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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/180855">180855</a></dd>
<dt>Author</dt> <dd>carlosgc@webkit.org</dd>
<dt>Date</dt> <dd>2015-03-01 00:45:32 -0800 (Sun, 01 Mar 2015)</dd>
</dl>
<h3>Log Message</h3>
<pre>Merge <a href="http://trac.webkit.org/projects/webkit/changeset/180688">r180688</a> - bmalloc: free up a bit in BoundaryTag
https://bugs.webkit.org/show_bug.cgi?id=142048
Reviewed by Brady Eidson.
We were wasting a bit by accident, and I need one now.
* bmalloc/Algorithm.h:
(bmalloc::rightShift): Deleted. Not needed, now that I've simplified
the math.
* bmalloc/BoundaryTag.h: Since each boundary tag bucket is 1024 bytes
long, the maximum offset into a bucket is 1023.
You need 5 bits to count up to 1024, but only 4 to count up to 1023.
Math is hard.
(bmalloc::BoundaryTag::compactBegin): Switched to division because it
is simpler, and easier to match up with our ASSERT. The compiler will
turn division by constant power of two into a shift for us.
(bmalloc::BoundaryTag::setRange): Added an ASSERT for compactBegin
because we do encode it, so we should ASSERT that encoding did not
lose information.
* bmalloc/Sizes.h: Shifting is no longer used since we use division
instead.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#releasesWebKitGTKwebkit28SourcebmallocChangeLog">releases/WebKitGTK/webkit-2.8/Source/bmalloc/ChangeLog</a></li>
<li><a href="#releasesWebKitGTKwebkit28SourcebmallocbmallocAlgorithmh">releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/Algorithm.h</a></li>
<li><a href="#releasesWebKitGTKwebkit28SourcebmallocbmallocBoundaryTagh">releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/BoundaryTag.h</a></li>
<li><a href="#releasesWebKitGTKwebkit28SourcebmallocbmallocSizesh">releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/Sizes.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="releasesWebKitGTKwebkit28SourcebmallocChangeLog"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.8/Source/bmalloc/ChangeLog (180854 => 180855)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.8/Source/bmalloc/ChangeLog 2015-03-01 08:43:46 UTC (rev 180854)
+++ releases/WebKitGTK/webkit-2.8/Source/bmalloc/ChangeLog 2015-03-01 08:45:32 UTC (rev 180855)
</span><span class="lines">@@ -1,3 +1,34 @@
</span><ins>+2015-02-26 Geoffrey Garen <ggaren@apple.com>
+
+ bmalloc: free up a bit in BoundaryTag
+ https://bugs.webkit.org/show_bug.cgi?id=142048
+
+ Reviewed by Brady Eidson.
+
+ We were wasting a bit by accident, and I need one now.
+
+ * bmalloc/Algorithm.h:
+ (bmalloc::rightShift): Deleted. Not needed, now that I've simplified
+ the math.
+
+ * bmalloc/BoundaryTag.h: Since each boundary tag bucket is 1024 bytes
+ long, the maximum offset into a bucket is 1023.
+
+ You need 5 bits to count up to 1024, but only 4 to count up to 1023.
+
+ Math is hard.
+
+ (bmalloc::BoundaryTag::compactBegin): Switched to division because it
+ is simpler, and easier to match up with our ASSERT. The compiler will
+ turn division by constant power of two into a shift for us.
+
+ (bmalloc::BoundaryTag::setRange): Added an ASSERT for compactBegin
+ because we do encode it, so we should ASSERT that encoding did not
+ lose information.
+
+ * bmalloc/Sizes.h: Shifting is no longer used since we use division
+ instead.
+
</ins><span class="cx"> 2015-02-24 Stephanie Lewis <slewis@apple.com>
</span><span class="cx">
</span><span class="cx"> Rolling out http://trac.webkit.org/changeset/180430 as it causes the PLT to crash.
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit28SourcebmallocbmallocAlgorithmh"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/Algorithm.h (180854 => 180855)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/Algorithm.h 2015-03-01 08:43:46 UTC (rev 180854)
+++ releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/Algorithm.h 2015-03-01 08:45:32 UTC (rev 180855)
</span><span class="lines">@@ -53,11 +53,6 @@
</span><span class="cx"> return reinterpret_cast<T>(reinterpret_cast<uintptr_t>(value) & mask);
</span><span class="cx"> }
</span><span class="cx">
</span><del>-template<typename T> inline constexpr T rightShift(T value, uintptr_t shift)
-{
- return reinterpret_cast<T>(reinterpret_cast<uintptr_t>(value) >> shift);
-}
-
</del><span class="cx"> template<typename T> inline constexpr bool test(T value, uintptr_t mask)
</span><span class="cx"> {
</span><span class="cx"> return !!(reinterpret_cast<uintptr_t>(value) & mask);
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit28SourcebmallocbmallocBoundaryTagh"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/BoundaryTag.h (180854 => 180855)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/BoundaryTag.h 2015-03-01 08:43:46 UTC (rev 180854)
+++ releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/BoundaryTag.h 2015-03-01 08:45:32 UTC (rev 180855)
</span><span class="lines">@@ -68,12 +68,17 @@
</span><span class="cx">
</span><span class="cx"> private:
</span><span class="cx"> static const size_t flagBits = 3;
</span><del>- static const size_t compactBeginBits = 5;
</del><ins>+ static const size_t compactBeginBits = 4;
</ins><span class="cx"> static const size_t sizeBits = bitCount<unsigned>() - flagBits - compactBeginBits;
</span><span class="cx">
</span><del>- static_assert((1 << compactBeginBits) - 1 >= largeMin / largeAlignment, "compactBegin must be encodable in a BoundaryTag.");
- static_assert((1 << sizeBits) - 1 >= largeMax, "largeMax must be encodable in a BoundaryTag.");
</del><ins>+ static_assert(
+ (1 << compactBeginBits) - 1 >= (largeMin - 1) / largeAlignment,
+ "compactBegin must be encodable in a BoundaryTag.");
</ins><span class="cx">
</span><ins>+ static_assert(
+ (1 << sizeBits) - 1 >= largeMax,
+ "largeMax must be encodable in a BoundaryTag.");
+
</ins><span class="cx"> bool m_isFree: 1;
</span><span class="cx"> bool m_isEnd: 1;
</span><span class="cx"> bool m_hasPhysicalPages: 1;
</span><span class="lines">@@ -84,14 +89,14 @@
</span><span class="cx"> inline unsigned BoundaryTag::compactBegin(void* object)
</span><span class="cx"> {
</span><span class="cx"> return static_cast<unsigned>(
</span><del>- reinterpret_cast<uintptr_t>(
- rightShift(
- mask(object, largeMin - 1), largeAlignmentShift)));
</del><ins>+ reinterpret_cast<uintptr_t>(mask(object, largeMin - 1)) / largeAlignment);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> inline void BoundaryTag::setRange(const Range& range)
</span><span class="cx"> {
</span><span class="cx"> m_compactBegin = compactBegin(range.begin());
</span><ins>+ BASSERT(this->compactBegin() == compactBegin(range.begin()));
+
</ins><span class="cx"> m_size = static_cast<unsigned>(range.size());
</span><span class="cx"> BASSERT(this->size() == range.size());
</span><span class="cx"> }
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit28SourcebmallocbmallocSizesh"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/Sizes.h (180854 => 180855)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/Sizes.h 2015-03-01 08:43:46 UTC (rev 180854)
+++ releases/WebKitGTK/webkit-2.8/Source/bmalloc/bmalloc/Sizes.h 2015-03-01 08:45:32 UTC (rev 180855)
</span><span class="lines">@@ -76,8 +76,6 @@
</span><span class="cx"> static const size_t largeChunkMask = ~(largeChunkSize - 1ul);
</span><span class="cx">
</span><span class="cx"> static const size_t largeAlignment = 64;
</span><del>- static const size_t largeAlignmentShift = 6;
- static_assert(1 << largeAlignmentShift == largeAlignment, "largeAlignmentShift be log2(largeAlignment).");
</del><span class="cx"> static const size_t largeMax = largeChunkSize * 99 / 100; // Plenty of room for metadata.
</span><span class="cx"> static const size_t largeMin = mediumMax;
</span><span class="cx">
</span></span></pre>
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