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

[via llvm-commits]

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@@ -7191,6 +7194,19 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   VPlanTransforms::optimizeForVFAndUF(BestVPlan, BestVF, BestUF, PSE);
   VPlanTransforms::simplifyRecipes(BestVPlan);
   VPlanTransforms::removeBranchOnConst(BestVPlan);
+  if (BestVPlan.getEntry()->getSingleSuccessor() ==
+      BestVPlan.getScalarPreheader()) {
+    // TODO: The vector loop would be dead, should not even try to vectorize.
+    ORE->emit([&]() {
+      return OptimizationRemarkAnalysis(DEBUG_TYPE, "VectorizationDead",
+                                        OrigLoop->getStartLoc(),
+                                        OrigLoop->getHeader())
+             << "Created vector loop never executes due insufficient trip "
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ayalz wrote:

```suggestion
             << "Created vector loop never executes due to insufficient trip "
```

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