RFR: 8314124: RISC-V: implement Base64 intrinsic - decoding [v3]

[Hamlin Li]

On Thu, 22 Aug 2024 14:46:26 GMT, Antonios Printezis <tonyp at openjdk.org> wrote:

>> Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   revert misc
>
> src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 5462:
> 
>> 5460:     __ sub(length, send, soff);
>> 5461:     // it's not guaranteed by java level, so do it explicitly
>> 5462:     __ andi(length, length, -4);
> 
> Is it possible for `length == 0` here?

No, this is guaranteed at java level.

> src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 5470:
> 
>> 5468: 
>> 5469:     // load the codec base address
>> 5470:     __ la(codec, ExternalAddress((address) fromBase64));
> 
> any way to avoid the double `la` when `isURL == true`? I guess you'd need one more label and an extra branch? Not sure it's worth it.

Seems not necessary, and I see other places, also on other cpus do the similar things.

> src/hotspot/cpu/riscv/stubGenerator_riscv.cpp line 5497:
> 
>> 5495: 
>> 5496:         // load 4 bytes encoded src data
>> 5497:         __ lbu(byte0, Address(src, 0));
> 
> Is it faster to issue four 8-bit loads instead of one 32-bit load and getting the four values with shifting and masking?

Yeh, it could be, I will test it later.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20026#discussion_r1727403705
PR Review Comment: https://git.openjdk.org/jdk/pull/20026#discussion_r1727401431
PR Review Comment: https://git.openjdk.org/jdk/pull/20026#discussion_r1727399419