RFR: 8295948: Support for Zicbop/prefetch instructions on RISC-V [v4]

[Yadong Wang]

On Fri, 4 Nov 2022 05:00:36 GMT, Fei Yang <fyang at openjdk.org> wrote:

>> Ludovic Henry has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - fixup! remove dead code
>>  - remove dead code
>
> src/hotspot/cpu/riscv/riscv.ad line 5190:
> 
>> 5188: 
>> 5189: instruct prefetchalloc( memory mem ) %{
>> 5190:   match(PrefetchAllocation mem);
> 
> PS: Should we also put this under control of option UseZicbop like you do in Prefetch::read/write? Did you checked whether those (prefetchalloc and Prefetch::read/write) will ever be used/called when AllocatePrefetchStyle is 0 (which is the case when UseZicbop is false).

The generation of PrefetchAllocationNode is controlled by AllocatePrefetchStyle. It should be fine if UseZicbop is associated with this option.

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PR: https://git.openjdk.org/jdk/pull/10884