org.jikesrvm.compilers.opt

Class LocalCastOptimization

java.lang.Object

org.jikesrvm.compilers.opt.driver.CompilerPhase

org.jikesrvm.compilers.opt.LocalCastOptimization

public final class LocalCastOptimization
extends CompilerPhase

Perform simple peephole optimizations to reduce the overhead of checking casts. This code was inspired by some special cases in handling checkcast in HIR2LIR, but the actual code is all different.

There are currently the following optimizations:

• 1. If a checkcast is just before a nullcheck, invert them and convert the checkcast into a checkcast_not_null
• 2. If a checkcast is followed by a branch based on a null test of the same variable, then push the cast below the conditional on the path where the obejct is known not to be null. And convert it to a checkcast_not_null

Field Summary

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

container

Constructor Summary

Constructors

Constructor and Description
LocalCastOptimization()

Method Summary

Modifier and Type	Method and Description
String	getName()
private boolean	invertNullAndTypeChecks(Instruction s) If there's a checkcast followed by a null check, move the checkcast after the null check, since the null pointer exception must be thrown anyway.
CompilerPhase	newExecution(IR ir) Return this instance of this phase.
void	perform(IR ir) Main routine: perform the transformation.
private boolean	pushTypeCheckBelowIf(Instruction s, IR ir) Where legal, move a type check below an if instruction.
void	reportAdditionalStats() Called when printing a measure compilation report to enable a phase to report additional phase-specific statistics.

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

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

Methods inherited from class java.lang.Object

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

Constructor Detail

LocalCastOptimization

public LocalCastOptimization()

Method Detail

getName

public String getName()

Specified by:

getName in class CompilerPhase

Returns:

a String which is the name of the phase.

reportAdditionalStats

public void reportAdditionalStats()

Description copied from class: CompilerPhase

Called when printing a measure compilation report to enable a phase to report additional phase-specific statistics.

Overrides:

reportAdditionalStats in class CompilerPhase

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

perform

public void perform(IR ir)

Main routine: perform the transformation.

Specified by:

perform in class CompilerPhase

Parameters:

ir - the IR to transform

invertNullAndTypeChecks

private boolean invertNullAndTypeChecks(Instruction s)

If there's a checkcast followed by a null check, move the checkcast after the null check, since the null pointer exception must be thrown anyway.

Parameters:

s - the potential checkcast instruction

Returns:

true iff the transformation happened

pushTypeCheckBelowIf

private boolean pushTypeCheckBelowIf(Instruction s,
                                     IR ir)

Where legal, move a type check below an if instruction.

Parameters:

s - the potential typecheck instruction

ir - the governing IR

Returns:

true if and only if a type check was moved