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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - small improvement to switch compilation"
href="https://bugs.llvm.org/show_bug.cgi?id=34471">34471</a>
</td>
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<th>Summary</th>
<td>small improvement to switch compilation
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>Dave@Yost.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>This code
int switcher(int x) {
switch(x) {
case 17: return 17;
case 42: return 42;
default: break;
}
return 0;
}
generates this:
switch i32 %4, label %7 [
i32 17, label %5
i32 42, label %6
]
; <label>:5: ; preds = %1
store i32 17, i32* %2, align 4
br label %9
; <label>:6: ; preds = %1
store i32 42, i32* %2, align 4
br label %9
I suspect that most targets would generate better code from equivalent llvm
output in which both cases jump to a common label that returns x instead of
jumping to separate labels that eventually return the constants 17 and 42.
Certainly the Mill compiler would generate better code. :)
See <a href="https://www.youtube.com/watch?time_continue=2191&v=FeYsKF3a14k">https://www.youtube.com/watch?time_continue=2191&v=FeYsKF3a14k</a></pre>
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</p>
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