[Truffle] Rename UndefinedPlaceholder U as it causes very long filena…

…mes.
jruby · Jan 19, 2015 · 8b84e49 · 8b84e49
1 parent 2d033dc
commit 8b84e49
Showing 24 changed files with 157 additions and 169 deletions.
diff --git a/core/src/main/java/org/jruby/truffle/nodes/RubyNode.java b/core/src/main/java/org/jruby/truffle/nodes/RubyNode.java
@@ -23,7 +23,7 @@
 import org.jruby.truffle.nodes.yield.YieldDispatchNode;
 import org.jruby.truffle.runtime.LexicalScope;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.core.*;
 
 import java.math.BigInteger;
@@ -174,8 +174,8 @@ public RubyEncoding executeRubyEncoding(VirtualFrame frame) throws UnexpectedRes
         return RubyTypesGen.RUBYTYPES.expectRubyEncoding(execute(frame));
     }
 
-    public UndefinedPlaceholder executeUndefinedPlaceholder(VirtualFrame frame) throws UnexpectedResultException {
-        return RubyTypesGen.RUBYTYPES.expectUndefinedPlaceholder(execute(frame));
+    public U executeUndefinedPlaceholder(VirtualFrame frame) throws UnexpectedResultException {
+        return RubyTypesGen.RUBYTYPES.expectU(execute(frame));
     }
 
     public RubyEncodingConverter executeRubyEncodingConverter(VirtualFrame frame) throws UnexpectedResultException {
@@ -285,7 +285,7 @@ public boolean isLexicalScope(Object value) {
 
     @SuppressWarnings("static-method")
     public boolean isUndefinedPlaceholder(Object value) {
-        return value instanceof UndefinedPlaceholder;
+        return value instanceof U;
     }
 
     @SuppressWarnings("static-method")

diff --git a/core/src/main/java/org/jruby/truffle/nodes/RubyTypes.java b/core/src/main/java/org/jruby/truffle/nodes/RubyTypes.java
@@ -10,17 +10,15 @@
 package org.jruby.truffle.nodes;
 
 import com.oracle.truffle.api.dsl.TypeSystem;
-import org.jruby.truffle.nodes.dispatch.DispatchAction;
-import org.jruby.truffle.runtime.LexicalScope;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.core.*;
 
 /**
  * The list of types and type conversions that the AST interpreter knows about and can specialise
  * using. Used by the DSL.
  */
 @TypeSystem({ //
-                UndefinedPlaceholder.class, //
+                U.class, //
                 boolean.class, //
                 byte.class, //
                 int.class, //

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/ArrayNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/ArrayNodes.java
@@ -35,7 +35,7 @@
 import org.jruby.truffle.nodes.core.ArrayNodesFactory.AtNodeFactory;
 import org.jruby.truffle.runtime.RubyArguments;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.control.BreakException;
 import org.jruby.truffle.runtime.control.NextException;
 import org.jruby.truffle.runtime.control.RaiseException;
@@ -654,7 +654,7 @@ public IndexNode(IndexNode prev) {
         }
 
         @Specialization
-        public Object index(RubyArray array, int index, UndefinedPlaceholder undefined) {
+        public Object index(RubyArray array, int index, U undefined) {
             return atNode.executeAt(array, index);
         }
 
@@ -715,7 +715,7 @@ public Object sliceObject(RubyArray array, int start, int length) {
         }
 
         @Specialization(guards = "isObject")
-        public Object sliceObject(RubyArray array, RubyRange.IntegerFixnumRange range, UndefinedPlaceholder undefined) {
+        public Object sliceObject(RubyArray array, RubyRange.IntegerFixnumRange range, U undefined) {
             notDesignedForCompilation();
 
             final int normalisedIndex = array.normaliseIndex(range.getBegin());
@@ -750,7 +750,7 @@ public IndexSetNode(IndexSetNode prev) {
         }
 
         @Specialization(guards = "isNull")
-        public Object setNullIntegerFixnum(RubyArray array, int index, int value, UndefinedPlaceholder unused) {
+        public Object setNullIntegerFixnum(RubyArray array, int index, int value, U unused) {
             if (index == 0) {
                 array.setStore(new int[]{value}, 1);
             } else {
@@ -762,7 +762,7 @@ public Object setNullIntegerFixnum(RubyArray array, int index, int value, Undefi
         }
 
         @Specialization(guards = "isNull")
-        public Object setNullLongFixnum(RubyArray array, int index, long value, UndefinedPlaceholder unused) {
+        public Object setNullLongFixnum(RubyArray array, int index, long value, U unused) {
             if (index == 0) {
                 array.setStore(new long[]{value}, 1);
             } else {
@@ -774,7 +774,7 @@ public Object setNullLongFixnum(RubyArray array, int index, long value, Undefine
         }
 
         @Specialization(guards = "isNull")
-        public Object setNullObject(RubyArray array, int index, Object value, UndefinedPlaceholder unused) {
+        public Object setNullObject(RubyArray array, int index, Object value, U unused) {
             notDesignedForCompilation();
 
             if (index == 0) {
@@ -787,7 +787,7 @@ public Object setNullObject(RubyArray array, int index, Object value, UndefinedP
         }
 
         @Specialization(guards = "isIntegerFixnum")
-        public int setIntegerFixnum(RubyArray array, int index, int value, UndefinedPlaceholder unused) {
+        public int setIntegerFixnum(RubyArray array, int index, int value, U unused) {
             final int normalisedIndex = array.normaliseIndex(index);
             int[] store = (int[]) array.getStore();
 
@@ -820,7 +820,7 @@ public int setIntegerFixnum(RubyArray array, int index, int value, UndefinedPlac
         }
 
         @Specialization(guards = "isIntegerFixnum")
-        public long setLongInIntegerFixnum(RubyArray array, int index, long value, UndefinedPlaceholder unused) {
+        public long setLongInIntegerFixnum(RubyArray array, int index, long value, U unused) {
             if (array.getAllocationSite() != null) {
                 array.getAllocationSite().convertedIntToLong();
             }
@@ -891,13 +891,13 @@ public RubyArray setIntegerFixnum(RubyArray array, int start, int length, RubyAr
         }
 
         @Specialization(guards = "isLongFixnum")
-        public int setLongFixnum(RubyArray array, int index, int value, UndefinedPlaceholder unused) {
+        public int setLongFixnum(RubyArray array, int index, int value, U unused) {
             setLongFixnum(array, index, (long) value, unused);
             return value;
         }
 
         @Specialization(guards = "isLongFixnum")
-        public long setLongFixnum(RubyArray array, int index, long value, UndefinedPlaceholder unused) {
+        public long setLongFixnum(RubyArray array, int index, long value, U unused) {
             final int normalisedIndex = array.normaliseIndex(index);
             long[] store = (long[]) array.getStore();
 
@@ -930,7 +930,7 @@ public long setLongFixnum(RubyArray array, int index, long value, UndefinedPlace
         }
 
         @Specialization(guards = "isFloat")
-        public double setFloat(RubyArray array, int index, double value, UndefinedPlaceholder unused) {
+        public double setFloat(RubyArray array, int index, double value, U unused) {
             final int normalisedIndex = array.normaliseIndex(index);
             double[] store = (double[]) array.getStore();
 
@@ -963,7 +963,7 @@ public double setFloat(RubyArray array, int index, double value, UndefinedPlaceh
         }
 
         @Specialization(guards = "isObject")
-        public Object setObject(RubyArray array, int index, Object value, UndefinedPlaceholder unused) {
+        public Object setObject(RubyArray array, int index, Object value, U unused) {
             final int normalisedIndex = array.normaliseIndex(index);
             Object[] store = (Object[]) array.getStore();
 
@@ -1008,14 +1008,14 @@ public Object setObject(RubyArray array, int start, int length, Object value) {
 
             if (begin >= array.getSize()) {
                 // We don't care of length in this case
-                return setObject(array, start, value, UndefinedPlaceholder.INSTANCE);
+                return setObject(array, start, value, U.INSTANCE);
             } else {
                 throw  new UnsupportedOperationException();
             }
         }
 
         @Specialization(guards = "isIntegerFixnum")
-        public RubyArray setIntegerFixnumRange(RubyArray array, RubyRange.IntegerFixnumRange range, RubyArray other, UndefinedPlaceholder unused) {
+        public RubyArray setIntegerFixnumRange(RubyArray array, RubyRange.IntegerFixnumRange range, RubyArray other, U unused) {
             if (range.doesExcludeEnd()) {
                 CompilerDirectives.transferToInterpreter();
                 throw new UnsupportedOperationException();
@@ -1898,52 +1898,52 @@ public InitializeNode(InitializeNode prev) {
         }
 
         @Specialization
-        public RubyArray initialize(RubyArray array, int size, UndefinedPlaceholder defaultValue, UndefinedPlaceholder block) {
+        public RubyArray initialize(RubyArray array, int size, U defaultValue, U block) {
             return initialize(array, size, getContext().getCoreLibrary().getNilObject(), block);
         }
 
         @Specialization
-        public RubyArray initialize(RubyArray array, long size, UndefinedPlaceholder defaultValue, UndefinedPlaceholder block) {
+        public RubyArray initialize(RubyArray array, long size, U defaultValue, U block) {
             if (size > Integer.MAX_VALUE) {
                 throw new IllegalStateException();
             }
             return initialize(array, (int) size, getContext().getCoreLibrary().getNilObject(), block);
         }
 
         @Specialization
-        public RubyArray initialize(RubyArray array, int size, int defaultValue, UndefinedPlaceholder block) {
+        public RubyArray initialize(RubyArray array, int size, int defaultValue, U block) {
             final int[] store = new int[size];
             Arrays.fill(store, defaultValue);
             array.setStore(store, size);
             return array;
         }
 
         @Specialization
-        public RubyArray initialize(RubyArray array, int size, long defaultValue, UndefinedPlaceholder block) {
+        public RubyArray initialize(RubyArray array, int size, long defaultValue, U block) {
             final long[] store = new long[size];
             Arrays.fill(store, defaultValue);
             array.setStore(store, size);
             return array;
         }
 
         @Specialization
-        public RubyArray initialize(RubyArray array, int size, double defaultValue, UndefinedPlaceholder block) {
+        public RubyArray initialize(RubyArray array, int size, double defaultValue, U block) {
             final double[] store = new double[size];
             Arrays.fill(store, defaultValue);
             array.setStore(store, size);
             return array;
         }
 
         @Specialization
-        public RubyArray initialize(RubyArray array, int size, Object defaultValue, UndefinedPlaceholder block) {
+        public RubyArray initialize(RubyArray array, int size, Object defaultValue, U block) {
             final Object[] store = new Object[size];
             Arrays.fill(store, defaultValue);
             array.setStore(store, size);
             return array;
         }
 
         @Specialization
-        public RubyArray initialize(VirtualFrame frame, RubyArray array, int size, UndefinedPlaceholder defaultValue, RubyProc block) {
+        public RubyArray initialize(VirtualFrame frame, RubyArray array, int size, U defaultValue, RubyProc block) {
             Object store = arrayBuilder.start(size);
 
             int count = 0;
@@ -1966,7 +1966,7 @@ public RubyArray initialize(VirtualFrame frame, RubyArray array, int size, Undef
         }
 
         @Specialization
-        public RubyArray initialize(RubyArray array, RubyArray copy, UndefinedPlaceholder defaultValue, UndefinedPlaceholder block) {
+        public RubyArray initialize(RubyArray array, RubyArray copy, U defaultValue, U block) {
             notDesignedForCompilation();
             array.setStore(copy.slowToArray(), copy.getSize());
             return array;
@@ -2094,7 +2094,7 @@ public Object inject(VirtualFrame frame, RubyArray array, Object initial, RubyPr
         }
 
         @Specialization
-        public Object inject(VirtualFrame frame, RubyArray array, RubySymbol symbol, UndefinedPlaceholder unused) {
+        public Object inject(VirtualFrame frame, RubyArray array, RubySymbol symbol, U unused) {
             notDesignedForCompilation();
 
             final Object[] store = array.slowToArray();
@@ -2214,7 +2214,7 @@ public JoinNode(JoinNode prev) {
         }
 
         @Specialization
-        public RubyString join(RubyArray array, UndefinedPlaceholder unused) {
+        public RubyString join(RubyArray array, U unused) {
             Object separator = getContext().getCoreLibrary().getGlobalVariablesObject().getInstanceVariable("$,");
             if (separator == getContext().getCoreLibrary().getNilObject()) {
                 separator = getContext().makeString("");
@@ -3434,15 +3434,15 @@ public SortNode(SortNode prev) {
         }
 
         @Specialization(guards = "isNull")
-        public RubyArray sortNull(RubyArray array, UndefinedPlaceholder block) {
+        public RubyArray sortNull(RubyArray array, U block) {
             notDesignedForCompilation();
 
             return new RubyArray(getContext().getCoreLibrary().getArrayClass());
         }
 
         @ExplodeLoop
         @Specialization(guards = {"isIntegerFixnum", "isSmall"})
-        public RubyArray sortVeryShortIntegerFixnum(VirtualFrame frame, RubyArray array, UndefinedPlaceholder block) {
+        public RubyArray sortVeryShortIntegerFixnum(VirtualFrame frame, RubyArray array, U block) {
             final int[] store = (int[]) array.getStore();
 
             final int size = array.getSize();
@@ -3467,7 +3467,7 @@ public RubyArray sortVeryShortIntegerFixnum(VirtualFrame frame, RubyArray array,
         }
 
         @Specialization(guards = "isIntegerFixnum")
-        public RubyArray sortIntegerFixnum(VirtualFrame frame, RubyArray array, UndefinedPlaceholder block) {
+        public RubyArray sortIntegerFixnum(VirtualFrame frame, RubyArray array, U block) {
             notDesignedForCompilation();
 
             final Object[] boxed = ArrayUtils.box((int[]) array.getStore());
@@ -3478,7 +3478,7 @@ public RubyArray sortIntegerFixnum(VirtualFrame frame, RubyArray array, Undefine
 
         @ExplodeLoop
         @Specialization(guards = {"isLongFixnum", "isSmall"})
-        public RubyArray sortVeryShortLongFixnum(VirtualFrame frame, RubyArray array, UndefinedPlaceholder block) {
+        public RubyArray sortVeryShortLongFixnum(VirtualFrame frame, RubyArray array, U block) {
             final long[] store = (long[]) array.getStore();
 
             final int size = array.getSize();
@@ -3503,7 +3503,7 @@ public RubyArray sortVeryShortLongFixnum(VirtualFrame frame, RubyArray array, Un
         }
 
         @Specialization(guards = "isLongFixnum")
-        public RubyArray sortLongFixnum(VirtualFrame frame, RubyArray array, UndefinedPlaceholder block) {
+        public RubyArray sortLongFixnum(VirtualFrame frame, RubyArray array, U block) {
             notDesignedForCompilation();
 
             final Object[] boxed = ArrayUtils.box((long[]) array.getStore());
@@ -3513,7 +3513,7 @@ public RubyArray sortLongFixnum(VirtualFrame frame, RubyArray array, UndefinedPl
         }
 
         @Specialization(guards = "isFloat")
-        public RubyArray sortDouble(VirtualFrame frame, RubyArray array, UndefinedPlaceholder block) {
+        public RubyArray sortDouble(VirtualFrame frame, RubyArray array, U block) {
             notDesignedForCompilation();
 
             final Object[] boxed = ArrayUtils.box((double[]) array.getStore());
@@ -3523,7 +3523,7 @@ public RubyArray sortDouble(VirtualFrame frame, RubyArray array, UndefinedPlaceh
         }
 
         @Specialization(guards = {"isObject", "isSmall"})
-        public RubyArray sortVeryShortObject(VirtualFrame frame, RubyArray array, UndefinedPlaceholder block) {
+        public RubyArray sortVeryShortObject(VirtualFrame frame, RubyArray array, U block) {
             final Object[] store = (Object[]) array.getStore();
 
             // Insertion sort
@@ -3545,7 +3545,7 @@ public RubyArray sortVeryShortObject(VirtualFrame frame, RubyArray array, Undefi
         }
 
         @Specialization(guards = "isObject")
-        public RubyArray sortObject(VirtualFrame frame, RubyArray array, UndefinedPlaceholder block) {
+        public RubyArray sortObject(VirtualFrame frame, RubyArray array, U block) {
             notDesignedForCompilation();
 
             final Object[] store = Arrays.copyOf((Object[]) array.getStore(), array.getSize());

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/BasicObjectNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/BasicObjectNodes.java
@@ -24,7 +24,7 @@
 import org.jruby.truffle.nodes.yield.YieldDispatchHeadNode;
 import org.jruby.truffle.runtime.ObjectIDOperations;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.control.RaiseException;
 import org.jruby.truffle.runtime.core.*;
 import org.jruby.truffle.runtime.util.ArrayUtils;
@@ -232,14 +232,14 @@ public InstanceEvalNode(InstanceEvalNode prev) {
         }
 
         @Specialization
-        public Object instanceEval(VirtualFrame frame, Object receiver, RubyString string, UndefinedPlaceholder block) {
+        public Object instanceEval(VirtualFrame frame, Object receiver, RubyString string, U block) {
             notDesignedForCompilation();
 
             return getContext().eval(string.getBytes(), receiver, this);
         }
 
         @Specialization
-        public Object instanceEval(VirtualFrame frame, Object receiver, UndefinedPlaceholder string, RubyProc block) {
+        public Object instanceEval(VirtualFrame frame, Object receiver, U string, RubyProc block) {
             notDesignedForCompilation();
 
             return yield.dispatchWithModifiedSelf(frame, block, receiver);
@@ -259,7 +259,7 @@ public MethodMissingNode(MethodMissingNode prev) {
         }
 
         @Specialization
-        public Object methodMissing(Object self, Object[] args, @SuppressWarnings("unused") UndefinedPlaceholder block) {
+        public Object methodMissing(Object self, Object[] args, @SuppressWarnings("unused") U block) {
             notDesignedForCompilation();
 
             return methodMissing(self, args, (RubyProc) null);
@@ -325,7 +325,7 @@ public SendNode(SendNode prev) {
         }
 
         @Specialization
-        public Object send(VirtualFrame frame, Object self, Object[] args, UndefinedPlaceholder block) {
+        public Object send(VirtualFrame frame, Object self, Object[] args, U block) {
             return send(frame, self, args, (RubyProc) null);
         }
 

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/ClassNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/ClassNodes.java
@@ -16,10 +16,9 @@
 import org.jruby.runtime.Visibility;
 import org.jruby.truffle.nodes.RubyNode;
 import org.jruby.truffle.nodes.dispatch.CallDispatchHeadNode;
-import org.jruby.truffle.nodes.dispatch.DispatchHeadNode;
 import org.jruby.truffle.nodes.dispatch.DispatchHeadNodeFactory;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.control.RaiseException;
 import org.jruby.truffle.runtime.core.RubyBasicObject;
 import org.jruby.truffle.runtime.core.RubyClass;
@@ -74,7 +73,7 @@ public NewNode(NewNode prev) {
         }
 
         @Specialization
-        public RubyBasicObject newInstance(VirtualFrame frame, RubyClass rubyClass, Object[] args, @SuppressWarnings("unused") UndefinedPlaceholder block) {
+        public RubyBasicObject newInstance(VirtualFrame frame, RubyClass rubyClass, Object[] args, @SuppressWarnings("unused") U block) {
             return doNewInstance(frame, rubyClass, args, null);
         }
 
@@ -112,18 +111,18 @@ void moduleInitialize(VirtualFrame frame, RubyClass rubyClass, RubyProc block) {
         }
 
         @Specialization
-        public RubyClass initialize(RubyClass rubyClass, UndefinedPlaceholder superclass, UndefinedPlaceholder block) {
+        public RubyClass initialize(RubyClass rubyClass, U superclass, U block) {
             return initialize(rubyClass, getContext().getCoreLibrary().getObjectClass(), block);
         }
 
         @Specialization
-        public RubyClass initialize(RubyClass rubyClass, RubyClass superclass, UndefinedPlaceholder block) {
+        public RubyClass initialize(RubyClass rubyClass, RubyClass superclass, U block) {
             rubyClass.initialize(superclass);
             return rubyClass;
         }
 
         @Specialization
-        public RubyClass initialize(VirtualFrame frame, RubyClass rubyClass, UndefinedPlaceholder superclass, RubyProc block) {
+        public RubyClass initialize(VirtualFrame frame, RubyClass rubyClass, U superclass, RubyProc block) {
             return initialize(frame, rubyClass, getContext().getCoreLibrary().getObjectClass(), block);
         }
 

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/CoreMethodNodeManager.java b/core/src/main/java/org/jruby/truffle/nodes/core/CoreMethodNodeManager.java
@@ -168,7 +168,7 @@ private static RubyRootNode makeGenericMethod(RubyContext context, MethodDetails
         }
 
         if (methodDetails.getMethodAnnotation().needsBlock()) {
-            argumentsNodes.add(new ReadBlockNode(context, sourceSection, UndefinedPlaceholder.INSTANCE));
+            argumentsNodes.add(new ReadBlockNode(context, sourceSection, U.INSTANCE));
         }
 
         RubyNode methodNode = null;

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/ExceptionNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/ExceptionNodes.java
@@ -13,7 +13,7 @@
 import com.oracle.truffle.api.source.SourceSection;
 import org.jruby.truffle.runtime.RubyCallStack;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.core.RubyArray;
 import org.jruby.truffle.runtime.core.RubyException;
 import org.jruby.truffle.runtime.core.RubyNilClass;
@@ -34,7 +34,7 @@ public InitializeNode(InitializeNode prev) {
         }
 
         @Specialization
-        public RubyNilClass initialize(RubyException exception, UndefinedPlaceholder message) {
+        public RubyNilClass initialize(RubyException exception, U message) {
             notDesignedForCompilation();
 
             exception.initialize(getContext().makeString(" "), RubyCallStack.getBacktrace(this));

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/FileNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/FileNodes.java
@@ -15,7 +15,7 @@
 import com.oracle.truffle.api.source.SourceSection;
 import jnr.posix.FileStat;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.core.*;
 import org.jruby.util.ByteList;
 
@@ -232,7 +232,7 @@ public ExpandPathNode(ExpandPathNode prev) {
         }
 
         @Specialization
-        public RubyString expandPath(RubyString path, @SuppressWarnings("unused") UndefinedPlaceholder dir) {
+        public RubyString expandPath(RubyString path, @SuppressWarnings("unused") U dir) {
             return getContext().makeString(RubyFile.expandPath(path.toString()));
         }
 

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/FixnumLowerNode.java b/core/src/main/java/org/jruby/truffle/nodes/core/FixnumLowerNode.java
@@ -13,7 +13,7 @@
 import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.nodes.UnexpectedResultException;
 import org.jruby.truffle.nodes.RubyNode;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.control.RaiseException;
 import org.jruby.truffle.runtime.core.CoreLibrary;
 import org.jruby.truffle.runtime.core.RubyBasicObject;
@@ -70,7 +70,7 @@ public Object execute(VirtualFrame frame) {
             }
         }
 
-        if (hasSeenUndefined && value instanceof UndefinedPlaceholder) {
+        if (hasSeenUndefined && value instanceof U) {
             return value;
         }
 
@@ -104,7 +104,7 @@ public Object execute(VirtualFrame frame) {
             }
         }
 
-        if (value instanceof UndefinedPlaceholder) {
+        if (value instanceof U) {
             hasSeenUndefined = true;
             return value;
         }
@@ -179,7 +179,7 @@ public RubyRange.LongFixnumRange executeLongFixnumRange(VirtualFrame frame) thro
     }
 
     @Override
-    public UndefinedPlaceholder executeUndefinedPlaceholder(VirtualFrame frame) throws UnexpectedResultException {
+    public U executeUndefinedPlaceholder(VirtualFrame frame) throws UnexpectedResultException {
         try {
             return super.executeUndefinedPlaceholder(frame);
         } catch (UnexpectedResultException e) {

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/FixnumNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/FixnumNodes.java
@@ -19,11 +19,10 @@
 import com.oracle.truffle.api.utilities.ConditionProfile;
 import org.jruby.truffle.nodes.RubyNode;
 import org.jruby.truffle.nodes.dispatch.CallDispatchHeadNode;
-import org.jruby.truffle.nodes.dispatch.DispatchHeadNode;
 import org.jruby.truffle.nodes.dispatch.DispatchHeadNodeFactory;
 import org.jruby.truffle.nodes.methods.UnsupportedOperationBehavior;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.control.RaiseException;
 import org.jruby.truffle.runtime.core.RubyArray;
 import org.jruby.truffle.runtime.core.RubyBasicObject;
@@ -1621,13 +1620,13 @@ public ToSNode(ToSNode prev) {
 
         @CompilerDirectives.TruffleBoundary
         @Specialization
-        public RubyString toS(int n, UndefinedPlaceholder undefined) {
+        public RubyString toS(int n, U undefined) {
             return getContext().makeString(Integer.toString(n));
         }
 
         @CompilerDirectives.TruffleBoundary
         @Specialization
-        public RubyString toS(long n, UndefinedPlaceholder undefined) {
+        public RubyString toS(long n, U undefined) {
             return getContext().makeString(Long.toString(n));
         }
 

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/HashNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/HashNodes.java
@@ -23,7 +23,7 @@
 import org.jruby.truffle.nodes.yield.YieldDispatchHeadNode;
 import org.jruby.truffle.runtime.DebugOperations;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.core.*;
 import org.jruby.truffle.runtime.hash.Entry;
 import org.jruby.truffle.runtime.hash.HashOperations;
@@ -606,23 +606,23 @@ public InitializeNode(InitializeNode prev) {
         }
 
         @Specialization
-        public RubyNilClass initialize(RubyHash hash, UndefinedPlaceholder defaultValue, UndefinedPlaceholder block) {
+        public RubyNilClass initialize(RubyHash hash, U defaultValue, U block) {
             notDesignedForCompilation();
             hash.setStore(null, 0, null, null);
             hash.setDefaultBlock(null);
             return getContext().getCoreLibrary().getNilObject();
         }
 
         @Specialization
-        public RubyNilClass initialize(RubyHash hash, UndefinedPlaceholder defaultValue, RubyProc block) {
+        public RubyNilClass initialize(RubyHash hash, U defaultValue, RubyProc block) {
             notDesignedForCompilation();
             hash.setStore(null, 0, null, null);
             hash.setDefaultBlock(block);
             return getContext().getCoreLibrary().getNilObject();
         }
 
         @Specialization
-        public RubyNilClass initialize(RubyHash hash, Object defaultValue, UndefinedPlaceholder block) {
+        public RubyNilClass initialize(RubyHash hash, Object defaultValue, U block) {
             notDesignedForCompilation();
             hash.setDefaultValue(defaultValue);
             return getContext().getCoreLibrary().getNilObject();
@@ -1044,7 +1044,7 @@ public DefaultNode(DefaultNode prev) {
         }
 
         @Specialization
-        public Object defaultElement(VirtualFrame frame, RubyHash hash, UndefinedPlaceholder undefined) {
+        public Object defaultElement(VirtualFrame frame, RubyHash hash, U undefined) {
             Object ret = hash.getDefaultValue();
 
             // TODO (nirvdrum Dec. 1, 2014): This needs to evaluate the defaultProc if it exists before it tries defaultValue.

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/IntegerNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/IntegerNodes.java
@@ -15,7 +15,7 @@
 import com.oracle.truffle.api.source.SourceSection;
 import com.oracle.truffle.api.utilities.BranchProfile;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.control.BreakException;
 import org.jruby.truffle.runtime.control.NextException;
 import org.jruby.truffle.runtime.control.RedoException;
@@ -92,7 +92,7 @@ public TimesNode(TimesNode prev) {
         }
 
         @Specialization
-        public RubyArray times(VirtualFrame frame, int n, UndefinedPlaceholder block) {
+        public RubyArray times(VirtualFrame frame, int n, U block) {
             notDesignedForCompilation();
 
             final int[] array = new int[n];

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/KernelNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/KernelNodes.java
@@ -355,7 +355,7 @@ public CallerNode(CallerNode prev) {
         }
 
         @Specialization
-        public Object caller(UndefinedPlaceholder omit) {
+        public Object caller(U omit) {
             return caller(1);
         }
 
@@ -561,21 +561,21 @@ protected RubyBinding getCallerBinding(VirtualFrame frame) {
         }
 
         @Specialization
-        public Object eval(VirtualFrame frame, RubyString source, UndefinedPlaceholder binding, UndefinedPlaceholder filename, UndefinedPlaceholder lineNumber) {
+        public Object eval(VirtualFrame frame, RubyString source, U binding, U filename, U lineNumber) {
             notDesignedForCompilation();
 
             return eval(source, getCallerBinding(frame), filename, lineNumber);
         }
 
         @Specialization
-        public Object eval(RubyString source, RubyBinding binding, UndefinedPlaceholder filename, UndefinedPlaceholder lineNumber) {
+        public Object eval(RubyString source, RubyBinding binding, U filename, U lineNumber) {
             notDesignedForCompilation();
 
             return getContext().eval(source.getBytes(), binding, this);
         }
 
         @Specialization
-        public Object eval(RubyString source, RubyBinding binding, RubyString filename, UndefinedPlaceholder lineNumber) {
+        public Object eval(RubyString source, RubyBinding binding, RubyString filename, U lineNumber) {
             notDesignedForCompilation();
 
             // TODO (nirvdrum Dec. 29, 2014) Do something with the supplied filename.
@@ -591,14 +591,14 @@ public Object eval(RubyString source, RubyBinding binding, RubyString filename,
         }
 
         @Specialization(guards = "!isRubyString(arguments[0])")
-        public Object eval(VirtualFrame frame, RubyBasicObject object, UndefinedPlaceholder binding, UndefinedPlaceholder filename, UndefinedPlaceholder lineNumber) {
+        public Object eval(VirtualFrame frame, RubyBasicObject object, U binding, U filename, U lineNumber) {
             notDesignedForCompilation();
 
             return eval(frame, object, getCallerBinding(frame), filename, lineNumber);
         }
 
         @Specialization(guards = "!isRubyString(arguments[0])")
-        public Object eval(VirtualFrame frame, RubyBasicObject object, RubyBinding binding, UndefinedPlaceholder filename, UndefinedPlaceholder lineNumber) {
+        public Object eval(VirtualFrame frame, RubyBasicObject object, RubyBinding binding, U filename, U lineNumber) {
             notDesignedForCompilation();
 
             Object coerced;
@@ -630,7 +630,7 @@ public Object eval(VirtualFrame frame, RubyBasicObject object, RubyBinding bindi
         }
 
         @Specialization(guards = "!isRubyBinding(arguments[1])")
-        public Object eval(RubyBasicObject source, RubyBasicObject badBinding, UndefinedPlaceholder filename, UndefinedPlaceholder lineNumber) {
+        public Object eval(RubyBasicObject source, RubyBasicObject badBinding, U filename, U lineNumber) {
             throw new RaiseException(
                     getContext().getCoreLibrary().typeError(
                             String.format("wrong argument type %s (expected binding)",
@@ -713,7 +713,7 @@ public ExitNode(ExitNode prev) {
         }
 
         @Specialization
-        public Object exit(UndefinedPlaceholder exitCode) {
+        public Object exit(U exitCode) {
             notDesignedForCompilation();
 
             getContext().shutdown();
@@ -744,7 +744,7 @@ public ExitBangNode(ExitBangNode prev) {
         }
 
         @Specialization
-        public RubyNilClass exit(UndefinedPlaceholder exitCode) {
+        public RubyNilClass exit(U exitCode) {
             return exit(1);
         }
 
@@ -1361,7 +1361,7 @@ public MethodsNode(MethodsNode prev) {
         }
 
         @Specialization
-        public RubyArray methods(RubyBasicObject self, UndefinedPlaceholder unused) {
+        public RubyArray methods(RubyBasicObject self, U unused) {
             return methods(self, true);
         }
 
@@ -1479,7 +1479,7 @@ public PrivateMethodsNode(PrivateMethodsNode prev) {
         }
 
         @Specialization
-        public RubyArray private_methods(RubyBasicObject self, UndefinedPlaceholder unused) {
+        public RubyArray private_methods(RubyBasicObject self, U unused) {
             return private_methods(self, true);
         }
 
@@ -1549,11 +1549,11 @@ public RubyArray methods(RubyBasicObject self, boolean includeInherited) {
                 getContext().getRuntime().getWarnings().warn(IRubyWarnings.ID.TRUFFLE, Truffle.getRuntime().getCallerFrame().getCallNode().getEncapsulatingSourceSection().getSource().getName(), Truffle.getRuntime().getCallerFrame().getCallNode().getEncapsulatingSourceSection().getStartLine(), "Object#methods always returns inherited methods at the moment");
             }
 
-            return methods(self, UndefinedPlaceholder.INSTANCE);
+            return methods(self, U.INSTANCE);
         }
 
         @Specialization
-        public RubyArray methods(RubyBasicObject self, UndefinedPlaceholder includeInherited) {
+        public RubyArray methods(RubyBasicObject self, U includeInherited) {
             notDesignedForCompilation();
 
             final RubyArray array = new RubyArray(self.getContext().getCoreLibrary().getArrayClass());
@@ -1587,21 +1587,21 @@ public RaiseNode(RaiseNode prev) {
         }
 
         @Specialization
-        public Object raise(VirtualFrame frame, UndefinedPlaceholder undefined1, UndefinedPlaceholder undefined2, Object undefined3) {
+        public Object raise(VirtualFrame frame, U undefined1, U undefined2, Object undefined3) {
             notDesignedForCompilation();
 
             return raise(frame, getContext().getCoreLibrary().getRuntimeErrorClass(), getContext().makeString("re-raised - don't have the current exception yet!"), undefined1);
         }
 
         @Specialization
-        public Object raise(VirtualFrame frame, RubyString message, UndefinedPlaceholder undefined1, Object undefined2) {
+        public Object raise(VirtualFrame frame, RubyString message, U undefined1, Object undefined2) {
             notDesignedForCompilation();
 
             return raise(frame, getContext().getCoreLibrary().getRuntimeErrorClass(), message, undefined1);
         }
 
         @Specialization
-        public Object raise(VirtualFrame frame, RubyClass exceptionClass, UndefinedPlaceholder undefined1, Object undefined2) {
+        public Object raise(VirtualFrame frame, RubyClass exceptionClass, U undefined1, Object undefined2) {
             notDesignedForCompilation();
 
             return raise(frame, exceptionClass, getContext().makeString(""), undefined1);
@@ -1623,7 +1623,7 @@ public Object raise(VirtualFrame frame, RubyClass exceptionClass, RubyString mes
         }
 
         @Specialization
-        public Object raise(RubyException exception, UndefinedPlaceholder undefined1, Object undefined2) {
+        public Object raise(RubyException exception, U undefined1, Object undefined2) {
             throw new RaiseException(exception);
         }
 
@@ -1641,7 +1641,7 @@ public RandNode(RandNode prev) {
         }
 
         @Specialization
-        public double rand(UndefinedPlaceholder undefined) {
+        public double rand(U undefined) {
             return getContext().getRandom().nextDouble();
         }
 
@@ -1745,7 +1745,7 @@ public RespondToNode(RespondToNode prev) {
         public abstract boolean executeDoesRespondTo(VirtualFrame frame, Object object, Object name, boolean includePrivate);
 
         @Specialization
-        public boolean doesRespondTo(VirtualFrame frame, Object object, RubyString name, UndefinedPlaceholder checkVisibility) {
+        public boolean doesRespondTo(VirtualFrame frame, Object object, RubyString name, U checkVisibility) {
             return dispatch.doesRespondTo(frame, name, object);
         }
 
@@ -1759,7 +1759,7 @@ public boolean doesRespondTo(VirtualFrame frame, Object object, RubyString name,
         }
 
         @Specialization
-        public boolean doesRespondTo(VirtualFrame frame, Object object, RubySymbol name, UndefinedPlaceholder checkVisibility) {
+        public boolean doesRespondTo(VirtualFrame frame, Object object, RubySymbol name, U checkVisibility) {
             return dispatch.doesRespondTo(frame, name, object);
         }
 
@@ -1785,12 +1785,12 @@ public RespondToMissingNode(RespondToMissingNode prev) {
         }
 
         @Specialization
-        public boolean doesRespondToMissing(Object object, RubyString name, UndefinedPlaceholder includeAll) {
+        public boolean doesRespondToMissing(Object object, RubyString name, U includeAll) {
             return false;
         }
 
         @Specialization
-        public boolean doesRespondToMissing(Object object, RubySymbol name, UndefinedPlaceholder includeAll) {
+        public boolean doesRespondToMissing(Object object, RubySymbol name, U includeAll) {
             return false;
         }
 
@@ -1902,7 +1902,7 @@ public RubyArray singletonMethods(RubyBasicObject self, boolean includeInherited
         }
 
         @Specialization
-        public RubyArray singletonMethods(RubyBasicObject self, UndefinedPlaceholder includeInherited) {
+        public RubyArray singletonMethods(RubyBasicObject self, U includeInherited) {
             return singletonMethods(self, false);
         }
 
@@ -1947,7 +1947,7 @@ public SleepNode(SleepNode prev) {
         }
 
         @Specialization
-        public double sleep(UndefinedPlaceholder duration) {
+        public double sleep(U duration) {
             return doSleep(0);
         }
 
@@ -2177,7 +2177,7 @@ public ThrowNode(ThrowNode prev) {
         }
 
         @Specialization
-        public Object doThrow(Object tag, UndefinedPlaceholder value) {
+        public Object doThrow(Object tag, U value) {
             return doThrow(tag, (Object) value);
         }
 
@@ -2192,7 +2192,7 @@ public Object doThrow(Object tag, Object value) {
                         RubyCallStack.getBacktrace(this)));
             }
 
-            if (value instanceof UndefinedPlaceholder) {
+            if (value instanceof U) {
                 throw new ThrowException(tag, getContext().getCoreLibrary().getNilObject());
             } else {
                 throw new ThrowException(tag, value);

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/MathNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/MathNodes.java
@@ -18,7 +18,7 @@
 import org.jruby.truffle.nodes.RubyNode;
 import org.jruby.truffle.nodes.dispatch.*;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.control.RaiseException;
 import org.jruby.truffle.runtime.core.RubyArray;
 import org.jruby.truffle.runtime.core.RubyBignum;
@@ -710,27 +710,27 @@ public LogNode(LogNode prev) {
         }
 
         @Specialization
-        public double function(int a, UndefinedPlaceholder b) {
+        public double function(int a, U b) {
             return doFunction(a);
         }
 
         @Specialization
-        public double function(long a, UndefinedPlaceholder b) {
+        public double function(long a, U b) {
             return doFunction(a);
         }
 
         @Specialization
-        public double function(RubyBignum a, UndefinedPlaceholder b) {
+        public double function(RubyBignum a, U b) {
             return doFunction(a.doubleValue());
         }
 
         @Specialization
-        public double function(double a, UndefinedPlaceholder b) {
+        public double function(double a, U b) {
             return doFunction(a);
         }
 
         @Specialization
-        public double function(VirtualFrame frame, Object a, UndefinedPlaceholder b) {
+        public double function(VirtualFrame frame, Object a, U b) {
             if (isANode.executeIsA(frame, a, getContext().getCoreLibrary().getNumericClass())) {
                 try {
                     return doFunction(

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/ModuleNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/ModuleNodes.java
@@ -396,23 +396,23 @@ public ClassEvalNode(ClassEvalNode prev) {
         }
 
         @Specialization
-        public Object classEval(VirtualFrame frame, RubyModule module, RubyString code, @SuppressWarnings("unused") UndefinedPlaceholder file, @SuppressWarnings("unused") UndefinedPlaceholder line, @SuppressWarnings("unused") UndefinedPlaceholder block) {
+        public Object classEval(VirtualFrame frame, RubyModule module, RubyString code, @SuppressWarnings("unused") U file, @SuppressWarnings("unused") U line, @SuppressWarnings("unused") U block) {
             notDesignedForCompilation();
 
             final Source source = Source.fromText(code.getBytes(), "(eval)");
             return classEvalSource(frame, module, source, code.getBytes().getEncoding());
         }
 
         @Specialization
-        public Object classEval(VirtualFrame frame, RubyModule module, RubyString code, RubyString file, @SuppressWarnings("unused") UndefinedPlaceholder line, @SuppressWarnings("unused") UndefinedPlaceholder block) {
+        public Object classEval(VirtualFrame frame, RubyModule module, RubyString code, RubyString file, @SuppressWarnings("unused") U line, @SuppressWarnings("unused") U block) {
             notDesignedForCompilation();
 
             final Source source = Source.asPseudoFile(code.getBytes(), file.toString());
             return classEvalSource(frame, module, source, code.getBytes().getEncoding());
         }
 
         @Specialization
-        public Object classEval(VirtualFrame frame, RubyModule module, RubyString code, RubyString file, @SuppressWarnings("unused") int line, @SuppressWarnings("unused") UndefinedPlaceholder block) {
+        public Object classEval(VirtualFrame frame, RubyModule module, RubyString code, RubyString file, @SuppressWarnings("unused") int line, @SuppressWarnings("unused") U block) {
             notDesignedForCompilation();
 
             final Source source = Source.asPseudoFile(code.getBytes(), file.toString());
@@ -429,14 +429,14 @@ public RubyNode wrap(RubyNode node) {
         }
 
         @Specialization
-        public Object classEval(VirtualFrame frame, RubyModule self, @SuppressWarnings("unused") UndefinedPlaceholder code, @SuppressWarnings("unused") UndefinedPlaceholder file, @SuppressWarnings("unused") UndefinedPlaceholder line, RubyProc block) {
+        public Object classEval(VirtualFrame frame, RubyModule self, @SuppressWarnings("unused") U code, @SuppressWarnings("unused") U file, @SuppressWarnings("unused") U line, RubyProc block) {
             notDesignedForCompilation();
 
             return yield.dispatchWithModifiedSelf(frame, block, self);
         }
 
         @Specialization
-        public Object classEval(RubyModule self, UndefinedPlaceholder code, UndefinedPlaceholder file, UndefinedPlaceholder line, UndefinedPlaceholder block) {
+        public Object classEval(RubyModule self, U code, U file, U line, U block) {
             notDesignedForCompilation();
 
             throw new RaiseException(getContext().getCoreLibrary().argumentError(0, 1, 2, this));
@@ -560,7 +560,7 @@ public ConstantsNode(ConstantsNode prev) {
         }
 
         @Specialization
-        public RubyArray constants(RubyModule module, UndefinedPlaceholder unused) {
+        public RubyArray constants(RubyModule module, U unused) {
             return constants(module, true);
         }
 
@@ -591,7 +591,7 @@ public ConstDefinedNode(ConstDefinedNode prev) {
         }
 
         @Specialization
-        public boolean isConstDefined(RubyModule module, RubyString name, @SuppressWarnings("unused") UndefinedPlaceholder inherit) {
+        public boolean isConstDefined(RubyModule module, RubyString name, @SuppressWarnings("unused") U inherit) {
             notDesignedForCompilation();
 
             return ModuleOperations.lookupConstant(getContext(), LexicalScope.NONE, module, name.toString()) != null;
@@ -609,7 +609,7 @@ public boolean isConstDefined(RubyModule module, RubyString name, boolean inheri
         }
 
         @Specialization
-        public boolean isConstDefined(RubyModule module, RubySymbol name, @SuppressWarnings("unused") UndefinedPlaceholder inherit) {
+        public boolean isConstDefined(RubyModule module, RubySymbol name, @SuppressWarnings("unused") U inherit) {
             notDesignedForCompilation();
 
             return ModuleOperations.lookupConstant(getContext(), LexicalScope.NONE, module, name.toString()) != null;
@@ -730,14 +730,14 @@ public DefineMethodNode(DefineMethodNode prev) {
         }
 
         @Specialization
-        public RubySymbol defineMethod(RubyModule module, RubyString name, @SuppressWarnings("unused") UndefinedPlaceholder proc, RubyProc block) {
+        public RubySymbol defineMethod(RubyModule module, RubyString name, @SuppressWarnings("unused") U proc, RubyProc block) {
             notDesignedForCompilation();
 
-            return defineMethod(module, name, block, UndefinedPlaceholder.INSTANCE);
+            return defineMethod(module, name, block, U.INSTANCE);
         }
 
         @Specialization
-        public RubySymbol defineMethod(RubyModule module, RubyString name, RubyProc proc, @SuppressWarnings("unused") UndefinedPlaceholder block) {
+        public RubySymbol defineMethod(RubyModule module, RubyString name, RubyProc proc, @SuppressWarnings("unused") U block) {
             notDesignedForCompilation();
 
             final RubySymbol symbol = getContext().getSymbolTable().getSymbol(name.getBytes());
@@ -746,22 +746,22 @@ public RubySymbol defineMethod(RubyModule module, RubyString name, RubyProc proc
         }
 
         @Specialization
-        public RubySymbol defineMethod(RubyModule module, RubySymbol name, @SuppressWarnings("unused") UndefinedPlaceholder proc, RubyProc block) {
+        public RubySymbol defineMethod(RubyModule module, RubySymbol name, @SuppressWarnings("unused") U proc, RubyProc block) {
             notDesignedForCompilation();
 
-            return defineMethod(module, name, block, UndefinedPlaceholder.INSTANCE);
+            return defineMethod(module, name, block, U.INSTANCE);
         }
 
         @Specialization
-        public RubySymbol defineMethod(RubyModule module, RubySymbol name, RubyProc proc, @SuppressWarnings("unused") UndefinedPlaceholder block) {
+        public RubySymbol defineMethod(RubyModule module, RubySymbol name, RubyProc proc, @SuppressWarnings("unused") U block) {
             notDesignedForCompilation();
 
             defineMethod(module, name, proc);
             return name;
         }
 
         @Specialization
-        public RubySymbol defineMethod(RubyModule module, RubySymbol name, RubyMethod method, UndefinedPlaceholder block) {
+        public RubySymbol defineMethod(RubyModule module, RubySymbol name, RubyMethod method, U block) {
             notDesignedForCompilation();
 
             module.addMethod(this, method.getMethod().withNewName(name.toString()));
@@ -803,7 +803,7 @@ void classEval(VirtualFrame frame, RubyModule module, RubyProc block) {
         }
 
         @Specialization
-        public RubyModule initialize(RubyModule module, UndefinedPlaceholder block) {
+        public RubyModule initialize(RubyModule module, U block) {
             return module;
         }
 
@@ -916,7 +916,7 @@ public MethodDefinedNode(MethodDefinedNode prev) {
         }
 
         @Specialization
-        public boolean isMethodDefined(RubyModule module, RubyString name, @SuppressWarnings("unused") UndefinedPlaceholder inherit) {
+        public boolean isMethodDefined(RubyModule module, RubyString name, @SuppressWarnings("unused") U inherit) {
             notDesignedForCompilation();
 
             return ModuleOperations.lookupMethod(module, name.toString()) != null;
@@ -934,7 +934,7 @@ public boolean isMethodDefined(RubyModule module, RubyString name, boolean inher
         }
 
         @Specialization
-        public boolean isMethodDefined(RubyModule module, RubySymbol name, @SuppressWarnings("unused") UndefinedPlaceholder inherit) {
+        public boolean isMethodDefined(RubyModule module, RubySymbol name, @SuppressWarnings("unused") U inherit) {
             notDesignedForCompilation();
 
             return ModuleOperations.lookupMethod(module, name.toString()) != null;
@@ -1163,7 +1163,7 @@ public PrivateInstanceMethodsNode(PrivateInstanceMethodsNode prev) {
         }
 
         @Specialization
-        public RubyArray privateInstanceMethods(RubyModule module, UndefinedPlaceholder argument) {
+        public RubyArray privateInstanceMethods(RubyModule module, U argument) {
             return privateInstanceMethods(module, false);
         }
 
@@ -1201,7 +1201,7 @@ public PublicInstanceMethodsNode(PublicInstanceMethodsNode prev) {
         }
 
         @Specialization
-        public RubyArray publicInstanceMethods(RubyModule module, UndefinedPlaceholder argument) {
+        public RubyArray publicInstanceMethods(RubyModule module, U argument) {
             return publicInstanceMethods(module, false);
         }
 
@@ -1238,7 +1238,7 @@ public InstanceMethodsNode(InstanceMethodsNode prev) {
         }
 
         @Specialization
-        public RubyArray instanceMethods(RubyModule module, UndefinedPlaceholder argument) {
+        public RubyArray instanceMethods(RubyModule module, U argument) {
             notDesignedForCompilation();
 
             return instanceMethods(module, true);

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/ObjectSpaceNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/ObjectSpaceNodes.java
@@ -15,7 +15,7 @@
 import org.jruby.truffle.runtime.ModuleOperations;
 import org.jruby.truffle.runtime.ObjectIDOperations;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.core.RubyBasicObject;
 import org.jruby.truffle.runtime.core.RubyBignum;
 import org.jruby.truffle.runtime.core.RubyClass;
@@ -97,7 +97,7 @@ public EachObjectNode(EachObjectNode prev) {
         }
 
         @Specialization
-        public int eachObject(VirtualFrame frame, @SuppressWarnings("unused") UndefinedPlaceholder ofClass, RubyProc block) {
+        public int eachObject(VirtualFrame frame, @SuppressWarnings("unused") U ofClass, RubyProc block) {
             notDesignedForCompilation();
 
             final Collection<RubyBasicObject> liveObjects = getContext().getObjectSpaceManager().collectLiveObjects().values();

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/ProcNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/ProcNodes.java
@@ -19,7 +19,7 @@
 import org.jruby.truffle.nodes.yield.YieldDispatchHeadNode;
 import org.jruby.truffle.runtime.RubyArguments;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.core.RubyArray;
 import org.jruby.truffle.runtime.core.RubyBinding;
 import org.jruby.truffle.runtime.core.RubyNilClass;
@@ -89,7 +89,7 @@ public CallNode(CallNode prev) {
         }
 
         @Specialization
-        public Object call(VirtualFrame frame, RubyProc proc, Object[] args, UndefinedPlaceholder block) {
+        public Object call(VirtualFrame frame, RubyProc proc, Object[] args, U block) {
             return yieldNode.dispatch(frame, proc, args);
         }
 

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/RegexpNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/RegexpNodes.java
@@ -18,7 +18,7 @@
 import org.jruby.runtime.Visibility;
 import org.jruby.truffle.nodes.RubyNode;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.control.RaiseException;
 import org.jruby.truffle.runtime.core.RubyBasicObject;
 import org.jruby.truffle.runtime.core.RubyEncoding;
@@ -197,7 +197,7 @@ public InitializeNode(InitializeNode prev) {
         }
 
         @Specialization
-        public RubyRegexp initialize(RubyRegexp regexp, RubyString string, @SuppressWarnings("unused") UndefinedPlaceholder options) {
+        public RubyRegexp initialize(RubyRegexp regexp, RubyString string, @SuppressWarnings("unused") U options) {
             notDesignedForCompilation();
 
             regexp.initialize(this, string.getBytes());
@@ -208,7 +208,7 @@ public RubyRegexp initialize(RubyRegexp regexp, RubyString string, @SuppressWarn
         public RubyRegexp initialize(RubyRegexp regexp, RubyString string, @SuppressWarnings("unused") RubyNilClass options) {
             notDesignedForCompilation();
 
-            return initialize(regexp, string, UndefinedPlaceholder.INSTANCE);
+            return initialize(regexp, string, U.INSTANCE);
         }
 
         @Specialization
@@ -218,7 +218,7 @@ public RubyRegexp initialize(RubyRegexp regexp, RubyString string, boolean optio
             if (booleanOptionsProfile.profile(options)) {
                 return initialize(regexp, string, Option.IGNORECASE);
             } else {
-                return initialize(regexp, string, UndefinedPlaceholder.INSTANCE);
+                return initialize(regexp, string, U.INSTANCE);
             }
         }
 
@@ -238,7 +238,7 @@ public RubyRegexp initialize(RubyRegexp regexp, RubyString string, @SuppressWarn
         }
 
         @Specialization
-        public RubyRegexp initialize(RubyRegexp regexp, RubyRegexp from, @SuppressWarnings("unused") UndefinedPlaceholder options) {
+        public RubyRegexp initialize(RubyRegexp regexp, RubyRegexp from, @SuppressWarnings("unused") U options) {
             notDesignedForCompilation();
 
             regexp.initialize(this, from.getSource(), from.getRegex().getOptions()); // TODO: is copying needed?
@@ -251,7 +251,7 @@ public RubyRegexp initialize(RubyRegexp regexp, RubyRegexp from, @SuppressWarnin
 
             getContext().getWarnings().warn("flags ignored");
 
-            return initialize(regexp, from, UndefinedPlaceholder.INSTANCE);
+            return initialize(regexp, from, U.INSTANCE);
         }
     }
 

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/SignalNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/SignalNodes.java
@@ -14,7 +14,7 @@
 import com.oracle.truffle.api.source.SourceSection;
 import org.jruby.common.IRubyWarnings;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.core.RubyProc;
 import org.jruby.truffle.runtime.core.RubyString;
 import org.jruby.truffle.runtime.signal.ProcSignalHandler;
@@ -36,7 +36,7 @@ public SignalNode(SignalNode prev) {
         }
 
         @Specialization
-        public Object trap(RubyString signalName, UndefinedPlaceholder command, final RubyProc block) {
+        public Object trap(RubyString signalName, U command, final RubyProc block) {
             notDesignedForCompilation();
 
             final Signal signal = new Signal(signalName.toString());
@@ -52,7 +52,7 @@ public Object trap(RubyString signalName, UndefinedPlaceholder command, final Ru
         }
 
         @Specialization
-        public Object trap(RubyString signalName, RubyString command, UndefinedPlaceholder block) {
+        public Object trap(RubyString signalName, RubyString command, U block) {
             notDesignedForCompilation();
             getContext().getRuntime().getWarnings().warn(IRubyWarnings.ID.TRUFFLE, Truffle.getRuntime().getCallerFrame().getCallNode().getEncapsulatingSourceSection().getSource().getName(), Truffle.getRuntime().getCallerFrame().getCallNode().getEncapsulatingSourceSection().getStartLine(), "Signal#trap with a string command not implemented yet");
             return getContext().getCoreLibrary().getNilObject();

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/StringNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/StringNodes.java
@@ -24,13 +24,11 @@
 import org.jruby.runtime.Visibility;
 import org.jruby.truffle.nodes.RubyNode;
 import org.jruby.truffle.nodes.dispatch.CallDispatchHeadNode;
-import org.jruby.truffle.nodes.dispatch.DispatchHeadNode;
 import org.jruby.truffle.nodes.dispatch.DispatchHeadNodeFactory;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.control.RaiseException;
 import org.jruby.truffle.runtime.core.*;
-import org.jruby.truffle.runtime.util.ArrayUtils;
 import org.jruby.util.ByteList;
 import org.jruby.util.Pack;
 import org.jruby.util.StringSupport;
@@ -200,7 +198,7 @@ public GetIndexNode(GetIndexNode prev) {
         }
 
         @Specialization(rewriteOn = UnexpectedResultException.class)
-        public RubyString getIndexInBounds(RubyString string, int index, UndefinedPlaceholder undefined) throws UnexpectedResultException {
+        public RubyString getIndexInBounds(RubyString string, int index, U undefined) throws UnexpectedResultException {
             final int normalisedIndex = string.normaliseIndex(index);
             final ByteList bytes = string.getBytes();
 
@@ -212,7 +210,7 @@ public RubyString getIndexInBounds(RubyString string, int index, UndefinedPlaceh
         }
 
         @Specialization(contains = "getIndexInBounds")
-        public Object getIndex(RubyString string, int index, UndefinedPlaceholder undefined) {
+        public Object getIndex(RubyString string, int index, U undefined) {
             int normalisedIndex = string.normaliseIndex(index);
             final ByteList bytes = string.getBytes();
 
@@ -225,7 +223,7 @@ public Object getIndex(RubyString string, int index, UndefinedPlaceholder undefi
         }
 
         @Specialization
-        public Object slice(RubyString string, RubyRange.IntegerFixnumRange range, UndefinedPlaceholder undefined) {
+        public Object slice(RubyString string, RubyRange.IntegerFixnumRange range, U undefined) {
             notDesignedForCompilation();
 
             final String javaString = string.toString();
@@ -431,7 +429,7 @@ public ChompNode(ChompNode prev) {
         }
 
         @Specialization
-        public RubyString chomp(RubyString string, UndefinedPlaceholder undefined) {
+        public RubyString chomp(RubyString string, U undefined) {
             notDesignedForCompilation();
             return string.getContext().makeString(StringNodesHelper.chomp(string));
         }
@@ -744,15 +742,15 @@ public GsubNode(GsubNode prev) {
         }
 
         @Specialization
-        public RubyString gsub(VirtualFrame frame, RubyString string, RubyString regexpString, RubyString replacement, UndefinedPlaceholder block) {
+        public RubyString gsub(VirtualFrame frame, RubyString string, RubyString regexpString, RubyString replacement, U block) {
             notDesignedForCompilation();
 
             final RubyRegexp regexp = new RubyRegexp(this, getContext().getCoreLibrary().getRegexpClass(), escape(frame, regexpString).getBytes(), Option.DEFAULT);
             return gsub(string, regexp, replacement, block);
         }
 
         @Specialization
-        public RubyString gsub(RubyString string, RubyRegexp regexp, RubyString replacement, @SuppressWarnings("unused") UndefinedPlaceholder block) {
+        public RubyString gsub(RubyString string, RubyRegexp regexp, RubyString replacement, @SuppressWarnings("unused") U block) {
             notDesignedForCompilation();
 
             return regexp.gsub(string, replacement.toString());
@@ -774,15 +772,15 @@ public RubyString gsub(RubyString string, RubyRegexp regexp, RubyString replacem
         }
 
         @Specialization
-        public RubyString gsub(VirtualFrame frame, RubyString string, RubyString regexpString, @SuppressWarnings("unused") UndefinedPlaceholder replacement, RubyProc block) {
+        public RubyString gsub(VirtualFrame frame, RubyString string, RubyString regexpString, @SuppressWarnings("unused") U replacement, RubyProc block) {
             notDesignedForCompilation();
 
             final RubyRegexp regexp = new RubyRegexp(this, getContext().getCoreLibrary().getRegexpClass(), escape(frame, regexpString).getBytes(), Option.DEFAULT);
             return gsub(frame, string, regexp, replacement, block);
         }
 
         @Specialization
-        public RubyString gsub(VirtualFrame frame, RubyString string, RubyRegexp regexp, @SuppressWarnings("unused") UndefinedPlaceholder replacement, RubyProc block) {
+        public RubyString gsub(VirtualFrame frame, RubyString string, RubyRegexp regexp, @SuppressWarnings("unused") U replacement, RubyProc block) {
             notDesignedForCompilation();
 
             final RubyContext context = getContext();
@@ -881,7 +879,7 @@ public InitializeNode(InitializeNode prev) {
         }
 
         @Specialization
-        public RubyString initialize(RubyString self, UndefinedPlaceholder from) {
+        public RubyString initialize(RubyString self, U from) {
             return self;
         }
 
@@ -996,7 +994,7 @@ public LjustNode(LjustNode prev) {
         }
 
         @Specialization
-        public RubyString ljust(RubyString string, int length, @SuppressWarnings("unused") UndefinedPlaceholder padding) {
+        public RubyString ljust(RubyString string, int length, @SuppressWarnings("unused") U padding) {
             notDesignedForCompilation();
 
             return getContext().makeString(RubyString.ljust(string.toString(), length, " "));
@@ -1066,7 +1064,7 @@ public RindexNode(RindexNode prev) {
         }
 
         @Specialization
-        public Object rindex(RubyString string, RubyString subString, @SuppressWarnings("unused") UndefinedPlaceholder endPosition) {
+        public Object rindex(RubyString string, RubyString subString, @SuppressWarnings("unused") U endPosition) {
             notDesignedForCompilation();
 
             return rindex(string, subString, string.length());
@@ -1112,7 +1110,7 @@ public RjustNode(RjustNode prev) {
         }
 
         @Specialization
-        public RubyString rjust(RubyString string, int length, @SuppressWarnings("unused") UndefinedPlaceholder padding) {
+        public RubyString rjust(RubyString string, int length, @SuppressWarnings("unused") U padding) {
             notDesignedForCompilation();
 
             return getContext().makeString(RubyString.rjust(string.toString(), length, " "));
@@ -1185,7 +1183,7 @@ public ScanNode(ScanNode prev) {
         }
 
         @Specialization
-        public RubyArray scan(RubyString string, RubyString regexpString, UndefinedPlaceholder block) {
+        public RubyArray scan(RubyString string, RubyString regexpString, U block) {
             notDesignedForCompilation();
 
             final RubyRegexp regexp = new RubyRegexp(this, getContext().getCoreLibrary().getRegexpClass(), regexpString.getBytes(), Option.DEFAULT);
@@ -1201,7 +1199,7 @@ public RubyString scan(VirtualFrame frame, RubyString string, RubyString regexpS
         }
 
         @Specialization
-        public RubyArray scan(RubyString string, RubyRegexp regexp, UndefinedPlaceholder block) {
+        public RubyArray scan(RubyString string, RubyRegexp regexp, U block) {
             notDesignedForCompilation();
 
             return RubyArray.fromObjects(getContext().getCoreLibrary().getArrayClass(), (Object[]) regexp.scan(string));
@@ -1329,7 +1327,7 @@ public RubyArray split(RubyString string, RubyRegexp sep) {
         }
 
         @Specialization
-        public RubyArray split(RubyString string, UndefinedPlaceholder sep) {
+        public RubyArray split(RubyString string, U sep) {
             notDesignedForCompilation();
 
             return splitHelper(string, " ");

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/ThreadNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/ThreadNodes.java
@@ -15,10 +15,9 @@
 import com.oracle.truffle.api.source.SourceSection;
 import org.jruby.RubyThread.Status;
 import org.jruby.truffle.nodes.dispatch.CallDispatchHeadNode;
-import org.jruby.truffle.nodes.dispatch.DispatchHeadNode;
 import org.jruby.truffle.nodes.dispatch.DispatchHeadNodeFactory;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 import org.jruby.truffle.runtime.control.RaiseException;
 import org.jruby.truffle.runtime.control.ThreadExitException;
 import org.jruby.truffle.runtime.core.*;
@@ -214,7 +213,7 @@ public RaiseNode(RaiseNode prev) {
         }
 
         @Specialization
-        public RubyNilClass raise(VirtualFrame frame, RubyThread thread, RubyString message, UndefinedPlaceholder undefined) {
+        public RubyNilClass raise(VirtualFrame frame, RubyThread thread, RubyString message, U undefined) {
             return raise(frame, thread, getContext().getCoreLibrary().getRuntimeErrorClass(), message);
         }
 

diff --git a/core/src/main/java/org/jruby/truffle/nodes/core/UnboundMethodNodes.java b/core/src/main/java/org/jruby/truffle/nodes/core/UnboundMethodNodes.java
@@ -10,14 +10,9 @@
 package org.jruby.truffle.nodes.core;
 
 import com.oracle.truffle.api.dsl.Specialization;
-import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.source.SourceSection;
-import org.jruby.truffle.nodes.yield.YieldDispatchHeadNode;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
-import org.jruby.truffle.runtime.core.RubyBignum;
 import org.jruby.truffle.runtime.core.RubyMethod;
-import org.jruby.truffle.runtime.core.RubyProc;
 import org.jruby.truffle.runtime.core.RubyUnboundMethod;
 
 @CoreClass(name = "UnboundMethod")

diff --git a/core/src/main/java/org/jruby/truffle/nodes/methods/arguments/ReadPreArgumentNode.java b/core/src/main/java/org/jruby/truffle/nodes/methods/arguments/ReadPreArgumentNode.java
@@ -16,7 +16,7 @@
 import org.jruby.truffle.nodes.RubyNode;
 import org.jruby.truffle.runtime.RubyArguments;
 import org.jruby.truffle.runtime.RubyContext;
-import org.jruby.truffle.runtime.UndefinedPlaceholder;
+import org.jruby.truffle.runtime.U;
 
 /**
  * Read pre-optional argument.
@@ -46,7 +46,7 @@ public Object execute(VirtualFrame frame) {
                     break;
 
                 case UNDEFINED:
-                    return UndefinedPlaceholder.INSTANCE;
+                    return U.INSTANCE;
 
                 case NIL:
                     return getContext().getCoreLibrary().getNilObject();

diff --git a/...truffle/runtime/UndefinedPlaceholder.java → ...ain/java/org/jruby/truffle/runtime/U.java b/...truffle/runtime/UndefinedPlaceholder.java → ...ain/java/org/jruby/truffle/runtime/U.java
@@ -10,15 +10,15 @@
 package org.jruby.truffle.runtime;
 
 /**
- * The {@link UndefinedPlaceholder} is a value that represents an undefined value in Ruby. This is
+ * The {@link U} is a value that represents an undefined value in Ruby. This is
  * used to differentiate between nil and the true absence of a value, such as an argument that has
  * not been passed.
  */
-public final class UndefinedPlaceholder {
+public final class U {
 
-    public static final UndefinedPlaceholder INSTANCE = new UndefinedPlaceholder();
+    public static final U INSTANCE = new U();
 
-    private UndefinedPlaceholder() {
+    private U() {
     }
 
 }