[llvm] [VPlan] Add VPlan-based addMinIterCheck, replace ILV for non-epilogue. (PR #153643)

[Florian Hahn via llvm-commits]

================
@@ -7327,6 +7257,17 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
       BestVPlan.resetTripCount(Exp);
     ExpSCEV->eraseFromParent();
   }
+  // SCEV expansion will add new instructions in the IRBB wrapped by Entry.
+  // Remove existing VPIRInstructions/VPIRPhi and re-create them to make sure
+  // all IR instructions are wrapped. Otherwise VPInstructions may be inserted
+  // at the wrong place.
----------------
fhahn wrote:

The original code also expanded everything at the end of the entry block, although it was not as clear. Before calling VPExpandSCEVRecipe::execute, the insert point of the build is set the the block's terminator:   `State.Builder.SetInsertPoint(Entry->getIRBasicBlock()->getTerminator());`

We can adjust that separately.

https://github.com/llvm/llvm-project/pull/153643