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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 --- - [InstCombine] missing folds for bit manipulation intrinsics"
href="https://llvm.org/bugs/show_bug.cgi?id=28668">28668</a>
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<tr>
<th>Summary</th>
<td>[InstCombine] missing folds for bit manipulation intrinsics
</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>All
</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>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>define i1 @ctlz_cmp(i32 %a) {
%x = tail call i32 @llvm.ctlz.i32(i32 %a, i1 false) #0
%cmp = icmp eq i32 %x, 0 ; no zeros? --> all ones
ret i1 %cmp
}
define i1 @cttz_cmp(i32 %a) {
%x = tail call i32 @llvm.cttz.i32(i32 %a, i1 false) #0
%cmp = icmp eq i32 %x, 0 ; no zeros? --> all ones
ret i1 %cmp
}
define i1 @ctpop_cmp(i32 %a) {
%x = tail call i32 @llvm.ctpop.i32(i32 %a) #0
%cmp = icmp eq i32 %x, 32 ; all ones? --> no zeros
ret i1 %cmp
}
-----------------------------------------------------------------------------
$ ./opt -instcombine more_bitz.ll -S
(doesn't change anything)
Note that these all work:
define i1 @ctlz_cmp(i32 %a) {
%x = tail call i32 @llvm.ctlz.i32(i32 %a, i1 false) nounwind readnone
%cmp = icmp eq i32 %x, 32 ; all zeros? --> no ones
ret i1 %cmp
}
define i1 @cttz_cmp(i32 %a) {
%x = tail call i32 @llvm.cttz.i32(i32 %a, i1 false) nounwind readnone
%cmp = icmp eq i32 %x, 32 ; all zeros? --> no ones
ret i1 %cmp
}
define i1 @ctpop_cmp(i32 %a) {
%x = tail call i32 @llvm.ctpop.i32(i32 %a) nounwind readnone
%cmp = icmp eq i32 %x, 0 ; no ones? --> all zeros
ret i1 %cmp
}
$ ./opt -instcombine more_bitz.ll -S
...
define i1 @ctlz_cmp(i32 %a) {
%cmp = icmp eq i32 %a, 0
ret i1 %cmp
}
define i1 @cttz_cmp(i32 %a) {
%cmp = icmp eq i32 %a, 0
ret i1 %cmp
}
define i1 @ctpop_cmp(i32 %a) {
%cmp = icmp eq i32 %a, 0
ret i1 %cmp
}</pre>
</div>
</p>
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