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

[Florian Hahn via llvm-commits]

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@@ -7377,6 +7387,16 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
       addRuntimeUnrollDisableMetaData(L);
   }
 
+  if (BestVPlan.getScalarPreheader()->getNumPredecessors() == 0) {
+    // If the original loop became unreachable, we need to delete it.
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fhahn wrote:

Yep, unfortunately we cannot do this when the VPIRBasicBlock for the scalar preheader gets executed, as we only execute reachable VPBBs.

I moved it for now to VPlan::execute. Unfortunately doing in the destructor of VPIRBasicBlock won't work either, because we need access to LoopInfo.

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