ScalarReplAggregates.cpp revision 2ca5c8644e6c35b3a7910a576ed89cddb7b82c3b
1//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This transformation implements the well known scalar replacement of 11// aggregates transformation. This xform breaks up alloca instructions of 12// aggregate type (structure or array) into individual alloca instructions for 13// each member (if possible). Then, if possible, it transforms the individual 14// alloca instructions into nice clean scalar SSA form. 15// 16// This combines a simple SRoA algorithm with the Mem2Reg algorithm because 17// often interact, especially for C++ programs. As such, iterating between 18// SRoA, then Mem2Reg until we run out of things to promote works well. 19// 20//===----------------------------------------------------------------------===// 21 22#define DEBUG_TYPE "scalarrepl" 23#include "llvm/Transforms/Scalar.h" 24#include "llvm/Constants.h" 25#include "llvm/DerivedTypes.h" 26#include "llvm/Function.h" 27#include "llvm/GlobalVariable.h" 28#include "llvm/Instructions.h" 29#include "llvm/IntrinsicInst.h" 30#include "llvm/LLVMContext.h" 31#include "llvm/Module.h" 32#include "llvm/Pass.h" 33#include "llvm/Analysis/Dominators.h" 34#include "llvm/Analysis/Loads.h" 35#include "llvm/Analysis/ValueTracking.h" 36#include "llvm/Target/TargetData.h" 37#include "llvm/Transforms/Utils/PromoteMemToReg.h" 38#include "llvm/Transforms/Utils/Local.h" 39#include "llvm/Transforms/Utils/SSAUpdater.h" 40#include "llvm/Support/CallSite.h" 41#include "llvm/Support/Debug.h" 42#include "llvm/Support/ErrorHandling.h" 43#include "llvm/Support/GetElementPtrTypeIterator.h" 44#include "llvm/Support/IRBuilder.h" 45#include "llvm/Support/MathExtras.h" 46#include "llvm/Support/raw_ostream.h" 47#include "llvm/ADT/SetVector.h" 48#include "llvm/ADT/SmallVector.h" 49#include "llvm/ADT/Statistic.h" 50using namespace llvm; 51 52STATISTIC(NumReplaced, "Number of allocas broken up"); 53STATISTIC(NumPromoted, "Number of allocas promoted"); 54STATISTIC(NumAdjusted, "Number of scalar allocas adjusted to allow promotion"); 55STATISTIC(NumConverted, "Number of aggregates converted to scalar"); 56STATISTIC(NumGlobals, "Number of allocas copied from constant global"); 57 58namespace { 59 struct SROA : public FunctionPass { 60 SROA(int T, bool hasDT, char &ID) 61 : FunctionPass(ID), HasDomTree(hasDT) { 62 if (T == -1) 63 SRThreshold = 128; 64 else 65 SRThreshold = T; 66 } 67 68 bool runOnFunction(Function &F); 69 70 bool performScalarRepl(Function &F); 71 bool performPromotion(Function &F); 72 73 private: 74 bool HasDomTree; 75 TargetData *TD; 76 77 /// DeadInsts - Keep track of instructions we have made dead, so that 78 /// we can remove them after we are done working. 79 SmallVector<Value*, 32> DeadInsts; 80 81 /// AllocaInfo - When analyzing uses of an alloca instruction, this captures 82 /// information about the uses. All these fields are initialized to false 83 /// and set to true when something is learned. 84 struct AllocaInfo { 85 /// The alloca to promote. 86 AllocaInst *AI; 87 88 /// CheckedPHIs - This is a set of verified PHI nodes, to prevent infinite 89 /// looping and avoid redundant work. 90 SmallPtrSet<PHINode*, 8> CheckedPHIs; 91 92 /// isUnsafe - This is set to true if the alloca cannot be SROA'd. 93 bool isUnsafe : 1; 94 95 /// isMemCpySrc - This is true if this aggregate is memcpy'd from. 96 bool isMemCpySrc : 1; 97 98 /// isMemCpyDst - This is true if this aggregate is memcpy'd into. 99 bool isMemCpyDst : 1; 100 101 /// hasSubelementAccess - This is true if a subelement of the alloca is 102 /// ever accessed, or false if the alloca is only accessed with mem 103 /// intrinsics or load/store that only access the entire alloca at once. 104 bool hasSubelementAccess : 1; 105 106 /// hasALoadOrStore - This is true if there are any loads or stores to it. 107 /// The alloca may just be accessed with memcpy, for example, which would 108 /// not set this. 109 bool hasALoadOrStore : 1; 110 111 explicit AllocaInfo(AllocaInst *ai) 112 : AI(ai), isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false), 113 hasSubelementAccess(false), hasALoadOrStore(false) {} 114 }; 115 116 unsigned SRThreshold; 117 118 void MarkUnsafe(AllocaInfo &I, Instruction *User) { 119 I.isUnsafe = true; 120 DEBUG(dbgs() << " Transformation preventing inst: " << *User << '\n'); 121 } 122 123 bool isSafeAllocaToScalarRepl(AllocaInst *AI); 124 125 void isSafeForScalarRepl(Instruction *I, uint64_t Offset, AllocaInfo &Info); 126 void isSafePHISelectUseForScalarRepl(Instruction *User, uint64_t Offset, 127 AllocaInfo &Info); 128 void isSafeGEP(GetElementPtrInst *GEPI, uint64_t &Offset, AllocaInfo &Info); 129 void isSafeMemAccess(uint64_t Offset, uint64_t MemSize, 130 const Type *MemOpType, bool isStore, AllocaInfo &Info, 131 Instruction *TheAccess, bool AllowWholeAccess); 132 bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size); 133 uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset, 134 const Type *&IdxTy); 135 136 void DoScalarReplacement(AllocaInst *AI, 137 std::vector<AllocaInst*> &WorkList); 138 void DeleteDeadInstructions(); 139 140 void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 141 SmallVector<AllocaInst*, 32> &NewElts); 142 void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 143 SmallVector<AllocaInst*, 32> &NewElts); 144 void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 145 SmallVector<AllocaInst*, 32> &NewElts); 146 void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 147 AllocaInst *AI, 148 SmallVector<AllocaInst*, 32> &NewElts); 149 void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 150 SmallVector<AllocaInst*, 32> &NewElts); 151 void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 152 SmallVector<AllocaInst*, 32> &NewElts); 153 154 static MemTransferInst *isOnlyCopiedFromConstantGlobal(AllocaInst *AI); 155 }; 156 157 // SROA_DT - SROA that uses DominatorTree. 158 struct SROA_DT : public SROA { 159 static char ID; 160 public: 161 SROA_DT(int T = -1) : SROA(T, true, ID) { 162 initializeSROA_DTPass(*PassRegistry::getPassRegistry()); 163 } 164 165 // getAnalysisUsage - This pass does not require any passes, but we know it 166 // will not alter the CFG, so say so. 167 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 168 AU.addRequired<DominatorTree>(); 169 AU.setPreservesCFG(); 170 } 171 }; 172 173 // SROA_SSAUp - SROA that uses SSAUpdater. 174 struct SROA_SSAUp : public SROA { 175 static char ID; 176 public: 177 SROA_SSAUp(int T = -1) : SROA(T, false, ID) { 178 initializeSROA_SSAUpPass(*PassRegistry::getPassRegistry()); 179 } 180 181 // getAnalysisUsage - This pass does not require any passes, but we know it 182 // will not alter the CFG, so say so. 183 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 184 AU.setPreservesCFG(); 185 } 186 }; 187 188} 189 190char SROA_DT::ID = 0; 191char SROA_SSAUp::ID = 0; 192 193INITIALIZE_PASS_BEGIN(SROA_DT, "scalarrepl", 194 "Scalar Replacement of Aggregates (DT)", false, false) 195INITIALIZE_PASS_DEPENDENCY(DominatorTree) 196INITIALIZE_PASS_END(SROA_DT, "scalarrepl", 197 "Scalar Replacement of Aggregates (DT)", false, false) 198 199INITIALIZE_PASS_BEGIN(SROA_SSAUp, "scalarrepl-ssa", 200 "Scalar Replacement of Aggregates (SSAUp)", false, false) 201INITIALIZE_PASS_END(SROA_SSAUp, "scalarrepl-ssa", 202 "Scalar Replacement of Aggregates (SSAUp)", false, false) 203 204// Public interface to the ScalarReplAggregates pass 205FunctionPass *llvm::createScalarReplAggregatesPass(int Threshold, 206 bool UseDomTree) { 207 if (UseDomTree) 208 return new SROA_DT(Threshold); 209 return new SROA_SSAUp(Threshold); 210} 211 212 213//===----------------------------------------------------------------------===// 214// Convert To Scalar Optimization. 215//===----------------------------------------------------------------------===// 216 217namespace { 218/// ConvertToScalarInfo - This class implements the "Convert To Scalar" 219/// optimization, which scans the uses of an alloca and determines if it can 220/// rewrite it in terms of a single new alloca that can be mem2reg'd. 221class ConvertToScalarInfo { 222 /// AllocaSize - The size of the alloca being considered. 223 unsigned AllocaSize; 224 const TargetData &TD; 225 226 /// IsNotTrivial - This is set to true if there is some access to the object 227 /// which means that mem2reg can't promote it. 228 bool IsNotTrivial; 229 230 /// VectorTy - This tracks the type that we should promote the vector to if 231 /// it is possible to turn it into a vector. This starts out null, and if it 232 /// isn't possible to turn into a vector type, it gets set to VoidTy. 233 const Type *VectorTy; 234 235 /// HadAVector - True if there is at least one vector access to the alloca. 236 /// We don't want to turn random arrays into vectors and use vector element 237 /// insert/extract, but if there are element accesses to something that is 238 /// also declared as a vector, we do want to promote to a vector. 239 bool HadAVector; 240 241public: 242 explicit ConvertToScalarInfo(unsigned Size, const TargetData &td) 243 : AllocaSize(Size), TD(td) { 244 IsNotTrivial = false; 245 VectorTy = 0; 246 HadAVector = false; 247 } 248 249 AllocaInst *TryConvert(AllocaInst *AI); 250 251private: 252 bool CanConvertToScalar(Value *V, uint64_t Offset); 253 void MergeInType(const Type *In, uint64_t Offset); 254 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset); 255 256 Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType, 257 uint64_t Offset, IRBuilder<> &Builder); 258 Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal, 259 uint64_t Offset, IRBuilder<> &Builder); 260}; 261} // end anonymous namespace. 262 263 264/// TryConvert - Analyze the specified alloca, and if it is safe to do so, 265/// rewrite it to be a new alloca which is mem2reg'able. This returns the new 266/// alloca if possible or null if not. 267AllocaInst *ConvertToScalarInfo::TryConvert(AllocaInst *AI) { 268 // If we can't convert this scalar, or if mem2reg can trivially do it, bail 269 // out. 270 if (!CanConvertToScalar(AI, 0) || !IsNotTrivial) 271 return 0; 272 273 // If we were able to find a vector type that can handle this with 274 // insert/extract elements, and if there was at least one use that had 275 // a vector type, promote this to a vector. We don't want to promote 276 // random stuff that doesn't use vectors (e.g. <9 x double>) because then 277 // we just get a lot of insert/extracts. If at least one vector is 278 // involved, then we probably really do have a union of vector/array. 279 const Type *NewTy; 280 if (VectorTy && VectorTy->isVectorTy() && HadAVector) { 281 DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = " 282 << *VectorTy << '\n'); 283 NewTy = VectorTy; // Use the vector type. 284 } else { 285 DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n"); 286 // Create and insert the integer alloca. 287 NewTy = IntegerType::get(AI->getContext(), AllocaSize*8); 288 } 289 AllocaInst *NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin()); 290 ConvertUsesToScalar(AI, NewAI, 0); 291 return NewAI; 292} 293 294/// MergeInType - Add the 'In' type to the accumulated vector type (VectorTy) 295/// so far at the offset specified by Offset (which is specified in bytes). 296/// 297/// There are two cases we handle here: 298/// 1) A union of vector types of the same size and potentially its elements. 299/// Here we turn element accesses into insert/extract element operations. 300/// This promotes a <4 x float> with a store of float to the third element 301/// into a <4 x float> that uses insert element. 302/// 2) A fully general blob of memory, which we turn into some (potentially 303/// large) integer type with extract and insert operations where the loads 304/// and stores would mutate the memory. We mark this by setting VectorTy 305/// to VoidTy. 306void ConvertToScalarInfo::MergeInType(const Type *In, uint64_t Offset) { 307 // If we already decided to turn this into a blob of integer memory, there is 308 // nothing to be done. 309 if (VectorTy && VectorTy->isVoidTy()) 310 return; 311 312 // If this could be contributing to a vector, analyze it. 313 314 // If the In type is a vector that is the same size as the alloca, see if it 315 // matches the existing VecTy. 316 if (const VectorType *VInTy = dyn_cast<VectorType>(In)) { 317 // Remember if we saw a vector type. 318 HadAVector = true; 319 320 if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) { 321 // If we're storing/loading a vector of the right size, allow it as a 322 // vector. If this the first vector we see, remember the type so that 323 // we know the element size. If this is a subsequent access, ignore it 324 // even if it is a differing type but the same size. Worst case we can 325 // bitcast the resultant vectors. 326 if (VectorTy == 0) 327 VectorTy = VInTy; 328 return; 329 } 330 } else if (In->isFloatTy() || In->isDoubleTy() || 331 (In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 && 332 isPowerOf2_32(In->getPrimitiveSizeInBits()))) { 333 // If we're accessing something that could be an element of a vector, see 334 // if the implied vector agrees with what we already have and if Offset is 335 // compatible with it. 336 unsigned EltSize = In->getPrimitiveSizeInBits()/8; 337 if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 && 338 (VectorTy == 0 || 339 cast<VectorType>(VectorTy)->getElementType() 340 ->getPrimitiveSizeInBits()/8 == EltSize)) { 341 if (VectorTy == 0) 342 VectorTy = VectorType::get(In, AllocaSize/EltSize); 343 return; 344 } 345 } 346 347 // Otherwise, we have a case that we can't handle with an optimized vector 348 // form. We can still turn this into a large integer. 349 VectorTy = Type::getVoidTy(In->getContext()); 350} 351 352/// CanConvertToScalar - V is a pointer. If we can convert the pointee and all 353/// its accesses to a single vector type, return true and set VecTy to 354/// the new type. If we could convert the alloca into a single promotable 355/// integer, return true but set VecTy to VoidTy. Further, if the use is not a 356/// completely trivial use that mem2reg could promote, set IsNotTrivial. Offset 357/// is the current offset from the base of the alloca being analyzed. 358/// 359/// If we see at least one access to the value that is as a vector type, set the 360/// SawVec flag. 361bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset) { 362 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 363 Instruction *User = cast<Instruction>(*UI); 364 365 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 366 // Don't break volatile loads. 367 if (LI->isVolatile()) 368 return false; 369 // Don't touch MMX operations. 370 if (LI->getType()->isX86_MMXTy()) 371 return false; 372 MergeInType(LI->getType(), Offset); 373 continue; 374 } 375 376 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 377 // Storing the pointer, not into the value? 378 if (SI->getOperand(0) == V || SI->isVolatile()) return false; 379 // Don't touch MMX operations. 380 if (SI->getOperand(0)->getType()->isX86_MMXTy()) 381 return false; 382 MergeInType(SI->getOperand(0)->getType(), Offset); 383 continue; 384 } 385 386 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { 387 IsNotTrivial = true; // Can't be mem2reg'd. 388 if (!CanConvertToScalar(BCI, Offset)) 389 return false; 390 continue; 391 } 392 393 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 394 // If this is a GEP with a variable indices, we can't handle it. 395 if (!GEP->hasAllConstantIndices()) 396 return false; 397 398 // Compute the offset that this GEP adds to the pointer. 399 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 400 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 401 &Indices[0], Indices.size()); 402 // See if all uses can be converted. 403 if (!CanConvertToScalar(GEP, Offset+GEPOffset)) 404 return false; 405 IsNotTrivial = true; // Can't be mem2reg'd. 406 continue; 407 } 408 409 // If this is a constant sized memset of a constant value (e.g. 0) we can 410 // handle it. 411 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 412 // Store of constant value and constant size. 413 if (!isa<ConstantInt>(MSI->getValue()) || 414 !isa<ConstantInt>(MSI->getLength())) 415 return false; 416 IsNotTrivial = true; // Can't be mem2reg'd. 417 continue; 418 } 419 420 // If this is a memcpy or memmove into or out of the whole allocation, we 421 // can handle it like a load or store of the scalar type. 422 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 423 ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()); 424 if (Len == 0 || Len->getZExtValue() != AllocaSize || Offset != 0) 425 return false; 426 427 IsNotTrivial = true; // Can't be mem2reg'd. 428 continue; 429 } 430 431 // Otherwise, we cannot handle this! 432 return false; 433 } 434 435 return true; 436} 437 438/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca 439/// directly. This happens when we are converting an "integer union" to a 440/// single integer scalar, or when we are converting a "vector union" to a 441/// vector with insert/extractelement instructions. 442/// 443/// Offset is an offset from the original alloca, in bits that need to be 444/// shifted to the right. By the end of this, there should be no uses of Ptr. 445void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, 446 uint64_t Offset) { 447 while (!Ptr->use_empty()) { 448 Instruction *User = cast<Instruction>(Ptr->use_back()); 449 450 if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 451 ConvertUsesToScalar(CI, NewAI, Offset); 452 CI->eraseFromParent(); 453 continue; 454 } 455 456 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 457 // Compute the offset that this GEP adds to the pointer. 458 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 459 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 460 &Indices[0], Indices.size()); 461 ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8); 462 GEP->eraseFromParent(); 463 continue; 464 } 465 466 IRBuilder<> Builder(User); 467 468 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 469 // The load is a bit extract from NewAI shifted right by Offset bits. 470 Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp"); 471 Value *NewLoadVal 472 = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder); 473 LI->replaceAllUsesWith(NewLoadVal); 474 LI->eraseFromParent(); 475 continue; 476 } 477 478 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 479 assert(SI->getOperand(0) != Ptr && "Consistency error!"); 480 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 481 Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset, 482 Builder); 483 Builder.CreateStore(New, NewAI); 484 SI->eraseFromParent(); 485 486 // If the load we just inserted is now dead, then the inserted store 487 // overwrote the entire thing. 488 if (Old->use_empty()) 489 Old->eraseFromParent(); 490 continue; 491 } 492 493 // If this is a constant sized memset of a constant value (e.g. 0) we can 494 // transform it into a store of the expanded constant value. 495 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 496 assert(MSI->getRawDest() == Ptr && "Consistency error!"); 497 unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue(); 498 if (NumBytes != 0) { 499 unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue(); 500 501 // Compute the value replicated the right number of times. 502 APInt APVal(NumBytes*8, Val); 503 504 // Splat the value if non-zero. 505 if (Val) 506 for (unsigned i = 1; i != NumBytes; ++i) 507 APVal |= APVal << 8; 508 509 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 510 Value *New = ConvertScalar_InsertValue( 511 ConstantInt::get(User->getContext(), APVal), 512 Old, Offset, Builder); 513 Builder.CreateStore(New, NewAI); 514 515 // If the load we just inserted is now dead, then the memset overwrote 516 // the entire thing. 517 if (Old->use_empty()) 518 Old->eraseFromParent(); 519 } 520 MSI->eraseFromParent(); 521 continue; 522 } 523 524 // If this is a memcpy or memmove into or out of the whole allocation, we 525 // can handle it like a load or store of the scalar type. 526 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 527 assert(Offset == 0 && "must be store to start of alloca"); 528 529 // If the source and destination are both to the same alloca, then this is 530 // a noop copy-to-self, just delete it. Otherwise, emit a load and store 531 // as appropriate. 532 AllocaInst *OrigAI = cast<AllocaInst>(GetUnderlyingObject(Ptr, &TD, 0)); 533 534 if (GetUnderlyingObject(MTI->getSource(), &TD, 0) != OrigAI) { 535 // Dest must be OrigAI, change this to be a load from the original 536 // pointer (bitcasted), then a store to our new alloca. 537 assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?"); 538 Value *SrcPtr = MTI->getSource(); 539 const PointerType* SPTy = cast<PointerType>(SrcPtr->getType()); 540 const PointerType* AIPTy = cast<PointerType>(NewAI->getType()); 541 if (SPTy->getAddressSpace() != AIPTy->getAddressSpace()) { 542 AIPTy = PointerType::get(AIPTy->getElementType(), 543 SPTy->getAddressSpace()); 544 } 545 SrcPtr = Builder.CreateBitCast(SrcPtr, AIPTy); 546 547 LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval"); 548 SrcVal->setAlignment(MTI->getAlignment()); 549 Builder.CreateStore(SrcVal, NewAI); 550 } else if (GetUnderlyingObject(MTI->getDest(), &TD, 0) != OrigAI) { 551 // Src must be OrigAI, change this to be a load from NewAI then a store 552 // through the original dest pointer (bitcasted). 553 assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?"); 554 LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval"); 555 556 const PointerType* DPTy = cast<PointerType>(MTI->getDest()->getType()); 557 const PointerType* AIPTy = cast<PointerType>(NewAI->getType()); 558 if (DPTy->getAddressSpace() != AIPTy->getAddressSpace()) { 559 AIPTy = PointerType::get(AIPTy->getElementType(), 560 DPTy->getAddressSpace()); 561 } 562 Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), AIPTy); 563 564 StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr); 565 NewStore->setAlignment(MTI->getAlignment()); 566 } else { 567 // Noop transfer. Src == Dst 568 } 569 570 MTI->eraseFromParent(); 571 continue; 572 } 573 574 llvm_unreachable("Unsupported operation!"); 575 } 576} 577 578/// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer 579/// or vector value FromVal, extracting the bits from the offset specified by 580/// Offset. This returns the value, which is of type ToType. 581/// 582/// This happens when we are converting an "integer union" to a single 583/// integer scalar, or when we are converting a "vector union" to a vector with 584/// insert/extractelement instructions. 585/// 586/// Offset is an offset from the original alloca, in bits that need to be 587/// shifted to the right. 588Value *ConvertToScalarInfo:: 589ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType, 590 uint64_t Offset, IRBuilder<> &Builder) { 591 // If the load is of the whole new alloca, no conversion is needed. 592 if (FromVal->getType() == ToType && Offset == 0) 593 return FromVal; 594 595 // If the result alloca is a vector type, this is either an element 596 // access or a bitcast to another vector type of the same size. 597 if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) { 598 if (ToType->isVectorTy()) 599 return Builder.CreateBitCast(FromVal, ToType, "tmp"); 600 601 // Otherwise it must be an element access. 602 unsigned Elt = 0; 603 if (Offset) { 604 unsigned EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 605 Elt = Offset/EltSize; 606 assert(EltSize*Elt == Offset && "Invalid modulus in validity checking"); 607 } 608 // Return the element extracted out of it. 609 Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get( 610 Type::getInt32Ty(FromVal->getContext()), Elt), "tmp"); 611 if (V->getType() != ToType) 612 V = Builder.CreateBitCast(V, ToType, "tmp"); 613 return V; 614 } 615 616 // If ToType is a first class aggregate, extract out each of the pieces and 617 // use insertvalue's to form the FCA. 618 if (const StructType *ST = dyn_cast<StructType>(ToType)) { 619 const StructLayout &Layout = *TD.getStructLayout(ST); 620 Value *Res = UndefValue::get(ST); 621 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 622 Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i), 623 Offset+Layout.getElementOffsetInBits(i), 624 Builder); 625 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 626 } 627 return Res; 628 } 629 630 if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) { 631 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 632 Value *Res = UndefValue::get(AT); 633 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 634 Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(), 635 Offset+i*EltSize, Builder); 636 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 637 } 638 return Res; 639 } 640 641 // Otherwise, this must be a union that was converted to an integer value. 642 const IntegerType *NTy = cast<IntegerType>(FromVal->getType()); 643 644 // If this is a big-endian system and the load is narrower than the 645 // full alloca type, we need to do a shift to get the right bits. 646 int ShAmt = 0; 647 if (TD.isBigEndian()) { 648 // On big-endian machines, the lowest bit is stored at the bit offset 649 // from the pointer given by getTypeStoreSizeInBits. This matters for 650 // integers with a bitwidth that is not a multiple of 8. 651 ShAmt = TD.getTypeStoreSizeInBits(NTy) - 652 TD.getTypeStoreSizeInBits(ToType) - Offset; 653 } else { 654 ShAmt = Offset; 655 } 656 657 // Note: we support negative bitwidths (with shl) which are not defined. 658 // We do this to support (f.e.) loads off the end of a structure where 659 // only some bits are used. 660 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth()) 661 FromVal = Builder.CreateLShr(FromVal, 662 ConstantInt::get(FromVal->getType(), 663 ShAmt), "tmp"); 664 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) 665 FromVal = Builder.CreateShl(FromVal, 666 ConstantInt::get(FromVal->getType(), 667 -ShAmt), "tmp"); 668 669 // Finally, unconditionally truncate the integer to the right width. 670 unsigned LIBitWidth = TD.getTypeSizeInBits(ToType); 671 if (LIBitWidth < NTy->getBitWidth()) 672 FromVal = 673 Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(), 674 LIBitWidth), "tmp"); 675 else if (LIBitWidth > NTy->getBitWidth()) 676 FromVal = 677 Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(), 678 LIBitWidth), "tmp"); 679 680 // If the result is an integer, this is a trunc or bitcast. 681 if (ToType->isIntegerTy()) { 682 // Should be done. 683 } else if (ToType->isFloatingPointTy() || ToType->isVectorTy()) { 684 // Just do a bitcast, we know the sizes match up. 685 FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp"); 686 } else { 687 // Otherwise must be a pointer. 688 FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp"); 689 } 690 assert(FromVal->getType() == ToType && "Didn't convert right?"); 691 return FromVal; 692} 693 694/// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer 695/// or vector value "Old" at the offset specified by Offset. 696/// 697/// This happens when we are converting an "integer union" to a 698/// single integer scalar, or when we are converting a "vector union" to a 699/// vector with insert/extractelement instructions. 700/// 701/// Offset is an offset from the original alloca, in bits that need to be 702/// shifted to the right. 703Value *ConvertToScalarInfo:: 704ConvertScalar_InsertValue(Value *SV, Value *Old, 705 uint64_t Offset, IRBuilder<> &Builder) { 706 // Convert the stored type to the actual type, shift it left to insert 707 // then 'or' into place. 708 const Type *AllocaType = Old->getType(); 709 LLVMContext &Context = Old->getContext(); 710 711 if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) { 712 uint64_t VecSize = TD.getTypeAllocSizeInBits(VTy); 713 uint64_t ValSize = TD.getTypeAllocSizeInBits(SV->getType()); 714 715 // Changing the whole vector with memset or with an access of a different 716 // vector type? 717 if (ValSize == VecSize) 718 return Builder.CreateBitCast(SV, AllocaType, "tmp"); 719 720 uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 721 722 // Must be an element insertion. 723 unsigned Elt = Offset/EltSize; 724 725 if (SV->getType() != VTy->getElementType()) 726 SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp"); 727 728 SV = Builder.CreateInsertElement(Old, SV, 729 ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt), 730 "tmp"); 731 return SV; 732 } 733 734 // If SV is a first-class aggregate value, insert each value recursively. 735 if (const StructType *ST = dyn_cast<StructType>(SV->getType())) { 736 const StructLayout &Layout = *TD.getStructLayout(ST); 737 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 738 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 739 Old = ConvertScalar_InsertValue(Elt, Old, 740 Offset+Layout.getElementOffsetInBits(i), 741 Builder); 742 } 743 return Old; 744 } 745 746 if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) { 747 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 748 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 749 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 750 Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder); 751 } 752 return Old; 753 } 754 755 // If SV is a float, convert it to the appropriate integer type. 756 // If it is a pointer, do the same. 757 unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType()); 758 unsigned DestWidth = TD.getTypeSizeInBits(AllocaType); 759 unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType()); 760 unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType); 761 if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy()) 762 SV = Builder.CreateBitCast(SV, 763 IntegerType::get(SV->getContext(),SrcWidth), "tmp"); 764 else if (SV->getType()->isPointerTy()) 765 SV = Builder.CreatePtrToInt(SV, TD.getIntPtrType(SV->getContext()), "tmp"); 766 767 // Zero extend or truncate the value if needed. 768 if (SV->getType() != AllocaType) { 769 if (SV->getType()->getPrimitiveSizeInBits() < 770 AllocaType->getPrimitiveSizeInBits()) 771 SV = Builder.CreateZExt(SV, AllocaType, "tmp"); 772 else { 773 // Truncation may be needed if storing more than the alloca can hold 774 // (undefined behavior). 775 SV = Builder.CreateTrunc(SV, AllocaType, "tmp"); 776 SrcWidth = DestWidth; 777 SrcStoreWidth = DestStoreWidth; 778 } 779 } 780 781 // If this is a big-endian system and the store is narrower than the 782 // full alloca type, we need to do a shift to get the right bits. 783 int ShAmt = 0; 784 if (TD.isBigEndian()) { 785 // On big-endian machines, the lowest bit is stored at the bit offset 786 // from the pointer given by getTypeStoreSizeInBits. This matters for 787 // integers with a bitwidth that is not a multiple of 8. 788 ShAmt = DestStoreWidth - SrcStoreWidth - Offset; 789 } else { 790 ShAmt = Offset; 791 } 792 793 // Note: we support negative bitwidths (with shr) which are not defined. 794 // We do this to support (f.e.) stores off the end of a structure where 795 // only some bits in the structure are set. 796 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth)); 797 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) { 798 SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(), 799 ShAmt), "tmp"); 800 Mask <<= ShAmt; 801 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { 802 SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(), 803 -ShAmt), "tmp"); 804 Mask = Mask.lshr(-ShAmt); 805 } 806 807 // Mask out the bits we are about to insert from the old value, and or 808 // in the new bits. 809 if (SrcWidth != DestWidth) { 810 assert(DestWidth > SrcWidth); 811 Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask"); 812 SV = Builder.CreateOr(Old, SV, "ins"); 813 } 814 return SV; 815} 816 817 818//===----------------------------------------------------------------------===// 819// SRoA Driver 820//===----------------------------------------------------------------------===// 821 822 823bool SROA::runOnFunction(Function &F) { 824 TD = getAnalysisIfAvailable<TargetData>(); 825 826 bool Changed = performPromotion(F); 827 828 // FIXME: ScalarRepl currently depends on TargetData more than it 829 // theoretically needs to. It should be refactored in order to support 830 // target-independent IR. Until this is done, just skip the actual 831 // scalar-replacement portion of this pass. 832 if (!TD) return Changed; 833 834 while (1) { 835 bool LocalChange = performScalarRepl(F); 836 if (!LocalChange) break; // No need to repromote if no scalarrepl 837 Changed = true; 838 LocalChange = performPromotion(F); 839 if (!LocalChange) break; // No need to re-scalarrepl if no promotion 840 } 841 842 return Changed; 843} 844 845namespace { 846class AllocaPromoter : public LoadAndStorePromoter { 847 AllocaInst *AI; 848public: 849 AllocaPromoter(const SmallVectorImpl<Instruction*> &Insts, SSAUpdater &S) 850 : LoadAndStorePromoter(Insts, S), AI(0) {} 851 852 void run(AllocaInst *AI, const SmallVectorImpl<Instruction*> &Insts) { 853 // Remember which alloca we're promoting (for isInstInList). 854 this->AI = AI; 855 LoadAndStorePromoter::run(Insts); 856 AI->eraseFromParent(); 857 } 858 859 virtual bool isInstInList(Instruction *I, 860 const SmallVectorImpl<Instruction*> &Insts) const { 861 if (LoadInst *LI = dyn_cast<LoadInst>(I)) 862 return LI->getOperand(0) == AI; 863 return cast<StoreInst>(I)->getPointerOperand() == AI; 864 } 865}; 866} // end anon namespace 867 868/// isSafeSelectToSpeculate - Select instructions that use an alloca and are 869/// subsequently loaded can be rewritten to load both input pointers and then 870/// select between the result, allowing the load of the alloca to be promoted. 871/// From this: 872/// %P2 = select i1 %cond, i32* %Alloca, i32* %Other 873/// %V = load i32* %P2 874/// to: 875/// %V1 = load i32* %Alloca -> will be mem2reg'd 876/// %V2 = load i32* %Other 877/// %V = select i1 %cond, i32 %V1, i32 %V2 878/// 879/// We can do this to a select if its only uses are loads and if the operand to 880/// the select can be loaded unconditionally. 881static bool isSafeSelectToSpeculate(SelectInst *SI, const TargetData *TD) { 882 bool TDerefable = SI->getTrueValue()->isDereferenceablePointer(); 883 bool FDerefable = SI->getFalseValue()->isDereferenceablePointer(); 884 885 for (Value::use_iterator UI = SI->use_begin(), UE = SI->use_end(); 886 UI != UE; ++UI) { 887 LoadInst *LI = dyn_cast<LoadInst>(*UI); 888 if (LI == 0 || LI->isVolatile()) return false; 889 890 // Both operands to the select need to be dereferencable, either absolutely 891 // (e.g. allocas) or at this point because we can see other accesses to it. 892 if (!TDerefable && !isSafeToLoadUnconditionally(SI->getTrueValue(), LI, 893 LI->getAlignment(), TD)) 894 return false; 895 if (!FDerefable && !isSafeToLoadUnconditionally(SI->getFalseValue(), LI, 896 LI->getAlignment(), TD)) 897 return false; 898 } 899 900 return true; 901} 902 903/// isSafePHIToSpeculate - PHI instructions that use an alloca and are 904/// subsequently loaded can be rewritten to load both input pointers in the pred 905/// blocks and then PHI the results, allowing the load of the alloca to be 906/// promoted. 907/// From this: 908/// %P2 = phi [i32* %Alloca, i32* %Other] 909/// %V = load i32* %P2 910/// to: 911/// %V1 = load i32* %Alloca -> will be mem2reg'd 912/// ... 913/// %V2 = load i32* %Other 914/// ... 915/// %V = phi [i32 %V1, i32 %V2] 916/// 917/// We can do this to a select if its only uses are loads and if the operand to 918/// the select can be loaded unconditionally. 919static bool isSafePHIToSpeculate(PHINode *PN, const TargetData *TD) { 920 // For now, we can only do this promotion if the load is in the same block as 921 // the PHI, and if there are no stores between the phi and load. 922 // TODO: Allow recursive phi users. 923 // TODO: Allow stores. 924 BasicBlock *BB = PN->getParent(); 925 unsigned MaxAlign = 0; 926 for (Value::use_iterator UI = PN->use_begin(), UE = PN->use_end(); 927 UI != UE; ++UI) { 928 LoadInst *LI = dyn_cast<LoadInst>(*UI); 929 if (LI == 0 || LI->isVolatile()) return false; 930 931 // For now we only allow loads in the same block as the PHI. This is a 932 // common case that happens when instcombine merges two loads through a PHI. 933 if (LI->getParent() != BB) return false; 934 935 // Ensure that there are no instructions between the PHI and the load that 936 // could store. 937 for (BasicBlock::iterator BBI = PN; &*BBI != LI; ++BBI) 938 if (BBI->mayWriteToMemory()) 939 return false; 940 941 MaxAlign = std::max(MaxAlign, LI->getAlignment()); 942 } 943 944 // Okay, we know that we have one or more loads in the same block as the PHI. 945 // We can transform this if it is safe to push the loads into the predecessor 946 // blocks. The only thing to watch out for is that we can't put a possibly 947 // trapping load in the predecessor if it is a critical edge. 948 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 949 BasicBlock *Pred = PN->getIncomingBlock(i); 950 951 // If the predecessor has a single successor, then the edge isn't critical. 952 if (Pred->getTerminator()->getNumSuccessors() == 1) 953 continue; 954 955 Value *InVal = PN->getIncomingValue(i); 956 957 // If the InVal is an invoke in the pred, we can't put a load on the edge. 958 if (InvokeInst *II = dyn_cast<InvokeInst>(InVal)) 959 if (II->getParent() == Pred) 960 return false; 961 962 // If this pointer is always safe to load, or if we can prove that there is 963 // already a load in the block, then we can move the load to the pred block. 964 if (InVal->isDereferenceablePointer() || 965 isSafeToLoadUnconditionally(InVal, Pred->getTerminator(), MaxAlign, TD)) 966 continue; 967 968 return false; 969 } 970 971 return true; 972} 973 974 975/// tryToMakeAllocaBePromotable - This returns true if the alloca only has 976/// direct (non-volatile) loads and stores to it. If the alloca is close but 977/// not quite there, this will transform the code to allow promotion. As such, 978/// it is a non-pure predicate. 979static bool tryToMakeAllocaBePromotable(AllocaInst *AI, const TargetData *TD) { 980 SetVector<Instruction*, SmallVector<Instruction*, 4>, 981 SmallPtrSet<Instruction*, 4> > InstsToRewrite; 982 983 for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end(); 984 UI != UE; ++UI) { 985 User *U = *UI; 986 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 987 if (LI->isVolatile()) 988 return false; 989 continue; 990 } 991 992 if (StoreInst *SI = dyn_cast<StoreInst>(U)) { 993 if (SI->getOperand(0) == AI || SI->isVolatile()) 994 return false; // Don't allow a store OF the AI, only INTO the AI. 995 continue; 996 } 997 998 if (SelectInst *SI = dyn_cast<SelectInst>(U)) { 999 // If the condition being selected on is a constant, fold the select, yes 1000 // this does (rarely) happen early on. 1001 if (ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition())) { 1002 Value *Result = SI->getOperand(1+CI->isZero()); 1003 SI->replaceAllUsesWith(Result); 1004 SI->eraseFromParent(); 1005 1006 // This is very rare and we just scrambled the use list of AI, start 1007 // over completely. 1008 return tryToMakeAllocaBePromotable(AI, TD); 1009 } 1010 1011 // If it is safe to turn "load (select c, AI, ptr)" into a select of two 1012 // loads, then we can transform this by rewriting the select. 1013 if (!isSafeSelectToSpeculate(SI, TD)) 1014 return false; 1015 1016 InstsToRewrite.insert(SI); 1017 continue; 1018 } 1019 1020 if (PHINode *PN = dyn_cast<PHINode>(U)) { 1021 if (PN->use_empty()) { // Dead PHIs can be stripped. 1022 InstsToRewrite.insert(PN); 1023 continue; 1024 } 1025 1026 // If it is safe to turn "load (phi [AI, ptr, ...])" into a PHI of loads 1027 // in the pred blocks, then we can transform this by rewriting the PHI. 1028 if (!isSafePHIToSpeculate(PN, TD)) 1029 return false; 1030 1031 InstsToRewrite.insert(PN); 1032 continue; 1033 } 1034 1035 return false; 1036 } 1037 1038 // If there are no instructions to rewrite, then all uses are load/stores and 1039 // we're done! 1040 if (InstsToRewrite.empty()) 1041 return true; 1042 1043 // If we have instructions that need to be rewritten for this to be promotable 1044 // take care of it now. 1045 for (unsigned i = 0, e = InstsToRewrite.size(); i != e; ++i) { 1046 if (SelectInst *SI = dyn_cast<SelectInst>(InstsToRewrite[i])) { 1047 // Selects in InstsToRewrite only have load uses. Rewrite each as two 1048 // loads with a new select. 1049 while (!SI->use_empty()) { 1050 LoadInst *LI = cast<LoadInst>(SI->use_back()); 1051 1052 IRBuilder<> Builder(LI); 1053 LoadInst *TrueLoad = 1054 Builder.CreateLoad(SI->getTrueValue(), LI->getName()+".t"); 1055 LoadInst *FalseLoad = 1056 Builder.CreateLoad(SI->getFalseValue(), LI->getName()+".t"); 1057 1058 // Transfer alignment and TBAA info if present. 1059 TrueLoad->setAlignment(LI->getAlignment()); 1060 FalseLoad->setAlignment(LI->getAlignment()); 1061 if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) { 1062 TrueLoad->setMetadata(LLVMContext::MD_tbaa, Tag); 1063 FalseLoad->setMetadata(LLVMContext::MD_tbaa, Tag); 1064 } 1065 1066 Value *V = Builder.CreateSelect(SI->getCondition(), TrueLoad, FalseLoad); 1067 V->takeName(LI); 1068 LI->replaceAllUsesWith(V); 1069 LI->eraseFromParent(); 1070 } 1071 1072 // Now that all the loads are gone, the select is gone too. 1073 SI->eraseFromParent(); 1074 continue; 1075 } 1076 1077 // Otherwise, we have a PHI node which allows us to push the loads into the 1078 // predecessors. 1079 PHINode *PN = cast<PHINode>(InstsToRewrite[i]); 1080 if (PN->use_empty()) { 1081 PN->eraseFromParent(); 1082 continue; 1083 } 1084 1085 const Type *LoadTy = cast<PointerType>(PN->getType())->getElementType(); 1086 PHINode *NewPN = PHINode::Create(LoadTy, PN->getName()+".ld", PN); 1087 1088 // Get the TBAA tag and alignment to use from one of the loads. It doesn't 1089 // matter which one we get and if any differ, it doesn't matter. 1090 LoadInst *SomeLoad = cast<LoadInst>(PN->use_back()); 1091 MDNode *TBAATag = SomeLoad->getMetadata(LLVMContext::MD_tbaa); 1092 unsigned Align = SomeLoad->getAlignment(); 1093 1094 // Rewrite all loads of the PN to use the new PHI. 1095 while (!PN->use_empty()) { 1096 LoadInst *LI = cast<LoadInst>(PN->use_back()); 1097 LI->replaceAllUsesWith(NewPN); 1098 LI->eraseFromParent(); 1099 } 1100 1101 // Inject loads into all of the pred blocks. Keep track of which blocks we 1102 // insert them into in case we have multiple edges from the same block. 1103 DenseMap<BasicBlock*, LoadInst*> InsertedLoads; 1104 1105 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 1106 BasicBlock *Pred = PN->getIncomingBlock(i); 1107 LoadInst *&Load = InsertedLoads[Pred]; 1108 if (Load == 0) { 1109 Load = new LoadInst(PN->getIncomingValue(i), 1110 PN->getName() + "." + Pred->getName(), 1111 Pred->getTerminator()); 1112 Load->setAlignment(Align); 1113 if (TBAATag) Load->setMetadata(LLVMContext::MD_tbaa, TBAATag); 1114 } 1115 1116 NewPN->addIncoming(Load, Pred); 1117 } 1118 1119 PN->eraseFromParent(); 1120 } 1121 1122 ++NumAdjusted; 1123 return true; 1124} 1125 1126 1127bool SROA::performPromotion(Function &F) { 1128 std::vector<AllocaInst*> Allocas; 1129 DominatorTree *DT = 0; 1130 if (HasDomTree) 1131 DT = &getAnalysis<DominatorTree>(); 1132 1133 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function 1134 1135 bool Changed = false; 1136 SmallVector<Instruction*, 64> Insts; 1137 while (1) { 1138 Allocas.clear(); 1139 1140 // Find allocas that are safe to promote, by looking at all instructions in 1141 // the entry node 1142 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) 1143 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? 1144 if (tryToMakeAllocaBePromotable(AI, TD)) 1145 Allocas.push_back(AI); 1146 1147 if (Allocas.empty()) break; 1148 1149 if (HasDomTree) 1150 PromoteMemToReg(Allocas, *DT); 1151 else { 1152 SSAUpdater SSA; 1153 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) { 1154 AllocaInst *AI = Allocas[i]; 1155 1156 // Build list of instructions to promote. 1157 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 1158 UI != E; ++UI) 1159 Insts.push_back(cast<Instruction>(*UI)); 1160 1161 AllocaPromoter(Insts, SSA).run(AI, Insts); 1162 Insts.clear(); 1163 } 1164 } 1165 NumPromoted += Allocas.size(); 1166 Changed = true; 1167 } 1168 1169 return Changed; 1170} 1171 1172 1173/// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for 1174/// SROA. It must be a struct or array type with a small number of elements. 1175static bool ShouldAttemptScalarRepl(AllocaInst *AI) { 1176 const Type *T = AI->getAllocatedType(); 1177 // Do not promote any struct into more than 32 separate vars. 1178 if (const StructType *ST = dyn_cast<StructType>(T)) 1179 return ST->getNumElements() <= 32; 1180 // Arrays are much less likely to be safe for SROA; only consider 1181 // them if they are very small. 1182 if (const ArrayType *AT = dyn_cast<ArrayType>(T)) 1183 return AT->getNumElements() <= 8; 1184 return false; 1185} 1186 1187 1188// performScalarRepl - This algorithm is a simple worklist driven algorithm, 1189// which runs on all of the malloc/alloca instructions in the function, removing 1190// them if they are only used by getelementptr instructions. 1191// 1192bool SROA::performScalarRepl(Function &F) { 1193 std::vector<AllocaInst*> WorkList; 1194 1195 // Scan the entry basic block, adding allocas to the worklist. 1196 BasicBlock &BB = F.getEntryBlock(); 1197 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) 1198 if (AllocaInst *A = dyn_cast<AllocaInst>(I)) 1199 WorkList.push_back(A); 1200 1201 // Process the worklist 1202 bool Changed = false; 1203 while (!WorkList.empty()) { 1204 AllocaInst *AI = WorkList.back(); 1205 WorkList.pop_back(); 1206 1207 // Handle dead allocas trivially. These can be formed by SROA'ing arrays 1208 // with unused elements. 1209 if (AI->use_empty()) { 1210 AI->eraseFromParent(); 1211 Changed = true; 1212 continue; 1213 } 1214 1215 // If this alloca is impossible for us to promote, reject it early. 1216 if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized()) 1217 continue; 1218 1219 // Check to see if this allocation is only modified by a memcpy/memmove from 1220 // a constant global. If this is the case, we can change all users to use 1221 // the constant global instead. This is commonly produced by the CFE by 1222 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A' 1223 // is only subsequently read. 1224 if (MemTransferInst *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) { 1225 DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n'); 1226 DEBUG(dbgs() << " memcpy = " << *TheCopy << '\n'); 1227 Constant *TheSrc = cast<Constant>(TheCopy->getSource()); 1228 AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType())); 1229 TheCopy->eraseFromParent(); // Don't mutate the global. 1230 AI->eraseFromParent(); 1231 ++NumGlobals; 1232 Changed = true; 1233 continue; 1234 } 1235 1236 // Check to see if we can perform the core SROA transformation. We cannot 1237 // transform the allocation instruction if it is an array allocation 1238 // (allocations OF arrays are ok though), and an allocation of a scalar 1239 // value cannot be decomposed at all. 1240 uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType()); 1241 1242 // Do not promote [0 x %struct]. 1243 if (AllocaSize == 0) continue; 1244 1245 // Do not promote any struct whose size is too big. 1246 if (AllocaSize > SRThreshold) continue; 1247 1248 // If the alloca looks like a good candidate for scalar replacement, and if 1249 // all its users can be transformed, then split up the aggregate into its 1250 // separate elements. 1251 if (ShouldAttemptScalarRepl(AI) && isSafeAllocaToScalarRepl(AI)) { 1252 DoScalarReplacement(AI, WorkList); 1253 Changed = true; 1254 continue; 1255 } 1256 1257 // If we can turn this aggregate value (potentially with casts) into a 1258 // simple scalar value that can be mem2reg'd into a register value. 1259 // IsNotTrivial tracks whether this is something that mem2reg could have 1260 // promoted itself. If so, we don't want to transform it needlessly. Note 1261 // that we can't just check based on the type: the alloca may be of an i32 1262 // but that has pointer arithmetic to set byte 3 of it or something. 1263 if (AllocaInst *NewAI = 1264 ConvertToScalarInfo((unsigned)AllocaSize, *TD).TryConvert(AI)) { 1265 NewAI->takeName(AI); 1266 AI->eraseFromParent(); 1267 ++NumConverted; 1268 Changed = true; 1269 continue; 1270 } 1271 1272 // Otherwise, couldn't process this alloca. 1273 } 1274 1275 return Changed; 1276} 1277 1278/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl 1279/// predicate, do SROA now. 1280void SROA::DoScalarReplacement(AllocaInst *AI, 1281 std::vector<AllocaInst*> &WorkList) { 1282 DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n'); 1283 SmallVector<AllocaInst*, 32> ElementAllocas; 1284 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 1285 ElementAllocas.reserve(ST->getNumContainedTypes()); 1286 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { 1287 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 1288 AI->getAlignment(), 1289 AI->getName() + "." + Twine(i), AI); 1290 ElementAllocas.push_back(NA); 1291 WorkList.push_back(NA); // Add to worklist for recursive processing 1292 } 1293 } else { 1294 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); 1295 ElementAllocas.reserve(AT->getNumElements()); 1296 const Type *ElTy = AT->getElementType(); 1297 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 1298 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(), 1299 AI->getName() + "." + Twine(i), AI); 1300 ElementAllocas.push_back(NA); 1301 WorkList.push_back(NA); // Add to worklist for recursive processing 1302 } 1303 } 1304 1305 // Now that we have created the new alloca instructions, rewrite all the 1306 // uses of the old alloca. 1307 RewriteForScalarRepl(AI, AI, 0, ElementAllocas); 1308 1309 // Now erase any instructions that were made dead while rewriting the alloca. 1310 DeleteDeadInstructions(); 1311 AI->eraseFromParent(); 1312 1313 ++NumReplaced; 1314} 1315 1316/// DeleteDeadInstructions - Erase instructions on the DeadInstrs list, 1317/// recursively including all their operands that become trivially dead. 1318void SROA::DeleteDeadInstructions() { 1319 while (!DeadInsts.empty()) { 1320 Instruction *I = cast<Instruction>(DeadInsts.pop_back_val()); 1321 1322 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) 1323 if (Instruction *U = dyn_cast<Instruction>(*OI)) { 1324 // Zero out the operand and see if it becomes trivially dead. 1325 // (But, don't add allocas to the dead instruction list -- they are 1326 // already on the worklist and will be deleted separately.) 1327 *OI = 0; 1328 if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U)) 1329 DeadInsts.push_back(U); 1330 } 1331 1332 I->eraseFromParent(); 1333 } 1334} 1335 1336/// isSafeForScalarRepl - Check if instruction I is a safe use with regard to 1337/// performing scalar replacement of alloca AI. The results are flagged in 1338/// the Info parameter. Offset indicates the position within AI that is 1339/// referenced by this instruction. 1340void SROA::isSafeForScalarRepl(Instruction *I, uint64_t Offset, 1341 AllocaInfo &Info) { 1342 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 1343 Instruction *User = cast<Instruction>(*UI); 1344 1345 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1346 isSafeForScalarRepl(BC, Offset, Info); 1347 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1348 uint64_t GEPOffset = Offset; 1349 isSafeGEP(GEPI, GEPOffset, Info); 1350 if (!Info.isUnsafe) 1351 isSafeForScalarRepl(GEPI, GEPOffset, Info); 1352 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 1353 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 1354 if (Length == 0) 1355 return MarkUnsafe(Info, User); 1356 isSafeMemAccess(Offset, Length->getZExtValue(), 0, 1357 UI.getOperandNo() == 0, Info, MI, 1358 true /*AllowWholeAccess*/); 1359 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1360 if (LI->isVolatile()) 1361 return MarkUnsafe(Info, User); 1362 const Type *LIType = LI->getType(); 1363 isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType), 1364 LIType, false, Info, LI, true /*AllowWholeAccess*/); 1365 Info.hasALoadOrStore = true; 1366 1367 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1368 // Store is ok if storing INTO the pointer, not storing the pointer 1369 if (SI->isVolatile() || SI->getOperand(0) == I) 1370 return MarkUnsafe(Info, User); 1371 1372 const Type *SIType = SI->getOperand(0)->getType(); 1373 isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType), 1374 SIType, true, Info, SI, true /*AllowWholeAccess*/); 1375 Info.hasALoadOrStore = true; 1376 } else if (isa<PHINode>(User) || isa<SelectInst>(User)) { 1377 isSafePHISelectUseForScalarRepl(User, Offset, Info); 1378 } else { 1379 return MarkUnsafe(Info, User); 1380 } 1381 if (Info.isUnsafe) return; 1382 } 1383} 1384 1385 1386/// isSafePHIUseForScalarRepl - If we see a PHI node or select using a pointer 1387/// derived from the alloca, we can often still split the alloca into elements. 1388/// This is useful if we have a large alloca where one element is phi'd 1389/// together somewhere: we can SRoA and promote all the other elements even if 1390/// we end up not being able to promote this one. 1391/// 1392/// All we require is that the uses of the PHI do not index into other parts of 1393/// the alloca. The most important use case for this is single load and stores 1394/// that are PHI'd together, which can happen due to code sinking. 1395void SROA::isSafePHISelectUseForScalarRepl(Instruction *I, uint64_t Offset, 1396 AllocaInfo &Info) { 1397 // If we've already checked this PHI, don't do it again. 1398 if (PHINode *PN = dyn_cast<PHINode>(I)) 1399 if (!Info.CheckedPHIs.insert(PN)) 1400 return; 1401 1402 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 1403 Instruction *User = cast<Instruction>(*UI); 1404 1405 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1406 isSafePHISelectUseForScalarRepl(BC, Offset, Info); 1407 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1408 // Only allow "bitcast" GEPs for simplicity. We could generalize this, 1409 // but would have to prove that we're staying inside of an element being 1410 // promoted. 1411 if (!GEPI->hasAllZeroIndices()) 1412 return MarkUnsafe(Info, User); 1413 isSafePHISelectUseForScalarRepl(GEPI, Offset, Info); 1414 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1415 if (LI->isVolatile()) 1416 return MarkUnsafe(Info, User); 1417 const Type *LIType = LI->getType(); 1418 isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType), 1419 LIType, false, Info, LI, false /*AllowWholeAccess*/); 1420 Info.hasALoadOrStore = true; 1421 1422 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1423 // Store is ok if storing INTO the pointer, not storing the pointer 1424 if (SI->isVolatile() || SI->getOperand(0) == I) 1425 return MarkUnsafe(Info, User); 1426 1427 const Type *SIType = SI->getOperand(0)->getType(); 1428 isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType), 1429 SIType, true, Info, SI, false /*AllowWholeAccess*/); 1430 Info.hasALoadOrStore = true; 1431 } else if (isa<PHINode>(User) || isa<SelectInst>(User)) { 1432 isSafePHISelectUseForScalarRepl(User, Offset, Info); 1433 } else { 1434 return MarkUnsafe(Info, User); 1435 } 1436 if (Info.isUnsafe) return; 1437 } 1438} 1439 1440/// isSafeGEP - Check if a GEP instruction can be handled for scalar 1441/// replacement. It is safe when all the indices are constant, in-bounds 1442/// references, and when the resulting offset corresponds to an element within 1443/// the alloca type. The results are flagged in the Info parameter. Upon 1444/// return, Offset is adjusted as specified by the GEP indices. 1445void SROA::isSafeGEP(GetElementPtrInst *GEPI, 1446 uint64_t &Offset, AllocaInfo &Info) { 1447 gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI); 1448 if (GEPIt == E) 1449 return; 1450 1451 // Walk through the GEP type indices, checking the types that this indexes 1452 // into. 1453 for (; GEPIt != E; ++GEPIt) { 1454 // Ignore struct elements, no extra checking needed for these. 1455 if ((*GEPIt)->isStructTy()) 1456 continue; 1457 1458 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand()); 1459 if (!IdxVal) 1460 return MarkUnsafe(Info, GEPI); 1461 } 1462 1463 // Compute the offset due to this GEP and check if the alloca has a 1464 // component element at that offset. 1465 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 1466 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 1467 &Indices[0], Indices.size()); 1468 if (!TypeHasComponent(Info.AI->getAllocatedType(), Offset, 0)) 1469 MarkUnsafe(Info, GEPI); 1470} 1471 1472/// isHomogeneousAggregate - Check if type T is a struct or array containing 1473/// elements of the same type (which is always true for arrays). If so, 1474/// return true with NumElts and EltTy set to the number of elements and the 1475/// element type, respectively. 1476static bool isHomogeneousAggregate(const Type *T, unsigned &NumElts, 1477 const Type *&EltTy) { 1478 if (const ArrayType *AT = dyn_cast<ArrayType>(T)) { 1479 NumElts = AT->getNumElements(); 1480 EltTy = (NumElts == 0 ? 0 : AT->getElementType()); 1481 return true; 1482 } 1483 if (const StructType *ST = dyn_cast<StructType>(T)) { 1484 NumElts = ST->getNumContainedTypes(); 1485 EltTy = (NumElts == 0 ? 0 : ST->getContainedType(0)); 1486 for (unsigned n = 1; n < NumElts; ++n) { 1487 if (ST->getContainedType(n) != EltTy) 1488 return false; 1489 } 1490 return true; 1491 } 1492 return false; 1493} 1494 1495/// isCompatibleAggregate - Check if T1 and T2 are either the same type or are 1496/// "homogeneous" aggregates with the same element type and number of elements. 1497static bool isCompatibleAggregate(const Type *T1, const Type *T2) { 1498 if (T1 == T2) 1499 return true; 1500 1501 unsigned NumElts1, NumElts2; 1502 const Type *EltTy1, *EltTy2; 1503 if (isHomogeneousAggregate(T1, NumElts1, EltTy1) && 1504 isHomogeneousAggregate(T2, NumElts2, EltTy2) && 1505 NumElts1 == NumElts2 && 1506 EltTy1 == EltTy2) 1507 return true; 1508 1509 return false; 1510} 1511 1512/// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI 1513/// alloca or has an offset and size that corresponds to a component element 1514/// within it. The offset checked here may have been formed from a GEP with a 1515/// pointer bitcasted to a different type. 1516/// 1517/// If AllowWholeAccess is true, then this allows uses of the entire alloca as a 1518/// unit. If false, it only allows accesses known to be in a single element. 1519void SROA::isSafeMemAccess(uint64_t Offset, uint64_t MemSize, 1520 const Type *MemOpType, bool isStore, 1521 AllocaInfo &Info, Instruction *TheAccess, 1522 bool AllowWholeAccess) { 1523 // Check if this is a load/store of the entire alloca. 1524 if (Offset == 0 && AllowWholeAccess && 1525 MemSize == TD->getTypeAllocSize(Info.AI->getAllocatedType())) { 1526 // This can be safe for MemIntrinsics (where MemOpType is 0) and integer 1527 // loads/stores (which are essentially the same as the MemIntrinsics with 1528 // regard to copying padding between elements). But, if an alloca is 1529 // flagged as both a source and destination of such operations, we'll need 1530 // to check later for padding between elements. 1531 if (!MemOpType || MemOpType->isIntegerTy()) { 1532 if (isStore) 1533 Info.isMemCpyDst = true; 1534 else 1535 Info.isMemCpySrc = true; 1536 return; 1537 } 1538 // This is also safe for references using a type that is compatible with 1539 // the type of the alloca, so that loads/stores can be rewritten using 1540 // insertvalue/extractvalue. 1541 if (isCompatibleAggregate(MemOpType, Info.AI->getAllocatedType())) { 1542 Info.hasSubelementAccess = true; 1543 return; 1544 } 1545 } 1546 // Check if the offset/size correspond to a component within the alloca type. 1547 const Type *T = Info.AI->getAllocatedType(); 1548 if (TypeHasComponent(T, Offset, MemSize)) { 1549 Info.hasSubelementAccess = true; 1550 return; 1551 } 1552 1553 return MarkUnsafe(Info, TheAccess); 1554} 1555 1556/// TypeHasComponent - Return true if T has a component type with the 1557/// specified offset and size. If Size is zero, do not check the size. 1558bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) { 1559 const Type *EltTy; 1560 uint64_t EltSize; 1561 if (const StructType *ST = dyn_cast<StructType>(T)) { 1562 const StructLayout *Layout = TD->getStructLayout(ST); 1563 unsigned EltIdx = Layout->getElementContainingOffset(Offset); 1564 EltTy = ST->getContainedType(EltIdx); 1565 EltSize = TD->getTypeAllocSize(EltTy); 1566 Offset -= Layout->getElementOffset(EltIdx); 1567 } else if (const ArrayType *AT = dyn_cast<ArrayType>(T)) { 1568 EltTy = AT->getElementType(); 1569 EltSize = TD->getTypeAllocSize(EltTy); 1570 if (Offset >= AT->getNumElements() * EltSize) 1571 return false; 1572 Offset %= EltSize; 1573 } else { 1574 return false; 1575 } 1576 if (Offset == 0 && (Size == 0 || EltSize == Size)) 1577 return true; 1578 // Check if the component spans multiple elements. 1579 if (Offset + Size > EltSize) 1580 return false; 1581 return TypeHasComponent(EltTy, Offset, Size); 1582} 1583 1584/// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite 1585/// the instruction I, which references it, to use the separate elements. 1586/// Offset indicates the position within AI that is referenced by this 1587/// instruction. 1588void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 1589 SmallVector<AllocaInst*, 32> &NewElts) { 1590 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E;) { 1591 Use &TheUse = UI.getUse(); 1592 Instruction *User = cast<Instruction>(*UI++); 1593 1594 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1595 RewriteBitCast(BC, AI, Offset, NewElts); 1596 continue; 1597 } 1598 1599 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1600 RewriteGEP(GEPI, AI, Offset, NewElts); 1601 continue; 1602 } 1603 1604 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 1605 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 1606 uint64_t MemSize = Length->getZExtValue(); 1607 if (Offset == 0 && 1608 MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) 1609 RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts); 1610 // Otherwise the intrinsic can only touch a single element and the 1611 // address operand will be updated, so nothing else needs to be done. 1612 continue; 1613 } 1614 1615 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1616 const Type *LIType = LI->getType(); 1617 1618 if (isCompatibleAggregate(LIType, AI->getAllocatedType())) { 1619 // Replace: 1620 // %res = load { i32, i32 }* %alloc 1621 // with: 1622 // %load.0 = load i32* %alloc.0 1623 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0 1624 // %load.1 = load i32* %alloc.1 1625 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1 1626 // (Also works for arrays instead of structs) 1627 Value *Insert = UndefValue::get(LIType); 1628 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1629 Value *Load = new LoadInst(NewElts[i], "load", LI); 1630 Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI); 1631 } 1632 LI->replaceAllUsesWith(Insert); 1633 DeadInsts.push_back(LI); 1634 } else if (LIType->isIntegerTy() && 1635 TD->getTypeAllocSize(LIType) == 1636 TD->getTypeAllocSize(AI->getAllocatedType())) { 1637 // If this is a load of the entire alloca to an integer, rewrite it. 1638 RewriteLoadUserOfWholeAlloca(LI, AI, NewElts); 1639 } 1640 continue; 1641 } 1642 1643 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1644 Value *Val = SI->getOperand(0); 1645 const Type *SIType = Val->getType(); 1646 if (isCompatibleAggregate(SIType, AI->getAllocatedType())) { 1647 // Replace: 1648 // store { i32, i32 } %val, { i32, i32 }* %alloc 1649 // with: 1650 // %val.0 = extractvalue { i32, i32 } %val, 0 1651 // store i32 %val.0, i32* %alloc.0 1652 // %val.1 = extractvalue { i32, i32 } %val, 1 1653 // store i32 %val.1, i32* %alloc.1 1654 // (Also works for arrays instead of structs) 1655 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1656 Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI); 1657 new StoreInst(Extract, NewElts[i], SI); 1658 } 1659 DeadInsts.push_back(SI); 1660 } else if (SIType->isIntegerTy() && 1661 TD->getTypeAllocSize(SIType) == 1662 TD->getTypeAllocSize(AI->getAllocatedType())) { 1663 // If this is a store of the entire alloca from an integer, rewrite it. 1664 RewriteStoreUserOfWholeAlloca(SI, AI, NewElts); 1665 } 1666 continue; 1667 } 1668 1669 if (isa<SelectInst>(User) || isa<PHINode>(User)) { 1670 // If we have a PHI user of the alloca itself (as opposed to a GEP or 1671 // bitcast) we have to rewrite it. GEP and bitcast uses will be RAUW'd to 1672 // the new pointer. 1673 if (!isa<AllocaInst>(I)) continue; 1674 1675 assert(Offset == 0 && NewElts[0] && 1676 "Direct alloca use should have a zero offset"); 1677 1678 // If we have a use of the alloca, we know the derived uses will be 1679 // utilizing just the first element of the scalarized result. Insert a 1680 // bitcast of the first alloca before the user as required. 1681 AllocaInst *NewAI = NewElts[0]; 1682 BitCastInst *BCI = new BitCastInst(NewAI, AI->getType(), "", NewAI); 1683 NewAI->moveBefore(BCI); 1684 TheUse = BCI; 1685 continue; 1686 } 1687 } 1688} 1689 1690/// RewriteBitCast - Update a bitcast reference to the alloca being replaced 1691/// and recursively continue updating all of its uses. 1692void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 1693 SmallVector<AllocaInst*, 32> &NewElts) { 1694 RewriteForScalarRepl(BC, AI, Offset, NewElts); 1695 if (BC->getOperand(0) != AI) 1696 return; 1697 1698 // The bitcast references the original alloca. Replace its uses with 1699 // references to the first new element alloca. 1700 Instruction *Val = NewElts[0]; 1701 if (Val->getType() != BC->getDestTy()) { 1702 Val = new BitCastInst(Val, BC->getDestTy(), "", BC); 1703 Val->takeName(BC); 1704 } 1705 BC->replaceAllUsesWith(Val); 1706 DeadInsts.push_back(BC); 1707} 1708 1709/// FindElementAndOffset - Return the index of the element containing Offset 1710/// within the specified type, which must be either a struct or an array. 1711/// Sets T to the type of the element and Offset to the offset within that 1712/// element. IdxTy is set to the type of the index result to be used in a 1713/// GEP instruction. 1714uint64_t SROA::FindElementAndOffset(const Type *&T, uint64_t &Offset, 1715 const Type *&IdxTy) { 1716 uint64_t Idx = 0; 1717 if (const StructType *ST = dyn_cast<StructType>(T)) { 1718 const StructLayout *Layout = TD->getStructLayout(ST); 1719 Idx = Layout->getElementContainingOffset(Offset); 1720 T = ST->getContainedType(Idx); 1721 Offset -= Layout->getElementOffset(Idx); 1722 IdxTy = Type::getInt32Ty(T->getContext()); 1723 return Idx; 1724 } 1725 const ArrayType *AT = cast<ArrayType>(T); 1726 T = AT->getElementType(); 1727 uint64_t EltSize = TD->getTypeAllocSize(T); 1728 Idx = Offset / EltSize; 1729 Offset -= Idx * EltSize; 1730 IdxTy = Type::getInt64Ty(T->getContext()); 1731 return Idx; 1732} 1733 1734/// RewriteGEP - Check if this GEP instruction moves the pointer across 1735/// elements of the alloca that are being split apart, and if so, rewrite 1736/// the GEP to be relative to the new element. 1737void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 1738 SmallVector<AllocaInst*, 32> &NewElts) { 1739 uint64_t OldOffset = Offset; 1740 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 1741 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 1742 &Indices[0], Indices.size()); 1743 1744 RewriteForScalarRepl(GEPI, AI, Offset, NewElts); 1745 1746 const Type *T = AI->getAllocatedType(); 1747 const Type *IdxTy; 1748 uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy); 1749 if (GEPI->getOperand(0) == AI) 1750 OldIdx = ~0ULL; // Force the GEP to be rewritten. 1751 1752 T = AI->getAllocatedType(); 1753 uint64_t EltOffset = Offset; 1754 uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy); 1755 1756 // If this GEP does not move the pointer across elements of the alloca 1757 // being split, then it does not needs to be rewritten. 1758 if (Idx == OldIdx) 1759 return; 1760 1761 const Type *i32Ty = Type::getInt32Ty(AI->getContext()); 1762 SmallVector<Value*, 8> NewArgs; 1763 NewArgs.push_back(Constant::getNullValue(i32Ty)); 1764 while (EltOffset != 0) { 1765 uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy); 1766 NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx)); 1767 } 1768 Instruction *Val = NewElts[Idx]; 1769 if (NewArgs.size() > 1) { 1770 Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(), 1771 NewArgs.end(), "", GEPI); 1772 Val->takeName(GEPI); 1773 } 1774 if (Val->getType() != GEPI->getType()) 1775 Val = new BitCastInst(Val, GEPI->getType(), Val->getName(), GEPI); 1776 GEPI->replaceAllUsesWith(Val); 1777 DeadInsts.push_back(GEPI); 1778} 1779 1780/// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI. 1781/// Rewrite it to copy or set the elements of the scalarized memory. 1782void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 1783 AllocaInst *AI, 1784 SmallVector<AllocaInst*, 32> &NewElts) { 1785 // If this is a memcpy/memmove, construct the other pointer as the 1786 // appropriate type. The "Other" pointer is the pointer that goes to memory 1787 // that doesn't have anything to do with the alloca that we are promoting. For 1788 // memset, this Value* stays null. 1789 Value *OtherPtr = 0; 1790 unsigned MemAlignment = MI->getAlignment(); 1791 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy 1792 if (Inst == MTI->getRawDest()) 1793 OtherPtr = MTI->getRawSource(); 1794 else { 1795 assert(Inst == MTI->getRawSource()); 1796 OtherPtr = MTI->getRawDest(); 1797 } 1798 } 1799 1800 // If there is an other pointer, we want to convert it to the same pointer 1801 // type as AI has, so we can GEP through it safely. 1802 if (OtherPtr) { 1803 unsigned AddrSpace = 1804 cast<PointerType>(OtherPtr->getType())->getAddressSpace(); 1805 1806 // Remove bitcasts and all-zero GEPs from OtherPtr. This is an 1807 // optimization, but it's also required to detect the corner case where 1808 // both pointer operands are referencing the same memory, and where 1809 // OtherPtr may be a bitcast or GEP that currently being rewritten. (This 1810 // function is only called for mem intrinsics that access the whole 1811 // aggregate, so non-zero GEPs are not an issue here.) 1812 OtherPtr = OtherPtr->stripPointerCasts(); 1813 1814 // Copying the alloca to itself is a no-op: just delete it. 1815 if (OtherPtr == AI || OtherPtr == NewElts[0]) { 1816 // This code will run twice for a no-op memcpy -- once for each operand. 1817 // Put only one reference to MI on the DeadInsts list. 1818 for (SmallVector<Value*, 32>::const_iterator I = DeadInsts.begin(), 1819 E = DeadInsts.end(); I != E; ++I) 1820 if (*I == MI) return; 1821 DeadInsts.push_back(MI); 1822 return; 1823 } 1824 1825 // If the pointer is not the right type, insert a bitcast to the right 1826 // type. 1827 const Type *NewTy = 1828 PointerType::get(AI->getType()->getElementType(), AddrSpace); 1829 1830 if (OtherPtr->getType() != NewTy) 1831 OtherPtr = new BitCastInst(OtherPtr, NewTy, OtherPtr->getName(), MI); 1832 } 1833 1834 // Process each element of the aggregate. 1835 bool SROADest = MI->getRawDest() == Inst; 1836 1837 Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext())); 1838 1839 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1840 // If this is a memcpy/memmove, emit a GEP of the other element address. 1841 Value *OtherElt = 0; 1842 unsigned OtherEltAlign = MemAlignment; 1843 1844 if (OtherPtr) { 1845 Value *Idx[2] = { Zero, 1846 ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) }; 1847 OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2, 1848 OtherPtr->getName()+"."+Twine(i), 1849 MI); 1850 uint64_t EltOffset; 1851 const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType()); 1852 const Type *OtherTy = OtherPtrTy->getElementType(); 1853 if (const StructType *ST = dyn_cast<StructType>(OtherTy)) { 1854 EltOffset = TD->getStructLayout(ST)->getElementOffset(i); 1855 } else { 1856 const Type *EltTy = cast<SequentialType>(OtherTy)->getElementType(); 1857 EltOffset = TD->getTypeAllocSize(EltTy)*i; 1858 } 1859 1860 // The alignment of the other pointer is the guaranteed alignment of the 1861 // element, which is affected by both the known alignment of the whole 1862 // mem intrinsic and the alignment of the element. If the alignment of 1863 // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the 1864 // known alignment is just 4 bytes. 1865 OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset); 1866 } 1867 1868 Value *EltPtr = NewElts[i]; 1869 const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType(); 1870 1871 // If we got down to a scalar, insert a load or store as appropriate. 1872 if (EltTy->isSingleValueType()) { 1873 if (isa<MemTransferInst>(MI)) { 1874 if (SROADest) { 1875 // From Other to Alloca. 1876 Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI); 1877 new StoreInst(Elt, EltPtr, MI); 1878 } else { 1879 // From Alloca to Other. 1880 Value *Elt = new LoadInst(EltPtr, "tmp", MI); 1881 new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI); 1882 } 1883 continue; 1884 } 1885 assert(isa<MemSetInst>(MI)); 1886 1887 // If the stored element is zero (common case), just store a null 1888 // constant. 1889 Constant *StoreVal; 1890 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getArgOperand(1))) { 1891 if (CI->isZero()) { 1892 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0> 1893 } else { 1894 // If EltTy is a vector type, get the element type. 1895 const Type *ValTy = EltTy->getScalarType(); 1896 1897 // Construct an integer with the right value. 1898 unsigned EltSize = TD->getTypeSizeInBits(ValTy); 1899 APInt OneVal(EltSize, CI->getZExtValue()); 1900 APInt TotalVal(OneVal); 1901 // Set each byte. 1902 for (unsigned i = 0; 8*i < EltSize; ++i) { 1903 TotalVal = TotalVal.shl(8); 1904 TotalVal |= OneVal; 1905 } 1906 1907 // Convert the integer value to the appropriate type. 1908 StoreVal = ConstantInt::get(CI->getContext(), TotalVal); 1909 if (ValTy->isPointerTy()) 1910 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); 1911 else if (ValTy->isFloatingPointTy()) 1912 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy); 1913 assert(StoreVal->getType() == ValTy && "Type mismatch!"); 1914 1915 // If the requested value was a vector constant, create it. 1916 if (EltTy != ValTy) { 1917 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements(); 1918 SmallVector<Constant*, 16> Elts(NumElts, StoreVal); 1919 StoreVal = ConstantVector::get(Elts); 1920 } 1921 } 1922 new StoreInst(StoreVal, EltPtr, MI); 1923 continue; 1924 } 1925 // Otherwise, if we're storing a byte variable, use a memset call for 1926 // this element. 1927 } 1928 1929 unsigned EltSize = TD->getTypeAllocSize(EltTy); 1930 1931 IRBuilder<> Builder(MI); 1932 1933 // Finally, insert the meminst for this element. 1934 if (isa<MemSetInst>(MI)) { 1935 Builder.CreateMemSet(EltPtr, MI->getArgOperand(1), EltSize, 1936 MI->isVolatile()); 1937 } else { 1938 assert(isa<MemTransferInst>(MI)); 1939 Value *Dst = SROADest ? EltPtr : OtherElt; // Dest ptr 1940 Value *Src = SROADest ? OtherElt : EltPtr; // Src ptr 1941 1942 if (isa<MemCpyInst>(MI)) 1943 Builder.CreateMemCpy(Dst, Src, EltSize, OtherEltAlign,MI->isVolatile()); 1944 else 1945 Builder.CreateMemMove(Dst, Src, EltSize,OtherEltAlign,MI->isVolatile()); 1946 } 1947 } 1948 DeadInsts.push_back(MI); 1949} 1950 1951/// RewriteStoreUserOfWholeAlloca - We found a store of an integer that 1952/// overwrites the entire allocation. Extract out the pieces of the stored 1953/// integer and store them individually. 1954void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 1955 SmallVector<AllocaInst*, 32> &NewElts){ 1956 // Extract each element out of the integer according to its structure offset 1957 // and store the element value to the individual alloca. 1958 Value *SrcVal = SI->getOperand(0); 1959 const Type *AllocaEltTy = AI->getAllocatedType(); 1960 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 1961 1962 IRBuilder<> Builder(SI); 1963 1964 // Handle tail padding by extending the operand 1965 if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits) 1966 SrcVal = Builder.CreateZExt(SrcVal, 1967 IntegerType::get(SI->getContext(), AllocaSizeBits)); 1968 1969 DEBUG(dbgs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI 1970 << '\n'); 1971 1972 // There are two forms here: AI could be an array or struct. Both cases 1973 // have different ways to compute the element offset. 1974 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 1975 const StructLayout *Layout = TD->getStructLayout(EltSTy); 1976 1977 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1978 // Get the number of bits to shift SrcVal to get the value. 1979 const Type *FieldTy = EltSTy->getElementType(i); 1980 uint64_t Shift = Layout->getElementOffsetInBits(i); 1981 1982 if (TD->isBigEndian()) 1983 Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy); 1984 1985 Value *EltVal = SrcVal; 1986 if (Shift) { 1987 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 1988 EltVal = Builder.CreateLShr(EltVal, ShiftVal, "sroa.store.elt"); 1989 } 1990 1991 // Truncate down to an integer of the right size. 1992 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 1993 1994 // Ignore zero sized fields like {}, they obviously contain no data. 1995 if (FieldSizeBits == 0) continue; 1996 1997 if (FieldSizeBits != AllocaSizeBits) 1998 EltVal = Builder.CreateTrunc(EltVal, 1999 IntegerType::get(SI->getContext(), FieldSizeBits)); 2000 Value *DestField = NewElts[i]; 2001 if (EltVal->getType() == FieldTy) { 2002 // Storing to an integer field of this size, just do it. 2003 } else if (FieldTy->isFloatingPointTy() || FieldTy->isVectorTy()) { 2004 // Bitcast to the right element type (for fp/vector values). 2005 EltVal = Builder.CreateBitCast(EltVal, FieldTy); 2006 } else { 2007 // Otherwise, bitcast the dest pointer (for aggregates). 2008 DestField = Builder.CreateBitCast(DestField, 2009 PointerType::getUnqual(EltVal->getType())); 2010 } 2011 new StoreInst(EltVal, DestField, SI); 2012 } 2013 2014 } else { 2015 const ArrayType *ATy = cast<ArrayType>(AllocaEltTy); 2016 const Type *ArrayEltTy = ATy->getElementType(); 2017 uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 2018 uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy); 2019 2020 uint64_t Shift; 2021 2022 if (TD->isBigEndian()) 2023 Shift = AllocaSizeBits-ElementOffset; 2024 else 2025 Shift = 0; 2026 2027 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 2028 // Ignore zero sized fields like {}, they obviously contain no data. 2029 if (ElementSizeBits == 0) continue; 2030 2031 Value *EltVal = SrcVal; 2032 if (Shift) { 2033 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 2034 EltVal = Builder.CreateLShr(EltVal, ShiftVal, "sroa.store.elt"); 2035 } 2036 2037 // Truncate down to an integer of the right size. 2038 if (ElementSizeBits != AllocaSizeBits) 2039 EltVal = Builder.CreateTrunc(EltVal, 2040 IntegerType::get(SI->getContext(), 2041 ElementSizeBits)); 2042 Value *DestField = NewElts[i]; 2043 if (EltVal->getType() == ArrayEltTy) { 2044 // Storing to an integer field of this size, just do it. 2045 } else if (ArrayEltTy->isFloatingPointTy() || 2046 ArrayEltTy->isVectorTy()) { 2047 // Bitcast to the right element type (for fp/vector values). 2048 EltVal = Builder.CreateBitCast(EltVal, ArrayEltTy); 2049 } else { 2050 // Otherwise, bitcast the dest pointer (for aggregates). 2051 DestField = Builder.CreateBitCast(DestField, 2052 PointerType::getUnqual(EltVal->getType())); 2053 } 2054 new StoreInst(EltVal, DestField, SI); 2055 2056 if (TD->isBigEndian()) 2057 Shift -= ElementOffset; 2058 else 2059 Shift += ElementOffset; 2060 } 2061 } 2062 2063 DeadInsts.push_back(SI); 2064} 2065 2066/// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to 2067/// an integer. Load the individual pieces to form the aggregate value. 2068void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 2069 SmallVector<AllocaInst*, 32> &NewElts) { 2070 // Extract each element out of the NewElts according to its structure offset 2071 // and form the result value. 2072 const Type *AllocaEltTy = AI->getAllocatedType(); 2073 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 2074 2075 DEBUG(dbgs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI 2076 << '\n'); 2077 2078 // There are two forms here: AI could be an array or struct. Both cases 2079 // have different ways to compute the element offset. 2080 const StructLayout *Layout = 0; 2081 uint64_t ArrayEltBitOffset = 0; 2082 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 2083 Layout = TD->getStructLayout(EltSTy); 2084 } else { 2085 const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType(); 2086 ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 2087 } 2088 2089 Value *ResultVal = 2090 Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits)); 2091 2092 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 2093 // Load the value from the alloca. If the NewElt is an aggregate, cast 2094 // the pointer to an integer of the same size before doing the load. 2095 Value *SrcField = NewElts[i]; 2096 const Type *FieldTy = 2097 cast<PointerType>(SrcField->getType())->getElementType(); 2098 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 2099 2100 // Ignore zero sized fields like {}, they obviously contain no data. 2101 if (FieldSizeBits == 0) continue; 2102 2103 const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(), 2104 FieldSizeBits); 2105 if (!FieldTy->isIntegerTy() && !FieldTy->isFloatingPointTy() && 2106 !FieldTy->isVectorTy()) 2107 SrcField = new BitCastInst(SrcField, 2108 PointerType::getUnqual(FieldIntTy), 2109 "", LI); 2110 SrcField = new LoadInst(SrcField, "sroa.load.elt", LI); 2111 2112 // If SrcField is a fp or vector of the right size but that isn't an 2113 // integer type, bitcast to an integer so we can shift it. 2114 if (SrcField->getType() != FieldIntTy) 2115 SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI); 2116 2117 // Zero extend the field to be the same size as the final alloca so that 2118 // we can shift and insert it. 2119 if (SrcField->getType() != ResultVal->getType()) 2120 SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI); 2121 2122 // Determine the number of bits to shift SrcField. 2123 uint64_t Shift; 2124 if (Layout) // Struct case. 2125 Shift = Layout->getElementOffsetInBits(i); 2126 else // Array case. 2127 Shift = i*ArrayEltBitOffset; 2128 2129 if (TD->isBigEndian()) 2130 Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth(); 2131 2132 if (Shift) { 2133 Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift); 2134 SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI); 2135 } 2136 2137 // Don't create an 'or x, 0' on the first iteration. 2138 if (!isa<Constant>(ResultVal) || 2139 !cast<Constant>(ResultVal)->isNullValue()) 2140 ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI); 2141 else 2142 ResultVal = SrcField; 2143 } 2144 2145 // Handle tail padding by truncating the result 2146 if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits) 2147 ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI); 2148 2149 LI->replaceAllUsesWith(ResultVal); 2150 DeadInsts.push_back(LI); 2151} 2152 2153/// HasPadding - Return true if the specified type has any structure or 2154/// alignment padding in between the elements that would be split apart 2155/// by SROA; return false otherwise. 2156static bool HasPadding(const Type *Ty, const TargetData &TD) { 2157 if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 2158 Ty = ATy->getElementType(); 2159 return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty); 2160 } 2161 2162 // SROA currently handles only Arrays and Structs. 2163 const StructType *STy = cast<StructType>(Ty); 2164 const StructLayout *SL = TD.getStructLayout(STy); 2165 unsigned PrevFieldBitOffset = 0; 2166 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 2167 unsigned FieldBitOffset = SL->getElementOffsetInBits(i); 2168 2169 // Check to see if there is any padding between this element and the 2170 // previous one. 2171 if (i) { 2172 unsigned PrevFieldEnd = 2173 PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1)); 2174 if (PrevFieldEnd < FieldBitOffset) 2175 return true; 2176 } 2177 PrevFieldBitOffset = FieldBitOffset; 2178 } 2179 // Check for tail padding. 2180 if (unsigned EltCount = STy->getNumElements()) { 2181 unsigned PrevFieldEnd = PrevFieldBitOffset + 2182 TD.getTypeSizeInBits(STy->getElementType(EltCount-1)); 2183 if (PrevFieldEnd < SL->getSizeInBits()) 2184 return true; 2185 } 2186 return false; 2187} 2188 2189/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of 2190/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, 2191/// or 1 if safe after canonicalization has been performed. 2192bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) { 2193 // Loop over the use list of the alloca. We can only transform it if all of 2194 // the users are safe to transform. 2195 AllocaInfo Info(AI); 2196 2197 isSafeForScalarRepl(AI, 0, Info); 2198 if (Info.isUnsafe) { 2199 DEBUG(dbgs() << "Cannot transform: " << *AI << '\n'); 2200 return false; 2201 } 2202 2203 // Okay, we know all the users are promotable. If the aggregate is a memcpy 2204 // source and destination, we have to be careful. In particular, the memcpy 2205 // could be moving around elements that live in structure padding of the LLVM 2206 // types, but may actually be used. In these cases, we refuse to promote the 2207 // struct. 2208 if (Info.isMemCpySrc && Info.isMemCpyDst && 2209 HasPadding(AI->getAllocatedType(), *TD)) 2210 return false; 2211 2212 // If the alloca never has an access to just *part* of it, but is accessed 2213 // via loads and stores, then we should use ConvertToScalarInfo to promote 2214 // the alloca instead of promoting each piece at a time and inserting fission 2215 // and fusion code. 2216 if (!Info.hasSubelementAccess && Info.hasALoadOrStore) { 2217 // If the struct/array just has one element, use basic SRoA. 2218 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 2219 if (ST->getNumElements() > 1) return false; 2220 } else { 2221 if (cast<ArrayType>(AI->getAllocatedType())->getNumElements() > 1) 2222 return false; 2223 } 2224 } 2225 2226 return true; 2227} 2228 2229 2230 2231/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to 2232/// some part of a constant global variable. This intentionally only accepts 2233/// constant expressions because we don't can't rewrite arbitrary instructions. 2234static bool PointsToConstantGlobal(Value *V) { 2235 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) 2236 return GV->isConstant(); 2237 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 2238 if (CE->getOpcode() == Instruction::BitCast || 2239 CE->getOpcode() == Instruction::GetElementPtr) 2240 return PointsToConstantGlobal(CE->getOperand(0)); 2241 return false; 2242} 2243 2244/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived) 2245/// pointer to an alloca. Ignore any reads of the pointer, return false if we 2246/// see any stores or other unknown uses. If we see pointer arithmetic, keep 2247/// track of whether it moves the pointer (with isOffset) but otherwise traverse 2248/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to 2249/// the alloca, and if the source pointer is a pointer to a constant global, we 2250/// can optimize this. 2251static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy, 2252 bool isOffset) { 2253 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 2254 User *U = cast<Instruction>(*UI); 2255 2256 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 2257 // Ignore non-volatile loads, they are always ok. 2258 if (LI->isVolatile()) return false; 2259 continue; 2260 } 2261 2262 if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) { 2263 // If uses of the bitcast are ok, we are ok. 2264 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) 2265 return false; 2266 continue; 2267 } 2268 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 2269 // If the GEP has all zero indices, it doesn't offset the pointer. If it 2270 // doesn't, it does. 2271 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy, 2272 isOffset || !GEP->hasAllZeroIndices())) 2273 return false; 2274 continue; 2275 } 2276 2277 if (CallSite CS = U) { 2278 // If this is a readonly/readnone call site, then we know it is just a 2279 // load and we can ignore it. 2280 if (CS.onlyReadsMemory()) 2281 continue; 2282 2283 // If this is the function being called then we treat it like a load and 2284 // ignore it. 2285 if (CS.isCallee(UI)) 2286 continue; 2287 2288 // If this is being passed as a byval argument, the caller is making a 2289 // copy, so it is only a read of the alloca. 2290 unsigned ArgNo = CS.getArgumentNo(UI); 2291 if (CS.paramHasAttr(ArgNo+1, Attribute::ByVal)) 2292 continue; 2293 } 2294 2295 // If this is isn't our memcpy/memmove, reject it as something we can't 2296 // handle. 2297 MemTransferInst *MI = dyn_cast<MemTransferInst>(U); 2298 if (MI == 0) 2299 return false; 2300 2301 // If the transfer is using the alloca as a source of the transfer, then 2302 // ignore it since it is a load (unless the transfer is volatile). 2303 if (UI.getOperandNo() == 1) { 2304 if (MI->isVolatile()) return false; 2305 continue; 2306 } 2307 2308 // If we already have seen a copy, reject the second one. 2309 if (TheCopy) return false; 2310 2311 // If the pointer has been offset from the start of the alloca, we can't 2312 // safely handle this. 2313 if (isOffset) return false; 2314 2315 // If the memintrinsic isn't using the alloca as the dest, reject it. 2316 if (UI.getOperandNo() != 0) return false; 2317 2318 // If the source of the memcpy/move is not a constant global, reject it. 2319 if (!PointsToConstantGlobal(MI->getSource())) 2320 return false; 2321 2322 // Otherwise, the transform is safe. Remember the copy instruction. 2323 TheCopy = MI; 2324 } 2325 return true; 2326} 2327 2328/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only 2329/// modified by a copy from a constant global. If we can prove this, we can 2330/// replace any uses of the alloca with uses of the global directly. 2331MemTransferInst *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) { 2332 MemTransferInst *TheCopy = 0; 2333 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) 2334 return TheCopy; 2335 return 0; 2336} 2337