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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - The add instruction is incorrectly folded into icmp when there is an overflow by instcombine"
href="https://llvm.org/bugs/show_bug.cgi?id=25986">25986</a>
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<th>Summary</th>
<td>The add instruction is incorrectly folded into icmp when there is an overflow by instcombine
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>3.7
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>new bugs
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>yuanrui.zhang@intel.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Given the following reduced test:
define i32 @f(i32 %j) {
entry:
%inc = add nsw i32 %j, 1
%cmp = icmp sgt i32 %inc, 0
%conv = zext i1 %cmp to i32
ret i32 %conv
}
define i32 @main() {
entry:
%call = call i32 @f(i32 2147483647)
ret i32 0
}
InstCombine folds the following 2 instructions
%inc = add nsw i32 %j, 1
%cmp = icmp sgt i32 %inc, 0
into:
<badref> = icmp sgt i32 %j, -1
and the IR becomes wrong after InstCombine as below:
define i32 @f(i32 %j) {
entry:
%j.lobit = lshr i32 %j, 31
%j.lobit.not = xor i32 %j.lobit, 1
ret i32 %j.lobit.not
}
define i32 @main() {
entry:
%call = call i32 @f(i32 2147483647)
ret i32 0
}
The error comes from visitICmpInst</pre>
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