[Bug debug/47991] New: [4.6 Regression] Var-tracking ICE on s390x *setmem_long insn

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47991

           Summary: [4.6 Regression] Var-tracking ICE on s390x
                    *setmem_long insn
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: jakub@gcc.gnu.org
        ReportedBy: jakub@gcc.gnu.org
            Target: s390x-linux


/* { dg-do compile } */
/* { dg-options "-g -Os" } */

typedef __SIZE_TYPE__ size_t;
extern inline __attribute__ ((__always_inline__))
void *
memset (void *x, int y, size_t z)
{
  return __builtin___memset_chk (x, y, z, __builtin_object_size (x, 0));
}

void
foo (unsigned char *x, unsigned char *y, unsigned char *z,
     unsigned char *w, unsigned int v, int u, int t)
{
  int i;
  for (i = 0; i < t; i++)
    {
      memset (z, x[0], v);
      memset (w, y[0], v);
      x += u;
    }
  __builtin_memcpy (z, x, u);
}

ICEs on s390x-linux in var-tracking, because
(insn 56 71 57 5 (parallel [
            (clobber (reg:TI 6 %r6))
            (set (mem:BLK (subreg:DI (reg:TI 6 %r6) 0) [0 A8])
                (reg:DI 10 %r10 [95]))
            (use (reg:TI 6 %r6))
            (use (reg:TI 2 %r2))
            (clobber (reg:CC 33 %cc))
        ]) pr47372.i:9 115 {*setmem_long}
     (expr_list:REG_DEAD (reg:DI 10 %r10 [95])
        (expr_list:REG_DEAD (reg:DI 7 %r7)
            (expr_list:REG_UNUSED (reg:CC 33 %cc)
                (expr_list:REG_UNUSED (reg:TI 6 %r6)
                    (nil))))))
is really weird.  But we already allow (set (mem:BLK ...) (const_int ...))
for memset, and while this one is much worse than that, let's workaround it in
var-tracking too.
Not sure if this is a problem in 4.5 too, certainly not in 4.4 which didn't
have VTA.