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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 @llvm.assume lack of unsigned overflow"
href="https://bugs.llvm.org/show_bug.cgi?id=42661">42661</a>
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<tr>
<th>Summary</th>
<td>Failure to @llvm.assume lack of unsigned overflow
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<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>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Global Analyses
</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><a href="https://godbolt.org/z/K-Ts7V">https://godbolt.org/z/K-Ts7V</a>
int t0(int x) {
__builtin_assume(x > 0);
__builtin_assume((3u*unsigned(x)) > unsigned(x));
return (3 * x) / 2;
}
int t1(int x) {
__builtin_assume(x > 0);
__builtin_assume((12u*unsigned(x)) > unsigned(x));
return (12 * x) / 8;
}
results in
define dso_local i32 @_Z2t0i(i32) local_unnamed_addr #0 {
%2 = icmp sgt i32 %0, 0
tail call void @llvm.assume(i1 %2)
%3 = mul i32 %0, 3
%4 = icmp ugt i32 %3, %0
tail call void @llvm.assume(i1 %4)
%5 = sdiv i32 %3, 2
ret i32 %5
}
declare void @llvm.assume(i1) #1
define dso_local i32 @_Z2t1i(i32) local_unnamed_addr #0 {
%2 = icmp sgt i32 %0, 0
tail call void @llvm.assume(i1 %2)
%3 = mul i32 %0, 12
%4 = icmp ugt i32 %3, %0
tail call void @llvm.assume(i1 %4)
%5 = sdiv i32 %3, 8
ret i32 %5
}
So the 'mul' is both feeding the @llvm.assume (that would signify that it
didn't overflow),
and is being used in the datapath.
I guess this could be due too aggressive CSE?</pre>
</div>
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