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The ANTLR 4 grammar compiler.
/*
* Copyright (c) 2012 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.runtime.atn.ATN;
import org.antlr.v4.runtime.atn.ATNState;
import org.antlr.v4.runtime.atn.BlockEndState;
import org.antlr.v4.runtime.atn.EpsilonTransition;
import org.antlr.v4.runtime.atn.PlusLoopbackState;
import org.antlr.v4.runtime.atn.RuleTransition;
import org.antlr.v4.runtime.atn.StarLoopbackState;
import org.antlr.v4.runtime.atn.Transition;
import org.antlr.v4.runtime.misc.NotNull;
/**
*
* @author Terence Parr
*/
public class TailEpsilonRemover extends ATNVisitor {
@NotNull
private final ATN _atn;
public TailEpsilonRemover(@NotNull ATN atn) {
this._atn = atn;
}
@Override
public void visitState(@NotNull ATNState p) {
if (p.getStateType() == ATNState.BASIC && p.getNumberOfTransitions() == 1) {
ATNState q = p.transition(0).target;
if (p.transition(0) instanceof RuleTransition) {
q = ((RuleTransition) p.transition(0)).followState;
}
if (q.getStateType() == ATNState.BASIC) {
// we have p-x->q for x in {rule, action, pred, token, ...}
// if edge out of q is single epsilon to block end
// we can strip epsilon p-x->q-eps->r
Transition trans = q.transition(0);
if (q.getNumberOfTransitions() == 1 && trans instanceof EpsilonTransition) {
ATNState r = trans.target;
if (r instanceof BlockEndState || r instanceof PlusLoopbackState || r instanceof StarLoopbackState) {
// skip over q
if (p.transition(0) instanceof RuleTransition) {
((RuleTransition) p.transition(0)).followState = r;
}
else {
p.transition(0).target = r;
}
_atn.removeState(q);
}
}
}
}
}
}