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Re: [PATCH 2/7] Don't disable SSE in x86-64 ld.so


On Tue, Aug 25, 2015 at 2:48 PM, Roland McGrath <roland@hack.frob.com> wrote:
>> We use -mno-mmx on i386 since mm registers are passed to pass
>> __m64 arguments.  On x86-64, I can't think of a good reason to use
>> MMX in ld.so.
>
> The patch is OK now since -mno-mmx was the status quo ante for x86_64.
>
> But the rationale for -mno-mmx is being stated in a backwards fashion.
> We should add special options only if there is a good reason to have
> them.  If you just don't think it's optimal to use MMX, then that is not
> a good reason to use -mno-mmx; it's a good reason to make some compiler
> change to improve optimization.  If there is a specific, known,
> pathological optimization issue, then there should be a GCC bug filed
> for that and the comments in the makefile should point to that bug.  If
> there is no such reason to specifically use -mno-mmx, then we should
> drop it.

Here is a partial list of MMX bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48397
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47759
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40983


-- 
H.J.


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