ScalarReplAggregates.cpp revision 593375d04ab32be0161607a741d310172f142b93
1//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This transformation implements the well known scalar replacement of 11// aggregates transformation. This xform breaks up alloca instructions of 12// aggregate type (structure or array) into individual alloca instructions for 13// each member (if possible). Then, if possible, it transforms the individual 14// alloca instructions into nice clean scalar SSA form. 15// 16// This combines a simple SRoA algorithm with the Mem2Reg algorithm because 17// often interact, especially for C++ programs. As such, iterating between 18// SRoA, then Mem2Reg until we run out of things to promote works well. 19// 20//===----------------------------------------------------------------------===// 21 22#define DEBUG_TYPE "scalarrepl" 23#include "llvm/Transforms/Scalar.h" 24#include "llvm/Constants.h" 25#include "llvm/DerivedTypes.h" 26#include "llvm/Function.h" 27#include "llvm/GlobalVariable.h" 28#include "llvm/Instructions.h" 29#include "llvm/IntrinsicInst.h" 30#include "llvm/LLVMContext.h" 31#include "llvm/Pass.h" 32#include "llvm/Analysis/Dominators.h" 33#include "llvm/Target/TargetData.h" 34#include "llvm/Transforms/Utils/PromoteMemToReg.h" 35#include "llvm/Transforms/Utils/Local.h" 36#include "llvm/Support/Debug.h" 37#include "llvm/Support/ErrorHandling.h" 38#include "llvm/Support/GetElementPtrTypeIterator.h" 39#include "llvm/Support/IRBuilder.h" 40#include "llvm/Support/MathExtras.h" 41#include "llvm/Support/raw_ostream.h" 42#include "llvm/ADT/SmallVector.h" 43#include "llvm/ADT/Statistic.h" 44using namespace llvm; 45 46STATISTIC(NumReplaced, "Number of allocas broken up"); 47STATISTIC(NumPromoted, "Number of allocas promoted"); 48STATISTIC(NumConverted, "Number of aggregates converted to scalar"); 49STATISTIC(NumGlobals, "Number of allocas copied from constant global"); 50 51namespace { 52 struct ConvertToScalarInfo; 53 54 struct SROA : public FunctionPass { 55 static char ID; // Pass identification, replacement for typeid 56 explicit SROA(signed T = -1) : FunctionPass(&ID) { 57 if (T == -1) 58 SRThreshold = 128; 59 else 60 SRThreshold = T; 61 } 62 63 bool runOnFunction(Function &F); 64 65 bool performScalarRepl(Function &F); 66 bool performPromotion(Function &F); 67 68 // getAnalysisUsage - This pass does not require any passes, but we know it 69 // will not alter the CFG, so say so. 70 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 71 AU.addRequired<DominatorTree>(); 72 AU.addRequired<DominanceFrontier>(); 73 AU.setPreservesCFG(); 74 } 75 76 private: 77 TargetData *TD; 78 79 /// DeadInsts - Keep track of instructions we have made dead, so that 80 /// we can remove them after we are done working. 81 SmallVector<Value*, 32> DeadInsts; 82 83 /// AllocaInfo - When analyzing uses of an alloca instruction, this captures 84 /// information about the uses. All these fields are initialized to false 85 /// and set to true when something is learned. 86 struct AllocaInfo { 87 /// isUnsafe - This is set to true if the alloca cannot be SROA'd. 88 bool isUnsafe : 1; 89 90 /// isMemCpySrc - This is true if this aggregate is memcpy'd from. 91 bool isMemCpySrc : 1; 92 93 /// isMemCpyDst - This is true if this aggregate is memcpy'd into. 94 bool isMemCpyDst : 1; 95 96 AllocaInfo() 97 : isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false) {} 98 }; 99 100 unsigned SRThreshold; 101 102 void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; } 103 104 bool isSafeAllocaToScalarRepl(AllocaInst *AI); 105 106 void isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 107 AllocaInfo &Info); 108 void isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t &Offset, 109 AllocaInfo &Info); 110 void isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize, 111 const Type *MemOpType, bool isStore, AllocaInfo &Info); 112 bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size); 113 uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset, 114 const Type *&IdxTy); 115 116 void DoScalarReplacement(AllocaInst *AI, 117 std::vector<AllocaInst*> &WorkList); 118 void DeleteDeadInstructions(); 119 AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocaInst *Base); 120 121 void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 122 SmallVector<AllocaInst*, 32> &NewElts); 123 void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 124 SmallVector<AllocaInst*, 32> &NewElts); 125 void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 126 SmallVector<AllocaInst*, 32> &NewElts); 127 void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 128 AllocaInst *AI, 129 SmallVector<AllocaInst*, 32> &NewElts); 130 void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 131 SmallVector<AllocaInst*, 32> &NewElts); 132 void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 133 SmallVector<AllocaInst*, 32> &NewElts); 134 135 static MemTransferInst *isOnlyCopiedFromConstantGlobal(AllocaInst *AI); 136 }; 137} 138 139char SROA::ID = 0; 140static RegisterPass<SROA> X("scalarrepl", "Scalar Replacement of Aggregates"); 141 142// Public interface to the ScalarReplAggregates pass 143FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) { 144 return new SROA(Threshold); 145} 146 147 148bool SROA::runOnFunction(Function &F) { 149 TD = getAnalysisIfAvailable<TargetData>(); 150 151 bool Changed = performPromotion(F); 152 153 // FIXME: ScalarRepl currently depends on TargetData more than it 154 // theoretically needs to. It should be refactored in order to support 155 // target-independent IR. Until this is done, just skip the actual 156 // scalar-replacement portion of this pass. 157 if (!TD) return Changed; 158 159 while (1) { 160 bool LocalChange = performScalarRepl(F); 161 if (!LocalChange) break; // No need to repromote if no scalarrepl 162 Changed = true; 163 LocalChange = performPromotion(F); 164 if (!LocalChange) break; // No need to re-scalarrepl if no promotion 165 } 166 167 return Changed; 168} 169 170 171bool SROA::performPromotion(Function &F) { 172 std::vector<AllocaInst*> Allocas; 173 DominatorTree &DT = getAnalysis<DominatorTree>(); 174 DominanceFrontier &DF = getAnalysis<DominanceFrontier>(); 175 176 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function 177 178 bool Changed = false; 179 180 while (1) { 181 Allocas.clear(); 182 183 // Find allocas that are safe to promote, by looking at all instructions in 184 // the entry node 185 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) 186 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? 187 if (isAllocaPromotable(AI)) 188 Allocas.push_back(AI); 189 190 if (Allocas.empty()) break; 191 192 PromoteMemToReg(Allocas, DT, DF); 193 NumPromoted += Allocas.size(); 194 Changed = true; 195 } 196 197 return Changed; 198} 199 200/// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for 201/// SROA. It must be a struct or array type with a small number of elements. 202static bool ShouldAttemptScalarRepl(AllocaInst *AI) { 203 const Type *T = AI->getAllocatedType(); 204 // Do not promote any struct into more than 32 separate vars. 205 if (const StructType *ST = dyn_cast<StructType>(T)) 206 return ST->getNumElements() <= 32; 207 // Arrays are much less likely to be safe for SROA; only consider 208 // them if they are very small. 209 if (const ArrayType *AT = dyn_cast<ArrayType>(T)) 210 return AT->getNumElements() <= 8; 211 return false; 212} 213 214namespace { 215/// ConvertToScalarInfo - This struct is used by CanConvertToScalar 216struct ConvertToScalarInfo { 217 /// AllocaSize - The size of the alloca being considered. 218 unsigned AllocaSize; 219 const TargetData &TD; 220 221 bool IsNotTrivial; 222 const Type *VectorTy; 223 bool HadAVector; 224 225 explicit ConvertToScalarInfo(unsigned Size, const TargetData &td) 226 : AllocaSize(Size), TD(td) { 227 IsNotTrivial = false; 228 VectorTy = 0; 229 HadAVector = false; 230 } 231 232 bool shouldConvertToVector() const { 233 return VectorTy && VectorTy->isVectorTy() && HadAVector; 234 } 235 236 AllocaInst *TryConvert(AllocaInst *AI) { 237 // If we can't convert this scalar, or if mem2reg can trivially do it, bail 238 // out. 239 if (!CanConvertToScalar(AI, 0) || !IsNotTrivial) 240 // FIXME: In the trivial case, just use mem2reg. 241 return 0; 242 243 // If we were able to find a vector type that can handle this with 244 // insert/extract elements, and if there was at least one use that had 245 // a vector type, promote this to a vector. We don't want to promote 246 // random stuff that doesn't use vectors (e.g. <9 x double>) because then 247 // we just get a lot of insert/extracts. If at least one vector is 248 // involved, then we probably really do have a union of vector/array. 249 const Type *NewTy; 250 if (shouldConvertToVector()) { 251 DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = " 252 << *VectorTy << '\n'); 253 NewTy = VectorTy; // Use the vector type. 254 } else { 255 DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n"); 256 // Create and insert the integer alloca. 257 NewTy = IntegerType::get(AI->getContext(), AllocaSize*8); 258 } 259 AllocaInst *NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin()); 260 ConvertUsesToScalar(AI, NewAI, 0); 261 return NewAI; 262 } 263 264 bool CanConvertToScalar(Value *V, uint64_t Offset); 265 void MergeInType(const Type *In, uint64_t Offset); 266 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset); 267 268 Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType, 269 uint64_t Offset, IRBuilder<> &Builder); 270 Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal, 271 uint64_t Offset, IRBuilder<> &Builder); 272}; 273} // end anonymous namespace. 274 275 276 277// performScalarRepl - This algorithm is a simple worklist driven algorithm, 278// which runs on all of the malloc/alloca instructions in the function, removing 279// them if they are only used by getelementptr instructions. 280// 281bool SROA::performScalarRepl(Function &F) { 282 std::vector<AllocaInst*> WorkList; 283 284 // Scan the entry basic block, adding allocas to the worklist. 285 BasicBlock &BB = F.getEntryBlock(); 286 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) 287 if (AllocaInst *A = dyn_cast<AllocaInst>(I)) 288 WorkList.push_back(A); 289 290 // Process the worklist 291 bool Changed = false; 292 while (!WorkList.empty()) { 293 AllocaInst *AI = WorkList.back(); 294 WorkList.pop_back(); 295 296 // Handle dead allocas trivially. These can be formed by SROA'ing arrays 297 // with unused elements. 298 if (AI->use_empty()) { 299 AI->eraseFromParent(); 300 Changed = true; 301 continue; 302 } 303 304 // If this alloca is impossible for us to promote, reject it early. 305 if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized()) 306 continue; 307 308 // Check to see if this allocation is only modified by a memcpy/memmove from 309 // a constant global. If this is the case, we can change all users to use 310 // the constant global instead. This is commonly produced by the CFE by 311 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A' 312 // is only subsequently read. 313 if (MemTransferInst *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) { 314 DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n'); 315 DEBUG(dbgs() << " memcpy = " << *TheCopy << '\n'); 316 Constant *TheSrc = cast<Constant>(TheCopy->getSource()); 317 AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType())); 318 TheCopy->eraseFromParent(); // Don't mutate the global. 319 AI->eraseFromParent(); 320 ++NumGlobals; 321 Changed = true; 322 continue; 323 } 324 325 // Check to see if we can perform the core SROA transformation. We cannot 326 // transform the allocation instruction if it is an array allocation 327 // (allocations OF arrays are ok though), and an allocation of a scalar 328 // value cannot be decomposed at all. 329 uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType()); 330 331 // Do not promote [0 x %struct]. 332 if (AllocaSize == 0) continue; 333 334 // Do not promote any struct whose size is too big. 335 if (AllocaSize > SRThreshold) continue; 336 337 // If the alloca looks like a good candidate for scalar replacement, and if 338 // all its users can be transformed, then split up the aggregate into its 339 // separate elements. 340 if (ShouldAttemptScalarRepl(AI) && isSafeAllocaToScalarRepl(AI)) { 341 DoScalarReplacement(AI, WorkList); 342 Changed = true; 343 continue; 344 } 345 346 // If we can turn this aggregate value (potentially with casts) into a 347 // simple scalar value that can be mem2reg'd into a register value. 348 // IsNotTrivial tracks whether this is something that mem2reg could have 349 // promoted itself. If so, we don't want to transform it needlessly. Note 350 // that we can't just check based on the type: the alloca may be of an i32 351 // but that has pointer arithmetic to set byte 3 of it or something. 352 if (AllocaInst *NewAI = 353 ConvertToScalarInfo((unsigned)AllocaSize, *TD).TryConvert(AI)) { 354 NewAI->takeName(AI); 355 AI->eraseFromParent(); 356 ++NumConverted; 357 Changed = true; 358 continue; 359 } 360 361 // Otherwise, couldn't process this alloca. 362 } 363 364 return Changed; 365} 366 367/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl 368/// predicate, do SROA now. 369void SROA::DoScalarReplacement(AllocaInst *AI, 370 std::vector<AllocaInst*> &WorkList) { 371 DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n'); 372 SmallVector<AllocaInst*, 32> ElementAllocas; 373 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 374 ElementAllocas.reserve(ST->getNumContainedTypes()); 375 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { 376 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 377 AI->getAlignment(), 378 AI->getName() + "." + Twine(i), AI); 379 ElementAllocas.push_back(NA); 380 WorkList.push_back(NA); // Add to worklist for recursive processing 381 } 382 } else { 383 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); 384 ElementAllocas.reserve(AT->getNumElements()); 385 const Type *ElTy = AT->getElementType(); 386 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 387 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(), 388 AI->getName() + "." + Twine(i), AI); 389 ElementAllocas.push_back(NA); 390 WorkList.push_back(NA); // Add to worklist for recursive processing 391 } 392 } 393 394 // Now that we have created the new alloca instructions, rewrite all the 395 // uses of the old alloca. 396 RewriteForScalarRepl(AI, AI, 0, ElementAllocas); 397 398 // Now erase any instructions that were made dead while rewriting the alloca. 399 DeleteDeadInstructions(); 400 AI->eraseFromParent(); 401 402 NumReplaced++; 403} 404 405/// DeleteDeadInstructions - Erase instructions on the DeadInstrs list, 406/// recursively including all their operands that become trivially dead. 407void SROA::DeleteDeadInstructions() { 408 while (!DeadInsts.empty()) { 409 Instruction *I = cast<Instruction>(DeadInsts.pop_back_val()); 410 411 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) 412 if (Instruction *U = dyn_cast<Instruction>(*OI)) { 413 // Zero out the operand and see if it becomes trivially dead. 414 // (But, don't add allocas to the dead instruction list -- they are 415 // already on the worklist and will be deleted separately.) 416 *OI = 0; 417 if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U)) 418 DeadInsts.push_back(U); 419 } 420 421 I->eraseFromParent(); 422 } 423} 424 425/// isSafeForScalarRepl - Check if instruction I is a safe use with regard to 426/// performing scalar replacement of alloca AI. The results are flagged in 427/// the Info parameter. Offset indicates the position within AI that is 428/// referenced by this instruction. 429void SROA::isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 430 AllocaInfo &Info) { 431 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 432 Instruction *User = cast<Instruction>(*UI); 433 434 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 435 isSafeForScalarRepl(BC, AI, Offset, Info); 436 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 437 uint64_t GEPOffset = Offset; 438 isSafeGEP(GEPI, AI, GEPOffset, Info); 439 if (!Info.isUnsafe) 440 isSafeForScalarRepl(GEPI, AI, GEPOffset, Info); 441 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 442 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 443 if (Length) 444 isSafeMemAccess(AI, Offset, Length->getZExtValue(), 0, 445 UI.getOperandNo() == 0, Info); 446 else 447 MarkUnsafe(Info); 448 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 449 if (!LI->isVolatile()) { 450 const Type *LIType = LI->getType(); 451 isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(LIType), 452 LIType, false, Info); 453 } else 454 MarkUnsafe(Info); 455 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 456 // Store is ok if storing INTO the pointer, not storing the pointer 457 if (!SI->isVolatile() && SI->getOperand(0) != I) { 458 const Type *SIType = SI->getOperand(0)->getType(); 459 isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(SIType), 460 SIType, true, Info); 461 } else 462 MarkUnsafe(Info); 463 } else { 464 DEBUG(errs() << " Transformation preventing inst: " << *User << '\n'); 465 MarkUnsafe(Info); 466 } 467 if (Info.isUnsafe) return; 468 } 469} 470 471/// isSafeGEP - Check if a GEP instruction can be handled for scalar 472/// replacement. It is safe when all the indices are constant, in-bounds 473/// references, and when the resulting offset corresponds to an element within 474/// the alloca type. The results are flagged in the Info parameter. Upon 475/// return, Offset is adjusted as specified by the GEP indices. 476void SROA::isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI, 477 uint64_t &Offset, AllocaInfo &Info) { 478 gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI); 479 if (GEPIt == E) 480 return; 481 482 // Walk through the GEP type indices, checking the types that this indexes 483 // into. 484 for (; GEPIt != E; ++GEPIt) { 485 // Ignore struct elements, no extra checking needed for these. 486 if ((*GEPIt)->isStructTy()) 487 continue; 488 489 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand()); 490 if (!IdxVal) 491 return MarkUnsafe(Info); 492 } 493 494 // Compute the offset due to this GEP and check if the alloca has a 495 // component element at that offset. 496 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 497 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 498 &Indices[0], Indices.size()); 499 if (!TypeHasComponent(AI->getAllocatedType(), Offset, 0)) 500 MarkUnsafe(Info); 501} 502 503/// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI 504/// alloca or has an offset and size that corresponds to a component element 505/// within it. The offset checked here may have been formed from a GEP with a 506/// pointer bitcasted to a different type. 507void SROA::isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize, 508 const Type *MemOpType, bool isStore, 509 AllocaInfo &Info) { 510 // Check if this is a load/store of the entire alloca. 511 if (Offset == 0 && MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) { 512 bool UsesAggregateType = (MemOpType == AI->getAllocatedType()); 513 // This is safe for MemIntrinsics (where MemOpType is 0), integer types 514 // (which are essentially the same as the MemIntrinsics, especially with 515 // regard to copying padding between elements), or references using the 516 // aggregate type of the alloca. 517 if (!MemOpType || MemOpType->isIntegerTy() || UsesAggregateType) { 518 if (!UsesAggregateType) { 519 if (isStore) 520 Info.isMemCpyDst = true; 521 else 522 Info.isMemCpySrc = true; 523 } 524 return; 525 } 526 } 527 // Check if the offset/size correspond to a component within the alloca type. 528 const Type *T = AI->getAllocatedType(); 529 if (TypeHasComponent(T, Offset, MemSize)) 530 return; 531 532 return MarkUnsafe(Info); 533} 534 535/// TypeHasComponent - Return true if T has a component type with the 536/// specified offset and size. If Size is zero, do not check the size. 537bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) { 538 const Type *EltTy; 539 uint64_t EltSize; 540 if (const StructType *ST = dyn_cast<StructType>(T)) { 541 const StructLayout *Layout = TD->getStructLayout(ST); 542 unsigned EltIdx = Layout->getElementContainingOffset(Offset); 543 EltTy = ST->getContainedType(EltIdx); 544 EltSize = TD->getTypeAllocSize(EltTy); 545 Offset -= Layout->getElementOffset(EltIdx); 546 } else if (const ArrayType *AT = dyn_cast<ArrayType>(T)) { 547 EltTy = AT->getElementType(); 548 EltSize = TD->getTypeAllocSize(EltTy); 549 if (Offset >= AT->getNumElements() * EltSize) 550 return false; 551 Offset %= EltSize; 552 } else { 553 return false; 554 } 555 if (Offset == 0 && (Size == 0 || EltSize == Size)) 556 return true; 557 // Check if the component spans multiple elements. 558 if (Offset + Size > EltSize) 559 return false; 560 return TypeHasComponent(EltTy, Offset, Size); 561} 562 563/// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite 564/// the instruction I, which references it, to use the separate elements. 565/// Offset indicates the position within AI that is referenced by this 566/// instruction. 567void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, 568 SmallVector<AllocaInst*, 32> &NewElts) { 569 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { 570 Instruction *User = cast<Instruction>(*UI); 571 572 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { 573 RewriteBitCast(BC, AI, Offset, NewElts); 574 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { 575 RewriteGEP(GEPI, AI, Offset, NewElts); 576 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 577 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 578 uint64_t MemSize = Length->getZExtValue(); 579 if (Offset == 0 && 580 MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) 581 RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts); 582 // Otherwise the intrinsic can only touch a single element and the 583 // address operand will be updated, so nothing else needs to be done. 584 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 585 const Type *LIType = LI->getType(); 586 if (LIType == AI->getAllocatedType()) { 587 // Replace: 588 // %res = load { i32, i32 }* %alloc 589 // with: 590 // %load.0 = load i32* %alloc.0 591 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0 592 // %load.1 = load i32* %alloc.1 593 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1 594 // (Also works for arrays instead of structs) 595 Value *Insert = UndefValue::get(LIType); 596 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 597 Value *Load = new LoadInst(NewElts[i], "load", LI); 598 Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI); 599 } 600 LI->replaceAllUsesWith(Insert); 601 DeadInsts.push_back(LI); 602 } else if (LIType->isIntegerTy() && 603 TD->getTypeAllocSize(LIType) == 604 TD->getTypeAllocSize(AI->getAllocatedType())) { 605 // If this is a load of the entire alloca to an integer, rewrite it. 606 RewriteLoadUserOfWholeAlloca(LI, AI, NewElts); 607 } 608 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 609 Value *Val = SI->getOperand(0); 610 const Type *SIType = Val->getType(); 611 if (SIType == AI->getAllocatedType()) { 612 // Replace: 613 // store { i32, i32 } %val, { i32, i32 }* %alloc 614 // with: 615 // %val.0 = extractvalue { i32, i32 } %val, 0 616 // store i32 %val.0, i32* %alloc.0 617 // %val.1 = extractvalue { i32, i32 } %val, 1 618 // store i32 %val.1, i32* %alloc.1 619 // (Also works for arrays instead of structs) 620 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 621 Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI); 622 new StoreInst(Extract, NewElts[i], SI); 623 } 624 DeadInsts.push_back(SI); 625 } else if (SIType->isIntegerTy() && 626 TD->getTypeAllocSize(SIType) == 627 TD->getTypeAllocSize(AI->getAllocatedType())) { 628 // If this is a store of the entire alloca from an integer, rewrite it. 629 RewriteStoreUserOfWholeAlloca(SI, AI, NewElts); 630 } 631 } 632 } 633} 634 635/// RewriteBitCast - Update a bitcast reference to the alloca being replaced 636/// and recursively continue updating all of its uses. 637void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, 638 SmallVector<AllocaInst*, 32> &NewElts) { 639 RewriteForScalarRepl(BC, AI, Offset, NewElts); 640 if (BC->getOperand(0) != AI) 641 return; 642 643 // The bitcast references the original alloca. Replace its uses with 644 // references to the first new element alloca. 645 Instruction *Val = NewElts[0]; 646 if (Val->getType() != BC->getDestTy()) { 647 Val = new BitCastInst(Val, BC->getDestTy(), "", BC); 648 Val->takeName(BC); 649 } 650 BC->replaceAllUsesWith(Val); 651 DeadInsts.push_back(BC); 652} 653 654/// FindElementAndOffset - Return the index of the element containing Offset 655/// within the specified type, which must be either a struct or an array. 656/// Sets T to the type of the element and Offset to the offset within that 657/// element. IdxTy is set to the type of the index result to be used in a 658/// GEP instruction. 659uint64_t SROA::FindElementAndOffset(const Type *&T, uint64_t &Offset, 660 const Type *&IdxTy) { 661 uint64_t Idx = 0; 662 if (const StructType *ST = dyn_cast<StructType>(T)) { 663 const StructLayout *Layout = TD->getStructLayout(ST); 664 Idx = Layout->getElementContainingOffset(Offset); 665 T = ST->getContainedType(Idx); 666 Offset -= Layout->getElementOffset(Idx); 667 IdxTy = Type::getInt32Ty(T->getContext()); 668 return Idx; 669 } 670 const ArrayType *AT = cast<ArrayType>(T); 671 T = AT->getElementType(); 672 uint64_t EltSize = TD->getTypeAllocSize(T); 673 Idx = Offset / EltSize; 674 Offset -= Idx * EltSize; 675 IdxTy = Type::getInt64Ty(T->getContext()); 676 return Idx; 677} 678 679/// RewriteGEP - Check if this GEP instruction moves the pointer across 680/// elements of the alloca that are being split apart, and if so, rewrite 681/// the GEP to be relative to the new element. 682void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, 683 SmallVector<AllocaInst*, 32> &NewElts) { 684 uint64_t OldOffset = Offset; 685 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); 686 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), 687 &Indices[0], Indices.size()); 688 689 RewriteForScalarRepl(GEPI, AI, Offset, NewElts); 690 691 const Type *T = AI->getAllocatedType(); 692 const Type *IdxTy; 693 uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy); 694 if (GEPI->getOperand(0) == AI) 695 OldIdx = ~0ULL; // Force the GEP to be rewritten. 696 697 T = AI->getAllocatedType(); 698 uint64_t EltOffset = Offset; 699 uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy); 700 701 // If this GEP does not move the pointer across elements of the alloca 702 // being split, then it does not needs to be rewritten. 703 if (Idx == OldIdx) 704 return; 705 706 const Type *i32Ty = Type::getInt32Ty(AI->getContext()); 707 SmallVector<Value*, 8> NewArgs; 708 NewArgs.push_back(Constant::getNullValue(i32Ty)); 709 while (EltOffset != 0) { 710 uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy); 711 NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx)); 712 } 713 Instruction *Val = NewElts[Idx]; 714 if (NewArgs.size() > 1) { 715 Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(), 716 NewArgs.end(), "", GEPI); 717 Val->takeName(GEPI); 718 } 719 if (Val->getType() != GEPI->getType()) 720 Val = new BitCastInst(Val, GEPI->getType(), Val->getName(), GEPI); 721 GEPI->replaceAllUsesWith(Val); 722 DeadInsts.push_back(GEPI); 723} 724 725/// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI. 726/// Rewrite it to copy or set the elements of the scalarized memory. 727void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, 728 AllocaInst *AI, 729 SmallVector<AllocaInst*, 32> &NewElts) { 730 // If this is a memcpy/memmove, construct the other pointer as the 731 // appropriate type. The "Other" pointer is the pointer that goes to memory 732 // that doesn't have anything to do with the alloca that we are promoting. For 733 // memset, this Value* stays null. 734 Value *OtherPtr = 0; 735 LLVMContext &Context = MI->getContext(); 736 unsigned MemAlignment = MI->getAlignment(); 737 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy 738 if (Inst == MTI->getRawDest()) 739 OtherPtr = MTI->getRawSource(); 740 else { 741 assert(Inst == MTI->getRawSource()); 742 OtherPtr = MTI->getRawDest(); 743 } 744 } 745 746 // If there is an other pointer, we want to convert it to the same pointer 747 // type as AI has, so we can GEP through it safely. 748 if (OtherPtr) { 749 750 // Remove bitcasts and all-zero GEPs from OtherPtr. This is an 751 // optimization, but it's also required to detect the corner case where 752 // both pointer operands are referencing the same memory, and where 753 // OtherPtr may be a bitcast or GEP that currently being rewritten. (This 754 // function is only called for mem intrinsics that access the whole 755 // aggregate, so non-zero GEPs are not an issue here.) 756 while (1) { 757 if (BitCastInst *BC = dyn_cast<BitCastInst>(OtherPtr)) { 758 OtherPtr = BC->getOperand(0); 759 continue; 760 } 761 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(OtherPtr)) { 762 // All zero GEPs are effectively bitcasts. 763 if (GEP->hasAllZeroIndices()) { 764 OtherPtr = GEP->getOperand(0); 765 continue; 766 } 767 } 768 break; 769 } 770 // Copying the alloca to itself is a no-op: just delete it. 771 if (OtherPtr == AI || OtherPtr == NewElts[0]) { 772 // This code will run twice for a no-op memcpy -- once for each operand. 773 // Put only one reference to MI on the DeadInsts list. 774 for (SmallVector<Value*, 32>::const_iterator I = DeadInsts.begin(), 775 E = DeadInsts.end(); I != E; ++I) 776 if (*I == MI) return; 777 DeadInsts.push_back(MI); 778 return; 779 } 780 781 if (ConstantExpr *BCE = dyn_cast<ConstantExpr>(OtherPtr)) 782 if (BCE->getOpcode() == Instruction::BitCast) 783 OtherPtr = BCE->getOperand(0); 784 785 // If the pointer is not the right type, insert a bitcast to the right 786 // type. 787 if (OtherPtr->getType() != AI->getType()) 788 OtherPtr = new BitCastInst(OtherPtr, AI->getType(), OtherPtr->getName(), 789 MI); 790 } 791 792 // Process each element of the aggregate. 793 Value *TheFn = MI->getCalledValue(); 794 const Type *BytePtrTy = MI->getRawDest()->getType(); 795 bool SROADest = MI->getRawDest() == Inst; 796 797 Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext())); 798 799 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 800 // If this is a memcpy/memmove, emit a GEP of the other element address. 801 Value *OtherElt = 0; 802 unsigned OtherEltAlign = MemAlignment; 803 804 if (OtherPtr) { 805 Value *Idx[2] = { Zero, 806 ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) }; 807 OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2, 808 OtherPtr->getName()+"."+Twine(i), 809 MI); 810 uint64_t EltOffset; 811 const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType()); 812 if (const StructType *ST = 813 dyn_cast<StructType>(OtherPtrTy->getElementType())) { 814 EltOffset = TD->getStructLayout(ST)->getElementOffset(i); 815 } else { 816 const Type *EltTy = 817 cast<SequentialType>(OtherPtr->getType())->getElementType(); 818 EltOffset = TD->getTypeAllocSize(EltTy)*i; 819 } 820 821 // The alignment of the other pointer is the guaranteed alignment of the 822 // element, which is affected by both the known alignment of the whole 823 // mem intrinsic and the alignment of the element. If the alignment of 824 // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the 825 // known alignment is just 4 bytes. 826 OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset); 827 } 828 829 Value *EltPtr = NewElts[i]; 830 const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType(); 831 832 // If we got down to a scalar, insert a load or store as appropriate. 833 if (EltTy->isSingleValueType()) { 834 if (isa<MemTransferInst>(MI)) { 835 if (SROADest) { 836 // From Other to Alloca. 837 Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI); 838 new StoreInst(Elt, EltPtr, MI); 839 } else { 840 // From Alloca to Other. 841 Value *Elt = new LoadInst(EltPtr, "tmp", MI); 842 new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI); 843 } 844 continue; 845 } 846 assert(isa<MemSetInst>(MI)); 847 848 // If the stored element is zero (common case), just store a null 849 // constant. 850 Constant *StoreVal; 851 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getOperand(1))) { 852 if (CI->isZero()) { 853 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0> 854 } else { 855 // If EltTy is a vector type, get the element type. 856 const Type *ValTy = EltTy->getScalarType(); 857 858 // Construct an integer with the right value. 859 unsigned EltSize = TD->getTypeSizeInBits(ValTy); 860 APInt OneVal(EltSize, CI->getZExtValue()); 861 APInt TotalVal(OneVal); 862 // Set each byte. 863 for (unsigned i = 0; 8*i < EltSize; ++i) { 864 TotalVal = TotalVal.shl(8); 865 TotalVal |= OneVal; 866 } 867 868 // Convert the integer value to the appropriate type. 869 StoreVal = ConstantInt::get(Context, TotalVal); 870 if (ValTy->isPointerTy()) 871 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); 872 else if (ValTy->isFloatingPointTy()) 873 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy); 874 assert(StoreVal->getType() == ValTy && "Type mismatch!"); 875 876 // If the requested value was a vector constant, create it. 877 if (EltTy != ValTy) { 878 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements(); 879 SmallVector<Constant*, 16> Elts(NumElts, StoreVal); 880 StoreVal = ConstantVector::get(&Elts[0], NumElts); 881 } 882 } 883 new StoreInst(StoreVal, EltPtr, MI); 884 continue; 885 } 886 // Otherwise, if we're storing a byte variable, use a memset call for 887 // this element. 888 } 889 890 // Cast the element pointer to BytePtrTy. 891 if (EltPtr->getType() != BytePtrTy) 892 EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getName(), MI); 893 894 // Cast the other pointer (if we have one) to BytePtrTy. 895 if (OtherElt && OtherElt->getType() != BytePtrTy) { 896 // Preserve address space of OtherElt 897 const PointerType* OtherPTy = cast<PointerType>(OtherElt->getType()); 898 const PointerType* PTy = cast<PointerType>(BytePtrTy); 899 if (OtherPTy->getElementType() != PTy->getElementType()) { 900 Type *NewOtherPTy = PointerType::get(PTy->getElementType(), 901 OtherPTy->getAddressSpace()); 902 OtherElt = new BitCastInst(OtherElt, NewOtherPTy, 903 OtherElt->getNameStr(), MI); 904 } 905 } 906 907 unsigned EltSize = TD->getTypeAllocSize(EltTy); 908 909 // Finally, insert the meminst for this element. 910 if (isa<MemTransferInst>(MI)) { 911 Value *Ops[] = { 912 SROADest ? EltPtr : OtherElt, // Dest ptr 913 SROADest ? OtherElt : EltPtr, // Src ptr 914 ConstantInt::get(MI->getOperand(2)->getType(), EltSize), // Size 915 // Align 916 ConstantInt::get(Type::getInt32Ty(MI->getContext()), OtherEltAlign), 917 MI->getVolatileCst() 918 }; 919 // In case we fold the address space overloaded memcpy of A to B 920 // with memcpy of B to C, change the function to be a memcpy of A to C. 921 const Type *Tys[] = { Ops[0]->getType(), Ops[1]->getType(), 922 Ops[2]->getType() }; 923 Module *M = MI->getParent()->getParent()->getParent(); 924 TheFn = Intrinsic::getDeclaration(M, MI->getIntrinsicID(), Tys, 3); 925 CallInst::Create(TheFn, Ops, Ops + 5, "", MI); 926 } else { 927 assert(isa<MemSetInst>(MI)); 928 Value *Ops[] = { 929 EltPtr, MI->getOperand(1), // Dest, Value, 930 ConstantInt::get(MI->getOperand(2)->getType(), EltSize), // Size 931 Zero, // Align 932 ConstantInt::get(Type::getInt1Ty(MI->getContext()), 0) // isVolatile 933 }; 934 const Type *Tys[] = { Ops[0]->getType(), Ops[2]->getType() }; 935 Module *M = MI->getParent()->getParent()->getParent(); 936 TheFn = Intrinsic::getDeclaration(M, Intrinsic::memset, Tys, 2); 937 CallInst::Create(TheFn, Ops, Ops + 5, "", MI); 938 } 939 } 940 DeadInsts.push_back(MI); 941} 942 943/// RewriteStoreUserOfWholeAlloca - We found a store of an integer that 944/// overwrites the entire allocation. Extract out the pieces of the stored 945/// integer and store them individually. 946void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, 947 SmallVector<AllocaInst*, 32> &NewElts){ 948 // Extract each element out of the integer according to its structure offset 949 // and store the element value to the individual alloca. 950 Value *SrcVal = SI->getOperand(0); 951 const Type *AllocaEltTy = AI->getAllocatedType(); 952 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 953 954 // Handle tail padding by extending the operand 955 if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits) 956 SrcVal = new ZExtInst(SrcVal, 957 IntegerType::get(SI->getContext(), AllocaSizeBits), 958 "", SI); 959 960 DEBUG(dbgs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI 961 << '\n'); 962 963 // There are two forms here: AI could be an array or struct. Both cases 964 // have different ways to compute the element offset. 965 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 966 const StructLayout *Layout = TD->getStructLayout(EltSTy); 967 968 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 969 // Get the number of bits to shift SrcVal to get the value. 970 const Type *FieldTy = EltSTy->getElementType(i); 971 uint64_t Shift = Layout->getElementOffsetInBits(i); 972 973 if (TD->isBigEndian()) 974 Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy); 975 976 Value *EltVal = SrcVal; 977 if (Shift) { 978 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 979 EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal, 980 "sroa.store.elt", SI); 981 } 982 983 // Truncate down to an integer of the right size. 984 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 985 986 // Ignore zero sized fields like {}, they obviously contain no data. 987 if (FieldSizeBits == 0) continue; 988 989 if (FieldSizeBits != AllocaSizeBits) 990 EltVal = new TruncInst(EltVal, 991 IntegerType::get(SI->getContext(), FieldSizeBits), 992 "", SI); 993 Value *DestField = NewElts[i]; 994 if (EltVal->getType() == FieldTy) { 995 // Storing to an integer field of this size, just do it. 996 } else if (FieldTy->isFloatingPointTy() || FieldTy->isVectorTy()) { 997 // Bitcast to the right element type (for fp/vector values). 998 EltVal = new BitCastInst(EltVal, FieldTy, "", SI); 999 } else { 1000 // Otherwise, bitcast the dest pointer (for aggregates). 1001 DestField = new BitCastInst(DestField, 1002 PointerType::getUnqual(EltVal->getType()), 1003 "", SI); 1004 } 1005 new StoreInst(EltVal, DestField, SI); 1006 } 1007 1008 } else { 1009 const ArrayType *ATy = cast<ArrayType>(AllocaEltTy); 1010 const Type *ArrayEltTy = ATy->getElementType(); 1011 uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 1012 uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy); 1013 1014 uint64_t Shift; 1015 1016 if (TD->isBigEndian()) 1017 Shift = AllocaSizeBits-ElementOffset; 1018 else 1019 Shift = 0; 1020 1021 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1022 // Ignore zero sized fields like {}, they obviously contain no data. 1023 if (ElementSizeBits == 0) continue; 1024 1025 Value *EltVal = SrcVal; 1026 if (Shift) { 1027 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); 1028 EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal, 1029 "sroa.store.elt", SI); 1030 } 1031 1032 // Truncate down to an integer of the right size. 1033 if (ElementSizeBits != AllocaSizeBits) 1034 EltVal = new TruncInst(EltVal, 1035 IntegerType::get(SI->getContext(), 1036 ElementSizeBits),"",SI); 1037 Value *DestField = NewElts[i]; 1038 if (EltVal->getType() == ArrayEltTy) { 1039 // Storing to an integer field of this size, just do it. 1040 } else if (ArrayEltTy->isFloatingPointTy() || 1041 ArrayEltTy->isVectorTy()) { 1042 // Bitcast to the right element type (for fp/vector values). 1043 EltVal = new BitCastInst(EltVal, ArrayEltTy, "", SI); 1044 } else { 1045 // Otherwise, bitcast the dest pointer (for aggregates). 1046 DestField = new BitCastInst(DestField, 1047 PointerType::getUnqual(EltVal->getType()), 1048 "", SI); 1049 } 1050 new StoreInst(EltVal, DestField, SI); 1051 1052 if (TD->isBigEndian()) 1053 Shift -= ElementOffset; 1054 else 1055 Shift += ElementOffset; 1056 } 1057 } 1058 1059 DeadInsts.push_back(SI); 1060} 1061 1062/// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to 1063/// an integer. Load the individual pieces to form the aggregate value. 1064void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, 1065 SmallVector<AllocaInst*, 32> &NewElts) { 1066 // Extract each element out of the NewElts according to its structure offset 1067 // and form the result value. 1068 const Type *AllocaEltTy = AI->getAllocatedType(); 1069 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); 1070 1071 DEBUG(dbgs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI 1072 << '\n'); 1073 1074 // There are two forms here: AI could be an array or struct. Both cases 1075 // have different ways to compute the element offset. 1076 const StructLayout *Layout = 0; 1077 uint64_t ArrayEltBitOffset = 0; 1078 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { 1079 Layout = TD->getStructLayout(EltSTy); 1080 } else { 1081 const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType(); 1082 ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); 1083 } 1084 1085 Value *ResultVal = 1086 Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits)); 1087 1088 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 1089 // Load the value from the alloca. If the NewElt is an aggregate, cast 1090 // the pointer to an integer of the same size before doing the load. 1091 Value *SrcField = NewElts[i]; 1092 const Type *FieldTy = 1093 cast<PointerType>(SrcField->getType())->getElementType(); 1094 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); 1095 1096 // Ignore zero sized fields like {}, they obviously contain no data. 1097 if (FieldSizeBits == 0) continue; 1098 1099 const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(), 1100 FieldSizeBits); 1101 if (!FieldTy->isIntegerTy() && !FieldTy->isFloatingPointTy() && 1102 !FieldTy->isVectorTy()) 1103 SrcField = new BitCastInst(SrcField, 1104 PointerType::getUnqual(FieldIntTy), 1105 "", LI); 1106 SrcField = new LoadInst(SrcField, "sroa.load.elt", LI); 1107 1108 // If SrcField is a fp or vector of the right size but that isn't an 1109 // integer type, bitcast to an integer so we can shift it. 1110 if (SrcField->getType() != FieldIntTy) 1111 SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI); 1112 1113 // Zero extend the field to be the same size as the final alloca so that 1114 // we can shift and insert it. 1115 if (SrcField->getType() != ResultVal->getType()) 1116 SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI); 1117 1118 // Determine the number of bits to shift SrcField. 1119 uint64_t Shift; 1120 if (Layout) // Struct case. 1121 Shift = Layout->getElementOffsetInBits(i); 1122 else // Array case. 1123 Shift = i*ArrayEltBitOffset; 1124 1125 if (TD->isBigEndian()) 1126 Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth(); 1127 1128 if (Shift) { 1129 Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift); 1130 SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI); 1131 } 1132 1133 ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI); 1134 } 1135 1136 // Handle tail padding by truncating the result 1137 if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits) 1138 ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI); 1139 1140 LI->replaceAllUsesWith(ResultVal); 1141 DeadInsts.push_back(LI); 1142} 1143 1144/// HasPadding - Return true if the specified type has any structure or 1145/// alignment padding, false otherwise. 1146static bool HasPadding(const Type *Ty, const TargetData &TD) { 1147 if (const StructType *STy = dyn_cast<StructType>(Ty)) { 1148 const StructLayout *SL = TD.getStructLayout(STy); 1149 unsigned PrevFieldBitOffset = 0; 1150 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 1151 unsigned FieldBitOffset = SL->getElementOffsetInBits(i); 1152 1153 // Padding in sub-elements? 1154 if (HasPadding(STy->getElementType(i), TD)) 1155 return true; 1156 1157 // Check to see if there is any padding between this element and the 1158 // previous one. 1159 if (i) { 1160 unsigned PrevFieldEnd = 1161 PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1)); 1162 if (PrevFieldEnd < FieldBitOffset) 1163 return true; 1164 } 1165 1166 PrevFieldBitOffset = FieldBitOffset; 1167 } 1168 1169 // Check for tail padding. 1170 if (unsigned EltCount = STy->getNumElements()) { 1171 unsigned PrevFieldEnd = PrevFieldBitOffset + 1172 TD.getTypeSizeInBits(STy->getElementType(EltCount-1)); 1173 if (PrevFieldEnd < SL->getSizeInBits()) 1174 return true; 1175 } 1176 1177 } else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 1178 return HasPadding(ATy->getElementType(), TD); 1179 } else if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) { 1180 return HasPadding(VTy->getElementType(), TD); 1181 } 1182 return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty); 1183} 1184 1185/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of 1186/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, 1187/// or 1 if safe after canonicalization has been performed. 1188bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) { 1189 // Loop over the use list of the alloca. We can only transform it if all of 1190 // the users are safe to transform. 1191 AllocaInfo Info; 1192 1193 isSafeForScalarRepl(AI, AI, 0, Info); 1194 if (Info.isUnsafe) { 1195 DEBUG(dbgs() << "Cannot transform: " << *AI << '\n'); 1196 return false; 1197 } 1198 1199 // Okay, we know all the users are promotable. If the aggregate is a memcpy 1200 // source and destination, we have to be careful. In particular, the memcpy 1201 // could be moving around elements that live in structure padding of the LLVM 1202 // types, but may actually be used. In these cases, we refuse to promote the 1203 // struct. 1204 if (Info.isMemCpySrc && Info.isMemCpyDst && 1205 HasPadding(AI->getAllocatedType(), *TD)) 1206 return false; 1207 1208 return true; 1209} 1210 1211/// MergeInType - Add the 'In' type to the accumulated type (Accum) so far at 1212/// the offset specified by Offset (which is specified in bytes). 1213/// 1214/// There are two cases we handle here: 1215/// 1) A union of vector types of the same size and potentially its elements. 1216/// Here we turn element accesses into insert/extract element operations. 1217/// This promotes a <4 x float> with a store of float to the third element 1218/// into a <4 x float> that uses insert element. 1219/// 2) A fully general blob of memory, which we turn into some (potentially 1220/// large) integer type with extract and insert operations where the loads 1221/// and stores would mutate the memory. 1222void ConvertToScalarInfo::MergeInType(const Type *In, uint64_t Offset) { 1223 // Remember if we saw a vector type. 1224 HadAVector |= In->isVectorTy(); 1225 1226 if (VectorTy && VectorTy->isVoidTy()) 1227 return; 1228 1229 // If this could be contributing to a vector, analyze it. 1230 1231 // If the In type is a vector that is the same size as the alloca, see if it 1232 // matches the existing VecTy. 1233 if (const VectorType *VInTy = dyn_cast<VectorType>(In)) { 1234 if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) { 1235 // If we're storing/loading a vector of the right size, allow it as a 1236 // vector. If this the first vector we see, remember the type so that 1237 // we know the element size. 1238 if (VectorTy == 0) 1239 VectorTy = VInTy; 1240 return; 1241 } 1242 } else if (In->isFloatTy() || In->isDoubleTy() || 1243 (In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 && 1244 isPowerOf2_32(In->getPrimitiveSizeInBits()))) { 1245 // If we're accessing something that could be an element of a vector, see 1246 // if the implied vector agrees with what we already have and if Offset is 1247 // compatible with it. 1248 unsigned EltSize = In->getPrimitiveSizeInBits()/8; 1249 if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 && 1250 (VectorTy == 0 || 1251 cast<VectorType>(VectorTy)->getElementType() 1252 ->getPrimitiveSizeInBits()/8 == EltSize)) { 1253 if (VectorTy == 0) 1254 VectorTy = VectorType::get(In, AllocaSize/EltSize); 1255 return; 1256 } 1257 } 1258 1259 // Otherwise, we have a case that we can't handle with an optimized vector 1260 // form. We can still turn this into a large integer. 1261 VectorTy = Type::getVoidTy(In->getContext()); 1262} 1263 1264/// CanConvertToScalar - V is a pointer. If we can convert the pointee and all 1265/// its accesses to a single vector type, return true and set VecTy to 1266/// the new type. If we could convert the alloca into a single promotable 1267/// integer, return true but set VecTy to VoidTy. Further, if the use is not a 1268/// completely trivial use that mem2reg could promote, set IsNotTrivial. Offset 1269/// is the current offset from the base of the alloca being analyzed. 1270/// 1271/// If we see at least one access to the value that is as a vector type, set the 1272/// SawVec flag. 1273bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset) { 1274 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 1275 Instruction *User = cast<Instruction>(*UI); 1276 1277 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1278 // Don't break volatile loads. 1279 if (LI->isVolatile()) 1280 return false; 1281 MergeInType(LI->getType(), Offset); 1282 continue; 1283 } 1284 1285 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1286 // Storing the pointer, not into the value? 1287 if (SI->getOperand(0) == V || SI->isVolatile()) return false; 1288 MergeInType(SI->getOperand(0)->getType(), Offset); 1289 continue; 1290 } 1291 1292 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { 1293 if (!CanConvertToScalar(BCI, Offset)) 1294 return false; 1295 IsNotTrivial = true; 1296 continue; 1297 } 1298 1299 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 1300 // If this is a GEP with a variable indices, we can't handle it. 1301 if (!GEP->hasAllConstantIndices()) 1302 return false; 1303 1304 // Compute the offset that this GEP adds to the pointer. 1305 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 1306 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 1307 &Indices[0], Indices.size()); 1308 // See if all uses can be converted. 1309 if (!CanConvertToScalar(GEP, Offset+GEPOffset)) 1310 return false; 1311 IsNotTrivial = true; 1312 continue; 1313 } 1314 1315 // If this is a constant sized memset of a constant value (e.g. 0) we can 1316 // handle it. 1317 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 1318 // Store of constant value and constant size. 1319 if (isa<ConstantInt>(MSI->getValue()) && 1320 isa<ConstantInt>(MSI->getLength())) { 1321 IsNotTrivial = true; 1322 continue; 1323 } 1324 } 1325 1326 // If this is a memcpy or memmove into or out of the whole allocation, we 1327 // can handle it like a load or store of the scalar type. 1328 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 1329 if (ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength())) 1330 if (Len->getZExtValue() == AllocaSize && Offset == 0) { 1331 IsNotTrivial = true; 1332 continue; 1333 } 1334 } 1335 1336 // Otherwise, we cannot handle this! 1337 return false; 1338 } 1339 1340 return true; 1341} 1342 1343/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca 1344/// directly. This happens when we are converting an "integer union" to a 1345/// single integer scalar, or when we are converting a "vector union" to a 1346/// vector with insert/extractelement instructions. 1347/// 1348/// Offset is an offset from the original alloca, in bits that need to be 1349/// shifted to the right. By the end of this, there should be no uses of Ptr. 1350void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, 1351 uint64_t Offset) { 1352 while (!Ptr->use_empty()) { 1353 Instruction *User = cast<Instruction>(Ptr->use_back()); 1354 1355 if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 1356 ConvertUsesToScalar(CI, NewAI, Offset); 1357 CI->eraseFromParent(); 1358 continue; 1359 } 1360 1361 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 1362 // Compute the offset that this GEP adds to the pointer. 1363 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); 1364 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), 1365 &Indices[0], Indices.size()); 1366 ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8); 1367 GEP->eraseFromParent(); 1368 continue; 1369 } 1370 1371 IRBuilder<> Builder(User->getParent(), User); 1372 1373 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1374 // The load is a bit extract from NewAI shifted right by Offset bits. 1375 Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp"); 1376 Value *NewLoadVal 1377 = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder); 1378 LI->replaceAllUsesWith(NewLoadVal); 1379 LI->eraseFromParent(); 1380 continue; 1381 } 1382 1383 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1384 assert(SI->getOperand(0) != Ptr && "Consistency error!"); 1385 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 1386 Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset, 1387 Builder); 1388 Builder.CreateStore(New, NewAI); 1389 SI->eraseFromParent(); 1390 1391 // If the load we just inserted is now dead, then the inserted store 1392 // overwrote the entire thing. 1393 if (Old->use_empty()) 1394 Old->eraseFromParent(); 1395 continue; 1396 } 1397 1398 // If this is a constant sized memset of a constant value (e.g. 0) we can 1399 // transform it into a store of the expanded constant value. 1400 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { 1401 assert(MSI->getRawDest() == Ptr && "Consistency error!"); 1402 unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue(); 1403 if (NumBytes != 0) { 1404 unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue(); 1405 1406 // Compute the value replicated the right number of times. 1407 APInt APVal(NumBytes*8, Val); 1408 1409 // Splat the value if non-zero. 1410 if (Val) 1411 for (unsigned i = 1; i != NumBytes; ++i) 1412 APVal |= APVal << 8; 1413 1414 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); 1415 Value *New = ConvertScalar_InsertValue( 1416 ConstantInt::get(User->getContext(), APVal), 1417 Old, Offset, Builder); 1418 Builder.CreateStore(New, NewAI); 1419 1420 // If the load we just inserted is now dead, then the memset overwrote 1421 // the entire thing. 1422 if (Old->use_empty()) 1423 Old->eraseFromParent(); 1424 } 1425 MSI->eraseFromParent(); 1426 continue; 1427 } 1428 1429 // If this is a memcpy or memmove into or out of the whole allocation, we 1430 // can handle it like a load or store of the scalar type. 1431 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { 1432 assert(Offset == 0 && "must be store to start of alloca"); 1433 1434 // If the source and destination are both to the same alloca, then this is 1435 // a noop copy-to-self, just delete it. Otherwise, emit a load and store 1436 // as appropriate. 1437 AllocaInst *OrigAI = cast<AllocaInst>(Ptr->getUnderlyingObject(0)); 1438 1439 if (MTI->getSource()->getUnderlyingObject(0) != OrigAI) { 1440 // Dest must be OrigAI, change this to be a load from the original 1441 // pointer (bitcasted), then a store to our new alloca. 1442 assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?"); 1443 Value *SrcPtr = MTI->getSource(); 1444 SrcPtr = Builder.CreateBitCast(SrcPtr, NewAI->getType()); 1445 1446 LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval"); 1447 SrcVal->setAlignment(MTI->getAlignment()); 1448 Builder.CreateStore(SrcVal, NewAI); 1449 } else if (MTI->getDest()->getUnderlyingObject(0) != OrigAI) { 1450 // Src must be OrigAI, change this to be a load from NewAI then a store 1451 // through the original dest pointer (bitcasted). 1452 assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?"); 1453 LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval"); 1454 1455 Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), NewAI->getType()); 1456 StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr); 1457 NewStore->setAlignment(MTI->getAlignment()); 1458 } else { 1459 // Noop transfer. Src == Dst 1460 } 1461 1462 MTI->eraseFromParent(); 1463 continue; 1464 } 1465 1466 llvm_unreachable("Unsupported operation!"); 1467 } 1468} 1469 1470/// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer 1471/// or vector value FromVal, extracting the bits from the offset specified by 1472/// Offset. This returns the value, which is of type ToType. 1473/// 1474/// This happens when we are converting an "integer union" to a single 1475/// integer scalar, or when we are converting a "vector union" to a vector with 1476/// insert/extractelement instructions. 1477/// 1478/// Offset is an offset from the original alloca, in bits that need to be 1479/// shifted to the right. 1480Value *ConvertToScalarInfo:: 1481ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType, 1482 uint64_t Offset, IRBuilder<> &Builder) { 1483 // If the load is of the whole new alloca, no conversion is needed. 1484 if (FromVal->getType() == ToType && Offset == 0) 1485 return FromVal; 1486 1487 // If the result alloca is a vector type, this is either an element 1488 // access or a bitcast to another vector type of the same size. 1489 if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) { 1490 if (ToType->isVectorTy()) 1491 return Builder.CreateBitCast(FromVal, ToType, "tmp"); 1492 1493 // Otherwise it must be an element access. 1494 unsigned Elt = 0; 1495 if (Offset) { 1496 unsigned EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 1497 Elt = Offset/EltSize; 1498 assert(EltSize*Elt == Offset && "Invalid modulus in validity checking"); 1499 } 1500 // Return the element extracted out of it. 1501 Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get( 1502 Type::getInt32Ty(FromVal->getContext()), Elt), "tmp"); 1503 if (V->getType() != ToType) 1504 V = Builder.CreateBitCast(V, ToType, "tmp"); 1505 return V; 1506 } 1507 1508 // If ToType is a first class aggregate, extract out each of the pieces and 1509 // use insertvalue's to form the FCA. 1510 if (const StructType *ST = dyn_cast<StructType>(ToType)) { 1511 const StructLayout &Layout = *TD.getStructLayout(ST); 1512 Value *Res = UndefValue::get(ST); 1513 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 1514 Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i), 1515 Offset+Layout.getElementOffsetInBits(i), 1516 Builder); 1517 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 1518 } 1519 return Res; 1520 } 1521 1522 if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) { 1523 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 1524 Value *Res = UndefValue::get(AT); 1525 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 1526 Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(), 1527 Offset+i*EltSize, Builder); 1528 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); 1529 } 1530 return Res; 1531 } 1532 1533 // Otherwise, this must be a union that was converted to an integer value. 1534 const IntegerType *NTy = cast<IntegerType>(FromVal->getType()); 1535 1536 // If this is a big-endian system and the load is narrower than the 1537 // full alloca type, we need to do a shift to get the right bits. 1538 int ShAmt = 0; 1539 if (TD.isBigEndian()) { 1540 // On big-endian machines, the lowest bit is stored at the bit offset 1541 // from the pointer given by getTypeStoreSizeInBits. This matters for 1542 // integers with a bitwidth that is not a multiple of 8. 1543 ShAmt = TD.getTypeStoreSizeInBits(NTy) - 1544 TD.getTypeStoreSizeInBits(ToType) - Offset; 1545 } else { 1546 ShAmt = Offset; 1547 } 1548 1549 // Note: we support negative bitwidths (with shl) which are not defined. 1550 // We do this to support (f.e.) loads off the end of a structure where 1551 // only some bits are used. 1552 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth()) 1553 FromVal = Builder.CreateLShr(FromVal, 1554 ConstantInt::get(FromVal->getType(), 1555 ShAmt), "tmp"); 1556 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) 1557 FromVal = Builder.CreateShl(FromVal, 1558 ConstantInt::get(FromVal->getType(), 1559 -ShAmt), "tmp"); 1560 1561 // Finally, unconditionally truncate the integer to the right width. 1562 unsigned LIBitWidth = TD.getTypeSizeInBits(ToType); 1563 if (LIBitWidth < NTy->getBitWidth()) 1564 FromVal = 1565 Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(), 1566 LIBitWidth), "tmp"); 1567 else if (LIBitWidth > NTy->getBitWidth()) 1568 FromVal = 1569 Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(), 1570 LIBitWidth), "tmp"); 1571 1572 // If the result is an integer, this is a trunc or bitcast. 1573 if (ToType->isIntegerTy()) { 1574 // Should be done. 1575 } else if (ToType->isFloatingPointTy() || ToType->isVectorTy()) { 1576 // Just do a bitcast, we know the sizes match up. 1577 FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp"); 1578 } else { 1579 // Otherwise must be a pointer. 1580 FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp"); 1581 } 1582 assert(FromVal->getType() == ToType && "Didn't convert right?"); 1583 return FromVal; 1584} 1585 1586/// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer 1587/// or vector value "Old" at the offset specified by Offset. 1588/// 1589/// This happens when we are converting an "integer union" to a 1590/// single integer scalar, or when we are converting a "vector union" to a 1591/// vector with insert/extractelement instructions. 1592/// 1593/// Offset is an offset from the original alloca, in bits that need to be 1594/// shifted to the right. 1595Value *ConvertToScalarInfo:: 1596ConvertScalar_InsertValue(Value *SV, Value *Old, 1597 uint64_t Offset, IRBuilder<> &Builder) { 1598 // Convert the stored type to the actual type, shift it left to insert 1599 // then 'or' into place. 1600 const Type *AllocaType = Old->getType(); 1601 LLVMContext &Context = Old->getContext(); 1602 1603 if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) { 1604 uint64_t VecSize = TD.getTypeAllocSizeInBits(VTy); 1605 uint64_t ValSize = TD.getTypeAllocSizeInBits(SV->getType()); 1606 1607 // Changing the whole vector with memset or with an access of a different 1608 // vector type? 1609 if (ValSize == VecSize) 1610 return Builder.CreateBitCast(SV, AllocaType, "tmp"); 1611 1612 uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); 1613 1614 // Must be an element insertion. 1615 unsigned Elt = Offset/EltSize; 1616 1617 if (SV->getType() != VTy->getElementType()) 1618 SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp"); 1619 1620 SV = Builder.CreateInsertElement(Old, SV, 1621 ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt), 1622 "tmp"); 1623 return SV; 1624 } 1625 1626 // If SV is a first-class aggregate value, insert each value recursively. 1627 if (const StructType *ST = dyn_cast<StructType>(SV->getType())) { 1628 const StructLayout &Layout = *TD.getStructLayout(ST); 1629 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { 1630 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 1631 Old = ConvertScalar_InsertValue(Elt, Old, 1632 Offset+Layout.getElementOffsetInBits(i), 1633 Builder); 1634 } 1635 return Old; 1636 } 1637 1638 if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) { 1639 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); 1640 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 1641 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); 1642 Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder); 1643 } 1644 return Old; 1645 } 1646 1647 // If SV is a float, convert it to the appropriate integer type. 1648 // If it is a pointer, do the same. 1649 unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType()); 1650 unsigned DestWidth = TD.getTypeSizeInBits(AllocaType); 1651 unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType()); 1652 unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType); 1653 if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy()) 1654 SV = Builder.CreateBitCast(SV, 1655 IntegerType::get(SV->getContext(),SrcWidth), "tmp"); 1656 else if (SV->getType()->isPointerTy()) 1657 SV = Builder.CreatePtrToInt(SV, TD.getIntPtrType(SV->getContext()), "tmp"); 1658 1659 // Zero extend or truncate the value if needed. 1660 if (SV->getType() != AllocaType) { 1661 if (SV->getType()->getPrimitiveSizeInBits() < 1662 AllocaType->getPrimitiveSizeInBits()) 1663 SV = Builder.CreateZExt(SV, AllocaType, "tmp"); 1664 else { 1665 // Truncation may be needed if storing more than the alloca can hold 1666 // (undefined behavior). 1667 SV = Builder.CreateTrunc(SV, AllocaType, "tmp"); 1668 SrcWidth = DestWidth; 1669 SrcStoreWidth = DestStoreWidth; 1670 } 1671 } 1672 1673 // If this is a big-endian system and the store is narrower than the 1674 // full alloca type, we need to do a shift to get the right bits. 1675 int ShAmt = 0; 1676 if (TD.isBigEndian()) { 1677 // On big-endian machines, the lowest bit is stored at the bit offset 1678 // from the pointer given by getTypeStoreSizeInBits. This matters for 1679 // integers with a bitwidth that is not a multiple of 8. 1680 ShAmt = DestStoreWidth - SrcStoreWidth - Offset; 1681 } else { 1682 ShAmt = Offset; 1683 } 1684 1685 // Note: we support negative bitwidths (with shr) which are not defined. 1686 // We do this to support (f.e.) stores off the end of a structure where 1687 // only some bits in the structure are set. 1688 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth)); 1689 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) { 1690 SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(), 1691 ShAmt), "tmp"); 1692 Mask <<= ShAmt; 1693 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { 1694 SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(), 1695 -ShAmt), "tmp"); 1696 Mask = Mask.lshr(-ShAmt); 1697 } 1698 1699 // Mask out the bits we are about to insert from the old value, and or 1700 // in the new bits. 1701 if (SrcWidth != DestWidth) { 1702 assert(DestWidth > SrcWidth); 1703 Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask"); 1704 SV = Builder.CreateOr(Old, SV, "ins"); 1705 } 1706 return SV; 1707} 1708 1709 1710 1711/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to 1712/// some part of a constant global variable. This intentionally only accepts 1713/// constant expressions because we don't can't rewrite arbitrary instructions. 1714static bool PointsToConstantGlobal(Value *V) { 1715 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) 1716 return GV->isConstant(); 1717 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 1718 if (CE->getOpcode() == Instruction::BitCast || 1719 CE->getOpcode() == Instruction::GetElementPtr) 1720 return PointsToConstantGlobal(CE->getOperand(0)); 1721 return false; 1722} 1723 1724/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived) 1725/// pointer to an alloca. Ignore any reads of the pointer, return false if we 1726/// see any stores or other unknown uses. If we see pointer arithmetic, keep 1727/// track of whether it moves the pointer (with isOffset) but otherwise traverse 1728/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to 1729/// the alloca, and if the source pointer is a pointer to a constant global, we 1730/// can optimize this. 1731static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy, 1732 bool isOffset) { 1733 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 1734 User *U = cast<Instruction>(*UI); 1735 1736 if (LoadInst *LI = dyn_cast<LoadInst>(U)) 1737 // Ignore non-volatile loads, they are always ok. 1738 if (!LI->isVolatile()) 1739 continue; 1740 1741 if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) { 1742 // If uses of the bitcast are ok, we are ok. 1743 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) 1744 return false; 1745 continue; 1746 } 1747 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 1748 // If the GEP has all zero indices, it doesn't offset the pointer. If it 1749 // doesn't, it does. 1750 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy, 1751 isOffset || !GEP->hasAllZeroIndices())) 1752 return false; 1753 continue; 1754 } 1755 1756 // If this is isn't our memcpy/memmove, reject it as something we can't 1757 // handle. 1758 MemTransferInst *MI = dyn_cast<MemTransferInst>(U); 1759 if (MI == 0) 1760 return false; 1761 1762 // If we already have seen a copy, reject the second one. 1763 if (TheCopy) return false; 1764 1765 // If the pointer has been offset from the start of the alloca, we can't 1766 // safely handle this. 1767 if (isOffset) return false; 1768 1769 // If the memintrinsic isn't using the alloca as the dest, reject it. 1770 if (UI.getOperandNo() != 0) return false; 1771 1772 // If the source of the memcpy/move is not a constant global, reject it. 1773 if (!PointsToConstantGlobal(MI->getSource())) 1774 return false; 1775 1776 // Otherwise, the transform is safe. Remember the copy instruction. 1777 TheCopy = MI; 1778 } 1779 return true; 1780} 1781 1782/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only 1783/// modified by a copy from a constant global. If we can prove this, we can 1784/// replace any uses of the alloca with uses of the global directly. 1785MemTransferInst *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) { 1786 MemTransferInst *TheCopy = 0; 1787 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) 1788 return TheCopy; 1789 return 0; 1790} 1791