Move coroutine upvars into locals for better memory economy

compiler/rustc_abi/src/layout.rs

@@ -3,6 +3,7 @@ use std::fmt::{self, Write};
 use std::ops::{Bound, Deref};
 use std::{cmp, iter};
 
+pub use coroutine::PackCoroutineLayout;
 use rustc_hashes::Hash64;
 use rustc_index::Idx;
 use rustc_index::bit_set::BitMatrix;
@@ -210,17 +211,21 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
     >(
         &self,
         local_layouts: &IndexSlice<LocalIdx, F>,
-        prefix_layouts: IndexVec<FieldIdx, F>,
+        relocated_upvars: &IndexSlice<LocalIdx, Option<LocalIdx>>,
+        upvar_layouts: IndexVec<FieldIdx, F>,
         variant_fields: &IndexSlice<VariantIdx, IndexVec<FieldIdx, LocalIdx>>,
         storage_conflicts: &BitMatrix<LocalIdx, LocalIdx>,
+        pack: PackCoroutineLayout,
         tag_to_layout: impl Fn(Scalar) -> F,
     ) -> LayoutCalculatorResult<FieldIdx, VariantIdx, F> {
         coroutine::layout(
             self,
             local_layouts,
-            prefix_layouts,
+            relocated_upvars,
+            upvar_layouts,
             variant_fields,
             storage_conflicts,
+            pack,
             tag_to_layout,
         )
     }

compiler/rustc_abi/src/layout/coroutine.rs

@@ -30,6 +30,17 @@ use crate::{
     StructKind, TagEncoding, Variants, WrappingRange,
 };
 
+/// This option controls how coroutine saved locals are packed
+/// into the coroutine state data
+#[derive(Debug, Clone, Copy)]
+pub enum PackCoroutineLayout {
+    /// The classic layout where captures are always promoted to coroutine state prefix
+    Classic,
+    /// Captures are first saved into the `UNRESUME` state and promoted
+    /// when they are used across more than one suspension
+    CapturesOnly,
+}
+
 /// Overlap eligibility and variant assignment for each CoroutineSavedLocal.
 #[derive(Clone, Debug, PartialEq)]
 enum SavedLocalEligibility<VariantIdx, FieldIdx> {
@@ -145,20 +156,23 @@ 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>>,
+    upvar_layouts: IndexVec<FieldIdx, F>,
     variant_fields: &IndexSlice<VariantIdx, IndexVec<FieldIdx, LocalIdx>>,
     storage_conflicts: &BitMatrix<LocalIdx, LocalIdx>,
+    pack: PackCoroutineLayout,
     tag_to_layout: impl Fn(Scalar) -> F,
 ) -> super::LayoutCalculatorResult<FieldIdx, VariantIdx, F> {
     use SavedLocalEligibility::*;
 
     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.next_index();
+    // Build a prefix layout, consisting of only the state tag and, as per request, upvars
+    let tag_index = match pack {
+        PackCoroutineLayout::CapturesOnly => FieldIdx::new(0),
+        PackCoroutineLayout::Classic => upvar_layouts.next_index(),
+    };
 
     // `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 +183,28 @@ 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);
+    // FIXME: when we introduce more pack scheme, we need to change the prefix layout here
+    let prefix_layouts: IndexVec<_, _> = match pack {
+        PackCoroutineLayout::Classic => {
+            // Classic scheme packs the states as follows
+            // [ <upvars>.. , <state tag>, <promoted ineligibles>] ++ <variant data>
+            // In addition, UNRESUME overlaps with the <upvars> part
+            upvar_layouts.into_iter().chain([tag_to_layout(tag)]).chain(promoted_layouts).collect()
+        }
+        PackCoroutineLayout::CapturesOnly => {
+            [tag_to_layout(tag)].into_iter().chain(promoted_layouts).collect()
+        }
+    };
+    debug!(?prefix_layouts, ?pack);
     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 } => {
@@ -218,19 +243,67 @@ pub(super) fn layout<
     let variants = variant_fields
         .iter_enumerated()
         .map(|(index, variant_fields)| {
+            let is_unresumed = index == VariantIdx::new(0);
+            if is_unresumed && matches!(pack, PackCoroutineLayout::Classic) {
+                let fields = FieldsShape::Arbitrary {
+                    offsets: (0..tag_index.index()).map(|i| outer_fields.offset(i)).collect(),
+                    memory_index: (0..tag_index.index())
+                        .map(|i| {
+                            (outer_fields.memory_index(i) + promoted_memory_index.len()) as u32
+                        })
+                        .collect(),
+                };
+                let align = prefix.align;
+                let size = prefix.size;
+                return Ok(LayoutData {
+                    fields,
+                    variants: Variants::Single { index },
+                    backend_repr: BackendRepr::Memory { sized: true },
+                    largest_niche: None,
+                    uninhabited: false,
+                    align,
+                    size,
+                    max_repr_align: None,
+                    unadjusted_abi_align: align.abi,
+                    randomization_seed: Default::default(),
+                });
+            }
+            let mut is_ineligible = IndexVec::from_elem_n(None, variant_fields.len());
+            for (field, &local) in variant_fields.iter_enumerated() {
+                if is_unresumed {
+                    if 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 +327,14 @@ 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

compiler/rustc_abi/src/lib.rs

@@ -67,7 +67,9 @@ pub use canon_abi::{ArmCall, CanonAbi, InterruptKind, X86Call};
 pub use extern_abi::CVariadicStatus;
 pub use extern_abi::{ExternAbi, all_names};
 #[cfg(feature = "nightly")]
-pub use layout::{FIRST_VARIANT, FieldIdx, Layout, TyAbiInterface, TyAndLayout, VariantIdx};
+pub use layout::{
+    FIRST_VARIANT, FieldIdx, Layout, PackCoroutineLayout, TyAbiInterface, TyAndLayout, VariantIdx,
+};
 pub use layout::{LayoutCalculator, LayoutCalculatorError};
 
 /// Requirements for a `StableHashingContext` to be used in this crate.

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -421,49 +421,7 @@ 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,
-                        );
-                    }
-                }
-
-                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);
-                }
+                self.suggest_mutable_upvar(*upvar_index, the_place_err, &mut err, span, act);
             }
 
             // Complete hack to approximate old AST-borrowck diagnostic: if the span starts
@@ -569,6 +527,58 @@ 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

@@ -2495,7 +2495,7 @@ 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
+                if !matches!(is_local_mutation_allowed, LocalMutationIsAllowed::Yes)
                     && self.is_local_ever_initialized(local, state).is_some()
                 {
                     self.used_mut.insert(local);

compiler/rustc_borrowck/src/path_utils.rs

@@ -3,7 +3,7 @@ use std::ops::ControlFlow;
 use rustc_abi::FieldIdx;
 use rustc_data_structures::graph::dominators::Dominators;
 use rustc_middle::mir::{BasicBlock, Body, Location, Place, PlaceRef, ProjectionElem};
-use rustc_middle::ty::TyCtxt;
+use rustc_middle::ty::{CapturedPlace, TyCtxt};
 use tracing::debug;
 
 use crate::borrow_set::{BorrowData, BorrowSet, TwoPhaseActivation};
@@ -133,7 +133,7 @@ pub(super) fn borrow_of_local_data(place: Place<'_>) -> bool {
 /// of a closure type.
 pub(crate) fn is_upvar_field_projection<'tcx>(
     tcx: TyCtxt<'tcx>,
-    upvars: &[&rustc_middle::ty::CapturedPlace<'tcx>],
+    upvars: &[&CapturedPlace<'tcx>],
     place_ref: PlaceRef<'tcx>,
     body: &Body<'tcx>,
 ) -> Option<FieldIdx> {