1 use crate::{LateContext, LateLintPass, LintContext};
3 use rustc_attr as attr;
4 use rustc_data_structures::fx::FxHashSet;
5 use rustc_errors::Applicability;
7 use rustc_hir::def_id::DefId;
8 use rustc_hir::{is_range_literal, Expr, ExprKind, Node};
9 use rustc_middle::ty::layout::{IntegerExt, LayoutOf, SizeSkeleton};
10 use rustc_middle::ty::subst::SubstsRef;
11 use rustc_middle::ty::{self, AdtKind, DefIdTree, Ty, TyCtxt, TypeFoldable};
12 use rustc_span::source_map;
13 use rustc_span::symbol::sym;
14 use rustc_span::{Span, Symbol, DUMMY_SP};
15 use rustc_target::abi::Abi;
16 use rustc_target::abi::{Integer, TagEncoding, Variants};
17 use rustc_target::spec::abi::Abi as SpecAbi;
19 use if_chain::if_chain;
22 use std::ops::ControlFlow;
26 /// The `unused_comparisons` lint detects comparisons made useless by
27 /// limits of the types involved.
41 /// A useless comparison may indicate a mistake, and should be fixed or
45 "comparisons made useless by limits of the types involved"
49 /// The `overflowing_literals` lint detects literal out of range for its
54 /// ```rust,compile_fail
62 /// It is usually a mistake to use a literal that overflows the type where
63 /// it is used. Either use a literal that is within range, or change the
64 /// type to be within the range of the literal.
67 "literal out of range for its type"
71 /// The `variant_size_differences` lint detects enums with widely varying
76 /// ```rust,compile_fail
77 /// #![deny(variant_size_differences)]
88 /// It can be a mistake to add a variant to an enum that is much larger
89 /// than the other variants, bloating the overall size required for all
90 /// variants. This can impact performance and memory usage. This is
91 /// triggered if one variant is more than 3 times larger than the
92 /// second-largest variant.
94 /// Consider placing the large variant's contents on the heap (for example
95 /// via [`Box`]) to keep the overall size of the enum itself down.
97 /// This lint is "allow" by default because it can be noisy, and may not be
98 /// an actual problem. Decisions about this should be guided with
99 /// profiling and benchmarking.
101 /// [`Box`]: https://doc.rust-lang.org/std/boxed/index.html
102 VARIANT_SIZE_DIFFERENCES,
104 "detects enums with widely varying variant sizes"
107 #[derive(Copy, Clone)]
108 pub struct TypeLimits {
109 /// Id of the last visited negated expression
110 negated_expr_id: Option<hir::HirId>,
113 impl_lint_pass!(TypeLimits => [UNUSED_COMPARISONS, OVERFLOWING_LITERALS]);
116 pub fn new() -> TypeLimits {
117 TypeLimits { negated_expr_id: None }
121 /// Attempts to special-case the overflowing literal lint when it occurs as a range endpoint.
122 /// Returns `true` iff the lint was overridden.
123 fn lint_overflowing_range_endpoint<'tcx>(
124 cx: &LateContext<'tcx>,
128 expr: &'tcx hir::Expr<'tcx>,
129 parent_expr: &'tcx hir::Expr<'tcx>,
132 // We only want to handle exclusive (`..`) ranges,
133 // which are represented as `ExprKind::Struct`.
134 let mut overwritten = false;
135 if let ExprKind::Struct(_, eps, _) = &parent_expr.kind {
139 // We can suggest using an inclusive range
140 // (`..=`) instead only if it is the `end` that is
141 // overflowing and only by 1.
142 if eps[1].expr.hir_id == expr.hir_id && lit_val - 1 == max {
143 cx.struct_span_lint(OVERFLOWING_LITERALS, parent_expr.span, |lint| {
144 let mut err = lint.build(&format!("range endpoint is out of range for `{}`", ty));
145 if let Ok(start) = cx.sess().source_map().span_to_snippet(eps[0].span) {
146 use ast::{LitIntType, LitKind};
147 // We need to preserve the literal's suffix,
148 // as it may determine typing information.
149 let suffix = match lit.node {
150 LitKind::Int(_, LitIntType::Signed(s)) => s.name_str(),
151 LitKind::Int(_, LitIntType::Unsigned(s)) => s.name_str(),
152 LitKind::Int(_, LitIntType::Unsuffixed) => "",
155 let suggestion = format!("{}..={}{}", start, lit_val - 1, suffix);
158 &"use an inclusive range instead",
160 Applicability::MachineApplicable,
171 // For `isize` & `usize`, be conservative with the warnings, so that the
172 // warnings are consistent between 32- and 64-bit platforms.
173 fn int_ty_range(int_ty: ty::IntTy) -> (i128, i128) {
175 ty::IntTy::Isize => (i64::MIN.into(), i64::MAX.into()),
176 ty::IntTy::I8 => (i8::MIN.into(), i8::MAX.into()),
177 ty::IntTy::I16 => (i16::MIN.into(), i16::MAX.into()),
178 ty::IntTy::I32 => (i32::MIN.into(), i32::MAX.into()),
179 ty::IntTy::I64 => (i64::MIN.into(), i64::MAX.into()),
180 ty::IntTy::I128 => (i128::MIN, i128::MAX),
184 fn uint_ty_range(uint_ty: ty::UintTy) -> (u128, u128) {
185 let max = match uint_ty {
186 ty::UintTy::Usize => u64::MAX.into(),
187 ty::UintTy::U8 => u8::MAX.into(),
188 ty::UintTy::U16 => u16::MAX.into(),
189 ty::UintTy::U32 => u32::MAX.into(),
190 ty::UintTy::U64 => u64::MAX.into(),
191 ty::UintTy::U128 => u128::MAX,
196 fn get_bin_hex_repr(cx: &LateContext<'_>, lit: &hir::Lit) -> Option<String> {
197 let src = cx.sess().source_map().span_to_snippet(lit.span).ok()?;
198 let firstch = src.chars().next()?;
201 match src.chars().nth(1) {
202 Some('x' | 'b') => return Some(src),
210 fn report_bin_hex_error(
211 cx: &LateContext<'_>,
212 expr: &hir::Expr<'_>,
218 let size = Integer::from_attr(&cx.tcx, ty).size();
219 cx.struct_span_lint(OVERFLOWING_LITERALS, expr.span, |lint| {
220 let (t, actually) = match ty {
221 attr::IntType::SignedInt(t) => {
222 let actually = if negative {
223 -(size.sign_extend(val) as i128)
225 size.sign_extend(val) as i128
227 (t.name_str(), actually.to_string())
229 attr::IntType::UnsignedInt(t) => {
230 let actually = size.truncate(val);
231 (t.name_str(), actually.to_string())
234 let mut err = lint.build(&format!("literal out of range for `{}`", t));
236 // If the value is negative,
237 // emits a note about the value itself, apart from the literal.
239 "the literal `{}` (decimal `{}`) does not fit into \
243 err.note(&format!("and the value `-{}` will become `{}{}`", repr_str, actually, t));
246 "the literal `{}` (decimal `{}`) does not fit into \
247 the type `{}` and will become `{}{}`",
248 repr_str, val, t, actually, t
251 if let Some(sugg_ty) =
252 get_type_suggestion(&cx.typeck_results().node_type(expr.hir_id), val, negative)
254 if let Some(pos) = repr_str.chars().position(|c| c == 'i' || c == 'u') {
255 let (sans_suffix, _) = repr_str.split_at(pos);
258 &format!("consider using the type `{}` instead", sugg_ty),
259 format!("{}{}", sans_suffix, sugg_ty),
260 Applicability::MachineApplicable,
263 err.help(&format!("consider using the type `{}` instead", sugg_ty));
270 // This function finds the next fitting type and generates a suggestion string.
271 // It searches for fitting types in the following way (`X < Y`):
272 // - `iX`: if literal fits in `uX` => `uX`, else => `iY`
276 // No suggestion for: `isize`, `usize`.
277 fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static str> {
280 macro_rules! find_fit {
281 ($ty:expr, $val:expr, $negative:expr,
282 $($type:ident => [$($utypes:expr),*] => [$($itypes:expr),*]),+) => {
284 let _neg = if negative { 1 } else { 0 };
287 $(if !negative && val <= uint_ty_range($utypes).1 {
288 return Some($utypes.name_str())
290 $(if val <= int_ty_range($itypes).1 as u128 + _neg {
291 return Some($itypes.name_str())
301 ty::Int(i) => find_fit!(i, val, negative,
302 I8 => [U8] => [I16, I32, I64, I128],
303 I16 => [U16] => [I32, I64, I128],
304 I32 => [U32] => [I64, I128],
305 I64 => [U64] => [I128],
306 I128 => [U128] => []),
307 ty::Uint(u) => find_fit!(u, val, negative,
308 U8 => [U8, U16, U32, U64, U128] => [],
309 U16 => [U16, U32, U64, U128] => [],
310 U32 => [U32, U64, U128] => [],
311 U64 => [U64, U128] => [],
312 U128 => [U128] => []),
317 fn lint_int_literal<'tcx>(
318 cx: &LateContext<'tcx>,
319 type_limits: &TypeLimits,
320 e: &'tcx hir::Expr<'tcx>,
325 let int_type = t.normalize(cx.sess().target.pointer_width);
326 let (min, max) = int_ty_range(int_type);
327 let max = max as u128;
328 let negative = type_limits.negated_expr_id == Some(e.hir_id);
330 // Detect literal value out of range [min, max] inclusive
331 // avoiding use of -min to prevent overflow/panic
332 if (negative && v > max + 1) || (!negative && v > max) {
333 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
334 report_bin_hex_error(
337 attr::IntType::SignedInt(ty::ast_int_ty(t)),
345 let par_id = cx.tcx.hir().get_parent_node(e.hir_id);
346 if let Node::Expr(par_e) = cx.tcx.hir().get(par_id) {
347 if let hir::ExprKind::Struct(..) = par_e.kind {
348 if is_range_literal(par_e)
349 && lint_overflowing_range_endpoint(cx, lit, v, max, e, par_e, t.name_str())
351 // The overflowing literal lint was overridden.
357 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
358 let mut err = lint.build(&format!("literal out of range for `{}`", t.name_str()));
360 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
363 .span_to_snippet(lit.span)
364 .expect("must get snippet from literal"),
369 if let Some(sugg_ty) =
370 get_type_suggestion(&cx.typeck_results().node_type(e.hir_id), v, negative)
372 err.help(&format!("consider using the type `{}` instead", sugg_ty));
379 fn lint_uint_literal<'tcx>(
380 cx: &LateContext<'tcx>,
381 e: &'tcx hir::Expr<'tcx>,
385 let uint_type = t.normalize(cx.sess().target.pointer_width);
386 let (min, max) = uint_ty_range(uint_type);
387 let lit_val: u128 = match lit.node {
388 // _v is u8, within range by definition
389 ast::LitKind::Byte(_v) => return,
390 ast::LitKind::Int(v, _) => v,
393 if lit_val < min || lit_val > max {
394 let parent_id = cx.tcx.hir().get_parent_node(e.hir_id);
395 if let Node::Expr(par_e) = cx.tcx.hir().get(parent_id) {
397 hir::ExprKind::Cast(..) => {
398 if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
399 cx.struct_span_lint(OVERFLOWING_LITERALS, par_e.span, |lint| {
400 lint.build("only `u8` can be cast into `char`")
403 &"use a `char` literal instead",
404 format!("'\\u{{{:X}}}'", lit_val),
405 Applicability::MachineApplicable,
412 hir::ExprKind::Struct(..) if is_range_literal(par_e) => {
413 let t = t.name_str();
414 if lint_overflowing_range_endpoint(cx, lit, lit_val, max, e, par_e, t) {
415 // The overflowing literal lint was overridden.
422 if let Some(repr_str) = get_bin_hex_repr(cx, lit) {
423 report_bin_hex_error(
426 attr::IntType::UnsignedInt(ty::ast_uint_ty(t)),
433 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
434 lint.build(&format!("literal out of range for `{}`", t.name_str()))
436 "the literal `{}` does not fit into the type `{}` whose range is `{}..={}`",
439 .span_to_snippet(lit.span)
440 .expect("must get snippet from literal"),
450 fn lint_literal<'tcx>(
451 cx: &LateContext<'tcx>,
452 type_limits: &TypeLimits,
453 e: &'tcx hir::Expr<'tcx>,
456 match *cx.typeck_results().node_type(e.hir_id).kind() {
459 ast::LitKind::Int(v, ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed) => {
460 lint_int_literal(cx, type_limits, e, lit, t, v)
465 ty::Uint(t) => lint_uint_literal(cx, e, lit, t),
467 let is_infinite = match lit.node {
468 ast::LitKind::Float(v, _) => match t {
469 ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
470 ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
474 if is_infinite == Ok(true) {
475 cx.struct_span_lint(OVERFLOWING_LITERALS, e.span, |lint| {
476 lint.build(&format!("literal out of range for `{}`", t.name_str()))
478 "the literal `{}` does not fit into the type `{}` and will be converted to `{}::INFINITY`",
481 .span_to_snippet(lit.span)
482 .expect("must get snippet from literal"),
494 impl<'tcx> LateLintPass<'tcx> for TypeLimits {
495 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
497 hir::ExprKind::Unary(hir::UnOp::Neg, ref expr) => {
498 // propagate negation, if the negation itself isn't negated
499 if self.negated_expr_id != Some(e.hir_id) {
500 self.negated_expr_id = Some(expr.hir_id);
503 hir::ExprKind::Binary(binop, ref l, ref r) => {
504 if is_comparison(binop) && !check_limits(cx, binop, &l, &r) {
505 cx.struct_span_lint(UNUSED_COMPARISONS, e.span, |lint| {
506 lint.build("comparison is useless due to type limits").emit()
510 hir::ExprKind::Lit(ref lit) => lint_literal(cx, self, e, lit),
514 fn is_valid<T: cmp::PartialOrd>(binop: hir::BinOp, v: T, min: T, max: T) -> bool {
516 hir::BinOpKind::Lt => v > min && v <= max,
517 hir::BinOpKind::Le => v >= min && v < max,
518 hir::BinOpKind::Gt => v >= min && v < max,
519 hir::BinOpKind::Ge => v > min && v <= max,
520 hir::BinOpKind::Eq | hir::BinOpKind::Ne => v >= min && v <= max,
525 fn rev_binop(binop: hir::BinOp) -> hir::BinOp {
529 hir::BinOpKind::Lt => hir::BinOpKind::Gt,
530 hir::BinOpKind::Le => hir::BinOpKind::Ge,
531 hir::BinOpKind::Gt => hir::BinOpKind::Lt,
532 hir::BinOpKind::Ge => hir::BinOpKind::Le,
539 cx: &LateContext<'_>,
544 let (lit, expr, swap) = match (&l.kind, &r.kind) {
545 (&hir::ExprKind::Lit(_), _) => (l, r, true),
546 (_, &hir::ExprKind::Lit(_)) => (r, l, false),
549 // Normalize the binop so that the literal is always on the RHS in
551 let norm_binop = if swap { rev_binop(binop) } else { binop };
552 match *cx.typeck_results().node_type(expr.hir_id).kind() {
554 let (min, max) = int_ty_range(int_ty);
555 let lit_val: i128 = match lit.kind {
556 hir::ExprKind::Lit(ref li) => match li.node {
559 ast::LitIntType::Signed(_) | ast::LitIntType::Unsuffixed,
565 is_valid(norm_binop, lit_val, min, max)
567 ty::Uint(uint_ty) => {
568 let (min, max): (u128, u128) = uint_ty_range(uint_ty);
569 let lit_val: u128 = match lit.kind {
570 hir::ExprKind::Lit(ref li) => match li.node {
571 ast::LitKind::Int(v, _) => v,
576 is_valid(norm_binop, lit_val, min, max)
582 fn is_comparison(binop: hir::BinOp) -> bool {
597 /// The `improper_ctypes` lint detects incorrect use of types in foreign
604 /// static STATIC: String;
612 /// The compiler has several checks to verify that types used in `extern`
613 /// blocks are safe and follow certain rules to ensure proper
614 /// compatibility with the foreign interfaces. This lint is issued when it
615 /// detects a probable mistake in a definition. The lint usually should
616 /// provide a description of the issue, along with possibly a hint on how
620 "proper use of libc types in foreign modules"
623 declare_lint_pass!(ImproperCTypesDeclarations => [IMPROPER_CTYPES]);
626 /// The `improper_ctypes_definitions` lint detects incorrect use of
627 /// [`extern` function] definitions.
629 /// [`extern` function]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
634 /// # #![allow(unused)]
635 /// pub extern "C" fn str_type(p: &str) { }
642 /// There are many parameter and return types that may be specified in an
643 /// `extern` function that are not compatible with the given ABI. This
644 /// lint is an alert that these types should not be used. The lint usually
645 /// should provide a description of the issue, along with possibly a hint
646 /// on how to resolve it.
647 IMPROPER_CTYPES_DEFINITIONS,
649 "proper use of libc types in foreign item definitions"
652 declare_lint_pass!(ImproperCTypesDefinitions => [IMPROPER_CTYPES_DEFINITIONS]);
654 #[derive(Clone, Copy)]
655 crate enum CItemKind {
660 struct ImproperCTypesVisitor<'a, 'tcx> {
661 cx: &'a LateContext<'tcx>,
665 enum FfiResult<'tcx> {
667 FfiPhantom(Ty<'tcx>),
668 FfiUnsafe { ty: Ty<'tcx>, reason: String, help: Option<String> },
671 crate fn nonnull_optimization_guaranteed<'tcx>(tcx: TyCtxt<'tcx>, def: &ty::AdtDef) -> bool {
672 tcx.get_attrs(def.did).iter().any(|a| a.has_name(sym::rustc_nonnull_optimization_guaranteed))
675 /// `repr(transparent)` structs can have a single non-ZST field, this function returns that
677 pub fn transparent_newtype_field<'a, 'tcx>(
679 variant: &'a ty::VariantDef,
680 ) -> Option<&'a ty::FieldDef> {
681 let param_env = tcx.param_env(variant.def_id);
682 variant.fields.iter().find(|field| {
683 let field_ty = tcx.type_of(field.did);
684 let is_zst = tcx.layout_of(param_env.and(field_ty)).map_or(false, |layout| layout.is_zst());
689 /// Is type known to be non-null?
690 fn ty_is_known_nonnull<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, mode: CItemKind) -> bool {
693 ty::FnPtr(_) => true,
695 ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
696 ty::Adt(def, substs) if def.repr.transparent() && !def.is_union() => {
697 let marked_non_null = nonnull_optimization_guaranteed(tcx, &def);
703 // Types with a `#[repr(no_niche)]` attribute have their niche hidden.
704 // The attribute is used by the UnsafeCell for example (the only use so far).
705 if def.repr.hide_niche() {
711 .filter_map(|variant| transparent_newtype_field(cx.tcx, variant))
712 .any(|field| ty_is_known_nonnull(cx, field.ty(tcx, substs), mode))
718 /// Given a non-null scalar (or transparent) type `ty`, return the nullable version of that type.
719 /// If the type passed in was not scalar, returns None.
720 fn get_nullable_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
722 Some(match *ty.kind() {
723 ty::Adt(field_def, field_substs) => {
724 let inner_field_ty = {
725 let first_non_zst_ty =
726 field_def.variants.iter().filter_map(|v| transparent_newtype_field(cx.tcx, v));
728 first_non_zst_ty.clone().count(),
730 "Wrong number of fields for transparent type"
734 .expect("No non-zst fields in transparent type.")
735 .ty(tcx, field_substs)
737 return get_nullable_type(cx, inner_field_ty);
739 ty::Int(ty) => tcx.mk_mach_int(ty),
740 ty::Uint(ty) => tcx.mk_mach_uint(ty),
741 ty::RawPtr(ty_mut) => tcx.mk_ptr(ty_mut),
742 // As these types are always non-null, the nullable equivalent of
743 // Option<T> of these types are their raw pointer counterparts.
744 ty::Ref(_region, ty, mutbl) => tcx.mk_ptr(ty::TypeAndMut { ty, mutbl }),
746 // There is no nullable equivalent for Rust's function pointers -- you
747 // must use an Option<fn(..) -> _> to represent it.
751 // We should only ever reach this case if ty_is_known_nonnull is extended
755 "get_nullable_type: Unhandled scalar kind: {:?} while checking {:?}",
763 /// Check if this enum can be safely exported based on the "nullable pointer optimization". If it
764 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
765 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero*`,
766 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
767 /// FIXME: This duplicates code in codegen.
768 crate fn repr_nullable_ptr<'tcx>(
769 cx: &LateContext<'tcx>,
772 ) -> Option<Ty<'tcx>> {
773 debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
774 if let ty::Adt(ty_def, substs) = ty.kind() {
775 let field_ty = match &ty_def.variants.raw[..] {
776 [var_one, var_two] => match (&var_one.fields[..], &var_two.fields[..]) {
777 ([], [field]) | ([field], []) => field.ty(cx.tcx, substs),
783 if !ty_is_known_nonnull(cx, field_ty, ckind) {
787 // At this point, the field's type is known to be nonnull and the parent enum is Option-like.
788 // If the computed size for the field and the enum are different, the nonnull optimization isn't
789 // being applied (and we've got a problem somewhere).
790 let compute_size_skeleton = |t| SizeSkeleton::compute(t, cx.tcx, cx.param_env).unwrap();
791 if !compute_size_skeleton(ty).same_size(compute_size_skeleton(field_ty)) {
792 bug!("improper_ctypes: Option nonnull optimization not applied?");
795 // Return the nullable type this Option-like enum can be safely represented with.
796 let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi;
797 if let Abi::Scalar(field_ty_scalar) = field_ty_abi {
798 match (field_ty_scalar.valid_range.start, field_ty_scalar.valid_range.end) {
799 (0, _) => unreachable!("Non-null optimisation extended to a non-zero value."),
801 return Some(get_nullable_type(cx, field_ty).unwrap());
803 (start, end) => unreachable!("Unhandled start and end range: ({}, {})", start, end),
810 impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
811 /// Check if the type is array and emit an unsafe type lint.
812 fn check_for_array_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
813 if let ty::Array(..) = ty.kind() {
814 self.emit_ffi_unsafe_type_lint(
817 "passing raw arrays by value is not FFI-safe",
818 Some("consider passing a pointer to the array"),
826 /// Checks if the given field's type is "ffi-safe".
827 fn check_field_type_for_ffi(
829 cache: &mut FxHashSet<Ty<'tcx>>,
830 field: &ty::FieldDef,
831 substs: SubstsRef<'tcx>,
832 ) -> FfiResult<'tcx> {
833 let field_ty = field.ty(self.cx.tcx, substs);
834 if field_ty.has_opaque_types() {
835 self.check_type_for_ffi(cache, field_ty)
837 let field_ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, field_ty);
838 self.check_type_for_ffi(cache, field_ty)
842 /// Checks if the given `VariantDef`'s field types are "ffi-safe".
843 fn check_variant_for_ffi(
845 cache: &mut FxHashSet<Ty<'tcx>>,
848 variant: &ty::VariantDef,
849 substs: SubstsRef<'tcx>,
850 ) -> FfiResult<'tcx> {
853 if def.repr.transparent() {
854 // Can assume that at most one field is not a ZST, so only check
855 // that field's type for FFI-safety.
856 if let Some(field) = transparent_newtype_field(self.cx.tcx, variant) {
857 self.check_field_type_for_ffi(cache, field, substs)
859 // All fields are ZSTs; this means that the type should behave
860 // like (), which is FFI-unsafe
863 reason: "this struct contains only zero-sized fields".into(),
868 // We can't completely trust repr(C) markings; make sure the fields are
870 let mut all_phantom = !variant.fields.is_empty();
871 for field in &variant.fields {
872 match self.check_field_type_for_ffi(cache, &field, substs) {
876 FfiPhantom(..) if def.is_enum() => {
879 reason: "this enum contains a PhantomData field".into(),
888 if all_phantom { FfiPhantom(ty) } else { FfiSafe }
892 /// Checks if the given type is "ffi-safe" (has a stable, well-defined
893 /// representation which can be exported to C code).
894 fn check_type_for_ffi(&self, cache: &mut FxHashSet<Ty<'tcx>>, ty: Ty<'tcx>) -> FfiResult<'tcx> {
897 let tcx = self.cx.tcx;
899 // Protect against infinite recursion, for example
900 // `struct S(*mut S);`.
901 // FIXME: A recursion limit is necessary as well, for irregular
903 if !cache.insert(ty) {
908 ty::Adt(def, substs) => {
909 if def.is_box() && matches!(self.mode, CItemKind::Definition) {
910 if ty.boxed_ty().is_sized(tcx.at(DUMMY_SP), self.cx.param_env) {
915 reason: "box cannot be represented as a single pointer".to_string(),
920 if def.is_phantom_data() {
921 return FfiPhantom(ty);
923 match def.adt_kind() {
924 AdtKind::Struct | AdtKind::Union => {
925 let kind = if def.is_struct() { "struct" } else { "union" };
927 if !def.repr.c() && !def.repr.transparent() {
930 reason: format!("this {} has unspecified layout", kind),
932 "consider adding a `#[repr(C)]` or \
933 `#[repr(transparent)]` attribute to this {}",
939 let is_non_exhaustive =
940 def.non_enum_variant().is_field_list_non_exhaustive();
941 if is_non_exhaustive && !def.did.is_local() {
944 reason: format!("this {} is non-exhaustive", kind),
949 if def.non_enum_variant().fields.is_empty() {
952 reason: format!("this {} has no fields", kind),
953 help: Some(format!("consider adding a member to this {}", kind)),
957 self.check_variant_for_ffi(cache, ty, def, def.non_enum_variant(), substs)
960 if def.variants.is_empty() {
961 // Empty enums are okay... although sort of useless.
965 // Check for a repr() attribute to specify the size of the
967 if !def.repr.c() && !def.repr.transparent() && def.repr.int.is_none() {
968 // Special-case types like `Option<extern fn()>`.
969 if repr_nullable_ptr(self.cx, ty, self.mode).is_none() {
972 reason: "enum has no representation hint".into(),
974 "consider adding a `#[repr(C)]`, \
975 `#[repr(transparent)]`, or integer `#[repr(...)]` \
976 attribute to this enum"
983 if def.is_variant_list_non_exhaustive() && !def.did.is_local() {
986 reason: "this enum is non-exhaustive".into(),
991 // Check the contained variants.
992 for variant in &def.variants {
993 let is_non_exhaustive = variant.is_field_list_non_exhaustive();
994 if is_non_exhaustive && !variant.def_id.is_local() {
997 reason: "this enum has non-exhaustive variants".into(),
1002 match self.check_variant_for_ffi(cache, ty, def, variant, substs) {
1013 ty::Char => FfiUnsafe {
1015 reason: "the `char` type has no C equivalent".into(),
1016 help: Some("consider using `u32` or `libc::wchar_t` instead".into()),
1019 ty::Int(ty::IntTy::I128) | ty::Uint(ty::UintTy::U128) => FfiUnsafe {
1021 reason: "128-bit integers don't currently have a known stable ABI".into(),
1025 // Primitive types with a stable representation.
1026 ty::Bool | ty::Int(..) | ty::Uint(..) | ty::Float(..) | ty::Never => FfiSafe,
1028 ty::Slice(_) => FfiUnsafe {
1030 reason: "slices have no C equivalent".into(),
1031 help: Some("consider using a raw pointer instead".into()),
1034 ty::Dynamic(..) => {
1035 FfiUnsafe { ty, reason: "trait objects have no C equivalent".into(), help: None }
1038 ty::Str => FfiUnsafe {
1040 reason: "string slices have no C equivalent".into(),
1041 help: Some("consider using `*const u8` and a length instead".into()),
1044 ty::Tuple(..) => FfiUnsafe {
1046 reason: "tuples have unspecified layout".into(),
1047 help: Some("consider using a struct instead".into()),
1050 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _)
1052 matches!(self.mode, CItemKind::Definition)
1053 && ty.is_sized(self.cx.tcx.at(DUMMY_SP), self.cx.param_env)
1059 ty::RawPtr(ty::TypeAndMut { ty, .. })
1060 if match ty.kind() {
1061 ty::Tuple(tuple) => tuple.is_empty(),
1068 ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
1069 self.check_type_for_ffi(cache, ty)
1072 ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
1075 if self.is_internal_abi(sig.abi()) {
1078 reason: "this function pointer has Rust-specific calling convention".into(),
1080 "consider using an `extern fn(...) -> ...` \
1081 function pointer instead"
1087 let sig = tcx.erase_late_bound_regions(sig);
1088 if !sig.output().is_unit() {
1089 let r = self.check_type_for_ffi(cache, sig.output());
1097 for arg in sig.inputs() {
1098 let r = self.check_type_for_ffi(cache, arg);
1109 ty::Foreign(..) => FfiSafe,
1111 // While opaque types are checked for earlier, if a projection in a struct field
1112 // normalizes to an opaque type, then it will reach this branch.
1114 FfiUnsafe { ty, reason: "opaque types have no C equivalent".into(), help: None }
1117 // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
1118 // so they are currently ignored for the purposes of this lint.
1119 ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
1124 | ty::Projection(..)
1130 | ty::GeneratorWitness(..)
1131 | ty::Placeholder(..)
1132 | ty::FnDef(..) => bug!("unexpected type in foreign function: {:?}", ty),
1136 fn emit_ffi_unsafe_type_lint(
1143 let lint = match self.mode {
1144 CItemKind::Declaration => IMPROPER_CTYPES,
1145 CItemKind::Definition => IMPROPER_CTYPES_DEFINITIONS,
1148 self.cx.struct_span_lint(lint, sp, |lint| {
1149 let item_description = match self.mode {
1150 CItemKind::Declaration => "block",
1151 CItemKind::Definition => "fn",
1153 let mut diag = lint.build(&format!(
1154 "`extern` {} uses type `{}`, which is not FFI-safe",
1155 item_description, ty
1157 diag.span_label(sp, "not FFI-safe");
1158 if let Some(help) = help {
1162 if let ty::Adt(def, _) = ty.kind() {
1163 if let Some(sp) = self.cx.tcx.hir().span_if_local(def.did) {
1164 diag.span_note(sp, "the type is defined here");
1171 fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
1172 struct ProhibitOpaqueTypes<'a, 'tcx> {
1173 cx: &'a LateContext<'tcx>,
1176 impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
1177 type BreakTy = Ty<'tcx>;
1178 fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
1182 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1184 ty::Opaque(..) => ControlFlow::Break(ty),
1185 // Consider opaque types within projections FFI-safe if they do not normalize
1186 // to more opaque types.
1187 ty::Projection(..) => {
1188 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1190 // If `ty` is an opaque type directly then `super_visit_with` won't invoke
1191 // this function again.
1192 if ty.has_opaque_types() {
1195 ControlFlow::CONTINUE
1198 _ => ty.super_visit_with(self),
1203 if let Some(ty) = ty.visit_with(&mut ProhibitOpaqueTypes { cx: self.cx }).break_value() {
1204 self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);
1211 fn check_type_for_ffi_and_report_errors(
1216 is_return_type: bool,
1218 // We have to check for opaque types before `normalize_erasing_regions`,
1219 // which will replace opaque types with their underlying concrete type.
1220 if self.check_for_opaque_ty(sp, ty) {
1221 // We've already emitted an error due to an opaque type.
1225 // it is only OK to use this function because extern fns cannot have
1226 // any generic types right now:
1227 let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
1229 // C doesn't really support passing arrays by value - the only way to pass an array by value
1230 // is through a struct. So, first test that the top level isn't an array, and then
1231 // recursively check the types inside.
1232 if !is_static && self.check_for_array_ty(sp, ty) {
1236 // Don't report FFI errors for unit return types. This check exists here, and not in
1237 // `check_foreign_fn` (where it would make more sense) so that normalization has definitely
1239 if is_return_type && ty.is_unit() {
1243 match self.check_type_for_ffi(&mut FxHashSet::default(), ty) {
1244 FfiResult::FfiSafe => {}
1245 FfiResult::FfiPhantom(ty) => {
1246 self.emit_ffi_unsafe_type_lint(ty, sp, "composed only of `PhantomData`", None);
1248 // If `ty` is a `repr(transparent)` newtype, and the non-zero-sized type is a generic
1249 // argument, which after substitution, is `()`, then this branch can be hit.
1250 FfiResult::FfiUnsafe { ty, .. } if is_return_type && ty.is_unit() => {}
1251 FfiResult::FfiUnsafe { ty, reason, help } => {
1252 self.emit_ffi_unsafe_type_lint(ty, sp, &reason, help.as_deref());
1257 fn check_foreign_fn(&mut self, id: hir::HirId, decl: &hir::FnDecl<'_>) {
1258 let def_id = self.cx.tcx.hir().local_def_id(id);
1259 let sig = self.cx.tcx.fn_sig(def_id);
1260 let sig = self.cx.tcx.erase_late_bound_regions(sig);
1262 for (input_ty, input_hir) in iter::zip(sig.inputs(), decl.inputs) {
1263 self.check_type_for_ffi_and_report_errors(input_hir.span, input_ty, false, false);
1266 if let hir::FnRetTy::Return(ref ret_hir) = decl.output {
1267 let ret_ty = sig.output();
1268 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty, false, true);
1272 fn check_foreign_static(&mut self, id: hir::HirId, span: Span) {
1273 let def_id = self.cx.tcx.hir().local_def_id(id);
1274 let ty = self.cx.tcx.type_of(def_id);
1275 self.check_type_for_ffi_and_report_errors(span, ty, true, false);
1278 fn is_internal_abi(&self, abi: SpecAbi) -> bool {
1281 SpecAbi::Rust | SpecAbi::RustCall | SpecAbi::RustIntrinsic | SpecAbi::PlatformIntrinsic
1286 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDeclarations {
1287 fn check_foreign_item(&mut self, cx: &LateContext<'_>, it: &hir::ForeignItem<'_>) {
1288 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Declaration };
1289 let abi = cx.tcx.hir().get_foreign_abi(it.hir_id());
1291 if !vis.is_internal_abi(abi) {
1293 hir::ForeignItemKind::Fn(ref decl, _, _) => {
1294 vis.check_foreign_fn(it.hir_id(), decl);
1296 hir::ForeignItemKind::Static(ref ty, _) => {
1297 vis.check_foreign_static(it.hir_id(), ty.span);
1299 hir::ForeignItemKind::Type => (),
1305 impl<'tcx> LateLintPass<'tcx> for ImproperCTypesDefinitions {
1308 cx: &LateContext<'tcx>,
1309 kind: hir::intravisit::FnKind<'tcx>,
1310 decl: &'tcx hir::FnDecl<'_>,
1311 _: &'tcx hir::Body<'_>,
1315 use hir::intravisit::FnKind;
1317 let abi = match kind {
1318 FnKind::ItemFn(_, _, header, ..) => header.abi,
1319 FnKind::Method(_, sig, ..) => sig.header.abi,
1323 let mut vis = ImproperCTypesVisitor { cx, mode: CItemKind::Definition };
1324 if !vis.is_internal_abi(abi) {
1325 vis.check_foreign_fn(hir_id, decl);
1330 declare_lint_pass!(VariantSizeDifferences => [VARIANT_SIZE_DIFFERENCES]);
1332 impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
1333 fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
1334 if let hir::ItemKind::Enum(ref enum_definition, _) = it.kind {
1335 let t = cx.tcx.type_of(it.def_id);
1336 let ty = cx.tcx.erase_regions(t);
1337 let layout = match cx.layout_of(ty) {
1338 Ok(layout) => layout,
1340 ty::layout::LayoutError::Unknown(_)
1341 | ty::layout::LayoutError::SizeOverflow(_)
1342 | ty::layout::LayoutError::NormalizationFailure(_, _),
1345 let Variants::Multiple {
1346 tag_encoding: TagEncoding::Direct, tag, ref variants, ..
1347 } = &layout.variants else {
1351 let tag_size = tag.value.size(&cx.tcx).bytes();
1354 "enum `{}` is {} bytes large with layout:\n{:#?}",
1356 layout.size.bytes(),
1360 let (largest, slargest, largest_index) = iter::zip(enum_definition.variants, variants)
1361 .map(|(variant, variant_layout)| {
1362 // Subtract the size of the enum tag.
1363 let bytes = variant_layout.size.bytes().saturating_sub(tag_size);
1365 debug!("- variant `{}` is {} bytes large", variant.ident, bytes);
1369 .fold((0, 0, 0), |(l, s, li), (idx, size)| {
1372 } else if size > s {
1379 // We only warn if the largest variant is at least thrice as large as
1380 // the second-largest.
1381 if largest > slargest * 3 && slargest > 0 {
1382 cx.struct_span_lint(
1383 VARIANT_SIZE_DIFFERENCES,
1384 enum_definition.variants[largest_index].span,
1386 lint.build(&format!(
1387 "enum variant is more than three times \
1388 larger ({} bytes) than the next largest",
1400 /// The `invalid_atomic_ordering` lint detects passing an `Ordering`
1401 /// to an atomic operation that does not support that ordering.
1405 /// ```rust,compile_fail
1406 /// # use core::sync::atomic::{AtomicU8, Ordering};
1407 /// let atom = AtomicU8::new(0);
1408 /// let value = atom.load(Ordering::Release);
1409 /// # let _ = value;
1416 /// Some atomic operations are only supported for a subset of the
1417 /// `atomic::Ordering` variants. Passing an unsupported variant will cause
1418 /// an unconditional panic at runtime, which is detected by this lint.
1420 /// This lint will trigger in the following cases: (where `AtomicType` is an
1421 /// atomic type from `core::sync::atomic`, such as `AtomicBool`,
1422 /// `AtomicPtr`, `AtomicUsize`, or any of the other integer atomics).
1424 /// - Passing `Ordering::Acquire` or `Ordering::AcqRel` to
1425 /// `AtomicType::store`.
1427 /// - Passing `Ordering::Release` or `Ordering::AcqRel` to
1428 /// `AtomicType::load`.
1430 /// - Passing `Ordering::Relaxed` to `core::sync::atomic::fence` or
1431 /// `core::sync::atomic::compiler_fence`.
1433 /// - Passing `Ordering::Release` or `Ordering::AcqRel` as the failure
1434 /// ordering for any of `AtomicType::compare_exchange`,
1435 /// `AtomicType::compare_exchange_weak`, or `AtomicType::fetch_update`.
1437 /// - Passing in a pair of orderings to `AtomicType::compare_exchange`,
1438 /// `AtomicType::compare_exchange_weak`, or `AtomicType::fetch_update`
1439 /// where the failure ordering is stronger than the success ordering.
1440 INVALID_ATOMIC_ORDERING,
1442 "usage of invalid atomic ordering in atomic operations and memory fences"
1445 declare_lint_pass!(InvalidAtomicOrdering => [INVALID_ATOMIC_ORDERING]);
1447 impl InvalidAtomicOrdering {
1448 fn inherent_atomic_method_call<'hir>(
1449 cx: &LateContext<'_>,
1451 recognized_names: &[Symbol], // used for fast path calculation
1452 ) -> Option<(Symbol, &'hir [Expr<'hir>])> {
1453 const ATOMIC_TYPES: &[Symbol] = &[
1470 if let ExprKind::MethodCall(ref method_path, _, args, _) = &expr.kind;
1471 if recognized_names.contains(&method_path.ident.name);
1472 if let Some(m_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
1473 if let Some(impl_did) = cx.tcx.impl_of_method(m_def_id);
1474 if let Some(adt) = cx.tcx.type_of(impl_did).ty_adt_def();
1475 // skip extension traits, only lint functions from the standard library
1476 if cx.tcx.trait_id_of_impl(impl_did).is_none();
1478 if let Some(parent) = cx.tcx.parent(adt.did);
1479 if cx.tcx.is_diagnostic_item(sym::atomic_mod, parent);
1480 if ATOMIC_TYPES.contains(&cx.tcx.item_name(adt.did));
1482 return Some((method_path.ident.name, args));
1488 fn matches_ordering(cx: &LateContext<'_>, did: DefId, orderings: &[Symbol]) -> bool {
1490 let atomic_ordering = tcx.get_diagnostic_item(sym::Ordering);
1491 orderings.iter().any(|ordering| {
1492 tcx.item_name(did) == *ordering && {
1493 let parent = tcx.parent(did);
1494 parent == atomic_ordering
1495 // needed in case this is a ctor, not a variant
1496 || parent.map_or(false, |parent| tcx.parent(parent) == atomic_ordering)
1501 fn opt_ordering_defid(cx: &LateContext<'_>, ord_arg: &Expr<'_>) -> Option<DefId> {
1502 if let ExprKind::Path(ref ord_qpath) = ord_arg.kind {
1503 cx.qpath_res(ord_qpath, ord_arg.hir_id).opt_def_id()
1509 fn check_atomic_load_store(cx: &LateContext<'_>, expr: &Expr<'_>) {
1510 use rustc_hir::def::{DefKind, Res};
1511 use rustc_hir::QPath;
1513 if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::load, sym::store]);
1514 if let Some((ordering_arg, invalid_ordering)) = match method {
1515 sym::load => Some((&args[1], sym::Release)),
1516 sym::store => Some((&args[2], sym::Acquire)),
1520 if let ExprKind::Path(QPath::Resolved(_, path)) = ordering_arg.kind;
1521 if let Res::Def(DefKind::Ctor(..), ctor_id) = path.res;
1522 if Self::matches_ordering(cx, ctor_id, &[invalid_ordering, sym::AcqRel]);
1524 cx.struct_span_lint(INVALID_ATOMIC_ORDERING, ordering_arg.span, |diag| {
1525 if method == sym::load {
1526 diag.build("atomic loads cannot have `Release` or `AcqRel` ordering")
1527 .help("consider using ordering modes `Acquire`, `SeqCst` or `Relaxed`")
1530 debug_assert_eq!(method, sym::store);
1531 diag.build("atomic stores cannot have `Acquire` or `AcqRel` ordering")
1532 .help("consider using ordering modes `Release`, `SeqCst` or `Relaxed`")
1540 fn check_memory_fence(cx: &LateContext<'_>, expr: &Expr<'_>) {
1542 if let ExprKind::Call(ref func, ref args) = expr.kind;
1543 if let ExprKind::Path(ref func_qpath) = func.kind;
1544 if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
1545 if matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::fence | sym::compiler_fence));
1546 if let ExprKind::Path(ref ordering_qpath) = &args[0].kind;
1547 if let Some(ordering_def_id) = cx.qpath_res(ordering_qpath, args[0].hir_id).opt_def_id();
1548 if Self::matches_ordering(cx, ordering_def_id, &[sym::Relaxed]);
1550 cx.struct_span_lint(INVALID_ATOMIC_ORDERING, args[0].span, |diag| {
1551 diag.build("memory fences cannot have `Relaxed` ordering")
1552 .help("consider using ordering modes `Acquire`, `Release`, `AcqRel` or `SeqCst`")
1559 fn check_atomic_compare_exchange(cx: &LateContext<'_>, expr: &Expr<'_>) {
1561 if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::fetch_update, sym::compare_exchange, sym::compare_exchange_weak]);
1562 if let Some((success_order_arg, failure_order_arg)) = match method {
1563 sym::fetch_update => Some((&args[1], &args[2])),
1564 sym::compare_exchange | sym::compare_exchange_weak => Some((&args[3], &args[4])),
1568 if let Some(fail_ordering_def_id) = Self::opt_ordering_defid(cx, failure_order_arg);
1570 // Helper type holding on to some checking and error reporting data. Has
1571 // - (success ordering,
1572 // - list of failure orderings forbidden by the success order,
1573 // - suggestion message)
1574 type OrdLintInfo = (Symbol, &'static [Symbol], &'static str);
1575 const RELAXED: OrdLintInfo = (sym::Relaxed, &[sym::SeqCst, sym::Acquire], "ordering mode `Relaxed`");
1576 const ACQUIRE: OrdLintInfo = (sym::Acquire, &[sym::SeqCst], "ordering modes `Acquire` or `Relaxed`");
1577 const SEQ_CST: OrdLintInfo = (sym::SeqCst, &[], "ordering modes `Acquire`, `SeqCst` or `Relaxed`");
1578 const RELEASE: OrdLintInfo = (sym::Release, RELAXED.1, RELAXED.2);
1579 const ACQREL: OrdLintInfo = (sym::AcqRel, ACQUIRE.1, ACQUIRE.2);
1580 const SEARCH: [OrdLintInfo; 5] = [RELAXED, ACQUIRE, SEQ_CST, RELEASE, ACQREL];
1582 let success_lint_info = Self::opt_ordering_defid(cx, success_order_arg)
1583 .and_then(|success_ord_def_id| -> Option<OrdLintInfo> {
1587 .find(|(ordering, ..)| {
1588 Self::matches_ordering(cx, success_ord_def_id, &[*ordering])
1591 if Self::matches_ordering(cx, fail_ordering_def_id, &[sym::Release, sym::AcqRel]) {
1592 // If we don't know the success order is, use what we'd suggest
1593 // if it were maximally permissive.
1594 let suggested = success_lint_info.unwrap_or(SEQ_CST).2;
1595 cx.struct_span_lint(INVALID_ATOMIC_ORDERING, failure_order_arg.span, |diag| {
1597 "{}'s failure ordering may not be `Release` or `AcqRel`",
1601 .help(&format!("consider using {} instead", suggested))
1604 } else if let Some((success_ord, bad_ords_given_success, suggested)) = success_lint_info {
1605 if Self::matches_ordering(cx, fail_ordering_def_id, bad_ords_given_success) {
1606 cx.struct_span_lint(INVALID_ATOMIC_ORDERING, failure_order_arg.span, |diag| {
1608 "{}'s failure ordering may not be stronger than the success ordering of `{}`",
1613 .help(&format!("consider using {} instead", suggested))
1623 impl<'tcx> LateLintPass<'tcx> for InvalidAtomicOrdering {
1624 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1625 Self::check_atomic_load_store(cx, expr);
1626 Self::check_memory_fence(cx, expr);
1627 Self::check_atomic_compare_exchange(cx, expr);