[Bug d/106977] [13 regression] d21 dies with SIGBUS on 32-bit Darwin

["ibuclaw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106977

--- Comment #26 from ibuclaw at gcc dot gnu.org ---
Comparing the D and C++ trees side by side.

At the point of `finish_function` for the ::vis() method, I see the following:

D:   type <record_type 0x7ffff6f91888 Visibility cxx-odr-p BLK
C++: type <record_type 0x7ffff700aa80 Visibility cxx-odr-p type_5 DI

When does TYPE_MODE get set, and why is it that value?

Setting watchers in both language compilers...

- C++/D: make_node() sets the memory to E_VOIDmode
- C++/D: entrypoint to compute_record_type() sets BLKmode
- D:     returns early because all fields still have DECL_SIZE = null
- C++:   exit to compute_record_type() sets E_DImode 

In D, this is finish_aggregate_type() which calls compute_record_mode() before
calling layout_decl() on all fields.  This was not the 

Looking at history between 2022/06/10 .. 2022/06/24, I think we have a clear
commit that introduced this wrong code/behaviour - r13-1104.

The loop added in r13-1104 that sets DECL_SIZE on all fields was added after
the call to compute_record_mode.

Looks like this is the mistake, it should have been put before
compute_record_mode.

So then, I think we finally have a fix:

--- a/gcc/d/types.cc
+++ b/gcc/d/types.cc
@@ -615,9 +615,6 @@ finish_aggregate_type (unsigned structsize, unsigned
alignsize, tree type)
   SET_TYPE_ALIGN (type, alignsize * BITS_PER_UNIT);
   TYPE_PACKED (type) = (alignsize == 1);

-  /* Set the back-end type mode.  */
-  compute_record_mode (type);
-
   /* Layout all fields now the type is complete.  */
   for (tree field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
     {
@@ -662,6 +659,9 @@ finish_aggregate_type (unsigned structsize, unsigned
alignsize, tree type)
        }
     }

+  /* Set the back-end type mode after all fields have had their size set.  */
+  compute_record_mode (type);
+
   /* Fix up all forward-referenced variants of this aggregate type.  */
   for (tree t = TYPE_MAIN_VARIANT (type); t; t = TYPE_NEXT_VARIANT (t))
     {