GlobalOpt.cpp revision 081ce940e7351e90fff829320b7dc6738a6b3815
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/Target/TargetData.h" 27#include "llvm/Support/Compiler.h" 28#include "llvm/Support/Debug.h" 29#include "llvm/ADT/SmallPtrSet.h" 30#include "llvm/ADT/SmallVector.h" 31#include "llvm/ADT/Statistic.h" 32#include "llvm/ADT/StringExtras.h" 33#include <algorithm> 34#include <set> 35using namespace llvm; 36 37STATISTIC(NumMarked , "Number of globals marked constant"); 38STATISTIC(NumSRA , "Number of aggregate globals broken into scalars"); 39STATISTIC(NumHeapSRA , "Number of heap objects SRA'd"); 40STATISTIC(NumSubstitute,"Number of globals with initializers stored into them"); 41STATISTIC(NumDeleted , "Number of globals deleted"); 42STATISTIC(NumFnDeleted , "Number of functions deleted"); 43STATISTIC(NumGlobUses , "Number of global uses devirtualized"); 44STATISTIC(NumLocalized , "Number of globals localized"); 45STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans"); 46STATISTIC(NumFastCallFns , "Number of functions converted to fastcc"); 47STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated"); 48 49namespace { 50 struct VISIBILITY_HIDDEN GlobalOpt : public ModulePass { 51 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 52 AU.addRequired<TargetData>(); 53 } 54 static char ID; // Pass identification, replacement for typeid 55 GlobalOpt() : ModulePass((intptr_t)&ID) {} 56 57 bool runOnModule(Module &M); 58 59 private: 60 GlobalVariable *FindGlobalCtors(Module &M); 61 bool OptimizeFunctions(Module &M); 62 bool OptimizeGlobalVars(Module &M); 63 bool OptimizeGlobalCtorsList(GlobalVariable *&GCL); 64 bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI); 65 }; 66 67 char GlobalOpt::ID = 0; 68 RegisterPass<GlobalOpt> X("globalopt", "Global Variable Optimizer"); 69} 70 71ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); } 72 73/// GlobalStatus - As we analyze each global, keep track of some information 74/// about it. If we find out that the address of the global is taken, none of 75/// this info will be accurate. 76struct VISIBILITY_HIDDEN GlobalStatus { 77 /// isLoaded - True if the global is ever loaded. If the global isn't ever 78 /// loaded it can be deleted. 79 bool isLoaded; 80 81 /// StoredType - Keep track of what stores to the global look like. 82 /// 83 enum StoredType { 84 /// NotStored - There is no store to this global. It can thus be marked 85 /// constant. 86 NotStored, 87 88 /// isInitializerStored - This global is stored to, but the only thing 89 /// stored is the constant it was initialized with. This is only tracked 90 /// for scalar globals. 91 isInitializerStored, 92 93 /// isStoredOnce - This global is stored to, but only its initializer and 94 /// one other value is ever stored to it. If this global isStoredOnce, we 95 /// track the value stored to it in StoredOnceValue below. This is only 96 /// tracked for scalar globals. 97 isStoredOnce, 98 99 /// isStored - This global is stored to by multiple values or something else 100 /// that we cannot track. 101 isStored 102 } StoredType; 103 104 /// StoredOnceValue - If only one value (besides the initializer constant) is 105 /// ever stored to this global, keep track of what value it is. 106 Value *StoredOnceValue; 107 108 /// AccessingFunction/HasMultipleAccessingFunctions - These start out 109 /// null/false. When the first accessing function is noticed, it is recorded. 110 /// When a second different accessing function is noticed, 111 /// HasMultipleAccessingFunctions is set to true. 112 Function *AccessingFunction; 113 bool HasMultipleAccessingFunctions; 114 115 /// HasNonInstructionUser - Set to true if this global has a user that is not 116 /// an instruction (e.g. a constant expr or GV initializer). 117 bool HasNonInstructionUser; 118 119 /// HasPHIUser - Set to true if this global has a user that is a PHI node. 120 bool HasPHIUser; 121 122 /// isNotSuitableForSRA - Keep track of whether any SRA preventing users of 123 /// the global exist. Such users include GEP instruction with variable 124 /// indexes, and non-gep/load/store users like constant expr casts. 125 bool isNotSuitableForSRA; 126 127 GlobalStatus() : isLoaded(false), StoredType(NotStored), StoredOnceValue(0), 128 AccessingFunction(0), HasMultipleAccessingFunctions(false), 129 HasNonInstructionUser(false), HasPHIUser(false), 130 isNotSuitableForSRA(false) {} 131}; 132 133 134 135/// ConstantIsDead - Return true if the specified constant is (transitively) 136/// dead. The constant may be used by other constants (e.g. constant arrays and 137/// constant exprs) as long as they are dead, but it cannot be used by anything 138/// else. 139static bool ConstantIsDead(Constant *C) { 140 if (isa<GlobalValue>(C)) return false; 141 142 for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI) 143 if (Constant *CU = dyn_cast<Constant>(*UI)) { 144 if (!ConstantIsDead(CU)) return false; 145 } else 146 return false; 147 return true; 148} 149 150 151/// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus 152/// structure. If the global has its address taken, return true to indicate we 153/// can't do anything with it. 154/// 155static bool AnalyzeGlobal(Value *V, GlobalStatus &GS, 156 std::set<PHINode*> &PHIUsers) { 157 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) 158 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) { 159 GS.HasNonInstructionUser = true; 160 161 if (AnalyzeGlobal(CE, GS, PHIUsers)) return true; 162 if (CE->getOpcode() != Instruction::GetElementPtr) 163 GS.isNotSuitableForSRA = true; 164 else if (!GS.isNotSuitableForSRA) { 165 // Check to see if this ConstantExpr GEP is SRA'able. In particular, we 166 // don't like < 3 operand CE's, and we don't like non-constant integer 167 // indices. 168 if (CE->getNumOperands() < 3 || !CE->getOperand(1)->isNullValue()) 169 GS.isNotSuitableForSRA = true; 170 else { 171 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) 172 if (!isa<ConstantInt>(CE->getOperand(i))) { 173 GS.isNotSuitableForSRA = true; 174 break; 175 } 176 } 177 } 178 179 } else if (Instruction *I = dyn_cast<Instruction>(*UI)) { 180 if (!GS.HasMultipleAccessingFunctions) { 181 Function *F = I->getParent()->getParent(); 182 if (GS.AccessingFunction == 0) 183 GS.AccessingFunction = F; 184 else if (GS.AccessingFunction != F) 185 GS.HasMultipleAccessingFunctions = true; 186 } 187 if (isa<LoadInst>(I)) { 188 GS.isLoaded = true; 189 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 190 // Don't allow a store OF the address, only stores TO the address. 191 if (SI->getOperand(0) == V) return true; 192 193 // If this is a direct store to the global (i.e., the global is a scalar 194 // value, not an aggregate), keep more specific information about 195 // stores. 196 if (GS.StoredType != GlobalStatus::isStored) 197 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(SI->getOperand(1))){ 198 Value *StoredVal = SI->getOperand(0); 199 if (StoredVal == GV->getInitializer()) { 200 if (GS.StoredType < GlobalStatus::isInitializerStored) 201 GS.StoredType = GlobalStatus::isInitializerStored; 202 } else if (isa<LoadInst>(StoredVal) && 203 cast<LoadInst>(StoredVal)->getOperand(0) == GV) { 204 // G = G 205 if (GS.StoredType < GlobalStatus::isInitializerStored) 206 GS.StoredType = GlobalStatus::isInitializerStored; 207 } else if (GS.StoredType < GlobalStatus::isStoredOnce) { 208 GS.StoredType = GlobalStatus::isStoredOnce; 209 GS.StoredOnceValue = StoredVal; 210 } else if (GS.StoredType == GlobalStatus::isStoredOnce && 211 GS.StoredOnceValue == StoredVal) { 212 // noop. 213 } else { 214 GS.StoredType = GlobalStatus::isStored; 215 } 216 } else { 217 GS.StoredType = GlobalStatus::isStored; 218 } 219 } else if (isa<GetElementPtrInst>(I)) { 220 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 221 222 // If the first two indices are constants, this can be SRA'd. 223 if (isa<GlobalVariable>(I->getOperand(0))) { 224 if (I->getNumOperands() < 3 || !isa<Constant>(I->getOperand(1)) || 225 !cast<Constant>(I->getOperand(1))->isNullValue() || 226 !isa<ConstantInt>(I->getOperand(2))) 227 GS.isNotSuitableForSRA = true; 228 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(I->getOperand(0))){ 229 if (CE->getOpcode() != Instruction::GetElementPtr || 230 CE->getNumOperands() < 3 || I->getNumOperands() < 2 || 231 !isa<Constant>(I->getOperand(0)) || 232 !cast<Constant>(I->getOperand(0))->isNullValue()) 233 GS.isNotSuitableForSRA = true; 234 } else { 235 GS.isNotSuitableForSRA = true; 236 } 237 } else if (isa<SelectInst>(I)) { 238 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 239 GS.isNotSuitableForSRA = true; 240 } else if (PHINode *PN = dyn_cast<PHINode>(I)) { 241 // PHI nodes we can check just like select or GEP instructions, but we 242 // have to be careful about infinite recursion. 243 if (PHIUsers.insert(PN).second) // Not already visited. 244 if (AnalyzeGlobal(I, GS, PHIUsers)) return true; 245 GS.isNotSuitableForSRA = true; 246 GS.HasPHIUser = true; 247 } else if (isa<CmpInst>(I)) { 248 GS.isNotSuitableForSRA = true; 249 } else if (isa<MemCpyInst>(I) || isa<MemMoveInst>(I)) { 250 if (I->getOperand(1) == V) 251 GS.StoredType = GlobalStatus::isStored; 252 if (I->getOperand(2) == V) 253 GS.isLoaded = true; 254 GS.isNotSuitableForSRA = true; 255 } else if (isa<MemSetInst>(I)) { 256 assert(I->getOperand(1) == V && "Memset only takes one pointer!"); 257 GS.StoredType = GlobalStatus::isStored; 258 GS.isNotSuitableForSRA = true; 259 } else { 260 return true; // Any other non-load instruction might take address! 261 } 262 } else if (Constant *C = dyn_cast<Constant>(*UI)) { 263 GS.HasNonInstructionUser = true; 264 // We might have a dead and dangling constant hanging off of here. 265 if (!ConstantIsDead(C)) 266 return true; 267 } else { 268 GS.HasNonInstructionUser = true; 269 // Otherwise must be some other user. 270 return true; 271 } 272 273 return false; 274} 275 276static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx) { 277 ConstantInt *CI = dyn_cast<ConstantInt>(Idx); 278 if (!CI) return 0; 279 unsigned IdxV = CI->getZExtValue(); 280 281 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) { 282 if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV); 283 } else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) { 284 if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV); 285 } else if (ConstantVector *CP = dyn_cast<ConstantVector>(Agg)) { 286 if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV); 287 } else if (isa<ConstantAggregateZero>(Agg)) { 288 if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) { 289 if (IdxV < STy->getNumElements()) 290 return Constant::getNullValue(STy->getElementType(IdxV)); 291 } else if (const SequentialType *STy = 292 dyn_cast<SequentialType>(Agg->getType())) { 293 return Constant::getNullValue(STy->getElementType()); 294 } 295 } else if (isa<UndefValue>(Agg)) { 296 if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) { 297 if (IdxV < STy->getNumElements()) 298 return UndefValue::get(STy->getElementType(IdxV)); 299 } else if (const SequentialType *STy = 300 dyn_cast<SequentialType>(Agg->getType())) { 301 return UndefValue::get(STy->getElementType()); 302 } 303 } 304 return 0; 305} 306 307 308/// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all 309/// users of the global, cleaning up the obvious ones. This is largely just a 310/// quick scan over the use list to clean up the easy and obvious cruft. This 311/// returns true if it made a change. 312static bool CleanupConstantGlobalUsers(Value *V, Constant *Init) { 313 bool Changed = false; 314 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) { 315 User *U = *UI++; 316 317 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 318 if (Init) { 319 // Replace the load with the initializer. 320 LI->replaceAllUsesWith(Init); 321 LI->eraseFromParent(); 322 Changed = true; 323 } 324 } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 325 // Store must be unreachable or storing Init into the global. 326 SI->eraseFromParent(); 327 Changed = true; 328 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { 329 if (CE->getOpcode() == Instruction::GetElementPtr) { 330 Constant *SubInit = 0; 331 if (Init) 332 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); 333 Changed |= CleanupConstantGlobalUsers(CE, SubInit); 334 } else if (CE->getOpcode() == Instruction::BitCast && 335 isa<PointerType>(CE->getType())) { 336 // Pointer cast, delete any stores and memsets to the global. 337 Changed |= CleanupConstantGlobalUsers(CE, 0); 338 } 339 340 if (CE->use_empty()) { 341 CE->destroyConstant(); 342 Changed = true; 343 } 344 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 345 // Do not transform "gepinst (gep constexpr (GV))" here, because forming 346 // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold 347 // and will invalidate our notion of what Init is. 348 Constant *SubInit = 0; 349 if (!isa<ConstantExpr>(GEP->getOperand(0))) { 350 ConstantExpr *CE = 351 dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP)); 352 if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr) 353 SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); 354 } 355 Changed |= CleanupConstantGlobalUsers(GEP, SubInit); 356 357 if (GEP->use_empty()) { 358 GEP->eraseFromParent(); 359 Changed = true; 360 } 361 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv 362 if (MI->getRawDest() == V) { 363 MI->eraseFromParent(); 364 Changed = true; 365 } 366 367 } else if (Constant *C = dyn_cast<Constant>(U)) { 368 // If we have a chain of dead constantexprs or other things dangling from 369 // us, and if they are all dead, nuke them without remorse. 370 if (ConstantIsDead(C)) { 371 C->destroyConstant(); 372 // This could have invalidated UI, start over from scratch. 373 CleanupConstantGlobalUsers(V, Init); 374 return true; 375 } 376 } 377 } 378 return Changed; 379} 380 381/// SRAGlobal - Perform scalar replacement of aggregates on the specified global 382/// variable. This opens the door for other optimizations by exposing the 383/// behavior of the program in a more fine-grained way. We have determined that 384/// this transformation is safe already. We return the first global variable we 385/// insert so that the caller can reprocess it. 386static GlobalVariable *SRAGlobal(GlobalVariable *GV) { 387 assert(GV->hasInternalLinkage() && !GV->isConstant()); 388 Constant *Init = GV->getInitializer(); 389 const Type *Ty = Init->getType(); 390 391 std::vector<GlobalVariable*> NewGlobals; 392 Module::GlobalListType &Globals = GV->getParent()->getGlobalList(); 393 394 if (const StructType *STy = dyn_cast<StructType>(Ty)) { 395 NewGlobals.reserve(STy->getNumElements()); 396 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 397 Constant *In = getAggregateConstantElement(Init, 398 ConstantInt::get(Type::Int32Ty, i)); 399 assert(In && "Couldn't get element of initializer?"); 400 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false, 401 GlobalVariable::InternalLinkage, 402 In, GV->getName()+"."+utostr(i), 403 (Module *)NULL, 404 GV->isThreadLocal()); 405 Globals.insert(GV, NGV); 406 NewGlobals.push_back(NGV); 407 } 408 } else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) { 409 unsigned NumElements = 0; 410 if (const ArrayType *ATy = dyn_cast<ArrayType>(STy)) 411 NumElements = ATy->getNumElements(); 412 else if (const VectorType *PTy = dyn_cast<VectorType>(STy)) 413 NumElements = PTy->getNumElements(); 414 else 415 assert(0 && "Unknown aggregate sequential type!"); 416 417 if (NumElements > 16 && GV->hasNUsesOrMore(16)) 418 return 0; // It's not worth it. 419 NewGlobals.reserve(NumElements); 420 for (unsigned i = 0, e = NumElements; i != e; ++i) { 421 Constant *In = getAggregateConstantElement(Init, 422 ConstantInt::get(Type::Int32Ty, i)); 423 assert(In && "Couldn't get element of initializer?"); 424 425 GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false, 426 GlobalVariable::InternalLinkage, 427 In, GV->getName()+"."+utostr(i), 428 (Module *)NULL, 429 GV->isThreadLocal()); 430 Globals.insert(GV, NGV); 431 NewGlobals.push_back(NGV); 432 } 433 } 434 435 if (NewGlobals.empty()) 436 return 0; 437 438 DOUT << "PERFORMING GLOBAL SRA ON: " << *GV; 439 440 Constant *NullInt = Constant::getNullValue(Type::Int32Ty); 441 442 // Loop over all of the uses of the global, replacing the constantexpr geps, 443 // with smaller constantexpr geps or direct references. 444 while (!GV->use_empty()) { 445 User *GEP = GV->use_back(); 446 assert(((isa<ConstantExpr>(GEP) && 447 cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)|| 448 isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!"); 449 450 // Ignore the 1th operand, which has to be zero or else the program is quite 451 // broken (undefined). Get the 2nd operand, which is the structure or array 452 // index. 453 unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 454 if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access. 455 456 Value *NewPtr = NewGlobals[Val]; 457 458 // Form a shorter GEP if needed. 459 if (GEP->getNumOperands() > 3) 460 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) { 461 SmallVector<Constant*, 8> Idxs; 462 Idxs.push_back(NullInt); 463 for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i) 464 Idxs.push_back(CE->getOperand(i)); 465 NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr), 466 &Idxs[0], Idxs.size()); 467 } else { 468 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP); 469 SmallVector<Value*, 8> Idxs; 470 Idxs.push_back(NullInt); 471 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) 472 Idxs.push_back(GEPI->getOperand(i)); 473 NewPtr = new GetElementPtrInst(NewPtr, Idxs.begin(), Idxs.end(), 474 GEPI->getName()+"."+utostr(Val), GEPI); 475 } 476 GEP->replaceAllUsesWith(NewPtr); 477 478 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP)) 479 GEPI->eraseFromParent(); 480 else 481 cast<ConstantExpr>(GEP)->destroyConstant(); 482 } 483 484 // Delete the old global, now that it is dead. 485 Globals.erase(GV); 486 ++NumSRA; 487 488 // Loop over the new globals array deleting any globals that are obviously 489 // dead. This can arise due to scalarization of a structure or an array that 490 // has elements that are dead. 491 unsigned FirstGlobal = 0; 492 for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i) 493 if (NewGlobals[i]->use_empty()) { 494 Globals.erase(NewGlobals[i]); 495 if (FirstGlobal == i) ++FirstGlobal; 496 } 497 498 return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0; 499} 500 501/// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified 502/// value will trap if the value is dynamically null. PHIs keeps track of any 503/// phi nodes we've seen to avoid reprocessing them. 504static bool AllUsesOfValueWillTrapIfNull(Value *V, 505 SmallPtrSet<PHINode*, 8> &PHIs) { 506 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) 507 if (isa<LoadInst>(*UI)) { 508 // Will trap. 509 } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) { 510 if (SI->getOperand(0) == V) { 511 //cerr << "NONTRAPPING USE: " << **UI; 512 return false; // Storing the value. 513 } 514 } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) { 515 if (CI->getOperand(0) != V) { 516 //cerr << "NONTRAPPING USE: " << **UI; 517 return false; // Not calling the ptr 518 } 519 } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) { 520 if (II->getOperand(0) != V) { 521 //cerr << "NONTRAPPING USE: " << **UI; 522 return false; // Not calling the ptr 523 } 524 } else if (BitCastInst *CI = dyn_cast<BitCastInst>(*UI)) { 525 if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false; 526 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) { 527 if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false; 528 } else if (PHINode *PN = dyn_cast<PHINode>(*UI)) { 529 // If we've already seen this phi node, ignore it, it has already been 530 // checked. 531 if (PHIs.insert(PN)) 532 return AllUsesOfValueWillTrapIfNull(PN, PHIs); 533 } else if (isa<ICmpInst>(*UI) && 534 isa<ConstantPointerNull>(UI->getOperand(1))) { 535 // Ignore setcc X, null 536 } else { 537 //cerr << "NONTRAPPING USE: " << **UI; 538 return false; 539 } 540 return true; 541} 542 543/// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads 544/// from GV will trap if the loaded value is null. Note that this also permits 545/// comparisons of the loaded value against null, as a special case. 546static bool AllUsesOfLoadedValueWillTrapIfNull(GlobalVariable *GV) { 547 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI!=E; ++UI) 548 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 549 SmallPtrSet<PHINode*, 8> PHIs; 550 if (!AllUsesOfValueWillTrapIfNull(LI, PHIs)) 551 return false; 552 } else if (isa<StoreInst>(*UI)) { 553 // Ignore stores to the global. 554 } else { 555 // We don't know or understand this user, bail out. 556 //cerr << "UNKNOWN USER OF GLOBAL!: " << **UI; 557 return false; 558 } 559 560 return true; 561} 562 563static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) { 564 bool Changed = false; 565 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) { 566 Instruction *I = cast<Instruction>(*UI++); 567 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 568 LI->setOperand(0, NewV); 569 Changed = true; 570 } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 571 if (SI->getOperand(1) == V) { 572 SI->setOperand(1, NewV); 573 Changed = true; 574 } 575 } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) { 576 if (I->getOperand(0) == V) { 577 // Calling through the pointer! Turn into a direct call, but be careful 578 // that the pointer is not also being passed as an argument. 579 I->setOperand(0, NewV); 580 Changed = true; 581 bool PassedAsArg = false; 582 for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i) 583 if (I->getOperand(i) == V) { 584 PassedAsArg = true; 585 I->setOperand(i, NewV); 586 } 587 588 if (PassedAsArg) { 589 // Being passed as an argument also. Be careful to not invalidate UI! 590 UI = V->use_begin(); 591 } 592 } 593 } else if (CastInst *CI = dyn_cast<CastInst>(I)) { 594 Changed |= OptimizeAwayTrappingUsesOfValue(CI, 595 ConstantExpr::getCast(CI->getOpcode(), 596 NewV, CI->getType())); 597 if (CI->use_empty()) { 598 Changed = true; 599 CI->eraseFromParent(); 600 } 601 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { 602 // Should handle GEP here. 603 SmallVector<Constant*, 8> Idxs; 604 Idxs.reserve(GEPI->getNumOperands()-1); 605 for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i) 606 if (Constant *C = dyn_cast<Constant>(GEPI->getOperand(i))) 607 Idxs.push_back(C); 608 else 609 break; 610 if (Idxs.size() == GEPI->getNumOperands()-1) 611 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI, 612 ConstantExpr::getGetElementPtr(NewV, &Idxs[0], 613 Idxs.size())); 614 if (GEPI->use_empty()) { 615 Changed = true; 616 GEPI->eraseFromParent(); 617 } 618 } 619 } 620 621 return Changed; 622} 623 624 625/// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null 626/// value stored into it. If there are uses of the loaded value that would trap 627/// if the loaded value is dynamically null, then we know that they cannot be 628/// reachable with a null optimize away the load. 629static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV) { 630 std::vector<LoadInst*> Loads; 631 bool Changed = false; 632 633 // Replace all uses of loads with uses of uses of the stored value. 634 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); 635 GUI != E; ++GUI) 636 if (LoadInst *LI = dyn_cast<LoadInst>(*GUI)) { 637 Loads.push_back(LI); 638 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV); 639 } else { 640 // If we get here we could have stores, selects, or phi nodes whose values 641 // are loaded. 642 assert((isa<StoreInst>(*GUI) || isa<PHINode>(*GUI) || 643 isa<SelectInst>(*GUI)) && 644 "Only expect load and stores!"); 645 } 646 647 if (Changed) { 648 DOUT << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV; 649 ++NumGlobUses; 650 } 651 652 // Delete all of the loads we can, keeping track of whether we nuked them all! 653 bool AllLoadsGone = true; 654 while (!Loads.empty()) { 655 LoadInst *L = Loads.back(); 656 if (L->use_empty()) { 657 L->eraseFromParent(); 658 Changed = true; 659 } else { 660 AllLoadsGone = false; 661 } 662 Loads.pop_back(); 663 } 664 665 // If we nuked all of the loads, then none of the stores are needed either, 666 // nor is the global. 667 if (AllLoadsGone) { 668 DOUT << " *** GLOBAL NOW DEAD!\n"; 669 CleanupConstantGlobalUsers(GV, 0); 670 if (GV->use_empty()) { 671 GV->eraseFromParent(); 672 ++NumDeleted; 673 } 674 Changed = true; 675 } 676 return Changed; 677} 678 679/// ConstantPropUsersOf - Walk the use list of V, constant folding all of the 680/// instructions that are foldable. 681static void ConstantPropUsersOf(Value *V) { 682 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) 683 if (Instruction *I = dyn_cast<Instruction>(*UI++)) 684 if (Constant *NewC = ConstantFoldInstruction(I)) { 685 I->replaceAllUsesWith(NewC); 686 687 // Advance UI to the next non-I use to avoid invalidating it! 688 // Instructions could multiply use V. 689 while (UI != E && *UI == I) 690 ++UI; 691 I->eraseFromParent(); 692 } 693} 694 695/// OptimizeGlobalAddressOfMalloc - This function takes the specified global 696/// variable, and transforms the program as if it always contained the result of 697/// the specified malloc. Because it is always the result of the specified 698/// malloc, there is no reason to actually DO the malloc. Instead, turn the 699/// malloc into a global, and any loads of GV as uses of the new global. 700static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, 701 MallocInst *MI) { 702 DOUT << "PROMOTING MALLOC GLOBAL: " << *GV << " MALLOC = " << *MI; 703 ConstantInt *NElements = cast<ConstantInt>(MI->getArraySize()); 704 705 if (NElements->getZExtValue() != 1) { 706 // If we have an array allocation, transform it to a single element 707 // allocation to make the code below simpler. 708 Type *NewTy = ArrayType::get(MI->getAllocatedType(), 709 NElements->getZExtValue()); 710 MallocInst *NewMI = 711 new MallocInst(NewTy, Constant::getNullValue(Type::Int32Ty), 712 MI->getAlignment(), MI->getName(), MI); 713 Value* Indices[2]; 714 Indices[0] = Indices[1] = Constant::getNullValue(Type::Int32Ty); 715 Value *NewGEP = new GetElementPtrInst(NewMI, Indices, Indices + 2, 716 NewMI->getName()+".el0", MI); 717 MI->replaceAllUsesWith(NewGEP); 718 MI->eraseFromParent(); 719 MI = NewMI; 720 } 721 722 // Create the new global variable. The contents of the malloc'd memory is 723 // undefined, so initialize with an undef value. 724 Constant *Init = UndefValue::get(MI->getAllocatedType()); 725 GlobalVariable *NewGV = new GlobalVariable(MI->getAllocatedType(), false, 726 GlobalValue::InternalLinkage, Init, 727 GV->getName()+".body", 728 (Module *)NULL, 729 GV->isThreadLocal()); 730 GV->getParent()->getGlobalList().insert(GV, NewGV); 731 732 // Anything that used the malloc now uses the global directly. 733 MI->replaceAllUsesWith(NewGV); 734 735 Constant *RepValue = NewGV; 736 if (NewGV->getType() != GV->getType()->getElementType()) 737 RepValue = ConstantExpr::getBitCast(RepValue, 738 GV->getType()->getElementType()); 739 740 // If there is a comparison against null, we will insert a global bool to 741 // keep track of whether the global was initialized yet or not. 742 GlobalVariable *InitBool = 743 new GlobalVariable(Type::Int1Ty, false, GlobalValue::InternalLinkage, 744 ConstantInt::getFalse(), GV->getName()+".init", 745 (Module *)NULL, GV->isThreadLocal()); 746 bool InitBoolUsed = false; 747 748 // Loop over all uses of GV, processing them in turn. 749 std::vector<StoreInst*> Stores; 750 while (!GV->use_empty()) 751 if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) { 752 while (!LI->use_empty()) { 753 Use &LoadUse = LI->use_begin().getUse(); 754 if (!isa<ICmpInst>(LoadUse.getUser())) 755 LoadUse = RepValue; 756 else { 757 ICmpInst *CI = cast<ICmpInst>(LoadUse.getUser()); 758 // Replace the cmp X, 0 with a use of the bool value. 759 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", CI); 760 InitBoolUsed = true; 761 switch (CI->getPredicate()) { 762 default: assert(0 && "Unknown ICmp Predicate!"); 763 case ICmpInst::ICMP_ULT: 764 case ICmpInst::ICMP_SLT: 765 LV = ConstantInt::getFalse(); // X < null -> always false 766 break; 767 case ICmpInst::ICMP_ULE: 768 case ICmpInst::ICMP_SLE: 769 case ICmpInst::ICMP_EQ: 770 LV = BinaryOperator::createNot(LV, "notinit", CI); 771 break; 772 case ICmpInst::ICMP_NE: 773 case ICmpInst::ICMP_UGE: 774 case ICmpInst::ICMP_SGE: 775 case ICmpInst::ICMP_UGT: 776 case ICmpInst::ICMP_SGT: 777 break; // no change. 778 } 779 CI->replaceAllUsesWith(LV); 780 CI->eraseFromParent(); 781 } 782 } 783 LI->eraseFromParent(); 784 } else { 785 StoreInst *SI = cast<StoreInst>(GV->use_back()); 786 // The global is initialized when the store to it occurs. 787 new StoreInst(ConstantInt::getTrue(), InitBool, SI); 788 SI->eraseFromParent(); 789 } 790 791 // If the initialization boolean was used, insert it, otherwise delete it. 792 if (!InitBoolUsed) { 793 while (!InitBool->use_empty()) // Delete initializations 794 cast<Instruction>(InitBool->use_back())->eraseFromParent(); 795 delete InitBool; 796 } else 797 GV->getParent()->getGlobalList().insert(GV, InitBool); 798 799 800 // Now the GV is dead, nuke it and the malloc. 801 GV->eraseFromParent(); 802 MI->eraseFromParent(); 803 804 // To further other optimizations, loop over all users of NewGV and try to 805 // constant prop them. This will promote GEP instructions with constant 806 // indices into GEP constant-exprs, which will allow global-opt to hack on it. 807 ConstantPropUsersOf(NewGV); 808 if (RepValue != NewGV) 809 ConstantPropUsersOf(RepValue); 810 811 return NewGV; 812} 813 814/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking 815/// to make sure that there are no complex uses of V. We permit simple things 816/// like dereferencing the pointer, but not storing through the address, unless 817/// it is to the specified global. 818static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Instruction *V, 819 GlobalVariable *GV, 820 SmallPtrSet<PHINode*, 8> &PHIs) { 821 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) 822 if (isa<LoadInst>(*UI) || isa<CmpInst>(*UI)) { 823 // Fine, ignore. 824 } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) { 825 if (SI->getOperand(0) == V && SI->getOperand(1) != GV) 826 return false; // Storing the pointer itself... bad. 827 // Otherwise, storing through it, or storing into GV... fine. 828 } else if (isa<GetElementPtrInst>(*UI)) { 829 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(cast<Instruction>(*UI), 830 GV, PHIs)) 831 return false; 832 } else if (PHINode *PN = dyn_cast<PHINode>(*UI)) { 833 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI 834 // cycles. 835 if (PHIs.insert(PN)) 836 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs)) 837 return false; 838 } else { 839 return false; 840 } 841 return true; 842} 843 844/// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV 845/// somewhere. Transform all uses of the allocation into loads from the 846/// global and uses of the resultant pointer. Further, delete the store into 847/// GV. This assumes that these value pass the 848/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate. 849static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, 850 GlobalVariable *GV) { 851 while (!Alloc->use_empty()) { 852 Instruction *U = cast<Instruction>(*Alloc->use_begin()); 853 Instruction *InsertPt = U; 854 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 855 // If this is the store of the allocation into the global, remove it. 856 if (SI->getOperand(1) == GV) { 857 SI->eraseFromParent(); 858 continue; 859 } 860 } else if (PHINode *PN = dyn_cast<PHINode>(U)) { 861 // Insert the load in the corresponding predecessor, not right before the 862 // PHI. 863 unsigned PredNo = Alloc->use_begin().getOperandNo()/2; 864 InsertPt = PN->getIncomingBlock(PredNo)->getTerminator(); 865 } 866 867 // Insert a load from the global, and use it instead of the malloc. 868 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt); 869 U->replaceUsesOfWith(Alloc, NL); 870 } 871} 872 873/// GlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from 874/// GV are simple enough to perform HeapSRA, return true. 875static bool GlobalLoadUsesSimpleEnoughForHeapSRA(GlobalVariable *GV, 876 MallocInst *MI) { 877 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E; 878 ++UI) 879 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 880 // We permit two users of the load: setcc comparing against the null 881 // pointer, and a getelementptr of a specific form. 882 for (Value::use_iterator UI = LI->use_begin(), E = LI->use_end(); UI != E; 883 ++UI) { 884 // Comparison against null is ok. 885 if (ICmpInst *ICI = dyn_cast<ICmpInst>(*UI)) { 886 if (!isa<ConstantPointerNull>(ICI->getOperand(1))) 887 return false; 888 continue; 889 } 890 891 // getelementptr is also ok, but only a simple form. 892 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) { 893 // Must index into the array and into the struct. 894 if (GEPI->getNumOperands() < 3) 895 return false; 896 897 // Otherwise the GEP is ok. 898 continue; 899 } 900 901 if (PHINode *PN = dyn_cast<PHINode>(*UI)) { 902 // We have a phi of a load from the global. We can only handle this 903 // if the other PHI'd values are actually the same. In this case, 904 // the rewriter will just drop the phi entirely. 905 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 906 Value *IV = PN->getIncomingValue(i); 907 if (IV == LI) continue; // Trivial the same. 908 909 // If the phi'd value is from the malloc that initializes the value, 910 // we can xform it. 911 if (IV == MI) continue; 912 913 // Otherwise, we don't know what it is. 914 return false; 915 } 916 return true; 917 } 918 919 // Otherwise we don't know what this is, not ok. 920 return false; 921 } 922 } 923 return true; 924} 925 926/// GetHeapSROALoad - Return the load for the specified field of the HeapSROA'd 927/// value, lazily creating it on demand. 928static Value *GetHeapSROALoad(Instruction *Load, unsigned FieldNo, 929 const std::vector<GlobalVariable*> &FieldGlobals, 930 std::vector<Value *> &InsertedLoadsForPtr) { 931 if (InsertedLoadsForPtr.size() <= FieldNo) 932 InsertedLoadsForPtr.resize(FieldNo+1); 933 if (InsertedLoadsForPtr[FieldNo] == 0) 934 InsertedLoadsForPtr[FieldNo] = new LoadInst(FieldGlobals[FieldNo], 935 Load->getName()+".f" + 936 utostr(FieldNo), Load); 937 return InsertedLoadsForPtr[FieldNo]; 938} 939 940/// RewriteHeapSROALoadUser - Given a load instruction and a value derived from 941/// the load, rewrite the derived value to use the HeapSRoA'd load. 942static void RewriteHeapSROALoadUser(LoadInst *Load, Instruction *LoadUser, 943 const std::vector<GlobalVariable*> &FieldGlobals, 944 std::vector<Value *> &InsertedLoadsForPtr) { 945 // If this is a comparison against null, handle it. 946 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) { 947 assert(isa<ConstantPointerNull>(SCI->getOperand(1))); 948 // If we have a setcc of the loaded pointer, we can use a setcc of any 949 // field. 950 Value *NPtr; 951 if (InsertedLoadsForPtr.empty()) { 952 NPtr = GetHeapSROALoad(Load, 0, FieldGlobals, InsertedLoadsForPtr); 953 } else { 954 NPtr = InsertedLoadsForPtr.back(); 955 } 956 957 Value *New = new ICmpInst(SCI->getPredicate(), NPtr, 958 Constant::getNullValue(NPtr->getType()), 959 SCI->getName(), SCI); 960 SCI->replaceAllUsesWith(New); 961 SCI->eraseFromParent(); 962 return; 963 } 964 965 // Handle 'getelementptr Ptr, Idx, uint FieldNo ...' 966 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) { 967 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2)) 968 && "Unexpected GEPI!"); 969 970 // Load the pointer for this field. 971 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 972 Value *NewPtr = GetHeapSROALoad(Load, FieldNo, 973 FieldGlobals, InsertedLoadsForPtr); 974 975 // Create the new GEP idx vector. 976 SmallVector<Value*, 8> GEPIdx; 977 GEPIdx.push_back(GEPI->getOperand(1)); 978 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end()); 979 980 Value *NGEPI = new GetElementPtrInst(NewPtr, GEPIdx.begin(), GEPIdx.end(), 981 GEPI->getName(), GEPI); 982 GEPI->replaceAllUsesWith(NGEPI); 983 GEPI->eraseFromParent(); 984 return; 985 } 986 987 // Handle PHI nodes. PHI nodes must be merging in the same values, plus 988 // potentially the original malloc. Insert phi nodes for each field, then 989 // process uses of the PHI. 990 PHINode *PN = cast<PHINode>(LoadUser); 991 std::vector<Value *> PHIsForField; 992 PHIsForField.resize(FieldGlobals.size()); 993 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 994 Value *LoadV = GetHeapSROALoad(Load, i, FieldGlobals, InsertedLoadsForPtr); 995 996 PHINode *FieldPN = new PHINode(LoadV->getType(), 997 PN->getName()+"."+utostr(i), PN); 998 // Fill in the predecessor values. 999 for (unsigned pred = 0, e = PN->getNumIncomingValues(); pred != e; ++pred) { 1000 // Each predecessor either uses the load or the original malloc. 1001 Value *InVal = PN->getIncomingValue(pred); 1002 BasicBlock *BB = PN->getIncomingBlock(pred); 1003 Value *NewVal; 1004 if (isa<MallocInst>(InVal)) { 1005 // Insert a reload from the global in the predecessor. 1006 NewVal = GetHeapSROALoad(BB->getTerminator(), i, FieldGlobals, 1007 PHIsForField); 1008 } else { 1009 NewVal = InsertedLoadsForPtr[i]; 1010 } 1011 FieldPN->addIncoming(NewVal, BB); 1012 } 1013 PHIsForField[i] = FieldPN; 1014 } 1015 1016 // Since PHIsForField specifies a phi for every input value, the lazy inserter 1017 // will never insert a load. 1018 while (!PN->use_empty()) 1019 RewriteHeapSROALoadUser(Load, PN->use_back(), FieldGlobals, PHIsForField); 1020 PN->eraseFromParent(); 1021} 1022 1023/// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr 1024/// is a value loaded from the global. Eliminate all uses of Ptr, making them 1025/// use FieldGlobals instead. All uses of loaded values satisfy 1026/// GlobalLoadUsesSimpleEnoughForHeapSRA. 1027static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load, 1028 const std::vector<GlobalVariable*> &FieldGlobals) { 1029 std::vector<Value *> InsertedLoadsForPtr; 1030 //InsertedLoadsForPtr.resize(FieldGlobals.size()); 1031 while (!Load->use_empty()) 1032 RewriteHeapSROALoadUser(Load, Load->use_back(), 1033 FieldGlobals, InsertedLoadsForPtr); 1034} 1035 1036/// PerformHeapAllocSRoA - MI is an allocation of an array of structures. Break 1037/// it up into multiple allocations of arrays of the fields. 1038static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, MallocInst *MI){ 1039 DOUT << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *MI; 1040 const StructType *STy = cast<StructType>(MI->getAllocatedType()); 1041 1042 // There is guaranteed to be at least one use of the malloc (storing 1043 // it into GV). If there are other uses, change them to be uses of 1044 // the global to simplify later code. This also deletes the store 1045 // into GV. 1046 ReplaceUsesOfMallocWithGlobal(MI, GV); 1047 1048 // Okay, at this point, there are no users of the malloc. Insert N 1049 // new mallocs at the same place as MI, and N globals. 1050 std::vector<GlobalVariable*> FieldGlobals; 1051 std::vector<MallocInst*> FieldMallocs; 1052 1053 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ 1054 const Type *FieldTy = STy->getElementType(FieldNo); 1055 const Type *PFieldTy = PointerType::getUnqual(FieldTy); 1056 1057 GlobalVariable *NGV = 1058 new GlobalVariable(PFieldTy, false, GlobalValue::InternalLinkage, 1059 Constant::getNullValue(PFieldTy), 1060 GV->getName() + ".f" + utostr(FieldNo), GV, 1061 GV->isThreadLocal()); 1062 FieldGlobals.push_back(NGV); 1063 1064 MallocInst *NMI = new MallocInst(FieldTy, MI->getArraySize(), 1065 MI->getName() + ".f" + utostr(FieldNo),MI); 1066 FieldMallocs.push_back(NMI); 1067 new StoreInst(NMI, NGV, MI); 1068 } 1069 1070 // The tricky aspect of this transformation is handling the case when malloc 1071 // fails. In the original code, malloc failing would set the result pointer 1072 // of malloc to null. In this case, some mallocs could succeed and others 1073 // could fail. As such, we emit code that looks like this: 1074 // F0 = malloc(field0) 1075 // F1 = malloc(field1) 1076 // F2 = malloc(field2) 1077 // if (F0 == 0 || F1 == 0 || F2 == 0) { 1078 // if (F0) { free(F0); F0 = 0; } 1079 // if (F1) { free(F1); F1 = 0; } 1080 // if (F2) { free(F2); F2 = 0; } 1081 // } 1082 Value *RunningOr = 0; 1083 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) { 1084 Value *Cond = new ICmpInst(ICmpInst::ICMP_EQ, FieldMallocs[i], 1085 Constant::getNullValue(FieldMallocs[i]->getType()), 1086 "isnull", MI); 1087 if (!RunningOr) 1088 RunningOr = Cond; // First seteq 1089 else 1090 RunningOr = BinaryOperator::createOr(RunningOr, Cond, "tmp", MI); 1091 } 1092 1093 // Split the basic block at the old malloc. 1094 BasicBlock *OrigBB = MI->getParent(); 1095 BasicBlock *ContBB = OrigBB->splitBasicBlock(MI, "malloc_cont"); 1096 1097 // Create the block to check the first condition. Put all these blocks at the 1098 // end of the function as they are unlikely to be executed. 1099 BasicBlock *NullPtrBlock = new BasicBlock("malloc_ret_null", 1100 OrigBB->getParent()); 1101 1102 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond 1103 // branch on RunningOr. 1104 OrigBB->getTerminator()->eraseFromParent(); 1105 new BranchInst(NullPtrBlock, ContBB, RunningOr, OrigBB); 1106 1107 // Within the NullPtrBlock, we need to emit a comparison and branch for each 1108 // pointer, because some may be null while others are not. 1109 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1110 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock); 1111 Value *Cmp = new ICmpInst(ICmpInst::ICMP_NE, GVVal, 1112 Constant::getNullValue(GVVal->getType()), 1113 "tmp", NullPtrBlock); 1114 BasicBlock *FreeBlock = new BasicBlock("free_it", OrigBB->getParent()); 1115 BasicBlock *NextBlock = new BasicBlock("next", OrigBB->getParent()); 1116 new BranchInst(FreeBlock, NextBlock, Cmp, NullPtrBlock); 1117 1118 // Fill in FreeBlock. 1119 new FreeInst(GVVal, FreeBlock); 1120 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i], 1121 FreeBlock); 1122 new BranchInst(NextBlock, FreeBlock); 1123 1124 NullPtrBlock = NextBlock; 1125 } 1126 1127 new BranchInst(ContBB, NullPtrBlock); 1128 1129 1130 // MI is no longer needed, remove it. 1131 MI->eraseFromParent(); 1132 1133 1134 // Okay, the malloc site is completely handled. All of the uses of GV are now 1135 // loads, and all uses of those loads are simple. Rewrite them to use loads 1136 // of the per-field globals instead. 1137 while (!GV->use_empty()) { 1138 if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) { 1139 RewriteUsesOfLoadForHeapSRoA(LI, FieldGlobals); 1140 LI->eraseFromParent(); 1141 } else { 1142 // Must be a store of null. 1143 StoreInst *SI = cast<StoreInst>(GV->use_back()); 1144 assert(isa<Constant>(SI->getOperand(0)) && 1145 cast<Constant>(SI->getOperand(0))->isNullValue() && 1146 "Unexpected heap-sra user!"); 1147 1148 // Insert a store of null into each global. 1149 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1150 Constant *Null = 1151 Constant::getNullValue(FieldGlobals[i]->getType()->getElementType()); 1152 new StoreInst(Null, FieldGlobals[i], SI); 1153 } 1154 // Erase the original store. 1155 SI->eraseFromParent(); 1156 } 1157 } 1158 1159 // The old global is now dead, remove it. 1160 GV->eraseFromParent(); 1161 1162 ++NumHeapSRA; 1163 return FieldGlobals[0]; 1164} 1165 1166 1167// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge 1168// that only one value (besides its initializer) is ever stored to the global. 1169static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal, 1170 Module::global_iterator &GVI, 1171 TargetData &TD) { 1172 if (CastInst *CI = dyn_cast<CastInst>(StoredOnceVal)) 1173 StoredOnceVal = CI->getOperand(0); 1174 else if (GetElementPtrInst *GEPI =dyn_cast<GetElementPtrInst>(StoredOnceVal)){ 1175 // "getelementptr Ptr, 0, 0, 0" is really just a cast. 1176 bool IsJustACast = true; 1177 for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i) 1178 if (!isa<Constant>(GEPI->getOperand(i)) || 1179 !cast<Constant>(GEPI->getOperand(i))->isNullValue()) { 1180 IsJustACast = false; 1181 break; 1182 } 1183 if (IsJustACast) 1184 StoredOnceVal = GEPI->getOperand(0); 1185 } 1186 1187 // If we are dealing with a pointer global that is initialized to null and 1188 // only has one (non-null) value stored into it, then we can optimize any 1189 // users of the loaded value (often calls and loads) that would trap if the 1190 // value was null. 1191 if (isa<PointerType>(GV->getInitializer()->getType()) && 1192 GV->getInitializer()->isNullValue()) { 1193 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { 1194 if (GV->getInitializer()->getType() != SOVC->getType()) 1195 SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType()); 1196 1197 // Optimize away any trapping uses of the loaded value. 1198 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC)) 1199 return true; 1200 } else if (MallocInst *MI = dyn_cast<MallocInst>(StoredOnceVal)) { 1201 // If this is a malloc of an abstract type, don't touch it. 1202 if (!MI->getAllocatedType()->isSized()) 1203 return false; 1204 1205 // We can't optimize this global unless all uses of it are *known* to be 1206 // of the malloc value, not of the null initializer value (consider a use 1207 // that compares the global's value against zero to see if the malloc has 1208 // been reached). To do this, we check to see if all uses of the global 1209 // would trap if the global were null: this proves that they must all 1210 // happen after the malloc. 1211 if (!AllUsesOfLoadedValueWillTrapIfNull(GV)) 1212 return false; 1213 1214 // We can't optimize this if the malloc itself is used in a complex way, 1215 // for example, being stored into multiple globals. This allows the 1216 // malloc to be stored into the specified global, loaded setcc'd, and 1217 // GEP'd. These are all things we could transform to using the global 1218 // for. 1219 { 1220 SmallPtrSet<PHINode*, 8> PHIs; 1221 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(MI, GV, PHIs)) 1222 return false; 1223 } 1224 1225 1226 // If we have a global that is only initialized with a fixed size malloc, 1227 // transform the program to use global memory instead of malloc'd memory. 1228 // This eliminates dynamic allocation, avoids an indirection accessing the 1229 // data, and exposes the resultant global to further GlobalOpt. 1230 if (ConstantInt *NElements = dyn_cast<ConstantInt>(MI->getArraySize())) { 1231 // Restrict this transformation to only working on small allocations 1232 // (2048 bytes currently), as we don't want to introduce a 16M global or 1233 // something. 1234 if (NElements->getZExtValue()* 1235 TD.getABITypeSize(MI->getAllocatedType()) < 2048) { 1236 GVI = OptimizeGlobalAddressOfMalloc(GV, MI); 1237 return true; 1238 } 1239 } 1240 1241 // If the allocation is an array of structures, consider transforming this 1242 // into multiple malloc'd arrays, one for each field. This is basically 1243 // SRoA for malloc'd memory. 1244 if (const StructType *AllocTy = 1245 dyn_cast<StructType>(MI->getAllocatedType())) { 1246 // This the structure has an unreasonable number of fields, leave it 1247 // alone. 1248 if (AllocTy->getNumElements() <= 16 && AllocTy->getNumElements() > 0 && 1249 GlobalLoadUsesSimpleEnoughForHeapSRA(GV, MI)) { 1250 GVI = PerformHeapAllocSRoA(GV, MI); 1251 return true; 1252 } 1253 } 1254 } 1255 } 1256 1257 return false; 1258} 1259 1260/// ShrinkGlobalToBoolean - At this point, we have learned that the only two 1261/// values ever stored into GV are its initializer and OtherVal. 1262static void ShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) { 1263 // Create the new global, initializing it to false. 1264 GlobalVariable *NewGV = new GlobalVariable(Type::Int1Ty, false, 1265 GlobalValue::InternalLinkage, ConstantInt::getFalse(), 1266 GV->getName()+".b", 1267 (Module *)NULL, 1268 GV->isThreadLocal()); 1269 GV->getParent()->getGlobalList().insert(GV, NewGV); 1270 1271 Constant *InitVal = GV->getInitializer(); 1272 assert(InitVal->getType() != Type::Int1Ty && "No reason to shrink to bool!"); 1273 1274 // If initialized to zero and storing one into the global, we can use a cast 1275 // instead of a select to synthesize the desired value. 1276 bool IsOneZero = false; 1277 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) 1278 IsOneZero = InitVal->isNullValue() && CI->isOne(); 1279 1280 while (!GV->use_empty()) { 1281 Instruction *UI = cast<Instruction>(GV->use_back()); 1282 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { 1283 // Change the store into a boolean store. 1284 bool StoringOther = SI->getOperand(0) == OtherVal; 1285 // Only do this if we weren't storing a loaded value. 1286 Value *StoreVal; 1287 if (StoringOther || SI->getOperand(0) == InitVal) 1288 StoreVal = ConstantInt::get(Type::Int1Ty, StoringOther); 1289 else { 1290 // Otherwise, we are storing a previously loaded copy. To do this, 1291 // change the copy from copying the original value to just copying the 1292 // bool. 1293 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); 1294 1295 // If we're already replaced the input, StoredVal will be a cast or 1296 // select instruction. If not, it will be a load of the original 1297 // global. 1298 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { 1299 assert(LI->getOperand(0) == GV && "Not a copy!"); 1300 // Insert a new load, to preserve the saved value. 1301 StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI); 1302 } else { 1303 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && 1304 "This is not a form that we understand!"); 1305 StoreVal = StoredVal->getOperand(0); 1306 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); 1307 } 1308 } 1309 new StoreInst(StoreVal, NewGV, SI); 1310 } else if (!UI->use_empty()) { 1311 // Change the load into a load of bool then a select. 1312 LoadInst *LI = cast<LoadInst>(UI); 1313 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", LI); 1314 Value *NSI; 1315 if (IsOneZero) 1316 NSI = new ZExtInst(NLI, LI->getType(), "", LI); 1317 else 1318 NSI = new SelectInst(NLI, OtherVal, InitVal, "", LI); 1319 NSI->takeName(LI); 1320 LI->replaceAllUsesWith(NSI); 1321 } 1322 UI->eraseFromParent(); 1323 } 1324 1325 GV->eraseFromParent(); 1326} 1327 1328 1329/// ProcessInternalGlobal - Analyze the specified global variable and optimize 1330/// it if possible. If we make a change, return true. 1331bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV, 1332 Module::global_iterator &GVI) { 1333 std::set<PHINode*> PHIUsers; 1334 GlobalStatus GS; 1335 GV->removeDeadConstantUsers(); 1336 1337 if (GV->use_empty()) { 1338 DOUT << "GLOBAL DEAD: " << *GV; 1339 GV->eraseFromParent(); 1340 ++NumDeleted; 1341 return true; 1342 } 1343 1344 if (!AnalyzeGlobal(GV, GS, PHIUsers)) { 1345#if 0 1346 cerr << "Global: " << *GV; 1347 cerr << " isLoaded = " << GS.isLoaded << "\n"; 1348 cerr << " StoredType = "; 1349 switch (GS.StoredType) { 1350 case GlobalStatus::NotStored: cerr << "NEVER STORED\n"; break; 1351 case GlobalStatus::isInitializerStored: cerr << "INIT STORED\n"; break; 1352 case GlobalStatus::isStoredOnce: cerr << "STORED ONCE\n"; break; 1353 case GlobalStatus::isStored: cerr << "stored\n"; break; 1354 } 1355 if (GS.StoredType == GlobalStatus::isStoredOnce && GS.StoredOnceValue) 1356 cerr << " StoredOnceValue = " << *GS.StoredOnceValue << "\n"; 1357 if (GS.AccessingFunction && !GS.HasMultipleAccessingFunctions) 1358 cerr << " AccessingFunction = " << GS.AccessingFunction->getName() 1359 << "\n"; 1360 cerr << " HasMultipleAccessingFunctions = " 1361 << GS.HasMultipleAccessingFunctions << "\n"; 1362 cerr << " HasNonInstructionUser = " << GS.HasNonInstructionUser<<"\n"; 1363 cerr << " isNotSuitableForSRA = " << GS.isNotSuitableForSRA << "\n"; 1364 cerr << "\n"; 1365#endif 1366 1367 // If this is a first class global and has only one accessing function 1368 // and this function is main (which we know is not recursive we can make 1369 // this global a local variable) we replace the global with a local alloca 1370 // in this function. 1371 // 1372 // NOTE: It doesn't make sense to promote non first class types since we 1373 // are just replacing static memory to stack memory. 1374 if (!GS.HasMultipleAccessingFunctions && 1375 GS.AccessingFunction && !GS.HasNonInstructionUser && 1376 GV->getType()->getElementType()->isFirstClassType() && 1377 GS.AccessingFunction->getName() == "main" && 1378 GS.AccessingFunction->hasExternalLinkage()) { 1379 DOUT << "LOCALIZING GLOBAL: " << *GV; 1380 Instruction* FirstI = GS.AccessingFunction->getEntryBlock().begin(); 1381 const Type* ElemTy = GV->getType()->getElementType(); 1382 // FIXME: Pass Global's alignment when globals have alignment 1383 AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), FirstI); 1384 if (!isa<UndefValue>(GV->getInitializer())) 1385 new StoreInst(GV->getInitializer(), Alloca, FirstI); 1386 1387 GV->replaceAllUsesWith(Alloca); 1388 GV->eraseFromParent(); 1389 ++NumLocalized; 1390 return true; 1391 } 1392 1393 // If the global is never loaded (but may be stored to), it is dead. 1394 // Delete it now. 1395 if (!GS.isLoaded) { 1396 DOUT << "GLOBAL NEVER LOADED: " << *GV; 1397 1398 // Delete any stores we can find to the global. We may not be able to 1399 // make it completely dead though. 1400 bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1401 1402 // If the global is dead now, delete it. 1403 if (GV->use_empty()) { 1404 GV->eraseFromParent(); 1405 ++NumDeleted; 1406 Changed = true; 1407 } 1408 return Changed; 1409 1410 } else if (GS.StoredType <= GlobalStatus::isInitializerStored) { 1411 DOUT << "MARKING CONSTANT: " << *GV; 1412 GV->setConstant(true); 1413 1414 // Clean up any obviously simplifiable users now. 1415 CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1416 1417 // If the global is dead now, just nuke it. 1418 if (GV->use_empty()) { 1419 DOUT << " *** Marking constant allowed us to simplify " 1420 << "all users and delete global!\n"; 1421 GV->eraseFromParent(); 1422 ++NumDeleted; 1423 } 1424 1425 ++NumMarked; 1426 return true; 1427 } else if (!GS.isNotSuitableForSRA && 1428 !GV->getInitializer()->getType()->isFirstClassType()) { 1429 if (GlobalVariable *FirstNewGV = SRAGlobal(GV)) { 1430 GVI = FirstNewGV; // Don't skip the newly produced globals! 1431 return true; 1432 } 1433 } else if (GS.StoredType == GlobalStatus::isStoredOnce) { 1434 // If the initial value for the global was an undef value, and if only 1435 // one other value was stored into it, we can just change the 1436 // initializer to be an undef value, then delete all stores to the 1437 // global. This allows us to mark it constant. 1438 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1439 if (isa<UndefValue>(GV->getInitializer())) { 1440 // Change the initial value here. 1441 GV->setInitializer(SOVConstant); 1442 1443 // Clean up any obviously simplifiable users now. 1444 CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1445 1446 if (GV->use_empty()) { 1447 DOUT << " *** Substituting initializer allowed us to " 1448 << "simplify all users and delete global!\n"; 1449 GV->eraseFromParent(); 1450 ++NumDeleted; 1451 } else { 1452 GVI = GV; 1453 } 1454 ++NumSubstitute; 1455 return true; 1456 } 1457 1458 // Try to optimize globals based on the knowledge that only one value 1459 // (besides its initializer) is ever stored to the global. 1460 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI, 1461 getAnalysis<TargetData>())) 1462 return true; 1463 1464 // Otherwise, if the global was not a boolean, we can shrink it to be a 1465 // boolean. 1466 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1467 if (GV->getType()->getElementType() != Type::Int1Ty && 1468 !GV->getType()->getElementType()->isFloatingPoint() && 1469 !isa<VectorType>(GV->getType()->getElementType()) && 1470 !GS.HasPHIUser && !GS.isNotSuitableForSRA) { 1471 DOUT << " *** SHRINKING TO BOOL: " << *GV; 1472 ShrinkGlobalToBoolean(GV, SOVConstant); 1473 ++NumShrunkToBool; 1474 return true; 1475 } 1476 } 1477 } 1478 return false; 1479} 1480 1481/// OnlyCalledDirectly - Return true if the specified function is only called 1482/// directly. In other words, its address is never taken. 1483static bool OnlyCalledDirectly(Function *F) { 1484 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1485 Instruction *User = dyn_cast<Instruction>(*UI); 1486 if (!User) return false; 1487 if (!isa<CallInst>(User) && !isa<InvokeInst>(User)) return false; 1488 1489 // See if the function address is passed as an argument. 1490 for (unsigned i = 1, e = User->getNumOperands(); i != e; ++i) 1491 if (User->getOperand(i) == F) return false; 1492 } 1493 return true; 1494} 1495 1496/// ChangeCalleesToFastCall - Walk all of the direct calls of the specified 1497/// function, changing them to FastCC. 1498static void ChangeCalleesToFastCall(Function *F) { 1499 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1500 Instruction *User = cast<Instruction>(*UI); 1501 if (CallInst *CI = dyn_cast<CallInst>(User)) 1502 CI->setCallingConv(CallingConv::Fast); 1503 else 1504 cast<InvokeInst>(User)->setCallingConv(CallingConv::Fast); 1505 } 1506} 1507 1508bool GlobalOpt::OptimizeFunctions(Module &M) { 1509 bool Changed = false; 1510 // Optimize functions. 1511 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { 1512 Function *F = FI++; 1513 F->removeDeadConstantUsers(); 1514 if (F->use_empty() && (F->hasInternalLinkage() || 1515 F->hasLinkOnceLinkage())) { 1516 M.getFunctionList().erase(F); 1517 Changed = true; 1518 ++NumFnDeleted; 1519 } else if (F->hasInternalLinkage() && 1520 F->getCallingConv() == CallingConv::C && !F->isVarArg() && 1521 OnlyCalledDirectly(F)) { 1522 // If this function has C calling conventions, is not a varargs 1523 // function, and is only called directly, promote it to use the Fast 1524 // calling convention. 1525 F->setCallingConv(CallingConv::Fast); 1526 ChangeCalleesToFastCall(F); 1527 ++NumFastCallFns; 1528 Changed = true; 1529 } 1530 } 1531 return Changed; 1532} 1533 1534bool GlobalOpt::OptimizeGlobalVars(Module &M) { 1535 bool Changed = false; 1536 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); 1537 GVI != E; ) { 1538 GlobalVariable *GV = GVI++; 1539 if (!GV->isConstant() && GV->hasInternalLinkage() && 1540 GV->hasInitializer()) 1541 Changed |= ProcessInternalGlobal(GV, GVI); 1542 } 1543 return Changed; 1544} 1545 1546/// FindGlobalCtors - Find the llvm.globalctors list, verifying that all 1547/// initializers have an init priority of 65535. 1548GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) { 1549 for (Module::global_iterator I = M.global_begin(), E = M.global_end(); 1550 I != E; ++I) 1551 if (I->getName() == "llvm.global_ctors") { 1552 // Found it, verify it's an array of { int, void()* }. 1553 const ArrayType *ATy =dyn_cast<ArrayType>(I->getType()->getElementType()); 1554 if (!ATy) return 0; 1555 const StructType *STy = dyn_cast<StructType>(ATy->getElementType()); 1556 if (!STy || STy->getNumElements() != 2 || 1557 STy->getElementType(0) != Type::Int32Ty) return 0; 1558 const PointerType *PFTy = dyn_cast<PointerType>(STy->getElementType(1)); 1559 if (!PFTy) return 0; 1560 const FunctionType *FTy = dyn_cast<FunctionType>(PFTy->getElementType()); 1561 if (!FTy || FTy->getReturnType() != Type::VoidTy || FTy->isVarArg() || 1562 FTy->getNumParams() != 0) 1563 return 0; 1564 1565 // Verify that the initializer is simple enough for us to handle. 1566 if (!I->hasInitializer()) return 0; 1567 ConstantArray *CA = dyn_cast<ConstantArray>(I->getInitializer()); 1568 if (!CA) return 0; 1569 for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i) 1570 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(CA->getOperand(i))) { 1571 if (isa<ConstantPointerNull>(CS->getOperand(1))) 1572 continue; 1573 1574 // Must have a function or null ptr. 1575 if (!isa<Function>(CS->getOperand(1))) 1576 return 0; 1577 1578 // Init priority must be standard. 1579 ConstantInt *CI = dyn_cast<ConstantInt>(CS->getOperand(0)); 1580 if (!CI || CI->getZExtValue() != 65535) 1581 return 0; 1582 } else { 1583 return 0; 1584 } 1585 1586 return I; 1587 } 1588 return 0; 1589} 1590 1591/// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand, 1592/// return a list of the functions and null terminator as a vector. 1593static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) { 1594 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer()); 1595 std::vector<Function*> Result; 1596 Result.reserve(CA->getNumOperands()); 1597 for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i) { 1598 ConstantStruct *CS = cast<ConstantStruct>(CA->getOperand(i)); 1599 Result.push_back(dyn_cast<Function>(CS->getOperand(1))); 1600 } 1601 return Result; 1602} 1603 1604/// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the 1605/// specified array, returning the new global to use. 1606static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL, 1607 const std::vector<Function*> &Ctors) { 1608 // If we made a change, reassemble the initializer list. 1609 std::vector<Constant*> CSVals; 1610 CSVals.push_back(ConstantInt::get(Type::Int32Ty, 65535)); 1611 CSVals.push_back(0); 1612 1613 // Create the new init list. 1614 std::vector<Constant*> CAList; 1615 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) { 1616 if (Ctors[i]) { 1617 CSVals[1] = Ctors[i]; 1618 } else { 1619 const Type *FTy = FunctionType::get(Type::VoidTy, 1620 std::vector<const Type*>(), false); 1621 const PointerType *PFTy = PointerType::getUnqual(FTy); 1622 CSVals[1] = Constant::getNullValue(PFTy); 1623 CSVals[0] = ConstantInt::get(Type::Int32Ty, 2147483647); 1624 } 1625 CAList.push_back(ConstantStruct::get(CSVals)); 1626 } 1627 1628 // Create the array initializer. 1629 const Type *StructTy = 1630 cast<ArrayType>(GCL->getType()->getElementType())->getElementType(); 1631 Constant *CA = ConstantArray::get(ArrayType::get(StructTy, CAList.size()), 1632 CAList); 1633 1634 // If we didn't change the number of elements, don't create a new GV. 1635 if (CA->getType() == GCL->getInitializer()->getType()) { 1636 GCL->setInitializer(CA); 1637 return GCL; 1638 } 1639 1640 // Create the new global and insert it next to the existing list. 1641 GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(), 1642 GCL->getLinkage(), CA, "", 1643 (Module *)NULL, 1644 GCL->isThreadLocal()); 1645 GCL->getParent()->getGlobalList().insert(GCL, NGV); 1646 NGV->takeName(GCL); 1647 1648 // Nuke the old list, replacing any uses with the new one. 1649 if (!GCL->use_empty()) { 1650 Constant *V = NGV; 1651 if (V->getType() != GCL->getType()) 1652 V = ConstantExpr::getBitCast(V, GCL->getType()); 1653 GCL->replaceAllUsesWith(V); 1654 } 1655 GCL->eraseFromParent(); 1656 1657 if (Ctors.size()) 1658 return NGV; 1659 else 1660 return 0; 1661} 1662 1663 1664static Constant *getVal(std::map<Value*, Constant*> &ComputedValues, 1665 Value *V) { 1666 if (Constant *CV = dyn_cast<Constant>(V)) return CV; 1667 Constant *R = ComputedValues[V]; 1668 assert(R && "Reference to an uncomputed value!"); 1669 return R; 1670} 1671 1672/// isSimpleEnoughPointerToCommit - Return true if this constant is simple 1673/// enough for us to understand. In particular, if it is a cast of something, 1674/// we punt. We basically just support direct accesses to globals and GEP's of 1675/// globals. This should be kept up to date with CommitValueTo. 1676static bool isSimpleEnoughPointerToCommit(Constant *C) { 1677 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) { 1678 if (!GV->hasExternalLinkage() && !GV->hasInternalLinkage()) 1679 return false; // do not allow weak/linkonce/dllimport/dllexport linkage. 1680 return !GV->isDeclaration(); // reject external globals. 1681 } 1682 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 1683 // Handle a constantexpr gep. 1684 if (CE->getOpcode() == Instruction::GetElementPtr && 1685 isa<GlobalVariable>(CE->getOperand(0))) { 1686 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 1687 if (!GV->hasExternalLinkage() && !GV->hasInternalLinkage()) 1688 return false; // do not allow weak/linkonce/dllimport/dllexport linkage. 1689 return GV->hasInitializer() && 1690 ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 1691 } 1692 return false; 1693} 1694 1695/// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global 1696/// initializer. This returns 'Init' modified to reflect 'Val' stored into it. 1697/// At this point, the GEP operands of Addr [0, OpNo) have been stepped into. 1698static Constant *EvaluateStoreInto(Constant *Init, Constant *Val, 1699 ConstantExpr *Addr, unsigned OpNo) { 1700 // Base case of the recursion. 1701 if (OpNo == Addr->getNumOperands()) { 1702 assert(Val->getType() == Init->getType() && "Type mismatch!"); 1703 return Val; 1704 } 1705 1706 if (const StructType *STy = dyn_cast<StructType>(Init->getType())) { 1707 std::vector<Constant*> Elts; 1708 1709 // Break up the constant into its elements. 1710 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) { 1711 for (unsigned i = 0, e = CS->getNumOperands(); i != e; ++i) 1712 Elts.push_back(CS->getOperand(i)); 1713 } else if (isa<ConstantAggregateZero>(Init)) { 1714 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 1715 Elts.push_back(Constant::getNullValue(STy->getElementType(i))); 1716 } else if (isa<UndefValue>(Init)) { 1717 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 1718 Elts.push_back(UndefValue::get(STy->getElementType(i))); 1719 } else { 1720 assert(0 && "This code is out of sync with " 1721 " ConstantFoldLoadThroughGEPConstantExpr"); 1722 } 1723 1724 // Replace the element that we are supposed to. 1725 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo)); 1726 unsigned Idx = CU->getZExtValue(); 1727 assert(Idx < STy->getNumElements() && "Struct index out of range!"); 1728 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1); 1729 1730 // Return the modified struct. 1731 return ConstantStruct::get(&Elts[0], Elts.size(), STy->isPacked()); 1732 } else { 1733 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo)); 1734 const ArrayType *ATy = cast<ArrayType>(Init->getType()); 1735 1736 // Break up the array into elements. 1737 std::vector<Constant*> Elts; 1738 if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) { 1739 for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i) 1740 Elts.push_back(CA->getOperand(i)); 1741 } else if (isa<ConstantAggregateZero>(Init)) { 1742 Constant *Elt = Constant::getNullValue(ATy->getElementType()); 1743 Elts.assign(ATy->getNumElements(), Elt); 1744 } else if (isa<UndefValue>(Init)) { 1745 Constant *Elt = UndefValue::get(ATy->getElementType()); 1746 Elts.assign(ATy->getNumElements(), Elt); 1747 } else { 1748 assert(0 && "This code is out of sync with " 1749 " ConstantFoldLoadThroughGEPConstantExpr"); 1750 } 1751 1752 assert(CI->getZExtValue() < ATy->getNumElements()); 1753 Elts[CI->getZExtValue()] = 1754 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1); 1755 return ConstantArray::get(ATy, Elts); 1756 } 1757} 1758 1759/// CommitValueTo - We have decided that Addr (which satisfies the predicate 1760/// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen. 1761static void CommitValueTo(Constant *Val, Constant *Addr) { 1762 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) { 1763 assert(GV->hasInitializer()); 1764 GV->setInitializer(Val); 1765 return; 1766 } 1767 1768 ConstantExpr *CE = cast<ConstantExpr>(Addr); 1769 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 1770 1771 Constant *Init = GV->getInitializer(); 1772 Init = EvaluateStoreInto(Init, Val, CE, 2); 1773 GV->setInitializer(Init); 1774} 1775 1776/// ComputeLoadResult - Return the value that would be computed by a load from 1777/// P after the stores reflected by 'memory' have been performed. If we can't 1778/// decide, return null. 1779static Constant *ComputeLoadResult(Constant *P, 1780 const std::map<Constant*, Constant*> &Memory) { 1781 // If this memory location has been recently stored, use the stored value: it 1782 // is the most up-to-date. 1783 std::map<Constant*, Constant*>::const_iterator I = Memory.find(P); 1784 if (I != Memory.end()) return I->second; 1785 1786 // Access it. 1787 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) { 1788 if (GV->hasInitializer()) 1789 return GV->getInitializer(); 1790 return 0; 1791 } 1792 1793 // Handle a constantexpr getelementptr. 1794 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) 1795 if (CE->getOpcode() == Instruction::GetElementPtr && 1796 isa<GlobalVariable>(CE->getOperand(0))) { 1797 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 1798 if (GV->hasInitializer()) 1799 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 1800 } 1801 1802 return 0; // don't know how to evaluate. 1803} 1804 1805/// EvaluateFunction - Evaluate a call to function F, returning true if 1806/// successful, false if we can't evaluate it. ActualArgs contains the formal 1807/// arguments for the function. 1808static bool EvaluateFunction(Function *F, Constant *&RetVal, 1809 const std::vector<Constant*> &ActualArgs, 1810 std::vector<Function*> &CallStack, 1811 std::map<Constant*, Constant*> &MutatedMemory, 1812 std::vector<GlobalVariable*> &AllocaTmps) { 1813 // Check to see if this function is already executing (recursion). If so, 1814 // bail out. TODO: we might want to accept limited recursion. 1815 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end()) 1816 return false; 1817 1818 CallStack.push_back(F); 1819 1820 /// Values - As we compute SSA register values, we store their contents here. 1821 std::map<Value*, Constant*> Values; 1822 1823 // Initialize arguments to the incoming values specified. 1824 unsigned ArgNo = 0; 1825 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E; 1826 ++AI, ++ArgNo) 1827 Values[AI] = ActualArgs[ArgNo]; 1828 1829 /// ExecutedBlocks - We only handle non-looping, non-recursive code. As such, 1830 /// we can only evaluate any one basic block at most once. This set keeps 1831 /// track of what we have executed so we can detect recursive cases etc. 1832 std::set<BasicBlock*> ExecutedBlocks; 1833 1834 // CurInst - The current instruction we're evaluating. 1835 BasicBlock::iterator CurInst = F->begin()->begin(); 1836 1837 // This is the main evaluation loop. 1838 while (1) { 1839 Constant *InstResult = 0; 1840 1841 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) { 1842 if (SI->isVolatile()) return false; // no volatile accesses. 1843 Constant *Ptr = getVal(Values, SI->getOperand(1)); 1844 if (!isSimpleEnoughPointerToCommit(Ptr)) 1845 // If this is too complex for us to commit, reject it. 1846 return false; 1847 Constant *Val = getVal(Values, SI->getOperand(0)); 1848 MutatedMemory[Ptr] = Val; 1849 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) { 1850 InstResult = ConstantExpr::get(BO->getOpcode(), 1851 getVal(Values, BO->getOperand(0)), 1852 getVal(Values, BO->getOperand(1))); 1853 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) { 1854 InstResult = ConstantExpr::getCompare(CI->getPredicate(), 1855 getVal(Values, CI->getOperand(0)), 1856 getVal(Values, CI->getOperand(1))); 1857 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) { 1858 InstResult = ConstantExpr::getCast(CI->getOpcode(), 1859 getVal(Values, CI->getOperand(0)), 1860 CI->getType()); 1861 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) { 1862 InstResult = ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)), 1863 getVal(Values, SI->getOperand(1)), 1864 getVal(Values, SI->getOperand(2))); 1865 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) { 1866 Constant *P = getVal(Values, GEP->getOperand(0)); 1867 SmallVector<Constant*, 8> GEPOps; 1868 for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i) 1869 GEPOps.push_back(getVal(Values, GEP->getOperand(i))); 1870 InstResult = ConstantExpr::getGetElementPtr(P, &GEPOps[0], GEPOps.size()); 1871 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) { 1872 if (LI->isVolatile()) return false; // no volatile accesses. 1873 InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)), 1874 MutatedMemory); 1875 if (InstResult == 0) return false; // Could not evaluate load. 1876 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) { 1877 if (AI->isArrayAllocation()) return false; // Cannot handle array allocs. 1878 const Type *Ty = AI->getType()->getElementType(); 1879 AllocaTmps.push_back(new GlobalVariable(Ty, false, 1880 GlobalValue::InternalLinkage, 1881 UndefValue::get(Ty), 1882 AI->getName())); 1883 InstResult = AllocaTmps.back(); 1884 } else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) { 1885 // Cannot handle inline asm. 1886 if (isa<InlineAsm>(CI->getOperand(0))) return false; 1887 1888 // Resolve function pointers. 1889 Function *Callee = dyn_cast<Function>(getVal(Values, CI->getOperand(0))); 1890 if (!Callee) return false; // Cannot resolve. 1891 1892 std::vector<Constant*> Formals; 1893 for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i) 1894 Formals.push_back(getVal(Values, CI->getOperand(i))); 1895 1896 if (Callee->isDeclaration()) { 1897 // If this is a function we can constant fold, do it. 1898 if (Constant *C = ConstantFoldCall(Callee, &Formals[0], 1899 Formals.size())) { 1900 InstResult = C; 1901 } else { 1902 return false; 1903 } 1904 } else { 1905 if (Callee->getFunctionType()->isVarArg()) 1906 return false; 1907 1908 Constant *RetVal; 1909 1910 // Execute the call, if successful, use the return value. 1911 if (!EvaluateFunction(Callee, RetVal, Formals, CallStack, 1912 MutatedMemory, AllocaTmps)) 1913 return false; 1914 InstResult = RetVal; 1915 } 1916 } else if (isa<TerminatorInst>(CurInst)) { 1917 BasicBlock *NewBB = 0; 1918 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) { 1919 if (BI->isUnconditional()) { 1920 NewBB = BI->getSuccessor(0); 1921 } else { 1922 ConstantInt *Cond = 1923 dyn_cast<ConstantInt>(getVal(Values, BI->getCondition())); 1924 if (!Cond) return false; // Cannot determine. 1925 1926 NewBB = BI->getSuccessor(!Cond->getZExtValue()); 1927 } 1928 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) { 1929 ConstantInt *Val = 1930 dyn_cast<ConstantInt>(getVal(Values, SI->getCondition())); 1931 if (!Val) return false; // Cannot determine. 1932 NewBB = SI->getSuccessor(SI->findCaseValue(Val)); 1933 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) { 1934 if (RI->getNumOperands()) 1935 RetVal = getVal(Values, RI->getOperand(0)); 1936 1937 CallStack.pop_back(); // return from fn. 1938 return true; // We succeeded at evaluating this ctor! 1939 } else { 1940 // invoke, unwind, unreachable. 1941 return false; // Cannot handle this terminator. 1942 } 1943 1944 // Okay, we succeeded in evaluating this control flow. See if we have 1945 // executed the new block before. If so, we have a looping function, 1946 // which we cannot evaluate in reasonable time. 1947 if (!ExecutedBlocks.insert(NewBB).second) 1948 return false; // looped! 1949 1950 // Okay, we have never been in this block before. Check to see if there 1951 // are any PHI nodes. If so, evaluate them with information about where 1952 // we came from. 1953 BasicBlock *OldBB = CurInst->getParent(); 1954 CurInst = NewBB->begin(); 1955 PHINode *PN; 1956 for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst) 1957 Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB)); 1958 1959 // Do NOT increment CurInst. We know that the terminator had no value. 1960 continue; 1961 } else { 1962 // Did not know how to evaluate this! 1963 return false; 1964 } 1965 1966 if (!CurInst->use_empty()) 1967 Values[CurInst] = InstResult; 1968 1969 // Advance program counter. 1970 ++CurInst; 1971 } 1972} 1973 1974/// EvaluateStaticConstructor - Evaluate static constructors in the function, if 1975/// we can. Return true if we can, false otherwise. 1976static bool EvaluateStaticConstructor(Function *F) { 1977 /// MutatedMemory - For each store we execute, we update this map. Loads 1978 /// check this to get the most up-to-date value. If evaluation is successful, 1979 /// this state is committed to the process. 1980 std::map<Constant*, Constant*> MutatedMemory; 1981 1982 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable 1983 /// to represent its body. This vector is needed so we can delete the 1984 /// temporary globals when we are done. 1985 std::vector<GlobalVariable*> AllocaTmps; 1986 1987 /// CallStack - This is used to detect recursion. In pathological situations 1988 /// we could hit exponential behavior, but at least there is nothing 1989 /// unbounded. 1990 std::vector<Function*> CallStack; 1991 1992 // Call the function. 1993 Constant *RetValDummy; 1994 bool EvalSuccess = EvaluateFunction(F, RetValDummy, std::vector<Constant*>(), 1995 CallStack, MutatedMemory, AllocaTmps); 1996 if (EvalSuccess) { 1997 // We succeeded at evaluation: commit the result. 1998 DOUT << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" 1999 << F->getName() << "' to " << MutatedMemory.size() 2000 << " stores.\n"; 2001 for (std::map<Constant*, Constant*>::iterator I = MutatedMemory.begin(), 2002 E = MutatedMemory.end(); I != E; ++I) 2003 CommitValueTo(I->second, I->first); 2004 } 2005 2006 // At this point, we are done interpreting. If we created any 'alloca' 2007 // temporaries, release them now. 2008 while (!AllocaTmps.empty()) { 2009 GlobalVariable *Tmp = AllocaTmps.back(); 2010 AllocaTmps.pop_back(); 2011 2012 // If there are still users of the alloca, the program is doing something 2013 // silly, e.g. storing the address of the alloca somewhere and using it 2014 // later. Since this is undefined, we'll just make it be null. 2015 if (!Tmp->use_empty()) 2016 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType())); 2017 delete Tmp; 2018 } 2019 2020 return EvalSuccess; 2021} 2022 2023 2024 2025/// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible. 2026/// Return true if anything changed. 2027bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) { 2028 std::vector<Function*> Ctors = ParseGlobalCtors(GCL); 2029 bool MadeChange = false; 2030 if (Ctors.empty()) return false; 2031 2032 // Loop over global ctors, optimizing them when we can. 2033 for (unsigned i = 0; i != Ctors.size(); ++i) { 2034 Function *F = Ctors[i]; 2035 // Found a null terminator in the middle of the list, prune off the rest of 2036 // the list. 2037 if (F == 0) { 2038 if (i != Ctors.size()-1) { 2039 Ctors.resize(i+1); 2040 MadeChange = true; 2041 } 2042 break; 2043 } 2044 2045 // We cannot simplify external ctor functions. 2046 if (F->empty()) continue; 2047 2048 // If we can evaluate the ctor at compile time, do. 2049 if (EvaluateStaticConstructor(F)) { 2050 Ctors.erase(Ctors.begin()+i); 2051 MadeChange = true; 2052 --i; 2053 ++NumCtorsEvaluated; 2054 continue; 2055 } 2056 } 2057 2058 if (!MadeChange) return false; 2059 2060 GCL = InstallGlobalCtors(GCL, Ctors); 2061 return true; 2062} 2063 2064 2065bool GlobalOpt::runOnModule(Module &M) { 2066 bool Changed = false; 2067 2068 // Try to find the llvm.globalctors list. 2069 GlobalVariable *GlobalCtors = FindGlobalCtors(M); 2070 2071 bool LocalChange = true; 2072 while (LocalChange) { 2073 LocalChange = false; 2074 2075 // Delete functions that are trivially dead, ccc -> fastcc 2076 LocalChange |= OptimizeFunctions(M); 2077 2078 // Optimize global_ctors list. 2079 if (GlobalCtors) 2080 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors); 2081 2082 // Optimize non-address-taken globals. 2083 LocalChange |= OptimizeGlobalVars(M); 2084 Changed |= LocalChange; 2085 } 2086 2087 // TODO: Move all global ctors functions to the end of the module for code 2088 // layout. 2089 2090 return Changed; 2091} 2092