[Bug debug/95835] New: Wrong line information at Og

[Bug debug/95835] New: Wrong line information at Og

[massarelli at diag dot uniroma1.it]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95835

            Bug ID: 95835
           Summary: Wrong line information at Og
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: massarelli at diag dot uniroma1.it
  Target Milestone: ---

Line information is wrong at line 6. 
Line 6 should not be hit as it is the declaration of variables. 
>From the disassembly, it seems that the program is actually executing line 5.

$ cat a.c
int a ;
int main () {
   for (;
        a < 2;
        a++)  {
        int i, j, k;
   }
}

$ cat -n a.c
     1  int a ;
     2  int main () {
     3     for (;
     4          a < 2;
     5          a++)  {
     6          int i, j, k;
     7     }
     8  }

$ gcc -v 
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/bin/../libexec/gcc/x86_64-pc-linux-gnu/11.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --prefix=/tmp/gcc_build --disable-multilib
--enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 11.0.0 20200619 (experimental) (GCC) 

$ gdb -v
GNU gdb (Ubuntu 8.1-0ubuntu3.2) 8.1.0.20180409-git

$ gcc -Og -g -o opt a.c

$ gdb opt
(gdb) b main
Breakpoint 1 at 0x400486: file a.c, line 3.
(gdb) r
Starting program: opt 
Breakpoint 1, main () at aaa.c:3
3          for (;
(gdb) s
4               a < 2;
(gdb) s
6               int i, j, k;
(gdb) disassemble
Dump of assembler code for function main:
   0x0000000000400486 <+0>:     jmp    0x400491 <main+11>
=> 0x0000000000400488 <+2>:     add    $0x1,%eax
   0x000000000040048b <+5>:     mov    %eax,0x200b9b(%rip)        # 0x60102c
<a>
   0x0000000000400491 <+11>:    mov    0x200b95(%rip),%eax        # 0x60102c
<a>
   0x0000000000400497 <+17>:    cmp    $0x1,%eax
   0x000000000040049a <+20>:    jle    0x400488 <main+2>
   0x000000000040049c <+22>:    mov    $0x0,%eax
   0x00000000004004a1 <+27>:    retq   
End of assembler dump.
(gdb)

[Bug c/95835] Wrong line information at Og

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95835

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-06-23
          Component|debug                       |c
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |wrong-debug

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
In the .gimple dump there's no line 6 on stmt locations but .lower has a new
debug stmt with that line, likely from the goto location of the backedge.

I'm not sure this is "easy" to fix.  Oddly enough at -O0 we don't have
debug stmts and thus this line is not mentioned.