MIR move elimination

[Amanieu]

This RFC proposes changes to Rust's operational semantics and MIR representation to enable elimination of unnecessary copies of local variables. Specifically, it makes accessing memory after a move undefined behavior, and redefines the allocation lifetime of local variables to be tied to their initialized state rather than their lexical scope. Finally, it introduces a new MIR optimization pass which exploits these guarantees to eliminate copies between locals when it is safe to do so.

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Rendered

[NobodyXu]

For Copy-iable types, can rust mir just drop them after the last usage, given that it cannot have a Drop implementation?

It seems to be extremely strange to say I need a move keyword on a Copy-iable type just so the compiler can optimize it