RFR: 8351016: RA support for EVEX to REX/REX2 demotion to optimize NDD instructions [v18]

[Jatin Bhateja]

On Tue, 25 Nov 2025 06:56:54 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> src/hotspot/share/opto/chaitin.cpp line 1538:
>> 
>>> 1536: 
>>> 1537:   // Try biasing the color with non-interfering bias live range[s].
>>> 1538:   if (lrg._copy_bias != 0 || lrg._copy_bias2 != 0) {
>> 
>> IMO you can drop `(lrg._copy_bias != 0 || lrg._copy_bias2 != 0)` guard. Original code didn't check it and there are enough guard in `select_bias_lrg_color` to catch it.
>
> The check you pointed at is performed on the result on LRG lookup (which is placed in `select_bias_lrg_color()` now) and not the original index stored in `_copy_bias`/`_copy_bias2`.

Correct, I have re-structured it now.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26283#discussion_r2559911773