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

[Andrew Trick]

On Sep 19, 2013, at 10:24 AM, Chandler Carruth <chandlerc at google.com> wrote:

> 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?

Yes.

> 
> 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.

Agreed. I reverted and will follow up on the original thread.

-Andy
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