[lworld] RFR: 8371993: [lworld] Aarch64: save bad values instead of rfp and lr above the extension space [v2]

[Marc Chevalier]

On Fri, 28 Nov 2025 12:26:50 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> I agree it's busy, but I like explicit braces, rust-style. Especially with `#ifdef` in the middle, it looks easy to do something wrong with un-braced blocks. I'm not so shocked by the current style but another option I see would be
>> 
>> if (DEBUG_ONLY(save_fake_rfp_lr) NOT_DEBUG(false)) {
>>   mov_immediate64(rscratch1, ((uint64_t)badRegWordVal) << 32 | (uint64_t)badRegWordVal);
>>   stp(rscratch1, rscratch1, Address(sp, framesize - 2 * wordSize));
>> } else {
>>   stp(rfp, lr, Address(sp, framesize - 2 * wordSize));
>> }
>> 
>> I am very confident gcc will remove the branch entirely in non-debug.
>
> Regarding Manuel's proposal: I don't think omitting brackets is a good idea. Alternative:
> 
>   } else
> #endif
>   {
>     stp ...
>   }

I've done what I proposed. I think it looks nice. Does anyone strongly prefer

#ifdef ASSERT
    if (save_fake_rfp_lr) {
      mov_immediate64(rscratch1, ((uint64_t)badRegWordVal) << 32 | (uint64_t)badRegWordVal);
      stp(rscratch1, rscratch1, Address(sp, framesize - 2 * wordSize));
    } else
#endif
    {
      stp(rfp, lr, Address(sp, framesize - 2 * wordSize));
    }

?

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1764#discussion_r2571799515