[llvm-bugs] [Bug 43949] New: Wrong debug info generated at -O3 (-O0 is correct)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43949

            Bug ID: 43949
           Summary: Wrong debug info generated at -O3 (-O0 is correct)
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: shuo.d at outlook.com
                CC: davide at freebsd.org, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

The expected output from lldb should be 0. However, compiled with "-O3", lldb
outputs 5.



$ clang-trunk -v
clang version 10.0.0 (trunk 375507)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.4.0
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/9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64



$ clang-trunk -g abc.c -O3
$ lldb-trunk -s cmds -b a.out 
(lldb) target create "a.out"
Current executable set to '/home/sding/LLDB-testing/reduce/32221/report/a.out'
(x86_64).
(lldb) command source -s 0 'cmds'
Executing commands in '/home/sding/LLDB-testing/reduce/32221/report/cmds'.
(lldb) b 22
Breakpoint 1: where = a.out`main + 671 at abc.c:22:7, address =
0x00000000004007df
(lldb) r
Process 24738 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x00000000004007df a.out`main at abc.c:22:7
   19       h((char)i);
   20     i = 0;
   21     for (; i < 2; i++) {
-> 22       h(d[i]); // optimize_me_not0
   23     }
   24   }

Process 24738 launched: '/home/sding/LLDB-testing/reduce/32221/report/a.out'
(x86_64)
(lldb) p i
(int) $0 = 5



$ clang-trunk -g abc.c -O0
$ lldb-trunk -s cmds -b a.out
(lldb) target create "a.out"
Current executable set to '/home/sding/LLDB-testing/reduce/32221/report/a.out'
(x86_64).
(lldb) command source -s 0 'cmds'
Executing commands in '/home/sding/LLDB-testing/reduce/32221/report/cmds'.
(lldb) b 22
Breakpoint 1: where = a.out`main + 104 at abc.c:22:7, address =
0x00000000004005c8
(lldb) r
Process 30349 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x00000000004005c8 a.out`main at abc.c:22:7
   19       h((char)i);
   20     i = 0;
   21     for (; i < 2; i++) {
-> 22       h(d[i]); // optimize_me_not0
   23     }
   24   }

Process 30349 launched: '/home/sding/LLDB-testing/reduce/32221/report/a.out'
(x86_64)
(lldb) p i
(int) $0 = 0



$ cat abc.c
int a[256];
int b, c;
static int d[] = {0, -4L};
void e(f) { b = b & 4095 ^ a[(b ^ f) & 5]; }
void h(f) {
  unsigned long g = f;
  b = b & 4095 ^ a[(b ^ g) & 255];
  e(g >> 8);
  e(g >> 6);
  e(g >> 4);
  e(g >> 2);
  e(g >> 56);
}
int main() {
  int i = 0;
  if (c)
    d[1] = 3;
  for (; i < 5; i++)
    h((char)i);
  i = 0;
  for (; i < 2; i++) {
    h(d[i]); // optimize_me_not0
  }
}



$ cat cmds
b 22
r
p i
kill
q

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