Add 'remark' diagnostic type in clang

[Chris Lattner]

On Feb 26, 2014, at 2:22 AM, Tobias Grosser <tobias at grosser.es> wrote:
> 2) Adding the new severity level / the name of the diagnostic
> 
> Only small issues have been found in the patch. All of them have been addressed. The last open issues was the name of the diagnostic. Richard
> proposed 'info' or 'remark'. Chris and Eric prefer to call the severity 'info', in case there is no prior art. However, Alexander and Arthur mentioned prior art for 'remark' in both icc and edg. Also the comment from Arthur sounds right:
> 
>  I don't know of any compiler that uses the term "informative".
>  Besides, that's redundant; *all* compiler diagnostics are purely
>  "informative" by definition. The variable here is //severity//:
>  fatal-error, recoverable-error, warning, remark, silent.
> 
> I personally preferred 'info' first, but now came to the conclusion
> that 'remark' is the better option, except someone sees strong reasons to ignore the prior art.

“remark” is fine with me.

> 3) How to enable 'remarks'
> 
> We need a way to enable 'remark' diagnostics. Quentin proposed to go
> for an approach similar to the warning flags. Where we control remarks
> with '-Rvector', '-Rloop-vector', ...
> 
> I will read a little bit through the existing option system to better understand what it is doing, possibly adding documentation / cleanups on my way. I will come back with a proposal here.

It’s a bit odd, but since these are diagnostics, why not use the existing -W flags?  You should be able to -Werror one of these, control them with #pragma clang diagnostics, etc.  It doesn’t seem like we need more complexity in this space.

-Chris