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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Emitted binary code changes at -O0 when compiling through -S"
href="https://bugs.llvm.org/show_bug.cgi?id=51571">51571</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Emitted binary code changes at -O0 when compiling through -S
</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>Common Code Generator Code
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>tlwang@uwaterloo.ca
</td>
</tr>
<tr>
<th>CC</th>
<td>cnsun@uwaterloo.ca, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>The .text section of program.c changes when the program is compiled through -S.
$ cat program.c
int a;
void b() {
if (a)
;
}
int main() {}
$
$ clang-trunk -v
clang version 14.0.0 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
3890ce708d4f94d0326172650ce22262f6b56661)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/cnsun/usr/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$
$ clang-trunk -O0 -c program.c ; objdump --disassemble --section=.text
program.o > no_s.txt
$ clang-trunk -O0 -S program.c ; clang-trunk -O0 -c program.s ; objdump
--disassemble --section=.text program.o > s.txt
$ diff s.txt no_s.txt
12,18c12,16
< c: 74 02 je 10 <b+0x10>
< e: eb 00 jmp 10 <b+0x10>
< 10: 5d pop %rbp
< 11: c3 retq
< 12: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
< 19: 00 00 00
< 1c: 0f 1f 40 00 nopl 0x0(%rax)
---
<span class="quote">> c: 0f 84 05 00 00 00 je 17 <b+0x17>
> 12: e9 00 00 00 00 jmpq 17 <b+0x17>
> 17: 5d pop %rbp
> 18: c3 retq
> 19: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)</span ></pre>
</div>
</p>
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