com.oracle.truffle.api.nodes

Interface BytecodeOSRNode

All Superinterfaces:

NodeInterface

public interface BytecodeOSRNode
extends NodeInterface

Interface for Truffle bytecode nodes which can be on-stack replaced (OSR). There are a few restrictions Bytecode OSR nodes must satisfy in order for OSR to work correctly:

1. The node must extend Node or a subclass of Node.
2. The node must provide storage for the OSR metadata maintained by the runtime using an instance field. The field must be @CompilationFinal, and the BytecodeOSRNode.getOSRMetadata() and BytecodeOSRNode.setOSRMetadata(java.lang.Object) methods must proxy accesses to it.
3. The node should call BytecodeOSRNode.pollOSRBackEdge(com.oracle.truffle.api.nodes.BytecodeOSRNode) and BytecodeOSRNode.tryOSR(com.oracle.truffle.api.nodes.BytecodeOSRNode, int, java.lang.Object, java.lang.Runnable, com.oracle.truffle.api.frame.VirtualFrame) as described by their documentation.

For performance reasons, the parent frame may be copied into a new frame used for OSR. If this happens, BytecodeOSRNode.copyIntoOSRFrame(com.oracle.truffle.api.frame.VirtualFrame, com.oracle.truffle.api.frame.VirtualFrame, int) is used to perform the copy, and BytecodeOSRNode.restoreParentFrame(com.oracle.truffle.api.frame.VirtualFrame, com.oracle.truffle.api.frame.VirtualFrame) is used to copy the OSR frame contents back into the parent frame after OSR. A node may override these methods; by default, they perform slot-wise copies.

A node may also wish to override BytecodeOSRNode.prepareOSR(int) to perform initialization. This method will be called before compilation, and can be useful to avoid deoptimizing inside compiled code.

Since:

21.3

Method Summary

Modifier and Type	Method and Description
default void	copyIntoOSRFrame(VirtualFrame osrFrame, VirtualFrame parentFrame, int target) Copies the contents of the parentFrame into the osrFrame used to execute OSR.
Object	executeOSR(VirtualFrame osrFrame, int target, Object interpreterState) Entrypoint to invoke this node through OSR.
Object	getOSRMetadata() Gets the OSR metadata for this instance.
static boolean	pollOSRBackEdge(BytecodeOSRNode osrNode) Reports a back edge, returning whether to try performing OSR.
default void	prepareOSR(int target) Initialization hook which will be invoked before OSR compilation.
default void	restoreParentFrame(VirtualFrame osrFrame, VirtualFrame parentFrame) Restores the contents of the osrFrame back into the parentFrame after OSR.
void	setOSRMetadata(Object osrMetadata) Sets the OSR metadata for this instance.
static Object	tryOSR(BytecodeOSRNode osrNode, int target, Object interpreterState, Runnable beforeTransfer, VirtualFrame parentFrame) Tries to perform OSR.

Method Detail

executeOSR

Object executeOSR(VirtualFrame osrFrame,
                  int target,
                  Object interpreterState)

Entrypoint to invoke this node through OSR. This method should execute from the target location.

The osrFrame may be the parent frame, but for performance reasons could also be a new frame. The frame's arguments are undefined and should not be used directly.

Typically, a bytecode node's execute(VirtualFrame) method already contains a dispatch loop. This loop can be extracted into a separate method which can also be used by this method. For example:

 Object execute(VirtualFrame frame) {
   return dispatchFromBCI(frame, 0);
 }
 Object executeOSR(VirtualFrame osrFrame, int target, Object interpreterState) {
   return dispatchFromBCI(osrFrame, target);
 }
 Object dispatchFromBCI(VirtualFrame frame, int bci) {
     // main dispatch loop
     while(true) {
         switch(instructions[bci]) {
             ...
         }
     }
 }
 

Parameters:

osrFrame - the frame to use for OSR.

target - the target location to execute from (e.g., bytecode index).

interpreterState - other interpreter state used to resume execution. See BytecodeOSRNode.tryOSR(com.oracle.truffle.api.nodes.BytecodeOSRNode, int, java.lang.Object, java.lang.Runnable, com.oracle.truffle.api.frame.VirtualFrame) for more details.

Returns:

the result of execution.

Since:

21.3

getOSRMetadata

Object getOSRMetadata()

Gets the OSR metadata for this instance. The metadata must be stored on a @CompilationFinal instance field. Refer to the documentation for this interface for a more complete description.

Returns:

the OSR metadata.

Since:

21.3

setOSRMetadata

void setOSRMetadata(Object osrMetadata)

Sets the OSR metadata for this instance. The metadata must be stored on a @CompilationFinal instance field. Refer to the documentation for this interface for a more complete description.

Parameters:

osrMetadata - the OSR metadata.

Since:

21.3

copyIntoOSRFrame

default void copyIntoOSRFrame(VirtualFrame osrFrame,
                              VirtualFrame parentFrame,
                              int target)

Copies the contents of the parentFrame into the osrFrame used to execute OSR. By default, performs a slot-wise copy of the frame.

NOTE: This method is only used if the Truffle runtime decides to copy the frame. OSR may also reuse the parent frame directly.

Parameters:

osrFrame - the frame to use for OSR.

parentFrame - the frame used before performing OSR.

target - the target location OSR will execute from (e.g., bytecode index).

Since:

21.3

restoreParentFrame

default void restoreParentFrame(VirtualFrame osrFrame,
                                VirtualFrame parentFrame)

Restores the contents of the osrFrame back into the parentFrame after OSR. By default, performs a slot-wise copy of the frame. Though a bytecode interpreter might not explicitly use parentFrame after OSR, it is necessary to restore the state into parentFrame if it may be accessed through instrumentation.

NOTE: This method is only used if the Truffle runtime decided to copy the frame using BytecodeOSRNode.copyIntoOSRFrame(com.oracle.truffle.api.frame.VirtualFrame, com.oracle.truffle.api.frame.VirtualFrame, int).

Parameters:

osrFrame - the frame which was used for OSR.

parentFrame - the frame which will be used by the parent after returning from OSR.

Since:

21.3

prepareOSR

default void prepareOSR(int target)

Initialization hook which will be invoked before OSR compilation. This hook can be used to perform any necessary initialization before compilation happens.

For example, consider a field which must be initialized in the interpreter:

  @CompilationFinal Object field;
 Object getField() {
     if (field == null) {
         CompilerDirectives.transferToInterpreterAndInvalidate();
         field = new Object();
     }
     return field;
 }
 

If the field is accessed from compiled OSR code, it may trigger a deoptimization in order to initialize the field. Using BytecodeOSRNode.prepareOSR(int) to initialize the field can prevent this.

Parameters:

target - the target location OSR will execute from (e.g., bytecode index).

Since:

21.3

pollOSRBackEdge

static boolean pollOSRBackEdge(BytecodeOSRNode osrNode)

Reports a back edge, returning whether to try performing OSR.

An interpreter must ensure this method returns true immediately before calling BytecodeOSRNode.tryOSR(com.oracle.truffle.api.nodes.BytecodeOSRNode, int, java.lang.Object, java.lang.Runnable, com.oracle.truffle.api.frame.VirtualFrame). For example:

 if (BytecodeOSRNode.pollOSRBackEdge(this)) {
   Object osrResult = BytecodeOSRNode.tryOSR(...);
   ...
 }
 

Parameters:

osrNode - the node to report a back-edge for.

Returns:

whether to try OSR.

Since:

21.3

tryOSR

static Object tryOSR(BytecodeOSRNode osrNode,
                     int target,
                     Object interpreterState,
                     Runnable beforeTransfer,
                     VirtualFrame parentFrame)

Tries to perform OSR. This method must only be called immediately after a true result from BytecodeOSRNode.pollOSRBackEdge(com.oracle.truffle.api.nodes.BytecodeOSRNode).

Depending on the Truffle runtime, this method can trigger OSR compilation and then (typically in a subsequent call) transfer to OSR code. If OSR occurs, this method returns the result of OSR execution. The caller of this method can forward the result back to its caller rather than continuing execution from the target. For example:

 if (BytecodeOSRNode.pollOSRBackEdge(this)) {
   Object osrResult = BytecodeOSRNode.tryOSR(...);
   if (osrResult != null) return osrResult;
 }
 

The optional interpreterState parameter will be forwarded to BytecodeOSRNode.executeOSR(com.oracle.truffle.api.frame.VirtualFrame, int, java.lang.Object) when OSR is performed. It should consist of additional interpreter state (e.g., data pointers) needed to resume execution from target. The state should be fixed (i.e., final) for the given target. For example:

 // class definition
 class InterpreterState {
     final int dataPtr;
     InterpreterState(int dataPtr) { ... }
 }

 // call site
 Object osrResult = BytecodeOSRNode.tryOSR(this, target, new InterpreterState(dataPtr), ...);

 // executeOSR
 Object executeOSR(VirtualFrame osrFrame, int target, Object interpreterState) {
     InterpreterState state = (InterpreterState) interpreterState;
     return dispatchFromBCI(osrFrame, target, interpreterState.dataPtr);
 }
 

The optional beforeTransfer callback will be called before transferring control to the OSR target. Since this method may or may not perform a transfer, it is a way to ensure certain actions (e.g., instrumentation events) occur before transferring to OSR code. For example:

 // call site
 Object osrResult = BytecodeNode.tryOSR(this, target, ..., () -> {
    instrument.notify(current, target);
 });
 

Parameters:

osrNode - the node to try OSR for.

target - the target location OSR will execute from (e.g., bytecode index).

interpreterState - other interpreter state used to resume execution.

beforeTransfer - a callback invoked before OSR. Can be null.

parentFrame - frame at the current point of execution.

Returns:

the result if OSR was performed, or null otherwise.

Since:

21.3