[PATCH] x86: VCVTNEPS2BF16{X,Y} should permit broadcasting

[Jan Beulich]

On 20.01.2020 15:42, H.J. Lu wrote:
> On Mon, Jan 20, 2020 at 6:35 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 20.01.2020 14:58, H.J. Lu wrote:
>>> On Mon, Jan 20, 2020 at 4:00 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>>
>>>> Just like other VCVT*{X,Y} templates do, and to allow the programmer
>>>> flexibility (might be relevant in particular when heavily macro-izing
>>>> code), the two templates should also have Broadcast set, just like their
>>>> X/Y-suffix-less counterparts. This in turn requires them to also have
>>>> * Dword set on their memory operands, to cover the logic added to i386gen
>>>>   by 4a1b91eabbe7 ("x86: Expand Broadcast to 3 bits"),
>>>> * Xmmword/Ymmword set on their memory operands, to satisfy broadcast
>>>>   sizing logic in gas itself.
>>>> Otherwise ATTSyntax templates wouldn't need such operand size attributes.
>>>>
>>>> While extending the test cases, also add Intel syntax broadcast forms
>>>> without explicit size specifiers.
>>>>
>>>> gas/
>>>> 2020-01-XX  Jan Beulich  <jbeulich@suse.com>
>>>>
>>>>         * testsuite/gas/i386/avx512_bf16_vl.s,
>>>>         testsuite/gas/i386/x86-64-avx512_bf16_vl.s: Add broadcast forms
>>>>         of VCVTNEPS2BF16{X,Y}. Add operand-size less Intel syntax
>>>>         broadcast forms of VCVTNEPS2BF16.
>>>>         * testsuite/gas/i386/avx512_bf16_vl.d,
>>>>         testsuite/gas/i386/x86-64-avx512_bf16_vl.d: Adjust expectations.
>>>>
>>>> opcodes/
>>>> 2020-01-XX  Jan Beulich  <jbeulich@suse.com>
>>>>
>>>>         * i386-opc.tbl (vcvtneps2bf16x): Add Broadcast, Xmmword, and
>>>>         Dword.
>>>>         (vcvtneps2bf16y): Add Broadcast, Ymmword, and Dword.
>>>>         * i386-tbl.h: Re-generate.
>>>>
>>>
>>> OK.
>>
>> Thanks. What about this remark
>>
>>>> ---
>>>> Arguably, just like other VCVT*{X,Y}, the ones here could then also be
>>>> made permit RegXMM/RegYMM as source operand. Personally I'd prefer this,
>>>> but there was resistance to such in similar earlier cases.
>>
>> that the original mail had? I think I've meanwhile found a case where
>> it would actually help if all such templates were consistent in this
>> regard.
> 
> Are you referring to use AVX512VL for suffix check? I don't we should
> do that.

No. I think there might be a broadcast handling anomaly when there's no
RegXMM (or RegYMM/RegZMM) on such templates. And I also think that the
same argument (might be used in heavily macro-ized code) calls for
register operands to be allowed even with these artificial x/y suffixes,
and despite there then being some redundancy at the source level.

Jan