diff options
| -rw-r--r-- | compiler/rustc_mir_dataflow/src/impls/borrowed_locals.rs | 45 | ||||
| -rw-r--r-- | compiler/rustc_mir_transform/src/generator.rs | 6 |
2 files changed, 13 insertions, 38 deletions
diff --git a/compiler/rustc_mir_dataflow/src/impls/borrowed_locals.rs b/compiler/rustc_mir_dataflow/src/impls/borrowed_locals.rs index bb9755e4f48..4981ab5152c 100644 --- a/compiler/rustc_mir_dataflow/src/impls/borrowed_locals.rs +++ b/compiler/rustc_mir_dataflow/src/impls/borrowed_locals.rs @@ -10,38 +10,11 @@ use rustc_middle::mir::*; /// At present, this is used as a very limited form of alias analysis. For example, /// `MaybeBorrowedLocals` is used to compute which locals are live during a yield expression for /// immovable generators. -pub struct MaybeBorrowedLocals { - ignore_borrow_on_drop: bool, -} - -impl MaybeBorrowedLocals { - /// A dataflow analysis that records whether a pointer or reference exists that may alias the - /// given local. - pub fn all_borrows() -> Self { - MaybeBorrowedLocals { ignore_borrow_on_drop: false } - } -} +pub struct MaybeBorrowedLocals; impl MaybeBorrowedLocals { - /// During dataflow analysis, ignore the borrow that may occur when a place is dropped. - /// - /// Drop terminators may call custom drop glue (`Drop::drop`), which takes `&mut self` as a - /// parameter. In the general case, a drop impl could launder that reference into the - /// surrounding environment through a raw pointer, thus creating a valid `*mut` pointing to the - /// dropped local. We are not yet willing to declare this particular case UB, so we must treat - /// all dropped locals as mutably borrowed for now. See discussion on [#61069]. - /// - /// In some contexts, we know that this borrow will never occur. For example, during - /// const-eval, custom drop glue cannot be run. Code that calls this should document the - /// assumptions that justify ignoring `Drop` terminators in this way. - /// - /// [#61069]: https://github.com/rust-lang/rust/pull/61069 - pub fn unsound_ignore_borrow_on_drop(self) -> Self { - MaybeBorrowedLocals { ignore_borrow_on_drop: true, ..self } - } - fn transfer_function<'a, T>(&'a self, trans: &'a mut T) -> TransferFunction<'a, T> { - TransferFunction { trans, ignore_borrow_on_drop: self.ignore_borrow_on_drop } + TransferFunction { trans } } } @@ -92,7 +65,6 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeBorrowedLocals { /// A `Visitor` that defines the transfer function for `MaybeBorrowedLocals`. struct TransferFunction<'a, T> { trans: &'a mut T, - ignore_borrow_on_drop: bool, } impl<'tcx, T> Visitor<'tcx> for TransferFunction<'_, T> @@ -146,10 +118,15 @@ where match terminator.kind { mir::TerminatorKind::Drop { place: dropped_place, .. } | mir::TerminatorKind::DropAndReplace { place: dropped_place, .. } => { - // See documentation for `unsound_ignore_borrow_on_drop` for an explanation. - if !self.ignore_borrow_on_drop { - self.trans.gen(dropped_place.local); - } + // Drop terminators may call custom drop glue (`Drop::drop`), which takes `&mut + // self` as a parameter. In the general case, a drop impl could launder that + // reference into the surrounding environment through a raw pointer, thus creating + // a valid `*mut` pointing to the dropped local. We are not yet willing to declare + // this particular case UB, so we must treat all dropped locals as mutably borrowed + // for now. See discussion on [#61069]. + // + // [#61069]: https://github.com/rust-lang/rust/pull/61069 + self.trans.gen(dropped_place.local); } TerminatorKind::Abort diff --git a/compiler/rustc_mir_transform/src/generator.rs b/compiler/rustc_mir_transform/src/generator.rs index 388bb7d3436..d9a66cace52 100644 --- a/compiler/rustc_mir_transform/src/generator.rs +++ b/compiler/rustc_mir_transform/src/generator.rs @@ -463,10 +463,8 @@ fn locals_live_across_suspend_points<'tcx>( // Calculate the MIR locals which have been previously // borrowed (even if they are still active). - let borrowed_locals_results = MaybeBorrowedLocals::all_borrows() - .into_engine(tcx, body_ref) - .pass_name("generator") - .iterate_to_fixpoint(); + let borrowed_locals_results = + MaybeBorrowedLocals.into_engine(tcx, body_ref).pass_name("generator").iterate_to_fixpoint(); let mut borrowed_locals_cursor = rustc_mir_dataflow::ResultsCursor::new(body_ref, &borrowed_locals_results); |