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Re: [PATCH] x86: also suppress use of MMX insns
- To: Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <amc96@xxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Wed, 20 Jul 2022 13:39:19 +0000
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- Cc: Wei Liu <wl@xxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, ChrisD <chris@xxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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- Thread-topic: [PATCH] x86: also suppress use of MMX insns
On 20/07/2022 14:36, Jan Beulich wrote:
> On 20.07.2022 15:33, Andrew Cooper wrote:
>> On 20/07/2022 14:30, Jan Beulich wrote:
>>> Passing -mno-sse alone is not enough: The compiler may still find
>>> (questionable) reasons to use MMX insns. In particular with gcc12 use
>>> of MOVD+PUNPCKLDQ+MOVQ was observed in an apparent attempt to auto-
>>> vectorize the storing of two adjacent zeroes, 32 bits each.
>>>
>>> Reported-by: ChrisD <chris@xxxxxxxxxxxx>
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Thanks.
>
>> But while we're at it, what else might we have to clobber to stop
>> nonsense like this? x87 and avx come to mind.
> AVX is taking SSE as a prereq (with -mno-sse %xmm etc registers simply
> are unavailable). And with -msoft-float I would very much hope we have
> clearly indicated to the compiler that we want no x87 insns whatsoever.
Ok. Sounds plausible.
~Andrew
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