot know that the user isn't doing invalid things like 448 // allowing i to index an out-of-range subscript that accesses A[1]. 449 // 450 // Scalar replacing *just* the outer index of the array is probably not 451 // going to be a win anyway, so just give up. 452 for (++GEPI; // Skip array index. 453 GEPI != E; 454 ++GEPI) { 455 uint64_t NumElements; 456 if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI)) 457 NumElements = SubArrayTy->getNumElements(); 458 else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI)) 459 NumElements = SubVectorTy->getNumElements(); 460 else { 461 assert((*GEPI)->isStructTy() && 462 "Indexed GEP type is not array, vector, or struct!"); 463 continue; 464 } 465 466 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand()); 467 if (!IdxVal || IdxVal->getZExtValue() >= NumElements) 468 return false; 469 } 470 } 471 472 for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I) 473 if (!isSafeSROAElementUse(*I)) 474 return false; 475 return true; 476} 477 478/// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it 479/// is safe for us to perform this transformation. 480/// 481static bool GlobalUsersSafeToSRA(GlobalValue *GV) { 482 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); 483 UI != E; ++UI) { 484 if (!IsUserOfGlobalSafeForSRA(*UI, GV)) 485 return false; 486 } 487 return true; 488} 489 490 491/// SRAGlobal - Perform scalar replacement of aggregates on the specified global 492/// variable. This opens the door for other optimizations by exposing the 493/// behavior of the program in a more fine-grained way. We have determined that 494/// this transformation is safe already. We return the first global variable we 495/// insert so that the caller can reprocess it. 496static GlobalVariable *SRAGlobal(GlobalVariable *GV, const TargetData &TD) { 497 // Make sure this global only has simple uses that we can SRA. 498 if (!GlobalUsersSafeToSRA(GV)) 499 return 0; 500 501 assert(GV->hasLocalLinkage() && !GV->isConstant()); 502 Constant *Init = GV->getInitializer(); 503 Type *Ty = Init->getType(); 504 505 std::vector<GlobalVariable*> NewGlobals; 506 Module::GlobalListType &Globals = GV->getParent()->getGlobalList(); 507 508 // Get the alignment of the global, either explicit or target-specific. 509 unsigned StartAlignment = GV->getAlignment(); 510 if (StartAlignment == 0) 511 StartAlignment = TD.getABITypeAlignment(GV->getType()); 512 513 if (StructType *STy = dyn_cast<StructType>(Ty)) { 514 NewGlobals.reserve(STy->getNumElements()); 515 const StructLayout &Layout = *TD.getStructLayout(STy); 516 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 517 Constant *In = getAggregateConstantElement(Init, 518 ConstantInt::get(Type::getInt32Ty(STy->getContext()), i)); 519 assert(In && "Couldn't get element of initializer?"); 520 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false, 521 GlobalVariable::InternalLinkage, 522 In, GV->getName()+"."+Twine(i), 523 GV->isThreadLocal(), 524 GV->getType()->getAddressSpace()); 525 Globals.insert(GV, NGV); 526 NewGlobals.push_back(NGV); 527 528 // Calculate the known alignment of the field. If the original aggregate 529 // had 256 byte alignment for example, something might depend on that: 530 // propagate info to each field. 531 uint64_t FieldOffset = Layout.getElementOffset(i); 532 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset); 533 if (NewAlign > TD.getABITypeAlignment(STy->getElementType(i))) 534 NGV->setAlignment(NewAlign); 535 } 536 } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) { 537 unsigned NumElements = 0; 538 if (ArrayType *ATy = dyn_cast<ArrayType>(STy)) 539 NumElements = ATy->getNumElements(); 540 else 541 NumElements = cast<VectorType>(STy)->getNumElements(); 542 543 if (NumElements > 16 && GV->hasNUsesOrMore(16)) 544 return 0; // It's not worth it. 545 NewGlobals.reserve(NumElements); 546 547 uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType()); 548 unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType()); 549 for (unsigned i = 0, e = NumElements; i != e; ++i) { 550 Constant *In = getAggregateConstantElement(Init, 551 ConstantInt::get(Type::getInt32Ty(Init->getContext()), i)); 552 assert(In && "Couldn't get element of initializer?"); 553 554 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false, 555 GlobalVariable::InternalLinkage, 556 In, GV->getName()+"."+Twine(i), 557 GV->isThreadLocal(), 558 GV->getType()->getAddressSpace()); 559 Globals.insert(GV, NGV); 560 NewGlobals.push_back(NGV); 561 562 // Calculate the known alignment of the field. If the original aggregate 563 // had 256 byte alignment for example, something might depend on that: 564 // propagate info to each field. 565 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i); 566 if (NewAlign > EltAlign) 567 NGV->setAlignment(NewAlign); 568 } 569 } 570 571 if (NewGlobals.empty()) 572 return 0; 573 574 DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV); 575 576 Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext())); 577 578 // Loop over all of the uses of the global, replacing the constantexpr geps, 579 // with smaller constantexpr geps or direct references. 580 while (!GV->use_empty()) { 581 User *GEP = GV->use_back(); 582 assert(((isa<ConstantExpr>(GEP) && 583 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)|| 584 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!"); 585 586 // Ignore the 1th operand, which has to be zero or else the program is quite 587 // broken (undefined). Get the 2nd operand, which is the structure or array 588 // index. 589 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 590 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access. 591 592 Value *NewPtr = NewGlobals[Val]; 593 594 // Form a shorter GEP if needed. 595 if (GEP->getNumOperands() > 3) { 596 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) { 597 SmallVector<Constant*, 8> Idxs; 598 Idxs.push_back(NullInt); 599 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i) 600 Idxs.push_back(CE->getOperand(i)); 601 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), Idxs); 602 } else { 603 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP); 604 SmallVector<Value*, 8> Idxs; 605 Idxs.push_back(NullInt); 606 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) 607 Idxs.push_back(GEPI->getOperand(i)); 608 NewPtr = GetElementPtrInst::Create(NewPtr, Idxs, 609 GEPI->getName()+"."+Twine(Val),GEPI); 610 } 611 } 612 GEP->replaceAllUsesWith(NewPtr); 613 614 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP)) 615 GEPI->eraseFromParent(); 616 else 617 cast<ConstantExpr>(GEP)->destroyConstant(); 618 } 619 620 // Delete the old global, now that it is dead. 621 Globals.erase(GV); 622 ++NumSRA; 623 624 // Loop over the new globals array deleting any globals that are obviously 625 // dead. This can arise due to scalarization of a structure or an array that 626 // has elements that are dead. 627 unsigned FirstGlobal = 0; 628 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i) 629 if (NewGlobals[i]->use_empty()) { 630 Globals.erase(NewGlobals[i]); 631 if (FirstGlobal == i) ++FirstGlobal; 632 } 633 634 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0; 635} 636 637/// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified 638/// value will trap if the value is dynamically null. PHIs keeps track of any 639/// phi nodes we've seen to avoid reprocessing them. 640static bool AllUsesOfValueWillTrapIfNull(const Value *V, 641 SmallPtrSet<const PHINode*, 8> &PHIs) { 642 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; 643 ++UI) { 644 const User *U = *UI; 645 646 if (isa<LoadInst>(U)) { 647 // Will trap. 648 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) { 649 if (SI->getOperand(0) == V) { 650 //cerr << "NONTRAPPING USE: " << *U; 651 return false; // Storing the value. 652 } 653 } else if (const CallInst *CI = dyn_cast<CallInst>(U)) { 654 if (CI->getCalledValue() != V) { 655 //cerr << "NONTRAPPING USE: " << *U; 656 return false; // Not calling the ptr 657 } 658 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) { 659 if (II->getCalledValue() != V) { 660 //cerr << "NONTRAPPING USE: " << *U; 661 return false; // Not calling the ptr 662 } 663 } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) { 664 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false; 665 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { 666 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false; 667 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) { 668 // If we've already seen this phi node, ignore it, it has already been 669 // checked. 670 if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs)) 671 return false; 672 } else if (isa<ICmpInst>(U) && 673 isa<ConstantPointerNull>(UI->getOperand(1))) { 674 // Ignore icmp X, null 675 } else { 676 //cerr << "NONTRAPPING USE: " << *U; 677 return false; 678 } 679 } 680 return true; 681} 682 683/// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads 684/// from GV will trap if the loaded value is null. Note that this also permits 685/// comparisons of the loaded value against null, as a special case. 686static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) { 687 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end(); 688 UI != E; ++UI) { 689 const User *U = *UI; 690 691 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) { 692 SmallPtrSet<const PHINode*, 8> PHIs; 693 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs)) 694 return false; 695 } else if (isa<StoreInst>(U)) { 696 // Ignore stores to the global. 697 } else { 698 // We don't know or understand this user, bail out. 699 //cerr << "UNKNOWN USER OF GLOBAL!: " << *U; 700 return false; 701 } 702 } 703 return true; 704} 705 706static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) { 707 bool Changed = false; 708 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) { 709 Instruction *I = cast<Instruction>(*UI++); 710 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 711 LI->setOperand(0, NewV); 712 Changed = true; 713 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 714 if (SI->getOperand(1) == V) { 715 SI->setOperand(1, NewV); 716 Changed = true; 717 } 718 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) { 719 CallSite CS(I); 720 if (CS.getCalledValue() == V) { 721 // Calling through the pointer! Turn into a direct call, but be careful 722 // that the pointer is not also being passed as an argument. 723 CS.setCalledFunction(NewV); 724 Changed = true; 725 bool PassedAsArg = false; 726 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) 727 if (CS.getArgument(i) == V) { 728 PassedAsArg = true; 729 CS.setArgument(i, NewV); 730 } 731 732 if (PassedAsArg) { 733 // Being passed as an argument also. Be careful to not invalidate UI! 734 UI = V->use_begin(); 735 } 736 } 737 } else if (CastInst *CI = dyn_cast<CastInst>(I)) { 738 Changed |= OptimizeAwayTrappingUsesOfValue(CI, 739 ConstantExpr::getCast(CI->getOpcode(), 740 NewV, CI->getType())); 741 if (CI->use_empty()) { 742 Changed = true; 743 CI->eraseFromParent(); 744 } 745 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { 746 // Should handle GEP here. 747 SmallVector<Constant*, 8> Idxs; 748 Idxs.reserve(GEPI->getNumOperands()-1); 749 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end(); 750 i != e; ++i) 751 if (Constant *C = dyn_cast<Constant>(*i)) 752 Idxs.push_back(C); 753 else 754 break; 755 if (Idxs.size() == GEPI->getNumOperands()-1) 756 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI, 757 ConstantExpr::getGetElementPtr(NewV, Idxs)); 758 if (GEPI->use_empty()) { 759 Changed = true; 760 GEPI->eraseFromParent(); 761 } 762 } 763 } 764 765 return Changed; 766} 767 768 769/// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null 770/// value stored into it. If there are uses of the loaded value that would trap 771/// if the loaded value is dynamically null, then we know that they cannot be 772/// reachable with a null optimize away the load. 773static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV) { 774 bool Changed = false; 775 776 // Keep track of whether we are able to remove all the uses of the global 777 // other than the store that defines it. 778 bool AllNonStoreUsesGone = true; 779 780 // Replace all uses of loads with uses of uses of the stored value. 781 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){ 782 User *GlobalUser = *GUI++; 783 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) { 784 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV); 785 // If we were able to delete all uses of the loads 786 if (LI->use_empty()) { 787 LI->eraseFromParent(); 788 Changed = true; 789 } else { 790 AllNonStoreUsesGone = false; 791 } 792 } else if (isa<StoreInst>(GlobalUser)) { 793 // Ignore the store that stores "LV" to the global. 794 assert(GlobalUser->getOperand(1) == GV && 795 "Must be storing *to* the global"); 796 } else { 797 AllNonStoreUsesGone = false; 798 799 // If we get here we could have other crazy uses that are transitively 800 // loaded. 801 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) || 802 isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser)) && 803 "Only expect load and stores!"); 804 } 805 } 806 807 if (Changed) { 808 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV); 809 ++NumGlobUses; 810 } 811 812 // If we nuked all of the loads, then none of the stores are needed either, 813 // nor is the global. 814 if (AllNonStoreUsesGone) { 815 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n"); 816 CleanupConstantGlobalUsers(GV, 0); 817 if (GV->use_empty()) { 818 GV->eraseFromParent(); 819 ++NumDeleted; 820 } 821 Changed = true; 822 } 823 return Changed; 824} 825 826/// ConstantPropUsersOf - Walk the use list of V, constant folding all of the 827/// instructions that are foldable. 828static void ConstantPropUsersOf(Value *V) { 829 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) 830 if (Instruction *I = dyn_cast<Instruction>(*UI++)) 831 if (Constant *NewC = ConstantFoldInstruction(I)) { 832 I->replaceAllUsesWith(NewC); 833 834 // Advance UI to the next non-I use to avoid invalidating it! 835 // Instructions could multiply use V. 836 while (UI != E && *UI == I) 837 ++UI; 838 I->eraseFromParent(); 839 } 840} 841 842/// OptimizeGlobalAddressOfMalloc - This function takes the specified global 843/// variable, and transforms the program as if it always contained the result of 844/// the specified malloc. Because it is always the result of the specified 845/// malloc, there is no reason to actually DO the malloc. Instead, turn the 846/// malloc into a global, and any loads of GV as uses of the new global. 847static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, 848 CallInst *CI, 849 Type *AllocTy, 850 ConstantInt *NElements, 851 TargetData* TD) { 852 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n'); 853 854 Type *GlobalType; 855 if (NElements->getZExtValue() == 1) 856 GlobalType = AllocTy; 857 else 858 // If we have an array allocation, the global variable is of an array. 859 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue()); 860 861 // Create the new global variable. The contents of the malloc'd memory is 862 // undefined, so initialize with an undef value. 863 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(), 864 GlobalType, false, 865 GlobalValue::InternalLinkage, 866 UndefValue::get(GlobalType), 867 GV->getName()+".body", 868 GV, 869 GV->isThreadLocal()); 870 871 // If there are bitcast users of the malloc (which is typical, usually we have 872 // a malloc + bitcast) then replace them with uses of the new global. Update 873 // other users to use the global as well. 874 BitCastInst *TheBC = 0; 875 while (!CI->use_empty()) { 876 Instruction *User = cast<Instruction>(CI->use_back()); 877 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { 878 if (BCI->getType() == NewGV->getType()) { 879 BCI->replaceAllUsesWith(NewGV); 880 BCI->eraseFromParent(); 881 } else { 882 BCI->setOperand(0, NewGV); 883 } 884 } else { 885 if (TheBC == 0) 886 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI); 887 User->replaceUsesOfWith(CI, TheBC); 888 } 889 } 890 891 Constant *RepValue = NewGV; 892 if (NewGV->getType() != GV->getType()->getElementType()) 893 RepValue = ConstantExpr::getBitCast(RepValue, 894 GV->getType()->getElementType()); 895 896 // If there is a comparison against null, we will insert a global bool to 897 // keep track of whether the global was initialized yet or not. 898 GlobalVariable *InitBool = 899 new GlobalVariable(Type::getInt1Ty(GV->getContext()), false, 900 GlobalValue::InternalLinkage, 901 ConstantInt::getFalse(GV->getContext()), 902 GV->getName()+".init", GV->isThreadLocal()); 903 bool InitBoolUsed = false; 904 905 // Loop over all uses of GV, processing them in turn. 906 while (!GV->use_empty()) { 907 if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) { 908 // The global is initialized when the store to it occurs. 909 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, SI); 910 SI->eraseFromParent(); 911 continue; 912 } 913 914 LoadInst *LI = cast<LoadInst>(GV->use_back()); 915 while (!LI->use_empty()) { 916 Use &LoadUse = LI->use_begin().getUse(); 917 if (!isa<ICmpInst>(LoadUse.getUser())) { 918 LoadUse = RepValue; 919 continue; 920 } 921 922 ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser()); 923 // Replace the cmp X, 0 with a use of the bool value. 924 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", ICI); 925 InitBoolUsed = true; 926 switch (ICI->getPredicate()) { 927 default: llvm_unreachable("Unknown ICmp Predicate!"); 928 case ICmpInst::ICMP_ULT: 929 case ICmpInst::ICMP_SLT: // X < null -> always false 930 LV = ConstantInt::getFalse(GV->getContext()); 931 break; 932 case ICmpInst::ICMP_ULE: 933 case ICmpInst::ICMP_SLE: 934 case ICmpInst::ICMP_EQ: 935 LV = BinaryOperator::CreateNot(LV, "notinit", ICI); 936 break; 937 case ICmpInst::ICMP_NE: 938 case ICmpInst::ICMP_UGE: 939 case ICmpInst::ICMP_SGE: 940 case ICmpInst::ICMP_UGT: 941 case ICmpInst::ICMP_SGT: 942 break; // no change. 943 } 944 ICI->replaceAllUsesWith(LV); 945 ICI->eraseFromParent(); 946 } 947 LI->eraseFromParent(); 948 } 949 950 // If the initialization boolean was used, insert it, otherwise delete it. 951 if (!InitBoolUsed) { 952 while (!InitBool->use_empty()) // Delete initializations 953 cast<StoreInst>(InitBool->use_back())->eraseFromParent(); 954 delete InitBool; 955 } else 956 GV->getParent()->getGlobalList().insert(GV, InitBool); 957 958 // Now the GV is dead, nuke it and the malloc.. 959 GV->eraseFromParent(); 960 CI->eraseFromParent(); 961 962 // To further other optimizations, loop over all users of NewGV and try to 963 // constant prop them. This will promote GEP instructions with constant 964 // indices into GEP constant-exprs, which will allow global-opt to hack on it. 965 ConstantPropUsersOf(NewGV); 966 if (RepValue != NewGV) 967 ConstantPropUsersOf(RepValue); 968 969 return NewGV; 970} 971 972/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking 973/// to make sure that there are no complex uses of V. We permit simple things 974/// like dereferencing the pointer, but not storing through the address, unless 975/// it is to the specified global. 976static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V, 977 const GlobalVariable *GV, 978 SmallPtrSet<const PHINode*, 8> &PHIs) { 979 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); 980 UI != E; ++UI) { 981 const Instruction *Inst = cast<Instruction>(*UI); 982 983 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) { 984 continue; // Fine, ignore. 985 } 986 987 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 988 if (SI->getOperand(0) == V && SI->getOperand(1) != GV) 989 return false; // Storing the pointer itself... bad. 990 continue; // Otherwise, storing through it, or storing into GV... fine. 991 } 992 993 // Must index into the array and into the struct. 994 if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) { 995 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs)) 996 return false; 997 continue; 998 } 999 1000 if (const PHINode *PN = dyn_cast<PHINode>(Inst)) { 1001 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI 1002 // cycles. 1003 if (PHIs.insert(PN)) 1004 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs)) 1005 return false; 1006 continue; 1007 } 1008 1009 if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) { 1010 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) 1011 return false; 1012 continue; 1013 } 1014 1015 return false; 1016 } 1017 return true; 1018} 1019 1020/// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV 1021/// somewhere. Transform all uses of the allocation into loads from the 1022/// global and uses of the resultant pointer. Further, delete the store into 1023/// GV. This assumes that these value pass the 1024/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate. 1025static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, 1026 GlobalVariable *GV) { 1027 while (!Alloc->use_empty()) { 1028 Instruction *U = cast<Instruction>(*Alloc->use_begin()); 1029 Instruction *InsertPt = U; 1030 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 1031 // If this is the store of the allocation into the global, remove it. 1032 if (SI->getOperand(1) == GV) { 1033 SI->eraseFromParent(); 1034 continue; 1035 } 1036 } else if (PHINode *PN = dyn_cast<PHINode>(U)) { 1037 // Insert the load in the corresponding predecessor, not right before the 1038 // PHI. 1039 InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator(); 1040 } else if (isa<BitCastInst>(U)) { 1041 // Must be bitcast between the malloc and store to initialize the global. 1042 ReplaceUsesOfMallocWithGlobal(U, GV); 1043 U->eraseFromParent(); 1044 continue; 1045 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { 1046 // If this is a "GEP bitcast" and the user is a store to the global, then 1047 // just process it as a bitcast. 1048 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse()) 1049 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back())) 1050 if (SI->getOperand(1) == GV) { 1051 // Must be bitcast GEP between the malloc and store to initialize 1052 // the global. 1053 ReplaceUsesOfMallocWithGlobal(GEPI, GV); 1054 GEPI->eraseFromParent(); 1055 continue; 1056 } 1057 } 1058 1059 // Insert a load from the global, and use it instead of the malloc. 1060 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt); 1061 U->replaceUsesOfWith(Alloc, NL); 1062 } 1063} 1064 1065/// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi 1066/// of a load) are simple enough to perform heap SRA on. This permits GEP's 1067/// that index through the array and struct field, icmps of null, and PHIs. 1068static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V, 1069 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs, 1070 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIsPerLoad) { 1071 // We permit two users of the load: setcc comparing against the null 1072 // pointer, and a getelementptr of a specific form. 1073 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; 1074 ++UI) { 1075 const Instruction *User = cast<Instruction>(*UI); 1076 1077 // Comparison against null is ok. 1078 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(User)) { 1079 if (!isa<ConstantPointerNull>(ICI->getOperand(1))) 1080 return false; 1081 continue; 1082 } 1083 1084 // getelementptr is also ok, but only a simple form. 1085 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1086 // Must index into the array and into the struct. 1087 if (GEPI->getNumOperands() < 3) 1088 return false; 1089 1090 // Otherwise the GEP is ok. 1091 continue; 1092 } 1093 1094 if (const PHINode *PN = dyn_cast<PHINode>(User)) { 1095 if (!LoadUsingPHIsPerLoad.insert(PN)) 1096 // This means some phi nodes are dependent on each other. 1097 // Avoid infinite looping! 1098 return false; 1099 if (!LoadUsingPHIs.insert(PN)) 1100 // If we have already analyzed this PHI, then it is safe. 1101 continue; 1102 1103 // Make sure all uses of the PHI are simple enough to transform. 1104 if (!LoadUsesSimpleEnoughForHeapSRA(PN, 1105 LoadUsingPHIs, LoadUsingPHIsPerLoad)) 1106 return false; 1107 1108 continue; 1109 } 1110 1111 // Otherwise we don't know what this is, not ok. 1112 return false; 1113 } 1114 1115 return true; 1116} 1117 1118 1119/// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from 1120/// GV are simple enough to perform HeapSRA, return true. 1121static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV, 1122 Instruction *StoredVal) { 1123 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs; 1124 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad; 1125 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end(); 1126 UI != E; ++UI) 1127 if (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 1128 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs, 1129 LoadUsingPHIsPerLoad)) 1130 return false; 1131 LoadUsingPHIsPerLoad.clear(); 1132 } 1133 1134 // If we reach here, we know that all uses of the loads and transitive uses 1135 // (through PHI nodes) are simple enough to transform. However, we don't know 1136 // that all inputs the to the PHI nodes are in the same equivalence sets. 1137 // Check to verify that all operands of the PHIs are either PHIS that can be 1138 // transformed, loads from GV, or MI itself. 1139 for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin() 1140 , E = LoadUsingPHIs.end(); I != E; ++I) { 1141 const PHINode *PN = *I; 1142 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) { 1143 Value *InVal = PN->getIncomingValue(op); 1144 1145 // PHI of the stored value itself is ok. 1146 if (InVal == StoredVal) continue; 1147 1148 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) { 1149 // One of the PHIs in our set is (optimistically) ok. 1150 if (LoadUsingPHIs.count(InPN)) 1151 continue; 1152 return false; 1153 } 1154 1155 // Load from GV is ok. 1156 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal)) 1157 if (LI->getOperand(0) == GV) 1158 continue; 1159 1160 // UNDEF? NULL? 1161 1162 // Anything else is rejected. 1163 return false; 1164 } 1165 } 1166 1167 return true; 1168} 1169 1170static Value *GetHeapSROAValue(Value *V, unsigned FieldNo, 1171 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1172 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 1173 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V]; 1174 1175 if (FieldNo >= FieldVals.size()) 1176 FieldVals.resize(FieldNo+1); 1177 1178 // If we already have this value, just reuse the previously scalarized 1179 // version. 1180 if (Value *FieldVal = FieldVals[FieldNo]) 1181 return FieldVal; 1182 1183 // Depending on what instruction this is, we have several cases. 1184 Value *Result; 1185 if (LoadInst *LI = dyn_cast<LoadInst>(V)) { 1186 // This is a scalarized version of the load from the global. Just create 1187 // a new Load of the scalarized global. 1188 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo, 1189 InsertedScalarizedValues, 1190 PHIsToRewrite), 1191 LI->getName()+".f"+Twine(FieldNo), LI); 1192 } else if (PHINode *PN = dyn_cast<PHINode>(V)) { 1193 // PN's type is pointer to struct. Make a new PHI of pointer to struct 1194 // field. 1195 StructType *ST = 1196 cast<StructType>(cast<PointerType>(PN->getType())->getElementType()); 1197 1198 PHINode *NewPN = 1199 PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)), 1200 PN->getNumIncomingValues(), 1201 PN->getName()+".f"+Twine(FieldNo), PN); 1202 Result = NewPN; 1203 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo)); 1204 } else { 1205 llvm_unreachable("Unknown usable value"); 1206 Result = 0; 1207 } 1208 1209 return FieldVals[FieldNo] = Result; 1210} 1211 1212/// RewriteHeapSROALoadUser - Given a load instruction and a value derived from 1213/// the load, rewrite the derived value to use the HeapSRoA'd load. 1214static void RewriteHeapSROALoadUser(Instruction *LoadUser, 1215 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1216 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 1217 // If this is a comparison against null, handle it. 1218 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) { 1219 assert(isa<ConstantPointerNull>(SCI->getOperand(1))); 1220 // If we have a setcc of the loaded pointer, we can use a setcc of any 1221 // field. 1222 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0, 1223 InsertedScalarizedValues, PHIsToRewrite); 1224 1225 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr, 1226 Constant::getNullValue(NPtr->getType()), 1227 SCI->getName()); 1228 SCI->replaceAllUsesWith(New); 1229 SCI->eraseFromParent(); 1230 return; 1231 } 1232 1233 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...' 1234 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) { 1235 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2)) 1236 && "Unexpected GEPI!"); 1237 1238 // Load the pointer for this field. 1239 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 1240 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo, 1241 InsertedScalarizedValues, PHIsToRewrite); 1242 1243 // Create the new GEP idx vector. 1244 SmallVector<Value*, 8> GEPIdx; 1245 GEPIdx.push_back(GEPI->getOperand(1)); 1246 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end()); 1247 1248 Value *NGEPI = GetElementPtrInst::Create(NewPtr, GEPIdx, 1249 GEPI->getName(), GEPI); 1250 GEPI->replaceAllUsesWith(NGEPI); 1251 GEPI->eraseFromParent(); 1252 return; 1253 } 1254 1255 // Recursively transform the users of PHI nodes. This will lazily create the 1256 // PHIs that are needed for individual elements. Keep track of what PHIs we 1257 // see in InsertedScalarizedValues so that we don't get infinite loops (very 1258 // antisocial). If the PHI is already in InsertedScalarizedValues, it has 1259 // already been seen first by another load, so its uses have already been 1260 // processed. 1261 PHINode *PN = cast<PHINode>(LoadUser); 1262 if (!InsertedScalarizedValues.insert(std::make_pair(PN, 1263 std::vector<Value*>())).second) 1264 return; 1265 1266 // If this is the first time we've seen this PHI, recursively process all 1267 // users. 1268 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) { 1269 Instruction *User = cast<Instruction>(*UI++); 1270 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); 1271 } 1272} 1273 1274/// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr 1275/// is a value loaded from the global. Eliminate all uses of Ptr, making them 1276/// use FieldGlobals instead. All uses of loaded values satisfy 1277/// AllGlobalLoadUsesSimpleEnoughForHeapSRA. 1278static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load, 1279 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1280 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 1281 for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end(); 1282 UI != E; ) { 1283 Instruction *User = cast<Instruction>(*UI++); 1284 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); 1285 } 1286 1287 if (Load->use_empty()) { 1288 Load->eraseFromParent(); 1289 InsertedScalarizedValues.erase(Load); 1290 } 1291} 1292 1293/// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break 1294/// it up into multiple allocations of arrays of the fields. 1295static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI, 1296 Value* NElems, TargetData *TD) { 1297 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n'); 1298 Type* MAT = getMallocAllocatedType(CI); 1299 StructType *STy = cast<StructType>(MAT); 1300 1301 // There is guaranteed to be at least one use of the malloc (storing 1302 // it into GV). If there are other uses, change them to be uses of 1303 // the global to simplify later code. This also deletes the store 1304 // into GV. 1305 ReplaceUsesOfMallocWithGlobal(CI, GV); 1306 1307 // Okay, at this point, there are no users of the malloc. Insert N 1308 // new mallocs at the same place as CI, and N globals. 1309 std::vector<Value*> FieldGlobals; 1310 std::vector<Value*> FieldMallocs; 1311 1312 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ 1313 Type *FieldTy = STy->getElementType(FieldNo); 1314 PointerType *PFieldTy = PointerType::getUnqual(FieldTy); 1315 1316 GlobalVariable *NGV = 1317 new GlobalVariable(*GV->getParent(), 1318 PFieldTy, false, GlobalValue::InternalLinkage, 1319 Constant::getNullValue(PFieldTy), 1320 GV->getName() + ".f" + Twine(FieldNo), GV, 1321 GV->isThreadLocal()); 1322 FieldGlobals.push_back(NGV); 1323 1324 unsigned TypeSize = TD->getTypeAllocSize(FieldTy); 1325 if (StructType *ST = dyn_cast<StructType>(FieldTy)) 1326 TypeSize = TD->getStructLayout(ST)->getSizeInBytes(); 1327 Type *IntPtrTy = TD->getIntPtrType(CI->getContext()); 1328 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy, 1329 ConstantInt::get(IntPtrTy, TypeSize), 1330 NElems, 0, 1331 CI->getName() + ".f" + Twine(FieldNo)); 1332 FieldMallocs.push_back(NMI); 1333 new StoreInst(NMI, NGV, CI); 1334 } 1335 1336 // The tricky aspect of this transformation is handling the case when malloc 1337 // fails. In the original code, malloc failing would set the result pointer 1338 // of malloc to null. In this case, some mallocs could succeed and others 1339 // could fail. As such, we emit code that looks like this: 1340 // F0 = malloc(field0) 1341 // F1 = malloc(field1) 1342 // F2 = malloc(field2) 1343 // if (F0 == 0 || F1 == 0 || F2 == 0) { 1344 // if (F0) { free(F0); F0 = 0; } 1345 // if (F1) { free(F1); F1 = 0; } 1346 // if (F2) { free(F2); F2 = 0; } 1347 // } 1348 // The malloc can also fail if its argument is too large. 1349 Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0); 1350 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0), 1351 ConstantZero, "isneg"); 1352 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) { 1353 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i], 1354 Constant::getNullValue(FieldMallocs[i]->getType()), 1355 "isnull"); 1356 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI); 1357 } 1358 1359 // Split the basic block at the old malloc. 1360 BasicBlock *OrigBB = CI->getParent(); 1361 BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont"); 1362 1363 // Create the block to check the first condition. Put all these blocks at the 1364 // end of the function as they are unlikely to be executed. 1365 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(), 1366 "malloc_ret_null", 1367 OrigBB->getParent()); 1368 1369 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond 1370 // branch on RunningOr. 1371 OrigBB->getTerminator()->eraseFromParent(); 1372 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB); 1373 1374 // Within the NullPtrBlock, we need to emit a comparison and branch for each 1375 // pointer, because some may be null while others are not. 1376 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1377 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock); 1378 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal, 1379 Constant::getNullValue(GVVal->getType())); 1380 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it", 1381 OrigBB->getParent()); 1382 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next", 1383 OrigBB->getParent()); 1384 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock, 1385 Cmp, NullPtrBlock); 1386 1387 // Fill in FreeBlock. 1388 CallInst::CreateFree(GVVal, BI); 1389 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i], 1390 FreeBlock); 1391 BranchInst::Create(NextBlock, FreeBlock); 1392 1393 NullPtrBlock = NextBlock; 1394 } 1395 1396 BranchInst::Create(ContBB, NullPtrBlock); 1397 1398 // CI is no longer needed, remove it. 1399 CI->eraseFromParent(); 1400 1401 /// InsertedScalarizedLoads - As we process loads, if we can't immediately 1402 /// update all uses of the load, keep track of what scalarized loads are 1403 /// inserted for a given load. 1404 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues; 1405 InsertedScalarizedValues[GV] = FieldGlobals; 1406 1407 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite; 1408 1409 // Okay, the malloc site is completely handled. All of the uses of GV are now 1410 // loads, and all uses of those loads are simple. Rewrite them to use loads 1411 // of the per-field globals instead. 1412 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) { 1413 Instruction *User = cast<Instruction>(*UI++); 1414 1415 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1416 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite); 1417 continue; 1418 } 1419 1420 // Must be a store of null. 1421 StoreInst *SI = cast<StoreInst>(User); 1422 assert(isa<ConstantPointerNull>(SI->getOperand(0)) && 1423 "Unexpected heap-sra user!"); 1424 1425 // Insert a store of null into each global. 1426 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1427 PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType()); 1428 Constant *Null = Constant::getNullValue(PT->getElementType()); 1429 new StoreInst(Null, FieldGlobals[i], SI); 1430 } 1431 // Erase the original store. 1432 SI->eraseFromParent(); 1433 } 1434 1435 // While we have PHIs that are interesting to rewrite, do it. 1436 while (!PHIsToRewrite.empty()) { 1437 PHINode *PN = PHIsToRewrite.back().first; 1438 unsigned FieldNo = PHIsToRewrite.back().second; 1439 PHIsToRewrite.pop_back(); 1440 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]); 1441 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi"); 1442 1443 // Add all the incoming values. This can materialize more phis. 1444 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1445 Value *InVal = PN->getIncomingValue(i); 1446 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues, 1447 PHIsToRewrite); 1448 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i)); 1449 } 1450 } 1451 1452 // Drop all inter-phi links and any loads that made it this far. 1453 for (DenseMap<Value*, std::vector<Value*> >::iterator 1454 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1455 I != E; ++I) { 1456 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1457 PN->dropAllReferences(); 1458 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1459 LI->dropAllReferences(); 1460 } 1461 1462 // Delete all the phis and loads now that inter-references are dead. 1463 for (DenseMap<Value*, std::vector<Value*> >::iterator 1464 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1465 I != E; ++I) { 1466 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1467 PN->eraseFromParent(); 1468 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1469 LI->eraseFromParent(); 1470 } 1471 1472 // The old global is now dead, remove it. 1473 GV->eraseFromParent(); 1474 1475 ++NumHeapSRA; 1476 return cast<GlobalVariable>(FieldGlobals[0]); 1477} 1478 1479/// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a 1480/// pointer global variable with a single value stored it that is a malloc or 1481/// cast of malloc. 1482static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, 1483 CallInst *CI, 1484 Type *AllocTy, 1485 Module::global_iterator &GVI, 1486 TargetData *TD) { 1487 if (!TD) 1488 return false; 1489 1490 // If this is a malloc of an abstract type, don't touch it. 1491 if (!AllocTy->isSized()) 1492 return false; 1493 1494 // We can't optimize this global unless all uses of it are *known* to be 1495 // of the malloc value, not of the null initializer value (consider a use 1496 // that compares the global's value against zero to see if the malloc has 1497 // been reached). To do this, we check to see if all uses of the global 1498 // would trap if the global were null: this proves that they must all 1499 // happen after the malloc. 1500 if (!AllUsesOfLoadedValueWillTrapIfNull(GV)) 1501 return false; 1502 1503 // We can't optimize this if the malloc itself is used in a complex way, 1504 // for example, being stored into multiple globals. This allows the 1505 // malloc to be stored into the specified global, loaded setcc'd, and 1506 // GEP'd. These are all things we could transform to using the global 1507 // for. 1508 SmallPtrSet<const PHINode*, 8> PHIs; 1509 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs)) 1510 return false; 1511 1512 // If we have a global that is only initialized with a fixed size malloc, 1513 // transform the program to use global memory instead of malloc'd memory. 1514 // This eliminates dynamic allocation, avoids an indirection accessing the 1515 // data, and exposes the resultant global to further GlobalOpt. 1516 // We cannot optimize the malloc if we cannot determine malloc array size. 1517 Value *NElems = getMallocArraySize(CI, TD, true); 1518 if (!NElems) 1519 return false; 1520 1521 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems)) 1522 // Restrict this transformation to only working on small allocations 1523 // (2048 bytes currently), as we don't want to introduce a 16M global or 1524 // something. 1525 if (NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) { 1526 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD); 1527 return true; 1528 } 1529 1530 // If the allocation is an array of structures, consider transforming this 1531 // into multiple malloc'd arrays, one for each field. This is basically 1532 // SRoA for malloc'd memory. 1533 1534 // If this is an allocation of a fixed size array of structs, analyze as a 1535 // variable size array. malloc [100 x struct],1 -> malloc struct, 100 1536 if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1)) 1537 if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy)) 1538 AllocTy = AT->getElementType(); 1539 1540 StructType *AllocSTy = dyn_cast<StructType>(AllocTy); 1541 if (!AllocSTy) 1542 return false; 1543 1544 // This the structure has an unreasonable number of fields, leave it 1545 // alone. 1546 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 && 1547 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) { 1548 1549 // If this is a fixed size array, transform the Malloc to be an alloc of 1550 // structs. malloc [100 x struct],1 -> malloc struct, 100 1551 if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI))) { 1552 Type *IntPtrTy = TD->getIntPtrType(CI->getContext()); 1553 unsigned TypeSize = TD->getStructLayout(AllocSTy)->getSizeInBytes(); 1554 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize); 1555 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements()); 1556 Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy, 1557 AllocSize, NumElements, 1558 0, CI->getName()); 1559 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI); 1560 CI->replaceAllUsesWith(Cast); 1561 CI->eraseFromParent(); 1562 CI = dyn_cast<BitCastInst>(Malloc) ? 1563 extractMallocCallFromBitCast(Malloc) : cast<CallInst>(Malloc); 1564 } 1565 1566 GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, true),TD); 1567 return true; 1568 } 1569 1570 return false; 1571} 1572 1573// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge 1574// that only one value (besides its initializer) is ever stored to the global. 1575static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal, 1576 Module::global_iterator &GVI, 1577 TargetData *TD) { 1578 // Ignore no-op GEPs and bitcasts. 1579 StoredOnceVal = StoredOnceVal->stripPointerCasts(); 1580 1581 // If we are dealing with a pointer global that is initialized to null and 1582 // only has one (non-null) value stored into it, then we can optimize any 1583 // users of the loaded value (often calls and loads) that would trap if the 1584 // value was null. 1585 if (GV->getInitializer()->getType()->isPointerTy() && 1586 GV->getInitializer()->isNullValue()) { 1587 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { 1588 if (GV->getInitializer()->getType() != SOVC->getType()) 1589 SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType()); 1590 1591 // Optimize away any trapping uses of the loaded value. 1592 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC)) 1593 return true; 1594 } else if (CallInst *CI = extractMallocCall(StoredOnceVal)) { 1595 Type* MallocType = getMallocAllocatedType(CI); 1596 if (MallocType && TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, 1597 GVI, TD)) 1598 return true; 1599 } 1600 } 1601 1602 return false; 1603} 1604 1605/// TryToShrinkGlobalToBoolean - At this point, we have learned that the only 1606/// two values ever stored into GV are its initializer and OtherVal. See if we 1607/// can shrink the global into a boolean and select between the two values 1608/// whenever it is used. This exposes the values to other scalar optimizations. 1609static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) { 1610 Type *GVElType = GV->getType()->getElementType(); 1611 1612 // If GVElType is already i1, it is already shrunk. If the type of the GV is 1613 // an FP value, pointer or vector, don't do this optimization because a select 1614 // between them is very expensive and unlikely to lead to later 1615 // simplification. In these cases, we typically end up with "cond ? v1 : v2" 1616 // where v1 and v2 both require constant pool loads, a big loss. 1617 if (GVElType == Type::getInt1Ty(GV->getContext()) || 1618 GVElType->isFloatingPointTy() || 1619 GVElType->isPointerTy() || GVElType->isVectorTy()) 1620 return false; 1621 1622 // Walk the use list of the global seeing if all the uses are load or store. 1623 // If there is anything else, bail out. 1624 for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){ 1625 User *U = *I; 1626 if (!isa<LoadInst>(U) && !isa<StoreInst>(U)) 1627 return false; 1628 } 1629 1630 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV); 1631 1632 // Create the new global, initializing it to false. 1633 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()), 1634 false, 1635 GlobalValue::InternalLinkage, 1636 ConstantInt::getFalse(GV->getContext()), 1637 GV->getName()+".b", 1638 GV->isThreadLocal()); 1639 GV->getParent()->getGlobalList().insert(GV, NewGV); 1640 1641 Constant *InitVal = GV->getInitializer(); 1642 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) && 1643 "No reason to shrink to bool!"); 1644 1645 // If initialized to zero and storing one into the global, we can use a cast 1646 // instead of a select to synthesize the desired value. 1647 bool IsOneZero = false; 1648 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) 1649 IsOneZero = InitVal->isNullValue() && CI->isOne(); 1650 1651 while (!GV->use_empty()) { 1652 Instruction *UI = cast<Instruction>(GV->use_back()); 1653 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { 1654 // Change the store into a boolean store. 1655 bool StoringOther = SI->getOperand(0) == OtherVal; 1656 // Only do this if we weren't storing a loaded value. 1657 Value *StoreVal; 1658 if (StoringOther || SI->getOperand(0) == InitVal) 1659 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()), 1660 StoringOther); 1661 else { 1662 // Otherwise, we are storing a previously loaded copy. To do this, 1663 // change the copy from copying the original value to just copying the 1664 // bool. 1665 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); 1666 1667 // If we've already replaced the input, StoredVal will be a cast or 1668 // select instruction. If not, it will be a load of the original 1669 // global. 1670 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { 1671 assert(LI->getOperand(0) == GV && "Not a copy!"); 1672 // Insert a new load, to preserve the saved value. 1673 StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI); 1674 } else { 1675 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && 1676 "This is not a form that we understand!"); 1677 StoreVal = StoredVal->getOperand(0); 1678 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); 1679 } 1680 } 1681 new StoreInst(StoreVal, NewGV, SI); 1682 } else { 1683 // Change the load into a load of bool then a select. 1684 LoadInst *LI = cast<LoadInst>(UI); 1685 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", LI); 1686 Value *NSI; 1687 if (IsOneZero) 1688 NSI = new ZExtInst(NLI, LI->getType(), "", LI); 1689 else 1690 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI); 1691 NSI->takeName(LI); 1692 LI->replaceAllUsesWith(NSI); 1693 } 1694 UI->eraseFromParent(); 1695 } 1696 1697 GV->eraseFromParent(); 1698 return true; 1699} 1700 1701 1702/// ProcessInternalGlobal - Analyze the specified global variable and optimize 1703/// it if possible. If we make a change, return true. 1704bool GlobalOpt::ProcessGlobal(GlobalVariable *GV, 1705 Module::global_iterator &GVI) { 1706 if (!GV->hasLocalLinkage()) 1707 return false; 1708 1709 // Do more involved optimizations if the global is internal. 1710 GV->removeDeadConstantUsers(); 1711 1712 if (GV->use_empty()) { 1713 DEBUG(dbgs() << "GLOBAL DEAD: " << *GV); 1714 GV->eraseFromParent(); 1715 ++NumDeleted; 1716 return true; 1717 } 1718 1719 SmallPtrSet<const PHINode*, 16> PHIUsers; 1720 GlobalStatus GS; 1721 1722 if (AnalyzeGlobal(GV, GS, PHIUsers)) 1723 return false; 1724 1725 if (!GS.isCompared && !GV->hasUnnamedAddr()) { 1726 GV->setUnnamedAddr(true); 1727 NumUnnamed++; 1728 } 1729 1730 if (GV->isConstant() || !GV->hasInitializer()) 1731 return false; 1732 1733 return ProcessInternalGlobal(GV, GVI, PHIUsers, GS); 1734} 1735 1736/// ProcessInternalGlobal - Analyze the specified global variable and optimize 1737/// it if possible. If we make a change, return true. 1738bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV, 1739 Module::global_iterator &GVI, 1740 const SmallPtrSet<const PHINode*, 16> &PHIUsers, 1741 const GlobalStatus &GS) { 1742 // If this is a first class global and has only one accessing function 1743 // and this function is main (which we know is not recursive we can make 1744 // this global a local variable) we replace the global with a local alloca 1745 // in this function. 1746 // 1747 // NOTE: It doesn't make sense to promote non single-value types since we 1748 // are just replacing static memory to stack memory. 1749 // 1750 // If the global is in different address space, don't bring it to stack. 1751 if (!GS.HasMultipleAccessingFunctions && 1752 GS.AccessingFunction && !GS.HasNonInstructionUser && 1753 GV->getType()->getElementType()->isSingleValueType() && 1754 GS.AccessingFunction->getName() == "main" && 1755 GS.AccessingFunction->hasExternalLinkage() && 1756 GV->getType()->getAddressSpace() == 0) { 1757 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV); 1758 Instruction& FirstI = const_cast<Instruction&>(*GS.AccessingFunction 1759 ->getEntryBlock().begin()); 1760 Type* ElemTy = GV->getType()->getElementType(); 1761 // FIXME: Pass Global's alignment when globals have alignment 1762 AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), &FirstI); 1763 if (!isa<UndefValue>(GV->getInitializer())) 1764 new StoreInst(GV->getInitializer(), Alloca, &FirstI); 1765 1766 GV->replaceAllUsesWith(Alloca); 1767 GV->eraseFromParent(); 1768 ++NumLocalized; 1769 return true; 1770 } 1771 1772 // If the global is never loaded (but may be stored to), it is dead. 1773 // Delete it now. 1774 if (!GS.isLoaded) { 1775 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV); 1776 1777 // Delete any stores we can find to the global. We may not be able to 1778 // make it completely dead though. 1779 bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1780 1781 // If the global is dead now, delete it. 1782 if (GV->use_empty()) { 1783 GV->eraseFromParent(); 1784 ++NumDeleted; 1785 Changed = true; 1786 } 1787 return Changed; 1788 1789 } else if (GS.StoredType <= GlobalStatus::isInitializerStored) { 1790 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV); 1791 GV->setConstant(true); 1792 1793 // Clean up any obviously simplifiable users now. 1794 CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1795 1796 // If the global is dead now, just nuke it. 1797 if (GV->use_empty()) { 1798 DEBUG(dbgs() << " *** Marking constant allowed us to simplify " 1799 << "all users and delete global!\n"); 1800 GV->eraseFromParent(); 1801 ++NumDeleted; 1802 } 1803 1804 ++NumMarked; 1805 return true; 1806 } else if (!GV->getInitializer()->getType()->isSingleValueType()) { 1807 if (TargetData *TD = getAnalysisIfAvailable<TargetData>()) 1808 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) { 1809 GVI = FirstNewGV; // Don't skip the newly produced globals! 1810 return true; 1811 } 1812 } else if (GS.StoredType == GlobalStatus::isStoredOnce) { 1813 // If the initial value for the global was an undef value, and if only 1814 // one other value was stored into it, we can just change the 1815 // initializer to be the stored value, then delete all stores to the 1816 // global. This allows us to mark it constant. 1817 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1818 if (isa<UndefValue>(GV->getInitializer())) { 1819 // Change the initial value here. 1820 GV->setInitializer(SOVConstant); 1821 1822 // Clean up any obviously simplifiable users now. 1823 CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1824 1825 if (GV->use_empty()) { 1826 DEBUG(dbgs() << " *** Substituting initializer allowed us to " 1827 << "simplify all users and delete global!\n"); 1828 GV->eraseFromParent(); 1829 ++NumDeleted; 1830 } else { 1831 GVI = GV; 1832 } 1833 ++NumSubstitute; 1834 return true; 1835 } 1836 1837 // Try to optimize globals based on the knowledge that only one value 1838 // (besides its initializer) is ever stored to the global. 1839 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI, 1840 getAnalysisIfAvailable<TargetData>())) 1841 return true; 1842 1843 // Otherwise, if the global was not a boolean, we can shrink it to be a 1844 // boolean. 1845 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1846 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) { 1847 ++NumShrunkToBool; 1848 return true; 1849 } 1850 } 1851 1852 return false; 1853} 1854 1855/// ChangeCalleesToFastCall - Walk all of the direct calls of the specified 1856/// function, changing them to FastCC. 1857static void ChangeCalleesToFastCall(Function *F) { 1858 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1859 CallSite User(cast<Instruction>(*UI)); 1860 User.setCallingConv(CallingConv::Fast); 1861 } 1862} 1863 1864static AttrListPtr StripNest(const AttrListPtr &Attrs) { 1865 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) { 1866 if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0) 1867 continue; 1868 1869 // There can be only one. 1870 return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest); 1871 } 1872 1873 return Attrs; 1874} 1875 1876static void RemoveNestAttribute(Function *F) { 1877 F->setAttributes(StripNest(F->getAttributes())); 1878 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1879 CallSite User(cast<Instruction>(*UI)); 1880 User.setAttributes(StripNest(User.getAttributes())); 1881 } 1882} 1883 1884bool GlobalOpt::OptimizeFunctions(Module &M) { 1885 bool Changed = false; 1886 // Optimize functions. 1887 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { 1888 Function *F = FI++; 1889 // Functions without names cannot be referenced outside this module. 1890 if (!F->hasName() && !F->isDeclaration()) 1891 F->setLinkage(GlobalValue::InternalLinkage); 1892 F->removeDeadConstantUsers(); 1893 if (F->use_empty() && (F->hasLocalLinkage() || F->hasLinkOnceLinkage())) { 1894 F->eraseFromParent(); 1895 Changed = true; 1896 ++NumFnDeleted; 1897 } else if (F->hasLocalLinkage()) { 1898 if (F->getCallingConv() == CallingConv::C && !F->isVarArg() && 1899 !F->hasAddressTaken()) { 1900 // If this function has C calling conventions, is not a varargs 1901 // function, and is only called directly, promote it to use the Fast 1902 // calling convention. 1903 F->setCallingConv(CallingConv::Fast); 1904 ChangeCalleesToFastCall(F); 1905 ++NumFastCallFns; 1906 Changed = true; 1907 } 1908 1909 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) && 1910 !F->hasAddressTaken()) { 1911 // The function is not used by a trampoline intrinsic, so it is safe 1912 // to remove the 'nest' attribute. 1913 RemoveNestAttribute(F); 1914 ++NumNestRemoved; 1915 Changed = true; 1916 } 1917 } 1918 } 1919 return Changed; 1920} 1921 1922bool GlobalOpt::OptimizeGlobalVars(Module &M) { 1923 bool Changed = false; 1924 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); 1925 GVI != E; ) { 1926 GlobalVariable *GV = GVI++; 1927 // Global variables without names cannot be referenced outside this module. 1928 if (!GV->hasName() && !GV->isDeclaration()) 1929 GV->setLinkage(GlobalValue::InternalLinkage); 1930 // Simplify the initializer. 1931 if (GV->hasInitializer()) 1932 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) { 1933 TargetData *TD = getAnalysisIfAvailable<TargetData>(); 1934 Constant *New = ConstantFoldConstantExpression(CE, TD); 1935 if (New && New != CE) 1936 GV->setInitializer(New); 1937 } 1938 1939 Changed |= ProcessGlobal(GV, GVI); 1940 } 1941 return Changed; 1942} 1943 1944/// FindGlobalCtors - Find the llvm.global_ctors list, verifying that all 1945/// initializers have an init priority of 65535. 1946GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) { 1947 GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors"); 1948 if (GV == 0) return 0; 1949 1950 // Verify that the initializer is simple enough for us to handle. We are 1951 // only allowed to optimize the initializer if it is unique. 1952 if (!GV->hasUniqueInitializer()) return 0; 1953 1954 if (isa<ConstantAggregateZero>(GV->getInitializer())) 1955 return GV; 1956 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer()); 1957 1958 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) { 1959 if (isa<ConstantAggregateZero>(*i)) 1960 continue; 1961 ConstantStruct *CS = cast<ConstantStruct>(*i); 1962 if (isa<ConstantPointerNull>(CS->getOperand(1))) 1963 continue; 1964 1965 // Must have a function or null ptr. 1966 if (!isa<Function>(CS->getOperand(1))) 1967 return 0; 1968 1969 // Init priority must be standard. 1970 ConstantInt *CI = cast<ConstantInt>(CS->getOperand(0)); 1971 if (CI->getZExtValue() != 65535) 1972 return 0; 1973 } 1974 1975 return GV; 1976} 1977 1978/// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand, 1979/// return a list of the functions and null terminator as a vector. 1980static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) { 1981 if (GV->getInitializer()->isNullValue()) 1982 return std::vector<Function*>(); 1983 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer()); 1984 std::vector<Function*> Result; 1985 Result.reserve(CA->getNumOperands()); 1986 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) { 1987 ConstantStruct *CS = cast<ConstantStruct>(*i); 1988 Result.push_back(dyn_cast<Function>(CS->getOperand(1))); 1989 } 1990 return Result; 1991} 1992 1993/// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the 1994/// specified array, returning the new global to use. 1995static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL, 1996 const std::vector<Function*> &Ctors) { 1997 // If we made a change, reassemble the initializer list. 1998 Constant *CSVals[2]; 1999 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 65535); 2000 CSVals[1] = 0; 2001 2002 StructType *StructTy = 2003 cast <StructType>( 2004 cast<ArrayType>(GCL->getType()->getElementType())->getElementType()); 2005 2006 // Create the new init list. 2007 std::vector<Constant*> CAList; 2008 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) { 2009 if (Ctors[i]) { 2010 CSVals[1] = Ctors[i]; 2011 } else { 2012 Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()), 2013 false); 2014 PointerType *PFTy = PointerType::getUnqual(FTy); 2015 CSVals[1] = Constant::getNullValue(PFTy); 2016 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 2017 0x7fffffff); 2018 } 2019 CAList.push_back(ConstantStruct::get(StructTy, CSVals)); 2020 } 2021 2022 // Create the array initializer. 2023 Constant *CA = ConstantArray::get(ArrayType::get(StructTy, 2024 CAList.size()), CAList); 2025 2026 // If we didn't change the number of elements, don't create a new GV. 2027 if (CA->getType() == GCL->getInitializer()->getType()) { 2028 GCL->setInitializer(CA); 2029 return GCL; 2030 } 2031 2032 // Create the new global and insert it next to the existing list. 2033 GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(), 2034 GCL->getLinkage(), CA, "", 2035 GCL->isThreadLocal()); 2036 GCL->getParent()->getGlobalList().insert(GCL, NGV); 2037 NGV->takeName(GCL); 2038 2039 // Nuke the old list, replacing any uses with the new one. 2040 if (!GCL->use_empty()) { 2041 Constant *V = NGV; 2042 if (V->getType() != GCL->getType()) 2043 V = ConstantExpr::getBitCast(V, GCL->getType()); 2044 GCL->replaceAllUsesWith(V); 2045 } 2046 GCL->eraseFromParent(); 2047 2048 if (Ctors.size()) 2049 return NGV; 2050 else 2051 return 0; 2052} 2053 2054 2055static Constant *getVal(DenseMap<Value*, Constant*> &ComputedValues, Value *V) { 2056 if (Constant *CV = dyn_cast<Constant>(V)) return CV; 2057 Constant *R = ComputedValues[V]; 2058 assert(R && "Reference to an uncomputed value!"); 2059 return R; 2060} 2061 2062static inline bool 2063isSimpleEnoughValueToCommit(Constant *C, 2064 SmallPtrSet<Constant*, 8> &SimpleConstants); 2065 2066 2067/// isSimpleEnoughValueToCommit - Return true if the specified constant can be 2068/// handled by the code generator. We don't want to generate something like: 2069/// void *X = &X/42; 2070/// because the code generator doesn't have a relocation that can handle that. 2071/// 2072/// This function should be called if C was not found (but just got inserted) 2073/// in SimpleConstants to avoid having to rescan the same constants all the 2074/// time. 2075static bool isSimpleEnoughValueToCommitHelper(Constant *C, 2076 SmallPtrSet<Constant*, 8> &SimpleConstants) { 2077 // Simple integer, undef, constant aggregate zero, global addresses, etc are 2078 // all supported. 2079 if (C->getNumOperands() == 0 || isa<BlockAddress>(C) || 2080 isa<GlobalValue>(C)) 2081 return true; 2082 2083 // Aggregate values are safe if all their elements are. 2084 if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) || 2085 isa<ConstantVector>(C)) { 2086 for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) { 2087 Constant *Op = cast<Constant>(C->getOperand(i)); 2088 if (!isSimpleEnoughValueToCommit(Op, SimpleConstants)) 2089 return false; 2090 } 2091 return true; 2092 } 2093 2094 // We don't know exactly what relocations are allowed in constant expressions, 2095 // so we allow &global+constantoffset, which is safe and uniformly supported 2096 // across targets. 2097 ConstantExpr *CE = cast<ConstantExpr>(C); 2098 switch (CE->getOpcode()) { 2099 case Instruction::BitCast: 2100 case Instruction::IntToPtr: 2101 case Instruction::PtrToInt: 2102 // These casts are always fine if the casted value is. 2103 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants); 2104 2105 // GEP is fine if it is simple + constant offset. 2106 case Instruction::GetElementPtr: 2107 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) 2108 if (!isa<ConstantInt>(CE->getOperand(i))) 2109 return false; 2110 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants); 2111 2112 case Instruction::Add: 2113 // We allow simple+cst. 2114 if (!isa<ConstantInt>(CE->getOperand(1))) 2115 return false; 2116 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants); 2117 } 2118 return false; 2119} 2120 2121static inline bool 2122isSimpleEnoughValueToCommit(Constant *C, 2123 SmallPtrSet<Constant*, 8> &SimpleConstants) { 2124 // If we already checked this constant, we win. 2125 if (!SimpleConstants.insert(C)) return true; 2126 // Check the constant. 2127 return isSimpleEnoughValueToCommitHelper(C, SimpleConstants); 2128} 2129 2130 2131/// isSimpleEnoughPointerToCommit - Return true if this constant is simple 2132/// enough for us to understand. In particular, if it is a cast to anything 2133/// other than from one pointer type to another pointer type, we punt. 2134/// We basically just support direct accesses to globals and GEP's of 2135/// globals. This should be kept up to date with CommitValueTo. 2136static bool isSimpleEnoughPointerToCommit(Constant *C) { 2137 // Conservatively, avoid aggregate types. This is because we don't 2138 // want to worry about them partially overlapping other stores. 2139 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType()) 2140 return false; 2141 2142 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) 2143 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or 2144 // external globals. 2145 return GV->hasUniqueInitializer(); 2146 2147 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) { 2148 // Handle a constantexpr gep. 2149 if (CE->getOpcode() == Instruction::GetElementPtr && 2150 isa<GlobalVariable>(CE->getOperand(0)) && 2151 cast<GEPOperator>(CE)->isInBounds()) { 2152 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2153 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or 2154 // external globals. 2155 if (!GV->hasUniqueInitializer()) 2156 return false; 2157 2158 // The first index must be zero. 2159 ConstantInt *CI = dyn_cast<ConstantInt>(*llvm::next(CE->op_begin())); 2160 if (!CI || !CI->isZero()) return false; 2161 2162 // The remaining indices must be compile-time known integers within the 2163 // notional bounds of the corresponding static array types. 2164 if (!CE->isGEPWithNoNotionalOverIndexing()) 2165 return false; 2166 2167 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2168 2169 // A constantexpr bitcast from a pointer to another pointer is a no-op, 2170 // and we know how to evaluate it by moving the bitcast from the pointer 2171 // operand to the value operand. 2172 } else if (CE->getOpcode() == Instruction::BitCast && 2173 isa<GlobalVariable>(CE->getOperand(0))) { 2174 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or 2175 // external globals. 2176 return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer(); 2177 } 2178 } 2179 2180 return false; 2181} 2182 2183/// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global 2184/// initializer. This returns 'Init' modified to reflect 'Val' stored into it. 2185/// At this point, the GEP operands of Addr [0, OpNo) have been stepped into. 2186static Constant *EvaluateStoreInto(Constant *Init, Constant *Val, 2187 ConstantExpr *Addr, unsigned OpNo) { 2188 // Base case of the recursion. 2189 if (OpNo == Addr->getNumOperands()) { 2190 assert(Val->getType() == Init->getType() && "Type mismatch!"); 2191 return Val; 2192 } 2193 2194 std::vector<Constant*> Elts; 2195 if (StructType *STy = dyn_cast<StructType>(Init->getType())) { 2196 2197 // Break up the constant into its elements. 2198 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) { 2199 for (User::op_iterator i = CS->op_begin(), e = CS->op_end(); i != e; ++i) 2200 Elts.push_back(cast<Constant>(*i)); 2201 } else if (isa<ConstantAggregateZero>(Init)) { 2202 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2203 Elts.push_back(Constant::getNullValue(STy->getElementType(i))); 2204 } else if (isa<UndefValue>(Init)) { 2205 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2206 Elts.push_back(UndefValue::get(STy->getElementType(i))); 2207 } else { 2208 llvm_unreachable("This code is out of sync with " 2209 " ConstantFoldLoadThroughGEPConstantExpr"); 2210 } 2211 2212 // Replace the element that we are supposed to. 2213 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo)); 2214 unsigned Idx = CU->getZExtValue(); 2215 assert(Idx < STy->getNumElements() && "Struct index out of range!"); 2216 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1); 2217 2218 // Return the modified struct. 2219 return ConstantStruct::get(STy, Elts); 2220 } 2221 2222 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo)); 2223 SequentialType *InitTy = cast<SequentialType>(Init->getType()); 2224 2225 uint64_t NumElts; 2226 if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy)) 2227 NumElts = ATy->getNumElements(); 2228 else 2229 NumElts = cast<VectorType>(InitTy)->getNumElements(); 2230 2231 // Break up the array into elements. 2232 if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) { 2233 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 2234 Elts.push_back(cast<Constant>(*i)); 2235 } else if (ConstantVector *CV = dyn_cast<ConstantVector>(Init)) { 2236 for (User::op_iterator i = CV->op_begin(), e = CV->op_end(); i != e; ++i) 2237 Elts.push_back(cast<Constant>(*i)); 2238 } else if (isa<ConstantAggregateZero>(Init)) { 2239 Elts.assign(NumElts, Constant::getNullValue(InitTy->getElementType())); 2240 } else { 2241 assert(isa<UndefValue>(Init) && "This code is out of sync with " 2242 " ConstantFoldLoadThroughGEPConstantExpr"); 2243 Elts.assign(NumElts, UndefValue::get(InitTy->getElementType())); 2244 } 2245 2246 assert(CI->getZExtValue() < NumElts); 2247 Elts[CI->getZExtValue()] = 2248 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1); 2249 2250 if (Init->getType()->isArrayTy()) 2251 return ConstantArray::get(cast<ArrayType>(InitTy), Elts); 2252 return ConstantVector::get(Elts); 2253} 2254 2255/// CommitValueTo - We have decided that Addr (which satisfies the predicate 2256/// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen. 2257static void CommitValueTo(Constant *Val, Constant *Addr) { 2258 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) { 2259 assert(GV->hasInitializer()); 2260 GV->setInitializer(Val); 2261 return; 2262 } 2263 2264 ConstantExpr *CE = cast<ConstantExpr>(Addr); 2265 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2266 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2)); 2267} 2268 2269/// ComputeLoadResult - Return the value that would be computed by a load from 2270/// P after the stores reflected by 'memory' have been performed. If we can't 2271/// decide, return null. 2272static Constant *ComputeLoadResult(Constant *P, 2273 const DenseMap<Constant*, Constant*> &Memory) { 2274 // If this memory location has been recently stored, use the stored value: it 2275 // is the most up-to-date. 2276 DenseMap<Constant*, Constant*>::const_iterator I = Memory.find(P); 2277 if (I != Memory.end()) return I->second; 2278 2279 // Access it. 2280 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) { 2281 if (GV->hasDefinitiveInitializer()) 2282 return GV->getInitializer(); 2283 return 0; 2284 } 2285 2286 // Handle a constantexpr getelementptr. 2287 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) 2288 if (CE->getOpcode() == Instruction::GetElementPtr && 2289 isa<GlobalVariable>(CE->getOperand(0))) { 2290 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2291 if (GV->hasDefinitiveInitializer()) 2292 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2293 } 2294 2295 return 0; // don't know how to evaluate. 2296} 2297 2298/// EvaluateFunction - Evaluate a call to function F, returning true if 2299/// successful, false if we can't evaluate it. ActualArgs contains the formal 2300/// arguments for the function. 2301static bool EvaluateFunction(Function *F, Constant *&RetVal, 2302 const SmallVectorImpl<Constant*> &ActualArgs, 2303 std::vector<Function*> &CallStack, 2304 DenseMap<Constant*, Constant*> &MutatedMemory, 2305 std::vector<GlobalVariable*> &AllocaTmps, 2306 SmallPtrSet<Constant*, 8> &SimpleConstants, 2307 const TargetData *TD) { 2308 // Check to see if this function is already executing (recursion). If so, 2309 // bail out. TODO: we might want to accept limited recursion. 2310 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end()) 2311 return false; 2312 2313 CallStack.push_back(F); 2314 2315 /// Values - As we compute SSA register values, we store their contents here. 2316 DenseMap<Value*, Constant*> Values; 2317 2318 // Initialize arguments to the incoming values specified. 2319 unsigned ArgNo = 0; 2320 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E; 2321 ++AI, ++ArgNo) 2322 Values[AI] = ActualArgs[ArgNo]; 2323 2324 /// ExecutedBlocks - We only handle non-looping, non-recursive code. As such, 2325 /// we can only evaluate any one basic block at most once. This set keeps 2326 /// track of what we have executed so we can detect recursive cases etc. 2327 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks; 2328 2329 // CurInst - The current instruction we're evaluating. 2330 BasicBlock::iterator CurInst = F->begin()->begin(); 2331 2332 // This is the main evaluation loop. 2333 while (1) { 2334 Constant *InstResult = 0; 2335 2336 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) { 2337 if (!SI->isSimple()) return false; // no volatile/atomic accesses. 2338 Constant *Ptr = getVal(Values, SI->getOperand(1)); 2339 if (!isSimpleEnoughPointerToCommit(Ptr)) 2340 // If this is too complex for us to commit, reject it. 2341 return false; 2342 2343 Constant *Val = getVal(Values, SI->getOperand(0)); 2344 2345 // If this might be too difficult for the backend to handle (e.g. the addr 2346 // of one global variable divided by another) then we can't commit it. 2347 if (!isSimpleEnoughValueToCommit(Val, SimpleConstants)) 2348 return false; 2349 2350 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) 2351 if (CE->getOpcode() == Instruction::BitCast) { 2352 // If we're evaluating a store through a bitcast, then we need 2353 // to pull the bitcast off the pointer type and push it onto the 2354 // stored value. 2355 Ptr = CE->getOperand(0); 2356 2357 Type *NewTy=cast<PointerType>(Ptr->getType())->getElementType(); 2358 2359 // In order to push the bitcast onto the stored value, a bitcast 2360 // from NewTy to Val's type must be legal. If it's not, we can try 2361 // introspecting NewTy to find a legal conversion. 2362 while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) { 2363 // If NewTy is a struct, we can convert the pointer to the struct 2364 // into a pointer to its first member. 2365 // FIXME: This could be extended to support arrays as well. 2366 if (StructType *STy = dyn_cast<StructType>(NewTy)) { 2367 NewTy = STy->getTypeAtIndex(0U); 2368 2369 IntegerType *IdxTy =IntegerType::get(NewTy->getContext(), 32); 2370 Constant *IdxZero = ConstantInt::get(IdxTy, 0, false); 2371 Constant * const IdxList[] = {IdxZero, IdxZero}; 2372 2373 Ptr = ConstantExpr::getGetElementPtr(Ptr, IdxList); 2374 2375 // If we can't improve the situation by introspecting NewTy, 2376 // we have to give up. 2377 } else { 2378 return 0; 2379 } 2380 } 2381 2382 // If we found compatible types, go ahead and push the bitcast 2383 // onto the stored value. 2384 Val = ConstantExpr::getBitCast(Val, NewTy); 2385 } 2386 2387 MutatedMemory[Ptr] = Val; 2388 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) { 2389 InstResult = ConstantExpr::get(BO->getOpcode(), 2390 getVal(Values, BO->getOperand(0)), 2391 getVal(Values, BO->getOperand(1))); 2392 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) { 2393 InstResult = ConstantExpr::getCompare(CI->getPredicate(), 2394 getVal(Values, CI->getOperand(0)), 2395 getVal(Values, CI->getOperand(1))); 2396 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) { 2397 InstResult = ConstantExpr::getCast(CI->getOpcode(), 2398 getVal(Values, CI->getOperand(0)), 2399 CI->getType()); 2400 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) { 2401 InstResult = ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)), 2402 getVal(Values, SI->getOperand(1)), 2403 getVal(Values, SI->getOperand(2))); 2404 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) { 2405 Constant *P = getVal(Values, GEP->getOperand(0)); 2406 SmallVector<Constant*, 8> GEPOps; 2407 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); 2408 i != e; ++i) 2409 GEPOps.push_back(getVal(Values, *i)); 2410 InstResult = 2411 ConstantExpr::getGetElementPtr(P, GEPOps, 2412 cast<GEPOperator>(GEP)->isInBounds()); 2413 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) { 2414 if (!LI->isSimple()) return false; // no volatile/atomic accesses. 2415 InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)), 2416 MutatedMemory); 2417 if (InstResult == 0) return false; // Could not evaluate load. 2418 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) { 2419 if (AI->isArrayAllocation()) return false; // Cannot handle array allocs. 2420 Type *Ty = AI->getType()->getElementType(); 2421 AllocaTmps.push_back(new GlobalVariable(Ty, false, 2422 GlobalValue::InternalLinkage, 2423 UndefValue::get(Ty), 2424 AI->getName())); 2425 InstResult = AllocaTmps.back(); 2426 } else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) { 2427 2428 // Debug info can safely be ignored here. 2429 if (isa<DbgInfoIntrinsic>(CI)) { 2430 ++CurInst; 2431 continue; 2432 } 2433 2434 // Cannot handle inline asm. 2435 if (isa<InlineAsm>(CI->getCalledValue())) return false; 2436 2437 if (MemSetInst *MSI = dyn_cast<MemSetInst>(CI)) { 2438 if (MSI->isVolatile()) return false; 2439 Constant *Ptr = getVal(Values, MSI->getDest()); 2440 Constant *Val = getVal(Values, MSI->getValue()); 2441 Constant *DestVal = ComputeLoadResult(getVal(Values, Ptr), 2442 MutatedMemory); 2443 if (Val->isNullValue() && DestVal && DestVal->isNullValue()) { 2444 // This memset is a no-op. 2445 ++CurInst; 2446 continue; 2447 } 2448 return false; 2449 } 2450 2451 // Resolve function pointers. 2452 Function *Callee = dyn_cast<Function>(getVal(Values, 2453 CI->getCalledValue())); 2454 if (!Callee) return false; // Cannot resolve. 2455 2456 SmallVector<Constant*, 8> Formals; 2457 CallSite CS(CI); 2458 for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); 2459 i != e; ++i) 2460 Formals.push_back(getVal(Values, *i)); 2461 2462 if (Callee->isDeclaration()) { 2463 // If this is a function we can constant fold, do it. 2464 if (Constant *C = ConstantFoldCall(Callee, Formals)) { 2465 InstResult = C; 2466 } else { 2467 return false; 2468 } 2469 } else { 2470 if (Callee->getFunctionType()->isVarArg()) 2471 return false; 2472 2473 Constant *RetVal; 2474 // Execute the call, if successful, use the return value. 2475 if (!EvaluateFunction(Callee, RetVal, Formals, CallStack, 2476 MutatedMemory, AllocaTmps, SimpleConstants, TD)) 2477 return false; 2478 InstResult = RetVal; 2479 } 2480 } else if (isa<TerminatorInst>(CurInst)) { 2481 BasicBlock *NewBB = 0; 2482 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) { 2483 if (BI->isUnconditional()) { 2484 NewBB = BI->getSuccessor(0); 2485 } else { 2486 ConstantInt *Cond = 2487 dyn_cast<ConstantInt>(getVal(Values, BI->getCondition())); 2488 if (!Cond) return false; // Cannot determine. 2489 2490 NewBB = BI->getSuccessor(!Cond->getZExtValue()); 2491 } 2492 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) { 2493 ConstantInt *Val = 2494 dyn_cast<ConstantInt>(getVal(Values, SI->getCondition())); 2495 if (!Val) return false; // Cannot determine. 2496 NewBB = SI->getSuccessor(SI->findCaseValue(Val)); 2497 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) { 2498 Value *Val = getVal(Values, IBI->getAddress())->stripPointerCasts(); 2499 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val)) 2500 NewBB = BA->getBasicBlock(); 2501 else 2502 return false; // Cannot determine. 2503 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) { 2504 if (RI->getNumOperands()) 2505 RetVal = getVal(Values, RI->getOperand(0)); 2506 2507 CallStack.pop_back(); // return from fn. 2508 return true; // We succeeded at evaluating this ctor! 2509 } else { 2510 // invoke, unwind, resume, unreachable. 2511 return false; // Cannot handle this terminator. 2512 } 2513 2514 // Okay, we succeeded in evaluating this control flow. See if we have 2515 // executed the new block before. If so, we have a looping function, 2516 // which we cannot evaluate in reasonable time. 2517 if (!ExecutedBlocks.insert(NewBB)) 2518 return false; // looped! 2519 2520 // Okay, we have never been in this block before. Check to see if there 2521 // are any PHI nodes. If so, evaluate them with information about where 2522 // we came from. 2523 BasicBlock *OldBB = CurInst->getParent(); 2524 CurInst = NewBB->begin(); 2525 PHINode *PN; 2526 for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst) 2527 Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB)); 2528 2529 // Do NOT increment CurInst. We know that the terminator had no value. 2530 continue; 2531 } else { 2532 // Did not know how to evaluate this! 2533 return false; 2534 } 2535 2536 if (!CurInst->use_empty()) { 2537 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult)) 2538 InstResult = ConstantFoldConstantExpression(CE, TD); 2539 2540 Values[CurInst] = InstResult; 2541 } 2542 2543 // Advance program counter. 2544 ++CurInst; 2545 } 2546} 2547 2548/// EvaluateStaticConstructor - Evaluate static constructors in the function, if 2549/// we can. Return true if we can, false otherwise. 2550static bool EvaluateStaticConstructor(Function *F, const TargetData *TD) { 2551 /// MutatedMemory - For each store we execute, we update this map. Loads 2552 /// check this to get the most up-to-date value. If evaluation is successful, 2553 /// this state is committed to the process. 2554 DenseMap<Constant*, Constant*> MutatedMemory; 2555 2556 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable 2557 /// to represent its body. This vector is needed so we can delete the 2558 /// temporary globals when we are done. 2559 std::vector<GlobalVariable*> AllocaTmps; 2560 2561 /// CallStack - This is used to detect recursion. In pathological situations 2562 /// we could hit exponential behavior, but at least there is nothing 2563 /// unbounded. 2564 std::vector<Function*> CallStack; 2565 2566 /// SimpleConstants - These are constants we have checked and know to be 2567 /// simple enough to live in a static initializer of a global. 2568 SmallPtrSet<Constant*, 8> SimpleConstants; 2569 2570 // Call the function. 2571 Constant *RetValDummy; 2572 bool EvalSuccess = EvaluateFunction(F, RetValDummy, 2573 SmallVector<Constant*, 0>(), CallStack, 2574 MutatedMemory, AllocaTmps, 2575 SimpleConstants, TD); 2576 2577 if (EvalSuccess) { 2578 // We succeeded at evaluation: commit the result. 2579 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" 2580 << F->getName() << "' to " << MutatedMemory.size() 2581 << " stores.\n"); 2582 for (DenseMap<Constant*, Constant*>::iterator I = MutatedMemory.begin(), 2583 E = MutatedMemory.end(); I != E; ++I) 2584 CommitValueTo(I->second, I->first); 2585 } 2586 2587 // At this point, we are done interpreting. If we created any 'alloca' 2588 // temporaries, release them now. 2589 while (!AllocaTmps.empty()) { 2590 GlobalVariable *Tmp = AllocaTmps.back(); 2591 AllocaTmps.pop_back(); 2592 2593 // If there are still users of the alloca, the program is doing something 2594 // silly, e.g. storing the address of the alloca somewhere and using it 2595 // later. Since this is undefined, we'll just make it be null. 2596 if (!Tmp->use_empty()) 2597 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType())); 2598 delete Tmp; 2599 } 2600 2601 return EvalSuccess; 2602} 2603 2604 2605 2606/// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible. 2607/// Return true if anything changed. 2608bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) { 2609 std::vector<Function*> Ctors = ParseGlobalCtors(GCL); 2610 bool MadeChange = false; 2611 if (Ctors.empty()) return false; 2612 2613 const TargetData *TD = getAnalysisIfAvailable<TargetData>(); 2614 // Loop over global ctors, optimizing them when we can. 2615 for (unsigned i = 0; i != Ctors.size(); ++i) { 2616 Function *F = Ctors[i]; 2617 // Found a null terminator in the middle of the list, prune off the rest of 2618 // the list. 2619 if (F == 0) { 2620 if (i != Ctors.size()-1) { 2621 Ctors.resize(i+1); 2622 MadeChange = true; 2623 } 2624 break; 2625 } 2626 2627 // We cannot simplify external ctor functions. 2628 if (F->empty()) continue; 2629 2630 // If we can evaluate the ctor at compile time, do. 2631 if (EvaluateStaticConstructor(F, TD)) { 2632 Ctors.erase(Ctors.begin()+i); 2633 MadeChange = true; 2634 --i; 2635 ++NumCtorsEvaluated; 2636 continue; 2637 } 2638 } 2639 2640 if (!MadeChange) return false; 2641 2642 GCL = InstallGlobalCtors(GCL, Ctors); 2643 return true; 2644} 2645 2646bool GlobalOpt::OptimizeGlobalAliases(Module &M) { 2647 bool Changed = false; 2648 2649 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); 2650 I != E;) { 2651 Module::alias_iterator J = I++; 2652 // Aliases without names cannot be referenced outside this module. 2653 if (!J->hasName() && !J->isDeclaration()) 2654 J->setLinkage(GlobalValue::InternalLinkage); 2655 // If the aliasee may change at link time, nothing can be done - bail out. 2656 if (J->mayBeOverridden()) 2657 continue; 2658 2659 Constant *Aliasee = J->getAliasee(); 2660 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts()); 2661 Target->removeDeadConstantUsers(); 2662 bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse(); 2663 2664 // Make all users of the alias use the aliasee instead. 2665 if (!J->use_empty()) { 2666 J->replaceAllUsesWith(Aliasee); 2667 ++NumAliasesResolved; 2668 Changed = true; 2669 } 2670 2671 // If the alias is externally visible, we may still be able to simplify it. 2672 if (!J->hasLocalLinkage()) { 2673 // If the aliasee has internal linkage, give it the name and linkage 2674 // of the alias, and delete the alias. This turns: 2675 // define internal ... @f(...) 2676 // @a = alias ... @f 2677 // into: 2678 // define ... @a(...) 2679 if (!Target->hasLocalLinkage()) 2680 continue; 2681 2682 // Do not perform the transform if multiple aliases potentially target the 2683 // aliasee. This check also ensures that it is safe to replace the section 2684 // and other attributes of the aliasee with those of the alias. 2685 if (!hasOneUse) 2686 continue; 2687 2688 // Give the aliasee the name, linkage and other attributes of the alias. 2689 Target->takeName(J); 2690 Target->setLinkage(J->getLinkage()); 2691 Target->GlobalValue::copyAttributesFrom(J); 2692 } 2693 2694 // Delete the alias. 2695 M.getAliasList().erase(J); 2696 ++NumAliasesRemoved; 2697 Changed = true; 2698 } 2699 2700 return Changed; 2701} 2702 2703static Function *FindCXAAtExit(Module &M) { 2704 Function *Fn = M.getFunction("__cxa_atexit"); 2705 2706 if (!Fn) 2707 return 0; 2708 2709 FunctionType *FTy = Fn->getFunctionType(); 2710 2711 // Checking that the function has the right return type, the right number of 2712 // parameters and that they all have pointer types should be enough. 2713 if (!FTy->getReturnType()->isIntegerTy() || 2714 FTy->getNumParams() != 3 || 2715 !FTy->getParamType(0)->isPointerTy() || 2716 !FTy->getParamType(1)->isPointerTy() || 2717 !FTy->getParamType(2)->isPointerTy()) 2718 return 0; 2719 2720 return Fn; 2721} 2722 2723/// cxxDtorIsEmpty - Returns whether the given function is an empty C++ 2724/// destructor and can therefore be eliminated. 2725/// Note that we assume that other optimization passes have already simplified 2726/// the code so we only look for a function with a single basic block, where 2727/// the only allowed instructions are 'ret' or 'call' to empty C++ dtor. 2728static bool cxxDtorIsEmpty(const Function &Fn, 2729 SmallPtrSet<const Function *, 8> &CalledFunctions) { 2730 // FIXME: We could eliminate C++ destructors if they're readonly/readnone and 2731 // nounwind, but that doesn't seem worth doing. 2732 if (Fn.isDeclaration()) 2733 return false; 2734 2735 if (++Fn.begin() != Fn.end()) 2736 return false; 2737 2738 const BasicBlock &EntryBlock = Fn.getEntryBlock(); 2739 for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end(); 2740 I != E; ++I) { 2741 if (const CallInst *CI = dyn_cast<CallInst>(I)) { 2742 // Ignore debug intrinsics. 2743 if (isa<DbgInfoIntrinsic>(CI)) 2744 continue; 2745 2746 const Function *CalledFn = CI->getCalledFunction(); 2747 2748 if (!CalledFn) 2749 return false; 2750 2751 SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions); 2752 2753 // Don't treat recursive functions as empty. 2754 if (!NewCalledFunctions.insert(CalledFn)) 2755 return false; 2756 2757 if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions)) 2758 return false; 2759 } else if (isa<ReturnInst>(*I)) 2760 return true; 2761 else 2762 return false; 2763 } 2764 2765 return false; 2766} 2767 2768bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) { 2769 /// Itanium C++ ABI p3.3.5: 2770 /// 2771 /// After constructing a global (or local static) object, that will require 2772 /// destruction on exit, a termination function is registered as follows: 2773 /// 2774 /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d ); 2775 /// 2776 /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the 2777 /// call f(p) when DSO d is unloaded, before all such termination calls 2778 /// registered before this one. It returns zero if registration is 2779 /// successful, nonzero on failure. 2780 2781 // This pass will look for calls to __cxa_atexit where the function is trivial 2782 // and remove them. 2783 bool Changed = false; 2784 2785 for (Function::use_iterator I = CXAAtExitFn->use_begin(), 2786 E = CXAAtExitFn->use_end(); I != E;) { 2787 // We're only interested in calls. Theoretically, we could handle invoke 2788 // instructions as well, but neither llvm-gcc nor clang generate invokes 2789 // to __cxa_atexit. 2790 CallInst *CI = dyn_cast<CallInst>(*I++); 2791 if (!CI) 2792 continue; 2793 2794 Function *DtorFn = 2795 dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts()); 2796 if (!DtorFn) 2797 continue; 2798 2799 SmallPtrSet<const Function *, 8> CalledFunctions; 2800 if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions)) 2801 continue; 2802 2803 // Just remove the call. 2804 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType())); 2805 CI->eraseFromParent(); 2806 2807 ++NumCXXDtorsRemoved; 2808 2809 Changed |= true; 2810 } 2811 2812 return Changed; 2813} 2814 2815bool GlobalOpt::runOnModule(Module &M) { 2816 bool Changed = false; 2817 2818 // Try to find the llvm.globalctors list. 2819 GlobalVariable *GlobalCtors = FindGlobalCtors(M); 2820 2821 Function *CXAAtExitFn = FindCXAAtExit(M); 2822 2823 bool LocalChange = true; 2824 while (LocalChange) { 2825 LocalChange = false; 2826 2827 // Delete functions that are trivially dead, ccc -> fastcc 2828 LocalChange |= OptimizeFunctions(M); 2829 2830 // Optimize global_ctors list. 2831 if (GlobalCtors) 2832 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors); 2833 2834 // Optimize non-address-taken globals. 2835 LocalChange |= OptimizeGlobalVars(M); 2836 2837 // Resolve aliases, when possible. 2838 LocalChange |= OptimizeGlobalAliases(M); 2839 2840 // Try to remove trivial global destructors. 2841 if (CXAAtExitFn) 2842 LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn); 2843 2844 Changed |= LocalChange; 2845 } 2846 2847 // TODO: Move all global ctors functions to the end of the module for code 2848 // layout. 2849 2850 return Changed; 2851} 2852