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

[Tobias Hartmann]

On Fri, 28 Nov 2025 12:19:03 GMT, Marc Chevalier <mchevalier at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 5915:
>> 
>>> 5913: #ifdef ASSERT
>>> 5914:     }
>>> 5915: #endif
>> 
>> Not sure if this is a good idea, but you could omit the braces on the else to make this a bit less busy.
>
> 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 ...
  }

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1764#discussion_r2571507484