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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - _mm_set_ps is lowered badly with sse4"
href="https://bugs.llvm.org/show_bug.cgi?id=37502">37502</a>
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<th>Summary</th>
<td>_mm_set_ps is lowered badly with sse4
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>jmuizelaar@mozilla.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>__m128 f(float aYScale, float aXScale) {
return _mm_set_ps(aYScale, aXScale, aYScale, aXScale);
}
With -mssse3 this compiles to:
unpcklps %xmm0, %xmm1 # xmm1 =
xmm1[0],xmm0[0],xmm1[1],xmm0[1]
movddup %xmm1, %xmm0 # xmm0 = xmm1[0,0]
with -mssse4 this compiles to:
movaps %xmm1, %xmm2
insertps $16, %xmm0, %xmm2 # xmm2 = xmm2[0],xmm0[0],xmm2[2,3]
insertps $32, %xmm1, %xmm2 # xmm2 = xmm2[0,1],xmm1[0],xmm2[3]
insertps $48, %xmm0, %xmm2 # xmm2 = xmm2[0,1,2],xmm0[0]
movaps %xmm2, %xmm0
llvm-mca -mcpu=haswell agrees that the ssse3 version is better:
Iterations: 1
Instructions: 2
Total Cycles: 5
Dispatch Width: 4
IPC: 0.40
vs
Iterations: 1
Instructions: 5
Total Cycles: 8
Dispatch Width: 4
IPC: 0.62</pre>
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