jit/BinarySwitch.h

   1 /*
   2  * Copyright (C) 2013, 2015 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,
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  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef BinarySwitch_h
  27 #define BinarySwitch_h
  28
  29 #if ENABLE(JIT)
  30
  31 #include "GPRInfo.h"
  32 #include "MacroAssembler.h"
  33 #include "WeakRandom.h"
  34
  35 namespace JSC {
  36
  37 // The BinarySwitch class makes it easy to emit a switch statement over either
  38 // 32-bit integers or pointers, where the switch uses a tree of branches
  39 // rather than a jump table. This makes it particularly useful if the case
  40 // values are too far apart to make a jump table practical, or if there are
  41 // sufficiently few cases that the total cost of log(numCases) branches is
  42 // less than the cost of an indirected jump.
  43 //
  44 // In an effort to simplify the logic of emitting code for each case, this
  45 // uses an iterator style, rather than a functor callback style. This makes
  46 // sense because even the iterator implementation found herein is relatively
  47 // simple, whereas the code it's used from is usually quite complex - one
  48 // example being the trie-of-trees string switch implementation, where the
  49 // code emitted for each case involves recursing to emit code for a sub-trie.
  50 //
  51 // Use this like so:
  52 //
  53 // BinarySwitch switch(valueReg, casesVector, BinarySwitch::Int32);
  54 // while (switch.advance(jit)) {
  55 //     int value = switch.caseValue();
  56 //     unsigned index = switch.caseIndex(); // index into casesVector, above
  57 //     ... // generate code for this case
  58 //     ... = jit.jump(); // you have to jump out yourself; falling through causes undefined behavior
  59 // }
  60 // switch.fallThrough().link(&jit);
  61
  62 class BinarySwitch {
  63 public:
  64     enum Type {
  65         Int32,
  66         IntPtr
  67     };
  68
  69     BinarySwitch(GPRReg value, const Vector<int64_t>& cases, Type);
  70     ~BinarySwitch();
  71
  72     unsigned caseIndex() const { return m_cases[m_caseIndex].index; }
  73     int64_t caseValue() const { return m_cases[m_caseIndex].value; }
  74
  75     bool advance(MacroAssembler&);
  76
  77     MacroAssembler::JumpList& fallThrough() { return m_fallThrough; }
  78
  79 private:
  80     void build(unsigned start, bool hardStart, unsigned end);
  81
  82     GPRReg m_value;
  83
  84     struct Case {
  85         Case() { }
  86
  87         Case(int64_t value, unsigned index)
  88             : value(value)
  89             , index(index)
  90         {
  91         }
  92
  93         bool operator<(const Case& other) const
  94         {
  95             return value < other.value;
  96         }
  97
  98         int64_t value;
  99         unsigned index;
 100     };
 101
 102     Vector<Case> m_cases;
 103
 104     enum BranchKind {
 105         NotEqualToFallThrough,
 106         NotEqualToPush,
 107         LessThanToPush,
 108         Pop,
 109         ExecuteCase
 110     };
 111
 112     struct BranchCode {
 113         BranchCode() { }
 114
 115         BranchCode(BranchKind kind, unsigned index = UINT_MAX)
 116             : kind(kind)
 117             , index(index)
 118         {
 119         }
 120
 121         BranchKind kind;
 122         unsigned index;
 123     };
 124
 125     WeakRandom m_weakRandom;
 126
 127     Vector<BranchCode> m_branches;
 128
 129     unsigned m_index;
 130     unsigned m_caseIndex;
 131     Vector<MacroAssembler::Jump> m_jumpStack;
 132
 133     MacroAssembler::JumpList m_fallThrough;
 134
 135     Type m_type;
 136 };
 137
 138 } // namespace JSC
 139
 140 #endif // ENABLE(JIT)
 141
 142 #endif // BinarySwitch_h
 143