/*
* 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.constants;
import com.google.gwt.dev.jjs.ast.Context;
import com.google.gwt.dev.jjs.ast.JBooleanLiteral;
import com.google.gwt.dev.jjs.ast.JExpression;
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.CfgCaseNode;
import com.google.gwt.dev.jjs.impl.gflow.cfg.CfgConditionalNode;
import com.google.gwt.dev.jjs.impl.gflow.cfg.CfgEdge;
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.thirdparty.guava.common.base.Preconditions;
/**
* Transformation to be applied when CfgConditionalNode's condition is constant
* value. Transformation replaces conditional node with CfgNop node depending
* on condition value. It leaves the edge, which will be never executed
* unconnected at source, thus making sure that it will be unreachable.
*
* Doesn't try to optimize unreachable branches, since this is subject to other
* optimizations.
*/
final class ConstantConditionTransformation implements
Transformation<CfgTransformer, Cfg> {
private final boolean conditionValue;
private final CfgConditionalNode<?> node;
private final Cfg graph;
ConstantConditionTransformation(Cfg graph, boolean conditionValue,
CfgConditionalNode<?> node) {
this.graph = graph;
this.conditionValue = conditionValue;
this.node = node;
}
@Override
public CfgTransformer getGraphTransformer() {
return new CfgTransformer() {
@Override
public boolean transform(CfgNode<?> cfgNode, Cfg cfgGraph) {
Preconditions.checkArgument(cfgNode == node);
if (cfgNode instanceof CfgCaseNode) {
// TODO: support case node optimization
return false;
}
final JExpression oldCondition = node.getCondition();
final JExpression newCondition = JBooleanLiteral.get(conditionValue);
JModVisitor visitor = new JModVisitor() {
@Override
public boolean visit(JExpression x, Context ctx) {
if (x == oldCondition) {
ctx.replaceMe(newCondition);
return false;
}
return true;
}
};
JNode startNode = node.getJNode();
visitor.accept(startNode);
Preconditions.checkState(visitor.didChange(),
"Couldn't replace %s with %s in %s",
oldCondition, newCondition, startNode);
return visitor.didChange();
}
};
}
@Override
public Cfg getNewSubgraph() {
Cfg newSubgraph = new Cfg();
CfgNode<?> newNode = new CfgNopNode(node.getParent(), node.getJNode());
newSubgraph.addNode(newNode);
// Add all incoming edges.
for (int i = 0; i < graph.getInEdges(node).size(); ++i) {
CfgEdge edge = new CfgEdge();
newSubgraph.addIn(newNode, edge);
newSubgraph.addGraphInEdge(edge);
}
for (CfgEdge e : graph.getOutEdges(node)) {
CfgEdge edge = new CfgEdge(e.getRole());
newSubgraph.addGraphOutEdge(edge);
if (e.getRole() != null
&& ((e.getRole().equals(CfgConditionalNode.ELSE) && conditionValue) ||
(e.getRole().equals(CfgConditionalNode.THEN) && !conditionValue))) {
// Do not connect this edge due to constant condition.
} else {
newSubgraph.addOut(newNode, edge);
}
}
return newSubgraph;
}
@Override
public String toString() {
return "ConstantConditionTransformation(node=" + node +
", conditionValue=" + conditionValue + ")";
}
}