[llvm] [VPlan] Scalarize to first-lane-only directly on VPlan (PR #184267)

[Andrei Elovikov via llvm-commits]

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@@ -6541,3 +6541,60 @@ void VPlanTransforms::makeMemOpWideningDecisions(
     ReplaceWith(Recipe);
   }
 }
+
+void VPlanTransforms::makeScalarizationDecisions(VPlan &Plan, VFRange &Range) {
+  if (LoopVectorizationPlanner::getDecisionAndClampRange(
+          [&](ElementCount VF) { return VF.isScalar(); }, Range))
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eas wrote:

* That would be a function change from the current behavior
* My understanding is we try to keep scalar VPlan unmodified for costing, so we do need to clamp range here.

https://github.com/llvm/llvm-project/pull/184267