rustc_codegen_ssa/
codegen_attrs.rs

1use std::str::FromStr;
2
3use rustc_abi::{Align, ExternAbi};
4use rustc_ast::expand::autodiff_attrs::{AutoDiffAttrs, DiffActivity, DiffMode};
5use rustc_ast::{LitKind, MetaItem, MetaItemInner, attr};
6use rustc_hir::attrs::{AttributeKind, InlineAttr, InstructionSetAttr, UsedBy};
7use rustc_hir::def::DefKind;
8use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
9use rustc_hir::{self as hir, Attribute, LangItem, find_attr, lang_items};
10use rustc_middle::middle::codegen_fn_attrs::{
11    CodegenFnAttrFlags, CodegenFnAttrs, PatchableFunctionEntry,
12};
13use rustc_middle::query::Providers;
14use rustc_middle::span_bug;
15use rustc_middle::ty::{self as ty, TyCtxt};
16use rustc_session::lint;
17use rustc_session::parse::feature_err;
18use rustc_span::{Ident, Span, sym};
19use rustc_target::spec::SanitizerSet;
20
21use crate::errors;
22use crate::target_features::{
23    check_target_feature_trait_unsafe, check_tied_features, from_target_feature_attr,
24};
25
26/// In some cases, attributes are only valid on functions, but it's the `check_attr`
27/// pass that checks that they aren't used anywhere else, rather than this module.
28/// In these cases, we bail from performing further checks that are only meaningful for
29/// functions (such as calling `fn_sig`, which ICEs if given a non-function). We also
30/// report a delayed bug, just in case `check_attr` isn't doing its job.
31fn try_fn_sig<'tcx>(
32    tcx: TyCtxt<'tcx>,
33    did: LocalDefId,
34    attr_span: Span,
35) -> Option<ty::EarlyBinder<'tcx, ty::PolyFnSig<'tcx>>> {
36    use DefKind::*;
37
38    let def_kind = tcx.def_kind(did);
39    if let Fn | AssocFn | Variant | Ctor(..) = def_kind {
40        Some(tcx.fn_sig(did))
41    } else {
42        tcx.dcx().span_delayed_bug(attr_span, "this attribute can only be applied to functions");
43        None
44    }
45}
46
47// FIXME(jdonszelmann): remove when instruction_set becomes a parsed attr
48fn parse_instruction_set_attr(tcx: TyCtxt<'_>, attr: &Attribute) -> Option<InstructionSetAttr> {
49    let list = attr.meta_item_list()?;
50
51    match &list[..] {
52        [MetaItemInner::MetaItem(set)] => {
53            let segments = set.path.segments.iter().map(|x| x.ident.name).collect::<Vec<_>>();
54            match segments.as_slice() {
55                [sym::arm, sym::a32 | sym::t32] if !tcx.sess.target.has_thumb_interworking => {
56                    tcx.dcx().emit_err(errors::UnsupportedInstructionSet { span: attr.span() });
57                    None
58                }
59                [sym::arm, sym::a32] => Some(InstructionSetAttr::ArmA32),
60                [sym::arm, sym::t32] => Some(InstructionSetAttr::ArmT32),
61                _ => {
62                    tcx.dcx().emit_err(errors::InvalidInstructionSet { span: attr.span() });
63                    None
64                }
65            }
66        }
67        [] => {
68            tcx.dcx().emit_err(errors::BareInstructionSet { span: attr.span() });
69            None
70        }
71        _ => {
72            tcx.dcx().emit_err(errors::MultipleInstructionSet { span: attr.span() });
73            None
74        }
75    }
76}
77
78// FIXME(jdonszelmann): remove when patchable_function_entry becomes a parsed attr
79fn parse_patchable_function_entry(
80    tcx: TyCtxt<'_>,
81    attr: &Attribute,
82) -> Option<PatchableFunctionEntry> {
83    attr.meta_item_list().and_then(|l| {
84        let mut prefix = None;
85        let mut entry = None;
86        for item in l {
87            let Some(meta_item) = item.meta_item() else {
88                tcx.dcx().emit_err(errors::ExpectedNameValuePair { span: item.span() });
89                continue;
90            };
91
92            let Some(name_value_lit) = meta_item.name_value_literal() else {
93                tcx.dcx().emit_err(errors::ExpectedNameValuePair { span: item.span() });
94                continue;
95            };
96
97            let attrib_to_write = match meta_item.name() {
98                Some(sym::prefix_nops) => &mut prefix,
99                Some(sym::entry_nops) => &mut entry,
100                _ => {
101                    tcx.dcx().emit_err(errors::UnexpectedParameterName {
102                        span: item.span(),
103                        prefix_nops: sym::prefix_nops,
104                        entry_nops: sym::entry_nops,
105                    });
106                    continue;
107                }
108            };
109
110            let rustc_ast::LitKind::Int(val, _) = name_value_lit.kind else {
111                tcx.dcx().emit_err(errors::InvalidLiteralValue { span: name_value_lit.span });
112                continue;
113            };
114
115            let Ok(val) = val.get().try_into() else {
116                tcx.dcx().emit_err(errors::OutOfRangeInteger { span: name_value_lit.span });
117                continue;
118            };
119
120            *attrib_to_write = Some(val);
121        }
122
123        if let (None, None) = (prefix, entry) {
124            tcx.dcx().span_err(attr.span(), "must specify at least one parameter");
125        }
126
127        Some(PatchableFunctionEntry::from_prefix_and_entry(prefix.unwrap_or(0), entry.unwrap_or(0)))
128    })
129}
130
131/// Spans that are collected when processing built-in attributes,
132/// that are useful for emitting diagnostics later.
133#[derive(Default)]
134struct InterestingAttributeDiagnosticSpans {
135    link_ordinal: Option<Span>,
136    sanitize: Option<Span>,
137    inline: Option<Span>,
138    no_mangle: Option<Span>,
139}
140
141/// Process the builtin attrs ([`hir::Attribute`]) on the item.
142/// Many of them directly translate to codegen attrs.
143fn process_builtin_attrs(
144    tcx: TyCtxt<'_>,
145    did: LocalDefId,
146    attrs: &[Attribute],
147    codegen_fn_attrs: &mut CodegenFnAttrs,
148) -> InterestingAttributeDiagnosticSpans {
149    let mut interesting_spans = InterestingAttributeDiagnosticSpans::default();
150    let rust_target_features = tcx.rust_target_features(LOCAL_CRATE);
151
152    for attr in attrs.iter() {
153        if let hir::Attribute::Parsed(p) = attr {
154            match p {
155                AttributeKind::Cold(_) => codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD,
156                AttributeKind::ExportName { name, .. } => {
157                    codegen_fn_attrs.symbol_name = Some(*name)
158                }
159                AttributeKind::Inline(inline, span) => {
160                    codegen_fn_attrs.inline = *inline;
161                    interesting_spans.inline = Some(*span);
162                }
163                AttributeKind::Naked(_) => codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED,
164                AttributeKind::Align { align, .. } => codegen_fn_attrs.alignment = Some(*align),
165                AttributeKind::LinkName { name, .. } => {
166                    // FIXME Remove check for foreign functions once #[link_name] on non-foreign
167                    // functions is a hard error
168                    if tcx.is_foreign_item(did) {
169                        codegen_fn_attrs.symbol_name = Some(*name);
170                    }
171                }
172                AttributeKind::LinkOrdinal { ordinal, span } => {
173                    codegen_fn_attrs.link_ordinal = Some(*ordinal);
174                    interesting_spans.link_ordinal = Some(*span);
175                }
176                AttributeKind::LinkSection { name, .. } => {
177                    codegen_fn_attrs.link_section = Some(*name)
178                }
179                AttributeKind::NoMangle(attr_span) => {
180                    interesting_spans.no_mangle = Some(*attr_span);
181                    if tcx.opt_item_name(did.to_def_id()).is_some() {
182                        codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
183                    } else {
184                        tcx.dcx().span_delayed_bug(
185                            *attr_span,
186                            "no_mangle should be on a named function",
187                        );
188                    }
189                }
190                AttributeKind::Optimize(optimize, _) => codegen_fn_attrs.optimize = *optimize,
191                AttributeKind::TargetFeature { features, attr_span, was_forced } => {
192                    let Some(sig) = tcx.hir_node_by_def_id(did).fn_sig() else {
193                        tcx.dcx().span_delayed_bug(*attr_span, "target_feature applied to non-fn");
194                        continue;
195                    };
196                    let safe_target_features =
197                        matches!(sig.header.safety, hir::HeaderSafety::SafeTargetFeatures);
198                    codegen_fn_attrs.safe_target_features = safe_target_features;
199                    if safe_target_features && !was_forced {
200                        if tcx.sess.target.is_like_wasm || tcx.sess.opts.actually_rustdoc {
201                            // The `#[target_feature]` attribute is allowed on
202                            // WebAssembly targets on all functions. Prior to stabilizing
203                            // the `target_feature_11` feature, `#[target_feature]` was
204                            // only permitted on unsafe functions because on most targets
205                            // execution of instructions that are not supported is
206                            // considered undefined behavior. For WebAssembly which is a
207                            // 100% safe target at execution time it's not possible to
208                            // execute undefined instructions, and even if a future
209                            // feature was added in some form for this it would be a
210                            // deterministic trap. There is no undefined behavior when
211                            // executing WebAssembly so `#[target_feature]` is allowed
212                            // on safe functions (but again, only for WebAssembly)
213                            //
214                            // Note that this is also allowed if `actually_rustdoc` so
215                            // if a target is documenting some wasm-specific code then
216                            // it's not spuriously denied.
217                            //
218                            // Now that `#[target_feature]` is permitted on safe functions,
219                            // this exception must still exist for allowing the attribute on
220                            // `main`, `start`, and other functions that are not usually
221                            // allowed.
222                        } else {
223                            check_target_feature_trait_unsafe(tcx, did, *attr_span);
224                        }
225                    }
226                    from_target_feature_attr(
227                        tcx,
228                        did,
229                        features,
230                        *was_forced,
231                        rust_target_features,
232                        &mut codegen_fn_attrs.target_features,
233                    );
234                }
235                AttributeKind::TrackCaller(attr_span) => {
236                    let is_closure = tcx.is_closure_like(did.to_def_id());
237
238                    if !is_closure
239                        && let Some(fn_sig) = try_fn_sig(tcx, did, *attr_span)
240                        && fn_sig.skip_binder().abi() != ExternAbi::Rust
241                    {
242                        tcx.dcx().emit_err(errors::RequiresRustAbi { span: *attr_span });
243                    }
244                    if is_closure
245                        && !tcx.features().closure_track_caller()
246                        && !attr_span.allows_unstable(sym::closure_track_caller)
247                    {
248                        feature_err(
249                            &tcx.sess,
250                            sym::closure_track_caller,
251                            *attr_span,
252                            "`#[track_caller]` on closures is currently unstable",
253                        )
254                        .emit();
255                    }
256                    codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER
257                }
258                AttributeKind::Used { used_by, .. } => match used_by {
259                    UsedBy::Compiler => codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_COMPILER,
260                    UsedBy::Linker => codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_LINKER,
261                    UsedBy::Default => {
262                        let used_form = if tcx.sess.target.os == "illumos" {
263                            // illumos' `ld` doesn't support a section header that would represent
264                            // `#[used(linker)]`, see
265                            // https://github.com/rust-lang/rust/issues/146169. For that target,
266                            // downgrade as if `#[used(compiler)]` was requested and hope for the
267                            // best.
268                            CodegenFnAttrFlags::USED_COMPILER
269                        } else {
270                            CodegenFnAttrFlags::USED_LINKER
271                        };
272                        codegen_fn_attrs.flags |= used_form;
273                    }
274                },
275                AttributeKind::FfiConst(_) => {
276                    codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_CONST
277                }
278                AttributeKind::FfiPure(_) => codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_PURE,
279                AttributeKind::StdInternalSymbol(_) => {
280                    codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL
281                }
282                AttributeKind::Linkage(linkage, span) => {
283                    let linkage = Some(*linkage);
284
285                    if tcx.is_foreign_item(did) {
286                        codegen_fn_attrs.import_linkage = linkage;
287
288                        if tcx.is_mutable_static(did.into()) {
289                            let mut diag = tcx.dcx().struct_span_err(
290                                *span,
291                                "extern mutable statics are not allowed with `#[linkage]`",
292                            );
293                            diag.note(
294                                "marking the extern static mutable would allow changing which \
295                                symbol the static references rather than make the target of the \
296                                symbol mutable",
297                            );
298                            diag.emit();
299                        }
300                    } else {
301                        codegen_fn_attrs.linkage = linkage;
302                    }
303                }
304                AttributeKind::Sanitize { span, .. } => {
305                    interesting_spans.sanitize = Some(*span);
306                }
307                AttributeKind::ObjcClass { classname, .. } => {
308                    codegen_fn_attrs.objc_class = Some(*classname);
309                }
310                AttributeKind::ObjcSelector { methname, .. } => {
311                    codegen_fn_attrs.objc_selector = Some(*methname);
312                }
313                _ => {}
314            }
315        }
316
317        let Some(Ident { name, .. }) = attr.ident() else {
318            continue;
319        };
320
321        match name {
322            sym::rustc_allocator => codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR,
323            sym::rustc_nounwind => codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND,
324            sym::rustc_reallocator => codegen_fn_attrs.flags |= CodegenFnAttrFlags::REALLOCATOR,
325            sym::rustc_deallocator => codegen_fn_attrs.flags |= CodegenFnAttrFlags::DEALLOCATOR,
326            sym::rustc_allocator_zeroed => {
327                codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR_ZEROED
328            }
329            sym::thread_local => codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL,
330            sym::instruction_set => {
331                codegen_fn_attrs.instruction_set = parse_instruction_set_attr(tcx, attr)
332            }
333            sym::patchable_function_entry => {
334                codegen_fn_attrs.patchable_function_entry =
335                    parse_patchable_function_entry(tcx, attr);
336            }
337            _ => {}
338        }
339    }
340
341    interesting_spans
342}
343
344/// Applies overrides for codegen fn attrs. These often have a specific reason why they're necessary.
345/// Please comment why when adding a new one!
346fn apply_overrides(tcx: TyCtxt<'_>, did: LocalDefId, codegen_fn_attrs: &mut CodegenFnAttrs) {
347    // Apply the minimum function alignment here. This ensures that a function's alignment is
348    // determined by the `-C` flags of the crate it is defined in, not the `-C` flags of the crate
349    // it happens to be codegen'd (or const-eval'd) in.
350    codegen_fn_attrs.alignment =
351        Ord::max(codegen_fn_attrs.alignment, tcx.sess.opts.unstable_opts.min_function_alignment);
352
353    // Compute the disabled sanitizers.
354    codegen_fn_attrs.no_sanitize |= tcx.disabled_sanitizers_for(did);
355    // On trait methods, inherit the `#[align]` of the trait's method prototype.
356    codegen_fn_attrs.alignment = Ord::max(codegen_fn_attrs.alignment, tcx.inherited_align(did));
357
358    // naked function MUST NOT be inlined! This attribute is required for the rust compiler itself,
359    // but not for the code generation backend because at that point the naked function will just be
360    // a declaration, with a definition provided in global assembly.
361    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
362        codegen_fn_attrs.inline = InlineAttr::Never;
363    }
364
365    // #73631: closures inherit `#[target_feature]` annotations
366    //
367    // If this closure is marked `#[inline(always)]`, simply skip adding `#[target_feature]`.
368    //
369    // At this point, `unsafe` has already been checked and `#[target_feature]` only affects codegen.
370    // Due to LLVM limitations, emitting both `#[inline(always)]` and `#[target_feature]` is *unsound*:
371    // the function may be inlined into a caller with fewer target features. Also see
372    // <https://github.com/rust-lang/rust/issues/116573>.
373    //
374    // Using `#[inline(always)]` implies that this closure will most likely be inlined into
375    // its parent function, which effectively inherits the features anyway. Boxing this closure
376    // would result in this closure being compiled without the inherited target features, but this
377    // is probably a poor usage of `#[inline(always)]` and easily avoided by not using the attribute.
378    if tcx.is_closure_like(did.to_def_id()) && codegen_fn_attrs.inline != InlineAttr::Always {
379        let owner_id = tcx.parent(did.to_def_id());
380        if tcx.def_kind(owner_id).has_codegen_attrs() {
381            codegen_fn_attrs
382                .target_features
383                .extend(tcx.codegen_fn_attrs(owner_id).target_features.iter().copied());
384        }
385    }
386
387    // When `no_builtins` is applied at the crate level, we should add the
388    // `no-builtins` attribute to each function to ensure it takes effect in LTO.
389    let crate_attrs = tcx.hir_attrs(rustc_hir::CRATE_HIR_ID);
390    let no_builtins = attr::contains_name(crate_attrs, sym::no_builtins);
391    if no_builtins {
392        codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_BUILTINS;
393    }
394
395    // inherit track-caller properly
396    if tcx.should_inherit_track_caller(did) {
397        codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
398    }
399
400    // Foreign items by default use no mangling for their symbol name.
401    if tcx.is_foreign_item(did) {
402        codegen_fn_attrs.flags |= CodegenFnAttrFlags::FOREIGN_ITEM;
403
404        // There's a few exceptions to this rule though:
405        if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
406            // * `#[rustc_std_internal_symbol]` mangles the symbol name in a special way
407            //   both for exports and imports through foreign items. This is handled further,
408            //   during symbol mangling logic.
409        } else if codegen_fn_attrs.symbol_name.is_some() {
410            // * This can be overridden with the `#[link_name]` attribute
411        } else {
412            // NOTE: there's one more exception that we cannot apply here. On wasm,
413            // some items cannot be `no_mangle`.
414            // However, we don't have enough information here to determine that.
415            // As such, no_mangle foreign items on wasm that have the same defid as some
416            // import will *still* be mangled despite this.
417            //
418            // if none of the exceptions apply; apply no_mangle
419            codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
420        }
421    }
422}
423
424fn check_result(
425    tcx: TyCtxt<'_>,
426    did: LocalDefId,
427    interesting_spans: InterestingAttributeDiagnosticSpans,
428    codegen_fn_attrs: &CodegenFnAttrs,
429) {
430    // If a function uses `#[target_feature]` it can't be inlined into general
431    // purpose functions as they wouldn't have the right target features
432    // enabled. For that reason we also forbid `#[inline(always)]` as it can't be
433    // respected.
434    //
435    // `#[rustc_force_inline]` doesn't need to be prohibited here, only
436    // `#[inline(always)]`, as forced inlining is implemented entirely within
437    // rustc (and so the MIR inliner can do any necessary checks for compatible target
438    // features).
439    //
440    // This sidesteps the LLVM blockers in enabling `target_features` +
441    // `inline(always)` to be used together (see rust-lang/rust#116573 and
442    // llvm/llvm-project#70563).
443    if !codegen_fn_attrs.target_features.is_empty()
444        && matches!(codegen_fn_attrs.inline, InlineAttr::Always)
445        && !tcx.features().target_feature_inline_always()
446        && let Some(span) = interesting_spans.inline
447    {
448        feature_err(
449            tcx.sess,
450            sym::target_feature_inline_always,
451            span,
452            "cannot use `#[inline(always)]` with `#[target_feature]`",
453        )
454        .emit();
455    }
456
457    // warn that inline has no effect when no_sanitize is present
458    if !codegen_fn_attrs.no_sanitize.is_empty()
459        && codegen_fn_attrs.inline.always()
460        && let (Some(no_sanitize_span), Some(inline_span)) =
461            (interesting_spans.sanitize, interesting_spans.inline)
462    {
463        let hir_id = tcx.local_def_id_to_hir_id(did);
464        tcx.node_span_lint(lint::builtin::INLINE_NO_SANITIZE, hir_id, no_sanitize_span, |lint| {
465            lint.primary_message("setting `sanitize` off will have no effect after inlining");
466            lint.span_note(inline_span, "inlining requested here");
467        })
468    }
469
470    // error when specifying link_name together with link_ordinal
471    if let Some(_) = codegen_fn_attrs.symbol_name
472        && let Some(_) = codegen_fn_attrs.link_ordinal
473    {
474        let msg = "cannot use `#[link_name]` with `#[link_ordinal]`";
475        if let Some(span) = interesting_spans.link_ordinal {
476            tcx.dcx().span_err(span, msg);
477        } else {
478            tcx.dcx().err(msg);
479        }
480    }
481
482    if let Some(features) = check_tied_features(
483        tcx.sess,
484        &codegen_fn_attrs
485            .target_features
486            .iter()
487            .map(|features| (features.name.as_str(), true))
488            .collect(),
489    ) {
490        let span =
491            find_attr!(tcx.get_all_attrs(did), AttributeKind::TargetFeature{attr_span: span, ..} => *span)
492                .unwrap_or_else(|| tcx.def_span(did));
493
494        tcx.dcx()
495            .create_err(errors::TargetFeatureDisableOrEnable {
496                features,
497                span: Some(span),
498                missing_features: Some(errors::MissingFeatures),
499            })
500            .emit();
501    }
502}
503
504fn handle_lang_items(
505    tcx: TyCtxt<'_>,
506    did: LocalDefId,
507    interesting_spans: &InterestingAttributeDiagnosticSpans,
508    attrs: &[Attribute],
509    codegen_fn_attrs: &mut CodegenFnAttrs,
510) {
511    let lang_item = lang_items::extract(attrs).and_then(|(name, _)| LangItem::from_name(name));
512
513    // Weak lang items have the same semantics as "std internal" symbols in the
514    // sense that they're preserved through all our LTO passes and only
515    // strippable by the linker.
516    //
517    // Additionally weak lang items have predetermined symbol names.
518    if let Some(lang_item) = lang_item
519        && let Some(link_name) = lang_item.link_name()
520    {
521        codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
522        codegen_fn_attrs.symbol_name = Some(link_name);
523    }
524
525    // error when using no_mangle on a lang item item
526    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
527        && codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE)
528    {
529        let mut err = tcx
530            .dcx()
531            .struct_span_err(
532                interesting_spans.no_mangle.unwrap_or_default(),
533                "`#[no_mangle]` cannot be used on internal language items",
534            )
535            .with_note("Rustc requires this item to have a specific mangled name.")
536            .with_span_label(tcx.def_span(did), "should be the internal language item");
537        if let Some(lang_item) = lang_item
538            && let Some(link_name) = lang_item.link_name()
539        {
540            err = err
541                .with_note("If you are trying to prevent mangling to ease debugging, many")
542                .with_note(format!("debuggers support a command such as `rbreak {link_name}` to"))
543                .with_note(format!(
544                    "match `.*{link_name}.*` instead of `break {link_name}` on a specific name"
545                ))
546        }
547        err.emit();
548    }
549}
550
551/// Generate the [`CodegenFnAttrs`] for an item (identified by the [`LocalDefId`]).
552///
553/// This happens in 4 stages:
554/// - apply built-in attributes that directly translate to codegen attributes.
555/// - handle lang items. These have special codegen attrs applied to them.
556/// - apply overrides, like minimum requirements for alignment and other settings that don't rely directly the built-in attrs on the item.
557///   overrides come after applying built-in attributes since they may only apply when certain attributes were already set in the stage before.
558/// - check that the result is valid. There's various ways in which this may not be the case, such as certain combinations of attrs.
559fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
560    if cfg!(debug_assertions) {
561        let def_kind = tcx.def_kind(did);
562        assert!(
563            def_kind.has_codegen_attrs(),
564            "unexpected `def_kind` in `codegen_fn_attrs`: {def_kind:?}",
565        );
566    }
567
568    let mut codegen_fn_attrs = CodegenFnAttrs::new();
569    let attrs = tcx.hir_attrs(tcx.local_def_id_to_hir_id(did));
570
571    let interesting_spans = process_builtin_attrs(tcx, did, attrs, &mut codegen_fn_attrs);
572    handle_lang_items(tcx, did, &interesting_spans, attrs, &mut codegen_fn_attrs);
573    apply_overrides(tcx, did, &mut codegen_fn_attrs);
574    check_result(tcx, did, interesting_spans, &codegen_fn_attrs);
575
576    codegen_fn_attrs
577}
578
579fn disabled_sanitizers_for(tcx: TyCtxt<'_>, did: LocalDefId) -> SanitizerSet {
580    // Backtrack to the crate root.
581    let mut disabled = match tcx.opt_local_parent(did) {
582        // Check the parent (recursively).
583        Some(parent) => tcx.disabled_sanitizers_for(parent),
584        // We reached the crate root without seeing an attribute, so
585        // there is no sanitizers to exclude.
586        None => SanitizerSet::empty(),
587    };
588
589    // Check for a sanitize annotation directly on this def.
590    if let Some((on_set, off_set)) = find_attr!(tcx.get_all_attrs(did), AttributeKind::Sanitize {on_set, off_set, ..} => (on_set, off_set))
591    {
592        // the on set is the set of sanitizers explicitly enabled.
593        // we mask those out since we want the set of disabled sanitizers here
594        disabled &= !*on_set;
595        // the off set is the set of sanitizers explicitly disabled.
596        // we or those in here.
597        disabled |= *off_set;
598        // the on set and off set are distjoint since there's a third option: unset.
599        // a node may not set the sanitizer setting in which case it inherits from parents.
600        // the code above in this function does this backtracking
601    }
602    disabled
603}
604
605/// Checks if the provided DefId is a method in a trait impl for a trait which has track_caller
606/// applied to the method prototype.
607fn should_inherit_track_caller(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
608    tcx.trait_item_of(def_id).is_some_and(|id| {
609        tcx.codegen_fn_attrs(id).flags.intersects(CodegenFnAttrFlags::TRACK_CALLER)
610    })
611}
612
613/// If the provided DefId is a method in a trait impl, return the value of the `#[align]`
614/// attribute on the method prototype (if any).
615fn inherited_align<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Option<Align> {
616    tcx.codegen_fn_attrs(tcx.trait_item_of(def_id)?).alignment
617}
618
619/// We now check the #\[rustc_autodiff\] attributes which we generated from the #[autodiff(...)]
620/// macros. There are two forms. The pure one without args to mark primal functions (the functions
621/// being differentiated). The other form is #[rustc_autodiff(Mode, ActivityList)] on top of the
622/// placeholder functions. We wrote the rustc_autodiff attributes ourself, so this should never
623/// panic, unless we introduced a bug when parsing the autodiff macro.
624//FIXME(jdonszelmann): put in the main loop. No need to have two..... :/ Let's do that when we make autodiff parsed.
625pub fn autodiff_attrs(tcx: TyCtxt<'_>, id: DefId) -> Option<AutoDiffAttrs> {
626    let attrs = tcx.get_attrs(id, sym::rustc_autodiff);
627
628    let attrs = attrs.filter(|attr| attr.has_name(sym::rustc_autodiff)).collect::<Vec<_>>();
629
630    // check for exactly one autodiff attribute on placeholder functions.
631    // There should only be one, since we generate a new placeholder per ad macro.
632    let attr = match &attrs[..] {
633        [] => return None,
634        [attr] => attr,
635        _ => {
636            span_bug!(attrs[1].span(), "cg_ssa: rustc_autodiff should only exist once per source");
637        }
638    };
639
640    let list = attr.meta_item_list().unwrap_or_default();
641
642    // empty autodiff attribute macros (i.e. `#[autodiff]`) are used to mark source functions
643    if list.is_empty() {
644        return Some(AutoDiffAttrs::source());
645    }
646
647    let [mode, width_meta, input_activities @ .., ret_activity] = &list[..] else {
648        span_bug!(attr.span(), "rustc_autodiff attribute must contain mode, width and activities");
649    };
650    let mode = if let MetaItemInner::MetaItem(MetaItem { path: p1, .. }) = mode {
651        p1.segments.first().unwrap().ident
652    } else {
653        span_bug!(attr.span(), "rustc_autodiff attribute must contain mode");
654    };
655
656    // parse mode
657    let mode = match mode.as_str() {
658        "Forward" => DiffMode::Forward,
659        "Reverse" => DiffMode::Reverse,
660        _ => {
661            span_bug!(mode.span, "rustc_autodiff attribute contains invalid mode");
662        }
663    };
664
665    let width: u32 = match width_meta {
666        MetaItemInner::MetaItem(MetaItem { path: p1, .. }) => {
667            let w = p1.segments.first().unwrap().ident;
668            match w.as_str().parse() {
669                Ok(val) => val,
670                Err(_) => {
671                    span_bug!(w.span, "rustc_autodiff width should fit u32");
672                }
673            }
674        }
675        MetaItemInner::Lit(lit) => {
676            if let LitKind::Int(val, _) = lit.kind {
677                match val.get().try_into() {
678                    Ok(val) => val,
679                    Err(_) => {
680                        span_bug!(lit.span, "rustc_autodiff width should fit u32");
681                    }
682                }
683            } else {
684                span_bug!(lit.span, "rustc_autodiff width should be an integer");
685            }
686        }
687    };
688
689    // First read the ret symbol from the attribute
690    let ret_symbol = if let MetaItemInner::MetaItem(MetaItem { path: p1, .. }) = ret_activity {
691        p1.segments.first().unwrap().ident
692    } else {
693        span_bug!(attr.span(), "rustc_autodiff attribute must contain the return activity");
694    };
695
696    // Then parse it into an actual DiffActivity
697    let Ok(ret_activity) = DiffActivity::from_str(ret_symbol.as_str()) else {
698        span_bug!(ret_symbol.span, "invalid return activity");
699    };
700
701    // Now parse all the intermediate (input) activities
702    let mut arg_activities: Vec<DiffActivity> = vec![];
703    for arg in input_activities {
704        let arg_symbol = if let MetaItemInner::MetaItem(MetaItem { path: p2, .. }) = arg {
705            match p2.segments.first() {
706                Some(x) => x.ident,
707                None => {
708                    span_bug!(
709                        arg.span(),
710                        "rustc_autodiff attribute must contain the input activity"
711                    );
712                }
713            }
714        } else {
715            span_bug!(arg.span(), "rustc_autodiff attribute must contain the input activity");
716        };
717
718        match DiffActivity::from_str(arg_symbol.as_str()) {
719            Ok(arg_activity) => arg_activities.push(arg_activity),
720            Err(_) => {
721                span_bug!(arg_symbol.span, "invalid input activity");
722            }
723        }
724    }
725
726    Some(AutoDiffAttrs { mode, width, ret_activity, input_activity: arg_activities })
727}
728
729pub(crate) fn provide(providers: &mut Providers) {
730    *providers = Providers {
731        codegen_fn_attrs,
732        should_inherit_track_caller,
733        inherited_align,
734        disabled_sanitizers_for,
735        ..*providers
736    };
737}
rustc_codegen_ssa/codegen_attrs.rs

rustc_codegen_ssa/
codegen_attrs.rs
