[llvm] [VPlan] Handle early exit before forming regions. (NFC) (PR #138393)

[via llvm-commits]

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@@ -9383,7 +9383,8 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
   VPlanTransforms::prepareForVectorization(
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ayalz wrote:

(Independent) Should `prepareForVectorization` be renamed to a more informative name, perhaps `canonicalizeTopLoop`, as it takes care of canonicalizing header and latch blocks, introducing and connecting preheader, middle-block,  scalar preheader, canonical IV recipes and trip-count value. 

https://github.com/llvm/llvm-project/pull/138393