LLVM API Documentation
00001 //===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // This transformation implements the well known scalar replacement of 00011 // aggregates transformation. This xform breaks up alloca instructions of 00012 // aggregate type (structure or array) into individual alloca instructions for 00013 // each member (if possible). Then, if possible, it transforms the individual 00014 // alloca instructions into nice clean scalar SSA form. 00015 // 00016 // This combines a simple SRoA algorithm with the Mem2Reg algorithm because 00017 // often interact, especially for C++ programs. As such, iterating between 00018 // SRoA, then Mem2Reg until we run out of things to promote works well. 00019 // 00020 //===----------------------------------------------------------------------===// 00021 00022 #include "llvm/Transforms/Scalar.h" 00023 #include "llvm/Constants.h" 00024 #include "llvm/DerivedTypes.h" 00025 #include "llvm/Function.h" 00026 #include "llvm/Pass.h" 00027 #include "llvm/Instructions.h" 00028 #include "llvm/Analysis/Dominators.h" 00029 #include "llvm/Target/TargetData.h" 00030 #include "llvm/Transforms/Utils/PromoteMemToReg.h" 00031 #include "llvm/Support/Debug.h" 00032 #include "llvm/Support/GetElementPtrTypeIterator.h" 00033 #include "llvm/Support/MathExtras.h" 00034 #include "llvm/Support/Visibility.h" 00035 #include "llvm/ADT/Statistic.h" 00036 #include "llvm/ADT/StringExtras.h" 00037 #include <iostream> 00038 using namespace llvm; 00039 00040 namespace { 00041 Statistic<> NumReplaced("scalarrepl", "Number of allocas broken up"); 00042 Statistic<> NumPromoted("scalarrepl", "Number of allocas promoted"); 00043 Statistic<> NumConverted("scalarrepl", 00044 "Number of aggregates converted to scalar"); 00045 00046 struct VISIBILITY_HIDDEN SROA : public FunctionPass { 00047 bool runOnFunction(Function &F); 00048 00049 bool performScalarRepl(Function &F); 00050 bool performPromotion(Function &F); 00051 00052 // getAnalysisUsage - This pass does not require any passes, but we know it 00053 // will not alter the CFG, so say so. 00054 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 00055 AU.addRequired<DominatorTree>(); 00056 AU.addRequired<DominanceFrontier>(); 00057 AU.addRequired<TargetData>(); 00058 AU.setPreservesCFG(); 00059 } 00060 00061 private: 00062 int isSafeElementUse(Value *Ptr); 00063 int isSafeUseOfAllocation(Instruction *User); 00064 int isSafeAllocaToScalarRepl(AllocationInst *AI); 00065 void CanonicalizeAllocaUsers(AllocationInst *AI); 00066 AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocationInst *Base); 00067 00068 const Type *CanConvertToScalar(Value *V, bool &IsNotTrivial); 00069 void ConvertToScalar(AllocationInst *AI, const Type *Ty); 00070 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, unsigned Offset); 00071 }; 00072 00073 RegisterOpt<SROA> X("scalarrepl", "Scalar Replacement of Aggregates"); 00074 } 00075 00076 // Public interface to the ScalarReplAggregates pass 00077 FunctionPass *llvm::createScalarReplAggregatesPass() { return new SROA(); } 00078 00079 00080 bool SROA::runOnFunction(Function &F) { 00081 bool Changed = performPromotion(F); 00082 while (1) { 00083 bool LocalChange = performScalarRepl(F); 00084 if (!LocalChange) break; // No need to repromote if no scalarrepl 00085 Changed = true; 00086 LocalChange = performPromotion(F); 00087 if (!LocalChange) break; // No need to re-scalarrepl if no promotion 00088 } 00089 00090 return Changed; 00091 } 00092 00093 00094 bool SROA::performPromotion(Function &F) { 00095 std::vector<AllocaInst*> Allocas; 00096 const TargetData &TD = getAnalysis<TargetData>(); 00097 DominatorTree &DT = getAnalysis<DominatorTree>(); 00098 DominanceFrontier &DF = getAnalysis<DominanceFrontier>(); 00099 00100 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function 00101 00102 bool Changed = false; 00103 00104 while (1) { 00105 Allocas.clear(); 00106 00107 // Find allocas that are safe to promote, by looking at all instructions in 00108 // the entry node 00109 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) 00110 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? 00111 if (isAllocaPromotable(AI, TD)) 00112 Allocas.push_back(AI); 00113 00114 if (Allocas.empty()) break; 00115 00116 PromoteMemToReg(Allocas, DT, DF, TD); 00117 NumPromoted += Allocas.size(); 00118 Changed = true; 00119 } 00120 00121 return Changed; 00122 } 00123 00124 // performScalarRepl - This algorithm is a simple worklist driven algorithm, 00125 // which runs on all of the malloc/alloca instructions in the function, removing 00126 // them if they are only used by getelementptr instructions. 00127 // 00128 bool SROA::performScalarRepl(Function &F) { 00129 std::vector<AllocationInst*> WorkList; 00130 00131 // Scan the entry basic block, adding any alloca's and mallocs to the worklist 00132 BasicBlock &BB = F.getEntryBlock(); 00133 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) 00134 if (AllocationInst *A = dyn_cast<AllocationInst>(I)) 00135 WorkList.push_back(A); 00136 00137 // Process the worklist 00138 bool Changed = false; 00139 while (!WorkList.empty()) { 00140 AllocationInst *AI = WorkList.back(); 00141 WorkList.pop_back(); 00142 00143 // If we can turn this aggregate value (potentially with casts) into a 00144 // simple scalar value that can be mem2reg'd into a register value. 00145 bool IsNotTrivial = false; 00146 if (const Type *ActualType = CanConvertToScalar(AI, IsNotTrivial)) 00147 if (IsNotTrivial && ActualType != Type::VoidTy) { 00148 ConvertToScalar(AI, ActualType); 00149 Changed = true; 00150 continue; 00151 } 00152 00153 // We cannot transform the allocation instruction if it is an array 00154 // allocation (allocations OF arrays are ok though), and an allocation of a 00155 // scalar value cannot be decomposed at all. 00156 // 00157 if (AI->isArrayAllocation() || 00158 (!isa<StructType>(AI->getAllocatedType()) && 00159 !isa<ArrayType>(AI->getAllocatedType()))) continue; 00160 00161 // Check that all of the users of the allocation are capable of being 00162 // transformed. 00163 switch (isSafeAllocaToScalarRepl(AI)) { 00164 default: assert(0 && "Unexpected value!"); 00165 case 0: // Not safe to scalar replace. 00166 continue; 00167 case 1: // Safe, but requires cleanup/canonicalizations first 00168 CanonicalizeAllocaUsers(AI); 00169 case 3: // Safe to scalar replace. 00170 break; 00171 } 00172 00173 DEBUG(std::cerr << "Found inst to xform: " << *AI); 00174 Changed = true; 00175 00176 std::vector<AllocaInst*> ElementAllocas; 00177 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { 00178 ElementAllocas.reserve(ST->getNumContainedTypes()); 00179 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { 00180 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 00181 AI->getAlignment(), 00182 AI->getName() + "." + utostr(i), AI); 00183 ElementAllocas.push_back(NA); 00184 WorkList.push_back(NA); // Add to worklist for recursive processing 00185 } 00186 } else { 00187 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); 00188 ElementAllocas.reserve(AT->getNumElements()); 00189 const Type *ElTy = AT->getElementType(); 00190 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { 00191 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(), 00192 AI->getName() + "." + utostr(i), AI); 00193 ElementAllocas.push_back(NA); 00194 WorkList.push_back(NA); // Add to worklist for recursive processing 00195 } 00196 } 00197 00198 // Now that we have created the alloca instructions that we want to use, 00199 // expand the getelementptr instructions to use them. 00200 // 00201 while (!AI->use_empty()) { 00202 Instruction *User = cast<Instruction>(AI->use_back()); 00203 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User); 00204 // We now know that the GEP is of the form: GEP <ptr>, 0, <cst> 00205 unsigned Idx = 00206 (unsigned)cast<ConstantInt>(GEPI->getOperand(2))->getRawValue(); 00207 00208 assert(Idx < ElementAllocas.size() && "Index out of range?"); 00209 AllocaInst *AllocaToUse = ElementAllocas[Idx]; 00210 00211 Value *RepValue; 00212 if (GEPI->getNumOperands() == 3) { 00213 // Do not insert a new getelementptr instruction with zero indices, only 00214 // to have it optimized out later. 00215 RepValue = AllocaToUse; 00216 } else { 00217 // We are indexing deeply into the structure, so we still need a 00218 // getelement ptr instruction to finish the indexing. This may be 00219 // expanded itself once the worklist is rerun. 00220 // 00221 std::string OldName = GEPI->getName(); // Steal the old name. 00222 std::vector<Value*> NewArgs; 00223 NewArgs.push_back(Constant::getNullValue(Type::IntTy)); 00224 NewArgs.insert(NewArgs.end(), GEPI->op_begin()+3, GEPI->op_end()); 00225 GEPI->setName(""); 00226 RepValue = new GetElementPtrInst(AllocaToUse, NewArgs, OldName, GEPI); 00227 } 00228 00229 // Move all of the users over to the new GEP. 00230 GEPI->replaceAllUsesWith(RepValue); 00231 // Delete the old GEP 00232 GEPI->eraseFromParent(); 00233 } 00234 00235 // Finally, delete the Alloca instruction 00236 AI->getParent()->getInstList().erase(AI); 00237 NumReplaced++; 00238 } 00239 00240 return Changed; 00241 } 00242 00243 00244 /// isSafeElementUse - Check to see if this use is an allowed use for a 00245 /// getelementptr instruction of an array aggregate allocation. 00246 /// 00247 int SROA::isSafeElementUse(Value *Ptr) { 00248 for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); 00249 I != E; ++I) { 00250 Instruction *User = cast<Instruction>(*I); 00251 switch (User->getOpcode()) { 00252 case Instruction::Load: break; 00253 case Instruction::Store: 00254 // Store is ok if storing INTO the pointer, not storing the pointer 00255 if (User->getOperand(0) == Ptr) return 0; 00256 break; 00257 case Instruction::GetElementPtr: { 00258 GetElementPtrInst *GEP = cast<GetElementPtrInst>(User); 00259 if (GEP->getNumOperands() > 1) { 00260 if (!isa<Constant>(GEP->getOperand(1)) || 00261 !cast<Constant>(GEP->getOperand(1))->isNullValue()) 00262 return 0; // Using pointer arithmetic to navigate the array... 00263 } 00264 if (!isSafeElementUse(GEP)) return 0; 00265 break; 00266 } 00267 default: 00268 DEBUG(std::cerr << " Transformation preventing inst: " << *User); 00269 return 0; 00270 } 00271 } 00272 return 3; // All users look ok :) 00273 } 00274 00275 /// AllUsersAreLoads - Return true if all users of this value are loads. 00276 static bool AllUsersAreLoads(Value *Ptr) { 00277 for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); 00278 I != E; ++I) 00279 if (cast<Instruction>(*I)->getOpcode() != Instruction::Load) 00280 return false; 00281 return true; 00282 } 00283 00284 /// isSafeUseOfAllocation - Check to see if this user is an allowed use for an 00285 /// aggregate allocation. 00286 /// 00287 int SROA::isSafeUseOfAllocation(Instruction *User) { 00288 if (!isa<GetElementPtrInst>(User)) return 0; 00289 00290 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User); 00291 gep_type_iterator I = gep_type_begin(GEPI), E = gep_type_end(GEPI); 00292 00293 // The GEP is not safe to transform if not of the form "GEP <ptr>, 0, <cst>". 00294 if (I == E || 00295 I.getOperand() != Constant::getNullValue(I.getOperand()->getType())) 00296 return 0; 00297 00298 ++I; 00299 if (I == E) return 0; // ran out of GEP indices?? 00300 00301 // If this is a use of an array allocation, do a bit more checking for sanity. 00302 if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) { 00303 uint64_t NumElements = AT->getNumElements(); 00304 00305 if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) { 00306 // Check to make sure that index falls within the array. If not, 00307 // something funny is going on, so we won't do the optimization. 00308 // 00309 if (cast<ConstantInt>(GEPI->getOperand(2))->getRawValue() >= NumElements) 00310 return 0; 00311 00312 // We cannot scalar repl this level of the array unless any array 00313 // sub-indices are in-range constants. In particular, consider: 00314 // A[0][i]. We cannot know that the user isn't doing invalid things like 00315 // allowing i to index an out-of-range subscript that accesses A[1]. 00316 // 00317 // Scalar replacing *just* the outer index of the array is probably not 00318 // going to be a win anyway, so just give up. 00319 for (++I; I != E && isa<ArrayType>(*I); ++I) { 00320 const ArrayType *SubArrayTy = cast<ArrayType>(*I); 00321 uint64_t NumElements = SubArrayTy->getNumElements(); 00322 if (!isa<ConstantInt>(I.getOperand())) return 0; 00323 if (cast<ConstantInt>(I.getOperand())->getRawValue() >= NumElements) 00324 return 0; 00325 } 00326 00327 } else { 00328 // If this is an array index and the index is not constant, we cannot 00329 // promote... that is unless the array has exactly one or two elements in 00330 // it, in which case we CAN promote it, but we have to canonicalize this 00331 // out if this is the only problem. 00332 if ((NumElements == 1 || NumElements == 2) && 00333 AllUsersAreLoads(GEPI)) 00334 return 1; // Canonicalization required! 00335 return 0; 00336 } 00337 } 00338 00339 // If there are any non-simple uses of this getelementptr, make sure to reject 00340 // them. 00341 return isSafeElementUse(GEPI); 00342 } 00343 00344 /// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of 00345 /// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, 00346 /// or 1 if safe after canonicalization has been performed. 00347 /// 00348 int SROA::isSafeAllocaToScalarRepl(AllocationInst *AI) { 00349 // Loop over the use list of the alloca. We can only transform it if all of 00350 // the users are safe to transform. 00351 // 00352 int isSafe = 3; 00353 for (Value::use_iterator I = AI->use_begin(), E = AI->use_end(); 00354 I != E; ++I) { 00355 isSafe &= isSafeUseOfAllocation(cast<Instruction>(*I)); 00356 if (isSafe == 0) { 00357 DEBUG(std::cerr << "Cannot transform: " << *AI << " due to user: " 00358 << **I); 00359 return 0; 00360 } 00361 } 00362 // If we require cleanup, isSafe is now 1, otherwise it is 3. 00363 return isSafe; 00364 } 00365 00366 /// CanonicalizeAllocaUsers - If SROA reported that it can promote the specified 00367 /// allocation, but only if cleaned up, perform the cleanups required. 00368 void SROA::CanonicalizeAllocaUsers(AllocationInst *AI) { 00369 // At this point, we know that the end result will be SROA'd and promoted, so 00370 // we can insert ugly code if required so long as sroa+mem2reg will clean it 00371 // up. 00372 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); 00373 UI != E; ) { 00374 GetElementPtrInst *GEPI = cast<GetElementPtrInst>(*UI++); 00375 gep_type_iterator I = gep_type_begin(GEPI); 00376 ++I; 00377 00378 if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) { 00379 uint64_t NumElements = AT->getNumElements(); 00380 00381 if (!isa<ConstantInt>(I.getOperand())) { 00382 if (NumElements == 1) { 00383 GEPI->setOperand(2, Constant::getNullValue(Type::IntTy)); 00384 } else { 00385 assert(NumElements == 2 && "Unhandled case!"); 00386 // All users of the GEP must be loads. At each use of the GEP, insert 00387 // two loads of the appropriate indexed GEP and select between them. 00388 Value *IsOne = BinaryOperator::createSetNE(I.getOperand(), 00389 Constant::getNullValue(I.getOperand()->getType()), 00390 "isone", GEPI); 00391 // Insert the new GEP instructions, which are properly indexed. 00392 std::vector<Value*> Indices(GEPI->op_begin()+1, GEPI->op_end()); 00393 Indices[1] = Constant::getNullValue(Type::IntTy); 00394 Value *ZeroIdx = new GetElementPtrInst(GEPI->getOperand(0), Indices, 00395 GEPI->getName()+".0", GEPI); 00396 Indices[1] = ConstantInt::get(Type::IntTy, 1); 00397 Value *OneIdx = new GetElementPtrInst(GEPI->getOperand(0), Indices, 00398 GEPI->getName()+".1", GEPI); 00399 // Replace all loads of the variable index GEP with loads from both 00400 // indexes and a select. 00401 while (!GEPI->use_empty()) { 00402 LoadInst *LI = cast<LoadInst>(GEPI->use_back()); 00403 Value *Zero = new LoadInst(ZeroIdx, LI->getName()+".0", LI); 00404 Value *One = new LoadInst(OneIdx , LI->getName()+".1", LI); 00405 Value *R = new SelectInst(IsOne, One, Zero, LI->getName(), LI); 00406 LI->replaceAllUsesWith(R); 00407 LI->eraseFromParent(); 00408 } 00409 GEPI->eraseFromParent(); 00410 } 00411 } 00412 } 00413 } 00414 } 00415 00416 /// MergeInType - Add the 'In' type to the accumulated type so far. If the 00417 /// types are incompatible, return true, otherwise update Accum and return 00418 /// false. 00419 /// 00420 /// There are two cases we handle here: 00421 /// 1) An effectively integer union, where the pieces are stored into as 00422 /// smaller integers (common with byte swap and other idioms). 00423 /// 2) A union of a vector and its elements. Here we turn element accesses 00424 /// into insert/extract element operations. 00425 static bool MergeInType(const Type *In, const Type *&Accum) { 00426 // If this is our first type, just use it. 00427 const PackedType *PTy; 00428 if (Accum == Type::VoidTy || In == Accum) { 00429 Accum = In; 00430 } else if (In->isIntegral() && Accum->isIntegral()) { // integer union. 00431 // Otherwise pick whichever type is larger. 00432 if (In->getTypeID() > Accum->getTypeID()) 00433 Accum = In; 00434 } else if ((PTy = dyn_cast<PackedType>(Accum)) && 00435 PTy->getElementType() == In) { 00436 // Accum is a vector, and we are accessing an element: ok. 00437 } else if ((PTy = dyn_cast<PackedType>(In)) && 00438 PTy->getElementType() == Accum) { 00439 // In is a vector, and accum is an element: ok, remember In. 00440 Accum = In; 00441 } else { 00442 return true; 00443 } 00444 return false; 00445 } 00446 00447 /// getUIntAtLeastAsBitAs - Return an unsigned integer type that is at least 00448 /// as big as the specified type. If there is no suitable type, this returns 00449 /// null. 00450 const Type *getUIntAtLeastAsBitAs(unsigned NumBits) { 00451 if (NumBits > 64) return 0; 00452 if (NumBits > 32) return Type::ULongTy; 00453 if (NumBits > 16) return Type::UIntTy; 00454 if (NumBits > 8) return Type::UShortTy; 00455 return Type::UByteTy; 00456 } 00457 00458 /// CanConvertToScalar - V is a pointer. If we can convert the pointee to a 00459 /// single scalar integer type, return that type. Further, if the use is not 00460 /// a completely trivial use that mem2reg could promote, set IsNotTrivial. If 00461 /// there are no uses of this pointer, return Type::VoidTy to differentiate from 00462 /// failure. 00463 /// 00464 const Type *SROA::CanConvertToScalar(Value *V, bool &IsNotTrivial) { 00465 const Type *UsedType = Type::VoidTy; // No uses, no forced type. 00466 const TargetData &TD = getAnalysis<TargetData>(); 00467 const PointerType *PTy = cast<PointerType>(V->getType()); 00468 00469 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { 00470 Instruction *User = cast<Instruction>(*UI); 00471 00472 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 00473 if (MergeInType(LI->getType(), UsedType)) 00474 return 0; 00475 00476 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 00477 // Storing the pointer, not the into the value? 00478 if (SI->getOperand(0) == V) return 0; 00479 00480 // NOTE: We could handle storing of FP imms into integers here! 00481 00482 if (MergeInType(SI->getOperand(0)->getType(), UsedType)) 00483 return 0; 00484 } else if (CastInst *CI = dyn_cast<CastInst>(User)) { 00485 if (!isa<PointerType>(CI->getType())) return 0; 00486 IsNotTrivial = true; 00487 const Type *SubTy = CanConvertToScalar(CI, IsNotTrivial); 00488 if (!SubTy || MergeInType(SubTy, UsedType)) return 0; 00489 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 00490 // Check to see if this is stepping over an element: GEP Ptr, int C 00491 if (GEP->getNumOperands() == 2 && isa<ConstantInt>(GEP->getOperand(1))) { 00492 unsigned Idx = cast<ConstantInt>(GEP->getOperand(1))->getRawValue(); 00493 unsigned ElSize = TD.getTypeSize(PTy->getElementType()); 00494 unsigned BitOffset = Idx*ElSize*8; 00495 if (BitOffset > 64 || !isPowerOf2_32(ElSize)) return 0; 00496 00497 IsNotTrivial = true; 00498 const Type *SubElt = CanConvertToScalar(GEP, IsNotTrivial); 00499 if (SubElt == 0) return 0; 00500 if (SubElt != Type::VoidTy && SubElt->isInteger()) { 00501 const Type *NewTy = 00502 getUIntAtLeastAsBitAs(SubElt->getPrimitiveSizeInBits()+BitOffset); 00503 if (NewTy == 0 || MergeInType(NewTy, UsedType)) return 0; 00504 continue; 00505 } 00506 } else if (GEP->getNumOperands() == 3 && 00507 isa<ConstantInt>(GEP->getOperand(1)) && 00508 isa<ConstantInt>(GEP->getOperand(2)) && 00509 cast<Constant>(GEP->getOperand(1))->isNullValue()) { 00510 // We are stepping into an element, e.g. a structure or an array: 00511 // GEP Ptr, int 0, uint C 00512 const Type *AggTy = PTy->getElementType(); 00513 unsigned Idx = cast<ConstantInt>(GEP->getOperand(2))->getRawValue(); 00514 00515 if (const ArrayType *ATy = dyn_cast<ArrayType>(AggTy)) { 00516 if (Idx >= ATy->getNumElements()) return 0; // Out of range. 00517 } else if (const PackedType *PackedTy = dyn_cast<PackedType>(AggTy)) { 00518 // Getting an element of the packed vector. 00519 if (Idx >= PackedTy->getNumElements()) return 0; // Out of range. 00520 00521 // Merge in the packed type. 00522 if (MergeInType(PackedTy, UsedType)) return 0; 00523 00524 const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial); 00525 if (SubTy == 0) return 0; 00526 00527 if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType)) 00528 return 0; 00529 00530 // We'll need to change this to an insert/extract element operation. 00531 IsNotTrivial = true; 00532 continue; // Everything looks ok 00533 00534 } else if (isa<StructType>(AggTy)) { 00535 // Structs are always ok. 00536 } else { 00537 return 0; 00538 } 00539 const Type *NTy = getUIntAtLeastAsBitAs(TD.getTypeSize(AggTy)*8); 00540 if (NTy == 0 || MergeInType(NTy, UsedType)) return 0; 00541 const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial); 00542 if (SubTy == 0) return 0; 00543 if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType)) 00544 return 0; 00545 continue; // Everything looks ok 00546 } 00547 return 0; 00548 } else { 00549 // Cannot handle this! 00550 return 0; 00551 } 00552 } 00553 00554 return UsedType; 00555 } 00556 00557 /// ConvertToScalar - The specified alloca passes the CanConvertToScalar 00558 /// predicate and is non-trivial. Convert it to something that can be trivially 00559 /// promoted into a register by mem2reg. 00560 void SROA::ConvertToScalar(AllocationInst *AI, const Type *ActualTy) { 00561 DEBUG(std::cerr << "CONVERT TO SCALAR: " << *AI << " TYPE = " 00562 << *ActualTy << "\n"); 00563 ++NumConverted; 00564 00565 BasicBlock *EntryBlock = AI->getParent(); 00566 assert(EntryBlock == &EntryBlock->getParent()->front() && 00567 "Not in the entry block!"); 00568 EntryBlock->getInstList().remove(AI); // Take the alloca out of the program. 00569 00570 if (ActualTy->isInteger()) 00571 ActualTy = ActualTy->getUnsignedVersion(); 00572 00573 // Create and insert the alloca. 00574 AllocaInst *NewAI = new AllocaInst(ActualTy, 0, AI->getName(), 00575 EntryBlock->begin()); 00576 ConvertUsesToScalar(AI, NewAI, 0); 00577 delete AI; 00578 } 00579 00580 00581 /// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca 00582 /// directly. This happens when we are converting an "integer union" to a 00583 /// single integer scalar, or when we are converting a "vector union" to a 00584 /// vector with insert/extractelement instructions. 00585 /// 00586 /// Offset is an offset from the original alloca, in bits that need to be 00587 /// shifted to the right. By the end of this, there should be no uses of Ptr. 00588 void SROA::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, unsigned Offset) { 00589 bool isVectorInsert = isa<PackedType>(NewAI->getType()->getElementType()); 00590 while (!Ptr->use_empty()) { 00591 Instruction *User = cast<Instruction>(Ptr->use_back()); 00592 00593 if (LoadInst *LI = dyn_cast<LoadInst>(User)) { 00594 // The load is a bit extract from NewAI shifted right by Offset bits. 00595 Value *NV = new LoadInst(NewAI, LI->getName(), LI); 00596 if (NV->getType() != LI->getType()) { 00597 if (const PackedType *PTy = dyn_cast<PackedType>(NV->getType())) { 00598 // Must be an element access. 00599 unsigned Elt = Offset/PTy->getElementType()->getPrimitiveSizeInBits(); 00600 NV = new ExtractElementInst(NV, ConstantUInt::get(Type::UIntTy, Elt), 00601 "tmp", LI); 00602 } else { 00603 assert(NV->getType()->isInteger() && "Unknown promotion!"); 00604 if (Offset && Offset < NV->getType()->getPrimitiveSizeInBits()) 00605 NV = new ShiftInst(Instruction::Shr, NV, 00606 ConstantUInt::get(Type::UByteTy, Offset), 00607 LI->getName(), LI); 00608 NV = new CastInst(NV, LI->getType(), LI->getName(), LI); 00609 } 00610 } 00611 LI->replaceAllUsesWith(NV); 00612 LI->eraseFromParent(); 00613 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { 00614 assert(SI->getOperand(0) != Ptr && "Consistency error!"); 00615 00616 // Convert the stored type to the actual type, shift it left to insert 00617 // then 'or' into place. 00618 Value *SV = SI->getOperand(0); 00619 const Type *AllocaType = NewAI->getType()->getElementType(); 00620 if (SV->getType() != AllocaType) { 00621 Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI); 00622 00623 if (const PackedType *PTy = dyn_cast<PackedType>(AllocaType)) { 00624 // Must be an element insertion. 00625 unsigned Elt = Offset/PTy->getElementType()->getPrimitiveSizeInBits(); 00626 SV = new InsertElementInst(Old, SV, 00627 ConstantUInt::get(Type::UIntTy, Elt), 00628 "tmp", SI); 00629 } else { 00630 // If SV is signed, convert it to unsigned, so that the next cast zero 00631 // extends the value. 00632 if (SV->getType()->isSigned()) 00633 SV = new CastInst(SV, SV->getType()->getUnsignedVersion(), 00634 SV->getName(), SI); 00635 SV = new CastInst(SV, Old->getType(), SV->getName(), SI); 00636 if (Offset && Offset < SV->getType()->getPrimitiveSizeInBits()) 00637 SV = new ShiftInst(Instruction::Shl, SV, 00638 ConstantUInt::get(Type::UByteTy, Offset), 00639 SV->getName()+".adj", SI); 00640 // Mask out the bits we are about to insert from the old value. 00641 unsigned TotalBits = SV->getType()->getPrimitiveSizeInBits(); 00642 unsigned InsertBits = 00643 SI->getOperand(0)->getType()->getPrimitiveSizeInBits(); 00644 if (TotalBits != InsertBits) { 00645 assert(TotalBits > InsertBits); 00646 uint64_t Mask = ~(((1ULL << InsertBits)-1) << Offset); 00647 if (TotalBits != 64) 00648 Mask = Mask & ((1ULL << TotalBits)-1); 00649 Old = BinaryOperator::createAnd(Old, 00650 ConstantUInt::get(Old->getType(), Mask), 00651 Old->getName()+".mask", SI); 00652 SV = BinaryOperator::createOr(Old, SV, SV->getName()+".ins", SI); 00653 } 00654 } 00655 } 00656 new StoreInst(SV, NewAI, SI); 00657 SI->eraseFromParent(); 00658 00659 } else if (CastInst *CI = dyn_cast<CastInst>(User)) { 00660 unsigned NewOff = Offset; 00661 const TargetData &TD = getAnalysis<TargetData>(); 00662 if (TD.isBigEndian() && !isVectorInsert) { 00663 // Adjust the pointer. For example, storing 16-bits into a 32-bit 00664 // alloca with just a cast makes it modify the top 16-bits. 00665 const Type *SrcTy = cast<PointerType>(Ptr->getType())->getElementType(); 00666 const Type *DstTy = cast<PointerType>(CI->getType())->getElementType(); 00667 int PtrDiffBits = TD.getTypeSize(SrcTy)*8-TD.getTypeSize(DstTy)*8; 00668 NewOff += PtrDiffBits; 00669 } 00670 ConvertUsesToScalar(CI, NewAI, NewOff); 00671 CI->eraseFromParent(); 00672 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { 00673 const PointerType *AggPtrTy = 00674 cast<PointerType>(GEP->getOperand(0)->getType()); 00675 const TargetData &TD = getAnalysis<TargetData>(); 00676 unsigned AggSizeInBits = TD.getTypeSize(AggPtrTy->getElementType())*8; 00677 00678 // Check to see if this is stepping over an element: GEP Ptr, int C 00679 unsigned NewOffset = Offset; 00680 if (GEP->getNumOperands() == 2) { 00681 unsigned Idx = cast<ConstantInt>(GEP->getOperand(1))->getRawValue(); 00682 unsigned BitOffset = Idx*AggSizeInBits; 00683 00684 if (TD.isLittleEndian() || isVectorInsert) 00685 NewOffset += BitOffset; 00686 else 00687 NewOffset -= BitOffset; 00688 00689 } else if (GEP->getNumOperands() == 3) { 00690 // We know that operand #2 is zero. 00691 unsigned Idx = cast<ConstantInt>(GEP->getOperand(2))->getRawValue(); 00692 const Type *AggTy = AggPtrTy->getElementType(); 00693 if (const SequentialType *SeqTy = dyn_cast<SequentialType>(AggTy)) { 00694 unsigned ElSizeBits = TD.getTypeSize(SeqTy->getElementType())*8; 00695 00696 if (TD.isLittleEndian() || isVectorInsert) 00697 NewOffset += ElSizeBits*Idx; 00698 else 00699 NewOffset += AggSizeInBits-ElSizeBits*(Idx+1); 00700 } else if (const StructType *STy = dyn_cast<StructType>(AggTy)) { 00701 unsigned EltBitOffset = TD.getStructLayout(STy)->MemberOffsets[Idx]*8; 00702 00703 if (TD.isLittleEndian() || isVectorInsert) 00704 NewOffset += EltBitOffset; 00705 else { 00706 const PointerType *ElPtrTy = cast<PointerType>(GEP->getType()); 00707 unsigned ElSizeBits = TD.getTypeSize(ElPtrTy->getElementType())*8; 00708 NewOffset += AggSizeInBits-(EltBitOffset+ElSizeBits); 00709 } 00710 00711 } else { 00712 assert(0 && "Unsupported operation!"); 00713 abort(); 00714 } 00715 } else { 00716 assert(0 && "Unsupported operation!"); 00717 abort(); 00718 } 00719 ConvertUsesToScalar(GEP, NewAI, NewOffset); 00720 GEP->eraseFromParent(); 00721 } else { 00722 assert(0 && "Unsupported operation!"); 00723 abort(); 00724 } 00725 } 00726 }