RFR: 8313779: RISC-V: use andn / orn in the MD5 instrinsic [v2]

[Fei Yang]

On Fri, 4 Aug 2023 15:15:06 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.
>
> Antonios Printezis has updated the pull request incrementally with one additional commit since the last revision:
> 
>   changes based on code review feedback

Looks good.
BTW: I noticed that two `li` are used in your previous PR to implement MD5 intrinsic:

./stubGenerator_riscv.cpp:    __ li(rtmp2, t);
./stubGenerator_riscv.cpp:    __ li(rmask32, MASK_32);

I think It should be more consistent if you use 'mv' instead as we did in other places when moving an immediate into register. 

template<typename T, ENABLE_IF(std::is_integral<T>::value)>
inline void mv(Register Rd, T o)                    { li(Rd, (int64_t)o); }

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Marked as reviewed by fyang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/15156#pullrequestreview-1564049901