GlobalOpt.cpp revision 4200f2c815159e939351d5d447f7f68fb557e600
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 Value* NElems, 827 LLVMContext &Context, 828 TargetData* TD) { 829 DEBUG(errs() << "PROMOTING MALLOC GLOBAL: " << *GV 830 << " CALL = " << *CI << " BCI = " << *BCI << '\n'); 831 832 const Type *IntPtrTy = TD->getIntPtrType(Context); 833 834 ConstantInt *NElements = cast<ConstantInt>(NElems); 835 if (NElements->getZExtValue() != 1) { 836 // If we have an array allocation, transform it to a single element 837 // allocation to make the code below simpler. 838 Type *NewTy = ArrayType::get(getMallocAllocatedType(CI), 839 NElements->getZExtValue()); 840 Value* NewM = CallInst::CreateMalloc(CI, IntPtrTy, NewTy); 841 Instruction* NewMI = cast<Instruction>(NewM); 842 Value* Indices[2]; 843 Indices[0] = Indices[1] = Constant::getNullValue(IntPtrTy); 844 Value *NewGEP = GetElementPtrInst::Create(NewMI, Indices, Indices + 2, 845 NewMI->getName()+".el0", CI); 846 BCI->replaceAllUsesWith(NewGEP); 847 BCI->eraseFromParent(); 848 CI->eraseFromParent(); 849 BCI = cast<BitCastInst>(NewMI); 850 CI = extractMallocCallFromBitCast(NewMI); 851 } 852 853 // Create the new global variable. The contents of the malloc'd memory is 854 // undefined, so initialize with an undef value. 855 const Type *MAT = getMallocAllocatedType(CI); 856 Constant *Init = UndefValue::get(MAT); 857 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(), 858 MAT, false, 859 GlobalValue::InternalLinkage, Init, 860 GV->getName()+".body", 861 GV, 862 GV->isThreadLocal()); 863 864 // Anything that used the malloc now uses the global directly. 865 BCI->replaceAllUsesWith(NewGV); 866 867 Constant *RepValue = NewGV; 868 if (NewGV->getType() != GV->getType()->getElementType()) 869 RepValue = ConstantExpr::getBitCast(RepValue, 870 GV->getType()->getElementType()); 871 872 // If there is a comparison against null, we will insert a global bool to 873 // keep track of whether the global was initialized yet or not. 874 GlobalVariable *InitBool = 875 new GlobalVariable(Context, Type::getInt1Ty(Context), false, 876 GlobalValue::InternalLinkage, 877 ConstantInt::getFalse(Context), GV->getName()+".init", 878 GV->isThreadLocal()); 879 bool InitBoolUsed = false; 880 881 // Loop over all uses of GV, processing them in turn. 882 std::vector<StoreInst*> Stores; 883 while (!GV->use_empty()) 884 if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) { 885 while (!LI->use_empty()) { 886 Use &LoadUse = LI->use_begin().getUse(); 887 if (!isa<ICmpInst>(LoadUse.getUser())) 888 LoadUse = RepValue; 889 else { 890 ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser()); 891 // Replace the cmp X, 0 with a use of the bool value. 892 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", ICI); 893 InitBoolUsed = true; 894 switch (ICI->getPredicate()) { 895 default: llvm_unreachable("Unknown ICmp Predicate!"); 896 case ICmpInst::ICMP_ULT: 897 case ICmpInst::ICMP_SLT: 898 LV = ConstantInt::getFalse(Context); // X < null -> always false 899 break; 900 case ICmpInst::ICMP_ULE: 901 case ICmpInst::ICMP_SLE: 902 case ICmpInst::ICMP_EQ: 903 LV = BinaryOperator::CreateNot(LV, "notinit", ICI); 904 break; 905 case ICmpInst::ICMP_NE: 906 case ICmpInst::ICMP_UGE: 907 case ICmpInst::ICMP_SGE: 908 case ICmpInst::ICMP_UGT: 909 case ICmpInst::ICMP_SGT: 910 break; // no change. 911 } 912 ICI->replaceAllUsesWith(LV); 913 ICI->eraseFromParent(); 914 } 915 } 916 LI->eraseFromParent(); 917 } else { 918 StoreInst *SI = cast<StoreInst>(GV->use_back()); 919 // The global is initialized when the store to it occurs. 920 new StoreInst(ConstantInt::getTrue(Context), InitBool, SI); 921 SI->eraseFromParent(); 922 } 923 924 // If the initialization boolean was used, insert it, otherwise delete it. 925 if (!InitBoolUsed) { 926 while (!InitBool->use_empty()) // Delete initializations 927 cast<Instruction>(InitBool->use_back())->eraseFromParent(); 928 delete InitBool; 929 } else 930 GV->getParent()->getGlobalList().insert(GV, InitBool); 931 932 933 // Now the GV is dead, nuke it and the malloc. 934 GV->eraseFromParent(); 935 BCI->eraseFromParent(); 936 CI->eraseFromParent(); 937 938 // To further other optimizations, loop over all users of NewGV and try to 939 // constant prop them. This will promote GEP instructions with constant 940 // indices into GEP constant-exprs, which will allow global-opt to hack on it. 941 ConstantPropUsersOf(NewGV, Context); 942 if (RepValue != NewGV) 943 ConstantPropUsersOf(RepValue, Context); 944 945 return NewGV; 946} 947 948/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking 949/// to make sure that there are no complex uses of V. We permit simple things 950/// like dereferencing the pointer, but not storing through the address, unless 951/// it is to the specified global. 952static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Instruction *V, 953 GlobalVariable *GV, 954 SmallPtrSet<PHINode*, 8> &PHIs) { 955 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 956 Instruction *Inst = cast<Instruction>(*UI); 957 958 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) { 959 continue; // Fine, ignore. 960 } 961 962 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 963 if (SI->getOperand(0) == V && SI->getOperand(1) != GV) 964 return false; // Storing the pointer itself... bad. 965 continue; // Otherwise, storing through it, or storing into GV... fine. 966 } 967 968 if (isa<GetElementPtrInst>(Inst)) { 969 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs)) 970 return false; 971 continue; 972 } 973 974 if (PHINode *PN = dyn_cast<PHINode>(Inst)) { 975 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI 976 // cycles. 977 if (PHIs.insert(PN)) 978 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs)) 979 return false; 980 continue; 981 } 982 983 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) { 984 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) 985 return false; 986 continue; 987 } 988 989 return false; 990 } 991 return true; 992} 993 994/// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV 995/// somewhere. Transform all uses of the allocation into loads from the 996/// global and uses of the resultant pointer. Further, delete the store into 997/// GV. This assumes that these value pass the 998/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate. 999static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, 1000 GlobalVariable *GV) { 1001 while (!Alloc->use_empty()) { 1002 Instruction *U = cast<Instruction>(*Alloc->use_begin()); 1003 Instruction *InsertPt = U; 1004 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 1005 // If this is the store of the allocation into the global, remove it. 1006 if (SI->getOperand(1) == GV) { 1007 SI->eraseFromParent(); 1008 continue; 1009 } 1010 } else if (PHINode *PN = dyn_cast<PHINode>(U)) { 1011 // Insert the load in the corresponding predecessor, not right before the 1012 // PHI. 1013 InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator(); 1014 } else if (isa<BitCastInst>(U)) { 1015 // Must be bitcast between the malloc and store to initialize the global. 1016 ReplaceUsesOfMallocWithGlobal(U, GV); 1017 U->eraseFromParent(); 1018 continue; 1019 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { 1020 // If this is a "GEP bitcast" and the user is a store to the global, then 1021 // just process it as a bitcast. 1022 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse()) 1023 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back())) 1024 if (SI->getOperand(1) == GV) { 1025 // Must be bitcast GEP between the malloc and store to initialize 1026 // the global. 1027 ReplaceUsesOfMallocWithGlobal(GEPI, GV); 1028 GEPI->eraseFromParent(); 1029 continue; 1030 } 1031 } 1032 1033 // Insert a load from the global, and use it instead of the malloc. 1034 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt); 1035 U->replaceUsesOfWith(Alloc, NL); 1036 } 1037} 1038 1039/// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi 1040/// of a load) are simple enough to perform heap SRA on. This permits GEP's 1041/// that index through the array and struct field, icmps of null, and PHIs. 1042static bool LoadUsesSimpleEnoughForHeapSRA(Value *V, 1043 SmallPtrSet<PHINode*, 32> &LoadUsingPHIs, 1044 SmallPtrSet<PHINode*, 32> &LoadUsingPHIsPerLoad) { 1045 // We permit two users of the load: setcc comparing against the null 1046 // pointer, and a getelementptr of a specific form. 1047 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 1048 Instruction *User = cast<Instruction>(*UI); 1049 1050 // Comparison against null is ok. 1051 if (ICmpInst *ICI = dyn_cast<ICmpInst>(User)) { 1052 if (!isa<ConstantPointerNull>(ICI->getOperand(1))) 1053 return false; 1054 continue; 1055 } 1056 1057 // getelementptr is also ok, but only a simple form. 1058 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1059 // Must index into the array and into the struct. 1060 if (GEPI->getNumOperands() < 3) 1061 return false; 1062 1063 // Otherwise the GEP is ok. 1064 continue; 1065 } 1066 1067 if (PHINode *PN = dyn_cast<PHINode>(User)) { 1068 if (!LoadUsingPHIsPerLoad.insert(PN)) 1069 // This means some phi nodes are dependent on each other. 1070 // Avoid infinite looping! 1071 return false; 1072 if (!LoadUsingPHIs.insert(PN)) 1073 // If we have already analyzed this PHI, then it is safe. 1074 continue; 1075 1076 // Make sure all uses of the PHI are simple enough to transform. 1077 if (!LoadUsesSimpleEnoughForHeapSRA(PN, 1078 LoadUsingPHIs, LoadUsingPHIsPerLoad)) 1079 return false; 1080 1081 continue; 1082 } 1083 1084 // Otherwise we don't know what this is, not ok. 1085 return false; 1086 } 1087 1088 return true; 1089} 1090 1091 1092/// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from 1093/// GV are simple enough to perform HeapSRA, return true. 1094static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(GlobalVariable *GV, 1095 Instruction *StoredVal) { 1096 SmallPtrSet<PHINode*, 32> LoadUsingPHIs; 1097 SmallPtrSet<PHINode*, 32> LoadUsingPHIsPerLoad; 1098 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E; 1099 ++UI) 1100 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 1101 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs, 1102 LoadUsingPHIsPerLoad)) 1103 return false; 1104 LoadUsingPHIsPerLoad.clear(); 1105 } 1106 1107 // If we reach here, we know that all uses of the loads and transitive uses 1108 // (through PHI nodes) are simple enough to transform. However, we don't know 1109 // that all inputs the to the PHI nodes are in the same equivalence sets. 1110 // Check to verify that all operands of the PHIs are either PHIS that can be 1111 // transformed, loads from GV, or MI itself. 1112 for (SmallPtrSet<PHINode*, 32>::iterator I = LoadUsingPHIs.begin(), 1113 E = LoadUsingPHIs.end(); I != E; ++I) { 1114 PHINode *PN = *I; 1115 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) { 1116 Value *InVal = PN->getIncomingValue(op); 1117 1118 // PHI of the stored value itself is ok. 1119 if (InVal == StoredVal) continue; 1120 1121 if (PHINode *InPN = dyn_cast<PHINode>(InVal)) { 1122 // One of the PHIs in our set is (optimistically) ok. 1123 if (LoadUsingPHIs.count(InPN)) 1124 continue; 1125 return false; 1126 } 1127 1128 // Load from GV is ok. 1129 if (LoadInst *LI = dyn_cast<LoadInst>(InVal)) 1130 if (LI->getOperand(0) == GV) 1131 continue; 1132 1133 // UNDEF? NULL? 1134 1135 // Anything else is rejected. 1136 return false; 1137 } 1138 } 1139 1140 return true; 1141} 1142 1143static Value *GetHeapSROAValue(Value *V, unsigned FieldNo, 1144 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1145 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite, 1146 LLVMContext &Context) { 1147 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V]; 1148 1149 if (FieldNo >= FieldVals.size()) 1150 FieldVals.resize(FieldNo+1); 1151 1152 // If we already have this value, just reuse the previously scalarized 1153 // version. 1154 if (Value *FieldVal = FieldVals[FieldNo]) 1155 return FieldVal; 1156 1157 // Depending on what instruction this is, we have several cases. 1158 Value *Result; 1159 if (LoadInst *LI = dyn_cast<LoadInst>(V)) { 1160 // This is a scalarized version of the load from the global. Just create 1161 // a new Load of the scalarized global. 1162 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo, 1163 InsertedScalarizedValues, 1164 PHIsToRewrite, Context), 1165 LI->getName()+".f"+Twine(FieldNo), LI); 1166 } else if (PHINode *PN = dyn_cast<PHINode>(V)) { 1167 // PN's type is pointer to struct. Make a new PHI of pointer to struct 1168 // field. 1169 const StructType *ST = 1170 cast<StructType>(cast<PointerType>(PN->getType())->getElementType()); 1171 1172 Result = 1173 PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)), 1174 PN->getName()+".f"+Twine(FieldNo), PN); 1175 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo)); 1176 } else { 1177 llvm_unreachable("Unknown usable value"); 1178 Result = 0; 1179 } 1180 1181 return FieldVals[FieldNo] = Result; 1182} 1183 1184/// RewriteHeapSROALoadUser - Given a load instruction and a value derived from 1185/// the load, rewrite the derived value to use the HeapSRoA'd load. 1186static void RewriteHeapSROALoadUser(Instruction *LoadUser, 1187 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1188 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite, 1189 LLVMContext &Context) { 1190 // If this is a comparison against null, handle it. 1191 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) { 1192 assert(isa<ConstantPointerNull>(SCI->getOperand(1))); 1193 // If we have a setcc of the loaded pointer, we can use a setcc of any 1194 // field. 1195 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0, 1196 InsertedScalarizedValues, PHIsToRewrite, 1197 Context); 1198 1199 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr, 1200 Constant::getNullValue(NPtr->getType()), 1201 SCI->getName()); 1202 SCI->replaceAllUsesWith(New); 1203 SCI->eraseFromParent(); 1204 return; 1205 } 1206 1207 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...' 1208 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) { 1209 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2)) 1210 && "Unexpected GEPI!"); 1211 1212 // Load the pointer for this field. 1213 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 1214 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo, 1215 InsertedScalarizedValues, PHIsToRewrite, 1216 Context); 1217 1218 // Create the new GEP idx vector. 1219 SmallVector<Value*, 8> GEPIdx; 1220 GEPIdx.push_back(GEPI->getOperand(1)); 1221 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end()); 1222 1223 Value *NGEPI = GetElementPtrInst::Create(NewPtr, 1224 GEPIdx.begin(), GEPIdx.end(), 1225 GEPI->getName(), GEPI); 1226 GEPI->replaceAllUsesWith(NGEPI); 1227 GEPI->eraseFromParent(); 1228 return; 1229 } 1230 1231 // Recursively transform the users of PHI nodes. This will lazily create the 1232 // PHIs that are needed for individual elements. Keep track of what PHIs we 1233 // see in InsertedScalarizedValues so that we don't get infinite loops (very 1234 // antisocial). If the PHI is already in InsertedScalarizedValues, it has 1235 // already been seen first by another load, so its uses have already been 1236 // processed. 1237 PHINode *PN = cast<PHINode>(LoadUser); 1238 bool Inserted; 1239 DenseMap<Value*, std::vector<Value*> >::iterator InsertPos; 1240 tie(InsertPos, Inserted) = 1241 InsertedScalarizedValues.insert(std::make_pair(PN, std::vector<Value*>())); 1242 if (!Inserted) return; 1243 1244 // If this is the first time we've seen this PHI, recursively process all 1245 // users. 1246 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) { 1247 Instruction *User = cast<Instruction>(*UI++); 1248 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite, 1249 Context); 1250 } 1251} 1252 1253/// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr 1254/// is a value loaded from the global. Eliminate all uses of Ptr, making them 1255/// use FieldGlobals instead. All uses of loaded values satisfy 1256/// AllGlobalLoadUsesSimpleEnoughForHeapSRA. 1257static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load, 1258 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1259 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite, 1260 LLVMContext &Context) { 1261 for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end(); 1262 UI != E; ) { 1263 Instruction *User = cast<Instruction>(*UI++); 1264 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite, 1265 Context); 1266 } 1267 1268 if (Load->use_empty()) { 1269 Load->eraseFromParent(); 1270 InsertedScalarizedValues.erase(Load); 1271 } 1272} 1273 1274/// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break 1275/// it up into multiple allocations of arrays of the fields. 1276static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, 1277 CallInst *CI, BitCastInst* BCI, 1278 Value* NElems, 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 1286 // There is guaranteed to be at least one use of the malloc (storing 1287 // it into GV). If there are other uses, change them to be uses of 1288 // the global to simplify later code. This also deletes the store 1289 // into GV. 1290 ReplaceUsesOfMallocWithGlobal(BCI, GV); 1291 1292 // Okay, at this point, there are no users of the malloc. Insert N 1293 // new mallocs at the same place as CI, and N globals. 1294 std::vector<Value*> FieldGlobals; 1295 std::vector<Value*> FieldMallocs; 1296 1297 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ 1298 const Type *FieldTy = STy->getElementType(FieldNo); 1299 const PointerType *PFieldTy = PointerType::getUnqual(FieldTy); 1300 1301 GlobalVariable *NGV = 1302 new GlobalVariable(*GV->getParent(), 1303 PFieldTy, false, GlobalValue::InternalLinkage, 1304 Constant::getNullValue(PFieldTy), 1305 GV->getName() + ".f" + Twine(FieldNo), GV, 1306 GV->isThreadLocal()); 1307 FieldGlobals.push_back(NGV); 1308 1309 Value *NMI = CallInst::CreateMalloc(CI, TD->getIntPtrType(Context), 1310 FieldTy, NElems, 1311 BCI->getName() + ".f" + Twine(FieldNo)); 1312 FieldMallocs.push_back(NMI); 1313 new StoreInst(NMI, NGV, BCI); 1314 } 1315 1316 // The tricky aspect of this transformation is handling the case when malloc 1317 // fails. In the original code, malloc failing would set the result pointer 1318 // of malloc to null. In this case, some mallocs could succeed and others 1319 // could fail. As such, we emit code that looks like this: 1320 // F0 = malloc(field0) 1321 // F1 = malloc(field1) 1322 // F2 = malloc(field2) 1323 // if (F0 == 0 || F1 == 0 || F2 == 0) { 1324 // if (F0) { free(F0); F0 = 0; } 1325 // if (F1) { free(F1); F1 = 0; } 1326 // if (F2) { free(F2); F2 = 0; } 1327 // } 1328 Value *RunningOr = 0; 1329 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) { 1330 Value *Cond = new ICmpInst(BCI, ICmpInst::ICMP_EQ, FieldMallocs[i], 1331 Constant::getNullValue(FieldMallocs[i]->getType()), 1332 "isnull"); 1333 if (!RunningOr) 1334 RunningOr = Cond; // First seteq 1335 else 1336 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", BCI); 1337 } 1338 1339 // Split the basic block at the old malloc. 1340 BasicBlock *OrigBB = BCI->getParent(); 1341 BasicBlock *ContBB = OrigBB->splitBasicBlock(BCI, "malloc_cont"); 1342 1343 // Create the block to check the first condition. Put all these blocks at the 1344 // end of the function as they are unlikely to be executed. 1345 BasicBlock *NullPtrBlock = BasicBlock::Create(Context, "malloc_ret_null", 1346 OrigBB->getParent()); 1347 1348 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond 1349 // branch on RunningOr. 1350 OrigBB->getTerminator()->eraseFromParent(); 1351 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB); 1352 1353 // Within the NullPtrBlock, we need to emit a comparison and branch for each 1354 // pointer, because some may be null while others are not. 1355 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1356 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock); 1357 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal, 1358 Constant::getNullValue(GVVal->getType()), 1359 "tmp"); 1360 BasicBlock *FreeBlock = BasicBlock::Create(Context, "free_it", 1361 OrigBB->getParent()); 1362 BasicBlock *NextBlock = BasicBlock::Create(Context, "next", 1363 OrigBB->getParent()); 1364 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock, 1365 Cmp, NullPtrBlock); 1366 1367 // Fill in FreeBlock. 1368 CallInst::CreateFree(GVVal, BI); 1369 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i], 1370 FreeBlock); 1371 BranchInst::Create(NextBlock, FreeBlock); 1372 1373 NullPtrBlock = NextBlock; 1374 } 1375 1376 BranchInst::Create(ContBB, NullPtrBlock); 1377 1378 // CI and BCI are no longer needed, remove them. 1379 BCI->eraseFromParent(); 1380 CI->eraseFromParent(); 1381 1382 /// InsertedScalarizedLoads - As we process loads, if we can't immediately 1383 /// update all uses of the load, keep track of what scalarized loads are 1384 /// inserted for a given load. 1385 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues; 1386 InsertedScalarizedValues[GV] = FieldGlobals; 1387 1388 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite; 1389 1390 // Okay, the malloc site is completely handled. All of the uses of GV are now 1391 // loads, and all uses of those loads are simple. Rewrite them to use loads 1392 // of the per-field globals instead. 1393 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) { 1394 Instruction *User = cast<Instruction>(*UI++); 1395 1396 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1397 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite, 1398 Context); 1399 continue; 1400 } 1401 1402 // Must be a store of null. 1403 StoreInst *SI = cast<StoreInst>(User); 1404 assert(isa<ConstantPointerNull>(SI->getOperand(0)) && 1405 "Unexpected heap-sra user!"); 1406 1407 // Insert a store of null into each global. 1408 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1409 const PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType()); 1410 Constant *Null = Constant::getNullValue(PT->getElementType()); 1411 new StoreInst(Null, FieldGlobals[i], SI); 1412 } 1413 // Erase the original store. 1414 SI->eraseFromParent(); 1415 } 1416 1417 // While we have PHIs that are interesting to rewrite, do it. 1418 while (!PHIsToRewrite.empty()) { 1419 PHINode *PN = PHIsToRewrite.back().first; 1420 unsigned FieldNo = PHIsToRewrite.back().second; 1421 PHIsToRewrite.pop_back(); 1422 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]); 1423 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi"); 1424 1425 // Add all the incoming values. This can materialize more phis. 1426 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1427 Value *InVal = PN->getIncomingValue(i); 1428 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues, 1429 PHIsToRewrite, Context); 1430 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i)); 1431 } 1432 } 1433 1434 // Drop all inter-phi links and any loads that made it this far. 1435 for (DenseMap<Value*, std::vector<Value*> >::iterator 1436 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1437 I != E; ++I) { 1438 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1439 PN->dropAllReferences(); 1440 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1441 LI->dropAllReferences(); 1442 } 1443 1444 // Delete all the phis and loads now that inter-references are dead. 1445 for (DenseMap<Value*, std::vector<Value*> >::iterator 1446 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1447 I != E; ++I) { 1448 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1449 PN->eraseFromParent(); 1450 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1451 LI->eraseFromParent(); 1452 } 1453 1454 // The old global is now dead, remove it. 1455 GV->eraseFromParent(); 1456 1457 ++NumHeapSRA; 1458 return cast<GlobalVariable>(FieldGlobals[0]); 1459} 1460 1461/// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a 1462/// pointer global variable with a single value stored it that is a malloc or 1463/// cast of malloc. 1464static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, 1465 CallInst *CI, 1466 BitCastInst *BCI, 1467 Module::global_iterator &GVI, 1468 TargetData *TD, 1469 LLVMContext &Context) { 1470 // If we can't figure out the type being malloced, then we can't optimize. 1471 const Type *AllocTy = getMallocAllocatedType(CI); 1472 assert(AllocTy); 1473 1474 // If this is a malloc of an abstract type, don't touch it. 1475 if (!AllocTy->isSized()) 1476 return false; 1477 1478 // We can't optimize this global unless all uses of it are *known* to be 1479 // of the malloc value, not of the null initializer value (consider a use 1480 // that compares the global's value against zero to see if the malloc has 1481 // been reached). To do this, we check to see if all uses of the global 1482 // would trap if the global were null: this proves that they must all 1483 // happen after the malloc. 1484 if (!AllUsesOfLoadedValueWillTrapIfNull(GV)) 1485 return false; 1486 1487 // We can't optimize this if the malloc itself is used in a complex way, 1488 // for example, being stored into multiple globals. This allows the 1489 // malloc to be stored into the specified global, loaded setcc'd, and 1490 // GEP'd. These are all things we could transform to using the global 1491 // for. 1492 { 1493 SmallPtrSet<PHINode*, 8> PHIs; 1494 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) 1495 return false; 1496 } 1497 1498 // If we have a global that is only initialized with a fixed size malloc, 1499 // transform the program to use global memory instead of malloc'd memory. 1500 // This eliminates dynamic allocation, avoids an indirection accessing the 1501 // data, and exposes the resultant global to further GlobalOpt. 1502 Value *NElems = getMallocArraySize(CI, Context, TD); 1503 // We cannot optimize the malloc if we cannot determine malloc array size. 1504 if (NElems) { 1505 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems)) 1506 // Restrict this transformation to only working on small allocations 1507 // (2048 bytes currently), as we don't want to introduce a 16M global or 1508 // something. 1509 if (TD && 1510 NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) { 1511 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, BCI, NElems, Context, TD); 1512 return true; 1513 } 1514 1515 // If the allocation is an array of structures, consider transforming this 1516 // into multiple malloc'd arrays, one for each field. This is basically 1517 // SRoA for malloc'd memory. 1518 1519 // If this is an allocation of a fixed size array of structs, analyze as a 1520 // variable size array. malloc [100 x struct],1 -> malloc struct, 100 1521 if (NElems == ConstantInt::get(CI->getOperand(1)->getType(), 1)) 1522 if (const ArrayType *AT = dyn_cast<ArrayType>(AllocTy)) 1523 AllocTy = AT->getElementType(); 1524 1525 if (const StructType *AllocSTy = dyn_cast<StructType>(AllocTy)) { 1526 // This the structure has an unreasonable number of fields, leave it 1527 // alone. 1528 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 && 1529 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, BCI)) { 1530 1531 // If this is a fixed size array, transform the Malloc to be an alloc of 1532 // structs. malloc [100 x struct],1 -> malloc struct, 100 1533 if (const ArrayType *AT = 1534 dyn_cast<ArrayType>(getMallocAllocatedType(CI))) { 1535 Value* NumElements = ConstantInt::get(Type::getInt32Ty(Context), 1536 AT->getNumElements()); 1537 Value* NewMI = CallInst::CreateMalloc(CI, TD->getIntPtrType(Context), 1538 AllocSTy, NumElements, 1539 BCI->getName()); 1540 Value *Cast = new BitCastInst(NewMI, getMallocType(CI), "tmp", CI); 1541 BCI->replaceAllUsesWith(Cast); 1542 BCI->eraseFromParent(); 1543 CI->eraseFromParent(); 1544 BCI = cast<BitCastInst>(NewMI); 1545 CI = extractMallocCallFromBitCast(NewMI); 1546 } 1547 1548 GVI = PerformHeapAllocSRoA(GV, CI, BCI, NElems, Context, TD); 1549 return true; 1550 } 1551 } 1552 } 1553 1554 return false; 1555} 1556 1557// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge 1558// that only one value (besides its initializer) is ever stored to the global. 1559static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal, 1560 Module::global_iterator &GVI, 1561 TargetData *TD, LLVMContext &Context) { 1562 // Ignore no-op GEPs and bitcasts. 1563 StoredOnceVal = StoredOnceVal->stripPointerCasts(); 1564 1565 // If we are dealing with a pointer global that is initialized to null and 1566 // only has one (non-null) value stored into it, then we can optimize any 1567 // users of the loaded value (often calls and loads) that would trap if the 1568 // value was null. 1569 if (isa<PointerType>(GV->getInitializer()->getType()) && 1570 GV->getInitializer()->isNullValue()) { 1571 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { 1572 if (GV->getInitializer()->getType() != SOVC->getType()) 1573 SOVC = 1574 ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType()); 1575 1576 // Optimize away any trapping uses of the loaded value. 1577 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, Context)) 1578 return true; 1579 } else if (CallInst *CI = extractMallocCall(StoredOnceVal)) { 1580 if (getMallocAllocatedType(CI)) { 1581 BitCastInst* BCI = NULL; 1582 for (Value::use_iterator UI = CI->use_begin(), E = CI->use_end(); 1583 UI != E; ) 1584 BCI = dyn_cast<BitCastInst>(cast<Instruction>(*UI++)); 1585 if (BCI && 1586 TryToOptimizeStoreOfMallocToGlobal(GV, CI, BCI, GVI, TD, Context)) 1587 return true; 1588 } 1589 } 1590 } 1591 1592 return false; 1593} 1594 1595/// TryToShrinkGlobalToBoolean - At this point, we have learned that the only 1596/// two values ever stored into GV are its initializer and OtherVal. See if we 1597/// can shrink the global into a boolean and select between the two values 1598/// whenever it is used. This exposes the values to other scalar optimizations. 1599static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal, 1600 LLVMContext &Context) { 1601 const Type *GVElType = GV->getType()->getElementType(); 1602 1603 // If GVElType is already i1, it is already shrunk. If the type of the GV is 1604 // an FP value, pointer or vector, don't do this optimization because a select 1605 // between them is very expensive and unlikely to lead to later 1606 // simplification. In these cases, we typically end up with "cond ? v1 : v2" 1607 // where v1 and v2 both require constant pool loads, a big loss. 1608 if (GVElType == Type::getInt1Ty(Context) || GVElType->isFloatingPoint() || 1609 isa<PointerType>(GVElType) || isa<VectorType>(GVElType)) 1610 return false; 1611 1612 // Walk the use list of the global seeing if all the uses are load or store. 1613 // If there is anything else, bail out. 1614 for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I) 1615 if (!isa<LoadInst>(I) && !isa<StoreInst>(I)) 1616 return false; 1617 1618 DEBUG(errs() << " *** SHRINKING TO BOOL: " << *GV); 1619 1620 // Create the new global, initializing it to false. 1621 GlobalVariable *NewGV = new GlobalVariable(Context, 1622 Type::getInt1Ty(Context), false, 1623 GlobalValue::InternalLinkage, ConstantInt::getFalse(Context), 1624 GV->getName()+".b", 1625 GV->isThreadLocal()); 1626 GV->getParent()->getGlobalList().insert(GV, NewGV); 1627 1628 Constant *InitVal = GV->getInitializer(); 1629 assert(InitVal->getType() != Type::getInt1Ty(Context) && 1630 "No reason to shrink to bool!"); 1631 1632 // If initialized to zero and storing one into the global, we can use a cast 1633 // instead of a select to synthesize the desired value. 1634 bool IsOneZero = false; 1635 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) 1636 IsOneZero = InitVal->isNullValue() && CI->isOne(); 1637 1638 while (!GV->use_empty()) { 1639 Instruction *UI = cast<Instruction>(GV->use_back()); 1640 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { 1641 // Change the store into a boolean store. 1642 bool StoringOther = SI->getOperand(0) == OtherVal; 1643 // Only do this if we weren't storing a loaded value. 1644 Value *StoreVal; 1645 if (StoringOther || SI->getOperand(0) == InitVal) 1646 StoreVal = ConstantInt::get(Type::getInt1Ty(Context), StoringOther); 1647 else { 1648 // Otherwise, we are storing a previously loaded copy. To do this, 1649 // change the copy from copying the original value to just copying the 1650 // bool. 1651 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); 1652 1653 // If we're already replaced the input, StoredVal will be a cast or 1654 // select instruction. If not, it will be a load of the original 1655 // global. 1656 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { 1657 assert(LI->getOperand(0) == GV && "Not a copy!"); 1658 // Insert a new load, to preserve the saved value. 1659 StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI); 1660 } else { 1661 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && 1662 "This is not a form that we understand!"); 1663 StoreVal = StoredVal->getOperand(0); 1664 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); 1665 } 1666 } 1667 new StoreInst(StoreVal, NewGV, SI); 1668 } else { 1669 // Change the load into a load of bool then a select. 1670 LoadInst *LI = cast<LoadInst>(UI); 1671 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", LI); 1672 Value *NSI; 1673 if (IsOneZero) 1674 NSI = new ZExtInst(NLI, LI->getType(), "", LI); 1675 else 1676 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI); 1677 NSI->takeName(LI); 1678 LI->replaceAllUsesWith(NSI); 1679 } 1680 UI->eraseFromParent(); 1681 } 1682 1683 GV->eraseFromParent(); 1684 return true; 1685} 1686 1687 1688/// ProcessInternalGlobal - Analyze the specified global variable and optimize 1689/// it if possible. If we make a change, return true. 1690bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV, 1691 Module::global_iterator &GVI) { 1692 SmallPtrSet<PHINode*, 16> PHIUsers; 1693 GlobalStatus GS; 1694 GV->removeDeadConstantUsers(); 1695 1696 if (GV->use_empty()) { 1697 DEBUG(errs() << "GLOBAL DEAD: " << *GV); 1698 GV->eraseFromParent(); 1699 ++NumDeleted; 1700 return true; 1701 } 1702 1703 if (!AnalyzeGlobal(GV, GS, PHIUsers)) { 1704#if 0 1705 cerr << "Global: " << *GV; 1706 cerr << " isLoaded = " << GS.isLoaded << "\n"; 1707 cerr << " StoredType = "; 1708 switch (GS.StoredType) { 1709 case GlobalStatus::NotStored: cerr << "NEVER STORED\n"; break; 1710 case GlobalStatus::isInitializerStored: cerr << "INIT STORED\n"; break; 1711 case GlobalStatus::isStoredOnce: cerr << "STORED ONCE\n"; break; 1712 case GlobalStatus::isStored: cerr << "stored\n"; break; 1713 } 1714 if (GS.StoredType == GlobalStatus::isStoredOnce && GS.StoredOnceValue) 1715 cerr << " StoredOnceValue = " << *GS.StoredOnceValue << "\n"; 1716 if (GS.AccessingFunction && !GS.HasMultipleAccessingFunctions) 1717 cerr << " AccessingFunction = " << GS.AccessingFunction->getName() 1718 << "\n"; 1719 cerr << " HasMultipleAccessingFunctions = " 1720 << GS.HasMultipleAccessingFunctions << "\n"; 1721 cerr << " HasNonInstructionUser = " << GS.HasNonInstructionUser<<"\n"; 1722 cerr << "\n"; 1723#endif 1724 1725 // If this is a first class global and has only one accessing function 1726 // and this function is main (which we know is not recursive we can make 1727 // this global a local variable) we replace the global with a local alloca 1728 // in this function. 1729 // 1730 // NOTE: It doesn't make sense to promote non single-value types since we 1731 // are just replacing static memory to stack memory. 1732 // 1733 // If the global is in different address space, don't bring it to stack. 1734 if (!GS.HasMultipleAccessingFunctions && 1735 GS.AccessingFunction && !GS.HasNonInstructionUser && 1736 GV->getType()->getElementType()->isSingleValueType() && 1737 GS.AccessingFunction->getName() == "main" && 1738 GS.AccessingFunction->hasExternalLinkage() && 1739 GV->getType()->getAddressSpace() == 0) { 1740 DEBUG(errs() << "LOCALIZING GLOBAL: " << *GV); 1741 Instruction* FirstI = GS.AccessingFunction->getEntryBlock().begin(); 1742 const Type* ElemTy = GV->getType()->getElementType(); 1743 // FIXME: Pass Global's alignment when globals have alignment 1744 AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), FirstI); 1745 if (!isa<UndefValue>(GV->getInitializer())) 1746 new StoreInst(GV->getInitializer(), Alloca, FirstI); 1747 1748 GV->replaceAllUsesWith(Alloca); 1749 GV->eraseFromParent(); 1750 ++NumLocalized; 1751 return true; 1752 } 1753 1754 // If the global is never loaded (but may be stored to), it is dead. 1755 // Delete it now. 1756 if (!GS.isLoaded) { 1757 DEBUG(errs() << "GLOBAL NEVER LOADED: " << *GV); 1758 1759 // Delete any stores we can find to the global. We may not be able to 1760 // make it completely dead though. 1761 bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), 1762 GV->getContext()); 1763 1764 // If the global is dead now, delete it. 1765 if (GV->use_empty()) { 1766 GV->eraseFromParent(); 1767 ++NumDeleted; 1768 Changed = true; 1769 } 1770 return Changed; 1771 1772 } else if (GS.StoredType <= GlobalStatus::isInitializerStored) { 1773 DEBUG(errs() << "MARKING CONSTANT: " << *GV); 1774 GV->setConstant(true); 1775 1776 // Clean up any obviously simplifiable users now. 1777 CleanupConstantGlobalUsers(GV, GV->getInitializer(), GV->getContext()); 1778 1779 // If the global is dead now, just nuke it. 1780 if (GV->use_empty()) { 1781 DEBUG(errs() << " *** Marking constant allowed us to simplify " 1782 << "all users and delete global!\n"); 1783 GV->eraseFromParent(); 1784 ++NumDeleted; 1785 } 1786 1787 ++NumMarked; 1788 return true; 1789 } else if (!GV->getInitializer()->getType()->isSingleValueType()) { 1790 if (TargetData *TD = getAnalysisIfAvailable<TargetData>()) 1791 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD, 1792 GV->getContext())) { 1793 GVI = FirstNewGV; // Don't skip the newly produced globals! 1794 return true; 1795 } 1796 } else if (GS.StoredType == GlobalStatus::isStoredOnce) { 1797 // If the initial value for the global was an undef value, and if only 1798 // one other value was stored into it, we can just change the 1799 // initializer to be the stored value, then delete all stores to the 1800 // global. This allows us to mark it constant. 1801 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1802 if (isa<UndefValue>(GV->getInitializer())) { 1803 // Change the initial value here. 1804 GV->setInitializer(SOVConstant); 1805 1806 // Clean up any obviously simplifiable users now. 1807 CleanupConstantGlobalUsers(GV, GV->getInitializer(), 1808 GV->getContext()); 1809 1810 if (GV->use_empty()) { 1811 DEBUG(errs() << " *** Substituting initializer allowed us to " 1812 << "simplify all users and delete global!\n"); 1813 GV->eraseFromParent(); 1814 ++NumDeleted; 1815 } else { 1816 GVI = GV; 1817 } 1818 ++NumSubstitute; 1819 return true; 1820 } 1821 1822 // Try to optimize globals based on the knowledge that only one value 1823 // (besides its initializer) is ever stored to the global. 1824 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI, 1825 getAnalysisIfAvailable<TargetData>(), 1826 GV->getContext())) 1827 return true; 1828 1829 // Otherwise, if the global was not a boolean, we can shrink it to be a 1830 // boolean. 1831 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1832 if (TryToShrinkGlobalToBoolean(GV, SOVConstant, GV->getContext())) { 1833 ++NumShrunkToBool; 1834 return true; 1835 } 1836 } 1837 } 1838 return false; 1839} 1840 1841/// ChangeCalleesToFastCall - Walk all of the direct calls of the specified 1842/// function, changing them to FastCC. 1843static void ChangeCalleesToFastCall(Function *F) { 1844 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1845 CallSite User(cast<Instruction>(*UI)); 1846 User.setCallingConv(CallingConv::Fast); 1847 } 1848} 1849 1850static AttrListPtr StripNest(const AttrListPtr &Attrs) { 1851 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) { 1852 if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0) 1853 continue; 1854 1855 // There can be only one. 1856 return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest); 1857 } 1858 1859 return Attrs; 1860} 1861 1862static void RemoveNestAttribute(Function *F) { 1863 F->setAttributes(StripNest(F->getAttributes())); 1864 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1865 CallSite User(cast<Instruction>(*UI)); 1866 User.setAttributes(StripNest(User.getAttributes())); 1867 } 1868} 1869 1870bool GlobalOpt::OptimizeFunctions(Module &M) { 1871 bool Changed = false; 1872 // Optimize functions. 1873 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { 1874 Function *F = FI++; 1875 // Functions without names cannot be referenced outside this module. 1876 if (!F->hasName() && !F->isDeclaration()) 1877 F->setLinkage(GlobalValue::InternalLinkage); 1878 F->removeDeadConstantUsers(); 1879 if (F->use_empty() && (F->hasLocalLinkage() || 1880 F->hasLinkOnceLinkage())) { 1881 M.getFunctionList().erase(F); 1882 Changed = true; 1883 ++NumFnDeleted; 1884 } else if (F->hasLocalLinkage()) { 1885 if (F->getCallingConv() == CallingConv::C && !F->isVarArg() && 1886 !F->hasAddressTaken()) { 1887 // If this function has C calling conventions, is not a varargs 1888 // function, and is only called directly, promote it to use the Fast 1889 // calling convention. 1890 F->setCallingConv(CallingConv::Fast); 1891 ChangeCalleesToFastCall(F); 1892 ++NumFastCallFns; 1893 Changed = true; 1894 } 1895 1896 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) && 1897 !F->hasAddressTaken()) { 1898 // The function is not used by a trampoline intrinsic, so it is safe 1899 // to remove the 'nest' attribute. 1900 RemoveNestAttribute(F); 1901 ++NumNestRemoved; 1902 Changed = true; 1903 } 1904 } 1905 } 1906 return Changed; 1907} 1908 1909bool GlobalOpt::OptimizeGlobalVars(Module &M) { 1910 bool Changed = false; 1911 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); 1912 GVI != E; ) { 1913 GlobalVariable *GV = GVI++; 1914 // Global variables without names cannot be referenced outside this module. 1915 if (!GV->hasName() && !GV->isDeclaration()) 1916 GV->setLinkage(GlobalValue::InternalLinkage); 1917 if (!GV->isConstant() && GV->hasLocalLinkage() && 1918 GV->hasInitializer()) 1919 Changed |= ProcessInternalGlobal(GV, GVI); 1920 } 1921 return Changed; 1922} 1923 1924/// FindGlobalCtors - Find the llvm.globalctors list, verifying that all 1925/// initializers have an init priority of 65535. 1926GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) { 1927 for (Module::global_iterator I = M.global_begin(), E = M.global_end(); 1928 I != E; ++I) 1929 if (I->getName() == "llvm.global_ctors") { 1930 // Found it, verify it's an array of { int, void()* }. 1931 const ArrayType *ATy =dyn_cast<ArrayType>(I->getType()->getElementType()); 1932 if (!ATy) return 0; 1933 const StructType *STy = dyn_cast<StructType>(ATy->getElementType()); 1934 if (!STy || STy->getNumElements() != 2 || 1935 STy->getElementType(0) != Type::getInt32Ty(M.getContext())) return 0; 1936 const PointerType *PFTy = dyn_cast<PointerType>(STy->getElementType(1)); 1937 if (!PFTy) return 0; 1938 const FunctionType *FTy = dyn_cast<FunctionType>(PFTy->getElementType()); 1939 if (!FTy || FTy->getReturnType() != Type::getVoidTy(M.getContext()) || 1940 FTy->isVarArg() || FTy->getNumParams() != 0) 1941 return 0; 1942 1943 // Verify that the initializer is simple enough for us to handle. 1944 if (!I->hasDefinitiveInitializer()) return 0; 1945 ConstantArray *CA = dyn_cast<ConstantArray>(I->getInitializer()); 1946 if (!CA) return 0; 1947 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 1948 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(*i)) { 1949 if (isa<ConstantPointerNull>(CS->getOperand(1))) 1950 continue; 1951 1952 // Must have a function or null ptr. 1953 if (!isa<Function>(CS->getOperand(1))) 1954 return 0; 1955 1956 // Init priority must be standard. 1957 ConstantInt *CI = dyn_cast<ConstantInt>(CS->getOperand(0)); 1958 if (!CI || CI->getZExtValue() != 65535) 1959 return 0; 1960 } else { 1961 return 0; 1962 } 1963 1964 return I; 1965 } 1966 return 0; 1967} 1968 1969/// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand, 1970/// return a list of the functions and null terminator as a vector. 1971static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) { 1972 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer()); 1973 std::vector<Function*> Result; 1974 Result.reserve(CA->getNumOperands()); 1975 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) { 1976 ConstantStruct *CS = cast<ConstantStruct>(*i); 1977 Result.push_back(dyn_cast<Function>(CS->getOperand(1))); 1978 } 1979 return Result; 1980} 1981 1982/// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the 1983/// specified array, returning the new global to use. 1984static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL, 1985 const std::vector<Function*> &Ctors, 1986 LLVMContext &Context) { 1987 // If we made a change, reassemble the initializer list. 1988 std::vector<Constant*> CSVals; 1989 CSVals.push_back(ConstantInt::get(Type::getInt32Ty(Context), 65535)); 1990 CSVals.push_back(0); 1991 1992 // Create the new init list. 1993 std::vector<Constant*> CAList; 1994 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) { 1995 if (Ctors[i]) { 1996 CSVals[1] = Ctors[i]; 1997 } else { 1998 const Type *FTy = FunctionType::get(Type::getVoidTy(Context), false); 1999 const PointerType *PFTy = PointerType::getUnqual(FTy); 2000 CSVals[1] = Constant::getNullValue(PFTy); 2001 CSVals[0] = ConstantInt::get(Type::getInt32Ty(Context), 2147483647); 2002 } 2003 CAList.push_back(ConstantStruct::get(Context, CSVals, false)); 2004 } 2005 2006 // Create the array initializer. 2007 const Type *StructTy = 2008 cast<ArrayType>(GCL->getType()->getElementType())->getElementType(); 2009 Constant *CA = ConstantArray::get(ArrayType::get(StructTy, 2010 CAList.size()), CAList); 2011 2012 // If we didn't change the number of elements, don't create a new GV. 2013 if (CA->getType() == GCL->getInitializer()->getType()) { 2014 GCL->setInitializer(CA); 2015 return GCL; 2016 } 2017 2018 // Create the new global and insert it next to the existing list. 2019 GlobalVariable *NGV = new GlobalVariable(Context, CA->getType(), 2020 GCL->isConstant(), 2021 GCL->getLinkage(), CA, "", 2022 GCL->isThreadLocal()); 2023 GCL->getParent()->getGlobalList().insert(GCL, NGV); 2024 NGV->takeName(GCL); 2025 2026 // Nuke the old list, replacing any uses with the new one. 2027 if (!GCL->use_empty()) { 2028 Constant *V = NGV; 2029 if (V->getType() != GCL->getType()) 2030 V = ConstantExpr::getBitCast(V, GCL->getType()); 2031 GCL->replaceAllUsesWith(V); 2032 } 2033 GCL->eraseFromParent(); 2034 2035 if (Ctors.size()) 2036 return NGV; 2037 else 2038 return 0; 2039} 2040 2041 2042static Constant *getVal(DenseMap<Value*, Constant*> &ComputedValues, 2043 Value *V) { 2044 if (Constant *CV = dyn_cast<Constant>(V)) return CV; 2045 Constant *R = ComputedValues[V]; 2046 assert(R && "Reference to an uncomputed value!"); 2047 return R; 2048} 2049 2050/// isSimpleEnoughPointerToCommit - Return true if this constant is simple 2051/// enough for us to understand. In particular, if it is a cast of something, 2052/// we punt. We basically just support direct accesses to globals and GEP's of 2053/// globals. This should be kept up to date with CommitValueTo. 2054static bool isSimpleEnoughPointerToCommit(Constant *C, LLVMContext &Context) { 2055 // Conservatively, avoid aggregate types. This is because we don't 2056 // want to worry about them partially overlapping other stores. 2057 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType()) 2058 return false; 2059 2060 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) 2061 // Do not allow weak/linkonce/dllimport/dllexport linkage or 2062 // external globals. 2063 return GV->hasDefinitiveInitializer(); 2064 2065 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 2066 // Handle a constantexpr gep. 2067 if (CE->getOpcode() == Instruction::GetElementPtr && 2068 isa<GlobalVariable>(CE->getOperand(0)) && 2069 cast<GEPOperator>(CE)->isInBounds()) { 2070 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2071 // Do not allow weak/linkonce/dllimport/dllexport linkage or 2072 // external globals. 2073 if (!GV->hasDefinitiveInitializer()) 2074 return false; 2075 2076 // The first index must be zero. 2077 ConstantInt *CI = dyn_cast<ConstantInt>(*next(CE->op_begin())); 2078 if (!CI || !CI->isZero()) return false; 2079 2080 // The remaining indices must be compile-time known integers within the 2081 // notional bounds of the corresponding static array types. 2082 if (!CE->isGEPWithNoNotionalOverIndexing()) 2083 return false; 2084 2085 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2086 } 2087 return false; 2088} 2089 2090/// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global 2091/// initializer. This returns 'Init' modified to reflect 'Val' stored into it. 2092/// At this point, the GEP operands of Addr [0, OpNo) have been stepped into. 2093static Constant *EvaluateStoreInto(Constant *Init, Constant *Val, 2094 ConstantExpr *Addr, unsigned OpNo, 2095 LLVMContext &Context) { 2096 // Base case of the recursion. 2097 if (OpNo == Addr->getNumOperands()) { 2098 assert(Val->getType() == Init->getType() && "Type mismatch!"); 2099 return Val; 2100 } 2101 2102 if (const StructType *STy = dyn_cast<StructType>(Init->getType())) { 2103 std::vector<Constant*> Elts; 2104 2105 // Break up the constant into its elements. 2106 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) { 2107 for (User::op_iterator i = CS->op_begin(), e = CS->op_end(); i != e; ++i) 2108 Elts.push_back(cast<Constant>(*i)); 2109 } else if (isa<ConstantAggregateZero>(Init)) { 2110 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2111 Elts.push_back(Constant::getNullValue(STy->getElementType(i))); 2112 } else if (isa<UndefValue>(Init)) { 2113 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2114 Elts.push_back(UndefValue::get(STy->getElementType(i))); 2115 } else { 2116 llvm_unreachable("This code is out of sync with " 2117 " ConstantFoldLoadThroughGEPConstantExpr"); 2118 } 2119 2120 // Replace the element that we are supposed to. 2121 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo)); 2122 unsigned Idx = CU->getZExtValue(); 2123 assert(Idx < STy->getNumElements() && "Struct index out of range!"); 2124 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1, Context); 2125 2126 // Return the modified struct. 2127 return ConstantStruct::get(Context, &Elts[0], Elts.size(), STy->isPacked()); 2128 } else { 2129 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo)); 2130 const ArrayType *ATy = cast<ArrayType>(Init->getType()); 2131 2132 // Break up the array into elements. 2133 std::vector<Constant*> Elts; 2134 if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) { 2135 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 2136 Elts.push_back(cast<Constant>(*i)); 2137 } else if (isa<ConstantAggregateZero>(Init)) { 2138 Constant *Elt = Constant::getNullValue(ATy->getElementType()); 2139 Elts.assign(ATy->getNumElements(), Elt); 2140 } else if (isa<UndefValue>(Init)) { 2141 Constant *Elt = UndefValue::get(ATy->getElementType()); 2142 Elts.assign(ATy->getNumElements(), Elt); 2143 } else { 2144 llvm_unreachable("This code is out of sync with " 2145 " ConstantFoldLoadThroughGEPConstantExpr"); 2146 } 2147 2148 assert(CI->getZExtValue() < ATy->getNumElements()); 2149 Elts[CI->getZExtValue()] = 2150 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1, Context); 2151 return ConstantArray::get(ATy, Elts); 2152 } 2153} 2154 2155/// CommitValueTo - We have decided that Addr (which satisfies the predicate 2156/// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen. 2157static void CommitValueTo(Constant *Val, Constant *Addr, 2158 LLVMContext &Context) { 2159 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) { 2160 assert(GV->hasInitializer()); 2161 GV->setInitializer(Val); 2162 return; 2163 } 2164 2165 ConstantExpr *CE = cast<ConstantExpr>(Addr); 2166 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2167 2168 Constant *Init = GV->getInitializer(); 2169 Init = EvaluateStoreInto(Init, Val, CE, 2, Context); 2170 GV->setInitializer(Init); 2171} 2172 2173/// ComputeLoadResult - Return the value that would be computed by a load from 2174/// P after the stores reflected by 'memory' have been performed. If we can't 2175/// decide, return null. 2176static Constant *ComputeLoadResult(Constant *P, 2177 const DenseMap<Constant*, Constant*> &Memory, 2178 LLVMContext &Context) { 2179 // If this memory location has been recently stored, use the stored value: it 2180 // is the most up-to-date. 2181 DenseMap<Constant*, Constant*>::const_iterator I = Memory.find(P); 2182 if (I != Memory.end()) return I->second; 2183 2184 // Access it. 2185 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) { 2186 if (GV->hasDefinitiveInitializer()) 2187 return GV->getInitializer(); 2188 return 0; 2189 } 2190 2191 // Handle a constantexpr getelementptr. 2192 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) 2193 if (CE->getOpcode() == Instruction::GetElementPtr && 2194 isa<GlobalVariable>(CE->getOperand(0))) { 2195 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2196 if (GV->hasDefinitiveInitializer()) 2197 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2198 } 2199 2200 return 0; // don't know how to evaluate. 2201} 2202 2203/// EvaluateFunction - Evaluate a call to function F, returning true if 2204/// successful, false if we can't evaluate it. ActualArgs contains the formal 2205/// arguments for the function. 2206static bool EvaluateFunction(Function *F, Constant *&RetVal, 2207 const SmallVectorImpl<Constant*> &ActualArgs, 2208 std::vector<Function*> &CallStack, 2209 DenseMap<Constant*, Constant*> &MutatedMemory, 2210 std::vector<GlobalVariable*> &AllocaTmps) { 2211 // Check to see if this function is already executing (recursion). If so, 2212 // bail out. TODO: we might want to accept limited recursion. 2213 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end()) 2214 return false; 2215 2216 LLVMContext &Context = F->getContext(); 2217 2218 CallStack.push_back(F); 2219 2220 /// Values - As we compute SSA register values, we store their contents here. 2221 DenseMap<Value*, Constant*> Values; 2222 2223 // Initialize arguments to the incoming values specified. 2224 unsigned ArgNo = 0; 2225 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E; 2226 ++AI, ++ArgNo) 2227 Values[AI] = ActualArgs[ArgNo]; 2228 2229 /// ExecutedBlocks - We only handle non-looping, non-recursive code. As such, 2230 /// we can only evaluate any one basic block at most once. This set keeps 2231 /// track of what we have executed so we can detect recursive cases etc. 2232 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks; 2233 2234 // CurInst - The current instruction we're evaluating. 2235 BasicBlock::iterator CurInst = F->begin()->begin(); 2236 2237 // This is the main evaluation loop. 2238 while (1) { 2239 Constant *InstResult = 0; 2240 2241 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) { 2242 if (SI->isVolatile()) return false; // no volatile accesses. 2243 Constant *Ptr = getVal(Values, SI->getOperand(1)); 2244 if (!isSimpleEnoughPointerToCommit(Ptr, Context)) 2245 // If this is too complex for us to commit, reject it. 2246 return false; 2247 Constant *Val = getVal(Values, SI->getOperand(0)); 2248 MutatedMemory[Ptr] = Val; 2249 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) { 2250 InstResult = ConstantExpr::get(BO->getOpcode(), 2251 getVal(Values, BO->getOperand(0)), 2252 getVal(Values, BO->getOperand(1))); 2253 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) { 2254 InstResult = ConstantExpr::getCompare(CI->getPredicate(), 2255 getVal(Values, CI->getOperand(0)), 2256 getVal(Values, CI->getOperand(1))); 2257 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) { 2258 InstResult = ConstantExpr::getCast(CI->getOpcode(), 2259 getVal(Values, CI->getOperand(0)), 2260 CI->getType()); 2261 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) { 2262 InstResult = 2263 ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)), 2264 getVal(Values, SI->getOperand(1)), 2265 getVal(Values, SI->getOperand(2))); 2266 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) { 2267 Constant *P = getVal(Values, GEP->getOperand(0)); 2268 SmallVector<Constant*, 8> GEPOps; 2269 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); 2270 i != e; ++i) 2271 GEPOps.push_back(getVal(Values, *i)); 2272 InstResult = cast<GEPOperator>(GEP)->isInBounds() ? 2273 ConstantExpr::getInBoundsGetElementPtr(P, &GEPOps[0], GEPOps.size()) : 2274 ConstantExpr::getGetElementPtr(P, &GEPOps[0], GEPOps.size()); 2275 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) { 2276 if (LI->isVolatile()) return false; // no volatile accesses. 2277 InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)), 2278 MutatedMemory, Context); 2279 if (InstResult == 0) return false; // Could not evaluate load. 2280 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) { 2281 if (AI->isArrayAllocation()) return false; // Cannot handle array allocs. 2282 const Type *Ty = AI->getType()->getElementType(); 2283 AllocaTmps.push_back(new GlobalVariable(Context, Ty, false, 2284 GlobalValue::InternalLinkage, 2285 UndefValue::get(Ty), 2286 AI->getName())); 2287 InstResult = AllocaTmps.back(); 2288 } else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) { 2289 2290 // Debug info can safely be ignored here. 2291 if (isa<DbgInfoIntrinsic>(CI)) { 2292 ++CurInst; 2293 continue; 2294 } 2295 2296 // Cannot handle inline asm. 2297 if (isa<InlineAsm>(CI->getOperand(0))) return false; 2298 2299 // Resolve function pointers. 2300 Function *Callee = dyn_cast<Function>(getVal(Values, CI->getOperand(0))); 2301 if (!Callee) return false; // Cannot resolve. 2302 2303 SmallVector<Constant*, 8> Formals; 2304 for (User::op_iterator i = CI->op_begin() + 1, e = CI->op_end(); 2305 i != e; ++i) 2306 Formals.push_back(getVal(Values, *i)); 2307 2308 if (Callee->isDeclaration()) { 2309 // If this is a function we can constant fold, do it. 2310 if (Constant *C = ConstantFoldCall(Callee, Formals.data(), 2311 Formals.size())) { 2312 InstResult = C; 2313 } else { 2314 return false; 2315 } 2316 } else { 2317 if (Callee->getFunctionType()->isVarArg()) 2318 return false; 2319 2320 Constant *RetVal; 2321 // Execute the call, if successful, use the return value. 2322 if (!EvaluateFunction(Callee, RetVal, Formals, CallStack, 2323 MutatedMemory, AllocaTmps)) 2324 return false; 2325 InstResult = RetVal; 2326 } 2327 } else if (isa<TerminatorInst>(CurInst)) { 2328 BasicBlock *NewBB = 0; 2329 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) { 2330 if (BI->isUnconditional()) { 2331 NewBB = BI->getSuccessor(0); 2332 } else { 2333 ConstantInt *Cond = 2334 dyn_cast<ConstantInt>(getVal(Values, BI->getCondition())); 2335 if (!Cond) return false; // Cannot determine. 2336 2337 NewBB = BI->getSuccessor(!Cond->getZExtValue()); 2338 } 2339 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) { 2340 ConstantInt *Val = 2341 dyn_cast<ConstantInt>(getVal(Values, SI->getCondition())); 2342 if (!Val) return false; // Cannot determine. 2343 NewBB = SI->getSuccessor(SI->findCaseValue(Val)); 2344 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) { 2345 Value *Val = getVal(Values, IBI->getAddress())->stripPointerCasts(); 2346 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val)) 2347 NewBB = BA->getBasicBlock(); 2348 if (NewBB == 0) return false; // Cannot determine. 2349 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) { 2350 if (RI->getNumOperands()) 2351 RetVal = getVal(Values, RI->getOperand(0)); 2352 2353 CallStack.pop_back(); // return from fn. 2354 return true; // We succeeded at evaluating this ctor! 2355 } else { 2356 // invoke, unwind, unreachable. 2357 return false; // Cannot handle this terminator. 2358 } 2359 2360 // Okay, we succeeded in evaluating this control flow. See if we have 2361 // executed the new block before. If so, we have a looping function, 2362 // which we cannot evaluate in reasonable time. 2363 if (!ExecutedBlocks.insert(NewBB)) 2364 return false; // looped! 2365 2366 // Okay, we have never been in this block before. Check to see if there 2367 // are any PHI nodes. If so, evaluate them with information about where 2368 // we came from. 2369 BasicBlock *OldBB = CurInst->getParent(); 2370 CurInst = NewBB->begin(); 2371 PHINode *PN; 2372 for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst) 2373 Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB)); 2374 2375 // Do NOT increment CurInst. We know that the terminator had no value. 2376 continue; 2377 } else { 2378 // Did not know how to evaluate this! 2379 return false; 2380 } 2381 2382 if (!CurInst->use_empty()) 2383 Values[CurInst] = InstResult; 2384 2385 // Advance program counter. 2386 ++CurInst; 2387 } 2388} 2389 2390/// EvaluateStaticConstructor - Evaluate static constructors in the function, if 2391/// we can. Return true if we can, false otherwise. 2392static bool EvaluateStaticConstructor(Function *F) { 2393 /// MutatedMemory - For each store we execute, we update this map. Loads 2394 /// check this to get the most up-to-date value. If evaluation is successful, 2395 /// this state is committed to the process. 2396 DenseMap<Constant*, Constant*> MutatedMemory; 2397 2398 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable 2399 /// to represent its body. This vector is needed so we can delete the 2400 /// temporary globals when we are done. 2401 std::vector<GlobalVariable*> AllocaTmps; 2402 2403 /// CallStack - This is used to detect recursion. In pathological situations 2404 /// we could hit exponential behavior, but at least there is nothing 2405 /// unbounded. 2406 std::vector<Function*> CallStack; 2407 2408 // Call the function. 2409 Constant *RetValDummy; 2410 bool EvalSuccess = EvaluateFunction(F, RetValDummy, 2411 SmallVector<Constant*, 0>(), CallStack, 2412 MutatedMemory, AllocaTmps); 2413 if (EvalSuccess) { 2414 // We succeeded at evaluation: commit the result. 2415 DEBUG(errs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" 2416 << F->getName() << "' to " << MutatedMemory.size() 2417 << " stores.\n"); 2418 for (DenseMap<Constant*, Constant*>::iterator I = MutatedMemory.begin(), 2419 E = MutatedMemory.end(); I != E; ++I) 2420 CommitValueTo(I->second, I->first, F->getContext()); 2421 } 2422 2423 // At this point, we are done interpreting. If we created any 'alloca' 2424 // temporaries, release them now. 2425 while (!AllocaTmps.empty()) { 2426 GlobalVariable *Tmp = AllocaTmps.back(); 2427 AllocaTmps.pop_back(); 2428 2429 // If there are still users of the alloca, the program is doing something 2430 // silly, e.g. storing the address of the alloca somewhere and using it 2431 // later. Since this is undefined, we'll just make it be null. 2432 if (!Tmp->use_empty()) 2433 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType())); 2434 delete Tmp; 2435 } 2436 2437 return EvalSuccess; 2438} 2439 2440 2441 2442/// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible. 2443/// Return true if anything changed. 2444bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) { 2445 std::vector<Function*> Ctors = ParseGlobalCtors(GCL); 2446 bool MadeChange = false; 2447 if (Ctors.empty()) return false; 2448 2449 // Loop over global ctors, optimizing them when we can. 2450 for (unsigned i = 0; i != Ctors.size(); ++i) { 2451 Function *F = Ctors[i]; 2452 // Found a null terminator in the middle of the list, prune off the rest of 2453 // the list. 2454 if (F == 0) { 2455 if (i != Ctors.size()-1) { 2456 Ctors.resize(i+1); 2457 MadeChange = true; 2458 } 2459 break; 2460 } 2461 2462 // We cannot simplify external ctor functions. 2463 if (F->empty()) continue; 2464 2465 // If we can evaluate the ctor at compile time, do. 2466 if (EvaluateStaticConstructor(F)) { 2467 Ctors.erase(Ctors.begin()+i); 2468 MadeChange = true; 2469 --i; 2470 ++NumCtorsEvaluated; 2471 continue; 2472 } 2473 } 2474 2475 if (!MadeChange) return false; 2476 2477 GCL = InstallGlobalCtors(GCL, Ctors, GCL->getContext()); 2478 return true; 2479} 2480 2481bool GlobalOpt::OptimizeGlobalAliases(Module &M) { 2482 bool Changed = false; 2483 2484 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); 2485 I != E;) { 2486 Module::alias_iterator J = I++; 2487 // Aliases without names cannot be referenced outside this module. 2488 if (!J->hasName() && !J->isDeclaration()) 2489 J->setLinkage(GlobalValue::InternalLinkage); 2490 // If the aliasee may change at link time, nothing can be done - bail out. 2491 if (J->mayBeOverridden()) 2492 continue; 2493 2494 Constant *Aliasee = J->getAliasee(); 2495 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts()); 2496 Target->removeDeadConstantUsers(); 2497 bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse(); 2498 2499 // Make all users of the alias use the aliasee instead. 2500 if (!J->use_empty()) { 2501 J->replaceAllUsesWith(Aliasee); 2502 ++NumAliasesResolved; 2503 Changed = true; 2504 } 2505 2506 // If the aliasee has internal linkage, give it the name and linkage 2507 // of the alias, and delete the alias. This turns: 2508 // define internal ... @f(...) 2509 // @a = alias ... @f 2510 // into: 2511 // define ... @a(...) 2512 if (!Target->hasLocalLinkage()) 2513 continue; 2514 2515 // The transform is only useful if the alias does not have internal linkage. 2516 if (J->hasLocalLinkage()) 2517 continue; 2518 2519 // Do not perform the transform if multiple aliases potentially target the 2520 // aliasee. This check also ensures that it is safe to replace the section 2521 // and other attributes of the aliasee with those of the alias. 2522 if (!hasOneUse) 2523 continue; 2524 2525 // Give the aliasee the name, linkage and other attributes of the alias. 2526 Target->takeName(J); 2527 Target->setLinkage(J->getLinkage()); 2528 Target->GlobalValue::copyAttributesFrom(J); 2529 2530 // Delete the alias. 2531 M.getAliasList().erase(J); 2532 ++NumAliasesRemoved; 2533 Changed = true; 2534 } 2535 2536 return Changed; 2537} 2538 2539bool GlobalOpt::runOnModule(Module &M) { 2540 bool Changed = false; 2541 2542 // Try to find the llvm.globalctors list. 2543 GlobalVariable *GlobalCtors = FindGlobalCtors(M); 2544 2545 bool LocalChange = true; 2546 while (LocalChange) { 2547 LocalChange = false; 2548 2549 // Delete functions that are trivially dead, ccc -> fastcc 2550 LocalChange |= OptimizeFunctions(M); 2551 2552 // Optimize global_ctors list. 2553 if (GlobalCtors) 2554 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors); 2555 2556 // Optimize non-address-taken globals. 2557 LocalChange |= OptimizeGlobalVars(M); 2558 2559 // Resolve aliases, when possible. 2560 LocalChange |= OptimizeGlobalAliases(M); 2561 Changed |= LocalChange; 2562 } 2563 2564 // TODO: Move all global ctors functions to the end of the module for code 2565 // layout. 2566 2567 return Changed; 2568} 2569