[Mesa-dev] [PATCH v3] glsl/linker: location aliasing requires types to have the same width
Iago Toral
itoral at igalia.com
Thu Nov 9 14:31:51 UTC 2017
On Thu, 2017-11-09 at 08:41 -0500, Ilia Mirkin wrote:
> On Tue, Nov 7, 2017 at 4:50 AM, Iago Toral Quiroga <itoral at igalia.com
> > wrote:
> > Regarding location aliasing requirements, the OpenGL spec says:
> >
> > "Further, when location aliasing, the aliases sharing the
> > location
> > must have the same underlying numerical type (floating-point or
> > integer)."
> >
> > Khronos has further clarified that this also requires the
> > underlying
> > types to have the same width, so we can't put a float and a double
> > in the same location slot for example. Future versions of the spec
> > will
> > be corrected to make this clear.
> >
> > This patch amends our implementation to account for this
> > restriction.
> >
> > In the process of doing this, I also noticed that we would attempt
> > to check aliasing requirements for record variables (including the
> > test
> > for the numerical type) which is not allowed, instead, we should be
> > producing a linker error as soon as we see any attempt to do
> > location
> > aliasing on non-numerical variables. For the particular case of
> > structs,
> > we were producing a linker error in this case, but only because we
> > assumed that struct fields use all components in each location, so
> > any attempt to alias locations consumed by struct fields would
> > produce
> > a link error due to component aliasing, which is not accurate of
> > the
> > actual problem. This patch would make it produce an error for
> > attempting
> > to alias a non-numerical variable instead, which is always
> > accurate.
> >
> > v2:
> > - Do not assert if we see invalid numerical types. These come
> > straight from shader code, so we should produce linker errors
> > if
> > shaders attempt to do location aliasing on variables that are
> > not
> > numerical such as records.
> > - While we are at it, improve error reporting for the case of
> > numerical type mismatch to include the shader stage.
> >
> > v3:
> > - Allow location aliasing of images and samplers. If we get these
> > it means bindless support is active and they should be handled
> > as 64-bit integers (Ilia)
> > - Make sure we produce link errors for any non-numerical type
> > for which we attempt location aliasing, not just structs.
> > ---
> > src/compiler/glsl/link_varyings.cpp | 64
> > ++++++++++++++++++++++++++-----------
> > 1 file changed, 46 insertions(+), 18 deletions(-)
> >
> > diff --git a/src/compiler/glsl/link_varyings.cpp
> > b/src/compiler/glsl/link_varyings.cpp
> > index 1a9894baab..e0d757eaaf 100644
> > --- a/src/compiler/glsl/link_varyings.cpp
> > +++ b/src/compiler/glsl/link_varyings.cpp
> > @@ -405,15 +405,15 @@ compute_variable_location_slot(ir_variable
> > *var, gl_shader_stage stage)
> >
> > struct explicit_location_info {
> > ir_variable *var;
> > - unsigned numerical_type;
> > + int numerical_type;
> > unsigned interpolation;
> > bool centroid;
> > bool sample;
> > bool patch;
> > };
> >
> > -static inline unsigned
> > -get_numerical_type(const glsl_type *type)
> > +static inline int
> > +get_numerical_sized_type(const glsl_type *type)
> > {
> > /* From the OpenGL 4.6 spec, section 4.4.1 Input Layout
> > Qualifiers, Page 68,
> > * (Location aliasing):
> > @@ -421,10 +421,25 @@ get_numerical_type(const glsl_type *type)
> > * "Further, when location aliasing, the aliases sharing the
> > location
> > * must have the same underlying numerical type (floating-
> > point or
> > * integer)
> > + *
> > + * Khronos has further clarified that this also requires the
> > underlying
> > + * types to have the same width, so we can't put a float and a
> > double
> > + * in the same location slot for example. Future versions of
> > the spec will
> > + * be corrected to make this clear.
> > + *
> > + * Notice that we allow location aliasing for bindless
> > image/samplers too
> > + * since these are defined as 64-bit integers.
> > */
> > - if (type->is_float() || type->is_double())
> > + if (type->is_float())
> > return GLSL_TYPE_FLOAT;
> > - return GLSL_TYPE_INT;
> > + else if (type->is_integer())
> > + return GLSL_TYPE_INT;
> > + else if (type->is_double())
> > + return GLSL_TYPE_DOUBLE;
> > + else if (type->is_integer_64() || type->is_sampler() || type-
> > >is_image())
> > + return GLSL_TYPE_INT64;
> > +
> > + return -1; /* Not a numerical type */
> > }
> >
> > static bool
> > @@ -442,14 +457,17 @@ check_location_aliasing(struct
> > explicit_location_info explicit_locations[][4],
> > gl_shader_stage stage)
> > {
> > unsigned last_comp;
> > - if (type->without_array()->is_record()) {
> > - /* The component qualifier can't be used on structs so just
> > treat
> > - * all component slots as used.
> > + const glsl_type *type_without_array = type->without_array();
> > + int numerical_type =
> > get_numerical_sized_type(type_without_array);
> > + if (numerical_type == -1) {
> > + /* The component qualifier can't be used on non-numerical
> > types so just
> > + * treat all component slots as used. This will also make it
> > so that
> > + * any location aliasing attempt on non-numerical types is
> > detected.
> > */
>
> But you don't really prevent this here...
>
> layout(component=2) out S foo;
>
> won't run into problems that I can see (at least not due to this
> code). Only if something else ends up in that location for the other
> comps. Is something else preventing the above?
This code only tests for location aliasing, so it only fails if
something else uses that location.
The component layout qualifier is forbidden on structs and is correctly
detected at compile time. I've just tested it and get this errors:
"error: component layout qualifier cannot be applied to a matrix, a
structure, a block, or an array containing any of these."
> > last_comp = 4;
> > } else {
> > - unsigned dmul = type->without_array()->is_64bit() ? 2 : 1;
> > - last_comp = component + type->without_array()-
> > >vector_elements * dmul;
> > + unsigned dmul = type_without_array->is_64bit() ? 2 : 1;
> > + last_comp = component + type_without_array->vector_elements
> > * dmul;
> > }
> >
> > while (location < location_limit) {
> > @@ -459,8 +477,18 @@ check_location_aliasing(struct
> > explicit_location_info explicit_locations[][4],
> > &explicit_locations[location][comp];
> >
> > if (info->var) {
> > - /* Component aliasing is not alloed */
> > - if (comp >= component && comp < last_comp) {
> > + if (numerical_type == -1 || info->numerical_type ==
> > -1) {
> > + /* Location aliasing is only allowed for numerical
> > variables */
> > + linker_error(prog,
> > + "%s shader has location aliasing for "
> > + "non-numerical variable '%s'. Location
> > %u "
> > + "component %u\n",
> > + _mesa_shader_stage_to_string(stage),
> > + numerical_type == -1 ? var->name :
> > info->var->name,
> > + location, comp);
> > + return false;
> > + } else if (comp >= component && comp < last_comp) {
> > + /* Component aliasing is not allowed */
> > linker_error(prog,
> > "%s shader has multiple outputs
> > explicitly "
> > "assigned to location %d and component
> > %d\n",
> > @@ -471,12 +499,12 @@ check_location_aliasing(struct
> > explicit_location_info explicit_locations[][4],
> > /* For all other used components we need to have
> > matching
> > * types, interpolation and auxiliary storage
> > */
> > - if (info->numerical_type !=
> > - get_numerical_type(type->without_array())) {
> > + if (info->numerical_type != numerical_type) {
> > linker_error(prog,
> > - "Varyings sharing the same location
> > must "
> > - "have the same underlying numerical
> > type. "
> > - "Location %u component %u\n",
> > + "%s shader has varyings sharing the
> > same "
> > + "location that don't have the same
> > underlying "
> > + "numerical type. Location %u
> > component %u\n",
> > + _mesa_shader_stage_to_string(stage)
> > ,
> > location, comp);
> > return false;
> > }
> > @@ -502,7 +530,7 @@ check_location_aliasing(struct
> > explicit_location_info explicit_locations[][4],
> > }
> > } else if (comp >= component && comp < last_comp) {
> > info->var = var;
> > - info->numerical_type = get_numerical_type(type-
> > >without_array());
> > + info->numerical_type = numerical_type;
> > info->interpolation = interpolation;
> > info->centroid = centroid;
> > info->sample = sample;
> > --
> > 2.11.0
> >
>
>
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