org.jikesrvm.compilers.opt

Class NullCheckCombining

java.lang.Object

org.jikesrvm.compilers.opt.driver.CompilerPhase

org.jikesrvm.compilers.opt.NullCheckCombining

public class NullCheckCombining
extends CompilerPhase

This module performs two tasks:

• (1) When possible, it folds null checks into the first load/store that is being guarded by the null check
• (2) It removes all validation registers from the IR

Doing (1) more or less implies either (a) doing (2) or (b) making large changes to the MIR operator set such that all load/stores produce validation results. Although this would be possible, it would not be a trivial change. So, until we have an urgent need to preserve guard operands all the way through the MIR, we'll take the easy way out.

Field Summary

Fields inherited from class org.jikesrvm.compilers.opt.driver.CompilerPhase

container

Constructor Summary

Constructors

Constructor and Description
NullCheckCombining()

Method Summary

Modifier and Type	Method and Description
private boolean	canFold(Instruction s, Operand activeGuard, boolean isStore)
String	getName()
private boolean	isExplicitLoad(Instruction s, Operator op)
private boolean	isExplicitStore(Instruction s, Operator op)
CompilerPhase	newExecution(IR ir) Return this instance of this phase.
void	perform(IR ir) Perform nullcheck combining and validation register removal.

Methods inherited from class org.jikesrvm.compilers.opt.driver.CompilerPhase

dumpIR, dumpIR, getClassConstructor, getCompilerPhaseConstructor, getCompilerPhaseConstructor, performPhase, printingEnabled, reportAdditionalStats, setContainer, shouldPerform, verify

Methods inherited from class java.lang.Object

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

Constructor Detail

NullCheckCombining

public NullCheckCombining()

Method Detail

newExecution

public CompilerPhase newExecution(IR ir)

Return this instance of this phase. This phase contains no per-compilation instance fields.

Overrides:

newExecution in class CompilerPhase

Parameters:

ir - not used

Returns:

this

getName

public final String getName()

Specified by:

getName in class CompilerPhase

Returns:

a String which is the name of the phase.

perform

public void perform(IR ir)

Perform nullcheck combining and validation register removal.

Specified by:

perform in class CompilerPhase

Parameters:

ir - the IR to transform

isExplicitStore

private boolean isExplicitStore(Instruction s,
                                Operator op)

isExplicitLoad

private boolean isExplicitLoad(Instruction s,
                               Operator op)

canFold

private boolean canFold(Instruction s,
                        Operand activeGuard,
                        boolean isStore)