[Patch, Fortran] PR51308 - fix bogus c_null_ptr error

[Tobias Burnus <burnus at net-b dot de>]

gfortran printed an error that "c_null_ptr" couldn't be SAVE an 
PARAMETER at the same time; removing the SAVE attribute causes an error 
that a BIND(C) variable may not be a PARAMETER, thus that has to be 
fixed as well.
(Patch based on the one of Steven

Build and regtested on x86-64-linux.
OK for the trunk?

Tobias
2011-11-28  Tobias Burnus  <burnus@net-b.de>
	    Steven G. Kargl  <kargl@gcc.gnu.org>

	PR fortran/51308
	* symbol.c (check_conflict): Ignore BIND(C) + PARAMETER
	conflicts for ISO_C_BINDING variables.
	(gen_special_c_interop_ptr): Don't mark c_ptr_null/c_funptr_null
	as SAVE.

2011-11-28  Tobias Burnus  <burnus@net-b.de>

	PR fortran/51308
	* gfortran.dg/iso_c_binding_compiler_4.f90: New.

diff --git a/gcc/fortran/symbol.c b/gcc/fortran/symbol.c
index 9bd6ed4..67009c5 100644
--- a/gcc/fortran/symbol.c
+++ b/gcc/fortran/symbol.c
@@ -742,9 +742,10 @@ check_conflict (symbol_attribute *attr, const char *name, locus *where)
       conf2 (asynchronous);
       conf2 (threadprivate);
       conf2 (value);
-      conf2 (is_bind_c);
       conf2 (codimension);
       conf2 (result);
+      if (!attr->is_iso_c)
+	conf2 (is_bind_c);
       break;
 
     default:
@@ -3763,13 +3764,12 @@ gen_special_c_interop_ptr (int ptr_id, const char *ptr_name,
                           "create symbol for %s", ptr_name);
     }
 
-  /* Set up the symbol's important fields.  Save attr required so we can
-     initialize the ptr to NULL.  */
-  tmp_sym->attr.save = SAVE_EXPLICIT;
+  /* Set up the symbol's important fields. */
   tmp_sym->ts.is_c_interop = 1;
   tmp_sym->attr.is_c_interop = 1;
   tmp_sym->ts.is_iso_c = 1;
   tmp_sym->ts.type = BT_DERIVED;
+  tmp_sym->attr.flavor = FL_PARAMETER;
 
   /* The c_ptr and c_funptr derived types will provide the
      definition for c_null_ptr and c_null_funptr, respectively.  */
@@ -3817,9 +3817,6 @@ gen_special_c_interop_ptr (int ptr_id, const char *ptr_name,
   c->expr = gfc_get_expr ();
   c->expr->expr_type = EXPR_NULL;
   c->expr->ts.is_iso_c = 1;
-  /* Must declare c_null_ptr and c_null_funptr as having the
-     PARAMETER attribute so they can be used in init expressions.  */
-  tmp_sym->attr.flavor = FL_PARAMETER;
 
   return SUCCESS;
 }
--- /dev/null	2011-11-28 07:33:54.995528670 +0100
+++ gcc/gcc/testsuite/gfortran.dg/iso_c_binding_compiler_4.f90	2011-11-28 14:27:05.000000000 +0100
@@ -0,0 +1,18 @@
+! { dg-do compile }
+!
+! PR fortran/51308
+!
+! Contributed by Matthias Moeller
+!
+
+module mymod
+  use iso_c_binding
+  implicit none
+
+  private
+  public :: c_ptr
+  public :: c_null_ptr
+
+end module mymod
+
+! { dg-final { cleanup-modules "mymod" } }