OptGCMap (Jikes RVM API)

java.lang.Object
- org.jikesrvm.compilers.opt.runtimesupport.OptGCMap

```
public final class OptGCMap
extends Object
```
A class that encapsulates the GCMap portion of the machine code maps. An instance of this class is created to encode and instance of a GCIRMap into an int[]. The int[] is stored persistently, but the instance of the OptGCMap is NOT.
- each map will be a sequence of 1 or more ints
- the first int in each map is a bit map of registers that contain references (the MSB is used for chaining, we assume it will never contain a reference)
- the remaining ints will be spill locations
- the sequence will continue as long as the most significant bit is set to 1
Note: This file contains two types of methods
- 1) methods called during compilation to create the GC maps these methods are virtual
- 2) methods called at GC time (no allocation allowed!) these methods are static

Field Summary

Fields
Modifier and Type	Field and Description
`static boolean`	`DEBUG`
`static int`	`ERROR`
`static int`	`FIRST_GCMAP_REG`
`private int[]`	`gcMapInformation` The gc map array, a sequence of gc maps.
`static int`	`INITIAL_MAP_SIZE` The initial allocation size for a map
`static int`	`LAST_GCMAP_REG`
`private int`	`lastGCMapEntry` the index of the last map entry in use
`private static int`	`NEXT_BIT` bit pattern for the "next" bit in the GC maps array
`static int`	`NO_MAP_ENTRY`

Constructor Summary

Constructors
Constructor and Description

OptGCMap()
Constructor, called during compilation

Constructors
Constructor and Description
`OptGCMap()` Constructor, called during compilation

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`private void`	`addAllSpills(int[] spillArray)` If we will be looking for missed references we need to sort the list of spills and then add them to the map, otherwise, nothing to do
`private void`	`addSpillLocation(int spill)` Adds the passed spill value to the current map
`static void`	`dumpMap(int entry, int[] gcMap)` Dumps the GCmap that starts at entry.
`private int`	`endCurrentMap(int firstIndex)` Ends the current map
`int[]`	`finish()` Completes the encoding of the map.
`static int`	`gcMapInformation(int mapEntry, int[] gcMap)`
`int`	`generateGCMapEntry(GCIRMapElement irMapElem)` Construct the GCMap for the argument GCIRMapElement
`private int`	`getNextMapEntry()` Returns the next GC map entry for use
`private static int`	`getRegBitPosition(int registerNumber)`
`private static boolean`	`nextBitSet(int entry, int[] gcMap)` Determines if the next bit is set for the entry passed in the gc map passed
`static int`	`nextLocation(int currentIndex, int[] gcMap)`
`static boolean`	`registerIsSet(int entry, int registerNumber, int[] gcMap)`
`private void`	`resizeMapInformation(int newSize)` Resize the map array
`private int`	`setRegisterBitMap(int bitMap)` Sets the register map information at the next available entry

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - NO_MAP_ENTRY
```
public static final int NO_MAP_ENTRY
```
    See Also:
    
    Constant Field Values
  - ERROR
```
public static final int ERROR
```
    See Also:
    
    Constant Field Values
  - INITIAL_MAP_SIZE
```
public static final int INITIAL_MAP_SIZE
```
    The initial allocation size for a map
    
    See Also:
    
    Constant Field Values
  - NEXT_BIT
```
private static final int NEXT_BIT
```
    bit pattern for the "next" bit in the GC maps array
    
    See Also:
    
    Constant Field Values
  - lastGCMapEntry
```
private int lastGCMapEntry
```
    the index of the last map entry in use
  - gcMapInformation
```
private int[] gcMapInformation
```
    The gc map array, a sequence of gc maps. Each sequence starts with a register bit mask and is followed by a list of spills. The most significant bit of the spill location is used to chain the list.
  - DEBUG
```
public static final boolean DEBUG
```
    See Also:
    
    Constant Field Values
  - FIRST_GCMAP_REG
```
public static final int FIRST_GCMAP_REG
```
  - LAST_GCMAP_REG
```
public static final int LAST_GCMAP_REG
```
- Constructor Detail
  - OptGCMap
```
OptGCMap()
```
    Constructor, called during compilation
- Method Detail
  - finish
```
public int[] finish()
```
    Completes the encoding of the map.
    
    Returns:
    
    the final GC map
  - generateGCMapEntry
```
public int generateGCMapEntry(GCIRMapElement irMapElem)
```
    Construct the GCMap for the argument GCIRMapElement
    
    Parameters:
    
    irMapElem - The IR Map element to create a GCMap for
    
    Returns:
    
    the GCMap index.
  - gcMapInformation
```
public static int gcMapInformation(int mapEntry,
                                   int[] gcMap)
```
  - registerIsSet
```
public static boolean registerIsSet(int entry,
                                    int registerNumber,
                                    int[] gcMap)
```
  - nextLocation
```
public static int nextLocation(int currentIndex,
                               int[] gcMap)
```
    Parameters:
    
    currentIndex - the index of the current location
    
    gcMap - the encoded GCMap
    
    Returns:
    
    the next (relative) location or -1 for no more locations
  - getRegBitPosition
```
private static int getRegBitPosition(int registerNumber)
```
  - nextBitSet
```
private static boolean nextBitSet(int entry,
                                  int[] gcMap)
```
    Determines if the next bit is set for the entry passed in the gc map passed
    
    Parameters:
    
    entry - the entry (index) to check
    
    gcMap - the gcmap
    
    Returns:
    
    whether the next bit is set
  - dumpMap
```
public static void dumpMap(int entry,
                           int[] gcMap)
```
    Dumps the GCmap that starts at entry.
    
    Parameters:
    
    entry - the entry where the map begins
    
    gcMap - the encoded GCmaps
  - getNextMapEntry
```
private int getNextMapEntry()
```
    Returns the next GC map entry for use
    
    Returns:
    
    the entry in the map table that can be used
  - resizeMapInformation
```
private void resizeMapInformation(int newSize)
```
    Resize the map array
    
    Parameters:
    
    newSize - the new size for the map array
  - setRegisterBitMap
```
private int setRegisterBitMap(int bitMap)
```
    Sets the register map information at the next available entry
    
    Parameters:
    
    bitMap - map entry
    
    Returns:
    
    The index of that entry.
  - addAllSpills
```
private void addAllSpills(int[] spillArray)
```
    If we will be looking for missed references we need to sort the list of spills and then add them to the map, otherwise, nothing to do
    
    Parameters:
    
    spillArray - an array of spills
  - addSpillLocation
```
private void addSpillLocation(int spill)
```
    Adds the passed spill value to the current map
    
    Parameters:
    
    spill - the spill location
  - endCurrentMap
```
private int endCurrentMap(int firstIndex)
```
    Ends the current map
    
    Parameters:
    
    firstIndex - the index of the beginning of the map
    
    Returns:
    
    the index of the beginning of the map (may be different)

Class OptGCMap

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

NO_MAP_ENTRY

ERROR

INITIAL_MAP_SIZE

NEXT_BIT

lastGCMapEntry

gcMapInformation

DEBUG

FIRST_GCMAP_REG

LAST_GCMAP_REG

Constructor Detail

OptGCMap

Method Detail

finish

generateGCMapEntry

gcMapInformation

registerIsSet

nextLocation

getRegBitPosition

nextBitSet

dumpMap

getNextMapEntry

resizeMapInformation

setRegisterBitMap

addAllSpills

addSpillLocation

endCurrentMap