[llvm] [VPlan] Model epilogue skeleton in VPlan by wrapping in VPIRBBs (NFCI). (PR #222312)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -1461,6 +1429,58 @@ static void insertCheckBlockBeforeVectorLoop(VPlan &Plan,
   addIncomingForLastPredecessor(ScalarPH);
 }
 
+void VPlanTransforms::modelGeneratedMainLoopBlocks(
+    VPlan &Plan, VPlan &MainPlan, VPIRBasicBlock *EnteredFrom) {
+  // Map blocks from MainPlan to new, empty VPIRBasicBlocks in Plan, so the
+  // skeleton CFG can be modeled explicitly. MainPlan's entry maps to Plan's
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artagnon wrote:

```suggestion
  // skeleton CFG can be modeled explicitly. MainPlan's entry maps to EpiPlan's
```

https://github.com/llvm/llvm-project/pull/222312