<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - __attribute__((alias)) should prevent DCE"
href="https://bugs.llvm.org/show_bug.cgi?id=39088">39088</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>__attribute__((alias)) should prevent DCE
</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>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Interprocedural Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>ndesaulniers@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>george.burgess.iv@gmail.com, jyknight@google.com, llozano@chromium.org, llvm-bugs@lists.llvm.org, manojgupta@google.com, niravd@google.com, srhines@google.com
</td>
</tr></table>
<p>
<div>
<pre>Consider this test case, from the Linux kernel's heavily used
MODULE_DEVICE_TABLE macro: <a href="https://godbolt.org/z/Dpxnbp">https://godbolt.org/z/Dpxnbp</a>
static int foo [] = { 42, 0xDEAD };
extern typeof(foo) bar __attribute__((unused, alias("foo")));
At -O2, GCC emits essentially:
.type foo, @object
.size foo, 8
foo:
.long 42
.long 57005
.globl bar
.set bar,fo
Clang with -Wall (and thus -Wunneeded-internal-declaration) warns for
-Wunneeded-internal-declaration, then at -O1 and up produces:
.type bar,@object # @bar
.globl bar
bar:
.long 42 # 0x2a
.long 57005 # 0xdead
.size bar, 8
indeed dropping all references to foo. Removing the `static` type qualifier
can work around this, but it seems that DCE should not remove variables that
are referenced by alias attributes.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>