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LibJS: Fast non-local variable access :^)
This patch introduces the "environment coordinate" concept, which encodes the distance from a variable access to the binding it ends up resolving to. EnvironmentCoordinate has two fields: - hops: The number of hops up the lexical environment chain we have to make before getting to the resolved binding. - index: The index of the resolved binding within its declarative environment record. Whenever a variable lookup resolves somewhere inside a declarative environment, we now cache the coordinates and reuse them in subsequent lookups. This is achieved via a coordinate cache in JS::Identifier. Note that non-strict direct eval() breaks this optimization and so it will not be performed if the resolved environment has been permanently screwed by eval(). This makes variable access *significantly* faster. :^)
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Userland/Libraries/LibJS/Runtime/EnvironmentCoordinate.h
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Userland/Libraries/LibJS/Runtime/EnvironmentCoordinate.h
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/*
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* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <LibJS/Forward.h>
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namespace JS {
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struct EnvironmentCoordinate {
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size_t hops { 0 };
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size_t index { 0 };
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};
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}
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