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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed optimization in math expression: pow(cbrt(x), y) == pow(x, y / 3)"
href="https://bugs.llvm.org/show_bug.cgi?id=35605">35605</a>
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<th>Summary</th>
<td>Missed optimization in math expression: pow(cbrt(x), y) == pow(x, y / 3)
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</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>
<tr>
<th>Reporter</th>
<td>zamazan4ik@tut.by
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>clang(trunk) with '--std=c++17 -O3 -march=native -ffast-math' flags for this
code:
#include <cmath>
double test(double x, double y)
{
return pow(cbrt(x),y);
}
generates this assembly:
test(double, double): # @test(double, double)
push rax
vmovsd qword ptr [rsp], xmm1 # 8-byte Spill
call cbrt
vmovsd xmm1, qword ptr [rsp] # 8-byte Reload
pop rax
jmp pow # TAILCALL
As you can see, we can simplify it by calling pow(x, y/3). It should be faster.</pre>
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