RFR: 8253843: AArch64: Use ishst for storestore barrier

[Alan Hayward]

On Wed, 30 Sep 2020 08:34:14 GMT, Alan Hayward <github.com+4146708+a74nh at openjdk.org> wrote:

> AArch64 orderAccess uses gcc built in atomic functions, which expand
> inline to DMB barrier instructions.  Specifically, they call the following:
> 
> FULL_MEM_BARRIER -> DMB ISH
> READ_MEM_BARRIER -> DMB ISHLD
> WRITE_MEM_BARRIER -> DMB ISH
> 
> However, storestore should be optimised to use ISHST.
> 
> In addition, __sync_synchronize is marked as legacy. See:
> https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html
> 
> In order for the code to match, I switched everything to call dmbs directly.
> 
> Also, add AArch64 to the orderAccess documentation table.

> /signed

this was a mistake. Meant to do /covered

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PR: https://git.openjdk.java.net/jdk/pull/427