C++: Consider representing value-initialized POD classes as `ClassAggregateLiteral`s

[dbartol]

Consider code like:

struct Test {};
const Test t = Test();

We represent the Test() object as a Literal node with type const Test and value 0. This is basically correct, but it's somewhat odd to have an expression of class type with an integer value. It might be less confusing to represent that temporary object as a ClassAggregateLiteral instead. I believe they should have the same semantics, although it could be argued that ClassAggregateLiteral is intended solely for the syntax that uses a braced initializer list.

[dbartol]

Another option would be to have a class that extends either Literal or AggregateLiteral specifically for this case.

[jbj]

IIRC, the C++ IR uses "a 0 of the appropriate size" to initialize something like the second element in

MyStruct arr[2] = { MyStruct(...) };

That seems to be consistent with the (confusing, I agree) current modelling of Test() as 0.