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Author: cloud-fan

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

@@ -73,6 +73,8 @@ class EquivalentExpressions {
     //   1. CodegenFallback: it's children will not be used to generate code (call eval() instead)
     //   2. ReferenceToExpressions: it's kind of an explicit sub-expression elimination.
     val shouldRecurse = root match {
+      // TODO: some expressions implements `CodegenFallback` but can still do codegen,
+      // e.g. `CaseWhen`, we should support them.
       case _: CodegenFallback => false
       case _: ReferenceToExpressions => false
       case _ => true

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala

@@ -110,12 +110,16 @@ class CodegenContext {
   }
 
   def declareMutableStates(): String = {
+    // It's possible that we add same mutable state twice, e.g. the `mergeExpressions` in
+    // `TypedAggregateExpression`, we should call `distinct` here to remove the duplicated ones.
     mutableStates.distinct.map { case (javaType, variableName, _) =>
       s"private $javaType $variableName;"
     }.mkString("\n")
   }
 
   def initMutableStates(): String = {
+    // It's possible that we add same mutable state twice, e.g. the `mergeExpressions` in
+    // `TypedAggregateExpression`, we should call `distinct` here to remove the duplicated ones.
     mutableStates.distinct.map(_._3).mkString("\n")
   }