RFR: 8313779: RISC-V: use andn / orn in the MD5 instrinsic

[Antonios Printezis]

On Fri, 4 Aug 2023 13:10:06 GMT, Antonios Printezis <tonyp at openjdk.org> wrote:

> Small improvement of the MD5 intrinsic when the Zbb extension is available. Performance comparison (with thanks again to @robehn for this!):
> 
> before:
> 
> 
> MessageDigests.digest                   md5        64     DEFAULT  avgt    6    1835.246 ±  252.071  ns/op
> MessageDigests.digest                   md5     16384     DEFAULT  avgt    6  145386.522 ±  444.446  ns/op
> MessageDigests.getAndDigest             md5        64     DEFAULT  avgt    6    2555.515 ±  639.491  ns/op
> MessageDigests.getAndDigest             md5     16384     DEFAULT  avgt    6  149045.631 ± 6658.545  ns/op
> 
> 
> after:
> 
> 
> MessageDigests.digest                   md5        64     DEFAULT  avgt    6    1779.637 ±  207.869  ns/op
> MessageDigests.digest                   md5     16384     DEFAULT  avgt    6  137147.179 ±  706.396  ns/op
> MessageDigests.getAndDigest             md5        64     DEFAULT  avgt    6    2645.354 ± 1245.318  ns/op
> MessageDigests.getAndDigest             md5     16384     DEFAULT  avgt    6  141306.966 ± 7000.576  ns/op
> 
> 
> (only line 3 is not an improvement, but it has higher variation)
> 
> It seems to save around 5% of executed instructions.

Was not sure how to differentiate between the `andn` and `orn` in the assembler and the macro assembler. I added an `r` suffix. If there's a better way, let me know!

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

PR Comment: https://git.openjdk.org/jdk/pull/15156#issuecomment-1665673427