RFR: 8253284: Zero OrderAccess barrier mappings are incorrect [v2]

[Andrew John Hughes]

On Fri, 18 Sep 2020 12:52:57 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix copy-paste omission in bsd_zero
>
> Marked as reviewed by aph (Reviewer).

> > Is the #if defined(ARM) referring to ARM in general here, or just 32-bit ARM? Because there appears to be no change to
> > its definition, just rearrangement.
> 
> No, there is `ARM` (32) and then there is `AARCH64` (64). This is why AArch64 fails: it effectively uses compiler
> barriers only through the confusing application of #else branches.

Ok, patch looks ok then. That seems to differ from the other architectures, where 'PPC' and 'X86' are referring to both
32- and 64-bit variants.

> 
> > The patch is quite hard to follow, and made even more difficult by multiple versions being attached to this PR.
> 
> These are not multiple versions, those commits would be squashed into one on push -- that is how Skara workflow works.
> Look at the final version, which basically enables default (implicitly used by `ALPHA` and `AARCH64`) strong
> barriers -- that is the bug fix. It also keeps the light-weight barrier light for `X86` by calling it out explicitly.

If there are not multiple versions, how is there a 'final version'? :-)

I eventually found the webrev with the full and final patch. One would normally rebase the patch with amendments, not
pile commit on commit and then leave it to a bot to rebase. I don't like the idea that the final commit will look
different to what is being reviewed.

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PR: https://git.openjdk.java.net/jdk/pull/224