[Bug tree-optimization/84577] New: snprintf with null buffer not eliminated when return value is in a known range

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84577

            Bug ID: 84577
           Summary: snprintf with null buffer not eliminated when return
                    value is in a known range
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The sprintf pass eliminates snprintf calls with a null buffer and zero size
when whose return value is a constant but it does not eliminate calls whose
return value is in some range.  Both calls can be eliminated.

$ cat b.c && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout b.c
void f (void)
{
  int n = __builtin_snprintf (0, 0, "%hhx", 123);   // eliminated
  if (n < 0 || 2 < n)
    __builtin_abort ();
}

void g (int i)
{
  int n = __builtin_snprintf (0, 0, "%hhx", i);   // not eliminated but could
be
  if (n < 0 || 2 < n)
    __builtin_abort ();
}


;; Function f (f, funcdef_no=0, decl_uid=1957, cgraph_uid=0, symbol_order=0)

f ()
{
  <bb 2> [local count: 1073741825]:
  return;

}



;; Function g (g, funcdef_no=1, decl_uid=1961, cgraph_uid=1, symbol_order=1)

g (int i)
{
  <bb 2> [local count: 1073741825]:
  __builtin_snprintf (0B, 0, "%hhx", i_3(D)); [tail call]
  return;

}