[SLP][NFC] Simplify count_if to count (#149072)

Author: pfusik

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -5540,8 +5540,7 @@ BoUpSLP::findReusedOrderedScalars(const BoUpSLP::TreeEntry &TE,
       return std::max(Entries[I].front()->getVectorFactor(),
                       Entries[I].back()->getVectorFactor());
     });
-  unsigned NumUndefs =
-      count_if(CurrentOrder, [&](unsigned Idx) { return Idx == NumScalars; });
+  unsigned NumUndefs = count(CurrentOrder, NumScalars);
   if (ShuffledSubMasks.all() || (NumScalars > 2 && NumUndefs >= NumScalars / 2))
     return std::nullopt;
   return std::move(CurrentOrder);