Source/JavaScriptCore/b3/B3EnsureLoopPreHeaders.cpp

/*
 * Copyright (C) 2017 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
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 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 */

#include "config.h"
#include "B3EnsureLoopPreHeaders.h"

#if ENABLE(B3_JIT)

#include "B3BasicBlockInlines.h"
#include "B3BlockInsertionSet.h"
#include "B3NaturalLoops.h"
#include "B3ValueInlines.h"

namespace JSC { namespace B3 {

bool ensureLoopPreHeaders(Procedure& proc)
{
    NaturalLoops& loops = proc.naturalLoops();
    
    BlockInsertionSet insertionSet(proc);
    
    for (unsigned loopIndex = loops.numLoops(); loopIndex--;) {
        const NaturalLoop& loop = loops.loop(loopIndex);
        
        Vector<BasicBlock*, 4> outOfBodyPredecessors;
        double totalFrequency = 0;
        for (BasicBlock* predecessor : loop.header()->predecessors()) {
            if (loops.belongsTo(predecessor, loop))
                continue;
            
            outOfBodyPredecessors.append(predecessor);
            totalFrequency += predecessor->frequency();
        }
        
        if (outOfBodyPredecessors.size() <= 1)
            continue;
        
        BasicBlock* preHeader = insertionSet.insertBefore(loop.header(), totalFrequency);
        preHeader->appendNew<Value>(proc, Jump, loop.header()->at(0)->origin());
        preHeader->setSuccessors(FrequentedBlock(loop.header()));
        
        for (BasicBlock* predecessor : outOfBodyPredecessors) {
            predecessor->replaceSuccessor(loop.header(), preHeader);
            preHeader->addPredecessor(predecessor);
            loop.header()->removePredecessor(predecessor);
        }
        
        loop.header()->addPredecessor(preHeader);
    }
    
    if (insertionSet.execute()) {
        proc.invalidateCFG();
        return true;
    }
    
    return false;
}

} } // namespace JSC::B3

#endif // ENABLE(B3_JIT)