diff options
Diffstat (limited to 'contrib/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp | 850 |
1 files changed, 850 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/contrib/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp new file mode 100644 index 000000000000..e9c25d32c281 --- /dev/null +++ b/contrib/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp @@ -0,0 +1,850 @@ +//===- InstCombineLoadStoreAlloca.cpp -------------------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements the visit functions for load, store and alloca. +// +//===----------------------------------------------------------------------===// + +#include "InstCombine.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/Loads.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Local.h" +using namespace llvm; + +#define DEBUG_TYPE "instcombine" + +STATISTIC(NumDeadStore, "Number of dead stores eliminated"); +STATISTIC(NumGlobalCopies, "Number of allocas copied from constant global"); + +/// pointsToConstantGlobal - Return true if V (possibly indirectly) points to +/// some part of a constant global variable. This intentionally only accepts +/// constant expressions because we can't rewrite arbitrary instructions. +static bool pointsToConstantGlobal(Value *V) { + if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) + return GV->isConstant(); + + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) { + if (CE->getOpcode() == Instruction::BitCast || + CE->getOpcode() == Instruction::AddrSpaceCast || + 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, + SmallVectorImpl<Instruction *> &ToDelete) { + // We track lifetime intrinsics as we encounter them. If we decide to go + // ahead and replace the value with the global, this lets the caller quickly + // eliminate the markers. + + SmallVector<std::pair<Value *, bool>, 35> ValuesToInspect; + ValuesToInspect.push_back(std::make_pair(V, false)); + while (!ValuesToInspect.empty()) { + auto ValuePair = ValuesToInspect.pop_back_val(); + const bool IsOffset = ValuePair.second; + for (auto &U : ValuePair.first->uses()) { + Instruction *I = cast<Instruction>(U.getUser()); + + if (LoadInst *LI = dyn_cast<LoadInst>(I)) { + // Ignore non-volatile loads, they are always ok. + if (!LI->isSimple()) return false; + continue; + } + + if (isa<BitCastInst>(I) || isa<AddrSpaceCastInst>(I)) { + // If uses of the bitcast are ok, we are ok. + ValuesToInspect.push_back(std::make_pair(I, IsOffset)); + continue; + } + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) { + // If the GEP has all zero indices, it doesn't offset the pointer. If it + // doesn't, it does. + ValuesToInspect.push_back( + std::make_pair(I, IsOffset || !GEP->hasAllZeroIndices())); + continue; + } + + if (CallSite CS = I) { + // If this is the function being called then we treat it like a load and + // ignore it. + if (CS.isCallee(&U)) + continue; + + // Inalloca arguments are clobbered by the call. + unsigned ArgNo = CS.getArgumentNo(&U); + if (CS.isInAllocaArgument(ArgNo)) + return false; + + // If this is a readonly/readnone call site, then we know it is just a + // load (but one that potentially returns the value itself), so we can + // ignore it if we know that the value isn't captured. + if (CS.onlyReadsMemory() && + (CS.getInstruction()->use_empty() || CS.doesNotCapture(ArgNo))) + 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. + if (CS.isByValArgument(ArgNo)) + continue; + } + + // Lifetime intrinsics can be handled by the caller. + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { + if (II->getIntrinsicID() == Intrinsic::lifetime_start || + II->getIntrinsicID() == Intrinsic::lifetime_end) { + assert(II->use_empty() && "Lifetime markers have no result to use!"); + ToDelete.push_back(II); + continue; + } + } + + // If this is isn't our memcpy/memmove, reject it as something we can't + // handle. + MemTransferInst *MI = dyn_cast<MemTransferInst>(I); + if (!MI) + 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 (U.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 (U.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. +static MemTransferInst * +isOnlyCopiedFromConstantGlobal(AllocaInst *AI, + SmallVectorImpl<Instruction *> &ToDelete) { + MemTransferInst *TheCopy = nullptr; + if (isOnlyCopiedFromConstantGlobal(AI, TheCopy, ToDelete)) + return TheCopy; + return nullptr; +} + +Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) { + // Ensure that the alloca array size argument has type intptr_t, so that + // any casting is exposed early. + if (DL) { + Type *IntPtrTy = DL->getIntPtrType(AI.getType()); + if (AI.getArraySize()->getType() != IntPtrTy) { + Value *V = Builder->CreateIntCast(AI.getArraySize(), + IntPtrTy, false); + AI.setOperand(0, V); + return &AI; + } + } + + // Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1 + if (AI.isArrayAllocation()) { // Check C != 1 + if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) { + Type *NewTy = + ArrayType::get(AI.getAllocatedType(), C->getZExtValue()); + AllocaInst *New = Builder->CreateAlloca(NewTy, nullptr, AI.getName()); + New->setAlignment(AI.getAlignment()); + + // Scan to the end of the allocation instructions, to skip over a block of + // allocas if possible...also skip interleaved debug info + // + BasicBlock::iterator It = New; + while (isa<AllocaInst>(*It) || isa<DbgInfoIntrinsic>(*It)) ++It; + + // Now that I is pointing to the first non-allocation-inst in the block, + // insert our getelementptr instruction... + // + Type *IdxTy = DL + ? DL->getIntPtrType(AI.getType()) + : Type::getInt64Ty(AI.getContext()); + Value *NullIdx = Constant::getNullValue(IdxTy); + Value *Idx[2] = { NullIdx, NullIdx }; + Instruction *GEP = + GetElementPtrInst::CreateInBounds(New, Idx, New->getName() + ".sub"); + InsertNewInstBefore(GEP, *It); + + // Now make everything use the getelementptr instead of the original + // allocation. + return ReplaceInstUsesWith(AI, GEP); + } else if (isa<UndefValue>(AI.getArraySize())) { + return ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType())); + } + } + + if (DL && AI.getAllocatedType()->isSized()) { + // If the alignment is 0 (unspecified), assign it the preferred alignment. + if (AI.getAlignment() == 0) + AI.setAlignment(DL->getPrefTypeAlignment(AI.getAllocatedType())); + + // Move all alloca's of zero byte objects to the entry block and merge them + // together. Note that we only do this for alloca's, because malloc should + // allocate and return a unique pointer, even for a zero byte allocation. + if (DL->getTypeAllocSize(AI.getAllocatedType()) == 0) { + // For a zero sized alloca there is no point in doing an array allocation. + // This is helpful if the array size is a complicated expression not used + // elsewhere. + if (AI.isArrayAllocation()) { + AI.setOperand(0, ConstantInt::get(AI.getArraySize()->getType(), 1)); + return &AI; + } + + // Get the first instruction in the entry block. + BasicBlock &EntryBlock = AI.getParent()->getParent()->getEntryBlock(); + Instruction *FirstInst = EntryBlock.getFirstNonPHIOrDbg(); + if (FirstInst != &AI) { + // If the entry block doesn't start with a zero-size alloca then move + // this one to the start of the entry block. There is no problem with + // dominance as the array size was forced to a constant earlier already. + AllocaInst *EntryAI = dyn_cast<AllocaInst>(FirstInst); + if (!EntryAI || !EntryAI->getAllocatedType()->isSized() || + DL->getTypeAllocSize(EntryAI->getAllocatedType()) != 0) { + AI.moveBefore(FirstInst); + return &AI; + } + + // If the alignment of the entry block alloca is 0 (unspecified), + // assign it the preferred alignment. + if (EntryAI->getAlignment() == 0) + EntryAI->setAlignment( + DL->getPrefTypeAlignment(EntryAI->getAllocatedType())); + // Replace this zero-sized alloca with the one at the start of the entry + // block after ensuring that the address will be aligned enough for both + // types. + unsigned MaxAlign = std::max(EntryAI->getAlignment(), + AI.getAlignment()); + EntryAI->setAlignment(MaxAlign); + if (AI.getType() != EntryAI->getType()) + return new BitCastInst(EntryAI, AI.getType()); + return ReplaceInstUsesWith(AI, EntryAI); + } + } + } + + if (AI.getAlignment()) { + // Check to see if this allocation is only modified by a memcpy/memmove from + // a constant global whose alignment is equal to or exceeds that of the + // allocation. 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. + SmallVector<Instruction *, 4> ToDelete; + if (MemTransferInst *Copy = isOnlyCopiedFromConstantGlobal(&AI, ToDelete)) { + unsigned SourceAlign = getOrEnforceKnownAlignment(Copy->getSource(), + AI.getAlignment(), DL); + if (AI.getAlignment() <= SourceAlign) { + DEBUG(dbgs() << "Found alloca equal to global: " << AI << '\n'); + DEBUG(dbgs() << " memcpy = " << *Copy << '\n'); + for (unsigned i = 0, e = ToDelete.size(); i != e; ++i) + EraseInstFromFunction(*ToDelete[i]); + Constant *TheSrc = cast<Constant>(Copy->getSource()); + Constant *Cast + = ConstantExpr::getPointerBitCastOrAddrSpaceCast(TheSrc, AI.getType()); + Instruction *NewI = ReplaceInstUsesWith(AI, Cast); + EraseInstFromFunction(*Copy); + ++NumGlobalCopies; + return NewI; + } + } + } + + // At last, use the generic allocation site handler to aggressively remove + // unused allocas. + return visitAllocSite(AI); +} + + +/// InstCombineLoadCast - Fold 'load (cast P)' -> cast (load P)' when possible. +static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI, + const DataLayout *DL) { + User *CI = cast<User>(LI.getOperand(0)); + Value *CastOp = CI->getOperand(0); + + PointerType *DestTy = cast<PointerType>(CI->getType()); + Type *DestPTy = DestTy->getElementType(); + if (PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType())) { + + // If the address spaces don't match, don't eliminate the cast. + if (DestTy->getAddressSpace() != SrcTy->getAddressSpace()) + return nullptr; + + Type *SrcPTy = SrcTy->getElementType(); + + if (DestPTy->isIntegerTy() || DestPTy->isPointerTy() || + DestPTy->isVectorTy()) { + // If the source is an array, the code below will not succeed. Check to + // see if a trivial 'gep P, 0, 0' will help matters. Only do this for + // constants. + if (ArrayType *ASrcTy = dyn_cast<ArrayType>(SrcPTy)) + if (Constant *CSrc = dyn_cast<Constant>(CastOp)) + if (ASrcTy->getNumElements() != 0) { + Type *IdxTy = DL + ? DL->getIntPtrType(SrcTy) + : Type::getInt64Ty(SrcTy->getContext()); + Value *Idx = Constant::getNullValue(IdxTy); + Value *Idxs[2] = { Idx, Idx }; + CastOp = ConstantExpr::getGetElementPtr(CSrc, Idxs); + SrcTy = cast<PointerType>(CastOp->getType()); + SrcPTy = SrcTy->getElementType(); + } + + if (IC.getDataLayout() && + (SrcPTy->isIntegerTy() || SrcPTy->isPointerTy() || + SrcPTy->isVectorTy()) && + // Do not allow turning this into a load of an integer, which is then + // casted to a pointer, this pessimizes pointer analysis a lot. + (SrcPTy->isPtrOrPtrVectorTy() == + LI.getType()->isPtrOrPtrVectorTy()) && + IC.getDataLayout()->getTypeSizeInBits(SrcPTy) == + IC.getDataLayout()->getTypeSizeInBits(DestPTy)) { + + // Okay, we are casting from one integer or pointer type to another of + // the same size. Instead of casting the pointer before the load, cast + // the result of the loaded value. + LoadInst *NewLoad = + IC.Builder->CreateLoad(CastOp, LI.isVolatile(), CI->getName()); + NewLoad->setAlignment(LI.getAlignment()); + NewLoad->setAtomic(LI.getOrdering(), LI.getSynchScope()); + // Now cast the result of the load. + PointerType *OldTy = dyn_cast<PointerType>(NewLoad->getType()); + PointerType *NewTy = dyn_cast<PointerType>(LI.getType()); + if (OldTy && NewTy && + OldTy->getAddressSpace() != NewTy->getAddressSpace()) { + return new AddrSpaceCastInst(NewLoad, LI.getType()); + } + + return new BitCastInst(NewLoad, LI.getType()); + } + } + } + return nullptr; +} + +Instruction *InstCombiner::visitLoadInst(LoadInst &LI) { + Value *Op = LI.getOperand(0); + + // Attempt to improve the alignment. + if (DL) { + unsigned KnownAlign = + getOrEnforceKnownAlignment(Op, DL->getPrefTypeAlignment(LI.getType()),DL); + unsigned LoadAlign = LI.getAlignment(); + unsigned EffectiveLoadAlign = LoadAlign != 0 ? LoadAlign : + DL->getABITypeAlignment(LI.getType()); + + if (KnownAlign > EffectiveLoadAlign) + LI.setAlignment(KnownAlign); + else if (LoadAlign == 0) + LI.setAlignment(EffectiveLoadAlign); + } + + // load (cast X) --> cast (load X) iff safe. + if (isa<CastInst>(Op)) + if (Instruction *Res = InstCombineLoadCast(*this, LI, DL)) + return Res; + + // None of the following transforms are legal for volatile/atomic loads. + // FIXME: Some of it is okay for atomic loads; needs refactoring. + if (!LI.isSimple()) return nullptr; + + // Do really simple store-to-load forwarding and load CSE, to catch cases + // where there are several consecutive memory accesses to the same location, + // separated by a few arithmetic operations. + BasicBlock::iterator BBI = &LI; + if (Value *AvailableVal = FindAvailableLoadedValue(Op, LI.getParent(), BBI,6)) + return ReplaceInstUsesWith(LI, AvailableVal); + + // load(gep null, ...) -> unreachable + if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) { + const Value *GEPI0 = GEPI->getOperand(0); + // TODO: Consider a target hook for valid address spaces for this xform. + if (isa<ConstantPointerNull>(GEPI0) && GEPI->getPointerAddressSpace() == 0){ + // Insert a new store to null instruction before the load to indicate + // that this code is not reachable. We do this instead of inserting + // an unreachable instruction directly because we cannot modify the + // CFG. + new StoreInst(UndefValue::get(LI.getType()), + Constant::getNullValue(Op->getType()), &LI); + return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType())); + } + } + + // load null/undef -> unreachable + // TODO: Consider a target hook for valid address spaces for this xform. + if (isa<UndefValue>(Op) || + (isa<ConstantPointerNull>(Op) && LI.getPointerAddressSpace() == 0)) { + // Insert a new store to null instruction before the load to indicate that + // this code is not reachable. We do this instead of inserting an + // unreachable instruction directly because we cannot modify the CFG. + new StoreInst(UndefValue::get(LI.getType()), + Constant::getNullValue(Op->getType()), &LI); + return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType())); + } + + // Instcombine load (constantexpr_cast global) -> cast (load global) + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op)) + if (CE->isCast()) + if (Instruction *Res = InstCombineLoadCast(*this, LI, DL)) + return Res; + + if (Op->hasOneUse()) { + // Change select and PHI nodes to select values instead of addresses: this + // helps alias analysis out a lot, allows many others simplifications, and + // exposes redundancy in the code. + // + // Note that we cannot do the transformation unless we know that the + // introduced loads cannot trap! Something like this is valid as long as + // the condition is always false: load (select bool %C, int* null, int* %G), + // but it would not be valid if we transformed it to load from null + // unconditionally. + // + if (SelectInst *SI = dyn_cast<SelectInst>(Op)) { + // load (select (Cond, &V1, &V2)) --> select(Cond, load &V1, load &V2). + unsigned Align = LI.getAlignment(); + if (isSafeToLoadUnconditionally(SI->getOperand(1), SI, Align, DL) && + isSafeToLoadUnconditionally(SI->getOperand(2), SI, Align, DL)) { + LoadInst *V1 = Builder->CreateLoad(SI->getOperand(1), + SI->getOperand(1)->getName()+".val"); + LoadInst *V2 = Builder->CreateLoad(SI->getOperand(2), + SI->getOperand(2)->getName()+".val"); + V1->setAlignment(Align); + V2->setAlignment(Align); + return SelectInst::Create(SI->getCondition(), V1, V2); + } + + // load (select (cond, null, P)) -> load P + if (Constant *C = dyn_cast<Constant>(SI->getOperand(1))) + if (C->isNullValue()) { + LI.setOperand(0, SI->getOperand(2)); + return &LI; + } + + // load (select (cond, P, null)) -> load P + if (Constant *C = dyn_cast<Constant>(SI->getOperand(2))) + if (C->isNullValue()) { + LI.setOperand(0, SI->getOperand(1)); + return &LI; + } + } + } + return nullptr; +} + +/// InstCombineStoreToCast - Fold store V, (cast P) -> store (cast V), P +/// when possible. This makes it generally easy to do alias analysis and/or +/// SROA/mem2reg of the memory object. +static Instruction *InstCombineStoreToCast(InstCombiner &IC, StoreInst &SI) { + User *CI = cast<User>(SI.getOperand(1)); + Value *CastOp = CI->getOperand(0); + + Type *DestPTy = CI->getType()->getPointerElementType(); + PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType()); + if (!SrcTy) return nullptr; + + Type *SrcPTy = SrcTy->getElementType(); + + if (!DestPTy->isIntegerTy() && !DestPTy->isPointerTy()) + return nullptr; + + /// NewGEPIndices - If SrcPTy is an aggregate type, we can emit a "noop gep" + /// to its first element. This allows us to handle things like: + /// store i32 xxx, (bitcast {foo*, float}* %P to i32*) + /// on 32-bit hosts. + SmallVector<Value*, 4> NewGEPIndices; + + // If the source is an array, the code below will not succeed. Check to + // see if a trivial 'gep P, 0, 0' will help matters. Only do this for + // constants. + if (SrcPTy->isArrayTy() || SrcPTy->isStructTy()) { + // Index through pointer. + Constant *Zero = Constant::getNullValue(Type::getInt32Ty(SI.getContext())); + NewGEPIndices.push_back(Zero); + + while (1) { + if (StructType *STy = dyn_cast<StructType>(SrcPTy)) { + if (!STy->getNumElements()) /* Struct can be empty {} */ + break; + NewGEPIndices.push_back(Zero); + SrcPTy = STy->getElementType(0); + } else if (ArrayType *ATy = dyn_cast<ArrayType>(SrcPTy)) { + NewGEPIndices.push_back(Zero); + SrcPTy = ATy->getElementType(); + } else { + break; + } + } + + SrcTy = PointerType::get(SrcPTy, SrcTy->getAddressSpace()); + } + + if (!SrcPTy->isIntegerTy() && !SrcPTy->isPointerTy()) + return nullptr; + + // If the pointers point into different address spaces don't do the + // transformation. + if (SrcTy->getAddressSpace() != CI->getType()->getPointerAddressSpace()) + return nullptr; + + // If the pointers point to values of different sizes don't do the + // transformation. + if (!IC.getDataLayout() || + IC.getDataLayout()->getTypeSizeInBits(SrcPTy) != + IC.getDataLayout()->getTypeSizeInBits(DestPTy)) + return nullptr; + + // If the pointers point to pointers to different address spaces don't do the + // transformation. It is not safe to introduce an addrspacecast instruction in + // this case since, depending on the target, addrspacecast may not be a no-op + // cast. + if (SrcPTy->isPointerTy() && DestPTy->isPointerTy() && + SrcPTy->getPointerAddressSpace() != DestPTy->getPointerAddressSpace()) + return nullptr; + + // Okay, we are casting from one integer or pointer type to another of + // the same size. Instead of casting the pointer before + // the store, cast the value to be stored. + Value *NewCast; + Instruction::CastOps opcode = Instruction::BitCast; + Type* CastSrcTy = DestPTy; + Type* CastDstTy = SrcPTy; + if (CastDstTy->isPointerTy()) { + if (CastSrcTy->isIntegerTy()) + opcode = Instruction::IntToPtr; + } else if (CastDstTy->isIntegerTy()) { + if (CastSrcTy->isPointerTy()) + opcode = Instruction::PtrToInt; + } + + // SIOp0 is a pointer to aggregate and this is a store to the first field, + // emit a GEP to index into its first field. + if (!NewGEPIndices.empty()) + CastOp = IC.Builder->CreateInBoundsGEP(CastOp, NewGEPIndices); + + Value *SIOp0 = SI.getOperand(0); + NewCast = IC.Builder->CreateCast(opcode, SIOp0, CastDstTy, + SIOp0->getName()+".c"); + SI.setOperand(0, NewCast); + SI.setOperand(1, CastOp); + return &SI; +} + +/// equivalentAddressValues - Test if A and B will obviously have the same +/// value. This includes recognizing that %t0 and %t1 will have the same +/// value in code like this: +/// %t0 = getelementptr \@a, 0, 3 +/// store i32 0, i32* %t0 +/// %t1 = getelementptr \@a, 0, 3 +/// %t2 = load i32* %t1 +/// +static bool equivalentAddressValues(Value *A, Value *B) { + // Test if the values are trivially equivalent. + if (A == B) return true; + + // Test if the values come form identical arithmetic instructions. + // This uses isIdenticalToWhenDefined instead of isIdenticalTo because + // its only used to compare two uses within the same basic block, which + // means that they'll always either have the same value or one of them + // will have an undefined value. + if (isa<BinaryOperator>(A) || + isa<CastInst>(A) || + isa<PHINode>(A) || + isa<GetElementPtrInst>(A)) + if (Instruction *BI = dyn_cast<Instruction>(B)) + if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI)) + return true; + + // Otherwise they may not be equivalent. + return false; +} + +Instruction *InstCombiner::visitStoreInst(StoreInst &SI) { + Value *Val = SI.getOperand(0); + Value *Ptr = SI.getOperand(1); + + // Attempt to improve the alignment. + if (DL) { + unsigned KnownAlign = + getOrEnforceKnownAlignment(Ptr, DL->getPrefTypeAlignment(Val->getType()), + DL); + unsigned StoreAlign = SI.getAlignment(); + unsigned EffectiveStoreAlign = StoreAlign != 0 ? StoreAlign : + DL->getABITypeAlignment(Val->getType()); + + if (KnownAlign > EffectiveStoreAlign) + SI.setAlignment(KnownAlign); + else if (StoreAlign == 0) + SI.setAlignment(EffectiveStoreAlign); + } + + // Don't hack volatile/atomic stores. + // FIXME: Some bits are legal for atomic stores; needs refactoring. + if (!SI.isSimple()) return nullptr; + + // If the RHS is an alloca with a single use, zapify the store, making the + // alloca dead. + if (Ptr->hasOneUse()) { + if (isa<AllocaInst>(Ptr)) + return EraseInstFromFunction(SI); + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) { + if (isa<AllocaInst>(GEP->getOperand(0))) { + if (GEP->getOperand(0)->hasOneUse()) + return EraseInstFromFunction(SI); + } + } + } + + // Do really simple DSE, to catch cases where there are several consecutive + // stores to the same location, separated by a few arithmetic operations. This + // situation often occurs with bitfield accesses. + BasicBlock::iterator BBI = &SI; + for (unsigned ScanInsts = 6; BBI != SI.getParent()->begin() && ScanInsts; + --ScanInsts) { + --BBI; + // Don't count debug info directives, lest they affect codegen, + // and we skip pointer-to-pointer bitcasts, which are NOPs. + if (isa<DbgInfoIntrinsic>(BBI) || + (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) { + ScanInsts++; + continue; + } + + if (StoreInst *PrevSI = dyn_cast<StoreInst>(BBI)) { + // Prev store isn't volatile, and stores to the same location? + if (PrevSI->isSimple() && equivalentAddressValues(PrevSI->getOperand(1), + SI.getOperand(1))) { + ++NumDeadStore; + ++BBI; + EraseInstFromFunction(*PrevSI); + continue; + } + break; + } + + // If this is a load, we have to stop. However, if the loaded value is from + // the pointer we're loading and is producing the pointer we're storing, + // then *this* store is dead (X = load P; store X -> P). + if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) { + if (LI == Val && equivalentAddressValues(LI->getOperand(0), Ptr) && + LI->isSimple()) + return EraseInstFromFunction(SI); + + // Otherwise, this is a load from some other location. Stores before it + // may not be dead. + break; + } + + // Don't skip over loads or things that can modify memory. + if (BBI->mayWriteToMemory() || BBI->mayReadFromMemory()) + break; + } + + // store X, null -> turns into 'unreachable' in SimplifyCFG + if (isa<ConstantPointerNull>(Ptr) && SI.getPointerAddressSpace() == 0) { + if (!isa<UndefValue>(Val)) { + SI.setOperand(0, UndefValue::get(Val->getType())); + if (Instruction *U = dyn_cast<Instruction>(Val)) + Worklist.Add(U); // Dropped a use. + } + return nullptr; // Do not modify these! + } + + // store undef, Ptr -> noop + if (isa<UndefValue>(Val)) + return EraseInstFromFunction(SI); + + // If the pointer destination is a cast, see if we can fold the cast into the + // source instead. + if (isa<CastInst>(Ptr)) + if (Instruction *Res = InstCombineStoreToCast(*this, SI)) + return Res; + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) + if (CE->isCast()) + if (Instruction *Res = InstCombineStoreToCast(*this, SI)) + return Res; + + + // If this store is the last instruction in the basic block (possibly + // excepting debug info instructions), and if the block ends with an + // unconditional branch, try to move it to the successor block. + BBI = &SI; + do { + ++BBI; + } while (isa<DbgInfoIntrinsic>(BBI) || + (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())); + if (BranchInst *BI = dyn_cast<BranchInst>(BBI)) + if (BI->isUnconditional()) + if (SimplifyStoreAtEndOfBlock(SI)) + return nullptr; // xform done! + + return nullptr; +} + +/// SimplifyStoreAtEndOfBlock - Turn things like: +/// if () { *P = v1; } else { *P = v2 } +/// into a phi node with a store in the successor. +/// +/// Simplify things like: +/// *P = v1; if () { *P = v2; } +/// into a phi node with a store in the successor. +/// +bool InstCombiner::SimplifyStoreAtEndOfBlock(StoreInst &SI) { + BasicBlock *StoreBB = SI.getParent(); + + // Check to see if the successor block has exactly two incoming edges. If + // so, see if the other predecessor contains a store to the same location. + // if so, insert a PHI node (if needed) and move the stores down. + BasicBlock *DestBB = StoreBB->getTerminator()->getSuccessor(0); + + // Determine whether Dest has exactly two predecessors and, if so, compute + // the other predecessor. + pred_iterator PI = pred_begin(DestBB); + BasicBlock *P = *PI; + BasicBlock *OtherBB = nullptr; + + if (P != StoreBB) + OtherBB = P; + + if (++PI == pred_end(DestBB)) + return false; + + P = *PI; + if (P != StoreBB) { + if (OtherBB) + return false; + OtherBB = P; + } + if (++PI != pred_end(DestBB)) + return false; + + // Bail out if all the relevant blocks aren't distinct (this can happen, + // for example, if SI is in an infinite loop) + if (StoreBB == DestBB || OtherBB == DestBB) + return false; + + // Verify that the other block ends in a branch and is not otherwise empty. + BasicBlock::iterator BBI = OtherBB->getTerminator(); + BranchInst *OtherBr = dyn_cast<BranchInst>(BBI); + if (!OtherBr || BBI == OtherBB->begin()) + return false; + + // If the other block ends in an unconditional branch, check for the 'if then + // else' case. there is an instruction before the branch. + StoreInst *OtherStore = nullptr; + if (OtherBr->isUnconditional()) { + --BBI; + // Skip over debugging info. + while (isa<DbgInfoIntrinsic>(BBI) || + (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) { + if (BBI==OtherBB->begin()) + return false; + --BBI; + } + // If this isn't a store, isn't a store to the same location, or is not the + // right kind of store, bail out. + OtherStore = dyn_cast<StoreInst>(BBI); + if (!OtherStore || OtherStore->getOperand(1) != SI.getOperand(1) || + !SI.isSameOperationAs(OtherStore)) + return false; + } else { + // Otherwise, the other block ended with a conditional branch. If one of the + // destinations is StoreBB, then we have the if/then case. + if (OtherBr->getSuccessor(0) != StoreBB && + OtherBr->getSuccessor(1) != StoreBB) + return false; + + // Okay, we know that OtherBr now goes to Dest and StoreBB, so this is an + // if/then triangle. See if there is a store to the same ptr as SI that + // lives in OtherBB. + for (;; --BBI) { + // Check to see if we find the matching store. + if ((OtherStore = dyn_cast<StoreInst>(BBI))) { + if (OtherStore->getOperand(1) != SI.getOperand(1) || + !SI.isSameOperationAs(OtherStore)) + return false; + break; + } + // If we find something that may be using or overwriting the stored + // value, or if we run out of instructions, we can't do the xform. + if (BBI->mayReadFromMemory() || BBI->mayWriteToMemory() || + BBI == OtherBB->begin()) + return false; + } + + // In order to eliminate the store in OtherBr, we have to + // make sure nothing reads or overwrites the stored value in + // StoreBB. + for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) { + // FIXME: This should really be AA driven. + if (I->mayReadFromMemory() || I->mayWriteToMemory()) + return false; + } + } + + // Insert a PHI node now if we need it. + Value *MergedVal = OtherStore->getOperand(0); + if (MergedVal != SI.getOperand(0)) { + PHINode *PN = PHINode::Create(MergedVal->getType(), 2, "storemerge"); + PN->addIncoming(SI.getOperand(0), SI.getParent()); + PN->addIncoming(OtherStore->getOperand(0), OtherBB); + MergedVal = InsertNewInstBefore(PN, DestBB->front()); + } + + // Advance to a place where it is safe to insert the new store and + // insert it. + BBI = DestBB->getFirstInsertionPt(); + StoreInst *NewSI = new StoreInst(MergedVal, SI.getOperand(1), + SI.isVolatile(), + SI.getAlignment(), + SI.getOrdering(), + SI.getSynchScope()); + InsertNewInstBefore(NewSI, *BBI); + NewSI->setDebugLoc(OtherStore->getDebugLoc()); + + // If the two stores had the same TBAA tag, preserve it. + if (MDNode *TBAATag = SI.getMetadata(LLVMContext::MD_tbaa)) + if ((TBAATag = MDNode::getMostGenericTBAA(TBAATag, + OtherStore->getMetadata(LLVMContext::MD_tbaa)))) + NewSI->setMetadata(LLVMContext::MD_tbaa, TBAATag); + + + // Nuke the old stores. + EraseInstFromFunction(SI); + EraseInstFromFunction(*OtherStore); + return true; +} |