Auto merge of rust-lang#129881 - veluca93:struct_tf, r=<try>

Implement struct_target_features for non-generic functions.

This PR implements a first version of RFC 3525. In particular, the current code does not handle structs with target features being passed to generic functions correctly.

This is a roll-up of rust-lang#129764, rust-lang#129783 and rust-lang#129764, which will hopefully result in a PR that does not introduce perf regressions in the first place.

r? Kobzol

Tracking issue: rust-lang#129107

Author: bors

compiler/rustc_codegen_ssa/messages.ftl

@@ -238,7 +238,7 @@ codegen_ssa_stripping_debug_info_failed = stripping debug info with `{$util}` fa
 
 codegen_ssa_symbol_file_write_failure = failed to write symbols file: {$error}
 
-codegen_ssa_target_feature_safe_trait = `#[target_feature(..)]` cannot be applied to safe trait method
+codegen_ssa_target_feature_safe_trait = `#[target_feature(enable = ..)]` cannot be applied to safe trait method
     .label = cannot be applied to safe trait method
     .label_def = not an `unsafe` function
 

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -8,11 +8,11 @@ use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
 use rustc_hir::weak_lang_items::WEAK_LANG_ITEMS;
 use rustc_hir::{lang_items, LangItem};
 use rustc_middle::middle::codegen_fn_attrs::{
-    CodegenFnAttrFlags, CodegenFnAttrs, PatchableFunctionEntry,
+    CodegenFnAttrFlags, CodegenFnAttrs, PatchableFunctionEntry, TargetFeature,
 };
 use rustc_middle::mir::mono::Linkage;
 use rustc_middle::query::Providers;
-use rustc_middle::ty::{self as ty, TyCtxt};
+use rustc_middle::ty::{self as ty, Ty, TyCtxt};
 use rustc_session::lint;
 use rustc_session::parse::feature_err;
 use rustc_span::symbol::Ident;
@@ -78,23 +78,26 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
     let mut link_ordinal_span = None;
     let mut no_sanitize_span = None;
 
+    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 {
@@ -264,7 +267,12 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                     && let Some(fn_sig) = fn_sig()
                     && fn_sig.skip_binder().safety() == hir::Safety::Safe
                 {
-                    if tcx.sess.target.is_like_wasm || tcx.sess.opts.actually_rustdoc {
+                    if attr.meta_item_list().is_some_and(|list| {
+                        list.len() == 1 && list[0].ident().is_some_and(|x| x.name == sym::from_args)
+                    }) {
+                        // #[target_feature(from_args)] can be applied to safe functions and safe
+                        // trait methods.
+                    } else if tcx.sess.target.is_like_wasm || tcx.sess.opts.actually_rustdoc {
                         // The `#[target_feature]` attribute is allowed on
                         // WebAssembly targets on all functions, including safe
                         // ones. Other targets require that `#[target_feature]` is
@@ -303,6 +311,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                     attr,
                     supported_target_features,
                     &mut codegen_fn_attrs.target_features,
+                    Some(&mut codegen_fn_attrs.target_features_from_args),
                 );
             }
             sym::linkage => {
@@ -613,7 +622,29 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
         }
     }
 
-    // If a function uses #[target_feature] it can't be inlined into general
+    if let Some(sig) = fn_sig_outer()
+        && codegen_fn_attrs.target_features_from_args
+    {
+        let mut additional_tf = vec![];
+        for ty in sig.skip_binder().inputs().skip_binder() {
+            extend_with_struct_target_features(
+                tcx,
+                tcx.param_env(did.to_def_id()).and(*ty),
+                &mut additional_tf,
+            )
+        }
+        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(additional_tf.iter().map(|tf| TargetFeature { implied: true, ..*tf }));
+    }
+
+    // If a function uses non-default target_features 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
     // respected.
@@ -755,6 +786,44 @@ fn check_link_name_xor_ordinal(
     }
 }
 
+fn struct_target_features(tcx: TyCtxt<'_>, def_id: LocalDefId) -> &[TargetFeature] {
+    let mut features = vec![];
+    let supported_features = tcx.supported_target_features(LOCAL_CRATE);
+    for attr in tcx.get_attrs(def_id, sym::target_feature) {
+        from_target_feature(tcx, attr, supported_features, &mut features, None);
+    }
+    tcx.arena.alloc_slice(&features)
+}
+
+fn extend_with_struct_target_features<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
+    target_features: &mut Vec<TargetFeature>,
+) {
+    // Collect target features from types reachable from `env.value` by dereferencing a certain
+    // number of references and resolving aliases.
+
+    let mut ty = env.value;
+    if matches!(ty.kind(), ty::Alias(..)) {
+        ty = match tcx.try_normalize_erasing_regions(env.param_env, ty) {
+            Ok(ty) => ty,
+            Err(_) => return,
+        };
+    }
+    while let ty::Ref(_, inner, _) = ty.kind() {
+        ty = *inner;
+    }
+
+    if let ty::Adt(adt_def, ..) = ty.kind() {
+        target_features.extend_from_slice(&tcx.struct_target_features(adt_def.did()));
+    }
+}
+
 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_codegen_ssa/src/target_features.rs

@@ -20,6 +20,7 @@ pub fn from_target_feature(
     attr: &ast::Attribute,
     supported_target_features: &UnordMap<String, Option<Symbol>>,
     target_features: &mut Vec<TargetFeature>,
+    mut features_from_args: Option<&mut bool>,
 ) {
     let Some(list) = attr.meta_item_list() else { return };
     let bad_item = |span| {
@@ -33,6 +34,14 @@ pub fn from_target_feature(
     let rust_features = tcx.features();
     let mut added_target_features = Vec::new();
     for item in list {
+        if let Some(ref mut from_args) = features_from_args
+            && item.ident().is_some_and(|x| x.name == sym::from_args)
+            && tcx.features().struct_target_features
+        {
+            **from_args = true;
+            continue;
+        }
+
         // Only `enable = ...` is accepted in the meta-item list.
         if !item.has_name(sym::enable) {
             bad_item(item.span());
@@ -144,7 +153,7 @@ fn asm_target_features(tcx: TyCtxt<'_>, did: DefId) -> &FxIndexSet<Symbol> {
     tcx.arena.alloc(target_features)
 }
 
-/// Checks the function annotated with `#[target_feature]` is not a safe
+/// Checks the function annotated with `#[target_feature(enable = ...)]` is not a safe
 /// trait method implementation, reporting an error if it is.
 pub fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId, attr_span: Span) {
     if let DefKind::AssocFn = tcx.def_kind(id) {

compiler/rustc_feature/src/unstable.rs

@@ -597,6 +597,8 @@ 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.
+    (incomplete, struct_target_features, "CURRENT_RUSTC_VERSION", Some(129107)),
     /// 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/src/def.rs

@@ -326,6 +326,43 @@ impl DefKind {
             | DefKind::ExternCrate => false,
         }
     }
+
+    /// Whether `query struct_target_features` should be used with this definition.
+    pub fn has_struct_target_features(self) -> bool {
+        match self {
+            DefKind::Struct => true,
+            DefKind::Fn
+            | DefKind::Union
+            | DefKind::Enum
+            | DefKind::AssocFn
+            | DefKind::Ctor(..)
+            | DefKind::Closure
+            | DefKind::Static { .. }
+            | DefKind::Mod
+            | DefKind::Variant
+            | DefKind::Trait
+            | DefKind::TyAlias
+            | DefKind::ForeignTy
+            | DefKind::TraitAlias
+            | DefKind::AssocTy
+            | DefKind::Const
+            | DefKind::AssocConst
+            | DefKind::Macro(..)
+            | DefKind::Use
+            | DefKind::ForeignMod
+            | DefKind::OpaqueTy
+            | DefKind::Impl { .. }
+            | DefKind::Field
+            | DefKind::TyParam
+            | DefKind::ConstParam
+            | DefKind::LifetimeParam
+            | DefKind::AnonConst
+            | DefKind::InlineConst
+            | DefKind::SyntheticCoroutineBody
+            | DefKind::GlobalAsm
+            | DefKind::ExternCrate => false,
+        }
+    }
 }
 
 /// The resolution of a path or export.

compiler/rustc_hir_typeck/src/coercion.rs

@@ -850,10 +850,15 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                         return Err(TypeError::IntrinsicCast);
                     }
 
-                    // Safe `#[target_feature]` functions are not assignable to safe fn pointers (RFC 2396).
-
+                    // Safe functions with explicit `#[target_feature]` attributes are not
+                    // assignable to safe fn pointers (RFC 2396).
                     if b_hdr.safety == hir::Safety::Safe
-                        && !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
+                        && self
+                            .tcx
+                            .codegen_fn_attrs(def_id)
+                            .target_features
+                            .iter()
+                            .any(|x| !x.implied)
                     {
                         return Err(TypeError::TargetFeatureCast(def_id));
                     }

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -254,6 +254,7 @@ provide! { tcx, def_id, other, cdata,
     variances_of => { table }
     fn_sig => { table }
     codegen_fn_attrs => { table }
+    struct_target_features => { table_defaulted_array }
     impl_trait_header => { table }
     const_param_default => { table }
     object_lifetime_default => { table }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1398,6 +1398,9 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             if def_kind.has_codegen_attrs() {
                 record!(self.tables.codegen_fn_attrs[def_id] <- self.tcx.codegen_fn_attrs(def_id));
             }
+            if def_kind.has_struct_target_features() {
+                record_defaulted_array!(self.tables.struct_target_features[def_id] <- self.tcx.struct_target_features(def_id));
+            }
             if should_encode_visibility(def_kind) {
                 let vis =
                     self.tcx.local_visibility(local_id).map_id(|def_id| def_id.local_def_index);

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -19,7 +19,7 @@ use rustc_macros::{
     Decodable, Encodable, MetadataDecodable, MetadataEncodable, TyDecodable, TyEncodable,
 };
 use rustc_middle::metadata::ModChild;
-use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
+use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrs, TargetFeature};
 use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerFile;
 use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo};
 use rustc_middle::middle::lib_features::FeatureStability;
@@ -404,6 +404,7 @@ define_tables! {
     // individually instead of `DefId`s.
     module_children_reexports: Table<DefIndex, LazyArray<ModChild>>,
     cross_crate_inlinable: Table<DefIndex, bool>,
+    struct_target_features: Table<DefIndex, LazyArray<TargetFeature>>,
 
 - optional:
     attributes: Table<DefIndex, LazyArray<ast::Attribute>>,

compiler/rustc_middle/src/middle/codegen_fn_attrs.rs

@@ -26,8 +26,8 @@ pub struct CodegenFnAttrs {
     /// be set when `link_name` is set. This is for foreign items with the
     /// "raw-dylib" kind.
     pub link_ordinal: Option<u16>,
-    /// The `#[target_feature(enable = "...")]` attribute and the enabled
-    /// features (only enabled features are supported right now).
+    /// All the target features that are enabled for this function. Some features might be enabled
+    /// implicitly.
     pub target_features: Vec<TargetFeature>,
     /// The `#[linkage = "..."]` attribute on Rust-defined items and the value we found.
     pub linkage: Option<Linkage>,
@@ -49,14 +49,16 @@ pub struct CodegenFnAttrs {
     /// The `#[patchable_function_entry(...)]` attribute. Indicates how many nops should be around
     /// the function entry.
     pub patchable_function_entry: Option<PatchableFunctionEntry>,
+    /// Whether the target features can be extended through the arguments of the function.
+    pub target_features_from_args: bool,
 }
 
 #[derive(Copy, Clone, Debug, TyEncodable, TyDecodable, HashStable)]
 pub struct TargetFeature {
     /// The name of the target feature (e.g. "avx")
     pub name: Symbol,
-    /// The feature is implied by another feature, rather than explicitly added by the
-    /// `#[target_feature]` attribute
+    /// The feature is implied by another feature or by an argument, rather than explicitly
+    /// added by the `#[target_feature]` attribute
     pub implied: bool,
 }
 
@@ -158,6 +160,7 @@ impl CodegenFnAttrs {
             instruction_set: None,
             alignment: None,
             patchable_function_entry: None,
+            target_features_from_args: false,
         }
     }