[Bug tree-optimization/50382] New: Reassoc doesn't optimize pointer arithmetics

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50382

             Bug #: 50382
           Summary: Reassoc doesn't optimize pointer arithmetics
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: ja...@gcc.gnu.org


This is something I've noticed while writing strlen optimization.
Reassoc doesn't optimize:
typedef __UINTPTR_TYPE__ uintptr_t;

char *
foo (char *p, const char *q, const char *r)
{
  char *a = p + __builtin_strlen (p);
  char *b = __builtin_stpcpy (a, q);
  uintptr_t c = (uintptr_t) b - (uintptr_t) p;
  __builtin_memcpy (b, "abcd", 4);
  uintptr_t d = c + 4;
  return __builtin_stpcpy (p + d, r);
}

and only RTL passes figure out that p + d is b + 4.