https://bugs.freedesktop.org/show_bug.cgi?id=90523
--- Comment #2 from acab@digitalfuture.it --- I am sorry, but while trying to get a crash I've realized it's not mesa. The culprit appears to be llvm.
In short: llvm 3.5.2 + mesa 10.5.5 -> ok llvm 3.6.0 + mesa 10.5.5 -> lockup
I'm going to attach the logs anyway. Feel free to close this bug if it doesn't belong in here.