Comment # 6 on bug 103743 from Nicolai Hähnle

Thanks. To give you an update, this is a super subtle control flow handling bug
in LLVM -- and the difference between the original shader and your modification
at the LLVM input is merely that the sense of one branch is (correctly)
inverted, leading LLVM down a subtly different path in the end.

A sledge-hammer fix is quite simple, but I'm still thinking about how to get a
better fix which doesn't pessimize a bunch of cases.