[llvm] [VPlan] Introduce child regions as VPlan transform. (PR #129402)

[via llvm-commits]

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@@ -54,15 +53,12 @@ class VPlanHCFGBuilder {
   /// created for a input IR basic block.
   DenseMap<VPBlockBase *, BasicBlock *> VPB2IRBB;
 
-  /// Build plain CFG for TheLoop and connects it to Plan's entry.
-  void buildPlainCFG();
-
 public:
   VPlanHCFGBuilder(Loop *Lp, LoopInfo *LI, VPlan &P)
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ayalz wrote:

```suggestion
  VPlanCFGBuilder(Loop *Lp, LoopInfo *LI, VPlan &P)
```
but better be consistent with VPlanHCFGBuilder.h file name, i.e., do so when moving to VPlanConstruction?

https://github.com/llvm/llvm-project/pull/129402