Upgrade to ASM master (including early support for Java 22 bytecode)

Closes gh-30845

spring-core/src/main/java/org/springframework/asm/ClassReader.java

@@ -194,7 +194,7 @@ public class ClassReader {
     this.b = classFileBuffer;
     // Check the class' major_version. This field is after the magic and minor_version fields, which
     // use 4 and 2 bytes respectively.
-    if (checkClassVersion && readShort(classFileOffset + 6) > Opcodes.V21) {
+    if (checkClassVersion && readShort(classFileOffset + 6) > Opcodes.V22) {
       throw new IllegalArgumentException(
           "Unsupported class file major version " + readShort(classFileOffset + 6));
     }
@@ -2052,6 +2052,7 @@ public class ClassReader {
     currentOffset = bytecodeStartOffset;
     while (currentOffset < bytecodeEndOffset) {
       final int currentBytecodeOffset = currentOffset - bytecodeStartOffset;
+      readBytecodeInstructionOffset(currentBytecodeOffset);
 
       // Visit the label and the line number(s) for this bytecode offset, if any.
       Label currentLabel = labels[currentBytecodeOffset];
@@ -2667,6 +2668,20 @@ public class ClassReader {
     methodVisitor.visitMaxs(maxStack, maxLocals);
   }
 
+  /**
+   * Handles the bytecode offset of the next instruction to be visited in {@link
+   * #accept(ClassVisitor,int)}. This method is called just before the instruction and before its
+   * associated label and stack map frame, if any. The default implementation of this method does
+   * nothing. Subclasses can override this method to store the argument in a mutable field, for
+   * instance, so that {@link MethodVisitor} instances can get the bytecode offset of each visited
+   * instruction (if so, the usual concurrency issues related to mutable data should be addressed).
+   *
+   * @param bytecodeOffset the bytecode offset of the next instruction to be visited.
+   */
+  protected void readBytecodeInstructionOffset(final int bytecodeOffset) {
+    // Do nothing by default.
+  }
+
   /**
    * Returns the label corresponding to the given bytecode offset. The default implementation of
    * this method creates a label for the given offset if it has not been already created.

spring-core/src/main/java/org/springframework/asm/ClassWriter.java

@@ -217,6 +217,7 @@ public class ClassWriter extends ClassVisitor {
   /**
    * Indicates what must be automatically computed in {@link MethodWriter}. Must be one of {@link
    * MethodWriter#COMPUTE_NOTHING}, {@link MethodWriter#COMPUTE_MAX_STACK_AND_LOCAL}, {@link
+   * MethodWriter#COMPUTE_MAX_STACK_AND_LOCAL_FROM_FRAMES}, {@link
    * MethodWriter#COMPUTE_INSERTED_FRAMES}, or {@link MethodWriter#COMPUTE_ALL_FRAMES}.
    */
   private int compute;

spring-core/src/main/java/org/springframework/asm/Frame.java

@@ -64,8 +64,8 @@ package org.springframework.asm;
  *       right shift of {@link #DIM_SHIFT}.
  *   <li>the KIND field, stored in 4 bits, indicates the kind of VALUE used. These 4 bits can be
  *       retrieved with {@link #KIND_MASK} and, without any shift, must be equal to {@link
- *       #CONSTANT_KIND}, {@link #REFERENCE_KIND}, {@link #UNINITIALIZED_KIND}, {@link #LOCAL_KIND}
+ *       #CONSTANT_KIND}, {@link #REFERENCE_KIND}, {@link #UNINITIALIZED_KIND}, {@link
- *       or {@link #STACK_KIND}.
+ *       #FORWARD_UNINITIALIZED_KIND},{@link #LOCAL_KIND} or {@link #STACK_KIND}.
  *   <li>the FLAGS field, stored in 2 bits, contains up to 2 boolean flags. Currently only one flag
  *       is defined, namely {@link #TOP_IF_LONG_OR_DOUBLE_FLAG}.
  *   <li>the VALUE field, stored in the remaining 20 bits, contains either
@@ -78,7 +78,10 @@ package org.springframework.asm;
  *         <li>the index of a {@link Symbol#TYPE_TAG} {@link Symbol} in the type table of a {@link
  *             SymbolTable}, if KIND is equal to {@link #REFERENCE_KIND}.
  *         <li>the index of an {@link Symbol#UNINITIALIZED_TYPE_TAG} {@link Symbol} in the type
- *             table of a SymbolTable, if KIND is equal to {@link #UNINITIALIZED_KIND}.
+ *             table of a {@link SymbolTable}, if KIND is equal to {@link #UNINITIALIZED_KIND}.
+ *         <li>the index of a {@link Symbol#FORWARD_UNINITIALIZED_TYPE_TAG} {@link Symbol} in the
+ *             type table of a {@link SymbolTable}, if KIND is equal to {@link
+ *             #FORWARD_UNINITIALIZED_KIND}.
  *         <li>the index of a local variable in the input stack frame, if KIND is equal to {@link
  *             #LOCAL_KIND}.
  *         <li>a position relatively to the top of the stack of the input stack frame, if KIND is
@@ -88,10 +91,10 @@ package org.springframework.asm;
  *
  * <p>Output frames can contain abstract types of any kind and with a positive or negative array
  * dimension (and even unassigned types, represented by 0 - which does not correspond to any valid
- * abstract type value). Input frames can only contain CONSTANT_KIND, REFERENCE_KIND or
+ * abstract type value). Input frames can only contain CONSTANT_KIND, REFERENCE_KIND,
- * UNINITIALIZED_KIND abstract types of positive or {@literal null} array dimension. In all cases
+ * UNINITIALIZED_KIND or FORWARD_UNINITIALIZED_KIND abstract types of positive or {@literal null}
- * the type table contains only internal type names (array type descriptors are forbidden - array
+ * array dimension. In all cases the type table contains only internal type names (array type
- * dimensions must be represented through the DIM field).
+ * descriptors are forbidden - array dimensions must be represented through the DIM field).
  *
  * <p>The LONG and DOUBLE types are always represented by using two slots (LONG + TOP or DOUBLE +
  * TOP), for local variables as well as in the operand stack. This is necessary to be able to
@@ -159,8 +162,9 @@ class Frame {
   private static final int CONSTANT_KIND = 1 << KIND_SHIFT;
   private static final int REFERENCE_KIND = 2 << KIND_SHIFT;
   private static final int UNINITIALIZED_KIND = 3 << KIND_SHIFT;
-  private static final int LOCAL_KIND = 4 << KIND_SHIFT;
+  private static final int FORWARD_UNINITIALIZED_KIND = 4 << KIND_SHIFT;
-  private static final int STACK_KIND = 5 << KIND_SHIFT;
+  private static final int LOCAL_KIND = 5 << KIND_SHIFT;
+  private static final int STACK_KIND = 6 << KIND_SHIFT;
 
   // Possible flags for the FLAGS field of an abstract type.
 
@@ -220,13 +224,13 @@ class Frame {
 
   /**
    * The abstract types that are initialized in the basic block. A constructor invocation on an
-   * UNINITIALIZED or UNINITIALIZED_THIS abstract type must replace <i>every occurrence</i> of this
+   * UNINITIALIZED, FORWARD_UNINITIALIZED or UNINITIALIZED_THIS abstract type must replace <i>every
-   * type in the local variables and in the operand stack. This cannot be done during the first step
+   * occurrence</i> of this type in the local variables and in the operand stack. This cannot be
-   * of the algorithm since, during this step, the local variables and the operand stack types are
+   * done during the first step of the algorithm since, during this step, the local variables and
-   * still abstract. It is therefore necessary to store the abstract types of the constructors which
+   * the operand stack types are still abstract. It is therefore necessary to store the abstract
-   * are invoked in the basic block, in order to do this replacement during the second step of the
+   * types of the constructors which are invoked in the basic block, in order to do this replacement
-   * algorithm, where the frames are fully computed. Note that this array can contain abstract types
+   * during the second step of the algorithm, where the frames are fully computed. Note that this
-   * that are relative to the input locals or to the input stack.
+   * array can contain abstract types that are relative to the input locals or to the input stack.
    */
   private int[] initializations;
 
@@ -284,8 +288,12 @@ class Frame {
       String descriptor = Type.getObjectType((String) type).getDescriptor();
       return getAbstractTypeFromDescriptor(symbolTable, descriptor, 0);
     } else {
-      return UNINITIALIZED_KIND
+      Label label = (Label) type;
-          | symbolTable.addUninitializedType("", ((Label) type).bytecodeOffset);
+      if ((label.flags & Label.FLAG_RESOLVED) != 0) {
+        return UNINITIALIZED_KIND | symbolTable.addUninitializedType("", label.bytecodeOffset);
+      } else {
+        return FORWARD_UNINITIALIZED_KIND | symbolTable.addForwardUninitializedType("", label);
+      }
     }
   }
 
@@ -637,12 +645,14 @@ class Frame {
    * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
    * @param abstractType an abstract type.
    * @return the REFERENCE_KIND abstract type corresponding to abstractType if it is
-   *     UNINITIALIZED_THIS or an UNINITIALIZED_KIND abstract type for one of the types on which a
+   *     UNINITIALIZED_THIS or an UNINITIALIZED_KIND or FORWARD_UNINITIALIZED_KIND abstract type for
-   *     constructor is invoked in the basic block. Otherwise returns abstractType.
+   *     one of the types on which a constructor is invoked in the basic block. Otherwise returns
+   *     abstractType.
    */
   private int getInitializedType(final SymbolTable symbolTable, final int abstractType) {
     if (abstractType == UNINITIALIZED_THIS
-        || (abstractType & (DIM_MASK | KIND_MASK)) == UNINITIALIZED_KIND) {
+        || (abstractType & (DIM_MASK | KIND_MASK)) == UNINITIALIZED_KIND
+        || (abstractType & (DIM_MASK | KIND_MASK)) == FORWARD_UNINITIALIZED_KIND) {
       for (int i = 0; i < initializationCount; ++i) {
         int initializedType = initializations[i];
         int dim = initializedType & DIM_MASK;
@@ -1253,11 +1263,12 @@ class Frame {
    *
    * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
    * @param sourceType the abstract type with which the abstract type array element must be merged.
-   *     This type should be of {@link #CONSTANT_KIND}, {@link #REFERENCE_KIND} or {@link
+   *     This type should be of {@link #CONSTANT_KIND}, {@link #REFERENCE_KIND}, {@link
-   *     #UNINITIALIZED_KIND} kind, with positive or {@literal null} array dimensions.
+   *     #UNINITIALIZED_KIND} or {@link #FORWARD_UNINITIALIZED_KIND} kind, with positive or
+   *     {@literal null} array dimensions.
    * @param dstTypes an array of abstract types. These types should be of {@link #CONSTANT_KIND},
-   *     {@link #REFERENCE_KIND} or {@link #UNINITIALIZED_KIND} kind, with positive or {@literal
+   *     {@link #REFERENCE_KIND}, {@link #UNINITIALIZED_KIND} or {@link #FORWARD_UNINITIALIZED_KIND}
-   *     null} array dimensions.
+   *     kind, with positive or {@literal null} array dimensions.
    * @param dstIndex the index of the type that must be merged in dstTypes.
    * @return {@literal true} if the type array has been modified by this operation.
    */
@@ -1400,7 +1411,8 @@ class Frame {
    *
    * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
    * @param abstractType an abstract type, restricted to {@link Frame#CONSTANT_KIND}, {@link
-   *     Frame#REFERENCE_KIND} or {@link Frame#UNINITIALIZED_KIND} types.
+   *     Frame#REFERENCE_KIND}, {@link Frame#UNINITIALIZED_KIND} or {@link
+   *     Frame#FORWARD_UNINITIALIZED_KIND} types.
    * @param output where the abstract type must be put.
    * @see <a href="https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.4">JVMS
    *     4.7.4</a>
@@ -1422,6 +1434,10 @@ class Frame {
         case UNINITIALIZED_KIND:
           output.putByte(ITEM_UNINITIALIZED).putShort((int) symbolTable.getType(typeValue).data);
           break;
+        case FORWARD_UNINITIALIZED_KIND:
+          output.putByte(ITEM_UNINITIALIZED);
+          symbolTable.getForwardUninitializedLabel(typeValue).put(output);
+          break;
         default:
           throw new AssertionError();
       }

spring-core/src/main/java/org/springframework/asm/Label.java

@@ -81,6 +81,9 @@ public class Label {
   /** A flag indicating that the basic block corresponding to a label is the end of a subroutine. */
   static final int FLAG_SUBROUTINE_END = 64;
 
+  /** A flag indicating that this label has at least one associated line number. */
+  static final int FLAG_LINE_NUMBER = 128;
+
   /**
    * The number of elements to add to the {@link #otherLineNumbers} array when it needs to be
    * resized to store a new source line number.
@@ -113,6 +116,13 @@ public class Label {
    */
   static final int FORWARD_REFERENCE_TYPE_WIDE = 0x20000000;
 
+  /**
+   * The type of forward references stored in two bytes in the <i>stack map table</i>. This is the
+   * case of the labels of {@link Frame#ITEM_UNINITIALIZED} stack map frame elements, when the NEW
+   * instruction is after the &lt;init&gt; constructor call (in bytecode offset order).
+   */
+  static final int FORWARD_REFERENCE_TYPE_STACK_MAP = 0x30000000;
+
   /**
    * The bit mask to extract the 'handle' of a forward reference to this label. The extracted handle
    * is the bytecode offset where the forward reference value is stored (using either 2 or 4 bytes,
@@ -145,9 +155,9 @@ public class Label {
   short flags;
 
   /**
-   * The source line number corresponding to this label, or 0. If there are several source line
+   * The source line number corresponding to this label, if {@link #FLAG_LINE_NUMBER} is set. If
-   * numbers corresponding to this label, the first one is stored in this field, and the remaining
+   * there are several source line numbers corresponding to this label, the first one is stored in
-   * ones are stored in {@link #otherLineNumbers}.
+   * this field, and the remaining ones are stored in {@link #otherLineNumbers}.
    */
   private short lineNumber;
 
@@ -332,7 +342,8 @@ public class Label {
    * @param lineNumber a source line number (which should be strictly positive).
    */
   final void addLineNumber(final int lineNumber) {
-    if (this.lineNumber == 0) {
+    if ((flags & FLAG_LINE_NUMBER) == 0) {
+      flags |= FLAG_LINE_NUMBER;
       this.lineNumber = (short) lineNumber;
     } else {
       if (otherLineNumbers == null) {
@@ -356,7 +367,7 @@ public class Label {
    */
   final void accept(final MethodVisitor methodVisitor, final boolean visitLineNumbers) {
     methodVisitor.visitLabel(this);
-    if (visitLineNumbers && lineNumber != 0) {
+    if (visitLineNumbers && (flags & FLAG_LINE_NUMBER) != 0) {
       methodVisitor.visitLineNumber(lineNumber & 0xFFFF, this);
       if (otherLineNumbers != null) {
         for (int i = 1; i <= otherLineNumbers[0]; ++i) {
@@ -400,6 +411,20 @@ public class Label {
     }
   }
 
+  /**
+   * Puts a reference to this label in the <i>stack map table</i> of a method. If the bytecode
+   * offset of the label is known, it is written directly. Otherwise, a null relative offset is
+   * written and a new forward reference is declared for this label.
+   *
+   * @param stackMapTableEntries the stack map table where the label offset must be added.
+   */
+  final void put(final ByteVector stackMapTableEntries) {
+    if ((flags & FLAG_RESOLVED) == 0) {
+      addForwardReference(0, FORWARD_REFERENCE_TYPE_STACK_MAP, stackMapTableEntries.length);
+    }
+    stackMapTableEntries.putShort(bytecodeOffset);
+  }
+
   /**
    * Adds a forward reference to this label. This method must be called only for a true forward
    * reference, i.e. only if this label is not resolved yet. For backward references, the relative
@@ -432,9 +457,12 @@ public class Label {
    * Sets the bytecode offset of this label to the given value and resolves the forward references
    * to this label, if any. This method must be called when this label is added to the bytecode of
    * the method, i.e. when its bytecode offset becomes known. This method fills in the blanks that
-   * where left in the bytecode by each forward reference previously added to this label.
+   * where left in the bytecode (and optionally in the stack map table) by each forward reference
+   * previously added to this label.
    *
    * @param code the bytecode of the method.
+   * @param stackMapTableEntries the 'entries' array of the StackMapTable code attribute of the
+   *     method. Maybe {@literal null}.
    * @param bytecodeOffset the bytecode offset of this label.
    * @return {@literal true} if a blank that was left for this label was too small to store the
    *     offset. In such a case the corresponding jump instruction is replaced with an equivalent
@@ -442,7 +470,8 @@ public class Label {
    *     instructions are later replaced with standard bytecode instructions with wider offsets (4
    *     bytes instead of 2), in ClassReader.
    */
-  final boolean resolve(final byte[] code, final int bytecodeOffset) {
+  final boolean resolve(
+      final byte[] code, final ByteVector stackMapTableEntries, final int bytecodeOffset) {
     this.flags |= FLAG_RESOLVED;
     this.bytecodeOffset = bytecodeOffset;
     if (forwardReferences == null) {
@@ -472,11 +501,14 @@ public class Label {
         }
         code[handle++] = (byte) (relativeOffset >>> 8);
         code[handle] = (byte) relativeOffset;
-      } else {
+      } else if ((reference & FORWARD_REFERENCE_TYPE_MASK) == FORWARD_REFERENCE_TYPE_WIDE) {
         code[handle++] = (byte) (relativeOffset >>> 24);
         code[handle++] = (byte) (relativeOffset >>> 16);
         code[handle++] = (byte) (relativeOffset >>> 8);
         code[handle] = (byte) relativeOffset;
+      } else {
+        stackMapTableEntries.data[handle++] = (byte) (bytecodeOffset >>> 8);
+        stackMapTableEntries.data[handle] = (byte) bytecodeOffset;
       }
     }
     return hasAsmInstructions;

spring-core/src/main/java/org/springframework/asm/MethodWriter.java

@@ -534,8 +534,9 @@ final class MethodWriter extends MethodVisitor {
    * the number of stack elements. The local variables start at index 3 and are followed by the
    * operand stack elements. In summary frame[0] = offset, frame[1] = numLocal, frame[2] = numStack.
    * Local variables and operand stack entries contain abstract types, as defined in {@link Frame},
-   * but restricted to {@link Frame#CONSTANT_KIND}, {@link Frame#REFERENCE_KIND} or {@link
+   * but restricted to {@link Frame#CONSTANT_KIND}, {@link Frame#REFERENCE_KIND}, {@link
-   * Frame#UNINITIALIZED_KIND} abstract types. Long and double types use only one array entry.
+   * Frame#UNINITIALIZED_KIND} or {@link Frame#FORWARD_UNINITIALIZED_KIND} abstract types. Long and
+   * double types use only one array entry.
    */
   private int[] currentFrame;
 
@@ -1199,7 +1200,7 @@ final class MethodWriter extends MethodVisitor {
   @Override
   public void visitLabel(final Label label) {
     // Resolve the forward references to this label, if any.
-    hasAsmInstructions |= label.resolve(code.data, code.length);
+    hasAsmInstructions |= label.resolve(code.data, stackMapTableEntries, code.length);
     // visitLabel starts a new basic block (except for debug only labels), so we need to update the
     // previous and current block references and list of successors.
     if ((label.flags & Label.FLAG_DEBUG_ONLY) != 0) {
@@ -1795,7 +1796,7 @@ final class MethodWriter extends MethodVisitor {
     if (compute == COMPUTE_ALL_FRAMES) {
       Label nextBasicBlock = new Label();
       nextBasicBlock.frame = new Frame(nextBasicBlock);
-      nextBasicBlock.resolve(code.data, code.length);
+      nextBasicBlock.resolve(code.data, stackMapTableEntries, code.length);
       lastBasicBlock.nextBasicBlock = nextBasicBlock;
       lastBasicBlock = nextBasicBlock;
       currentBasicBlock = null;
@@ -1979,9 +1980,8 @@ final class MethodWriter extends MethodVisitor {
           .putByte(Frame.ITEM_OBJECT)
           .putShort(symbolTable.addConstantClass((String) type).index);
     } else {
-      stackMapTableEntries
+      stackMapTableEntries.putByte(Frame.ITEM_UNINITIALIZED);
-          .putByte(Frame.ITEM_UNINITIALIZED)
+      ((Label) type).put(stackMapTableEntries);
-          .putShort(((Label) type).bytecodeOffset);
     }
   }
 

spring-core/src/main/java/org/springframework/asm/Opcodes.java

@@ -286,6 +286,7 @@ public interface Opcodes {
   int V19 = 0 << 16 | 63;
   int V20 = 0 << 16 | 64;
   int V21 = 0 << 16 | 65;
+  int V22 = 0 << 16 | 66;
 
   /**
    * Version flag indicating that the class is using 'preview' features.

spring-core/src/main/java/org/springframework/asm/Symbol.java

@@ -103,12 +103,25 @@ abstract class Symbol {
   static final int TYPE_TAG = 128;
 
   /**
-   * The tag value of an {@link Frame#ITEM_UNINITIALIZED} type entry in the type table of a class.
+   * The tag value of an uninitialized type entry in the type table of a class. This type is used
+   * for the normal case where the NEW instruction is before the <init> constructor call (in
+   * bytecode offset order), i.e. when the label of the NEW instruction is resolved when the
+   * constructor call is visited. If the NEW instruction is after the constructor call, use the
+   * {@link #FORWARD_UNINITIALIZED_TYPE_TAG} tag value instead.
    */
   static final int UNINITIALIZED_TYPE_TAG = 129;
 
+  /**
+   * The tag value of an uninitialized type entry in the type table of a class. This type is used
+   * for the unusual case where the NEW instruction is after the <init> constructor call (in
+   * bytecode offset order), i.e. when the label of the NEW instruction is not resolved when the
+   * constructor call is visited. If the NEW instruction is before the constructor call, use the
+   * {@link #UNINITIALIZED_TYPE_TAG} tag value instead.
+   */
+  static final int FORWARD_UNINITIALIZED_TYPE_TAG = 130;
+
   /** The tag value of a merged type entry in the (ASM specific) type table of a class. */
-  static final int MERGED_TYPE_TAG = 130;
+  static final int MERGED_TYPE_TAG = 131;
 
   // Instance fields.
 
@@ -151,8 +164,8 @@ abstract class Symbol {
    *       #CONSTANT_INVOKE_DYNAMIC_TAG} symbols,
    *   <li>an arbitrary string for {@link #CONSTANT_UTF8_TAG} and {@link #CONSTANT_STRING_TAG}
    *       symbols,
-   *   <li>an internal class name for {@link #CONSTANT_CLASS_TAG}, {@link #TYPE_TAG} and {@link
+   *   <li>an internal class name for {@link #CONSTANT_CLASS_TAG}, {@link #TYPE_TAG}, {@link
-   *       #UNINITIALIZED_TYPE_TAG} symbols,
+   *       #UNINITIALIZED_TYPE_TAG} and {@link #FORWARD_UNINITIALIZED_TYPE_TAG} symbols,
    *   <li>{@literal null} for the other types of symbol.
    * </ul>
    */
@@ -172,6 +185,9 @@ abstract class Symbol {
    *       {@link #CONSTANT_DYNAMIC_TAG} or {@link #BOOTSTRAP_METHOD_TAG} symbols,
    *   <li>the bytecode offset of the NEW instruction that created an {@link
    *       Frame#ITEM_UNINITIALIZED} type for {@link #UNINITIALIZED_TYPE_TAG} symbols,
+   *   <li>the index of the {@link Label} (in the {@link SymbolTable#labelTable} table) of the NEW
+   *       instruction that created an {@link Frame#ITEM_UNINITIALIZED} type for {@link
+   *       #FORWARD_UNINITIALIZED_TYPE_TAG} symbols,
    *   <li>the indices (in the class' type table) of two {@link #TYPE_TAG} source types for {@link
    *       #MERGED_TYPE_TAG} symbols,
    *   <li>0 for the other types of symbol.

spring-core/src/main/java/org/springframework/asm/SymbolTable.java

@@ -108,11 +108,35 @@ final class SymbolTable {
    * An ASM specific type table used to temporarily store internal names that will not necessarily
    * be stored in the constant pool. This type table is used by the control flow and data flow
    * analysis algorithm used to compute stack map frames from scratch. This array stores {@link
-   * Symbol#TYPE_TAG} and {@link Symbol#UNINITIALIZED_TYPE_TAG}) Symbol. The type symbol at index
+   * Symbol#TYPE_TAG}, {@link Symbol#UNINITIALIZED_TYPE_TAG},{@link
-   * {@code i} has its {@link Symbol#index} equal to {@code i} (and vice versa).
+   * Symbol#FORWARD_UNINITIALIZED_TYPE_TAG} and {@link Symbol#MERGED_TYPE_TAG} entries. The type
+   * symbol at index {@code i} has its {@link Symbol#index} equal to {@code i} (and vice versa).
    */
   private Entry[] typeTable;
 
+  /**
+   * The actual number of {@link LabelEntry} in {@link #labelTable}. These elements are stored from
+   * index 0 to labelCount (excluded). The other array entries are empty. These label entries are
+   * also stored in the {@link #labelEntries} hash set.
+   */
+  private int labelCount;
+
+  /**
+   * The labels corresponding to the "forward uninitialized" types in the ASM specific {@link
+   * typeTable} (see {@link Symbol#FORWARD_UNINITIALIZED_TYPE_TAG}). The label entry at index {@code
+   * i} has its {@link LabelEntry#index} equal to {@code i} (and vice versa).
+   */
+  private LabelEntry[] labelTable;
+
+  /**
+   * A hash set of all the {@link LabelEntry} elements in the {@link #labelTable}. Each {@link
+   * LabelEntry} instance is stored at the array index given by its hash code modulo the array size.
+   * If several entries must be stored at the same array index, they are linked together via their
+   * {@link LabelEntry#next} field. The {@link #getOrAddLabelEntry(Label)} method ensures that this
+   * table does not contain duplicated entries.
+   */
+  private LabelEntry[] labelEntries;
+
   /**
    * Constructs a new, empty SymbolTable for the given ClassWriter.
    *
@@ -1129,6 +1153,18 @@ final class SymbolTable {
     return typeTable[typeIndex];
   }
 
+  /**
+   * Returns the label corresponding to the "forward uninitialized" type table element whose index
+   * is given.
+   *
+   * @param typeIndex the type table index of a "forward uninitialized" type table element.
+   * @return the label corresponding of the NEW instruction which created this "forward
+   *     uninitialized" type.
+   */
+  Label getForwardUninitializedLabel(final int typeIndex) {
+    return labelTable[(int) typeTable[typeIndex].data].label;
+  }
+
   /**
    * Adds a type in the type table of this symbol table. Does nothing if the type table already
    * contains a similar type.
@@ -1149,13 +1185,13 @@ final class SymbolTable {
   }
 
   /**
-   * Adds an {@link Frame#ITEM_UNINITIALIZED} type in the type table of this symbol table. Does
+   * Adds an uninitialized type in the type table of this symbol table. Does nothing if the type
-   * nothing if the type table already contains a similar type.
+   * table already contains a similar type.
    *
    * @param value an internal class name.
-   * @param bytecodeOffset the bytecode offset of the NEW instruction that created this {@link
+   * @param bytecodeOffset the bytecode offset of the NEW instruction that created this
-   *     Frame#ITEM_UNINITIALIZED} type value.
+   *     uninitialized type value.
-   * @return the index of a new or already existing type Symbol with the given value.
+   * @return the index of a new or already existing type #@link Symbol} with the given value.
    */
   int addUninitializedType(final String value, final int bytecodeOffset) {
     int hashCode = hash(Symbol.UNINITIALIZED_TYPE_TAG, value, bytecodeOffset);
@@ -1173,6 +1209,32 @@ final class SymbolTable {
         new Entry(typeCount, Symbol.UNINITIALIZED_TYPE_TAG, value, bytecodeOffset, hashCode));
   }
 
+  /**
+   * Adds a "forward uninitialized" type in the type table of this symbol table. Does nothing if the
+   * type table already contains a similar type.
+   *
+   * @param value an internal class name.
+   * @param label the label of the NEW instruction that created this uninitialized type value. If
+   *     the label is resolved, use the {@link #addUninitializedType} method instead.
+   * @return the index of a new or already existing type {@link Symbol} with the given value.
+   */
+  int addForwardUninitializedType(final String value, final Label label) {
+    int labelIndex = getOrAddLabelEntry(label).index;
+    int hashCode = hash(Symbol.FORWARD_UNINITIALIZED_TYPE_TAG, value, labelIndex);
+    Entry entry = get(hashCode);
+    while (entry != null) {
+      if (entry.tag == Symbol.FORWARD_UNINITIALIZED_TYPE_TAG
+          && entry.hashCode == hashCode
+          && entry.data == labelIndex
+          && entry.value.equals(value)) {
+        return entry.index;
+      }
+      entry = entry.next;
+    }
+    return addTypeInternal(
+        new Entry(typeCount, Symbol.FORWARD_UNINITIALIZED_TYPE_TAG, value, labelIndex, hashCode));
+  }
+
   /**
    * Adds a merged type in the type table of this symbol table. Does nothing if the type table
    * already contains a similar type.
@@ -1225,6 +1287,59 @@ final class SymbolTable {
     return put(entry).index;
   }
 
+  /**
+   * Returns the {@link LabelEntry} corresponding to the given label. Creates a new one if there is
+   * no such entry.
+   *
+   * @param label the {@link Label} of a NEW instruction which created an uninitialized type, in the
+   *     case where this NEW instruction is after the <init> constructor call (in bytecode
+   *     offset order). See {@link Symbol#FORWARD_UNINITIALIZED_TYPE_TAG}.
+   * @return the {@link LabelEntry} corresponding to {@code label}.
+   */
+  private LabelEntry getOrAddLabelEntry(final Label label) {
+    if (labelEntries == null) {
+      labelEntries = new LabelEntry[16];
+      labelTable = new LabelEntry[16];
+    }
+    int hashCode = System.identityHashCode(label);
+    LabelEntry labelEntry = labelEntries[hashCode % labelEntries.length];
+    while (labelEntry != null && labelEntry.label != label) {
+      labelEntry = labelEntry.next;
+    }
+    if (labelEntry != null) {
+      return labelEntry;
+    }
+
+    if (labelCount > (labelEntries.length * 3) / 4) {
+      int currentCapacity = labelEntries.length;
+      int newCapacity = currentCapacity * 2 + 1;
+      LabelEntry[] newLabelEntries = new LabelEntry[newCapacity];
+      for (int i = currentCapacity - 1; i >= 0; --i) {
+        LabelEntry currentEntry = labelEntries[i];
+        while (currentEntry != null) {
+          int newCurrentEntryIndex = System.identityHashCode(currentEntry.label) % newCapacity;
+          LabelEntry nextEntry = currentEntry.next;
+          currentEntry.next = newLabelEntries[newCurrentEntryIndex];
+          newLabelEntries[newCurrentEntryIndex] = currentEntry;
+          currentEntry = nextEntry;
+        }
+      }
+      labelEntries = newLabelEntries;
+    }
+    if (labelCount == labelTable.length) {
+      LabelEntry[] newLabelTable = new LabelEntry[2 * labelTable.length];
+      System.arraycopy(labelTable, 0, newLabelTable, 0, labelTable.length);
+      labelTable = newLabelTable;
+    }
+
+    labelEntry = new LabelEntry(labelCount, label);
+    int index = hashCode % labelEntries.length;
+    labelEntry.next = labelEntries[index];
+    labelEntries[index] = labelEntry;
+    labelTable[labelCount++] = labelEntry;
+    return labelEntry;
+  }
+
   // -----------------------------------------------------------------------------------------------
   // Static helper methods to compute hash codes.
   // -----------------------------------------------------------------------------------------------
@@ -1275,7 +1390,7 @@ final class SymbolTable {
    *
    * @author Eric Bruneton
    */
-  private static class Entry extends Symbol {
+  private static final class Entry extends Symbol {
 
     /** The hash code of this entry. */
     final int hashCode;
@@ -1319,4 +1434,30 @@ final class SymbolTable {
       this.hashCode = hashCode;
     }
   }
+
+  /**
+   * A label corresponding to a "forward uninitialized" type in the ASM specific {@link
+   * SymbolTable#typeTable} (see {@link Symbol#FORWARD_UNINITIALIZED_TYPE_TAG}).
+   *
+   * @author Eric Bruneton
+   */
+  private static final class LabelEntry {
+
+    /** The index of this label entry in the {@link SymbolTable#labelTable} array. */
+    final int index;
+
+    /** The value of this label entry. */
+    final Label label;
+
+    /**
+     * Another entry (and so on recursively) having the same hash code (modulo the size of {@link
+     * SymbolTable#labelEntries}}) as this one.
+     */
+    LabelEntry next;
+
+    LabelEntry(final int index, final Label label) {
+      this.index = index;
+      this.label = label;
+    }
+  }
 }