exp_attr.adb (Expand_N_Attribute_Reference): Rewrite the processing for Descriptor_Size.

2011-09-06  Hristian Kirtchev  <kirtchev@adacore.com>

	* exp_attr.adb (Expand_N_Attribute_Reference): Rewrite the
	processing for Descriptor_Size.
	* gnat_rm.texi: Rephrase the wording for attribute Descriptor_Size
	to account for its broader usage.
	* sem_attr.adb (Analyze_Attribute): Change the error detection
	circuitry for Descriptor_Size as the attribute is now applicable
	to all types.

From-SVN: r178590

gcc/ada/ChangeLog

@@ -1,3 +1,13 @@
+2011-09-06  Hristian Kirtchev  <kirtchev@adacore.com>
+
+	* exp_attr.adb (Expand_N_Attribute_Reference): Rewrite the
+	processing for Descriptor_Size.
+	* gnat_rm.texi: Rephrase the wording for attribute Descriptor_Size
+	to account for its broader usage.
+	* sem_attr.adb (Analyze_Attribute): Change the error detection
+	circuitry for Descriptor_Size as the attribute is now applicable
+	to all types.
+
 2011-09-06  Robert Dewar  <dewar@adacore.com>
 
 	* sem_attr.adb, prj-nmsc.adb, exp_aggr.adb: Minor reformatting.

gcc/ada/exp_attr.adb

@@ -1803,10 +1803,23 @@ package body Exp_Attr is
       -- Descriptor_Size --
       ---------------------
 
-      --  This attribute is handled entirely by the back end
-
       when Attribute_Descriptor_Size =>
-         Apply_Universal_Integer_Attribute_Checks (N);
+
+         --  Attribute Descriptor_Size is handled by the back end when applied
+         --  to an unconstrained array type.
+
+         if Is_Array_Type (Ptyp)
+           and then not Is_Constrained (Ptyp)
+         then
+            Apply_Universal_Integer_Attribute_Checks (N);
+
+         --  For any other type, the descriptor size is 0 because there is no
+         --  actual descriptor.
+
+         else
+            Rewrite (N, Make_Integer_Literal (Loc, 0));
+            Analyze (N);
+         end if;
 
       ---------------
       -- Elab_Body --

gcc/ada/gnat_rm.texi

@@ -5941,9 +5941,10 @@ as a @code{Pos} value (0 for @code{High_Order_First}, 1 for
 @findex Descriptor_Size
 @noindent
 Attribute @code{Descriptor_Size} returns the size in bits of the descriptor
-allocated for an unconstrained array type. An array descriptor contains bounds
-information and is located immediately before the first element of the array.
-The value of attribute @code{Descriptor_Size} is of type universal integer.
+allocated for a type.  The result is non-zero only for unconstrained array
+types and the returned value is of type universal integer.  In GNAT, an array
+descriptor contains bounds information and is located immediately before the
+first element of the array.
 
 @smallexample @c ada
 type Unconstr_Array is array (Positive range <>) of Boolean;
@@ -5953,7 +5954,7 @@ Put_Line ("Descriptor size = " & Unconstr_Array'Descriptor_Size'Img);
 @noindent
 The attribute takes into account any additional padding due to type alignment.
 In the example above, the descriptor contains two values of type
-@code{Positive} representing the low and high bound. Since @code{Positive} has
+@code{Positive} representing the low and high bound.  Since @code{Positive} has
 a size of 31 bits and an alignment of 4, the descriptor size is @code{2 *
 Positive'Size + 2} or 64 bits.
 

gcc/ada/sem_attr.adb

@@ -1906,7 +1906,7 @@ package body Sem_Attr is
          end if;
       end Validate_Non_Static_Attribute_Function_Call;
 
-   --   Start of processing for Analyze_Attribute
+   --  Start of processing for Analyze_Attribute
 
    begin
       --  Immediate return if unrecognized attribute (already diagnosed
@@ -3021,19 +3021,10 @@ package body Sem_Attr is
       when Attribute_Descriptor_Size =>
          Check_E0;
 
-         --  Attribute Descriptor_Size is relevant only in the context of an
-         --  unconstrained array type.
-
-         --  Shouldn't it just return zero for types other than arrays or
-         --  constrained arrays ???
-
-         if Is_Entity_Name (P)
-           and then Is_Array_Type (Entity (P))
-           and then not Is_Constrained (Entity (P))
+         if not Is_Entity_Name (P)
+           or else not Is_Type (Entity (P))
          then
-            null;
-         else
-            Error_Attr_P ("invalid prefix for % attribute");
+            Error_Attr_P ("prefix of attribute % must denote a type");
          end if;
 
          Set_Etype (N, Universal_Integer);