Re: [PATCH v3 4/7] x86-64: further re-work insn/suffix recognition to also cover MOVSL

[Jan Beulich <jbeulich@suse.com>]

On 13.10.2022 19:00, H.J. Lu wrote:
> On Wed, Oct 12, 2022 at 11:08 PM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 12.10.2022 19:10, H.J. Lu wrote:
>>> On Wed, Oct 12, 2022 at 12:08 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>>
>>>> On 11.10.2022 19:44, H.J. Lu wrote:
>>>>> On Wed, Oct 5, 2022 at 12:24 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>>>>
>>>>>> PR gas/29524
>>>>>> In order to make MOVSL{,Q} behave similarly to MOVSB{W,L,Q} and
>>>>>> MOVSW{L,Q} we need to defer parse_insn()'s emitting of errors unrelated
>>>>>> to prefix parsing. Utilize i.error just like match_template() does.
>>>>>
>>>>> Since movs{b,w,l,q} are string instructions, integer sign extensions
>>>>> require a suffix to specify the destination size.  This is different from other
>>>>> integer instructions.  Since only the new assembler allows the implicit suffix,
>>>>> it won't be easy to use.  We should improve error messages, but allowing
>>>>> new syntax doesn't help much.
>>>>
>>>> It is an earlier change making most of this consistent with MOVZ*; it is
>>>
>>> MOVZ is different.  There are no MOVZ string instructions.  MOVS has
>>> different meanings in ISA.   MOVS difference from MOVZ in assembly
>>> syntax should be expected.
>>
>> You've said so before, yes, but I continue to disagree. And as we can see
>> from the series things can be made work consistently (and imo nothing else
>> should have been done right from the beginning).
>>
> 
> There are inconsistencies in ISA.

Sure. But we shouldn't add further ones in the assembler.

>  AT&T syntax makes things more complex.
> People should either deal with it or leave it to compilers.   I don't think we
> should make assembler more complex.

The complexity added here isn't all that bad. You've added far more
complexity in the past for things which arguably shouldn't even be
dealt with by the assembler (I'm thinking of -malign-branch* and
-mlfence-* first of all).

Jan