https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82569
--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Eric Botcazou from comment #7)
> It's a conflict with the out-of-ssa pass: this pass implicitly expects every
> pseudo associated with a partition to be always fully initialized, including
> a DImode pseudo for a partition attached to a SImode variable. And this is
> guaranteed for promoted SUBREGs because expand_gimple_stmt_1 makes sure
> that, if one of the them is on the LHS of an assignment, then the whole
> SUBREG_REG is assigned (with the appropriate extension). But this falls for
> other SUBREGs.
>
> So an immediate fix would be to generate the glue code between partitions
> with undefined values and other partitions in insert_partition_copy_on_edge,
> but I'm starting to wonder whether the entire approach shouldn't be scrapped
> instead.
Sounds indeed like a hack ontop of a hack :/
But I don't fully understand the new issue - what are "other SUBREGs"? The
SUBREG_PROMOTED_VAR setting is set per subreg so we should be able to handle
those okish?
Like change
temp = gen_lowpart_SUBREG (mode, decl_rtl);
/* We cannot assume anything about an existing extension if the
register may contain uninitialized bits. */
if (always_initialized_rtx)
{
SUBREG_PROMOTED_VAR_P (temp) = 1;
SUBREG_PROMOTED_SET (temp, unsignedp);
}
to
if (always_initialized_rtx
&& mode == TYPE_MODE (TREE_TYPE (exp)))
? Not sure if this captures the issue as said.
