InstOptUtils.cpp

//===--- InstOptUtils.cpp - SILOptimizer instruction utilities ------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#include "swift/SILOptimizer/Utils/InstOptUtils.h"
#include "swift/AST/CanTypeVisitor.h"
#include "swift/AST/GenericSignature.h"
#include "swift/AST/SemanticAttrs.h"
#include "swift/AST/SubstitutionMap.h"
#include "swift/Basic/Assertions.h"
#include "swift/Basic/SmallPtrSetVector.h"
#include "swift/SIL/ApplySite.h"
#include "swift/SIL/BasicBlockUtils.h"
#include "swift/SIL/DebugUtils.h"
#include "swift/SIL/DynamicCasts.h"
#include "swift/SIL/InstructionUtils.h"
#include "swift/SIL/SILArgument.h"
#include "swift/SIL/SILBridging.h"
#include "swift/SIL/SILBuilder.h"
#include "swift/SIL/SILDebugInfoExpression.h"
#include "swift/SIL/SILModule.h"
#include "swift/SIL/SILUndef.h"
#include "swift/SIL/ScopedAddressUtils.h"
#include "swift/SIL/TypeLowering.h"
#include "swift/SILOptimizer/Analysis/ARCAnalysis.h"
#include "swift/SILOptimizer/Analysis/Analysis.h"
#include "swift/SILOptimizer/Analysis/ArraySemantic.h"
#include "swift/SILOptimizer/Analysis/BasicCalleeAnalysis.h"
#include "swift/SILOptimizer/Analysis/DominanceAnalysis.h"
#include "swift/SILOptimizer/OptimizerBridging.h"
#include "swift/SILOptimizer/Utils/CFGOptUtils.h"
#include "swift/SILOptimizer/Utils/DebugOptUtils.h"
#include "swift/SILOptimizer/Utils/OwnershipOptUtils.h"
#include "swift/SILOptimizer/Utils/ValueLifetime.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include <deque>
#include <optional>

using namespace swift;

static llvm::cl::opt<bool> EnableExpandAll("enable-expand-all",
                                           llvm::cl::init(false));

static llvm::cl::opt<bool> KeepWillThrowCall(
    "keep-will-throw-call", llvm::cl::init(false),
    llvm::cl::desc(
      "Keep calls to swift_willThrow, even if the throw is optimized away"));

std::optional<SILBasicBlock::iterator>
swift::getInsertAfterPoint(SILValue val) {
  if (auto *inst = val->getDefiningInstruction()) {
    return std::next(inst->getIterator());
  }
  if (isa<SILArgument>(val)) {
    return cast<SILArgument>(val)->getParentBlock()->begin();
  }
  return std::nullopt;
}

/// Creates an increment on \p Ptr before insertion point \p InsertPt that
/// creates a strong_retain if \p Ptr has reference semantics itself or a
/// retain_value if \p Ptr is a non-trivial value without reference-semantics.
NullablePtr<SILInstruction>
swift::createIncrementBefore(SILValue ptr, SILInstruction *insertPt) {
  // Set up the builder we use to insert at our insertion point.
  SILBuilder builder(insertPt);
  auto loc = RegularLocation::getAutoGeneratedLocation();

  // If we have a trivial type, just bail, there is no work to do.
  if (ptr->getType().isTrivial(builder.getFunction()))
    return nullptr;

  // If Ptr is refcounted itself, create the strong_retain and
  // return.
  if (ptr->getType().isReferenceCounted(builder.getModule())) {
#define ALWAYS_OR_SOMETIMES_LOADABLE_CHECKED_REF_STORAGE(Name, ...)            \
    if (ptr->getType().is<Name##StorageType>())                                \
      return builder.create##Name##Retain(loc, ptr,                            \
                                          builder.getDefaultAtomicity());
#include "swift/AST/ReferenceStorage.def"

    return builder.createStrongRetain(loc, ptr,
                                      builder.getDefaultAtomicity());
  }

  // Otherwise, create the retain_value.
  return builder.createRetainValue(loc, ptr, builder.getDefaultAtomicity());
}

/// Creates a decrement on \p ptr before insertion point \p InsertPt that
/// creates a strong_release if \p ptr has reference semantics itself or
/// a release_value if \p ptr is a non-trivial value without
/// reference-semantics.
NullablePtr<SILInstruction>
swift::createDecrementBefore(SILValue ptr, SILInstruction *insertPt) {
  // Setup the builder we will use to insert at our insertion point.
  SILBuilder builder(insertPt);
  auto loc = RegularLocation::getAutoGeneratedLocation();

  if (ptr->getType().isTrivial(builder.getFunction()))
    return nullptr;

  // If ptr has reference semantics itself, create a strong_release.
  if (ptr->getType().isReferenceCounted(builder.getModule())) {
#define ALWAYS_OR_SOMETIMES_LOADABLE_CHECKED_REF_STORAGE(Name, ...)            \
    if (ptr->getType().is<Name##StorageType>())                                \
      return builder.create##Name##Release(loc, ptr,                           \
                                          builder.getDefaultAtomicity());
#include "swift/AST/ReferenceStorage.def"

    return builder.createStrongRelease(loc, ptr,
                                       builder.getDefaultAtomicity());
  }

  // Otherwise create a release value.
  return builder.createReleaseValue(loc, ptr, builder.getDefaultAtomicity());
}

/// Returns true if OSSA scope ending instructions end_borrow/destroy_value can
/// be deleted trivially
bool swift::canTriviallyDeleteOSSAEndScopeInst(SILInstruction *i) {
  if (!isa<EndBorrowInst>(i) && !isa<DestroyValueInst>(i))
    return false;
  if (isa<StoreBorrowInst>(i->getOperand(0)))
    return false;

  auto opValue = i->getOperand(0);
  // We can delete destroy_value with operands of none ownership unless
  // they are move-only values, which can have custom deinit
  return opValue->getOwnershipKind() == OwnershipKind::None &&
         !opValue->getType().isMoveOnly();
}

/// Perform a fast local check to see if the instruction is dead.
///
/// This routine only examines the state of the instruction at hand.
bool swift::isInstructionTriviallyDead(SILInstruction *inst) {
  // At Onone, consider all uses, including the debug_info.
  // This way, debug_info is preserved at Onone.
  if (inst->hasUsesOfAnyResult()
      && inst->getFunction()->getEffectiveOptimizationMode()
             <= OptimizationMode::NoOptimization)
    return false;

  if (!onlyHaveDebugUsesOfAllResults(inst) || isa<TermInst>(inst))
    return false;

  if (auto *bi = dyn_cast<BuiltinInst>(inst)) {
    // Although the onFastPath builtin has no side-effects we don't want to
    // remove it.
    if (bi->getBuiltinInfo().ID == BuiltinValueKind::OnFastPath)
      return false;
    return !bi->mayHaveSideEffects();
  }

  // condfail instructions that obviously can't fail are dead.
  if (auto *cfi = dyn_cast<CondFailInst>(inst))
    if (auto *ili = dyn_cast<IntegerLiteralInst>(cfi->getOperand()))
      if (!ili->getValue())
        return true;

  // mark_uninitialized is never dead.
  if (isa<MarkUninitializedInst>(inst))
    return false;

  if (isa<DebugValueInst>(inst))
    return false;

  // A dead borrowed-from can only be removed if the argument (= operand) is also removed.
  if (isa<BorrowedFromInst>(inst))
    return false;

  // These invalidate enums so "write" memory, but that is not an essential
  // operation so we can remove these if they are trivially dead.
  if (isa<UncheckedTakeEnumDataAddrInst>(inst))
    return true;

  // An ossa end scope instruction is trivially dead if its operand has
  // OwnershipKind::None. This can occur after CFG simplification in the
  // presence of non-payloaded or trivial payload cases of non-trivial enums.
  //
  // Examples of ossa end_scope instructions: end_borrow, destroy_value.
  if (inst->getFunction()->hasOwnership() &&
      canTriviallyDeleteOSSAEndScopeInst(inst))
    return true;

  if (!inst->mayHaveSideEffects())
    return true;

  return false;
}

/// Return true if this is a release instruction and the released value
/// is a part of a guaranteed parameter.
bool swift::isIntermediateRelease(SILInstruction *inst,
                                  EpilogueARCFunctionInfo *eafi) {
  // Check whether this is a release instruction.
  if (!isa<StrongReleaseInst>(inst) && !isa<ReleaseValueInst>(inst))
    return false;

  // OK. we have a release instruction.
  // Check whether this is a release on part of a guaranteed function argument.
  SILValue Op = stripValueProjections(inst->getOperand(0));
  auto *arg = dyn_cast<SILFunctionArgument>(Op);
  if (!arg)
    return false;

  // This is a release on a guaranteed parameter. Its not the final release.
  if (arg->hasConvention(SILArgumentConvention::Direct_Guaranteed))
    return true;

  // This is a release on an owned parameter and its not the epilogue release.
  // Its not the final release.
  auto rel = eafi->computeEpilogueARCInstructions(
      EpilogueARCContext::EpilogueARCKind::Release, arg);
  if (rel.size() && !rel.count(inst))
    return true;

  // Failed to prove anything.
  return false;
}

bool swift::hasOnlyEndOfScopeOrEndOfLifetimeUses(SILInstruction *inst) {
  for (SILValue result : inst->getResults()) {
    for (Operand *use : result->getUses()) {
      SILInstruction *user = use->getUser();
      bool isDebugUser = user->isDebugInstruction();
      if (!isa<DestroyValueInst>(user) && !isa<EndLifetimeInst>(user)
          && !isa<DeallocStackInst>(user) && !isEndOfScopeMarker(user)
          && !isDebugUser) {
        return false;
      }
      // Include debug uses only in Onone mode.
      if (isDebugUser && inst->getFunction()->getEffectiveOptimizationMode() <=
                             OptimizationMode::NoOptimization)
        return false;
    }
  }
  return true;
}

unsigned swift::getNumInOutArguments(FullApplySite applySite) {
  assert(applySite);
  auto substConv = applySite.getSubstCalleeConv();
  unsigned numIndirectResults = substConv.getNumIndirectSILResults();
  unsigned numInOutArguments = 0;
  for (unsigned argIndex = 0; argIndex < applySite.getNumArguments();
       argIndex++) {
    // Skip indirect results.
    if (argIndex < numIndirectResults) {
      continue;
    }
    auto paramNumber = argIndex - numIndirectResults;
    auto ParamConvention =
        substConv.getParameters()[paramNumber].getConvention();
    switch (ParamConvention) {
    case ParameterConvention::Indirect_Inout:
    case ParameterConvention::Indirect_InoutAliasable: {
      ++numInOutArguments;
      break;
    default:
      break;
    }
    }
  }
  return numInOutArguments;
}

/// If the given instruction is dead, delete it along with its dead
/// operands.
///
/// \param inst The instruction to be deleted.
/// \param force If force is set, don't check if the top level instruction is
///        considered dead - delete it regardless.
void swift::recursivelyDeleteTriviallyDeadInstructions(
    SILInstruction *inst, bool force, InstModCallbacks callbacks) {
  ArrayRef<SILInstruction *> ai = ArrayRef<SILInstruction *>(inst);
  recursivelyDeleteTriviallyDeadInstructions(ai, force, callbacks);
}

void swift::collectUsesOfValue(SILValue v,
                               llvm::SmallPtrSetImpl<SILInstruction *> &insts) {
  for (auto ui = v->use_begin(), E = v->use_end(); ui != E; ++ui) {
    auto *user = ui->getUser();
    // Instruction has been processed.
    if (!insts.insert(user).second)
      continue;

    // Collect the users of this instruction.
    for (auto result : user->getResults())
      collectUsesOfValue(result, insts);
  }
}

void swift::eraseUsesOfValue(SILValue v) {
  llvm::SmallPtrSet<SILInstruction *, 4> insts;
  // Collect the uses.
  collectUsesOfValue(v, insts);
  // Erase the uses, we can have instructions that become dead because
  // of the removal of these instructions, leave to DCE to cleanup.
  // Its not safe to do recursively delete here as some of the SILInstruction
  // maybe tracked by this set.
  for (auto inst : insts) {
    inst->replaceAllUsesOfAllResultsWithUndef();
    inst->eraseFromParent();
  }
}

bool swift::hasValueDeinit(SILType type) {
  // Do not look inside an aggregate type that has a user-deinit, for which
  // memberwise-destruction is not equivalent to aggregate destruction.
  if (auto *nominal = type.getNominalOrBoundGenericNominal()) {
    return nominal->getValueTypeDestructor() != nullptr;
  }
  return false;
}

SILValue swift::
getConcreteValueOfExistentialBox(AllocExistentialBoxInst *existentialBox,
                                  SILInstruction *ignoreUser) {
  StoreInst *singleStore = nullptr;
  SmallPtrSetVector<Operand *, 32> worklist;
  for (auto *use : getNonDebugUses(existentialBox)) {
    worklist.insert(use);
  }

  while (!worklist.empty()) {
    auto *use = worklist.pop_back_val();
    SILInstruction *user = use->getUser();
    switch (user->getKind()) {
    case SILInstructionKind::StrongRetainInst:
    case SILInstructionKind::StrongReleaseInst:
    case SILInstructionKind::DestroyValueInst:
    case SILInstructionKind::EndBorrowInst:
      break;
    case SILInstructionKind::CopyValueInst:
    case SILInstructionKind::BeginBorrowInst:
      // Look through copy_value, begin_borrow
      for (SILValue result : user->getResults())
        for (auto *transitiveUse : result->getUses())
          worklist.insert(transitiveUse);
      break;
    case SILInstructionKind::ProjectExistentialBoxInst: {
      auto *projectedAddr = cast<ProjectExistentialBoxInst>(user);
      for (Operand *addrUse : getNonDebugUses(projectedAddr)) {
        if (auto *store = dyn_cast<StoreInst>(addrUse->getUser())) {
          assert(store->getSrc() != projectedAddr && "cannot store an address");
          // Bail if there are multiple stores.
          if (singleStore)
            return SILValue();
          singleStore = store;
          continue;
        }
        // If there are other users to the box value address then bail out.
        return SILValue();
      }
      break;
    }
    case SILInstructionKind::BuiltinInst: {
      auto *builtin = cast<BuiltinInst>(user);
      if (KeepWillThrowCall ||
          builtin->getBuiltinInfo().ID != BuiltinValueKind::WillThrow) {
        return SILValue();
      }
      break;
    }
    default:
      if (user != ignoreUser)
        return SILValue();
      break;
    }
  }
  if (!singleStore)
    return SILValue();
  return singleStore->getSrc();
}

SILValue swift::
getConcreteValueOfExistentialBoxAddr(SILValue addr, SILInstruction *ignoreUser) {
  auto *stackLoc = dyn_cast<AllocStackInst>(addr);
  if (!stackLoc)
    return SILValue();

  StoreInst *singleStackStore = nullptr;
  for (Operand *stackUse : stackLoc->getUses()) {
    SILInstruction *stackUser = stackUse->getUser();
    switch (stackUser->getKind()) {
    case SILInstructionKind::DestroyAddrInst: {
      // Make sure the destroy_addr is the instruction before one of our
      // dealloc_stack insts and is directly on the stack location.
      auto next = std::next(stackUser->getIterator());
      if (auto *dsi = dyn_cast<DeallocStackInst>(next))
        if (dsi->getOperand() != stackLoc)
          return SILValue();
      break;
    }
    case SILInstructionKind::DeallocStackInst:
    case SILInstructionKind::LoadInst:
      break;
    case SILInstructionKind::DebugValueInst:
      if (!DebugValueInst::hasAddrVal(stackUser)) {
        if (stackUser != ignoreUser)
          return SILValue();
      }
      break;
    case SILInstructionKind::StoreInst: {
      auto *store = cast<StoreInst>(stackUser);
      assert(store->getSrc() != stackLoc && "cannot store an address");
      // Bail if there are multiple stores.
      if (singleStackStore)
        return SILValue();
      singleStackStore = store;
      break;
    }
    default:
      if (stackUser != ignoreUser)
        return SILValue();
      break;
    }
  }
  if (!singleStackStore)
    return SILValue();

  // Look through copy value insts.
  SILValue val = singleStackStore->getSrc();
  while (auto *cvi = dyn_cast<CopyValueInst>(val))
    val = cvi->getOperand();
  auto *box = dyn_cast<AllocExistentialBoxInst>(val);
  if (!box)
    return SILValue();

  return getConcreteValueOfExistentialBox(box, singleStackStore);
}

bool swift::mayBindDynamicSelf(SILFunction *F) {
  if (!F->hasDynamicSelfMetadata())
    return false;

  SILValue mdArg = F->getDynamicSelfMetadata();

  for (Operand *mdUse : mdArg->getUses()) {
    SILInstruction *mdUser = mdUse->getUser();
    for (Operand &typeDepOp : mdUser->getTypeDependentOperands()) {
      if (typeDepOp.get() == mdArg)
        return true;
    }
  }
  return false;
}

static SILValue skipAddrProjections(SILValue v) {
  for (;;) {
    switch (v->getKind()) {
    case ValueKind::IndexAddrInst:
    case ValueKind::IndexRawPointerInst:
    case ValueKind::StructElementAddrInst:
    case ValueKind::TupleElementAddrInst:
      v = cast<SingleValueInstruction>(v)->getOperand(0);
      break;
    default:
      return v;
    }
  }
  llvm_unreachable("there is no escape from an infinite loop");
}

/// Check whether the \p addr is an address of a tail-allocated array element.
bool swift::isAddressOfArrayElement(SILValue addr) {
  addr = stripAddressProjections(addr);
  if (auto *md = dyn_cast<MarkDependenceInst>(addr))
    addr = stripAddressProjections(md->getValue());

  // High-level SIL: check for an get_element_address array semantics call.
  if (auto *ptrToAddr = dyn_cast<PointerToAddressInst>(addr))
    if (auto *sei = dyn_cast<StructExtractInst>(ptrToAddr->getOperand())) {
      ArraySemanticsCall call(sei->getOperand());
      if (call && call.getKind() == ArrayCallKind::kGetElementAddress)
        return true;
    }

  // Check for an tail-address (of an array buffer object).
  if (isa<RefTailAddrInst>(skipAddrProjections(addr)))
    return true;

  return false;
}

/// Find a new position for an ApplyInst's FuncRef so that it dominates its
/// use. Not that FunctionRefInsts may be shared by multiple ApplyInsts.
void swift::placeFuncRef(ApplyInst *ai, DominanceInfo *domInfo) {
  FunctionRefInst *funcRef = cast<FunctionRefInst>(ai->getCallee());
  SILBasicBlock *domBB = domInfo->findNearestCommonDominator(
      ai->getParent(), funcRef->getParent());
  if (domBB == ai->getParent() && domBB != funcRef->getParent())
    // Prefer to place the FuncRef immediately before the call. Since we're
    // moving FuncRef up, this must be the only call to it in the block.
    funcRef->moveBefore(ai);
  else
    // Otherwise, conservatively stick it at the beginning of the block.
    funcRef->moveBefore(&*domBB->begin());
}

/// Add an argument, \p val, to the branch-edge that is pointing into
/// block \p Dest. Return a new instruction and do not erase the old
/// instruction.
TermInst *swift::addArgumentsToBranch(ArrayRef<SILValue> vals,
                                      SILBasicBlock *dest, TermInst *branch) {
  SILBuilderWithScope builder(branch);

  if (auto *cbi = dyn_cast<CondBranchInst>(branch)) {
    SmallVector<SILValue, 8> trueArgs;
    SmallVector<SILValue, 8> falseArgs;

    for (auto arg : cbi->getTrueArgs())
      trueArgs.push_back(arg);

    for (auto arg : cbi->getFalseArgs())
      falseArgs.push_back(arg);

    if (dest == cbi->getTrueBB()) {
      for (auto val : vals)
        trueArgs.push_back(val);
      assert(trueArgs.size() == dest->getNumArguments());
    } else {
      for (auto val : vals)
        falseArgs.push_back(val);
      assert(falseArgs.size() == dest->getNumArguments());
    }

    return builder.createCondBranch(
        cbi->getLoc(), cbi->getCondition(), cbi->getTrueBB(), trueArgs,
        cbi->getFalseBB(), falseArgs, cbi->getTrueBBCount(),
        cbi->getFalseBBCount());
  }

  if (auto *bi = dyn_cast<BranchInst>(branch)) {
    SmallVector<SILValue, 8> args;

    for (auto arg : bi->getArgs())
      args.push_back(arg);

    for (auto val : vals)
      args.push_back(val);
    assert(args.size() == dest->getNumArguments());
    return builder.createBranch(bi->getLoc(), bi->getDestBB(), args);
  }

  llvm_unreachable("unsupported terminator");
}

SILLinkage swift::getSpecializedLinkage(SILFunction *f, SILLinkage linkage) {
  if (hasPrivateVisibility(linkage) && !f->isAnySerialized()) {
    // Specializations of private symbols should remain so, unless
    // they were serialized, which can only happen when specializing
    // definitions from a standard library built with -sil-serialize-all.
    return SILLinkage::Private;
  }

  return SILLinkage::Shared;
}

/// Cast a value into the expected, ABI compatible type if necessary.
/// This may happen e.g. when:
/// - a type of the return value is a subclass of the expected return type.
/// - actual return type and expected return type differ in optionality.
/// - both types are tuple-types and some of the elements need to be casted.
/// Return the cast value and true if a CFG modification was required
/// NOTE: We intentionally combine the checking of the cast's handling
/// possibility and the transformation performing the cast in the same function,
/// to avoid any divergence between the check and the implementation in the
/// future.
///
/// \p usePoints are required when \p value has guaranteed ownership. It must be
/// the last users of the returned, casted value. A usePoint cannot be a
/// BranchInst (a phi is never the last guaranteed user). \p builder's current
/// insertion point must dominate all \p usePoints. \p usePoints must
/// collectively post-dominate \p builder's current insertion point.
///
/// NOTE: The implementation of this function is very closely related to the
/// rules checked by SILVerifier::requireABICompatibleFunctionTypes. It must
/// handle all cases recognized by SILFunctionType::isABICompatibleWith (see
/// areABICompatibleParamsOrReturns()).
std::pair<SILValue, bool /* changedCFG */>
swift::castValueToABICompatibleType(SILBuilder *builder, SILPassManager *pm,
                                    SILLocation loc,
                                    SILValue value, SILType srcTy,
                                    SILType destTy,
                                    ArrayRef<SILInstruction *> usePoints) {
  assert(value->getOwnershipKind() != OwnershipKind::Guaranteed ||
         !usePoints.empty() && "guaranteed value must have use points");

  // No cast is required if types are the same.
  if (srcTy == destTy)
    return {value, false};

  if (srcTy.isAddress() && destTy.isAddress()) {
    // Cast between two addresses and that's it.
    return {builder->createUncheckedAddrCast(loc, value, destTy), false};
  }

  // If both types are classes and dest is the superclass of src,
  // simply perform an upcast.
  if (destTy.isExactSuperclassOf(srcTy)) {
    return {builder->createUpcast(loc, value, destTy), false};
  }

  if (srcTy.isHeapObjectReferenceType() && destTy.isHeapObjectReferenceType()) {
    return {builder->createUncheckedRefCast(loc, value, destTy), false};
  }

  if (auto mt1 = srcTy.getAs<AnyMetatypeType>()) {
    if (auto mt2 = destTy.getAs<AnyMetatypeType>()) {
      if (mt1->getRepresentation() == mt2->getRepresentation()) {
        // If builder.Type needs to be casted to A.Type and
        // A is a superclass of builder, then it can be done by means
        // of a simple upcast.
        if (mt2.getInstanceType()->isExactSuperclassOf(mt1.getInstanceType())) {
          return {builder->createUpcast(loc, value, destTy), false};
        }

        // Cast between two metatypes and that's it.
        return {builder->createUncheckedReinterpretCast(loc, value, destTy),
                false};
      }
    }
  }

  // Check if src and dest types are optional.
  auto optionalSrcTy = srcTy.getOptionalObjectType();
  auto optionalDestTy = destTy.getOptionalObjectType();

  // Both types are optional.
  if (optionalDestTy && optionalSrcTy) {
    // If both wrapped types are classes and dest is the superclass of src,
    // simply perform an upcast.
    if (optionalDestTy.isExactSuperclassOf(optionalSrcTy)) {
      // Insert upcast.
      return {builder->createUpcast(loc, value, destTy), false};
    }

    // Unwrap the original optional value.
    auto *someDecl = builder->getASTContext().getOptionalSomeDecl();
    auto *curBB = builder->getInsertionPoint()->getParent();
    auto *contBB = curBB->split(builder->getInsertionPoint());
    auto *someBB = builder->getFunction().createBasicBlockAfter(curBB);
    auto *noneBB = builder->getFunction().createBasicBlockAfter(someBB);

    auto *phi = contBB->createPhiArgument(destTy, value->getOwnershipKind());

    SmallVector<std::pair<EnumElementDecl *, SILBasicBlock *>, 1> caseBBs;
    caseBBs.push_back(std::make_pair(someDecl, someBB));
    builder->setInsertionPoint(curBB);
    auto *switchEnum = builder->createSwitchEnum(loc, value, noneBB, caseBBs);
    // In OSSA switch_enum destinations have terminator results.
    //
    // TODO: This should be in a switchEnum utility.
    SILValue unwrappedValue;
    if (builder->hasOwnership()) {
      unwrappedValue = switchEnum->createOptionalSomeResult();
      builder->setInsertionPoint(someBB);
    } else {
      builder->setInsertionPoint(someBB);
      unwrappedValue = builder->createUncheckedEnumData(loc, value, someDecl);
    }
    // Cast the unwrapped value.
    SILValue castedUnwrappedValue;
    std::tie(castedUnwrappedValue, std::ignore) = castValueToABICompatibleType(
      builder, pm, loc, unwrappedValue, optionalSrcTy, optionalDestTy, usePoints);
    // Wrap into optional. An owned value is forwarded through the cast and into
    // the Optional. A borrowed value will have a nested borrow for the
    // rewrapped Optional.
    SILValue someValue =
        builder->createOptionalSome(loc, castedUnwrappedValue, destTy);
    builder->createBranch(loc, contBB, {someValue});

    // Handle the None case.
    builder->setInsertionPoint(noneBB);
    SILValue noneValue = builder->createOptionalNone(loc, destTy);
    builder->createBranch(loc, contBB, {noneValue});
    builder->setInsertionPoint(contBB->begin());

    updateBorrowedFromPhis(pm, { phi });

    return {lookThroughBorrowedFromUser(phi), true};
  }

  // Src is not optional, but dest is optional.
  if (!optionalSrcTy && optionalDestTy) {
    auto optionalSrcCanTy =
        OptionalType::get(srcTy.getASTType())->getCanonicalType();
    auto loweredOptionalSrcType =
        SILType::getPrimitiveObjectType(optionalSrcCanTy);

    // Wrap the source value into an optional first.
    SILValue wrappedValue =
        builder->createOptionalSome(loc, value, loweredOptionalSrcType);
    // Cast the wrapped value.
    return castValueToABICompatibleType(builder, pm, loc, wrappedValue,
                                        wrappedValue->getType(), destTy,
                                        usePoints);
  }

  // Handle tuple types.
  // Extract elements, cast each of them, create a new tuple.
  if (auto srcTupleTy = srcTy.getAs<TupleType>()) {
    SmallVector<SILValue, 8> expectedTuple;
    bool changedCFG = false;
    auto castElement = [&](unsigned idx, SILValue element) {
      // Cast the value if necessary.
      bool neededCFGChange;
      std::tie(element, neededCFGChange) = castValueToABICompatibleType(
          builder, pm, loc, element, srcTy.getTupleElementType(idx),
          destTy.getTupleElementType(idx), usePoints);
      changedCFG |= neededCFGChange;
      expectedTuple.push_back(element);
    };
    builder->emitDestructureValueOperation(loc, value, castElement);
    return {builder->createTuple(loc, destTy, expectedTuple), changedCFG};
  }

  // Function types are interchangeable if they're also ABI-compatible.
  if (srcTy.is<SILFunctionType>()) {
    if (destTy.is<SILFunctionType>()) {
      assert(srcTy.getAs<SILFunctionType>()->isNoEscape()
                 == destTy.getAs<SILFunctionType>()->isNoEscape()
             || srcTy.getAs<SILFunctionType>()->getRepresentation()
                        != SILFunctionType::Representation::Thick
                    && "Swift thick functions that differ in escapeness are "
                       "not ABI "
                       "compatible");
      // Insert convert_function.
      return {builder->createConvertFunction(loc, value, destTy,
                                             /*WithoutActuallyEscaping=*/false),
              false};
    }
  }
  NominalTypeDecl *srcNominal = srcTy.getNominalOrBoundGenericNominal();
  NominalTypeDecl *destNominal = destTy.getNominalOrBoundGenericNominal();
  if (srcNominal && srcNominal == destNominal &&
      !layoutIsTypeDependent(srcNominal) &&
      srcTy.isObject() && destTy.isObject()) {

    // This can be a result from whole-module reasoning of protocol conformances.
    // If a protocol only has a single conformance where the associated type (`ID`) is some
    // concrete type (e.g. `Int`), then the devirtualizer knows that `p.get()`
    // can only return an `Int`:
    // ```
    //   public struct X2<ID> {
    //     let p: any P2<ID>
    //     public func testit(i: ID, x: ID) -> S2<ID> {
    //       return p.get(x: x)
    //     }
    //   }
    // ```
    // and after devirtualizing the `get` function, its result must be cast from `Int` to `ID`.
    //
    // The `layoutIsTypeDependent` utility is basically only used here to assert that this
    // cast can only happen between layout compatible types.
    return {builder->createUncheckedForwardingCast(loc, value, destTy), false};
  }

  llvm::errs() << "Source type: " << srcTy << "\n";
  llvm::errs() << "Destination type: " << destTy << "\n";
  llvm_unreachable("Unknown combination of types for casting");
}

namespace {
  class TypeDependentVisitor : public CanTypeVisitor<TypeDependentVisitor, bool> {
  public:
    // If the type isn't actually dependent, we're okay.
    bool visit(CanType type) {
      if (!type->hasArchetype() && !type->hasTypeParameter())
        return false;
      return CanTypeVisitor::visit(type);
    }

    bool visitStructType(CanStructType type) {
      return visitStructDecl(type->getDecl());
    }
    bool visitBoundGenericStructType(CanBoundGenericStructType type) {
      return visitStructDecl(type->getDecl());
    }
    bool visitStructDecl(StructDecl *decl) {
      auto rawLayout = decl->getAttrs().getAttribute<RawLayoutAttr>();
      if (rawLayout) {
        if (auto likeType = rawLayout->getResolvedScalarLikeType(decl)) {
          return visit((*likeType)->getCanonicalType());
        } else if (auto likeArray = rawLayout->getResolvedArrayLikeTypeAndCount(decl)) {
          return visit(likeArray->first->getCanonicalType());
        }
      }

      for (auto field : decl->getStoredProperties()) {
        if (visit(field->getInterfaceType()->getCanonicalType()))
          return true;
      }
      return false;
    }

    bool visitEnumType(CanEnumType type) {
      return visitEnumDecl(type->getDecl());
    }
    bool visitBoundGenericEnumType(CanBoundGenericEnumType type) {
      return visitEnumDecl(type->getDecl());
    }
    bool visitEnumDecl(EnumDecl *decl) {
      if (decl->isIndirect())
        return false;

      for (auto elt : decl->getAllElements()) {
        if (!elt->hasAssociatedValues() || elt->isIndirect())
          continue;

        if (visit(elt->getArgumentInterfaceType()->getCanonicalType()))
          return true;
      }
      return false;
    }

    bool visitTupleType(CanTupleType type) {
      for (auto eltTy : type.getElementTypes()) {
        if (visit(eltTy->getCanonicalType()))
          return true;
      }
      return false;
    }

    // A class reference does not depend on the layout of the class.
    bool visitClassType(CanClassType type) {
      return false;
     }
    bool visitBoundGenericClassType(CanBoundGenericClassType type) {
      return false;
    }

    // The same for non-strong references.
    bool visitReferenceStorageType(CanReferenceStorageType type) {
      return false;
    }

    // All function types have the same layout.
    bool visitAnyFunctionType(CanAnyFunctionType type) {
      return false;
    }

    // The safe default for types we didn't handle above.
    bool visitType(CanType type) {
      return true;
    }
  };
} // end anonymous namespace

bool swift::layoutIsTypeDependent(NominalTypeDecl *decl) {
  if (auto *classDecl = dyn_cast<ClassDecl>(decl)) {
    return false;
  } else if (auto *structDecl = dyn_cast<StructDecl>(decl)) {
    return TypeDependentVisitor().visitStructDecl(structDecl);
  } else {
    auto *enumDecl = cast<EnumDecl>(decl);
    return TypeDependentVisitor().visitEnumDecl(enumDecl);
  }
}

ProjectBoxInst *swift::getOrCreateProjectBox(AllocBoxInst *abi,
                                             unsigned index) {
  SILBasicBlock::iterator iter(abi);
  ++iter;
  assert(iter != abi->getParent()->end()
         && "alloc_box cannot be the last instruction of a block");
  SILInstruction *nextInst = &*iter;
  if (auto *pbi = dyn_cast<ProjectBoxInst>(nextInst)) {
    if (pbi->getOperand() == abi && pbi->getFieldIndex() == index)
      return pbi;
  }

  SILBuilder builder(nextInst);
  return builder.createProjectBox(abi->getLoc(), abi, index);
}

// Peek through trivial Enum initialization, typically for pointless
// Optionals.
//
// Given an UncheckedTakeEnumDataAddrInst, check that there are no
// other uses of the Enum value and return the address used to initialized the
// enum's payload:
//
//   %stack_adr = alloc_stack
//   %data_adr  = init_enum_data_addr %stk_adr
//   %enum_adr  = inject_enum_addr %stack_adr
//   %copy_src  = unchecked_take_enum_data_addr %enum_adr
//   dealloc_stack %stack_adr
//   (No other uses of %stack_adr.)
InitEnumDataAddrInst *
swift::findInitAddressForTrivialEnum(UncheckedTakeEnumDataAddrInst *utedai) {
  auto *asi = dyn_cast<AllocStackInst>(utedai->getOperand());
  if (!asi)
    return nullptr;

  SILInstruction *singleUser = nullptr;
  for (auto use : asi->getUses()) {
    auto *user = use->getUser();
    if (user == utedai)
      continue;

    // As long as there's only one UncheckedTakeEnumDataAddrInst and one
    // InitEnumDataAddrInst, we don't care how many InjectEnumAddr and
    // DeallocStack users there are.
    if (isa<InjectEnumAddrInst>(user) || isa<DeallocStackInst>(user))
      continue;

    if (singleUser)
      return nullptr;

    singleUser = user;
  }
  if (!singleUser)
    return nullptr;

  // Assume, without checking, that the returned InitEnumDataAddr dominates the
  // given UncheckedTakeEnumDataAddrInst, because that's how SIL is defined. I
  // don't know where this is actually verified.
  return dyn_cast<InitEnumDataAddrInst>(singleUser);
}

//===----------------------------------------------------------------------===//
//                              Closure Deletion
//===----------------------------------------------------------------------===//

/// NOTE: Instructions with transitive ownership kind are assumed to not keep
/// the underlying value alive as well. This is meant for instructions only
/// with non-transitive users.
static bool useDoesNotKeepValueAlive(const SILInstruction *inst) {
  switch (inst->getKind()) {
  case SILInstructionKind::StrongRetainInst:
  case SILInstructionKind::StrongReleaseInst:
  case SILInstructionKind::DestroyValueInst:
  case SILInstructionKind::RetainValueInst:
  case SILInstructionKind::ReleaseValueInst:
  case SILInstructionKind::DebugValueInst:
  case SILInstructionKind::EndBorrowInst:
    return true;
  default:
    return false;
  }
}

static bool useHasTransitiveOwnership(const SILInstruction *inst) {
  // convert_escape_to_noescape is used to convert to a @noescape function type.
  // It does not change ownership of the function value.
  if (isa<ConvertEscapeToNoEscapeInst>(inst))
    return true;

  // Look through copy_value, begin_borrow, move_value. They are inert for our
  // purposes, but we need to look through it.
  return isa<CopyValueInst>(inst) || isa<BeginBorrowInst>(inst) ||
         isa<MoveValueInst>(inst);
}

static bool shouldDestroyPartialApplyCapturedArg(SILValue arg,
                                                 SILParameterInfo paramInfo,
                                                 const SILFunction &F) {
  // If we have a non-trivial type and the argument is passed in @inout, we do
  // not need to destroy it here. This is something that is implicit in the
  // partial_apply design that will be revisited when partial_apply is
  // redesigned.
  if (paramInfo.isIndirectMutating())
    return false;

  // If we have a trivial type, we do not need to put in any extra releases.
  if (arg->getType().isTrivial(F))
    return false;

  // We handle all other cases.
  return true;
}

void swift::emitDestroyOperation(SILBuilder &builder, SILLocation loc,
                                 SILValue operand, InstModCallbacks callbacks) {
  // If we have an address, we insert a destroy_addr and return. Any live range
  // issues must have been dealt with by our caller.
  if (operand->getType().isAddress()) {
    // Then emit the destroy_addr for this operand. This function does not
    // delete any instructions
    SILInstruction *newInst = builder.emitDestroyAddrAndFold(loc, operand);
    if (newInst != nullptr)
      callbacks.createdNewInst(newInst);
    return;
  }

  // Otherwise, we have an object. We emit the most optimized form of release
  // possible for that value.

  // If we have qualified ownership, we should just emit a destroy value.
  if (builder.getFunction().hasOwnership()) {
    callbacks.createdNewInst(builder.createDestroyValue(loc, operand));
    return;
  }

  if (operand->getType().isReferenceCounted(builder.getModule())) {
    auto u = builder.emitStrongRelease(loc, operand);
    if (u.isNull())
      return;

    if (auto *SRI = u.dyn_cast<StrongRetainInst *>()) {
      callbacks.deleteInst(SRI);
      return;
    }

    callbacks.createdNewInst(u.get<StrongReleaseInst *>());
    return;
  }

  auto u = builder.emitReleaseValue(loc, operand);
  if (u.isNull())
    return;

  if (auto *rvi = u.dyn_cast<RetainValueInst *>()) {
    callbacks.deleteInst(rvi);
    return;
  }

  callbacks.createdNewInst(u.get<ReleaseValueInst *>());
}

// NOTE: The ownership of the partial_apply argument does not match the
// convention of the closed over function. All non-inout arguments to a
// partial_apply are passed at +1 for regular escaping closures and +0 for
// closures that have been promoted to partial_apply [on_stack]. An escaping
// partial apply stores each capture in an owned box, even for guaranteed and
// in_guaranteed argument convention. A non-escaping/on-stack closure either
// borrows its arguments or takes an inout_aliasable address. Non-escaping
// closures do not support owned arguments.
void swift::releasePartialApplyCapturedArg(SILBuilder &builder, SILLocation loc,
                                           SILValue arg,
                                           SILParameterInfo paramInfo,
                                           InstModCallbacks callbacks) {
  if (!shouldDestroyPartialApplyCapturedArg(arg, paramInfo,
                                            builder.getFunction()))
    return;

  emitDestroyOperation(builder, loc, arg, callbacks);
}

static bool
deadMarkDependenceUser(SILInstruction *inst,
                       SmallVectorImpl<SILInstruction *> &deleteInsts) {
  if (!isa<MarkDependenceInst>(inst))
    return false;
  deleteInsts.push_back(inst);
  for (auto *use : cast<SingleValueInstruction>(inst)->getUses()) {
    if (!deadMarkDependenceUser(use->getUser(), deleteInsts))
      return false;
  }
  return true;
}

void swift::getConsumedPartialApplyArgs(PartialApplyInst *pai,
                                        SmallVectorImpl<Operand *> &argOperands,
                                        bool includeTrivialAddrArgs) {
  ApplySite applySite(pai);
  SILFunctionConventions calleeConv = applySite.getSubstCalleeConv();
  unsigned firstCalleeArgIdx = applySite.getCalleeArgIndexOfFirstAppliedArg();
  auto argList = pai->getArgumentOperands();
  SILFunction *F = pai->getFunction();

  for (unsigned i : indices(argList)) {
    auto argConv = calleeConv.getSILArgumentConvention(firstCalleeArgIdx + i);
    if (argConv.isInoutConvention())
      continue;

    Operand &argOp = argList[i];
    SILType ty = argOp.get()->getType();
    if (!ty.isTrivial(*F) || (includeTrivialAddrArgs && ty.isAddress()))
      argOperands.push_back(&argOp);
  }
}

bool swift::collectDestroys(SingleValueInstruction *inst,
                            SmallVectorImpl<Operand *> &destroys) {
  bool isDead = true;
  for (Operand *use : inst->getUses()) {
    SILInstruction *user = use->getUser();
    if (useHasTransitiveOwnership(user)) {
      if (!collectDestroys(cast<SingleValueInstruction>(user), destroys))
        isDead = false;
      destroys.push_back(use);
    } else if (useDoesNotKeepValueAlive(user)) {
      destroys.push_back(use);
    } else {
      isDead = false;
    }
  }
  return isDead;
}

/// Move the original arguments of the partial_apply into newly created
/// temporaries to extend the lifetime of the arguments until the partial_apply
/// is finally destroyed.
///
/// TODO: figure out why this is needed at all. Probably because of some
///       weirdness of the old retain/release ARC model. Most likely this will
///       not be needed anymore with OSSA.
static bool keepArgsOfPartialApplyAlive(PartialApplyInst *pai,
                                        ArrayRef<Operand *> paiUses,
                                        SILBuilderContext &builderCtxt,
                                        InstModCallbacks callbacks) {
  SmallVector<Operand *, 8> argsToHandle;
  getConsumedPartialApplyArgs(pai, argsToHandle,
                              /*includeTrivialAddrArgs*/ false);
  if (argsToHandle.empty())
    return true;

  // Compute the set of endpoints, which will be used to insert destroys of
  // temporaries. This may fail if the frontier is located on a critical edge
  // which we may not split.
  ValueLifetimeAnalysis vla(pai, paiUses);

  ValueLifetimeAnalysis::Frontier partialApplyFrontier;
  if (!vla.computeFrontier(partialApplyFrontier,
                           ValueLifetimeAnalysis::DontModifyCFG)) {
    return false;
  }

  // We must not introduce copies for move only types.
  // TODO: in OSSA, instead of bailing, it's possible to destroy the arguments
  //       without the need of copies.
  for (Operand *argOp : argsToHandle) {
    if (argOp->get()->getType().isMoveOnly())
      return false;
  }

  for (Operand *argOp : argsToHandle) {
    SILValue arg = argOp->get();

    SILValue tmp = arg;
    if (arg->getType().isAddress()) {
      // Move the value to a stack-allocated temporary.
      SILBuilderWithScope builder(pai, builderCtxt);
      tmp = builder.createAllocStack(pai->getLoc(), arg->getType());
      builder.createCopyAddr(pai->getLoc(), arg, tmp, IsTake_t::IsTake,
                             IsInitialization_t::IsInitialization);
    }

    // Delay the destroy of the value (either as SSA value or in the stack-
    // allocated temporary) at the end of the partial_apply's lifetime.
    endLifetimeAtFrontier(tmp, partialApplyFrontier, builderCtxt, callbacks);
  }
  return true;
}

bool swift::tryDeleteDeadClosure(SingleValueInstruction *closure,
                                 InstModCallbacks callbacks,
                                 bool needKeepArgsAlive) {
  auto *pa = dyn_cast<PartialApplyInst>(closure);

  // We currently only handle locally identified values that do not escape. We
  // also assume that the partial apply does not capture any addresses.
  if (!pa && !isa<ThinToThickFunctionInst>(closure))
    return false;

  // A stack allocated partial apply does not have any release users. Delete it
  // if the only users are the dealloc_stack and mark_dependence instructions.
  if (pa && pa->isOnStack()) {
    SmallVector<SILInstruction *, 8> deleteInsts;
    for (auto *use : pa->getUses()) {
      SILInstruction *user = use->getUser();
      if (isa<DeallocStackInst>(user)
          || isa<DebugValueInst>(user)
          || isa<DestroyValueInst>(user)) {
        deleteInsts.push_back(user);
      } else if (!deadMarkDependenceUser(user, deleteInsts)) {
        return false;
      }
    }
    for (auto *inst : reverse(deleteInsts))
      callbacks.deleteInst(inst);
    callbacks.deleteInst(pa);

    // Note: the lifetime of the captured arguments is managed outside of the
    // trivial closure value i.e: there will already be releases for the
    // captured arguments. Releasing captured arguments is not necessary.
    return true;
  }

  // Collect all destroys of the closure (transitively including destroys of
  // copies) and check if those are the only uses of the closure.
  SmallVector<Operand *, 16> closureDestroys;
  if (!collectDestroys(closure, closureDestroys))
    return false;

  // If we have a partial_apply, release each captured argument at each one of
  // the final release locations of the partial apply.
  if (auto *pai = dyn_cast<PartialApplyInst>(closure)) {
    assert(!pa->isOnStack() &&
           "partial_apply [stack] should have been handled before");
    SILBuilderContext builderCtxt(pai->getModule());
    if (needKeepArgsAlive) {
      if (!keepArgsOfPartialApplyAlive(pai, closureDestroys, builderCtxt,
                                       callbacks))
        return false;
    } else {
      // A preceding partial_apply -> apply conversion (done in
      // tryOptimizeApplyOfPartialApply) already ensured that the arguments are
      // kept alive until the end of the partial_apply's lifetime.
      SmallVector<Operand *, 8> argsToHandle;
      getConsumedPartialApplyArgs(pai, argsToHandle,
                                  /*includeTrivialAddrArgs*/ false);

      // We can just destroy the arguments at the point of the partial_apply
      // (remember: partial_apply consumes all arguments).
      for (Operand *argOp : argsToHandle) {
        SILValue arg = argOp->get();
        SILBuilderWithScope builder(pai, builderCtxt);
        emitDestroyOperation(builder, pai->getLoc(), arg, callbacks);
      }
    }
  }

  // Delete all copy and destroy instructions in order so that leaf uses are
  // deleted first.
  for (auto *use : closureDestroys) {
    auto *user = use->getUser();
    assert(
        (useDoesNotKeepValueAlive(user) || useHasTransitiveOwnership(user)) &&
        "We expect only ARC operations without "
        "results or a cast from escape to noescape without users");
    callbacks.deleteInst(user);
  }

  callbacks.deleteInst(closure);
  return true;
}

bool swift::simplifyUsers(SingleValueInstruction *inst) {
  bool changed = false;
  InstModCallbacks callbacks;

  for (auto ui = inst->use_begin(), ue = inst->use_end(); ui != ue;) {
    SILInstruction *user = ui->getUser();
    ++ui;

    auto svi = dyn_cast<SingleValueInstruction>(user);
    if (!svi)
      continue;

    callbacks.resetHadCallbackInvocation();
    simplifyAndReplaceAllSimplifiedUsesAndErase(svi, callbacks);
    changed |= callbacks.hadCallbackInvocation();
  }

  return changed;
}

// True if a type can be expanded without a significant increase to code size.
//
// False if expanding a type is invalid. For example, expanding a
// struct-with-deinit drops the deinit.
bool swift::shouldExpand(SILModule &module, SILType ty) {
  // FIXME: Expansion
  auto expansion = TypeExpansionContext::minimal();

  if (module.Types.getTypeLowering(ty, expansion).isAddressOnly()) {
    return false;
  }
  // A move-only-with-deinit type cannot be SROA.
  //
  // TODO: we could loosen this requirement if all paths lead to a drop_deinit.
  if (auto *nominalTy = ty.getNominalOrBoundGenericNominal()) {
    if (nominalTy->getValueTypeDestructor())
      return false;
  }
  if (EnableExpandAll) {
    return true;
  }

  unsigned numFields = module.Types.countNumberOfFields(ty, expansion);
  return (numFields <= 6);
}

/// Some support functions for the global-opt and let-properties-opts

// Encapsulate the state used for recursive analysis of a static
// initializer. Discover all the instruction in a use-def graph and return them
// in topological order.
//
// TODO: We should have a DFS utility for this sort of thing so it isn't
// recursive.
class StaticInitializerAnalysis {
  SmallVectorImpl<SILInstruction *> &postOrderInstructions;
  llvm::SmallDenseSet<SILValue, 8> visited;
  int recursionLevel = 0;

public:
  StaticInitializerAnalysis(
      SmallVectorImpl<SILInstruction *> &postOrderInstructions)
      : postOrderInstructions(postOrderInstructions) {}

  // Perform a recursive DFS on on the use-def graph rooted at `V`. Insert
  // values in the `visited` set in preorder. Insert values in
  // `postOrderInstructions` in postorder so that the instructions are
  // topologically def-use ordered (in execution order).
  bool analyze(SILValue rootValue) {
    return recursivelyAnalyzeOperand(rootValue);
  }

protected:
  bool recursivelyAnalyzeOperand(SILValue v) {
    if (!visited.insert(v).second)
      return true;

    if (++recursionLevel > 50)
      return false;

    // TODO: For multi-result instructions, we could simply insert all result
    // values in the visited set here.
    auto *inst = dyn_cast<SingleValueInstruction>(v);
    if (!inst)
      return false;

    if (!recursivelyAnalyzeInstruction(inst))
      return false;

    postOrderInstructions.push_back(inst);
    --recursionLevel;
    return true;
  }

  bool recursivelyAnalyzeInstruction(SILInstruction *inst) {
    if (auto *si = dyn_cast<StructInst>(inst)) {
      // If it is not a struct which is a simple type, bail.
      if (!si->getType().isTrivial(*si->getFunction()))
        return false;

      return llvm::all_of(si->getAllOperands(), [&](Operand &operand) -> bool {
        return recursivelyAnalyzeOperand(operand.get());
      });
    }
    if (auto *ti = dyn_cast<TupleInst>(inst)) {
      // If it is not a tuple which is a simple type, bail.
      if (!ti->getType().isTrivial(*ti->getFunction()))
        return false;

      return llvm::all_of(ti->getAllOperands(), [&](Operand &operand) -> bool {
        return recursivelyAnalyzeOperand(operand.get());
      });
    }
    if (auto *bi = dyn_cast<BuiltinInst>(inst)) {
      switch (bi->getBuiltinInfo().ID) {
      case BuiltinValueKind::FPTrunc:
        if (auto *li = dyn_cast<LiteralInst>(bi->getArguments()[0])) {
          return recursivelyAnalyzeOperand(li);
        }
        return false;
      default:
        return false;
      }
    }
    return isa<IntegerLiteralInst>(inst) || isa<FloatLiteralInst>(inst)
           || isa<StringLiteralInst>(inst);
  }
};

/// Check if the value of v is computed by means of a simple initialization.
/// Populate `forwardInstructions` with references to all the instructions
/// that participate in the use-def graph required to compute `V`. The
/// instructions will be in def-use topological order.
bool swift::analyzeStaticInitializer(
    SILValue v, SmallVectorImpl<SILInstruction *> &forwardInstructions) {
  return StaticInitializerAnalysis(forwardInstructions).analyze(v);
}

/// FIXME: This must be kept in sync with replaceLoadSequence()
/// below. What a horrible design.
bool swift::canReplaceLoadSequence(SILInstruction *inst) {
  if (auto *cai = dyn_cast<CopyAddrInst>(inst))
    return true;

  if (auto *li = dyn_cast<LoadInst>(inst))
    return true;

  if (auto *seai = dyn_cast<StructElementAddrInst>(inst)) {
    for (auto seaiUse : seai->getUses()) {
      if (!canReplaceLoadSequence(seaiUse->getUser()))
        return false;
    }
    return true;
  }

  if (auto *teai = dyn_cast<TupleElementAddrInst>(inst)) {
    for (auto teaiUse : teai->getUses()) {
      if (!canReplaceLoadSequence(teaiUse->getUser()))
        return false;
    }
    return true;
  }

  if (auto *ba = dyn_cast<BeginAccessInst>(inst)) {
    for (auto use : ba->getUses()) {
      if (!canReplaceLoadSequence(use->getUser()))
        return false;
    }
    return true;
  }

  // Incidental uses of an address are meaningless with regard to the loaded
  // value.
  if (isIncidentalUse(inst) || isa<BeginUnpairedAccessInst>(inst))
    return true;

  return false;
}

/// Replace load sequence which may contain
/// a chain of struct_element_addr followed by a load.
/// The sequence is traversed inside out, i.e.
/// starting with the innermost struct_element_addr
/// Move into utils.
///
/// FIXME: this utility does not make sense as an API. How can the caller
/// guarantee that the only uses of `I` are struct_element_addr and
/// tuple_element_addr?
void swift::replaceLoadSequence(SILInstruction *inst, SILValue value) {
  if (auto *cai = dyn_cast<CopyAddrInst>(inst)) {
    SILBuilder builder(cai);
    builder.createStore(cai->getLoc(), value, cai->getDest(),
                        StoreOwnershipQualifier::Unqualified);
    return;
  }

  if (auto *li = dyn_cast<LoadInst>(inst)) {
    li->replaceAllUsesWith(value);
    return;
  }

  if (auto *seai = dyn_cast<StructElementAddrInst>(inst)) {
    SILBuilder builder(seai);
    auto *sei =
        builder.createStructExtract(seai->getLoc(), value, seai->getField());
    for (auto seaiUse : seai->getUses()) {
      replaceLoadSequence(seaiUse->getUser(), sei);
    }
    return;
  }

  if (auto *teai = dyn_cast<TupleElementAddrInst>(inst)) {
    SILBuilder builder(teai);
    auto *tei =
        builder.createTupleExtract(teai->getLoc(), value, teai->getFieldIndex());
    for (auto teaiUse : teai->getUses()) {
      replaceLoadSequence(teaiUse->getUser(), tei);
    }
    return;
  }

  if (auto *ba = dyn_cast<BeginAccessInst>(inst)) {
    for (auto use : ba->getUses()) {
      replaceLoadSequence(use->getUser(), value);
    }
    return;
  }

  // Incidental uses of an address are meaningless with regard to the loaded
  // value.
  if (isIncidentalUse(inst) || isa<BeginUnpairedAccessInst>(inst))
    return;

  llvm_unreachable("Unknown instruction sequence for reading from a global");
}

std::optional<FindLocalApplySitesResult>
swift::findLocalApplySites(FunctionRefBaseInst *fri) {
  SmallVector<Operand *, 32> worklist(fri->use_begin(), fri->use_end());

  std::optional<FindLocalApplySitesResult> f;
  f.emplace();

  // Optimistically state that we have no escapes before our def-use dataflow.
  f->escapes = false;

  while (!worklist.empty()) {
    auto *op = worklist.pop_back_val();
    auto *user = op->getUser();

    // If we have a full apply site as our user.
    if (auto apply = FullApplySite::isa(user)) {
      if (apply.getCallee() == op->get()) {
        f->fullApplySites.push_back(apply);
        continue;
      }
    }

    // If we have a partial apply as a user, start tracking it, but also look at
    // its users.
    if (auto *pai = dyn_cast<PartialApplyInst>(user)) {
      if (pai->getCallee() == op->get()) {
        // Track the partial apply that we saw so we can potentially eliminate
        // dead closure arguments.
        f->partialApplySites.push_back(pai);
        // Look to see if we can find a full application of this partial apply
        // as well.
        llvm::copy(pai->getUses(), std::back_inserter(worklist));
        continue;
      }
    }

    // Otherwise, see if we have any function casts to look through...
    switch (user->getKind()) {
    case SILInstructionKind::ThinToThickFunctionInst:
    case SILInstructionKind::ConvertFunctionInst:
    case SILInstructionKind::ConvertEscapeToNoEscapeInst:
      llvm::copy(cast<SingleValueInstruction>(user)->getUses(),
                 std::back_inserter(worklist));
      continue;

    // A partial_apply [stack] marks its captured arguments with
    // mark_dependence.
    case SILInstructionKind::MarkDependenceInst:
      llvm::copy(cast<SingleValueInstruction>(user)->getUses(),
                 std::back_inserter(worklist));
      continue;

    // Look through any reference count instructions since these are not
    // escapes:
    case SILInstructionKind::CopyValueInst:
      llvm::copy(cast<CopyValueInst>(user)->getUses(),
                 std::back_inserter(worklist));
      continue;
    case SILInstructionKind::StrongRetainInst:
    case SILInstructionKind::StrongReleaseInst:
    case SILInstructionKind::RetainValueInst:
    case SILInstructionKind::ReleaseValueInst:
    case SILInstructionKind::DestroyValueInst:
    // A partial_apply [stack] is deallocated with a dealloc_stack.
    case SILInstructionKind::DeallocStackInst:
      continue;
    default:
      break;
    }

    // But everything else is considered an escape.
    f->escapes = true;
  }

  // If we did escape and didn't find any apply sites, then we have no
  // information for our users that is interesting.
  if (f->escapes && f->partialApplySites.empty() && f->fullApplySites.empty())
    return std::nullopt;
  return f;
}

/// Insert destroys of captured arguments of partial_apply [stack].
void swift::insertDestroyOfCapturedArguments(
    PartialApplyInst *pai, SILBuilder &builder,
    llvm::function_ref<SILValue(SILValue)> getValueToDestroy,
    SILLocation origLoc) {
  assert(pai->isOnStack());

  ApplySite site(pai);
  SILFunctionConventions calleeConv(site.getSubstCalleeType(),
                                    pai->getModule());
  auto loc = CleanupLocation(origLoc);
  for (auto &arg : pai->getArgumentOperands()) {
    SILValue argValue = getValueToDestroy(arg.get());
    if (!argValue)
      continue;

    assert(!pai->getFunction()->hasOwnership()
           || (argValue->getOwnershipKind().isCompatibleWith(
                 OwnershipKind::Owned)));

    unsigned calleeArgumentIndex = site.getCalleeArgIndex(arg);
    assert(calleeArgumentIndex >= calleeConv.getSILArgIndexOfFirstParam());
    auto paramInfo = calleeConv.getParamInfoForSILArg(calleeArgumentIndex);
    releasePartialApplyCapturedArg(builder, loc, argValue, paramInfo);
  }
}

void swift::insertDeallocOfCapturedArguments(
  PartialApplyInst *pai,
  DominanceInfo *domInfo,
  llvm::function_ref<SILValue(SILValue)> getAddressToDealloc)
{
  assert(pai->isOnStack());

  ApplySite site(pai);
  SILFunctionConventions calleeConv(site.getSubstCalleeType(),
                                    pai->getModule());
  for (auto &arg : pai->getArgumentOperands()) {
    unsigned calleeArgumentIndex = site.getCalleeArgIndex(arg);
    assert(calleeArgumentIndex >= calleeConv.getSILArgIndexOfFirstParam());
    auto paramInfo = calleeConv.getParamInfoForSILArg(calleeArgumentIndex);
    if (!paramInfo.isIndirectInGuaranteed())
      continue;

    SILValue argValue = getAddressToDealloc(arg.get());
    if (!argValue) {
      continue;
    }

    SmallVector<SILBasicBlock *, 4> boundary;
    auto *asi = cast<AllocStackInst>(argValue);
    computeDominatedBoundaryBlocks(asi->getParent(), domInfo, boundary);

    SmallVector<Operand *, 2> uses;
    auto useFinding = findTransitiveUsesForAddress(asi, &uses);
    InstructionSet users(asi->getFunction());
    if (useFinding != AddressUseKind::Unknown) {
      for (auto use : uses) {
        users.insert(use->getUser());
      }
    }

    for (auto *block : boundary) {
      auto *terminator = block->getTerminator();
      if (isa<UnreachableInst>(terminator))
        continue;
      SILInstruction *insertionPoint = nullptr;
      if (useFinding != AddressUseKind::Unknown) {
        insertionPoint = &block->front();
        for (auto &instruction : llvm::reverse(*block)) {
          if (users.contains(&instruction)) {
            insertionPoint = instruction.getNextInstruction();
            break;
          }
        }
      } else {
        insertionPoint = terminator;
      }
      SILBuilderWithScope builder(insertionPoint);
      builder.createDeallocStack(CleanupLocation(insertionPoint->getLoc()),
                                 argValue);
    }
  }
}

AbstractFunctionDecl *swift::getBaseMethod(AbstractFunctionDecl *FD) {
  while (FD->getOverriddenDecl()) {
    FD = FD->getOverriddenDecl();
  }
  return FD;
}

FullApplySite
swift::cloneFullApplySiteReplacingCallee(FullApplySite applySite,
                                         SILValue newCallee,
                                         SILBuilderContext &builderCtx) {
  SmallVector<SILValue, 16> arguments;
  llvm::copy(applySite.getArguments(), std::back_inserter(arguments));

  SILBuilderWithScope builder(applySite.getInstruction(), builderCtx);

  switch (applySite.getKind()) {
  case FullApplySiteKind::TryApplyInst: {
    auto *tai = cast<TryApplyInst>(applySite.getInstruction());
    return builder.createTryApply(tai->getLoc(), newCallee,
                                  tai->getSubstitutionMap(), arguments,
                                  tai->getNormalBB(), tai->getErrorBB(),
                                  tai->getApplyOptions());
  }
  case FullApplySiteKind::ApplyInst: {
    auto *ai = cast<ApplyInst>(applySite);
    auto fTy = newCallee->getType().getAs<SILFunctionType>();

    auto options = ai->getApplyOptions();
    // The optimizer can generate a thin_to_thick_function from a throwing thin
    // to a non-throwing thick function (in case it can prove that the function
    // is not throwing).
    // Therefore we have to check if the new callee (= the argument of the
    // thin_to_thick_function) is a throwing function and set the not-throwing
    // flag in this case.
    if (fTy->hasErrorResult())
      options |= ApplyFlags::DoesNotThrow;
    return builder.createApply(applySite.getLoc(), newCallee,
                               applySite.getSubstitutionMap(), arguments,
                               options);
  }
  case FullApplySiteKind::BeginApplyInst: {
    llvm_unreachable("begin_apply support not implemented?!");
  }
  }
  llvm_unreachable("Unhandled case?!");
}

// FIXME: For any situation where this may be called on an unbounded number of
// uses, it should perform a single callback invocation to notify the client
// that newValue has new uses rather than a callback for every new use.
//
// FIXME: This should almost certainly replace end_lifetime uses rather than
// deleting them.
SILBasicBlock::iterator swift::replaceAllUses(SILValue oldValue,
                                              SILValue newValue,
                                              SILBasicBlock::iterator nextii,
                                              InstModCallbacks &callbacks) {
  assert(oldValue != newValue && "Cannot RAUW a value with itself");
  while (!oldValue->use_empty()) {
    Operand *use = *oldValue->use_begin();
    SILInstruction *user = use->getUser();
    // Erase the end of scope marker.
    if (isEndOfScopeMarker(user)) {
      if (&*nextii == user)
        ++nextii;
      callbacks.deleteInst(user);
      continue;
    }
    callbacks.setUseValue(use, newValue);
  }
  return nextii;
}

SILBasicBlock::iterator
swift::replaceAllUsesAndErase(SingleValueInstruction *svi, SILValue newValue,
                              InstModCallbacks &callbacks) {
  SILBasicBlock::iterator nextii = replaceAllUses(
      svi, newValue, std::next(svi->getIterator()), callbacks);

  callbacks.deleteInst(svi);

  return nextii;
}

SILBasicBlock::iterator
swift::replaceAllUsesAndErase(SILValue oldValue, SILValue newValue,
                              InstModCallbacks &callbacks) {
  auto *blockArg = dyn_cast<SILPhiArgument>(oldValue);
  if (!blockArg) {
    // SingleValueInstruction SSA replacement.
    return replaceAllUsesAndErase(cast<SingleValueInstruction>(oldValue),
                                  newValue, callbacks);
  }
  llvm_unreachable("Untested");
#if 0 // FIXME: to be enabled in a following commit
  TermInst *oldTerm = blockArg->getTerminatorForResult();
  assert(oldTerm && "can only replace and erase terminators, not phis");

  // Before:
  //     oldTerm bb1, bb2
  //   bb1(%oldValue):
  //     use %oldValue
  //   bb2:
  //
  // After:
  //     br bb1
  //   bb1:
  //     use %newValue
  //   bb2:

  auto nextii = replaceAllUses(blockArg, newValue,
                               oldTerm->getParent()->end(), callbacks);
  // Now that oldValue is replaced, the terminator should have no uses
  // left. The caller should have removed uses from other results.
  for (auto *succBB : oldTerm->getSuccessorBlocks()) {
    assert(succBB->getNumArguments() == 1 && "expected terminator result");
    succBB->eraseArgument(0);
  }
  auto *newBr = SILBuilderWithScope(oldTerm).createBranch(
    oldTerm->getLoc(), blockArg->getParent());
  callbacks.createdNewInst(newBr);
  callbacks.deleteInst(oldTerm);
  return nextii;
#endif
}

/// Given that we are going to replace use's underlying value, if the use is a
/// lifetime ending use, insert an end scope use for the underlying value
/// before we RAUW.
static void cleanupUseOldValueBeforeRAUW(Operand *use, SILBuilder &builder,
                                         SILLocation loc,
                                         InstModCallbacks &callbacks) {
  if (!use->isLifetimeEnding()) {
    return;
  }

  switch (use->get()->getOwnershipKind()) {
  case OwnershipKind::Any:
    llvm_unreachable("Invalid ownership for value");
  case OwnershipKind::Owned: {
    auto *dvi = builder.createDestroyValue(loc, use->get());
    callbacks.createdNewInst(dvi);
    return;
  }
  case OwnershipKind::Guaranteed: {
    // Should only happen once we model destructures as true reborrows.
    auto *ebi = builder.createEndBorrow(loc, use->get());
    callbacks.createdNewInst(ebi);
    return;
  }
  case OwnershipKind::None:
    return;
  case OwnershipKind::Unowned:
    llvm_unreachable("Unowned object can never be consumed?!");
  }
  llvm_unreachable("Covered switch isn't covered");
}

SILBasicBlock::iterator swift::replaceSingleUse(Operand *use, SILValue newValue,
                                                InstModCallbacks &callbacks) {
  auto oldValue = use->get();
  assert(oldValue != newValue && "Cannot RAUW a value with itself");

  auto *user = use->getUser();
  auto nextII = std::next(user->getIterator());

  // If we have an end of scope marker, just return next. We are done.
  if (isEndOfScopeMarker(user)) {
    return nextII;
  }

  // Otherwise, first insert clean up our use's value if we need to and then set
  // use to have a new value.
  SILBuilderWithScope builder(user);
  cleanupUseOldValueBeforeRAUW(use, builder, user->getLoc(), callbacks);
  callbacks.setUseValue(use, newValue);

  return nextII;
}

SILValue swift::makeCopiedValueAvailable(SILValue value, SILBasicBlock *inBlock) {
  if (isa<SILUndef>(value))
    return value;

  if (!value->getFunction()->hasOwnership())
    return value;

  if (value->getOwnershipKind() == OwnershipKind::None)
    return value;

  auto insertPt = getInsertAfterPoint(value).value();
  SILBuilderWithScope builder(insertPt);
  auto *copy = builder.createCopyValue(
      RegularLocation::getAutoGeneratedLocation(), value);

  return makeValueAvailable(copy, inBlock);
}

SILValue swift::makeValueAvailable(SILValue value, SILBasicBlock *inBlock) {
  if (isa<SILUndef>(value))
    return value;

  if (!value->getFunction()->hasOwnership())
    return value;

  if (value->getOwnershipKind() == OwnershipKind::None)
    return value;

  assert(value->getOwnershipKind() == OwnershipKind::Owned);

  SmallVector<SILBasicBlock *, 4> userBBs;
  for (auto use : value->getUses()) {
    userBBs.push_back(use->getParentBlock());
  }
  userBBs.push_back(inBlock);

  // Use \p jointPostDomComputer to:
  // 1. Create a control equivalent copy at \p inBlock if needed
  // 2. Insert destroy_value at leaking blocks
  SILValue controlEqCopy;
  findJointPostDominatingSet(
      value->getParentBlock(), userBBs,
      [&](SILBasicBlock *loopBlock) {
        assert(loopBlock == inBlock);
        auto front = loopBlock->begin();
        SILBuilderWithScope newBuilder(front);
        controlEqCopy = newBuilder.createCopyValue(
            RegularLocation::getAutoGeneratedLocation(), value);
      },
      [&](SILBasicBlock *postDomBlock) {
        // Insert a destroy_value in the leaking block
        auto front = postDomBlock->begin();
        SILBuilderWithScope newBuilder(front);
        newBuilder.createDestroyValue(
            RegularLocation::getAutoGeneratedLocation(), value);
      });

  return controlEqCopy ? controlEqCopy : value;
}

bool swift::tryEliminateOnlyOwnershipUsedForwardingInst(
    SingleValueInstruction *forwardingInst, InstModCallbacks &callbacks) {
  auto fwdOp = ForwardingOperation(forwardingInst);
  if (!fwdOp) {
    return false;
  }
  auto *singleFwdOp = fwdOp.getSingleForwardingOperand();
  if (!singleFwdOp) {
    return false;
  }

  SmallVector<Operand *, 32> worklist(getNonDebugUses(forwardingInst));
  while (!worklist.empty()) {
    auto *use = worklist.pop_back_val();
    auto *user = use->getUser();

    if (isa<EndBorrowInst>(user) || isa<DestroyValueInst>(user) ||
        isa<RefCountingInst>(user))
      continue;

    if (isa<CopyValueInst>(user) || isa<BeginBorrowInst>(user)) {
      for (auto result : user->getResults())
        for (auto *resultUse : getNonDebugUses(result))
          worklist.push_back(resultUse);
      continue;
    }

    return false;
  }

  // Now that we know we can perform our transform, set all uses of
  // forwardingInst to be used of its operand and then delete \p forwardingInst.
  auto newValue = singleFwdOp->get();
  while (!forwardingInst->use_empty()) {
    auto *use = *(forwardingInst->use_begin());
    use->set(newValue);
  }

  callbacks.deleteInst(forwardingInst);
  return true;
}

// The consuming use blocks are assumed either not to inside a loop relative to
// \p value or they must have their own copies.
void swift::endLifetimeAtLeakingBlocks(SILValue value,
                                       ArrayRef<SILBasicBlock *> uses) {
  if (!value->getFunction()->hasOwnership())
    return;

  if (value->getOwnershipKind() != OwnershipKind::Owned)
    return;

  findJointPostDominatingSet(
      value->getParentBlock(), uses, [&](SILBasicBlock *loopBlock) {},
      [&](SILBasicBlock *postDomBlock) {
        // Insert a destroy_value in the leaking block
        auto front = postDomBlock->begin();
        SILBuilderWithScope newBuilder(front);
        newBuilder.createDestroyValue(
            RegularLocation::getAutoGeneratedLocation(), value);
      });
}

/// Create a new debug value from a store and a debug variable.
static void transferStoreDebugValue(DebugVarCarryingInst DefiningInst,
                                    SILInstruction *SI,
                                    SILValue original) {
  auto VarInfo = DefiningInst.getVarInfo();
  if (!VarInfo)
    return;
  // Fix the op_deref.
  if (!isa<CopyAddrInst>(SI) && VarInfo->DIExpr.startsWithDeref())
    VarInfo->DIExpr.eraseElement(VarInfo->DIExpr.element_begin());
  else if (isa<CopyAddrInst>(SI) && !VarInfo->DIExpr.startsWithDeref())
    VarInfo->DIExpr.prependElements({
      SILDIExprElement::createOperator(SILDIExprOperator::Dereference)});
  // Note: The instruction should logically be in the SI's scope.
  // However, LLVM does not support variables and stores in different scopes,
  // so we use the variable's scope.
  SILBuilder(SI, DefiningInst->getDebugScope())
    .createDebugValue(SI->getLoc(), original, *VarInfo);
}

void swift::salvageStoreDebugInfo(SILInstruction *SI,
                                  SILValue SrcVal, SILValue DestVal) {
  if (auto *ASI = dyn_cast_or_null<AllocStackInst>(
          DestVal.getDefiningInstruction())) {
    transferStoreDebugValue(ASI, SI, SrcVal);
    for (Operand *U : getDebugUses(ASI))
      transferStoreDebugValue(U->getUser(), SI, SrcVal);
  }
}

// TODO: this currently fails to notify the pass with notifyNewInstruction.
//
// TODO: whenever a debug_value is inserted at a new location, check that no
// other debug_value instructions exist between the old and new location for
// the same variable.
void swift::salvageDebugInfo(SILInstruction *I) {
  if (!I)
    return;

  if (auto *SI = dyn_cast<StoreInst>(I)) {
    if (SILValue DestVal = SI->getDest())
      salvageStoreDebugInfo(SI, SI->getSrc(), DestVal);
  }
  if (auto *SI = dyn_cast<StoreBorrowInst>(I)) {
    if (SILValue DestVal = SI->getDest())
      salvageStoreDebugInfo(SI, SI->getSrc(), DestVal);
    for (Operand *U : getDebugUses(SI))
      transferStoreDebugValue(U->getUser(), SI, SI->getSrc());
  }
  // If a `struct` SIL instruction is "unwrapped" and removed,
  // for instance, in favor of using its enclosed value directly,
  // we need to make sure any of its related `debug_value` instructions
  // are preserved.
  if (auto *STI = dyn_cast<StructInst>(I)) {
    auto STVal = STI->getResult(0);
    llvm::ArrayRef<VarDecl *> FieldDecls =
      STI->getStructDecl()->getStoredProperties();
    for (Operand *U : getDebugUses(STVal)) {
      auto *DbgInst = cast<DebugValueInst>(U->getUser());
      auto VarInfo = DbgInst->getVarInfo();
      if (!VarInfo)
        continue;
      for (VarDecl *FD : FieldDecls) {
        SILDebugVariable NewVarInfo = *VarInfo;
        auto FieldVal = STI->getFieldValue(FD);
        // Build the corresponding fragment DIExpression
        auto FragDIExpr = SILDebugInfoExpression::createFragment(FD);
        NewVarInfo.DIExpr.append(FragDIExpr);

        if (!NewVarInfo.Type)
          NewVarInfo.Type = STI->getType();

        // Create a new debug_value
        SILBuilder(STI, DbgInst->getDebugScope())
          .createDebugValue(DbgInst->getLoc(), FieldVal, NewVarInfo);
      }
    }
  }
  // Similarly, if a `tuple` SIL instruction is "unwrapped" and removed,
  // we need to make sure any of its related `debug_value` instructions
  // are preserved.
  if (auto *TTI = dyn_cast<TupleInst>(I)) {
    auto TTVal = TTI->getResult(0);
    for (Operand *U : getDebugUses(TTVal)) {
      auto *DbgInst = cast<DebugValueInst>(U->getUser());
      auto VarInfo = DbgInst->getVarInfo();
      if (!VarInfo)
        continue;
      TupleType *TT = TTI->getTupleType();
      for (auto i : indices(TT->getElements())) {
        SILDebugVariable NewVarInfo = *VarInfo;
        auto FragDIExpr = SILDebugInfoExpression::createTupleFragment(TT, i);
        NewVarInfo.DIExpr.append(FragDIExpr);

        if (!NewVarInfo.Type)
          NewVarInfo.Type = TTI->getType();

        // Create a new debug_value
        SILBuilder(TTI, DbgInst->getDebugScope())
          .createDebugValue(DbgInst->getLoc(), TTI->getElement(i), NewVarInfo);
      }
    }
  }

  if (auto *IA = dyn_cast<IndexAddrInst>(I)) {
    if (IA->getBase() && IA->getIndex())
      // Only handle cases where offset is constant.
      if (const auto *LiteralInst =
            dyn_cast<IntegerLiteralInst>(IA->getIndex())) {
        SILValue Base = IA->getBase();
        SILValue ResultAddr = IA->getResult(0);
        APInt OffsetVal = LiteralInst->getValue();
        const SILDIExprElement ExprElements[3] = {
          SILDIExprElement::createOperator(OffsetVal.isNegative() ?
            SILDIExprOperator::ConstSInt : SILDIExprOperator::ConstUInt),
          SILDIExprElement::createConstInt(OffsetVal.getLimitedValue()),
          SILDIExprElement::createOperator(SILDIExprOperator::Plus)
        };
        for (Operand *U : getDebugUses(ResultAddr)) {
          auto *DbgInst = cast<DebugValueInst>(U->getUser());
          auto VarInfo = DbgInst->getVarInfo();
          if (!VarInfo)
            continue;
          VarInfo->DIExpr.prependElements(ExprElements);
          // Create a new debug_value
          SILBuilder(IA, DbgInst->getDebugScope())
            .createDebugValue(DbgInst->getLoc(), Base, *VarInfo);
        }
      }
  }

  if (auto *IL = dyn_cast<IntegerLiteralInst>(I)) {
    APInt value = IL->getValue();
    const SILDIExprElement ExprElements[2] = {
      SILDIExprElement::createOperator(value.isNegative() ?
        SILDIExprOperator::ConstSInt : SILDIExprOperator::ConstUInt),
      SILDIExprElement::createConstInt(value.getLimitedValue()),
    };
    for (Operand *U : getDebugUses(IL)) {
      auto *DbgInst = cast<DebugValueInst>(U->getUser());
      auto VarInfo = DbgInst->getVarInfo();
      if (!VarInfo)
        continue;
      VarInfo->DIExpr.prependElements(ExprElements);
      // Create a new debug_value, with undef, and the correct const int
      SILBuilder(DbgInst, DbgInst->getDebugScope())
        .createDebugValue(DbgInst->getLoc(), SILUndef::get(IL), *VarInfo);
    }
  }
}

void swift::salvageLoadDebugInfo(LoadOperation load) {
  for (Operand *debugUse : getDebugUses(load.getLoadInst())) {
    // Create a new debug_value rather than reusing the old one so the
    // SILBuilder adds 'expr(deref)' to account for the indirection.
    auto *debugInst = cast<DebugValueInst>(debugUse->getUser());
    auto varInfo = debugInst->getVarInfo();
    if (!varInfo)
      continue;

    // The new debug_value must be "hoisted" to the load to ensure that the
    // address is still valid.
    SILBuilder(load.getLoadInst(), debugInst->getDebugScope())
      .createDebugValueAddr(debugInst->getLoc(), load.getOperand(),
                            varInfo.value());
  }
}

// TODO: this currently fails to notify the pass with notifyNewInstruction.
void swift::createDebugFragments(SILValue oldValue, Projection proj,
                                 SILValue newValue) {
  if (proj.getKind() != ProjectionKind::Struct)
    return;

  for (auto *use : getDebugUses(oldValue)) {
    auto debugVal = dyn_cast<DebugValueInst>(use->getUser());
    if (!debugVal)
      continue;

    auto varInfo = debugVal->getVarInfo();

    SILType baseType = oldValue->getType();

    // Copy VarInfo and add the corresponding fragment DIExpression.
    SILDebugVariable newVarInfo = *varInfo;
    newVarInfo.DIExpr.append(
        SILDebugInfoExpression::createFragment(proj.getVarDecl(baseType)));

    if (!newVarInfo.Type)
      newVarInfo.Type = baseType;

    // Create a new debug_value
    SILBuilder(debugVal, debugVal->getDebugScope())
        .createDebugValue(debugVal->getLoc(), newValue, newVarInfo);
  }
}

IntegerLiteralInst *swift::optimizeBuiltinCanBeObjCClass(BuiltinInst *bi,
                                                         SILBuilder &builder) {
  assert(bi->getBuiltinInfo().ID == BuiltinValueKind::CanBeObjCClass);
  assert(bi->hasSubstitutions() && "Expected substitutions for canBeClass");

  auto const &subs = bi->getSubstitutions();
  assert((subs.getReplacementTypes().size() == 1) &&
         "Expected one substitution in call to canBeClass");

  auto ty = subs.getReplacementTypes()[0]->getCanonicalType();
  switch (ty->canBeClass()) {
  case TypeTraitResult::IsNot:
    return builder.createIntegerLiteral(bi->getLoc(), bi->getType(),
                                        APInt(8, 0));
  case TypeTraitResult::Is:
    return builder.createIntegerLiteral(bi->getLoc(), bi->getType(),
                                        APInt(8, 1));
  case TypeTraitResult::CanBe:
    return nullptr;
  }
  llvm_unreachable("Unhandled TypeTraitResult in switch.");
}

SILValue swift::createEmptyAndUndefValue(SILType ty,
                                         SILInstruction *insertionPoint,
                                         SILBuilderContext &ctx,
                                         bool noUndef) {
  auto *function = insertionPoint->getFunction();
  if (auto tupleTy = ty.getAs<TupleType>()) {
    SmallVector<SILValue, 4> elements;
    for (unsigned idx : range(tupleTy->getNumElements())) {
      SILType elementTy = ty.getTupleElementType(idx);
      auto element = createEmptyAndUndefValue(elementTy, insertionPoint, ctx);
      elements.push_back(element);
    }
    SILBuilderWithScope builder(insertionPoint, ctx);
    return builder.createTuple(insertionPoint->getLoc(), ty, elements);
  }
  if (auto *decl = ty.getStructOrBoundGenericStruct()) {
    TypeExpansionContext tec = *function;
    auto &module = function->getModule();
    if (decl->isResilient(tec.getContext()->getParentModule(),
                          tec.getResilienceExpansion())) {
      llvm::errs() << "Attempting to create value for illegal empty type:\n";
      ty.print(llvm::errs());
      llvm::report_fatal_error("illegal empty type: resilient struct");
    }
    SmallVector<SILValue, 4> elements;
    for (auto *field : decl->getStoredProperties()) {
      auto elementTy = ty.getFieldType(field, module, tec);
      auto element = createEmptyAndUndefValue(elementTy, insertionPoint, ctx);
      elements.push_back(element);
    }
    SILBuilderWithScope builder(insertionPoint, ctx);
    return builder.createStruct(insertionPoint->getLoc(), ty, elements);
  }
  assert(!noUndef);
  return SILUndef::get(insertionPoint->getFunction(), ty);
}

bool swift::findUnreferenceableStorage(StructDecl *decl, SILType structType,
                                       SILFunction *func) {
  if (decl->hasUnreferenceableStorage()) {
    return true;
  }
  // Check if any fields have unreferenceable stoage
  for (auto *field : decl->getStoredProperties()) {
    TypeExpansionContext tec = *func;
    auto fieldTy = structType.getFieldType(field, func->getModule(), tec);
    if (auto *fieldStructDecl = fieldTy.getStructOrBoundGenericStruct()) {
      if (findUnreferenceableStorage(fieldStructDecl, fieldTy, func)) {
        return true;
      }
    }
  }
  return false;
}

//===----------------------------------------------------------------------===//
//          MARK: Find Initialization Value Of Temporary Alloc Stack
//===----------------------------------------------------------------------===//

namespace {
struct AddressWalkerState {
  bool foundError = false;
  InstructionSet writes;
  AddressWalkerState(SILFunction *fn) : writes(fn) {}
};
} // namespace

static SILValue
findRootValueForNonTupleTempAllocation(AllocationInst *allocInst,
                                       AddressWalkerState &state) {
  // These are instructions which we are ok with looking through when
  // identifying our allocation. It must always refer to the entire allocation.
  auto isAlloc = [&](SILValue value) -> bool {
    if (auto *ieai = dyn_cast<InitExistentialAddrInst>(value))
      value = ieai->getOperand();
    return value == SILValue(allocInst);
  };

  // Walk from our allocation to one of our writes. Then make sure that the
  // write writes to our entire value.
  for (auto &inst : allocInst->getParent()->getRangeStartingAtInst(allocInst)) {
    // See if we have a full tuple value.

    if (!state.writes.contains(&inst))
      continue;

    if (auto *copyAddr = dyn_cast<CopyAddrInst>(&inst)) {
      if (isAlloc(copyAddr->getDest()) && copyAddr->isInitializationOfDest()) {
        return copyAddr->getSrc();
      }
    }

    if (auto *si = dyn_cast<StoreInst>(&inst)) {
      if (isAlloc(si->getDest()) &&
          si->getOwnershipQualifier() != StoreOwnershipQualifier::Assign) {
        return si->getSrc();
      }
    }

    if (auto *sbi = dyn_cast<StoreBorrowInst>(&inst)) {
      if (isAlloc(sbi->getDest()))
        return sbi->getSrc();
    }

    // If we do not identify the write... return SILValue(). We weren't able
    // to understand the write.
    break;
  }

  return SILValue();
}

static SILValue findRootValueForTupleTempAllocation(AllocationInst *allocInst,
                                                    AddressWalkerState &state) {
  SmallVector<SILValue, 8> tupleValues;

  for (unsigned i : range(allocInst->getType().getNumTupleElements())) {
    (void)i;
    tupleValues.push_back(nullptr);
  }

  unsigned numEltsLeft = tupleValues.size();

  // If we have an empty tuple, just return SILValue() for now.
  //
  // TODO: What does this pattern look like out of SILGen?
  if (!numEltsLeft)
    return SILValue();

  // Walk from our allocation to one of our writes. Then make sure that the
  // write writes to our entire value.
  DestructureTupleInst *foundDestructure = nullptr;
  SILValue foundRootAddress;
  for (auto &inst : allocInst->getParent()->getRangeStartingAtInst(allocInst)) {
    if (!state.writes.contains(&inst))
      continue;

    if (auto *copyAddr = dyn_cast<CopyAddrInst>(&inst)) {
      if (copyAddr->isInitializationOfDest()) {
        if (auto *tei = dyn_cast<TupleElementAddrInst>(copyAddr->getDest())) {
          if (tei->getOperand() == allocInst) {
            unsigned i = tei->getFieldIndex();
            if (auto *otherTei = dyn_cast_or_null<TupleElementAddrInst>(
                    copyAddr->getSrc()->getDefiningInstruction())) {
              // If we already were processing destructures, then we have a mix
              // of struct/destructures... we do not support that, so bail.
              if (foundDestructure)
                return SILValue();

              // Otherwise, update our root address. If we already had a root
              // address and it doesn't match our tuple_element_addr's operand,
              // bail. There is some sort of mix/match of tuple addresses that
              // we do not support. We are looking for a specific SILGen
              // pattern.
              if (!foundRootAddress) {
                foundRootAddress = otherTei->getOperand();
              } else if (foundRootAddress != otherTei->getOperand()) {
                return SILValue();
              }

              if (i != otherTei->getFieldIndex())
                return SILValue();
              if (tupleValues[i])
                return SILValue();
              tupleValues[i] = otherTei;

              // If we have completely covered the tuple, break.
              --numEltsLeft;
              if (!numEltsLeft)
                break;

              // Otherwise, continue so we keep processing.
              continue;
            }
          }
        }
      }
    }

    if (auto *si = dyn_cast<StoreInst>(&inst)) {
      if (si->getOwnershipQualifier() != StoreOwnershipQualifier::Assign) {
        // Check if we are updating the entire tuple value.
        if (si->getDest() == allocInst) {
          // If we already found a root address (meaning we were processing
          // tuple_elt_addr), bail. We have some sort of unhandled mix of
          // copy_addr and store.
          if (foundRootAddress)
            return SILValue();

          // If we already found a destructure, return SILValue(). We are
          // initializing twice.
          if (foundDestructure)
            return SILValue();

          // We are looking for a pattern where we construct a tuple from
          // destructured parts.
          if (auto *ti = dyn_cast<TupleInst>(si->getSrc())) {
            for (auto p : llvm::enumerate(ti->getOperandValues())) {
              SILValue value = lookThroughOwnershipInsts(p.value());
              if (auto *dti = dyn_cast_or_null<DestructureTupleInst>(
                      value->getDefiningInstruction())) {
                // We should always go through the same dti.
                if (foundDestructure && foundDestructure != dti)
                  return SILValue();
                if (!foundDestructure)
                  foundDestructure = dti;

                // If we have a mixmatch of indices, we cannot look through.
                if (p.index() != dti->getIndexOfResult(value))
                  return SILValue();
                if (tupleValues[p.index()])
                  return SILValue();
                tupleValues[p.index()] = value;

                // If we have completely covered the tuple, break.
                --numEltsLeft;
                if (!numEltsLeft)
                  break;
              }
            }

            // If we haven't completely covered the tuple, return SILValue(). We
            // should completely cover the tuple.
            if (numEltsLeft)
              return SILValue();

            // Otherwise, break since we are done.
            break;
          }
        }

        // If we store to a tuple_element_addr, update for a single value.
        if (auto *tei = dyn_cast<TupleElementAddrInst>(si->getDest())) {
          if (tei->getOperand() == allocInst) {
            unsigned i = tei->getFieldIndex();
            if (auto *dti = dyn_cast_or_null<DestructureTupleInst>(
                    si->getSrc()->getDefiningInstruction())) {
              // If we already found a root address (meaning we were processing
              // tuple_elt_addr), bail. We have some sort of unhandled mix of
              // copy_addr and store [init].
              if (foundRootAddress)
                return SILValue();
              if (!foundDestructure) {
                foundDestructure = dti;
              } else if (foundDestructure != dti) {
                return SILValue();
              }

              if (i != dti->getIndexOfResult(si->getSrc()))
                return SILValue();
              if (tupleValues[i])
                return SILValue();
              tupleValues[i] = si->getSrc();

              // If we have completely covered the tuple, break.
              --numEltsLeft;
              if (!numEltsLeft)
                break;

              // Otherwise, continue so we keep processing.
              continue;
            }
          }
        }
      }
    }

    // Found a write that we did not understand... bail.
    break;
  }

  // Now check if we have a complete tuple with all elements coming from the
  // same destructure_tuple. In such a case, we can look through the
  // destructure_tuple.
  if (numEltsLeft)
    return SILValue();

  if (foundDestructure)
    return foundDestructure->getOperand();
  if (foundRootAddress)
    return foundRootAddress;

  return SILValue();
}

SILValue swift::getInitOfTemporaryAllocStack(AllocStackInst *asi) {
  // If we are from a VarDecl, bail.
  if (asi->isFromVarDecl())
    return SILValue();

  struct AddressWalker final : public TransitiveAddressWalker<AddressWalker> {
    AddressWalkerState &state;

    AddressWalker(AddressWalkerState &state) : state(state) {}

    bool visitUse(Operand *use) {
      if (use->getUser()->mayWriteToMemory())
        state.writes.insert(use->getUser());
      return true;
    }

    TransitiveUseVisitation visitTransitiveUseAsEndPointUse(Operand *use) {
      if (auto *sbi = dyn_cast<StoreBorrowInst>(use->getUser()))
        return TransitiveUseVisitation::OnlyUser;
      return TransitiveUseVisitation::OnlyUses;
    }

    void onError(Operand *use) { state.foundError = true; }
  };

  AddressWalkerState state(asi->getFunction());
  AddressWalker walker(state);
  if (std::move(walker).walk(asi) == AddressUseKind::Unknown ||
      state.foundError)
    return SILValue();

  if (asi->getType().is<TupleType>())
    return findRootValueForTupleTempAllocation(asi, state);
  return findRootValueForNonTupleTempAllocation(asi, state);
}