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Commit9fe1803

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Auto merge ofrust-lang#124662 - zetanumbers:needs_async_drop, r=oli-obk
Implement `needs_async_drop` in rustc and optimize async drop glueThis PR expands onrust-lang#121801 and implements `Ty::needs_async_drop` which works almost exactly the same as `Ty::needs_drop`, which is needed forrust-lang#123948.Also made compiler's async drop code to look more like compiler's regular drop code, which enabled me to write an optimization where types which do not use `AsyncDrop` can simply forward async drop glue to `drop_in_place`. This made size of the async block from the [async_drop test](https://github.com/zetanumbers/rust/blob/67980dd6fb11917d23d01a19c2cf4cfc3978aac8/tests/ui/async-await/async-drop.rs) to decrease by 12%.
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‎core/src/future/async_drop.rs‎

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@@ -161,6 +161,11 @@ async unsafe fn surface_drop_in_place<T: Drop + ?Sized>(ptr: *mut T) {
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/// wrapped future completes by returning `Poll::Ready(())` on poll. This
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/// is useful for constructing async destructors to guarantee this
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/// "fuse" property
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//
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// FIXME: Consider optimizing combinators to not have to use fuse in majority
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// of cases, perhaps by adding `#[(rustc_)idempotent(_future)]` attribute for
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// async functions and blocks with the unit return type. However current layout
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// optimizations currently encode `None` case into the async block's discriminant.
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structFuse<T>{
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inner:Option<T>,
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}
@@ -251,6 +256,14 @@ async unsafe fn either<O: IntoFuture<Output = ()>, M: IntoFuture<Output = ()>, T
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}
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}
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#[cfg(not(bootstrap))]
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#[lang ="async_drop_deferred_drop_in_place"]
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asyncunsafefndeferred_drop_in_place<T>(to_drop:*mutT){
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// SAFETY: same safety requirements as with drop_in_place (implied by
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// function's name)
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unsafe{crate::ptr::drop_in_place(to_drop)}
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}
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/// Used for noop async destructors. We don't use [`core::future::Ready`]
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/// because it panics after its second poll, which could be potentially
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/// bad if that would happen during the cleanup.

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