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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 - Failure to reduce indvarsimplify modulo loop output to a simple AND mask"
href="https://bugs.llvm.org/show_bug.cgi?id=40878">40878</a>
</td>
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<th>Summary</th>
<td>Failure to reduce indvarsimplify modulo loop output to a simple AND mask
</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>
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<th>Component</th>
<td>Loop Optimizer
</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>greened@obbligato.org, lebedev.ri@gmail.com, llvm-bugs@lists.llvm.org, spatel+llvm@rotateright.com
</td>
</tr>
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<th>Blocks</th>
<td>38280
</td>
</tr></table>
<p>
<div>
<pre>Pulled out of [<a class="bz_bug_link
bz_status_NEW "
title="NEW - Pointless loop unroll / vectorization"
href="show_bug.cgi?id=38280#c1">Bug #38280 Comment #1</a>]:
<span class="quote">> On a perhaps related note, the very simple example
> (<a href="https://godbolt.org/g/MToVLm">https://godbolt.org/g/MToVLm</a>):
> unsigned func(unsigned count)
> {
> while (count >= 32)
> count -= 32;
> return count;
> }
>
> Currently produces something like (thanks to indvarsimplify):
>
> define i32 @test(i32 %size) {
> entry:
> %0 = xor i32 %size, -1
> %1 = icmp ugt i32 %0, -32
> %umax = select i1 %1, i32 %0, i32 -32
> %2 = add i32 %umax, %size
> %3 = add i32 %2, 32
> %4 = and i32 %3, -32
> %5 = sub i32 %size, %4
> ret i32 %5
> }
>
> Which is really just:
> <a href="https://rise4fun.com/Alive/lKL">https://rise4fun.com/Alive/lKL</a>
>
> define i32 @test(i32 %size) {
> %0 = and i32 %size, 31
> ret i32 %0
> }</span ></pre>
</div>
</p>
<div id="referenced">
<hr style="border: 1px dashed #969696">
<b>Referenced Bugs:</b>
<ul>
<li>
[<a class="bz_bug_link
bz_status_NEW "
title="NEW - Pointless loop unroll / vectorization"
href="https://bugs.llvm.org/show_bug.cgi?id=38280">Bug 38280</a>] Pointless loop unroll / vectorization
</li>
</ul>
</div>
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