On 01/18/2016 02:12 PM, Patrick Palka wrote:
On Mon, Jan 18, 2016 at 10:34 AM, Jason Merrill <ja...@redhat.com> wrote:
On 12/25/2015 12:37 PM, Patrick Palka wrote:
That alone would not be sufficient because more_specialized_fn()
doesn't call maybe_adjust_types_for_deduction() beforehand, yet we
have to do the decaying there too (and on both types, not just one of
them).
And maybe_adjust_types_for_deduction() seems to operate on the
presumption that one type is the parameter type and one is the
argument type. But in more_specialized_fn() and in get_bindings() we
are really working with two parameter types and have to decay them
both. So sometimes we have to decay one of the types that are
eventually going to get passed to unify(), and other times we want to
decay both types that are going to get passed to unify().
maybe_adjust_types_for_deduction() seems to only expect the former
case.
Finally, maybe_adjust_types_for_deduction() is not called when
unifying a nested function declarator (because it is guarded by the
subr flag in unify_one_argument), so doing it there we would also
regress in the following test case:
Ah, that makes sense.
How about keeping the un-decayed type in the PARM_DECLs, so that we get the
substitution failure in instantiate_template, but having the decayed type in
the TYPE_ARG_TYPES, probably by doing the decay in grokparms, so it's
already decayed when we're doing unification?
I just tried this, and it works well! With this approach, all but one
of the test cases pass. The failing test case is unify17.C:
-- 8< --
void foo (int *);
template <typename T>
void bar (void (T[5])); // { dg-error "array of 'void'" }
void
baz (void)
{
bar<void> (0); // { dg-error "no matching function" }
}
-- 8< --
Here, we don't get a substitution failure because we don't have a
corresponding FUNCTION_DECL for the nested function specifier, only a
FUNCTION_TYPE. So there is no PARM_DECL to recurse into during
substitution, that retains the un-decayed argument type "T[5]" of the
nested function specifier.
Then your original patch is OK. Thanks for indulging me.
Jason
