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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [InstSimplify] rotating all-ones is still all-ones"
href="https://bugs.llvm.org/show_bug.cgi?id=51575">51575</a>
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<th>Summary</th>
<td>[InstSimplify] rotating all-ones is still all-ones
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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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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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
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<pre>I'm not sure if there's overlap between this and related rotate bugs, but
filing it so we have a reference:
define i32 @src(i32 %shamt) {
%r = lshr i32 -1, %shamt
%s = sub i32 32, %shamt
%l = shl i32 -1, %s
%o = or i32 %r, %l
ret i32 %o
}
define i32 @tgt(i32 %shamt) {
ret i32 -1
}
<a href="https://alive2.llvm.org/ce/z/gDke_c">https://alive2.llvm.org/ce/z/gDke_c</a>
We do handle the sibling rotate-of-zero (probably via known bits or simpler
folds since all bits are the same in that case).</pre>
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