[C++ PATCH] Clear TYPE_TRANSPARENT_AGGR if there are no fields (PR c++/46862)

[Jakub Jelinek]

Hi!

TYPE_TRANSPARENT_AGGR types are passed and mangled as its first field.
But if somebody errorneously doesn't put any types in its definition,
the FE marks it TYPE_TRANSPARENT_AGGR early (e.g. even on a forward
declaration), but during mangling or in middle-end when trying to find out
how it will be passed we ICE because first_field is NULL.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux.
Ok for trunk/4.6?

2011-08-22  Jakub Jelinek  <ja...@redhat.com>

        PR c++/46862
        * class.c (finish_struct_1): If TYPE_TRANSPARENT_AGGR is set on a type
        which doesn't have any fields, clear it and diagnose.

        * g++.dg/ext/decimal1.C: New test.

--- gcc/cp/class.c.jj   2011-08-18 08:35:38.000000000 +0200
+++ gcc/cp/class.c      2011-08-22 12:52:13.000000000 +0200
@@ -1,6 +1,6 @@
 /* Functions related to building classes and their related objects.
    Copyright (C) 1987, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
-   1999, 2000, 2001, 2002, 2003, 2004, 2005, 2007, 2008, 2009, 2010
+   1999, 2000, 2001, 2002, 2003, 2004, 2005, 2007, 2008, 2009, 2010, 2011
    Free Software Foundation, Inc.
    Contributed by Michael Tiemann (tiem...@cygnus.com)
 
@@ -5794,6 +5794,12 @@ finish_struct_1 (tree t)
 
   /* Finish debugging output for this type.  */
   rest_of_type_compilation (t, ! LOCAL_CLASS_P (t));
+
+  if (TYPE_TRANSPARENT_AGGR (t) && first_field (t) == NULL_TREE)
+    {
+      error ("type transparent class %qT does not have any fields", t);
+      TYPE_TRANSPARENT_AGGR (t) = 0;
+    }
 }
 
 /* When T was built up, the member declarations were added in reverse
--- gcc/testsuite/g++.dg/ext/decimal1.C.jj      2011-08-22 13:22:01.000000000 
+0200
+++ gcc/testsuite/g++.dg/ext/decimal1.C 2011-08-22 13:16:30.000000000 +0200
@@ -0,0 +1,19 @@
+// PR c++/46862
+// { dg-do compile }
+
+namespace std
+{
+  namespace decimal
+  {
+    class decimal32 { };       // { dg-error "does not have any fields" }
+    class decimal64 { };       // { dg-error "does not have any fields" }
+    class decimal128 { };      // { dg-error "does not have any fields" }
+  }
+}
+
+void
+foo (std::decimal::decimal32 x,
+     std::decimal::decimal64 y,
+     std::decimal::decimal128 z)
+{
+}

        Jakub