1/*
2 * Copyright (C) 2018 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#include "config.h"
27#include "ExecutableToCodeBlockEdge.h"
28
29#include "CodeBlock.h"
30#include "IsoCellSetInlines.h"
31
32namespace JSC {
33
34const ClassInfo ExecutableToCodeBlockEdge::s_info = { "ExecutableToCodeBlockEdge", nullptr, nullptr, nullptr, CREATE_METHOD_TABLE(ExecutableToCodeBlockEdge) };
35
36Structure* ExecutableToCodeBlockEdge::createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
37{
38 return Structure::create(vm, globalObject, prototype, TypeInfo(CellType, StructureFlags), info());
39}
40
41ExecutableToCodeBlockEdge* ExecutableToCodeBlockEdge::create(VM& vm, CodeBlock* codeBlock)
42{
43 ExecutableToCodeBlockEdge* result = new (NotNull, allocateCell<ExecutableToCodeBlockEdge>(vm.heap)) ExecutableToCodeBlockEdge(vm, codeBlock);
44 result->finishCreation(vm);
45 return result;
46}
47
48void ExecutableToCodeBlockEdge::finishCreation(VM& vm)
49{
50 Base::finishCreation(vm);
51 ASSERT(!isActive());
52}
53
54void ExecutableToCodeBlockEdge::visitChildren(JSCell* cell, SlotVisitor& visitor)
55{
56 VM& vm = visitor.vm();
57 ExecutableToCodeBlockEdge* edge = jsCast<ExecutableToCodeBlockEdge*>(cell);
58 Base::visitChildren(cell, visitor);
59
60 CodeBlock* codeBlock = edge->m_codeBlock.get();
61
62 // It's possible for someone to hold a pointer to the edge after the edge has cleared its weak
63 // reference to the codeBlock. In a conservative GC like ours, that could happen at random for
64 // no good reason and it's Totally OK (TM). See finalizeUnconditionally() for where we clear
65 // m_codeBlock.
66 if (!codeBlock)
67 return;
68
69 if (!edge->isActive()) {
70 visitor.appendUnbarriered(codeBlock);
71 return;
72 }
73
74 ConcurrentJSLocker locker(codeBlock->m_lock);
75
76 if (codeBlock->shouldVisitStrongly(locker))
77 visitor.appendUnbarriered(codeBlock);
78
79 if (!vm.heap.isMarked(codeBlock))
80 vm.executableToCodeBlockEdgesWithFinalizers.add(edge);
81
82 if (JITCode::isOptimizingJIT(codeBlock->jitType())) {
83 // If we jettison ourselves we'll install our alternative, so make sure that it
84 // survives GC even if we don't.
85 visitor.append(codeBlock->m_alternative);
86 }
87
88 // NOTE: There are two sides to this constraint, with different requirements for correctness.
89 // Because everything is ultimately protected with weak references and jettisoning, it's
90 // always "OK" to claim that something is dead prematurely and it's "OK" to keep things alive.
91 // But both choices could lead to bad perf - either recomp cycles or leaks.
92 //
93 // Determining CodeBlock liveness: This part is the most consequential. We want to keep the
94 // output constraint active so long as we think that we may yet prove that the CodeBlock is
95 // live but we haven't done it yet.
96 //
97 // Marking Structures if profitable: It's important that we do a pass of this. Logically, this
98 // seems like it is a constraint of CodeBlock. But we have always first run this as a result
99 // of the edge being marked even before we determine the liveness of the CodeBlock. This
100 // allows a CodeBlock to mark itself by first proving that all of the Structures it weakly
101 // depends on could be strongly marked. (This part is also called propagateTransitions.)
102 //
103 // As a weird caveat, we only fixpoint the constraints so long as the CodeBlock is not live.
104 // This means that we may overlook structure marking opportunities created by other marking
105 // that happens after the CodeBlock is marked. This was an accidental policy decision from a
106 // long time ago, but it is probably OK, since it's only worthwhile to keep fixpointing the
107 // structure marking if we still have unmarked structures after the first round. We almost
108 // never will because we will mark-if-profitable based on the owning global object being
109 // already marked. We mark it just in case that hadn't happened yet. And if the CodeBlock is
110 // not yet marked because it weakly depends on a structure that we did not yet mark, then we
111 // will keep fixpointing until the end.
112 visitor.appendUnbarriered(codeBlock->globalObject());
113 vm.executableToCodeBlockEdgesWithConstraints.add(edge);
114 edge->runConstraint(locker, vm, visitor);
115}
116
117void ExecutableToCodeBlockEdge::visitOutputConstraints(JSCell* cell, SlotVisitor& visitor)
118{
119 VM& vm = visitor.vm();
120 ExecutableToCodeBlockEdge* edge = jsCast<ExecutableToCodeBlockEdge*>(cell);
121
122 edge->runConstraint(NoLockingNecessary, vm, visitor);
123}
124
125void ExecutableToCodeBlockEdge::finalizeUnconditionally(VM& vm)
126{
127 CodeBlock* codeBlock = m_codeBlock.get();
128
129 if (!vm.heap.isMarked(codeBlock)) {
130 if (codeBlock->shouldJettisonDueToWeakReference(vm))
131 codeBlock->jettison(Profiler::JettisonDueToWeakReference);
132 else
133 codeBlock->jettison(Profiler::JettisonDueToOldAge);
134 m_codeBlock.clear();
135 }
136
137 vm.executableToCodeBlockEdgesWithFinalizers.remove(this);
138 vm.executableToCodeBlockEdgesWithConstraints.remove(this);
139}
140
141inline void ExecutableToCodeBlockEdge::activate()
142{
143 setPerCellBit(true);
144}
145
146inline void ExecutableToCodeBlockEdge::deactivate()
147{
148 setPerCellBit(false);
149}
150
151inline bool ExecutableToCodeBlockEdge::isActive() const
152{
153 return perCellBit();
154}
155
156CodeBlock* ExecutableToCodeBlockEdge::deactivateAndUnwrap(ExecutableToCodeBlockEdge* edge)
157{
158 if (!edge)
159 return nullptr;
160 edge->deactivate();
161 return edge->codeBlock();
162}
163
164ExecutableToCodeBlockEdge* ExecutableToCodeBlockEdge::wrap(CodeBlock* codeBlock)
165{
166 if (!codeBlock)
167 return nullptr;
168 return codeBlock->ownerEdge();
169}
170
171ExecutableToCodeBlockEdge* ExecutableToCodeBlockEdge::wrapAndActivate(CodeBlock* codeBlock)
172{
173 if (!codeBlock)
174 return nullptr;
175 ExecutableToCodeBlockEdge* result = codeBlock->ownerEdge();
176 result->activate();
177 return result;
178}
179
180ExecutableToCodeBlockEdge::ExecutableToCodeBlockEdge(VM& vm, CodeBlock* codeBlock)
181 : Base(vm, vm.executableToCodeBlockEdgeStructure.get())
182 , m_codeBlock(vm, this, codeBlock)
183{
184}
185
186void ExecutableToCodeBlockEdge::runConstraint(const ConcurrentJSLocker& locker, VM& vm, SlotVisitor& visitor)
187{
188 CodeBlock* codeBlock = m_codeBlock.get();
189
190 codeBlock->propagateTransitions(locker, visitor);
191 codeBlock->determineLiveness(locker, visitor);
192
193 if (vm.heap.isMarked(codeBlock))
194 vm.executableToCodeBlockEdgesWithConstraints.remove(this);
195}
196
197} // namespace JSC
198
199