[clang] [llvm] [RISCV] Add -mcpu=sifive-p550. (PR #122164)

[Craig Topper via llvm-commits]

topperc wrote:

> > > > I thought the P550 was supposed to support RV64GCB, but that would require Zbs support, which isn't listed here.
> > > 
> > > 
> > > The P550 version in the HiFive Premier board does not support Zbs. ISA string from /proc/cpuinfo is `rv64imafdch_zicsr_zifencei_zba_zbb_sscofpmf`
> > 
> > 
> > That's weird. Basically, remving `Zbs` won't save any area. Is it because the kernel is using wrong device tree without Zbs?
> 
> The hardware does not implement Zbs. SiFive originally announced a P550 based board 2 years ago. The design has been frozen for a while and Zbs was not included. It's taken longer than intended to get a board out.

The ISA is specified in this document too https://www.sifive.com/document-file/eic7700x-datasheet available here https://www.sifive.com/boards/hifive-premier-p550

https://github.com/llvm/llvm-project/pull/122164