rustc_codegen_llvm/
attributes.rs

1//! Set and unset common attributes on LLVM values.
2use rustc_hir::attrs::{InlineAttr, InstructionSetAttr, OptimizeAttr};
3use rustc_hir::def_id::DefId;
4use rustc_middle::middle::codegen_fn_attrs::{
5    CodegenFnAttrFlags, CodegenFnAttrs, PatchableFunctionEntry,
6};
7use rustc_middle::ty::{self, TyCtxt};
8use rustc_session::config::{BranchProtection, FunctionReturn, OptLevel, PAuthKey, PacRet};
9use rustc_symbol_mangling::mangle_internal_symbol;
10use rustc_target::spec::{FramePointer, SanitizerSet, StackProbeType, StackProtector};
11use smallvec::SmallVec;
12
13use crate::context::SimpleCx;
14use crate::errors::SanitizerMemtagRequiresMte;
15use crate::llvm::AttributePlace::Function;
16use crate::llvm::{
17    self, AllocKindFlags, Attribute, AttributeKind, AttributePlace, MemoryEffects, Value,
18};
19use crate::{Session, attributes, llvm_util};
20
21pub(crate) fn apply_to_llfn(llfn: &Value, idx: AttributePlace, attrs: &[&Attribute]) {
22    if !attrs.is_empty() {
23        llvm::AddFunctionAttributes(llfn, idx, attrs);
24    }
25}
26
27pub(crate) fn apply_to_callsite(callsite: &Value, idx: AttributePlace, attrs: &[&Attribute]) {
28    if !attrs.is_empty() {
29        llvm::AddCallSiteAttributes(callsite, idx, attrs);
30    }
31}
32
33/// Get LLVM attribute for the provided inline heuristic.
34pub(crate) fn inline_attr<'ll, 'tcx>(
35    cx: &SimpleCx<'ll>,
36    tcx: TyCtxt<'tcx>,
37    instance: ty::Instance<'tcx>,
38) -> Option<&'ll Attribute> {
39    // `optnone` requires `noinline`
40    let codegen_fn_attrs = tcx.codegen_fn_attrs(instance.def_id());
41    let inline = match (codegen_fn_attrs.inline, &codegen_fn_attrs.optimize) {
42        (_, OptimizeAttr::DoNotOptimize) => InlineAttr::Never,
43        (InlineAttr::None, _) if instance.def.requires_inline(tcx) => InlineAttr::Hint,
44        (inline, _) => inline,
45    };
46
47    if !tcx.sess.opts.unstable_opts.inline_llvm {
48        // disable LLVM inlining
49        return Some(AttributeKind::NoInline.create_attr(cx.llcx));
50    }
51    match inline {
52        InlineAttr::Hint => Some(AttributeKind::InlineHint.create_attr(cx.llcx)),
53        InlineAttr::Always | InlineAttr::Force { .. } => {
54            Some(AttributeKind::AlwaysInline.create_attr(cx.llcx))
55        }
56        InlineAttr::Never => {
57            if tcx.sess.target.arch != "amdgpu" {
58                Some(AttributeKind::NoInline.create_attr(cx.llcx))
59            } else {
60                None
61            }
62        }
63        InlineAttr::None => None,
64    }
65}
66
67#[inline]
68fn patchable_function_entry_attrs<'ll>(
69    cx: &SimpleCx<'ll>,
70    sess: &Session,
71    attr: Option<PatchableFunctionEntry>,
72) -> SmallVec<[&'ll Attribute; 2]> {
73    let mut attrs = SmallVec::new();
74    let patchable_spec = attr.unwrap_or_else(|| {
75        PatchableFunctionEntry::from_config(sess.opts.unstable_opts.patchable_function_entry)
76    });
77    let entry = patchable_spec.entry();
78    let prefix = patchable_spec.prefix();
79    if entry > 0 {
80        attrs.push(llvm::CreateAttrStringValue(
81            cx.llcx,
82            "patchable-function-entry",
83            &format!("{}", entry),
84        ));
85    }
86    if prefix > 0 {
87        attrs.push(llvm::CreateAttrStringValue(
88            cx.llcx,
89            "patchable-function-prefix",
90            &format!("{}", prefix),
91        ));
92    }
93    attrs
94}
95
96/// Get LLVM sanitize attributes.
97#[inline]
98pub(crate) fn sanitize_attrs<'ll, 'tcx>(
99    cx: &SimpleCx<'ll>,
100    tcx: TyCtxt<'tcx>,
101    no_sanitize: SanitizerSet,
102) -> SmallVec<[&'ll Attribute; 4]> {
103    let mut attrs = SmallVec::new();
104    let enabled = tcx.sess.opts.unstable_opts.sanitizer - no_sanitize;
105    if enabled.contains(SanitizerSet::ADDRESS) || enabled.contains(SanitizerSet::KERNELADDRESS) {
106        attrs.push(llvm::AttributeKind::SanitizeAddress.create_attr(cx.llcx));
107    }
108    if enabled.contains(SanitizerSet::MEMORY) {
109        attrs.push(llvm::AttributeKind::SanitizeMemory.create_attr(cx.llcx));
110    }
111    if enabled.contains(SanitizerSet::THREAD) {
112        attrs.push(llvm::AttributeKind::SanitizeThread.create_attr(cx.llcx));
113    }
114    if enabled.contains(SanitizerSet::HWADDRESS) {
115        attrs.push(llvm::AttributeKind::SanitizeHWAddress.create_attr(cx.llcx));
116    }
117    if enabled.contains(SanitizerSet::SHADOWCALLSTACK) {
118        attrs.push(llvm::AttributeKind::ShadowCallStack.create_attr(cx.llcx));
119    }
120    if enabled.contains(SanitizerSet::MEMTAG) {
121        // Check to make sure the mte target feature is actually enabled.
122        let features = tcx.global_backend_features(());
123        let mte_feature =
124            features.iter().map(|s| &s[..]).rfind(|n| ["+mte", "-mte"].contains(&&n[..]));
125        if let None | Some("-mte") = mte_feature {
126            tcx.dcx().emit_err(SanitizerMemtagRequiresMte);
127        }
128
129        attrs.push(llvm::AttributeKind::SanitizeMemTag.create_attr(cx.llcx));
130    }
131    if enabled.contains(SanitizerSet::SAFESTACK) {
132        attrs.push(llvm::AttributeKind::SanitizeSafeStack.create_attr(cx.llcx));
133    }
134    attrs
135}
136
137/// Tell LLVM to emit or not emit the information necessary to unwind the stack for the function.
138#[inline]
139pub(crate) fn uwtable_attr(llcx: &llvm::Context, use_sync_unwind: Option<bool>) -> &Attribute {
140    // NOTE: We should determine if we even need async unwind tables, as they
141    // take have more overhead and if we can use sync unwind tables we
142    // probably should.
143    let async_unwind = !use_sync_unwind.unwrap_or(false);
144    llvm::CreateUWTableAttr(llcx, async_unwind)
145}
146
147pub(crate) fn frame_pointer_type_attr<'ll>(
148    cx: &SimpleCx<'ll>,
149    sess: &Session,
150) -> Option<&'ll Attribute> {
151    let mut fp = sess.target.frame_pointer;
152    let opts = &sess.opts;
153    // "mcount" function relies on stack pointer.
154    // See <https://sourceware.org/binutils/docs/gprof/Implementation.html>.
155    if opts.unstable_opts.instrument_mcount {
156        fp.ratchet(FramePointer::Always);
157    }
158    fp.ratchet(opts.cg.force_frame_pointers);
159    let attr_value = match fp {
160        FramePointer::Always => "all",
161        FramePointer::NonLeaf => "non-leaf",
162        FramePointer::MayOmit => return None,
163    };
164    Some(llvm::CreateAttrStringValue(cx.llcx, "frame-pointer", attr_value))
165}
166
167fn function_return_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> Option<&'ll Attribute> {
168    let function_return_attr = match sess.opts.unstable_opts.function_return {
169        FunctionReturn::Keep => return None,
170        FunctionReturn::ThunkExtern => AttributeKind::FnRetThunkExtern,
171    };
172
173    Some(function_return_attr.create_attr(cx.llcx))
174}
175
176/// Tell LLVM what instrument function to insert.
177#[inline]
178fn instrument_function_attr<'ll>(
179    cx: &SimpleCx<'ll>,
180    sess: &Session,
181) -> SmallVec<[&'ll Attribute; 4]> {
182    let mut attrs = SmallVec::new();
183    if sess.opts.unstable_opts.instrument_mcount {
184        // Similar to `clang -pg` behavior. Handled by the
185        // `post-inline-ee-instrument` LLVM pass.
186
187        // The function name varies on platforms.
188        // See test/CodeGen/mcount.c in clang.
189        let mcount_name = match &sess.target.llvm_mcount_intrinsic {
190            Some(llvm_mcount_intrinsic) => llvm_mcount_intrinsic.as_ref(),
191            None => sess.target.mcount.as_ref(),
192        };
193
194        attrs.push(llvm::CreateAttrStringValue(
195            cx.llcx,
196            "instrument-function-entry-inlined",
197            mcount_name,
198        ));
199    }
200    if let Some(options) = &sess.opts.unstable_opts.instrument_xray {
201        // XRay instrumentation is similar to __cyg_profile_func_{enter,exit}.
202        // Function prologue and epilogue are instrumented with NOP sleds,
203        // a runtime library later replaces them with detours into tracing code.
204        if options.always {
205            attrs.push(llvm::CreateAttrStringValue(cx.llcx, "function-instrument", "xray-always"));
206        }
207        if options.never {
208            attrs.push(llvm::CreateAttrStringValue(cx.llcx, "function-instrument", "xray-never"));
209        }
210        if options.ignore_loops {
211            attrs.push(llvm::CreateAttrString(cx.llcx, "xray-ignore-loops"));
212        }
213        // LLVM will not choose the default for us, but rather requires specific
214        // threshold in absence of "xray-always". Use the same default as Clang.
215        let threshold = options.instruction_threshold.unwrap_or(200);
216        attrs.push(llvm::CreateAttrStringValue(
217            cx.llcx,
218            "xray-instruction-threshold",
219            &threshold.to_string(),
220        ));
221        if options.skip_entry {
222            attrs.push(llvm::CreateAttrString(cx.llcx, "xray-skip-entry"));
223        }
224        if options.skip_exit {
225            attrs.push(llvm::CreateAttrString(cx.llcx, "xray-skip-exit"));
226        }
227    }
228    attrs
229}
230
231fn nojumptables_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> Option<&'ll Attribute> {
232    if !sess.opts.unstable_opts.no_jump_tables {
233        return None;
234    }
235
236    Some(llvm::CreateAttrStringValue(cx.llcx, "no-jump-tables", "true"))
237}
238
239fn probestack_attr<'ll, 'tcx>(cx: &SimpleCx<'ll>, tcx: TyCtxt<'tcx>) -> Option<&'ll Attribute> {
240    // Currently stack probes seem somewhat incompatible with the address
241    // sanitizer and thread sanitizer. With asan we're already protected from
242    // stack overflow anyway so we don't really need stack probes regardless.
243    if tcx
244        .sess
245        .opts
246        .unstable_opts
247        .sanitizer
248        .intersects(SanitizerSet::ADDRESS | SanitizerSet::THREAD)
249    {
250        return None;
251    }
252
253    // probestack doesn't play nice either with `-C profile-generate`.
254    if tcx.sess.opts.cg.profile_generate.enabled() {
255        return None;
256    }
257
258    let attr_value = match tcx.sess.target.stack_probes {
259        StackProbeType::None => return None,
260        // Request LLVM to generate the probes inline. If the given LLVM version does not support
261        // this, no probe is generated at all (even if the attribute is specified).
262        StackProbeType::Inline => "inline-asm",
263        // Flag our internal `__rust_probestack` function as the stack probe symbol.
264        // This is defined in the `compiler-builtins` crate for each architecture.
265        StackProbeType::Call => &mangle_internal_symbol(tcx, "__rust_probestack"),
266        // Pick from the two above based on the LLVM version.
267        StackProbeType::InlineOrCall { min_llvm_version_for_inline } => {
268            if llvm_util::get_version() < min_llvm_version_for_inline {
269                &mangle_internal_symbol(tcx, "__rust_probestack")
270            } else {
271                "inline-asm"
272            }
273        }
274    };
275    Some(llvm::CreateAttrStringValue(cx.llcx, "probe-stack", attr_value))
276}
277
278fn stackprotector_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> Option<&'ll Attribute> {
279    let sspattr = match sess.stack_protector() {
280        StackProtector::None => return None,
281        StackProtector::All => AttributeKind::StackProtectReq,
282        StackProtector::Strong => AttributeKind::StackProtectStrong,
283        StackProtector::Basic => AttributeKind::StackProtect,
284    };
285
286    Some(sspattr.create_attr(cx.llcx))
287}
288
289fn backchain_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> Option<&'ll Attribute> {
290    if sess.target.arch != "s390x" {
291        return None;
292    }
293
294    let requested_features = sess.opts.cg.target_feature.split(',');
295    let found_positive = requested_features.clone().any(|r| r == "+backchain");
296
297    if found_positive { Some(llvm::CreateAttrString(cx.llcx, "backchain")) } else { None }
298}
299
300pub(crate) fn target_cpu_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> &'ll Attribute {
301    let target_cpu = llvm_util::target_cpu(sess);
302    llvm::CreateAttrStringValue(cx.llcx, "target-cpu", target_cpu)
303}
304
305pub(crate) fn tune_cpu_attr<'ll>(cx: &SimpleCx<'ll>, sess: &Session) -> Option<&'ll Attribute> {
306    llvm_util::tune_cpu(sess)
307        .map(|tune_cpu| llvm::CreateAttrStringValue(cx.llcx, "tune-cpu", tune_cpu))
308}
309
310/// Get the `target-features` LLVM attribute.
311pub(crate) fn target_features_attr<'ll, 'tcx>(
312    cx: &SimpleCx<'ll>,
313    tcx: TyCtxt<'tcx>,
314    function_features: Vec<String>,
315) -> Option<&'ll Attribute> {
316    let global_features = tcx.global_backend_features(()).iter().map(String::as_str);
317    let function_features = function_features.iter().map(String::as_str);
318    let target_features =
319        global_features.chain(function_features).intersperse(",").collect::<String>();
320    (!target_features.is_empty())
321        .then(|| llvm::CreateAttrStringValue(cx.llcx, "target-features", &target_features))
322}
323
324/// Get the `NonLazyBind` LLVM attribute,
325/// if the codegen options allow skipping the PLT.
326pub(crate) fn non_lazy_bind_attr<'ll>(
327    cx: &SimpleCx<'ll>,
328    sess: &Session,
329) -> Option<&'ll Attribute> {
330    // Don't generate calls through PLT if it's not necessary
331    if !sess.needs_plt() { Some(AttributeKind::NonLazyBind.create_attr(cx.llcx)) } else { None }
332}
333
334/// Get the default optimizations attrs for a function.
335#[inline]
336pub(crate) fn default_optimisation_attrs<'ll>(
337    cx: &SimpleCx<'ll>,
338    sess: &Session,
339) -> SmallVec<[&'ll Attribute; 2]> {
340    let mut attrs = SmallVec::new();
341    match sess.opts.optimize {
342        OptLevel::Size => {
343            attrs.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
344        }
345        OptLevel::SizeMin => {
346            attrs.push(llvm::AttributeKind::MinSize.create_attr(cx.llcx));
347            attrs.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
348        }
349        _ => {}
350    }
351    attrs
352}
353
354fn create_alloc_family_attr(llcx: &llvm::Context) -> &llvm::Attribute {
355    llvm::CreateAttrStringValue(llcx, "alloc-family", "__rust_alloc")
356}
357
358/// Helper for `FnAbi::apply_attrs_llfn`:
359/// Composite function which sets LLVM attributes for function depending on its AST (`#[attribute]`)
360/// attributes.
361pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
362    cx: &SimpleCx<'ll>,
363    tcx: TyCtxt<'tcx>,
364    llfn: &'ll Value,
365    codegen_fn_attrs: &CodegenFnAttrs,
366    instance: Option<ty::Instance<'tcx>>,
367) {
368    let sess = tcx.sess;
369    let mut to_add = SmallVec::<[_; 16]>::new();
370
371    match codegen_fn_attrs.optimize {
372        OptimizeAttr::Default => {
373            to_add.extend(default_optimisation_attrs(cx, sess));
374        }
375        OptimizeAttr::DoNotOptimize => {
376            to_add.push(llvm::AttributeKind::OptimizeNone.create_attr(cx.llcx));
377        }
378        OptimizeAttr::Size => {
379            to_add.push(llvm::AttributeKind::MinSize.create_attr(cx.llcx));
380            to_add.push(llvm::AttributeKind::OptimizeForSize.create_attr(cx.llcx));
381        }
382        OptimizeAttr::Speed => {}
383    }
384
385    if sess.must_emit_unwind_tables() {
386        to_add.push(uwtable_attr(cx.llcx, sess.opts.unstable_opts.use_sync_unwind));
387    }
388
389    if sess.opts.unstable_opts.profile_sample_use.is_some() {
390        to_add.push(llvm::CreateAttrString(cx.llcx, "use-sample-profile"));
391    }
392
393    // FIXME: none of these functions interact with source level attributes.
394    to_add.extend(frame_pointer_type_attr(cx, sess));
395    to_add.extend(function_return_attr(cx, sess));
396    to_add.extend(instrument_function_attr(cx, sess));
397    to_add.extend(nojumptables_attr(cx, sess));
398    to_add.extend(probestack_attr(cx, tcx));
399    to_add.extend(stackprotector_attr(cx, sess));
400
401    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NO_BUILTINS) {
402        to_add.push(llvm::CreateAttrString(cx.llcx, "no-builtins"));
403    }
404
405    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
406        to_add.push(AttributeKind::Cold.create_attr(cx.llcx));
407    }
408    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_PURE) {
409        to_add.push(MemoryEffects::ReadOnly.create_attr(cx.llcx));
410    }
411    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_CONST) {
412        to_add.push(MemoryEffects::None.create_attr(cx.llcx));
413    }
414    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
415        // do nothing; a naked function is converted into an extern function
416        // and a global assembly block. LLVM's support for naked functions is
417        // not used.
418    } else {
419        // Do not set sanitizer attributes for naked functions.
420        to_add.extend(sanitize_attrs(cx, tcx, codegen_fn_attrs.no_sanitize));
421
422        // For non-naked functions, set branch protection attributes on aarch64.
423        if let Some(BranchProtection { bti, pac_ret, gcs }) =
424            sess.opts.unstable_opts.branch_protection
425        {
426            assert!(sess.target.arch == "aarch64");
427            if bti {
428                to_add.push(llvm::CreateAttrString(cx.llcx, "branch-target-enforcement"));
429            }
430            if gcs {
431                to_add.push(llvm::CreateAttrString(cx.llcx, "guarded-control-stack"));
432            }
433            if let Some(PacRet { leaf, pc, key }) = pac_ret {
434                if pc {
435                    to_add.push(llvm::CreateAttrString(cx.llcx, "branch-protection-pauth-lr"));
436                }
437                to_add.push(llvm::CreateAttrStringValue(
438                    cx.llcx,
439                    "sign-return-address",
440                    if leaf { "all" } else { "non-leaf" },
441                ));
442                to_add.push(llvm::CreateAttrStringValue(
443                    cx.llcx,
444                    "sign-return-address-key",
445                    if key == PAuthKey::A { "a_key" } else { "b_key" },
446                ));
447            }
448        }
449    }
450    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR)
451        || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR_ZEROED)
452    {
453        to_add.push(create_alloc_family_attr(cx.llcx));
454        if let Some(instance) = instance
455            && let Some(zv) =
456                tcx.get_attr(instance.def_id(), rustc_span::sym::rustc_allocator_zeroed_variant)
457            && let Some(name) = zv.value_str()
458        {
459            to_add.push(llvm::CreateAttrStringValue(
460                cx.llcx,
461                "alloc-variant-zeroed",
462                &mangle_internal_symbol(tcx, name.as_str()),
463            ));
464        }
465        // apply to argument place instead of function
466        let alloc_align = AttributeKind::AllocAlign.create_attr(cx.llcx);
467        attributes::apply_to_llfn(llfn, AttributePlace::Argument(1), &[alloc_align]);
468        to_add.push(llvm::CreateAllocSizeAttr(cx.llcx, 0));
469        let mut flags = AllocKindFlags::Alloc | AllocKindFlags::Aligned;
470        if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR) {
471            flags |= AllocKindFlags::Uninitialized;
472        } else {
473            flags |= AllocKindFlags::Zeroed;
474        }
475        to_add.push(llvm::CreateAllocKindAttr(cx.llcx, flags));
476        // apply to return place instead of function (unlike all other attributes applied in this
477        // function)
478        let no_alias = AttributeKind::NoAlias.create_attr(cx.llcx);
479        attributes::apply_to_llfn(llfn, AttributePlace::ReturnValue, &[no_alias]);
480    }
481    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::REALLOCATOR) {
482        to_add.push(create_alloc_family_attr(cx.llcx));
483        to_add.push(llvm::CreateAllocKindAttr(
484            cx.llcx,
485            AllocKindFlags::Realloc | AllocKindFlags::Aligned,
486        ));
487        // applies to argument place instead of function place
488        let allocated_pointer = AttributeKind::AllocatedPointer.create_attr(cx.llcx);
489        attributes::apply_to_llfn(llfn, AttributePlace::Argument(0), &[allocated_pointer]);
490        // apply to argument place instead of function
491        let alloc_align = AttributeKind::AllocAlign.create_attr(cx.llcx);
492        attributes::apply_to_llfn(llfn, AttributePlace::Argument(2), &[alloc_align]);
493        to_add.push(llvm::CreateAllocSizeAttr(cx.llcx, 3));
494        let no_alias = AttributeKind::NoAlias.create_attr(cx.llcx);
495        attributes::apply_to_llfn(llfn, AttributePlace::ReturnValue, &[no_alias]);
496    }
497    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::DEALLOCATOR) {
498        to_add.push(create_alloc_family_attr(cx.llcx));
499        to_add.push(llvm::CreateAllocKindAttr(cx.llcx, AllocKindFlags::Free));
500        // applies to argument place instead of function place
501        let allocated_pointer = AttributeKind::AllocatedPointer.create_attr(cx.llcx);
502        attributes::apply_to_llfn(llfn, AttributePlace::Argument(0), &[allocated_pointer]);
503    }
504    if let Some(align) = codegen_fn_attrs.alignment {
505        llvm::set_alignment(llfn, align);
506    }
507    if let Some(backchain) = backchain_attr(cx, sess) {
508        to_add.push(backchain);
509    }
510    to_add.extend(patchable_function_entry_attrs(
511        cx,
512        sess,
513        codegen_fn_attrs.patchable_function_entry,
514    ));
515
516    // Always annotate functions with the target-cpu they are compiled for.
517    // Without this, ThinLTO won't inline Rust functions into Clang generated
518    // functions (because Clang annotates functions this way too).
519    to_add.push(target_cpu_attr(cx, sess));
520    // tune-cpu is only conveyed through the attribute for our purpose.
521    // The target doesn't care; the subtarget reads our attribute.
522    to_add.extend(tune_cpu_attr(cx, sess));
523
524    let function_features =
525        codegen_fn_attrs.target_features.iter().map(|f| f.name.as_str()).collect::<Vec<&str>>();
526
527    // Apply function attributes as per usual if there are no user defined
528    // target features otherwise this will get applied at the callsite.
529    if function_features.is_empty() {
530        if let Some(instance) = instance
531            && let Some(inline_attr) = inline_attr(cx, tcx, instance)
532        {
533            to_add.push(inline_attr);
534        }
535    }
536
537    let function_features = function_features
538        .iter()
539        // Convert to LLVMFeatures and filter out unavailable ones
540        .flat_map(|feat| llvm_util::to_llvm_features(sess, feat))
541        // Convert LLVMFeatures & dependencies to +<feats>s
542        .flat_map(|feat| feat.into_iter().map(|f| format!("+{f}")))
543        .chain(codegen_fn_attrs.instruction_set.iter().map(|x| match x {
544            InstructionSetAttr::ArmA32 => "-thumb-mode".to_string(),
545            InstructionSetAttr::ArmT32 => "+thumb-mode".to_string(),
546        }))
547        .collect::<Vec<String>>();
548
549    if sess.target.is_like_wasm {
550        // If this function is an import from the environment but the wasm
551        // import has a specific module/name, apply them here.
552        if let Some(instance) = instance
553            && let Some(module) = wasm_import_module(tcx, instance.def_id())
554        {
555            to_add.push(llvm::CreateAttrStringValue(cx.llcx, "wasm-import-module", module));
556
557            let name =
558                codegen_fn_attrs.symbol_name.unwrap_or_else(|| tcx.item_name(instance.def_id()));
559            let name = name.as_str();
560            to_add.push(llvm::CreateAttrStringValue(cx.llcx, "wasm-import-name", name));
561        }
562    }
563
564    to_add.extend(target_features_attr(cx, tcx, function_features));
565
566    attributes::apply_to_llfn(llfn, Function, &to_add);
567}
568
569fn wasm_import_module(tcx: TyCtxt<'_>, id: DefId) -> Option<&String> {
570    tcx.wasm_import_module_map(id.krate).get(&id)
571}
rustc_codegen_llvm/attributes.rs

rustc_codegen_llvm/
attributes.rs
