jyknight added a comment.

In D55150#1321046 <https://reviews.llvm.org/D55150#1321046>, @kristina wrote:

> Personally I'm against this type of warning as it's likely anyone using 
> `-mllvm` is actually intending to adjust certain behaviors across one or more 
> passes with a lot of switches supported by it being intentionally hidden from 
> `<llvm_tool> --help` output requiring explicitly specifying that hidden flags 
> be shown.


There is a cost to having people encode these flags into their build systems -- 
it can then cause issues if we ever change these internal flags. I do not think 
any Clang maintainer intends to support these as stable APIs, unlike most of 
the driver command-line. But, neither -Xclang nor -mllvm obviously scream out 
"don't use this!", and so people may then add them to their buildsystems 
without causing reviewers to say "Wait...really? Are you sure that's a good 
idea?".

That's why I think a warning is useful -- it'll discourage people from using 
them when they haven't properly understand the consequences, but does not 
prevent them from doing so, when they actually do.

> For example, I routinely use the following with SEH (excuse some of the 
> naming, this is just a downstream fork however):
>  `-mllvm -target-enable-seh=true -mllvm -force-msvc-seh=true -mllvm 
> -wtfabi-opts=0x1EF77F`

If you already are passing that, do you see a problem with instead passing
 `-mllvm -target-enable-seh=true -mllvm -force-msvc-seh=true -mllvm 
-wtfabi-opts=0x1EF77F -Wno-experimental-driver-option`
?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D55150/new/

https://reviews.llvm.org/D55150



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