lib/AST/Interp/Block.h

//===--- Block.h - Allocated blocks for the interpreter ---------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Defines the classes describing allocated blocks.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_AST_INTERP_BLOCK_H
#define LLVM_CLANG_AST_INTERP_BLOCK_H

#include "Descriptor.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ComparisonCategories.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/Support/raw_ostream.h"

namespace clang {
namespace interp {
class Block;
class DeadBlock;
class Context;
class InterpState;
class Pointer;
class Function;
enum PrimType : unsigned;

/// A memory block, either on the stack or in the heap.
///
/// The storage described by the block immediately follows it in memory.
class Block {
public:
  // Creates a new block.
  Block(const llvm::Optional<unsigned> &DeclID, Descriptor *Desc,
        bool IsStatic = false, bool IsExtern = false)
      : DeclID(DeclID), IsStatic(IsStatic), IsExtern(IsExtern), Desc(Desc) {}

  Block(Descriptor *Desc, bool IsStatic = false, bool IsExtern = false)
      : DeclID((unsigned)-1), IsStatic(IsStatic), IsExtern(IsExtern),
        Desc(Desc) {}

  /// Returns the block's descriptor.
  Descriptor *getDescriptor() const { return Desc; }
  /// Checks if the block has any live pointers.
  bool hasPointers() const { return Pointers; }
  /// Checks if the block is extern.
  bool isExtern() const { return IsExtern; }
  /// Checks if the block has static storage duration.
  bool isStatic() const { return IsStatic; }
  /// Checks if the block is temporary.
  bool isTemporary() const { return Desc->IsTemporary; }
  /// Returns the size of the block.
  InterpSize getSize() const { return Desc->getAllocSize(); }
  /// Returns the declaration ID.
  llvm::Optional<unsigned> getDeclID() const { return DeclID; }

  /// Returns a pointer to the stored data.
  char *data() { return reinterpret_cast<char *>(this + 1); }

  /// Returns a view over the data.
  template <typename T>
  T &deref() { return *reinterpret_cast<T *>(data()); }

  /// Invokes the constructor.
  void invokeCtor() {
    std::memset(data(), 0, getSize());
    if (Desc->CtorFn)
      Desc->CtorFn(this, data(), Desc->IsConst, Desc->IsMutable,
                   /*isActive=*/true, Desc);
  }

protected:
  friend class Pointer;
  friend class DeadBlock;
  friend class InterpState;

  Block(Descriptor *Desc, bool IsExtern, bool IsStatic, bool IsDead)
    : IsStatic(IsStatic), IsExtern(IsExtern), IsDead(true), Desc(Desc) {}

  // Deletes a dead block at the end of its lifetime.
  void cleanup();

  // Pointer chain management.
  void addPointer(Pointer *P);
  void removePointer(Pointer *P);
  void movePointer(Pointer *From, Pointer *To);

  /// Start of the chain of pointers.
  Pointer *Pointers = nullptr;
  /// Unique identifier of the declaration.
  llvm::Optional<unsigned> DeclID;
  /// Flag indicating if the block has static storage duration.
  bool IsStatic = false;
  /// Flag indicating if the block is an extern.
  bool IsExtern = false;
  /// Flag indicating if the pointer is dead.
  bool IsDead = false;
  /// Pointer to the stack slot descriptor.
  Descriptor *Desc;
};

/// Descriptor for a dead block.
///
/// Dead blocks are chained in a double-linked list to deallocate them
/// whenever pointers become dead.
class DeadBlock {
public:
  /// Copies the block.
  DeadBlock(DeadBlock *&Root, Block *Blk);

  /// Returns a pointer to the stored data.
  char *data() { return B.data(); }

private:
  friend class Block;
  friend class InterpState;

  void free();

  /// Root pointer of the list.
  DeadBlock *&Root;
  /// Previous block in the list.
  DeadBlock *Prev;
  /// Next block in the list.
  DeadBlock *Next;

  /// Actual block storing data and tracking pointers.
  Block B;
};

} // namespace interp
} // namespace clang

#endif