[Bug middle-end/30778] New: [4.3 Regression] invalid code generation for memset() with -mtune=k8

["belyshev at depni dot sinp dot msu dot ru" <gcc-bugzilla@gcc.gnu.org>]

Reduced from combine.c, fails if compiled with "-O1 -mtune=k8", doesn't fail
with "-O1 -mtune=generic".
possibly introduced between r119211 and r119769 (not sure about this).

// -------------------8<-------------------------------------------------------
extern void *memset (void *, int, unsigned long);
extern void abort (void);

struct reg_stat {
  void *last_death;
  void *last_set;
  void *last_set_value;
  int   last_set_label;
  char  last_set_sign_bit_copies;
  int   last_set_mode : 8;
  char  last_set_invalid;
  char sign_bit_copies;
  long nonzero_bits;
};

static struct reg_stat *reg_stat;

void __attribute__((noinline))
init_reg_last (void)
{
  memset (reg_stat, 0, __builtin_offsetof (struct reg_stat, sign_bit_copies));
}

int main (void)
{
  struct reg_stat r;

  reg_stat = &r;
  r.nonzero_bits = -1;
  init_reg_last ();
  if (r.nonzero_bits != -1)
    abort ();
  return 0;
}
// ------------------->8-------------------------------------------------------


-- 
           Summary: [4.3 Regression] invalid code generation for memset()
                    with -mtune=k8
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: belyshev at depni dot sinp dot msu dot ru
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30778