polyglot.visit
Class DeadCodeEliminator

java.lang.Object
  polyglot.visit.NodeVisitor
      polyglot.visit.HaltingVisitor
          polyglot.visit.ErrorHandlingVisitor
              polyglot.visit.DataFlow
                  polyglot.visit.DeadCodeEliminator

All Implemented Interfaces:

java.lang.Cloneable, Copy

public class DeadCodeEliminator
extends DataFlow

Visitor which performs dead code elimination.

Nested Class Summary

protected static class	DeadCodeEliminator.DataFlowItem
protected static class	DeadCodeEliminator.DefUseFinder

Nested classes/interfaces inherited from class polyglot.visit.DataFlow

DataFlow.BoolItem, DataFlow.ConditionNavigator, DataFlow.FlowGraphSource, DataFlow.Item

Field Summary

Fields inherited from class polyglot.visit.DataFlow

dataflowOnEntry, flowCounter, flowgraphStack, forward

Fields inherited from class polyglot.visit.ErrorHandlingVisitor

error, job, nf, ts

Constructor Summary

DeadCodeEliminator(Job job, TypeSystem ts, NodeFactory nf)

Method Summary

void	check(FlowGraph graph, Term n, DataFlow.Item inItem, java.util.Map outItems) Check that the term n satisfies whatever properties this dataflow is checking for.
DataFlow.Item	confluence(java.util.List inItems, Term node, FlowGraph graph) The confluence operator for many flows.
protected NodeVisitor	createDefUseFinder(java.util.Set def, java.util.Set use)
DataFlow.Item	createInitialItem(FlowGraph graph, Term node) Create an initial Item for the term node.
protected DeadCodeEliminator.DataFlowItem	flow(DataFlow.Item in, FlowGraph graph, Term t)
java.util.Map	flow(DataFlow.Item in, FlowGraph graph, Term t, java.util.Set succEdgeKeys) Produce new Items as appropriate for the Term n and the input Item in.
protected java.util.Set[]	getDefUse(Node n) Returns array of sets of local instances.
protected Stmt	getEffects(Expr expr) Returns a statement that is side-effect-equivalent to the given expression.
Node	leaveCall(Node old, Node n, NodeVisitor v) Contains all of the functionality that can be done in the leave method, but allows SemanticExceptions to be thrown.
void	post(FlowGraph graph, Term root) Check all of the Peers in the graph, after the dataflow analysis has been performed.

Methods inherited from class polyglot.visit.DataFlow

confluence, constructItemsFromCondition, createCFGBuilder, currentFlowGraph, dataflow, dataflow, dumpFlowGraph, enterCall, filterItems, filterItemsExceptionSubclass, filterItemsNonError, filterItemsNonException, findSCCs, flow, flow, flowBooleanConditions, flowToBooleanFlow, hasTrueFalseBranches, initGraph, itemsToMap, itemToMap, leave, leaveCall, safeConfluence, safeConfluence, safeConfluence

Methods inherited from class polyglot.visit.ErrorHandlingVisitor

begin, catchErrors, enter, enterCall, enterError, errorQueue, job, nodeFactory, typeSystem

Methods inherited from class polyglot.visit.HaltingVisitor

bypass, bypass, bypassChildren, copy, override, visitChildren

Methods inherited from class polyglot.visit.NodeVisitor

enter, finish, finish, leave, override, toString, visitEdge

Methods inherited from class java.lang.Object

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

Constructor Detail

DeadCodeEliminator

public DeadCodeEliminator(Job job,
                          TypeSystem ts,
                          NodeFactory nf)

Method Detail

createInitialItem

public DataFlow.Item createInitialItem(FlowGraph graph,
                                       Term node)

Description copied from class: DataFlow

Create an initial Item for the term node. This is generally how the Item that will be given to the start node of a graph is created, although this method may also be called for other (non-start) nodes.

Specified by:

createInitialItem in class DataFlow

Returns:

a (possibly null) Item.

confluence

public DataFlow.Item confluence(java.util.List inItems,
                                Term node,
                                FlowGraph graph)

Description copied from class: DataFlow

The confluence operator for many flows. This method produces a single Item from a List of Items, for the confluence just before flow enters node.

Specified by:

confluence in class DataFlow

Parameters:

inItems - List of Items that flow into node. this method will only be called if the list has at least 2 elements.

node - Term for which the items are flowing into.

Returns:

a non-null Item.

flow

public java.util.Map flow(DataFlow.Item in,
                          FlowGraph graph,
                          Term t,
                          java.util.Set succEdgeKeys)

Description copied from class: DataFlow

Produce new Items as appropriate for the Term n and the input Item in.

Overrides:

flow in class DataFlow

Parameters:

in - the Item flowing into the node. Note that if the Term n has many flows going into it, the Item in may be the result of a call to confluence(List, List, Term)

graph - the FlowGraph which the dataflow is operating on

t - the Term which this method must calculate the flow for.

succEdgeKeys - a set of FlowGraph.EdgeKeys, being all the EdgeKeys of the edges leaving this node. The returned Map must have mappings for all objects in this set.

Returns:

a Map from FlowGraph.EdgeKeys to Items. The map must have entries for all EdgeKeys in edgeKeys.

flow

protected DeadCodeEliminator.DataFlowItem flow(DataFlow.Item in,
                                               FlowGraph graph,
                                               Term t)

post

public void post(FlowGraph graph,
                 Term root)
          throws SemanticException

Description copied from class: DataFlow

Check all of the Peers in the graph, after the dataflow analysis has been performed.

Overrides:

post in class DataFlow

Throws:

SemanticException

check

public void check(FlowGraph graph,
                  Term n,
                  DataFlow.Item inItem,
                  java.util.Map outItems)
           throws SemanticException

Description copied from class: DataFlow

Check that the term n satisfies whatever properties this dataflow is checking for. This method is called for each term in a code declaration block after the dataflow for that block of code has been performed.

Specified by:

check in class DataFlow

Throws:

SemanticException

leaveCall

public Node leaveCall(Node old,
                      Node n,
                      NodeVisitor v)
               throws SemanticException

Description copied from class: ErrorHandlingVisitor

Contains all of the functionality that can be done in the leave method, but allows SemanticExceptions to be thrown. This method is in addition to the leave method, and allows the compiler writer to write code that can throw errors and let the polyglot infrastructure handle the exceptions.

Overrides:

leaveCall in class ErrorHandlingVisitor

Parameters:

old - The original state of root of the current subtree.

n - The current state of the root of the current subtree.

v - The NodeVisitor object used to visit the children.

Returns:

The final result of the traversal of the tree rooted at n.

Throws:

SemanticException

See Also:

NodeVisitor.leave(Node, Node, NodeVisitor)

getDefUse

protected java.util.Set[] getDefUse(Node n)

Returns array of sets of local instances. Element 0 is the set of local instances DEFined by the node. Element 1 is the set of local instances USEd by the node.

createDefUseFinder

protected NodeVisitor createDefUseFinder(java.util.Set def,
                                         java.util.Set use)

getEffects

protected Stmt getEffects(Expr expr)

Returns a statement that is side-effect-equivalent to the given expression.