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Truffle is a multi-language framework for executing dynamic languages
that achieves high performance when combined with Graal.
/*
* Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
* 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. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* 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.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package com.oracle.truffle.api.profiles;
import com.oracle.truffle.api.CompilerDirectives;
import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;
/**
*
* LoopConditionProfiles are designed to profile the outcome of loop conditions. Loop profiles can
* be used to profile unpredictable loops as well as predictable loops.
*
*
*
* Arbitrary loop usage example:
*
*
* class LoopNode extends Node {
*
* final LoopConditionProfile loopProfile = LoopConditionProfile.createCountingProfile();
*
* void execute() {
* // loop count cannot be predicted
* while (loopProfile.profile(Math.random() >= 0.9)) {
* // work
* }
* }
* }
*
*
*
*
*
* Counted loop usage example:
*
*
* class CountedLoopNode extends Node {
*
* final LoopConditionProfile loopProfile = LoopConditionProfile.createCountingProfile();
*
* void execute(int length) {
* // loop count can be predicted
* loopProfile.profileCounted(length);
* for (int i = 0; loopProfile.inject(i < length); i++) {
* // work
* }
* }
* }
*
*
*
*
* The advantage of using {@link #profileCounted(long)} to using {@link #profile(boolean)} is that
* it incurs less overhead in the interpreter. Using {@link LoopConditionProfile#inject(boolean)} is
* a no-op in the interpreter while {@link #profile(boolean)} needs to use a counter for each
* iteration.
*
*
*
* {@inheritDoc}
*
* @see #createBinaryProfile()
* @see #createCountingProfile()
* @see LoopConditionProfile
* @since 0.10
*/
public abstract class LoopConditionProfile extends ConditionProfile {
LoopConditionProfile() {
}
/** @since 0.10 */
@Override
public abstract boolean profile(boolean value);
/**
* Provides an alternative way to profile counted loops with less interpreter footprint. Please
* see {@link LoopConditionProfile} for an usage example.
*
* @see #inject(boolean)
* @since 0.10
*/
public abstract void profileCounted(long length);
/**
* Provides an alternative way to profile counted loops with less interpreter footprint. Please
* see {@link LoopConditionProfile} for an usage example.
*
* @see #inject(boolean)
* @since 0.10
*/
public abstract boolean inject(boolean condition);
/**
* Returns a {@link LoopConditionProfile} that speculates on loop conditions to be never
* true. It also captures loop probabilities for the compiler. Loop condition
* profiles are intended to be used for loop conditions.
*
* @see LoopConditionProfile
* @since 0.10
*/
public static LoopConditionProfile createCountingProfile() {
if (Profile.isProfilingEnabled()) {
return Enabled.create();
} else {
return Disabled.INSTANCE;
}
}
static final class Enabled extends LoopConditionProfile {
@CompilationFinal private long trueCount; // long for long running loops.
@CompilationFinal private int falseCount;
@Override
public boolean profile(boolean condition) {
// locals required to guarantee no overflow in multi-threaded environments
long trueCountLocal = trueCount;
int falseCountLocal = falseCount;
if (trueCountLocal == 0) {
// Deopt for never entering the loop.
if (condition) {
CompilerDirectives.transferToInterpreterAndInvalidate();
}
}
// No deopt for not entering the loop.
if (CompilerDirectives.inInterpreter()) {
if (condition) {
if (trueCountLocal < Long.MAX_VALUE) {
trueCount = trueCountLocal + 1;
}
} else {
if (falseCountLocal < Integer.MAX_VALUE) {
falseCount = falseCountLocal + 1;
}
}
// no branch probability calculation in the interpreter
return condition;
} else {
return CompilerDirectives.injectBranchProbability(calculateProbability(trueCountLocal, falseCountLocal), condition);
}
}
@Override
public void profileCounted(long length) {
if (CompilerDirectives.inInterpreter()) {
long trueCountLocal = trueCount + length;
if (trueCountLocal >= 0) { // don't write overflow values
trueCount = trueCountLocal;
int falseCountLocal = falseCount;
if (falseCountLocal < Integer.MAX_VALUE) {
falseCount = falseCountLocal + 1;
}
}
}
}
@Override
public boolean inject(boolean condition) {
if (CompilerDirectives.inCompiledCode()) {
return CompilerDirectives.injectBranchProbability(calculateProbability(trueCount, falseCount), condition);
} else {
return condition;
}
}
private static double calculateProbability(long trueCountLocal, int falseCountLocal) {
if (falseCountLocal == 0 && trueCountLocal == 0) {
/* Avoid division by zero if profile was never used. */
return 0.0;
} else {
return (double) trueCountLocal / (double) (trueCountLocal + falseCountLocal);
}
}
/* for testing */
long getTrueCount() {
return trueCount;
}
/* for testing */
int getFalseCount() {
return falseCount;
}
@Override
public String toString() {
return toString(LoopConditionProfile.class, falseCount == 0, false, //
String.format("trueProbability=%s (trueCount=%s, falseCount=%s)", calculateProbability(trueCount, falseCount), trueCount, falseCount));
}
/* Needed for lazy class loading. */
static LoopConditionProfile create() {
return new Enabled();
}
}
static final class Disabled extends LoopConditionProfile {
static final LoopConditionProfile INSTANCE = new Disabled();
@Override
protected Object clone() {
return INSTANCE;
}
@Override
public boolean profile(boolean condition) {
return condition;
}
@Override
public void profileCounted(long length) {
}
@Override
public boolean inject(boolean condition) {
return condition;
}
@Override
public String toString() {
return toStringDisabled(LoopConditionProfile.class);
}
}
}
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