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

[Florian Hahn via llvm-commits]

================
@@ -2429,6 +2429,30 @@ InnerLoopVectorizer::getOrCreateVectorTripCount(BasicBlock *InsertBlock) {
   return VectorTripCount;
 }
 
+/// Helper to connect both the vector and scalar preheaders to the Plan's
+/// entry. This is used when adjusting \p Plan during skeleton
+/// creation, i.e. adjusting the plan after introducing an initial runtime
+/// check.
+static void connectScalarPreheaderInVPlan(VPlan &Plan) {
+  VPBlockBase *VectorPH = Plan.getVectorPreheader();
+  VPBlockBase *ScalarPH = Plan.getScalarPreheader();
+  VPBlockBase *PredVPB = Plan.getEntry();
+  VPBlockUtils::connectBlocks(PredVPB, ScalarPH, -1, 0);
+  VPBlockUtils::connectBlocks(PredVPB, VectorPH, 0, -1);
----------------
fhahn wrote:

Updated to connect + swap, thanks.

> Furthermore, TCCheckBlock could then be inserted on this Entry-->vector_PH edge, so that connectScalarPreheaderInVPlan() assimilates introduceCheckBlockInVPlan().

Not sure how exactly, left as is for now.

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