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<body><span class="vcard"><a class="email" href="mailto:florian_hahn@apple.com" title="Florian Hahn <florian_hahn@apple.com>"> <span class="fn">Florian Hahn</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Miscompilation of single loop with two assignments"
href="https://bugs.llvm.org/show_bug.cgi?id=47793">bug 47793</a>
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<th>What</th>
<th>Removed</th>
<th>Added</th>
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<td style="text-align:right;">Resolution</td>
<td>---
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<td>INVALID
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<td style="text-align:right;">Status</td>
<td>NEW
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<td>RESOLVED
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<td style="text-align:right;">CC</td>
<td>
</td>
<td>florian_hahn@apple.com
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Miscompilation of single loop with two assignments"
href="https://bugs.llvm.org/show_bug.cgi?id=47793#c3">Comment # 3</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Miscompilation of single loop with two assignments"
href="https://bugs.llvm.org/show_bug.cgi?id=47793">bug 47793</a>
from <span class="vcard"><a class="email" href="mailto:florian_hahn@apple.com" title="Florian Hahn <florian_hahn@apple.com>"> <span class="fn">Florian Hahn</span></a>
</span></b>
<pre>(In reply to Tuom Larsen from <a href="show_bug.cgi?id=47793#c2">comment #2</a>)
<span class="quote">> Sorry, I'm new to all this. Could you please point me to where you see the
> undefined behaviour? I'm just copying bunch of uint16_t's. Even if I could
> use memcpy, who knows what memcpy would in fact do and this is what broke(?).</span >
The problem is likely that you are accessing the same memory through uint16_t
and uint64_t pointers. Clang assumes 'strict aliasing' by default IIRC and
under those rules I think that is not allowed. See
<a href="http://dbp-consulting.com/tutorials/StrictAliasing.html">http://dbp-consulting.com/tutorials/StrictAliasing.html</a> for an explanation.
Please try your example with -fno-strict-aliasing. Your code should work as
expected with that option. If not, please re-open the issue.</pre>
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