llvm-project/clang/lib/CIR/CodeGen/CIRGenRecordLayoutBuilder.cpp

//===----------------------------------------------------------------------===//
//
// 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 "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 "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 { Field } kind;
    mlir::Type data;
    union {
      const FieldDecl *fieldDecl;
      // CXXRecordDecl will be used here when base types are supported.
    };
    MemberInfo(CharUnits offset, InfoKind kind, mlir::Type data,
               const FieldDecl *fieldDecl = nullptr)
        : offset(offset), kind(kind), data(data), fieldDecl(fieldDecl) {};
    // MemberInfos are sorted so we define a < operator.
    bool operator<(const MemberInfo &other) const {
      return offset < other.offset;
    }
  };
  // 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) {
    return MemberInfo(offset, MemberInfo::InfoKind::Field, data);
  }

  void lower();
  void lowerUnion();

  /// Determines if we need a packed llvm struct.
  void determinePacked();
  /// Inserts padding everywhere it's needed.
  void insertPadding();

  void accumulateFields();

  CharUnits bitsToCharUnits(uint64_t bitOffset) {
    return astContext.toCharUnitsFromBits(bitOffset);
  }

  CharUnits getSize(mlir::Type Ty) {
    return CharUnits::fromQuantity(dataLayout.layout.getTypeSize(Ty));
  }
  CharUnits getAlignment(mlir::Type Ty) {
    return CharUnits::fromQuantity(dataLayout.layout.getTypeABIAlignment(Ty));
  }

  bool isZeroInitializable(const FieldDecl *fd) {
    return cirGenTypes.isZeroInitializable(fd->getType());
  }

  /// 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());
  }

  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()) {
      fieldTypes.push_back(getByteArrayType(size));
      padded = true;
    }
  }

  CIRGenTypes &cirGenTypes;
  CIRGenBuilderTy &builder;
  const ASTContext &astContext;
  const RecordDecl *recordDecl;
  const ASTRecordLayout &astRecordLayout;
  // Helpful intermediate data-structures
  std::vector<MemberInfo> members;
  // Output fields, consumed by CIRGenTypes::computeRecordLayout
  llvm::SmallVector<mlir::Type, 16> fieldTypes;
  llvm::DenseMap<const FieldDecl *, unsigned> fieldIdxMap;
  cir::CIRDataLayout dataLayout;

  LLVM_PREFERRED_TYPE(bool)
  unsigned zeroInitializable : 1;
  LLVM_PREFERRED_TYPE(bool)
  unsigned zeroInitializableAsBase : 1;
  LLVM_PREFERRED_TYPE(bool)
  unsigned packed : 1;
  LLVM_PREFERRED_TYPE(bool)
  unsigned padded : 1;

private:
  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),
      astRecordLayout(
          cirGenTypes.getASTContext().getASTRecordLayout(recordDecl)),
      dataLayout(cirGenTypes.getCGModule().getModule()),
      zeroInitializable(true), zeroInitializableAsBase(true), packed(packed),
      padded(false) {}

void CIRRecordLowering::lower() {
  if (recordDecl->isUnion()) {
    lowerUnion();
    assert(!cir::MissingFeatures::bitfields());
    return;
  }

  if (isa<CXXRecordDecl>(recordDecl)) {
    cirGenTypes.getCGModule().errorNYI(recordDecl->getSourceRange(),
                                       "lower: class");
    return;
  }

  assert(!cir::MissingFeatures::cxxSupport());

  CharUnits size = astRecordLayout.getSize();

  accumulateFields();

  llvm::stable_sort(members);
  // TODO: implement clipTailPadding once bitfields are implemented
  assert(!cir::MissingFeatures::bitfields());
  assert(!cir::MissingFeatures::recordZeroInit());

  members.push_back(makeStorageInfo(size, getUIntNType(8)));
  determinePacked();
  insertPadding();
  members.pop_back();

  fillOutputFields();
}

void CIRRecordLowering::fillOutputFields() {
  for (const MemberInfo &member : members) {
    if (member.data)
      fieldTypes.push_back(member.data);
    if (member.kind == MemberInfo::InfoKind::Field) {
      if (member.fieldDecl)
        fieldIdxMap[member.fieldDecl->getCanonicalDecl()] =
            fieldTypes.size() - 1;
      // A field without storage must be a bitfield.
      assert(!cir::MissingFeatures::bitfields());
    }
    assert(!cir::MissingFeatures::cxxSupport());
  }
}

void CIRRecordLowering::accumulateFields() {
  for (const FieldDecl *field : recordDecl->fields()) {
    if (field->isBitField()) {
      cirGenTypes.getCGModule().errorNYI(recordDecl->getSourceRange(),
                                         "accumulate bitfields");
      ++field;
    } else if (!field->isZeroSize(astContext)) {
      members.push_back(MemberInfo(bitsToCharUnits(getFieldBitOffset(field)),
                                   MemberInfo::InfoKind::Field,
                                   getStorageType(field), field));
      ++field;
    } else {
      // TODO(cir): do we want to do anything special about zero size members?
      assert(!cir::MissingFeatures::zeroSizeRecordMembers());
      ++field;
    }
  }
}

void CIRRecordLowering::determinePacked() {
  if (packed)
    return;
  CharUnits alignment = CharUnits::One();

  // TODO(cir): handle non-virtual base types
  assert(!cir::MissingFeatures::cxxSupport());

  for (const MemberInfo &member : members) {
    if (!member.data)
      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 % getAlignment(member.data))
      packed = true;
    alignment = std::max(alignment, getAlignment(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 % alignment)
    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;
    CharUnits offset = member.offset;
    assert(offset >= size);
    // Insert padding if we need to.
    if (offset !=
        size.alignTo(packed ? CharUnits::One() : getAlignment(member.data)))
      padding.push_back(std::make_pair(size, offset - size));
    size = offset + getSize(member.data);
  }
  if (padding.empty())
    return;
  padded = true;
  // 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)));
  llvm::stable_sort(members);
}

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();

  // If we're in C++, compute the base subobject type.
  if (llvm::isa<CXXRecordDecl>(rd) && !rd->isUnion() &&
      !rd->hasAttr<FinalAttr>()) {
    cgm.errorNYI(rd->getSourceRange(), "computeRecordLayout: CXXRecordDecl");
  }

  // 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.fieldTypes, lowering.packed, lowering.padded);

  auto rl = std::make_unique<CIRGenRecordLayout>(ty ? *ty : cir::RecordType());

  assert(!cir::MissingFeatures::recordZeroInit());
  assert(!cir::MissingFeatures::cxxSupport());
  assert(!cir::MissingFeatures::bitfields());

  // Add all the field numbers.
  rl->fieldIdxMap.swap(lowering.fieldIdxMap);

  // Dump the layout, if requested.
  if (getASTContext().getLangOpts().DumpRecordLayouts) {
    cgm.errorNYI(rd->getSourceRange(), "computeRecordLayout: dump layout");
  }

  // TODO: implement verification
  return rl;
}

void CIRRecordLowering::lowerUnion() {
  CharUnits layoutSize = astRecordLayout.getSize();
  mlir::Type storageType = nullptr;
  bool seenNamedMember = false;

  // Iterate through the fields setting bitFieldInfo and the Fields array. Also
  // locate the "most appropriate" storage type.
  for (const FieldDecl *field : recordDecl->fields()) {
    mlir::Type fieldType;
    if (field->isBitField())
      cirGenTypes.getCGModule().errorNYI(recordDecl->getSourceRange(),
                                         "bitfields in lowerUnion");
    else
      fieldType = getStorageType(field);

    // This maps a field to its index. For unions, the index is always 0.
    fieldIdxMap[field->getCanonicalDecl()] = 0;

    // 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.
    // If this is the case, then we ought not to try and come up with a "better"
    // type, it might not be very easy to come up with a Constant which
    // correctly initializes it.
    if (!seenNamedMember) {
      seenNamedMember = field->getIdentifier();
      if (!seenNamedMember)
        if (const RecordDecl *fieldRD = field->getType()->getAsRecordDecl())
          seenNamedMember = fieldRD->findFirstNamedDataMember();
      if (seenNamedMember && !isZeroInitializable(field)) {
        zeroInitializable = zeroInitializableAsBase = false;
        storageType = fieldType;
      }
    }

    // Because our union isn't zero initializable, we won't be getting a better
    // storage type.
    if (!zeroInitializable)
      continue;

    // Conditionally update our storage type if we've got a new "better" one.
    if (!storageType || getAlignment(fieldType) > getAlignment(storageType) ||
        (getAlignment(fieldType) == getAlignment(storageType) &&
         getSize(fieldType) > getSize(storageType)))
      storageType = fieldType;

    // NOTE(cir): Track all union member's types, not just the largest one. It
    // allows for proper type-checking and retain more info for analisys.
    fieldTypes.push_back(fieldType);
  }

  if (!storageType)
    cirGenTypes.getCGModule().errorNYI(recordDecl->getSourceRange(),
                                       "No-storage Union NYI");

  if (layoutSize < getSize(storageType))
    storageType = getByteArrayType(layoutSize);
  else
    appendPaddingBytes(layoutSize - getSize(storageType));

  // Set packed if we need it.
  if (layoutSize % getAlignment(storageType))
    packed = true;
}