ScalarReplAggregates.cpp revision 88e6dc8bf14e8a98888f62173a6581386b8d29a0
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: 317 // %res = load { i32, i32 }* %alloc 318 // with: 319 // %load.0 = load i32* %alloc.0 320 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0 321 // %load.1 = load i32* %alloc.1 322 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1 323 // (Also works for arrays instead of structs) 324 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 325 Value *Insert = UndefValue::get(LI->getType()); 326 for (unsigned i = 0, e = ElementAllocas.size(); i != e; ++i) { 327 Value *Load = new LoadInst(ElementAllocas[i], "load", LI); 328 Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI); 329 } 330 LI->replaceAllUsesWith(Insert); 331 LI->eraseFromParent(); 332 continue; 333 } 334 335 // Replace: 336 // store { i32, i32 } %val, { i32, i32 }* %alloc 337 // with: 338 // %val.0 = extractvalue { i32, i32 } %val, 0 339 // store i32 %val.0, i32* %alloc.0 340 // %val.1 = extractvalue { i32, i32 } %val, 1 341 // store i32 %val.1, i32* %alloc.1 342 // (Also works for arrays instead of structs) 343 if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 344 Value *Val = SI->getOperand(0); 345 for (unsigned i = 0, e = ElementAllocas.size(); i != e; ++i) { 346 Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI); 347 new StoreInst(Extract, ElementAllocas[i], SI); 348 } 349 SI->eraseFromParent(); 350 continue; 351 } 352 353 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User); 354 // We now know that the GEP is of the form: GEP <ptr>, 0, <cst> 355 unsigned Idx = 356 (unsigned)cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 357 358 assert(Idx < ElementAllocas.size() && "Index out of range?"); 359 AllocaInst *AllocaToUse = ElementAllocas[Idx]; 360 361 Value *RepValue; 362 if (GEPI->getNumOperands() == 3) { 363 // Do not insert a new getelementptr instruction with zero indices, only 364 // to have it optimized out later. 365 RepValue = AllocaToUse; 366 } else { 367 // We are indexing deeply into the structure, so we still need a 368 // getelement ptr instruction to finish the indexing. This may be 369 // expanded itself once the worklist is rerun. 370 // 371 SmallVector<Value*, 8> NewArgs; 372 NewArgs.push_back(Constant::getNullValue(Type::Int32Ty)); 373 NewArgs.append(GEPI->op_begin()+3, GEPI->op_end()); 374 RepValue = GetElementPtrInst::Create(AllocaToUse, NewArgs.begin(), 375 NewArgs.end(), "", GEPI); 376 RepValue->takeName(GEPI); 377 } 378 379 // If this GEP is to the start of the aggregate, check for memcpys. 380 if (Idx == 0) { 381 bool IsStartOfAggregateGEP = true; 382 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) { 383 if (!isa<ConstantInt>(GEPI->getOperand(i))) { 384 IsStartOfAggregateGEP = false; 385 break; 386 } 387 if (!cast<ConstantInt>(GEPI->getOperand(i))->isZero()) { 388 IsStartOfAggregateGEP = false; 389 break; 390 } 391 } 392 393 if (IsStartOfAggregateGEP) 394 RewriteBitCastUserOfAlloca(GEPI, AI, ElementAllocas); 395 } 396 397 398 // Move all of the users over to the new GEP. 399 GEPI->replaceAllUsesWith(RepValue); 400 // Delete the old GEP 401 GEPI->eraseFromParent(); 402 } 403 404 // Finally, delete the Alloca instruction 405 AI->eraseFromParent(); 406 NumReplaced++; 407} 408 409 410/// isSafeElementUse - Check to see if this use is an allowed use for a 411/// getelementptr instruction of an array aggregate allocation. isFirstElt 412/// indicates whether Ptr is known to the start of the aggregate. 413/// 414void SROA::isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI, 415 AllocaInfo &Info) { 416 for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); 417 I != E; ++I) { 418 Instruction *User = cast<Instruction>(*I); 419 switch (User->getOpcode()) { 420 case Instruction::Load: break; 421 case Instruction::Store: 422 // Store is ok if storing INTO the pointer, not storing the pointer 423 if (User->getOperand(0) == Ptr) return MarkUnsafe(Info); 424 break; 425 case Instruction::GetElementPtr: { 426 GetElementPtrInst *GEP = cast<GetElementPtrInst>(User); 427 bool AreAllZeroIndices = isFirstElt; 428 if (GEP->getNumOperands() > 1) { 429 if (!isa<ConstantInt>(GEP->getOperand(1)) || 430 !cast<ConstantInt>(GEP->getOperand(1))->isZero()) 431 // Using pointer arithmetic to navigate the array. 432 return MarkUnsafe(Info); 433 434 if (AreAllZeroIndices) { 435 for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) { 436 if (!isa<ConstantInt>(GEP->getOperand(i)) || 437 !cast<ConstantInt>(GEP->getOperand(i))->isZero()) { 438 AreAllZeroIndices = false; 439 break; 440 } 441 } 442 } 443 } 444 isSafeElementUse(GEP, AreAllZeroIndices, AI, Info); 445 if (Info.isUnsafe) return; 446 break; 447 } 448 case Instruction::BitCast: 449 if (isFirstElt) { 450 isSafeUseOfBitCastedAllocation(cast<BitCastInst>(User), AI, Info); 451 if (Info.isUnsafe) return; 452 break; 453 } 454 DOUT << " Transformation preventing inst: " << *User; 455 return MarkUnsafe(Info); 456 case Instruction::Call: 457 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 458 if (isFirstElt) { 459 isSafeMemIntrinsicOnAllocation(MI, AI, I.getOperandNo(), Info); 460 if (Info.isUnsafe) return; 461 break; 462 } 463 } 464 DOUT << " Transformation preventing inst: " << *User; 465 return MarkUnsafe(Info); 466 default: 467 DOUT << " Transformation preventing inst: " << *User; 468 return MarkUnsafe(Info); 469 } 470 } 471 return; // All users look ok :) 472} 473 474/// AllUsersAreLoads - Return true if all users of this value are loads. 475static bool AllUsersAreLoads(Value *Ptr) { 476 for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); 477 I != E; ++I) 478 if (cast<Instruction>(*I)->getOpcode() != Instruction::Load) 479 return false; 480 return true; 481} 482 483/// isSafeUseOfAllocation - Check to see if this user is an allowed use for an 484/// aggregate allocation. 485/// 486void SROA::isSafeUseOfAllocation(Instruction *User, AllocationInst *AI, 487 AllocaInfo &Info) { 488 if (BitCastInst *C = dyn_cast<BitCastInst>(User)) 489 return isSafeUseOfBitCastedAllocation(C, AI, Info); 490 491 if (isa<LoadInst>(User)) 492 return; // Loads (returning a first class aggregrate) are always rewritable 493 494 if (isa<StoreInst>(User) && User->getOperand(0) != AI) 495 return; // Store is ok if storing INTO the pointer, not storing the pointer 496 497 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User); 498 if (GEPI == 0) 499 return MarkUnsafe(Info); 500 501 gep_type_iterator I = gep_type_begin(GEPI), E = gep_type_end(GEPI); 502 503 // The GEP is not safe to transform if not of the form "GEP <ptr>, 0, <cst>". 504 if (I == E || 505 I.getOperand() != Constant::getNullValue(I.getOperand()->getType())) { 506 return MarkUnsafe(Info); 507 } 508 509 ++I; 510 if (I == E) return MarkUnsafe(Info); // ran out of GEP indices?? 511 512 bool IsAllZeroIndices = true; 513 514 // If the first index is a non-constant index into an array, see if we can 515 // handle it as a special case. 516 if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) { 517 if (!isa<ConstantInt>(I.getOperand())) { 518 IsAllZeroIndices = 0; 519 uint64_t NumElements = AT->getNumElements(); 520 521 // If this is an array index and the index is not constant, we cannot 522 // promote... that is unless the array has exactly one or two elements in 523 // it, in which case we CAN promote it, but we have to canonicalize this 524 // out if this is the only problem. 525 if ((NumElements == 1 || NumElements == 2) && 526 AllUsersAreLoads(GEPI)) { 527 Info.needsCanon = true; 528 return; // Canonicalization required! 529 } 530 return MarkUnsafe(Info); 531 } 532 } 533 534 535 // Walk through the GEP type indices, checking the types that this indexes 536 // into. 537 for (; I != E; ++I) { 538 // Ignore struct elements, no extra checking needed for these. 539 if (isa<StructType>(*I)) 540 continue; 541 542 // Don't SROA pointers into vectors. 543 if (isa<VectorType>(*I)) 544 return MarkUnsafe(Info); 545 546 // Otherwise, we must have an index into an array type. Verify that this is 547 // an in-range constant integer. Specifically, consider A[0][i]. We 548 // cannot know that the user isn't doing invalid things like allowing i to 549 // index an out-of-range subscript that accesses A[1]. Because of this, we 550 // have to reject SROA of any accesses into structs where any of the 551 // components are variables. 552 ConstantInt *IdxVal = dyn_cast<ConstantInt>(I.getOperand()); 553 if (!IdxVal) return MarkUnsafe(Info); 554 if (IdxVal->getZExtValue() >= cast<ArrayType>(*I)->getNumElements()) 555 return MarkUnsafe(Info); 556 557 IsAllZeroIndices &= IdxVal->isZero(); 558 } 559 560 // If there are any non-simple uses of this getelementptr, make sure to reject 561 // them. 562 return isSafeElementUse(GEPI, IsAllZeroIndices, AI, Info); 563} 564 565/// isSafeMemIntrinsicOnAllocation - Return true if the specified memory 566/// intrinsic can be promoted by SROA. At this point, we know that the operand 567/// of the memintrinsic is a pointer to the beginning of the allocation. 568void SROA::isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI, 569 unsigned OpNo, AllocaInfo &Info) { 570 // If not constant length, give up. 571 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 572 if (!Length) return MarkUnsafe(Info); 573 574 // If not the whole aggregate, give up. 575 const TargetData &TD = getAnalysis<TargetData>(); 576 if (Length->getZExtValue() != 577 TD.getABITypeSize(AI->getType()->getElementType())) 578 return MarkUnsafe(Info); 579 580 // We only know about memcpy/memset/memmove. 581 if (!isa<MemCpyInst>(MI) && !isa<MemSetInst>(MI) && !isa<MemMoveInst>(MI)) 582 return MarkUnsafe(Info); 583 584 // Otherwise, we can transform it. Determine whether this is a memcpy/set 585 // into or out of the aggregate. 586 if (OpNo == 1) 587 Info.isMemCpyDst = true; 588 else { 589 assert(OpNo == 2); 590 Info.isMemCpySrc = true; 591 } 592} 593 594/// isSafeUseOfBitCastedAllocation - Return true if all users of this bitcast 595/// are 596void SROA::isSafeUseOfBitCastedAllocation(BitCastInst *BC, AllocationInst *AI, 597 AllocaInfo &Info) { 598 for (Value::use_iterator UI = BC->use_begin(), E = BC->use_end(); 599 UI != E; ++UI) { 600 if (BitCastInst *BCU = dyn_cast<BitCastInst>(UI)) { 601 isSafeUseOfBitCastedAllocation(BCU, AI, Info); 602 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(UI)) { 603 isSafeMemIntrinsicOnAllocation(MI, AI, UI.getOperandNo(), Info); 604 } else { 605 return MarkUnsafe(Info); 606 } 607 if (Info.isUnsafe) return; 608 } 609} 610 611/// RewriteBitCastUserOfAlloca - BCInst (transitively) bitcasts AI, or indexes 612/// to its first element. Transform users of the cast to use the new values 613/// instead. 614void SROA::RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI, 615 SmallVector<AllocaInst*, 32> &NewElts) { 616 Constant *Zero = Constant::getNullValue(Type::Int32Ty); 617 const TargetData &TD = getAnalysis<TargetData>(); 618 619 Value::use_iterator UI = BCInst->use_begin(), UE = BCInst->use_end(); 620 while (UI != UE) { 621 if (BitCastInst *BCU = dyn_cast<BitCastInst>(*UI)) { 622 RewriteBitCastUserOfAlloca(BCU, AI, NewElts); 623 ++UI; 624 BCU->eraseFromParent(); 625 continue; 626 } 627 628 // Otherwise, must be memcpy/memmove/memset of the entire aggregate. Split 629 // into one per element. 630 MemIntrinsic *MI = dyn_cast<MemIntrinsic>(*UI); 631 632 // If it's not a mem intrinsic, it must be some other user of a gep of the 633 // first pointer. Just leave these alone. 634 if (!MI) { 635 ++UI; 636 continue; 637 } 638 639 // If this is a memcpy/memmove, construct the other pointer as the 640 // appropriate type. 641 Value *OtherPtr = 0; 642 if (MemCpyInst *MCI = dyn_cast<MemCpyInst>(MI)) { 643 if (BCInst == MCI->getRawDest()) 644 OtherPtr = MCI->getRawSource(); 645 else { 646 assert(BCInst == MCI->getRawSource()); 647 OtherPtr = MCI->getRawDest(); 648 } 649 } else if (MemMoveInst *MMI = dyn_cast<MemMoveInst>(MI)) { 650 if (BCInst == MMI->getRawDest()) 651 OtherPtr = MMI->getRawSource(); 652 else { 653 assert(BCInst == MMI->getRawSource()); 654 OtherPtr = MMI->getRawDest(); 655 } 656 } 657 658 // If there is an other pointer, we want to convert it to the same pointer 659 // type as AI has, so we can GEP through it. 660 if (OtherPtr) { 661 // It is likely that OtherPtr is a bitcast, if so, remove it. 662 if (BitCastInst *BC = dyn_cast<BitCastInst>(OtherPtr)) 663 OtherPtr = BC->getOperand(0); 664 if (ConstantExpr *BCE = dyn_cast<ConstantExpr>(OtherPtr)) 665 if (BCE->getOpcode() == Instruction::BitCast) 666 OtherPtr = BCE->getOperand(0); 667 668 // If the pointer is not the right type, insert a bitcast to the right 669 // type. 670 if (OtherPtr->getType() != AI->getType()) 671 OtherPtr = new BitCastInst(OtherPtr, AI->getType(), OtherPtr->getName(), 672 MI); 673 } 674 675 // Process each element of the aggregate. 676 Value *TheFn = MI->getOperand(0); 677 const Type *BytePtrTy = MI->getRawDest()->getType(); 678 bool SROADest = MI->getRawDest() == BCInst; 679 680 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 681 // If this is a memcpy/memmove, emit a GEP of the other element address. 682 Value *OtherElt = 0; 683 if (OtherPtr) { 684 Value *Idx[2] = { Zero, ConstantInt::get(Type::Int32Ty, i) }; 685 OtherElt = GetElementPtrInst::Create(OtherPtr, Idx, Idx + 2, 686 OtherPtr->getNameStr()+"."+utostr(i), 687 MI); 688 } 689 690 Value *EltPtr = NewElts[i]; 691 const Type *EltTy =cast<PointerType>(EltPtr->getType())->getElementType(); 692 693 // If we got down to a scalar, insert a load or store as appropriate. 694 if (EltTy->isSingleValueType()) { 695 if (isa<MemCpyInst>(MI) || isa<MemMoveInst>(MI)) { 696 Value *Elt = new LoadInst(SROADest ? OtherElt : EltPtr, "tmp", 697 MI); 698 new StoreInst(Elt, SROADest ? EltPtr : OtherElt, MI); 699 continue; 700 } else { 701 assert(isa<MemSetInst>(MI)); 702 703 // If the stored element is zero (common case), just store a null 704 // constant. 705 Constant *StoreVal; 706 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getOperand(2))) { 707 if (CI->isZero()) { 708 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0> 709 } else { 710 // If EltTy is a vector type, get the element type. 711 const Type *ValTy = EltTy; 712 if (const VectorType *VTy = dyn_cast<VectorType>(ValTy)) 713 ValTy = VTy->getElementType(); 714 715 // Construct an integer with the right value. 716 unsigned EltSize = TD.getTypeSizeInBits(ValTy); 717 APInt OneVal(EltSize, CI->getZExtValue()); 718 APInt TotalVal(OneVal); 719 // Set each byte. 720 for (unsigned i = 0; 8*i < EltSize; ++i) { 721 TotalVal = TotalVal.shl(8); 722 TotalVal |= OneVal; 723 } 724 725 // Convert the integer value to the appropriate type. 726 StoreVal = ConstantInt::get(TotalVal); 727 if (isa<PointerType>(ValTy)) 728 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); 729 else if (ValTy->isFloatingPoint()) 730 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy); 731 assert(StoreVal->getType() == ValTy && "Type mismatch!"); 732 733 // If the requested value was a vector constant, create it. 734 if (EltTy != ValTy) { 735 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements(); 736 SmallVector<Constant*, 16> Elts(NumElts, StoreVal); 737 StoreVal = ConstantVector::get(&Elts[0], NumElts); 738 } 739 } 740 new StoreInst(StoreVal, EltPtr, MI); 741 continue; 742 } 743 // Otherwise, if we're storing a byte variable, use a memset call for 744 // this element. 745 } 746 } 747 748 // Cast the element pointer to BytePtrTy. 749 if (EltPtr->getType() != BytePtrTy) 750 EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getNameStr(), MI); 751 752 // Cast the other pointer (if we have one) to BytePtrTy. 753 if (OtherElt && OtherElt->getType() != BytePtrTy) 754 OtherElt = new BitCastInst(OtherElt, BytePtrTy,OtherElt->getNameStr(), 755 MI); 756 757 unsigned EltSize = TD.getABITypeSize(EltTy); 758 759 // Finally, insert the meminst for this element. 760 if (isa<MemCpyInst>(MI) || isa<MemMoveInst>(MI)) { 761 Value *Ops[] = { 762 SROADest ? EltPtr : OtherElt, // Dest ptr 763 SROADest ? OtherElt : EltPtr, // Src ptr 764 ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size 765 Zero // Align 766 }; 767 CallInst::Create(TheFn, Ops, Ops + 4, "", MI); 768 } else { 769 assert(isa<MemSetInst>(MI)); 770 Value *Ops[] = { 771 EltPtr, MI->getOperand(2), // Dest, Value, 772 ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size 773 Zero // Align 774 }; 775 CallInst::Create(TheFn, Ops, Ops + 4, "", MI); 776 } 777 } 778 779 // Finally, MI is now dead, as we've modified its actions to occur on all of 780 // the elements of the aggregate. 781 ++UI; 782 MI->eraseFromParent(); 783 } 784} 785 786/// HasPadding - Return true if the specified type has any structure or 787/// alignment padding, false otherwise. 788static bool HasPadding(const Type *Ty, const TargetData &TD) { 789 if (const StructType *STy = dyn_cast<StructType>(Ty)) { 790 const StructLayout *SL = TD.getStructLayout(STy); 791 unsigned PrevFieldBitOffset = 0; 792 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 793 unsigned FieldBitOffset = SL->getElementOffsetInBits(i); 794 795 // Padding in sub-elements? 796 if (HasPadding(STy->getElementType(i), TD)) 797 return true; 798 799 // Check to see if there is any padding between this element and the 800 // previous one. 801 if (i) { 802 unsigned PrevFieldEnd = 803 PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1)); 804 if (PrevFieldEnd < FieldBitOffset) 805 return true; 806 } 807 808 PrevFieldBitOffset = FieldBitOffset; 809 } 810 811 // Check for tail padding. 812 if (unsigned EltCount = STy->getNumElements()) { 813 unsigned PrevFieldEnd = PrevFieldBitOffset + 814 TD.getTypeSizeInBits(STy->getElementType(EltCount-1)); 815 if (PrevFieldEnd < SL->getSizeInBits()) 816 return true; 817 } 818 819 } else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 820 return HasPadding(ATy->getElementType(), TD); 821 } else if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) { 822 return HasPadding(VTy->getElementType(), TD); 823 } 824 return TD.getTypeSizeInBits(Ty) != TD.getABITypeSizeInBits(Ty); 825} 826 827/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of 828/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, 829/// or 1 if safe after canonicalization has been performed. 830/// 831int SROA::isSafeAllocaToScalarRepl(AllocationInst *AI) { 832 // Loop over the use list of the alloca. We can only transform it if all of 833 // the users are safe to transform. 834 AllocaInfo Info; 835 836 for (Value::use_iterator I = AI->use_begin(), E = AI->use_end(); 837 I != E; ++I) { 838 isSafeUseOfAllocation(cast<Instruction>(*I), AI, Info); 839 if (Info.isUnsafe) { 840 DOUT << "Cannot transform: " << *AI << " due to user: " << **I; 841 return 0; 842 } 843 } 844 845 // Okay, we know all the users are promotable. If the aggregate is a memcpy 846 // source and destination, we have to be careful. In particular, the memcpy 847 // could be moving around elements that live in structure padding of the LLVM 848 // types, but may actually be used. In these cases, we refuse to promote the 849 // struct. 850 if (Info.isMemCpySrc && Info.isMemCpyDst && 851 HasPadding(AI->getType()->getElementType(), getAnalysis<TargetData>())) 852 return 0; 853 854 // If we require cleanup, return 1, otherwise return 3. 855 return Info.needsCanon ? 1 : 3; 856} 857 858/// CanonicalizeAllocaUsers - If SROA reported that it can promote the specified 859/// allocation, but only if cleaned up, perform the cleanups required. 860void SROA::CanonicalizeAllocaUsers(AllocationInst *AI) { 861 // At this point, we know that the end result will be SROA'd and promoted, so 862 // we can insert ugly code if required so long as sroa+mem2reg will clean it 863 // up. 864 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 865 UI != E; ) { 866 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI++); 867 if (!GEPI) continue; 868 gep_type_iterator I = gep_type_begin(GEPI); 869 ++I; 870 871 if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) { 872 uint64_t NumElements = AT->getNumElements(); 873 874 if (!isa<ConstantInt>(I.getOperand())) { 875 if (NumElements == 1) { 876 GEPI->setOperand(2, Constant::getNullValue(Type::Int32Ty)); 877 } else { 878 assert(NumElements == 2 && "Unhandled case!"); 879 // All users of the GEP must be loads. At each use of the GEP, insert 880 // two loads of the appropriate indexed GEP and select between them. 881 Value *IsOne = new ICmpInst(ICmpInst::ICMP_NE, I.getOperand(), 882 Constant::getNullValue(I.getOperand()->getType()), 883 "isone", GEPI); 884 // Insert the new GEP instructions, which are properly indexed. 885 SmallVector<Value*, 8> Indices(GEPI->op_begin()+1, GEPI->op_end()); 886 Indices[1] = Constant::getNullValue(Type::Int32Ty); 887 Value *ZeroIdx = GetElementPtrInst::Create(GEPI->getOperand(0), 888 Indices.begin(), 889 Indices.end(), 890 GEPI->getName()+".0", GEPI); 891 Indices[1] = ConstantInt::get(Type::Int32Ty, 1); 892 Value *OneIdx = GetElementPtrInst::Create(GEPI->getOperand(0), 893 Indices.begin(), 894 Indices.end(), 895 GEPI->getName()+".1", GEPI); 896 // Replace all loads of the variable index GEP with loads from both 897 // indexes and a select. 898 while (!GEPI->use_empty()) { 899 LoadInst *LI = cast<LoadInst>(GEPI->use_back()); 900 Value *Zero = new LoadInst(ZeroIdx, LI->getName()+".0", LI); 901 Value *One = new LoadInst(OneIdx , LI->getName()+".1", LI); 902 Value *R = SelectInst::Create(IsOne, One, Zero, LI->getName(), LI); 903 LI->replaceAllUsesWith(R); 904 LI->eraseFromParent(); 905 } 906 GEPI->eraseFromParent(); 907 } 908 } 909 } 910 } 911} 912 913/// MergeInType - Add the 'In' type to the accumulated type so far. If the 914/// types are incompatible, return true, otherwise update Accum and return 915/// false. 916/// 917/// There are three cases we handle here: 918/// 1) An effectively-integer union, where the pieces are stored into as 919/// smaller integers (common with byte swap and other idioms). 920/// 2) A union of vector types of the same size and potentially its elements. 921/// Here we turn element accesses into insert/extract element operations. 922/// 3) A union of scalar types, such as int/float or int/pointer. Here we 923/// merge together into integers, allowing the xform to work with #1 as 924/// well. 925static bool MergeInType(const Type *In, const Type *&Accum, 926 const TargetData &TD) { 927 // If this is our first type, just use it. 928 const VectorType *PTy; 929 if (Accum == Type::VoidTy || In == Accum) { 930 Accum = In; 931 } else if (In == Type::VoidTy) { 932 // Noop. 933 } else if (In->isInteger() && Accum->isInteger()) { // integer union. 934 // Otherwise pick whichever type is larger. 935 if (cast<IntegerType>(In)->getBitWidth() > 936 cast<IntegerType>(Accum)->getBitWidth()) 937 Accum = In; 938 } else if (isa<PointerType>(In) && isa<PointerType>(Accum)) { 939 // Pointer unions just stay as one of the pointers. 940 } else if (isa<VectorType>(In) || isa<VectorType>(Accum)) { 941 if ((PTy = dyn_cast<VectorType>(Accum)) && 942 PTy->getElementType() == In) { 943 // Accum is a vector, and we are accessing an element: ok. 944 } else if ((PTy = dyn_cast<VectorType>(In)) && 945 PTy->getElementType() == Accum) { 946 // In is a vector, and accum is an element: ok, remember In. 947 Accum = In; 948 } else if ((PTy = dyn_cast<VectorType>(In)) && isa<VectorType>(Accum) && 949 PTy->getBitWidth() == cast<VectorType>(Accum)->getBitWidth()) { 950 // Two vectors of the same size: keep Accum. 951 } else { 952 // Cannot insert an short into a <4 x int> or handle 953 // <2 x int> -> <4 x int> 954 return true; 955 } 956 } else { 957 // Pointer/FP/Integer unions merge together as integers. 958 switch (Accum->getTypeID()) { 959 case Type::PointerTyID: Accum = TD.getIntPtrType(); break; 960 case Type::FloatTyID: Accum = Type::Int32Ty; break; 961 case Type::DoubleTyID: Accum = Type::Int64Ty; break; 962 case Type::X86_FP80TyID: return true; 963 case Type::FP128TyID: return true; 964 case Type::PPC_FP128TyID: return true; 965 default: 966 assert(Accum->isInteger() && "Unknown FP type!"); 967 break; 968 } 969 970 switch (In->getTypeID()) { 971 case Type::PointerTyID: In = TD.getIntPtrType(); break; 972 case Type::FloatTyID: In = Type::Int32Ty; break; 973 case Type::DoubleTyID: In = Type::Int64Ty; break; 974 case Type::X86_FP80TyID: return true; 975 case Type::FP128TyID: return true; 976 case Type::PPC_FP128TyID: return true; 977 default: 978 assert(In->isInteger() && "Unknown FP type!"); 979 break; 980 } 981 return MergeInType(In, Accum, TD); 982 } 983 return false; 984} 985 986/// getUIntAtLeastAsBigAs - Return an unsigned integer type that is at least 987/// as big as the specified type. If there is no suitable type, this returns 988/// null. 989const Type *getUIntAtLeastAsBigAs(unsigned NumBits) { 990 if (NumBits > 64) return 0; 991 if (NumBits > 32) return Type::Int64Ty; 992 if (NumBits > 16) return Type::Int32Ty; 993 if (NumBits > 8) return Type::Int16Ty; 994 return Type::Int8Ty; 995} 996 997/// CanConvertToScalar - V is a pointer. If we can convert the pointee to a 998/// single scalar integer type, return that type. Further, if the use is not 999/// a completely trivial use that mem2reg could promote, set IsNotTrivial. If 1000/// there are no uses of this pointer, return Type::VoidTy to differentiate from 1001/// failure. 1002/// 1003const Type *SROA::CanConvertToScalar(Value *V, bool &IsNotTrivial) { 1004 const Type *UsedType = Type::VoidTy; // No uses, no forced type. 1005 const TargetData &TD = getAnalysis<TargetData>(); 1006 const PointerType *PTy = cast<PointerType>(V->getType()); 1007 1008 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 1009 Instruction *User = cast<Instruction>(*UI); 1010 1011 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1012 // FIXME: Loads of a first class aggregrate value could be converted to a 1013 // series of loads and insertvalues 1014 if (!LI->getType()->isSingleValueType()) 1015 return 0; 1016 1017 if (MergeInType(LI->getType(), UsedType, TD)) 1018 return 0; 1019 1020 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1021 // Storing the pointer, not into the value? 1022 if (SI->getOperand(0) == V) return 0; 1023 1024 // FIXME: Stores of a first class aggregrate value could be converted to a 1025 // series of extractvalues and stores 1026 if (!SI->getOperand(0)->getType()->isSingleValueType()) 1027 return 0; 1028 1029 // NOTE: We could handle storing of FP imms into integers here! 1030 1031 if (MergeInType(SI->getOperand(0)->getType(), UsedType, TD)) 1032 return 0; 1033 } else if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 1034 IsNotTrivial = true; 1035 const Type *SubTy = CanConvertToScalar(CI, IsNotTrivial); 1036 if (!SubTy || MergeInType(SubTy, UsedType, TD)) return 0; 1037 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 1038 // Check to see if this is stepping over an element: GEP Ptr, int C 1039 if (GEP->getNumOperands() == 2 && isa<ConstantInt>(GEP->getOperand(1))) { 1040 unsigned Idx = cast<ConstantInt>(GEP->getOperand(1))->getZExtValue(); 1041 unsigned ElSize = TD.getABITypeSize(PTy->getElementType()); 1042 unsigned BitOffset = Idx*ElSize*8; 1043 if (BitOffset > 64 || !isPowerOf2_32(ElSize)) return 0; 1044 1045 IsNotTrivial = true; 1046 const Type *SubElt = CanConvertToScalar(GEP, IsNotTrivial); 1047 if (SubElt == 0) return 0; 1048 if (SubElt != Type::VoidTy && SubElt->isInteger()) { 1049 const Type *NewTy = 1050 getUIntAtLeastAsBigAs(TD.getABITypeSizeInBits(SubElt)+BitOffset); 1051 if (NewTy == 0 || MergeInType(NewTy, UsedType, TD)) return 0; 1052 continue; 1053 } 1054 } else if (GEP->getNumOperands() == 3 && 1055 isa<ConstantInt>(GEP->getOperand(1)) && 1056 isa<ConstantInt>(GEP->getOperand(2)) && 1057 cast<ConstantInt>(GEP->getOperand(1))->isZero()) { 1058 // We are stepping into an element, e.g. a structure or an array: 1059 // GEP Ptr, int 0, uint C 1060 const Type *AggTy = PTy->getElementType(); 1061 unsigned Idx = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 1062 1063 if (const ArrayType *ATy = dyn_cast<ArrayType>(AggTy)) { 1064 if (Idx >= ATy->getNumElements()) return 0; // Out of range. 1065 } else if (const VectorType *VectorTy = dyn_cast<VectorType>(AggTy)) { 1066 // Getting an element of the vector. 1067 if (Idx >= VectorTy->getNumElements()) return 0; // Out of range. 1068 1069 // Merge in the vector type. 1070 if (MergeInType(VectorTy, UsedType, TD)) return 0; 1071 1072 const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial); 1073 if (SubTy == 0) return 0; 1074 1075 if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType, TD)) 1076 return 0; 1077 1078 // We'll need to change this to an insert/extract element operation. 1079 IsNotTrivial = true; 1080 continue; // Everything looks ok 1081 1082 } else if (isa<StructType>(AggTy)) { 1083 // Structs are always ok. 1084 } else { 1085 return 0; 1086 } 1087 const Type *NTy = getUIntAtLeastAsBigAs(TD.getABITypeSizeInBits(AggTy)); 1088 if (NTy == 0 || MergeInType(NTy, UsedType, TD)) return 0; 1089 const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial); 1090 if (SubTy == 0) return 0; 1091 if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType, TD)) 1092 return 0; 1093 continue; // Everything looks ok 1094 } 1095 return 0; 1096 } else { 1097 // Cannot handle this! 1098 return 0; 1099 } 1100 } 1101 1102 return UsedType; 1103} 1104 1105/// ConvertToScalar - The specified alloca passes the CanConvertToScalar 1106/// predicate and is non-trivial. Convert it to something that can be trivially 1107/// promoted into a register by mem2reg. 1108void SROA::ConvertToScalar(AllocationInst *AI, const Type *ActualTy) { 1109 DOUT << "CONVERT TO SCALAR: " << *AI << " TYPE = " 1110 << *ActualTy << "\n"; 1111 ++NumConverted; 1112 1113 BasicBlock *EntryBlock = AI->getParent(); 1114 assert(EntryBlock == &EntryBlock->getParent()->getEntryBlock() && 1115 "Not in the entry block!"); 1116 EntryBlock->getInstList().remove(AI); // Take the alloca out of the program. 1117 1118 // Create and insert the alloca. 1119 AllocaInst *NewAI = new AllocaInst(ActualTy, 0, AI->getName(), 1120 EntryBlock->begin()); 1121 ConvertUsesToScalar(AI, NewAI, 0); 1122 delete AI; 1123} 1124 1125 1126/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca 1127/// directly. This happens when we are converting an "integer union" to a 1128/// single integer scalar, or when we are converting a "vector union" to a 1129/// vector with insert/extractelement instructions. 1130/// 1131/// Offset is an offset from the original alloca, in bits that need to be 1132/// shifted to the right. By the end of this, there should be no uses of Ptr. 1133void SROA::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, unsigned Offset) { 1134 while (!Ptr->use_empty()) { 1135 Instruction *User = cast<Instruction>(Ptr->use_back()); 1136 1137 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 1138 Value *NV = ConvertUsesOfLoadToScalar(LI, NewAI, Offset); 1139 LI->replaceAllUsesWith(NV); 1140 LI->eraseFromParent(); 1141 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1142 assert(SI->getOperand(0) != Ptr && "Consistency error!"); 1143 1144 Value *SV = ConvertUsesOfStoreToScalar(SI, NewAI, Offset); 1145 new StoreInst(SV, NewAI, SI); 1146 SI->eraseFromParent(); 1147 1148 } else if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 1149 ConvertUsesToScalar(CI, NewAI, Offset); 1150 CI->eraseFromParent(); 1151 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 1152 const PointerType *AggPtrTy = 1153 cast<PointerType>(GEP->getOperand(0)->getType()); 1154 const TargetData &TD = getAnalysis<TargetData>(); 1155 unsigned AggSizeInBits = 1156 TD.getABITypeSizeInBits(AggPtrTy->getElementType()); 1157 1158 // Check to see if this is stepping over an element: GEP Ptr, int C 1159 unsigned NewOffset = Offset; 1160 if (GEP->getNumOperands() == 2) { 1161 unsigned Idx = cast<ConstantInt>(GEP->getOperand(1))->getZExtValue(); 1162 unsigned BitOffset = Idx*AggSizeInBits; 1163 1164 NewOffset += BitOffset; 1165 } else if (GEP->getNumOperands() == 3) { 1166 // We know that operand #2 is zero. 1167 unsigned Idx = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 1168 const Type *AggTy = AggPtrTy->getElementType(); 1169 if (const SequentialType *SeqTy = dyn_cast<SequentialType>(AggTy)) { 1170 unsigned ElSizeBits = 1171 TD.getABITypeSizeInBits(SeqTy->getElementType()); 1172 1173 NewOffset += ElSizeBits*Idx; 1174 } else if (const StructType *STy = dyn_cast<StructType>(AggTy)) { 1175 unsigned EltBitOffset = 1176 TD.getStructLayout(STy)->getElementOffsetInBits(Idx); 1177 1178 NewOffset += EltBitOffset; 1179 } else { 1180 assert(0 && "Unsupported operation!"); 1181 abort(); 1182 } 1183 } else { 1184 assert(0 && "Unsupported operation!"); 1185 abort(); 1186 } 1187 ConvertUsesToScalar(GEP, NewAI, NewOffset); 1188 GEP->eraseFromParent(); 1189 } else { 1190 assert(0 && "Unsupported operation!"); 1191 abort(); 1192 } 1193 } 1194} 1195 1196/// ConvertUsesOfLoadToScalar - Convert all of the users the specified load to 1197/// use the new alloca directly, returning the value that should replace the 1198/// load. This happens when we are converting an "integer union" to a 1199/// single integer scalar, or when we are converting a "vector union" to a 1200/// vector with insert/extractelement instructions. 1201/// 1202/// Offset is an offset from the original alloca, in bits that need to be 1203/// shifted to the right. By the end of this, there should be no uses of Ptr. 1204Value *SROA::ConvertUsesOfLoadToScalar(LoadInst *LI, AllocaInst *NewAI, 1205 unsigned Offset) { 1206 // The load is a bit extract from NewAI shifted right by Offset bits. 1207 Value *NV = new LoadInst(NewAI, LI->getName(), LI); 1208 1209 if (NV->getType() == LI->getType() && Offset == 0) { 1210 // We win, no conversion needed. 1211 return NV; 1212 } 1213 1214 // If the result type of the 'union' is a pointer, then this must be ptr->ptr 1215 // cast. Anything else would result in NV being an integer. 1216 if (isa<PointerType>(NV->getType())) { 1217 assert(isa<PointerType>(LI->getType())); 1218 return new BitCastInst(NV, LI->getType(), LI->getName(), LI); 1219 } 1220 1221 if (const VectorType *VTy = dyn_cast<VectorType>(NV->getType())) { 1222 // If the result alloca is a vector type, this is either an element 1223 // access or a bitcast to another vector type. 1224 if (isa<VectorType>(LI->getType())) 1225 return new BitCastInst(NV, LI->getType(), LI->getName(), LI); 1226 1227 // Otherwise it must be an element access. 1228 const TargetData &TD = getAnalysis<TargetData>(); 1229 unsigned Elt = 0; 1230 if (Offset) { 1231 unsigned EltSize = TD.getABITypeSizeInBits(VTy->getElementType()); 1232 Elt = Offset/EltSize; 1233 Offset -= EltSize*Elt; 1234 } 1235 NV = new ExtractElementInst(NV, ConstantInt::get(Type::Int32Ty, Elt), 1236 "tmp", LI); 1237 1238 // If we're done, return this element. 1239 if (NV->getType() == LI->getType() && Offset == 0) 1240 return NV; 1241 } 1242 1243 const IntegerType *NTy = cast<IntegerType>(NV->getType()); 1244 1245 // If this is a big-endian system and the load is narrower than the 1246 // full alloca type, we need to do a shift to get the right bits. 1247 int ShAmt = 0; 1248 const TargetData &TD = getAnalysis<TargetData>(); 1249 if (TD.isBigEndian()) { 1250 // On big-endian machines, the lowest bit is stored at the bit offset 1251 // from the pointer given by getTypeStoreSizeInBits. This matters for 1252 // integers with a bitwidth that is not a multiple of 8. 1253 ShAmt = TD.getTypeStoreSizeInBits(NTy) - 1254 TD.getTypeStoreSizeInBits(LI->getType()) - Offset; 1255 } else { 1256 ShAmt = Offset; 1257 } 1258 1259 // Note: we support negative bitwidths (with shl) which are not defined. 1260 // We do this to support (f.e.) loads off the end of a structure where 1261 // only some bits are used. 1262 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth()) 1263 NV = BinaryOperator::CreateLShr(NV, 1264 ConstantInt::get(NV->getType(),ShAmt), 1265 LI->getName(), LI); 1266 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) 1267 NV = BinaryOperator::CreateShl(NV, 1268 ConstantInt::get(NV->getType(),-ShAmt), 1269 LI->getName(), LI); 1270 1271 // Finally, unconditionally truncate the integer to the right width. 1272 unsigned LIBitWidth = TD.getTypeSizeInBits(LI->getType()); 1273 if (LIBitWidth < NTy->getBitWidth()) 1274 NV = new TruncInst(NV, IntegerType::get(LIBitWidth), 1275 LI->getName(), LI); 1276 1277 // If the result is an integer, this is a trunc or bitcast. 1278 if (isa<IntegerType>(LI->getType())) { 1279 // Should be done. 1280 } else if (LI->getType()->isFloatingPoint()) { 1281 // Just do a bitcast, we know the sizes match up. 1282 NV = new BitCastInst(NV, LI->getType(), LI->getName(), LI); 1283 } else { 1284 // Otherwise must be a pointer. 1285 NV = new IntToPtrInst(NV, LI->getType(), LI->getName(), LI); 1286 } 1287 assert(NV->getType() == LI->getType() && "Didn't convert right?"); 1288 return NV; 1289} 1290 1291 1292/// ConvertUsesOfStoreToScalar - Convert the specified store to a load+store 1293/// pair of the new alloca directly, returning the value that should be stored 1294/// to the alloca. This happens when we are converting an "integer union" to a 1295/// single integer scalar, or when we are converting a "vector union" to a 1296/// vector with insert/extractelement instructions. 1297/// 1298/// Offset is an offset from the original alloca, in bits that need to be 1299/// shifted to the right. By the end of this, there should be no uses of Ptr. 1300Value *SROA::ConvertUsesOfStoreToScalar(StoreInst *SI, AllocaInst *NewAI, 1301 unsigned Offset) { 1302 1303 // Convert the stored type to the actual type, shift it left to insert 1304 // then 'or' into place. 1305 Value *SV = SI->getOperand(0); 1306 const Type *AllocaType = NewAI->getType()->getElementType(); 1307 if (SV->getType() == AllocaType && Offset == 0) { 1308 // All is well. 1309 } else if (const VectorType *PTy = dyn_cast<VectorType>(AllocaType)) { 1310 Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI); 1311 1312 // If the result alloca is a vector type, this is either an element 1313 // access or a bitcast to another vector type. 1314 if (isa<VectorType>(SV->getType())) { 1315 SV = new BitCastInst(SV, AllocaType, SV->getName(), SI); 1316 } else { 1317 // Must be an element insertion. 1318 const TargetData &TD = getAnalysis<TargetData>(); 1319 unsigned Elt = Offset/TD.getABITypeSizeInBits(PTy->getElementType()); 1320 SV = InsertElementInst::Create(Old, SV, 1321 ConstantInt::get(Type::Int32Ty, Elt), 1322 "tmp", SI); 1323 } 1324 } else if (isa<PointerType>(AllocaType)) { 1325 // If the alloca type is a pointer, then all the elements must be 1326 // pointers. 1327 if (SV->getType() != AllocaType) 1328 SV = new BitCastInst(SV, AllocaType, SV->getName(), SI); 1329 } else { 1330 Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI); 1331 1332 // If SV is a float, convert it to the appropriate integer type. 1333 // If it is a pointer, do the same, and also handle ptr->ptr casts 1334 // here. 1335 const TargetData &TD = getAnalysis<TargetData>(); 1336 unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType()); 1337 unsigned DestWidth = TD.getTypeSizeInBits(AllocaType); 1338 unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType()); 1339 unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType); 1340 if (SV->getType()->isFloatingPoint()) 1341 SV = new BitCastInst(SV, IntegerType::get(SrcWidth), 1342 SV->getName(), SI); 1343 else if (isa<PointerType>(SV->getType())) 1344 SV = new PtrToIntInst(SV, TD.getIntPtrType(), SV->getName(), SI); 1345 1346 // Always zero extend the value if needed. 1347 if (SV->getType() != AllocaType) 1348 SV = new ZExtInst(SV, AllocaType, SV->getName(), SI); 1349 1350 // If this is a big-endian system and the store is narrower than the 1351 // full alloca type, we need to do a shift to get the right bits. 1352 int ShAmt = 0; 1353 if (TD.isBigEndian()) { 1354 // On big-endian machines, the lowest bit is stored at the bit offset 1355 // from the pointer given by getTypeStoreSizeInBits. This matters for 1356 // integers with a bitwidth that is not a multiple of 8. 1357 ShAmt = DestStoreWidth - SrcStoreWidth - Offset; 1358 } else { 1359 ShAmt = Offset; 1360 } 1361 1362 // Note: we support negative bitwidths (with shr) which are not defined. 1363 // We do this to support (f.e.) stores off the end of a structure where 1364 // only some bits in the structure are set. 1365 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth)); 1366 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) { 1367 SV = BinaryOperator::CreateShl(SV, 1368 ConstantInt::get(SV->getType(), ShAmt), 1369 SV->getName(), SI); 1370 Mask <<= ShAmt; 1371 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { 1372 SV = BinaryOperator::CreateLShr(SV, 1373 ConstantInt::get(SV->getType(),-ShAmt), 1374 SV->getName(), SI); 1375 Mask = Mask.lshr(ShAmt); 1376 } 1377 1378 // Mask out the bits we are about to insert from the old value, and or 1379 // in the new bits. 1380 if (SrcWidth != DestWidth) { 1381 assert(DestWidth > SrcWidth); 1382 Old = BinaryOperator::CreateAnd(Old, ConstantInt::get(~Mask), 1383 Old->getName()+".mask", SI); 1384 SV = BinaryOperator::CreateOr(Old, SV, SV->getName()+".ins", SI); 1385 } 1386 } 1387 return SV; 1388} 1389 1390 1391 1392/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to 1393/// some part of a constant global variable. This intentionally only accepts 1394/// constant expressions because we don't can't rewrite arbitrary instructions. 1395static bool PointsToConstantGlobal(Value *V) { 1396 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) 1397 return GV->isConstant(); 1398 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 1399 if (CE->getOpcode() == Instruction::BitCast || 1400 CE->getOpcode() == Instruction::GetElementPtr) 1401 return PointsToConstantGlobal(CE->getOperand(0)); 1402 return false; 1403} 1404 1405/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived) 1406/// pointer to an alloca. Ignore any reads of the pointer, return false if we 1407/// see any stores or other unknown uses. If we see pointer arithmetic, keep 1408/// track of whether it moves the pointer (with isOffset) but otherwise traverse 1409/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to 1410/// the alloca, and if the source pointer is a pointer to a constant global, we 1411/// can optimize this. 1412static bool isOnlyCopiedFromConstantGlobal(Value *V, Instruction *&TheCopy, 1413 bool isOffset) { 1414 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 1415 if (isa<LoadInst>(*UI)) { 1416 // Ignore loads, they are always ok. 1417 continue; 1418 } 1419 if (BitCastInst *BCI = dyn_cast<BitCastInst>(*UI)) { 1420 // If uses of the bitcast are ok, we are ok. 1421 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) 1422 return false; 1423 continue; 1424 } 1425 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) { 1426 // If the GEP has all zero indices, it doesn't offset the pointer. If it 1427 // doesn't, it does. 1428 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy, 1429 isOffset || !GEP->hasAllZeroIndices())) 1430 return false; 1431 continue; 1432 } 1433 1434 // If this is isn't our memcpy/memmove, reject it as something we can't 1435 // handle. 1436 if (!isa<MemCpyInst>(*UI) && !isa<MemMoveInst>(*UI)) 1437 return false; 1438 1439 // If we already have seen a copy, reject the second one. 1440 if (TheCopy) return false; 1441 1442 // If the pointer has been offset from the start of the alloca, we can't 1443 // safely handle this. 1444 if (isOffset) return false; 1445 1446 // If the memintrinsic isn't using the alloca as the dest, reject it. 1447 if (UI.getOperandNo() != 1) return false; 1448 1449 MemIntrinsic *MI = cast<MemIntrinsic>(*UI); 1450 1451 // If the source of the memcpy/move is not a constant global, reject it. 1452 if (!PointsToConstantGlobal(MI->getOperand(2))) 1453 return false; 1454 1455 // Otherwise, the transform is safe. Remember the copy instruction. 1456 TheCopy = MI; 1457 } 1458 return true; 1459} 1460 1461/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only 1462/// modified by a copy from a constant global. If we can prove this, we can 1463/// replace any uses of the alloca with uses of the global directly. 1464Instruction *SROA::isOnlyCopiedFromConstantGlobal(AllocationInst *AI) { 1465 Instruction *TheCopy = 0; 1466 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) 1467 return TheCopy; 1468 return 0; 1469} 1470