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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.spark.sql.catalyst.expressions
import scala.collection.mutable
import org.apache.spark.sql.catalyst.expressions.codegen.CodegenFallback
/**
* This class is used to compute equality of (sub)expression trees. Expressions can be added
* to this class and they subsequently query for expression equality. Expression trees are
* considered equal if for the same input(s), the same result is produced.
*/
class EquivalentExpressions {
/**
* Wrapper around an Expression that provides semantic equality.
*/
case class Expr(e: Expression) {
override def equals(o: Any): Boolean = o match {
case other: Expr => e.semanticEquals(other.e)
case _ => false
}
override val hashCode: Int = e.semanticHash()
}
// For each expression, the set of equivalent expressions.
private val equivalenceMap = mutable.HashMap.empty[Expr, mutable.MutableList[Expression]]
/**
* Adds each expression to this data structure, grouping them with existing equivalent
* expressions. Non-recursive.
* Returns true if there was already a matching expression.
*/
def addExpr(expr: Expression): Boolean = {
if (expr.deterministic) {
val e: Expr = Expr(expr)
val f = equivalenceMap.get(e)
if (f.isDefined) {
f.get += expr
true
} else {
equivalenceMap.put(e, mutable.MutableList(expr))
false
}
} else {
false
}
}
/**
* Adds the expression to this data structure recursively. Stops if a matching expression
* is found. That is, if `expr` has already been added, its children are not added.
* If ignoreLeaf is true, leaf nodes are ignored.
*/
def addExprTree(root: Expression, ignoreLeaf: Boolean = true): Unit = {
val skip = root.isInstanceOf[LeafExpression] && ignoreLeaf
// the children of CodegenFallback will not be used to generate code (call eval() instead)
if (!skip && !addExpr(root) && !root.isInstanceOf[CodegenFallback]) {
root.children.foreach(addExprTree(_, ignoreLeaf))
}
}
/**
* Returns all of the expression trees that are equivalent to `e`. Returns
* an empty collection if there are none.
*/
def getEquivalentExprs(e: Expression): Seq[Expression] = {
equivalenceMap.getOrElse(Expr(e), mutable.MutableList())
}
/**
* Returns all the equivalent sets of expressions.
*/
def getAllEquivalentExprs: Seq[Seq[Expression]] = {
equivalenceMap.values.map(_.toSeq).toSeq
}
/**
* Returns the state of the data structure as a string. If `all` is false, skips sets of
* equivalent expressions with cardinality 1.
*/
def debugString(all: Boolean = false): String = {
val sb: mutable.StringBuilder = new StringBuilder()
sb.append("Equivalent expressions:\n")
equivalenceMap.foreach { case (k, v) => {
if (all || v.length > 1) {
sb.append(" " + v.mkString(", ")).append("\n")
}
}}
sb.toString()
}
}
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