Rollup of 8 pull requests

compiler/rustc_abi/src/callconv.rs

@@ -65,8 +65,6 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {
         Ty: TyAbiInterface<'a, C> + Copy,
     {
         match self.backend_repr {
-            BackendRepr::Uninhabited => Err(Heterogeneous),
-
             // The primitive for this algorithm.
             BackendRepr::Scalar(scalar) => {
                 let kind = match scalar.primitive() {

compiler/rustc_abi/src/layout.rs

@@ -130,6 +130,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
             },
             backend_repr: BackendRepr::ScalarPair(a, b),
             largest_niche,
+            uninhabited: false,
             align,
             size,
             max_repr_align: None,
@@ -221,8 +222,9 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
         LayoutData {
             variants: Variants::Empty,
             fields: FieldsShape::Primitive,
-            backend_repr: BackendRepr::Uninhabited,
+            backend_repr: BackendRepr::Memory { sized: true },
             largest_niche: None,
+            uninhabited: true,
             align: dl.i8_align,
             size: Size::ZERO,
             max_repr_align: None,
@@ -400,6 +402,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
             fields: FieldsShape::Union(union_field_count),
             backend_repr: abi,
             largest_niche: None,
+            uninhabited: false,
             align,
             size: size.align_to(align.abi),
             max_repr_align,
@@ -447,7 +450,6 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
                 Scalar::Union { .. } => {}
             };
             match &mut st.backend_repr {
-                BackendRepr::Uninhabited => {}
                 BackendRepr::Scalar(scalar) => hide_niches(scalar),
                 BackendRepr::ScalarPair(a, b) => {
                     hide_niches(a);
@@ -639,9 +641,8 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
             let same_size = size == variant_layouts[largest_variant_index].size;
             let same_align = align == variant_layouts[largest_variant_index].align;
 
-            let abi = if variant_layouts.iter().all(|v| v.is_uninhabited()) {
-                BackendRepr::Uninhabited
-            } else if same_size && same_align && others_zst {
+            let uninhabited = variant_layouts.iter().all(|v| v.is_uninhabited());
+            let abi = if same_size && same_align && others_zst {
                 match variant_layouts[largest_variant_index].backend_repr {
                     // When the total alignment and size match, we can use the
                     // same ABI as the scalar variant with the reserved niche.
@@ -683,6 +684,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
                 },
                 backend_repr: abi,
                 largest_niche,
+                uninhabited,
                 size,
                 align,
                 max_repr_align,
@@ -853,9 +855,8 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
         };
         let mut abi = BackendRepr::Memory { sized: true };
 
-        if layout_variants.iter().all(|v| v.is_uninhabited()) {
-            abi = BackendRepr::Uninhabited;
-        } else if tag.size(dl) == size {
+        let uninhabited = layout_variants.iter().all(|v| v.is_uninhabited());
+        if tag.size(dl) == size {
             // Make sure we only use scalar layout when the enum is entirely its
             // own tag (i.e. it has no padding nor any non-ZST variant fields).
             abi = BackendRepr::Scalar(tag);
@@ -995,6 +996,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
                 memory_index: [0].into(),
             },
             largest_niche,
+            uninhabited,
             backend_repr: abi,
             align,
             size,
@@ -1355,9 +1357,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
                 _ => {}
             }
         }
-        if fields.iter().any(|f| f.is_uninhabited()) {
-            abi = BackendRepr::Uninhabited;
-        }
+        let uninhabited = fields.iter().any(|f| f.is_uninhabited());
 
         let unadjusted_abi_align = if repr.transparent() {
             match layout_of_single_non_zst_field {
@@ -1378,6 +1378,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
             fields: FieldsShape::Arbitrary { offsets, memory_index },
             backend_repr: abi,
             largest_niche,
+            uninhabited,
             align,
             size,
             max_repr_align,

compiler/rustc_abi/src/lib.rs

@@ -1404,7 +1404,6 @@ impl AddressSpace {
 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
 #[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
 pub enum BackendRepr {
-    Uninhabited,
     Scalar(Scalar),
     ScalarPair(Scalar, Scalar),
     Vector {
@@ -1423,10 +1422,9 @@ impl BackendRepr {
     #[inline]
     pub fn is_unsized(&self) -> bool {
         match *self {
-            BackendRepr::Uninhabited
-            | BackendRepr::Scalar(_)
-            | BackendRepr::ScalarPair(..)
-            | BackendRepr::Vector { .. } => false,
+            BackendRepr::Scalar(_) | BackendRepr::ScalarPair(..) | BackendRepr::Vector { .. } => {
+                false
+            }
             BackendRepr::Memory { sized } => !sized,
         }
     }
@@ -1445,12 +1443,6 @@ impl BackendRepr {
         }
     }
 
-    /// Returns `true` if this is an uninhabited type
-    #[inline]
-    pub fn is_uninhabited(&self) -> bool {
-        matches!(*self, BackendRepr::Uninhabited)
-    }
-
     /// Returns `true` if this is a scalar type
     #[inline]
     pub fn is_scalar(&self) -> bool {
@@ -1471,7 +1463,7 @@ impl BackendRepr {
             BackendRepr::Vector { element, count } => {
                 cx.data_layout().vector_align(element.size(cx) * count)
             }
-            BackendRepr::Uninhabited | BackendRepr::Memory { .. } => return None,
+            BackendRepr::Memory { .. } => return None,
         })
     }
 
@@ -1492,7 +1484,7 @@ impl BackendRepr {
                 // to make the size a multiple of align (e.g. for vectors of size 3).
                 (element.size(cx) * count).align_to(self.inherent_align(cx)?.abi)
             }
-            BackendRepr::Uninhabited | BackendRepr::Memory { .. } => return None,
+            BackendRepr::Memory { .. } => return None,
         })
     }
 
@@ -1506,9 +1498,7 @@ impl BackendRepr {
             BackendRepr::Vector { element, count } => {
                 BackendRepr::Vector { element: element.to_union(), count }
             }
-            BackendRepr::Uninhabited | BackendRepr::Memory { .. } => {
-                BackendRepr::Memory { sized: true }
-            }
+            BackendRepr::Memory { .. } => BackendRepr::Memory { sized: true },
         }
     }
 
@@ -1704,6 +1694,11 @@ pub struct LayoutData<FieldIdx: Idx, VariantIdx: Idx> {
     /// The leaf scalar with the largest number of invalid values
     /// (i.e. outside of its `valid_range`), if it exists.
     pub largest_niche: Option<Niche>,
+    /// Is this type known to be uninhabted?
+    ///
+    /// This is separate from BackendRepr because uninhabited return types can affect ABI,
+    /// especially in the case of by-pointer struct returns, which allocate stack even when unused.
+    pub uninhabited: bool,
 
     pub align: AbiAndPrefAlign,
     pub size: Size,
@@ -1735,14 +1730,14 @@ impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx> {
     /// Returns `true` if this is an aggregate type (including a ScalarPair!)
     pub fn is_aggregate(&self) -> bool {
         match self.backend_repr {
-            BackendRepr::Uninhabited | BackendRepr::Scalar(_) | BackendRepr::Vector { .. } => false,
+            BackendRepr::Scalar(_) | BackendRepr::Vector { .. } => false,
             BackendRepr::ScalarPair(..) | BackendRepr::Memory { .. } => true,
         }
     }
 
     /// Returns `true` if this is an uninhabited type
     pub fn is_uninhabited(&self) -> bool {
-        self.backend_repr.is_uninhabited()
+        self.uninhabited
     }
 
     pub fn scalar<C: HasDataLayout>(cx: &C, scalar: Scalar) -> Self {
@@ -1778,6 +1773,7 @@ impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx> {
             fields: FieldsShape::Primitive,
             backend_repr: BackendRepr::Scalar(scalar),
             largest_niche,
+            uninhabited: false,
             size,
             align,
             max_repr_align: None,
@@ -1802,6 +1798,7 @@ where
             backend_repr,
             fields,
             largest_niche,
+            uninhabited,
             variants,
             max_repr_align,
             unadjusted_abi_align,
@@ -1813,6 +1810,7 @@ where
             .field("abi", backend_repr)
             .field("fields", fields)
             .field("largest_niche", largest_niche)
+            .field("uninhabited", uninhabited)
             .field("variants", variants)
             .field("max_repr_align", max_repr_align)
             .field("unadjusted_abi_align", unadjusted_abi_align)
@@ -1877,7 +1875,6 @@ impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx> {
             BackendRepr::Scalar(_) | BackendRepr::ScalarPair(..) | BackendRepr::Vector { .. } => {
                 false
             }
-            BackendRepr::Uninhabited => self.size.bytes() == 0,
             BackendRepr::Memory { sized } => sized && self.size.bytes() == 0,
         }
     }

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -386,8 +386,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 hir::intravisit::walk_pat(self, p);
             }
         }
+        let tcx = self.infcx.tcx;
         let hir = self.infcx.tcx.hir();
-        if let Some(body) = hir.maybe_body_owned_by(self.mir_def_id()) {
+        if let Some(body) = tcx.hir_maybe_body_owned_by(self.mir_def_id()) {
             let expr = body.value;
             let place = &self.move_data.move_paths[mpi].place;
             let span = place.as_local().map(|local| self.body.local_decls[local].source_info.span);
@@ -396,7 +397,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 expr: None,
                 pat: None,
                 parent_pat: None,
-                tcx: self.infcx.tcx,
+                tcx,
             };
             finder.visit_expr(expr);
             if let Some(span) = span
@@ -782,9 +783,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
         // We use the statements were the binding was initialized, and inspect the HIR to look
         // for the branching codepaths that aren't covered, to point at them.
-        let map = self.infcx.tcx.hir();
-        let body = map.body_owned_by(self.mir_def_id());
-        let mut visitor = ConditionVisitor { tcx: self.infcx.tcx, spans, name, errors: vec![] };
+        let tcx = self.infcx.tcx;
+        let body = tcx.hir_body_owned_by(self.mir_def_id());
+        let mut visitor = ConditionVisitor { tcx, spans, name, errors: vec![] };
         visitor.visit_body(&body);
         let spans = visitor.spans;
 
@@ -2443,7 +2444,6 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     ) {
         let &UseSpans::ClosureUse { capture_kind_span, .. } = issued_spans else { return };
         let tcx = self.infcx.tcx;
-        let hir = tcx.hir();
 
         // Get the type of the local that we are trying to borrow
         let local = borrowed_place.local;
@@ -2522,7 +2522,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
         // Find the first argument with a matching type, get its name
         let Some((_, this_name)) =
-            params.iter().zip(hir.body_param_names(closure.body)).find(|(param_ty, name)| {
+            params.iter().zip(tcx.hir_body_param_names(closure.body)).find(|(param_ty, name)| {
                 // FIXME: also support deref for stuff like `Rc` arguments
                 param_ty.peel_refs() == local_ty && name != &Ident::empty()
             })
@@ -4178,7 +4178,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         debug!("annotate_fn_sig: did={:?} sig={:?}", did, sig);
         let is_closure = self.infcx.tcx.is_closure_like(did.to_def_id());
         let fn_hir_id = self.infcx.tcx.local_def_id_to_hir_id(did);
-        let fn_decl = self.infcx.tcx.hir().fn_decl_by_hir_id(fn_hir_id)?;
+        let fn_decl = self.infcx.tcx.hir_fn_decl_by_hir_id(fn_hir_id)?;
 
         // We need to work out which arguments to highlight. We do this by looking
         // at the return type, where there are three cases:

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -777,12 +777,12 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         }
         let Some(pat_span) = pat_span else { return };
 
-        let hir = self.infcx.tcx.hir();
-        let Some(body) = hir.maybe_body_owned_by(self.mir_def_id()) else { return };
+        let tcx = self.infcx.tcx;
+        let Some(body) = tcx.hir_maybe_body_owned_by(self.mir_def_id()) else { return };
         let typeck_results = self.infcx.tcx.typeck(self.mir_def_id());
         let mut finder = BindingFinder {
             typeck_results,
-            tcx: self.infcx.tcx,
+            tcx,
             pat_span,
             binding_spans,
             found_pat: false,

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -648,10 +648,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                     }
                 }
             }
-            let hir_map = self.infcx.tcx.hir();
             let def_id = self.body.source.def_id();
             let Some(local_def_id) = def_id.as_local() else { return };
-            let Some(body) = hir_map.maybe_body_owned_by(local_def_id) else { return };
+            let Some(body) = self.infcx.tcx.hir_maybe_body_owned_by(local_def_id) else { return };
 
             let mut v = SuggestIndexOperatorAlternativeVisitor {
                 assign_span: span,
@@ -749,7 +748,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         // `fn foo(&x: &i32)` -> `fn foo(&(mut x): &i32)`
         let def_id = self.body.source.def_id();
         if let Some(local_def_id) = def_id.as_local()
-            && let Some(body) = self.infcx.tcx.hir().maybe_body_owned_by(local_def_id)
+            && let Some(body) = self.infcx.tcx.hir_maybe_body_owned_by(local_def_id)
             && let Some(hir_id) = (BindingFinder { span: pat_span }).visit_body(&body).break_value()
             && let node = self.infcx.tcx.hir_node(hir_id)
             && let hir::Node::LetStmt(hir::LetStmt {
@@ -856,7 +855,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         use hir::ExprKind::{AddrOf, Block, Call, MethodCall};
         use hir::{BorrowKind, Expr};
 
-        let hir_map = self.infcx.tcx.hir();
+        let tcx = self.infcx.tcx;
         struct Finder {
             span: Span,
         }
@@ -871,7 +870,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 }
             }
         }
-        if let Some(body) = hir_map.maybe_body_owned_by(self.mir_def_id())
+        if let Some(body) = tcx.hir_maybe_body_owned_by(self.mir_def_id())
             && let Block(block, _) = body.value.kind
         {
             // `span` corresponds to the expression being iterated, find the `for`-loop desugared
@@ -884,17 +883,15 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                     MethodCall(path_segment, _, _, span) => {
                         // We have `for _ in iter.read_only_iter()`, try to
                         // suggest `for _ in iter.mutable_iter()` instead.
-                        let opt_suggestions = self
-                            .infcx
-                            .tcx
+                        let opt_suggestions = tcx
                             .typeck(path_segment.hir_id.owner.def_id)
                             .type_dependent_def_id(expr.hir_id)
-                            .and_then(|def_id| self.infcx.tcx.impl_of_method(def_id))
-                            .map(|def_id| self.infcx.tcx.associated_items(def_id))
+                            .and_then(|def_id| tcx.impl_of_method(def_id))
+                            .map(|def_id| tcx.associated_items(def_id))
                             .map(|assoc_items| {
                                 assoc_items
                                     .in_definition_order()
-                                    .map(|assoc_item_def| assoc_item_def.ident(self.infcx.tcx))
+                                    .map(|assoc_item_def| assoc_item_def.ident(tcx))
                                     .filter(|&ident| {
                                         let original_method_ident = path_segment.ident;
                                         original_method_ident != ident
@@ -942,7 +939,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         let closure_span = tcx.def_span(self.mir_def_id());
         let fn_call_id = tcx.parent_hir_id(closure_id);
         let node = tcx.hir_node(fn_call_id);
-        let def_id = hir.enclosing_body_owner(fn_call_id);
+        let def_id = tcx.hir_enclosing_body_owner(fn_call_id);
         let mut look_at_return = true;
 
         // If the HIR node is a function or method call gets the def ID
@@ -1275,7 +1272,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             }) => {
                 let def_id = self.body.source.def_id();
                 let hir_id = if let Some(local_def_id) = def_id.as_local()
-                    && let Some(body) = self.infcx.tcx.hir().maybe_body_owned_by(local_def_id)
+                    && let Some(body) = self.infcx.tcx.hir_maybe_body_owned_by(local_def_id)
                 {
                     BindingFinder { span: err_label_span }.visit_body(&body).break_value()
                 } else {

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -1169,8 +1169,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
     #[allow(rustc::diagnostic_outside_of_impl)]
     fn suggest_move_on_borrowing_closure(&self, diag: &mut Diag<'_>) {
-        let map = self.infcx.tcx.hir();
-        let body = map.body_owned_by(self.mir_def_id());
+        let body = self.infcx.tcx.hir_body_owned_by(self.mir_def_id());
         let expr = &body.value.peel_blocks();
         let mut closure_span = None::<rustc_span::Span>;
         match expr.kind {