[llvm-dev] cmpxchg on floats

[Nicolai Hähnle via llvm-dev]

We've relaxed `atomicrmw xchg` to support floating point types but not
cmpxchg -- the cmpxchg comparison behavior is not a floating point
comparison, so that would be potentially misleading. I'd say adding
the assertion is a good idea.

Cheers,
Nicolai

On Thu, Aug 13, 2020 at 10:59 PM Chris Lattner via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> Does the code generator support this?  If not, we should add an assertion to the verifier.  If so, we can consider relaxing langref or making it more specific about floats.
>
> -Chris
>
> On Aug 13, 2020, at 6:35 AM, Alex Zinenko via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>
> Hi LLVM-dev,
>
> when working on MLIR-to-LLVM-IR conversion, I noticed that it is possible to programmatically construct a cmpxchg instruction operating on floats (or actually any type since there is no assertion on pointer element type here https://github.com/llvm/llvm-project/blob/9c2e708f0dc547d386ea528450a33ef4bd2a750b/llvm/lib/IR/Instructions.cpp#L1501), but LangRef specifies that only integers and pointers are accepted (https://llvm.org/docs/LangRef.html#cmpxchg-instruction). Does somebody rely on other types being accepted in cmpxchg or should we add an assertion for the element type to match the LangRef?
>
> --
> Alex
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev



-- 
Lerne, wie die Welt wirklich ist,
aber vergiss niemals, wie sie sein sollte.