[Bug debug/79289] DWARF info for typeof of C function with no args and no prototype is empty pointer

["ian at airs dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79289

Ian Lance Taylor <ian at airs dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |aoliva at gcc dot gnu.org,
                   |                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org

--- Comment #1 from Ian Lance Taylor <ian at airs dot com> ---
I think the bug is a mismatch in how the code determines the base type to use
for the DIE in this change:

2016-11-03  Jakub Jelinek  <jakub@redhat.com>
            Alexandre Oliva  <aoliva@redhat.com>
            Jason Merrill  <jason@redhat.com>

        PR debug/28767
        PR debug/56974
        * langhooks.h (struct lang_hooks_for_types): Add type_dwarf_attribute
        langhook.
        * langhooks.c (lhd_type_dwarf_attribute): New function.
        * langhooks-def.h (lhd_type_dwarf_attribute): Declare.
        (LANG_HOOKS_TYPE_DWARF_ATTRIBUTE): Define.
        (LANG_HOOKS_FOR_TYPES_INITIALIZER): Add
        LANG_HOOKS_TYPE_DWARF_ATTRIBUTE.
        (check_qualified_type, check_aligned_type): Call it.
        * dwarf2out.c (modified_type_die): Don't use type_main_variant
        for FUNCTION_TYPE or METHOD_TYPE, instead walk over variants with
        check_base_type and check_lang_type.
        (gen_ptr_to_mbr_type_die): If lookup_type_die is already non-NULL,
        return early.  For pointer-to-data-member add DW_AT_use_location
        attribute.
        (gen_subroutine_type_die): Add DW_AT_{,rvalue_}reference attribute
        if needed.
        (gen_type_die_with_usage): Don't use type_main_variant
        for FUNCTION_TYPE or METHOD_TYPE, instead walk over variants with
        check_base_type and check_lang_type.  Formatting fixes. Call
        get_debug_type langhook.

The problem is that the DIE is stored with one type variant in
gen_type_die_with_usage (the last matching variant), but looked up with a
different type variant in modified_type_die (the first matching variant).

This patch seems to fix the problem, but I can't tell whether this is correct
or whether the other obvious change is correct.


Index: gcc/dwarf2out.c
===================================================================
--- gcc/dwarf2out.c     (revision 244166)
+++ gcc/dwarf2out.c     (working copy)
@@ -24395,8 +24395,13 @@ gen_type_die_with_usage (tree type, dw_d
         but try to canonicalize.  */
       tree main = TYPE_MAIN_VARIANT (type);
       for (tree t = main; t; t = TYPE_NEXT_VARIANT (t))
-       if (check_base_type (t, main) && check_lang_type (t, type))
-         type = t;
+       {
+         if (check_base_type (t, main) && check_lang_type (t, type))
+           {
+             type = t;
+             break;
+           }
+       }
     }
   else if (TREE_CODE (type) != VECTOR_TYPE
           && TREE_CODE (type) != ARRAY_TYPE)