[llvm] [VPlan] Hook IR blocks into VPlan during skeleton creation (NFC) (PR #114292)

[via llvm-commits]

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@@ -8074,6 +8090,15 @@ EpilogueVectorizerEpilogueLoop::emitMinimumVectorEpilogueIterCountCheck(
   }
   ReplaceInstWithInst(Insert->getTerminator(), &BI);
   LoopBypassBlocks.push_back(Insert);
+
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ayalz wrote:

All VPlans are initialized with the original scalar preheader as their Entry, but this works only when vectorizing the main loop (w/ or w/o vectorizing the epilog). When vectorizing the epilog loop, Entry no longer serves to host SCEV-expand recipes but should instead refer to the block between Middle and "Vector Epilog PreHeader" (called "Vector Epilogue Trip Count Check", but that's also how the first block is named), as depicted in https://llvm.org/docs/Vectorizers.html#epilogue-vectorization. The documentation of Entry in createInitialVPlan() deserves update?

https://github.com/llvm/llvm-project/pull/114292