[Bug c++/84642] [6/7/8 Regression] ICE: segfault reading through NULL current_template_parms in synthesize_implicit_template_parm

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84642

--- Comment #2 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
(In reply to Vegard Nossum from comment #0)
> Seems potentially related to bug #84610?

Similar backtraces - and they both started with same commit - though this one
is a read-through-NULL, whereas bug #84610 is an assertion failure.