[Bug tree-optimization/85724] New: strspn of one-element arrays can be assumed to return zero

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85724

            Bug ID: 85724
           Summary: strspn of one-element arrays can be assumed to return
                    zero
           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: ---

GCC folds strlen() calls with one-element array arguments to zero but it
doesn't do that same for calls to strspn and strcspn with the same arguments
even though they too must return zero (they return the length of a substring in
the first argument).

$ cat u.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout u.c
extern char a[1];

int f (void)
{
  return __builtin_strlen (a);   // folded to 0
}

int g (const char *s)
{
  return __builtin_strspn (a, s);   // not folded
}

int h (const char *s)
{
  return __builtin_strcspn (a, s);   // not folded
}


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

f ()
{
  <bb 2> [local count: 1073741825]:
  return 0;

}



;; Function g (g, funcdef_no=1, decl_uid=1960, cgraph_uid=1, symbol_order=1)

g (const char * s)
{
  long unsigned int _1;
  int _4;

  <bb 2> [local count: 1073741825]:
  _1 = __builtin_strspn (&a, s_3(D));
  _4 = (int) _1;
  return _4;

}



;; Function h (h, funcdef_no=2, decl_uid=1963, cgraph_uid=2, symbol_order=2)

h (const char * s)
{
  long unsigned int _1;
  int _4;

  <bb 2> [local count: 1073741825]:
  _1 = __builtin_strcspn (&a, s_3(D));
  _4 = (int) _1;
  return _4;

}