[Mesa-dev] Extension to get Mesa IRs (Was: [Bug 91173])

Ilia Mirkin imirkin at alum.mit.edu
Thu Jul 2 08:34:44 PDT 2015

On Thu, Jul 2, 2015 at 1:55 AM, Jose Fonseca <jfonseca at vmware.com> wrote:
> On 01/07/15 22:30, bugzilla-daemon at freedesktop.org wrote:> *Comment # 14
> <https://bugs.freedesktop.org/show_bug.cgi?id=91173#c14>
>> on bug 91173 <https://bugs.freedesktop.org/show_bug.cgi?id=91173> from
>> Ilia Mirkin <mailto:imirkin at alum.mit.edu> *
>> Erm... ok...
>> MOV R0.zw, c[A0.x + 9];
>> MOV R1.x, c[0].w;
>> ADD R0.x, c[A0.x + 9].y, R1;
>> FLR R0.y, R0.x;
>> vs
>>    0: MAD TEMP[0].xy, IN[1], CONST[7].yyyy, CONST[7].xxxx
>>    3: MOV TEMP[0].zw, CONST[ADDR[0].x+9]
>>    7: FLR TEMP[0].y, CONST[0].wwww
>> Could be that I'm matching the wrong shaders. But this seems highly
>> suspect.
>> Need to see if there's a good way of dumping mesa ir... I wonder if it
>> doesn't
>> notice the write-mask on the MOV R0.zw and thinks that R0 contains the
>> value it
>> wants.
> Nice detective work on this bug, Ilia.
>> Could be that I'm matching the wrong shaders.
> I think it could be quite useful if there was a
> "GL_MESAX_get_internal_representation" Mesa specific extension to extract a
> text representation of the current bound GLSL, TGSI, hardware speicfic, etc,
> exclusively for debugging purposes.
> It doesn't even need to be advertised on non-debug builds of Mesa.  But
> merely being able to see next to each other all the IRs at a given call in a
> trace, will probably save some time / grief for us developers on similar
> situations.
> I did something akin to this for NVIDIA prioprietary drivers on
> https://github.com/apitrace/apitrace/commit/49192a4e48d080e44a0d66f059e6897f07cf67f8
> but I don't think GetProgramBinary is apropriate for Mesa (only one format.)
> Instead, for Mesa we could have something like
>    GLint n;
>    // this will trigget IRs being collected into an array internally
>    glGetIntegerv(GL_NUM_ACTIVE_IRS, &n);
>    for (i=0; i < n; ++i) {
>        GLint nameLength;
>        char *name;
>        GLint sourceLength;
>        char *source;
>        glGetActiveInternalRepr(&nameLength, NULL, &sourceLength, NULL);
>        name = malloc(nameLength)
>        source = malloc(sourceLength)
>        glGetActiveInternalRepr(NULL, name, NULL, source);
>    }
> And this would need to be plumbed through all the way inside the drivers,
> each layer would  advertise additional IRs.
> And the information here would only be obtainable/valid immediately after a
> draw call.
> A completely different tack, is that apitrace's glretrace would advertise an
> unique environment variable (e.g,MESA_IR_DUMP_ALL=fd), and all
> drivers/layers would write shaders repres, and when they are
> bound/unbound/destroyed on  a preestablished format:
> ...
> BIND HW/789
> I don't feel strongly either way, but I suspect that having a proper
> extension, even if a little more work at start, will be more robust on the
> long term.  And less runtime overhead.  GL extensions also give a mechanism
> to revise/deprecate this functionality in the future.

This would still require fairly extensive changes as you'd have to
track all the bindings together.

Anyways, *something* would be fantastic. It's also incredibly
difficult to tell what shader is being used for a particular draw...
I've resorted to taking mmt traces of nouveau to see what it's
actually drawing with. Sometimes qapitrace doesn't show a shader,
sometimes it's a fixed function shader, etc. Note that among other
things, this has to account for any shader keys that might exist at
any of the levels. And since bugs are often in optimization passes,
being able to see both pre- and post-opt shaders would be *really*



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