Building Clang as a standalone project depending on LLVM binary - build

Question

I want to build Clang from source but not LLVM. Clang has LLVM as a hard dependency, but instead of building LLVM from source, it should be possible to depend on a pre-installed(pre-built) LLVM binary.
I know this is possible because clang has the following CMake flags -
LLVM_DIR
LLVM_LIBRARY_DIR
LLVM_MAIN_INCLUDE_DIR
LLVM_TOOLS_BINARY_DIR
and Clang's CMakeLists.txt also has provisions to rely on a previously installed version of LLVM. (https://github.com/llvm-mirror/clang/blob/master/CMakeLists.txt#L14)
I got the LLVM 9 binary and Clang 9 source code from here - http://releases.llvm.org/download.html#9.0.0
I am trying to build Clang with -
cmake -DLLVM_BUILD_TOOLS=Off -DCMAKE_BUILD_TYPE=Release -DLLVM_TARGETS_TO_BUILD=host ../
But, I get the following errors -
CMake Error at /home/reik/Downloads/clang/lib/cmake/llvm/AddLLVM.cmake:467 (add_library):
add_library cannot create target "SampleAnalyzerPlugin" because an imported
target with the same name already exists.
Call Stack (most recent call first):
/home/reik/Downloads/clang/lib/cmake/llvm/AddLLVM.cmake:665 (llvm_add_library)
lib/Analysis/plugins/SampleAnalyzer/CMakeLists.txt:6 (add_llvm_library)
CMake Error at /home/reik/Downloads/clang/lib/cmake/llvm/AddLLVM.cmake:585 (target_link_libraries):
Cannot specify link libraries for target "SampleAnalyzerPlugin" which is
not built by this project.
Call Stack (most recent call first):
/home/reik/Downloads/clang/lib/cmake/llvm/AddLLVM.cmake:665 (llvm_add_library)
lib/Analysis/plugins/SampleAnalyzer/CMakeLists.txt:6 (add_llvm_library)
In the above code snippet, /home/reik/Downloads/clang is the LLVM binary. (To note, the LLVM binary comes with Clang binary)
It seems like since the LLVM binary comes with Clang installed, there is some sort of conflict in add_library since some things already exist (Found a related thread here - http://lists.llvm.org/pipermail/llvm-dev/2016-November/107616.html) -> So I think I am missing some sort of configuration steps when building Clang as a standalone project.
Or maybe I just need an LLVM binary that comes without clang installed but I have been unable to find any such thing on LLVM's official website.
Could anyone please help me with this?

Answer 1

i build clang standalone with these commands, then it worked.
on macos 10.15.6, xcode12.1, cmake 3.18.3
1.
wget https://github.com/llvm/llvm-project/releases/download/llvmorg-11.0.0/clang-11.0.0.src.tar.xz
wget https://github.com/llvm/llvm-project/releases/download/llvmorg-11.0.0/clang+llvm-11.0.0-x86_64-apple-darwin.tar.xz
tar xvjf clang+llvm-11.0.0-x86_64-apple-darwin.tar.xz
tar xjvf clang-11.0.0.src.tar.xz
mkdir build && cd build
cmake ../clang-11.0.0.src -DLLVM_CONFIG=../clang+llvm-11.0.0-x86_64-apple-darwin/bin/llvm-config
make -j2

Answer 2

I think you are giving the wrong path to cmake. I think you were pointing to the sub-directory named clang. You should instead point to llvm-project-llvmorg-9.0.0/llvm itself.
Run something like the following:
cmake -DLLVM_BUILD_TOOLS=Off -DCMAKE_BUILD_TYPE=Release -DLLVM_TARGETS_TO_BUILD=host $LLVM_SRC