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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 --- - inefficient floating point register ld/st instructions are generated when -mcpu=power8 is specified"
href="https://llvm.org/bugs/show_bug.cgi?id=24817">24817</a>
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<th>Summary</th>
<td>inefficient floating point register ld/st instructions are generated when -mcpu=power8 is specified
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: PowerPC
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
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<th>Reporter</th>
<td>carrot@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>The simple test case is:
int foo(float *p)
{
float f1 = p[1];
float f2 = p[2];
return f1 > f2;
}
Compiler command line and output
clang -S t8.c --target=powerpc -m64 -mcpu=power8 -O2
li 4, 4 // A
li 5, 8 // B
lxsspx 0, 3, 4 // C
lxsspx 1, 3, 5 // D
li 3, 0
li 4, 1
fcmpu 0, 0, 1
isel 3, 4, 3, 1
blr
If I change -mcpu=power8 to -mcpu=power7, I got
lfs 0, 4(3) // E
lfs 1, 8(3) // F
li 3, 0
li 4, 1
fcmpu 0, 0, 1
isel 3, 4, 3, 1
blr
Instructions AC are replaced by E
Instructions BD are replaced by F</pre>
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</p>
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