com.apptelemetry.apm.org.objectweb.asm.commons

Class LocalVariablesSorter

java.lang.Object

com.apptelemetry.apm.org.objectweb.asm.MethodVisitor

com.apptelemetry.apm.org.objectweb.asm.commons.LocalVariablesSorter

Direct Known Subclasses:

GeneratorAdapter, RemappingMethodAdapter

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(com.apptelemetry.apm.org.objectweb.asm.Type) on this adapter (this requires a reference back to this LocalVariablesSorter).

Author:

Chris Nokleberg, Eugene Kuleshov, Eric Bruneton

Constructor Summary

Constructors

Constructor and Description
LocalVariablesSorter(int access, java.lang.String desc, MethodVisitor mv) Creates a new LocalVariablesSorter.

Method Summary

Modifier and Type	Method and Description
int	newLocal(Type type) Creates a new local variable of the given type.
void	visitFrame(int type, int nLocal, java.lang.Object[] local, int nStack, java.lang.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(java.lang.String name, java.lang.String desc, java.lang.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 com.apptelemetry.apm.org.objectweb.asm.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 java.lang.Object

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

Constructor Detail

LocalVariablesSorter

public LocalVariablesSorter(int access,
                            java.lang.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.

Method Detail

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(java.lang.String name,
                               java.lang.String desc,
                               java.lang.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,
                       java.lang.Object[] local,
                       int nStack,
                       java.lang.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.

Packed frames are basically "deltas" from the state of the previous frame (very first frame is implicitly defined by the method's parameters and access flags):

• 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.

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.