Aliaksandr Kalenik 2171563daf LibJS: Avoid function envs for lexical-this arrows ...

Track whether a function needs environment-backed this resolution
separately from whether it needs to allocate its own function
environment. Arrow functions that only capture lexical this can now
resolve through the outer environment without allocating an empty
function environment for every call.

Keep the asm Call path conservative by routing functions that still need
lexical-this resolution through the C++ inline-call helper, so the call
receiver is not cached as the arrow function's this value.

Microbenchmark:

    function makeLexicalThisArrow() {
        return () => this.value;
    }

    let object = { value: 1, makeLexicalThisArrow };
    let fn = object.makeLexicalThisArrow();
    for (let i = 0; i < 20_000_000; ++i)
        fn();

Measured with the same Release build toggling this patch:

    baseline:  1069.2 ms mean over 12 runs
    optimized:  501.2 ms mean over 12 runs
    speedup:    2.13 times faster

2026-04-30 18:44:34 +02:00

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