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

[Florian Hahn via llvm-commits]

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@@ -972,12 +972,14 @@ 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()->getNumPredecessors() > 0) {
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fhahn wrote:

The issue is that the updater than would try to apply an update to a disconnected part of the CFG, which will result in a crash, as the edge we are trying to update won't exist.

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