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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - O3 pass pipeline does not remove trivial LCSSA node"
href="https://llvm.org/bugs/show_bug.cgi?id=27620">27620</a>
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</tr>
<tr>
<th>Summary</th>
<td>O3 pass pipeline does not remove trivial LCSSA node
</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>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>me@manueljacob.de
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Given this IR:
define i64 @test() {
entry:
br label %loop
loop:
%i = phi i64 [ 0, %entry ], [ %inc, %loop ]
%inc = add i64 %i, 1
%cond = tail call i1 @check()
br i1 %cond, label %loop, label %exit
exit:
ret i64 %i
}
declare i1 @check()
Running opt -S -O3 on it gives the following output:
define i64 @test() {
entry:
br label %loop
loop: ; preds = %loop, %entry
%i = phi i64 [ 0, %entry ], [ %inc, %loop ]
%inc = add i64 %i, 1
%cond = tail call i1 @check()
br i1 %cond, label %loop, label %exit
exit: ; preds = %loop
%i.lcssa = phi i64 [ %i, %loop ]
ret i64 %i.lcssa
}
declare i1 @check()
Here, the LCSSA pass introduces a trivially removable PHI node in the exit
block. However, InstCombine (or a similar pass) isn't run after LCSSA in the
pass pipeline.</pre>
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