//===- 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/Pass.h" #include "llvm/Analysis/Dominators.h" #include "llvm/Target/TargetData.h" #include "llvm/Transforms/Utils/PromoteMemToReg.h" #include "llvm/Support/Debug.h" #include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/MathExtras.h" #include "llvm/Support/Compiler.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/ADT/StringExtras.h" using namespace llvm; STATISTIC(NumReplaced, "Number of allocas broken up"); STATISTIC(NumPromoted, "Number of allocas promoted"); STATISTIC(NumConverted, "Number of aggregates converted to scalar"); STATISTIC(NumGlobals, "Number of allocas copied from constant global"); namespace { struct VISIBILITY_HIDDEN SROA : public FunctionPass { static char ID; // Pass identification, replacement for typeid explicit SROA(signed T = -1) : FunctionPass(&ID) { if (T == -1) SRThreshold = 128; else SRThreshold = T; } bool runOnFunction(Function &F); bool performScalarRepl(Function &F); bool performPromotion(Function &F); // 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.addRequired(); AU.addRequired(); AU.setPreservesCFG(); } private: /// 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 { /// isUnsafe - This is set to true if the alloca cannot be SROA'd. bool isUnsafe : 1; /// needsCanon - This is set to true if there is some use of the alloca /// that requires canonicalization. bool needsCanon : 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; AllocaInfo() : isUnsafe(false), needsCanon(false), isMemCpySrc(false), isMemCpyDst(false) {} }; unsigned SRThreshold; void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; } int isSafeAllocaToScalarRepl(AllocationInst *AI); void isSafeUseOfAllocation(Instruction *User, AllocationInst *AI, AllocaInfo &Info); void isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI, AllocaInfo &Info); void isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI, unsigned OpNo, AllocaInfo &Info); void isSafeUseOfBitCastedAllocation(BitCastInst *User, AllocationInst *AI, AllocaInfo &Info); void DoScalarReplacement(AllocationInst *AI, std::vector &WorkList); void CanonicalizeAllocaUsers(AllocationInst *AI); AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocationInst *Base); void RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI, SmallVector &NewElts); const Type *CanConvertToScalar(Value *V, bool &IsNotTrivial); void ConvertToScalar(AllocationInst *AI, const Type *Ty); void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, unsigned Offset); Value *ConvertUsesOfLoadToScalar(LoadInst *LI, AllocaInst *NewAI, unsigned Offset); Value *ConvertUsesOfStoreToScalar(StoreInst *SI, AllocaInst *NewAI, unsigned Offset); static Instruction *isOnlyCopiedFromConstantGlobal(AllocationInst *AI); }; } char SROA::ID = 0; static RegisterPass X("scalarrepl", "Scalar Replacement of Aggregates"); // Public interface to the ScalarReplAggregates pass FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) { return new SROA(Threshold); } bool SROA::runOnFunction(Function &F) { bool Changed = performPromotion(F); 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; } bool SROA::performPromotion(Function &F) { std::vector Allocas; DominatorTree &DT = getAnalysis(); DominanceFrontier &DF = getAnalysis(); BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function bool Changed = false; 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 (isAllocaPromotable(AI)) Allocas.push_back(AI); if (Allocas.empty()) break; PromoteMemToReg(Allocas, DT, DF); NumPromoted += Allocas.size(); Changed = true; } return Changed; } /// getNumSAElements - Return the number of elements in the specific struct or /// array. static uint64_t getNumSAElements(const Type *T) { if (const StructType *ST = dyn_cast(T)) return ST->getNumElements(); return cast(T)->getNumElements(); } // 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 any alloca's and mallocs to the worklist BasicBlock &BB = F.getEntryBlock(); for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) if (AllocationInst *A = dyn_cast(I)) WorkList.push_back(A); const TargetData &TD = getAnalysis(); // Process the worklist bool Changed = false; while (!WorkList.empty()) { AllocationInst *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(); 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. bool IsNotTrivial = false; if (const Type *ActualType = CanConvertToScalar(AI, IsNotTrivial)) if (IsNotTrivial && ActualType != Type::VoidTy) { ConvertToScalar(AI, ActualType); 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. if (!AI->isArrayAllocation() && (isa(AI->getAllocatedType()) || isa(AI->getAllocatedType())) && AI->getAllocatedType()->isSized() && // Do not promote any struct whose size is larger than "128" bytes. TD.getABITypeSize(AI->getAllocatedType()) < SRThreshold && // Do not promote any struct into more than "32" separate vars. getNumSAElements(AI->getAllocatedType()) < SRThreshold/4) { // Check that all of the users of the allocation are capable of being // transformed. switch (isSafeAllocaToScalarRepl(AI)) { default: assert(0 && "Unexpected value!"); case 0: // Not safe to scalar replace. break; case 1: // Safe, but requires cleanup/canonicalizations first CanonicalizeAllocaUsers(AI); // FALL THROUGH. case 3: // Safe to scalar replace. DoScalarReplacement(AI, WorkList); Changed = true; 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 (Instruction *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) { DOUT << "Found alloca equal to global: " << *AI; DOUT << " memcpy = " << *TheCopy; Constant *TheSrc = cast(TheCopy->getOperand(2)); AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType())); TheCopy->eraseFromParent(); // Don't mutate the global. AI->eraseFromParent(); ++NumGlobals; Changed = true; continue; } // Otherwise, couldn't process this. } return Changed; } /// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl /// predicate, do SROA now. void SROA::DoScalarReplacement(AllocationInst *AI, std::vector &WorkList) { DOUT << "Found inst to SROA: " << *AI; 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() + "." + utostr(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() + "." + utostr(i), AI); ElementAllocas.push_back(NA); WorkList.push_back(NA); // Add to worklist for recursive processing } } // Now that we have created the alloca instructions that we want to use, // expand the getelementptr instructions to use them. // while (!AI->use_empty()) { Instruction *User = cast(AI->use_back()); if (BitCastInst *BCInst = dyn_cast(User)) { RewriteBitCastUserOfAlloca(BCInst, AI, ElementAllocas); BCInst->eraseFromParent(); continue; } // 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) if (LoadInst *LI = dyn_cast(User)) { Value *Insert = UndefValue::get(LI->getType()); for (unsigned i = 0, e = ElementAllocas.size(); i != e; ++i) { Value *Load = new LoadInst(ElementAllocas[i], "load", LI); Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI); } LI->replaceAllUsesWith(Insert); LI->eraseFromParent(); continue; } // 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) if (StoreInst *SI = dyn_cast(User)) { Value *Val = SI->getOperand(0); for (unsigned i = 0, e = ElementAllocas.size(); i != e; ++i) { Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI); new StoreInst(Extract, ElementAllocas[i], SI); } SI->eraseFromParent(); continue; } GetElementPtrInst *GEPI = cast(User); // We now know that the GEP is of the form: GEP , 0, unsigned Idx = (unsigned)cast(GEPI->getOperand(2))->getZExtValue(); assert(Idx < ElementAllocas.size() && "Index out of range?"); AllocaInst *AllocaToUse = ElementAllocas[Idx]; Value *RepValue; if (GEPI->getNumOperands() == 3) { // Do not insert a new getelementptr instruction with zero indices, only // to have it optimized out later. RepValue = AllocaToUse; } else { // We are indexing deeply into the structure, so we still need a // getelement ptr instruction to finish the indexing. This may be // expanded itself once the worklist is rerun. // SmallVector NewArgs; NewArgs.push_back(Constant::getNullValue(Type::Int32Ty)); NewArgs.append(GEPI->op_begin()+3, GEPI->op_end()); RepValue = GetElementPtrInst::Create(AllocaToUse, NewArgs.begin(), NewArgs.end(), "", GEPI); RepValue->takeName(GEPI); } // If this GEP is to the start of the aggregate, check for memcpys. if (Idx == 0) { bool IsStartOfAggregateGEP = true; for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) { if (!isa(GEPI->getOperand(i))) { IsStartOfAggregateGEP = false; break; } if (!cast(GEPI->getOperand(i))->isZero()) { IsStartOfAggregateGEP = false; break; } } if (IsStartOfAggregateGEP) RewriteBitCastUserOfAlloca(GEPI, AI, ElementAllocas); } // Move all of the users over to the new GEP. GEPI->replaceAllUsesWith(RepValue); // Delete the old GEP GEPI->eraseFromParent(); } // Finally, delete the Alloca instruction AI->eraseFromParent(); NumReplaced++; } /// isSafeElementUse - Check to see if this use is an allowed use for a /// getelementptr instruction of an array aggregate allocation. isFirstElt /// indicates whether Ptr is known to the start of the aggregate. /// void SROA::isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI, AllocaInfo &Info) { for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); I != E; ++I) { Instruction *User = cast(*I); switch (User->getOpcode()) { case Instruction::Load: break; case Instruction::Store: // Store is ok if storing INTO the pointer, not storing the pointer if (User->getOperand(0) == Ptr) return MarkUnsafe(Info); break; case Instruction::GetElementPtr: { GetElementPtrInst *GEP = cast(User); bool AreAllZeroIndices = isFirstElt; if (GEP->getNumOperands() > 1) { if (!isa(GEP->getOperand(1)) || !cast(GEP->getOperand(1))->isZero()) // Using pointer arithmetic to navigate the array. return MarkUnsafe(Info); if (AreAllZeroIndices) { for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) { if (!isa(GEP->getOperand(i)) || !cast(GEP->getOperand(i))->isZero()) { AreAllZeroIndices = false; break; } } } } isSafeElementUse(GEP, AreAllZeroIndices, AI, Info); if (Info.isUnsafe) return; break; } case Instruction::BitCast: if (isFirstElt) { isSafeUseOfBitCastedAllocation(cast(User), AI, Info); if (Info.isUnsafe) return; break; } DOUT << " Transformation preventing inst: " << *User; return MarkUnsafe(Info); case Instruction::Call: if (MemIntrinsic *MI = dyn_cast(User)) { if (isFirstElt) { isSafeMemIntrinsicOnAllocation(MI, AI, I.getOperandNo(), Info); if (Info.isUnsafe) return; break; } } DOUT << " Transformation preventing inst: " << *User; return MarkUnsafe(Info); default: DOUT << " Transformation preventing inst: " << *User; return MarkUnsafe(Info); } } return; // All users look ok :) } /// AllUsersAreLoads - Return true if all users of this value are loads. static bool AllUsersAreLoads(Value *Ptr) { for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); I != E; ++I) if (cast(*I)->getOpcode() != Instruction::Load) return false; return true; } /// isSafeUseOfAllocation - Check to see if this user is an allowed use for an /// aggregate allocation. /// void SROA::isSafeUseOfAllocation(Instruction *User, AllocationInst *AI, AllocaInfo &Info) { if (BitCastInst *C = dyn_cast(User)) return isSafeUseOfBitCastedAllocation(C, AI, Info); if (isa(User)) return; // Loads (returning a first class aggregrate) are always rewritable if (isa(User) && User->getOperand(0) != AI) return; // Store is ok if storing INTO the pointer, not storing the pointer GetElementPtrInst *GEPI = dyn_cast(User); if (GEPI == 0) return MarkUnsafe(Info); gep_type_iterator I = gep_type_begin(GEPI), E = gep_type_end(GEPI); // The GEP is not safe to transform if not of the form "GEP , 0, ". if (I == E || I.getOperand() != Constant::getNullValue(I.getOperand()->getType())) { return MarkUnsafe(Info); } ++I; if (I == E) return MarkUnsafe(Info); // ran out of GEP indices?? bool IsAllZeroIndices = true; // If the first index is a non-constant index into an array, see if we can // handle it as a special case. if (const ArrayType *AT = dyn_cast(*I)) { if (!isa(I.getOperand())) { IsAllZeroIndices = 0; uint64_t NumElements = AT->getNumElements(); // If this is an array index and the index is not constant, we cannot // promote... that is unless the array has exactly one or two elements in // it, in which case we CAN promote it, but we have to canonicalize this // out if this is the only problem. if ((NumElements == 1 || NumElements == 2) && AllUsersAreLoads(GEPI)) { Info.needsCanon = true; return; // Canonicalization required! } return MarkUnsafe(Info); } } bool hasVector = false; // Walk through the GEP type indices, checking the types that this indexes // into. for (; I != E; ++I) { // Ignore struct elements, no extra checking needed for these. if (isa(*I)) continue; ConstantInt *IdxVal = dyn_cast(I.getOperand()); if (!IdxVal) return MarkUnsafe(Info); // Are all indices still zero? IsAllZeroIndices &= IdxVal->isZero(); if (const ArrayType *AT = dyn_cast(*I)) { // This GEP indexes an array. Verify that this is an in-range constant // integer. Specifically, consider A[0][i]. We cannot know that the user // isn't doing invalid things like allowing i to index an out-of-range // subscript that accesses A[1]. Because of this, we have to reject SROA // of any accesses into structs where any of the components are variables. if (IdxVal->getZExtValue() >= AT->getNumElements()) return MarkUnsafe(Info); } // Note if we've seen a vector type yet hasVector |= isa(*I); // Don't SROA pointers into vectors, unless all indices are zero. When all // indices are zero, we only consider this GEP as a bitcast, but will still // not consider breaking up the vector. if (hasVector && !IsAllZeroIndices) return MarkUnsafe(Info); } // If there are any non-simple uses of this getelementptr, make sure to reject // them. return isSafeElementUse(GEPI, IsAllZeroIndices, AI, Info); } /// isSafeMemIntrinsicOnAllocation - Return true if the specified memory /// intrinsic can be promoted by SROA. At this point, we know that the operand /// of the memintrinsic is a pointer to the beginning of the allocation. void SROA::isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI, unsigned OpNo, AllocaInfo &Info) { // If not constant length, give up. ConstantInt *Length = dyn_cast(MI->getLength()); if (!Length) return MarkUnsafe(Info); // If not the whole aggregate, give up. const TargetData &TD = getAnalysis(); if (Length->getZExtValue() != TD.getABITypeSize(AI->getType()->getElementType())) return MarkUnsafe(Info); // We only know about memcpy/memset/memmove. if (!isa(MI) && !isa(MI) && !isa(MI)) return MarkUnsafe(Info); // Otherwise, we can transform it. Determine whether this is a memcpy/set // into or out of the aggregate. if (OpNo == 1) Info.isMemCpyDst = true; else { assert(OpNo == 2); Info.isMemCpySrc = true; } } /// isSafeUseOfBitCastedAllocation - Return true if all users of this bitcast /// are void SROA::isSafeUseOfBitCastedAllocation(BitCastInst *BC, AllocationInst *AI, AllocaInfo &Info) { for (Value::use_iterator UI = BC->use_begin(), E = BC->use_end(); UI != E; ++UI) { if (BitCastInst *BCU = dyn_cast(UI)) { isSafeUseOfBitCastedAllocation(BCU, AI, Info); } else if (MemIntrinsic *MI = dyn_cast(UI)) { isSafeMemIntrinsicOnAllocation(MI, AI, UI.getOperandNo(), Info); } else { return MarkUnsafe(Info); } if (Info.isUnsafe) return; } } /// RewriteBitCastUserOfAlloca - BCInst (transitively) bitcasts AI, or indexes /// to its first element. Transform users of the cast to use the new values /// instead. void SROA::RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI, SmallVector &NewElts) { Constant *Zero = Constant::getNullValue(Type::Int32Ty); const TargetData &TD = getAnalysis(); Value::use_iterator UI = BCInst->use_begin(), UE = BCInst->use_end(); while (UI != UE) { if (BitCastInst *BCU = dyn_cast(*UI)) { RewriteBitCastUserOfAlloca(BCU, AI, NewElts); ++UI; BCU->eraseFromParent(); continue; } // Otherwise, must be memcpy/memmove/memset of the entire aggregate. Split // into one per element. MemIntrinsic *MI = dyn_cast(*UI); // If it's not a mem intrinsic, it must be some other user of a gep of the // first pointer. Just leave these alone. if (!MI) { ++UI; continue; } // If this is a memcpy/memmove, construct the other pointer as the // appropriate type. Value *OtherPtr = 0; if (MemCpyInst *MCI = dyn_cast(MI)) { if (BCInst == MCI->getRawDest()) OtherPtr = MCI->getRawSource(); else { assert(BCInst == MCI->getRawSource()); OtherPtr = MCI->getRawDest(); } } else if (MemMoveInst *MMI = dyn_cast(MI)) { if (BCInst == MMI->getRawDest()) OtherPtr = MMI->getRawSource(); else { assert(BCInst == MMI->getRawSource()); OtherPtr = MMI->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. if (OtherPtr) { // It is likely that OtherPtr is a bitcast, if so, remove it. if (BitCastInst *BC = dyn_cast(OtherPtr)) OtherPtr = BC->getOperand(0); // All zero GEPs are effectively casts if (GetElementPtrInst *GEP = dyn_cast(OtherPtr)) if (GEP->hasAllZeroIndices()) OtherPtr = GEP->getOperand(0); if (ConstantExpr *BCE = dyn_cast(OtherPtr)) if (BCE->getOpcode() == Instruction::BitCast) OtherPtr = BCE->getOperand(0); // If the pointer is not the right type, insert a bitcast to the right // type. if (OtherPtr->getType() != AI->getType()) OtherPtr = new BitCastInst(OtherPtr, AI->getType(), OtherPtr->getName(), MI); } // Process each element of the aggregate. Value *TheFn = MI->getOperand(0); const Type *BytePtrTy = MI->getRawDest()->getType(); bool SROADest = MI->getRawDest() == BCInst; 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; if (OtherPtr) { Value *Idx[2] = { Zero, ConstantInt::get(Type::Int32Ty, i) }; OtherElt = GetElementPtrInst::Create(OtherPtr, Idx, Idx + 2, OtherPtr->getNameStr()+"."+utostr(i), MI); } 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) || isa(MI)) { Value *Elt = new LoadInst(SROADest ? OtherElt : EltPtr, "tmp", MI); new StoreInst(Elt, SROADest ? EltPtr : OtherElt, MI); continue; } else { assert(isa(MI)); // If the stored element is zero (common case), just store a null // constant. Constant *StoreVal; if (ConstantInt *CI = dyn_cast(MI->getOperand(2))) { 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; if (const VectorType *VTy = dyn_cast(ValTy)) ValTy = VTy->getElementType(); // 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(TotalVal); if (isa(ValTy)) StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy); else if (ValTy->isFloatingPoint()) 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[0], NumElts); } } new StoreInst(StoreVal, EltPtr, MI); continue; } // Otherwise, if we're storing a byte variable, use a memset call for // this element. } } // Cast the element pointer to BytePtrTy. if (EltPtr->getType() != BytePtrTy) EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getNameStr(), MI); // Cast the other pointer (if we have one) to BytePtrTy. if (OtherElt && OtherElt->getType() != BytePtrTy) OtherElt = new BitCastInst(OtherElt, BytePtrTy,OtherElt->getNameStr(), MI); unsigned EltSize = TD.getABITypeSize(EltTy); // Finally, insert the meminst for this element. if (isa(MI) || isa(MI)) { Value *Ops[] = { SROADest ? EltPtr : OtherElt, // Dest ptr SROADest ? OtherElt : EltPtr, // Src ptr ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size Zero // Align }; CallInst::Create(TheFn, Ops, Ops + 4, "", MI); } else { assert(isa(MI)); Value *Ops[] = { EltPtr, MI->getOperand(2), // Dest, Value, ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size Zero // Align }; CallInst::Create(TheFn, Ops, Ops + 4, "", MI); } } // Finally, MI is now dead, as we've modified its actions to occur on all of // the elements of the aggregate. ++UI; MI->eraseFromParent(); } } /// HasPadding - Return true if the specified type has any structure or /// alignment padding, false otherwise. static bool HasPadding(const Type *Ty, const TargetData &TD) { if (const StructType *STy = dyn_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); // Padding in sub-elements? if (HasPadding(STy->getElementType(i), TD)) return true; // 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; } } else if (const ArrayType *ATy = dyn_cast(Ty)) { return HasPadding(ATy->getElementType(), TD); } else if (const VectorType *VTy = dyn_cast(Ty)) { return HasPadding(VTy->getElementType(), TD); } return TD.getTypeSizeInBits(Ty) != TD.getABITypeSizeInBits(Ty); } /// 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. /// int SROA::isSafeAllocaToScalarRepl(AllocationInst *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; for (Value::use_iterator I = AI->use_begin(), E = AI->use_end(); I != E; ++I) { isSafeUseOfAllocation(cast(*I), AI, Info); if (Info.isUnsafe) { DOUT << "Cannot transform: " << *AI << " due to user: " << **I; return 0; } } // 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->getType()->getElementType(), getAnalysis())) return 0; // If we require cleanup, return 1, otherwise return 3. return Info.needsCanon ? 1 : 3; } /// CanonicalizeAllocaUsers - If SROA reported that it can promote the specified /// allocation, but only if cleaned up, perform the cleanups required. void SROA::CanonicalizeAllocaUsers(AllocationInst *AI) { // At this point, we know that the end result will be SROA'd and promoted, so // we can insert ugly code if required so long as sroa+mem2reg will clean it // up. for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E; ) { GetElementPtrInst *GEPI = dyn_cast(*UI++); if (!GEPI) continue; gep_type_iterator I = gep_type_begin(GEPI); ++I; if (const ArrayType *AT = dyn_cast(*I)) { uint64_t NumElements = AT->getNumElements(); if (!isa(I.getOperand())) { if (NumElements == 1) { GEPI->setOperand(2, Constant::getNullValue(Type::Int32Ty)); } else { assert(NumElements == 2 && "Unhandled case!"); // All users of the GEP must be loads. At each use of the GEP, insert // two loads of the appropriate indexed GEP and select between them. Value *IsOne = new ICmpInst(ICmpInst::ICMP_NE, I.getOperand(), Constant::getNullValue(I.getOperand()->getType()), "isone", GEPI); // Insert the new GEP instructions, which are properly indexed. SmallVector Indices(GEPI->op_begin()+1, GEPI->op_end()); Indices[1] = Constant::getNullValue(Type::Int32Ty); Value *ZeroIdx = GetElementPtrInst::Create(GEPI->getOperand(0), Indices.begin(), Indices.end(), GEPI->getName()+".0", GEPI); Indices[1] = ConstantInt::get(Type::Int32Ty, 1); Value *OneIdx = GetElementPtrInst::Create(GEPI->getOperand(0), Indices.begin(), Indices.end(), GEPI->getName()+".1", GEPI); // Replace all loads of the variable index GEP with loads from both // indexes and a select. while (!GEPI->use_empty()) { LoadInst *LI = cast(GEPI->use_back()); Value *Zero = new LoadInst(ZeroIdx, LI->getName()+".0", LI); Value *One = new LoadInst(OneIdx , LI->getName()+".1", LI); Value *R = SelectInst::Create(IsOne, One, Zero, LI->getName(), LI); LI->replaceAllUsesWith(R); LI->eraseFromParent(); } GEPI->eraseFromParent(); } } } } } /// MergeInType - Add the 'In' type to the accumulated type so far. If the /// types are incompatible, return true, otherwise update Accum and return /// false. /// /// There are three cases we handle here: /// 1) An effectively-integer union, where the pieces are stored into as /// smaller integers (common with byte swap and other idioms). /// 2) A union of vector types of the same size and potentially its elements. /// Here we turn element accesses into insert/extract element operations. /// 3) A union of scalar types, such as int/float or int/pointer. Here we /// merge together into integers, allowing the xform to work with #1 as /// well. static bool MergeInType(const Type *In, const Type *&Accum, const TargetData &TD) { // If this is our first type, just use it. const VectorType *PTy; if (Accum == Type::VoidTy || In == Accum) { Accum = In; } else if (In == Type::VoidTy) { // Noop. } else if (In->isInteger() && Accum->isInteger()) { // integer union. // Otherwise pick whichever type is larger. if (cast(In)->getBitWidth() > cast(Accum)->getBitWidth()) Accum = In; } else if (isa(In) && isa(Accum)) { // Pointer unions just stay as one of the pointers. } else if (isa(In) || isa(Accum)) { if ((PTy = dyn_cast(Accum)) && PTy->getElementType() == In) { // Accum is a vector, and we are accessing an element: ok. } else if ((PTy = dyn_cast(In)) && PTy->getElementType() == Accum) { // In is a vector, and accum is an element: ok, remember In. Accum = In; } else if ((PTy = dyn_cast(In)) && isa(Accum) && PTy->getBitWidth() == cast(Accum)->getBitWidth()) { // Two vectors of the same size: keep Accum. } else { // Cannot insert an short into a <4 x int> or handle // <2 x int> -> <4 x int> return true; } } else { // Pointer/FP/Integer unions merge together as integers. switch (Accum->getTypeID()) { case Type::PointerTyID: Accum = TD.getIntPtrType(); break; case Type::FloatTyID: Accum = Type::Int32Ty; break; case Type::DoubleTyID: Accum = Type::Int64Ty; break; case Type::X86_FP80TyID: return true; case Type::FP128TyID: return true; case Type::PPC_FP128TyID: return true; default: assert(Accum->isInteger() && "Unknown FP type!"); break; } switch (In->getTypeID()) { case Type::PointerTyID: In = TD.getIntPtrType(); break; case Type::FloatTyID: In = Type::Int32Ty; break; case Type::DoubleTyID: In = Type::Int64Ty; break; case Type::X86_FP80TyID: return true; case Type::FP128TyID: return true; case Type::PPC_FP128TyID: return true; default: assert(In->isInteger() && "Unknown FP type!"); break; } return MergeInType(In, Accum, TD); } return false; } /// getUIntAtLeastAsBigAs - Return an unsigned integer type that is at least /// as big as the specified type. If there is no suitable type, this returns /// null. const Type *getUIntAtLeastAsBigAs(unsigned NumBits) { if (NumBits > 64) return 0; if (NumBits > 32) return Type::Int64Ty; if (NumBits > 16) return Type::Int32Ty; if (NumBits > 8) return Type::Int16Ty; return Type::Int8Ty; } /// CanConvertToScalar - V is a pointer. If we can convert the pointee to a /// single scalar integer type, return that type. Further, if the use is not /// a completely trivial use that mem2reg could promote, set IsNotTrivial. If /// there are no uses of this pointer, return Type::VoidTy to differentiate from /// failure. /// const Type *SROA::CanConvertToScalar(Value *V, bool &IsNotTrivial) { const Type *UsedType = Type::VoidTy; // No uses, no forced type. const TargetData &TD = getAnalysis(); const PointerType *PTy = cast(V->getType()); 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)) { // FIXME: Loads of a first class aggregrate value could be converted to a // series of loads and insertvalues if (!LI->getType()->isSingleValueType()) return 0; if (MergeInType(LI->getType(), UsedType, TD)) return 0; } else if (StoreInst *SI = dyn_cast(User)) { // Storing the pointer, not into the value? if (SI->getOperand(0) == V) return 0; // FIXME: Stores of a first class aggregrate value could be converted to a // series of extractvalues and stores if (!SI->getOperand(0)->getType()->isSingleValueType()) return 0; // NOTE: We could handle storing of FP imms into integers here! if (MergeInType(SI->getOperand(0)->getType(), UsedType, TD)) return 0; } else if (BitCastInst *CI = dyn_cast(User)) { IsNotTrivial = true; const Type *SubTy = CanConvertToScalar(CI, IsNotTrivial); if (!SubTy || MergeInType(SubTy, UsedType, TD)) return 0; } else if (GetElementPtrInst *GEP = dyn_cast(User)) { // Check to see if this is stepping over an element: GEP Ptr, int C if (GEP->getNumOperands() == 2 && isa(GEP->getOperand(1))) { unsigned Idx = cast(GEP->getOperand(1))->getZExtValue(); unsigned ElSize = TD.getABITypeSize(PTy->getElementType()); unsigned BitOffset = Idx*ElSize*8; if (BitOffset > 64 || !isPowerOf2_32(ElSize)) return 0; IsNotTrivial = true; const Type *SubElt = CanConvertToScalar(GEP, IsNotTrivial); if (SubElt == 0) return 0; if (SubElt != Type::VoidTy && SubElt->isInteger()) { const Type *NewTy = getUIntAtLeastAsBigAs(TD.getABITypeSizeInBits(SubElt)+BitOffset); if (NewTy == 0 || MergeInType(NewTy, UsedType, TD)) return 0; continue; } } else if (GEP->getNumOperands() == 3 && isa(GEP->getOperand(1)) && isa(GEP->getOperand(2)) && cast(GEP->getOperand(1))->isZero()) { // We are stepping into an element, e.g. a structure or an array: // GEP Ptr, int 0, uint C const Type *AggTy = PTy->getElementType(); unsigned Idx = cast(GEP->getOperand(2))->getZExtValue(); if (const ArrayType *ATy = dyn_cast(AggTy)) { if (Idx >= ATy->getNumElements()) return 0; // Out of range. } else if (const VectorType *VectorTy = dyn_cast(AggTy)) { // Getting an element of the vector. if (Idx >= VectorTy->getNumElements()) return 0; // Out of range. // Merge in the vector type. if (MergeInType(VectorTy, UsedType, TD)) return 0; const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial); if (SubTy == 0) return 0; if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType, TD)) return 0; // We'll need to change this to an insert/extract element operation. IsNotTrivial = true; continue; // Everything looks ok } else if (isa(AggTy)) { // Structs are always ok. } else { return 0; } const Type *NTy = getUIntAtLeastAsBigAs(TD.getABITypeSizeInBits(AggTy)); if (NTy == 0 || MergeInType(NTy, UsedType, TD)) return 0; const Type *SubTy = CanConvertToScalar(GEP, IsNotTrivial); if (SubTy == 0) return 0; if (SubTy != Type::VoidTy && MergeInType(SubTy, UsedType, TD)) return 0; continue; // Everything looks ok } return 0; } else { // Cannot handle this! return 0; } } return UsedType; } /// ConvertToScalar - The specified alloca passes the CanConvertToScalar /// predicate and is non-trivial. Convert it to something that can be trivially /// promoted into a register by mem2reg. void SROA::ConvertToScalar(AllocationInst *AI, const Type *ActualTy) { DOUT << "CONVERT TO SCALAR: " << *AI << " TYPE = " << *ActualTy << "\n"; ++NumConverted; BasicBlock *EntryBlock = AI->getParent(); assert(EntryBlock == &EntryBlock->getParent()->getEntryBlock() && "Not in the entry block!"); EntryBlock->getInstList().remove(AI); // Take the alloca out of the program. // Create and insert the alloca. AllocaInst *NewAI = new AllocaInst(ActualTy, 0, AI->getName(), EntryBlock->begin()); ConvertUsesToScalar(AI, NewAI, 0); delete AI; } /// 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 SROA::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, unsigned Offset) { while (!Ptr->use_empty()) { Instruction *User = cast(Ptr->use_back()); if (LoadInst *LI = dyn_cast(User)) { Value *NV = ConvertUsesOfLoadToScalar(LI, NewAI, Offset); LI->replaceAllUsesWith(NV); LI->eraseFromParent(); } else if (StoreInst *SI = dyn_cast(User)) { assert(SI->getOperand(0) != Ptr && "Consistency error!"); Value *SV = ConvertUsesOfStoreToScalar(SI, NewAI, Offset); new StoreInst(SV, NewAI, SI); SI->eraseFromParent(); } else if (BitCastInst *CI = dyn_cast(User)) { ConvertUsesToScalar(CI, NewAI, Offset); CI->eraseFromParent(); } else if (GetElementPtrInst *GEP = dyn_cast(User)) { const PointerType *AggPtrTy = cast(GEP->getOperand(0)->getType()); const TargetData &TD = getAnalysis(); unsigned AggSizeInBits = TD.getABITypeSizeInBits(AggPtrTy->getElementType()); // Check to see if this is stepping over an element: GEP Ptr, int C unsigned NewOffset = Offset; if (GEP->getNumOperands() == 2) { unsigned Idx = cast(GEP->getOperand(1))->getZExtValue(); unsigned BitOffset = Idx*AggSizeInBits; NewOffset += BitOffset; } else if (GEP->getNumOperands() == 3) { // We know that operand #2 is zero. unsigned Idx = cast(GEP->getOperand(2))->getZExtValue(); const Type *AggTy = AggPtrTy->getElementType(); if (const SequentialType *SeqTy = dyn_cast(AggTy)) { unsigned ElSizeBits = TD.getABITypeSizeInBits(SeqTy->getElementType()); NewOffset += ElSizeBits*Idx; } else if (const StructType *STy = dyn_cast(AggTy)) { unsigned EltBitOffset = TD.getStructLayout(STy)->getElementOffsetInBits(Idx); NewOffset += EltBitOffset; } else { assert(0 && "Unsupported operation!"); abort(); } } else { assert(0 && "Unsupported operation!"); abort(); } ConvertUsesToScalar(GEP, NewAI, NewOffset); GEP->eraseFromParent(); } else { assert(0 && "Unsupported operation!"); abort(); } } } /// ConvertUsesOfLoadToScalar - Convert all of the users the specified load to /// use the new alloca directly, returning the value that should replace the /// load. 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. Value *SROA::ConvertUsesOfLoadToScalar(LoadInst *LI, AllocaInst *NewAI, unsigned Offset) { // The load is a bit extract from NewAI shifted right by Offset bits. Value *NV = new LoadInst(NewAI, LI->getName(), LI); if (NV->getType() == LI->getType() && Offset == 0) { // We win, no conversion needed. return NV; } // If the result type of the 'union' is a pointer, then this must be ptr->ptr // cast. Anything else would result in NV being an integer. if (isa(NV->getType())) { assert(isa(LI->getType())); return new BitCastInst(NV, LI->getType(), LI->getName(), LI); } if (const VectorType *VTy = dyn_cast(NV->getType())) { // If the result alloca is a vector type, this is either an element // access or a bitcast to another vector type. if (isa(LI->getType())) return new BitCastInst(NV, LI->getType(), LI->getName(), LI); // Otherwise it must be an element access. const TargetData &TD = getAnalysis(); unsigned Elt = 0; if (Offset) { unsigned EltSize = TD.getABITypeSizeInBits(VTy->getElementType()); Elt = Offset/EltSize; Offset -= EltSize*Elt; } NV = new ExtractElementInst(NV, ConstantInt::get(Type::Int32Ty, Elt), "tmp", LI); // If we're done, return this element. if (NV->getType() == LI->getType() && Offset == 0) return NV; } const IntegerType *NTy = cast(NV->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; const TargetData &TD = getAnalysis(); 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(LI->getType()) - 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()) NV = BinaryOperator::CreateLShr(NV, ConstantInt::get(NV->getType(),ShAmt), LI->getName(), LI); else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth()) NV = BinaryOperator::CreateShl(NV, ConstantInt::get(NV->getType(),-ShAmt), LI->getName(), LI); // Finally, unconditionally truncate the integer to the right width. unsigned LIBitWidth = TD.getTypeSizeInBits(LI->getType()); if (LIBitWidth < NTy->getBitWidth()) NV = new TruncInst(NV, IntegerType::get(LIBitWidth), LI->getName(), LI); // If the result is an integer, this is a trunc or bitcast. if (isa(LI->getType())) { // Should be done. } else if (LI->getType()->isFloatingPoint()) { // Just do a bitcast, we know the sizes match up. NV = new BitCastInst(NV, LI->getType(), LI->getName(), LI); } else { // Otherwise must be a pointer. NV = new IntToPtrInst(NV, LI->getType(), LI->getName(), LI); } assert(NV->getType() == LI->getType() && "Didn't convert right?"); return NV; } /// ConvertUsesOfStoreToScalar - Convert the specified store to a load+store /// pair of the new alloca directly, returning the value that should be stored /// to the alloca. 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. Value *SROA::ConvertUsesOfStoreToScalar(StoreInst *SI, AllocaInst *NewAI, unsigned Offset) { // Convert the stored type to the actual type, shift it left to insert // then 'or' into place. Value *SV = SI->getOperand(0); const Type *AllocaType = NewAI->getType()->getElementType(); if (SV->getType() == AllocaType && Offset == 0) { // All is well. } else if (const VectorType *PTy = dyn_cast(AllocaType)) { Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI); // If the result alloca is a vector type, this is either an element // access or a bitcast to another vector type. if (isa(SV->getType())) { SV = new BitCastInst(SV, AllocaType, SV->getName(), SI); } else { // Must be an element insertion. const TargetData &TD = getAnalysis(); unsigned Elt = Offset/TD.getABITypeSizeInBits(PTy->getElementType()); SV = InsertElementInst::Create(Old, SV, ConstantInt::get(Type::Int32Ty, Elt), "tmp", SI); } } else if (isa(AllocaType)) { // If the alloca type is a pointer, then all the elements must be // pointers. if (SV->getType() != AllocaType) SV = new BitCastInst(SV, AllocaType, SV->getName(), SI); } else { Value *Old = new LoadInst(NewAI, NewAI->getName()+".in", SI); // If SV is a float, convert it to the appropriate integer type. // If it is a pointer, do the same, and also handle ptr->ptr casts // here. const TargetData &TD = getAnalysis(); 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()->isFloatingPoint()) SV = new BitCastInst(SV, IntegerType::get(SrcWidth), SV->getName(), SI); else if (isa(SV->getType())) SV = new PtrToIntInst(SV, TD.getIntPtrType(), SV->getName(), SI); // Always zero extend the value if needed. if (SV->getType() != AllocaType) SV = new ZExtInst(SV, AllocaType, SV->getName(), SI); // 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 = BinaryOperator::CreateShl(SV, ConstantInt::get(SV->getType(), ShAmt), SV->getName(), SI); Mask <<= ShAmt; } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) { SV = BinaryOperator::CreateLShr(SV, ConstantInt::get(SV->getType(),-ShAmt), SV->getName(), SI); 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 = BinaryOperator::CreateAnd(Old, ConstantInt::get(~Mask), Old->getName()+".mask", SI); SV = BinaryOperator::CreateOr(Old, SV, SV->getName()+".ins", SI); } } return SV; } /// 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, Instruction *&TheCopy, bool isOffset) { for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) { if (isa(*UI)) { // Ignore loads, they are always ok. continue; } if (BitCastInst *BCI = dyn_cast(*UI)) { // If uses of the bitcast are ok, we are ok. if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset)) return false; continue; } if (GetElementPtrInst *GEP = dyn_cast(*UI)) { // 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 this is isn't our memcpy/memmove, reject it as something we can't // handle. if (!isa(*UI) && !isa(*UI)) return false; // 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() != 1) return false; MemIntrinsic *MI = cast(*UI); // If the source of the memcpy/move is not a constant global, reject it. if (!PointsToConstantGlobal(MI->getOperand(2))) 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. Instruction *SROA::isOnlyCopiedFromConstantGlobal(AllocationInst *AI) { Instruction *TheCopy = 0; if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false)) return TheCopy; return 0; }