glsl: Track existence of default float precision in GLSL ES fragment shaders

This is required by the spec, and it's a bit tricky because the default
precision is scoped.  As a result, I'm slightly abusing the symbol
table.

Fixes piglit no-default-float-precision.frag tests and the piglit
default-precision-nested-scope-0[1234].frag tests that are currently on
the piglit mailing list for review.

On IRC I got confirmation from cwabbot that ARM (Mali T6xx and T400)
enforces this requirement and from kusma that NVIDIA (Tegra2) enforces
this requirement.  We should be safe from regressing shipping
applications.

Signed-off-by: Ian Romanick <[email protected]>
Reviewed-by: Kenneth Graunke <[email protected]>
Cc: "9.2" <[email protected]>

2 files changed, 68 insertions, 4 deletions

diff --git a/src/glsl/ast.h b/src/glsl/ast.h
index 9b194dbd043..335374de16b 100644
--- a/src/glsl/ast.h
+++ b/src/glsl/ast.h
@@ -610,6 +610,10 @@ public:
    virtual void print(void) const;
    bool has_qualifiers() const;
 
+   const struct glsl_type *glsl_type(const char **name,
+				     struct _mesa_glsl_parse_state *state)
+      const;
+
    ast_type_qualifier qualifier;
    ast_type_specifier *specifier;
 };
diff --git a/src/glsl/ast_to_hir.cpp b/src/glsl/ast_to_hir.cpp
index 88d9fd60b56..d94faa885b5 100644
--- a/src/glsl/ast_to_hir.cpp
+++ b/src/glsl/ast_to_hir.cpp
@@ -1797,6 +1797,28 @@ ast_type_specifier::glsl_type(const char **name,
    return type;
 }
 
+const glsl_type *
+ast_fully_specified_type::glsl_type(const char **name,
+                                    struct _mesa_glsl_parse_state *state) const
+{
+   const struct glsl_type *type = this->specifier->glsl_type(name, state);
+
+   if (type == NULL)
+      return NULL;
+
+   if (type->base_type == GLSL_TYPE_FLOAT
+       && state->es_shader
+       && state->target == fragment_shader
+       && this->qualifier.precision == ast_precision_none
+       && state->symbols->get_variable("#default precision") == NULL) {
+      YYLTYPE loc = this->get_location();
+      _mesa_glsl_error(&loc, state,
+                       "no precision specified this scope for type `%s'",
+                       type->name);
+   }
+
+   return type;
+}
 
 /**
  * Determine whether a toplevel variable declaration declares a varying.  This
@@ -2693,7 +2715,7 @@ ast_declarator_list::hir(exec_list *instructions,
     */
    (void) this->type->specifier->hir(instructions, state);
 
-   decl_type = this->type->specifier->glsl_type(& type_name, state);
+   decl_type = this->type->glsl_type(& type_name, state);
    if (this->declarations.is_empty()) {
       /* If there is no structure involved in the program text, there are two
        * possible scenarios:
@@ -3277,7 +3299,7 @@ ast_parameter_declarator::hir(exec_list *instructions,
    const char *name = NULL;
    YYLTYPE loc = this->get_location();
 
-   type = this->type->specifier->glsl_type(& name, state);
+   type = this->type->glsl_type(& name, state);
 
    if (type == NULL) {
       if (name != NULL) {
@@ -3484,7 +3506,7 @@ ast_function::hir(exec_list *instructions,
 
    const char *return_type_name;
    const glsl_type *return_type =
-      this->return_type->specifier->glsl_type(& return_type_name, state);
+      this->return_type->glsl_type(& return_type_name, state);
 
    if (!return_type) {
       YYLTYPE loc = this->get_location();
@@ -4288,6 +4310,44 @@ ast_type_specifier::hir(exec_list *instructions,
          return NULL;
       }
 
+      if (type->base_type == GLSL_TYPE_FLOAT
+          && state->es_shader
+          && state->target == fragment_shader) {
+         /* Section 4.5.3 (Default Precision Qualifiers) of the GLSL ES 1.00
+          * spec says:
+          *
+          *     "The fragment language has no default precision qualifier for
+          *     floating point types."
+          *
+          * As a result, we have to track whether or not default precision has
+          * been specified for float in GLSL ES fragment shaders.
+          *
+          * Earlier in that same section, the spec says:
+          *
+          *     "Non-precision qualified declarations will use the precision
+          *     qualifier specified in the most recent precision statement
+          *     that is still in scope. The precision statement has the same
+          *     scoping rules as variable declarations. If it is declared
+          *     inside a compound statement, its effect stops at the end of
+          *     the innermost statement it was declared in. Precision
+          *     statements in nested scopes override precision statements in
+          *     outer scopes. Multiple precision statements for the same basic
+          *     type can appear inside the same scope, with later statements
+          *     overriding earlier statements within that scope."
+          *
+          * Default precision specifications follow the same scope rules as
+          * variables.  So, we can track the state of the default float
+          * precision in the symbol table, and the rules will just work.  This
+          * is a slight abuse of the symbol table, but it has the semantics
+          * that we want.
+          */
+         ir_variable *const junk =
+            new(state) ir_variable(type, "#default precision",
+                                   ir_var_temporary);
+
+         state->symbols->add_variable(junk);
+      }
+
       /* FINISHME: Translate precision statements into IR. */
       return NULL;
    }
@@ -4368,7 +4428,7 @@ ast_process_structure_or_interface_block(exec_list *instructions,
       }
 
       const glsl_type *decl_type =
-	 decl_list->type->specifier->glsl_type(& type_name, state);
+         decl_list->type->glsl_type(& type_name, state);
 
       foreach_list_typed (ast_declaration, decl, link,
 			  &decl_list->declarations) {