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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 - [x86] After 16f3d698f2af, -march=amdfam10 incorrectly implies SSSE3 instructions"
href="https://bugs.llvm.org/show_bug.cgi?id=47464">47464</a>
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<th>Summary</th>
<td>[x86] After 16f3d698f2af, -march=amdfam10 incorrectly implies SSSE3 instructions
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>11.0
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</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>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>dimitry@andric.com
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>After <a href="https://reviews.llvm.org/D83273">https://reviews.llvm.org/D83273</a> /
<a href="https://github.com/llvm/llvm-project/commit/16f3d698f2af">https://github.com/llvm/llvm-project/commit/16f3d698f2af</a> ("[X86] Move
the feature dependency handling in X86TargetInfo::setFeatureEnabledImpl
to a table based lookup in X86TargetParser.cpp"), compiling with
-march=amdfam10 incorrectly starts using SSSE3 instructions, in particular
pshufb.
Test case:
#include <xmmintrin.h>
__m128i foo(unsigned char c) {
return _mm_set1_epi8(c);
}
Asm output before:
foo: # @foo
.cfi_startproc
# %bb.0: # %entry
movd %edi, %xmm0
punpcklbw %xmm0, %xmm0 # xmm0 =
xmm0[0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7]
pshuflw $224, %xmm0, %xmm0 # xmm0 = xmm0[0,0,2,3,4,5,6,7]
pshufd $0, %xmm0, %xmm0 # xmm0 = xmm0[0,0,0,0]
retq
After:
foo: # @foo
.cfi_startproc
# %bb.0: # %entry
movd %edi, %xmm0
pxor %xmm1, %xmm1
pshufb %xmm1, %xmm0
retq
Apparently
<a href="https://github.com/llvm/llvm-project/commit/16f3d698f2afbbea43e0c3df81df6f2a640ce806#diff-045a11495d5fad4e01af59c60f6a387aR500">https://github.com/llvm/llvm-project/commit/16f3d698f2afbbea43e0c3df81df6f2a640ce806#diff-045a11495d5fad4e01af59c60f6a387aR500</a>
makes SSE4_A now imply SSSE3, which is not correct (at least not always, I
think).</pre>
</div>
</p>
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