GlobalOpt.cpp revision 3be3ab75d6545698dc54d1197b8bd93ed4325add
1//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass transforms simple global variables that never have their address 11// taken. If obviously true, it marks read/write globals as constant, deletes 12// variables only stored to, etc. 13// 14//===----------------------------------------------------------------------===// 15 16#define DEBUG_TYPE "globalopt" 17#include "llvm/Transforms/IPO.h" 18#include "llvm/CallingConv.h" 19#include "llvm/Constants.h" 20#include "llvm/DerivedTypes.h" 21#include "llvm/Instructions.h" 22#include "llvm/IntrinsicInst.h" 23#include "llvm/Module.h" 24#include "llvm/Pass.h" 25#include "llvm/Analysis/ConstantFolding.h" 26#include "llvm/Analysis/MemoryBuiltins.h" 27#include "llvm/Target/TargetData.h" 28#include "llvm/Support/CallSite.h" 29#include "llvm/Support/Debug.h" 30#include "llvm/Support/ErrorHandling.h" 31#include "llvm/Support/GetElementPtrTypeIterator.h" 32#include "llvm/Support/MathExtras.h" 33#include "llvm/Support/raw_ostream.h" 34#include "llvm/ADT/DenseMap.h" 35#include "llvm/ADT/SmallPtrSet.h" 36#include "llvm/ADT/SmallVector.h" 37#include "llvm/ADT/Statistic.h" 38#include "llvm/ADT/STLExtras.h" 39#include <algorithm> 40using namespace llvm; 41 42STATISTIC(NumMarked , "Number of globals marked constant"); 43STATISTIC(NumSRA , "Number of aggregate globals broken into scalars"); 44STATISTIC(NumHeapSRA , "Number of heap objects SRA'd"); 45STATISTIC(NumSubstitute,"Number of globals with initializers stored into them"); 46STATISTIC(NumDeleted , "Number of globals deleted"); 47STATISTIC(NumFnDeleted , "Number of functions deleted"); 48STATISTIC(NumGlobUses , "Number of global uses devirtualized"); 49STATISTIC(NumLocalized , "Number of globals localized"); 50STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans"); 51STATISTIC(NumFastCallFns , "Number of functions converted to fastcc"); 52STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated"); 53STATISTIC(NumNestRemoved , "Number of nest attributes removed"); 54STATISTIC(NumAliasesResolved, "Number of global aliases resolved"); 55STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated"); 56 57namespace { 58 struct GlobalOpt : public ModulePass { 59 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 60 } 61 static char ID; // Pass identification, replacement for typeid 62 GlobalOpt() : ModulePass(&ID) {} 63 64 bool runOnModule(Module &M); 65 66 private: 67 GlobalVariable *FindGlobalCtors(Module &M); 68 bool OptimizeFunctions(Module &M); 69 bool OptimizeGlobalVars(Module &M); 70 bool OptimizeGlobalAliases(Module &M); 71 bool OptimizeGlobalCtorsList(GlobalVariable *&GCL); 72 bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI); 73 }; 74} 75 76char GlobalOpt::ID = 0; 77static RegisterPass<GlobalOpt> X("globalopt", "Global Variable Optimizer"); 78 79ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); } 80 81namespace { 82 83/// GlobalStatus - As we analyze each global, keep track of some information 84/// about it. If we find out that the address of the global is taken, none of 85/// this info will be accurate. 86struct GlobalStatus { 87 /// isLoaded - True if the global is ever loaded. If the global isn't ever 88 /// loaded it can be deleted. 89 bool isLoaded; 90 91 /// StoredType - Keep track of what stores to the global look like. 92 /// 93 enum StoredType { 94 /// NotStored - There is no store to this global. It can thus be marked 95 /// constant. 96 NotStored, 97 98 /// isInitializerStored - This global is stored to, but the only thing 99 /// stored is the constant it was initialized with. This is only tracked 100 /// for scalar globals. 101 isInitializerStored, 102 103 /// isStoredOnce - This global is stored to, but only its initializer and 104 /// one other value is ever stored to it. If this global isStoredOnce, we 105 /// track the value stored to it in StoredOnceValue below. This is only 106 /// tracked for scalar globals. 107 isStoredOnce, 108 109 /// isStored - This global is stored to by multiple values or something else 110 /// that we cannot track. 111 isStored 112 } StoredType; 113 114 /// StoredOnceValue - If only one value (besides the initializer constant) is 115 /// ever stored to this global, keep track of what value it is. 116 Value *StoredOnceValue; 117 118 /// AccessingFunction/HasMultipleAccessingFunctions - These start out 119 /// null/false. When the first accessing function is noticed, it is recorded. 120 /// When a second different accessing function is noticed, 121 /// HasMultipleAccessingFunctions is set to true. 122 const Function *AccessingFunction; 123 bool HasMultipleAccessingFunctions; 124 125 /// HasNonInstructionUser - Set to true if this global has a user that is not 126 /// an instruction (e.g. a constant expr or GV initializer). 127 bool HasNonInstructionUser; 128 129 /// HasPHIUser - Set to true if this global has a user that is a PHI node. 130 bool HasPHIUser; 131 132 GlobalStatus() : isLoaded(false), StoredType(NotStored), StoredOnceValue(0), 133 AccessingFunction(0), HasMultipleAccessingFunctions(false), 134 HasNonInstructionUser(false), HasPHIUser(false) {} 135}; 136 137} 138 139// SafeToDestroyConstant - It is safe to destroy a constant iff it is only used 140// by constants itself. Note that constants cannot be cyclic, so this test is 141// pretty easy to implement recursively. 142// 143static bool SafeToDestroyConstant(const Constant *C) { 144 if (isa<GlobalValue>(C)) return false; 145 146 for (Value::const_use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI) 147 if (const Constant *CU = dyn_cast<Constant>(*UI)) { 148 if (!SafeToDestroyConstant(CU)) return false; 149 } else 150 return false; 151 return true; 152} 153 154 155/// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus 156/// structure. If the global has its address taken, return true to indicate we 157/// can't do anything with it. 158/// 159static bool AnalyzeGlobal(const Value *V, GlobalStatus &GS, 160 SmallPtrSet<const PHINode*, 16> &PHIUsers) { 161 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) 162 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) { 163 GS.HasNonInstructionUser = true; 164 165 if (AnalyzeGlobal(CE, GS, PHIUsers)) return true; 166 167 } else if (const Instruction *I = dyn_cast<Instruction>(*UI)) { 168 if (!GS.HasMultipleAccessingFunctions) { 169 const Function *F = I->getParent()->getParent(); 170 if (GS.AccessingFunction == 0) 171 GS.AccessingFunction = F; 172 else if (GS.AccessingFunction != F) 173 GS.HasMultipleAccessingFunctions = true; 174 } 175 if (const LoadInst *LI = dyn_cast<LoadInst>(I)) { 176 GS.isLoaded = true; 177 if (LI->isVolatile()) return true; // Don't hack on volatile loads. 178 } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) { 179 // Don't allow a store OF the address, only stores TO the address. 180 if (SI->getOperand(0) == V) return true; 181 182 if (SI->isVolatile()) return true; // Don't hack on volatile stores. 183 184 // If this is a direct store to the global (i.e., the global is a scalar 185 // value, not an aggregate), keep more specific information about 186 // stores. 187 if (GS.StoredType != GlobalStatus::isStored) { 188 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(SI->getOperand(1))){ 189 Value *StoredVal = SI->getOperand(0); 190 if (StoredVal == GV->getInitializer()) { 191 if (GS.StoredType < GlobalStatus::isInitializerStored) 192 GS.StoredType = GlobalStatus::isInitializerStored; 193 } else if (isa<LoadInst>(StoredVal) && 194 cast<LoadInst>(StoredVal)->getOperand(0) == GV) { 195 if (GS.StoredType < GlobalStatus::isInitializerStored) 196 GS.StoredType = GlobalStatus::isInitializerStored; 197 } else if (GS.StoredType < GlobalStatus::isStoredOnce) { 198 GS.StoredType = GlobalStatus::isStoredOnce; 199 GS.StoredOnceValue = StoredVal; 200 } else if (GS.StoredType == GlobalStatus::isStoredOnce && 201 GS.StoredOnceValue == StoredVal) { 202 // noop. 203 } else { 204 GS.StoredType = GlobalStatus::isStored; 205 } 206 } else { 207 GS.StoredType = GlobalStatus::isStored; 208 } 209 } 210 } else if (isa<GetElementPtrInst>(I)) { 211 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 212 } else if (isa<SelectInst>(I)) { 213 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 214 } else if (const PHINode *PN = dyn_cast<PHINode>(I)) { 215 // PHI nodes we can check just like select or GEP instructions, but we 216 // have to be careful about infinite recursion. 217 if (PHIUsers.insert(PN)) // Not already visited. 218 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 219 GS.HasPHIUser = true; 220 } else if (isa<CmpInst>(I)) { 221 } else if (isa<MemTransferInst>(I)) { 222 if (I->getOperand(1) == V) 223 GS.StoredType = GlobalStatus::isStored; 224 if (I->getOperand(2) == V) 225 GS.isLoaded = true; 226 } else if (isa<MemSetInst>(I)) { 227 assert(I->getOperand(1) == V && "Memset only takes one pointer!"); 228 GS.StoredType = GlobalStatus::isStored; 229 } else { 230 return true; // Any other non-load instruction might take address! 231 } 232 } else if (const Constant *C = dyn_cast<Constant>(*UI)) { 233 GS.HasNonInstructionUser = true; 234 // We might have a dead and dangling constant hanging off of here. 235 if (!SafeToDestroyConstant(C)) 236 return true; 237 } else { 238 GS.HasNonInstructionUser = true; 239 // Otherwise must be some other user. 240 return true; 241 } 242 243 return false; 244} 245 246static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx) { 247 ConstantInt *CI = dyn_cast<ConstantInt>(Idx); 248 if (!CI) return 0; 249 unsigned IdxV = CI->getZExtValue(); 250 251 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) { 252 if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV); 253 } else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) { 254 if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV); 255 } else if (ConstantVector *CP = dyn_cast<ConstantVector>(Agg)) { 256 if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV); 257 } else if (isa<ConstantAggregateZero>(Agg)) { 258 if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) { 259 if (IdxV < STy->getNumElements()) 260 return Constant::getNullValue(STy->getElementType(IdxV)); 261 } else if (const SequentialType *STy = 262 dyn_cast<SequentialType>(Agg->getType())) { 263 return Constant::getNullValue(STy->getElementType()); 264 } 265 } else if (isa<UndefValue>(Agg)) { 266 if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) { 267 if (IdxV < STy->getNumElements()) 268 return UndefValue::get(STy->getElementType(IdxV)); 269 } else if (const SequentialType *STy = 270 dyn_cast<SequentialType>(Agg->getType())) { 271 return UndefValue::get(STy->getElementType()); 272 } 273 } 274 return 0; 275} 276 277 278/// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all 279/// users of the global, cleaning up the obvious ones. This is largely just a 280/// quick scan over the use list to clean up the easy and obvious cruft. This 281/// returns true if it made a change. 282static bool CleanupConstantGlobalUsers(Value *V, Constant *Init) { 283 bool Changed = false; 284 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) { 285 User *U = *UI++; 286 287 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 288 if (Init) { 289 // Replace the load with the initializer. 290 LI->replaceAllUsesWith(Init); 291 LI->eraseFromParent(); 292 Changed = true; 293 } 294 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 295 // Store must be unreachable or storing Init into the global. 296 SI->eraseFromParent(); 297 Changed = true; 298 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { 299 if (CE->getOpcode() == Instruction::GetElementPtr) { 300 Constant *SubInit = 0; 301 if (Init) 302 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); 303 Changed |= CleanupConstantGlobalUsers(CE, SubInit); 304 } else if (CE->getOpcode() == Instruction::BitCast && 305 CE->getType()->isPointerTy()) { 306 // Pointer cast, delete any stores and memsets to the global. 307 Changed |= CleanupConstantGlobalUsers(CE, 0); 308 } 309 310 if (CE->use_empty()) { 311 CE->destroyConstant(); 312 Changed = true; 313 } 314 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 315 // Do not transform "gepinst (gep constexpr (GV))" here, because forming 316 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold 317 // and will invalidate our notion of what Init is. 318 Constant *SubInit = 0; 319 if (!isa<ConstantExpr>(GEP->getOperand(0))) { 320 ConstantExpr *CE = 321 dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP)); 322 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr) 323 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); 324 } 325 Changed |= CleanupConstantGlobalUsers(GEP, SubInit); 326 327 if (GEP->use_empty()) { 328 GEP->eraseFromParent(); 329 Changed = true; 330 } 331 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv 332 if (MI->getRawDest() == V) { 333 MI->eraseFromParent(); 334 Changed = true; 335 } 336 337 } else if (Constant *C = dyn_cast<Constant>(U)) { 338 // If we have a chain of dead constantexprs or other things dangling from 339 // us, and if they are all dead, nuke them without remorse. 340 if (SafeToDestroyConstant(C)) { 341 C->destroyConstant(); 342 // This could have invalidated UI, start over from scratch. 343 CleanupConstantGlobalUsers(V, Init); 344 return true; 345 } 346 } 347 } 348 return Changed; 349} 350 351/// isSafeSROAElementUse - Return true if the specified instruction is a safe 352/// user of a derived expression from a global that we want to SROA. 353static bool isSafeSROAElementUse(Value *V) { 354 // We might have a dead and dangling constant hanging off of here. 355 if (Constant *C = dyn_cast<Constant>(V)) 356 return SafeToDestroyConstant(C); 357 358 Instruction *I = dyn_cast<Instruction>(V); 359 if (!I) return false; 360 361 // Loads are ok. 362 if (isa<LoadInst>(I)) return true; 363 364 // Stores *to* the pointer are ok. 365 if (StoreInst *SI = dyn_cast<StoreInst>(I)) 366 return SI->getOperand(0) != V; 367 368 // Otherwise, it must be a GEP. 369 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I); 370 if (GEPI == 0) return false; 371 372 if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) || 373 !cast<Constant>(GEPI->getOperand(1))->isNullValue()) 374 return false; 375 376 for (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end(); 377 I != E; ++I) 378 if (!isSafeSROAElementUse(*I)) 379 return false; 380 return true; 381} 382 383 384/// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value. 385/// Look at it and its uses and decide whether it is safe to SROA this global. 386/// 387static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) { 388 // The user of the global must be a GEP Inst or a ConstantExpr GEP. 389 if (!isa<GetElementPtrInst>(U) && 390 (!isa<ConstantExpr>(U) || 391 cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr)) 392 return false; 393 394 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we 395 // don't like < 3 operand CE's, and we don't like non-constant integer 396 // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some 397 // value of C. 398 if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) || 399 !cast<Constant>(U->getOperand(1))->isNullValue() || 400 !isa<ConstantInt>(U->getOperand(2))) 401 return false; 402 403 gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U); 404 ++GEPI; // Skip over the pointer index. 405 406 // If this is a use of an array allocation, do a bit more checking for sanity. 407 if (const ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) { 408 uint64_t NumElements = AT->getNumElements(); 409 ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2)); 410 411 // Check to make sure that index falls within the array. If not, 412 // something funny is going on, so we won't do the optimization. 413 // 414 if (Idx->getZExtValue() >= NumElements) 415 return false; 416 417 // We cannot scalar repl this level of the array unless any array 418 // sub-indices are in-range constants. In particular, consider: 419 // A[0][i]. We cannot know that the user isn't doing invalid things like 420 // allowing i to index an out-of-range subscript that accesses A[1]. 421 // 422 // Scalar replacing *just* the outer index of the array is probably not 423 // going to be a win anyway, so just give up. 424 for (++GEPI; // Skip array index. 425 GEPI != E; 426 ++GEPI) { 427 uint64_t NumElements; 428 if (const ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI)) 429 NumElements = SubArrayTy->getNumElements(); 430 else if (const VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI)) 431 NumElements = SubVectorTy->getNumElements(); 432 else { 433 assert((*GEPI)->isStructTy() && 434 "Indexed GEP type is not array, vector, or struct!"); 435 continue; 436 } 437 438 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand()); 439 if (!IdxVal || IdxVal->getZExtValue() >= NumElements) 440 return false; 441 } 442 } 443 444 for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I) 445 if (!isSafeSROAElementUse(*I)) 446 return false; 447 return true; 448} 449 450/// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it 451/// is safe for us to perform this transformation. 452/// 453static bool GlobalUsersSafeToSRA(GlobalValue *GV) { 454 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); 455 UI != E; ++UI) { 456 if (!IsUserOfGlobalSafeForSRA(*UI, GV)) 457 return false; 458 } 459 return true; 460} 461 462 463/// SRAGlobal - Perform scalar replacement of aggregates on the specified global 464/// variable. This opens the door for other optimizations by exposing the 465/// behavior of the program in a more fine-grained way. We have determined that 466/// this transformation is safe already. We return the first global variable we 467/// insert so that the caller can reprocess it. 468static GlobalVariable *SRAGlobal(GlobalVariable *GV, const TargetData &TD) { 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(STy->getContext()), i)); 491 assert(In && "Couldn't get element of initializer?"); 492 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false, 493 GlobalVariable::InternalLinkage, 494 In, GV->getName()+"."+Twine(i), 495 GV->isThreadLocal(), 496 GV->getType()->getAddressSpace()); 497 Globals.insert(GV, NGV); 498 NewGlobals.push_back(NGV); 499 500 // Calculate the known alignment of the field. If the original aggregate 501 // had 256 byte alignment for example, something might depend on that: 502 // propagate info to each field. 503 uint64_t FieldOffset = Layout.getElementOffset(i); 504 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset); 505 if (NewAlign > TD.getABITypeAlignment(STy->getElementType(i))) 506 NGV->setAlignment(NewAlign); 507 } 508 } else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) { 509 unsigned NumElements = 0; 510 if (const ArrayType *ATy = dyn_cast<ArrayType>(STy)) 511 NumElements = ATy->getNumElements(); 512 else 513 NumElements = cast<VectorType>(STy)->getNumElements(); 514 515 if (NumElements > 16 && GV->hasNUsesOrMore(16)) 516 return 0; // It's not worth it. 517 NewGlobals.reserve(NumElements); 518 519 uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType()); 520 unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType()); 521 for (unsigned i = 0, e = NumElements; i != e; ++i) { 522 Constant *In = getAggregateConstantElement(Init, 523 ConstantInt::get(Type::getInt32Ty(Init->getContext()), i)); 524 assert(In && "Couldn't get element of initializer?"); 525 526 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false, 527 GlobalVariable::InternalLinkage, 528 In, GV->getName()+"."+Twine(i), 529 GV->isThreadLocal(), 530 GV->getType()->getAddressSpace()); 531 Globals.insert(GV, NGV); 532 NewGlobals.push_back(NGV); 533 534 // Calculate the known alignment of the field. If the original aggregate 535 // had 256 byte alignment for example, something might depend on that: 536 // propagate info to each field. 537 unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i); 538 if (NewAlign > EltAlign) 539 NGV->setAlignment(NewAlign); 540 } 541 } 542 543 if (NewGlobals.empty()) 544 return 0; 545 546 DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV); 547 548 Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext())); 549 550 // Loop over all of the uses of the global, replacing the constantexpr geps, 551 // with smaller constantexpr geps or direct references. 552 while (!GV->use_empty()) { 553 User *GEP = GV->use_back(); 554 assert(((isa<ConstantExpr>(GEP) && 555 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)|| 556 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!"); 557 558 // Ignore the 1th operand, which has to be zero or else the program is quite 559 // broken (undefined). Get the 2nd operand, which is the structure or array 560 // index. 561 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 562 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access. 563 564 Value *NewPtr = NewGlobals[Val]; 565 566 // Form a shorter GEP if needed. 567 if (GEP->getNumOperands() > 3) { 568 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) { 569 SmallVector<Constant*, 8> Idxs; 570 Idxs.push_back(NullInt); 571 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i) 572 Idxs.push_back(CE->getOperand(i)); 573 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), 574 &Idxs[0], Idxs.size()); 575 } else { 576 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP); 577 SmallVector<Value*, 8> Idxs; 578 Idxs.push_back(NullInt); 579 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) 580 Idxs.push_back(GEPI->getOperand(i)); 581 NewPtr = GetElementPtrInst::Create(NewPtr, Idxs.begin(), Idxs.end(), 582 GEPI->getName()+"."+Twine(Val),GEPI); 583 } 584 } 585 GEP->replaceAllUsesWith(NewPtr); 586 587 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP)) 588 GEPI->eraseFromParent(); 589 else 590 cast<ConstantExpr>(GEP)->destroyConstant(); 591 } 592 593 // Delete the old global, now that it is dead. 594 Globals.erase(GV); 595 ++NumSRA; 596 597 // Loop over the new globals array deleting any globals that are obviously 598 // dead. This can arise due to scalarization of a structure or an array that 599 // has elements that are dead. 600 unsigned FirstGlobal = 0; 601 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i) 602 if (NewGlobals[i]->use_empty()) { 603 Globals.erase(NewGlobals[i]); 604 if (FirstGlobal == i) ++FirstGlobal; 605 } 606 607 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0; 608} 609 610/// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified 611/// value will trap if the value is dynamically null. PHIs keeps track of any 612/// phi nodes we've seen to avoid reprocessing them. 613static bool AllUsesOfValueWillTrapIfNull(Value *V, 614 SmallPtrSet<PHINode*, 8> &PHIs) { 615 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) 616 if (isa<LoadInst>(*UI)) { 617 // Will trap. 618 } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) { 619 if (SI->getOperand(0) == V) { 620 //cerr << "NONTRAPPING USE: " << **UI; 621 return false; // Storing the value. 622 } 623 } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) { 624 if (CI->getCalledValue() != V) { 625 //cerr << "NONTRAPPING USE: " << **UI; 626 return false; // Not calling the ptr 627 } 628 } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) { 629 if (II->getCalledValue() != V) { 630 //cerr << "NONTRAPPING USE: " << **UI; 631 return false; // Not calling the ptr 632 } 633 } else if (BitCastInst *CI = dyn_cast<BitCastInst>(*UI)) { 634 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false; 635 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) { 636 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false; 637 } else if (PHINode *PN = dyn_cast<PHINode>(*UI)) { 638 // If we've already seen this phi node, ignore it, it has already been 639 // checked. 640 if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs)) 641 return false; 642 } else if (isa<ICmpInst>(*UI) && 643 isa<ConstantPointerNull>(UI->getOperand(1))) { 644 // Ignore icmp X, null 645 } else { 646 //cerr << "NONTRAPPING USE: " << **UI; 647 return false; 648 } 649 return true; 650} 651 652/// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads 653/// from GV will trap if the loaded value is null. Note that this also permits 654/// comparisons of the loaded value against null, as a special case. 655static bool AllUsesOfLoadedValueWillTrapIfNull(GlobalVariable *GV) { 656 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI!=E; ++UI) 657 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 658 SmallPtrSet<PHINode*, 8> PHIs; 659 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs)) 660 return false; 661 } else if (isa<StoreInst>(*UI)) { 662 // Ignore stores to the global. 663 } else { 664 // We don't know or understand this user, bail out. 665 //cerr << "UNKNOWN USER OF GLOBAL!: " << **UI; 666 return false; 667 } 668 669 return true; 670} 671 672static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) { 673 bool Changed = false; 674 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) { 675 Instruction *I = cast<Instruction>(*UI++); 676 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 677 LI->setOperand(0, NewV); 678 Changed = true; 679 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 680 if (SI->getOperand(1) == V) { 681 SI->setOperand(1, NewV); 682 Changed = true; 683 } 684 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) { 685 CallSite CS(I); 686 if (CS.getCalledValue() == V) { 687 // Calling through the pointer! Turn into a direct call, but be careful 688 // that the pointer is not also being passed as an argument. 689 CS.setCalledFunction(NewV); 690 Changed = true; 691 bool PassedAsArg = false; 692 for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) 693 if (CS.getArgument(i) == V) { 694 PassedAsArg = true; 695 CS.setArgument(i, NewV); 696 } 697 698 if (PassedAsArg) { 699 // Being passed as an argument also. Be careful to not invalidate UI! 700 UI = V->use_begin(); 701 } 702 } 703 } else if (CastInst *CI = dyn_cast<CastInst>(I)) { 704 Changed |= OptimizeAwayTrappingUsesOfValue(CI, 705 ConstantExpr::getCast(CI->getOpcode(), 706 NewV, CI->getType())); 707 if (CI->use_empty()) { 708 Changed = true; 709 CI->eraseFromParent(); 710 } 711 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { 712 // Should handle GEP here. 713 SmallVector<Constant*, 8> Idxs; 714 Idxs.reserve(GEPI->getNumOperands()-1); 715 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end(); 716 i != e; ++i) 717 if (Constant *C = dyn_cast<Constant>(*i)) 718 Idxs.push_back(C); 719 else 720 break; 721 if (Idxs.size() == GEPI->getNumOperands()-1) 722 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI, 723 ConstantExpr::getGetElementPtr(NewV, &Idxs[0], 724 Idxs.size())); 725 if (GEPI->use_empty()) { 726 Changed = true; 727 GEPI->eraseFromParent(); 728 } 729 } 730 } 731 732 return Changed; 733} 734 735 736/// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null 737/// value stored into it. If there are uses of the loaded value that would trap 738/// if the loaded value is dynamically null, then we know that they cannot be 739/// reachable with a null optimize away the load. 740static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV) { 741 bool Changed = false; 742 743 // Keep track of whether we are able to remove all the uses of the global 744 // other than the store that defines it. 745 bool AllNonStoreUsesGone = true; 746 747 // Replace all uses of loads with uses of uses of the stored value. 748 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){ 749 User *GlobalUser = *GUI++; 750 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) { 751 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV); 752 // If we were able to delete all uses of the loads 753 if (LI->use_empty()) { 754 LI->eraseFromParent(); 755 Changed = true; 756 } else { 757 AllNonStoreUsesGone = false; 758 } 759 } else if (isa<StoreInst>(GlobalUser)) { 760 // Ignore the store that stores "LV" to the global. 761 assert(GlobalUser->getOperand(1) == GV && 762 "Must be storing *to* the global"); 763 } else { 764 AllNonStoreUsesGone = false; 765 766 // If we get here we could have other crazy uses that are transitively 767 // loaded. 768 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) || 769 isa<ConstantExpr>(GlobalUser)) && "Only expect load and stores!"); 770 } 771 } 772 773 if (Changed) { 774 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV); 775 ++NumGlobUses; 776 } 777 778 // If we nuked all of the loads, then none of the stores are needed either, 779 // nor is the global. 780 if (AllNonStoreUsesGone) { 781 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n"); 782 CleanupConstantGlobalUsers(GV, 0); 783 if (GV->use_empty()) { 784 GV->eraseFromParent(); 785 ++NumDeleted; 786 } 787 Changed = true; 788 } 789 return Changed; 790} 791 792/// ConstantPropUsersOf - Walk the use list of V, constant folding all of the 793/// instructions that are foldable. 794static void ConstantPropUsersOf(Value *V) { 795 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) 796 if (Instruction *I = dyn_cast<Instruction>(*UI++)) 797 if (Constant *NewC = ConstantFoldInstruction(I)) { 798 I->replaceAllUsesWith(NewC); 799 800 // Advance UI to the next non-I use to avoid invalidating it! 801 // Instructions could multiply use V. 802 while (UI != E && *UI == I) 803 ++UI; 804 I->eraseFromParent(); 805 } 806} 807 808/// OptimizeGlobalAddressOfMalloc - This function takes the specified global 809/// variable, and transforms the program as if it always contained the result of 810/// the specified malloc. Because it is always the result of the specified 811/// malloc, there is no reason to actually DO the malloc. Instead, turn the 812/// malloc into a global, and any loads of GV as uses of the new global. 813static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, 814 CallInst *CI, 815 const Type *AllocTy, 816 ConstantInt *NElements, 817 TargetData* TD) { 818 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n'); 819 820 const Type *GlobalType; 821 if (NElements->getZExtValue() == 1) 822 GlobalType = AllocTy; 823 else 824 // If we have an array allocation, the global variable is of an array. 825 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue()); 826 827 // Create the new global variable. The contents of the malloc'd memory is 828 // undefined, so initialize with an undef value. 829 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(), 830 GlobalType, false, 831 GlobalValue::InternalLinkage, 832 UndefValue::get(GlobalType), 833 GV->getName()+".body", 834 GV, 835 GV->isThreadLocal()); 836 837 // If there are bitcast users of the malloc (which is typical, usually we have 838 // a malloc + bitcast) then replace them with uses of the new global. Update 839 // other users to use the global as well. 840 BitCastInst *TheBC = 0; 841 while (!CI->use_empty()) { 842 Instruction *User = cast<Instruction>(CI->use_back()); 843 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { 844 if (BCI->getType() == NewGV->getType()) { 845 BCI->replaceAllUsesWith(NewGV); 846 BCI->eraseFromParent(); 847 } else { 848 BCI->setOperand(0, NewGV); 849 } 850 } else { 851 if (TheBC == 0) 852 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI); 853 User->replaceUsesOfWith(CI, TheBC); 854 } 855 } 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(Type::getInt1Ty(GV->getContext()), false, 866 GlobalValue::InternalLinkage, 867 ConstantInt::getFalse(GV->getContext()), 868 GV->getName()+".init", GV->isThreadLocal()); 869 bool InitBoolUsed = false; 870 871 // Loop over all uses of GV, processing them in turn. 872 while (!GV->use_empty()) { 873 if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) { 874 // The global is initialized when the store to it occurs. 875 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, SI); 876 SI->eraseFromParent(); 877 continue; 878 } 879 880 LoadInst *LI = cast<LoadInst>(GV->use_back()); 881 while (!LI->use_empty()) { 882 Use &LoadUse = LI->use_begin().getUse(); 883 if (!isa<ICmpInst>(LoadUse.getUser())) { 884 LoadUse = RepValue; 885 continue; 886 } 887 888 ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser()); 889 // Replace the cmp X, 0 with a use of the bool value. 890 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", ICI); 891 InitBoolUsed = true; 892 switch (ICI->getPredicate()) { 893 default: llvm_unreachable("Unknown ICmp Predicate!"); 894 case ICmpInst::ICMP_ULT: 895 case ICmpInst::ICMP_SLT: // X < null -> always false 896 LV = ConstantInt::getFalse(GV->getContext()); 897 break; 898 case ICmpInst::ICMP_ULE: 899 case ICmpInst::ICMP_SLE: 900 case ICmpInst::ICMP_EQ: 901 LV = BinaryOperator::CreateNot(LV, "notinit", ICI); 902 break; 903 case ICmpInst::ICMP_NE: 904 case ICmpInst::ICMP_UGE: 905 case ICmpInst::ICMP_SGE: 906 case ICmpInst::ICMP_UGT: 907 case ICmpInst::ICMP_SGT: 908 break; // no change. 909 } 910 ICI->replaceAllUsesWith(LV); 911 ICI->eraseFromParent(); 912 } 913 LI->eraseFromParent(); 914 } 915 916 // If the initialization boolean was used, insert it, otherwise delete it. 917 if (!InitBoolUsed) { 918 while (!InitBool->use_empty()) // Delete initializations 919 cast<StoreInst>(InitBool->use_back())->eraseFromParent(); 920 delete InitBool; 921 } else 922 GV->getParent()->getGlobalList().insert(GV, InitBool); 923 924 // Now the GV is dead, nuke it and the malloc.. 925 GV->eraseFromParent(); 926 CI->eraseFromParent(); 927 928 // To further other optimizations, loop over all users of NewGV and try to 929 // constant prop them. This will promote GEP instructions with constant 930 // indices into GEP constant-exprs, which will allow global-opt to hack on it. 931 ConstantPropUsersOf(NewGV); 932 if (RepValue != NewGV) 933 ConstantPropUsersOf(RepValue); 934 935 return NewGV; 936} 937 938/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking 939/// to make sure that there are no complex uses of V. We permit simple things 940/// like dereferencing the pointer, but not storing through the address, unless 941/// it is to the specified global. 942static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Instruction *V, 943 GlobalVariable *GV, 944 SmallPtrSet<PHINode*, 8> &PHIs) { 945 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 946 Instruction *Inst = cast<Instruction>(*UI); 947 948 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) { 949 continue; // Fine, ignore. 950 } 951 952 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 953 if (SI->getOperand(0) == V && SI->getOperand(1) != GV) 954 return false; // Storing the pointer itself... bad. 955 continue; // Otherwise, storing through it, or storing into GV... fine. 956 } 957 958 if (isa<GetElementPtrInst>(Inst)) { 959 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs)) 960 return false; 961 continue; 962 } 963 964 if (PHINode *PN = dyn_cast<PHINode>(Inst)) { 965 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI 966 // cycles. 967 if (PHIs.insert(PN)) 968 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs)) 969 return false; 970 continue; 971 } 972 973 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) { 974 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) 975 return false; 976 continue; 977 } 978 979 return false; 980 } 981 return true; 982} 983 984/// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV 985/// somewhere. Transform all uses of the allocation into loads from the 986/// global and uses of the resultant pointer. Further, delete the store into 987/// GV. This assumes that these value pass the 988/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate. 989static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, 990 GlobalVariable *GV) { 991 while (!Alloc->use_empty()) { 992 Instruction *U = cast<Instruction>(*Alloc->use_begin()); 993 Instruction *InsertPt = U; 994 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 995 // If this is the store of the allocation into the global, remove it. 996 if (SI->getOperand(1) == GV) { 997 SI->eraseFromParent(); 998 continue; 999 } 1000 } else if (PHINode *PN = dyn_cast<PHINode>(U)) { 1001 // Insert the load in the corresponding predecessor, not right before the 1002 // PHI. 1003 InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator(); 1004 } else if (isa<BitCastInst>(U)) { 1005 // Must be bitcast between the malloc and store to initialize the global. 1006 ReplaceUsesOfMallocWithGlobal(U, GV); 1007 U->eraseFromParent(); 1008 continue; 1009 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { 1010 // If this is a "GEP bitcast" and the user is a store to the global, then 1011 // just process it as a bitcast. 1012 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse()) 1013 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back())) 1014 if (SI->getOperand(1) == GV) { 1015 // Must be bitcast GEP between the malloc and store to initialize 1016 // the global. 1017 ReplaceUsesOfMallocWithGlobal(GEPI, GV); 1018 GEPI->eraseFromParent(); 1019 continue; 1020 } 1021 } 1022 1023 // Insert a load from the global, and use it instead of the malloc. 1024 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt); 1025 U->replaceUsesOfWith(Alloc, NL); 1026 } 1027} 1028 1029/// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi 1030/// of a load) are simple enough to perform heap SRA on. This permits GEP's 1031/// that index through the array and struct field, icmps of null, and PHIs. 1032static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V, 1033 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs, 1034 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIsPerLoad) { 1035 // We permit two users of the load: setcc comparing against the null 1036 // pointer, and a getelementptr of a specific form. 1037 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 1038 const Instruction *User = cast<Instruction>(*UI); 1039 1040 // Comparison against null is ok. 1041 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(User)) { 1042 if (!isa<ConstantPointerNull>(ICI->getOperand(1))) 1043 return false; 1044 continue; 1045 } 1046 1047 // getelementptr is also ok, but only a simple form. 1048 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1049 // Must index into the array and into the struct. 1050 if (GEPI->getNumOperands() < 3) 1051 return false; 1052 1053 // Otherwise the GEP is ok. 1054 continue; 1055 } 1056 1057 if (const PHINode *PN = dyn_cast<PHINode>(User)) { 1058 if (!LoadUsingPHIsPerLoad.insert(PN)) 1059 // This means some phi nodes are dependent on each other. 1060 // Avoid infinite looping! 1061 return false; 1062 if (!LoadUsingPHIs.insert(PN)) 1063 // If we have already analyzed this PHI, then it is safe. 1064 continue; 1065 1066 // Make sure all uses of the PHI are simple enough to transform. 1067 if (!LoadUsesSimpleEnoughForHeapSRA(PN, 1068 LoadUsingPHIs, LoadUsingPHIsPerLoad)) 1069 return false; 1070 1071 continue; 1072 } 1073 1074 // Otherwise we don't know what this is, not ok. 1075 return false; 1076 } 1077 1078 return true; 1079} 1080 1081 1082/// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from 1083/// GV are simple enough to perform HeapSRA, return true. 1084static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV, 1085 Instruction *StoredVal) { 1086 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs; 1087 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad; 1088 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E; 1089 ++UI) 1090 if (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 1091 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs, 1092 LoadUsingPHIsPerLoad)) 1093 return false; 1094 LoadUsingPHIsPerLoad.clear(); 1095 } 1096 1097 // If we reach here, we know that all uses of the loads and transitive uses 1098 // (through PHI nodes) are simple enough to transform. However, we don't know 1099 // that all inputs the to the PHI nodes are in the same equivalence sets. 1100 // Check to verify that all operands of the PHIs are either PHIS that can be 1101 // transformed, loads from GV, or MI itself. 1102 for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin(), 1103 E = LoadUsingPHIs.end(); I != E; ++I) { 1104 const PHINode *PN = *I; 1105 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) { 1106 Value *InVal = PN->getIncomingValue(op); 1107 1108 // PHI of the stored value itself is ok. 1109 if (InVal == StoredVal) continue; 1110 1111 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) { 1112 // One of the PHIs in our set is (optimistically) ok. 1113 if (LoadUsingPHIs.count(InPN)) 1114 continue; 1115 return false; 1116 } 1117 1118 // Load from GV is ok. 1119 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal)) 1120 if (LI->getOperand(0) == GV) 1121 continue; 1122 1123 // UNDEF? NULL? 1124 1125 // Anything else is rejected. 1126 return false; 1127 } 1128 } 1129 1130 return true; 1131} 1132 1133static Value *GetHeapSROAValue(Value *V, unsigned FieldNo, 1134 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1135 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 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), 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 // If this is a comparison against null, handle it. 1179 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) { 1180 assert(isa<ConstantPointerNull>(SCI->getOperand(1))); 1181 // If we have a setcc of the loaded pointer, we can use a setcc of any 1182 // field. 1183 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0, 1184 InsertedScalarizedValues, PHIsToRewrite); 1185 1186 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr, 1187 Constant::getNullValue(NPtr->getType()), 1188 SCI->getName()); 1189 SCI->replaceAllUsesWith(New); 1190 SCI->eraseFromParent(); 1191 return; 1192 } 1193 1194 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...' 1195 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) { 1196 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2)) 1197 && "Unexpected GEPI!"); 1198 1199 // Load the pointer for this field. 1200 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 1201 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo, 1202 InsertedScalarizedValues, PHIsToRewrite); 1203 1204 // Create the new GEP idx vector. 1205 SmallVector<Value*, 8> GEPIdx; 1206 GEPIdx.push_back(GEPI->getOperand(1)); 1207 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end()); 1208 1209 Value *NGEPI = GetElementPtrInst::Create(NewPtr, 1210 GEPIdx.begin(), GEPIdx.end(), 1211 GEPI->getName(), GEPI); 1212 GEPI->replaceAllUsesWith(NGEPI); 1213 GEPI->eraseFromParent(); 1214 return; 1215 } 1216 1217 // Recursively transform the users of PHI nodes. This will lazily create the 1218 // PHIs that are needed for individual elements. Keep track of what PHIs we 1219 // see in InsertedScalarizedValues so that we don't get infinite loops (very 1220 // antisocial). If the PHI is already in InsertedScalarizedValues, it has 1221 // already been seen first by another load, so its uses have already been 1222 // processed. 1223 PHINode *PN = cast<PHINode>(LoadUser); 1224 bool Inserted; 1225 DenseMap<Value*, std::vector<Value*> >::iterator InsertPos; 1226 tie(InsertPos, Inserted) = 1227 InsertedScalarizedValues.insert(std::make_pair(PN, std::vector<Value*>())); 1228 if (!Inserted) return; 1229 1230 // If this is the first time we've seen this PHI, recursively process all 1231 // users. 1232 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) { 1233 Instruction *User = cast<Instruction>(*UI++); 1234 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); 1235 } 1236} 1237 1238/// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr 1239/// is a value loaded from the global. Eliminate all uses of Ptr, making them 1240/// use FieldGlobals instead. All uses of loaded values satisfy 1241/// AllGlobalLoadUsesSimpleEnoughForHeapSRA. 1242static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load, 1243 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1244 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 1245 for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end(); 1246 UI != E; ) { 1247 Instruction *User = cast<Instruction>(*UI++); 1248 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); 1249 } 1250 1251 if (Load->use_empty()) { 1252 Load->eraseFromParent(); 1253 InsertedScalarizedValues.erase(Load); 1254 } 1255} 1256 1257/// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break 1258/// it up into multiple allocations of arrays of the fields. 1259static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI, 1260 Value* NElems, TargetData *TD) { 1261 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n'); 1262 const Type* MAT = getMallocAllocatedType(CI); 1263 const StructType *STy = cast<StructType>(MAT); 1264 1265 // There is guaranteed to be at least one use of the malloc (storing 1266 // it into GV). If there are other uses, change them to be uses of 1267 // the global to simplify later code. This also deletes the store 1268 // into GV. 1269 ReplaceUsesOfMallocWithGlobal(CI, GV); 1270 1271 // Okay, at this point, there are no users of the malloc. Insert N 1272 // new mallocs at the same place as CI, and N globals. 1273 std::vector<Value*> FieldGlobals; 1274 std::vector<Value*> FieldMallocs; 1275 1276 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ 1277 const Type *FieldTy = STy->getElementType(FieldNo); 1278 const PointerType *PFieldTy = PointerType::getUnqual(FieldTy); 1279 1280 GlobalVariable *NGV = 1281 new GlobalVariable(*GV->getParent(), 1282 PFieldTy, false, GlobalValue::InternalLinkage, 1283 Constant::getNullValue(PFieldTy), 1284 GV->getName() + ".f" + Twine(FieldNo), GV, 1285 GV->isThreadLocal()); 1286 FieldGlobals.push_back(NGV); 1287 1288 unsigned TypeSize = TD->getTypeAllocSize(FieldTy); 1289 if (const StructType *ST = dyn_cast<StructType>(FieldTy)) 1290 TypeSize = TD->getStructLayout(ST)->getSizeInBytes(); 1291 const Type *IntPtrTy = TD->getIntPtrType(CI->getContext()); 1292 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy, 1293 ConstantInt::get(IntPtrTy, TypeSize), 1294 NElems, 1295 CI->getName() + ".f" + Twine(FieldNo)); 1296 FieldMallocs.push_back(NMI); 1297 new StoreInst(NMI, NGV, CI); 1298 } 1299 1300 // The tricky aspect of this transformation is handling the case when malloc 1301 // fails. In the original code, malloc failing would set the result pointer 1302 // of malloc to null. In this case, some mallocs could succeed and others 1303 // could fail. As such, we emit code that looks like this: 1304 // F0 = malloc(field0) 1305 // F1 = malloc(field1) 1306 // F2 = malloc(field2) 1307 // if (F0 == 0 || F1 == 0 || F2 == 0) { 1308 // if (F0) { free(F0); F0 = 0; } 1309 // if (F1) { free(F1); F1 = 0; } 1310 // if (F2) { free(F2); F2 = 0; } 1311 // } 1312 // The malloc can also fail if its argument is too large. 1313 Constant *ConstantZero = ConstantInt::get(CI->getOperand(1)->getType(), 0); 1314 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getOperand(1), 1315 ConstantZero, "isneg"); 1316 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) { 1317 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i], 1318 Constant::getNullValue(FieldMallocs[i]->getType()), 1319 "isnull"); 1320 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI); 1321 } 1322 1323 // Split the basic block at the old malloc. 1324 BasicBlock *OrigBB = CI->getParent(); 1325 BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont"); 1326 1327 // Create the block to check the first condition. Put all these blocks at the 1328 // end of the function as they are unlikely to be executed. 1329 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(), 1330 "malloc_ret_null", 1331 OrigBB->getParent()); 1332 1333 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond 1334 // branch on RunningOr. 1335 OrigBB->getTerminator()->eraseFromParent(); 1336 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB); 1337 1338 // Within the NullPtrBlock, we need to emit a comparison and branch for each 1339 // pointer, because some may be null while others are not. 1340 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1341 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock); 1342 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal, 1343 Constant::getNullValue(GVVal->getType()), 1344 "tmp"); 1345 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it", 1346 OrigBB->getParent()); 1347 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next", 1348 OrigBB->getParent()); 1349 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock, 1350 Cmp, NullPtrBlock); 1351 1352 // Fill in FreeBlock. 1353 CallInst::CreateFree(GVVal, BI); 1354 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i], 1355 FreeBlock); 1356 BranchInst::Create(NextBlock, FreeBlock); 1357 1358 NullPtrBlock = NextBlock; 1359 } 1360 1361 BranchInst::Create(ContBB, NullPtrBlock); 1362 1363 // CI is no longer needed, remove it. 1364 CI->eraseFromParent(); 1365 1366 /// InsertedScalarizedLoads - As we process loads, if we can't immediately 1367 /// update all uses of the load, keep track of what scalarized loads are 1368 /// inserted for a given load. 1369 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues; 1370 InsertedScalarizedValues[GV] = FieldGlobals; 1371 1372 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite; 1373 1374 // Okay, the malloc site is completely handled. All of the uses of GV are now 1375 // loads, and all uses of those loads are simple. Rewrite them to use loads 1376 // of the per-field globals instead. 1377 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) { 1378 Instruction *User = cast<Instruction>(*UI++); 1379 1380 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1381 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite); 1382 continue; 1383 } 1384 1385 // Must be a store of null. 1386 StoreInst *SI = cast<StoreInst>(User); 1387 assert(isa<ConstantPointerNull>(SI->getOperand(0)) && 1388 "Unexpected heap-sra user!"); 1389 1390 // Insert a store of null into each global. 1391 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1392 const PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType()); 1393 Constant *Null = Constant::getNullValue(PT->getElementType()); 1394 new StoreInst(Null, FieldGlobals[i], SI); 1395 } 1396 // Erase the original store. 1397 SI->eraseFromParent(); 1398 } 1399 1400 // While we have PHIs that are interesting to rewrite, do it. 1401 while (!PHIsToRewrite.empty()) { 1402 PHINode *PN = PHIsToRewrite.back().first; 1403 unsigned FieldNo = PHIsToRewrite.back().second; 1404 PHIsToRewrite.pop_back(); 1405 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]); 1406 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi"); 1407 1408 // Add all the incoming values. This can materialize more phis. 1409 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1410 Value *InVal = PN->getIncomingValue(i); 1411 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues, 1412 PHIsToRewrite); 1413 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i)); 1414 } 1415 } 1416 1417 // Drop all inter-phi links and any loads that made it this far. 1418 for (DenseMap<Value*, std::vector<Value*> >::iterator 1419 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1420 I != E; ++I) { 1421 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1422 PN->dropAllReferences(); 1423 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1424 LI->dropAllReferences(); 1425 } 1426 1427 // Delete all the phis and loads now that inter-references are dead. 1428 for (DenseMap<Value*, std::vector<Value*> >::iterator 1429 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1430 I != E; ++I) { 1431 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1432 PN->eraseFromParent(); 1433 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1434 LI->eraseFromParent(); 1435 } 1436 1437 // The old global is now dead, remove it. 1438 GV->eraseFromParent(); 1439 1440 ++NumHeapSRA; 1441 return cast<GlobalVariable>(FieldGlobals[0]); 1442} 1443 1444/// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a 1445/// pointer global variable with a single value stored it that is a malloc or 1446/// cast of malloc. 1447static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, 1448 CallInst *CI, 1449 const Type *AllocTy, 1450 Module::global_iterator &GVI, 1451 TargetData *TD) { 1452 // If this is a malloc of an abstract type, don't touch it. 1453 if (!AllocTy->isSized()) 1454 return false; 1455 1456 // We can't optimize this global unless all uses of it are *known* to be 1457 // of the malloc value, not of the null initializer value (consider a use 1458 // that compares the global's value against zero to see if the malloc has 1459 // been reached). To do this, we check to see if all uses of the global 1460 // would trap if the global were null: this proves that they must all 1461 // happen after the malloc. 1462 if (!AllUsesOfLoadedValueWillTrapIfNull(GV)) 1463 return false; 1464 1465 // We can't optimize this if the malloc itself is used in a complex way, 1466 // for example, being stored into multiple globals. This allows the 1467 // malloc to be stored into the specified global, loaded setcc'd, and 1468 // GEP'd. These are all things we could transform to using the global 1469 // for. 1470 { 1471 SmallPtrSet<PHINode*, 8> PHIs; 1472 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs)) 1473 return false; 1474 } 1475 1476 // If we have a global that is only initialized with a fixed size malloc, 1477 // transform the program to use global memory instead of malloc'd memory. 1478 // This eliminates dynamic allocation, avoids an indirection accessing the 1479 // data, and exposes the resultant global to further GlobalOpt. 1480 // We cannot optimize the malloc if we cannot determine malloc array size. 1481 if (Value *NElems = getMallocArraySize(CI, TD, true)) { 1482 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems)) 1483 // Restrict this transformation to only working on small allocations 1484 // (2048 bytes currently), as we don't want to introduce a 16M global or 1485 // something. 1486 if (TD && 1487 NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) { 1488 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD); 1489 return true; 1490 } 1491 1492 // If the allocation is an array of structures, consider transforming this 1493 // into multiple malloc'd arrays, one for each field. This is basically 1494 // SRoA for malloc'd memory. 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 (NElems == ConstantInt::get(CI->getOperand(1)->getType(), 1)) 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, CI)) { 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 = 1511 dyn_cast<ArrayType>(getMallocAllocatedType(CI))) { 1512 const Type *IntPtrTy = TD->getIntPtrType(CI->getContext()); 1513 unsigned TypeSize = TD->getStructLayout(AllocSTy)->getSizeInBytes(); 1514 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize); 1515 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements()); 1516 Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy, 1517 AllocSize, NumElements, 1518 CI->getName()); 1519 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI); 1520 CI->replaceAllUsesWith(Cast); 1521 CI->eraseFromParent(); 1522 CI = dyn_cast<BitCastInst>(Malloc) ? 1523 extractMallocCallFromBitCast(Malloc) : cast<CallInst>(Malloc); 1524 } 1525 1526 GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, true),TD); 1527 return true; 1528 } 1529 } 1530 } 1531 1532 return false; 1533} 1534 1535// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge 1536// that only one value (besides its initializer) is ever stored to the global. 1537static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal, 1538 Module::global_iterator &GVI, 1539 TargetData *TD) { 1540 // Ignore no-op GEPs and bitcasts. 1541 StoredOnceVal = StoredOnceVal->stripPointerCasts(); 1542 1543 // If we are dealing with a pointer global that is initialized to null and 1544 // only has one (non-null) value stored into it, then we can optimize any 1545 // users of the loaded value (often calls and loads) that would trap if the 1546 // value was null. 1547 if (GV->getInitializer()->getType()->isPointerTy() && 1548 GV->getInitializer()->isNullValue()) { 1549 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { 1550 if (GV->getInitializer()->getType() != SOVC->getType()) 1551 SOVC = 1552 ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType()); 1553 1554 // Optimize away any trapping uses of the loaded value. 1555 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC)) 1556 return true; 1557 } else if (CallInst *CI = extractMallocCall(StoredOnceVal)) { 1558 const Type* MallocType = getMallocAllocatedType(CI); 1559 if (MallocType && TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, 1560 GVI, TD)) 1561 return true; 1562 } 1563 } 1564 1565 return false; 1566} 1567 1568/// TryToShrinkGlobalToBoolean - At this point, we have learned that the only 1569/// two values ever stored into GV are its initializer and OtherVal. See if we 1570/// can shrink the global into a boolean and select between the two values 1571/// whenever it is used. This exposes the values to other scalar optimizations. 1572static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) { 1573 const Type *GVElType = GV->getType()->getElementType(); 1574 1575 // If GVElType is already i1, it is already shrunk. If the type of the GV is 1576 // an FP value, pointer or vector, don't do this optimization because a select 1577 // between them is very expensive and unlikely to lead to later 1578 // simplification. In these cases, we typically end up with "cond ? v1 : v2" 1579 // where v1 and v2 both require constant pool loads, a big loss. 1580 if (GVElType == Type::getInt1Ty(GV->getContext()) || 1581 GVElType->isFloatingPointTy() || 1582 GVElType->isPointerTy() || GVElType->isVectorTy()) 1583 return false; 1584 1585 // Walk the use list of the global seeing if all the uses are load or store. 1586 // If there is anything else, bail out. 1587 for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I) 1588 if (!isa<LoadInst>(I) && !isa<StoreInst>(I)) 1589 return false; 1590 1591 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV); 1592 1593 // Create the new global, initializing it to false. 1594 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()), 1595 false, 1596 GlobalValue::InternalLinkage, 1597 ConstantInt::getFalse(GV->getContext()), 1598 GV->getName()+".b", 1599 GV->isThreadLocal()); 1600 GV->getParent()->getGlobalList().insert(GV, NewGV); 1601 1602 Constant *InitVal = GV->getInitializer(); 1603 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) && 1604 "No reason to shrink to bool!"); 1605 1606 // If initialized to zero and storing one into the global, we can use a cast 1607 // instead of a select to synthesize the desired value. 1608 bool IsOneZero = false; 1609 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) 1610 IsOneZero = InitVal->isNullValue() && CI->isOne(); 1611 1612 while (!GV->use_empty()) { 1613 Instruction *UI = cast<Instruction>(GV->use_back()); 1614 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { 1615 // Change the store into a boolean store. 1616 bool StoringOther = SI->getOperand(0) == OtherVal; 1617 // Only do this if we weren't storing a loaded value. 1618 Value *StoreVal; 1619 if (StoringOther || SI->getOperand(0) == InitVal) 1620 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()), 1621 StoringOther); 1622 else { 1623 // Otherwise, we are storing a previously loaded copy. To do this, 1624 // change the copy from copying the original value to just copying the 1625 // bool. 1626 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); 1627 1628 // If we're already replaced the input, StoredVal will be a cast or 1629 // select instruction. If not, it will be a load of the original 1630 // global. 1631 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { 1632 assert(LI->getOperand(0) == GV && "Not a copy!"); 1633 // Insert a new load, to preserve the saved value. 1634 StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI); 1635 } else { 1636 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && 1637 "This is not a form that we understand!"); 1638 StoreVal = StoredVal->getOperand(0); 1639 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); 1640 } 1641 } 1642 new StoreInst(StoreVal, NewGV, SI); 1643 } else { 1644 // Change the load into a load of bool then a select. 1645 LoadInst *LI = cast<LoadInst>(UI); 1646 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", LI); 1647 Value *NSI; 1648 if (IsOneZero) 1649 NSI = new ZExtInst(NLI, LI->getType(), "", LI); 1650 else 1651 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI); 1652 NSI->takeName(LI); 1653 LI->replaceAllUsesWith(NSI); 1654 } 1655 UI->eraseFromParent(); 1656 } 1657 1658 GV->eraseFromParent(); 1659 return true; 1660} 1661 1662 1663/// ProcessInternalGlobal - Analyze the specified global variable and optimize 1664/// it if possible. If we make a change, return true. 1665bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV, 1666 Module::global_iterator &GVI) { 1667 SmallPtrSet<const PHINode*, 16> PHIUsers; 1668 GlobalStatus GS; 1669 GV->removeDeadConstantUsers(); 1670 1671 if (GV->use_empty()) { 1672 DEBUG(dbgs() << "GLOBAL DEAD: " << *GV); 1673 GV->eraseFromParent(); 1674 ++NumDeleted; 1675 return true; 1676 } 1677 1678 if (!AnalyzeGlobal(GV, GS, PHIUsers)) { 1679#if 0 1680 DEBUG(dbgs() << "Global: " << *GV); 1681 DEBUG(dbgs() << " isLoaded = " << GS.isLoaded << "\n"); 1682 DEBUG(dbgs() << " StoredType = "); 1683 switch (GS.StoredType) { 1684 case GlobalStatus::NotStored: DEBUG(dbgs() << "NEVER STORED\n"); break; 1685 case GlobalStatus::isInitializerStored: DEBUG(dbgs() << "INIT STORED\n"); 1686 break; 1687 case GlobalStatus::isStoredOnce: DEBUG(dbgs() << "STORED ONCE\n"); break; 1688 case GlobalStatus::isStored: DEBUG(dbgs() << "stored\n"); break; 1689 } 1690 if (GS.StoredType == GlobalStatus::isStoredOnce && GS.StoredOnceValue) 1691 DEBUG(dbgs() << " StoredOnceValue = " << *GS.StoredOnceValue << "\n"); 1692 if (GS.AccessingFunction && !GS.HasMultipleAccessingFunctions) 1693 DEBUG(dbgs() << " AccessingFunction = " << GS.AccessingFunction->getName() 1694 << "\n"); 1695 DEBUG(dbgs() << " HasMultipleAccessingFunctions = " 1696 << GS.HasMultipleAccessingFunctions << "\n"); 1697 DEBUG(dbgs() << " HasNonInstructionUser = " 1698 << GS.HasNonInstructionUser<<"\n"); 1699 DEBUG(dbgs() << "\n"); 1700#endif 1701 1702 // If this is a first class global and has only one accessing function 1703 // and this function is main (which we know is not recursive we can make 1704 // this global a local variable) we replace the global with a local alloca 1705 // in this function. 1706 // 1707 // NOTE: It doesn't make sense to promote non single-value types since we 1708 // are just replacing static memory to stack memory. 1709 // 1710 // If the global is in different address space, don't bring it to stack. 1711 if (!GS.HasMultipleAccessingFunctions && 1712 GS.AccessingFunction && !GS.HasNonInstructionUser && 1713 GV->getType()->getElementType()->isSingleValueType() && 1714 GS.AccessingFunction->getName() == "main" && 1715 GS.AccessingFunction->hasExternalLinkage() && 1716 GV->getType()->getAddressSpace() == 0) { 1717 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV); 1718 Instruction& FirstI = const_cast<Instruction&>(*GS.AccessingFunction 1719 ->getEntryBlock().begin()); 1720 const Type* ElemTy = GV->getType()->getElementType(); 1721 // FIXME: Pass Global's alignment when globals have alignment 1722 AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), &FirstI); 1723 if (!isa<UndefValue>(GV->getInitializer())) 1724 new StoreInst(GV->getInitializer(), Alloca, &FirstI); 1725 1726 GV->replaceAllUsesWith(Alloca); 1727 GV->eraseFromParent(); 1728 ++NumLocalized; 1729 return true; 1730 } 1731 1732 // If the global is never loaded (but may be stored to), it is dead. 1733 // Delete it now. 1734 if (!GS.isLoaded) { 1735 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV); 1736 1737 // Delete any stores we can find to the global. We may not be able to 1738 // make it completely dead though. 1739 bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1740 1741 // If the global is dead now, delete it. 1742 if (GV->use_empty()) { 1743 GV->eraseFromParent(); 1744 ++NumDeleted; 1745 Changed = true; 1746 } 1747 return Changed; 1748 1749 } else if (GS.StoredType <= GlobalStatus::isInitializerStored) { 1750 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV); 1751 GV->setConstant(true); 1752 1753 // Clean up any obviously simplifiable users now. 1754 CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1755 1756 // If the global is dead now, just nuke it. 1757 if (GV->use_empty()) { 1758 DEBUG(dbgs() << " *** Marking constant allowed us to simplify " 1759 << "all users and delete global!\n"); 1760 GV->eraseFromParent(); 1761 ++NumDeleted; 1762 } 1763 1764 ++NumMarked; 1765 return true; 1766 } else if (!GV->getInitializer()->getType()->isSingleValueType()) { 1767 if (TargetData *TD = getAnalysisIfAvailable<TargetData>()) 1768 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) { 1769 GVI = FirstNewGV; // Don't skip the newly produced globals! 1770 return true; 1771 } 1772 } else if (GS.StoredType == GlobalStatus::isStoredOnce) { 1773 // If the initial value for the global was an undef value, and if only 1774 // one other value was stored into it, we can just change the 1775 // initializer to be the stored value, then delete all stores to the 1776 // global. This allows us to mark it constant. 1777 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1778 if (isa<UndefValue>(GV->getInitializer())) { 1779 // Change the initial value here. 1780 GV->setInitializer(SOVConstant); 1781 1782 // Clean up any obviously simplifiable users now. 1783 CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1784 1785 if (GV->use_empty()) { 1786 DEBUG(dbgs() << " *** Substituting initializer allowed us to " 1787 << "simplify all users and delete global!\n"); 1788 GV->eraseFromParent(); 1789 ++NumDeleted; 1790 } else { 1791 GVI = GV; 1792 } 1793 ++NumSubstitute; 1794 return true; 1795 } 1796 1797 // Try to optimize globals based on the knowledge that only one value 1798 // (besides its initializer) is ever stored to the global. 1799 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI, 1800 getAnalysisIfAvailable<TargetData>())) 1801 return true; 1802 1803 // Otherwise, if the global was not a boolean, we can shrink it to be a 1804 // boolean. 1805 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1806 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) { 1807 ++NumShrunkToBool; 1808 return true; 1809 } 1810 } 1811 } 1812 return false; 1813} 1814 1815/// ChangeCalleesToFastCall - Walk all of the direct calls of the specified 1816/// function, changing them to FastCC. 1817static void ChangeCalleesToFastCall(Function *F) { 1818 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1819 CallSite User(cast<Instruction>(*UI)); 1820 User.setCallingConv(CallingConv::Fast); 1821 } 1822} 1823 1824static AttrListPtr StripNest(const AttrListPtr &Attrs) { 1825 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) { 1826 if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0) 1827 continue; 1828 1829 // There can be only one. 1830 return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest); 1831 } 1832 1833 return Attrs; 1834} 1835 1836static void RemoveNestAttribute(Function *F) { 1837 F->setAttributes(StripNest(F->getAttributes())); 1838 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1839 CallSite User(cast<Instruction>(*UI)); 1840 User.setAttributes(StripNest(User.getAttributes())); 1841 } 1842} 1843 1844bool GlobalOpt::OptimizeFunctions(Module &M) { 1845 bool Changed = false; 1846 // Optimize functions. 1847 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { 1848 Function *F = FI++; 1849 // Functions without names cannot be referenced outside this module. 1850 if (!F->hasName() && !F->isDeclaration()) 1851 F->setLinkage(GlobalValue::InternalLinkage); 1852 F->removeDeadConstantUsers(); 1853 if (F->use_empty() && (F->hasLocalLinkage() || F->hasLinkOnceLinkage())) { 1854 F->eraseFromParent(); 1855 Changed = true; 1856 ++NumFnDeleted; 1857 } else if (F->hasLocalLinkage()) { 1858 if (F->getCallingConv() == CallingConv::C && !F->isVarArg() && 1859 !F->hasAddressTaken()) { 1860 // If this function has C calling conventions, is not a varargs 1861 // function, and is only called directly, promote it to use the Fast 1862 // calling convention. 1863 F->setCallingConv(CallingConv::Fast); 1864 ChangeCalleesToFastCall(F); 1865 ++NumFastCallFns; 1866 Changed = true; 1867 } 1868 1869 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) && 1870 !F->hasAddressTaken()) { 1871 // The function is not used by a trampoline intrinsic, so it is safe 1872 // to remove the 'nest' attribute. 1873 RemoveNestAttribute(F); 1874 ++NumNestRemoved; 1875 Changed = true; 1876 } 1877 } 1878 } 1879 return Changed; 1880} 1881 1882bool GlobalOpt::OptimizeGlobalVars(Module &M) { 1883 bool Changed = false; 1884 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); 1885 GVI != E; ) { 1886 GlobalVariable *GV = GVI++; 1887 // Global variables without names cannot be referenced outside this module. 1888 if (!GV->hasName() && !GV->isDeclaration()) 1889 GV->setLinkage(GlobalValue::InternalLinkage); 1890 // Simplify the initializer. 1891 if (GV->hasInitializer()) 1892 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) { 1893 TargetData *TD = getAnalysisIfAvailable<TargetData>(); 1894 Constant *New = ConstantFoldConstantExpression(CE, TD); 1895 if (New && New != CE) 1896 GV->setInitializer(New); 1897 } 1898 // Do more involved optimizations if the global is internal. 1899 if (!GV->isConstant() && GV->hasLocalLinkage() && 1900 GV->hasInitializer()) 1901 Changed |= ProcessInternalGlobal(GV, GVI); 1902 } 1903 return Changed; 1904} 1905 1906/// FindGlobalCtors - Find the llvm.globalctors list, verifying that all 1907/// initializers have an init priority of 65535. 1908GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) { 1909 for (Module::global_iterator I = M.global_begin(), E = M.global_end(); 1910 I != E; ++I) 1911 if (I->getName() == "llvm.global_ctors") { 1912 // Found it, verify it's an array of { int, void()* }. 1913 const ArrayType *ATy =dyn_cast<ArrayType>(I->getType()->getElementType()); 1914 if (!ATy) return 0; 1915 const StructType *STy = dyn_cast<StructType>(ATy->getElementType()); 1916 if (!STy || STy->getNumElements() != 2 || 1917 !STy->getElementType(0)->isIntegerTy(32)) return 0; 1918 const PointerType *PFTy = dyn_cast<PointerType>(STy->getElementType(1)); 1919 if (!PFTy) return 0; 1920 const FunctionType *FTy = dyn_cast<FunctionType>(PFTy->getElementType()); 1921 if (!FTy || !FTy->getReturnType()->isVoidTy() || 1922 FTy->isVarArg() || FTy->getNumParams() != 0) 1923 return 0; 1924 1925 // Verify that the initializer is simple enough for us to handle. 1926 if (!I->hasDefinitiveInitializer()) return 0; 1927 ConstantArray *CA = dyn_cast<ConstantArray>(I->getInitializer()); 1928 if (!CA) return 0; 1929 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 1930 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(*i)) { 1931 if (isa<ConstantPointerNull>(CS->getOperand(1))) 1932 continue; 1933 1934 // Must have a function or null ptr. 1935 if (!isa<Function>(CS->getOperand(1))) 1936 return 0; 1937 1938 // Init priority must be standard. 1939 ConstantInt *CI = dyn_cast<ConstantInt>(CS->getOperand(0)); 1940 if (!CI || CI->getZExtValue() != 65535) 1941 return 0; 1942 } else { 1943 return 0; 1944 } 1945 1946 return I; 1947 } 1948 return 0; 1949} 1950 1951/// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand, 1952/// return a list of the functions and null terminator as a vector. 1953static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) { 1954 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer()); 1955 std::vector<Function*> Result; 1956 Result.reserve(CA->getNumOperands()); 1957 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) { 1958 ConstantStruct *CS = cast<ConstantStruct>(*i); 1959 Result.push_back(dyn_cast<Function>(CS->getOperand(1))); 1960 } 1961 return Result; 1962} 1963 1964/// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the 1965/// specified array, returning the new global to use. 1966static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL, 1967 const std::vector<Function*> &Ctors) { 1968 // If we made a change, reassemble the initializer list. 1969 std::vector<Constant*> CSVals; 1970 CSVals.push_back(ConstantInt::get(Type::getInt32Ty(GCL->getContext()),65535)); 1971 CSVals.push_back(0); 1972 1973 // Create the new init list. 1974 std::vector<Constant*> CAList; 1975 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) { 1976 if (Ctors[i]) { 1977 CSVals[1] = Ctors[i]; 1978 } else { 1979 const Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()), 1980 false); 1981 const PointerType *PFTy = PointerType::getUnqual(FTy); 1982 CSVals[1] = Constant::getNullValue(PFTy); 1983 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 1984 2147483647); 1985 } 1986 CAList.push_back(ConstantStruct::get(GCL->getContext(), CSVals, false)); 1987 } 1988 1989 // Create the array initializer. 1990 const Type *StructTy = 1991 cast<ArrayType>(GCL->getType()->getElementType())->getElementType(); 1992 Constant *CA = ConstantArray::get(ArrayType::get(StructTy, 1993 CAList.size()), CAList); 1994 1995 // If we didn't change the number of elements, don't create a new GV. 1996 if (CA->getType() == GCL->getInitializer()->getType()) { 1997 GCL->setInitializer(CA); 1998 return GCL; 1999 } 2000 2001 // Create the new global and insert it next to the existing list. 2002 GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(), 2003 GCL->getLinkage(), CA, "", 2004 GCL->isThreadLocal()); 2005 GCL->getParent()->getGlobalList().insert(GCL, NGV); 2006 NGV->takeName(GCL); 2007 2008 // Nuke the old list, replacing any uses with the new one. 2009 if (!GCL->use_empty()) { 2010 Constant *V = NGV; 2011 if (V->getType() != GCL->getType()) 2012 V = ConstantExpr::getBitCast(V, GCL->getType()); 2013 GCL->replaceAllUsesWith(V); 2014 } 2015 GCL->eraseFromParent(); 2016 2017 if (Ctors.size()) 2018 return NGV; 2019 else 2020 return 0; 2021} 2022 2023 2024static Constant *getVal(DenseMap<Value*, Constant*> &ComputedValues, 2025 Value *V) { 2026 if (Constant *CV = dyn_cast<Constant>(V)) return CV; 2027 Constant *R = ComputedValues[V]; 2028 assert(R && "Reference to an uncomputed value!"); 2029 return R; 2030} 2031 2032/// isSimpleEnoughPointerToCommit - Return true if this constant is simple 2033/// enough for us to understand. In particular, if it is a cast of something, 2034/// we punt. We basically just support direct accesses to globals and GEP's of 2035/// globals. This should be kept up to date with CommitValueTo. 2036static bool isSimpleEnoughPointerToCommit(Constant *C) { 2037 // Conservatively, avoid aggregate types. This is because we don't 2038 // want to worry about them partially overlapping other stores. 2039 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType()) 2040 return false; 2041 2042 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) 2043 // Do not allow weak/linkonce/dllimport/dllexport linkage or 2044 // external globals. 2045 return GV->hasDefinitiveInitializer(); 2046 2047 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 2048 // Handle a constantexpr gep. 2049 if (CE->getOpcode() == Instruction::GetElementPtr && 2050 isa<GlobalVariable>(CE->getOperand(0)) && 2051 cast<GEPOperator>(CE)->isInBounds()) { 2052 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2053 // Do not allow weak/linkonce/dllimport/dllexport linkage or 2054 // external globals. 2055 if (!GV->hasDefinitiveInitializer()) 2056 return false; 2057 2058 // The first index must be zero. 2059 ConstantInt *CI = dyn_cast<ConstantInt>(*next(CE->op_begin())); 2060 if (!CI || !CI->isZero()) return false; 2061 2062 // The remaining indices must be compile-time known integers within the 2063 // notional bounds of the corresponding static array types. 2064 if (!CE->isGEPWithNoNotionalOverIndexing()) 2065 return false; 2066 2067 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2068 } 2069 return false; 2070} 2071 2072/// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global 2073/// initializer. This returns 'Init' modified to reflect 'Val' stored into it. 2074/// At this point, the GEP operands of Addr [0, OpNo) have been stepped into. 2075static Constant *EvaluateStoreInto(Constant *Init, Constant *Val, 2076 ConstantExpr *Addr, unsigned OpNo) { 2077 // Base case of the recursion. 2078 if (OpNo == Addr->getNumOperands()) { 2079 assert(Val->getType() == Init->getType() && "Type mismatch!"); 2080 return Val; 2081 } 2082 2083 std::vector<Constant*> Elts; 2084 if (const StructType *STy = dyn_cast<StructType>(Init->getType())) { 2085 2086 // Break up the constant into its elements. 2087 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) { 2088 for (User::op_iterator i = CS->op_begin(), e = CS->op_end(); i != e; ++i) 2089 Elts.push_back(cast<Constant>(*i)); 2090 } else if (isa<ConstantAggregateZero>(Init)) { 2091 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2092 Elts.push_back(Constant::getNullValue(STy->getElementType(i))); 2093 } else if (isa<UndefValue>(Init)) { 2094 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2095 Elts.push_back(UndefValue::get(STy->getElementType(i))); 2096 } else { 2097 llvm_unreachable("This code is out of sync with " 2098 " ConstantFoldLoadThroughGEPConstantExpr"); 2099 } 2100 2101 // Replace the element that we are supposed to. 2102 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo)); 2103 unsigned Idx = CU->getZExtValue(); 2104 assert(Idx < STy->getNumElements() && "Struct index out of range!"); 2105 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1); 2106 2107 // Return the modified struct. 2108 return ConstantStruct::get(Init->getContext(), &Elts[0], Elts.size(), 2109 STy->isPacked()); 2110 } else { 2111 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo)); 2112 const SequentialType *InitTy = cast<SequentialType>(Init->getType()); 2113 2114 uint64_t NumElts; 2115 if (const ArrayType *ATy = dyn_cast<ArrayType>(InitTy)) 2116 NumElts = ATy->getNumElements(); 2117 else 2118 NumElts = cast<VectorType>(InitTy)->getNumElements(); 2119 2120 2121 // Break up the array into elements. 2122 if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) { 2123 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 2124 Elts.push_back(cast<Constant>(*i)); 2125 } else if (ConstantVector *CV = dyn_cast<ConstantVector>(Init)) { 2126 for (User::op_iterator i = CV->op_begin(), e = CV->op_end(); i != e; ++i) 2127 Elts.push_back(cast<Constant>(*i)); 2128 } else if (isa<ConstantAggregateZero>(Init)) { 2129 Elts.assign(NumElts, Constant::getNullValue(InitTy->getElementType())); 2130 } else { 2131 assert(isa<UndefValue>(Init) && "This code is out of sync with " 2132 " ConstantFoldLoadThroughGEPConstantExpr"); 2133 Elts.assign(NumElts, UndefValue::get(InitTy->getElementType())); 2134 } 2135 2136 assert(CI->getZExtValue() < NumElts); 2137 Elts[CI->getZExtValue()] = 2138 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1); 2139 2140 if (Init->getType()->isArrayTy()) 2141 return ConstantArray::get(cast<ArrayType>(InitTy), Elts); 2142 else 2143 return ConstantVector::get(&Elts[0], Elts.size()); 2144 } 2145} 2146 2147/// CommitValueTo - We have decided that Addr (which satisfies the predicate 2148/// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen. 2149static void CommitValueTo(Constant *Val, Constant *Addr) { 2150 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) { 2151 assert(GV->hasInitializer()); 2152 GV->setInitializer(Val); 2153 return; 2154 } 2155 2156 ConstantExpr *CE = cast<ConstantExpr>(Addr); 2157 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2158 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2)); 2159} 2160 2161/// ComputeLoadResult - Return the value that would be computed by a load from 2162/// P after the stores reflected by 'memory' have been performed. If we can't 2163/// decide, return null. 2164static Constant *ComputeLoadResult(Constant *P, 2165 const DenseMap<Constant*, Constant*> &Memory) { 2166 // If this memory location has been recently stored, use the stored value: it 2167 // is the most up-to-date. 2168 DenseMap<Constant*, Constant*>::const_iterator I = Memory.find(P); 2169 if (I != Memory.end()) return I->second; 2170 2171 // Access it. 2172 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) { 2173 if (GV->hasDefinitiveInitializer()) 2174 return GV->getInitializer(); 2175 return 0; 2176 } 2177 2178 // Handle a constantexpr getelementptr. 2179 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) 2180 if (CE->getOpcode() == Instruction::GetElementPtr && 2181 isa<GlobalVariable>(CE->getOperand(0))) { 2182 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2183 if (GV->hasDefinitiveInitializer()) 2184 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2185 } 2186 2187 return 0; // don't know how to evaluate. 2188} 2189 2190/// EvaluateFunction - Evaluate a call to function F, returning true if 2191/// successful, false if we can't evaluate it. ActualArgs contains the formal 2192/// arguments for the function. 2193static bool EvaluateFunction(Function *F, Constant *&RetVal, 2194 const SmallVectorImpl<Constant*> &ActualArgs, 2195 std::vector<Function*> &CallStack, 2196 DenseMap<Constant*, Constant*> &MutatedMemory, 2197 std::vector<GlobalVariable*> &AllocaTmps) { 2198 // Check to see if this function is already executing (recursion). If so, 2199 // bail out. TODO: we might want to accept limited recursion. 2200 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end()) 2201 return false; 2202 2203 CallStack.push_back(F); 2204 2205 /// Values - As we compute SSA register values, we store their contents here. 2206 DenseMap<Value*, Constant*> Values; 2207 2208 // Initialize arguments to the incoming values specified. 2209 unsigned ArgNo = 0; 2210 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E; 2211 ++AI, ++ArgNo) 2212 Values[AI] = ActualArgs[ArgNo]; 2213 2214 /// ExecutedBlocks - We only handle non-looping, non-recursive code. As such, 2215 /// we can only evaluate any one basic block at most once. This set keeps 2216 /// track of what we have executed so we can detect recursive cases etc. 2217 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks; 2218 2219 // CurInst - The current instruction we're evaluating. 2220 BasicBlock::iterator CurInst = F->begin()->begin(); 2221 2222 // This is the main evaluation loop. 2223 while (1) { 2224 Constant *InstResult = 0; 2225 2226 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) { 2227 if (SI->isVolatile()) return false; // no volatile accesses. 2228 Constant *Ptr = getVal(Values, SI->getOperand(1)); 2229 if (!isSimpleEnoughPointerToCommit(Ptr)) 2230 // If this is too complex for us to commit, reject it. 2231 return false; 2232 Constant *Val = getVal(Values, SI->getOperand(0)); 2233 MutatedMemory[Ptr] = Val; 2234 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) { 2235 InstResult = ConstantExpr::get(BO->getOpcode(), 2236 getVal(Values, BO->getOperand(0)), 2237 getVal(Values, BO->getOperand(1))); 2238 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) { 2239 InstResult = ConstantExpr::getCompare(CI->getPredicate(), 2240 getVal(Values, CI->getOperand(0)), 2241 getVal(Values, CI->getOperand(1))); 2242 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) { 2243 InstResult = ConstantExpr::getCast(CI->getOpcode(), 2244 getVal(Values, CI->getOperand(0)), 2245 CI->getType()); 2246 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) { 2247 InstResult = 2248 ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)), 2249 getVal(Values, SI->getOperand(1)), 2250 getVal(Values, SI->getOperand(2))); 2251 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) { 2252 Constant *P = getVal(Values, GEP->getOperand(0)); 2253 SmallVector<Constant*, 8> GEPOps; 2254 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); 2255 i != e; ++i) 2256 GEPOps.push_back(getVal(Values, *i)); 2257 InstResult = cast<GEPOperator>(GEP)->isInBounds() ? 2258 ConstantExpr::getInBoundsGetElementPtr(P, &GEPOps[0], GEPOps.size()) : 2259 ConstantExpr::getGetElementPtr(P, &GEPOps[0], GEPOps.size()); 2260 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) { 2261 if (LI->isVolatile()) return false; // no volatile accesses. 2262 InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)), 2263 MutatedMemory); 2264 if (InstResult == 0) return false; // Could not evaluate load. 2265 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) { 2266 if (AI->isArrayAllocation()) return false; // Cannot handle array allocs. 2267 const Type *Ty = AI->getType()->getElementType(); 2268 AllocaTmps.push_back(new GlobalVariable(Ty, false, 2269 GlobalValue::InternalLinkage, 2270 UndefValue::get(Ty), 2271 AI->getName())); 2272 InstResult = AllocaTmps.back(); 2273 } else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) { 2274 2275 // Debug info can safely be ignored here. 2276 if (isa<DbgInfoIntrinsic>(CI)) { 2277 ++CurInst; 2278 continue; 2279 } 2280 2281 // Cannot handle inline asm. 2282 if (isa<InlineAsm>(CI->getOperand(0))) return false; 2283 2284 // Resolve function pointers. 2285 Function *Callee = dyn_cast<Function>(getVal(Values, CI->getOperand(0))); 2286 if (!Callee) return false; // Cannot resolve. 2287 2288 SmallVector<Constant*, 8> Formals; 2289 for (User::op_iterator i = CI->op_begin() + 1, e = CI->op_end(); 2290 i != e; ++i) 2291 Formals.push_back(getVal(Values, *i)); 2292 2293 if (Callee->isDeclaration()) { 2294 // If this is a function we can constant fold, do it. 2295 if (Constant *C = ConstantFoldCall(Callee, Formals.data(), 2296 Formals.size())) { 2297 InstResult = C; 2298 } else { 2299 return false; 2300 } 2301 } else { 2302 if (Callee->getFunctionType()->isVarArg()) 2303 return false; 2304 2305 Constant *RetVal; 2306 // Execute the call, if successful, use the return value. 2307 if (!EvaluateFunction(Callee, RetVal, Formals, CallStack, 2308 MutatedMemory, AllocaTmps)) 2309 return false; 2310 InstResult = RetVal; 2311 } 2312 } else if (isa<TerminatorInst>(CurInst)) { 2313 BasicBlock *NewBB = 0; 2314 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) { 2315 if (BI->isUnconditional()) { 2316 NewBB = BI->getSuccessor(0); 2317 } else { 2318 ConstantInt *Cond = 2319 dyn_cast<ConstantInt>(getVal(Values, BI->getCondition())); 2320 if (!Cond) return false; // Cannot determine. 2321 2322 NewBB = BI->getSuccessor(!Cond->getZExtValue()); 2323 } 2324 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) { 2325 ConstantInt *Val = 2326 dyn_cast<ConstantInt>(getVal(Values, SI->getCondition())); 2327 if (!Val) return false; // Cannot determine. 2328 NewBB = SI->getSuccessor(SI->findCaseValue(Val)); 2329 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) { 2330 Value *Val = getVal(Values, IBI->getAddress())->stripPointerCasts(); 2331 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val)) 2332 NewBB = BA->getBasicBlock(); 2333 else 2334 return false; // Cannot determine. 2335 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) { 2336 if (RI->getNumOperands()) 2337 RetVal = getVal(Values, RI->getOperand(0)); 2338 2339 CallStack.pop_back(); // return from fn. 2340 return true; // We succeeded at evaluating this ctor! 2341 } else { 2342 // invoke, unwind, unreachable. 2343 return false; // Cannot handle this terminator. 2344 } 2345 2346 // Okay, we succeeded in evaluating this control flow. See if we have 2347 // executed the new block before. If so, we have a looping function, 2348 // which we cannot evaluate in reasonable time. 2349 if (!ExecutedBlocks.insert(NewBB)) 2350 return false; // looped! 2351 2352 // Okay, we have never been in this block before. Check to see if there 2353 // are any PHI nodes. If so, evaluate them with information about where 2354 // we came from. 2355 BasicBlock *OldBB = CurInst->getParent(); 2356 CurInst = NewBB->begin(); 2357 PHINode *PN; 2358 for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst) 2359 Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB)); 2360 2361 // Do NOT increment CurInst. We know that the terminator had no value. 2362 continue; 2363 } else { 2364 // Did not know how to evaluate this! 2365 return false; 2366 } 2367 2368 if (!CurInst->use_empty()) 2369 Values[CurInst] = InstResult; 2370 2371 // Advance program counter. 2372 ++CurInst; 2373 } 2374} 2375 2376/// EvaluateStaticConstructor - Evaluate static constructors in the function, if 2377/// we can. Return true if we can, false otherwise. 2378static bool EvaluateStaticConstructor(Function *F) { 2379 /// MutatedMemory - For each store we execute, we update this map. Loads 2380 /// check this to get the most up-to-date value. If evaluation is successful, 2381 /// this state is committed to the process. 2382 DenseMap<Constant*, Constant*> MutatedMemory; 2383 2384 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable 2385 /// to represent its body. This vector is needed so we can delete the 2386 /// temporary globals when we are done. 2387 std::vector<GlobalVariable*> AllocaTmps; 2388 2389 /// CallStack - This is used to detect recursion. In pathological situations 2390 /// we could hit exponential behavior, but at least there is nothing 2391 /// unbounded. 2392 std::vector<Function*> CallStack; 2393 2394 // Call the function. 2395 Constant *RetValDummy; 2396 bool EvalSuccess = EvaluateFunction(F, RetValDummy, 2397 SmallVector<Constant*, 0>(), CallStack, 2398 MutatedMemory, AllocaTmps); 2399 if (EvalSuccess) { 2400 // We succeeded at evaluation: commit the result. 2401 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" 2402 << F->getName() << "' to " << MutatedMemory.size() 2403 << " stores.\n"); 2404 for (DenseMap<Constant*, Constant*>::iterator I = MutatedMemory.begin(), 2405 E = MutatedMemory.end(); I != E; ++I) 2406 CommitValueTo(I->second, I->first); 2407 } 2408 2409 // At this point, we are done interpreting. If we created any 'alloca' 2410 // temporaries, release them now. 2411 while (!AllocaTmps.empty()) { 2412 GlobalVariable *Tmp = AllocaTmps.back(); 2413 AllocaTmps.pop_back(); 2414 2415 // If there are still users of the alloca, the program is doing something 2416 // silly, e.g. storing the address of the alloca somewhere and using it 2417 // later. Since this is undefined, we'll just make it be null. 2418 if (!Tmp->use_empty()) 2419 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType())); 2420 delete Tmp; 2421 } 2422 2423 return EvalSuccess; 2424} 2425 2426 2427 2428/// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible. 2429/// Return true if anything changed. 2430bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) { 2431 std::vector<Function*> Ctors = ParseGlobalCtors(GCL); 2432 bool MadeChange = false; 2433 if (Ctors.empty()) return false; 2434 2435 // Loop over global ctors, optimizing them when we can. 2436 for (unsigned i = 0; i != Ctors.size(); ++i) { 2437 Function *F = Ctors[i]; 2438 // Found a null terminator in the middle of the list, prune off the rest of 2439 // the list. 2440 if (F == 0) { 2441 if (i != Ctors.size()-1) { 2442 Ctors.resize(i+1); 2443 MadeChange = true; 2444 } 2445 break; 2446 } 2447 2448 // We cannot simplify external ctor functions. 2449 if (F->empty()) continue; 2450 2451 // If we can evaluate the ctor at compile time, do. 2452 if (EvaluateStaticConstructor(F)) { 2453 Ctors.erase(Ctors.begin()+i); 2454 MadeChange = true; 2455 --i; 2456 ++NumCtorsEvaluated; 2457 continue; 2458 } 2459 } 2460 2461 if (!MadeChange) return false; 2462 2463 GCL = InstallGlobalCtors(GCL, Ctors); 2464 return true; 2465} 2466 2467bool GlobalOpt::OptimizeGlobalAliases(Module &M) { 2468 bool Changed = false; 2469 2470 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); 2471 I != E;) { 2472 Module::alias_iterator J = I++; 2473 // Aliases without names cannot be referenced outside this module. 2474 if (!J->hasName() && !J->isDeclaration()) 2475 J->setLinkage(GlobalValue::InternalLinkage); 2476 // If the aliasee may change at link time, nothing can be done - bail out. 2477 if (J->mayBeOverridden()) 2478 continue; 2479 2480 Constant *Aliasee = J->getAliasee(); 2481 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts()); 2482 Target->removeDeadConstantUsers(); 2483 bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse(); 2484 2485 // Make all users of the alias use the aliasee instead. 2486 if (!J->use_empty()) { 2487 J->replaceAllUsesWith(Aliasee); 2488 ++NumAliasesResolved; 2489 Changed = true; 2490 } 2491 2492 // If the alias is externally visible, we may still be able to simplify it. 2493 if (!J->hasLocalLinkage()) { 2494 // If the aliasee has internal linkage, give it the name and linkage 2495 // of the alias, and delete the alias. This turns: 2496 // define internal ... @f(...) 2497 // @a = alias ... @f 2498 // into: 2499 // define ... @a(...) 2500 if (!Target->hasLocalLinkage()) 2501 continue; 2502 2503 // Do not perform the transform if multiple aliases potentially target the 2504 // aliasee. This check also ensures that it is safe to replace the section 2505 // and other attributes of the aliasee with those of the alias. 2506 if (!hasOneUse) 2507 continue; 2508 2509 // Give the aliasee the name, linkage and other attributes of the alias. 2510 Target->takeName(J); 2511 Target->setLinkage(J->getLinkage()); 2512 Target->GlobalValue::copyAttributesFrom(J); 2513 } 2514 2515 // Delete the alias. 2516 M.getAliasList().erase(J); 2517 ++NumAliasesRemoved; 2518 Changed = true; 2519 } 2520 2521 return Changed; 2522} 2523 2524bool GlobalOpt::runOnModule(Module &M) { 2525 bool Changed = false; 2526 2527 // Try to find the llvm.globalctors list. 2528 GlobalVariable *GlobalCtors = FindGlobalCtors(M); 2529 2530 bool LocalChange = true; 2531 while (LocalChange) { 2532 LocalChange = false; 2533 2534 // Delete functions that are trivially dead, ccc -> fastcc 2535 LocalChange |= OptimizeFunctions(M); 2536 2537 // Optimize global_ctors list. 2538 if (GlobalCtors) 2539 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors); 2540 2541 // Optimize non-address-taken globals. 2542 LocalChange |= OptimizeGlobalVars(M); 2543 2544 // Resolve aliases, when possible. 2545 LocalChange |= OptimizeGlobalAliases(M); 2546 Changed |= LocalChange; 2547 } 2548 2549 // TODO: Move all global ctors functions to the end of the module for code 2550 // layout. 2551 2552 return Changed; 2553} 2554