RFR: 8256245: AArch64: Implement Base64 decoding intrinsic

[Dong Bo]

On Mon, 29 Mar 2021 08:38:59 GMT, Andrew Haley <aph at openjdk.org> wrote:

> > With an intial implemention, we can have almost half of the code size reduced (1312B -> 748B). Sounds OK to you?
> 
> Sounds great, but I'm still somewhat concerned that the non-SIMD case only offers 3-12% performance gain. Make it just 748 bytes, and therefore not icache-hostile, then perhaps the balance of risk and reward is justified.

Hi, @theRealAph @nick-arm 

The code is updated. The error handling in SIMD case was rewriten as loops.

Also combined the two non-SIMD code blocks into one.
Due to we have only one non-SIMD loop now, it is moved into `generate_base64_decodeBlock`.
The size of the stub is 692 bytes, the non-SIMD loop takes about 92 bytes if my calculation is right.

Verified with tests `test/jdk/java/util/Base64/` and `compiler/intrinsics/base64/TestBase64.java`.
Compared with previous implementation, the performance changes are negligible.

Other comments are addressed too. Thanks.

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PR: https://git.openjdk.java.net/jdk/pull/3228