[PATCH] Emit DWARF5 DW_AT_export_symbols for namespaces

[PATCH] Emit DWARF5 DW_AT_export_symbols for namespaces

[Jakub Jelinek]

Hi!

DWARF5 introduced DW_AT_export_symbols that may be preset on
DW_TAG_namespace or DW_TAG_{structure,union,class}_type to signalize
inline or anonymous namespaces or anonymous structures/unions/classes.

What we were emitting instead is an implicit DW_TAG_imported_module
in the outer namespace.

The following patch changes nothing for -gdwarf-4 and below with
-gstrict-dwarf, for -gdwarf-4 and below -gno-strict-dwarf it
just adds DW_AT_export_symbols to inline namespaces (so that interested
consumers can find out it is inline namespace, but consumers not knowing
about DW_AT_export_symbols still have the implicit DW_TAG_imported_module).
In that mode, no changes for anonymous namespaces, because those
are already easily detectable by the consumers (missing DW_AT_name).
For -gdwarf-5 it emits DW_AT_export_symbols on both inline namespaces
and anonymous namespaces and doesn't emit the implicit
DW_TAG_imported_module, which is shorter.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

This patch doesn't do anything about anon struct/union/class, I've tried
to handle it, the problem is that ANON_AGGR_TYPE_P flag is set too late,
after the debug hook adds the type DIE.  Any thoughts on how to handle that?
And I wonder what is the counterpart of ANON_AGGR_TYPE_P in the C FE, CCing
Marek on that.

2017-07-21  Jakub Jelinek  <jakub@redhat.com>

	* debug.h (struct gcc_debug_hooks): Add IMPLICIT argument
	to imported_module_or_decl hook.
	(debug_nothing_tree_tree_tree_bool): Remove.
	(debug_nothing_tree_tree_tree_bool_bool): New declaration.
	* debug.c (do_nothing_debug_hooks): Use
	debug_nothing_tree_tree_tree_bool_bool instead of
	debug_nothing_tree_tree_tree_bool.
	* vmsdbgout.c (vmsdbg_debug_hooks): Likewise.
	* dbxout.c (dbx_debug_hooks, xcoff_debug_hooks): Likewise.
	* sdbout.c (sdb_debug_hooks): Likewise.
	* dwarf2out.c (dwarf2_lineno_debug_hooks): Likewise.
	(gen_namespace_die): Add DW_AT_export_symbols attribute if
	langhook wants it.
	(dwarf2out_imported_module_or_decl): Add IMPLICIT argument,
	if true, -gdwarf-5 and decl will have DW_AT_export_symbols
	attribute, don't add anything.
cp/
	* cp-objcp-common.c (cp_decl_dwarf_attribute): Handle
	DW_AT_export_symbols.
	* name-lookup.c (emit_debug_info_using_namespace): Add IMPLICIT
	argument, pass it through to the debug hook.
	(finish_namespace_using_directive): Adjust
	emit_debug_info_using_namespace caller.
	(push_namespace): Likewise.  Call it after setting
	DECL_NAMESPACE_INLINE_P.
	(cp_emit_debug_info_for_using): Pass false as new argument to
	the imported_module_or_decl debug hook.
fortran/
	* trans-decl.c (gfc_trans_use_stmts): Pass false as new argument to
	the imported_module_or_decl debug hook.
ada/
	* gcc-interface/utils.c (gnat_write_global_declarations): Pass false
	as new argument to the imported_module_or_decl debug hook.
testsuite/
	* g++.dg/debug/dwarf2/inline-ns-1.C: New test.
	* g++.dg/debug/dwarf2/inline-ns-2.C: New test.

--- gcc/debug.h.jj	2017-02-18 17:11:18.000000000 +0100
+++ gcc/debug.h	2017-07-21 12:19:09.486576092 +0200
@@ -145,7 +145,8 @@ struct gcc_debug_hooks
 
   /* Debug information for imported modules and declarations.  */
   void (* imported_module_or_decl) (tree decl, tree name,
-				    tree context, bool child);
+				    tree context, bool child,
+				    bool implicit);
 
   /* DECL is an inline function, whose body is present, but which is
      not being output at this point.  */
@@ -206,7 +207,8 @@ extern void debug_nothing_int_int (unsig
 extern void debug_nothing_tree (tree);
 extern void debug_nothing_tree_tree (tree, tree);
 extern void debug_nothing_tree_int (tree, int);
-extern void debug_nothing_tree_tree_tree_bool (tree, tree, tree, bool);
+extern void debug_nothing_tree_tree_tree_bool_bool (tree, tree, tree,
+						    bool, bool);
 extern bool debug_true_const_tree (const_tree);
 extern void debug_nothing_rtx_insn (rtx_insn *);
 extern void debug_nothing_rtx_code_label (rtx_code_label *);
--- gcc/debug.c.jj	2017-02-18 17:11:18.000000000 +0100
+++ gcc/debug.c	2017-07-21 11:53:45.452383785 +0200
@@ -47,7 +47,7 @@ const struct gcc_debug_hooks do_nothing_
   debug_nothing_tree,	         	 /* early_global_decl */
   debug_nothing_tree,	         	 /* late_global_decl */
   debug_nothing_tree_int,		 /* type_decl */
-  debug_nothing_tree_tree_tree_bool,	 /* imported_module_or_decl */
+  debug_nothing_tree_tree_tree_bool_bool,/* imported_module_or_decl */
   debug_nothing_tree,		         /* deferred_inline_function */
   debug_nothing_tree,		         /* outlining_inline_function */
   debug_nothing_rtx_code_label,	         /* label */
@@ -80,10 +80,11 @@ debug_nothing_tree_tree (tree t1 ATTRIBU
 }
 
 void
-debug_nothing_tree_tree_tree_bool (tree t1 ATTRIBUTE_UNUSED,
-				   tree t2 ATTRIBUTE_UNUSED,
-				   tree t3 ATTRIBUTE_UNUSED,
-				   bool b1 ATTRIBUTE_UNUSED)
+debug_nothing_tree_tree_tree_bool_bool (tree t1 ATTRIBUTE_UNUSED,
+					tree t2 ATTRIBUTE_UNUSED,
+					tree t3 ATTRIBUTE_UNUSED,
+					bool b1 ATTRIBUTE_UNUSED,
+					bool b2 ATTRIBUTE_UNUSED)
 {
 }
 
--- gcc/vmsdbgout.c.jj	2017-02-18 17:11:18.000000000 +0100
+++ gcc/vmsdbgout.c	2017-07-21 11:54:50.757609629 +0200
@@ -197,7 +197,7 @@ const struct gcc_debug_hooks vmsdbg_debu
    vmsdbgout_early_global_decl,
    vmsdbgout_late_global_decl,
    vmsdbgout_type_decl,		  /* type_decl */
-   debug_nothing_tree_tree_tree_bool, /* imported_module_or_decl */
+   debug_nothing_tree_tree_tree_bool_bool, /* imported_module_or_decl */
    debug_nothing_tree,		  /* deferred_inline_function */
    vmsdbgout_abstract_function,
    debug_nothing_rtx_code_label,  /* label */
--- gcc/dbxout.c.jj	2017-07-21 10:28:12.000000000 +0200
+++ gcc/dbxout.c	2017-07-21 11:54:03.115174403 +0200
@@ -371,7 +371,7 @@ const struct gcc_debug_hooks dbx_debug_h
   dbxout_early_global_decl,		 /* early_global_decl */
   dbxout_late_global_decl,		 /* late_global_decl */
   dbxout_type_decl,			 /* type_decl */
-  debug_nothing_tree_tree_tree_bool,	 /* imported_module_or_decl */
+  debug_nothing_tree_tree_tree_bool_bool,/* imported_module_or_decl */
   debug_nothing_tree,		         /* deferred_inline_function */
   debug_nothing_tree,		         /* outlining_inline_function */
   debug_nothing_rtx_code_label,	         /* label */
@@ -411,7 +411,7 @@ const struct gcc_debug_hooks xcoff_debug
   dbxout_early_global_decl,		 /* early_global_decl */
   dbxout_late_global_decl,		 /* late_global_decl */
   dbxout_type_decl,			 /* type_decl */
-  debug_nothing_tree_tree_tree_bool,	 /* imported_module_or_decl */
+  debug_nothing_tree_tree_tree_bool_bool,/* imported_module_or_decl */
   debug_nothing_tree,		         /* deferred_inline_function */
   debug_nothing_tree,		         /* outlining_inline_function */
   debug_nothing_rtx_code_label,	         /* label */
--- gcc/sdbout.c.jj	2017-02-18 17:11:18.000000000 +0100
+++ gcc/sdbout.c	2017-07-21 11:54:32.259828909 +0200
@@ -301,7 +301,7 @@ const struct gcc_debug_hooks sdb_debug_h
   sdbout_early_global_decl,		 /* early_global_decl */
   sdbout_late_global_decl,		 /* late_global_decl */
   sdbout_symbol,			 /* type_decl */
-  debug_nothing_tree_tree_tree_bool,	 /* imported_module_or_decl */
+  debug_nothing_tree_tree_tree_bool_bool,/* imported_module_or_decl */
   debug_nothing_tree,		         /* deferred_inline_function */
   debug_nothing_tree,		         /* outlining_inline_function */
   sdbout_label,			         /* label */
--- gcc/dwarf2out.c.jj	2017-07-21 10:28:12.659136982 +0200
+++ gcc/dwarf2out.c	2017-07-21 12:01:14.052065893 +0200
@@ -2680,7 +2680,7 @@ static bool dwarf2out_ignore_block (cons
 static void dwarf2out_early_global_decl (tree);
 static void dwarf2out_late_global_decl (tree);
 static void dwarf2out_type_decl (tree, int);
-static void dwarf2out_imported_module_or_decl (tree, tree, tree, bool);
+static void dwarf2out_imported_module_or_decl (tree, tree, tree, bool, bool);
 static void dwarf2out_imported_module_or_decl_1 (tree, tree, tree,
 						 dw_die_ref);
 static void dwarf2out_abstract_function (tree);
@@ -2764,7 +2764,7 @@ const struct gcc_debug_hooks dwarf2_line
   debug_nothing_tree,		         /* early_global_decl */
   debug_nothing_tree,		         /* late_global_decl */
   debug_nothing_tree_int,		 /* type_decl */
-  debug_nothing_tree_tree_tree_bool,	 /* imported_module_or_decl */
+  debug_nothing_tree_tree_tree_bool_bool,/* imported_module_or_decl */
   debug_nothing_tree,		         /* deferred_inline_function */
   debug_nothing_tree,		         /* outlining_inline_function */
   debug_nothing_rtx_code_label,	         /* label */
@@ -25166,6 +25172,11 @@ gen_namespace_die (tree decl, dw_die_ref
       add_AT_die_ref (namespace_die, DW_AT_import, origin_die);
       equate_decl_number_to_die (decl, namespace_die);
     }
+  if ((dwarf_version >= 5 || !dwarf_strict)
+      && lang_hooks.decls.decl_dwarf_attribute (decl,
+						DW_AT_export_symbols) == 1)
+    add_AT_flag (namespace_die, DW_AT_export_symbols, 1);
+
   /* Bypass dwarf2_name's check for DECL_NAMELESS.  */
   if (want_pubnames ())
     add_pubname_string (lang_hooks.dwarf_name (decl, 1), namespace_die);
@@ -25579,11 +25590,13 @@ dwarf2out_imported_module_or_decl_1 (tre
 /* Output debug information for imported module or decl DECL.
    NAME is non-NULL name in context if the decl has been renamed.
    CHILD is true if decl is one of the renamed decls as part of
-   importing whole module.  */
+   importing whole module.
+   IMPLICIT is set if this hook is called for an implicit import
+   such as inline namespace.  */
 
 static void
 dwarf2out_imported_module_or_decl (tree decl, tree name, tree context,
-				   bool child)
+				   bool child, bool implicit)
 {
   /* dw_die_ref at_import_die;  */
   dw_die_ref scope_die;
@@ -25593,6 +25606,16 @@ dwarf2out_imported_module_or_decl (tree
 
   gcc_assert (decl);
 
+  /* For DWARF5, just DW_AT_export_symbols on the DW_TAG_namespace
+     should be enough, for DWARF4 and older even if we emit as extension
+     DW_AT_export_symbols add the implicit DW_TAG_imported_module anyway
+     for the benefit of consumers unaware of DW_AT_export_symbols.  */
+  if (implicit
+      && dwarf_version >= 5
+      && lang_hooks.decls.decl_dwarf_attribute (decl,
+						DW_AT_export_symbols) == 1)
+    return;
+
   set_early_dwarf s;
 
   /* To emit DW_TAG_imported_module or DW_TAG_imported_decl, we need two DIEs.
--- gcc/cp/cp-objcp-common.c.jj	2017-07-19 14:01:18.866064325 +0200
+++ gcc/cp/cp-objcp-common.c	2017-07-21 12:18:28.031066986 +0200
@@ -212,6 +212,13 @@ cp_decl_dwarf_attribute (const_tree decl
 	}
       break;
 
+    case DW_AT_export_symbols:
+      if (TREE_CODE (decl) == NAMESPACE_DECL
+	  && (DECL_NAMESPACE_INLINE_P (decl)
+	      || (DECL_NAME (decl) == NULL_TREE && dwarf_version >= 5)))
+	return 1;
+      break;
+
     default:
       break;
     }
--- gcc/cp/name-lookup.c.jj	2017-07-19 14:01:18.887064085 +0200
+++ gcc/cp/name-lookup.c	2017-07-21 12:06:27.525349847 +0200
@@ -6045,11 +6045,12 @@ add_using_namespace (vec<tree, va_gc> *&
 /* Tell the debug system of a using directive.  */
 
 static void
-emit_debug_info_using_namespace (tree from, tree target)
+emit_debug_info_using_namespace (tree from, tree target, bool implicit)
 {
   /* Emit debugging info.  */
   tree context = from != global_namespace ? from : NULL_TREE;
-  debug_hooks->imported_module_or_decl (target, NULL_TREE, context, false);
+  debug_hooks->imported_module_or_decl (target, NULL_TREE, context, false,
+					implicit);
 }
 
 /* Process a namespace-scope using directive.  */
@@ -6064,7 +6065,7 @@ finish_namespace_using_directive (tree t
   add_using_namespace (DECL_NAMESPACE_USING (current_namespace),
 		       ORIGINAL_NAMESPACE (target));
   emit_debug_info_using_namespace (current_namespace,
-				   ORIGINAL_NAMESPACE (target));
+				   ORIGINAL_NAMESPACE (target), false);
 
   if (attribs == error_mark_node)
     return;
@@ -6223,14 +6224,14 @@ push_namespace (tree name, bool make_inl
 	  else if (TREE_PUBLIC (current_namespace))
 	    TREE_PUBLIC (ns) = 1;
 
-	  if (name == anon_identifier || make_inline)
-	    emit_debug_info_using_namespace (current_namespace, ns);
-
 	  if (make_inline)
 	    {
 	      DECL_NAMESPACE_INLINE_P (ns) = true;
 	      vec_safe_push (DECL_NAMESPACE_INLINEES (current_namespace), ns);
 	    }
+
+	  if (name == anon_identifier || make_inline)
+	    emit_debug_info_using_namespace (current_namespace, ns, true);
 	}
     }
 
@@ -6358,8 +6359,8 @@ cp_emit_debug_info_for_using (tree t, tr
 	  if (building_stmt_list_p ())
 	    add_stmt (build_stmt (input_location, USING_STMT, fn));
 	  else
-	    debug_hooks->imported_module_or_decl (fn,
-						  NULL_TREE, context, false);
+	    debug_hooks->imported_module_or_decl (fn, NULL_TREE, context,
+						  false, false);
 	}
     }
 }
--- gcc/fortran/trans-decl.c.jj	2017-05-12 14:34:55.000000000 +0200
+++ gcc/fortran/trans-decl.c	2017-07-21 12:11:53.917733772 +0200
@@ -4875,7 +4875,7 @@ gfc_trans_use_stmts (gfc_namespace * ns)
 	(*debug_hooks->imported_module_or_decl) (entry->namespace_decl,
 						 NULL_TREE,
 						 ns->proc_name->backend_decl,
-						 false);
+						 false, false);
       for (rent = use_stmt->rename; rent; rent = rent->next)
 	{
 	  tree decl, local_name;
@@ -4952,7 +4952,8 @@ gfc_trans_use_stmts (gfc_namespace * ns)
 	  gfc_set_backend_locus (&rent->where);
 	  (*debug_hooks->imported_module_or_decl) (decl, local_name,
 						   ns->proc_name->backend_decl,
-						   !use_stmt->only_flag);
+						   !use_stmt->only_flag,
+						   false);
 	}
     }
 }
--- gcc/ada/gcc-interface/utils.c.jj	2017-06-21 16:53:37.000000000 +0200
+++ gcc/ada/gcc-interface/utils.c	2017-07-21 12:12:22.569394503 +0200
@@ -5553,7 +5553,7 @@ gnat_write_global_declarations (void)
   FOR_EACH_VEC_SAFE_ELT (global_decls, i, iter)
    if (TREE_CODE (iter) == IMPORTED_DECL && !DECL_IGNORED_P (iter))
      debug_hooks->imported_module_or_decl (iter, DECL_NAME (iter),
-					   DECL_CONTEXT (iter), 0);
+					   DECL_CONTEXT (iter), false, false);
 }
 
 /* ************************************************************************
--- gcc/testsuite/g++.dg/debug/dwarf2/inline-ns-1.C.jj	2017-07-21 13:36:41.589158999 +0200
+++ gcc/testsuite/g++.dg/debug/dwarf2/inline-ns-1.C	2017-07-21 13:51:34.353524052 +0200
@@ -0,0 +1,23 @@
+// { dg-options "-O2 -gdwarf-4 -dA -gno-strict-dwarf" }
+// { dg-final { scan-assembler-times " DW_AT_export_symbols" 1 } }
+// { dg-final { scan-assembler-times "DIE \\(\[^\n\r\]*\\) DW_TAG_imported_module" 2 } }
+
+namespace A
+{
+  int i = 5;
+  inline namespace B
+  {
+    int j = 6;
+    namespace C
+    {
+      int k = 7;
+    };
+  };
+};
+int l = A::i + A::j + A::C::k;
+int m = A::i + A::B::j + A::B::C::k;
+namespace
+{
+  int n = 8;
+};
+int o = n;
--- gcc/testsuite/g++.dg/debug/dwarf2/inline-ns-2.C.jj	2017-07-21 13:40:16.689595957 +0200
+++ gcc/testsuite/g++.dg/debug/dwarf2/inline-ns-2.C	2017-07-21 13:52:20.043981081 +0200
@@ -0,0 +1,23 @@
+// { dg-options "-O2 -gdwarf-5 -dA" }
+// { dg-final { scan-assembler-times " DW_AT_export_symbols" 2 } }
+// { dg-final { scan-assembler-not "DIE \\(\[^\n\r\]*\\) DW_TAG_imported_module" } }
+
+namespace A
+{
+  int i = 5;
+  inline namespace B
+  {
+    int j = 6;
+    namespace C
+    {
+      int k = 7;
+    };
+  };
+};
+int l = A::i + A::j + A::C::k;
+int m = A::i + A::B::j + A::B::C::k;
+namespace
+{
+  int n = 8;
+};
+int o = n;

	Jakub

Re: [PATCH] Emit DWARF5 DW_AT_export_symbols for namespaces

[Marek Polacek]

On Fri, Jul 21, 2017 at 10:33:12PM +0200, Jakub Jelinek wrote:
> Hi!
> 
> DWARF5 introduced DW_AT_export_symbols that may be preset on
> DW_TAG_namespace or DW_TAG_{structure,union,class}_type to signalize
> inline or anonymous namespaces or anonymous structures/unions/classes.
> 
> What we were emitting instead is an implicit DW_TAG_imported_module
> in the outer namespace.
> 
> The following patch changes nothing for -gdwarf-4 and below with
> -gstrict-dwarf, for -gdwarf-4 and below -gno-strict-dwarf it
> just adds DW_AT_export_symbols to inline namespaces (so that interested
> consumers can find out it is inline namespace, but consumers not knowing
> about DW_AT_export_symbols still have the implicit DW_TAG_imported_module).
> In that mode, no changes for anonymous namespaces, because those
> are already easily detectable by the consumers (missing DW_AT_name).
> For -gdwarf-5 it emits DW_AT_export_symbols on both inline namespaces
> and anonymous namespaces and doesn't emit the implicit
> DW_TAG_imported_module, which is shorter.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> 
> This patch doesn't do anything about anon struct/union/class, I've tried
> to handle it, the problem is that ANON_AGGR_TYPE_P flag is set too late,
> after the debug hook adds the type DIE.  Any thoughts on how to handle that?
> And I wonder what is the counterpart of ANON_AGGR_TYPE_P in the C FE, CCing
> Marek on that.

I think you need to check RECORD_OR_UNION_TYPE_P && DECL_NAME == NULL_TREE.
Or do it in grokfield -- would that work?

	Marek

Re: [PATCH] Emit DWARF5 DW_AT_export_symbols for namespaces

[Jakub Jelinek]

On Tue, Jul 25, 2017 at 01:45:31PM +0200, Marek Polacek wrote:
> > This patch doesn't do anything about anon struct/union/class, I've tried
> > to handle it, the problem is that ANON_AGGR_TYPE_P flag is set too late,
> > after the debug hook adds the type DIE.  Any thoughts on how to handle that?
> > And I wonder what is the counterpart of ANON_AGGR_TYPE_P in the C FE, CCing
> > Marek on that.
> 
> I think you need to check RECORD_OR_UNION_TYPE_P && DECL_NAME == NULL_TREE.
> Or do it in grokfield -- would that work?

One thing is that the information needs to be propagated from the FE to
dwarf2out somehow.

And the second thing is that it isn't really clear to me when exactly do we
want to use DW_AT_export_symbols on types with no name.

Consider:

struct { int a, b; } c;
typedef struct { int d, e; } f;
struct S {
  f h;
#ifdef MS_EXTENSIONS
  f;
#endif
  struct { int i, j; };
  struct { int k, l; } m;
} g;

with -g -dA {,-DMS_EXTENSIONS -fms-extensions}
(or -fplan9-extensions).
For the struct with i/j fields we clearly want the DW_AT_export_symbols
on it, for the struct with k/l fields I think we don't, the fields of that
structure aren't exported into the outer namespace.
And then there is the case of the misdesigned Plan9 and Microsoft
extensions, the same type then can be used once as not really exporting
stuff out of it and another time as doing that.

Guess my preference would be to only mark i+j struct here, i.e. struct/union
with DECL_NAME NULL with DECL_CONTEXT of some aggregate where there are no
named fields with that type in the aggregate.
It might be a good idea to change DWARF6 so that DW_AT_export_symbols is
also allowed on DW_TAG_member and emit it that way for the f; case above.

Another issue is that DWARF5 D.2.5 lists the anonymous structure nested
as child of the outer structure, so just for:
struct T { struct { int n; }; };
DW_TAG_structure_type
  DW_AT_name T
  DW_TAG_structure_type
    DW_AT_export_symbols
    DW_TAG_member
      DW_AT_name n
but what GCC emits is:
1: DW_TAG_structure_type
  DW_TAG_member
    DW_AT_name n
DW_TAG_structure_type
  DW_AT_name T
    DW_TAG_member
      DW_AT_type 1b

Maybe at least for -gdwarf-5 we should start moving stuff into the right
context.

	Jakub

Re: [PATCH] Emit DWARF5 DW_AT_export_symbols for namespaces

[Jason Merrill]

On Fri, Jul 21, 2017 at 4:33 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> DWARF5 introduced DW_AT_export_symbols that may be preset on
> DW_TAG_namespace or DW_TAG_{structure,union,class}_type to signalize
> inline or anonymous namespaces or anonymous structures/unions/classes.
>
> What we were emitting instead is an implicit DW_TAG_imported_module
> in the outer namespace.
>
> The following patch changes nothing for -gdwarf-4 and below with
> -gstrict-dwarf, for -gdwarf-4 and below -gno-strict-dwarf it
> just adds DW_AT_export_symbols to inline namespaces (so that interested
> consumers can find out it is inline namespace, but consumers not knowing
> about DW_AT_export_symbols still have the implicit DW_TAG_imported_module).
> In that mode, no changes for anonymous namespaces, because those
> are already easily detectable by the consumers (missing DW_AT_name).
> For -gdwarf-5 it emits DW_AT_export_symbols on both inline namespaces
> and anonymous namespaces and doesn't emit the implicit
> DW_TAG_imported_module, which is shorter.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

> This patch doesn't do anything about anon struct/union/class, I've tried
> to handle it, the problem is that ANON_AGGR_TYPE_P flag is set too late,
> after the debug hook adds the type DIE.  Any thoughts on how to handle that?

Hmm, I guess we want to call rest_of_type_compilation again after we
set ANON_AGGR_TYPE_P, and adjust the debug back-ends to handle that; I
see that gen_struct_or_union_type_die already handles being called
again to fill in variable-length fields.

Jason