RFR: 8329597: C2: Intrinsify Reference.clear

[Kim Barrett]

On Mon, 15 Jul 2024 16:09:39 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> > Aw, nice usability landmine. I thought C2 barrier set would assert on me if it cannot deliver. Apparently not, [...]
> 
> Reference.refersTo has similar issues. See refersToImpl and refersTo0 in both Reference and PhantomReference. I think you should be able to model on those and the intrinsic implementation for refersTo to get what you want.
> 
> One additional complication is that Reference.enqueue intentionally calls clear0. If implementing clear similarly to refersTo, then enqueue should be changed to call clearImpl.

I should have read what I was replying to more carefully, rather than focusing on what was further up in the thread.
Looks like you (@shipilev) already spotted the refersTo stuff.  But the enqueue => clear0 could have easily been missed,
so perhaps not an entirely unneeded suggestion.

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PR Comment: https://git.openjdk.org/jdk/pull/20139#issuecomment-2231464762