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Optimisation of Java Bytecode via EOLANG
/*
* The MIT License (MIT)
*
* Copyright (c) 2016-2024 Objectionary.com
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
package org.eolang.jeo.representation.bytecode;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;
import org.eolang.jeo.representation.xmir.AllLabels;
import org.objectweb.asm.Label;
/**
* Data-flow analysis.
* This class knows how to compute the maximum value of a reducible element based
* on the instruction flow.
* @param Type of the reducible element.
* @since 0.6
*/
public final class InstructionsFlow> {
/**
* Method instructions.
*/
private final List instructions;
/**
* Try-catch blocks.
*/
private final List blocks;
/**
* Constructor.
* @param instr Instructions.
* @param catches Try-catch blocks.
*/
InstructionsFlow(
final List instr, final List catches
) {
this.instructions = instr;
this.blocks = new ArrayList<>(catches);
}
/**
* Compute the maximum value.
* @param initial Initial value.
* @param generator Function to generate the reducible element from the instruction.
* @return Maximum value.
*/
@SuppressWarnings("PMD.CognitiveComplexity")
public T max(final T initial, final Function generator) {
final Map visited = new HashMap<>(0);
final Map worklist = new HashMap<>(0);
worklist.put(0, initial);
final int total = this.instructions.size();
T current;
while (!worklist.isEmpty()) {
final Map.Entry curr = worklist.entrySet()
.stream()
.findFirst()
.orElseThrow(() -> new IllegalStateException("Cannot find first worklist element"));
int index = curr.getKey();
current = curr.getValue();
worklist.remove(index);
if (visited.get(index) != null && visited.get(index).compareTo(current) >= 0) {
continue;
}
while (index < total) {
final BytecodeEntry entry = this.instructions.get(index);
if (entry instanceof BytecodeInstruction) {
final BytecodeInstruction instruction = BytecodeInstruction.class.cast(entry);
current = current.add(generator.apply(instruction));
final T updated = current;
if (instruction.isSwitch()) {
instruction.offsets()
.stream()
.map(this::index)
.forEach(ind -> worklist.put(ind, updated));
visited.put(index, updated);
break;
} else if (instruction.isBranch()) {
final Label label = instruction.jump();
final int jump = this.index(label);
worklist.put(jump, updated);
final int next = index + 1;
worklist.put(next, updated);
visited.put(index, updated);
break;
} else if (instruction.isJump()) {
final Label label = instruction.jump();
final int jump = this.index(label);
worklist.put(jump, updated);
visited.put(index, updated);
break;
} else if (instruction.isReturn()) {
visited.put(index, updated);
break;
}
this.suitableBlocks(index)
.forEach(ind -> worklist.put(ind, updated.enterBlock()));
visited.putIfAbsent(index, updated);
visited.computeIfPresent(index, (k, v) -> InstructionsFlow.max(v, updated));
} else {
visited.put(index, current);
}
++index;
}
}
return visited.values()
.stream()
.max(T::compareTo)
.orElseThrow(() -> new IllegalStateException("Cannot find max value"));
}
/**
* Which try-catch-blocks cover the instruction.
* @param instruction Instruction index.
* @return List of block indexes.
*/
private List suitableBlocks(final int instruction) {
return this.blocks.stream()
.map(BytecodeTryCatchBlock.class::cast)
.filter(block -> this.index(block.startLabel()) <= instruction)
.filter(block -> this.index(block.endLabel()) >= instruction)
.map(block -> this.index(block.handlerLabel()))
.collect(Collectors.toList());
}
/**
* Index of the label.
* @param label Label.
* @return Index.
*/
private int index(final Label label) {
for (int index = 0; index < this.instructions.size(); ++index) {
if (this.instructions.get(index).equals(new BytecodeLabel(label, new AllLabels()))) {
return index;
}
}
throw new IllegalStateException(String.format("Label %s not found", label));
}
/**
* Max of two reducible elements.
* @param first First element.
* @param second Second element.
* @param Type of the element.
* @return Max element.
*/
private static > T max(final T first, final T second) {
final T result;
if (first.compareTo(second) > 0) {
result = first;
} else {
result = second;
}
return result;
}
/**
* Reducible element in the data-flow analysis.
* @param Type of the element.
* @since 0.6
*/
interface Reducible extends Comparable {
T add(T other);
T enterBlock();
}
}