ScalarReplAggregates.cpp revision aab3ea244cb014beb21c112729034879a5d4e5ee
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/DIBuilder.h" 34#include "llvm/Analysis/Dominators.h" 35#include "llvm/Analysis/Loads.h" 36#include "llvm/Analysis/ValueTracking.h" 37#include "llvm/Target/TargetData.h" 38#include "llvm/Transforms/Utils/PromoteMemToReg.h" 39#include "llvm/Transforms/Utils/Local.h" 40#include "llvm/Transforms/Utils/SSAUpdater.h" 41#include "llvm/Support/CallSite.h" 42#include "llvm/Support/Debug.h" 43#include "llvm/Support/ErrorHandling.h" 44#include "llvm/Support/GetElementPtrTypeIterator.h" 45#include "llvm/Support/IRBuilder.h" 46#include "llvm/Support/MathExtras.h" 47#include "llvm/Support/raw_ostream.h" 48#include "llvm/ADT/SetVector.h" 49#include "llvm/ADT/SmallVector.h" 50#include "llvm/ADT/Statistic.h" 51using namespace llvm; 52 53STATISTIC(NumReplaced, "Number of allocas broken up"); 54STATISTIC(NumPromoted, "Number of allocas promoted"); 55STATISTIC(NumAdjusted, "Number of scalar allocas adjusted to allow promotion"); 56STATISTIC(NumConverted, "Number of aggregates converted to scalar"); 57STATISTIC(NumGlobals, "Number of allocas copied from constant global"); 58 59namespace { 60 struct SROA : public FunctionPass { 61 SROA(int T, bool hasDT, char &ID) 62 : FunctionPass(ID), HasDomTree(hasDT) { 63 if (T == -1) 64 SRThreshold = 128; 65 else 66 SRThreshold = T; 67 } 68 69 bool runOnFunction(Function &F); 70 71 bool performScalarRepl(Function &F); 72 bool performPromotion(Function &F); 73 74 private: 75 bool HasDomTree; 76 TargetData *TD; 77 78 /// DeadInsts - Keep track of instructions we have made dead, so that 79 /// we can remove them after we are done working. 80 SmallVector<Value*, 32> DeadInsts; 81 82 /// AllocaInfo - When analyzing uses of an alloca instruction, this captures 83 /// information about the uses. All these fields are initialized to false 84 /// and set to true when something is learned. 85 struct AllocaInfo { 86 /// The alloca to promote. 87 AllocaInst *AI; 88 89 /// CheckedPHIs - This is a set of verified PHI nodes, to prevent infinite 90 /// looping and avoid redundant work. 91 SmallPtrSet<PHINode*, 8> CheckedPHIs; 92 93 /// isUnsafe - This is set to true if the alloca cannot be SROA'd. 94 bool isUnsafe : 1; 95 96 /// isMemCpySrc - This is true if this aggregate is memcpy'd from. 97 bool isMemCpySrc : 1; 98 99 /// isMemCpyDst - This is true if this aggregate is memcpy'd into. 100 bool isMemCpyDst : 1; 101 102 /// hasSubelementAccess - This is true if a subelement of the alloca is 103 /// ever accessed, or false if the alloca is only accessed with mem 104 /// intrinsics or load/store that only access the entire alloca at once. 105 bool hasSubelementAccess : 1; 106 107 /// hasALoadOrStore - This is true if there are any loads or stores to it. 108 /// The alloca may just be accessed with memcpy, for example, which would 109 /// not set this. 110 bool hasALoadOrStore : 1; 111 112 explicit AllocaInfo(AllocaInst *ai) 113 : AI(ai), isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false), 114 hasSubelementAccess(false), hasALoadOrStore(false) {} 115 }; 116 117 unsigned SRThreshold; 118 119 void MarkUnsafe(AllocaInfo &I, Instruction *User) { 120 I.isUnsafe = true; 121 DEBUG(dbgs() << " Transformation preventing inst: " << *User << '\n'); 122 } 123 124 bool isSafeAllocaToScalarRepl(AllocaInst *AI); 125 126 void isSafeForScalarRepl(Instruction *I, uint64_t Offset, AllocaInfo &Info); 127 void isSafePHISelectUseForScalarRepl(Instruction *User, uint64_t Offset, 128 AllocaInfo &Info); 129 void isSafeGEP(GetElementPtrInst *GEPI, uint64_t &Offset, AllocaInfo &Info); 130 void isSafeMemAccess(uint64_t Offset, uint64_t MemSize, 131 const Type *MemOpType, bool isStore, AllocaInfo &Info, 132 Instruction *TheAccess, bool AllowWholeAccess); 133 bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size); 134 uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset, 135 const Type *&IdxTy); 136 137 void DoScalarReplacement(AllocaInst *AI, 138 std::vector<AllocaInst*> &WorkList); 139 void DeleteDeadInstructions(); 140 141 void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 142 SmallVector<AllocaInst*, 32> &NewElts); 143 void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 144 SmallVector<AllocaInst*, 32> &NewElts); 145 void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 146 SmallVector<AllocaInst*, 32> &NewElts); 147 void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 148 AllocaInst *AI, 149 SmallVector<AllocaInst*, 32> &NewElts); 150 void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 151 SmallVector<AllocaInst*, 32> &NewElts); 152 void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 153 SmallVector<AllocaInst*, 32> &NewElts); 154 155 static MemTransferInst *isOnlyCopiedFromConstantGlobal(AllocaInst *AI); 156 }; 157 158 // SROA_DT - SROA that uses DominatorTree. 159 struct SROA_DT : public SROA { 160 static char ID; 161 public: 162 SROA_DT(int T = -1) : SROA(T, true, ID) { 163 initializeSROA_DTPass(*PassRegistry::getPassRegistry()); 164 } 165 166 // getAnalysisUsage - This pass does not require any passes, but we know it 167 // will not alter the CFG, so say so. 168 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 169 AU.addRequired<DominatorTree>(); 170 AU.setPreservesCFG(); 171 } 172 }; 173 174 // SROA_SSAUp - SROA that uses SSAUpdater. 175 struct SROA_SSAUp : public SROA { 176 static char ID; 177 public: 178 SROA_SSAUp(int T = -1) : SROA(T, false, ID) { 179 initializeSROA_SSAUpPass(*PassRegistry::getPassRegistry()); 180 } 181 182 // getAnalysisUsage - This pass does not require any passes, but we know it 183 // will not alter the CFG, so say so. 184 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 185 AU.setPreservesCFG(); 186 } 187 }; 188 189} 190 191char SROA_DT::ID = 0; 192char SROA_SSAUp::ID = 0; 193 194INITIALIZE_PASS_BEGIN(SROA_DT, "scalarrepl", 195 "Scalar Replacement of Aggregates (DT)", false, false) 196INITIALIZE_PASS_DEPENDENCY(DominatorTree) 197INITIALIZE_PASS_END(SROA_DT, "scalarrepl", 198 "Scalar Replacement of Aggregates (DT)", false, false) 199 200INITIALIZE_PASS_BEGIN(SROA_SSAUp, "scalarrepl-ssa", 201 "Scalar Replacement of Aggregates (SSAUp)", false, false) 202INITIALIZE_PASS_END(SROA_SSAUp, "scalarrepl-ssa", 203 "Scalar Replacement of Aggregates (SSAUp)", false, false) 204 205// Public interface to the ScalarReplAggregates pass 206FunctionPass *llvm::createScalarReplAggregatesPass(int Threshold, 207 bool UseDomTree) { 208 if (UseDomTree) 209 return new SROA_DT(Threshold); 210 return new SROA_SSAUp(Threshold); 211} 212 213 214//===----------------------------------------------------------------------===// 215// Convert To Scalar Optimization. 216//===----------------------------------------------------------------------===// 217 218namespace { 219/// ConvertToScalarInfo - This class implements the "Convert To Scalar" 220/// optimization, which scans the uses of an alloca and determines if it can 221/// rewrite it in terms of a single new alloca that can be mem2reg'd. 222class ConvertToScalarInfo { 223 /// AllocaSize - The size of the alloca being considered in bytes. 224 unsigned AllocaSize; 225 const TargetData &TD; 226 227 /// IsNotTrivial - This is set to true if there is some access to the object 228 /// which means that mem2reg can't promote it. 229 bool IsNotTrivial; 230 231 /// ScalarKind - Tracks the kind of alloca being considered for promotion, 232 /// computed based on the uses of the alloca rather than the LLVM type system. 233 enum { 234 Unknown, 235 236 // Accesses via GEPs that are consistent with element access of a vector 237 // type. This will not be converted into a vector unless there is a later 238 // access using an actual vector type. 239 ImplicitVector, 240 241 // Accesses via vector operations and GEPs that are consistent with the 242 // layout of a vector type. 243 Vector, 244 245 // An integer bag-of-bits with bitwise operations for insertion and 246 // extraction. Any combination of types can be converted into this kind 247 // of scalar. 248 Integer 249 } ScalarKind; 250 251 /// VectorTy - This tracks the type that we should promote the vector to if 252 /// it is possible to turn it into a vector. This starts out null, and if it 253 /// isn't possible to turn into a vector type, it gets set to VoidTy. 254 const VectorType *VectorTy; 255 256 /// HadNonMemTransferAccess - True if there is at least one access to the 257 /// alloca that is not a MemTransferInst. We don't want to turn structs into 258 /// large integers unless there is some potential for optimization. 259 bool HadNonMemTransferAccess; 260 261public: 262 explicit ConvertToScalarInfo(unsigned Size, const TargetData &td) 263 : AllocaSize(Size), TD(td), IsNotTrivial(false), ScalarKind(Unknown), 264 VectorTy(0), HadNonMemTransferAccess(false) { } 265 266 AllocaInst *TryConvert(AllocaInst *AI); 267 268private: 269 bool CanConvertToScalar(Value *V, uint64_t Offset); 270 void MergeInTypeForLoadOrStore(const Type *In, uint64_t Offset); 271 bool MergeInVectorType(const VectorType *VInTy, uint64_t Offset); 272 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset); 273 274 Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType, 275 uint64_t Offset, IRBuilder<> &Builder); 276 Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal, 277 uint64_t Offset, IRBuilder<> &Builder); 278}; 279} // end anonymous namespace. 280 281 282/// TryConvert - Analyze the specified alloca, and if it is safe to do so, 283/// rewrite it to be a new alloca which is mem2reg'able. This returns the new 284/// alloca if possible or null if not. 285AllocaInst *ConvertToScalarInfo::TryConvert(AllocaInst *AI) { 286 // If we can't convert this scalar, or if mem2reg can trivially do it, bail 287 // out. 288 if (!CanConvertToScalar(AI, 0) || !IsNotTrivial) 289 return 0; 290 291 // If an alloca has only memset / memcpy uses, it may still have an Unknown 292 // ScalarKind. Treat it as an Integer below. 293 if (ScalarKind == Unknown) 294 ScalarKind = Integer; 295 296 // If we were able to find a vector type that can handle this with 297 // insert/extract elements, and if there was at least one use that had 298 // a vector type, promote this to a vector. We don't want to promote 299 // random stuff that doesn't use vectors (e.g. <9 x double>) because then 300 // we just get a lot of insert/extracts. If at least one vector is 301 // involved, then we probably really do have a union of vector/array. 302 const Type *NewTy; 303 if (ScalarKind == Vector) { 304 assert(VectorTy && "Missing type for vector scalar."); 305 DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = " 306 << *VectorTy << '\n'); 307 NewTy = VectorTy; // Use the vector type. 308 } else { 309 unsigned BitWidth = AllocaSize * 8; 310 if ((ScalarKind == ImplicitVector || ScalarKind == Integer) && 311 !HadNonMemTransferAccess && !TD.fitsInLegalInteger(BitWidth)) 312 return 0; 313 314 DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n"); 315 // Create and insert the integer alloca. 316 NewTy = IntegerType::get(AI->getContext(), BitWidth); 317 } 318 AllocaInst *NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin()); 319 ConvertUsesToScalar(AI, NewAI, 0); 320 return NewAI; 321} 322 323/// MergeInTypeForLoadOrStore - Add the 'In' type to the accumulated vector type 324/// (VectorTy) so far at the offset specified by Offset (which is specified in 325/// bytes). 326/// 327/// There are three cases we handle here: 328/// 1) A union of vector types of the same size and potentially its elements. 329/// Here we turn element accesses into insert/extract element operations. 330/// This promotes a <4 x float> with a store of float to the third element 331/// into a <4 x float> that uses insert element. 332/// 2) A union of vector types with power-of-2 size differences, e.g. a float, 333/// <2 x float> and <4 x float>. Here we turn element accesses into insert 334/// and extract element operations, and <2 x float> accesses into a cast to 335/// <2 x double>, an extract, and a cast back to <2 x float>. 336/// 3) A fully general blob of memory, which we turn into some (potentially 337/// large) integer type with extract and insert operations where the loads 338/// and stores would mutate the memory. We mark this by setting VectorTy 339/// to VoidTy. 340void ConvertToScalarInfo::MergeInTypeForLoadOrStore(const Type *In, 341 uint64_t Offset) { 342 // If we already decided to turn this into a blob of integer memory, there is 343 // nothing to be done. 344 if (ScalarKind == Integer) 345 return; 346 347 // If this could be contributing to a vector, analyze it. 348 349 // If the In type is a vector that is the same size as the alloca, see if it 350 // matches the existing VecTy. 351 if (const VectorType *VInTy = dyn_cast<VectorType>(In)) { 352 if (MergeInVectorType(VInTy, Offset)) 353 return; 354 } else if (In->isFloatTy() || In->isDoubleTy() || 355 (In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 && 356 isPowerOf2_32(In->getPrimitiveSizeInBits()))) { 357 // Full width accesses can be ignored, because they can always be turned 358 // into bitcasts. 359 unsigned EltSize = In->getPrimitiveSizeInBits()/8; 360 if (EltSize == AllocaSize) 361 return; 362 363 // If we're accessing something that could be an element of a vector, see 364 // if the implied vector agrees with what we already have and if Offset is 365 // compatible with it. 366 if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 && 367 (!VectorTy || Offset * 8 < VectorTy->getPrimitiveSizeInBits())) { 368 if (!VectorTy) { 369 ScalarKind = ImplicitVector; 370 VectorTy = VectorType::get(In, AllocaSize/EltSize); 371 return; 372 } 373 374 unsigned CurrentEltSize = VectorTy->getElementType() 375 ->getPrimitiveSizeInBits()/8; 376 if (EltSize == CurrentEltSize) 377 return; 378 379 if (In->isIntegerTy() && isPowerOf2_32(AllocaSize / EltSize)) 380 return; 381 } 382 } 383 384 // Otherwise, we have a case that we can't handle with an optimized vector 385 // form. We can still turn this into a large integer. 386 ScalarKind = Integer; 387} 388 389/// MergeInVectorType - Handles the vector case of MergeInTypeForLoadOrStore, 390/// returning true if the type was successfully merged and false otherwise. 391bool ConvertToScalarInfo::MergeInVectorType(const VectorType *VInTy, 392 uint64_t Offset) { 393 // TODO: Support nonzero offsets? 394 if (Offset != 0) 395 return false; 396 397 // Only allow vectors that are a power-of-2 away from the size of the alloca. 398 if (!isPowerOf2_64(AllocaSize / (VInTy->getBitWidth() / 8))) 399 return false; 400 401 // If this the first vector we see, remember the type so that we know the 402 // element size. 403 if (!VectorTy) { 404 ScalarKind = Vector; 405 VectorTy = VInTy; 406 return true; 407 } 408 409 unsigned BitWidth = VectorTy->getBitWidth(); 410 unsigned InBitWidth = VInTy->getBitWidth(); 411 412 // Vectors of the same size can be converted using a simple bitcast. 413 if (InBitWidth == BitWidth && AllocaSize == (InBitWidth / 8)) { 414 ScalarKind = Vector; 415 return true; 416 } 417 418 const Type *ElementTy = VectorTy->getElementType(); 419 const Type *InElementTy = VInTy->getElementType(); 420 421 // Do not allow mixed integer and floating-point accesses from vectors of 422 // different sizes. 423 if (ElementTy->isFloatingPointTy() != InElementTy->isFloatingPointTy()) 424 return false; 425 426 if (ElementTy->isFloatingPointTy()) { 427 // Only allow floating-point vectors of different sizes if they have the 428 // same element type. 429 // TODO: This could be loosened a bit, but would anything benefit? 430 if (ElementTy != InElementTy) 431 return false; 432 433 // There are no arbitrary-precision floating-point types, which limits the 434 // number of legal vector types with larger element types that we can form 435 // to bitcast and extract a subvector. 436 // TODO: We could support some more cases with mixed fp128 and double here. 437 if (!(BitWidth == 64 || BitWidth == 128) || 438 !(InBitWidth == 64 || InBitWidth == 128)) 439 return false; 440 } else { 441 assert(ElementTy->isIntegerTy() && "Vector elements must be either integer " 442 "or floating-point."); 443 unsigned BitWidth = ElementTy->getPrimitiveSizeInBits(); 444 unsigned InBitWidth = InElementTy->getPrimitiveSizeInBits(); 445 446 // Do not allow integer types smaller than a byte or types whose widths are 447 // not a multiple of a byte. 448 if (BitWidth < 8 || InBitWidth < 8 || 449 BitWidth % 8 != 0 || InBitWidth % 8 != 0) 450 return false; 451 } 452 453 // Pick the largest of the two vector types. 454 ScalarKind = Vector; 455 if (InBitWidth > BitWidth) 456 VectorTy = VInTy; 457 458 return true; 459} 460 461/// CanConvertToScalar - V is a pointer. If we can convert the pointee and all 462/// its accesses to a single vector type, return true and set VecTy to 463/// the new type. If we could convert the alloca into a single promotable 464/// integer, return true but set VecTy to VoidTy. Further, if the use is not a 465/// completely trivial use that mem2reg could promote, set IsNotTrivial. Offset 466/// is the current offset from the base of the alloca being analyzed. 467/// 468/// If we see at least one access to the value that is as a vector type, set the 469/// SawVec flag. 470bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset) { 471 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 472 Instruction *User = cast<Instruction>(*UI); 473 474 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 475 // Don't break volatile loads. 476 if (LI->isVolatile()) 477 return false; 478 // Don't touch MMX operations. 479 if (LI->getType()->isX86_MMXTy()) 480 return false; 481 HadNonMemTransferAccess = true; 482 MergeInTypeForLoadOrStore(LI->getType(), Offset); 483 continue; 484 } 485 486 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 487 // Storing the pointer, not into the value? 488 if (SI->getOperand(0) == V || SI->isVolatile()) return false; 489 // Don't touch MMX operations. 490 if (SI->getOperand(0)->getType()->isX86_MMXTy()) 491 return false; 492 HadNonMemTransferAccess = true; 493 MergeInTypeForLoadOrStore(SI->getOperand(0)->getType(), Offset); 494 continue; 495 } 496 497 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { 498 IsNotTrivial = true; // Can't be mem2reg'd. 499 if (!CanConvertToScalar(BCI, Offset)) 500 return false; 501 continue; 502 } 503 504 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 505 // If this is a GEP with a variable indices, we can't handle it. 506 if (!GEP->hasAllConstantIndices()) 507 return false; 508 509 // Compute the offset that this GEP adds to the pointer. 510 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 511 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 512 &Indices[0], Indices.size()); 513 // See if all uses can be converted. 514 if (!CanConvertToScalar(GEP, Offset+GEPOffset)) 515 return false; 516 IsNotTrivial = true; // Can't be mem2reg'd. 517 HadNonMemTransferAccess = true; 518 continue; 519 } 520 521 // If this is a constant sized memset of a constant value (e.g. 0) we can 522 // handle it. 523 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 524 // Store of constant value and constant size. 525 if (!isa<ConstantInt>(MSI->getValue()) || 526 !isa<ConstantInt>(MSI->getLength())) 527 return false; 528 IsNotTrivial = true; // Can't be mem2reg'd. 529 HadNonMemTransferAccess = true; 530 continue; 531 } 532 533 // If this is a memcpy or memmove into or out of the whole allocation, we 534 // can handle it like a load or store of the scalar type. 535 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 536 ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()); 537 if (Len == 0 || Len->getZExtValue() != AllocaSize || Offset != 0) 538 return false; 539 540 IsNotTrivial = true; // Can't be mem2reg'd. 541 continue; 542 } 543 544 // Otherwise, we cannot handle this! 545 return false; 546 } 547 548 return true; 549} 550 551/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca 552/// directly. This happens when we are converting an "integer union" to a 553/// single integer scalar, or when we are converting a "vector union" to a 554/// vector with insert/extractelement instructions. 555/// 556/// Offset is an offset from the original alloca, in bits that need to be 557/// shifted to the right. By the end of this, there should be no uses of Ptr. 558void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, 559 uint64_t Offset) { 560 while (!Ptr->use_empty()) { 561 Instruction *User = cast<Instruction>(Ptr->use_back()); 562 563 if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 564 ConvertUsesToScalar(CI, NewAI, Offset); 565 CI->eraseFromParent(); 566 continue; 567 } 568 569 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 570 // Compute the offset that this GEP adds to the pointer. 571 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 572 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 573 &Indices[0], Indices.size()); 574 ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8); 575 GEP->eraseFromParent(); 576 continue; 577 } 578 579 IRBuilder<> Builder(User); 580 581 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 582 // The load is a bit extract from NewAI shifted right by Offset bits. 583 Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp"); 584 Value *NewLoadVal 585 = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder); 586 LI->replaceAllUsesWith(NewLoadVal); 587 LI->eraseFromParent(); 588 continue; 589 } 590 591 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 592 assert(SI->getOperand(0) != Ptr && "Consistency error!"); 593 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 594 Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset, 595 Builder); 596 Builder.CreateStore(New, NewAI); 597 SI->eraseFromParent(); 598 599 // If the load we just inserted is now dead, then the inserted store 600 // overwrote the entire thing. 601 if (Old->use_empty()) 602 Old->eraseFromParent(); 603 continue; 604 } 605 606 // If this is a constant sized memset of a constant value (e.g. 0) we can 607 // transform it into a store of the expanded constant value. 608 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 609 assert(MSI->getRawDest() == Ptr && "Consistency error!"); 610 unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue(); 611 if (NumBytes != 0) { 612 unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue(); 613 614 // Compute the value replicated the right number of times. 615 APInt APVal(NumBytes*8, Val); 616 617 // Splat the value if non-zero. 618 if (Val) 619 for (unsigned i = 1; i != NumBytes; ++i) 620 APVal |= APVal << 8; 621 622 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 623 Value *New = ConvertScalar_InsertValue( 624 ConstantInt::get(User->getContext(), APVal), 625 Old, Offset, Builder); 626 Builder.CreateStore(New, NewAI); 627 628 // If the load we just inserted is now dead, then the memset overwrote 629 // the entire thing. 630 if (Old->use_empty()) 631 Old->eraseFromParent(); 632 } 633 MSI->eraseFromParent(); 634 continue; 635 } 636 637 // If this is a memcpy or memmove into or out of the whole allocation, we 638 // can handle it like a load or store of the scalar type. 639 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 640 assert(Offset == 0 && "must be store to start of alloca"); 641 642 // If the source and destination are both to the same alloca, then this is 643 // a noop copy-to-self, just delete it. Otherwise, emit a load and store 644 // as appropriate. 645 AllocaInst *OrigAI = cast<AllocaInst>(GetUnderlyingObject(Ptr, &TD, 0)); 646 647 if (GetUnderlyingObject(MTI->getSource(), &TD, 0) != OrigAI) { 648 // Dest must be OrigAI, change this to be a load from the original 649 // pointer (bitcasted), then a store to our new alloca. 650 assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?"); 651 Value *SrcPtr = MTI->getSource(); 652 const PointerType* SPTy = cast<PointerType>(SrcPtr->getType()); 653 const PointerType* AIPTy = cast<PointerType>(NewAI->getType()); 654 if (SPTy->getAddressSpace() != AIPTy->getAddressSpace()) { 655 AIPTy = PointerType::get(AIPTy->getElementType(), 656 SPTy->getAddressSpace()); 657 } 658 SrcPtr = Builder.CreateBitCast(SrcPtr, AIPTy); 659 660 LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval"); 661 SrcVal->setAlignment(MTI->getAlignment()); 662 Builder.CreateStore(SrcVal, NewAI); 663 } else if (GetUnderlyingObject(MTI->getDest(), &TD, 0) != OrigAI) { 664 // Src must be OrigAI, change this to be a load from NewAI then a store 665 // through the original dest pointer (bitcasted). 666 assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?"); 667 LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval"); 668 669 const PointerType* DPTy = cast<PointerType>(MTI->getDest()->getType()); 670 const PointerType* AIPTy = cast<PointerType>(NewAI->getType()); 671 if (DPTy->getAddressSpace() != AIPTy->getAddressSpace()) { 672 AIPTy = PointerType::get(AIPTy->getElementType(), 673 DPTy->getAddressSpace()); 674 } 675 Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), AIPTy); 676 677 StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr); 678 NewStore->setAlignment(MTI->getAlignment()); 679 } else { 680 // Noop transfer. Src == Dst 681 } 682 683 MTI->eraseFromParent(); 684 continue; 685 } 686 687 llvm_unreachable("Unsupported operation!"); 688 } 689} 690 691/// getScaledElementType - Gets a scaled element type for a partial vector 692/// access of an alloca. The input types must be integer or floating-point 693/// scalar or vector types, and the resulting type is an integer, float or 694/// double. 695static const Type *getScaledElementType(const Type *Ty1, const Type *Ty2, 696 unsigned NewBitWidth) { 697 bool IsFP1 = Ty1->isFloatingPointTy() || 698 (Ty1->isVectorTy() && 699 cast<VectorType>(Ty1)->getElementType()->isFloatingPointTy()); 700 bool IsFP2 = Ty2->isFloatingPointTy() || 701 (Ty2->isVectorTy() && 702 cast<VectorType>(Ty2)->getElementType()->isFloatingPointTy()); 703 704 LLVMContext &Context = Ty1->getContext(); 705 706 // Prefer floating-point types over integer types, as integer types may have 707 // been created by earlier scalar replacement. 708 if (IsFP1 || IsFP2) { 709 if (NewBitWidth == 32) 710 return Type::getFloatTy(Context); 711 if (NewBitWidth == 64) 712 return Type::getDoubleTy(Context); 713 } 714 715 return Type::getIntNTy(Context, NewBitWidth); 716} 717 718/// CreateShuffleVectorCast - Creates a shuffle vector to convert one vector 719/// to another vector of the same element type which has the same allocation 720/// size but different primitive sizes (e.g. <3 x i32> and <4 x i32>). 721static Value *CreateShuffleVectorCast(Value *FromVal, const Type *ToType, 722 IRBuilder<> &Builder) { 723 const Type *FromType = FromVal->getType(); 724 const VectorType *FromVTy = cast<VectorType>(FromType); 725 const VectorType *ToVTy = cast<VectorType>(ToType); 726 assert((ToVTy->getElementType() == FromVTy->getElementType()) && 727 "Vectors must have the same element type"); 728 Value *UnV = UndefValue::get(FromType); 729 unsigned numEltsFrom = FromVTy->getNumElements(); 730 unsigned numEltsTo = ToVTy->getNumElements(); 731 732 SmallVector<Constant*, 3> Args; 733 const Type* Int32Ty = Builder.getInt32Ty(); 734 unsigned minNumElts = std::min(numEltsFrom, numEltsTo); 735 unsigned i; 736 for (i=0; i != minNumElts; ++i) 737 Args.push_back(ConstantInt::get(Int32Ty, i)); 738 739 if (i < numEltsTo) { 740 Constant* UnC = UndefValue::get(Int32Ty); 741 for (; i != numEltsTo; ++i) 742 Args.push_back(UnC); 743 } 744 Constant *Mask = ConstantVector::get(Args); 745 return Builder.CreateShuffleVector(FromVal, UnV, Mask, "tmpV"); 746} 747 748/// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer 749/// or vector value FromVal, extracting the bits from the offset specified by 750/// Offset. This returns the value, which is of type ToType. 751/// 752/// This happens when we are converting an "integer union" to a single 753/// integer scalar, or when we are converting a "vector union" to a vector with 754/// insert/extractelement instructions. 755/// 756/// Offset is an offset from the original alloca, in bits that need to be 757/// shifted to the right. 758Value *ConvertToScalarInfo:: 759ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType, 760 uint64_t Offset, IRBuilder<> &Builder) { 761 // If the load is of the whole new alloca, no conversion is needed. 762 const Type *FromType = FromVal->getType(); 763 if (FromType == ToType && Offset == 0) 764 return FromVal; 765 766 // If the result alloca is a vector type, this is either an element 767 // access or a bitcast to another vector type of the same size. 768 if (const VectorType *VTy = dyn_cast<VectorType>(FromType)) { 769 unsigned FromTypeSize = TD.getTypeAllocSize(FromType); 770 unsigned ToTypeSize = TD.getTypeAllocSize(ToType); 771 if (FromTypeSize == ToTypeSize) { 772 // If the two types have the same primitive size, use a bit cast. 773 // Otherwise, it is two vectors with the same element type that has 774 // the same allocation size but different number of elements so use 775 // a shuffle vector. 776 if (FromType->getPrimitiveSizeInBits() == 777 ToType->getPrimitiveSizeInBits()) 778 return Builder.CreateBitCast(FromVal, ToType, "tmp"); 779 else 780 return CreateShuffleVectorCast(FromVal, ToType, Builder); 781 } 782 783 if (isPowerOf2_64(FromTypeSize / ToTypeSize)) { 784 assert(!(ToType->isVectorTy() && Offset != 0) && "Can't extract a value " 785 "of a smaller vector type at a nonzero offset."); 786 787 const Type *CastElementTy = getScaledElementType(FromType, ToType, 788 ToTypeSize * 8); 789 unsigned NumCastVectorElements = FromTypeSize / ToTypeSize; 790 791 LLVMContext &Context = FromVal->getContext(); 792 const Type *CastTy = VectorType::get(CastElementTy, 793 NumCastVectorElements); 794 Value *Cast = Builder.CreateBitCast(FromVal, CastTy, "tmp"); 795 796 unsigned EltSize = TD.getTypeAllocSizeInBits(CastElementTy); 797 unsigned Elt = Offset/EltSize; 798 assert(EltSize*Elt == Offset && "Invalid modulus in validity checking"); 799 Value *Extract = Builder.CreateExtractElement(Cast, ConstantInt::get( 800 Type::getInt32Ty(Context), Elt), "tmp"); 801 return Builder.CreateBitCast(Extract, ToType, "tmp"); 802 } 803 804 // Otherwise it must be an element access. 805 unsigned Elt = 0; 806 if (Offset) { 807 unsigned EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 808 Elt = Offset/EltSize; 809 assert(EltSize*Elt == Offset && "Invalid modulus in validity checking"); 810 } 811 // Return the element extracted out of it. 812 Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get( 813 Type::getInt32Ty(FromVal->getContext()), Elt), "tmp"); 814 if (V->getType() != ToType) 815 V = Builder.CreateBitCast(V, ToType, "tmp"); 816 return V; 817 } 818 819 // If ToType is a first class aggregate, extract out each of the pieces and 820 // use insertvalue's to form the FCA. 821 if (const StructType *ST = dyn_cast<StructType>(ToType)) { 822 const StructLayout &Layout = *TD.getStructLayout(ST); 823 Value *Res = UndefValue::get(ST); 824 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 825 Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i), 826 Offset+Layout.getElementOffsetInBits(i), 827 Builder); 828 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 829 } 830 return Res; 831 } 832 833 if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) { 834 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 835 Value *Res = UndefValue::get(AT); 836 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 837 Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(), 838 Offset+i*EltSize, Builder); 839 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 840 } 841 return Res; 842 } 843 844 // Otherwise, this must be a union that was converted to an integer value. 845 const IntegerType *NTy = cast<IntegerType>(FromVal->getType()); 846 847 // If this is a big-endian system and the load is narrower than the 848 // full alloca type, we need to do a shift to get the right bits. 849 int ShAmt = 0; 850 if (TD.isBigEndian()) { 851 // On big-endian machines, the lowest bit is stored at the bit offset 852 // from the pointer given by getTypeStoreSizeInBits. This matters for 853 // integers with a bitwidth that is not a multiple of 8. 854 ShAmt = TD.getTypeStoreSizeInBits(NTy) - 855 TD.getTypeStoreSizeInBits(ToType) - Offset; 856 } else { 857 ShAmt = Offset; 858 } 859 860 // Note: we support negative bitwidths (with shl) which are not defined. 861 // We do this to support (f.e.) loads off the end of a structure where 862 // only some bits are used. 863 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth()) 864 FromVal = Builder.CreateLShr(FromVal, 865 ConstantInt::get(FromVal->getType(), 866 ShAmt), "tmp"); 867 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) 868 FromVal = Builder.CreateShl(FromVal, 869 ConstantInt::get(FromVal->getType(), 870 -ShAmt), "tmp"); 871 872 // Finally, unconditionally truncate the integer to the right width. 873 unsigned LIBitWidth = TD.getTypeSizeInBits(ToType); 874 if (LIBitWidth < NTy->getBitWidth()) 875 FromVal = 876 Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(), 877 LIBitWidth), "tmp"); 878 else if (LIBitWidth > NTy->getBitWidth()) 879 FromVal = 880 Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(), 881 LIBitWidth), "tmp"); 882 883 // If the result is an integer, this is a trunc or bitcast. 884 if (ToType->isIntegerTy()) { 885 // Should be done. 886 } else if (ToType->isFloatingPointTy() || ToType->isVectorTy()) { 887 // Just do a bitcast, we know the sizes match up. 888 FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp"); 889 } else { 890 // Otherwise must be a pointer. 891 FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp"); 892 } 893 assert(FromVal->getType() == ToType && "Didn't convert right?"); 894 return FromVal; 895} 896 897/// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer 898/// or vector value "Old" at the offset specified by Offset. 899/// 900/// This happens when we are converting an "integer union" to a 901/// single integer scalar, or when we are converting a "vector union" to a 902/// vector with insert/extractelement instructions. 903/// 904/// Offset is an offset from the original alloca, in bits that need to be 905/// shifted to the right. 906Value *ConvertToScalarInfo:: 907ConvertScalar_InsertValue(Value *SV, Value *Old, 908 uint64_t Offset, IRBuilder<> &Builder) { 909 // Convert the stored type to the actual type, shift it left to insert 910 // then 'or' into place. 911 const Type *AllocaType = Old->getType(); 912 LLVMContext &Context = Old->getContext(); 913 914 if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) { 915 uint64_t VecSize = TD.getTypeAllocSizeInBits(VTy); 916 uint64_t ValSize = TD.getTypeAllocSizeInBits(SV->getType()); 917 918 // Changing the whole vector with memset or with an access of a different 919 // vector type? 920 if (ValSize == VecSize) { 921 // If the two types have the same primitive size, use a bit cast. 922 // Otherwise, it is two vectors with the same element type that has 923 // the same allocation size but different number of elements so use 924 // a shuffle vector. 925 if (VTy->getPrimitiveSizeInBits() == 926 SV->getType()->getPrimitiveSizeInBits()) 927 return Builder.CreateBitCast(SV, AllocaType, "tmp"); 928 else 929 return CreateShuffleVectorCast(SV, VTy, Builder); 930 } 931 932 if (isPowerOf2_64(VecSize / ValSize)) { 933 assert(!(SV->getType()->isVectorTy() && Offset != 0) && "Can't insert a " 934 "value of a smaller vector type at a nonzero offset."); 935 936 const Type *CastElementTy = getScaledElementType(VTy, SV->getType(), 937 ValSize); 938 unsigned NumCastVectorElements = VecSize / ValSize; 939 940 LLVMContext &Context = SV->getContext(); 941 const Type *OldCastTy = VectorType::get(CastElementTy, 942 NumCastVectorElements); 943 Value *OldCast = Builder.CreateBitCast(Old, OldCastTy, "tmp"); 944 945 Value *SVCast = Builder.CreateBitCast(SV, CastElementTy, "tmp"); 946 947 unsigned EltSize = TD.getTypeAllocSizeInBits(CastElementTy); 948 unsigned Elt = Offset/EltSize; 949 assert(EltSize*Elt == Offset && "Invalid modulus in validity checking"); 950 Value *Insert = 951 Builder.CreateInsertElement(OldCast, SVCast, ConstantInt::get( 952 Type::getInt32Ty(Context), Elt), "tmp"); 953 return Builder.CreateBitCast(Insert, AllocaType, "tmp"); 954 } 955 956 // Must be an element insertion. 957 assert(SV->getType() == VTy->getElementType()); 958 uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 959 unsigned Elt = Offset/EltSize; 960 return Builder.CreateInsertElement(Old, SV, 961 ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt), 962 "tmp"); 963 } 964 965 // If SV is a first-class aggregate value, insert each value recursively. 966 if (const StructType *ST = dyn_cast<StructType>(SV->getType())) { 967 const StructLayout &Layout = *TD.getStructLayout(ST); 968 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 969 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 970 Old = ConvertScalar_InsertValue(Elt, Old, 971 Offset+Layout.getElementOffsetInBits(i), 972 Builder); 973 } 974 return Old; 975 } 976 977 if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) { 978 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 979 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 980 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 981 Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder); 982 } 983 return Old; 984 } 985 986 // If SV is a float, convert it to the appropriate integer type. 987 // If it is a pointer, do the same. 988 unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType()); 989 unsigned DestWidth = TD.getTypeSizeInBits(AllocaType); 990 unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType()); 991 unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType); 992 if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy()) 993 SV = Builder.CreateBitCast(SV, 994 IntegerType::get(SV->getContext(),SrcWidth), "tmp"); 995 else if (SV->getType()->isPointerTy()) 996 SV = Builder.CreatePtrToInt(SV, TD.getIntPtrType(SV->getContext()), "tmp"); 997 998 // Zero extend or truncate the value if needed. 999 if (SV->getType() != AllocaType) { 1000 if (SV->getType()->getPrimitiveSizeInBits() < 1001 AllocaType->getPrimitiveSizeInBits()) 1002 SV = Builder.CreateZExt(SV, AllocaType, "tmp"); 1003 else { 1004 // Truncation may be needed if storing more than the alloca can hold 1005 // (undefined behavior). 1006 SV = Builder.CreateTrunc(SV, AllocaType, "tmp"); 1007 SrcWidth = DestWidth; 1008 SrcStoreWidth = DestStoreWidth; 1009 } 1010 } 1011 1012 // If this is a big-endian system and the store is narrower than the 1013 // full alloca type, we need to do a shift to get the right bits. 1014 int ShAmt = 0; 1015 if (TD.isBigEndian()) { 1016 // On big-endian machines, the lowest bit is stored at the bit offset 1017 // from the pointer given by getTypeStoreSizeInBits. This matters for 1018 // integers with a bitwidth that is not a multiple of 8. 1019 ShAmt = DestStoreWidth - SrcStoreWidth - Offset; 1020 } else { 1021 ShAmt = Offset; 1022 } 1023 1024 // Note: we support negative bitwidths (with shr) which are not defined. 1025 // We do this to support (f.e.) stores off the end of a structure where 1026 // only some bits in the structure are set. 1027 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth)); 1028 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) { 1029 SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(), 1030 ShAmt), "tmp"); 1031 Mask <<= ShAmt; 1032 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { 1033 SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(), 1034 -ShAmt), "tmp"); 1035 Mask = Mask.lshr(-ShAmt); 1036 } 1037 1038 // Mask out the bits we are about to insert from the old value, and or 1039 // in the new bits. 1040 if (SrcWidth != DestWidth) { 1041 assert(DestWidth > SrcWidth); 1042 Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask"); 1043 SV = Builder.CreateOr(Old, SV, "ins"); 1044 } 1045 return SV; 1046} 1047 1048 1049//===----------------------------------------------------------------------===// 1050// SRoA Driver 1051//===----------------------------------------------------------------------===// 1052 1053 1054bool SROA::runOnFunction(Function &F) { 1055 TD = getAnalysisIfAvailable<TargetData>(); 1056 1057 bool Changed = performPromotion(F); 1058 1059 // FIXME: ScalarRepl currently depends on TargetData more than it 1060 // theoretically needs to. It should be refactored in order to support 1061 // target-independent IR. Until this is done, just skip the actual 1062 // scalar-replacement portion of this pass. 1063 if (!TD) return Changed; 1064 1065 while (1) { 1066 bool LocalChange = performScalarRepl(F); 1067 if (!LocalChange) break; // No need to repromote if no scalarrepl 1068 Changed = true; 1069 LocalChange = performPromotion(F); 1070 if (!LocalChange) break; // No need to re-scalarrepl if no promotion 1071 } 1072 1073 return Changed; 1074} 1075 1076namespace { 1077class AllocaPromoter : public LoadAndStorePromoter { 1078 AllocaInst *AI; 1079public: 1080 AllocaPromoter(const SmallVectorImpl<Instruction*> &Insts, SSAUpdater &S, 1081 DbgDeclareInst *DD, DIBuilder *&DB) 1082 : LoadAndStorePromoter(Insts, S, DD, DB), AI(0) {} 1083 1084 void run(AllocaInst *AI, const SmallVectorImpl<Instruction*> &Insts) { 1085 // Remember which alloca we're promoting (for isInstInList). 1086 this->AI = AI; 1087 LoadAndStorePromoter::run(Insts); 1088 AI->eraseFromParent(); 1089 } 1090 1091 virtual bool isInstInList(Instruction *I, 1092 const SmallVectorImpl<Instruction*> &Insts) const { 1093 if (LoadInst *LI = dyn_cast<LoadInst>(I)) 1094 return LI->getOperand(0) == AI; 1095 return cast<StoreInst>(I)->getPointerOperand() == AI; 1096 } 1097}; 1098} // end anon namespace 1099 1100/// isSafeSelectToSpeculate - Select instructions that use an alloca and are 1101/// subsequently loaded can be rewritten to load both input pointers and then 1102/// select between the result, allowing the load of the alloca to be promoted. 1103/// From this: 1104/// %P2 = select i1 %cond, i32* %Alloca, i32* %Other 1105/// %V = load i32* %P2 1106/// to: 1107/// %V1 = load i32* %Alloca -> will be mem2reg'd 1108/// %V2 = load i32* %Other 1109/// %V = select i1 %cond, i32 %V1, i32 %V2 1110/// 1111/// We can do this to a select if its only uses are loads and if the operand to 1112/// the select can be loaded unconditionally. 1113static bool isSafeSelectToSpeculate(SelectInst *SI, const TargetData *TD) { 1114 bool TDerefable = SI->getTrueValue()->isDereferenceablePointer(); 1115 bool FDerefable = SI->getFalseValue()->isDereferenceablePointer(); 1116 1117 for (Value::use_iterator UI = SI->use_begin(), UE = SI->use_end(); 1118 UI != UE; ++UI) { 1119 LoadInst *LI = dyn_cast<LoadInst>(*UI); 1120 if (LI == 0 || LI->isVolatile()) return false; 1121 1122 // Both operands to the select need to be dereferencable, either absolutely 1123 // (e.g. allocas) or at this point because we can see other accesses to it. 1124 if (!TDerefable && !isSafeToLoadUnconditionally(SI->getTrueValue(), LI, 1125 LI->getAlignment(), TD)) 1126 return false; 1127 if (!FDerefable && !isSafeToLoadUnconditionally(SI->getFalseValue(), LI, 1128 LI->getAlignment(), TD)) 1129 return false; 1130 } 1131 1132 return true; 1133} 1134 1135/// isSafePHIToSpeculate - PHI instructions that use an alloca and are 1136/// subsequently loaded can be rewritten to load both input pointers in the pred 1137/// blocks and then PHI the results, allowing the load of the alloca to be 1138/// promoted. 1139/// From this: 1140/// %P2 = phi [i32* %Alloca, i32* %Other] 1141/// %V = load i32* %P2 1142/// to: 1143/// %V1 = load i32* %Alloca -> will be mem2reg'd 1144/// ... 1145/// %V2 = load i32* %Other 1146/// ... 1147/// %V = phi [i32 %V1, i32 %V2] 1148/// 1149/// We can do this to a select if its only uses are loads and if the operand to 1150/// the select can be loaded unconditionally. 1151static bool isSafePHIToSpeculate(PHINode *PN, const TargetData *TD) { 1152 // For now, we can only do this promotion if the load is in the same block as 1153 // the PHI, and if there are no stores between the phi and load. 1154 // TODO: Allow recursive phi users. 1155 // TODO: Allow stores. 1156 BasicBlock *BB = PN->getParent(); 1157 unsigned MaxAlign = 0; 1158 for (Value::use_iterator UI = PN->use_begin(), UE = PN->use_end(); 1159 UI != UE; ++UI) { 1160 LoadInst *LI = dyn_cast<LoadInst>(*UI); 1161 if (LI == 0 || LI->isVolatile()) return false; 1162 1163 // For now we only allow loads in the same block as the PHI. This is a 1164 // common case that happens when instcombine merges two loads through a PHI. 1165 if (LI->getParent() != BB) return false; 1166 1167 // Ensure that there are no instructions between the PHI and the load that 1168 // could store. 1169 for (BasicBlock::iterator BBI = PN; &*BBI != LI; ++BBI) 1170 if (BBI->mayWriteToMemory()) 1171 return false; 1172 1173 MaxAlign = std::max(MaxAlign, LI->getAlignment()); 1174 } 1175 1176 // Okay, we know that we have one or more loads in the same block as the PHI. 1177 // We can transform this if it is safe to push the loads into the predecessor 1178 // blocks. The only thing to watch out for is that we can't put a possibly 1179 // trapping load in the predecessor if it is a critical edge. 1180 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1181 BasicBlock *Pred = PN->getIncomingBlock(i); 1182 1183 // If the predecessor has a single successor, then the edge isn't critical. 1184 if (Pred->getTerminator()->getNumSuccessors() == 1) 1185 continue; 1186 1187 Value *InVal = PN->getIncomingValue(i); 1188 1189 // If the InVal is an invoke in the pred, we can't put a load on the edge. 1190 if (InvokeInst *II = dyn_cast<InvokeInst>(InVal)) 1191 if (II->getParent() == Pred) 1192 return false; 1193 1194 // If this pointer is always safe to load, or if we can prove that there is 1195 // already a load in the block, then we can move the load to the pred block. 1196 if (InVal->isDereferenceablePointer() || 1197 isSafeToLoadUnconditionally(InVal, Pred->getTerminator(), MaxAlign, TD)) 1198 continue; 1199 1200 return false; 1201 } 1202 1203 return true; 1204} 1205 1206 1207/// tryToMakeAllocaBePromotable - This returns true if the alloca only has 1208/// direct (non-volatile) loads and stores to it. If the alloca is close but 1209/// not quite there, this will transform the code to allow promotion. As such, 1210/// it is a non-pure predicate. 1211static bool tryToMakeAllocaBePromotable(AllocaInst *AI, const TargetData *TD) { 1212 SetVector<Instruction*, SmallVector<Instruction*, 4>, 1213 SmallPtrSet<Instruction*, 4> > InstsToRewrite; 1214 1215 for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end(); 1216 UI != UE; ++UI) { 1217 User *U = *UI; 1218 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 1219 if (LI->isVolatile()) 1220 return false; 1221 continue; 1222 } 1223 1224 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 1225 if (SI->getOperand(0) == AI || SI->isVolatile()) 1226 return false; // Don't allow a store OF the AI, only INTO the AI. 1227 continue; 1228 } 1229 1230 if (SelectInst *SI = dyn_cast<SelectInst>(U)) { 1231 // If the condition being selected on is a constant, fold the select, yes 1232 // this does (rarely) happen early on. 1233 if (ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition())) { 1234 Value *Result = SI->getOperand(1+CI->isZero()); 1235 SI->replaceAllUsesWith(Result); 1236 SI->eraseFromParent(); 1237 1238 // This is very rare and we just scrambled the use list of AI, start 1239 // over completely. 1240 return tryToMakeAllocaBePromotable(AI, TD); 1241 } 1242 1243 // If it is safe to turn "load (select c, AI, ptr)" into a select of two 1244 // loads, then we can transform this by rewriting the select. 1245 if (!isSafeSelectToSpeculate(SI, TD)) 1246 return false; 1247 1248 InstsToRewrite.insert(SI); 1249 continue; 1250 } 1251 1252 if (PHINode *PN = dyn_cast<PHINode>(U)) { 1253 if (PN->use_empty()) { // Dead PHIs can be stripped. 1254 InstsToRewrite.insert(PN); 1255 continue; 1256 } 1257 1258 // If it is safe to turn "load (phi [AI, ptr, ...])" into a PHI of loads 1259 // in the pred blocks, then we can transform this by rewriting the PHI. 1260 if (!isSafePHIToSpeculate(PN, TD)) 1261 return false; 1262 1263 InstsToRewrite.insert(PN); 1264 continue; 1265 } 1266 1267 return false; 1268 } 1269 1270 // If there are no instructions to rewrite, then all uses are load/stores and 1271 // we're done! 1272 if (InstsToRewrite.empty()) 1273 return true; 1274 1275 // If we have instructions that need to be rewritten for this to be promotable 1276 // take care of it now. 1277 for (unsigned i = 0, e = InstsToRewrite.size(); i != e; ++i) { 1278 if (SelectInst *SI = dyn_cast<SelectInst>(InstsToRewrite[i])) { 1279 // Selects in InstsToRewrite only have load uses. Rewrite each as two 1280 // loads with a new select. 1281 while (!SI->use_empty()) { 1282 LoadInst *LI = cast<LoadInst>(SI->use_back()); 1283 1284 IRBuilder<> Builder(LI); 1285 LoadInst *TrueLoad = 1286 Builder.CreateLoad(SI->getTrueValue(), LI->getName()+".t"); 1287 LoadInst *FalseLoad = 1288 Builder.CreateLoad(SI->getFalseValue(), LI->getName()+".t"); 1289 1290 // Transfer alignment and TBAA info if present. 1291 TrueLoad->setAlignment(LI->getAlignment()); 1292 FalseLoad->setAlignment(LI->getAlignment()); 1293 if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) { 1294 TrueLoad->setMetadata(LLVMContext::MD_tbaa, Tag); 1295 FalseLoad->setMetadata(LLVMContext::MD_tbaa, Tag); 1296 } 1297 1298 Value *V = Builder.CreateSelect(SI->getCondition(), TrueLoad, FalseLoad); 1299 V->takeName(LI); 1300 LI->replaceAllUsesWith(V); 1301 LI->eraseFromParent(); 1302 } 1303 1304 // Now that all the loads are gone, the select is gone too. 1305 SI->eraseFromParent(); 1306 continue; 1307 } 1308 1309 // Otherwise, we have a PHI node which allows us to push the loads into the 1310 // predecessors. 1311 PHINode *PN = cast<PHINode>(InstsToRewrite[i]); 1312 if (PN->use_empty()) { 1313 PN->eraseFromParent(); 1314 continue; 1315 } 1316 1317 const Type *LoadTy = cast<PointerType>(PN->getType())->getElementType(); 1318 PHINode *NewPN = PHINode::Create(LoadTy, PN->getNumIncomingValues(), 1319 PN->getName()+".ld", PN); 1320 1321 // Get the TBAA tag and alignment to use from one of the loads. It doesn't 1322 // matter which one we get and if any differ, it doesn't matter. 1323 LoadInst *SomeLoad = cast<LoadInst>(PN->use_back()); 1324 MDNode *TBAATag = SomeLoad->getMetadata(LLVMContext::MD_tbaa); 1325 unsigned Align = SomeLoad->getAlignment(); 1326 1327 // Rewrite all loads of the PN to use the new PHI. 1328 while (!PN->use_empty()) { 1329 LoadInst *LI = cast<LoadInst>(PN->use_back()); 1330 LI->replaceAllUsesWith(NewPN); 1331 LI->eraseFromParent(); 1332 } 1333 1334 // Inject loads into all of the pred blocks. Keep track of which blocks we 1335 // insert them into in case we have multiple edges from the same block. 1336 DenseMap<BasicBlock*, LoadInst*> InsertedLoads; 1337 1338 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1339 BasicBlock *Pred = PN->getIncomingBlock(i); 1340 LoadInst *&Load = InsertedLoads[Pred]; 1341 if (Load == 0) { 1342 Load = new LoadInst(PN->getIncomingValue(i), 1343 PN->getName() + "." + Pred->getName(), 1344 Pred->getTerminator()); 1345 Load->setAlignment(Align); 1346 if (TBAATag) Load->setMetadata(LLVMContext::MD_tbaa, TBAATag); 1347 } 1348 1349 NewPN->addIncoming(Load, Pred); 1350 } 1351 1352 PN->eraseFromParent(); 1353 } 1354 1355 ++NumAdjusted; 1356 return true; 1357} 1358 1359bool SROA::performPromotion(Function &F) { 1360 std::vector<AllocaInst*> Allocas; 1361 DominatorTree *DT = 0; 1362 if (HasDomTree) 1363 DT = &getAnalysis<DominatorTree>(); 1364 1365 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function 1366 1367 bool Changed = false; 1368 SmallVector<Instruction*, 64> Insts; 1369 DIBuilder *DIB = 0; 1370 while (1) { 1371 Allocas.clear(); 1372 1373 // Find allocas that are safe to promote, by looking at all instructions in 1374 // the entry node 1375 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) 1376 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? 1377 if (tryToMakeAllocaBePromotable(AI, TD)) 1378 Allocas.push_back(AI); 1379 1380 if (Allocas.empty()) break; 1381 1382 if (HasDomTree) 1383 PromoteMemToReg(Allocas, *DT); 1384 else { 1385 SSAUpdater SSA; 1386 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) { 1387 AllocaInst *AI = Allocas[i]; 1388 1389 // Build list of instructions to promote. 1390 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 1391 UI != E; ++UI) 1392 Insts.push_back(cast<Instruction>(*UI)); 1393 1394 DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI); 1395 if (DDI && !DIB) 1396 DIB = new DIBuilder(*AI->getParent()->getParent()->getParent()); 1397 AllocaPromoter(Insts, SSA, DDI, DIB).run(AI, Insts); 1398 Insts.clear(); 1399 } 1400 } 1401 NumPromoted += Allocas.size(); 1402 Changed = true; 1403 } 1404 1405 // FIXME: Is there a better way to handle the lazy initialization of DIB 1406 // so that there doesn't need to be an explicit delete? 1407 delete DIB; 1408 1409 return Changed; 1410} 1411 1412 1413/// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for 1414/// SROA. It must be a struct or array type with a small number of elements. 1415static bool ShouldAttemptScalarRepl(AllocaInst *AI) { 1416 const Type *T = AI->getAllocatedType(); 1417 // Do not promote any struct into more than 32 separate vars. 1418 if (const StructType *ST = dyn_cast<StructType>(T)) 1419 return ST->getNumElements() <= 32; 1420 // Arrays are much less likely to be safe for SROA; only consider 1421 // them if they are very small. 1422 if (const ArrayType *AT = dyn_cast<ArrayType>(T)) 1423 return AT->getNumElements() <= 8; 1424 return false; 1425} 1426 1427 1428// performScalarRepl - This algorithm is a simple worklist driven algorithm, 1429// which runs on all of the malloc/alloca instructions in the function, removing 1430// them if they are only used by getelementptr instructions. 1431// 1432bool SROA::performScalarRepl(Function &F) { 1433 std::vector<AllocaInst*> WorkList; 1434 1435 // Scan the entry basic block, adding allocas to the worklist. 1436 BasicBlock &BB = F.getEntryBlock(); 1437 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) 1438 if (AllocaInst *A = dyn_cast<AllocaInst>(I)) 1439 WorkList.push_back(A); 1440 1441 // Process the worklist 1442 bool Changed = false; 1443 while (!WorkList.empty()) { 1444 AllocaInst *AI = WorkList.back(); 1445 WorkList.pop_back(); 1446 1447 // Handle dead allocas trivially. These can be formed by SROA'ing arrays 1448 // with unused elements. 1449 if (AI->use_empty()) { 1450 AI->eraseFromParent(); 1451 Changed = true; 1452 continue; 1453 } 1454 1455 // If this alloca is impossible for us to promote, reject it early. 1456 if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized()) 1457 continue; 1458 1459 // Check to see if this allocation is only modified by a memcpy/memmove from 1460 // a constant global. If this is the case, we can change all users to use 1461 // the constant global instead. This is commonly produced by the CFE by 1462 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A' 1463 // is only subsequently read. 1464 if (MemTransferInst *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) { 1465 DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n'); 1466 DEBUG(dbgs() << " memcpy = " << *TheCopy << '\n'); 1467 Constant *TheSrc = cast<Constant>(TheCopy->getSource()); 1468 AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType())); 1469 TheCopy->eraseFromParent(); // Don't mutate the global. 1470 AI->eraseFromParent(); 1471 ++NumGlobals; 1472 Changed = true; 1473 continue; 1474 } 1475 1476 // Check to see if we can perform the core SROA transformation. We cannot 1477 // transform the allocation instruction if it is an array allocation 1478 // (allocations OF arrays are ok though), and an allocation of a scalar 1479 // value cannot be decomposed at all. 1480 uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType()); 1481 1482 // Do not promote [0 x %struct]. 1483 if (AllocaSize == 0) continue; 1484 1485 // Do not promote any struct whose size is too big. 1486 if (AllocaSize > SRThreshold) continue; 1487 1488 // If the alloca looks like a good candidate for scalar replacement, and if 1489 // all its users can be transformed, then split up the aggregate into its 1490 // separate elements. 1491 if (ShouldAttemptScalarRepl(AI) && isSafeAllocaToScalarRepl(AI)) { 1492 DoScalarReplacement(AI, WorkList); 1493 Changed = true; 1494 continue; 1495 } 1496 1497 // If we can turn this aggregate value (potentially with casts) into a 1498 // simple scalar value that can be mem2reg'd into a register value. 1499 // IsNotTrivial tracks whether this is something that mem2reg could have 1500 // promoted itself. If so, we don't want to transform it needlessly. Note 1501 // that we can't just check based on the type: the alloca may be of an i32 1502 // but that has pointer arithmetic to set byte 3 of it or something. 1503 if (AllocaInst *NewAI = 1504 ConvertToScalarInfo((unsigned)AllocaSize, *TD).TryConvert(AI)) { 1505 NewAI->takeName(AI); 1506 AI->eraseFromParent(); 1507 ++NumConverted; 1508 Changed = true; 1509 continue; 1510 } 1511 1512 // Otherwise, couldn't process this alloca. 1513 } 1514 1515 return Changed; 1516} 1517 1518/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl 1519/// predicate, do SROA now. 1520void SROA::DoScalarReplacement(AllocaInst *AI, 1521 std::vector<AllocaInst*> &WorkList) { 1522 DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n'); 1523 SmallVector<AllocaInst*, 32> ElementAllocas; 1524 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 1525 ElementAllocas.reserve(ST->getNumContainedTypes()); 1526 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { 1527 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 1528 AI->getAlignment(), 1529 AI->getName() + "." + Twine(i), AI); 1530 ElementAllocas.push_back(NA); 1531 WorkList.push_back(NA); // Add to worklist for recursive processing 1532 } 1533 } else { 1534 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); 1535 ElementAllocas.reserve(AT->getNumElements()); 1536 const Type *ElTy = AT->getElementType(); 1537 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 1538 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(), 1539 AI->getName() + "." + Twine(i), AI); 1540 ElementAllocas.push_back(NA); 1541 WorkList.push_back(NA); // Add to worklist for recursive processing 1542 } 1543 } 1544 1545 // Now that we have created the new alloca instructions, rewrite all the 1546 // uses of the old alloca. 1547 RewriteForScalarRepl(AI, AI, 0, ElementAllocas); 1548 1549 // Now erase any instructions that were made dead while rewriting the alloca. 1550 DeleteDeadInstructions(); 1551 AI->eraseFromParent(); 1552 1553 ++NumReplaced; 1554} 1555 1556/// DeleteDeadInstructions - Erase instructions on the DeadInstrs list, 1557/// recursively including all their operands that become trivially dead. 1558void SROA::DeleteDeadInstructions() { 1559 while (!DeadInsts.empty()) { 1560 Instruction *I = cast<Instruction>(DeadInsts.pop_back_val()); 1561 1562 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) 1563 if (Instruction *U = dyn_cast<Instruction>(*OI)) { 1564 // Zero out the operand and see if it becomes trivially dead. 1565 // (But, don't add allocas to the dead instruction list -- they are 1566 // already on the worklist and will be deleted separately.) 1567 *OI = 0; 1568 if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U)) 1569 DeadInsts.push_back(U); 1570 } 1571 1572 I->eraseFromParent(); 1573 } 1574} 1575 1576/// isSafeForScalarRepl - Check if instruction I is a safe use with regard to 1577/// performing scalar replacement of alloca AI. The results are flagged in 1578/// the Info parameter. Offset indicates the position within AI that is 1579/// referenced by this instruction. 1580void SROA::isSafeForScalarRepl(Instruction *I, uint64_t Offset, 1581 AllocaInfo &Info) { 1582 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 1583 Instruction *User = cast<Instruction>(*UI); 1584 1585 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1586 isSafeForScalarRepl(BC, Offset, Info); 1587 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1588 uint64_t GEPOffset = Offset; 1589 isSafeGEP(GEPI, GEPOffset, Info); 1590 if (!Info.isUnsafe) 1591 isSafeForScalarRepl(GEPI, GEPOffset, Info); 1592 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 1593 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 1594 if (Length == 0) 1595 return MarkUnsafe(Info, User); 1596 isSafeMemAccess(Offset, Length->getZExtValue(), 0, 1597 UI.getOperandNo() == 0, Info, MI, 1598 true /*AllowWholeAccess*/); 1599 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1600 if (LI->isVolatile()) 1601 return MarkUnsafe(Info, User); 1602 const Type *LIType = LI->getType(); 1603 isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType), 1604 LIType, false, Info, LI, true /*AllowWholeAccess*/); 1605 Info.hasALoadOrStore = true; 1606 1607 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1608 // Store is ok if storing INTO the pointer, not storing the pointer 1609 if (SI->isVolatile() || SI->getOperand(0) == I) 1610 return MarkUnsafe(Info, User); 1611 1612 const Type *SIType = SI->getOperand(0)->getType(); 1613 isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType), 1614 SIType, true, Info, SI, true /*AllowWholeAccess*/); 1615 Info.hasALoadOrStore = true; 1616 } else if (isa<PHINode>(User) || isa<SelectInst>(User)) { 1617 isSafePHISelectUseForScalarRepl(User, Offset, Info); 1618 } else { 1619 return MarkUnsafe(Info, User); 1620 } 1621 if (Info.isUnsafe) return; 1622 } 1623} 1624 1625 1626/// isSafePHIUseForScalarRepl - If we see a PHI node or select using a pointer 1627/// derived from the alloca, we can often still split the alloca into elements. 1628/// This is useful if we have a large alloca where one element is phi'd 1629/// together somewhere: we can SRoA and promote all the other elements even if 1630/// we end up not being able to promote this one. 1631/// 1632/// All we require is that the uses of the PHI do not index into other parts of 1633/// the alloca. The most important use case for this is single load and stores 1634/// that are PHI'd together, which can happen due to code sinking. 1635void SROA::isSafePHISelectUseForScalarRepl(Instruction *I, uint64_t Offset, 1636 AllocaInfo &Info) { 1637 // If we've already checked this PHI, don't do it again. 1638 if (PHINode *PN = dyn_cast<PHINode>(I)) 1639 if (!Info.CheckedPHIs.insert(PN)) 1640 return; 1641 1642 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 1643 Instruction *User = cast<Instruction>(*UI); 1644 1645 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1646 isSafePHISelectUseForScalarRepl(BC, Offset, Info); 1647 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1648 // Only allow "bitcast" GEPs for simplicity. We could generalize this, 1649 // but would have to prove that we're staying inside of an element being 1650 // promoted. 1651 if (!GEPI->hasAllZeroIndices()) 1652 return MarkUnsafe(Info, User); 1653 isSafePHISelectUseForScalarRepl(GEPI, Offset, Info); 1654 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1655 if (LI->isVolatile()) 1656 return MarkUnsafe(Info, User); 1657 const Type *LIType = LI->getType(); 1658 isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType), 1659 LIType, false, Info, LI, false /*AllowWholeAccess*/); 1660 Info.hasALoadOrStore = true; 1661 1662 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1663 // Store is ok if storing INTO the pointer, not storing the pointer 1664 if (SI->isVolatile() || SI->getOperand(0) == I) 1665 return MarkUnsafe(Info, User); 1666 1667 const Type *SIType = SI->getOperand(0)->getType(); 1668 isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType), 1669 SIType, true, Info, SI, false /*AllowWholeAccess*/); 1670 Info.hasALoadOrStore = true; 1671 } else if (isa<PHINode>(User) || isa<SelectInst>(User)) { 1672 isSafePHISelectUseForScalarRepl(User, Offset, Info); 1673 } else { 1674 return MarkUnsafe(Info, User); 1675 } 1676 if (Info.isUnsafe) return; 1677 } 1678} 1679 1680/// isSafeGEP - Check if a GEP instruction can be handled for scalar 1681/// replacement. It is safe when all the indices are constant, in-bounds 1682/// references, and when the resulting offset corresponds to an element within 1683/// the alloca type. The results are flagged in the Info parameter. Upon 1684/// return, Offset is adjusted as specified by the GEP indices. 1685void SROA::isSafeGEP(GetElementPtrInst *GEPI, 1686 uint64_t &Offset, AllocaInfo &Info) { 1687 gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI); 1688 if (GEPIt == E) 1689 return; 1690 1691 // Walk through the GEP type indices, checking the types that this indexes 1692 // into. 1693 for (; GEPIt != E; ++GEPIt) { 1694 // Ignore struct elements, no extra checking needed for these. 1695 if ((*GEPIt)->isStructTy()) 1696 continue; 1697 1698 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand()); 1699 if (!IdxVal) 1700 return MarkUnsafe(Info, GEPI); 1701 } 1702 1703 // Compute the offset due to this GEP and check if the alloca has a 1704 // component element at that offset. 1705 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 1706 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 1707 &Indices[0], Indices.size()); 1708 if (!TypeHasComponent(Info.AI->getAllocatedType(), Offset, 0)) 1709 MarkUnsafe(Info, GEPI); 1710} 1711 1712/// isHomogeneousAggregate - Check if type T is a struct or array containing 1713/// elements of the same type (which is always true for arrays). If so, 1714/// return true with NumElts and EltTy set to the number of elements and the 1715/// element type, respectively. 1716static bool isHomogeneousAggregate(const Type *T, unsigned &NumElts, 1717 const Type *&EltTy) { 1718 if (const ArrayType *AT = dyn_cast<ArrayType>(T)) { 1719 NumElts = AT->getNumElements(); 1720 EltTy = (NumElts == 0 ? 0 : AT->getElementType()); 1721 return true; 1722 } 1723 if (const StructType *ST = dyn_cast<StructType>(T)) { 1724 NumElts = ST->getNumContainedTypes(); 1725 EltTy = (NumElts == 0 ? 0 : ST->getContainedType(0)); 1726 for (unsigned n = 1; n < NumElts; ++n) { 1727 if (ST->getContainedType(n) != EltTy) 1728 return false; 1729 } 1730 return true; 1731 } 1732 return false; 1733} 1734 1735/// isCompatibleAggregate - Check if T1 and T2 are either the same type or are 1736/// "homogeneous" aggregates with the same element type and number of elements. 1737static bool isCompatibleAggregate(const Type *T1, const Type *T2) { 1738 if (T1 == T2) 1739 return true; 1740 1741 unsigned NumElts1, NumElts2; 1742 const Type *EltTy1, *EltTy2; 1743 if (isHomogeneousAggregate(T1, NumElts1, EltTy1) && 1744 isHomogeneousAggregate(T2, NumElts2, EltTy2) && 1745 NumElts1 == NumElts2 && 1746 EltTy1 == EltTy2) 1747 return true; 1748 1749 return false; 1750} 1751 1752/// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI 1753/// alloca or has an offset and size that corresponds to a component element 1754/// within it. The offset checked here may have been formed from a GEP with a 1755/// pointer bitcasted to a different type. 1756/// 1757/// If AllowWholeAccess is true, then this allows uses of the entire alloca as a 1758/// unit. If false, it only allows accesses known to be in a single element. 1759void SROA::isSafeMemAccess(uint64_t Offset, uint64_t MemSize, 1760 const Type *MemOpType, bool isStore, 1761 AllocaInfo &Info, Instruction *TheAccess, 1762 bool AllowWholeAccess) { 1763 // Check if this is a load/store of the entire alloca. 1764 if (Offset == 0 && AllowWholeAccess && 1765 MemSize == TD->getTypeAllocSize(Info.AI->getAllocatedType())) { 1766 // This can be safe for MemIntrinsics (where MemOpType is 0) and integer 1767 // loads/stores (which are essentially the same as the MemIntrinsics with 1768 // regard to copying padding between elements). But, if an alloca is 1769 // flagged as both a source and destination of such operations, we'll need 1770 // to check later for padding between elements. 1771 if (!MemOpType || MemOpType->isIntegerTy()) { 1772 if (isStore) 1773 Info.isMemCpyDst = true; 1774 else 1775 Info.isMemCpySrc = true; 1776 return; 1777 } 1778 // This is also safe for references using a type that is compatible with 1779 // the type of the alloca, so that loads/stores can be rewritten using 1780 // insertvalue/extractvalue. 1781 if (isCompatibleAggregate(MemOpType, Info.AI->getAllocatedType())) { 1782 Info.hasSubelementAccess = true; 1783 return; 1784 } 1785 } 1786 // Check if the offset/size correspond to a component within the alloca type. 1787 const Type *T = Info.AI->getAllocatedType(); 1788 if (TypeHasComponent(T, Offset, MemSize)) { 1789 Info.hasSubelementAccess = true; 1790 return; 1791 } 1792 1793 return MarkUnsafe(Info, TheAccess); 1794} 1795 1796/// TypeHasComponent - Return true if T has a component type with the 1797/// specified offset and size. If Size is zero, do not check the size. 1798bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) { 1799 const Type *EltTy; 1800 uint64_t EltSize; 1801 if (const StructType *ST = dyn_cast<StructType>(T)) { 1802 const StructLayout *Layout = TD->getStructLayout(ST); 1803 unsigned EltIdx = Layout->getElementContainingOffset(Offset); 1804 EltTy = ST->getContainedType(EltIdx); 1805 EltSize = TD->getTypeAllocSize(EltTy); 1806 Offset -= Layout->getElementOffset(EltIdx); 1807 } else if (const ArrayType *AT = dyn_cast<ArrayType>(T)) { 1808 EltTy = AT->getElementType(); 1809 EltSize = TD->getTypeAllocSize(EltTy); 1810 if (Offset >= AT->getNumElements() * EltSize) 1811 return false; 1812 Offset %= EltSize; 1813 } else { 1814 return false; 1815 } 1816 if (Offset == 0 && (Size == 0 || EltSize == Size)) 1817 return true; 1818 // Check if the component spans multiple elements. 1819 if (Offset + Size > EltSize) 1820 return false; 1821 return TypeHasComponent(EltTy, Offset, Size); 1822} 1823 1824/// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite 1825/// the instruction I, which references it, to use the separate elements. 1826/// Offset indicates the position within AI that is referenced by this 1827/// instruction. 1828void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 1829 SmallVector<AllocaInst*, 32> &NewElts) { 1830 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E;) { 1831 Use &TheUse = UI.getUse(); 1832 Instruction *User = cast<Instruction>(*UI++); 1833 1834 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1835 RewriteBitCast(BC, AI, Offset, NewElts); 1836 continue; 1837 } 1838 1839 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1840 RewriteGEP(GEPI, AI, Offset, NewElts); 1841 continue; 1842 } 1843 1844 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 1845 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 1846 uint64_t MemSize = Length->getZExtValue(); 1847 if (Offset == 0 && 1848 MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) 1849 RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts); 1850 // Otherwise the intrinsic can only touch a single element and the 1851 // address operand will be updated, so nothing else needs to be done. 1852 continue; 1853 } 1854 1855 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1856 const Type *LIType = LI->getType(); 1857 1858 if (isCompatibleAggregate(LIType, AI->getAllocatedType())) { 1859 // Replace: 1860 // %res = load { i32, i32 }* %alloc 1861 // with: 1862 // %load.0 = load i32* %alloc.0 1863 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0 1864 // %load.1 = load i32* %alloc.1 1865 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1 1866 // (Also works for arrays instead of structs) 1867 Value *Insert = UndefValue::get(LIType); 1868 IRBuilder<> Builder(LI); 1869 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1870 Value *Load = Builder.CreateLoad(NewElts[i], "load"); 1871 Insert = Builder.CreateInsertValue(Insert, Load, i, "insert"); 1872 } 1873 LI->replaceAllUsesWith(Insert); 1874 DeadInsts.push_back(LI); 1875 } else if (LIType->isIntegerTy() && 1876 TD->getTypeAllocSize(LIType) == 1877 TD->getTypeAllocSize(AI->getAllocatedType())) { 1878 // If this is a load of the entire alloca to an integer, rewrite it. 1879 RewriteLoadUserOfWholeAlloca(LI, AI, NewElts); 1880 } 1881 continue; 1882 } 1883 1884 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1885 Value *Val = SI->getOperand(0); 1886 const Type *SIType = Val->getType(); 1887 if (isCompatibleAggregate(SIType, AI->getAllocatedType())) { 1888 // Replace: 1889 // store { i32, i32 } %val, { i32, i32 }* %alloc 1890 // with: 1891 // %val.0 = extractvalue { i32, i32 } %val, 0 1892 // store i32 %val.0, i32* %alloc.0 1893 // %val.1 = extractvalue { i32, i32 } %val, 1 1894 // store i32 %val.1, i32* %alloc.1 1895 // (Also works for arrays instead of structs) 1896 IRBuilder<> Builder(SI); 1897 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1898 Value *Extract = Builder.CreateExtractValue(Val, i, Val->getName()); 1899 Builder.CreateStore(Extract, NewElts[i]); 1900 } 1901 DeadInsts.push_back(SI); 1902 } else if (SIType->isIntegerTy() && 1903 TD->getTypeAllocSize(SIType) == 1904 TD->getTypeAllocSize(AI->getAllocatedType())) { 1905 // If this is a store of the entire alloca from an integer, rewrite it. 1906 RewriteStoreUserOfWholeAlloca(SI, AI, NewElts); 1907 } 1908 continue; 1909 } 1910 1911 if (isa<SelectInst>(User) || isa<PHINode>(User)) { 1912 // If we have a PHI user of the alloca itself (as opposed to a GEP or 1913 // bitcast) we have to rewrite it. GEP and bitcast uses will be RAUW'd to 1914 // the new pointer. 1915 if (!isa<AllocaInst>(I)) continue; 1916 1917 assert(Offset == 0 && NewElts[0] && 1918 "Direct alloca use should have a zero offset"); 1919 1920 // If we have a use of the alloca, we know the derived uses will be 1921 // utilizing just the first element of the scalarized result. Insert a 1922 // bitcast of the first alloca before the user as required. 1923 AllocaInst *NewAI = NewElts[0]; 1924 BitCastInst *BCI = new BitCastInst(NewAI, AI->getType(), "", NewAI); 1925 NewAI->moveBefore(BCI); 1926 TheUse = BCI; 1927 continue; 1928 } 1929 } 1930} 1931 1932/// RewriteBitCast - Update a bitcast reference to the alloca being replaced 1933/// and recursively continue updating all of its uses. 1934void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 1935 SmallVector<AllocaInst*, 32> &NewElts) { 1936 RewriteForScalarRepl(BC, AI, Offset, NewElts); 1937 if (BC->getOperand(0) != AI) 1938 return; 1939 1940 // The bitcast references the original alloca. Replace its uses with 1941 // references to the first new element alloca. 1942 Instruction *Val = NewElts[0]; 1943 if (Val->getType() != BC->getDestTy()) { 1944 Val = new BitCastInst(Val, BC->getDestTy(), "", BC); 1945 Val->takeName(BC); 1946 } 1947 BC->replaceAllUsesWith(Val); 1948 DeadInsts.push_back(BC); 1949} 1950 1951/// FindElementAndOffset - Return the index of the element containing Offset 1952/// within the specified type, which must be either a struct or an array. 1953/// Sets T to the type of the element and Offset to the offset within that 1954/// element. IdxTy is set to the type of the index result to be used in a 1955/// GEP instruction. 1956uint64_t SROA::FindElementAndOffset(const Type *&T, uint64_t &Offset, 1957 const Type *&IdxTy) { 1958 uint64_t Idx = 0; 1959 if (const StructType *ST = dyn_cast<StructType>(T)) { 1960 const StructLayout *Layout = TD->getStructLayout(ST); 1961 Idx = Layout->getElementContainingOffset(Offset); 1962 T = ST->getContainedType(Idx); 1963 Offset -= Layout->getElementOffset(Idx); 1964 IdxTy = Type::getInt32Ty(T->getContext()); 1965 return Idx; 1966 } 1967 const ArrayType *AT = cast<ArrayType>(T); 1968 T = AT->getElementType(); 1969 uint64_t EltSize = TD->getTypeAllocSize(T); 1970 Idx = Offset / EltSize; 1971 Offset -= Idx * EltSize; 1972 IdxTy = Type::getInt64Ty(T->getContext()); 1973 return Idx; 1974} 1975 1976/// RewriteGEP - Check if this GEP instruction moves the pointer across 1977/// elements of the alloca that are being split apart, and if so, rewrite 1978/// the GEP to be relative to the new element. 1979void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 1980 SmallVector<AllocaInst*, 32> &NewElts) { 1981 uint64_t OldOffset = Offset; 1982 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 1983 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 1984 &Indices[0], Indices.size()); 1985 1986 RewriteForScalarRepl(GEPI, AI, Offset, NewElts); 1987 1988 const Type *T = AI->getAllocatedType(); 1989 const Type *IdxTy; 1990 uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy); 1991 if (GEPI->getOperand(0) == AI) 1992 OldIdx = ~0ULL; // Force the GEP to be rewritten. 1993 1994 T = AI->getAllocatedType(); 1995 uint64_t EltOffset = Offset; 1996 uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy); 1997 1998 // If this GEP does not move the pointer across elements of the alloca 1999 // being split, then it does not needs to be rewritten. 2000 if (Idx == OldIdx) 2001 return; 2002 2003 const Type *i32Ty = Type::getInt32Ty(AI->getContext()); 2004 SmallVector<Value*, 8> NewArgs; 2005 NewArgs.push_back(Constant::getNullValue(i32Ty)); 2006 while (EltOffset != 0) { 2007 uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy); 2008 NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx)); 2009 } 2010 Instruction *Val = NewElts[Idx]; 2011 if (NewArgs.size() > 1) { 2012 Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(), 2013 NewArgs.end(), "", GEPI); 2014 Val->takeName(GEPI); 2015 } 2016 if (Val->getType() != GEPI->getType()) 2017 Val = new BitCastInst(Val, GEPI->getType(), Val->getName(), GEPI); 2018 GEPI->replaceAllUsesWith(Val); 2019 DeadInsts.push_back(GEPI); 2020} 2021 2022/// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI. 2023/// Rewrite it to copy or set the elements of the scalarized memory. 2024void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 2025 AllocaInst *AI, 2026 SmallVector<AllocaInst*, 32> &NewElts) { 2027 // If this is a memcpy/memmove, construct the other pointer as the 2028 // appropriate type. The "Other" pointer is the pointer that goes to memory 2029 // that doesn't have anything to do with the alloca that we are promoting. For 2030 // memset, this Value* stays null. 2031 Value *OtherPtr = 0; 2032 unsigned MemAlignment = MI->getAlignment(); 2033 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy 2034 if (Inst == MTI->getRawDest()) 2035 OtherPtr = MTI->getRawSource(); 2036 else { 2037 assert(Inst == MTI->getRawSource()); 2038 OtherPtr = MTI->getRawDest(); 2039 } 2040 } 2041 2042 // If there is an other pointer, we want to convert it to the same pointer 2043 // type as AI has, so we can GEP through it safely. 2044 if (OtherPtr) { 2045 unsigned AddrSpace = 2046 cast<PointerType>(OtherPtr->getType())->getAddressSpace(); 2047 2048 // Remove bitcasts and all-zero GEPs from OtherPtr. This is an 2049 // optimization, but it's also required to detect the corner case where 2050 // both pointer operands are referencing the same memory, and where 2051 // OtherPtr may be a bitcast or GEP that currently being rewritten. (This 2052 // function is only called for mem intrinsics that access the whole 2053 // aggregate, so non-zero GEPs are not an issue here.) 2054 OtherPtr = OtherPtr->stripPointerCasts(); 2055 2056 // Copying the alloca to itself is a no-op: just delete it. 2057 if (OtherPtr == AI || OtherPtr == NewElts[0]) { 2058 // This code will run twice for a no-op memcpy -- once for each operand. 2059 // Put only one reference to MI on the DeadInsts list. 2060 for (SmallVector<Value*, 32>::const_iterator I = DeadInsts.begin(), 2061 E = DeadInsts.end(); I != E; ++I) 2062 if (*I == MI) return; 2063 DeadInsts.push_back(MI); 2064 return; 2065 } 2066 2067 // If the pointer is not the right type, insert a bitcast to the right 2068 // type. 2069 const Type *NewTy = 2070 PointerType::get(AI->getType()->getElementType(), AddrSpace); 2071 2072 if (OtherPtr->getType() != NewTy) 2073 OtherPtr = new BitCastInst(OtherPtr, NewTy, OtherPtr->getName(), MI); 2074 } 2075 2076 // Process each element of the aggregate. 2077 bool SROADest = MI->getRawDest() == Inst; 2078 2079 Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext())); 2080 2081 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 2082 // If this is a memcpy/memmove, emit a GEP of the other element address. 2083 Value *OtherElt = 0; 2084 unsigned OtherEltAlign = MemAlignment; 2085 2086 if (OtherPtr) { 2087 Value *Idx[2] = { Zero, 2088 ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) }; 2089 OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2, 2090 OtherPtr->getName()+"."+Twine(i), 2091 MI); 2092 uint64_t EltOffset; 2093 const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType()); 2094 const Type *OtherTy = OtherPtrTy->getElementType(); 2095 if (const StructType *ST = dyn_cast<StructType>(OtherTy)) { 2096 EltOffset = TD->getStructLayout(ST)->getElementOffset(i); 2097 } else { 2098 const Type *EltTy = cast<SequentialType>(OtherTy)->getElementType(); 2099 EltOffset = TD->getTypeAllocSize(EltTy)*i; 2100 } 2101 2102 // The alignment of the other pointer is the guaranteed alignment of the 2103 // element, which is affected by both the known alignment of the whole 2104 // mem intrinsic and the alignment of the element. If the alignment of 2105 // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the 2106 // known alignment is just 4 bytes. 2107 OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset); 2108 } 2109 2110 Value *EltPtr = NewElts[i]; 2111 const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType(); 2112 2113 // If we got down to a scalar, insert a load or store as appropriate. 2114 if (EltTy->isSingleValueType()) { 2115 if (isa<MemTransferInst>(MI)) { 2116 if (SROADest) { 2117 // From Other to Alloca. 2118 Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI); 2119 new StoreInst(Elt, EltPtr, MI); 2120 } else { 2121 // From Alloca to Other. 2122 Value *Elt = new LoadInst(EltPtr, "tmp", MI); 2123 new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI); 2124 } 2125 continue; 2126 } 2127 assert(isa<MemSetInst>(MI)); 2128 2129 // If the stored element is zero (common case), just store a null 2130 // constant. 2131 Constant *StoreVal; 2132 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getArgOperand(1))) { 2133 if (CI->isZero()) { 2134 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0> 2135 } else { 2136 // If EltTy is a vector type, get the element type. 2137 const Type *ValTy = EltTy->getScalarType(); 2138 2139 // Construct an integer with the right value. 2140 unsigned EltSize = TD->getTypeSizeInBits(ValTy); 2141 APInt OneVal(EltSize, CI->getZExtValue()); 2142 APInt TotalVal(OneVal); 2143 // Set each byte. 2144 for (unsigned i = 0; 8*i < EltSize; ++i) { 2145 TotalVal = TotalVal.shl(8); 2146 TotalVal |= OneVal; 2147 } 2148 2149 // Convert the integer value to the appropriate type. 2150 StoreVal = ConstantInt::get(CI->getContext(), TotalVal); 2151 if (ValTy->isPointerTy()) 2152 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); 2153 else if (ValTy->isFloatingPointTy()) 2154 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy); 2155 assert(StoreVal->getType() == ValTy && "Type mismatch!"); 2156 2157 // If the requested value was a vector constant, create it. 2158 if (EltTy != ValTy) { 2159 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements(); 2160 SmallVector<Constant*, 16> Elts(NumElts, StoreVal); 2161 StoreVal = ConstantVector::get(Elts); 2162 } 2163 } 2164 new StoreInst(StoreVal, EltPtr, MI); 2165 continue; 2166 } 2167 // Otherwise, if we're storing a byte variable, use a memset call for 2168 // this element. 2169 } 2170 2171 unsigned EltSize = TD->getTypeAllocSize(EltTy); 2172 2173 IRBuilder<> Builder(MI); 2174 2175 // Finally, insert the meminst for this element. 2176 if (isa<MemSetInst>(MI)) { 2177 Builder.CreateMemSet(EltPtr, MI->getArgOperand(1), EltSize, 2178 MI->isVolatile()); 2179 } else { 2180 assert(isa<MemTransferInst>(MI)); 2181 Value *Dst = SROADest ? EltPtr : OtherElt; // Dest ptr 2182 Value *Src = SROADest ? OtherElt : EltPtr; // Src ptr 2183 2184 if (isa<MemCpyInst>(MI)) 2185 Builder.CreateMemCpy(Dst, Src, EltSize, OtherEltAlign,MI->isVolatile()); 2186 else 2187 Builder.CreateMemMove(Dst, Src, EltSize,OtherEltAlign,MI->isVolatile()); 2188 } 2189 } 2190 DeadInsts.push_back(MI); 2191} 2192 2193/// RewriteStoreUserOfWholeAlloca - We found a store of an integer that 2194/// overwrites the entire allocation. Extract out the pieces of the stored 2195/// integer and store them individually. 2196void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 2197 SmallVector<AllocaInst*, 32> &NewElts){ 2198 // Extract each element out of the integer according to its structure offset 2199 // and store the element value to the individual alloca. 2200 Value *SrcVal = SI->getOperand(0); 2201 const Type *AllocaEltTy = AI->getAllocatedType(); 2202 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 2203 2204 IRBuilder<> Builder(SI); 2205 2206 // Handle tail padding by extending the operand 2207 if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits) 2208 SrcVal = Builder.CreateZExt(SrcVal, 2209 IntegerType::get(SI->getContext(), AllocaSizeBits)); 2210 2211 DEBUG(dbgs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI 2212 << '\n'); 2213 2214 // There are two forms here: AI could be an array or struct. Both cases 2215 // have different ways to compute the element offset. 2216 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 2217 const StructLayout *Layout = TD->getStructLayout(EltSTy); 2218 2219 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 2220 // Get the number of bits to shift SrcVal to get the value. 2221 const Type *FieldTy = EltSTy->getElementType(i); 2222 uint64_t Shift = Layout->getElementOffsetInBits(i); 2223 2224 if (TD->isBigEndian()) 2225 Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy); 2226 2227 Value *EltVal = SrcVal; 2228 if (Shift) { 2229 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 2230 EltVal = Builder.CreateLShr(EltVal, ShiftVal, "sroa.store.elt"); 2231 } 2232 2233 // Truncate down to an integer of the right size. 2234 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 2235 2236 // Ignore zero sized fields like {}, they obviously contain no data. 2237 if (FieldSizeBits == 0) continue; 2238 2239 if (FieldSizeBits != AllocaSizeBits) 2240 EltVal = Builder.CreateTrunc(EltVal, 2241 IntegerType::get(SI->getContext(), FieldSizeBits)); 2242 Value *DestField = NewElts[i]; 2243 if (EltVal->getType() == FieldTy) { 2244 // Storing to an integer field of this size, just do it. 2245 } else if (FieldTy->isFloatingPointTy() || FieldTy->isVectorTy()) { 2246 // Bitcast to the right element type (for fp/vector values). 2247 EltVal = Builder.CreateBitCast(EltVal, FieldTy); 2248 } else { 2249 // Otherwise, bitcast the dest pointer (for aggregates). 2250 DestField = Builder.CreateBitCast(DestField, 2251 PointerType::getUnqual(EltVal->getType())); 2252 } 2253 new StoreInst(EltVal, DestField, SI); 2254 } 2255 2256 } else { 2257 const ArrayType *ATy = cast<ArrayType>(AllocaEltTy); 2258 const Type *ArrayEltTy = ATy->getElementType(); 2259 uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 2260 uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy); 2261 2262 uint64_t Shift; 2263 2264 if (TD->isBigEndian()) 2265 Shift = AllocaSizeBits-ElementOffset; 2266 else 2267 Shift = 0; 2268 2269 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 2270 // Ignore zero sized fields like {}, they obviously contain no data. 2271 if (ElementSizeBits == 0) continue; 2272 2273 Value *EltVal = SrcVal; 2274 if (Shift) { 2275 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 2276 EltVal = Builder.CreateLShr(EltVal, ShiftVal, "sroa.store.elt"); 2277 } 2278 2279 // Truncate down to an integer of the right size. 2280 if (ElementSizeBits != AllocaSizeBits) 2281 EltVal = Builder.CreateTrunc(EltVal, 2282 IntegerType::get(SI->getContext(), 2283 ElementSizeBits)); 2284 Value *DestField = NewElts[i]; 2285 if (EltVal->getType() == ArrayEltTy) { 2286 // Storing to an integer field of this size, just do it. 2287 } else if (ArrayEltTy->isFloatingPointTy() || 2288 ArrayEltTy->isVectorTy()) { 2289 // Bitcast to the right element type (for fp/vector values). 2290 EltVal = Builder.CreateBitCast(EltVal, ArrayEltTy); 2291 } else { 2292 // Otherwise, bitcast the dest pointer (for aggregates). 2293 DestField = Builder.CreateBitCast(DestField, 2294 PointerType::getUnqual(EltVal->getType())); 2295 } 2296 new StoreInst(EltVal, DestField, SI); 2297 2298 if (TD->isBigEndian()) 2299 Shift -= ElementOffset; 2300 else 2301 Shift += ElementOffset; 2302 } 2303 } 2304 2305 DeadInsts.push_back(SI); 2306} 2307 2308/// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to 2309/// an integer. Load the individual pieces to form the aggregate value. 2310void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 2311 SmallVector<AllocaInst*, 32> &NewElts) { 2312 // Extract each element out of the NewElts according to its structure offset 2313 // and form the result value. 2314 const Type *AllocaEltTy = AI->getAllocatedType(); 2315 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 2316 2317 DEBUG(dbgs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI 2318 << '\n'); 2319 2320 // There are two forms here: AI could be an array or struct. Both cases 2321 // have different ways to compute the element offset. 2322 const StructLayout *Layout = 0; 2323 uint64_t ArrayEltBitOffset = 0; 2324 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 2325 Layout = TD->getStructLayout(EltSTy); 2326 } else { 2327 const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType(); 2328 ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 2329 } 2330 2331 Value *ResultVal = 2332 Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits)); 2333 2334 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 2335 // Load the value from the alloca. If the NewElt is an aggregate, cast 2336 // the pointer to an integer of the same size before doing the load. 2337 Value *SrcField = NewElts[i]; 2338 const Type *FieldTy = 2339 cast<PointerType>(SrcField->getType())->getElementType(); 2340 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 2341 2342 // Ignore zero sized fields like {}, they obviously contain no data. 2343 if (FieldSizeBits == 0) continue; 2344 2345 const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(), 2346 FieldSizeBits); 2347 if (!FieldTy->isIntegerTy() && !FieldTy->isFloatingPointTy() && 2348 !FieldTy->isVectorTy()) 2349 SrcField = new BitCastInst(SrcField, 2350 PointerType::getUnqual(FieldIntTy), 2351 "", LI); 2352 SrcField = new LoadInst(SrcField, "sroa.load.elt", LI); 2353 2354 // If SrcField is a fp or vector of the right size but that isn't an 2355 // integer type, bitcast to an integer so we can shift it. 2356 if (SrcField->getType() != FieldIntTy) 2357 SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI); 2358 2359 // Zero extend the field to be the same size as the final alloca so that 2360 // we can shift and insert it. 2361 if (SrcField->getType() != ResultVal->getType()) 2362 SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI); 2363 2364 // Determine the number of bits to shift SrcField. 2365 uint64_t Shift; 2366 if (Layout) // Struct case. 2367 Shift = Layout->getElementOffsetInBits(i); 2368 else // Array case. 2369 Shift = i*ArrayEltBitOffset; 2370 2371 if (TD->isBigEndian()) 2372 Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth(); 2373 2374 if (Shift) { 2375 Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift); 2376 SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI); 2377 } 2378 2379 // Don't create an 'or x, 0' on the first iteration. 2380 if (!isa<Constant>(ResultVal) || 2381 !cast<Constant>(ResultVal)->isNullValue()) 2382 ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI); 2383 else 2384 ResultVal = SrcField; 2385 } 2386 2387 // Handle tail padding by truncating the result 2388 if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits) 2389 ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI); 2390 2391 LI->replaceAllUsesWith(ResultVal); 2392 DeadInsts.push_back(LI); 2393} 2394 2395/// HasPadding - Return true if the specified type has any structure or 2396/// alignment padding in between the elements that would be split apart 2397/// by SROA; return false otherwise. 2398static bool HasPadding(const Type *Ty, const TargetData &TD) { 2399 if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 2400 Ty = ATy->getElementType(); 2401 return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty); 2402 } 2403 2404 // SROA currently handles only Arrays and Structs. 2405 const StructType *STy = cast<StructType>(Ty); 2406 const StructLayout *SL = TD.getStructLayout(STy); 2407 unsigned PrevFieldBitOffset = 0; 2408 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 2409 unsigned FieldBitOffset = SL->getElementOffsetInBits(i); 2410 2411 // Check to see if there is any padding between this element and the 2412 // previous one. 2413 if (i) { 2414 unsigned PrevFieldEnd = 2415 PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1)); 2416 if (PrevFieldEnd < FieldBitOffset) 2417 return true; 2418 } 2419 PrevFieldBitOffset = FieldBitOffset; 2420 } 2421 // Check for tail padding. 2422 if (unsigned EltCount = STy->getNumElements()) { 2423 unsigned PrevFieldEnd = PrevFieldBitOffset + 2424 TD.getTypeSizeInBits(STy->getElementType(EltCount-1)); 2425 if (PrevFieldEnd < SL->getSizeInBits()) 2426 return true; 2427 } 2428 return false; 2429} 2430 2431/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of 2432/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, 2433/// or 1 if safe after canonicalization has been performed. 2434bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) { 2435 // Loop over the use list of the alloca. We can only transform it if all of 2436 // the users are safe to transform. 2437 AllocaInfo Info(AI); 2438 2439 isSafeForScalarRepl(AI, 0, Info); 2440 if (Info.isUnsafe) { 2441 DEBUG(dbgs() << "Cannot transform: " << *AI << '\n'); 2442 return false; 2443 } 2444 2445 // Okay, we know all the users are promotable. If the aggregate is a memcpy 2446 // source and destination, we have to be careful. In particular, the memcpy 2447 // could be moving around elements that live in structure padding of the LLVM 2448 // types, but may actually be used. In these cases, we refuse to promote the 2449 // struct. 2450 if (Info.isMemCpySrc && Info.isMemCpyDst && 2451 HasPadding(AI->getAllocatedType(), *TD)) 2452 return false; 2453 2454 // If the alloca never has an access to just *part* of it, but is accessed 2455 // via loads and stores, then we should use ConvertToScalarInfo to promote 2456 // the alloca instead of promoting each piece at a time and inserting fission 2457 // and fusion code. 2458 if (!Info.hasSubelementAccess && Info.hasALoadOrStore) { 2459 // If the struct/array just has one element, use basic SRoA. 2460 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 2461 if (ST->getNumElements() > 1) return false; 2462 } else { 2463 if (cast<ArrayType>(AI->getAllocatedType())->getNumElements() > 1) 2464 return false; 2465 } 2466 } 2467 2468 return true; 2469} 2470 2471 2472 2473/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to 2474/// some part of a constant global variable. This intentionally only accepts 2475/// constant expressions because we don't can't rewrite arbitrary instructions. 2476static bool PointsToConstantGlobal(Value *V) { 2477 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) 2478 return GV->isConstant(); 2479 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 2480 if (CE->getOpcode() == Instruction::BitCast || 2481 CE->getOpcode() == Instruction::GetElementPtr) 2482 return PointsToConstantGlobal(CE->getOperand(0)); 2483 return false; 2484} 2485 2486/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived) 2487/// pointer to an alloca. Ignore any reads of the pointer, return false if we 2488/// see any stores or other unknown uses. If we see pointer arithmetic, keep 2489/// track of whether it moves the pointer (with isOffset) but otherwise traverse 2490/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to 2491/// the alloca, and if the source pointer is a pointer to a constant global, we 2492/// can optimize this. 2493static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy, 2494 bool isOffset) { 2495 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 2496 User *U = cast<Instruction>(*UI); 2497 2498 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 2499 // Ignore non-volatile loads, they are always ok. 2500 if (LI->isVolatile()) return false; 2501 continue; 2502 } 2503 2504 if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) { 2505 // If uses of the bitcast are ok, we are ok. 2506 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) 2507 return false; 2508 continue; 2509 } 2510 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 2511 // If the GEP has all zero indices, it doesn't offset the pointer. If it 2512 // doesn't, it does. 2513 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy, 2514 isOffset || !GEP->hasAllZeroIndices())) 2515 return false; 2516 continue; 2517 } 2518 2519 if (CallSite CS = U) { 2520 // If this is the function being called then we treat it like a load and 2521 // ignore it. 2522 if (CS.isCallee(UI)) 2523 continue; 2524 2525 // If this is a readonly/readnone call site, then we know it is just a 2526 // load (but one that potentially returns the value itself), so we can 2527 // ignore it if we know that the value isn't captured. 2528 unsigned ArgNo = CS.getArgumentNo(UI); 2529 if (CS.onlyReadsMemory() && 2530 (CS.getInstruction()->use_empty() || 2531 CS.paramHasAttr(ArgNo+1, Attribute::NoCapture))) 2532 continue; 2533 2534 // If this is being passed as a byval argument, the caller is making a 2535 // copy, so it is only a read of the alloca. 2536 if (CS.paramHasAttr(ArgNo+1, Attribute::ByVal)) 2537 continue; 2538 } 2539 2540 // If this is isn't our memcpy/memmove, reject it as something we can't 2541 // handle. 2542 MemTransferInst *MI = dyn_cast<MemTransferInst>(U); 2543 if (MI == 0) 2544 return false; 2545 2546 // If the transfer is using the alloca as a source of the transfer, then 2547 // ignore it since it is a load (unless the transfer is volatile). 2548 if (UI.getOperandNo() == 1) { 2549 if (MI->isVolatile()) return false; 2550 continue; 2551 } 2552 2553 // If we already have seen a copy, reject the second one. 2554 if (TheCopy) return false; 2555 2556 // If the pointer has been offset from the start of the alloca, we can't 2557 // safely handle this. 2558 if (isOffset) return false; 2559 2560 // If the memintrinsic isn't using the alloca as the dest, reject it. 2561 if (UI.getOperandNo() != 0) return false; 2562 2563 // If the source of the memcpy/move is not a constant global, reject it. 2564 if (!PointsToConstantGlobal(MI->getSource())) 2565 return false; 2566 2567 // Otherwise, the transform is safe. Remember the copy instruction. 2568 TheCopy = MI; 2569 } 2570 return true; 2571} 2572 2573/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only 2574/// modified by a copy from a constant global. If we can prove this, we can 2575/// replace any uses of the alloca with uses of the global directly. 2576MemTransferInst *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) { 2577 MemTransferInst *TheCopy = 0; 2578 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) 2579 return TheCopy; 2580 return 0; 2581} 2582