Similar to the bmethod optimization, this avoids using CALLER_ARG_SPLAT if not necessary. As long as the method argument can be shifted off, other arguments are passed through as-is. This optimizes the following types of calls: * send(meth, arg) ~5% * send(meth, *args) ~75% for args.length == 200 * send(meth, *args, **kw) ~50% for args.length == 200 * send(meth, **kw) ~25% * send(meth, kw: 1) ~115% Note that empty argument splats do get slower with this approach, by about 20%. 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: * send(*args) * send(*args, **kw) This is because the you cannot shift the method argument off without first splatting the arg.