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Re: [committed, PATCH] x86: Don't disable SSE4a when disabling SSE4
On 17.02.2020 16:44, H.J. Lu wrote:
> On Mon, Feb 17, 2020 at 7:32 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 17.02.2020 16:30, H.J. Lu wrote:
>>> On Mon, Feb 17, 2020 at 7:27 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>>
>>>> On 16.02.2020 17:47, H.J. Lu wrote:
>>>>> On Wed, Feb 12, 2020 at 9:18 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>>
>>>>>> On Wed, Feb 12, 2020 at 9:08 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>>>>>
>>>>>>> Since ".arch sse4a" enables SSE3 and earlier, disabling SSE3 should also
>>>>>>> disable SSE4a. And as per its name, ".arch .nosse4" should also do so.
>>>>>>>
>>>>>>> gas/
>>>>>>> 2020-02-XX Jan Beulich <jbeulich@suse.com>
>>>>>>>
>>>>>>> * config/tc-i386.c (cpu_noarch): Use CPU_ANY_SSE4_FLAGS in
>>>>>>> "nosse4" entry.
>>>>>>>
>>>>>>> opcodes/
>>>>>>> 2020-02-XX Jan Beulich <jbeulich@suse.com>
>>>>>>>
>>>>>>> * i386-gen.c (cpu_flag_init): Move CpuSSE4a from
>>>>>>> CPU_ANY_SSE_FLAGS entry to CPU_ANY_SSE3_FLAGS one. Add
>>>>>>> CPU_ANY_SSE4_FLAGS entry.
>>>>>>> * i386-init.h: Re-generate.
>>>>>>>
>>>>>>
>>>>>> OK.
>>>>>>
>>>>>> Thanks.
>>>>>
>>>>> commit 7deea9aad8 changed nosse4 to include CpuSSE4a. But AMD SSE4a is
>>>>> a superset of SSE3 and Intel SSE4 is a superset of SSSE3. Disable Intel
>>>>> SSE4 shouldn't disable AMD SSE4a. This patch restores nosse4. It also
>>>>> adds .sse4a and nosse4a.
>>>>
>>>> And where is it said that "nosse4" means only the Intel flavors? As
>>>> said in the commit message of said change, to me the clear implication
>>>> is that anything called SSE4* will get disabled.
>>>>
>>>
>>> SSE4 refers to SSE4 from Intel, which includes SSE4.1 and SSE4.2.
>>> SSE4a from AMD is unrelated from Intel SSE4.
>>
>> Repeating my question then: Where is this being said? (Best imo
>> would be to delete ".arch .nosse4" support then, eliminating
>> the ambiguity.)
>
> We have both .sse4 and nosse4 which are aliases for SSE4.2. Please
> feel free to add documentation.
If it's not documented, then it's not clear at all what the intention
is. I'm certainly not going to add documentation saying something that
I don't believe should be said. I.e. if I were to add documentation
here, it'd say .nosse4 covers all three SSE4* variants (and it would
then be a bug of the implementation that this isn't the case).
Just like for the MOVSX/MOVZX issue, I really dislike you making
statements of things that were (apparently) never settled on.
Jan