Source/JavaScriptCore/dfg/DFGCriticalEdgeBreakingPhase.cpp

/*
 * Copyright (C) 2013 Apple Inc. All rights reserved.
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 * modification, are permitted provided that the following conditions
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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#include "config.h"
#include "DFGCriticalEdgeBreakingPhase.h"

#if ENABLE(DFG_JIT)

#include "DFGBasicBlockInlines.h"
#include "DFGBlockInsertionSet.h"
#include "DFGGraph.h"
#include "DFGPhase.h"
#include "JSCInlines.h"
#include <wtf/HashMap.h>

namespace JSC { namespace DFG {

class CriticalEdgeBreakingPhase : public Phase {
public:
    CriticalEdgeBreakingPhase(Graph& graph)
        : Phase(graph, "critical edge breaking")
        , m_insertionSet(graph)
    {
    }
    
    bool run()
    {
        for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex) {
            BasicBlock* block = m_graph.block(blockIndex);
            if (!block)
                continue;
            
            // An edge A->B is critical if A has multiple successor and B has multiple
            // predecessors. Thus we fail early if we don't have multiple successors.
            
            if (block->numSuccessors() <= 1)
                continue;
            
            for (unsigned i = block->numSuccessors(); i--;) {
                BasicBlock** successor = &block->successor(i);
                if ((*successor)->predecessors.size() <= 1)
                    continue;
                
                breakCriticalEdge(block, successor); 
            }
        }
        
        return m_insertionSet.execute();
    }

private:
    void breakCriticalEdge(BasicBlock* predecessor, BasicBlock** successor)
    {
        BasicBlock* pad = m_insertionSet.insertBefore(*successor);
        pad->appendNode(
            m_graph, SpecNone, Jump, (*successor)->at(0)->origin, OpInfo(*successor));
        pad->predecessors.append(predecessor);
        (*successor)->replacePredecessor(predecessor, pad);
        
        *successor = pad;
    }
    
    BlockInsertionSet m_insertionSet;
};

bool performCriticalEdgeBreaking(Graph& graph)
{
    SamplingRegion samplingRegion("DFG Critical Edge Breaking Phase");
    return runPhase<CriticalEdgeBreakingPhase>(graph);
}

} } // namespace JSC::DFG

#endif // ENABLE(DFG_JIT)