https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89410
--- Comment #11 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Jonny Grant from comment #9)
> Maybe zero could be disallowed too.
Yes, but maybe we need that for historical reasons.
> Not sure what is best here, I'm not knowledgeable of GCC, but maybe setting
> it to -1 if it goes above, and then never increment again if(-1 == line) ...
The testcase will still ICE then... The assert is
/* The spans must be ordered. */
gcc_assert (prev->m_first_line < next->m_first_line);
