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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Optimization of loop via loop peeling does not occur for float and double"
href="https://llvm.org/bugs/show_bug.cgi?id=31930">31930</a>
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<th>Summary</th>
<td>Optimization of loop via loop peeling does not occur for float and double
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<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>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>drraph@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Consider:
float f(float x[]) {
float p = 1.0;
for (int i = 0; i < 960; i++)
p += 1;
return p;
}
When compiled with -march=core-avx2 -O3 -ffast-math the assembly loops round
adding until it gets to 961.
However:
int f(int x[]) {
int p = 1;
for (int i = 0; i < 960; i++)
p += 1;
return p;
}
gives:
f: # @f
mov eax, 961
ret
I don't know how hard it would be to add the same optimization for floats and
double.
As a side note, there are in fact a number of interesting details with the
first (float) loop. First, if we reduce the i < 960 limit to i < 959 the loop
is optimized out. Second if we change the type to 'double' this upper limit
goes down to i < 479. My guess is that this corresponds to an unpeeling cost
model that is incorporated into the compiler.</pre>
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</p>
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