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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - LLVM 10 regression in gep inbounds of zero-offset gep"
href="https://bugs.llvm.org/show_bug.cgi?id=44423">44423</a>
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<th>Summary</th>
<td>LLVM 10 regression in gep inbounds of zero-offset gep
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<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>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>nikita.ppv@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>define i32* @test([0 x i32]* %base, i64 %idx) {
%base2 = bitcast [0 x i32]* %base to i32*
;%base2 = getelementptr [0 x i32], [0 x i32]* %base, i64 0, i64 0
%ptr = getelementptr inbounds i32, i32* %base2, i64 %idx
ret i32* %ptr
}
opt -instcombine now gives:
define i32* @test([0 x i32]* %base, i64 %idx) {
%ptr = getelementptr [0 x i32], [0 x i32]* %base, i64 0, i64 %idx
ret i32* %ptr
}
while previously:
define i32* @test([0 x i32]* %base, i64 %idx) {
%ptr = getelementptr inbounds [0 x i32], [0 x i32]* %base, i64 0, i64 %idx
ret i32* %ptr
}
This is because bitcasts are now converted to gep rather than gep inbounds, and
we drop the inbounds when combining both geps.
I believe that in this case the inbounds should be preserved, as the base gep
is zero-offset, so it has no impact on the overall inbounds-ness of the
operation.</pre>
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