[Bug debug/90232] gcc drops top-level dies with -fdebug-types-section

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90232

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
With this demonstrator patch:
...
diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index b9a624e1ac7..1e818973fae 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -8400,10 +8400,11 @@ generate_skeleton (dw_die_ref die)
   /* If this type definition is nested inside another type,
      and is not an instantiation of a template, always leave
      at least a declaration in its place.  */
-  if (die->die_parent != NULL
-      && is_type_die (die->die_parent)
-      && !is_template_instantiation (die))
-    node.new_die = clone_as_declaration (die);
+  if (true || (die->die_parent != NULL
+              && is_type_die (die->die_parent)
+              && !is_template_instantiation (die)))
+      node.new_die = clone_as_declaration (die);
+  node.new_die->die_perennial_p = 1;

   generate_skeleton_bottom_up (&node);
   return node.new_die;
...
instead we get the desired:
...
 <0><d2>: Abbrev Number: 5 (DW_TAG_compile_unit)
    <d8>   DW_AT_name        : (indirect string, offset: 0x1f8): 36.c
 <1><f4>: Abbrev Number: 6 (DW_TAG_structure_type)
    <f5>   DW_AT_name        : s
    <f7>   DW_AT_signature   : signature: 0xfd1462823bb6f7b7
 <1><106>: Abbrev Number: 7 (DW_TAG_subprogram)
    <107>   DW_AT_name        : (indirect string, offset: 0x2b8): main
 <2><124>: Abbrev Number: 8 (DW_TAG_variable)
    <125>   DW_AT_name        : a
    <12a>   DW_AT_type        : <0xf4>
Contents of the .debug_types section:
   Signature:     0xfd1462823bb6f7b7
 <1><1d>: Abbrev Number: 2 (DW_TAG_structure_type)
    <1e>   DW_AT_name        : s
...
and:
...
 <0><13e>: Abbrev Number: 5 (DW_TAG_compile_unit)
    <144>   DW_AT_name        : (indirect string, offset: 0x2bd): 36b.c
 <1><160>: Abbrev Number: 6 (DW_TAG_structure_type)
    <161>   DW_AT_name        : s
    <163>   DW_AT_signature   : signature: 0x534310fbefba324d
 <1><172>: Abbrev Number: 7 (DW_TAG_subprogram)
    <173>   DW_AT_name        : f
 <2><18a>: Abbrev Number: 8 (DW_TAG_variable)
    <18b>   DW_AT_name        : b
Contents of the .debug_types section:
   Signature:     0x534310fbefba324d
 <1><59>: Abbrev Number: 2 (DW_TAG_structure_type)
    <5a>   DW_AT_name        : s
...