src/v8/src/builtins/constants-table-builder.h

// Copyright 2018 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_BUILTINS_CONSTANTS_TABLE_BUILDER_H_
#define V8_BUILTINS_CONSTANTS_TABLE_BUILDER_H_

#include "src/base/macros.h"
#include "src/utils/allocation.h"
#include "src/utils/identity-map.h"
#include "src/handles/handles.h"

namespace v8 {
namespace internal {

class Isolate;
class Object;

// Utility class to build the builtins constants table and store it on the root
// list. The constants table contains constants used by builtins, and is there
// to avoid directly embedding them into code objects, which would not be
// possible for off-heap (and thus immutable) code objects.
class BuiltinsConstantsTableBuilder final {
 public:
  explicit BuiltinsConstantsTableBuilder(Isolate* isolate);

  // Returns the index within the builtins constants table for the given
  // object, possibly adding the object to the table. Objects are deduplicated.
  uint32_t AddObject(Handle<Object> object);

  // Self-references during code generation start out by referencing a handle
  // with a temporary dummy object. Once the final Code object exists, such
  // entries in the constants map must be patched up.
  void PatchSelfReference(Handle<Object> self_reference,
                          Handle<Code> code_object);

  // Should be called after all affected code (e.g. builtins and bytecode
  // handlers) has been generated.
  void Finalize();

 private:
  Isolate* isolate_;

  // Maps objects to corresponding indices within the constants list.
  using ConstantsMap = IdentityMap<uint32_t, FreeStoreAllocationPolicy>;
  ConstantsMap map_;

  DISALLOW_COPY_AND_ASSIGN(BuiltinsConstantsTableBuilder);
};

}  // namespace internal
}  // namespace v8

#endif  // V8_BUILTINS_CONSTANTS_TABLE_BUILDER_H_