Auto merge of rust-lang#135227 - matthiaskrgr:rollup-5itqccr, r=matthiaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#134389 (Condvar: implement wait_timeout for targets without threads)
 - rust-lang#134920 (Convert typeck constraints in location-sensitive polonius)
 - rust-lang#135032 (triagebot: register `relnotes-interest-group` ping group)
 - rust-lang#135176 (More compelling env_clear() examples)
 - rust-lang#135184 (Reserve x18 register for aarch64 wrs vxworks target)
 - rust-lang#135203 (arm: add unstable soft-float target feature)
 - rust-lang#135219 (warn about broken simd not only on structs but also enums and unions when we didn't opt in to it)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -242,7 +242,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
             }
 
-            ast::ItemKind::Struct(..) => {
+            ast::ItemKind::Struct(..) | ast::ItemKind::Enum(..) | ast::ItemKind::Union(..) => {
                 for attr in attr::filter_by_name(&i.attrs, sym::repr) {
                     for item in attr.meta_item_list().unwrap_or_else(ThinVec::new) {
                         if item.has_name(sym::simd) {

compiler/rustc_borrowck/src/borrow_set.rs

@@ -11,7 +11,6 @@ use rustc_mir_dataflow::move_paths::MoveData;
 use tracing::debug;
 
 use crate::BorrowIndex;
-use crate::path_utils::allow_two_phase_borrow;
 use crate::place_ext::PlaceExt;
 
 pub struct BorrowSet<'tcx> {
@@ -350,7 +349,7 @@ impl<'a, 'tcx> GatherBorrows<'a, 'tcx> {
             start_location, assigned_place, borrow_index,
         );
 
-        if !allow_two_phase_borrow(kind) {
+        if !kind.allows_two_phase_borrow() {
             debug!("  -> {:?}", start_location);
             return;
         }

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -10,6 +10,7 @@ use rustc_hir::intravisit::Visitor;
 use rustc_hir::{self as hir, BindingMode, ByRef, Node};
 use rustc_middle::bug;
 use rustc_middle::hir::place::PlaceBase;
+use rustc_middle::mir::visit::PlaceContext;
 use rustc_middle::mir::{
     self, BindingForm, Local, LocalDecl, LocalInfo, LocalKind, Location, Mutability, Place,
     PlaceRef, ProjectionElem,
@@ -22,7 +23,6 @@ use rustc_trait_selection::traits;
 use tracing::debug;
 
 use crate::diagnostics::BorrowedContentSource;
-use crate::util::FindAssignments;
 use crate::{MirBorrowckCtxt, session_diagnostics};
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
@@ -1088,6 +1088,38 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         }
     }
 
+    /// Finds all statements that assign directly to local (i.e., X = ...) and returns their
+    /// locations.
+    fn find_assignments(&self, local: Local) -> Vec<Location> {
+        use rustc_middle::mir::visit::Visitor;
+
+        struct FindLocalAssignmentVisitor {
+            needle: Local,
+            locations: Vec<Location>,
+        }
+
+        impl<'tcx> Visitor<'tcx> for FindLocalAssignmentVisitor {
+            fn visit_local(
+                &mut self,
+                local: Local,
+                place_context: PlaceContext,
+                location: Location,
+            ) {
+                if self.needle != local {
+                    return;
+                }
+
+                if place_context.is_place_assignment() {
+                    self.locations.push(location);
+                }
+            }
+        }
+
+        let mut visitor = FindLocalAssignmentVisitor { needle: local, locations: vec![] };
+        visitor.visit_body(self.body);
+        visitor.locations
+    }
+
     fn suggest_make_local_mut(&self, err: &mut Diag<'_>, local: Local, name: Symbol) {
         let local_decl = &self.body.local_decls[local];
 
@@ -1121,7 +1153,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             })) => {
                 // check if the RHS is from desugaring
                 let opt_assignment_rhs_span =
-                    self.body.find_assignments(local).first().map(|&location| {
+                    self.find_assignments(local).first().map(|&location| {
                         if let Some(mir::Statement {
                             source_info: _,
                             kind:

compiler/rustc_borrowck/src/lib.rs

@@ -17,7 +17,7 @@
 
 use std::cell::RefCell;
 use std::marker::PhantomData;
-use std::ops::Deref;
+use std::ops::{ControlFlow, Deref};
 
 use rustc_abi::FieldIdx;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
@@ -81,7 +81,6 @@ mod session_diagnostics;
 mod type_check;
 mod universal_regions;
 mod used_muts;
-mod util;
 
 /// A public API provided for the Rust compiler consumers.
 pub mod consumers;
@@ -1054,31 +1053,31 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                         rw,
                         (borrow_index, borrow),
                     );
-                    Control::Continue
+                    ControlFlow::Continue(())
                 }
 
                 (Read(_), BorrowKind::Shared | BorrowKind::Fake(_))
                 | (
                     Read(ReadKind::Borrow(BorrowKind::Fake(FakeBorrowKind::Shallow))),
                     BorrowKind::Mut { .. },
-                ) => Control::Continue,
+                ) => ControlFlow::Continue(()),
 
                 (Reservation(_), BorrowKind::Fake(_) | BorrowKind::Shared) => {
                     // This used to be a future compatibility warning (to be
                     // disallowed on NLL). See rust-lang/rust#56254
-                    Control::Continue
+                    ControlFlow::Continue(())
                 }
 
                 (Write(WriteKind::Move), BorrowKind::Fake(FakeBorrowKind::Shallow)) => {
                     // Handled by initialization checks.
-                    Control::Continue
+                    ControlFlow::Continue(())
                 }
 
                 (Read(kind), BorrowKind::Mut { .. }) => {
                     // Reading from mere reservations of mutable-borrows is OK.
                     if !is_active(this.dominators(), borrow, location) {
-                        assert!(allow_two_phase_borrow(borrow.kind));
-                        return Control::Continue;
+                        assert!(borrow.kind.allows_two_phase_borrow());
+                        return ControlFlow::Continue(());
                     }
 
                     error_reported = true;
@@ -1094,7 +1093,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                             this.buffer_error(err);
                         }
                     }
-                    Control::Break
+                    ControlFlow::Break(())
                 }
 
                 (Reservation(kind) | Activation(kind, _) | Write(kind), _) => {
@@ -1141,7 +1140,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                             this.report_illegal_mutation_of_borrowed(location, place_span, borrow)
                         }
                     }
-                    Control::Break
+                    ControlFlow::Break(())
                 }
             },
         );
@@ -1185,7 +1184,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                     }
                     BorrowKind::Mut { .. } => {
                         let wk = WriteKind::MutableBorrow(bk);
-                        if allow_two_phase_borrow(bk) {
+                        if bk.allows_two_phase_borrow() {
                             (Deep, Reservation(wk))
                         } else {
                             (Deep, Write(wk))

compiler/rustc_borrowck/src/nll.rs

@@ -142,9 +142,9 @@ pub(crate) fn compute_regions<'a, 'tcx>(
 
     // If requested for `-Zpolonius=next`, convert NLL constraints to localized outlives
     // constraints.
-    let localized_outlives_constraints = polonius_context
-        .as_mut()
-        .map(|polonius_context| polonius_context.create_localized_constraints(&mut regioncx, body));
+    let localized_outlives_constraints = polonius_context.as_mut().map(|polonius_context| {
+        polonius_context.create_localized_constraints(infcx.tcx, &regioncx, body)
+    });
 
     // If requested: dump NLL facts, and run legacy polonius analysis.
     let polonius_output = all_facts.as_ref().and_then(|all_facts| {

compiler/rustc_borrowck/src/path_utils.rs

@@ -1,26 +1,14 @@
+use std::ops::ControlFlow;
+
 use rustc_abi::FieldIdx;
 use rustc_data_structures::graph::dominators::Dominators;
-use rustc_middle::mir::{BasicBlock, Body, BorrowKind, Location, Place, PlaceRef, ProjectionElem};
+use rustc_middle::mir::{BasicBlock, Body, Location, Place, PlaceRef, ProjectionElem};
 use rustc_middle::ty::TyCtxt;
 use tracing::debug;
 
 use crate::borrow_set::{BorrowData, BorrowSet, TwoPhaseActivation};
 use crate::{AccessDepth, BorrowIndex, places_conflict};
 
-/// Returns `true` if the borrow represented by `kind` is
-/// allowed to be split into separate Reservation and
-/// Activation phases.
-pub(super) fn allow_two_phase_borrow(kind: BorrowKind) -> bool {
-    kind.allows_two_phase_borrow()
-}
-
-/// Control for the path borrow checking code
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
-pub(super) enum Control {
-    Continue,
-    Break,
-}
-
 /// Encapsulates the idea of iterating over every borrow that involves a particular path
 pub(super) fn each_borrow_involving_path<'tcx, F, I, S>(
     s: &mut S,
@@ -31,7 +19,7 @@ pub(super) fn each_borrow_involving_path<'tcx, F, I, S>(
     is_candidate: I,
     mut op: F,
 ) where
-    F: FnMut(&mut S, BorrowIndex, &BorrowData<'tcx>) -> Control,
+    F: FnMut(&mut S, BorrowIndex, &BorrowData<'tcx>) -> ControlFlow<()>,
     I: Fn(BorrowIndex) -> bool,
 {
     let (access, place) = access_place;
@@ -62,7 +50,7 @@ pub(super) fn each_borrow_involving_path<'tcx, F, I, S>(
                 i, borrowed, place, access
             );
             let ctrl = op(s, i, borrowed);
-            if ctrl == Control::Break {
+            if matches!(ctrl, ControlFlow::Break(_)) {
                 return;
             }
         }

compiler/rustc_borrowck/src/polonius/legacy/loan_invalidations.rs

@@ -1,3 +1,5 @@
+use std::ops::ControlFlow;
+
 use rustc_data_structures::graph::dominators::Dominators;
 use rustc_middle::bug;
 use rustc_middle::mir::visit::Visitor;
@@ -260,7 +262,7 @@ impl<'a, 'tcx> LoanInvalidationsGenerator<'a, 'tcx> {
                     }
                     BorrowKind::Mut { .. } => {
                         let wk = WriteKind::MutableBorrow(bk);
-                        if allow_two_phase_borrow(bk) {
+                        if bk.allows_two_phase_borrow() {
                             (Deep, Reservation(wk))
                         } else {
                             (Deep, Write(wk))
@@ -378,8 +380,8 @@ impl<'a, 'tcx> LoanInvalidationsGenerator<'a, 'tcx> {
                         // Reading from mere reservations of mutable-borrows is OK.
                         if !is_active(this.dominators, borrow, location) {
                             // If the borrow isn't active yet, reads don't invalidate it
-                            assert!(allow_two_phase_borrow(borrow.kind));
-                            return Control::Continue;
+                            assert!(borrow.kind.allows_two_phase_borrow());
+                            return ControlFlow::Continue(());
                         }
 
                         // Unique and mutable borrows are invalidated by reads from any
@@ -395,7 +397,7 @@ impl<'a, 'tcx> LoanInvalidationsGenerator<'a, 'tcx> {
                         this.emit_loan_invalidated_at(borrow_index, location);
                     }
                 }
-                Control::Continue
+                ControlFlow::Continue(())
             },
         );
     }

compiler/rustc_borrowck/src/polonius/mod.rs

@@ -37,21 +37,20 @@ mod constraints;
 mod dump;
 pub(crate) mod legacy;
 mod liveness_constraints;
+mod typeck_constraints;
 
 use std::collections::BTreeMap;
 
 use rustc_index::bit_set::SparseBitMatrix;
-use rustc_middle::mir::{Body, Location};
-use rustc_middle::ty::RegionVid;
+use rustc_middle::mir::Body;
+use rustc_middle::ty::{RegionVid, TyCtxt};
 use rustc_mir_dataflow::points::PointIndex;
 
 pub(crate) use self::constraints::*;
 pub(crate) use self::dump::dump_polonius_mir;
 use self::liveness_constraints::create_liveness_constraints;
+use self::typeck_constraints::convert_typeck_constraints;
 use crate::RegionInferenceContext;
-use crate::constraints::OutlivesConstraint;
-use crate::region_infer::values::LivenessValues;
-use crate::type_check::Locations;
 
 /// This struct holds the data needed to create the Polonius localized constraints.
 pub(crate) struct PoloniusContext {
@@ -88,14 +87,17 @@ impl PoloniusContext {
     /// - encoding liveness constraints
     pub(crate) fn create_localized_constraints<'tcx>(
         &self,
+        tcx: TyCtxt<'tcx>,
         regioncx: &RegionInferenceContext<'tcx>,
         body: &Body<'tcx>,
     ) -> LocalizedOutlivesConstraintSet {
         let mut localized_outlives_constraints = LocalizedOutlivesConstraintSet::default();
         convert_typeck_constraints(
+            tcx,
             body,
             regioncx.liveness_constraints(),
             regioncx.outlives_constraints(),
+            regioncx.universal_regions(),
             &mut localized_outlives_constraints,
         );
 
@@ -117,38 +119,3 @@ impl PoloniusContext {
         localized_outlives_constraints
     }
 }
-
-/// Propagate loans throughout the subset graph at a given point (with some subtleties around the
-/// location where effects start to be visible).
-fn convert_typeck_constraints<'tcx>(
-    body: &Body<'tcx>,
-    liveness: &LivenessValues,
-    outlives_constraints: impl Iterator<Item = OutlivesConstraint<'tcx>>,
-    localized_outlives_constraints: &mut LocalizedOutlivesConstraintSet,
-) {
-    for outlives_constraint in outlives_constraints {
-        match outlives_constraint.locations {
-            Locations::All(_) => {
-                // For now, turn logical constraints holding at all points into physical edges at
-                // every point in the graph.
-                // FIXME: encode this into *traversal* instead.
-                for (block, bb) in body.basic_blocks.iter_enumerated() {
-                    let statement_count = bb.statements.len();
-                    for statement_index in 0..=statement_count {
-                        let current_location = Location { block, statement_index };
-                        let current_point = liveness.point_from_location(current_location);
-
-                        localized_outlives_constraints.push(LocalizedOutlivesConstraint {
-                            source: outlives_constraint.sup,
-                            from: current_point,
-                            target: outlives_constraint.sub,
-                            to: current_point,
-                        });
-                    }
-                }
-            }
-
-            _ => {}
-        }
-    }
-}

compiler/rustc_borrowck/src/polonius/typeck_constraints.rs

@@ -0,0 +1,241 @@
+use rustc_data_structures::fx::FxHashSet;
+use rustc_middle::mir::{Body, Location, Statement, StatementKind, Terminator, TerminatorKind};
+use rustc_middle::ty::{TyCtxt, TypeVisitable};
+use rustc_mir_dataflow::points::PointIndex;
+
+use super::{LocalizedOutlivesConstraint, LocalizedOutlivesConstraintSet};
+use crate::constraints::OutlivesConstraint;
+use crate::region_infer::values::LivenessValues;
+use crate::type_check::Locations;
+use crate::universal_regions::UniversalRegions;
+
+/// Propagate loans throughout the subset graph at a given point (with some subtleties around the
+/// location where effects start to be visible).
+pub(super) fn convert_typeck_constraints<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    body: &Body<'tcx>,
+    liveness: &LivenessValues,
+    outlives_constraints: impl Iterator<Item = OutlivesConstraint<'tcx>>,
+    universal_regions: &UniversalRegions<'tcx>,
+    localized_outlives_constraints: &mut LocalizedOutlivesConstraintSet,
+) {
+    for outlives_constraint in outlives_constraints {
+        match outlives_constraint.locations {
+            Locations::All(_) => {
+                // For now, turn logical constraints holding at all points into physical edges at
+                // every point in the graph.
+                // FIXME: encode this into *traversal* instead.
+                for (block, bb) in body.basic_blocks.iter_enumerated() {
+                    let statement_count = bb.statements.len();
+                    for statement_index in 0..=statement_count {
+                        let current_location = Location { block, statement_index };
+                        let current_point = liveness.point_from_location(current_location);
+
+                        localized_outlives_constraints.push(LocalizedOutlivesConstraint {
+                            source: outlives_constraint.sup,
+                            from: current_point,
+                            target: outlives_constraint.sub,
+                            to: current_point,
+                        });
+                    }
+                }
+            }
+
+            Locations::Single(location) => {
+                // This constraint is marked as holding at one location, we localize it to that
+                // location or its successor, depending on the corresponding MIR
+                // statement/terminator. Unfortunately, they all show up from typeck as coming "on
+                // entry", so for now we modify them to take effects that should apply "on exit"
+                // into account.
+                //
+                // FIXME: this approach is subtle, complicated, and hard to test, so we should track
+                // this information better in MIR typeck instead, for example with a new `Locations`
+                // variant that contains which node is crossing over between entry and exit.
+                let point = liveness.point_from_location(location);
+                let localized_constraint = if let Some(stmt) =
+                    body[location.block].statements.get(location.statement_index)
+                {
+                    localize_statement_constraint(
+                        tcx,
+                        body,
+                        stmt,
+                        liveness,
+                        &outlives_constraint,
+                        location,
+                        point,
+                        universal_regions,
+                    )
+                } else {
+                    assert_eq!(location.statement_index, body[location.block].statements.len());
+                    let terminator = body[location.block].terminator();
+                    localize_terminator_constraint(
+                        tcx,
+                        body,
+                        terminator,
+                        liveness,
+                        &outlives_constraint,
+                        point,
+                        universal_regions,
+                    )
+                };
+                localized_outlives_constraints.push(localized_constraint);
+            }
+        }
+    }
+}
+
+/// For a given outlives constraint arising from a MIR statement, localize the constraint with the
+/// needed CFG `from`-`to` intra-block nodes.
+fn localize_statement_constraint<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    body: &Body<'tcx>,
+    stmt: &Statement<'tcx>,
+    liveness: &LivenessValues,
+    outlives_constraint: &OutlivesConstraint<'tcx>,
+    current_location: Location,
+    current_point: PointIndex,
+    universal_regions: &UniversalRegions<'tcx>,
+) -> LocalizedOutlivesConstraint {
+    match &stmt.kind {
+        StatementKind::Assign(box (lhs, rhs)) => {
+            // To create localized outlives constraints without midpoints, we rely on the property
+            // that no input regions from the RHS of the assignment will flow into themselves: they
+            // should not appear in the output regions in the LHS. We believe this to be true by
+            // construction of the MIR, via temporaries, and assert it here.
+            //
+            // We think we don't need midpoints because:
+            // - every LHS Place has a unique set of regions that don't appear elsewhere
+            // - this implies that for them to be part of the RHS, the same Place must be read and
+            //   written
+            // - and that should be impossible in MIR
+            //
+            // When we have a more complete implementation in the future, tested with crater, etc,
+            // we can relax this to a debug assert instead, or remove it.
+            assert!(
+                {
+                    let mut lhs_regions = FxHashSet::default();
+                    tcx.for_each_free_region(lhs, |region| {
+                        let region = universal_regions.to_region_vid(region);
+                        lhs_regions.insert(region);
+                    });
+
+                    let mut rhs_regions = FxHashSet::default();
+                    tcx.for_each_free_region(rhs, |region| {
+                        let region = universal_regions.to_region_vid(region);
+                        rhs_regions.insert(region);
+                    });
+
+                    // The intersection between LHS and RHS regions should be empty.
+                    lhs_regions.is_disjoint(&rhs_regions)
+                },
+                "there should be no common regions between the LHS and RHS of an assignment"
+            );
+
+            // As mentioned earlier, we should be tracking these better upstream but: we want to
+            // relate the types on entry to the type of the place on exit. That is, outlives
+            // constraints on the RHS are on entry, and outlives constraints to/from the LHS are on
+            // exit (i.e. on entry to the successor location).
+            let lhs_ty = body.local_decls[lhs.local].ty;
+            let successor_location = Location {
+                block: current_location.block,
+                statement_index: current_location.statement_index + 1,
+            };
+            let successor_point = liveness.point_from_location(successor_location);
+            compute_constraint_direction(
+                tcx,
+                outlives_constraint,
+                &lhs_ty,
+                current_point,
+                successor_point,
+                universal_regions,
+            )
+        }
+        _ => {
+            // For the other cases, we localize an outlives constraint to where it arises.
+            LocalizedOutlivesConstraint {
+                source: outlives_constraint.sup,
+                from: current_point,
+                target: outlives_constraint.sub,
+                to: current_point,
+            }
+        }
+    }
+}
+
+/// For a given outlives constraint arising from a MIR terminator, localize the constraint with the
+/// needed CFG `from`-`to` inter-block nodes.
+fn localize_terminator_constraint<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    body: &Body<'tcx>,
+    terminator: &Terminator<'tcx>,
+    liveness: &LivenessValues,
+    outlives_constraint: &OutlivesConstraint<'tcx>,
+    current_point: PointIndex,
+    universal_regions: &UniversalRegions<'tcx>,
+) -> LocalizedOutlivesConstraint {
+    // FIXME: check if other terminators need the same handling as `Call`s, in particular
+    // Assert/Yield/Drop. A handful of tests are failing with Drop related issues, as well as some
+    // coroutine tests, and that may be why.
+    match &terminator.kind {
+        // FIXME: also handle diverging calls.
+        TerminatorKind::Call { destination, target: Some(target), .. } => {
+            // Calls are similar to assignments, and thus follow the same pattern. If there is a
+            // target for the call we also relate what flows into the destination here to entry to
+            // that successor.
+            let destination_ty = destination.ty(&body.local_decls, tcx);
+            let successor_location = Location { block: *target, statement_index: 0 };
+            let successor_point = liveness.point_from_location(successor_location);
+            compute_constraint_direction(
+                tcx,
+                outlives_constraint,
+                &destination_ty,
+                current_point,
+                successor_point,
+                universal_regions,
+            )
+        }
+        _ => {
+            // Typeck constraints guide loans between regions at the current point, so we do that in
+            // the general case, and liveness will take care of making them flow to the terminator's
+            // successors.
+            LocalizedOutlivesConstraint {
+                source: outlives_constraint.sup,
+                from: current_point,
+                target: outlives_constraint.sub,
+                to: current_point,
+            }
+        }
+    }
+}
+/// For a given outlives constraint and CFG edge, returns the localized constraint with the
+/// appropriate `from`-`to` direction. This is computed according to whether the constraint flows to
+/// or from a free region in the given `value`, some kind of result for an effectful operation, like
+/// the LHS of an assignment.
+fn compute_constraint_direction<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    outlives_constraint: &OutlivesConstraint<'tcx>,
+    value: &impl TypeVisitable<TyCtxt<'tcx>>,
+    current_point: PointIndex,
+    successor_point: PointIndex,
+    universal_regions: &UniversalRegions<'tcx>,
+) -> LocalizedOutlivesConstraint {
+    let mut to = current_point;
+    let mut from = current_point;
+    tcx.for_each_free_region(value, |region| {
+        let region = universal_regions.to_region_vid(region);
+        if region == outlives_constraint.sub {
+            // This constraint flows into the result, its effects start becoming visible on exit.
+            to = successor_point;
+        } else if region == outlives_constraint.sup {
+            // This constraint flows from the result, its effects start becoming visible on exit.
+            from = successor_point;
+        }
+    });
+
+    LocalizedOutlivesConstraint {
+        source: outlives_constraint.sup,
+        from,
+        target: outlives_constraint.sub,
+        to,
+    }
+}

compiler/rustc_borrowck/src/util/collect_writes.rs

@@ -455,6 +455,8 @@ impl BorrowKind {
         }
     }
 
+    /// Returns whether borrows represented by this kind are allowed to be split into separate
+    /// Reservation and Activation phases.
     pub fn allows_two_phase_borrow(&self) -> bool {
         match *self {
             BorrowKind::Shared

compiler/rustc_borrowck/src/util/mod.rs

@@ -13,7 +13,7 @@ pub(crate) fn target() -> Target {
         data_layout: "e-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32".into(),
         arch: "aarch64".into(),
         options: TargetOptions {
-            features: "+v8a".into(),
+            features: "+v8a,+reserve-x18".into(),
             max_atomic_width: Some(128),
             stack_probes: StackProbeType::Inline,
             ..base::vxworks::opts()

compiler/rustc_middle/src/mir/statement.rs

@@ -148,6 +148,11 @@ const ARM_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("neon", Unstable(sym::arm_target_feature), &["vfp3"]),
     ("rclass", Unstable(sym::arm_target_feature), &[]),
     ("sha2", Unstable(sym::arm_target_feature), &["neon"]),
+    // This can be *disabled* on non-`hf` targets to enable the use
+    // of hardfloats while keeping the softfloat ABI.
+    // FIXME before stabilization: Should we expose this as a `hard-float` target feature instead of
+    // matching the odd negative feature LLVM uses?
+    ("soft-float", Unstable(sym::arm_target_feature), &[]),
     // This is needed for inline assembly, but shouldn't be stabilized as-is
     // since it should be enabled per-function using #[instruction_set], not
     // #[target_feature].
@@ -790,6 +795,9 @@ impl Target {
                 match self.llvm_floatabi.unwrap() {
                     FloatAbi::Soft => {
                         // Nothing special required, will use soft-float ABI throughout.
+                        // We can even allow `-soft-float` here; in fact that is useful as it lets
+                        // people use FPU instructions with a softfloat ABI (corresponds to
+                        // `-mfloat-abi=softfp` in GCC/clang).
                         NOTHING
                     }
                     FloatAbi::Hard => {

compiler/rustc_target/src/spec/targets/aarch64_wrs_vxworks.rs

@@ -868,13 +868,17 @@ impl Command {
     ///
     /// # Examples
     ///
+    /// Prevent any inherited `GIT_DIR` variable from changing the target of the `git` command,
+    /// while allowing all other variables, like `GIT_AUTHOR_NAME`.
+    ///
     /// ```no_run
     /// use std::process::Command;
     ///
-    /// Command::new("ls")
-    ///     .env_remove("PATH")
-    ///     .spawn()
-    ///     .expect("ls command failed to start");
+    /// Command::new("git")
+    ///     .arg("commit")
+    ///     .env_remove("GIT_DIR")
+    ///     .spawn()?;
+    /// # std::io::Result::Ok(())
     /// ```
     #[stable(feature = "process", since = "1.0.0")]
     pub fn env_remove<K: AsRef<OsStr>>(&mut self, key: K) -> &mut Command {
@@ -896,13 +900,17 @@ impl Command {
     ///
     /// # Examples
     ///
+    /// The behavior of `sort` is affected by `LANG` and `LC_*` environment variables.
+    /// Clearing the environment makes `sort`'s behavior independent of the parent processes' language.
+    ///
     /// ```no_run
     /// use std::process::Command;
     ///
-    /// Command::new("ls")
+    /// Command::new("sort")
+    ///     .arg("file.txt")
     ///     .env_clear()
-    ///     .spawn()
-    ///     .expect("ls command failed to start");
+    ///     .spawn()?;
+    /// # std::io::Result::Ok(())
     /// ```
     #[stable(feature = "process", since = "1.0.0")]
     pub fn env_clear(&mut self) -> &mut Command {

compiler/rustc_target/src/target_features.rs

@@ -1,4 +1,5 @@
 use crate::sys::sync::Mutex;
+use crate::thread::sleep;
 use crate::time::Duration;
 
 pub struct Condvar {}
@@ -19,7 +20,8 @@ impl Condvar {
         panic!("condvar wait not supported")
     }
 
-    pub unsafe fn wait_timeout(&self, _mutex: &Mutex, _dur: Duration) -> bool {
-        panic!("condvar wait not supported");
+    pub unsafe fn wait_timeout(&self, _mutex: &Mutex, dur: Duration) -> bool {
+        sleep(dur);
+        false
     }
 }

library/std/src/process.rs

@@ -202,6 +202,7 @@ LL |     cfg!(target_feature = "_UNEXPECTED_VALUE");
 `sme-lutv2`
 `sme2`
 `sme2p1`
+`soft-float`
 `spe`
 `ssbs`
 `sse`

library/std/src/sys/sync/condvar/no_threads.rs

@@ -1,9 +1,17 @@
-#[repr(simd)] //~ error: SIMD types are experimental
+#[repr(simd)] //~ ERROR: SIMD types are experimental
 struct Foo([u64; 2]);
 
 #[repr(C)] //~ ERROR conflicting representation hints
 //~^ WARN this was previously accepted
-#[repr(simd)] //~ error: SIMD types are experimental
+#[repr(simd)] //~ ERROR: SIMD types are experimental
 struct Bar([u64; 2]);
 
+#[repr(simd)] //~ ERROR: SIMD types are experimental
+//~^ ERROR: attribute should be applied to a struct
+union U {f: u32}
+
+#[repr(simd)] //~ ERROR: SIMD types are experimental
+//~^ error: attribute should be applied to a struct
+enum E { X }
+
 fn main() {}

tests/ui/check-cfg/target_feature.stderr

@@ -18,6 +18,26 @@ LL | #[repr(simd)]
    = help: add `#![feature(repr_simd)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
+error[E0658]: SIMD types are experimental and possibly buggy
+  --> $DIR/feature-gate-repr-simd.rs:9:1
+   |
+LL | #[repr(simd)]
+   | ^^^^^^^^^^^^^
+   |
+   = note: see issue #27731 <https://github.com/rust-lang/rust/issues/27731> for more information
+   = help: add `#![feature(repr_simd)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: SIMD types are experimental and possibly buggy
+  --> $DIR/feature-gate-repr-simd.rs:13:1
+   |
+LL | #[repr(simd)]
+   | ^^^^^^^^^^^^^
+   |
+   = note: see issue #27731 <https://github.com/rust-lang/rust/issues/27731> for more information
+   = help: add `#![feature(repr_simd)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
 error[E0566]: conflicting representation hints
   --> $DIR/feature-gate-repr-simd.rs:4:8
    |
@@ -31,10 +51,28 @@ LL | #[repr(simd)]
    = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
    = note: `#[deny(conflicting_repr_hints)]` on by default
 
-error: aborting due to 3 previous errors
+error[E0517]: attribute should be applied to a struct
+  --> $DIR/feature-gate-repr-simd.rs:9:8
+   |
+LL | #[repr(simd)]
+   |        ^^^^
+LL |
+LL | union U {f: u32}
+   | ---------------- not a struct
+
+error[E0517]: attribute should be applied to a struct
+  --> $DIR/feature-gate-repr-simd.rs:13:8
+   |
+LL | #[repr(simd)]
+   |        ^^^^
+LL |
+LL | enum E { X }
+   | ------------ not a struct
+
+error: aborting due to 7 previous errors
 
-Some errors have detailed explanations: E0566, E0658.
-For more information about an error, try `rustc --explain E0566`.
+Some errors have detailed explanations: E0517, E0566, E0658.
+For more information about an error, try `rustc --explain E0517`.
 Future incompatibility report: Future breakage diagnostic:
 error[E0566]: conflicting representation hints
   --> $DIR/feature-gate-repr-simd.rs:4:8

tests/ui/feature-gates/feature-gate-repr-simd.rs

@@ -5,6 +5,8 @@
 #[repr(simd)]
 //~^ ERROR: attribute should be applied to a struct [E0517]
 //~| ERROR: unsupported representation for zero-variant enum [E0084]
+//~| ERROR: SIMD types are experimental and possibly buggy [E0658]
+
 enum Es {}
 static CLs: Es;
 //~^ ERROR: free static item without body

tests/ui/feature-gates/feature-gate-repr-simd.stderr

@@ -1,11 +1,21 @@
 error: free static item without body
-  --> $DIR/issue-83505-repr-simd.rs:9:1
+  --> $DIR/issue-83505-repr-simd.rs:11:1
    |
 LL | static CLs: Es;
    | ^^^^^^^^^^^^^^-
    |               |
    |               help: provide a definition for the static: `= <expr>;`
 
+error[E0658]: SIMD types are experimental and possibly buggy
+  --> $DIR/issue-83505-repr-simd.rs:5:1
+   |
+LL | #[repr(simd)]
+   | ^^^^^^^^^^^^^
+   |
+   = note: see issue #27731 <https://github.com/rust-lang/rust/issues/27731> for more information
+   = help: add `#![feature(repr_simd)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
 error[E0517]: attribute should be applied to a struct
   --> $DIR/issue-83505-repr-simd.rs:5:8
    |
@@ -24,7 +34,7 @@ LL | #[repr(simd)]
 LL | enum Es {}
    | ------- zero-variant enum
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0084, E0517.
+Some errors have detailed explanations: E0084, E0517, E0658.
 For more information about an error, try `rustc --explain E0084`.

tests/ui/repr/issue-83505-repr-simd.rs

@@ -172,6 +172,12 @@ issues).
 """
 label = "O-emscripten"
 
+[ping.relnotes-interest-group]
+message = """\
+Hi relnotes-interest-group, this PR adds release notes. Could you review this PR
+if you have time? Thanks <3
+"""
+
 [prioritize]
 label = "I-prioritize"