[llvm-bugs] [Bug 41628] New: Clang-trunk Generates Wrong Debug values with -O1

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41628

            Bug ID: 41628
           Summary: Clang-trunk Generates Wrong Debug values with -O1
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Keywords: wrong-debug
          Severity: enhancement
          Priority: P
         Component: DebugInfo
          Assignee: unassignedbugs at nondot.org
          Reporter: yuanboli233 at gmail.com
                CC: davide at freebsd.org, jdevlieghere at apple.com,
                    keith.walker at arm.com, llvm-bugs at lists.llvm.org,
                    paul_robinson at playstation.sony.com

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 (https://llvm.org/svn/llvm-project/lldb/trunk 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)

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