Integrated: 8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier

[kuaiwei]

On Fri, 17 May 2024 08:57:20 GMT, kuaiwei <duke at openjdk.org> wrote:

> he origin patch for https://bugs.openjdk.org/browse/JDK-8324186 has 2 issues:
> 1 It show regression in some platform, like Apple silicon in mac os
> 2 Can not handle instruction sequence like "dmb.ishld; dmb.ishst; dmb.ishld; dmb.ishld"
> 
> It can be fixed by:
> 1 Enable AlwaysMergeDMB by default, only disable it in architecture we can see performance improvement (N1 or N2)
> 2 Check the special pattern and merge the subsequent dmb.
> 
> It also fix a bug when code buffer is expanding, st/ld/dmb can not be merged. I added unit tests for these.
> 
> This patch still has a unhandled case. Insts like "dmb.ishld; dmb.ishst; dmb.ish", it will merge the last 2 instructions and can not merge all three. Because when emitting dmb.ish, if merge all previous dmbs, the code buffer will shrink the size. I think it may break some resumption and think it's not a common pattern.
> 
> In previous PR https://github.com/openjdk/jdk/pull/18467 , I tried an implementation to use state machine for merging. But it looks risky to pending instruction during emitting.

This pull request has now been integrated.

Changeset: 2a242db0
Author:    Kuai Wei <kuaiwei.kw at alibaba-inc.com>
Committer: Aleksey Shipilev <shade at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/2a242db01ed1d502affa4a954e601266fa98dfbe
Stats:     523 lines in 9 files changed: 510 ins; 0 del; 13 mod

8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier

Reviewed-by: shade, aph

-------------

PR: https://git.openjdk.org/jdk/pull/19278