dfg/DFGCFAPhase.cpp

   1 /*
   2  * Copyright (C) 2011, 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,
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  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "config.h"
  27 #include "DFGCFAPhase.h"
  28
  29 #if ENABLE(DFG_JIT)
  30
  31 #include "DFGAbstractState.h"
  32 #include "DFGGraph.h"
  33 #include "DFGPhase.h"
  34 #include "Operations.h"
  35
  36 namespace JSC { namespace DFG {
  37
  38 class CFAPhase : public Phase {
  39 public:
  40     CFAPhase(Graph& graph)
  41         : Phase(graph, "control flow analysis")
  42         , m_state(graph)
  43     {
  44     }
  45
  46     bool run()
  47     {
  48         ASSERT(m_graph.m_form == ThreadedCPS);
  49         ASSERT(m_graph.m_unificationState == GloballyUnified);
  50         ASSERT(m_graph.m_refCountState == EverythingIsLive);
  51
  52 #if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
  53         m_count = 0;
  54 #endif
  55
  56         // This implements a pseudo-worklist-based forward CFA, except that the visit order
  57         // of blocks is the bytecode program order (which is nearly topological), and
  58         // instead of a worklist we just walk all basic blocks checking if cfaShouldRevisit
  59         // is set to true. This is likely to balance the efficiency properties of both
  60         // worklist-based and forward fixpoint-based approaches. Like a worklist-based
  61         // approach, it won't visit code if it's meaningless to do so (nothing changed at
  62         // the head of the block or the predecessors have not been visited). Like a forward
  63         // fixpoint-based approach, it has a high probability of only visiting a block
  64         // after all predecessors have been visited. Only loops will cause this analysis to
  65         // revisit blocks, and the amount of revisiting is proportional to loop depth.
  66
  67         AbstractState::initialize(m_graph);
  68
  69         do {
  70             m_changed = false;
  71             performForwardCFA();
  72         } while (m_changed);
  73
  74         return true;
  75     }
  76
  77 private:
  78     void performBlockCFA(BlockIndex blockIndex)
  79     {
  80         BasicBlock* block = m_graph.m_blocks[blockIndex].get();
  81         if (!block)
  82             return;
  83         if (!block->cfaShouldRevisit)
  84             return;
  85 #if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
  86         dataLogF("   Block #%u (bc#%u):\n", blockIndex, block->bytecodeBegin);
  87 #endif
  88         m_state.beginBasicBlock(block);
  89 #if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
  90         dataLogF("      head vars: ");
  91         dumpOperands(block->valuesAtHead, WTF::dataFile());
  92         dataLogF("\n");
  93 #endif
  94         for (unsigned i = 0; i < block->size(); ++i) {
  95 #if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
  96             Node* node = block->at(i);
  97             dataLogF("      %s @%u: ", Graph::opName(node->op()), node->index());
  98             m_state.dump(WTF::dataFile());
  99             dataLogF("\n");
 100 #endif
 101             if (!m_state.execute(i)) {
 102 #if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
 103                 dataLogF("         Expect OSR exit.\n");
 104 #endif
 105                 break;
 106             }
 107         }
 108 #if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
 109         dataLogF("      tail regs: ");
 110         m_state.dump(WTF::dataFile());
 111         dataLogF("\n");
 112 #endif
 113         m_changed |= m_state.endBasicBlock(AbstractState::MergeToSuccessors);
 114 #if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
 115         dataLogF("      tail vars: ");
 116         dumpOperands(block->valuesAtTail, WTF::dataFile());
 117         dataLogF("\n");
 118 #endif
 119     }
 120
 121     void performForwardCFA()
 122     {
 123 #if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
 124         dataLogF("CFA [%u]\n", ++m_count);
 125 #endif
 126
 127         for (BlockIndex block = 0; block < m_graph.m_blocks.size(); ++block)
 128             performBlockCFA(block);
 129     }
 130
 131 private:
 132     AbstractState m_state;
 133
 134     bool m_changed;
 135 #if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
 136     unsigned m_count;
 137 #endif
 138 };
 139
 140 bool performCFA(Graph& graph)
 141 {
 142     SamplingRegion samplingRegion("DFG CFA Phase");
 143     return runPhase<CFAPhase>(graph);
 144 }
 145
 146 } } // namespace JSC::DFG
 147
 148 #endif // ENABLE(DFG_JIT)