[Mesa-dev] [PATCH V5] mesa: add SSE optimisation for glDrawElements

[Ian Romanick]

On 11/07/2014 06:09 AM, Siavash Eliasi wrote:
> 
> On 11/07/2014 03:14 PM, Steven Newbury wrote:
>> On Thu, 2014-11-06 at 21:00 -0800, Matt Turner wrote:
>>> On Thu, Nov 6, 2014 at 8:56 PM, Siavash Eliasi <
>>> siavashserver at gmail.com> wrote:
>>>> Then I do recommend removing the "if (cpu_has_sse4_1)" from this
>>>> patch and similar places, because there is no runtime CPU
>>>> dispatching happening for SSE optimized code paths in action and
>>>> just adds extra overhead (unnecessary branches) to the generated
>>>> code.
>>> No. Sorry, I realize I misread your previous question:
>>>
>>>>> I guess checking for "cpu_has_sse4_1" is unnecessary if it isn't
>>>>> controllable by user at runtime; because "USE_SSE41" is a
>>>>> compile time check and requires the target machine to be SSE 4.1
>>>>> capable already.
>>> USE_SSE41 is set if the *compiler* supports SSE 4.1. This allows you
>>> to build the code and then use it only on systems that actually
>>> support it.
>>>
>>> All of this could have been pretty easily answered by a few greps
>>> though...
>> I wonder what difference it would make to have an option to compile
>> out the run-time check code to avoid the additional overhead in cases
>> where the builder *knows* at compile time what the run-time system is?
>> (ie Gentoo)
> I think that's possible. Since "cpu_has_sse4_1" and friends are simply
> macros, one can set them to "true" or "1" during compile time if it's
> going to be built for an SSE 4.1 capable target so your smart compiler
> will totally get rid of the unnecessary runtime check.
> 
> I guess "common_x86_features.h" should be modified to something like this:
> 
> #ifdef __SSE4_1__
> #define cpu_has_sse4_1 1
> #else
> #define cpu_has_sse4_1        (_mesa_x86_cpu_features & X86_FEATURE_SSE4_1)
> #endif

I was thinking about doing something similar for cpu_has_xmm and
cpu_has_xmm2 for x64.  SSE and SSE2 are required parts of that
instruction set, so they're always there.

> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/mesa-dev
>