GoingNative 6: The D Episode with Walter Bright and Andrei Alexandrescu

[Walter Bright]

On 2/23/2012 8:57 AM, Alex Rønne Petersen wrote:
>> > System languages are implemented with LLVM.
>>
>> That works if your language is expressible as C, because LLVM is a C/C++
>> back end. If your language has different semantics (like how Go does
>> stacks), using LLVM can be a large problem.
>
> I don't think that's true. D, Rust, C# (CIL in general), Cray, ActionScript,
> Python, Java, Lua, Haskell, and many others have been compiled with LLVM
> successfully.
>
> LLVM is very much engineered for C and C++, but it has many other features that
> those languages don't make use of at all (see for example the precise GC
> support; and this is not even something Apple uses, as their Obj-C GC is
> conservative). There is also the language-specific support for OCaml's precise
> stack maps. Also, LLVM has segmented stacks on x86 these days. That said, LLVM
> is definitely not as easy to use for managed languages as it is for
> systems/native languages.
>
> So, while the design of LLVM certainly is driven by Clang primarily, it's not as
> if they don't welcome non-C family features.

What you're saying is they add support here and there for non-C languages, 
meaning someone has to do it if it isn't there already.


> In Mono, we found that ABC removal was actually beneficial in some code;
> consider for example allocating small static arrays locally and indexing them
> with constants (or very simple expressions).

This is done already by standard data flow optimization techniques.