(In reply to comment #2)
> I can't reproduce this with LLVM r179895 and Mesa
> 12eab7cc564a6928197f9b87ded9e368e56976f0
> 
> Have you done full rebuilds of both projects?

Yes, I always do make [dist]clean and git clean -dfx.

I have just deleted both trees and re-cloned to be sure, but the segfault is
still there.

When I was on my working commits moving either llvm or mesa to head while
keeping the other on "working" produced the segfault (which is why I didn't do
a proper bisect).

I always clean and rebuild mesa after llvm has changed.