Installation

Refer to https://llvm.org/docs/GettingStarted.html#requirements

git clone --depth 1 https://github.com/llvm/llvm-project.git
cd llvm-project
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release -G Ninja ../llvm
# cmake -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang;lld" -G Ninja ../llvm

cmake --build . --target <target>
# or
export PATH=$PWD/build/bin:$PATH
export LD_LIBRARY_PATH=$PWD/build/lib:$LD_LIBRARY_PATH

https://llvm.org/docs/GettingStarted.html#getting-a-modern-host-c-toolchain describes how to install GCC from source.

Use of a user provided GCC:

mkdir build
cd build
CC=$HOME/toolchains/bin/gcc CXX=$HOME/toolchains/bin/g++ \
  cmake .. -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$HOME/toolchains/lib64 -L$HOME/toolchains/lib64"

Useful tools that can be found in build/bin:

$ llvm-config --cxxflags
-I/ceph-fj/fangjun/open-source-2/llvm-project/llvm/include -I/ceph-fj/fangjun/open-source-2/llvm-project/build/include -std=c++14   -fno-exceptions -fno-rtti -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS

$ llvm-config --libdir
/ceph-fj/fangjun/open-source-2/llvm-project/build/lib

$ llvm-config --cflags
-I/ceph-fj/fangjun/open-source-2/llvm-project/llvm/include -I/ceph-fj/fangjun/open-source-2/llvm-project/build/include  -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS

$ llvm-config --ldflags
-L/ceph-fj/fangjun/open-source-2/llvm-project/build/lib

$ llvm-config --src-root
/ceph-fj/fangjun/open-source-2/llvm-project/llvm

$ llvm-config --obj-root
/ceph-fj/fangjun/open-source-2/llvm-project/build

$ llvm-config --version
15.0.0git

$ llvm-config --bindir
/ceph-fj/fangjun/open-source-2/llvm-project/build/bin