RFR: 8295282: Use Zicboz/cbo.zero to zero-out memory on RISC-V [v6]

[Ludovic Henry]

On Thu, 20 Oct 2022 14:07:23 GMT, Fei Yang <fyang at openjdk.org> wrote:

>> Ludovic Henry has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Explicit use of temp registers
>>  - fixup! Add -XX:CacheLineSize= to set cache line size
>
> src/hotspot/cpu/riscv/macroAssembler_riscv.cpp line 4127:
> 
>> 4125:   sub(cnt, cnt, tmp2);
>> 4126:   add(tmp3, zr, zr);
>> 4127:   movptr(tmp3, initial_table_end);
> 
> I think it will be more efficient if we make use of 'auipc' instruction here for this purpose. The current version which makes use of 'movptr' will emits 6 instructions.

I'm using `la` which I've modified with `wrap_label`.

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PR: https://git.openjdk.org/jdk/pull/10718