org.graalvm.compiler.java

Class BciBlockMapping

java.lang.Object

org.graalvm.compiler.java.BciBlockMapping

All Implemented Interfaces:

JavaMethodContext

public class BciBlockMapping
extends Object
implements JavaMethodContext

Builds a mapping between bytecodes and basic blocks and builds a conservative control flow graph (CFG). It makes one linear pass over the bytecodes to build the CFG where it detects block headers and connects them.

It also creates exception dispatch blocks for exception handling. These blocks are between a bytecode that might throw an exception, and the actual exception handler entries, and are later used to create the type checks with the exception handler catch types. If a bytecode is covered by an exception handler, this bytecode ends the basic block. This guarantees that a) control flow cannot be transferred to an exception dispatch block in the middle of a block, and b) that every block has at most one exception dispatch block (which is always the last entry in the successor list).

If a bytecode is covered by multiple exception handlers, a chain of exception dispatch blocks is created so that multiple exception handler types can be checked.

Note that exception unwinds, i.e., bytecodes that can throw an exception but the exception is not handled in this method, do not end a basic block. Not modeling the exception unwind block reduces the complexity of the CFG, and there is no algorithm yet where the exception unwind block would matter.

The class also handles subroutines (jsr and ret bytecodes): subroutines are inlined by duplicating the subroutine blocks. This is limited to simple, structured subroutines with a maximum subroutine nesting of 4. Otherwise, a bailout is thrown.

Loops in the methods are detected. If a method contains an irreducible loop (a loop with more than one entry), a bailout is thrown or, if BciBlockMapping.Options.MaxDuplicationFactor > 1, block duplication is attempted to make the loop reducible. This simplifies the compiler later on since only structured loops need to be supported.

A data flow analysis computes the live local variables from the point of view of the interpreter. The result is used later to prune frame states, i.e., remove local variable entries that are guaranteed to be never used again (even in the case of deoptimization).

The algorithms and analysis in this class are conservative and do not use any assumptions or profiling information.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	BciBlockMapping.BciBlock
static class	BciBlockMapping.ExceptionDispatchBlock
static class	BciBlockMapping.Options

Field Summary

Fields

Modifier and Type	Field and Description
protected BitSet[]	bciExceptionHandlerIDs
protected BciBlockMapping.BciBlock[]	blockMap
protected int	blocksNotYetAssignedId
Bytecode	code
protected ExceptionHandler[]	exceptionHandlers
boolean	hasJsrBytecodes
protected static int	UNASSIGNED_ID

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	BciBlockMapping(Bytecode code, DebugContext debug) Creates a new BlockMap instance from code.
protected	BciBlockMapping(Bytecode code, DebugContext debug, int maxDuplicationBoost) Creates a new BlockMap instance from code.

Method Summary

Modifier and Type	Method and Description
protected void	addInvokeNormalSuccessor(int invokeBci, BciBlockMapping.BciBlock sux) Logic for adding an the "normal" invoke successor link.
JavaMethod	asJavaMethod()
boolean	bciUnique()
void	build(BytecodeStream stream, OptionValues options, boolean splitExceptionRanges) Builds the block map and conservative CFG and numbers blocks.
protected static void	buildMap(BytecodeStream stream, Bytecode code, OptionValues options, DebugContext debug, BciBlockMapping map, boolean splitExceptionRanges)
void	clearLivenessMetadata() After local liveness has been computed, some metadata no longer needs to be retained.
static BciBlockMapping	create(BytecodeStream stream, Bytecode code, OptionValues options, DebugContext debug, boolean hasAsyncExceptions)
static BciBlockMapping	create(BytecodeStream stream, Bytecode code, OptionValues options, DebugContext debug, boolean hasAsyncExceptions, int maxDuplicationBoost)
BitSet	getBciExceptionHandlerIDs(int bci)
int	getBlockCount()
BciBlockMapping.BciBlock[]	getBlocks()
BciBlockMapping.BciBlock	getHandlerBlock(int handlerID)
protected BciBlockMapping.BciBlock	getInstructionBlock(int bci) Retrieve the instruction block corresponding to this bci.
int	getLoopCount()
BciBlockMapping.BciBlock	getLoopHeader(int index) Get the header block for a loop index.
BciBlockMapping.BciBlock[]	getLoopHeaders()
BciBlockMapping.BciBlock	getStartBlock()
BciBlockMapping.ExceptionDispatchBlock	getUnwindBlock()
protected BciBlockMapping.ExceptionDispatchBlock	handleExceptions(int bci, boolean processNewBlock, boolean isInvoke)
protected boolean	isStartOfNewBlock(BciBlockMapping.BciBlock current, int bci) Check whether this bci should be the start of a new block.
void	log(BciBlockMapping.BciBlock[] blockArray, String name)
protected Set<BciBlockMapping.BciBlock>	makeExceptionEntries(boolean splitRanges) Makes exception entries and splits blocks at exception handlers if requested.
protected BciBlockMapping.BciBlock	processNewBciBlock(int bci, BciBlockMapping.BciBlock newBlock) A hook for subclasses to insert additional blocks around a newly created BciBlock.
protected BciBlockMapping.ExceptionDispatchBlock	processNewExceptionDispatchBlock(int bci, boolean isInvoke, BciBlockMapping.ExceptionDispatchBlock handler) A hook for subclasses to insert additional blocks around a newly created ExceptionDispatchBlock.
protected BciBlockMapping.BciBlock	startNewBlock(int bci) Wrapper around makeBlock.
String	toString()
static String	toString(BciBlockMapping.BciBlock[] blockMap, BciBlockMapping.BciBlock[] loopHeadersMap)
protected boolean	verify()

Methods inherited from class java.lang.Object

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

Field Detail

UNASSIGNED_ID

protected static final int UNASSIGNED_ID

See Also:

Constant Field Values

blockMap

protected BciBlockMapping.BciBlock[] blockMap

code

public final Bytecode code

hasJsrBytecodes

public boolean hasJsrBytecodes

exceptionHandlers

protected final ExceptionHandler[] exceptionHandlers

bciExceptionHandlerIDs

protected BitSet[] bciExceptionHandlerIDs

blocksNotYetAssignedId

protected int blocksNotYetAssignedId

Constructor Detail

BciBlockMapping

protected BciBlockMapping(Bytecode code,
                          DebugContext debug)

Creates a new BlockMap instance from code.

BciBlockMapping

protected BciBlockMapping(Bytecode code,
                          DebugContext debug,
                          int maxDuplicationBoost)

Creates a new BlockMap instance from code.

Parameters:

maxDuplicationBoost - amount by which to multiply BciBlockMapping.Options.MaxDuplicationFactor

Method Detail

getBlocks

public BciBlockMapping.BciBlock[] getBlocks()

getBciExceptionHandlerIDs

public BitSet getBciExceptionHandlerIDs(int bci)

getHandlerBlock

public BciBlockMapping.BciBlock getHandlerBlock(int handlerID)

bciUnique

public boolean bciUnique()

clearLivenessMetadata

public void clearLivenessMetadata()

After local liveness has been computed, some metadata no longer needs to be retained.

build

public void build(BytecodeStream stream,
                  OptionValues options,
                  boolean splitExceptionRanges)

Builds the block map and conservative CFG and numbers blocks.

verify

protected boolean verify()

startNewBlock

protected BciBlockMapping.BciBlock startNewBlock(int bci)

Wrapper around makeBlock. This serves as a hook for subclasses.

makeExceptionEntries

protected Set<BciBlockMapping.BciBlock> makeExceptionEntries(boolean splitRanges)

Makes exception entries and splits blocks at exception handlers if requested.

Returns:

blocks that were requested to be the start of new blocks.

isStartOfNewBlock

protected boolean isStartOfNewBlock(BciBlockMapping.BciBlock current,
                                    int bci)

Check whether this bci should be the start of a new block.

getInstructionBlock

protected BciBlockMapping.BciBlock getInstructionBlock(int bci)

Retrieve the instruction block corresponding to this bci. The criteria for being an instruction block is defined at BlockMap.isInstructionBlock.

processNewBciBlock

protected BciBlockMapping.BciBlock processNewBciBlock(int bci,
                                                      BciBlockMapping.BciBlock newBlock)

A hook for subclasses to insert additional blocks around a newly created BciBlock.

addInvokeNormalSuccessor

protected void addInvokeNormalSuccessor(int invokeBci,
                                        BciBlockMapping.BciBlock sux)

Logic for adding an the "normal" invoke successor link.

processNewExceptionDispatchBlock

protected BciBlockMapping.ExceptionDispatchBlock processNewExceptionDispatchBlock(int bci,
                                                                                  boolean isInvoke,
                                                                                  BciBlockMapping.ExceptionDispatchBlock handler)

A hook for subclasses to insert additional blocks around a newly created ExceptionDispatchBlock.

handleExceptions

protected BciBlockMapping.ExceptionDispatchBlock handleExceptions(int bci,
                                                                  boolean processNewBlock,
                                                                  boolean isInvoke)

log

public void log(BciBlockMapping.BciBlock[] blockArray,
                String name)

toString

public static String toString(BciBlockMapping.BciBlock[] blockMap,
                              BciBlockMapping.BciBlock[] loopHeadersMap)

toString

public String toString()

Overrides:

toString in class Object

getLoopHeader

public BciBlockMapping.BciBlock getLoopHeader(int index)

Get the header block for a loop index.

create

public static BciBlockMapping create(BytecodeStream stream,
                                     Bytecode code,
                                     OptionValues options,
                                     DebugContext debug,
                                     boolean hasAsyncExceptions)

create

public static BciBlockMapping create(BytecodeStream stream,
                                     Bytecode code,
                                     OptionValues options,
                                     DebugContext debug,
                                     boolean hasAsyncExceptions,
                                     int maxDuplicationBoost)

buildMap

protected static void buildMap(BytecodeStream stream,
                               Bytecode code,
                               OptionValues options,
                               DebugContext debug,
                               BciBlockMapping map,
                               boolean splitExceptionRanges)

getLoopHeaders

public BciBlockMapping.BciBlock[] getLoopHeaders()

getStartBlock

public BciBlockMapping.BciBlock getStartBlock()

getUnwindBlock

public BciBlockMapping.ExceptionDispatchBlock getUnwindBlock()

getLoopCount

public int getLoopCount()

getBlockCount

public int getBlockCount()

asJavaMethod

public JavaMethod asJavaMethod()

Specified by:

asJavaMethod in interface JavaMethodContext