https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92948
--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> --- Because of the alias template build_converted_constant_expr produces a TARGET_EXPR containing a TEMPLATE_PARM_INDEX which makes it value-dependent. So we don't call get_template_parm_object here 7449 /* Replace the argument with a reference to the corresponding template 7450 parameter object. */ 7451 if (!value_dependent_expression_p (expr)) 7452 expr = get_template_parm_object (expr, complain); we crash in pt.c: 16396 /* Wrapper to make a C++20 template parameter object const. */ 16397 op = tsubst_copy (op, args, complain, in_decl); ... 16405 gcc_assert (CP_TYPE_CONST_P (TREE_TYPE (op))); because tsubst_copy didn't turn op into one of those _ZT... VAR_DECLs. Poking more.
