[SPARK-47319][SQL] Improve missingInput calculation

### What changes were proposed in this pull request?
This PR improves `QueryPlan.missingInput()` calculation.

### Why are the changes needed?
This seems to be the root cause of `DeduplicateRelations` slowness in some cases.

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
Existing UTs.

### Was this patch authored or co-authored using generative AI tooling?
No.

Closes apache#45424 from peter-toth/fix-missinginput.

Authored-by: Peter Toth <peter.toth@gmail.com>
Signed-off-by: Kent Yao <yao@apache.org>

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/AttributeSet.scala

@@ -104,13 +104,19 @@ class AttributeSet private (private val baseSet: mutable.LinkedHashSet[Attribute
    * in `other`.
    */
   def --(other: Iterable[NamedExpression]): AttributeSet = {
-    other match {
-      // SPARK-32755: `--` method behave differently under scala 2.12 and 2.13,
-      // use a Scala 2.12 based code to maintains the insertion order in Scala 2.13
-      case otherSet: AttributeSet =>
-        new AttributeSet(baseSet.clone() --= otherSet.baseSet)
-      case _ =>
-        new AttributeSet(baseSet.clone() --= other.map(a => new AttributeEquals(a.toAttribute)))
+    if (isEmpty) {
+      AttributeSet.empty
+    } else if (other.isEmpty) {
+      this
+    } else {
+      other match {
+        // SPARK-32755: `--` method behave differently under scala 2.12 and 2.13,
+        // use a Scala 2.12 based code to maintains the insertion order in Scala 2.13
+        case otherSet: AttributeSet =>
+          new AttributeSet(baseSet.clone() --= otherSet.baseSet)
+        case _ =>
+          new AttributeSet(baseSet.clone() --= other.map(a => new AttributeEquals(a.toAttribute)))
+      }
     }
   }
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/QueryPlan.scala

@@ -102,7 +102,13 @@ abstract class QueryPlan[PlanType <: QueryPlan[PlanType]]
   /**
    * Attributes that are referenced by expressions but not provided by this node's children.
    */
-  final def missingInput: AttributeSet = references -- inputSet
+  final def missingInput: AttributeSet = {
+    if (references.isEmpty) {
+      AttributeSet.empty
+    } else {
+      references -- inputSet
+    }
+  }
 
   /**
    * Runs [[transformExpressionsDown]] with `rule` on all expressions present