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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Add warning to indicate when ARC implicit writeback occurs"
href="http://llvm.org/bugs/show_bug.cgi?id=19009">19009</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Add warning to indicate when ARC implicit writeback occurs
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>Macintosh
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>tjw@me.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=12171" name="attach_12171" title="patch">attachment 12171</a> <a href="attachment.cgi?id=12171&action=edit" title="patch">[details]</a></span>
patch
Split out from <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Warn about using a variable as __strong and __autoreleasing at the same time"
href="show_bug.cgi?id=15649">http://llvm.org/bugs/show_bug.cgi?id=15649</a>
In some cases, ARC implicit writeback can result in loss of what the user
likely intended. For example:
int main(int argc, char *argv[])
{
__block id value = @"initial value";
void (^block)(id *outValue) = ^(id *outValue){
value = @"hello";
};
block(&value);
NSLog(@"value = %@", value);
return 0;
}
With ARC, this reports:
2013-04-24 13:55:35.814 block-local-address[28013:707] value = initial
value
but with MRR:
2013-04-24 13:57:26.058 block-local-address[28046:707] value = hello
Attached is a patch vs trunk r202532 that adds -Warc-implicit-writeback and
test cases for the ObjC and ObjC++ compilers (which each seem to have their own
support for writeback).</pre>
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