Back in 2010, we imported the YARR regular expression engine from JSC [0]. It has served us well over the years, but with all the optimizations to the rest of the engine, regular expression performance is becoming a bottleneck again. When YARR is able to JIT a regular expression, performance is mostly on par with V8. However, when we can't compile a regexp, we're stuck in the interpreter and become very slow.
Unfortunately, YARR is unable to JIT some regular expressions used in popular JS libraries like jQuery [1]. The main problem is that YARR can't compile regexps with nested parenthesized groups. As I understand it, this is a pretty fundamental issue that requires a major refactoring. The upstream WebKit bug has had no activity for over 3 years [2]. There's also a problem with "quantity 1 subpatterns that are copies" that affects a Peacekeeper email validation regular expression [3] and is the only reason for us being slower than Chrome on the Peacekeeper stringValidateForm test [4]. To address these issues, we have the following options: (1) Fix YARR ourselves, either upstream or locally. (2) Switch from YARR to V8's irregexp engine. (3) Write something ourselves, probably based on V8's irregexp. (1) will be hard; I don't think we have somebody familiar enough with YARR to do a refactoring of this size. It could be an option though. For (2), we'd have to write a layer mapping V8's macro assembler calls to our own macro assembler. Unfortunately, unlike SM and JSC, V8 has more platform-specific code and we'd have to do this work for different platforms. I'm not sure what other dependencies there are on other parts of the V8 engine. Personally, I like (3): it's not a small task, but it'd finally give us a regexp engine that integrates well with the rest of the engine. This also means we can dump JSC's macro-assembler (JM used it as well, but is also gone) and use the one we wrote for the baseline/Ion JITs. It'd also integrate much better than Yarr in terms of code style and data structures. If we base it on irregexp, we should be able to avoid most pitfalls or design problems. What do people think? Jan [0] https://bugzilla.mozilla.org/show_bug.cgi?id=564953 [1] https://bugzilla.mozilla.org/show_bug.cgi?id=929507 [2] https://bugs.webkit.org/show_bug.cgi?id=42264 [3] https://bugs.webkit.org/show_bug.cgi?id=122891 [4] https://bugzilla.mozilla.org/show_bug.cgi?id=692009 _______________________________________________ dev-tech-js-engine-internals mailing list [email protected] https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals
