GlobalOpt.cpp revision fa6a1cf1ed4282145269b12578f687b3869d6476
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/Target/TargetData.h" 28#include "llvm/Support/CallSite.h" 29#include "llvm/Support/Compiler.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 VISIBILITY_HIDDEN 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 VISIBILITY_HIDDEN 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, Context); 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, Context); 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 && (isa<ArrayType>(*GEPI) || isa<VectorType>(*GEPI)); 430 ++GEPI) { 431 uint64_t NumElements; 432 if (const ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI)) 433 NumElements = SubArrayTy->getNumElements(); 434 else 435 NumElements = cast<VectorType>(*GEPI)->getNumElements(); 436 437 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand()); 438 if (!IdxVal || IdxVal->getZExtValue() >= NumElements) 439 return false; 440 } 441 } 442 443 for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I) 444 if (!isSafeSROAElementUse(*I)) 445 return false; 446 return true; 447} 448 449/// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it 450/// is safe for us to perform this transformation. 451/// 452static bool GlobalUsersSafeToSRA(GlobalValue *GV) { 453 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); 454 UI != E; ++UI) { 455 if (!IsUserOfGlobalSafeForSRA(*UI, GV)) 456 return false; 457 } 458 return true; 459} 460 461 462/// SRAGlobal - Perform scalar replacement of aggregates on the specified global 463/// variable. This opens the door for other optimizations by exposing the 464/// behavior of the program in a more fine-grained way. We have determined that 465/// this transformation is safe already. We return the first global variable we 466/// insert so that the caller can reprocess it. 467static GlobalVariable *SRAGlobal(GlobalVariable *GV, const TargetData &TD, 468 LLVMContext &Context) { 469 // Make sure this global only has simple uses that we can SRA. 470 if (!GlobalUsersSafeToSRA(GV)) 471 return 0; 472 473 assert(GV->hasLocalLinkage() && !GV->isConstant()); 474 Constant *Init = GV->getInitializer(); 475 const Type *Ty = Init->getType(); 476 477 std::vector<GlobalVariable*> NewGlobals; 478 Module::GlobalListType &Globals = GV->getParent()->getGlobalList(); 479 480 // Get the alignment of the global, either explicit or target-specific. 481 unsigned StartAlignment = GV->getAlignment(); 482 if (StartAlignment == 0) 483 StartAlignment = TD.getABITypeAlignment(GV->getType()); 484 485 if (const StructType *STy = dyn_cast<StructType>(Ty)) { 486 NewGlobals.reserve(STy->getNumElements()); 487 const StructLayout &Layout = *TD.getStructLayout(STy); 488 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 489 Constant *In = getAggregateConstantElement(Init, 490 ConstantInt::get(Type::getInt32Ty(Context), i), 491 Context); 492 assert(In && "Couldn't get element of initializer?"); 493 GlobalVariable *NGV = new GlobalVariable(Context, 494 STy->getElementType(i), false, 495 GlobalVariable::InternalLinkage, 496 In, GV->getName()+"."+Twine(i), 497 GV->isThreadLocal(), 498 GV->getType()->getAddressSpace()); 499 Globals.insert(GV, NGV); 500 NewGlobals.push_back(NGV); 501 502 // Calculate the known alignment of the field. If the original aggregate 503 // had 256 byte alignment for example, something might depend on that: 504 // propagate info to each field. 505 uint64_t FieldOffset = Layout.getElementOffset(i); 506 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset); 507 if (NewAlign > TD.getABITypeAlignment(STy->getElementType(i))) 508 NGV->setAlignment(NewAlign); 509 } 510 } else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) { 511 unsigned NumElements = 0; 512 if (const ArrayType *ATy = dyn_cast<ArrayType>(STy)) 513 NumElements = ATy->getNumElements(); 514 else 515 NumElements = cast<VectorType>(STy)->getNumElements(); 516 517 if (NumElements > 16 && GV->hasNUsesOrMore(16)) 518 return 0; // It's not worth it. 519 NewGlobals.reserve(NumElements); 520 521 uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType()); 522 unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType()); 523 for (unsigned i = 0, e = NumElements; i != e; ++i) { 524 Constant *In = getAggregateConstantElement(Init, 525 ConstantInt::get(Type::getInt32Ty(Context), i), 526 Context); 527 assert(In && "Couldn't get element of initializer?"); 528 529 GlobalVariable *NGV = new GlobalVariable(Context, 530 STy->getElementType(), false, 531 GlobalVariable::InternalLinkage, 532 In, GV->getName()+"."+Twine(i), 533 GV->isThreadLocal(), 534 GV->getType()->getAddressSpace()); 535 Globals.insert(GV, NGV); 536 NewGlobals.push_back(NGV); 537 538 // Calculate the known alignment of the field. If the original aggregate 539 // had 256 byte alignment for example, something might depend on that: 540 // propagate info to each field. 541 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i); 542 if (NewAlign > EltAlign) 543 NGV->setAlignment(NewAlign); 544 } 545 } 546 547 if (NewGlobals.empty()) 548 return 0; 549 550 DOUT << "PERFORMING GLOBAL SRA ON: " << *GV; 551 552 Constant *NullInt = Constant::getNullValue(Type::getInt32Ty(Context)); 553 554 // Loop over all of the uses of the global, replacing the constantexpr geps, 555 // with smaller constantexpr geps or direct references. 556 while (!GV->use_empty()) { 557 User *GEP = GV->use_back(); 558 assert(((isa<ConstantExpr>(GEP) && 559 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)|| 560 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!"); 561 562 // Ignore the 1th operand, which has to be zero or else the program is quite 563 // broken (undefined). Get the 2nd operand, which is the structure or array 564 // index. 565 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 566 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access. 567 568 Value *NewPtr = NewGlobals[Val]; 569 570 // Form a shorter GEP if needed. 571 if (GEP->getNumOperands() > 3) { 572 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) { 573 SmallVector<Constant*, 8> Idxs; 574 Idxs.push_back(NullInt); 575 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i) 576 Idxs.push_back(CE->getOperand(i)); 577 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), 578 &Idxs[0], Idxs.size()); 579 } else { 580 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP); 581 SmallVector<Value*, 8> Idxs; 582 Idxs.push_back(NullInt); 583 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) 584 Idxs.push_back(GEPI->getOperand(i)); 585 NewPtr = GetElementPtrInst::Create(NewPtr, Idxs.begin(), Idxs.end(), 586 GEPI->getName()+"."+Twine(Val),GEPI); 587 } 588 } 589 GEP->replaceAllUsesWith(NewPtr); 590 591 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP)) 592 GEPI->eraseFromParent(); 593 else 594 cast<ConstantExpr>(GEP)->destroyConstant(); 595 } 596 597 // Delete the old global, now that it is dead. 598 Globals.erase(GV); 599 ++NumSRA; 600 601 // Loop over the new globals array deleting any globals that are obviously 602 // dead. This can arise due to scalarization of a structure or an array that 603 // has elements that are dead. 604 unsigned FirstGlobal = 0; 605 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i) 606 if (NewGlobals[i]->use_empty()) { 607 Globals.erase(NewGlobals[i]); 608 if (FirstGlobal == i) ++FirstGlobal; 609 } 610 611 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0; 612} 613 614/// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified 615/// value will trap if the value is dynamically null. PHIs keeps track of any 616/// phi nodes we've seen to avoid reprocessing them. 617static bool AllUsesOfValueWillTrapIfNull(Value *V, 618 SmallPtrSet<PHINode*, 8> &PHIs) { 619 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) 620 if (isa<LoadInst>(*UI)) { 621 // Will trap. 622 } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) { 623 if (SI->getOperand(0) == V) { 624 //cerr << "NONTRAPPING USE: " << **UI; 625 return false; // Storing the value. 626 } 627 } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) { 628 if (CI->getOperand(0) != V) { 629 //cerr << "NONTRAPPING USE: " << **UI; 630 return false; // Not calling the ptr 631 } 632 } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) { 633 if (II->getOperand(0) != V) { 634 //cerr << "NONTRAPPING USE: " << **UI; 635 return false; // Not calling the ptr 636 } 637 } else if (BitCastInst *CI = dyn_cast<BitCastInst>(*UI)) { 638 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false; 639 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) { 640 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false; 641 } else if (PHINode *PN = dyn_cast<PHINode>(*UI)) { 642 // If we've already seen this phi node, ignore it, it has already been 643 // checked. 644 if (PHIs.insert(PN)) 645 return AllUsesOfValueWillTrapIfNull(PN, PHIs); 646 } else if (isa<ICmpInst>(*UI) && 647 isa<ConstantPointerNull>(UI->getOperand(1))) { 648 // Ignore setcc X, null 649 } else { 650 //cerr << "NONTRAPPING USE: " << **UI; 651 return false; 652 } 653 return true; 654} 655 656/// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads 657/// from GV will trap if the loaded value is null. Note that this also permits 658/// comparisons of the loaded value against null, as a special case. 659static bool AllUsesOfLoadedValueWillTrapIfNull(GlobalVariable *GV) { 660 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI!=E; ++UI) 661 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 662 SmallPtrSet<PHINode*, 8> PHIs; 663 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs)) 664 return false; 665 } else if (isa<StoreInst>(*UI)) { 666 // Ignore stores to the global. 667 } else { 668 // We don't know or understand this user, bail out. 669 //cerr << "UNKNOWN USER OF GLOBAL!: " << **UI; 670 return false; 671 } 672 673 return true; 674} 675 676static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV, 677 LLVMContext &Context) { 678 bool Changed = false; 679 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) { 680 Instruction *I = cast<Instruction>(*UI++); 681 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 682 LI->setOperand(0, NewV); 683 Changed = true; 684 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 685 if (SI->getOperand(1) == V) { 686 SI->setOperand(1, NewV); 687 Changed = true; 688 } 689 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) { 690 if (I->getOperand(0) == V) { 691 // Calling through the pointer! Turn into a direct call, but be careful 692 // that the pointer is not also being passed as an argument. 693 I->setOperand(0, NewV); 694 Changed = true; 695 bool PassedAsArg = false; 696 for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i) 697 if (I->getOperand(i) == V) { 698 PassedAsArg = true; 699 I->setOperand(i, NewV); 700 } 701 702 if (PassedAsArg) { 703 // Being passed as an argument also. Be careful to not invalidate UI! 704 UI = V->use_begin(); 705 } 706 } 707 } else if (CastInst *CI = dyn_cast<CastInst>(I)) { 708 Changed |= OptimizeAwayTrappingUsesOfValue(CI, 709 ConstantExpr::getCast(CI->getOpcode(), 710 NewV, CI->getType()), Context); 711 if (CI->use_empty()) { 712 Changed = true; 713 CI->eraseFromParent(); 714 } 715 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { 716 // Should handle GEP here. 717 SmallVector<Constant*, 8> Idxs; 718 Idxs.reserve(GEPI->getNumOperands()-1); 719 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end(); 720 i != e; ++i) 721 if (Constant *C = dyn_cast<Constant>(*i)) 722 Idxs.push_back(C); 723 else 724 break; 725 if (Idxs.size() == GEPI->getNumOperands()-1) 726 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI, 727 ConstantExpr::getGetElementPtr(NewV, &Idxs[0], 728 Idxs.size()), Context); 729 if (GEPI->use_empty()) { 730 Changed = true; 731 GEPI->eraseFromParent(); 732 } 733 } 734 } 735 736 return Changed; 737} 738 739 740/// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null 741/// value stored into it. If there are uses of the loaded value that would trap 742/// if the loaded value is dynamically null, then we know that they cannot be 743/// reachable with a null optimize away the load. 744static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV, 745 LLVMContext &Context) { 746 bool Changed = false; 747 748 // Keep track of whether we are able to remove all the uses of the global 749 // other than the store that defines it. 750 bool AllNonStoreUsesGone = true; 751 752 // Replace all uses of loads with uses of uses of the stored value. 753 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){ 754 User *GlobalUser = *GUI++; 755 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) { 756 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV, Context); 757 // If we were able to delete all uses of the loads 758 if (LI->use_empty()) { 759 LI->eraseFromParent(); 760 Changed = true; 761 } else { 762 AllNonStoreUsesGone = false; 763 } 764 } else if (isa<StoreInst>(GlobalUser)) { 765 // Ignore the store that stores "LV" to the global. 766 assert(GlobalUser->getOperand(1) == GV && 767 "Must be storing *to* the global"); 768 } else { 769 AllNonStoreUsesGone = false; 770 771 // If we get here we could have other crazy uses that are transitively 772 // loaded. 773 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) || 774 isa<ConstantExpr>(GlobalUser)) && "Only expect load and stores!"); 775 } 776 } 777 778 if (Changed) { 779 DOUT << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV; 780 ++NumGlobUses; 781 } 782 783 // If we nuked all of the loads, then none of the stores are needed either, 784 // nor is the global. 785 if (AllNonStoreUsesGone) { 786 DOUT << " *** GLOBAL NOW DEAD!\n"; 787 CleanupConstantGlobalUsers(GV, 0, Context); 788 if (GV->use_empty()) { 789 GV->eraseFromParent(); 790 ++NumDeleted; 791 } 792 Changed = true; 793 } 794 return Changed; 795} 796 797/// ConstantPropUsersOf - Walk the use list of V, constant folding all of the 798/// instructions that are foldable. 799static void ConstantPropUsersOf(Value *V, LLVMContext &Context) { 800 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) 801 if (Instruction *I = dyn_cast<Instruction>(*UI++)) 802 if (Constant *NewC = ConstantFoldInstruction(I, Context)) { 803 I->replaceAllUsesWith(NewC); 804 805 // Advance UI to the next non-I use to avoid invalidating it! 806 // Instructions could multiply use V. 807 while (UI != E && *UI == I) 808 ++UI; 809 I->eraseFromParent(); 810 } 811} 812 813/// OptimizeGlobalAddressOfMalloc - This function takes the specified global 814/// variable, and transforms the program as if it always contained the result of 815/// the specified malloc. Because it is always the result of the specified 816/// malloc, there is no reason to actually DO the malloc. Instead, turn the 817/// malloc into a global, and any loads of GV as uses of the new global. 818static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, 819 MallocInst *MI, 820 LLVMContext &Context) { 821 DOUT << "PROMOTING MALLOC GLOBAL: " << *GV << " MALLOC = " << *MI; 822 ConstantInt *NElements = cast<ConstantInt>(MI->getArraySize()); 823 824 if (NElements->getZExtValue() != 1) { 825 // If we have an array allocation, transform it to a single element 826 // allocation to make the code below simpler. 827 Type *NewTy = ArrayType::get(MI->getAllocatedType(), 828 NElements->getZExtValue()); 829 MallocInst *NewMI = 830 new MallocInst(NewTy, Constant::getNullValue(Type::getInt32Ty(Context)), 831 MI->getAlignment(), MI->getName(), MI); 832 Value* Indices[2]; 833 Indices[0] = Indices[1] = Constant::getNullValue(Type::getInt32Ty(Context)); 834 Value *NewGEP = GetElementPtrInst::Create(NewMI, Indices, Indices + 2, 835 NewMI->getName()+".el0", MI); 836 MI->replaceAllUsesWith(NewGEP); 837 MI->eraseFromParent(); 838 MI = NewMI; 839 } 840 841 // Create the new global variable. The contents of the malloc'd memory is 842 // undefined, so initialize with an undef value. 843 // FIXME: This new global should have the alignment returned by malloc. Code 844 // could depend on malloc returning large alignment (on the mac, 16 bytes) but 845 // this would only guarantee some lower alignment. 846 Constant *Init = UndefValue::get(MI->getAllocatedType()); 847 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(), 848 MI->getAllocatedType(), false, 849 GlobalValue::InternalLinkage, Init, 850 GV->getName()+".body", 851 GV, 852 GV->isThreadLocal()); 853 854 // Anything that used the malloc now uses the global directly. 855 MI->replaceAllUsesWith(NewGV); 856 857 Constant *RepValue = NewGV; 858 if (NewGV->getType() != GV->getType()->getElementType()) 859 RepValue = ConstantExpr::getBitCast(RepValue, 860 GV->getType()->getElementType()); 861 862 // If there is a comparison against null, we will insert a global bool to 863 // keep track of whether the global was initialized yet or not. 864 GlobalVariable *InitBool = 865 new GlobalVariable(Context, Type::getInt1Ty(Context), false, 866 GlobalValue::InternalLinkage, 867 ConstantInt::getFalse(Context), GV->getName()+".init", 868 GV->isThreadLocal()); 869 bool InitBoolUsed = false; 870 871 // Loop over all uses of GV, processing them in turn. 872 std::vector<StoreInst*> Stores; 873 while (!GV->use_empty()) 874 if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) { 875 while (!LI->use_empty()) { 876 Use &LoadUse = LI->use_begin().getUse(); 877 if (!isa<ICmpInst>(LoadUse.getUser())) 878 LoadUse = RepValue; 879 else { 880 ICmpInst *CI = cast<ICmpInst>(LoadUse.getUser()); 881 // Replace the cmp X, 0 with a use of the bool value. 882 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", CI); 883 InitBoolUsed = true; 884 switch (CI->getPredicate()) { 885 default: llvm_unreachable("Unknown ICmp Predicate!"); 886 case ICmpInst::ICMP_ULT: 887 case ICmpInst::ICMP_SLT: 888 LV = ConstantInt::getFalse(Context); // X < null -> always false 889 break; 890 case ICmpInst::ICMP_ULE: 891 case ICmpInst::ICMP_SLE: 892 case ICmpInst::ICMP_EQ: 893 LV = BinaryOperator::CreateNot(LV, "notinit", CI); 894 break; 895 case ICmpInst::ICMP_NE: 896 case ICmpInst::ICMP_UGE: 897 case ICmpInst::ICMP_SGE: 898 case ICmpInst::ICMP_UGT: 899 case ICmpInst::ICMP_SGT: 900 break; // no change. 901 } 902 CI->replaceAllUsesWith(LV); 903 CI->eraseFromParent(); 904 } 905 } 906 LI->eraseFromParent(); 907 } else { 908 StoreInst *SI = cast<StoreInst>(GV->use_back()); 909 // The global is initialized when the store to it occurs. 910 new StoreInst(ConstantInt::getTrue(Context), InitBool, SI); 911 SI->eraseFromParent(); 912 } 913 914 // If the initialization boolean was used, insert it, otherwise delete it. 915 if (!InitBoolUsed) { 916 while (!InitBool->use_empty()) // Delete initializations 917 cast<Instruction>(InitBool->use_back())->eraseFromParent(); 918 delete InitBool; 919 } else 920 GV->getParent()->getGlobalList().insert(GV, InitBool); 921 922 923 // Now the GV is dead, nuke it and the malloc. 924 GV->eraseFromParent(); 925 MI->eraseFromParent(); 926 927 // To further other optimizations, loop over all users of NewGV and try to 928 // constant prop them. This will promote GEP instructions with constant 929 // indices into GEP constant-exprs, which will allow global-opt to hack on it. 930 ConstantPropUsersOf(NewGV, Context); 931 if (RepValue != NewGV) 932 ConstantPropUsersOf(RepValue, Context); 933 934 return NewGV; 935} 936 937/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking 938/// to make sure that there are no complex uses of V. We permit simple things 939/// like dereferencing the pointer, but not storing through the address, unless 940/// it is to the specified global. 941static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Instruction *V, 942 GlobalVariable *GV, 943 SmallPtrSet<PHINode*, 8> &PHIs) { 944 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 945 Instruction *Inst = cast<Instruction>(*UI); 946 947 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) { 948 continue; // Fine, ignore. 949 } 950 951 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 952 if (SI->getOperand(0) == V && SI->getOperand(1) != GV) 953 return false; // Storing the pointer itself... bad. 954 continue; // Otherwise, storing through it, or storing into GV... fine. 955 } 956 957 if (isa<GetElementPtrInst>(Inst)) { 958 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs)) 959 return false; 960 continue; 961 } 962 963 if (PHINode *PN = dyn_cast<PHINode>(Inst)) { 964 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI 965 // cycles. 966 if (PHIs.insert(PN)) 967 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs)) 968 return false; 969 continue; 970 } 971 972 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) { 973 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) 974 return false; 975 continue; 976 } 977 978 return false; 979 } 980 return true; 981} 982 983/// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV 984/// somewhere. Transform all uses of the allocation into loads from the 985/// global and uses of the resultant pointer. Further, delete the store into 986/// GV. This assumes that these value pass the 987/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate. 988static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, 989 GlobalVariable *GV) { 990 while (!Alloc->use_empty()) { 991 Instruction *U = cast<Instruction>(*Alloc->use_begin()); 992 Instruction *InsertPt = U; 993 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 994 // If this is the store of the allocation into the global, remove it. 995 if (SI->getOperand(1) == GV) { 996 SI->eraseFromParent(); 997 continue; 998 } 999 } else if (PHINode *PN = dyn_cast<PHINode>(U)) { 1000 // Insert the load in the corresponding predecessor, not right before the 1001 // PHI. 1002 InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator(); 1003 } else if (isa<BitCastInst>(U)) { 1004 // Must be bitcast between the malloc and store to initialize the global. 1005 ReplaceUsesOfMallocWithGlobal(U, GV); 1006 U->eraseFromParent(); 1007 continue; 1008 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { 1009 // If this is a "GEP bitcast" and the user is a store to the global, then 1010 // just process it as a bitcast. 1011 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse()) 1012 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back())) 1013 if (SI->getOperand(1) == GV) { 1014 // Must be bitcast GEP between the malloc and store to initialize 1015 // the global. 1016 ReplaceUsesOfMallocWithGlobal(GEPI, GV); 1017 GEPI->eraseFromParent(); 1018 continue; 1019 } 1020 } 1021 1022 // Insert a load from the global, and use it instead of the malloc. 1023 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt); 1024 U->replaceUsesOfWith(Alloc, NL); 1025 } 1026} 1027 1028/// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi 1029/// of a load) are simple enough to perform heap SRA on. This permits GEP's 1030/// that index through the array and struct field, icmps of null, and PHIs. 1031static bool LoadUsesSimpleEnoughForHeapSRA(Value *V, 1032 SmallPtrSet<PHINode*, 32> &LoadUsingPHIs, 1033 SmallPtrSet<PHINode*, 32> &LoadUsingPHIsPerLoad) { 1034 // We permit two users of the load: setcc comparing against the null 1035 // pointer, and a getelementptr of a specific form. 1036 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 1037 Instruction *User = cast<Instruction>(*UI); 1038 1039 // Comparison against null is ok. 1040 if (ICmpInst *ICI = dyn_cast<ICmpInst>(User)) { 1041 if (!isa<ConstantPointerNull>(ICI->getOperand(1))) 1042 return false; 1043 continue; 1044 } 1045 1046 // getelementptr is also ok, but only a simple form. 1047 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1048 // Must index into the array and into the struct. 1049 if (GEPI->getNumOperands() < 3) 1050 return false; 1051 1052 // Otherwise the GEP is ok. 1053 continue; 1054 } 1055 1056 if (PHINode *PN = dyn_cast<PHINode>(User)) { 1057 if (!LoadUsingPHIsPerLoad.insert(PN)) 1058 // This means some phi nodes are dependent on each other. 1059 // Avoid infinite looping! 1060 return false; 1061 if (!LoadUsingPHIs.insert(PN)) 1062 // If we have already analyzed this PHI, then it is safe. 1063 continue; 1064 1065 // Make sure all uses of the PHI are simple enough to transform. 1066 if (!LoadUsesSimpleEnoughForHeapSRA(PN, 1067 LoadUsingPHIs, LoadUsingPHIsPerLoad)) 1068 return false; 1069 1070 continue; 1071 } 1072 1073 // Otherwise we don't know what this is, not ok. 1074 return false; 1075 } 1076 1077 return true; 1078} 1079 1080 1081/// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from 1082/// GV are simple enough to perform HeapSRA, return true. 1083static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(GlobalVariable *GV, 1084 MallocInst *MI) { 1085 SmallPtrSet<PHINode*, 32> LoadUsingPHIs; 1086 SmallPtrSet<PHINode*, 32> LoadUsingPHIsPerLoad; 1087 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E; 1088 ++UI) 1089 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 1090 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs, 1091 LoadUsingPHIsPerLoad)) 1092 return false; 1093 LoadUsingPHIsPerLoad.clear(); 1094 } 1095 1096 // If we reach here, we know that all uses of the loads and transitive uses 1097 // (through PHI nodes) are simple enough to transform. However, we don't know 1098 // that all inputs the to the PHI nodes are in the same equivalence sets. 1099 // Check to verify that all operands of the PHIs are either PHIS that can be 1100 // transformed, loads from GV, or MI itself. 1101 for (SmallPtrSet<PHINode*, 32>::iterator I = LoadUsingPHIs.begin(), 1102 E = LoadUsingPHIs.end(); I != E; ++I) { 1103 PHINode *PN = *I; 1104 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) { 1105 Value *InVal = PN->getIncomingValue(op); 1106 1107 // PHI of the stored value itself is ok. 1108 if (InVal == MI) continue; 1109 1110 if (PHINode *InPN = dyn_cast<PHINode>(InVal)) { 1111 // One of the PHIs in our set is (optimistically) ok. 1112 if (LoadUsingPHIs.count(InPN)) 1113 continue; 1114 return false; 1115 } 1116 1117 // Load from GV is ok. 1118 if (LoadInst *LI = dyn_cast<LoadInst>(InVal)) 1119 if (LI->getOperand(0) == GV) 1120 continue; 1121 1122 // UNDEF? NULL? 1123 1124 // Anything else is rejected. 1125 return false; 1126 } 1127 } 1128 1129 return true; 1130} 1131 1132static Value *GetHeapSROAValue(Value *V, unsigned FieldNo, 1133 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1134 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite, 1135 LLVMContext &Context) { 1136 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V]; 1137 1138 if (FieldNo >= FieldVals.size()) 1139 FieldVals.resize(FieldNo+1); 1140 1141 // If we already have this value, just reuse the previously scalarized 1142 // version. 1143 if (Value *FieldVal = FieldVals[FieldNo]) 1144 return FieldVal; 1145 1146 // Depending on what instruction this is, we have several cases. 1147 Value *Result; 1148 if (LoadInst *LI = dyn_cast<LoadInst>(V)) { 1149 // This is a scalarized version of the load from the global. Just create 1150 // a new Load of the scalarized global. 1151 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo, 1152 InsertedScalarizedValues, 1153 PHIsToRewrite, Context), 1154 LI->getName()+".f"+Twine(FieldNo), LI); 1155 } else if (PHINode *PN = dyn_cast<PHINode>(V)) { 1156 // PN's type is pointer to struct. Make a new PHI of pointer to struct 1157 // field. 1158 const StructType *ST = 1159 cast<StructType>(cast<PointerType>(PN->getType())->getElementType()); 1160 1161 Result = 1162 PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)), 1163 PN->getName()+".f"+Twine(FieldNo), PN); 1164 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo)); 1165 } else { 1166 llvm_unreachable("Unknown usable value"); 1167 Result = 0; 1168 } 1169 1170 return FieldVals[FieldNo] = Result; 1171} 1172 1173/// RewriteHeapSROALoadUser - Given a load instruction and a value derived from 1174/// the load, rewrite the derived value to use the HeapSRoA'd load. 1175static void RewriteHeapSROALoadUser(Instruction *LoadUser, 1176 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1177 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite, 1178 LLVMContext &Context) { 1179 // If this is a comparison against null, handle it. 1180 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) { 1181 assert(isa<ConstantPointerNull>(SCI->getOperand(1))); 1182 // If we have a setcc of the loaded pointer, we can use a setcc of any 1183 // field. 1184 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0, 1185 InsertedScalarizedValues, PHIsToRewrite, 1186 Context); 1187 1188 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr, 1189 Constant::getNullValue(NPtr->getType()), 1190 SCI->getName()); 1191 SCI->replaceAllUsesWith(New); 1192 SCI->eraseFromParent(); 1193 return; 1194 } 1195 1196 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...' 1197 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) { 1198 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2)) 1199 && "Unexpected GEPI!"); 1200 1201 // Load the pointer for this field. 1202 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 1203 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo, 1204 InsertedScalarizedValues, PHIsToRewrite, 1205 Context); 1206 1207 // Create the new GEP idx vector. 1208 SmallVector<Value*, 8> GEPIdx; 1209 GEPIdx.push_back(GEPI->getOperand(1)); 1210 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end()); 1211 1212 Value *NGEPI = GetElementPtrInst::Create(NewPtr, 1213 GEPIdx.begin(), GEPIdx.end(), 1214 GEPI->getName(), GEPI); 1215 GEPI->replaceAllUsesWith(NGEPI); 1216 GEPI->eraseFromParent(); 1217 return; 1218 } 1219 1220 // Recursively transform the users of PHI nodes. This will lazily create the 1221 // PHIs that are needed for individual elements. Keep track of what PHIs we 1222 // see in InsertedScalarizedValues so that we don't get infinite loops (very 1223 // antisocial). If the PHI is already in InsertedScalarizedValues, it has 1224 // already been seen first by another load, so its uses have already been 1225 // processed. 1226 PHINode *PN = cast<PHINode>(LoadUser); 1227 bool Inserted; 1228 DenseMap<Value*, std::vector<Value*> >::iterator InsertPos; 1229 tie(InsertPos, Inserted) = 1230 InsertedScalarizedValues.insert(std::make_pair(PN, std::vector<Value*>())); 1231 if (!Inserted) return; 1232 1233 // If this is the first time we've seen this PHI, recursively process all 1234 // users. 1235 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) { 1236 Instruction *User = cast<Instruction>(*UI++); 1237 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite, 1238 Context); 1239 } 1240} 1241 1242/// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr 1243/// is a value loaded from the global. Eliminate all uses of Ptr, making them 1244/// use FieldGlobals instead. All uses of loaded values satisfy 1245/// AllGlobalLoadUsesSimpleEnoughForHeapSRA. 1246static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load, 1247 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1248 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite, 1249 LLVMContext &Context) { 1250 for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end(); 1251 UI != E; ) { 1252 Instruction *User = cast<Instruction>(*UI++); 1253 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite, 1254 Context); 1255 } 1256 1257 if (Load->use_empty()) { 1258 Load->eraseFromParent(); 1259 InsertedScalarizedValues.erase(Load); 1260 } 1261} 1262 1263/// PerformHeapAllocSRoA - MI is an allocation of an array of structures. Break 1264/// it up into multiple allocations of arrays of the fields. 1265static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, MallocInst *MI, 1266 LLVMContext &Context){ 1267 DOUT << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *MI; 1268 const StructType *STy = cast<StructType>(MI->getAllocatedType()); 1269 1270 // There is guaranteed to be at least one use of the malloc (storing 1271 // it into GV). If there are other uses, change them to be uses of 1272 // the global to simplify later code. This also deletes the store 1273 // into GV. 1274 ReplaceUsesOfMallocWithGlobal(MI, GV); 1275 1276 // Okay, at this point, there are no users of the malloc. Insert N 1277 // new mallocs at the same place as MI, and N globals. 1278 std::vector<Value*> FieldGlobals; 1279 std::vector<MallocInst*> FieldMallocs; 1280 1281 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ 1282 const Type *FieldTy = STy->getElementType(FieldNo); 1283 const Type *PFieldTy = PointerType::getUnqual(FieldTy); 1284 1285 GlobalVariable *NGV = 1286 new GlobalVariable(*GV->getParent(), 1287 PFieldTy, false, GlobalValue::InternalLinkage, 1288 Constant::getNullValue(PFieldTy), 1289 GV->getName() + ".f" + Twine(FieldNo), GV, 1290 GV->isThreadLocal()); 1291 FieldGlobals.push_back(NGV); 1292 1293 MallocInst *NMI = new MallocInst(FieldTy, MI->getArraySize(), 1294 MI->getName() + ".f" + Twine(FieldNo), MI); 1295 FieldMallocs.push_back(NMI); 1296 new StoreInst(NMI, NGV, MI); 1297 } 1298 1299 // The tricky aspect of this transformation is handling the case when malloc 1300 // fails. In the original code, malloc failing would set the result pointer 1301 // of malloc to null. In this case, some mallocs could succeed and others 1302 // could fail. As such, we emit code that looks like this: 1303 // F0 = malloc(field0) 1304 // F1 = malloc(field1) 1305 // F2 = malloc(field2) 1306 // if (F0 == 0 || F1 == 0 || F2 == 0) { 1307 // if (F0) { free(F0); F0 = 0; } 1308 // if (F1) { free(F1); F1 = 0; } 1309 // if (F2) { free(F2); F2 = 0; } 1310 // } 1311 Value *RunningOr = 0; 1312 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) { 1313 Value *Cond = new ICmpInst(MI, ICmpInst::ICMP_EQ, FieldMallocs[i], 1314 Constant::getNullValue(FieldMallocs[i]->getType()), 1315 "isnull"); 1316 if (!RunningOr) 1317 RunningOr = Cond; // First seteq 1318 else 1319 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", MI); 1320 } 1321 1322 // Split the basic block at the old malloc. 1323 BasicBlock *OrigBB = MI->getParent(); 1324 BasicBlock *ContBB = OrigBB->splitBasicBlock(MI, "malloc_cont"); 1325 1326 // Create the block to check the first condition. Put all these blocks at the 1327 // end of the function as they are unlikely to be executed. 1328 BasicBlock *NullPtrBlock = BasicBlock::Create(Context, "malloc_ret_null", 1329 OrigBB->getParent()); 1330 1331 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond 1332 // branch on RunningOr. 1333 OrigBB->getTerminator()->eraseFromParent(); 1334 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB); 1335 1336 // Within the NullPtrBlock, we need to emit a comparison and branch for each 1337 // pointer, because some may be null while others are not. 1338 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1339 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock); 1340 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal, 1341 Constant::getNullValue(GVVal->getType()), 1342 "tmp"); 1343 BasicBlock *FreeBlock = BasicBlock::Create(Context, "free_it", 1344 OrigBB->getParent()); 1345 BasicBlock *NextBlock = BasicBlock::Create(Context, "next", 1346 OrigBB->getParent()); 1347 BranchInst::Create(FreeBlock, NextBlock, Cmp, NullPtrBlock); 1348 1349 // Fill in FreeBlock. 1350 new FreeInst(GVVal, FreeBlock); 1351 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i], 1352 FreeBlock); 1353 BranchInst::Create(NextBlock, FreeBlock); 1354 1355 NullPtrBlock = NextBlock; 1356 } 1357 1358 BranchInst::Create(ContBB, NullPtrBlock); 1359 1360 // MI is no longer needed, remove it. 1361 MI->eraseFromParent(); 1362 1363 /// InsertedScalarizedLoads - As we process loads, if we can't immediately 1364 /// update all uses of the load, keep track of what scalarized loads are 1365 /// inserted for a given load. 1366 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues; 1367 InsertedScalarizedValues[GV] = FieldGlobals; 1368 1369 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite; 1370 1371 // Okay, the malloc site is completely handled. All of the uses of GV are now 1372 // loads, and all uses of those loads are simple. Rewrite them to use loads 1373 // of the per-field globals instead. 1374 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) { 1375 Instruction *User = cast<Instruction>(*UI++); 1376 1377 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1378 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite, 1379 Context); 1380 continue; 1381 } 1382 1383 // Must be a store of null. 1384 StoreInst *SI = cast<StoreInst>(User); 1385 assert(isa<ConstantPointerNull>(SI->getOperand(0)) && 1386 "Unexpected heap-sra user!"); 1387 1388 // Insert a store of null into each global. 1389 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1390 const PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType()); 1391 Constant *Null = Constant::getNullValue(PT->getElementType()); 1392 new StoreInst(Null, FieldGlobals[i], SI); 1393 } 1394 // Erase the original store. 1395 SI->eraseFromParent(); 1396 } 1397 1398 // While we have PHIs that are interesting to rewrite, do it. 1399 while (!PHIsToRewrite.empty()) { 1400 PHINode *PN = PHIsToRewrite.back().first; 1401 unsigned FieldNo = PHIsToRewrite.back().second; 1402 PHIsToRewrite.pop_back(); 1403 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]); 1404 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi"); 1405 1406 // Add all the incoming values. This can materialize more phis. 1407 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1408 Value *InVal = PN->getIncomingValue(i); 1409 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues, 1410 PHIsToRewrite, Context); 1411 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i)); 1412 } 1413 } 1414 1415 // Drop all inter-phi links and any loads that made it this far. 1416 for (DenseMap<Value*, std::vector<Value*> >::iterator 1417 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1418 I != E; ++I) { 1419 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1420 PN->dropAllReferences(); 1421 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1422 LI->dropAllReferences(); 1423 } 1424 1425 // Delete all the phis and loads now that inter-references are dead. 1426 for (DenseMap<Value*, std::vector<Value*> >::iterator 1427 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1428 I != E; ++I) { 1429 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1430 PN->eraseFromParent(); 1431 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1432 LI->eraseFromParent(); 1433 } 1434 1435 // The old global is now dead, remove it. 1436 GV->eraseFromParent(); 1437 1438 ++NumHeapSRA; 1439 return cast<GlobalVariable>(FieldGlobals[0]); 1440} 1441 1442/// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a 1443/// pointer global variable with a single value stored it that is a malloc or 1444/// cast of malloc. 1445static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, 1446 MallocInst *MI, 1447 Module::global_iterator &GVI, 1448 TargetData *TD, 1449 LLVMContext &Context) { 1450 // If this is a malloc of an abstract type, don't touch it. 1451 if (!MI->getAllocatedType()->isSized()) 1452 return false; 1453 1454 // We can't optimize this global unless all uses of it are *known* to be 1455 // of the malloc value, not of the null initializer value (consider a use 1456 // that compares the global's value against zero to see if the malloc has 1457 // been reached). To do this, we check to see if all uses of the global 1458 // would trap if the global were null: this proves that they must all 1459 // happen after the malloc. 1460 if (!AllUsesOfLoadedValueWillTrapIfNull(GV)) 1461 return false; 1462 1463 // We can't optimize this if the malloc itself is used in a complex way, 1464 // for example, being stored into multiple globals. This allows the 1465 // malloc to be stored into the specified global, loaded setcc'd, and 1466 // GEP'd. These are all things we could transform to using the global 1467 // for. 1468 { 1469 SmallPtrSet<PHINode*, 8> PHIs; 1470 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(MI, GV, PHIs)) 1471 return false; 1472 } 1473 1474 1475 // If we have a global that is only initialized with a fixed size malloc, 1476 // transform the program to use global memory instead of malloc'd memory. 1477 // This eliminates dynamic allocation, avoids an indirection accessing the 1478 // data, and exposes the resultant global to further GlobalOpt. 1479 if (ConstantInt *NElements = dyn_cast<ConstantInt>(MI->getArraySize())) { 1480 // Restrict this transformation to only working on small allocations 1481 // (2048 bytes currently), as we don't want to introduce a 16M global or 1482 // something. 1483 if (TD && 1484 NElements->getZExtValue()* 1485 TD->getTypeAllocSize(MI->getAllocatedType()) < 2048) { 1486 GVI = OptimizeGlobalAddressOfMalloc(GV, MI, Context); 1487 return true; 1488 } 1489 } 1490 1491 // If the allocation is an array of structures, consider transforming this 1492 // into multiple malloc'd arrays, one for each field. This is basically 1493 // SRoA for malloc'd memory. 1494 const Type *AllocTy = MI->getAllocatedType(); 1495 1496 // If this is an allocation of a fixed size array of structs, analyze as a 1497 // variable size array. malloc [100 x struct],1 -> malloc struct, 100 1498 if (!MI->isArrayAllocation()) 1499 if (const ArrayType *AT = dyn_cast<ArrayType>(AllocTy)) 1500 AllocTy = AT->getElementType(); 1501 1502 if (const StructType *AllocSTy = dyn_cast<StructType>(AllocTy)) { 1503 // This the structure has an unreasonable number of fields, leave it 1504 // alone. 1505 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 && 1506 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, MI)) { 1507 1508 // If this is a fixed size array, transform the Malloc to be an alloc of 1509 // structs. malloc [100 x struct],1 -> malloc struct, 100 1510 if (const ArrayType *AT = dyn_cast<ArrayType>(MI->getAllocatedType())) { 1511 MallocInst *NewMI = 1512 new MallocInst(AllocSTy, 1513 ConstantInt::get(Type::getInt32Ty(Context), 1514 AT->getNumElements()), 1515 "", MI); 1516 NewMI->takeName(MI); 1517 Value *Cast = new BitCastInst(NewMI, MI->getType(), "tmp", MI); 1518 MI->replaceAllUsesWith(Cast); 1519 MI->eraseFromParent(); 1520 MI = NewMI; 1521 } 1522 1523 GVI = PerformHeapAllocSRoA(GV, MI, Context); 1524 return true; 1525 } 1526 } 1527 1528 return false; 1529} 1530 1531// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge 1532// that only one value (besides its initializer) is ever stored to the global. 1533static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal, 1534 Module::global_iterator &GVI, 1535 TargetData *TD, LLVMContext &Context) { 1536 // Ignore no-op GEPs and bitcasts. 1537 StoredOnceVal = StoredOnceVal->stripPointerCasts(); 1538 1539 // If we are dealing with a pointer global that is initialized to null and 1540 // only has one (non-null) value stored into it, then we can optimize any 1541 // users of the loaded value (often calls and loads) that would trap if the 1542 // value was null. 1543 if (isa<PointerType>(GV->getInitializer()->getType()) && 1544 GV->getInitializer()->isNullValue()) { 1545 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { 1546 if (GV->getInitializer()->getType() != SOVC->getType()) 1547 SOVC = 1548 ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType()); 1549 1550 // Optimize away any trapping uses of the loaded value. 1551 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, Context)) 1552 return true; 1553 } else if (MallocInst *MI = dyn_cast<MallocInst>(StoredOnceVal)) { 1554 if (TryToOptimizeStoreOfMallocToGlobal(GV, MI, GVI, TD, Context)) 1555 return true; 1556 } 1557 } 1558 1559 return false; 1560} 1561 1562/// TryToShrinkGlobalToBoolean - At this point, we have learned that the only 1563/// two values ever stored into GV are its initializer and OtherVal. See if we 1564/// can shrink the global into a boolean and select between the two values 1565/// whenever it is used. This exposes the values to other scalar optimizations. 1566static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal, 1567 LLVMContext &Context) { 1568 const Type *GVElType = GV->getType()->getElementType(); 1569 1570 // If GVElType is already i1, it is already shrunk. If the type of the GV is 1571 // an FP value, pointer or vector, don't do this optimization because a select 1572 // between them is very expensive and unlikely to lead to later 1573 // simplification. In these cases, we typically end up with "cond ? v1 : v2" 1574 // where v1 and v2 both require constant pool loads, a big loss. 1575 if (GVElType == Type::getInt1Ty(Context) || GVElType->isFloatingPoint() || 1576 isa<PointerType>(GVElType) || isa<VectorType>(GVElType)) 1577 return false; 1578 1579 // Walk the use list of the global seeing if all the uses are load or store. 1580 // If there is anything else, bail out. 1581 for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I) 1582 if (!isa<LoadInst>(I) && !isa<StoreInst>(I)) 1583 return false; 1584 1585 DOUT << " *** SHRINKING TO BOOL: " << *GV; 1586 1587 // Create the new global, initializing it to false. 1588 GlobalVariable *NewGV = new GlobalVariable(Context, 1589 Type::getInt1Ty(Context), false, 1590 GlobalValue::InternalLinkage, ConstantInt::getFalse(Context), 1591 GV->getName()+".b", 1592 GV->isThreadLocal()); 1593 GV->getParent()->getGlobalList().insert(GV, NewGV); 1594 1595 Constant *InitVal = GV->getInitializer(); 1596 assert(InitVal->getType() != Type::getInt1Ty(Context) && 1597 "No reason to shrink to bool!"); 1598 1599 // If initialized to zero and storing one into the global, we can use a cast 1600 // instead of a select to synthesize the desired value. 1601 bool IsOneZero = false; 1602 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) 1603 IsOneZero = InitVal->isNullValue() && CI->isOne(); 1604 1605 while (!GV->use_empty()) { 1606 Instruction *UI = cast<Instruction>(GV->use_back()); 1607 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { 1608 // Change the store into a boolean store. 1609 bool StoringOther = SI->getOperand(0) == OtherVal; 1610 // Only do this if we weren't storing a loaded value. 1611 Value *StoreVal; 1612 if (StoringOther || SI->getOperand(0) == InitVal) 1613 StoreVal = ConstantInt::get(Type::getInt1Ty(Context), StoringOther); 1614 else { 1615 // Otherwise, we are storing a previously loaded copy. To do this, 1616 // change the copy from copying the original value to just copying the 1617 // bool. 1618 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); 1619 1620 // If we're already replaced the input, StoredVal will be a cast or 1621 // select instruction. If not, it will be a load of the original 1622 // global. 1623 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { 1624 assert(LI->getOperand(0) == GV && "Not a copy!"); 1625 // Insert a new load, to preserve the saved value. 1626 StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI); 1627 } else { 1628 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && 1629 "This is not a form that we understand!"); 1630 StoreVal = StoredVal->getOperand(0); 1631 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); 1632 } 1633 } 1634 new StoreInst(StoreVal, NewGV, SI); 1635 } else { 1636 // Change the load into a load of bool then a select. 1637 LoadInst *LI = cast<LoadInst>(UI); 1638 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", LI); 1639 Value *NSI; 1640 if (IsOneZero) 1641 NSI = new ZExtInst(NLI, LI->getType(), "", LI); 1642 else 1643 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI); 1644 NSI->takeName(LI); 1645 LI->replaceAllUsesWith(NSI); 1646 } 1647 UI->eraseFromParent(); 1648 } 1649 1650 GV->eraseFromParent(); 1651 return true; 1652} 1653 1654 1655/// ProcessInternalGlobal - Analyze the specified global variable and optimize 1656/// it if possible. If we make a change, return true. 1657bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV, 1658 Module::global_iterator &GVI) { 1659 SmallPtrSet<PHINode*, 16> PHIUsers; 1660 GlobalStatus GS; 1661 GV->removeDeadConstantUsers(); 1662 1663 if (GV->use_empty()) { 1664 DOUT << "GLOBAL DEAD: " << *GV; 1665 GV->eraseFromParent(); 1666 ++NumDeleted; 1667 return true; 1668 } 1669 1670 if (!AnalyzeGlobal(GV, GS, PHIUsers)) { 1671#if 0 1672 cerr << "Global: " << *GV; 1673 cerr << " isLoaded = " << GS.isLoaded << "\n"; 1674 cerr << " StoredType = "; 1675 switch (GS.StoredType) { 1676 case GlobalStatus::NotStored: cerr << "NEVER STORED\n"; break; 1677 case GlobalStatus::isInitializerStored: cerr << "INIT STORED\n"; break; 1678 case GlobalStatus::isStoredOnce: cerr << "STORED ONCE\n"; break; 1679 case GlobalStatus::isStored: cerr << "stored\n"; break; 1680 } 1681 if (GS.StoredType == GlobalStatus::isStoredOnce && GS.StoredOnceValue) 1682 cerr << " StoredOnceValue = " << *GS.StoredOnceValue << "\n"; 1683 if (GS.AccessingFunction && !GS.HasMultipleAccessingFunctions) 1684 cerr << " AccessingFunction = " << GS.AccessingFunction->getName() 1685 << "\n"; 1686 cerr << " HasMultipleAccessingFunctions = " 1687 << GS.HasMultipleAccessingFunctions << "\n"; 1688 cerr << " HasNonInstructionUser = " << GS.HasNonInstructionUser<<"\n"; 1689 cerr << "\n"; 1690#endif 1691 1692 // If this is a first class global and has only one accessing function 1693 // and this function is main (which we know is not recursive we can make 1694 // this global a local variable) we replace the global with a local alloca 1695 // in this function. 1696 // 1697 // NOTE: It doesn't make sense to promote non single-value types since we 1698 // are just replacing static memory to stack memory. 1699 // 1700 // If the global is in different address space, don't bring it to stack. 1701 if (!GS.HasMultipleAccessingFunctions && 1702 GS.AccessingFunction && !GS.HasNonInstructionUser && 1703 GV->getType()->getElementType()->isSingleValueType() && 1704 GS.AccessingFunction->getName() == "main" && 1705 GS.AccessingFunction->hasExternalLinkage() && 1706 GV->getType()->getAddressSpace() == 0) { 1707 DOUT << "LOCALIZING GLOBAL: " << *GV; 1708 Instruction* FirstI = GS.AccessingFunction->getEntryBlock().begin(); 1709 const Type* ElemTy = GV->getType()->getElementType(); 1710 // FIXME: Pass Global's alignment when globals have alignment 1711 AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), FirstI); 1712 if (!isa<UndefValue>(GV->getInitializer())) 1713 new StoreInst(GV->getInitializer(), Alloca, FirstI); 1714 1715 GV->replaceAllUsesWith(Alloca); 1716 GV->eraseFromParent(); 1717 ++NumLocalized; 1718 return true; 1719 } 1720 1721 // If the global is never loaded (but may be stored to), it is dead. 1722 // Delete it now. 1723 if (!GS.isLoaded) { 1724 DOUT << "GLOBAL NEVER LOADED: " << *GV; 1725 1726 // Delete any stores we can find to the global. We may not be able to 1727 // make it completely dead though. 1728 bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer(), 1729 GV->getContext()); 1730 1731 // If the global is dead now, delete it. 1732 if (GV->use_empty()) { 1733 GV->eraseFromParent(); 1734 ++NumDeleted; 1735 Changed = true; 1736 } 1737 return Changed; 1738 1739 } else if (GS.StoredType <= GlobalStatus::isInitializerStored) { 1740 DOUT << "MARKING CONSTANT: " << *GV; 1741 GV->setConstant(true); 1742 1743 // Clean up any obviously simplifiable users now. 1744 CleanupConstantGlobalUsers(GV, GV->getInitializer(), GV->getContext()); 1745 1746 // If the global is dead now, just nuke it. 1747 if (GV->use_empty()) { 1748 DOUT << " *** Marking constant allowed us to simplify " 1749 << "all users and delete global!\n"; 1750 GV->eraseFromParent(); 1751 ++NumDeleted; 1752 } 1753 1754 ++NumMarked; 1755 return true; 1756 } else if (!GV->getInitializer()->getType()->isSingleValueType()) { 1757 if (TargetData *TD = getAnalysisIfAvailable<TargetData>()) 1758 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD, 1759 GV->getContext())) { 1760 GVI = FirstNewGV; // Don't skip the newly produced globals! 1761 return true; 1762 } 1763 } else if (GS.StoredType == GlobalStatus::isStoredOnce) { 1764 // If the initial value for the global was an undef value, and if only 1765 // one other value was stored into it, we can just change the 1766 // initializer to be the stored value, then delete all stores to the 1767 // global. This allows us to mark it constant. 1768 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1769 if (isa<UndefValue>(GV->getInitializer())) { 1770 // Change the initial value here. 1771 GV->setInitializer(SOVConstant); 1772 1773 // Clean up any obviously simplifiable users now. 1774 CleanupConstantGlobalUsers(GV, GV->getInitializer(), 1775 GV->getContext()); 1776 1777 if (GV->use_empty()) { 1778 DOUT << " *** Substituting initializer allowed us to " 1779 << "simplify all users and delete global!\n"; 1780 GV->eraseFromParent(); 1781 ++NumDeleted; 1782 } else { 1783 GVI = GV; 1784 } 1785 ++NumSubstitute; 1786 return true; 1787 } 1788 1789 // Try to optimize globals based on the knowledge that only one value 1790 // (besides its initializer) is ever stored to the global. 1791 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI, 1792 getAnalysisIfAvailable<TargetData>(), 1793 GV->getContext())) 1794 return true; 1795 1796 // Otherwise, if the global was not a boolean, we can shrink it to be a 1797 // boolean. 1798 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1799 if (TryToShrinkGlobalToBoolean(GV, SOVConstant, GV->getContext())) { 1800 ++NumShrunkToBool; 1801 return true; 1802 } 1803 } 1804 } 1805 return false; 1806} 1807 1808/// ChangeCalleesToFastCall - Walk all of the direct calls of the specified 1809/// function, changing them to FastCC. 1810static void ChangeCalleesToFastCall(Function *F) { 1811 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1812 CallSite User(cast<Instruction>(*UI)); 1813 User.setCallingConv(CallingConv::Fast); 1814 } 1815} 1816 1817static AttrListPtr StripNest(const AttrListPtr &Attrs) { 1818 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) { 1819 if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0) 1820 continue; 1821 1822 // There can be only one. 1823 return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest); 1824 } 1825 1826 return Attrs; 1827} 1828 1829static void RemoveNestAttribute(Function *F) { 1830 F->setAttributes(StripNest(F->getAttributes())); 1831 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1832 CallSite User(cast<Instruction>(*UI)); 1833 User.setAttributes(StripNest(User.getAttributes())); 1834 } 1835} 1836 1837bool GlobalOpt::OptimizeFunctions(Module &M) { 1838 bool Changed = false; 1839 // Optimize functions. 1840 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { 1841 Function *F = FI++; 1842 // Functions without names cannot be referenced outside this module. 1843 if (!F->hasName() && !F->isDeclaration()) 1844 F->setLinkage(GlobalValue::InternalLinkage); 1845 F->removeDeadConstantUsers(); 1846 if (F->use_empty() && (F->hasLocalLinkage() || 1847 F->hasLinkOnceLinkage())) { 1848 M.getFunctionList().erase(F); 1849 Changed = true; 1850 ++NumFnDeleted; 1851 } else if (F->hasLocalLinkage()) { 1852 if (F->getCallingConv() == CallingConv::C && !F->isVarArg() && 1853 !F->hasAddressTaken()) { 1854 // If this function has C calling conventions, is not a varargs 1855 // function, and is only called directly, promote it to use the Fast 1856 // calling convention. 1857 F->setCallingConv(CallingConv::Fast); 1858 ChangeCalleesToFastCall(F); 1859 ++NumFastCallFns; 1860 Changed = true; 1861 } 1862 1863 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) && 1864 !F->hasAddressTaken()) { 1865 // The function is not used by a trampoline intrinsic, so it is safe 1866 // to remove the 'nest' attribute. 1867 RemoveNestAttribute(F); 1868 ++NumNestRemoved; 1869 Changed = true; 1870 } 1871 } 1872 } 1873 return Changed; 1874} 1875 1876bool GlobalOpt::OptimizeGlobalVars(Module &M) { 1877 bool Changed = false; 1878 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); 1879 GVI != E; ) { 1880 GlobalVariable *GV = GVI++; 1881 // Global variables without names cannot be referenced outside this module. 1882 if (!GV->hasName() && !GV->isDeclaration()) 1883 GV->setLinkage(GlobalValue::InternalLinkage); 1884 if (!GV->isConstant() && GV->hasLocalLinkage() && 1885 GV->hasInitializer()) 1886 Changed |= ProcessInternalGlobal(GV, GVI); 1887 } 1888 return Changed; 1889} 1890 1891/// FindGlobalCtors - Find the llvm.globalctors list, verifying that all 1892/// initializers have an init priority of 65535. 1893GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) { 1894 for (Module::global_iterator I = M.global_begin(), E = M.global_end(); 1895 I != E; ++I) 1896 if (I->getName() == "llvm.global_ctors") { 1897 // Found it, verify it's an array of { int, void()* }. 1898 const ArrayType *ATy =dyn_cast<ArrayType>(I->getType()->getElementType()); 1899 if (!ATy) return 0; 1900 const StructType *STy = dyn_cast<StructType>(ATy->getElementType()); 1901 if (!STy || STy->getNumElements() != 2 || 1902 STy->getElementType(0) != Type::getInt32Ty(M.getContext())) return 0; 1903 const PointerType *PFTy = dyn_cast<PointerType>(STy->getElementType(1)); 1904 if (!PFTy) return 0; 1905 const FunctionType *FTy = dyn_cast<FunctionType>(PFTy->getElementType()); 1906 if (!FTy || FTy->getReturnType() != Type::getVoidTy(M.getContext()) || 1907 FTy->isVarArg() || FTy->getNumParams() != 0) 1908 return 0; 1909 1910 // Verify that the initializer is simple enough for us to handle. 1911 if (!I->hasInitializer()) return 0; 1912 ConstantArray *CA = dyn_cast<ConstantArray>(I->getInitializer()); 1913 if (!CA) return 0; 1914 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 1915 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(*i)) { 1916 if (isa<ConstantPointerNull>(CS->getOperand(1))) 1917 continue; 1918 1919 // Must have a function or null ptr. 1920 if (!isa<Function>(CS->getOperand(1))) 1921 return 0; 1922 1923 // Init priority must be standard. 1924 ConstantInt *CI = dyn_cast<ConstantInt>(CS->getOperand(0)); 1925 if (!CI || CI->getZExtValue() != 65535) 1926 return 0; 1927 } else { 1928 return 0; 1929 } 1930 1931 return I; 1932 } 1933 return 0; 1934} 1935 1936/// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand, 1937/// return a list of the functions and null terminator as a vector. 1938static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) { 1939 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer()); 1940 std::vector<Function*> Result; 1941 Result.reserve(CA->getNumOperands()); 1942 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) { 1943 ConstantStruct *CS = cast<ConstantStruct>(*i); 1944 Result.push_back(dyn_cast<Function>(CS->getOperand(1))); 1945 } 1946 return Result; 1947} 1948 1949/// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the 1950/// specified array, returning the new global to use. 1951static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL, 1952 const std::vector<Function*> &Ctors, 1953 LLVMContext &Context) { 1954 // If we made a change, reassemble the initializer list. 1955 std::vector<Constant*> CSVals; 1956 CSVals.push_back(ConstantInt::get(Type::getInt32Ty(Context), 65535)); 1957 CSVals.push_back(0); 1958 1959 // Create the new init list. 1960 std::vector<Constant*> CAList; 1961 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) { 1962 if (Ctors[i]) { 1963 CSVals[1] = Ctors[i]; 1964 } else { 1965 const Type *FTy = FunctionType::get(Type::getVoidTy(Context), false); 1966 const PointerType *PFTy = PointerType::getUnqual(FTy); 1967 CSVals[1] = Constant::getNullValue(PFTy); 1968 CSVals[0] = ConstantInt::get(Type::getInt32Ty(Context), 2147483647); 1969 } 1970 CAList.push_back(ConstantStruct::get(Context, CSVals)); 1971 } 1972 1973 // Create the array initializer. 1974 const Type *StructTy = 1975 cast<ArrayType>(GCL->getType()->getElementType())->getElementType(); 1976 Constant *CA = ConstantArray::get(ArrayType::get(StructTy, 1977 CAList.size()), CAList); 1978 1979 // If we didn't change the number of elements, don't create a new GV. 1980 if (CA->getType() == GCL->getInitializer()->getType()) { 1981 GCL->setInitializer(CA); 1982 return GCL; 1983 } 1984 1985 // Create the new global and insert it next to the existing list. 1986 GlobalVariable *NGV = new GlobalVariable(Context, CA->getType(), 1987 GCL->isConstant(), 1988 GCL->getLinkage(), CA, "", 1989 GCL->isThreadLocal()); 1990 GCL->getParent()->getGlobalList().insert(GCL, NGV); 1991 NGV->takeName(GCL); 1992 1993 // Nuke the old list, replacing any uses with the new one. 1994 if (!GCL->use_empty()) { 1995 Constant *V = NGV; 1996 if (V->getType() != GCL->getType()) 1997 V = ConstantExpr::getBitCast(V, GCL->getType()); 1998 GCL->replaceAllUsesWith(V); 1999 } 2000 GCL->eraseFromParent(); 2001 2002 if (Ctors.size()) 2003 return NGV; 2004 else 2005 return 0; 2006} 2007 2008 2009static Constant *getVal(DenseMap<Value*, Constant*> &ComputedValues, 2010 Value *V) { 2011 if (Constant *CV = dyn_cast<Constant>(V)) return CV; 2012 Constant *R = ComputedValues[V]; 2013 assert(R && "Reference to an uncomputed value!"); 2014 return R; 2015} 2016 2017/// isSimpleEnoughPointerToCommit - Return true if this constant is simple 2018/// enough for us to understand. In particular, if it is a cast of something, 2019/// we punt. We basically just support direct accesses to globals and GEP's of 2020/// globals. This should be kept up to date with CommitValueTo. 2021static bool isSimpleEnoughPointerToCommit(Constant *C, LLVMContext &Context) { 2022 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) { 2023 if (!GV->hasExternalLinkage() && !GV->hasLocalLinkage()) 2024 return false; // do not allow weak/linkonce/dllimport/dllexport linkage. 2025 return !GV->isDeclaration(); // reject external globals. 2026 } 2027 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 2028 // Handle a constantexpr gep. 2029 if (CE->getOpcode() == Instruction::GetElementPtr && 2030 isa<GlobalVariable>(CE->getOperand(0))) { 2031 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2032 if (!GV->hasExternalLinkage() && !GV->hasLocalLinkage()) 2033 return false; // do not allow weak/linkonce/dllimport/dllexport linkage. 2034 return GV->hasInitializer() && 2035 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE, 2036 Context); 2037 } 2038 return false; 2039} 2040 2041/// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global 2042/// initializer. This returns 'Init' modified to reflect 'Val' stored into it. 2043/// At this point, the GEP operands of Addr [0, OpNo) have been stepped into. 2044static Constant *EvaluateStoreInto(Constant *Init, Constant *Val, 2045 ConstantExpr *Addr, unsigned OpNo, 2046 LLVMContext &Context) { 2047 // Base case of the recursion. 2048 if (OpNo == Addr->getNumOperands()) { 2049 assert(Val->getType() == Init->getType() && "Type mismatch!"); 2050 return Val; 2051 } 2052 2053 if (const StructType *STy = dyn_cast<StructType>(Init->getType())) { 2054 std::vector<Constant*> Elts; 2055 2056 // Break up the constant into its elements. 2057 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) { 2058 for (User::op_iterator i = CS->op_begin(), e = CS->op_end(); i != e; ++i) 2059 Elts.push_back(cast<Constant>(*i)); 2060 } else if (isa<ConstantAggregateZero>(Init)) { 2061 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2062 Elts.push_back(Constant::getNullValue(STy->getElementType(i))); 2063 } else if (isa<UndefValue>(Init)) { 2064 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2065 Elts.push_back(UndefValue::get(STy->getElementType(i))); 2066 } else { 2067 llvm_unreachable("This code is out of sync with " 2068 " ConstantFoldLoadThroughGEPConstantExpr"); 2069 } 2070 2071 // Replace the element that we are supposed to. 2072 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo)); 2073 unsigned Idx = CU->getZExtValue(); 2074 assert(Idx < STy->getNumElements() && "Struct index out of range!"); 2075 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1, Context); 2076 2077 // Return the modified struct. 2078 return ConstantStruct::get(Context, &Elts[0], Elts.size(), STy->isPacked()); 2079 } else { 2080 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo)); 2081 const ArrayType *ATy = cast<ArrayType>(Init->getType()); 2082 2083 // Break up the array into elements. 2084 std::vector<Constant*> Elts; 2085 if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) { 2086 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 2087 Elts.push_back(cast<Constant>(*i)); 2088 } else if (isa<ConstantAggregateZero>(Init)) { 2089 Constant *Elt = Constant::getNullValue(ATy->getElementType()); 2090 Elts.assign(ATy->getNumElements(), Elt); 2091 } else if (isa<UndefValue>(Init)) { 2092 Constant *Elt = UndefValue::get(ATy->getElementType()); 2093 Elts.assign(ATy->getNumElements(), Elt); 2094 } else { 2095 llvm_unreachable("This code is out of sync with " 2096 " ConstantFoldLoadThroughGEPConstantExpr"); 2097 } 2098 2099 assert(CI->getZExtValue() < ATy->getNumElements()); 2100 Elts[CI->getZExtValue()] = 2101 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1, Context); 2102 return ConstantArray::get(ATy, Elts); 2103 } 2104} 2105 2106/// CommitValueTo - We have decided that Addr (which satisfies the predicate 2107/// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen. 2108static void CommitValueTo(Constant *Val, Constant *Addr, 2109 LLVMContext &Context) { 2110 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) { 2111 assert(GV->hasInitializer()); 2112 GV->setInitializer(Val); 2113 return; 2114 } 2115 2116 ConstantExpr *CE = cast<ConstantExpr>(Addr); 2117 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2118 2119 Constant *Init = GV->getInitializer(); 2120 Init = EvaluateStoreInto(Init, Val, CE, 2, Context); 2121 GV->setInitializer(Init); 2122} 2123 2124/// ComputeLoadResult - Return the value that would be computed by a load from 2125/// P after the stores reflected by 'memory' have been performed. If we can't 2126/// decide, return null. 2127static Constant *ComputeLoadResult(Constant *P, 2128 const DenseMap<Constant*, Constant*> &Memory, 2129 LLVMContext &Context) { 2130 // If this memory location has been recently stored, use the stored value: it 2131 // is the most up-to-date. 2132 DenseMap<Constant*, Constant*>::const_iterator I = Memory.find(P); 2133 if (I != Memory.end()) return I->second; 2134 2135 // Access it. 2136 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) { 2137 if (GV->hasInitializer()) 2138 return GV->getInitializer(); 2139 return 0; 2140 } 2141 2142 // Handle a constantexpr getelementptr. 2143 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) 2144 if (CE->getOpcode() == Instruction::GetElementPtr && 2145 isa<GlobalVariable>(CE->getOperand(0))) { 2146 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2147 if (GV->hasInitializer()) 2148 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE, 2149 Context); 2150 } 2151 2152 return 0; // don't know how to evaluate. 2153} 2154 2155/// EvaluateFunction - Evaluate a call to function F, returning true if 2156/// successful, false if we can't evaluate it. ActualArgs contains the formal 2157/// arguments for the function. 2158static bool EvaluateFunction(Function *F, Constant *&RetVal, 2159 const SmallVectorImpl<Constant*> &ActualArgs, 2160 std::vector<Function*> &CallStack, 2161 DenseMap<Constant*, Constant*> &MutatedMemory, 2162 std::vector<GlobalVariable*> &AllocaTmps) { 2163 // Check to see if this function is already executing (recursion). If so, 2164 // bail out. TODO: we might want to accept limited recursion. 2165 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end()) 2166 return false; 2167 2168 LLVMContext &Context = F->getContext(); 2169 2170 CallStack.push_back(F); 2171 2172 /// Values - As we compute SSA register values, we store their contents here. 2173 DenseMap<Value*, Constant*> Values; 2174 2175 // Initialize arguments to the incoming values specified. 2176 unsigned ArgNo = 0; 2177 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E; 2178 ++AI, ++ArgNo) 2179 Values[AI] = ActualArgs[ArgNo]; 2180 2181 /// ExecutedBlocks - We only handle non-looping, non-recursive code. As such, 2182 /// we can only evaluate any one basic block at most once. This set keeps 2183 /// track of what we have executed so we can detect recursive cases etc. 2184 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks; 2185 2186 // CurInst - The current instruction we're evaluating. 2187 BasicBlock::iterator CurInst = F->begin()->begin(); 2188 2189 // This is the main evaluation loop. 2190 while (1) { 2191 Constant *InstResult = 0; 2192 2193 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) { 2194 if (SI->isVolatile()) return false; // no volatile accesses. 2195 Constant *Ptr = getVal(Values, SI->getOperand(1)); 2196 if (!isSimpleEnoughPointerToCommit(Ptr, Context)) 2197 // If this is too complex for us to commit, reject it. 2198 return false; 2199 Constant *Val = getVal(Values, SI->getOperand(0)); 2200 MutatedMemory[Ptr] = Val; 2201 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) { 2202 InstResult = ConstantExpr::get(BO->getOpcode(), 2203 getVal(Values, BO->getOperand(0)), 2204 getVal(Values, BO->getOperand(1))); 2205 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) { 2206 InstResult = ConstantExpr::getCompare(CI->getPredicate(), 2207 getVal(Values, CI->getOperand(0)), 2208 getVal(Values, CI->getOperand(1))); 2209 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) { 2210 InstResult = ConstantExpr::getCast(CI->getOpcode(), 2211 getVal(Values, CI->getOperand(0)), 2212 CI->getType()); 2213 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) { 2214 InstResult = 2215 ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)), 2216 getVal(Values, SI->getOperand(1)), 2217 getVal(Values, SI->getOperand(2))); 2218 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) { 2219 Constant *P = getVal(Values, GEP->getOperand(0)); 2220 SmallVector<Constant*, 8> GEPOps; 2221 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); 2222 i != e; ++i) 2223 GEPOps.push_back(getVal(Values, *i)); 2224 InstResult = 2225 ConstantExpr::getGetElementPtr(P, &GEPOps[0], GEPOps.size()); 2226 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) { 2227 if (LI->isVolatile()) return false; // no volatile accesses. 2228 InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)), 2229 MutatedMemory, Context); 2230 if (InstResult == 0) return false; // Could not evaluate load. 2231 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) { 2232 if (AI->isArrayAllocation()) return false; // Cannot handle array allocs. 2233 const Type *Ty = AI->getType()->getElementType(); 2234 AllocaTmps.push_back(new GlobalVariable(Context, Ty, false, 2235 GlobalValue::InternalLinkage, 2236 UndefValue::get(Ty), 2237 AI->getName())); 2238 InstResult = AllocaTmps.back(); 2239 } else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) { 2240 2241 // Debug info can safely be ignored here. 2242 if (isa<DbgInfoIntrinsic>(CI)) { 2243 ++CurInst; 2244 continue; 2245 } 2246 2247 // Cannot handle inline asm. 2248 if (isa<InlineAsm>(CI->getOperand(0))) return false; 2249 2250 // Resolve function pointers. 2251 Function *Callee = dyn_cast<Function>(getVal(Values, CI->getOperand(0))); 2252 if (!Callee) return false; // Cannot resolve. 2253 2254 SmallVector<Constant*, 8> Formals; 2255 for (User::op_iterator i = CI->op_begin() + 1, e = CI->op_end(); 2256 i != e; ++i) 2257 Formals.push_back(getVal(Values, *i)); 2258 2259 if (Callee->isDeclaration()) { 2260 // If this is a function we can constant fold, do it. 2261 if (Constant *C = ConstantFoldCall(Callee, Formals.data(), 2262 Formals.size())) { 2263 InstResult = C; 2264 } else { 2265 return false; 2266 } 2267 } else { 2268 if (Callee->getFunctionType()->isVarArg()) 2269 return false; 2270 2271 Constant *RetVal; 2272 // Execute the call, if successful, use the return value. 2273 if (!EvaluateFunction(Callee, RetVal, Formals, CallStack, 2274 MutatedMemory, AllocaTmps)) 2275 return false; 2276 InstResult = RetVal; 2277 } 2278 } else if (isa<TerminatorInst>(CurInst)) { 2279 BasicBlock *NewBB = 0; 2280 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) { 2281 if (BI->isUnconditional()) { 2282 NewBB = BI->getSuccessor(0); 2283 } else { 2284 ConstantInt *Cond = 2285 dyn_cast<ConstantInt>(getVal(Values, BI->getCondition())); 2286 if (!Cond) return false; // Cannot determine. 2287 2288 NewBB = BI->getSuccessor(!Cond->getZExtValue()); 2289 } 2290 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) { 2291 ConstantInt *Val = 2292 dyn_cast<ConstantInt>(getVal(Values, SI->getCondition())); 2293 if (!Val) return false; // Cannot determine. 2294 NewBB = SI->getSuccessor(SI->findCaseValue(Val)); 2295 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) { 2296 if (RI->getNumOperands()) 2297 RetVal = getVal(Values, RI->getOperand(0)); 2298 2299 CallStack.pop_back(); // return from fn. 2300 return true; // We succeeded at evaluating this ctor! 2301 } else { 2302 // invoke, unwind, unreachable. 2303 return false; // Cannot handle this terminator. 2304 } 2305 2306 // Okay, we succeeded in evaluating this control flow. See if we have 2307 // executed the new block before. If so, we have a looping function, 2308 // which we cannot evaluate in reasonable time. 2309 if (!ExecutedBlocks.insert(NewBB)) 2310 return false; // looped! 2311 2312 // Okay, we have never been in this block before. Check to see if there 2313 // are any PHI nodes. If so, evaluate them with information about where 2314 // we came from. 2315 BasicBlock *OldBB = CurInst->getParent(); 2316 CurInst = NewBB->begin(); 2317 PHINode *PN; 2318 for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst) 2319 Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB)); 2320 2321 // Do NOT increment CurInst. We know that the terminator had no value. 2322 continue; 2323 } else { 2324 // Did not know how to evaluate this! 2325 return false; 2326 } 2327 2328 if (!CurInst->use_empty()) 2329 Values[CurInst] = InstResult; 2330 2331 // Advance program counter. 2332 ++CurInst; 2333 } 2334} 2335 2336/// EvaluateStaticConstructor - Evaluate static constructors in the function, if 2337/// we can. Return true if we can, false otherwise. 2338static bool EvaluateStaticConstructor(Function *F) { 2339 /// MutatedMemory - For each store we execute, we update this map. Loads 2340 /// check this to get the most up-to-date value. If evaluation is successful, 2341 /// this state is committed to the process. 2342 DenseMap<Constant*, Constant*> MutatedMemory; 2343 2344 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable 2345 /// to represent its body. This vector is needed so we can delete the 2346 /// temporary globals when we are done. 2347 std::vector<GlobalVariable*> AllocaTmps; 2348 2349 /// CallStack - This is used to detect recursion. In pathological situations 2350 /// we could hit exponential behavior, but at least there is nothing 2351 /// unbounded. 2352 std::vector<Function*> CallStack; 2353 2354 // Call the function. 2355 Constant *RetValDummy; 2356 bool EvalSuccess = EvaluateFunction(F, RetValDummy, 2357 SmallVector<Constant*, 0>(), CallStack, 2358 MutatedMemory, AllocaTmps); 2359 if (EvalSuccess) { 2360 // We succeeded at evaluation: commit the result. 2361 DEBUG(errs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" 2362 << F->getName() << "' to " << MutatedMemory.size() 2363 << " stores.\n"); 2364 for (DenseMap<Constant*, Constant*>::iterator I = MutatedMemory.begin(), 2365 E = MutatedMemory.end(); I != E; ++I) 2366 CommitValueTo(I->second, I->first, F->getContext()); 2367 } 2368 2369 // At this point, we are done interpreting. If we created any 'alloca' 2370 // temporaries, release them now. 2371 while (!AllocaTmps.empty()) { 2372 GlobalVariable *Tmp = AllocaTmps.back(); 2373 AllocaTmps.pop_back(); 2374 2375 // If there are still users of the alloca, the program is doing something 2376 // silly, e.g. storing the address of the alloca somewhere and using it 2377 // later. Since this is undefined, we'll just make it be null. 2378 if (!Tmp->use_empty()) 2379 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType())); 2380 delete Tmp; 2381 } 2382 2383 return EvalSuccess; 2384} 2385 2386 2387 2388/// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible. 2389/// Return true if anything changed. 2390bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) { 2391 std::vector<Function*> Ctors = ParseGlobalCtors(GCL); 2392 bool MadeChange = false; 2393 if (Ctors.empty()) return false; 2394 2395 // Loop over global ctors, optimizing them when we can. 2396 for (unsigned i = 0; i != Ctors.size(); ++i) { 2397 Function *F = Ctors[i]; 2398 // Found a null terminator in the middle of the list, prune off the rest of 2399 // the list. 2400 if (F == 0) { 2401 if (i != Ctors.size()-1) { 2402 Ctors.resize(i+1); 2403 MadeChange = true; 2404 } 2405 break; 2406 } 2407 2408 // We cannot simplify external ctor functions. 2409 if (F->empty()) continue; 2410 2411 // If we can evaluate the ctor at compile time, do. 2412 if (EvaluateStaticConstructor(F)) { 2413 Ctors.erase(Ctors.begin()+i); 2414 MadeChange = true; 2415 --i; 2416 ++NumCtorsEvaluated; 2417 continue; 2418 } 2419 } 2420 2421 if (!MadeChange) return false; 2422 2423 GCL = InstallGlobalCtors(GCL, Ctors, GCL->getContext()); 2424 return true; 2425} 2426 2427bool GlobalOpt::OptimizeGlobalAliases(Module &M) { 2428 bool Changed = false; 2429 2430 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); 2431 I != E;) { 2432 Module::alias_iterator J = I++; 2433 // Aliases without names cannot be referenced outside this module. 2434 if (!J->hasName() && !J->isDeclaration()) 2435 J->setLinkage(GlobalValue::InternalLinkage); 2436 // If the aliasee may change at link time, nothing can be done - bail out. 2437 if (J->mayBeOverridden()) 2438 continue; 2439 2440 Constant *Aliasee = J->getAliasee(); 2441 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts()); 2442 Target->removeDeadConstantUsers(); 2443 bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse(); 2444 2445 // Make all users of the alias use the aliasee instead. 2446 if (!J->use_empty()) { 2447 J->replaceAllUsesWith(Aliasee); 2448 ++NumAliasesResolved; 2449 Changed = true; 2450 } 2451 2452 // If the aliasee has internal linkage, give it the name and linkage 2453 // of the alias, and delete the alias. This turns: 2454 // define internal ... @f(...) 2455 // @a = alias ... @f 2456 // into: 2457 // define ... @a(...) 2458 if (!Target->hasLocalLinkage()) 2459 continue; 2460 2461 // The transform is only useful if the alias does not have internal linkage. 2462 if (J->hasLocalLinkage()) 2463 continue; 2464 2465 // Do not perform the transform if multiple aliases potentially target the 2466 // aliasee. This check also ensures that it is safe to replace the section 2467 // and other attributes of the aliasee with those of the alias. 2468 if (!hasOneUse) 2469 continue; 2470 2471 // Give the aliasee the name, linkage and other attributes of the alias. 2472 Target->takeName(J); 2473 Target->setLinkage(J->getLinkage()); 2474 Target->GlobalValue::copyAttributesFrom(J); 2475 2476 // Delete the alias. 2477 M.getAliasList().erase(J); 2478 ++NumAliasesRemoved; 2479 Changed = true; 2480 } 2481 2482 return Changed; 2483} 2484 2485bool GlobalOpt::runOnModule(Module &M) { 2486 bool Changed = false; 2487 2488 // Try to find the llvm.globalctors list. 2489 GlobalVariable *GlobalCtors = FindGlobalCtors(M); 2490 2491 bool LocalChange = true; 2492 while (LocalChange) { 2493 LocalChange = false; 2494 2495 // Delete functions that are trivially dead, ccc -> fastcc 2496 LocalChange |= OptimizeFunctions(M); 2497 2498 // Optimize global_ctors list. 2499 if (GlobalCtors) 2500 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors); 2501 2502 // Optimize non-address-taken globals. 2503 LocalChange |= OptimizeGlobalVars(M); 2504 2505 // Resolve aliases, when possible. 2506 LocalChange |= OptimizeGlobalAliases(M); 2507 Changed |= LocalChange; 2508 } 2509 2510 // TODO: Move all global ctors functions to the end of the module for code 2511 // layout. 2512 2513 return Changed; 2514} 2515