[jdk17u] RFR: 8261495: Shenandoah: reconsider update references memory ordering

[Roman Kennke]

On Fri, 12 Nov 2021 08:21:51 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Clean backport to improve Shenandoah performance.
> 
> Additional testing: 
>  - [x] Linux x86_64 fastdebug `hotspot_gc_shenandoah`
>  - [x] Linux x86_64 fastdebug `tier1`

Looks good, thank you!

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Marked as reviewed by rkennke (Reviewer).

PR: https://git.openjdk.java.net/jdk17u/pull/254