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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [X86] Failing to tail call with bool parameter"
href="https://llvm.org/bugs/show_bug.cgi?id=26305">26305</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[X86] Failing to tail call with bool parameter
</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>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>hans@chromium.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Blocks</th>
<td>26299
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Consider:
void f(bool);
void g(bool x) {
f(x);
}
Clang will generate:
00000000 <_Z1gb>:
0: 83 ec 0c sub $0xc,%esp
3: 0f b6 44 24 10 movzbl 0x10(%esp),%eax
8: 89 04 24 mov %eax,(%esp)
b: e8 fc ff ff ff call c <_Z1gb+0xc>
10: 83 c4 0c add $0xc,%esp
13: c3 ret
GCC 5.3 will do the tail call, but still insists on zexting:
g(bool):
movzbl 4(%esp), %eax
movl %eax, 4(%esp)
jmp f(bool)
MSVC hits the spot and emits a single jmp:
?g@@YAX_N@Z (void __cdecl g(bool)):
00000000: E9 00 00 00 00 jmp ?f@@YAX_N@Z </pre>
</div>
</p>
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