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 "DFGLoopPreHeaderCreationPhase.h"
28
29#if ENABLE(DFG_JIT)
30
31#include "DFGBasicBlockInlines.h"
32#include "DFGBlockInsertionSet.h"
33#include "DFGGraph.h"
34#include "DFGPhase.h"
35#include "JSCInlines.h"
36#include <wtf/HashMap.h>
37
38namespace JSC { namespace DFG {
39
40BasicBlock* createPreHeader(Graph& graph, BlockInsertionSet& insertionSet, BasicBlock* block)
41{
42    // Don't bother to preserve execution frequencies for now.
43    BasicBlock* preHeader = insertionSet.insertBefore(block, PNaN);
44    preHeader->appendNode(
45        graph, SpecNone, Jump, block->at(0)->origin, OpInfo(block));
46
47    for (unsigned predecessorIndex = 0; predecessorIndex < block->predecessors.size(); predecessorIndex++) {
48        BasicBlock* predecessor = block->predecessors[predecessorIndex];
49        if (graph.m_dominators.dominates(block, predecessor))
50            continue;
51        block->predecessors[predecessorIndex--] = block->predecessors.last();
52        block->predecessors.removeLast();
53        for (unsigned successorIndex = predecessor->numSuccessors(); successorIndex--;) {
54            BasicBlock*& successor = predecessor->successor(successorIndex);
55            if (successor != block)
56                continue;
57            successor = preHeader;
58            preHeader->predecessors.append(predecessor);
59        }
60    }
61
62    block->predecessors.append(preHeader);
63    return preHeader;
64}
65
66class LoopPreHeaderCreationPhase : public Phase {
67public:
68    LoopPreHeaderCreationPhase(Graph& graph)
69        : Phase(graph, "loop pre-header creation")
70        , m_insertionSet(graph)
71    {
72    }
73
74    bool run()
75    {
76        m_graph.m_dominators.computeIfNecessary(m_graph);
77        m_graph.m_naturalLoops.computeIfNecessary(m_graph);
78
79        for (unsigned loopIndex = m_graph.m_naturalLoops.numLoops(); loopIndex--;) {
80            const NaturalLoop& loop = m_graph.m_naturalLoops.loop(loopIndex);
81            BasicBlock* existingPreHeader = 0;
82            bool needsNewPreHeader = false;
83            for (unsigned predecessorIndex = loop.header()->predecessors.size(); predecessorIndex--;) {
84                BasicBlock* predecessor = loop.header()->predecessors[predecessorIndex];
85                if (m_graph.m_dominators.dominates(loop.header(), predecessor))
86                    continue;
87                if (!existingPreHeader) {
88                    existingPreHeader = predecessor;
89                    continue;
90                }
91                if (existingPreHeader == predecessor)
92                    continue;
93                needsNewPreHeader = true;
94                break;
95            }
96            if (!needsNewPreHeader)
97                continue;
98
99            createPreHeader(m_graph, m_insertionSet, loop.header());
100        }
101
102        return m_insertionSet.execute();
103    }
104
105    BlockInsertionSet m_insertionSet;
106};
107
108bool performLoopPreHeaderCreation(Graph& graph)
109{
110    SamplingRegion samplingRegion("DFG Loop Pre-Header Creation Phase");
111    return runPhase<LoopPreHeaderCreationPhase>(graph);
112}
113
114} } // namespace JSC::DFG
115
116#endif // ENABLE(DFG_JIT)
117
118
119