ISA change proposal: allow predicate manipulation in second issue slot

[Emoun]

This issue will track the discussion into changing the Patmos ISA to allow predicate manipulation instructions in the second issue slot.

Motivation

Like #73, there is no technical reason for disallowing predicate manipulation instructions in the second issue slot. Allowing them could bring benefit in many ways, however, for single-path code especially, which has many independent predicate manipulation instructions, this could bring significant improvements

Todo:

• Implement in simulator
• Benchmark on simulator

[Emoun]

Did some quick testing using inline assembly and it seems to me that both the new compiler and the simulator accept bit-manipulation instructions in the second issue slot. Tested comparisons, pand, and por and they were accepted and worked correctly.

[schoeberl]

Ok, then "only" the hardware has to implement it ;-)