dfg/DFGLivenessAnalysisPhase.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 "DFGLivenessAnalysisPhase.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 LivenessAnalysisPhase : public Phase {
  40 public:
  41     LivenessAnalysisPhase(Graph& graph)
  42         : Phase(graph, "liveness analysis")
  43     {
  44     }
  45
  46     bool run()
  47     {
  48         ASSERT(m_graph.m_form == SSA);
  49
  50         // Liveness is a backwards analysis; the roots are the blocks that
  51         // end in a terminal (Return/Throw/ThrowReferenceError). For now, we
  52         // use a fixpoint formulation since liveness is a rapid analysis with
  53         // convergence guaranteed after O(connectivity).
  54
  55         // Start by assuming that everything is dead.
  56         for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
  57             BasicBlock* block = m_graph.block(blockIndex);
  58             if (!block)
  59                 continue;
  60             block->ssa->liveAtHead.clear();
  61             block->ssa->liveAtTail.clear();
  62         }
  63
  64         do {
  65             m_changed = false;
  66             for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;)
  67                 process(blockIndex);
  68         } while (m_changed);
  69
  70         if (!m_graph.block(0)->ssa->liveAtHead.isEmpty()) {
  71             startCrashing();
  72             dataLog(
  73                 "Bad liveness analysis result: live at root is not empty: ",
  74                 nodeListDump(m_graph.block(0)->ssa->liveAtHead), "\n");
  75             dataLog("IR at time of error:\n");
  76             m_graph.dump();
  77             CRASH();
  78         }
  79
  80         return true;
  81     }
  82
  83 private:
  84     void process(BlockIndex blockIndex)
  85     {
  86         BasicBlock* block = m_graph.block(blockIndex);
  87         if (!block)
  88             return;
  89
  90         // FIXME: It's likely that this can be improved, for static analyses that use
  91         // HashSets. https://bugs.webkit.org/show_bug.cgi?id=118455
  92         m_live = block->ssa->liveAtTail;
  93
  94         for (unsigned nodeIndex = block->size(); nodeIndex--;) {
  95             Node* node = block->at(nodeIndex);
  96
  97             // Given an Upsilon:
  98             //
  99             //    n: Upsilon(@x, ^p)
 100             //
 101             // We say that it def's @p and @n and uses @x.
 102             //
 103             // Given a Phi:
 104             //
 105             //    p: Phi()
 106             //
 107             // We say nothing. It's neither a use nor a def.
 108             //
 109             // Given a node:
 110             //
 111             //    n: Thingy(@a, @b, @c)
 112             //
 113             // We say that it def's @n and uses @a, @b, @c.
 114
 115             switch (node->op()) {
 116             case Upsilon: {
 117                 Node* phi = node->phi();
 118                 m_live.remove(phi);
 119                 m_live.remove(node);
 120                 m_live.add(node->child1().node());
 121                 break;
 122             }
 123
 124             case Phi: {
 125                 break;
 126             }
 127
 128             default:
 129                 m_live.remove(node);
 130                 DFG_NODE_DO_TO_CHILDREN(m_graph, node, addChildUse);
 131                 break;
 132             }
 133         }
 134
 135         if (m_live == block->ssa->liveAtHead)
 136             return;
 137
 138         m_changed = true;
 139         block->ssa->liveAtHead = m_live;
 140         for (unsigned i = block->predecessors.size(); i--;)
 141             block->predecessors[i]->ssa->liveAtTail.add(m_live.begin(), m_live.end());
 142     }
 143
 144     void addChildUse(Node*, Edge& edge)
 145     {
 146         addChildUse(edge);
 147     }
 148
 149     void addChildUse(Edge& edge)
 150     {
 151         edge.setKillStatus(m_live.add(edge.node()).isNewEntry ? DoesKill : DoesNotKill);
 152     }
 153
 154     bool m_changed;
 155     HashSet<Node*> m_live;
 156 };
 157
 158 bool performLivenessAnalysis(Graph& graph)
 159 {
 160     SamplingRegion samplingRegion("DFG Liveness Analysis Phase");
 161     return runPhase<LivenessAnalysisPhase>(graph);
 162 }
 163
 164 } } // namespace JSC::DFG
 165
 166 #endif // ENABLE(DFG_JIT)
 167