On Wed, 19 Jul 2023, Jason Merrill wrote:
> On 7/19/23 14:05, Patrick Palka wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > trunk/13?
> >
> > -- >8 --
> >
> > Since the arguments 'pargs' passed to the coerce_template_parms from
> > coerce_template_template_parms are always a full set, we need to make sure
> > we always pass the parameters of the most general template because if the
> > template is partially instantiated then the levels won't match up.
>
> Hmm, so then my comment "In that case we might end up adding more levels than
> needed, but that shouldn't be a problem; any args we need to refer to are at
> the right level." is wrong for auto template parms?
I suppose, but only for the ttp case I think? It seems all is well when
passing an ordinary template as a ttp as long as we use the parameters of the
most general template for the coercion. I can't come up with a counterexample
at least.
>
> So I guess we likely need to do more to assure that pargs has the right number
> of levels if there are autos in the innermost arg parms.
>
> Also, most_general_template doesn't work for TTPs, so that probably won't help
> handle their partial instantiations.
Ah, yeah :( Here's an analagous testcase that we still ICE on due to this:
template<template<int N, int M> class>
struct A;
template<class U>
struct B {
template<class T>
struct C {
template<template<auto X, auto Y> class TT>
using type = A<TT>;
};
};
template struct B<int>::C<int>;
I think I have a fix using get_innermost_template_args.
>
> And is it right for an alias template in a partial specialization?
IIUC yes, e.g. tsubst directly relies on most_general_template to work
for alias templates (when substituting an alias template specialization).
>
> > In the
> > testcase below during said call to coerce_template_parms the parameters
> > are {X, Y} both level 1, but the arguments are {{int}, {N, M}}, which
> > leads to a crash during auto deduction of X and Y.
> >
> > PR c++/110566
>
> Since this is a regression from the patch for PR c++/108179, please list that
> PR here as well, to help avoid backporting that patch without this one.
>
> > gcc/cp/ChangeLog:
> >
> > * pt.cc (coerce_template_template_parms): Simplify by using
> > DECL_INNERMOST_TEMPLATE_PARMS and removing redundant asserts.
> > Always pass the parameters of the most general template to
> > coerce_template_parms.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/template/ttp38.C: New test.
> > ---
> > gcc/cp/pt.cc | 12 +++++-------
> > gcc/testsuite/g++.dg/template/ttp38.C | 12 ++++++++++++
> > 2 files changed, 17 insertions(+), 7 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/template/ttp38.C
> >
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index d882e9dd117..8723868823e 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -8073,12 +8073,10 @@ coerce_template_template_parms (tree parm_tmpl,
> > tree parm, arg;
> > int variadic_p = 0;
> > - tree parm_parms = INNERMOST_TEMPLATE_PARMS (DECL_TEMPLATE_PARMS
> > (parm_tmpl));
> > - tree arg_parms_full = DECL_TEMPLATE_PARMS (arg_tmpl);
> > - tree arg_parms = INNERMOST_TEMPLATE_PARMS (arg_parms_full);
> > -
> > - gcc_assert (TREE_CODE (parm_parms) == TREE_VEC);
> > - gcc_assert (TREE_CODE (arg_parms) == TREE_VEC);
> > + tree parm_parms = DECL_INNERMOST_TEMPLATE_PARMS (parm_tmpl);
> > + tree arg_parms = DECL_INNERMOST_TEMPLATE_PARMS (arg_tmpl);
> > + tree gen_arg_tmpl = most_general_template (arg_tmpl);
> > + tree gen_arg_parms = DECL_INNERMOST_TEMPLATE_PARMS (gen_arg_tmpl);
> > nparms = TREE_VEC_LENGTH (parm_parms);
> > nargs = TREE_VEC_LENGTH (arg_parms);
> > @@ -8134,7 +8132,7 @@ coerce_template_template_parms (tree parm_tmpl,
> > scope_args = TI_ARGS (tinfo);
> > pargs = add_to_template_args (scope_args, pargs);
> > - pargs = coerce_template_parms (arg_parms, pargs, NULL_TREE,
> > tf_none);
> > + pargs = coerce_template_parms (gen_arg_parms, pargs, NULL_TREE,
> > tf_none);
> > if (pargs != error_mark_node)
> > {
> > tree targs = make_tree_vec (nargs);
> > diff --git a/gcc/testsuite/g++.dg/template/ttp38.C
> > b/gcc/testsuite/g++.dg/template/ttp38.C
> > new file mode 100644
> > index 00000000000..7d25d291e81
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/template/ttp38.C
> > @@ -0,0 +1,12 @@
> > +// PR c++/110566
> > +// { dg-do compile { target c++20 } }
> > +
> > +template<template<int N, int M> class>
> > +struct A;
> > +
> > +template<class T>
> > +struct B {
> > + template<int X, int Y> struct C;
> > +};
> > +
> > +using type = A<B<int>::C>;
>
>
