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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - UB in APInt::slt"
href="https://llvm.org/bugs/show_bug.cgi?id=28294">28294</a>
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<th>Summary</th>
<td>UB in APInt::slt
</td>
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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
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Support Libraries
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>jonathan@codesourcery.com
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</tr>
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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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</tr></table>
<p>
<div>
<pre>When VAL has its MSbit set, the left shift on line 558 shifts a negative value
leftward, which is UB. Similarly for RHS.VAL on line 559:
555: bool APInt::slt(const APInt& RHS) const {
556: assert(BitWidth == RHS.BitWidth && "Bit widths must be same for
comparison");
557: if (isSingleWord()) {
558: int64_t lhsSext = (int64_t(VAL) << (64-BitWidth)) >> (64-BitWidth);
559: int64_t rhsSext = (int64_t(RHS.VAL) << (64-BitWidth)) >>
(64-BitWidth);
560: return lhsSext < rhsSext;
561: }</pre>
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