RFR: 8270340: Base64 decodeBlock intrinsic for Power64 needs cleanup [v2]

[Corey Ashford]

On Thu, 15 Jul 2021 17:27:18 GMT, Corey Ashford <cashford at openjdk.org> wrote:

>> src/hotspot/cpu/ppc/stubGenerator_ppc.cpp line 3869:
>> 
>>> 3867:     VectorSRegister M                       = VSR8;
>>> 3868: 
>>> 3869:     // P10+ VSR lookup variables
>> 
>> "P10+" should better be "P10 or above" (or something grammatically correct) because it appears like an enhanced version of P10, like P7+.  Although IBM didn't released "+" models after P8, they have manufactured with reduced semiconductor process and apply enhancements, including larger caches, higher clock frequency, etc.
>
> Good point.  Will fix.

I believe I have resolved this with my latest commit to this PR.  Please double check.

>> src/hotspot/cpu/ppc/stubGenerator_ppc.cpp line 4038:
>> 
>>> 4036:       __ bne_predict_not_taken(CCR6, unrolled_loop_exit);
>>> 4037: 
>>> 4038:       // The Base64 characters had no errors, so add the offsets
>> 
>> It may be helpful to add comments for P10 case, where each byte of input contains (decoded 6-bit binary | 0x80) and offsets contains 0x80, and vaddubm  is used to clear the MSB.
>
> Good point.  I'll update the comment.

I believe I have resolved this with my latest commit to this PR.  Please double check.

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PR: https://git.openjdk.java.net/jdk/pull/4762