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LibJS: Remove dedicated iterator result instructions in favor of GetById

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When iterating over an iterable, we get back a JS object with the fields
"value" and "done".

Before this change, we've had two dedicated instructions for retrieving
the two fields: IteratorResultValue and IteratorResultDone. These had no
fast path whatsoever and just did a generic [[Get]] access to fetch the
corresponding property values.

By replacing the instructions with GetById("value") and GetById("done"),
they instantly get caching and JIT fast paths for free, making iterating
over iterables much faster. :^)

26% speed-up on this microbenchmark:

    function go(a) {
        for (const p of a) {
        }
    }
    const a = [];
    a.length = 1_000_000;
    go(a);
This commit is contained in:
Andreas Kling 2023-12-07 16:12:12 +01:00
parent 8d68f94282
commit 350e6c54d7
8 changed files with 26 additions and 96 deletions
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3
Userland/Libraries/LibJS/Bytecode/Generator.h
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@ -234,6 +234,9 @@ public:
void emit_get_by_id(IdentifierTableIndex);
void emit_get_by_id_with_this(IdentifierTableIndex, Register);
void emit_iterator_value();
void emit_iterator_complete();
[[nodiscard]] size_t next_global_variable_cache() { return m_next_global_variable_cache++; }
[[nodiscard]] size_t next_environment_variable_cache() { return m_next_environment_variable_cache++; }
[[nodiscard]] size_t next_property_lookup_cache() { return m_next_property_lookup_cache++; }