The ABI seems to sacrifice performance for the sake of simplicity, which IMHO has little value at such a low level. There's a reason why the x86-64 ABI passes 6

The ABI seems to sacrifice performance for the sake of simplicity, which IMHO has little value at such a low level. There's a reason why the x86-64 ABI passes 6 (4 for the MS variant) machine words via registers! Disappointing. Both D and Go use an unusual convention. The GCC maintainers raised issues over D's ABI during discussions regarding integrating the GCC-based D compiler. I wonder how did this apply to Go's inclusion? Or did GCC support the Plan9 ABI before Go's inclusion?