[PATCH] ARM: Fix VEXT encoding

[Tim Northover]

Hi Amaury,

> This patch enforces the following rule at the MC layer for the VEXT instruction:
> 
> A8.8.316 VEXT
> if Q == '0' && imm4<3> == '1' then UNDEFINED;

Looks good to me with one modification: "index" is now only three bits so you should probably change its declaration to "bits<3> index". Just might stop someone scratching their head a bit later.

> When not used as a quadword operation, VEXT's imm4 operand must be of the form 0b1xxx.

Don't you mean 0b0xxx? If not, I may have misunderstood everything.

Tim.