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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - misaligned placement of function arguments of over-aligned type on the stack (ABI incompatibility)"
href="https://llvm.org/bugs/show_bug.cgi?id=26830">26830</a>
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<th>Summary</th>
<td>misaligned placement of function arguments of over-aligned type on the stack (ABI incompatibility)
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>3.7
</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>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>kretz@kde.org
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Testcase:
#include <xmmintrin.h>
struct X { __m128 x; };
X f(X a, X b) { return {_mm_add_ps(a.x, b.x)}; }
Compiles to (-msse -m32 -O2):
00000000 <f(X, X)>:
0:· mov 0x4(%esp),%eax
4:· movups 0x8(%esp),%xmm0
9:· movups 0x18(%esp),%xmm1
e:· addps %xmm0,%xmm1
11:· movaps %xmm1,(%eax)
14:· ret $0x4
This is incorrect according to the x86 psABI document, which states that
padding must be added so that the placement of the argument matches its
alignment. GCC compiles the code to:
00000000 <f(X, X)>:
0:· movaps 0x24(%esp),%xmm0
5:· mov 0x4(%esp),%eax
9:· addps 0x14(%esp),%xmm0
e:· movaps %xmm0,(%eax)
11:· ret $0x4</pre>
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