// Copyright 2017 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_OBJECTS_ARGUMENTS_H_
#define V8_OBJECTS_ARGUMENTS_H_
#include "src/objects/fixed-array.h"
#include "src/objects/hole.h"
#include "src/objects/js-objects.h"
#include "src/objects/struct.h"
// Has to be the last include (doesn't have include guards):
#include "src/objects/object-macros.h"
namespace v8 {
namespace internal {
class StructBodyDescriptor;
// Superclass for all objects with instance type {JS_ARGUMENTS_OBJECT_TYPE}
V8_OBJECT class JSArgumentsObject : public JSObject {
public:
V8_IT_OWN_TYPE;
DECL_VERIFIER(JSArgumentsObject)
DECL_PRINTER(JSArgumentsObject)
// Defined out-of-line below the class so `sizeof` on the still-incomplete
// type can appear in an initializer.
static const int kHeaderSize;
} V8_OBJECT_END;
inline constexpr int JSArgumentsObject::kHeaderSize = sizeof(JSArgumentsObject);
// JSSloppyArgumentsObject is just a JSArgumentsObject with specific initial
// map. This initial map adds in-object properties for "length" and "callee".
// Shape-style: no own C++ storage; fields live in the parent
// JSArgumentsObject's in-object property slots at fixed offsets past
// JSArgumentsObject::kHeaderSize.
class JSSloppyArgumentsObject : public JSArgumentsObject {
public:
V8_IT_REUSE_PARENT;
// Slot indices of the in-object properties, relative to the parent's
// kHeaderSize.
static constexpr int kLengthSlotIndex = 0;
static constexpr int kCalleeSlotIndex = 1;
static constexpr int kInObjectPropertyCount = 2;
static constexpr int kLengthOffset =
JSArgumentsObject::kHeaderSize + kLengthSlotIndex * kTaggedSize;
static constexpr int kCalleeOffset =
JSArgumentsObject::kHeaderSize + kCalleeSlotIndex * kTaggedSize;
static constexpr int kSize =
JSArgumentsObject::kHeaderSize + kInObjectPropertyCount * kTaggedSize;
private:
DISALLOW_IMPLICIT_CONSTRUCTORS(JSSloppyArgumentsObject);
};
// JSStrictArgumentsObject is just a JSArgumentsObject with specific initial
// map. This initial map adds an in-object property for "length".
class JSStrictArgumentsObject : public JSArgumentsObject {
V8_IT_REUSE_PARENT;
public:
static constexpr int kLengthSlotIndex = 0;
static constexpr int kInObjectPropertyCount = 1;
static constexpr int kLengthOffset =
JSArgumentsObject::kHeaderSize + kLengthSlotIndex * kTaggedSize;
static constexpr int kSize =
JSArgumentsObject::kHeaderSize + kInObjectPropertyCount * kTaggedSize;
private:
DISALLOW_IMPLICIT_CONSTRUCTORS(JSStrictArgumentsObject);
};
// Representation of a slow alias as part of a sloppy arguments objects.
// For fast aliases (if HasSloppyArgumentsElements()):
// - the parameter map contains an index into the context
// - all attributes of the element have default values
// For slow aliases (if HasDictionaryArgumentsElements()):
// - the parameter map contains no fast alias mapping (i.e. the hole)
// - this struct (in the slow backing store) contains an index into the context
// - all attributes are available as part if the property details
V8_OBJECT class AliasedArgumentsEntry : public Struct {
public:
inline int aliased_context_slot() const;
inline void set_aliased_context_slot(int value);
using BodyDescriptor = StructBodyDescriptor;
DECL_PRINTER(AliasedArgumentsEntry)
DECL_VERIFIER(AliasedArgumentsEntry)
public:
TaggedMember<Smi> aliased_context_slot_;
} V8_OBJECT_END;
// Helper class to access FAST_ and SLOW_SLOPPY_ARGUMENTS_ELEMENTS, dividing
// arguments into two types for a given SloppyArgumentsElements object:
// mapped and unmapped.
//
// For clarity SloppyArgumentsElements fields are qualified with "elements."
// below.
//
// Mapped arguments are actual arguments. Unmapped arguments are values added
// to the arguments object after it was created for the call. Mapped arguments
// are stored in the context at indexes given by elements.mapped_entries[key].
// Unmapped arguments are stored as regular indexed properties in the arguments
// array which can be accessed from elements.arguments.
//
// elements.length is min(number_of_actual_arguments,
// number_of_formal_arguments) for a concrete call to a function.
//
// Once a SloppyArgumentsElements is generated, lookup of an argument with index
// |key| in |elements| works as follows:
//
// If key >= elements.length then attempt to look in the unmapped arguments
// array and return the value at key, missing to the runtime if the unmapped
// arguments array is not a fixed array or if key >= elements.arguments.length.
//
// Otherwise, t = elements.mapped_entries[key]. If t is the hole, then the
// entry has been deleted from the arguments object, and value is looked up in
// the unmapped arguments array, as described above. Otherwise, t is a Smi
// index into the context array specified at elements.context, and the return
// value is elements.context[t].
//
// A graphic representation of a SloppyArgumentsElements object and a
// corresponding unmapped arguments FixedArray:
//
// SloppyArgumentsElements
// +---+-----------------------+
// | Context context |
// +---------------------------+
// | FixedArray arguments +----+ HOLEY_ELEMENTS
// +---------------------------+ v-----+-----------+
// | 0 | Object mapped_entries | | 0 | the_hole |
// |...| ... | | ... | ... |
// |n-1| Object mapped_entries | | n-1 | the_hole |
// +---------------------------+ | n | element_1 |
// | ... | ... |
// |n+m-1| element_m |
// +-----------------+
//
// The elements.arguments backing store kind depends on the ElementsKind of
// the outer JSArgumentsObject:
// - FAST_SLOPPY_ARGUMENTS_ELEMENTS: HOLEY_ELEMENTS
// - SLOW_SLOPPY_ARGUMENTS_ELEMENTS: DICTIONARY_ELEMENTS
V8_OBJECT class SloppyArgumentsElements
: public TaggedArrayBase<SloppyArgumentsElements, UnionOf<Smi, Hole>> {
using Super = TaggedArrayBase<SloppyArgumentsElements, UnionOf<Smi, Hole>>;
public:
static constexpr RootIndex kMapRootIndex =
RootIndex::kSloppyArgumentsElementsMap;
inline Tagged<Context> context() const;
inline void set_context(Tagged<Context> value,
WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
inline Tagged<UnionOf<FixedArray, NumberDictionary>> arguments() const;
inline void set_arguments(Tagged<UnionOf<FixedArray, NumberDictionary>> value,
WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
// Returns: Smi|TheHole.
inline Tagged<UnionOf<Smi, Hole>> mapped_entries(uint32_t index,
RelaxedLoadTag) const;
inline void set_mapped_entries(uint32_t index,
Tagged<UnionOf<Smi, Hole>> value);
inline void set_mapped_entries(uint32_t index,
Tagged<UnionOf<Smi, Hole>> value,
RelaxedStoreTag);
DECL_PRINTER(SloppyArgumentsElements)
DECL_VERIFIER(SloppyArgumentsElements)
class BodyDescriptor;
static constexpr uint32_t kLengthOffset = sizeof(HeapObject);
static constexpr uint32_t kHeaderSize =
kLengthOffset + (TAGGED_SIZE_8_BYTES ? kTaggedSize : kApiInt32Size) +
2 * kTaggedSize;
public:
// length_ / optional_padding_ live in FixedArrayBase.
TaggedMember<Context> context_;
TaggedMember<UnionOf<FixedArray, NumberDictionary>> arguments_;
FLEXIBLE_ARRAY_MEMBER(typename Super::ElementMemberT, objects);
} V8_OBJECT_END;
} // namespace internal
} // namespace v8
#include "src/objects/object-macros-undef.h"
#endif // V8_OBJECTS_ARGUMENTS_H_