[Bug tree-optimization/80934] New: bzero should be assumed not to escape pointer argument

["msebor at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80934

            Bug ID: 80934
           Summary: bzero should be assumed not to escape pointer argument
           Product: gcc
           Version: 7.0
            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: ---

Similarly to a call to memset, a call to bzero can be assumed not to escape its
pointer argument.  GCC takes advantage of this knowledge by optimizing function
h() below but it doesn't do the same for function g(), even though it could. 
See also bug 80933 for another missed optimization related to bzero.

$ cat a.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout a.c
void f (void);

void g (void)
{
  char d[32];
  __builtin_bzero (d, sizeof d);
  f ();
  if (*d != 0)
    __builtin_abort ();
}

void h (void)
{
  char d[32];
  __builtin_memset (d, 0, sizeof d);
  f ();
  if (*d != 0)
    __builtin_abort ();
}



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

g ()
{
  char d[32];
  char _1;

  <bb 2> [100.00%]:
  __builtin_bzero (&d, 32);
  f ();
  _1 = d[0];
  if (_1 != 0)
    goto <bb 3>; [0.04%]
  else
    goto <bb 4>; [99.96%]

  <bb 3> [0.04%]:
  __builtin_abort ();

  <bb 4> [99.96%]:
  d ={v} {CLOBBER};
  return;

}



;; Function h (h, funcdef_no=1, decl_uid=1799, cgraph_uid=1, symbol_order=1)

h ()
{
  <bb 2> [100.00%]:
  f (); [tail call]
  return;

}