RFR: 8367692: RISC-V: Align post call nop [v6]

[Hamlin Li]

On Mon, 29 Sep 2025 12:38:10 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> src/hotspot/cpu/riscv/macroAssembler_riscv.cpp line 363:
>> 
>>> 361:     return;
>>> 362:   }
>>> 363:   relocate(post_call_nop_Relocation::spec());
>> 
>> What's the reason for this change? Does it make difference from the previous code?
>
> The code is location independent, meaning it will be the exact same encoding regardless of what addresses it's placed on. But we need a reloc spec to keep track of where we did place them.
> So we don't need to regenerate the instructions after move.

Just checked the code, seems either `relocate` w/wo `Callback` will be treated in the same way when relocation happens.

For the version with `Callback` argument, the code will be in an `IncompressibleScope`.
But this pr you put an `assert(!in_compressible_scope()` at the beginning, so seems it's also fine.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27467#discussion_r2387899135