[Bug fortran/79165] [7 Regression] 100% compile-time increase for polyhedron aermod by r244581

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79165

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ok, so the reason for the slowness is that the Fortran frontend emits full
diagnostics to a temporary buffer for gfc_match_rvalue:

    /* Match a function reference.  */
    function0:
      m = gfc_match_actual_arglist (0, &actual_arglist);
      if (m == MATCH_NO)
        {
          if (sym->attr.proc == PROC_ST_FUNCTION)
            gfc_error ("Statement function %qs requires argument list at %C",
                       sym->name);
          else
            gfc_error ("Function %qs requires an argument list at %C",
                       sym->name);

          m = MATCH_ERROR;
          break;
        }

for aermod that's 18748 times.  And what slows down with the linemap mangling
is showing of the caret location (location_get_source_line/get_next_line
and thus the fcache I suppose).

Tentatively remembering an error like above is of course quite broken (read:
expensive).

So somehow with the tree.c hunk of the patch location_get_source_line
(inclusive callees) gets 90 times more expensive (when using callgrind on
aermod).