variable.java

linux下建立JAVA虚拟机的源码KAFFE

// Copyright (c) 1997, 2004  Per M.A. Bothner.
// This is free software;  for terms and warranty disclaimer see ./COPYING.

package gnu.bytecodecvssnap;

public class Variable extends Location implements java.util.Enumeration
{
  /* Variables in a Scope are linked together in a linked list. */
  Variable next;
  public final Variable nextVar () { return next; }
  public final boolean hasMoreElements () { return next != null; }
  public Object nextElement ()
  {
    if (next == null)
      throw new java.util.NoSuchElementException("Variable enumeration");
    return next;
  }

  public Variable ()
  {
  }

  public Variable (String name)
  {
    setName(name);
  }

  public Variable (String name, Type type)
  {
    setName(name);
    setType(type);
  }

  private int flags = SIMPLE_FLAG;
  /** The SIMPLE_FLAG records the isSimple (q.v.) state. */
  private static final int SIMPLE_FLAG = 0x1;
  /** The PARAMETER_FLAG bit is true for parameters. */
  private static final int PARAMETER_FLAG = 0x2;
  private static final int LIVE_FLAG = 0x4;

  static final int UNASSIGNED = -1;
  /** The local variable slot number used by this variable.
   * Not used (by the codegen layer) if !isSimple(). */
  int offset = UNASSIGNED;
  /** Returns true iff assigned to a local variable slot.
   * Only relevant if isSimple (). */
  public final boolean isAssigned () { return offset != UNASSIGNED; }

  Scope scope;

  final boolean dead () { return (flags & LIVE_FLAG) == 0; }

  private void setFlag (boolean setting, int flag)
  {
    if (setting) flags |= flag;
    else flags &= ~flag;
  }

  /** Returns true for a "simple" variable.
   * A "simple" Variable can be stack-allocated using standard local
   * variable slots.  It is allocated by the codegen package.
   * A non-simple variable may need heap allocation, or more more
   * complex access;  it is basically ignored by the codegen package,
   * and must be managed by higher layers.  */
  public final boolean isSimple ()
  {
    return (flags & SIMPLE_FLAG) != 0;
  }
  
  public final void setSimple (boolean simple)
  { setFlag(simple, SIMPLE_FLAG); }

  public final boolean isParameter ()
  {
    return (flags & PARAMETER_FLAG) != 0;
  }
  
  public final void setParameter (boolean parameter)
  {
    setFlag(parameter, PARAMETER_FLAG);
  }

  /** Assign a local variable to a given local variable slot.
   * @param varIndex the index of the local variables.
   * @return true iff we succeeded (i.e. the slot was unused) */
  public boolean reserveLocal (int varIndex, CodeAttr code)
  {
    int size = getType().size > 4 ? 2 : 1;
    if (code.locals.used == null)
      code.locals.used = new Variable[20+size];
    else if (code.getMaxLocals() + size >= code.locals.used.length) {
      Variable[] new_locals = new Variable [2 * code.locals.used.length + size];
      System.arraycopy (code.locals.used, 0, new_locals, 0, code.getMaxLocals());
      code.locals.used = new_locals;
    }
    for (int j = 0; j < size; j++)
      {
	if (code.locals.used[varIndex+j] != null)
	  return false;
      }
    for (int j = 0; j < size; j++)
      code.locals.used[varIndex + j] = this;
    if (varIndex + size > code.getMaxLocals())
      code.setMaxLocals(varIndex + size);
    offset = varIndex;
    flags |= LIVE_FLAG;
    return true;
  }

  /**
   * Allocate slots for a local variable (or parameter).
   */
  public void allocateLocal (CodeAttr code)
  {
    if (offset != UNASSIGNED)
      return;
    for (int i = 0; ; i++)
      {
	if (reserveLocal (i, code))
	  return;
      }
  }

  public void freeLocal (CodeAttr code)
  {
    flags &= ~LIVE_FLAG;
    int size = getType().size > 4 ? 2 : 1;
    while (--size >= 0)
      code.locals.used [offset + size] = null;
  }

  boolean shouldEmit ()
  {
    Scope sc = scope;  // Cache
    Label start, end;
    int pos;
    return (isSimple () && name != null && sc != null
	    && (start = sc.start) != null
	    && (pos = start.position) >= 0
	    && (end = sc.end) != null
	    && end.position > pos);
  }

  public String toString()
  {
    return "Variable["+getName()+" offset:"+offset+']';
  }
}