profiledbootstrap currently fails on i386, with --enable-checking=release rtl.c (copy_rtx) is miscompiled (after giving a bogus warning that copy is uninitialized (well, in the generated code it is), with checking it ICEs:
../../gcc/rtl.c: In function ‘copy_rtx’:
../../gcc/rtl.c:236:1: error: SSA_NAME_DEF_STMT is wrong
Expected definition statement:
# .MEM_93 = VDEF <.MEM_91>
    D.27976_89 = memcpy (copy.26_86, orig.25_85, 12);

Actual definition statement:
# .MEM_92 = VDEF <.MEM_91>
    D.27976_89 = memcpy (copy.26_86, orig.25_85, D.27973_83);
../../gcc/rtl.c:236:1: internal compiler error: verify_ssa failed
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.

This is caused by a bug in gimple_stringop_fixed_value where it doesn't handle lhs properly.  Small testcase:
char buf[64];
char buf2[64];

void *
foo (char *p, long size)
{
  return __builtin_memcpy (buf, p, size);
}

int
main (void)
{
  long i;
  for (i = 0; i < 65536; i++)
    if (foo ("abcdefghijkl", 12) != buf)
      __builtin_abort ();
  if (foo (buf2, 64) != buf)
    __builtin_abort ();
  return 0;
}

./xgcc -B ./ -O2 -fprofile-generate test.c -o test
./test
./xgcc -B ./ -O2 -fprofile-use test.c -o test