[C++ PATCH] Fix ICE with builtin redefinition (PR c++/84843)

[Jason Merrill]

OK.

On Tue, Mar 13, 2018 at 4:17 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> If we return olddecl on an (invalid) builtin function redefinition rather
> than redeclaration, we ICE shortly afterwards, because we assume we have
> non-NULL DECL_INITIAL on whatever is returned (except for error_mark_node).
>
> The following patch errors unconditionally for definitions of builtin
> functions, and also makes sure to return error_mark_node if we've emitted
> an error from the permerror.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2018-03-13  Jakub Jelinek  <jakub@redhat.com>
>
>         PR c++/84843
>         * decl.c (duplicate_decls): For redefinition of built-in, use error
>         and return error_mark_node.  For redeclaration, return error_mark_node
>         rather than olddecl if !flag_permissive.
>
>         * g++.dg/ext/pr84843-1.C: New test.
>         * g++.dg/ext/pr84843-2.C: New test.
>
> --- gcc/cp/decl.c.jj    2018-03-09 19:00:44.350969146 +0100
> +++ gcc/cp/decl.c       2018-03-13 14:56:45.244872506 +0100
> @@ -1583,13 +1583,20 @@ next_arg:;
>                           || memcmp (name + len - strlen ("_chk"),
>                                      "_chk", strlen ("_chk") + 1) != 0))
>                     {
> +                     if (DECL_INITIAL (newdecl))
> +                       {
> +                         error_at (DECL_SOURCE_LOCATION (newdecl),
> +                                   "definition of %q#D ambiguates built-in "
> +                                   "declaration %q#D", newdecl, olddecl);
> +                         return error_mark_node;
> +                       }
>                       if (permerror (DECL_SOURCE_LOCATION (newdecl),
>                                      "new declaration %q#D ambiguates built-in"
>                                      " declaration %q#D", newdecl, olddecl)
>                           && flag_permissive)
>                         inform (DECL_SOURCE_LOCATION (newdecl),
>                                 "ignoring the %q#D declaration", newdecl);
> -                     return olddecl;
> +                     return flag_permissive ? olddecl : error_mark_node;
>                     }
>                 }
>
> --- gcc/testsuite/g++.dg/ext/pr84843-1.C.jj     2018-03-13 14:55:15.927831678 +0100
> +++ gcc/testsuite/g++.dg/ext/pr84843-1.C        2018-03-13 14:57:51.652902862 +0100
> @@ -0,0 +1,9 @@
> +// PR c++/84843
> +// { dg-do compile }
> +// { dg-options "-fpermissive" }
> +
> +extern "C" int
> +__atomic_compare_exchange (int x, int y)       // { dg-error "ambiguates built-in declaration" }
> +{
> +  return x + y;
> +}
> --- gcc/testsuite/g++.dg/ext/pr84843-2.C.jj     2018-03-13 14:55:19.349833246 +0100
> +++ gcc/testsuite/g++.dg/ext/pr84843-2.C        2018-03-13 14:57:58.205905859 +0100
> @@ -0,0 +1,9 @@
> +// PR c++/84843
> +// { dg-do compile }
> +// { dg-options "" }
> +
> +extern "C" int
> +__atomic_compare_exchange (int x, int y)       // { dg-error "ambiguates built-in declaration" }
> +{
> +  return x + y;
> +}
>
>         Jakub