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

[via llvm-commits]

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@@ -2426,6 +2426,26 @@ InnerLoopVectorizer::getOrCreateVectorTripCount(BasicBlock *InsertBlock) {
   return VectorTripCount;
 }
 
+static void connectScalarPreheaderInVPlan(VPlan &Plan) {
+  VPBlockBase *VectorPH = Plan.getVectorPreheader();
+  VPBlockBase *ScalarPH = Plan.getScalarPreheader();
+  VPBlockBase *PredVPB = VectorPH->getSinglePredecessor();
+  VPBlockUtils::disconnectBlocks(Plan.getEntry(), VectorPH);
+  VPBlockUtils::connectBlocks(PredVPB, ScalarPH);
+  VPBlockUtils::connectBlocks(PredVPB, VectorPH);
+}
+
+static void connectCheckBlockInVPlan(VPlan &Plan, BasicBlock *CheckIRBB) {
+  VPBlockBase *ScalarPH = Plan.getScalarPreheader();
+  VPBlockBase *VectorPH = Plan.getVectorPreheader();
+  VPBlockBase *PredVPB = VectorPH->getSinglePredecessor();
+  VPBlockUtils::disconnectBlocks(PredVPB, VectorPH);
+  VPIRBasicBlock *CheckVPIRBB = VPIRBasicBlock::fromBasicBlock(CheckIRBB);
+  VPBlockUtils::connectBlocks(PredVPB, CheckVPIRBB);
+  VPBlockUtils::connectBlocks(CheckVPIRBB, ScalarPH);
+  VPBlockUtils::connectBlocks(CheckVPIRBB, VectorPH);
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ayalz wrote:

Perhaps worth having an `insertBlockOnEdge()` function that takes block B and edge A->C, and produces A->B->C.

Followed by adding the scalar PH as another (the first) successor of B.

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