[PATCH] D117238: [C2x] Add BITINT_MAXWIDTH support

Tue Feb 22 11:32:31 PST 2022

mariospr added a comment.

In D117238#3338205 <https://reviews.llvm.org/D117238#3338205>, @aaron.ballman wrote:

> In D117238#3338092 <https://reviews.llvm.org/D117238#3338092>, @erichkeane wrote:
>
>> Hi Mario!  Thank you for inquiring!  As you may know, we disabled _BitInt this large since we couldn't handle division/modulus in the code generators.  There is an RFC currently underway (as of today, we have the patches to start supporting this in the backend!) here: https://discourse.llvm.org/t/rfc-add-support-for-division-of-large-bitint-builtins-selectiondag-globalisel-clang/60329
>>
>> I'm hopeful that the answer here is 'in the near future'.  @mgehre-amd should be able to at least partially revert this patch once the library changes/llvm code generator changes make it in.
>
> I agree with what Erich is saying here. My intention is to increase back to the LLVM maximum again once the IR we generate stops crashing LLVM. However, there's likely to be performance issues with "very large" bit-precise integer types until we've gone through the backend and optimized for those cases (both compile time and runtime performance concerns), so we might want to bump up to something lower than the theoretical max for a while still (though hopefully usefully bigger than 128!).

Wow, this is some seriously quick response time, kudos for that!

Also, thanks a lot for the clarification: it's more clear to me now what the situation actually is, and I'm happy to see there's already an ongoing plan to get this fixed, even if it will take some time. It was not clear to me when I read this ticket the first time whether there was some active work going on already, so thanks a lot for the pointers, that makes things more clear.

Again, thanks a lot for your help, much appreciated! I'll keep an eye on this ticket and the RFC to be aware when things change.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D117238/new/

https://reviews.llvm.org/D117238