Development/GCC
| Description | Content |
|---|---|
| module load | compiler/gnu/xxx |
| License | GPL |
| Citing | n/a |
| Links | GNU-Homepage |
| Graphical Interface | No |
| Included modules | gcc | g++ | gfortran |
Introduction
The GNU Compiler Collection (GCC) consists of tools to compile C, C++ and Fortran programs:
| gcc | GNU C compiler |
| g++ | GNU C++ compiler |
| gfortran | GNU Fortran compiler |
More information about the MPI versions of the GCC Compiler is available here:
Versions and Availability
A list of versions currently available on all bwHPC-C5-Clusters can be obtained from the
Cluster Information System CIS
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There is a version of GCC available on the system without loading a module but it may be outdated and it is recommended to load the GNU compiler module.
On the command line interface of any bwHPC cluster you'll get a list of available versions
by using the command 'module avail compiler/gnu'.
$ : bwUniCluster $ module avail compiler/gnu -------------------- /opt/bwhpc/common/modulefiles --------------------- compiler/gnu/4.5 compiler/gnu/4.8 compiler/gnu/5.2 compiler/gnu/4.7(default) compiler/gnu/4.9
Loading the module
Default Version
Load the version of GCC with the command 'module load compiler/gnu'.
$ module avail compiler/gnu ------------------ /opt/bwhpc/common/modulefiles ------------------- compiler/gnu/4.5 compiler/gnu/4.8 compiler/gnu/5.2 compiler/gnu/4.7(default) compiler/gnu/4.9 $ module load compiler/gnu $ module list Currently Loaded Modulefiles: 1) compiler/gnu/4.7(default)
Here, we got the "default" version 4.7 (example).
The module will try to load modules it needs to function.
If loading the module fails, check if you have already loaded the module
with 'module list'.
Specific (newer or older) Version
If you wish to load a specific (older or newer) version (if available), you can do so using e.g. 'module load compiler/gnu/version' to load the version you desires.
$ module list Currently Loaded Modulefiles: 1) compiler/gnu/4.7(default) $ module clear Are you sure you want to clear all loaded modules!? [n] y $ : New version will be used : $ module load compiler/gnu/5.2 $ module list Currently Loaded Modulefiles: 1) compiler/gnu/5.2
GCC "version 5.2" is loaded now.
GCC-Specific Environments
To see a list of all GCC environments set by the 'module load'-command use
'env | grep GNU'.
Or use the command 'module show compiler/gnu/version'.
Example (Version 5.2)
/opt/bwhpc/common/modulefiles/compiler/gnu/5.2: GNU_VERSION = 5.2.0 GNU_HOME = /opt/bwhpc/common/compiler/gnu/5.2.0 GNU_BIN_DIR = /opt/bwhpc/common/compiler/gnu/5.2.0/bin GNU_MAN_DIR = /opt/bwhpc/common/compiler/gnu/5.2.0/man GNU_LIB_DIR = /opt/bwhpc/common/compiler/gnu/5.2.0/lib64 PATH = $PATH:/opt/bwhpc/common/compiler/gnu/5.2.0/bin MANPATH = $MANPATH:/opt/bwhpc/common/compiler/gnu/5.2.0/man LD_LIBRARY_PATH = $LD_LIBRARY_PATH:/opt/bwhpc/common/compiler/gnu/5.2.0/lib64 CC = gcc CXX = g++ F77 = gfortran FC = gfortran F90 = gfortran
Documentation
Online documentation
Local documentation
For version specific documentation see the help page of the module.
Show informations for the default version by using the command
'module help compiler/gnu'.
$ module help compiler/gnu
----------- Module Specific Help for 'compiler/gnu/4.7' -----------
This module provides the GNU compiler suite version 4.7.3
via commands 'gcc', 'g++' and 'gfortran' (see also 'http://gcc.gnu.org/').
The GNU compiler has been build with gmp-4.3.2, mpfr-2.4.2 and mpc-0.8.1.
Commands:
cpp - GNU pre processor
gcc - GNU C compiler
g++ - GNU C++ compiler
gfortran - GNU Fortran compiler (Fortran 77, 90 and 95)
Libraries can be found in
$GNU_LIB_DIR = /opt/bwhpc/common/compiler/gnu/4.7.3/x86_64/lib64
Local documentation:
See commands 'man cpp', 'man gcc', 'man g++' and 'man gfortran'.
Online documentation:
http://gcc.gnu.org/onlinedocs/
For details on library and include dirs please call
module show compiler/gnu/4.7
Please do not add the gnu compiler module to any automatic environment setup
procedure (neither to ~/.profile nor to ~/.bashrc).
[...]
Manual Pages
For detailed lists of the different program options consult the particular man page.
$ man gcc $ man g++ $ man gfortran
Optimizations
You can turn on various optimization options to enhance the performance of your program. Which options are the best depends on the specific program and can be determined by benchmarking your code. A command which gives good performance and a decent file size is
$ gcc -march=native -O2 ex.c -o ex
There are more aggressive optimization flags but the compiled programs can get quite large and the compilation process will probably take much longer. Moreover it can happen that the so compiled program is even slower. Such a command would be for example
$ gcc -march=native -O3 ex.c -o ex
For a complete list of all the optimization options execute
$ gcc --help=optimizers
Profiling with Gprof
Gprof is the profiler which belongs to the gcc compiler. Gprof is also installed on the system and can be used to profile your code. The profiler supports C, C++, Pascal and Fortran 77 program code. With this tool it is possible to analyse call times and time spent within program functions.
The first required step is to compile your program with the profiling flag "-pg".
$ gcc -pg ex.c -o ex
Compiled in this way your program will generate profiling data during execution. By default a file named gmon.out can be found in the work directory after running the program.
$ ./ex
The next step is to run the gprof program to analyse the gmon.out profiling data file. This file contains profiling data concerning the program execution, like an overview, time information or the call graph, in human readable format.
$ gprof gmon.out ex > outputfile.txt