bors e9f29a8519 Auto merge of #89030 - nbdd0121:box2, r=jonas-schievink ... Introduce `Rvalue::ShallowInitBox` Polished version of #88700. Implements MCP rust-lang/compiler-team#460, and should allow #43596 to go forward. In short, creating an empty box is split from a nullary-op `NullOp::Box` into two steps, first a call to `exchange_malloc`, then a `Rvalue::ShallowInitBox` which transmutes `*mut u8` to a shallow-initialized `Box<T>`. This allows the `exchange_malloc` call to unwind. Details can be found in the MCP. `NullOp::Box` is not yet removed, purely to make reverting easier in case anything goes wrong as the result of this PR. If revert is needed a reversion of "Use Rvalue::ShallowInitBox for box expression" commit followed by a test bless should be sufficient. Experiments in #88700 showed a very slight compile-time perf regression due to (supposedly) slightly more time spent in LLVM. We could omit unwind edge generation (in non-`oom=panic` case) in box expression MIR construction to restore perf; but I don't think it's necessary since runtime perf isn't affected and perf difference is rather small.		2021-09-25 11:01:13 +00:00
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src	Auto merge of #89030 - nbdd0121:box2, r=jonas-schievink	2021-09-25 11:01:13 +00:00
Cargo.toml	Migrate to 2021	2021-09-20 22:21:42 -04:00