This document describes how to configure a LLVM http://llvm.org/ build for use with JitCat.
JitCat uses the LLVM 10.0.0 release that you will have to build from source. The binary release cannot be used because it is compiled with the C++14 standard and JitCat is targeting C++17. Download the source from github: https://github.com/llvm/llvm-project/archive/llvmorg-10.0.0.zip
For building LLVM first of all refer to LLVM build documentation:
Getting started
Building LLVM with Cmake
Getting Started with the LLVM System using Microsoft Visual Studio
Set CMAKE_CXX_STANDARD to 17. LLVM currently targets C++14 but will build under C++17 as well. Building LLVM with C++14 will possibly lead to incompatibilities. For example, see this issue.
Except for the CMAKE_CCXX_STANDARD, the default CMake configuration of LLVM will work fine. It is possible to greatly reduce build time and diskspace usage of the LLVM build by disabling certain features (see below).
Use CMake to generate your Visual Studio project files. (I highly recommend using the CMake gui.)
Make sure you select the proper project generator for your use case. There are separate generators for 64 bit and 32 bit projects.
Add /D_SILENCE_ALL_CXX17_DEPRECATION_WARNINGS to CMAKE_CXX_FLAGS. Without this MSVC will generate an enormous amount of deprecation warnings and a few errors as well.
By default, JitCat is built with /MT (Multithread - statically linked runtime library), however LLVM is built with /MD (Multithreaded DLL runtime library) by default.
Either change JitCat to /MD if you are ok with the external dependency on a C++ runtime DLL, or change LLVM to build with /MT.
In order to do that, change MD to MT and MDd to MTd in the following settings:
LLVM_USE_CRT_DEBUG
LLVM_USE_CRT_MINSIZEREL
LLVM_USE_CRT_RELEASE
LLVM_USE_CRT_RELWITHDEBINFO
CMAKE_CXX_FLAGS
CMAKE_CXX_FLAGS_DEBUG
CMAKE_CXX_FLAGS_MINSIZEREL
CMAKE_CXX_FLAGS_RELWITHDEBINFO
CMAKE_C_FLAGS
CMAKE_C_FLAGS_DEBUG
CMAKE_C_FLAGS_MINSIZEREL
CMAKE_C_FLAGS_RELWITHDEBINFO
LLVM is a huge project and JitCat only needs part of it.
In order to minimize build time, a lot of things can be disabled.
Disable tools, tests, benchmarks, etc by turning off these options:
LLVM_INCLUDE_BENCHMARKS
LLVM_INCLUDE_DOCS
LLVM_INCLUDE_EXAMPLES
LLVM_INCLUDE_GO_TESTS
LLVM_INCLUDE_TEST
LLVM_INCLUDE_TOOLS
LLVM_INCLUDE_UTILS
LLVM can generate code for many target platforms, but we only need one.
For JitCat, select the same target for which you are building JitCat.
Most likely, this should be X86.
Change LLVM_TARGETS_TO_BUILD from ‘all’ to your target platform.