Sounds like a solid plan. It combines the best of both worlds (we don't have to reinvent the wheel but we minimize how much code we import). The fact that the code is pretty stable definitely supports this approach.
Andreas On Jan 2, 2014, at 12:28 PM, Luke Wagner <[email protected]> wrote: > I don't think a pure (2) approach is our cheapest option. Even with Yarr, it > took Chris a whole bunch of work to import and it also took Dave/Dave a long > time each time they pulled a new version. It sounds like irregexp would be > much worse. Furthermore, having a whole hunk of code you can't just change > means everybody goes to lengths to avoid touching it and it becomes a big sad > sinkhole. > > Perhaps we could use a modified (2) approach: fork irregexp. In particular, > we'd: > - significantly refactor the code to use SM rooting, assembler, Vector, > LifoAlloc, etc APIs > - declare open season on stylistic refactorings to make irregexp match SM > > The obvious concern is that we'd miss updates/fixes in V8. However, looking > at the V8 svn repo, the irregexp files change infrequently (almost nothing in > the last 6 months) so we could just as well, every month or so, just look at > all the changes to the 9 *regexp* files and manually apply the diffs. > > One thing, though, is we'd really need an owner for this code who took the > time to fully understand irregexp so they could fix what may come as it came > and review patches. > > Cheers, > Luke > > ----- Original Message ----- >> 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 >> > _______________________________________________ > dev-tech-js-engine-internals mailing list > [email protected] > https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals _______________________________________________ dev-tech-js-engine-internals mailing list [email protected] https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals
