[llvm-dev] What is compiler-rt for?

[mats petersson via llvm-dev]

Thanks for the clarification, David!

I didn't even think about atomics - or floating point, for that matter.

--
Mats

On 2 September 2015 at 11:22, David Chisnall <David.Chisnall at cl.cam.ac.uk>
wrote:

> On 2 Sep 2015, at 10:59, mats petersson via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > It is there to allow the compiler to run on platforms that would
> otherwise not have the relevant functionality. If you already have a C++
> compiler to build Clang with on the target system, you (most likely) have
> everything you need. But what if you are cross-compiling to a target with
> limited/no support for C++ on the target?
>
> It’s not just cross compiling.  On most operating systems, the OS vendor
> is responsible for providing a set of libraries that perform functionality
> expected by the compiler.  This includes functions that provide missing CPU
> functionality (and which would be too expensive to inline everywhere, or
> which all programs must do in precisely the same way, irrespective of the
> compiler used), for example some complex floating point operations or
> atomics, and the generic unwind frameworks.
>
> Most OS vendors *do* provide these (and so do some third-party toolchains,
> such as MinGW).  GCC provides an implementation of these that most Linux
> distributions ship.  On FreeBSD or OS X, these are provided by
> compiler-rt.  If you are bringing up a new platform, then compiler-rt gives
> you some of these components.
>
> Note that nothing in compiler-rt is specific to C++.  The closest thing is
> the unwind library, which provides the generic part of the unwinder, which
> is also used for other languages (Objective-C, Ada, Java with GCJ, and so
> on).
>
> David
>
>
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