18 ms·
> Is there any benefit to it? Well, in theory yes. When determining whether a specific function can be inlined into its call site, V8 looks at the length of th
by phpnode 11y ago
> Is there any benefit to it?
Well, in theory yes. When determining whether a specific function can be inlined into its call site, V8 looks at the length of the function source code to try and guess whether it's worth it. Functions longer than 600 characters (including comments) cannot be inlined and therefore they will typically be slower.
Whether that makes any meaningful difference to your application performance really depends on the application. In most cases it won't.
- nitrogen 11y agoInteresting. Is there a reason why the parsed AST size isn't used instead of raw source code size?
- phpnode 11y agoV8 doesn't use an AST, it uses a CFG, but I believe it comes down to efficiency - it's far cheaper to look at the length of a string than to traverse a graph, and by its nature JS needs very fast compilation times. This is probably one of those heuristics that works well enough on enough real world code, even though everyone knows it's suboptimal. I've heard that the turbofan compiler will remove this limitation but that's still very much work in progress.
- teacup50 11y ago... and people wonder why we want a web bytecode so, so badly.
- barrkel 11y agoV8 AST: https://code.google.com/p/v8/source/browse/branches/bleeding_edge/src/ast.h https://code.google.com/p/v8/source/browse/branches/bleeding...
- phpnode 11y agothanks
- barrkel 11y agoOnly reason I brought it up was the assertion that V8 didn't have an AST. Only the most trivial of compilers avoid building an AST; V8 may not use an AST for interpretation, but interpretation / compilation will be downstream of the AST and could use info from the AST for optimization heuristics. A non-IDE AST would not normally include comments.
- phpnode 11y agoI remember thinking that it was odd when I first read about it, I think it must have been in relation to one of the other compilers and I got my wires crossed, but I can't find the source now. Thanks for the correction anyway.
- Kenji 11y agoThat's really odd. In my eyes, source code length is not a good way to measure the semantic size of a function. But what you're saying is very interesting; I learned something new.
- nallerooth 11y agoI did not know that, thanks!
- StavrosK 11y agoWait, what if you have really really long comments? Or do they get stripped out beforehand?
- phpnode 11y agoComments affect this heuristic, so yeah, commented code can be slower.
- hiou 11y agoSome libraries use annotations in comments. Therefore they cannot be stripped. Off the top of my head I know of some JavaScript testing libraries that do this.
- wolf550e 11y agoThis slide deck has a nice example of using a comment to fix a performance bug in a js implementation of the chacha20 cipher: http://mrale.ph/talks/goto2015/#/14 http://mrale.ph/talks/goto2015/#/14
- bcrypt 11y agoThat's really surprising. Thanks!
- rezacks 11y agoI never know this before! Thanks for sharing.
- joepie91_ 11y agoYou can also just set a flag that changes that maximum length - there's more about that here: https://www.youtube.com/watch?v=FXyM1yrtloc https://www.youtube.com/watch?v=FXyM1yrtloc You certainly don't need server-side minification.