[Bug tree-optimization/84339] New: [8 Regression] Wrong-code with optimizing strlen

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84339

            Bug ID: 84339
           Summary: [8 Regression] Wrong-code with optimizing strlen
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
  Target Milestone: ---

Hunspell's test alias3 fails.  Distilled testcase:

typedef __SIZE_TYPE__ size_t;
struct S { int a; char b[1]; };

__attribute__((noipa)) size_t
foo (struct S *p)
{
  return __builtin_strlen (&p->b[0]);
}

__attribute__((noipa)) size_t
bar (struct S *p)
{
  return __builtin_strlen (p->b);
}

int
main ()
{
  struct S *p = __builtin_malloc (sizeof (struct S) + 16);
  if (p)
    {
      p->a = 1;
      __builtin_strcpy (p->b, "abcdefg");
      if (foo (p) != 7 || bar (p) != 7)
        __builtin_abort ();
      __builtin_free (p);
    }
  return 0;
}

Started with r256457.