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

[dmalcolm at gcc dot gnu.org]

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

--- Comment #17 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
I added some instrumentation (covering all files read by input.c) and did some
crude timing:

Release build, with bogus linemap:

nb_read: 1869916
calls to: location_get_source_line: 37494
calls to: read_data: 10
calls to: get_next_line: 577038786
calls to: read_line_num: 37098

real    1m10.032s
user    1m9.293s
sys     0m0.507s


Release build, with bogus linemap, with -fno-diagnostics-show-caret:

nb_read: 0
calls to: location_get_source_line: 0
calls to: read_data: 0
calls to: get_next_line: 0
calls to: read_line_num: 0

real    0m37.035s
user    0m36.355s
sys     0m0.522s

Release build, without bogus linemap:

nb_read: 1869916
calls to: location_get_source_line: 37494
calls to: read_data: 10
calls to: get_next_line: 5773019
calls to: read_line_num: 37098

real    0m39.018s
user    0m38.321s
sys     0m0.532s


Release build, without bogus linemap, with -fno-diagnostics-show-caret:

nb_read: 0
calls to: location_get_source_line: 0
calls to: read_data: 0
calls to: get_next_line: 0
calls to: read_line_num: 0

real    0m38.295s
user    0m37.652s
sys     0m0.498s

Note how with the bogus linemap, without -fno-diagnostics-show-caret, the # of
calls to get_next_line increases from 5.7 * 10^6 to 5.7 * 10^8, a 100x
increase.