[llvm] [VPlan] Simplify Plan's entry in removeBranchOnConst. (PR #154510)

[Florian Hahn via llvm-commits]

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@@ -969,12 +969,25 @@ void VPlan::execute(VPTransformState *State) {
   setName("Final VPlan");
   LLVM_DEBUG(dump());
 
-  // Disconnect scalar preheader and scalar header, as the dominator tree edge
-  // will be updated as part of VPlan execution. This allows keeping the DTU
-  // logic generic during VPlan execution.
   BasicBlock *ScalarPh = State->CFG.ExitBB;
-  State->CFG.DTU.applyUpdates(
-      {{DominatorTree::Delete, ScalarPh, ScalarPh->getSingleSuccessor()}});
+  if (getScalarPreheader()->hasPredecessors()) {
+    // Disconnect scalar preheader and scalar header, as the dominator tree edge
+    // will be updated as part of VPlan execution. This allows keeping the DTU
+    // logic generic during VPlan execution.
+    State->CFG.DTU.applyUpdates(
+        {{DominatorTree::Delete, ScalarPh, ScalarPh->getSingleSuccessor()}});
+  } else {
+    Loop *OrigLoop = State->LI->getLoopFor(
+        cast<VPIRBasicBlock>(getScalarPreheader()->getSingleSuccessor())
+            ->getIRBasicBlock());
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fhahn wrote:

done thanks

https://github.com/llvm/llvm-project/pull/154510