asb added a comment.

@ym1813382441 thanks for the contribution. In many cases, this kind of 
incremental and tightly focused patch is a good way to start things. But in 
this case, there's a few bigger issues.

- As has been pointed out, the discussion about supporting multiple ISA 
versions has been started before. The barrier isn't the code change required, 
but more about agreeing we actually want/need to support multiple extension 
versions simultaneously (RISC-V International seem to have indicated they'd add 
new named extensions rather than add instructions to an existing extension in 
the future), and perhaps the biggest blocker has been around the handling of 
build attributes, what is accepted / produces an error / produces a warning by 
what tool and so on. We've been discussing this in the recent RISC-V LLVM 
sync-up calls and a few people who've been thinking about these issues for a 
while are hoping to come up with a proposal in the coming weeks.
- If the ultimate intention is to support V0.7, then as Craig suggests that's a 
much bigger discussion. We really need to understand what the level of changes 
would be required, how this would impact in-tree code for V1.0, what the burden 
might be going forwards and so on. Not all points are relevant, but I've often 
thought that the considerations for Contributing Extensions to Clang 
<https://clang.llvm.org/get_involved.html> provide a good starting point. e.g.
  - Evidence of a significant user community
  - A specific need to reside within the upstream tree
  - A long term support plan
  - A high quality implementation
  - Testing


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D144696/new/

https://reviews.llvm.org/D144696

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