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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/163416">163416</a></dd>
<dt>Author</dt> <dd>andersca@apple.com</dd>
<dt>Date</dt> <dd>2014-02-04 16:23:26 -0800 (Tue, 04 Feb 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>Store StringImpl substring backpointers as tail data
https://bugs.webkit.org/show_bug.cgi?id=128220
Reviewed by Geoffrey Garen.
This lets us get rid of m_substringBuffer from the union.
* wtf/text/StringImpl.cpp:
(WTF::StringImpl::~StringImpl):
(WTF::StringImpl::getData16SlowCase):
* wtf/text/StringImpl.h:
(WTF::StringImpl::StringImpl):
(WTF::StringImpl::createSubstringSharingImpl8):
(WTF::StringImpl::createSubstringSharingImpl):
(WTF::StringImpl::cost):
(WTF::StringImpl::costDuringGC):
(WTF::StringImpl::substringBuffer):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWTFChangeLog">trunk/Source/WTF/ChangeLog</a></li>
<li><a href="#trunkSourceWTFwtftextStringImplcpp">trunk/Source/WTF/wtf/text/StringImpl.cpp</a></li>
<li><a href="#trunkSourceWTFwtftextStringImplh">trunk/Source/WTF/wtf/text/StringImpl.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWTFChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/ChangeLog (163415 => 163416)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/ChangeLog 2014-02-05 00:09:15 UTC (rev 163415)
+++ trunk/Source/WTF/ChangeLog 2014-02-05 00:23:26 UTC (rev 163416)
</span><span class="lines">@@ -1,5 +1,25 @@
</span><span class="cx"> 2014-02-04 Anders Carlsson <andersca@apple.com>
</span><span class="cx">
</span><ins>+ Store StringImpl substring backpointers as tail data
+ https://bugs.webkit.org/show_bug.cgi?id=128220
+
+ Reviewed by Geoffrey Garen.
+
+ This lets us get rid of m_substringBuffer from the union.
+
+ * wtf/text/StringImpl.cpp:
+ (WTF::StringImpl::~StringImpl):
+ (WTF::StringImpl::getData16SlowCase):
+ * wtf/text/StringImpl.h:
+ (WTF::StringImpl::StringImpl):
+ (WTF::StringImpl::createSubstringSharingImpl8):
+ (WTF::StringImpl::createSubstringSharingImpl):
+ (WTF::StringImpl::cost):
+ (WTF::StringImpl::costDuringGC):
+ (WTF::StringImpl::substringBuffer):
+
+2014-02-04 Anders Carlsson <andersca@apple.com>
+
</ins><span class="cx"> Rename the substring sharing StringImpl::create variants to better indicate what they do
</span><span class="cx"> https://bugs.webkit.org/show_bug.cgi?id=128214
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceWTFwtftextStringImplcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/wtf/text/StringImpl.cpp (163415 => 163416)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/wtf/text/StringImpl.cpp 2014-02-05 00:09:15 UTC (rev 163415)
+++ trunk/Source/WTF/wtf/text/StringImpl.cpp 2014-02-05 00:23:26 UTC (rev 163416)
</span><span class="lines">@@ -137,8 +137,8 @@
</span><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> ASSERT(ownership == BufferSubstring);
</span><del>- ASSERT(m_substringBuffer);
- m_substringBuffer->deref();
</del><ins>+ ASSERT(substringBuffer());
+ substringBuffer()->deref();
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void StringImpl::destroy(StringImpl* stringImpl)
</span><span class="lines">@@ -307,8 +307,8 @@
</span><span class="cx"> if (bufferOwnership() == BufferSubstring) {
</span><span class="cx"> // If this is a substring, return a pointer into the parent string.
</span><span class="cx"> // TODO: Consider severing this string from the parent string
</span><del>- unsigned offset = m_data8 - m_substringBuffer->characters8();
- return m_substringBuffer->deprecatedCharacters() + offset;
</del><ins>+ unsigned offset = m_data8 - substringBuffer()->characters8();
+ return substringBuffer()->deprecatedCharacters() + offset;
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> STRING_STATS_ADD_UPCONVERTED_STRING(m_length);
</span></span></pre></div>
<a id="trunkSourceWTFwtftextStringImplh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/wtf/text/StringImpl.h (163415 => 163416)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/wtf/text/StringImpl.h 2014-02-05 00:09:15 UTC (rev 163415)
+++ trunk/Source/WTF/wtf/text/StringImpl.h 2014-02-05 00:23:26 UTC (rev 163416)
</span><span class="lines">@@ -273,14 +273,15 @@
</span><span class="cx"> : m_refCount(s_refCountIncrement)
</span><span class="cx"> , m_length(length)
</span><span class="cx"> , m_data8(characters)
</span><del>- , m_substringBuffer(base.leakRef())
</del><span class="cx"> , m_hashAndFlags(s_hashFlag8BitBuffer | BufferSubstring)
</span><span class="cx"> {
</span><span class="cx"> ASSERT(is8Bit());
</span><span class="cx"> ASSERT(m_data8);
</span><span class="cx"> ASSERT(m_length);
</span><del>- ASSERT(m_substringBuffer->bufferOwnership() != BufferSubstring);
</del><ins>+ ASSERT(base->bufferOwnership() != BufferSubstring);
</ins><span class="cx">
</span><ins>+ substringBuffer() = base.leakRef();
+
</ins><span class="cx"> STRING_STATS_ADD_8BIT_STRING2(m_length, true);
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -289,14 +290,15 @@
</span><span class="cx"> : m_refCount(s_refCountIncrement)
</span><span class="cx"> , m_length(length)
</span><span class="cx"> , m_data16(characters)
</span><del>- , m_substringBuffer(base.leakRef())
</del><span class="cx"> , m_hashAndFlags(BufferSubstring)
</span><span class="cx"> {
</span><span class="cx"> ASSERT(!is8Bit());
</span><span class="cx"> ASSERT(m_data16);
</span><span class="cx"> ASSERT(m_length);
</span><del>- ASSERT(m_substringBuffer->bufferOwnership() != BufferSubstring);
</del><ins>+ ASSERT(base->bufferOwnership() != BufferSubstring);
</ins><span class="cx">
</span><ins>+ substringBuffer() = base.leakRef();
+
</ins><span class="cx"> STRING_STATS_ADD_16BIT_STRING2(m_length, true);
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -351,8 +353,11 @@
</span><span class="cx"> return *empty();
</span><span class="cx">
</span><span class="cx"> ASSERT(rep->is8Bit());
</span><del>- StringImpl* ownerRep = (rep->bufferOwnership() == BufferSubstring) ? rep->m_substringBuffer : rep.get();
- return adoptRef(*new StringImpl(rep->m_data8 + offset, length, ownerRep));
</del><ins>+ StringImpl* ownerRep = (rep->bufferOwnership() == BufferSubstring) ? rep->substringBuffer() : rep.get();
+
+ // We allocate a buffer that contains both the StringImpl struct as well as the pointer to the owner string.
+ StringImpl* stringImpl = static_cast<StringImpl*>(fastMalloc(allocationSize<StringImpl*>(1)));
+ return adoptRef(*new (NotNull, stringImpl) StringImpl(rep->m_data8 + offset, length, ownerRep));
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> static ALWAYS_INLINE PassRef<StringImpl> createSubstringSharingImpl(PassRefPtr<StringImpl> rep, unsigned offset, unsigned length)
</span><span class="lines">@@ -363,10 +368,13 @@
</span><span class="cx"> if (!length)
</span><span class="cx"> return *empty();
</span><span class="cx">
</span><del>- StringImpl* ownerRep = (rep->bufferOwnership() == BufferSubstring) ? rep->m_substringBuffer : rep.get();
</del><ins>+ StringImpl* ownerRep = (rep->bufferOwnership() == BufferSubstring) ? rep->substringBuffer() : rep.get();
+
+ // We allocate a buffer that contains both the StringImpl struct as well as the pointer to the owner string.
+ StringImpl* stringImpl = static_cast<StringImpl*>(fastMalloc(allocationSize<StringImpl*>(1)));
</ins><span class="cx"> if (rep->is8Bit())
</span><del>- return adoptRef(*new StringImpl(rep->m_data8 + offset, length, ownerRep));
- return adoptRef(*new StringImpl(rep->m_data16 + offset, length, ownerRep));
</del><ins>+ return adoptRef(*new (NotNull, stringImpl) StringImpl(rep->m_data8 + offset, length, ownerRep));
+ return adoptRef(*new (NotNull, stringImpl) StringImpl(rep->m_data16 + offset, length, ownerRep));
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> template<unsigned charactersCount>
</span><span class="lines">@@ -459,7 +467,7 @@
</span><span class="cx"> {
</span><span class="cx"> // For substrings, return the cost of the base string.
</span><span class="cx"> if (bufferOwnership() == BufferSubstring)
</span><del>- return m_substringBuffer->cost();
</del><ins>+ return substringBuffer()->cost();
</ins><span class="cx">
</span><span class="cx"> if (m_hashAndFlags & s_hashFlagDidReportCost)
</span><span class="cx"> return 0;
</span><span class="lines">@@ -477,7 +485,7 @@
</span><span class="cx"> return 0;
</span><span class="cx">
</span><span class="cx"> if (bufferOwnership() == BufferSubstring)
</span><del>- return divideRoundedUp(m_substringBuffer->costDuringGC(), refCount());
</del><ins>+ return divideRoundedUp(substringBuffer()->costDuringGC(), refCount());
</ins><span class="cx">
</span><span class="cx"> size_t result = m_length;
</span><span class="cx"> if (!is8Bit())
</span><span class="lines">@@ -789,6 +797,20 @@
</span><span class="cx"> return reinterpret_cast<T*>(reinterpret_cast<uint8_t*>(this) + tailOffset<T>());
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+ StringImpl* const& substringBuffer() const
+ {
+ ASSERT(bufferOwnership() == BufferSubstring);
+
+ return *tailPointer<StringImpl*>();
+ }
+
+ StringImpl*& substringBuffer()
+ {
+ ASSERT(bufferOwnership() == BufferSubstring);
+
+ return *tailPointer<StringImpl*>();
+ }
+
</ins><span class="cx"> // This number must be at least 2 to avoid sharing empty, null as well as 1 character strings from SmallStrings.
</span><span class="cx"> static const unsigned s_copyCharsInlineCutOff = 20;
</span><span class="cx">
</span><span class="lines">@@ -854,10 +876,7 @@
</span><span class="cx"> const LChar* m_data8;
</span><span class="cx"> const UChar* m_data16;
</span><span class="cx"> };
</span><del>- union {
- StringImpl* m_substringBuffer;
- mutable UChar* m_copyData16;
- };
</del><ins>+ mutable UChar* m_copyData16;
</ins><span class="cx"> mutable unsigned m_hashAndFlags;
</span><span class="cx"> };
</span><span class="cx">
</span></span></pre>
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