On Tue, 6 Oct 2020, Jason Merrill wrote:
> On 10/5/20 4:30 PM, Patrick Palka wrote:
> > On Wed, 30 Sep 2020, Jason Merrill wrote:
> >
> > > On 9/29/20 5:01 PM, Patrick Palka wrote:
> > > > This patch fixes an "unguarded" call to coerce_template_parms in
> > > > build_standard_check: processing_template_decl could be zero if we
> > > > we get here during processing of the first 'auto' parameter of an
> > > > abbreviated function template. In the testcase below, this leads to an
> > > > ICE when coerce_template_parms substitutes into C's dependent default
> > > > template argument.
> > > >
> > > > Bootstrapped and regtested on x86_64-pc-linux-gnu and tested by building
> > > > cmcstl2 and range-v3. Does this look OK for trunk?
> > >
> > > This looks OK, but is there a place higher in the call stack where we
> > > should
> > > have already set processing_template_decl?
> >
> > The call stack at that point is:
> >
> > build_variable_check
> > build_concept_check
> > build_type_constraint
> > finish_type_constraints
> > cp_parser_placeholder_type_specifier
> > cp_parser_simple_type_specifier
> > ...
> >
> > So it seems the most natural place to set processing_template_decl would
> > be in build_type_constraint, around the call to build_concept_check,
> > since that's where we create the WILDCARD_DECL that eventually reaches
> > coerce_template_parms.
> >
> > And in order to additionally avoid a similar ICE when processing the
> > type constraint of a non-templated variable, we also need to guard the
> > call to build_concept check in make_constrained_placeholder_type. The
> > testcase below now contains such an example.
>
> Setting the flag in cp_parser_placeholder_type_specifier would cover both of
> those, right?
That doesn't quite work unfortunately, because if we set
processing_template_decl to non-zero around the call to
make_constrained_auto within cp_parser_placeholder_type_specifier, then
that will skew the level of the 'auto' parm built by make_auto_1,
causing the auto deduction of the non-templated variable to later fail
it seems.
>
> > So something like this perhaps:
> >
> > -- >8 --
> >
> > Subject: [PATCH] c++: ICE in dependent_type_p with constrained auto
> > [PR97052]
> >
> > This patch fixes an "unguarded" call to coerce_template_parms in
> > build_standard_check: processing_template_decl could be zero if we
> > get here during processing of the first 'auto' parameter of an
> > abbreviated function template, or if we're processing the type
> > constraint of a non-templated variable. In the testcase below, this
> > leads to an ICE when coerce_template_parms instantiates C's dependent
> > default template argument.
> >
> > gcc/cp/ChangeLog:
> >
> > PR c++/97052
> > * constraint.cc (build_type_constraint): Temporarily increment
> > processing_template_decl before calling build_concept_check.
> > * pt.c (make_constrained_placeholder_type): Likewise.
> >
> > gcc/testsuite/ChangeLog:
> >
> > PR c++/97052
> > * g++.dg/cpp2a/concepts-defarg2: New test.
> > ---
> > gcc/cp/constraint.cc | 2 ++
> > gcc/cp/pt.c | 2 ++
> > gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C | 13 +++++++++++++
> > 3 files changed, 17 insertions(+)
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C
> >
> > diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> > index d49957a6c4a..050b55ce092 100644
> > --- a/gcc/cp/constraint.cc
> > +++ b/gcc/cp/constraint.cc
> > @@ -1427,7 +1427,9 @@ tree
> > build_type_constraint (tree decl, tree args, tsubst_flags_t complain)
> > {
> > tree wildcard = build_nt (WILDCARD_DECL);
> > + ++processing_template_decl;
> > tree check = build_concept_check (decl, wildcard, args, complain);
> > + --processing_template_decl;
> > if (check == error_mark_node)
> > return error_mark_node;
> > return unpack_concept_check (check);
> > diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> > index 72efecff37f..efdd017a4d5 100644
> > --- a/gcc/cp/pt.c
> > +++ b/gcc/cp/pt.c
> > @@ -27914,7 +27914,9 @@ make_constrained_placeholder_type (tree type, tree
> > con, tree args)
> > tree expr = tmpl;
> > if (TREE_CODE (con) == FUNCTION_DECL)
> > expr = ovl_make (tmpl);
> > + ++processing_template_decl;
> > expr = build_concept_check (expr, type, args, tf_warning_or_error);
> > + --processing_template_decl;
> > PLACEHOLDER_TYPE_CONSTRAINTS (type) = expr;
> > diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C
> > b/gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C
> > new file mode 100644
> > index 00000000000..a63ca4e133d
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C
> > @@ -0,0 +1,13 @@
> > +// PR c++/97052
> > +// { dg-do compile { target c++20 } }
> > +
> > +template<typename T, typename U = typename T::type>
> > +concept C = true;
> > +
> > +constexpr bool f(C auto) {
> > + return true;
> > +}
> > +
> > +static_assert(f(0));
> > +
> > +C auto x = 0;
> >
>
>
