[Bug tree-optimization/86428] New: strlen of const array initialized with a string of the same length not folded

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86428

            Bug ID: 86428
           Summary: strlen of const array initialized with a string of the
                    same length not folded
           Product: gcc
           Version: 9.0
            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 constant array arguments initialized with strings
fewer elements than the size of the array, but not those initialized with
strings with either a) the same number of elements or b) more.  (a) is a
missing optimization opportunity, (b) results in unsafe code (reading past the
end of the array).

Clang folds all three kinds of strlen calls.

$ cat c.c && gcc -O2 -S -Wall -Wextra -fdump-tree-strlen=/dev/stdout c.c
const char a[4] = "123";

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

const char b[4] = "123\0";       // no warning

int g (void)
{
  return __builtin_strlen (b);   // not folded
}


;; Function f (f, funcdef_no=0, decl_uid=1899, cgraph_uid=1, symbol_order=1)

f ()
{
  <bb 2> [local count: 1073741825]:
  return 3;

}



;; Function g (g, funcdef_no=1, decl_uid=1903, cgraph_uid=2, symbol_order=3)

g ()
{
  long unsigned int _1;
  int _3;

  <bb 2> [local count: 1073741825]:
  _1 = __builtin_strlen (&b);
  _3 = (int) _1;
  return _3;

}