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Auto merge of #103957 - JakobDegen:drop-retag, r=RalfJung

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Retag as FnEntry on `drop_in_place`

This commit changes the mir drop shim to always retag its argument as if it were a `&mut`.

cc rust-lang/unsafe-code-guidelines#373
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bors 2022-12-22 17:48:43 +00:00
commit cca80b9a81
10 changed files with 199 additions and 15 deletions
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13
compiler/rustc_middle/src/mir/syntax.rs
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@ -564,14 +564,13 @@ pub enum TerminatorKind<'tcx> {
Unreachable,
/// The behavior of this statement differs significantly before and after drop elaboration.
/// After drop elaboration, `Drop` executes the drop glue for the specified place, after which
/// it continues execution/unwinds at the given basic blocks. It is possible that executing drop
/// glue is special - this would be part of Rust's memory model. (**FIXME**: due we have an
/// issue tracking if drop glue has any interesting semantics in addition to those of a function
/// call?)
///
/// `Drop` before drop elaboration is a *conditional* execution of the drop glue. Specifically, the
/// `Drop` will be executed if...
/// After drop elaboration: `Drop` terminators are a complete nop for types that have no drop
/// glue. For other types, `Drop` terminators behave exactly like a call to
/// `core::mem::drop_in_place` with a pointer to the given place.
///
/// `Drop` before drop elaboration is a *conditional* execution of the drop glue. Specifically,
/// the `Drop` will be executed if...
///
/// **Needs clarification**: End of that sentence. This in effect should document the exact
/// behavior of drop elaboration. The following sounds vaguely right, but I'm not quite sure: