CIRGenRecordLayoutBuilder.cpp

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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This contains code to compute the layout of a record.
//
//===----------------------------------------------------------------------===//
 
#include "CIRGenBuilder.h"
#include "CIRGenModule.h"
#include "CIRGenTypes.h"
#include "TargetInfo.h"
 
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/RecordLayout.h"
#include "clang/CIR/Dialect/IR/CIRAttrs.h"
#include "clang/CIR/Dialect/IR/CIRDataLayout.h"
#include "clang/CIR/MissingFeatures.h"
#include "clang/CodeGenUtils/CodeGenUtils.h"
#include "llvm/Support/Casting.h"
 
#include <memory>
 
using namespace llvm;
using namespace clang;
using namespace clang::CIRGen;
 
namespace {
/// The CIRRecordLowering is responsible for lowering an ASTRecordLayout to an
/// mlir::Type. Some of the lowering is straightforward, some is not.
// TODO: Detail some of the complexities and weirdnesses?
// (See CGRecordLayoutBuilder.cpp)
struct CIRRecordLowering final {
 
  // MemberInfo is a helper structure that contains information about a record
  // member. In addition to the standard member types, there exists a sentinel
  // member type that ensures correct rounding.
  struct MemberInfo final {
    CharUnits offset;
    enum class InfoKind { VFPtr, Field, Base, VBase } kind;
    mlir::Type data;
    /// What this member holds, recorded on the CIR record type.
    cir::RecordMemberKind memberKind;
    union {
      const FieldDecl *fieldDecl;
      const CXXRecordDecl *cxxRecordDecl;
    };
    MemberInfo(CharUnits offset, InfoKind kind, mlir::Type data,
               cir::RecordMemberKind memberKind,
               const FieldDecl *fieldDecl = nullptr)
        : offset{offset}, kind{kind}, data{data}, memberKind{memberKind},
          fieldDecl{fieldDecl} {}
    MemberInfo(CharUnits offset, InfoKind kind, mlir::Type data,
               cir::RecordMemberKind memberKind, const CXXRecordDecl *rd)
        : offset{offset}, kind{kind}, data{data}, memberKind{memberKind},
          cxxRecordDecl{rd} {}
    // MemberInfos are sorted so we define a < operator.
    bool operator<(const MemberInfo &other) const {
      return offset < other.offset;
    }
  };
 
  static bool ownsBytes(const MemberInfo &member) {
    return member.data && cir::memberOwnsBytes(member.data);
  }
 
  cir::BitFieldDeclAttr getBitFieldDecl(const FieldDecl *field) {
    return cir::BitFieldDeclAttr::get(
        cirGenTypes.convertTypeForMem(field->getType()),
        field->getBitWidthValue(), field->isUnnamedBitField());
  }
 
  MemberInfo makeAccessUnitInfo(CharUnits offset, mlir::Type storage,
                                llvm::ArrayRef<cir::BitFieldDeclAttr> fields) {
    mlir::Type unitTy =
        cir::BitFieldType::get(&cirGenTypes.getMLIRContext(), storage, fields);
    // If the access unit doesn't hold any named fields, it's empty.
    const bool holdsNamedField =
        mlir::cast<cir::BitFieldType>(unitTy).holdsNamedField();
    return makeStorageInfo(offset, unitTy,
                           holdsNamedField ? cir::RecordMemberKind::BitField
                                           : cir::RecordMemberKind::Empty);
  }
 
  /// The member for a zero-width bit-field, which belongs to no access unit
  /// and owns no bytes.  It sits at its own offset, where the run it ended
  /// stops.
  MemberInfo makeZeroWidthBitFieldInfo(const FieldDecl *field) {
    assert(field->isZeroLengthBitField() && "not a zero-width bit-field");
    return makeAccessUnitInfo(bitsToCharUnits(getFieldBitOffset(field)),
                              /*storage=*/mlir::Type{}, getBitFieldDecl(field));
  }
 
  // The constructor.
  CIRRecordLowering(CIRGenTypes &cirGenTypes, const RecordDecl *recordDecl,
                    bool packed);
 
  /// Constructs a MemberInfo instance from an offset and mlir::Type.
  MemberInfo makeStorageInfo(CharUnits offset, mlir::Type data,
                             cir::RecordMemberKind memberKind) {
    return MemberInfo(offset, MemberInfo::InfoKind::Field, data, memberKind);
  }
 
  // Layout routines.
  void setBitFieldInfo(const FieldDecl *fd, CharUnits startOffset,
                       mlir::Type storageType);
 
  void lower(bool nonVirtualBaseType);
  void lowerUnion(bool nonVirtualBaseType);
 
  /// Determines if we need a packed llvm struct.
  void determinePacked(bool nvBaseType);
  /// Inserts padding everywhere it's needed.
  void insertPadding();
 
  void computeVolatileBitfields();
  void accumulateBases();
  void accumulateVPtrs();
  void accumulateVBases();
  void accumulateFields(bool nonVirtualBaseType);
  RecordDecl::field_iterator
  accumulateBitFields(RecordDecl::field_iterator field,
                      RecordDecl::field_iterator fieldEnd);
 
  mlir::Type getVFPtrType();
 
  /// Helper function to check if the target machine is BigEndian.
  bool isBigEndian() const { return astContext.getTargetInfo().isBigEndian(); }
 
  // The Itanium base layout rule allows virtual bases to overlap
  // other bases, which complicates layout in specific ways.
  //
  // Note specifically that the ms_struct attribute doesn't change this.
  bool isOverlappingVBaseABI() {
    return !astContext.getTargetInfo().getCXXABI().isMicrosoft();
  }
  // Recursively searches all of the bases to find out if a vbase is
  // not the primary vbase of some base class.
  bool hasOwnStorage(const CXXRecordDecl *decl, const CXXRecordDecl *query);
 
  /// The Microsoft bitfield layout rule allocates discrete storage
  /// units of the field's formal type and only combines adjacent
  /// fields of the same formal type.  We want to emit a layout with
  /// these discrete storage units instead of combining them into a
  /// continuous run.
  bool isDiscreteBitFieldABI() {
    return astContext.getTargetInfo().getCXXABI().isMicrosoft() ||
           recordDecl->isMsStruct(astContext);
  }
 
  CharUnits bitsToCharUnits(uint64_t bitOffset) {
    return astContext.toCharUnitsFromBits(bitOffset);
  }
 
  void calculateZeroInit();
 
  CharUnits getSize(mlir::Type Ty) {
    return CharUnits::fromQuantity(dataLayout.layout.getTypeSize(Ty));
  }
  CharUnits getSizeInBits(mlir::Type ty) {
    return CharUnits::fromQuantity(dataLayout.layout.getTypeSizeInBits(ty));
  }
 
  CharUnits getMemberAlignment(mlir::Type Ty) {
    // An access unit takes the alignment of its storage type. A zero-width
    // bit-field has no storage and so imposes no alignment.
    if (auto bitFieldTy = mlir::dyn_cast<cir::BitFieldType>(Ty)) {
      if (mlir::Type storage = bitFieldTy.getStorageType())
        return getMemberAlignment(storage);
      return CharUnits::One();
    }
    // Recurse on Arrays, they have the member alignment of their element type.
    if (auto arrayTy = mlir::dyn_cast<cir::ArrayType>(Ty))
      return getMemberAlignment(arrayTy.getElementType());
    // Int types (_BitInt in particular) share the alignment of their storage
    // type.
    if (auto intTy = mlir::dyn_cast<cir::IntType>(Ty))
      return CharUnits::fromQuantity(
          intTy.getStorageTypeAlignment(dataLayout.layout));
 
    return CharUnits::fromQuantity(dataLayout.layout.getTypeABIAlignment(Ty));
  }
 
  bool isZeroInitializable(const FieldDecl *fd) {
    return cirGenTypes.isZeroInitializable(fd->getType());
  }
  bool isZeroInitializable(const RecordDecl *rd) {
    return cirGenTypes.isZeroInitializable(rd);
  }
 
  /// The mark for a member, given whether it holds data for argument passing
  /// and whether it is a bit-field.  A run of bit-fields shares one access
  /// unit whose width can be narrower than the declared type of the bit-field
  /// it holds.
  static cir::RecordMemberKind makeMemberKind(bool holdsData,
                                              bool isNamedBitField) {
    if (!holdsData)
      return cir::RecordMemberKind::Empty;
    return isNamedBitField ? cir::RecordMemberKind::BitField
                           : cir::RecordMemberKind::Data;
  }
 
  /// The mark for a field that is not a bit-field.  A run of bit-fields is one
  /// member per access unit rather than one per field, so a bit-field is
  /// marked where its unit is built.
  cir::RecordMemberKind getFieldMemberKind(const FieldDecl *fd) {
    assert(!fd->isBitField() && "a bit-field is marked with its access unit");
    return makeMemberKind(/*holdsData=*/!isEmptyFieldForABI(astContext, fd),
                          /*isNamedBitField=*/false);
  }
 
  /// The mark for a base subobject.  A base contributes no ABI data when it is
  /// empty for the ABI, which is not the same as CXXRecordDecl::isEmpty(): a
  /// base holding only unnamed bit-fields is laid out but carries no data.
  cir::RecordMemberKind getBaseMemberKind(const CXXRecordDecl *baseDecl) {
    return isEmptyRecordForABI(astContext,
                               astContext.getCanonicalTagType(baseDecl))
               ? cir::RecordMemberKind::Empty
               : cir::RecordMemberKind::Data;
  }
 
  /// Wraps cir::IntType with some implicit arguments.
  mlir::Type getUIntNType(uint64_t numBits) {
    unsigned alignedBits = llvm::PowerOf2Ceil(numBits);
    alignedBits = std::max(8u, alignedBits);
    return cir::IntType::get(&cirGenTypes.getMLIRContext(), alignedBits,
                             /*isSigned=*/false);
  }
 
  mlir::Type getCharType() {
    return cir::IntType::get(&cirGenTypes.getMLIRContext(),
                             astContext.getCharWidth(),
                             /*isSigned=*/false);
  }
 
  mlir::Type getByteArrayType(CharUnits numberOfChars) {
    assert(!numberOfChars.isZero() && "Empty byte arrays aren't allowed.");
    mlir::Type type = getCharType();
    return numberOfChars == CharUnits::One()
               ? type
               : cir::ArrayType::get(type, numberOfChars.getQuantity());
  }
 
  // Gets the CIR BaseSubobject type from a CXXRecordDecl.
  mlir::Type getStorageType(const CXXRecordDecl *RD) {
    return cirGenTypes.getCIRGenRecordLayout(RD).getBaseSubobjectCIRType();
  }
  // This is different from LLVM traditional codegen because CIRGen uses arrays
  // of bytes instead of arbitrary-sized integers. This is important for packed
  // structures support.
  mlir::Type getBitfieldStorageType(unsigned numBits) {
    unsigned alignedBits = llvm::alignTo(numBits, astContext.getCharWidth());
    if (cir::isValidFundamentalIntWidth(alignedBits))
      return builder.getUIntNTy(alignedBits);
 
    mlir::Type type = getCharType();
    return cir::ArrayType::get(type, alignedBits / astContext.getCharWidth());
  }
 
  mlir::Type getStorageType(const FieldDecl *fieldDecl) {
    mlir::Type type = cirGenTypes.convertTypeForMem(fieldDecl->getType());
    if (fieldDecl->isBitField()) {
      cirGenTypes.getCGModule().errorNYI(recordDecl->getSourceRange(),
                                         "getStorageType for bitfields");
    }
    return type;
  }
 
  uint64_t getFieldBitOffset(const FieldDecl *fieldDecl) {
    return astRecordLayout.getFieldOffset(fieldDecl->getFieldIndex());
  }
 
  /// Fills out the structures that are ultimately consumed.
  void fillOutputFields();
 
  void appendPaddingBytes(CharUnits size) {
    if (size.isZero())
      return;
    mlir::Type padTy = getByteArrayType(size);
    if (recordDecl->isUnion()) {
      assert(!unionPadding && "at most one union tail-padding type");
      unionPadding = padTy;
    } else {
      addField(padTy, cir::RecordMemberKind::Pad);
    }
  }
 
  void addField(mlir::Type ty, cir::RecordMemberKind memberKind) {
    fieldTypes.push_back(ty);
    fieldKinds.push_back(memberKind);
  }
 
  void clearFields() {
    fieldTypes.clear();
    fieldKinds.clear();
  }
 
  llvm::ArrayRef<mlir::Type> getFieldTypes() const { return fieldTypes; }
  llvm::ArrayRef<cir::RecordMemberKind> getFieldKinds() const {
    return fieldKinds;
  }
 
  CIRGenTypes &cirGenTypes;
  CIRGenBuilderTy &builder;
  const ASTContext &astContext;
  const RecordDecl *recordDecl;
  const CXXRecordDecl *cxxRecordDecl;
  const ASTRecordLayout &astRecordLayout;
  // Helpful intermediate data-structures
  std::vector<MemberInfo> members;
  mlir::Type unionPadding;
  llvm::DenseMap<const FieldDecl *, CIRGenBitFieldInfo> bitFields;
  llvm::DenseMap<const FieldDecl *, unsigned> fieldIdxMap;
  llvm::DenseMap<const CXXRecordDecl *, unsigned> nonVirtualBases;
  llvm::DenseMap<const CXXRecordDecl *, unsigned> virtualBases;
  cir::CIRDataLayout dataLayout;
 
  LLVM_PREFERRED_TYPE(bool)
  unsigned zeroInitializable : 1;
  LLVM_PREFERRED_TYPE(bool)
  unsigned zeroInitializableAsBase : 1;
  LLVM_PREFERRED_TYPE(bool)
  unsigned packed : 1;
 
private:
  // Output fields, consumed by CIRGenTypes::computeRecordLayout.  Private so
  // that every append goes through addField and fieldKinds stays parallel to
  // fieldTypes.
  llvm::SmallVector<mlir::Type, 16> fieldTypes;
  llvm::SmallVector<cir::RecordMemberKind> fieldKinds;
 
  CIRRecordLowering(const CIRRecordLowering &) = delete;
  void operator=(const CIRRecordLowering &) = delete;
}; // CIRRecordLowering
} // namespace
 
CIRRecordLowering::CIRRecordLowering(CIRGenTypes &cirGenTypes,
                                     const RecordDecl *recordDecl, bool packed)
    : cirGenTypes{cirGenTypes}, builder{cirGenTypes.getBuilder()},
      astContext{cirGenTypes.getASTContext()}, recordDecl{recordDecl},
      cxxRecordDecl{llvm::dyn_cast<CXXRecordDecl>(recordDecl)},
      astRecordLayout{
          cirGenTypes.getASTContext().getASTRecordLayout(recordDecl)},
      dataLayout{cirGenTypes.getCGModule().getModule()},
      zeroInitializable{true}, zeroInitializableAsBase{true}, packed{packed} {}
 
void CIRRecordLowering::setBitFieldInfo(const FieldDecl *fd,
                                        CharUnits startOffset,
                                        mlir::Type storageType) {
  CIRGenBitFieldInfo &info = bitFields[fd->getCanonicalDecl()];
  info.isSigned = fd->getType()->isSignedIntegerOrEnumerationType();
  info.offset =
      (unsigned)(getFieldBitOffset(fd) - astContext.toBits(startOffset));
  info.size = fd->getBitWidthValue();
  info.storageSize = getSizeInBits(storageType).getQuantity();
  info.storageOffset = startOffset;
  info.storageType = storageType;
  info.name = fd->getName();
 
  if (info.size > info.storageSize)
    info.size = info.storageSize;
  // Reverse the bit offsets for big endian machines. Since bitfields are laid
  // out as packed bits within an integer-sized unit, we can imagine the bits
  // counting from the most-significant-bit instead of the
  // least-significant-bit.
  if (dataLayout.isBigEndian())
    info.offset = info.storageSize - (info.offset + info.size);
 
  info.volatileStorageSize = 0;
  info.volatileOffset = 0;
  info.volatileStorageOffset = CharUnits::Zero();
}
 
void CIRRecordLowering::lower(bool nonVirtualBaseType) {
  if (recordDecl->isUnion()) {
    lowerUnion(nonVirtualBaseType);
    computeVolatileBitfields();
    return;
  }
 
  CharUnits size = nonVirtualBaseType ? astRecordLayout.getNonVirtualSize()
                                      : astRecordLayout.getSize();
 
  accumulateFields(nonVirtualBaseType);
 
  if (cxxRecordDecl) {
    accumulateVPtrs();
    accumulateBases();
    if (members.empty()) {
      appendPaddingBytes(size);
      computeVolatileBitfields();
      return;
    }
    if (!nonVirtualBaseType)
      accumulateVBases();
  }
 
  llvm::stable_sort(members);
  // TODO: Verify bitfield clipping
  assert(!cir::MissingFeatures::checkBitfieldClipping());
 
  // The sentinel is popped before fillOutputFields, so its kind never reaches
  // the type.
  members.push_back(
      makeStorageInfo(size, getUIntNType(8), cir::RecordMemberKind::Data));
  determinePacked(nonVirtualBaseType);
  insertPadding();
  members.pop_back();
 
  calculateZeroInit();
  fillOutputFields();
  computeVolatileBitfields();
}
 
void CIRRecordLowering::fillOutputFields() {
  for (const MemberInfo &member : members) {
    if (member.data)
      addField(member.data, member.memberKind);
    if (member.kind == MemberInfo::InfoKind::Field) {
      if (member.fieldDecl)
        fieldIdxMap[member.fieldDecl->getCanonicalDecl()] =
            fieldTypes.size() - 1;
      // A bit-field carries no member of its own. It is numbered as the access
      // unit ahead of it, whose storage it is read and written through.
      if (!member.data) {
        assert(member.fieldDecl &&
               "member.data is a nullptr so member.fieldDecl should not be");
        setBitFieldInfo(member.fieldDecl, member.offset,
                        cir::memberStorageType(fieldTypes.back()));
      }
    } else if (member.kind == MemberInfo::InfoKind::Base) {
      nonVirtualBases[member.cxxRecordDecl] = fieldTypes.size() - 1;
    } else if (member.kind == MemberInfo::InfoKind::VBase) {
      virtualBases[member.cxxRecordDecl] = fieldTypes.size() - 1;
    }
  }
}
 
RecordDecl::field_iterator
CIRRecordLowering::accumulateBitFields(RecordDecl::field_iterator field,
                                       RecordDecl::field_iterator fieldEnd) {
  if (isDiscreteBitFieldABI()) {
    // run stores the first element of the current run of bitfields. fieldEnd is
    // used as a special value to note that we don't have a current run. A
    // bitfield run is a contiguous collection of bitfields that can be stored
    // in the same storage block. Zero-sized bitfields and bitfields that would
    // cross an alignment boundary break a run and start a new one.
    RecordDecl::field_iterator run = fieldEnd;
    // tail is the offset of the first bit off the end of the current run. It's
    // used to determine if the ASTRecordLayout is treating these two bitfields
    // as contiguous. StartBitOffset is offset of the beginning of the Run.
    uint64_t startBitOffset, tail = 0;
    // Where the current run's access unit sits in members, and the bit-fields
    // it holds so far.  The unit grows as new bit-fields are added.
    size_t unitIdx = 0;
    mlir::Type unitStorage;
    llvm::SmallVector<cir::BitFieldDeclAttr> unitFields;
    for (; field != fieldEnd && field->isBitField(); ++field) {
      // Zero-width bitfields end runs.
      if (field->isZeroLengthBitField()) {
        members.push_back(makeZeroWidthBitFieldInfo(*field));
        run = fieldEnd;
        continue;
      }
      uint64_t bitOffset = getFieldBitOffset(*field);
      mlir::Type type = cirGenTypes.convertTypeForMem(field->getType());
      cir::BitFieldDeclAttr decl = getBitFieldDecl(*field);
      // If we don't have a run yet, or don't live within the previous run's
      // allocated storage then we allocate some storage and start a new run.
      if (run == fieldEnd || bitOffset >= tail) {
        run = field;
        startBitOffset = bitOffset;
        tail = startBitOffset + dataLayout.getTypeAllocSizeInBits(type);
        // The access unit is added to the record before the bit-fields it
        // holds so that it gets laid out ahead of them.
        unitIdx = members.size();
        unitStorage = type;
        unitFields.assign(1, decl);
        members.push_back(makeAccessUnitInfo(bitsToCharUnits(startBitOffset),
                                             unitStorage, unitFields));
      } else {
        unitFields.push_back(decl);
        members[unitIdx] = makeAccessUnitInfo(bitsToCharUnits(startBitOffset),
                                              unitStorage, unitFields);
      }
      assert(members[unitIdx].offset == bitsToCharUnits(startBitOffset) &&
             "unitIdx must name the current run's access unit");
      // Bitfields get the offset of their access unit but come afterward and
      // remain there after a stable sort.
      members.push_back(MemberInfo(bitsToCharUnits(startBitOffset),
                                   MemberInfo::InfoKind::Field, nullptr,
                                   cir::RecordMemberKind::Data, *field));
    }
    return field;
  }
 
  CharUnits regSize =
      bitsToCharUnits(astContext.getTargetInfo().getRegisterWidth());
  unsigned charBits = astContext.getCharWidth();
 
  // Data about the start of the span we're accumulating to create an access
  // unit from. 'Begin' is the first bitfield of the span. If 'begin' is
  // 'fieldEnd', we've not got a current span. The span starts at the
  // 'beginOffset' character boundary. 'bitSizeSinceBegin' is the size (in bits)
  // of the span -- this might include padding when we've advanced to a
  // subsequent bitfield run.
  RecordDecl::field_iterator begin = fieldEnd;
  CharUnits beginOffset;
  uint64_t bitSizeSinceBegin;
 
  // The (non-inclusive) end of the largest acceptable access unit we've found
  // since 'begin'. If this is 'begin', we're gathering the initial set of
  // bitfields of a new span. 'bestEndOffset' is the end of that acceptable
  // access unit -- it might extend beyond the last character of the bitfield
  // run, using available padding characters.
  RecordDecl::field_iterator bestEnd = begin;
  CharUnits bestEndOffset;
  bool bestClipped; // Whether the representation must be in a byte array.
 
  for (;;) {
    // atAlignedBoundary is true if 'field' is the (potential) start of a new
    // span (or the end of the bitfields). When true, limitOffset is the
    // character offset of that span and barrier indicates whether the new
    // span cannot be merged into the current one.
    bool atAlignedBoundary = false;
    bool barrier = false; // a barrier can be a zero Bit Width or non bit member
    if (field != fieldEnd && field->isBitField()) {
      uint64_t bitOffset = getFieldBitOffset(*field);
      if (begin == fieldEnd) {
        // Beginning a new span.
        begin = field;
        bestEnd = begin;
 
        assert((bitOffset % charBits) == 0 && "Not at start of char");
        beginOffset = bitsToCharUnits(bitOffset);
        bitSizeSinceBegin = 0;
      } else if ((bitOffset % charBits) != 0) {
        // Bitfield occupies the same character as previous bitfield, it must be
        // part of the same span. This can include zero-length bitfields, should
        // the target not align them to character boundaries. Such non-alignment
        // is at variance with the standards, which require zero-length
        // bitfields be a barrier between access units. But of course we can't
        // achieve that in the middle of a character.
        assert(bitOffset ==
                   astContext.toBits(beginOffset) + bitSizeSinceBegin &&
               "Concatenating non-contiguous bitfields");
      } else {
        // Bitfield potentially begins a new span. This includes zero-length
        // bitfields on non-aligning targets that lie at character boundaries
        // (those are barriers to merging).
        if (field->isZeroLengthBitField())
          barrier = true;
        atAlignedBoundary = true;
      }
    } else {
      // We've reached the end of the bitfield run. Either we're done, or this
      // is a barrier for the current span.
      if (begin == fieldEnd)
        break;
 
      barrier = true;
      atAlignedBoundary = true;
    }
 
    // 'installBest' indicates whether we should create an access unit for the
    // current best span: fields ['begin', 'bestEnd') occupying characters
    // ['beginOffset', 'bestEndOffset').
    bool installBest = false;
    if (atAlignedBoundary) {
      // 'field' is the start of a new span or the end of the bitfields. The
      // just-seen span now extends to 'bitSizeSinceBegin'.
 
      // Determine if we can accumulate that just-seen span into the current
      // accumulation.
      CharUnits accessSize = bitsToCharUnits(bitSizeSinceBegin + charBits - 1);
      if (bestEnd == begin) {
        // This is the initial run at the start of a new span. By definition,
        // this is the best seen so far.
        bestEnd = field;
        bestEndOffset = beginOffset + accessSize;
        // Assume clipped until proven not below.
        bestClipped = true;
        if (!bitSizeSinceBegin)
          // A zero-sized initial span -- this will install nothing and reset
          // for another.
          installBest = true;
      } else if (accessSize > regSize) {
        // Accumulating the just-seen span would create a multi-register access
        // unit, which would increase register pressure.
        installBest = true;
      }
 
      if (!installBest) {
        // Determine if accumulating the just-seen span will create an expensive
        // access unit or not.
        mlir::Type type = getUIntNType(astContext.toBits(accessSize));
        if (!astContext.getTargetInfo().hasCheapUnalignedBitFieldAccess())
          cirGenTypes.getCGModule().errorNYI(
              field->getSourceRange(), "NYI CheapUnalignedBitFieldAccess");
 
        if (!installBest) {
          // Find the next used storage offset to determine what the limit of
          // the current span is. That's either the offset of the next field
          // with storage (which might be field itself) or the end of the
          // non-reusable tail padding.
          CharUnits limitOffset;
          for (auto probe = field; probe != fieldEnd; ++probe)
            if (!isEmptyFieldForLayout(astContext, *probe)) {
              // A member with storage sets the limit.
              assert((getFieldBitOffset(*probe) % charBits) == 0 &&
                     "Next storage is not byte-aligned");
              limitOffset = bitsToCharUnits(getFieldBitOffset(*probe));
              goto FoundLimit;
            }
          limitOffset = cxxRecordDecl ? astRecordLayout.getNonVirtualSize()
                                      : astRecordLayout.getDataSize();
 
        FoundLimit:
          CharUnits typeSize = getSize(type);
          if (beginOffset + typeSize <= limitOffset) {
            // There is space before limitOffset to create a naturally-sized
            // access unit.
            bestEndOffset = beginOffset + typeSize;
            bestEnd = field;
            bestClipped = false;
          }
          if (barrier) {
            // The next field is a barrier that we cannot merge across.
            installBest = true;
          } else if (cirGenTypes.getCGModule()
                         .getCodeGenOpts()
                         .FineGrainedBitfieldAccesses) {
            installBest = true;
          } else {
            // Otherwise, we're not installing. Update the bit size
            // of the current span to go all the way to limitOffset, which is
            // the (aligned) offset of next bitfield to consider.
            bitSizeSinceBegin = astContext.toBits(limitOffset - beginOffset);
          }
        }
      }
    }
 
    if (installBest) {
      assert((field == fieldEnd || !field->isBitField() ||
              (getFieldBitOffset(*field) % charBits) == 0) &&
             "Installing but not at an aligned bitfield or limit");
      CharUnits accessSize = bestEndOffset - beginOffset;
      if (!accessSize.isZero()) {
        // Add the storage member for the access unit to the record. The
        // bitfields get the offset of their storage but come afterward and
        // remain there after a stable sort.
        mlir::Type type;
        if (bestClipped) {
          assert(getSize(getUIntNType(astContext.toBits(accessSize))) >
                     accessSize &&
                 "Clipped access need not be clipped");
          type = getByteArrayType(accessSize);
        } else {
          type = getUIntNType(astContext.toBits(accessSize));
          assert(getSize(type) == accessSize &&
                 "Unclipped access must be clipped");
        }
        // A zero-length bit-field in the span was given a member of its own
        // when it was accumulated, and belongs to no access unit, so it is not
        // one of the fields this unit holds.
        llvm::SmallVector<cir::BitFieldDeclAttr> unitFields;
        for (auto occupant = begin; occupant != bestEnd; ++occupant)
          if (!occupant->isZeroLengthBitField())
            unitFields.push_back(getBitFieldDecl(*occupant));
        assert(!unitFields.empty() && "an access unit holds a bit-field");
        members.push_back(makeAccessUnitInfo(beginOffset, type, unitFields));
 
        for (; begin != bestEnd; ++begin)
          if (!begin->isZeroLengthBitField())
            members.push_back(MemberInfo(beginOffset,
                                         MemberInfo::InfoKind::Field, nullptr,
                                         cir::RecordMemberKind::Data, *begin));
      }
      // Reset to start a new span.
      field = bestEnd;
      begin = fieldEnd;
    } else {
      assert(field != fieldEnd && field->isBitField() &&
             "Accumulating past end of bitfields");
      assert(!barrier && "Accumulating across barrier");
      if (field->isZeroLengthBitField())
        members.push_back(makeZeroWidthBitFieldInfo(*field));
      // Accumulate this bitfield into the current (potential) span.
      bitSizeSinceBegin += field->getBitWidthValue();
      ++field;
    }
  }
 
  return field;
}
 
void CIRRecordLowering::accumulateFields(bool nonVirtualBaseType) {
  for (RecordDecl::field_iterator field = recordDecl->field_begin(),
                                  fieldEnd = recordDecl->field_end();
       field != fieldEnd;) {
    if (field->isBitField()) {
      field = accumulateBitFields(field, fieldEnd);
      assert((field == fieldEnd || !field->isBitField()) &&
             "Failed to accumulate all the bitfields");
    } else if (isEmptyFieldForLayout(astContext, *field) &&
               field->isPotentiallyOverlapping()) {
      // We lay out normal empty fields, as they are required for GEPs/getting
      // function pointers. However 'no-unique-address' lends some additional
      // complexity. These fields take up no real space, but would also have to
      // be the correct 'GEP' offset to work here, but then mess with the
      // layout.  We likely need to come up with a new 'type' to support these,
      // then figure out some way to lower these to the correct offset, likely
      // by calculating the correct offset into the struct, and forming a
      // replacement by-byte GEP in LowerToLLVM.  However, this is only a
      // problem with taking the address of one of these, so it is in practice
      // not a horrifyingly problematic issue.
      assert(!cir::MissingFeatures::noUniqueAddressLayout());
      // Dropping the field leaves no member to mark, so its bytes read as
      // padding.  That is only sound when the field carries no ABI data, so
      // make sure we add a member for it. if it does.
      if (!isEmptyFieldForABI(astContext, *field))
        members.push_back(
            MemberInfo(bitsToCharUnits(getFieldBitOffset(*field)),
                       MemberInfo::InfoKind::Field,
                       getStorageType(field->getType()->getAsCXXRecordDecl()),
                       getFieldMemberKind(*field), *field));
      ++field;
    } else {
      // Use base subobject layout for potentially-overlapping fields,
      // as it is done in RecordLayoutBuilder.
      //
      // The mark comes from isEmptyFieldForABI, not the isEmptyFieldForLayout
      // above.  Neither predicate subsumes the other.
      members.push_back(MemberInfo(
          bitsToCharUnits(getFieldBitOffset(*field)),
          MemberInfo::InfoKind::Field,
          field->isPotentiallyOverlapping()
              ? getStorageType(field->getType()->getAsCXXRecordDecl())
              : getStorageType(*field),
          getFieldMemberKind(*field), *field));
      ++field;
    }
  }
}
 
void CIRRecordLowering::calculateZeroInit() {
  for (const MemberInfo &member : members) {
    if (member.kind == MemberInfo::InfoKind::Field) {
      if (!member.fieldDecl || isZeroInitializable(member.fieldDecl))
        continue;
      zeroInitializable = zeroInitializableAsBase = false;
      return;
    } else if (member.kind == MemberInfo::InfoKind::Base ||
               member.kind == MemberInfo::InfoKind::VBase) {
      if (isZeroInitializable(member.cxxRecordDecl))
        continue;
      zeroInitializable = false;
      if (member.kind == MemberInfo::InfoKind::Base)
        zeroInitializableAsBase = false;
    }
  }
}
 
void CIRRecordLowering::determinePacked(bool nvBaseType) {
  if (packed)
    return;
  CharUnits alignment = CharUnits::One();
  CharUnits nvAlignment = CharUnits::One();
  CharUnits nvSize = !nvBaseType && cxxRecordDecl
                         ? astRecordLayout.getNonVirtualSize()
                         : CharUnits::Zero();
 
  for (const MemberInfo &member : members) {
    // A member that owns no bytes sits inside another member's storage, whose
    // own offset and alignment are what decide packing.
    if (!ownsBytes(member))
      continue;
    // If any member falls at an offset that it not a multiple of its alignment,
    // then the entire record must be packed.
    if (!member.offset.isMultipleOf(getMemberAlignment(member.data)))
      packed = true;
    if (member.offset < nvSize)
      nvAlignment = std::max(nvAlignment, getMemberAlignment(member.data));
    alignment = std::max(alignment, getMemberAlignment(member.data));
  }
  // If the size of the record (the capstone's offset) is not a multiple of the
  // record's alignment, it must be packed.
  if (!members.back().offset.isMultipleOf(alignment))
    packed = true;
  // If the non-virtual sub-object is not a multiple of the non-virtual
  // sub-object's alignment, it must be packed.  We cannot have a packed
  // non-virtual sub-object and an unpacked complete object or vise versa.
  if (!nvSize.isMultipleOf(nvAlignment))
    packed = true;
  // Update the alignment of the sentinel.
  if (!packed)
    members.back().data = getUIntNType(astContext.toBits(alignment));
}
 
void CIRRecordLowering::insertPadding() {
  std::vector<std::pair<CharUnits, CharUnits>> padding;
  CharUnits size = CharUnits::Zero();
  for (const MemberInfo &member : members) {
    if (!member.data)
      continue;
    // A consumer recovers a member's offset by accumulating the sizes of the
    // members before it, so the padding a zero-width bit-field sits inside has
    // to be split at its offset for that sum to come out right.  The offset
    // can sit behind the running size, since the access unit covering the bits
    // around it may be wider than the offset it was declared at.
    if (!ownsBytes(member)) {
      if (member.offset > size) {
        padding.push_back(std::make_pair(size, member.offset - size));
        size = member.offset;
      }
      continue;
    }
    CharUnits offset = member.offset;
    assert(offset >= size);
    // Insert padding if we need to.
    if (offset != size.alignTo(packed ? CharUnits::One()
                                      : getMemberAlignment(member.data)))
      padding.push_back(std::make_pair(size, offset - size));
    size = offset + getSize(member.data);
  }
  if (padding.empty())
    return;
  // Add the padding to the Members list and sort it.
  for (const std::pair<CharUnits, CharUnits> &paddingPair : padding)
    members.push_back(makeStorageInfo(paddingPair.first,
                                      getByteArrayType(paddingPair.second),
                                      cir::RecordMemberKind::Pad));
  llvm::stable_sort(members);
}
 
static cir::ArgPassingKind
convertRecordArgPassingKind(RecordArgPassingKind kind) {
  switch (kind) {
  case RecordArgPassingKind::CanPassInRegs:
    return cir::ArgPassingKind::CanPassInRegs;
  case RecordArgPassingKind::CannotPassInRegs:
    return cir::ArgPassingKind::CannotPassInRegs;
  case RecordArgPassingKind::CanNeverPassInRegs:
    return cir::ArgPassingKind::CanNeverPassInRegs;
  }
  llvm_unreachable("unknown RecordArgPassingKind");
}
 
/// Whether the member kinds on \p recordTy answer the record's ABI emptiness
/// the same way the AST predicate does.
[[maybe_unused]] static bool
marksMatchABIEmptiness(const ASTContext &astContext, const RecordDecl *rd,
                       cir::RecordType recordTy) {
  return recordTy.isEmptyForABI() ==
         isEmptyRecordForABI(astContext, astContext.getCanonicalTagType(rd));
}
 
std::unique_ptr<CIRGenRecordLayout>
CIRGenTypes::computeRecordLayout(const RecordDecl *rd, cir::RecordType *ty) {
  CIRRecordLowering lowering(*this, rd, /*packed=*/false);
  assert(ty->isIncomplete() && "recomputing record layout?");
  lowering.lower(/*nonVirtualBaseType=*/false);
 
  // If we're in C++, compute the base subobject type. For C++ records baseTy
  // defaults to the complete object type and is replaced by a distinct,
  // smaller record only when the record has tail padding an enclosing
  // [[no_unique_address]] field can reuse. We must populate baseTy even when
  // it equals ty because callers such as getStorageType(const CXXRecordDecl *)
  // read it unconditionally when laying out potentially-overlapping
  // ([[no_unique_address]]) fields; a null baseTy would otherwise propagate as
  // a null mlir::Type into the members vector and trip the !empty() assertion
  // in fillOutputFields.
  cir::RecordType baseTy;
  if (llvm::isa<CXXRecordDecl>(rd)) {
    baseTy = *ty;
    // A record needs a distinct base-subobject type when its tail padding can
    // be reused by an enclosing [[no_unique_address]] field, i.e. when the
    // non-virtual size differs from the complete size.  This matches classic
    // CodeGen and covers unions too: a union's non-virtual size already tracks
    // its reusable tail padding (and stays at the minimum union size when the
    // union is empty, so a zero-data union does not spuriously qualify).
    if (lowering.astRecordLayout.getNonVirtualSize() !=
        lowering.astRecordLayout.getSize()) {
      CIRRecordLowering baseLowering(*this, rd, /*Packed=*/lowering.packed);
      baseLowering.lower(/*nonVirtualBaseType=*/true);
      std::string baseIdentifier = getRecordTypeName(rd, ".base");
      baseTy = builder.getCompleteNamedRecordType(
          baseLowering.getFieldTypes(), baseLowering.packed, baseIdentifier,
          baseLowering.getFieldKinds());
      // TODO(cir): add something like addRecordTypeName
 
      // BaseTy and Ty must agree on their packedness for getCIRFieldNo to work
      // on both of them with the same index.  Unions are exempt: CIR derives a
      // union's packedness from its layout size, which is the data size for the
      // base subobject but the full size for the complete object, so the two
      // can legitimately disagree.  (Classic CodeGen derives both from the data
      // size and so needs no such exemption.)
      assert((rd->isUnion() || lowering.packed == baseLowering.packed) &&
             "Non-virtual and complete types must agree on packedness");
      // Emptiness is a property of the decl, so the base subobject must answer
      // the same way the complete object does.  The two are not comparable
      // mark by mark: they see different sizes and so different tail padding.
      assert((marksMatchABIEmptiness(astContext, rd, baseTy) ||
              cgm.getDiags().hasErrorOccurred()) &&
             "base subobject member kinds must reproduce its ABI emptiness");
    }
  }
 
  // Fill in the record *after* computing the base type.  Filling in the body
  // signifies that the type is no longer opaque and record layout is complete,
  // but we may need to recursively layout rd while laying D out as a base type.
  assert(!cir::MissingFeatures::astRecordDeclAttr());
  ty->complete(lowering.getFieldTypes(), lowering.packed, lowering.unionPadding,
               lowering.getFieldKinds());
 
  // The marks exist so that emptiness can be read off the type, so check that
  // answer against the AST predicate on every record CIRGen lays out.  This
  // does not check the individual marks, only what they add up to.  The marks
  // themselves are pinned by clang/test/CIR/CodeGen/record-member-kinds.*.
  assert((marksMatchABIEmptiness(astContext, rd, *ty) ||
          cgm.getDiags().hasErrorOccurred()) &&
         "member kinds must reproduce the ABI emptiness of the record");
 
  // Queue ABI metadata for the module-level cir.record_layouts attribute.
  if (ty->getName()) {
    mlir::MLIRContext *mlirCtx = ty->getContext();
    cir::ArgPassingKind apk =
        convertRecordArgPassingKind(rd->getArgPassingRestrictions());
 
    bool hasTrivialDestructor = true;
    if (auto *cxxRD = dyn_cast<CXXRecordDecl>(rd))
      hasTrivialDestructor = cxxRD->hasTrivialDestructor();
    const auto &astLayout = astContext.getASTRecordLayout(rd);
    uint64_t recordAlignInBytes = astLayout.getAlignment().getQuantity();
 
    cgm.addRecordLayout(ty->getName(), cir::RecordLayoutAttr::get(
                                           mlirCtx, apk, hasTrivialDestructor,
                                           recordAlignInBytes));
  }
 
  auto rl = std::make_unique<CIRGenRecordLayout>(
      ty ? *ty : cir::RecordType{}, baseTy ? baseTy : cir::RecordType{},
      (bool)lowering.zeroInitializable, (bool)lowering.zeroInitializableAsBase);
 
  rl->nonVirtualBases.swap(lowering.nonVirtualBases);
  rl->completeObjectVirtualBases.swap(lowering.virtualBases);
 
  // Add all the field numbers.
  rl->fieldIdxMap.swap(lowering.fieldIdxMap);
 
  rl->bitFields.swap(lowering.bitFields);
 
  // Dump the layout, if requested.
  if (getASTContext().getLangOpts().DumpRecordLayouts) {
    llvm::outs() << "\n*** Dumping CIRgen Record Layout\n";
    llvm::outs() << "Record: ";
    rd->dump(llvm::outs());
    llvm::outs() << "\nLayout: ";
    rl->print(llvm::outs());
  }
 
  // TODO: implement verification
  return rl;
}
 
void CIRGenRecordLayout::print(raw_ostream &os) const {
  os << "<CIRecordLayout\n";
  os << "   CIR Type:" << completeObjectType << "\n";
  if (baseSubobjectType)
    os << "   NonVirtualBaseCIRType:" << baseSubobjectType << "\n";
  os << "   IsZeroInitializable:" << zeroInitializable << "\n";
  os << "   BitFields:[\n";
  std::vector<std::pair<unsigned, const CIRGenBitFieldInfo *>> bitInfo;
  for (auto &[decl, info] : bitFields) {
    const RecordDecl *rd = decl->getParent();
    unsigned index = 0;
    for (RecordDecl::field_iterator it = rd->field_begin(); *it != decl; ++it)
      ++index;
    bitInfo.push_back(std::make_pair(index, &info));
  }
  llvm::array_pod_sort(bitInfo.begin(), bitInfo.end());
  for (std::pair<unsigned, const CIRGenBitFieldInfo *> &info : bitInfo) {
    os.indent(4);
    info.second->print(os);
    os << "\n";
  }
  os << "   ]>\n";
}
 
void CIRGenBitFieldInfo::print(raw_ostream &os) const {
  os << "<CIRBitFieldInfo" << " name:" << name << " offset:" << offset
     << " size:" << size << " isSigned:" << isSigned
     << " storageSize:" << storageSize
     << " storageOffset:" << storageOffset.getQuantity()
     << " volatileOffset:" << volatileOffset
     << " volatileStorageSize:" << volatileStorageSize
     << " volatileStorageOffset:" << volatileStorageOffset.getQuantity() << ">";
}
 
void CIRGenRecordLayout::dump() const { print(llvm::errs()); }
 
void CIRGenBitFieldInfo::dump() const { print(llvm::errs()); }
 
void CIRRecordLowering::lowerUnion(bool nonVirtualBaseType) {
  // The base-subobject layout of a union is sized to its data size rather than
  // its full size.  A union can have reusable tail padding when one of its
  // members is a [[no_unique_address]] field that itself has tail padding, so
  // an enclosing [[no_unique_address]] union field must use this smaller type.
  CharUnits layoutSize = nonVirtualBaseType ? astRecordLayout.getDataSize()
                                            : astRecordLayout.getSize();
  // Accumulate bitfields and fields, and figure out what our difference between
  // storage type and padding is.
 
  // First, accumulate all the types.
  for (const FieldDecl *field : recordDecl->fields()) {
    mlir::Type fieldType;
    cir::RecordMemberKind fieldKind;
    if (field->isBitField()) {
      if (field->isZeroLengthBitField())
        continue;
      // Every variant starts at offset zero, so a bit-field variant is an
      // access unit of its own, holding that one field.
      mlir::Type unitStorage =
          getBitfieldStorageType(field->getBitWidthValue());
      setBitFieldInfo(field, CharUnits::Zero(), unitStorage);
      MemberInfo unit = makeAccessUnitInfo(CharUnits::Zero(), unitStorage,
                                           getBitFieldDecl(field));
      fieldType = unit.data;
      fieldKind = unit.memberKind;
    } else {
      fieldType = getStorageType(field);
      fieldKind = getFieldMemberKind(field);
    }
 
    fieldIdxMap[field->getCanonicalDecl()] = 0;
    addField(fieldType, fieldKind);
  }
 
  // Compute zero-initializable status.
  // This union might not be zero initialized: it may contain a pointer to
  // data member which might have some exotic initialization sequence.
  // This chooses the first 'named' member and is zero-initializable based on
  // that.
  auto hasNamedMember = [](const FieldDecl *curField) -> bool {
    const auto *rd = curField->getType()->getAsRecordDecl();
    return rd && rd->findFirstNamedDataMember();
  };
  // Whether this is usable for zero-init as a 'named member'. It is a field
  // with a name (or a record type with a named member itself), that isn't a
  // zero-width bitfield.
  auto isNamedMember = [hasNamedMember](const FieldDecl *curField) -> bool {
    if (curField->isZeroLengthBitField())
      return false;
    return curField->getIdentifier() || hasNamedMember(curField);
  };
  auto firstNamedMemberItr = llvm::find_if(recordDecl->fields(), isNamedMember);
 
  if (firstNamedMemberItr != recordDecl->fields().end() &&
      !isZeroInitializable(*firstNamedMemberItr))
    zeroInitializable = zeroInitializableAsBase = false;
 
  // If we have no candidates for storage, we are JUST padding.
  if (getFieldTypes().empty()) {
    appendPaddingBytes(layoutSize);
    return;
  }
 
  mlir::Type storageType =
      cir::UnionType::getUnionStorageType(dataLayout.layout, getFieldTypes());
 
  // If our storage size was bigger than our required size (can happen in the
  // case of packed bitfields on Itanium) then just use an I8 array.
  if (layoutSize < getSize(storageType))
    storageType = getByteArrayType(layoutSize);
 
  // The base-subobject record is built as a struct from fieldTypes, so add
  // the storage type and any trailing padding as ordinary fields rather than
  // routing padding through the union's single tail-padding slot.
  if (nonVirtualBaseType) {
    // A bit-field mark here says the stand-in's extent is not a declared
    // extent, not that its storage came from a bit-field: UnionBitAndWide in
    // clang/test/CIR/CodeGen/no-unique-address.cpp takes its double as storage
    // and still marks bitfield.  The stand-in describes every variant, so it
    // takes the storage type rather than any one variant's `!cir.bitfield`,
    // and is the one bit-field-marked member that is not one.  Computed before
    // clearFields() drops the variant marks.
    const cir::RecordMemberKind storageKind = makeMemberKind(
        /*holdsData=*/cir::anyMemberHoldsDataForABI(getFieldKinds()),
        /*isNamedBitField=*/llvm::any_of(getFieldKinds(),
                                         cir::isNamedBitField));
    clearFields();
    addField(storageType, storageKind);
    CharUnits padding = layoutSize - getSize(storageType);
    if (!padding.isZero())
      addField(getByteArrayType(padding), cir::RecordMemberKind::Pad);
  } else {
    // Else we just add padding normally.
    appendPaddingBytes(layoutSize - getSize(storageType));
  }
  packed = !layoutSize.isMultipleOf(getMemberAlignment(storageType));
}
 
bool CIRRecordLowering::hasOwnStorage(const CXXRecordDecl *decl,
                                      const CXXRecordDecl *query) {
  const ASTRecordLayout &declLayout = astContext.getASTRecordLayout(decl);
  if (declLayout.isPrimaryBaseVirtual() && declLayout.getPrimaryBase() == query)
    return false;
  for (const auto &base : decl->bases())
    if (!hasOwnStorage(base.getType()->getAsCXXRecordDecl(), query))
      return false;
  return true;
}
 
/// The AAPCS that defines that, when possible, bit-fields should
/// be accessed using containers of the declared type width:
/// When a volatile bit-field is read, and its container does not overlap with
/// any non-bit-field member or any zero length bit-field member, its container
/// must be read exactly once using the access width appropriate to the type of
/// the container. When a volatile bit-field is written, and its container does
/// not overlap with any non-bit-field member or any zero-length bit-field
/// member, its container must be read exactly once and written exactly once
/// using the access width appropriate to the type of the container. The two
/// accesses are not atomic.
///
/// Enforcing the width restriction can be disabled using
/// -fno-aapcs-bitfield-width.
void CIRRecordLowering::computeVolatileBitfields() {
  if (!CodeGenUtils::isAAPCS(astContext.getTargetInfo()) ||
      !cirGenTypes.getCGModule().getCodeGenOpts().AAPCSBitfieldWidth)
    return;
 
  for (auto &[field, info] : bitFields) {
    mlir::Type resLTy = cirGenTypes.convertTypeForMem(field->getType());
 
    if (astContext.toBits(astRecordLayout.getAlignment()) <
        getSizeInBits(resLTy).getQuantity())
      continue;
 
    // CIRRecordLowering::setBitFieldInfo() pre-adjusts the bit-field offsets
    // for big-endian targets, but it assumes a container of width
    // info.storageSize. Since AAPCS uses a different container size (width
    // of the type), we first undo that calculation here and redo it once
    // the bit-field offset within the new container is calculated.
    const unsigned oldOffset =
        isBigEndian() ? info.storageSize - (info.offset + info.size)
                      : info.offset;
    // Offset to the bit-field from the beginning of the struct.
    const unsigned absoluteOffset =
        astContext.toBits(info.storageOffset) + oldOffset;
 
    // Container size is the width of the bit-field type.
    const unsigned storageSize = getSizeInBits(resLTy).getQuantity();
    // Nothing to do if the access uses the desired
    // container width and is naturally aligned.
    if (info.storageSize == storageSize && (oldOffset % storageSize == 0))
      continue;
 
    // Offset within the container.
    unsigned offset = absoluteOffset & (storageSize - 1);
    // Bail out if an aligned load of the container cannot cover the entire
    // bit-field. This can happen for example, if the bit-field is part of a
    // packed struct. AAPCS does not define access rules for such cases, we let
    // clang to follow its own rules.
    if (offset + info.size > storageSize)
      continue;
 
    // Re-adjust offsets for big-endian targets.
    if (isBigEndian())
      offset = storageSize - (offset + info.size);
 
    const CharUnits storageOffset =
        astContext.toCharUnitsFromBits(absoluteOffset & ~(storageSize - 1));
    const CharUnits end = storageOffset +
                          astContext.toCharUnitsFromBits(storageSize) -
                          CharUnits::One();
 
    const ASTRecordLayout &layout =
        astContext.getASTRecordLayout(field->getParent());
    // If we access outside memory outside the record, than bail out.
    const CharUnits recordSize = layout.getSize();
    if (end >= recordSize)
      continue;
 
    // Bail out if performing this load would access non-bit-fields members.
    bool conflict = false;
    for (const auto *f : recordDecl->fields()) {
      // Allow sized bit-fields overlaps.
      if (f->isBitField() && !f->isZeroLengthBitField())
        continue;
 
      const CharUnits fOffset = astContext.toCharUnitsFromBits(
          layout.getFieldOffset(f->getFieldIndex()));
 
      // As C11 defines, a zero sized bit-field defines a barrier, so
      // fields after and before it should be race condition free.
      // The AAPCS acknowledges it and imposes no restritions when the
      // natural container overlaps a zero-length bit-field.
      if (f->isZeroLengthBitField()) {
        if (end > fOffset && storageOffset < fOffset) {
          conflict = true;
          break;
        }
      }
 
      const CharUnits fEnd =
          fOffset +
          astContext.toCharUnitsFromBits(
              getSizeInBits(cirGenTypes.convertTypeForMem(f->getType()))
                  .getQuantity()) -
          CharUnits::One();
      // If no overlap, continue.
      if (end < fOffset || fEnd < storageOffset)
        continue;
 
      // The desired load overlaps a non-bit-field member, bail out.
      conflict = true;
      break;
    }
 
    if (conflict)
      continue;
    // Write the new bit-field access parameters.
    // As the storage offset now is defined as the number of elements from the
    // start of the structure, we should divide the Offset by the element size.
    info.volatileStorageOffset =
        storageOffset /
        astContext.toCharUnitsFromBits(storageSize).getQuantity();
    info.volatileStorageSize = storageSize;
    info.volatileOffset = offset;
  }
}
 
void CIRRecordLowering::accumulateBases() {
  // If we've got a primary virtual base, we need to add it with the bases.
  if (astRecordLayout.isPrimaryBaseVirtual()) {
    const CXXRecordDecl *baseDecl = astRecordLayout.getPrimaryBase();
    members.push_back(MemberInfo(CharUnits::Zero(), MemberInfo::InfoKind::Base,
                                 getStorageType(baseDecl),
                                 getBaseMemberKind(baseDecl), baseDecl));
  }
 
  // Accumulate the non-virtual bases.
  for (const auto &base : cxxRecordDecl->bases()) {
    if (base.isVirtual())
      continue;
    // Bases can be zero-sized even if not technically empty if they
    // contain only a trailing array member.
    const CXXRecordDecl *baseDecl = base.getType()->getAsCXXRecordDecl();
    if (!baseDecl->isEmpty() &&
        !astContext.getASTRecordLayout(baseDecl).getNonVirtualSize().isZero()) {
      members.push_back(MemberInfo(astRecordLayout.getBaseClassOffset(baseDecl),
                                   MemberInfo::InfoKind::Base,
                                   getStorageType(baseDecl),
                                   getBaseMemberKind(baseDecl), baseDecl));
    }
  }
}
 
void CIRRecordLowering::accumulateVBases() {
  for (const auto &base : cxxRecordDecl->vbases()) {
    const CXXRecordDecl *baseDecl = base.getType()->getAsCXXRecordDecl();
    if (isEmptyRecordForLayout(astContext, base.getType()))
      continue;
    CharUnits offset = astRecordLayout.getVBaseClassOffset(baseDecl);
    // If the vbase is a primary virtual base of some base, then it doesn't
    // get its own storage location but instead lives inside of that base.
    if (isOverlappingVBaseABI() && astContext.isNearlyEmpty(baseDecl) &&
        !hasOwnStorage(cxxRecordDecl, baseDecl)) {
      members.push_back(MemberInfo(offset, MemberInfo::InfoKind::VBase, nullptr,
                                   cir::RecordMemberKind::Data, baseDecl));
      continue;
    }
    // If we've got a vtordisp, add it as a storage type.
    if (astRecordLayout.getVBaseOffsetsMap()
            .find(baseDecl)
            ->second.hasVtorDisp())
      members.push_back(makeStorageInfo(offset - CharUnits::fromQuantity(4),
                                        getUIntNType(32),
                                        cir::RecordMemberKind::Data));
    members.push_back(MemberInfo(offset, MemberInfo::InfoKind::VBase,
                                 getStorageType(baseDecl),
                                 getBaseMemberKind(baseDecl), baseDecl));
  }
}
 
void CIRRecordLowering::accumulateVPtrs() {
  if (astRecordLayout.hasOwnVFPtr())
    members.push_back(MemberInfo(CharUnits::Zero(), MemberInfo::InfoKind::VFPtr,
                                 getVFPtrType(), cir::RecordMemberKind::Data));
 
  if (astRecordLayout.hasOwnVBPtr())
    cirGenTypes.getCGModule().errorNYI(recordDecl->getSourceRange(),
                                       "accumulateVPtrs: hasOwnVBPtr");
}
 
mlir::Type CIRRecordLowering::getVFPtrType() {
  return cir::VPtrType::get(builder.getContext());
}