dfg/DFGDCEPhase.cpp

   1 /*
   2  * Copyright (C) 2013-2015 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 "DFGDCEPhase.h"
  28
  29 #if ENABLE(DFG_JIT)
  30
  31 #include "DFGBasicBlockInlines.h"
  32 #include "DFGGraph.h"
  33 #include "DFGInsertionSet.h"
  34 #include "DFGPhase.h"
  35 #include "JSCInlines.h"
  36
  37 namespace JSC { namespace DFG {
  38
  39 class DCEPhase : public Phase {
  40 public:
  41     DCEPhase(Graph& graph)
  42         : Phase(graph, "dead code elimination")
  43         , m_insertionSet(graph)
  44     {
  45     }
  46
  47     bool run()
  48     {
  49         ASSERT(m_graph.m_form == ThreadedCPS || m_graph.m_form == SSA);
  50
  51         m_graph.computeRefCounts();
  52
  53         for (BasicBlock* block : m_graph.blocksInPreOrder())
  54             fixupBlock(block);
  55
  56         cleanVariables(m_graph.m_arguments);
  57
  58         // Just do a basic Phantom/Check clean-up.
  59         for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
  60             BasicBlock* block = m_graph.block(blockIndex);
  61             if (!block)
  62                 continue;
  63             unsigned sourceIndex = 0;
  64             unsigned targetIndex = 0;
  65             while (sourceIndex < block->size()) {
  66                 Node* node = block->at(sourceIndex++);
  67                 switch (node->op()) {
  68                 case Check:
  69                 case Phantom:
  70                     if (node->children.isEmpty())
  71                         continue;
  72                     break;
  73                 default:
  74                     break;
  75                 }
  76                 block->at(targetIndex++) = node;
  77             }
  78             block->resize(targetIndex);
  79         }
  80
  81         m_graph.m_refCountState = ExactRefCount;
  82
  83         return true;
  84     }
  85
  86 private:
  87     void fixupBlock(BasicBlock* block)
  88     {
  89         if (!block)
  90             return;
  91
  92         if (m_graph.m_form == ThreadedCPS) {
  93             for (unsigned phiIndex = 0; phiIndex < block->phis.size(); ++phiIndex) {
  94                 Node* phi = block->phis[phiIndex];
  95                 if (!phi->shouldGenerate()) {
  96                     m_graph.m_allocator.free(phi);
  97                     block->phis[phiIndex--] = block->phis.last();
  98                     block->phis.removeLast();
  99                 }
 100             }
 101
 102             cleanVariables(block->variablesAtHead);
 103             cleanVariables(block->variablesAtTail);
 104         }
 105
 106         // This has to be a forward loop because we are using the insertion set.
 107         for (unsigned indexInBlock = 0; indexInBlock < block->size(); ++indexInBlock) {
 108             Node* node = block->at(indexInBlock);
 109             if (node->shouldGenerate())
 110                 continue;
 111
 112             if (node->flags() & NodeHasVarArgs) {
 113                 for (unsigned childIdx = node->firstChild(); childIdx < node->firstChild() + node->numChildren(); childIdx++) {
 114                     Edge edge = m_graph.m_varArgChildren[childIdx];
 115
 116                     if (!edge || edge.willNotHaveCheck())
 117                         continue;
 118
 119                     m_insertionSet.insertNode(indexInBlock, SpecNone, Check, node->origin, edge);
 120                 }
 121
 122                 node->setOpAndDefaultFlags(Check);
 123                 node->children.reset();
 124                 node->setRefCount(1);
 125                 continue;
 126             }
 127
 128             node->remove();
 129             node->setRefCount(1);
 130         }
 131
 132         m_insertionSet.execute(block);
 133     }
 134
 135     template<typename VariablesVectorType>
 136     void cleanVariables(VariablesVectorType& variables)
 137     {
 138         for (unsigned i = variables.size(); i--;) {
 139             Node* node = variables[i];
 140             if (!node)
 141                 continue;
 142             if (node->op() != Check && node->shouldGenerate())
 143                 continue;
 144             variables[i] = nullptr;
 145         }
 146     }
 147
 148     InsertionSet m_insertionSet;
 149 };
 150
 151 bool performDCE(Graph& graph)
 152 {
 153     SamplingRegion samplingRegion("DFG DCE Phase");
 154     return runPhase<DCEPhase>(graph);
 155 }
 156
 157 } } // namespace JSC::DFG
 158
 159 #endif // ENABLE(DFG_JIT)
 160