Jon Coppeard
f24562cc04
This involved a bit more work. Getting the exact number of object slots can be quite involved but we don't need this for conucrrent marking. I added functions to get slot count accurate up to SMALL_SLOTSPAN_MAX for use when calculating the number of used fixed slots, as we don't need accuracy beyond MAX_FIXED_SLOTS (16) for this anyway. Differential Revision: https://phabricator.services.mozilla.com/D307519
89 lines
2.2 KiB
C++
89 lines
2.2 KiB
C++
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/*
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* Shadow definition of |JSObject| innards. Do not use this directly!
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*/
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#ifndef js_shadow_Object_h
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#define js_shadow_Object_h
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#include "mozilla/Assertions.h" // MOZ_ASSERT
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#include <stddef.h> // size_t
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#include "js/shadow/Shape.h" // JS::shadow::Shape
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#include "js/Value.h" // JS::Value
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class JS_PUBLIC_API JSObject;
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namespace JS {
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class JS_PUBLIC_API Value;
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namespace shadow {
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inline size_t NumNativeObjectFixedSlots(Shape* shape) {
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return (shape->immutableFlags & shadow::Shape::FIXED_SLOTS_MASK) >>
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shadow::Shape::FIXED_SLOTS_SHIFT;
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}
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/**
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* Layout shared by all JSObjects.
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*/
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struct Object {
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shadow::Shape* shape;
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static constexpr size_t MAX_FIXED_SLOTS = 16;
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};
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/**
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* Layout for all NativeObjects.
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*/
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struct NativeObject : public Object {
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#ifndef JS_64BIT
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uint32_t padding_;
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#endif
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Value* slots;
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void* _1;
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size_t numFixedSlots() const { return NumNativeObjectFixedSlots(shape); }
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Value* fixedSlots() const {
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auto address = reinterpret_cast<uintptr_t>(this);
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return reinterpret_cast<JS::Value*>(address + sizeof(NativeObject));
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}
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Value& slotRef(size_t slot) const {
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size_t nfixed = numFixedSlots();
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if (slot < nfixed) {
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return fixedSlots()[slot];
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}
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return slots[slot - nfixed];
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}
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// Like slotRef, but optimized for reserved slots. This relies on the fact
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// that the first reserved slots (up to MAX_FIXED_SLOTS) are always stored in
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// fixed slots. This lets the compiler optimize away the branch below when
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// |slot| is a constant (after inlining).
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MOZ_ALWAYS_INLINE Value& reservedSlotRef(size_t slot) const {
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MOZ_ASSERT((slot < numFixedSlots()) == (slot < MAX_FIXED_SLOTS));
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if (slot < MAX_FIXED_SLOTS) {
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return fixedSlots()[slot];
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}
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return slots[slot - MAX_FIXED_SLOTS];
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}
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};
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} // namespace shadow
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/** Get the |JSClass| of an object. */
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inline const JSClass* GetClass(const JSObject* obj) {
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return reinterpret_cast<const shadow::Object*>(obj)->shape->base->clasp;
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}
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} // namespace JS
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#endif // js_shadow_Object_h
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