RFR: 8352159: RISC-V: add more zfa support [v4]

[Fei Yang]

On Wed, 19 Mar 2025 09:27:44 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> src/hotspot/cpu/riscv/assembler_riscv.hpp line 446:
>> 
>>> 444:       case 0x7c00 : return 29;
>>> 445:       // case 0x7c00 : return 30; // redundant with 29
>>> 446:       case 0x7e00 : return 31;
>> 
>> This switch-case seems nontrivial (Same for for all S & D variants). One possible enhancement to speed up might be putting the values in a table and doing a binary search.
>
> In this case, I think the compiler (gcc or clang) will be able to automatically generate a binary research rather than a linear search, so we don't have to write the code manually. And keep the code as it is is more readable.

Interesting! I tried several recent GCC versions and I see it is doing a binary search. Then I think we are OK with the current shape. Thanks.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24081#discussion_r2002980368