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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Comparisons against last enum are optimizable (found via LLVM classof() analysis)"
href="https://bugs.llvm.org/show_bug.cgi?id=35906">35906</a>
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<th>Summary</th>
<td>Comparisons against last enum are optimizable (found via LLVM classof() analysis)
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>All
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>LLVM Codegen
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>dave@znu.io
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>In LLVM and derived projects, exhaustive enums are common. For example, from
the casting machinery, an abstract class might have code roughly like this:
static bool classof(Thing *t) {
return t->getKind() >= ThingKind::First_AbstractFoo &&
t->getKind() <= ThingKind::Last_AbstractFoo;
}
If ThingKind::Last_AbstractFoo equals the last enumeration, then "t->getKind()
<= ThingKind::Last_AbstractFoo" will always be true. (Similarly, "t->getKind()
<span class="quote">> ThingKind::Last_AbstractFoo" will always fail). That being said, clang</span >
generates the IR for the pointless comparison above.
This seems like an easy optimization opportunity.</pre>
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