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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.vespa.indexinglanguage;
import com.yahoo.vespa.indexinglanguage.expressions.*;
import java.util.ArrayList;
import java.util.List;
/**
* Optimizes expressions by removing expressions that have no effect.
* Typical examples are statements that come before a statement that
* generates a new execution value without regard for the existing one.
*/
public class ExpressionOptimizer extends ExpressionConverter {
@Override
protected boolean shouldConvert(Expression exp) {
return exp instanceof StatementExpression;
}
@Override
protected Expression doConvert(Expression exp) {
return optimizeStatement((StatementExpression) exp);
}
private Expression optimizeStatement(StatementExpression statement) {
List<Expression> expressionList = new ArrayList<>();
List<Expression> candidateList = new ArrayList<>();
for (Expression exp : statement) {
if (ignoresInput(exp)) {
candidateList.clear();
}
candidateList.add(convert(exp));
if (hasSideEffect(exp)) {
expressionList.addAll(candidateList);
candidateList.clear();
}
}
expressionList.addAll(candidateList);
return new StatementExpression(expressionList);
}
static boolean hasSideEffect(Expression exp) {
HasSideEffectVisitor visitor = new HasSideEffectVisitor();
visitor.visit(exp);
return visitor.hasSideEffect;
}
private static class HasSideEffectVisitor extends ExpressionVisitor {
boolean hasSideEffect = false;
@Override
protected void doVisit(Expression exp) {
hasSideEffect |= exp instanceof OutputExpression ||
exp instanceof SetVarExpression ||
exp instanceof EchoExpression;
}
}
static boolean ignoresInput(Expression exp) {
if (exp instanceof SwitchExpression || exp instanceof ScriptExpression) {
return false; // Switch and script never ignores input.
}
if (exp instanceof CompositeExpression) {
return new IgnoresInputVisitor().ignoresInput(exp);
}
if (exp instanceof RandomExpression) {
return ((RandomExpression)exp).getMaxValue() != null;
}
return exp instanceof InputExpression ||
exp instanceof NowExpression ||
exp instanceof ConstantExpression ||
exp instanceof HostNameExpression ||
exp instanceof GetVarExpression;
}
private static class IgnoresInputVisitor extends ExpressionConverter {
private boolean ignoresInput = true;
private Expression root = null;
public boolean ignoresInput(Expression root) {
this.root = root;
convert(root);
return ignoresInput;
}
@Override
protected boolean shouldConvert(Expression exp) {
if (!ignoresInput) {
return true; // Answer found, skip ahead
}
if (exp == root) {
return false; // Skip root, check children
}
if (exp instanceof StatementExpression) {
for (Expression expression : (StatementExpression) exp) {
if (ExpressionOptimizer.ignoresInput(expression)) {
return true; // Skip children
}
}
ignoresInput = false;
return true; // Answer found, skip children
}
ignoresInput &= ExpressionOptimizer.ignoresInput(exp);
return true; // Children already checked. Skip them.
}
@Override
protected Expression doConvert(Expression exp) {
return exp;
}
}
}
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