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 "DFGAbstractState.h"
32#include "DFGGraph.h"
33#include "DFGPhase.h"
34#include "Operations.h"
35
36namespace JSC { namespace DFG {
37
38class CFAPhase : public Phase {
39public:
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
77private:
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
131private:
132    AbstractState m_state;
133
134    bool m_changed;
135#if DFG_ENABLE(DEBUG_PROPAGATION_VERBOSE)
136    unsigned m_count;
137#endif
138};
139
140bool 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)
149