GlobalOpt.cpp revision 28f4d2fb94b9057d8daba2128867fde276a37d1b
1//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass transforms simple global variables that never have their address 11// taken. If obviously true, it marks read/write globals as constant, deletes 12// variables only stored to, etc. 13// 14//===----------------------------------------------------------------------===// 15 16#define DEBUG_TYPE "globalopt" 17#include "llvm/Transforms/IPO.h" 18#include "llvm/CallingConv.h" 19#include "llvm/Constants.h" 20#include "llvm/DerivedTypes.h" 21#include "llvm/Instructions.h" 22#include "llvm/IntrinsicInst.h" 23#include "llvm/LLVMContext.h" 24#include "llvm/Module.h" 25#include "llvm/Pass.h" 26#include "llvm/Analysis/ConstantFolding.h" 27#include "llvm/Analysis/MemoryBuiltins.h" 28#include "llvm/Target/TargetData.h" 29#include "llvm/Support/CallSite.h" 30#include "llvm/Support/Debug.h" 31#include "llvm/Support/ErrorHandling.h" 32#include "llvm/Support/GetElementPtrTypeIterator.h" 33#include "llvm/Support/MathExtras.h" 34#include "llvm/Support/raw_ostream.h" 35#include "llvm/ADT/DenseMap.h" 36#include "llvm/ADT/SmallPtrSet.h" 37#include "llvm/ADT/SmallVector.h" 38#include "llvm/ADT/Statistic.h" 39#include "llvm/ADT/STLExtras.h" 40#include <algorithm> 41using namespace llvm; 42 43STATISTIC(NumMarked , "Number of globals marked constant"); 44STATISTIC(NumSRA , "Number of aggregate globals broken into scalars"); 45STATISTIC(NumHeapSRA , "Number of heap objects SRA'd"); 46STATISTIC(NumSubstitute,"Number of globals with initializers stored into them"); 47STATISTIC(NumDeleted , "Number of globals deleted"); 48STATISTIC(NumFnDeleted , "Number of functions deleted"); 49STATISTIC(NumGlobUses , "Number of global uses devirtualized"); 50STATISTIC(NumLocalized , "Number of globals localized"); 51STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans"); 52STATISTIC(NumFastCallFns , "Number of functions converted to fastcc"); 53STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated"); 54STATISTIC(NumNestRemoved , "Number of nest attributes removed"); 55STATISTIC(NumAliasesResolved, "Number of global aliases resolved"); 56STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated"); 57 58namespace { 59 struct GlobalOpt : public ModulePass { 60 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 61 } 62 static char ID; // Pass identification, replacement for typeid 63 GlobalOpt() : ModulePass(&ID) {} 64 65 bool runOnModule(Module &M); 66 67 private: 68 GlobalVariable *FindGlobalCtors(Module &M); 69 bool OptimizeFunctions(Module &M); 70 bool OptimizeGlobalVars(Module &M); 71 bool OptimizeGlobalAliases(Module &M); 72 bool OptimizeGlobalCtorsList(GlobalVariable *&GCL); 73 bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI); 74 }; 75} 76 77char GlobalOpt::ID = 0; 78static RegisterPass<GlobalOpt> X("globalopt", "Global Variable Optimizer"); 79 80ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); } 81 82namespace { 83 84/// GlobalStatus - As we analyze each global, keep track of some information 85/// about it. If we find out that the address of the global is taken, none of 86/// this info will be accurate. 87struct GlobalStatus { 88 /// isLoaded - True if the global is ever loaded. If the global isn't ever 89 /// loaded it can be deleted. 90 bool isLoaded; 91 92 /// StoredType - Keep track of what stores to the global look like. 93 /// 94 enum StoredType { 95 /// NotStored - There is no store to this global. It can thus be marked 96 /// constant. 97 NotStored, 98 99 /// isInitializerStored - This global is stored to, but the only thing 100 /// stored is the constant it was initialized with. This is only tracked 101 /// for scalar globals. 102 isInitializerStored, 103 104 /// isStoredOnce - This global is stored to, but only its initializer and 105 /// one other value is ever stored to it. If this global isStoredOnce, we 106 /// track the value stored to it in StoredOnceValue below. This is only 107 /// tracked for scalar globals. 108 isStoredOnce, 109 110 /// isStored - This global is stored to by multiple values or something else 111 /// that we cannot track. 112 isStored 113 } StoredType; 114 115 /// StoredOnceValue - If only one value (besides the initializer constant) is 116 /// ever stored to this global, keep track of what value it is. 117 Value *StoredOnceValue; 118 119 /// AccessingFunction/HasMultipleAccessingFunctions - These start out 120 /// null/false. When the first accessing function is noticed, it is recorded. 121 /// When a second different accessing function is noticed, 122 /// HasMultipleAccessingFunctions is set to true. 123 Function *AccessingFunction; 124 bool HasMultipleAccessingFunctions; 125 126 /// HasNonInstructionUser - Set to true if this global has a user that is not 127 /// an instruction (e.g. a constant expr or GV initializer). 128 bool HasNonInstructionUser; 129 130 /// HasPHIUser - Set to true if this global has a user that is a PHI node. 131 bool HasPHIUser; 132 133 GlobalStatus() : isLoaded(false), StoredType(NotStored), StoredOnceValue(0), 134 AccessingFunction(0), HasMultipleAccessingFunctions(false), 135 HasNonInstructionUser(false), HasPHIUser(false) {} 136}; 137 138} 139 140// SafeToDestroyConstant - It is safe to destroy a constant iff it is only used 141// by constants itself. Note that constants cannot be cyclic, so this test is 142// pretty easy to implement recursively. 143// 144static bool SafeToDestroyConstant(Constant *C) { 145 if (isa<GlobalValue>(C)) return false; 146 147 for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI) 148 if (Constant *CU = dyn_cast<Constant>(*UI)) { 149 if (!SafeToDestroyConstant(CU)) return false; 150 } else 151 return false; 152 return true; 153} 154 155 156/// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus 157/// structure. If the global has its address taken, return true to indicate we 158/// can't do anything with it. 159/// 160static bool AnalyzeGlobal(Value *V, GlobalStatus &GS, 161 SmallPtrSet<PHINode*, 16> &PHIUsers) { 162 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) 163 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) { 164 GS.HasNonInstructionUser = true; 165 166 if (AnalyzeGlobal(CE, GS, PHIUsers)) return true; 167 168 } else if (Instruction *I = dyn_cast<Instruction>(*UI)) { 169 if (!GS.HasMultipleAccessingFunctions) { 170 Function *F = I->getParent()->getParent(); 171 if (GS.AccessingFunction == 0) 172 GS.AccessingFunction = F; 173 else if (GS.AccessingFunction != F) 174 GS.HasMultipleAccessingFunctions = true; 175 } 176 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 177 GS.isLoaded = true; 178 if (LI->isVolatile()) return true; // Don't hack on volatile loads. 179 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 180 // Don't allow a store OF the address, only stores TO the address. 181 if (SI->getOperand(0) == V) return true; 182 183 if (SI->isVolatile()) return true; // Don't hack on volatile stores. 184 185 // If this is a direct store to the global (i.e., the global is a scalar 186 // value, not an aggregate), keep more specific information about 187 // stores. 188 if (GS.StoredType != GlobalStatus::isStored) { 189 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(SI->getOperand(1))){ 190 Value *StoredVal = SI->getOperand(0); 191 if (StoredVal == GV->getInitializer()) { 192 if (GS.StoredType < GlobalStatus::isInitializerStored) 193 GS.StoredType = GlobalStatus::isInitializerStored; 194 } else if (isa<LoadInst>(StoredVal) && 195 cast<LoadInst>(StoredVal)->getOperand(0) == GV) { 196 // G = G 197 if (GS.StoredType < GlobalStatus::isInitializerStored) 198 GS.StoredType = GlobalStatus::isInitializerStored; 199 } else if (GS.StoredType < GlobalStatus::isStoredOnce) { 200 GS.StoredType = GlobalStatus::isStoredOnce; 201 GS.StoredOnceValue = StoredVal; 202 } else if (GS.StoredType == GlobalStatus::isStoredOnce && 203 GS.StoredOnceValue == StoredVal) { 204 // noop. 205 } else { 206 GS.StoredType = GlobalStatus::isStored; 207 } 208 } else { 209 GS.StoredType = GlobalStatus::isStored; 210 } 211 } 212 } else if (isa<GetElementPtrInst>(I)) { 213 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 214 } else if (isa<SelectInst>(I)) { 215 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 216 } else if (PHINode *PN = dyn_cast<PHINode>(I)) { 217 // PHI nodes we can check just like select or GEP instructions, but we 218 // have to be careful about infinite recursion. 219 if (PHIUsers.insert(PN)) // Not already visited. 220 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 221 GS.HasPHIUser = true; 222 } else if (isa<CmpInst>(I)) { 223 } else if (isa<MemTransferInst>(I)) { 224 if (I->getOperand(1) == V) 225 GS.StoredType = GlobalStatus::isStored; 226 if (I->getOperand(2) == V) 227 GS.isLoaded = true; 228 } else if (isa<MemSetInst>(I)) { 229 assert(I->getOperand(1) == V && "Memset only takes one pointer!"); 230 GS.StoredType = GlobalStatus::isStored; 231 } else { 232 return true; // Any other non-load instruction might take address! 233 } 234 } else if (Constant *C = dyn_cast<Constant>(*UI)) { 235 GS.HasNonInstructionUser = true; 236 // We might have a dead and dangling constant hanging off of here. 237 if (!SafeToDestroyConstant(C)) 238 return true; 239 } else { 240 GS.HasNonInstructionUser = true; 241 // Otherwise must be some other user. 242 return true; 243 } 244 245 return false; 246} 247 248static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx, 249 LLVMContext &Context) { 250 ConstantInt *CI = dyn_cast<ConstantInt>(Idx); 251 if (!CI) return 0; 252 unsigned IdxV = CI->getZExtValue(); 253 254 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) { 255 if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV); 256 } else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) { 257 if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV); 258 } else if (ConstantVector *CP = dyn_cast<ConstantVector>(Agg)) { 259 if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV); 260 } else if (isa<ConstantAggregateZero>(Agg)) { 261 if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) { 262 if (IdxV < STy->getNumElements()) 263 return Constant::getNullValue(STy->getElementType(IdxV)); 264 } else if (const SequentialType *STy = 265 dyn_cast<SequentialType>(Agg->getType())) { 266 return Constant::getNullValue(STy->getElementType()); 267 } 268 } else if (isa<UndefValue>(Agg)) { 269 if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) { 270 if (IdxV < STy->getNumElements()) 271 return UndefValue::get(STy->getElementType(IdxV)); 272 } else if (const SequentialType *STy = 273 dyn_cast<SequentialType>(Agg->getType())) { 274 return UndefValue::get(STy->getElementType()); 275 } 276 } 277 return 0; 278} 279 280 281/// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all 282/// users of the global, cleaning up the obvious ones. This is largely just a 283/// quick scan over the use list to clean up the easy and obvious cruft. This 284/// returns true if it made a change. 285static bool CleanupConstantGlobalUsers(Value *V, Constant *Init, 286 LLVMContext &Context) { 287 bool Changed = false; 288 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) { 289 User *U = *UI++; 290 291 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 292 if (Init) { 293 // Replace the load with the initializer. 294 LI->replaceAllUsesWith(Init); 295 LI->eraseFromParent(); 296 Changed = true; 297 } 298 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 299 // Store must be unreachable or storing Init into the global. 300 SI->eraseFromParent(); 301 Changed = true; 302 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { 303 if (CE->getOpcode() == Instruction::GetElementPtr) { 304 Constant *SubInit = 0; 305 if (Init) 306 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); 307 Changed |= CleanupConstantGlobalUsers(CE, SubInit, Context); 308 } else if (CE->getOpcode() == Instruction::BitCast && 309 isa<PointerType>(CE->getType())) { 310 // Pointer cast, delete any stores and memsets to the global. 311 Changed |= CleanupConstantGlobalUsers(CE, 0, Context); 312 } 313 314 if (CE->use_empty()) { 315 CE->destroyConstant(); 316 Changed = true; 317 } 318 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 319 // Do not transform "gepinst (gep constexpr (GV))" here, because forming 320 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold 321 // and will invalidate our notion of what Init is. 322 Constant *SubInit = 0; 323 if (!isa<ConstantExpr>(GEP->getOperand(0))) { 324 ConstantExpr *CE = 325 dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, Context)); 326 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr) 327 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); 328 } 329 Changed |= CleanupConstantGlobalUsers(GEP, SubInit, Context); 330 331 if (GEP->use_empty()) { 332 GEP->eraseFromParent(); 333 Changed = true; 334 } 335 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv 336 if (MI->getRawDest() == V) { 337 MI->eraseFromParent(); 338 Changed = true; 339 } 340 341 } else if (Constant *C = dyn_cast<Constant>(U)) { 342 // If we have a chain of dead constantexprs or other things dangling from 343 // us, and if they are all dead, nuke them without remorse. 344 if (SafeToDestroyConstant(C)) { 345 C->destroyConstant(); 346 // This could have invalidated UI, start over from scratch. 347 CleanupConstantGlobalUsers(V, Init, Context); 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 SafeToDestroyConstant(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 == 0) 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 (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end(); 381 I != E; ++I) 382 if (!isSafeSROAElementUse(*I)) 383 return false; 384 return true; 385} 386 387 388/// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value. 389/// Look at it and its uses and decide whether it is safe to SROA this global. 390/// 391static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) { 392 // The user of the global must be a GEP Inst or a ConstantExpr GEP. 393 if (!isa<GetElementPtrInst>(U) && 394 (!isa<ConstantExpr>(U) || 395 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr)) 396 return false; 397 398 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we 399 // don't like < 3 operand CE's, and we don't like non-constant integer 400 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some 401 // value of C. 402 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) || 403 !cast<Constant>(U->getOperand(1))->isNullValue() || 404 !isa<ConstantInt>(U->getOperand(2))) 405 return false; 406 407 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U); 408 ++GEPI; // Skip over the pointer index. 409 410 // If this is a use of an array allocation, do a bit more checking for sanity. 411 if (const ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) { 412 uint64_t NumElements = AT->getNumElements(); 413 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2)); 414 415 // Check to make sure that index falls within the array. If not, 416 // something funny is going on, so we won't do the optimization. 417 // 418 if (Idx->getZExtValue() >= NumElements) 419 return false; 420 421 // We cannot scalar repl this level of the array unless any array 422 // sub-indices are in-range constants. In particular, consider: 423 // A[0][i]. We cannot know that the user isn't doing invalid things like 424 // allowing i to index an out-of-range subscript that accesses A[1]. 425 // 426 // Scalar replacing *just* the outer index of the array is probably not 427 // going to be a win anyway, so just give up. 428 for (++GEPI; // Skip array index. 429 GEPI != E; 430 ++GEPI) { 431 uint64_t NumElements; 432 if (const ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI)) 433 NumElements = SubArrayTy->getNumElements(); 434 else if (const VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI)) 435 NumElements = SubVectorTy->getNumElements(); 436 else { 437 assert(isa<StructType>(*GEPI) && 438 "Indexed GEP type is not array, vector, or struct!"); 439 continue; 440 } 441 442 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand()); 443 if (!IdxVal || IdxVal->getZExtValue() >= NumElements) 444 return false; 445 } 446 } 447 448 for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I) 449 if (!isSafeSROAElementUse(*I)) 450 return false; 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 (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); 459 UI != E; ++UI) { 460 if (!IsUserOfGlobalSafeForSRA(*UI, GV)) 461 return false; 462 } 463 return true; 464} 465 466 467/// SRAGlobal - Perform scalar replacement of aggregates on the specified global 468/// variable. This opens the door for other optimizations by exposing the 469/// behavior of the program in a more fine-grained way. We have determined that 470/// this transformation is safe already. We return the first global variable we 471/// insert so that the caller can reprocess it. 472static GlobalVariable *SRAGlobal(GlobalVariable *GV, const TargetData &TD, 473 LLVMContext &Context) { 474 // Make sure this global only has simple uses that we can SRA. 475 if (!GlobalUsersSafeToSRA(GV)) 476 return 0; 477 478 assert(GV->hasLocalLinkage() && !GV->isConstant()); 479 Constant *Init = GV->getInitializer(); 480 const Type *Ty = Init->getType(); 481 482 std::vector<GlobalVariable*> NewGlobals; 483 Module::GlobalListType &Globals = GV->getParent()->getGlobalList(); 484 485 // Get the alignment of the global, either explicit or target-specific. 486 unsigned StartAlignment = GV->getAlignment(); 487 if (StartAlignment == 0) 488 StartAlignment = TD.getABITypeAlignment(GV->getType()); 489 490 if (const StructType *STy = dyn_cast<StructType>(Ty)) { 491 NewGlobals.reserve(STy->getNumElements()); 492 const StructLayout &Layout = *TD.getStructLayout(STy); 493 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 494 Constant *In = getAggregateConstantElement(Init, 495 ConstantInt::get(Type::getInt32Ty(Context), i), 496 Context); 497 assert(In && "Couldn't get element of initializer?"); 498 GlobalVariable *NGV = new GlobalVariable(Context, 499 STy->getElementType(i), false, 500 GlobalVariable::InternalLinkage, 501 In, GV->getName()+"."+Twine(i), 502 GV->isThreadLocal(), 503 GV->getType()->getAddressSpace()); 504 Globals.insert(GV, NGV); 505 NewGlobals.push_back(NGV); 506 507 // Calculate the known alignment of the field. If the original aggregate 508 // had 256 byte alignment for example, something might depend on that: 509 // propagate info to each field. 510 uint64_t FieldOffset = Layout.getElementOffset(i); 511 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset); 512 if (NewAlign > TD.getABITypeAlignment(STy->getElementType(i))) 513 NGV->setAlignment(NewAlign); 514 } 515 } else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) { 516 unsigned NumElements = 0; 517 if (const ArrayType *ATy = dyn_cast<ArrayType>(STy)) 518 NumElements = ATy->getNumElements(); 519 else 520 NumElements = cast<VectorType>(STy)->getNumElements(); 521 522 if (NumElements > 16 && GV->hasNUsesOrMore(16)) 523 return 0; // It's not worth it. 524 NewGlobals.reserve(NumElements); 525 526 uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType()); 527 unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType()); 528 for (unsigned i = 0, e = NumElements; i != e; ++i) { 529 Constant *In = getAggregateConstantElement(Init, 530 ConstantInt::get(Type::getInt32Ty(Context), i), 531 Context); 532 assert(In && "Couldn't get element of initializer?"); 533 534 GlobalVariable *NGV = new GlobalVariable(Context, 535 STy->getElementType(), false, 536 GlobalVariable::InternalLinkage, 537 In, GV->getName()+"."+Twine(i), 538 GV->isThreadLocal(), 539 GV->getType()->getAddressSpace()); 540 Globals.insert(GV, NGV); 541 NewGlobals.push_back(NGV); 542 543 // Calculate the known alignment of the field. If the original aggregate 544 // had 256 byte alignment for example, something might depend on that: 545 // propagate info to each field. 546 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i); 547 if (NewAlign > EltAlign) 548 NGV->setAlignment(NewAlign); 549 } 550 } 551 552 if (NewGlobals.empty()) 553 return 0; 554 555 DEBUG(errs() << "PERFORMING GLOBAL SRA ON: " << *GV); 556 557 Constant *NullInt = Constant::getNullValue(Type::getInt32Ty(Context)); 558 559 // Loop over all of the uses of the global, replacing the constantexpr geps, 560 // with smaller constantexpr geps or direct references. 561 while (!GV->use_empty()) { 562 User *GEP = GV->use_back(); 563 assert(((isa<ConstantExpr>(GEP) && 564 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)|| 565 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!"); 566 567 // Ignore the 1th operand, which has to be zero or else the program is quite 568 // broken (undefined). Get the 2nd operand, which is the structure or array 569 // index. 570 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 571 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access. 572 573 Value *NewPtr = NewGlobals[Val]; 574 575 // Form a shorter GEP if needed. 576 if (GEP->getNumOperands() > 3) { 577 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) { 578 SmallVector<Constant*, 8> Idxs; 579 Idxs.push_back(NullInt); 580 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i) 581 Idxs.push_back(CE->getOperand(i)); 582 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), 583 &Idxs[0], Idxs.size()); 584 } else { 585 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP); 586 SmallVector<Value*, 8> Idxs; 587 Idxs.push_back(NullInt); 588 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) 589 Idxs.push_back(GEPI->getOperand(i)); 590 NewPtr = GetElementPtrInst::Create(NewPtr, Idxs.begin(), Idxs.end(), 591 GEPI->getName()+"."+Twine(Val),GEPI); 592 } 593 } 594 GEP->replaceAllUsesWith(NewPtr); 595 596 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP)) 597 GEPI->eraseFromParent(); 598 else 599 cast<ConstantExpr>(GEP)->destroyConstant(); 600 } 601 602 // Delete the old global, now that it is dead. 603 Globals.erase(GV); 604 ++NumSRA; 605 606 // Loop over the new globals array deleting any globals that are obviously 607 // dead. This can arise due to scalarization of a structure or an array that 608 // has elements that are dead. 609 unsigned FirstGlobal = 0; 610 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i) 611 if (NewGlobals[i]->use_empty()) { 612 Globals.erase(NewGlobals[i]); 613 if (FirstGlobal == i) ++FirstGlobal; 614 } 615 616 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0; 617} 618 619/// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified 620/// value will trap if the value is dynamically null. PHIs keeps track of any 621/// phi nodes we've seen to avoid reprocessing them. 622static bool AllUsesOfValueWillTrapIfNull(Value *V, 623 SmallPtrSet<PHINode*, 8> &PHIs) { 624 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) 625 if (isa<LoadInst>(*UI)) { 626 // Will trap. 627 } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) { 628 if (SI->getOperand(0) == V) { 629 //cerr << "NONTRAPPING USE: " << **UI; 630 return false; // Storing the value. 631 } 632 } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) { 633 if (CI->getOperand(0) != V) { 634 //cerr << "NONTRAPPING USE: " << **UI; 635 return false; // Not calling the ptr 636 } 637 } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) { 638 if (II->getOperand(0) != V) { 639 //cerr << "NONTRAPPING USE: " << **UI; 640 return false; // Not calling the ptr 641 } 642 } else if (BitCastInst *CI = dyn_cast<BitCastInst>(*UI)) { 643 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false; 644 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) { 645 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false; 646 } else if (PHINode *PN = dyn_cast<PHINode>(*UI)) { 647 // If we've already seen this phi node, ignore it, it has already been 648 // checked. 649 if (PHIs.insert(PN)) 650 return AllUsesOfValueWillTrapIfNull(PN, PHIs); 651 } else if (isa<ICmpInst>(*UI) && 652 isa<ConstantPointerNull>(UI->getOperand(1))) { 653 // Ignore setcc X, null 654 } else { 655 //cerr << "NONTRAPPING USE: " << **UI; 656 return false; 657 } 658 return true; 659} 660 661/// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads 662/// from GV will trap if the loaded value is null. Note that this also permits 663/// comparisons of the loaded value against null, as a special case. 664static bool AllUsesOfLoadedValueWillTrapIfNull(GlobalVariable *GV) { 665 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI!=E; ++UI) 666 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 667 SmallPtrSet<PHINode*, 8> PHIs; 668 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs)) 669 return false; 670 } else if (isa<StoreInst>(*UI)) { 671 // Ignore stores to the global. 672 } else { 673 // We don't know or understand this user, bail out. 674 //cerr << "UNKNOWN USER OF GLOBAL!: " << **UI; 675 return false; 676 } 677 678 return true; 679} 680 681static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV, 682 LLVMContext &Context) { 683 bool Changed = false; 684 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) { 685 Instruction *I = cast<Instruction>(*UI++); 686 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 687 LI->setOperand(0, NewV); 688 Changed = true; 689 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 690 if (SI->getOperand(1) == V) { 691 SI->setOperand(1, NewV); 692 Changed = true; 693 } 694 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) { 695 if (I->getOperand(0) == V) { 696 // Calling through the pointer! Turn into a direct call, but be careful 697 // that the pointer is not also being passed as an argument. 698 I->setOperand(0, NewV); 699 Changed = true; 700 bool PassedAsArg = false; 701 for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i) 702 if (I->getOperand(i) == V) { 703 PassedAsArg = true; 704 I->setOperand(i, NewV); 705 } 706 707 if (PassedAsArg) { 708 // Being passed as an argument also. Be careful to not invalidate UI! 709 UI = V->use_begin(); 710 } 711 } 712 } else if (CastInst *CI = dyn_cast<CastInst>(I)) { 713 Changed |= OptimizeAwayTrappingUsesOfValue(CI, 714 ConstantExpr::getCast(CI->getOpcode(), 715 NewV, CI->getType()), Context); 716 if (CI->use_empty()) { 717 Changed = true; 718 CI->eraseFromParent(); 719 } 720 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { 721 // Should handle GEP here. 722 SmallVector<Constant*, 8> Idxs; 723 Idxs.reserve(GEPI->getNumOperands()-1); 724 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end(); 725 i != e; ++i) 726 if (Constant *C = dyn_cast<Constant>(*i)) 727 Idxs.push_back(C); 728 else 729 break; 730 if (Idxs.size() == GEPI->getNumOperands()-1) 731 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI, 732 ConstantExpr::getGetElementPtr(NewV, &Idxs[0], 733 Idxs.size()), Context); 734 if (GEPI->use_empty()) { 735 Changed = true; 736 GEPI->eraseFromParent(); 737 } 738 } 739 } 740 741 return Changed; 742} 743 744 745/// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null 746/// value stored into it. If there are uses of the loaded value that would trap 747/// if the loaded value is dynamically null, then we know that they cannot be 748/// reachable with a null optimize away the load. 749static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV, 750 LLVMContext &Context) { 751 bool Changed = false; 752 753 // Keep track of whether we are able to remove all the uses of the global 754 // other than the store that defines it. 755 bool AllNonStoreUsesGone = true; 756 757 // Replace all uses of loads with uses of uses of the stored value. 758 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){ 759 User *GlobalUser = *GUI++; 760 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) { 761 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV, Context); 762 // If we were able to delete all uses of the loads 763 if (LI->use_empty()) { 764 LI->eraseFromParent(); 765 Changed = true; 766 } else { 767 AllNonStoreUsesGone = false; 768 } 769 } else if (isa<StoreInst>(GlobalUser)) { 770 // Ignore the store that stores "LV" to the global. 771 assert(GlobalUser->getOperand(1) == GV && 772 "Must be storing *to* the global"); 773 } else { 774 AllNonStoreUsesGone = false; 775 776 // If we get here we could have other crazy uses that are transitively 777 // loaded. 778 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) || 779 isa<ConstantExpr>(GlobalUser)) && "Only expect load and stores!"); 780 } 781 } 782 783 if (Changed) { 784 DEBUG(errs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV); 785 ++NumGlobUses; 786 } 787 788 // If we nuked all of the loads, then none of the stores are needed either, 789 // nor is the global. 790 if (AllNonStoreUsesGone) { 791 DEBUG(errs() << " *** GLOBAL NOW DEAD!\n"); 792 CleanupConstantGlobalUsers(GV, 0, Context); 793 if (GV->use_empty()) { 794 GV->eraseFromParent(); 795 ++NumDeleted; 796 } 797 Changed = true; 798 } 799 return Changed; 800} 801 802/// ConstantPropUsersOf - Walk the use list of V, constant folding all of the 803/// instructions that are foldable. 804static void ConstantPropUsersOf(Value *V, LLVMContext &Context) { 805 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) 806 if (Instruction *I = dyn_cast<Instruction>(*UI++)) 807 if (Constant *NewC = ConstantFoldInstruction(I, Context)) { 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 BitCastInst *BCI, 826 LLVMContext &Context, 827 TargetData* TD) { 828 DEBUG(errs() << "PROMOTING MALLOC GLOBAL: " << *GV 829 << " CALL = " << *CI << " BCI = " << *BCI << '\n'); 830 831 const Type *IntPtrTy = TD->getIntPtrType(Context); 832 833 Value* ArraySize = getMallocArraySize(CI, Context, TD); 834 assert(ArraySize && "not a malloc whose array size can be determined"); 835 ConstantInt *NElements = cast<ConstantInt>(ArraySize); 836 if (NElements->getZExtValue() != 1) { 837 // If we have an array allocation, transform it to a single element 838 // allocation to make the code below simpler. 839 Type *NewTy = ArrayType::get(getMallocAllocatedType(CI), 840 NElements->getZExtValue()); 841 Value* NewM = CallInst::CreateMalloc(CI, IntPtrTy, NewTy); 842 Instruction* NewMI = cast<Instruction>(NewM); 843 Value* Indices[2]; 844 Indices[0] = Indices[1] = Constant::getNullValue(IntPtrTy); 845 Value *NewGEP = GetElementPtrInst::Create(NewMI, Indices, Indices + 2, 846 NewMI->getName()+".el0", CI); 847 BCI->replaceAllUsesWith(NewGEP); 848 BCI->eraseFromParent(); 849 CI->eraseFromParent(); 850 BCI = cast<BitCastInst>(NewMI); 851 CI = extractMallocCallFromBitCast(NewMI); 852 } 853 854 // Create the new global variable. The contents of the malloc'd memory is 855 // undefined, so initialize with an undef value. 856 const Type *MAT = getMallocAllocatedType(CI); 857 Constant *Init = UndefValue::get(MAT); 858 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(), 859 MAT, false, 860 GlobalValue::InternalLinkage, Init, 861 GV->getName()+".body", 862 GV, 863 GV->isThreadLocal()); 864 865 // Anything that used the malloc now uses the global directly. 866 BCI->replaceAllUsesWith(NewGV); 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(Context, Type::getInt1Ty(Context), false, 877 GlobalValue::InternalLinkage, 878 ConstantInt::getFalse(Context), GV->getName()+".init", 879 GV->isThreadLocal()); 880 bool InitBoolUsed = false; 881 882 // Loop over all uses of GV, processing them in turn. 883 std::vector<StoreInst*> Stores; 884 while (!GV->use_empty()) 885 if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) { 886 while (!LI->use_empty()) { 887 Use &LoadUse = LI->use_begin().getUse(); 888 if (!isa<ICmpInst>(LoadUse.getUser())) 889 LoadUse = RepValue; 890 else { 891 ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser()); 892 // Replace the cmp X, 0 with a use of the bool value. 893 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", ICI); 894 InitBoolUsed = true; 895 switch (ICI->getPredicate()) { 896 default: llvm_unreachable("Unknown ICmp Predicate!"); 897 case ICmpInst::ICMP_ULT: 898 case ICmpInst::ICMP_SLT: 899 LV = ConstantInt::getFalse(Context); // X < null -> always false 900 break; 901 case ICmpInst::ICMP_ULE: 902 case ICmpInst::ICMP_SLE: 903 case ICmpInst::ICMP_EQ: 904 LV = BinaryOperator::CreateNot(LV, "notinit", ICI); 905 break; 906 case ICmpInst::ICMP_NE: 907 case ICmpInst::ICMP_UGE: 908 case ICmpInst::ICMP_SGE: 909 case ICmpInst::ICMP_UGT: 910 case ICmpInst::ICMP_SGT: 911 break; // no change. 912 } 913 ICI->replaceAllUsesWith(LV); 914 ICI->eraseFromParent(); 915 } 916 } 917 LI->eraseFromParent(); 918 } else { 919 StoreInst *SI = cast<StoreInst>(GV->use_back()); 920 // The global is initialized when the store to it occurs. 921 new StoreInst(ConstantInt::getTrue(Context), InitBool, SI); 922 SI->eraseFromParent(); 923 } 924 925 // If the initialization boolean was used, insert it, otherwise delete it. 926 if (!InitBoolUsed) { 927 while (!InitBool->use_empty()) // Delete initializations 928 cast<Instruction>(InitBool->use_back())->eraseFromParent(); 929 delete InitBool; 930 } else 931 GV->getParent()->getGlobalList().insert(GV, InitBool); 932 933 934 // Now the GV is dead, nuke it and the malloc. 935 GV->eraseFromParent(); 936 BCI->eraseFromParent(); 937 CI->eraseFromParent(); 938 939 // To further other optimizations, loop over all users of NewGV and try to 940 // constant prop them. This will promote GEP instructions with constant 941 // indices into GEP constant-exprs, which will allow global-opt to hack on it. 942 ConstantPropUsersOf(NewGV, Context); 943 if (RepValue != NewGV) 944 ConstantPropUsersOf(RepValue, Context); 945 946 return NewGV; 947} 948 949/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking 950/// to make sure that there are no complex uses of V. We permit simple things 951/// like dereferencing the pointer, but not storing through the address, unless 952/// it is to the specified global. 953static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Instruction *V, 954 GlobalVariable *GV, 955 SmallPtrSet<PHINode*, 8> &PHIs) { 956 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 957 Instruction *Inst = cast<Instruction>(*UI); 958 959 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) { 960 continue; // Fine, ignore. 961 } 962 963 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 964 if (SI->getOperand(0) == V && SI->getOperand(1) != GV) 965 return false; // Storing the pointer itself... bad. 966 continue; // Otherwise, storing through it, or storing into GV... fine. 967 } 968 969 if (isa<GetElementPtrInst>(Inst)) { 970 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs)) 971 return false; 972 continue; 973 } 974 975 if (PHINode *PN = dyn_cast<PHINode>(Inst)) { 976 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI 977 // cycles. 978 if (PHIs.insert(PN)) 979 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs)) 980 return false; 981 continue; 982 } 983 984 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) { 985 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) 986 return false; 987 continue; 988 } 989 990 return false; 991 } 992 return true; 993} 994 995/// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV 996/// somewhere. Transform all uses of the allocation into loads from the 997/// global and uses of the resultant pointer. Further, delete the store into 998/// GV. This assumes that these value pass the 999/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate. 1000static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, 1001 GlobalVariable *GV) { 1002 while (!Alloc->use_empty()) { 1003 Instruction *U = cast<Instruction>(*Alloc->use_begin()); 1004 Instruction *InsertPt = U; 1005 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 1006 // If this is the store of the allocation into the global, remove it. 1007 if (SI->getOperand(1) == GV) { 1008 SI->eraseFromParent(); 1009 continue; 1010 } 1011 } else if (PHINode *PN = dyn_cast<PHINode>(U)) { 1012 // Insert the load in the corresponding predecessor, not right before the 1013 // PHI. 1014 InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator(); 1015 } else if (isa<BitCastInst>(U)) { 1016 // Must be bitcast between the malloc and store to initialize the global. 1017 ReplaceUsesOfMallocWithGlobal(U, GV); 1018 U->eraseFromParent(); 1019 continue; 1020 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { 1021 // If this is a "GEP bitcast" and the user is a store to the global, then 1022 // just process it as a bitcast. 1023 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse()) 1024 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back())) 1025 if (SI->getOperand(1) == GV) { 1026 // Must be bitcast GEP between the malloc and store to initialize 1027 // the global. 1028 ReplaceUsesOfMallocWithGlobal(GEPI, GV); 1029 GEPI->eraseFromParent(); 1030 continue; 1031 } 1032 } 1033 1034 // Insert a load from the global, and use it instead of the malloc. 1035 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt); 1036 U->replaceUsesOfWith(Alloc, NL); 1037 } 1038} 1039 1040/// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi 1041/// of a load) are simple enough to perform heap SRA on. This permits GEP's 1042/// that index through the array and struct field, icmps of null, and PHIs. 1043static bool LoadUsesSimpleEnoughForHeapSRA(Value *V, 1044 SmallPtrSet<PHINode*, 32> &LoadUsingPHIs, 1045 SmallPtrSet<PHINode*, 32> &LoadUsingPHIsPerLoad) { 1046 // We permit two users of the load: setcc comparing against the null 1047 // pointer, and a getelementptr of a specific form. 1048 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 1049 Instruction *User = cast<Instruction>(*UI); 1050 1051 // Comparison against null is ok. 1052 if (ICmpInst *ICI = dyn_cast<ICmpInst>(User)) { 1053 if (!isa<ConstantPointerNull>(ICI->getOperand(1))) 1054 return false; 1055 continue; 1056 } 1057 1058 // getelementptr is also ok, but only a simple form. 1059 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1060 // Must index into the array and into the struct. 1061 if (GEPI->getNumOperands() < 3) 1062 return false; 1063 1064 // Otherwise the GEP is ok. 1065 continue; 1066 } 1067 1068 if (PHINode *PN = dyn_cast<PHINode>(User)) { 1069 if (!LoadUsingPHIsPerLoad.insert(PN)) 1070 // This means some phi nodes are dependent on each other. 1071 // Avoid infinite looping! 1072 return false; 1073 if (!LoadUsingPHIs.insert(PN)) 1074 // If we have already analyzed this PHI, then it is safe. 1075 continue; 1076 1077 // Make sure all uses of the PHI are simple enough to transform. 1078 if (!LoadUsesSimpleEnoughForHeapSRA(PN, 1079 LoadUsingPHIs, LoadUsingPHIsPerLoad)) 1080 return false; 1081 1082 continue; 1083 } 1084 1085 // Otherwise we don't know what this is, not ok. 1086 return false; 1087 } 1088 1089 return true; 1090} 1091 1092 1093/// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from 1094/// GV are simple enough to perform HeapSRA, return true. 1095static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(GlobalVariable *GV, 1096 Instruction *StoredVal) { 1097 SmallPtrSet<PHINode*, 32> LoadUsingPHIs; 1098 SmallPtrSet<PHINode*, 32> LoadUsingPHIsPerLoad; 1099 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E; 1100 ++UI) 1101 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 1102 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs, 1103 LoadUsingPHIsPerLoad)) 1104 return false; 1105 LoadUsingPHIsPerLoad.clear(); 1106 } 1107 1108 // If we reach here, we know that all uses of the loads and transitive uses 1109 // (through PHI nodes) are simple enough to transform. However, we don't know 1110 // that all inputs the to the PHI nodes are in the same equivalence sets. 1111 // Check to verify that all operands of the PHIs are either PHIS that can be 1112 // transformed, loads from GV, or MI itself. 1113 for (SmallPtrSet<PHINode*, 32>::iterator I = LoadUsingPHIs.begin(), 1114 E = LoadUsingPHIs.end(); I != E; ++I) { 1115 PHINode *PN = *I; 1116 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) { 1117 Value *InVal = PN->getIncomingValue(op); 1118 1119 // PHI of the stored value itself is ok. 1120 if (InVal == StoredVal) continue; 1121 1122 if (PHINode *InPN = dyn_cast<PHINode>(InVal)) { 1123 // One of the PHIs in our set is (optimistically) ok. 1124 if (LoadUsingPHIs.count(InPN)) 1125 continue; 1126 return false; 1127 } 1128 1129 // Load from GV is ok. 1130 if (LoadInst *LI = dyn_cast<LoadInst>(InVal)) 1131 if (LI->getOperand(0) == GV) 1132 continue; 1133 1134 // UNDEF? NULL? 1135 1136 // Anything else is rejected. 1137 return false; 1138 } 1139 } 1140 1141 return true; 1142} 1143 1144static Value *GetHeapSROAValue(Value *V, unsigned FieldNo, 1145 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1146 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite, 1147 LLVMContext &Context) { 1148 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V]; 1149 1150 if (FieldNo >= FieldVals.size()) 1151 FieldVals.resize(FieldNo+1); 1152 1153 // If we already have this value, just reuse the previously scalarized 1154 // version. 1155 if (Value *FieldVal = FieldVals[FieldNo]) 1156 return FieldVal; 1157 1158 // Depending on what instruction this is, we have several cases. 1159 Value *Result; 1160 if (LoadInst *LI = dyn_cast<LoadInst>(V)) { 1161 // This is a scalarized version of the load from the global. Just create 1162 // a new Load of the scalarized global. 1163 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo, 1164 InsertedScalarizedValues, 1165 PHIsToRewrite, Context), 1166 LI->getName()+".f"+Twine(FieldNo), LI); 1167 } else if (PHINode *PN = dyn_cast<PHINode>(V)) { 1168 // PN's type is pointer to struct. Make a new PHI of pointer to struct 1169 // field. 1170 const StructType *ST = 1171 cast<StructType>(cast<PointerType>(PN->getType())->getElementType()); 1172 1173 Result = 1174 PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)), 1175 PN->getName()+".f"+Twine(FieldNo), PN); 1176 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo)); 1177 } else { 1178 llvm_unreachable("Unknown usable value"); 1179 Result = 0; 1180 } 1181 1182 return FieldVals[FieldNo] = Result; 1183} 1184 1185/// RewriteHeapSROALoadUser - Given a load instruction and a value derived from 1186/// the load, rewrite the derived value to use the HeapSRoA'd load. 1187static void RewriteHeapSROALoadUser(Instruction *LoadUser, 1188 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1189 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite, 1190 LLVMContext &Context) { 1191 // If this is a comparison against null, handle it. 1192 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) { 1193 assert(isa<ConstantPointerNull>(SCI->getOperand(1))); 1194 // If we have a setcc of the loaded pointer, we can use a setcc of any 1195 // field. 1196 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0, 1197 InsertedScalarizedValues, PHIsToRewrite, 1198 Context); 1199 1200 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr, 1201 Constant::getNullValue(NPtr->getType()), 1202 SCI->getName()); 1203 SCI->replaceAllUsesWith(New); 1204 SCI->eraseFromParent(); 1205 return; 1206 } 1207 1208 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...' 1209 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) { 1210 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2)) 1211 && "Unexpected GEPI!"); 1212 1213 // Load the pointer for this field. 1214 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 1215 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo, 1216 InsertedScalarizedValues, PHIsToRewrite, 1217 Context); 1218 1219 // Create the new GEP idx vector. 1220 SmallVector<Value*, 8> GEPIdx; 1221 GEPIdx.push_back(GEPI->getOperand(1)); 1222 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end()); 1223 1224 Value *NGEPI = GetElementPtrInst::Create(NewPtr, 1225 GEPIdx.begin(), GEPIdx.end(), 1226 GEPI->getName(), GEPI); 1227 GEPI->replaceAllUsesWith(NGEPI); 1228 GEPI->eraseFromParent(); 1229 return; 1230 } 1231 1232 // Recursively transform the users of PHI nodes. This will lazily create the 1233 // PHIs that are needed for individual elements. Keep track of what PHIs we 1234 // see in InsertedScalarizedValues so that we don't get infinite loops (very 1235 // antisocial). If the PHI is already in InsertedScalarizedValues, it has 1236 // already been seen first by another load, so its uses have already been 1237 // processed. 1238 PHINode *PN = cast<PHINode>(LoadUser); 1239 bool Inserted; 1240 DenseMap<Value*, std::vector<Value*> >::iterator InsertPos; 1241 tie(InsertPos, Inserted) = 1242 InsertedScalarizedValues.insert(std::make_pair(PN, std::vector<Value*>())); 1243 if (!Inserted) return; 1244 1245 // If this is the first time we've seen this PHI, recursively process all 1246 // users. 1247 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) { 1248 Instruction *User = cast<Instruction>(*UI++); 1249 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite, 1250 Context); 1251 } 1252} 1253 1254/// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr 1255/// is a value loaded from the global. Eliminate all uses of Ptr, making them 1256/// use FieldGlobals instead. All uses of loaded values satisfy 1257/// AllGlobalLoadUsesSimpleEnoughForHeapSRA. 1258static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load, 1259 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1260 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite, 1261 LLVMContext &Context) { 1262 for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end(); 1263 UI != E; ) { 1264 Instruction *User = cast<Instruction>(*UI++); 1265 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite, 1266 Context); 1267 } 1268 1269 if (Load->use_empty()) { 1270 Load->eraseFromParent(); 1271 InsertedScalarizedValues.erase(Load); 1272 } 1273} 1274 1275/// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break 1276/// it up into multiple allocations of arrays of the fields. 1277static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, 1278 CallInst *CI, BitCastInst* BCI, 1279 LLVMContext &Context, 1280 TargetData *TD){ 1281 DEBUG(errs() << "SROA HEAP ALLOC: " << *GV << " MALLOC CALL = " << *CI 1282 << " BITCAST = " << *BCI << '\n'); 1283 const Type* MAT = getMallocAllocatedType(CI); 1284 const StructType *STy = cast<StructType>(MAT); 1285 Value* ArraySize = getMallocArraySize(CI, Context, TD); 1286 assert(ArraySize && "not a malloc whose array size can be determined"); 1287 1288 // There is guaranteed to be at least one use of the malloc (storing 1289 // it into GV). If there are other uses, change them to be uses of 1290 // the global to simplify later code. This also deletes the store 1291 // into GV. 1292 ReplaceUsesOfMallocWithGlobal(BCI, GV); 1293 1294 // Okay, at this point, there are no users of the malloc. Insert N 1295 // new mallocs at the same place as CI, and N globals. 1296 std::vector<Value*> FieldGlobals; 1297 std::vector<Value*> FieldMallocs; 1298 1299 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ 1300 const Type *FieldTy = STy->getElementType(FieldNo); 1301 const PointerType *PFieldTy = PointerType::getUnqual(FieldTy); 1302 1303 GlobalVariable *NGV = 1304 new GlobalVariable(*GV->getParent(), 1305 PFieldTy, false, GlobalValue::InternalLinkage, 1306 Constant::getNullValue(PFieldTy), 1307 GV->getName() + ".f" + Twine(FieldNo), GV, 1308 GV->isThreadLocal()); 1309 FieldGlobals.push_back(NGV); 1310 1311 Value *NMI = CallInst::CreateMalloc(CI, TD->getIntPtrType(Context), 1312 FieldTy, ArraySize, 1313 BCI->getName() + ".f" + Twine(FieldNo)); 1314 FieldMallocs.push_back(NMI); 1315 new StoreInst(NMI, NGV, BCI); 1316 } 1317 1318 // The tricky aspect of this transformation is handling the case when malloc 1319 // fails. In the original code, malloc failing would set the result pointer 1320 // of malloc to null. In this case, some mallocs could succeed and others 1321 // could fail. As such, we emit code that looks like this: 1322 // F0 = malloc(field0) 1323 // F1 = malloc(field1) 1324 // F2 = malloc(field2) 1325 // if (F0 == 0 || F1 == 0 || F2 == 0) { 1326 // if (F0) { free(F0); F0 = 0; } 1327 // if (F1) { free(F1); F1 = 0; } 1328 // if (F2) { free(F2); F2 = 0; } 1329 // } 1330 Value *RunningOr = 0; 1331 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) { 1332 Value *Cond = new ICmpInst(BCI, ICmpInst::ICMP_EQ, FieldMallocs[i], 1333 Constant::getNullValue(FieldMallocs[i]->getType()), 1334 "isnull"); 1335 if (!RunningOr) 1336 RunningOr = Cond; // First seteq 1337 else 1338 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", BCI); 1339 } 1340 1341 // Split the basic block at the old malloc. 1342 BasicBlock *OrigBB = BCI->getParent(); 1343 BasicBlock *ContBB = OrigBB->splitBasicBlock(BCI, "malloc_cont"); 1344 1345 // Create the block to check the first condition. Put all these blocks at the 1346 // end of the function as they are unlikely to be executed. 1347 BasicBlock *NullPtrBlock = BasicBlock::Create(Context, "malloc_ret_null", 1348 OrigBB->getParent()); 1349 1350 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond 1351 // branch on RunningOr. 1352 OrigBB->getTerminator()->eraseFromParent(); 1353 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB); 1354 1355 // Within the NullPtrBlock, we need to emit a comparison and branch for each 1356 // pointer, because some may be null while others are not. 1357 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1358 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock); 1359 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal, 1360 Constant::getNullValue(GVVal->getType()), 1361 "tmp"); 1362 BasicBlock *FreeBlock = BasicBlock::Create(Context, "free_it", 1363 OrigBB->getParent()); 1364 BasicBlock *NextBlock = BasicBlock::Create(Context, "next", 1365 OrigBB->getParent()); 1366 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock, 1367 Cmp, NullPtrBlock); 1368 1369 // Fill in FreeBlock. 1370 CallInst::CreateFree(GVVal, BI); 1371 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i], 1372 FreeBlock); 1373 BranchInst::Create(NextBlock, FreeBlock); 1374 1375 NullPtrBlock = NextBlock; 1376 } 1377 1378 BranchInst::Create(ContBB, NullPtrBlock); 1379 1380 // CI and BCI are no longer needed, remove them. 1381 BCI->eraseFromParent(); 1382 CI->eraseFromParent(); 1383 1384 /// InsertedScalarizedLoads - As we process loads, if we can't immediately 1385 /// update all uses of the load, keep track of what scalarized loads are 1386 /// inserted for a given load. 1387 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues; 1388 InsertedScalarizedValues[GV] = FieldGlobals; 1389 1390 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite; 1391 1392 // Okay, the malloc site is completely handled. All of the uses of GV are now 1393 // loads, and all uses of those loads are simple. Rewrite them to use loads 1394 // of the per-field globals instead. 1395 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) { 1396 Instruction *User = cast<Instruction>(*UI++); 1397 1398 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1399 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite, 1400 Context); 1401 continue; 1402 } 1403 1404 // Must be a store of null. 1405 StoreInst *SI = cast<StoreInst>(User); 1406 assert(isa<ConstantPointerNull>(SI->getOperand(0)) && 1407 "Unexpected heap-sra user!"); 1408 1409 // Insert a store of null into each global. 1410 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1411 const PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType()); 1412 Constant *Null = Constant::getNullValue(PT->getElementType()); 1413 new StoreInst(Null, FieldGlobals[i], SI); 1414 } 1415 // Erase the original store. 1416 SI->eraseFromParent(); 1417 } 1418 1419 // While we have PHIs that are interesting to rewrite, do it. 1420 while (!PHIsToRewrite.empty()) { 1421 PHINode *PN = PHIsToRewrite.back().first; 1422 unsigned FieldNo = PHIsToRewrite.back().second; 1423 PHIsToRewrite.pop_back(); 1424 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]); 1425 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi"); 1426 1427 // Add all the incoming values. This can materialize more phis. 1428 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1429 Value *InVal = PN->getIncomingValue(i); 1430 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues, 1431 PHIsToRewrite, Context); 1432 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i)); 1433 } 1434 } 1435 1436 // Drop all inter-phi links and any loads that made it this far. 1437 for (DenseMap<Value*, std::vector<Value*> >::iterator 1438 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1439 I != E; ++I) { 1440 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1441 PN->dropAllReferences(); 1442 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1443 LI->dropAllReferences(); 1444 } 1445 1446 // Delete all the phis and loads now that inter-references are dead. 1447 for (DenseMap<Value*, std::vector<Value*> >::iterator 1448 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1449 I != E; ++I) { 1450 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1451 PN->eraseFromParent(); 1452 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1453 LI->eraseFromParent(); 1454 } 1455 1456 // The old global is now dead, remove it. 1457 GV->eraseFromParent(); 1458 1459 ++NumHeapSRA; 1460 return cast<GlobalVariable>(FieldGlobals[0]); 1461} 1462 1463/// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a 1464/// pointer global variable with a single value stored it that is a malloc or 1465/// cast of malloc. 1466static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, 1467 CallInst *CI, 1468 BitCastInst *BCI, 1469 Module::global_iterator &GVI, 1470 TargetData *TD, 1471 LLVMContext &Context) { 1472 // If we can't figure out the type being malloced, then we can't optimize. 1473 const Type *AllocTy = getMallocAllocatedType(CI); 1474 assert(AllocTy); 1475 1476 // If this is a malloc of an abstract type, don't touch it. 1477 if (!AllocTy->isSized()) 1478 return false; 1479 1480 // We can't optimize this global unless all uses of it are *known* to be 1481 // of the malloc value, not of the null initializer value (consider a use 1482 // that compares the global's value against zero to see if the malloc has 1483 // been reached). To do this, we check to see if all uses of the global 1484 // would trap if the global were null: this proves that they must all 1485 // happen after the malloc. 1486 if (!AllUsesOfLoadedValueWillTrapIfNull(GV)) 1487 return false; 1488 1489 // We can't optimize this if the malloc itself is used in a complex way, 1490 // for example, being stored into multiple globals. This allows the 1491 // malloc to be stored into the specified global, loaded setcc'd, and 1492 // GEP'd. These are all things we could transform to using the global 1493 // for. 1494 { 1495 SmallPtrSet<PHINode*, 8> PHIs; 1496 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) 1497 return false; 1498 } 1499 1500 // If we have a global that is only initialized with a fixed size malloc, 1501 // transform the program to use global memory instead of malloc'd memory. 1502 // This eliminates dynamic allocation, avoids an indirection accessing the 1503 // data, and exposes the resultant global to further GlobalOpt. 1504 Value *NElems = getMallocArraySize(CI, Context, TD); 1505 // We cannot optimize the malloc if we cannot determine malloc array size. 1506 if (NElems) { 1507 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems)) 1508 // Restrict this transformation to only working on small allocations 1509 // (2048 bytes currently), as we don't want to introduce a 16M global or 1510 // something. 1511 if (TD && 1512 NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) { 1513 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, BCI, Context, TD); 1514 return true; 1515 } 1516 1517 // If the allocation is an array of structures, consider transforming this 1518 // into multiple malloc'd arrays, one for each field. This is basically 1519 // SRoA for malloc'd memory. 1520 1521 // If this is an allocation of a fixed size array of structs, analyze as a 1522 // variable size array. malloc [100 x struct],1 -> malloc struct, 100 1523 if (!isArrayMalloc(CI, Context, TD)) 1524 if (const ArrayType *AT = dyn_cast<ArrayType>(AllocTy)) 1525 AllocTy = AT->getElementType(); 1526 1527 if (const StructType *AllocSTy = dyn_cast<StructType>(AllocTy)) { 1528 // This the structure has an unreasonable number of fields, leave it 1529 // alone. 1530 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 && 1531 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, BCI)) { 1532 1533 // If this is a fixed size array, transform the Malloc to be an alloc of 1534 // structs. malloc [100 x struct],1 -> malloc struct, 100 1535 if (const ArrayType *AT = 1536 dyn_cast<ArrayType>(getMallocAllocatedType(CI))) { 1537 Value* NumElements = ConstantInt::get(Type::getInt32Ty(Context), 1538 AT->getNumElements()); 1539 Value* NewMI = CallInst::CreateMalloc(CI, TD->getIntPtrType(Context), 1540 AllocSTy, NumElements, 1541 BCI->getName()); 1542 Value *Cast = new BitCastInst(NewMI, getMallocType(CI), "tmp", CI); 1543 BCI->replaceAllUsesWith(Cast); 1544 BCI->eraseFromParent(); 1545 CI->eraseFromParent(); 1546 BCI = cast<BitCastInst>(NewMI); 1547 CI = extractMallocCallFromBitCast(NewMI); 1548 } 1549 1550 GVI = PerformHeapAllocSRoA(GV, CI, BCI, Context, TD); 1551 return true; 1552 } 1553 } 1554 } 1555 1556 return false; 1557} 1558 1559// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge 1560// that only one value (besides its initializer) is ever stored to the global. 1561static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal, 1562 Module::global_iterator &GVI, 1563 TargetData *TD, LLVMContext &Context) { 1564 // Ignore no-op GEPs and bitcasts. 1565 StoredOnceVal = StoredOnceVal->stripPointerCasts(); 1566 1567 // If we are dealing with a pointer global that is initialized to null and 1568 // only has one (non-null) value stored into it, then we can optimize any 1569 // users of the loaded value (often calls and loads) that would trap if the 1570 // value was null. 1571 if (isa<PointerType>(GV->getInitializer()->getType()) && 1572 GV->getInitializer()->isNullValue()) { 1573 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { 1574 if (GV->getInitializer()->getType() != SOVC->getType()) 1575 SOVC = 1576 ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType()); 1577 1578 // Optimize away any trapping uses of the loaded value. 1579 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, Context)) 1580 return true; 1581 } else if (CallInst *CI = extractMallocCall(StoredOnceVal)) { 1582 if (getMallocAllocatedType(CI)) { 1583 BitCastInst* BCI = NULL; 1584 for (Value::use_iterator UI = CI->use_begin(), E = CI->use_end(); 1585 UI != E; ) 1586 BCI = dyn_cast<BitCastInst>(cast<Instruction>(*UI++)); 1587 if (BCI && 1588 TryToOptimizeStoreOfMallocToGlobal(GV, CI, BCI, GVI, TD, Context)) 1589 return true; 1590 } 1591 } 1592 } 1593 1594 return false; 1595} 1596 1597/// TryToShrinkGlobalToBoolean - At this point, we have learned that the only 1598/// two values ever stored into GV are its initializer and OtherVal. See if we 1599/// can shrink the global into a boolean and select between the two values 1600/// whenever it is used. This exposes the values to other scalar optimizations. 1601static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal, 1602 LLVMContext &Context) { 1603 const Type *GVElType = GV->getType()->getElementType(); 1604 1605 // If GVElType is already i1, it is already shrunk. If the type of the GV is 1606 // an FP value, pointer or vector, don't do this optimization because a select 1607 // between them is very expensive and unlikely to lead to later 1608 // simplification. In these cases, we typically end up with "cond ? v1 : v2" 1609 // where v1 and v2 both require constant pool loads, a big loss. 1610 if (GVElType == Type::getInt1Ty(Context) || GVElType->isFloatingPoint() || 1611 isa<PointerType>(GVElType) || isa<VectorType>(GVElType)) 1612 return false; 1613 1614 // Walk the use list of the global seeing if all the uses are load or store. 1615 // If there is anything else, bail out. 1616 for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I) 1617 if (!isa<LoadInst>(I) && !isa<StoreInst>(I)) 1618 return false; 1619 1620 DEBUG(errs() << " *** SHRINKING TO BOOL: " << *GV); 1621 1622 // Create the new global, initializing it to false. 1623 GlobalVariable *NewGV = new GlobalVariable(Context, 1624 Type::getInt1Ty(Context), false, 1625 GlobalValue::InternalLinkage, ConstantInt::getFalse(Context), 1626 GV->getName()+".b", 1627 GV->isThreadLocal()); 1628 GV->getParent()->getGlobalList().insert(GV, NewGV); 1629 1630 Constant *InitVal = GV->getInitializer(); 1631 assert(InitVal->getType() != Type::getInt1Ty(Context) && 1632 "No reason to shrink to bool!"); 1633 1634 // If initialized to zero and storing one into the global, we can use a cast 1635 // instead of a select to synthesize the desired value. 1636 bool IsOneZero = false; 1637 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) 1638 IsOneZero = InitVal->isNullValue() && CI->isOne(); 1639 1640 while (!GV->use_empty()) { 1641 Instruction *UI = cast<Instruction>(GV->use_back()); 1642 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { 1643 // Change the store into a boolean store. 1644 bool StoringOther = SI->getOperand(0) == OtherVal; 1645 // Only do this if we weren't storing a loaded value. 1646 Value *StoreVal; 1647 if (StoringOther || SI->getOperand(0) == InitVal) 1648 StoreVal = ConstantInt::get(Type::getInt1Ty(Context), StoringOther); 1649 else { 1650 // Otherwise, we are storing a previously loaded copy. To do this, 1651 // change the copy from copying the original value to just copying the 1652 // bool. 1653 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); 1654 1655 // If we're already replaced the input, StoredVal will be a cast or 1656 // select instruction. If not, it will be a load of the original 1657 // global. 1658 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { 1659 assert(LI->getOperand(0) == GV && "Not a copy!"); 1660 // Insert a new load, to preserve the saved value. 1661 StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI); 1662 } else { 1663 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && 1664 "This is not a form that we understand!"); 1665 StoreVal = StoredVal->getOperand(0); 1666 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); 1667 } 1668 } 1669 new StoreInst(StoreVal, NewGV, SI); 1670 } else { 1671 // Change the load into a load of bool then a select. 1672 LoadInst *LI = cast<LoadInst>(UI); 1673 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", LI); 1674 Value *NSI; 1675 if (IsOneZero) 1676 NSI = new ZExtInst(NLI, LI->getType(), "", LI); 1677 else 1678 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI); 1679 NSI->takeName(LI); 1680 LI->replaceAllUsesWith(NSI); 1681 } 1682 UI->eraseFromParent(); 1683 } 1684 1685 GV->eraseFromParent(); 1686 return true; 1687} 1688 1689 1690/// ProcessInternalGlobal - Analyze the specified global variable and optimize 1691/// it if possible. If we make a change, return true. 1692bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV, 1693 Module::global_iterator &GVI) { 1694 SmallPtrSet<PHINode*, 16> PHIUsers; 1695 GlobalStatus GS; 1696 GV->removeDeadConstantUsers(); 1697 1698 if (GV->use_empty()) { 1699 DEBUG(errs() << "GLOBAL DEAD: " << *GV); 1700 GV->eraseFromParent(); 1701 ++NumDeleted; 1702 return true; 1703 } 1704 1705 if (!AnalyzeGlobal(GV, GS, PHIUsers)) { 1706#if 0 1707 cerr << "Global: " << *GV; 1708 cerr << " isLoaded = " << GS.isLoaded << "\n"; 1709 cerr << " StoredType = "; 1710 switch (GS.StoredType) { 1711 case GlobalStatus::NotStored: cerr << "NEVER STORED\n"; break; 1712 case GlobalStatus::isInitializerStored: cerr << "INIT STORED\n"; break; 1713 case GlobalStatus::isStoredOnce: cerr << "STORED ONCE\n"; break; 1714 case GlobalStatus::isStored: cerr << "stored\n"; break; 1715 } 1716 if (GS.StoredType == GlobalStatus::isStoredOnce && GS.StoredOnceValue) 1717 cerr << " StoredOnceValue = " << *GS.StoredOnceValue << "\n"; 1718 if (GS.AccessingFunction && !GS.HasMultipleAccessingFunctions) 1719 cerr << " AccessingFunction = " << GS.AccessingFunction->getName() 1720 << "\n"; 1721 cerr << " HasMultipleAccessingFunctions = " 1722 << GS.HasMultipleAccessingFunctions << "\n"; 1723 cerr << " HasNonInstructionUser = " << GS.HasNonInstructionUser<<"\n"; 1724 cerr << "\n"; 1725#endif 1726 1727 // If this is a first class global and has only one accessing function 1728 // and this function is main (which we know is not recursive we can make 1729 // this global a local variable) we replace the global with a local alloca 1730 // in this function. 1731 // 1732 // NOTE: It doesn't make sense to promote non single-value types since we 1733 // are just replacing static memory to stack memory. 1734 // 1735 // If the global is in different address space, don't bring it to stack. 1736 if (!GS.HasMultipleAccessingFunctions && 1737 GS.AccessingFunction && !GS.HasNonInstructionUser && 1738 GV->getType()->getElementType()->isSingleValueType() && 1739 GS.AccessingFunction->getName() == "main" && 1740 GS.AccessingFunction->hasExternalLinkage() && 1741 GV->getType()->getAddressSpace() == 0) { 1742 DEBUG(errs() << "LOCALIZING GLOBAL: " << *GV); 1743 Instruction* FirstI = GS.AccessingFunction->getEntryBlock().begin(); 1744 const Type* ElemTy = GV->getType()->getElementType(); 1745 // FIXME: Pass Global's alignment when globals have alignment 1746 AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), FirstI); 1747 if (!isa<UndefValue>(GV->getInitializer())) 1748 new StoreInst(GV->getInitializer(), Alloca, FirstI); 1749 1750 GV->replaceAllUsesWith(Alloca); 1751 GV->eraseFromParent(); 1752 ++NumLocalized; 1753 return true; 1754 } 1755 1756 // If the global is never loaded (but may be stored to), it is dead. 1757 // Delete it now. 1758 if (!GS.isLoaded) { 1759 DEBUG(errs() << "GLOBAL NEVER LOADED: " << *GV); 1760 1761 // Delete any stores we can find to the global. We may not be able to 1762 // make it completely dead though. 1763 bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), 1764 GV->getContext()); 1765 1766 // If the global is dead now, delete it. 1767 if (GV->use_empty()) { 1768 GV->eraseFromParent(); 1769 ++NumDeleted; 1770 Changed = true; 1771 } 1772 return Changed; 1773 1774 } else if (GS.StoredType <= GlobalStatus::isInitializerStored) { 1775 DEBUG(errs() << "MARKING CONSTANT: " << *GV); 1776 GV->setConstant(true); 1777 1778 // Clean up any obviously simplifiable users now. 1779 CleanupConstantGlobalUsers(GV, GV->getInitializer(), GV->getContext()); 1780 1781 // If the global is dead now, just nuke it. 1782 if (GV->use_empty()) { 1783 DEBUG(errs() << " *** Marking constant allowed us to simplify " 1784 << "all users and delete global!\n"); 1785 GV->eraseFromParent(); 1786 ++NumDeleted; 1787 } 1788 1789 ++NumMarked; 1790 return true; 1791 } else if (!GV->getInitializer()->getType()->isSingleValueType()) { 1792 if (TargetData *TD = getAnalysisIfAvailable<TargetData>()) 1793 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD, 1794 GV->getContext())) { 1795 GVI = FirstNewGV; // Don't skip the newly produced globals! 1796 return true; 1797 } 1798 } else if (GS.StoredType == GlobalStatus::isStoredOnce) { 1799 // If the initial value for the global was an undef value, and if only 1800 // one other value was stored into it, we can just change the 1801 // initializer to be the stored value, then delete all stores to the 1802 // global. This allows us to mark it constant. 1803 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1804 if (isa<UndefValue>(GV->getInitializer())) { 1805 // Change the initial value here. 1806 GV->setInitializer(SOVConstant); 1807 1808 // Clean up any obviously simplifiable users now. 1809 CleanupConstantGlobalUsers(GV, GV->getInitializer(), 1810 GV->getContext()); 1811 1812 if (GV->use_empty()) { 1813 DEBUG(errs() << " *** Substituting initializer allowed us to " 1814 << "simplify all users and delete global!\n"); 1815 GV->eraseFromParent(); 1816 ++NumDeleted; 1817 } else { 1818 GVI = GV; 1819 } 1820 ++NumSubstitute; 1821 return true; 1822 } 1823 1824 // Try to optimize globals based on the knowledge that only one value 1825 // (besides its initializer) is ever stored to the global. 1826 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI, 1827 getAnalysisIfAvailable<TargetData>(), 1828 GV->getContext())) 1829 return true; 1830 1831 // Otherwise, if the global was not a boolean, we can shrink it to be a 1832 // boolean. 1833 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1834 if (TryToShrinkGlobalToBoolean(GV, SOVConstant, GV->getContext())) { 1835 ++NumShrunkToBool; 1836 return true; 1837 } 1838 } 1839 } 1840 return false; 1841} 1842 1843/// ChangeCalleesToFastCall - Walk all of the direct calls of the specified 1844/// function, changing them to FastCC. 1845static void ChangeCalleesToFastCall(Function *F) { 1846 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1847 CallSite User(cast<Instruction>(*UI)); 1848 User.setCallingConv(CallingConv::Fast); 1849 } 1850} 1851 1852static AttrListPtr StripNest(const AttrListPtr &Attrs) { 1853 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) { 1854 if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0) 1855 continue; 1856 1857 // There can be only one. 1858 return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest); 1859 } 1860 1861 return Attrs; 1862} 1863 1864static void RemoveNestAttribute(Function *F) { 1865 F->setAttributes(StripNest(F->getAttributes())); 1866 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1867 CallSite User(cast<Instruction>(*UI)); 1868 User.setAttributes(StripNest(User.getAttributes())); 1869 } 1870} 1871 1872bool GlobalOpt::OptimizeFunctions(Module &M) { 1873 bool Changed = false; 1874 // Optimize functions. 1875 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { 1876 Function *F = FI++; 1877 // Functions without names cannot be referenced outside this module. 1878 if (!F->hasName() && !F->isDeclaration()) 1879 F->setLinkage(GlobalValue::InternalLinkage); 1880 F->removeDeadConstantUsers(); 1881 if (F->use_empty() && (F->hasLocalLinkage() || 1882 F->hasLinkOnceLinkage())) { 1883 M.getFunctionList().erase(F); 1884 Changed = true; 1885 ++NumFnDeleted; 1886 } else if (F->hasLocalLinkage()) { 1887 if (F->getCallingConv() == CallingConv::C && !F->isVarArg() && 1888 !F->hasAddressTaken()) { 1889 // If this function has C calling conventions, is not a varargs 1890 // function, and is only called directly, promote it to use the Fast 1891 // calling convention. 1892 F->setCallingConv(CallingConv::Fast); 1893 ChangeCalleesToFastCall(F); 1894 ++NumFastCallFns; 1895 Changed = true; 1896 } 1897 1898 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) && 1899 !F->hasAddressTaken()) { 1900 // The function is not used by a trampoline intrinsic, so it is safe 1901 // to remove the 'nest' attribute. 1902 RemoveNestAttribute(F); 1903 ++NumNestRemoved; 1904 Changed = true; 1905 } 1906 } 1907 } 1908 return Changed; 1909} 1910 1911bool GlobalOpt::OptimizeGlobalVars(Module &M) { 1912 bool Changed = false; 1913 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); 1914 GVI != E; ) { 1915 GlobalVariable *GV = GVI++; 1916 // Global variables without names cannot be referenced outside this module. 1917 if (!GV->hasName() && !GV->isDeclaration()) 1918 GV->setLinkage(GlobalValue::InternalLinkage); 1919 if (!GV->isConstant() && GV->hasLocalLinkage() && 1920 GV->hasInitializer()) 1921 Changed |= ProcessInternalGlobal(GV, GVI); 1922 } 1923 return Changed; 1924} 1925 1926/// FindGlobalCtors - Find the llvm.globalctors list, verifying that all 1927/// initializers have an init priority of 65535. 1928GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) { 1929 for (Module::global_iterator I = M.global_begin(), E = M.global_end(); 1930 I != E; ++I) 1931 if (I->getName() == "llvm.global_ctors") { 1932 // Found it, verify it's an array of { int, void()* }. 1933 const ArrayType *ATy =dyn_cast<ArrayType>(I->getType()->getElementType()); 1934 if (!ATy) return 0; 1935 const StructType *STy = dyn_cast<StructType>(ATy->getElementType()); 1936 if (!STy || STy->getNumElements() != 2 || 1937 STy->getElementType(0) != Type::getInt32Ty(M.getContext())) return 0; 1938 const PointerType *PFTy = dyn_cast<PointerType>(STy->getElementType(1)); 1939 if (!PFTy) return 0; 1940 const FunctionType *FTy = dyn_cast<FunctionType>(PFTy->getElementType()); 1941 if (!FTy || FTy->getReturnType() != Type::getVoidTy(M.getContext()) || 1942 FTy->isVarArg() || FTy->getNumParams() != 0) 1943 return 0; 1944 1945 // Verify that the initializer is simple enough for us to handle. 1946 if (!I->hasDefinitiveInitializer()) return 0; 1947 ConstantArray *CA = dyn_cast<ConstantArray>(I->getInitializer()); 1948 if (!CA) return 0; 1949 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 1950 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(*i)) { 1951 if (isa<ConstantPointerNull>(CS->getOperand(1))) 1952 continue; 1953 1954 // Must have a function or null ptr. 1955 if (!isa<Function>(CS->getOperand(1))) 1956 return 0; 1957 1958 // Init priority must be standard. 1959 ConstantInt *CI = dyn_cast<ConstantInt>(CS->getOperand(0)); 1960 if (!CI || CI->getZExtValue() != 65535) 1961 return 0; 1962 } else { 1963 return 0; 1964 } 1965 1966 return I; 1967 } 1968 return 0; 1969} 1970 1971/// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand, 1972/// return a list of the functions and null terminator as a vector. 1973static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) { 1974 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer()); 1975 std::vector<Function*> Result; 1976 Result.reserve(CA->getNumOperands()); 1977 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) { 1978 ConstantStruct *CS = cast<ConstantStruct>(*i); 1979 Result.push_back(dyn_cast<Function>(CS->getOperand(1))); 1980 } 1981 return Result; 1982} 1983 1984/// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the 1985/// specified array, returning the new global to use. 1986static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL, 1987 const std::vector<Function*> &Ctors, 1988 LLVMContext &Context) { 1989 // If we made a change, reassemble the initializer list. 1990 std::vector<Constant*> CSVals; 1991 CSVals.push_back(ConstantInt::get(Type::getInt32Ty(Context), 65535)); 1992 CSVals.push_back(0); 1993 1994 // Create the new init list. 1995 std::vector<Constant*> CAList; 1996 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) { 1997 if (Ctors[i]) { 1998 CSVals[1] = Ctors[i]; 1999 } else { 2000 const Type *FTy = FunctionType::get(Type::getVoidTy(Context), false); 2001 const PointerType *PFTy = PointerType::getUnqual(FTy); 2002 CSVals[1] = Constant::getNullValue(PFTy); 2003 CSVals[0] = ConstantInt::get(Type::getInt32Ty(Context), 2147483647); 2004 } 2005 CAList.push_back(ConstantStruct::get(Context, CSVals, false)); 2006 } 2007 2008 // Create the array initializer. 2009 const Type *StructTy = 2010 cast<ArrayType>(GCL->getType()->getElementType())->getElementType(); 2011 Constant *CA = ConstantArray::get(ArrayType::get(StructTy, 2012 CAList.size()), CAList); 2013 2014 // If we didn't change the number of elements, don't create a new GV. 2015 if (CA->getType() == GCL->getInitializer()->getType()) { 2016 GCL->setInitializer(CA); 2017 return GCL; 2018 } 2019 2020 // Create the new global and insert it next to the existing list. 2021 GlobalVariable *NGV = new GlobalVariable(Context, CA->getType(), 2022 GCL->isConstant(), 2023 GCL->getLinkage(), CA, "", 2024 GCL->isThreadLocal()); 2025 GCL->getParent()->getGlobalList().insert(GCL, NGV); 2026 NGV->takeName(GCL); 2027 2028 // Nuke the old list, replacing any uses with the new one. 2029 if (!GCL->use_empty()) { 2030 Constant *V = NGV; 2031 if (V->getType() != GCL->getType()) 2032 V = ConstantExpr::getBitCast(V, GCL->getType()); 2033 GCL->replaceAllUsesWith(V); 2034 } 2035 GCL->eraseFromParent(); 2036 2037 if (Ctors.size()) 2038 return NGV; 2039 else 2040 return 0; 2041} 2042 2043 2044static Constant *getVal(DenseMap<Value*, Constant*> &ComputedValues, 2045 Value *V) { 2046 if (Constant *CV = dyn_cast<Constant>(V)) return CV; 2047 Constant *R = ComputedValues[V]; 2048 assert(R && "Reference to an uncomputed value!"); 2049 return R; 2050} 2051 2052/// isSimpleEnoughPointerToCommit - Return true if this constant is simple 2053/// enough for us to understand. In particular, if it is a cast of something, 2054/// we punt. We basically just support direct accesses to globals and GEP's of 2055/// globals. This should be kept up to date with CommitValueTo. 2056static bool isSimpleEnoughPointerToCommit(Constant *C, LLVMContext &Context) { 2057 // Conservatively, avoid aggregate types. This is because we don't 2058 // want to worry about them partially overlapping other stores. 2059 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType()) 2060 return false; 2061 2062 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) 2063 // Do not allow weak/linkonce/dllimport/dllexport linkage or 2064 // external globals. 2065 return GV->hasDefinitiveInitializer(); 2066 2067 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 2068 // Handle a constantexpr gep. 2069 if (CE->getOpcode() == Instruction::GetElementPtr && 2070 isa<GlobalVariable>(CE->getOperand(0)) && 2071 cast<GEPOperator>(CE)->isInBounds()) { 2072 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2073 // Do not allow weak/linkonce/dllimport/dllexport linkage or 2074 // external globals. 2075 if (!GV->hasDefinitiveInitializer()) 2076 return false; 2077 2078 // The first index must be zero. 2079 ConstantInt *CI = dyn_cast<ConstantInt>(*next(CE->op_begin())); 2080 if (!CI || !CI->isZero()) return false; 2081 2082 // The remaining indices must be compile-time known integers within the 2083 // notional bounds of the corresponding static array types. 2084 if (!CE->isGEPWithNoNotionalOverIndexing()) 2085 return false; 2086 2087 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2088 } 2089 return false; 2090} 2091 2092/// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global 2093/// initializer. This returns 'Init' modified to reflect 'Val' stored into it. 2094/// At this point, the GEP operands of Addr [0, OpNo) have been stepped into. 2095static Constant *EvaluateStoreInto(Constant *Init, Constant *Val, 2096 ConstantExpr *Addr, unsigned OpNo, 2097 LLVMContext &Context) { 2098 // Base case of the recursion. 2099 if (OpNo == Addr->getNumOperands()) { 2100 assert(Val->getType() == Init->getType() && "Type mismatch!"); 2101 return Val; 2102 } 2103 2104 if (const StructType *STy = dyn_cast<StructType>(Init->getType())) { 2105 std::vector<Constant*> Elts; 2106 2107 // Break up the constant into its elements. 2108 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) { 2109 for (User::op_iterator i = CS->op_begin(), e = CS->op_end(); i != e; ++i) 2110 Elts.push_back(cast<Constant>(*i)); 2111 } else if (isa<ConstantAggregateZero>(Init)) { 2112 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2113 Elts.push_back(Constant::getNullValue(STy->getElementType(i))); 2114 } else if (isa<UndefValue>(Init)) { 2115 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2116 Elts.push_back(UndefValue::get(STy->getElementType(i))); 2117 } else { 2118 llvm_unreachable("This code is out of sync with " 2119 " ConstantFoldLoadThroughGEPConstantExpr"); 2120 } 2121 2122 // Replace the element that we are supposed to. 2123 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo)); 2124 unsigned Idx = CU->getZExtValue(); 2125 assert(Idx < STy->getNumElements() && "Struct index out of range!"); 2126 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1, Context); 2127 2128 // Return the modified struct. 2129 return ConstantStruct::get(Context, &Elts[0], Elts.size(), STy->isPacked()); 2130 } else { 2131 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo)); 2132 const ArrayType *ATy = cast<ArrayType>(Init->getType()); 2133 2134 // Break up the array into elements. 2135 std::vector<Constant*> Elts; 2136 if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) { 2137 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 2138 Elts.push_back(cast<Constant>(*i)); 2139 } else if (isa<ConstantAggregateZero>(Init)) { 2140 Constant *Elt = Constant::getNullValue(ATy->getElementType()); 2141 Elts.assign(ATy->getNumElements(), Elt); 2142 } else if (isa<UndefValue>(Init)) { 2143 Constant *Elt = UndefValue::get(ATy->getElementType()); 2144 Elts.assign(ATy->getNumElements(), Elt); 2145 } else { 2146 llvm_unreachable("This code is out of sync with " 2147 " ConstantFoldLoadThroughGEPConstantExpr"); 2148 } 2149 2150 assert(CI->getZExtValue() < ATy->getNumElements()); 2151 Elts[CI->getZExtValue()] = 2152 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1, Context); 2153 return ConstantArray::get(ATy, Elts); 2154 } 2155} 2156 2157/// CommitValueTo - We have decided that Addr (which satisfies the predicate 2158/// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen. 2159static void CommitValueTo(Constant *Val, Constant *Addr, 2160 LLVMContext &Context) { 2161 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) { 2162 assert(GV->hasInitializer()); 2163 GV->setInitializer(Val); 2164 return; 2165 } 2166 2167 ConstantExpr *CE = cast<ConstantExpr>(Addr); 2168 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2169 2170 Constant *Init = GV->getInitializer(); 2171 Init = EvaluateStoreInto(Init, Val, CE, 2, Context); 2172 GV->setInitializer(Init); 2173} 2174 2175/// ComputeLoadResult - Return the value that would be computed by a load from 2176/// P after the stores reflected by 'memory' have been performed. If we can't 2177/// decide, return null. 2178static Constant *ComputeLoadResult(Constant *P, 2179 const DenseMap<Constant*, Constant*> &Memory, 2180 LLVMContext &Context) { 2181 // If this memory location has been recently stored, use the stored value: it 2182 // is the most up-to-date. 2183 DenseMap<Constant*, Constant*>::const_iterator I = Memory.find(P); 2184 if (I != Memory.end()) return I->second; 2185 2186 // Access it. 2187 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) { 2188 if (GV->hasDefinitiveInitializer()) 2189 return GV->getInitializer(); 2190 return 0; 2191 } 2192 2193 // Handle a constantexpr getelementptr. 2194 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) 2195 if (CE->getOpcode() == Instruction::GetElementPtr && 2196 isa<GlobalVariable>(CE->getOperand(0))) { 2197 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2198 if (GV->hasDefinitiveInitializer()) 2199 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2200 } 2201 2202 return 0; // don't know how to evaluate. 2203} 2204 2205/// EvaluateFunction - Evaluate a call to function F, returning true if 2206/// successful, false if we can't evaluate it. ActualArgs contains the formal 2207/// arguments for the function. 2208static bool EvaluateFunction(Function *F, Constant *&RetVal, 2209 const SmallVectorImpl<Constant*> &ActualArgs, 2210 std::vector<Function*> &CallStack, 2211 DenseMap<Constant*, Constant*> &MutatedMemory, 2212 std::vector<GlobalVariable*> &AllocaTmps) { 2213 // Check to see if this function is already executing (recursion). If so, 2214 // bail out. TODO: we might want to accept limited recursion. 2215 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end()) 2216 return false; 2217 2218 LLVMContext &Context = F->getContext(); 2219 2220 CallStack.push_back(F); 2221 2222 /// Values - As we compute SSA register values, we store their contents here. 2223 DenseMap<Value*, Constant*> Values; 2224 2225 // Initialize arguments to the incoming values specified. 2226 unsigned ArgNo = 0; 2227 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E; 2228 ++AI, ++ArgNo) 2229 Values[AI] = ActualArgs[ArgNo]; 2230 2231 /// ExecutedBlocks - We only handle non-looping, non-recursive code. As such, 2232 /// we can only evaluate any one basic block at most once. This set keeps 2233 /// track of what we have executed so we can detect recursive cases etc. 2234 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks; 2235 2236 // CurInst - The current instruction we're evaluating. 2237 BasicBlock::iterator CurInst = F->begin()->begin(); 2238 2239 // This is the main evaluation loop. 2240 while (1) { 2241 Constant *InstResult = 0; 2242 2243 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) { 2244 if (SI->isVolatile()) return false; // no volatile accesses. 2245 Constant *Ptr = getVal(Values, SI->getOperand(1)); 2246 if (!isSimpleEnoughPointerToCommit(Ptr, Context)) 2247 // If this is too complex for us to commit, reject it. 2248 return false; 2249 Constant *Val = getVal(Values, SI->getOperand(0)); 2250 MutatedMemory[Ptr] = Val; 2251 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) { 2252 InstResult = ConstantExpr::get(BO->getOpcode(), 2253 getVal(Values, BO->getOperand(0)), 2254 getVal(Values, BO->getOperand(1))); 2255 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) { 2256 InstResult = ConstantExpr::getCompare(CI->getPredicate(), 2257 getVal(Values, CI->getOperand(0)), 2258 getVal(Values, CI->getOperand(1))); 2259 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) { 2260 InstResult = ConstantExpr::getCast(CI->getOpcode(), 2261 getVal(Values, CI->getOperand(0)), 2262 CI->getType()); 2263 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) { 2264 InstResult = 2265 ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)), 2266 getVal(Values, SI->getOperand(1)), 2267 getVal(Values, SI->getOperand(2))); 2268 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) { 2269 Constant *P = getVal(Values, GEP->getOperand(0)); 2270 SmallVector<Constant*, 8> GEPOps; 2271 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); 2272 i != e; ++i) 2273 GEPOps.push_back(getVal(Values, *i)); 2274 InstResult = cast<GEPOperator>(GEP)->isInBounds() ? 2275 ConstantExpr::getInBoundsGetElementPtr(P, &GEPOps[0], GEPOps.size()) : 2276 ConstantExpr::getGetElementPtr(P, &GEPOps[0], GEPOps.size()); 2277 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) { 2278 if (LI->isVolatile()) return false; // no volatile accesses. 2279 InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)), 2280 MutatedMemory, Context); 2281 if (InstResult == 0) return false; // Could not evaluate load. 2282 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) { 2283 if (AI->isArrayAllocation()) return false; // Cannot handle array allocs. 2284 const Type *Ty = AI->getType()->getElementType(); 2285 AllocaTmps.push_back(new GlobalVariable(Context, Ty, false, 2286 GlobalValue::InternalLinkage, 2287 UndefValue::get(Ty), 2288 AI->getName())); 2289 InstResult = AllocaTmps.back(); 2290 } else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) { 2291 2292 // Debug info can safely be ignored here. 2293 if (isa<DbgInfoIntrinsic>(CI)) { 2294 ++CurInst; 2295 continue; 2296 } 2297 2298 // Cannot handle inline asm. 2299 if (isa<InlineAsm>(CI->getOperand(0))) return false; 2300 2301 // Resolve function pointers. 2302 Function *Callee = dyn_cast<Function>(getVal(Values, CI->getOperand(0))); 2303 if (!Callee) return false; // Cannot resolve. 2304 2305 SmallVector<Constant*, 8> Formals; 2306 for (User::op_iterator i = CI->op_begin() + 1, e = CI->op_end(); 2307 i != e; ++i) 2308 Formals.push_back(getVal(Values, *i)); 2309 2310 if (Callee->isDeclaration()) { 2311 // If this is a function we can constant fold, do it. 2312 if (Constant *C = ConstantFoldCall(Callee, Formals.data(), 2313 Formals.size())) { 2314 InstResult = C; 2315 } else { 2316 return false; 2317 } 2318 } else { 2319 if (Callee->getFunctionType()->isVarArg()) 2320 return false; 2321 2322 Constant *RetVal; 2323 // Execute the call, if successful, use the return value. 2324 if (!EvaluateFunction(Callee, RetVal, Formals, CallStack, 2325 MutatedMemory, AllocaTmps)) 2326 return false; 2327 InstResult = RetVal; 2328 } 2329 } else if (isa<TerminatorInst>(CurInst)) { 2330 BasicBlock *NewBB = 0; 2331 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) { 2332 if (BI->isUnconditional()) { 2333 NewBB = BI->getSuccessor(0); 2334 } else { 2335 ConstantInt *Cond = 2336 dyn_cast<ConstantInt>(getVal(Values, BI->getCondition())); 2337 if (!Cond) return false; // Cannot determine. 2338 2339 NewBB = BI->getSuccessor(!Cond->getZExtValue()); 2340 } 2341 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) { 2342 ConstantInt *Val = 2343 dyn_cast<ConstantInt>(getVal(Values, SI->getCondition())); 2344 if (!Val) return false; // Cannot determine. 2345 NewBB = SI->getSuccessor(SI->findCaseValue(Val)); 2346 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) { 2347 if (RI->getNumOperands()) 2348 RetVal = getVal(Values, RI->getOperand(0)); 2349 2350 CallStack.pop_back(); // return from fn. 2351 return true; // We succeeded at evaluating this ctor! 2352 } else { 2353 // invoke, unwind, unreachable. 2354 return false; // Cannot handle this terminator. 2355 } 2356 2357 // Okay, we succeeded in evaluating this control flow. See if we have 2358 // executed the new block before. If so, we have a looping function, 2359 // which we cannot evaluate in reasonable time. 2360 if (!ExecutedBlocks.insert(NewBB)) 2361 return false; // looped! 2362 2363 // Okay, we have never been in this block before. Check to see if there 2364 // are any PHI nodes. If so, evaluate them with information about where 2365 // we came from. 2366 BasicBlock *OldBB = CurInst->getParent(); 2367 CurInst = NewBB->begin(); 2368 PHINode *PN; 2369 for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst) 2370 Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB)); 2371 2372 // Do NOT increment CurInst. We know that the terminator had no value. 2373 continue; 2374 } else { 2375 // Did not know how to evaluate this! 2376 return false; 2377 } 2378 2379 if (!CurInst->use_empty()) 2380 Values[CurInst] = InstResult; 2381 2382 // Advance program counter. 2383 ++CurInst; 2384 } 2385} 2386 2387/// EvaluateStaticConstructor - Evaluate static constructors in the function, if 2388/// we can. Return true if we can, false otherwise. 2389static bool EvaluateStaticConstructor(Function *F) { 2390 /// MutatedMemory - For each store we execute, we update this map. Loads 2391 /// check this to get the most up-to-date value. If evaluation is successful, 2392 /// this state is committed to the process. 2393 DenseMap<Constant*, Constant*> MutatedMemory; 2394 2395 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable 2396 /// to represent its body. This vector is needed so we can delete the 2397 /// temporary globals when we are done. 2398 std::vector<GlobalVariable*> AllocaTmps; 2399 2400 /// CallStack - This is used to detect recursion. In pathological situations 2401 /// we could hit exponential behavior, but at least there is nothing 2402 /// unbounded. 2403 std::vector<Function*> CallStack; 2404 2405 // Call the function. 2406 Constant *RetValDummy; 2407 bool EvalSuccess = EvaluateFunction(F, RetValDummy, 2408 SmallVector<Constant*, 0>(), CallStack, 2409 MutatedMemory, AllocaTmps); 2410 if (EvalSuccess) { 2411 // We succeeded at evaluation: commit the result. 2412 DEBUG(errs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" 2413 << F->getName() << "' to " << MutatedMemory.size() 2414 << " stores.\n"); 2415 for (DenseMap<Constant*, Constant*>::iterator I = MutatedMemory.begin(), 2416 E = MutatedMemory.end(); I != E; ++I) 2417 CommitValueTo(I->second, I->first, F->getContext()); 2418 } 2419 2420 // At this point, we are done interpreting. If we created any 'alloca' 2421 // temporaries, release them now. 2422 while (!AllocaTmps.empty()) { 2423 GlobalVariable *Tmp = AllocaTmps.back(); 2424 AllocaTmps.pop_back(); 2425 2426 // If there are still users of the alloca, the program is doing something 2427 // silly, e.g. storing the address of the alloca somewhere and using it 2428 // later. Since this is undefined, we'll just make it be null. 2429 if (!Tmp->use_empty()) 2430 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType())); 2431 delete Tmp; 2432 } 2433 2434 return EvalSuccess; 2435} 2436 2437 2438 2439/// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible. 2440/// Return true if anything changed. 2441bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) { 2442 std::vector<Function*> Ctors = ParseGlobalCtors(GCL); 2443 bool MadeChange = false; 2444 if (Ctors.empty()) return false; 2445 2446 // Loop over global ctors, optimizing them when we can. 2447 for (unsigned i = 0; i != Ctors.size(); ++i) { 2448 Function *F = Ctors[i]; 2449 // Found a null terminator in the middle of the list, prune off the rest of 2450 // the list. 2451 if (F == 0) { 2452 if (i != Ctors.size()-1) { 2453 Ctors.resize(i+1); 2454 MadeChange = true; 2455 } 2456 break; 2457 } 2458 2459 // We cannot simplify external ctor functions. 2460 if (F->empty()) continue; 2461 2462 // If we can evaluate the ctor at compile time, do. 2463 if (EvaluateStaticConstructor(F)) { 2464 Ctors.erase(Ctors.begin()+i); 2465 MadeChange = true; 2466 --i; 2467 ++NumCtorsEvaluated; 2468 continue; 2469 } 2470 } 2471 2472 if (!MadeChange) return false; 2473 2474 GCL = InstallGlobalCtors(GCL, Ctors, GCL->getContext()); 2475 return true; 2476} 2477 2478bool GlobalOpt::OptimizeGlobalAliases(Module &M) { 2479 bool Changed = false; 2480 2481 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); 2482 I != E;) { 2483 Module::alias_iterator J = I++; 2484 // Aliases without names cannot be referenced outside this module. 2485 if (!J->hasName() && !J->isDeclaration()) 2486 J->setLinkage(GlobalValue::InternalLinkage); 2487 // If the aliasee may change at link time, nothing can be done - bail out. 2488 if (J->mayBeOverridden()) 2489 continue; 2490 2491 Constant *Aliasee = J->getAliasee(); 2492 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts()); 2493 Target->removeDeadConstantUsers(); 2494 bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse(); 2495 2496 // Make all users of the alias use the aliasee instead. 2497 if (!J->use_empty()) { 2498 J->replaceAllUsesWith(Aliasee); 2499 ++NumAliasesResolved; 2500 Changed = true; 2501 } 2502 2503 // If the aliasee has internal linkage, give it the name and linkage 2504 // of the alias, and delete the alias. This turns: 2505 // define internal ... @f(...) 2506 // @a = alias ... @f 2507 // into: 2508 // define ... @a(...) 2509 if (!Target->hasLocalLinkage()) 2510 continue; 2511 2512 // The transform is only useful if the alias does not have internal linkage. 2513 if (J->hasLocalLinkage()) 2514 continue; 2515 2516 // Do not perform the transform if multiple aliases potentially target the 2517 // aliasee. This check also ensures that it is safe to replace the section 2518 // and other attributes of the aliasee with those of the alias. 2519 if (!hasOneUse) 2520 continue; 2521 2522 // Give the aliasee the name, linkage and other attributes of the alias. 2523 Target->takeName(J); 2524 Target->setLinkage(J->getLinkage()); 2525 Target->GlobalValue::copyAttributesFrom(J); 2526 2527 // Delete the alias. 2528 M.getAliasList().erase(J); 2529 ++NumAliasesRemoved; 2530 Changed = true; 2531 } 2532 2533 return Changed; 2534} 2535 2536bool GlobalOpt::runOnModule(Module &M) { 2537 bool Changed = false; 2538 2539 // Try to find the llvm.globalctors list. 2540 GlobalVariable *GlobalCtors = FindGlobalCtors(M); 2541 2542 bool LocalChange = true; 2543 while (LocalChange) { 2544 LocalChange = false; 2545 2546 // Delete functions that are trivially dead, ccc -> fastcc 2547 LocalChange |= OptimizeFunctions(M); 2548 2549 // Optimize global_ctors list. 2550 if (GlobalCtors) 2551 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors); 2552 2553 // Optimize non-address-taken globals. 2554 LocalChange |= OptimizeGlobalVars(M); 2555 2556 // Resolve aliases, when possible. 2557 LocalChange |= OptimizeGlobalAliases(M); 2558 Changed |= LocalChange; 2559 } 2560 2561 // TODO: Move all global ctors functions to the end of the module for code 2562 // layout. 2563 2564 return Changed; 2565} 2566