jodd-proxetta/src/main/java/jodd/asm7/Frame.java
private static boolean merge(
      final SymbolTable symbolTable,
      final int sourceType,
      final int[] dstTypes,
      final int dstIndex) {
    int dstType = dstTypes[dstIndex];
    if (dstType == sourceType) {
      // If the types are equal, merge(sourceType, dstType) = dstType, so there is no change.
      return false;
    }
    int srcType = sourceType;
    if ((sourceType & ~DIM_MASK) == NULL) {
      if (dstType == NULL) {
        return false;
      }
      srcType = NULL;
    }
    if (dstType == 0) {
      // If dstTypes[dstIndex] has never been assigned, merge(srcType, dstType) = srcType.
      dstTypes[dstIndex] = srcType;
      return true;
    }
    int mergedType;
    if ((dstType & DIM_MASK) != 0 || (dstType & KIND_MASK) == REFERENCE_KIND) {
      // If dstType is a reference type of any array dimension.
      if (srcType == NULL) {
        // If srcType is the NULL type, merge(srcType, dstType) = dstType, so there is no change.
        return false;
      } else if ((srcType & (DIM_MASK | KIND_MASK)) == (dstType & (DIM_MASK | KIND_MASK))) {
        // If srcType has the same array dimension and the same kind as dstType.
        if ((dstType & KIND_MASK) == REFERENCE_KIND) {
          // If srcType and dstType are reference types with the same array dimension,
          // merge(srcType, dstType) = dim(srcType) | common super class of srcType and dstType.
          mergedType =
              (srcType & DIM_MASK)
                  | REFERENCE_KIND
                  | symbolTable.addMergedType(srcType & VALUE_MASK, dstType & VALUE_MASK);
        } else {
          // If srcType and dstType are array types of equal dimension but different element types,
          // merge(srcType, dstType) = dim(srcType) - 1 | java/lang/Object.
          int mergedDim = ELEMENT_OF + (srcType & DIM_MASK);
          mergedType = mergedDim | REFERENCE_KIND | symbolTable.addType("java/lang/Object");
        }
      } else if ((srcType & DIM_MASK) != 0 || (srcType & KIND_MASK) == REFERENCE_KIND) {
        // If srcType is any other reference or array type,
        // merge(srcType, dstType) = min(srcDdim, dstDim) | java/lang/Object
        // where srcDim is the array dimension of srcType, minus 1 if srcType is an array type
        // with a non reference element type (and similarly for dstDim).
        int srcDim = srcType & DIM_MASK;
        if (srcDim != 0 && (srcType & KIND_MASK) != REFERENCE_KIND) {
          srcDim = ELEMENT_OF + srcDim;
        }
        int dstDim = dstType & DIM_MASK;
        if (dstDim != 0 && (dstType & KIND_MASK) != REFERENCE_KIND) {
          dstDim = ELEMENT_OF + dstDim;
        }
        mergedType =
            Math.min(srcDim, dstDim) | REFERENCE_KIND | symbolTable.addType("java/lang/Object");
      } else {
        // If srcType is any other type, merge(srcType, dstType) = TOP.
        mergedType = TOP;
      }
    } else if (dstType == NULL) {
      // If dstType is the NULL type, merge(srcType, dstType) = srcType, or TOP if srcType is not a
      // an array type or a reference type.
      mergedType =
          (srcType & DIM_MASK) != 0 || (srcType & KIND_MASK) == REFERENCE_KIND ? srcType : TOP;
    } else {
      // If dstType is any other type, merge(srcType, dstType) = TOP whatever srcType.
      mergedType = TOP;
    }
    if (mergedType != dstType) {
      dstTypes[dstIndex] = mergedType;
      return true;
    }
    return false;
  }
private static boolean merge(
      final SymbolTable symbolTable,
      final int sourceType,
      final int[] dstTypes,
      final int dstIndex) {
    int dstType = dstTypes[dstIndex];
    if (dstType == sourceType) {
      // If the types are equal, merge(sourceType, dstType) = dstType, so there is no change.
      return false;
    }
    int srcType = sourceType;
    if ((sourceType & ~DIM_MASK) == NULL) {
      if (dstType == NULL) {
        return false;
      }
      srcType = NULL;
    }
    if (dstType == 0) {
      // If dstTypes[dstIndex] has never been assigned, merge(srcType, dstType) = srcType.
      dstTypes[dstIndex] = srcType;
      return true;
    }
    int mergedType;
    if ((dstType & DIM_MASK) != 0 || (dstType & KIND_MASK) == REFERENCE_KIND) {
      // If dstType is a reference type of any array dimension.
      if (srcType == NULL) {
        // If srcType is the NULL type, merge(srcType, dstType) = dstType, so there is no change.
        return false;
      } else if ((srcType & (DIM_MASK | KIND_MASK)) == (dstType & (DIM_MASK | KIND_MASK))) {
        // If srcType has the same array dimension and the same kind as dstType.
        if ((dstType & KIND_MASK) == REFERENCE_KIND) {
          // If srcType and dstType are reference types with the same array dimension,
          // merge(srcType, dstType) = dim(srcType) | common super class of srcType and dstType.
          mergedType =
              (srcType & DIM_MASK)
                  | REFERENCE_KIND
                  | symbolTable.addMergedType(srcType & VALUE_MASK, dstType & VALUE_MASK);
        } else {
          // If srcType and dstType are array types of equal dimension but different element types,
          // merge(srcType, dstType) = dim(srcType) - 1 | java/lang/Object.
          int mergedDim = ELEMENT_OF + (srcType & DIM_MASK);
          mergedType = mergedDim | REFERENCE_KIND | symbolTable.addType("java/lang/Object");
        }
      } else if ((srcType & DIM_MASK) != 0 || (srcType & KIND_MASK) == REFERENCE_KIND) {
        // If srcType is any other reference or array type,
        // merge(srcType, dstType) = min(srcDdim, dstDim) | java/lang/Object
        // where srcDim is the array dimension of srcType, minus 1 if srcType is an array type
        // with a non reference element type (and similarly for dstDim).
        int srcDim = srcType & DIM_MASK;
        if (srcDim != 0 && (srcType & KIND_MASK) != REFERENCE_KIND) {
          srcDim = ELEMENT_OF + srcDim;
        }
        int dstDim = dstType & DIM_MASK;
        if (dstDim != 0 && (dstType & KIND_MASK) != REFERENCE_KIND) {
          dstDim = ELEMENT_OF + dstDim;
        }
        mergedType =
            Math.min(srcDim, dstDim) | REFERENCE_KIND | symbolTable.addType("java/lang/Object");
      } else {
        // If srcType is any other type, merge(srcType, dstType) = TOP.
        mergedType = TOP;
      }
    } else if (dstType == NULL) {
      // If dstType is the NULL type, merge(srcType, dstType) = srcType, or TOP if srcType is not a
      // an array type or a reference type.
      mergedType =
          (srcType & DIM_MASK) != 0 || (srcType & KIND_MASK) == REFERENCE_KIND ? srcType : TOP;
    } else {
      // If dstType is any other type, merge(srcType, dstType) = TOP whatever srcType.
      mergedType = TOP;
    }
    if (mergedType != dstType) {
      dstTypes[dstIndex] = mergedType;
      return true;
    }
    return false;
  }
Merges the type at the given index in the given abstract type array with the given type.
Returns {@literal true} if the type array has been modified by this operation.

@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
#UNINITIALIZED_KIND} kind, with positive or 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 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.