org.jikesrvm.compilers.opt.ssa
Class GlobalCSE

java.lang.Object
  org.jikesrvm.compilers.opt.driver.CompilerPhase
      org.jikesrvm.compilers.opt.ssa.GlobalCSE

public final class GlobalCSE
extends CompilerPhase

This class provides global common sub expression elimination.

verbose

public boolean verbose

Output debug messages

ir

private IR ir

Cache of IR being processed by this phase

valueNumbers

private GlobalValueNumberState valueNumbers

Cache of the value numbers from the IR

dominator

private DominatorTree dominator

Cache of dominator tree that should be computed prior to this phase

avail

private final HashMap<Integer,Instruction> avail

Available expressions. From Muchnick, "an expression expis said to be available at the entry to a basic block if along every control-flow path from the entry block to this block there is an evaluation of exp that is not subsequently killed by having one or more of its operands assigned a new value." Our available expressions are a mapping from a value number to the first instruction to define it as we traverse the dominator tree.

constructor

private static final Constructor<CompilerPhase> constructor

Constructor for this compiler phase

GlobalCSE

public GlobalCSE()

Constructor

shouldPerform

public boolean shouldPerform(OptOptions options)

Redefine shouldPerform so that none of the subphases will occur unless we pass through this test.

Overrides:

shouldPerform in class CompilerPhase

Parameters:

options - the compiler options for the compilation

Returns:

true if the phase should be performed

getClassConstructor

public Constructor<CompilerPhase> getClassConstructor()

Get a constructor object for this compiler phase

Overrides:

getClassConstructor in class CompilerPhase

Returns:

compiler phase constructor

getName

public String getName()

Returns the name of the phase

Specified by:

getName in class CompilerPhase

Returns:

a String which is the name of the phase.

perform

public void perform(IR ir)

Perform the GlobalCSE compiler phase

Specified by:

perform in class CompilerPhase

Parameters:

ir - the IR on which to apply the phase

globalCSE

private void globalCSE(BasicBlock b)

Recursively descend over all blocks dominated by b. For each instruction in the block, if it defines a GVN then record it in the available expressions. If the GVN already exists in the available expressions then eliminate the instruction and change all uses of the result of the instruction to be uses of the first instruction to define the result of this expression.

Parameters:

b - the current block to process

getResult

private RegisterOperand getResult(Instruction inst)

Get the result operand of the instruction

Parameters:

inst -

shouldCSE

private boolean shouldCSE(Instruction inst)

should this instruction be cse'd ?

Parameters:

inst -