decl.c (gnat_to_gnu_param): Add comment about double reference and DECL_POINTS_TO_READONLY_P.

	* gcc-interface/decl.c (gnat_to_gnu_param): Add comment about double
	reference and DECL_POINTS_TO_READONLY_P.
	* gcc-interface/trans.c (Identifier_to_gnu) <by_ref>: Always set the
	TREE_READONLY flag on the first dereference of a double dereference.

From-SVN: r182460

gcc/ada/ChangeLog

+2011-12-18  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* gcc-interface/decl.c (gnat_to_gnu_param): Add comment about double
+	reference and DECL_POINTS_TO_READONLY_P.
+	* gcc-interface/trans.c (Identifier_to_gnu) <by_ref>: Always set the
+	TREE_READONLY flag on the first dereference of a double dereference.
+
 2011-12-15  Arnaud Charlet  <charlet@adacore.com>
 
 	* a-numaux-vms.ads, s-asthan-vms-ia64.adb, s-auxdec-vms-ia64.adb,

gcc/ada/gcc-interface/decl.c

@@ -5587,6 +5587,10 @@ gnat_to_gnu_param (Entity_Id gnat_param, Mechanism_Type mech,
   DECL_BY_COMPONENT_PTR_P (gnu_param) = by_component_ptr;
   DECL_BY_DESCRIPTOR_P (gnu_param) = (mech == By_Descriptor ||
                                       mech == By_Short_Descriptor);
+  /* Note that, in case of a parameter passed by double reference, the
+     DECL_POINTS_TO_READONLY_P flag is meant for the second reference.
+     The first reference always points to read-only, as it points to
+     the second reference, i.e. the reference to the actual parameter.  */
   DECL_POINTS_TO_READONLY_P (gnu_param)
     = (ro_param && (by_ref || by_component_ptr));
   DECL_CAN_NEVER_BE_NULL_P (gnu_param) = Can_Never_Be_Null (gnat_param);

gcc/ada/gcc-interface/trans.c

@@ -1038,8 +1038,9 @@ Identifier_to_gnu (Node_Id gnat_node, tree *gnu_result_type_p)
 	  if (TREE_CODE (gnu_result) == INDIRECT_REF)
 	    TREE_THIS_NOTRAP (gnu_result) = 1;
 
-	  if (read_only)
-	    TREE_READONLY (gnu_result) = 1;
+	  /* The first reference, in case of a double reference, always points
+	     to read-only, see gnat_to_gnu_param for the rationale.  */
+	  TREE_READONLY (gnu_result) = 1;
 	}
 
       /* If it's a PARM_DECL to foreign convention subprogram, convert it.  */