```
class Generic<T> {
@objc dynamic func method() {}
}
extension Generic {
@_dynamicReplacement(for:method())
func replacement() {}
}
```
The standard mechanism of using Objective-C categories for dynamically
replacing @objc methods in generic classes does not work.
Instead we mark the native entry point as replaceable.
Because this affects all @objc methods in generic classes (whether there
is a replacement or not) by making the native entry point
`[dynamically_replaceable]` (regardless of optimization mode) we guard this by
the -enable-implicit-dynamic flag because we are late in the release cycle.
* Replace isNativeDynamic and isObjcDynamic by calls to shouldUse*Dispatch and
shouldUse*Replacement
This disambiguates between which dispatch method we should use at call
sites and how these methods should implement dynamic function
replacement.
* Don't emit the method entry for @_dynamicReplacement(for:) of generic class
methods
There is not way to call this entry point since we can't generate an
objective-c category for generic classes.
rdar://63679357
Specifically, I split it into 3 initial categories: IR, Utils, Verifier. I just
did this quickly, we can always split it more later if we want.
I followed the model that we use in SILOptimizer: ./lib/SIL/CMakeLists.txt vends
a macro (sil_register_sources) to the sub-folders that register the sources of
the subdirectory with a global state variable that ./lib/SIL/CMakeLists.txt
defines. Then after including those subdirs, the parent cmake declares the SIL
library. So the output is the same, but we have the flexibility of having
subdirectories to categorize source files.
