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/*
* Copyright (C) 2007 The Android Open Source Project
*
* 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.android.dx.ssa;
import com.android.dx.util.IntSet;
import com.android.dx.util.BitIntSet;
import com.android.dx.util.ListIntSet;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.BitSet;
/**
* Calculates the dominance-frontiers of a methot's basic blocks.
* Algorithm from "A Simple, Fast Dominance Algorithm" by Cooper,
* Harvey, and Kennedy; transliterated to Java.
*/
public class DomFront {
/** local debug flag */
private static boolean DEBUG = false;
/** {@code non-null;} method being processed */
private final SsaMethod meth;
private final ArrayList<SsaBasicBlock> nodes;
private final DomInfo[] domInfos;
/**
* Dominance-frontier information for a single basic block.
*/
public static class DomInfo {
/**
* {@code null-ok;} the dominance frontier set indexed by
* block index
*/
public IntSet dominanceFrontiers;
/** {@code >= 0 after run();} the index of the immediate dominator */
public int idom = -1;
}
/**
* Constructs instance. Call {@link DomFront#run} to process.
*
* @param meth {@code non-null;} method to process
*/
public DomFront(SsaMethod meth) {
this.meth = meth;
nodes = meth.getBlocks();
int szNodes = nodes.size();
domInfos = new DomInfo[szNodes];
for (int i = 0; i < szNodes; i++) {
domInfos[i] = new DomInfo();
}
}
/**
* Calculates the dominance frontier information for the method.
*
* @return {@code non-null;} an array of DomInfo structures
*/
public DomInfo[] run() {
int szNodes = nodes.size();
if (DEBUG) {
for (int i = 0; i < szNodes; i++) {
SsaBasicBlock node = nodes.get(i);
System.out.println("pred[" + i + "]: "
+ node.getPredecessors());
}
}
Dominators methDom = Dominators.make(meth, domInfos, false);
if (DEBUG) {
for (int i = 0; i < szNodes; i++) {
DomInfo info = domInfos[i];
System.out.println("idom[" + i + "]: "
+ info.idom);
}
}
buildDomTree();
if (DEBUG) {
debugPrintDomChildren();
}
for (int i = 0; i < szNodes; i++) {
domInfos[i].dominanceFrontiers
= SetFactory.makeDomFrontSet(szNodes);
}
calcDomFronts();
if (DEBUG) {
for (int i = 0; i < szNodes; i++) {
System.out.println("df[" + i + "]: "
+ domInfos[i].dominanceFrontiers);
}
}
return domInfos;
}
private void debugPrintDomChildren() {
int szNodes = nodes.size();
for (int i = 0; i < szNodes; i++) {
SsaBasicBlock node = nodes.get(i);
StringBuffer sb = new StringBuffer();
sb.append('{');
boolean comma = false;
for (SsaBasicBlock child : node.getDomChildren()) {
if (comma) {
sb.append(',');
}
sb.append(child);
comma = true;
}
sb.append('}');
System.out.println("domChildren[" + node + "]: "
+ sb);
}
}
/**
* The dominators algorithm leaves us knowing who the immediate dominator
* is for each node. This sweeps the node list and builds the proper
* dominance tree.
*/
private void buildDomTree() {
int szNodes = nodes.size();
for (int i = 0; i < szNodes; i++) {
DomInfo info = domInfos[i];
if (info.idom == -1) continue;
SsaBasicBlock domParent = nodes.get(info.idom);
domParent.addDomChild(nodes.get(i));
}
}
/**
* Calculates the dominance-frontier set.
* from "A Simple, Fast Dominance Algorithm" by Cooper,
* Harvey, and Kennedy; transliterated to Java.
*/
private void calcDomFronts() {
int szNodes = nodes.size();
for (int b = 0; b < szNodes; b++) {
SsaBasicBlock nb = nodes.get(b);
DomInfo nbInfo = domInfos[b];
BitSet pred = nb.getPredecessors();
if (pred.cardinality() > 1) {
for (int i = pred.nextSetBit(0); i >= 0;
i = pred.nextSetBit(i + 1)) {
for (int runnerIndex = i;
runnerIndex != nbInfo.idom; /* empty */) {
/*
* We can stop if we hit a block we already
* added label to, since we must be at a part
* of the dom tree we have seen before.
*/
if (runnerIndex == -1) break;
DomInfo runnerInfo = domInfos[runnerIndex];
if (runnerInfo.dominanceFrontiers.has(b)) {
break;
}
// Add b to runner's dominance frontier set.
runnerInfo.dominanceFrontiers.add(b);
runnerIndex = runnerInfo.idom;
}
}
}
}
}
}
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