wipe out config lookup in ATNConfigSet when it goes readonly.

runtime/Java/src/org/antlr/v4/runtime/atn/ATNConfigSet.java

@@ -63,7 +63,7 @@ import java.util.Set;
    1 12
    1 119 <- max size
 
- 322 set size for SLL parser java.*
+ 322 set size for SLL parser java.* in DFA states:
 
  888 1
  411 54
@@ -142,6 +142,91 @@ import java.util.Set;
     1 9
     1 2
 
+ javalr, java.* all atnconfigsets; max size = 322, num sets = 269088
+
+ 114186 1    <-- optimize
+ 35712 6
+ 28081 78
+ 15252 54
+ 14171 56
+ 13159 12
+ 11810 88
+ 6873 86
+ 6158 80
+ 5169 4
+ 3773 118
+ 2350 16
+ 1002 112
+  915 28
+  898 44
+  734 2
+  632 62
+  575 8
+  566 59
+  474 20
+  388 84
+  343 48
+  333 55
+  328 47
+  311 41
+  306 38
+  277 81
+  263 79
+  255 66
+  245 90
+  245 87
+  234 50
+  224 10
+  220 60
+  194 64
+  186 32
+  184 82
+  150 18
+  125 7
+  121 132
+  116 30
+  103 51
+   95 114
+   84 36
+   82 40
+   78 22
+   77 89
+   55 9
+   53 174
+   48 152
+   44 67
+   44 5
+   42 115
+   41 58
+   38 122
+   37 134
+   34 13
+   34 116
+   29 45
+   29 3
+   29 24
+   27 144
+   26 146
+   25 91
+   24 113
+   20 27
+   ...
+
+ number with 1-9 elements:
+
+ 114186 1
+ 35712 6
+ 5169 4
+  734 2
+  575 8
+  125 7
+   55 9
+   44 5
+   29 3
+
+ Can cover 60% of sizes with size up to 6
+ Can cover 44% of sizes with size up to 4
+ Can cover 42% of sizes with size up to 1
  */
 public class ATNConfigSet implements Set<ATNConfig> {
 	/*
@@ -366,6 +451,7 @@ public class ATNConfigSet implements Set<ATNConfig> {
 
 	public void setReadonly(boolean readonly) {
 		this.readonly = readonly;
+		configLookup.clear();
 	}
 
 	@Override

runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java

@@ -651,9 +651,6 @@ public class ParserATNSimulator<Symbol extends Token> extends ATNSimulator {
 		}
 
 		if ( reach.size()==0 ) return null;
-
-//		reach.setConflictingAlts(getConflictingAlts(reach, false));
-//
 		return reach;
 	}
 

runtime/Java/src/org/antlr/v4/runtime/misc/Array2DHashSet.java

@@ -270,7 +270,7 @@ public class Array2DHashSet<T> implements Set<T> {
 
 	@Override
 	public void clear() {
-		buckets = (T[][])new Object[buckets.length][];
+		buckets = (T[][])new Object[INITAL_CAPACITY][];
 		n = 0;
 	}