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             DFG_CRASH(
  72                 m_graph, nullptr,
  73                 toCString(
  74                     "Bad liveness analysis result: live at root is not empty: ",
  75                     nodeListDump(m_graph.block(0)->ssa->liveAtHead)).data());
  76         }
  77
  78         return true;
  79     }
  80
  81 private:
  82     void process(BlockIndex blockIndex)
  83     {
  84         BasicBlock* block = m_graph.block(blockIndex);
  85         if (!block)
  86             return;
  87
  88         // FIXME: It's likely that this can be improved, for static analyses that use
  89         // HashSets. https://bugs.webkit.org/show_bug.cgi?id=118455
  90         m_live = block->ssa->liveAtTail;
  91
  92         for (unsigned nodeIndex = block->size(); nodeIndex--;) {
  93             Node* node = block->at(nodeIndex);
  94
  95             // Given an Upsilon:
  96             //
  97             //    n: Upsilon(@x, ^p)
  98             //
  99             // We say that it def's @p and @n and uses @x.
 100             //
 101             // Given a Phi:
 102             //
 103             //    p: Phi()
 104             //
 105             // We say nothing. It's neither a use nor a def.
 106             //
 107             // Given a node:
 108             //
 109             //    n: Thingy(@a, @b, @c)
 110             //
 111             // We say that it def's @n and uses @a, @b, @c.
 112
 113             switch (node->op()) {
 114             case Upsilon: {
 115                 Node* phi = node->phi();
 116                 m_live.remove(phi);
 117                 m_live.remove(node);
 118                 m_live.add(node->child1().node());
 119                 break;
 120             }
 121
 122             case Phi: {
 123                 break;
 124             }
 125
 126             default:
 127                 m_live.remove(node);
 128                 DFG_NODE_DO_TO_CHILDREN(m_graph, node, addChildUse);
 129                 break;
 130             }
 131         }
 132
 133         if (m_live == block->ssa->liveAtHead)
 134             return;
 135
 136         m_changed = true;
 137         block->ssa->liveAtHead = m_live;
 138         for (unsigned i = block->predecessors.size(); i--;)
 139             block->predecessors[i]->ssa->liveAtTail.add(m_live.begin(), m_live.end());
 140     }
 141
 142     void addChildUse(Node*, Edge& edge)
 143     {
 144         addChildUse(edge);
 145     }
 146
 147     void addChildUse(Edge& edge)
 148     {
 149         edge.setKillStatus(m_live.add(edge.node()).isNewEntry ? DoesKill : DoesNotKill);
 150     }
 151
 152     bool m_changed;
 153     HashSet<Node*> m_live;
 154 };
 155
 156 bool performLivenessAnalysis(Graph& graph)
 157 {
 158     SamplingRegion samplingRegion("DFG Liveness Analysis Phase");
 159     return runPhase<LivenessAnalysisPhase>(graph);
 160 }
 161
 162 } } // namespace JSC::DFG
 163
 164 #endif // ENABLE(DFG_JIT)
 165