RFR: 8314125: RISC-V: implement Base64 intrinsic - encoding [v7]

[Hamlin Li]

> Hi,
> Can you help to review the patch?
> 
> I'm also working a base64 decode instrinsic, but there is some performance regression in some cases, and decode and encode are totally independent with each other, so I will send out review of decode in another pr when I fix the performance regression in it.
> 
> Thanks.
> 
> ## Test
> benchmarks run on CanVM-K230 (vlenb == 16), and banana-pi (vlenb == 32)
> 
> I've tried several implementations, respectively with vector group
> * m2+m1+scalar
> * m2+scalar
> * m1+scalar
> * pure scalar
> The best one is combination of m2+m1, it have best performance in all source size.
> 
> ### K230
> 
> this implementation (m2+m1)
> <google-sheets-html-origin style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">
> Benchmark | (maxNumBytes) | Mode | Cnt | Score -intrinsic | Score + instrinsic, m1+m2 | Error | Units | -intrinsic/+intrinsic
> -- | -- | -- | -- | -- | -- | -- | -- | --
> Base64Encode.testBase64Encode | 1 | avgt | 10 | 86.784 | 86.996 | 0.459 | ns/op | 0.9975631063
> Base64Encode.testBase64Encode | 2 | avgt | 10 | 93.603 | 94.026 | 1.081 | ns/op | 0.9955012443
> Base64Encode.testBase64Encode | 3 | avgt | 10 | 121.927 | 123.227 | 0.342 | ns/op | 0.989450364
> Base64Encode.testBase64Encode | 6 | avgt | 10 | 139.554 | 137.4 | 1.221 | ns/op | 1.015676856
> Base64Encode.testBase64Encode | 7 | avgt | 10 | 160.698 | 162.25 | 2.36 | ns/op | 0.9904345146
> Base64Encode.testBase64Encode | 9 | avgt | 10 | 161.085 | 153.772 | 1.505 | ns/op | 1.047557423
> Base64Encode.testBase64Encode | 10 | avgt | 10 | 187.963 | 174.763 | 1.204 | ns/op | 1.075530862
> Base64Encode.testBase64Encode | 48 | avgt | 10 | 405.212 | 199.4 | 6.374 | ns/op | 2.032156469
> Base64Encode.testBase64Encode | 512 | avgt | 10 | 3652.555 | 1111.009 | 3.462 | ns/op | 3.287601631
> Base64Encode.testBase64Encode | 1000 | avgt | 10 | 7217.187 | 2011.943 | 227.784 | ns/op | 3.587172698
> Base64Encode.testBase64Encode | 20000 | avgt | 10 | 135165.706 | 33864.592 | 57.557 | ns/op | 3.991357876
> 
> </google-sheets-html-origin>
> 
> vector with only m2
> <google-sheets-html-origin style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px...

Hamlin Li has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains ten commits:

 - minor
 - merge master
 - merge master
 - Merge branch 'master' into baes64-encode-integrated
 - move label
 - refine code
 - use pure scalar version when rvv is not supported
 - clean code
 - Initial commit

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

Changes: https://git.openjdk.org/jdk/pull/19973/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19973&range=06
  Stats: 242 lines in 3 files changed: 242 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19973.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19973/head:pull/19973

PR: https://git.openjdk.org/jdk/pull/19973