rustc_codegen_ssa/
target_features.rs

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1use rustc_attr_parsing::InstructionSetAttr;
2use rustc_data_structures::fx::FxIndexSet;
3use rustc_data_structures::unord::{UnordMap, UnordSet};
4use rustc_errors::Applicability;
5use rustc_hir as hir;
6use rustc_hir::def::DefKind;
7use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
8use rustc_middle::middle::codegen_fn_attrs::TargetFeature;
9use rustc_middle::query::Providers;
10use rustc_middle::ty::TyCtxt;
11use rustc_session::parse::feature_err;
12use rustc_span::{Span, Symbol, sym};
13use rustc_target::target_features::{self, Stability};
14
15use crate::errors;
16
17/// Compute the enabled target features from the `#[target_feature]` function attribute.
18/// Enabled target features are added to `target_features`.
19pub(crate) fn from_target_feature_attr(
20    tcx: TyCtxt<'_>,
21    attr: &hir::Attribute,
22    rust_target_features: &UnordMap<String, target_features::Stability>,
23    target_features: &mut Vec<TargetFeature>,
24) {
25    let Some(list) = attr.meta_item_list() else { return };
26    let bad_item = |span| {
27        let msg = "malformed `target_feature` attribute input";
28        let code = "enable = \"..\"";
29        tcx.dcx()
30            .struct_span_err(span, msg)
31            .with_span_suggestion(span, "must be of the form", code, Applicability::HasPlaceholders)
32            .emit();
33    };
34    let rust_features = tcx.features();
35    let abi_feature_constraints = tcx.sess.target.abi_required_features();
36    for item in list {
37        // Only `enable = ...` is accepted in the meta-item list.
38        if !item.has_name(sym::enable) {
39            bad_item(item.span());
40            continue;
41        }
42
43        // Must be of the form `enable = "..."` (a string).
44        let Some(value) = item.value_str() else {
45            bad_item(item.span());
46            continue;
47        };
48
49        // We allow comma separation to enable multiple features.
50        for feature in value.as_str().split(',') {
51            let Some(stability) = rust_target_features.get(feature) else {
52                let msg = format!("the feature named `{feature}` is not valid for this target");
53                let mut err = tcx.dcx().struct_span_err(item.span(), msg);
54                err.span_label(item.span(), format!("`{feature}` is not valid for this target"));
55                if let Some(stripped) = feature.strip_prefix('+') {
56                    let valid = rust_target_features.contains_key(stripped);
57                    if valid {
58                        err.help("consider removing the leading `+` in the feature name");
59                    }
60                }
61                err.emit();
62                continue;
63            };
64
65            // Only allow target features whose feature gates have been enabled
66            // and which are permitted to be toggled.
67            if let Err(reason) = stability.toggle_allowed() {
68                tcx.dcx().emit_err(errors::ForbiddenTargetFeatureAttr {
69                    span: item.span(),
70                    feature,
71                    reason,
72                });
73            } else if let Some(nightly_feature) = stability.requires_nightly()
74                && !rust_features.enabled(nightly_feature)
75            {
76                feature_err(
77                    &tcx.sess,
78                    nightly_feature,
79                    item.span(),
80                    format!("the target feature `{feature}` is currently unstable"),
81                )
82                .emit();
83            } else {
84                // Add this and the implied features.
85                let feature_sym = Symbol::intern(feature);
86                for &name in tcx.implied_target_features(feature_sym) {
87                    // But ensure the ABI does not forbid enabling this.
88                    // Here we do assume that LLVM doesn't add even more implied features
89                    // we don't know about, at least no features that would have ABI effects!
90                    // We skip this logic in rustdoc, where we want to allow all target features of
91                    // all targets, so we can't check their ABI compatibility and anyway we are not
92                    // generating code so "it's fine".
93                    if !tcx.sess.opts.actually_rustdoc {
94                        if abi_feature_constraints.incompatible.contains(&name.as_str()) {
95                            tcx.dcx().emit_err(errors::ForbiddenTargetFeatureAttr {
96                                span: item.span(),
97                                feature: name.as_str(),
98                                reason: "this feature is incompatible with the target ABI",
99                            });
100                        }
101                    }
102                    target_features.push(TargetFeature { name, implied: name != feature_sym })
103                }
104            }
105        }
106    }
107}
108
109/// Computes the set of target features used in a function for the purposes of
110/// inline assembly.
111fn asm_target_features(tcx: TyCtxt<'_>, did: DefId) -> &FxIndexSet<Symbol> {
112    let mut target_features = tcx.sess.unstable_target_features.clone();
113    if tcx.def_kind(did).has_codegen_attrs() {
114        let attrs = tcx.codegen_fn_attrs(did);
115        target_features.extend(attrs.target_features.iter().map(|feature| feature.name));
116        match attrs.instruction_set {
117            None => {}
118            Some(InstructionSetAttr::ArmA32) => {
119                // FIXME(#120456) - is `swap_remove` correct?
120                target_features.swap_remove(&sym::thumb_mode);
121            }
122            Some(InstructionSetAttr::ArmT32) => {
123                target_features.insert(sym::thumb_mode);
124            }
125        }
126    }
127
128    tcx.arena.alloc(target_features)
129}
130
131/// Checks the function annotated with `#[target_feature]` is not a safe
132/// trait method implementation, reporting an error if it is.
133pub(crate) fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId, attr_span: Span) {
134    if let DefKind::AssocFn = tcx.def_kind(id) {
135        let parent_id = tcx.local_parent(id);
136        if let DefKind::Trait | DefKind::Impl { of_trait: true } = tcx.def_kind(parent_id) {
137            tcx.dcx().emit_err(errors::TargetFeatureSafeTrait {
138                span: attr_span,
139                def: tcx.def_span(id),
140            });
141        }
142    }
143}
144
145pub(crate) fn provide(providers: &mut Providers) {
146    *providers = Providers {
147        rust_target_features: |tcx, cnum| {
148            assert_eq!(cnum, LOCAL_CRATE);
149            if tcx.sess.opts.actually_rustdoc {
150                // HACK: rustdoc would like to pretend that we have all the target features, so we
151                // have to merge all the lists into one. To ensure an unstable target never prevents
152                // a stable one from working, we merge the stability info of all instances of the
153                // same target feature name, with the "most stable" taking precedence. And then we
154                // hope that this doesn't cause issues anywhere else in the compiler...
155                let mut result: UnordMap<String, Stability> = Default::default();
156                for (name, stability) in rustc_target::target_features::all_rust_features() {
157                    use std::collections::hash_map::Entry;
158                    match result.entry(name.to_owned()) {
159                        Entry::Vacant(vacant_entry) => {
160                            vacant_entry.insert(stability);
161                        }
162                        Entry::Occupied(mut occupied_entry) => {
163                            // Merge the two stabilities, "more stable" taking precedence.
164                            match (occupied_entry.get(), stability) {
165                                (Stability::Stable, _)
166                                | (
167                                    Stability::Unstable { .. },
168                                    Stability::Unstable { .. } | Stability::Forbidden { .. },
169                                )
170                                | (Stability::Forbidden { .. }, Stability::Forbidden { .. }) => {
171                                    // The stability in the entry is at least as good as the new one, just keep it.
172                                }
173                                _ => {
174                                    // Overwrite stabilite.
175                                    occupied_entry.insert(stability);
176                                }
177                            }
178                        }
179                    }
180                }
181                result
182            } else {
183                tcx.sess
184                    .target
185                    .rust_target_features()
186                    .iter()
187                    .map(|(a, b, _)| (a.to_string(), *b))
188                    .collect()
189            }
190        },
191        implied_target_features: |tcx, feature: Symbol| {
192            let feature = feature.as_str();
193            UnordSet::from(tcx.sess.target.implied_target_features(std::iter::once(feature)))
194                .into_sorted_stable_ord()
195                .into_iter()
196                .map(|s| Symbol::intern(s))
197                .collect()
198        },
199        asm_target_features,
200        ..*providers
201    }
202}
rustc_codegen_ssa/target_features.rs

rustc_codegen_ssa/
target_features.rs
