//===- 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 // often interact, especially for C++ programs. As such, iterating between // SRoA, then Mem2Reg until we run out of things to promote works well. // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "scalarrepl" #include "llvm/Transforms/Scalar.h" #include "llvm/Constants.h" #include "llvm/DerivedTypes.h" #include "llvm/Function.h" #include "llvm/GlobalVariable.h" #include "llvm/Instructions.h" #include "llvm/IntrinsicInst.h" #include "llvm/LLVMContext.h" #include "llvm/Module.h" #include "llvm/Pass.h" #include "llvm/Analysis/Dominators.h" #include "llvm/Analysis/Loads.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/Target/TargetData.h" #include "llvm/Transforms/Utils/PromoteMemToReg.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Transforms/Utils/SSAUpdater.h" #include "llvm/Support/CallSite.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/IRBuilder.h" #include "llvm/Support/MathExtras.h" #include "llvm/Support/raw_ostream.h" #include "llvm/ADT/SetVector.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" using namespace llvm; 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"); STATISTIC(NumGlobals, "Number of allocas copied from constant global"); namespace { struct SROA : public FunctionPass { SROA(int T, bool hasDT, char &ID) : FunctionPass(ID), HasDomTree(hasDT) { if (T == -1) SRThreshold = 128; else SRThreshold = T; } bool runOnFunction(Function &F); bool performScalarRepl(Function &F); bool performPromotion(Function &F); private: bool HasDomTree; TargetData *TD; /// DeadInsts - Keep track of instructions we have made dead, so that /// we can remove them after we are done working. SmallVector 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 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) {} }; unsigned SRThreshold; 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, const Type *MemOpType, bool isStore, AllocaInfo &Info, Instruction *TheAccess, bool AllowWholeAccess); bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size); uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset, const Type *&IdxTy); void DoScalarReplacement(AllocaInst *AI, std::vector &WorkList); void DeleteDeadInstructions(); void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset, SmallVector &NewElts); void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset, SmallVector &NewElts); void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset, SmallVector &NewElts); void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst, AllocaInst *AI, SmallVector &NewElts); void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI, SmallVector &NewElts); void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI, SmallVector &NewElts); static MemTransferInst *isOnlyCopiedFromConstantGlobal(AllocaInst *AI); }; // SROA_DT - SROA that uses DominatorTree. struct SROA_DT : public SROA { static char ID; public: SROA_DT(int T = -1) : SROA(T, true, ID) { initializeSROA_DTPass(*PassRegistry::getPassRegistry()); } // getAnalysisUsage - This pass does not require any passes, but we know it // will not alter the CFG, so say so. virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.addRequired(); AU.setPreservesCFG(); } }; // SROA_SSAUp - SROA that uses SSAUpdater. struct SROA_SSAUp : public SROA { static char ID; public: SROA_SSAUp(int T = -1) : SROA(T, false, ID) { initializeSROA_SSAUpPass(*PassRegistry::getPassRegistry()); } // getAnalysisUsage - This pass does not require any passes, but we know it // will not alter the CFG, so say so. virtual void getAnalysisUsage(AnalysisUsage &AU) const { 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(DominatorTree) 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) { if (UseDomTree) return new SROA_DT(Threshold); return new SROA_SSAUp(Threshold); } //===----------------------------------------------------------------------===// // 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 TargetData &TD; /// IsNotTrivial - This is set to true if there is some access to the object /// which means that mem2reg can't promote it. bool IsNotTrivial; /// 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. const Type *VectorTy; /// HadAVector - True if there is at least one vector access to the alloca. /// We don't want to turn random arrays into vectors and use vector element /// insert/extract, but if there are element accesses to something that is /// also declared as a vector, we do want to promote to a vector. bool HadAVector; /// 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; public: explicit ConvertToScalarInfo(unsigned Size, const TargetData &td) : AllocaSize(Size), TD(td), IsNotTrivial(false), VectorTy(0), HadAVector(false), HadNonMemTransferAccess(false) { } AllocaInst *TryConvert(AllocaInst *AI); private: bool CanConvertToScalar(Value *V, uint64_t Offset); void MergeInType(const Type *In, uint64_t Offset, bool IsLoadOrStore); bool MergeInVectorType(const VectorType *VInTy, uint64_t Offset); void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset); Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType, uint64_t Offset, IRBuilder<> &Builder); Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal, uint64_t Offset, 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) || !IsNotTrivial) return 0; // 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. const Type *NewTy; if (VectorTy && VectorTy->isVectorTy() && HadAVector) { DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = " << *VectorTy << '\n'); NewTy = VectorTy; // Use the vector type. } else { unsigned BitWidth = AllocaSize * 8; if (!HadAVector && !HadNonMemTransferAccess && !TD.fitsInLegalInteger(BitWidth)) return 0; 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, 0, "", AI->getParent()->begin()); ConvertUsesToScalar(AI, NewAI, 0); return NewAI; } /// MergeInType - 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 three 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 union of vector types with power-of-2 size differences, e.g. a float, /// <2 x float> and <4 x float>. Here we turn element accesses into insert /// and extract element operations, and <2 x float> accesses into a cast to /// <2 x double>, an extract, and a cast back to <2 x float>. /// 3) 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::MergeInType(const Type *In, uint64_t Offset, bool IsLoadOrStore) { // If we already decided to turn this into a blob of integer memory, there is // nothing to be done. if (VectorTy && VectorTy->isVoidTy()) 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 (const VectorType *VInTy = dyn_cast(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 (IsLoadOrStore && 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 == 0 || cast(VectorTy)->getElementType() ->getPrimitiveSizeInBits()/8 == EltSize)) { if (VectorTy == 0) 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. VectorTy = Type::getVoidTy(In->getContext()); } /// MergeInVectorType - Handles the vector case of MergeInType, returning true /// if the type was successfully merged and false otherwise. bool ConvertToScalarInfo::MergeInVectorType(const VectorType *VInTy, uint64_t Offset) { // Remember if we saw a vector type. HadAVector = true; // TODO: Support nonzero offsets? if (Offset != 0) return false; // Only allow vectors that are a power-of-2 away from the size of the alloca. if (!isPowerOf2_64(AllocaSize / (VInTy->getBitWidth() / 8))) return false; // If this the first vector we see, remember the type so that we know the // element size. if (!VectorTy) { VectorTy = VInTy; return true; } unsigned BitWidth = cast(VectorTy)->getBitWidth(); unsigned InBitWidth = VInTy->getBitWidth(); // Vectors of the same size can be converted using a simple bitcast. if (InBitWidth == BitWidth && AllocaSize == (InBitWidth / 8)) return true; const Type *ElementTy = cast(VectorTy)->getElementType(); const Type *InElementTy = cast(VInTy)->getElementType(); // Do not allow mixed integer and floating-point accesses from vectors of // different sizes. if (ElementTy->isFloatingPointTy() != InElementTy->isFloatingPointTy()) return false; if (ElementTy->isFloatingPointTy()) { // Only allow floating-point vectors of different sizes if they have the // same element type. // TODO: This could be loosened a bit, but would anything benefit? if (ElementTy != InElementTy) return false; // There are no arbitrary-precision floating-point types, which limits the // number of legal vector types with larger element types that we can form // to bitcast and extract a subvector. // TODO: We could support some more cases with mixed fp128 and double here. if (!(BitWidth == 64 || BitWidth == 128) || !(InBitWidth == 64 || InBitWidth == 128)) return false; } else { assert(ElementTy->isIntegerTy() && "Vector elements must be either integer " "or floating-point."); unsigned BitWidth = ElementTy->getPrimitiveSizeInBits(); unsigned InBitWidth = InElementTy->getPrimitiveSizeInBits(); // Do not allow integer types smaller than a byte or types whose widths are // not a multiple of a byte. if (BitWidth < 8 || InBitWidth < 8 || BitWidth % 8 != 0 || InBitWidth % 8 != 0) return false; } // Pick the largest of the two vector types. if (InBitWidth > BitWidth) VectorTy = VInTy; return true; } /// 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) { for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { Instruction *User = cast(*UI); if (LoadInst *LI = dyn_cast(User)) { // Don't break volatile loads. if (LI->isVolatile()) return false; // Don't touch MMX operations. if (LI->getType()->isX86_MMXTy()) return false; HadNonMemTransferAccess = true; MergeInType(LI->getType(), Offset, true); continue; } if (StoreInst *SI = dyn_cast(User)) { // Storing the pointer, not into the value? if (SI->getOperand(0) == V || SI->isVolatile()) return false; // Don't touch MMX operations. if (SI->getOperand(0)->getType()->isX86_MMXTy()) return false; HadNonMemTransferAccess = true; MergeInType(SI->getOperand(0)->getType(), Offset, true); continue; } if (BitCastInst *BCI = dyn_cast(User)) { IsNotTrivial = true; // Can't be mem2reg'd. if (!CanConvertToScalar(BCI, Offset)) return false; continue; } if (GetElementPtrInst *GEP = dyn_cast(User)) { // If this is a GEP with a variable indices, we can't handle it. if (!GEP->hasAllConstantIndices()) return false; // Compute the offset that this GEP adds to the pointer. SmallVector Indices(GEP->op_begin()+1, GEP->op_end()); uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), &Indices[0], Indices.size()); // See if all uses can be converted. if (!CanConvertToScalar(GEP, Offset+GEPOffset)) 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(User)) { // Store of constant value and constant size. if (!isa(MSI->getValue()) || !isa(MSI->getLength())) return false; 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(User)) { ConstantInt *Len = dyn_cast(MTI->getLength()); if (Len == 0 || Len->getZExtValue() != AllocaSize || Offset != 0) return false; IsNotTrivial = true; // Can't be mem2reg'd. 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) { while (!Ptr->use_empty()) { Instruction *User = cast(Ptr->use_back()); if (BitCastInst *CI = dyn_cast(User)) { ConvertUsesToScalar(CI, NewAI, Offset); CI->eraseFromParent(); continue; } if (GetElementPtrInst *GEP = dyn_cast(User)) { // Compute the offset that this GEP adds to the pointer. SmallVector Indices(GEP->op_begin()+1, GEP->op_end()); uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(), &Indices[0], Indices.size()); ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8); GEP->eraseFromParent(); continue; } IRBuilder<> Builder(User); if (LoadInst *LI = dyn_cast(User)) { // The load is a bit extract from NewAI shifted right by Offset bits. Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp"); Value *NewLoadVal = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder); LI->replaceAllUsesWith(NewLoadVal); LI->eraseFromParent(); continue; } if (StoreInst *SI = dyn_cast(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, 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(User)) { assert(MSI->getRawDest() == Ptr && "Consistency error!"); unsigned NumBytes = cast(MSI->getLength())->getZExtValue(); if (NumBytes != 0) { unsigned Val = cast(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, 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(User)) { assert(Offset == 0 && "must be store to start of alloca"); // 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(GetUnderlyingObject(Ptr, &TD, 0)); if (GetUnderlyingObject(MTI->getSource(), &TD, 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(); const PointerType* SPTy = cast(SrcPtr->getType()); const PointerType* AIPTy = cast(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(), &TD, 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"); const PointerType* DPTy = cast(MTI->getDest()->getType()); const PointerType* AIPTy = cast(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; } llvm_unreachable("Unsupported operation!"); } } /// getScaledElementType - Gets a scaled element type for a partial vector /// access of an alloca. The input type must be an integer or float, and /// the resulting type must be an integer, float or double. static const Type *getScaledElementType(const Type *OldTy, unsigned NewBitWidth) { assert((OldTy->isIntegerTy() || OldTy->isFloatTy()) && "Partial vector " "accesses must be scaled from integer or float elements."); LLVMContext &Context = OldTy->getContext(); if (OldTy->isIntegerTy()) return Type::getIntNTy(Context, NewBitWidth); if (NewBitWidth == 32) return Type::getFloatTy(Context); if (NewBitWidth == 64) return Type::getDoubleTy(Context); llvm_unreachable("Invalid type for a partial vector access of an alloca!"); } /// CreateShuffleVectorCast - Creates a shuffle vector to convert one vector /// to another vector of the same element type which has the same allocation /// size but different primitive sizes (e.g. <3 x i32> and <4 x i32>). static Value *CreateShuffleVectorCast(Value *FromVal, const Type *ToType, IRBuilder<> &Builder) { const Type *FromType = FromVal->getType(); const VectorType *FromVTy = cast(FromType); const VectorType *ToVTy = cast(ToType); assert((ToVTy->getElementType() == FromVTy->getElementType()) && "Vectors must have the same element type"); Value *UnV = UndefValue::get(FromType); unsigned numEltsFrom = FromVTy->getNumElements(); unsigned numEltsTo = ToVTy->getNumElements(); SmallVector Args; const Type* Int32Ty = Builder.getInt32Ty(); unsigned minNumElts = std::min(numEltsFrom, numEltsTo); unsigned i; for (i=0; i != minNumElts; ++i) Args.push_back(ConstantInt::get(Int32Ty, i)); if (i < numEltsTo) { Constant* UnC = UndefValue::get(Int32Ty); for (; i != numEltsTo; ++i) Args.push_back(UnC); } Constant *Mask = ConstantVector::get(Args); return Builder.CreateShuffleVector(FromVal, UnV, Mask, "tmpV"); } /// 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, const Type *ToType, uint64_t Offset, IRBuilder<> &Builder) { // If the load is of the whole new alloca, no conversion is needed. const 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 (const VectorType *VTy = dyn_cast(FromType)) { unsigned ToTypeSize = TD.getTypeAllocSize(ToType); if (ToTypeSize == AllocaSize) { // If the two types have the same primitive size, use a bit cast. // Otherwise, it is two vectors with the same element type that has // the same allocation size but different number of elements so use // a shuffle vector. if (FromType->getPrimitiveSizeInBits() == ToType->getPrimitiveSizeInBits()) return Builder.CreateBitCast(FromVal, ToType, "tmp"); else return CreateShuffleVectorCast(FromVal, ToType, Builder); } if (ToType->isVectorTy()) { assert(isPowerOf2_64(AllocaSize / ToTypeSize) && "Partial vector access of an alloca must have a power-of-2 size " "ratio."); assert(Offset == 0 && "Can't extract a value of a smaller vector type " "from a nonzero offset."); const Type *ToElementTy = cast(ToType)->getElementType(); const Type *CastElementTy = getScaledElementType(ToElementTy, ToTypeSize * 8); unsigned NumCastVectorElements = AllocaSize / ToTypeSize; LLVMContext &Context = FromVal->getContext(); const Type *CastTy = VectorType::get(CastElementTy, NumCastVectorElements); Value *Cast = Builder.CreateBitCast(FromVal, CastTy, "tmp"); Value *Extract = Builder.CreateExtractElement(Cast, ConstantInt::get( Type::getInt32Ty(Context), 0), "tmp"); return Builder.CreateBitCast(Extract, ToType, "tmp"); } // Otherwise it must be an element access. unsigned Elt = 0; if (Offset) { unsigned EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); Elt = Offset/EltSize; assert(EltSize*Elt == Offset && "Invalid modulus in validity checking"); } // Return the element extracted out of it. Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get( Type::getInt32Ty(FromVal->getContext()), Elt), "tmp"); if (V->getType() != ToType) V = Builder.CreateBitCast(V, ToType, "tmp"); return V; } // If ToType is a first class aggregate, extract out each of the pieces and // use insertvalue's to form the FCA. if (const StructType *ST = dyn_cast(ToType)) { const StructLayout &Layout = *TD.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), Builder); Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); } return Res; } if (const ArrayType *AT = dyn_cast(ToType)) { uint64_t EltSize = TD.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, Builder); Res = Builder.CreateInsertValue(Res, Elt, i, "tmp"); } return Res; } // Otherwise, this must be a union that was converted to an integer value. const IntegerType *NTy = cast(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 (TD.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 = TD.getTypeStoreSizeInBits(NTy) - TD.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), "tmp"); else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) FromVal = Builder.CreateShl(FromVal, ConstantInt::get(FromVal->getType(), -ShAmt), "tmp"); // Finally, unconditionally truncate the integer to the right width. unsigned LIBitWidth = TD.getTypeSizeInBits(ToType); if (LIBitWidth < NTy->getBitWidth()) FromVal = Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(), LIBitWidth), "tmp"); else if (LIBitWidth > NTy->getBitWidth()) FromVal = Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(), LIBitWidth), "tmp"); // 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, "tmp"); } else { // Otherwise must be a pointer. FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp"); } 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. Value *ConvertToScalarInfo:: ConvertScalar_InsertValue(Value *SV, Value *Old, uint64_t Offset, IRBuilder<> &Builder) { // Convert the stored type to the actual type, shift it left to insert // then 'or' into place. const Type *AllocaType = Old->getType(); LLVMContext &Context = Old->getContext(); if (const VectorType *VTy = dyn_cast(AllocaType)) { uint64_t VecSize = TD.getTypeAllocSizeInBits(VTy); uint64_t ValSize = TD.getTypeAllocSizeInBits(SV->getType()); // Changing the whole vector with memset or with an access of a different // vector type? if (ValSize == VecSize) { // If the two types have the same primitive size, use a bit cast. // Otherwise, it is two vectors with the same element type that has // the same allocation size but different number of elements so use // a shuffle vector. if (VTy->getPrimitiveSizeInBits() == SV->getType()->getPrimitiveSizeInBits()) return Builder.CreateBitCast(SV, AllocaType, "tmp"); else return CreateShuffleVectorCast(SV, VTy, Builder); } if (SV->getType()->isVectorTy() && isPowerOf2_64(VecSize / ValSize)) { assert(Offset == 0 && "Can't insert a value of a smaller vector type at " "a nonzero offset."); const Type *ToElementTy = cast(SV->getType())->getElementType(); const Type *CastElementTy = getScaledElementType(ToElementTy, ValSize); unsigned NumCastVectorElements = VecSize / ValSize; LLVMContext &Context = SV->getContext(); const Type *OldCastTy = VectorType::get(CastElementTy, NumCastVectorElements); Value *OldCast = Builder.CreateBitCast(Old, OldCastTy, "tmp"); Value *SVCast = Builder.CreateBitCast(SV, CastElementTy, "tmp"); Value *Insert = Builder.CreateInsertElement(OldCast, SVCast, ConstantInt::get( Type::getInt32Ty(Context), 0), "tmp"); return Builder.CreateBitCast(Insert, AllocaType, "tmp"); } uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType()); // Must be an element insertion. unsigned Elt = Offset/EltSize; if (SV->getType() != VTy->getElementType()) SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp"); SV = Builder.CreateInsertElement(Old, SV, ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt), "tmp"); return SV; } // If SV is a first-class aggregate value, insert each value recursively. if (const StructType *ST = dyn_cast(SV->getType())) { const StructLayout &Layout = *TD.getStructLayout(ST); for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) { Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); Old = ConvertScalar_InsertValue(Elt, Old, Offset+Layout.getElementOffsetInBits(i), Builder); } return Old; } if (const ArrayType *AT = dyn_cast(SV->getType())) { uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType()); for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { Value *Elt = Builder.CreateExtractValue(SV, i, "tmp"); Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, 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 = TD.getTypeSizeInBits(SV->getType()); unsigned DestWidth = TD.getTypeSizeInBits(AllocaType); unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType()); unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType); if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy()) SV = Builder.CreateBitCast(SV, IntegerType::get(SV->getContext(),SrcWidth), "tmp"); else if (SV->getType()->isPointerTy()) SV = Builder.CreatePtrToInt(SV, TD.getIntPtrType(SV->getContext()), "tmp"); // Zero extend or truncate the value if needed. if (SV->getType() != AllocaType) { if (SV->getType()->getPrimitiveSizeInBits() < AllocaType->getPrimitiveSizeInBits()) SV = Builder.CreateZExt(SV, AllocaType, "tmp"); else { // Truncation may be needed if storing more than the alloca can hold // (undefined behavior). SV = Builder.CreateTrunc(SV, AllocaType, "tmp"); 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 (TD.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), "tmp"); Mask <<= ShAmt; } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(), -ShAmt), "tmp"); 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) { TD = getAnalysisIfAvailable(); bool Changed = performPromotion(F); // FIXME: ScalarRepl currently depends on TargetData 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 (!TD) 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; public: AllocaPromoter(const SmallVectorImpl &Insts, SSAUpdater &S) : LoadAndStorePromoter(Insts, S), AI(0) {} void run(AllocaInst *AI, const SmallVectorImpl &Insts) { // Remember which alloca we're promoting (for isInstInList). this->AI = AI; LoadAndStorePromoter::run(Insts); AI->eraseFromParent(); } virtual bool isInstInList(Instruction *I, const SmallVectorImpl &Insts) const { if (LoadInst *LI = dyn_cast(I)) return LI->getOperand(0) == AI; return cast(I)->getPointerOperand() == AI; } }; } // 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 TargetData *TD) { bool TDerefable = SI->getTrueValue()->isDereferenceablePointer(); bool FDerefable = SI->getFalseValue()->isDereferenceablePointer(); for (Value::use_iterator UI = SI->use_begin(), UE = SI->use_end(); UI != UE; ++UI) { LoadInst *LI = dyn_cast(*UI); if (LI == 0 || LI->isVolatile()) 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(), TD)) return false; if (!FDerefable && !isSafeToLoadUnconditionally(SI->getFalseValue(), LI, LI->getAlignment(), TD)) 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 TargetData *TD) { // 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 (Value::use_iterator UI = PN->use_begin(), UE = PN->use_end(); UI != UE; ++UI) { LoadInst *LI = dyn_cast(*UI); if (LI == 0 || LI->isVolatile()) 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); // If the predecessor has a single successor, then the edge isn't critical. if (Pred->getTerminator()->getNumSuccessors() == 1) continue; Value *InVal = PN->getIncomingValue(i); // If the InVal is an invoke in the pred, we can't put a load on the edge. if (InvokeInst *II = dyn_cast(InVal)) if (II->getParent() == Pred) return false; // 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() || isSafeToLoadUnconditionally(InVal, Pred->getTerminator(), MaxAlign, TD)) 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 TargetData *TD) { SetVector, SmallPtrSet > InstsToRewrite; for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end(); UI != UE; ++UI) { User *U = *UI; if (LoadInst *LI = dyn_cast(U)) { if (LI->isVolatile()) return false; continue; } if (StoreInst *SI = dyn_cast(U)) { if (SI->getOperand(0) == AI || SI->isVolatile()) return false; // Don't allow a store OF the AI, only INTO the AI. continue; } if (SelectInst *SI = dyn_cast(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(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, TD); } // 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, TD)) return false; InstsToRewrite.insert(SI); continue; } if (PHINode *PN = dyn_cast(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, TD)) return false; InstsToRewrite.insert(PN); 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 (SelectInst *SI = dyn_cast(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(SI->use_back()); IRBuilder<> Builder(LI); LoadInst *TrueLoad = Builder.CreateLoad(SI->getTrueValue(), LI->getName()+".t"); LoadInst *FalseLoad = Builder.CreateLoad(SI->getFalseValue(), LI->getName()+".t"); // 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(InstsToRewrite[i]); if (PN->use_empty()) { PN->eraseFromParent(); continue; } const Type *LoadTy = cast(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(PN->use_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(PN->use_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 InsertedLoads; for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { BasicBlock *Pred = PN->getIncomingBlock(i); LoadInst *&Load = InsertedLoads[Pred]; if (Load == 0) { 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 Allocas; DominatorTree *DT = 0; if (HasDomTree) DT = &getAnalysis(); BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function bool Changed = false; SmallVector 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(I)) // Is it an alloca? if (tryToMakeAllocaBePromotable(AI, TD)) 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 (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E; ++UI) Insts.push_back(cast(*UI)); AllocaPromoter(Insts, SSA).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. static bool ShouldAttemptScalarRepl(AllocaInst *AI) { const Type *T = AI->getAllocatedType(); // Do not promote any struct into more than 32 separate vars. if (const StructType *ST = dyn_cast(T)) return ST->getNumElements() <= 32; // Arrays are much less likely to be safe for SROA; only consider // them if they are very small. if (const ArrayType *AT = dyn_cast(T)) return AT->getNumElements() <= 8; return false; } // performScalarRepl - This algorithm is a simple worklist driven algorithm, // which runs on all of the malloc/alloca instructions in the function, removing // them if they are only used by getelementptr instructions. // bool SROA::performScalarRepl(Function &F) { std::vector 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(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 this allocation is only modified by a memcpy/memmove from // a constant global. If this is the case, we can change all users to use // the constant global instead. This is commonly produced by the CFE by // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A' // is only subsequently read. if (MemTransferInst *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) { DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n'); DEBUG(dbgs() << " memcpy = " << *TheCopy << '\n'); Constant *TheSrc = cast(TheCopy->getSource()); AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType())); TheCopy->eraseFromParent(); // Don't mutate the global. AI->eraseFromParent(); ++NumGlobals; Changed = true; 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 = TD->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, *TD).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 &WorkList) { DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n'); SmallVector ElementAllocas; if (const StructType *ST = dyn_cast(AI->getAllocatedType())) { ElementAllocas.reserve(ST->getNumContainedTypes()); for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, AI->getAlignment(), AI->getName() + "." + Twine(i), AI); ElementAllocas.push_back(NA); WorkList.push_back(NA); // Add to worklist for recursive processing } } else { const ArrayType *AT = cast(AI->getAllocatedType()); ElementAllocas.reserve(AT->getNumElements()); const Type *ElTy = AT->getElementType(); for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { AllocaInst *NA = new AllocaInst(ElTy, 0, 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(DeadInsts.pop_back_val()); for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) if (Instruction *U = dyn_cast(*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 = 0; if (isInstructionTriviallyDead(U) && !isa(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 (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { Instruction *User = cast(*UI); if (BitCastInst *BC = dyn_cast(User)) { isSafeForScalarRepl(BC, Offset, Info); } else if (GetElementPtrInst *GEPI = dyn_cast(User)) { uint64_t GEPOffset = Offset; isSafeGEP(GEPI, GEPOffset, Info); if (!Info.isUnsafe) isSafeForScalarRepl(GEPI, GEPOffset, Info); } else if (MemIntrinsic *MI = dyn_cast(User)) { ConstantInt *Length = dyn_cast(MI->getLength()); if (Length == 0) return MarkUnsafe(Info, User); isSafeMemAccess(Offset, Length->getZExtValue(), 0, UI.getOperandNo() == 0, Info, MI, true /*AllowWholeAccess*/); } else if (LoadInst *LI = dyn_cast(User)) { if (LI->isVolatile()) return MarkUnsafe(Info, User); const Type *LIType = LI->getType(); isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType), LIType, false, Info, LI, true /*AllowWholeAccess*/); Info.hasALoadOrStore = true; } else if (StoreInst *SI = dyn_cast(User)) { // Store is ok if storing INTO the pointer, not storing the pointer if (SI->isVolatile() || SI->getOperand(0) == I) return MarkUnsafe(Info, User); const Type *SIType = SI->getOperand(0)->getType(); isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType), SIType, true, Info, SI, true /*AllowWholeAccess*/); Info.hasALoadOrStore = true; } else if (isa(User) || isa(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(I)) if (!Info.CheckedPHIs.insert(PN)) return; for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) { Instruction *User = cast(*UI); if (BitCastInst *BC = dyn_cast(User)) { isSafePHISelectUseForScalarRepl(BC, Offset, Info); } else if (GetElementPtrInst *GEPI = dyn_cast(User)) { // 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, User); isSafePHISelectUseForScalarRepl(GEPI, Offset, Info); } else if (LoadInst *LI = dyn_cast(User)) { if (LI->isVolatile()) return MarkUnsafe(Info, User); const Type *LIType = LI->getType(); isSafeMemAccess(Offset, TD->getTypeAllocSize(LIType), LIType, false, Info, LI, false /*AllowWholeAccess*/); Info.hasALoadOrStore = true; } else if (StoreInst *SI = dyn_cast(User)) { // Store is ok if storing INTO the pointer, not storing the pointer if (SI->isVolatile() || SI->getOperand(0) == I) return MarkUnsafe(Info, User); const Type *SIType = SI->getOperand(0)->getType(); isSafeMemAccess(Offset, TD->getTypeAllocSize(SIType), SIType, true, Info, SI, false /*AllowWholeAccess*/); Info.hasALoadOrStore = true; } else if (isa(User) || isa(User)) { isSafePHISelectUseForScalarRepl(User, Offset, Info); } else { return MarkUnsafe(Info, User); } 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; // 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(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 Indices(GEPI->op_begin() + 1, GEPI->op_end()); Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), &Indices[0], Indices.size()); if (!TypeHasComponent(Info.AI->getAllocatedType(), Offset, 0)) 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(const Type *T, unsigned &NumElts, const Type *&EltTy) { if (const ArrayType *AT = dyn_cast(T)) { NumElts = AT->getNumElements(); EltTy = (NumElts == 0 ? 0 : AT->getElementType()); return true; } if (const StructType *ST = dyn_cast(T)) { NumElts = ST->getNumContainedTypes(); EltTy = (NumElts == 0 ? 0 : 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(const Type *T1, const Type *T2) { if (T1 == T2) return true; unsigned NumElts1, NumElts2; const 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, const 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 == TD->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. const 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(const Type *T, uint64_t Offset, uint64_t Size) { const Type *EltTy; uint64_t EltSize; if (const StructType *ST = dyn_cast(T)) { const StructLayout *Layout = TD->getStructLayout(ST); unsigned EltIdx = Layout->getElementContainingOffset(Offset); EltTy = ST->getContainedType(EltIdx); EltSize = TD->getTypeAllocSize(EltTy); Offset -= Layout->getElementOffset(EltIdx); } else if (const ArrayType *AT = dyn_cast(T)) { EltTy = AT->getElementType(); EltSize = TD->getTypeAllocSize(EltTy); if (Offset >= AT->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, SmallVector &NewElts) { for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E;) { Use &TheUse = UI.getUse(); Instruction *User = cast(*UI++); if (BitCastInst *BC = dyn_cast(User)) { RewriteBitCast(BC, AI, Offset, NewElts); continue; } if (GetElementPtrInst *GEPI = dyn_cast(User)) { RewriteGEP(GEPI, AI, Offset, NewElts); continue; } if (MemIntrinsic *MI = dyn_cast(User)) { ConstantInt *Length = dyn_cast(MI->getLength()); uint64_t MemSize = Length->getZExtValue(); if (Offset == 0 && MemSize == TD->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 (LoadInst *LI = dyn_cast(User)) { const 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); for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { Value *Load = new LoadInst(NewElts[i], "load", LI); Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI); } LI->replaceAllUsesWith(Insert); DeadInsts.push_back(LI); } else if (LIType->isIntegerTy() && TD->getTypeAllocSize(LIType) == TD->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(User)) { Value *Val = SI->getOperand(0); const 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) for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI); new StoreInst(Extract, NewElts[i], SI); } DeadInsts.push_back(SI); } else if (SIType->isIntegerTy() && TD->getTypeAllocSize(SIType) == TD->getTypeAllocSize(AI->getAllocatedType())) { // If this is a store of the entire alloca from an integer, rewrite it. RewriteStoreUserOfWholeAlloca(SI, AI, NewElts); } continue; } if (isa(User) || isa(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(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, SmallVector &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 first new element alloca. Instruction *Val = NewElts[0]; 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(const Type *&T, uint64_t &Offset, const Type *&IdxTy) { uint64_t Idx = 0; if (const StructType *ST = dyn_cast(T)) { const StructLayout *Layout = TD->getStructLayout(ST); Idx = Layout->getElementContainingOffset(Offset); T = ST->getContainedType(Idx); Offset -= Layout->getElementOffset(Idx); IdxTy = Type::getInt32Ty(T->getContext()); return Idx; } const ArrayType *AT = cast(T); T = AT->getElementType(); uint64_t EltSize = TD->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, SmallVector &NewElts) { uint64_t OldOffset = Offset; SmallVector Indices(GEPI->op_begin() + 1, GEPI->op_end()); Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(), &Indices[0], Indices.size()); RewriteForScalarRepl(GEPI, AI, Offset, NewElts); const Type *T = AI->getAllocatedType(); const 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; const Type *i32Ty = Type::getInt32Ty(AI->getContext()); SmallVector NewArgs; NewArgs.push_back(Constant::getNullValue(i32Ty)); while (EltOffset != 0) { uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy); NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx)); } Instruction *Val = NewElts[Idx]; if (NewArgs.size() > 1) { Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(), NewArgs.end(), "", 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); } /// 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, SmallVector &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 = 0; unsigned MemAlignment = MI->getAlignment(); if (MemTransferInst *MTI = dyn_cast(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(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 (SmallVector::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. const 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 = 0; unsigned OtherEltAlign = MemAlignment; if (OtherPtr) { Value *Idx[2] = { Zero, ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) }; OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2, OtherPtr->getName()+"."+Twine(i), MI); uint64_t EltOffset; const PointerType *OtherPtrTy = cast(OtherPtr->getType()); const Type *OtherTy = OtherPtrTy->getElementType(); if (const StructType *ST = dyn_cast(OtherTy)) { EltOffset = TD->getStructLayout(ST)->getElementOffset(i); } else { const Type *EltTy = cast(OtherTy)->getElementType(); EltOffset = TD->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]; const Type *EltTy = cast(EltPtr->getType())->getElementType(); // If we got down to a scalar, insert a load or store as appropriate. if (EltTy->isSingleValueType()) { if (isa(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(MI)); // If the stored element is zero (common case), just store a null // constant. Constant *StoreVal; if (ConstantInt *CI = dyn_cast(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. const Type *ValTy = EltTy->getScalarType(); // Construct an integer with the right value. unsigned EltSize = TD->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 != ValTy) { unsigned NumElts = cast(ValTy)->getNumElements(); SmallVector Elts(NumElts, StoreVal); StoreVal = ConstantVector::get(Elts); } } new StoreInst(StoreVal, EltPtr, MI); continue; } // Otherwise, if we're storing a byte variable, use a memset call for // this element. } unsigned EltSize = TD->getTypeAllocSize(EltTy); IRBuilder<> Builder(MI); // Finally, insert the meminst for this element. if (isa(MI)) { Builder.CreateMemSet(EltPtr, MI->getArgOperand(1), EltSize, MI->isVolatile()); } else { assert(isa(MI)); Value *Dst = SROADest ? EltPtr : OtherElt; // Dest ptr Value *Src = SROADest ? OtherElt : EltPtr; // Src ptr if (isa(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, SmallVector &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); const Type *AllocaEltTy = AI->getAllocatedType(); uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy); IRBuilder<> Builder(SI); // Handle tail padding by extending the operand if (TD->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 (const StructType *EltSTy = dyn_cast(AllocaEltTy)) { const StructLayout *Layout = TD->getStructLayout(EltSTy); for (unsigned i = 0, e = NewElts.size(); i != e; ++i) { // Get the number of bits to shift SrcVal to get the value. const Type *FieldTy = EltSTy->getElementType(i); uint64_t Shift = Layout->getElementOffsetInBits(i); if (TD->isBigEndian()) Shift = AllocaSizeBits-Shift-TD->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 = TD->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 { const ArrayType *ATy = cast(AllocaEltTy); const Type *ArrayEltTy = ATy->getElementType(); uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy); uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy); uint64_t Shift; if (TD->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 (TD->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, SmallVector &NewElts) { // Extract each element out of the NewElts according to its structure offset // and form the result value. const Type *AllocaEltTy = AI->getAllocatedType(); uint64_t AllocaSizeBits = TD->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 = 0; uint64_t ArrayEltBitOffset = 0; if (const StructType *EltSTy = dyn_cast(AllocaEltTy)) { Layout = TD->getStructLayout(EltSTy); } else { const Type *ArrayEltTy = cast(AllocaEltTy)->getElementType(); ArrayEltBitOffset = TD->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]; const Type *FieldTy = cast(SrcField->getType())->getElementType(); uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy); // Ignore zero sized fields like {}, they obviously contain no data. if (FieldSizeBits == 0) continue; const 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 (TD->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(ResultVal) || !cast(ResultVal)->isNullValue()) ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI); else ResultVal = SrcField; } // Handle tail padding by truncating the result if (TD->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(const Type *Ty, const TargetData &TD) { if (const ArrayType *ATy = dyn_cast(Ty)) { Ty = ATy->getElementType(); return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty); } // SROA currently handles only Arrays and Structs. const StructType *STy = cast(Ty); const StructLayout *SL = TD.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+TD.getTypeSizeInBits(STy->getElementType(i-1)); if (PrevFieldEnd < FieldBitOffset) return true; } PrevFieldBitOffset = FieldBitOffset; } // Check for tail padding. if (unsigned EltCount = STy->getNumElements()) { unsigned PrevFieldEnd = PrevFieldBitOffset + TD.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(), *TD)) 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 (const StructType *ST = dyn_cast(AI->getAllocatedType())) { if (ST->getNumElements() > 1) return false; } else { if (cast(AI->getAllocatedType())->getNumElements() > 1) return false; } } return true; } /// PointsToConstantGlobal - Return true if V (possibly indirectly) points to /// some part of a constant global variable. This intentionally only accepts /// constant expressions because we don't can't rewrite arbitrary instructions. static bool PointsToConstantGlobal(Value *V) { if (GlobalVariable *GV = dyn_cast(V)) return GV->isConstant(); if (ConstantExpr *CE = dyn_cast(V)) if (CE->getOpcode() == Instruction::BitCast || CE->getOpcode() == Instruction::GetElementPtr) return PointsToConstantGlobal(CE->getOperand(0)); return false; } /// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived) /// pointer to an alloca. Ignore any reads of the pointer, return false if we /// see any stores or other unknown uses. If we see pointer arithmetic, keep /// track of whether it moves the pointer (with isOffset) but otherwise traverse /// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to /// the alloca, and if the source pointer is a pointer to a constant global, we /// can optimize this. static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy, bool isOffset) { for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { User *U = cast(*UI); if (LoadInst *LI = dyn_cast(U)) { // Ignore non-volatile loads, they are always ok. if (LI->isVolatile()) return false; continue; } if (BitCastInst *BCI = dyn_cast(U)) { // If uses of the bitcast are ok, we are ok. if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) return false; continue; } if (GetElementPtrInst *GEP = dyn_cast(U)) { // If the GEP has all zero indices, it doesn't offset the pointer. If it // doesn't, it does. if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy, isOffset || !GEP->hasAllZeroIndices())) return false; continue; } if (CallSite CS = U) { // If this is a readonly/readnone call site, then we know it is just a // load and we can ignore it. if (CS.onlyReadsMemory()) continue; // If this is the function being called then we treat it like a load and // ignore it. if (CS.isCallee(UI)) continue; // If this is being passed as a byval argument, the caller is making a // copy, so it is only a read of the alloca. unsigned ArgNo = CS.getArgumentNo(UI); if (CS.paramHasAttr(ArgNo+1, Attribute::ByVal)) continue; } // If this is isn't our memcpy/memmove, reject it as something we can't // handle. MemTransferInst *MI = dyn_cast(U); if (MI == 0) return false; // If the transfer is using the alloca as a source of the transfer, then // ignore it since it is a load (unless the transfer is volatile). if (UI.getOperandNo() == 1) { if (MI->isVolatile()) return false; continue; } // If we already have seen a copy, reject the second one. if (TheCopy) return false; // If the pointer has been offset from the start of the alloca, we can't // safely handle this. if (isOffset) return false; // If the memintrinsic isn't using the alloca as the dest, reject it. if (UI.getOperandNo() != 0) return false; // If the source of the memcpy/move is not a constant global, reject it. if (!PointsToConstantGlobal(MI->getSource())) return false; // Otherwise, the transform is safe. Remember the copy instruction. TheCopy = MI; } return true; } /// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only /// modified by a copy from a constant global. If we can prove this, we can /// replace any uses of the alloca with uses of the global directly. MemTransferInst *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) { MemTransferInst *TheCopy = 0; if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) return TheCopy; return 0; }