ScalarReplAggregates.cpp revision 90c579de5a383cee278acc3f7e7b9d0a656e6a35
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/Pass.h" 32#include "llvm/Analysis/Dominators.h" 33#include "llvm/Target/TargetData.h" 34#include "llvm/Transforms/Utils/PromoteMemToReg.h" 35#include "llvm/Transforms/Utils/Local.h" 36#include "llvm/Support/Debug.h" 37#include "llvm/Support/ErrorHandling.h" 38#include "llvm/Support/GetElementPtrTypeIterator.h" 39#include "llvm/Support/IRBuilder.h" 40#include "llvm/Support/MathExtras.h" 41#include "llvm/Support/raw_ostream.h" 42#include "llvm/ADT/SmallVector.h" 43#include "llvm/ADT/Statistic.h" 44using namespace llvm; 45 46STATISTIC(NumReplaced, "Number of allocas broken up"); 47STATISTIC(NumPromoted, "Number of allocas promoted"); 48STATISTIC(NumConverted, "Number of aggregates converted to scalar"); 49STATISTIC(NumGlobals, "Number of allocas copied from constant global"); 50 51namespace { 52 struct SROA : public FunctionPass { 53 static char ID; // Pass identification, replacement for typeid 54 explicit SROA(signed T = -1) : FunctionPass(ID) { 55 if (T == -1) 56 SRThreshold = 128; 57 else 58 SRThreshold = T; 59 } 60 61 bool runOnFunction(Function &F); 62 63 bool performScalarRepl(Function &F); 64 bool performPromotion(Function &F); 65 66 // getAnalysisUsage - This pass does not require any passes, but we know it 67 // will not alter the CFG, so say so. 68 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 69 AU.addRequired<DominatorTree>(); 70 AU.addRequired<DominanceFrontier>(); 71 AU.setPreservesCFG(); 72 } 73 74 private: 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 /// isUnsafe - This is set to true if the alloca cannot be SROA'd. 86 bool isUnsafe : 1; 87 88 /// isMemCpySrc - This is true if this aggregate is memcpy'd from. 89 bool isMemCpySrc : 1; 90 91 /// isMemCpyDst - This is true if this aggregate is memcpy'd into. 92 bool isMemCpyDst : 1; 93 94 AllocaInfo() 95 : isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false) {} 96 }; 97 98 unsigned SRThreshold; 99 100 void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; } 101 102 bool isSafeAllocaToScalarRepl(AllocaInst *AI); 103 104 void isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 105 AllocaInfo &Info); 106 void isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t &Offset, 107 AllocaInfo &Info); 108 void isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize, 109 const Type *MemOpType, bool isStore, AllocaInfo &Info); 110 bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size); 111 uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset, 112 const Type *&IdxTy); 113 114 void DoScalarReplacement(AllocaInst *AI, 115 std::vector<AllocaInst*> &WorkList); 116 void DeleteDeadInstructions(); 117 AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocaInst *Base); 118 119 void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 120 SmallVector<AllocaInst*, 32> &NewElts); 121 void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 122 SmallVector<AllocaInst*, 32> &NewElts); 123 void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 124 SmallVector<AllocaInst*, 32> &NewElts); 125 void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 126 AllocaInst *AI, 127 SmallVector<AllocaInst*, 32> &NewElts); 128 void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 129 SmallVector<AllocaInst*, 32> &NewElts); 130 void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 131 SmallVector<AllocaInst*, 32> &NewElts); 132 133 static MemTransferInst *isOnlyCopiedFromConstantGlobal(AllocaInst *AI); 134 }; 135} 136 137char SROA::ID = 0; 138INITIALIZE_PASS(SROA, "scalarrepl", 139 "Scalar Replacement of Aggregates", false, false); 140 141// Public interface to the ScalarReplAggregates pass 142FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) { 143 return new SROA(Threshold); 144} 145 146 147//===----------------------------------------------------------------------===// 148// Convert To Scalar Optimization. 149//===----------------------------------------------------------------------===// 150 151namespace { 152/// ConvertToScalarInfo - This class implements the "Convert To Scalar" 153/// optimization, which scans the uses of an alloca and determines if it can 154/// rewrite it in terms of a single new alloca that can be mem2reg'd. 155class ConvertToScalarInfo { 156 /// AllocaSize - The size of the alloca being considered. 157 unsigned AllocaSize; 158 const TargetData &TD; 159 160 /// IsNotTrivial - This is set to true if there is some access to the object 161 /// which means that mem2reg can't promote it. 162 bool IsNotTrivial; 163 164 /// VectorTy - This tracks the type that we should promote the vector to if 165 /// it is possible to turn it into a vector. This starts out null, and if it 166 /// isn't possible to turn into a vector type, it gets set to VoidTy. 167 const Type *VectorTy; 168 169 /// HadAVector - True if there is at least one vector access to the alloca. 170 /// We don't want to turn random arrays into vectors and use vector element 171 /// insert/extract, but if there are element accesses to something that is 172 /// also declared as a vector, we do want to promote to a vector. 173 bool HadAVector; 174 175public: 176 explicit ConvertToScalarInfo(unsigned Size, const TargetData &td) 177 : AllocaSize(Size), TD(td) { 178 IsNotTrivial = false; 179 VectorTy = 0; 180 HadAVector = false; 181 } 182 183 AllocaInst *TryConvert(AllocaInst *AI); 184 185private: 186 bool CanConvertToScalar(Value *V, uint64_t Offset); 187 void MergeInType(const Type *In, uint64_t Offset); 188 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset); 189 190 Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType, 191 uint64_t Offset, IRBuilder<> &Builder); 192 Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal, 193 uint64_t Offset, IRBuilder<> &Builder); 194}; 195} // end anonymous namespace. 196 197/// TryConvert - Analyze the specified alloca, and if it is safe to do so, 198/// rewrite it to be a new alloca which is mem2reg'able. This returns the new 199/// alloca if possible or null if not. 200AllocaInst *ConvertToScalarInfo::TryConvert(AllocaInst *AI) { 201 // If we can't convert this scalar, or if mem2reg can trivially do it, bail 202 // out. 203 if (!CanConvertToScalar(AI, 0) || !IsNotTrivial) 204 return 0; 205 206 // If we were able to find a vector type that can handle this with 207 // insert/extract elements, and if there was at least one use that had 208 // a vector type, promote this to a vector. We don't want to promote 209 // random stuff that doesn't use vectors (e.g. <9 x double>) because then 210 // we just get a lot of insert/extracts. If at least one vector is 211 // involved, then we probably really do have a union of vector/array. 212 const Type *NewTy; 213 if (VectorTy && VectorTy->isVectorTy() && HadAVector) { 214 DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = " 215 << *VectorTy << '\n'); 216 NewTy = VectorTy; // Use the vector type. 217 } else { 218 DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n"); 219 // Create and insert the integer alloca. 220 NewTy = IntegerType::get(AI->getContext(), AllocaSize*8); 221 } 222 AllocaInst *NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin()); 223 ConvertUsesToScalar(AI, NewAI, 0); 224 return NewAI; 225} 226 227/// MergeInType - Add the 'In' type to the accumulated vector type (VectorTy) 228/// so far at the offset specified by Offset (which is specified in bytes). 229/// 230/// There are two cases we handle here: 231/// 1) A union of vector types of the same size and potentially its elements. 232/// Here we turn element accesses into insert/extract element operations. 233/// This promotes a <4 x float> with a store of float to the third element 234/// into a <4 x float> that uses insert element. 235/// 2) A fully general blob of memory, which we turn into some (potentially 236/// large) integer type with extract and insert operations where the loads 237/// and stores would mutate the memory. We mark this by setting VectorTy 238/// to VoidTy. 239void ConvertToScalarInfo::MergeInType(const Type *In, uint64_t Offset) { 240 // If we already decided to turn this into a blob of integer memory, there is 241 // nothing to be done. 242 if (VectorTy && VectorTy->isVoidTy()) 243 return; 244 245 // If this could be contributing to a vector, analyze it. 246 247 // If the In type is a vector that is the same size as the alloca, see if it 248 // matches the existing VecTy. 249 if (const VectorType *VInTy = dyn_cast<VectorType>(In)) { 250 // Remember if we saw a vector type. 251 HadAVector = true; 252 253 if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) { 254 // If we're storing/loading a vector of the right size, allow it as a 255 // vector. If this the first vector we see, remember the type so that 256 // we know the element size. If this is a subsequent access, ignore it 257 // even if it is a differing type but the same size. Worst case we can 258 // bitcast the resultant vectors. 259 if (VectorTy == 0) 260 VectorTy = VInTy; 261 return; 262 } 263 } else if (In->isFloatTy() || In->isDoubleTy() || 264 (In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 && 265 isPowerOf2_32(In->getPrimitiveSizeInBits()))) { 266 // If we're accessing something that could be an element of a vector, see 267 // if the implied vector agrees with what we already have and if Offset is 268 // compatible with it. 269 unsigned EltSize = In->getPrimitiveSizeInBits()/8; 270 if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 && 271 (VectorTy == 0 || 272 cast<VectorType>(VectorTy)->getElementType() 273 ->getPrimitiveSizeInBits()/8 == EltSize)) { 274 if (VectorTy == 0) 275 VectorTy = VectorType::get(In, AllocaSize/EltSize); 276 return; 277 } 278 } 279 280 // Otherwise, we have a case that we can't handle with an optimized vector 281 // form. We can still turn this into a large integer. 282 VectorTy = Type::getVoidTy(In->getContext()); 283} 284 285/// CanConvertToScalar - V is a pointer. If we can convert the pointee and all 286/// its accesses to a single vector type, return true and set VecTy to 287/// the new type. If we could convert the alloca into a single promotable 288/// integer, return true but set VecTy to VoidTy. Further, if the use is not a 289/// completely trivial use that mem2reg could promote, set IsNotTrivial. Offset 290/// is the current offset from the base of the alloca being analyzed. 291/// 292/// If we see at least one access to the value that is as a vector type, set the 293/// SawVec flag. 294bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset) { 295 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 296 Instruction *User = cast<Instruction>(*UI); 297 298 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 299 // Don't break volatile loads. 300 if (LI->isVolatile()) 301 return false; 302 MergeInType(LI->getType(), Offset); 303 continue; 304 } 305 306 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 307 // Storing the pointer, not into the value? 308 if (SI->getOperand(0) == V || SI->isVolatile()) return false; 309 MergeInType(SI->getOperand(0)->getType(), Offset); 310 continue; 311 } 312 313 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { 314 IsNotTrivial = true; // Can't be mem2reg'd. 315 if (!CanConvertToScalar(BCI, Offset)) 316 return false; 317 continue; 318 } 319 320 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 321 // If this is a GEP with a variable indices, we can't handle it. 322 if (!GEP->hasAllConstantIndices()) 323 return false; 324 325 // Compute the offset that this GEP adds to the pointer. 326 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 327 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 328 &Indices[0], Indices.size()); 329 // See if all uses can be converted. 330 if (!CanConvertToScalar(GEP, Offset+GEPOffset)) 331 return false; 332 IsNotTrivial = true; // Can't be mem2reg'd. 333 continue; 334 } 335 336 // If this is a constant sized memset of a constant value (e.g. 0) we can 337 // handle it. 338 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 339 // Store of constant value and constant size. 340 if (!isa<ConstantInt>(MSI->getValue()) || 341 !isa<ConstantInt>(MSI->getLength())) 342 return false; 343 IsNotTrivial = true; // Can't be mem2reg'd. 344 continue; 345 } 346 347 // If this is a memcpy or memmove into or out of the whole allocation, we 348 // can handle it like a load or store of the scalar type. 349 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 350 ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()); 351 if (Len == 0 || Len->getZExtValue() != AllocaSize || Offset != 0) 352 return false; 353 354 IsNotTrivial = true; // Can't be mem2reg'd. 355 continue; 356 } 357 358 // Otherwise, we cannot handle this! 359 return false; 360 } 361 362 return true; 363} 364 365/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca 366/// directly. This happens when we are converting an "integer union" to a 367/// single integer scalar, or when we are converting a "vector union" to a 368/// vector with insert/extractelement instructions. 369/// 370/// Offset is an offset from the original alloca, in bits that need to be 371/// shifted to the right. By the end of this, there should be no uses of Ptr. 372void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, 373 uint64_t Offset) { 374 while (!Ptr->use_empty()) { 375 Instruction *User = cast<Instruction>(Ptr->use_back()); 376 377 if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 378 ConvertUsesToScalar(CI, NewAI, Offset); 379 CI->eraseFromParent(); 380 continue; 381 } 382 383 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 384 // Compute the offset that this GEP adds to the pointer. 385 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 386 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 387 &Indices[0], Indices.size()); 388 ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8); 389 GEP->eraseFromParent(); 390 continue; 391 } 392 393 IRBuilder<> Builder(User->getParent(), User); 394 395 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 396 // The load is a bit extract from NewAI shifted right by Offset bits. 397 Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp"); 398 Value *NewLoadVal 399 = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder); 400 LI->replaceAllUsesWith(NewLoadVal); 401 LI->eraseFromParent(); 402 continue; 403 } 404 405 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 406 assert(SI->getOperand(0) != Ptr && "Consistency error!"); 407 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 408 Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset, 409 Builder); 410 Builder.CreateStore(New, NewAI); 411 SI->eraseFromParent(); 412 413 // If the load we just inserted is now dead, then the inserted store 414 // overwrote the entire thing. 415 if (Old->use_empty()) 416 Old->eraseFromParent(); 417 continue; 418 } 419 420 // If this is a constant sized memset of a constant value (e.g. 0) we can 421 // transform it into a store of the expanded constant value. 422 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 423 assert(MSI->getRawDest() == Ptr && "Consistency error!"); 424 unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue(); 425 if (NumBytes != 0) { 426 unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue(); 427 428 // Compute the value replicated the right number of times. 429 APInt APVal(NumBytes*8, Val); 430 431 // Splat the value if non-zero. 432 if (Val) 433 for (unsigned i = 1; i != NumBytes; ++i) 434 APVal |= APVal << 8; 435 436 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 437 Value *New = ConvertScalar_InsertValue( 438 ConstantInt::get(User->getContext(), APVal), 439 Old, Offset, Builder); 440 Builder.CreateStore(New, NewAI); 441 442 // If the load we just inserted is now dead, then the memset overwrote 443 // the entire thing. 444 if (Old->use_empty()) 445 Old->eraseFromParent(); 446 } 447 MSI->eraseFromParent(); 448 continue; 449 } 450 451 // If this is a memcpy or memmove into or out of the whole allocation, we 452 // can handle it like a load or store of the scalar type. 453 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 454 assert(Offset == 0 && "must be store to start of alloca"); 455 456 // If the source and destination are both to the same alloca, then this is 457 // a noop copy-to-self, just delete it. Otherwise, emit a load and store 458 // as appropriate. 459 AllocaInst *OrigAI = cast<AllocaInst>(Ptr->getUnderlyingObject(0)); 460 461 if (MTI->getSource()->getUnderlyingObject(0) != OrigAI) { 462 // Dest must be OrigAI, change this to be a load from the original 463 // pointer (bitcasted), then a store to our new alloca. 464 assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?"); 465 Value *SrcPtr = MTI->getSource(); 466 SrcPtr = Builder.CreateBitCast(SrcPtr, NewAI->getType()); 467 468 LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval"); 469 SrcVal->setAlignment(MTI->getAlignment()); 470 Builder.CreateStore(SrcVal, NewAI); 471 } else if (MTI->getDest()->getUnderlyingObject(0) != OrigAI) { 472 // Src must be OrigAI, change this to be a load from NewAI then a store 473 // through the original dest pointer (bitcasted). 474 assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?"); 475 LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval"); 476 477 Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), NewAI->getType()); 478 StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr); 479 NewStore->setAlignment(MTI->getAlignment()); 480 } else { 481 // Noop transfer. Src == Dst 482 } 483 484 MTI->eraseFromParent(); 485 continue; 486 } 487 488 llvm_unreachable("Unsupported operation!"); 489 } 490} 491 492/// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer 493/// or vector value FromVal, extracting the bits from the offset specified by 494/// Offset. This returns the value, which is of type ToType. 495/// 496/// This happens when we are converting an "integer union" to a single 497/// integer scalar, or when we are converting a "vector union" to a vector with 498/// insert/extractelement instructions. 499/// 500/// Offset is an offset from the original alloca, in bits that need to be 501/// shifted to the right. 502Value *ConvertToScalarInfo:: 503ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType, 504 uint64_t Offset, IRBuilder<> &Builder) { 505 // If the load is of the whole new alloca, no conversion is needed. 506 if (FromVal->getType() == ToType && Offset == 0) 507 return FromVal; 508 509 // If the result alloca is a vector type, this is either an element 510 // access or a bitcast to another vector type of the same size. 511 if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) { 512 if (ToType->isVectorTy()) 513 return Builder.CreateBitCast(FromVal, ToType, "tmp"); 514 515 // Otherwise it must be an element access. 516 unsigned Elt = 0; 517 if (Offset) { 518 unsigned EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 519 Elt = Offset/EltSize; 520 assert(EltSize*Elt == Offset && "Invalid modulus in validity checking"); 521 } 522 // Return the element extracted out of it. 523 Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get( 524 Type::getInt32Ty(FromVal->getContext()), Elt), "tmp"); 525 if (V->getType() != ToType) 526 V = Builder.CreateBitCast(V, ToType, "tmp"); 527 return V; 528 } 529 530 // If ToType is a first class aggregate, extract out each of the pieces and 531 // use insertvalue's to form the FCA. 532 if (const StructType *ST = dyn_cast<StructType>(ToType)) { 533 const StructLayout &Layout = *TD.getStructLayout(ST); 534 Value *Res = UndefValue::get(ST); 535 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 536 Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i), 537 Offset+Layout.getElementOffsetInBits(i), 538 Builder); 539 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 540 } 541 return Res; 542 } 543 544 if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) { 545 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 546 Value *Res = UndefValue::get(AT); 547 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 548 Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(), 549 Offset+i*EltSize, Builder); 550 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 551 } 552 return Res; 553 } 554 555 // Otherwise, this must be a union that was converted to an integer value. 556 const IntegerType *NTy = cast<IntegerType>(FromVal->getType()); 557 558 // If this is a big-endian system and the load is narrower than the 559 // full alloca type, we need to do a shift to get the right bits. 560 int ShAmt = 0; 561 if (TD.isBigEndian()) { 562 // On big-endian machines, the lowest bit is stored at the bit offset 563 // from the pointer given by getTypeStoreSizeInBits. This matters for 564 // integers with a bitwidth that is not a multiple of 8. 565 ShAmt = TD.getTypeStoreSizeInBits(NTy) - 566 TD.getTypeStoreSizeInBits(ToType) - Offset; 567 } else { 568 ShAmt = Offset; 569 } 570 571 // Note: we support negative bitwidths (with shl) which are not defined. 572 // We do this to support (f.e.) loads off the end of a structure where 573 // only some bits are used. 574 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth()) 575 FromVal = Builder.CreateLShr(FromVal, 576 ConstantInt::get(FromVal->getType(), 577 ShAmt), "tmp"); 578 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) 579 FromVal = Builder.CreateShl(FromVal, 580 ConstantInt::get(FromVal->getType(), 581 -ShAmt), "tmp"); 582 583 // Finally, unconditionally truncate the integer to the right width. 584 unsigned LIBitWidth = TD.getTypeSizeInBits(ToType); 585 if (LIBitWidth < NTy->getBitWidth()) 586 FromVal = 587 Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(), 588 LIBitWidth), "tmp"); 589 else if (LIBitWidth > NTy->getBitWidth()) 590 FromVal = 591 Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(), 592 LIBitWidth), "tmp"); 593 594 // If the result is an integer, this is a trunc or bitcast. 595 if (ToType->isIntegerTy()) { 596 // Should be done. 597 } else if (ToType->isFloatingPointTy() || ToType->isVectorTy()) { 598 // Just do a bitcast, we know the sizes match up. 599 FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp"); 600 } else { 601 // Otherwise must be a pointer. 602 FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp"); 603 } 604 assert(FromVal->getType() == ToType && "Didn't convert right?"); 605 return FromVal; 606} 607 608/// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer 609/// or vector value "Old" at the offset specified by Offset. 610/// 611/// This happens when we are converting an "integer union" to a 612/// single integer scalar, or when we are converting a "vector union" to a 613/// vector with insert/extractelement instructions. 614/// 615/// Offset is an offset from the original alloca, in bits that need to be 616/// shifted to the right. 617Value *ConvertToScalarInfo:: 618ConvertScalar_InsertValue(Value *SV, Value *Old, 619 uint64_t Offset, IRBuilder<> &Builder) { 620 // Convert the stored type to the actual type, shift it left to insert 621 // then 'or' into place. 622 const Type *AllocaType = Old->getType(); 623 LLVMContext &Context = Old->getContext(); 624 625 if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) { 626 uint64_t VecSize = TD.getTypeAllocSizeInBits(VTy); 627 uint64_t ValSize = TD.getTypeAllocSizeInBits(SV->getType()); 628 629 // Changing the whole vector with memset or with an access of a different 630 // vector type? 631 if (ValSize == VecSize) 632 return Builder.CreateBitCast(SV, AllocaType, "tmp"); 633 634 uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 635 636 // Must be an element insertion. 637 unsigned Elt = Offset/EltSize; 638 639 if (SV->getType() != VTy->getElementType()) 640 SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp"); 641 642 SV = Builder.CreateInsertElement(Old, SV, 643 ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt), 644 "tmp"); 645 return SV; 646 } 647 648 // If SV is a first-class aggregate value, insert each value recursively. 649 if (const StructType *ST = dyn_cast<StructType>(SV->getType())) { 650 const StructLayout &Layout = *TD.getStructLayout(ST); 651 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 652 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 653 Old = ConvertScalar_InsertValue(Elt, Old, 654 Offset+Layout.getElementOffsetInBits(i), 655 Builder); 656 } 657 return Old; 658 } 659 660 if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) { 661 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 662 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 663 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 664 Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder); 665 } 666 return Old; 667 } 668 669 // If SV is a float, convert it to the appropriate integer type. 670 // If it is a pointer, do the same. 671 unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType()); 672 unsigned DestWidth = TD.getTypeSizeInBits(AllocaType); 673 unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType()); 674 unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType); 675 if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy()) 676 SV = Builder.CreateBitCast(SV, 677 IntegerType::get(SV->getContext(),SrcWidth), "tmp"); 678 else if (SV->getType()->isPointerTy()) 679 SV = Builder.CreatePtrToInt(SV, TD.getIntPtrType(SV->getContext()), "tmp"); 680 681 // Zero extend or truncate the value if needed. 682 if (SV->getType() != AllocaType) { 683 if (SV->getType()->getPrimitiveSizeInBits() < 684 AllocaType->getPrimitiveSizeInBits()) 685 SV = Builder.CreateZExt(SV, AllocaType, "tmp"); 686 else { 687 // Truncation may be needed if storing more than the alloca can hold 688 // (undefined behavior). 689 SV = Builder.CreateTrunc(SV, AllocaType, "tmp"); 690 SrcWidth = DestWidth; 691 SrcStoreWidth = DestStoreWidth; 692 } 693 } 694 695 // If this is a big-endian system and the store is narrower than the 696 // full alloca type, we need to do a shift to get the right bits. 697 int ShAmt = 0; 698 if (TD.isBigEndian()) { 699 // On big-endian machines, the lowest bit is stored at the bit offset 700 // from the pointer given by getTypeStoreSizeInBits. This matters for 701 // integers with a bitwidth that is not a multiple of 8. 702 ShAmt = DestStoreWidth - SrcStoreWidth - Offset; 703 } else { 704 ShAmt = Offset; 705 } 706 707 // Note: we support negative bitwidths (with shr) which are not defined. 708 // We do this to support (f.e.) stores off the end of a structure where 709 // only some bits in the structure are set. 710 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth)); 711 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) { 712 SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(), 713 ShAmt), "tmp"); 714 Mask <<= ShAmt; 715 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { 716 SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(), 717 -ShAmt), "tmp"); 718 Mask = Mask.lshr(-ShAmt); 719 } 720 721 // Mask out the bits we are about to insert from the old value, and or 722 // in the new bits. 723 if (SrcWidth != DestWidth) { 724 assert(DestWidth > SrcWidth); 725 Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask"); 726 SV = Builder.CreateOr(Old, SV, "ins"); 727 } 728 return SV; 729} 730 731 732//===----------------------------------------------------------------------===// 733// SRoA Driver 734//===----------------------------------------------------------------------===// 735 736 737bool SROA::runOnFunction(Function &F) { 738 TD = getAnalysisIfAvailable<TargetData>(); 739 740 bool Changed = performPromotion(F); 741 742 // FIXME: ScalarRepl currently depends on TargetData more than it 743 // theoretically needs to. It should be refactored in order to support 744 // target-independent IR. Until this is done, just skip the actual 745 // scalar-replacement portion of this pass. 746 if (!TD) return Changed; 747 748 while (1) { 749 bool LocalChange = performScalarRepl(F); 750 if (!LocalChange) break; // No need to repromote if no scalarrepl 751 Changed = true; 752 LocalChange = performPromotion(F); 753 if (!LocalChange) break; // No need to re-scalarrepl if no promotion 754 } 755 756 return Changed; 757} 758 759 760bool SROA::performPromotion(Function &F) { 761 std::vector<AllocaInst*> Allocas; 762 DominatorTree &DT = getAnalysis<DominatorTree>(); 763 DominanceFrontier &DF = getAnalysis<DominanceFrontier>(); 764 765 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function 766 767 bool Changed = false; 768 769 while (1) { 770 Allocas.clear(); 771 772 // Find allocas that are safe to promote, by looking at all instructions in 773 // the entry node 774 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) 775 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? 776 if (isAllocaPromotable(AI)) 777 Allocas.push_back(AI); 778 779 if (Allocas.empty()) break; 780 781 PromoteMemToReg(Allocas, DT, DF); 782 NumPromoted += Allocas.size(); 783 Changed = true; 784 } 785 786 return Changed; 787} 788 789 790/// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for 791/// SROA. It must be a struct or array type with a small number of elements. 792static bool ShouldAttemptScalarRepl(AllocaInst *AI) { 793 const Type *T = AI->getAllocatedType(); 794 // Do not promote any struct into more than 32 separate vars. 795 if (const StructType *ST = dyn_cast<StructType>(T)) 796 return ST->getNumElements() <= 32; 797 // Arrays are much less likely to be safe for SROA; only consider 798 // them if they are very small. 799 if (const ArrayType *AT = dyn_cast<ArrayType>(T)) 800 return AT->getNumElements() <= 8; 801 return false; 802} 803 804 805// performScalarRepl - This algorithm is a simple worklist driven algorithm, 806// which runs on all of the malloc/alloca instructions in the function, removing 807// them if they are only used by getelementptr instructions. 808// 809bool SROA::performScalarRepl(Function &F) { 810 std::vector<AllocaInst*> WorkList; 811 812 // Scan the entry basic block, adding allocas to the worklist. 813 BasicBlock &BB = F.getEntryBlock(); 814 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) 815 if (AllocaInst *A = dyn_cast<AllocaInst>(I)) 816 WorkList.push_back(A); 817 818 // Process the worklist 819 bool Changed = false; 820 while (!WorkList.empty()) { 821 AllocaInst *AI = WorkList.back(); 822 WorkList.pop_back(); 823 824 // Handle dead allocas trivially. These can be formed by SROA'ing arrays 825 // with unused elements. 826 if (AI->use_empty()) { 827 AI->eraseFromParent(); 828 Changed = true; 829 continue; 830 } 831 832 // If this alloca is impossible for us to promote, reject it early. 833 if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized()) 834 continue; 835 836 // Check to see if this allocation is only modified by a memcpy/memmove from 837 // a constant global. If this is the case, we can change all users to use 838 // the constant global instead. This is commonly produced by the CFE by 839 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A' 840 // is only subsequently read. 841 if (MemTransferInst *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) { 842 DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n'); 843 DEBUG(dbgs() << " memcpy = " << *TheCopy << '\n'); 844 Constant *TheSrc = cast<Constant>(TheCopy->getSource()); 845 AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType())); 846 TheCopy->eraseFromParent(); // Don't mutate the global. 847 AI->eraseFromParent(); 848 ++NumGlobals; 849 Changed = true; 850 continue; 851 } 852 853 // Check to see if we can perform the core SROA transformation. We cannot 854 // transform the allocation instruction if it is an array allocation 855 // (allocations OF arrays are ok though), and an allocation of a scalar 856 // value cannot be decomposed at all. 857 uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType()); 858 859 // Do not promote [0 x %struct]. 860 if (AllocaSize == 0) continue; 861 862 // Do not promote any struct whose size is too big. 863 if (AllocaSize > SRThreshold) continue; 864 865 // If the alloca looks like a good candidate for scalar replacement, and if 866 // all its users can be transformed, then split up the aggregate into its 867 // separate elements. 868 if (ShouldAttemptScalarRepl(AI) && isSafeAllocaToScalarRepl(AI)) { 869 DoScalarReplacement(AI, WorkList); 870 Changed = true; 871 continue; 872 } 873 874 // If we can turn this aggregate value (potentially with casts) into a 875 // simple scalar value that can be mem2reg'd into a register value. 876 // IsNotTrivial tracks whether this is something that mem2reg could have 877 // promoted itself. If so, we don't want to transform it needlessly. Note 878 // that we can't just check based on the type: the alloca may be of an i32 879 // but that has pointer arithmetic to set byte 3 of it or something. 880 if (AllocaInst *NewAI = 881 ConvertToScalarInfo((unsigned)AllocaSize, *TD).TryConvert(AI)) { 882 NewAI->takeName(AI); 883 AI->eraseFromParent(); 884 ++NumConverted; 885 Changed = true; 886 continue; 887 } 888 889 // Otherwise, couldn't process this alloca. 890 } 891 892 return Changed; 893} 894 895/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl 896/// predicate, do SROA now. 897void SROA::DoScalarReplacement(AllocaInst *AI, 898 std::vector<AllocaInst*> &WorkList) { 899 DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n'); 900 SmallVector<AllocaInst*, 32> ElementAllocas; 901 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 902 ElementAllocas.reserve(ST->getNumContainedTypes()); 903 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { 904 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 905 AI->getAlignment(), 906 AI->getName() + "." + Twine(i), AI); 907 ElementAllocas.push_back(NA); 908 WorkList.push_back(NA); // Add to worklist for recursive processing 909 } 910 } else { 911 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); 912 ElementAllocas.reserve(AT->getNumElements()); 913 const Type *ElTy = AT->getElementType(); 914 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 915 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(), 916 AI->getName() + "." + Twine(i), AI); 917 ElementAllocas.push_back(NA); 918 WorkList.push_back(NA); // Add to worklist for recursive processing 919 } 920 } 921 922 // Now that we have created the new alloca instructions, rewrite all the 923 // uses of the old alloca. 924 RewriteForScalarRepl(AI, AI, 0, ElementAllocas); 925 926 // Now erase any instructions that were made dead while rewriting the alloca. 927 DeleteDeadInstructions(); 928 AI->eraseFromParent(); 929 930 ++NumReplaced; 931} 932 933/// DeleteDeadInstructions - Erase instructions on the DeadInstrs list, 934/// recursively including all their operands that become trivially dead. 935void SROA::DeleteDeadInstructions() { 936 while (!DeadInsts.empty()) { 937 Instruction *I = cast<Instruction>(DeadInsts.pop_back_val()); 938 939 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) 940 if (Instruction *U = dyn_cast<Instruction>(*OI)) { 941 // Zero out the operand and see if it becomes trivially dead. 942 // (But, don't add allocas to the dead instruction list -- they are 943 // already on the worklist and will be deleted separately.) 944 *OI = 0; 945 if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U)) 946 DeadInsts.push_back(U); 947 } 948 949 I->eraseFromParent(); 950 } 951} 952 953/// isSafeForScalarRepl - Check if instruction I is a safe use with regard to 954/// performing scalar replacement of alloca AI. The results are flagged in 955/// the Info parameter. Offset indicates the position within AI that is 956/// referenced by this instruction. 957void SROA::isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 958 AllocaInfo &Info) { 959 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 960 Instruction *User = cast<Instruction>(*UI); 961 962 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 963 isSafeForScalarRepl(BC, AI, Offset, Info); 964 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 965 uint64_t GEPOffset = Offset; 966 isSafeGEP(GEPI, AI, GEPOffset, Info); 967 if (!Info.isUnsafe) 968 isSafeForScalarRepl(GEPI, AI, GEPOffset, Info); 969 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 970 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 971 if (Length) 972 isSafeMemAccess(AI, Offset, Length->getZExtValue(), 0, 973 UI.getOperandNo() == 0, Info); 974 else 975 MarkUnsafe(Info); 976 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 977 if (!LI->isVolatile()) { 978 const Type *LIType = LI->getType(); 979 isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(LIType), 980 LIType, false, Info); 981 } else 982 MarkUnsafe(Info); 983 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 984 // Store is ok if storing INTO the pointer, not storing the pointer 985 if (!SI->isVolatile() && SI->getOperand(0) != I) { 986 const Type *SIType = SI->getOperand(0)->getType(); 987 isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(SIType), 988 SIType, true, Info); 989 } else 990 MarkUnsafe(Info); 991 } else { 992 DEBUG(errs() << " Transformation preventing inst: " << *User << '\n'); 993 MarkUnsafe(Info); 994 } 995 if (Info.isUnsafe) return; 996 } 997} 998 999/// isSafeGEP - Check if a GEP instruction can be handled for scalar 1000/// replacement. It is safe when all the indices are constant, in-bounds 1001/// references, and when the resulting offset corresponds to an element within 1002/// the alloca type. The results are flagged in the Info parameter. Upon 1003/// return, Offset is adjusted as specified by the GEP indices. 1004void SROA::isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI, 1005 uint64_t &Offset, AllocaInfo &Info) { 1006 gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI); 1007 if (GEPIt == E) 1008 return; 1009 1010 // Walk through the GEP type indices, checking the types that this indexes 1011 // into. 1012 for (; GEPIt != E; ++GEPIt) { 1013 // Ignore struct elements, no extra checking needed for these. 1014 if ((*GEPIt)->isStructTy()) 1015 continue; 1016 1017 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand()); 1018 if (!IdxVal) 1019 return MarkUnsafe(Info); 1020 } 1021 1022 // Compute the offset due to this GEP and check if the alloca has a 1023 // component element at that offset. 1024 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 1025 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 1026 &Indices[0], Indices.size()); 1027 if (!TypeHasComponent(AI->getAllocatedType(), Offset, 0)) 1028 MarkUnsafe(Info); 1029} 1030 1031/// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI 1032/// alloca or has an offset and size that corresponds to a component element 1033/// within it. The offset checked here may have been formed from a GEP with a 1034/// pointer bitcasted to a different type. 1035void SROA::isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize, 1036 const Type *MemOpType, bool isStore, 1037 AllocaInfo &Info) { 1038 // Check if this is a load/store of the entire alloca. 1039 if (Offset == 0 && MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) { 1040 bool UsesAggregateType = (MemOpType == AI->getAllocatedType()); 1041 // This is safe for MemIntrinsics (where MemOpType is 0), integer types 1042 // (which are essentially the same as the MemIntrinsics, especially with 1043 // regard to copying padding between elements), or references using the 1044 // aggregate type of the alloca. 1045 if (!MemOpType || MemOpType->isIntegerTy() || UsesAggregateType) { 1046 if (!UsesAggregateType) { 1047 if (isStore) 1048 Info.isMemCpyDst = true; 1049 else 1050 Info.isMemCpySrc = true; 1051 } 1052 return; 1053 } 1054 } 1055 // Check if the offset/size correspond to a component within the alloca type. 1056 const Type *T = AI->getAllocatedType(); 1057 if (TypeHasComponent(T, Offset, MemSize)) 1058 return; 1059 1060 return MarkUnsafe(Info); 1061} 1062 1063/// TypeHasComponent - Return true if T has a component type with the 1064/// specified offset and size. If Size is zero, do not check the size. 1065bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) { 1066 const Type *EltTy; 1067 uint64_t EltSize; 1068 if (const StructType *ST = dyn_cast<StructType>(T)) { 1069 const StructLayout *Layout = TD->getStructLayout(ST); 1070 unsigned EltIdx = Layout->getElementContainingOffset(Offset); 1071 EltTy = ST->getContainedType(EltIdx); 1072 EltSize = TD->getTypeAllocSize(EltTy); 1073 Offset -= Layout->getElementOffset(EltIdx); 1074 } else if (const ArrayType *AT = dyn_cast<ArrayType>(T)) { 1075 EltTy = AT->getElementType(); 1076 EltSize = TD->getTypeAllocSize(EltTy); 1077 if (Offset >= AT->getNumElements() * EltSize) 1078 return false; 1079 Offset %= EltSize; 1080 } else { 1081 return false; 1082 } 1083 if (Offset == 0 && (Size == 0 || EltSize == Size)) 1084 return true; 1085 // Check if the component spans multiple elements. 1086 if (Offset + Size > EltSize) 1087 return false; 1088 return TypeHasComponent(EltTy, Offset, Size); 1089} 1090 1091/// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite 1092/// the instruction I, which references it, to use the separate elements. 1093/// Offset indicates the position within AI that is referenced by this 1094/// instruction. 1095void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 1096 SmallVector<AllocaInst*, 32> &NewElts) { 1097 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 1098 Instruction *User = cast<Instruction>(*UI); 1099 1100 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1101 RewriteBitCast(BC, AI, Offset, NewElts); 1102 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1103 RewriteGEP(GEPI, AI, Offset, NewElts); 1104 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 1105 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 1106 uint64_t MemSize = Length->getZExtValue(); 1107 if (Offset == 0 && 1108 MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) 1109 RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts); 1110 // Otherwise the intrinsic can only touch a single element and the 1111 // address operand will be updated, so nothing else needs to be done. 1112 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1113 const Type *LIType = LI->getType(); 1114 if (LIType == AI->getAllocatedType()) { 1115 // Replace: 1116 // %res = load { i32, i32 }* %alloc 1117 // with: 1118 // %load.0 = load i32* %alloc.0 1119 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0 1120 // %load.1 = load i32* %alloc.1 1121 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1 1122 // (Also works for arrays instead of structs) 1123 Value *Insert = UndefValue::get(LIType); 1124 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1125 Value *Load = new LoadInst(NewElts[i], "load", LI); 1126 Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI); 1127 } 1128 LI->replaceAllUsesWith(Insert); 1129 DeadInsts.push_back(LI); 1130 } else if (LIType->isIntegerTy() && 1131 TD->getTypeAllocSize(LIType) == 1132 TD->getTypeAllocSize(AI->getAllocatedType())) { 1133 // If this is a load of the entire alloca to an integer, rewrite it. 1134 RewriteLoadUserOfWholeAlloca(LI, AI, NewElts); 1135 } 1136 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1137 Value *Val = SI->getOperand(0); 1138 const Type *SIType = Val->getType(); 1139 if (SIType == AI->getAllocatedType()) { 1140 // Replace: 1141 // store { i32, i32 } %val, { i32, i32 }* %alloc 1142 // with: 1143 // %val.0 = extractvalue { i32, i32 } %val, 0 1144 // store i32 %val.0, i32* %alloc.0 1145 // %val.1 = extractvalue { i32, i32 } %val, 1 1146 // store i32 %val.1, i32* %alloc.1 1147 // (Also works for arrays instead of structs) 1148 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1149 Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI); 1150 new StoreInst(Extract, NewElts[i], SI); 1151 } 1152 DeadInsts.push_back(SI); 1153 } else if (SIType->isIntegerTy() && 1154 TD->getTypeAllocSize(SIType) == 1155 TD->getTypeAllocSize(AI->getAllocatedType())) { 1156 // If this is a store of the entire alloca from an integer, rewrite it. 1157 RewriteStoreUserOfWholeAlloca(SI, AI, NewElts); 1158 } 1159 } 1160 } 1161} 1162 1163/// RewriteBitCast - Update a bitcast reference to the alloca being replaced 1164/// and recursively continue updating all of its uses. 1165void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 1166 SmallVector<AllocaInst*, 32> &NewElts) { 1167 RewriteForScalarRepl(BC, AI, Offset, NewElts); 1168 if (BC->getOperand(0) != AI) 1169 return; 1170 1171 // The bitcast references the original alloca. Replace its uses with 1172 // references to the first new element alloca. 1173 Instruction *Val = NewElts[0]; 1174 if (Val->getType() != BC->getDestTy()) { 1175 Val = new BitCastInst(Val, BC->getDestTy(), "", BC); 1176 Val->takeName(BC); 1177 } 1178 BC->replaceAllUsesWith(Val); 1179 DeadInsts.push_back(BC); 1180} 1181 1182/// FindElementAndOffset - Return the index of the element containing Offset 1183/// within the specified type, which must be either a struct or an array. 1184/// Sets T to the type of the element and Offset to the offset within that 1185/// element. IdxTy is set to the type of the index result to be used in a 1186/// GEP instruction. 1187uint64_t SROA::FindElementAndOffset(const Type *&T, uint64_t &Offset, 1188 const Type *&IdxTy) { 1189 uint64_t Idx = 0; 1190 if (const StructType *ST = dyn_cast<StructType>(T)) { 1191 const StructLayout *Layout = TD->getStructLayout(ST); 1192 Idx = Layout->getElementContainingOffset(Offset); 1193 T = ST->getContainedType(Idx); 1194 Offset -= Layout->getElementOffset(Idx); 1195 IdxTy = Type::getInt32Ty(T->getContext()); 1196 return Idx; 1197 } 1198 const ArrayType *AT = cast<ArrayType>(T); 1199 T = AT->getElementType(); 1200 uint64_t EltSize = TD->getTypeAllocSize(T); 1201 Idx = Offset / EltSize; 1202 Offset -= Idx * EltSize; 1203 IdxTy = Type::getInt64Ty(T->getContext()); 1204 return Idx; 1205} 1206 1207/// RewriteGEP - Check if this GEP instruction moves the pointer across 1208/// elements of the alloca that are being split apart, and if so, rewrite 1209/// the GEP to be relative to the new element. 1210void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 1211 SmallVector<AllocaInst*, 32> &NewElts) { 1212 uint64_t OldOffset = Offset; 1213 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 1214 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 1215 &Indices[0], Indices.size()); 1216 1217 RewriteForScalarRepl(GEPI, AI, Offset, NewElts); 1218 1219 const Type *T = AI->getAllocatedType(); 1220 const Type *IdxTy; 1221 uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy); 1222 if (GEPI->getOperand(0) == AI) 1223 OldIdx = ~0ULL; // Force the GEP to be rewritten. 1224 1225 T = AI->getAllocatedType(); 1226 uint64_t EltOffset = Offset; 1227 uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy); 1228 1229 // If this GEP does not move the pointer across elements of the alloca 1230 // being split, then it does not needs to be rewritten. 1231 if (Idx == OldIdx) 1232 return; 1233 1234 const Type *i32Ty = Type::getInt32Ty(AI->getContext()); 1235 SmallVector<Value*, 8> NewArgs; 1236 NewArgs.push_back(Constant::getNullValue(i32Ty)); 1237 while (EltOffset != 0) { 1238 uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy); 1239 NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx)); 1240 } 1241 Instruction *Val = NewElts[Idx]; 1242 if (NewArgs.size() > 1) { 1243 Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(), 1244 NewArgs.end(), "", GEPI); 1245 Val->takeName(GEPI); 1246 } 1247 if (Val->getType() != GEPI->getType()) 1248 Val = new BitCastInst(Val, GEPI->getType(), Val->getName(), GEPI); 1249 GEPI->replaceAllUsesWith(Val); 1250 DeadInsts.push_back(GEPI); 1251} 1252 1253/// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI. 1254/// Rewrite it to copy or set the elements of the scalarized memory. 1255void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 1256 AllocaInst *AI, 1257 SmallVector<AllocaInst*, 32> &NewElts) { 1258 // If this is a memcpy/memmove, construct the other pointer as the 1259 // appropriate type. The "Other" pointer is the pointer that goes to memory 1260 // that doesn't have anything to do with the alloca that we are promoting. For 1261 // memset, this Value* stays null. 1262 Value *OtherPtr = 0; 1263 unsigned MemAlignment = MI->getAlignment(); 1264 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy 1265 if (Inst == MTI->getRawDest()) 1266 OtherPtr = MTI->getRawSource(); 1267 else { 1268 assert(Inst == MTI->getRawSource()); 1269 OtherPtr = MTI->getRawDest(); 1270 } 1271 } 1272 1273 // If there is an other pointer, we want to convert it to the same pointer 1274 // type as AI has, so we can GEP through it safely. 1275 if (OtherPtr) { 1276 unsigned AddrSpace = 1277 cast<PointerType>(OtherPtr->getType())->getAddressSpace(); 1278 1279 // Remove bitcasts and all-zero GEPs from OtherPtr. This is an 1280 // optimization, but it's also required to detect the corner case where 1281 // both pointer operands are referencing the same memory, and where 1282 // OtherPtr may be a bitcast or GEP that currently being rewritten. (This 1283 // function is only called for mem intrinsics that access the whole 1284 // aggregate, so non-zero GEPs are not an issue here.) 1285 OtherPtr = OtherPtr->stripPointerCasts(); 1286 1287 // Copying the alloca to itself is a no-op: just delete it. 1288 if (OtherPtr == AI || OtherPtr == NewElts[0]) { 1289 // This code will run twice for a no-op memcpy -- once for each operand. 1290 // Put only one reference to MI on the DeadInsts list. 1291 for (SmallVector<Value*, 32>::const_iterator I = DeadInsts.begin(), 1292 E = DeadInsts.end(); I != E; ++I) 1293 if (*I == MI) return; 1294 DeadInsts.push_back(MI); 1295 return; 1296 } 1297 1298 // If the pointer is not the right type, insert a bitcast to the right 1299 // type. 1300 const Type *NewTy = 1301 PointerType::get(AI->getType()->getElementType(), AddrSpace); 1302 1303 if (OtherPtr->getType() != NewTy) 1304 OtherPtr = new BitCastInst(OtherPtr, NewTy, OtherPtr->getName(), MI); 1305 } 1306 1307 // Process each element of the aggregate. 1308 Value *TheFn = MI->getCalledValue(); 1309 const Type *BytePtrTy = MI->getRawDest()->getType(); 1310 bool SROADest = MI->getRawDest() == Inst; 1311 1312 Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext())); 1313 1314 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1315 // If this is a memcpy/memmove, emit a GEP of the other element address. 1316 Value *OtherElt = 0; 1317 unsigned OtherEltAlign = MemAlignment; 1318 1319 if (OtherPtr) { 1320 Value *Idx[2] = { Zero, 1321 ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) }; 1322 OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2, 1323 OtherPtr->getName()+"."+Twine(i), 1324 MI); 1325 uint64_t EltOffset; 1326 const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType()); 1327 const Type *OtherTy = OtherPtrTy->getElementType(); 1328 if (const StructType *ST = dyn_cast<StructType>(OtherTy)) { 1329 EltOffset = TD->getStructLayout(ST)->getElementOffset(i); 1330 } else { 1331 const Type *EltTy = cast<SequentialType>(OtherTy)->getElementType(); 1332 EltOffset = TD->getTypeAllocSize(EltTy)*i; 1333 } 1334 1335 // The alignment of the other pointer is the guaranteed alignment of the 1336 // element, which is affected by both the known alignment of the whole 1337 // mem intrinsic and the alignment of the element. If the alignment of 1338 // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the 1339 // known alignment is just 4 bytes. 1340 OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset); 1341 } 1342 1343 Value *EltPtr = NewElts[i]; 1344 const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType(); 1345 1346 // If we got down to a scalar, insert a load or store as appropriate. 1347 if (EltTy->isSingleValueType()) { 1348 if (isa<MemTransferInst>(MI)) { 1349 if (SROADest) { 1350 // From Other to Alloca. 1351 Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI); 1352 new StoreInst(Elt, EltPtr, MI); 1353 } else { 1354 // From Alloca to Other. 1355 Value *Elt = new LoadInst(EltPtr, "tmp", MI); 1356 new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI); 1357 } 1358 continue; 1359 } 1360 assert(isa<MemSetInst>(MI)); 1361 1362 // If the stored element is zero (common case), just store a null 1363 // constant. 1364 Constant *StoreVal; 1365 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getArgOperand(1))) { 1366 if (CI->isZero()) { 1367 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0> 1368 } else { 1369 // If EltTy is a vector type, get the element type. 1370 const Type *ValTy = EltTy->getScalarType(); 1371 1372 // Construct an integer with the right value. 1373 unsigned EltSize = TD->getTypeSizeInBits(ValTy); 1374 APInt OneVal(EltSize, CI->getZExtValue()); 1375 APInt TotalVal(OneVal); 1376 // Set each byte. 1377 for (unsigned i = 0; 8*i < EltSize; ++i) { 1378 TotalVal = TotalVal.shl(8); 1379 TotalVal |= OneVal; 1380 } 1381 1382 // Convert the integer value to the appropriate type. 1383 StoreVal = ConstantInt::get(CI->getContext(), TotalVal); 1384 if (ValTy->isPointerTy()) 1385 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); 1386 else if (ValTy->isFloatingPointTy()) 1387 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy); 1388 assert(StoreVal->getType() == ValTy && "Type mismatch!"); 1389 1390 // If the requested value was a vector constant, create it. 1391 if (EltTy != ValTy) { 1392 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements(); 1393 SmallVector<Constant*, 16> Elts(NumElts, StoreVal); 1394 StoreVal = ConstantVector::get(&Elts[0], NumElts); 1395 } 1396 } 1397 new StoreInst(StoreVal, EltPtr, MI); 1398 continue; 1399 } 1400 // Otherwise, if we're storing a byte variable, use a memset call for 1401 // this element. 1402 } 1403 1404 // Cast the element pointer to BytePtrTy. 1405 if (EltPtr->getType() != BytePtrTy) 1406 EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getName(), MI); 1407 1408 // Cast the other pointer (if we have one) to BytePtrTy. 1409 if (OtherElt && OtherElt->getType() != BytePtrTy) { 1410 // Preserve address space of OtherElt 1411 const PointerType* OtherPTy = cast<PointerType>(OtherElt->getType()); 1412 const PointerType* PTy = cast<PointerType>(BytePtrTy); 1413 if (OtherPTy->getElementType() != PTy->getElementType()) { 1414 Type *NewOtherPTy = PointerType::get(PTy->getElementType(), 1415 OtherPTy->getAddressSpace()); 1416 OtherElt = new BitCastInst(OtherElt, NewOtherPTy, 1417 OtherElt->getNameStr(), MI); 1418 } 1419 } 1420 1421 unsigned EltSize = TD->getTypeAllocSize(EltTy); 1422 1423 // Finally, insert the meminst for this element. 1424 if (isa<MemTransferInst>(MI)) { 1425 Value *Ops[] = { 1426 SROADest ? EltPtr : OtherElt, // Dest ptr 1427 SROADest ? OtherElt : EltPtr, // Src ptr 1428 ConstantInt::get(MI->getArgOperand(2)->getType(), EltSize), // Size 1429 // Align 1430 ConstantInt::get(Type::getInt32Ty(MI->getContext()), OtherEltAlign), 1431 MI->getVolatileCst() 1432 }; 1433 // In case we fold the address space overloaded memcpy of A to B 1434 // with memcpy of B to C, change the function to be a memcpy of A to C. 1435 const Type *Tys[] = { Ops[0]->getType(), Ops[1]->getType(), 1436 Ops[2]->getType() }; 1437 Module *M = MI->getParent()->getParent()->getParent(); 1438 TheFn = Intrinsic::getDeclaration(M, MI->getIntrinsicID(), Tys, 3); 1439 CallInst::Create(TheFn, Ops, Ops + 5, "", MI); 1440 } else { 1441 assert(isa<MemSetInst>(MI)); 1442 Value *Ops[] = { 1443 EltPtr, MI->getArgOperand(1), // Dest, Value, 1444 ConstantInt::get(MI->getArgOperand(2)->getType(), EltSize), // Size 1445 Zero, // Align 1446 ConstantInt::get(Type::getInt1Ty(MI->getContext()), 0) // isVolatile 1447 }; 1448 const Type *Tys[] = { Ops[0]->getType(), Ops[2]->getType() }; 1449 Module *M = MI->getParent()->getParent()->getParent(); 1450 TheFn = Intrinsic::getDeclaration(M, Intrinsic::memset, Tys, 2); 1451 CallInst::Create(TheFn, Ops, Ops + 5, "", MI); 1452 } 1453 } 1454 DeadInsts.push_back(MI); 1455} 1456 1457/// RewriteStoreUserOfWholeAlloca - We found a store of an integer that 1458/// overwrites the entire allocation. Extract out the pieces of the stored 1459/// integer and store them individually. 1460void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 1461 SmallVector<AllocaInst*, 32> &NewElts){ 1462 // Extract each element out of the integer according to its structure offset 1463 // and store the element value to the individual alloca. 1464 Value *SrcVal = SI->getOperand(0); 1465 const Type *AllocaEltTy = AI->getAllocatedType(); 1466 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 1467 1468 // Handle tail padding by extending the operand 1469 if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits) 1470 SrcVal = new ZExtInst(SrcVal, 1471 IntegerType::get(SI->getContext(), AllocaSizeBits), 1472 "", SI); 1473 1474 DEBUG(dbgs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI 1475 << '\n'); 1476 1477 // There are two forms here: AI could be an array or struct. Both cases 1478 // have different ways to compute the element offset. 1479 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 1480 const StructLayout *Layout = TD->getStructLayout(EltSTy); 1481 1482 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1483 // Get the number of bits to shift SrcVal to get the value. 1484 const Type *FieldTy = EltSTy->getElementType(i); 1485 uint64_t Shift = Layout->getElementOffsetInBits(i); 1486 1487 if (TD->isBigEndian()) 1488 Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy); 1489 1490 Value *EltVal = SrcVal; 1491 if (Shift) { 1492 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 1493 EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal, 1494 "sroa.store.elt", SI); 1495 } 1496 1497 // Truncate down to an integer of the right size. 1498 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 1499 1500 // Ignore zero sized fields like {}, they obviously contain no data. 1501 if (FieldSizeBits == 0) continue; 1502 1503 if (FieldSizeBits != AllocaSizeBits) 1504 EltVal = new TruncInst(EltVal, 1505 IntegerType::get(SI->getContext(), FieldSizeBits), 1506 "", SI); 1507 Value *DestField = NewElts[i]; 1508 if (EltVal->getType() == FieldTy) { 1509 // Storing to an integer field of this size, just do it. 1510 } else if (FieldTy->isFloatingPointTy() || FieldTy->isVectorTy()) { 1511 // Bitcast to the right element type (for fp/vector values). 1512 EltVal = new BitCastInst(EltVal, FieldTy, "", SI); 1513 } else { 1514 // Otherwise, bitcast the dest pointer (for aggregates). 1515 DestField = new BitCastInst(DestField, 1516 PointerType::getUnqual(EltVal->getType()), 1517 "", SI); 1518 } 1519 new StoreInst(EltVal, DestField, SI); 1520 } 1521 1522 } else { 1523 const ArrayType *ATy = cast<ArrayType>(AllocaEltTy); 1524 const Type *ArrayEltTy = ATy->getElementType(); 1525 uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 1526 uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy); 1527 1528 uint64_t Shift; 1529 1530 if (TD->isBigEndian()) 1531 Shift = AllocaSizeBits-ElementOffset; 1532 else 1533 Shift = 0; 1534 1535 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1536 // Ignore zero sized fields like {}, they obviously contain no data. 1537 if (ElementSizeBits == 0) continue; 1538 1539 Value *EltVal = SrcVal; 1540 if (Shift) { 1541 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 1542 EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal, 1543 "sroa.store.elt", SI); 1544 } 1545 1546 // Truncate down to an integer of the right size. 1547 if (ElementSizeBits != AllocaSizeBits) 1548 EltVal = new TruncInst(EltVal, 1549 IntegerType::get(SI->getContext(), 1550 ElementSizeBits),"",SI); 1551 Value *DestField = NewElts[i]; 1552 if (EltVal->getType() == ArrayEltTy) { 1553 // Storing to an integer field of this size, just do it. 1554 } else if (ArrayEltTy->isFloatingPointTy() || 1555 ArrayEltTy->isVectorTy()) { 1556 // Bitcast to the right element type (for fp/vector values). 1557 EltVal = new BitCastInst(EltVal, ArrayEltTy, "", SI); 1558 } else { 1559 // Otherwise, bitcast the dest pointer (for aggregates). 1560 DestField = new BitCastInst(DestField, 1561 PointerType::getUnqual(EltVal->getType()), 1562 "", SI); 1563 } 1564 new StoreInst(EltVal, DestField, SI); 1565 1566 if (TD->isBigEndian()) 1567 Shift -= ElementOffset; 1568 else 1569 Shift += ElementOffset; 1570 } 1571 } 1572 1573 DeadInsts.push_back(SI); 1574} 1575 1576/// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to 1577/// an integer. Load the individual pieces to form the aggregate value. 1578void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 1579 SmallVector<AllocaInst*, 32> &NewElts) { 1580 // Extract each element out of the NewElts according to its structure offset 1581 // and form the result value. 1582 const Type *AllocaEltTy = AI->getAllocatedType(); 1583 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 1584 1585 DEBUG(dbgs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI 1586 << '\n'); 1587 1588 // There are two forms here: AI could be an array or struct. Both cases 1589 // have different ways to compute the element offset. 1590 const StructLayout *Layout = 0; 1591 uint64_t ArrayEltBitOffset = 0; 1592 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 1593 Layout = TD->getStructLayout(EltSTy); 1594 } else { 1595 const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType(); 1596 ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 1597 } 1598 1599 Value *ResultVal = 1600 Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits)); 1601 1602 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1603 // Load the value from the alloca. If the NewElt is an aggregate, cast 1604 // the pointer to an integer of the same size before doing the load. 1605 Value *SrcField = NewElts[i]; 1606 const Type *FieldTy = 1607 cast<PointerType>(SrcField->getType())->getElementType(); 1608 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 1609 1610 // Ignore zero sized fields like {}, they obviously contain no data. 1611 if (FieldSizeBits == 0) continue; 1612 1613 const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(), 1614 FieldSizeBits); 1615 if (!FieldTy->isIntegerTy() && !FieldTy->isFloatingPointTy() && 1616 !FieldTy->isVectorTy()) 1617 SrcField = new BitCastInst(SrcField, 1618 PointerType::getUnqual(FieldIntTy), 1619 "", LI); 1620 SrcField = new LoadInst(SrcField, "sroa.load.elt", LI); 1621 1622 // If SrcField is a fp or vector of the right size but that isn't an 1623 // integer type, bitcast to an integer so we can shift it. 1624 if (SrcField->getType() != FieldIntTy) 1625 SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI); 1626 1627 // Zero extend the field to be the same size as the final alloca so that 1628 // we can shift and insert it. 1629 if (SrcField->getType() != ResultVal->getType()) 1630 SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI); 1631 1632 // Determine the number of bits to shift SrcField. 1633 uint64_t Shift; 1634 if (Layout) // Struct case. 1635 Shift = Layout->getElementOffsetInBits(i); 1636 else // Array case. 1637 Shift = i*ArrayEltBitOffset; 1638 1639 if (TD->isBigEndian()) 1640 Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth(); 1641 1642 if (Shift) { 1643 Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift); 1644 SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI); 1645 } 1646 1647 // Don't create an 'or x, 0' on the first iteration. 1648 if (!isa<Constant>(ResultVal) || 1649 !cast<Constant>(ResultVal)->isNullValue()) 1650 ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI); 1651 else 1652 ResultVal = SrcField; 1653 } 1654 1655 // Handle tail padding by truncating the result 1656 if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits) 1657 ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI); 1658 1659 LI->replaceAllUsesWith(ResultVal); 1660 DeadInsts.push_back(LI); 1661} 1662 1663/// HasPadding - Return true if the specified type has any structure or 1664/// alignment padding, false otherwise. 1665static bool HasPadding(const Type *Ty, const TargetData &TD) { 1666 if (const StructType *STy = dyn_cast<StructType>(Ty)) { 1667 const StructLayout *SL = TD.getStructLayout(STy); 1668 unsigned PrevFieldBitOffset = 0; 1669 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 1670 unsigned FieldBitOffset = SL->getElementOffsetInBits(i); 1671 1672 // Padding in sub-elements? 1673 if (HasPadding(STy->getElementType(i), TD)) 1674 return true; 1675 1676 // Check to see if there is any padding between this element and the 1677 // previous one. 1678 if (i) { 1679 unsigned PrevFieldEnd = 1680 PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1)); 1681 if (PrevFieldEnd < FieldBitOffset) 1682 return true; 1683 } 1684 1685 PrevFieldBitOffset = FieldBitOffset; 1686 } 1687 1688 // Check for tail padding. 1689 if (unsigned EltCount = STy->getNumElements()) { 1690 unsigned PrevFieldEnd = PrevFieldBitOffset + 1691 TD.getTypeSizeInBits(STy->getElementType(EltCount-1)); 1692 if (PrevFieldEnd < SL->getSizeInBits()) 1693 return true; 1694 } 1695 1696 } else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 1697 return HasPadding(ATy->getElementType(), TD); 1698 } else if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) { 1699 return HasPadding(VTy->getElementType(), TD); 1700 } 1701 return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty); 1702} 1703 1704/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of 1705/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, 1706/// or 1 if safe after canonicalization has been performed. 1707bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) { 1708 // Loop over the use list of the alloca. We can only transform it if all of 1709 // the users are safe to transform. 1710 AllocaInfo Info; 1711 1712 isSafeForScalarRepl(AI, AI, 0, Info); 1713 if (Info.isUnsafe) { 1714 DEBUG(dbgs() << "Cannot transform: " << *AI << '\n'); 1715 return false; 1716 } 1717 1718 // Okay, we know all the users are promotable. If the aggregate is a memcpy 1719 // source and destination, we have to be careful. In particular, the memcpy 1720 // could be moving around elements that live in structure padding of the LLVM 1721 // types, but may actually be used. In these cases, we refuse to promote the 1722 // struct. 1723 if (Info.isMemCpySrc && Info.isMemCpyDst && 1724 HasPadding(AI->getAllocatedType(), *TD)) 1725 return false; 1726 1727 return true; 1728} 1729 1730 1731 1732/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to 1733/// some part of a constant global variable. This intentionally only accepts 1734/// constant expressions because we don't can't rewrite arbitrary instructions. 1735static bool PointsToConstantGlobal(Value *V) { 1736 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) 1737 return GV->isConstant(); 1738 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 1739 if (CE->getOpcode() == Instruction::BitCast || 1740 CE->getOpcode() == Instruction::GetElementPtr) 1741 return PointsToConstantGlobal(CE->getOperand(0)); 1742 return false; 1743} 1744 1745/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived) 1746/// pointer to an alloca. Ignore any reads of the pointer, return false if we 1747/// see any stores or other unknown uses. If we see pointer arithmetic, keep 1748/// track of whether it moves the pointer (with isOffset) but otherwise traverse 1749/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to 1750/// the alloca, and if the source pointer is a pointer to a constant global, we 1751/// can optimize this. 1752static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy, 1753 bool isOffset) { 1754 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 1755 User *U = cast<Instruction>(*UI); 1756 1757 if (LoadInst *LI = dyn_cast<LoadInst>(U)) 1758 // Ignore non-volatile loads, they are always ok. 1759 if (!LI->isVolatile()) 1760 continue; 1761 1762 if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) { 1763 // If uses of the bitcast are ok, we are ok. 1764 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) 1765 return false; 1766 continue; 1767 } 1768 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 1769 // If the GEP has all zero indices, it doesn't offset the pointer. If it 1770 // doesn't, it does. 1771 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy, 1772 isOffset || !GEP->hasAllZeroIndices())) 1773 return false; 1774 continue; 1775 } 1776 1777 // If this is isn't our memcpy/memmove, reject it as something we can't 1778 // handle. 1779 MemTransferInst *MI = dyn_cast<MemTransferInst>(U); 1780 if (MI == 0) 1781 return false; 1782 1783 // If we already have seen a copy, reject the second one. 1784 if (TheCopy) return false; 1785 1786 // If the pointer has been offset from the start of the alloca, we can't 1787 // safely handle this. 1788 if (isOffset) return false; 1789 1790 // If the memintrinsic isn't using the alloca as the dest, reject it. 1791 if (UI.getOperandNo() != 0) return false; 1792 1793 // If the source of the memcpy/move is not a constant global, reject it. 1794 if (!PointsToConstantGlobal(MI->getSource())) 1795 return false; 1796 1797 // Otherwise, the transform is safe. Remember the copy instruction. 1798 TheCopy = MI; 1799 } 1800 return true; 1801} 1802 1803/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only 1804/// modified by a copy from a constant global. If we can prove this, we can 1805/// replace any uses of the alloca with uses of the global directly. 1806MemTransferInst *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) { 1807 MemTransferInst *TheCopy = 0; 1808 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) 1809 return TheCopy; 1810 return 0; 1811} 1812