1266764 - Make finding sticky "y" from `flags` faster in RegExpSplit.

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Tooru Fujisawa [:arai]]

Related to bug 1263490.

We're searching "y" character from `flags` string.

>        if (callFunction(std_String_includes, flags, "y"))

std_String_includes is also not inlinable.

Searching single character should be optimizable more with JS loop or length check or JIT inlining.

Especially, flags string should always be short, at most 5 chars (unless someone introduces extra many flags in their library), so JS loop with charCodeAt could be faster.

Comment 1

[Tooru Fujisawa [:arai]]

About bug 1263340 comment #24, if we could use flags slot instead of flags for all optimizable case, std_String_includes will be used only in non-optimizable case, like subclass or monkey-patched RegExp ctor/prototype.

Comment 2

[Tooru Fujisawa [:arai]]

Now std_String_includes is called only for the following non-optimizable cases:
  * call on subclassed RegExp instance
  * when RegExp prototype is modified

https://dxr.mozilla.org/mozilla-central/rev/c67dc1f9fab86d4f2cf3224307809c44fe3ce820/js/src/builtin/RegExp.js#615

Comment 3

[Till Schneidereit [:till]]

Excellent, let's call this fixed: there will come a time when some framework uses RegExp subclasses for ... something. Until then, there's no need to worry about it at all.