protected virtual void OptimizeExitBranches(DFAState d)
{
int sI = d.stateNumber;
if (_visited.Contains(sI))
{
return; // already visited
}
_visited.Add(sI);
int nAlts = d.dfa.NumberOfAlts;
for (int i = 0; i < d.NumberOfTransitions; i++)
{
Transition edge = (Transition)d.Transition(i);
DFAState edgeTarget = ((DFAState)edge.target);
/*
* [email protected](d.stateNumber+"-"+
* edge.label.toString(d.dfa.nfa.grammar)+"->"+
* edgeTarget.stateNumber);
*/
// if target is an accept state and that alt is the exit alt
if (edgeTarget.IsAcceptState &&
edgeTarget.GetUniquelyPredictedAlt() == nAlts)
{
/*
* [email protected]("ignoring transition "+i+" to max alt "+
* d.dfa.getNumberOfAlts());
*/
d.RemoveTransition(i);
i--; // back up one so that i++ of loop iteration stays within bounds
}
OptimizeExitBranches(edgeTarget);
}
}
protected virtual void OptimizeEOTBranches(DFAState state)
{
if (state == null)
{
throw new ArgumentNullException("state");
}
int sI = state.StateNumber;
if (_visited.Contains(sI))
{
return; // already visited
}
_visited.Add(sI);
for (int i = 0; i < state.NumberOfTransitions; i++)
{
Transition edge = state.GetTransition(i);
DFAState edgeTarget = ((DFAState)edge.Target);
/*
* [email protected](d.stateNumber+"-"+
* edge.label.toString(d.dfa.nfa.grammar)+"->"+
* edgeTarget.stateNumber);
*/
// if only one edge coming out, it is EOT, and target is accept prune
if (PRUNE_TOKENS_RULE_SUPERFLUOUS_EOT_EDGES &&
edgeTarget.IsAcceptState &&
state.NumberOfTransitions == 1 &&
edge.Label.IsAtom &&
edge.Label.Atom == Label.EOT)
{
//[email protected]("state "+d+" can be pruned");
// remove the superfluous EOT edge
state.RemoveTransition(i);
state.IsAcceptState = true; // make it an accept state
// force it to uniquely predict the originally predicted state
state.CachedUniquelyPredicatedAlt = edgeTarget.GetUniquelyPredictedAlt();
i--; // back up one so that i++ of loop iteration stays within bounds
}
OptimizeEOTBranches(edgeTarget);
}
}
/** figure out if this state eventually reaches an accept state and
* modify the instance variable 'reduced' to indicate if we find
* at least one state that cannot reach an accept state. This implies
* that the overall DFA is not reduced. This algorithm should be
* linear in the number of DFA states.
*
* The algorithm also tracks which alternatives have no accept state,
* indicating a nondeterminism.
*
* Also computes whether the DFA is cyclic.
*
* TODO: I call getUniquelyPredicatedAlt too much; cache predicted alt
*/
protected virtual bool DoesStateReachAcceptState( DFAState d )
{
if ( d.IsAcceptState )
{
// accept states have no edges emanating from them so we can return
d.AcceptStateReachable = Reachable.Yes;
// this alt is uniquely predicted, remove from nondeterministic list
int predicts = d.GetUniquelyPredictedAlt();
UnreachableAlts.Remove( predicts );
return true;
}
// avoid infinite loops
d.AcceptStateReachable = Reachable.Busy;
bool anEdgeReachesAcceptState = false;
// Visit every transition, track if at least one edge reaches stop state
// Cannot terminate when we know this state reaches stop state since
// all transitions must be traversed to set status of each DFA state.
for ( int i = 0; i < d.NumberOfTransitions; i++ )
{
Transition t = d.GetTransition( i );
DFAState edgeTarget = (DFAState)t.Target;
Reachable targetStatus = edgeTarget.AcceptStateReachable;
if ( targetStatus == Reachable.Busy )
{
// avoid cycles; they say nothing
_cyclic = true;
continue;
}
if ( targetStatus == Reachable.Yes )
{
// avoid unnecessary work
anEdgeReachesAcceptState = true;
continue;
}
if ( targetStatus == Reachable.No )
{
// avoid unnecessary work
continue;
}
// target must be REACHABLE_UNKNOWN (i.e., unvisited)
if ( DoesStateReachAcceptState( edgeTarget ) )
{
anEdgeReachesAcceptState = true;
// have to keep looking so don't break loop
// must cover all states even if we find a path for this state
}
}
if ( anEdgeReachesAcceptState )
{
d.AcceptStateReachable = Reachable.Yes;
}
else
{
d.AcceptStateReachable = Reachable.No;
_reduced = false;
}
return anEdgeReachesAcceptState;
}
protected virtual StringTemplate WalkFixedDFAGeneratingStateMachine(
TemplateGroup templates,
DFA dfa,
DFAState s,
int k )
{
//System.Console.Out.WriteLine( "walk " + s.stateNumber + " in dfa for decision " + dfa.decisionNumber );
if ( s.IsAcceptState )
{
StringTemplate dfaST2 = templates.GetInstanceOf( "dfaAcceptState" );
dfaST2.SetAttribute( "alt", s.GetUniquelyPredictedAlt() );
return dfaST2;
}
// the default templates for generating a state and its edges
// can be an if-then-else structure or a switch
string dfaStateName = "dfaState";
string dfaLoopbackStateName = "dfaLoopbackState";
string dfaOptionalBlockStateName = "dfaOptionalBlockState";
string dfaEdgeName = "dfaEdge";
if ( _parentGenerator.CanGenerateSwitch( s ) )
{
dfaStateName = "dfaStateSwitch";
dfaLoopbackStateName = "dfaLoopbackStateSwitch";
dfaOptionalBlockStateName = "dfaOptionalBlockStateSwitch";
dfaEdgeName = "dfaEdgeSwitch";
}
StringTemplate dfaST = templates.GetInstanceOf( dfaStateName );
if ( dfa.NFADecisionStartState.decisionStateType == NFAState.LOOPBACK )
{
dfaST = templates.GetInstanceOf( dfaLoopbackStateName );
}
else if ( dfa.NFADecisionStartState.decisionStateType == NFAState.OPTIONAL_BLOCK_START )
{
dfaST = templates.GetInstanceOf( dfaOptionalBlockStateName );
}
dfaST.SetAttribute( "k", k );
dfaST.SetAttribute( "stateNumber", s.StateNumber );
dfaST.SetAttribute( "semPredState",
s.IsResolvedWithPredicates );
/*
string description = dfa.getNFADecisionStartState().Description;
description = parentGenerator.target.getTargetStringLiteralFromString( description );
//System.Console.Out.WriteLine( "DFA: " + description + " associated with AST " + dfa.getNFADecisionStartState() );
if ( description != null )
{
dfaST.SetAttribute( "description", description );
}
*/
int EOTPredicts = NFA.INVALID_ALT_NUMBER;
DFAState EOTTarget = null;
//System.Console.Out.WriteLine( "DFA state " + s.stateNumber );
for ( int i = 0; i < s.NumberOfTransitions; i++ )
{
Transition edge = (Transition)s.GetTransition( i );
//System.Console.Out.WriteLine( "edge " + s.stateNumber + "-" + edge.label.ToString() + "->" + edge.target.stateNumber );
if ( edge.Label.Atom == Label.EOT )
{
// don't generate a real edge for EOT; track alt EOT predicts
// generate that prediction in the else clause as default case
EOTTarget = (DFAState)edge.Target;
EOTPredicts = EOTTarget.GetUniquelyPredictedAlt();
/*
System.Console.Out.WriteLine("DFA s"+s.stateNumber+" EOT goes to s"+
edge.target.stateNumber+" predicates alt "+
EOTPredicts);
*/
continue;
}
StringTemplate edgeST = templates.GetInstanceOf( dfaEdgeName );
// If the template wants all the label values delineated, do that
if ( edgeST.impl.TryGetFormalArgument( "labels" ) != null )
{
List<string> labels = edge.Label.Set.Select( value => _parentGenerator.GetTokenTypeAsTargetLabel( value ) ).ToList();
edgeST.SetAttribute( "labels", labels );
}
else
{ // else create an expression to evaluate (the general case)
edgeST.SetAttribute( "labelExpr",
_parentGenerator.GenLabelExpr( templates, edge, k ) );
}
// stick in any gated predicates for any edge if not already a pred
if ( !edge.Label.IsSemanticPredicate )
{
DFAState target = (DFAState)edge.Target;
SemanticContext preds =
target.GetGatedPredicatesInNFAConfigurations();
if ( preds != null )
{
//System.Console.Out.WriteLine( "preds=" + target.getGatedPredicatesInNFAConfigurations() );
StringTemplate predST = preds.GenExpr( _parentGenerator,
_parentGenerator.Templates,
dfa );
edgeST.SetAttribute( "predicates", predST );
}
}
StringTemplate targetST =
WalkFixedDFAGeneratingStateMachine( templates,
dfa,
(DFAState)edge.Target,
k + 1 );
edgeST.SetAttribute( "targetState", targetST );
dfaST.SetAttribute( "edges", edgeST );
//System.Console.Out.WriteLine( "back to DFA " + dfa.decisionNumber + "." + s.stateNumber );
}
// HANDLE EOT EDGE
if ( EOTPredicts != NFA.INVALID_ALT_NUMBER )
{
// EOT unique predicts an alt
dfaST.SetAttribute( "eotPredictsAlt", EOTPredicts );
}
else if ( EOTTarget != null && EOTTarget.NumberOfTransitions > 0 )
{
// EOT state has transitions so must split on predicates.
// Generate predicate else-if clauses and then generate
// NoViableAlt exception as else clause.
// Note: these predicates emanate from the EOT target state
// rather than the current DFAState s so the error message
// might be slightly misleading if you are looking at the
// state number. Predicates emanating from EOT targets are
// hoisted up to the state that has the EOT edge.
for ( int i = 0; i < EOTTarget.NumberOfTransitions; i++ )
{
Transition predEdge = (Transition)EOTTarget.GetTransition( i );
StringTemplate edgeST = templates.GetInstanceOf( dfaEdgeName );
edgeST.SetAttribute( "labelExpr",
_parentGenerator.GenSemanticPredicateExpr( templates, predEdge ) );
// the target must be an accept state
//System.Console.Out.WriteLine( "EOT edge" );
StringTemplate targetST =
WalkFixedDFAGeneratingStateMachine( templates,
dfa,
(DFAState)predEdge.Target,
k + 1 );
edgeST.SetAttribute( "targetState", targetST );
dfaST.SetAttribute( "edges", edgeST );
}
}
return dfaST;
}
