https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71821
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- TEMPLATE_ID_EXPR is considered to be potential_constant_expression_1, so require_potential_rvalue_constant_expression (e) at the start of cxx_alignas_expr. But cxx_eval_constant_expression does not handle it. So, shall potential_constant_expression_1 return false for TEMPLATE_ID_EXPR and similar if !processing_template_decl (or always)? Or shall cxx_eval_constant_expression handle it (how?)?
