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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - adding min signed value constant does not result in expected 'unsigned add with overflow' codegen"
href="https://bugs.llvm.org/show_bug.cgi?id=40842">40842</a>
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<th>Summary</th>
<td>adding min signed value constant does not result in expected 'unsigned add with overflow' codegen
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
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</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Forking this reduced example from <a class="bz_bug_link
bz_status_NEW "
title="NEW - CodeGenPrepare::CombineUAddWithOverflow - improve icmp eq/ne matching"
href="show_bug.cgi?id=40486">bug 40486</a>:
#include <x86intrin.h>
using u64 = unsigned;
template<u64 K>
void test(u64& alo, u64& ahi)
{
u64 blo = K;
u64 bhi = 0;
bool cf = (alo += blo) < blo;
_addcarry_u32(cf, ahi, bhi, &ahi);
}
template void test<0x80000000u>(u64&, u64&);
--------------------------------------------------------------------------
<a href="https://godbolt.org/z/lPSSir">https://godbolt.org/z/lPSSir</a>
Either we've prematurely formed bit magic from icmp or we need to recognize
this as another special-case form of uaddo:</pre>
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