ScalarReplAggregates.cpp revision 963a97f1a365c8d09ca681e922371f9ec3473ee8
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/Pass.h" 31#include "llvm/Analysis/Dominators.h" 32#include "llvm/Target/TargetData.h" 33#include "llvm/Transforms/Utils/PromoteMemToReg.h" 34#include "llvm/Support/Debug.h" 35#include "llvm/Support/GetElementPtrTypeIterator.h" 36#include "llvm/Support/MathExtras.h" 37#include "llvm/Support/Compiler.h" 38#include "llvm/ADT/SmallVector.h" 39#include "llvm/ADT/Statistic.h" 40#include "llvm/ADT/StringExtras.h" 41using namespace llvm; 42 43STATISTIC(NumReplaced, "Number of allocas broken up"); 44STATISTIC(NumPromoted, "Number of allocas promoted"); 45STATISTIC(NumConverted, "Number of aggregates converted to scalar"); 46STATISTIC(NumGlobals, "Number of allocas copied from constant global"); 47 48namespace { 49 struct VISIBILITY_HIDDEN SROA : public FunctionPass { 50 static char ID; // Pass identification, replacement for typeid 51 explicit SROA(signed T = -1) : FunctionPass((intptr_t)&ID) { 52 if (T == -1) 53 SRThreshold = 128; 54 else 55 SRThreshold = T; 56 } 57 58 bool runOnFunction(Function &F); 59 60 bool performScalarRepl(Function &F); 61 bool performPromotion(Function &F); 62 63 // getAnalysisUsage - This pass does not require any passes, but we know it 64 // will not alter the CFG, so say so. 65 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 66 AU.addRequired<DominatorTree>(); 67 AU.addRequired<DominanceFrontier>(); 68 AU.addRequired<TargetData>(); 69 AU.setPreservesCFG(); 70 } 71 72 private: 73 /// AllocaInfo - When analyzing uses of an alloca instruction, this captures 74 /// information about the uses. All these fields are initialized to false 75 /// and set to true when something is learned. 76 struct AllocaInfo { 77 /// isUnsafe - This is set to true if the alloca cannot be SROA'd. 78 bool isUnsafe : 1; 79 80 /// needsCanon - This is set to true if there is some use of the alloca 81 /// that requires canonicalization. 82 bool needsCanon : 1; 83 84 /// isMemCpySrc - This is true if this aggregate is memcpy'd from. 85 bool isMemCpySrc : 1; 86 87 /// isMemCpyDst - This is true if this aggregate is memcpy'd into. 88 bool isMemCpyDst : 1; 89 90 AllocaInfo() 91 : isUnsafe(false), needsCanon(false), 92 isMemCpySrc(false), isMemCpyDst(false) {} 93 }; 94 95 unsigned SRThreshold; 96 97 void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; } 98 99 int isSafeAllocaToScalarRepl(AllocationInst *AI); 100 101 void isSafeUseOfAllocation(Instruction *User, AllocationInst *AI, 102 AllocaInfo &Info); 103 void isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI, 104 AllocaInfo &Info); 105 void isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI, 106 unsigned OpNo, AllocaInfo &Info); 107 void isSafeUseOfBitCastedAllocation(BitCastInst *User, AllocationInst *AI, 108 AllocaInfo &Info); 109 110 void DoScalarReplacement(AllocationInst *AI, 111 std::vector<AllocationInst*> &WorkList); 112 void CanonicalizeAllocaUsers(AllocationInst *AI); 113 AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocationInst *Base); 114 115 void RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI, 116 SmallVector<AllocaInst*, 32> &NewElts); 117 118 const Type *CanConvertToScalar(Value *V, bool &IsNotTrivial); 119 void ConvertToScalar(AllocationInst *AI, const Type *Ty); 120 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, unsigned Offset); 121 Value *ConvertUsesOfLoadToScalar(LoadInst *LI, AllocaInst *NewAI, 122 unsigned Offset); 123 Value *ConvertUsesOfStoreToScalar(StoreInst *SI, AllocaInst *NewAI, 124 unsigned Offset); 125 static Instruction *isOnlyCopiedFromConstantGlobal(AllocationInst *AI); 126 }; 127} 128 129char SROA::ID = 0; 130static RegisterPass<SROA> X("scalarrepl", "Scalar Replacement of Aggregates"); 131 132// Public interface to the ScalarReplAggregates pass 133FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) { 134 return new SROA(Threshold); 135} 136 137 138bool SROA::runOnFunction(Function &F) { 139 bool Changed = performPromotion(F); 140 while (1) { 141 bool LocalChange = performScalarRepl(F); 142 if (!LocalChange) break; // No need to repromote if no scalarrepl 143 Changed = true; 144 LocalChange = performPromotion(F); 145 if (!LocalChange) break; // No need to re-scalarrepl if no promotion 146 } 147 148 return Changed; 149} 150 151 152bool SROA::performPromotion(Function &F) { 153 std::vector<AllocaInst*> Allocas; 154 DominatorTree &DT = getAnalysis<DominatorTree>(); 155 DominanceFrontier &DF = getAnalysis<DominanceFrontier>(); 156 157 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function 158 159 bool Changed = false; 160 161 while (1) { 162 Allocas.clear(); 163 164 // Find allocas that are safe to promote, by looking at all instructions in 165 // the entry node 166 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) 167 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? 168 if (isAllocaPromotable(AI)) 169 Allocas.push_back(AI); 170 171 if (Allocas.empty()) break; 172 173 PromoteMemToReg(Allocas, DT, DF); 174 NumPromoted += Allocas.size(); 175 Changed = true; 176 } 177 178 return Changed; 179} 180 181/// getNumSAElements - Return the number of elements in the specific struct or 182/// array. 183static uint64_t getNumSAElements(const Type *T) { 184 if (const StructType *ST = dyn_cast<StructType>(T)) 185 return ST->getNumElements(); 186 return cast<ArrayType>(T)->getNumElements(); 187} 188 189// performScalarRepl - This algorithm is a simple worklist driven algorithm, 190// which runs on all of the malloc/alloca instructions in the function, removing 191// them if they are only used by getelementptr instructions. 192// 193bool SROA::performScalarRepl(Function &F) { 194 std::vector<AllocationInst*> WorkList; 195 196 // Scan the entry basic block, adding any alloca's and mallocs to the worklist 197 BasicBlock &BB = F.getEntryBlock(); 198 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) 199 if (AllocationInst *A = dyn_cast<AllocationInst>(I)) 200 WorkList.push_back(A); 201 202 const TargetData &TD = getAnalysis<TargetData>(); 203 204 // Process the worklist 205 bool Changed = false; 206 while (!WorkList.empty()) { 207 AllocationInst *AI = WorkList.back(); 208 WorkList.pop_back(); 209 210 // Handle dead allocas trivially. These can be formed by SROA'ing arrays 211 // with unused elements. 212 if (AI->use_empty()) { 213 AI->eraseFromParent(); 214 continue; 215 } 216 217 // If we can turn this aggregate value (potentially with casts) into a 218 // simple scalar value that can be mem2reg'd into a register value. 219 bool IsNotTrivial = false; 220 if (const Type *ActualType = CanConvertToScalar(AI, IsNotTrivial)) 221 if (IsNotTrivial && ActualType != Type::VoidTy) { 222 ConvertToScalar(AI, ActualType); 223 Changed = true; 224 continue; 225 } 226 227 // Check to see if we can perform the core SROA transformation. We cannot 228 // transform the allocation instruction if it is an array allocation 229 // (allocations OF arrays are ok though), and an allocation of a scalar 230 // value cannot be decomposed at all. 231 if (!AI->isArrayAllocation() && 232 (isa<StructType>(AI->getAllocatedType()) || 233 isa<ArrayType>(AI->getAllocatedType())) && 234 AI->getAllocatedType()->isSized() && 235 // Do not promote any struct whose size is larger than "128" bytes. 236 TD.getABITypeSize(AI->getAllocatedType()) < SRThreshold && 237 // Do not promote any struct into more than "32" separate vars. 238 getNumSAElements(AI->getAllocatedType()) < SRThreshold/4) { 239 // Check that all of the users of the allocation are capable of being 240 // transformed. 241 switch (isSafeAllocaToScalarRepl(AI)) { 242 default: assert(0 && "Unexpected value!"); 243 case 0: // Not safe to scalar replace. 244 break; 245 case 1: // Safe, but requires cleanup/canonicalizations first 246 CanonicalizeAllocaUsers(AI); 247 // FALL THROUGH. 248 case 3: // Safe to scalar replace. 249 DoScalarReplacement(AI, WorkList); 250 Changed = true; 251 continue; 252 } 253 } 254 255 // Check to see if this allocation is only modified by a memcpy/memmove from 256 // a constant global. If this is the case, we can change all users to use 257 // the constant global instead. This is commonly produced by the CFE by 258 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A' 259 // is only subsequently read. 260 if (Instruction *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) { 261 DOUT << "Found alloca equal to global: " << *AI; 262 DOUT << " memcpy = " << *TheCopy; 263 Constant *TheSrc = cast<Constant>(TheCopy->getOperand(2)); 264 AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType())); 265 TheCopy->eraseFromParent(); // Don't mutate the global. 266 AI->eraseFromParent(); 267 ++NumGlobals; 268 Changed = true; 269 continue; 270 } 271 272 // Otherwise, couldn't process this. 273 } 274 275 return Changed; 276} 277 278/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl 279/// predicate, do SROA now. 280void SROA::DoScalarReplacement(AllocationInst *AI, 281 std::vector<AllocationInst*> &WorkList) { 282 DOUT << "Found inst to SROA: " << *AI; 283 SmallVector<AllocaInst*, 32> ElementAllocas; 284 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 285 ElementAllocas.reserve(ST->getNumContainedTypes()); 286 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { 287 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 288 AI->getAlignment(), 289 AI->getName() + "." + utostr(i), AI); 290 ElementAllocas.push_back(NA); 291 WorkList.push_back(NA); // Add to worklist for recursive processing 292 } 293 } else { 294 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); 295 ElementAllocas.reserve(AT->getNumElements()); 296 const Type *ElTy = AT->getElementType(); 297 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 298 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(), 299 AI->getName() + "." + utostr(i), AI); 300 ElementAllocas.push_back(NA); 301 WorkList.push_back(NA); // Add to worklist for recursive processing 302 } 303 } 304 305 // Now that we have created the alloca instructions that we want to use, 306 // expand the getelementptr instructions to use them. 307 // 308 while (!AI->use_empty()) { 309 Instruction *User = cast<Instruction>(AI->use_back()); 310 if (BitCastInst *BCInst = dyn_cast<BitCastInst>(User)) { 311 RewriteBitCastUserOfAlloca(BCInst, AI, ElementAllocas); 312 BCInst->eraseFromParent(); 313 continue; 314 } 315 316 // Replace %res = load { i32, i32 }* %alloc 317 // by 318 // %load.0 = load i32* %alloc.0 319 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0 320 // %load.1 = load i32* %alloc.1 321 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1 322 // (Also works for arrays instead of structs) 323 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 324 Value *Insert = UndefValue::get(LI->getType()); 325 for (unsigned i = 0, e = ElementAllocas.size(); i != e; ++i) { 326 Value *Load = new LoadInst(ElementAllocas[i], "load", LI); 327 Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI); 328 } 329 LI->replaceAllUsesWith(Insert); 330 LI->eraseFromParent(); 331 continue; 332 } 333 334 // Replace store { i32, i32 } %val, { i32, i32 }* %alloc 335 // by 336 // %val.0 = extractvalue { i32, i32 } %val, 0 337 // store i32 %val.0, i32* %alloc.0 338 // %val.1 = extractvalue { i32, i32 } %val, 1 339 // store i32 %val.1, i32* %alloc.1 340 // (Also works for arrays instead of structs) 341 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 342 Value *Val = SI->getOperand(0); 343 for (unsigned i = 0, e = ElementAllocas.size(); i != e; ++i) { 344 Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI); 345 new StoreInst(Extract, ElementAllocas[i], SI); 346 } 347 SI->eraseFromParent(); 348 continue; 349 } 350 351 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User); 352 // We now know that the GEP is of the form: GEP <ptr>, 0, <cst> 353 unsigned Idx = 354 (unsigned)cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 355 356 assert(Idx < ElementAllocas.size() && "Index out of range?"); 357 AllocaInst *AllocaToUse = ElementAllocas[Idx]; 358 359 Value *RepValue; 360 if (GEPI->getNumOperands() == 3) { 361 // Do not insert a new getelementptr instruction with zero indices, only 362 // to have it optimized out later. 363 RepValue = AllocaToUse; 364 } else { 365 // We are indexing deeply into the structure, so we still need a 366 // getelement ptr instruction to finish the indexing. This may be 367 // expanded itself once the worklist is rerun. 368 // 369 SmallVector<Value*, 8> NewArgs; 370 NewArgs.push_back(Constant::getNullValue(Type::Int32Ty)); 371 NewArgs.append(GEPI->op_begin()+3, GEPI->op_end()); 372 RepValue = GetElementPtrInst::Create(AllocaToUse, NewArgs.begin(), 373 NewArgs.end(), "", GEPI); 374 RepValue->takeName(GEPI); 375 } 376 377 // If this GEP is to the start of the aggregate, check for memcpys. 378 if (Idx == 0) { 379 bool IsStartOfAggregateGEP = true; 380 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) { 381 if (!isa<ConstantInt>(GEPI->getOperand(i))) { 382 IsStartOfAggregateGEP = false; 383 break; 384 } 385 if (!cast<ConstantInt>(GEPI->getOperand(i))->isZero()) { 386 IsStartOfAggregateGEP = false; 387 break; 388 } 389 } 390 391 if (IsStartOfAggregateGEP) 392 RewriteBitCastUserOfAlloca(GEPI, AI, ElementAllocas); 393 } 394 395 396 // Move all of the users over to the new GEP. 397 GEPI->replaceAllUsesWith(RepValue); 398 // Delete the old GEP 399 GEPI->eraseFromParent(); 400 } 401 402 // Finally, delete the Alloca instruction 403 AI->eraseFromParent(); 404 NumReplaced++; 405} 406 407 408/// isSafeElementUse - Check to see if this use is an allowed use for a 409/// getelementptr instruction of an array aggregate allocation. isFirstElt 410/// indicates whether Ptr is known to the start of the aggregate. 411/// 412void SROA::isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI, 413 AllocaInfo &Info) { 414 for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); 415 I != E; ++I) { 416 Instruction *User = cast<Instruction>(*I); 417 switch (User->getOpcode()) { 418 case Instruction::Load: break; 419 case Instruction::Store: 420 // Store is ok if storing INTO the pointer, not storing the pointer 421 if (User->getOperand(0) == Ptr) return MarkUnsafe(Info); 422 break; 423 case Instruction::GetElementPtr: { 424 GetElementPtrInst *GEP = cast<GetElementPtrInst>(User); 425 bool AreAllZeroIndices = isFirstElt; 426 if (GEP->getNumOperands() > 1) { 427 if (!isa<ConstantInt>(GEP->getOperand(1)) || 428 !cast<ConstantInt>(GEP->getOperand(1))->isZero()) 429 // Using pointer arithmetic to navigate the array. 430 return MarkUnsafe(Info); 431 432 if (AreAllZeroIndices) { 433 for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) { 434 if (!isa<ConstantInt>(GEP->getOperand(i)) || 435 !cast<ConstantInt>(GEP->getOperand(i))->isZero()) { 436 AreAllZeroIndices = false; 437 break; 438 } 439 } 440 } 441 } 442 isSafeElementUse(GEP, AreAllZeroIndices, AI, Info); 443 if (Info.isUnsafe) return; 444 break; 445 } 446 case Instruction::BitCast: 447 if (isFirstElt) { 448 isSafeUseOfBitCastedAllocation(cast<BitCastInst>(User), AI, Info); 449 if (Info.isUnsafe) return; 450 break; 451 } 452 DOUT << " Transformation preventing inst: " << *User; 453 return MarkUnsafe(Info); 454 case Instruction::Call: 455 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 456 if (isFirstElt) { 457 isSafeMemIntrinsicOnAllocation(MI, AI, I.getOperandNo(), Info); 458 if (Info.isUnsafe) return; 459 break; 460 } 461 } 462 DOUT << " Transformation preventing inst: " << *User; 463 return MarkUnsafe(Info); 464 default: 465 DOUT << " Transformation preventing inst: " << *User; 466 return MarkUnsafe(Info); 467 } 468 } 469 return; // All users look ok :) 470} 471 472/// AllUsersAreLoads - Return true if all users of this value are loads. 473static bool AllUsersAreLoads(Value *Ptr) { 474 for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); 475 I != E; ++I) 476 if (cast<Instruction>(*I)->getOpcode() != Instruction::Load) 477 return false; 478 return true; 479} 480 481/// isSafeUseOfAllocation - Check to see if this user is an allowed use for an 482/// aggregate allocation. 483/// 484void SROA::isSafeUseOfAllocation(Instruction *User, AllocationInst *AI, 485 AllocaInfo &Info) { 486 if (BitCastInst *C = dyn_cast<BitCastInst>(User)) 487 return isSafeUseOfBitCastedAllocation(C, AI, Info); 488 489 if (isa<LoadInst>(User)) 490 return; // Loads (returning a first class aggregrate) are always rewritable 491 492 if (isa<StoreInst>(User) && User->getOperand(0) != AI) 493 return; // Store is ok if storing INTO the pointer, not storing the pointer 494 495 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User); 496 if (GEPI == 0) 497 return MarkUnsafe(Info); 498 499 gep_type_iterator I = gep_type_begin(GEPI), E = gep_type_end(GEPI); 500 501 // The GEP is not safe to transform if not of the form "GEP <ptr>, 0, <cst>". 502 if (I == E || 503 I.getOperand() != Constant::getNullValue(I.getOperand()->getType())) { 504 return MarkUnsafe(Info); 505 } 506 507 ++I; 508 if (I == E) return MarkUnsafe(Info); // ran out of GEP indices?? 509 510 bool IsAllZeroIndices = true; 511 512 // If this is a use of an array allocation, do a bit more checking for sanity. 513 if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) { 514 uint64_t NumElements = AT->getNumElements(); 515 516 if (ConstantInt *Idx = dyn_cast<ConstantInt>(I.getOperand())) { 517 IsAllZeroIndices &= Idx->isZero(); 518 519 // Check to make sure that index falls within the array. If not, 520 // something funny is going on, so we won't do the optimization. 521 // 522 if (Idx->getZExtValue() >= NumElements) 523 return MarkUnsafe(Info); 524 525 // We cannot scalar repl this level of the array unless any array 526 // sub-indices are in-range constants. In particular, consider: 527 // A[0][i]. We cannot know that the user isn't doing invalid things like 528 // allowing i to index an out-of-range subscript that accesses A[1]. 529 // 530 // Scalar replacing *just* the outer index of the array is probably not 531 // going to be a win anyway, so just give up. 532 for (++I; I != E && (isa<ArrayType>(*I) || isa<VectorType>(*I)); ++I) { 533 uint64_t NumElements; 534 if (const ArrayType *SubArrayTy = dyn_cast<ArrayType>(*I)) 535 NumElements = SubArrayTy->getNumElements(); 536 else 537 NumElements = cast<VectorType>(*I)->getNumElements(); 538 539 ConstantInt *IdxVal = dyn_cast<ConstantInt>(I.getOperand()); 540 if (!IdxVal) return MarkUnsafe(Info); 541 if (IdxVal->getZExtValue() >= NumElements) 542 return MarkUnsafe(Info); 543 IsAllZeroIndices &= IdxVal->isZero(); 544 } 545 546 } else { 547 IsAllZeroIndices = 0; 548 549 // If this is an array index and the index is not constant, we cannot 550 // promote... that is unless the array has exactly one or two elements in 551 // it, in which case we CAN promote it, but we have to canonicalize this 552 // out if this is the only problem. 553 if ((NumElements == 1 || NumElements == 2) && 554 AllUsersAreLoads(GEPI)) { 555 Info.needsCanon = true; 556 return; // Canonicalization required! 557 } 558 return MarkUnsafe(Info); 559 } 560 } 561 562 // If there are any non-simple uses of this getelementptr, make sure to reject 563 // them. 564 return isSafeElementUse(GEPI, IsAllZeroIndices, AI, Info); 565} 566 567/// isSafeMemIntrinsicOnAllocation - Return true if the specified memory 568/// intrinsic can be promoted by SROA. At this point, we know that the operand 569/// of the memintrinsic is a pointer to the beginning of the allocation. 570void SROA::isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI, 571 unsigned OpNo, AllocaInfo &Info) { 572 // If not constant length, give up. 573 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 574 if (!Length) return MarkUnsafe(Info); 575 576 // If not the whole aggregate, give up. 577 const TargetData &TD = getAnalysis<TargetData>(); 578 if (Length->getZExtValue() != 579 TD.getABITypeSize(AI->getType()->getElementType())) 580 return MarkUnsafe(Info); 581 582 // We only know about memcpy/memset/memmove. 583 if (!isa<MemCpyInst>(MI) && !isa<MemSetInst>(MI) && !isa<MemMoveInst>(MI)) 584 return MarkUnsafe(Info); 585 586 // Otherwise, we can transform it. Determine whether this is a memcpy/set 587 // into or out of the aggregate. 588 if (OpNo == 1) 589 Info.isMemCpyDst = true; 590 else { 591 assert(OpNo == 2); 592 Info.isMemCpySrc = true; 593 } 594} 595 596/// isSafeUseOfBitCastedAllocation - Return true if all users of this bitcast 597/// are 598void SROA::isSafeUseOfBitCastedAllocation(BitCastInst *BC, AllocationInst *AI, 599 AllocaInfo &Info) { 600 for (Value::use_iterator UI = BC->use_begin(), E = BC->use_end(); 601 UI != E; ++UI) { 602 if (BitCastInst *BCU = dyn_cast<BitCastInst>(UI)) { 603 isSafeUseOfBitCastedAllocation(BCU, AI, Info); 604 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(UI)) { 605 isSafeMemIntrinsicOnAllocation(MI, AI, UI.getOperandNo(), Info); 606 } else { 607 return MarkUnsafe(Info); 608 } 609 if (Info.isUnsafe) return; 610 } 611} 612 613/// RewriteBitCastUserOfAlloca - BCInst (transitively) bitcasts AI, or indexes 614/// to its first element. Transform users of the cast to use the new values 615/// instead. 616void SROA::RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI, 617 SmallVector<AllocaInst*, 32> &NewElts) { 618 Constant *Zero = Constant::getNullValue(Type::Int32Ty); 619 const TargetData &TD = getAnalysis<TargetData>(); 620 621 Value::use_iterator UI = BCInst->use_begin(), UE = BCInst->use_end(); 622 while (UI != UE) { 623 if (BitCastInst *BCU = dyn_cast<BitCastInst>(*UI)) { 624 RewriteBitCastUserOfAlloca(BCU, AI, NewElts); 625 ++UI; 626 BCU->eraseFromParent(); 627 continue; 628 } 629 630 // Otherwise, must be memcpy/memmove/memset of the entire aggregate. Split 631 // into one per element. 632 MemIntrinsic *MI = dyn_cast<MemIntrinsic>(*UI); 633 634 // If it's not a mem intrinsic, it must be some other user of a gep of the 635 // first pointer. Just leave these alone. 636 if (!MI) { 637 ++UI; 638 continue; 639 } 640 641 // If this is a memcpy/memmove, construct the other pointer as the 642 // appropriate type. 643 Value *OtherPtr = 0; 644 if (MemCpyInst *MCI = dyn_cast<MemCpyInst>(MI)) { 645 if (BCInst == MCI->getRawDest()) 646 OtherPtr = MCI->getRawSource(); 647 else { 648 assert(BCInst == MCI->getRawSource()); 649 OtherPtr = MCI->getRawDest(); 650 } 651 } else if (MemMoveInst *MMI = dyn_cast<MemMoveInst>(MI)) { 652 if (BCInst == MMI->getRawDest()) 653 OtherPtr = MMI->getRawSource(); 654 else { 655 assert(BCInst == MMI->getRawSource()); 656 OtherPtr = MMI->getRawDest(); 657 } 658 } 659 660 // If there is an other pointer, we want to convert it to the same pointer 661 // type as AI has, so we can GEP through it. 662 if (OtherPtr) { 663 // It is likely that OtherPtr is a bitcast, if so, remove it. 664 if (BitCastInst *BC = dyn_cast<BitCastInst>(OtherPtr)) 665 OtherPtr = BC->getOperand(0); 666 if (ConstantExpr *BCE = dyn_cast<ConstantExpr>(OtherPtr)) 667 if (BCE->getOpcode() == Instruction::BitCast) 668 OtherPtr = BCE->getOperand(0); 669 670 // If the pointer is not the right type, insert a bitcast to the right 671 // type. 672 if (OtherPtr->getType() != AI->getType()) 673 OtherPtr = new BitCastInst(OtherPtr, AI->getType(), OtherPtr->getName(), 674 MI); 675 } 676 677 // Process each element of the aggregate. 678 Value *TheFn = MI->getOperand(0); 679 const Type *BytePtrTy = MI->getRawDest()->getType(); 680 bool SROADest = MI->getRawDest() == BCInst; 681 682 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 683 // If this is a memcpy/memmove, emit a GEP of the other element address. 684 Value *OtherElt = 0; 685 if (OtherPtr) { 686 Value *Idx[2] = { Zero, ConstantInt::get(Type::Int32Ty, i) }; 687 OtherElt = GetElementPtrInst::Create(OtherPtr, Idx, Idx + 2, 688 OtherPtr->getNameStr()+"."+utostr(i), 689 MI); 690 } 691 692 Value *EltPtr = NewElts[i]; 693 const Type *EltTy =cast<PointerType>(EltPtr->getType())->getElementType(); 694 695 // If we got down to a scalar, insert a load or store as appropriate. 696 if (EltTy->isSingleValueType()) { 697 if (isa<MemCpyInst>(MI) || isa<MemMoveInst>(MI)) { 698 Value *Elt = new LoadInst(SROADest ? OtherElt : EltPtr, "tmp", 699 MI); 700 new StoreInst(Elt, SROADest ? EltPtr : OtherElt, MI); 701 continue; 702 } else { 703 assert(isa<MemSetInst>(MI)); 704 705 // If the stored element is zero (common case), just store a null 706 // constant. 707 Constant *StoreVal; 708 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getOperand(2))) { 709 if (CI->isZero()) { 710 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0> 711 } else { 712 // If EltTy is a vector type, get the element type. 713 const Type *ValTy = EltTy; 714 if (const VectorType *VTy = dyn_cast<VectorType>(ValTy)) 715 ValTy = VTy->getElementType(); 716 717 // Construct an integer with the right value. 718 unsigned EltSize = TD.getTypeSizeInBits(ValTy); 719 APInt OneVal(EltSize, CI->getZExtValue()); 720 APInt TotalVal(OneVal); 721 // Set each byte. 722 for (unsigned i = 0; 8*i < EltSize; ++i) { 723 TotalVal = TotalVal.shl(8); 724 TotalVal |= OneVal; 725 } 726 727 // Convert the integer value to the appropriate type. 728 StoreVal = ConstantInt::get(TotalVal); 729 if (isa<PointerType>(ValTy)) 730 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); 731 else if (ValTy->isFloatingPoint()) 732 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy); 733 assert(StoreVal->getType() == ValTy && "Type mismatch!"); 734 735 // If the requested value was a vector constant, create it. 736 if (EltTy != ValTy) { 737 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements(); 738 SmallVector<Constant*, 16> Elts(NumElts, StoreVal); 739 StoreVal = ConstantVector::get(&Elts[0], NumElts); 740 } 741 } 742 new StoreInst(StoreVal, EltPtr, MI); 743 continue; 744 } 745 // Otherwise, if we're storing a byte variable, use a memset call for 746 // this element. 747 } 748 } 749 750 // Cast the element pointer to BytePtrTy. 751 if (EltPtr->getType() != BytePtrTy) 752 EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getNameStr(), MI); 753 754 // Cast the other pointer (if we have one) to BytePtrTy. 755 if (OtherElt && OtherElt->getType() != BytePtrTy) 756 OtherElt = new BitCastInst(OtherElt, BytePtrTy,OtherElt->getNameStr(), 757 MI); 758 759 unsigned EltSize = TD.getABITypeSize(EltTy); 760 761 // Finally, insert the meminst for this element. 762 if (isa<MemCpyInst>(MI) || isa<MemMoveInst>(MI)) { 763 Value *Ops[] = { 764 SROADest ? EltPtr : OtherElt, // Dest ptr 765 SROADest ? OtherElt : EltPtr, // Src ptr 766 ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size 767 Zero // Align 768 }; 769 CallInst::Create(TheFn, Ops, Ops + 4, "", MI); 770 } else { 771 assert(isa<MemSetInst>(MI)); 772 Value *Ops[] = { 773 EltPtr, MI->getOperand(2), // Dest, Value, 774 ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size 775 Zero // Align 776 }; 777 CallInst::Create(TheFn, Ops, Ops + 4, "", MI); 778 } 779 } 780 781 // Finally, MI is now dead, as we've modified its actions to occur on all of 782 // the elements of the aggregate. 783 ++UI; 784 MI->eraseFromParent(); 785 } 786} 787 788/// HasPadding - Return true if the specified type has any structure or 789/// alignment padding, false otherwise. 790static bool HasPadding(const Type *Ty, const TargetData &TD) { 791 if (const StructType *STy = dyn_cast<StructType>(Ty)) { 792 const StructLayout *SL = TD.getStructLayout(STy); 793 unsigned PrevFieldBitOffset = 0; 794 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 795 unsigned FieldBitOffset = SL->getElementOffsetInBits(i); 796 797 // Padding in sub-elements? 798 if (HasPadding(STy->getElementType(i), TD)) 799 return true; 800 801 // Check to see if there is any padding between this element and the 802 // previous one. 803 if (i) { 804 unsigned PrevFieldEnd = 805 PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1)); 806 if (PrevFieldEnd < FieldBitOffset) 807 return true; 808 } 809 810 PrevFieldBitOffset = FieldBitOffset; 811 } 812 813 // Check for tail padding. 814 if (unsigned EltCount = STy->getNumElements()) { 815 unsigned PrevFieldEnd = PrevFieldBitOffset + 816 TD.getTypeSizeInBits(STy->getElementType(EltCount-1)); 817 if (PrevFieldEnd < SL->getSizeInBits()) 818 return true; 819 } 820 821 } else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 822 return HasPadding(ATy->getElementType(), TD); 823 } else if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) { 824 return HasPadding(VTy->getElementType(), TD); 825 } 826 return TD.getTypeSizeInBits(Ty) != TD.getABITypeSizeInBits(Ty); 827} 828 829/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of 830/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, 831/// or 1 if safe after canonicalization has been performed. 832/// 833int SROA::isSafeAllocaToScalarRepl(AllocationInst *AI) { 834 // Loop over the use list of the alloca. We can only transform it if all of 835 // the users are safe to transform. 836 AllocaInfo Info; 837 838 for (Value::use_iterator I = AI->use_begin(), E = AI->use_end(); 839 I != E; ++I) { 840 isSafeUseOfAllocation(cast<Instruction>(*I), AI, Info); 841 if (Info.isUnsafe) { 842 DOUT << "Cannot transform: " << *AI << " due to user: " << **I; 843 return 0; 844 } 845 } 846 847 // Okay, we know all the users are promotable. If the aggregate is a memcpy 848 // source and destination, we have to be careful. In particular, the memcpy 849 // could be moving around elements that live in structure padding of the LLVM 850 // types, but may actually be used. In these cases, we refuse to promote the 851 // struct. 852 if (Info.isMemCpySrc && Info.isMemCpyDst && 853 HasPadding(AI->getType()->getElementType(), getAnalysis<TargetData>())) 854 return 0; 855 856 // If we require cleanup, return 1, otherwise return 3. 857 return Info.needsCanon ? 1 : 3; 858} 859 860/// CanonicalizeAllocaUsers - If SROA reported that it can promote the specified 861/// allocation, but only if cleaned up, perform the cleanups required. 862void SROA::CanonicalizeAllocaUsers(AllocationInst *AI) { 863 // At this point, we know that the end result will be SROA'd and promoted, so 864 // we can insert ugly code if required so long as sroa+mem2reg will clean it 865 // up. 866 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 867 UI != E; ) { 868 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI++); 869 if (!GEPI) continue; 870 gep_type_iterator I = gep_type_begin(GEPI); 871 ++I; 872 873 if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) { 874 uint64_t NumElements = AT->getNumElements(); 875 876 if (!isa<ConstantInt>(I.getOperand())) { 877 if (NumElements == 1) { 878 GEPI->setOperand(2, Constant::getNullValue(Type::Int32Ty)); 879 } else { 880 assert(NumElements == 2 && "Unhandled case!"); 881 // All users of the GEP must be loads. At each use of the GEP, insert 882 // two loads of the appropriate indexed GEP and select between them. 883 Value *IsOne = new ICmpInst(ICmpInst::ICMP_NE, I.getOperand(), 884 Constant::getNullValue(I.getOperand()->getType()), 885 "isone", GEPI); 886 // Insert the new GEP instructions, which are properly indexed. 887 SmallVector<Value*, 8> Indices(GEPI->op_begin()+1, GEPI->op_end()); 888 Indices[1] = Constant::getNullValue(Type::Int32Ty); 889 Value *ZeroIdx = GetElementPtrInst::Create(GEPI->getOperand(0), 890 Indices.begin(), 891 Indices.end(), 892 GEPI->getName()+".0", GEPI); 893 Indices[1] = ConstantInt::get(Type::Int32Ty, 1); 894 Value *OneIdx = GetElementPtrInst::Create(GEPI->getOperand(0), 895 Indices.begin(), 896 Indices.end(), 897 GEPI->getName()+".1", GEPI); 898 // Replace all loads of the variable index GEP with loads from both 899 // indexes and a select. 900 while (!GEPI->use_empty()) { 901 LoadInst *LI = cast<LoadInst>(GEPI->use_back()); 902 Value *Zero = new LoadInst(ZeroIdx, LI->getName()+".0", LI); 903 Value *One = new LoadInst(OneIdx , LI->getName()+".1", LI); 904 Value *R = SelectInst::Create(IsOne, One, Zero, LI->getName(), LI); 905 LI->replaceAllUsesWith(R); 906 LI->eraseFromParent(); 907 } 908 GEPI->eraseFromParent(); 909 } 910 } 911 } 912 } 913} 914 915/// MergeInType - Add the 'In' type to the accumulated type so far. If the 916/// types are incompatible, return true, otherwise update Accum and return 917/// false. 918/// 919/// There are three cases we handle here: 920/// 1) An effectively-integer union, where the pieces are stored into as 921/// smaller integers (common with byte swap and other idioms). 922/// 2) A union of vector types of the same size and potentially its elements. 923/// Here we turn element accesses into insert/extract element operations. 924/// 3) A union of scalar types, such as int/float or int/pointer. Here we 925/// merge together into integers, allowing the xform to work with #1 as 926/// well. 927static bool MergeInType(const Type *In, const Type *&Accum, 928 const TargetData &TD) { 929 // If this is our first type, just use it. 930 const VectorType *PTy; 931 if (Accum == Type::VoidTy || In == Accum) { 932 Accum = In; 933 } else if (In == Type::VoidTy) { 934 // Noop. 935 } else if (In->isInteger() && Accum->isInteger()) { // integer union. 936 // Otherwise pick whichever type is larger. 937 if (cast<IntegerType>(In)->getBitWidth() > 938 cast<IntegerType>(Accum)->getBitWidth()) 939 Accum = In; 940 } else if (isa<PointerType>(In) && isa<PointerType>(Accum)) { 941 // Pointer unions just stay as one of the pointers. 942 } else if (isa<VectorType>(In) || isa<VectorType>(Accum)) { 943 if ((PTy = dyn_cast<VectorType>(Accum)) && 944 PTy->getElementType() == In) { 945 // Accum is a vector, and we are accessing an element: ok. 946 } else if ((PTy = dyn_cast<VectorType>(In)) && 947 PTy->getElementType() == Accum) { 948 // In is a vector, and accum is an element: ok, remember In. 949 Accum = In; 950 } else if ((PTy = dyn_cast<VectorType>(In)) && isa<VectorType>(Accum) && 951 PTy->getBitWidth() == cast<VectorType>(Accum)->getBitWidth()) { 952 // Two vectors of the same size: keep Accum. 953 } else { 954 // Cannot insert an short into a <4 x int> or handle 955 // <2 x int> -> <4 x int> 956 return true; 957 } 958 } else { 959 // Pointer/FP/Integer unions merge together as integers. 960 switch (Accum->getTypeID()) { 961 case Type::PointerTyID: Accum = TD.getIntPtrType(); break; 962 case Type::FloatTyID: Accum = Type::Int32Ty; break; 963 case Type::DoubleTyID: Accum = Type::Int64Ty; break; 964 case Type::X86_FP80TyID: return true; 965 case Type::FP128TyID: return true; 966 case Type::PPC_FP128TyID: return true; 967 default: 968 assert(Accum->isInteger() && "Unknown FP type!"); 969 break; 970 } 971 972 switch (In->getTypeID()) { 973 case Type::PointerTyID: In = TD.getIntPtrType(); break; 974 case Type::FloatTyID: In = Type::Int32Ty; break; 975 case Type::DoubleTyID: In = Type::Int64Ty; break; 976 case Type::X86_FP80TyID: return true; 977 case Type::FP128TyID: return true; 978 case Type::PPC_FP128TyID: return true; 979 default: 980 assert(In->isInteger() && "Unknown FP type!"); 981 break; 982 } 983 return MergeInType(In, Accum, TD); 984 } 985 return false; 986} 987 988/// getUIntAtLeastAsBigAs - Return an unsigned integer type that is at least 989/// as big as the specified type. If there is no suitable type, this returns 990/// null. 991const Type *getUIntAtLeastAsBigAs(unsigned NumBits) { 992 if (NumBits > 64) return 0; 993 if (NumBits > 32) return Type::Int64Ty; 994 if (NumBits > 16) return Type::Int32Ty; 995 if (NumBits > 8) return Type::Int16Ty; 996 return Type::Int8Ty; 997} 998 999/// CanConvertToScalar - V is a pointer. If we can convert the pointee to a 1000/// single scalar integer type, return that type. Further, if the use is not 1001/// a completely trivial use that mem2reg could promote, set IsNotTrivial. If 1002/// there are no uses of this pointer, return Type::VoidTy to differentiate from 1003/// failure. 1004/// 1005const Type *SROA::CanConvertToScalar(Value *V, bool &IsNotTrivial) { 1006 const Type *UsedType = Type::VoidTy; // No uses, no forced type. 1007 const TargetData &TD = getAnalysis<TargetData>(); 1008 const PointerType *PTy = cast<PointerType>(V->getType()); 1009 1010 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 1011 Instruction *User = cast<Instruction>(*UI); 1012 1013 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1014 // FIXME: Loads of a first class aggregrate value could be converted to a 1015 // series of loads and insertvalues 1016 if (!LI->getType()->isSingleValueType()) 1017 return 0; 1018 1019 if (MergeInType(LI->getType(), UsedType, TD)) 1020 return 0; 1021 1022 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1023 // Storing the pointer, not into the value? 1024 if (SI->getOperand(0) == V) return 0; 1025 1026 // FIXME: Stores of a first class aggregrate value could be converted to a 1027 // series of extractvalues and stores 1028 if (!SI->getOperand(0)->getType()->isSingleValueType()) 1029 return 0; 1030 1031 // NOTE: We could handle storing of FP imms into integers here! 1032 1033 if (MergeInType(SI->getOperand(0)->getType(), UsedType, TD)) 1034 return 0; 1035 } else if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 1036 IsNotTrivial = true; 1037 const Type *SubTy = CanConvertToScalar(CI, IsNotTrivial); 1038 if (!SubTy || MergeInType(SubTy, UsedType, TD)) return 0; 1039 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 1040 // Check to see if this is stepping over an element: GEP Ptr, int C 1041 if (GEP->getNumOperands() == 2 && isa<ConstantInt>(GEP->getOperand(1))) { 1042 unsigned Idx = cast<ConstantInt>(GEP->getOperand(1))->getZExtValue(); 1043 unsigned ElSize = TD.getABITypeSize(PTy->getElementType()); 1044 unsigned BitOffset = Idx*ElSize*8; 1045 if (BitOffset > 64 || !isPowerOf2_32(ElSize)) return 0; 1046 1047 IsNotTrivial = true; 1048 const Type *SubElt = CanConvertToScalar(GEP, IsNotTrivial); 1049 if (SubElt == 0) return 0; 1050 if (SubElt != Type::VoidTy && SubElt->isInteger()) { 1051 const Type *NewTy = 1052 getUIntAtLeastAsBigAs(TD.getABITypeSizeInBits(SubElt)+BitOffset); 1053 if (NewTy == 0 || MergeInType(NewTy, UsedType, TD)) return 0; 1054 continue; 1055 } 1056 } else if (GEP->getNumOperands() == 3 && 1057 isa<ConstantInt>(GEP->getOperand(1)) && 1058 isa<ConstantInt>(GEP->getOperand(2)) && 1059 cast<ConstantInt>(GEP->getOperand(1))->isZero()) { 1060 // We are stepping into an element, e.g. a structure or an array: 1061 // GEP Ptr, int 0, uint C 1062 const Type *AggTy = PTy->getElementType(); 1063 unsigned Idx = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 1064 1065 if (const ArrayType *ATy = dyn_cast<ArrayType>(AggTy)) { 1066 if (Idx >= ATy->getNumElements()) return 0; // Out of range. 1067 } else if (const VectorType *VectorTy = dyn_cast<VectorType>(AggTy)) { 1068 // Getting an element of the vector. 1069 if (Idx >= VectorTy->getNumElements()) return 0; // Out of range. 1070 1071 // Merge in the vector type. 1072 if (MergeInType(VectorTy, UsedType, TD)) return 0; 1073 1074 const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial); 1075 if (SubTy == 0) return 0; 1076 1077 if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType, TD)) 1078 return 0; 1079 1080 // We'll need to change this to an insert/extract element operation. 1081 IsNotTrivial = true; 1082 continue; // Everything looks ok 1083 1084 } else if (isa<StructType>(AggTy)) { 1085 // Structs are always ok. 1086 } else { 1087 return 0; 1088 } 1089 const Type *NTy = getUIntAtLeastAsBigAs(TD.getABITypeSizeInBits(AggTy)); 1090 if (NTy == 0 || MergeInType(NTy, UsedType, TD)) return 0; 1091 const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial); 1092 if (SubTy == 0) return 0; 1093 if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType, TD)) 1094 return 0; 1095 continue; // Everything looks ok 1096 } 1097 return 0; 1098 } else { 1099 // Cannot handle this! 1100 return 0; 1101 } 1102 } 1103 1104 return UsedType; 1105} 1106 1107/// ConvertToScalar - The specified alloca passes the CanConvertToScalar 1108/// predicate and is non-trivial. Convert it to something that can be trivially 1109/// promoted into a register by mem2reg. 1110void SROA::ConvertToScalar(AllocationInst *AI, const Type *ActualTy) { 1111 DOUT << "CONVERT TO SCALAR: " << *AI << " TYPE = " 1112 << *ActualTy << "\n"; 1113 ++NumConverted; 1114 1115 BasicBlock *EntryBlock = AI->getParent(); 1116 assert(EntryBlock == &EntryBlock->getParent()->getEntryBlock() && 1117 "Not in the entry block!"); 1118 EntryBlock->getInstList().remove(AI); // Take the alloca out of the program. 1119 1120 // Create and insert the alloca. 1121 AllocaInst *NewAI = new AllocaInst(ActualTy, 0, AI->getName(), 1122 EntryBlock->begin()); 1123 ConvertUsesToScalar(AI, NewAI, 0); 1124 delete AI; 1125} 1126 1127 1128/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca 1129/// directly. This happens when we are converting an "integer union" to a 1130/// single integer scalar, or when we are converting a "vector union" to a 1131/// vector with insert/extractelement instructions. 1132/// 1133/// Offset is an offset from the original alloca, in bits that need to be 1134/// shifted to the right. By the end of this, there should be no uses of Ptr. 1135void SROA::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, unsigned Offset) { 1136 while (!Ptr->use_empty()) { 1137 Instruction *User = cast<Instruction>(Ptr->use_back()); 1138 1139 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1140 Value *NV = ConvertUsesOfLoadToScalar(LI, NewAI, Offset); 1141 LI->replaceAllUsesWith(NV); 1142 LI->eraseFromParent(); 1143 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1144 assert(SI->getOperand(0) != Ptr && "Consistency error!"); 1145 1146 Value *SV = ConvertUsesOfStoreToScalar(SI, NewAI, Offset); 1147 new StoreInst(SV, NewAI, SI); 1148 SI->eraseFromParent(); 1149 1150 } else if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 1151 ConvertUsesToScalar(CI, NewAI, Offset); 1152 CI->eraseFromParent(); 1153 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 1154 const PointerType *AggPtrTy = 1155 cast<PointerType>(GEP->getOperand(0)->getType()); 1156 const TargetData &TD = getAnalysis<TargetData>(); 1157 unsigned AggSizeInBits = 1158 TD.getABITypeSizeInBits(AggPtrTy->getElementType()); 1159 1160 // Check to see if this is stepping over an element: GEP Ptr, int C 1161 unsigned NewOffset = Offset; 1162 if (GEP->getNumOperands() == 2) { 1163 unsigned Idx = cast<ConstantInt>(GEP->getOperand(1))->getZExtValue(); 1164 unsigned BitOffset = Idx*AggSizeInBits; 1165 1166 NewOffset += BitOffset; 1167 } else if (GEP->getNumOperands() == 3) { 1168 // We know that operand #2 is zero. 1169 unsigned Idx = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 1170 const Type *AggTy = AggPtrTy->getElementType(); 1171 if (const SequentialType *SeqTy = dyn_cast<SequentialType>(AggTy)) { 1172 unsigned ElSizeBits = 1173 TD.getABITypeSizeInBits(SeqTy->getElementType()); 1174 1175 NewOffset += ElSizeBits*Idx; 1176 } else if (const StructType *STy = dyn_cast<StructType>(AggTy)) { 1177 unsigned EltBitOffset = 1178 TD.getStructLayout(STy)->getElementOffsetInBits(Idx); 1179 1180 NewOffset += EltBitOffset; 1181 } else { 1182 assert(0 && "Unsupported operation!"); 1183 abort(); 1184 } 1185 } else { 1186 assert(0 && "Unsupported operation!"); 1187 abort(); 1188 } 1189 ConvertUsesToScalar(GEP, NewAI, NewOffset); 1190 GEP->eraseFromParent(); 1191 } else { 1192 assert(0 && "Unsupported operation!"); 1193 abort(); 1194 } 1195 } 1196} 1197 1198/// ConvertUsesOfLoadToScalar - Convert all of the users the specified load to 1199/// use the new alloca directly, returning the value that should replace the 1200/// load. This happens when we are converting an "integer union" to a 1201/// single integer scalar, or when we are converting a "vector union" to a 1202/// vector with insert/extractelement instructions. 1203/// 1204/// Offset is an offset from the original alloca, in bits that need to be 1205/// shifted to the right. By the end of this, there should be no uses of Ptr. 1206Value *SROA::ConvertUsesOfLoadToScalar(LoadInst *LI, AllocaInst *NewAI, 1207 unsigned Offset) { 1208 // The load is a bit extract from NewAI shifted right by Offset bits. 1209 Value *NV = new LoadInst(NewAI, LI->getName(), LI); 1210 1211 if (NV->getType() == LI->getType() && Offset == 0) { 1212 // We win, no conversion needed. 1213 return NV; 1214 } 1215 1216 // If the result type of the 'union' is a pointer, then this must be ptr->ptr 1217 // cast. Anything else would result in NV being an integer. 1218 if (isa<PointerType>(NV->getType())) { 1219 assert(isa<PointerType>(LI->getType())); 1220 return new BitCastInst(NV, LI->getType(), LI->getName(), LI); 1221 } 1222 1223 if (const VectorType *VTy = dyn_cast<VectorType>(NV->getType())) { 1224 // If the result alloca is a vector type, this is either an element 1225 // access or a bitcast to another vector type. 1226 if (isa<VectorType>(LI->getType())) 1227 return new BitCastInst(NV, LI->getType(), LI->getName(), LI); 1228 1229 // Otherwise it must be an element access. 1230 const TargetData &TD = getAnalysis<TargetData>(); 1231 unsigned Elt = 0; 1232 if (Offset) { 1233 unsigned EltSize = TD.getABITypeSizeInBits(VTy->getElementType()); 1234 Elt = Offset/EltSize; 1235 Offset -= EltSize*Elt; 1236 } 1237 NV = new ExtractElementInst(NV, ConstantInt::get(Type::Int32Ty, Elt), 1238 "tmp", LI); 1239 1240 // If we're done, return this element. 1241 if (NV->getType() == LI->getType() && Offset == 0) 1242 return NV; 1243 } 1244 1245 const IntegerType *NTy = cast<IntegerType>(NV->getType()); 1246 1247 // If this is a big-endian system and the load is narrower than the 1248 // full alloca type, we need to do a shift to get the right bits. 1249 int ShAmt = 0; 1250 const TargetData &TD = getAnalysis<TargetData>(); 1251 if (TD.isBigEndian()) { 1252 // On big-endian machines, the lowest bit is stored at the bit offset 1253 // from the pointer given by getTypeStoreSizeInBits. This matters for 1254 // integers with a bitwidth that is not a multiple of 8. 1255 ShAmt = TD.getTypeStoreSizeInBits(NTy) - 1256 TD.getTypeStoreSizeInBits(LI->getType()) - Offset; 1257 } else { 1258 ShAmt = Offset; 1259 } 1260 1261 // Note: we support negative bitwidths (with shl) which are not defined. 1262 // We do this to support (f.e.) loads off the end of a structure where 1263 // only some bits are used. 1264 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth()) 1265 NV = BinaryOperator::CreateLShr(NV, 1266 ConstantInt::get(NV->getType(),ShAmt), 1267 LI->getName(), LI); 1268 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) 1269 NV = BinaryOperator::CreateShl(NV, 1270 ConstantInt::get(NV->getType(),-ShAmt), 1271 LI->getName(), LI); 1272 1273 // Finally, unconditionally truncate the integer to the right width. 1274 unsigned LIBitWidth = TD.getTypeSizeInBits(LI->getType()); 1275 if (LIBitWidth < NTy->getBitWidth()) 1276 NV = new TruncInst(NV, IntegerType::get(LIBitWidth), 1277 LI->getName(), LI); 1278 1279 // If the result is an integer, this is a trunc or bitcast. 1280 if (isa<IntegerType>(LI->getType())) { 1281 // Should be done. 1282 } else if (LI->getType()->isFloatingPoint()) { 1283 // Just do a bitcast, we know the sizes match up. 1284 NV = new BitCastInst(NV, LI->getType(), LI->getName(), LI); 1285 } else { 1286 // Otherwise must be a pointer. 1287 NV = new IntToPtrInst(NV, LI->getType(), LI->getName(), LI); 1288 } 1289 assert(NV->getType() == LI->getType() && "Didn't convert right?"); 1290 return NV; 1291} 1292 1293 1294/// ConvertUsesOfStoreToScalar - Convert the specified store to a load+store 1295/// pair of the new alloca directly, returning the value that should be stored 1296/// to the alloca. This happens when we are converting an "integer union" to a 1297/// single integer scalar, or when we are converting a "vector union" to a 1298/// vector with insert/extractelement instructions. 1299/// 1300/// Offset is an offset from the original alloca, in bits that need to be 1301/// shifted to the right. By the end of this, there should be no uses of Ptr. 1302Value *SROA::ConvertUsesOfStoreToScalar(StoreInst *SI, AllocaInst *NewAI, 1303 unsigned Offset) { 1304 1305 // Convert the stored type to the actual type, shift it left to insert 1306 // then 'or' into place. 1307 Value *SV = SI->getOperand(0); 1308 const Type *AllocaType = NewAI->getType()->getElementType(); 1309 if (SV->getType() == AllocaType && Offset == 0) { 1310 // All is well. 1311 } else if (const VectorType *PTy = dyn_cast<VectorType>(AllocaType)) { 1312 Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI); 1313 1314 // If the result alloca is a vector type, this is either an element 1315 // access or a bitcast to another vector type. 1316 if (isa<VectorType>(SV->getType())) { 1317 SV = new BitCastInst(SV, AllocaType, SV->getName(), SI); 1318 } else { 1319 // Must be an element insertion. 1320 const TargetData &TD = getAnalysis<TargetData>(); 1321 unsigned Elt = Offset/TD.getABITypeSizeInBits(PTy->getElementType()); 1322 SV = InsertElementInst::Create(Old, SV, 1323 ConstantInt::get(Type::Int32Ty, Elt), 1324 "tmp", SI); 1325 } 1326 } else if (isa<PointerType>(AllocaType)) { 1327 // If the alloca type is a pointer, then all the elements must be 1328 // pointers. 1329 if (SV->getType() != AllocaType) 1330 SV = new BitCastInst(SV, AllocaType, SV->getName(), SI); 1331 } else { 1332 Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI); 1333 1334 // If SV is a float, convert it to the appropriate integer type. 1335 // If it is a pointer, do the same, and also handle ptr->ptr casts 1336 // here. 1337 const TargetData &TD = getAnalysis<TargetData>(); 1338 unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType()); 1339 unsigned DestWidth = TD.getTypeSizeInBits(AllocaType); 1340 unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType()); 1341 unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType); 1342 if (SV->getType()->isFloatingPoint()) 1343 SV = new BitCastInst(SV, IntegerType::get(SrcWidth), 1344 SV->getName(), SI); 1345 else if (isa<PointerType>(SV->getType())) 1346 SV = new PtrToIntInst(SV, TD.getIntPtrType(), SV->getName(), SI); 1347 1348 // Always zero extend the value if needed. 1349 if (SV->getType() != AllocaType) 1350 SV = new ZExtInst(SV, AllocaType, SV->getName(), SI); 1351 1352 // If this is a big-endian system and the store is narrower than the 1353 // full alloca type, we need to do a shift to get the right bits. 1354 int ShAmt = 0; 1355 if (TD.isBigEndian()) { 1356 // On big-endian machines, the lowest bit is stored at the bit offset 1357 // from the pointer given by getTypeStoreSizeInBits. This matters for 1358 // integers with a bitwidth that is not a multiple of 8. 1359 ShAmt = DestStoreWidth - SrcStoreWidth - Offset; 1360 } else { 1361 ShAmt = Offset; 1362 } 1363 1364 // Note: we support negative bitwidths (with shr) which are not defined. 1365 // We do this to support (f.e.) stores off the end of a structure where 1366 // only some bits in the structure are set. 1367 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth)); 1368 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) { 1369 SV = BinaryOperator::CreateShl(SV, 1370 ConstantInt::get(SV->getType(), ShAmt), 1371 SV->getName(), SI); 1372 Mask <<= ShAmt; 1373 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { 1374 SV = BinaryOperator::CreateLShr(SV, 1375 ConstantInt::get(SV->getType(),-ShAmt), 1376 SV->getName(), SI); 1377 Mask = Mask.lshr(ShAmt); 1378 } 1379 1380 // Mask out the bits we are about to insert from the old value, and or 1381 // in the new bits. 1382 if (SrcWidth != DestWidth) { 1383 assert(DestWidth > SrcWidth); 1384 Old = BinaryOperator::CreateAnd(Old, ConstantInt::get(~Mask), 1385 Old->getName()+".mask", SI); 1386 SV = BinaryOperator::CreateOr(Old, SV, SV->getName()+".ins", SI); 1387 } 1388 } 1389 return SV; 1390} 1391 1392 1393 1394/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to 1395/// some part of a constant global variable. This intentionally only accepts 1396/// constant expressions because we don't can't rewrite arbitrary instructions. 1397static bool PointsToConstantGlobal(Value *V) { 1398 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) 1399 return GV->isConstant(); 1400 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 1401 if (CE->getOpcode() == Instruction::BitCast || 1402 CE->getOpcode() == Instruction::GetElementPtr) 1403 return PointsToConstantGlobal(CE->getOperand(0)); 1404 return false; 1405} 1406 1407/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived) 1408/// pointer to an alloca. Ignore any reads of the pointer, return false if we 1409/// see any stores or other unknown uses. If we see pointer arithmetic, keep 1410/// track of whether it moves the pointer (with isOffset) but otherwise traverse 1411/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to 1412/// the alloca, and if the source pointer is a pointer to a constant global, we 1413/// can optimize this. 1414static bool isOnlyCopiedFromConstantGlobal(Value *V, Instruction *&TheCopy, 1415 bool isOffset) { 1416 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 1417 if (isa<LoadInst>(*UI)) { 1418 // Ignore loads, they are always ok. 1419 continue; 1420 } 1421 if (BitCastInst *BCI = dyn_cast<BitCastInst>(*UI)) { 1422 // If uses of the bitcast are ok, we are ok. 1423 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) 1424 return false; 1425 continue; 1426 } 1427 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) { 1428 // If the GEP has all zero indices, it doesn't offset the pointer. If it 1429 // doesn't, it does. 1430 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy, 1431 isOffset || !GEP->hasAllZeroIndices())) 1432 return false; 1433 continue; 1434 } 1435 1436 // If this is isn't our memcpy/memmove, reject it as something we can't 1437 // handle. 1438 if (!isa<MemCpyInst>(*UI) && !isa<MemMoveInst>(*UI)) 1439 return false; 1440 1441 // If we already have seen a copy, reject the second one. 1442 if (TheCopy) return false; 1443 1444 // If the pointer has been offset from the start of the alloca, we can't 1445 // safely handle this. 1446 if (isOffset) return false; 1447 1448 // If the memintrinsic isn't using the alloca as the dest, reject it. 1449 if (UI.getOperandNo() != 1) return false; 1450 1451 MemIntrinsic *MI = cast<MemIntrinsic>(*UI); 1452 1453 // If the source of the memcpy/move is not a constant global, reject it. 1454 if (!PointsToConstantGlobal(MI->getOperand(2))) 1455 return false; 1456 1457 // Otherwise, the transform is safe. Remember the copy instruction. 1458 TheCopy = MI; 1459 } 1460 return true; 1461} 1462 1463/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only 1464/// modified by a copy from a constant global. If we can prove this, we can 1465/// replace any uses of the alloca with uses of the global directly. 1466Instruction *SROA::isOnlyCopiedFromConstantGlobal(AllocationInst *AI) { 1467 Instruction *TheCopy = 0; 1468 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) 1469 return TheCopy; 1470 return 0; 1471} 1472