tree 79276348cd132f9c10a3d8d7477f1f5e48c4a7b5
parent cfa7eebb88b38cd68b611e043a70a44bc6460b54
author Dominik Inführ <dinfuehr@chromium.org> 1741609184 +0100
committer V8 LUCI CQ <v8-scoped@luci-project-accounts.iam.gserviceaccount.com> 1741612591 -0700

[heap] Get rid of discovered_ephemerons worklist

This CL drops `discovered_ephemerons` and simply pushes newly
discovered ephemerons into `next_ephemerons` instead. Conceptually
marking with ephemeron semantics will operate like this until
fixpoint:

1) Move `next_ephemerons` into `current_ephemerons`
2) Apply ephemeron semantics on all ephemerons in
   `current_ephemerons`
3) Drain marking worklist
4) Goto 1) if any object was marked

`discovered_ephemerons` was intended as an optimization and since we
anyways have to perform another iteration when we marked any object,
this also means that we will always perform another iteration as soon
when discovered_ephemerons is non-empty. So `discovered_ephemerons`
does not help us anymore.

The fixpoint iteration will behave like this:

0) `current_ephemerons` is empty and will not be used.
1) Add all `next_ephemerons` to key_to_values.
2) Drain marking worklist
3) Add new `next_ephemerons` to key_to_values.
4a) Good case: All discovered objects fit into vector. Simply iterate
               all discovered objects and perform map lookup in
               key_to_values_.
4b) Bad case:  Too many discovered objects. Iterate over all of
               key_to_values_ and apply ephemeron semantics if key
               is marked now.
5) Goto 2) if there is more work

Bug: 401897607
Change-Id: I637e210cf36eb8e5b74d5341ef6f295ab3e2f78b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/6329481
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#99149}