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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Different encoding using direct object emission"
href="http://llvm.org/bugs/show_bug.cgi?id=22854">22854</a>
</td>
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<tr>
<th>Summary</th>
<td>Different encoding using direct object emission
</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>MC
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>russell_gallop@sn.scee.net
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>For the following source the generated code is different between direct object
emission and .s. Using r231635.
The code using direct object emissions seems to be less efficient.
$ cat test.c
void foo (void) {
for (int s = 0; s != 1 ; s++)
;
}
$ clang -c test.c -o test.o
$ clang -S test.c -o test.s && clang -c test.s -o test_via_s.o
$ objdump -d test.o
test.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <foo>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: c7 45 fc 00 00 00 00 movl $0x0,-0x4(%rbp)
b: 81 7d fc 01 00 00 00 cmpl $0x1,-0x4(%rbp)
12: 0f 84 15 00 00 00 je 2d <foo+0x2d>
18: e9 00 00 00 00 jmpq 1d <foo+0x1d>
1d: 8b 45 fc mov -0x4(%rbp),%eax
20: 05 01 00 00 00 add $0x1,%eax
25: 89 45 fc mov %eax,-0x4(%rbp)
28: e9 de ff ff ff jmpq b <foo+0xb>
2d: 5d pop %rbp
2e: c3 retq
$ objdump -d test_via_s.o
test_via_s.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <foo>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: c7 45 fc 00 00 00 00 movl $0x0,-0x4(%rbp)
b: 83 7d fc 01 cmpl $0x1,-0x4(%rbp)
f: 74 0d je 1e <foo+0x1e>
11: eb 00 jmp 13 <foo+0x13>
13: 8b 45 fc mov -0x4(%rbp),%eax
16: 83 c0 01 add $0x1,%eax
19: 89 45 fc mov %eax,-0x4(%rbp)
1c: eb ed jmp b <foo+0xb>
1e: 5d pop %rbp
1f: c3 retq</pre>
</div>
</p>
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