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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/242441">242441</a></dd>
<dt>Author</dt> <dd>carlosgc@webkit.org</dd>
<dt>Date</dt> <dd>2019-03-05 04:40:35 -0800 (Tue, 05 Mar 2019)</dd>
</dl>

<h3>Log Message</h3>
<pre>Merge <a href="http://trac.webkit.org/projects/webkit/changeset/241954">r241954</a>,<a href="http://trac.webkit.org/projects/webkit/changeset/241955">r241955</a> - [JSC] SmallStringsStorage is unnecessary
https://bugs.webkit.org/show_bug.cgi?id=194939

Reviewed by Mark Lam.

SmallStrings hold common small JSStrings. Their underlying StringImpl is also held by SmallStringsStorage.
But it is duplicate since we can get StringImpl from small JSStrings. This patch removes SmallStringsStorage,
and get StringImpls from JSStrings if necessary.

We also add m_canAccessHeap flag to SmallStrings. At the time of VM destruction, JSStrings are destroyed when
VM's Heap is finalized. We must not touch JSStrings before VM's heap (and JSStrings in SmallStrings) is initialized,
and after VM's Heap is destroyed. We add this m_canAccessHeap flag to allow users to get StringImpl during the
this sensitive period. If m_canAccessHeap is false, we get StringImpl from AtomicStringImpl::add.

* runtime/SmallStrings.cpp:
(JSC::SmallStrings::initializeCommonStrings):
(JSC::SmallStrings::singleCharacterStringRep):
(JSC::SmallStringsStorage::rep): Deleted.
(JSC::SmallStringsStorage::SmallStringsStorage): Deleted.
(JSC::SmallStrings::createSingleCharacterString): Deleted.
* runtime/SmallStrings.h:
(JSC::SmallStrings::setCanAccessHeap):
* runtime/VM.cpp:
(JSC::VM::VM):
(JSC::VM::~VM):</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#releasesWebKitGTKwebkit224SourceJavaScriptCoreChangeLog">releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#releasesWebKitGTKwebkit224SourceJavaScriptCoreruntimeSmallStringscpp">releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/SmallStrings.cpp</a></li>
<li><a href="#releasesWebKitGTKwebkit224SourceJavaScriptCoreruntimeSmallStringsh">releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/SmallStrings.h</a></li>
<li><a href="#releasesWebKitGTKwebkit224SourceJavaScriptCoreruntimeVMcpp">releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/VM.cpp</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="releasesWebKitGTKwebkit224SourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/ChangeLog (242440 => 242441)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/ChangeLog   2019-03-05 12:40:31 UTC (rev 242440)
+++ releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/ChangeLog      2019-03-05 12:40:35 UTC (rev 242441)
</span><span class="lines">@@ -1,3 +1,43 @@
</span><ins>+2019-02-22  Yusuke Suzuki  <ysuzuki@apple.com>
+
+        Unreviewed, build fix after r241954
+        https://bugs.webkit.org/show_bug.cgi?id=194939
+
+        Renaming setCanAccessHeap was incomplete.
+
+        * runtime/SmallStrings.cpp:
+        (JSC::SmallStrings::initializeCommonStrings):
+        * runtime/VM.cpp:
+        (JSC::VM::~VM):
+
+2019-02-22  Yusuke Suzuki  <ysuzuki@apple.com>
+
+        [JSC] SmallStringsStorage is unnecessary
+        https://bugs.webkit.org/show_bug.cgi?id=194939
+
+        Reviewed by Mark Lam.
+
+        SmallStrings hold common small JSStrings. Their underlying StringImpl is also held by SmallStringsStorage.
+        But it is duplicate since we can get StringImpl from small JSStrings. This patch removes SmallStringsStorage,
+        and get StringImpls from JSStrings if necessary.
+
+        We also add m_canAccessHeap flag to SmallStrings. At the time of VM destruction, JSStrings are destroyed when
+        VM's Heap is finalized. We must not touch JSStrings before VM's heap (and JSStrings in SmallStrings) is initialized,
+        and after VM's Heap is destroyed. We add this m_canAccessHeap flag to allow users to get StringImpl during the
+        this sensitive period. If m_canAccessHeap is false, we get StringImpl from AtomicStringImpl::add.
+
+        * runtime/SmallStrings.cpp:
+        (JSC::SmallStrings::initializeCommonStrings):
+        (JSC::SmallStrings::singleCharacterStringRep):
+        (JSC::SmallStringsStorage::rep): Deleted.
+        (JSC::SmallStringsStorage::SmallStringsStorage): Deleted.
+        (JSC::SmallStrings::createSingleCharacterString): Deleted.
+        * runtime/SmallStrings.h:
+        (JSC::SmallStrings::setCanAccessHeap):
+        * runtime/VM.cpp:
+        (JSC::VM::VM):
+        (JSC::VM::~VM):
+
</ins><span class="cx"> 2019-02-21  Mark Lam  <mark.lam@apple.com>
</span><span class="cx"> 
</span><span class="cx">         Add more doesGC() assertions.
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit224SourceJavaScriptCoreruntimeSmallStringscpp"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/SmallStrings.cpp (242440 => 242441)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/SmallStrings.cpp    2019-03-05 12:40:31 UTC (rev 242440)
+++ releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/SmallStrings.cpp       2019-03-05 12:40:35 UTC (rev 242441)
</span><span class="lines">@@ -34,30 +34,6 @@
</span><span class="cx"> 
</span><span class="cx"> namespace JSC {
</span><span class="cx"> 
</span><del>-class SmallStringsStorage {
-    WTF_MAKE_NONCOPYABLE(SmallStringsStorage); WTF_MAKE_FAST_ALLOCATED;
-public:
-    SmallStringsStorage();
-
-    StringImpl& rep(unsigned char character)
-    {
-        return *m_reps[character].get();
-    }
-
-private:
-    static const unsigned singleCharacterStringCount = maxSingleCharacterString + 1;
-
-    RefPtr<StringImpl> m_reps[singleCharacterStringCount];
-};
-
-SmallStringsStorage::SmallStringsStorage()
-{
-    for (unsigned i = 0; i < singleCharacterStringCount; ++i) {
-        const LChar string[] = { static_cast<LChar>(i) };
-        m_reps[i] = AtomicStringImpl::add(StringImpl::create(string, 1).ptr());
-    }
-}
-
</del><span class="cx"> SmallStrings::SmallStrings()
</span><span class="cx"> {
</span><span class="cx">     COMPILE_ASSERT(singleCharacterStringCount == sizeof(m_singleCharacterStrings) / sizeof(m_singleCharacterStrings[0]), IsNumCharactersConstInSyncWithClassUsage);
</span><span class="lines">@@ -69,8 +45,14 @@
</span><span class="cx"> void SmallStrings::initializeCommonStrings(VM& vm)
</span><span class="cx"> {
</span><span class="cx">     createEmptyString(&vm);
</span><del>-    for (unsigned i = 0; i <= maxSingleCharacterString; ++i)
-        createSingleCharacterString(&vm, i);
</del><ins>+
+    for (unsigned i = 0; i < singleCharacterStringCount; ++i) {
+        ASSERT(!m_singleCharacterStrings[i]);
+        const LChar string[] = { static_cast<LChar>(i) };
+        m_singleCharacterStrings[i] = JSString::createHasOtherOwner(vm, AtomicStringImpl::add(string, 1).releaseNonNull());
+        ASSERT(m_needsToBeVisited);
+    }
+
</ins><span class="cx"> #define JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE(name) initialize(&vm, m_##name, #name);
</span><span class="cx">     JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE)
</span><span class="cx"> #undef JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE
</span><span class="lines">@@ -77,6 +59,8 @@
</span><span class="cx">     initialize(&vm, m_objectStringStart, "[object ");
</span><span class="cx">     initialize(&vm, m_nullObjectString, "[object Null]");
</span><span class="cx">     initialize(&vm, m_undefinedObjectString, "[object Undefined]");
</span><ins>+
+    setIsInitialized(true);
</ins><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> void SmallStrings::visitStrongReferences(SlotVisitor& visitor)
</span><span class="lines">@@ -104,22 +88,14 @@
</span><span class="cx">     ASSERT(m_needsToBeVisited);
</span><span class="cx"> }
</span><span class="cx"> 
</span><del>-void SmallStrings::createSingleCharacterString(VM* vm, unsigned char character)
</del><ins>+Ref<StringImpl> SmallStrings::singleCharacterStringRep(unsigned char character)
</ins><span class="cx"> {
</span><del>-    if (!m_storage)
-        m_storage = std::make_unique<SmallStringsStorage>();
-    ASSERT(!m_singleCharacterStrings[character]);
-    m_singleCharacterStrings[character] = JSString::createHasOtherOwner(*vm, m_storage->rep(character));
-    ASSERT(m_needsToBeVisited);
</del><ins>+    if (LIKELY(m_isInitialized))
+        return *const_cast<StringImpl*>(m_singleCharacterStrings[character]->tryGetValueImpl());
+    const LChar string[] = { static_cast<LChar>(character) };
+    return AtomicStringImpl::add(string, 1).releaseNonNull();
</ins><span class="cx"> }
</span><span class="cx"> 
</span><del>-StringImpl& SmallStrings::singleCharacterStringRep(unsigned char character)
-{
-    if (!m_storage)
-        m_storage = std::make_unique<SmallStringsStorage>();
-    return m_storage->rep(character);
-}
-
</del><span class="cx"> void SmallStrings::initialize(VM* vm, JSString*& string, const char* value)
</span><span class="cx"> {
</span><span class="cx">     string = JSString::create(*vm, AtomicStringImpl::add(value).releaseNonNull());
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit224SourceJavaScriptCoreruntimeSmallStringsh"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/SmallStrings.h (242440 => 242441)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/SmallStrings.h      2019-03-05 12:40:31 UTC (rev 242440)
+++ releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/SmallStrings.h 2019-03-05 12:40:35 UTC (rev 242441)
</span><span class="lines">@@ -51,7 +51,6 @@
</span><span class="cx"> 
</span><span class="cx"> class VM;
</span><span class="cx"> class JSString;
</span><del>-class SmallStringsStorage;
</del><span class="cx"> class SlotVisitor;
</span><span class="cx"> 
</span><span class="cx"> static const unsigned maxSingleCharacterString = 0xFF;
</span><span class="lines">@@ -72,8 +71,10 @@
</span><span class="cx">         return m_singleCharacterStrings[character];
</span><span class="cx">     }
</span><span class="cx"> 
</span><del>-    JS_EXPORT_PRIVATE WTF::StringImpl& singleCharacterStringRep(unsigned char character);
</del><ins>+    JS_EXPORT_PRIVATE Ref<StringImpl> singleCharacterStringRep(unsigned char character);
</ins><span class="cx"> 
</span><ins>+    void setIsInitialized(bool isInitialized) { m_isInitialized = isInitialized; }
+
</ins><span class="cx">     JSString** singleCharacterStrings() { return &m_singleCharacterStrings[0]; }
</span><span class="cx"> 
</span><span class="cx">     void initializeCommonStrings(VM&);
</span><span class="lines">@@ -127,7 +128,6 @@
</span><span class="cx">     static const unsigned singleCharacterStringCount = maxSingleCharacterString + 1;
</span><span class="cx"> 
</span><span class="cx">     void createEmptyString(VM*);
</span><del>-    void createSingleCharacterString(VM*, unsigned char);
</del><span class="cx"> 
</span><span class="cx">     void initialize(VM*, JSString*&, const char* value);
</span><span class="cx"> 
</span><span class="lines">@@ -139,8 +139,8 @@
</span><span class="cx">     JSString* m_nullObjectString { nullptr };
</span><span class="cx">     JSString* m_undefinedObjectString { nullptr };
</span><span class="cx">     JSString* m_singleCharacterStrings[singleCharacterStringCount] { nullptr };
</span><del>-    std::unique_ptr<SmallStringsStorage> m_storage;
</del><span class="cx">     bool m_needsToBeVisited { true };
</span><ins>+    bool m_isInitialized { false };
</ins><span class="cx"> };
</span><span class="cx"> 
</span><span class="cx"> } // namespace JSC
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit224SourceJavaScriptCoreruntimeVMcpp"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/VM.cpp (242440 => 242441)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/VM.cpp      2019-03-05 12:40:31 UTC (rev 242440)
+++ releases/WebKitGTK/webkit-2.24/Source/JavaScriptCore/runtime/VM.cpp 2019-03-05 12:40:35 UTC (rev 242441)
</span><span class="lines">@@ -340,11 +340,14 @@
</span><span class="cx">     // Need to be careful to keep everything consistent here
</span><span class="cx">     JSLockHolder lock(this);
</span><span class="cx">     AtomicStringTable* existingEntryAtomicStringTable = Thread::current().setCurrentAtomicStringTable(m_atomicStringTable);
</span><del>-    propertyNames = new CommonIdentifiers(this);
</del><span class="cx">     structureStructure.set(*this, Structure::createStructure(*this));
</span><span class="cx">     structureRareDataStructure.set(*this, StructureRareData::createStructure(*this, 0, jsNull()));
</span><ins>+    stringStructure.set(*this, JSString::createStructure(*this, 0, jsNull()));
+
+    smallStrings.initializeCommonStrings(*this);
+
+    propertyNames = new CommonIdentifiers(this);
</ins><span class="cx">     terminatedExecutionErrorStructure.set(*this, TerminatedExecutionError::createStructure(*this, 0, jsNull()));
</span><del>-    stringStructure.set(*this, JSString::createStructure(*this, 0, jsNull()));
</del><span class="cx">     propertyNameEnumeratorStructure.set(*this, JSPropertyNameEnumerator::createStructure(*this, 0, jsNull()));
</span><span class="cx">     customGetterSetterStructure.set(*this, CustomGetterSetter::createStructure(*this, 0, jsNull()));
</span><span class="cx">     domAttributeGetterSetterStructure.set(*this, DOMAttributeGetterSetter::createStructure(*this, 0, jsNull()));
</span><span class="lines">@@ -401,8 +404,6 @@
</span><span class="cx">     sentinelSetBucket.set(*this, JSSet::BucketType::createSentinel(*this));
</span><span class="cx">     sentinelMapBucket.set(*this, JSMap::BucketType::createSentinel(*this));
</span><span class="cx"> 
</span><del>-    smallStrings.initializeCommonStrings(*this);
-
</del><span class="cx">     Thread::current().setCurrentAtomicStringTable(existingEntryAtomicStringTable);
</span><span class="cx"> 
</span><span class="cx"> #if ENABLE(JIT)
</span><span class="lines">@@ -539,6 +540,7 @@
</span><span class="cx"> 
</span><span class="cx">     ASSERT(currentThreadIsHoldingAPILock());
</span><span class="cx">     m_apiLock->willDestroyVM(this);
</span><ins>+    smallStrings.setIsInitialized(false);
</ins><span class="cx">     heap.lastChanceToFinalize();
</span><span class="cx"> 
</span><span class="cx">     JSRunLoopTimer::Manager::shared().unregisterVM(*this);
</span></span></pre>
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