Added implementation for aarch64 NEGS instruction

[su-vikas]

I have added implementation for negs instruction. As per ARM ARM, NEGS is an alias of SUBS instruction.

I have copied the CMP instruction, as CMP is also an alias of SUBS. Let me know if I got it right.

[su-vikas]

For your testing purposes, instruction is "FF 03 0A 6B", IDA shows it as CMP WZR, W10, probably aliasing it. The encoding looks to be of NEGS.

[commial]

I have copied the CMP instruction, as CMP is also an alias of SUBS

Does CMP also update the destination?

[su-vikas]

No, CMP discards the results and just updates the condition flags.

[commial]

So it isn't an alias of SUBS, right? Or maybe I misunderstood your sentence

[su-vikas]

As per ARM documentation, NEGS and CMP are alias of SUBS - but NEGS and CMP discard the result. http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0802b/NEGS_SUBS_addsub_shift.html

If you ask me, I don't think alias is the right word to use. But documentation states so, thus I use it as well.