[PATCH] D62079: [MBP] Rotate should bring more fallthrough

[Guozhi Wei via Phabricator via llvm-commits]

Carrot added a comment.

Precisely compute the fallthrough frequency is very helpful in layout of loop header and exit BB. It is included in my next patch.

Current implementation of findBestLoopExit finds the exit edge with most frequency, and rotateLoop exposes that edge as fallthrough. This patch fixed a problem in a very common case

- The loop header has only one out-of-loop predecessor
- The bottom of the loop chain doesn't exit the  loop

In this case, the exit edge can't have larger frequency than the fallthrough to header, so the loop chain should not be rotated.


Repository:
  rL LLVM

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  https://reviews.llvm.org/D62079/new/

https://reviews.llvm.org/D62079