<html>
<head>
<base href="https://llvm.org/bugs/" />
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_ASSIGNED "
title="ASSIGNED --- - OptimizeLEAPass is too slow"
href="https://llvm.org/bugs/show_bug.cgi?id=25843">25843</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>OptimizeLEAPass is too slow
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>ASSIGNED
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>a.bataev@hotmail.com
</td>
</tr>
<tr>
<th>Reporter</th>
<td>vonosmas@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, nadav256@gmail.com, qcolombet@apple.com
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>OptimizeLEAPass added in r254712 and triggered by -Os on X86 platforms is
unacceptably slow. Its algorithm complexity is at least
O(MBB * ACCESS * LEA)
where MBB is the number of machine basic blocks in a function,
ACCESS is the number of load/stores in a basic block,
LEA is the number of lea instructions in a basic block.
The last two numbers can easily grow to thousands in real-life code (especially
in auto-generated functions), exploding the compile time.
Please investigate optimization improvements, or add a bound to avoid
triggering this pass. To reproduce:
$ cat a.py
import sys
def foo(n):
print '#include <unordered_map>'
print 'std::unordered_map<int, int> m;'
print 'void foo() {'
for i in range(n):
print ' m[%d] = %d;' % (i, i + 100);
print '}'
if __name__ == '__main__':
foo(int(sys.argv[1]))
$ python a.py 200 > a.cc ; time ./bin/clang++ -std=c++11 -c a.cc -o a.o -Os
real 0m0.892s
user 0m0.852s
sys 0m0.040s
$ python a.py 400 > a.cc ; time ./bin/clang++ -std=c++11 -c a.cc -o a.o -Os
real 0m3.438s
user 0m3.412s
sys 0m0.030s
$ python a.py 800 > a.cc ; time ./bin/clang++ -std=c++11 -c a.cc -o a.o -Os
real 0m23.815s
user 0m23.709s
sys 0m0.116s</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>