Error when using CMake with LLVM

Question

So I'm trying to build a toy compiler using LLVM and I'd like to use CMake as my build system. I tried using the sample CMakeLists.txt from LLVM's website, but I encounter the following error when running cmake:

CMake Error at /usr/share/llvm-3.8/cmake/LLVMConfig.cmake:178  (include):
  include could not find load file:

    /usr/share/llvm/cmake/LLVMExports.cmake
Call Stack (most recent call first):
  CMakeLists.txt:4 (find_package)


CMake Error at /usr/share/llvm-3.8/cmake/LLVMConfig.cmake:181 (include):
  include could not find load file:

    /usr/share/llvm/cmake/LLVM-Config.cmake
Call Stack (most recent call first):
  CMakeLists.txt:4 (find_package)

When I went to go investigate the problem, I discovered that the path on my system is actually /usr/share/llvm-3.8/. When I tried changing the path to /usr/share/llvm/ like it expects, I get another error:

CMake Error at /usr/share/llvm/cmake/LLVMExports.cmake:1034 (message):
  The imported target "LLVMSupport" references the file

     "/usr/lib/libLLVMSupport.a"

  but this file does not exist.  Possible reasons include:

  * The file was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and contained

     "/usr/share/llvm/cmake/LLVMExports.cmake"

  but not all the files it references.

I'm not really an expert on how exactly CMake works, so I'm not sure where to go from here. I'm running Ubuntu 16.04, and I've tried installing LLVM through various different packages with the same results. Is this a problem with Ubuntu's packaging system, or is something that I can fix?

Answer 1

AFAIK, this is a well-known bug in Ubuntu's packaging. The original issue still persists in llvm-3.8-dev on Ubuntu 16.04 see here and here.

When attempting to fix LLVMExports.cmake by manually setting the import prefix

set(_IMPORT_PREFIX "/usr/lib/llvm-3.8")

CMake was able to find libLLVMSupport.a and other libraries. However, I was faced with the following issue

 The imported target "PollyISL" references the file

    "/usr/lib/llvm-3.8/lib/libPollyISL.a"

 but this file does not exist.  Possible reasons include:

Surprisingly, library libPollyISL.a does not even exist in LLVM installation directory. Therefore, the problem is more than CMake config.

To save time, build LLVM yourself from source and set LLVM_DIR env variable. See this tutorial.

Answer 2

The easiest option is to install a version of LLVM that doesn't have that problem: the error disappeared for me after doing:

apt-get remove llvm
apt-get autoremove
apt-get install llvm-3.9

(Tested on Ubuntu 16.04.)