GC: Register None

Implement chained comparisons

Merges #88

Conflicts:
	src/core/threading.cpp

Not sure why greg_t got changed from 'long' to 'long long' in newer versions of glibc; just cast it to be compatible

Build fix

Signed-off-by: Vinzenz Feenstra <evilissimo@gmail.com>

Implementation is pretty straightforward for now:
- find all names that get accessed from a nested function
- if any, create a closure object at function entry
- any time we set a name accessed from a nested function,
  update its value in the closure
- when evaluating a functiondef that needs a closure, attach
  the created closure to the created function object.

Closures are currently passed as an extra argument before any
python-level args, which I'm not convinced is the right strategy.
It's works out fine but it feels messy to say that functions
can have different C-level calling conventions.
It felt worse to include the closure as part of the python-level arg
passing.
Maybe it should be passed after all the other arguments?

Closures are currently just simple objects, on which we set and get
Python-level attributes.  The performance (which I haven't tested)
relies on attribute access being made fast through the hidden-class
inline caches.

There are a number of ways that this could be improved:
- be smarter about when we create the closure object, or when we
  update it.
- not create empty pass-through closures
- give the closures a pre-defined shape, since we know at irgen-time
  what names can get set.  could probably avoid the inline cache
  machinery and also have better code.

Enable the VTune JIT support in llvm, and add it as a jit
listener.

I think it's mostly confirming my suspicion that the slowdown is
cache-related... it's not being very helpful with determining why
(it's in some function that it can't analyze).

I updated the memory allocator to have strong thread-affinity
(ie a thread now generally gets back memory that it had previously freed),
but that doesn't seem to have any effect.

Going to punt on further investigations for now, pretty happy though that there's
an overall speedup with the grwl, even if there are still issues.

Turns out a large amount of thread contention was coming from these shared counters -- disable some of them and add some thread-local caching

insert full blocks back at the end of the free list to hopefully reduce the amount of times we have to check them

Now, threads will claim an entire block at a time, and
put it in a thread-local cache.  In the common case, they
can allocate out of this block, and only need to take out
a lock if they run out.

Trying to add a generic PerThread class has involved
a journey into the wonderful world of template programming,
including C++11 variadic templates.

Make rules more general, and generate rules that can't be patterns
Made it easy to add a pyston_grwl target

Add some basic locking to:
- code generation (one lock for all of it)
- garbage collection (spin lock for allocations, global serialization for collections)
- lists (mutex per list object)

Can run the GRWL on some simple tests (microbenchmarks/thread_contention.py and thread_uncontended.py)
Performance is not great yet

And then use that register info rather than sending a signal to the
thread; this lets the thread that called AllowThreads avoid receiving
signals ex during a syscall.

I'm not sure if this is valid though; are we really guaranteed that
the thread can't invalidate the saved state?

Once the GRWL is added, will also be for GC safepoints.

We always want to crawl the entire stack, and it's
possible to determine the extents of the stack, so just
do a scan over the entire memory range.

Also, change the way the interpreter keeps track of its roots;
we don't really need to associate the roots with a specific
interpreter frame.

This should hopefully clear up the weirdness about libunwind
trying to unwind through the pthreads assembly code, and potentially
also make stack crawling faster.

I think threading now "works" ie doesn't crash Pyston,
though we don't release the GIL until the thread exits.

Don't worry, a non-gil version is coming.
Use a gil for now so we can start working on the other threading
requirements, such as GC.

Well, the thread-creating should work, but nothing is threadsafe.

Remove read from freed memory

Update chr to be compatible with CPython