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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed optimization in math expression: simplify calls std::pow functions"
href="https://bugs.llvm.org/show_bug.cgi?id=35593">35593</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missed optimization in math expression: simplify calls std::pow functions
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</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>
<tr>
<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>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@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 f(double a, double b, double c)
{
return std::pow(a, b) * std::pow(a, c);
}
generates this assembly:
f(double, double, double): # @f(double, double, double)
sub rsp, 24
vmovsd qword ptr [rsp + 16], xmm2 # 8-byte Spill
vmovsd qword ptr [rsp], xmm0 # 8-byte Spill
call pow
vmovsd qword ptr [rsp + 8], xmm0 # 8-byte Spill
vmovsd xmm0, qword ptr [rsp] # 8-byte Reload
vmovsd xmm1, qword ptr [rsp + 16] # 8-byte Reload
call pow
vmulsd xmm0, xmm0, qword ptr [rsp + 8] # 8-byte Folded Reload
add rsp, 24
ret
GCC (trunk) with '--std=c++17 -O3 -march=native -ffast-math' flags generates
more optimal code:
f(double, double, double):
vaddsd xmm1, xmm1, xmm2
jmp __pow_finite</pre>
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