You can also pass structs of floating point or SIMD types by register. They have to be 2-4 elements and all of the same type. These are called HFA (Homogeneous

You can also pass structs of floating point or SIMD types by register. They have to be 2-4 elements and all of the same type. These are called HFA (Homogeneous Floating-point Aggregate) and HVA (Homogeneous Short-Vector Aggregate). Source: the Procedure Call Standard for the Arm 64-bit Architecture https://github.com/ARM-software/abi-aa/blob/2021Q1/aapcs64/aapcs64.rst https://github.com/ARM-software/abi-aa/blob/2021Q1/aapcs64/a...