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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Power i32/i64 atomic acquire load lowers to lwsync, not isync"
href="http://bugs.llvm.org/show_bug.cgi?id=32392">32392</a>
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<th>Summary</th>
<td>Power i32/i64 atomic acquire load lowers to lwsync, not isync
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</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>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: PowerPC
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>timshen91@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
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<pre>GCC lowers acquire load of i32/i64 to isync, but llvm lowers them to lwsync.
Here's the explanation:
<a href="http://www.rdrop.com/~paulmck/scalability/paper/N2745r.2011.03.04a.html">http://www.rdrop.com/~paulmck/scalability/paper/N2745r.2011.03.04a.html</a>
A casually written benchmark also shows that isync approach is faster:
GCC:
Benchmark Time(ns) CPU(ns) Iterations
---------------------------------------------------------------------
BM_Acquire32/threads:1 2.74 2.74 256555796
BM_Acquire32/threads:2 1.40 2.80 228185266
BM_Acquire32/threads:4 1.25 4.98 124786836
BM_Acquire32/threads:176 0.240 8.17 78115312
BM_Acquire64/threads:1 5.42 5.41 166593868
BM_Acquire64/threads:2 2.47 4.07 199450866
BM_Acquire64/threads:4 1.17 3.22 182357912
BM_Acquire64/threads:176 0.209 6.76 94368384
LLVM:
Benchmark Time(ns) CPU(ns) Iterations
---------------------------------------------------------------------
BM_Acquire32/threads:1 8.45 8.44 70487873
BM_Acquire32/threads:2 2.75 5.49 93091058
BM_Acquire32/threads:4 5.56 22.2 31810768
BM_Acquire32/threads:176 1.14 37.4 17600000
BM_Acquire64/threads:1 6.71 6.71 100000000
BM_Acquire64/threads:2 4.01 8.00 63776730
BM_Acquire64/threads:4 5.57 22.2 31363992
BM_Acquire64/threads:176 1.41 36.9 17600000</pre>
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