re PR ada/56474 (bogus Storage_Error raised for record containing empty zero-based array)

	PR ada/56474
	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Array_Subtype>: Use
	int_const_binop to shift bounds by 1 when they are integer constants.

From-SVN: r198663

gcc/ada/ChangeLog

+2013-05-07  Eric Botcazou  <ebotcazou@adacore.com>
+
+	PR ada/56474
+	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Array_Subtype>: Use
+	int_const_binop to shift bounds by 1 when they are integer constants.
+
 2013-04-25  Arnaud Charlet  <charlet@adacore.com>
 
 	* gcc-interface/Makefile.in (ADA_EXCLUDE_SRCS): Exclude s-init.ad{s,b}

gcc/ada/gcc-interface/decl.c

@@ -2447,7 +2447,7 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, int definition)
 							gnu_orig_max,
 							gnu_orig_min),
 				       gnu_min,
-				       size_binop (PLUS_EXPR, gnu_max,
+				       int_const_binop (PLUS_EXPR, gnu_max,
 							size_one_node));
 		}
 
@@ -2455,7 +2455,9 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, int definition)
 		 in all the other cases.  Note that, here as well as above,
 		 the condition used in the comparison must be equivalent to
 		 the condition (length != 0).  This is relied upon in order
-		 to optimize array comparisons in compare_arrays.  */
+		 to optimize array comparisons in compare_arrays.  Moreover
+		 we use int_const_binop for the shift by 1 if the bound is
+		 constant to avoid any unwanted overflow.  */
 	      else
 		gnu_high
 		  = build_cond_expr (sizetype,
@@ -2464,7 +2466,10 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, int definition)
 						      gnu_orig_max,
 						      gnu_orig_min),
 				     gnu_max,
-				     size_binop (MINUS_EXPR, gnu_min,
+				     TREE_CODE (gnu_min) == INTEGER_CST
+				     ? int_const_binop (MINUS_EXPR, gnu_min,
+							size_one_node)
+				     : size_binop (MINUS_EXPR, gnu_min,
 						   size_one_node));
 
 	      /* Reuse the index type for the range type.  Then make an index

gcc/testsuite/ChangeLog

+2013-05-07  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* gnat.dg/specs/array3.ads: New test.
+
 2013-05-06  Marc Glisse  <marc.glisse@inria.fr>
 
 	* c-c++-common/vector-scalar-2.c: New testcase.

gcc/testsuite/gnat.dg/specs/array3.ads

+-- PR middle-end/56474
+-- Reported by Pavel Zhukov <pavel@zhukoff.net>
+
+-- { dg-do compile }
+
+with Ada.Streams;
+
+package Array3 is
+
+   use type Ada.Streams.Stream_Element_Offset;
+
+   type Vector (Size : Ada.Streams.Stream_Element_Offset) is record
+      Value : Ada.Streams.Stream_Element_Array (0 .. Size);
+   end record;
+
+   Empty_Vector : Vector (-1);
+
+end Array3;