[patch c/c++]: Fix for PR c/52991 issue about ignored packed-attribute for ms-structure-layout

[Kai Tietz]

Hello,

This fixes an old regression about ms-structure-layout in combination
with packed-attribute.

ChangeLog

2012-12-11  Kai Tietz

        PR c/52991
        * stor-layout.c (start_record_layout): Handle
        packed-attribute for ms-structure-layout.
        (update_alignment_for_field): Likewise.
        (place_field): Likewise.


Tested for i686-w64-mingw32, x86_64-w64-mingw32, and for
x86_64-unknown-linux-gnu.  Ok for apply?

Regards,
Kai

Index: stor-layout.c
===================================================================
--- stor-layout.c       (Revision 194386)
+++ stor-layout.c       (Arbeitskopie)
@@ -756,7 +756,10 @@ start_record_layout (tree t)
   /* If the type has a minimum specified alignment (via an attribute
      declaration, for example) use it -- otherwise, start with a
      one-byte alignment.  */
-  rli->record_align = MAX (BITS_PER_UNIT, TYPE_ALIGN (t));
+  if (TYPE_PACKED (t))
+    rli->record_align = BITS_PER_UNIT;
+  else
+    rli->record_align = MAX (BITS_PER_UNIT, TYPE_ALIGN (t));
   rli->unpacked_align = rli->record_align;
   rli->offset_align = MAX (rli->record_align, BIGGEST_ALIGNMENT);

@@ -952,15 +955,20 @@ update_alignment_for_field (record_layout_info rli
      meaningless.  */
   if (targetm.ms_bitfield_layout_p (rli->t))
     {
+      if (rli->t && TYPE_PACKED (rli->t)
+          && (is_bitfield || !DECL_PACKED (field)
+              || DECL_SIZE (field) == NULL_TREE
+              || !integer_zerop (DECL_SIZE (field))))
+        desired_align = BITS_PER_UNIT;
       /* Here, the alignment of the underlying type of a bitfield can
         affect the alignment of a record; even a zero-sized field
         can do this.  The alignment should be to the alignment of
         the type, except that for zero-size bitfields this only
         applies if there was an immediately prior, nonzero-size
         bitfield.  (That's the way it is, experimentally.) */
-      if ((!is_bitfield && !DECL_PACKED (field))
-         || ((DECL_SIZE (field) == NULL_TREE
-              || !integer_zerop (DECL_SIZE (field)))
+      else if ((!is_bitfield && !DECL_PACKED (field))
+              || ((DECL_SIZE (field) == NULL_TREE
+                  || !integer_zerop (DECL_SIZE (field)))
              ? !DECL_PACKED (field)
              : (rli->prev_field
                 && DECL_BIT_FIELD_TYPE (rli->prev_field)
@@ -1414,7 +1422,13 @@ place_field (record_layout_info rli, tree field)
            }

          /* Now align (conventionally) for the new type.  */
-         type_align = TYPE_ALIGN (TREE_TYPE (field));
+         if (!TYPE_PACKED (rli->t))
+           {
+             type_align = TYPE_ALIGN (TREE_TYPE (field));
+             if (DECL_PACKED (field))
+               type_align = MIN (type_align, BITS_PER_UNIT);
+       
+           }

          if (maximum_field_alignment != 0)
            type_align = MIN (type_align, maximum_field_alignment);