[PATCH] x86: support -Ofast

[Jiang, Haochen]

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Friday, August 28, 2026 4:40 PM
> 
> ... in analogy to gcc's option of the same name: It relaxes constraints
> on (the lack of) commutativity of V{ADD,MAX,MIN,MUL}{P,S}{S,D}. They're
> not fully commutative solely because of their NaN treatment. If the
> programmer indicates that's benign to them, we can apply the VEX3->VEX2
> encoding transformation for these AVX insns as well.

I am not against the option and the behavior of this patch since it fits what
its goal.

Maybe others will have concerns on whether it is out of scope for assembler
hence we need to leave some time for others.

> ---
> If we wanted to also use this to control optimization of NOP-like insns
> (e.g. the XCHG -> MOV one), the variable would want renaming. Question is:
> _Do_ we (perhaps) want that?
> 

NOP insns might be another topic. It is still vague to me. I will lean on if we
have -Ofast, we could include that. And which variable would want renaming?
I did not get that.

Thx,
Haochen