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DFGBinarySwitch.h
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142 lines (111 loc) · 4.23 KB
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/*
* Copyright (C) 2013 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef DFGBinarySwitch_h
#define DFGBinarySwitch_h
#include <wtf/Platform.h>
#if ENABLE(DFG_JIT)
#include "GPRInfo.h"
#include "MacroAssembler.h"
namespace JSC { namespace DFG {
// The BinarySwitch class makes it easy to emit a switch statement over either
// 32-bit integers or pointers, where the switch uses a tree of branches
// rather than a jump table. This makes it particularly useful if the case
// values are too far apart to make a jump table practical, or if there are
// sufficiently few cases that the total cost of log(numCases) branches is
// less than the cost of an indirected jump.
//
// In an effort to simplify the logic of emitting code for each case, this
// uses an iterator style, rather than a functor callback style. This makes
// sense because even the iterator implementation found herein is relatively
// simple, whereas the code it's used from is usually quite complex - one
// example being the trie-of-trees string switch implementation, where the
// code emitted for each case involves recursing to emit code for a sub-trie.
//
// Use this like so:
//
// BinarySwitch switch(valueReg, casesVector, BinarySwitch::Int32);
// while (switch.advance(jit)) {
// int value = switch.caseValue();
// unsigned index = switch.caseIndex(); // index into casesVector, above
// ... // generate code for this case
// }
// switch.fallThrough().link(&jit);
class BinarySwitch {
public:
enum Type {
Int32,
IntPtr
};
BinarySwitch(GPRReg value, const Vector<int64_t>& cases, Type);
unsigned caseIndex() const { return m_cases[m_caseIndex].index; }
int64_t caseValue() const { return m_cases[m_caseIndex].value; }
bool advance(MacroAssembler&);
MacroAssembler::JumpList& fallThrough() { return m_fallThrough; }
private:
void build(unsigned start, unsigned end);
GPRReg m_value;
struct Case {
Case() { }
Case(int64_t value, unsigned index)
: value(value)
, index(index)
{
}
bool operator<(const Case& other) const
{
return value < other.value;
}
int64_t value;
unsigned index;
};
Vector<Case> m_cases;
enum BranchKind {
NotEqualToFallThrough,
NotEqualToPush,
LessThanToPush,
Pop,
ExecuteCase
};
struct BranchCode {
BranchCode() { }
BranchCode(BranchKind kind, unsigned index = UINT_MAX)
: kind(kind)
, index(index)
{
}
BranchKind kind;
unsigned index;
};
Vector<BranchCode> m_branches;
unsigned m_index;
unsigned m_caseIndex;
Vector<MacroAssembler::Jump> m_jumpStack;
MacroAssembler::JumpList m_fallThrough;
unsigned m_medianBias;
Type m_type;
};
} } // namespace JSC::DFG
#endif // ENABLE(DFG_JIT)
#endif // DFGBinarySwitch_h