com.sleepycat.asm
Class Label

java.lang.Object
  com.sleepycat.asm.Label

public class Label
extends Object

A label represents a position in the bytecode of a method. Labels are used for jump, goto, and switch instructions, and for try catch blocks.

Author:

Eric Bruneton

Field Summary

(package private) int	beginStackSize The stack size at the beginning of this basic block.
(package private) int	line The line number corresponding to this label, if known.
(package private) int	maxStackSize The (relative) maximum stack size corresponding to this basic block.
(package private) Label	next The next basic block in the basic block stack.
(package private) int	position The position of this label in the code, if known.
(package private) boolean	pushed true if this basic block has been pushed in the basic block stack.
(package private) boolean	resized If the label position has been updated, after instruction resizing.
(package private) boolean	resolved Indicates if the position of this label is known.
(package private) Edge	successors The successors of this node in the control flow graph.

Constructor Summary

Label()
Constructs a new label.

Method Summary

int	getOffset() Returns the offset corresponding to this label.
(package private) void	put(MethodWriter owner, ByteVector out, int source, boolean wideOffset) Puts a reference to this label in the bytecode of a method.
(package private) boolean	resolve(MethodWriter owner, int position, byte[] data) Resolves all forward references to this label.
String	toString() Returns a string representation of this label.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

line

int line

The line number corresponding to this label, if known.

resolved

boolean resolved

Indicates if the position of this label is known.

position

int position

The position of this label in the code, if known.

resized

boolean resized

If the label position has been updated, after instruction resizing.

beginStackSize

int beginStackSize

The stack size at the beginning of this basic block. This size is initially unknown. It is computed by the control flow analysis algorithm (see visitMaxs).

maxStackSize

int maxStackSize

The (relative) maximum stack size corresponding to this basic block. This size is relative to the stack size at the beginning of the basic block, i.e., the true maximum stack size is equal to beginStackSize + maxStackSize.

successors

Edge successors

The successors of this node in the control flow graph. These successors are stored in a linked list of Edge objects, linked to each other by their Edge.next field.

next

Label next

The next basic block in the basic block stack. See visitMaxs.

pushed

boolean pushed

true if this basic block has been pushed in the basic block stack. See visitMaxs.

Constructor Detail

Label

public Label()

Constructs a new label.

Method Detail

getOffset

public int getOffset()

Returns the offset corresponding to this label. This offset is computed from the start of the method's bytecode. This method is intended for Attribute sub classes, and is normally not needed by class generators or adapters.

Returns:

the offset corresponding to this label.

Throws:

IllegalStateException - if this label is not resolved yet.

put

void put(MethodWriter owner,
         ByteVector out,
         int source,
         boolean wideOffset)

Puts a reference to this label in the bytecode of a method. If the position of the label is known, the offset is computed and written directly. Otherwise, a null offset is written and a new forward reference is declared for this label.

Parameters:

owner - the code writer that calls this method.

out - the bytecode of the method.

source - the position of first byte of the bytecode instruction that contains this label.

wideOffset - true if the reference must be stored in 4 bytes, or false if it must be stored with 2 bytes.

Throws:

IllegalArgumentException - if this label has not been created by the given code writer.

resolve

boolean resolve(MethodWriter owner,
                int position,
                byte[] data)

Resolves all forward references to this label. This method must be called when this label is added to the bytecode of the method, i.e. when its position becomes known. This method fills in the blanks that where left in the bytecode by each forward reference previously added to this label.

Parameters:

owner - the code writer that calls this method.

position - the position of this label in the bytecode.

data - the bytecode of the method.

Returns:

true if a blank that was left for this label was to small to store the offset. In such a case the corresponding jump instruction is replaced with a pseudo instruction (using unused opcodes) using an unsigned two bytes offset. These pseudo instructions will need to be replaced with true instructions with wider offsets (4 bytes instead of 2). This is done in MethodWriter.resizeInstructions(int[], int[], int).

Throws:

IllegalArgumentException - if this label has already been resolved, or if it has not been created by the given code writer.

toString

public String toString()

Returns a string representation of this label.

Overrides:

toString in class Object

Returns:

a string representation of this label.