[PATCH] x86: Support BHI_CTRL instruction

[Jiang, Haochen]

> From: Christian Ludloff <ludloff@gmail.com>
> Sent: Friday, June 5, 2026 12:46 AM
> 
> On Thu, Jun 4, 2026 at 12:39 AM Jiang, Haochen <haochen.jiang@intel.com>
> wrote:
> > > From: Christian Ludloff <ludloff@gmail.com>
> > > Arguably RDSSP{D,Q} is a litmus test – can it REX2 or EVEX?
> >
> > I suppose it should be a REX2, not EVEX MAP4.
> 
> From the perspective of the ISA, the W for D-vs-Q
> can come from REX or REX2 or EVEX – it should
> not matter which of the three encodings gets used
> for RDSSP. If that is not the case, then please get
> it documented too, together with IBHF behavior.
> 

APX documentation has mentioned which instructions could be
promoted to EVEX MAP4. Only the inst mentioned in chart could
use EVEX MAP4. Actually, those EVEX MAP4 insts are all listed
one by one in EAS since the encoding are quite different.

Thx,
Haochen