runtime/JSSegmentedVariableObject.h

   1 /*
   2  * Copyright (C) 2012 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 Computer, 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
  18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  20  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
  21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  24  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  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 "JSObject.h"
  33 #include "JSSymbolTableObject.h"
  34 #include "Register.h"
  35 #include "SymbolTable.h"
  36 #include <wtf/OwnArrayPtr.h>
  37 #include <wtf/SegmentedVector.h>
  38
  39 namespace JSC {
  40
  41 class LLIntOffsetsExtractor;
  42 class Register;
  43
  44 // This is a mostly drop-in replacement for JSVariableObject, 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 // JSVariableObject, 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
  53 class JSSegmentedVariableObject : public JSSymbolTableObject {
  54     friend class JIT;
  55     friend class LLIntOffsetsExtractor;
  56
  57 public:
  58     typedef JSSymbolTableObject Base;
  59
  60     WriteBarrier<Unknown>& registerAt(int index) { return m_registers[index]; }
  61
  62     // This is a slow method call, which searches the register bank to find the index
  63     // given a pointer. It will CRASH() if it does not find the register. Only use this
  64     // in debug code (like bytecode dumping).
  65     JS_EXPORT_PRIVATE int findRegisterIndex(void*);
  66
  67     WriteBarrier<Unknown>* assertRegisterIsInThisObject(WriteBarrier<Unknown>* registerPointer)
  68     {
  69 #if !ASSERT_DISABLED
  70         findRegisterIndex(registerPointer);
  71 #endif
  72         return registerPointer;
  73     }
  74
  75     // Adds numberOfRegistersToAdd registers, initializes them to Undefined, and returns
  76     // the index of the first one added.
  77     JS_EXPORT_PRIVATE int addRegisters(int numberOfRegistersToAdd);
  78
  79     JS_EXPORT_PRIVATE static void visitChildren(JSCell*, SlotVisitor&);
  80
  81 protected:
  82     static const unsigned StructureFlags = OverridesVisitChildren | JSSymbolTableObject::StructureFlags;
  83
  84     JSSegmentedVariableObject(VM& vm, Structure* structure, JSScope* scope)
  85         : JSSymbolTableObject(vm, structure, scope)
  86     {
  87     }
  88
  89     void finishCreation(VM& vm)
  90     {
  91         Base::finishCreation(vm);
  92     }
  93
  94     SegmentedVector<WriteBarrier<Unknown>, 16> m_registers;
  95 };
  96
  97 } // namespace JSC
  98
  99 #endif // JSSegmentedVariableObject_h
 100