RFR: 8339910: RISC-V: crc32 intrinsic with carry-less multiplication [v3]

[Robbin Ehn]

On Thu, 5 Dec 2024 15:10:24 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   add some background description
>
> src/hotspot/cpu/riscv/vm_version_riscv.cpp line 360:
> 
>> 358:   // UseZvbc (depends on RVV).
>> 359:   if (UseZvbc && !UseRVV) {
>> 360:     FLAG_SET_DEFAULT(UseZvbc, false);
> 
> If Zvbc is picked up via hwprobe and user uses:
> `java -XX:-UseRVV ...`
> wouldn't they get the warning forcing them to add -UseZvbc?

I tested:

qemu-riscv64 -cpu "rv64,v=true,vext_spec=v1.0,zvbc=true" java -XX:-UseRVV -version

Gives me this warning about zvcb.

I think if zvcb is default, just turn it off if rvv is off.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22475#discussion_r1871591614