[PATCH] Fix initialization problems with PassRegistry

[David Blaikie]

On Wed, Jun 11, 2014 at 11:54 AM, Zachary Turner <zturner at google.com> wrote:
> I might be able to solve the lock problem by just deleting the lock access from the destructor, as you mention, or making the lock an instance variable of the PassRegistry class.  But I still think the way I've done is the only real way to solve the problem with the PassRegistrationListener.

It seems like the problem with PassRegistrationListener would be
solved by having a static device (other than
PassRegistrationListener's ctor itself) that simply doesn't remove the
listener in its dtor. The problem being then you change the behavior
of non-static PassRegistrationListeners (since you have to remove the
registration machinery from PassRegistrationListener's ctor/dtor).
Global registration devices are pretty common.

All that being said, removing global ctors is a soft goal of the
project, so I'm OK doing it for those reasons - I'm just trying not to
conflate different goals/problems & understand which things we're
doing for what reasons.

> Ultimately, the root of the problem is that ManagedStatics are being accessed during static initialization and shutdown.

I don't actually see those things as inherently wrong. Something like
a ManagedStatic is the only way to resolve ordering in global init
(yes, the alternative is to restrict the project to never have globals
that access other globals - but that's not the only correct answer).
During destruction is more subtle, certainly.

> This needs to be prevented, and I think we need to try to get to a point where we can actually enforce, by way of asserts, that you cannot touch a ManagedStatic before main is entered or after it returns.
>
> http://reviews.llvm.org/D3996
>
>