[Ada] Fix wrong code with biased subtype

[Eric Botcazou]

This is a regression present on all active branches for a subtype of a biased 
type declared with explicit constraints, which is itself biased.  The compiler 
generates code that computes a wrong value for the conversion to an integer.

Tested on x86_64-suse-linux, applied on all active branches.


2016-10-10  Eric Botcazou  <ebotca...@adacore.com>

        * gcc-interface/utils.c (convert): For a biased input type, convert
        the bias itself to the base type before adding it.


2016-10-10  Eric Botcazou  <ebotca...@adacore.com>

        * gnat.dg/biased_subtype.adb: New test.

-- 
Eric Botcazou
Index: gcc-interface/utils.c
===================================================================
--- gcc-interface/utils.c	(revision 240890)
+++ gcc-interface/utils.c	(working copy)
@@ -4193,12 +4193,15 @@ convert (tree type, tree expr)
       return convert (type, unpadded);
     }
 
-  /* If the input is a biased type, adjust first.  */
+  /* If the input is a biased type, convert first to the base type and add
+     the bias.  Note that the bias must go through a full conversion to the
+     base type, lest it is itself a biased value; this happens for subtypes
+     of biased types.  */
   if (ecode == INTEGER_TYPE && TYPE_BIASED_REPRESENTATION_P (etype))
     return convert (type, fold_build2 (PLUS_EXPR, TREE_TYPE (etype),
 				       fold_convert (TREE_TYPE (etype), expr),
-				       fold_convert (TREE_TYPE (etype),
-						     TYPE_MIN_VALUE (etype))));
+				       convert (TREE_TYPE (etype),
+						TYPE_MIN_VALUE (etype))));
 
   /* If the input is a justified modular type, we need to extract the actual
      object before converting it to any other type with the exceptions of an
@@ -4502,7 +4505,12 @@ convert (tree type, tree expr)
 	  && (ecode == ARRAY_TYPE || ecode == UNCONSTRAINED_ARRAY_TYPE
 	      || (ecode == RECORD_TYPE && TYPE_CONTAINS_TEMPLATE_P (etype))))
 	return unchecked_convert (type, expr, false);
-      else if (TYPE_BIASED_REPRESENTATION_P (type))
+
+      /* If the output is a biased type, convert first to the base type and
+	 subtract the bias.  Note that the bias itself must go through a full
+	 conversion to the base type, lest it is a biased value; this happens
+	 for subtypes of biased types.  */
+      if (TYPE_BIASED_REPRESENTATION_P (type))
 	return fold_convert (type,
 			     fold_build2 (MINUS_EXPR, TREE_TYPE (type),
 					  convert (TREE_TYPE (type), expr),

-- { dg-do run }
-- { dg-options "-gnatws" }

procedure Biased_Subtype is

   CIM_Max_AA : constant := 9_999_999;
   CIM_Min_AA : constant := -999_999;

   type TIM_AA is range CIM_Min_AA..CIM_Max_AA + 1;
   for TIM_AA'Size use 24;

   subtype STIM_AA is TIM_AA range TIM_AA(CIM_Min_AA)..TIM_AA(CIM_Max_AA);

   SAA : STIM_AA := 1;

begin
   if Integer(SAA) /= 1 then
     raise Program_Error;
   end if;
end;