[Mesa-dev] Testing optimizer

[Patrick Baggett]

On Tue, Dec 17, 2013 at 10:59 AM, Paul Berry <stereotype441 at gmail.com>wrote:

> On 17 December 2013 08:46, Tom Stellard <tom at stellard.net> wrote:
>
>> On Tue, Dec 17, 2013 at 09:57:31AM -0600, Patrick Baggett wrote:
>> > Hi all,
>> >
>> > Is there a way to see the machine code that is generated by the GLSL
>> > compiler for all GPU instruction sets? For example, I would like to
>> know if
>> > the optimizer optimizes certain (equivalent) constructs (or not), and
>> avoid
>> > them if possible. I know there is a lot to optimization on GPUs that I
>> > don't know, but I'd still like to get some ballpark estimates. For
>> example,
>> > I'm curious whether:
>>
>> Each driver has its own environment variable for dumping machine code.
>>
>> llvmpipe: GALLIVM_DEBUG=asm (I think you need to build mesa
>>                              with --enable-debug for this to work)
>> r300g: RADEON_DEBUG=fp,vp
>> r600g, radeonsi: R600_DEBUG=ps,vs
>>
>> I'm not sure what the other drivers use.
>>
>> -Tom
>>
>
> I believe every driver also supports MESA_GLSL=dump, which prints out the
> IR both before and after linking (you'll want to look at the version after
> linking to see what optimizations have been applied, since some
> optimizations happen at link time).  Looking at the IR rather than the
> machine code is more likely to give you the information you need, since
> Mesa performs the same IR-level optimizations on all architectures, whereas
> the optimizations that happen at machine code level are vastly different
> from one driver to the next.
>
>
I do want to see both, actually. For example, if a driver implements a
specific optimization (machine code level) and another driver clearly does
not, then that would be considered "interesting" to me.



> Another thing which might be useful to you is Aras Pranckevičius's
> "glsl-optimizer" project (https://github.com/aras-p/glsl-optimizer),
> which performs Mesa's IR-level optimizations on a shader and then
> translates it from IR back to GLSL.
>
> Paul
>
>
Thanks to everyone for the great tips!


>
>> >
>> >     //let p1, p2, p3 be vec2 uniforms
>> >
>> >     vec4(p1, 0, 0) + vec4(p2, 0, 0) + vec4(p3, 0, 1)
>> >
>> > produces identical machine code as:
>> >
>> >     vec4(p1+p2+p3, 0, 1);
>> >
>> > for all architectures supported by Mesa.
>>
>> > _______________________________________________
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>> > mesa-dev at lists.freedesktop.org
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>>
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>
>
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