Class LocalVariablesSorter

java.lang.Object

com.googlecode.aviator.asm.MethodVisitor

com.googlecode.aviator.asm.commons.LocalVariablesSorter

Direct Known Subclasses:

GeneratorAdapter

public class LocalVariablesSorter
extends MethodVisitor

A MethodVisitor that renumbers local variables in their order of appearance. This adapter allows one to easily add new local variables to a method. It may be used by inheriting from this class, but the preferred way of using it is via delegation: the next visitor in the chain can indeed add new locals when needed by calling newLocal(Type) on this adapter (this requires a reference back to this LocalVariablesSorter).

Field Summary

Fields

Modifier and Type	Field	Description
private boolean	changed	Indicates if at least one local variable has moved due to remapping.
protected final int	firstLocal	Index of the first local variable, after formal parameters.
private int[]	mapping	Mapping from old to new local variable indexes.
private Object[]	newLocals	Array used to store stack map local variable types after remapping.
protected int	nextLocal	Index of the next local variable to be created by newLocal(Type).
private static final Type	OBJECT_TYPE

Fields inherited from class MethodVisitor

api, mv

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	LocalVariablesSorter(int api, int access, String desc, MethodVisitor mv)	Creates a new LocalVariablesSorter.
	LocalVariablesSorter(int access, String desc, MethodVisitor mv)	Creates a new LocalVariablesSorter.

Method Summary

Modifier and Type	Method	Description
int	newLocal(Type type)	Creates a new local variable of the given type.
protected int	newLocalMapping(Type type)
private int	remap(int var, Type type)
private void	setFrameLocal(int local, Object type)
protected void	setLocalType(int local, Type type)	Notifies subclasses that a local variable has been added or remapped.
protected void	updateNewLocals(Object[] newLocals)	Notifies subclasses that a new stack map frame is being visited.
void	visitFrame(int type, int nLocal, Object[] local, int nStack, Object[] stack)	Visits the current state of the local variables and operand stack elements.
void	visitIincInsn(int var, int increment)	Visits an IINC instruction.
void	visitLocalVariable(String name, String desc, String signature, Label start, Label end, int index)	Visits a local variable declaration.
void	visitMaxs(int maxStack, int maxLocals)	Visits the maximum stack size and the maximum number of local variables of the method.
void	visitVarInsn(int opcode, int var)	Visits a local variable instruction.

Methods inherited from class MethodVisitor

visitAnnotation, visitAnnotationDefault, visitAttribute, visitCode, visitEnd, visitFieldInsn, visitInsn, visitIntInsn, visitInvokeDynamicInsn, visitJumpInsn, visitLabel, visitLdcInsn, visitLineNumber, visitLookupSwitchInsn, visitMethodInsn, visitMultiANewArrayInsn, visitParameterAnnotation, visitTableSwitchInsn, visitTryCatchBlock, visitTypeInsn

Methods inherited from class Object

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

Field Details

OBJECT_TYPE

private static final Type OBJECT_TYPE

mapping

private int[] mapping

Mapping from old to new local variable indexes. A local variable at index i of size 1 is remapped to 'mapping[2*i]', while a local variable at index i of size 2 is remapped to 'mapping[2*i+1]'.

newLocals

private Object[] newLocals

Array used to store stack map local variable types after remapping.

firstLocal

protected final int firstLocal

Index of the first local variable, after formal parameters.

nextLocal

protected int nextLocal

Index of the next local variable to be created by newLocal(Type).

changed

private boolean changed

Indicates if at least one local variable has moved due to remapping.

Constructor Details

LocalVariablesSorter

public LocalVariablesSorter(int access,
 String desc,
 MethodVisitor mv)

Creates a new LocalVariablesSorter. Subclasses must not use this constructor. Instead, they must use the LocalVariablesSorter(int, int, String, MethodVisitor) version.

Parameters:

access - access flags of the adapted method.

desc - the method's descriptor (see Type).

mv - the method visitor to which this adapter delegates calls.

LocalVariablesSorter

protected LocalVariablesSorter(int api,
 int access,
 String desc,
 MethodVisitor mv)

Creates a new LocalVariablesSorter.

Parameters:

api - the ASM API version implemented by this visitor. Must be one of Opcodes.ASM4.

access - access flags of the adapted method.

desc - the method's descriptor (see Type).

mv - the method visitor to which this adapter delegates calls.

Method Details

visitVarInsn

public void visitVarInsn(int opcode,
 int var)

Description copied from class: MethodVisitor

Visits a local variable instruction. A local variable instruction is an instruction that loads or stores the value of a local variable.

Overrides:

visitVarInsn in class MethodVisitor

Parameters:

opcode - the opcode of the local variable instruction to be visited. This opcode is either ILOAD, LLOAD, FLOAD, DLOAD, ALOAD, ISTORE, LSTORE, FSTORE, DSTORE, ASTORE or RET.

var - the operand of the instruction to be visited. This operand is the index of a local variable.

visitIincInsn

public void visitIincInsn(int var,
 int increment)

Description copied from class: MethodVisitor

Visits an IINC instruction.

Overrides:

visitIincInsn in class MethodVisitor

Parameters:

var - index of the local variable to be incremented.

increment - amount to increment the local variable by.

visitMaxs

public void visitMaxs(int maxStack,
 int maxLocals)

Description copied from class: MethodVisitor

Visits the maximum stack size and the maximum number of local variables of the method.

Overrides:

visitMaxs in class MethodVisitor

Parameters:

maxStack - maximum stack size of the method.

maxLocals - maximum number of local variables for the method.

visitLocalVariable

public void visitLocalVariable(String name,
 String desc,
 String signature,
 Label start,
 Label end,
 int index)

Description copied from class: MethodVisitor

Visits a local variable declaration.

Overrides:

visitLocalVariable in class MethodVisitor

Parameters:

name - the name of a local variable.

desc - the type descriptor of this local variable.

signature - the type signature of this local variable. May be null if the local variable type does not use generic types.

start - the first instruction corresponding to the scope of this local variable (inclusive).

end - the last instruction corresponding to the scope of this local variable (exclusive).

index - the local variable's index.

visitFrame

public void visitFrame(int type,
 int nLocal,
 Object[] local,
 int nStack,
 Object[] stack)

Description copied from class: MethodVisitor

Visits the current state of the local variables and operand stack elements. This method must(*) be called just before any instruction i that follows an unconditional branch instruction such as GOTO or THROW, that is the target of a jump instruction, or that starts an exception handler block. The visited types must describe the values of the local variables and of the operand stack elements just before i is executed.

(*) this is mandatory only for classes whose version is greater than or equal to V1_6.

The frames of a method must be given either in expanded form, or in compressed form (all frames must use the same format, i.e. you must not mix expanded and compressed frames within a single method):

• In expanded form, all frames must have the F_NEW type.
• In compressed form, frames are basically "deltas" from the state of the previous frame:
  • Opcodes.F_SAME representing frame with exactly the same locals as the previous frame and with the empty stack.
  • Opcodes.F_SAME1 representing frame with exactly the same locals as the previous frame and with single value on the stack ( nStack is 1 and stack[0] contains value for the type of the stack item).
  • Opcodes.F_APPEND representing frame with current locals are the same as the locals in the previous frame, except that additional locals are defined (nLocal is 1, 2 or 3 and local elements contains values representing added types).
  • Opcodes.F_CHOP representing frame with current locals are the same as the locals in the previous frame, except that the last 1-3 locals are absent and with the empty stack (nLocals is 1, 2 or 3).
  • Opcodes.F_FULL representing complete frame data.

In both cases the first frame, corresponding to the method's parameters and access flags, is implicit and must not be visited. Also, it is illegal to visit two or more frames for the same code location (i.e., at least one instruction must be visited between two calls to visitFrame).

Overrides:

visitFrame in class MethodVisitor

Parameters:

type - the type of this stack map frame. Must be Opcodes.F_NEW for expanded frames, or Opcodes.F_FULL, Opcodes.F_APPEND, Opcodes.F_CHOP, Opcodes.F_SAME or Opcodes.F_APPEND, Opcodes.F_SAME1 for compressed frames.

nLocal - the number of local variables in the visited frame.

local - the local variable types in this frame. This array must not be modified. Primitive types are represented by Opcodes.TOP, Opcodes.INTEGER, Opcodes.FLOAT, Opcodes.LONG, Opcodes.DOUBLE,Opcodes.NULL or Opcodes.UNINITIALIZED_THIS (long and double are represented by a single element). Reference types are represented by String objects (representing internal names), and uninitialized types by Label objects (this label designates the NEW instruction that created this uninitialized value).

nStack - the number of operand stack elements in the visited frame.

stack - the operand stack types in this frame. This array must not be modified. Its content has the same format as the "local" array.

newLocal

public int newLocal(Type type)

Creates a new local variable of the given type.

Parameters:

type - the type of the local variable to be created.

Returns:

the identifier of the newly created local variable.

updateNewLocals

protected void updateNewLocals(Object[] newLocals)

Notifies subclasses that a new stack map frame is being visited. The array argument contains the stack map frame types corresponding to the local variables added with newLocal(Type). This method can update these types in place for the stack map frame being visited. The default implementation of this method does nothing, i.e. a local variable added with newLocal(Type) will have the same type in all stack map frames. But this behavior is not always the desired one, for instance if a local variable is added in the middle of a try/catch block: the frame for the exception handler should have a TOP type for this new local.

Parameters:

newLocals - the stack map frame types corresponding to the local variables added with newLocal(Type) (and null for the others). The format of this array is the same as in MethodVisitor.visitFrame(int, int, Object[], int, Object[]), except that long and double types use two slots. The types for the current stack map frame must be updated in place in this array.

setLocalType

protected void setLocalType(int local,
 Type type)

Notifies subclasses that a local variable has been added or remapped. The default implementation of this method does nothing.

Parameters:

local - a local variable identifier, as returned by newLocal().

type - the type of the value being stored in the local variable.

setFrameLocal

private void setFrameLocal(int local,
 Object type)

remap

private int remap(int var,
 Type type)

newLocalMapping

protected int newLocalMapping(Type type)