asb added a comment.

In D148066#4294924 <https://reviews.llvm.org/D148066#4294924>, @kito-cheng 
wrote:

>> My concern would be that as we don't gate CSR names on enabling the relevant 
>> extension, people could start using CSR names and encodings that could 
>> change, without opting in via -menable-experimental-extensions, perhaps not 
>> realising that they're using the unratified version. OTOH, you could argue 
>> it was user error from the start by not trying to specify all the needed 
>> extensions in the ISA naming string.
>
> We decide don't gate CSR before, but I am wondering maybe we should gate 
> those CSR if they are defined by a unratified/experimental ext., and remove 
> the checking once it ratified, since it might change the name or CSR number 
> before ratified.

That's definitely a risk, but at least when people try to do the "right" thing 
and specify the extension name in the ISA string, they'll quickly find out that 
the version supported in the compiler is experimental. Given the cost of 
marking such CSR extensions as experimental is near-zero, I think we might as 
well. I agree gating the CSR names might also make sense, but then we're back 
to the effort of testing this. I think our conclusions before were that nobody 
is particularly opposed to doing finer grained control of CSRs for new 
extensions at least (it's more problematic for the older CSRs given spec 
changes to move CSRs to separate extensions), so I think it would be find if 
someone wanted to implement that. I don't think we need that as a pre-requisite 
for this patch though, IMHO.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D148066/new/

https://reviews.llvm.org/D148066

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