ko1: thank you for checking, any comment on the extra jumps insns which
I hack around by disabling peephole optimization?

It seems caused by the following in iseq_set_sequence:

		    else if (orig_sp - sp == 0) {
			/* jump to next insn */
			if (last_line != (unsigned int)adjust->line_no) {
			    line_info_table[k].line_no = last_line = adjust->line_no;
			    line_info_table[k].position = pos;
			    k++;
			}
			generated_iseq[pos++] = BIN(jump);
			generated_iseq[pos++] = 0;

My roundtrip test fails because:

	1. iseq_peephole_optimize called in original
	2. iseq_set_sequence generates useless jump (above)
	3. ISeq#to_a called (showing useless jump)
	4. ISeq#load on 3. array
	5. iseq_peephole_optimize now deletes jump emitted in 2.
	6. ISeq#to_a now has no useless jumps

So now I'm trying to figure out how to eliminate the useless jump in 2
so roundtrip test always succeeds (and my normal Ruby code has
no useless jump insns)