[Bug ipa/62051] [4.9/5/6 Regression] Undefined reference to vtable with -O2 and -fdevirtualize-speculatively

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62051

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> ---
Created attachment 36480
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36480&action=edit
visibility flag patch

Is this the sort of thing you had in mind?