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Re: [PATCH] x86: also suppress use of MMX insns
- To: Andrew Cooper <amc96@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 20 Jul 2022 15:36:50 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, ChrisD <chris@xxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 20 Jul 2022 13:37:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
Jan
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