[cfe-dev] Small patches to allow fully independent clang/llvm/compiler-rt/libc++

[Jonathan Roelofs via cfe-dev]

On 10/14/15 7:11 AM, Vasileios Kalintiris wrote:
>> Some people may disagree on the principle, even if it doesn't affect
>> current builds. But I'll let them voice their concerns.
>
> IMHO, the "correct" approach for a GNU-free/independent clang package requires
> a new ToolChain class for LLVM-based toolchains. Maybe, this class could
> inherit from the Linux ToolChain and use most of the existing infrastructure
> for paths, options & tools invocations. Otherwise, we could use these
> configuration-time options for most of the GNU-dependencies that we want to
> replace. However, I think that we would be duplicating effort/functionality
> at two different places (cmake & clang source code). Additionally, other than
> compiler-rt, libcxx, libcxxabi, etc., we'd need a non-GLIBC/GNU C library
> which might have a different set of CRT files with its own naming scheme for the
> dynamic linker/loader.

Something along these ^ lines is the "correct" way to do it. You'd have 
to add your own vendor to Triple.h, and then specialize these defaults 
based on seeing that particular vendor.  Baking these decisions in at 
compile-time is an anti-pattern driver-wise.

If you do it this way, then you'll be able to write testcases for your 
changes, and those tests will get run by all the buildbots (not just one 
configured to have one particular set of defaults).  This has the added 
benefit of not requiring more builders to test more configurations.

Please don't commit these patches as-is.


Jon

>
> Having said all that, I don't explicitly disagree with these set of patches.
> They could offer a reasonable trade-off for the time being.
>
> - Vasileios
>

-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded