Similar to the bmethod/send optimization, this avoids using CALLER_ARG_SPLAT if not necessary. As long as the receiver argument can be shifted off, other arguments are passed through as-is. This optimizes the following types of calls: * symproc.(recv) ~5% * symproc.(recv, *args) ~65% for args.length == 200 * symproc.(recv, *args, **kw) ~45% for args.length == 200 * symproc.(recv, **kw) ~30% * symproc.(recv, kw: 1) ~100% Note that empty argument splats do get slower with this approach, by about 2-3%. This is probably because iseq argument setup is slower for empty argument splats than CALLER_SETUP_ARG is. Other than non-empty argument splats, other argument splats are faster, with the speedup depending on the number of arguments. The following types of calls are not optimized: * symproc.(*args) * symproc.(*args, **kw) This is because the you cannot shift the receiver argument off without first splatting the arg.