Source/JavaScriptCore/dfg/DFGNaturalLoops.h

/*
 * Copyright (C) 2013 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.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``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 INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#ifndef DFGNaturalLoops_h
#define DFGNaturalLoops_h

#if ENABLE(DFG_JIT)

#include "DFGAnalysis.h"
#include "DFGBasicBlock.h"
#include "DFGCommon.h"

namespace JSC { namespace DFG {

class NaturalLoops;

class NaturalLoop {
public:
    NaturalLoop()
        : m_header(0)
        , m_outerLoopIndex(UINT_MAX)
    {
    }
    
    NaturalLoop(BasicBlock* header, unsigned index)
        : m_header(header)
        , m_outerLoopIndex(UINT_MAX)
        , m_index(index)
    {
    }
    
    BasicBlock* header() const { return m_header; }
    
    unsigned size() const { return m_body.size(); }
    BasicBlock* at(unsigned i) const { return m_body[i]; }
    BasicBlock* operator[](unsigned i) const { return at(i); }

    // This is the slower, but simpler, way of asking if a block belongs to
    // a natural loop. It's faster to call NaturalLoops::belongsTo(), which
    // tries to be O(loop depth) rather than O(loop size). Loop depth is
    // almost always smaller than loop size. A *lot* smaller.
    bool contains(BasicBlock* block) const
    {
        for (unsigned i = m_body.size(); i--;) {
            if (m_body[i] == block)
                return true;
        }
        ASSERT(block != header()); // Header should be contained.
        return false;
    }

    // The index of this loop in NaturalLoops.
    unsigned index() const { return m_index; }
    
    bool isOuterMostLoop() const { return m_outerLoopIndex == UINT_MAX; }
    
    void dump(PrintStream&) const;
private:
    friend class NaturalLoops;
    
    void addBlock(BasicBlock* block) { m_body.append(block); }
    
    BasicBlock* m_header;
    Vector<BasicBlock*, 4> m_body;
    unsigned m_outerLoopIndex;
    unsigned m_index;
};

class NaturalLoops : public Analysis<NaturalLoops> {
public:
    NaturalLoops();
    ~NaturalLoops();
    
    void computeDependencies(Graph&);
    void compute(Graph&);
    
    unsigned numLoops() const
    {
        ASSERT(isValid());
        return m_loops.size();
    }
    const NaturalLoop& loop(unsigned i) const
    {
        ASSERT(isValid());
        return m_loops[i];
    }
    
    // Return either null if the block isn't a loop header, or the
    // loop it belongs to.
    const NaturalLoop* headerOf(BasicBlock* block) const
    {
        ASSERT(isValid());
        const NaturalLoop* loop = innerMostLoopOf(block);
        if (!loop)
            return 0;
        if (loop->header() == block)
            return loop;
        if (!ASSERT_DISABLED) {
            for (; loop; loop = innerMostOuterLoop(*loop))
                ASSERT(loop->header() != block);
        }
        return 0;
    }
    
    const NaturalLoop* innerMostLoopOf(BasicBlock* block) const
    {
        ASSERT(isValid());
        unsigned index = block->innerMostLoopIndices[0];
        if (index == UINT_MAX)
            return 0;
        return &m_loops[index];
    }
    
    const NaturalLoop* innerMostOuterLoop(const NaturalLoop& loop) const
    {
        ASSERT(isValid());
        if (loop.m_outerLoopIndex == UINT_MAX)
            return 0;
        return &m_loops[loop.m_outerLoopIndex];
    }
    
    bool belongsTo(BasicBlock* block, const NaturalLoop& candidateLoop) const
    {
        ASSERT(isValid());
        // It's faster to do this test using the loop itself, if it's small.
        if (candidateLoop.size() < 4)
            return candidateLoop.contains(block);
        
        for (const NaturalLoop* loop = innerMostLoopOf(block); loop; loop = innerMostOuterLoop(*loop)) {
            if (loop == &candidateLoop)
                return true;
        }
        return false;
    }
    
    unsigned loopDepth(BasicBlock* block) const
    {
        unsigned depth = 0;
        for (const NaturalLoop* loop = innerMostLoopOf(block); loop; loop = innerMostOuterLoop(*loop))
            depth++;
        return depth;
    }
    
    // Return the indices of all loops this belongs to.
    Vector<const NaturalLoop*> loopsOf(BasicBlock*) const;

    void dump(PrintStream&) const;
private:
    // If we ever had a scalability problem in our natural loop finder, we could
    // use some HashMap's here. But it just feels a heck of a lot less convenient.
    Vector<NaturalLoop, 4> m_loops;
};

} } // namespace JSC::DFG

#endif // ENABLE(DFG_JIT)

#endif // DFGNaturalLoops_h