[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 #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
It doesn't help that the ADDR_EXPR is rendered as &*a.1_9[2] when it should be
&(*a.1_9)[2] because a.1_9 is a pointer to a char[n] array.  With the
parenthesization the problem becomes more apparent (to me, anyway): the strlen
pass doesn't handle pointers to arrays:

$ cat a.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout a.c
typedef char A8[8];

void f (A8 *pa)
{
  __builtin_strcpy (*pa, "12345");
  if (__builtin_strlen (&(*pa)[2]) != 3)   // not folded
    __builtin_abort ();
}

;; Function f (f, funcdef_no=0, decl_uid=1907, cgraph_uid=1, symbol_order=0)

f (char[8] * pa)
{
  char * _1;
  long unsigned int _2;

  <bb 2> [local count: 1073741824]:
  __builtin_memcpy (pa_4(D), "12345", 6);
  _1 = &*pa_4(D)[2];
  _2 = __builtin_strlen (_1);
  if (_2 != 3)
    goto <bb 3>; [0.00%]
  else
    goto <bb 4>; [100.00%]

  <bb 3> [count: 0]:
  __builtin_abort ();

  <bb 4> [local count: 1073741824]:
  return;

}