[llvm-bugs] [Bug 42170] New: Clang-trunk produce incorrect debug info under O1

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42170

            Bug ID: 42170
           Summary: Clang-trunk produce incorrect debug info under 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: aprantl at apple.com, 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, vsk at apple.com

$ 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
int b;
short(a)(c) { return c; }
int main() {
  short d;
  int e, p_40 = 0;
  e = b + 1;
  d = 26900 + e;
  p_40 = d;
  optimize_me_not();
  a(p_40);
}

$ cat outer.c
optimize_me_not() {}

$ cat cmds
b 9
r
p p_40
kill
q

The debug info is correct under O0:

$ clang-trunk abc.c outer.c -O0 -g

$ 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 9
Breakpoint 1: where = a.out`main + 50 at abc.c:9:3, address =
0x00000000004004c2
(lldb) r
Process 27402 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x00000000004004c2 a.out`main at abc.c:9:3
   6      e = b + 1;
   7      d = 26900 + e;
   8      p_40 = d;
-> 9      optimize_me_not();
   10     a(p_40);
   11   }

Process 27402 launched: '/home/ybli/Projects/LLDB-testing/reduce.llvm/a.out'
(x86_64)
(lldb) p p_40
(int) $0 = 26901
(lldb) kill
Process 27402 exited with status = 9 (0x00000009) 
(lldb) q

Under O1 the debug info is not correct:

$ clang-trunk abc.c outer.c -O1 -g

$ 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 9
Breakpoint 1: where = a.out`main + 1 at abc.c:9:3, address = 0x0000000000400491
(lldb) r
Process 9582 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x0000000000400491 a.out`main at abc.c:9:3
   6      e = b + 1;
   7      d = 26900 + e;
   8      p_40 = d;
-> 9      optimize_me_not();
   10     a(p_40);
   11   }

Process 9582 launched: '/home/ybli/Projects/LLDB-testing/reduce.llvm/a.out'
(x86_64)
(lldb) p p_40
(int) $0 = 0
(lldb) kill
Process 9582 exited with status = 9 (0x00000009) 
(lldb) q

Bisection suggest it is possibly related to "Deduce function attributes on SCC"
produce correct results:
BISECT: running pass (18) Remove unused exception handling info on SCC (a)
BISECT: NOT running pass (19) Deduce function attributes on SCC (a)

produce inccorect results:
BISECT: running pass (18) Remove unused exception handling info on SCC (a)
BISECT: running pass (19) Deduce function attributes on SCC (a)

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