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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [InstCombine] ((~x) + y) + 1 -> y - x fold"
href="https://bugs.llvm.org/show_bug.cgi?id=42459">42459</a>
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<th>Summary</th>
<td>[InstCombine] ((~x) + y) + 1 -> y - x fold
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>lebedev.ri@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>While this fold is nominally supported, it only happens due to some other
folds,
so it is missed if there are extra uses:
<a href="https://godbolt.org/z/ujsxHs">https://godbolt.org/z/ujsxHs</a>
<a href="https://rise4fun.com/Alive/EPO0">https://rise4fun.com/Alive/EPO0</a>
declare void @use32(i32)
define i32 @t2(i32 %x, i32 %y) {
%o0 = xor i32 %x, -1
%o1 = add i32 %o0, %y
call void @use32(i32 %o1)
%o2 = add i32 %o1, 1
ret i32 %o2
}
Name: ((~x) + y) + 1 -> y - x
%o0 = xor i32 %x, -1
%o1 = add i32 %o0, %y
%r = add i32 %o1, 1
=>
%r = sub i32 %y, %x</pre>
</div>
</p>
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