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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed optimization in math expression: aggressive optimization with std::pow"
href="https://bugs.llvm.org/show_bug.cgi?id=35595">35595</a>
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</tr>
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<th>Summary</th>
<td>Missed optimization in math expression: aggressive optimization with std::pow
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<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>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Common Code Generator Code
</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 a, double x)
{
return pow(a, x) * a * a * a * a;
}
generates this assembly:
test(double, double): # @test(double, double)
push rax
vmovsd qword ptr [rsp], xmm0 # 8-byte Spill
call pow
vmovsd xmm1, qword ptr [rsp] # 8-byte Reload
vmulsd xmm1, xmm1, xmm1
vmulsd xmm1, xmm1, xmm1
vmulsd xmm0, xmm1, xmm0
pop rax
ret
As you can see, me can simplify it by adding 4 to 'x' variable and after call
std::pow.</pre>
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