[Bug c++/71821] [5/6/7 regression] ICE on invalid C++11 code (incorrect argument for alignas): unexpected expression ‘f<int>’ of kind template_id_expr

[jakub at gcc dot gnu.org]

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?)?