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With inspiration from other libraries
/*
* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
* Use of this file is governed by the BSD 3-clause license that
* can be found in the LICENSE.txt file in the project root.
*/
package org.antlr.v4.automata;
import org.antlr.v4.misc.CharSupport;
import org.antlr.v4.runtime.atn.ATN;
import org.antlr.v4.runtime.atn.ATNState;
import org.antlr.v4.runtime.atn.AtomTransition;
import org.antlr.v4.runtime.atn.BlockEndState;
import org.antlr.v4.runtime.atn.CodePointTransitions;
import org.antlr.v4.runtime.atn.DecisionState;
import org.antlr.v4.runtime.atn.EpsilonTransition;
import org.antlr.v4.runtime.atn.NotSetTransition;
import org.antlr.v4.runtime.atn.RangeTransition;
import org.antlr.v4.runtime.atn.SetTransition;
import org.antlr.v4.runtime.atn.Transition;
import org.antlr.v4.runtime.misc.Interval;
import org.antlr.v4.runtime.misc.IntervalSet;
import org.antlr.v4.tool.ErrorType;
import org.antlr.v4.tool.Grammar;
import org.antlr.v4.tool.Rule;
import java.util.ArrayList;
import java.util.List;
/**
*
* @author Sam Harwell
*/
public class ATNOptimizer {
public static void optimize(Grammar g, ATN atn) {
optimizeSets(g, atn);
optimizeStates(atn);
}
private static void optimizeSets(Grammar g, ATN atn) {
if (g.isParser()) {
// parser codegen doesn't currently support SetTransition
return;
}
int removedStates = 0;
List decisions = atn.decisionToState;
for (DecisionState decision : decisions) {
if (decision.ruleIndex >= 0) {
Rule rule = g.getRule(decision.ruleIndex);
if (Character.isLowerCase(rule.name.charAt(0))) {
// parser codegen doesn't currently support SetTransition
continue;
}
}
IntervalSet setTransitions = new IntervalSet();
for (int i = 0; i < decision.getNumberOfTransitions(); i++) {
Transition epsTransition = decision.transition(i);
if (!(epsTransition instanceof EpsilonTransition)) {
continue;
}
if (epsTransition.target.getNumberOfTransitions() != 1) {
continue;
}
Transition transition = epsTransition.target.transition(0);
if (!(transition.target instanceof BlockEndState)) {
continue;
}
if (transition instanceof NotSetTransition) {
// TODO: not yet implemented
continue;
}
if (transition instanceof AtomTransition
|| transition instanceof RangeTransition
|| transition instanceof SetTransition)
{
setTransitions.add(i);
}
}
// due to min alt resolution policies, can only collapse sequential alts
for (int i = setTransitions.getIntervals().size() - 1; i >= 0; i--) {
Interval interval = setTransitions.getIntervals().get(i);
if (interval.length() <= 1) {
continue;
}
ATNState blockEndState = decision.transition(interval.a).target.transition(0).target;
IntervalSet matchSet = new IntervalSet();
for (int j = interval.a; j <= interval.b; j++) {
Transition matchTransition = decision.transition(j).target.transition(0);
if (matchTransition instanceof NotSetTransition) {
throw new UnsupportedOperationException("Not yet implemented.");
}
IntervalSet set = matchTransition.label();
List intervals = set.getIntervals();
int n = intervals.size();
for (int k = 0; k < n; k++) {
Interval setInterval = intervals.get(k);
int a = setInterval.a;
int b = setInterval.b;
if (a != -1 && b != -1) {
for (int v = a; v <= b; v++) {
if (matchSet.contains(v)) {
// TODO: Token is missing (i.e. position in source will not be displayed).
g.tool.errMgr.grammarError(ErrorType.CHARACTERS_COLLISION_IN_SET, g.fileName,
null,
CharSupport.getANTLRCharLiteralForChar(v),
CharSupport.getIntervalSetEscapedString(matchSet));
break;
}
}
}
}
matchSet.addAll(set);
}
Transition newTransition;
if (matchSet.getIntervals().size() == 1) {
if (matchSet.size() == 1) {
newTransition = CodePointTransitions.createWithCodePoint(blockEndState, matchSet.getMinElement());
}
else {
Interval matchInterval = matchSet.getIntervals().get(0);
newTransition = CodePointTransitions.createWithCodePointRange(blockEndState, matchInterval.a, matchInterval.b);
}
}
else {
newTransition = new SetTransition(blockEndState, matchSet);
}
decision.transition(interval.a).target.setTransition(0, newTransition);
for (int j = interval.a + 1; j <= interval.b; j++) {
Transition removed = decision.removeTransition(interval.a + 1);
atn.removeState(removed.target);
removedStates++;
}
}
}
// System.out.println("ATN optimizer removed " + removedStates + " states by collapsing sets.");
}
private static void optimizeStates(ATN atn) {
// System.out.println(atn.states);
List compressed = new ArrayList();
int i = 0; // new state number
for (ATNState s : atn.states) {
if ( s!=null ) {
compressed.add(s);
s.stateNumber = i; // reset state number as we shift to new position
i++;
}
}
// System.out.println(compressed);
// System.out.println("ATN optimizer removed " + (atn.states.size() - compressed.size()) + " null states.");
atn.states.clear();
atn.states.addAll(compressed);
}
private ATNOptimizer() {
}
}
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