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

Pawel Wodnicki root at 32bitmicro.com
Wed Jan 9 22:11:55 PST 2013


 I have been following this discussion for a while and I think the
question we should be asking is:

 Why do we want to even bother with all these other broken C++
compilers in a first place?

 Clang is good enough to bootstrap itself on practically
any platform I can think of or it can be cross-bootstrapped
if needed.

 I think usage of any language features should be decided
based on support from a either clang(n-j) release or a
reference version (3.2 being my personal favorite)
rather then on a common unbroken subset from a motley
collection of other compilers.

Just my 0.02$ after 2 months of building clang+llvm.


> On Jan 9, 2013, at 2:38 AM, David Chisnall <David.Chisnall at cl.cam.ac.uk> wrote:
>> On 9 Jan 2013, at 04:49, Marc J. Driftmeyer wrote:
>>> It's not a coincidence that GCC 4.2.1 is the baseline on FreeBSD considering the licensing of GPL restrictions on new releases.
>> [With my FreeBSD hat on]
>> Our plan for 10.0 is to ship clang only, with gcc 4.2.1 relegated to a compat package for tier 1 architectures.  This should be x86, x86-64, and ARMv6/7 (and maybe v8 if we're very lucky, but probably not).  MIPS and PowerPC are slowly migrating to clang, but will probably take a little bit longer (although given the progress that these are making, possibly not).  As these are tier 2 architectures, I don't have a problem requiring an external compiler or a cross compiler for the initial bootstrap build.  
> Ok, that's good news!

Kudos to FreeBSD!

>> However, our release cycle is (in theory) 6 months, but is out of phase with LLVM's and so at any given point we are likely to be one or two releases behind.
>> As such, it's important to us to be able to build trunk clang with clang from at least two releases ago, and ideally four.  Losing this ability makes it very difficult for us to do the bootstrap toolchain build

Since Thursday, February 4, 2010 we can always do
clang(n-j) ... clang(n-1)clang(n) -> clang(n+1)

> Can you make this more concrete for me?  If we made this change in LLVM 3.3, what version of Clang would you need us to be compatible with?  Would it be ok to require Clang 3.1 or later, or do you need clang 3.0 support?
> -Chris

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