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Treat Drop as a rmw operation
Previously, a Drop terminator was considered a move in MIR. This commit changes the behavior to only treat Drop as a mutable access to the dropped place.
In order for this change to be correct, we need to guarantee that
1. A dropped value won't be used again
2. Places that appear in a drop won't be used again before a
subsequent initialization.
We can ensure this to be correct at MIR construction because Drop will only be emitted when a variable goes out of scope, thus having:
* (1) as there is no way of reaching the old value. drop-elaboration
will also remove any uninitialized drop.
* (2) as the place can't be named following the end of the scope.
However, the initialization status, previously tracked by moves, should also be tied to the execution of a Drop, hence the additional logic in the dataflow analyses.
From discussion in [this thread](https://rust-lang.zulipchat.com/#narrow/stream/233931-t-compiler.2Fmajor-changes/topic/.60DROP.60.20to.20.60DROP_IF.60.20compiler-team.23558), originating from https://github.com/rust-lang/compiler-team/issues/558.
See also https://github.com/rust-lang/rust/pull/104488#discussion_r1085556010
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