How to define vzero and vreinterpret

[WilliamWangPeng]

How to define vzero and vreinterpret

[rdolbeau]

Those intrinsics don't correspond to an actual instruction. They are here to help with writing high-level code.

̀vzero outputs an all-zero vector (of the appropriate type), i.e. __builtin_riscv_vzero_i8m1() outputs a zero-valued vint8m1_t. The compiler has some freedom on how to achieve that (using a zero-generating idiom like xor a,a,a, reusing a previously-known-to-be-zero vector, etc.)

vreinterpret like ___builtin_riscv_vreinterpret_i64_u64m2 merely changes the high-level types without changing any bit in the vector. In this case it merely changes the 'signedness' of the type, reinterpreting vint64m2_t to vuint64m2_t.

Both are described as 'utilisy functions' in https://github.com/riscv/rvv-intrinsic-doc/blob/master/rvv-intrinsic-rfc.md#utility-functions