glsl: add update_array_sizes() helper to the NIR uniform linker

This will be used to reduce the size of uniform arrays and replace
the current glsl ir pass. Doing this in NIR allows us to better
optimise the size of uniform arrays.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4910>

src/compiler/glsl/gl_nir_link_uniforms.c

@@ -84,6 +84,109 @@ uniform_storage_size(const struct glsl_type *type)
    }
 }
 
+/**
+ * Update the sizes of linked shader uniform arrays to the maximum
+ * array index used.
+ *
+ * From page 81 (page 95 of the PDF) of the OpenGL 2.1 spec:
+ *
+ *     If one or more elements of an array are active,
+ *     GetActiveUniform will return the name of the array in name,
+ *     subject to the restrictions listed above. The type of the array
+ *     is returned in type. The size parameter contains the highest
+ *     array element index used, plus one. The compiler or linker
+ *     determines the highest index used.  There will be only one
+ *     active uniform reported by the GL per uniform array.
+ */
+static void
+update_array_sizes(struct gl_shader_program *prog, nir_variable *var,
+                   struct hash_table **referenced_uniforms)
+{
+   /* For now we only resize 1D arrays.
+    * TODO: add support for resizing more complex array types ??
+    */
+   if (!glsl_type_is_array(var->type) ||
+       glsl_type_is_array(glsl_get_array_element(var->type)))
+      return;
+
+   /* GL_ARB_uniform_buffer_object says that std140 uniforms
+    * will not be eliminated.  Since we always do std140, just
+    * don't resize arrays in UBOs.
+    *
+    * Atomic counters are supposed to get deterministic
+    * locations assigned based on the declaration ordering and
+    * sizes, array compaction would mess that up.
+    *
+    * Subroutine uniforms are not removed.
+    */
+   if (nir_variable_is_in_block(var) || glsl_contains_atomic(var->type) ||
+       glsl_get_base_type(glsl_without_array(var->type)) == GLSL_TYPE_SUBROUTINE ||
+       var->constant_initializer)
+      return;
+
+   struct uniform_array_info *ainfo = NULL;
+   int words = BITSET_WORDS(glsl_array_size(var->type));
+   int max_array_size = 0;
+   for (unsigned stage = 0; stage < MESA_SHADER_STAGES; stage++) {
+      struct gl_linked_shader *sh = prog->_LinkedShaders[stage];
+      if (!sh)
+         continue;
+
+      struct hash_entry *entry =
+         _mesa_hash_table_search(referenced_uniforms[stage], var);
+      if (entry) {
+         ainfo = (struct uniform_array_info *)  entry->data;
+         if (ainfo->resized)
+            return;
+
+         max_array_size = MAX2(BITSET_LAST_BIT(ainfo->indices, words),
+                               max_array_size);
+      }
+
+      if (max_array_size == glsl_array_size(var->type))
+         return;
+   }
+
+   if (max_array_size != glsl_array_size(var->type)) {
+      /* If this is a built-in uniform (i.e., it's backed by some
+       * fixed-function state), adjust the number of state slots to
+       * match the new array size.  The number of slots per array entry
+       * is not known.  It seems safe to assume that the total number of
+       * slots is an integer multiple of the number of array elements.
+       * Determine the number of slots per array element by dividing by
+       * the old (total) size.
+       */
+      const unsigned num_slots = var->num_state_slots;
+      if (num_slots > 0) {
+         var->num_state_slots =
+            (max_array_size * (num_slots / glsl_array_size(var->type)));
+      }
+
+      var->type = glsl_array_type(glsl_get_array_element(var->type),
+                                  max_array_size, 0);
+
+      /* Update the types of dereferences in case we changed any. */
+      for (unsigned stage = 0; stage < MESA_SHADER_STAGES; stage++) {
+         struct gl_linked_shader *sh = prog->_LinkedShaders[stage];
+         if (!sh)
+            continue;
+
+         struct hash_entry *entry =
+            _mesa_hash_table_search(referenced_uniforms[stage], var);
+         if (entry) {
+            struct uniform_array_info *ainfo =
+               (struct uniform_array_info *) entry->data;
+            util_dynarray_foreach(ainfo->deref_list, nir_deref_instr *, deref) {
+               (*deref)->type = var->type;
+            }
+         }
+      }
+
+      if (ainfo)
+         ainfo->resized = true;
+   }
+}
+
 static void
 nir_setup_uniform_remap_tables(struct gl_context *ctx,
                                struct gl_shader_program *prog)