[Mesa-dev] [PATCH 2/2] glsl/linker: location aliasing requires types to have the same width

[Iago Toral Quiroga]

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 a record variable.
---
 src/compiler/glsl/link_varyings.cpp | 41 ++++++++++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
index af938611f4..1d17deaffe 100644
--- a/src/compiler/glsl/link_varyings.cpp
+++ b/src/compiler/glsl/link_varyings.cpp
@@ -413,7 +413,7 @@ struct explicit_location_info {
 };
 
 static inline unsigned
-get_numerical_type(const glsl_type *type)
+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 +421,22 @@ 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.
     */
-   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())
+      return GLSL_TYPE_INT64;
+
+   unreachable("Type is not numerical");
 }
 
 static bool
@@ -442,14 +454,17 @@ check_location_aliasing(struct explicit_location_info explicit_locations[][4],
                         gl_shader_stage stage)
 {
    unsigned last_comp;
+   bool is_record;
    if (type->without_array()->is_record()) {
       /* The component qualifier can't be used on structs so just treat
        * all component slots as used.
        */
       last_comp = 4;
+      is_record = true;
    } else {
       unsigned dmul = type->without_array()->is_64bit() ? 2 : 1;
       last_comp = component + type->without_array()->vector_elements * dmul;
+      is_record = false;
    }
 
    while (location < location_limit) {
@@ -459,8 +474,17 @@ 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 (is_record) {
+               /* Disallow location aliasing for record variables */
+               linker_error(prog,
+                            "%s shader uses explicit location on record "
+                            "variable %s that generates location aliasing "
+                            "for location %u, component %u\n",
+                            _mesa_shader_stage_to_string(stage),
+                            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",
@@ -472,7 +496,7 @@ check_location_aliasing(struct explicit_location_info explicit_locations[][4],
                 * types, interpolation and auxiliary storage
                 */
                if (info->numerical_type !=
-                   get_numerical_type(type->without_array())) {
+                   get_numerical_sized_type(type->without_array())) {
                   linker_error(prog,
                                "Varyings sharing the same location must "
                                "have the same underlying numerical type. "
@@ -502,7 +526,10 @@ 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());
+            if (!is_record) {
+               info->numerical_type =
+                  get_numerical_sized_type(type->without_array());
+            }
             info->interpolation = interpolation;
             info->centroid = centroid;
             info->sample = sample;
-- 
2.11.0