DWARF: make it possible to emit debug info for declarations only

The DWARF back-end used to systematically ignore file-scope function and
variable declarations.  While this is justified in language like C/C++,
where such declarations can appear in several translation units and thus
bloat uselessly the debug info, this behavior is counter-productive in
languages with a well-defined module system.  Specifically, it prevents
the description of imported entities, that belong to foreign languages,
making them unavailable from debuggers.

Take for instance:

    package C_Binding is
        function My_C_Function (I : Integer) return Integer;
        pragma Import (C, My_C_Function, "my_c_function");
    end C_Binding;

This makes available for Ada programs the C function "my_c_function"
under the following name: C_Binding.My_C_Function.  When GCC compiles
it, though, it is represented as a FUNCTION_DECL node with DECL_EXTERNAL
set and a null DECL_INITIAL, which used to be discarded unconditionally
in the DWARF back-end.

This patch moves such filter from the DWARF back-end to the relevant
callers: passes.c:rest_of_decl_compilation and
godump.c:go_early_global_decl. It also This patch also updates the Ada
front-end to call debug hooks for functions such as in the above
example, so that we do generate debugging information for them.

gcc/
	* dwarf2out.c (gen_decl_die): Remove the guard to skip file-scope
	FUNCTION_DECL declarations.
	(dwarf2out_early_global_decl): Remove the guard to skip FUNCTION_DECL
	declarations.
	(dwaf2out_decl): Likewise.
	* godump.c (go_early_global_decl): Skip call to the real debug hook
	for FUNCTION_DECL declarations.
	* passes.c (rest_of_decl_compilation): Skip call to the
	early_global_decl debug hook for FUNCTION_DECL declarations, unless
	-fdump-go-spec is passed.

gcc/ada/
	* gcc-interface/ada-tree.h (DECL_FUNCTION_IS_DEF): Update copyright
	notice.  New macro.
	* gcc-interface/trans.c (Subprogram_Body_to_gnu): Tag the subprogram
	as a definition.
	(Compilation_Unit_to_gnu): Tag the elaboration procedure as a
	definition.
	* gcc-interface/decl.c (gnat_to_gnu_entity): Tag declarations of
	imported subprograms for the current compilation unit as
	definitions.  Disable debug info for references to variables.
	* gcc-interface/gigi.h (create_subprog_decl): Update declaration.
	* gcc-interface/utils.c (gnat_pushdecl): Add external DECLs that are
	not built-in functions to their binding scope.
	(create_subprog_decl): Add a DEFINITION parameter.  If it is true, tag
	the function as a definition.  Update all callers.
	(gnat_write_global_declarations): Emit debug info for imported
	functions.  Filter out external variables for which debug info
	is disabled.

gcc/testsuite/
	* gnat.dg/debug11_pkg.adb, gnat.dg/debug11_pkg.ads,
	gnat.dg/debug11_pkg2.ads: New testcase.

From-SVN: r249449

1 files changed, 12 insertions, 7 deletions

diff --git a/gcc/ada/gcc-interface/decl.c b/gcc/ada/gcc-interface/decl.c
index eab244e..83b9d07 100644
--- a/gcc/ada/gcc-interface/decl.c
+++ b/gcc/ada/gcc-interface/decl.c
@@ -1392,7 +1392,8 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
 	      = create_var_decl (create_concat_name (gnat_entity, "ALIGN"),
 				 NULL_TREE, gnu_new_type, NULL_TREE,
 				 false, false, false, false, false,
-				 true, debug_info_p, NULL, gnat_entity);
+				 true, debug_info_p && definition, NULL,
+				 gnat_entity);
 
 	    /* Initialize the aligned field if we have an initializer.  */
 	    if (gnu_expr)
@@ -1441,7 +1442,8 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
 				      NULL_TREE, gnu_type, gnu_expr,
 				      const_flag, Is_Public (gnat_entity),
 				      imported_p || !definition, static_flag,
-				      volatile_flag, true, debug_info_p,
+				      volatile_flag, true,
+				      debug_info_p && definition,
 				      NULL, gnat_entity);
 		gnu_expr = build_unary_op (ADDR_EXPR, NULL_TREE, gnu_unc_var);
 		TREE_CONSTANT (gnu_expr) = 1;
@@ -1492,8 +1494,9 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
 	  = create_var_decl (gnu_entity_name, gnu_ext_name, gnu_type,
 			     gnu_expr, const_flag, Is_Public (gnat_entity),
 			     imported_p || !definition, static_flag,
-			     volatile_flag, artificial_p, debug_info_p,
-			     attr_list, gnat_entity, !renamed_obj);
+			     volatile_flag, artificial_p,
+			     debug_info_p && definition, attr_list,
+			     gnat_entity, !renamed_obj);
 	DECL_BY_REF_P (gnu_decl) = used_by_ref;
 	DECL_POINTS_TO_READONLY_P (gnu_decl) = used_by_ref && inner_const_flag;
 	DECL_CAN_NEVER_BE_NULL_P (gnu_decl) = Can_Never_Be_Null (gnat_entity);
@@ -1545,8 +1548,8 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
 	      = create_var_decl (gnu_entity_name, gnu_ext_name, gnu_type,
 				 gnu_expr, true, Is_Public (gnat_entity),
 				 !definition, static_flag, volatile_flag,
-				 artificial_p, debug_info_p, attr_list,
-				 gnat_entity, false);
+				 artificial_p, debug_info_p && definition,
+				 attr_list, gnat_entity, false);
 
 	    SET_DECL_CONST_CORRESPONDING_VAR (gnu_decl, gnu_corr_var);
 	  }
@@ -4083,7 +4086,9 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
 					 gnu_type, gnu_param_list,
 					 inline_status, public_flag,
 					 extern_flag, artificial_p,
-					 debug_info_p, attr_list, gnat_entity);
+					 debug_info_p,
+					 definition && imported_p, attr_list,
+					 gnat_entity);
 
 		DECL_STUBBED_P (gnu_decl)
 		  = (Convention (gnat_entity) == Convention_Stubbed);