Yesterday I discovered that 78% of all selectors in "Cocoa.h" take 0/1 argument.

This motivated implementing a devious clattner inspired solution:-)

This approach uses a small value "Selector" class to point to an IdentifierInfo for the 0/1 case. For multi-keyword selectors, we instantiate a MultiKeywordSelector object (previously known as SelectorInfo). Now, the incremental cost for selectors is only 24,800 for Cocoa.h! This saves 156,592 bytes, or 86%!! The size reduction is also the result of getting rid of the AST slot, which was not strictly necessary (we will associate a selector with it's method using another table...most likely in Sema).

This change was critical to make now, before we have too many clients.

I still need to add some comments to the Selector class...will likely add later today/tomorrow.

llvm-svn: 42452