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::errors::NoMangleNameless;
23use crate::target_features::{
24    check_target_feature_trait_unsafe, check_tied_features, from_target_feature_attr,
25};
26
27/// In some cases, attributes are only valid on functions, but it's the `check_attr`
28/// pass that checks that they aren't used anywhere else, rather than this module.
29/// In these cases, we bail from performing further checks that are only meaningful for
30/// functions (such as calling `fn_sig`, which ICEs if given a non-function). We also
31/// report a delayed bug, just in case `check_attr` isn't doing its job.
32fn try_fn_sig<'tcx>(
33    tcx: TyCtxt<'tcx>,
34    did: LocalDefId,
35    attr_span: Span,
36) -> Option<ty::EarlyBinder<'tcx, ty::PolyFnSig<'tcx>>> {
37    use DefKind::*;
38
39    let def_kind = tcx.def_kind(did);
40    if let Fn | AssocFn | Variant | Ctor(..) = def_kind {
41        Some(tcx.fn_sig(did))
42    } else {
43        tcx.dcx().span_delayed_bug(attr_span, "this attribute can only be applied to functions");
44        None
45    }
46}
47
48// FIXME(jdonszelmann): remove when instruction_set becomes a parsed attr
49fn parse_instruction_set_attr(tcx: TyCtxt<'_>, attr: &Attribute) -> Option<InstructionSetAttr> {
50    let list = attr.meta_item_list()?;
51
52    match &list[..] {
53        [MetaItemInner::MetaItem(set)] => {
54            let segments = set.path.segments.iter().map(|x| x.ident.name).collect::<Vec<_>>();
55            match segments.as_slice() {
56                [sym::arm, sym::a32 | sym::t32] if !tcx.sess.target.has_thumb_interworking => {
57                    tcx.dcx().emit_err(errors::UnsupportedInstructionSet { span: attr.span() });
58                    None
59                }
60                [sym::arm, sym::a32] => Some(InstructionSetAttr::ArmA32),
61                [sym::arm, sym::t32] => Some(InstructionSetAttr::ArmT32),
62                _ => {
63                    tcx.dcx().emit_err(errors::InvalidInstructionSet { span: attr.span() });
64                    None
65                }
66            }
67        }
68        [] => {
69            tcx.dcx().emit_err(errors::BareInstructionSet { span: attr.span() });
70            None
71        }
72        _ => {
73            tcx.dcx().emit_err(errors::MultipleInstructionSet { span: attr.span() });
74            None
75        }
76    }
77}
78
79// FIXME(jdonszelmann): remove when patchable_function_entry becomes a parsed attr
80fn parse_patchable_function_entry(
81    tcx: TyCtxt<'_>,
82    attr: &Attribute,
83) -> Option<PatchableFunctionEntry> {
84    attr.meta_item_list().and_then(|l| {
85        let mut prefix = None;
86        let mut entry = None;
87        for item in l {
88            let Some(meta_item) = item.meta_item() else {
89                tcx.dcx().emit_err(errors::ExpectedNameValuePair { span: item.span() });
90                continue;
91            };
92
93            let Some(name_value_lit) = meta_item.name_value_literal() else {
94                tcx.dcx().emit_err(errors::ExpectedNameValuePair { span: item.span() });
95                continue;
96            };
97
98            let attrib_to_write = match meta_item.name() {
99                Some(sym::prefix_nops) => &mut prefix,
100                Some(sym::entry_nops) => &mut entry,
101                _ => {
102                    tcx.dcx().emit_err(errors::UnexpectedParameterName {
103                        span: item.span(),
104                        prefix_nops: sym::prefix_nops,
105                        entry_nops: sym::entry_nops,
106                    });
107                    continue;
108                }
109            };
110
111            let rustc_ast::LitKind::Int(val, _) = name_value_lit.kind else {
112                tcx.dcx().emit_err(errors::InvalidLiteralValue { span: name_value_lit.span });
113                continue;
114            };
115
116            let Ok(val) = val.get().try_into() else {
117                tcx.dcx().emit_err(errors::OutOfRangeInteger { span: name_value_lit.span });
118                continue;
119            };
120
121            *attrib_to_write = Some(val);
122        }
123
124        if let (None, None) = (prefix, entry) {
125            tcx.dcx().span_err(attr.span(), "must specify at least one parameter");
126        }
127
128        Some(PatchableFunctionEntry::from_prefix_and_entry(prefix.unwrap_or(0), entry.unwrap_or(0)))
129    })
130}
131
132/// Spans that are collected when processing built-in attributes,
133/// that are useful for emitting diagnostics later.
134#[derive(Default)]
135struct InterestingAttributeDiagnosticSpans {
136    link_ordinal: Option<Span>,
137    sanitize: Option<Span>,
138    inline: Option<Span>,
139    no_mangle: Option<Span>,
140}
141
142/// Process the builtin attrs ([`hir::Attribute`]) on the item.
143/// Many of them directly translate to codegen attrs.
144fn process_builtin_attrs(
145    tcx: TyCtxt<'_>,
146    did: LocalDefId,
147    attrs: &[Attribute],
148    codegen_fn_attrs: &mut CodegenFnAttrs,
149) -> InterestingAttributeDiagnosticSpans {
150    let mut interesting_spans = InterestingAttributeDiagnosticSpans::default();
151    let rust_target_features = tcx.rust_target_features(LOCAL_CRATE);
152
153    for attr in attrs.iter() {
154        if let hir::Attribute::Parsed(p) = attr {
155            match p {
156                AttributeKind::Cold(_) => codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD,
157                AttributeKind::ExportName { name, .. } => {
158                    codegen_fn_attrs.symbol_name = Some(*name)
159                }
160                AttributeKind::Inline(inline, span) => {
161                    codegen_fn_attrs.inline = *inline;
162                    interesting_spans.inline = Some(*span);
163                }
164                AttributeKind::Naked(_) => codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED,
165                AttributeKind::Align { align, .. } => codegen_fn_attrs.alignment = Some(*align),
166                AttributeKind::LinkName { name, .. } => {
167                    // FIXME Remove check for foreign functions once #[link_name] on non-foreign
168                    // functions is a hard error
169                    if tcx.is_foreign_item(did) {
170                        codegen_fn_attrs.symbol_name = Some(*name);
171                    }
172                }
173                AttributeKind::LinkOrdinal { ordinal, span } => {
174                    codegen_fn_attrs.link_ordinal = Some(*ordinal);
175                    interesting_spans.link_ordinal = Some(*span);
176                }
177                AttributeKind::LinkSection { name, .. } => {
178                    codegen_fn_attrs.link_section = Some(*name)
179                }
180                AttributeKind::NoMangle(attr_span) => {
181                    interesting_spans.no_mangle = Some(*attr_span);
182                    if tcx.opt_item_name(did.to_def_id()).is_some() {
183                        codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
184                    } else {
185                        tcx.dcx().emit_err(NoMangleNameless {
186                            span: *attr_span,
187                            definition: format!(
188                                "{} {}",
189                                tcx.def_descr_article(did.to_def_id()),
190                                tcx.def_descr(did.to_def_id())
191                            ),
192                        });
193                    }
194                }
195                AttributeKind::Optimize(optimize, _) => codegen_fn_attrs.optimize = *optimize,
196                AttributeKind::TargetFeature { features, attr_span, was_forced } => {
197                    let Some(sig) = tcx.hir_node_by_def_id(did).fn_sig() else {
198                        tcx.dcx().span_delayed_bug(*attr_span, "target_feature applied to non-fn");
199                        continue;
200                    };
201                    let safe_target_features =
202                        matches!(sig.header.safety, hir::HeaderSafety::SafeTargetFeatures);
203                    codegen_fn_attrs.safe_target_features = safe_target_features;
204                    if safe_target_features && !was_forced {
205                        if tcx.sess.target.is_like_wasm || tcx.sess.opts.actually_rustdoc {
206                            // The `#[target_feature]` attribute is allowed on
207                            // WebAssembly targets on all functions. Prior to stabilizing
208                            // the `target_feature_11` feature, `#[target_feature]` was
209                            // only permitted on unsafe functions because on most targets
210                            // execution of instructions that are not supported is
211                            // considered undefined behavior. For WebAssembly which is a
212                            // 100% safe target at execution time it's not possible to
213                            // execute undefined instructions, and even if a future
214                            // feature was added in some form for this it would be a
215                            // deterministic trap. There is no undefined behavior when
216                            // executing WebAssembly so `#[target_feature]` is allowed
217                            // on safe functions (but again, only for WebAssembly)
218                            //
219                            // Note that this is also allowed if `actually_rustdoc` so
220                            // if a target is documenting some wasm-specific code then
221                            // it's not spuriously denied.
222                            //
223                            // Now that `#[target_feature]` is permitted on safe functions,
224                            // this exception must still exist for allowing the attribute on
225                            // `main`, `start`, and other functions that are not usually
226                            // allowed.
227                        } else {
228                            check_target_feature_trait_unsafe(tcx, did, *attr_span);
229                        }
230                    }
231                    from_target_feature_attr(
232                        tcx,
233                        did,
234                        features,
235                        *was_forced,
236                        rust_target_features,
237                        &mut codegen_fn_attrs.target_features,
238                    );
239                }
240                AttributeKind::TrackCaller(attr_span) => {
241                    let is_closure = tcx.is_closure_like(did.to_def_id());
242
243                    if !is_closure
244                        && let Some(fn_sig) = try_fn_sig(tcx, did, *attr_span)
245                        && fn_sig.skip_binder().abi() != ExternAbi::Rust
246                    {
247                        tcx.dcx().emit_err(errors::RequiresRustAbi { span: *attr_span });
248                    }
249                    if is_closure
250                        && !tcx.features().closure_track_caller()
251                        && !attr_span.allows_unstable(sym::closure_track_caller)
252                    {
253                        feature_err(
254                            &tcx.sess,
255                            sym::closure_track_caller,
256                            *attr_span,
257                            "`#[track_caller]` on closures is currently unstable",
258                        )
259                        .emit();
260                    }
261                    codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER
262                }
263                AttributeKind::Used { used_by, .. } => match used_by {
264                    UsedBy::Compiler => codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_COMPILER,
265                    UsedBy::Linker => codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED_LINKER,
266                    UsedBy::Default => {
267                        let used_form = if tcx.sess.target.os == "illumos" {
268                            // illumos' `ld` doesn't support a section header that would represent
269                            // `#[used(linker)]`, see
270                            // https://github.com/rust-lang/rust/issues/146169. For that target,
271                            // downgrade as if `#[used(compiler)]` was requested and hope for the
272                            // best.
273                            CodegenFnAttrFlags::USED_COMPILER
274                        } else {
275                            CodegenFnAttrFlags::USED_LINKER
276                        };
277                        codegen_fn_attrs.flags |= used_form;
278                    }
279                },
280                AttributeKind::FfiConst(_) => {
281                    codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_CONST
282                }
283                AttributeKind::FfiPure(_) => codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_PURE,
284                AttributeKind::StdInternalSymbol(_) => {
285                    codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL
286                }
287                AttributeKind::Linkage(linkage, _) => {
288                    let linkage = Some(*linkage);
289
290                    if tcx.is_foreign_item(did) {
291                        codegen_fn_attrs.import_linkage = linkage;
292
293                        if tcx.is_mutable_static(did.into()) {
294                            let mut diag = tcx.dcx().struct_span_err(
295                                attr.span(),
296                                "extern mutable statics are not allowed with `#[linkage]`",
297                            );
298                            diag.note(
299                                "marking the extern static mutable would allow changing which \
300                                symbol the static references rather than make the target of the \
301                                symbol mutable",
302                            );
303                            diag.emit();
304                        }
305                    } else {
306                        codegen_fn_attrs.linkage = linkage;
307                    }
308                }
309                AttributeKind::Sanitize { span, .. } => {
310                    interesting_spans.sanitize = Some(*span);
311                }
312                AttributeKind::ObjcClass { classname, .. } => {
313                    codegen_fn_attrs.objc_class = Some(*classname);
314                }
315                AttributeKind::ObjcSelector { methname, .. } => {
316                    codegen_fn_attrs.objc_selector = Some(*methname);
317                }
318                _ => {}
319            }
320        }
321
322        let Some(Ident { name, .. }) = attr.ident() else {
323            continue;
324        };
325
326        match name {
327            sym::rustc_allocator => codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR,
328            sym::rustc_nounwind => codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND,
329            sym::rustc_reallocator => codegen_fn_attrs.flags |= CodegenFnAttrFlags::REALLOCATOR,
330            sym::rustc_deallocator => codegen_fn_attrs.flags |= CodegenFnAttrFlags::DEALLOCATOR,
331            sym::rustc_allocator_zeroed => {
332                codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR_ZEROED
333            }
334            sym::thread_local => codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL,
335            sym::instruction_set => {
336                codegen_fn_attrs.instruction_set = parse_instruction_set_attr(tcx, attr)
337            }
338            sym::patchable_function_entry => {
339                codegen_fn_attrs.patchable_function_entry =
340                    parse_patchable_function_entry(tcx, attr);
341            }
342            _ => {}
343        }
344    }
345
346    interesting_spans
347}
348
349/// Applies overrides for codegen fn attrs. These often have a specific reason why they're necessary.
350/// Please comment why when adding a new one!
351fn apply_overrides(tcx: TyCtxt<'_>, did: LocalDefId, codegen_fn_attrs: &mut CodegenFnAttrs) {
352    // Apply the minimum function alignment here. This ensures that a function's alignment is
353    // determined by the `-C` flags of the crate it is defined in, not the `-C` flags of the crate
354    // it happens to be codegen'd (or const-eval'd) in.
355    codegen_fn_attrs.alignment =
356        Ord::max(codegen_fn_attrs.alignment, tcx.sess.opts.unstable_opts.min_function_alignment);
357
358    // Compute the disabled sanitizers.
359    codegen_fn_attrs.no_sanitize |= tcx.disabled_sanitizers_for(did);
360    // On trait methods, inherit the `#[align]` of the trait's method prototype.
361    codegen_fn_attrs.alignment = Ord::max(codegen_fn_attrs.alignment, tcx.inherited_align(did));
362
363    // naked function MUST NOT be inlined! This attribute is required for the rust compiler itself,
364    // but not for the code generation backend because at that point the naked function will just be
365    // a declaration, with a definition provided in global assembly.
366    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
367        codegen_fn_attrs.inline = InlineAttr::Never;
368    }
369
370    // #73631: closures inherit `#[target_feature]` annotations
371    //
372    // If this closure is marked `#[inline(always)]`, simply skip adding `#[target_feature]`.
373    //
374    // At this point, `unsafe` has already been checked and `#[target_feature]` only affects codegen.
375    // Due to LLVM limitations, emitting both `#[inline(always)]` and `#[target_feature]` is *unsound*:
376    // the function may be inlined into a caller with fewer target features. Also see
377    // <https://github.com/rust-lang/rust/issues/116573>.
378    //
379    // Using `#[inline(always)]` implies that this closure will most likely be inlined into
380    // its parent function, which effectively inherits the features anyway. Boxing this closure
381    // would result in this closure being compiled without the inherited target features, but this
382    // is probably a poor usage of `#[inline(always)]` and easily avoided by not using the attribute.
383    if tcx.is_closure_like(did.to_def_id()) && codegen_fn_attrs.inline != InlineAttr::Always {
384        let owner_id = tcx.parent(did.to_def_id());
385        if tcx.def_kind(owner_id).has_codegen_attrs() {
386            codegen_fn_attrs
387                .target_features
388                .extend(tcx.codegen_fn_attrs(owner_id).target_features.iter().copied());
389        }
390    }
391
392    // When `no_builtins` is applied at the crate level, we should add the
393    // `no-builtins` attribute to each function to ensure it takes effect in LTO.
394    let crate_attrs = tcx.hir_attrs(rustc_hir::CRATE_HIR_ID);
395    let no_builtins = attr::contains_name(crate_attrs, sym::no_builtins);
396    if no_builtins {
397        codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_BUILTINS;
398    }
399
400    // inherit track-caller properly
401    if tcx.should_inherit_track_caller(did) {
402        codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
403    }
404
405    // Foreign items by default use no mangling for their symbol name.
406    if tcx.is_foreign_item(did) {
407        codegen_fn_attrs.flags |= CodegenFnAttrFlags::FOREIGN_ITEM;
408
409        // There's a few exceptions to this rule though:
410        if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
411            // * `#[rustc_std_internal_symbol]` mangles the symbol name in a special way
412            //   both for exports and imports through foreign items. This is handled further,
413            //   during symbol mangling logic.
414        } else if codegen_fn_attrs.symbol_name.is_some() {
415            // * This can be overridden with the `#[link_name]` attribute
416        } else {
417            // NOTE: there's one more exception that we cannot apply here. On wasm,
418            // some items cannot be `no_mangle`.
419            // However, we don't have enough information here to determine that.
420            // As such, no_mangle foreign items on wasm that have the same defid as some
421            // import will *still* be mangled despite this.
422            //
423            // if none of the exceptions apply; apply no_mangle
424            codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
425        }
426    }
427}
428
429fn check_result(
430    tcx: TyCtxt<'_>,
431    did: LocalDefId,
432    interesting_spans: InterestingAttributeDiagnosticSpans,
433    codegen_fn_attrs: &CodegenFnAttrs,
434) {
435    // If a function uses `#[target_feature]` it can't be inlined into general
436    // purpose functions as they wouldn't have the right target features
437    // enabled. For that reason we also forbid `#[inline(always)]` as it can't be
438    // respected.
439    //
440    // `#[rustc_force_inline]` doesn't need to be prohibited here, only
441    // `#[inline(always)]`, as forced inlining is implemented entirely within
442    // rustc (and so the MIR inliner can do any necessary checks for compatible target
443    // features).
444    //
445    // This sidesteps the LLVM blockers in enabling `target_features` +
446    // `inline(always)` to be used together (see rust-lang/rust#116573 and
447    // llvm/llvm-project#70563).
448    if !codegen_fn_attrs.target_features.is_empty()
449        && matches!(codegen_fn_attrs.inline, InlineAttr::Always)
450        && !tcx.features().target_feature_inline_always()
451        && let Some(span) = interesting_spans.inline
452    {
453        feature_err(
454            tcx.sess,
455            sym::target_feature_inline_always,
456            span,
457            "cannot use `#[inline(always)]` with `#[target_feature]`",
458        )
459        .emit();
460    }
461
462    // warn that inline has no effect when no_sanitize is present
463    if !codegen_fn_attrs.no_sanitize.is_empty()
464        && codegen_fn_attrs.inline.always()
465        && let (Some(no_sanitize_span), Some(inline_span)) =
466            (interesting_spans.sanitize, interesting_spans.inline)
467    {
468        let hir_id = tcx.local_def_id_to_hir_id(did);
469        tcx.node_span_lint(lint::builtin::INLINE_NO_SANITIZE, hir_id, no_sanitize_span, |lint| {
470            lint.primary_message("setting `sanitize` off will have no effect after inlining");
471            lint.span_note(inline_span, "inlining requested here");
472        })
473    }
474
475    // error when specifying link_name together with link_ordinal
476    if let Some(_) = codegen_fn_attrs.symbol_name
477        && let Some(_) = codegen_fn_attrs.link_ordinal
478    {
479        let msg = "cannot use `#[link_name]` with `#[link_ordinal]`";
480        if let Some(span) = interesting_spans.link_ordinal {
481            tcx.dcx().span_err(span, msg);
482        } else {
483            tcx.dcx().err(msg);
484        }
485    }
486
487    if let Some(features) = check_tied_features(
488        tcx.sess,
489        &codegen_fn_attrs
490            .target_features
491            .iter()
492            .map(|features| (features.name.as_str(), true))
493            .collect(),
494    ) {
495        let span =
496            find_attr!(tcx.get_all_attrs(did), AttributeKind::TargetFeature{attr_span: span, ..} => *span)
497                .unwrap_or_else(|| tcx.def_span(did));
498
499        tcx.dcx()
500            .create_err(errors::TargetFeatureDisableOrEnable {
501                features,
502                span: Some(span),
503                missing_features: Some(errors::MissingFeatures),
504            })
505            .emit();
506    }
507}
508
509fn handle_lang_items(
510    tcx: TyCtxt<'_>,
511    did: LocalDefId,
512    interesting_spans: &InterestingAttributeDiagnosticSpans,
513    attrs: &[Attribute],
514    codegen_fn_attrs: &mut CodegenFnAttrs,
515) {
516    let lang_item = lang_items::extract(attrs).and_then(|(name, _)| LangItem::from_name(name));
517
518    // Weak lang items have the same semantics as "std internal" symbols in the
519    // sense that they're preserved through all our LTO passes and only
520    // strippable by the linker.
521    //
522    // Additionally weak lang items have predetermined symbol names.
523    if let Some(lang_item) = lang_item
524        && let Some(link_name) = lang_item.link_name()
525    {
526        codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
527        codegen_fn_attrs.symbol_name = Some(link_name);
528    }
529
530    // error when using no_mangle on a lang item item
531    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
532        && codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE)
533    {
534        let mut err = tcx
535            .dcx()
536            .struct_span_err(
537                interesting_spans.no_mangle.unwrap_or_default(),
538                "`#[no_mangle]` cannot be used on internal language items",
539            )
540            .with_note("Rustc requires this item to have a specific mangled name.")
541            .with_span_label(tcx.def_span(did), "should be the internal language item");
542        if let Some(lang_item) = lang_item
543            && let Some(link_name) = lang_item.link_name()
544        {
545            err = err
546                .with_note("If you are trying to prevent mangling to ease debugging, many")
547                .with_note(format!("debuggers support a command such as `rbreak {link_name}` to"))
548                .with_note(format!(
549                    "match `.*{link_name}.*` instead of `break {link_name}` on a specific name"
550                ))
551        }
552        err.emit();
553    }
554}
555
556/// Generate the [`CodegenFnAttrs`] for an item (identified by the [`LocalDefId`]).
557///
558/// This happens in 4 stages:
559/// - apply built-in attributes that directly translate to codegen attributes.
560/// - handle lang items. These have special codegen attrs applied to them.
561/// - apply overrides, like minimum requirements for alignment and other settings that don't rely directly the built-in attrs on the item.
562///   overrides come after applying built-in attributes since they may only apply when certain attributes were already set in the stage before.
563/// - check that the result is valid. There's various ways in which this may not be the case, such as certain combinations of attrs.
564fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
565    if cfg!(debug_assertions) {
566        let def_kind = tcx.def_kind(did);
567        assert!(
568            def_kind.has_codegen_attrs(),
569            "unexpected `def_kind` in `codegen_fn_attrs`: {def_kind:?}",
570        );
571    }
572
573    let mut codegen_fn_attrs = CodegenFnAttrs::new();
574    let attrs = tcx.hir_attrs(tcx.local_def_id_to_hir_id(did));
575
576    let interesting_spans = process_builtin_attrs(tcx, did, attrs, &mut codegen_fn_attrs);
577    handle_lang_items(tcx, did, &interesting_spans, attrs, &mut codegen_fn_attrs);
578    apply_overrides(tcx, did, &mut codegen_fn_attrs);
579    check_result(tcx, did, interesting_spans, &codegen_fn_attrs);
580
581    codegen_fn_attrs
582}
583
584fn disabled_sanitizers_for(tcx: TyCtxt<'_>, did: LocalDefId) -> SanitizerSet {
585    // Backtrack to the crate root.
586    let mut disabled = match tcx.opt_local_parent(did) {
587        // Check the parent (recursively).
588        Some(parent) => tcx.disabled_sanitizers_for(parent),
589        // We reached the crate root without seeing an attribute, so
590        // there is no sanitizers to exclude.
591        None => SanitizerSet::empty(),
592    };
593
594    // Check for a sanitize annotation directly on this def.
595    if let Some((on_set, off_set)) = find_attr!(tcx.get_all_attrs(did), AttributeKind::Sanitize {on_set, off_set, ..} => (on_set, off_set))
596    {
597        // the on set is the set of sanitizers explicitly enabled.
598        // we mask those out since we want the set of disabled sanitizers here
599        disabled &= !*on_set;
600        // the off set is the set of sanitizers explicitly disabled.
601        // we or those in here.
602        disabled |= *off_set;
603        // the on set and off set are distjoint since there's a third option: unset.
604        // a node may not set the sanitizer setting in which case it inherits from parents.
605        // the code above in this function does this backtracking
606    }
607    disabled
608}
609
610/// Checks if the provided DefId is a method in a trait impl for a trait which has track_caller
611/// applied to the method prototype.
612fn should_inherit_track_caller(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
613    tcx.trait_item_of(def_id).is_some_and(|id| {
614        tcx.codegen_fn_attrs(id).flags.intersects(CodegenFnAttrFlags::TRACK_CALLER)
615    })
616}
617
618/// If the provided DefId is a method in a trait impl, return the value of the `#[align]`
619/// attribute on the method prototype (if any).
620fn inherited_align<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Option<Align> {
621    tcx.codegen_fn_attrs(tcx.trait_item_of(def_id)?).alignment
622}
623
624/// We now check the #\[rustc_autodiff\] attributes which we generated from the #[autodiff(...)]
625/// macros. There are two forms. The pure one without args to mark primal functions (the functions
626/// being differentiated). The other form is #[rustc_autodiff(Mode, ActivityList)] on top of the
627/// placeholder functions. We wrote the rustc_autodiff attributes ourself, so this should never
628/// panic, unless we introduced a bug when parsing the autodiff macro.
629//FIXME(jdonszelmann): put in the main loop. No need to have two..... :/ Let's do that when we make autodiff parsed.
630pub fn autodiff_attrs(tcx: TyCtxt<'_>, id: DefId) -> Option<AutoDiffAttrs> {
631    let attrs = tcx.get_attrs(id, sym::rustc_autodiff);
632
633    let attrs = attrs.filter(|attr| attr.has_name(sym::rustc_autodiff)).collect::<Vec<_>>();
634
635    // check for exactly one autodiff attribute on placeholder functions.
636    // There should only be one, since we generate a new placeholder per ad macro.
637    let attr = match &attrs[..] {
638        [] => return None,
639        [attr] => attr,
640        _ => {
641            span_bug!(attrs[1].span(), "cg_ssa: rustc_autodiff should only exist once per source");
642        }
643    };
644
645    let list = attr.meta_item_list().unwrap_or_default();
646
647    // empty autodiff attribute macros (i.e. `#[autodiff]`) are used to mark source functions
648    if list.is_empty() {
649        return Some(AutoDiffAttrs::source());
650    }
651
652    let [mode, width_meta, input_activities @ .., ret_activity] = &list[..] else {
653        span_bug!(attr.span(), "rustc_autodiff attribute must contain mode, width and activities");
654    };
655    let mode = if let MetaItemInner::MetaItem(MetaItem { path: p1, .. }) = mode {
656        p1.segments.first().unwrap().ident
657    } else {
658        span_bug!(attr.span(), "rustc_autodiff attribute must contain mode");
659    };
660
661    // parse mode
662    let mode = match mode.as_str() {
663        "Forward" => DiffMode::Forward,
664        "Reverse" => DiffMode::Reverse,
665        _ => {
666            span_bug!(mode.span, "rustc_autodiff attribute contains invalid mode");
667        }
668    };
669
670    let width: u32 = match width_meta {
671        MetaItemInner::MetaItem(MetaItem { path: p1, .. }) => {
672            let w = p1.segments.first().unwrap().ident;
673            match w.as_str().parse() {
674                Ok(val) => val,
675                Err(_) => {
676                    span_bug!(w.span, "rustc_autodiff width should fit u32");
677                }
678            }
679        }
680        MetaItemInner::Lit(lit) => {
681            if let LitKind::Int(val, _) = lit.kind {
682                match val.get().try_into() {
683                    Ok(val) => val,
684                    Err(_) => {
685                        span_bug!(lit.span, "rustc_autodiff width should fit u32");
686                    }
687                }
688            } else {
689                span_bug!(lit.span, "rustc_autodiff width should be an integer");
690            }
691        }
692    };
693
694    // First read the ret symbol from the attribute
695    let ret_symbol = if let MetaItemInner::MetaItem(MetaItem { path: p1, .. }) = ret_activity {
696        p1.segments.first().unwrap().ident
697    } else {
698        span_bug!(attr.span(), "rustc_autodiff attribute must contain the return activity");
699    };
700
701    // Then parse it into an actual DiffActivity
702    let Ok(ret_activity) = DiffActivity::from_str(ret_symbol.as_str()) else {
703        span_bug!(ret_symbol.span, "invalid return activity");
704    };
705
706    // Now parse all the intermediate (input) activities
707    let mut arg_activities: Vec<DiffActivity> = vec![];
708    for arg in input_activities {
709        let arg_symbol = if let MetaItemInner::MetaItem(MetaItem { path: p2, .. }) = arg {
710            match p2.segments.first() {
711                Some(x) => x.ident,
712                None => {
713                    span_bug!(
714                        arg.span(),
715                        "rustc_autodiff attribute must contain the input activity"
716                    );
717                }
718            }
719        } else {
720            span_bug!(arg.span(), "rustc_autodiff attribute must contain the input activity");
721        };
722
723        match DiffActivity::from_str(arg_symbol.as_str()) {
724            Ok(arg_activity) => arg_activities.push(arg_activity),
725            Err(_) => {
726                span_bug!(arg_symbol.span, "invalid input activity");
727            }
728        }
729    }
730
731    Some(AutoDiffAttrs { mode, width, ret_activity, input_activity: arg_activities })
732}
733
734pub(crate) fn provide(providers: &mut Providers) {
735    *providers = Providers {
736        codegen_fn_attrs,
737        should_inherit_track_caller,
738        inherited_align,
739        disabled_sanitizers_for,
740        ..*providers
741    };
742}
rustc_codegen_ssa/codegen_attrs.rs

rustc_codegen_ssa/
codegen_attrs.rs
