Uninitialized memory + trivial types

[scanon (Steve Canon)]

Reading uninitialized¹ memory (via pointee or load or any other mechanism) is undefined behavior.

@Karl

When reading from the pointee property, the instance referenced by this pointer must already be initialized. When pointee is used as the left side of an assignment, the instance is updated. The instance must be initialized or this pointer’s Pointee type must be a trivial type.

This should be clarified, but the correct interpretation is as follows:

1. When reading, the pointed-to instance must already be initialized.
2. When assigning, the pointed-to instance must either already be initialized or be trivial.

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¹ what exactly qualifies as "initialization" here is quite subtle, because we have to allow for memory initialized by non-Swift code that doesn't have the same notion of "initialization" as Swift. "Must either be initialized in the Swift sense or contain a valid value of compatible type" is probably close enough if we wave our hands a little bit.