[cfe-dev] RFC: A proposal to move toward using C++11 features in LLVM & Clang / bounding support for old host compilers

["C. Bergström"]

For those driving c++11 in clang/llvm - Would it generally be acceptable 
to have a "sunrise" period where the preliminary evaluation has been 
done (buildbots, compiler evaluate.. etc) and the 1st actual c++11 
commit hits the repo. (30-60 days?)
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My concern/thoughts - When we swap out STDCXX for libc++ - We aren't 
able to self host clang. This could be entirely *our* fault, but it 
hasn't been investigated extensively. (We also see Perennial C++ 
testsuite regressions which appear to come from libc++, but also not 
investiaged/confirmed) Having a sunrise period would allow us to 
investigate this as well as report any potentially blocking problems.

Having a gnu-free self hosting[1] policy attached to this would also be 
great - that makes a potentially easier backup solution to anyone on 
[linux] with older gnu compilers

[1] My simple explanation of self hosting
Stage 1 - g++ builds clang - bootstrapped clang builds it's own runtime 
libs -> clang-stage1
Stage 2 - clang-stage1 builds -> clang-stage2
Stage 3 - clang-stage2 builds -> clang-stage3

Typically in such a large c++ codebase like clang - any bad code 
generation issues would make stage3 fail. (Not guaranteed, but it's a 
pretty good sanity check and way to "dogfood" your own compiler)