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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. :^)
13 lines
345 B
JavaScript
13 lines
345 B
JavaScript
test("basic that non-strict direct eval() prevents non-local access caching", () => {
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function foo(do_eval) {
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var c = 1;
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function bar(do_eval) {
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if (do_eval) eval("var c = 2;");
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return c;
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}
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return bar(do_eval);
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}
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expect(foo(false)).toBe(1);
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expect(foo(true)).toBe(2);
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});
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