Extended Description

When compiling the attached code, clang doesn't emit 'this' adjustment code for
'static_cast<A*>(z)' expression and ends up using a wrong vtable for the virtual call. As a result, B.g() is called instead of Z.f().

Inspection of CodeGenFunction::EmitCXXMemberCallExpr() code shows that clang can stop devirtualization in the middle if it finds out that return types are covariant. At that moment, 'Base' expression that is later used for emission of 'this' pointer has already been assigned to 'Inner' expression (with casts stripped), so no 'this' adjustment code is generated.