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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 - @sdiv3 and @sdiv5 tests in test/Transforms/InstCombine/exact.ll are miscompiles for undef"
href="https://bugs.llvm.org/show_bug.cgi?id=44327">44327</a>
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<th>Summary</th>
<td>@sdiv3 and @sdiv5 tests in test/Transforms/InstCombine/exact.ll are miscompiles for undef
</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>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<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>lebedev.ri@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Noticed accidentally when looking at <a href="https://reviews.llvm.org/D71568">https://reviews.llvm.org/D71568</a> and trying
to ensure that the baseline udiv-by-select tests aren't miscompiles also.
----------------------------------------
define i32 @sdiv3(i32 %x) {
%0:
%y = sdiv i32 %x, 3
%z = mul i32 %y, 3
ret i32 %z
}
=>
define i32 @sdiv3(i32 %x) {
%0:
%1 = srem i32 %x, 3
%z = sub i32 %x, %1
ret i32 %z
}
Transformation doesn't verify!
ERROR: Value mismatch
Example:
i32 %x = undef
Source:
i32 %y = #x00000000 (0) [based on undef value]
i32 %z = #x00000000 (0)
Target:
i32 %1 = #x00000000 (0)
i32 %z = #x00010000 (65536)
Source value: #x00000000 (0)
Target value: #x00010000 (65536)
----------------------------------------
define i32 @sdiv5(i32 %x) {
%0:
%y = sdiv i32 %x, 3
%z = mul i32 %y, 4294967293
ret i32 %z
}
=>
define i32 @sdiv5(i32 %x) {
%0:
%1 = srem i32 %x, 3
%z = sub i32 %1, %x
ret i32 %z
}
Transformation doesn't verify!
ERROR: Value mismatch
Example:
i32 %x = undef
Source:
i32 %y = #x00000000 (0) [based on undef value]
i32 %z = #x00000000 (0)
Target:
i32 %1 = #x00000000 (0)
i32 %z = #x10000000 (268435456)
Source value: #x00000000 (0)
Target value: #x10000000 (268435456)</pre>
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