I just tested with Mesa latest from git (2f175bfe5d8ca59a8a68b6d6d072cd7bf2f8baa9) and LLVM 7.0 revision 328838 (anything newer and Mesa won't compile due to a known issue) and the problem is gone. Either a later Mesa commit already fixed it, or my LLVM version was too old. This ticket can be closed as the problem can no longer be reproduced. Thanks and Cheers