[LLVMdev] Using C++'11 language features in LLVM itself

[Chris Lattner]

On Jan 8, 2013, at 4:24 PM, dag at cray.com wrote:
> I am personally very much in favor of this.  C++11 really is a huge leap
> from C++03 in terms of readability, maintainability and safety.

I agree completely.

> Why not C++11 libraries?  Implementation/capatability reasons?  I don't
> know anything about how the various implementation compare in terms of
> completeness.  But the libraries use the new language features and
> theoretically you get a performance boost "for free."

It's mostly about only changing one thing at a time.  It's already possible to build LLVM in C++'11 mode and with a C++'11 library.  Adding a dependency to *require* C++'11 compiler and/or C++'11 library are two orthogonal changes, and I'd like to tackle them one at a time.
 
> I'm assuming we wouldn't release an llvm with C++11 until 3.4 at least
> which gives folks a good 8 months to a year to prepare.  Doing it in a
> 3.3 release shortens that considerably but it might be ok.  The biggest
> issue for groups like ours is upgrading the compiler we use to build our
> compiler.  We have a LOT of components and they all have to work with
> the new build environment.  It involves a lot of testing and assurance
> which is where we might bump up against a 3.3 release, not having a new
> compiler in place before 3.3 is out.
> 
> As for gcc version, it looks like 4.7.2 is in Debian Wheezy and that's
> usually the most common distribution to lag behind in these kinds of
> things.  I think that's sufficiently new for Linux but someone correct
> me if that's wrong.

Wow, requiring GCC 4.7 would be really aggressive, it was just released in March 2012.  Call me conservative, but I was thinking that a reasonable GCC baseline would be GCC 4.4 or something (which is ~3.5 years old).

-Chris