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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - PowerPC64: issue passing packed bitfield to function"
href="https://llvm.org/bugs/show_bug.cgi?id=30280">30280</a>
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<tr>
<th>Summary</th>
<td>PowerPC64: issue passing packed bitfield to function
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</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>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: PowerPC
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>anton@samba.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>I was looking at a csmith fail with packed bitfields. A reduced test case looks
like:
#pragma pack(1)
struct S0 {
unsigned int f1;
unsigned int f2 : 31;
unsigned int f3 : 7;
};
int foo(struct S0 a)
{
return a.f3;
}
-O0 looks ok, but at -O1 and above we seem to pull the last byte out of the
wrong spot on the stack:
std 3, -24(1)
stb 4, -16(1)
ori 2, 2, 0
lbz 3, -20(1) <---- expecting offset -16
lwz 4, -20(1)
sldi 3, 3, 32
or 3, 4, 3
rldicl 3, 3, 33, 57
blr
It also seems a bit silly to do all this work when the values were in GPRs to
start with.</pre>
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</p>
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