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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.rop.code.RegisterSpecSet;
import com.android.dx.rop.code.RegisterSpec;
import com.android.dx.util.IntList;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.List;
/**
* Code to figure out which local variables are active at which points in
* a method. Stolen and retrofitted from
* com.android.dx.rop.code.LocalVariableExtractor
*
* TODO remove this. Allow Rop-form LocalVariableInfo to be passed in,
* converted, and adapted through edge-splitting.
*/
public class LocalVariableExtractor {
/** {@code non-null;} method being extracted from */
private final SsaMethod method;
/** {@code non-null;} block list for the method */
private final ArrayList<SsaBasicBlock> blocks;
/** {@code non-null;} result in-progress */
private final LocalVariableInfo resultInfo;
/** {@code non-null;} work set indicating blocks needing to be processed */
private final BitSet workSet;
/**
* Extracts out all the local variable information from the given method.
*
* @param method {@code non-null;} the method to extract from
* @return {@code non-null;} the extracted information
*/
public static LocalVariableInfo extract(SsaMethod method) {
LocalVariableExtractor lve = new LocalVariableExtractor(method);
return lve.doit();
}
/**
* Constructs an instance. This method is private. Use {@link #extract}.
*
* @param method {@code non-null;} the method to extract from
*/
private LocalVariableExtractor(SsaMethod method) {
if (method == null) {
throw new NullPointerException("method == null");
}
ArrayList<SsaBasicBlock> blocks = method.getBlocks();
this.method = method;
this.blocks = blocks;
this.resultInfo = new LocalVariableInfo(method);
this.workSet = new BitSet(blocks.size());
}
/**
* Does the extraction.
*
* @return {@code non-null;} the extracted information
*/
private LocalVariableInfo doit() {
//FIXME why is this needed here?
if (method.getRegCount() > 0 ) {
for (int bi = method.getEntryBlockIndex();
bi >= 0;
bi = workSet.nextSetBit(0)) {
workSet.clear(bi);
processBlock(bi);
}
}
resultInfo.setImmutable();
return resultInfo;
}
/**
* Processes a single block.
*
* @param blockIndex {@code >= 0;} block index of the block to process
*/
private void processBlock(int blockIndex) {
RegisterSpecSet primaryState
= resultInfo.mutableCopyOfStarts(blockIndex);
SsaBasicBlock block = blocks.get(blockIndex);
List<SsaInsn> insns = block.getInsns();
int insnSz = insns.size();
// The exit block has no insns and no successors
if (blockIndex == method.getExitBlockIndex()) {
return;
}
/*
* We may have to treat the last instruction specially: If it
* can (but doesn't always) throw, and the exception can be
* caught within the same method, then we need to use the
* state *before* executing it to be what is merged into
* exception targets.
*/
SsaInsn lastInsn = insns.get(insnSz - 1);
boolean hasExceptionHandlers
= lastInsn.getOriginalRopInsn().getCatches().size() !=0 ;
boolean canThrowDuringLastInsn = hasExceptionHandlers
&& (lastInsn.getResult() != null);
int freezeSecondaryStateAt = insnSz - 1;
RegisterSpecSet secondaryState = primaryState;
/*
* Iterate over the instructions, adding information for each place
* that the active variable set changes.
*/
for (int i = 0; i < insnSz; i++) {
if (canThrowDuringLastInsn && (i == freezeSecondaryStateAt)) {
// Until this point, primaryState == secondaryState.
primaryState.setImmutable();
primaryState = primaryState.mutableCopy();
}
SsaInsn insn = insns.get(i);
RegisterSpec result;
result = insn.getLocalAssignment();
if (result == null) {
// We may be nuking an existing local
result = insn.getResult();
if (result != null && primaryState.get(result.getReg()) != null) {
primaryState.remove(primaryState.get(result.getReg()));
}
continue;
}
result = result.withSimpleType();
RegisterSpec already = primaryState.get(result);
/*
* The equals() check ensures we only add new info if
* the instruction causes a change to the set of
* active variables.
*/
if (!result.equals(already)) {
/*
* If this insn represents a local moving from one register
* to another, remove the association between the old register
* and the local.
*/
RegisterSpec previous
= primaryState.localItemToSpec(result.getLocalItem());
if (previous != null
&& (previous.getReg() != result.getReg())) {
primaryState.remove(previous);
}
resultInfo.addAssignment(insn, result);
primaryState.put(result);
}
}
primaryState.setImmutable();
/*
* Merge this state into the start state for each successor,
* and update the work set where required (that is, in cases
* where the start state for a block changes).
*/
IntList successors = block.getSuccessorList();
int succSz = successors.size();
int primarySuccessor = block.getPrimarySuccessorIndex();
for (int i = 0; i < succSz; i++) {
int succ = successors.get(i);
RegisterSpecSet state = (succ == primarySuccessor) ?
primaryState : secondaryState;
if (resultInfo.mergeStarts(succ, state)) {
workSet.set(succ);
}
}
}
}
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