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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 - Missing fold cttz(zext(x)) -> zext(cttz(x))"
href="https://bugs.llvm.org/show_bug.cgi?id=50172">50172</a>
</td>
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<tr>
<th>Summary</th>
<td>Missing fold cttz(zext(x)) -> zext(cttz(x))
</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>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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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>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>define i32 @src(i16 %x) {
%z = zext i16 %x to i32
%p = call i32 @llvm.cttz.i32(i32 %z, i1 true)
ret i32 %p
}
define i32 @tgt(i16 %x) {
%p = call i16 @llvm.cttz.i16(i16 %x, i1 true)
%z = zext i16 %p to i32
ret i32 %z
}
declare i32 @llvm.cttz.i32(i32, i1)
declare i16 @llvm.cttz.i16(i16, i1)
----------------------------------------
define i32 @src(i16 %x) {
%0:
%z = zext i16 %x to i32
%p = cttz i32 %z, 1
ret i32 %p
}
=>
define i32 @tgt(i16 %x) {
%0:
%p = cttz i16 %x, 0
%z = zext i16 %p to i32
ret i32 %z
}
Transformation seems to be correct!
src: # @src
movzx eax, di
bsf eax, eax
ret
tgt: # @tgt
bsf ax, di
movzx eax, ax
ret</pre>
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