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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed optimization in math expression: (x+x)/x == 2"
href="https://bugs.llvm.org/show_bug.cgi?id=35709">35709</a>
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<th>Summary</th>
<td>Missed optimization in math expression: (x+x)/x == 2
</td>
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<th>Product</th>
<td>clang
</td>
</tr>
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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>
</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>LLVM Codegen
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>zamazan4ik@tut.by
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>clang (trunk) with '-O3 -std=c++17 -ffast-math -funsafe-math-optimizations' for
this code:
int test(int x)
{
return (x+x)/x;
}
generates:
test(int): # @test(int)
lea eax, [rdi + rdi]
cdq
idiv edi
ret
Why? In this case we can return simply 2. Because there are only two corner
cases: when x is 0 and we have division by zero (it's UB), and when x+x is
integer overflow (it's also UB).
So we can simply optimize it. There are a lot of similar cases.</pre>
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