trans.c (Attribute_to_gnu): Add kludge to avoid generating an overflow for -1.

	* gcc-interface/trans.c (Attribute_to_gnu) <Attr_Last_Bit>: Add kludge
	to avoid generating an overflow for -1.

From-SVN: r199339

gcc/ada/ChangeLog

 2013-05-26  Eric Botcazou  <ebotcazou@adacore.com>
 
+	* gcc-interface/trans.c (Attribute_to_gnu) <Attr_Last_Bit>: Add kludge
+	to avoid generating an overflow for -1.
+
+2013-05-26  Eric Botcazou  <ebotcazou@adacore.com>
+
 	* gcc-interface/gigi.h (create_type_decl): Adjust prototype.
 	(create_label_decl): Complete prototype.
 	(process_attributes): Declare.

gcc/ada/gcc-interface/trans.c

@@ -2080,14 +2080,19 @@ Attribute_to_gnu (Node_Id gnat_node, tree *gnu_result_type_p, int attribute)
 	    gnu_result = bitsize_int (bitpos % BITS_PER_UNIT);
 	    gnu_result = size_binop (PLUS_EXPR, gnu_result,
 				     TYPE_SIZE (TREE_TYPE (gnu_prefix)));
-	    gnu_result = size_binop (MINUS_EXPR, gnu_result,
-				     bitsize_one_node);
+	    /* ??? Avoid a large unsigned result that will overflow when
+	       converted to the signed universal_integer.  */
+	    if (integer_zerop (gnu_result))
+	      gnu_result = integer_minus_one_node;
+	    else
+	      gnu_result
+		= size_binop (MINUS_EXPR, gnu_result, bitsize_one_node);
 	    break;
 
 	  case Attr_Bit_Position:
 	    gnu_result = gnu_field_bitpos;
 	    break;
-		}
+	  }
 
 	/* If this has a PLACEHOLDER_EXPR, qualify it by the object we are
 	   handling.  */

gcc/testsuite/ChangeLog

 2013-05-26  Eric Botcazou  <ebotcazou@adacore.com>
 
+	* gnat.dg/specs/last_bit.ads: New test.
+
+2013-05-26  Eric Botcazou  <ebotcazou@adacore.com>
+
 	* gnat.dg/specs/machine_attribute.ads: New test.
 
 2013-05-26  Eric Botcazou  <ebotcazou@adacore.com>

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

+-- { dg-do compile }
+
+package Last_Bit is
+
+   Max_Components : constant := 100;
+   type Count_Type is new Natural range 0 .. Max_Components;
+   subtype Index_Type is Count_Type range 1 .. Count_Type'Last;
+   
+   type List_Type is array (Index_Type range <>) of Integer;
+
+   type Record_Type (Count : Count_Type := 0) is record
+      List : List_Type (1 .. Count);
+   end record;
+
+   Null_Record : Record_Type (Count => 0);
+
+   List_Last_Bit : Integer := Null_Record.List'Last_Bit;
+
+end Last_Bit;