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

[Jose Fonseca]

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:

CREATE "GLSL/123"
...
EOF

CREATE TGSI/456
EOF

BIND GLSL/123
BIND TGSI/456
BIND HW/789

UNBIND GLSL/123
UNBIND TGSI/456
UNBIND HW/789

DESTROY GLSL/123
DESTROY TGSI/456
DESTROY 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.


Jose