http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54315
Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2012-09-14
CC| |ebotcazou at gcc dot
| |gnu.org
Ever Confirmed|0 |1
--- Comment #3 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-09-14
14:54:53 UTC ---
The big discrepancy between structures and unions comes from:
/* Compute the TYPE_MODE for the TYPE (which is a RECORD_TYPE). */
void
compute_record_mode (tree type)
{
[...]
/* If we only have one real field; use its mode if that mode's size
matches the type's size. This only applies to RECORD_TYPE. This
does not apply to unions. */
if (TREE_CODE (type) == RECORD_TYPE && mode != VOIDmode
&& host_integerp (TYPE_SIZE (type), 1)
&& GET_MODE_BITSIZE (mode) == TREE_INT_CST_LOW (TYPE_SIZE (type)))
SET_TYPE_MODE (type, mode);
else
SET_TYPE_MODE (type, mode_for_size_tree (TYPE_SIZE (type), MODE_INT, 1));
so the structure is given XFmode but the union is given BKLmode.
Apparently someone has attempted to bridge the gap but this was reverted by:
------------------------------------------------------------------------
r37041 | wilson | 2000-10-25 03:30:25 +0200 (Wed, 25 Oct 2000) | 6 lines
Fixes for C++ structure layout breakage.
* expmed.c (store_bit_field): Move integer pun code down after
code that calls emit_move_insn for entire register move.
* stor-layout.c (compute_record_mode): Revert Mar 25, Aug 18, and
Oct 20 changes. Only store mode in TYPE_MODE if RECORD_TYPE.
