[PATCH] D30631: [BPI] Use metadata info before any other heuristics

[Philip Reames via Phabricator via llvm-commits]

reames added a comment.

FYI: Serguei is going to file an upstream bug with a clear illustration of where loop rotations goes wrong due to the issue identified here.  Essentially, for a sufficiently long running loop, the static heuristic for unreached blocks is not strongly biased enough.  In our case, we have branch weights specified which are more strongly biased than the static heuristic result.  Using the static heuristic by itself is clearly wrong, but I do see Chandler's point about the static heuristics providing useful information.  Possibly we should be using the stronger of the two sources of information?


https://reviews.llvm.org/D30631