[llvm] r227300 - [LPM] Rip all of ManagedStatic and ThreadLocal out of the pretty stack

[Chandler Carruth]

On Wed, Jan 28, 2015 at 2:14 PM, Owen Anderson <resistor at mac.com> wrote:

> Hi Chandler,
>
> On Jan 28, 2015, at 1:52 AM, Chandler Carruth <chandlerc at gmail.com> wrote:
>
> -static ManagedStatic<sys::ThreadLocal<const PrettyStackTraceEntry> >
> PrettyStackTraceHead;
> +// We need a thread local pointer to manage the stack of our stack trace
> +// objects, but we *really* cannot tolerate destructors running and do
> not want
> +// to pay any overhead of synchronizing. As a consequence, we use a raw
> +// thread-local variable. Some day, we should be able to use a limited
> subset
> +// of C++11's thread_local, but compilers aren't up for it today.
> +// FIXME: This should be moved to a Compiler.h abstraction.
> +#ifdef _MSC_VER // MSVC supports this with a __declspec.
> +static __declspec(thread) const PrettyStackTraceEntry
> +    *PrettyStackTraceHead = nullptr;
> +#else // Clang, GCC, and all compatible compilers tend to use __thread.
> +static __thread const PrettyStackTraceEntry *PrettyStackTraceHead =
> nullptr;
> +#endif
>
>
> Darwin doesn’t support __thread or thread_local on armv7 or arm64.  This
> is breaking all Darwin embedded builds.  :-(
>

So, this is part of C++11 and threading... I don't know how to support a
system which wants a threaded LLVM but doesn't support TLS. I'm happy to
make these compile out when threading is disabled of course. Do you have
any other suggestions?
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