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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed optimization in math expression: missing cube of the sum formula"
href="https://bugs.llvm.org/show_bug.cgi?id=35597">35597</a>
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<th>Summary</th>
<td>Missed optimization in math expression: missing cube of the sum formula
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<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>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<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>
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<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:
double test(double a, double b)
{
return a*a*a + 3.0*a*a*b + 3.0*a*b*b + b*b*b;
}
generates this assembly:
.LCPI0_0:
.quad 4613937818241073152 # double 3
test(double, double): # @test(double, double)
vmulsd xmm2, xmm0, qword ptr [rip + .LCPI0_0]
vmulsd xmm3, xmm0, xmm0
vmulsd xmm4, xmm1, xmm1
vaddsd xmm5, xmm2, xmm1
vmulsd xmm4, xmm4, xmm5
vfmadd231sd xmm3, xmm2, xmm1
vfmadd213sd xmm0, xmm3, xmm4
ret
But there is formula: a*a*a + 3.0*a*a*b + 3.0*a*b*b + b*b*b == (a + b)^3. And
it can be compiled in faster way.</pre>
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