| 00:41 | <ljharb> | oh. well then yeah fair, i'm sure that's super rare :-) |
| 00:42 | <ljharb> | it's just very unfortunate that you can basically slow down any large-enough codebase for the entire life of the program if you sneak a ;[][Symbol.isConcatSpreadable] = false; in there |
| 00:50 | <bakkot> | there's lots of other things with similar effect |
| 00:53 | <bakkot> | https://chromium.googlesource.com/v8/v8.git/+/HEAD/src/execution/protectors.h |
| 00:54 | <bakkot> | not as many as I recalled actually |
| 00:54 | <bakkot> | but yeah still a handful |
| 00:56 | <ljharb> | do other engines have similar global, permanent perf cliffs? |
| 00:59 | <bakkot> | I know JSC has watchpoints, which amount to the same thing, yes |
| 00:59 | <bakkot> | I suspect SpiderMonkey also does but don't know offhand; shu might remember |
| 01:00 | <bakkot> | It's kind of inevitable if you want to make a performant engine - the language has lots of stupid dynamism and it's impossible to optimize in the face of full dynamism, so you have to know if certain things are intact |
| 01:01 | <bakkot> | and while I guess you could in principle check to see if something is mutated and then restored, that's expensive and rare so there's not that much reason to bother |
| 01:04 | <bakkot> | JSC also famously has the "have a bad time" watchpoint, which makes many things slow https://github.com/WebKit/WebKit/blob/eb65814e9baa483a2fb87b099ab1ba905b9389c9/Source/JavaScriptCore/runtime/JSGlobalObject.cpp#L2249 |