Michael Gottesman ac7e28a57e [alloc-stack-hoisting] Handle alloc_stack [move] correctly. ...

This is just a quick fix to stop us from dropping live values such as m in the
following example:

```
public func addressOnlyVarTest<T : P>(_ x: T) {
    var k = x
    k.doSomething()
    let m = _move(k)
    m.doSomething()
    k = x
    k.doSomething()
}
```

Before this change, we would just drop m and one wouldn't even see it in the
debugger.

I am only doing this currently for cases where when we merge at least one
alloc_stack was moved. The reason why is that to implement this correctly, I
need to use llvm.dbg.addr and changing the debug info from using
llvm.dbg.declare -> llvm.dbg.addr requires statistics and needs to be done a
little later in the swift development process. If one of these alloc_stack had
the [moved] marker attached to it, we know the user /did/ use move so they have
in a sense opted into having a move function effect its program so we are only
changing how new code appears in the debugger.

2022-02-22 20:36:19 -08:00

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