relocate upvars to Unresumed state and make coroutine prefix trivial

Co-authored-by: Dario Nieuwenhuis <dirbaio@dirbaio.net>

compiler/rustc_abi/src/layout.rs

@@ -215,15 +215,15 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
     >(
         &self,
         local_layouts: &IndexSlice<LocalIdx, F>,
-        prefix_layouts: IndexVec<FieldIdx, F>,
+        relocated_upvars: &IndexSlice<LocalIdx, Option<LocalIdx>>,
         variant_fields: &IndexSlice<VariantIdx, IndexVec<FieldIdx, LocalIdx>>,
         storage_conflicts: &BitMatrix<LocalIdx, LocalIdx>,
         tag_to_layout: impl Fn(Scalar) -> F,
     ) -> LayoutCalculatorResult<FieldIdx, VariantIdx, F> {
         coroutine::layout(
             self,
             local_layouts,
-            prefix_layouts,
+            relocated_upvars,
             variant_fields,
             storage_conflicts,
             tag_to_layout,

compiler/rustc_abi/src/layout/coroutine.rs

@@ -145,7 +145,7 @@ pub(super) fn layout<
 >(
     calc: &super::LayoutCalculator<impl HasDataLayout>,
     local_layouts: &IndexSlice<LocalIdx, F>,
-    mut prefix_layouts: IndexVec<FieldIdx, F>,
+    relocated_upvars: &IndexSlice<LocalIdx, Option<LocalIdx>>,
     variant_fields: &IndexSlice<VariantIdx, IndexVec<FieldIdx, LocalIdx>>,
     storage_conflicts: &BitMatrix<LocalIdx, LocalIdx>,
     tag_to_layout: impl Fn(Scalar) -> F,
@@ -155,10 +155,8 @@ pub(super) fn layout<
     let (ineligible_locals, assignments) =
         coroutine_saved_local_eligibility(local_layouts.len(), variant_fields, storage_conflicts);
 
-    // Build a prefix layout, including "promoting" all ineligible
-    // locals as part of the prefix. We compute the layout of all of
-    // these fields at once to get optimal packing.
-    let tag_index = prefix_layouts.len();
+    // Build a prefix layout, consisting of only the state tag.
+    let tag_index = 0;
 
     // `variant_fields` already accounts for the reserved variants, so no need to add them.
     let max_discr = (variant_fields.len() - 1) as u128;
@@ -169,17 +167,17 @@ pub(super) fn layout<
     };
 
     let promoted_layouts = ineligible_locals.iter().map(|local| local_layouts[local]);
-    prefix_layouts.push(tag_to_layout(tag));
-    prefix_layouts.extend(promoted_layouts);
+    let prefix_layouts: IndexVec<_, _> =
+        [tag_to_layout(tag)].into_iter().chain(promoted_layouts).collect();
     let prefix =
         calc.univariant(&prefix_layouts, &ReprOptions::default(), StructKind::AlwaysSized)?;
 
     let (prefix_size, prefix_align) = (prefix.size, prefix.align);
 
-    // Split the prefix layout into the "outer" fields (upvars and
-    // discriminant) and the "promoted" fields. Promoted fields will
-    // get included in each variant that requested them in
-    // CoroutineLayout.
+    // Split the prefix layout into the discriminant and
+    // the "promoted" fields.
+    // Promoted fields will get included in each variant
+    // that requested them in CoroutineLayout.
     debug!("prefix = {:#?}", prefix);
     let (outer_fields, promoted_offsets, promoted_memory_index) = match prefix.fields {
         FieldsShape::Arbitrary { mut offsets, memory_index } => {
@@ -215,22 +213,45 @@ pub(super) fn layout<
 
     let mut size = prefix.size;
     let mut align = prefix.align;
-    let variants = variant_fields
+    let variants: IndexVec<VariantIdx, _> = variant_fields
         .iter_enumerated()
         .map(|(index, variant_fields)| {
+            let is_unresumed = index == VariantIdx::new(0);
+            let mut is_ineligible = IndexVec::from_elem_n(None, variant_fields.len());
+            for (field, &local) in variant_fields.iter_enumerated() {
+                if is_unresumed
+                    && let Some(inner_local) = relocated_upvars[local]
+                    && let Ineligible(Some(promoted_field)) = assignments[inner_local]
+                {
+                    is_ineligible.insert(field, promoted_field);
+                    continue;
+                }
+                match assignments[local] {
+                    Assigned(v) if v == index => {}
+                    Ineligible(Some(promoted_field)) => {
+                        is_ineligible.insert(field, promoted_field);
+                    }
+                    Ineligible(None) => {
+                        panic!("an ineligible local should have been promoted into the prefix")
+                    }
+                    Assigned(_) => {
+                        panic!("an eligible local should have been assigned to exactly one variant")
+                    }
+                    Unassigned => {
+                        panic!("each saved local should have been inspected at least once")
+                    }
+                }
+            }
             // Only include overlap-eligible fields when we compute our variant layout.
-            let variant_only_tys = variant_fields
-                .iter()
-                .filter(|local| match assignments[**local] {
-                    Unassigned => unreachable!(),
-                    Assigned(v) if v == index => true,
-                    Assigned(_) => unreachable!("assignment does not match variant"),
-                    Ineligible(_) => false,
+            let fields: IndexVec<_, _> = variant_fields
+                .iter_enumerated()
+                .filter_map(|(field, &local)| {
+                    if is_ineligible.contains(field) { None } else { Some(local_layouts[local]) }
                 })
-                .map(|local| local_layouts[*local]);
+                .collect();
 
             let mut variant = calc.univariant(
-                &variant_only_tys.collect::<IndexVec<_, _>>(),
+                &fields,
                 &ReprOptions::default(),
                 StructKind::Prefixed(prefix_size, prefix_align.abi),
             )?;
@@ -254,19 +275,14 @@ pub(super) fn layout<
                 IndexVec::from_elem_n(FieldIdx::new(invalid_field_idx), invalid_field_idx);
 
             let mut offsets_and_memory_index = iter::zip(offsets, memory_index);
-            let combined_offsets = variant_fields
+            let combined_offsets = is_ineligible
                 .iter_enumerated()
-                .map(|(i, local)| {
-                    let (offset, memory_index) = match assignments[*local] {
-                        Unassigned => unreachable!(),
-                        Assigned(_) => {
-                            let (offset, memory_index) = offsets_and_memory_index.next().unwrap();
-                            (offset, promoted_memory_index.len() as u32 + memory_index)
-                        }
-                        Ineligible(field_idx) => {
-                            let field_idx = field_idx.unwrap();
-                            (promoted_offsets[field_idx], promoted_memory_index[field_idx])
-                        }
+                .map(|(i, &is_ineligible)| {
+                    let (offset, memory_index) = if let Some(field_idx) = is_ineligible {
+                        (promoted_offsets[field_idx], promoted_memory_index[field_idx])
+                    } else {
+                        let (offset, memory_index) = offsets_and_memory_index.next().unwrap();
+                        (offset, promoted_memory_index.len() as u32 + memory_index)
                     };
                     combined_inverse_memory_index[memory_index] = i;
                     offset
@@ -287,7 +303,7 @@ pub(super) fn layout<
             align = align.max(variant.align);
             Ok(variant)
         })
-        .collect::<Result<IndexVec<VariantIdx, _>, _>>()?;
+        .try_collect()?;
 
     size = size.align_to(align.abi);
 

compiler/rustc_abi/src/lib.rs

@@ -2,6 +2,8 @@
 #![cfg_attr(feature = "nightly", allow(internal_features))]
 #![cfg_attr(feature = "nightly", doc(rust_logo))]
 #![cfg_attr(feature = "nightly", feature(assert_matches))]
+#![cfg_attr(feature = "nightly", feature(iterator_try_collect))]
+#![cfg_attr(feature = "nightly", feature(let_chains))]
 #![cfg_attr(feature = "nightly", feature(rustc_attrs))]
 #![cfg_attr(feature = "nightly", feature(rustdoc_internals))]
 #![cfg_attr(feature = "nightly", feature(step_trait))]

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -393,49 +393,18 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                     Place::ty_from(local, proj_base, self.body, self.infcx.tcx).ty
                 ));
 
-                let captured_place = self.upvars[upvar_index.index()];
-
-                err.span_label(span, format!("cannot {act}"));
-
-                let upvar_hir_id = captured_place.get_root_variable();
-
-                if let Node::Pat(pat) = self.infcx.tcx.hir_node(upvar_hir_id)
-                    && let hir::PatKind::Binding(hir::BindingMode::NONE, _, upvar_ident, _) =
-                        pat.kind
-                {
-                    if upvar_ident.name == kw::SelfLower {
-                        for (_, node) in self.infcx.tcx.hir_parent_iter(upvar_hir_id) {
-                            if let Some(fn_decl) = node.fn_decl() {
-                                if !matches!(
-                                    fn_decl.implicit_self,
-                                    hir::ImplicitSelfKind::RefImm | hir::ImplicitSelfKind::RefMut
-                                ) {
-                                    err.span_suggestion_verbose(
-                                        upvar_ident.span.shrink_to_lo(),
-                                        "consider changing this to be mutable",
-                                        "mut ",
-                                        Applicability::MachineApplicable,
-                                    );
-                                    break;
-                                }
-                            }
-                        }
-                    } else {
-                        err.span_suggestion_verbose(
-                            upvar_ident.span.shrink_to_lo(),
-                            "consider changing this to be mutable",
-                            "mut ",
-                            Applicability::MachineApplicable,
-                        );
-                    }
-                }
+                self.suggest_mutable_upvar(*upvar_index, the_place_err, &mut err, span, act);
+            }
 
-                let tcx = self.infcx.tcx;
-                if let ty::Ref(_, ty, Mutability::Mut) = the_place_err.ty(self.body, tcx).ty.kind()
-                    && let ty::Closure(id, _) = *ty.kind()
-                {
-                    self.show_mutating_upvar(tcx, id.expect_local(), the_place_err, &mut err);
-                }
+            PlaceRef { local, projection: [] }
+                if let Some(upvar_index) = self
+                    .body
+                    .local_upvar_map
+                    .iter_enumerated()
+                    .filter_map(|(field, &local)| local.map(|local| (field, local)))
+                    .find_map(|(field, relocated)| (relocated == local).then_some(field)) =>
+            {
+                self.suggest_mutable_upvar(upvar_index, the_place_err, &mut err, span, act);
             }
 
             // complete hack to approximate old AST-borrowck
@@ -542,6 +511,58 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         }
     }
 
+    fn suggest_mutable_upvar(
+        &self,
+        upvar_index: FieldIdx,
+        the_place_err: PlaceRef<'tcx>,
+        err: &mut Diag<'infcx>,
+        span: Span,
+        act: &str,
+    ) {
+        let captured_place = self.upvars[upvar_index.index()];
+
+        err.span_label(span, format!("cannot {act}"));
+
+        let upvar_hir_id = captured_place.get_root_variable();
+
+        if let Node::Pat(pat) = self.infcx.tcx.hir_node(upvar_hir_id)
+            && let hir::PatKind::Binding(hir::BindingMode::NONE, _, upvar_ident, _) = pat.kind
+        {
+            if upvar_ident.name == kw::SelfLower {
+                for (_, node) in self.infcx.tcx.hir_parent_iter(upvar_hir_id) {
+                    if let Some(fn_decl) = node.fn_decl() {
+                        if !matches!(
+                            fn_decl.implicit_self,
+                            hir::ImplicitSelfKind::RefImm | hir::ImplicitSelfKind::RefMut
+                        ) {
+                            err.span_suggestion_verbose(
+                                upvar_ident.span.shrink_to_lo(),
+                                "consider changing this to be mutable",
+                                "mut ",
+                                Applicability::MachineApplicable,
+                            );
+                            break;
+                        }
+                    }
+                }
+            } else {
+                err.span_suggestion_verbose(
+                    upvar_ident.span.shrink_to_lo(),
+                    "consider changing this to be mutable",
+                    "mut ",
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+
+        let tcx = self.infcx.tcx;
+        if let ty::Ref(_, ty, Mutability::Mut) = the_place_err.ty(self.body, tcx).ty.kind()
+            && let ty::Closure(id, _) = *ty.kind()
+        {
+            self.show_mutating_upvar(tcx, id.expect_local(), the_place_err, err);
+        }
+    }
+
     /// Suggest `map[k] = v` => `map.insert(k, v)` and the like.
     fn suggest_map_index_mut_alternatives(&self, ty: Ty<'tcx>, err: &mut Diag<'infcx>, span: Span) {
         let Some(adt) = ty.ty_adt_def() else { return };

compiler/rustc_borrowck/src/lib.rs

@@ -23,6 +23,7 @@ use std::ops::{ControlFlow, Deref};
 use rustc_abi::FieldIdx;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::graph::dominators::Dominators;
+use rustc_data_structures::unord::UnordMap;
 use rustc_errors::LintDiagnostic;
 use rustc_hir as hir;
 use rustc_hir::CRATE_HIR_ID;
@@ -261,6 +262,7 @@ fn do_mir_borrowck<'tcx>(
             regioncx: &regioncx,
             used_mut: Default::default(),
             used_mut_upvars: SmallVec::new(),
+            local_from_upvars: UnordMap::default(),
             borrow_set: &borrow_set,
             upvars: &[],
             local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
@@ -286,6 +288,11 @@ fn do_mir_borrowck<'tcx>(
         promoted_mbcx.report_move_errors();
     }
 
+    let mut local_from_upvars = UnordMap::default();
+    for (field, &local) in body.local_upvar_map.iter_enumerated() {
+        let Some(local) = local else { continue };
+        local_from_upvars.insert(local, field);
+    }
     let mut mbcx = MirBorrowckCtxt {
         infcx: &infcx,
         body,
@@ -300,6 +307,7 @@ fn do_mir_borrowck<'tcx>(
         regioncx: &regioncx,
         used_mut: Default::default(),
         used_mut_upvars: SmallVec::new(),
+        local_from_upvars,
         borrow_set: &borrow_set,
         upvars: tcx.closure_captures(def),
         local_names,
@@ -555,6 +563,9 @@ struct MirBorrowckCtxt<'a, 'infcx, 'tcx> {
     /// If the function we're checking is a closure, then we'll need to report back the list of
     /// mutable upvars that have been used. This field keeps track of them.
     used_mut_upvars: SmallVec<[FieldIdx; 8]>,
+    /// Since upvars are moved to real locals, we need to map mutations to the locals back to
+    /// the upvars, so that used_mut_upvars is up-to-date.
+    local_from_upvars: UnordMap<Local, FieldIdx>,
     /// Region inference context. This contains the results from region inference and lets us e.g.
     /// find out which CFG points are contained in each borrow region.
     regioncx: &'a RegionInferenceContext<'tcx>,
@@ -2265,7 +2276,9 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
 
         // at this point, we have set up the error reporting state.
         if let Some(init_index) = previously_initialized {
-            if let (AccessKind::Mutate, Some(_)) = (error_access, place.as_local()) {
+            if let (AccessKind::Mutate, Some(local)) = (error_access, place.as_local())
+                && self.body.local_upvar_map.iter().flatten().all(|upvar| upvar != &local)
+            {
                 // If this is a mutate access to an immutable local variable with no projections
                 // report the error as an illegal reassignment
                 let init = &self.move_data.inits[init_index];
@@ -2293,10 +2306,12 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                 // If the local may have been initialized, and it is now currently being
                 // mutated, then it is justified to be annotated with the `mut`
                 // keyword, since the mutation may be a possible reassignment.
-                if is_local_mutation_allowed != LocalMutationIsAllowed::Yes
-                    && self.is_local_ever_initialized(local, state).is_some()
-                {
-                    self.used_mut.insert(local);
+                if !matches!(is_local_mutation_allowed, LocalMutationIsAllowed::Yes) {
+                    if self.is_local_ever_initialized(local, state).is_some() {
+                        self.used_mut.insert(local);
+                    } else if let Some(&field) = self.local_from_upvars.get(&local) {
+                        self.used_mut_upvars.push(field);
+                    }
                 }
             }
             RootPlace {
@@ -2314,6 +2329,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
                     projection: place_projection,
                 }) {
                     self.used_mut_upvars.push(field);
+                } else if let Some(&field) = self.local_from_upvars.get(&place_local) {
+                    self.used_mut_upvars.push(field);
                 }
             }
         }

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -27,8 +27,8 @@ use rustc_middle::ty::cast::CastTy;
 use rustc_middle::ty::fold::fold_regions;
 use rustc_middle::ty::visit::TypeVisitableExt;
 use rustc_middle::ty::{
-    self, Binder, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, CoroutineArgsExt,
-    Dynamic, GenericArgsRef, OpaqueHiddenType, OpaqueTypeKey, RegionVid, Ty, TyCtxt, UserArgs,
+    self, Binder, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations, Dynamic,
+    GenericArgsRef, OpaqueHiddenType, OpaqueTypeKey, RegionVid, Ty, TyCtxt, UserArgs,
     UserTypeAnnotationIndex,
 };
 use rustc_middle::{bug, span_bug};
@@ -1544,11 +1544,11 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 // It doesn't make sense to look at a field beyond the prefix;
                 // these require a variant index, and are not initialized in
                 // aggregate rvalues.
-                match args.as_coroutine().prefix_tys().get(field_index.as_usize()) {
-                    Some(ty) => Ok(*ty),
-                    None => Err(FieldAccessError::OutOfRange {
-                        field_count: args.as_coroutine().prefix_tys().len(),
-                    }),
+                let upvar_tys = &args.as_coroutine().upvar_tys();
+                if let Some(ty) = upvar_tys.get(field_index.as_usize()) {
+                    Ok(*ty)
+                } else {
+                    Err(FieldAccessError::OutOfRange { field_count: upvar_tys.len() })
                 }
             }
             AggregateKind::CoroutineClosure(_, args) => {