[llvm] [CodeGen] Perform early program return instead of using indirect branch (PR #102127)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> The RB (BB'ssuccessor) should be post dominating i.e. the control should reach RB from all possible path from BB till the graph end.

Tail duplication can help if the return isn't a post dominator
 
We need IR test examples to determine if there is any need to do anything here. There are several interacting MIR passes, and we only care about the net result 

https://github.com/llvm/llvm-project/pull/102127