The beta ARMv8.3 ISA specifications have been released for AArch64 and AArch32, these can be found at:
https://developer.arm.com/products/architecture/a-profile/exploration-tools
An introduction to this architecture update can be found at:
https://community.arm.com/processors/b/blog/posts/armv8-a-architecture-2016-additions
This patch is the first in a series which will add ARM v8.3-A support in LLVM and Clang. It adds the necessary changes that create targets for both the ARM and AArch64 backends.