glsl: validate sampler array indexing for 'constant-index-expression'

Desktop GLSL < 130 and GLSL ES < 300 allow sampler array indexing where
index can contain a loop induction variable. This extra check will warn
during linking if some of the indexes could not be turned in to constant
expressions.

v2: warning instead of error for backends that did not enable
    EmitNoIndirectSampler option (have dynamic indexing)

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Cc: "10.5" and "10.6" <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 9350ea6979)

src/glsl/linker.cpp

@@ -346,6 +346,39 @@ private:
    bool uses_non_zero_stream;
 };
 
+/* Class that finds array derefs and check if indexes are dynamic. */
+class dynamic_sampler_array_indexing_visitor : public ir_hierarchical_visitor
+{
+public:
+   dynamic_sampler_array_indexing_visitor() :
+      dynamic_sampler_array_indexing(false)
+   {
+   }
+
+   ir_visitor_status visit_enter(ir_dereference_array *ir)
+   {
+      if (!ir->variable_referenced())
+         return visit_continue;
+
+      if (!ir->variable_referenced()->type->contains_sampler())
+         return visit_continue;
+
+      if (!ir->array_index->constant_expression_value()) {
+         dynamic_sampler_array_indexing = true;
+         return visit_stop;
+      }
+      return visit_continue;
+   }
+
+   bool uses_dynamic_sampler_array_indexing()
+   {
+      return dynamic_sampler_array_indexing;
+   }
+
+private:
+   bool dynamic_sampler_array_indexing;
+};
+
 } /* anonymous namespace */
 
 void
@@ -2738,6 +2771,40 @@ build_program_resource_list(struct gl_context *ctx,
     */
 }
 
+/**
+ * This check is done to make sure we allow only constant expression
+ * indexing and "constant-index-expression" (indexing with an expression
+ * that includes loop induction variable).
+ */
+static bool
+validate_sampler_array_indexing(struct gl_context *ctx,
+                                struct gl_shader_program *prog)
+{
+   dynamic_sampler_array_indexing_visitor v;
+   for (unsigned i = 0; i < MESA_SHADER_STAGES; i++) {
+      if (prog->_LinkedShaders[i] == NULL)
+	 continue;
+
+      bool no_dynamic_indexing =
+         ctx->Const.ShaderCompilerOptions[i].EmitNoIndirectSampler;
+
+      /* Search for array derefs in shader. */
+      v.run(prog->_LinkedShaders[i]->ir);
+      if (v.uses_dynamic_sampler_array_indexing()) {
+         const char *msg = "sampler arrays indexed with non-constant "
+                           "expressions is forbidden in GLSL %s %u";
+         /* Backend has indicated that it has no dynamic indexing support. */
+         if (no_dynamic_indexing) {
+            linker_error(prog, msg, prog->IsES ? "ES" : "", prog->Version);
+            return false;
+         } else {
+            linker_warning(prog, msg, prog->IsES ? "ES" : "", prog->Version);
+         }
+      }
+   }
+   return true;
+}
+
 
 void
 link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
@@ -2956,6 +3023,16 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
       lower_const_arrays_to_uniforms(prog->_LinkedShaders[i]->ir);
    }
 
+   /* Validation for special cases where we allow sampler array indexing
+    * with loop induction variable. This check emits a warning or error
+    * depending if backend can handle dynamic indexing.
+    */
+   if ((!prog->IsES && prog->Version < 130) ||
+       (prog->IsES && prog->Version < 300)) {
+      if (!validate_sampler_array_indexing(ctx, prog))
+         goto done;
+   }
+
    /* Check and validate stream emissions in geometry shaders */
    validate_geometry_shader_emissions(ctx, prog);