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full LL is always correct now, if slower. Stops prediction when resolvesToJustOneViableAlt(). SLL always uses heuristic

This commit is contained in:
Terence Parr 2012-10-14 13:25:34 -07:00
parent e7ece0e90a
commit 01bbce6952
5 changed files with 82 additions and 212 deletions
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258
runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java
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@ -44,7 +44,6 @@ import org.antlr.v4.runtime.misc.Interval;
import org.antlr.v4.runtime.misc.IntervalSet;
import org.antlr.v4.runtime.misc.NotNull;
import org.antlr.v4.runtime.misc.Nullable;
import org.stringtemplate.v4.misc.MultiMap;
import java.util.ArrayList;
import java.util.Arrays;
@ -268,9 +267,7 @@ public class ParserATNSimulator extends ATNSimulator {
public static int retry_with_context_predicts_same_as_alt = 0;
public static int retry_with_context_from_dfa = 0;
/** A Map that uses just the state and the stack context as the key.
* Used by needMoreLookaheadLL.
*/
/** A Map that uses just the state and the stack context as the key. */
class AltAndContextMap extends FlexibleHashMap<ATNConfig,BitSet> {
/** Code is function of (s, _, ctx, _) */
@Override
@ -297,18 +294,7 @@ public class ParserATNSimulator extends ATNSimulator {
@NotNull
public final DFA[] decisionToDFA;
/** Do only local context prediction (SLL(k) style). */
protected boolean SLL = false;
/** Tell the full LL prediction algorithm to pursue lookahead until
* it has uniquely predicted alternative without conflict or it's
* certain that it's found and ambiguous input sequence. For speed
* reasons, we terminate the prediction process early when this
* variable is false. When true, the prediction process will
* continue looking for the exact ambiguous sequence even if
* it has already figured out which alternative to predict.
*/
protected boolean exactAmbig = false;
protected PredictionMode mode = PredictionMode.LL;
/** Each prediction operation uses a cache for merge of prediction contexts.
* Don't keep around as it wastes huge amounts of memory. DoubleKeyMap
@ -458,7 +444,7 @@ public class ParserATNSimulator extends ATNSimulator {
loop:
while ( true ) {
if ( dfa_debug ) System.out.println("DFA state "+s.stateNumber+" LA(1)=="+getLookaheadName(input));
if ( s.requiresFullContext && !SLL ) {
if ( s.requiresFullContext && mode != PredictionMode.SLL ) {
if ( dfa_debug ) System.out.println("ctx sensitive state "+outerContext+" in "+s);
boolean fullCtx = true;
ATNConfigSet s0_closure =
@ -612,7 +598,6 @@ public class ParserATNSimulator extends ATNSimulator {
ATNConfigSet previous = s0.configs;
DFAState previousD = s0;
ATNConfigSet fullCtxSet;
if ( debug ) System.out.println("s0 = "+s0);
@ -685,30 +670,29 @@ public class ParserATNSimulator extends ATNSimulator {
}
else {
// MORE THAN ONE VIABLE ALTERNATIVE
if ( hasConflictingAltSet(altSubSets) && !hasStateAssociatedWithOneAlt(reach) ) {
if ( hasSLLConflictTerminatingPrediction(reach) ) {
D.configs.conflictingAlts = getConflictingAlts(reach);
if ( outerContext == ParserRuleContext.EMPTY || // in grammar start rule
!D.configs.dipsIntoOuterContext || // didn't fall out of rule
SLL ) // forcing SLL only
{
// SPECIAL CASE WHERE SLL KNOWS CONFLICT IS AMBIGUITY
if ( !D.configs.hasSemanticContext ) {
reportAmbiguity(dfa, D, startIndex, input.index(),
D.configs.conflictingAlts, D.configs);
if ( mode == PredictionMode.SLL ) {
// stop w/o failover for sure
if ( outerContext == ParserRuleContext.EMPTY || // in grammar start rule
!D.configs.dipsIntoOuterContext ) // didn't fall out of rule
{
// SPECIAL CASE WHERE SLL KNOWS CONFLICT IS AMBIGUITY
if ( !D.configs.hasSemanticContext ) {
reportAmbiguity(dfa, D, startIndex, input.index(),
D.configs.conflictingAlts, D.configs);
}
}
// always stop at D
D.isAcceptState = true;
D.prediction = D.configs.conflictingAlts.nextSetBit(0);
if ( debug ) System.out.println("RESOLVED TO "+D.prediction+" for "+D);
if ( debug ) System.out.println("SLL RESOLVED TO "+D.prediction+" for "+D);
predictedAlt = D.prediction;
// Falls through to check predicates below
}
else {
// SLL CONFLICT; RETRY WITH FULL LL CONTEXT
// (it's possible SLL with preds could resolve to single alt
// which would mean we could avoid full LL, but not worth
// code complexity.)
// RETRY WITH FULL LL CONTEXT
if ( debug ) System.out.println("RETRY with outerContext="+outerContext);
// don't look up context in cache now since we're just creating state D
ATNConfigSet s0_closure =
computeStartState(dfa.atnStartState,
outerContext,
@ -831,15 +815,12 @@ public class ParserATNSimulator extends ATNSimulator {
// System.out.println("altSubSets: "+altSubSets);
reach.uniqueAlt = getUniqueAlt(altSubSets);
if ( reach.uniqueAlt!=ATN.INVALID_ALT_NUMBER ) break;
if ( exactAmbig ) {
if ( mode == PredictionMode.LL_EXACT_AMBIG ) {
if ( allSubsetsConflict(altSubSets) && allSubsetsEqual(altSubSets) ) {
break;
}
}
else if ( (hasConflictingAltSet(altSubSets) &&
!hasStateAssociatedWithOneAlt(reach)) ||
resolvesToJustOneViableAlt(altSubSets) )
{
else if ( resolvesToJustOneViableAlt(altSubSets) ) {
break;
}
previous = reach;
@ -882,7 +863,7 @@ public class ParserATNSimulator extends ATNSimulator {
// reportAmbiguity(dfa, D, startIndex, input.index(), getConflictingAlts(reach), reach);
// }
if ( exactAmbig ) {
if ( mode == PredictionMode.LL_EXACT_AMBIG ) {
reportAmbiguity(dfa, D, startIndex, input.index(), getConflictingAlts(reach), reach);
}
@ -1440,9 +1421,9 @@ public class ParserATNSimulator extends ATNSimulator {
return false; # all sets conflict with len(viable_alts)>1, stop
*/
public boolean needMoreLookaheadSLL(@NotNull ATNConfigSet configs) {
public boolean hasSLLConflictTerminatingPrediction(@NotNull ATNConfigSet configs) {
// pure SLL mode parsing
if ( SLL ) {
if ( mode == PredictionMode.SLL ) {
if ( configs.hasSemanticContext ) {
// dup configs, tossing out semantic predicates
ATNConfigSet dup = new ATNConfigSet();
@ -1452,15 +1433,15 @@ public class ParserATNSimulator extends ATNSimulator {
}
configs = dup;
}
// do usual full LL termination test
return needMoreLookaheadLL(configs);
// now we have combined contexts for configs with dissimilar preds
}
// combined SLL+LL mode parsing
// System.out.println("SLL configs: "+configs);
// map (s,_,x,_) -> altset for all configs
// pure SLL or combined SLL+LL mode parsing
Collection<BitSet> altsets = getConflictingAltSubsets(configs);
// System.out.println("SLL altsets: "+altsets);
return hasNonConflictingAltSet(altsets);
boolean heuristic =
hasConflictingAltSet(altsets) && !hasStateAssociatedWithOneAlt(configs);
return heuristic;
}
public boolean allSubsetsConflict(Collection<BitSet> altsets) {
@ -1637,20 +1618,16 @@ public class ParserATNSimulator extends ATNSimulator {
return false; # len(viable_alts)==1, stop
*/
public boolean needMoreLookaheadLL(@NotNull ATNConfigSet configs) {
// System.out.println("configs: "+configs);
// map (s,_,x,_) -> altset for all configs
Collection<BitSet> altsets = getConflictingAltSubsets(configs);
// System.out.println("altsets: "+altsets);
BitSet viableAlts = new BitSet();
for (BitSet alts : altsets) {
int minAlt = alts.nextSetBit(0);
viableAlts.set(minAlt);
if ( viableAlts.cardinality()>1 ) { // more than 1 viable alt
// System.out.println("go; viableAlts="+viableAlts);
return true; // try using more lookahead
}
}
// System.out.println("stop");
return false; // len(viable_alts)==1, stop
}
@ -1712,33 +1689,29 @@ public class ParserATNSimulator extends ATNSimulator {
return false;
}
int n = 0;
boolean[] viableAlts = new boolean[100];
public boolean hasMoreThanOneViableAlt2(Collection<BitSet> altsets) {
n = 0;
Arrays.fill(viableAlts, false);
for (BitSet alts : altsets) {
int minAlt = alts.nextSetBit(0);
if ( !viableAlts[minAlt] ) n++;
viableAlts[minAlt] = true;
if ( n > 1 ) { // more than 1 viable alt
return true;
}
}
return false;
}
public BitSet getConflictingAlts(ATNConfigSet configs) {
Collection<BitSet> altsets = getConflictingAltSubsets(configs);
return getAlts(altsets);
}
/**
* From grammar:
s' : s s ;
s : x? | x ;
x : 'a' ;
config list: (4,1), (11,1,4), (7,1), (3,1,1), (4,1,1), (8,1,1), (7,1,1),
(8,2), (11,2,8), (11,1,[8 1])
state to config list:
3 -> (3,1,1)
4 -> (4,1), (4,1,1)
7 -> (7,1), (7,1,1)
8 -> (8,1,1), (8,2)
11 -> (11,1,4), (11,2,8), (11,1,8 1)
Walk and find state config lists with > 1 alt. If none, no conflict.
return null. Here, states 11 and 8 have lists with both alts 1 and 2.
Must check these config lists for conflicting configs.
Sam pointed out a problem with the previous definition, v3, of
ambiguous states. If we have another state associated with conflicting
alternatives, we should keep going. For example, the following grammar
@ -1773,118 +1746,8 @@ public class ParserATNSimulator extends ATNSimulator {
looking for input reasonably, I don't declare the state done. We
ignore a set of conflicting alts when we have an alternative
that we still need to pursue.
So, in summary, as long as there is a single configuration that is
not conflicting with any other configuration for that state, then
there is more input we can use to keep going. E.g.,
s->[(s,1,[x]), (s,2,[x]), (s,2,[y])]
s->[(s,1,_)]
s->[(s,1,[y]), (s,2,[x])]
Regardless of what goes on for the other states, this is
sufficient to force us to add this new state to the ATN-to-DFA work list.
TODO: split into "has nonconflict config--add to work list" and getambigalts functions
TODO: now we know contexts are merged, can we optimize? Use big int -> config array?
*/
@Nullable
public IntervalSet getConflictingAlts_old(@NotNull ATNConfigSet configs) {
if ( debug ) System.out.println("### check ambiguous "+configs);
// System.out.println("getConflictingAlts; set size="+configs.size());
// First get a list of configurations for each state.
// Most of the time, each state will have one associated configuration.
MultiMap<Integer, ATNConfig> stateToConfigListMap = new MultiMap<Integer, ATNConfig>();
Map<Integer, IntervalSet> stateToAltListMap = new HashMap<Integer, IntervalSet>();
for (ATNConfig c : configs) {
stateToConfigListMap.map(c.state.stateNumber, c);
IntervalSet alts = stateToAltListMap.get(c.state.stateNumber);
if ( alts==null ) {
alts = new IntervalSet();
stateToAltListMap.put(c.state.stateNumber, alts);
}
alts.add(c.alt);
}
// potential conflicts are states, s, with > 1 configurations and diff alts
// find all alts with potential conflicts
int numPotentialConflicts = 0;
IntervalSet altsToIgnore = new IntervalSet();
for (int state : stateToConfigListMap.keySet()) { // for each state
IntervalSet alts = stateToAltListMap.get(state);
if ( alts.size()==1 ) {
if ( !atn.states.get(state).onlyHasEpsilonTransitions() ) {
List<ATNConfig> configsPerState = stateToConfigListMap.get(state);
ATNConfig anyConfig = configsPerState.get(0);
altsToIgnore.add(anyConfig.alt);
if ( debug ) System.out.println("### one alt and all non-ep: "+configsPerState);
}
// remove state's configurations from further checking; no issues with them.
// (can't remove as it's concurrent modification; set to null)
// return null;
stateToConfigListMap.put(state, null);
}
else {
numPotentialConflicts++;
}
}
if ( debug ) System.out.println("### altsToIgnore: "+altsToIgnore);
if ( debug ) System.out.println("### stateToConfigListMap="+stateToConfigListMap);
if ( numPotentialConflicts==0 ) {
return null;
}
// compare each pair of configs in sets for states with > 1 alt in config list, looking for
// (s, i, ctx) and (s, j, ctx') where ctx==ctx' or one is suffix of the other.
IntervalSet ambigAlts = new IntervalSet();
for (int state : stateToConfigListMap.keySet()) {
List<ATNConfig> configsPerState = stateToConfigListMap.get(state);
if (configsPerState == null) continue;
IntervalSet alts = stateToAltListMap.get(state);
// Sam's correction to ambig def is here:
if ( !altsToIgnore.isNil() && alts.and(altsToIgnore).size()<=1 ) {
// System.err.println("ignoring alt since "+alts+"&"+altsToIgnore+
// ".size is "+alts.and(altsToIgnore).size());
continue;
}
int size = configsPerState.size();
for (int i = 0; i < size; i++) {
ATNConfig c = configsPerState.get(i);
for (int j = i+1; j < size; j++) {
ATNConfig d = configsPerState.get(j);
if ( c.alt != d.alt ) {
boolean conflicting = c.context.equals(d.context);
if ( conflicting ) {
if ( debug ) {
System.out.println("we reach state "+c.state.stateNumber+
" in rule "+
(parser !=null ? getRuleName(c.state.ruleIndex) :"n/a")+
" alts "+c.alt+","+d.alt+" from ctx "+c.context.toString(parser)
+" and "+ d.context.toString(parser));
}
ambigAlts.add(c.alt);
ambigAlts.add(d.alt);
}
}
}
}
}
if ( debug ) System.out.println("### ambigAlts="+ambigAlts);
if ( ambigAlts.isNil() ) return null;
// are any configs not represented in ambig alt sets
// for (ATNConfig config : configs) {
// if (!ambigAlts.contains(config.alt)) {
// return null;
// }
// }
return ambigAlts;
}
protected BitSet getConflictingAltsOrUniqueAlt(ATNConfigSet configs) {
BitSet conflictingAlts;
if ( configs.uniqueAlt!= ATN.INVALID_ALT_NUMBER ) {
@ -1897,27 +1760,6 @@ public class ParserATNSimulator extends ATNSimulator {
return conflictingAlts;
}
// protected int resolveToMinAlt(@NotNull DFAState D, IntervalSet conflictingAlts) {
// // kill dead alts so we don't chase them ever
//// killAlts(conflictingAlts, D.configset);
// D.prediction = conflictingAlts.getMinElement();
// if ( debug ) System.out.println("RESOLVED TO "+D.prediction+" for "+D);
// return D.prediction;
// }
protected int resolveNongreedyToExitBranch(@NotNull ATNConfigSet reach,
@NotNull IntervalSet conflictingAlts)
{
// exit branch is alt 2 always; alt 1 is entry or loopback branch
// since we're predicting, create DFA accept state for exit alt
int exitAlt = 2;
conflictingAlts.remove(exitAlt);
// kill dead alts so we don't chase them ever
// killAlts(conflictingAlts, reach);
if ( debug ) System.out.println("RESOLVED TO "+reach);
return exitAlt;
}
@NotNull
public String getTokenName(int t) {
if ( t==Token.EOF ) return "EOF";
@ -2078,11 +1920,9 @@ public class ParserATNSimulator extends ATNSimulator {
ambigAlts, configs);
}
public void setSLL(boolean SLL) {
this.SLL = SLL;
public void setPredictionMode(PredictionMode mode) {
this.mode = mode;
}
public void setExactAmbig(boolean exactAmbig) {
this.exactAmbig = exactAmbig;
}
public PredictionMode getPredictionMode() { return mode; }
}

27
runtime/Java/src/org/antlr/v4/runtime/atn/PredictionMode.java Normal file
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@ -0,0 +1,27 @@
package org.antlr.v4.runtime.atn;
public enum PredictionMode {
/** Do only local context prediction (SLL(k) style) and using
* heuristic which almost always works but is much faster
* than precise answer.
*/
SLL(1),
/** Full LL that always gets right answer */
LL(2),
/** Tell the full LL prediction algorithm to pursue lookahead until
* it has uniquely predicted alternative without conflict or it's
* certain that it's found and ambiguous input sequence. For speed
* reasons, we terminate the prediction process early when this
* variable is false. When true, the prediction process will
* continue looking for the exact ambiguous sequence even if
* it has already figured out which alternative to predict.
*/
LL_EXACT_AMBIG(4);
int v;
private PredictionMode(int v) {
this.v = v;
}
}

3
runtime/Java/src/org/antlr/v4/runtime/misc/TestRig.java
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@ -38,6 +38,7 @@ import org.antlr.v4.runtime.Parser;
import org.antlr.v4.runtime.ParserRuleContext;
import org.antlr.v4.runtime.Token;
import org.antlr.v4.runtime.TokenStream;
import org.antlr.v4.runtime.atn.PredictionMode;
import javax.print.PrintException;
import java.io.FileInputStream;
@ -224,7 +225,7 @@ public class TestRig {
}
if ( SLL ) {
parser.getInterpreter().setSLL(true);
parser.getInterpreter().setPredictionMode(PredictionMode.SLL);
}
parser.setTokenStream(tokens);

3
tool/playground/TestJava.java
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@ -6,6 +6,7 @@ import org.antlr.v4.runtime.ParserRuleContext;
import org.antlr.v4.runtime.Token;
import org.antlr.v4.runtime.atn.LexerATNSimulator;
import org.antlr.v4.runtime.atn.ParserATNSimulator;
import org.antlr.v4.runtime.atn.PredictionMode;
import java.io.File;
@ -127,7 +128,7 @@ class TestJava {
parser.setTokenStream(tokens);
if ( diag ) parser.addErrorListener(new DiagnosticErrorListener());
if ( SLL ) parser.getInterpreter().setSLL(true);
if ( SLL ) parser.getInterpreter().setPredictionMode(PredictionMode.SLL);
// start parsing at the compilationUnit rule
ParserRuleContext<Token> tree = parser.compilationUnit();
if ( showTree ) tree.inspect(parser);

3
tool/playground/TestJavaLR.java
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@ -36,6 +36,7 @@ import org.antlr.v4.runtime.ParserRuleContext;
import org.antlr.v4.runtime.Token;
import org.antlr.v4.runtime.atn.LexerATNSimulator;
import org.antlr.v4.runtime.atn.ParserATNSimulator;
import org.antlr.v4.runtime.atn.PredictionMode;
import java.io.File;
import java.util.ArrayList;
@ -260,7 +261,7 @@ class TestJavaLR {
JavaLRParser parser = new JavaLRParser(tokens);
if ( diag ) parser.addErrorListener(new DiagnosticErrorListener());
if ( bail ) parser.setErrorHandler(new BailErrorStrategy());
if ( SLL ) parser.getInterpreter().setSLL(true);
if ( SLL ) parser.getInterpreter().setPredictionMode(PredictionMode.SLL);
// start parsing at the compilationUnit rule
ParserRuleContext<Token> t = parser.compilationUnit();