In the following function:

bool Compile::can_generate_C2I(ciMethod* method, int compiled_arg_size) {
  int slots = in_preserve_stack_slots();
  slots = round_to(slots, 1UL << (Matcher::stack_alignment() - LogBitsPerInt));
  // slots == reg2stack(_old_SP of adapter)
  slots += out_preserve_stack_slots();
  slots += round_to(compiled_arg_size, RegMask::SlotsPerLong);
  // slots == reg2stack(_new_SP of adapter)
  slots += out_preserve_stack_slots();
  slots += method->arg_size() * (wordSize/jintSize);
  // All of the preceding stack slots must be bind-able in a regmask.
  return RegMask::can_represent(SharedInfo::stack2reg(slots));
}

The last line should use "slot - 1" instead of "slot", because the slots are 0 based.