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<base href="https://bugs.llvm.org/">
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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 - Incorrect register allocation for inline assembly with 4 outputs"
href="https://bugs.llvm.org/show_bug.cgi?id=42830">42830</a>
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<th>Summary</th>
<td>Incorrect register allocation for inline assembly with 4 outputs
</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>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>glider@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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<pre>When compiling the following code:
$ cat bar.c
char foo();
int bar() {
char x1 = foo();
char x2 = foo();
char x3 = foo();
char y1, y2, y3, y4;
asm("mov $1, %k0\nmov $2, %k1\nmov $3, %k2\nmov $4, %k3" : "=r"(y1),
"=r"(y2), "=r"(y3), "=r"(y4));
return x1 + x2 + y1 + y2 + y3 + y4;
}
with -m32, Clang uses EAX twice to return 1 and 4 from the inline assembly:
$ clang bar.c -c -m32
$ objdump -dr bar.o
00000000 <bar>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 57 push %edi
4: 56 push %esi
5: 83 ec 10 sub $0x10,%esp
8: e8 fc ff ff ff call 9 <bar+0x9>
9: R_386_PC32 foo
d: 88 45 f7 mov %al,-0x9(%ebp)
10: e8 fc ff ff ff call 11 <bar+0x11>
11: R_386_PC32 foo
15: 88 45 f6 mov %al,-0xa(%ebp)
18: e8 fc ff ff ff call 19 <bar+0x19>
19: R_386_PC32 foo
1d: 88 45 f5 mov %al,-0xb(%ebp)
20: b8 01 00 00 00 mov $0x1,%eax
25: b9 02 00 00 00 mov $0x2,%ecx
2a: ba 03 00 00 00 mov $0x3,%edx
2f: b8 04 00 00 00 mov $0x4,%eax
Without -m32 Clang returns 1 and 4 in EAX and ESI, respectively.</pre>
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