RFR: 8227369: pd_disjoint_words_atomic() needs to be atomic [v2]

[David Holmes]

> Replace the common "atomic" switch+loop code chunks in the pd code with a shared version that uses Atomic::load/store.
> 
> See details in the bug report that show how current code is actually replaced by `memcpy` (in some places at least) whereas the new code is not.
> 
> Platforms affected:
>  - all x86
>  - Zero
>  - Windows Aarch64
>  - PPC
> 
> Testing: tiers 1-3
> Additional builds: tiers 4 and 5
>  - builds covered: x86 and Zero
> 
> GHA
> - builds covered:  Windows-Aarch64
> 
> The only build affected and not tested is PPC. It would be great if someone could take this for a spin on PPC.
> 
> For platforms not affected by this change, i.e. those that already specialise the code, I make not claims regarding the atomicity or otherwise of those specialized versions. That would be for someone interested in those specific platforms to check out.
> 
> Thanks,
> David

David Holmes has updated the pull request incrementally with one additional commit since the last revision:

  Remove underscore from name

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7567/files
  - new: https://git.openjdk.java.net/jdk/pull/7567/files/a34aee31..46ecdd29

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7567&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7567&range=00-01

  Stats: 6 lines in 5 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7567.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7567/head:pull/7567

PR: https://git.openjdk.java.net/jdk/pull/7567