1/*
2 * Copyright (C) 2014, 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,
18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#pragma once
27
28#include "ObjectPropertyConditionSet.h"
29#include "PropertyOffset.h"
30
31namespace JSC {
32
33class CodeBlock;
34class StructureChain;
35
36// This class is useful for figuring out how to inline a cached get-like access. We
37// say "get-like" because this is appropriate for loading the GetterSetter object in
38// a put_by_id that hits a setter. Notably, this doesn't figure out how to call
39// accessors, or even whether they should be called. What it gives us, is a way of
40// determining how to load the value from the requested property (identified by a
41// StringImpl* uid) from an object of the given structure in the given CodeBlock,
42// assuming that such an access had already been cached by Repatch (and so Repatch had
43// already done a bunch of safety checks). This doesn't reexecute any checks that
44// Repatch would have executed, and for prototype chain accesses, it doesn't ask the
45// objects in the prototype chain whether their getOwnPropertySlot would attempt to
46// intercept the access - so this really is only appropriate if you already know that
47// one of the JITOperations had OK'd this for caching and that Repatch concurred.
48//
49// The typical use pattern is something like:
50//
51// ComplexGetStatus status = ComplexGetStatus::computeFor(...);
52// switch (status.kind()) {
53// case ComplexGetStatus::ShouldSkip:
54// // Handle the case where this kind of access is possibly safe but wouldn't
55// // pass the required safety checks. For example, if an IC gives us a list of
56// // accesses and one of them is ShouldSkip, then we should pretend as if it
57// // wasn't even there.
58// break;
59// case ComplexGetStatus::TakesSlowPath:
60// // This kind of access is not safe to inline. Bail out of any attempst to
61// // inline.
62// break;
63// case ComplexGetStatus::Inlineable:
64// // The good stuff goes here. If it's Inlineable then the other properties of
65// // the 'status' object will tell you everything you need to know about how
66// // to execute the get-like operation.
67// break;
68// }
69
70class ComplexGetStatus {
71public:
72 enum Kind {
73 ShouldSkip,
74 TakesSlowPath,
75 Inlineable
76 };
77
78 ComplexGetStatus()
79 : m_kind(ShouldSkip)
80 , m_offset(invalidOffset)
81 {
82 }
83
84 static ComplexGetStatus skip()
85 {
86 return ComplexGetStatus();
87 }
88
89 static ComplexGetStatus takesSlowPath()
90 {
91 ComplexGetStatus result;
92 result.m_kind = TakesSlowPath;
93 return result;
94 }
95
96 static ComplexGetStatus computeFor(
97 Structure* headStructure, const ObjectPropertyConditionSet&, UniquedStringImpl* uid);
98
99 Kind kind() const { return m_kind; }
100 PropertyOffset offset() const { return m_offset; }
101 const ObjectPropertyConditionSet& conditionSet() const { return m_conditionSet; }
102
103private:
104 Kind m_kind;
105 PropertyOffset m_offset;
106 ObjectPropertyConditionSet m_conditionSet;
107};
108
109} // namespace JSC
110