GlobalOpt.cpp revision dce4a407a24b04eebc6a376f8e62b41aaa7b071f
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#include "llvm/Transforms/IPO.h" 17#include "llvm/ADT/DenseMap.h" 18#include "llvm/ADT/STLExtras.h" 19#include "llvm/ADT/SmallPtrSet.h" 20#include "llvm/ADT/SmallVector.h" 21#include "llvm/ADT/Statistic.h" 22#include "llvm/Analysis/ConstantFolding.h" 23#include "llvm/Analysis/MemoryBuiltins.h" 24#include "llvm/IR/CallSite.h" 25#include "llvm/IR/CallingConv.h" 26#include "llvm/IR/Constants.h" 27#include "llvm/IR/DataLayout.h" 28#include "llvm/IR/DerivedTypes.h" 29#include "llvm/IR/GetElementPtrTypeIterator.h" 30#include "llvm/IR/Instructions.h" 31#include "llvm/IR/IntrinsicInst.h" 32#include "llvm/IR/Module.h" 33#include "llvm/IR/Operator.h" 34#include "llvm/IR/ValueHandle.h" 35#include "llvm/Pass.h" 36#include "llvm/Support/Debug.h" 37#include "llvm/Support/ErrorHandling.h" 38#include "llvm/Support/MathExtras.h" 39#include "llvm/Support/raw_ostream.h" 40#include "llvm/Target/TargetLibraryInfo.h" 41#include "llvm/Transforms/Utils/CtorUtils.h" 42#include "llvm/Transforms/Utils/GlobalStatus.h" 43#include "llvm/Transforms/Utils/ModuleUtils.h" 44#include <algorithm> 45#include <deque> 46using namespace llvm; 47 48#define DEBUG_TYPE "globalopt" 49 50STATISTIC(NumMarked , "Number of globals marked constant"); 51STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr"); 52STATISTIC(NumSRA , "Number of aggregate globals broken into scalars"); 53STATISTIC(NumHeapSRA , "Number of heap objects SRA'd"); 54STATISTIC(NumSubstitute,"Number of globals with initializers stored into them"); 55STATISTIC(NumDeleted , "Number of globals deleted"); 56STATISTIC(NumFnDeleted , "Number of functions deleted"); 57STATISTIC(NumGlobUses , "Number of global uses devirtualized"); 58STATISTIC(NumLocalized , "Number of globals localized"); 59STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans"); 60STATISTIC(NumFastCallFns , "Number of functions converted to fastcc"); 61STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated"); 62STATISTIC(NumNestRemoved , "Number of nest attributes removed"); 63STATISTIC(NumAliasesResolved, "Number of global aliases resolved"); 64STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated"); 65STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed"); 66 67namespace { 68 struct GlobalOpt : public ModulePass { 69 void getAnalysisUsage(AnalysisUsage &AU) const override { 70 AU.addRequired<TargetLibraryInfo>(); 71 } 72 static char ID; // Pass identification, replacement for typeid 73 GlobalOpt() : ModulePass(ID) { 74 initializeGlobalOptPass(*PassRegistry::getPassRegistry()); 75 } 76 77 bool runOnModule(Module &M) override; 78 79 private: 80 bool OptimizeFunctions(Module &M); 81 bool OptimizeGlobalVars(Module &M); 82 bool OptimizeGlobalAliases(Module &M); 83 bool ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI); 84 bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI, 85 const GlobalStatus &GS); 86 bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn); 87 88 const DataLayout *DL; 89 TargetLibraryInfo *TLI; 90 }; 91} 92 93char GlobalOpt::ID = 0; 94INITIALIZE_PASS_BEGIN(GlobalOpt, "globalopt", 95 "Global Variable Optimizer", false, false) 96INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) 97INITIALIZE_PASS_END(GlobalOpt, "globalopt", 98 "Global Variable Optimizer", false, false) 99 100ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); } 101 102/// isLeakCheckerRoot - Is this global variable possibly used by a leak checker 103/// as a root? If so, we might not really want to eliminate the stores to it. 104static bool isLeakCheckerRoot(GlobalVariable *GV) { 105 // A global variable is a root if it is a pointer, or could plausibly contain 106 // a pointer. There are two challenges; one is that we could have a struct 107 // the has an inner member which is a pointer. We recurse through the type to 108 // detect these (up to a point). The other is that we may actually be a union 109 // of a pointer and another type, and so our LLVM type is an integer which 110 // gets converted into a pointer, or our type is an [i8 x #] with a pointer 111 // potentially contained here. 112 113 if (GV->hasPrivateLinkage()) 114 return false; 115 116 SmallVector<Type *, 4> Types; 117 Types.push_back(cast<PointerType>(GV->getType())->getElementType()); 118 119 unsigned Limit = 20; 120 do { 121 Type *Ty = Types.pop_back_val(); 122 switch (Ty->getTypeID()) { 123 default: break; 124 case Type::PointerTyID: return true; 125 case Type::ArrayTyID: 126 case Type::VectorTyID: { 127 SequentialType *STy = cast<SequentialType>(Ty); 128 Types.push_back(STy->getElementType()); 129 break; 130 } 131 case Type::StructTyID: { 132 StructType *STy = cast<StructType>(Ty); 133 if (STy->isOpaque()) return true; 134 for (StructType::element_iterator I = STy->element_begin(), 135 E = STy->element_end(); I != E; ++I) { 136 Type *InnerTy = *I; 137 if (isa<PointerType>(InnerTy)) return true; 138 if (isa<CompositeType>(InnerTy)) 139 Types.push_back(InnerTy); 140 } 141 break; 142 } 143 } 144 if (--Limit == 0) return true; 145 } while (!Types.empty()); 146 return false; 147} 148 149/// Given a value that is stored to a global but never read, determine whether 150/// it's safe to remove the store and the chain of computation that feeds the 151/// store. 152static bool IsSafeComputationToRemove(Value *V, const TargetLibraryInfo *TLI) { 153 do { 154 if (isa<Constant>(V)) 155 return true; 156 if (!V->hasOneUse()) 157 return false; 158 if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) || 159 isa<GlobalValue>(V)) 160 return false; 161 if (isAllocationFn(V, TLI)) 162 return true; 163 164 Instruction *I = cast<Instruction>(V); 165 if (I->mayHaveSideEffects()) 166 return false; 167 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) { 168 if (!GEP->hasAllConstantIndices()) 169 return false; 170 } else if (I->getNumOperands() != 1) { 171 return false; 172 } 173 174 V = I->getOperand(0); 175 } while (1); 176} 177 178/// CleanupPointerRootUsers - This GV is a pointer root. Loop over all users 179/// of the global and clean up any that obviously don't assign the global a 180/// value that isn't dynamically allocated. 181/// 182static bool CleanupPointerRootUsers(GlobalVariable *GV, 183 const TargetLibraryInfo *TLI) { 184 // A brief explanation of leak checkers. The goal is to find bugs where 185 // pointers are forgotten, causing an accumulating growth in memory 186 // usage over time. The common strategy for leak checkers is to whitelist the 187 // memory pointed to by globals at exit. This is popular because it also 188 // solves another problem where the main thread of a C++ program may shut down 189 // before other threads that are still expecting to use those globals. To 190 // handle that case, we expect the program may create a singleton and never 191 // destroy it. 192 193 bool Changed = false; 194 195 // If Dead[n].first is the only use of a malloc result, we can delete its 196 // chain of computation and the store to the global in Dead[n].second. 197 SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead; 198 199 // Constants can't be pointers to dynamically allocated memory. 200 for (Value::user_iterator UI = GV->user_begin(), E = GV->user_end(); 201 UI != E;) { 202 User *U = *UI++; 203 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 204 Value *V = SI->getValueOperand(); 205 if (isa<Constant>(V)) { 206 Changed = true; 207 SI->eraseFromParent(); 208 } else if (Instruction *I = dyn_cast<Instruction>(V)) { 209 if (I->hasOneUse()) 210 Dead.push_back(std::make_pair(I, SI)); 211 } 212 } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) { 213 if (isa<Constant>(MSI->getValue())) { 214 Changed = true; 215 MSI->eraseFromParent(); 216 } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) { 217 if (I->hasOneUse()) 218 Dead.push_back(std::make_pair(I, MSI)); 219 } 220 } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) { 221 GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource()); 222 if (MemSrc && MemSrc->isConstant()) { 223 Changed = true; 224 MTI->eraseFromParent(); 225 } else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) { 226 if (I->hasOneUse()) 227 Dead.push_back(std::make_pair(I, MTI)); 228 } 229 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { 230 if (CE->use_empty()) { 231 CE->destroyConstant(); 232 Changed = true; 233 } 234 } else if (Constant *C = dyn_cast<Constant>(U)) { 235 if (isSafeToDestroyConstant(C)) { 236 C->destroyConstant(); 237 // This could have invalidated UI, start over from scratch. 238 Dead.clear(); 239 CleanupPointerRootUsers(GV, TLI); 240 return true; 241 } 242 } 243 } 244 245 for (int i = 0, e = Dead.size(); i != e; ++i) { 246 if (IsSafeComputationToRemove(Dead[i].first, TLI)) { 247 Dead[i].second->eraseFromParent(); 248 Instruction *I = Dead[i].first; 249 do { 250 if (isAllocationFn(I, TLI)) 251 break; 252 Instruction *J = dyn_cast<Instruction>(I->getOperand(0)); 253 if (!J) 254 break; 255 I->eraseFromParent(); 256 I = J; 257 } while (1); 258 I->eraseFromParent(); 259 } 260 } 261 262 return Changed; 263} 264 265/// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all 266/// users of the global, cleaning up the obvious ones. This is largely just a 267/// quick scan over the use list to clean up the easy and obvious cruft. This 268/// returns true if it made a change. 269static bool CleanupConstantGlobalUsers(Value *V, Constant *Init, 270 const DataLayout *DL, 271 TargetLibraryInfo *TLI) { 272 bool Changed = false; 273 // Note that we need to use a weak value handle for the worklist items. When 274 // we delete a constant array, we may also be holding pointer to one of its 275 // elements (or an element of one of its elements if we're dealing with an 276 // array of arrays) in the worklist. 277 SmallVector<WeakVH, 8> WorkList(V->user_begin(), V->user_end()); 278 while (!WorkList.empty()) { 279 Value *UV = WorkList.pop_back_val(); 280 if (!UV) 281 continue; 282 283 User *U = cast<User>(UV); 284 285 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 286 if (Init) { 287 // Replace the load with the initializer. 288 LI->replaceAllUsesWith(Init); 289 LI->eraseFromParent(); 290 Changed = true; 291 } 292 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 293 // Store must be unreachable or storing Init into the global. 294 SI->eraseFromParent(); 295 Changed = true; 296 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { 297 if (CE->getOpcode() == Instruction::GetElementPtr) { 298 Constant *SubInit = nullptr; 299 if (Init) 300 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); 301 Changed |= CleanupConstantGlobalUsers(CE, SubInit, DL, TLI); 302 } else if ((CE->getOpcode() == Instruction::BitCast && 303 CE->getType()->isPointerTy()) || 304 CE->getOpcode() == Instruction::AddrSpaceCast) { 305 // Pointer cast, delete any stores and memsets to the global. 306 Changed |= CleanupConstantGlobalUsers(CE, nullptr, DL, TLI); 307 } 308 309 if (CE->use_empty()) { 310 CE->destroyConstant(); 311 Changed = true; 312 } 313 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 314 // Do not transform "gepinst (gep constexpr (GV))" here, because forming 315 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold 316 // and will invalidate our notion of what Init is. 317 Constant *SubInit = nullptr; 318 if (!isa<ConstantExpr>(GEP->getOperand(0))) { 319 ConstantExpr *CE = 320 dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, DL, TLI)); 321 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr) 322 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); 323 324 // If the initializer is an all-null value and we have an inbounds GEP, 325 // we already know what the result of any load from that GEP is. 326 // TODO: Handle splats. 327 if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds()) 328 SubInit = Constant::getNullValue(GEP->getType()->getElementType()); 329 } 330 Changed |= CleanupConstantGlobalUsers(GEP, SubInit, DL, TLI); 331 332 if (GEP->use_empty()) { 333 GEP->eraseFromParent(); 334 Changed = true; 335 } 336 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv 337 if (MI->getRawDest() == V) { 338 MI->eraseFromParent(); 339 Changed = true; 340 } 341 342 } else if (Constant *C = dyn_cast<Constant>(U)) { 343 // If we have a chain of dead constantexprs or other things dangling from 344 // us, and if they are all dead, nuke them without remorse. 345 if (isSafeToDestroyConstant(C)) { 346 C->destroyConstant(); 347 CleanupConstantGlobalUsers(V, Init, DL, TLI); 348 return true; 349 } 350 } 351 } 352 return Changed; 353} 354 355/// isSafeSROAElementUse - Return true if the specified instruction is a safe 356/// user of a derived expression from a global that we want to SROA. 357static bool isSafeSROAElementUse(Value *V) { 358 // We might have a dead and dangling constant hanging off of here. 359 if (Constant *C = dyn_cast<Constant>(V)) 360 return isSafeToDestroyConstant(C); 361 362 Instruction *I = dyn_cast<Instruction>(V); 363 if (!I) return false; 364 365 // Loads are ok. 366 if (isa<LoadInst>(I)) return true; 367 368 // Stores *to* the pointer are ok. 369 if (StoreInst *SI = dyn_cast<StoreInst>(I)) 370 return SI->getOperand(0) != V; 371 372 // Otherwise, it must be a GEP. 373 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I); 374 if (!GEPI) return false; 375 376 if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) || 377 !cast<Constant>(GEPI->getOperand(1))->isNullValue()) 378 return false; 379 380 for (User *U : GEPI->users()) 381 if (!isSafeSROAElementUse(U)) 382 return false; 383 return true; 384} 385 386 387/// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value. 388/// Look at it and its uses and decide whether it is safe to SROA this global. 389/// 390static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) { 391 // The user of the global must be a GEP Inst or a ConstantExpr GEP. 392 if (!isa<GetElementPtrInst>(U) && 393 (!isa<ConstantExpr>(U) || 394 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr)) 395 return false; 396 397 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we 398 // don't like < 3 operand CE's, and we don't like non-constant integer 399 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some 400 // value of C. 401 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) || 402 !cast<Constant>(U->getOperand(1))->isNullValue() || 403 !isa<ConstantInt>(U->getOperand(2))) 404 return false; 405 406 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U); 407 ++GEPI; // Skip over the pointer index. 408 409 // If this is a use of an array allocation, do a bit more checking for sanity. 410 if (ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) { 411 uint64_t NumElements = AT->getNumElements(); 412 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2)); 413 414 // Check to make sure that index falls within the array. If not, 415 // something funny is going on, so we won't do the optimization. 416 // 417 if (Idx->getZExtValue() >= NumElements) 418 return false; 419 420 // We cannot scalar repl this level of the array unless any array 421 // sub-indices are in-range constants. In particular, consider: 422 // A[0][i]. We cannot know that the user isn't doing invalid things like 423 // allowing i to index an out-of-range subscript that accesses A[1]. 424 // 425 // Scalar replacing *just* the outer index of the array is probably not 426 // going to be a win anyway, so just give up. 427 for (++GEPI; // Skip array index. 428 GEPI != E; 429 ++GEPI) { 430 uint64_t NumElements; 431 if (ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI)) 432 NumElements = SubArrayTy->getNumElements(); 433 else if (VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI)) 434 NumElements = SubVectorTy->getNumElements(); 435 else { 436 assert((*GEPI)->isStructTy() && 437 "Indexed GEP type is not array, vector, or struct!"); 438 continue; 439 } 440 441 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand()); 442 if (!IdxVal || IdxVal->getZExtValue() >= NumElements) 443 return false; 444 } 445 } 446 447 for (User *UU : U->users()) 448 if (!isSafeSROAElementUse(UU)) 449 return false; 450 451 return true; 452} 453 454/// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it 455/// is safe for us to perform this transformation. 456/// 457static bool GlobalUsersSafeToSRA(GlobalValue *GV) { 458 for (User *U : GV->users()) 459 if (!IsUserOfGlobalSafeForSRA(U, GV)) 460 return false; 461 462 return true; 463} 464 465 466/// SRAGlobal - Perform scalar replacement of aggregates on the specified global 467/// variable. This opens the door for other optimizations by exposing the 468/// behavior of the program in a more fine-grained way. We have determined that 469/// this transformation is safe already. We return the first global variable we 470/// insert so that the caller can reprocess it. 471static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) { 472 // Make sure this global only has simple uses that we can SRA. 473 if (!GlobalUsersSafeToSRA(GV)) 474 return nullptr; 475 476 assert(GV->hasLocalLinkage() && !GV->isConstant()); 477 Constant *Init = GV->getInitializer(); 478 Type *Ty = Init->getType(); 479 480 std::vector<GlobalVariable*> NewGlobals; 481 Module::GlobalListType &Globals = GV->getParent()->getGlobalList(); 482 483 // Get the alignment of the global, either explicit or target-specific. 484 unsigned StartAlignment = GV->getAlignment(); 485 if (StartAlignment == 0) 486 StartAlignment = DL.getABITypeAlignment(GV->getType()); 487 488 if (StructType *STy = dyn_cast<StructType>(Ty)) { 489 NewGlobals.reserve(STy->getNumElements()); 490 const StructLayout &Layout = *DL.getStructLayout(STy); 491 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 492 Constant *In = Init->getAggregateElement(i); 493 assert(In && "Couldn't get element of initializer?"); 494 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false, 495 GlobalVariable::InternalLinkage, 496 In, GV->getName()+"."+Twine(i), 497 GV->getThreadLocalMode(), 498 GV->getType()->getAddressSpace()); 499 Globals.insert(GV, NGV); 500 NewGlobals.push_back(NGV); 501 502 // Calculate the known alignment of the field. If the original aggregate 503 // had 256 byte alignment for example, something might depend on that: 504 // propagate info to each field. 505 uint64_t FieldOffset = Layout.getElementOffset(i); 506 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset); 507 if (NewAlign > DL.getABITypeAlignment(STy->getElementType(i))) 508 NGV->setAlignment(NewAlign); 509 } 510 } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) { 511 unsigned NumElements = 0; 512 if (ArrayType *ATy = dyn_cast<ArrayType>(STy)) 513 NumElements = ATy->getNumElements(); 514 else 515 NumElements = cast<VectorType>(STy)->getNumElements(); 516 517 if (NumElements > 16 && GV->hasNUsesOrMore(16)) 518 return nullptr; // It's not worth it. 519 NewGlobals.reserve(NumElements); 520 521 uint64_t EltSize = DL.getTypeAllocSize(STy->getElementType()); 522 unsigned EltAlign = DL.getABITypeAlignment(STy->getElementType()); 523 for (unsigned i = 0, e = NumElements; i != e; ++i) { 524 Constant *In = Init->getAggregateElement(i); 525 assert(In && "Couldn't get element of initializer?"); 526 527 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false, 528 GlobalVariable::InternalLinkage, 529 In, GV->getName()+"."+Twine(i), 530 GV->getThreadLocalMode(), 531 GV->getType()->getAddressSpace()); 532 Globals.insert(GV, NGV); 533 NewGlobals.push_back(NGV); 534 535 // Calculate the known alignment of the field. If the original aggregate 536 // had 256 byte alignment for example, something might depend on that: 537 // propagate info to each field. 538 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i); 539 if (NewAlign > EltAlign) 540 NGV->setAlignment(NewAlign); 541 } 542 } 543 544 if (NewGlobals.empty()) 545 return nullptr; 546 547 DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV); 548 549 Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext())); 550 551 // Loop over all of the uses of the global, replacing the constantexpr geps, 552 // with smaller constantexpr geps or direct references. 553 while (!GV->use_empty()) { 554 User *GEP = GV->user_back(); 555 assert(((isa<ConstantExpr>(GEP) && 556 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)|| 557 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!"); 558 559 // Ignore the 1th operand, which has to be zero or else the program is quite 560 // broken (undefined). Get the 2nd operand, which is the structure or array 561 // index. 562 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 563 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access. 564 565 Value *NewPtr = NewGlobals[Val]; 566 567 // Form a shorter GEP if needed. 568 if (GEP->getNumOperands() > 3) { 569 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) { 570 SmallVector<Constant*, 8> Idxs; 571 Idxs.push_back(NullInt); 572 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i) 573 Idxs.push_back(CE->getOperand(i)); 574 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), Idxs); 575 } else { 576 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP); 577 SmallVector<Value*, 8> Idxs; 578 Idxs.push_back(NullInt); 579 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) 580 Idxs.push_back(GEPI->getOperand(i)); 581 NewPtr = GetElementPtrInst::Create(NewPtr, Idxs, 582 GEPI->getName()+"."+Twine(Val),GEPI); 583 } 584 } 585 GEP->replaceAllUsesWith(NewPtr); 586 587 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP)) 588 GEPI->eraseFromParent(); 589 else 590 cast<ConstantExpr>(GEP)->destroyConstant(); 591 } 592 593 // Delete the old global, now that it is dead. 594 Globals.erase(GV); 595 ++NumSRA; 596 597 // Loop over the new globals array deleting any globals that are obviously 598 // dead. This can arise due to scalarization of a structure or an array that 599 // has elements that are dead. 600 unsigned FirstGlobal = 0; 601 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i) 602 if (NewGlobals[i]->use_empty()) { 603 Globals.erase(NewGlobals[i]); 604 if (FirstGlobal == i) ++FirstGlobal; 605 } 606 607 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : nullptr; 608} 609 610/// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified 611/// value will trap if the value is dynamically null. PHIs keeps track of any 612/// phi nodes we've seen to avoid reprocessing them. 613static bool AllUsesOfValueWillTrapIfNull(const Value *V, 614 SmallPtrSet<const PHINode*, 8> &PHIs) { 615 for (const User *U : V->users()) 616 if (isa<LoadInst>(U)) { 617 // Will trap. 618 } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) { 619 if (SI->getOperand(0) == V) { 620 //cerr << "NONTRAPPING USE: " << *U; 621 return false; // Storing the value. 622 } 623 } else if (const CallInst *CI = dyn_cast<CallInst>(U)) { 624 if (CI->getCalledValue() != V) { 625 //cerr << "NONTRAPPING USE: " << *U; 626 return false; // Not calling the ptr 627 } 628 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) { 629 if (II->getCalledValue() != V) { 630 //cerr << "NONTRAPPING USE: " << *U; 631 return false; // Not calling the ptr 632 } 633 } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) { 634 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false; 635 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { 636 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false; 637 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) { 638 // If we've already seen this phi node, ignore it, it has already been 639 // checked. 640 if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs)) 641 return false; 642 } else if (isa<ICmpInst>(U) && 643 isa<ConstantPointerNull>(U->getOperand(1))) { 644 // Ignore icmp X, null 645 } else { 646 //cerr << "NONTRAPPING USE: " << *U; 647 return false; 648 } 649 650 return true; 651} 652 653/// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads 654/// from GV will trap if the loaded value is null. Note that this also permits 655/// comparisons of the loaded value against null, as a special case. 656static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) { 657 for (const User *U : GV->users()) 658 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) { 659 SmallPtrSet<const PHINode*, 8> PHIs; 660 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs)) 661 return false; 662 } else if (isa<StoreInst>(U)) { 663 // Ignore stores to the global. 664 } else { 665 // We don't know or understand this user, bail out. 666 //cerr << "UNKNOWN USER OF GLOBAL!: " << *U; 667 return false; 668 } 669 return true; 670} 671 672static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) { 673 bool Changed = false; 674 for (auto UI = V->user_begin(), E = V->user_end(); UI != E; ) { 675 Instruction *I = cast<Instruction>(*UI++); 676 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 677 LI->setOperand(0, NewV); 678 Changed = true; 679 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 680 if (SI->getOperand(1) == V) { 681 SI->setOperand(1, NewV); 682 Changed = true; 683 } 684 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) { 685 CallSite CS(I); 686 if (CS.getCalledValue() == V) { 687 // Calling through the pointer! Turn into a direct call, but be careful 688 // that the pointer is not also being passed as an argument. 689 CS.setCalledFunction(NewV); 690 Changed = true; 691 bool PassedAsArg = false; 692 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) 693 if (CS.getArgument(i) == V) { 694 PassedAsArg = true; 695 CS.setArgument(i, NewV); 696 } 697 698 if (PassedAsArg) { 699 // Being passed as an argument also. Be careful to not invalidate UI! 700 UI = V->user_begin(); 701 } 702 } 703 } else if (CastInst *CI = dyn_cast<CastInst>(I)) { 704 Changed |= OptimizeAwayTrappingUsesOfValue(CI, 705 ConstantExpr::getCast(CI->getOpcode(), 706 NewV, CI->getType())); 707 if (CI->use_empty()) { 708 Changed = true; 709 CI->eraseFromParent(); 710 } 711 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { 712 // Should handle GEP here. 713 SmallVector<Constant*, 8> Idxs; 714 Idxs.reserve(GEPI->getNumOperands()-1); 715 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end(); 716 i != e; ++i) 717 if (Constant *C = dyn_cast<Constant>(*i)) 718 Idxs.push_back(C); 719 else 720 break; 721 if (Idxs.size() == GEPI->getNumOperands()-1) 722 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI, 723 ConstantExpr::getGetElementPtr(NewV, Idxs)); 724 if (GEPI->use_empty()) { 725 Changed = true; 726 GEPI->eraseFromParent(); 727 } 728 } 729 } 730 731 return Changed; 732} 733 734 735/// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null 736/// value stored into it. If there are uses of the loaded value that would trap 737/// if the loaded value is dynamically null, then we know that they cannot be 738/// reachable with a null optimize away the load. 739static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV, 740 const DataLayout *DL, 741 TargetLibraryInfo *TLI) { 742 bool Changed = false; 743 744 // Keep track of whether we are able to remove all the uses of the global 745 // other than the store that defines it. 746 bool AllNonStoreUsesGone = true; 747 748 // Replace all uses of loads with uses of uses of the stored value. 749 for (Value::user_iterator GUI = GV->user_begin(), E = GV->user_end(); GUI != E;){ 750 User *GlobalUser = *GUI++; 751 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) { 752 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV); 753 // If we were able to delete all uses of the loads 754 if (LI->use_empty()) { 755 LI->eraseFromParent(); 756 Changed = true; 757 } else { 758 AllNonStoreUsesGone = false; 759 } 760 } else if (isa<StoreInst>(GlobalUser)) { 761 // Ignore the store that stores "LV" to the global. 762 assert(GlobalUser->getOperand(1) == GV && 763 "Must be storing *to* the global"); 764 } else { 765 AllNonStoreUsesGone = false; 766 767 // If we get here we could have other crazy uses that are transitively 768 // loaded. 769 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) || 770 isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser) || 771 isa<BitCastInst>(GlobalUser) || 772 isa<GetElementPtrInst>(GlobalUser)) && 773 "Only expect load and stores!"); 774 } 775 } 776 777 if (Changed) { 778 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV); 779 ++NumGlobUses; 780 } 781 782 // If we nuked all of the loads, then none of the stores are needed either, 783 // nor is the global. 784 if (AllNonStoreUsesGone) { 785 if (isLeakCheckerRoot(GV)) { 786 Changed |= CleanupPointerRootUsers(GV, TLI); 787 } else { 788 Changed = true; 789 CleanupConstantGlobalUsers(GV, nullptr, DL, TLI); 790 } 791 if (GV->use_empty()) { 792 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n"); 793 Changed = true; 794 GV->eraseFromParent(); 795 ++NumDeleted; 796 } 797 } 798 return Changed; 799} 800 801/// ConstantPropUsersOf - Walk the use list of V, constant folding all of the 802/// instructions that are foldable. 803static void ConstantPropUsersOf(Value *V, const DataLayout *DL, 804 TargetLibraryInfo *TLI) { 805 for (Value::user_iterator UI = V->user_begin(), E = V->user_end(); UI != E; ) 806 if (Instruction *I = dyn_cast<Instruction>(*UI++)) 807 if (Constant *NewC = ConstantFoldInstruction(I, DL, TLI)) { 808 I->replaceAllUsesWith(NewC); 809 810 // Advance UI to the next non-I use to avoid invalidating it! 811 // Instructions could multiply use V. 812 while (UI != E && *UI == I) 813 ++UI; 814 I->eraseFromParent(); 815 } 816} 817 818/// OptimizeGlobalAddressOfMalloc - This function takes the specified global 819/// variable, and transforms the program as if it always contained the result of 820/// the specified malloc. Because it is always the result of the specified 821/// malloc, there is no reason to actually DO the malloc. Instead, turn the 822/// malloc into a global, and any loads of GV as uses of the new global. 823static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, 824 CallInst *CI, 825 Type *AllocTy, 826 ConstantInt *NElements, 827 const DataLayout *DL, 828 TargetLibraryInfo *TLI) { 829 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n'); 830 831 Type *GlobalType; 832 if (NElements->getZExtValue() == 1) 833 GlobalType = AllocTy; 834 else 835 // If we have an array allocation, the global variable is of an array. 836 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue()); 837 838 // Create the new global variable. The contents of the malloc'd memory is 839 // undefined, so initialize with an undef value. 840 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(), 841 GlobalType, false, 842 GlobalValue::InternalLinkage, 843 UndefValue::get(GlobalType), 844 GV->getName()+".body", 845 GV, 846 GV->getThreadLocalMode()); 847 848 // If there are bitcast users of the malloc (which is typical, usually we have 849 // a malloc + bitcast) then replace them with uses of the new global. Update 850 // other users to use the global as well. 851 BitCastInst *TheBC = nullptr; 852 while (!CI->use_empty()) { 853 Instruction *User = cast<Instruction>(CI->user_back()); 854 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { 855 if (BCI->getType() == NewGV->getType()) { 856 BCI->replaceAllUsesWith(NewGV); 857 BCI->eraseFromParent(); 858 } else { 859 BCI->setOperand(0, NewGV); 860 } 861 } else { 862 if (!TheBC) 863 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI); 864 User->replaceUsesOfWith(CI, TheBC); 865 } 866 } 867 868 Constant *RepValue = NewGV; 869 if (NewGV->getType() != GV->getType()->getElementType()) 870 RepValue = ConstantExpr::getBitCast(RepValue, 871 GV->getType()->getElementType()); 872 873 // If there is a comparison against null, we will insert a global bool to 874 // keep track of whether the global was initialized yet or not. 875 GlobalVariable *InitBool = 876 new GlobalVariable(Type::getInt1Ty(GV->getContext()), false, 877 GlobalValue::InternalLinkage, 878 ConstantInt::getFalse(GV->getContext()), 879 GV->getName()+".init", GV->getThreadLocalMode()); 880 bool InitBoolUsed = false; 881 882 // Loop over all uses of GV, processing them in turn. 883 while (!GV->use_empty()) { 884 if (StoreInst *SI = dyn_cast<StoreInst>(GV->user_back())) { 885 // The global is initialized when the store to it occurs. 886 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0, 887 SI->getOrdering(), SI->getSynchScope(), SI); 888 SI->eraseFromParent(); 889 continue; 890 } 891 892 LoadInst *LI = cast<LoadInst>(GV->user_back()); 893 while (!LI->use_empty()) { 894 Use &LoadUse = *LI->use_begin(); 895 ICmpInst *ICI = dyn_cast<ICmpInst>(LoadUse.getUser()); 896 if (!ICI) { 897 LoadUse = RepValue; 898 continue; 899 } 900 901 // Replace the cmp X, 0 with a use of the bool value. 902 // Sink the load to where the compare was, if atomic rules allow us to. 903 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0, 904 LI->getOrdering(), LI->getSynchScope(), 905 LI->isUnordered() ? (Instruction*)ICI : LI); 906 InitBoolUsed = true; 907 switch (ICI->getPredicate()) { 908 default: llvm_unreachable("Unknown ICmp Predicate!"); 909 case ICmpInst::ICMP_ULT: 910 case ICmpInst::ICMP_SLT: // X < null -> always false 911 LV = ConstantInt::getFalse(GV->getContext()); 912 break; 913 case ICmpInst::ICMP_ULE: 914 case ICmpInst::ICMP_SLE: 915 case ICmpInst::ICMP_EQ: 916 LV = BinaryOperator::CreateNot(LV, "notinit", ICI); 917 break; 918 case ICmpInst::ICMP_NE: 919 case ICmpInst::ICMP_UGE: 920 case ICmpInst::ICMP_SGE: 921 case ICmpInst::ICMP_UGT: 922 case ICmpInst::ICMP_SGT: 923 break; // no change. 924 } 925 ICI->replaceAllUsesWith(LV); 926 ICI->eraseFromParent(); 927 } 928 LI->eraseFromParent(); 929 } 930 931 // If the initialization boolean was used, insert it, otherwise delete it. 932 if (!InitBoolUsed) { 933 while (!InitBool->use_empty()) // Delete initializations 934 cast<StoreInst>(InitBool->user_back())->eraseFromParent(); 935 delete InitBool; 936 } else 937 GV->getParent()->getGlobalList().insert(GV, InitBool); 938 939 // Now the GV is dead, nuke it and the malloc.. 940 GV->eraseFromParent(); 941 CI->eraseFromParent(); 942 943 // To further other optimizations, loop over all users of NewGV and try to 944 // constant prop them. This will promote GEP instructions with constant 945 // indices into GEP constant-exprs, which will allow global-opt to hack on it. 946 ConstantPropUsersOf(NewGV, DL, TLI); 947 if (RepValue != NewGV) 948 ConstantPropUsersOf(RepValue, DL, TLI); 949 950 return NewGV; 951} 952 953/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking 954/// to make sure that there are no complex uses of V. We permit simple things 955/// like dereferencing the pointer, but not storing through the address, unless 956/// it is to the specified global. 957static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V, 958 const GlobalVariable *GV, 959 SmallPtrSet<const PHINode*, 8> &PHIs) { 960 for (const User *U : V->users()) { 961 const Instruction *Inst = cast<Instruction>(U); 962 963 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) { 964 continue; // Fine, ignore. 965 } 966 967 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 968 if (SI->getOperand(0) == V && SI->getOperand(1) != GV) 969 return false; // Storing the pointer itself... bad. 970 continue; // Otherwise, storing through it, or storing into GV... fine. 971 } 972 973 // Must index into the array and into the struct. 974 if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) { 975 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs)) 976 return false; 977 continue; 978 } 979 980 if (const PHINode *PN = dyn_cast<PHINode>(Inst)) { 981 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI 982 // cycles. 983 if (PHIs.insert(PN)) 984 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs)) 985 return false; 986 continue; 987 } 988 989 if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) { 990 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) 991 return false; 992 continue; 993 } 994 995 return false; 996 } 997 return true; 998} 999 1000/// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV 1001/// somewhere. Transform all uses of the allocation into loads from the 1002/// global and uses of the resultant pointer. Further, delete the store into 1003/// GV. This assumes that these value pass the 1004/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate. 1005static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, 1006 GlobalVariable *GV) { 1007 while (!Alloc->use_empty()) { 1008 Instruction *U = cast<Instruction>(*Alloc->user_begin()); 1009 Instruction *InsertPt = U; 1010 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 1011 // If this is the store of the allocation into the global, remove it. 1012 if (SI->getOperand(1) == GV) { 1013 SI->eraseFromParent(); 1014 continue; 1015 } 1016 } else if (PHINode *PN = dyn_cast<PHINode>(U)) { 1017 // Insert the load in the corresponding predecessor, not right before the 1018 // PHI. 1019 InsertPt = PN->getIncomingBlock(*Alloc->use_begin())->getTerminator(); 1020 } else if (isa<BitCastInst>(U)) { 1021 // Must be bitcast between the malloc and store to initialize the global. 1022 ReplaceUsesOfMallocWithGlobal(U, GV); 1023 U->eraseFromParent(); 1024 continue; 1025 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { 1026 // If this is a "GEP bitcast" and the user is a store to the global, then 1027 // just process it as a bitcast. 1028 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse()) 1029 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->user_back())) 1030 if (SI->getOperand(1) == GV) { 1031 // Must be bitcast GEP between the malloc and store to initialize 1032 // the global. 1033 ReplaceUsesOfMallocWithGlobal(GEPI, GV); 1034 GEPI->eraseFromParent(); 1035 continue; 1036 } 1037 } 1038 1039 // Insert a load from the global, and use it instead of the malloc. 1040 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt); 1041 U->replaceUsesOfWith(Alloc, NL); 1042 } 1043} 1044 1045/// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi 1046/// of a load) are simple enough to perform heap SRA on. This permits GEP's 1047/// that index through the array and struct field, icmps of null, and PHIs. 1048static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V, 1049 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs, 1050 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIsPerLoad) { 1051 // We permit two users of the load: setcc comparing against the null 1052 // pointer, and a getelementptr of a specific form. 1053 for (const User *U : V->users()) { 1054 const Instruction *UI = cast<Instruction>(U); 1055 1056 // Comparison against null is ok. 1057 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(UI)) { 1058 if (!isa<ConstantPointerNull>(ICI->getOperand(1))) 1059 return false; 1060 continue; 1061 } 1062 1063 // getelementptr is also ok, but only a simple form. 1064 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(UI)) { 1065 // Must index into the array and into the struct. 1066 if (GEPI->getNumOperands() < 3) 1067 return false; 1068 1069 // Otherwise the GEP is ok. 1070 continue; 1071 } 1072 1073 if (const PHINode *PN = dyn_cast<PHINode>(UI)) { 1074 if (!LoadUsingPHIsPerLoad.insert(PN)) 1075 // This means some phi nodes are dependent on each other. 1076 // Avoid infinite looping! 1077 return false; 1078 if (!LoadUsingPHIs.insert(PN)) 1079 // If we have already analyzed this PHI, then it is safe. 1080 continue; 1081 1082 // Make sure all uses of the PHI are simple enough to transform. 1083 if (!LoadUsesSimpleEnoughForHeapSRA(PN, 1084 LoadUsingPHIs, LoadUsingPHIsPerLoad)) 1085 return false; 1086 1087 continue; 1088 } 1089 1090 // Otherwise we don't know what this is, not ok. 1091 return false; 1092 } 1093 1094 return true; 1095} 1096 1097 1098/// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from 1099/// GV are simple enough to perform HeapSRA, return true. 1100static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV, 1101 Instruction *StoredVal) { 1102 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs; 1103 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad; 1104 for (const User *U : GV->users()) 1105 if (const LoadInst *LI = dyn_cast<LoadInst>(U)) { 1106 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs, 1107 LoadUsingPHIsPerLoad)) 1108 return false; 1109 LoadUsingPHIsPerLoad.clear(); 1110 } 1111 1112 // If we reach here, we know that all uses of the loads and transitive uses 1113 // (through PHI nodes) are simple enough to transform. However, we don't know 1114 // that all inputs the to the PHI nodes are in the same equivalence sets. 1115 // Check to verify that all operands of the PHIs are either PHIS that can be 1116 // transformed, loads from GV, or MI itself. 1117 for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin() 1118 , E = LoadUsingPHIs.end(); I != E; ++I) { 1119 const PHINode *PN = *I; 1120 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) { 1121 Value *InVal = PN->getIncomingValue(op); 1122 1123 // PHI of the stored value itself is ok. 1124 if (InVal == StoredVal) continue; 1125 1126 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) { 1127 // One of the PHIs in our set is (optimistically) ok. 1128 if (LoadUsingPHIs.count(InPN)) 1129 continue; 1130 return false; 1131 } 1132 1133 // Load from GV is ok. 1134 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal)) 1135 if (LI->getOperand(0) == GV) 1136 continue; 1137 1138 // UNDEF? NULL? 1139 1140 // Anything else is rejected. 1141 return false; 1142 } 1143 } 1144 1145 return true; 1146} 1147 1148static Value *GetHeapSROAValue(Value *V, unsigned FieldNo, 1149 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1150 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 1151 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V]; 1152 1153 if (FieldNo >= FieldVals.size()) 1154 FieldVals.resize(FieldNo+1); 1155 1156 // If we already have this value, just reuse the previously scalarized 1157 // version. 1158 if (Value *FieldVal = FieldVals[FieldNo]) 1159 return FieldVal; 1160 1161 // Depending on what instruction this is, we have several cases. 1162 Value *Result; 1163 if (LoadInst *LI = dyn_cast<LoadInst>(V)) { 1164 // This is a scalarized version of the load from the global. Just create 1165 // a new Load of the scalarized global. 1166 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo, 1167 InsertedScalarizedValues, 1168 PHIsToRewrite), 1169 LI->getName()+".f"+Twine(FieldNo), LI); 1170 } else if (PHINode *PN = dyn_cast<PHINode>(V)) { 1171 // PN's type is pointer to struct. Make a new PHI of pointer to struct 1172 // field. 1173 1174 PointerType *PTy = cast<PointerType>(PN->getType()); 1175 StructType *ST = cast<StructType>(PTy->getElementType()); 1176 1177 unsigned AS = PTy->getAddressSpace(); 1178 PHINode *NewPN = 1179 PHINode::Create(PointerType::get(ST->getElementType(FieldNo), AS), 1180 PN->getNumIncomingValues(), 1181 PN->getName()+".f"+Twine(FieldNo), PN); 1182 Result = NewPN; 1183 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo)); 1184 } else { 1185 llvm_unreachable("Unknown usable value"); 1186 } 1187 1188 return FieldVals[FieldNo] = Result; 1189} 1190 1191/// RewriteHeapSROALoadUser - Given a load instruction and a value derived from 1192/// the load, rewrite the derived value to use the HeapSRoA'd load. 1193static void RewriteHeapSROALoadUser(Instruction *LoadUser, 1194 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1195 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 1196 // If this is a comparison against null, handle it. 1197 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) { 1198 assert(isa<ConstantPointerNull>(SCI->getOperand(1))); 1199 // If we have a setcc of the loaded pointer, we can use a setcc of any 1200 // field. 1201 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0, 1202 InsertedScalarizedValues, PHIsToRewrite); 1203 1204 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr, 1205 Constant::getNullValue(NPtr->getType()), 1206 SCI->getName()); 1207 SCI->replaceAllUsesWith(New); 1208 SCI->eraseFromParent(); 1209 return; 1210 } 1211 1212 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...' 1213 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) { 1214 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2)) 1215 && "Unexpected GEPI!"); 1216 1217 // Load the pointer for this field. 1218 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 1219 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo, 1220 InsertedScalarizedValues, PHIsToRewrite); 1221 1222 // Create the new GEP idx vector. 1223 SmallVector<Value*, 8> GEPIdx; 1224 GEPIdx.push_back(GEPI->getOperand(1)); 1225 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end()); 1226 1227 Value *NGEPI = GetElementPtrInst::Create(NewPtr, GEPIdx, 1228 GEPI->getName(), GEPI); 1229 GEPI->replaceAllUsesWith(NGEPI); 1230 GEPI->eraseFromParent(); 1231 return; 1232 } 1233 1234 // Recursively transform the users of PHI nodes. This will lazily create the 1235 // PHIs that are needed for individual elements. Keep track of what PHIs we 1236 // see in InsertedScalarizedValues so that we don't get infinite loops (very 1237 // antisocial). If the PHI is already in InsertedScalarizedValues, it has 1238 // already been seen first by another load, so its uses have already been 1239 // processed. 1240 PHINode *PN = cast<PHINode>(LoadUser); 1241 if (!InsertedScalarizedValues.insert(std::make_pair(PN, 1242 std::vector<Value*>())).second) 1243 return; 1244 1245 // If this is the first time we've seen this PHI, recursively process all 1246 // users. 1247 for (auto UI = PN->user_begin(), E = PN->user_end(); UI != E;) { 1248 Instruction *User = cast<Instruction>(*UI++); 1249 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); 1250 } 1251} 1252 1253/// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr 1254/// is a value loaded from the global. Eliminate all uses of Ptr, making them 1255/// use FieldGlobals instead. All uses of loaded values satisfy 1256/// AllGlobalLoadUsesSimpleEnoughForHeapSRA. 1257static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load, 1258 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1259 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 1260 for (auto UI = Load->user_begin(), E = Load->user_end(); UI != E;) { 1261 Instruction *User = cast<Instruction>(*UI++); 1262 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); 1263 } 1264 1265 if (Load->use_empty()) { 1266 Load->eraseFromParent(); 1267 InsertedScalarizedValues.erase(Load); 1268 } 1269} 1270 1271/// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break 1272/// it up into multiple allocations of arrays of the fields. 1273static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI, 1274 Value *NElems, const DataLayout *DL, 1275 const TargetLibraryInfo *TLI) { 1276 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n'); 1277 Type *MAT = getMallocAllocatedType(CI, TLI); 1278 StructType *STy = cast<StructType>(MAT); 1279 1280 // There is guaranteed to be at least one use of the malloc (storing 1281 // it into GV). If there are other uses, change them to be uses of 1282 // the global to simplify later code. This also deletes the store 1283 // into GV. 1284 ReplaceUsesOfMallocWithGlobal(CI, GV); 1285 1286 // Okay, at this point, there are no users of the malloc. Insert N 1287 // new mallocs at the same place as CI, and N globals. 1288 std::vector<Value*> FieldGlobals; 1289 std::vector<Value*> FieldMallocs; 1290 1291 unsigned AS = GV->getType()->getPointerAddressSpace(); 1292 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ 1293 Type *FieldTy = STy->getElementType(FieldNo); 1294 PointerType *PFieldTy = PointerType::get(FieldTy, AS); 1295 1296 GlobalVariable *NGV = 1297 new GlobalVariable(*GV->getParent(), 1298 PFieldTy, false, GlobalValue::InternalLinkage, 1299 Constant::getNullValue(PFieldTy), 1300 GV->getName() + ".f" + Twine(FieldNo), GV, 1301 GV->getThreadLocalMode()); 1302 FieldGlobals.push_back(NGV); 1303 1304 unsigned TypeSize = DL->getTypeAllocSize(FieldTy); 1305 if (StructType *ST = dyn_cast<StructType>(FieldTy)) 1306 TypeSize = DL->getStructLayout(ST)->getSizeInBytes(); 1307 Type *IntPtrTy = DL->getIntPtrType(CI->getType()); 1308 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy, 1309 ConstantInt::get(IntPtrTy, TypeSize), 1310 NElems, nullptr, 1311 CI->getName() + ".f" + Twine(FieldNo)); 1312 FieldMallocs.push_back(NMI); 1313 new StoreInst(NMI, NGV, CI); 1314 } 1315 1316 // The tricky aspect of this transformation is handling the case when malloc 1317 // fails. In the original code, malloc failing would set the result pointer 1318 // of malloc to null. In this case, some mallocs could succeed and others 1319 // could fail. As such, we emit code that looks like this: 1320 // F0 = malloc(field0) 1321 // F1 = malloc(field1) 1322 // F2 = malloc(field2) 1323 // if (F0 == 0 || F1 == 0 || F2 == 0) { 1324 // if (F0) { free(F0); F0 = 0; } 1325 // if (F1) { free(F1); F1 = 0; } 1326 // if (F2) { free(F2); F2 = 0; } 1327 // } 1328 // The malloc can also fail if its argument is too large. 1329 Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0); 1330 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0), 1331 ConstantZero, "isneg"); 1332 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) { 1333 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i], 1334 Constant::getNullValue(FieldMallocs[i]->getType()), 1335 "isnull"); 1336 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI); 1337 } 1338 1339 // Split the basic block at the old malloc. 1340 BasicBlock *OrigBB = CI->getParent(); 1341 BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont"); 1342 1343 // Create the block to check the first condition. Put all these blocks at the 1344 // end of the function as they are unlikely to be executed. 1345 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(), 1346 "malloc_ret_null", 1347 OrigBB->getParent()); 1348 1349 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond 1350 // branch on RunningOr. 1351 OrigBB->getTerminator()->eraseFromParent(); 1352 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB); 1353 1354 // Within the NullPtrBlock, we need to emit a comparison and branch for each 1355 // pointer, because some may be null while others are not. 1356 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1357 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock); 1358 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal, 1359 Constant::getNullValue(GVVal->getType())); 1360 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it", 1361 OrigBB->getParent()); 1362 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next", 1363 OrigBB->getParent()); 1364 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock, 1365 Cmp, NullPtrBlock); 1366 1367 // Fill in FreeBlock. 1368 CallInst::CreateFree(GVVal, BI); 1369 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i], 1370 FreeBlock); 1371 BranchInst::Create(NextBlock, FreeBlock); 1372 1373 NullPtrBlock = NextBlock; 1374 } 1375 1376 BranchInst::Create(ContBB, NullPtrBlock); 1377 1378 // CI is no longer needed, remove it. 1379 CI->eraseFromParent(); 1380 1381 /// InsertedScalarizedLoads - As we process loads, if we can't immediately 1382 /// update all uses of the load, keep track of what scalarized loads are 1383 /// inserted for a given load. 1384 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues; 1385 InsertedScalarizedValues[GV] = FieldGlobals; 1386 1387 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite; 1388 1389 // Okay, the malloc site is completely handled. All of the uses of GV are now 1390 // loads, and all uses of those loads are simple. Rewrite them to use loads 1391 // of the per-field globals instead. 1392 for (auto UI = GV->user_begin(), E = GV->user_end(); UI != E;) { 1393 Instruction *User = cast<Instruction>(*UI++); 1394 1395 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1396 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite); 1397 continue; 1398 } 1399 1400 // Must be a store of null. 1401 StoreInst *SI = cast<StoreInst>(User); 1402 assert(isa<ConstantPointerNull>(SI->getOperand(0)) && 1403 "Unexpected heap-sra user!"); 1404 1405 // Insert a store of null into each global. 1406 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1407 PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType()); 1408 Constant *Null = Constant::getNullValue(PT->getElementType()); 1409 new StoreInst(Null, FieldGlobals[i], SI); 1410 } 1411 // Erase the original store. 1412 SI->eraseFromParent(); 1413 } 1414 1415 // While we have PHIs that are interesting to rewrite, do it. 1416 while (!PHIsToRewrite.empty()) { 1417 PHINode *PN = PHIsToRewrite.back().first; 1418 unsigned FieldNo = PHIsToRewrite.back().second; 1419 PHIsToRewrite.pop_back(); 1420 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]); 1421 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi"); 1422 1423 // Add all the incoming values. This can materialize more phis. 1424 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1425 Value *InVal = PN->getIncomingValue(i); 1426 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues, 1427 PHIsToRewrite); 1428 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i)); 1429 } 1430 } 1431 1432 // Drop all inter-phi links and any loads that made it this far. 1433 for (DenseMap<Value*, std::vector<Value*> >::iterator 1434 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1435 I != E; ++I) { 1436 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1437 PN->dropAllReferences(); 1438 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1439 LI->dropAllReferences(); 1440 } 1441 1442 // Delete all the phis and loads now that inter-references are dead. 1443 for (DenseMap<Value*, std::vector<Value*> >::iterator 1444 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1445 I != E; ++I) { 1446 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1447 PN->eraseFromParent(); 1448 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1449 LI->eraseFromParent(); 1450 } 1451 1452 // The old global is now dead, remove it. 1453 GV->eraseFromParent(); 1454 1455 ++NumHeapSRA; 1456 return cast<GlobalVariable>(FieldGlobals[0]); 1457} 1458 1459/// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a 1460/// pointer global variable with a single value stored it that is a malloc or 1461/// cast of malloc. 1462static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, 1463 CallInst *CI, 1464 Type *AllocTy, 1465 AtomicOrdering Ordering, 1466 Module::global_iterator &GVI, 1467 const DataLayout *DL, 1468 TargetLibraryInfo *TLI) { 1469 if (!DL) 1470 return false; 1471 1472 // If this is a malloc of an abstract type, don't touch it. 1473 if (!AllocTy->isSized()) 1474 return false; 1475 1476 // We can't optimize this global unless all uses of it are *known* to be 1477 // of the malloc value, not of the null initializer value (consider a use 1478 // that compares the global's value against zero to see if the malloc has 1479 // been reached). To do this, we check to see if all uses of the global 1480 // would trap if the global were null: this proves that they must all 1481 // happen after the malloc. 1482 if (!AllUsesOfLoadedValueWillTrapIfNull(GV)) 1483 return false; 1484 1485 // We can't optimize this if the malloc itself is used in a complex way, 1486 // for example, being stored into multiple globals. This allows the 1487 // malloc to be stored into the specified global, loaded icmp'd, and 1488 // GEP'd. These are all things we could transform to using the global 1489 // for. 1490 SmallPtrSet<const PHINode*, 8> PHIs; 1491 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs)) 1492 return false; 1493 1494 // If we have a global that is only initialized with a fixed size malloc, 1495 // transform the program to use global memory instead of malloc'd memory. 1496 // This eliminates dynamic allocation, avoids an indirection accessing the 1497 // data, and exposes the resultant global to further GlobalOpt. 1498 // We cannot optimize the malloc if we cannot determine malloc array size. 1499 Value *NElems = getMallocArraySize(CI, DL, TLI, true); 1500 if (!NElems) 1501 return false; 1502 1503 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems)) 1504 // Restrict this transformation to only working on small allocations 1505 // (2048 bytes currently), as we don't want to introduce a 16M global or 1506 // something. 1507 if (NElements->getZExtValue() * DL->getTypeAllocSize(AllocTy) < 2048) { 1508 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, DL, TLI); 1509 return true; 1510 } 1511 1512 // If the allocation is an array of structures, consider transforming this 1513 // into multiple malloc'd arrays, one for each field. This is basically 1514 // SRoA for malloc'd memory. 1515 1516 if (Ordering != NotAtomic) 1517 return false; 1518 1519 // If this is an allocation of a fixed size array of structs, analyze as a 1520 // variable size array. malloc [100 x struct],1 -> malloc struct, 100 1521 if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1)) 1522 if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy)) 1523 AllocTy = AT->getElementType(); 1524 1525 StructType *AllocSTy = dyn_cast<StructType>(AllocTy); 1526 if (!AllocSTy) 1527 return false; 1528 1529 // This the structure has an unreasonable number of fields, leave it 1530 // alone. 1531 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 && 1532 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) { 1533 1534 // If this is a fixed size array, transform the Malloc to be an alloc of 1535 // structs. malloc [100 x struct],1 -> malloc struct, 100 1536 if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) { 1537 Type *IntPtrTy = DL->getIntPtrType(CI->getType()); 1538 unsigned TypeSize = DL->getStructLayout(AllocSTy)->getSizeInBytes(); 1539 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize); 1540 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements()); 1541 Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy, 1542 AllocSize, NumElements, 1543 nullptr, CI->getName()); 1544 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI); 1545 CI->replaceAllUsesWith(Cast); 1546 CI->eraseFromParent(); 1547 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc)) 1548 CI = cast<CallInst>(BCI->getOperand(0)); 1549 else 1550 CI = cast<CallInst>(Malloc); 1551 } 1552 1553 GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, DL, TLI, true), 1554 DL, TLI); 1555 return true; 1556 } 1557 1558 return false; 1559} 1560 1561// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge 1562// that only one value (besides its initializer) is ever stored to the global. 1563static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal, 1564 AtomicOrdering Ordering, 1565 Module::global_iterator &GVI, 1566 const DataLayout *DL, 1567 TargetLibraryInfo *TLI) { 1568 // Ignore no-op GEPs and bitcasts. 1569 StoredOnceVal = StoredOnceVal->stripPointerCasts(); 1570 1571 // If we are dealing with a pointer global that is initialized to null and 1572 // only has one (non-null) value stored into it, then we can optimize any 1573 // users of the loaded value (often calls and loads) that would trap if the 1574 // value was null. 1575 if (GV->getInitializer()->getType()->isPointerTy() && 1576 GV->getInitializer()->isNullValue()) { 1577 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { 1578 if (GV->getInitializer()->getType() != SOVC->getType()) 1579 SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType()); 1580 1581 // Optimize away any trapping uses of the loaded value. 1582 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, DL, TLI)) 1583 return true; 1584 } else if (CallInst *CI = extractMallocCall(StoredOnceVal, TLI)) { 1585 Type *MallocType = getMallocAllocatedType(CI, TLI); 1586 if (MallocType && 1587 TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, Ordering, GVI, 1588 DL, TLI)) 1589 return true; 1590 } 1591 } 1592 1593 return false; 1594} 1595 1596/// TryToShrinkGlobalToBoolean - At this point, we have learned that the only 1597/// two values ever stored into GV are its initializer and OtherVal. See if we 1598/// can shrink the global into a boolean and select between the two values 1599/// whenever it is used. This exposes the values to other scalar optimizations. 1600static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) { 1601 Type *GVElType = GV->getType()->getElementType(); 1602 1603 // If GVElType is already i1, it is already shrunk. If the type of the GV is 1604 // an FP value, pointer or vector, don't do this optimization because a select 1605 // between them is very expensive and unlikely to lead to later 1606 // simplification. In these cases, we typically end up with "cond ? v1 : v2" 1607 // where v1 and v2 both require constant pool loads, a big loss. 1608 if (GVElType == Type::getInt1Ty(GV->getContext()) || 1609 GVElType->isFloatingPointTy() || 1610 GVElType->isPointerTy() || GVElType->isVectorTy()) 1611 return false; 1612 1613 // Walk the use list of the global seeing if all the uses are load or store. 1614 // If there is anything else, bail out. 1615 for (User *U : GV->users()) 1616 if (!isa<LoadInst>(U) && !isa<StoreInst>(U)) 1617 return false; 1618 1619 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV); 1620 1621 // Create the new global, initializing it to false. 1622 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()), 1623 false, 1624 GlobalValue::InternalLinkage, 1625 ConstantInt::getFalse(GV->getContext()), 1626 GV->getName()+".b", 1627 GV->getThreadLocalMode(), 1628 GV->getType()->getAddressSpace()); 1629 GV->getParent()->getGlobalList().insert(GV, NewGV); 1630 1631 Constant *InitVal = GV->getInitializer(); 1632 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) && 1633 "No reason to shrink to bool!"); 1634 1635 // If initialized to zero and storing one into the global, we can use a cast 1636 // instead of a select to synthesize the desired value. 1637 bool IsOneZero = false; 1638 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) 1639 IsOneZero = InitVal->isNullValue() && CI->isOne(); 1640 1641 while (!GV->use_empty()) { 1642 Instruction *UI = cast<Instruction>(GV->user_back()); 1643 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { 1644 // Change the store into a boolean store. 1645 bool StoringOther = SI->getOperand(0) == OtherVal; 1646 // Only do this if we weren't storing a loaded value. 1647 Value *StoreVal; 1648 if (StoringOther || SI->getOperand(0) == InitVal) { 1649 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()), 1650 StoringOther); 1651 } else { 1652 // Otherwise, we are storing a previously loaded copy. To do this, 1653 // change the copy from copying the original value to just copying the 1654 // bool. 1655 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); 1656 1657 // If we've already replaced the input, StoredVal will be a cast or 1658 // select instruction. If not, it will be a load of the original 1659 // global. 1660 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { 1661 assert(LI->getOperand(0) == GV && "Not a copy!"); 1662 // Insert a new load, to preserve the saved value. 1663 StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0, 1664 LI->getOrdering(), LI->getSynchScope(), LI); 1665 } else { 1666 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && 1667 "This is not a form that we understand!"); 1668 StoreVal = StoredVal->getOperand(0); 1669 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); 1670 } 1671 } 1672 new StoreInst(StoreVal, NewGV, false, 0, 1673 SI->getOrdering(), SI->getSynchScope(), SI); 1674 } else { 1675 // Change the load into a load of bool then a select. 1676 LoadInst *LI = cast<LoadInst>(UI); 1677 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0, 1678 LI->getOrdering(), LI->getSynchScope(), LI); 1679 Value *NSI; 1680 if (IsOneZero) 1681 NSI = new ZExtInst(NLI, LI->getType(), "", LI); 1682 else 1683 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI); 1684 NSI->takeName(LI); 1685 LI->replaceAllUsesWith(NSI); 1686 } 1687 UI->eraseFromParent(); 1688 } 1689 1690 // Retain the name of the old global variable. People who are debugging their 1691 // programs may expect these variables to be named the same. 1692 NewGV->takeName(GV); 1693 GV->eraseFromParent(); 1694 return true; 1695} 1696 1697 1698/// ProcessGlobal - Analyze the specified global variable and optimize it if 1699/// possible. If we make a change, return true. 1700bool GlobalOpt::ProcessGlobal(GlobalVariable *GV, 1701 Module::global_iterator &GVI) { 1702 if (!GV->isDiscardableIfUnused()) 1703 return false; 1704 1705 // Do more involved optimizations if the global is internal. 1706 GV->removeDeadConstantUsers(); 1707 1708 if (GV->use_empty()) { 1709 DEBUG(dbgs() << "GLOBAL DEAD: " << *GV); 1710 GV->eraseFromParent(); 1711 ++NumDeleted; 1712 return true; 1713 } 1714 1715 if (!GV->hasLocalLinkage()) 1716 return false; 1717 1718 GlobalStatus GS; 1719 1720 if (GlobalStatus::analyzeGlobal(GV, GS)) 1721 return false; 1722 1723 if (!GS.IsCompared && !GV->hasUnnamedAddr()) { 1724 GV->setUnnamedAddr(true); 1725 NumUnnamed++; 1726 } 1727 1728 if (GV->isConstant() || !GV->hasInitializer()) 1729 return false; 1730 1731 return ProcessInternalGlobal(GV, GVI, GS); 1732} 1733 1734/// ProcessInternalGlobal - Analyze the specified global variable and optimize 1735/// it if possible. If we make a change, return true. 1736bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV, 1737 Module::global_iterator &GVI, 1738 const GlobalStatus &GS) { 1739 // If this is a first class global and has only one accessing function 1740 // and this function is main (which we know is not recursive), we replace 1741 // the global with a local alloca in this function. 1742 // 1743 // NOTE: It doesn't make sense to promote non-single-value types since we 1744 // are just replacing static memory to stack memory. 1745 // 1746 // If the global is in different address space, don't bring it to stack. 1747 if (!GS.HasMultipleAccessingFunctions && 1748 GS.AccessingFunction && !GS.HasNonInstructionUser && 1749 GV->getType()->getElementType()->isSingleValueType() && 1750 GS.AccessingFunction->getName() == "main" && 1751 GS.AccessingFunction->hasExternalLinkage() && 1752 GV->getType()->getAddressSpace() == 0) { 1753 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV); 1754 Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction 1755 ->getEntryBlock().begin()); 1756 Type *ElemTy = GV->getType()->getElementType(); 1757 // FIXME: Pass Global's alignment when globals have alignment 1758 AllocaInst *Alloca = new AllocaInst(ElemTy, nullptr, 1759 GV->getName(), &FirstI); 1760 if (!isa<UndefValue>(GV->getInitializer())) 1761 new StoreInst(GV->getInitializer(), Alloca, &FirstI); 1762 1763 GV->replaceAllUsesWith(Alloca); 1764 GV->eraseFromParent(); 1765 ++NumLocalized; 1766 return true; 1767 } 1768 1769 // If the global is never loaded (but may be stored to), it is dead. 1770 // Delete it now. 1771 if (!GS.IsLoaded) { 1772 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV); 1773 1774 bool Changed; 1775 if (isLeakCheckerRoot(GV)) { 1776 // Delete any constant stores to the global. 1777 Changed = CleanupPointerRootUsers(GV, TLI); 1778 } else { 1779 // Delete any stores we can find to the global. We may not be able to 1780 // make it completely dead though. 1781 Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI); 1782 } 1783 1784 // If the global is dead now, delete it. 1785 if (GV->use_empty()) { 1786 GV->eraseFromParent(); 1787 ++NumDeleted; 1788 Changed = true; 1789 } 1790 return Changed; 1791 1792 } else if (GS.StoredType <= GlobalStatus::InitializerStored) { 1793 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n"); 1794 GV->setConstant(true); 1795 1796 // Clean up any obviously simplifiable users now. 1797 CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI); 1798 1799 // If the global is dead now, just nuke it. 1800 if (GV->use_empty()) { 1801 DEBUG(dbgs() << " *** Marking constant allowed us to simplify " 1802 << "all users and delete global!\n"); 1803 GV->eraseFromParent(); 1804 ++NumDeleted; 1805 } 1806 1807 ++NumMarked; 1808 return true; 1809 } else if (!GV->getInitializer()->getType()->isSingleValueType()) { 1810 if (DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>()) { 1811 const DataLayout &DL = DLP->getDataLayout(); 1812 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, DL)) { 1813 GVI = FirstNewGV; // Don't skip the newly produced globals! 1814 return true; 1815 } 1816 } 1817 } else if (GS.StoredType == GlobalStatus::StoredOnce) { 1818 // If the initial value for the global was an undef value, and if only 1819 // one other value was stored into it, we can just change the 1820 // initializer to be the stored value, then delete all stores to the 1821 // global. This allows us to mark it constant. 1822 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1823 if (isa<UndefValue>(GV->getInitializer())) { 1824 // Change the initial value here. 1825 GV->setInitializer(SOVConstant); 1826 1827 // Clean up any obviously simplifiable users now. 1828 CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, TLI); 1829 1830 if (GV->use_empty()) { 1831 DEBUG(dbgs() << " *** Substituting initializer allowed us to " 1832 << "simplify all users and delete global!\n"); 1833 GV->eraseFromParent(); 1834 ++NumDeleted; 1835 } else { 1836 GVI = GV; 1837 } 1838 ++NumSubstitute; 1839 return true; 1840 } 1841 1842 // Try to optimize globals based on the knowledge that only one value 1843 // (besides its initializer) is ever stored to the global. 1844 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, GVI, 1845 DL, TLI)) 1846 return true; 1847 1848 // Otherwise, if the global was not a boolean, we can shrink it to be a 1849 // boolean. 1850 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) { 1851 if (GS.Ordering == NotAtomic) { 1852 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) { 1853 ++NumShrunkToBool; 1854 return true; 1855 } 1856 } 1857 } 1858 } 1859 1860 return false; 1861} 1862 1863/// ChangeCalleesToFastCall - Walk all of the direct calls of the specified 1864/// function, changing them to FastCC. 1865static void ChangeCalleesToFastCall(Function *F) { 1866 for (User *U : F->users()) { 1867 if (isa<BlockAddress>(U)) 1868 continue; 1869 CallSite CS(cast<Instruction>(U)); 1870 CS.setCallingConv(CallingConv::Fast); 1871 } 1872} 1873 1874static AttributeSet StripNest(LLVMContext &C, const AttributeSet &Attrs) { 1875 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) { 1876 unsigned Index = Attrs.getSlotIndex(i); 1877 if (!Attrs.getSlotAttributes(i).hasAttribute(Index, Attribute::Nest)) 1878 continue; 1879 1880 // There can be only one. 1881 return Attrs.removeAttribute(C, Index, Attribute::Nest); 1882 } 1883 1884 return Attrs; 1885} 1886 1887static void RemoveNestAttribute(Function *F) { 1888 F->setAttributes(StripNest(F->getContext(), F->getAttributes())); 1889 for (User *U : F->users()) { 1890 if (isa<BlockAddress>(U)) 1891 continue; 1892 CallSite CS(cast<Instruction>(U)); 1893 CS.setAttributes(StripNest(F->getContext(), CS.getAttributes())); 1894 } 1895} 1896 1897/// Return true if this is a calling convention that we'd like to change. The 1898/// idea here is that we don't want to mess with the convention if the user 1899/// explicitly requested something with performance implications like coldcc, 1900/// GHC, or anyregcc. 1901static bool isProfitableToMakeFastCC(Function *F) { 1902 CallingConv::ID CC = F->getCallingConv(); 1903 // FIXME: Is it worth transforming x86_stdcallcc and x86_fastcallcc? 1904 return CC == CallingConv::C || CC == CallingConv::X86_ThisCall; 1905} 1906 1907bool GlobalOpt::OptimizeFunctions(Module &M) { 1908 bool Changed = false; 1909 // Optimize functions. 1910 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { 1911 Function *F = FI++; 1912 // Functions without names cannot be referenced outside this module. 1913 if (!F->hasName() && !F->isDeclaration()) 1914 F->setLinkage(GlobalValue::InternalLinkage); 1915 F->removeDeadConstantUsers(); 1916 if (F->isDefTriviallyDead()) { 1917 F->eraseFromParent(); 1918 Changed = true; 1919 ++NumFnDeleted; 1920 } else if (F->hasLocalLinkage()) { 1921 if (isProfitableToMakeFastCC(F) && !F->isVarArg() && 1922 !F->hasAddressTaken()) { 1923 // If this function has a calling convention worth changing, is not a 1924 // varargs function, and is only called directly, promote it to use the 1925 // Fast calling convention. 1926 F->setCallingConv(CallingConv::Fast); 1927 ChangeCalleesToFastCall(F); 1928 ++NumFastCallFns; 1929 Changed = true; 1930 } 1931 1932 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) && 1933 !F->hasAddressTaken()) { 1934 // The function is not used by a trampoline intrinsic, so it is safe 1935 // to remove the 'nest' attribute. 1936 RemoveNestAttribute(F); 1937 ++NumNestRemoved; 1938 Changed = true; 1939 } 1940 } 1941 } 1942 return Changed; 1943} 1944 1945bool GlobalOpt::OptimizeGlobalVars(Module &M) { 1946 bool Changed = false; 1947 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); 1948 GVI != E; ) { 1949 GlobalVariable *GV = GVI++; 1950 // Global variables without names cannot be referenced outside this module. 1951 if (!GV->hasName() && !GV->isDeclaration()) 1952 GV->setLinkage(GlobalValue::InternalLinkage); 1953 // Simplify the initializer. 1954 if (GV->hasInitializer()) 1955 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) { 1956 Constant *New = ConstantFoldConstantExpression(CE, DL, TLI); 1957 if (New && New != CE) 1958 GV->setInitializer(New); 1959 } 1960 1961 Changed |= ProcessGlobal(GV, GVI); 1962 } 1963 return Changed; 1964} 1965 1966static inline bool 1967isSimpleEnoughValueToCommit(Constant *C, 1968 SmallPtrSet<Constant*, 8> &SimpleConstants, 1969 const DataLayout *DL); 1970 1971 1972/// isSimpleEnoughValueToCommit - Return true if the specified constant can be 1973/// handled by the code generator. We don't want to generate something like: 1974/// void *X = &X/42; 1975/// because the code generator doesn't have a relocation that can handle that. 1976/// 1977/// This function should be called if C was not found (but just got inserted) 1978/// in SimpleConstants to avoid having to rescan the same constants all the 1979/// time. 1980static bool isSimpleEnoughValueToCommitHelper(Constant *C, 1981 SmallPtrSet<Constant*, 8> &SimpleConstants, 1982 const DataLayout *DL) { 1983 // Simple integer, undef, constant aggregate zero, global addresses, etc are 1984 // all supported. 1985 if (C->getNumOperands() == 0 || isa<BlockAddress>(C) || 1986 isa<GlobalValue>(C)) 1987 return true; 1988 1989 // Aggregate values are safe if all their elements are. 1990 if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) || 1991 isa<ConstantVector>(C)) { 1992 for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) { 1993 Constant *Op = cast<Constant>(C->getOperand(i)); 1994 if (!isSimpleEnoughValueToCommit(Op, SimpleConstants, DL)) 1995 return false; 1996 } 1997 return true; 1998 } 1999 2000 // We don't know exactly what relocations are allowed in constant expressions, 2001 // so we allow &global+constantoffset, which is safe and uniformly supported 2002 // across targets. 2003 ConstantExpr *CE = cast<ConstantExpr>(C); 2004 switch (CE->getOpcode()) { 2005 case Instruction::BitCast: 2006 // Bitcast is fine if the casted value is fine. 2007 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); 2008 2009 case Instruction::IntToPtr: 2010 case Instruction::PtrToInt: 2011 // int <=> ptr is fine if the int type is the same size as the 2012 // pointer type. 2013 if (!DL || DL->getTypeSizeInBits(CE->getType()) != 2014 DL->getTypeSizeInBits(CE->getOperand(0)->getType())) 2015 return false; 2016 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); 2017 2018 // GEP is fine if it is simple + constant offset. 2019 case Instruction::GetElementPtr: 2020 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) 2021 if (!isa<ConstantInt>(CE->getOperand(i))) 2022 return false; 2023 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); 2024 2025 case Instruction::Add: 2026 // We allow simple+cst. 2027 if (!isa<ConstantInt>(CE->getOperand(1))) 2028 return false; 2029 return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants, DL); 2030 } 2031 return false; 2032} 2033 2034static inline bool 2035isSimpleEnoughValueToCommit(Constant *C, 2036 SmallPtrSet<Constant*, 8> &SimpleConstants, 2037 const DataLayout *DL) { 2038 // If we already checked this constant, we win. 2039 if (!SimpleConstants.insert(C)) return true; 2040 // Check the constant. 2041 return isSimpleEnoughValueToCommitHelper(C, SimpleConstants, DL); 2042} 2043 2044 2045/// isSimpleEnoughPointerToCommit - Return true if this constant is simple 2046/// enough for us to understand. In particular, if it is a cast to anything 2047/// other than from one pointer type to another pointer type, we punt. 2048/// We basically just support direct accesses to globals and GEP's of 2049/// globals. This should be kept up to date with CommitValueTo. 2050static bool isSimpleEnoughPointerToCommit(Constant *C) { 2051 // Conservatively, avoid aggregate types. This is because we don't 2052 // want to worry about them partially overlapping other stores. 2053 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType()) 2054 return false; 2055 2056 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) 2057 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or 2058 // external globals. 2059 return GV->hasUniqueInitializer(); 2060 2061 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) { 2062 // Handle a constantexpr gep. 2063 if (CE->getOpcode() == Instruction::GetElementPtr && 2064 isa<GlobalVariable>(CE->getOperand(0)) && 2065 cast<GEPOperator>(CE)->isInBounds()) { 2066 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2067 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or 2068 // external globals. 2069 if (!GV->hasUniqueInitializer()) 2070 return false; 2071 2072 // The first index must be zero. 2073 ConstantInt *CI = dyn_cast<ConstantInt>(*std::next(CE->op_begin())); 2074 if (!CI || !CI->isZero()) return false; 2075 2076 // The remaining indices must be compile-time known integers within the 2077 // notional bounds of the corresponding static array types. 2078 if (!CE->isGEPWithNoNotionalOverIndexing()) 2079 return false; 2080 2081 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2082 2083 // A constantexpr bitcast from a pointer to another pointer is a no-op, 2084 // and we know how to evaluate it by moving the bitcast from the pointer 2085 // operand to the value operand. 2086 } else if (CE->getOpcode() == Instruction::BitCast && 2087 isa<GlobalVariable>(CE->getOperand(0))) { 2088 // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or 2089 // external globals. 2090 return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer(); 2091 } 2092 } 2093 2094 return false; 2095} 2096 2097/// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global 2098/// initializer. This returns 'Init' modified to reflect 'Val' stored into it. 2099/// At this point, the GEP operands of Addr [0, OpNo) have been stepped into. 2100static Constant *EvaluateStoreInto(Constant *Init, Constant *Val, 2101 ConstantExpr *Addr, unsigned OpNo) { 2102 // Base case of the recursion. 2103 if (OpNo == Addr->getNumOperands()) { 2104 assert(Val->getType() == Init->getType() && "Type mismatch!"); 2105 return Val; 2106 } 2107 2108 SmallVector<Constant*, 32> Elts; 2109 if (StructType *STy = dyn_cast<StructType>(Init->getType())) { 2110 // Break up the constant into its elements. 2111 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2112 Elts.push_back(Init->getAggregateElement(i)); 2113 2114 // Replace the element that we are supposed to. 2115 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo)); 2116 unsigned Idx = CU->getZExtValue(); 2117 assert(Idx < STy->getNumElements() && "Struct index out of range!"); 2118 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1); 2119 2120 // Return the modified struct. 2121 return ConstantStruct::get(STy, Elts); 2122 } 2123 2124 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo)); 2125 SequentialType *InitTy = cast<SequentialType>(Init->getType()); 2126 2127 uint64_t NumElts; 2128 if (ArrayType *ATy = dyn_cast<ArrayType>(InitTy)) 2129 NumElts = ATy->getNumElements(); 2130 else 2131 NumElts = InitTy->getVectorNumElements(); 2132 2133 // Break up the array into elements. 2134 for (uint64_t i = 0, e = NumElts; i != e; ++i) 2135 Elts.push_back(Init->getAggregateElement(i)); 2136 2137 assert(CI->getZExtValue() < NumElts); 2138 Elts[CI->getZExtValue()] = 2139 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1); 2140 2141 if (Init->getType()->isArrayTy()) 2142 return ConstantArray::get(cast<ArrayType>(InitTy), Elts); 2143 return ConstantVector::get(Elts); 2144} 2145 2146/// CommitValueTo - We have decided that Addr (which satisfies the predicate 2147/// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen. 2148static void CommitValueTo(Constant *Val, Constant *Addr) { 2149 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) { 2150 assert(GV->hasInitializer()); 2151 GV->setInitializer(Val); 2152 return; 2153 } 2154 2155 ConstantExpr *CE = cast<ConstantExpr>(Addr); 2156 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2157 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2)); 2158} 2159 2160namespace { 2161 2162/// Evaluator - This class evaluates LLVM IR, producing the Constant 2163/// representing each SSA instruction. Changes to global variables are stored 2164/// in a mapping that can be iterated over after the evaluation is complete. 2165/// Once an evaluation call fails, the evaluation object should not be reused. 2166class Evaluator { 2167public: 2168 Evaluator(const DataLayout *DL, const TargetLibraryInfo *TLI) 2169 : DL(DL), TLI(TLI) { 2170 ValueStack.emplace_back(); 2171 } 2172 2173 ~Evaluator() { 2174 for (auto &Tmp : AllocaTmps) 2175 // If there are still users of the alloca, the program is doing something 2176 // silly, e.g. storing the address of the alloca somewhere and using it 2177 // later. Since this is undefined, we'll just make it be null. 2178 if (!Tmp->use_empty()) 2179 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType())); 2180 } 2181 2182 /// EvaluateFunction - Evaluate a call to function F, returning true if 2183 /// successful, false if we can't evaluate it. ActualArgs contains the formal 2184 /// arguments for the function. 2185 bool EvaluateFunction(Function *F, Constant *&RetVal, 2186 const SmallVectorImpl<Constant*> &ActualArgs); 2187 2188 /// EvaluateBlock - Evaluate all instructions in block BB, returning true if 2189 /// successful, false if we can't evaluate it. NewBB returns the next BB that 2190 /// control flows into, or null upon return. 2191 bool EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB); 2192 2193 Constant *getVal(Value *V) { 2194 if (Constant *CV = dyn_cast<Constant>(V)) return CV; 2195 Constant *R = ValueStack.back().lookup(V); 2196 assert(R && "Reference to an uncomputed value!"); 2197 return R; 2198 } 2199 2200 void setVal(Value *V, Constant *C) { 2201 ValueStack.back()[V] = C; 2202 } 2203 2204 const DenseMap<Constant*, Constant*> &getMutatedMemory() const { 2205 return MutatedMemory; 2206 } 2207 2208 const SmallPtrSet<GlobalVariable*, 8> &getInvariants() const { 2209 return Invariants; 2210 } 2211 2212private: 2213 Constant *ComputeLoadResult(Constant *P); 2214 2215 /// ValueStack - As we compute SSA register values, we store their contents 2216 /// here. The back of the deque contains the current function and the stack 2217 /// contains the values in the calling frames. 2218 std::deque<DenseMap<Value*, Constant*>> ValueStack; 2219 2220 /// CallStack - This is used to detect recursion. In pathological situations 2221 /// we could hit exponential behavior, but at least there is nothing 2222 /// unbounded. 2223 SmallVector<Function*, 4> CallStack; 2224 2225 /// MutatedMemory - For each store we execute, we update this map. Loads 2226 /// check this to get the most up-to-date value. If evaluation is successful, 2227 /// this state is committed to the process. 2228 DenseMap<Constant*, Constant*> MutatedMemory; 2229 2230 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable 2231 /// to represent its body. This vector is needed so we can delete the 2232 /// temporary globals when we are done. 2233 SmallVector<std::unique_ptr<GlobalVariable>, 32> AllocaTmps; 2234 2235 /// Invariants - These global variables have been marked invariant by the 2236 /// static constructor. 2237 SmallPtrSet<GlobalVariable*, 8> Invariants; 2238 2239 /// SimpleConstants - These are constants we have checked and know to be 2240 /// simple enough to live in a static initializer of a global. 2241 SmallPtrSet<Constant*, 8> SimpleConstants; 2242 2243 const DataLayout *DL; 2244 const TargetLibraryInfo *TLI; 2245}; 2246 2247} // anonymous namespace 2248 2249/// ComputeLoadResult - Return the value that would be computed by a load from 2250/// P after the stores reflected by 'memory' have been performed. If we can't 2251/// decide, return null. 2252Constant *Evaluator::ComputeLoadResult(Constant *P) { 2253 // If this memory location has been recently stored, use the stored value: it 2254 // is the most up-to-date. 2255 DenseMap<Constant*, Constant*>::const_iterator I = MutatedMemory.find(P); 2256 if (I != MutatedMemory.end()) return I->second; 2257 2258 // Access it. 2259 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) { 2260 if (GV->hasDefinitiveInitializer()) 2261 return GV->getInitializer(); 2262 return nullptr; 2263 } 2264 2265 // Handle a constantexpr getelementptr. 2266 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) 2267 if (CE->getOpcode() == Instruction::GetElementPtr && 2268 isa<GlobalVariable>(CE->getOperand(0))) { 2269 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2270 if (GV->hasDefinitiveInitializer()) 2271 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2272 } 2273 2274 return nullptr; // don't know how to evaluate. 2275} 2276 2277/// EvaluateBlock - Evaluate all instructions in block BB, returning true if 2278/// successful, false if we can't evaluate it. NewBB returns the next BB that 2279/// control flows into, or null upon return. 2280bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst, 2281 BasicBlock *&NextBB) { 2282 // This is the main evaluation loop. 2283 while (1) { 2284 Constant *InstResult = nullptr; 2285 2286 DEBUG(dbgs() << "Evaluating Instruction: " << *CurInst << "\n"); 2287 2288 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) { 2289 if (!SI->isSimple()) { 2290 DEBUG(dbgs() << "Store is not simple! Can not evaluate.\n"); 2291 return false; // no volatile/atomic accesses. 2292 } 2293 Constant *Ptr = getVal(SI->getOperand(1)); 2294 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) { 2295 DEBUG(dbgs() << "Folding constant ptr expression: " << *Ptr); 2296 Ptr = ConstantFoldConstantExpression(CE, DL, TLI); 2297 DEBUG(dbgs() << "; To: " << *Ptr << "\n"); 2298 } 2299 if (!isSimpleEnoughPointerToCommit(Ptr)) { 2300 // If this is too complex for us to commit, reject it. 2301 DEBUG(dbgs() << "Pointer is too complex for us to evaluate store."); 2302 return false; 2303 } 2304 2305 Constant *Val = getVal(SI->getOperand(0)); 2306 2307 // If this might be too difficult for the backend to handle (e.g. the addr 2308 // of one global variable divided by another) then we can't commit it. 2309 if (!isSimpleEnoughValueToCommit(Val, SimpleConstants, DL)) { 2310 DEBUG(dbgs() << "Store value is too complex to evaluate store. " << *Val 2311 << "\n"); 2312 return false; 2313 } 2314 2315 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) { 2316 if (CE->getOpcode() == Instruction::BitCast) { 2317 DEBUG(dbgs() << "Attempting to resolve bitcast on constant ptr.\n"); 2318 // If we're evaluating a store through a bitcast, then we need 2319 // to pull the bitcast off the pointer type and push it onto the 2320 // stored value. 2321 Ptr = CE->getOperand(0); 2322 2323 Type *NewTy = cast<PointerType>(Ptr->getType())->getElementType(); 2324 2325 // In order to push the bitcast onto the stored value, a bitcast 2326 // from NewTy to Val's type must be legal. If it's not, we can try 2327 // introspecting NewTy to find a legal conversion. 2328 while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) { 2329 // If NewTy is a struct, we can convert the pointer to the struct 2330 // into a pointer to its first member. 2331 // FIXME: This could be extended to support arrays as well. 2332 if (StructType *STy = dyn_cast<StructType>(NewTy)) { 2333 NewTy = STy->getTypeAtIndex(0U); 2334 2335 IntegerType *IdxTy = IntegerType::get(NewTy->getContext(), 32); 2336 Constant *IdxZero = ConstantInt::get(IdxTy, 0, false); 2337 Constant * const IdxList[] = {IdxZero, IdxZero}; 2338 2339 Ptr = ConstantExpr::getGetElementPtr(Ptr, IdxList); 2340 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) 2341 Ptr = ConstantFoldConstantExpression(CE, DL, TLI); 2342 2343 // If we can't improve the situation by introspecting NewTy, 2344 // we have to give up. 2345 } else { 2346 DEBUG(dbgs() << "Failed to bitcast constant ptr, can not " 2347 "evaluate.\n"); 2348 return false; 2349 } 2350 } 2351 2352 // If we found compatible types, go ahead and push the bitcast 2353 // onto the stored value. 2354 Val = ConstantExpr::getBitCast(Val, NewTy); 2355 2356 DEBUG(dbgs() << "Evaluated bitcast: " << *Val << "\n"); 2357 } 2358 } 2359 2360 MutatedMemory[Ptr] = Val; 2361 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) { 2362 InstResult = ConstantExpr::get(BO->getOpcode(), 2363 getVal(BO->getOperand(0)), 2364 getVal(BO->getOperand(1))); 2365 DEBUG(dbgs() << "Found a BinaryOperator! Simplifying: " << *InstResult 2366 << "\n"); 2367 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) { 2368 InstResult = ConstantExpr::getCompare(CI->getPredicate(), 2369 getVal(CI->getOperand(0)), 2370 getVal(CI->getOperand(1))); 2371 DEBUG(dbgs() << "Found a CmpInst! Simplifying: " << *InstResult 2372 << "\n"); 2373 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) { 2374 InstResult = ConstantExpr::getCast(CI->getOpcode(), 2375 getVal(CI->getOperand(0)), 2376 CI->getType()); 2377 DEBUG(dbgs() << "Found a Cast! Simplifying: " << *InstResult 2378 << "\n"); 2379 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) { 2380 InstResult = ConstantExpr::getSelect(getVal(SI->getOperand(0)), 2381 getVal(SI->getOperand(1)), 2382 getVal(SI->getOperand(2))); 2383 DEBUG(dbgs() << "Found a Select! Simplifying: " << *InstResult 2384 << "\n"); 2385 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) { 2386 Constant *P = getVal(GEP->getOperand(0)); 2387 SmallVector<Constant*, 8> GEPOps; 2388 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); 2389 i != e; ++i) 2390 GEPOps.push_back(getVal(*i)); 2391 InstResult = 2392 ConstantExpr::getGetElementPtr(P, GEPOps, 2393 cast<GEPOperator>(GEP)->isInBounds()); 2394 DEBUG(dbgs() << "Found a GEP! Simplifying: " << *InstResult 2395 << "\n"); 2396 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) { 2397 2398 if (!LI->isSimple()) { 2399 DEBUG(dbgs() << "Found a Load! Not a simple load, can not evaluate.\n"); 2400 return false; // no volatile/atomic accesses. 2401 } 2402 2403 Constant *Ptr = getVal(LI->getOperand(0)); 2404 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) { 2405 Ptr = ConstantFoldConstantExpression(CE, DL, TLI); 2406 DEBUG(dbgs() << "Found a constant pointer expression, constant " 2407 "folding: " << *Ptr << "\n"); 2408 } 2409 InstResult = ComputeLoadResult(Ptr); 2410 if (!InstResult) { 2411 DEBUG(dbgs() << "Failed to compute load result. Can not evaluate load." 2412 "\n"); 2413 return false; // Could not evaluate load. 2414 } 2415 2416 DEBUG(dbgs() << "Evaluated load: " << *InstResult << "\n"); 2417 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) { 2418 if (AI->isArrayAllocation()) { 2419 DEBUG(dbgs() << "Found an array alloca. Can not evaluate.\n"); 2420 return false; // Cannot handle array allocs. 2421 } 2422 Type *Ty = AI->getType()->getElementType(); 2423 AllocaTmps.push_back( 2424 make_unique<GlobalVariable>(Ty, false, GlobalValue::InternalLinkage, 2425 UndefValue::get(Ty), AI->getName())); 2426 InstResult = AllocaTmps.back().get(); 2427 DEBUG(dbgs() << "Found an alloca. Result: " << *InstResult << "\n"); 2428 } else if (isa<CallInst>(CurInst) || isa<InvokeInst>(CurInst)) { 2429 CallSite CS(CurInst); 2430 2431 // Debug info can safely be ignored here. 2432 if (isa<DbgInfoIntrinsic>(CS.getInstruction())) { 2433 DEBUG(dbgs() << "Ignoring debug info.\n"); 2434 ++CurInst; 2435 continue; 2436 } 2437 2438 // Cannot handle inline asm. 2439 if (isa<InlineAsm>(CS.getCalledValue())) { 2440 DEBUG(dbgs() << "Found inline asm, can not evaluate.\n"); 2441 return false; 2442 } 2443 2444 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) { 2445 if (MemSetInst *MSI = dyn_cast<MemSetInst>(II)) { 2446 if (MSI->isVolatile()) { 2447 DEBUG(dbgs() << "Can not optimize a volatile memset " << 2448 "intrinsic.\n"); 2449 return false; 2450 } 2451 Constant *Ptr = getVal(MSI->getDest()); 2452 Constant *Val = getVal(MSI->getValue()); 2453 Constant *DestVal = ComputeLoadResult(getVal(Ptr)); 2454 if (Val->isNullValue() && DestVal && DestVal->isNullValue()) { 2455 // This memset is a no-op. 2456 DEBUG(dbgs() << "Ignoring no-op memset.\n"); 2457 ++CurInst; 2458 continue; 2459 } 2460 } 2461 2462 if (II->getIntrinsicID() == Intrinsic::lifetime_start || 2463 II->getIntrinsicID() == Intrinsic::lifetime_end) { 2464 DEBUG(dbgs() << "Ignoring lifetime intrinsic.\n"); 2465 ++CurInst; 2466 continue; 2467 } 2468 2469 if (II->getIntrinsicID() == Intrinsic::invariant_start) { 2470 // We don't insert an entry into Values, as it doesn't have a 2471 // meaningful return value. 2472 if (!II->use_empty()) { 2473 DEBUG(dbgs() << "Found unused invariant_start. Can't evaluate.\n"); 2474 return false; 2475 } 2476 ConstantInt *Size = cast<ConstantInt>(II->getArgOperand(0)); 2477 Value *PtrArg = getVal(II->getArgOperand(1)); 2478 Value *Ptr = PtrArg->stripPointerCasts(); 2479 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) { 2480 Type *ElemTy = cast<PointerType>(GV->getType())->getElementType(); 2481 if (DL && !Size->isAllOnesValue() && 2482 Size->getValue().getLimitedValue() >= 2483 DL->getTypeStoreSize(ElemTy)) { 2484 Invariants.insert(GV); 2485 DEBUG(dbgs() << "Found a global var that is an invariant: " << *GV 2486 << "\n"); 2487 } else { 2488 DEBUG(dbgs() << "Found a global var, but can not treat it as an " 2489 "invariant.\n"); 2490 } 2491 } 2492 // Continue even if we do nothing. 2493 ++CurInst; 2494 continue; 2495 } 2496 2497 DEBUG(dbgs() << "Unknown intrinsic. Can not evaluate.\n"); 2498 return false; 2499 } 2500 2501 // Resolve function pointers. 2502 Function *Callee = dyn_cast<Function>(getVal(CS.getCalledValue())); 2503 if (!Callee || Callee->mayBeOverridden()) { 2504 DEBUG(dbgs() << "Can not resolve function pointer.\n"); 2505 return false; // Cannot resolve. 2506 } 2507 2508 SmallVector<Constant*, 8> Formals; 2509 for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end(); i != e; ++i) 2510 Formals.push_back(getVal(*i)); 2511 2512 if (Callee->isDeclaration()) { 2513 // If this is a function we can constant fold, do it. 2514 if (Constant *C = ConstantFoldCall(Callee, Formals, TLI)) { 2515 InstResult = C; 2516 DEBUG(dbgs() << "Constant folded function call. Result: " << 2517 *InstResult << "\n"); 2518 } else { 2519 DEBUG(dbgs() << "Can not constant fold function call.\n"); 2520 return false; 2521 } 2522 } else { 2523 if (Callee->getFunctionType()->isVarArg()) { 2524 DEBUG(dbgs() << "Can not constant fold vararg function call.\n"); 2525 return false; 2526 } 2527 2528 Constant *RetVal = nullptr; 2529 // Execute the call, if successful, use the return value. 2530 ValueStack.emplace_back(); 2531 if (!EvaluateFunction(Callee, RetVal, Formals)) { 2532 DEBUG(dbgs() << "Failed to evaluate function.\n"); 2533 return false; 2534 } 2535 ValueStack.pop_back(); 2536 InstResult = RetVal; 2537 2538 if (InstResult) { 2539 DEBUG(dbgs() << "Successfully evaluated function. Result: " << 2540 InstResult << "\n\n"); 2541 } else { 2542 DEBUG(dbgs() << "Successfully evaluated function. Result: 0\n\n"); 2543 } 2544 } 2545 } else if (isa<TerminatorInst>(CurInst)) { 2546 DEBUG(dbgs() << "Found a terminator instruction.\n"); 2547 2548 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) { 2549 if (BI->isUnconditional()) { 2550 NextBB = BI->getSuccessor(0); 2551 } else { 2552 ConstantInt *Cond = 2553 dyn_cast<ConstantInt>(getVal(BI->getCondition())); 2554 if (!Cond) return false; // Cannot determine. 2555 2556 NextBB = BI->getSuccessor(!Cond->getZExtValue()); 2557 } 2558 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) { 2559 ConstantInt *Val = 2560 dyn_cast<ConstantInt>(getVal(SI->getCondition())); 2561 if (!Val) return false; // Cannot determine. 2562 NextBB = SI->findCaseValue(Val).getCaseSuccessor(); 2563 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) { 2564 Value *Val = getVal(IBI->getAddress())->stripPointerCasts(); 2565 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val)) 2566 NextBB = BA->getBasicBlock(); 2567 else 2568 return false; // Cannot determine. 2569 } else if (isa<ReturnInst>(CurInst)) { 2570 NextBB = nullptr; 2571 } else { 2572 // invoke, unwind, resume, unreachable. 2573 DEBUG(dbgs() << "Can not handle terminator."); 2574 return false; // Cannot handle this terminator. 2575 } 2576 2577 // We succeeded at evaluating this block! 2578 DEBUG(dbgs() << "Successfully evaluated block.\n"); 2579 return true; 2580 } else { 2581 // Did not know how to evaluate this! 2582 DEBUG(dbgs() << "Failed to evaluate block due to unhandled instruction." 2583 "\n"); 2584 return false; 2585 } 2586 2587 if (!CurInst->use_empty()) { 2588 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult)) 2589 InstResult = ConstantFoldConstantExpression(CE, DL, TLI); 2590 2591 setVal(CurInst, InstResult); 2592 } 2593 2594 // If we just processed an invoke, we finished evaluating the block. 2595 if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) { 2596 NextBB = II->getNormalDest(); 2597 DEBUG(dbgs() << "Found an invoke instruction. Finished Block.\n\n"); 2598 return true; 2599 } 2600 2601 // Advance program counter. 2602 ++CurInst; 2603 } 2604} 2605 2606/// EvaluateFunction - Evaluate a call to function F, returning true if 2607/// successful, false if we can't evaluate it. ActualArgs contains the formal 2608/// arguments for the function. 2609bool Evaluator::EvaluateFunction(Function *F, Constant *&RetVal, 2610 const SmallVectorImpl<Constant*> &ActualArgs) { 2611 // Check to see if this function is already executing (recursion). If so, 2612 // bail out. TODO: we might want to accept limited recursion. 2613 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end()) 2614 return false; 2615 2616 CallStack.push_back(F); 2617 2618 // Initialize arguments to the incoming values specified. 2619 unsigned ArgNo = 0; 2620 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E; 2621 ++AI, ++ArgNo) 2622 setVal(AI, ActualArgs[ArgNo]); 2623 2624 // ExecutedBlocks - We only handle non-looping, non-recursive code. As such, 2625 // we can only evaluate any one basic block at most once. This set keeps 2626 // track of what we have executed so we can detect recursive cases etc. 2627 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks; 2628 2629 // CurBB - The current basic block we're evaluating. 2630 BasicBlock *CurBB = F->begin(); 2631 2632 BasicBlock::iterator CurInst = CurBB->begin(); 2633 2634 while (1) { 2635 BasicBlock *NextBB = nullptr; // Initialized to avoid compiler warnings. 2636 DEBUG(dbgs() << "Trying to evaluate BB: " << *CurBB << "\n"); 2637 2638 if (!EvaluateBlock(CurInst, NextBB)) 2639 return false; 2640 2641 if (!NextBB) { 2642 // Successfully running until there's no next block means that we found 2643 // the return. Fill it the return value and pop the call stack. 2644 ReturnInst *RI = cast<ReturnInst>(CurBB->getTerminator()); 2645 if (RI->getNumOperands()) 2646 RetVal = getVal(RI->getOperand(0)); 2647 CallStack.pop_back(); 2648 return true; 2649 } 2650 2651 // Okay, we succeeded in evaluating this control flow. See if we have 2652 // executed the new block before. If so, we have a looping function, 2653 // which we cannot evaluate in reasonable time. 2654 if (!ExecutedBlocks.insert(NextBB)) 2655 return false; // looped! 2656 2657 // Okay, we have never been in this block before. Check to see if there 2658 // are any PHI nodes. If so, evaluate them with information about where 2659 // we came from. 2660 PHINode *PN = nullptr; 2661 for (CurInst = NextBB->begin(); 2662 (PN = dyn_cast<PHINode>(CurInst)); ++CurInst) 2663 setVal(PN, getVal(PN->getIncomingValueForBlock(CurBB))); 2664 2665 // Advance to the next block. 2666 CurBB = NextBB; 2667 } 2668} 2669 2670/// EvaluateStaticConstructor - Evaluate static constructors in the function, if 2671/// we can. Return true if we can, false otherwise. 2672static bool EvaluateStaticConstructor(Function *F, const DataLayout *DL, 2673 const TargetLibraryInfo *TLI) { 2674 // Call the function. 2675 Evaluator Eval(DL, TLI); 2676 Constant *RetValDummy; 2677 bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy, 2678 SmallVector<Constant*, 0>()); 2679 2680 if (EvalSuccess) { 2681 ++NumCtorsEvaluated; 2682 2683 // We succeeded at evaluation: commit the result. 2684 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" 2685 << F->getName() << "' to " << Eval.getMutatedMemory().size() 2686 << " stores.\n"); 2687 for (DenseMap<Constant*, Constant*>::const_iterator I = 2688 Eval.getMutatedMemory().begin(), E = Eval.getMutatedMemory().end(); 2689 I != E; ++I) 2690 CommitValueTo(I->second, I->first); 2691 for (SmallPtrSet<GlobalVariable*, 8>::const_iterator I = 2692 Eval.getInvariants().begin(), E = Eval.getInvariants().end(); 2693 I != E; ++I) 2694 (*I)->setConstant(true); 2695 } 2696 2697 return EvalSuccess; 2698} 2699 2700static int compareNames(Constant *const *A, Constant *const *B) { 2701 return (*A)->getName().compare((*B)->getName()); 2702} 2703 2704static void setUsedInitializer(GlobalVariable &V, 2705 SmallPtrSet<GlobalValue *, 8> Init) { 2706 if (Init.empty()) { 2707 V.eraseFromParent(); 2708 return; 2709 } 2710 2711 // Type of pointer to the array of pointers. 2712 PointerType *Int8PtrTy = Type::getInt8PtrTy(V.getContext(), 0); 2713 2714 SmallVector<llvm::Constant *, 8> UsedArray; 2715 for (SmallPtrSet<GlobalValue *, 8>::iterator I = Init.begin(), E = Init.end(); 2716 I != E; ++I) { 2717 Constant *Cast 2718 = ConstantExpr::getPointerBitCastOrAddrSpaceCast(*I, Int8PtrTy); 2719 UsedArray.push_back(Cast); 2720 } 2721 // Sort to get deterministic order. 2722 array_pod_sort(UsedArray.begin(), UsedArray.end(), compareNames); 2723 ArrayType *ATy = ArrayType::get(Int8PtrTy, UsedArray.size()); 2724 2725 Module *M = V.getParent(); 2726 V.removeFromParent(); 2727 GlobalVariable *NV = 2728 new GlobalVariable(*M, ATy, false, llvm::GlobalValue::AppendingLinkage, 2729 llvm::ConstantArray::get(ATy, UsedArray), ""); 2730 NV->takeName(&V); 2731 NV->setSection("llvm.metadata"); 2732 delete &V; 2733} 2734 2735namespace { 2736/// \brief An easy to access representation of llvm.used and llvm.compiler.used. 2737class LLVMUsed { 2738 SmallPtrSet<GlobalValue *, 8> Used; 2739 SmallPtrSet<GlobalValue *, 8> CompilerUsed; 2740 GlobalVariable *UsedV; 2741 GlobalVariable *CompilerUsedV; 2742 2743public: 2744 LLVMUsed(Module &M) { 2745 UsedV = collectUsedGlobalVariables(M, Used, false); 2746 CompilerUsedV = collectUsedGlobalVariables(M, CompilerUsed, true); 2747 } 2748 typedef SmallPtrSet<GlobalValue *, 8>::iterator iterator; 2749 iterator usedBegin() { return Used.begin(); } 2750 iterator usedEnd() { return Used.end(); } 2751 iterator compilerUsedBegin() { return CompilerUsed.begin(); } 2752 iterator compilerUsedEnd() { return CompilerUsed.end(); } 2753 bool usedCount(GlobalValue *GV) const { return Used.count(GV); } 2754 bool compilerUsedCount(GlobalValue *GV) const { 2755 return CompilerUsed.count(GV); 2756 } 2757 bool usedErase(GlobalValue *GV) { return Used.erase(GV); } 2758 bool compilerUsedErase(GlobalValue *GV) { return CompilerUsed.erase(GV); } 2759 bool usedInsert(GlobalValue *GV) { return Used.insert(GV); } 2760 bool compilerUsedInsert(GlobalValue *GV) { return CompilerUsed.insert(GV); } 2761 2762 void syncVariablesAndSets() { 2763 if (UsedV) 2764 setUsedInitializer(*UsedV, Used); 2765 if (CompilerUsedV) 2766 setUsedInitializer(*CompilerUsedV, CompilerUsed); 2767 } 2768}; 2769} 2770 2771static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) { 2772 if (GA.use_empty()) // No use at all. 2773 return false; 2774 2775 assert((!U.usedCount(&GA) || !U.compilerUsedCount(&GA)) && 2776 "We should have removed the duplicated " 2777 "element from llvm.compiler.used"); 2778 if (!GA.hasOneUse()) 2779 // Strictly more than one use. So at least one is not in llvm.used and 2780 // llvm.compiler.used. 2781 return true; 2782 2783 // Exactly one use. Check if it is in llvm.used or llvm.compiler.used. 2784 return !U.usedCount(&GA) && !U.compilerUsedCount(&GA); 2785} 2786 2787static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V, 2788 const LLVMUsed &U) { 2789 unsigned N = 2; 2790 assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) && 2791 "We should have removed the duplicated " 2792 "element from llvm.compiler.used"); 2793 if (U.usedCount(&V) || U.compilerUsedCount(&V)) 2794 ++N; 2795 return V.hasNUsesOrMore(N); 2796} 2797 2798static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) { 2799 if (!GA.hasLocalLinkage()) 2800 return true; 2801 2802 return U.usedCount(&GA) || U.compilerUsedCount(&GA); 2803} 2804 2805static bool hasUsesToReplace(GlobalAlias &GA, LLVMUsed &U, bool &RenameTarget) { 2806 RenameTarget = false; 2807 bool Ret = false; 2808 if (hasUseOtherThanLLVMUsed(GA, U)) 2809 Ret = true; 2810 2811 // If the alias is externally visible, we may still be able to simplify it. 2812 if (!mayHaveOtherReferences(GA, U)) 2813 return Ret; 2814 2815 // If the aliasee has internal linkage, give it the name and linkage 2816 // of the alias, and delete the alias. This turns: 2817 // define internal ... @f(...) 2818 // @a = alias ... @f 2819 // into: 2820 // define ... @a(...) 2821 Constant *Aliasee = GA.getAliasee(); 2822 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts()); 2823 if (!Target->hasLocalLinkage()) 2824 return Ret; 2825 2826 // Do not perform the transform if multiple aliases potentially target the 2827 // aliasee. This check also ensures that it is safe to replace the section 2828 // and other attributes of the aliasee with those of the alias. 2829 if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U)) 2830 return Ret; 2831 2832 RenameTarget = true; 2833 return true; 2834} 2835 2836bool GlobalOpt::OptimizeGlobalAliases(Module &M) { 2837 bool Changed = false; 2838 LLVMUsed Used(M); 2839 2840 for (SmallPtrSet<GlobalValue *, 8>::iterator I = Used.usedBegin(), 2841 E = Used.usedEnd(); 2842 I != E; ++I) 2843 Used.compilerUsedErase(*I); 2844 2845 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); 2846 I != E;) { 2847 Module::alias_iterator J = I++; 2848 // Aliases without names cannot be referenced outside this module. 2849 if (!J->hasName() && !J->isDeclaration()) 2850 J->setLinkage(GlobalValue::InternalLinkage); 2851 // If the aliasee may change at link time, nothing can be done - bail out. 2852 if (J->mayBeOverridden()) 2853 continue; 2854 2855 Constant *Aliasee = J->getAliasee(); 2856 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts()); 2857 Target->removeDeadConstantUsers(); 2858 2859 // Make all users of the alias use the aliasee instead. 2860 bool RenameTarget; 2861 if (!hasUsesToReplace(*J, Used, RenameTarget)) 2862 continue; 2863 2864 J->replaceAllUsesWith(ConstantExpr::getBitCast(Aliasee, J->getType())); 2865 ++NumAliasesResolved; 2866 Changed = true; 2867 2868 if (RenameTarget) { 2869 // Give the aliasee the name, linkage and other attributes of the alias. 2870 Target->takeName(J); 2871 Target->setLinkage(J->getLinkage()); 2872 Target->setVisibility(J->getVisibility()); 2873 Target->setDLLStorageClass(J->getDLLStorageClass()); 2874 2875 if (Used.usedErase(J)) 2876 Used.usedInsert(Target); 2877 2878 if (Used.compilerUsedErase(J)) 2879 Used.compilerUsedInsert(Target); 2880 } else if (mayHaveOtherReferences(*J, Used)) 2881 continue; 2882 2883 // Delete the alias. 2884 M.getAliasList().erase(J); 2885 ++NumAliasesRemoved; 2886 Changed = true; 2887 } 2888 2889 Used.syncVariablesAndSets(); 2890 2891 return Changed; 2892} 2893 2894static Function *FindCXAAtExit(Module &M, TargetLibraryInfo *TLI) { 2895 if (!TLI->has(LibFunc::cxa_atexit)) 2896 return nullptr; 2897 2898 Function *Fn = M.getFunction(TLI->getName(LibFunc::cxa_atexit)); 2899 2900 if (!Fn) 2901 return nullptr; 2902 2903 FunctionType *FTy = Fn->getFunctionType(); 2904 2905 // Checking that the function has the right return type, the right number of 2906 // parameters and that they all have pointer types should be enough. 2907 if (!FTy->getReturnType()->isIntegerTy() || 2908 FTy->getNumParams() != 3 || 2909 !FTy->getParamType(0)->isPointerTy() || 2910 !FTy->getParamType(1)->isPointerTy() || 2911 !FTy->getParamType(2)->isPointerTy()) 2912 return nullptr; 2913 2914 return Fn; 2915} 2916 2917/// cxxDtorIsEmpty - Returns whether the given function is an empty C++ 2918/// destructor and can therefore be eliminated. 2919/// Note that we assume that other optimization passes have already simplified 2920/// the code so we only look for a function with a single basic block, where 2921/// the only allowed instructions are 'ret', 'call' to an empty C++ dtor and 2922/// other side-effect free instructions. 2923static bool cxxDtorIsEmpty(const Function &Fn, 2924 SmallPtrSet<const Function *, 8> &CalledFunctions) { 2925 // FIXME: We could eliminate C++ destructors if they're readonly/readnone and 2926 // nounwind, but that doesn't seem worth doing. 2927 if (Fn.isDeclaration()) 2928 return false; 2929 2930 if (++Fn.begin() != Fn.end()) 2931 return false; 2932 2933 const BasicBlock &EntryBlock = Fn.getEntryBlock(); 2934 for (BasicBlock::const_iterator I = EntryBlock.begin(), E = EntryBlock.end(); 2935 I != E; ++I) { 2936 if (const CallInst *CI = dyn_cast<CallInst>(I)) { 2937 // Ignore debug intrinsics. 2938 if (isa<DbgInfoIntrinsic>(CI)) 2939 continue; 2940 2941 const Function *CalledFn = CI->getCalledFunction(); 2942 2943 if (!CalledFn) 2944 return false; 2945 2946 SmallPtrSet<const Function *, 8> NewCalledFunctions(CalledFunctions); 2947 2948 // Don't treat recursive functions as empty. 2949 if (!NewCalledFunctions.insert(CalledFn)) 2950 return false; 2951 2952 if (!cxxDtorIsEmpty(*CalledFn, NewCalledFunctions)) 2953 return false; 2954 } else if (isa<ReturnInst>(*I)) 2955 return true; // We're done. 2956 else if (I->mayHaveSideEffects()) 2957 return false; // Destructor with side effects, bail. 2958 } 2959 2960 return false; 2961} 2962 2963bool GlobalOpt::OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) { 2964 /// Itanium C++ ABI p3.3.5: 2965 /// 2966 /// After constructing a global (or local static) object, that will require 2967 /// destruction on exit, a termination function is registered as follows: 2968 /// 2969 /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d ); 2970 /// 2971 /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the 2972 /// call f(p) when DSO d is unloaded, before all such termination calls 2973 /// registered before this one. It returns zero if registration is 2974 /// successful, nonzero on failure. 2975 2976 // This pass will look for calls to __cxa_atexit where the function is trivial 2977 // and remove them. 2978 bool Changed = false; 2979 2980 for (auto I = CXAAtExitFn->user_begin(), E = CXAAtExitFn->user_end(); 2981 I != E;) { 2982 // We're only interested in calls. Theoretically, we could handle invoke 2983 // instructions as well, but neither llvm-gcc nor clang generate invokes 2984 // to __cxa_atexit. 2985 CallInst *CI = dyn_cast<CallInst>(*I++); 2986 if (!CI) 2987 continue; 2988 2989 Function *DtorFn = 2990 dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts()); 2991 if (!DtorFn) 2992 continue; 2993 2994 SmallPtrSet<const Function *, 8> CalledFunctions; 2995 if (!cxxDtorIsEmpty(*DtorFn, CalledFunctions)) 2996 continue; 2997 2998 // Just remove the call. 2999 CI->replaceAllUsesWith(Constant::getNullValue(CI->getType())); 3000 CI->eraseFromParent(); 3001 3002 ++NumCXXDtorsRemoved; 3003 3004 Changed |= true; 3005 } 3006 3007 return Changed; 3008} 3009 3010bool GlobalOpt::runOnModule(Module &M) { 3011 bool Changed = false; 3012 3013 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); 3014 DL = DLP ? &DLP->getDataLayout() : nullptr; 3015 TLI = &getAnalysis<TargetLibraryInfo>(); 3016 3017 bool LocalChange = true; 3018 while (LocalChange) { 3019 LocalChange = false; 3020 3021 // Delete functions that are trivially dead, ccc -> fastcc 3022 LocalChange |= OptimizeFunctions(M); 3023 3024 // Optimize global_ctors list. 3025 LocalChange |= optimizeGlobalCtorsList(M, [&](Function *F) { 3026 return EvaluateStaticConstructor(F, DL, TLI); 3027 }); 3028 3029 // Optimize non-address-taken globals. 3030 LocalChange |= OptimizeGlobalVars(M); 3031 3032 // Resolve aliases, when possible. 3033 LocalChange |= OptimizeGlobalAliases(M); 3034 3035 // Try to remove trivial global destructors if they are not removed 3036 // already. 3037 Function *CXAAtExitFn = FindCXAAtExit(M, TLI); 3038 if (CXAAtExitFn) 3039 LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn); 3040 3041 Changed |= LocalChange; 3042 } 3043 3044 // TODO: Move all global ctors functions to the end of the module for code 3045 // layout. 3046 3047 return Changed; 3048} 3049