[Bug c/83448] [7/8 Regression] ice in get_source_location_for_substring, at input.c:1507

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83448

--- Comment #5 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
Created attachment 42907
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42907&action=edit
Work-in-progress patch, with reproducer, and more assertions