RFC: [SmallVector] Adding SVec<T> and Vec<T> convenience wrappers.

The LLVM codebase is designed with having exceptions disabled in mind. In such a world, having noexcept everywhere is just noise (“we don’t throw exceptions, so everything is noexcept! yay!”). Furthermore, we provide a CMake build flag to enable exceptions with the intention that user libs with exceptions enabled would link with LLVM and that user lib exceptions would flow through LLVM. If people start adding noexcept everywhere in order to please std::vector, then you will start seeing crashes.

Since the LLVM codebase largely pretends that exceptions don’t exist, I don’t think it should do anything that will change what actually happens in the presence of exceptions. If this means that we prefer llvm::SmallVector to std::vector for performance reasons, then I say “so be it”.

Thanks,

Christopher Tetreault