org.jikesrvm.compilers.opt.controlflow
Class ReorderingPhase

java.lang.Object
  org.jikesrvm.compilers.opt.driver.CompilerPhase
      org.jikesrvm.compilers.opt.controlflow.ReorderingPhase

public final class ReorderingPhase
extends CompilerPhase

Reorder code layout of basic blocks for improved I-cache locality and branch prediction. This code assumes that basic block frequencies have been computed and blocks have been marked infrequent. This pass actually implements two code placement algorithms:

• (1) A simple 'fluff' removal pass that moves all infrequent basic blocks to the end of the code order.
• (2) Pettis and Hansen Algo2.

DEBUG

private static final boolean DEBUG

See Also:

Constant Field Values

ReorderingPhase

public ReorderingPhase()

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

shouldPerform

public boolean shouldPerform(OptOptions options)

Description copied from class: CompilerPhase

This method determines if the phase should be run, based on the Options object it is passed. By default, phases are always performed. Subclasses should override this method if they only want to be performed conditionally.

Overrides:

shouldPerform in class CompilerPhase

Parameters:

options - the compiler options for the compilation

Returns:

true if the phase should be performed

printingEnabled

public boolean printingEnabled(OptOptions options,
                               boolean before)

Description copied from class: CompilerPhase

Returns true if the phase wants the IR dumped before and/or after it runs. By default, printing is not enabled. Subclasses should override this method if they want to provide IR dumping.

Overrides:

printingEnabled in class CompilerPhase

Parameters:

options - the compiler options for the compilation

before - true when invoked before perform, false otherwise.

Returns:

true if the IR should be printed, false otherwise.

getName

public String getName()

Specified by:

getName in class CompilerPhase

Returns:

a String which is the name of the phase.

perform

public void perform(IR ir)

Reorder basic blocks either by trivially moving infrequent blocks to the end of the code order or by applying Pettis and Hansen Algo2. We will rearrange basic blocks and insert/remove unconditional GOTO's if needed. It does not clean up branches, by reversing the branch condition, however. That is saved for BranchOptimizations.

Specified by:

perform in class CompilerPhase

Parameters:

ir - the IR on which to apply the phase

exileInfrequentBlocks

private void exileInfrequentBlocks(IR ir)

Select a new basic block ordering via a simple heuristic that moves all infrequent basic blocks to the end.

Parameters:

ir - the IR object to reorder

doPettisHansenAlgo2

private void doPettisHansenAlgo2(IR ir)

Reorder code using Algo2 (Bottom-Up Positioning) from Pettis and Hansen PLDI'90.

Parameters:

ir - the IR to reorder.

dumpChain

private void dumpChain(BasicBlock head)