//===--- Enum.cpp - Runtime declarations for enums ------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 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
//
//===----------------------------------------------------------------------===//
//
// Swift runtime functions in support of enums.
//
//===----------------------------------------------------------------------===//

#include "swift/Runtime/Metadata.h"
#include "swift/Runtime/Enum.h"
#include "swift/Runtime/Debug.h"
#include "Private.h"
#include "BytecodeLayouts.h"
#include "EnumImpl.h"
#include "MetadataCache.h"
#include <cstring>
#include <algorithm>

using namespace swift;

// So remote inspection/debugging tools can obtain
// information about this process.
SWIFT_RUNTIME_STDLIB_SPI
const uint64_t _swift_debug_multiPayloadEnumPointerSpareBitsMask
  = _swift_abi_SwiftSpareBitsMask;

static EnumValueWitnessTable *getMutableVWTableForInit(EnumMetadata *self,
                                                       EnumLayoutFlags flags) {
  auto oldTable =
    static_cast<const EnumValueWitnessTable *>(self->getValueWitnesses());

  // If we can alter the existing table in-place, do so.
  if (isValueWitnessTableMutable(flags))
    return const_cast<EnumValueWitnessTable*>(oldTable);

  // Otherwise, allocate permanent memory for it and copy the existing table.
  void *memory = allocateMetadata(sizeof(EnumValueWitnessTable),
                                  alignof(EnumValueWitnessTable));
  auto newTable = new (memory) EnumValueWitnessTable(*oldTable);
  self->setValueWitnesses(newTable);

  return newTable;
}

void
swift::swift_initEnumMetadataSingleCase(EnumMetadata *self,
                                        EnumLayoutFlags layoutFlags,
                                        const TypeLayout *payloadLayout) {
  auto vwtable = getMutableVWTableForInit(self, layoutFlags);

  TypeLayout layout;
  layout.size = payloadLayout->size;
  layout.stride = payloadLayout->stride;
  layout.flags = payloadLayout->flags.withEnumWitnesses(true);
  layout.extraInhabitantCount = payloadLayout->getNumExtraInhabitants();

  vwtable->publishLayout(layout);
}

void swift::swift_initEnumMetadataSingleCaseWithLayoutString(
    EnumMetadata *self, EnumLayoutFlags layoutFlags,
    const Metadata *payloadType) {
  assert(self->hasLayoutString());

  auto payloadLayout = payloadType->getTypeLayout();
  auto vwtable = getMutableVWTableForInit(self, layoutFlags);

  TypeLayout layout;
  layout.size = payloadLayout->size;
  layout.stride = payloadLayout->stride;
  layout.flags = payloadLayout->flags.withEnumWitnesses(true);
  layout.extraInhabitantCount = payloadLayout->getNumExtraInhabitants();

  auto refCountBytes = _swift_refCountBytesForMetatype(payloadType);
  const size_t fixedLayoutStringSize =
      layoutStringHeaderSize + sizeof(uint64_t);

  uint8_t *layoutStr =
      (uint8_t *)MetadataAllocator(LayoutStringTag)
          .Allocate(llvm::alignTo(fixedLayoutStringSize + refCountBytes,
                                  sizeof(void *)),
                    alignof(uint8_t));

  LayoutStringWriter writer{layoutStr, sizeof(uint64_t)};
  writer.writeBytes(refCountBytes);
  size_t fullOffset = 0;
  size_t previousFieldOffset = 0;
  LayoutStringFlags flags = LayoutStringFlags::Empty;

  _swift_addRefCountStringForMetatype(writer, flags, payloadType, fullOffset,
                                      previousFieldOffset);

  writer.writeBytes((uint64_t)previousFieldOffset);

  // we mask out HasRelativePointers, because at this point they have all been
  // resolved to metadata pointers
  writer.offset = 0;
  writer.writeBytes(((uint64_t)flags) &
                    ~((uint64_t)LayoutStringFlags::HasRelativePointers));

  vwtable->destroy = swift_generic_destroy;
  vwtable->initializeWithCopy = swift_generic_initWithCopy;
  vwtable->initializeWithTake = swift_generic_initWithTake;
  vwtable->assignWithCopy = swift_generic_assignWithCopy;
  vwtable->assignWithTake = swift_generic_assignWithTake;

  installCommonValueWitnesses(layout, vwtable);

  self->setLayoutString(layoutStr);

  vwtable->publishLayout(layout);
}

void
swift::swift_initEnumMetadataSinglePayload(EnumMetadata *self,
                                           EnumLayoutFlags layoutFlags,
                                           const TypeLayout *payloadLayout,
                                           unsigned emptyCases) {
  size_t payloadSize = payloadLayout->size;
  unsigned payloadNumExtraInhabitants
    = payloadLayout->getNumExtraInhabitants();
  
  unsigned unusedExtraInhabitants = 0;
  
  // If there are enough extra inhabitants for all of the cases, then the size
  // of the enum is the same as its payload.
  size_t size;
  if (payloadNumExtraInhabitants >= emptyCases) {
    size = payloadSize;
    unusedExtraInhabitants = payloadNumExtraInhabitants - emptyCases;
  } else {
    size = payloadSize + getEnumTagCounts(payloadSize,
                                      emptyCases - payloadNumExtraInhabitants,
                                        1 /*payload case*/).numTagBytes; ;
  }

  auto vwtable = getMutableVWTableForInit(self, layoutFlags);
  
  size_t align = payloadLayout->flags.getAlignment();
  bool isBT = payloadLayout->flags.isBitwiseTakable();
  TypeLayout layout;
  layout.size = size;
  layout.flags =
      payloadLayout->flags
          .withEnumWitnesses(true)
          .withInlineStorage(
              ValueWitnessTable::isValueInline(isBT, size, align));
  layout.extraInhabitantCount = unusedExtraInhabitants;
  auto rawStride = llvm::alignTo(size, align);
  layout.stride = rawStride == 0 ? 1 : rawStride;
  
  // Substitute in better common value witnesses if we have them.
  // If the payload type is a single-refcounted pointer, and the enum has
  // a single empty case, then we can borrow the witnesses of the single
  // refcounted pointer type, since swift_retain and objc_retain are both
  // nil-aware. Most single-refcounted types will use the standard
  // value witness tables for NativeObject or AnyObject. This isn't
  // foolproof but should catch the common case of optional class types.
#if OPTIONAL_OBJECT_OPTIMIZATION
  auto payloadVWT = payload->getValueWitnesses();
  if (emptyCases == 1
      && (payloadVWT == &VALUE_WITNESS_SYM(Bo)
#if SWIFT_OBJC_INTEROP
          || payloadVWT == &VALUE_WITNESS_SYM(BO)
#endif
          )) {
#define WANT_ONLY_REQUIRED_VALUE_WITNESSES
#define VALUE_WITNESS(LOWER_ID, UPPER_ID) \
    vwtable->LOWER_ID = payloadVWT->LOWER_ID;
#define DATA_VALUE_WITNESS(LOWER_ID, UPPER_ID, TYPE)
#include "swift/ABI/ValueWitness.def"
  } else {
#endif
    installCommonValueWitnesses(layout, vwtable);
#if OPTIONAL_OBJECT_OPTIMIZATION
  }
#endif

  vwtable->publishLayout(layout);
}

namespace {
struct XIElement {
  const Metadata *type;
  size_t offset;
};

XIElement findXIElement(const Metadata *type) {
  if (type->vw_getNumExtraInhabitants() == 0) {
    return {nullptr, 0};
  }

  if (auto *tuple = dyn_cast<TupleTypeMetadata>(type)) {
    assert(tuple->NumElements &&
           "Empty payloads can't store extra inhabitants");

    const TupleTypeMetadata::Element *current = tuple->getElements();
    for (InProcess::StoredSize i = 1; i < tuple->NumElements; i++) {
      auto &candidate = tuple->getElement(i);
      if (current->Type->vw_getNumExtraInhabitants() <
          candidate.Type->vw_getNumExtraInhabitants()) {
        current = &candidate;
      }
    }

    return {current->Type, current->Offset};
  } else {
    return {type, 0};
  }
}
} // namespace

void swift::swift_initEnumMetadataSinglePayloadWithLayoutString(
    EnumMetadata *self, EnumLayoutFlags layoutFlags,
    const Metadata *payloadType, unsigned emptyCases) {
  assert(self->hasLayoutString());

  auto *payloadLayout = payloadType->getTypeLayout();
  size_t payloadSize = payloadLayout->size;
  unsigned payloadNumExtraInhabitants = payloadLayout->getNumExtraInhabitants();

  unsigned unusedExtraInhabitants = 0;
  unsigned extraTagBytes = 0;

  // If there are enough extra inhabitants for all of the cases, then the size
  // of the enum is the same as its payload.
  size_t size;
  if (payloadNumExtraInhabitants >= emptyCases) {
    size = payloadSize;
    unusedExtraInhabitants = payloadNumExtraInhabitants - emptyCases;
  } else {
    extraTagBytes =
        getEnumTagCounts(payloadSize, emptyCases - payloadNumExtraInhabitants,
                         1 /*payload case*/)
            .numTagBytes;
    size = payloadSize + extraTagBytes;
  }

  auto vwtable = getMutableVWTableForInit(self, layoutFlags);

  size_t align = payloadLayout->flags.getAlignment();
  bool isBT = payloadLayout->flags.isBitwiseTakable();
  TypeLayout layout;
  layout.size = size;
  layout.flags = payloadLayout->flags.withEnumWitnesses(true).withInlineStorage(
      ValueWitnessTable::isValueInline(isBT, size, align));
  layout.extraInhabitantCount = unusedExtraInhabitants;
  auto rawStride = llvm::alignTo(size, align);
  layout.stride = rawStride == 0 ? 1 : rawStride;

  auto xiElement = findXIElement(payloadType);

  size_t payloadRefCountBytes = _swift_refCountBytesForMetatype(payloadType);
  size_t refCountBytes = payloadRefCountBytes +
                         sizeof(uint64_t) +  // tag + offset
                         sizeof(uint64_t) +  // extra tag bytes + XI offset
                         sizeof(size_t) +    // payload size
                         sizeof(uintptr_t) + // XI metadata
                         sizeof(unsigned) +  // num empty cases
                         sizeof(size_t) +    // payload ref count bytes
                         sizeof(size_t);     // bytes to skip if no payload case

  const size_t fixedLayoutStringSize =
      layoutStringHeaderSize + sizeof(uint64_t); // Last skip bytes

  uint8_t *layoutStr =
      (uint8_t *)MetadataAllocator(LayoutStringTag)
          .Allocate(llvm::alignTo(fixedLayoutStringSize + refCountBytes,
                                  sizeof(void *)),
                    alignof(uint8_t));

  LayoutStringWriter writer{layoutStr, sizeof(uint64_t)};

  writer.writeBytes(refCountBytes);

  uint64_t tagAndOffset = ((uint64_t)RefCountingKind::SinglePayloadEnumGeneric)
                          << 56;
  writer.writeBytes(tagAndOffset);

  uint64_t compactExtraTagByteCount = std::min(extraTagBytes, 3u);
  writer.writeBytes(compactExtraTagByteCount << 62 | xiElement.offset);

  writer.writeBytes(payloadSize);

  writer.writeBytes(xiElement.type);
  writer.writeBytes(emptyCases);
  writer.writeBytes(payloadRefCountBytes);

  // skip for now and fill in after writing the payload ref count string
  auto skipBytesOffset = writer.offset;
  writer.skip(sizeof(size_t));

  size_t fullOffset = 0;
  size_t previousFieldOffset = 0;
  LayoutStringFlags flags = LayoutStringFlags::Empty;

  _swift_addRefCountStringForMetatype(writer, flags, payloadType, fullOffset,
                                      previousFieldOffset);

  writer.writeBytes((uint64_t)previousFieldOffset + extraTagBytes);

  writer.offset = skipBytesOffset;
  writer.writeBytes(payloadSize - previousFieldOffset);

  // we mask out HasRelativePointers, because at this point they have all been
  // resolved to metadata pointers
  writer.offset = 0;
  writer.writeBytes(((uint64_t)flags) &
                    ~((uint64_t)LayoutStringFlags::HasRelativePointers));

  self->setLayoutString(layoutStr);
  vwtable->destroy = swift_generic_destroy;
  vwtable->initializeWithCopy = swift_generic_initWithCopy;
  vwtable->initializeWithTake = swift_generic_initWithTake;
  vwtable->assignWithCopy = swift_generic_assignWithCopy;
  vwtable->assignWithTake = swift_generic_assignWithTake;

  // Substitute in better common value witnesses if we have them.
  // If the payload type is a single-refcounted pointer, and the enum has
  // a single empty case, then we can borrow the witnesses of the single
  // refcounted pointer type, since swift_retain and objc_retain are both
  // nil-aware. Most single-refcounted types will use the standard
  // value witness tables for NativeObject or AnyObject. This isn't
  // foolproof but should catch the common case of optional class types.
#if OPTIONAL_OBJECT_OPTIMIZATION
  auto payloadVWT = payload->getValueWitnesses();
  if (emptyCases == 1 && (payloadVWT == &VALUE_WITNESS_SYM(Bo)
#if SWIFT_OBJC_INTEROP
                          || payloadVWT == &VALUE_WITNESS_SYM(BO)
#endif
                              )) {
#define WANT_ONLY_REQUIRED_VALUE_WITNESSES
#define VALUE_WITNESS(LOWER_ID, UPPER_ID)                                      \
  vwtable->LOWER_ID = payloadVWT->LOWER_ID;
#define DATA_VALUE_WITNESS(LOWER_ID, UPPER_ID, TYPE)
#include "swift/ABI/ValueWitness.def"
  } else {
#endif
    installCommonValueWitnesses(layout, vwtable);
#if OPTIONAL_OBJECT_OPTIMIZATION
  }
#endif

  vwtable->publishLayout(layout);
}

unsigned
swift::swift_getEnumTagSinglePayloadGeneric(const OpaqueValue *value,
                                            unsigned emptyCases,
                                            const Metadata *payloadType,
                               getExtraInhabitantTag_t *getExtraInhabitantTag) {
  auto size = payloadType->vw_size();
  auto numExtraInhabitants = payloadType->vw_getNumExtraInhabitants();
  return getEnumTagSinglePayloadImpl(value, emptyCases, payloadType, size,
                                     numExtraInhabitants,
                                     getExtraInhabitantTag);
}

void swift::swift_storeEnumTagSinglePayloadGeneric(OpaqueValue *value,
                                                   unsigned whichCase,
                                                   unsigned emptyCases,
                                                   const Metadata *payloadType,
                           storeExtraInhabitantTag_t *storeExtraInhabitantTag) {
  auto size = payloadType->vw_size();
  auto numExtraInhabitants = payloadType->vw_getNumExtraInhabitants();
  storeEnumTagSinglePayloadImpl(value, whichCase, emptyCases, payloadType, size,
                                numExtraInhabitants, storeExtraInhabitantTag);
}

void
swift::swift_initEnumMetadataMultiPayload(EnumMetadata *enumType,
                                     EnumLayoutFlags layoutFlags,
                                     unsigned numPayloads,
                                     const TypeLayout * const *payloadLayouts) {
  // Accumulate the layout requirements of the payloads.
  size_t payloadSize = 0, alignMask = 0;
  bool isPOD = true, isBT = true;
  for (unsigned i = 0; i < numPayloads; ++i) {
    const TypeLayout *payloadLayout = payloadLayouts[i];
    payloadSize
      = std::max(payloadSize, (size_t)payloadLayout->size);
    alignMask |= payloadLayout->flags.getAlignmentMask();
    isPOD &= payloadLayout->flags.isPOD();
    isBT &= payloadLayout->flags.isBitwiseTakable();
  }
  
  // Store the max payload size in the metadata.
  assignUnlessEqual(enumType->getPayloadSize(), payloadSize);
  
  // The total size includes space for the tag.
  auto tagCounts = getEnumTagCounts(payloadSize,
                                enumType->getDescription()->getNumEmptyCases(),
                                numPayloads);
  unsigned totalSize = payloadSize + tagCounts.numTagBytes;
  
  // See whether there are extra inhabitants in the tag.
  unsigned numExtraInhabitants = tagCounts.numTagBytes == 4
    ? INT_MAX
    : (1 << (tagCounts.numTagBytes * 8)) - tagCounts.numTags;
  numExtraInhabitants = std::min(numExtraInhabitants,
                          unsigned(ValueWitnessFlags::MaxNumExtraInhabitants));

  auto vwtable = getMutableVWTableForInit(enumType, layoutFlags);

  // Set up the layout info in the vwtable.
  auto rawStride = (totalSize + alignMask) & ~alignMask;
  TypeLayout layout{totalSize,
                    rawStride == 0 ? 1 : rawStride,
                    ValueWitnessFlags()
                     .withAlignmentMask(alignMask)
                     .withPOD(isPOD)
                     .withBitwiseTakable(isBT)
                     .withEnumWitnesses(true)
                     .withInlineStorage(ValueWitnessTable::isValueInline(
                         isBT, totalSize, alignMask + 1)),
                    numExtraInhabitants};

  installCommonValueWitnesses(layout, vwtable);

  // Unconditionally overwrite the enum-tag witnesses.
  // The compiler does not generate meaningful enum-tag witnesses for
  // enums in this state.
  vwtable->getEnumTagSinglePayload = swift_getMultiPayloadEnumTagSinglePayload;
  vwtable->storeEnumTagSinglePayload =
      swift_storeMultiPayloadEnumTagSinglePayload;

  vwtable->publishLayout(layout);
}

void swift::swift_initEnumMetadataMultiPayloadWithLayoutString(
    EnumMetadata *enumType,
    EnumLayoutFlags layoutFlags,
    unsigned numPayloads,
    const Metadata * const *payloadLayouts) {
  assert(enumType->hasLayoutString());

  // Accumulate the layout requirements of the payloads.
  size_t payloadSize = 0, alignMask = 0;
  bool isPOD = true, isBT = true;

  size_t payloadRefCountBytes = 0;
  for (unsigned i = 0; i < numPayloads; ++i) {
    const TypeLayout *payloadLayout = payloadLayouts[i]->getTypeLayout();
    payloadSize
      = std::max(payloadSize, (size_t)payloadLayout->size);
    alignMask |= payloadLayout->flags.getAlignmentMask();
    isPOD &= payloadLayout->flags.isPOD();
    isBT &= payloadLayout->flags.isBitwiseTakable();

    payloadRefCountBytes += _swift_refCountBytesForMetatype(payloadLayouts[i]);
    // NUL terminator
    payloadRefCountBytes += sizeof(uint64_t);
  }

  // Store the max payload size in the metadata.
  assignUnlessEqual(enumType->getPayloadSize(), payloadSize);

  // The total size includes space for the tag.
  auto tagCounts = getEnumTagCounts(payloadSize,
                                enumType->getDescription()->getNumEmptyCases(),
                                numPayloads);
  unsigned totalSize = payloadSize + tagCounts.numTagBytes;

  // See whether there are extra inhabitants in the tag.
  unsigned numExtraInhabitants = tagCounts.numTagBytes == 4
    ? INT_MAX
    : (1 << (tagCounts.numTagBytes * 8)) - tagCounts.numTags;
  numExtraInhabitants = std::min(numExtraInhabitants,
                          unsigned(ValueWitnessFlags::MaxNumExtraInhabitants));

  auto vwtable = getMutableVWTableForInit(enumType, layoutFlags);

  // Instantiate layout string
  {
    const size_t fixedLayoutHeaderSize = layoutStringHeaderSize +
                                         sizeof(uint64_t) +         // Tag + offset
                                         sizeof(size_t) +           // Extra tag byte count
                                         sizeof(size_t) * 3;        // Payload count, ref count bytes, enum size

    const size_t allocationSize =
        fixedLayoutHeaderSize +
        (numPayloads * sizeof(size_t)) +         // Payload ref count offsets
        payloadRefCountBytes + sizeof(uint64_t); // Last skip bytes

    uint8_t *layoutStr =
        (uint8_t *)MetadataAllocator(LayoutStringTag)
            .Allocate(llvm::alignTo(allocationSize, sizeof(void *)),
                      alignof(uint8_t));

    LayoutStringWriter writer{layoutStr, sizeof(uint64_t)};

    uint64_t tagAndOffset = ((uint64_t)RefCountingKind::MultiPayloadEnumGeneric)
                            << 56;

    size_t refCountBytes =
        allocationSize - layoutStringHeaderSize - (sizeof(uint64_t));
    writer.writeBytes(refCountBytes);
    writer.writeBytes(tagAndOffset);
    writer.writeBytes(size_t(tagCounts.numTagBytes));
    writer.writeBytes(size_t(numPayloads));
    writer.writeBytes(payloadRefCountBytes);
    writer.writeBytes(size_t(totalSize));

    LayoutStringFlags flags = LayoutStringFlags::Empty;

    LayoutStringWriter offsetWriter{layoutStr, writer.offset};
    size_t payloadRefCountOffset = 0;

    writer.skip(sizeof(size_t) * numPayloads);

    for (unsigned i = 0; i < numPayloads; ++i) {
      const Metadata *payloadType = payloadLayouts[i];

      offsetWriter.writeBytes(payloadRefCountOffset);

      size_t layoutStrOffsetBefore = writer.offset;
      size_t previousFieldOffset = 0;
      size_t fullOffset = 0;
      _swift_addRefCountStringForMetatype(writer, flags, payloadType,
                                          fullOffset, previousFieldOffset);

      // NUL terminator
      writer.writeBytes<uint64_t>(0);

      payloadRefCountOffset += (writer.offset - layoutStrOffsetBefore);
    }

    // Last skip bytes (always 0 for enums)
    writer.writeBytes<uint64_t>(0);

    // we mask out HasRelativePointers, because at this point they have all been
    // resolved to metadata pointers
    writer.offset = 0;
    writer.writeBytes(((uint64_t)flags) &
                      ~((uint64_t)LayoutStringFlags::HasRelativePointers));

    enumType->setLayoutString(layoutStr);

    vwtable->destroy = swift_generic_destroy;
    vwtable->initializeWithCopy = swift_generic_initWithCopy;
    vwtable->initializeWithTake = swift_generic_initWithTake;
    vwtable->assignWithCopy = swift_generic_assignWithCopy;
    vwtable->assignWithTake = swift_generic_assignWithTake;
  }

  // Set up the layout info in the vwtable.
  auto rawStride = (totalSize + alignMask) & ~alignMask;
  TypeLayout layout{totalSize,
                    rawStride == 0 ? 1 : rawStride,
                    ValueWitnessFlags()
                     .withAlignmentMask(alignMask)
                     .withPOD(isPOD)
                     .withBitwiseTakable(isBT)
                     .withEnumWitnesses(true)
                     .withInlineStorage(ValueWitnessTable::isValueInline(
                         isBT, totalSize, alignMask + 1)),
                    numExtraInhabitants};

  installCommonValueWitnesses(layout, vwtable);

  // Unconditionally overwrite the enum-tag witnesses.
  // The compiler does not generate meaningful enum-tag witnesses for
  // enums in this state.
  vwtable->getEnumTagSinglePayload = swift_getMultiPayloadEnumTagSinglePayload;
  vwtable->storeEnumTagSinglePayload =
      swift_storeMultiPayloadEnumTagSinglePayload;

  vwtable->publishLayout(layout);
}

namespace {
struct MultiPayloadLayout {
  size_t payloadSize;
  size_t numTagBytes;
};
} // end anonymous namespace

static MultiPayloadLayout getMultiPayloadLayout(const EnumMetadata *enumType) {
  size_t payloadSize = enumType->getPayloadSize();
  size_t totalSize = enumType->getValueWitnesses()->size;
  return {payloadSize, totalSize - payloadSize};
}

static void storeMultiPayloadTag(OpaqueValue *value,
                                 MultiPayloadLayout layout,
                                 unsigned tag) {
  auto tagBytes = reinterpret_cast<uint8_t *>(value) + layout.payloadSize;
  storeEnumElement(tagBytes, tag, layout.numTagBytes);
}

static void storeMultiPayloadValue(OpaqueValue *value,
                                   MultiPayloadLayout layout,
                                   unsigned payloadValue) {
  auto bytes = reinterpret_cast<uint8_t *>(value);
  storeEnumElement(bytes, payloadValue, layout.payloadSize);
}

static unsigned loadMultiPayloadTag(const OpaqueValue *value,
                                    MultiPayloadLayout layout,
                                    unsigned baseValue = 0) {
  auto tagBytes = reinterpret_cast<const uint8_t *>(value) +
                  layout.payloadSize;
  auto tag = loadEnumElement(tagBytes, layout.numTagBytes);

  // The maximum number of extra tag bytes is 4.
  // Note: return early to avoid shifting baseValue by 32 which is
  // undefined behaviour.
  if (layout.numTagBytes == 4) {
    return tag;
  }

  // Replace out-of-range bytes with the base value.
  return tag | (baseValue & (~0u << (layout.numTagBytes * 8)));
}

static unsigned loadMultiPayloadValue(const OpaqueValue *value,
                                      MultiPayloadLayout layout) {
  auto bytes = reinterpret_cast<const uint8_t *>(value);
  return loadEnumElement(bytes, layout.payloadSize);
}

SWIFT_CC(swift)
static unsigned getMultiPayloadExtraInhabitantTag(const OpaqueValue *value,
                                                  unsigned enumNumXI,
                                                  const Metadata *enumType) {
  auto layout = getMultiPayloadLayout(cast<EnumMetadata>(enumType));
  unsigned index = ~loadMultiPayloadTag(value, layout, ~0u);
  
  if (index >= enumType->getValueWitnesses()->getNumExtraInhabitants())
    return 0;
  return index + 1;
}

SWIFT_CC(swift)
static void storeMultiPayloadExtraInhabitantTag(OpaqueValue *value,
                                                unsigned tag,
                                                unsigned enumNumXI,
                                                const Metadata *enumType) {
  auto layout = getMultiPayloadLayout(cast<EnumMetadata>(enumType));
  storeMultiPayloadTag(value, layout, ~(tag - 1));
}

uint32_t
swift::swift_getMultiPayloadEnumTagSinglePayload(const OpaqueValue *value,
                                                 uint32_t numExtraCases,
                                                 const Metadata *enumType) {
  return getEnumTagSinglePayloadImpl(value, numExtraCases, enumType,
                                     enumType->vw_size(),
                                     enumType->vw_getNumExtraInhabitants(),
                                     getMultiPayloadExtraInhabitantTag);
}

void swift::swift_storeMultiPayloadEnumTagSinglePayload(
    OpaqueValue *value, uint32_t index, uint32_t numExtraCases,
    const Metadata *enumType) {
  storeEnumTagSinglePayloadImpl(value, index, numExtraCases, enumType,
                                enumType->vw_size(),
                                enumType->vw_getNumExtraInhabitants(),
                                storeMultiPayloadExtraInhabitantTag);
}

void
swift::swift_storeEnumTagMultiPayload(OpaqueValue *value,
                                      const EnumMetadata *enumType,
                                      unsigned whichCase) {
  auto layout = getMultiPayloadLayout(enumType);
  unsigned numPayloads = enumType->getDescription()->getNumPayloadCases();
  if (whichCase < numPayloads) {
    // For a payload case, store the tag after the payload area.
    storeMultiPayloadTag(value, layout, whichCase);
  } else {
    // For an empty case, factor out the parts that go in the payload and
    // tag areas.
    unsigned whichEmptyCase = whichCase - numPayloads;
    unsigned whichTag, whichPayloadValue;
    if (layout.payloadSize >= 4) {
      whichTag = numPayloads;
      whichPayloadValue = whichEmptyCase;
    } else {
      unsigned numPayloadBits = layout.payloadSize * CHAR_BIT;
      whichTag = numPayloads + (whichEmptyCase >> numPayloadBits);
      whichPayloadValue = whichEmptyCase & ((1U << numPayloadBits) - 1U);
    }
    storeMultiPayloadTag(value, layout, whichTag);
    storeMultiPayloadValue(value, layout, whichPayloadValue);
  }
}

unsigned
swift::swift_getEnumCaseMultiPayload(const OpaqueValue *value,
                                     const EnumMetadata *enumType) {
  auto layout = getMultiPayloadLayout(enumType);
  unsigned numPayloads = enumType->getDescription()->getNumPayloadCases();

  unsigned tag = loadMultiPayloadTag(value, layout);
  if (tag < numPayloads) {
    // If the tag indicates a payload, then we're done.
    return tag;
  } else {
    // Otherwise, the other part of the discriminator is in the payload.
    unsigned payloadValue = loadMultiPayloadValue(value, layout);
    
    if (layout.payloadSize >= 4) {
      return numPayloads + payloadValue;
    } else {
      unsigned numPayloadBits = layout.payloadSize * CHAR_BIT;
      return (payloadValue | (tag - numPayloads) << numPayloadBits)
             + numPayloads;
    }
  }
}