Interval inference in the compiler is now complete, as of a couple of days ago. The interval code I posted earlier has ballooned into something more complex, because I realized I needed something that supports intervals which exclude or include the endpoints.
On the YUV to RGB conversion benchmark, runtime decreased from 180ms to 90ms. This is still not good enough for real time video playback; open-coded inline intrinsics for alien accessor words should go a long way toward rectifying that; this is something I plan on working on in 0.90. Other benchmarks such as appending sequences show better performance as well, because interval inference is able to remove overflow checks in many situations.