> - Runtime information. The runtime needs accurate maps of stack frames for both GC and stack copying, something that is not available from standard backends today.

DannyBee addressed most of these points, however I just wanted to note that even if LLVM didn't provide stack maps, it's easy to recover stack information using lazy pointer stacks [1]

[1] http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.158....