org.jikesrvm.compilers.common.assembler

Class ForwardReference

java.lang.Object

org.jikesrvm.compilers.common.assembler.ForwardReference

Direct Known Subclasses:

ForwardReference.ConditionalBranch, ForwardReference.LoadReturnAddress, ForwardReference.ShortBranch, ForwardReference.SwitchCase, ForwardReference.UnconditionalBranch

public abstract class ForwardReference
extends Object

A forward reference has a machine-code-index source and optionally a bytecode-index target. The idea is to fix up the instruction at the source when the machine-code-index of the target is known. There need not be an explicit target, if the reference is used (by the compiler) within the machine-code for one bytecode.

There are three kinds of forward reference:

1. unconditional branches
2. conditional branches
3. switch cases

Each subclass must be able to resolve itself.

This class also includes the machinery for maintaining a priority queue of forward references, priorities being target bytecode addresses. The head of this priority queue is maintained by a Assembler object.

The priority queue is implemented as a one-way linked list of forward references with strictly increasing targets. The link for this list is "next". A separate linked list ("other" is the link) contains all forward references with the same target.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ForwardReference.ConditionalBranch
static class	ForwardReference.LoadReturnAddress
static class	ForwardReference.ShortBranch
static class	ForwardReference.SwitchCase
static class	ForwardReference.UnconditionalBranch

Field Summary

Fields

Modifier and Type	Field and Description
(package private) ForwardReference	next Has next larger targetBytecodeIndex
(package private) ForwardReference	other Has the same targetBytecodeIndex
(package private) int	sourceMachinecodeIndex
(package private) int	targetBytecodeIndex

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ForwardReference(int source)
protected	ForwardReference(int source, int btarget)

Method Summary

Modifier and Type	Method and Description
static ForwardReference	enqueue(ForwardReference q, ForwardReference r) Adds a new reference to a priority queue.
abstract void	resolve(AbstractAssembler asm) Rewrite source to reference current machine code (in asm's machineCodes)
static ForwardReference	resolveMatching(AbstractAssembler asm, ForwardReference q, int bi) Resolve any forward references on the priority queue for the given bytecode index.

Methods inherited from class java.lang.Object

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

Field Detail

sourceMachinecodeIndex

final int sourceMachinecodeIndex

targetBytecodeIndex

final int targetBytecodeIndex

next

ForwardReference next

Has next larger targetBytecodeIndex

other

ForwardReference other

Has the same targetBytecodeIndex

Constructor Detail

ForwardReference

protected ForwardReference(int source,
                           int btarget)

ForwardReference

protected ForwardReference(int source)

Method Detail

resolve

public abstract void resolve(AbstractAssembler asm)

Rewrite source to reference current machine code (in asm's machineCodes)

Parameters:

asm - the assembler to use to resolve the reference

enqueue

public static ForwardReference enqueue(ForwardReference q,
                                       ForwardReference r)

Adds a new reference to a priority queue.

Parameters:

q - a forward reference acting as a priority queue

r - a new reference to enqueue

Returns:

the updated queue

resolveMatching

public static ForwardReference resolveMatching(AbstractAssembler asm,
                                               ForwardReference q,
                                               int bi)

Resolve any forward references on the priority queue for the given bytecode index.

Parameters:

asm - assembler to use for resolution

q - priority queue

bi - bytecode index

Returns:

queue of unresolved references