1/*
2 * Copyright (C) 2012, 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 *
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of Apple Inc. ("Apple") nor the names of
14 * its contributors may be used to endorse or promote products derived
15 * from this software without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
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22 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28
29#ifndef JSSegmentedVariableObject_h
30#define JSSegmentedVariableObject_h
31
32#include "ConcurrentJITLock.h"
33#include "JSObject.h"
34#include "JSSymbolTableObject.h"
35#include "Register.h"
36#include "SymbolTable.h"
37#include <wtf/SegmentedVector.h>
38
39namespace JSC {
40
41class LLIntOffsetsExtractor;
42class Register;
43
44// This is a mostly drop-in replacement for JSEnvironmentRecord, except that it preserves
45// the invariant that after a variable is created, its address in memory will not change
46// so long as the JSSegmentedVariableObject is alive. This allows optimizations based
47// on getting the address of the variable and remembering it. As well, unlike a
48// JSEnvironmentRecord, this will manage the memory for the registers itself and neither
49// requires nor allows for the subclasses to manage that memory. Finally,
50// JSSegmentedVariableObject has its own GC tracing functionality, since it knows the
51// exact dimensions of the variables array at all times.
52
53class JSSegmentedVariableObject : public JSSymbolTableObject {
54 friend class JIT;
55 friend class LLIntOffsetsExtractor;
56
57public:
58 typedef JSSymbolTableObject Base;
59
60 bool isValidScopeOffset(ScopeOffset offset)
61 {
62 return !!offset && offset.offset() < m_variables.size();
63 }
64
65 // This is not thread-safe, since m_variables is a segmented vector, and its spine can resize with
66 // malloc/free if new variables - unrelated to the one you are accessing - are added. You can get
67 // around this by grabbing m_lock, or finding some other way to get to the variable pointer (global
68 // variable access bytecode instructions will have a direct pointer already).
69 WriteBarrier<Unknown>& variableAt(ScopeOffset offset) { return m_variables[offset.offset()]; }
70
71 // This is a slow method call, which searches the register bank to find the index
72 // given a pointer. It will CRASH() if it does not find the register. Only use this
73 // in debug code (like bytecode dumping).
74 JS_EXPORT_PRIVATE ScopeOffset findVariableIndex(void*);
75
76 WriteBarrier<Unknown>* assertVariableIsInThisObject(WriteBarrier<Unknown>* variablePointer)
77 {
78 if (!ASSERT_DISABLED)
79 findVariableIndex(variablePointer);
80 return variablePointer;
81 }
82
83 // Adds numberOfRegistersToAdd registers, initializes them to Undefined, and returns
84 // the index of the first one added.
85 JS_EXPORT_PRIVATE ScopeOffset addVariables(unsigned numberOfVariablesToAdd, JSValue);
86
87 JS_EXPORT_PRIVATE static void visitChildren(JSCell*, SlotVisitor&);
88
89protected:
90 JSSegmentedVariableObject(VM& vm, Structure* structure, JSScope* scope)
91 : JSSymbolTableObject(vm, structure, scope)
92 {
93 }
94
95 void finishCreation(VM& vm)
96 {
97 Base::finishCreation(vm);
98 setSymbolTable(vm, SymbolTable::create(vm));
99 }
100
101 SegmentedVector<WriteBarrier<Unknown>, 16> m_variables;
102 ConcurrentJITLock m_lock;
103};
104
105} // namespace JSC
106
107#endif // JSSegmentedVariableObject_h
108
109