dfg/DFGLoopPreHeaderCreationPhase.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. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "config.h"
  27 #include "DFGLoopPreHeaderCreationPhase.h"
  28
  29 #if ENABLE(DFG_JIT)
  30
  31 #include "DFGBasicBlockInlines.h"
  32 #include "DFGBlockInsertionSet.h"
  33 #include "DFGGraph.h"
  34 #include "DFGPhase.h"
  35 #include "JSCInlines.h"
  36 #include <wtf/HashMap.h>
  37
  38 namespace JSC { namespace DFG {
  39
  40 BasicBlock* createPreHeader(Graph& graph, BlockInsertionSet& insertionSet, BasicBlock* block)
  41 {
  42     // Don't bother to preserve execution frequencies for now.
  43     BasicBlock* preHeader = insertionSet.insertBefore(block, PNaN);
  44     preHeader->appendNode(
  45         graph, SpecNone, Jump, block->at(0)->origin, OpInfo(block));
  46
  47     for (unsigned predecessorIndex = 0; predecessorIndex < block->predecessors.size(); predecessorIndex++) {
  48         BasicBlock* predecessor = block->predecessors[predecessorIndex];
  49         if (graph.m_dominators.dominates(block, predecessor))
  50             continue;
  51         block->predecessors[predecessorIndex--] = block->predecessors.last();
  52         block->predecessors.removeLast();
  53         for (unsigned successorIndex = predecessor->numSuccessors(); successorIndex--;) {
  54             BasicBlock*& successor = predecessor->successor(successorIndex);
  55             if (successor != block)
  56                 continue;
  57             successor = preHeader;
  58             preHeader->predecessors.append(predecessor);
  59         }
  60     }
  61
  62     block->predecessors.append(preHeader);
  63     return preHeader;
  64 }
  65
  66 class LoopPreHeaderCreationPhase : public Phase {
  67 public:
  68     LoopPreHeaderCreationPhase(Graph& graph)
  69         : Phase(graph, "loop pre-header creation")
  70         , m_insertionSet(graph)
  71     {
  72     }
  73
  74     bool run()
  75     {
  76         m_graph.m_dominators.computeIfNecessary(m_graph);
  77         m_graph.m_naturalLoops.computeIfNecessary(m_graph);
  78
  79         for (unsigned loopIndex = m_graph.m_naturalLoops.numLoops(); loopIndex--;) {
  80             const NaturalLoop& loop = m_graph.m_naturalLoops.loop(loopIndex);
  81             BasicBlock* existingPreHeader = 0;
  82             bool needsNewPreHeader = false;
  83             for (unsigned predecessorIndex = loop.header()->predecessors.size(); predecessorIndex--;) {
  84                 BasicBlock* predecessor = loop.header()->predecessors[predecessorIndex];
  85                 if (m_graph.m_dominators.dominates(loop.header(), predecessor))
  86                     continue;
  87                 if (!existingPreHeader) {
  88                     existingPreHeader = predecessor;
  89                     continue;
  90                 }
  91                 if (existingPreHeader == predecessor)
  92                     continue;
  93                 needsNewPreHeader = true;
  94                 break;
  95             }
  96             if (!needsNewPreHeader)
  97                 continue;
  98
  99             createPreHeader(m_graph, m_insertionSet, loop.header());
 100         }
 101
 102         return m_insertionSet.execute();
 103     }
 104
 105     BlockInsertionSet m_insertionSet;
 106 };
 107
 108 bool performLoopPreHeaderCreation(Graph& graph)
 109 {
 110     SamplingRegion samplingRegion("DFG Loop Pre-Header Creation Phase");
 111     return runPhase<LoopPreHeaderCreationPhase>(graph);
 112 }
 113
 114 } } // namespace JSC::DFG
 115
 116 #endif // ENABLE(DFG_JIT)
 117
 118