[llvm] [VPlan] Add VPIRWrapperBlock, use to model pre-preheader. (PR #93398)

[via llvm-commits]

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@@ -3321,6 +3374,8 @@ class VPlanPrinter {
   /// its successor blocks.
   void dumpBasicBlock(const VPBasicBlock *BasicBlock);
 
+  void dumpIRWrapperBlock(const VPIRWrapperBlock *WrapperBlock);
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ayalz wrote:

Is dumpIRWrapperBlock() defined, called, needed or can dumpBasicBlock() be (or is) reused?
Add documentation. 

https://github.com/llvm/llvm-project/pull/93398