[Ada] Possibly bit aligned objects in assignments

[Ada] Possibly bit aligned objects in assignments

[Arnaud Charlet]

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If either the target or the expression in an array or record ssignment may be
bit-aligned, the assignment must be expanded into component assignments. The
object (or subcomponent) may be given by an unchecked conversion, in which case
we must examine its expression to determine potential mis-alignment.

The following must execute quietly:
   
    gnatmake -gnata -q test_conversion
    test_conversion

---
with Packing; use Packing;
with Interfaces; use Interfaces;

procedure Test_Conversion is
   Orig     : Table        := (1, (others => (others => (others => 4))));
   Dest     : Packed_Table;
   
begin
   Convert (Orig, Dest);
   
   pragma Assert (Dest.Data (1) (1, 1) = 4);
end Test_Conversion;
---
with Interfaces; use Interfaces;

package Packing is 
   subtype Index is Integer range 0 .. 32;
   
   type Element is array (1 .. 2, 1 .. 2) of Integer_32;
   
   type Container is array (1 .. 3) of Element;
   pragma Pack (Container);
   
   type Table is
      record
	 Padding : Index;
	 Data    : Container;
      end record;
   
   type Packed_Table is new Table;
   
   for Packed_Table use
      record
	 Padding at 0 range 0 ..           5;
	 Data    at 0 range 6 .. 12 * 32 + 5;
      end record;
   
   procedure Convert (Value_In : Table; Value_Out : out Packed_Table);
end Packing;
---
package body Packing is
   procedure Convert (Value_In : Table; Value_Out : out Packed_Table) is
   begin
      Value_Out := Packed_Table (Value_In);
   end Convert;
end Packing;

Tested on x86_64-pc-linux-gnu, committed on trunk

2011-09-02  Ed Schonberg  <schonberg@adacore.com>

	* exp_util.adb: (Possible_Bit_Aligned_Object): If the object
	is an unchecked conversion, apply test to its expression.


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Index: exp_util.adb
===================================================================
--- exp_util.adb	(revision 178438)
+++ exp_util.adb	(working copy)
@@ -5687,6 +5687,12 @@
          when N_Slice =>
             return Possible_Bit_Aligned_Component (Prefix (N));
 
+         --  For an unchecked conversion, check whether the expression may
+         --  be bit-aligned.
+
+         when N_Unchecked_Type_Conversion =>
+            return Possible_Bit_Aligned_Component (Expression (N));
+
          --  If we have none of the above, it means that we have fallen off the
          --  top testing prefixes recursively, and we now have a stand alone
          --  object, where we don't have a problem.