[llvm] [VPlan] Delay adding canonical IV increment and exit branches. (PR #82270)

[Kolya Panchenko via llvm-commits]

https://github.com/nikolaypanchenko commented:

I'm concerned that such  missed update till later phase make VPlan ill-formed for xforms and vplan-based cost model ? That is, that canonical IV can be seen as a dead recipe by xforms, i.e. requires special handling everywhere and possibly can break vendor's downstream. 
For the vplan-based cost model such implicit representation will require extra code to properly model the cost (even though it's simple 1 reg + 1 add).
What is a plan to handle these areas later ?

https://github.com/llvm/llvm-project/pull/82270