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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 - Clang-trunk Generates Wrong Debug values with -O1"
href="https://bugs.llvm.org/show_bug.cgi?id=41628">41628</a>
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<th>Summary</th>
<td>Clang-trunk Generates Wrong Debug values with -O1
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Keywords</th>
<td>wrong-debug
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>DebugInfo
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>yuanboli233@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>davide@freebsd.org, jdevlieghere@apple.com, keith.walker@arm.com, llvm-bugs@lists.llvm.org, paul_robinson@playstation.sony.com
</td>
</tr></table>
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<pre>This problem also affects O2 and O3
$ clang-trunk --version
clang version 9.0.0 (trunk 355785)
Target: x86_64-unknown-linux-gnu
Thread model: posix
$ lldb-trunk --version
lldb version 9.0.0 (<a href="https://llvm.org/svn/llvm-project/lldb/trunk">https://llvm.org/svn/llvm-project/lldb/trunk</a> revision
355785)
clang revision 355785
llvm revision 355785
$ cat abc.c
static char a(int p_15) {
optimize_me_not();
return p_15;
}
int main() { a(2534103781 | 1677553596); }
$ cat outer.c
optimize_me_not() {}
$ cat cmds
b 2
r
p p_15
kill
q
$ clang-trunk -g -O0 abc.c outer.c
$ lldb-trunk -s cmds -b a.out
(lldb) target create "a.out"
Current executable set to 'a.out' (x86_64).
(lldb) command source -s 0 'cmds'
Executing commands in '/home/ybli/Projects/LLDB-testing/reduce.llvm/cmds'.
(lldb) b 2
Breakpoint 1: where = a.out`a + 11 at abc.c:2:3, address = 0x00000000004004ab
(lldb) r
Process 31358 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
frame #0: 0x00000000004004ab a.out`a(p_15=-134250499) at abc.c:2:3
1 static char a(int p_15) {
-> 2 optimize_me_not();
3 return p_15;
4 }
5 int main() { a(2534103781 | 1677553596); }
Process 31358 launched: '/home/ybli/Projects/LLDB-testing/reduce.llvm/a.out'
(x86_64)
(lldb) p p_15
(int) $0 = -134250499
(lldb) kill
Process 31358 exited with status = 9 (0x00000009)
(lldb) q
$ clang-trunk -g -O1 abc.c outer.c
$ lldb-trunk -s cmds -b a.out
(lldb) target create "a.out"
Current executable set to 'a.out' (x86_64).
(lldb) command source -s 0 'cmds'
Executing commands in '/home/ybli/Projects/LLDB-testing/reduce.llvm/cmds'.
(lldb) b 2
Breakpoint 1: where = a.out`a at abc.c:2:3, address = 0x0000000000400490
(lldb) r
Process 21531 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
frame #0: 0x0000000000400490 a.out`a(p_15=-3) at abc.c:2:3
1 static char a(int p_15) {
-> 2 optimize_me_not();
3 return p_15;
4 }
5 int main() { a(2534103781 | 1677553596); }
Process 21531 launched: '/home/ybli/Projects/LLDB-testing/reduce.llvm/a.out'
(x86_64)
(lldb) p p_15
(int) $0 = -3
(lldb) kill
Process 21531 exited with status = 9 (0x00000009)
(lldb) q
pass bisection suggests that this problem is related to Tail Call Elimination:
working:
BISECT: running pass (30) Combine redundant instructions on function (a)
BISECT: NOT running pass (31) Tail Call Elimination on function (a)
not working:
BISECT: running pass (30) Combine redundant instructions on function (a)
BISECT: running pass (31) Tail Call Elimination on function (a)</pre>
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