decl.c (components_to_record): Add special case for single field with…

decl.c (components_to_record): Add special case for single field with representation clause at offset 0.

	* gcc-interface/decl.c (components_to_record): Add special case for     
	single field with representation clause at offset 0.

From-SVN: r234494

gcc/ada/ChangeLog

+2016-03-27  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* gcc-interface/decl.c (components_to_record): Add special case for     
+	single field with representation clause at offset 0.
+
 2016-03-16  Svante Signell  <svante.signell@gmail.com>
 
 	* gcc-interface/Makefile.in: Add support for x86 GNU/Hurd.

gcc/ada/gcc-interface/decl.c

@@ -7606,6 +7606,23 @@ components_to_record (tree gnu_record_type, Node_Id gnat_component_list,
   if (p_gnu_rep_list && gnu_rep_list)
     *p_gnu_rep_list = chainon (*p_gnu_rep_list, gnu_rep_list);
 
+  /* If only one field has a rep clause and it starts at 0, put back the field
+     at the head of the regular field list.  This will avoid creating a useless
+     REP part below and deal with the annoying case of an extension of a record
+     with variable size and rep clause, for which the _Parent field is forced
+     at offset 0 and has variable size, which we do not support below.  */
+  else if (gnu_rep_list
+	   && !DECL_CHAIN (gnu_rep_list)
+	   && !variants_have_rep
+	   && first_free_pos
+	   && integer_zerop (first_free_pos)
+	   && integer_zerop (bit_position (gnu_rep_list)))
+    {
+      DECL_CHAIN (gnu_rep_list) = gnu_field_list;
+      gnu_field_list = gnu_rep_list;
+      gnu_rep_list = NULL_TREE;
+    }
+
   /* Otherwise, sort the fields by bit position and put them into their own
      record, before the others, if we also have fields without rep clause.  */
   else if (gnu_rep_list)

gcc/testsuite/ChangeLog

+2016-03-27  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* gnat.dg/specs/double_record_extension3.ads: New test.
+
 2016-03-25  Richard Henderson  <rth@redhat.com>
 
 	PR target/70120

gcc/testsuite/gnat.dg/specs/double_record_extension3.ads

+-- { dg-do compile }
+
+package Double_Record_Extension3 is
+
+   type Rec1 is tagged record
+      Id : Integer;
+   end record;
+
+   for Rec1 use record
+      Id at 8 range 0 .. 31;
+   end record;
+
+   type Rec2 (Size : Integer) is new Rec1 with record
+      Data : String (1 .. Size);
+   end record;
+
+   type Rec3 is new Rec2 (Size => 128) with record
+      Valid : Boolean;
+   end record;
+
+end Double_Record_Extension3;
+