[IR] Avoid repeated hash lookups (NFC) (#138430)

Author: kazutakahirata

llvm/lib/IR/DroppedVariableStats.cpp

@@ -117,8 +117,7 @@ void DroppedVariableStats::removeVarFromAllSets(VarID Var, const Function *F) {
 bool DroppedVariableStats::isScopeChildOfOrEqualTo(const DIScope *Scope,
                                                    const DIScope *DbgValScope) {
   while (Scope != nullptr) {
-    if (VisitedScope.find(Scope) == VisitedScope.end()) {
-      VisitedScope.insert(Scope);
+    if (VisitedScope.insert(Scope).second) {
       if (Scope == DbgValScope) {
         VisitedScope.clear();
         return true;