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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Less efficient encoding using direct object emission"
href="https://llvm.org/bugs/show_bug.cgi?id=22947">22947</a>
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<tr>
<th>Summary</th>
<td>Less efficient encoding using direct object emission
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>MC
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>russell_gallop@sn.scee.net
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>For the following source the code generated by direct object emission is less
efficient than outputting to .s. Using r232386.
$ cat decrement.c
int foo(int a) {
return --a;
}
$ clang -c decrement.c -o decrement.o
$ clang -S decrement.c -o decrement.s && clang -c decrement.s -o
decrement_via_s.o
$ objdump -d decrement.o
decrement.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <foo>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 89 7d fc mov %edi,-0x4(%rbp)
7: 8b 7d fc mov -0x4(%rbp),%edi
a: 81 c7 ff ff ff ff add $0xffffffff,%edi
10: 89 7d fc mov %edi,-0x4(%rbp)
13: 89 f8 mov %edi,%eax
15: 5d pop %rbp
16: c3 retq
$ objdump -d decrement_via_s.o
decrement_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: 89 7d fc mov %edi,-0x4(%rbp)
7: 8b 7d fc mov -0x4(%rbp),%edi
a: 83 c7 ff add $0xffffffff,%edi
d: 89 7d fc mov %edi,-0x4(%rbp)
10: 89 f8 mov %edi,%eax
12: 5d pop %rbp
13: c3 retq</pre>
</div>
</p>
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