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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: fmax(-a, -b) -> -fmin(a, b)"
href="https://bugs.llvm.org/show_bug.cgi?id=37404">37404</a>
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<th>Summary</th>
<td>Missed optimization: fmax(-a, -b) -> -fmin(a, b)
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>6.0
</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>
<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>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>m-takahiro@jp.fujitsu.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>I compiled the following code by clang (tags/RELEASE_600/final 327104).
Option is '-Ofast -march=native'
#include <math.h>
double foo(double a, double b) {
return fmax(-a, -b);
}
Generated IRs are as follows.
; Function Attrs: nounwind readnone uwtable
define double @foo(double, double) local_unnamed_addr #0 {
%3 = fsub fast double -0.000000e+00, %0
%4 = fsub fast double -0.000000e+00, %1
%5 = tail call fast double @llvm.maxnum.f64(double %3, double %4)
ret double %5
}
I think the above IRs can be simplified like the following.
; Function Attrs: nounwind readnone uwtable
define double @foo(double, double) local_unnamed_addr #0 {
%2 = tail call fast double @llvm.minnum.f64(double %0, double %1)
%3 = fsub fast double -0.000000e+00, %2
ret double %3
}</pre>
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