[PATCH] x86: Disable XCHG to MOV optimization

[Jan Beulich]

On 13.07.2026 17:10, H.J. Lu wrote:
> On Mon, Jul 13, 2026 at 11:03 PM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 13.07.2026 14:08, H.J. Lu wrote:
>>> I am going to check this patch into master as well as 2.47 branch.
>>> I added optimize_for_unsafe, which is 0, and moved XCHG to MOV
>>> optimization under it.  We can add something like -Ounsafe later.
>>
>> But this is wrong, the optimization itself isn't unsafe. Please can we
> 
> You can change it to a different name.  But -O on master must work with
> today's valgrind.

That's your position. I continue to fail to see why -O needs to work on
anything (valgrind or not) that depends on getting to see specific
encodings for certain insns. Such uses of -O are simply wrong. Undoing
the change on the branch is, as previously indicated, merely to give them
some time to adjust their machinery.

Jan