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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [SCEV] Unable to determine precise trip multiple from assumes using URem."
href="https://bugs.llvm.org/show_bug.cgi?id=47904">47904</a>
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<th>Summary</th>
<td>[SCEV] Unable to determine precise trip multiple from assumes using URem.
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Loop Optimizer
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>florian_hahn@apple.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>We currently are unable to determine a precise trip multiple for loops using
information from assumes.
For example for the code below, we fail to determine a trip multiple of 4.
<a href="https://godbolt.org/z/9zMWKW">https://godbolt.org/z/9zMWKW</a>
define void @test_trip_multiple_4(i32 %num) {
entry:
%u = urem i32 %num, 4
%cmp = icmp eq i32 %u, 0
tail call void @llvm.assume(i1 %cmp)
%cmp.1 = icmp uge i32 %num, 4
tail call void @llvm.assume(i1 %cmp.1)
br label %for.body
for.body:
%i.010 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%inc = add nuw nsw i32 %i.010, 1
%cmp2 = icmp ult i32 %inc, %num
br i1 %cmp2, label %for.body, label %exit
exit:
ret void
}
declare void @llvm.assume(i1)
This is one issue causing sub-optimal optimizations for an example shared on
IRC <a href="https://godbolt.org/z/49erfa">https://godbolt.org/z/49erfa</a></pre>
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