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There is a newer version: 0.10.2
/*
 *  Copyright 2012 Alexey Andreev.
 *
 *  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 org.teavm.javascript;

import java.util.Arrays;
import org.teavm.common.Graph;
import org.teavm.common.GraphUtils;
import org.teavm.common.IntegerStack;
import org.teavm.model.*;
import org.teavm.model.util.DefinitionExtractor;
import org.teavm.model.util.ProgramUtils;
import org.teavm.model.util.UsageExtractor;

/**
 *
 * @author Alexey Andreev
 */
class ReadWriteStatsBuilder {
    public int[] reads;
    public int[] writes;

    private ReadWriteStatsBuilder() {
    }

    public ReadWriteStatsBuilder(int variableCount) {
        reads = new int[variableCount];
        writes = new int[variableCount];
    }

    public ReadWriteStatsBuilder copy() {
        ReadWriteStatsBuilder result = new ReadWriteStatsBuilder();
        result.reads = Arrays.copyOf(reads, reads.length);
        result.writes = Arrays.copyOf(writes, writes.length);
        return result;
    }

    public void analyze(Program program) {
        Graph cfg = ProgramUtils.buildControlFlowGraph(program);
        Graph dom = GraphUtils.buildDominatorGraph(GraphUtils.buildDominatorTree(cfg), cfg.size());
        DefinitionExtractor defExtractor = new DefinitionExtractor();
        UsageExtractor useExtractor = new UsageExtractor();
        IntegerStack stack = new IntegerStack(program.basicBlockCount());
        stack.push(0);
        while (!stack.isEmpty()) {
            int node = stack.pop();
            BasicBlock block = program.basicBlockAt(node);
            for (Instruction insn : block.getInstructions()) {
                insn.acceptVisitor(defExtractor);
                insn.acceptVisitor(useExtractor);
                for (Variable var : defExtractor.getDefinedVariables()) {
                    writes[var.getIndex()]++;
                }
                for (Variable var : useExtractor.getUsedVariables()) {
                    reads[var.getIndex()]++;
                }
            }
            for (Phi phi : block.getPhis()) {
                writes[phi.getReceiver().getIndex()] += phi.getIncomings().size();
                for (Incoming incoming : phi.getIncomings()) {
                    if (writes[incoming.getValue().getIndex()] == 0) {
                        reads[incoming.getValue().getIndex()]++;
                    }
                }
            }
            for (TryCatchBlock tryCatch : block.getTryCatchBlocks()) {
                writes[tryCatch.getExceptionVariable().getIndex()]++;
                reads[tryCatch.getExceptionVariable().getIndex()]++;
            }

            for (int succ : dom.outgoingEdges(node)) {
                stack.push(succ);
            }
        }
    }
}