Some people might want to run and test ug4 with different build configurations. For example a release build with full compiler optimizations and a development and debugging build with all debug symbols and profiler analysis. In addition it might be useful having these builds in both sequential and parallel builds.

The recommended way is to use multiple build directories. One for each build configuration:

build_release_sp (release build without parallelization)
build_release_mp (release build with parallelization)
build_debug_sp (debug build without parallelization)
build_debug_mp (debug build with parallelization)

Compile Time Speedup with ccache

ccache (https://ccache.samba.org/) is a wrapper around GCC compatible compilers (basically GCC itself and Clang) providing a cache for compiler objects to speedup recompilation. The average speedup for the second and any subsequent compile runs is between 5- and 40-fold.

Basic Setup for GCC

ccache should be available in your distributions repositories (on Mac via macports). Make sure it is in your $PATH (which ccache should print the location). We will assume its in /usr/bin/ccache.

The easiest way is to add symlinks for the GCC compiler executables cc, c++, cpp, gcc and g++ pointing to /usr/bin/ccache in a directory contained in $PATH prior to the location of the real compiler executables.

Assuming your $PATH is /usr/local/bin:/usr/bin and the compilers are found in /usr/bin. Add symlinks via ln -s /usr/bin/ccache /usr/local/bin/<gcc_exec> for each of the five GCC executables.

If you now run gcc (i.e. /usr/local/bin/gcc or any other of the five), ccache is executed which runs the real /usr/bin/gcc only if it does not find the resulting objects in its cache (i.e. the source file or any includes have changed).

Basic Setup for Clang

Though Clang is similar enough to GCC to be used with ccache, it needs some further tweaks to suppress myriads of annoying compiler warnings. It is also assumed that Clang's executables (clang and clang++) are in /usr/bin.

Instead of adding symlinks to /usr/bin/ccache we need two little Bash scripts for invoking ccache.

For clang save the following two lines as /usr/local/bin/clang:

#!/bin/bash
CCACHE_CPP2=yes ccache /usr/bin/clang -Qunused-arguments -fcolor-diagnostics "$@"

And for clang++ save the following two lines as /usr/local/bin/clang++:

#!/bin/bash
CCACHE_CPP2=yes ccache /usr/bin/clang++ -Qunused-arguments -fcolor-diagnostics "$@"

Using Multiple Caches

When using ccache for multiple build configurations the speedup is far from being optimal. This is due to the fact, that ccache overrides the compiler objects for a given source file if the compile parameters have changed. Switching back and forth between different build configurations causes more cache misses than hits in ccache and little to no speedup.

Luckily ccache allows us to specify the cache directory via the environment variable CCACHE_DIR. By default this is /home/USER/.ccache.

For the four build configurations mentioned at the beginning, we need four different caches. Create those in a directory writable by you, e.g. in /home/USER/.cache/ccache/ug4:

/home/USER/.cache/ccache/ug4/build_release_sp
/home/USER/.cache/ccache/ug4/build_release_mp
/home/USER/.cache/ccache/ug4/build_debug_sp
/home/USER/.cache/ccache/ug4/build_debug_mp

When executing make in one of the build dirs, simply set CCACHE_DIR to the appropriate cache directory:

cd build_debug_mp
CCACHE_DIR=/home/USER/.cache/ccache/ug4/build_debug_mp make

Note: In the case of ug4 ccache uses between 1.5GB and 2GB for its cache per build configuration.

Table of Contents

Compile Time Speedup with ccache

Basic Setup for GCC

Basic Setup for Clang

Using Multiple Caches