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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - recognize min/max patterns as commutative"
href="https://bugs.llvm.org/show_bug.cgi?id=35642">35642</a>
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<th>Summary</th>
<td>recognize min/max patterns as commutative
</td>
</tr>
<tr>
<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
</td>
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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
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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>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>#include <algorithm>
int maxmax(int a, int b) {
return std::max(a, b) - std::max(b, a);
}
Or as IR after -O2:
define i32 @_Z6maxmaxii(i32 %a, i32 %b) {
%cmp1 = icmp slt i32 %a, %b
%sel1 = select i1 %cmp1, i32 %b, i32 %a
%cmp2 = icmp slt i32 %b, %a
%sel2 = select i1 %cmp2, i32 %a, i32 %b
%sub = sub nsw i32 %sel1, %sel2
ret i32 %sub
}
<a href="https://godbolt.org/g/hG6HMR">https://godbolt.org/g/hG6HMR</a>
I think early-cse needs to know that max is commutative. We can't easily
instcombine or instsimplify our way out of this.</pre>
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