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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Failure to zextload due to unused bits"
href="https://bugs.llvm.org/show_bug.cgi?id=36689">36689</a>
</td>
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<tr>
<th>Summary</th>
<td>Failure to zextload due to unused bits
</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>Windows NT
</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>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, spatel+llvm@rotateright.com
</td>
</tr></table>
<p>
<div>
<pre>We correctly convert to a zextload for a basic load + mask, but this fails if
we set any extra bits, which I assume is due to SimplifyDemandedBits getting in
the way:
clang -g0 -O3 -march=btver2
int masklo(int *p) {
return (*p & 65535);
}
int masklo_set(int *p) {
return (*p & 65535) | 255;
}
define i32 @_Z6maskloPi(i32*) {
%2 = load i32, i32* %0
%3 = and i32 %2, 65535
ret i32 %3
}
define i32 @_Z10masklo_setPi(i32*) {
%2 = load i32, i32* %0
%3 = and i32 %2, 65280
%4 = or i32 %3, 255
ret i32 %4
}
_Z6maskloPi:
movzwl (%rdi), %eax
retq
_Z10masklo_setPi:
movl $65280, %eax # imm = 0xFF00
andl (%rdi), %eax
orl $255, %eax
retq
Ideally this should have been:
_Z10masklo_setPi:
movzwl (%rdi), %eax
orl $255, %eax
retq</pre>
</div>
</p>
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