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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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package com.sun.c1x.opt;
import static com.sun.c1x.ir.Value.Flag.*;
import com.sun.c1x.*;
import com.sun.c1x.graph.*;
import com.sun.c1x.ir.*;
import com.sun.c1x.value.*;
/**
* The {@code LivenessMarker} class walks over an IR graph and marks instructions
* whose values are live, either because they are needed to compute the method's result,
* may produce a side-effect, or are needed for deoptimization.
*/
public final class LivenessMarker {
final IR ir;
final InstructionMarker deoptMarker = new InstructionMarker(LiveDeopt);
final InstructionMarker valueMarker = new InstructionMarker(LiveValue);
int count;
/**
* Creates a new liveness marking instance and marks live instructions.
* @param ir the IR to mark
*/
public LivenessMarker(IR ir) {
this.ir = ir;
markRoots();
}
private void markRoots() {
// first pass: mark root instructions and their inputs
ir.startBlock.iteratePreOrder(new BlockClosure() {
public void apply(BlockBegin block) {
block.stateBefore().valuesDo(deoptMarker);
if (block.stateAfter() != null) {
block.stateAfter().valuesDo(deoptMarker);
}
Instruction i = block;
while ((i = i.next()) != null) {
// visit all instructions first, marking control dependent and side-effects
markRootInstr(i);
}
}
});
// propagate liveness flags to inputs of instructions
valueMarker.markAll();
deoptMarker.markAll();
}
public int liveCount() {
return count;
}
public void removeDeadCode() {
// second pass: remove dead instructions from blocks
ir.startBlock.iteratePreOrder(new BlockClosure() {
public void apply(BlockBegin block) {
Instruction prev = block;
Instruction i = block.next();
while (i != null) {
if (i.isLive()) {
prev.resetNext(i); // skip any previous dead instructions
prev = i;
} else {
C1XMetrics.DeadCodeEliminated++;
}
i = i.next();
}
}
});
// clear all marks on all instructions
valueMarker.clearAll();
deoptMarker.clearAll();
}
private static class Link {
final Value value;
Link next;
Link(Value v) {
this.value = v;
}
}
private final class InstructionMarker implements ValueClosure {
final Value.Flag reason;
Link head;
Link tail;
public InstructionMarker(Value.Flag reason) {
this.reason = reason;
}
public Value apply(Value i) {
if (!i.checkFlag(reason) && !i.isDeadPhi()) {
// set the flag and add to the queue
setFlag(i, reason);
if (head == null) {
head = tail = new Link(i);
} else {
tail.next = new Link(i);
tail = tail.next;
}
}
return i;
}
private void markAll() {
Link cursor = head;
while (cursor != null) {
markInputs(cursor.value);
cursor = cursor.next;
}
}
private void clearAll() {
Link cursor = head;
while (cursor != null) {
cursor.value.clearLive();
cursor = cursor.next;
}
}
private void markInputs(Value i) {
if (!i.isDeadPhi()) {
i.inputValuesDo(this);
if (i instanceof Phi) {
// phis are special
Phi phi = (Phi) i;
int max = phi.inputCount();
for (int j = 0; j < max; j++) {
apply(phi.inputAt(j));
}
}
}
}
}
void markRootInstr(Instruction i) {
FrameState stateBefore = i.stateBefore();
if (stateBefore != null) {
// stateBefore != null implies that this instruction may have side effects
stateBefore.valuesDo(deoptMarker);
i.inputValuesDo(valueMarker);
setFlag(i, LiveSideEffect);
} else if (i.checkFlag(LiveStore)) {
// instruction is a store that cannot be eliminated
i.inputValuesDo(valueMarker);
setFlag(i, LiveSideEffect);
} else if (i.checkFlag(LiveSideEffect)) {
// instruction has a side effect
i.inputValuesDo(valueMarker);
}
if (i instanceof BlockEnd) {
// input values to block ends are control dependencies
i.inputValuesDo(valueMarker);
setFlag(i, LiveControl);
}
FrameState stateAfter = i.stateAfter();
if (stateAfter != null) {
stateAfter.valuesDo(deoptMarker);
}
}
void setFlag(Value i, Value.Flag flag) {
if (!i.isLive()) {
count++;
}
i.setFlag(flag);
}
}