From ff9baa5f1c532a43d7d14a800f5a4a5c5757dca6 Mon Sep 17 00:00:00 2001
From: Pierre-Marie de Rodat <derodat@adacore.com>
Date: Wed, 21 Jun 2017 11:24:51 +0000
Subject: 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
---
 gcc/passes.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

(limited to 'gcc/passes.c')

diff --git a/gcc/passes.c b/gcc/passes.c
index 64493ba..374f6f7 100644
--- a/gcc/passes.c
+++ b/gcc/passes.c
@@ -262,17 +262,18 @@ rest_of_decl_compilation (tree decl,
      finalize_compilation_unit (and by consequence, locally scoped
      symbols), or by rest_of_type_compilation below.
 
-     Also, pick up function prototypes, which will be mostly ignored
-     by the different early_global_decl() hooks, but will at least be
-     used by Go's hijack of the debug_hooks to implement
-     -fdump-go-spec.  */
+     For Go's hijack of the debug_hooks to implement -fdump-go-spec, pick up
+     function prototypes.  Go's debug_hooks will not forward them to the
+     wrapped hooks.  */
   if (!in_lto_p
       && (TREE_CODE (decl) != FUNCTION_DECL
 	  /* This will pick up function prototypes with no bodies,
 	     which are not visible in finalize_compilation_unit()
 	     while iterating with FOR_EACH_*_FUNCTION through the
 	     symbol table.  */
-	  || !DECL_SAVED_TREE (decl))
+	  || (flag_dump_go_spec != NULL
+	      && !DECL_SAVED_TREE (decl)
+	      && DECL_STRUCT_FUNCTION (decl) == NULL))
 
       /* We need to check both decl_function_context and
 	 current_function_decl here to make sure local extern
-- 
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