[PATCH] D21720: Unroll for uncountable loops

[Michael Zolotukhin via Phabricator via llvm-commits]

mzolotukhin added a comment.

What is the case 1?

For loops with unknown trip count (that's the case 2, right?) I don't see why we need to add any additional analyzers (`analyzeLoopUnrollCost`). Removing one instruction by unrolling by 2 is not better than the worst case for partial unroll of a loop with a known trip count:

  for (i = 0; i < N; i++) {
    ...
  }

But since we sometimes partially unroll such loops, I don't currently see a reason why we can't do this for loops with unknown trip-count as well. However, we don't need additional thresholds/knobs for it, thresholds for partial unroll should do it already.


Repository:
  rL LLVM

https://reviews.llvm.org/D21720