more smarts in it. This is where most of the interesting logic that used
to live in the implicit-scheduling-hackery of the old pass manager will
live.

Like the previous commits, note that this is a very early prototype!
I expect substantial changes before this is ready to use.

The core of the design is the following:

- We have an AnalysisManager which can be used across a series of
  passes over a module.
- The code setting up a pass pipeline registers the analyses available
  with the manager.
- Individual transform passes can check than an analysis manager
  provides the analyses they require in order to fail-fast.
- There is *no* implicit registration or scheduling.
- Analysis passes are different from other passes: they produce an
  analysis result that is cached and made available via the analysis
  manager.
- Cached results are invalidated automatically by the pass managers.
- When a transform pass requests an analysis result, either the analysis
  is run to produce the result or a cached result is provided.

There are a few aspects of this design that I *know* will change in
subsequent commits:
- Currently there is no "preservation" system, that needs to be added.
- All of the analysis management should move up to the analysis library.
- The analysis management needs to support at least SCC passes. Maybe
  loop passes. Living in the analysis library will facilitate this.
- Need support for analyses which are *both* module and function passes.
- Need support for pro-actively running module analyses to have cached
  results within a function pass manager.
- Need a clear design for "immutable" passes.
- Need support for requesting cached results when available and not
  re-running the pass even if that would be necessary.
- Need more thorough testing of all of this infrastructure.

There are other aspects that I view as open questions I'm hoping to
resolve as I iterate a bit on the infrastructure, and especially as
I start writing actual passes against this.
- Should we have separate management layers for function, module, and
  SCC analyses? I think "yes", but I'm not yet ready to switch the code.
  Adding SCC support will likely resolve this definitively.
- How should the 'require' functionality work? Should *that* be the only
  way to request results to ensure that passes always require things?
- How should preservation work?
- Probably some other things I'm forgetting. =]

Look forward to more patches in shorter order now that this is in place.

llvm-svn: 194538