Provide a minimal set of RISC-V instructions that may be used to implement the following pseudoinstruction: not x5, x6 // bit-wise invert

The RISC-V ISA does not have a NOT instruction for bit-wise inversion of a register. However, we can still implement this operation using a combination of other RISC-V instructions. One possible set of instructions that can be used to implement the bit-wise inversion operation for registers x5 and x6 are:

    xori x5, x6, -1

Explanation:

The `xori` instruction performs a bit-wise Exclusive-OR operation between the source register `x6` and the immediate value `-1`, which is represented in binary as all 1's. This has the effect of inverting all the bits in `x6` and storing the result in `x5`. Therefore, the above instruction is equivalent to the pseudoinstruction `not x5, x6` in terms of bit-wise inversion.

Note that the above instruction assumes that the initial value of register `x6` is zero-extended to 32 bits. If `x6` contains a value that is sign-extended to 32 bits, we need to use a different immediate value for the `xori` instruction. For example, if `x6` contains the value -1 (represented in binary as all 1's), we can use the immediate value 0 instead of -1, like this:

    xori x5, x6, 0

This will perform the same bit-wise inversion operation as before, but with the correct immediate value for sign-extended register values.