[llvm] r190974 - Encapsulate PassManager debug flags to avoid static init and cxa_exit.

[Chandler Carruth]

On Wed, Sep 18, 2013 at 9:03 PM, Andrew Trick <atrick at apple.com> wrote:

>
> On Sep 18, 2013, at 5:51 PM, Chris Lattner <clattner at apple.com> wrote:
>
> On Sep 18, 2013, at 4:54 PM, Chandler Carruth <chandlerc at google.com>
> wrote:
>
> Andy, this really feels like a hack, and a bad hack at that.
>>
>> Where is the requirement for the core library to have no static
>> initializers coming from? What is the support plan here? What problem are
>> you actually trying to fix?
>>
>
> Just for clarity, I have read the llvmdev thread, and I understand the
> *general* goal, but this patch itself doesn't seem like a clean incremental
> step toward that goal, doesn't reference any of the constructs under
> discussion in that thread.
>
>
> I totally agree.  This seems like a hack that would be resolved by making
> cl::opt's get compiled out in non-assert builds, which you already
> described.
>
>
> I'll coalesce my responses to Chris and Chandler here:
>
> This fixes a particularly horrible bug where LLVM crashes during
> PassRegistry::removeRegistrationListener when a multi-threaded process
> exits while compiler threads are running.
>

OK, to make sure I understand correctly, this is the classical problem
where threads are live at the moment exit is called, and thus global
destructors are run out from under the threads?


>
> This patch was meant to
> (a) fix a bug
> (b) handle one of the handful of special cl::opt cases that won't be
> covered by the general approach I outlined in the RFC.
>
> The proposal talked about handling the majority of options incrementally
> without enormous churn. This case is an exception that I wanted to get out
> of the way first.
>
> This case is special because we want the PassManager options to be
> availabe in non-assert builds, or so I thought. These are clearly "tool"
> options that need to be exported to a number of LLVM-based tools.
>
> What about this patch is a hack, other than being a special case? Having
> tools call initializePassManager()? I can't think of any long-term solution
> where that can be avoided.
>
> I thought this fix would be general all-around goodness, but I'd be happy
> to revert this patch and wrap the whole thing in #ifndef LLVM_NO_STATICINIT
> if Chris and Chandler prefer.
>

I'd like to first figure out what the end state actually looks like. Maybe
that's better done on the original thread.
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