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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Example of missing overflow check folds"
href="https://bugs.llvm.org/show_bug.cgi?id=43172">43172</a>
</td>
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<tr>
<th>Summary</th>
<td>Example of missing overflow check folds
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<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>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>listmail@philipreames.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Here is a collection of overflow check idioms which we don't currently turn
into the op.with.overflow equivalents (or more importantly, generate op
w/following OF flag check on x86).
add i32, i32
%8 = add i32 %1, %0
%9 = xor i32 %8, %0
%10 = xor i32 %8, %1
%11 = and i32 %9, %10
%12 = icmp sgt i32 %11, -1
sub i32 i32
%8 = sub i32 %0, %1
%9 = xor i32 %1, %0
%10 = xor i32 %8, %0
%11 = and i32 %10, %9
%12 = icmp sgt i32 %11, -1
mul i32 i32
%8 = sext i32 %0 to i64
%9 = sext i32 %1 to i64
%10 = mul nsw i64 %9, %8
%11 = add nsw i64 %10, 2147483648
%12 = icmp ult i64 %11, 4294967296
increment i32 (i.e. add i32 1)
%7 = icmp eq i32 %0, 2147483647
...
%9 = add nsw i32 %0, 1
ret i32 %9
Note that in all cases, there's a branch on the overflow check leading to an
exception block. I left that out for simplicity.
All of these are derived from
<a href="https://github.com/AdoptOpenJDK/openjdk-jdk11/blob/master/src/java.base/share/classes/java/lang/Math.java">https://github.com/AdoptOpenJDK/openjdk-jdk11/blob/master/src/java.base/share/classes/java/lang/Math.java</a>
opExact family of methods.</pre>
</div>
</p>
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