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

[via llvm-commits]

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@@ -7877,6 +7899,12 @@ EpilogueVectorizerMainLoop::emitIterationCountCheck(BasicBlock *Bypass,
     setBranchWeights(BI, MinItersBypassWeights, /*IsExpected=*/false);
   ReplaceInstWithInst(TCCheckBlock->getTerminator(), &BI);
 
+  VPBlockBase *VectorPH = Plan.getVectorPreheader();
+  VPBlockBase *PredVPB = VectorPH->getSinglePredecessor();
+  if (PredVPB->getNumSuccessors() == 1)
+    connectScalarPreheaderInVPlan(Plan);
+  else
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ayalz wrote:

Worth introducing TCCheckBlock also when it appears first, rather than "folding" it into Entry?

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