codegen.c: add a comment that notice `rewind_pc` calling convention.
`rewind_pc` should not be called when `s->pc` is `0` (top).
@@ -463,8 +463,8 @@ mrb_prev_pc(codegen_scope *s, const mrb_code *pc)
static void
rewind_pc(codegen_scope *s)
{
- const mrb_code *pc = mrb_prev_pc(s, pc_addr(s));
- s->pc = addr_pc(s, pc);
+ /* should not be called when s->pc is 0 (top) */
+ s->pc = addr_pc(s, mrb_prev_pc(s, pc_addr(s)));
}
static struct mrb_insn_data
