[PM] Port SROA to the new pass manager.
In some ways this is a very boring port to the new pass manager as there
are no interesting analyses or dependencies or other oddities.
However, this does introduce the first good example of a transformation
pass with non-trivial state porting to the new pass manager. I've tried
to carve out patterns here to replicate elsewhere, and would appreciate
comments on whether folks like these patterns:
- A common need in the new pass manager is to effectively lift the pass class and some of its state into a public header file. Prior to this, LLVM used anonymous namespaces to provide "module private" types and utilities, but that doesn't scale to cases where a public header file is needed and the new pass manager will exacerbate that. The pattern I've adopted here is to use the namespace-cased-name of the core pass (what would be a module if we had them) as a module-private namespace. Then utility and other code can be declared and defined in this namespace. At some point in the future, we could even have (conditionally compiled) code that used modules features when available to do the same basic thing.
- I've split the actual pass run method in two in order to expose a private method usable by the old pass manager to wrap the new class with a minimum of duplicated code. I actually looked at a bunch of ways to automate or generate these, but they are all quite terrible IMO. The fundamental need is to extract the set of analyses which need to cross this interface boundary, and that will end up being too unpredictable to effectively encapsulate IMO. This is also a relatively small amount of boiler plate that will live a relatively short time, so I'm not too worried about the fact that it is boiler plate.
The rest of the patch is totally boring but results in a massive diff
(sorry). It just moves code around and removes or adds qualifiers to
reflect the new name and nesting structure.
Differential Revision: http://reviews.llvm.org/D12773