I've written a patch to fix the transparent_union attribute when the first
field in a union is MODE_PARTIAL_INT, but I noticed that the current code
only allows the TYPE_MODE of a UNION_TYPE to be of MODE_INT class.
See stor-layout.c (compute_record_mode), particularly this section:
/* 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
&& tree_fits_uhwi_p (TYPE_SIZE (type))
&& known_eq (GET_MODE_BITSIZE (mode), tree_to_uhwi (TYPE_SIZE
(type))))
;
else
mode = mode_for_size_tree (TYPE_SIZE (type), MODE_INT, 1).else_blk ();
Is there a reason the type of the union must be of MODE_INT class but a
RECORD_TYPE with one field can have the class of it's single field?
If the else clause is changed to the following, then transparent_union unions
with a first field of double (e.g. gcc/testsuite/g++.dg/ext/transparent-union.C)
no longer error.
mode = mode_for_size_tree (TYPE_SIZE (type),
(GET_MODE_CLASS (mode) != MODE_RANDOM
? GET_MODE_CLASS (mode) : MODE_INT),
1).else_blk ();
Could anyone provide some insight on whether the TYPE_MODE of a union should
stay as a MODE_INT class or if it would be acceptable for the TYPE_MODE to be
other classes e.g. MODE_FLOAT?
