[Mesa-dev] [RFC 2/2] i965: add support for image AoA

[Francisco Jerez]

Timothy Arceri <t_arceri at yahoo.com.au> writes:

> On Sun, 2015-08-16 at 13:15 +0300, Francisco Jerez wrote:
>> Timothy Arceri <t_arceri at yahoo.com.au> writes:
>> 
>> > On Sat, 2015-08-15 at 17:33 +0300, Francisco Jerez wrote:
>> > > Timothy Arceri <t_arceri at yahoo.com.au> writes:
>> > > 
>> > > > On Wed, 2015-08-12 at 19:39 +1000, Timothy Arceri wrote:
>> > > > > Cc: Francisco Jerez <currojerez at riseup.net>
>> > > > > ---
>> > > > >  This patch works for direct indexing of images, but I'm having some 
>> > > > > trouble
>> > > > >  getting indirect to work.
>> > > > > 
>> > > > >  For example for:
>> > > > >  tests/spec/arb_arrays_of_arrays/execution/image_store/basic
>> > > > > -imageStore
>> > > > >  -non-const-uniform-index.shader_test
>> > > > > 
>> > > > >  Which has and image writeonly uniform image2D tex[2][2]
>> > > > > 
>> > > > >  Indirect indexing will work for tex[0][0] and text[0][1] but not 
>> > > > > for
>> > > > >  tex[1][0] and tex[1][1] they seem to always end up refering to the
>> > > > >  image in 0.
>> > > > 
>> > > > Just to add some more to this, I'm pretty sure my code is generating 
>> > > > the
>> > > > correct offsets. If I hardcode the img_offset offset to 72 to get the 
>> > > > uniform
>> > > > value of tex[1][0] I get the value I expected, but if I set 
>> > > > image.reladdr 
>> > > > to a
>> > > > register that contains 72 I don't what I expect.
>> > > > 
>> > > > If I change the array to be a single dimension e.g. tex[4] and I 
>> > > > hardcode 
>> > > > the
>> > > > offset as described above then it works as expected for both 
>> > > > scenarios, it
>> > > > also works if I split the offset across img_offset and image.reladdr, 
>> > > > there is
>> > > > something going on with image.reladdr for multi-dimensional arrays 
>> > > > that I 
>> > > > can'
>> > > > t quite put my finger on.
>> > > > 
>> > > > Any hints appreciated.
>> > > > 
>> > > Odd, can you attach an assembly dump?
>> > > 
>> > > Thanks.
>> > 
>> > I wasn't sure what would be the most helpful so I've attached a few 
>> > different
>> > dumps.
>> > 
>> > image_dump = 1D array indirect piglit test, without this patch 
>> > (Result=pass)
>> > image_dump2 = 2D array indirect piglit test, with this patch (Result=fail)
>> > image_dump3 = 1D array indirect piglit test, with this patch (Result=pass)
>> > 
>> > image_dump4 = 1D array indirect piglit test, hardcoded register with 72 
>> > offset
>> >   (Result=pass)
>> > image_dump5 = 2D array indirect piglit test, hardcoded register with 72 
>> > offset
>> > (Result=fail)
>> > 
>> > image_dump4 vs image_dump5 is interesting because the output matches which 
>> > is
>> > what I would have expected, but the result differs. Then with the offset 
>> > below
>> > it seems to work as expected suggesting everything else is setup 
>> > correctly.
>> > 
>> > image_dump6 = 1D array indirect piglit test, hardcoded 72 offset in 
>> > img_offset
>> >    (Result=pass)
>> > image_dump7 = 2D array indirect piglit test, hardcoded 72 offset in 
>> > img_offset
>> >    (Result=pass)
>> >  
>> 
>> Yeah... The assembly output looks correct to me in the cases that fail.
>> AFAICT what all the failing cases have in common is that the array of
>> image uniforms is demoted to pull constants (see demote_pull_constants()
>> and move_uniform_array_access_to_pull_constants()),
>>  so most likely
>> something goes wrong while doing that for multidimensional arrays.  I
>> have the suspicion that this is the source of the problem:
>> 
>> > --- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
>> > +++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
>> > @@ -226,6 +226,7 @@ fs_visitor::nir_setup_uniform(nir_variable *var)
>> >        * our name.
>> >        */
>> >     unsigned index = var->data.driver_location;
>> > +   bool set_image_location = true;
>> >     for (unsigned u = 0; u < shader_prog->NumUniformStorage; u++) {
>> >        struct gl_uniform_storage *storage = &shader_prog
>> > ->UniformStorage[u];
>> > 
>> > @@ -244,7 +245,13 @@ fs_visitor::nir_setup_uniform(nir_variable *var)
>> >            * because their size is driver-specific, so we need to allocate
>> >            * space for them here at the end of the parameter array.
>> >            */
>> > -         var->data.driver_location = uniforms;
>> > +         if (set_image_location) {
>> > +            /* For arrays of arrays we only want to set this once at the 
>> > base
>> > +             * location.
>> > +             */
>> > +            var->data.driver_location = uniforms;
>> > +            set_image_location = false;
>> > +         }
>> >           param_size[uniforms] =
>> >              BRW_IMAGE_PARAM_SIZE * MAX2(storage->array_elements, 1);
>> 
>> The assumption that this code was previously making was that a given
>> image array would be stored in a single gl_uniform_storage entry,
>> otherwise param_size[var->data.driver_location] won't match the real
>> size of the array and move_uniform_array_access_to_pull_constants() will
>> have no idea how large the array really is, so it will only be able to
>> move part of the array to the pull constant buffer and later on the
>> indirect array access will read past the end of the initialized area of
>> the constant buffer.
>
> Thanks for the reply. I'm still getting to know the i965 backend it would have
> taken me a while to get to this point, make a lot more sense now. The code
> below does the trick all of the indirect tests now pass.
>
> Thanks so much for your help :)

No problem. :)

>
>> 
>> I think something like this would do what you want:
>> 
>> >     if (var->type->without_array()->is_image()) {
>> >        /* Images don't get a valid location assigned by nir_lower_io()
>> >         * because their size is driver-specific, so we need to allocate
>> >         * space for them here at the end of the parameter array.
>> >         */
>> >        var->data.driver_location = uniforms;
>> >     }
>> > [...]
>> >     for (unsigned u = 0; u < shader_prog->NumUniformStorage; u++) {
>> >        if (storage->type->is_image()) {
>> >           param_size[var->data.driver_location] +=
>> >              BRW_IMAGE_PARAM_SIZE * MAX2(storage->array_elements, 1);
>> >           setup_image_uniform_values(storage);
>> >        } else {
>> > [...]
>> >        }              
>> >     }
>> 
>> > [...]
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