//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This transformation implements the well known scalar replacement of // aggregates transformation. This xform breaks up alloca instructions of // aggregate type (structure or array) into individual alloca instructions for // each member (if possible). Then, if possible, it transforms the individual // alloca instructions into nice clean scalar SSA form. // // This combines a simple SRoA algorithm with the Mem2Reg algorithm because they // often interact, especially for C++ programs. As such, iterating between // SRoA, then Mem2Reg until we run out of things to promote works well. // //===----------------------------------------------------------------------===// #include "llvm/Transforms/Scalar.h" #include "llvm/ADT/SetVector.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/Loads.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/IR/CallSite.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DIBuilder.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/DebugInfo.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" #include "llvm/IR/GetElementPtrTypeIterator.h" #include "llvm/IR/GlobalVariable.h" #include "llvm/IR/IRBuilder.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Module.h" #include "llvm/IR/Operator.h" #include "llvm/Pass.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/MathExtras.h" #include "llvm/Support/raw_ostream.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Transforms/Utils/PromoteMemToReg.h" #include "llvm/Transforms/Utils/SSAUpdater.h" using namespace llvm; #define DEBUG_TYPE "scalarrepl" STATISTIC(NumReplaced, "Number of allocas broken up"); STATISTIC(NumPromoted, "Number of allocas promoted"); STATISTIC(NumAdjusted, "Number of scalar allocas adjusted to allow promotion"); STATISTIC(NumConverted, "Number of aggregates converted to scalar"); namespace { struct SROA : public FunctionPass { SROA(int T, bool hasDT, char &ID, int ST, int AT, int SLT) : FunctionPass(ID), HasDomTree(hasDT) { if (T == -1) SRThreshold = 128; else SRThreshold = T; if (ST == -1) StructMemberThreshold = 32; else StructMemberThreshold = ST; if (AT == -1) ArrayElementThreshold = 8; else ArrayElementThreshold = AT; if (SLT == -1) // Do not limit the scalar integer load size if no threshold is given. ScalarLoadThreshold = -1; else ScalarLoadThreshold = SLT; } bool runOnFunction(Function &F) override; bool performScalarRepl(Function &F); bool performPromotion(Function &F); private: bool HasDomTree; const DataLayout *DL; /// DeadInsts - Keep track of instructions we have made dead, so that /// we can remove them after we are done working. SmallVector<Value*, 32> DeadInsts; /// AllocaInfo - When analyzing uses of an alloca instruction, this captures /// information about the uses. All these fields are initialized to false /// and set to true when something is learned. struct AllocaInfo { /// The alloca to promote. AllocaInst *AI; /// CheckedPHIs - This is a set of verified PHI nodes, to prevent infinite /// looping and avoid redundant work. SmallPtrSet<PHINode*, 8> CheckedPHIs; /// isUnsafe - This is set to true if the alloca cannot be SROA'd. bool isUnsafe : 1; /// isMemCpySrc - This is true if this aggregate is memcpy'd from. bool isMemCpySrc : 1; /// isMemCpyDst - This is true if this aggregate is memcpy'd into. bool isMemCpyDst : 1; /// hasSubelementAccess - This is true if a subelement of the alloca is /// ever accessed, or false if the alloca is only accessed with mem /// intrinsics or load/store that only access the entire alloca at once. bool hasSubelementAccess : 1; /// hasALoadOrStore - This is true if there are any loads or stores to it. /// The alloca may just be accessed with memcpy, for example, which would /// not set this. bool hasALoadOrStore : 1; explicit AllocaInfo(AllocaInst *ai) : AI(ai), isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false), hasSubelementAccess(false), hasALoadOrStore(false) {} }; /// SRThreshold - The maximum alloca size to considered for SROA. unsigned SRThreshold; /// StructMemberThreshold - The maximum number of members a struct can /// contain to be considered for SROA. unsigned StructMemberThreshold; /// ArrayElementThreshold - The maximum number of elements an array can /// have to be considered for SROA. unsigned ArrayElementThreshold; /// ScalarLoadThreshold - The maximum size in bits of scalars to load when /// converting to scalar unsigned ScalarLoadThreshold; void MarkUnsafe(AllocaInfo &I, Instruction *User) { I.isUnsafe = true; DEBUG(dbgs() << " Transformation preventing inst: " << *User << '\n'); } bool isSafeAllocaToScalarRepl(AllocaInst *AI); void isSafeForScalarRepl(Instruction *I, uint64_t Offset, AllocaInfo &Info); void isSafePHISelectUseForScalarRepl(Instruction *User, uint64_t Offset, AllocaInfo &Info); void isSafeGEP(GetElementPtrInst *GEPI, uint64_t &Offset, AllocaInfo &Info); void isSafeMemAccess(uint64_t Offset, uint64_t MemSize, Type *MemOpType, bool isStore, AllocaInfo &Info, Instruction *TheAccess, bool AllowWholeAccess); bool TypeHasComponent(Type *T, uint64_t Offset, uint64_t Size); uint64_t FindElementAndOffset(Type *&T, uint64_t &Offset, Type *&IdxTy); void DoScalarReplacement(AllocaInst *AI, std::vector<AllocaInst*> &WorkList); void DeleteDeadInstructions(); void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, SmallVectorImpl<AllocaInst *> &NewElts); void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, SmallVectorImpl<AllocaInst *> &NewElts); void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, SmallVectorImpl<AllocaInst *> &NewElts); void RewriteLifetimeIntrinsic(IntrinsicInst *II, AllocaInst *AI, uint64_t Offset, SmallVectorImpl<AllocaInst *> &NewElts); void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, AllocaInst *AI, SmallVectorImpl<AllocaInst *> &NewElts); void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, SmallVectorImpl<AllocaInst *> &NewElts); void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, SmallVectorImpl<AllocaInst *> &NewElts); bool ShouldAttemptScalarRepl(AllocaInst *AI); }; // SROA_DT - SROA that uses DominatorTree. struct SROA_DT : public SROA { static char ID; public: SROA_DT(int T = -1, int ST = -1, int AT = -1, int SLT = -1) : SROA(T, true, ID, ST, AT, SLT) { initializeSROA_DTPass(*PassRegistry::getPassRegistry()); } // getAnalysisUsage - This pass does not require any passes, but we know it // will not alter the CFG, so say so. void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequired<DominatorTreeWrapperPass>(); AU.setPreservesCFG(); } }; // SROA_SSAUp - SROA that uses SSAUpdater. struct SROA_SSAUp : public SROA { static char ID; public: SROA_SSAUp(int T = -1, int ST = -1, int AT = -1, int SLT = -1) : SROA(T, false, ID, ST, AT, SLT) { initializeSROA_SSAUpPass(*PassRegistry::getPassRegistry()); } // getAnalysisUsage - This pass does not require any passes, but we know it // will not alter the CFG, so say so. void getAnalysisUsage(AnalysisUsage &AU) const override { AU.setPreservesCFG(); } }; } char SROA_DT::ID = 0; char SROA_SSAUp::ID = 0; INITIALIZE_PASS_BEGIN(SROA_DT, "scalarrepl", "Scalar Replacement of Aggregates (DT)", false, false) INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) INITIALIZE_PASS_END(SROA_DT, "scalarrepl", "Scalar Replacement of Aggregates (DT)", false, false) INITIALIZE_PASS_BEGIN(SROA_SSAUp, "scalarrepl-ssa", "Scalar Replacement of Aggregates (SSAUp)", false, false) INITIALIZE_PASS_END(SROA_SSAUp, "scalarrepl-ssa", "Scalar Replacement of Aggregates (SSAUp)", false, false) // Public interface to the ScalarReplAggregates pass FunctionPass *llvm::createScalarReplAggregatesPass(int Threshold, bool UseDomTree, int StructMemberThreshold, int ArrayElementThreshold, int ScalarLoadThreshold) { if (UseDomTree) return new SROA_DT(Threshold, StructMemberThreshold, ArrayElementThreshold, ScalarLoadThreshold); return new SROA_SSAUp(Threshold, StructMemberThreshold, ArrayElementThreshold, ScalarLoadThreshold); } //===----------------------------------------------------------------------===// // Convert To Scalar Optimization. //===----------------------------------------------------------------------===// namespace { /// ConvertToScalarInfo - This class implements the "Convert To Scalar" /// optimization, which scans the uses of an alloca and determines if it can /// rewrite it in terms of a single new alloca that can be mem2reg'd. class ConvertToScalarInfo { /// AllocaSize - The size of the alloca being considered in bytes. unsigned AllocaSize; const DataLayout &DL; unsigned ScalarLoadThreshold; /// IsNotTrivial - This is set to true if there is some access to the object /// which means that mem2reg can't promote it. bool IsNotTrivial; /// ScalarKind - Tracks the kind of alloca being considered for promotion, /// computed based on the uses of the alloca rather than the LLVM type system. enum { Unknown, // Accesses via GEPs that are consistent with element access of a vector // type. This will not be converted into a vector unless there is a later // access using an actual vector type. ImplicitVector, // Accesses via vector operations and GEPs that are consistent with the // layout of a vector type. Vector, // An integer bag-of-bits with bitwise operations for insertion and // extraction. Any combination of types can be converted into this kind // of scalar. Integer } ScalarKind; /// VectorTy - This tracks the type that we should promote the vector to if /// it is possible to turn it into a vector. This starts out null, and if it /// isn't possible to turn into a vector type, it gets set to VoidTy. VectorType *VectorTy; /// HadNonMemTransferAccess - True if there is at least one access to the /// alloca that is not a MemTransferInst. We don't want to turn structs into /// large integers unless there is some potential for optimization. bool HadNonMemTransferAccess; /// HadDynamicAccess - True if some element of this alloca was dynamic. /// We don't yet have support for turning a dynamic access into a large /// integer. bool HadDynamicAccess; public: explicit ConvertToScalarInfo(unsigned Size, const DataLayout &DL, unsigned SLT) : AllocaSize(Size), DL(DL), ScalarLoadThreshold(SLT), IsNotTrivial(false), ScalarKind(Unknown), VectorTy(nullptr), HadNonMemTransferAccess(false), HadDynamicAccess(false) { } AllocaInst *TryConvert(AllocaInst *AI); private: bool CanConvertToScalar(Value *V, uint64_t Offset, Value* NonConstantIdx); void MergeInTypeForLoadOrStore(Type *In, uint64_t Offset); bool MergeInVectorType(VectorType *VInTy, uint64_t Offset); void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset, Value *NonConstantIdx); Value *ConvertScalar_ExtractValue(Value *NV, Type *ToType, uint64_t Offset, Value* NonConstantIdx, IRBuilder<> &Builder); Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal, uint64_t Offset, Value* NonConstantIdx, IRBuilder<> &Builder); }; } // end anonymous namespace. /// TryConvert - Analyze the specified alloca, and if it is safe to do so, /// rewrite it to be a new alloca which is mem2reg'able. This returns the new /// alloca if possible or null if not. AllocaInst *ConvertToScalarInfo::TryConvert(AllocaInst *AI) { // If we can't convert this scalar, or if mem2reg can trivially do it, bail // out. if (!CanConvertToScalar(AI, 0, nullptr) || !IsNotTrivial) return nullptr; // If an alloca has only memset / memcpy uses, it may still have an Unknown // ScalarKind. Treat it as an Integer below. if (ScalarKind == Unknown) ScalarKind = Integer; if (ScalarKind == Vector && VectorTy->getBitWidth() != AllocaSize * 8) ScalarKind = Integer; // If we were able to find a vector type that can handle this with // insert/extract elements, and if there was at least one use that had // a vector type, promote this to a vector. We don't want to promote // random stuff that doesn't use vectors (e.g. <9 x double>) because then // we just get a lot of insert/extracts. If at least one vector is // involved, then we probably really do have a union of vector/array. Type *NewTy; if (ScalarKind == Vector) { assert(VectorTy && "Missing type for vector scalar."); DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = " << *VectorTy << '\n'); NewTy = VectorTy; // Use the vector type. } else { unsigned BitWidth = AllocaSize * 8; // Do not convert to scalar integer if the alloca size exceeds the // scalar load threshold. if (BitWidth > ScalarLoadThreshold) return nullptr; if ((ScalarKind == ImplicitVector || ScalarKind == Integer) && !HadNonMemTransferAccess && !DL.fitsInLegalInteger(BitWidth)) return nullptr; // Dynamic accesses on integers aren't yet supported. They need us to shift // by a dynamic amount which could be difficult to work out as we might not // know whether to use a left or right shift. if (ScalarKind == Integer && HadDynamicAccess) return nullptr; DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n"); // Create and insert the integer alloca. NewTy = IntegerType::get(AI->getContext(), BitWidth); } AllocaInst *NewAI = new AllocaInst(NewTy, nullptr, "", AI->getParent()->begin()); ConvertUsesToScalar(AI, NewAI, 0, nullptr); return NewAI; } /// MergeInTypeForLoadOrStore - Add the 'In' type to the accumulated vector type /// (VectorTy) so far at the offset specified by Offset (which is specified in /// bytes). /// /// There are two cases we handle here: /// 1) A union of vector types of the same size and potentially its elements. /// Here we turn element accesses into insert/extract element operations. /// This promotes a <4 x float> with a store of float to the third element /// into a <4 x float> that uses insert element. /// 2) A fully general blob of memory, which we turn into some (potentially /// large) integer type with extract and insert operations where the loads /// and stores would mutate the memory. We mark this by setting VectorTy /// to VoidTy. void ConvertToScalarInfo::MergeInTypeForLoadOrStore(Type *In, uint64_t Offset) { // If we already decided to turn this into a blob of integer memory, there is // nothing to be done. if (ScalarKind == Integer) return; // If this could be contributing to a vector, analyze it. // If the In type is a vector that is the same size as the alloca, see if it // matches the existing VecTy. if (VectorType *VInTy = dyn_cast<VectorType>(In)) { if (MergeInVectorType(VInTy, Offset)) return; } else if (In->isFloatTy() || In->isDoubleTy() || (In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 && isPowerOf2_32(In->getPrimitiveSizeInBits()))) { // Full width accesses can be ignored, because they can always be turned // into bitcasts. unsigned EltSize = In->getPrimitiveSizeInBits()/8; if (EltSize == AllocaSize) return; // If we're accessing something that could be an element of a vector, see // if the implied vector agrees with what we already have and if Offset is // compatible with it. if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 && (!VectorTy || EltSize == VectorTy->getElementType() ->getPrimitiveSizeInBits()/8)) { if (!VectorTy) { ScalarKind = ImplicitVector; VectorTy = VectorType::get(In, AllocaSize/EltSize); } return; } } // Otherwise, we have a case that we can't handle with an optimized vector // form. We can still turn this into a large integer. ScalarKind = Integer; } /// MergeInVectorType - Handles the vector case of MergeInTypeForLoadOrStore, /// returning true if the type was successfully merged and false otherwise. bool ConvertToScalarInfo::MergeInVectorType(VectorType *VInTy, uint64_t Offset) { if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) { // If we're storing/loading a vector of the right size, allow it as a // vector. If this the first vector we see, remember the type so that // we know the element size. If this is a subsequent access, ignore it // even if it is a differing type but the same size. Worst case we can // bitcast the resultant vectors. if (!VectorTy) VectorTy = VInTy; ScalarKind = Vector; return true; } return false; } /// CanConvertToScalar - V is a pointer. If we can convert the pointee and all /// its accesses to a single vector type, return true and set VecTy to /// the new type. If we could convert the alloca into a single promotable /// integer, return true but set VecTy to VoidTy. Further, if the use is not a /// completely trivial use that mem2reg could promote, set IsNotTrivial. Offset /// is the current offset from the base of the alloca being analyzed. /// /// If we see at least one access to the value that is as a vector type, set the /// SawVec flag. bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset, Value* NonConstantIdx) { for (User *U : V->users()) { Instruction *UI = cast<Instruction>(U); if (LoadInst *LI = dyn_cast<LoadInst>(UI)) { // Don't break volatile loads. if (!LI->isSimple()) return false; // Don't touch MMX operations. if (LI->getType()->isX86_MMXTy()) return false; HadNonMemTransferAccess = true; MergeInTypeForLoadOrStore(LI->getType(), Offset); continue; } if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { // Storing the pointer, not into the value? if (SI->getOperand(0) == V || !SI->isSimple()) return false; // Don't touch MMX operations. if (SI->getOperand(0)->getType()->isX86_MMXTy()) return false; HadNonMemTransferAccess = true; MergeInTypeForLoadOrStore(SI->getOperand(0)->getType(), Offset); continue; } if (BitCastInst *BCI = dyn_cast<BitCastInst>(UI)) { if (!onlyUsedByLifetimeMarkers(BCI)) IsNotTrivial = true; // Can't be mem2reg'd. if (!CanConvertToScalar(BCI, Offset, NonConstantIdx)) return false; continue; } if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(UI)) { // If this is a GEP with a variable indices, we can't handle it. PointerType* PtrTy = dyn_cast<PointerType>(GEP->getPointerOperandType()); if (!PtrTy) return false; // Compute the offset that this GEP adds to the pointer. SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); Value *GEPNonConstantIdx = nullptr; if (!GEP->hasAllConstantIndices()) { if (!isa<VectorType>(PtrTy->getElementType())) return false; if (NonConstantIdx) return false; GEPNonConstantIdx = Indices.pop_back_val(); if (!GEPNonConstantIdx->getType()->isIntegerTy(32)) return false; HadDynamicAccess = true; } else GEPNonConstantIdx = NonConstantIdx; uint64_t GEPOffset = DL.getIndexedOffset(PtrTy, Indices); // See if all uses can be converted. if (!CanConvertToScalar(GEP, Offset+GEPOffset, GEPNonConstantIdx)) return false; IsNotTrivial = true; // Can't be mem2reg'd. HadNonMemTransferAccess = true; continue; } // If this is a constant sized memset of a constant value (e.g. 0) we can // handle it. if (MemSetInst *MSI = dyn_cast<MemSetInst>(UI)) { // Store to dynamic index. if (NonConstantIdx) return false; // Store of constant value. if (!isa<ConstantInt>(MSI->getValue())) return false; // Store of constant size. ConstantInt *Len = dyn_cast<ConstantInt>(MSI->getLength()); if (!Len) return false; // If the size differs from the alloca, we can only convert the alloca to // an integer bag-of-bits. // FIXME: This should handle all of the cases that are currently accepted // as vector element insertions. if (Len->getZExtValue() != AllocaSize || Offset != 0) ScalarKind = Integer; IsNotTrivial = true; // Can't be mem2reg'd. HadNonMemTransferAccess = true; continue; } // If this is a memcpy or memmove into or out of the whole allocation, we // can handle it like a load or store of the scalar type. if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(UI)) { // Store to dynamic index. if (NonConstantIdx) return false; ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()); if (!Len || Len->getZExtValue() != AllocaSize || Offset != 0) return false; IsNotTrivial = true; // Can't be mem2reg'd. continue; } // If this is a lifetime intrinsic, we can handle it. if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(UI)) { if (II->getIntrinsicID() == Intrinsic::lifetime_start || II->getIntrinsicID() == Intrinsic::lifetime_end) { continue; } } // Otherwise, we cannot handle this! return false; } return true; } /// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca /// directly. This happens when we are converting an "integer union" to a /// single integer scalar, or when we are converting a "vector union" to a /// vector with insert/extractelement instructions. /// /// Offset is an offset from the original alloca, in bits that need to be /// shifted to the right. By the end of this, there should be no uses of Ptr. void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset, Value* NonConstantIdx) { while (!Ptr->use_empty()) { Instruction *User = cast<Instruction>(Ptr->user_back()); if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) { ConvertUsesToScalar(CI, NewAI, Offset, NonConstantIdx); CI->eraseFromParent(); continue; } if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) { // Compute the offset that this GEP adds to the pointer. SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end()); Value* GEPNonConstantIdx = nullptr; if (!GEP->hasAllConstantIndices()) { assert(!NonConstantIdx && "Dynamic GEP reading from dynamic GEP unsupported"); GEPNonConstantIdx = Indices.pop_back_val(); } else GEPNonConstantIdx = NonConstantIdx; uint64_t GEPOffset = DL.getIndexedOffset(GEP->getPointerOperandType(), Indices); ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8, GEPNonConstantIdx); GEP->eraseFromParent(); continue; } IRBuilder<> Builder(User); if (LoadInst *LI = dyn_cast<LoadInst>(User)) { // The load is a bit extract from NewAI shifted right by Offset bits. Value *LoadedVal = Builder.CreateLoad(NewAI); Value *NewLoadVal = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, NonConstantIdx, Builder); LI->replaceAllUsesWith(NewLoadVal); LI->eraseFromParent(); continue; } if (StoreInst *SI = dyn_cast<StoreInst>(User)) { assert(SI->getOperand(0) != Ptr && "Consistency error!"); Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset, NonConstantIdx, Builder); Builder.CreateStore(New, NewAI); SI->eraseFromParent(); // If the load we just inserted is now dead, then the inserted store // overwrote the entire thing. if (Old->use_empty()) Old->eraseFromParent(); continue; } // If this is a constant sized memset of a constant value (e.g. 0) we can // transform it into a store of the expanded constant value. if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) { assert(MSI->getRawDest() == Ptr && "Consistency error!"); assert(!NonConstantIdx && "Cannot replace dynamic memset with insert"); int64_t SNumBytes = cast<ConstantInt>(MSI->getLength())->getSExtValue(); if (SNumBytes > 0 && (SNumBytes >> 32) == 0) { unsigned NumBytes = static_cast<unsigned>(SNumBytes); unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue(); // Compute the value replicated the right number of times. APInt APVal(NumBytes*8, Val); // Splat the value if non-zero. if (Val) for (unsigned i = 1; i != NumBytes; ++i) APVal |= APVal << 8; Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in"); Value *New = ConvertScalar_InsertValue( ConstantInt::get(User->getContext(), APVal), Old, Offset, nullptr, Builder); Builder.CreateStore(New, NewAI); // If the load we just inserted is now dead, then the memset overwrote // the entire thing. if (Old->use_empty()) Old->eraseFromParent(); } MSI->eraseFromParent(); continue; } // If this is a memcpy or memmove into or out of the whole allocation, we // can handle it like a load or store of the scalar type. if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) { assert(Offset == 0 && "must be store to start of alloca"); assert(!NonConstantIdx && "Cannot replace dynamic transfer with insert"); // If the source and destination are both to the same alloca, then this is // a noop copy-to-self, just delete it. Otherwise, emit a load and store // as appropriate. AllocaInst *OrigAI = cast<AllocaInst>(GetUnderlyingObject(Ptr, &DL, 0)); if (GetUnderlyingObject(MTI->getSource(), &DL, 0) != OrigAI) { // Dest must be OrigAI, change this to be a load from the original // pointer (bitcasted), then a store to our new alloca. assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?"); Value *SrcPtr = MTI->getSource(); PointerType* SPTy = cast<PointerType>(SrcPtr->getType()); PointerType* AIPTy = cast<PointerType>(NewAI->getType()); if (SPTy->getAddressSpace() != AIPTy->getAddressSpace()) { AIPTy = PointerType::get(AIPTy->getElementType(), SPTy->getAddressSpace()); } SrcPtr = Builder.CreateBitCast(SrcPtr, AIPTy); LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval"); SrcVal->setAlignment(MTI->getAlignment()); Builder.CreateStore(SrcVal, NewAI); } else if (GetUnderlyingObject(MTI->getDest(), &DL, 0) != OrigAI) { // Src must be OrigAI, change this to be a load from NewAI then a store // through the original dest pointer (bitcasted). assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?"); LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval"); PointerType* DPTy = cast<PointerType>(MTI->getDest()->getType()); PointerType* AIPTy = cast<PointerType>(NewAI->getType()); if (DPTy->getAddressSpace() != AIPTy->getAddressSpace()) { AIPTy = PointerType::get(AIPTy->getElementType(), DPTy->getAddressSpace()); } Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), AIPTy); StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr); NewStore->setAlignment(MTI->getAlignment()); } else { // Noop transfer. Src == Dst } MTI->eraseFromParent(); continue; } if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(User)) { if (II->getIntrinsicID() == Intrinsic::lifetime_start || II->getIntrinsicID() == Intrinsic::lifetime_end) { // There's no need to preserve these, as the resulting alloca will be // converted to a register anyways. II->eraseFromParent(); continue; } } llvm_unreachable("Unsupported operation!"); } } /// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer /// or vector value FromVal, extracting the bits from the offset specified by /// Offset. This returns the value, which is of type ToType. /// /// This happens when we are converting an "integer union" to a single /// integer scalar, or when we are converting a "vector union" to a vector with /// insert/extractelement instructions. /// /// Offset is an offset from the original alloca, in bits that need to be /// shifted to the right. Value *ConvertToScalarInfo:: ConvertScalar_ExtractValue(Value *FromVal, Type *ToType, uint64_t Offset, Value* NonConstantIdx, IRBuilder<> &Builder) { // If the load is of the whole new alloca, no conversion is needed. Type *FromType = FromVal->getType(); if (FromType == ToType && Offset == 0) return FromVal; // If the result alloca is a vector type, this is either an element // access or a bitcast to another vector type of the same size. if (VectorType *VTy = dyn_cast<VectorType>(FromType)) { unsigned FromTypeSize = DL.getTypeAllocSize(FromType); unsigned ToTypeSize = DL.getTypeAllocSize(ToType); if (FromTypeSize == ToTypeSize) return Builder.CreateBitCast(FromVal, ToType); // Otherwise it must be an element access. unsigned Elt = 0; if (Offset) { unsigned EltSize = DL.getTypeAllocSizeInBits(VTy->getElementType()); Elt = Offset/EltSize; assert(EltSize*Elt == Offset && "Invalid modulus in validity checking"); } // Return the element extracted out of it. Value *Idx; if (NonConstantIdx) { if (Elt) Idx = Builder.CreateAdd(NonConstantIdx, Builder.getInt32(Elt), "dyn.offset"); else Idx = NonConstantIdx; } else Idx = Builder.getInt32(Elt); Value *V = Builder.CreateExtractElement(FromVal, Idx); if (V->getType() != ToType) V = Builder.CreateBitCast(V, ToType); return V; } // If ToType is a first class aggregate, extract out each of the pieces and // use insertvalue's to form the FCA. if (StructType *ST = dyn_cast<StructType>(ToType)) { assert(!NonConstantIdx && "Dynamic indexing into struct types not supported"); const StructLayout &Layout = *DL.getStructLayout(ST); Value *Res = UndefValue::get(ST); for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i), Offset+Layout.getElementOffsetInBits(i), nullptr, Builder); Res = Builder.CreateInsertValue(Res, Elt, i); } return Res; } if (ArrayType *AT = dyn_cast<ArrayType>(ToType)) { assert(!NonConstantIdx && "Dynamic indexing into array types not supported"); uint64_t EltSize = DL.getTypeAllocSizeInBits(AT->getElementType()); Value *Res = UndefValue::get(AT); for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(), Offset+i*EltSize, nullptr, Builder); Res = Builder.CreateInsertValue(Res, Elt, i); } return Res; } // Otherwise, this must be a union that was converted to an integer value. IntegerType *NTy = cast<IntegerType>(FromVal->getType()); // If this is a big-endian system and the load is narrower than the // full alloca type, we need to do a shift to get the right bits. int ShAmt = 0; if (DL.isBigEndian()) { // On big-endian machines, the lowest bit is stored at the bit offset // from the pointer given by getTypeStoreSizeInBits. This matters for // integers with a bitwidth that is not a multiple of 8. ShAmt = DL.getTypeStoreSizeInBits(NTy) - DL.getTypeStoreSizeInBits(ToType) - Offset; } else { ShAmt = Offset; } // Note: we support negative bitwidths (with shl) which are not defined. // We do this to support (f.e.) loads off the end of a structure where // only some bits are used. if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth()) FromVal = Builder.CreateLShr(FromVal, ConstantInt::get(FromVal->getType(), ShAmt)); else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) FromVal = Builder.CreateShl(FromVal, ConstantInt::get(FromVal->getType(), -ShAmt)); // Finally, unconditionally truncate the integer to the right width. unsigned LIBitWidth = DL.getTypeSizeInBits(ToType); if (LIBitWidth < NTy->getBitWidth()) FromVal = Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(), LIBitWidth)); else if (LIBitWidth > NTy->getBitWidth()) FromVal = Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(), LIBitWidth)); // If the result is an integer, this is a trunc or bitcast. if (ToType->isIntegerTy()) { // Should be done. } else if (ToType->isFloatingPointTy() || ToType->isVectorTy()) { // Just do a bitcast, we know the sizes match up. FromVal = Builder.CreateBitCast(FromVal, ToType); } else { // Otherwise must be a pointer. FromVal = Builder.CreateIntToPtr(FromVal, ToType); } assert(FromVal->getType() == ToType && "Didn't convert right?"); return FromVal; } /// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer /// or vector value "Old" at the offset specified by Offset. /// /// This happens when we are converting an "integer union" to a /// single integer scalar, or when we are converting a "vector union" to a /// vector with insert/extractelement instructions. /// /// Offset is an offset from the original alloca, in bits that need to be /// shifted to the right. /// /// NonConstantIdx is an index value if there was a GEP with a non-constant /// index value. If this is 0 then all GEPs used to find this insert address /// are constant. Value *ConvertToScalarInfo:: ConvertScalar_InsertValue(Value *SV, Value *Old, uint64_t Offset, Value* NonConstantIdx, IRBuilder<> &Builder) { // Convert the stored type to the actual type, shift it left to insert // then 'or' into place. Type *AllocaType = Old->getType(); LLVMContext &Context = Old->getContext(); if (VectorType *VTy = dyn_cast<VectorType>(AllocaType)) { uint64_t VecSize = DL.getTypeAllocSizeInBits(VTy); uint64_t ValSize = DL.getTypeAllocSizeInBits(SV->getType()); // Changing the whole vector with memset or with an access of a different // vector type? if (ValSize == VecSize) return Builder.CreateBitCast(SV, AllocaType); // Must be an element insertion. Type *EltTy = VTy->getElementType(); if (SV->getType() != EltTy) SV = Builder.CreateBitCast(SV, EltTy); uint64_t EltSize = DL.getTypeAllocSizeInBits(EltTy); unsigned Elt = Offset/EltSize; Value *Idx; if (NonConstantIdx) { if (Elt) Idx = Builder.CreateAdd(NonConstantIdx, Builder.getInt32(Elt), "dyn.offset"); else Idx = NonConstantIdx; } else Idx = Builder.getInt32(Elt); return Builder.CreateInsertElement(Old, SV, Idx); } // If SV is a first-class aggregate value, insert each value recursively. if (StructType *ST = dyn_cast<StructType>(SV->getType())) { assert(!NonConstantIdx && "Dynamic indexing into struct types not supported"); const StructLayout &Layout = *DL.getStructLayout(ST); for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { Value *Elt = Builder.CreateExtractValue(SV, i); Old = ConvertScalar_InsertValue(Elt, Old, Offset+Layout.getElementOffsetInBits(i), nullptr, Builder); } return Old; } if (ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) { assert(!NonConstantIdx && "Dynamic indexing into array types not supported"); uint64_t EltSize = DL.getTypeAllocSizeInBits(AT->getElementType()); for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { Value *Elt = Builder.CreateExtractValue(SV, i); Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, nullptr, Builder); } return Old; } // If SV is a float, convert it to the appropriate integer type. // If it is a pointer, do the same. unsigned SrcWidth = DL.getTypeSizeInBits(SV->getType()); unsigned DestWidth = DL.getTypeSizeInBits(AllocaType); unsigned SrcStoreWidth = DL.getTypeStoreSizeInBits(SV->getType()); unsigned DestStoreWidth = DL.getTypeStoreSizeInBits(AllocaType); if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy()) SV = Builder.CreateBitCast(SV, IntegerType::get(SV->getContext(),SrcWidth)); else if (SV->getType()->isPointerTy()) SV = Builder.CreatePtrToInt(SV, DL.getIntPtrType(SV->getType())); // Zero extend or truncate the value if needed. if (SV->getType() != AllocaType) { if (SV->getType()->getPrimitiveSizeInBits() < AllocaType->getPrimitiveSizeInBits()) SV = Builder.CreateZExt(SV, AllocaType); else { // Truncation may be needed if storing more than the alloca can hold // (undefined behavior). SV = Builder.CreateTrunc(SV, AllocaType); SrcWidth = DestWidth; SrcStoreWidth = DestStoreWidth; } } // If this is a big-endian system and the store is narrower than the // full alloca type, we need to do a shift to get the right bits. int ShAmt = 0; if (DL.isBigEndian()) { // On big-endian machines, the lowest bit is stored at the bit offset // from the pointer given by getTypeStoreSizeInBits. This matters for // integers with a bitwidth that is not a multiple of 8. ShAmt = DestStoreWidth - SrcStoreWidth - Offset; } else { ShAmt = Offset; } // Note: we support negative bitwidths (with shr) which are not defined. // We do this to support (f.e.) stores off the end of a structure where // only some bits in the structure are set. APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth)); if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) { SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(), ShAmt)); Mask <<= ShAmt; } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(), -ShAmt)); Mask = Mask.lshr(-ShAmt); } // Mask out the bits we are about to insert from the old value, and or // in the new bits. if (SrcWidth != DestWidth) { assert(DestWidth > SrcWidth); Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask"); SV = Builder.CreateOr(Old, SV, "ins"); } return SV; } //===----------------------------------------------------------------------===// // SRoA Driver //===----------------------------------------------------------------------===// bool SROA::runOnFunction(Function &F) { if (skipOptnoneFunction(F)) return false; DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); DL = DLP ? &DLP->getDataLayout() : nullptr; bool Changed = performPromotion(F); // FIXME: ScalarRepl currently depends on DataLayout more than it // theoretically needs to. It should be refactored in order to support // target-independent IR. Until this is done, just skip the actual // scalar-replacement portion of this pass. if (!DL) return Changed; while (1) { bool LocalChange = performScalarRepl(F); if (!LocalChange) break; // No need to repromote if no scalarrepl Changed = true; LocalChange = performPromotion(F); if (!LocalChange) break; // No need to re-scalarrepl if no promotion } return Changed; } namespace { class AllocaPromoter : public LoadAndStorePromoter { AllocaInst *AI; DIBuilder *DIB; SmallVector<DbgDeclareInst *, 4> DDIs; SmallVector<DbgValueInst *, 4> DVIs; public: AllocaPromoter(const SmallVectorImpl<Instruction*> &Insts, SSAUpdater &S, DIBuilder *DB) : LoadAndStorePromoter(Insts, S), AI(nullptr), DIB(DB) {} void run(AllocaInst *AI, const SmallVectorImpl<Instruction*> &Insts) { // Remember which alloca we're promoting (for isInstInList). this->AI = AI; if (MDNode *DebugNode = MDNode::getIfExists(AI->getContext(), AI)) { for (User *U : DebugNode->users()) if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U)) DDIs.push_back(DDI); else if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(U)) DVIs.push_back(DVI); } LoadAndStorePromoter::run(Insts); AI->eraseFromParent(); for (SmallVectorImpl<DbgDeclareInst *>::iterator I = DDIs.begin(), E = DDIs.end(); I != E; ++I) { DbgDeclareInst *DDI = *I; DDI->eraseFromParent(); } for (SmallVectorImpl<DbgValueInst *>::iterator I = DVIs.begin(), E = DVIs.end(); I != E; ++I) { DbgValueInst *DVI = *I; DVI->eraseFromParent(); } } bool isInstInList(Instruction *I, const SmallVectorImpl<Instruction*> &Insts) const override { if (LoadInst *LI = dyn_cast<LoadInst>(I)) return LI->getOperand(0) == AI; return cast<StoreInst>(I)->getPointerOperand() == AI; } void updateDebugInfo(Instruction *Inst) const override { for (SmallVectorImpl<DbgDeclareInst *>::const_iterator I = DDIs.begin(), E = DDIs.end(); I != E; ++I) { DbgDeclareInst *DDI = *I; if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) ConvertDebugDeclareToDebugValue(DDI, SI, *DIB); else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) ConvertDebugDeclareToDebugValue(DDI, LI, *DIB); } for (SmallVectorImpl<DbgValueInst *>::const_iterator I = DVIs.begin(), E = DVIs.end(); I != E; ++I) { DbgValueInst *DVI = *I; Value *Arg = nullptr; if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { // If an argument is zero extended then use argument directly. The ZExt // may be zapped by an optimization pass in future. if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) Arg = dyn_cast<Argument>(ZExt->getOperand(0)); if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) Arg = dyn_cast<Argument>(SExt->getOperand(0)); if (!Arg) Arg = SI->getOperand(0); } else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { Arg = LI->getOperand(0); } else { continue; } Instruction *DbgVal = DIB->insertDbgValueIntrinsic(Arg, 0, DIVariable(DVI->getVariable()), Inst); DbgVal->setDebugLoc(DVI->getDebugLoc()); } } }; } // end anon namespace /// isSafeSelectToSpeculate - Select instructions that use an alloca and are /// subsequently loaded can be rewritten to load both input pointers and then /// select between the result, allowing the load of the alloca to be promoted. /// From this: /// %P2 = select i1 %cond, i32* %Alloca, i32* %Other /// %V = load i32* %P2 /// to: /// %V1 = load i32* %Alloca -> will be mem2reg'd /// %V2 = load i32* %Other /// %V = select i1 %cond, i32 %V1, i32 %V2 /// /// We can do this to a select if its only uses are loads and if the operand to /// the select can be loaded unconditionally. static bool isSafeSelectToSpeculate(SelectInst *SI, const DataLayout *DL) { bool TDerefable = SI->getTrueValue()->isDereferenceablePointer(DL); bool FDerefable = SI->getFalseValue()->isDereferenceablePointer(DL); for (User *U : SI->users()) { LoadInst *LI = dyn_cast<LoadInst>(U); if (!LI || !LI->isSimple()) return false; // Both operands to the select need to be dereferencable, either absolutely // (e.g. allocas) or at this point because we can see other accesses to it. if (!TDerefable && !isSafeToLoadUnconditionally(SI->getTrueValue(), LI, LI->getAlignment(), DL)) return false; if (!FDerefable && !isSafeToLoadUnconditionally(SI->getFalseValue(), LI, LI->getAlignment(), DL)) return false; } return true; } /// isSafePHIToSpeculate - PHI instructions that use an alloca and are /// subsequently loaded can be rewritten to load both input pointers in the pred /// blocks and then PHI the results, allowing the load of the alloca to be /// promoted. /// From this: /// %P2 = phi [i32* %Alloca, i32* %Other] /// %V = load i32* %P2 /// to: /// %V1 = load i32* %Alloca -> will be mem2reg'd /// ... /// %V2 = load i32* %Other /// ... /// %V = phi [i32 %V1, i32 %V2] /// /// We can do this to a select if its only uses are loads and if the operand to /// the select can be loaded unconditionally. static bool isSafePHIToSpeculate(PHINode *PN, const DataLayout *DL) { // For now, we can only do this promotion if the load is in the same block as // the PHI, and if there are no stores between the phi and load. // TODO: Allow recursive phi users. // TODO: Allow stores. BasicBlock *BB = PN->getParent(); unsigned MaxAlign = 0; for (User *U : PN->users()) { LoadInst *LI = dyn_cast<LoadInst>(U); if (!LI || !LI->isSimple()) return false; // For now we only allow loads in the same block as the PHI. This is a // common case that happens when instcombine merges two loads through a PHI. if (LI->getParent() != BB) return false; // Ensure that there are no instructions between the PHI and the load that // could store. for (BasicBlock::iterator BBI = PN; &*BBI != LI; ++BBI) if (BBI->mayWriteToMemory()) return false; MaxAlign = std::max(MaxAlign, LI->getAlignment()); } // Okay, we know that we have one or more loads in the same block as the PHI. // We can transform this if it is safe to push the loads into the predecessor // blocks. The only thing to watch out for is that we can't put a possibly // trapping load in the predecessor if it is a critical edge. for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { BasicBlock *Pred = PN->getIncomingBlock(i); Value *InVal = PN->getIncomingValue(i); // If the terminator of the predecessor has side-effects (an invoke), // there is no safe place to put a load in the predecessor. if (Pred->getTerminator()->mayHaveSideEffects()) return false; // If the value is produced by the terminator of the predecessor // (an invoke), there is no valid place to put a load in the predecessor. if (Pred->getTerminator() == InVal) return false; // If the predecessor has a single successor, then the edge isn't critical. if (Pred->getTerminator()->getNumSuccessors() == 1) continue; // If this pointer is always safe to load, or if we can prove that there is // already a load in the block, then we can move the load to the pred block. if (InVal->isDereferenceablePointer(DL) || isSafeToLoadUnconditionally(InVal, Pred->getTerminator(), MaxAlign, DL)) continue; return false; } return true; } /// tryToMakeAllocaBePromotable - This returns true if the alloca only has /// direct (non-volatile) loads and stores to it. If the alloca is close but /// not quite there, this will transform the code to allow promotion. As such, /// it is a non-pure predicate. static bool tryToMakeAllocaBePromotable(AllocaInst *AI, const DataLayout *DL) { SetVector<Instruction*, SmallVector<Instruction*, 4>, SmallPtrSet<Instruction*, 4> > InstsToRewrite; for (User *U : AI->users()) { if (LoadInst *LI = dyn_cast<LoadInst>(U)) { if (!LI->isSimple()) return false; continue; } if (StoreInst *SI = dyn_cast<StoreInst>(U)) { if (SI->getOperand(0) == AI || !SI->isSimple()) return false; // Don't allow a store OF the AI, only INTO the AI. continue; } if (SelectInst *SI = dyn_cast<SelectInst>(U)) { // If the condition being selected on is a constant, fold the select, yes // this does (rarely) happen early on. if (ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition())) { Value *Result = SI->getOperand(1+CI->isZero()); SI->replaceAllUsesWith(Result); SI->eraseFromParent(); // This is very rare and we just scrambled the use list of AI, start // over completely. return tryToMakeAllocaBePromotable(AI, DL); } // If it is safe to turn "load (select c, AI, ptr)" into a select of two // loads, then we can transform this by rewriting the select. if (!isSafeSelectToSpeculate(SI, DL)) return false; InstsToRewrite.insert(SI); continue; } if (PHINode *PN = dyn_cast<PHINode>(U)) { if (PN->use_empty()) { // Dead PHIs can be stripped. InstsToRewrite.insert(PN); continue; } // If it is safe to turn "load (phi [AI, ptr, ...])" into a PHI of loads // in the pred blocks, then we can transform this by rewriting the PHI. if (!isSafePHIToSpeculate(PN, DL)) return false; InstsToRewrite.insert(PN); continue; } if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) { if (onlyUsedByLifetimeMarkers(BCI)) { InstsToRewrite.insert(BCI); continue; } } return false; } // If there are no instructions to rewrite, then all uses are load/stores and // we're done! if (InstsToRewrite.empty()) return true; // If we have instructions that need to be rewritten for this to be promotable // take care of it now. for (unsigned i = 0, e = InstsToRewrite.size(); i != e; ++i) { if (BitCastInst *BCI = dyn_cast<BitCastInst>(InstsToRewrite[i])) { // This could only be a bitcast used by nothing but lifetime intrinsics. for (BitCastInst::user_iterator I = BCI->user_begin(), E = BCI->user_end(); I != E;) cast<Instruction>(*I++)->eraseFromParent(); BCI->eraseFromParent(); continue; } if (SelectInst *SI = dyn_cast<SelectInst>(InstsToRewrite[i])) { // Selects in InstsToRewrite only have load uses. Rewrite each as two // loads with a new select. while (!SI->use_empty()) { LoadInst *LI = cast<LoadInst>(SI->user_back()); IRBuilder<> Builder(LI); LoadInst *TrueLoad = Builder.CreateLoad(SI->getTrueValue(), LI->getName()+".t"); LoadInst *FalseLoad = Builder.CreateLoad(SI->getFalseValue(), LI->getName()+".f"); // Transfer alignment and TBAA info if present. TrueLoad->setAlignment(LI->getAlignment()); FalseLoad->setAlignment(LI->getAlignment()); if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) { TrueLoad->setMetadata(LLVMContext::MD_tbaa, Tag); FalseLoad->setMetadata(LLVMContext::MD_tbaa, Tag); } Value *V = Builder.CreateSelect(SI->getCondition(), TrueLoad, FalseLoad); V->takeName(LI); LI->replaceAllUsesWith(V); LI->eraseFromParent(); } // Now that all the loads are gone, the select is gone too. SI->eraseFromParent(); continue; } // Otherwise, we have a PHI node which allows us to push the loads into the // predecessors. PHINode *PN = cast<PHINode>(InstsToRewrite[i]); if (PN->use_empty()) { PN->eraseFromParent(); continue; } Type *LoadTy = cast<PointerType>(PN->getType())->getElementType(); PHINode *NewPN = PHINode::Create(LoadTy, PN->getNumIncomingValues(), PN->getName()+".ld", PN); // Get the TBAA tag and alignment to use from one of the loads. It doesn't // matter which one we get and if any differ, it doesn't matter. LoadInst *SomeLoad = cast<LoadInst>(PN->user_back()); MDNode *TBAATag = SomeLoad->getMetadata(LLVMContext::MD_tbaa); unsigned Align = SomeLoad->getAlignment(); // Rewrite all loads of the PN to use the new PHI. while (!PN->use_empty()) { LoadInst *LI = cast<LoadInst>(PN->user_back()); LI->replaceAllUsesWith(NewPN); LI->eraseFromParent(); } // Inject loads into all of the pred blocks. Keep track of which blocks we // insert them into in case we have multiple edges from the same block. DenseMap<BasicBlock*, LoadInst*> InsertedLoads; for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { BasicBlock *Pred = PN->getIncomingBlock(i); LoadInst *&Load = InsertedLoads[Pred]; if (!Load) { Load = new LoadInst(PN->getIncomingValue(i), PN->getName() + "." + Pred->getName(), Pred->getTerminator()); Load->setAlignment(Align); if (TBAATag) Load->setMetadata(LLVMContext::MD_tbaa, TBAATag); } NewPN->addIncoming(Load, Pred); } PN->eraseFromParent(); } ++NumAdjusted; return true; } bool SROA::performPromotion(Function &F) { std::vector<AllocaInst*> Allocas; DominatorTree *DT = nullptr; if (HasDomTree) DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function DIBuilder DIB(*F.getParent()); bool Changed = false; SmallVector<Instruction*, 64> Insts; while (1) { Allocas.clear(); // Find allocas that are safe to promote, by looking at all instructions in // the entry node for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? if (tryToMakeAllocaBePromotable(AI, DL)) Allocas.push_back(AI); if (Allocas.empty()) break; if (HasDomTree) PromoteMemToReg(Allocas, *DT); else { SSAUpdater SSA; for (unsigned i = 0, e = Allocas.size(); i != e; ++i) { AllocaInst *AI = Allocas[i]; // Build list of instructions to promote. for (User *U : AI->users()) Insts.push_back(cast<Instruction>(U)); AllocaPromoter(Insts, SSA, &DIB).run(AI, Insts); Insts.clear(); } } NumPromoted += Allocas.size(); Changed = true; } return Changed; } /// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for /// SROA. It must be a struct or array type with a small number of elements. bool SROA::ShouldAttemptScalarRepl(AllocaInst *AI) { Type *T = AI->getAllocatedType(); // Do not promote any struct that has too many members. if (StructType *ST = dyn_cast<StructType>(T)) return ST->getNumElements() <= StructMemberThreshold; // Do not promote any array that has too many elements. if (ArrayType *AT = dyn_cast<ArrayType>(T)) return AT->getNumElements() <= ArrayElementThreshold; return false; } // performScalarRepl - This algorithm is a simple worklist driven algorithm, // which runs on all of the alloca instructions in the entry block, removing // them if they are only used by getelementptr instructions. // bool SROA::performScalarRepl(Function &F) { std::vector<AllocaInst*> WorkList; // Scan the entry basic block, adding allocas to the worklist. BasicBlock &BB = F.getEntryBlock(); for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) if (AllocaInst *A = dyn_cast<AllocaInst>(I)) WorkList.push_back(A); // Process the worklist bool Changed = false; while (!WorkList.empty()) { AllocaInst *AI = WorkList.back(); WorkList.pop_back(); // Handle dead allocas trivially. These can be formed by SROA'ing arrays // with unused elements. if (AI->use_empty()) { AI->eraseFromParent(); Changed = true; continue; } // If this alloca is impossible for us to promote, reject it early. if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized()) continue; // Check to see if we can perform the core SROA transformation. We cannot // transform the allocation instruction if it is an array allocation // (allocations OF arrays are ok though), and an allocation of a scalar // value cannot be decomposed at all. uint64_t AllocaSize = DL->getTypeAllocSize(AI->getAllocatedType()); // Do not promote [0 x %struct]. if (AllocaSize == 0) continue; // Do not promote any struct whose size is too big. if (AllocaSize > SRThreshold) continue; // If the alloca looks like a good candidate for scalar replacement, and if // all its users can be transformed, then split up the aggregate into its // separate elements. if (ShouldAttemptScalarRepl(AI) && isSafeAllocaToScalarRepl(AI)) { DoScalarReplacement(AI, WorkList); Changed = true; continue; } // If we can turn this aggregate value (potentially with casts) into a // simple scalar value that can be mem2reg'd into a register value. // IsNotTrivial tracks whether this is something that mem2reg could have // promoted itself. If so, we don't want to transform it needlessly. Note // that we can't just check based on the type: the alloca may be of an i32 // but that has pointer arithmetic to set byte 3 of it or something. if (AllocaInst *NewAI = ConvertToScalarInfo( (unsigned)AllocaSize, *DL, ScalarLoadThreshold).TryConvert(AI)) { NewAI->takeName(AI); AI->eraseFromParent(); ++NumConverted; Changed = true; continue; } // Otherwise, couldn't process this alloca. } return Changed; } /// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl /// predicate, do SROA now. void SROA::DoScalarReplacement(AllocaInst *AI, std::vector<AllocaInst*> &WorkList) { DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n'); SmallVector<AllocaInst*, 32> ElementAllocas; if (StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { ElementAllocas.reserve(ST->getNumContainedTypes()); for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { AllocaInst *NA = new AllocaInst(ST->getContainedType(i), nullptr, AI->getAlignment(), AI->getName() + "." + Twine(i), AI); ElementAllocas.push_back(NA); WorkList.push_back(NA); // Add to worklist for recursive processing } } else { ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); ElementAllocas.reserve(AT->getNumElements()); Type *ElTy = AT->getElementType(); for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { AllocaInst *NA = new AllocaInst(ElTy, nullptr, AI->getAlignment(), AI->getName() + "." + Twine(i), AI); ElementAllocas.push_back(NA); WorkList.push_back(NA); // Add to worklist for recursive processing } } // Now that we have created the new alloca instructions, rewrite all the // uses of the old alloca. RewriteForScalarRepl(AI, AI, 0, ElementAllocas); // Now erase any instructions that were made dead while rewriting the alloca. DeleteDeadInstructions(); AI->eraseFromParent(); ++NumReplaced; } /// DeleteDeadInstructions - Erase instructions on the DeadInstrs list, /// recursively including all their operands that become trivially dead. void SROA::DeleteDeadInstructions() { while (!DeadInsts.empty()) { Instruction *I = cast<Instruction>(DeadInsts.pop_back_val()); for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) if (Instruction *U = dyn_cast<Instruction>(*OI)) { // Zero out the operand and see if it becomes trivially dead. // (But, don't add allocas to the dead instruction list -- they are // already on the worklist and will be deleted separately.) *OI = nullptr; if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U)) DeadInsts.push_back(U); } I->eraseFromParent(); } } /// isSafeForScalarRepl - Check if instruction I is a safe use with regard to /// performing scalar replacement of alloca AI. The results are flagged in /// the Info parameter. Offset indicates the position within AI that is /// referenced by this instruction. void SROA::isSafeForScalarRepl(Instruction *I, uint64_t Offset, AllocaInfo &Info) { for (Use &U : I->uses()) { Instruction *User = cast<Instruction>(U.getUser()); if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { isSafeForScalarRepl(BC, Offset, Info); } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { uint64_t GEPOffset = Offset; isSafeGEP(GEPI, GEPOffset, Info); if (!Info.isUnsafe) isSafeForScalarRepl(GEPI, GEPOffset, Info); } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); if (!Length || Length->isNegative()) return MarkUnsafe(Info, User); isSafeMemAccess(Offset, Length->getZExtValue(), nullptr, U.getOperandNo() == 0, Info, MI, true /*AllowWholeAccess*/); } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) { if (!LI->isSimple()) return MarkUnsafe(Info, User); Type *LIType = LI->getType(); isSafeMemAccess(Offset, DL->getTypeAllocSize(LIType), LIType, false, Info, LI, true /*AllowWholeAccess*/); Info.hasALoadOrStore = true; } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) { // Store is ok if storing INTO the pointer, not storing the pointer if (!SI->isSimple() || SI->getOperand(0) == I) return MarkUnsafe(Info, User); Type *SIType = SI->getOperand(0)->getType(); isSafeMemAccess(Offset, DL->getTypeAllocSize(SIType), SIType, true, Info, SI, true /*AllowWholeAccess*/); Info.hasALoadOrStore = true; } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(User)) { if (II->getIntrinsicID() != Intrinsic::lifetime_start && II->getIntrinsicID() != Intrinsic::lifetime_end) return MarkUnsafe(Info, User); } else if (isa<PHINode>(User) || isa<SelectInst>(User)) { isSafePHISelectUseForScalarRepl(User, Offset, Info); } else { return MarkUnsafe(Info, User); } if (Info.isUnsafe) return; } } /// isSafePHIUseForScalarRepl - If we see a PHI node or select using a pointer /// derived from the alloca, we can often still split the alloca into elements. /// This is useful if we have a large alloca where one element is phi'd /// together somewhere: we can SRoA and promote all the other elements even if /// we end up not being able to promote this one. /// /// All we require is that the uses of the PHI do not index into other parts of /// the alloca. The most important use case for this is single load and stores /// that are PHI'd together, which can happen due to code sinking. void SROA::isSafePHISelectUseForScalarRepl(Instruction *I, uint64_t Offset, AllocaInfo &Info) { // If we've already checked this PHI, don't do it again. if (PHINode *PN = dyn_cast<PHINode>(I)) if (!Info.CheckedPHIs.insert(PN)) return; for (User *U : I->users()) { Instruction *UI = cast<Instruction>(U); if (BitCastInst *BC = dyn_cast<BitCastInst>(UI)) { isSafePHISelectUseForScalarRepl(BC, Offset, Info); } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(UI)) { // Only allow "bitcast" GEPs for simplicity. We could generalize this, // but would have to prove that we're staying inside of an element being // promoted. if (!GEPI->hasAllZeroIndices()) return MarkUnsafe(Info, UI); isSafePHISelectUseForScalarRepl(GEPI, Offset, Info); } else if (LoadInst *LI = dyn_cast<LoadInst>(UI)) { if (!LI->isSimple()) return MarkUnsafe(Info, UI); Type *LIType = LI->getType(); isSafeMemAccess(Offset, DL->getTypeAllocSize(LIType), LIType, false, Info, LI, false /*AllowWholeAccess*/); Info.hasALoadOrStore = true; } else if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { // Store is ok if storing INTO the pointer, not storing the pointer if (!SI->isSimple() || SI->getOperand(0) == I) return MarkUnsafe(Info, UI); Type *SIType = SI->getOperand(0)->getType(); isSafeMemAccess(Offset, DL->getTypeAllocSize(SIType), SIType, true, Info, SI, false /*AllowWholeAccess*/); Info.hasALoadOrStore = true; } else if (isa<PHINode>(UI) || isa<SelectInst>(UI)) { isSafePHISelectUseForScalarRepl(UI, Offset, Info); } else { return MarkUnsafe(Info, UI); } if (Info.isUnsafe) return; } } /// isSafeGEP - Check if a GEP instruction can be handled for scalar /// replacement. It is safe when all the indices are constant, in-bounds /// references, and when the resulting offset corresponds to an element within /// the alloca type. The results are flagged in the Info parameter. Upon /// return, Offset is adjusted as specified by the GEP indices. void SROA::isSafeGEP(GetElementPtrInst *GEPI, uint64_t &Offset, AllocaInfo &Info) { gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI); if (GEPIt == E) return; bool NonConstant = false; unsigned NonConstantIdxSize = 0; // Walk through the GEP type indices, checking the types that this indexes // into. for (; GEPIt != E; ++GEPIt) { // Ignore struct elements, no extra checking needed for these. if ((*GEPIt)->isStructTy()) continue; ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand()); if (!IdxVal) return MarkUnsafe(Info, GEPI); } // Compute the offset due to this GEP and check if the alloca has a // component element at that offset. SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); // If this GEP is non-constant then the last operand must have been a // dynamic index into a vector. Pop this now as it has no impact on the // constant part of the offset. if (NonConstant) Indices.pop_back(); Offset += DL->getIndexedOffset(GEPI->getPointerOperandType(), Indices); if (!TypeHasComponent(Info.AI->getAllocatedType(), Offset, NonConstantIdxSize)) MarkUnsafe(Info, GEPI); } /// isHomogeneousAggregate - Check if type T is a struct or array containing /// elements of the same type (which is always true for arrays). If so, /// return true with NumElts and EltTy set to the number of elements and the /// element type, respectively. static bool isHomogeneousAggregate(Type *T, unsigned &NumElts, Type *&EltTy) { if (ArrayType *AT = dyn_cast<ArrayType>(T)) { NumElts = AT->getNumElements(); EltTy = (NumElts == 0 ? nullptr : AT->getElementType()); return true; } if (StructType *ST = dyn_cast<StructType>(T)) { NumElts = ST->getNumContainedTypes(); EltTy = (NumElts == 0 ? nullptr : ST->getContainedType(0)); for (unsigned n = 1; n < NumElts; ++n) { if (ST->getContainedType(n) != EltTy) return false; } return true; } return false; } /// isCompatibleAggregate - Check if T1 and T2 are either the same type or are /// "homogeneous" aggregates with the same element type and number of elements. static bool isCompatibleAggregate(Type *T1, Type *T2) { if (T1 == T2) return true; unsigned NumElts1, NumElts2; Type *EltTy1, *EltTy2; if (isHomogeneousAggregate(T1, NumElts1, EltTy1) && isHomogeneousAggregate(T2, NumElts2, EltTy2) && NumElts1 == NumElts2 && EltTy1 == EltTy2) return true; return false; } /// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI /// alloca or has an offset and size that corresponds to a component element /// within it. The offset checked here may have been formed from a GEP with a /// pointer bitcasted to a different type. /// /// If AllowWholeAccess is true, then this allows uses of the entire alloca as a /// unit. If false, it only allows accesses known to be in a single element. void SROA::isSafeMemAccess(uint64_t Offset, uint64_t MemSize, Type *MemOpType, bool isStore, AllocaInfo &Info, Instruction *TheAccess, bool AllowWholeAccess) { // Check if this is a load/store of the entire alloca. if (Offset == 0 && AllowWholeAccess && MemSize == DL->getTypeAllocSize(Info.AI->getAllocatedType())) { // This can be safe for MemIntrinsics (where MemOpType is 0) and integer // loads/stores (which are essentially the same as the MemIntrinsics with // regard to copying padding between elements). But, if an alloca is // flagged as both a source and destination of such operations, we'll need // to check later for padding between elements. if (!MemOpType || MemOpType->isIntegerTy()) { if (isStore) Info.isMemCpyDst = true; else Info.isMemCpySrc = true; return; } // This is also safe for references using a type that is compatible with // the type of the alloca, so that loads/stores can be rewritten using // insertvalue/extractvalue. if (isCompatibleAggregate(MemOpType, Info.AI->getAllocatedType())) { Info.hasSubelementAccess = true; return; } } // Check if the offset/size correspond to a component within the alloca type. Type *T = Info.AI->getAllocatedType(); if (TypeHasComponent(T, Offset, MemSize)) { Info.hasSubelementAccess = true; return; } return MarkUnsafe(Info, TheAccess); } /// TypeHasComponent - Return true if T has a component type with the /// specified offset and size. If Size is zero, do not check the size. bool SROA::TypeHasComponent(Type *T, uint64_t Offset, uint64_t Size) { Type *EltTy; uint64_t EltSize; if (StructType *ST = dyn_cast<StructType>(T)) { const StructLayout *Layout = DL->getStructLayout(ST); unsigned EltIdx = Layout->getElementContainingOffset(Offset); EltTy = ST->getContainedType(EltIdx); EltSize = DL->getTypeAllocSize(EltTy); Offset -= Layout->getElementOffset(EltIdx); } else if (ArrayType *AT = dyn_cast<ArrayType>(T)) { EltTy = AT->getElementType(); EltSize = DL->getTypeAllocSize(EltTy); if (Offset >= AT->getNumElements() * EltSize) return false; Offset %= EltSize; } else if (VectorType *VT = dyn_cast<VectorType>(T)) { EltTy = VT->getElementType(); EltSize = DL->getTypeAllocSize(EltTy); if (Offset >= VT->getNumElements() * EltSize) return false; Offset %= EltSize; } else { return false; } if (Offset == 0 && (Size == 0 || EltSize == Size)) return true; // Check if the component spans multiple elements. if (Offset + Size > EltSize) return false; return TypeHasComponent(EltTy, Offset, Size); } /// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite /// the instruction I, which references it, to use the separate elements. /// Offset indicates the position within AI that is referenced by this /// instruction. void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, SmallVectorImpl<AllocaInst *> &NewElts) { for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E;) { Use &TheUse = *UI++; Instruction *User = cast<Instruction>(TheUse.getUser()); if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) { RewriteBitCast(BC, AI, Offset, NewElts); continue; } if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { RewriteGEP(GEPI, AI, Offset, NewElts); continue; } if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) { ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength()); uint64_t MemSize = Length->getZExtValue(); if (Offset == 0 && MemSize == DL->getTypeAllocSize(AI->getAllocatedType())) RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts); // Otherwise the intrinsic can only touch a single element and the // address operand will be updated, so nothing else needs to be done. continue; } if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(User)) { if (II->getIntrinsicID() == Intrinsic::lifetime_start || II->getIntrinsicID() == Intrinsic::lifetime_end) { RewriteLifetimeIntrinsic(II, AI, Offset, NewElts); } continue; } if (LoadInst *LI = dyn_cast<LoadInst>(User)) { Type *LIType = LI->getType(); if (isCompatibleAggregate(LIType, AI->getAllocatedType())) { // Replace: // %res = load { i32, i32 }* %alloc // with: // %load.0 = load i32* %alloc.0 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0 // %load.1 = load i32* %alloc.1 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1 // (Also works for arrays instead of structs) Value *Insert = UndefValue::get(LIType); IRBuilder<> Builder(LI); for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { Value *Load = Builder.CreateLoad(NewElts[i], "load"); Insert = Builder.CreateInsertValue(Insert, Load, i, "insert"); } LI->replaceAllUsesWith(Insert); DeadInsts.push_back(LI); } else if (LIType->isIntegerTy() && DL->getTypeAllocSize(LIType) == DL->getTypeAllocSize(AI->getAllocatedType())) { // If this is a load of the entire alloca to an integer, rewrite it. RewriteLoadUserOfWholeAlloca(LI, AI, NewElts); } continue; } if (StoreInst *SI = dyn_cast<StoreInst>(User)) { Value *Val = SI->getOperand(0); Type *SIType = Val->getType(); if (isCompatibleAggregate(SIType, AI->getAllocatedType())) { // Replace: // store { i32, i32 } %val, { i32, i32 }* %alloc // with: // %val.0 = extractvalue { i32, i32 } %val, 0 // store i32 %val.0, i32* %alloc.0 // %val.1 = extractvalue { i32, i32 } %val, 1 // store i32 %val.1, i32* %alloc.1 // (Also works for arrays instead of structs) IRBuilder<> Builder(SI); for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { Value *Extract = Builder.CreateExtractValue(Val, i, Val->getName()); Builder.CreateStore(Extract, NewElts[i]); } DeadInsts.push_back(SI); } else if (SIType->isIntegerTy() && DL->getTypeAllocSize(SIType) == DL->getTypeAllocSize(AI->getAllocatedType())) { // If this is a store of the entire alloca from an integer, rewrite it. RewriteStoreUserOfWholeAlloca(SI, AI, NewElts); } continue; } if (isa<SelectInst>(User) || isa<PHINode>(User)) { // If we have a PHI user of the alloca itself (as opposed to a GEP or // bitcast) we have to rewrite it. GEP and bitcast uses will be RAUW'd to // the new pointer. if (!isa<AllocaInst>(I)) continue; assert(Offset == 0 && NewElts[0] && "Direct alloca use should have a zero offset"); // If we have a use of the alloca, we know the derived uses will be // utilizing just the first element of the scalarized result. Insert a // bitcast of the first alloca before the user as required. AllocaInst *NewAI = NewElts[0]; BitCastInst *BCI = new BitCastInst(NewAI, AI->getType(), "", NewAI); NewAI->moveBefore(BCI); TheUse = BCI; continue; } } } /// RewriteBitCast - Update a bitcast reference to the alloca being replaced /// and recursively continue updating all of its uses. void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, SmallVectorImpl<AllocaInst *> &NewElts) { RewriteForScalarRepl(BC, AI, Offset, NewElts); if (BC->getOperand(0) != AI) return; // The bitcast references the original alloca. Replace its uses with // references to the alloca containing offset zero (which is normally at // index zero, but might not be in cases involving structs with elements // of size zero). Type *T = AI->getAllocatedType(); uint64_t EltOffset = 0; Type *IdxTy; uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy); Instruction *Val = NewElts[Idx]; if (Val->getType() != BC->getDestTy()) { Val = new BitCastInst(Val, BC->getDestTy(), "", BC); Val->takeName(BC); } BC->replaceAllUsesWith(Val); DeadInsts.push_back(BC); } /// FindElementAndOffset - Return the index of the element containing Offset /// within the specified type, which must be either a struct or an array. /// Sets T to the type of the element and Offset to the offset within that /// element. IdxTy is set to the type of the index result to be used in a /// GEP instruction. uint64_t SROA::FindElementAndOffset(Type *&T, uint64_t &Offset, Type *&IdxTy) { uint64_t Idx = 0; if (StructType *ST = dyn_cast<StructType>(T)) { const StructLayout *Layout = DL->getStructLayout(ST); Idx = Layout->getElementContainingOffset(Offset); T = ST->getContainedType(Idx); Offset -= Layout->getElementOffset(Idx); IdxTy = Type::getInt32Ty(T->getContext()); return Idx; } else if (ArrayType *AT = dyn_cast<ArrayType>(T)) { T = AT->getElementType(); uint64_t EltSize = DL->getTypeAllocSize(T); Idx = Offset / EltSize; Offset -= Idx * EltSize; IdxTy = Type::getInt64Ty(T->getContext()); return Idx; } VectorType *VT = cast<VectorType>(T); T = VT->getElementType(); uint64_t EltSize = DL->getTypeAllocSize(T); Idx = Offset / EltSize; Offset -= Idx * EltSize; IdxTy = Type::getInt64Ty(T->getContext()); return Idx; } /// RewriteGEP - Check if this GEP instruction moves the pointer across /// elements of the alloca that are being split apart, and if so, rewrite /// the GEP to be relative to the new element. void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, SmallVectorImpl<AllocaInst *> &NewElts) { uint64_t OldOffset = Offset; SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end()); // If the GEP was dynamic then it must have been a dynamic vector lookup. // In this case, it must be the last GEP operand which is dynamic so keep that // aside until we've found the constant GEP offset then add it back in at the // end. Value* NonConstantIdx = nullptr; if (!GEPI->hasAllConstantIndices()) NonConstantIdx = Indices.pop_back_val(); Offset += DL->getIndexedOffset(GEPI->getPointerOperandType(), Indices); RewriteForScalarRepl(GEPI, AI, Offset, NewElts); Type *T = AI->getAllocatedType(); Type *IdxTy; uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy); if (GEPI->getOperand(0) == AI) OldIdx = ~0ULL; // Force the GEP to be rewritten. T = AI->getAllocatedType(); uint64_t EltOffset = Offset; uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy); // If this GEP does not move the pointer across elements of the alloca // being split, then it does not needs to be rewritten. if (Idx == OldIdx) return; Type *i32Ty = Type::getInt32Ty(AI->getContext()); SmallVector<Value*, 8> NewArgs; NewArgs.push_back(Constant::getNullValue(i32Ty)); while (EltOffset != 0) { uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy); NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx)); } if (NonConstantIdx) { Type* GepTy = T; // This GEP has a dynamic index. We need to add "i32 0" to index through // any structs or arrays in the original type until we get to the vector // to index. while (!isa<VectorType>(GepTy)) { NewArgs.push_back(Constant::getNullValue(i32Ty)); GepTy = cast<CompositeType>(GepTy)->getTypeAtIndex(0U); } NewArgs.push_back(NonConstantIdx); } Instruction *Val = NewElts[Idx]; if (NewArgs.size() > 1) { Val = GetElementPtrInst::CreateInBounds(Val, NewArgs, "", GEPI); Val->takeName(GEPI); } if (Val->getType() != GEPI->getType()) Val = new BitCastInst(Val, GEPI->getType(), Val->getName(), GEPI); GEPI->replaceAllUsesWith(Val); DeadInsts.push_back(GEPI); } /// RewriteLifetimeIntrinsic - II is a lifetime.start/lifetime.end. Rewrite it /// to mark the lifetime of the scalarized memory. void SROA::RewriteLifetimeIntrinsic(IntrinsicInst *II, AllocaInst *AI, uint64_t Offset, SmallVectorImpl<AllocaInst *> &NewElts) { ConstantInt *OldSize = cast<ConstantInt>(II->getArgOperand(0)); // Put matching lifetime markers on everything from Offset up to // Offset+OldSize. Type *AIType = AI->getAllocatedType(); uint64_t NewOffset = Offset; Type *IdxTy; uint64_t Idx = FindElementAndOffset(AIType, NewOffset, IdxTy); IRBuilder<> Builder(II); uint64_t Size = OldSize->getLimitedValue(); if (NewOffset) { // Splice the first element and index 'NewOffset' bytes in. SROA will // split the alloca again later. unsigned AS = AI->getType()->getAddressSpace(); Value *V = Builder.CreateBitCast(NewElts[Idx], Builder.getInt8PtrTy(AS)); V = Builder.CreateGEP(V, Builder.getInt64(NewOffset)); IdxTy = NewElts[Idx]->getAllocatedType(); uint64_t EltSize = DL->getTypeAllocSize(IdxTy) - NewOffset; if (EltSize > Size) { EltSize = Size; Size = 0; } else { Size -= EltSize; } if (II->getIntrinsicID() == Intrinsic::lifetime_start) Builder.CreateLifetimeStart(V, Builder.getInt64(EltSize)); else Builder.CreateLifetimeEnd(V, Builder.getInt64(EltSize)); ++Idx; } for (; Idx != NewElts.size() && Size; ++Idx) { IdxTy = NewElts[Idx]->getAllocatedType(); uint64_t EltSize = DL->getTypeAllocSize(IdxTy); if (EltSize > Size) { EltSize = Size; Size = 0; } else { Size -= EltSize; } if (II->getIntrinsicID() == Intrinsic::lifetime_start) Builder.CreateLifetimeStart(NewElts[Idx], Builder.getInt64(EltSize)); else Builder.CreateLifetimeEnd(NewElts[Idx], Builder.getInt64(EltSize)); } DeadInsts.push_back(II); } /// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI. /// Rewrite it to copy or set the elements of the scalarized memory. void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, AllocaInst *AI, SmallVectorImpl<AllocaInst *> &NewElts) { // If this is a memcpy/memmove, construct the other pointer as the // appropriate type. The "Other" pointer is the pointer that goes to memory // that doesn't have anything to do with the alloca that we are promoting. For // memset, this Value* stays null. Value *OtherPtr = nullptr; unsigned MemAlignment = MI->getAlignment(); if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy if (Inst == MTI->getRawDest()) OtherPtr = MTI->getRawSource(); else { assert(Inst == MTI->getRawSource()); OtherPtr = MTI->getRawDest(); } } // If there is an other pointer, we want to convert it to the same pointer // type as AI has, so we can GEP through it safely. if (OtherPtr) { unsigned AddrSpace = cast<PointerType>(OtherPtr->getType())->getAddressSpace(); // Remove bitcasts and all-zero GEPs from OtherPtr. This is an // optimization, but it's also required to detect the corner case where // both pointer operands are referencing the same memory, and where // OtherPtr may be a bitcast or GEP that currently being rewritten. (This // function is only called for mem intrinsics that access the whole // aggregate, so non-zero GEPs are not an issue here.) OtherPtr = OtherPtr->stripPointerCasts(); // Copying the alloca to itself is a no-op: just delete it. if (OtherPtr == AI || OtherPtr == NewElts[0]) { // This code will run twice for a no-op memcpy -- once for each operand. // Put only one reference to MI on the DeadInsts list. for (SmallVectorImpl<Value *>::const_iterator I = DeadInsts.begin(), E = DeadInsts.end(); I != E; ++I) if (*I == MI) return; DeadInsts.push_back(MI); return; } // If the pointer is not the right type, insert a bitcast to the right // type. Type *NewTy = PointerType::get(AI->getType()->getElementType(), AddrSpace); if (OtherPtr->getType() != NewTy) OtherPtr = new BitCastInst(OtherPtr, NewTy, OtherPtr->getName(), MI); } // Process each element of the aggregate. bool SROADest = MI->getRawDest() == Inst; Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext())); for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { // If this is a memcpy/memmove, emit a GEP of the other element address. Value *OtherElt = nullptr; unsigned OtherEltAlign = MemAlignment; if (OtherPtr) { Value *Idx[2] = { Zero, ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) }; OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, OtherPtr->getName()+"."+Twine(i), MI); uint64_t EltOffset; PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType()); Type *OtherTy = OtherPtrTy->getElementType(); if (StructType *ST = dyn_cast<StructType>(OtherTy)) { EltOffset = DL->getStructLayout(ST)->getElementOffset(i); } else { Type *EltTy = cast<SequentialType>(OtherTy)->getElementType(); EltOffset = DL->getTypeAllocSize(EltTy)*i; } // The alignment of the other pointer is the guaranteed alignment of the // element, which is affected by both the known alignment of the whole // mem intrinsic and the alignment of the element. If the alignment of // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the // known alignment is just 4 bytes. OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset); } Value *EltPtr = NewElts[i]; Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType(); // If we got down to a scalar, insert a load or store as appropriate. if (EltTy->isSingleValueType()) { if (isa<MemTransferInst>(MI)) { if (SROADest) { // From Other to Alloca. Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI); new StoreInst(Elt, EltPtr, MI); } else { // From Alloca to Other. Value *Elt = new LoadInst(EltPtr, "tmp", MI); new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI); } continue; } assert(isa<MemSetInst>(MI)); // If the stored element is zero (common case), just store a null // constant. Constant *StoreVal; if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getArgOperand(1))) { if (CI->isZero()) { StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0> } else { // If EltTy is a vector type, get the element type. Type *ValTy = EltTy->getScalarType(); // Construct an integer with the right value. unsigned EltSize = DL->getTypeSizeInBits(ValTy); APInt OneVal(EltSize, CI->getZExtValue()); APInt TotalVal(OneVal); // Set each byte. for (unsigned i = 0; 8*i < EltSize; ++i) { TotalVal = TotalVal.shl(8); TotalVal |= OneVal; } // Convert the integer value to the appropriate type. StoreVal = ConstantInt::get(CI->getContext(), TotalVal); if (ValTy->isPointerTy()) StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); else if (ValTy->isFloatingPointTy()) StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy); assert(StoreVal->getType() == ValTy && "Type mismatch!"); // If the requested value was a vector constant, create it. if (EltTy->isVectorTy()) { unsigned NumElts = cast<VectorType>(EltTy)->getNumElements(); StoreVal = ConstantVector::getSplat(NumElts, StoreVal); } } new StoreInst(StoreVal, EltPtr, MI); continue; } // Otherwise, if we're storing a byte variable, use a memset call for // this element. } unsigned EltSize = DL->getTypeAllocSize(EltTy); if (!EltSize) continue; IRBuilder<> Builder(MI); // Finally, insert the meminst for this element. if (isa<MemSetInst>(MI)) { Builder.CreateMemSet(EltPtr, MI->getArgOperand(1), EltSize, MI->isVolatile()); } else { assert(isa<MemTransferInst>(MI)); Value *Dst = SROADest ? EltPtr : OtherElt; // Dest ptr Value *Src = SROADest ? OtherElt : EltPtr; // Src ptr if (isa<MemCpyInst>(MI)) Builder.CreateMemCpy(Dst, Src, EltSize, OtherEltAlign,MI->isVolatile()); else Builder.CreateMemMove(Dst, Src, EltSize,OtherEltAlign,MI->isVolatile()); } } DeadInsts.push_back(MI); } /// RewriteStoreUserOfWholeAlloca - We found a store of an integer that /// overwrites the entire allocation. Extract out the pieces of the stored /// integer and store them individually. void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, SmallVectorImpl<AllocaInst *> &NewElts) { // Extract each element out of the integer according to its structure offset // and store the element value to the individual alloca. Value *SrcVal = SI->getOperand(0); Type *AllocaEltTy = AI->getAllocatedType(); uint64_t AllocaSizeBits = DL->getTypeAllocSizeInBits(AllocaEltTy); IRBuilder<> Builder(SI); // Handle tail padding by extending the operand if (DL->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits) SrcVal = Builder.CreateZExt(SrcVal, IntegerType::get(SI->getContext(), AllocaSizeBits)); DEBUG(dbgs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI << '\n'); // There are two forms here: AI could be an array or struct. Both cases // have different ways to compute the element offset. if (StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { const StructLayout *Layout = DL->getStructLayout(EltSTy); for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { // Get the number of bits to shift SrcVal to get the value. Type *FieldTy = EltSTy->getElementType(i); uint64_t Shift = Layout->getElementOffsetInBits(i); if (DL->isBigEndian()) Shift = AllocaSizeBits-Shift-DL->getTypeAllocSizeInBits(FieldTy); Value *EltVal = SrcVal; if (Shift) { Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); EltVal = Builder.CreateLShr(EltVal, ShiftVal, "sroa.store.elt"); } // Truncate down to an integer of the right size. uint64_t FieldSizeBits = DL->getTypeSizeInBits(FieldTy); // Ignore zero sized fields like {}, they obviously contain no data. if (FieldSizeBits == 0) continue; if (FieldSizeBits != AllocaSizeBits) EltVal = Builder.CreateTrunc(EltVal, IntegerType::get(SI->getContext(), FieldSizeBits)); Value *DestField = NewElts[i]; if (EltVal->getType() == FieldTy) { // Storing to an integer field of this size, just do it. } else if (FieldTy->isFloatingPointTy() || FieldTy->isVectorTy()) { // Bitcast to the right element type (for fp/vector values). EltVal = Builder.CreateBitCast(EltVal, FieldTy); } else { // Otherwise, bitcast the dest pointer (for aggregates). DestField = Builder.CreateBitCast(DestField, PointerType::getUnqual(EltVal->getType())); } new StoreInst(EltVal, DestField, SI); } } else { ArrayType *ATy = cast<ArrayType>(AllocaEltTy); Type *ArrayEltTy = ATy->getElementType(); uint64_t ElementOffset = DL->getTypeAllocSizeInBits(ArrayEltTy); uint64_t ElementSizeBits = DL->getTypeSizeInBits(ArrayEltTy); uint64_t Shift; if (DL->isBigEndian()) Shift = AllocaSizeBits-ElementOffset; else Shift = 0; for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { // Ignore zero sized fields like {}, they obviously contain no data. if (ElementSizeBits == 0) continue; Value *EltVal = SrcVal; if (Shift) { Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift); EltVal = Builder.CreateLShr(EltVal, ShiftVal, "sroa.store.elt"); } // Truncate down to an integer of the right size. if (ElementSizeBits != AllocaSizeBits) EltVal = Builder.CreateTrunc(EltVal, IntegerType::get(SI->getContext(), ElementSizeBits)); Value *DestField = NewElts[i]; if (EltVal->getType() == ArrayEltTy) { // Storing to an integer field of this size, just do it. } else if (ArrayEltTy->isFloatingPointTy() || ArrayEltTy->isVectorTy()) { // Bitcast to the right element type (for fp/vector values). EltVal = Builder.CreateBitCast(EltVal, ArrayEltTy); } else { // Otherwise, bitcast the dest pointer (for aggregates). DestField = Builder.CreateBitCast(DestField, PointerType::getUnqual(EltVal->getType())); } new StoreInst(EltVal, DestField, SI); if (DL->isBigEndian()) Shift -= ElementOffset; else Shift += ElementOffset; } } DeadInsts.push_back(SI); } /// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to /// an integer. Load the individual pieces to form the aggregate value. void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, SmallVectorImpl<AllocaInst *> &NewElts) { // Extract each element out of the NewElts according to its structure offset // and form the result value. Type *AllocaEltTy = AI->getAllocatedType(); uint64_t AllocaSizeBits = DL->getTypeAllocSizeInBits(AllocaEltTy); DEBUG(dbgs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI << '\n'); // There are two forms here: AI could be an array or struct. Both cases // have different ways to compute the element offset. const StructLayout *Layout = nullptr; uint64_t ArrayEltBitOffset = 0; if (StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) { Layout = DL->getStructLayout(EltSTy); } else { Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType(); ArrayEltBitOffset = DL->getTypeAllocSizeInBits(ArrayEltTy); } Value *ResultVal = Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits)); for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { // Load the value from the alloca. If the NewElt is an aggregate, cast // the pointer to an integer of the same size before doing the load. Value *SrcField = NewElts[i]; Type *FieldTy = cast<PointerType>(SrcField->getType())->getElementType(); uint64_t FieldSizeBits = DL->getTypeSizeInBits(FieldTy); // Ignore zero sized fields like {}, they obviously contain no data. if (FieldSizeBits == 0) continue; IntegerType *FieldIntTy = IntegerType::get(LI->getContext(), FieldSizeBits); if (!FieldTy->isIntegerTy() && !FieldTy->isFloatingPointTy() && !FieldTy->isVectorTy()) SrcField = new BitCastInst(SrcField, PointerType::getUnqual(FieldIntTy), "", LI); SrcField = new LoadInst(SrcField, "sroa.load.elt", LI); // If SrcField is a fp or vector of the right size but that isn't an // integer type, bitcast to an integer so we can shift it. if (SrcField->getType() != FieldIntTy) SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI); // Zero extend the field to be the same size as the final alloca so that // we can shift and insert it. if (SrcField->getType() != ResultVal->getType()) SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI); // Determine the number of bits to shift SrcField. uint64_t Shift; if (Layout) // Struct case. Shift = Layout->getElementOffsetInBits(i); else // Array case. Shift = i*ArrayEltBitOffset; if (DL->isBigEndian()) Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth(); if (Shift) { Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift); SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI); } // Don't create an 'or x, 0' on the first iteration. if (!isa<Constant>(ResultVal) || !cast<Constant>(ResultVal)->isNullValue()) ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI); else ResultVal = SrcField; } // Handle tail padding by truncating the result if (DL->getTypeSizeInBits(LI->getType()) != AllocaSizeBits) ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI); LI->replaceAllUsesWith(ResultVal); DeadInsts.push_back(LI); } /// HasPadding - Return true if the specified type has any structure or /// alignment padding in between the elements that would be split apart /// by SROA; return false otherwise. static bool HasPadding(Type *Ty, const DataLayout &DL) { if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { Ty = ATy->getElementType(); return DL.getTypeSizeInBits(Ty) != DL.getTypeAllocSizeInBits(Ty); } // SROA currently handles only Arrays and Structs. StructType *STy = cast<StructType>(Ty); const StructLayout *SL = DL.getStructLayout(STy); unsigned PrevFieldBitOffset = 0; for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { unsigned FieldBitOffset = SL->getElementOffsetInBits(i); // Check to see if there is any padding between this element and the // previous one. if (i) { unsigned PrevFieldEnd = PrevFieldBitOffset+DL.getTypeSizeInBits(STy->getElementType(i-1)); if (PrevFieldEnd < FieldBitOffset) return true; } PrevFieldBitOffset = FieldBitOffset; } // Check for tail padding. if (unsigned EltCount = STy->getNumElements()) { unsigned PrevFieldEnd = PrevFieldBitOffset + DL.getTypeSizeInBits(STy->getElementType(EltCount-1)); if (PrevFieldEnd < SL->getSizeInBits()) return true; } return false; } /// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of /// an aggregate can be broken down into elements. Return 0 if not, 3 if safe, /// or 1 if safe after canonicalization has been performed. bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) { // Loop over the use list of the alloca. We can only transform it if all of // the users are safe to transform. AllocaInfo Info(AI); isSafeForScalarRepl(AI, 0, Info); if (Info.isUnsafe) { DEBUG(dbgs() << "Cannot transform: " << *AI << '\n'); return false; } // Okay, we know all the users are promotable. If the aggregate is a memcpy // source and destination, we have to be careful. In particular, the memcpy // could be moving around elements that live in structure padding of the LLVM // types, but may actually be used. In these cases, we refuse to promote the // struct. if (Info.isMemCpySrc && Info.isMemCpyDst && HasPadding(AI->getAllocatedType(), *DL)) return false; // If the alloca never has an access to just *part* of it, but is accessed // via loads and stores, then we should use ConvertToScalarInfo to promote // the alloca instead of promoting each piece at a time and inserting fission // and fusion code. if (!Info.hasSubelementAccess && Info.hasALoadOrStore) { // If the struct/array just has one element, use basic SRoA. if (StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { if (ST->getNumElements() > 1) return false; } else { if (cast<ArrayType>(AI->getAllocatedType())->getNumElements() > 1) return false; } } return true; }