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Optimize getSynValidOrSemInvalidAltThatFinishedDecisionEntryRule 

Implements the optimization identified by @garzon.

See antlr/antlr4#2366
This commit is contained in:
Sam Harwell 2019-02-11 11:05:56 -06:00
parent 1c6c62afc7
commit ae0bfc4d96
1 changed files with 32 additions and 46 deletions
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78
runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java
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@ -1297,65 +1297,51 @@ public class ParserATNSimulator extends ATNSimulator {
protected int getSynValidOrSemInvalidAltThatFinishedDecisionEntryRule(ATNConfigSet configs,
ParserRuleContext outerContext)
{
Pair<ATNConfigSet,ATNConfigSet> sets =
splitAccordingToSemanticValidity(configs, outerContext);
ATNConfigSet semValidConfigs = sets.a;
ATNConfigSet semInvalidConfigs = sets.b;
int alt = getAltThatFinishedDecisionEntryRule(semValidConfigs);
if ( alt!=ATN.INVALID_ALT_NUMBER ) { // semantically/syntactically viable path exists
return alt;
}
// Is there a syntactically valid path with a failed pred?
if ( semInvalidConfigs.size()>0 ) {
alt = getAltThatFinishedDecisionEntryRule(semInvalidConfigs);
if ( alt!=ATN.INVALID_ALT_NUMBER ) { // syntactically viable path exists
return alt;
}
}
return ATN.INVALID_ALT_NUMBER;
}
protected int getAltThatFinishedDecisionEntryRule(ATNConfigSet configs) {
IntervalSet alts = new IntervalSet();
// The minimum alternative that finished the decision entry rule and is
// valid according to semantic predicates.
int minAltSucceeded = Integer.MAX_VALUE;
// The minimum alternative that finished the decision entry rule but is
// not valid according to semantic predicates. Only considered if
// minAltSucceeded does not produce an alternative.
int minAltFailed = Integer.MAX_VALUE;
for (ATNConfig c : configs) {
if ( c.getOuterContextDepth()>0 || (c.state instanceof RuleStopState && c.context.hasEmptyPath()) ) {
alts.add(c.alt);
if (c.alt >= minAltSucceeded) {
// This alternative is no better than our current best
continue;
}
if (c.getOuterContextDepth() == 0 && !(c.state instanceof RuleStopState && c.context.hasEmptyPath())) {
// This configuration did not finish the decision entry rule
continue;
}
}
if ( alts.size()==0 ) return ATN.INVALID_ALT_NUMBER;
return alts.getMinElement();
}
/** Walk the list of configurations and split them according to
* those that have preds evaluating to true/false. If no pred, assume
* true pred and include in succeeded set. Returns Pair of sets.
*
* Create a new set so as not to alter the incoming parameter.
*
* Assumption: the input stream has been restored to the starting point
* prediction, which is where predicates need to evaluate.
*/
protected Pair<ATNConfigSet,ATNConfigSet> splitAccordingToSemanticValidity(
ATNConfigSet configs,
ParserRuleContext outerContext)
{
ATNConfigSet succeeded = new ATNConfigSet(configs.fullCtx);
ATNConfigSet failed = new ATNConfigSet(configs.fullCtx);
for (ATNConfig c : configs) {
if ( c.semanticContext!=SemanticContext.NONE ) {
boolean predicateEvaluationResult = evalSemanticContext(c.semanticContext, outerContext, c.alt, configs.fullCtx);
if ( predicateEvaluationResult ) {
succeeded.add(c);
minAltSucceeded = Math.min(minAltSucceeded, c.alt);
}
else {
failed.add(c);
minAltFailed = Math.min(minAltFailed, c.alt);
}
}
else {
succeeded.add(c);
minAltSucceeded = Math.min(minAltSucceeded, c.alt);
}
}
return new Pair<ATNConfigSet, ATNConfigSet>(succeeded,failed);
if (minAltSucceeded != Integer.MAX_VALUE) {
// A syntactically and semantically valid path to the end of the
// decision entry rule was found.
return minAltSucceeded;
}
else if (minAltFailed != Integer.MAX_VALUE) {
// A syntactically valid path to the end of the decision entry rule
// was found.
return minAltFailed;
}
else {
return ATN.INVALID_ALT_NUMBER;
}
}
/** Look through a list of predicate/alt pairs, returning alts for the