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,
  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 "DFGAbstractInterpreterInlines.h"
  32 #include "DFGGraph.h"
  33 #include "DFGInPlaceAbstractState.h"
  34 #include "DFGPhase.h"
  35 #include "DFGSafeToExecute.h"
  36 #include "OperandsInlines.h"
  37 #include "JSCInlines.h"
  38
  39 namespace JSC { namespace DFG {
  40
  41 class CFAPhase : public Phase {
  42 public:
  43     CFAPhase(Graph& graph)
  44         : Phase(graph, "control flow analysis")
  45         , m_state(graph)
  46         , m_interpreter(graph, m_state)
  47         , m_verbose(Options::verboseCFA())
  48     {
  49     }
  50
  51     bool run()
  52     {
  53         ASSERT(m_graph.m_form == ThreadedCPS || m_graph.m_form == SSA);
  54         ASSERT(m_graph.m_unificationState == GloballyUnified);
  55         ASSERT(m_graph.m_refCountState == EverythingIsLive);
  56
  57         m_count = 0;
  58
  59         if (m_verbose && !shouldDumpGraphAtEachPhase()) {
  60             dataLog("Graph before CFA:\n");
  61             m_graph.dump();
  62         }
  63
  64         // This implements a pseudo-worklist-based forward CFA, except that the visit order
  65         // of blocks is the bytecode program order (which is nearly topological), and
  66         // instead of a worklist we just walk all basic blocks checking if cfaShouldRevisit
  67         // is set to true. This is likely to balance the efficiency properties of both
  68         // worklist-based and forward fixpoint-based approaches. Like a worklist-based
  69         // approach, it won't visit code if it's meaningless to do so (nothing changed at
  70         // the head of the block or the predecessors have not been visited). Like a forward
  71         // fixpoint-based approach, it has a high probability of only visiting a block
  72         // after all predecessors have been visited. Only loops will cause this analysis to
  73         // revisit blocks, and the amount of revisiting is proportional to loop depth.
  74
  75         m_state.initialize();
  76
  77         do {
  78             m_changed = false;
  79             performForwardCFA();
  80         } while (m_changed);
  81
  82         return true;
  83     }
  84
  85 private:
  86     void performBlockCFA(BasicBlock* block)
  87     {
  88         if (!block)
  89             return;
  90         if (!block->cfaShouldRevisit)
  91             return;
  92         if (m_verbose)
  93             dataLog("   Block ", *block, ":\n");
  94         m_state.beginBasicBlock(block);
  95         if (m_verbose)
  96             dataLog("      head vars: ", block->valuesAtHead, "\n");
  97         for (unsigned i = 0; i < block->size(); ++i) {
  98             if (m_verbose) {
  99                 Node* node = block->at(i);
 100                 dataLogF("      %s @%u: ", Graph::opName(node->op()), node->index());
 101
 102                 if (!safeToExecute(m_state, m_graph, node))
 103                     dataLog("(UNSAFE) ");
 104
 105                 m_interpreter.dump(WTF::dataFile());
 106
 107                 if (m_state.haveStructures())
 108                     dataLog(" (Have Structures)");
 109                 dataLogF("\n");
 110             }
 111             if (!m_interpreter.execute(i)) {
 112                 if (m_verbose)
 113                     dataLogF("         Expect OSR exit.\n");
 114                 break;
 115             }
 116         }
 117         if (m_verbose) {
 118             dataLogF("      tail regs: ");
 119             m_interpreter.dump(WTF::dataFile());
 120             dataLogF("\n");
 121         }
 122         m_changed |= m_state.endBasicBlock(MergeToSuccessors);
 123
 124         if (m_verbose)
 125             dataLog("      tail vars: ", block->valuesAtTail, "\n");
 126     }
 127
 128     void performForwardCFA()
 129     {
 130         ++m_count;
 131         if (m_verbose)
 132             dataLogF("CFA [%u]\n", ++m_count);
 133
 134         for (BlockIndex blockIndex = 0; blockIndex < m_graph.numBlocks(); ++blockIndex)
 135             performBlockCFA(m_graph.block(blockIndex));
 136     }
 137
 138 private:
 139     InPlaceAbstractState m_state;
 140     AbstractInterpreter<InPlaceAbstractState> m_interpreter;
 141
 142     bool m_verbose;
 143
 144     bool m_changed;
 145     unsigned m_count;
 146 };
 147
 148 bool performCFA(Graph& graph)
 149 {
 150     SamplingRegion samplingRegion("DFG CFA Phase");
 151     return runPhase<CFAPhase>(graph);
 152 }
 153
 154 } } // namespace JSC::DFG
 155
 156 #endif // ENABLE(DFG_JIT)