/*
* Copyright 2008 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.gwt.dev.jjs.impl.gflow.liveness;
import com.google.gwt.dev.jjs.ast.Context;
import com.google.gwt.dev.jjs.ast.JBinaryOperation;
import com.google.gwt.dev.jjs.ast.JDeclarationStatement;
import com.google.gwt.dev.jjs.ast.JExpression;
import com.google.gwt.dev.jjs.ast.JExpressionStatement;
import com.google.gwt.dev.jjs.ast.JModVisitor;
import com.google.gwt.dev.jjs.ast.JNode;
import com.google.gwt.dev.jjs.impl.gflow.TransformationFunction.Transformation;
import com.google.gwt.dev.jjs.impl.gflow.cfg.Cfg;
import com.google.gwt.dev.jjs.impl.gflow.cfg.CfgNode;
import com.google.gwt.dev.jjs.impl.gflow.cfg.CfgNopNode;
import com.google.gwt.dev.jjs.impl.gflow.cfg.CfgTransformer;
import com.google.gwt.dev.jjs.impl.gflow.cfg.CfgUtil;
import com.google.gwt.dev.jjs.impl.gflow.cfg.CfgWriteNode;
import com.google.gwt.thirdparty.guava.common.base.Preconditions;
/**
* Kill assignment. Leave rhs expression evaluation if it has side effects.
*/
public class LivenessTransformation implements
Transformation<CfgTransformer, Cfg> {
private final Cfg graph;
private final CfgWriteNode writeToKill;
public LivenessTransformation(Cfg cfg, CfgWriteNode writeToKill) {
this.graph = cfg;
this.writeToKill = writeToKill;
}
@Override
public CfgTransformer getGraphTransformer() {
return new CfgTransformer() {
@Override
public boolean transform(CfgNode<?> node, Cfg cfgGraph) {
JModVisitor visitor = new JModVisitor() {
@Override
public void endVisit(JBinaryOperation x, Context ctx) {
if (!shouldKill(x)) {
return;
}
ctx.replaceMe(x.getRhs());
}
@Override
public void endVisit(JDeclarationStatement x, Context ctx) {
if (writeToKill.getValue() != x.getInitializer() ||
x != writeToKill.getJNode()) {
return;
}
if (x.getInitializer().hasSideEffects()) {
ctx.insertBefore(x.getInitializer().makeStatement());
}
x.initializer = null;
madeChanges();
}
@Override
public boolean visit(JExpressionStatement x, Context ctx) {
JExpression expr = x.getExpr();
if (expr instanceof JBinaryOperation) {
JBinaryOperation binop = (JBinaryOperation) expr;
if (shouldKill(binop) &&
!binop.getRhs().hasSideEffects()) {
ctx.removeMe();
return false;
}
}
return true;
}
private boolean shouldKill(JBinaryOperation x) {
return writeToKill.getJNode() == x;
}
};
CfgNode<?> parentNode = CfgUtil.findParentOfContainingStatement(node);
Preconditions.checkNotNull(parentNode,
"Can't find parent of stmt of %s", node);
JNode parentJNode = parentNode.getJNode();
visitor.accept(parentJNode);
Preconditions.checkState(visitor.didChange(),
"Can't remove write in %s", node.getJNode());
return visitor.didChange();
}
};
}
@Override
public Cfg getNewSubgraph() {
CfgNode<?> newNode = new CfgNopNode(writeToKill.getParent(),
writeToKill.getJNode());
return CfgUtil.createSingleNodeReplacementGraph(graph, writeToKill,
newNode);
}
}