This addresses SR-15272.
When you have a function (e.g. 'foo') which is used in a constructor
initializer (e.g. constructor of some class 'Bar'), and you use the
constructor from swift code without directly using the function (e.g.
Bar's ctor is used from swift but foo isn't, foo is used from Bar's ctor),
you will get a link error. My fix is as follows:
When walking the clangAST to be imported, make sure you look at each
CXXCtorInitializer for each CXXConstructorDecl you see.
Currently the following code doesn't work when `callConstructor()` is called from Swift:
```cc
inline int increment(int value) {
return value + 1;
}
struct Incrementor {
int incrementee;
Incrementor(int value) : incrementee(increment(value)) {}
}
int callConstructor(int value) {
return Incrementor(value).incrementee;
}
```
The issue is that we don't generate `IR` for the `increment()` function when it's only called from a constructor or a method.
Swift is aware of the existence of `increment()` and we see it in `IR` as `declare incrementEi`, however, as we don't to emit a definition, we get the following error:
```
Incrementor::Incrementor(int): error: undefined reference to 'increment(int)'
```
This PR fixes this by visiting constructors and methods in `IRGen` and calling `HandleTopLevelDecl()` with all used declarations, which results in emitting definitions for the used declarations.
Co-authored-by: Marcel Hlopko <hlopko@google.com>
