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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 - [Middle-end] Moving truncate before right-shift"
href="https://bugs.llvm.org/show_bug.cgi?id=46234">46234</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[Middle-end] Moving truncate before right-shift
</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>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>lebedev.ri@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>int src(long int num) {
num &= 0xFFFFFFF;
return num >> 2;
}
int tgt(long int num) {
return (((unsigned int)num) << 4) >> 6;
}
----------------------------------------
define i32 @src(i64 %0) {
%1:
%2 = lshr i64 %0, 2
%3 = trunc i64 %2 to i32
%4 = and i32 %3, 67108863
ret i32 %4
}
=>
define i32 @tgt(i64 %0) {
%1:
%2 = trunc i64 %0 to i32
%3 = lshr i32 %2, 2
%4 = and i32 %3, 67108863
ret i32 %4
}
Transformation seems to be correct!
<a href="https://godbolt.org/z/V7xRAy">https://godbolt.org/z/V7xRAy</a>
^ we do that in backend, but not middle-end.</pre>
</div>
</p>
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