dfg/DFGStoreBarrierElisionPhase.cpp

   1 /*
   2  * Copyright (C) 2013 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
  14  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  15  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
  17  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  18  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  19  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  20  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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  22  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  23  * THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "config.h"
  27 #include "DFGStoreBarrierElisionPhase.h"
  28
  29 #if ENABLE(DFG_JIT)
  30
  31 #include "DFGBasicBlock.h"
  32 #include "DFGClobberize.h"
  33 #include "DFGGraph.h"
  34 #include "DFGPhase.h"
  35 #include "JSCInlines.h"
  36 #include <wtf/HashSet.h>
  37
  38 namespace JSC { namespace DFG {
  39
  40 class StoreBarrierElisionPhase : public Phase {
  41 public:
  42     StoreBarrierElisionPhase(Graph& graph)
  43         : Phase(graph, "store barrier elision")
  44         , m_currentBlock(0)
  45         , m_currentIndex(0)
  46     {
  47     }
  48
  49     bool run()
  50     {
  51         for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex) {
  52             m_currentBlock = m_graph.block(blockIndex);
  53             if (!m_currentBlock)
  54                 continue;
  55             handleBlock(m_currentBlock);
  56         }
  57         return true;
  58     }
  59
  60 private:
  61     bool couldCauseGC(Node* node)
  62     {
  63         return writesOverlap(m_graph, node, GCState);
  64     }
  65
  66     bool allocatesFreshObject(Node* node)
  67     {
  68         switch (node->op()) {
  69         case NewObject:
  70         case NewArray:
  71         case NewArrayWithSize:
  72         case NewArrayBuffer:
  73         case NewTypedArray:
  74         case NewRegexp:
  75             return true;
  76         default:
  77             return false;
  78         }
  79     }
  80
  81     void noticeFreshObject(HashSet<Node*>& dontNeedBarriers, Node* node)
  82     {
  83         ASSERT(allocatesFreshObject(node));
  84         dontNeedBarriers.add(node);
  85     }
  86
  87     Node* getBaseOfStore(Node* barrierNode)
  88     {
  89         ASSERT(barrierNode->isStoreBarrier());
  90         return barrierNode->child1().node();
  91     }
  92
  93     bool shouldBeElided(HashSet<Node*>& dontNeedBarriers, Node* node)
  94     {
  95         ASSERT(node->isStoreBarrier());
  96         return dontNeedBarriers.contains(node->child1().node());
  97     }
  98
  99     void elideBarrier(Node* node)
 100     {
 101         ASSERT(node->isStoreBarrier());
 102         node->convertToPhantom();
 103     }
 104
 105     void handleNode(HashSet<Node*>& dontNeedBarriers, Node* node)
 106     {
 107         if (couldCauseGC(node))
 108             dontNeedBarriers.clear();
 109
 110         if (allocatesFreshObject(node))
 111             noticeFreshObject(dontNeedBarriers, node);
 112
 113         if (!node->isStoreBarrier())
 114             return;
 115
 116         if (shouldBeElided(dontNeedBarriers, node)) {
 117             elideBarrier(node);
 118             return;
 119         }
 120
 121         Node* base = getBaseOfStore(node);
 122         if (!base)
 123             return;
 124
 125         if (dontNeedBarriers.contains(base))
 126             return;
 127         dontNeedBarriers.add(base);
 128     }
 129
 130     bool handleBlock(BasicBlock* block)
 131     {
 132         HashSet<Node*> dontNeedBarriers;
 133         for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
 134             m_currentIndex = indexInBlock;
 135             Node* node = block->at(indexInBlock);
 136             handleNode(dontNeedBarriers, node);
 137         }
 138         return true;
 139     }
 140
 141     BasicBlock* m_currentBlock;
 142     unsigned m_currentIndex;
 143 };
 144
 145 bool performStoreBarrierElision(Graph& graph)
 146 {
 147     SamplingRegion samplingRegion("DFG Store Barrier Elision Phase");
 148     return runPhase<StoreBarrierElisionPhase>(graph);
 149 }
 150
 151
 152 } } // namespace JSC::DFG
 153
 154 #endif // ENABLE(DFG_JIT)