[Mesa-dev] [PATCH V3] glsl: fix atomic buffer index for bindings other than 0

[Timothy Arceri]

On Wed, 2015-07-29 at 09:57 +0200, Iago Toral wrote:
> On Sun, 2015-07-26 at 18:35 +1000, Timothy Arceri wrote:
> > Since commit c0cd5b var->data.binding was being used as a replacement
> > for atomic buffer index, but they don't have to be the same value they
> > just happen to end up the same when binding is 0.
> > 
> > Now we store atomic buffer index in the unused var->data.index
> > to avoid the extra memory of putting back the atmoic buffer index field.
> 
> Could this be a bit too restrictive? var->data.index has only a single
> bit of storage, so this would limit the number of buffers we can index
> to 2.

Your right I wasn't paying enough attention, the nir struct doesn't place the
same limits on index (although maybe it should) and I didn't notice it in the
glsl ir.

I have a new solution on the way as part on V3 of my AoA work, however its not
really suitable for stable.

If we want this fix in stable maybe putting back the atomic_index struct
member is the best solution after all.


>  The spec says that the minimum an implementation should support is
> 1, so it accomplishes that, but still... a quick look through the i965
> code reveals that it is prepared to support up to 16 for example (see
> BRW_MAX_ABO in brw_context.h).
> 
> Iago
> 
> > V3: Dont make unrelated changes to the uniform storage handling.
> > Cc the correct stable branch.
> > 
> > V2: store buffer index in var->data.index and uniform slot in
> > var->data.location to avoid issues when linking more than 2 shaders.
> > Also some small tidy ups.
> > 
> > Cc: Alejandro Piñeiro <apinheiro at igalia.com>
> > Cc: Ian Romanick <idr at freedesktop.org>
> > Cc: 10.6 <mesa-stable at lists.freedesktop.org>
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90175
> > ---
> >  src/glsl/ir.h                                  | 2 ++
> >  src/glsl/link_atomics.cpp                      | 2 ++
> >  src/glsl/nir/glsl_to_nir.cpp                   | 2 --
> >  src/glsl/nir/nir.h                             | 5 +++--
> >  src/glsl/nir/nir_lower_atomics.c               | 2 +-
> >  src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 2 +-
> >  6 files changed, 9 insertions(+), 6 deletions(-)
> > 
> > diff --git a/src/glsl/ir.h b/src/glsl/ir.h
> > index ede8caa..f77534c 100644
> > --- a/src/glsl/ir.h
> > +++ b/src/glsl/ir.h
> > @@ -757,6 +757,8 @@ public:
> >         * \note
> >         * The GLSL spec only allows the values 0 or 1 for the index in \b 
> > dual
> >         * source blending.
> > +       *
> > +       * For atomic counters this stores the atomic buffer index.
> >         */
> >        unsigned index:1;
> >  
> > diff --git a/src/glsl/link_atomics.cpp b/src/glsl/link_atomics.cpp
> > index 100d03c..5120564 100644
> > --- a/src/glsl/link_atomics.cpp
> > +++ b/src/glsl/link_atomics.cpp
> > @@ -204,6 +204,8 @@ link_assign_atomic_counter_resources(struct gl_context 
> > *ctx,
> >           if (!var->data.explicit_binding)
> >              var->data.binding = i;
> >  
> > +         var->data.index = i;
> > +
> >           storage->atomic_buffer_index = i;
> >           storage->offset = var->data.atomic.offset;
> >           storage->array_stride = (var->type->is_array() ?
> > diff --git a/src/glsl/nir/glsl_to_nir.cpp b/src/glsl/nir/glsl_to_nir.cpp
> > index 77327b6..6cb23c0 100644
> > --- a/src/glsl/nir/glsl_to_nir.cpp
> > +++ b/src/glsl/nir/glsl_to_nir.cpp
> > @@ -326,8 +326,6 @@ nir_visitor::visit(ir_variable *ir)
> >  
> >     var->data.index = ir->data.index;
> >     var->data.binding = ir->data.binding;
> > -   /* XXX Get rid of buffer_index */
> > -   var->data.atomic.buffer_index = ir->data.binding;
> >     var->data.atomic.offset = ir->data.atomic.offset;
> >     var->data.image.read_only = ir->data.image_read_only;
> >     var->data.image.write_only = ir->data.image_write_only;
> > diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
> > index 62cdbd4..837d197 100644
> > --- a/src/glsl/nir/nir.h
> > +++ b/src/glsl/nir/nir.h
> > @@ -292,7 +292,9 @@ typedef struct {
> >        unsigned int driver_location;
> >  
> >        /**
> > -       * output index for dual source blending.
> > +       * Output index for dual source blending.
> > +       *
> > +       * For atomic counters this stores the atomic buffer index.
> >         */
> >        int index;
> >  
> > @@ -307,7 +309,6 @@ typedef struct {
> >         * Location an atomic counter is stored at.
> >         */
> >        struct {
> > -         unsigned buffer_index;
> >           unsigned offset;
> >        } atomic;
> >  
> > diff --git a/src/glsl/nir/nir_lower_atomics.c 
> > b/src/glsl/nir/nir_lower_atomics.c
> > index ce3615a..6119f62 100644
> > --- a/src/glsl/nir/nir_lower_atomics.c
> > +++ b/src/glsl/nir/nir_lower_atomics.c
> > @@ -63,7 +63,7 @@ lower_instr(nir_intrinsic_instr *instr, 
> > nir_function_impl *impl)
> >  
> >     nir_intrinsic_instr *new_instr = nir_intrinsic_instr_create(mem_ctx, 
> > op);
> >     new_instr->const_index[0] =
> > -      (int) instr->variables[0]->var->data.atomic.buffer_index;
> > +      (int) instr->variables[0]->var->data.index;
> >  
> >     nir_load_const_instr *offset_const = 
> > nir_load_const_instr_create(mem_ctx, 1);
> >     offset_const->value.u[0] = instr->variables[0]->var
> > ->data.atomic.offset;
> > diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp 
> > b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> > index 6fee798..5e0bf1b 100644
> > --- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> > @@ -2407,7 +2407,7 @@ vec4_visitor::visit_atomic_counter_intrinsic(ir_call 
> > *ir)
> >        ir->actual_parameters.get_head());
> >     ir_variable *location = deref->variable_referenced();
> >     unsigned surf_index = (prog_data->base.binding_table.abo_start +
> > -                          location->data.binding);
> > +                          location->data.index);
> >  
> >     /* Calculate the surface offset */
> >     src_reg offset(this, glsl_type::uint_type);
> 
>