(In reply to comment #3)
> [...] after a few minutes from launching a game (I have tried with CKII,
> Witcher 2, Watelands 2, Cities in motion, Deadfall Adventures and Serious Sam
> 3) or just after a few seconds after exiting the game [...]

If you capture an apitrace of one of those games, does the problem also occur
after replaying the apitrace?

> I am using a llvm ppa to install llvm 3.5 git.

Do the ppa packages use any patches versus upstream?

> I've tried to compile llvm with no luck, so I cannot bisect.

What's the problem compiling LLVM? It would probably be best if you could
bisect yourself.