Rollup of 12 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_codegen_cranelift/src/value_and_place.rs

@@ -638,9 +638,7 @@ impl<'tcx> CPlace<'tcx> {
             }
             CPlaceInner::Addr(_, Some(_)) => bug!("Can't write value to unsized place {:?}", self),
             CPlaceInner::Addr(to_ptr, None) => {
-                if dst_layout.size == Size::ZERO
-                    || dst_layout.backend_repr == BackendRepr::Uninhabited
-                {
+                if dst_layout.size == Size::ZERO {
                     return;
                 }
 

compiler/rustc_codegen_gcc/src/intrinsic/mod.rs

@@ -315,7 +315,7 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tc
                 let layout = self.layout_of(tp_ty).layout;
                 let _use_integer_compare = match layout.backend_repr() {
                     Scalar(_) | ScalarPair(_, _) => true,
-                    Uninhabited | Vector { .. } => false,
+                    Vector { .. } => false,
                     Memory { .. } => {
                         // For rusty ABIs, small aggregates are actually passed
                         // as `RegKind::Integer` (see `FnAbi::adjust_for_abi`),

compiler/rustc_codegen_gcc/src/type_of.rs

@@ -84,7 +84,7 @@ fn uncached_gcc_type<'gcc, 'tcx>(
                 false,
             );
         }
-        BackendRepr::Uninhabited | BackendRepr::Memory { .. } => {}
+        BackendRepr::Memory { .. } => {}
     }
 
     let name = match *layout.ty.kind() {
@@ -179,19 +179,16 @@ impl<'tcx> LayoutGccExt<'tcx> for TyAndLayout<'tcx> {
     fn is_gcc_immediate(&self) -> bool {
         match self.backend_repr {
             BackendRepr::Scalar(_) | BackendRepr::Vector { .. } => true,
-            BackendRepr::ScalarPair(..) | BackendRepr::Uninhabited | BackendRepr::Memory { .. } => {
-                false
-            }
+            BackendRepr::ScalarPair(..) | BackendRepr::Memory { .. } => false,
         }
     }
 
     fn is_gcc_scalar_pair(&self) -> bool {
         match self.backend_repr {
             BackendRepr::ScalarPair(..) => true,
-            BackendRepr::Uninhabited
-            | BackendRepr::Scalar(_)
-            | BackendRepr::Vector { .. }
-            | BackendRepr::Memory { .. } => false,
+            BackendRepr::Scalar(_) | BackendRepr::Vector { .. } | BackendRepr::Memory { .. } => {
+                false
+            }
         }
     }
 

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -476,7 +476,7 @@ impl<'ll, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                 let layout = self.layout_of(tp_ty).layout;
                 let use_integer_compare = match layout.backend_repr() {
                     Scalar(_) | ScalarPair(_, _) => true,
-                    Uninhabited | Vector { .. } => false,
+                    Vector { .. } => false,
                     Memory { .. } => {
                         // For rusty ABIs, small aggregates are actually passed
                         // as `RegKind::Integer` (see `FnAbi::adjust_for_abi`),

compiler/rustc_codegen_llvm/src/type_of.rs

@@ -23,7 +23,7 @@ fn uncached_llvm_type<'a, 'tcx>(
             let element = layout.scalar_llvm_type_at(cx, element);
             return cx.type_vector(element, count);
         }
-        BackendRepr::Uninhabited | BackendRepr::Memory { .. } | BackendRepr::ScalarPair(..) => {}
+        BackendRepr::Memory { .. } | BackendRepr::ScalarPair(..) => {}
     }
 
     let name = match layout.ty.kind() {
@@ -172,19 +172,16 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
     fn is_llvm_immediate(&self) -> bool {
         match self.backend_repr {
             BackendRepr::Scalar(_) | BackendRepr::Vector { .. } => true,
-            BackendRepr::ScalarPair(..) | BackendRepr::Uninhabited | BackendRepr::Memory { .. } => {
-                false
-            }
+            BackendRepr::ScalarPair(..) | BackendRepr::Memory { .. } => false,
         }
     }
 
     fn is_llvm_scalar_pair(&self) -> bool {
         match self.backend_repr {
             BackendRepr::ScalarPair(..) => true,
-            BackendRepr::Uninhabited
-            | BackendRepr::Scalar(_)
-            | BackendRepr::Vector { .. }
-            | BackendRepr::Memory { .. } => false,
+            BackendRepr::Scalar(_) | BackendRepr::Vector { .. } | BackendRepr::Memory { .. } => {
+                false
+            }
         }
     }
 

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1990,6 +1990,7 @@ fn add_pre_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor)
     if let Some(args) = sess.target.pre_link_args.get(&flavor) {
         cmd.verbatim_args(args.iter().map(Deref::deref));
     }
+
     cmd.verbatim_args(&sess.opts.unstable_opts.pre_link_args);
 }
 
@@ -2518,6 +2519,12 @@ fn add_order_independent_options(
             "--target-cpu",
             &codegen_results.crate_info.target_cpu,
         ]);
+        if codegen_results.crate_info.target_features.len() > 0 {
+            cmd.link_arg(&format!(
+                "--target-feature={}",
+                &codegen_results.crate_info.target_features.join(",")
+            ));
+        }
     } else if flavor == LinkerFlavor::Ptx {
         cmd.link_args(&["--fallback-arch", &codegen_results.crate_info.target_cpu]);
     } else if flavor == LinkerFlavor::Bpf {

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -153,6 +153,7 @@ pub(crate) fn get_linker<'a>(
             hinted_static: None,
             is_ld: cc == Cc::No,
             is_gnu: flavor.is_gnu(),
+            uses_lld: flavor.uses_lld(),
         }) as Box<dyn Linker>,
         LinkerFlavor::Msvc(..) => Box::new(MsvcLinker { cmd, sess }) as Box<dyn Linker>,
         LinkerFlavor::EmCc => Box::new(EmLinker { cmd, sess }) as Box<dyn Linker>,
@@ -361,6 +362,7 @@ struct GccLinker<'a> {
     // Link as ld
     is_ld: bool,
     is_gnu: bool,
+    uses_lld: bool,
 }
 
 impl<'a> GccLinker<'a> {
@@ -552,6 +554,7 @@ impl<'a> Linker for GccLinker<'a> {
                 self.link_args(&["--entry", "_initialize"]);
             }
         }
+
         // VxWorks compiler driver introduced `--static-crt` flag specifically for rustc,
         // it switches linking for libc and similar system libraries to static without using
         // any `#[link]` attributes in the `libc` crate, see #72782 for details.
@@ -567,6 +570,15 @@ impl<'a> Linker for GccLinker<'a> {
         {
             self.cc_arg("--static-crt");
         }
+
+        // avr-none doesn't have default ISA, users must specify which specific
+        // CPU (well, microcontroller) they are targetting using `-Ctarget-cpu`.
+        //
+        // Currently this makes sense only when using avr-gcc as a linker, since
+        // it brings a couple of hand-written important intrinsics from libgcc.
+        if self.sess.target.arch == "avr" && !self.uses_lld {
+            self.verbatim_arg(format!("-mmcu={}", self.target_cpu));
+        }
     }
 
     fn link_dylib_by_name(&mut self, name: &str, verbatim: bool, as_needed: bool) {

compiler/rustc_codegen_ssa/src/base.rs

@@ -915,6 +915,7 @@ impl CrateInfo {
         let n_crates = crates.len();
         let mut info = CrateInfo {
             target_cpu,
+            target_features: tcx.global_backend_features(()).clone(),
             crate_types,
             exported_symbols,
             linked_symbols,