WIP: first try at implementing RFC 3525.

Author: veluca93

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -1,5 +1,6 @@
 use rustc_ast::{ast, attr, MetaItemKind, NestedMetaItem};
 use rustc_attr::{list_contains_name, InlineAttr, InstructionSetAttr, OptimizeAttr};
+use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{codes::*, struct_span_code_err, DiagMessage, SubdiagMessage};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
@@ -13,8 +14,10 @@ use rustc_middle::query::Providers;
 use rustc_middle::ty::{self as ty, TyCtxt};
 use rustc_session::{lint, parse::feature_err};
 use rustc_span::symbol::Ident;
-use rustc_span::{sym, Span};
+use rustc_span::{sym, Span, Symbol};
+use rustc_target::abi::VariantIdx;
 use rustc_target::spec::{abi, SanitizerSet};
+use rustc_type_ir::inherent::*;
 
 use crate::errors;
 use crate::target_features::{check_target_feature_trait_unsafe, from_target_feature};
@@ -75,23 +78,26 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
     let mut link_ordinal_span = None;
     let mut no_sanitize_span = None;
 
+    // In some cases, attribute are only valid on functions, but it's the `check_attr`
+    // pass that check that they aren't used anywhere else, rather this module.
+    // In these cases, we bail from performing further checks that are only meaningful for
+    // functions (such as calling `fn_sig`, which ICEs if given a non-function). We also
+    // report a delayed bug, just in case `check_attr` isn't doing its job.
+    let fn_sig_outer = || {
+        use DefKind::*;
+
+        let def_kind = tcx.def_kind(did);
+        if let Fn | AssocFn | Variant | Ctor(..) = def_kind { Some(tcx.fn_sig(did)) } else { None }
+    };
+
     for attr in attrs.iter() {
-        // In some cases, attribute are only valid on functions, but it's the `check_attr`
-        // pass that check that they aren't used anywhere else, rather this module.
-        // In these cases, we bail from performing further checks that are only meaningful for
-        // functions (such as calling `fn_sig`, which ICEs if given a non-function). We also
-        // report a delayed bug, just in case `check_attr` isn't doing its job.
         let fn_sig = || {
-            use DefKind::*;
-
-            let def_kind = tcx.def_kind(did);
-            if let Fn | AssocFn | Variant | Ctor(..) = def_kind {
-                Some(tcx.fn_sig(did))
-            } else {
+            let sig = fn_sig_outer();
+            if sig.is_none() {
                 tcx.dcx()
                     .span_delayed_bug(attr.span, "this attribute can only be applied to functions");
-                None
             }
+            sig
         };
 
         let Some(Ident { name, .. }) = attr.ident() else {
@@ -610,6 +616,57 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
         }
     }
 
+    if tcx.features().struct_target_features
+        && let Some(sig) = fn_sig_outer()
+    {
+        // Collect target features from types reachable from arguments.
+        // We define a type as "reachable" if:
+        //  - it is a function argument
+        //  - it is a field of a reachable struct
+        //  - there is a reachable reference to it
+        // FIXME: we may want to cache the result of this computation.
+        let mut visited_types = FxHashSet::default();
+        let mut reachable_types: Vec<_> = sig.skip_binder().inputs().skip_binder().to_owned();
+        let mut additional_tf = vec![];
+
+        while let Some(ty) = reachable_types.pop() {
+            if visited_types.contains(&ty) {
+                continue;
+            }
+            visited_types.insert(ty);
+            if ty.is_ref() {
+                reachable_types.push(ty.builtin_deref(false).unwrap());
+            } else if matches!(ty.kind(), ty::Tuple(_)) {
+                reachable_types.extend(ty.tuple_fields().iter());
+            } else if let ty::Adt(adt_def, args) = ty.kind() {
+                additional_tf.extend_from_slice(&adt_def.target_features());
+                if adt_def.is_struct() {
+                    reachable_types.extend(
+                        adt_def
+                            .variant(VariantIdx::from_usize(0))
+                            .fields
+                            .iter()
+                            .map(|field| field.ty(tcx, args)),
+                    );
+                }
+            }
+        }
+
+        if !additional_tf.is_empty() && !sig.skip_binder().abi().is_rust() {
+            tcx.dcx().span_err(
+                tcx.hir().span(tcx.local_def_id_to_hir_id(did)),
+                "cannot use a struct with target features in a function with non-Rust ABI",
+            );
+        }
+        if !additional_tf.is_empty() && codegen_fn_attrs.inline == InlineAttr::Always {
+            tcx.dcx().span_err(
+                tcx.hir().span(tcx.local_def_id_to_hir_id(did)),
+                "cannot use a struct with target features in a #[inline(always)] function",
+            );
+        }
+        codegen_fn_attrs.target_features.extend_from_slice(&additional_tf);
+    }
+
     // If a function uses #[target_feature] it can't be inlined into general
     // purpose functions as they wouldn't have the right target features
     // enabled. For that reason we also forbid #[inline(always)] as it can't be
@@ -755,6 +812,20 @@ fn check_link_name_xor_ordinal(
     }
 }
 
+fn struct_target_features(tcx: TyCtxt<'_>, def_id: DefId) -> Vec<Symbol> {
+    let mut features = vec![];
+    let supported_features = tcx.supported_target_features(def_id.krate);
+    for attr in tcx.get_attrs(def_id, sym::target_feature) {
+        from_target_feature(tcx, attr, supported_features, &mut features);
+    }
+    features
+}
+
 pub fn provide(providers: &mut Providers) {
-    *providers = Providers { codegen_fn_attrs, should_inherit_track_caller, ..*providers };
+    *providers = Providers {
+        codegen_fn_attrs,
+        should_inherit_track_caller,
+        struct_target_features,
+        ..*providers
+    };
 }

compiler/rustc_feature/src/unstable.rs

@@ -602,6 +602,8 @@ declare_features! (
     (unstable, strict_provenance, "1.61.0", Some(95228)),
     /// Allows string patterns to dereference values to match them.
     (unstable, string_deref_patterns, "1.67.0", Some(87121)),
+    /// Allows structs to carry target_feature information.
+    (unstable, struct_target_features, "CURRENT_RUSTC_VERSION", Some(871212)) /*FIXME*/,
     /// Allows the use of `#[target_feature]` on safe functions.
     (unstable, target_feature_11, "1.45.0", Some(69098)),
     /// Allows using `#[thread_local]` on `static` items.

compiler/rustc_hir_analysis/src/collect.rs

@@ -1147,7 +1147,7 @@ fn adt_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::AdtDef<'_> {
     } else {
         tcx.repr_options_of_def(def_id)
     };
-    let (kind, variants) = match &item.kind {
+    let (kind, variants, features) = match &item.kind {
         ItemKind::Enum(def, _) => {
             let mut distance_from_explicit = 0;
             let variants = def
@@ -1175,7 +1175,7 @@ fn adt_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::AdtDef<'_> {
                 })
                 .collect();
 
-            (AdtKind::Enum, variants)
+            (AdtKind::Enum, variants, vec![])
         }
         ItemKind::Struct(def, _) | ItemKind::Union(def, _) => {
             let adt_kind = match item.kind {
@@ -1194,11 +1194,11 @@ fn adt_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::AdtDef<'_> {
             ))
             .collect();
 
-            (adt_kind, variants)
+            (adt_kind, variants, tcx.struct_target_features(def_id).clone())
         }
         _ => bug!("{:?} is not an ADT", item.owner_id.def_id),
     };
-    tcx.mk_adt_def(def_id.to_def_id(), kind, variants, repr, is_anonymous)
+    tcx.mk_adt_def(def_id.to_def_id(), kind, variants, repr, features, is_anonymous)
 }
 
 fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -1179,6 +1179,13 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             adt_kind,
             variants.into_iter().map(|(_, variant)| variant).collect(),
             repr,
+            self.root
+                .tables
+                .adt_target_features
+                .get(self, item_id)
+                .expect("target features not encoded")
+                .decode(self)
+                .collect(),
             false,
         )
     }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1568,6 +1568,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 record!(self.tables.fn_sig[variant.def_id] <- fn_sig);
             }
         }
+        record_array!(self.tables.adt_target_features[def_id] <- adt_def.target_features());
     }
 
     #[instrument(level = "debug", skip(self))]

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -459,6 +459,7 @@ define_tables! {
     def_keys: Table<DefIndex, LazyValue<DefKey>>,
     proc_macro_quoted_spans: Table<usize, LazyValue<Span>>,
     variant_data: Table<DefIndex, LazyValue<VariantData>>,
+    adt_target_features: Table<DefIndex, LazyArray<Symbol>>,
     assoc_container: Table<DefIndex, ty::AssocItemContainer>,
     macro_definition: Table<DefIndex, LazyValue<ast::DelimArgs>>,
     proc_macro: Table<DefIndex, MacroKind>,

compiler/rustc_middle/src/query/mod.rs

@@ -1253,6 +1253,11 @@ rustc_queries! {
         feedable
     }
 
+    query struct_target_features(def_id: DefId) -> &'tcx Vec<Symbol> {
+        arena_cache
+        desc { |tcx| "computing target features for struct `{}`", tcx.def_path_str(def_id) }
+    }
+
     query asm_target_features(def_id: DefId) -> &'tcx FxIndexSet<Symbol> {
         desc { |tcx| "computing target features for inline asm of `{}`", tcx.def_path_str(def_id) }
     }

compiler/rustc_middle/src/ty/adt.rs

@@ -16,6 +16,7 @@ use rustc_macros::{HashStable, TyDecodable, TyEncodable};
 use rustc_query_system::ich::StableHashingContext;
 use rustc_session::DataTypeKind;
 use rustc_span::symbol::sym;
+use rustc_span::Symbol;
 use rustc_target::abi::{ReprOptions, VariantIdx, FIRST_VARIANT};
 use tracing::{debug, info, trace};
 
@@ -103,6 +104,8 @@ pub struct AdtDefData {
     flags: AdtFlags,
     /// Repr options provided by the user.
     repr: ReprOptions,
+    /// Target features that functions taking objects of this type by value will enable.
+    target_features: Vec<Symbol>,
 }
 
 impl PartialEq for AdtDefData {
@@ -115,8 +118,8 @@ impl PartialEq for AdtDefData {
         // definition of `AdtDefData` changes, a compile-error will be produced,
         // reminding us to revisit this assumption.
 
-        let Self { did: self_def_id, variants: _, flags: _, repr: _ } = self;
-        let Self { did: other_def_id, variants: _, flags: _, repr: _ } = other;
+        let Self { did: self_def_id, variants: _, flags: _, repr: _, target_features: _ } = self;
+        let Self { did: other_def_id, variants: _, flags: _, repr: _, target_features: _ } = other;
 
         let res = self_def_id == other_def_id;
 
@@ -153,13 +156,15 @@ impl<'a> HashStable<StableHashingContext<'a>> for AdtDefData {
             let addr = self as *const AdtDefData as usize;
             let hashing_controls = hcx.hashing_controls();
             *cache.borrow_mut().entry((addr, hashing_controls)).or_insert_with(|| {
-                let ty::AdtDefData { did, ref variants, ref flags, ref repr } = *self;
+                let ty::AdtDefData { did, ref variants, ref flags, ref repr, ref target_features } =
+                    *self;
 
                 let mut hasher = StableHasher::new();
                 did.hash_stable(hcx, &mut hasher);
                 variants.hash_stable(hcx, &mut hasher);
                 flags.hash_stable(hcx, &mut hasher);
                 repr.hash_stable(hcx, &mut hasher);
+                target_features.hash_stable(hcx, &mut hasher);
 
                 hasher.finish()
             })
@@ -198,6 +203,11 @@ impl<'tcx> AdtDef<'tcx> {
     pub fn repr(self) -> ReprOptions {
         self.0.0.repr
     }
+
+    #[inline]
+    pub fn target_features(self) -> &'tcx Vec<Symbol> {
+        &self.0.0.target_features
+    }
 }
 
 impl<'tcx> rustc_type_ir::inherent::AdtDef<TyCtxt<'tcx>> for AdtDef<'tcx> {
@@ -260,6 +270,7 @@ impl AdtDefData {
         kind: AdtKind,
         variants: IndexVec<VariantIdx, VariantDef>,
         repr: ReprOptions,
+        target_features: Vec<Symbol>,
         is_anonymous: bool,
     ) -> Self {
         debug!(
@@ -302,7 +313,7 @@ impl AdtDefData {
             flags |= AdtFlags::IS_ANONYMOUS;
         }
 
-        AdtDefData { did, variants, flags, repr }
+        AdtDefData { did, variants, flags, repr, target_features }
     }
 }
 

compiler/rustc_middle/src/ty/context.rs

@@ -1429,6 +1429,7 @@ impl<'tcx> TyCtxt<'tcx> {
         kind: AdtKind,
         variants: IndexVec<VariantIdx, ty::VariantDef>,
         repr: ReprOptions,
+        features: Vec<Symbol>,
         is_anonymous: bool,
     ) -> ty::AdtDef<'tcx> {
         self.mk_adt_def_from_data(ty::AdtDefData::new(
@@ -1437,6 +1438,7 @@ impl<'tcx> TyCtxt<'tcx> {
             kind,
             variants,
             repr,
+            features,
             is_anonymous,
         ))
     }

compiler/rustc_mir_build/messages.ftl

@@ -125,6 +125,17 @@ mir_build_initializing_type_with_requires_unsafe_unsafe_op_in_unsafe_fn_allowed
     .note = initializing a layout restricted type's field with a value outside the valid range is undefined behavior
     .label = initializing type with `rustc_layout_scalar_valid_range` attr
 
+mir_build_initializing_type_with_target_feature_requires_unsafe =
+    initializing type with `target_feature` attr is unsafe and requires unsafe block
+    .note = this struct can only be constructed if the corresponding `target_feature`s are available
+    .label = initializing type with `target_feature` attr
+
+mir_build_initializing_type_with_target_feature_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
+    initializing type with `target_feature` attr is unsafe and requires unsafe function or block
+    .note = this struct can only be constructed if the corresponding `target_feature`s are available
+    .label = initializing type with `target_feature` attr
+
+
 mir_build_inline_assembly_requires_unsafe =
     use of inline assembly is unsafe and requires unsafe block
     .note = inline assembly is entirely unchecked and can cause undefined behavior
@@ -377,6 +388,11 @@ mir_build_unsafe_op_in_unsafe_fn_initializing_type_with_requires_unsafe =
     .note = initializing a layout restricted type's field with a value outside the valid range is undefined behavior
     .label = initializing type with `rustc_layout_scalar_valid_range` attr
 
+mir_build_unsafe_op_in_unsafe_fn_initializing_type_with_target_feature_requires_unsafe =
+    initializing type with `target_feature` attr is unsafe and requires unsafe block
+    .note = this struct can only be constructed if the corresponding `target_feature`s are available
+    .label = initializing type with `target_feature` attr
+
 mir_build_unsafe_op_in_unsafe_fn_inline_assembly_requires_unsafe =
     use of inline assembly is unsafe and requires unsafe block
     .note = inline assembly is entirely unchecked and can cause undefined behavior