[cfe-dev] On the preferred use of C++ in the clang source code

[Chris Lattner]

On Nov 9, 2007, at 8:55 AM, James Widman wrote:

> I've heard that clang is meant to be implemented in a "subset of C+
> +" (which I guess means that some core language features are barred
> from use).
>
> Is there a document anywhere that describes and motivates that subset?

It is pretty subjective.  We do use almost all C++ features somewhere  
in the (greater llvm) code base.  It's really more about making clear  
and simple code than it is about banning specific language features.   
Some coding guidelines are available here:
http://llvm.org/docs/CodingStandards.html

That said, there are two features we don't like:  RTTI and EH.  This  
is because they violate the "don't pay for it if you don't use it"  
principle.  If building with GCC, clang disables both RTTI and EH  
support (-fno-rtti and -fno-exceptions).  The main llvm repository  
has a couple of places that still use RTTI, but we'd like to fix that.

The main problem with RTTI and EH is the impact on binary size.  Many  
clients of LLVM and at least one client of clang use them in a JIT  
context.  Having the binaries be as small as possible makes it easier  
for people to distribute them with their apps.

-Chris