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InliningContext.scala
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InliningContext.scala
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/*
* Copyright (c) 2002-2017 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.cypher.internal.compiler.v3_4.ast.rewriters
import org.neo4j.cypher.internal.util.v3_4.{Rewriter, TypedRewriter, bottomUp}
import org.neo4j.cypher.internal.compiler.v3_4.ast.rewriters.InliningContext._
import org.neo4j.cypher.internal.frontend.v3_4.ast.rewriters.copyVariables
import org.neo4j.cypher.internal.v3_4.expressions._
case class InliningContext(projections: Map[Variable, Expression] = Map.empty,
seenVariables: Set[Variable] = Set.empty,
usageCount: Map[Variable, Int] = Map.empty) {
def trackUsageOfVariable(id: Variable) =
copy(usageCount = usageCount + (id -> (usageCount.withDefaultValue(0)(id) + 1)))
def enterQueryPart(newProjections: Map[Variable, Expression]): InliningContext = {
val inlineExpressions = TypedRewriter[Expression](variableRewriter)
val containsAggregation = newProjections.values.exists(containsAggregate)
val shadowing = newProjections.filterKeys(seenVariables.contains).filter {
case (_, _: PathExpression) => false
case (key, value) => key != value
}
assert(shadowing.isEmpty, "Should have deduped by this point: " + shadowing)
val resultProjections = if (containsAggregation) {
projections
} else {
projections ++ newProjections.mapValues(inlineExpressions)
}
copy(projections = resultProjections, seenVariables = seenVariables ++ newProjections.keys)
}
def spoilVariable(variable: Variable): InliningContext =
copy(projections = projections - variable)
def variableRewriter: Rewriter = bottomUp(Rewriter.lift {
case variable: Variable if okToRewrite(variable) =>
projections.get(variable).map(_.endoRewrite(copyVariables)).getOrElse(variable.copyId)
})
def okToRewrite(i: Variable) =
projections.contains(i) &&
usageCount.withDefaultValue(0)(i) < INLINING_THRESHOLD
def patternRewriter: Rewriter = bottomUp(Rewriter.lift {
case node @ NodePattern(Some(ident), _, _) if okToRewrite(ident) =>
alias(ident) match {
case alias @ Some(_) => node.copy(variable = alias)(node.position)
case _ => node
}
case rel @ RelationshipPattern(Some(ident), _, _, _, _, _) if okToRewrite(ident) =>
alias(ident) match {
case alias @ Some(_) => rel.copy(variable = alias)(rel.position)
case _ => rel
}
})
def isAliasedVarible(variable: Variable) = alias(variable).nonEmpty
def alias(variable: Variable): Option[Variable] = projections.get(variable) match {
case Some(other: Variable) => Some(other.copyId)
case _ => None
}
}
object InliningContext {
private val INLINING_THRESHOLD = 3
}