[llvm-dev] Deprecating ADDC/ADDE/SUBC/SUBE

[Krzysztof Parzyszek via llvm-dev]

For targets where ADDCARRY and SUBCARRY are legal, would it make sense 
to expand ADDC/UADDO/ADDE/etc. into ADDCARRY (and same for sub)?

Are there plans to deprecate UADDO/USUBO in favor of ADDCARRY/SUBCARRY?

-Krzysztof


On 5/30/2018 11:57 AM, Amaury Séchet via llvm-dev wrote:
> These opcodes have been deprecated about a year ago, but still in use in 
> various backend.
> 
> In https://reviews.llvm.org/D47422 I would like to change the behavior 
> of the backend to not enable the use of these opcodes by default. The 
> opcode remains usable by any backend that wish to use them, but that 
> should limit the situation where newer backend just use them as they are 
> enabled by default.
> 
> This shouldn't break any out of tree backend, however, it may cause 
> misoptimisation if the backend dev do not activate these opcodes via 
> setOperationAction and rely on them for some of their optimizations.
> 
> I would like to gather some feedback about moving forward with that as 
> it can impact a wide range of users.
> 
> So, feedback ?
> 
> Thanks in advance for your answers,
> 
> Amaury Séchet
> 
> 
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