https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116834
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Jump threading introduces the code:
```
<bb 2> [local count: 1073741824]:
if (fmt_2(D) == 0B)
goto <bb 4>; [0.00%]
else
goto <bb 3>; [100.00%]
<bb 3> [local count: 1073741824]:
# .MEM_8 = VDEF <.MEM_1(D)>
vsnprintf (0B, 0, fmt_2(D), ap); [tail call]
# VUSE <.MEM_8>
return;
<bb 4> [count: 0]:
# .MEM_6 = VDEF <.MEM_1(D)>
__builtin___ubsan_handle_nonnull_arg (&*.Lubsan_data0);
# .MEM_3 = VDEF <.MEM_6>
vsnprintf (0B, 0, 0B, ap);
# .MEM_4 = VDEF <.MEM_3>
abort ();
```
Obvious if you place the check for fmt before the vsnprintf there will be no
warning.
Can you provide the original case?
