[LLVMdev] Cygwin bootstrap is incompatible with <mutex> (and most other threading C++11 libraries)

[Gabriel Dos Reis]

4) since you are doing the native windows work, why not just go with
mingw(64), and use that  as a native compiler under cygwin?


On Wed, Jun 25, 2014 at 4:14 AM, Chandler Carruth <chandlerc at gmail.com>
wrote:

> (sorry for the cross post, but this issue effects lots of people)
>
> Takumi diagnosed a problem when Zach switched LLVM to use compile-time
> multithreading, but it actually has little to do with the multithreading
> decisions.
>
> LLVM is rapidly moving to use more C++11 library features and more
> multithreading features. I think this is a good thing. However, we're
> hitting a specific issue on cygwin when bootstrapping: Clang doesn't
> support the Cygwin __thread implementation (it's different... sadly...). As
> a consequence, a *huge* amount of libstdc++'s multithreading primitives
> when bootstrapping, including <mutex>.
>
> I don't think the current situation is tenable -- we really shouldn't be
> increasingly using C++11 in LLVM while trying to keep all of the
> multithreading code away from the C++11 standard library. At some point, we
> will fail because some other part of the library needed <mutex> (or
> something), and get a really surprising breakage.
>
> I see three options:
> 1) Give up on cygwin bootstrapping (I don't really like this, and I
> suspect there are users of it)
> 2) Switch cygwin bootstrap to libc++ and fix libc++ to not require
> __thread (seems rather gross and lots of work)
> 3) Implement __thread in cygwin mode ASAP.
>
> Thoughts? I think we need to address this pretty quickly or we're just
> going to start running into more failure modes.
>
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