[Bug c/47939] Missing DW_TAG_typedef for qualified types

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47939

--- Comment #7 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-03-01 17:01:38 UTC ---
(In reply to comment #6)
> On Tue, 1 Mar 2011, rguenth at gcc dot gnu.org wrote:
> 
> > The patch bootstrapped and tested ok.  Removing
> > 
> >   if (!flag_gen_aux_info && (TYPE_QUALS (element_type)))
> >     type = TYPE_MAIN_VARIANT (type);
> > 
> > unconditionally breaks gcc.dg/array-quals-2.c (but nothing else).
> 
> The point of the logic removing qualifiers here is as described in the 
> comment
> 
>   /* Now figure out the structure of the declarator proper.
>      Descend through it, creating more complex types, until we reach
>      the declared identifier (or NULL_TREE, in an absolute declarator).
>      At each stage we maintain an unqualified version of the type
>      together with any qualifiers that should be applied to it with
>      c_build_qualified_type; this way, array types including
>      multidimensional array types are first built up in unqualified
>      form and then the qualified form is created with
>      TYPE_MAIN_VARIANT pointing to the unqualified form.  */
> 
> to ensure consistency in TYPE_MAIN_VARIANT for array types; see 
> <http://gcc.gnu.org/ml/gcc-patches/2005-01/msg02180.html>.
> 
> > Probably a better general approach would be to make c_build_qualified_type
> > also take a desired name as argument instead of using TYPE_NAME.
> 
> In general it's a desired name for an intermediate type at some level of 
> array derivation, not for the type being constructed by 
> c_build_qualified_type.  I suppose you could pass both the name and the 
> particular type that should have that name, or otherwise indicate the 
> qualifiers and level of array nesting where the name should be used if 
> possible.
> 
> If you have
> 
> typedef const int T[1];
> T array[2][3];
> 
> then "const" is being applied to "int [2][3][1]", and it's the 
> intermediate type "const int [1]" that you'd like to get the name T.

I see.  There is an alternative way to stripping qualifiers - build
an unqualified variant like with

Index: gcc/c-decl.c
===================================================================
--- gcc/c-decl.c        (revision 170594)
+++ gcc/c-decl.c        (working copy)
@@ -5038,8 +5038,8 @@ grokdeclarator (const struct c_declarato
     error_at (loc, "conflicting named address spaces (%s vs %s)",
              c_addr_space_name (as1), c_addr_space_name (as2));

-  if (!flag_gen_aux_info && (TYPE_QUALS (element_type)))
-    type = TYPE_MAIN_VARIANT (type);
+  if (TYPE_QUALS (element_type))
+    type = c_build_qualified_type (type, 0);
   type_quals = ((constp ? TYPE_QUAL_CONST : 0)
                | (restrictp ? TYPE_QUAL_RESTRICT : 0)
                | (volatilep ? TYPE_QUAL_VOLATILE : 0)

or alternatively using build_qualified_type directly to not strip
qualifiers recursively at this point.  That would preserve the
type-names but also introduce a unqualified variants with that name
if it doesn't exist already.  To avoid the latter in c_build_qualified_type
we could pass TYPE_MAIN_VARIANT to the build_qualified_type calls.

I don't know if I'm the correct person to try fixing this (I'm certainly
new to this part of the code), but at least the flag_gen_aux_info
checking looks suspicious and should be removed.