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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Loop unswitching stopped happening"
href="https://bugs.llvm.org/show_bug.cgi?id=34257">34257</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Loop unswitching stopped happening
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>aivchenk@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>foo.cpp:
int foo(bool x, int a) {
int s = a;
int i = 0;
while (i < 10000) {
int y = x ? a : i;
s += y;
i++;
}
return s;
}
<span class="quote">>clang++ foo.cpp -c -S -emit-llvm -o llvm_version.ll -O3</span >
Before <a href="https://reviews.llvm.org/D35811">https://reviews.llvm.org/D35811</a> we used to nicely unswitch this loop:
define i32 @_Z12llvm_versionbi(i1 zeroext %x, i32 %a) local_unnamed_addr #0 {
entry:
%0 = mul i32 %a, 10001
%1 = add i32 %a, 49995000
%s.0.lcssa = select i1 %x, i32 %0, i32 %1
ret i32 %s.0.lcssa
}
I guess that degradation is expected, though, but, I'm not 100% sure</pre>
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</p>
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