ScalarReplAggregates.cpp revision e0a1a5ba91df6817f9ffae7af65ed0bda66f7620
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/DominanceFrontier.h" 34#include "llvm/Analysis/ValueTracking.h" 35#include "llvm/Target/TargetData.h" 36#include "llvm/Transforms/Utils/PromoteMemToReg.h" 37#include "llvm/Transforms/Utils/Local.h" 38#include "llvm/Transforms/Utils/SSAUpdater.h" 39#include "llvm/Support/CallSite.h" 40#include "llvm/Support/Debug.h" 41#include "llvm/Support/ErrorHandling.h" 42#include "llvm/Support/GetElementPtrTypeIterator.h" 43#include "llvm/Support/IRBuilder.h" 44#include "llvm/Support/MathExtras.h" 45#include "llvm/Support/raw_ostream.h" 46#include "llvm/ADT/SmallVector.h" 47#include "llvm/ADT/Statistic.h" 48using namespace llvm; 49 50STATISTIC(NumReplaced, "Number of allocas broken up"); 51STATISTIC(NumPromoted, "Number of allocas promoted"); 52STATISTIC(NumConverted, "Number of aggregates converted to scalar"); 53STATISTIC(NumGlobals, "Number of allocas copied from constant global"); 54 55enum { 56 UsePromoteMemToReg = 1 57}; 58 59namespace { 60 struct SROA : public FunctionPass { 61 static char ID; // Pass identification, replacement for typeid 62 explicit SROA(signed T = -1) : FunctionPass(ID) { 63 initializeSROAPass(*PassRegistry::getPassRegistry()); 64 if (T == -1) 65 SRThreshold = 128; 66 else 67 SRThreshold = T; 68 } 69 70 bool runOnFunction(Function &F); 71 72 bool performScalarRepl(Function &F); 73 bool performPromotion(Function &F); 74 75 // getAnalysisUsage - This pass does not require any passes, but we know it 76 // will not alter the CFG, so say so. 77 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 78 if (UsePromoteMemToReg) { 79 AU.addRequired<DominatorTree>(); 80 AU.addRequired<DominanceFrontier>(); 81 } 82 AU.setPreservesCFG(); 83 } 84 85 private: 86 TargetData *TD; 87 88 /// DeadInsts - Keep track of instructions we have made dead, so that 89 /// we can remove them after we are done working. 90 SmallVector<Value*, 32> DeadInsts; 91 92 /// AllocaInfo - When analyzing uses of an alloca instruction, this captures 93 /// information about the uses. All these fields are initialized to false 94 /// and set to true when something is learned. 95 struct AllocaInfo { 96 /// isUnsafe - This is set to true if the alloca cannot be SROA'd. 97 bool isUnsafe : 1; 98 99 /// isMemCpySrc - This is true if this aggregate is memcpy'd from. 100 bool isMemCpySrc : 1; 101 102 /// isMemCpyDst - This is true if this aggregate is memcpy'd into. 103 bool isMemCpyDst : 1; 104 105 AllocaInfo() 106 : isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false) {} 107 }; 108 109 unsigned SRThreshold; 110 111 void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; } 112 113 bool isSafeAllocaToScalarRepl(AllocaInst *AI); 114 115 void isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 116 AllocaInfo &Info); 117 void isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t &Offset, 118 AllocaInfo &Info); 119 void isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize, 120 const Type *MemOpType, bool isStore, AllocaInfo &Info); 121 bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size); 122 uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset, 123 const Type *&IdxTy); 124 125 void DoScalarReplacement(AllocaInst *AI, 126 std::vector<AllocaInst*> &WorkList); 127 void DeleteDeadInstructions(); 128 129 void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 130 SmallVector<AllocaInst*, 32> &NewElts); 131 void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 132 SmallVector<AllocaInst*, 32> &NewElts); 133 void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 134 SmallVector<AllocaInst*, 32> &NewElts); 135 void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 136 AllocaInst *AI, 137 SmallVector<AllocaInst*, 32> &NewElts); 138 void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 139 SmallVector<AllocaInst*, 32> &NewElts); 140 void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 141 SmallVector<AllocaInst*, 32> &NewElts); 142 143 static MemTransferInst *isOnlyCopiedFromConstantGlobal(AllocaInst *AI); 144 }; 145} 146 147char SROA::ID = 0; 148INITIALIZE_PASS_BEGIN(SROA, "scalarrepl", 149 "Scalar Replacement of Aggregates", false, false) 150INITIALIZE_PASS_DEPENDENCY(DominatorTree) 151INITIALIZE_PASS_DEPENDENCY(DominanceFrontier) 152INITIALIZE_PASS_END(SROA, "scalarrepl", 153 "Scalar Replacement of Aggregates", false, false) 154 155// Public interface to the ScalarReplAggregates pass 156FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) { 157 return new SROA(Threshold); 158} 159 160 161//===----------------------------------------------------------------------===// 162// Convert To Scalar Optimization. 163//===----------------------------------------------------------------------===// 164 165namespace { 166/// ConvertToScalarInfo - This class implements the "Convert To Scalar" 167/// optimization, which scans the uses of an alloca and determines if it can 168/// rewrite it in terms of a single new alloca that can be mem2reg'd. 169class ConvertToScalarInfo { 170 /// AllocaSize - The size of the alloca being considered. 171 unsigned AllocaSize; 172 const TargetData &TD; 173 174 /// IsNotTrivial - This is set to true if there is some access to the object 175 /// which means that mem2reg can't promote it. 176 bool IsNotTrivial; 177 178 /// VectorTy - This tracks the type that we should promote the vector to if 179 /// it is possible to turn it into a vector. This starts out null, and if it 180 /// isn't possible to turn into a vector type, it gets set to VoidTy. 181 const Type *VectorTy; 182 183 /// HadAVector - True if there is at least one vector access to the alloca. 184 /// We don't want to turn random arrays into vectors and use vector element 185 /// insert/extract, but if there are element accesses to something that is 186 /// also declared as a vector, we do want to promote to a vector. 187 bool HadAVector; 188 189public: 190 explicit ConvertToScalarInfo(unsigned Size, const TargetData &td) 191 : AllocaSize(Size), TD(td) { 192 IsNotTrivial = false; 193 VectorTy = 0; 194 HadAVector = false; 195 } 196 197 AllocaInst *TryConvert(AllocaInst *AI); 198 199private: 200 bool CanConvertToScalar(Value *V, uint64_t Offset); 201 void MergeInType(const Type *In, uint64_t Offset); 202 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset); 203 204 Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType, 205 uint64_t Offset, IRBuilder<> &Builder); 206 Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal, 207 uint64_t Offset, IRBuilder<> &Builder); 208}; 209} // end anonymous namespace. 210 211 212/// IsVerbotenVectorType - Return true if this is a vector type ScalarRepl isn't 213/// allowed to form. We do this to avoid MMX types, which is a complete hack, 214/// but is required until the backend is fixed. 215static bool IsVerbotenVectorType(const VectorType *VTy, const Instruction *I) { 216 StringRef Triple(I->getParent()->getParent()->getParent()->getTargetTriple()); 217 if (!Triple.startswith("i386") && 218 !Triple.startswith("x86_64")) 219 return false; 220 221 // Reject all the MMX vector types. 222 switch (VTy->getNumElements()) { 223 default: return false; 224 case 1: return VTy->getElementType()->isIntegerTy(64); 225 case 2: return VTy->getElementType()->isIntegerTy(32); 226 case 4: return VTy->getElementType()->isIntegerTy(16); 227 case 8: return VTy->getElementType()->isIntegerTy(8); 228 } 229} 230 231 232/// TryConvert - Analyze the specified alloca, and if it is safe to do so, 233/// rewrite it to be a new alloca which is mem2reg'able. This returns the new 234/// alloca if possible or null if not. 235AllocaInst *ConvertToScalarInfo::TryConvert(AllocaInst *AI) { 236 // If we can't convert this scalar, or if mem2reg can trivially do it, bail 237 // out. 238 if (!CanConvertToScalar(AI, 0) || !IsNotTrivial) 239 return 0; 240 241 // If we were able to find a vector type that can handle this with 242 // insert/extract elements, and if there was at least one use that had 243 // a vector type, promote this to a vector. We don't want to promote 244 // random stuff that doesn't use vectors (e.g. <9 x double>) because then 245 // we just get a lot of insert/extracts. If at least one vector is 246 // involved, then we probably really do have a union of vector/array. 247 const Type *NewTy; 248 if (VectorTy && VectorTy->isVectorTy() && HadAVector && 249 !IsVerbotenVectorType(cast<VectorType>(VectorTy), AI)) { 250 DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = " 251 << *VectorTy << '\n'); 252 NewTy = VectorTy; // Use the vector type. 253 } else { 254 DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n"); 255 // Create and insert the integer alloca. 256 NewTy = IntegerType::get(AI->getContext(), AllocaSize*8); 257 } 258 AllocaInst *NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin()); 259 ConvertUsesToScalar(AI, NewAI, 0); 260 return NewAI; 261} 262 263/// MergeInType - Add the 'In' type to the accumulated vector type (VectorTy) 264/// so far at the offset specified by Offset (which is specified in bytes). 265/// 266/// There are two cases we handle here: 267/// 1) A union of vector types of the same size and potentially its elements. 268/// Here we turn element accesses into insert/extract element operations. 269/// This promotes a <4 x float> with a store of float to the third element 270/// into a <4 x float> that uses insert element. 271/// 2) A fully general blob of memory, which we turn into some (potentially 272/// large) integer type with extract and insert operations where the loads 273/// and stores would mutate the memory. We mark this by setting VectorTy 274/// to VoidTy. 275void ConvertToScalarInfo::MergeInType(const Type *In, uint64_t Offset) { 276 // If we already decided to turn this into a blob of integer memory, there is 277 // nothing to be done. 278 if (VectorTy && VectorTy->isVoidTy()) 279 return; 280 281 // If this could be contributing to a vector, analyze it. 282 283 // If the In type is a vector that is the same size as the alloca, see if it 284 // matches the existing VecTy. 285 if (const VectorType *VInTy = dyn_cast<VectorType>(In)) { 286 // Remember if we saw a vector type. 287 HadAVector = true; 288 289 if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) { 290 // If we're storing/loading a vector of the right size, allow it as a 291 // vector. If this the first vector we see, remember the type so that 292 // we know the element size. If this is a subsequent access, ignore it 293 // even if it is a differing type but the same size. Worst case we can 294 // bitcast the resultant vectors. 295 if (VectorTy == 0) 296 VectorTy = VInTy; 297 return; 298 } 299 } else if (In->isFloatTy() || In->isDoubleTy() || 300 (In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 && 301 isPowerOf2_32(In->getPrimitiveSizeInBits()))) { 302 // If we're accessing something that could be an element of a vector, see 303 // if the implied vector agrees with what we already have and if Offset is 304 // compatible with it. 305 unsigned EltSize = In->getPrimitiveSizeInBits()/8; 306 if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 && 307 (VectorTy == 0 || 308 cast<VectorType>(VectorTy)->getElementType() 309 ->getPrimitiveSizeInBits()/8 == EltSize)) { 310 if (VectorTy == 0) 311 VectorTy = VectorType::get(In, AllocaSize/EltSize); 312 return; 313 } 314 } 315 316 // Otherwise, we have a case that we can't handle with an optimized vector 317 // form. We can still turn this into a large integer. 318 VectorTy = Type::getVoidTy(In->getContext()); 319} 320 321/// CanConvertToScalar - V is a pointer. If we can convert the pointee and all 322/// its accesses to a single vector type, return true and set VecTy to 323/// the new type. If we could convert the alloca into a single promotable 324/// integer, return true but set VecTy to VoidTy. Further, if the use is not a 325/// completely trivial use that mem2reg could promote, set IsNotTrivial. Offset 326/// is the current offset from the base of the alloca being analyzed. 327/// 328/// If we see at least one access to the value that is as a vector type, set the 329/// SawVec flag. 330bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset) { 331 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 332 Instruction *User = cast<Instruction>(*UI); 333 334 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 335 // Don't break volatile loads. 336 if (LI->isVolatile()) 337 return false; 338 // Don't touch MMX operations. 339 if (LI->getType()->isX86_MMXTy()) 340 return false; 341 MergeInType(LI->getType(), Offset); 342 continue; 343 } 344 345 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 346 // Storing the pointer, not into the value? 347 if (SI->getOperand(0) == V || SI->isVolatile()) return false; 348 // Don't touch MMX operations. 349 if (SI->getOperand(0)->getType()->isX86_MMXTy()) 350 return false; 351 MergeInType(SI->getOperand(0)->getType(), Offset); 352 continue; 353 } 354 355 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { 356 IsNotTrivial = true; // Can't be mem2reg'd. 357 if (!CanConvertToScalar(BCI, Offset)) 358 return false; 359 continue; 360 } 361 362 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 363 // If this is a GEP with a variable indices, we can't handle it. 364 if (!GEP->hasAllConstantIndices()) 365 return false; 366 367 // Compute the offset that this GEP adds to the pointer. 368 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 369 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 370 &Indices[0], Indices.size()); 371 // See if all uses can be converted. 372 if (!CanConvertToScalar(GEP, Offset+GEPOffset)) 373 return false; 374 IsNotTrivial = true; // Can't be mem2reg'd. 375 continue; 376 } 377 378 // If this is a constant sized memset of a constant value (e.g. 0) we can 379 // handle it. 380 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 381 // Store of constant value and constant size. 382 if (!isa<ConstantInt>(MSI->getValue()) || 383 !isa<ConstantInt>(MSI->getLength())) 384 return false; 385 IsNotTrivial = true; // Can't be mem2reg'd. 386 continue; 387 } 388 389 // If this is a memcpy or memmove into or out of the whole allocation, we 390 // can handle it like a load or store of the scalar type. 391 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 392 ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()); 393 if (Len == 0 || Len->getZExtValue() != AllocaSize || Offset != 0) 394 return false; 395 396 IsNotTrivial = true; // Can't be mem2reg'd. 397 continue; 398 } 399 400 // Otherwise, we cannot handle this! 401 return false; 402 } 403 404 return true; 405} 406 407/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca 408/// directly. This happens when we are converting an "integer union" to a 409/// single integer scalar, or when we are converting a "vector union" to a 410/// vector with insert/extractelement instructions. 411/// 412/// Offset is an offset from the original alloca, in bits that need to be 413/// shifted to the right. By the end of this, there should be no uses of Ptr. 414void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, 415 uint64_t Offset) { 416 while (!Ptr->use_empty()) { 417 Instruction *User = cast<Instruction>(Ptr->use_back()); 418 419 if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 420 ConvertUsesToScalar(CI, NewAI, Offset); 421 CI->eraseFromParent(); 422 continue; 423 } 424 425 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 426 // Compute the offset that this GEP adds to the pointer. 427 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 428 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 429 &Indices[0], Indices.size()); 430 ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8); 431 GEP->eraseFromParent(); 432 continue; 433 } 434 435 IRBuilder<> Builder(User); 436 437 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 438 // The load is a bit extract from NewAI shifted right by Offset bits. 439 Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp"); 440 Value *NewLoadVal 441 = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder); 442 LI->replaceAllUsesWith(NewLoadVal); 443 LI->eraseFromParent(); 444 continue; 445 } 446 447 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 448 assert(SI->getOperand(0) != Ptr && "Consistency error!"); 449 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 450 Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset, 451 Builder); 452 Builder.CreateStore(New, NewAI); 453 SI->eraseFromParent(); 454 455 // If the load we just inserted is now dead, then the inserted store 456 // overwrote the entire thing. 457 if (Old->use_empty()) 458 Old->eraseFromParent(); 459 continue; 460 } 461 462 // If this is a constant sized memset of a constant value (e.g. 0) we can 463 // transform it into a store of the expanded constant value. 464 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 465 assert(MSI->getRawDest() == Ptr && "Consistency error!"); 466 unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue(); 467 if (NumBytes != 0) { 468 unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue(); 469 470 // Compute the value replicated the right number of times. 471 APInt APVal(NumBytes*8, Val); 472 473 // Splat the value if non-zero. 474 if (Val) 475 for (unsigned i = 1; i != NumBytes; ++i) 476 APVal |= APVal << 8; 477 478 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 479 Value *New = ConvertScalar_InsertValue( 480 ConstantInt::get(User->getContext(), APVal), 481 Old, Offset, Builder); 482 Builder.CreateStore(New, NewAI); 483 484 // If the load we just inserted is now dead, then the memset overwrote 485 // the entire thing. 486 if (Old->use_empty()) 487 Old->eraseFromParent(); 488 } 489 MSI->eraseFromParent(); 490 continue; 491 } 492 493 // If this is a memcpy or memmove into or out of the whole allocation, we 494 // can handle it like a load or store of the scalar type. 495 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 496 assert(Offset == 0 && "must be store to start of alloca"); 497 498 // If the source and destination are both to the same alloca, then this is 499 // a noop copy-to-self, just delete it. Otherwise, emit a load and store 500 // as appropriate. 501 AllocaInst *OrigAI = cast<AllocaInst>(GetUnderlyingObject(Ptr, 0)); 502 503 if (GetUnderlyingObject(MTI->getSource(), 0) != OrigAI) { 504 // Dest must be OrigAI, change this to be a load from the original 505 // pointer (bitcasted), then a store to our new alloca. 506 assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?"); 507 Value *SrcPtr = MTI->getSource(); 508 const PointerType* SPTy = cast<PointerType>(SrcPtr->getType()); 509 const PointerType* AIPTy = cast<PointerType>(NewAI->getType()); 510 if (SPTy->getAddressSpace() != AIPTy->getAddressSpace()) { 511 AIPTy = PointerType::get(AIPTy->getElementType(), 512 SPTy->getAddressSpace()); 513 } 514 SrcPtr = Builder.CreateBitCast(SrcPtr, AIPTy); 515 516 LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval"); 517 SrcVal->setAlignment(MTI->getAlignment()); 518 Builder.CreateStore(SrcVal, NewAI); 519 } else if (GetUnderlyingObject(MTI->getDest(), 0) != OrigAI) { 520 // Src must be OrigAI, change this to be a load from NewAI then a store 521 // through the original dest pointer (bitcasted). 522 assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?"); 523 LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval"); 524 525 const PointerType* DPTy = cast<PointerType>(MTI->getDest()->getType()); 526 const PointerType* AIPTy = cast<PointerType>(NewAI->getType()); 527 if (DPTy->getAddressSpace() != AIPTy->getAddressSpace()) { 528 AIPTy = PointerType::get(AIPTy->getElementType(), 529 DPTy->getAddressSpace()); 530 } 531 Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), AIPTy); 532 533 StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr); 534 NewStore->setAlignment(MTI->getAlignment()); 535 } else { 536 // Noop transfer. Src == Dst 537 } 538 539 MTI->eraseFromParent(); 540 continue; 541 } 542 543 llvm_unreachable("Unsupported operation!"); 544 } 545} 546 547/// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer 548/// or vector value FromVal, extracting the bits from the offset specified by 549/// Offset. This returns the value, which is of type ToType. 550/// 551/// This happens when we are converting an "integer union" to a single 552/// integer scalar, or when we are converting a "vector union" to a vector with 553/// insert/extractelement instructions. 554/// 555/// Offset is an offset from the original alloca, in bits that need to be 556/// shifted to the right. 557Value *ConvertToScalarInfo:: 558ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType, 559 uint64_t Offset, IRBuilder<> &Builder) { 560 // If the load is of the whole new alloca, no conversion is needed. 561 if (FromVal->getType() == ToType && Offset == 0) 562 return FromVal; 563 564 // If the result alloca is a vector type, this is either an element 565 // access or a bitcast to another vector type of the same size. 566 if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) { 567 if (ToType->isVectorTy()) 568 return Builder.CreateBitCast(FromVal, ToType, "tmp"); 569 570 // Otherwise it must be an element access. 571 unsigned Elt = 0; 572 if (Offset) { 573 unsigned EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 574 Elt = Offset/EltSize; 575 assert(EltSize*Elt == Offset && "Invalid modulus in validity checking"); 576 } 577 // Return the element extracted out of it. 578 Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get( 579 Type::getInt32Ty(FromVal->getContext()), Elt), "tmp"); 580 if (V->getType() != ToType) 581 V = Builder.CreateBitCast(V, ToType, "tmp"); 582 return V; 583 } 584 585 // If ToType is a first class aggregate, extract out each of the pieces and 586 // use insertvalue's to form the FCA. 587 if (const StructType *ST = dyn_cast<StructType>(ToType)) { 588 const StructLayout &Layout = *TD.getStructLayout(ST); 589 Value *Res = UndefValue::get(ST); 590 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 591 Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i), 592 Offset+Layout.getElementOffsetInBits(i), 593 Builder); 594 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 595 } 596 return Res; 597 } 598 599 if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) { 600 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 601 Value *Res = UndefValue::get(AT); 602 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 603 Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(), 604 Offset+i*EltSize, Builder); 605 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 606 } 607 return Res; 608 } 609 610 // Otherwise, this must be a union that was converted to an integer value. 611 const IntegerType *NTy = cast<IntegerType>(FromVal->getType()); 612 613 // If this is a big-endian system and the load is narrower than the 614 // full alloca type, we need to do a shift to get the right bits. 615 int ShAmt = 0; 616 if (TD.isBigEndian()) { 617 // On big-endian machines, the lowest bit is stored at the bit offset 618 // from the pointer given by getTypeStoreSizeInBits. This matters for 619 // integers with a bitwidth that is not a multiple of 8. 620 ShAmt = TD.getTypeStoreSizeInBits(NTy) - 621 TD.getTypeStoreSizeInBits(ToType) - Offset; 622 } else { 623 ShAmt = Offset; 624 } 625 626 // Note: we support negative bitwidths (with shl) which are not defined. 627 // We do this to support (f.e.) loads off the end of a structure where 628 // only some bits are used. 629 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth()) 630 FromVal = Builder.CreateLShr(FromVal, 631 ConstantInt::get(FromVal->getType(), 632 ShAmt), "tmp"); 633 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) 634 FromVal = Builder.CreateShl(FromVal, 635 ConstantInt::get(FromVal->getType(), 636 -ShAmt), "tmp"); 637 638 // Finally, unconditionally truncate the integer to the right width. 639 unsigned LIBitWidth = TD.getTypeSizeInBits(ToType); 640 if (LIBitWidth < NTy->getBitWidth()) 641 FromVal = 642 Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(), 643 LIBitWidth), "tmp"); 644 else if (LIBitWidth > NTy->getBitWidth()) 645 FromVal = 646 Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(), 647 LIBitWidth), "tmp"); 648 649 // If the result is an integer, this is a trunc or bitcast. 650 if (ToType->isIntegerTy()) { 651 // Should be done. 652 } else if (ToType->isFloatingPointTy() || ToType->isVectorTy()) { 653 // Just do a bitcast, we know the sizes match up. 654 FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp"); 655 } else { 656 // Otherwise must be a pointer. 657 FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp"); 658 } 659 assert(FromVal->getType() == ToType && "Didn't convert right?"); 660 return FromVal; 661} 662 663/// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer 664/// or vector value "Old" at the offset specified by Offset. 665/// 666/// This happens when we are converting an "integer union" to a 667/// single integer scalar, or when we are converting a "vector union" to a 668/// vector with insert/extractelement instructions. 669/// 670/// Offset is an offset from the original alloca, in bits that need to be 671/// shifted to the right. 672Value *ConvertToScalarInfo:: 673ConvertScalar_InsertValue(Value *SV, Value *Old, 674 uint64_t Offset, IRBuilder<> &Builder) { 675 // Convert the stored type to the actual type, shift it left to insert 676 // then 'or' into place. 677 const Type *AllocaType = Old->getType(); 678 LLVMContext &Context = Old->getContext(); 679 680 if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) { 681 uint64_t VecSize = TD.getTypeAllocSizeInBits(VTy); 682 uint64_t ValSize = TD.getTypeAllocSizeInBits(SV->getType()); 683 684 // Changing the whole vector with memset or with an access of a different 685 // vector type? 686 if (ValSize == VecSize) 687 return Builder.CreateBitCast(SV, AllocaType, "tmp"); 688 689 uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 690 691 // Must be an element insertion. 692 unsigned Elt = Offset/EltSize; 693 694 if (SV->getType() != VTy->getElementType()) 695 SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp"); 696 697 SV = Builder.CreateInsertElement(Old, SV, 698 ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt), 699 "tmp"); 700 return SV; 701 } 702 703 // If SV is a first-class aggregate value, insert each value recursively. 704 if (const StructType *ST = dyn_cast<StructType>(SV->getType())) { 705 const StructLayout &Layout = *TD.getStructLayout(ST); 706 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 707 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 708 Old = ConvertScalar_InsertValue(Elt, Old, 709 Offset+Layout.getElementOffsetInBits(i), 710 Builder); 711 } 712 return Old; 713 } 714 715 if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) { 716 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 717 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 718 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 719 Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder); 720 } 721 return Old; 722 } 723 724 // If SV is a float, convert it to the appropriate integer type. 725 // If it is a pointer, do the same. 726 unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType()); 727 unsigned DestWidth = TD.getTypeSizeInBits(AllocaType); 728 unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType()); 729 unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType); 730 if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy()) 731 SV = Builder.CreateBitCast(SV, 732 IntegerType::get(SV->getContext(),SrcWidth), "tmp"); 733 else if (SV->getType()->isPointerTy()) 734 SV = Builder.CreatePtrToInt(SV, TD.getIntPtrType(SV->getContext()), "tmp"); 735 736 // Zero extend or truncate the value if needed. 737 if (SV->getType() != AllocaType) { 738 if (SV->getType()->getPrimitiveSizeInBits() < 739 AllocaType->getPrimitiveSizeInBits()) 740 SV = Builder.CreateZExt(SV, AllocaType, "tmp"); 741 else { 742 // Truncation may be needed if storing more than the alloca can hold 743 // (undefined behavior). 744 SV = Builder.CreateTrunc(SV, AllocaType, "tmp"); 745 SrcWidth = DestWidth; 746 SrcStoreWidth = DestStoreWidth; 747 } 748 } 749 750 // If this is a big-endian system and the store is narrower than the 751 // full alloca type, we need to do a shift to get the right bits. 752 int ShAmt = 0; 753 if (TD.isBigEndian()) { 754 // On big-endian machines, the lowest bit is stored at the bit offset 755 // from the pointer given by getTypeStoreSizeInBits. This matters for 756 // integers with a bitwidth that is not a multiple of 8. 757 ShAmt = DestStoreWidth - SrcStoreWidth - Offset; 758 } else { 759 ShAmt = Offset; 760 } 761 762 // Note: we support negative bitwidths (with shr) which are not defined. 763 // We do this to support (f.e.) stores off the end of a structure where 764 // only some bits in the structure are set. 765 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth)); 766 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) { 767 SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(), 768 ShAmt), "tmp"); 769 Mask <<= ShAmt; 770 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { 771 SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(), 772 -ShAmt), "tmp"); 773 Mask = Mask.lshr(-ShAmt); 774 } 775 776 // Mask out the bits we are about to insert from the old value, and or 777 // in the new bits. 778 if (SrcWidth != DestWidth) { 779 assert(DestWidth > SrcWidth); 780 Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask"); 781 SV = Builder.CreateOr(Old, SV, "ins"); 782 } 783 return SV; 784} 785 786 787//===----------------------------------------------------------------------===// 788// SRoA Driver 789//===----------------------------------------------------------------------===// 790 791 792bool SROA::runOnFunction(Function &F) { 793 TD = getAnalysisIfAvailable<TargetData>(); 794 795 bool Changed = performPromotion(F); 796 797 // FIXME: ScalarRepl currently depends on TargetData more than it 798 // theoretically needs to. It should be refactored in order to support 799 // target-independent IR. Until this is done, just skip the actual 800 // scalar-replacement portion of this pass. 801 if (!TD) return Changed; 802 803 while (1) { 804 bool LocalChange = performScalarRepl(F); 805 if (!LocalChange) break; // No need to repromote if no scalarrepl 806 Changed = true; 807 LocalChange = performPromotion(F); 808 if (!LocalChange) break; // No need to re-scalarrepl if no promotion 809 } 810 811 return Changed; 812} 813 814/// PromoteAlloca - Promote an alloca to registers, using SSAUpdater. 815static void PromoteAlloca(AllocaInst *AI, SSAUpdater &SSA) { 816 SSA.Initialize(AI->getType()->getElementType(), AI->getName()); 817 818 // First step: bucket up uses of the alloca by the block they occur in. 819 // This is important because we have to handle multiple defs/uses in a block 820 // ourselves: SSAUpdater is purely for cross-block references. 821 // FIXME: Want a TinyVector<Instruction*> since there is often 0/1 element. 822 DenseMap<BasicBlock*, std::vector<Instruction*> > UsesByBlock; 823 824 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 825 UI != E; ++UI) { 826 Instruction *User = cast<Instruction>(*UI); 827 UsesByBlock[User->getParent()].push_back(User); 828 } 829 830 // Okay, now we can iterate over all the blocks in the function with uses, 831 // processing them. Keep track of which loads are loading a live-in value. 832 // Walk the uses in the use-list order to be determinstic. 833 SmallVector<LoadInst*, 32> LiveInLoads; 834 DenseMap<Value*, Value*> ReplacedLoads; 835 836 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 837 UI != E; ++UI) { 838 Instruction *User = cast<Instruction>(*UI); 839 BasicBlock *BB = User->getParent(); 840 std::vector<Instruction*> &BlockUses = UsesByBlock[BB]; 841 842 // If this block has already been processed, ignore this repeat use. 843 if (BlockUses.empty()) continue; 844 845 // Okay, this is the first use in the block. If this block just has a 846 // single user in it, we can rewrite it trivially. 847 if (BlockUses.size() == 1) { 848 // If it is a store, it is a trivial def of the value in the block. 849 if (StoreInst *SI = dyn_cast<StoreInst>(User)) 850 SSA.AddAvailableValue(BB, SI->getOperand(0)); 851 else 852 // Otherwise it is a load, queue it to rewrite as a live-in load. 853 LiveInLoads.push_back(cast<LoadInst>(User)); 854 BlockUses.clear(); 855 continue; 856 } 857 858 // Otherwise, check to see if this block is all loads. 859 bool HasStore = false; 860 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) { 861 if (isa<StoreInst>(BlockUses[i])) { 862 HasStore = true; 863 break; 864 } 865 } 866 867 // If so, we can queue them all as live in loads. We don't have an 868 // efficient way to tell which on is first in the block and don't want to 869 // scan large blocks, so just add all loads as live ins. 870 if (!HasStore) { 871 for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) 872 LiveInLoads.push_back(cast<LoadInst>(BlockUses[i])); 873 BlockUses.clear(); 874 continue; 875 } 876 877 // Otherwise, we have mixed loads and stores (or just a bunch of stores). 878 // Since SSAUpdater is purely for cross-block values, we need to determine 879 // the order of these instructions in the block. If the first use in the 880 // block is a load, then it uses the live in value. The last store defines 881 // the live out value. We handle this by doing a linear scan of the block. 882 Value *StoredValue = 0; 883 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) { 884 if (LoadInst *L = dyn_cast<LoadInst>(II)) { 885 // If this is a load from an unrelated pointer, ignore it. 886 if (L->getOperand(0) != AI) continue; 887 888 // If we haven't seen a store yet, this is a live in use, otherwise 889 // use the stored value. 890 if (StoredValue) { 891 L->replaceAllUsesWith(StoredValue); 892 ReplacedLoads[L] = StoredValue; 893 } else { 894 LiveInLoads.push_back(L); 895 } 896 continue; 897 } 898 899 if (StoreInst *S = dyn_cast<StoreInst>(II)) { 900 // If this is a store to an unrelated pointer, ignore it. 901 if (S->getPointerOperand() != AI) continue; 902 903 // Remember that this is the active value in the block. 904 StoredValue = S->getOperand(0); 905 } 906 } 907 908 // The last stored value that happened is the live-out for the block. 909 assert(StoredValue && "Already checked that there is a store in block"); 910 SSA.AddAvailableValue(BB, StoredValue); 911 BlockUses.clear(); 912 } 913 914 // Okay, now we rewrite all loads that use live-in values in the loop, 915 // inserting PHI nodes as necessary. 916 for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) { 917 LoadInst *ALoad = LiveInLoads[i]; 918 Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent()); 919 ALoad->replaceAllUsesWith(NewVal); 920 ReplacedLoads[ALoad] = NewVal; 921 } 922 923 // Now that everything is rewritten, delete the old instructions from the 924 // function. They should all be dead now. 925 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E; ) { 926 Instruction *User = cast<Instruction>(*UI++); 927 928 // If this is a load that still has uses, then the load must have been added 929 // as a live value in the SSAUpdate data structure for a block (e.g. because 930 // the loaded value was stored later). In this case, we need to recursively 931 // propagate the updates until we get to the real value. 932 if (!User->use_empty()) { 933 Value *NewVal = ReplacedLoads[User]; 934 assert(NewVal && "not a replaced load?"); 935 936 // Propagate down to the ultimate replacee. The intermediately loads 937 // could theoretically already have been deleted, so we don't want to 938 // dereference the Value*'s. 939 DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal); 940 while (RLI != ReplacedLoads.end()) { 941 NewVal = RLI->second; 942 RLI = ReplacedLoads.find(NewVal); 943 } 944 945 User->replaceAllUsesWith(NewVal); 946 } 947 948 User->eraseFromParent(); 949 } 950} 951 952 953bool SROA::performPromotion(Function &F) { 954 std::vector<AllocaInst*> Allocas; 955 DominatorTree *DT = 0; 956 DominanceFrontier *DF = 0; 957 if (UsePromoteMemToReg) { 958 DT = &getAnalysis<DominatorTree>(); 959 DF = &getAnalysis<DominanceFrontier>(); 960 } 961 962 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function 963 964 bool Changed = false; 965 966 while (1) { 967 Allocas.clear(); 968 969 // Find allocas that are safe to promote, by looking at all instructions in 970 // the entry node 971 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) 972 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? 973 if (isAllocaPromotable(AI)) 974 Allocas.push_back(AI); 975 976 if (Allocas.empty()) break; 977 978 if (UsePromoteMemToReg) 979 PromoteMemToReg(Allocas, *DT, *DF); 980 else { 981 SSAUpdater SSA; 982 for (unsigned i = 0, e = Allocas.size(); i != e; ++i) { 983 PromoteAlloca(Allocas[i], SSA); 984 Allocas[i]->eraseFromParent(); 985 } 986 } 987 NumPromoted += Allocas.size(); 988 Changed = true; 989 } 990 991 return Changed; 992} 993 994 995/// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for 996/// SROA. It must be a struct or array type with a small number of elements. 997static bool ShouldAttemptScalarRepl(AllocaInst *AI) { 998 const Type *T = AI->getAllocatedType(); 999 // Do not promote any struct into more than 32 separate vars. 1000 if (const StructType *ST = dyn_cast<StructType>(T)) 1001 return ST->getNumElements() <= 32; 1002 // Arrays are much less likely to be safe for SROA; only consider 1003 // them if they are very small. 1004 if (const ArrayType *AT = dyn_cast<ArrayType>(T)) 1005 return AT->getNumElements() <= 8; 1006 return false; 1007} 1008 1009 1010// performScalarRepl - This algorithm is a simple worklist driven algorithm, 1011// which runs on all of the malloc/alloca instructions in the function, removing 1012// them if they are only used by getelementptr instructions. 1013// 1014bool SROA::performScalarRepl(Function &F) { 1015 std::vector<AllocaInst*> WorkList; 1016 1017 // Scan the entry basic block, adding allocas to the worklist. 1018 BasicBlock &BB = F.getEntryBlock(); 1019 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) 1020 if (AllocaInst *A = dyn_cast<AllocaInst>(I)) 1021 WorkList.push_back(A); 1022 1023 // Process the worklist 1024 bool Changed = false; 1025 while (!WorkList.empty()) { 1026 AllocaInst *AI = WorkList.back(); 1027 WorkList.pop_back(); 1028 1029 // Handle dead allocas trivially. These can be formed by SROA'ing arrays 1030 // with unused elements. 1031 if (AI->use_empty()) { 1032 AI->eraseFromParent(); 1033 Changed = true; 1034 continue; 1035 } 1036 1037 // If this alloca is impossible for us to promote, reject it early. 1038 if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized()) 1039 continue; 1040 1041 // Check to see if this allocation is only modified by a memcpy/memmove from 1042 // a constant global. If this is the case, we can change all users to use 1043 // the constant global instead. This is commonly produced by the CFE by 1044 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A' 1045 // is only subsequently read. 1046 if (MemTransferInst *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) { 1047 DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n'); 1048 DEBUG(dbgs() << " memcpy = " << *TheCopy << '\n'); 1049 Constant *TheSrc = cast<Constant>(TheCopy->getSource()); 1050 AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType())); 1051 TheCopy->eraseFromParent(); // Don't mutate the global. 1052 AI->eraseFromParent(); 1053 ++NumGlobals; 1054 Changed = true; 1055 continue; 1056 } 1057 1058 // Check to see if we can perform the core SROA transformation. We cannot 1059 // transform the allocation instruction if it is an array allocation 1060 // (allocations OF arrays are ok though), and an allocation of a scalar 1061 // value cannot be decomposed at all. 1062 uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType()); 1063 1064 // Do not promote [0 x %struct]. 1065 if (AllocaSize == 0) continue; 1066 1067 // Do not promote any struct whose size is too big. 1068 if (AllocaSize > SRThreshold) continue; 1069 1070 // If the alloca looks like a good candidate for scalar replacement, and if 1071 // all its users can be transformed, then split up the aggregate into its 1072 // separate elements. 1073 if (ShouldAttemptScalarRepl(AI) && isSafeAllocaToScalarRepl(AI)) { 1074 DoScalarReplacement(AI, WorkList); 1075 Changed = true; 1076 continue; 1077 } 1078 1079 // If we can turn this aggregate value (potentially with casts) into a 1080 // simple scalar value that can be mem2reg'd into a register value. 1081 // IsNotTrivial tracks whether this is something that mem2reg could have 1082 // promoted itself. If so, we don't want to transform it needlessly. Note 1083 // that we can't just check based on the type: the alloca may be of an i32 1084 // but that has pointer arithmetic to set byte 3 of it or something. 1085 if (AllocaInst *NewAI = 1086 ConvertToScalarInfo((unsigned)AllocaSize, *TD).TryConvert(AI)) { 1087 NewAI->takeName(AI); 1088 AI->eraseFromParent(); 1089 ++NumConverted; 1090 Changed = true; 1091 continue; 1092 } 1093 1094 // Otherwise, couldn't process this alloca. 1095 } 1096 1097 return Changed; 1098} 1099 1100/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl 1101/// predicate, do SROA now. 1102void SROA::DoScalarReplacement(AllocaInst *AI, 1103 std::vector<AllocaInst*> &WorkList) { 1104 DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n'); 1105 SmallVector<AllocaInst*, 32> ElementAllocas; 1106 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 1107 ElementAllocas.reserve(ST->getNumContainedTypes()); 1108 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { 1109 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 1110 AI->getAlignment(), 1111 AI->getName() + "." + Twine(i), AI); 1112 ElementAllocas.push_back(NA); 1113 WorkList.push_back(NA); // Add to worklist for recursive processing 1114 } 1115 } else { 1116 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); 1117 ElementAllocas.reserve(AT->getNumElements()); 1118 const Type *ElTy = AT->getElementType(); 1119 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 1120 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(), 1121 AI->getName() + "." + Twine(i), AI); 1122 ElementAllocas.push_back(NA); 1123 WorkList.push_back(NA); // Add to worklist for recursive processing 1124 } 1125 } 1126 1127 // Now that we have created the new alloca instructions, rewrite all the 1128 // uses of the old alloca. 1129 RewriteForScalarRepl(AI, AI, 0, ElementAllocas); 1130 1131 // Now erase any instructions that were made dead while rewriting the alloca. 1132 DeleteDeadInstructions(); 1133 AI->eraseFromParent(); 1134 1135 ++NumReplaced; 1136} 1137 1138/// DeleteDeadInstructions - Erase instructions on the DeadInstrs list, 1139/// recursively including all their operands that become trivially dead. 1140void SROA::DeleteDeadInstructions() { 1141 while (!DeadInsts.empty()) { 1142 Instruction *I = cast<Instruction>(DeadInsts.pop_back_val()); 1143 1144 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) 1145 if (Instruction *U = dyn_cast<Instruction>(*OI)) { 1146 // Zero out the operand and see if it becomes trivially dead. 1147 // (But, don't add allocas to the dead instruction list -- they are 1148 // already on the worklist and will be deleted separately.) 1149 *OI = 0; 1150 if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U)) 1151 DeadInsts.push_back(U); 1152 } 1153 1154 I->eraseFromParent(); 1155 } 1156} 1157 1158/// isSafeForScalarRepl - Check if instruction I is a safe use with regard to 1159/// performing scalar replacement of alloca AI. The results are flagged in 1160/// the Info parameter. Offset indicates the position within AI that is 1161/// referenced by this instruction. 1162void SROA::isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 1163 AllocaInfo &Info) { 1164 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 1165 Instruction *User = cast<Instruction>(*UI); 1166 1167 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1168 isSafeForScalarRepl(BC, AI, Offset, Info); 1169 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1170 uint64_t GEPOffset = Offset; 1171 isSafeGEP(GEPI, AI, GEPOffset, Info); 1172 if (!Info.isUnsafe) 1173 isSafeForScalarRepl(GEPI, AI, GEPOffset, Info); 1174 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 1175 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 1176 if (Length) 1177 isSafeMemAccess(AI, Offset, Length->getZExtValue(), 0, 1178 UI.getOperandNo() == 0, Info); 1179 else 1180 MarkUnsafe(Info); 1181 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1182 if (!LI->isVolatile()) { 1183 const Type *LIType = LI->getType(); 1184 isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(LIType), 1185 LIType, false, Info); 1186 } else 1187 MarkUnsafe(Info); 1188 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1189 // Store is ok if storing INTO the pointer, not storing the pointer 1190 if (!SI->isVolatile() && SI->getOperand(0) != I) { 1191 const Type *SIType = SI->getOperand(0)->getType(); 1192 isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(SIType), 1193 SIType, true, Info); 1194 } else 1195 MarkUnsafe(Info); 1196 } else { 1197 DEBUG(errs() << " Transformation preventing inst: " << *User << '\n'); 1198 MarkUnsafe(Info); 1199 } 1200 if (Info.isUnsafe) return; 1201 } 1202} 1203 1204/// isSafeGEP - Check if a GEP instruction can be handled for scalar 1205/// replacement. It is safe when all the indices are constant, in-bounds 1206/// references, and when the resulting offset corresponds to an element within 1207/// the alloca type. The results are flagged in the Info parameter. Upon 1208/// return, Offset is adjusted as specified by the GEP indices. 1209void SROA::isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI, 1210 uint64_t &Offset, AllocaInfo &Info) { 1211 gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI); 1212 if (GEPIt == E) 1213 return; 1214 1215 // Walk through the GEP type indices, checking the types that this indexes 1216 // into. 1217 for (; GEPIt != E; ++GEPIt) { 1218 // Ignore struct elements, no extra checking needed for these. 1219 if ((*GEPIt)->isStructTy()) 1220 continue; 1221 1222 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand()); 1223 if (!IdxVal) 1224 return MarkUnsafe(Info); 1225 } 1226 1227 // Compute the offset due to this GEP and check if the alloca has a 1228 // component element at that offset. 1229 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 1230 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 1231 &Indices[0], Indices.size()); 1232 if (!TypeHasComponent(AI->getAllocatedType(), Offset, 0)) 1233 MarkUnsafe(Info); 1234} 1235 1236/// isHomogeneousAggregate - Check if type T is a struct or array containing 1237/// elements of the same type (which is always true for arrays). If so, 1238/// return true with NumElts and EltTy set to the number of elements and the 1239/// element type, respectively. 1240static bool isHomogeneousAggregate(const Type *T, unsigned &NumElts, 1241 const Type *&EltTy) { 1242 if (const ArrayType *AT = dyn_cast<ArrayType>(T)) { 1243 NumElts = AT->getNumElements(); 1244 EltTy = (NumElts == 0 ? 0 : AT->getElementType()); 1245 return true; 1246 } 1247 if (const StructType *ST = dyn_cast<StructType>(T)) { 1248 NumElts = ST->getNumContainedTypes(); 1249 EltTy = (NumElts == 0 ? 0 : ST->getContainedType(0)); 1250 for (unsigned n = 1; n < NumElts; ++n) { 1251 if (ST->getContainedType(n) != EltTy) 1252 return false; 1253 } 1254 return true; 1255 } 1256 return false; 1257} 1258 1259/// isCompatibleAggregate - Check if T1 and T2 are either the same type or are 1260/// "homogeneous" aggregates with the same element type and number of elements. 1261static bool isCompatibleAggregate(const Type *T1, const Type *T2) { 1262 if (T1 == T2) 1263 return true; 1264 1265 unsigned NumElts1, NumElts2; 1266 const Type *EltTy1, *EltTy2; 1267 if (isHomogeneousAggregate(T1, NumElts1, EltTy1) && 1268 isHomogeneousAggregate(T2, NumElts2, EltTy2) && 1269 NumElts1 == NumElts2 && 1270 EltTy1 == EltTy2) 1271 return true; 1272 1273 return false; 1274} 1275 1276/// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI 1277/// alloca or has an offset and size that corresponds to a component element 1278/// within it. The offset checked here may have been formed from a GEP with a 1279/// pointer bitcasted to a different type. 1280void SROA::isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize, 1281 const Type *MemOpType, bool isStore, 1282 AllocaInfo &Info) { 1283 // Check if this is a load/store of the entire alloca. 1284 if (Offset == 0 && MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) { 1285 // This can be safe for MemIntrinsics (where MemOpType is 0) and integer 1286 // loads/stores (which are essentially the same as the MemIntrinsics with 1287 // regard to copying padding between elements). But, if an alloca is 1288 // flagged as both a source and destination of such operations, we'll need 1289 // to check later for padding between elements. 1290 if (!MemOpType || MemOpType->isIntegerTy()) { 1291 if (isStore) 1292 Info.isMemCpyDst = true; 1293 else 1294 Info.isMemCpySrc = true; 1295 return; 1296 } 1297 // This is also safe for references using a type that is compatible with 1298 // the type of the alloca, so that loads/stores can be rewritten using 1299 // insertvalue/extractvalue. 1300 if (isCompatibleAggregate(MemOpType, AI->getAllocatedType())) 1301 return; 1302 } 1303 // Check if the offset/size correspond to a component within the alloca type. 1304 const Type *T = AI->getAllocatedType(); 1305 if (TypeHasComponent(T, Offset, MemSize)) 1306 return; 1307 1308 return MarkUnsafe(Info); 1309} 1310 1311/// TypeHasComponent - Return true if T has a component type with the 1312/// specified offset and size. If Size is zero, do not check the size. 1313bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) { 1314 const Type *EltTy; 1315 uint64_t EltSize; 1316 if (const StructType *ST = dyn_cast<StructType>(T)) { 1317 const StructLayout *Layout = TD->getStructLayout(ST); 1318 unsigned EltIdx = Layout->getElementContainingOffset(Offset); 1319 EltTy = ST->getContainedType(EltIdx); 1320 EltSize = TD->getTypeAllocSize(EltTy); 1321 Offset -= Layout->getElementOffset(EltIdx); 1322 } else if (const ArrayType *AT = dyn_cast<ArrayType>(T)) { 1323 EltTy = AT->getElementType(); 1324 EltSize = TD->getTypeAllocSize(EltTy); 1325 if (Offset >= AT->getNumElements() * EltSize) 1326 return false; 1327 Offset %= EltSize; 1328 } else { 1329 return false; 1330 } 1331 if (Offset == 0 && (Size == 0 || EltSize == Size)) 1332 return true; 1333 // Check if the component spans multiple elements. 1334 if (Offset + Size > EltSize) 1335 return false; 1336 return TypeHasComponent(EltTy, Offset, Size); 1337} 1338 1339/// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite 1340/// the instruction I, which references it, to use the separate elements. 1341/// Offset indicates the position within AI that is referenced by this 1342/// instruction. 1343void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 1344 SmallVector<AllocaInst*, 32> &NewElts) { 1345 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 1346 Instruction *User = cast<Instruction>(*UI); 1347 1348 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 1349 RewriteBitCast(BC, AI, Offset, NewElts); 1350 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 1351 RewriteGEP(GEPI, AI, Offset, NewElts); 1352 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 1353 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 1354 uint64_t MemSize = Length->getZExtValue(); 1355 if (Offset == 0 && 1356 MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) 1357 RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts); 1358 // Otherwise the intrinsic can only touch a single element and the 1359 // address operand will be updated, so nothing else needs to be done. 1360 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1361 const Type *LIType = LI->getType(); 1362 if (isCompatibleAggregate(LIType, AI->getAllocatedType())) { 1363 // Replace: 1364 // %res = load { i32, i32 }* %alloc 1365 // with: 1366 // %load.0 = load i32* %alloc.0 1367 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0 1368 // %load.1 = load i32* %alloc.1 1369 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1 1370 // (Also works for arrays instead of structs) 1371 Value *Insert = UndefValue::get(LIType); 1372 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1373 Value *Load = new LoadInst(NewElts[i], "load", LI); 1374 Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI); 1375 } 1376 LI->replaceAllUsesWith(Insert); 1377 DeadInsts.push_back(LI); 1378 } else if (LIType->isIntegerTy() && 1379 TD->getTypeAllocSize(LIType) == 1380 TD->getTypeAllocSize(AI->getAllocatedType())) { 1381 // If this is a load of the entire alloca to an integer, rewrite it. 1382 RewriteLoadUserOfWholeAlloca(LI, AI, NewElts); 1383 } 1384 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1385 Value *Val = SI->getOperand(0); 1386 const Type *SIType = Val->getType(); 1387 if (isCompatibleAggregate(SIType, AI->getAllocatedType())) { 1388 // Replace: 1389 // store { i32, i32 } %val, { i32, i32 }* %alloc 1390 // with: 1391 // %val.0 = extractvalue { i32, i32 } %val, 0 1392 // store i32 %val.0, i32* %alloc.0 1393 // %val.1 = extractvalue { i32, i32 } %val, 1 1394 // store i32 %val.1, i32* %alloc.1 1395 // (Also works for arrays instead of structs) 1396 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1397 Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI); 1398 new StoreInst(Extract, NewElts[i], SI); 1399 } 1400 DeadInsts.push_back(SI); 1401 } else if (SIType->isIntegerTy() && 1402 TD->getTypeAllocSize(SIType) == 1403 TD->getTypeAllocSize(AI->getAllocatedType())) { 1404 // If this is a store of the entire alloca from an integer, rewrite it. 1405 RewriteStoreUserOfWholeAlloca(SI, AI, NewElts); 1406 } 1407 } 1408 } 1409} 1410 1411/// RewriteBitCast - Update a bitcast reference to the alloca being replaced 1412/// and recursively continue updating all of its uses. 1413void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 1414 SmallVector<AllocaInst*, 32> &NewElts) { 1415 RewriteForScalarRepl(BC, AI, Offset, NewElts); 1416 if (BC->getOperand(0) != AI) 1417 return; 1418 1419 // The bitcast references the original alloca. Replace its uses with 1420 // references to the first new element alloca. 1421 Instruction *Val = NewElts[0]; 1422 if (Val->getType() != BC->getDestTy()) { 1423 Val = new BitCastInst(Val, BC->getDestTy(), "", BC); 1424 Val->takeName(BC); 1425 } 1426 BC->replaceAllUsesWith(Val); 1427 DeadInsts.push_back(BC); 1428} 1429 1430/// FindElementAndOffset - Return the index of the element containing Offset 1431/// within the specified type, which must be either a struct or an array. 1432/// Sets T to the type of the element and Offset to the offset within that 1433/// element. IdxTy is set to the type of the index result to be used in a 1434/// GEP instruction. 1435uint64_t SROA::FindElementAndOffset(const Type *&T, uint64_t &Offset, 1436 const Type *&IdxTy) { 1437 uint64_t Idx = 0; 1438 if (const StructType *ST = dyn_cast<StructType>(T)) { 1439 const StructLayout *Layout = TD->getStructLayout(ST); 1440 Idx = Layout->getElementContainingOffset(Offset); 1441 T = ST->getContainedType(Idx); 1442 Offset -= Layout->getElementOffset(Idx); 1443 IdxTy = Type::getInt32Ty(T->getContext()); 1444 return Idx; 1445 } 1446 const ArrayType *AT = cast<ArrayType>(T); 1447 T = AT->getElementType(); 1448 uint64_t EltSize = TD->getTypeAllocSize(T); 1449 Idx = Offset / EltSize; 1450 Offset -= Idx * EltSize; 1451 IdxTy = Type::getInt64Ty(T->getContext()); 1452 return Idx; 1453} 1454 1455/// RewriteGEP - Check if this GEP instruction moves the pointer across 1456/// elements of the alloca that are being split apart, and if so, rewrite 1457/// the GEP to be relative to the new element. 1458void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 1459 SmallVector<AllocaInst*, 32> &NewElts) { 1460 uint64_t OldOffset = Offset; 1461 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 1462 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 1463 &Indices[0], Indices.size()); 1464 1465 RewriteForScalarRepl(GEPI, AI, Offset, NewElts); 1466 1467 const Type *T = AI->getAllocatedType(); 1468 const Type *IdxTy; 1469 uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy); 1470 if (GEPI->getOperand(0) == AI) 1471 OldIdx = ~0ULL; // Force the GEP to be rewritten. 1472 1473 T = AI->getAllocatedType(); 1474 uint64_t EltOffset = Offset; 1475 uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy); 1476 1477 // If this GEP does not move the pointer across elements of the alloca 1478 // being split, then it does not needs to be rewritten. 1479 if (Idx == OldIdx) 1480 return; 1481 1482 const Type *i32Ty = Type::getInt32Ty(AI->getContext()); 1483 SmallVector<Value*, 8> NewArgs; 1484 NewArgs.push_back(Constant::getNullValue(i32Ty)); 1485 while (EltOffset != 0) { 1486 uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy); 1487 NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx)); 1488 } 1489 Instruction *Val = NewElts[Idx]; 1490 if (NewArgs.size() > 1) { 1491 Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(), 1492 NewArgs.end(), "", GEPI); 1493 Val->takeName(GEPI); 1494 } 1495 if (Val->getType() != GEPI->getType()) 1496 Val = new BitCastInst(Val, GEPI->getType(), Val->getName(), GEPI); 1497 GEPI->replaceAllUsesWith(Val); 1498 DeadInsts.push_back(GEPI); 1499} 1500 1501/// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI. 1502/// Rewrite it to copy or set the elements of the scalarized memory. 1503void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 1504 AllocaInst *AI, 1505 SmallVector<AllocaInst*, 32> &NewElts) { 1506 // If this is a memcpy/memmove, construct the other pointer as the 1507 // appropriate type. The "Other" pointer is the pointer that goes to memory 1508 // that doesn't have anything to do with the alloca that we are promoting. For 1509 // memset, this Value* stays null. 1510 Value *OtherPtr = 0; 1511 unsigned MemAlignment = MI->getAlignment(); 1512 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy 1513 if (Inst == MTI->getRawDest()) 1514 OtherPtr = MTI->getRawSource(); 1515 else { 1516 assert(Inst == MTI->getRawSource()); 1517 OtherPtr = MTI->getRawDest(); 1518 } 1519 } 1520 1521 // If there is an other pointer, we want to convert it to the same pointer 1522 // type as AI has, so we can GEP through it safely. 1523 if (OtherPtr) { 1524 unsigned AddrSpace = 1525 cast<PointerType>(OtherPtr->getType())->getAddressSpace(); 1526 1527 // Remove bitcasts and all-zero GEPs from OtherPtr. This is an 1528 // optimization, but it's also required to detect the corner case where 1529 // both pointer operands are referencing the same memory, and where 1530 // OtherPtr may be a bitcast or GEP that currently being rewritten. (This 1531 // function is only called for mem intrinsics that access the whole 1532 // aggregate, so non-zero GEPs are not an issue here.) 1533 OtherPtr = OtherPtr->stripPointerCasts(); 1534 1535 // Copying the alloca to itself is a no-op: just delete it. 1536 if (OtherPtr == AI || OtherPtr == NewElts[0]) { 1537 // This code will run twice for a no-op memcpy -- once for each operand. 1538 // Put only one reference to MI on the DeadInsts list. 1539 for (SmallVector<Value*, 32>::const_iterator I = DeadInsts.begin(), 1540 E = DeadInsts.end(); I != E; ++I) 1541 if (*I == MI) return; 1542 DeadInsts.push_back(MI); 1543 return; 1544 } 1545 1546 // If the pointer is not the right type, insert a bitcast to the right 1547 // type. 1548 const Type *NewTy = 1549 PointerType::get(AI->getType()->getElementType(), AddrSpace); 1550 1551 if (OtherPtr->getType() != NewTy) 1552 OtherPtr = new BitCastInst(OtherPtr, NewTy, OtherPtr->getName(), MI); 1553 } 1554 1555 // Process each element of the aggregate. 1556 bool SROADest = MI->getRawDest() == Inst; 1557 1558 Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext())); 1559 1560 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1561 // If this is a memcpy/memmove, emit a GEP of the other element address. 1562 Value *OtherElt = 0; 1563 unsigned OtherEltAlign = MemAlignment; 1564 1565 if (OtherPtr) { 1566 Value *Idx[2] = { Zero, 1567 ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) }; 1568 OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2, 1569 OtherPtr->getName()+"."+Twine(i), 1570 MI); 1571 uint64_t EltOffset; 1572 const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType()); 1573 const Type *OtherTy = OtherPtrTy->getElementType(); 1574 if (const StructType *ST = dyn_cast<StructType>(OtherTy)) { 1575 EltOffset = TD->getStructLayout(ST)->getElementOffset(i); 1576 } else { 1577 const Type *EltTy = cast<SequentialType>(OtherTy)->getElementType(); 1578 EltOffset = TD->getTypeAllocSize(EltTy)*i; 1579 } 1580 1581 // The alignment of the other pointer is the guaranteed alignment of the 1582 // element, which is affected by both the known alignment of the whole 1583 // mem intrinsic and the alignment of the element. If the alignment of 1584 // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the 1585 // known alignment is just 4 bytes. 1586 OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset); 1587 } 1588 1589 Value *EltPtr = NewElts[i]; 1590 const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType(); 1591 1592 // If we got down to a scalar, insert a load or store as appropriate. 1593 if (EltTy->isSingleValueType()) { 1594 if (isa<MemTransferInst>(MI)) { 1595 if (SROADest) { 1596 // From Other to Alloca. 1597 Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI); 1598 new StoreInst(Elt, EltPtr, MI); 1599 } else { 1600 // From Alloca to Other. 1601 Value *Elt = new LoadInst(EltPtr, "tmp", MI); 1602 new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI); 1603 } 1604 continue; 1605 } 1606 assert(isa<MemSetInst>(MI)); 1607 1608 // If the stored element is zero (common case), just store a null 1609 // constant. 1610 Constant *StoreVal; 1611 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getArgOperand(1))) { 1612 if (CI->isZero()) { 1613 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0> 1614 } else { 1615 // If EltTy is a vector type, get the element type. 1616 const Type *ValTy = EltTy->getScalarType(); 1617 1618 // Construct an integer with the right value. 1619 unsigned EltSize = TD->getTypeSizeInBits(ValTy); 1620 APInt OneVal(EltSize, CI->getZExtValue()); 1621 APInt TotalVal(OneVal); 1622 // Set each byte. 1623 for (unsigned i = 0; 8*i < EltSize; ++i) { 1624 TotalVal = TotalVal.shl(8); 1625 TotalVal |= OneVal; 1626 } 1627 1628 // Convert the integer value to the appropriate type. 1629 StoreVal = ConstantInt::get(CI->getContext(), TotalVal); 1630 if (ValTy->isPointerTy()) 1631 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); 1632 else if (ValTy->isFloatingPointTy()) 1633 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy); 1634 assert(StoreVal->getType() == ValTy && "Type mismatch!"); 1635 1636 // If the requested value was a vector constant, create it. 1637 if (EltTy != ValTy) { 1638 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements(); 1639 SmallVector<Constant*, 16> Elts(NumElts, StoreVal); 1640 StoreVal = ConstantVector::get(&Elts[0], NumElts); 1641 } 1642 } 1643 new StoreInst(StoreVal, EltPtr, MI); 1644 continue; 1645 } 1646 // Otherwise, if we're storing a byte variable, use a memset call for 1647 // this element. 1648 } 1649 1650 unsigned EltSize = TD->getTypeAllocSize(EltTy); 1651 1652 IRBuilder<> Builder(MI); 1653 1654 // Finally, insert the meminst for this element. 1655 if (isa<MemSetInst>(MI)) { 1656 Builder.CreateMemSet(EltPtr, MI->getArgOperand(1), EltSize, 1657 MI->isVolatile()); 1658 } else { 1659 assert(isa<MemTransferInst>(MI)); 1660 Value *Dst = SROADest ? EltPtr : OtherElt; // Dest ptr 1661 Value *Src = SROADest ? OtherElt : EltPtr; // Src ptr 1662 1663 if (isa<MemCpyInst>(MI)) 1664 Builder.CreateMemCpy(Dst, Src, EltSize, OtherEltAlign,MI->isVolatile()); 1665 else 1666 Builder.CreateMemMove(Dst, Src, EltSize,OtherEltAlign,MI->isVolatile()); 1667 } 1668 } 1669 DeadInsts.push_back(MI); 1670} 1671 1672/// RewriteStoreUserOfWholeAlloca - We found a store of an integer that 1673/// overwrites the entire allocation. Extract out the pieces of the stored 1674/// integer and store them individually. 1675void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 1676 SmallVector<AllocaInst*, 32> &NewElts){ 1677 // Extract each element out of the integer according to its structure offset 1678 // and store the element value to the individual alloca. 1679 Value *SrcVal = SI->getOperand(0); 1680 const Type *AllocaEltTy = AI->getAllocatedType(); 1681 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 1682 1683 // Handle tail padding by extending the operand 1684 if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits) 1685 SrcVal = new ZExtInst(SrcVal, 1686 IntegerType::get(SI->getContext(), AllocaSizeBits), 1687 "", SI); 1688 1689 DEBUG(dbgs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI 1690 << '\n'); 1691 1692 // There are two forms here: AI could be an array or struct. Both cases 1693 // have different ways to compute the element offset. 1694 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 1695 const StructLayout *Layout = TD->getStructLayout(EltSTy); 1696 1697 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1698 // Get the number of bits to shift SrcVal to get the value. 1699 const Type *FieldTy = EltSTy->getElementType(i); 1700 uint64_t Shift = Layout->getElementOffsetInBits(i); 1701 1702 if (TD->isBigEndian()) 1703 Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy); 1704 1705 Value *EltVal = SrcVal; 1706 if (Shift) { 1707 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 1708 EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal, 1709 "sroa.store.elt", SI); 1710 } 1711 1712 // Truncate down to an integer of the right size. 1713 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 1714 1715 // Ignore zero sized fields like {}, they obviously contain no data. 1716 if (FieldSizeBits == 0) continue; 1717 1718 if (FieldSizeBits != AllocaSizeBits) 1719 EltVal = new TruncInst(EltVal, 1720 IntegerType::get(SI->getContext(), FieldSizeBits), 1721 "", SI); 1722 Value *DestField = NewElts[i]; 1723 if (EltVal->getType() == FieldTy) { 1724 // Storing to an integer field of this size, just do it. 1725 } else if (FieldTy->isFloatingPointTy() || FieldTy->isVectorTy()) { 1726 // Bitcast to the right element type (for fp/vector values). 1727 EltVal = new BitCastInst(EltVal, FieldTy, "", SI); 1728 } else { 1729 // Otherwise, bitcast the dest pointer (for aggregates). 1730 DestField = new BitCastInst(DestField, 1731 PointerType::getUnqual(EltVal->getType()), 1732 "", SI); 1733 } 1734 new StoreInst(EltVal, DestField, SI); 1735 } 1736 1737 } else { 1738 const ArrayType *ATy = cast<ArrayType>(AllocaEltTy); 1739 const Type *ArrayEltTy = ATy->getElementType(); 1740 uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 1741 uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy); 1742 1743 uint64_t Shift; 1744 1745 if (TD->isBigEndian()) 1746 Shift = AllocaSizeBits-ElementOffset; 1747 else 1748 Shift = 0; 1749 1750 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1751 // Ignore zero sized fields like {}, they obviously contain no data. 1752 if (ElementSizeBits == 0) continue; 1753 1754 Value *EltVal = SrcVal; 1755 if (Shift) { 1756 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 1757 EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal, 1758 "sroa.store.elt", SI); 1759 } 1760 1761 // Truncate down to an integer of the right size. 1762 if (ElementSizeBits != AllocaSizeBits) 1763 EltVal = new TruncInst(EltVal, 1764 IntegerType::get(SI->getContext(), 1765 ElementSizeBits), "", SI); 1766 Value *DestField = NewElts[i]; 1767 if (EltVal->getType() == ArrayEltTy) { 1768 // Storing to an integer field of this size, just do it. 1769 } else if (ArrayEltTy->isFloatingPointTy() || 1770 ArrayEltTy->isVectorTy()) { 1771 // Bitcast to the right element type (for fp/vector values). 1772 EltVal = new BitCastInst(EltVal, ArrayEltTy, "", SI); 1773 } else { 1774 // Otherwise, bitcast the dest pointer (for aggregates). 1775 DestField = new BitCastInst(DestField, 1776 PointerType::getUnqual(EltVal->getType()), 1777 "", SI); 1778 } 1779 new StoreInst(EltVal, DestField, SI); 1780 1781 if (TD->isBigEndian()) 1782 Shift -= ElementOffset; 1783 else 1784 Shift += ElementOffset; 1785 } 1786 } 1787 1788 DeadInsts.push_back(SI); 1789} 1790 1791/// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to 1792/// an integer. Load the individual pieces to form the aggregate value. 1793void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 1794 SmallVector<AllocaInst*, 32> &NewElts) { 1795 // Extract each element out of the NewElts according to its structure offset 1796 // and form the result value. 1797 const Type *AllocaEltTy = AI->getAllocatedType(); 1798 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 1799 1800 DEBUG(dbgs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI 1801 << '\n'); 1802 1803 // There are two forms here: AI could be an array or struct. Both cases 1804 // have different ways to compute the element offset. 1805 const StructLayout *Layout = 0; 1806 uint64_t ArrayEltBitOffset = 0; 1807 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 1808 Layout = TD->getStructLayout(EltSTy); 1809 } else { 1810 const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType(); 1811 ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 1812 } 1813 1814 Value *ResultVal = 1815 Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits)); 1816 1817 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1818 // Load the value from the alloca. If the NewElt is an aggregate, cast 1819 // the pointer to an integer of the same size before doing the load. 1820 Value *SrcField = NewElts[i]; 1821 const Type *FieldTy = 1822 cast<PointerType>(SrcField->getType())->getElementType(); 1823 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 1824 1825 // Ignore zero sized fields like {}, they obviously contain no data. 1826 if (FieldSizeBits == 0) continue; 1827 1828 const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(), 1829 FieldSizeBits); 1830 if (!FieldTy->isIntegerTy() && !FieldTy->isFloatingPointTy() && 1831 !FieldTy->isVectorTy()) 1832 SrcField = new BitCastInst(SrcField, 1833 PointerType::getUnqual(FieldIntTy), 1834 "", LI); 1835 SrcField = new LoadInst(SrcField, "sroa.load.elt", LI); 1836 1837 // If SrcField is a fp or vector of the right size but that isn't an 1838 // integer type, bitcast to an integer so we can shift it. 1839 if (SrcField->getType() != FieldIntTy) 1840 SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI); 1841 1842 // Zero extend the field to be the same size as the final alloca so that 1843 // we can shift and insert it. 1844 if (SrcField->getType() != ResultVal->getType()) 1845 SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI); 1846 1847 // Determine the number of bits to shift SrcField. 1848 uint64_t Shift; 1849 if (Layout) // Struct case. 1850 Shift = Layout->getElementOffsetInBits(i); 1851 else // Array case. 1852 Shift = i*ArrayEltBitOffset; 1853 1854 if (TD->isBigEndian()) 1855 Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth(); 1856 1857 if (Shift) { 1858 Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift); 1859 SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI); 1860 } 1861 1862 // Don't create an 'or x, 0' on the first iteration. 1863 if (!isa<Constant>(ResultVal) || 1864 !cast<Constant>(ResultVal)->isNullValue()) 1865 ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI); 1866 else 1867 ResultVal = SrcField; 1868 } 1869 1870 // Handle tail padding by truncating the result 1871 if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits) 1872 ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI); 1873 1874 LI->replaceAllUsesWith(ResultVal); 1875 DeadInsts.push_back(LI); 1876} 1877 1878/// HasPadding - Return true if the specified type has any structure or 1879/// alignment padding in between the elements that would be split apart 1880/// by SROA; return false otherwise. 1881static bool HasPadding(const Type *Ty, const TargetData &TD) { 1882 if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 1883 Ty = ATy->getElementType(); 1884 return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty); 1885 } 1886 1887 // SROA currently handles only Arrays and Structs. 1888 const StructType *STy = cast<StructType>(Ty); 1889 const StructLayout *SL = TD.getStructLayout(STy); 1890 unsigned PrevFieldBitOffset = 0; 1891 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 1892 unsigned FieldBitOffset = SL->getElementOffsetInBits(i); 1893 1894 // Check to see if there is any padding between this element and the 1895 // previous one. 1896 if (i) { 1897 unsigned PrevFieldEnd = 1898 PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1)); 1899 if (PrevFieldEnd < FieldBitOffset) 1900 return true; 1901 } 1902 PrevFieldBitOffset = FieldBitOffset; 1903 } 1904 // Check for tail padding. 1905 if (unsigned EltCount = STy->getNumElements()) { 1906 unsigned PrevFieldEnd = PrevFieldBitOffset + 1907 TD.getTypeSizeInBits(STy->getElementType(EltCount-1)); 1908 if (PrevFieldEnd < SL->getSizeInBits()) 1909 return true; 1910 } 1911 return false; 1912} 1913 1914/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of 1915/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, 1916/// or 1 if safe after canonicalization has been performed. 1917bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) { 1918 // Loop over the use list of the alloca. We can only transform it if all of 1919 // the users are safe to transform. 1920 AllocaInfo Info; 1921 1922 isSafeForScalarRepl(AI, AI, 0, Info); 1923 if (Info.isUnsafe) { 1924 DEBUG(dbgs() << "Cannot transform: " << *AI << '\n'); 1925 return false; 1926 } 1927 1928 // Okay, we know all the users are promotable. If the aggregate is a memcpy 1929 // source and destination, we have to be careful. In particular, the memcpy 1930 // could be moving around elements that live in structure padding of the LLVM 1931 // types, but may actually be used. In these cases, we refuse to promote the 1932 // struct. 1933 if (Info.isMemCpySrc && Info.isMemCpyDst && 1934 HasPadding(AI->getAllocatedType(), *TD)) 1935 return false; 1936 1937 return true; 1938} 1939 1940 1941 1942/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to 1943/// some part of a constant global variable. This intentionally only accepts 1944/// constant expressions because we don't can't rewrite arbitrary instructions. 1945static bool PointsToConstantGlobal(Value *V) { 1946 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) 1947 return GV->isConstant(); 1948 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 1949 if (CE->getOpcode() == Instruction::BitCast || 1950 CE->getOpcode() == Instruction::GetElementPtr) 1951 return PointsToConstantGlobal(CE->getOperand(0)); 1952 return false; 1953} 1954 1955/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived) 1956/// pointer to an alloca. Ignore any reads of the pointer, return false if we 1957/// see any stores or other unknown uses. If we see pointer arithmetic, keep 1958/// track of whether it moves the pointer (with isOffset) but otherwise traverse 1959/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to 1960/// the alloca, and if the source pointer is a pointer to a constant global, we 1961/// can optimize this. 1962static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy, 1963 bool isOffset) { 1964 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 1965 User *U = cast<Instruction>(*UI); 1966 1967 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 1968 // Ignore non-volatile loads, they are always ok. 1969 if (LI->isVolatile()) return false; 1970 continue; 1971 } 1972 1973 if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) { 1974 // If uses of the bitcast are ok, we are ok. 1975 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) 1976 return false; 1977 continue; 1978 } 1979 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 1980 // If the GEP has all zero indices, it doesn't offset the pointer. If it 1981 // doesn't, it does. 1982 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy, 1983 isOffset || !GEP->hasAllZeroIndices())) 1984 return false; 1985 continue; 1986 } 1987 1988 if (CallSite CS = U) { 1989 // If this is a readonly/readnone call site, then we know it is just a 1990 // load and we can ignore it. 1991 if (CS.onlyReadsMemory()) 1992 continue; 1993 1994 // If this is the function being called then we treat it like a load and 1995 // ignore it. 1996 if (CS.isCallee(UI)) 1997 continue; 1998 1999 // If this is being passed as a byval argument, the caller is making a 2000 // copy, so it is only a read of the alloca. 2001 unsigned ArgNo = CS.getArgumentNo(UI); 2002 if (CS.paramHasAttr(ArgNo+1, Attribute::ByVal)) 2003 continue; 2004 } 2005 2006 // If this is isn't our memcpy/memmove, reject it as something we can't 2007 // handle. 2008 MemTransferInst *MI = dyn_cast<MemTransferInst>(U); 2009 if (MI == 0) 2010 return false; 2011 2012 // If the transfer is using the alloca as a source of the transfer, then 2013 // ignore it since it is a load (unless the transfer is volatile). 2014 if (UI.getOperandNo() == 1) { 2015 if (MI->isVolatile()) return false; 2016 continue; 2017 } 2018 2019 // If we already have seen a copy, reject the second one. 2020 if (TheCopy) return false; 2021 2022 // If the pointer has been offset from the start of the alloca, we can't 2023 // safely handle this. 2024 if (isOffset) return false; 2025 2026 // If the memintrinsic isn't using the alloca as the dest, reject it. 2027 if (UI.getOperandNo() != 0) return false; 2028 2029 // If the source of the memcpy/move is not a constant global, reject it. 2030 if (!PointsToConstantGlobal(MI->getSource())) 2031 return false; 2032 2033 // Otherwise, the transform is safe. Remember the copy instruction. 2034 TheCopy = MI; 2035 } 2036 return true; 2037} 2038 2039/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only 2040/// modified by a copy from a constant global. If we can prove this, we can 2041/// replace any uses of the alloca with uses of the global directly. 2042MemTransferInst *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) { 2043 MemTransferInst *TheCopy = 0; 2044 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) 2045 return TheCopy; 2046 return 0; 2047} 2048