diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/ArrayPredictionContext.java b/runtime/Java/src/org/antlr/v4/runtime/atn/ArrayPredictionContext.java
index b9dbea66f..7a0f779db 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/ArrayPredictionContext.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/ArrayPredictionContext.java
@@ -71,18 +71,33 @@ public class ArrayPredictionContext extends PredictionContext {
 		return Arrays.binarySearch(invokingStates, invokingState);
 	}
 
-	public ArrayPredictionContext trim() {
-		int i = parents.length-1;
-		while ( i>=0 && parents[i]==null ) { i--; }
-		// i is last non-null index
-		if ( i < parents.length-1 ) {
-			int n = i+1;
-			return new ArrayPredictionContext(
-				Arrays.copyOf(parents, n),
-				Arrays.copyOf(invokingStates, n)
-			);
+	/** Find invokingState parameter (call it x) in this.invokingStates,
+	 *  if present.  Call pop on all x's parent(s) and then pull other
+	 *  elements from this context and merge into new context.
+	 */
+	@Override
+	public PredictionContext popAll(int invokingState, boolean fullCtx) {
+		int index = Arrays.binarySearch(this.invokingStates, invokingState);
+		if ( index < 0 ) {
+			return this;
 		}
-		return this;
+
+		PredictionContext newCtx = this.parents[index].popAll(invokingState, fullCtx);
+		for (int i = 0; i < this.invokingStates.length; i++) {
+			if (i == index) continue;
+			PredictionContext next;
+			if ( this.invokingStates[i] == EMPTY_FULL_CTX_INVOKING_STATE ) {
+				next = PredictionContext.EMPTY;
+			}
+			else {
+				next = new SingletonPredictionContext(this.parents[i],
+													  this.invokingStates[i]);
+			}
+			boolean rootIsWildcard = fullCtx;
+			newCtx = merge(newCtx, next, rootIsWildcard);
+		}
+
+		return newCtx;
 	}
 
 	@Override
diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java b/runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java
index a95c82b9a..d00cc8a63 100755
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/ParserATNSimulator.java
@@ -956,19 +956,21 @@ public class ParserATNSimulator<Symbol extends Token> extends ATNSimulator {
 			// run thru all possible stack tops in ctx
 			if ( config.context!=null && !config.context.isEmpty() ) {
 				for (SingletonPredictionContext ctx : config.context) {
-					if ( !ctx.isEmpty() ) {
+//					if ( !ctx.isEmpty() ) {
 						ATNState invokingState = atn.states.get(ctx.invokingState);
 						RuleTransition rt = (RuleTransition)invokingState.transition(0);
 						ATNState retState = rt.followState;
 						PredictionContext newContext = ctx.parent; // "pop" invoking state
-						ATNConfig c = new ATNConfig(retState, config.alt, newContext, config.semanticContext);
+						ATNConfig c = new ATNConfig(retState, config.alt, newContext,
+													config.semanticContext);
 						// While we have context to pop back from, we may have
 						// gotten that context AFTER having falling off a rule.
 						// Make sure we track that we are now out of context.
 						c.reachesIntoOuterContext = config.reachesIntoOuterContext;
 						assert depth > Integer.MIN_VALUE;
-						closure(c, configs, closureBusy, collectPredicates, greedy, loopsSimulateTailRecursion, depth - 1);
-					}
+						closure(c, configs, closureBusy, collectPredicates, greedy,
+								loopsSimulateTailRecursion, depth - 1);
+//					}
 					return;
 				}
 			}
@@ -989,16 +991,9 @@ public class ParserATNSimulator<Symbol extends Token> extends ATNSimulator {
 			}
 			else if ( config.state.getClass()==LoopEndState.class ) {
 				if ( debug ) System.out.println("Loop end; pop, stack="+config.context);
-				// run thru all possible stack tops in ctx
-				for (SingletonPredictionContext ctx : config.context) {
-					SingletonPredictionContext p = ctx;
-					LoopEndState end = (LoopEndState) config.state;
-					// pop all the way back until we don't see the loopback state anymore
-					while ( !p.isEmpty() && p.invokingState == end.loopBackStateNumber ) {
-						// TODO: BROKEN. can't figure out how to leave config.context
-//						p = config.context = config.context.parent; // "pop"
-					}
-				}
+				LoopEndState end = (LoopEndState)config.state;
+				// pop all the way back until we don't see the loopback state anymore
+				config.context = config.context.popAll(end.loopBackStateNumber, configs.fullCtx);
 			}
 		}
 
diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionContext.java b/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionContext.java
index 4518c3674..d3cf5fd67 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionContext.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionContext.java
@@ -15,7 +15,7 @@ import java.util.Map;
 
 public abstract class PredictionContext implements Iterable<SingletonPredictionContext> {
 	public static final EmptyPredictionContext EMPTY = new EmptyPredictionContext();
-	public static final int EMPTY_FULL_INVOKING_STATE = Integer.MAX_VALUE;
+	public static final int EMPTY_FULL_CTX_INVOKING_STATE = Integer.MAX_VALUE;
 
 	public static int globalNodeCount = 0;
 	public final int id = globalNodeCount++;
@@ -61,9 +61,14 @@ public abstract class PredictionContext implements Iterable<SingletonPredictionC
 		return this == EMPTY;
 	}
 
+	public abstract PredictionContext popAll(int invokingState, boolean fullCtx);
+
 	protected static int calculateParentHashCode(PredictionContext[] parents) {
 		int hashCode = 1;
 		for (PredictionContext context : parents) {
+			if ( context==null ) {
+				System.out.println("WHAT!? "+parents.toString());
+			}
 			hashCode = hashCode * 31 ^ context.hashCode();
 		}
 
@@ -184,7 +189,7 @@ public abstract class PredictionContext implements Iterable<SingletonPredictionC
 					String ruleName = recognizer.getRuleNames()[s.ruleIndex];
 					localBuffer.append(ruleName);
 				}
-				else if ( p.getInvokingState(index)!=EMPTY_FULL_INVOKING_STATE ) {
+				else if ( p.getInvokingState(index)!= EMPTY_FULL_CTX_INVOKING_STATE) {
 					if ( !p.isEmpty() ) {
 						if (localBuffer.length() > 1) {
 							// first char is '[', if more than that this isn't the first rule
@@ -277,14 +282,14 @@ public abstract class PredictionContext implements Iterable<SingletonPredictionC
 		else {
 			if ( a == EMPTY && b == EMPTY ) return EMPTY; // $ + $ = $
 			if ( a == EMPTY ) { // $ + x = [$,x]
-				int[] payloads = {EMPTY_FULL_INVOKING_STATE, b.invokingState};
+				int[] payloads = {EMPTY_FULL_CTX_INVOKING_STATE, b.invokingState};
 				PredictionContext[] parents = {null, b.parent};
 				ArrayPredictionContext joined =
 					new ArrayPredictionContext(parents, payloads);
 				return joined;
 			}
 			if ( b == EMPTY ) { // x + $ = [$,x] ($ is always first if present)
-				int[] payloads = {EMPTY_FULL_INVOKING_STATE, a.invokingState};
+				int[] payloads = {EMPTY_FULL_CTX_INVOKING_STATE, a.invokingState};
 				PredictionContext[] parents = {null, a.parent};
 				ArrayPredictionContext joined =
 					new ArrayPredictionContext(parents, payloads);
@@ -302,9 +307,9 @@ public abstract class PredictionContext implements Iterable<SingletonPredictionC
 		int i = 0; // walks a
 		int j = 0; // walks b
 		int k = 0; // walks M target array
-		int[] mergedPayloads = new int[a.invokingStates.length + b.invokingStates.length];
+
+		int[] mergedInvokingStates = new int[a.invokingStates.length + b.invokingStates.length];
 		PredictionContext[] mergedParents = new PredictionContext[a.invokingStates.length + b.invokingStates.length];
-		ArrayPredictionContext M = new ArrayPredictionContext(mergedParents, mergedPayloads);
 		while ( i<a.invokingStates.length && j<b.invokingStates.length ) {
 			if ( a.invokingStates[i]==b.invokingStates[j] ) {
 				// same payload; stack tops are equal
@@ -315,28 +320,28 @@ public abstract class PredictionContext implements Iterable<SingletonPredictionC
 				SingletonPredictionContext r = (SingletonPredictionContext)mergeSingletons(a_, b_, rootIsWildcard);
 				// if r is same as a_ or b_, we get to keep existing, else new
 				if ( r==a_ ) {
-					M.parents[k] = a.parents[i];
-					M.invokingStates[k] = a.invokingStates[i];
+					mergedParents[k] = a.parents[i];
+					mergedInvokingStates[k] = a.invokingStates[i];
 				}
 				else if ( r==b_ ) {
-					M.parents[k] = b.parents[j];
-					M.invokingStates[k] = b.invokingStates[j];
+					mergedParents[k] = b.parents[j];
+					mergedInvokingStates[k] = b.invokingStates[j];
 				}
 				else {
-					M.parents[k] = r.parent;
-					M.invokingStates[k] = r.invokingState;
+					mergedParents[k] = r.parent;
+					mergedInvokingStates[k] = r.invokingState;
 				}
 				i++; // hop over left one as usual
 				j++; // but also skip one in right side since we merge
 			}
 			else if ( a.invokingStates[i]<b.invokingStates[j] ) {
-				M.parents[k] = a.parents[i];
-				M.invokingStates[k] = a.invokingStates[i];
+				mergedParents[k] = a.parents[i];
+				mergedInvokingStates[k] = a.invokingStates[i];
 				i++;
 			}
 			else {
-				M.parents[k] = a.parents[j];
-				M.invokingStates[k] = b.invokingStates[j];
+				mergedParents[k] = a.parents[j];
+				mergedInvokingStates[k] = b.invokingStates[j];
 				j++;
 			}
 			k++;
@@ -344,23 +349,34 @@ public abstract class PredictionContext implements Iterable<SingletonPredictionC
 		// copy over any payloads remaining in either array
 		if (i < a.invokingStates.length) {
 			for (int p = i; p < a.invokingStates.length; p++) {
-				M.parents[k] = a.parents[p];
-				M.invokingStates[k] = a.invokingStates[p];
+				mergedParents[k] = a.parents[p];
+				mergedInvokingStates[k] = a.invokingStates[p];
 				k++;
 			}
 		}
 		else {
 			for (int p = j; p < b.invokingStates.length; p++) {
-				M.parents[k] = b.parents[p];
-				M.invokingStates[k] = b.invokingStates[p];
+				mergedParents[k] = b.parents[p];
+				mergedInvokingStates[k] = b.invokingStates[p];
 				k++;
 			}
 		}
+
 		// trim merged
-		if ( k < M.size() ) { // write index < last position; trim
-			M = M.trim();
+		if ( k < mergedParents.length ) { // write index < last position; trim
+			int p = mergedParents.length-1;
+			while ( p>=0 && mergedParents[p]==null ) { p--; }
+			// p is now last non-null index
+			if ( p < mergedParents.length-1 ) {
+				int n = p+1;
+				mergedParents = Arrays.copyOf(mergedParents, n);
+				mergedInvokingStates = Arrays.copyOf(mergedInvokingStates, n);
+			}
 		}
 
+		ArrayPredictionContext M =
+			new ArrayPredictionContext(mergedParents, mergedInvokingStates);
+
 		// TODO: if we created same array as a or b, return that instead
 
 		// TODO: make pass over all M parents; merge any equal() ones
diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/SingletonPredictionContext.java b/runtime/Java/src/org/antlr/v4/runtime/atn/SingletonPredictionContext.java
index 92afe67a9..7a29fdeaa 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/SingletonPredictionContext.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/SingletonPredictionContext.java
@@ -50,6 +50,14 @@ public class SingletonPredictionContext extends PredictionContext {
 		return this.invokingState == invokingState ? 0 : -1;
 	}
 
+	@Override
+	public PredictionContext popAll(int invokingState, boolean fullCtx) {
+		if ( invokingState == this.invokingState ) {
+			return parent.popAll(invokingState, fullCtx);
+		}
+		return this;
+	}
+
 	@Override
 	public boolean equals(Object o) {
 		if (this == o) {
diff --git a/tool/playground/T.g b/tool/playground/T.g
index 83e79ba0f..31bea6bda 100644
--- a/tool/playground/T.g
+++ b/tool/playground/T.g
@@ -1,8 +1,7 @@
 grammar T;
-s : a a a;
+s : a+ ;
 a : {false}? ID {System.out.println("alt 1");}
   | {true}?  ID {System.out.println("alt 2");}
-  | INT         {System.out.println("alt 3");}
   ;
 ID : 'a'..'z'+ ;
 INT : '0'..'9'+;