ScalarReplAggregates.cpp revision 68c01b3cf35bb7ed2d3a3f63053e304e092bcfdd
1//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source 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 bool runOnFunction(Function &F); 51 52 bool performScalarRepl(Function &F); 53 bool performPromotion(Function &F); 54 55 // getAnalysisUsage - This pass does not require any passes, but we know it 56 // will not alter the CFG, so say so. 57 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 58 AU.addRequired<ETForest>(); 59 AU.addRequired<DominanceFrontier>(); 60 AU.addRequired<TargetData>(); 61 AU.setPreservesCFG(); 62 } 63 64 private: 65 int isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI); 66 int isSafeUseOfAllocation(Instruction *User, AllocationInst *AI); 67 bool isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI); 68 bool isSafeUseOfBitCastedAllocation(BitCastInst *User, AllocationInst *AI); 69 int isSafeAllocaToScalarRepl(AllocationInst *AI); 70 void DoScalarReplacement(AllocationInst *AI, 71 std::vector<AllocationInst*> &WorkList); 72 void CanonicalizeAllocaUsers(AllocationInst *AI); 73 AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocationInst *Base); 74 75 void RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI, 76 SmallVector<AllocaInst*, 32> &NewElts); 77 78 const Type *CanConvertToScalar(Value *V, bool &IsNotTrivial); 79 void ConvertToScalar(AllocationInst *AI, const Type *Ty); 80 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, unsigned Offset); 81 static Instruction *isOnlyCopiedFromConstantGlobal(AllocationInst *AI); 82 }; 83 84 RegisterPass<SROA> X("scalarrepl", "Scalar Replacement of Aggregates"); 85} 86 87// Public interface to the ScalarReplAggregates pass 88FunctionPass *llvm::createScalarReplAggregatesPass() { return new SROA(); } 89 90 91bool SROA::runOnFunction(Function &F) { 92 bool Changed = performPromotion(F); 93 while (1) { 94 bool LocalChange = performScalarRepl(F); 95 if (!LocalChange) break; // No need to repromote if no scalarrepl 96 Changed = true; 97 LocalChange = performPromotion(F); 98 if (!LocalChange) break; // No need to re-scalarrepl if no promotion 99 } 100 101 return Changed; 102} 103 104 105bool SROA::performPromotion(Function &F) { 106 std::vector<AllocaInst*> Allocas; 107 ETForest &ET = getAnalysis<ETForest>(); 108 DominanceFrontier &DF = getAnalysis<DominanceFrontier>(); 109 110 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function 111 112 bool Changed = false; 113 114 while (1) { 115 Allocas.clear(); 116 117 // Find allocas that are safe to promote, by looking at all instructions in 118 // the entry node 119 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) 120 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? 121 if (isAllocaPromotable(AI)) 122 Allocas.push_back(AI); 123 124 if (Allocas.empty()) break; 125 126 PromoteMemToReg(Allocas, ET, DF); 127 NumPromoted += Allocas.size(); 128 Changed = true; 129 } 130 131 return Changed; 132} 133 134// performScalarRepl - This algorithm is a simple worklist driven algorithm, 135// which runs on all of the malloc/alloca instructions in the function, removing 136// them if they are only used by getelementptr instructions. 137// 138bool SROA::performScalarRepl(Function &F) { 139 std::vector<AllocationInst*> WorkList; 140 141 // Scan the entry basic block, adding any alloca's and mallocs to the worklist 142 BasicBlock &BB = F.getEntryBlock(); 143 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) 144 if (AllocationInst *A = dyn_cast<AllocationInst>(I)) 145 WorkList.push_back(A); 146 147 // Process the worklist 148 bool Changed = false; 149 while (!WorkList.empty()) { 150 AllocationInst *AI = WorkList.back(); 151 WorkList.pop_back(); 152 153 // Handle dead allocas trivially. These can be formed by SROA'ing arrays 154 // with unused elements. 155 if (AI->use_empty()) { 156 AI->eraseFromParent(); 157 continue; 158 } 159 160 // If we can turn this aggregate value (potentially with casts) into a 161 // simple scalar value that can be mem2reg'd into a register value. 162 bool IsNotTrivial = false; 163 if (const Type *ActualType = CanConvertToScalar(AI, IsNotTrivial)) 164 if (IsNotTrivial && ActualType != Type::VoidTy) { 165 ConvertToScalar(AI, ActualType); 166 Changed = true; 167 continue; 168 } 169 170 // Check to see if we can perform the core SROA transformation. We cannot 171 // transform the allocation instruction if it is an array allocation 172 // (allocations OF arrays are ok though), and an allocation of a scalar 173 // value cannot be decomposed at all. 174 if (!AI->isArrayAllocation() && 175 (isa<StructType>(AI->getAllocatedType()) || 176 isa<ArrayType>(AI->getAllocatedType()))) { 177 // Check that all of the users of the allocation are capable of being 178 // transformed. 179 switch (isSafeAllocaToScalarRepl(AI)) { 180 default: assert(0 && "Unexpected value!"); 181 case 0: // Not safe to scalar replace. 182 break; 183 case 1: // Safe, but requires cleanup/canonicalizations first 184 CanonicalizeAllocaUsers(AI); 185 // FALL THROUGH. 186 case 3: // Safe to scalar replace. 187 DoScalarReplacement(AI, WorkList); 188 Changed = true; 189 continue; 190 } 191 } 192 193 // Check to see if this allocation is only modified by a memcpy/memmove from 194 // a constant global. If this is the case, we can change all users to use 195 // the constant global instead. This is commonly produced by the CFE by 196 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A' 197 // is only subsequently read. 198 if (Instruction *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) { 199 DOUT << "Found alloca equal to global: " << *AI; 200 DOUT << " memcpy = " << *TheCopy; 201 Constant *TheSrc = cast<Constant>(TheCopy->getOperand(2)); 202 AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType())); 203 TheCopy->eraseFromParent(); // Don't mutate the global. 204 AI->eraseFromParent(); 205 ++NumGlobals; 206 Changed = true; 207 continue; 208 } 209 210 // Otherwise, couldn't process this. 211 } 212 213 return Changed; 214} 215 216/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl 217/// predicate, do SROA now. 218void SROA::DoScalarReplacement(AllocationInst *AI, 219 std::vector<AllocationInst*> &WorkList) { 220 DOUT << "Found inst to SROA: " << *AI; 221 SmallVector<AllocaInst*, 32> ElementAllocas; 222 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 223 ElementAllocas.reserve(ST->getNumContainedTypes()); 224 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { 225 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 226 AI->getAlignment(), 227 AI->getName() + "." + utostr(i), AI); 228 ElementAllocas.push_back(NA); 229 WorkList.push_back(NA); // Add to worklist for recursive processing 230 } 231 } else { 232 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); 233 ElementAllocas.reserve(AT->getNumElements()); 234 const Type *ElTy = AT->getElementType(); 235 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 236 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(), 237 AI->getName() + "." + utostr(i), AI); 238 ElementAllocas.push_back(NA); 239 WorkList.push_back(NA); // Add to worklist for recursive processing 240 } 241 } 242 243 // Now that we have created the alloca instructions that we want to use, 244 // expand the getelementptr instructions to use them. 245 // 246 while (!AI->use_empty()) { 247 Instruction *User = cast<Instruction>(AI->use_back()); 248 if (BitCastInst *BCInst = dyn_cast<BitCastInst>(User)) { 249 RewriteBitCastUserOfAlloca(BCInst, AI, ElementAllocas); 250 BCInst->eraseFromParent(); 251 continue; 252 } 253 254 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User); 255 // We now know that the GEP is of the form: GEP <ptr>, 0, <cst> 256 unsigned Idx = 257 (unsigned)cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); 258 259 assert(Idx < ElementAllocas.size() && "Index out of range?"); 260 AllocaInst *AllocaToUse = ElementAllocas[Idx]; 261 262 Value *RepValue; 263 if (GEPI->getNumOperands() == 3) { 264 // Do not insert a new getelementptr instruction with zero indices, only 265 // to have it optimized out later. 266 RepValue = AllocaToUse; 267 } else { 268 // We are indexing deeply into the structure, so we still need a 269 // getelement ptr instruction to finish the indexing. This may be 270 // expanded itself once the worklist is rerun. 271 // 272 SmallVector<Value*, 8> NewArgs; 273 NewArgs.push_back(Constant::getNullValue(Type::Int32Ty)); 274 NewArgs.append(GEPI->op_begin()+3, GEPI->op_end()); 275 RepValue = new GetElementPtrInst(AllocaToUse, &NewArgs[0], 276 NewArgs.size(), "", GEPI); 277 RepValue->takeName(GEPI); 278 } 279 280 // If this GEP is to the start of the aggregate, check for memcpys. 281 if (Idx == 0) { 282 bool IsStartOfAggregateGEP = true; 283 for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) { 284 if (!isa<ConstantInt>(GEPI->getOperand(i))) { 285 IsStartOfAggregateGEP = false; 286 break; 287 } 288 if (!cast<ConstantInt>(GEPI->getOperand(i))->isZero()) { 289 IsStartOfAggregateGEP = false; 290 break; 291 } 292 } 293 294 if (IsStartOfAggregateGEP) 295 RewriteBitCastUserOfAlloca(GEPI, AI, ElementAllocas); 296 } 297 298 299 // Move all of the users over to the new GEP. 300 GEPI->replaceAllUsesWith(RepValue); 301 // Delete the old GEP 302 GEPI->eraseFromParent(); 303 } 304 305 // Finally, delete the Alloca instruction 306 AI->eraseFromParent(); 307 NumReplaced++; 308} 309 310 311/// isSafeElementUse - Check to see if this use is an allowed use for a 312/// getelementptr instruction of an array aggregate allocation. isFirstElt 313/// indicates whether Ptr is known to the start of the aggregate. 314/// 315int SROA::isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI) { 316 for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); 317 I != E; ++I) { 318 Instruction *User = cast<Instruction>(*I); 319 switch (User->getOpcode()) { 320 case Instruction::Load: break; 321 case Instruction::Store: 322 // Store is ok if storing INTO the pointer, not storing the pointer 323 if (User->getOperand(0) == Ptr) return 0; 324 break; 325 case Instruction::GetElementPtr: { 326 GetElementPtrInst *GEP = cast<GetElementPtrInst>(User); 327 bool AreAllZeroIndices = isFirstElt; 328 if (GEP->getNumOperands() > 1) { 329 if (!isa<ConstantInt>(GEP->getOperand(1)) || 330 !cast<ConstantInt>(GEP->getOperand(1))->isZero()) 331 return 0; // Using pointer arithmetic to navigate the array. 332 333 if (AreAllZeroIndices) { 334 for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) { 335 if (!isa<ConstantInt>(GEP->getOperand(i)) || 336 !cast<ConstantInt>(GEP->getOperand(i))->isZero()) { 337 AreAllZeroIndices = false; 338 break; 339 } 340 } 341 } 342 } 343 if (!isSafeElementUse(GEP, AreAllZeroIndices, AI)) return 0; 344 break; 345 } 346 case Instruction::BitCast: 347 if (isFirstElt && 348 isSafeUseOfBitCastedAllocation(cast<BitCastInst>(User), AI)) 349 break; 350 DOUT << " Transformation preventing inst: " << *User; 351 return 0; 352 case Instruction::Call: 353 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { 354 if (isFirstElt && isSafeMemIntrinsicOnAllocation(MI, AI)) 355 break; 356 } 357 DOUT << " Transformation preventing inst: " << *User; 358 return 0; 359 default: 360 DOUT << " Transformation preventing inst: " << *User; 361 return 0; 362 } 363 } 364 return 3; // All users look ok :) 365} 366 367/// AllUsersAreLoads - Return true if all users of this value are loads. 368static bool AllUsersAreLoads(Value *Ptr) { 369 for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); 370 I != E; ++I) 371 if (cast<Instruction>(*I)->getOpcode() != Instruction::Load) 372 return false; 373 return true; 374} 375 376/// isSafeUseOfAllocation - Check to see if this user is an allowed use for an 377/// aggregate allocation. 378/// 379int SROA::isSafeUseOfAllocation(Instruction *User, AllocationInst *AI) { 380 if (BitCastInst *C = dyn_cast<BitCastInst>(User)) 381 return isSafeUseOfBitCastedAllocation(C, AI) ? 3 : 0; 382 if (!isa<GetElementPtrInst>(User)) return 0; 383 384 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User); 385 gep_type_iterator I = gep_type_begin(GEPI), E = gep_type_end(GEPI); 386 387 // The GEP is not safe to transform if not of the form "GEP <ptr>, 0, <cst>". 388 if (I == E || 389 I.getOperand() != Constant::getNullValue(I.getOperand()->getType())) 390 return 0; 391 392 ++I; 393 if (I == E) return 0; // ran out of GEP indices?? 394 395 bool IsAllZeroIndices = true; 396 397 // If this is a use of an array allocation, do a bit more checking for sanity. 398 if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) { 399 uint64_t NumElements = AT->getNumElements(); 400 401 if (ConstantInt *Idx = dyn_cast<ConstantInt>(I.getOperand())) { 402 IsAllZeroIndices &= Idx->isZero(); 403 404 // Check to make sure that index falls within the array. If not, 405 // something funny is going on, so we won't do the optimization. 406 // 407 if (Idx->getZExtValue() >= NumElements) 408 return 0; 409 410 // We cannot scalar repl this level of the array unless any array 411 // sub-indices are in-range constants. In particular, consider: 412 // A[0][i]. We cannot know that the user isn't doing invalid things like 413 // allowing i to index an out-of-range subscript that accesses A[1]. 414 // 415 // Scalar replacing *just* the outer index of the array is probably not 416 // going to be a win anyway, so just give up. 417 for (++I; I != E && (isa<ArrayType>(*I) || isa<VectorType>(*I)); ++I) { 418 uint64_t NumElements; 419 if (const ArrayType *SubArrayTy = dyn_cast<ArrayType>(*I)) 420 NumElements = SubArrayTy->getNumElements(); 421 else 422 NumElements = cast<VectorType>(*I)->getNumElements(); 423 424 ConstantInt *IdxVal = dyn_cast<ConstantInt>(I.getOperand()); 425 if (!IdxVal) return 0; 426 if (IdxVal->getZExtValue() >= NumElements) 427 return 0; 428 IsAllZeroIndices &= IdxVal->isZero(); 429 } 430 431 } else { 432 IsAllZeroIndices = 0; 433 434 // If this is an array index and the index is not constant, we cannot 435 // promote... that is unless the array has exactly one or two elements in 436 // it, in which case we CAN promote it, but we have to canonicalize this 437 // out if this is the only problem. 438 if ((NumElements == 1 || NumElements == 2) && 439 AllUsersAreLoads(GEPI)) 440 return 1; // Canonicalization required! 441 return 0; 442 } 443 } 444 445 // If there are any non-simple uses of this getelementptr, make sure to reject 446 // them. 447 return isSafeElementUse(GEPI, IsAllZeroIndices, AI); 448} 449 450/// isSafeMemIntrinsicOnAllocation - Return true if the specified memory 451/// intrinsic can be promoted by SROA. At this point, we know that the operand 452/// of the memintrinsic is a pointer to the beginning of the allocation. 453bool SROA::isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI){ 454 // If not constant length, give up. 455 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); 456 if (!Length) return false; 457 458 // If not the whole aggregate, give up. 459 const TargetData &TD = getAnalysis<TargetData>(); 460 if (Length->getZExtValue() != TD.getTypeSize(AI->getType()->getElementType())) 461 return false; 462 463 // We only know about memcpy/memset/memmove. 464 if (!isa<MemCpyInst>(MI) && !isa<MemSetInst>(MI) && !isa<MemMoveInst>(MI)) 465 return false; 466 // Otherwise, we can transform it. 467 return true; 468} 469 470/// isSafeUseOfBitCastedAllocation - Return true if all users of this bitcast 471/// are 472bool SROA::isSafeUseOfBitCastedAllocation(BitCastInst *BC, AllocationInst *AI) { 473 for (Value::use_iterator UI = BC->use_begin(), E = BC->use_end(); 474 UI != E; ++UI) { 475 if (BitCastInst *BCU = dyn_cast<BitCastInst>(UI)) { 476 if (!isSafeUseOfBitCastedAllocation(BCU, AI)) 477 return false; 478 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(UI)) { 479 if (!isSafeMemIntrinsicOnAllocation(MI, AI)) 480 return false; 481 } else { 482 return false; 483 } 484 } 485 return true; 486} 487 488/// RewriteBitCastUserOfAlloca - BCInst (transitively) bitcasts AI, or indexes 489/// to its first element. Transform users of the cast to use the new values 490/// instead. 491void SROA::RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI, 492 SmallVector<AllocaInst*, 32> &NewElts) { 493 Constant *Zero = Constant::getNullValue(Type::Int32Ty); 494 const TargetData &TD = getAnalysis<TargetData>(); 495 496 Value::use_iterator UI = BCInst->use_begin(), UE = BCInst->use_end(); 497 while (UI != UE) { 498 if (BitCastInst *BCU = dyn_cast<BitCastInst>(*UI)) { 499 RewriteBitCastUserOfAlloca(BCU, AI, NewElts); 500 ++UI; 501 BCU->eraseFromParent(); 502 continue; 503 } 504 505 // Otherwise, must be memcpy/memmove/memset of the entire aggregate. Split 506 // into one per element. 507 MemIntrinsic *MI = dyn_cast<MemIntrinsic>(*UI); 508 509 // If it's not a mem intrinsic, it must be some other user of a gep of the 510 // first pointer. Just leave these alone. 511 if (!MI) { 512 ++UI; 513 continue; 514 } 515 516 // If this is a memcpy/memmove, construct the other pointer as the 517 // appropriate type. 518 Value *OtherPtr = 0; 519 if (MemCpyInst *MCI = dyn_cast<MemCpyInst>(MI)) { 520 if (BCInst == MCI->getRawDest()) 521 OtherPtr = MCI->getRawSource(); 522 else { 523 assert(BCInst == MCI->getRawSource()); 524 OtherPtr = MCI->getRawDest(); 525 } 526 } else if (MemMoveInst *MMI = dyn_cast<MemMoveInst>(MI)) { 527 if (BCInst == MMI->getRawDest()) 528 OtherPtr = MMI->getRawSource(); 529 else { 530 assert(BCInst == MMI->getRawSource()); 531 OtherPtr = MMI->getRawDest(); 532 } 533 } 534 535 // If there is an other pointer, we want to convert it to the same pointer 536 // type as AI has, so we can GEP through it. 537 if (OtherPtr) { 538 // It is likely that OtherPtr is a bitcast, if so, remove it. 539 if (BitCastInst *BC = dyn_cast<BitCastInst>(OtherPtr)) 540 OtherPtr = BC->getOperand(0); 541 if (ConstantExpr *BCE = dyn_cast<ConstantExpr>(OtherPtr)) 542 if (BCE->getOpcode() == Instruction::BitCast) 543 OtherPtr = BCE->getOperand(0); 544 545 // If the pointer is not the right type, insert a bitcast to the right 546 // type. 547 if (OtherPtr->getType() != AI->getType()) 548 OtherPtr = new BitCastInst(OtherPtr, AI->getType(), OtherPtr->getName(), 549 MI); 550 } 551 552 // Process each element of the aggregate. 553 Value *TheFn = MI->getOperand(0); 554 const Type *BytePtrTy = MI->getRawDest()->getType(); 555 bool SROADest = MI->getRawDest() == BCInst; 556 557 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { 558 // If this is a memcpy/memmove, emit a GEP of the other element address. 559 Value *OtherElt = 0; 560 if (OtherPtr) { 561 OtherElt = new GetElementPtrInst(OtherPtr, Zero, 562 ConstantInt::get(Type::Int32Ty, i), 563 OtherPtr->getNameStr()+"."+utostr(i), 564 MI); 565 } 566 567 Value *EltPtr = NewElts[i]; 568 const Type *EltTy =cast<PointerType>(EltPtr->getType())->getElementType(); 569 570 // If we got down to a scalar, insert a load or store as appropriate. 571 if (EltTy->isFirstClassType()) { 572 if (isa<MemCpyInst>(MI) || isa<MemMoveInst>(MI)) { 573 Value *Elt = new LoadInst(SROADest ? OtherElt : EltPtr, "tmp", 574 MI); 575 new StoreInst(Elt, SROADest ? EltPtr : OtherElt, MI); 576 continue; 577 } else { 578 assert(isa<MemSetInst>(MI)); 579 580 // If the stored element is zero (common case), just store a null 581 // constant. 582 Constant *StoreVal; 583 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getOperand(2))) { 584 if (CI->isZero()) { 585 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0> 586 } else { 587 // If EltTy is a packed type, get the element type. 588 const Type *ValTy = EltTy; 589 if (const VectorType *VTy = dyn_cast<VectorType>(ValTy)) 590 ValTy = VTy->getElementType(); 591 592 // Construct an integer with the right value. 593 unsigned EltSize = TD.getTypeSize(ValTy); 594 APInt OneVal(EltSize*8, CI->getZExtValue()); 595 APInt TotalVal(OneVal); 596 // Set each byte. 597 for (unsigned i = 0; i != EltSize-1; ++i) { 598 TotalVal = TotalVal.shl(8); 599 TotalVal |= OneVal; 600 } 601 602 // Convert the integer value to the appropriate type. 603 StoreVal = ConstantInt::get(TotalVal); 604 if (isa<PointerType>(ValTy)) 605 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); 606 else if (ValTy->isFloatingPoint()) 607 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy); 608 assert(StoreVal->getType() == ValTy && "Type mismatch!"); 609 610 // If the requested value was a vector constant, create it. 611 if (EltTy != ValTy) { 612 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements(); 613 SmallVector<Constant*, 16> Elts(NumElts, StoreVal); 614 StoreVal = ConstantVector::get(&Elts[0], NumElts); 615 } 616 } 617 new StoreInst(StoreVal, EltPtr, MI); 618 continue; 619 } 620 // Otherwise, if we're storing a byte variable, use a memset call for 621 // this element. 622 } 623 } 624 625 // Cast the element pointer to BytePtrTy. 626 if (EltPtr->getType() != BytePtrTy) 627 EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getNameStr(), MI); 628 629 // Cast the other pointer (if we have one) to BytePtrTy. 630 if (OtherElt && OtherElt->getType() != BytePtrTy) 631 OtherElt = new BitCastInst(OtherElt, BytePtrTy,OtherElt->getNameStr(), 632 MI); 633 634 unsigned EltSize = TD.getTypeSize(EltTy); 635 636 // Finally, insert the meminst for this element. 637 if (isa<MemCpyInst>(MI) || isa<MemMoveInst>(MI)) { 638 Value *Ops[] = { 639 SROADest ? EltPtr : OtherElt, // Dest ptr 640 SROADest ? OtherElt : EltPtr, // Src ptr 641 ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size 642 Zero // Align 643 }; 644 new CallInst(TheFn, Ops, 4, "", MI); 645 } else { 646 assert(isa<MemSetInst>(MI)); 647 Value *Ops[] = { 648 EltPtr, MI->getOperand(2), // Dest, Value, 649 ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size 650 Zero // Align 651 }; 652 new CallInst(TheFn, Ops, 4, "", MI); 653 } 654 } 655 656 // Finally, MI is now dead, as we've modified its actions to occur on all of 657 // the elements of the aggregate. 658 ++UI; 659 MI->eraseFromParent(); 660 } 661} 662 663 664/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of 665/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, 666/// or 1 if safe after canonicalization has been performed. 667/// 668int SROA::isSafeAllocaToScalarRepl(AllocationInst *AI) { 669 // Loop over the use list of the alloca. We can only transform it if all of 670 // the users are safe to transform. 671 // 672 int isSafe = 3; 673 for (Value::use_iterator I = AI->use_begin(), E = AI->use_end(); 674 I != E; ++I) { 675 isSafe &= isSafeUseOfAllocation(cast<Instruction>(*I), AI); 676 if (isSafe == 0) { 677 DOUT << "Cannot transform: " << *AI << " due to user: " << **I; 678 return 0; 679 } 680 } 681 // If we require cleanup, isSafe is now 1, otherwise it is 3. 682 return isSafe; 683} 684 685/// CanonicalizeAllocaUsers - If SROA reported that it can promote the specified 686/// allocation, but only if cleaned up, perform the cleanups required. 687void SROA::CanonicalizeAllocaUsers(AllocationInst *AI) { 688 // At this point, we know that the end result will be SROA'd and promoted, so 689 // we can insert ugly code if required so long as sroa+mem2reg will clean it 690 // up. 691 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 692 UI != E; ) { 693 GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI++); 694 if (!GEPI) continue; 695 gep_type_iterator I = gep_type_begin(GEPI); 696 ++I; 697 698 if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) { 699 uint64_t NumElements = AT->getNumElements(); 700 701 if (!isa<ConstantInt>(I.getOperand())) { 702 if (NumElements == 1) { 703 GEPI->setOperand(2, Constant::getNullValue(Type::Int32Ty)); 704 } else { 705 assert(NumElements == 2 && "Unhandled case!"); 706 // All users of the GEP must be loads. At each use of the GEP, insert 707 // two loads of the appropriate indexed GEP and select between them. 708 Value *IsOne = new ICmpInst(ICmpInst::ICMP_NE, I.getOperand(), 709 Constant::getNullValue(I.getOperand()->getType()), 710 "isone", GEPI); 711 // Insert the new GEP instructions, which are properly indexed. 712 SmallVector<Value*, 8> Indices(GEPI->op_begin()+1, GEPI->op_end()); 713 Indices[1] = Constant::getNullValue(Type::Int32Ty); 714 Value *ZeroIdx = new GetElementPtrInst(GEPI->getOperand(0), 715 &Indices[0], Indices.size(), 716 GEPI->getName()+".0", GEPI); 717 Indices[1] = ConstantInt::get(Type::Int32Ty, 1); 718 Value *OneIdx = new GetElementPtrInst(GEPI->getOperand(0), 719 &Indices[0], Indices.size(), 720 GEPI->getName()+".1", GEPI); 721 // Replace all loads of the variable index GEP with loads from both 722 // indexes and a select. 723 while (!GEPI->use_empty()) { 724 LoadInst *LI = cast<LoadInst>(GEPI->use_back()); 725 Value *Zero = new LoadInst(ZeroIdx, LI->getName()+".0", LI); 726 Value *One = new LoadInst(OneIdx , LI->getName()+".1", LI); 727 Value *R = new SelectInst(IsOne, One, Zero, LI->getName(), LI); 728 LI->replaceAllUsesWith(R); 729 LI->eraseFromParent(); 730 } 731 GEPI->eraseFromParent(); 732 } 733 } 734 } 735 } 736} 737 738/// MergeInType - Add the 'In' type to the accumulated type so far. If the 739/// types are incompatible, return true, otherwise update Accum and return 740/// false. 741/// 742/// There are three cases we handle here: 743/// 1) An effectively-integer union, where the pieces are stored into as 744/// smaller integers (common with byte swap and other idioms). 745/// 2) A union of vector types of the same size and potentially its elements. 746/// Here we turn element accesses into insert/extract element operations. 747/// 3) A union of scalar types, such as int/float or int/pointer. Here we 748/// merge together into integers, allowing the xform to work with #1 as 749/// well. 750static bool MergeInType(const Type *In, const Type *&Accum, 751 const TargetData &TD) { 752 // If this is our first type, just use it. 753 const VectorType *PTy; 754 if (Accum == Type::VoidTy || In == Accum) { 755 Accum = In; 756 } else if (In == Type::VoidTy) { 757 // Noop. 758 } else if (In->isInteger() && Accum->isInteger()) { // integer union. 759 // Otherwise pick whichever type is larger. 760 if (cast<IntegerType>(In)->getBitWidth() > 761 cast<IntegerType>(Accum)->getBitWidth()) 762 Accum = In; 763 } else if (isa<PointerType>(In) && isa<PointerType>(Accum)) { 764 // Pointer unions just stay as one of the pointers. 765 } else if (isa<VectorType>(In) || isa<VectorType>(Accum)) { 766 if ((PTy = dyn_cast<VectorType>(Accum)) && 767 PTy->getElementType() == In) { 768 // Accum is a vector, and we are accessing an element: ok. 769 } else if ((PTy = dyn_cast<VectorType>(In)) && 770 PTy->getElementType() == Accum) { 771 // In is a vector, and accum is an element: ok, remember In. 772 Accum = In; 773 } else if ((PTy = dyn_cast<VectorType>(In)) && isa<VectorType>(Accum) && 774 PTy->getBitWidth() == cast<VectorType>(Accum)->getBitWidth()) { 775 // Two vectors of the same size: keep Accum. 776 } else { 777 // Cannot insert an short into a <4 x int> or handle 778 // <2 x int> -> <4 x int> 779 return true; 780 } 781 } else { 782 // Pointer/FP/Integer unions merge together as integers. 783 switch (Accum->getTypeID()) { 784 case Type::PointerTyID: Accum = TD.getIntPtrType(); break; 785 case Type::FloatTyID: Accum = Type::Int32Ty; break; 786 case Type::DoubleTyID: Accum = Type::Int64Ty; break; 787 default: 788 assert(Accum->isInteger() && "Unknown FP type!"); 789 break; 790 } 791 792 switch (In->getTypeID()) { 793 case Type::PointerTyID: In = TD.getIntPtrType(); break; 794 case Type::FloatTyID: In = Type::Int32Ty; break; 795 case Type::DoubleTyID: In = Type::Int64Ty; break; 796 default: 797 assert(In->isInteger() && "Unknown FP type!"); 798 break; 799 } 800 return MergeInType(In, Accum, TD); 801 } 802 return false; 803} 804 805/// getUIntAtLeastAsBitAs - Return an unsigned integer type that is at least 806/// as big as the specified type. If there is no suitable type, this returns 807/// null. 808const Type *getUIntAtLeastAsBitAs(unsigned NumBits) { 809 if (NumBits > 64) return 0; 810 if (NumBits > 32) return Type::Int64Ty; 811 if (NumBits > 16) return Type::Int32Ty; 812 if (NumBits > 8) return Type::Int16Ty; 813 return Type::Int8Ty; 814} 815 816/// CanConvertToScalar - V is a pointer. If we can convert the pointee to a 817/// single scalar integer type, return that type. Further, if the use is not 818/// a completely trivial use that mem2reg could promote, set IsNotTrivial. If 819/// there are no uses of this pointer, return Type::VoidTy to differentiate from 820/// failure. 821/// 822const Type *SROA::CanConvertToScalar(Value *V, bool &IsNotTrivial) { 823 const Type *UsedType = Type::VoidTy; // No uses, no forced type. 824 const TargetData &TD = getAnalysis<TargetData>(); 825 const PointerType *PTy = cast<PointerType>(V->getType()); 826 827 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 828 Instruction *User = cast<Instruction>(*UI); 829 830 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 831 if (MergeInType(LI->getType(), UsedType, TD)) 832 return 0; 833 834 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 835 // Storing the pointer, not into the value? 836 if (SI->getOperand(0) == V) return 0; 837 838 // NOTE: We could handle storing of FP imms into integers here! 839 840 if (MergeInType(SI->getOperand(0)->getType(), UsedType, TD)) 841 return 0; 842 } else if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 843 IsNotTrivial = true; 844 const Type *SubTy = CanConvertToScalar(CI, IsNotTrivial); 845 if (!SubTy || MergeInType(SubTy, UsedType, TD)) return 0; 846 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 847 // Check to see if this is stepping over an element: GEP Ptr, int C 848 if (GEP->getNumOperands() == 2 && isa<ConstantInt>(GEP->getOperand(1))) { 849 unsigned Idx = cast<ConstantInt>(GEP->getOperand(1))->getZExtValue(); 850 unsigned ElSize = TD.getTypeSize(PTy->getElementType()); 851 unsigned BitOffset = Idx*ElSize*8; 852 if (BitOffset > 64 || !isPowerOf2_32(ElSize)) return 0; 853 854 IsNotTrivial = true; 855 const Type *SubElt = CanConvertToScalar(GEP, IsNotTrivial); 856 if (SubElt == 0) return 0; 857 if (SubElt != Type::VoidTy && SubElt->isInteger()) { 858 const Type *NewTy = 859 getUIntAtLeastAsBitAs(TD.getTypeSize(SubElt)*8+BitOffset); 860 if (NewTy == 0 || MergeInType(NewTy, UsedType, TD)) return 0; 861 continue; 862 } 863 } else if (GEP->getNumOperands() == 3 && 864 isa<ConstantInt>(GEP->getOperand(1)) && 865 isa<ConstantInt>(GEP->getOperand(2)) && 866 cast<ConstantInt>(GEP->getOperand(1))->isZero()) { 867 // We are stepping into an element, e.g. a structure or an array: 868 // GEP Ptr, int 0, uint C 869 const Type *AggTy = PTy->getElementType(); 870 unsigned Idx = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 871 872 if (const ArrayType *ATy = dyn_cast<ArrayType>(AggTy)) { 873 if (Idx >= ATy->getNumElements()) return 0; // Out of range. 874 } else if (const VectorType *VectorTy = dyn_cast<VectorType>(AggTy)) { 875 // Getting an element of the packed vector. 876 if (Idx >= VectorTy->getNumElements()) return 0; // Out of range. 877 878 // Merge in the vector type. 879 if (MergeInType(VectorTy, UsedType, TD)) return 0; 880 881 const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial); 882 if (SubTy == 0) return 0; 883 884 if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType, TD)) 885 return 0; 886 887 // We'll need to change this to an insert/extract element operation. 888 IsNotTrivial = true; 889 continue; // Everything looks ok 890 891 } else if (isa<StructType>(AggTy)) { 892 // Structs are always ok. 893 } else { 894 return 0; 895 } 896 const Type *NTy = getUIntAtLeastAsBitAs(TD.getTypeSize(AggTy)*8); 897 if (NTy == 0 || MergeInType(NTy, UsedType, TD)) return 0; 898 const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial); 899 if (SubTy == 0) return 0; 900 if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType, TD)) 901 return 0; 902 continue; // Everything looks ok 903 } 904 return 0; 905 } else { 906 // Cannot handle this! 907 return 0; 908 } 909 } 910 911 return UsedType; 912} 913 914/// ConvertToScalar - The specified alloca passes the CanConvertToScalar 915/// predicate and is non-trivial. Convert it to something that can be trivially 916/// promoted into a register by mem2reg. 917void SROA::ConvertToScalar(AllocationInst *AI, const Type *ActualTy) { 918 DOUT << "CONVERT TO SCALAR: " << *AI << " TYPE = " 919 << *ActualTy << "\n"; 920 ++NumConverted; 921 922 BasicBlock *EntryBlock = AI->getParent(); 923 assert(EntryBlock == &EntryBlock->getParent()->getEntryBlock() && 924 "Not in the entry block!"); 925 EntryBlock->getInstList().remove(AI); // Take the alloca out of the program. 926 927 // Create and insert the alloca. 928 AllocaInst *NewAI = new AllocaInst(ActualTy, 0, AI->getName(), 929 EntryBlock->begin()); 930 ConvertUsesToScalar(AI, NewAI, 0); 931 delete AI; 932} 933 934 935/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca 936/// directly. This happens when we are converting an "integer union" to a 937/// single integer scalar, or when we are converting a "vector union" to a 938/// vector with insert/extractelement instructions. 939/// 940/// Offset is an offset from the original alloca, in bits that need to be 941/// shifted to the right. By the end of this, there should be no uses of Ptr. 942void SROA::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, unsigned Offset) { 943 const TargetData &TD = getAnalysis<TargetData>(); 944 while (!Ptr->use_empty()) { 945 Instruction *User = cast<Instruction>(Ptr->use_back()); 946 947 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 948 // The load is a bit extract from NewAI shifted right by Offset bits. 949 Value *NV = new LoadInst(NewAI, LI->getName(), LI); 950 if (NV->getType() == LI->getType()) { 951 // We win, no conversion needed. 952 } else if (const VectorType *PTy = dyn_cast<VectorType>(NV->getType())) { 953 // If the result alloca is a vector type, this is either an element 954 // access or a bitcast to another vector type. 955 if (isa<VectorType>(LI->getType())) { 956 NV = new BitCastInst(NV, LI->getType(), LI->getName(), LI); 957 } else { 958 // Must be an element access. 959 unsigned Elt = Offset/(TD.getTypeSize(PTy->getElementType())*8); 960 NV = new ExtractElementInst( 961 NV, ConstantInt::get(Type::Int32Ty, Elt), "tmp", LI); 962 } 963 } else if (isa<PointerType>(NV->getType())) { 964 assert(isa<PointerType>(LI->getType())); 965 // Must be ptr->ptr cast. Anything else would result in NV being 966 // an integer. 967 NV = new BitCastInst(NV, LI->getType(), LI->getName(), LI); 968 } else { 969 const IntegerType *NTy = cast<IntegerType>(NV->getType()); 970 unsigned LIBitWidth = TD.getTypeSizeInBits(LI->getType()); 971 972 // If this is a big-endian system and the load is narrower than the 973 // full alloca type, we need to do a shift to get the right bits. 974 int ShAmt = 0; 975 if (TD.isBigEndian()) { 976 ShAmt = NTy->getBitWidth()-LIBitWidth-Offset; 977 } else { 978 ShAmt = Offset; 979 } 980 981 // Note: we support negative bitwidths (with shl) which are not defined. 982 // We do this to support (f.e.) loads off the end of a structure where 983 // only some bits are used. 984 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth()) 985 NV = BinaryOperator::createLShr(NV, 986 ConstantInt::get(NV->getType(),ShAmt), 987 LI->getName(), LI); 988 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) 989 NV = BinaryOperator::createShl(NV, 990 ConstantInt::get(NV->getType(),-ShAmt), 991 LI->getName(), LI); 992 993 // Finally, unconditionally truncate the integer to the right width. 994 if (LIBitWidth < NTy->getBitWidth()) 995 NV = new TruncInst(NV, IntegerType::get(LIBitWidth), 996 LI->getName(), LI); 997 998 // If the result is an integer, this is a trunc or bitcast. 999 if (isa<IntegerType>(LI->getType())) { 1000 assert(NV->getType() == LI->getType() && "Truncate wasn't enough?"); 1001 } else if (LI->getType()->isFloatingPoint()) { 1002 // Just do a bitcast, we know the sizes match up. 1003 NV = new BitCastInst(NV, LI->getType(), LI->getName(), LI); 1004 } else { 1005 // Otherwise must be a pointer. 1006 NV = new IntToPtrInst(NV, LI->getType(), LI->getName(), LI); 1007 } 1008 } 1009 LI->replaceAllUsesWith(NV); 1010 LI->eraseFromParent(); 1011 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 1012 assert(SI->getOperand(0) != Ptr && "Consistency error!"); 1013 1014 // Convert the stored type to the actual type, shift it left to insert 1015 // then 'or' into place. 1016 Value *SV = SI->getOperand(0); 1017 const Type *AllocaType = NewAI->getType()->getElementType(); 1018 if (SV->getType() == AllocaType) { 1019 // All is well. 1020 } else if (const VectorType *PTy = dyn_cast<VectorType>(AllocaType)) { 1021 Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI); 1022 1023 // If the result alloca is a vector type, this is either an element 1024 // access or a bitcast to another vector type. 1025 if (isa<VectorType>(SV->getType())) { 1026 SV = new BitCastInst(SV, AllocaType, SV->getName(), SI); 1027 } else { 1028 // Must be an element insertion. 1029 unsigned Elt = Offset/(TD.getTypeSize(PTy->getElementType())*8); 1030 SV = new InsertElementInst(Old, SV, 1031 ConstantInt::get(Type::Int32Ty, Elt), 1032 "tmp", SI); 1033 } 1034 } else if (isa<PointerType>(AllocaType)) { 1035 // If the alloca type is a pointer, then all the elements must be 1036 // pointers. 1037 if (SV->getType() != AllocaType) 1038 SV = new BitCastInst(SV, AllocaType, SV->getName(), SI); 1039 } else { 1040 Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI); 1041 1042 // If SV is a float, convert it to the appropriate integer type. 1043 // If it is a pointer, do the same, and also handle ptr->ptr casts 1044 // here. 1045 unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType()); 1046 unsigned DestWidth = AllocaType->getPrimitiveSizeInBits(); 1047 if (SV->getType()->isFloatingPoint()) 1048 SV = new BitCastInst(SV, IntegerType::get(SrcWidth), 1049 SV->getName(), SI); 1050 else if (isa<PointerType>(SV->getType())) 1051 SV = new PtrToIntInst(SV, TD.getIntPtrType(), SV->getName(), SI); 1052 1053 // Always zero extend the value if needed. 1054 if (SV->getType() != AllocaType) 1055 SV = new ZExtInst(SV, AllocaType, SV->getName(), SI); 1056 1057 // If this is a big-endian system and the store is narrower than the 1058 // full alloca type, we need to do a shift to get the right bits. 1059 int ShAmt = 0; 1060 if (TD.isBigEndian()) { 1061 ShAmt = DestWidth-SrcWidth-Offset; 1062 } else { 1063 ShAmt = Offset; 1064 } 1065 1066 // Note: we support negative bitwidths (with shr) which are not defined. 1067 // We do this to support (f.e.) stores off the end of a structure where 1068 // only some bits in the structure are set. 1069 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth)); 1070 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) { 1071 SV = BinaryOperator::createShl(SV, 1072 ConstantInt::get(SV->getType(), ShAmt), 1073 SV->getName(), SI); 1074 Mask <<= ShAmt; 1075 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { 1076 SV = BinaryOperator::createLShr(SV, 1077 ConstantInt::get(SV->getType(),-ShAmt), 1078 SV->getName(), SI); 1079 Mask = Mask.lshr(ShAmt); 1080 } 1081 1082 // Mask out the bits we are about to insert from the old value, and or 1083 // in the new bits. 1084 if (SrcWidth != DestWidth) { 1085 assert(DestWidth > SrcWidth); 1086 Old = BinaryOperator::createAnd(Old, ConstantInt::get(~Mask), 1087 Old->getName()+".mask", SI); 1088 SV = BinaryOperator::createOr(Old, SV, SV->getName()+".ins", SI); 1089 } 1090 } 1091 new StoreInst(SV, NewAI, SI); 1092 SI->eraseFromParent(); 1093 1094 } else if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { 1095 ConvertUsesToScalar(CI, NewAI, Offset); 1096 CI->eraseFromParent(); 1097 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 1098 const PointerType *AggPtrTy = 1099 cast<PointerType>(GEP->getOperand(0)->getType()); 1100 const TargetData &TD = getAnalysis<TargetData>(); 1101 unsigned AggSizeInBits = TD.getTypeSize(AggPtrTy->getElementType())*8; 1102 1103 // Check to see if this is stepping over an element: GEP Ptr, int C 1104 unsigned NewOffset = Offset; 1105 if (GEP->getNumOperands() == 2) { 1106 unsigned Idx = cast<ConstantInt>(GEP->getOperand(1))->getZExtValue(); 1107 unsigned BitOffset = Idx*AggSizeInBits; 1108 1109 NewOffset += BitOffset; 1110 } else if (GEP->getNumOperands() == 3) { 1111 // We know that operand #2 is zero. 1112 unsigned Idx = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); 1113 const Type *AggTy = AggPtrTy->getElementType(); 1114 if (const SequentialType *SeqTy = dyn_cast<SequentialType>(AggTy)) { 1115 unsigned ElSizeBits = TD.getTypeSize(SeqTy->getElementType())*8; 1116 1117 NewOffset += ElSizeBits*Idx; 1118 } else if (const StructType *STy = dyn_cast<StructType>(AggTy)) { 1119 unsigned EltBitOffset = 1120 TD.getStructLayout(STy)->getElementOffset(Idx)*8; 1121 1122 NewOffset += EltBitOffset; 1123 } else { 1124 assert(0 && "Unsupported operation!"); 1125 abort(); 1126 } 1127 } else { 1128 assert(0 && "Unsupported operation!"); 1129 abort(); 1130 } 1131 ConvertUsesToScalar(GEP, NewAI, NewOffset); 1132 GEP->eraseFromParent(); 1133 } else { 1134 assert(0 && "Unsupported operation!"); 1135 abort(); 1136 } 1137 } 1138} 1139 1140 1141/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to 1142/// some part of a constant global variable. This intentionally only accepts 1143/// constant expressions because we don't can't rewrite arbitrary instructions. 1144static bool PointsToConstantGlobal(Value *V) { 1145 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) 1146 return GV->isConstant(); 1147 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 1148 if (CE->getOpcode() == Instruction::BitCast || 1149 CE->getOpcode() == Instruction::GetElementPtr) 1150 return PointsToConstantGlobal(CE->getOperand(0)); 1151 return false; 1152} 1153 1154/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived) 1155/// pointer to an alloca. Ignore any reads of the pointer, return false if we 1156/// see any stores or other unknown uses. If we see pointer arithmetic, keep 1157/// track of whether it moves the pointer (with isOffset) but otherwise traverse 1158/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to 1159/// the alloca, and if the source pointer is a pointer to a constant global, we 1160/// can optimize this. 1161static bool isOnlyCopiedFromConstantGlobal(Value *V, Instruction *&TheCopy, 1162 bool isOffset) { 1163 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 1164 if (isa<LoadInst>(*UI)) { 1165 // Ignore loads, they are always ok. 1166 continue; 1167 } 1168 if (BitCastInst *BCI = dyn_cast<BitCastInst>(*UI)) { 1169 // If uses of the bitcast are ok, we are ok. 1170 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) 1171 return false; 1172 continue; 1173 } 1174 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) { 1175 // If the GEP has all zero indices, it doesn't offset the pointer. If it 1176 // doesn't, it does. 1177 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy, 1178 isOffset || !GEP->hasAllZeroIndices())) 1179 return false; 1180 continue; 1181 } 1182 1183 // If this is isn't our memcpy/memmove, reject it as something we can't 1184 // handle. 1185 if (!isa<MemCpyInst>(*UI) && !isa<MemMoveInst>(*UI)) 1186 return false; 1187 1188 // If we already have seen a copy, reject the second one. 1189 if (TheCopy) return false; 1190 1191 // If the pointer has been offset from the start of the alloca, we can't 1192 // safely handle this. 1193 if (isOffset) return false; 1194 1195 // If the memintrinsic isn't using the alloca as the dest, reject it. 1196 if (UI.getOperandNo() != 1) return false; 1197 1198 MemIntrinsic *MI = cast<MemIntrinsic>(*UI); 1199 1200 // If the source of the memcpy/move is not a constant global, reject it. 1201 if (!PointsToConstantGlobal(MI->getOperand(2))) 1202 return false; 1203 1204 // Otherwise, the transform is safe. Remember the copy instruction. 1205 TheCopy = MI; 1206 } 1207 return true; 1208} 1209 1210/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only 1211/// modified by a copy from a constant global. If we can prove this, we can 1212/// replace any uses of the alloca with uses of the global directly. 1213Instruction *SROA::isOnlyCopiedFromConstantGlobal(AllocationInst *AI) { 1214 Instruction *TheCopy = 0; 1215 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) 1216 return TheCopy; 1217 return 0; 1218} 1219