Re: GCC -msse2 portability question

[Loic Dachary <loic@dachary.org>]

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On 25/03/2014 20:13, Kevin Greenan wrote:
> +1 
> 
> Yeah, that sounds better...  Let's keep this as simple as possible.  

I'll rework the https://bitbucket.org/jimplank/gf-complete/pull-request/4/defer-the-decision-to-use-a-given-sse accordingly.

Would it be sensible to compile with SSE optimizations only if all are available ( SSE2, SSSE3, SSE4, SSE4_PCMUL ) and not attempt to distinguish betweel SSSE3 being available but not SSE4_PCMUL etc. From what I understand at this point that kind of distinction is going to be difficult to manage anyway.

Is it too simplistic ? 

> 
> -kevin
> 
> 
> On Tue, Mar 25, 2014 at 12:08 PM, Loic Dachary <loic@dachary.org <mailto:loic@dachary.org>> wrote:
> 
>     Andreas Peters suggested another approach, which makes sense to me : have one plugin with SSE optimizations enabled, another without them and chose at runtime between the two.
> 
>     What do you think ?
> 
>     On 23/03/2014 20:50, Loic Dachary wrote:
>     > Hi Laurent,
>     >
>     > In the context of optimizing erasure code functions implemented by Kevin Greenan (cc'ed) and James Plank at https://bitbucket.org/jimplank/gf-complete/ we ran accross a question you may have the answer to: can gcc -msse2 (or -msse* for that matter ) have a negative impact on the portability of the compiled binary code ?
>     >
>     > In other words, if a code is compiled without -msse* and runs fine on all intel processors it targets, could it be that adding -msse* to the compilation of the same source code generate a binary that would fail on some processors ? This is assuming no sse specific functions were used in the source code.
>     >
>     > In gf-complete, all sse specific instructions are carefully protected to not be run on a CPU that does not support them. The runtime detection is done by checking CPU id bits ( see https://bitbucket.org/jimplank/gf-complete/pull-request/7/probe-intel-sse-features-at-runtime/diff#Lsrc/gf_intel.cT28 )
>     >
>     > The corresponding thread is at:
>     >
>     > https://bitbucket.org/jimplank/gf-complete/pull-request/4/defer-the-decision-to-use-a-given-sse/diff#comment-1479296
>     >
>     > Cheers
>     >
> 
>     --
>     Loïc Dachary, Artisan Logiciel Libre
> 
> 

-- 
Loïc Dachary, Artisan Logiciel Libre


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