https://bugs.freedesktop.org/show_bug.cgi?id=82050
--- Comment #3 from Tom Stellard tstellar@gmail.com --- (In reply to comment #2)
There was a recent change to LLVM which increased conformance with OpenCL floating point semantics at some performance cost. That might explain at least some of the difference.
Pyrit doesn't use any floating-point operations, so this shouldn't be an issue.