RFR: 8315841: RISC-V: Check for hardware TSO support [v8]

[Fei Yang]

On Thu, 7 Sep 2023 17:24:28 GMT, Ludovic Henry <luhenry at openjdk.org> wrote:

>> With the Ztso extension [1], some hardware will support TSO on RISC-V. That allows us to reduce the generation of memory fences, given the stronger memory model compared to RVWMO.
>> 
>> [1] https://github.com/riscv/riscv-isa-manual/blob/6dcbc6da9ada01f0f57da83cda6059bdec57619f/src/ztso-st-ext.adoc#L1
>
> Ludovic Henry has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fixup! 8315841: RISC-V: Check for hardware TSO support

src/hotspot/cpu/riscv/vm_version_riscv.cpp line 213:

> 211:   }
> 212: 
> 213: #ifdef __riscv_ztso

May I ask where is this `__riscv_ztso` macro defined / specified? I tried to search it in the gcc user manual and gcc source code, but I found nothing about it.

[1] https://gcc.gnu.org/onlinedocs/gcc.pdf

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

PR Review Comment: https://git.openjdk.org/jdk/pull/15613#discussion_r1319404817