LCOV - app.info - js/src/vm/ArgumentsObject.h

LCOV - code coverage report
| Current view: | directory - js/src/vm - ArgumentsObject.h (source / functions) |  | Found | Hit | Coverage |
| Test: | app.info | Lines: | 9 | 9 | 100.0 %
| Date: | 2012-04-07 | Functions: | 3 | 3 | 100.0 %

           1                 : /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
           2                 :  * vim: set ts=8 sw=4 et tw=78:
           3                 :  *
           4                 :  * ***** BEGIN LICENSE BLOCK *****
           5                 :  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
           6                 :  *
           7                 :  * The contents of this file are subject to the Mozilla Public License Version
           8                 :  * 1.1 (the "License"); you may not use this file except in compliance with
           9                 :  * the License. You may obtain a copy of the License at
          10                 :  * http://www.mozilla.org/MPL/
          11                 :  *
          12                 :  * Software distributed under the License is distributed on an "AS IS" basis,
          13                 :  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
          14                 :  * for the specific language governing rights and limitations under the
          15                 :  * License.
          16                 :  *
          17                 :  * The Original Code is SpiderMonkey arguments object code.
          18                 :  *
          19                 :  * The Initial Developer of the Original Code is
          20                 :  * the Mozilla Foundation.
          21                 :  * Portions created by the Initial Developer are Copyright (C) 2011
          22                 :  * the Initial Developer. All Rights Reserved.
          23                 :  *
          24                 :  * Contributor(s):
          25                 :  *   Jeff Walden <jwalden+code@mit.edu> (original author)
          26                 :  *   Luke Wagner <luke@mozilla.com>
          27                 :  *
          28                 :  * Alternatively, the contents of this file may be used under the terms of
          29                 :  * either of the GNU General Public License Version 2 or later (the "GPL"),
          30                 :  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
          31                 :  * in which case the provisions of the GPL or the LGPL are applicable instead
          32                 :  * of those above. If you wish to allow use of your version of this file only
          33                 :  * under the terms of either the GPL or the LGPL, and not to allow others to
          34                 :  * use your version of this file under the terms of the MPL, indicate your
          35                 :  * decision by deleting the provisions above and replace them with the notice
          36                 :  * and other provisions required by the GPL or the LGPL. If you do not delete
          37                 :  * the provisions above, a recipient may use your version of this file under
          38                 :  * the terms of any one of the MPL, the GPL or the LGPL.
          39                 :  *
          40                 :  * ***** END LICENSE BLOCK ***** */
          41                 :
          42                 : #ifndef ArgumentsObject_h___
          43                 : #define ArgumentsObject_h___
          44                 :
          45                 : #include "jsfun.h"
          46                 :
          47                 : namespace js {
          48                 :
          49                 : /*
          50                 :  * ArgumentsData stores the initial indexed arguments provided to the
          51                 :  * corresponding and that function itself.  It is used to store arguments[i]
          52                 :  * and arguments.callee -- up until the corresponding property is modified,
          53                 :  * when the relevant value is overwritten with MagicValue(JS_ARGS_HOLE) to
          54                 :  * memorialize the modification.
          55                 :  */
          56                 : struct ArgumentsData
          57                 : {
          58                 :     /*
          59                 :      * arguments.callee, or MagicValue(JS_ARGS_HOLE) if arguments.callee has
          60                 :      * been modified.
          61                 :      */
          62                 :     HeapValue   callee;
          63                 :
          64                 :     /*
          65                 :      * Pointer to an array of bits indicating, for every argument in 'slots',
          66                 :      * whether the element has been deleted. See isElementDeleted comment.
          67                 :      */
          68                 :     size_t      *deletedBits;
          69                 :
          70                 :     /*
          71                 :      * Values of the arguments for this object, or MagicValue(JS_ARGS_HOLE) if
          72                 :      * the indexed argument has been modified.
          73                 :      */
          74                 :     HeapValue   slots[1];
          75                 : };
          76                 :
          77                 : /*
          78                 :  * ArgumentsObject instances represent |arguments| objects created to store
          79                 :  * function arguments when a function is called.  It's expensive to create such
          80                 :  * objects if they're never used, so they're only created lazily.  (See
          81                 :  * js::StackFrame::setArgsObj and friends.)
          82                 :  *
          83                 :  * Arguments objects are complicated because, for non-strict mode code, they
          84                 :  * must alias any named arguments which were provided to the function.  Gnarly
          85                 :  * example:
          86                 :  *
          87                 :  *   function f(a, b, c, d)
          88                 :  *   {
          89                 :  *     arguments[0] = "seta";
          90                 :  *     assertEq(a, "seta");
          91                 :  *     b = "setb";
          92                 :  *     assertEq(arguments[1], "setb");
          93                 :  *     c = "setc";
          94                 :  *     assertEq(arguments[2], undefined);
          95                 :  *     arguments[3] = "setd";
          96                 :  *     assertEq(d, undefined);
          97                 :  *   }
          98                 :  *   f("arga", "argb");
          99                 :  *
         100                 :  * ES5's strict mode behaves more sanely, and named arguments don't alias
         101                 :  * elements of an arguments object.
         102                 :  *
         103                 :  * ArgumentsObject instances use the following reserved slots:
         104                 :  *
         105                 :  *   INITIAL_LENGTH_SLOT
         106                 :  *     Stores the initial value of arguments.length, plus a bit indicating
         107                 :  *     whether arguments.length has been modified.  Use initialLength() and
         108                 :  *     hasOverriddenLength() to access these values.  If arguments.length has
         109                 :  *     been modified, then the current value of arguments.length is stored in
         110                 :  *     another slot associated with a new property.
         111                 :  *   DATA_SLOT
         112                 :  *     Stores an ArgumentsData* storing argument values and the callee, or
         113                 :  *     sentinels for any of these if the corresponding property is modified.
         114                 :  *     Use callee() to access the callee/sentinel, and use
         115                 :  *     element/addressOfElement/setElement to access the values stored in
         116                 :  *     the ArgumentsData.  If you're simply looking to get arguments[i],
         117                 :  *     however, use getElement or getElements to avoid spreading arguments
         118                 :  *     object implementation details around too much.
         119                 :  *   STACK_FRAME_SLOT
         120                 :  *     Stores the function's stack frame for non-strict arguments objects until
         121                 :  *     the function returns, when it is replaced with null.  When an arguments
         122                 :  *     object is created on-trace its private is JS_ARGUMENTS_OBJECT_ON_TRACE,
         123                 :  *     and when the trace exits its private is replaced with the stack frame or
         124                 :  *     null, as appropriate. This slot is used by strict arguments objects as
         125                 :  *     well, but the slot is always null. Conceptually it would be better to
         126                 :  *     remove this oddity, but preserving it allows us to work with arguments
         127                 :  *     objects of either kind more abstractly, so we keep it for now.
         128                 :  */
         129                 : class ArgumentsObject : public JSObject
         130                 : {
         131                 :     static const uint32_t INITIAL_LENGTH_SLOT = 0;
         132                 :     static const uint32_t DATA_SLOT = 1;
         133                 :     static const uint32_t STACK_FRAME_SLOT = 2;
         134                 :
         135                 :     /* Lower-order bit stolen from the length slot. */
         136                 :     static const uint32_t LENGTH_OVERRIDDEN_BIT = 0x1;
         137                 :     static const uint32_t PACKED_BITS_COUNT = 1;
         138                 :
         139                 :     void initInitialLength(uint32_t length);
         140                 :     void initData(ArgumentsData *data);
         141                 :     static ArgumentsObject *create(JSContext *cx, uint32_t argc, JSObject &callee);
         142                 :
         143                 :   public:
         144                 :     static const uint32_t RESERVED_SLOTS = 3;
         145                 :     static const gc::AllocKind FINALIZE_KIND = gc::FINALIZE_OBJECT4;
         146                 :
         147                 :     /* Create an arguments object for a frame that is expecting them. */
         148                 :     static bool create(JSContext *cx, StackFrame *fp);
         149                 :
         150                 :     /*
         151                 :      * Purposefully disconnect the returned arguments object from the frame
         152                 :      * by always creating a new copy that does not alias formal parameters.
         153                 :      * This allows function-local analysis to determine that formals are
         154                 :      * not aliased and generally simplifies arguments objects.
         155                 :      */
         156                 :     static ArgumentsObject *createUnexpected(JSContext *cx, StackFrame *fp);
         157                 :
         158                 :     /*
         159                 :      * Return the initial length of the arguments.  This may differ from the
         160                 :      * current value of arguments.length!
         161                 :      */
         162                 :     inline uint32_t initialLength() const;
         163                 :
         164                 :     /* True iff arguments.length has been assigned or its attributes changed. */
         165                 :     inline bool hasOverriddenLength() const;
         166                 :     inline void markLengthOverridden();
         167                 :
         168                 :     /*
         169                 :      * Attempt to speedily and efficiently access the i-th element of this
         170                 :      * arguments object.  Return true if the element was speedily returned.
         171                 :      * Return false if the element must be looked up more slowly using
         172                 :      * getProperty or some similar method.
         173                 :      *
         174                 :      * NB: Returning false does not indicate error!
         175                 :      */
         176                 :     inline bool getElement(uint32_t i, js::Value *vp);
         177                 :
         178                 :     /*
         179                 :      * Attempt to speedily and efficiently get elements [start, start + count)
         180                 :      * of this arguments object into the locations starting at |vp|.  Return
         181                 :      * true if all elements were copied.  Return false if the elements must be
         182                 :      * gotten more slowly, perhaps using a getProperty or some similar method
         183                 :      * in a loop.
         184                 :      *
         185                 :      * NB: Returning false does not indicate error!
         186                 :      */
         187                 :     inline bool getElements(uint32_t start, uint32_t count, js::Value *vp);
         188                 :
         189                 :     inline js::ArgumentsData *data() const;
         190                 :
         191                 :     /*
         192                 :      * Because the arguments object is a real object, its elements may be
         193                 :      * deleted. This is implemented by setting a 'deleted' flag for the arg
         194                 :      * which is read by argument object resolve and getter/setter hooks.
         195                 :      *
         196                 :      * NB: an element, once deleted, stays deleted. Thus:
         197                 :      *
         198                 :      *   function f(x) { delete arguments[0]; arguments[0] = 42; return x }
         199                 :      *   assertEq(f(1), 1);
         200                 :      *
         201                 :      * This works because, once a property is deleted from an arguments object,
         202                 :      * it gets regular properties with regular getters/setters that don't alias
         203                 :      * ArgumentsData::slots.
         204                 :      */
         205                 :     inline bool isElementDeleted(uint32_t i) const;
         206                 :     inline bool isAnyElementDeleted() const;
         207                 :     inline void markElementDeleted(uint32_t i);
         208                 :
         209                 :     inline const js::Value &element(uint32_t i) const;
         210                 :     inline void setElement(uint32_t i, const js::Value &v);
         211                 :
         212                 :     /* The stack frame for this ArgumentsObject, if the frame is still active. */
         213                 :     inline js::StackFrame *maybeStackFrame() const;
         214                 :     inline void setStackFrame(js::StackFrame *frame);
         215                 :
         216                 :     /*
         217                 :      * Measures things hanging off this ArgumentsObject that are counted by the
         218                 :      * |miscSize| argument in JSObject::sizeOfExcludingThis().
         219                 :      */
         220                 :     inline size_t sizeOfMisc(JSMallocSizeOfFun mallocSizeOf) const;
         221                 : };
         222                 :
         223                 : class NormalArgumentsObject : public ArgumentsObject
         224                 : {
         225                 :   public:
         226                 :     /*
         227                 :      * Stores arguments.callee, or MagicValue(JS_ARGS_HOLE) if the callee has
         228                 :      * been cleared.
         229                 :      */
         230                 :     inline const js::Value &callee() const;
         231                 :
         232                 :     /* Clear the location storing arguments.callee's initial value. */
         233                 :     inline void clearCallee();
         234                 :
         235                 :     /*
         236                 :      * Return 'arguments[index]' for some unmodified NormalArgumentsObject of
         237                 :      * 'fp' (the actual instance of 'arguments' doesn't matter so it does not
         238                 :      * have to be passed or even created).
         239                 :      */
         240                 :     static bool optimizedGetElem(JSContext *cx, StackFrame *fp, const Value &elem, Value *vp);
         241                 : };
         242                 :
         243                 : class StrictArgumentsObject : public ArgumentsObject
         244                 : {};
         245                 :
         246                 : } // namespace js
         247                 :
         248                 : js::NormalArgumentsObject &
         249            9034 : JSObject::asNormalArguments()
         250                 : {
         251            9034 :     JS_ASSERT(isNormalArguments());
         252            9034 :     return *static_cast<js::NormalArgumentsObject *>(this);
         253                 : }
         254                 :
         255                 : js::StrictArgumentsObject &
         256            1628 : JSObject::asStrictArguments()
         257                 : {
         258            1628 :     JS_ASSERT(isStrictArguments());
         259            1628 :     return *static_cast<js::StrictArgumentsObject *>(this);
         260                 : }
         261                 :
         262                 : js::ArgumentsObject &
         263         1286964 : JSObject::asArguments()
         264                 : {
         265         1286964 :     JS_ASSERT(isArguments());
         266         1286964 :     return *static_cast<js::ArgumentsObject *>(this);
         267                 : }
         268                 :
         269                 : const js::ArgumentsObject &
         270                 : JSObject::asArguments() const
         271                 : {
         272                 :     JS_ASSERT(isArguments());
         273                 :     return *static_cast<const js::ArgumentsObject *>(this);
         274                 : }
         275                 :
         276                 : #endif /* ArgumentsObject_h___ */

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