RFR: 8322790: RISC-V: Tune costs for shuffles with no conversion

[Fei Yang]

On Tue, 2 Jan 2024 10:57:22 GMT, Vladimir Kempik <vkempik at openjdk.org> wrote:

>> src/hotspot/cpu/riscv/riscv.ad line 8534:
>> 
>>> 8532:   effect(DEF dst, USE src);
>>> 8533: 
>>> 8534:   ins_cost(ALU_COST + LOAD_COST);
>> 
>> Adding an extra cost of `ALU_COST` for these load/store nodes looks a bit strange to me. I suppose only lowering the cost for those fmv.x.w/fmv.w.x/fmv.x.d/fmv.d.x nodes will do?
>
> those nodes need to go below 100 which then starts looking ugly

Seems that the performance gain is still there (tested on lichee-pi-4a board) when reverting part of the changes. I haven't checked the JIT code though. Try this addon change:

[addon-change.diff.txt](https://github.com/openjdk/jdk/files/13815870/addon-change.diff.txt)

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

PR Review Comment: https://git.openjdk.org/jdk/pull/17206#discussion_r1440083334