GlobalOpt.cpp revision 3ed470da2b05e027282e2f8c67b3739dad11745c
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 if (I->getOperand(0) == V) { 686 // Calling through the pointer! Turn into a direct call, but be careful 687 // that the pointer is not also being passed as an argument. 688 I->setOperand(0, NewV); 689 Changed = true; 690 bool PassedAsArg = false; 691 for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i) 692 if (I->getOperand(i) == V) { 693 PassedAsArg = true; 694 I->setOperand(i, NewV); 695 } 696 697 if (PassedAsArg) { 698 // Being passed as an argument also. Be careful to not invalidate UI! 699 UI = V->use_begin(); 700 } 701 } 702 } else if (CastInst *CI = dyn_cast<CastInst>(I)) { 703 Changed |= OptimizeAwayTrappingUsesOfValue(CI, 704 ConstantExpr::getCast(CI->getOpcode(), 705 NewV, CI->getType())); 706 if (CI->use_empty()) { 707 Changed = true; 708 CI->eraseFromParent(); 709 } 710 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { 711 // Should handle GEP here. 712 SmallVector<Constant*, 8> Idxs; 713 Idxs.reserve(GEPI->getNumOperands()-1); 714 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end(); 715 i != e; ++i) 716 if (Constant *C = dyn_cast<Constant>(*i)) 717 Idxs.push_back(C); 718 else 719 break; 720 if (Idxs.size() == GEPI->getNumOperands()-1) 721 Changed |= OptimizeAwayTrappingUsesOfValue(GEPI, 722 ConstantExpr::getGetElementPtr(NewV, &Idxs[0], 723 Idxs.size())); 724 if (GEPI->use_empty()) { 725 Changed = true; 726 GEPI->eraseFromParent(); 727 } 728 } 729 } 730 731 return Changed; 732} 733 734 735/// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null 736/// value stored into it. If there are uses of the loaded value that would trap 737/// if the loaded value is dynamically null, then we know that they cannot be 738/// reachable with a null optimize away the load. 739static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV) { 740 bool Changed = false; 741 742 // Keep track of whether we are able to remove all the uses of the global 743 // other than the store that defines it. 744 bool AllNonStoreUsesGone = true; 745 746 // Replace all uses of loads with uses of uses of the stored value. 747 for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){ 748 User *GlobalUser = *GUI++; 749 if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) { 750 Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV); 751 // If we were able to delete all uses of the loads 752 if (LI->use_empty()) { 753 LI->eraseFromParent(); 754 Changed = true; 755 } else { 756 AllNonStoreUsesGone = false; 757 } 758 } else if (isa<StoreInst>(GlobalUser)) { 759 // Ignore the store that stores "LV" to the global. 760 assert(GlobalUser->getOperand(1) == GV && 761 "Must be storing *to* the global"); 762 } else { 763 AllNonStoreUsesGone = false; 764 765 // If we get here we could have other crazy uses that are transitively 766 // loaded. 767 assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) || 768 isa<ConstantExpr>(GlobalUser)) && "Only expect load and stores!"); 769 } 770 } 771 772 if (Changed) { 773 DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV); 774 ++NumGlobUses; 775 } 776 777 // If we nuked all of the loads, then none of the stores are needed either, 778 // nor is the global. 779 if (AllNonStoreUsesGone) { 780 DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n"); 781 CleanupConstantGlobalUsers(GV, 0); 782 if (GV->use_empty()) { 783 GV->eraseFromParent(); 784 ++NumDeleted; 785 } 786 Changed = true; 787 } 788 return Changed; 789} 790 791/// ConstantPropUsersOf - Walk the use list of V, constant folding all of the 792/// instructions that are foldable. 793static void ConstantPropUsersOf(Value *V) { 794 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) 795 if (Instruction *I = dyn_cast<Instruction>(*UI++)) 796 if (Constant *NewC = ConstantFoldInstruction(I)) { 797 I->replaceAllUsesWith(NewC); 798 799 // Advance UI to the next non-I use to avoid invalidating it! 800 // Instructions could multiply use V. 801 while (UI != E && *UI == I) 802 ++UI; 803 I->eraseFromParent(); 804 } 805} 806 807/// OptimizeGlobalAddressOfMalloc - This function takes the specified global 808/// variable, and transforms the program as if it always contained the result of 809/// the specified malloc. Because it is always the result of the specified 810/// malloc, there is no reason to actually DO the malloc. Instead, turn the 811/// malloc into a global, and any loads of GV as uses of the new global. 812static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, 813 CallInst *CI, 814 const Type *AllocTy, 815 ConstantInt *NElements, 816 TargetData* TD) { 817 DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI << '\n'); 818 819 const Type *GlobalType; 820 if (NElements->getZExtValue() == 1) 821 GlobalType = AllocTy; 822 else 823 // If we have an array allocation, the global variable is of an array. 824 GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue()); 825 826 // Create the new global variable. The contents of the malloc'd memory is 827 // undefined, so initialize with an undef value. 828 GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(), 829 GlobalType, false, 830 GlobalValue::InternalLinkage, 831 UndefValue::get(GlobalType), 832 GV->getName()+".body", 833 GV, 834 GV->isThreadLocal()); 835 836 // If there are bitcast users of the malloc (which is typical, usually we have 837 // a malloc + bitcast) then replace them with uses of the new global. Update 838 // other users to use the global as well. 839 BitCastInst *TheBC = 0; 840 while (!CI->use_empty()) { 841 Instruction *User = cast<Instruction>(CI->use_back()); 842 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { 843 if (BCI->getType() == NewGV->getType()) { 844 BCI->replaceAllUsesWith(NewGV); 845 BCI->eraseFromParent(); 846 } else { 847 BCI->setOperand(0, NewGV); 848 } 849 } else { 850 if (TheBC == 0) 851 TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI); 852 User->replaceUsesOfWith(CI, TheBC); 853 } 854 } 855 856 Constant *RepValue = NewGV; 857 if (NewGV->getType() != GV->getType()->getElementType()) 858 RepValue = ConstantExpr::getBitCast(RepValue, 859 GV->getType()->getElementType()); 860 861 // If there is a comparison against null, we will insert a global bool to 862 // keep track of whether the global was initialized yet or not. 863 GlobalVariable *InitBool = 864 new GlobalVariable(Type::getInt1Ty(GV->getContext()), false, 865 GlobalValue::InternalLinkage, 866 ConstantInt::getFalse(GV->getContext()), 867 GV->getName()+".init", GV->isThreadLocal()); 868 bool InitBoolUsed = false; 869 870 // Loop over all uses of GV, processing them in turn. 871 while (!GV->use_empty()) { 872 if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) { 873 // The global is initialized when the store to it occurs. 874 new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, SI); 875 SI->eraseFromParent(); 876 continue; 877 } 878 879 LoadInst *LI = cast<LoadInst>(GV->use_back()); 880 while (!LI->use_empty()) { 881 Use &LoadUse = LI->use_begin().getUse(); 882 if (!isa<ICmpInst>(LoadUse.getUser())) { 883 LoadUse = RepValue; 884 continue; 885 } 886 887 ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser()); 888 // Replace the cmp X, 0 with a use of the bool value. 889 Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", ICI); 890 InitBoolUsed = true; 891 switch (ICI->getPredicate()) { 892 default: llvm_unreachable("Unknown ICmp Predicate!"); 893 case ICmpInst::ICMP_ULT: 894 case ICmpInst::ICMP_SLT: // X < null -> always false 895 LV = ConstantInt::getFalse(GV->getContext()); 896 break; 897 case ICmpInst::ICMP_ULE: 898 case ICmpInst::ICMP_SLE: 899 case ICmpInst::ICMP_EQ: 900 LV = BinaryOperator::CreateNot(LV, "notinit", ICI); 901 break; 902 case ICmpInst::ICMP_NE: 903 case ICmpInst::ICMP_UGE: 904 case ICmpInst::ICMP_SGE: 905 case ICmpInst::ICMP_UGT: 906 case ICmpInst::ICMP_SGT: 907 break; // no change. 908 } 909 ICI->replaceAllUsesWith(LV); 910 ICI->eraseFromParent(); 911 } 912 LI->eraseFromParent(); 913 } 914 915 // If the initialization boolean was used, insert it, otherwise delete it. 916 if (!InitBoolUsed) { 917 while (!InitBool->use_empty()) // Delete initializations 918 cast<StoreInst>(InitBool->use_back())->eraseFromParent(); 919 delete InitBool; 920 } else 921 GV->getParent()->getGlobalList().insert(GV, InitBool); 922 923 // Now the GV is dead, nuke it and the malloc.. 924 GV->eraseFromParent(); 925 CI->eraseFromParent(); 926 927 // To further other optimizations, loop over all users of NewGV and try to 928 // constant prop them. This will promote GEP instructions with constant 929 // indices into GEP constant-exprs, which will allow global-opt to hack on it. 930 ConstantPropUsersOf(NewGV); 931 if (RepValue != NewGV) 932 ConstantPropUsersOf(RepValue); 933 934 return NewGV; 935} 936 937/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking 938/// to make sure that there are no complex uses of V. We permit simple things 939/// like dereferencing the pointer, but not storing through the address, unless 940/// it is to the specified global. 941static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Instruction *V, 942 GlobalVariable *GV, 943 SmallPtrSet<PHINode*, 8> &PHIs) { 944 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 945 Instruction *Inst = cast<Instruction>(*UI); 946 947 if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) { 948 continue; // Fine, ignore. 949 } 950 951 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 952 if (SI->getOperand(0) == V && SI->getOperand(1) != GV) 953 return false; // Storing the pointer itself... bad. 954 continue; // Otherwise, storing through it, or storing into GV... fine. 955 } 956 957 if (isa<GetElementPtrInst>(Inst)) { 958 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs)) 959 return false; 960 continue; 961 } 962 963 if (PHINode *PN = dyn_cast<PHINode>(Inst)) { 964 // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI 965 // cycles. 966 if (PHIs.insert(PN)) 967 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs)) 968 return false; 969 continue; 970 } 971 972 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) { 973 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) 974 return false; 975 continue; 976 } 977 978 return false; 979 } 980 return true; 981} 982 983/// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV 984/// somewhere. Transform all uses of the allocation into loads from the 985/// global and uses of the resultant pointer. Further, delete the store into 986/// GV. This assumes that these value pass the 987/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate. 988static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, 989 GlobalVariable *GV) { 990 while (!Alloc->use_empty()) { 991 Instruction *U = cast<Instruction>(*Alloc->use_begin()); 992 Instruction *InsertPt = U; 993 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 994 // If this is the store of the allocation into the global, remove it. 995 if (SI->getOperand(1) == GV) { 996 SI->eraseFromParent(); 997 continue; 998 } 999 } else if (PHINode *PN = dyn_cast<PHINode>(U)) { 1000 // Insert the load in the corresponding predecessor, not right before the 1001 // PHI. 1002 InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator(); 1003 } else if (isa<BitCastInst>(U)) { 1004 // Must be bitcast between the malloc and store to initialize the global. 1005 ReplaceUsesOfMallocWithGlobal(U, GV); 1006 U->eraseFromParent(); 1007 continue; 1008 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { 1009 // If this is a "GEP bitcast" and the user is a store to the global, then 1010 // just process it as a bitcast. 1011 if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse()) 1012 if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back())) 1013 if (SI->getOperand(1) == GV) { 1014 // Must be bitcast GEP between the malloc and store to initialize 1015 // the global. 1016 ReplaceUsesOfMallocWithGlobal(GEPI, GV); 1017 GEPI->eraseFromParent(); 1018 continue; 1019 } 1020 } 1021 1022 // Insert a load from the global, and use it instead of the malloc. 1023 Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt); 1024 U->replaceUsesOfWith(Alloc, NL); 1025 } 1026} 1027 1028/// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi 1029/// of a load) are simple enough to perform heap SRA on. This permits GEP's 1030/// that index through the array and struct field, icmps of null, and PHIs. 1031static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V, 1032 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs, 1033 SmallPtrSet<const PHINode*, 32> &LoadUsingPHIsPerLoad) { 1034 // We permit two users of the load: setcc comparing against the null 1035 // pointer, and a getelementptr of a specific form. 1036 for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 1037 const Instruction *User = cast<Instruction>(*UI); 1038 1039 // Comparison against null is ok. 1040 if (const ICmpInst *ICI = dyn_cast<ICmpInst>(User)) { 1041 if (!isa<ConstantPointerNull>(ICI->getOperand(1))) 1042 return false; 1043 continue; 1044 } 1045 1046 // getelementptr is also ok, but only a simple form. 1047 if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1048 // Must index into the array and into the struct. 1049 if (GEPI->getNumOperands() < 3) 1050 return false; 1051 1052 // Otherwise the GEP is ok. 1053 continue; 1054 } 1055 1056 if (const PHINode *PN = dyn_cast<PHINode>(User)) { 1057 if (!LoadUsingPHIsPerLoad.insert(PN)) 1058 // This means some phi nodes are dependent on each other. 1059 // Avoid infinite looping! 1060 return false; 1061 if (!LoadUsingPHIs.insert(PN)) 1062 // If we have already analyzed this PHI, then it is safe. 1063 continue; 1064 1065 // Make sure all uses of the PHI are simple enough to transform. 1066 if (!LoadUsesSimpleEnoughForHeapSRA(PN, 1067 LoadUsingPHIs, LoadUsingPHIsPerLoad)) 1068 return false; 1069 1070 continue; 1071 } 1072 1073 // Otherwise we don't know what this is, not ok. 1074 return false; 1075 } 1076 1077 return true; 1078} 1079 1080 1081/// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from 1082/// GV are simple enough to perform HeapSRA, return true. 1083static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV, 1084 Instruction *StoredVal) { 1085 SmallPtrSet<const PHINode*, 32> LoadUsingPHIs; 1086 SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad; 1087 for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E; 1088 ++UI) 1089 if (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 1090 if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs, 1091 LoadUsingPHIsPerLoad)) 1092 return false; 1093 LoadUsingPHIsPerLoad.clear(); 1094 } 1095 1096 // If we reach here, we know that all uses of the loads and transitive uses 1097 // (through PHI nodes) are simple enough to transform. However, we don't know 1098 // that all inputs the to the PHI nodes are in the same equivalence sets. 1099 // Check to verify that all operands of the PHIs are either PHIS that can be 1100 // transformed, loads from GV, or MI itself. 1101 for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin(), 1102 E = LoadUsingPHIs.end(); I != E; ++I) { 1103 const PHINode *PN = *I; 1104 for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) { 1105 Value *InVal = PN->getIncomingValue(op); 1106 1107 // PHI of the stored value itself is ok. 1108 if (InVal == StoredVal) continue; 1109 1110 if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) { 1111 // One of the PHIs in our set is (optimistically) ok. 1112 if (LoadUsingPHIs.count(InPN)) 1113 continue; 1114 return false; 1115 } 1116 1117 // Load from GV is ok. 1118 if (const LoadInst *LI = dyn_cast<LoadInst>(InVal)) 1119 if (LI->getOperand(0) == GV) 1120 continue; 1121 1122 // UNDEF? NULL? 1123 1124 // Anything else is rejected. 1125 return false; 1126 } 1127 } 1128 1129 return true; 1130} 1131 1132static Value *GetHeapSROAValue(Value *V, unsigned FieldNo, 1133 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1134 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 1135 std::vector<Value*> &FieldVals = InsertedScalarizedValues[V]; 1136 1137 if (FieldNo >= FieldVals.size()) 1138 FieldVals.resize(FieldNo+1); 1139 1140 // If we already have this value, just reuse the previously scalarized 1141 // version. 1142 if (Value *FieldVal = FieldVals[FieldNo]) 1143 return FieldVal; 1144 1145 // Depending on what instruction this is, we have several cases. 1146 Value *Result; 1147 if (LoadInst *LI = dyn_cast<LoadInst>(V)) { 1148 // This is a scalarized version of the load from the global. Just create 1149 // a new Load of the scalarized global. 1150 Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo, 1151 InsertedScalarizedValues, 1152 PHIsToRewrite), 1153 LI->getName()+".f"+Twine(FieldNo), LI); 1154 } else if (PHINode *PN = dyn_cast<PHINode>(V)) { 1155 // PN's type is pointer to struct. Make a new PHI of pointer to struct 1156 // field. 1157 const StructType *ST = 1158 cast<StructType>(cast<PointerType>(PN->getType())->getElementType()); 1159 1160 Result = 1161 PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)), 1162 PN->getName()+".f"+Twine(FieldNo), PN); 1163 PHIsToRewrite.push_back(std::make_pair(PN, FieldNo)); 1164 } else { 1165 llvm_unreachable("Unknown usable value"); 1166 Result = 0; 1167 } 1168 1169 return FieldVals[FieldNo] = Result; 1170} 1171 1172/// RewriteHeapSROALoadUser - Given a load instruction and a value derived from 1173/// the load, rewrite the derived value to use the HeapSRoA'd load. 1174static void RewriteHeapSROALoadUser(Instruction *LoadUser, 1175 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1176 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 1177 // If this is a comparison against null, handle it. 1178 if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) { 1179 assert(isa<ConstantPointerNull>(SCI->getOperand(1))); 1180 // If we have a setcc of the loaded pointer, we can use a setcc of any 1181 // field. 1182 Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0, 1183 InsertedScalarizedValues, PHIsToRewrite); 1184 1185 Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr, 1186 Constant::getNullValue(NPtr->getType()), 1187 SCI->getName()); 1188 SCI->replaceAllUsesWith(New); 1189 SCI->eraseFromParent(); 1190 return; 1191 } 1192 1193 // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...' 1194 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) { 1195 assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2)) 1196 && "Unexpected GEPI!"); 1197 1198 // Load the pointer for this field. 1199 unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 1200 Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo, 1201 InsertedScalarizedValues, PHIsToRewrite); 1202 1203 // Create the new GEP idx vector. 1204 SmallVector<Value*, 8> GEPIdx; 1205 GEPIdx.push_back(GEPI->getOperand(1)); 1206 GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end()); 1207 1208 Value *NGEPI = GetElementPtrInst::Create(NewPtr, 1209 GEPIdx.begin(), GEPIdx.end(), 1210 GEPI->getName(), GEPI); 1211 GEPI->replaceAllUsesWith(NGEPI); 1212 GEPI->eraseFromParent(); 1213 return; 1214 } 1215 1216 // Recursively transform the users of PHI nodes. This will lazily create the 1217 // PHIs that are needed for individual elements. Keep track of what PHIs we 1218 // see in InsertedScalarizedValues so that we don't get infinite loops (very 1219 // antisocial). If the PHI is already in InsertedScalarizedValues, it has 1220 // already been seen first by another load, so its uses have already been 1221 // processed. 1222 PHINode *PN = cast<PHINode>(LoadUser); 1223 bool Inserted; 1224 DenseMap<Value*, std::vector<Value*> >::iterator InsertPos; 1225 tie(InsertPos, Inserted) = 1226 InsertedScalarizedValues.insert(std::make_pair(PN, std::vector<Value*>())); 1227 if (!Inserted) return; 1228 1229 // If this is the first time we've seen this PHI, recursively process all 1230 // users. 1231 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) { 1232 Instruction *User = cast<Instruction>(*UI++); 1233 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); 1234 } 1235} 1236 1237/// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global. Ptr 1238/// is a value loaded from the global. Eliminate all uses of Ptr, making them 1239/// use FieldGlobals instead. All uses of loaded values satisfy 1240/// AllGlobalLoadUsesSimpleEnoughForHeapSRA. 1241static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load, 1242 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues, 1243 std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) { 1244 for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end(); 1245 UI != E; ) { 1246 Instruction *User = cast<Instruction>(*UI++); 1247 RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); 1248 } 1249 1250 if (Load->use_empty()) { 1251 Load->eraseFromParent(); 1252 InsertedScalarizedValues.erase(Load); 1253 } 1254} 1255 1256/// PerformHeapAllocSRoA - CI is an allocation of an array of structures. Break 1257/// it up into multiple allocations of arrays of the fields. 1258static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI, 1259 Value* NElems, TargetData *TD) { 1260 DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI << '\n'); 1261 const Type* MAT = getMallocAllocatedType(CI); 1262 const StructType *STy = cast<StructType>(MAT); 1263 1264 // There is guaranteed to be at least one use of the malloc (storing 1265 // it into GV). If there are other uses, change them to be uses of 1266 // the global to simplify later code. This also deletes the store 1267 // into GV. 1268 ReplaceUsesOfMallocWithGlobal(CI, GV); 1269 1270 // Okay, at this point, there are no users of the malloc. Insert N 1271 // new mallocs at the same place as CI, and N globals. 1272 std::vector<Value*> FieldGlobals; 1273 std::vector<Value*> FieldMallocs; 1274 1275 for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ 1276 const Type *FieldTy = STy->getElementType(FieldNo); 1277 const PointerType *PFieldTy = PointerType::getUnqual(FieldTy); 1278 1279 GlobalVariable *NGV = 1280 new GlobalVariable(*GV->getParent(), 1281 PFieldTy, false, GlobalValue::InternalLinkage, 1282 Constant::getNullValue(PFieldTy), 1283 GV->getName() + ".f" + Twine(FieldNo), GV, 1284 GV->isThreadLocal()); 1285 FieldGlobals.push_back(NGV); 1286 1287 unsigned TypeSize = TD->getTypeAllocSize(FieldTy); 1288 if (const StructType *ST = dyn_cast<StructType>(FieldTy)) 1289 TypeSize = TD->getStructLayout(ST)->getSizeInBytes(); 1290 const Type *IntPtrTy = TD->getIntPtrType(CI->getContext()); 1291 Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy, 1292 ConstantInt::get(IntPtrTy, TypeSize), 1293 NElems, 1294 CI->getName() + ".f" + Twine(FieldNo)); 1295 FieldMallocs.push_back(NMI); 1296 new StoreInst(NMI, NGV, CI); 1297 } 1298 1299 // The tricky aspect of this transformation is handling the case when malloc 1300 // fails. In the original code, malloc failing would set the result pointer 1301 // of malloc to null. In this case, some mallocs could succeed and others 1302 // could fail. As such, we emit code that looks like this: 1303 // F0 = malloc(field0) 1304 // F1 = malloc(field1) 1305 // F2 = malloc(field2) 1306 // if (F0 == 0 || F1 == 0 || F2 == 0) { 1307 // if (F0) { free(F0); F0 = 0; } 1308 // if (F1) { free(F1); F1 = 0; } 1309 // if (F2) { free(F2); F2 = 0; } 1310 // } 1311 // The malloc can also fail if its argument is too large. 1312 Constant *ConstantZero = ConstantInt::get(CI->getOperand(1)->getType(), 0); 1313 Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getOperand(1), 1314 ConstantZero, "isneg"); 1315 for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) { 1316 Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i], 1317 Constant::getNullValue(FieldMallocs[i]->getType()), 1318 "isnull"); 1319 RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI); 1320 } 1321 1322 // Split the basic block at the old malloc. 1323 BasicBlock *OrigBB = CI->getParent(); 1324 BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont"); 1325 1326 // Create the block to check the first condition. Put all these blocks at the 1327 // end of the function as they are unlikely to be executed. 1328 BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(), 1329 "malloc_ret_null", 1330 OrigBB->getParent()); 1331 1332 // Remove the uncond branch from OrigBB to ContBB, turning it into a cond 1333 // branch on RunningOr. 1334 OrigBB->getTerminator()->eraseFromParent(); 1335 BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB); 1336 1337 // Within the NullPtrBlock, we need to emit a comparison and branch for each 1338 // pointer, because some may be null while others are not. 1339 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1340 Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock); 1341 Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal, 1342 Constant::getNullValue(GVVal->getType()), 1343 "tmp"); 1344 BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it", 1345 OrigBB->getParent()); 1346 BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next", 1347 OrigBB->getParent()); 1348 Instruction *BI = BranchInst::Create(FreeBlock, NextBlock, 1349 Cmp, NullPtrBlock); 1350 1351 // Fill in FreeBlock. 1352 CallInst::CreateFree(GVVal, BI); 1353 new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i], 1354 FreeBlock); 1355 BranchInst::Create(NextBlock, FreeBlock); 1356 1357 NullPtrBlock = NextBlock; 1358 } 1359 1360 BranchInst::Create(ContBB, NullPtrBlock); 1361 1362 // CI is no longer needed, remove it. 1363 CI->eraseFromParent(); 1364 1365 /// InsertedScalarizedLoads - As we process loads, if we can't immediately 1366 /// update all uses of the load, keep track of what scalarized loads are 1367 /// inserted for a given load. 1368 DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues; 1369 InsertedScalarizedValues[GV] = FieldGlobals; 1370 1371 std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite; 1372 1373 // Okay, the malloc site is completely handled. All of the uses of GV are now 1374 // loads, and all uses of those loads are simple. Rewrite them to use loads 1375 // of the per-field globals instead. 1376 for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) { 1377 Instruction *User = cast<Instruction>(*UI++); 1378 1379 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1380 RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite); 1381 continue; 1382 } 1383 1384 // Must be a store of null. 1385 StoreInst *SI = cast<StoreInst>(User); 1386 assert(isa<ConstantPointerNull>(SI->getOperand(0)) && 1387 "Unexpected heap-sra user!"); 1388 1389 // Insert a store of null into each global. 1390 for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { 1391 const PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType()); 1392 Constant *Null = Constant::getNullValue(PT->getElementType()); 1393 new StoreInst(Null, FieldGlobals[i], SI); 1394 } 1395 // Erase the original store. 1396 SI->eraseFromParent(); 1397 } 1398 1399 // While we have PHIs that are interesting to rewrite, do it. 1400 while (!PHIsToRewrite.empty()) { 1401 PHINode *PN = PHIsToRewrite.back().first; 1402 unsigned FieldNo = PHIsToRewrite.back().second; 1403 PHIsToRewrite.pop_back(); 1404 PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]); 1405 assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi"); 1406 1407 // Add all the incoming values. This can materialize more phis. 1408 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1409 Value *InVal = PN->getIncomingValue(i); 1410 InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues, 1411 PHIsToRewrite); 1412 FieldPN->addIncoming(InVal, PN->getIncomingBlock(i)); 1413 } 1414 } 1415 1416 // Drop all inter-phi links and any loads that made it this far. 1417 for (DenseMap<Value*, std::vector<Value*> >::iterator 1418 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1419 I != E; ++I) { 1420 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1421 PN->dropAllReferences(); 1422 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1423 LI->dropAllReferences(); 1424 } 1425 1426 // Delete all the phis and loads now that inter-references are dead. 1427 for (DenseMap<Value*, std::vector<Value*> >::iterator 1428 I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); 1429 I != E; ++I) { 1430 if (PHINode *PN = dyn_cast<PHINode>(I->first)) 1431 PN->eraseFromParent(); 1432 else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) 1433 LI->eraseFromParent(); 1434 } 1435 1436 // The old global is now dead, remove it. 1437 GV->eraseFromParent(); 1438 1439 ++NumHeapSRA; 1440 return cast<GlobalVariable>(FieldGlobals[0]); 1441} 1442 1443/// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a 1444/// pointer global variable with a single value stored it that is a malloc or 1445/// cast of malloc. 1446static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, 1447 CallInst *CI, 1448 const Type *AllocTy, 1449 Module::global_iterator &GVI, 1450 TargetData *TD) { 1451 // If this is a malloc of an abstract type, don't touch it. 1452 if (!AllocTy->isSized()) 1453 return false; 1454 1455 // We can't optimize this global unless all uses of it are *known* to be 1456 // of the malloc value, not of the null initializer value (consider a use 1457 // that compares the global's value against zero to see if the malloc has 1458 // been reached). To do this, we check to see if all uses of the global 1459 // would trap if the global were null: this proves that they must all 1460 // happen after the malloc. 1461 if (!AllUsesOfLoadedValueWillTrapIfNull(GV)) 1462 return false; 1463 1464 // We can't optimize this if the malloc itself is used in a complex way, 1465 // for example, being stored into multiple globals. This allows the 1466 // malloc to be stored into the specified global, loaded setcc'd, and 1467 // GEP'd. These are all things we could transform to using the global 1468 // for. 1469 { 1470 SmallPtrSet<PHINode*, 8> PHIs; 1471 if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs)) 1472 return false; 1473 } 1474 1475 // If we have a global that is only initialized with a fixed size malloc, 1476 // transform the program to use global memory instead of malloc'd memory. 1477 // This eliminates dynamic allocation, avoids an indirection accessing the 1478 // data, and exposes the resultant global to further GlobalOpt. 1479 // We cannot optimize the malloc if we cannot determine malloc array size. 1480 if (Value *NElems = getMallocArraySize(CI, TD, true)) { 1481 if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems)) 1482 // Restrict this transformation to only working on small allocations 1483 // (2048 bytes currently), as we don't want to introduce a 16M global or 1484 // something. 1485 if (TD && 1486 NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) { 1487 GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD); 1488 return true; 1489 } 1490 1491 // If the allocation is an array of structures, consider transforming this 1492 // into multiple malloc'd arrays, one for each field. This is basically 1493 // SRoA for malloc'd memory. 1494 1495 // If this is an allocation of a fixed size array of structs, analyze as a 1496 // variable size array. malloc [100 x struct],1 -> malloc struct, 100 1497 if (NElems == ConstantInt::get(CI->getOperand(1)->getType(), 1)) 1498 if (const ArrayType *AT = dyn_cast<ArrayType>(AllocTy)) 1499 AllocTy = AT->getElementType(); 1500 1501 if (const StructType *AllocSTy = dyn_cast<StructType>(AllocTy)) { 1502 // This the structure has an unreasonable number of fields, leave it 1503 // alone. 1504 if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 && 1505 AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) { 1506 1507 // If this is a fixed size array, transform the Malloc to be an alloc of 1508 // structs. malloc [100 x struct],1 -> malloc struct, 100 1509 if (const ArrayType *AT = 1510 dyn_cast<ArrayType>(getMallocAllocatedType(CI))) { 1511 const Type *IntPtrTy = TD->getIntPtrType(CI->getContext()); 1512 unsigned TypeSize = TD->getStructLayout(AllocSTy)->getSizeInBytes(); 1513 Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize); 1514 Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements()); 1515 Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy, 1516 AllocSize, NumElements, 1517 CI->getName()); 1518 Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI); 1519 CI->replaceAllUsesWith(Cast); 1520 CI->eraseFromParent(); 1521 CI = dyn_cast<BitCastInst>(Malloc) ? 1522 extractMallocCallFromBitCast(Malloc) : cast<CallInst>(Malloc); 1523 } 1524 1525 GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, true),TD); 1526 return true; 1527 } 1528 } 1529 } 1530 1531 return false; 1532} 1533 1534// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge 1535// that only one value (besides its initializer) is ever stored to the global. 1536static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal, 1537 Module::global_iterator &GVI, 1538 TargetData *TD) { 1539 // Ignore no-op GEPs and bitcasts. 1540 StoredOnceVal = StoredOnceVal->stripPointerCasts(); 1541 1542 // If we are dealing with a pointer global that is initialized to null and 1543 // only has one (non-null) value stored into it, then we can optimize any 1544 // users of the loaded value (often calls and loads) that would trap if the 1545 // value was null. 1546 if (GV->getInitializer()->getType()->isPointerTy() && 1547 GV->getInitializer()->isNullValue()) { 1548 if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { 1549 if (GV->getInitializer()->getType() != SOVC->getType()) 1550 SOVC = 1551 ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType()); 1552 1553 // Optimize away any trapping uses of the loaded value. 1554 if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC)) 1555 return true; 1556 } else if (CallInst *CI = extractMallocCall(StoredOnceVal)) { 1557 const Type* MallocType = getMallocAllocatedType(CI); 1558 if (MallocType && TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, 1559 GVI, TD)) 1560 return true; 1561 } 1562 } 1563 1564 return false; 1565} 1566 1567/// TryToShrinkGlobalToBoolean - At this point, we have learned that the only 1568/// two values ever stored into GV are its initializer and OtherVal. See if we 1569/// can shrink the global into a boolean and select between the two values 1570/// whenever it is used. This exposes the values to other scalar optimizations. 1571static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) { 1572 const Type *GVElType = GV->getType()->getElementType(); 1573 1574 // If GVElType is already i1, it is already shrunk. If the type of the GV is 1575 // an FP value, pointer or vector, don't do this optimization because a select 1576 // between them is very expensive and unlikely to lead to later 1577 // simplification. In these cases, we typically end up with "cond ? v1 : v2" 1578 // where v1 and v2 both require constant pool loads, a big loss. 1579 if (GVElType == Type::getInt1Ty(GV->getContext()) || 1580 GVElType->isFloatingPointTy() || 1581 GVElType->isPointerTy() || GVElType->isVectorTy()) 1582 return false; 1583 1584 // Walk the use list of the global seeing if all the uses are load or store. 1585 // If there is anything else, bail out. 1586 for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I) 1587 if (!isa<LoadInst>(I) && !isa<StoreInst>(I)) 1588 return false; 1589 1590 DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV); 1591 1592 // Create the new global, initializing it to false. 1593 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()), 1594 false, 1595 GlobalValue::InternalLinkage, 1596 ConstantInt::getFalse(GV->getContext()), 1597 GV->getName()+".b", 1598 GV->isThreadLocal()); 1599 GV->getParent()->getGlobalList().insert(GV, NewGV); 1600 1601 Constant *InitVal = GV->getInitializer(); 1602 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) && 1603 "No reason to shrink to bool!"); 1604 1605 // If initialized to zero and storing one into the global, we can use a cast 1606 // instead of a select to synthesize the desired value. 1607 bool IsOneZero = false; 1608 if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) 1609 IsOneZero = InitVal->isNullValue() && CI->isOne(); 1610 1611 while (!GV->use_empty()) { 1612 Instruction *UI = cast<Instruction>(GV->use_back()); 1613 if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { 1614 // Change the store into a boolean store. 1615 bool StoringOther = SI->getOperand(0) == OtherVal; 1616 // Only do this if we weren't storing a loaded value. 1617 Value *StoreVal; 1618 if (StoringOther || SI->getOperand(0) == InitVal) 1619 StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()), 1620 StoringOther); 1621 else { 1622 // Otherwise, we are storing a previously loaded copy. To do this, 1623 // change the copy from copying the original value to just copying the 1624 // bool. 1625 Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); 1626 1627 // If we're already replaced the input, StoredVal will be a cast or 1628 // select instruction. If not, it will be a load of the original 1629 // global. 1630 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { 1631 assert(LI->getOperand(0) == GV && "Not a copy!"); 1632 // Insert a new load, to preserve the saved value. 1633 StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI); 1634 } else { 1635 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && 1636 "This is not a form that we understand!"); 1637 StoreVal = StoredVal->getOperand(0); 1638 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); 1639 } 1640 } 1641 new StoreInst(StoreVal, NewGV, SI); 1642 } else { 1643 // Change the load into a load of bool then a select. 1644 LoadInst *LI = cast<LoadInst>(UI); 1645 LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", LI); 1646 Value *NSI; 1647 if (IsOneZero) 1648 NSI = new ZExtInst(NLI, LI->getType(), "", LI); 1649 else 1650 NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI); 1651 NSI->takeName(LI); 1652 LI->replaceAllUsesWith(NSI); 1653 } 1654 UI->eraseFromParent(); 1655 } 1656 1657 GV->eraseFromParent(); 1658 return true; 1659} 1660 1661 1662/// ProcessInternalGlobal - Analyze the specified global variable and optimize 1663/// it if possible. If we make a change, return true. 1664bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV, 1665 Module::global_iterator &GVI) { 1666 SmallPtrSet<const PHINode*, 16> PHIUsers; 1667 GlobalStatus GS; 1668 GV->removeDeadConstantUsers(); 1669 1670 if (GV->use_empty()) { 1671 DEBUG(dbgs() << "GLOBAL DEAD: " << *GV); 1672 GV->eraseFromParent(); 1673 ++NumDeleted; 1674 return true; 1675 } 1676 1677 if (!AnalyzeGlobal(GV, GS, PHIUsers)) { 1678#if 0 1679 DEBUG(dbgs() << "Global: " << *GV); 1680 DEBUG(dbgs() << " isLoaded = " << GS.isLoaded << "\n"); 1681 DEBUG(dbgs() << " StoredType = "); 1682 switch (GS.StoredType) { 1683 case GlobalStatus::NotStored: DEBUG(dbgs() << "NEVER STORED\n"); break; 1684 case GlobalStatus::isInitializerStored: DEBUG(dbgs() << "INIT STORED\n"); 1685 break; 1686 case GlobalStatus::isStoredOnce: DEBUG(dbgs() << "STORED ONCE\n"); break; 1687 case GlobalStatus::isStored: DEBUG(dbgs() << "stored\n"); break; 1688 } 1689 if (GS.StoredType == GlobalStatus::isStoredOnce && GS.StoredOnceValue) 1690 DEBUG(dbgs() << " StoredOnceValue = " << *GS.StoredOnceValue << "\n"); 1691 if (GS.AccessingFunction && !GS.HasMultipleAccessingFunctions) 1692 DEBUG(dbgs() << " AccessingFunction = " << GS.AccessingFunction->getName() 1693 << "\n"); 1694 DEBUG(dbgs() << " HasMultipleAccessingFunctions = " 1695 << GS.HasMultipleAccessingFunctions << "\n"); 1696 DEBUG(dbgs() << " HasNonInstructionUser = " 1697 << GS.HasNonInstructionUser<<"\n"); 1698 DEBUG(dbgs() << "\n"); 1699#endif 1700 1701 // If this is a first class global and has only one accessing function 1702 // and this function is main (which we know is not recursive we can make 1703 // this global a local variable) we replace the global with a local alloca 1704 // in this function. 1705 // 1706 // NOTE: It doesn't make sense to promote non single-value types since we 1707 // are just replacing static memory to stack memory. 1708 // 1709 // If the global is in different address space, don't bring it to stack. 1710 if (!GS.HasMultipleAccessingFunctions && 1711 GS.AccessingFunction && !GS.HasNonInstructionUser && 1712 GV->getType()->getElementType()->isSingleValueType() && 1713 GS.AccessingFunction->getName() == "main" && 1714 GS.AccessingFunction->hasExternalLinkage() && 1715 GV->getType()->getAddressSpace() == 0) { 1716 DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV); 1717 Instruction& FirstI = const_cast<Instruction&>(*GS.AccessingFunction 1718 ->getEntryBlock().begin()); 1719 const Type* ElemTy = GV->getType()->getElementType(); 1720 // FIXME: Pass Global's alignment when globals have alignment 1721 AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), &FirstI); 1722 if (!isa<UndefValue>(GV->getInitializer())) 1723 new StoreInst(GV->getInitializer(), Alloca, &FirstI); 1724 1725 GV->replaceAllUsesWith(Alloca); 1726 GV->eraseFromParent(); 1727 ++NumLocalized; 1728 return true; 1729 } 1730 1731 // If the global is never loaded (but may be stored to), it is dead. 1732 // Delete it now. 1733 if (!GS.isLoaded) { 1734 DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV); 1735 1736 // Delete any stores we can find to the global. We may not be able to 1737 // make it completely dead though. 1738 bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1739 1740 // If the global is dead now, delete it. 1741 if (GV->use_empty()) { 1742 GV->eraseFromParent(); 1743 ++NumDeleted; 1744 Changed = true; 1745 } 1746 return Changed; 1747 1748 } else if (GS.StoredType <= GlobalStatus::isInitializerStored) { 1749 DEBUG(dbgs() << "MARKING CONSTANT: " << *GV); 1750 GV->setConstant(true); 1751 1752 // Clean up any obviously simplifiable users now. 1753 CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1754 1755 // If the global is dead now, just nuke it. 1756 if (GV->use_empty()) { 1757 DEBUG(dbgs() << " *** Marking constant allowed us to simplify " 1758 << "all users and delete global!\n"); 1759 GV->eraseFromParent(); 1760 ++NumDeleted; 1761 } 1762 1763 ++NumMarked; 1764 return true; 1765 } else if (!GV->getInitializer()->getType()->isSingleValueType()) { 1766 if (TargetData *TD = getAnalysisIfAvailable<TargetData>()) 1767 if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) { 1768 GVI = FirstNewGV; // Don't skip the newly produced globals! 1769 return true; 1770 } 1771 } else if (GS.StoredType == GlobalStatus::isStoredOnce) { 1772 // If the initial value for the global was an undef value, and if only 1773 // one other value was stored into it, we can just change the 1774 // initializer to be the stored value, then delete all stores to the 1775 // global. This allows us to mark it constant. 1776 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1777 if (isa<UndefValue>(GV->getInitializer())) { 1778 // Change the initial value here. 1779 GV->setInitializer(SOVConstant); 1780 1781 // Clean up any obviously simplifiable users now. 1782 CleanupConstantGlobalUsers(GV, GV->getInitializer()); 1783 1784 if (GV->use_empty()) { 1785 DEBUG(dbgs() << " *** Substituting initializer allowed us to " 1786 << "simplify all users and delete global!\n"); 1787 GV->eraseFromParent(); 1788 ++NumDeleted; 1789 } else { 1790 GVI = GV; 1791 } 1792 ++NumSubstitute; 1793 return true; 1794 } 1795 1796 // Try to optimize globals based on the knowledge that only one value 1797 // (besides its initializer) is ever stored to the global. 1798 if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI, 1799 getAnalysisIfAvailable<TargetData>())) 1800 return true; 1801 1802 // Otherwise, if the global was not a boolean, we can shrink it to be a 1803 // boolean. 1804 if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) 1805 if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) { 1806 ++NumShrunkToBool; 1807 return true; 1808 } 1809 } 1810 } 1811 return false; 1812} 1813 1814/// ChangeCalleesToFastCall - Walk all of the direct calls of the specified 1815/// function, changing them to FastCC. 1816static void ChangeCalleesToFastCall(Function *F) { 1817 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1818 CallSite User(cast<Instruction>(*UI)); 1819 User.setCallingConv(CallingConv::Fast); 1820 } 1821} 1822 1823static AttrListPtr StripNest(const AttrListPtr &Attrs) { 1824 for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) { 1825 if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0) 1826 continue; 1827 1828 // There can be only one. 1829 return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest); 1830 } 1831 1832 return Attrs; 1833} 1834 1835static void RemoveNestAttribute(Function *F) { 1836 F->setAttributes(StripNest(F->getAttributes())); 1837 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){ 1838 CallSite User(cast<Instruction>(*UI)); 1839 User.setAttributes(StripNest(User.getAttributes())); 1840 } 1841} 1842 1843bool GlobalOpt::OptimizeFunctions(Module &M) { 1844 bool Changed = false; 1845 // Optimize functions. 1846 for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { 1847 Function *F = FI++; 1848 // Functions without names cannot be referenced outside this module. 1849 if (!F->hasName() && !F->isDeclaration()) 1850 F->setLinkage(GlobalValue::InternalLinkage); 1851 F->removeDeadConstantUsers(); 1852 if (F->use_empty() && (F->hasLocalLinkage() || F->hasLinkOnceLinkage())) { 1853 F->eraseFromParent(); 1854 Changed = true; 1855 ++NumFnDeleted; 1856 } else if (F->hasLocalLinkage()) { 1857 if (F->getCallingConv() == CallingConv::C && !F->isVarArg() && 1858 !F->hasAddressTaken()) { 1859 // If this function has C calling conventions, is not a varargs 1860 // function, and is only called directly, promote it to use the Fast 1861 // calling convention. 1862 F->setCallingConv(CallingConv::Fast); 1863 ChangeCalleesToFastCall(F); 1864 ++NumFastCallFns; 1865 Changed = true; 1866 } 1867 1868 if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) && 1869 !F->hasAddressTaken()) { 1870 // The function is not used by a trampoline intrinsic, so it is safe 1871 // to remove the 'nest' attribute. 1872 RemoveNestAttribute(F); 1873 ++NumNestRemoved; 1874 Changed = true; 1875 } 1876 } 1877 } 1878 return Changed; 1879} 1880 1881bool GlobalOpt::OptimizeGlobalVars(Module &M) { 1882 bool Changed = false; 1883 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); 1884 GVI != E; ) { 1885 GlobalVariable *GV = GVI++; 1886 // Global variables without names cannot be referenced outside this module. 1887 if (!GV->hasName() && !GV->isDeclaration()) 1888 GV->setLinkage(GlobalValue::InternalLinkage); 1889 // Simplify the initializer. 1890 if (GV->hasInitializer()) 1891 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) { 1892 TargetData *TD = getAnalysisIfAvailable<TargetData>(); 1893 Constant *New = ConstantFoldConstantExpression(CE, TD); 1894 if (New && New != CE) 1895 GV->setInitializer(New); 1896 } 1897 // Do more involved optimizations if the global is internal. 1898 if (!GV->isConstant() && GV->hasLocalLinkage() && 1899 GV->hasInitializer()) 1900 Changed |= ProcessInternalGlobal(GV, GVI); 1901 } 1902 return Changed; 1903} 1904 1905/// FindGlobalCtors - Find the llvm.globalctors list, verifying that all 1906/// initializers have an init priority of 65535. 1907GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) { 1908 for (Module::global_iterator I = M.global_begin(), E = M.global_end(); 1909 I != E; ++I) 1910 if (I->getName() == "llvm.global_ctors") { 1911 // Found it, verify it's an array of { int, void()* }. 1912 const ArrayType *ATy =dyn_cast<ArrayType>(I->getType()->getElementType()); 1913 if (!ATy) return 0; 1914 const StructType *STy = dyn_cast<StructType>(ATy->getElementType()); 1915 if (!STy || STy->getNumElements() != 2 || 1916 !STy->getElementType(0)->isIntegerTy(32)) return 0; 1917 const PointerType *PFTy = dyn_cast<PointerType>(STy->getElementType(1)); 1918 if (!PFTy) return 0; 1919 const FunctionType *FTy = dyn_cast<FunctionType>(PFTy->getElementType()); 1920 if (!FTy || !FTy->getReturnType()->isVoidTy() || 1921 FTy->isVarArg() || FTy->getNumParams() != 0) 1922 return 0; 1923 1924 // Verify that the initializer is simple enough for us to handle. 1925 if (!I->hasDefinitiveInitializer()) return 0; 1926 ConstantArray *CA = dyn_cast<ConstantArray>(I->getInitializer()); 1927 if (!CA) return 0; 1928 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 1929 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(*i)) { 1930 if (isa<ConstantPointerNull>(CS->getOperand(1))) 1931 continue; 1932 1933 // Must have a function or null ptr. 1934 if (!isa<Function>(CS->getOperand(1))) 1935 return 0; 1936 1937 // Init priority must be standard. 1938 ConstantInt *CI = dyn_cast<ConstantInt>(CS->getOperand(0)); 1939 if (!CI || CI->getZExtValue() != 65535) 1940 return 0; 1941 } else { 1942 return 0; 1943 } 1944 1945 return I; 1946 } 1947 return 0; 1948} 1949 1950/// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand, 1951/// return a list of the functions and null terminator as a vector. 1952static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) { 1953 ConstantArray *CA = cast<ConstantArray>(GV->getInitializer()); 1954 std::vector<Function*> Result; 1955 Result.reserve(CA->getNumOperands()); 1956 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) { 1957 ConstantStruct *CS = cast<ConstantStruct>(*i); 1958 Result.push_back(dyn_cast<Function>(CS->getOperand(1))); 1959 } 1960 return Result; 1961} 1962 1963/// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the 1964/// specified array, returning the new global to use. 1965static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL, 1966 const std::vector<Function*> &Ctors) { 1967 // If we made a change, reassemble the initializer list. 1968 std::vector<Constant*> CSVals; 1969 CSVals.push_back(ConstantInt::get(Type::getInt32Ty(GCL->getContext()),65535)); 1970 CSVals.push_back(0); 1971 1972 // Create the new init list. 1973 std::vector<Constant*> CAList; 1974 for (unsigned i = 0, e = Ctors.size(); i != e; ++i) { 1975 if (Ctors[i]) { 1976 CSVals[1] = Ctors[i]; 1977 } else { 1978 const Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()), 1979 false); 1980 const PointerType *PFTy = PointerType::getUnqual(FTy); 1981 CSVals[1] = Constant::getNullValue(PFTy); 1982 CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()), 1983 2147483647); 1984 } 1985 CAList.push_back(ConstantStruct::get(GCL->getContext(), CSVals, false)); 1986 } 1987 1988 // Create the array initializer. 1989 const Type *StructTy = 1990 cast<ArrayType>(GCL->getType()->getElementType())->getElementType(); 1991 Constant *CA = ConstantArray::get(ArrayType::get(StructTy, 1992 CAList.size()), CAList); 1993 1994 // If we didn't change the number of elements, don't create a new GV. 1995 if (CA->getType() == GCL->getInitializer()->getType()) { 1996 GCL->setInitializer(CA); 1997 return GCL; 1998 } 1999 2000 // Create the new global and insert it next to the existing list. 2001 GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(), 2002 GCL->getLinkage(), CA, "", 2003 GCL->isThreadLocal()); 2004 GCL->getParent()->getGlobalList().insert(GCL, NGV); 2005 NGV->takeName(GCL); 2006 2007 // Nuke the old list, replacing any uses with the new one. 2008 if (!GCL->use_empty()) { 2009 Constant *V = NGV; 2010 if (V->getType() != GCL->getType()) 2011 V = ConstantExpr::getBitCast(V, GCL->getType()); 2012 GCL->replaceAllUsesWith(V); 2013 } 2014 GCL->eraseFromParent(); 2015 2016 if (Ctors.size()) 2017 return NGV; 2018 else 2019 return 0; 2020} 2021 2022 2023static Constant *getVal(DenseMap<Value*, Constant*> &ComputedValues, 2024 Value *V) { 2025 if (Constant *CV = dyn_cast<Constant>(V)) return CV; 2026 Constant *R = ComputedValues[V]; 2027 assert(R && "Reference to an uncomputed value!"); 2028 return R; 2029} 2030 2031/// isSimpleEnoughPointerToCommit - Return true if this constant is simple 2032/// enough for us to understand. In particular, if it is a cast of something, 2033/// we punt. We basically just support direct accesses to globals and GEP's of 2034/// globals. This should be kept up to date with CommitValueTo. 2035static bool isSimpleEnoughPointerToCommit(Constant *C) { 2036 // Conservatively, avoid aggregate types. This is because we don't 2037 // want to worry about them partially overlapping other stores. 2038 if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType()) 2039 return false; 2040 2041 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) 2042 // Do not allow weak/linkonce/dllimport/dllexport linkage or 2043 // external globals. 2044 return GV->hasDefinitiveInitializer(); 2045 2046 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 2047 // Handle a constantexpr gep. 2048 if (CE->getOpcode() == Instruction::GetElementPtr && 2049 isa<GlobalVariable>(CE->getOperand(0)) && 2050 cast<GEPOperator>(CE)->isInBounds()) { 2051 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2052 // Do not allow weak/linkonce/dllimport/dllexport linkage or 2053 // external globals. 2054 if (!GV->hasDefinitiveInitializer()) 2055 return false; 2056 2057 // The first index must be zero. 2058 ConstantInt *CI = dyn_cast<ConstantInt>(*next(CE->op_begin())); 2059 if (!CI || !CI->isZero()) return false; 2060 2061 // The remaining indices must be compile-time known integers within the 2062 // notional bounds of the corresponding static array types. 2063 if (!CE->isGEPWithNoNotionalOverIndexing()) 2064 return false; 2065 2066 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2067 } 2068 return false; 2069} 2070 2071/// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global 2072/// initializer. This returns 'Init' modified to reflect 'Val' stored into it. 2073/// At this point, the GEP operands of Addr [0, OpNo) have been stepped into. 2074static Constant *EvaluateStoreInto(Constant *Init, Constant *Val, 2075 ConstantExpr *Addr, unsigned OpNo) { 2076 // Base case of the recursion. 2077 if (OpNo == Addr->getNumOperands()) { 2078 assert(Val->getType() == Init->getType() && "Type mismatch!"); 2079 return Val; 2080 } 2081 2082 std::vector<Constant*> Elts; 2083 if (const StructType *STy = dyn_cast<StructType>(Init->getType())) { 2084 2085 // Break up the constant into its elements. 2086 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) { 2087 for (User::op_iterator i = CS->op_begin(), e = CS->op_end(); i != e; ++i) 2088 Elts.push_back(cast<Constant>(*i)); 2089 } else if (isa<ConstantAggregateZero>(Init)) { 2090 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2091 Elts.push_back(Constant::getNullValue(STy->getElementType(i))); 2092 } else if (isa<UndefValue>(Init)) { 2093 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 2094 Elts.push_back(UndefValue::get(STy->getElementType(i))); 2095 } else { 2096 llvm_unreachable("This code is out of sync with " 2097 " ConstantFoldLoadThroughGEPConstantExpr"); 2098 } 2099 2100 // Replace the element that we are supposed to. 2101 ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo)); 2102 unsigned Idx = CU->getZExtValue(); 2103 assert(Idx < STy->getNumElements() && "Struct index out of range!"); 2104 Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1); 2105 2106 // Return the modified struct. 2107 return ConstantStruct::get(Init->getContext(), &Elts[0], Elts.size(), 2108 STy->isPacked()); 2109 } else { 2110 ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo)); 2111 const SequentialType *InitTy = cast<SequentialType>(Init->getType()); 2112 2113 uint64_t NumElts; 2114 if (const ArrayType *ATy = dyn_cast<ArrayType>(InitTy)) 2115 NumElts = ATy->getNumElements(); 2116 else 2117 NumElts = cast<VectorType>(InitTy)->getNumElements(); 2118 2119 2120 // Break up the array into elements. 2121 if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) { 2122 for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) 2123 Elts.push_back(cast<Constant>(*i)); 2124 } else if (ConstantVector *CV = dyn_cast<ConstantVector>(Init)) { 2125 for (User::op_iterator i = CV->op_begin(), e = CV->op_end(); i != e; ++i) 2126 Elts.push_back(cast<Constant>(*i)); 2127 } else if (isa<ConstantAggregateZero>(Init)) { 2128 Elts.assign(NumElts, Constant::getNullValue(InitTy->getElementType())); 2129 } else { 2130 assert(isa<UndefValue>(Init) && "This code is out of sync with " 2131 " ConstantFoldLoadThroughGEPConstantExpr"); 2132 Elts.assign(NumElts, UndefValue::get(InitTy->getElementType())); 2133 } 2134 2135 assert(CI->getZExtValue() < NumElts); 2136 Elts[CI->getZExtValue()] = 2137 EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1); 2138 2139 if (Init->getType()->isArrayTy()) 2140 return ConstantArray::get(cast<ArrayType>(InitTy), Elts); 2141 else 2142 return ConstantVector::get(&Elts[0], Elts.size()); 2143 } 2144} 2145 2146/// CommitValueTo - We have decided that Addr (which satisfies the predicate 2147/// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen. 2148static void CommitValueTo(Constant *Val, Constant *Addr) { 2149 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) { 2150 assert(GV->hasInitializer()); 2151 GV->setInitializer(Val); 2152 return; 2153 } 2154 2155 ConstantExpr *CE = cast<ConstantExpr>(Addr); 2156 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2157 GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2)); 2158} 2159 2160/// ComputeLoadResult - Return the value that would be computed by a load from 2161/// P after the stores reflected by 'memory' have been performed. If we can't 2162/// decide, return null. 2163static Constant *ComputeLoadResult(Constant *P, 2164 const DenseMap<Constant*, Constant*> &Memory) { 2165 // If this memory location has been recently stored, use the stored value: it 2166 // is the most up-to-date. 2167 DenseMap<Constant*, Constant*>::const_iterator I = Memory.find(P); 2168 if (I != Memory.end()) return I->second; 2169 2170 // Access it. 2171 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) { 2172 if (GV->hasDefinitiveInitializer()) 2173 return GV->getInitializer(); 2174 return 0; 2175 } 2176 2177 // Handle a constantexpr getelementptr. 2178 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P)) 2179 if (CE->getOpcode() == Instruction::GetElementPtr && 2180 isa<GlobalVariable>(CE->getOperand(0))) { 2181 GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); 2182 if (GV->hasDefinitiveInitializer()) 2183 return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE); 2184 } 2185 2186 return 0; // don't know how to evaluate. 2187} 2188 2189/// EvaluateFunction - Evaluate a call to function F, returning true if 2190/// successful, false if we can't evaluate it. ActualArgs contains the formal 2191/// arguments for the function. 2192static bool EvaluateFunction(Function *F, Constant *&RetVal, 2193 const SmallVectorImpl<Constant*> &ActualArgs, 2194 std::vector<Function*> &CallStack, 2195 DenseMap<Constant*, Constant*> &MutatedMemory, 2196 std::vector<GlobalVariable*> &AllocaTmps) { 2197 // Check to see if this function is already executing (recursion). If so, 2198 // bail out. TODO: we might want to accept limited recursion. 2199 if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end()) 2200 return false; 2201 2202 CallStack.push_back(F); 2203 2204 /// Values - As we compute SSA register values, we store their contents here. 2205 DenseMap<Value*, Constant*> Values; 2206 2207 // Initialize arguments to the incoming values specified. 2208 unsigned ArgNo = 0; 2209 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E; 2210 ++AI, ++ArgNo) 2211 Values[AI] = ActualArgs[ArgNo]; 2212 2213 /// ExecutedBlocks - We only handle non-looping, non-recursive code. As such, 2214 /// we can only evaluate any one basic block at most once. This set keeps 2215 /// track of what we have executed so we can detect recursive cases etc. 2216 SmallPtrSet<BasicBlock*, 32> ExecutedBlocks; 2217 2218 // CurInst - The current instruction we're evaluating. 2219 BasicBlock::iterator CurInst = F->begin()->begin(); 2220 2221 // This is the main evaluation loop. 2222 while (1) { 2223 Constant *InstResult = 0; 2224 2225 if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) { 2226 if (SI->isVolatile()) return false; // no volatile accesses. 2227 Constant *Ptr = getVal(Values, SI->getOperand(1)); 2228 if (!isSimpleEnoughPointerToCommit(Ptr)) 2229 // If this is too complex for us to commit, reject it. 2230 return false; 2231 Constant *Val = getVal(Values, SI->getOperand(0)); 2232 MutatedMemory[Ptr] = Val; 2233 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) { 2234 InstResult = ConstantExpr::get(BO->getOpcode(), 2235 getVal(Values, BO->getOperand(0)), 2236 getVal(Values, BO->getOperand(1))); 2237 } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) { 2238 InstResult = ConstantExpr::getCompare(CI->getPredicate(), 2239 getVal(Values, CI->getOperand(0)), 2240 getVal(Values, CI->getOperand(1))); 2241 } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) { 2242 InstResult = ConstantExpr::getCast(CI->getOpcode(), 2243 getVal(Values, CI->getOperand(0)), 2244 CI->getType()); 2245 } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) { 2246 InstResult = 2247 ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)), 2248 getVal(Values, SI->getOperand(1)), 2249 getVal(Values, SI->getOperand(2))); 2250 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) { 2251 Constant *P = getVal(Values, GEP->getOperand(0)); 2252 SmallVector<Constant*, 8> GEPOps; 2253 for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); 2254 i != e; ++i) 2255 GEPOps.push_back(getVal(Values, *i)); 2256 InstResult = cast<GEPOperator>(GEP)->isInBounds() ? 2257 ConstantExpr::getInBoundsGetElementPtr(P, &GEPOps[0], GEPOps.size()) : 2258 ConstantExpr::getGetElementPtr(P, &GEPOps[0], GEPOps.size()); 2259 } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) { 2260 if (LI->isVolatile()) return false; // no volatile accesses. 2261 InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)), 2262 MutatedMemory); 2263 if (InstResult == 0) return false; // Could not evaluate load. 2264 } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) { 2265 if (AI->isArrayAllocation()) return false; // Cannot handle array allocs. 2266 const Type *Ty = AI->getType()->getElementType(); 2267 AllocaTmps.push_back(new GlobalVariable(Ty, false, 2268 GlobalValue::InternalLinkage, 2269 UndefValue::get(Ty), 2270 AI->getName())); 2271 InstResult = AllocaTmps.back(); 2272 } else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) { 2273 2274 // Debug info can safely be ignored here. 2275 if (isa<DbgInfoIntrinsic>(CI)) { 2276 ++CurInst; 2277 continue; 2278 } 2279 2280 // Cannot handle inline asm. 2281 if (isa<InlineAsm>(CI->getOperand(0))) return false; 2282 2283 // Resolve function pointers. 2284 Function *Callee = dyn_cast<Function>(getVal(Values, CI->getOperand(0))); 2285 if (!Callee) return false; // Cannot resolve. 2286 2287 SmallVector<Constant*, 8> Formals; 2288 for (User::op_iterator i = CI->op_begin() + 1, e = CI->op_end(); 2289 i != e; ++i) 2290 Formals.push_back(getVal(Values, *i)); 2291 2292 if (Callee->isDeclaration()) { 2293 // If this is a function we can constant fold, do it. 2294 if (Constant *C = ConstantFoldCall(Callee, Formals.data(), 2295 Formals.size())) { 2296 InstResult = C; 2297 } else { 2298 return false; 2299 } 2300 } else { 2301 if (Callee->getFunctionType()->isVarArg()) 2302 return false; 2303 2304 Constant *RetVal; 2305 // Execute the call, if successful, use the return value. 2306 if (!EvaluateFunction(Callee, RetVal, Formals, CallStack, 2307 MutatedMemory, AllocaTmps)) 2308 return false; 2309 InstResult = RetVal; 2310 } 2311 } else if (isa<TerminatorInst>(CurInst)) { 2312 BasicBlock *NewBB = 0; 2313 if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) { 2314 if (BI->isUnconditional()) { 2315 NewBB = BI->getSuccessor(0); 2316 } else { 2317 ConstantInt *Cond = 2318 dyn_cast<ConstantInt>(getVal(Values, BI->getCondition())); 2319 if (!Cond) return false; // Cannot determine. 2320 2321 NewBB = BI->getSuccessor(!Cond->getZExtValue()); 2322 } 2323 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) { 2324 ConstantInt *Val = 2325 dyn_cast<ConstantInt>(getVal(Values, SI->getCondition())); 2326 if (!Val) return false; // Cannot determine. 2327 NewBB = SI->getSuccessor(SI->findCaseValue(Val)); 2328 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) { 2329 Value *Val = getVal(Values, IBI->getAddress())->stripPointerCasts(); 2330 if (BlockAddress *BA = dyn_cast<BlockAddress>(Val)) 2331 NewBB = BA->getBasicBlock(); 2332 else 2333 return false; // Cannot determine. 2334 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) { 2335 if (RI->getNumOperands()) 2336 RetVal = getVal(Values, RI->getOperand(0)); 2337 2338 CallStack.pop_back(); // return from fn. 2339 return true; // We succeeded at evaluating this ctor! 2340 } else { 2341 // invoke, unwind, unreachable. 2342 return false; // Cannot handle this terminator. 2343 } 2344 2345 // Okay, we succeeded in evaluating this control flow. See if we have 2346 // executed the new block before. If so, we have a looping function, 2347 // which we cannot evaluate in reasonable time. 2348 if (!ExecutedBlocks.insert(NewBB)) 2349 return false; // looped! 2350 2351 // Okay, we have never been in this block before. Check to see if there 2352 // are any PHI nodes. If so, evaluate them with information about where 2353 // we came from. 2354 BasicBlock *OldBB = CurInst->getParent(); 2355 CurInst = NewBB->begin(); 2356 PHINode *PN; 2357 for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst) 2358 Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB)); 2359 2360 // Do NOT increment CurInst. We know that the terminator had no value. 2361 continue; 2362 } else { 2363 // Did not know how to evaluate this! 2364 return false; 2365 } 2366 2367 if (!CurInst->use_empty()) 2368 Values[CurInst] = InstResult; 2369 2370 // Advance program counter. 2371 ++CurInst; 2372 } 2373} 2374 2375/// EvaluateStaticConstructor - Evaluate static constructors in the function, if 2376/// we can. Return true if we can, false otherwise. 2377static bool EvaluateStaticConstructor(Function *F) { 2378 /// MutatedMemory - For each store we execute, we update this map. Loads 2379 /// check this to get the most up-to-date value. If evaluation is successful, 2380 /// this state is committed to the process. 2381 DenseMap<Constant*, Constant*> MutatedMemory; 2382 2383 /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable 2384 /// to represent its body. This vector is needed so we can delete the 2385 /// temporary globals when we are done. 2386 std::vector<GlobalVariable*> AllocaTmps; 2387 2388 /// CallStack - This is used to detect recursion. In pathological situations 2389 /// we could hit exponential behavior, but at least there is nothing 2390 /// unbounded. 2391 std::vector<Function*> CallStack; 2392 2393 // Call the function. 2394 Constant *RetValDummy; 2395 bool EvalSuccess = EvaluateFunction(F, RetValDummy, 2396 SmallVector<Constant*, 0>(), CallStack, 2397 MutatedMemory, AllocaTmps); 2398 if (EvalSuccess) { 2399 // We succeeded at evaluation: commit the result. 2400 DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" 2401 << F->getName() << "' to " << MutatedMemory.size() 2402 << " stores.\n"); 2403 for (DenseMap<Constant*, Constant*>::iterator I = MutatedMemory.begin(), 2404 E = MutatedMemory.end(); I != E; ++I) 2405 CommitValueTo(I->second, I->first); 2406 } 2407 2408 // At this point, we are done interpreting. If we created any 'alloca' 2409 // temporaries, release them now. 2410 while (!AllocaTmps.empty()) { 2411 GlobalVariable *Tmp = AllocaTmps.back(); 2412 AllocaTmps.pop_back(); 2413 2414 // If there are still users of the alloca, the program is doing something 2415 // silly, e.g. storing the address of the alloca somewhere and using it 2416 // later. Since this is undefined, we'll just make it be null. 2417 if (!Tmp->use_empty()) 2418 Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType())); 2419 delete Tmp; 2420 } 2421 2422 return EvalSuccess; 2423} 2424 2425 2426 2427/// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible. 2428/// Return true if anything changed. 2429bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) { 2430 std::vector<Function*> Ctors = ParseGlobalCtors(GCL); 2431 bool MadeChange = false; 2432 if (Ctors.empty()) return false; 2433 2434 // Loop over global ctors, optimizing them when we can. 2435 for (unsigned i = 0; i != Ctors.size(); ++i) { 2436 Function *F = Ctors[i]; 2437 // Found a null terminator in the middle of the list, prune off the rest of 2438 // the list. 2439 if (F == 0) { 2440 if (i != Ctors.size()-1) { 2441 Ctors.resize(i+1); 2442 MadeChange = true; 2443 } 2444 break; 2445 } 2446 2447 // We cannot simplify external ctor functions. 2448 if (F->empty()) continue; 2449 2450 // If we can evaluate the ctor at compile time, do. 2451 if (EvaluateStaticConstructor(F)) { 2452 Ctors.erase(Ctors.begin()+i); 2453 MadeChange = true; 2454 --i; 2455 ++NumCtorsEvaluated; 2456 continue; 2457 } 2458 } 2459 2460 if (!MadeChange) return false; 2461 2462 GCL = InstallGlobalCtors(GCL, Ctors); 2463 return true; 2464} 2465 2466bool GlobalOpt::OptimizeGlobalAliases(Module &M) { 2467 bool Changed = false; 2468 2469 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); 2470 I != E;) { 2471 Module::alias_iterator J = I++; 2472 // Aliases without names cannot be referenced outside this module. 2473 if (!J->hasName() && !J->isDeclaration()) 2474 J->setLinkage(GlobalValue::InternalLinkage); 2475 // If the aliasee may change at link time, nothing can be done - bail out. 2476 if (J->mayBeOverridden()) 2477 continue; 2478 2479 Constant *Aliasee = J->getAliasee(); 2480 GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts()); 2481 Target->removeDeadConstantUsers(); 2482 bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse(); 2483 2484 // Make all users of the alias use the aliasee instead. 2485 if (!J->use_empty()) { 2486 J->replaceAllUsesWith(Aliasee); 2487 ++NumAliasesResolved; 2488 Changed = true; 2489 } 2490 2491 // If the alias is externally visible, we may still be able to simplify it. 2492 if (!J->hasLocalLinkage()) { 2493 // If the aliasee has internal linkage, give it the name and linkage 2494 // of the alias, and delete the alias. This turns: 2495 // define internal ... @f(...) 2496 // @a = alias ... @f 2497 // into: 2498 // define ... @a(...) 2499 if (!Target->hasLocalLinkage()) 2500 continue; 2501 2502 // Do not perform the transform if multiple aliases potentially target the 2503 // aliasee. This check also ensures that it is safe to replace the section 2504 // and other attributes of the aliasee with those of the alias. 2505 if (!hasOneUse) 2506 continue; 2507 2508 // Give the aliasee the name, linkage and other attributes of the alias. 2509 Target->takeName(J); 2510 Target->setLinkage(J->getLinkage()); 2511 Target->GlobalValue::copyAttributesFrom(J); 2512 } 2513 2514 // Delete the alias. 2515 M.getAliasList().erase(J); 2516 ++NumAliasesRemoved; 2517 Changed = true; 2518 } 2519 2520 return Changed; 2521} 2522 2523bool GlobalOpt::runOnModule(Module &M) { 2524 bool Changed = false; 2525 2526 // Try to find the llvm.globalctors list. 2527 GlobalVariable *GlobalCtors = FindGlobalCtors(M); 2528 2529 bool LocalChange = true; 2530 while (LocalChange) { 2531 LocalChange = false; 2532 2533 // Delete functions that are trivially dead, ccc -> fastcc 2534 LocalChange |= OptimizeFunctions(M); 2535 2536 // Optimize global_ctors list. 2537 if (GlobalCtors) 2538 LocalChange |= OptimizeGlobalCtorsList(GlobalCtors); 2539 2540 // Optimize non-address-taken globals. 2541 LocalChange |= OptimizeGlobalVars(M); 2542 2543 // Resolve aliases, when possible. 2544 LocalChange |= OptimizeGlobalAliases(M); 2545 Changed |= LocalChange; 2546 } 2547 2548 // TODO: Move all global ctors functions to the end of the module for code 2549 // layout. 2550 2551 return Changed; 2552} 2553