[cfe-dev] RFC: Removing clang-cl's /fallback option

[Hans Wennborg via cfe-dev]

clang-cl's /fallback option was added back in 2013 [1] as part of
bringing up clang's native Windows support.

Since then, the Windows support has become quite stable, and I'm not
aware of anyone using /fallback anymore. In Chromium we stopped using
it in 2015 [2].

While /fallback doesn't require a lot of code, it does add a bit of
complexity to the driver (for example it added a special type of Job),
and I worry about the code rotting since it's not getting updated to
handle new flags.

So, are there any objections to removing the /fallback mode? My
proposal is to put a note in the upcoming Clang 12 release, and then
delete the code after the branch point, meaning it would be gone in
Clang 13.

Please let me know what you think.

Thanks,
Hans

1. https://github.com/llvm/llvm-project/commit/87cfa71071d73c702a833f19c9fe035f31c1275d
2. http://crrev.com/340533