Function core::arch::x86::_blsfill_u64

pub unsafe fn _blsfill_u64(x: u64) -> u64

This is supported on (non-crate feature miri-test-libstd or test or doctest) and x86 and non-x86 and target feature tbm only.

Sets all bits of x below the least significant one.

If there is no set bit in x, it sets all the bits.