The POWER10 processor, which implements Power ISA 3.1 [1], supports new instruction formats where an instruction takes two 32bit words. The first word is called prefix, and the instructions with prefix are called prefixed instructions. With more bits in opcode and operand fields, POWER10 supports larger immediate value in an operand, as well as many new instructions.

This is the first changes to handle prefixed instructions, and this adds support of prefixed addi (= paddi) instruction as an example of prefix usage. paddi accepts 34bit immediate value, while original addi accepts 16bit value.

I ran jtreg test on POWER10 box by using "make test-tier1" and verified no additional fails.

[1] https://ibm.ent.box.com/s/hhjfw0x0lrbtyzmiaffnbxh2fuo0fog0