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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 - Huge compile time with loop unroll benchmark with -O3"
href="https://bugs.llvm.org/show_bug.cgi?id=39110">39110</a>
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<th>Summary</th>
<td>Huge compile time with loop unroll benchmark with -O3
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
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<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>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<pre>Created <span class=""><a href="attachment.cgi?id=20934" name="attach_20934" title="time report of passes">attachment 20934</a> <a href="attachment.cgi?id=20934&action=edit" title="time report of passes">[details]</a></span>
time report of passes
Bechmark:
<a href="https://gitlab.com/chriscox/CppPerformanceBenchmarks/blob/master/loop_unroll.cpp">https://gitlab.com/chriscox/CppPerformanceBenchmarks/blob/master/loop_unroll.cpp</a>
Both GCC and Clang versions are close to the top of trunk.
time clang++ -std=c++11 -O3 loop_unroll.cpp -o loop_unroll
real 0m37,371s
user 0m37,247s
sys 0m0,124s
time g++ -std=c++11 -O3 loop_unroll.cpp -o loop_unroll
real 0m17,509s
user 0m17,267s
sys 0m0,196s
time g++ -std=c++11 loop_unroll.cpp -o loop_unroll
real 0m2,567s
user 0m2,478s
sys 0m0,089s
time clang++ -std=c++11 loop_unroll.cpp -o loop_unroll
real 0m1,795s
user 0m1,744s
sys 0m0,050s
===-------------------------------------------------------------------------===
... Pass execution timing report ...
===-------------------------------------------------------------------------===
Total Execution Time: 38.8286 seconds (38.7849 wall clock)
---User Time--- --System Time-- --User+System-- ---Wall Time--- ---
Name ---
5.5111 ( 15.0%) 0.3874 ( 18.7%) 5.8985 ( 15.2%) 5.8983 ( 15.2%) X86
DAG->DAG Instruction Selection
2.0702 ( 5.6%) 0.0664 ( 3.2%) 2.1366 ( 5.5%) 2.1347 ( 5.5%) Loop
Strength Reduction
1.8916 ( 5.1%) 0.0472 ( 2.3%) 1.9388 ( 5.0%) 1.9379 ( 5.0%)
Combine redundant instructions #8
1.5240 ( 4.1%) 0.0868 ( 4.2%) 1.6108 ( 4.1%) 1.6097 ( 4.2%)
Function Integration/Inlining
1.3555 ( 3.7%) 0.0794 ( 3.8%) 1.4349 ( 3.7%) 1.4337 ( 3.7%)
Induction Variable Simplification
1.2232 ( 3.3%) 0.0651 ( 3.1%) 1.2882 ( 3.3%) 1.2872 ( 3.3%)
Global Value Numbering
1.1388 ( 3.1%) 0.0472 ( 2.3%) 1.1860 ( 3.1%) 1.1851 ( 3.1%)
Combine redundant instructions #6
1.0846 ( 3.0%) 0.0502 ( 2.4%) 1.1348 ( 2.9%) 1.1340 ( 2.9%)
Combine redundant instructions #2
1.0596 ( 2.9%) 0.0215 ( 1.0%) 1.0811 ( 2.8%) 1.0794 ( 2.8%)
Unroll loops #2
Full output of clang++ -std=c++11 -O3 loop_unroll.cpp -o loop_unroll
-ftime-report is attached.</pre>
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