RISC-V: Add vector state registers by a4lg · Pull Request #2005 · rust-lang/reference (original) (raw)

vxsat (vector fixed-point saturation flag) and vxrm (vector fixed-point rounding mode) are subset, readable/writable mirrors of the vcsr register. Still, adding them to the default preserved register list will improve clarity.

Note that, the reason vxrm (rounding mode register which normally the developer writes) is in the list is, it is not preserved across calls on all ratified ABIs.

Quoting asm.rules.preserves_flags,

As a general rule, the flags covered by preserves_flags are those which are not preserved when performing a function call.