[llvm-bugs] [Bug 43955] New: Wrong debug info generated at -O3 (-O0 is correct)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43955

            Bug ID: 43955
           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 5. However, compiled with "-O3", lldb
outputs 0.



$ 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
abc.c:6:13: warning: implicitly declaring library function 'printf' with type
'int (const char *, ...)' [-Wimplicit-function-declaration]
void f(g) { printf("%X\n", g); }
            ^
abc.c:6:13: note: include the header <stdio.h> or explicitly provide a
declaration for 'printf'
1 warning generated.
$ lldb-trunk -s cmds -b a.out 
(lldb) target create "a.out"
Current executable set to '/home/sding/LLDB-testing/reduce/30972/report/a.out'
(x86_64).
(lldb) command source -s 0 'cmds'
Executing commands in '/home/sding/LLDB-testing/reduce/30972/report/cmds'.
(lldb) b 25
Breakpoint 1: where = a.out`main + 781 at abc.c:25:7, address =
0x000000000040083d
(lldb) r
Process 21519 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x000000000040083d a.out`main at abc.c:25:7
   22     for (; i < 5; i++)
   23       h(e[i]);
   24     h(1);
-> 25     f(b ^ 5); // optimize_me_not0
   26   }

Process 21519 launched: '/home/sding/LLDB-testing/reduce/30972/report/a.out'
(x86_64)
(lldb) p i
(int) $0 = 0



$ clang-trunk -g abc.c -O0
abc.c:6:13: warning: implicitly declaring library function 'printf' with type
'int (const char *, ...)' [-Wimplicit-function-declaration]
void f(g) { printf("%X\n", g); }
            ^
abc.c:6:13: note: include the header <stdio.h> or explicitly provide a
declaration for 'printf'
1 warning generated.
$ lldb-trunk -s cmds -b a.out 
(lldb) target create "a.out"
Current executable set to '/home/sding/LLDB-testing/reduce/30972/report/a.out'
(x86_64).
(lldb) command source -s 0 'cmds'
Executing commands in '/home/sding/LLDB-testing/reduce/30972/report/cmds'.
(lldb) b 25
Breakpoint 1: where = a.out`main + 164 at abc.c:25:5, address =
0x0000000000400634
(lldb) r
Process 29588 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x0000000000400634 a.out`main at abc.c:25:5
   22     for (; i < 5; i++)
   23       h(e[i]);
   24     h(1);
-> 25     f(b ^ 5); // optimize_me_not0
   26   }

Process 29588 launched: '/home/sding/LLDB-testing/reduce/30972/report/a.out'
(x86_64)
(lldb) p i
(int) $0 = 5



$ cat abc.c 
int a[56];
int b;
short c;
static int d;
static int e[] = {4, 0, 4, 0, 4};
void f(g) { printf("%X\n", g); }
void h(g) {
  b = b & 4095 ^ a[(b ^ g) & 255];
  b = b & 4095 ^ a[(b ^ 8) & 255];
  b = b & 4095 ^ a[(b ^ 6) & 5];
}
int main() {
  int i, j;
  i = 0;
  h(c);
  for (; i < 3; i++) {
    j = 0;
    for (; j < 2; j++)
      h(d);
  }
  i = 0;
  for (; i < 5; i++)
    h(e[i]);
  h(1);
  f(b ^ 5); // optimize_me_not0
}



$ cat cmds
b 25
r
p i
kill
q

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