Class DeadCodeElimination

java.lang.Object

EDU.purdue.cs.bloat.trans.DeadCodeElimination

public class DeadCodeElimination
extends Object

DeadCodeElimination performs SSA-based dead code elimination as described in [Cytron, et. al. 91]. The idea behind dead code elimination is that there are some instructions that do not contribute anything useful to the result of the program. Most dead code is introduced by other optimizations. A program statement is live if one or more of the following holds:

1. The statement effects program output. In Java this is a lot more than just I/O. We must be conservative and assume that exceptions and monitor expression are always live.
2. The statement is an assignment statement whose target is used in a live statement.
3. The statement is a conditional branch and there are live statements whose execution depend on the conditional branch.
   Basically, the algorithm proceeds by marking a number of statements as being pre-live and then uses a worklist to determine which statements must also be live by the above three conditions.

Field Summary

Fields

Modifier and Type	Field	Description
static boolean	DEBUG

Constructor Summary

Constructors

Constructor	Description
DeadCodeElimination(FlowGraph cfg)	Constructor.

Method Summary

Modifier and Type	Method	Description
void	transform()	Performs dead code elimination.

Methods inherited from class Object

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

Field Details

DEBUG

public static boolean DEBUG

Constructor Details

DeadCodeElimination

public DeadCodeElimination(FlowGraph cfg)

Constructor.

Method Details

transform

public void transform()

Performs dead code elimination.