zapcc is a caching C++ compiler based on clang, designed to perform faster compilations. zapcc uses in-memory compilation cache in client-server architecture, remembering all compilation information between runs. zapcc is the client while zapccs is the server. Each zapcc run will reuse an existing server or if none was available will start a new one.

This open source release is licensed under the LLVM Release License (University of Illinois/NCSA).

The prerequisites and build process are identical to building LLVM.

mkdir build
cd build
cmake -G Ninja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_WARNINGS=OFF ../llvm
ninja

ninja check-all

zapcc command syntax is identical to clang with the command being zapcc.

zapcc ...

pkill zapcc

To kill the zapccs server to free memory or replace with newly-built zapcc

Typically re-compilations are 10x-50x faster Boost.Math, and full builds are 2x-5x faster WebKit.

Yes, zapcc is based on heavily-modified clang code.

Yes, to the extent clang is gcc compatible.

Please make sure first your project compiles successfully with Clang. If your project does not compile with Clang, Zapcc, being based on Clang, will not be able to compile any more than clang.

Currently, no.

zapcc builds on Linux x64. Windows x64 support with mingw-w64 is experimental.

Precompiled headers requires building your project to the exact precompiled headers rules. Most projects do not bother with using precompiled headers. Even then, precompiled headers do not cache as much as zapcc. Zapcc works within your existing build.

Precompiled headers are currently ignored by Zapcc.

Modules are not yet standard, rarely used and do not support well legacy code and macros found in most existing C++ code, such as Boost. Modules require significant code refactoring in bottom-up approach everything or are slow. Even then, modules do not cache template instantiations and generated code that are specific to your code like zapcc does.

To avoid killing the server by using endless memory, Zapcc server has a memory limit and will automatically reset after reaching it, restarting with an empty cache and low memory usage. The memory limit is set under [MaxMemory] at bin/zapccs.config, and you can change it to optimize memory usage and the number of servers you plan to use. Usually, you should not set the -j parameter to more than the number of physical cores + 2. This is especially important for Intel CPU with hyper-threading enabled, which report twice the number of physical cores. In such cases, Zapcc may run faster with fewer servers, each using a higher memory limit.

No.

This depends on the complexity of the header files vs. the complexity of the source files. It can range from no acceleration at all for plain C projects to x2-x5 for build-all of heavily templated projects, up to cases of x50 speedups in developer-build incremental change of one file.

As a reference number, Zapcc accelerates clang build-all about x2 faster compared to building clang using clang.

No, caching is disabled for C files.

This open-source release was last merged with LLVM r307021 on 2017-07-03.

There are patches all around LLVM & clang. Additional zapcc-only code in

tools/zapcc
tools/zapccs
tools/clang/test/zapcc