Source/JavaScriptCore/bytecode/ValueProfile.h

/*
 * Copyright (C) 2011 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef ValueProfile_h
#define ValueProfile_h

#include "JSArray.h"
#include "PredictedType.h"
#include "Structure.h"
#include "WriteBarrier.h"

namespace JSC {

#if ENABLE(VALUE_PROFILER)
struct ValueProfile {
    static const unsigned logNumberOfBuckets = 0; // 1 bucket
    static const unsigned numberOfBuckets = 1 << logNumberOfBuckets;
    static const unsigned numberOfSpecFailBuckets = 1;
    static const unsigned bucketIndexMask = numberOfBuckets - 1;
    static const unsigned totalNumberOfBuckets = numberOfBuckets + numberOfSpecFailBuckets;
    
    ValueProfile()
        : m_bytecodeOffset(-1)
        , m_prediction(PredictNone)
        , m_numberOfSamplesInPrediction(0)
    {
        for (unsigned i = 0; i < totalNumberOfBuckets; ++i)
            m_buckets[i] = JSValue::encode(JSValue());
    }
    
    ValueProfile(int bytecodeOffset)
        : m_bytecodeOffset(bytecodeOffset)
        , m_prediction(PredictNone)
        , m_numberOfSamplesInPrediction(0)
    {
        for (unsigned i = 0; i < totalNumberOfBuckets; ++i)
            m_buckets[i] = JSValue::encode(JSValue());
    }
    
    EncodedJSValue* specFailBucket(unsigned i)
    {
        ASSERT(numberOfBuckets + i < totalNumberOfBuckets);
        return m_buckets + numberOfBuckets + i;
    }
    
    const ClassInfo* classInfo(unsigned bucket) const
    {
        JSValue value = JSValue::decode(m_buckets[bucket]);
        if (!!value) {
            if (!value.isCell())
                return 0;
            return value.asCell()->structure()->classInfo();
        }
        return 0;
    }
    
    unsigned numberOfSamples() const
    {
        unsigned result = 0;
        for (unsigned i = 0; i < totalNumberOfBuckets; ++i) {
            if (!!JSValue::decode(m_buckets[i]))
                result++;
        }
        return result;
    }
    
    unsigned totalNumberOfSamples() const
    {
        return numberOfSamples() + m_numberOfSamplesInPrediction;
    }
    
    bool isLive() const
    {
        for (unsigned i = 0; i < totalNumberOfBuckets; ++i) {
            if (!!JSValue::decode(m_buckets[i]))
                return true;
        }
        return false;
    }
    
#ifndef NDEBUG
    void dump(FILE* out)
    {
        fprintf(out,
                "samples = %u, prediction = %s",
                totalNumberOfSamples(),
                predictionToString(m_prediction));
        bool first = true;
        for (unsigned i = 0; i < totalNumberOfBuckets; ++i) {
            JSValue value = JSValue::decode(m_buckets[i]);
            if (!!value) {
                if (first) {
                    fprintf(out, ": ");
                    first = false;
                } else
                    fprintf(out, ", ");
                fprintf(out, "%s", value.description());
            }
        }
    }
#endif
    
    // Updates the prediction and returns the new one.
    PredictedType computeUpdatedPrediction();
    
    int m_bytecodeOffset; // -1 for prologue
    
    PredictedType m_prediction;
    unsigned m_numberOfSamplesInPrediction;
    
    EncodedJSValue m_buckets[totalNumberOfBuckets];
};

inline int getValueProfileBytecodeOffset(ValueProfile* valueProfile)
{
    return valueProfile->m_bytecodeOffset;
}

// This is a mini value profile to catch pathologies. It is a counter that gets
// incremented when we take the slow path on any instruction.
struct RareCaseProfile {
    RareCaseProfile(int bytecodeOffset)
        : m_bytecodeOffset(bytecodeOffset)
        , m_counter(0)
    {
    }
    
    int m_bytecodeOffset;
    uint32_t m_counter;
};

inline int getRareCaseProfileBytecodeOffset(RareCaseProfile* rareCaseProfile)
{
    return rareCaseProfile->m_bytecodeOffset;
}
#endif

}

#endif