[Bug debug/95047] New: Wrong debug information for ternary operator at O0

[Bug debug/95047] New: Wrong debug information for ternary operator at O0

[massarelli at diag dot uniroma1.it]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95047

            Bug ID: 95047
           Summary: Wrong debug information for ternary operator at O0
           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: ---

Debug information for ternary operator seems wrong at O0.

$ 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 20200508 (experimental) (GCC) 

$ lldb -v
  lldb version 11.0.0
  clang revision 23cbea9a04e023d5b79dfee5964fae769340c993
  llvm revision 23cbea9a04e023d5b79dfee5964fae769340c993

$ cat a.c
short a;
short
b( left,  right )
{
  return
    ((left < 0) || (((int)right) < 0) || (((int)right) >= 32) || (left >
((32767) >> ((int)right)))) ?
    0 :
    left
;
}
int main ()
{
    a = b(4294967286 , 5);
}

$ gcc -O0 -g a.c

$ lldb a.out

* thread #1, name = 'a.out', stop reason = breakpoint 2.1
    frame #0: 0x00000000004004c1 unopt`main at a.c:13:9
   10   }
   11   int main ()
   12   {
-> 13       a = b(4294967286 , 5);
   14   }
(lldb) s
Process 78 stopped
* thread #1, name = 'a.out', stop reason = step in
    frame #0: 0x000000000040048c unopt`b(left=-10, right=5) at a.c:7:7
   4    {
   5      return
   6        ((left < 0) || (((int)right) < 0) || (((int)right) >= 32) || (left
> ((32767) >> ((int)right)))) ?
-> 7        0 :
   8        left
   9    ;
   10   }
(lldb) s
Process 78 stopped
* thread #1, name = 'a.out', stop reason = step in
    frame #0: 0x00000000004004bb unopt`b(left=-10, right=5) at a.c:10:1
   7        0 :
   8        left
   9    ;
-> 10   }
   11   int main ()
   12   {
   13       a = b(4294967286 , 5);
(lldb) s
Process 78 stopped
* thread #1, name = 'a.out', stop reason = step in
    frame #0: 0x00000000004004d5 unopt`main at a.c:13:7
   10   }
   11   int main ()
   12   {
-> 13       a = b(4294967286 , 5);
   14   }

[Bug debug/95047] Wrong debug information for ternary operator at O0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95047

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC puts the line information as the line/collumn as the ':' part of the
ternary 
 opertator.

  <bb 2> :
  [t666.c:7:7] if (left_3(D) >= 0)
    goto <bb 3>; [INV]
  else
    goto <bb 7>; [INV]

  <bb 3> :
  [t666.c:6:17] if (right_4(D) >= 0)
    goto <bb 4>; [INV]
  else
    goto <bb 7>; [INV]

  <bb 4> :
  [t666.c:6:39] if (right_4(D) <= 31)
    goto <bb 5>; [INV]
  else
    goto <bb 7>; [INV]

  <bb 5> :
  [t666.c:6:83] _1 = 32767 >> right_4(D);
  [t666.c:6:63] if (left_3(D) <= _1)
    goto <bb 6>; [INV]
  else
    goto <bb 7>; [INV]

  <bb 6> :
  [t666.c:7:7] iftmp.0_5 = (short int) left_3(D);
  [t666.c:7:7] goto <bb 8>; [INV]

  <bb 7> :
  [t666.c:7:7] iftmp.0_6 = 0;

  <bb 8> :
  # iftmp.0_2 = PHI <[t666.c:7:7] iftmp.0_5(6), [t666.c:7:7] iftmp.0_6(7)>
  [t666.c:7:7] _7 = iftmp.0_2;

[Bug debug/95047] Wrong debug information for ternary operator at O0

[massarelli at diag dot uniroma1.it]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95047

--- Comment #2 from Luca Massarelli <massarelli at diag dot uniroma1.it> ---
Ok, so it seems that there is an inconsistency with -Og:

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

$ lldb opt
* thread #1, name = 'opt', stop reason = breakpoint 1.1
    frame #0: 0x00000000004004bb opt`main at a.c:13:9
   10   }
   11   int main ()
   12   {
-> 13       a = b(4294967286 , 5);
   14   }
(lldb) s
Process 101 stopped
* thread #1, name = 'opt', stop reason = step in
    frame #0: 0x0000000000400482 opt`b(left=-10, right=5) at a.c:6:12
   3    b( left,  right )
   4    {
   5      return
-> 6        ((left < 0) || (((int)right) < 0) || (((int)right) >= 32) || (left
> ((32767) >> ((int)right)))) ?
   7        0 :
   8        left
   9    ;
(lldb) s
Process 101 stopped
* thread #1, name = 'opt', stop reason = step in
    frame #0: 0x0000000000400490 opt`b(left=-10, right=5) at a.c:7:7
   4    {
   5      return
   6        ((left < 0) || (((int)right) < 0) || (((int)right) >= 32) || (left
> ((32767) >> ((int)right)))) ?
-> 7        0 :
   8        left
   9    ;
   10   }
(lldb) s
Process 101 stopped
* thread #1, name = 'opt', stop reason = step in
    frame #0: 0x00000000004004cf opt`main at a.c:13:7
   10   }
   11   int main ()
   12   {
-> 13       a = b(4294967286 , 5);
   14   }

[Bug debug/95047] Wrong debug information for ternary operator at O0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95047

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
That is because when GCC does for -Og:
  [t666.c:6:12] _1 = left_6(D) >= 0;
  [t666.c:6:34] _2 = right_7(D) >= 0;
  [t666.c:6:17] _3 = _1 & _2;
  [t666.c:7:7] if (_3 != 0)

This "optimization" happens at early on.  I have not looked into why the line
numbers are different.