jdk.internal.jvmci.code

Class BytecodeFrame

java.lang.Object

jdk.internal.jvmci.code.BytecodePosition

jdk.internal.jvmci.code.BytecodeFrame

public class BytecodeFrame
extends BytecodePosition

Represents the Java bytecode frame state(s) at a given position including locations where to find the local variables, operand stack values and locked objects of the bytecode frame(s).

Field Summary

Fields

Modifier and Type	Field and Description
static int	AFTER_BCI The BCI for the state after finishing the execution of a method and returning normally.
static int	AFTER_EXCEPTION_BCI The BCI for exception unwind.
static int	BEFORE_BCI The BCI for the state before starting to execute a method.
boolean	duringCall
static int	INVALID_FRAMESTATE_BCI This BCI should be used for states that cannot be the target of a deoptimization, like snippet frame states.
int	numLocals The number of locals in the values array.
int	numLocks The number of locks in the values array.
int	numStack The number of stack slots in the values array.
boolean	rethrowException True if this is a position inside an exception handler before the exception object has been consumed.
static int	UNKNOWN_BCI This BCI should be used for frame states that are built for code with no meaningful BCI.
static int	UNWIND_BCI The BCI for exception unwind.
Value[]	values An array of values representing how to reconstruct the state of the Java frame.

Constructor Summary

Constructors

Constructor and Description
BytecodeFrame(BytecodeFrame caller, ResolvedJavaMethod method, int bci, boolean rethrowException, boolean duringCall, Value[] values, int numLocals, int numStack, int numLocks) Creates a new frame object.

Method Summary

Modifier and Type	Method and Description
BytecodeFrame	caller() Gets the caller of this frame.
boolean	equals(Object obj) Deep equality test.
Value	getLocalValue(int i) Gets the value representing the specified local variable.
Value	getLockValue(int i) Gets the value representing the specified lock.
static String	getPlaceholderBciName(int bci) Gets the name of a given placeholder BCI.
Value	getStackValue(int i) Gets the value representing the specified stack slot.
static boolean	isPlaceholderBci(int bci) Determines if a given BCI matches one of the placeholder BCI constants defined in this class.
String	toString() Converts this code position to a string representation.
boolean	validateFormat(boolean derivedOk) Ensure that the frame state is formatted as expected by the JVM, with null or Illegal in the slot following a double word item.

Methods inherited from class jdk.internal.jvmci.code.BytecodePosition

addCaller, getBCI, getCaller, getMethod, hashCode

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

values

public final Value[] values

An array of values representing how to reconstruct the state of the Java frame. This is array is partitioned as follows:

Start index (inclusive)	End index (exclusive)	Description
0	numLocals	Local variables
numLocals	numLocals + numStack	Operand stack
numLocals + numStack	values.length	Locked objects

Note that the number of locals and the number of stack slots may be smaller than the maximum number of locals and stack slots as specified in the compiled method.

numLocals

public final int numLocals

The number of locals in the values array.

numStack

public final int numStack

The number of stack slots in the values array.

numLocks

public final int numLocks

The number of locks in the values array.

rethrowException

public final boolean rethrowException

True if this is a position inside an exception handler before the exception object has been consumed. In this case, numStack == 1 and getStackValue(0) is the location of the exception object. If deoptimization happens at this position, the interpreter will rethrow the exception instead of executing the bytecode instruction at this position.

duringCall

public final boolean duringCall

UNKNOWN_BCI

public static final int UNKNOWN_BCI

This BCI should be used for frame states that are built for code with no meaningful BCI.

See Also:

Constant Field Values

UNWIND_BCI

public static final int UNWIND_BCI

The BCI for exception unwind. This is synthetic code and has no representation in bytecode. In contrast with AFTER_EXCEPTION_BCI, at this point, if the method is synchronized, the monitor is still held.

See Also:

Constant Field Values

BEFORE_BCI

public static final int BEFORE_BCI

The BCI for the state before starting to execute a method. Note that if the method is synchronized, the monitor is not yet held.

See Also:

Constant Field Values

AFTER_BCI

public static final int AFTER_BCI

The BCI for the state after finishing the execution of a method and returning normally. Note that if the method was synchronized the monitor is already released.

See Also:

Constant Field Values

AFTER_EXCEPTION_BCI

public static final int AFTER_EXCEPTION_BCI

The BCI for exception unwind. This is synthetic code and has no representation in bytecode. In contrast with UNWIND_BCI, at this point, if the method is synchronized, the monitor is already released.

See Also:

Constant Field Values

INVALID_FRAMESTATE_BCI

public static final int INVALID_FRAMESTATE_BCI

This BCI should be used for states that cannot be the target of a deoptimization, like snippet frame states.

See Also:

Constant Field Values

Constructor Detail

BytecodeFrame

public BytecodeFrame(BytecodeFrame caller,
                     ResolvedJavaMethod method,
                     int bci,
                     boolean rethrowException,
                     boolean duringCall,
                     Value[] values,
                     int numLocals,
                     int numStack,
                     int numLocks)

Creates a new frame object.

Parameters:

caller - the caller frame (which may be null)

method - the method

bci - a BCI within the method

rethrowException - specifies if the VM should re-throw the pending exception when deopt'ing using this frame

values - the frame state values

numLocals - the number of local variables

numStack - the depth of the stack

numLocks - the number of locked objects

Method Detail

isPlaceholderBci

public static boolean isPlaceholderBci(int bci)

Determines if a given BCI matches one of the placeholder BCI constants defined in this class.

getPlaceholderBciName

public static String getPlaceholderBciName(int bci)

Gets the name of a given placeholder BCI.

validateFormat

public boolean validateFormat(boolean derivedOk)

Ensure that the frame state is formatted as expected by the JVM, with null or Illegal in the slot following a double word item. This should really be checked in FrameState itself but because of Word type rewriting and alternative backends that can't be done.

getLocalValue

public Value getLocalValue(int i)

Gets the value representing the specified local variable.

Parameters:

i - the local variable index

Returns:

the value that can be used to reconstruct the local's current value

getStackValue

public Value getStackValue(int i)

Gets the value representing the specified stack slot.

Parameters:

i - the stack index

Returns:

the value that can be used to reconstruct the stack slot's current value

getLockValue

public Value getLockValue(int i)

Gets the value representing the specified lock.

Parameters:

i - the lock index

Returns:

the value that can be used to reconstruct the lock's current value

caller

public BytecodeFrame caller()

Gets the caller of this frame.

Returns:

null if this frame has no caller

equals

public boolean equals(Object obj)

Description copied from class: BytecodePosition

Deep equality test.

Overrides:

equals in class BytecodePosition

toString

public String toString()

Description copied from class: BytecodePosition

Converts this code position to a string representation.

Overrides:

toString in class BytecodePosition

Returns:

a string representation of this code position