# New instructions for CR/INT predication

See:

* <https://bugs.libre-soc.org/show_bug.cgi?id=533>

Basic concept:

* CR-based instructions that perform simple AND/OR/XOR from all four bits
  of a CR to create a single bit value (0/1) in an integer register
* Inverse of the same, taking a single bit value (0/1) from an integer
  register to selectively target all four bits of a given CR
* Vectorisation of the same

Purpose:

* To provide a merged version of what is currently a multi-sequence of
  CR operations (crand, cror, crxor) with mfcr and mtcrf
* To provide a vectorised version of the same, suitable for advanced
  predication

# Instruction form and pseudocode

    | 0-5 | 6-10 | 11 | 12-15 | 16-18 | 19-20 | 21-30 | 31 |
    | 19  | RT   | 0  | mask  | BB    |  m2   | XO    | /  |
    | 19  | RT   | 1  | mask  | BB    |  m2   | XO    | /  |

mode is encoded in XO and from m2 to produce 4 bits

bit 11=0:

    crweird: RT, BB, mask.mode

    creg = CRfile[32+BB*4:36+BB*4]
    n0 = mask[1] & (mode[0] == creg[0]
    n1 = mask[1] & (mode[1] == creg[1]
    n2 = mask[2] & (mode[2] == creg[2]
    n3 = mask[3] & (mode[3] == creg[3]
    RT[0] = n0 | n1 | n2 | b3