RFR: 8259822: [PPC64] Support the prefixed instruction format added in POWER10 [v4]

[Kazunori Ogata]

On Wed, 3 Feb 2021 21:00:34 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> Looks good!  Thanks for the additional formatting cleanup
>
> Sorry that I didn't review it, yet. I didn't have enough time.
> 
> Please note that C2 already has a mechanism to handle alignment:
> 
> Insert "ins_alignment(n);" into the instruct. This allows C2 to insert up to n-1 nop instructions. 
> Add a "compute_padding" function to determine the actual number of nops to insert given the current offset.
> They are used in s390.ad. Please take a look.

@TheRealMDoerr  Sorry to be late to update the patch.  It took time to debug my careless mistakes...

I updated the patch with using ins_alignment and verified there is no additional errors in jtreg tier1 tests.  Although there were intermittent failures in VarHandleTests using weakCompareAndSet, it was the same situation as the base build, so I think it is not related to my changes.

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PR: https://git.openjdk.java.net/jdk/pull/2095