ScalarReplAggregates.cpp revision c9ecd14cee020f884313b60f8696384d3e7848f7
1//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===// 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 transformation implements the well known scalar replacement of 11// aggregates transformation. This xform breaks up alloca instructions of 12// aggregate type (structure or array) into individual alloca instructions for 13// each member (if possible). Then, if possible, it transforms the individual 14// alloca instructions into nice clean scalar SSA form. 15// 16// This combines a simple SRoA algorithm with the Mem2Reg algorithm because 17// often interact, especially for C++ programs. As such, iterating between 18// SRoA, then Mem2Reg until we run out of things to promote works well. 19// 20//===----------------------------------------------------------------------===// 21 22#define DEBUG_TYPE "scalarrepl" 23#include "llvm/Transforms/Scalar.h" 24#include "llvm/Constants.h" 25#include "llvm/DerivedTypes.h" 26#include "llvm/Function.h" 27#include "llvm/GlobalVariable.h" 28#include "llvm/Instructions.h" 29#include "llvm/IntrinsicInst.h" 30#include "llvm/LLVMContext.h" 31#include "llvm/Module.h" 32#include "llvm/Pass.h" 33#include "llvm/Analysis/Dominators.h" 34#include "llvm/Analysis/Loads.h" 35#include "llvm/Analysis/ValueTracking.h" 36#include "llvm/Target/TargetData.h" 37#include "llvm/Transforms/Utils/PromoteMemToReg.h" 38#include "llvm/Transforms/Utils/Local.h" 39#include "llvm/Transforms/Utils/SSAUpdater.h" 40#include "llvm/Support/CallSite.h" 41#include "llvm/Support/Debug.h" 42#include "llvm/Support/ErrorHandling.h" 43#include "llvm/Support/GetElementPtrTypeIterator.h" 44#include "llvm/Support/IRBuilder.h" 45#include "llvm/Support/MathExtras.h" 46#include "llvm/Support/raw_ostream.h" 47#include "llvm/ADT/SetVector.h" 48#include "llvm/ADT/SmallVector.h" 49#include "llvm/ADT/Statistic.h" 50using namespace llvm; 51 52STATISTIC(NumReplaced, "Number of allocas broken up"); 53STATISTIC(NumPromoted, "Number of allocas promoted"); 54STATISTIC(NumAdjusted, "Number of scalar allocas adjusted to allow promotion"); 55STATISTIC(NumConverted, "Number of aggregates converted to scalar"); 56STATISTIC(NumGlobals, "Number of allocas copied from constant global"); 57 58namespace { 59 struct SROA : public FunctionPass { 60 SROA(int T, bool hasDT, char &ID) 61 : FunctionPass(ID), HasDomTree(hasDT) { 62 if (T == -1) 63 SRThreshold = 128; 64 else 65 SRThreshold = T; 66 } 67 68 bool runOnFunction(Function &F); 69 70 bool performScalarRepl(Function &F); 71 bool performPromotion(Function &F); 72 73 private: 74 bool HasDomTree; 75 TargetData *TD; 76 77 /// DeadInsts - Keep track of instructions we have made dead, so that 78 /// we can remove them after we are done working. 79 SmallVector<Value*, 32> DeadInsts; 80 81 /// AllocaInfo - When analyzing uses of an alloca instruction, this captures 82 /// information about the uses. All these fields are initialized to false 83 /// and set to true when something is learned. 84 struct AllocaInfo { 85 /// The alloca to promote. 86 AllocaInst *AI; 87 88 /// CheckedPHIs - This is a set of verified PHI nodes, to prevent infinite 89 /// looping and avoid redundant work. 90 SmallPtrSet<PHINode*, 8> CheckedPHIs; 91 92 /// isUnsafe - This is set to true if the alloca cannot be SROA'd. 93 bool isUnsafe : 1; 94 95 /// isMemCpySrc - This is true if this aggregate is memcpy'd from. 96 bool isMemCpySrc : 1; 97 98 /// isMemCpyDst - This is true if this aggregate is memcpy'd into. 99 bool isMemCpyDst : 1; 100 101 /// hasSubelementAccess - This is true if a subelement of the alloca is 102 /// ever accessed, or false if the alloca is only accessed with mem 103 /// intrinsics or load/store that only access the entire alloca at once. 104 bool hasSubelementAccess : 1; 105 106 /// hasALoadOrStore - This is true if there are any loads or stores to it. 107 /// The alloca may just be accessed with memcpy, for example, which would 108 /// not set this. 109 bool hasALoadOrStore : 1; 110 111 explicit AllocaInfo(AllocaInst *ai) 112 : AI(ai), isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false), 113 hasSubelementAccess(false), hasALoadOrStore(false) {} 114 }; 115 116 unsigned SRThreshold; 117 118 void MarkUnsafe(AllocaInfo &I, Instruction *User) { 119 I.isUnsafe = true; 120 DEBUG(dbgs() << " Transformation preventing inst: " << *User << '\n'); 121 } 122 123 bool isSafeAllocaToScalarRepl(AllocaInst *AI); 124 125 void isSafeForScalarRepl(Instruction *I, uint64_t Offset, AllocaInfo &Info); 126 void isSafePHISelectUseForScalarRepl(Instruction *User, uint64_t Offset, 127 AllocaInfo &Info); 128 void isSafeGEP(GetElementPtrInst *GEPI, uint64_t &Offset, AllocaInfo &Info); 129 void isSafeMemAccess(uint64_t Offset, uint64_t MemSize, 130 const Type *MemOpType, bool isStore, AllocaInfo &Info, 131 Instruction *TheAccess, bool AllowWholeAccess); 132 bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size); 133 uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset, 134 const Type *&IdxTy); 135 136 void DoScalarReplacement(AllocaInst *AI, 137 std::vector<AllocaInst*> &WorkList); 138 void DeleteDeadInstructions(); 139 140 void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 141 SmallVector<AllocaInst*, 32> &NewElts); 142 void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 143 SmallVector<AllocaInst*, 32> &NewElts); 144 void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 145 SmallVector<AllocaInst*, 32> &NewElts); 146 void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 147 AllocaInst *AI, 148 SmallVector<AllocaInst*, 32> &NewElts); 149 void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 150 SmallVector<AllocaInst*, 32> &NewElts); 151 void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 152 SmallVector<AllocaInst*, 32> &NewElts); 153 154 static MemTransferInst *isOnlyCopiedFromConstantGlobal(AllocaInst *AI); 155 }; 156 157 // SROA_DT - SROA that uses DominatorTree. 158 struct SROA_DT : public SROA { 159 static char ID; 160 public: 161 SROA_DT(int T = -1) : SROA(T, true, ID) { 162 initializeSROA_DTPass(*PassRegistry::getPassRegistry()); 163 } 164 165 // getAnalysisUsage - This pass does not require any passes, but we know it 166 // will not alter the CFG, so say so. 167 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 168 AU.addRequired<DominatorTree>(); 169 AU.setPreservesCFG(); 170 } 171 }; 172 173 // SROA_SSAUp - SROA that uses SSAUpdater. 174 struct SROA_SSAUp : public SROA { 175 static char ID; 176 public: 177 SROA_SSAUp(int T = -1) : SROA(T, false, ID) { 178 initializeSROA_SSAUpPass(*PassRegistry::getPassRegistry()); 179 } 180 181 // getAnalysisUsage - This pass does not require any passes, but we know it 182 // will not alter the CFG, so say so. 183 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 184 AU.setPreservesCFG(); 185 } 186 }; 187 188} 189 190char SROA_DT::ID = 0; 191char SROA_SSAUp::ID = 0; 192 193INITIALIZE_PASS_BEGIN(SROA_DT, "scalarrepl", 194 "Scalar Replacement of Aggregates (DT)", false, false) 195INITIALIZE_PASS_DEPENDENCY(DominatorTree) 196INITIALIZE_PASS_END(SROA_DT, "scalarrepl", 197 "Scalar Replacement of Aggregates (DT)", false, false) 198 199INITIALIZE_PASS_BEGIN(SROA_SSAUp, "scalarrepl-ssa", 200 "Scalar Replacement of Aggregates (SSAUp)", false, false) 201INITIALIZE_PASS_END(SROA_SSAUp, "scalarrepl-ssa", 202 "Scalar Replacement of Aggregates (SSAUp)", false, false) 203 204// Public interface to the ScalarReplAggregates pass 205FunctionPass *llvm::createScalarReplAggregatesPass(int Threshold, 206 bool UseDomTree) { 207 if (UseDomTree) 208 return new SROA_DT(Threshold); 209 return new SROA_SSAUp(Threshold); 210} 211 212 213//===----------------------------------------------------------------------===// 214// Convert To Scalar Optimization. 215//===----------------------------------------------------------------------===// 216 217namespace { 218/// ConvertToScalarInfo - This class implements the "Convert To Scalar" 219/// optimization, which scans the uses of an alloca and determines if it can 220/// rewrite it in terms of a single new alloca that can be mem2reg'd. 221class ConvertToScalarInfo { 222 /// AllocaSize - The size of the alloca being considered. 223 unsigned AllocaSize; 224 const TargetData &TD; 225 226 /// IsNotTrivial - This is set to true if there is some access to the object 227 /// which means that mem2reg can't promote it. 228 bool IsNotTrivial; 229 230 /// VectorTy - This tracks the type that we should promote the vector to if 231 /// it is possible to turn it into a vector. This starts out null, and if it 232 /// isn't possible to turn into a vector type, it gets set to VoidTy. 233 const Type *VectorTy; 234 235 /// HadAVector - True if there is at least one vector access to the alloca. 236 /// We don't want to turn random arrays into vectors and use vector element 237 /// insert/extract, but if there are element accesses to something that is 238 /// also declared as a vector, we do want to promote to a vector. 239 bool HadAVector; 240 241public: 242 explicit ConvertToScalarInfo(unsigned Size, const TargetData &td) 243 : AllocaSize(Size), TD(td) { 244 IsNotTrivial = false; 245 VectorTy = 0; 246 HadAVector = false; 247 } 248 249 AllocaInst *TryConvert(AllocaInst *AI); 250 251private: 252 bool CanConvertToScalar(Value *V, uint64_t Offset); 253 void MergeInType(const Type *In, uint64_t Offset); 254 bool MergeInVectorType(const VectorType *VInTy, uint64_t Offset); 255 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset); 256 257 Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType, 258 uint64_t Offset, IRBuilder<> &Builder); 259 Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal, 260 uint64_t Offset, IRBuilder<> &Builder); 261}; 262} // end anonymous namespace. 263 264 265/// TryConvert - Analyze the specified alloca, and if it is safe to do so, 266/// rewrite it to be a new alloca which is mem2reg'able. This returns the new 267/// alloca if possible or null if not. 268AllocaInst *ConvertToScalarInfo::TryConvert(AllocaInst *AI) { 269 // If we can't convert this scalar, or if mem2reg can trivially do it, bail 270 // out. 271 if (!CanConvertToScalar(AI, 0) || !IsNotTrivial) 272 return 0; 273 274 // If we were able to find a vector type that can handle this with 275 // insert/extract elements, and if there was at least one use that had 276 // a vector type, promote this to a vector. We don't want to promote 277 // random stuff that doesn't use vectors (e.g. <9 x double>) because then 278 // we just get a lot of insert/extracts. If at least one vector is 279 // involved, then we probably really do have a union of vector/array. 280 const Type *NewTy; 281 if (VectorTy && VectorTy->isVectorTy() && HadAVector) { 282 DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = " 283 << *VectorTy << '\n'); 284 NewTy = VectorTy; // Use the vector type. 285 } else { 286 DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n"); 287 // Create and insert the integer alloca. 288 NewTy = IntegerType::get(AI->getContext(), AllocaSize*8); 289 } 290 AllocaInst *NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin()); 291 ConvertUsesToScalar(AI, NewAI, 0); 292 return NewAI; 293} 294 295/// MergeInType - Add the 'In' type to the accumulated vector type (VectorTy) 296/// so far at the offset specified by Offset (which is specified in bytes). 297/// 298/// There are two cases we handle here: 299/// 1) A union of vector types of the same size and potentially its elements. 300/// Here we turn element accesses into insert/extract element operations. 301/// This promotes a <4 x float> with a store of float to the third element 302/// into a <4 x float> that uses insert element. 303/// 2) A fully general blob of memory, which we turn into some (potentially 304/// large) integer type with extract and insert operations where the loads 305/// and stores would mutate the memory. We mark this by setting VectorTy 306/// to VoidTy. 307void ConvertToScalarInfo::MergeInType(const Type *In, uint64_t Offset) { 308 // If we already decided to turn this into a blob of integer memory, there is 309 // nothing to be done. 310 if (VectorTy && VectorTy->isVoidTy()) 311 return; 312 313 // If this could be contributing to a vector, analyze it. 314 315 // If the In type is a vector that is the same size as the alloca, see if it 316 // matches the existing VecTy. 317 if (const VectorType *VInTy = dyn_cast<VectorType>(In)) { 318 if (MergeInVectorType(VInTy, Offset)) 319 return; 320 } else if (In->isFloatTy() || In->isDoubleTy() || 321 (In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 && 322 isPowerOf2_32(In->getPrimitiveSizeInBits()))) { 323 // If we're accessing something that could be an element of a vector, see 324 // if the implied vector agrees with what we already have and if Offset is 325 // compatible with it. 326 unsigned EltSize = In->getPrimitiveSizeInBits()/8; 327 if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 && 328 (VectorTy == 0 || 329 cast<VectorType>(VectorTy)->getElementType() 330 ->getPrimitiveSizeInBits()/8 == EltSize)) { 331 if (VectorTy == 0) 332 VectorTy = VectorType::get(In, AllocaSize/EltSize); 333 return; 334 } 335 } 336 337 // Otherwise, we have a case that we can't handle with an optimized vector 338 // form. We can still turn this into a large integer. 339 VectorTy = Type::getVoidTy(In->getContext()); 340} 341 342/// MergeInVectorType - Handles the vector case of MergeInType, returning true 343/// if the type was successfully merged and false otherwise. 344bool ConvertToScalarInfo::MergeInVectorType(const VectorType *VInTy, 345 uint64_t Offset) { 346 // Remember if we saw a vector type. 347 HadAVector = true; 348 349 if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) { 350 // If we're storing/loading a vector of the right size, allow it as a 351 // vector. If this the first vector we see, remember the type so that 352 // we know the element size. If this is a subsequent access, ignore it 353 // even if it is a differing type but the same size. Worst case we can 354 // bitcast the resultant vectors. 355 if (VectorTy == 0) 356 VectorTy = VInTy; 357 return true; 358 } 359 360 return false; 361} 362 363/// CanConvertToScalar - V is a pointer. If we can convert the pointee and all 364/// its accesses to a single vector type, return true and set VecTy to 365/// the new type. If we could convert the alloca into a single promotable 366/// integer, return true but set VecTy to VoidTy. Further, if the use is not a 367/// completely trivial use that mem2reg could promote, set IsNotTrivial. Offset 368/// is the current offset from the base of the alloca being analyzed. 369/// 370/// If we see at least one access to the value that is as a vector type, set the 371/// SawVec flag. 372bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset) { 373 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 374 Instruction *User = cast<Instruction>(*UI); 375 376 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 377 // Don't break volatile loads. 378 if (LI->isVolatile()) 379 return false; 380 // Don't touch MMX operations. 381 if (LI->getType()->isX86_MMXTy()) 382 return false; 383 MergeInType(LI->getType(), Offset); 384 continue; 385 } 386 387 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 388 // Storing the pointer, not into the value? 389 if (SI->getOperand(0) == V || SI->isVolatile()) return false; 390 // Don't touch MMX operations. 391 if (SI->getOperand(0)->getType()->isX86_MMXTy()) 392 return false; 393 MergeInType(SI->getOperand(0)->getType(), Offset); 394 continue; 395 } 396 397 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { 398 IsNotTrivial = true; // Can't be mem2reg'd. 399 if (!CanConvertToScalar(BCI, Offset)) 400 return false; 401 continue; 402 } 403 404 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 405 // If this is a GEP with a variable indices, we can't handle it. 406 if (!GEP->hasAllConstantIndices()) 407 return false; 408 409 // Compute the offset that this GEP adds to the pointer. 410 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 411 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 412 &Indices[0], Indices.size()); 413 // See if all uses can be converted. 414 if (!CanConvertToScalar(GEP, Offset+GEPOffset)) 415 return false; 416 IsNotTrivial = true; // Can't be mem2reg'd. 417 continue; 418 } 419 420 // If this is a constant sized memset of a constant value (e.g. 0) we can 421 // handle it. 422 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 423 // Store of constant value and constant size. 424 if (!isa<ConstantInt>(MSI->getValue()) || 425 !isa<ConstantInt>(MSI->getLength())) 426 return false; 427 IsNotTrivial = true; // Can't be mem2reg'd. 428 continue; 429 } 430 431 // If this is a memcpy or memmove into or out of the whole allocation, we 432 // can handle it like a load or store of the scalar type. 433 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 434 ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()); 435 if (Len == 0 || Len->getZExtValue() != AllocaSize || Offset != 0) 436 return false; 437 438 IsNotTrivial = true; // Can't be mem2reg'd. 439 continue; 440 } 441 442 // Otherwise, we cannot handle this! 443 return false; 444 } 445 446 return true; 447} 448 449/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca 450/// directly. This happens when we are converting an "integer union" to a 451/// single integer scalar, or when we are converting a "vector union" to a 452/// vector with insert/extractelement instructions. 453/// 454/// Offset is an offset from the original alloca, in bits that need to be 455/// shifted to the right. By the end of this, there should be no uses of Ptr. 456void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, 457 uint64_t Offset) { 458 while (!Ptr->use_empty()) { 459 Instruction *User = cast<Instruction>(Ptr->use_back()); 460 461 if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 462 ConvertUsesToScalar(CI, NewAI, Offset); 463 CI->eraseFromParent(); 464 continue; 465 } 466 467 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 468 // Compute the offset that this GEP adds to the pointer. 469 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 470 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 471 &Indices[0], Indices.size()); 472 ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8); 473 GEP->eraseFromParent(); 474 continue; 475 } 476 477 IRBuilder<> Builder(User); 478 479 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 480 // The load is a bit extract from NewAI shifted right by Offset bits. 481 Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp"); 482 Value *NewLoadVal 483 = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder); 484 LI->replaceAllUsesWith(NewLoadVal); 485 LI->eraseFromParent(); 486 continue; 487 } 488 489 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 490 assert(SI->getOperand(0) != Ptr && "Consistency error!"); 491 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 492 Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset, 493 Builder); 494 Builder.CreateStore(New, NewAI); 495 SI->eraseFromParent(); 496 497 // If the load we just inserted is now dead, then the inserted store 498 // overwrote the entire thing. 499 if (Old->use_empty()) 500 Old->eraseFromParent(); 501 continue; 502 } 503 504 // If this is a constant sized memset of a constant value (e.g. 0) we can 505 // transform it into a store of the expanded constant value. 506 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 507 assert(MSI->getRawDest() == Ptr && "Consistency error!"); 508 unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue(); 509 if (NumBytes != 0) { 510 unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue(); 511 512 // Compute the value replicated the right number of times. 513 APInt APVal(NumBytes*8, Val); 514 515 // Splat the value if non-zero. 516 if (Val) 517 for (unsigned i = 1; i != NumBytes; ++i) 518 APVal |= APVal << 8; 519 520 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 521 Value *New = ConvertScalar_InsertValue( 522 ConstantInt::get(User->getContext(), APVal), 523 Old, Offset, Builder); 524 Builder.CreateStore(New, NewAI); 525 526 // If the load we just inserted is now dead, then the memset overwrote 527 // the entire thing. 528 if (Old->use_empty()) 529 Old->eraseFromParent(); 530 } 531 MSI->eraseFromParent(); 532 continue; 533 } 534 535 // If this is a memcpy or memmove into or out of the whole allocation, we 536 // can handle it like a load or store of the scalar type. 537 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 538 assert(Offset == 0 && "must be store to start of alloca"); 539 540 // If the source and destination are both to the same alloca, then this is 541 // a noop copy-to-self, just delete it. Otherwise, emit a load and store 542 // as appropriate. 543 AllocaInst *OrigAI = cast<AllocaInst>(GetUnderlyingObject(Ptr, &TD, 0)); 544 545 if (GetUnderlyingObject(MTI->getSource(), &TD, 0) != OrigAI) { 546 // Dest must be OrigAI, change this to be a load from the original 547 // pointer (bitcasted), then a store to our new alloca. 548 assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?"); 549 Value *SrcPtr = MTI->getSource(); 550 const PointerType* SPTy = cast<PointerType>(SrcPtr->getType()); 551 const PointerType* AIPTy = cast<PointerType>(NewAI->getType()); 552 if (SPTy->getAddressSpace() != AIPTy->getAddressSpace()) { 553 AIPTy = PointerType::get(AIPTy->getElementType(), 554 SPTy->getAddressSpace()); 555 } 556 SrcPtr = Builder.CreateBitCast(SrcPtr, AIPTy); 557 558 LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval"); 559 SrcVal->setAlignment(MTI->getAlignment()); 560 Builder.CreateStore(SrcVal, NewAI); 561 } else if (GetUnderlyingObject(MTI->getDest(), &TD, 0) != OrigAI) { 562 // Src must be OrigAI, change this to be a load from NewAI then a store 563 // through the original dest pointer (bitcasted). 564 assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?"); 565 LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval"); 566 567 const PointerType* DPTy = cast<PointerType>(MTI->getDest()->getType()); 568 const PointerType* AIPTy = cast<PointerType>(NewAI->getType()); 569 if (DPTy->getAddressSpace() != AIPTy->getAddressSpace()) { 570 AIPTy = PointerType::get(AIPTy->getElementType(), 571 DPTy->getAddressSpace()); 572 } 573 Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), AIPTy); 574 575 StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr); 576 NewStore->setAlignment(MTI->getAlignment()); 577 } else { 578 // Noop transfer. Src == Dst 579 } 580 581 MTI->eraseFromParent(); 582 continue; 583 } 584 585 llvm_unreachable("Unsupported operation!"); 586 } 587} 588 589/// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer 590/// or vector value FromVal, extracting the bits from the offset specified by 591/// Offset. This returns the value, which is of type ToType. 592/// 593/// This happens when we are converting an "integer union" to a single 594/// integer scalar, or when we are converting a "vector union" to a vector with 595/// insert/extractelement instructions. 596/// 597/// Offset is an offset from the original alloca, in bits that need to be 598/// shifted to the right. 599Value *ConvertToScalarInfo:: 600ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType, 601 uint64_t Offset, IRBuilder<> &Builder) { 602 // If the load is of the whole new alloca, no conversion is needed. 603 if (FromVal->getType() == ToType && Offset == 0) 604 return FromVal; 605 606 // If the result alloca is a vector type, this is either an element 607 // access or a bitcast to another vector type of the same size. 608 if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) { 609 if (ToType->isVectorTy()) 610 return Builder.CreateBitCast(FromVal, ToType, "tmp"); 611 612 // Otherwise it must be an element access. 613 unsigned Elt = 0; 614 if (Offset) { 615 unsigned EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 616 Elt = Offset/EltSize; 617 assert(EltSize*Elt == Offset && "Invalid modulus in validity checking"); 618 } 619 // Return the element extracted out of it. 620 Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get( 621 Type::getInt32Ty(FromVal->getContext()), Elt), "tmp"); 622 if (V->getType() != ToType) 623 V = Builder.CreateBitCast(V, ToType, "tmp"); 624 return V; 625 } 626 627 // If ToType is a first class aggregate, extract out each of the pieces and 628 // use insertvalue's to form the FCA. 629 if (const StructType *ST = dyn_cast<StructType>(ToType)) { 630 const StructLayout &Layout = *TD.getStructLayout(ST); 631 Value *Res = UndefValue::get(ST); 632 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 633 Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i), 634 Offset+Layout.getElementOffsetInBits(i), 635 Builder); 636 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 637 } 638 return Res; 639 } 640 641 if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) { 642 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 643 Value *Res = UndefValue::get(AT); 644 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 645 Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(), 646 Offset+i*EltSize, Builder); 647 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 648 } 649 return Res; 650 } 651 652 // Otherwise, this must be a union that was converted to an integer value. 653 const IntegerType *NTy = cast<IntegerType>(FromVal->getType()); 654 655 // If this is a big-endian system and the load is narrower than the 656 // full alloca type, we need to do a shift to get the right bits. 657 int ShAmt = 0; 658 if (TD.isBigEndian()) { 659 // On big-endian machines, the lowest bit is stored at the bit offset 660 // from the pointer given by getTypeStoreSizeInBits. This matters for 661 // integers with a bitwidth that is not a multiple of 8. 662 ShAmt = TD.getTypeStoreSizeInBits(NTy) - 663 TD.getTypeStoreSizeInBits(ToType) - Offset; 664 } else { 665 ShAmt = Offset; 666 } 667 668 // Note: we support negative bitwidths (with shl) which are not defined. 669 // We do this to support (f.e.) loads off the end of a structure where 670 // only some bits are used. 671 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth()) 672 FromVal = Builder.CreateLShr(FromVal, 673 ConstantInt::get(FromVal->getType(), 674 ShAmt), "tmp"); 675 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) 676 FromVal = Builder.CreateShl(FromVal, 677 ConstantInt::get(FromVal->getType(), 678 -ShAmt), "tmp"); 679 680 // Finally, unconditionally truncate the integer to the right width. 681 unsigned LIBitWidth = TD.getTypeSizeInBits(ToType); 682 if (LIBitWidth < NTy->getBitWidth()) 683 FromVal = 684 Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(), 685 LIBitWidth), "tmp"); 686 else if (LIBitWidth > NTy->getBitWidth()) 687 FromVal = 688 Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(), 689 LIBitWidth), "tmp"); 690 691 // If the result is an integer, this is a trunc or bitcast. 692 if (ToType->isIntegerTy()) { 693 // Should be done. 694 } else if (ToType->isFloatingPointTy() || ToType->isVectorTy()) { 695 // Just do a bitcast, we know the sizes match up. 696 FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp"); 697 } else { 698 // Otherwise must be a pointer. 699 FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp"); 700 } 701 assert(FromVal->getType() == ToType && "Didn't convert right?"); 702 return FromVal; 703} 704 705/// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer 706/// or vector value "Old" at the offset specified by Offset. 707/// 708/// This happens when we are converting an "integer union" to a 709/// single integer scalar, or when we are converting a "vector union" to a 710/// vector with insert/extractelement instructions. 711/// 712/// Offset is an offset from the original alloca, in bits that need to be 713/// shifted to the right. 714Value *ConvertToScalarInfo:: 715ConvertScalar_InsertValue(Value *SV, Value *Old, 716 uint64_t Offset, IRBuilder<> &Builder) { 717 // Convert the stored type to the actual type, shift it left to insert 718 // then 'or' into place. 719 const Type *AllocaType = Old->getType(); 720 LLVMContext &Context = Old->getContext(); 721 722 if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) { 723 uint64_t VecSize = TD.getTypeAllocSizeInBits(VTy); 724 uint64_t ValSize = TD.getTypeAllocSizeInBits(SV->getType()); 725 726 // Changing the whole vector with memset or with an access of a different 727 // vector type? 728 if (ValSize == VecSize) 729 return Builder.CreateBitCast(SV, AllocaType, "tmp"); 730 731 uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 732 733 // Must be an element insertion. 734 unsigned Elt = Offset/EltSize; 735 736 if (SV->getType() != VTy->getElementType()) 737 SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp"); 738 739 SV = Builder.CreateInsertElement(Old, SV, 740 ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt), 741 "tmp"); 742 return SV; 743 } 744 745 // If SV is a first-class aggregate value, insert each value recursively. 746 if (const StructType *ST = dyn_cast<StructType>(SV->getType())) { 747 const StructLayout &Layout = *TD.getStructLayout(ST); 748 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 749 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 750 Old = ConvertScalar_InsertValue(Elt, Old, 751 Offset+Layout.getElementOffsetInBits(i), 752 Builder); 753 } 754 return Old; 755 } 756 757 if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) { 758 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 759 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 760 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 761 Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder); 762 } 763 return Old; 764 } 765 766 // If SV is a float, convert it to the appropriate integer type. 767 // If it is a pointer, do the same. 768 unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType()); 769 unsigned DestWidth = TD.getTypeSizeInBits(AllocaType); 770 unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType()); 771 unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType); 772 if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy()) 773 SV = Builder.CreateBitCast(SV, 774 IntegerType::get(SV->getContext(),SrcWidth), "tmp"); 775 else if (SV->getType()->isPointerTy()) 776 SV = Builder.CreatePtrToInt(SV, TD.getIntPtrType(SV->getContext()), "tmp"); 777 778 // Zero extend or truncate the value if needed. 779 if (SV->getType() != AllocaType) { 780 if (SV->getType()->getPrimitiveSizeInBits() < 781 AllocaType->getPrimitiveSizeInBits()) 782 SV = Builder.CreateZExt(SV, AllocaType, "tmp"); 783 else { 784 // Truncation may be needed if storing more than the alloca can hold 785 // (undefined behavior). 786 SV = Builder.CreateTrunc(SV, AllocaType, "tmp"); 787 SrcWidth = DestWidth; 788 SrcStoreWidth = DestStoreWidth; 789 } 790 } 791 792 // If this is a big-endian system and the store is narrower than the 793 // full alloca type, we need to do a shift to get the right bits. 794 int ShAmt = 0; 795 if (TD.isBigEndian()) { 796 // On big-endian machines, the lowest bit is stored at the bit offset 797 // from the pointer given by getTypeStoreSizeInBits. This matters for 798 // integers with a bitwidth that is not a multiple of 8. 799 ShAmt = DestStoreWidth - SrcStoreWidth - Offset; 800 } else { 801 ShAmt = Offset; 802 } 803 804 // Note: we support negative bitwidths (with shr) which are not defined. 805 // We do this to support (f.e.) stores off the end of a structure where 806 // only some bits in the structure are set. 807 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth)); 808 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) { 809 SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(), 810 ShAmt), "tmp"); 811 Mask <<= ShAmt; 812 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { 813 SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(), 814 -ShAmt), "tmp"); 815 Mask = Mask.lshr(-ShAmt); 816 } 817 818 // Mask out the bits we are about to insert from the old value, and or 819 // in the new bits. 820 if (SrcWidth != DestWidth) { 821 assert(DestWidth > SrcWidth); 822 Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask"); 823 SV = Builder.CreateOr(Old, SV, "ins"); 824 } 825 return SV; 826} 827 828 829//===----------------------------------------------------------------------===// 830// SRoA Driver 831//===----------------------------------------------------------------------===// 832 833 834bool SROA::runOnFunction(Function &F) { 835 TD = getAnalysisIfAvailable<TargetData>(); 836 837 bool Changed = performPromotion(F); 838 839 // FIXME: ScalarRepl currently depends on TargetData more than it 840 // theoretically needs to. It should be refactored in order to support 841 // target-independent IR. Until this is done, just skip the actual 842 // scalar-replacement portion of this pass. 843 if (!TD) return Changed; 844 845 while (1) { 846 bool LocalChange = performScalarRepl(F); 847 if (!LocalChange) break; // No need to repromote if no scalarrepl 848 Changed = true; 849 LocalChange = performPromotion(F); 850 if (!LocalChange) break; // No need to re-scalarrepl if no promotion 851 } 852 853 return Changed; 854} 855 856namespace { 857class AllocaPromoter : public LoadAndStorePromoter { 858 AllocaInst *AI; 859public: 860 AllocaPromoter(const SmallVectorImpl<Instruction*> &Insts, SSAUpdater &S) 861 : LoadAndStorePromoter(Insts, S), AI(0) {} 862 863 void run(AllocaInst *AI, const SmallVectorImpl<Instruction*> &Insts) { 864 // Remember which alloca we're promoting (for isInstInList). 865 this->AI = AI; 866 LoadAndStorePromoter::run(Insts); 867 AI->eraseFromParent(); 868 } 869 870 virtual bool isInstInList(Instruction *I, 871 const SmallVectorImpl<Instruction*> &Insts) const { 872 if (LoadInst *LI = dyn_cast<LoadInst>(I)) 873 return LI->getOperand(0) == AI; 874 return cast<StoreInst>(I)->getPointerOperand() == AI; 875 } 876}; 877} // end anon namespace 878 879/// isSafeSelectToSpeculate - Select instructions that use an alloca and are 880/// subsequently loaded can be rewritten to load both input pointers and then 881/// select between the result, allowing the load of the alloca to be promoted. 882/// From this: 883/// %P2 = select i1 %cond, i32* %Alloca, i32* %Other 884/// %V = load i32* %P2 885/// to: 886/// %V1 = load i32* %Alloca -> will be mem2reg'd 887/// %V2 = load i32* %Other 888/// %V = select i1 %cond, i32 %V1, i32 %V2 889/// 890/// We can do this to a select if its only uses are loads and if the operand to 891/// the select can be loaded unconditionally. 892static bool isSafeSelectToSpeculate(SelectInst *SI, const TargetData *TD) { 893 bool TDerefable = SI->getTrueValue()->isDereferenceablePointer(); 894 bool FDerefable = SI->getFalseValue()->isDereferenceablePointer(); 895 896 for (Value::use_iterator UI = SI->use_begin(), UE = SI->use_end(); 897 UI != UE; ++UI) { 898 LoadInst *LI = dyn_cast<LoadInst>(*UI); 899 if (LI == 0 || LI->isVolatile()) return false; 900 901 // Both operands to the select need to be dereferencable, either absolutely 902 // (e.g. allocas) or at this point because we can see other accesses to it. 903 if (!TDerefable && !isSafeToLoadUnconditionally(SI->getTrueValue(), LI, 904 LI->getAlignment(), TD)) 905 return false; 906 if (!FDerefable && !isSafeToLoadUnconditionally(SI->getFalseValue(), LI, 907 LI->getAlignment(), TD)) 908 return false; 909 } 910 911 return true; 912} 913 914/// isSafePHIToSpeculate - PHI instructions that use an alloca and are 915/// subsequently loaded can be rewritten to load both input pointers in the pred 916/// blocks and then PHI the results, allowing the load of the alloca to be 917/// promoted. 918/// From this: 919/// %P2 = phi [i32* %Alloca, i32* %Other] 920/// %V = load i32* %P2 921/// to: 922/// %V1 = load i32* %Alloca -> will be mem2reg'd 923/// ... 924/// %V2 = load i32* %Other 925/// ... 926/// %V = phi [i32 %V1, i32 %V2] 927/// 928/// We can do this to a select if its only uses are loads and if the operand to 929/// the select can be loaded unconditionally. 930static bool isSafePHIToSpeculate(PHINode *PN, const TargetData *TD) { 931 // For now, we can only do this promotion if the load is in the same block as 932 // the PHI, and if there are no stores between the phi and load. 933 // TODO: Allow recursive phi users. 934 // TODO: Allow stores. 935 BasicBlock *BB = PN->getParent(); 936 unsigned MaxAlign = 0; 937 for (Value::use_iterator UI = PN->use_begin(), UE = PN->use_end(); 938 UI != UE; ++UI) { 939 LoadInst *LI = dyn_cast<LoadInst>(*UI); 940 if (LI == 0 || LI->isVolatile()) return false; 941 942 // For now we only allow loads in the same block as the PHI. This is a 943 // common case that happens when instcombine merges two loads through a PHI. 944 if (LI->getParent() != BB) return false; 945 946 // Ensure that there are no instructions between the PHI and the load that 947 // could store. 948 for (BasicBlock::iterator BBI = PN; &*BBI != LI; ++BBI) 949 if (BBI->mayWriteToMemory()) 950 return false; 951 952 MaxAlign = std::max(MaxAlign, LI->getAlignment()); 953 } 954 955 // Okay, we know that we have one or more loads in the same block as the PHI. 956 // We can transform this if it is safe to push the loads into the predecessor 957 // blocks. The only thing to watch out for is that we can't put a possibly 958 // trapping load in the predecessor if it is a critical edge. 959 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 960 BasicBlock *Pred = PN->getIncomingBlock(i); 961 962 // If the predecessor has a single successor, then the edge isn't critical. 963 if (Pred->getTerminator()->getNumSuccessors() == 1) 964 continue; 965 966 Value *InVal = PN->getIncomingValue(i); 967 968 // If the InVal is an invoke in the pred, we can't put a load on the edge. 969 if (InvokeInst *II = dyn_cast<InvokeInst>(InVal)) 970 if (II->getParent() == Pred) 971 return false; 972 973 // If this pointer is always safe to load, or if we can prove that there is 974 // already a load in the block, then we can move the load to the pred block. 975 if (InVal->isDereferenceablePointer() || 976 isSafeToLoadUnconditionally(InVal, Pred->getTerminator(), MaxAlign, TD)) 977 continue; 978 979 return false; 980 } 981 982 return true; 983} 984 985 986/// tryToMakeAllocaBePromotable - This returns true if the alloca only has 987/// direct (non-volatile) loads and stores to it. If the alloca is close but 988/// not quite there, this will transform the code to allow promotion. As such, 989/// it is a non-pure predicate. 990static bool tryToMakeAllocaBePromotable(AllocaInst *AI, const TargetData *TD) { 991 SetVector<Instruction*, SmallVector<Instruction*, 4>, 992 SmallPtrSet<Instruction*, 4> > InstsToRewrite; 993 994 for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end(); 995 UI != UE; ++UI) { 996 User *U = *UI; 997 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 998 if (LI->isVolatile()) 999 return false; 1000 continue; 1001 } 1002 1003 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 1004 if (SI->getOperand(0) == AI || SI->isVolatile()) 1005 return false; // Don't allow a store OF the AI, only INTO the AI. 1006 continue; 1007 } 1008 1009 if (SelectInst *SI = dyn_cast<SelectInst>(U)) { 1010 // If the condition being selected on is a constant, fold the select, yes 1011 // this does (rarely) happen early on. 1012 if (ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition())) { 1013 Value *Result = SI->getOperand(1+CI->isZero()); 1014 SI->replaceAllUsesWith(Result); 1015 SI->eraseFromParent(); 1016 1017 // This is very rare and we just scrambled the use list of AI, start 1018 // over completely. 1019 return tryToMakeAllocaBePromotable(AI, TD); 1020 } 1021 1022 // If it is safe to turn "load (select c, AI, ptr)" into a select of two 1023 // loads, then we can transform this by rewriting the select. 1024 if (!isSafeSelectToSpeculate(SI, TD)) 1025 return false; 1026 1027 InstsToRewrite.insert(SI); 1028 continue; 1029 } 1030 1031 if (PHINode *PN = dyn_cast<PHINode>(U)) { 1032 if (PN->use_empty()) { // Dead PHIs can be stripped. 1033 InstsToRewrite.insert(PN); 1034 continue; 1035 } 1036 1037 // If it is safe to turn "load (phi [AI, ptr, ...])" into a PHI of loads 1038 // in the pred blocks, then we can transform this by rewriting the PHI. 1039 if (!isSafePHIToSpeculate(PN, TD)) 1040 return false; 1041 1042 InstsToRewrite.insert(PN); 1043 continue; 1044 } 1045 1046 return false; 1047 } 1048 1049 // If there are no instructions to rewrite, then all uses are load/stores and 1050 // we're done! 1051 if (InstsToRewrite.empty()) 1052 return true; 1053 1054 // If we have instructions that need to be rewritten for this to be promotable 1055 // take care of it now. 1056 for (unsigned i = 0, e = InstsToRewrite.size(); i != e; ++i) { 1057 if (SelectInst *SI = dyn_cast<SelectInst>(InstsToRewrite[i])) { 1058 // Selects in InstsToRewrite only have load uses. Rewrite each as two 1059 // loads with a new select. 1060 while (!SI->use_empty()) { 1061 LoadInst *LI = cast<LoadInst>(SI->use_back()); 1062 1063 IRBuilder<> Builder(LI); 1064 LoadInst *TrueLoad = 1065 Builder.CreateLoad(SI->getTrueValue(), LI->getName()+".t"); 1066 LoadInst *FalseLoad = 1067 Builder.CreateLoad(SI->getFalseValue(), LI->getName()+".t"); 1068 1069 // Transfer alignment and TBAA info if present. 1070 TrueLoad->setAlignment(LI->getAlignment()); 1071 FalseLoad->setAlignment(LI->getAlignment()); 1072 if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) { 1073 TrueLoad->setMetadata(LLVMContext::MD_tbaa, Tag); 1074 FalseLoad->setMetadata(LLVMContext::MD_tbaa, Tag); 1075 } 1076 1077 Value *V = Builder.CreateSelect(SI->getCondition(), TrueLoad, FalseLoad); 1078 V->takeName(LI); 1079 LI->replaceAllUsesWith(V); 1080 LI->eraseFromParent(); 1081 } 1082 1083 // Now that all the loads are gone, the select is gone too. 1084 SI->eraseFromParent(); 1085 continue; 1086 } 1087 1088 // Otherwise, we have a PHI node which allows us to push the loads into the 1089 // predecessors. 1090 PHINode *PN = cast<PHINode>(InstsToRewrite[i]); 1091 if (PN->use_empty()) { 1092 PN->eraseFromParent(); 1093 continue; 1094 } 1095 1096 const Type *LoadTy = cast<PointerType>(PN->getType())->getElementType(); 1097 PHINode *NewPN = PHINode::Create(LoadTy, PN->getName()+".ld", PN); 1098 1099 // Get the TBAA tag and alignment to use from one of the loads. It doesn't 1100 // matter which one we get and if any differ, it doesn't matter. 1101 LoadInst *SomeLoad = cast<LoadInst>(PN->use_back()); 1102 MDNode *TBAATag = SomeLoad->getMetadata(LLVMContext::MD_tbaa); 1103 unsigned Align = SomeLoad->getAlignment(); 1104 1105 // Rewrite all loads of the PN to use the new PHI. 1106 while (!PN->use_empty()) { 1107 LoadInst *LI = cast<LoadInst>(PN->use_back()); 1108 LI->replaceAllUsesWith(NewPN); 1109 LI->eraseFromParent(); 1110 } 1111 1112 // Inject loads into all of the pred blocks. Keep track of which blocks we 1113 // insert them into in case we have multiple edges from the same block. 1114 DenseMap<BasicBlock*, LoadInst*> InsertedLoads; 1115 1116 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1117 BasicBlock *Pred = PN->getIncomingBlock(i); 1118 LoadInst *&Load = InsertedLoads[Pred]; 1119 if (Load == 0) { 1120 Load = new LoadInst(PN->getIncomingValue(i), 1121 PN->getName() + "." + Pred->getName(), 1122 Pred->getTerminator()); 1123 Load->setAlignment(Align); 1124 if (TBAATag) Load->setMetadata(LLVMContext::MD_tbaa, TBAATag); 1125 } 1126 1127 NewPN->addIncoming(Load, Pred); 1128 } 1129 1130 PN->eraseFromParent(); 1131 } 1132 1133 ++NumAdjusted; 1134 return true; 1135} 1136 1137 1138bool SROA::performPromotion(Function &F) { 1139 std::vector<AllocaInst*> Allocas; 1140 DominatorTree *DT = 0; 1141 if (HasDomTree) 1142 DT = &getAnalysis<DominatorTree>(); 1143 1144 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function 1145 1146 bool Changed = false; 1147 SmallVector<Instruction*, 64> Insts; 1148 while (1) { 1149 Allocas.clear(); 1150 1151 // Find allocas that are safe to promote, by looking at all instructions in 1152 // the entry node 1153 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) 1154 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? 1155 if (tryToMakeAllocaBePromotable(AI, TD)) 1156 Allocas.push_back(AI); 1157 1158 if (Allocas.empty()) break; 1159 1160 if (HasDomTree) 1161 PromoteMemToReg(Allocas, *DT); 1162 else { 1163 SSAUpdater SSA; 1164 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) { 1165 AllocaInst *AI = Allocas[i]; 1166 1167 // Build list of instructions to promote. 1168 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 1169 UI != E; ++UI) 1170 Insts.push_back(cast<Instruction>(*UI)); 1171 1172 AllocaPromoter(Insts, SSA).run(AI, Insts); 1173 Insts.clear(); 1174 } 1175 } 1176 NumPromoted += Allocas.size(); 1177 Changed = true; 1178 } 1179 1180 return Changed; 1181} 1182 1183 1184/// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for 1185/// SROA. It must be a struct or array type with a small number of elements. 1186static bool ShouldAttemptScalarRepl(AllocaInst *AI) { 1187 const Type *T = AI->getAllocatedType(); 1188 // Do not promote any struct into more than 32 separate vars. 1189 if (const StructType *ST = dyn_cast<StructType>(T)) 1190 return ST->getNumElements() <= 32; 1191 // Arrays are much less likely to be safe for SROA; only consider 1192 // them if they are very small. 1193 if (const ArrayType *AT = dyn_cast<ArrayType>(T)) 1194 return AT->getNumElements() <= 8; 1195 return false; 1196} 1197 1198 1199// performScalarRepl - This algorithm is a simple worklist driven algorithm, 1200// which runs on all of the malloc/alloca instructions in the function, removing 1201// them if they are only used by getelementptr instructions. 1202// 1203bool SROA::performScalarRepl(Function &F) { 1204 std::vector<AllocaInst*> WorkList; 1205 1206 // Scan the entry basic block, adding allocas to the worklist. 1207 BasicBlock &BB = F.getEntryBlock(); 1208 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) 1209 if (AllocaInst *A = dyn_cast<AllocaInst>(I)) 1210 WorkList.push_back(A); 1211 1212 // Process the worklist 1213 bool Changed = false; 1214 while (!WorkList.empty()) { 1215 AllocaInst *AI = WorkList.back(); 1216 WorkList.pop_back(); 1217 1218 // Handle dead allocas trivially. These can be formed by SROA'ing arrays 1219 // with unused elements. 1220 if (AI->use_empty()) { 1221 AI->eraseFromParent(); 1222 Changed = true; 1223 continue; 1224 } 1225 1226 // If this alloca is impossible for us to promote, reject it early. 1227 if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized()) 1228 continue; 1229 1230 // Check to see if this allocation is only modified by a memcpy/memmove from 1231 // a constant global. If this is the case, we can change all users to use 1232 // the constant global instead. This is commonly produced by the CFE by 1233 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A' 1234 // is only subsequently read. 1235 if (MemTransferInst *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) { 1236 DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n'); 1237 DEBUG(dbgs() << " memcpy = " << *TheCopy << '\n'); 1238 Constant *TheSrc = cast<Constant>(TheCopy->getSource()); 1239 AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType())); 1240 TheCopy->eraseFromParent(); // Don't mutate the global. 1241 AI->eraseFromParent(); 1242 ++NumGlobals; 1243 Changed = true; 1244 continue; 1245 } 1246 1247 // Check to see if we can perform the core SROA transformation. We cannot 1248 // transform the allocation instruction if it is an array allocation 1249 // (allocations OF arrays are ok though), and an allocation of a scalar 1250 // value cannot be decomposed at all. 1251 uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType()); 1252 1253 // Do not promote [0 x %struct]. 1254 if (AllocaSize == 0) continue; 1255 1256 // Do not promote any struct whose size is too big. 1257 if (AllocaSize > SRThreshold) continue; 1258 1259 // If the alloca looks like a good candidate for scalar replacement, and if 1260 // all its users can be transformed, then split up the aggregate into its 1261 // separate elements. 1262 if (ShouldAttemptScalarRepl(AI) && isSafeAllocaToScalarRepl(AI)) { 1263 DoScalarReplacement(AI, WorkList); 1264 Changed = true; 1265 continue; 1266 } 1267 1268 // If we can turn this aggregate value (potentially with casts) into a 1269 // simple scalar value that can be mem2reg'd into a register value. 1270 // IsNotTrivial tracks whether this is something that mem2reg could have 1271 // promoted itself. If so, we don't want to transform it needlessly. Note 1272 // that we can't just check based on the type: the alloca may be of an i32 1273 // but that has pointer arithmetic to set byte 3 of it or something. 1274 if (AllocaInst *NewAI = 1275 ConvertToScalarInfo((unsigned)AllocaSize, *TD).TryConvert(AI)) { 1276 NewAI->takeName(AI); 1277 AI->eraseFromParent(); 1278 ++NumConverted; 1279 Changed = true; 1280 continue; 1281 } 1282 1283 // Otherwise, couldn't process this alloca. 1284 } 1285 1286 return Changed; 1287} 1288 1289/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl 1290/// predicate, do SROA now. 1291void SROA::DoScalarReplacement(AllocaInst *AI, 1292 std::vector<AllocaInst*> &WorkList) { 1293 DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n'); 1294 SmallVector<AllocaInst*, 32> ElementAllocas; 1295 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 1296 ElementAllocas.reserve(ST->getNumContainedTypes()); 1297 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { 1298 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 1299 AI->getAlignment(), 1300 AI->getName() + "." + Twine(i), AI); 1301 ElementAllocas.push_back(NA); 1302 WorkList.push_back(NA); // Add to worklist for recursive processing 1303 } 1304 } else { 1305 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); 1306 ElementAllocas.reserve(AT->getNumElements()); 1307 const Type *ElTy = AT->getElementType(); 1308 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 1309 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(), 1310 AI->getName() + "." + Twine(i), AI); 1311 ElementAllocas.push_back(NA); 1312 WorkList.push_back(NA); // Add to worklist for recursive processing 1313 } 1314 } 1315 1316 // Now that we have created the new alloca instructions, rewrite all the 1317 // uses of the old alloca. 1318 RewriteForScalarRepl(AI, AI, 0, ElementAllocas); 1319 1320 // Now erase any instructions that were made dead while rewriting the alloca. 1321 DeleteDeadInstructions(); 1322 AI->eraseFromParent(); 1323 1324 ++NumReplaced; 1325} 1326 1327/// DeleteDeadInstructions - Erase instructions on the DeadInstrs list, 1328/// recursively including all their operands that become trivially dead. 1329void SROA::DeleteDeadInstructions() { 1330 while (!DeadInsts.empty()) { 1331 Instruction *I = cast<Instruction>(DeadInsts.pop_back_val()); 1332 1333 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) 1334 if (Instruction *U = dyn_cast<Instruction>(*OI)) { 1335 // Zero out the operand and see if it becomes trivially dead. 1336 // (But, don't add allocas to the dead instruction list -- they are 1337 // already on the worklist and will be deleted separately.) 1338 *OI = 0; 1339 if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U)) 1340 DeadInsts.push_back(U); 1341 } 1342 1343 I->eraseFromParent(); 1344 } 1345} 1346 1347/// isSafeForScalarRepl - Check if instruction I is a safe use with regard to 1348/// performing scalar replacement of alloca AI. The results are flagged in 1349/// the Info parameter. Offset indicates the position within AI that is 1350/// referenced by this instruction. 1351void SROA::isSafeForScalarRepl(Instruction *I, uint64_t Offset, 1352 AllocaInfo &Info) { 1353 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 1354 Instruction *User = cast<Instruction>(*UI); 1355 1356 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1357 isSafeForScalarRepl(BC, Offset, Info); 1358 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1359 uint64_t GEPOffset = Offset; 1360 isSafeGEP(GEPI, GEPOffset, Info); 1361 if (!Info.isUnsafe) 1362 isSafeForScalarRepl(GEPI, GEPOffset, Info); 1363 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 1364 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 1365 if (Length == 0) 1366 return MarkUnsafe(Info, User); 1367 isSafeMemAccess(Offset, Length->getZExtValue(), 0, 1368 UI.getOperandNo() == 0, Info, MI, 1369 true /*AllowWholeAccess*/); 1370 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1371 if (LI->isVolatile()) 1372 return MarkUnsafe(Info, User); 1373 const Type *LIType = LI->getType(); 1374 isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType), 1375 LIType, false, Info, LI, true /*AllowWholeAccess*/); 1376 Info.hasALoadOrStore = true; 1377 1378 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1379 // Store is ok if storing INTO the pointer, not storing the pointer 1380 if (SI->isVolatile() || SI->getOperand(0) == I) 1381 return MarkUnsafe(Info, User); 1382 1383 const Type *SIType = SI->getOperand(0)->getType(); 1384 isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType), 1385 SIType, true, Info, SI, true /*AllowWholeAccess*/); 1386 Info.hasALoadOrStore = true; 1387 } else if (isa<PHINode>(User) || isa<SelectInst>(User)) { 1388 isSafePHISelectUseForScalarRepl(User, Offset, Info); 1389 } else { 1390 return MarkUnsafe(Info, User); 1391 } 1392 if (Info.isUnsafe) return; 1393 } 1394} 1395 1396 1397/// isSafePHIUseForScalarRepl - If we see a PHI node or select using a pointer 1398/// derived from the alloca, we can often still split the alloca into elements. 1399/// This is useful if we have a large alloca where one element is phi'd 1400/// together somewhere: we can SRoA and promote all the other elements even if 1401/// we end up not being able to promote this one. 1402/// 1403/// All we require is that the uses of the PHI do not index into other parts of 1404/// the alloca. The most important use case for this is single load and stores 1405/// that are PHI'd together, which can happen due to code sinking. 1406void SROA::isSafePHISelectUseForScalarRepl(Instruction *I, uint64_t Offset, 1407 AllocaInfo &Info) { 1408 // If we've already checked this PHI, don't do it again. 1409 if (PHINode *PN = dyn_cast<PHINode>(I)) 1410 if (!Info.CheckedPHIs.insert(PN)) 1411 return; 1412 1413 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 1414 Instruction *User = cast<Instruction>(*UI); 1415 1416 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1417 isSafePHISelectUseForScalarRepl(BC, Offset, Info); 1418 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1419 // Only allow "bitcast" GEPs for simplicity. We could generalize this, 1420 // but would have to prove that we're staying inside of an element being 1421 // promoted. 1422 if (!GEPI->hasAllZeroIndices()) 1423 return MarkUnsafe(Info, User); 1424 isSafePHISelectUseForScalarRepl(GEPI, Offset, Info); 1425 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1426 if (LI->isVolatile()) 1427 return MarkUnsafe(Info, User); 1428 const Type *LIType = LI->getType(); 1429 isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType), 1430 LIType, false, Info, LI, false /*AllowWholeAccess*/); 1431 Info.hasALoadOrStore = true; 1432 1433 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1434 // Store is ok if storing INTO the pointer, not storing the pointer 1435 if (SI->isVolatile() || SI->getOperand(0) == I) 1436 return MarkUnsafe(Info, User); 1437 1438 const Type *SIType = SI->getOperand(0)->getType(); 1439 isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType), 1440 SIType, true, Info, SI, false /*AllowWholeAccess*/); 1441 Info.hasALoadOrStore = true; 1442 } else if (isa<PHINode>(User) || isa<SelectInst>(User)) { 1443 isSafePHISelectUseForScalarRepl(User, Offset, Info); 1444 } else { 1445 return MarkUnsafe(Info, User); 1446 } 1447 if (Info.isUnsafe) return; 1448 } 1449} 1450 1451/// isSafeGEP - Check if a GEP instruction can be handled for scalar 1452/// replacement. It is safe when all the indices are constant, in-bounds 1453/// references, and when the resulting offset corresponds to an element within 1454/// the alloca type. The results are flagged in the Info parameter. Upon 1455/// return, Offset is adjusted as specified by the GEP indices. 1456void SROA::isSafeGEP(GetElementPtrInst *GEPI, 1457 uint64_t &Offset, AllocaInfo &Info) { 1458 gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI); 1459 if (GEPIt == E) 1460 return; 1461 1462 // Walk through the GEP type indices, checking the types that this indexes 1463 // into. 1464 for (; GEPIt != E; ++GEPIt) { 1465 // Ignore struct elements, no extra checking needed for these. 1466 if ((*GEPIt)->isStructTy()) 1467 continue; 1468 1469 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand()); 1470 if (!IdxVal) 1471 return MarkUnsafe(Info, GEPI); 1472 } 1473 1474 // Compute the offset due to this GEP and check if the alloca has a 1475 // component element at that offset. 1476 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 1477 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 1478 &Indices[0], Indices.size()); 1479 if (!TypeHasComponent(Info.AI->getAllocatedType(), Offset, 0)) 1480 MarkUnsafe(Info, GEPI); 1481} 1482 1483/// isHomogeneousAggregate - Check if type T is a struct or array containing 1484/// elements of the same type (which is always true for arrays). If so, 1485/// return true with NumElts and EltTy set to the number of elements and the 1486/// element type, respectively. 1487static bool isHomogeneousAggregate(const Type *T, unsigned &NumElts, 1488 const Type *&EltTy) { 1489 if (const ArrayType *AT = dyn_cast<ArrayType>(T)) { 1490 NumElts = AT->getNumElements(); 1491 EltTy = (NumElts == 0 ? 0 : AT->getElementType()); 1492 return true; 1493 } 1494 if (const StructType *ST = dyn_cast<StructType>(T)) { 1495 NumElts = ST->getNumContainedTypes(); 1496 EltTy = (NumElts == 0 ? 0 : ST->getContainedType(0)); 1497 for (unsigned n = 1; n < NumElts; ++n) { 1498 if (ST->getContainedType(n) != EltTy) 1499 return false; 1500 } 1501 return true; 1502 } 1503 return false; 1504} 1505 1506/// isCompatibleAggregate - Check if T1 and T2 are either the same type or are 1507/// "homogeneous" aggregates with the same element type and number of elements. 1508static bool isCompatibleAggregate(const Type *T1, const Type *T2) { 1509 if (T1 == T2) 1510 return true; 1511 1512 unsigned NumElts1, NumElts2; 1513 const Type *EltTy1, *EltTy2; 1514 if (isHomogeneousAggregate(T1, NumElts1, EltTy1) && 1515 isHomogeneousAggregate(T2, NumElts2, EltTy2) && 1516 NumElts1 == NumElts2 && 1517 EltTy1 == EltTy2) 1518 return true; 1519 1520 return false; 1521} 1522 1523/// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI 1524/// alloca or has an offset and size that corresponds to a component element 1525/// within it. The offset checked here may have been formed from a GEP with a 1526/// pointer bitcasted to a different type. 1527/// 1528/// If AllowWholeAccess is true, then this allows uses of the entire alloca as a 1529/// unit. If false, it only allows accesses known to be in a single element. 1530void SROA::isSafeMemAccess(uint64_t Offset, uint64_t MemSize, 1531 const Type *MemOpType, bool isStore, 1532 AllocaInfo &Info, Instruction *TheAccess, 1533 bool AllowWholeAccess) { 1534 // Check if this is a load/store of the entire alloca. 1535 if (Offset == 0 && AllowWholeAccess && 1536 MemSize == TD->getTypeAllocSize(Info.AI->getAllocatedType())) { 1537 // This can be safe for MemIntrinsics (where MemOpType is 0) and integer 1538 // loads/stores (which are essentially the same as the MemIntrinsics with 1539 // regard to copying padding between elements). But, if an alloca is 1540 // flagged as both a source and destination of such operations, we'll need 1541 // to check later for padding between elements. 1542 if (!MemOpType || MemOpType->isIntegerTy()) { 1543 if (isStore) 1544 Info.isMemCpyDst = true; 1545 else 1546 Info.isMemCpySrc = true; 1547 return; 1548 } 1549 // This is also safe for references using a type that is compatible with 1550 // the type of the alloca, so that loads/stores can be rewritten using 1551 // insertvalue/extractvalue. 1552 if (isCompatibleAggregate(MemOpType, Info.AI->getAllocatedType())) { 1553 Info.hasSubelementAccess = true; 1554 return; 1555 } 1556 } 1557 // Check if the offset/size correspond to a component within the alloca type. 1558 const Type *T = Info.AI->getAllocatedType(); 1559 if (TypeHasComponent(T, Offset, MemSize)) { 1560 Info.hasSubelementAccess = true; 1561 return; 1562 } 1563 1564 return MarkUnsafe(Info, TheAccess); 1565} 1566 1567/// TypeHasComponent - Return true if T has a component type with the 1568/// specified offset and size. If Size is zero, do not check the size. 1569bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) { 1570 const Type *EltTy; 1571 uint64_t EltSize; 1572 if (const StructType *ST = dyn_cast<StructType>(T)) { 1573 const StructLayout *Layout = TD->getStructLayout(ST); 1574 unsigned EltIdx = Layout->getElementContainingOffset(Offset); 1575 EltTy = ST->getContainedType(EltIdx); 1576 EltSize = TD->getTypeAllocSize(EltTy); 1577 Offset -= Layout->getElementOffset(EltIdx); 1578 } else if (const ArrayType *AT = dyn_cast<ArrayType>(T)) { 1579 EltTy = AT->getElementType(); 1580 EltSize = TD->getTypeAllocSize(EltTy); 1581 if (Offset >= AT->getNumElements() * EltSize) 1582 return false; 1583 Offset %= EltSize; 1584 } else { 1585 return false; 1586 } 1587 if (Offset == 0 && (Size == 0 || EltSize == Size)) 1588 return true; 1589 // Check if the component spans multiple elements. 1590 if (Offset + Size > EltSize) 1591 return false; 1592 return TypeHasComponent(EltTy, Offset, Size); 1593} 1594 1595/// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite 1596/// the instruction I, which references it, to use the separate elements. 1597/// Offset indicates the position within AI that is referenced by this 1598/// instruction. 1599void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 1600 SmallVector<AllocaInst*, 32> &NewElts) { 1601 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E;) { 1602 Use &TheUse = UI.getUse(); 1603 Instruction *User = cast<Instruction>(*UI++); 1604 1605 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1606 RewriteBitCast(BC, AI, Offset, NewElts); 1607 continue; 1608 } 1609 1610 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1611 RewriteGEP(GEPI, AI, Offset, NewElts); 1612 continue; 1613 } 1614 1615 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 1616 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 1617 uint64_t MemSize = Length->getZExtValue(); 1618 if (Offset == 0 && 1619 MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) 1620 RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts); 1621 // Otherwise the intrinsic can only touch a single element and the 1622 // address operand will be updated, so nothing else needs to be done. 1623 continue; 1624 } 1625 1626 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1627 const Type *LIType = LI->getType(); 1628 1629 if (isCompatibleAggregate(LIType, AI->getAllocatedType())) { 1630 // Replace: 1631 // %res = load { i32, i32 }* %alloc 1632 // with: 1633 // %load.0 = load i32* %alloc.0 1634 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0 1635 // %load.1 = load i32* %alloc.1 1636 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1 1637 // (Also works for arrays instead of structs) 1638 Value *Insert = UndefValue::get(LIType); 1639 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1640 Value *Load = new LoadInst(NewElts[i], "load", LI); 1641 Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI); 1642 } 1643 LI->replaceAllUsesWith(Insert); 1644 DeadInsts.push_back(LI); 1645 } else if (LIType->isIntegerTy() && 1646 TD->getTypeAllocSize(LIType) == 1647 TD->getTypeAllocSize(AI->getAllocatedType())) { 1648 // If this is a load of the entire alloca to an integer, rewrite it. 1649 RewriteLoadUserOfWholeAlloca(LI, AI, NewElts); 1650 } 1651 continue; 1652 } 1653 1654 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1655 Value *Val = SI->getOperand(0); 1656 const Type *SIType = Val->getType(); 1657 if (isCompatibleAggregate(SIType, AI->getAllocatedType())) { 1658 // Replace: 1659 // store { i32, i32 } %val, { i32, i32 }* %alloc 1660 // with: 1661 // %val.0 = extractvalue { i32, i32 } %val, 0 1662 // store i32 %val.0, i32* %alloc.0 1663 // %val.1 = extractvalue { i32, i32 } %val, 1 1664 // store i32 %val.1, i32* %alloc.1 1665 // (Also works for arrays instead of structs) 1666 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1667 Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI); 1668 new StoreInst(Extract, NewElts[i], SI); 1669 } 1670 DeadInsts.push_back(SI); 1671 } else if (SIType->isIntegerTy() && 1672 TD->getTypeAllocSize(SIType) == 1673 TD->getTypeAllocSize(AI->getAllocatedType())) { 1674 // If this is a store of the entire alloca from an integer, rewrite it. 1675 RewriteStoreUserOfWholeAlloca(SI, AI, NewElts); 1676 } 1677 continue; 1678 } 1679 1680 if (isa<SelectInst>(User) || isa<PHINode>(User)) { 1681 // If we have a PHI user of the alloca itself (as opposed to a GEP or 1682 // bitcast) we have to rewrite it. GEP and bitcast uses will be RAUW'd to 1683 // the new pointer. 1684 if (!isa<AllocaInst>(I)) continue; 1685 1686 assert(Offset == 0 && NewElts[0] && 1687 "Direct alloca use should have a zero offset"); 1688 1689 // If we have a use of the alloca, we know the derived uses will be 1690 // utilizing just the first element of the scalarized result. Insert a 1691 // bitcast of the first alloca before the user as required. 1692 AllocaInst *NewAI = NewElts[0]; 1693 BitCastInst *BCI = new BitCastInst(NewAI, AI->getType(), "", NewAI); 1694 NewAI->moveBefore(BCI); 1695 TheUse = BCI; 1696 continue; 1697 } 1698 } 1699} 1700 1701/// RewriteBitCast - Update a bitcast reference to the alloca being replaced 1702/// and recursively continue updating all of its uses. 1703void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 1704 SmallVector<AllocaInst*, 32> &NewElts) { 1705 RewriteForScalarRepl(BC, AI, Offset, NewElts); 1706 if (BC->getOperand(0) != AI) 1707 return; 1708 1709 // The bitcast references the original alloca. Replace its uses with 1710 // references to the first new element alloca. 1711 Instruction *Val = NewElts[0]; 1712 if (Val->getType() != BC->getDestTy()) { 1713 Val = new BitCastInst(Val, BC->getDestTy(), "", BC); 1714 Val->takeName(BC); 1715 } 1716 BC->replaceAllUsesWith(Val); 1717 DeadInsts.push_back(BC); 1718} 1719 1720/// FindElementAndOffset - Return the index of the element containing Offset 1721/// within the specified type, which must be either a struct or an array. 1722/// Sets T to the type of the element and Offset to the offset within that 1723/// element. IdxTy is set to the type of the index result to be used in a 1724/// GEP instruction. 1725uint64_t SROA::FindElementAndOffset(const Type *&T, uint64_t &Offset, 1726 const Type *&IdxTy) { 1727 uint64_t Idx = 0; 1728 if (const StructType *ST = dyn_cast<StructType>(T)) { 1729 const StructLayout *Layout = TD->getStructLayout(ST); 1730 Idx = Layout->getElementContainingOffset(Offset); 1731 T = ST->getContainedType(Idx); 1732 Offset -= Layout->getElementOffset(Idx); 1733 IdxTy = Type::getInt32Ty(T->getContext()); 1734 return Idx; 1735 } 1736 const ArrayType *AT = cast<ArrayType>(T); 1737 T = AT->getElementType(); 1738 uint64_t EltSize = TD->getTypeAllocSize(T); 1739 Idx = Offset / EltSize; 1740 Offset -= Idx * EltSize; 1741 IdxTy = Type::getInt64Ty(T->getContext()); 1742 return Idx; 1743} 1744 1745/// RewriteGEP - Check if this GEP instruction moves the pointer across 1746/// elements of the alloca that are being split apart, and if so, rewrite 1747/// the GEP to be relative to the new element. 1748void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 1749 SmallVector<AllocaInst*, 32> &NewElts) { 1750 uint64_t OldOffset = Offset; 1751 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 1752 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 1753 &Indices[0], Indices.size()); 1754 1755 RewriteForScalarRepl(GEPI, AI, Offset, NewElts); 1756 1757 const Type *T = AI->getAllocatedType(); 1758 const Type *IdxTy; 1759 uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy); 1760 if (GEPI->getOperand(0) == AI) 1761 OldIdx = ~0ULL; // Force the GEP to be rewritten. 1762 1763 T = AI->getAllocatedType(); 1764 uint64_t EltOffset = Offset; 1765 uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy); 1766 1767 // If this GEP does not move the pointer across elements of the alloca 1768 // being split, then it does not needs to be rewritten. 1769 if (Idx == OldIdx) 1770 return; 1771 1772 const Type *i32Ty = Type::getInt32Ty(AI->getContext()); 1773 SmallVector<Value*, 8> NewArgs; 1774 NewArgs.push_back(Constant::getNullValue(i32Ty)); 1775 while (EltOffset != 0) { 1776 uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy); 1777 NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx)); 1778 } 1779 Instruction *Val = NewElts[Idx]; 1780 if (NewArgs.size() > 1) { 1781 Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(), 1782 NewArgs.end(), "", GEPI); 1783 Val->takeName(GEPI); 1784 } 1785 if (Val->getType() != GEPI->getType()) 1786 Val = new BitCastInst(Val, GEPI->getType(), Val->getName(), GEPI); 1787 GEPI->replaceAllUsesWith(Val); 1788 DeadInsts.push_back(GEPI); 1789} 1790 1791/// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI. 1792/// Rewrite it to copy or set the elements of the scalarized memory. 1793void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 1794 AllocaInst *AI, 1795 SmallVector<AllocaInst*, 32> &NewElts) { 1796 // If this is a memcpy/memmove, construct the other pointer as the 1797 // appropriate type. The "Other" pointer is the pointer that goes to memory 1798 // that doesn't have anything to do with the alloca that we are promoting. For 1799 // memset, this Value* stays null. 1800 Value *OtherPtr = 0; 1801 unsigned MemAlignment = MI->getAlignment(); 1802 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy 1803 if (Inst == MTI->getRawDest()) 1804 OtherPtr = MTI->getRawSource(); 1805 else { 1806 assert(Inst == MTI->getRawSource()); 1807 OtherPtr = MTI->getRawDest(); 1808 } 1809 } 1810 1811 // If there is an other pointer, we want to convert it to the same pointer 1812 // type as AI has, so we can GEP through it safely. 1813 if (OtherPtr) { 1814 unsigned AddrSpace = 1815 cast<PointerType>(OtherPtr->getType())->getAddressSpace(); 1816 1817 // Remove bitcasts and all-zero GEPs from OtherPtr. This is an 1818 // optimization, but it's also required to detect the corner case where 1819 // both pointer operands are referencing the same memory, and where 1820 // OtherPtr may be a bitcast or GEP that currently being rewritten. (This 1821 // function is only called for mem intrinsics that access the whole 1822 // aggregate, so non-zero GEPs are not an issue here.) 1823 OtherPtr = OtherPtr->stripPointerCasts(); 1824 1825 // Copying the alloca to itself is a no-op: just delete it. 1826 if (OtherPtr == AI || OtherPtr == NewElts[0]) { 1827 // This code will run twice for a no-op memcpy -- once for each operand. 1828 // Put only one reference to MI on the DeadInsts list. 1829 for (SmallVector<Value*, 32>::const_iterator I = DeadInsts.begin(), 1830 E = DeadInsts.end(); I != E; ++I) 1831 if (*I == MI) return; 1832 DeadInsts.push_back(MI); 1833 return; 1834 } 1835 1836 // If the pointer is not the right type, insert a bitcast to the right 1837 // type. 1838 const Type *NewTy = 1839 PointerType::get(AI->getType()->getElementType(), AddrSpace); 1840 1841 if (OtherPtr->getType() != NewTy) 1842 OtherPtr = new BitCastInst(OtherPtr, NewTy, OtherPtr->getName(), MI); 1843 } 1844 1845 // Process each element of the aggregate. 1846 bool SROADest = MI->getRawDest() == Inst; 1847 1848 Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext())); 1849 1850 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1851 // If this is a memcpy/memmove, emit a GEP of the other element address. 1852 Value *OtherElt = 0; 1853 unsigned OtherEltAlign = MemAlignment; 1854 1855 if (OtherPtr) { 1856 Value *Idx[2] = { Zero, 1857 ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) }; 1858 OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2, 1859 OtherPtr->getName()+"."+Twine(i), 1860 MI); 1861 uint64_t EltOffset; 1862 const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType()); 1863 const Type *OtherTy = OtherPtrTy->getElementType(); 1864 if (const StructType *ST = dyn_cast<StructType>(OtherTy)) { 1865 EltOffset = TD->getStructLayout(ST)->getElementOffset(i); 1866 } else { 1867 const Type *EltTy = cast<SequentialType>(OtherTy)->getElementType(); 1868 EltOffset = TD->getTypeAllocSize(EltTy)*i; 1869 } 1870 1871 // The alignment of the other pointer is the guaranteed alignment of the 1872 // element, which is affected by both the known alignment of the whole 1873 // mem intrinsic and the alignment of the element. If the alignment of 1874 // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the 1875 // known alignment is just 4 bytes. 1876 OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset); 1877 } 1878 1879 Value *EltPtr = NewElts[i]; 1880 const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType(); 1881 1882 // If we got down to a scalar, insert a load or store as appropriate. 1883 if (EltTy->isSingleValueType()) { 1884 if (isa<MemTransferInst>(MI)) { 1885 if (SROADest) { 1886 // From Other to Alloca. 1887 Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI); 1888 new StoreInst(Elt, EltPtr, MI); 1889 } else { 1890 // From Alloca to Other. 1891 Value *Elt = new LoadInst(EltPtr, "tmp", MI); 1892 new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI); 1893 } 1894 continue; 1895 } 1896 assert(isa<MemSetInst>(MI)); 1897 1898 // If the stored element is zero (common case), just store a null 1899 // constant. 1900 Constant *StoreVal; 1901 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getArgOperand(1))) { 1902 if (CI->isZero()) { 1903 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0> 1904 } else { 1905 // If EltTy is a vector type, get the element type. 1906 const Type *ValTy = EltTy->getScalarType(); 1907 1908 // Construct an integer with the right value. 1909 unsigned EltSize = TD->getTypeSizeInBits(ValTy); 1910 APInt OneVal(EltSize, CI->getZExtValue()); 1911 APInt TotalVal(OneVal); 1912 // Set each byte. 1913 for (unsigned i = 0; 8*i < EltSize; ++i) { 1914 TotalVal = TotalVal.shl(8); 1915 TotalVal |= OneVal; 1916 } 1917 1918 // Convert the integer value to the appropriate type. 1919 StoreVal = ConstantInt::get(CI->getContext(), TotalVal); 1920 if (ValTy->isPointerTy()) 1921 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); 1922 else if (ValTy->isFloatingPointTy()) 1923 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy); 1924 assert(StoreVal->getType() == ValTy && "Type mismatch!"); 1925 1926 // If the requested value was a vector constant, create it. 1927 if (EltTy != ValTy) { 1928 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements(); 1929 SmallVector<Constant*, 16> Elts(NumElts, StoreVal); 1930 StoreVal = ConstantVector::get(Elts); 1931 } 1932 } 1933 new StoreInst(StoreVal, EltPtr, MI); 1934 continue; 1935 } 1936 // Otherwise, if we're storing a byte variable, use a memset call for 1937 // this element. 1938 } 1939 1940 unsigned EltSize = TD->getTypeAllocSize(EltTy); 1941 1942 IRBuilder<> Builder(MI); 1943 1944 // Finally, insert the meminst for this element. 1945 if (isa<MemSetInst>(MI)) { 1946 Builder.CreateMemSet(EltPtr, MI->getArgOperand(1), EltSize, 1947 MI->isVolatile()); 1948 } else { 1949 assert(isa<MemTransferInst>(MI)); 1950 Value *Dst = SROADest ? EltPtr : OtherElt; // Dest ptr 1951 Value *Src = SROADest ? OtherElt : EltPtr; // Src ptr 1952 1953 if (isa<MemCpyInst>(MI)) 1954 Builder.CreateMemCpy(Dst, Src, EltSize, OtherEltAlign,MI->isVolatile()); 1955 else 1956 Builder.CreateMemMove(Dst, Src, EltSize,OtherEltAlign,MI->isVolatile()); 1957 } 1958 } 1959 DeadInsts.push_back(MI); 1960} 1961 1962/// RewriteStoreUserOfWholeAlloca - We found a store of an integer that 1963/// overwrites the entire allocation. Extract out the pieces of the stored 1964/// integer and store them individually. 1965void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 1966 SmallVector<AllocaInst*, 32> &NewElts){ 1967 // Extract each element out of the integer according to its structure offset 1968 // and store the element value to the individual alloca. 1969 Value *SrcVal = SI->getOperand(0); 1970 const Type *AllocaEltTy = AI->getAllocatedType(); 1971 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 1972 1973 IRBuilder<> Builder(SI); 1974 1975 // Handle tail padding by extending the operand 1976 if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits) 1977 SrcVal = Builder.CreateZExt(SrcVal, 1978 IntegerType::get(SI->getContext(), AllocaSizeBits)); 1979 1980 DEBUG(dbgs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI 1981 << '\n'); 1982 1983 // There are two forms here: AI could be an array or struct. Both cases 1984 // have different ways to compute the element offset. 1985 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 1986 const StructLayout *Layout = TD->getStructLayout(EltSTy); 1987 1988 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1989 // Get the number of bits to shift SrcVal to get the value. 1990 const Type *FieldTy = EltSTy->getElementType(i); 1991 uint64_t Shift = Layout->getElementOffsetInBits(i); 1992 1993 if (TD->isBigEndian()) 1994 Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy); 1995 1996 Value *EltVal = SrcVal; 1997 if (Shift) { 1998 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 1999 EltVal = Builder.CreateLShr(EltVal, ShiftVal, "sroa.store.elt"); 2000 } 2001 2002 // Truncate down to an integer of the right size. 2003 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 2004 2005 // Ignore zero sized fields like {}, they obviously contain no data. 2006 if (FieldSizeBits == 0) continue; 2007 2008 if (FieldSizeBits != AllocaSizeBits) 2009 EltVal = Builder.CreateTrunc(EltVal, 2010 IntegerType::get(SI->getContext(), FieldSizeBits)); 2011 Value *DestField = NewElts[i]; 2012 if (EltVal->getType() == FieldTy) { 2013 // Storing to an integer field of this size, just do it. 2014 } else if (FieldTy->isFloatingPointTy() || FieldTy->isVectorTy()) { 2015 // Bitcast to the right element type (for fp/vector values). 2016 EltVal = Builder.CreateBitCast(EltVal, FieldTy); 2017 } else { 2018 // Otherwise, bitcast the dest pointer (for aggregates). 2019 DestField = Builder.CreateBitCast(DestField, 2020 PointerType::getUnqual(EltVal->getType())); 2021 } 2022 new StoreInst(EltVal, DestField, SI); 2023 } 2024 2025 } else { 2026 const ArrayType *ATy = cast<ArrayType>(AllocaEltTy); 2027 const Type *ArrayEltTy = ATy->getElementType(); 2028 uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 2029 uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy); 2030 2031 uint64_t Shift; 2032 2033 if (TD->isBigEndian()) 2034 Shift = AllocaSizeBits-ElementOffset; 2035 else 2036 Shift = 0; 2037 2038 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 2039 // Ignore zero sized fields like {}, they obviously contain no data. 2040 if (ElementSizeBits == 0) continue; 2041 2042 Value *EltVal = SrcVal; 2043 if (Shift) { 2044 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 2045 EltVal = Builder.CreateLShr(EltVal, ShiftVal, "sroa.store.elt"); 2046 } 2047 2048 // Truncate down to an integer of the right size. 2049 if (ElementSizeBits != AllocaSizeBits) 2050 EltVal = Builder.CreateTrunc(EltVal, 2051 IntegerType::get(SI->getContext(), 2052 ElementSizeBits)); 2053 Value *DestField = NewElts[i]; 2054 if (EltVal->getType() == ArrayEltTy) { 2055 // Storing to an integer field of this size, just do it. 2056 } else if (ArrayEltTy->isFloatingPointTy() || 2057 ArrayEltTy->isVectorTy()) { 2058 // Bitcast to the right element type (for fp/vector values). 2059 EltVal = Builder.CreateBitCast(EltVal, ArrayEltTy); 2060 } else { 2061 // Otherwise, bitcast the dest pointer (for aggregates). 2062 DestField = Builder.CreateBitCast(DestField, 2063 PointerType::getUnqual(EltVal->getType())); 2064 } 2065 new StoreInst(EltVal, DestField, SI); 2066 2067 if (TD->isBigEndian()) 2068 Shift -= ElementOffset; 2069 else 2070 Shift += ElementOffset; 2071 } 2072 } 2073 2074 DeadInsts.push_back(SI); 2075} 2076 2077/// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to 2078/// an integer. Load the individual pieces to form the aggregate value. 2079void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 2080 SmallVector<AllocaInst*, 32> &NewElts) { 2081 // Extract each element out of the NewElts according to its structure offset 2082 // and form the result value. 2083 const Type *AllocaEltTy = AI->getAllocatedType(); 2084 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 2085 2086 DEBUG(dbgs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI 2087 << '\n'); 2088 2089 // There are two forms here: AI could be an array or struct. Both cases 2090 // have different ways to compute the element offset. 2091 const StructLayout *Layout = 0; 2092 uint64_t ArrayEltBitOffset = 0; 2093 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 2094 Layout = TD->getStructLayout(EltSTy); 2095 } else { 2096 const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType(); 2097 ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 2098 } 2099 2100 Value *ResultVal = 2101 Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits)); 2102 2103 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 2104 // Load the value from the alloca. If the NewElt is an aggregate, cast 2105 // the pointer to an integer of the same size before doing the load. 2106 Value *SrcField = NewElts[i]; 2107 const Type *FieldTy = 2108 cast<PointerType>(SrcField->getType())->getElementType(); 2109 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 2110 2111 // Ignore zero sized fields like {}, they obviously contain no data. 2112 if (FieldSizeBits == 0) continue; 2113 2114 const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(), 2115 FieldSizeBits); 2116 if (!FieldTy->isIntegerTy() && !FieldTy->isFloatingPointTy() && 2117 !FieldTy->isVectorTy()) 2118 SrcField = new BitCastInst(SrcField, 2119 PointerType::getUnqual(FieldIntTy), 2120 "", LI); 2121 SrcField = new LoadInst(SrcField, "sroa.load.elt", LI); 2122 2123 // If SrcField is a fp or vector of the right size but that isn't an 2124 // integer type, bitcast to an integer so we can shift it. 2125 if (SrcField->getType() != FieldIntTy) 2126 SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI); 2127 2128 // Zero extend the field to be the same size as the final alloca so that 2129 // we can shift and insert it. 2130 if (SrcField->getType() != ResultVal->getType()) 2131 SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI); 2132 2133 // Determine the number of bits to shift SrcField. 2134 uint64_t Shift; 2135 if (Layout) // Struct case. 2136 Shift = Layout->getElementOffsetInBits(i); 2137 else // Array case. 2138 Shift = i*ArrayEltBitOffset; 2139 2140 if (TD->isBigEndian()) 2141 Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth(); 2142 2143 if (Shift) { 2144 Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift); 2145 SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI); 2146 } 2147 2148 // Don't create an 'or x, 0' on the first iteration. 2149 if (!isa<Constant>(ResultVal) || 2150 !cast<Constant>(ResultVal)->isNullValue()) 2151 ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI); 2152 else 2153 ResultVal = SrcField; 2154 } 2155 2156 // Handle tail padding by truncating the result 2157 if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits) 2158 ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI); 2159 2160 LI->replaceAllUsesWith(ResultVal); 2161 DeadInsts.push_back(LI); 2162} 2163 2164/// HasPadding - Return true if the specified type has any structure or 2165/// alignment padding in between the elements that would be split apart 2166/// by SROA; return false otherwise. 2167static bool HasPadding(const Type *Ty, const TargetData &TD) { 2168 if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 2169 Ty = ATy->getElementType(); 2170 return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty); 2171 } 2172 2173 // SROA currently handles only Arrays and Structs. 2174 const StructType *STy = cast<StructType>(Ty); 2175 const StructLayout *SL = TD.getStructLayout(STy); 2176 unsigned PrevFieldBitOffset = 0; 2177 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 2178 unsigned FieldBitOffset = SL->getElementOffsetInBits(i); 2179 2180 // Check to see if there is any padding between this element and the 2181 // previous one. 2182 if (i) { 2183 unsigned PrevFieldEnd = 2184 PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1)); 2185 if (PrevFieldEnd < FieldBitOffset) 2186 return true; 2187 } 2188 PrevFieldBitOffset = FieldBitOffset; 2189 } 2190 // Check for tail padding. 2191 if (unsigned EltCount = STy->getNumElements()) { 2192 unsigned PrevFieldEnd = PrevFieldBitOffset + 2193 TD.getTypeSizeInBits(STy->getElementType(EltCount-1)); 2194 if (PrevFieldEnd < SL->getSizeInBits()) 2195 return true; 2196 } 2197 return false; 2198} 2199 2200/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of 2201/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, 2202/// or 1 if safe after canonicalization has been performed. 2203bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) { 2204 // Loop over the use list of the alloca. We can only transform it if all of 2205 // the users are safe to transform. 2206 AllocaInfo Info(AI); 2207 2208 isSafeForScalarRepl(AI, 0, Info); 2209 if (Info.isUnsafe) { 2210 DEBUG(dbgs() << "Cannot transform: " << *AI << '\n'); 2211 return false; 2212 } 2213 2214 // Okay, we know all the users are promotable. If the aggregate is a memcpy 2215 // source and destination, we have to be careful. In particular, the memcpy 2216 // could be moving around elements that live in structure padding of the LLVM 2217 // types, but may actually be used. In these cases, we refuse to promote the 2218 // struct. 2219 if (Info.isMemCpySrc && Info.isMemCpyDst && 2220 HasPadding(AI->getAllocatedType(), *TD)) 2221 return false; 2222 2223 // If the alloca never has an access to just *part* of it, but is accessed 2224 // via loads and stores, then we should use ConvertToScalarInfo to promote 2225 // the alloca instead of promoting each piece at a time and inserting fission 2226 // and fusion code. 2227 if (!Info.hasSubelementAccess && Info.hasALoadOrStore) { 2228 // If the struct/array just has one element, use basic SRoA. 2229 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 2230 if (ST->getNumElements() > 1) return false; 2231 } else { 2232 if (cast<ArrayType>(AI->getAllocatedType())->getNumElements() > 1) 2233 return false; 2234 } 2235 } 2236 2237 return true; 2238} 2239 2240 2241 2242/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to 2243/// some part of a constant global variable. This intentionally only accepts 2244/// constant expressions because we don't can't rewrite arbitrary instructions. 2245static bool PointsToConstantGlobal(Value *V) { 2246 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) 2247 return GV->isConstant(); 2248 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 2249 if (CE->getOpcode() == Instruction::BitCast || 2250 CE->getOpcode() == Instruction::GetElementPtr) 2251 return PointsToConstantGlobal(CE->getOperand(0)); 2252 return false; 2253} 2254 2255/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived) 2256/// pointer to an alloca. Ignore any reads of the pointer, return false if we 2257/// see any stores or other unknown uses. If we see pointer arithmetic, keep 2258/// track of whether it moves the pointer (with isOffset) but otherwise traverse 2259/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to 2260/// the alloca, and if the source pointer is a pointer to a constant global, we 2261/// can optimize this. 2262static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy, 2263 bool isOffset) { 2264 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 2265 User *U = cast<Instruction>(*UI); 2266 2267 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 2268 // Ignore non-volatile loads, they are always ok. 2269 if (LI->isVolatile()) return false; 2270 continue; 2271 } 2272 2273 if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) { 2274 // If uses of the bitcast are ok, we are ok. 2275 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) 2276 return false; 2277 continue; 2278 } 2279 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 2280 // If the GEP has all zero indices, it doesn't offset the pointer. If it 2281 // doesn't, it does. 2282 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy, 2283 isOffset || !GEP->hasAllZeroIndices())) 2284 return false; 2285 continue; 2286 } 2287 2288 if (CallSite CS = U) { 2289 // If this is a readonly/readnone call site, then we know it is just a 2290 // load and we can ignore it. 2291 if (CS.onlyReadsMemory()) 2292 continue; 2293 2294 // If this is the function being called then we treat it like a load and 2295 // ignore it. 2296 if (CS.isCallee(UI)) 2297 continue; 2298 2299 // If this is being passed as a byval argument, the caller is making a 2300 // copy, so it is only a read of the alloca. 2301 unsigned ArgNo = CS.getArgumentNo(UI); 2302 if (CS.paramHasAttr(ArgNo+1, Attribute::ByVal)) 2303 continue; 2304 } 2305 2306 // If this is isn't our memcpy/memmove, reject it as something we can't 2307 // handle. 2308 MemTransferInst *MI = dyn_cast<MemTransferInst>(U); 2309 if (MI == 0) 2310 return false; 2311 2312 // If the transfer is using the alloca as a source of the transfer, then 2313 // ignore it since it is a load (unless the transfer is volatile). 2314 if (UI.getOperandNo() == 1) { 2315 if (MI->isVolatile()) return false; 2316 continue; 2317 } 2318 2319 // If we already have seen a copy, reject the second one. 2320 if (TheCopy) return false; 2321 2322 // If the pointer has been offset from the start of the alloca, we can't 2323 // safely handle this. 2324 if (isOffset) return false; 2325 2326 // If the memintrinsic isn't using the alloca as the dest, reject it. 2327 if (UI.getOperandNo() != 0) return false; 2328 2329 // If the source of the memcpy/move is not a constant global, reject it. 2330 if (!PointsToConstantGlobal(MI->getSource())) 2331 return false; 2332 2333 // Otherwise, the transform is safe. Remember the copy instruction. 2334 TheCopy = MI; 2335 } 2336 return true; 2337} 2338 2339/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only 2340/// modified by a copy from a constant global. If we can prove this, we can 2341/// replace any uses of the alloca with uses of the global directly. 2342MemTransferInst *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) { 2343 MemTransferInst *TheCopy = 0; 2344 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) 2345 return TheCopy; 2346 return 0; 2347} 2348