glsl: Emit function signatures at toplevel, even for built-ins.

The ast-to-hir conversion needs to emit function signatures in two
circumstances: when a function declaration (or definition) is
encountered, and when a built-in function is encountered.

To avoid emitting a function signature in an illegal place (such as
inside a function), emit_function() checked whether we were inside a
function definition, and if so, emitted the signature before the
function definition.

However, this didn't cover the case of emitting function signatures
for built-in functions when those built-in functions are called from
inside the constant integer expression that specifies the length of a
global array.  This failed because when processing an array length, we
are emitting IR into a dummy exec_list (see process_array_type() in
ast_to_hir.cpp).  process_array_type() later checks (via an assertion)
that no instructions were emitted to the dummy exec_list, based on the
reasonable assumption that we shouldn't need to emit instructions to
calculate the value of a constant.

This patch changes emit_function() so that it emits function
signatures at toplevel in all cases.

This partially fixes bug 38625
(https://bugs.freedesktop.org/show_bug.cgi?id=38625).  The remainder
of the fix is in the patch that follows.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/ast.h

@@ -730,7 +730,6 @@ _mesa_ast_field_selection_to_hir(const ast_expression *expr,
 				 struct _mesa_glsl_parse_state *state);
 
 void
-emit_function(_mesa_glsl_parse_state *state, exec_list *instructions,
-	      ir_function *f);
+emit_function(_mesa_glsl_parse_state *state, ir_function *f);
 
 #endif /* AST_H */

src/glsl/ast_function.cpp

@@ -125,7 +125,7 @@ match_function_by_name(exec_list *instructions, const char *name,
 	    if (f == NULL) {
 	       f = new(ctx) ir_function(name);
 	       state->symbols->add_global_function(f);
-	       emit_function(state, instructions, f);
+	       emit_function(state, f);
 	    }
 
 	    f->add_signature(sig->clone_prototype(f, NULL));

src/glsl/ast_to_hir.cpp

@@ -66,6 +66,8 @@ _mesa_ast_to_hir(exec_list *instructions, struct _mesa_glsl_parse_state *state)
 
    state->current_function = NULL;
 
+   state->toplevel_ir = instructions;
+
    /* Section 4.2 of the GLSL 1.20 specification states:
     * "The built-in functions are scoped in a scope outside the global scope
     *  users declare global variables in.  That is, a shader's global scope,
@@ -85,6 +87,8 @@ _mesa_ast_to_hir(exec_list *instructions, struct _mesa_glsl_parse_state *state)
       ast->hir(instructions, state);
 
    detect_recursion_unlinked(state, instructions);
+
+   state->toplevel_ir = NULL;
 }
 
 
@@ -2926,23 +2930,16 @@ ast_parameter_declarator::parameters_to_hir(exec_list *ast_parameters,
 
 
 void
-emit_function(_mesa_glsl_parse_state *state, exec_list *instructions,
-	      ir_function *f)
+emit_function(_mesa_glsl_parse_state *state, ir_function *f)
 {
-   /* Emit the new function header */
-   if (state->current_function == NULL) {
-      instructions->push_tail(f);
-   } else {
-      /* IR invariants disallow function declarations or definitions nested
-       * within other function definitions.  Insert the new ir_function
-       * block in the instruction sequence before the ir_function block
-       * containing the current ir_function_signature.
-       */
-      ir_function *const curr =
-	 const_cast<ir_function *>(state->current_function->function());
-
-      curr->insert_before(f);
-   }
+   /* IR invariants disallow function declarations or definitions
+    * nested within other function definitions.  But there is no
+    * requirement about the relative order of function declarations
+    * and definitions with respect to one another.  So simply insert
+    * the new ir_function block at the end of the toplevel instruction
+    * list.
+    */
+   state->toplevel_ir->push_tail(f);
 }
 
 
@@ -3069,7 +3066,7 @@ ast_function::hir(exec_list *instructions,
 	 return NULL;
       }
 
-      emit_function(state, instructions, f);
+      emit_function(state, f);
    }
 
    /* Verify the return type of main() */

src/glsl/glsl_parser_extras.h

@@ -129,6 +129,12 @@ struct _mesa_glsl_parse_state {
     */
    class ir_function_signature *current_function;
 
+   /**
+    * During AST to IR conversion, pointer to the toplevel IR
+    * instruction list being generated.
+    */
+   exec_list *toplevel_ir;
+
    /** Have we found a return statement in this function? */
    bool found_return;