org.jikesrvm.osr

Class BytecodeTraverser

java.lang.Object

org.jikesrvm.osr.BytecodeTraverser

public class BytecodeTraverser
extends Object

BytecodeTraverser does depth first search on a bytecode array, determines the type information of locals and stacks at Interesting point.

This class only intends to provide type information for on-stack replacement, which needs to know the type of a value. This class can only tells basic type information such as : REFERENCE, LONG, DOUBLE, FLOAT, INT, and ReturnAddress. Not like GCMap which tells GC a value is REFERENCE or NON-REFERENCE we also want to know it is INT or DOUBLE, and takes two words value or one word.

The produced type information has to be adjusted by consulting GC maps because two different types may merge at one program point (REF and non-REF types). Bytecode verifier will make the type info undefined in that case. But this class won't know. So the caller should check the GC map to validate a REF type variable.

More or less, this class needs to do the same work as a bytecode verifier, which tells the type and size of each locals and stacks. The JSR/RET instructions pose the difficulty to our case. However, we can assume the bytecode is verified. We use following assumptions:

1. After JSR, the stack was not changed, only local variable type needs to merge with FINALLY clause.
2. We need program-point specific stack type, but only need the summary of local types. Thus, after analysis, local types are same for all PCs.

Field Summary

Fields

Modifier and Type	Field and Description
private int	addr
private BytecodeStream	bytecodes
private boolean	ignoreGotos
private byte[]	ltypes
private int[]	retaddr
private byte[]	stypes
private boolean	TRACE
private byte[]	visitedpc

Constructor Summary

Constructors

Constructor and Description
BytecodeTraverser()

Method Summary

Modifier and Type	Method and Description
boolean	computeLocalStackTypes(NormalMethod method, int bcpoint) Computes types of local variable and stack slots at an interesting point for future querying.
void	computeStackHeights(NormalMethod method, BytecodeStream bcodes, int[] stackHeights, boolean adjustExptable)
byte[]	getLocalTypes() Returns an array of type information of locals at the registered program point.
private byte	getReturnCodeFromSignature(String sig)
byte[]	getStackTypes() Returns an array of type information of stacks at a program point.
void	prologueStackHeights(NormalMethod method, BytecodeStream bcodes, int[] stackHeights) Compute stack heights of bytecode stream (used for osr prologue)
private boolean	scanBlocks(NormalMethod method, BytecodeStream bytecodes, boolean doDFS, int pcs, byte[] ltypes, byte[] stypes, int startpc, TypeStack S, int[] stackHeights)

Methods inherited from class java.lang.Object

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

Field Detail

retaddr

private int[] retaddr

addr

private int addr

visitedpc

private byte[] visitedpc

TRACE

private final boolean TRACE

See Also:

Constant Field Values

ignoreGotos

private boolean ignoreGotos

bytecodes

private BytecodeStream bytecodes

ltypes

private byte[] ltypes

stypes

private byte[] stypes

Constructor Detail

BytecodeTraverser

public BytecodeTraverser()

Method Detail

computeLocalStackTypes

public boolean computeLocalStackTypes(NormalMethod method,
                                      int bcpoint)

Computes types of local variable and stack slots at an interesting point for future querying. Computing type info and retrieval should not be reentered. The type info of local variable is not accurate about reference types, see JVM SPEC (2nd edition) p 146. The caller can consult GC map to verify if a local is a reference or not.

Parameters:

method - whose bytecode to be queried

bcpoint - the bytecode index which is the interesting point at the mean time, we only support one PC.

Returns:

whether the pc is a valid program point of the method

getLocalTypes

public byte[] getLocalTypes()

Returns an array of type information of locals at the registered program point. The size of array is fixed by MAX_LOCALS, the type descriptor can be found in "ClassLoadConstants.java".

Returns:

an array of type information, or null

getStackTypes

public byte[] getStackTypes()

Returns an array of type information of stacks at a program point. The size of array is fixed by MAX_STACKS, the type descriptor can be found in "ClassLoadConstants.java".

Returns:

an array of type information, or null

computeStackHeights

public void computeStackHeights(NormalMethod method,
                                BytecodeStream bcodes,
                                int[] stackHeights,
                                boolean adjustExptable)

prologueStackHeights

public void prologueStackHeights(NormalMethod method,
                                 BytecodeStream bcodes,
                                 int[] stackHeights)

Compute stack heights of bytecode stream (used for osr prologue)

Parameters:

method - the method that's subject to OSR

bcodes - the bytecode stream for the OSR prologue

stackHeights - the original stack heights computed by the baseline compiler

getReturnCodeFromSignature

private byte getReturnCodeFromSignature(String sig)

scanBlocks

private boolean scanBlocks(NormalMethod method,
                           BytecodeStream bytecodes,
                           boolean doDFS,
                           int pcs,
                           byte[] ltypes,
                           byte[] stypes,
                           int startpc,
                           TypeStack S,
                           int[] stackHeights)