text: /*========================== begin_copyright_notice ============================
  
  Copyright (C) 2018-2021 Intel Corporation
  
  SPDX-License-Identifier: MIT
  
  ============================= end_copyright_notice ===========================*/
  
  /*========================== begin_copyright_notice ============================
  
  This file is distributed under the University of Illinois Open Source License.
  See LICENSE.TXT for details.
  
  ============================= end_copyright_notice ===========================*/
  
  // This file implements the visit functions for load, store and alloca.
  
  #include "common/LLVMWarningsPush.hpp"
  #include "InstCombineInternal.h"
  #include "llvm/ADT/SmallString.h"
  #include "llvm/ADT/Statistic.h"
  #include "llvm/Analysis/Loads.h"
  #include "llvm/IR/ConstantRange.h"
  #include "llvm/IR/DataLayout.h"
  #include "llvm/IR/LLVMContext.h"
  #include "llvm/IR/IntrinsicInst.h"
  #include "llvm/IR/MDBuilder.h"
  #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  #include "llvm/Transforms/Utils/Local.h"
  #include "Probe/Assertion.h"
  
  using namespace llvm;
  using namespace IGCombiner;
  
  #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.emplace_back(V, false);
    while (!ValuesToInspect.empty()) {
      auto ValuePair = ValuesToInspect.pop_back_val();
      const bool IsOffset = ValuePair.second;
      for (auto &U : ValuePair.first->uses()) {
        auto *I = cast<Instruction>(U.getUser());
  
        if (auto *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.emplace_back(I, IsOffset);
          continue;
        }
        if (auto *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.emplace_back(I, IsOffset || !GEP->hasAllZeroIndices());
          continue;
        }
  
        if (auto CS = CallSite(I)) {
          // If this is the function being called then we treat it like a load and
          // ignore it.
          if (CS.isCallee(&U))
            continue;
  
          unsigned DataOpNo = CS.getDataOperandNo(&U);
          bool IsArgOperand = CS.isArgOperand(&U);
  
          // Inalloca arguments are clobbered by the call.
          if (IsArgOperand && CS.isInAllocaArgument(DataOpNo))
            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(DataOpNo)))
            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 (IsArgOperand && CS.isByValArgument(DataOpNo))
            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) {
            IGC_ASSERT_MESSAGE(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;
  }
  
  static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
    // Check for array size of 1 (scalar allocation).
    if (!AI.isArrayAllocation()) {
      // i32 1 is the canonical array size for scalar allocations.
      if (AI.getArraySize()->getType()->isIntegerTy(32))
        return nullptr;
  
      // Canonicalize it.
      Value *V = IC.Builder->getInt32(1);
      AI.setOperand(0, V);
      return &AI;
    }
  
    // Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1
    if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
      Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getZExtValue());
      AllocaInst *New = IC.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 = IC.getDataLayout().getIntPtrType(AI.getType());
      Value *NullIdx = Constant::getNullValue(IdxTy);
      Value *Idx[2] = {NullIdx, NullIdx};
      Instruction *GEP =
          GetElementPtrInst::CreateInBounds(New, Idx, New->getName() + ".sub");
      IC.InsertNewInstBefore(GEP, *It);
  
      // Now make everything use the getelementptr instead of the original
      // allocation.
      return IC.replaceInstUsesWith(AI, GEP);
    }
  
    if (isa<UndefValue>(AI.getArraySize()))
      return IC.replaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
  
    // Ensure that the alloca array size argument has type intptr_t, so that
    // any casting is exposed early.
    Type *IntPtrTy = IC.getDataLayout().getIntPtrType(AI.getType());
    if (AI.getArraySize()->getType() != IntPtrTy) {
      Value *V = IC.Builder->CreateIntCast(AI.getArraySize(), IntPtrTy, false);
      AI.setOperand(0, V);
      return &AI;
    }
  
    return nullptr;
  }
  
  Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
    if (auto *I = simplifyAllocaArraySize(*this, AI))
      return I;
  
    if (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, &AI, &AC, &DT);
        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);
  }
  
  // Are we allowed to form a atomic load or store of this type?
  static bool isSupportedAtomicType(Type *Ty) {
    return Ty->isIntegerTy() || Ty->isPointerTy() || Ty->isFloatingPointTy();
  }
  
  /// \brief Helper to combine a load to a new type.
  ///
  /// This just does the work of combining a load to a new type. It handles
  /// metadata, etc., and returns the new instruction. The \c NewTy should be the
  /// loaded *value* type. This will convert it to a pointer, cast the operand to
  /// that pointer type, load it, etc.
  ///
  /// Note that this will create all of the instructions with whatever insert
  /// point the \c InstCombiner currently is using.
  static LoadInst *combineLoadToNewType(InstCombiner &IC, LoadInst &LI, Type *NewTy,
                                        const Twine &Suffix = "") {
    IGC_ASSERT_MESSAGE((!LI.isAtomic() || isSupportedAtomicType(NewTy)), "can't fold an atomic load to requested type");
  
    Value *Ptr = LI.getPointerOperand();
    unsigned AS = LI.getPointerAddressSpace();
    SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
    LI.getAllMetadata(MD);
  
    LoadInst *NewLoad = IC.Builder->CreateAlignedLoad(
        IC.Builder->CreateBitCast(Ptr, NewTy->getPointerTo(AS)),
        LI.getAlignment(), LI.isVolatile(), LI.getName() + Suffix);
    NewLoad->setAtomic(LI.getOrdering(), LI.getSynchScope());
    MDBuilder MDB(NewLoad->getContext());
    for (const auto &MDPair : MD) {
      unsigned ID = MDPair.first;
      MDNode *N = MDPair.second;
      // Note, essentially every kind of metadata should be preserved here! This
      // routine is supposed to clone a load instruction changing *only its type*.
      // The only metadata it makes sense to drop is metadata which is invalidated
      // when the pointer type changes. This should essentially never be the case
      // in LLVM, but we explicitly switch over only known metadata to be
      // conservatively correct. If you are adding metadata to LLVM which pertains
      // to loads, you almost certainly want to add it here.
      switch (ID) {
      case LLVMContext::MD_dbg:
      case LLVMContext::MD_tbaa:
      case LLVMContext::MD_prof:
      case LLVMContext::MD_fpmath:
      case LLVMContext::MD_tbaa_struct:
      case LLVMContext::MD_invariant_load:
      case LLVMContext::MD_alias_scope:
      case LLVMContext::MD_noalias:
      case LLVMContext::MD_nontemporal:
      case LLVMContext::MD_mem_parallel_loop_access:
        // All of these directly apply.
        NewLoad->setMetadata(ID, N);
        break;
  
      case LLVMContext::MD_nonnull:
        // This only directly applies if the new type is also a pointer.
        if (NewTy->isPointerTy()) {
          NewLoad->setMetadata(ID, N);
          break;
        }
        // If it's integral now, translate it to !range metadata.
        if (NewTy->isIntegerTy()) {
          auto *ITy = cast<IntegerType>(NewTy);
          auto *NullInt = ConstantExpr::getPtrToInt(
              ConstantPointerNull::get(cast<PointerType>(Ptr->getType())), ITy);
          auto *NonNullInt =
              ConstantExpr::getAdd(NullInt, ConstantInt::get(ITy, 1));
          NewLoad->setMetadata(LLVMContext::MD_range,
                               MDB.createRange(NonNullInt, NullInt));
        }
        break;
      case LLVMContext::MD_align:
      case LLVMContext::MD_dereferenceable:
      case LLVMContext::MD_dereferenceable_or_null:
        // These only directly apply if the new type is also a pointer.
        if (NewTy->isPointerTy())
          NewLoad->setMetadata(ID, N);
        break;
      case LLVMContext::MD_range:
        // FIXME: It would be nice to propagate this in some way, but the type
        // conversions make it hard.
  
        // If it's a pointer now and the range does not contain 0, make it !nonnull.
        if (NewTy->isPointerTy()) {
          unsigned BitWidth = IC.getDataLayout().getTypeSizeInBits(NewTy);
          if (!getConstantRangeFromMetadata(*N).contains(APInt(BitWidth, 0))) {
            MDNode *NN = MDNode::get(LI.getContext(), None);
            NewLoad->setMetadata(LLVMContext::MD_nonnull, NN);
          }
        }
        break;
      }
    }
    return NewLoad;
  }
  
  /// \brief Combine a store to a new type.
  ///
  /// Returns the newly created store instruction.
  static StoreInst *combineStoreToNewValue(InstCombiner &IC, StoreInst &SI, Value *V) {
    IGC_ASSERT_MESSAGE((!SI.isAtomic() || isSupportedAtomicType(V->getType())), "can't fold an atomic store of requested type");
  
    Value *Ptr = SI.getPointerOperand();
    unsigned AS = SI.getPointerAddressSpace();
    SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
    SI.getAllMetadata(MD);
  
    StoreInst *NewStore = IC.Builder->CreateAlignedStore(
        V, IC.Builder->CreateBitCast(Ptr, V->getType()->getPointerTo(AS)),
        SI.getAlignment(), SI.isVolatile());
    NewStore->setAtomic(SI.getOrdering(), SI.getSynchScope());
    for (const auto &MDPair : MD) {
      unsigned ID = MDPair.first;
      MDNode *N = MDPair.second;
      // Note, essentially every kind of metadata should be preserved here! This
      // routine is supposed to clone a store instruction changing *only its
      // type*. The only metadata it makes sense to drop is metadata which is
      // invalidated when the pointer type changes. This should essentially
      // never be the case in LLVM, but we explicitly switch over only known
      // metadata to be conservatively correct. If you are adding metadata to
      // LLVM which pertains to stores, you almost certainly want to add it
      // here.
      switch (ID) {
      case LLVMContext::MD_dbg:
      case LLVMContext::MD_tbaa:
      case LLVMContext::MD_prof:
      case LLVMContext::MD_fpmath:
      case LLVMContext::MD_tbaa_struct:
      case LLVMContext::MD_alias_scope:
      case LLVMContext::MD_noalias:
      case LLVMContext::MD_nontemporal:
      case LLVMContext::MD_mem_parallel_loop_access:
        // All of these directly apply.
        NewStore->setMetadata(ID, N);
        break;
  
      case LLVMContext::MD_invariant_load:
      case LLVMContext::MD_nonnull:
      case LLVMContext::MD_range:
      case LLVMContext::MD_align:
      case LLVMContext::MD_dereferenceable:
      case LLVMContext::MD_dereferenceable_or_null:
        // These don't apply for stores.
        break;
      }
    }
  
    return NewStore;
  }
  
  /// \brief Combine loads to match the type of their uses' value after looking
  /// through intervening bitcasts.
  ///
  /// The core idea here is that if the result of a load is used in an operation,
  /// we should load the type most conducive to that operation. For example, when
  /// loading an integer and converting that immediately to a pointer, we should
  /// instead directly load a pointer.
  ///
  /// However, this routine must never change the width of a load or the number of
  /// loads as that would introduce a semantic change. This combine is expected to
  /// be a semantic no-op which just allows loads to more closely model the types
  /// of their consuming operations.
  ///
  /// Currently, we also refuse to change the precise type used for an atomic load
  /// or a volatile load. This is debatable, and might be reasonable to change
  /// later. However, it is risky in case some backend or other part of LLVM is
  /// relying on the exact type loaded to select appropriate atomic operations.
  static Instruction *combineLoadToOperationType(InstCombiner &IC, LoadInst &LI) {
    // FIXME: We could probably with some care handle both volatile and ordered
    // atomic loads here but it isn't clear that this is important.
    if (!LI.isUnordered())
      return nullptr;
  
    if (LI.use_empty())
      return nullptr;
  
    // swifterror values can't be bitcasted.
    if (LI.getPointerOperand()->isSwiftError())
      return nullptr;
  
    Type *Ty = LI.getType();
    const DataLayout &DL = IC.getDataLayout();
  
    // Try to canonicalize loads which are only ever stored to operate over
    // integers instead of any other type. We only do this when the loaded type
    // is sized and has a size exactly the same as its store size and the store
    // size is a legal integer type.
    if (!Ty->isIntegerTy() && Ty->isSized() &&
        DL.isLegalInteger(DL.getTypeStoreSizeInBits(Ty)) &&
        DL.getTypeStoreSizeInBits(Ty) == DL.getTypeSizeInBits(Ty) &&
        !DL.isNonIntegralPointerType(Ty)) {
      if (all_of(LI.users(), [&LI](User *U) {
            auto *SI = dyn_cast<StoreInst>(U);
            return SI && SI->getPointerOperand() != &LI &&
                   !SI->getPointerOperand()->isSwiftError();
          })) {
        LoadInst *NewLoad = combineLoadToNewType(
            IC, LI,
            Type::getIntNTy(LI.getContext(), DL.getTypeStoreSizeInBits(Ty)));
        // Replace all the stores with stores of the newly loaded value.
        for (auto UI = LI.user_begin(), UE = LI.user_end(); UI != UE;) {
          auto *SI = cast<StoreInst>(*UI++);
          IC.Builder->SetInsertPoint(SI);
          combineStoreToNewValue(IC, *SI, NewLoad);
          IC.eraseInstFromFunction(*SI);
        }
        IGC_ASSERT_MESSAGE(LI.use_empty(), "Failed to remove all users of the load!");
        // Return the old load so the combiner can delete it safely.
        return &LI;
      }
    }
  
    // Fold away bit casts of the loaded value by loading the desired type.
    // We can do this for BitCastInsts as well as casts from and to pointer types,
    // as long as those are noops (i.e., the source or dest type have the same
    // bitwidth as the target's pointers).
    if (LI.hasOneUse())
      if (auto* CI = dyn_cast<CastInst>(LI.user_back()))
        if (CI->isNoopCast(DL))
          if (!LI.isAtomic() || isSupportedAtomicType(CI->getDestTy())) {
            LoadInst *NewLoad = combineLoadToNewType(IC, LI, CI->getDestTy());
            CI->replaceAllUsesWith(NewLoad);
            IC.eraseInstFromFunction(*CI);
            return &LI;
          }
  
    // FIXME: We should also canonicalize loads of vectors when their elements are
    // cast to other types.
    return nullptr;
  }
  
  static Instruction *unpackLoadToAggregate(InstCombiner &IC, LoadInst &LI) {
    // FIXME: We could probably with some care handle both volatile and atomic
    // stores here but it isn't clear that this is important.
    if (!LI.isSimple())
      return nullptr;
  
    Type *T = LI.getType();
    if (!T->isAggregateType())
      return nullptr;
  
    StringRef Name = LI.getName();
    IGC_ASSERT_MESSAGE(LI.getAlignment(), "Alignment must be set at this point");
  
    if (auto *ST = dyn_cast<StructType>(T)) {
      // If the struct only have one element, we unpack.
      auto NumElements = ST->getNumElements();
      if (NumElements == 1) {
        LoadInst *NewLoad = combineLoadToNewType(IC, LI, ST->getTypeAtIndex(0U),
                                                 ".unpack");
        return IC.replaceInstUsesWith(LI, IC.Builder->CreateInsertValue(
          UndefValue::get(T), NewLoad, 0, Name));
      }
  
      // We don't want to break loads with padding here as we'd loose
      // the knowledge that padding exists for the rest of the pipeline.
      const DataLayout &DL = IC.getDataLayout();
      auto *SL = DL.getStructLayout(ST);
      if (SL->hasPadding())
        return nullptr;
  
      auto Align = LI.getAlignment();
      if (!Align)
        Align = DL.getABITypeAlignment(ST);
  
      auto *Addr = LI.getPointerOperand();
      auto *IdxType = Type::getInt32Ty(T->getContext());
      auto *Zero = ConstantInt::get(IdxType, 0);
  
      Value *V = UndefValue::get(T);
      for (unsigned i = 0; i < NumElements; i++) {
        Value *Indices[2] = {
          Zero,
          ConstantInt::get(IdxType, i),
        };
        auto *Ptr = IC.Builder->CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices),
                                                  Name + ".elt");
        auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
        auto *L = IC.Builder->CreateAlignedLoad(Ptr, EltAlign, Name + ".unpack");
        V = IC.Builder->CreateInsertValue(V, L, i);
      }
  
      V->setName(Name);
      return IC.replaceInstUsesWith(LI, V);
    }
  
    if (auto *AT = dyn_cast<ArrayType>(T)) {
      auto *ET = AT->getElementType();
      auto NumElements = AT->getNumElements();
      if (NumElements == 1) {
        LoadInst *NewLoad = combineLoadToNewType(IC, LI, ET, ".unpack");
        return IC.replaceInstUsesWith(LI, IC.Builder->CreateInsertValue(
          UndefValue::get(T), NewLoad, 0, Name));
      }
  
      // Bail out if the array is too large. Ideally we would like to optimize
      // arrays of arbitrary size but this has a terrible impact on compile time.
      // The threshold here is chosen arbitrarily, maybe needs a little bit of
      // tuning.
      if (NumElements > 1024)
        return nullptr;
  
      const DataLayout &DL = IC.getDataLayout();
      auto EltSize = DL.getTypeAllocSize(ET);
      auto Align = LI.getAlignment();
      if (!Align)
        Align = DL.getABITypeAlignment(T);
  
      auto *Addr = LI.getPointerOperand();
      auto *IdxType = Type::getInt64Ty(T->getContext());
      auto *Zero = ConstantInt::get(IdxType, 0);
  
      Value *V = UndefValue::get(T);
      uint64_t Offset = 0;
      for (uint64_t i = 0; i < NumElements; i++) {
        Value *Indices[2] = {
          Zero,
          ConstantInt::get(IdxType, i),
        };
        auto *Ptr = IC.Builder->CreateInBoundsGEP(AT, Addr, makeArrayRef(Indices),
                                                  Name + ".elt");
        auto *L = IC.Builder->CreateAlignedLoad(Ptr, MinAlign(Align, Offset),
                                                Name + ".unpack");
        V = IC.Builder->CreateInsertValue(V, L, i);
        Offset += EltSize;
      }
  
      V->setName(Name);
      return IC.replaceInstUsesWith(LI, V);
    }
  
    return nullptr;
  }
  
  // If we can determine that all possible objects pointed to by the provided
  // pointer value are, not only dereferenceable, but also definitively less than
  // or equal to the provided maximum size, then return true. Otherwise, return
  // false (constant global values and allocas fall into this category).
  //
  // FIXME: This should probably live in ValueTracking (or similar).
  static bool isObjectSizeLessThanOrEq(Value *V, uint64_t MaxSize,
                                       const DataLayout &DL) {
    SmallPtrSet<Value *, 4> Visited;
    SmallVector<Value *, 4> Worklist(1, V);
  
    do {
      Value *P = Worklist.pop_back_val();
      P = P->stripPointerCasts();
  
      if (!Visited.insert(P).second)
        continue;
  
      if (SelectInst *SI = dyn_cast<SelectInst>(P)) {
        Worklist.push_back(SI->getTrueValue());
        Worklist.push_back(SI->getFalseValue());
        continue;
      }
  
      if (PHINode *PN = dyn_cast<PHINode>(P)) {
        for (Value *IncValue : PN->incoming_values())
          Worklist.push_back(IncValue);
        continue;
      }
  
      if (GlobalAlias *GA = dyn_cast<GlobalAlias>(P)) {
        if (GA->isInterposable())
          return false;
        Worklist.push_back(GA->getAliasee());
        continue;
      }
  
      // If we know how big this object is, and it is less than MaxSize, continue
      // searching. Otherwise, return false.
      if (AllocaInst *AI = dyn_cast<AllocaInst>(P)) {
        if (!AI->getAllocatedType()->isSized())
          return false;
  
        ConstantInt *CS = dyn_cast<ConstantInt>(AI->getArraySize());
        if (!CS)
          return false;
  
        uint64_t TypeSize = DL.getTypeAllocSize(AI->getAllocatedType());
        // Make sure that, even if the multiplication below would wrap as an
        // uint64_t, we still do the right thing.
        if ((CS->getValue().zextOrSelf(128)*APInt(128, TypeSize)).ugt(MaxSize))
          return false;
        continue;
      }
  
      if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
        if (!GV->hasDefinitiveInitializer() || !GV->isConstant())
          return false;
  
        uint64_t InitSize = DL.getTypeAllocSize(GV->getValueType());
        if (InitSize > MaxSize)
          return false;
        continue;
      }
  
      return false;
    } while (!Worklist.empty());
  
    return true;
  }
  
  // If we're indexing into an object of a known size, and the outer index is
  // not a constant, but having any value but zero would lead to undefined
  // behavior, replace it with zero.
  //
  // For example, if we have:
  // @f.a = private unnamed_addr constant [1 x i32] [i32 12], align 4
  // ...
  // %arrayidx = getelementptr inbounds [1 x i32]* @f.a, i64 0, i64 %x
  // ... = load i32* %arrayidx, align 4
  // Then we know that we can replace %x in the GEP with i64 0.
  //
  // FIXME: We could fold any GEP index to zero that would cause UB if it were
  // not zero. Currently, we only handle the first such index. Also, we could
  // also search through non-zero constant indices if we kept track of the
  // offsets those indices implied.
  static bool canReplaceGEPIdxWithZero(InstCombiner &IC, GetElementPtrInst *GEPI,
                                       Instruction *MemI, unsigned &Idx) {
    if (GEPI->getNumOperands() < 2)
      return false;
  
    // Find the first non-zero index of a GEP. If all indices are zero, return
    // one past the last index.
    auto FirstNZIdx = [](const GetElementPtrInst *GEPI) {
      unsigned I = 1;
      for (unsigned IE = GEPI->getNumOperands(); I != IE; ++I) {
        Value *V = GEPI->getOperand(I);
        if (const ConstantInt *CI = dyn_cast<ConstantInt>(V))
          if (CI->isZero())
            continue;
  
        break;
      }
  
      return I;
    };
  
    // Skip through initial 'zero' indices, and find the corresponding pointer
    // type. See if the next index is not a constant.
    Idx = FirstNZIdx(GEPI);
    if (Idx == GEPI->getNumOperands())
      return false;
    if (isa<Constant>(GEPI->getOperand(Idx)))
      return false;
  
    SmallVector<Value *, 4> Ops(GEPI->idx_begin(), GEPI->idx_begin() + Idx);
    Type *AllocTy =
      GetElementPtrInst::getIndexedType(GEPI->getSourceElementType(), Ops);
    if (!AllocTy || !AllocTy->isSized())
      return false;
    const DataLayout &DL = IC.getDataLayout();
    uint64_t TyAllocSize = DL.getTypeAllocSize(AllocTy);
  
    // If there are more indices after the one we might replace with a zero, make
    // sure they're all non-negative. If any of them are negative, the overall
    // address being computed might be before the base address determined by the
    // first non-zero index.
    auto IsAllNonNegative = [&]() {
      for (unsigned i = Idx+1, e = GEPI->getNumOperands(); i != e; ++i) {
        bool KnownNonNegative = false, KnownNegative = false;
        IC.ComputeSignBit(GEPI->getOperand(i), KnownNonNegative,
                          KnownNegative, 0, MemI);
        if (KnownNonNegative)
          continue;
        return false;
      }
  
      return true;
    };
  
    // FIXME: If the GEP is not inbounds, and there are extra indices after the
    // one we'll replace, those could cause the address computation to wrap
    // (rendering the IsAllNonNegative() check below insufficient). We can do
    // better, ignoring zero indices (and other indices we can prove small
    // enough not to wrap).
    if (Idx+1 != GEPI->getNumOperands() && !GEPI->isInBounds())
      return false;
  
    // Note that isObjectSizeLessThanOrEq will return true only if the pointer is
    // also known to be dereferenceable.
    return isObjectSizeLessThanOrEq(GEPI->getOperand(0), TyAllocSize, DL) &&
           IsAllNonNegative();
  }
  
  // If we're indexing into an object with a variable index for the memory
  // access, but the object has only one element, we can assume that the index
  // will always be zero. If we replace the GEP, return it.
  template <typename T>
  static Instruction *replaceGEPIdxWithZero(InstCombiner &IC, Value *Ptr,
                                            T &MemI) {
    if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr)) {
      unsigned Idx;
      if (canReplaceGEPIdxWithZero(IC, GEPI, &MemI, Idx)) {
        Instruction *NewGEPI = GEPI->clone();
        NewGEPI->setOperand(Idx,
          ConstantInt::get(GEPI->getOperand(Idx)->getType(), 0));
        NewGEPI->insertBefore(GEPI);
        MemI.setOperand(MemI.getPointerOperandIndex(), NewGEPI);
        return NewGEPI;
      }
    }
  
    return nullptr;
  }
  
  Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
    Value *Op = LI.getOperand(0);
  
    // Try to canonicalize the loaded type.
    if (Instruction *Res = combineLoadToOperationType(*this, LI))
      return Res;
  
    // Attempt to improve the alignment.
    unsigned KnownAlign = getOrEnforceKnownAlignment(
        Op, DL.getPrefTypeAlignment(LI.getType()), DL, &LI, &AC, &DT);
    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);
  
    // Replace GEP indices if possible.
    if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Op, LI)) {
        Worklist.Add(NewGEPI);
        return &LI;
    }
  
    if (Instruction *Res = unpackLoadToAggregate(*this, LI))
      return Res;
  
    // 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);
    bool IsLoadCSE = false;
    if (Value *AvailableVal = FindAvailableLoadedValue(
            &LI, LI.getParent(), BBI, DefMaxInstsToScan, AA, &IsLoadCSE)) {
      if (IsLoadCSE)
        combineMetadataForCSE(cast<LoadInst>(AvailableVal), &LI);
  
      return replaceInstUsesWith(
          LI, Builder->CreateBitOrPointerCast(AvailableVal, LI.getType(),
                                              LI.getName() + ".cast"));
    }
  
    // None of the following transforms are legal for volatile/ordered atomic
    // loads.  Most of them do apply for unordered atomics.
    if (!LI.isUnordered()) return nullptr;
  
    // 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()));
    }
  
    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), Align, DL, SI) &&
            isSafeToLoadUnconditionally(SI->getOperand(2), Align, DL, SI)) {
          LoadInst *V1 = Builder->CreateLoad(SI->getOperand(1),
                                             SI->getOperand(1)->getName()+".val");
          LoadInst *V2 = Builder->CreateLoad(SI->getOperand(2),
                                             SI->getOperand(2)->getName()+".val");
          IGC_ASSERT_MESSAGE(LI.isUnordered(), "implied by above");
          V1->setAlignment(Align);
          V1->setAtomic(LI.getOrdering(), LI.getSynchScope());
          V2->setAlignment(Align);
          V2->setAtomic(LI.getOrdering(), LI.getSynchScope());
          return SelectInst::Create(SI->getCondition(), V1, V2);
        }
  
        // load (select (cond, null, P)) -> load P
        if (isa<ConstantPointerNull>(SI->getOperand(1)) &&
            LI.getPointerAddressSpace() == 0) {
          LI.setOperand(0, SI->getOperand(2));
          return &LI;
        }
  
        // load (select (cond, P, null)) -> load P
        if (isa<ConstantPointerNull>(SI->getOperand(2)) &&
            LI.getPointerAddressSpace() == 0) {
          LI.setOperand(0, SI->getOperand(1));
          return &LI;
        }
      }
    }
    return nullptr;
  }
  
  /// \brief Look for extractelement/insertvalue sequence that acts like a bitcast.
  ///
  /// \returns underlying value that was "cast", or nullptr otherwise.
  ///
  /// For example, if we have:
  ///
  ///     %E0 = extractelement <2 x double> %U, i32 0
  ///     %V0 = insertvalue [2 x double] undef, double %E0, 0
  ///     %E1 = extractelement <2 x double> %U, i32 1
  ///     %V1 = insertvalue [2 x double] %V0, double %E1, 1
  ///
  /// and the layout of a <2 x double> is isomorphic to a [2 x double],
  /// then %V1 can be safely approximated by a conceptual "bitcast" of %U.
  /// Note that %U may contain non-undef values where %V1 has undef.
  static Value *likeBitCastFromVector(InstCombiner &IC, Value *V) {
    Value *U = nullptr;
    while (auto *IV = dyn_cast<InsertValueInst>(V)) {
      auto *E = dyn_cast<ExtractElementInst>(IV->getInsertedValueOperand());
      if (!E)
        return nullptr;
      auto *W = E->getVectorOperand();
      if (!U)
        U = W;
      else if (U != W)
        return nullptr;
      auto *CI = dyn_cast<ConstantInt>(E->getIndexOperand());
      if (!CI || IV->getNumIndices() != 1 || CI->getZExtValue() != *IV->idx_begin())
        return nullptr;
      V = IV->getAggregateOperand();
    }
    if (!isa<UndefValue>(V) ||!U)
      return nullptr;
  
    auto *UT = cast<VectorType>(U->getType());
    auto *VT = V->getType();
    // Check that types UT and VT are bitwise isomorphic.
    const auto &DL = IC.getDataLayout();
    if (DL.getTypeStoreSizeInBits(UT) != DL.getTypeStoreSizeInBits(VT)) {
      return nullptr;
    }
    if (auto *AT = dyn_cast<ArrayType>(VT)) {
      if (AT->getNumElements() != UT->getNumElements())
        return nullptr;
    } else {
      auto *ST = cast<StructType>(VT);
      if (ST->getNumElements() != UT->getNumElements())
        return nullptr;
      for (const auto *EltT : ST->elements()) {
        if (EltT != UT->getElementType())
          return nullptr;
      }
    }
    return U;
  }
  
  /// \brief Combine stores to match the type of value being stored.
  ///
  /// The core idea here is that the memory does not have any intrinsic type and
  /// where we can we should match the type of a store to the type of value being
  /// stored.
  ///
  /// However, this routine must never change the width of a store or the number of
  /// stores as that would introduce a semantic change. This combine is expected to
  /// be a semantic no-op which just allows stores to more closely model the types
  /// of their incoming values.
  ///
  /// Currently, we also refuse to change the precise type used for an atomic or
  /// volatile store. This is debatable, and might be reasonable to change later.
  /// However, it is risky in case some backend or other part of LLVM is relying
  /// on the exact type stored to select appropriate atomic operations.
  ///
  /// \returns true if the store was successfully combined away. This indicates
  /// the caller must erase the store instruction. We have to let the caller erase
  /// the store instruction as otherwise there is no way to signal whether it was
  /// combined or not: IC.EraseInstFromFunction returns a null pointer.
  static bool combineStoreToValueType(InstCombiner &IC, StoreInst &SI) {
    // FIXME: We could probably with some care handle both volatile and ordered
    // atomic stores here but it isn't clear that this is important.
    if (!SI.isUnordered())
      return false;
  
    // swifterror values can't be bitcasted.
    if (SI.getPointerOperand()->isSwiftError())
      return false;
  
    Value *V = SI.getValueOperand();
  
    // Fold away bit casts of the stored value by storing the original type.
    if (auto *BC = dyn_cast<BitCastInst>(V)) {
      V = BC->getOperand(0);
      if (!SI.isAtomic() || isSupportedAtomicType(V->getType())) {
        combineStoreToNewValue(IC, SI, V);
        return true;
      }
    }
  
    if (Value *U = likeBitCastFromVector(IC, V))
      if (!SI.isAtomic() || isSupportedAtomicType(U->getType())) {
        combineStoreToNewValue(IC, SI, U);
        return true;
      }
  
    // FIXME: We should also canonicalize stores of vectors when their elements
    // are cast to other types.
    return false;
  }
  
  static bool unpackStoreToAggregate(InstCombiner &IC, StoreInst &SI) {
    // FIXME: We could probably with some care handle both volatile and atomic
    // stores here but it isn't clear that this is important.
    if (!SI.isSimple())
      return false;
  
    Value *V = SI.getValueOperand();
    Type *T = V->getType();
  
    if (!T->isAggregateType())
      return false;
  
    if (auto *ST = dyn_cast<StructType>(T)) {
      // If the struct only have one element, we unpack.
      unsigned Count = ST->getNumElements();
      if (Count == 1) {
        V = IC.Builder->CreateExtractValue(V, 0);
        combineStoreToNewValue(IC, SI, V);
        return true;
      }
  
      // We don't want to break loads with padding here as we'd loose
      // the knowledge that padding exists for the rest of the pipeline.
      const DataLayout &DL = IC.getDataLayout();
      auto *SL = DL.getStructLayout(ST);
      if (SL->hasPadding())
        return false;
  
      auto Align = SI.getAlignment();
      if (!Align)
        Align = DL.getABITypeAlignment(ST);
  
      SmallString<16> EltName = V->getName();
      EltName += ".elt";
      auto *Addr = SI.getPointerOperand();
      SmallString<16> AddrName = Addr->getName();
      AddrName += ".repack";
  
      auto *IdxType = Type::getInt32Ty(ST->getContext());
      auto *Zero = ConstantInt::get(IdxType, 0);
      for (unsigned i = 0; i < Count; i++) {
        Value *Indices[2] = {
          Zero,
          ConstantInt::get(IdxType, i),
        };
        auto *Ptr = IC.Builder->CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices),
                                                  AddrName);
        auto *Val = IC.Builder->CreateExtractValue(V, i, EltName);
        auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
        IC.Builder->CreateAlignedStore(Val, Ptr, EltAlign);
      }
  
      return true;
    }
  
    if (auto *AT = dyn_cast<ArrayType>(T)) {
      // If the array only have one element, we unpack.
      auto NumElements = AT->getNumElements();
      if (NumElements == 1) {
        V = IC.Builder->CreateExtractValue(V, 0);
        combineStoreToNewValue(IC, SI, V);
        return true;
      }
  
      // Bail out if the array is too large. Ideally we would like to optimize
      // arrays of arbitrary size but this has a terrible impact on compile time.
      // The threshold here is chosen arbitrarily, maybe needs a little bit of
      // tuning.
      if (NumElements > 1024)
        return false;
  
      const DataLayout &DL = IC.getDataLayout();
      auto EltSize = DL.getTypeAllocSize(AT->getElementType());
      auto Align = SI.getAlignment();
      if (!Align)
        Align = DL.getABITypeAlignment(T);
  
      SmallString<16> EltName = V->getName();
      EltName += ".elt";
      auto *Addr = SI.getPointerOperand();
      SmallString<16> AddrName = Addr->getName();
      AddrName += ".repack";
  
      auto *IdxType = Type::getInt64Ty(T->getContext());
      auto *Zero = ConstantInt::get(IdxType, 0);
  
      uint64_t Offset = 0;
      for (uint64_t i = 0; i < NumElements; i++) {
        Value *Indices[2] = {
          Zero,
          ConstantInt::get(IdxType, i),
        };
        auto *Ptr = IC.Builder->CreateInBoundsGEP(AT, Addr, makeArrayRef(Indices),
                                                  AddrName);
        auto *Val = IC.Builder->CreateExtractValue(V, i, EltName);
        auto EltAlign = MinAlign(Align, Offset);
        IC.Builder->CreateAlignedStore(Val, Ptr, EltAlign);
        Offset += EltSize;
      }
  
      return true;
    }
  
    return false;
  }
  
  /// 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);
  
    // Try to canonicalize the stored type.
    if (combineStoreToValueType(*this, SI))
      return eraseInstFromFunction(SI);
  
    // Attempt to improve the alignment.
    unsigned KnownAlign = getOrEnforceKnownAlignment(
        Ptr, DL.getPrefTypeAlignment(Val->getType()), DL, &SI, &AC, &DT);
    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);
  
    // Try to canonicalize the stored type.
    if (unpackStoreToAggregate(*this, SI))
      return eraseInstFromFunction(SI);
  
    // Replace GEP indices if possible.
    if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Ptr, SI)) {
        Worklist.Add(NewGEPI);
        return &SI;
    }
  
    // Don't hack volatile/ordered stores.
    // FIXME: Some bits are legal for ordered atomic stores; needs refactoring.
    if (!SI.isUnordered()) 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->isUnordered() && 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)) {
          IGC_ASSERT_MESSAGE(SI.isUnordered(), "can't eliminate ordering operation");
          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 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.getIterator();
    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) {
    IGC_ASSERT_MESSAGE(SI.isUnordered(), "this code has not been auditted for volatile or ordered store case");
  
    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 AA tags, merge them.
    AAMDNodes AATags;
    SI.getAAMetadata(AATags);
    if (AATags) {
      OtherStore->getAAMetadata(AATags, /* Merge = */ true);
      NewSI->setAAMetadata(AATags);
    }
  
    // Nuke the old stores.
    eraseInstFromFunction(SI);
    eraseInstFromFunction(*OtherStore);
    return true;
  }
  #include "common/LLVMWarningsPop.hpp"