[clang] [llvm] [RISCV] Add support of Zibi experimental extension (PR #127463)

[Craig Topper via cfe-commits]

topperc wrote:

> > > This adds the support of Zibi v0.1 experimental extension.
> > > References:
> > > 
> > > * https://lf-riscv.atlassian.net/wiki/spaces/USXX/pages/599261201/Branch+with+Immediate+Zibi+Ratification+Plan
> > 
> > 
> > I cannot for the life of me find an actual specification linked from that page, nor from searching. Where is the GitHub repo in the riscv organisation with it?
> 
> Sorry, we are still working on the repo. This extension has been approved as fast-track, but we are not familiar with the process (and the process has some changes recently). You may refer to the mailing list (https://lists.riscv.org/g/sig-scalar-efficiency/topic/111893156). We will make all the resouces publicly accessible ASAP, sorry for the inconvenience.

Note the pdf linked there seems to be missing the image that contains the immediate format.

https://github.com/llvm/llvm-project/pull/127463