On Tue, 7 Jul 2020, Jason Merrill wrote:
> On 7/7/20 9:33 AM, Patrick Palka wrote:
> > We are ICEing in the testcase below because we pass the
> > yet-uninstantiated class type A<int> of the PARM_DECL b to
> > is_really_empty_class from potential_rvalue_constant_expression when
> > parsing the requirement t += b.
>
> Why are we getting to potential_rvalue_constant_expression? My guess is from
> build_non_dependent_expr because processing_constraint isn't set?
My mistake, I meant to write that we are calling is_really_empty_class
from is_rvalue_constant_expression, not from
potential_rvalue_constant_expression. And we're getting to
is_rvalue_constant_expression from cp_parser_constant_expression when
parsing the RHS of the assignment.
>
> > This patch fixes the ICE by guarding the problematic call to
> > is_really_empty_class with a COMPLETE_TYPE_P check, which should also
> > subsume the existing dependent_type_p check.
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK to
> > commit to trunk and to the 10 branch?
> >
> > gcc/cp/ChangeLog:
> >
> > PR c++/95497
> > * constexpr.c (potential_constant_expression_1): When
> > processing_template_decl, check COMPLETE_TYPE_P before calling
> > is_really_empty_class.
> >
> > gcc/testsuite/ChangeLog:
> >
> > PR c++/95497
> > * g++.dg/cpp2a/concepts-pr95497.C: New test.
> > ---
> > gcc/cp/constexpr.c | 2 +-
> > gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C | 12 ++++++++++++
> > 2 files changed, 13 insertions(+), 1 deletion(-)
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C
> >
> > diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
> > index 1939166e907..ff78ebda2dc 100644
> > --- a/gcc/cp/constexpr.c
> > +++ b/gcc/cp/constexpr.c
> > @@ -7443,7 +7443,7 @@ potential_constant_expression_1 (tree t, bool
> > want_rval, bool strict, bool now,
> > if (now && want_rval)
> > {
> > tree type = TREE_TYPE (t);
> > - if (dependent_type_p (type)
> > + if ((processing_template_decl && !COMPLETE_TYPE_P (type))
> > || is_really_empty_class (type, /*ignore_vptr*/false))
> > /* An empty class has no data to read. */
> > return true;
> > diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C
> > b/gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C
> > new file mode 100644
> > index 00000000000..4d7718ad5e8
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C
> > @@ -0,0 +1,12 @@
> > +// PR c++/95497
> > +// { dg-do compile { target c++20 } }
> > +
> > +template <typename T>
> > +struct A{};
> > +
> > +template <typename T>
> > +concept c =
> > + requires(T t, A<int> b) // note that A<int> is independent of T
> > + {
> > + { t += b };
> > + };
> >
>
>
