RVA23/RVB23 public review feedback and responses

[Krste Asanovic]

Public review has closed on the RVA23 and RVB23 profiles.

The following were the primary issues raised during public review of the RVA23
and RVB23 profiles, along with the action taken:

- Profile-defined extensions. Several reviewers were concerned about
new extensions that appear only in the profile definition. Notes
were added to explain that these are only adding missing names to
options that already existed in ratified specifications, and for
each extension, which section the text would move to when the
profiles are merged into the main ISA manual.

- Misaligned load/stores. A question was raised whether the Zicclsm
extension implied full hardware support for misaligned loads and
stores. As with other ISA extensions, no performance mandate is
given, and the Zicclsm extension just describes that misaligned
loads and stores execute correctly. A non-normative note on Zicclsm
warns that some implementations might be slow and to avoid
misaligned access, though this note is not specific to RVA23 but
rather applies to Zicclsm in general.

- Simplifying the profile text by adding new extension group
names. The now-ratified B extension was used to replace the
previously separately listed Zba, Zbb, Zbs extensions. A new Sha
extension was defined to capture all the mandates required along
with the hypervisor extension. These changes do not represent any
modifications to the profile, but just simplify the text.

- Request to add Zbkx extension (additional bit permutation
instructions). These instructions have limited utility except to
detect zeros in strings, which is already handled by the mandated
orc.b instruction. This extension was not added.

- Request to include performance information for vrgather and
vcompress instructions. The profile is an ISA specification and is
not intended to capture microarchitectural performance attributes.