[llvm-bugs] [Bug 46120] New: Odd stepping b

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46120

            Bug ID: 46120
           Summary: Odd stepping b
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: DebugInfo
          Assignee: unassignedbugs at nondot.org
          Reporter: massarelli at diag.uniroma1.it
                CC: jdevlieghere at apple.com, keith.walker at arm.com,
                    llvm-bugs at lists.llvm.org,
                    paul_robinson at playstation.sony.com

Line 24 is hit even if it is dead code. Moreover, the stepping behaviour is
odd: from line 13 it jumps to line 24 and then hit lines 18, 19, 21, 22.

$ cat -n a.c
     1  short a,  g_35,  b,  c;
     2  int d,  f ;
     3  static short *g = &g_35;
     4  char h,  i ;
     5  short ciriaco( j,  k ) {
     6       return k;
     7  }
     8  
     9  int main () {
    10  {
    11      int l = 1;
    12      int *l_258 = b;
    13      if (f)  h++;
    14      else {
    15         int *m = &l;
    16         *m = 0;
    17      }
    18      *g &= l;
    19      i = d;
    20      short e = l;
    21      c =  d * e;
    22      if (a)  {
    23         int l_305 ;
    24         (*l_258) = (ciriaco((l_305 != (void*)0), g_35));
    25      }
    26    }
    27  }


$ cat a.c
short a,  g_35,  b,  c;
int d,  f ;
static short *g = &g_35;
char h,  i ;
short ciriaco( j,  k ) {
     return k;
}

int main () {
{
    int l = 1;
    int *l_258 = b;
    if (f)  h++;
    else {
       int *m = &l;
       *m = 0;
    }
    *g &= l;
    i = d;
    short e = l;
    c =  d * e;
    if (a)  {
       int l_305 ;
       (*l_258) = (ciriaco((l_305 != (void*)0), g_35));
    }
  }
}

$ clang -v
clang version 11.0.0 (https://github.com/llvm/llvm-project.git
268fa40daa151d3b4bff1df12b62e5dae94685d7)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Candidate multilib: .;@m64
Selected multilib: .;@m64

$ lldb -v
lldb version 11.0.0
  clang revision 268fa40daa151d3b4bff1df12b62e5dae94685d7
  llvm revision 268fa40daa151d3b4bff1df12b62e5dae94685d7

$ lldb opt 
(lldb) target create "opt"
Current executable set to 'opt' (x86_64).
(lldb) b main
Breakpoint 1: where = opt`main + 1 at a.c:12:18, address = 0x0000000000400491
(lldb) r
Process 65 launched: 'opt' (x86_64)
Process 65 stopped
* thread #1, name = 'opt', stop reason = breakpoint 1.1
    frame #0: 0x0000000000400491 opt`main at a.c:12:18
   9    int main () {
   10   {
   11       int l = 1;
-> 12       int *l_258 = b;
   13       if (f)  h++;
   14       else {
   15          int *m = &l;
(lldb) s
Process 65 stopped
* thread #1, name = 'opt', stop reason = step in
    frame #0: 0x0000000000400499 opt`main at a.c:13:9
   10   {
   11       int l = 1;
   12       int *l_258 = b;
-> 13       if (f)  h++;
   14       else {
   15          int *m = &l;
   16          *m = 0;
(lldb) s
Process 65 stopped
* thread #1, name = 'opt', stop reason = step in
    frame #0: 0x00000000004004b1 opt`main at a.c:24:49
   21       c =  d * e;
   22       if (a)  {
   23          int l_305 ;
-> 24          (*l_258) = (ciriaco((l_305 != (void*)0), g_35));
   25       }
   26     }
   27   }
(lldb) s
Process 65 stopped
* thread #1, name = 'opt', stop reason = step in
    frame #0: 0x00000000004004bb opt`main at a.c:18:8
   15          int *m = &l;
   16          *m = 0;
   17       }
-> 18       *g &= l;
   19       i = d;
   20       short e = l;
   21       c =  d * e;
(lldb) s
Process 65 stopped
* thread #1, name = 'opt', stop reason = step in
    frame #0: 0x00000000004004c5 opt`main at a.c:19:9
   16          *m = 0;
   17       }
   18       *g &= l;
-> 19       i = d;
   20       short e = l;
   21       c =  d * e;
   22       if (a)  {
(lldb) s
Process 65 stopped
* thread #1, name = 'opt', stop reason = step in
    frame #0: 0x00000000004004d1 opt`main at a.c:21:10
   18       *g &= l;
   19       i = d;
   20       short e = l;
-> 21       c =  d * e;
   22       if (a)  {
   23          int l_305 ;
   24          (*l_258) = (ciriaco((l_305 != (void*)0), g_35));
(lldb) s
Process 65 stopped
* thread #1, name = 'opt', stop reason = step in
    frame #0: 0x00000000004004db opt`main at a.c:22:9
   19       i = d;
   20       short e = l;
   21       c =  d * e;
-> 22       if (a)  {
   23          int l_305 ;
   24          (*l_258) = (ciriaco((l_305 != (void*)0), g_35));
   25       }
(lldb) s
Process 65 stopped
* thread #1, name = 'opt', stop reason = step in
    frame #0: 0x00000000004004f0 opt`main at a.c:27:1
   24          (*l_258) = (ciriaco((l_305 != (void*)0), g_35));
   25       }
   26     }
-> 27   }

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