[VPlan] Wrap planContainsAdditionalSimplifications in NDEBUG (NFC)

Only used for an assertion.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7239,11 +7239,12 @@ InstructionCost LoopVectorizationPlanner::cost(VPlan &Plan,
   return Cost;
 }
 
+#ifndef NDEBUG
 /// Return true if the original loop \ TheLoop contains any instructions that do
 /// not have corresponding recipes in \p Plan and are not marked to be ignored
 /// in \p CostCtx. This means the VPlan contains simplification that the legacy
 /// cost-model did not account for.
-[[maybe_unused]] static bool
+static bool
 planContainsAdditionalSimplifications(VPlan &Plan, ElementCount VF,
                                       VPCostContext &CostCtx, Loop *TheLoop,
                                       LoopVectorizationCostModel &CM) {
@@ -7288,6 +7289,7 @@ planContainsAdditionalSimplifications(VPlan &Plan, ElementCount VF,
         });
       });
 }
+#endif
 
 VectorizationFactor LoopVectorizationPlanner::computeBestVF() {
   if (VPlans.empty())