[clang] [llvm] [RISCV] Remove B and Zbc extension from Andes series cpus. (PR #144022)

[Jim Lin via llvm-commits]

tclin914 wrote:

> Not related to this PR, but I'd like to raise the question here:
> 
> For configurable cores, what is the best way to specify the features? `-mcpu` is meant to support the base configuration, but how can we specify the additional optional extensions? Apparently, failing back to `-march` is silly.
> 
> My thought is: can we support `-march/-mcpu` where the values can be `{cpu}(_ext)*`? Will such use be problematic?

Unfortunately, we have to suggest our users to specify both `-march` and `-mcpu` when their processor includes additional optional extensions. Ideally,  we hope that code generated using `-mcpu` alone would always be compatible with processors that have varying configurations.

https://github.com/llvm/llvm-project/pull/144022