scale.score.trans
Class BasicBlockOps

java.lang.Object
  scale.score.trans.Optimization
      scale.score.trans.BasicBlockOps

public class BasicBlockOps
extends Optimization

Perform optimizations on each basic block.

$Id: BasicBlockOps.java,v 1.57 2007-10-04 19:58:35 burrill Exp $

Copyright 2008 by the Scale Compiler Group,
Department of Computer Science
University of Massachusetts,
Amherst MA. 01003, USA
All Rights Reserved.

This module performs optimizations that are local to a basic block. For this module a basic block ends at a function call as well as at a branch point in the CFG. These optimizations do not require use-def links and may be performed in or out of SSA form. Current basic block optimizations:

1. Eliminate duplicate loads from a structure field.
2. Eliminate duplicate loads from scalar variables (e.g., global or static scalar variables).
3. Eliminate duplicate memory address generation.
4. Eliminate un-needed stores into scalar variables.

Elimination of a store to a variable is legal if:

• it is followed by another store to the same variable in the same basic block,
• the variable is in memory,
• the variable has no hidden aliases,
• the variable's address is not taken, and
• the variable is not volatile.

It is always beneficial.

Eliminating a load increases the live range of any definition of a register value. This increases register pressure.

Elimination of a load from a variable is legal if:

• it is preceded by another load from the same variable in the same basic block,
• the variable is in memory,
• the variable has no hidden aliases, and
• the variable is not volatile.

If it is legal, it is always eliminated.

Replacing a reference to a constant with a reference to a variable is legal if the variable has been loaded with the constant value previously in the basic block. It is beneficial if the cost of generating the constant value in a register is greater than minimumExecutionCost.

Field Summary

static boolean	classTrace True if traces are to be performed.
static int	maxBlockSize Maximum number of CFG nodes that we will process in one "chunk".
static boolean	useHeuristics If true, use heuristics that prune the cases where the optimization is applied.

Fields inherited from class scale.score.trans.Optimization

dChanged, fpReorder, hasDummyAliases, IN_SSA, minimumExecutionCost, NA_SSA, NO_SSA, rChanged, scribble, signedIntsWrapOnOverflow, trace, un, unsafe, unsignedIntsWrapOnOverflow, VALID_SSA

Constructor Summary

BasicBlockOps(Scribble scribble)

Method Summary

static int	constantEliminated() Return the number of times the generation of a constant was eliminated.
static int	loadAddressEliminated() Return the number of times the generation of a memory address was eliminated.
static int	loadArrayAddressEliminated() Return the number of times the generation of an array element address was eliminated.
static int	loadEliminated() Return the number of times a load from memory was eliminated.
static int	loadFieldAddressEliminated() Return the number of times the generation of a structure field address was eliminated.
static int	loadFieldEliminated() Return the number of times a load from a structure field was eliminated.
static int	loadIndirectEliminated() Return the number of times a load indirect was eliminated.
static int	newCFGNodes() Return the number of new nodes created.
void	perform() Perform the actual basic block optimizations.
int	requiresSSA() Return whether this optimization requires that the CFG be in SSA form.
static int	storeEliminated() Return the number of times a load from memory was eliminated.

Methods inherited from class scale.score.trans.Optimization

assertTrace, assertTrace, assertTrace, assertTrace, assertTrace, genTemp, insertStores, setTrace, sort

Methods inherited from class java.lang.Object

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

Field Detail

classTrace

public static boolean classTrace

True if traces are to be performed.

useHeuristics

public static boolean useHeuristics

If true, use heuristics that prune the cases where the optimization is applied.

maxBlockSize

public static int maxBlockSize

Maximum number of CFG nodes that we will process in one "chunk".

Constructor Detail

BasicBlockOps

public BasicBlockOps(Scribble scribble)

Parameters:

scribble - is the CFG

Method Detail

newCFGNodes

public static int newCFGNodes()

Return the number of new nodes created.

loadEliminated

public static int loadEliminated()

Return the number of times a load from memory was eliminated.

constantEliminated

public static int constantEliminated()

Return the number of times the generation of a constant was eliminated.

storeEliminated

public static int storeEliminated()

Return the number of times a load from memory was eliminated.

loadFieldEliminated

public static int loadFieldEliminated()

Return the number of times a load from a structure field was eliminated.

loadIndirectEliminated

public static int loadIndirectEliminated()

Return the number of times a load indirect was eliminated.

loadAddressEliminated

public static int loadAddressEliminated()

Return the number of times the generation of a memory address was eliminated.

loadFieldAddressEliminated

public static int loadFieldAddressEliminated()

Return the number of times the generation of a structure field address was eliminated.

loadArrayAddressEliminated

public static int loadArrayAddressEliminated()

Return the number of times the generation of an array element address was eliminated.

perform

public void perform()

Perform the actual basic block optimizations.

Specified by:

perform in class Optimization

requiresSSA

public int requiresSSA()

Return whether this optimization requires that the CFG be in SSA form. It returns either

NO_SSA

the CFG must not be in SSA form,

IN_SSA

the CFG must be in SSA form,

VALID_SSA

the CFG must be in valid SSA form, or

NA_SSA

the CFG does not need to be in valid SSA form.

Overrides:

requiresSSA in class Optimization