On Sun, Aug 28, 2016 at 11:58:03PM -0400, P Levine wrote:
> Other distros like Ubuntu support the installation of multiple versions of
> LLVM/Clang side by side. One of the things Clang is really good at is
> support for the most recently approved upcoming features of the C++17
> standard. The best support for testing such features is with the latest
> sys-devel/llvm-9999. However if I want to compile Mesa against a stable
> version LLVM/Clang as well, I don't get that option.
I'm not sure such a configuration is fully supported upstream, but the way
ubuntu (and debian) does this is (was?) painfully broken. If I recall correctly
they first build it in one location and then move it around and try to
partially solve things through symlinks.
This totally destroys llvm-config and LLVM's cmake find_package module
meaning those things have hard-coded paths that have nothing to do with
where the things are installed on the system. Simple example, the
following CMakeLists.txt
cmake_minimum_required(VERSION 3.4)
project(llvm-test)
find_package(LLVM)
errors out on ubuntu with:
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)
-- Configuring incomplete, errors occurred!
Fixing this one path leads to more suffering further down the road.
The way gentoo maintainers package LLVM is much saner and developer friendly.
