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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. :^)
This commit is contained in:
Andreas Kling 2021-10-07 01:06:21 +02:00
parent 421845b0cd
commit 41a072bded
8 changed files with 65 additions and 12 deletions

View file

@ -17,6 +17,7 @@
#include <AK/Variant.h>
#include <AK/Vector.h>
#include <LibJS/Forward.h>
#include <LibJS/Runtime/EnvironmentCoordinate.h>
#include <LibJS/Runtime/PropertyName.h>
#include <LibJS/Runtime/Reference.h>
#include <LibJS/Runtime/Value.h>
@ -984,6 +985,7 @@ private:
virtual bool is_identifier() const override { return true; }
FlyString m_string;
mutable Optional<EnvironmentCoordinate> m_cached_environment_coordinate;
};
class ClassMethod final : public ASTNode {