[4.1] Outliner: Can't handle generic ObjC classes

[aschwaighofer]

The outliner can't handle outlining calls to generic objective c
classes resulting in crashes if it attempted so.

Explanation: The outliner can't handle outlining calls to generic objective c
classes resulting in crashes if it attempted so.

Scope: Use of Osize with swift code that uses generic objective c classes results in crashes.

Risk: Low. This disables the optimization if an objective c method call is encountered that is generic. We would have crashed before this fix.

Testing: Swift CI test added

rdar://36395452

[aschwaighofer]

@swift-ci Please test

[aschwaighofer]

Reviewed by Erik here: #13852

[aschwaighofer]

@swift-ci Please test source compatibility

[aschwaighofer]

@swift-ci Please nominate

[slavapestov]

Can you just solve the general case? The thunk should have the same generic signature as the bridging method that its calling. It should be @pseudogeneric so that no type metadata actually gets passed at runtime. When the thunk calls the bridging method, it uses SILFunction::getForwardingSubstitutions(). When the caller calls the thunk it uses the same substitutions that it used when it used to call the bridging method directly.

In general I'm not a huge fan of this pattern in the optimizer where we say "if this and that don't attempt this optimization". While solving the general case requires a bit more thought sometimes it makes the code simpler and easier to test because there are fewer possible paths through the code.

[aschwaighofer]

I don't agree that adding the code you describe would lead to simplifications. You just described the code that has to be added. This is more code than a bailout.

I agree with you that ultimately we want to add that code. But that is not going to happen for the swift-4.1-branch.