[Bug c/79691] -Wformat-truncation suppressed by (and only by) -Og

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79691

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic,
                   |                            |missed-optimization
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2017-02-23
                 CC|                            |msebor at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |msebor at gcc dot 
gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed for the missing diagnostic
(https://gcc.gnu.org/ml/gcc/2017-02/msg00105.html).

It's a also a missed optimization because, as can be seen in the test case
below, the sprintf return value optimization isn't done:

$ (set -x && cat t.c && for O in 1 g; do gcc -O$O -S -Wall -Wextra -Wpedantic
-fdump-tree-optimized=/dev/stdout t.c; done)
+ cat t.c
int f (void)
{
  return __builtin_snprintf (0, 0, "%i", 123);
} 
+ for O in 1 g
+ gcc -O1 -S -Wall -Wextra -Wpedantic -fdump-tree-optimized=/dev/stdout t.c

;; Function f (f, funcdef_no=0, decl_uid=1795, cgraph_uid=0, symbol_order=0)

f ()
{
  <bb 2> [100.00%]:
  return 3;

}


+ for O in 1 g
+ gcc -Og -S -Wall -Wextra -Wpedantic -fdump-tree-optimized=/dev/stdout t.c

;; Function f (f, funcdef_no=0, decl_uid=1795, cgraph_uid=0, symbol_order=0)

f ()
{
  int _3;

  <bb 2> [100.00%]:
  _3 = __builtin_snprintf (0B, 0, "%i", 123);
  return _3;

}