Event: 2020 LLVM Virtual Developers Meeting

The Program Repository (llvm-prepo) is an LLVM/Clang compiler with program repository support. It aims to improve turnaround times and eliminate duplication of effort by centralising program data in a repository. This reduces compilation time by reusing previously optimised functions and global variable fragments, including both sharing them across multiple translation units and reusing them even when other portions of the relevant source files have changed.

Ccache is a compiler caching tool that uses textual hashing of the source files. When used to build a large project, the ccache cache can quickly become invalid due to the frequency of header file changes.

Thus, llvm-prepo reduces the build time for changed files, whereas ccache reduces the build time for unchanged files. This lightning talk will focus on showing how using the llvm-prepo and ccache together achieves much faster builds than using either of them individually. We will show the benefits by building the LLVM+Clang project at points through its commit history.

Duration: 5 Minutes