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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed Optimization: redundant ternary expression not removed"
href="https://bugs.llvm.org/show_bug.cgi?id=42848">42848</a>
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<th>Summary</th>
<td>Missed Optimization: redundant ternary expression not removed
</td>
</tr>
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<th>Product</th>
<td>new-bugs
</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>Linux
</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>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>jameshamm1995@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Missed optimization on a ternary expression which has two equivalent output
paths.
Example code (<a href="https://godbolt.org/z/6dYE7d">https://godbolt.org/z/6dYE7d</a>) compiled with clang (trunk,
currently 10.0.0) -Ofast -march=skylake
int f(int a, int b) {
return (a == b) ? (a + b) : (a + a);
}
produces
f(int, int): # @f(int, int)
lea ecx, [rsi + rdi]
lea eax, [rdi + rdi]
cmp edi, esi
cmove eax, ecx
ret
Since a == b, the code can be reduced to
int f(int a, int b) {
return (a == b) ? (a + a) : (a + a);
}
which produces the much shorter assembly
f(int, int): # @f(int, int)
lea eax, [rdi + rdi]
ret
This result is correct according to alive (<a href="https://rise4fun.com/Alive/Ozp">https://rise4fun.com/Alive/Ozp</a>)</pre>
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