<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 - ThinLTO doesn't know about constant return values"
href="https://bugs.llvm.org/show_bug.cgi?id=33604">33604</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>ThinLTO doesn't know about constant return values
</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>All
</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>davide@freebsd.org
</td>
</tr>
<tr>
<th>CC</th>
<td>charles.saternos@gmail.com, davidxl@google.com, joker.eph@gmail.com, llvm-bugs@lists.llvm.org, tejohnson@google.com
</td>
</tr></table>
<p>
<div>
<pre>As Charles, our GSoC student working on ThinLTO was looking for opportunities
to improve ThinLTO, here's something that came to my mind.
I'm not sure whether we want to go in this direction, but it's a start.
$ cat a.c
__attribute__((noinline))
int patatino(void) {
return 47;
}
$ cat b.c
extern int patatino(void);
int main(void) {
return patatino();
}
$ ../clang a.c b.c -flto -fuse-ld=lld -Wl,-save-temps -o patatino-lto
$ objdump -d patatino-lto
[...]
0000000000201190 <main>:
201190: 55 push %rbp
201191: 48 89 e5 mov %rsp,%rbp
201194: 48 83 ec 10 sub $0x10,%rsp
201198: c7 45 fc 00 00 00 00 movl $0x0,-0x4(%rbp)
20119f: e8 dc ff ff ff callq 201180 <patatino>
2011a4: b8 2f 00 00 00 mov $0x2f,%eax
2011a9: 48 83 c4 10 add $0x10,%rsp
2011ad: 5d pop %rbp
2011ae: c3 retq
With ThinLTO:
$ ../clang a.c b.c -flto=thin -fuse-ld=lld -Wl,-save-temps -o patatino-thin
$ $ objdump -d ./patatino-thin
[...]
0000000000201190 <main>:
201190: 55 push %rbp
201191: 48 89 e5 mov %rsp,%rbp
201194: 48 83 ec 10 sub $0x10,%rsp
201198: c7 45 fc 00 00 00 00 movl $0x0,-0x4(%rbp)
20119f: e8 dc ff ff ff callq 201180 <patatino>
2011a4: 48 83 c4 10 add $0x10,%rsp
2011a8: 5d pop %rbp
2011a9: c3 retq</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>