Hi Matthew,
please have a look at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98426 but
ignore any patches I have attached there, because they are just wrong. It
definitely sound like you hit the same problem. As described there, if you have
a lot of symbols within the mod files pulled in by the use statements, then an
O(N^2) search increases compilation time considerably.
Best regards Martin
Gesendet: Mittwoch, 12. Mai 2021 um 15:52 Uhr
Von: "Thompson, Matt (GSFC-610.1)[SCIENCE SYSTEMS AND APPLICATIONS INC] via
Fortran"
An: "fortran@gcc.gnu.org"
Betreff: Help with long compile time of all-USE module
All,
I'm hoping to rely on the wisdom of the gfortran gurus for some help on this.
I've been looking at trying to speed up the compilation of a library I help
maintain because, well, always a worthy goal, especially with CI and Git. I did
some profiling and found that the most expensive file to compile in our library
(doing a debug build with GCC 10.3) is a "meta-module" that only has 'use foo'
statements:
https://github.com/GEOS-ESM/MAPL/blob/main/base/MAPL_Mod.F90
It allows us to "gather" many use-statements so users don't need to "use" 50
different modules.
This really surprised me as there are other files in this library that are
infinitely more complex and I can think of ways we could maybe refactor or
break them up, but this file is...boring. I guess I could split it up, but
almost doesn't seem worth the effort.
Now, it is the slowest compile when building with Debugging flags which are,
for this model:
FLAGS = -O0 -g -fcheck=all,no-array-temps -finit-real=snan
-ffree-line-length-none -fno-range-check -Wno-missing-include-dirs -fbacktrace
-ffpe-trap=zero,overflow -fbacktrace -fallow-argument-mismatch
-fallow-invalid-boz -falign-commons -Jinclude/MAPL.base -fPIC
-ffixed-line-length-132 -pthread -fopenmp
My naïve thought when I first saw this was the tall pole was "well, I'll
degrade the optimization" but, well, already at -O0. So perhaps one of these
other flags is triggering some sort of weirdness with an "only USE" file?
I might try a binary exclusion experiment to figure it out (remove half the
flags, etc.), but maybe it's obvious to the experts.
Thanks,
Matt
--
Matt Thompson, SSAI, Ld Scientific Programmer/Analyst
NASA GSFC, Global Modeling and Assimilation Office
Code 610.1, 8800 Greenbelt Rd, Greenbelt, MD 20771
Phone: 301-614-6712 Fax: 301-614-6246
http://science.gsfc.nasa.gov/sed/bio/matthew.thompson[http://science.gsfc.nasa.gov/sed/bio/matthew.thompson]
