[llvm] [LoopPeel] LCSSA form is destroyed by LoopPeel, preserve it (PR #78696)

[Vedant Paranjape via llvm-commits]

vedantparanjape-amd wrote:

> > Now we are unaware if such a transformation is expected of simplifyLoopIV and if it is also expected to maintain LCSSA.
> 
> simplifyLoopIV is supposed to maintain LCSSA form.

So, should we update the simplifyLoopIV or just call formLCSSAform after simplifyLoopIV ?

https://github.com/llvm/llvm-project/pull/78696