>
> Adding back the mode check is fine if all types with the same TYPE_CANONICAL
> have the same mode. Otherwise we'd regress here. I thought we do for
>
> Struct x { int i; };
> Typedef y x __attribute__((packed));
>
> And then doing
>
> X x;
> Y y;
> X = y;
Do you have any idea how to turn this into a testcase? I don't think we could
add packed attribute to typedef. Even in
gimple_canonical_types_compatible_p
/* Can't be the same type if they have different mode. */
if (TYPE_MODE (t1) != TYPE_MODE (t2))
return false;
(which IMO may be wrong WRT -mavx flags where modes of same types may be
different
in different TUs)
Therefore I would say that TYPE_CANONICAL determine mode modulo the fact that
incoplete variant of a complete type will have VOIDmode instead of complete
type's mode (during non-LTO). That is why I allow mode changes for casts from
complete to incomplete.
In longer run I think that every query to useless_type_conversion_p that
contains incomplete types is a confused query. useless_type_conversion_p is
about operations on the value and there are no operations for incomplete type
(and function types). I know that ipa-icf-gimple and the following code in
gimplify-stmt checks this frequently:
/* The FEs may end up building ADDR_EXPRs early on a decl with
an incomplete type. Re-build ADDR_EXPRs in canonical form
here. */
if (!types_compatible_p (TREE_TYPE (op0), TREE_TYPE (TREE_TYPE (expr))))
*expr_p = build_fold_addr_expr (op0);
Taking address of incomplete type or functions, naturally, makes sense. We may
want to check something else here, like simply
TREE_TYPE (op0) != TREE_TYPE (TREE_TYPE (expr))
and once ipa-icf is cleanded up start sanity checking in usless_type_conversion
that we use it to force equality only on types that do have values.
We also can trip it when checking TYPE_METHOD_BASETYPE which may be incomplete.
This is in the code checking useless_type_conversion on functions that I think
are confused querries anyway - we need the ABI matcher, I am looking into that.
Honza
>
> Richard.
>
>
> >Honza
> >>
> >> --
> >> Eric Botcazou
>
