[llvm] [VPlan] Move initial skeleton construction earlier (NFC). (PR #150848)

[Florian Hahn via llvm-commits]

================
@@ -58,17 +58,21 @@ struct VPlanTransforms {
                                                                 LoopInfo &LI);
 
   /// Prepare the plan for vectorization. It will introduce a dedicated
-  /// VPBasicBlock for the vector pre-header as well as a VPBasicBlock as exit
-  /// block of the main vector loop (middle.block). If a check is needed to
+  /// VPBasicBlock for the vector pre-header, a VPBasicBlock as exit
+  /// block of the main vector loop (middle.block) and a VPBaiscBlock for the
+  /// scalar preheader. It also adds a canonical IV and its increment, using \p
+  /// InductionTy and \p IVDL, and creates a VPValue expression for the original
+  /// trip count.
+  LLVM_ABI_FOR_TEST static void
----------------
fhahn wrote:

Yep, this is needed now for symbols used in the LLVM unit tests

https://github.com/llvm/llvm-project/pull/150848