[Bug tree-optimization/90662] strlen of a string in a vla plus offset not folded

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90662

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
The inequality in g() should be != 3, not != 5:

  void g (int n)
  {
    char a[n];
    __builtin_strcpy (a, "12345");
    if (__builtin_strlen (&a[2]) != 3)   // not folded
      __builtin_abort ();
  }

The expression '&*a.1_9[2]' in the GIMPLE can be traced to the original IL
(below).  I wonder how many other transformations make the same assumption as
strlen that such ADDR_EXPRs are simplified into POINTER_PLUS_EXPRs.

;; Function g (null)
;; enabled by -tree-original


{
  char a[0:(sizetype) ((long int) SAVE_EXPR <n> + -1)];

  (void) SAVE_EXPR <n>;
    char a[0:(sizetype) ((long int) SAVE_EXPR <n> + -1)];
  __builtin_strcpy ((char *) &a, (const char *) "12345");
  if (__builtin_strlen ((const char *) &a[2]) != 3)
    {
      __builtin_abort ();
    }
}


;; Function h (null)
;; enabled by -tree-original


{
  char * a = (char *) __builtin_malloc (6);

    char * a = (char *) __builtin_malloc (6);
  __builtin_strcpy (a, (const char *) "12345");
  if (__builtin_strlen ((const char *) (a + 2)) != 3)
    {
      __builtin_abort ();
    }
}