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LibJS: Allocate RegExp.{lastMatch,leftContext,rightContext} lazily

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These properties are always substrings of the RegExp input string,
and so we can store them as views and lazily construct strings if
they're actually accessed (which most of the time they aren't).

This avoids a bunch of unnecessary memory copying, saving roughly
2.1 seconds per iteration of Speedometer.
This commit is contained in:
Andreas Kling 2025-02-08 20:50:28 +01:00 • committed by Andreas Kling
commit dbf52a1b5f
Notes: github-actions[bot] 2025-02-08 23:29:09 +00:00
2 changed files with 47 additions and 12 deletions
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9
Libraries/LibJS/Runtime/RegExpLegacyStaticProperties.cpp
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@ -15,9 +15,12 @@ void RegExpLegacyStaticProperties::invalidate()
{
m_input = {};
m_last_match = {};
m_last_match_string = {};
m_last_paren = {};
m_left_context = {};
m_left_context_string = {};
m_right_context = {};
m_right_context_string = {};
m_$1 = {};
m_$2 = {};
m_$3 = {};
@ -92,7 +95,7 @@ void update_legacy_regexp_static_properties(RegExpConstructor& constructor, Utf1
// 8. Set the value of C’s [[RegExpLastMatch]] internal slot to a String whose length is endIndex - startIndex and containing the code units from S with indices startIndex through endIndex - 1, in ascending order.
auto last_match = string.view().substring_view(start_index, end_index - start_index);
legacy_static_properties.set_last_match(Utf16String::create(last_match));
legacy_static_properties.set_last_match(last_match);
// 9. If n > 0, set the value of C’s [[RegExpLastParen]] internal slot to the last element of capturedValues.
if (group_count > 0) {
@ -106,11 +109,11 @@ void update_legacy_regexp_static_properties(RegExpConstructor& constructor, Utf1
// 11. Set the value of C’s [[RegExpLeftContext]] internal slot to a String whose length is startIndex and containing the code units from S with indices 0 through startIndex - 1, in ascending order.
auto left_context = string.view().substring_view(0, start_index);
legacy_static_properties.set_left_context(Utf16String::create(left_context));
legacy_static_properties.set_left_context(left_context);
// 12. Set the value of C’s [[RegExpRightContext]] internal slot to a String whose length is len - endIndex and containing the code units from S with indices endIndex through len - 1, in ascending order.
auto right_context = string.view().substring_view(end_index, len - end_index);
legacy_static_properties.set_right_context(Utf16String::create(right_context));
legacy_static_properties.set_right_context(right_context);
// 13. For each integer i such that 1 ≤ i ≤ 9
for (size_t i = 1; i <= 9; i++) {