[Bug lto/88147] [9 Regression] ICE in linemap_line_start, at libcpp/line-map.c:781 starting from r265875

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88147

--- Comment #15 from Martin Liška <marxin at gcc dot gnu.org> ---
During the bug investigation I noticed a strange thing in line-map.c:

   700    if (line_delta < 0
   701        || (line_delta > 10
   702            && line_delta * map->m_column_and_range_bits > 1000)
   703        || (max_column_hint >= (1U << effective_column_bits))
   704        || (max_column_hint <= 80 && effective_column_bits >= 10)
   705        || (highest > LINE_MAP_MAX_LOCATION_WITH_PACKED_RANGES
   706            && map->m_range_bits > 0)
   707        || (highest > LINE_MAP_MAX_LOCATION_WITH_COLS
   708            && (set->max_column_hint || highest >=
LINE_MAP_MAX_LOCATION)))
   709      add_map = true;

m_column_and_range_bits > 1000 is always false as:

  /* Number of the low-order source_location bits used for column numbers
     and ranges.  */
  unsigned int m_column_and_range_bits : 8;

and the sub-expression on lines 701 and 702 is ugly as well.
What's the purpose of the check?