dfg/DFGCFAPhase.cpp

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