<div dir="ltr"><div class="gmail_default" style>On Fri, Jan 4, 2013 at 9:14 PM, NAKAMURA Takumi <span dir="ltr"><<a href="mailto:geek4civic@gmail.com" target="_blank" class="cremed">geek4civic@gmail.com</a>></span> wrote:<br>
</div><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: chapuni<br>
Date: Fri Jan  4 23:14:23 2013<br>
New Revision: 171600<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=171600&view=rev" target="_blank" class="cremed">http://llvm.org/viewvc/llvm-project?rev=171600&view=rev</a><br>
Log:<br>
DenseMap: Appease -fstrict-aliasing on g++-4.4.<br>
<br>
With DenseMapInfo<Enum>, it is miscompiled on g++-4.4.<br>
<br>
    static inline Enum getEmptyKey() { return Enum(<arbitrary int/unsigned value>); }<br>
<br>
    isEauql(getEmptyKey(), ...)<br>
<br>
The compiler mis-assumes the return value is not aliased to Enum.<br></blockquote><div><br></div><div style>This doesn't make a lot of sense to me.</div><div style><br></div><div style>Aliasing has to do with pointers and references. The return value is a value, and can't alias anything....</div>
<div style><br></div><div style>Not sure what is actually happening though.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
Modified:<br>
    llvm/trunk/include/llvm/ADT/DenseMap.h<br>
<br>
Modified: llvm/trunk/include/llvm/ADT/DenseMap.h<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/DenseMap.h?rev=171600&r1=171599&r2=171600&view=diff" target="_blank" class="cremed">http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/DenseMap.h?rev=171600&r1=171599&r2=171600&view=diff</a><br>

==============================================================================<br>
--- llvm/trunk/include/llvm/ADT/DenseMap.h (original)<br>
+++ llvm/trunk/include/llvm/ADT/DenseMap.h Fri Jan  4 23:14:23 2013<br>
@@ -430,7 +430,8 @@<br>
     incrementNumEntries();<br>
<br>
     // If we are writing over a tombstone, remember this.<br>
-    if (!KeyInfoT::isEqual(TheBucket->first, getEmptyKey()))<br>
+    const KeyT EmptyKey = getEmptyKey();<br>
+    if (!KeyInfoT::isEqual(TheBucket->first, EmptyKey))<br>
       decrementNumTombstones();<br>
<br>
     return TheBucket;<br>
<br>
<br>
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</blockquote></div><br></div></div>