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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 - Compiler no longer optimizing some horizontal add/sub patterns after r310260"
href="https://bugs.llvm.org/show_bug.cgi?id=34724">34724</a>
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<th>Summary</th>
<td>Compiler no longer optimizing some horizontal add/sub patterns after r310260
</td>
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<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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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>
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<th>Component</th>
<td>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>douglas_yung@playstation.sony.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>Prior to r310260, the compiler was optimizing some add/sub + shuffle patterns
to horizontal add/sub instructions, but no longer seems to do so.
Consider this example:
__attribute__((noinline))
__m128 add_ps_001(__m128 a, __m128 b) {
__m128 r = (__m128){ a[0] + a[1], a[2] + a[3], b[0] + b[1], b[2] + b[3] };
return __builtin_shufflevector(r, a, -1, 1, 2, 3);
}
When compiled with the options "-S -O2 -march=bdver2" using a compiler prior to
r310260, the compiler would generate the following assembly:
vmovaps (%rcx), %xmm0
vhaddps (%rdx), %xmm0, %xmm0
retq
After r310260, the compiler is now generating the following code for the same
function:
vmovaps (%rdx), %xmm0
vmovddup 8(%rcx), %xmm1 # xmm1 = mem[0,0]
vinsertps $28, %xmm0, %xmm1, %xmm2 # xmm2 = xmm1[0],xmm0[0],zero,zero
vinsertps $76, %xmm1, %xmm0, %xmm1 # xmm1 = xmm1[1],xmm0[1],zero,zero
vaddps %xmm1, %xmm2, %xmm1
vpermilpd $1, %xmm0, %xmm2 # xmm2 = xmm0[1,0]
vpermilps $231, %xmm0, %xmm0 # xmm0 = xmm0[3,1,2,3]
vaddss %xmm0, %xmm2, %xmm0
vpermilps $208, %xmm1, %xmm1 # xmm1 = xmm1[0,0,1,3]
vinsertps $48, %xmm0, %xmm1, %xmm0 # xmm0 = xmm1[0,1,2],xmm0[0]
retq</pre>
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</p>
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