org.jetbrains.java.decompiler.modules.code.DeadCodeHelper Maven / Gradle / Ivy
/*
* Copyright 2000-2015 JetBrains s.r.o.
*
* 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.jetbrains.java.decompiler.modules.code;
import org.jetbrains.java.decompiler.code.CodeConstants;
import org.jetbrains.java.decompiler.code.Instruction;
import org.jetbrains.java.decompiler.code.InstructionSequence;
import org.jetbrains.java.decompiler.code.cfg.BasicBlock;
import org.jetbrains.java.decompiler.code.cfg.ControlFlowGraph;
import org.jetbrains.java.decompiler.code.cfg.ExceptionRangeCFG;
import org.jetbrains.java.decompiler.main.DecompilerContext;
import org.jetbrains.java.decompiler.main.extern.IFernflowerPreferences;
import java.util.*;
public class DeadCodeHelper {
public static void removeDeadBlocks(ControlFlowGraph graph) {
LinkedList stack = new LinkedList();
HashSet setStacked = new HashSet();
stack.add(graph.getFirst());
setStacked.add(graph.getFirst());
while (!stack.isEmpty()) {
BasicBlock block = stack.removeFirst();
List lstSuccs = new ArrayList(block.getSuccs());
lstSuccs.addAll(block.getSuccExceptions());
for (BasicBlock succ : lstSuccs) {
if (!setStacked.contains(succ)) {
stack.add(succ);
setStacked.add(succ);
}
}
}
HashSet setAllBlocks = new HashSet(graph.getBlocks());
setAllBlocks.removeAll(setStacked);
for (BasicBlock block : setAllBlocks) {
graph.removeBlock(block);
}
}
public static void removeEmptyBlocks(ControlFlowGraph graph) {
List blocks = graph.getBlocks();
boolean cont;
do {
cont = false;
for (int i = blocks.size() - 1; i >= 0; i--) {
BasicBlock block = blocks.get(i);
if (removeEmptyBlock(graph, block, false)) {
cont = true;
break;
}
}
}
while (cont);
}
private static boolean removeEmptyBlock(ControlFlowGraph graph, BasicBlock block, boolean merging) {
boolean deletedRanges = false;
if (block.getSeq().isEmpty()) {
if (block.getSuccs().size() > 1) {
if (block.getPreds().size() > 1) {
// ambiguous block
throw new RuntimeException("ERROR: empty block with multiple predecessors and successors found");
}
else if (!merging) {
throw new RuntimeException("ERROR: empty block with multiple successors found");
}
}
HashSet setExits = new HashSet(graph.getLast().getPreds());
if (block.getPredExceptions().isEmpty() &&
(!setExits.contains(block) || block.getPreds().size() == 1)) {
if (setExits.contains(block)) {
BasicBlock pred = block.getPreds().get(0);
// FIXME: flag in the basic block
if (pred.getSuccs().size() != 1 || (!pred.getSeq().isEmpty()
&& pred.getSeq().getLastInstr().group == CodeConstants.GROUP_SWITCH)) {
return false;
}
}
HashSet setPreds = new HashSet(block.getPreds());
HashSet setSuccs = new HashSet(block.getSuccs());
// collect common exception ranges of predecessors and successors
HashSet setCommonExceptionHandlers = null;
for (int i = 0; i < 2; ++i) {
for (BasicBlock pred : i == 0 ? setPreds : setSuccs) {
if (setCommonExceptionHandlers == null) {
setCommonExceptionHandlers = new HashSet(pred.getSuccExceptions());
}
else {
setCommonExceptionHandlers.retainAll(pred.getSuccExceptions());
}
}
}
// check the block to be in each of the common ranges
if (setCommonExceptionHandlers != null && !setCommonExceptionHandlers.isEmpty()) {
for (BasicBlock handler : setCommonExceptionHandlers) {
if (!block.getSuccExceptions().contains(handler)) {
return false;
}
}
}
// remove ranges consisting of this one block
List lstRanges = graph.getExceptions();
for (int i = lstRanges.size() - 1; i >= 0; i--) {
ExceptionRangeCFG range = lstRanges.get(i);
List lst = range.getProtectedRange();
if (lst.size() == 1 && lst.get(0) == block) {
if (DecompilerContext.getOption(IFernflowerPreferences.REMOVE_EMPTY_RANGES)) {
block.removeSuccessorException(range.getHandler());
lstRanges.remove(i);
deletedRanges = true;
}
else {
return false;
}
}
}
// connect remaining nodes
if (merging) {
BasicBlock pred = block.getPreds().get(0);
pred.removeSuccessor(block);
List lstSuccs = new ArrayList(block.getSuccs());
for (BasicBlock succ : lstSuccs) {
block.removeSuccessor(succ);
pred.addSuccessor(succ);
}
}
else {
for (BasicBlock pred : setPreds) {
for (BasicBlock succ : setSuccs) {
pred.replaceSuccessor(block, succ);
}
}
}
// finally exit edges
Set setFinallyExits = graph.getFinallyExits();
if (setFinallyExits.contains(block)) {
setFinallyExits.remove(block);
setFinallyExits.add(setPreds.iterator().next());
}
// replace first if necessary
if (graph.getFirst() == block) {
if (setSuccs.size() != 1) {
throw new RuntimeException("multiple or no entry blocks!");
}
else {
graph.setFirst(setSuccs.iterator().next());
}
}
// remove this block
graph.removeBlock(block);
if (deletedRanges) {
removeDeadBlocks(graph);
}
}
}
return deletedRanges;
}
public static boolean isDominator(ControlFlowGraph graph, BasicBlock block, BasicBlock dom) {
HashSet marked = new HashSet();
if (block == dom) {
return true;
}
LinkedList lstNodes = new LinkedList();
lstNodes.add(block);
while (!lstNodes.isEmpty()) {
BasicBlock node = lstNodes.remove(0);
if (marked.contains(node)) {
continue;
}
else {
marked.add(node);
}
if (node == graph.getFirst()) {
return false;
}
for (int i = 0; i < node.getPreds().size(); i++) {
BasicBlock pred = node.getPreds().get(i);
if (!marked.contains(pred) && pred != dom) {
lstNodes.add(pred);
}
}
for (int i = 0; i < node.getPredExceptions().size(); i++) {
BasicBlock pred = node.getPredExceptions().get(i);
if (!marked.contains(pred) && pred != dom) {
lstNodes.add(pred);
}
}
}
return true;
}
public static void removeGotos(ControlFlowGraph graph) {
for (BasicBlock block : graph.getBlocks()) {
Instruction instr = block.getLastInstruction();
if (instr != null && instr.opcode == CodeConstants.opc_goto) {
block.getSeq().removeLast();
}
}
removeEmptyBlocks(graph);
}
public static void connectDummyExitBlock(ControlFlowGraph graph) {
BasicBlock exit = graph.getLast();
for (BasicBlock block : new HashSet(exit.getPreds())) {
exit.removePredecessor(block);
block.addSuccessor(exit);
}
}
public static void incorporateValueReturns(ControlFlowGraph graph) {
for (BasicBlock block : graph.getBlocks()) {
InstructionSequence seq = block.getSeq();
int len = seq.length();
if (len > 0 && len < 3) {
boolean ok = false;
if (seq.getLastInstr().opcode >= CodeConstants.opc_ireturn && seq.getLastInstr().opcode <= CodeConstants.opc_return) {
if (len == 1) {
ok = true;
}
else if (seq.getLastInstr().opcode != CodeConstants.opc_return) {
switch (seq.getInstr(0).opcode) {
case CodeConstants.opc_iload:
case CodeConstants.opc_lload:
case CodeConstants.opc_fload:
case CodeConstants.opc_dload:
case CodeConstants.opc_aload:
case CodeConstants.opc_aconst_null:
case CodeConstants.opc_bipush:
case CodeConstants.opc_sipush:
case CodeConstants.opc_lconst_0:
case CodeConstants.opc_lconst_1:
case CodeConstants.opc_fconst_0:
case CodeConstants.opc_fconst_1:
case CodeConstants.opc_fconst_2:
case CodeConstants.opc_dconst_0:
case CodeConstants.opc_dconst_1:
case CodeConstants.opc_ldc:
case CodeConstants.opc_ldc_w:
case CodeConstants.opc_ldc2_w:
ok = true;
}
}
}
if (ok) {
if (!block.getPreds().isEmpty()) {
HashSet setPredHandlersUnion = new HashSet();
HashSet setPredHandlersIntersection = new HashSet();
boolean firstpred = true;
for (BasicBlock pred : block.getPreds()) {
if (firstpred) {
setPredHandlersIntersection.addAll(pred.getSuccExceptions());
firstpred = false;
}
else {
setPredHandlersIntersection.retainAll(pred.getSuccExceptions());
}
setPredHandlersUnion.addAll(pred.getSuccExceptions());
}
// add exception ranges from predecessors
setPredHandlersIntersection.removeAll(block.getSuccExceptions());
BasicBlock predecessor = block.getPreds().get(0);
for (BasicBlock handler : setPredHandlersIntersection) {
ExceptionRangeCFG range = graph.getExceptionRange(handler, predecessor);
range.getProtectedRange().add(block);
block.addSuccessorException(handler);
}
// remove redundant ranges
HashSet setRangesToBeRemoved = new HashSet(block.getSuccExceptions());
setRangesToBeRemoved.removeAll(setPredHandlersUnion);
for (BasicBlock handler : setRangesToBeRemoved) {
ExceptionRangeCFG range = graph.getExceptionRange(handler, block);
if (range.getProtectedRange().size() > 1) {
range.getProtectedRange().remove(block);
block.removeSuccessorException(handler);
}
}
}
if (block.getPreds().size() == 1 && block.getPredExceptions().isEmpty()) {
BasicBlock bpred = block.getPreds().get(0);
if (bpred.getSuccs().size() == 1) {
// add exception ranges of predecessor
for (BasicBlock succ : bpred.getSuccExceptions()) {
if (!block.getSuccExceptions().contains(succ)) {
ExceptionRangeCFG range = graph.getExceptionRange(succ, bpred);
range.getProtectedRange().add(block);
block.addSuccessorException(succ);
}
}
// remove superfluous ranges from successors
for (BasicBlock succ : new HashSet(block.getSuccExceptions())) {
if (!bpred.getSuccExceptions().contains(succ)) {
ExceptionRangeCFG range = graph.getExceptionRange(succ, block);
if (range.getProtectedRange().size() > 1) {
range.getProtectedRange().remove(block);
block.removeSuccessorException(succ);
}
}
}
}
}
}
}
}
}
public static void mergeBasicBlocks(ControlFlowGraph graph) {
while (true) {
boolean merged = false;
for (BasicBlock block : graph.getBlocks()) {
InstructionSequence seq = block.getSeq();
if (block.getSuccs().size() == 1) {
BasicBlock next = block.getSuccs().get(0);
if (next != graph.getLast() && (seq.isEmpty() || seq.getLastInstr().group != CodeConstants.GROUP_SWITCH)) {
if (next.getPreds().size() == 1 && next.getPredExceptions().isEmpty()
&& next != graph.getFirst()) {
// TODO: implement a dummy start block
boolean sameRanges = true;
for (ExceptionRangeCFG range : graph.getExceptions()) {
if (range.getProtectedRange().contains(block) ^
range.getProtectedRange().contains(next)) {
sameRanges = false;
break;
}
}
if (sameRanges) {
seq.addSequence(next.getSeq());
block.getInstrOldOffsets().addAll(next.getInstrOldOffsets());
next.getSeq().clear();
removeEmptyBlock(graph, next, true);
merged = true;
break;
}
}
}
}
}
if (!merged) {
break;
}
}
}
}