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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 --- - Very recent regression when optimizing i128"
href="https://llvm.org/bugs/show_bug.cgi?id=27792">27792</a>
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<th>Summary</th>
<td>Very recent regression when optimizing i128
</td>
</tr>
<tr>
<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>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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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>yyc1992@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>According to our (julia) buildbot, this happened within the last 24 hours
<a href="http://buildbot.e.ip.saba.us:8010/builders/nightly_llvmsvn-x64">http://buildbot.e.ip.saba.us:8010/builders/nightly_llvmsvn-x64</a>
<a href="http://buildbot.e.ip.saba.us:8010/builders/nightly_llvmsvn-x86">http://buildbot.e.ip.saba.us:8010/builders/nightly_llvmsvn-x86</a>
So far all of the failing tests seems to be related to 128bit integer handling.
It is unclear if there is a single issue but one of the reduced test case is
(this is the code we emit for sign check)
```
define i32 @f(i128) {
top:
%1 = lshr i128 %0, 127
%2 = trunc i128 %1 to i1
%3 = xor i1 %2, true
br i1 %3, label %pass, label %fail
fail: ; preds = %top
ret i32 0
pass: ; preds = %top
ret i32 1
}
```
For -O1 to -O3 with opt on x64, this is mis-optimized to
```
yuyichao% usr/bin/opt -O3 -S -o - a.ll
; ModuleID = 'a.ll'
source_filename = "a.ll"
; Function Attrs: norecurse nounwind readnone
define i32 @f(i128) #0 {
top:
%1 = icmp sgt i128 %0, 18446744073709551615
%. = zext i1 %1 to i32
ret i32 %.
}
attributes #0 = { norecurse nounwind readnone }
```
Where `18446744073709551615` is the 64 bits representation of `-1`. The code is
correct if it is an 128 bits `-1` (which is what LLVM 3.8 optimized it to in a
similar case (not for this case))</pre>
</div>
</p>
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