[llvm] [TailDuplicator] Add a limit on the size of predecessors (PR #78582)

[via llvm-commits]

weiguozhi wrote:

> Hmm, CodeGen is not an area I know much about. Could you explain that? What does profile information refer to, the information provided by the PGO?

Right. Disable tail duplication for blocks with 8 predecessors may hurt performance of some applications. Duplicate blocks into hot predecessors only can still give you the benefit of tail duplication, and at the same time limit the number of duplication. MachineBlockPlacement does the same thing in the late tail duplication (embedded in the MBP).

https://github.com/llvm/llvm-project/pull/78582