ccache is a C/C++ compiler cache. It wraps calls to the compiler to cache results and detect previous compilation results.
ccache versions >= 3.2.x support clang.
Install the latest version with homebrew
brew install ccache
CMake will currently detect whether ccache is installed on your system and automatically start using it. If you don't want to customize your setup, you don't have to do anything.
The build system uses wrapper scripts:
Each of these contain the following settings:
export CCACHE_CPP2=true
export CCACHE_MAXSIZE=10G
export CCACHE_HARDLINK=true
All of these are optional, except for CACHE_CPP2=true, which is required for clang.
ccache creates a configuration file in ${HOME}/.ccache/ccache.conf on your computer. This file contains many settings that control ccache. See the website for a detailed description of config settings.
There are 2 important settings that you might want to change:
cache_dir
If you're using hard links and you build code on a partition that is separate from the one where you home directory is located, you need to either disable hard links, or move the cache dir to the same partition where the build occurs so that ccache can hard link to the cache dir.
base_dir
This can be set to a folder that is the parent of the root repo directory. This will cause ccache to replace absolute dirs in cached files with relative dirs to base_dir. This allows sharing cached results with builds of the same project in different directories. See the docs for a more thorough explanation of compiling in different directories. By default, base_dir is set to the root of the repo, which should do the right thing in most cases.
You can cause ccache to output a log file in order to determine the reasons for cache hits or misses. Export the following variable to your shell before building:
export CCACHE_LOGFILE=/tmp/ccache.log
You can bypass ccache by exporting the following variable in your shell before building:
export CCACHE_DISABLE=1