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

[via llvm-commits]

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@@ -7220,6 +7223,12 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   VPlanTransforms::optimizeForVFAndUF(BestVPlan, BestVF, BestUF, PSE);
   VPlanTransforms::simplifyRecipes(BestVPlan);
   VPlanTransforms::removeBranchOnConst(BestVPlan);
+  if (BestVPlan.getEntry()->getSingleSuccessor() ==
+      BestVPlan.getScalarPreheader()) {
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ayalz wrote:

ok, it appears the loop isn't vectorized because the Trip Count guard is known to always jump to the scalar loop, i.e., where VFxUF is known to exceed TC, so conceptually a smaller VFxUF could work. But tests include unvectorizable non-loop cases where TC<=1, which should better be cleaned up before calling LV, certainly before reaching LVP::executePlan().

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