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

[Amaury Séchet via llvm-dev]

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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