As long as a map is stable, no object with this map has changed map, which is a very useful property especially for optimized code. To be able to exploit this in optimized code, transitioning from a previously stable map will invalidate and deoptimize all optimized code that made use of the map being stable up to this point.
- Tobias On Tue, Dec 31, 2019 at 7:07 PM <janngodsp...@gmail.com> wrote: > Thanks! > > What is the point of marking a map as stable? If there was a normalization > isn't a new map created? So if types can't get mixed up after > normalization, what is the point of marking a map as stable? > > - Jann > > On Tuesday, December 31, 2019 at 1:33:36 AM UTC-6, Leszek Swirski wrote: >> >> Hi, >> >> A stable map is one from which a transition has never been observed, i.e. >> it's the leaf of the transition tree and objects with that map can be >> assumed to be "stable". Perhaps "is_leaf" or "never_transitioned_away_from" >> could be alternative names but it's a subtle concept to name and naming is >> hard anyway :) >> >> In the code you linked, I'm not 100% familiar with the reasoning but I >> assume that the compiler assumes that inferred stable maps are a "safe bet" >> as far as speculation is concerned, since they're a reliable end state, and >> can be assumed to be a correct inference even if the data is unreliable. >> That's mostly just a guess from the context though. >> >> - Leszek >> >> On Tue, 31 Dec 2019, 05:46 , <janngo...@gmail.com> wrote: >> >>> What is the difference between a stable and unstable map? >>> >>> Context: I'm trying to understand this line of code >>> https://cs.chromium.org/chromium/src/v8/src/compiler/js-native-context-specialization.cc?l=3227&rcl=4c53f9a51444393133ff303952f1296603d44ab7 >>> but can't seem to find any documentation about stable maps. Comments and >>> diffs are sparse on the subject as well. >>> >>> -- >>> -- >>> v8-dev mailing list >>> v8-...@googlegroups.com >>> http://groups.google.com/group/v8-dev >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "v8-dev" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to v8-...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/v8-dev/d8383180-787c-4bac-8ac3-d9295d400b2c%40googlegroups.com >>> <https://groups.google.com/d/msgid/v8-dev/d8383180-787c-4bac-8ac3-d9295d400b2c%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- > -- > v8-dev mailing list > v8-dev@googlegroups.com > http://groups.google.com/group/v8-dev > --- > You received this message because you are subscribed to the Google Groups > "v8-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to v8-dev+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/v8-dev/b2064f2a-93ea-4354-ac53-150a8eb56f68%40googlegroups.com > <https://groups.google.com/d/msgid/v8-dev/b2064f2a-93ea-4354-ac53-150a8eb56f68%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- -- v8-dev mailing list v8-dev@googlegroups.com http://groups.google.com/group/v8-dev --- You received this message because you are subscribed to the Google Groups "v8-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to v8-dev+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/v8-dev/CAN54oN7ViJc_KU9n%2BUxdGTG0bVvKUxwoN0WHgdS-qkK_3eOQRg%40mail.gmail.com.
