When encountering &SmallImplCopy < &SmallImplCopy, suggest copying

When encountering a binary operation for two `T: Copy` where `T` is as
small as a 64bit pointer, suggest dereferencing the expressions so the
binary operation is inlined.

Mitigate the effects of rust-lang#105259, particularly when match ergonomics is
involved.

Author: estebank

compiler/rustc_ast/src/token.rs

@@ -894,7 +894,7 @@ impl PartialEq for Nonterminal {
     fn eq(&self, rhs: &Self) -> bool {
         match (self, rhs) {
             (NtIdent(ident_lhs, is_raw_lhs), NtIdent(ident_rhs, is_raw_rhs)) => {
-                ident_lhs == ident_rhs && is_raw_lhs == is_raw_rhs
+                ident_lhs == ident_rhs && *is_raw_lhs == *is_raw_rhs
             }
             (NtLifetime(ident_lhs), NtLifetime(ident_rhs)) => ident_lhs == ident_rhs,
             // FIXME: Assume that all "complex" nonterminal are not equal, we can't compare them

compiler/rustc_ast/src/tokenstream.rs

@@ -65,7 +65,7 @@ impl TokenTree {
         match (self, other) {
             (TokenTree::Token(token, _), TokenTree::Token(token2, _)) => token.kind == token2.kind,
             (TokenTree::Delimited(_, delim, tts), TokenTree::Delimited(_, delim2, tts2)) => {
-                delim == delim2 && tts.eq_unspanned(tts2)
+                *delim == *delim2 && tts.eq_unspanned(tts2)
             }
             _ => false,
         }

compiler/rustc_ast_lowering/src/lib.rs

@@ -617,7 +617,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.impl_trait_defs = current_impl_trait_defs;
         self.impl_trait_bounds = current_impl_trait_bounds;
 
-        debug_assert!(!self.children.iter().any(|(id, _)| id == &def_id));
+        debug_assert!(!self.children.iter().any(|(id, _)| *id == def_id));
         self.children.push((def_id, hir::MaybeOwner::Owner(info)));
     }
 

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -688,8 +688,9 @@ fn check_incompatible_features(sess: &Session) {
         .iter()
         .filter(|&&(f1, f2)| features.enabled(f1) && features.enabled(f2))
     {
-        if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| name == f1) {
-            if let Some((f2_name, f2_span)) = declared_features.clone().find(|(name, _)| name == f2)
+        if let Some((f1_name, f1_span)) = declared_features.clone().find(|(name, _)| *name == *f1) {
+            if let Some((f2_name, f2_span)) =
+                declared_features.clone().find(|(name, _)| *name == *f2)
             {
                 let spans = vec![f1_span, f2_span];
                 sess.struct_span_err(

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2825,7 +2825,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 let mut arguments = Vec::new();
                 for (index, argument) in sig.inputs().skip_binder().iter().enumerate() {
                     if let ty::Ref(argument_region, _, _) = argument.kind() {
-                        if argument_region == return_region {
+                        if *argument_region == *return_region {
                             // Need to use the `rustc_middle::ty` types to compare against the
                             // `return_region`. Then use the `rustc_hir` type to get only
                             // the lifetime span.

compiler/rustc_codegen_ssa/src/base.rs

@@ -694,7 +694,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
             let cgus: Vec<_> = cgu_reuse
                 .iter()
                 .enumerate()
-                .filter(|&(_, reuse)| reuse == &CguReuse::No)
+                .filter(|&(_, reuse)| *reuse == CguReuse::No)
                 .take(tcx.sess.threads())
                 .collect();
 

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -258,15 +258,15 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             (PassMode::Pair(a1, b1), PassMode::Pair(a2, b2)) => {
                 arg_attr_compat(a1, a2) && arg_attr_compat(b1, b2)
             }
-            (PassMode::Cast(c1, pad1), PassMode::Cast(c2, pad2)) => c1 == c2 && pad1 == pad2,
+            (PassMode::Cast(c1, pad1), PassMode::Cast(c2, pad2)) => c1 == c2 && *pad1 == *pad2,
             (
                 PassMode::Indirect { attrs: a1, extra_attrs: None, on_stack: s1 },
                 PassMode::Indirect { attrs: a2, extra_attrs: None, on_stack: s2 },
-            ) => arg_attr_compat(a1, a2) && s1 == s2,
+            ) => arg_attr_compat(a1, a2) && *s1 == *s2,
             (
                 PassMode::Indirect { attrs: a1, extra_attrs: Some(e1), on_stack: s1 },
                 PassMode::Indirect { attrs: a2, extra_attrs: Some(e2), on_stack: s2 },
-            ) => arg_attr_compat(a1, a2) && arg_attr_compat(e1, e2) && s1 == s2,
+            ) => arg_attr_compat(a1, a2) && arg_attr_compat(e1, e2) && *s1 == *s2,
             _ => false,
         };
 

compiler/rustc_errors/src/emitter.rs

@@ -351,7 +351,7 @@ pub trait Emitter: Translate {
             if let Some((macro_kind, name)) = has_macro_spans.first() {
                 // Mark the actual macro this originates from
                 let and_then = if let Some((macro_kind, last_name)) = has_macro_spans.last()
-                    && last_name != name
+                    && *last_name != *name
                 {
                     let descr = macro_kind.descr();
                     format!(
@@ -2753,7 +2753,7 @@ pub fn is_case_difference(sm: &SourceMap, suggested: &str, sp: Span) -> bool {
     let ascii_confusables = &['c', 'f', 'i', 'k', 'o', 's', 'u', 'v', 'w', 'x', 'y', 'z'];
     // All the chars that differ in capitalization are confusable (above):
     let confusable = iter::zip(found.chars(), suggested.chars())
-        .filter(|(f, s)| f != s)
+        .filter(|(f, s)| *f != *s)
         .all(|(f, s)| (ascii_confusables.contains(&f) || ascii_confusables.contains(&s)));
     confusable && found.to_lowercase() == suggested.to_lowercase()
             // FIXME: We sometimes suggest the same thing we already have, which is a

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -123,7 +123,7 @@ pub(super) fn transcribe<'a>(
             if let Frame::Sequence { idx, sep, .. } = stack.last_mut().unwrap() {
                 let (repeat_idx, repeat_len) = repeats.last_mut().unwrap();
                 *repeat_idx += 1;
-                if repeat_idx < repeat_len {
+                if *repeat_idx < *repeat_len {
                     *idx = 0;
                     if let Some(sep) = sep {
                         result.push(TokenTree::Token(sep.clone(), Spacing::Alone));

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -579,7 +579,7 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
         for (region_b, region_b_idx) in &regions {
             // Again, skip `'static` because it outlives everything. Also, we trivially
             // know that a region outlives itself.
-            if ty::ReStatic == **region_b || region_a == region_b {
+            if ty::ReStatic == **region_b || *region_a == *region_b {
                 continue;
             }
             if region_known_to_outlive(

compiler/rustc_hir_pretty/src/lib.rs

@@ -2092,7 +2092,7 @@ impl<'a> State<'a> {
 
             match bound {
                 GenericBound::Trait(tref, modifier) => {
-                    if modifier == &TraitBoundModifier::Maybe {
+                    if *modifier == TraitBoundModifier::Maybe {
                         self.word("?");
                     }
                     self.print_poly_trait_ref(tref);

compiler/rustc_hir_typeck/src/demand.rs

@@ -321,7 +321,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // Remove one layer of references to account for `&mut self` and
                 // `&self`, so that we can compare it against the binding.
                 let (ty, def_self_ty) = match (ty.kind(), def_self_ty.kind()) {
-                    (ty::Ref(_, ty, a), ty::Ref(_, self_ty, b)) if a == b => (*ty, *self_ty),
+                    (ty::Ref(_, ty, a), ty::Ref(_, self_ty, b)) if *a == *b => (*ty, *self_ty),
                     _ => (ty, def_self_ty),
                 };
                 let mut param_args = FxHashMap::default();

compiler/rustc_hir_typeck/src/expr.rs

@@ -1739,7 +1739,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 self.check_expr_has_type_or_error(base_expr, adt_ty, |_| {
                     let base_ty = self.typeck_results.borrow().expr_ty(*base_expr);
                     let same_adt = match (adt_ty.kind(), base_ty.kind()) {
-                        (ty::Adt(adt, _), ty::Adt(base_adt, _)) if adt == base_adt => true,
+                        (ty::Adt(adt, _), ty::Adt(base_adt, _)) if *adt == *base_adt => true,
                         _ => false,
                     };
                     if self.tcx.sess.is_nightly_build() && same_adt {

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -815,7 +815,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 _ => None,
             })
             .map(|(ty, bounds)| match ty.kind() {
-                ty::Param(param_ty) if param_ty == expected_ty_as_param => Ok(Some(bounds)),
+                ty::Param(param_ty) if *param_ty == *expected_ty_as_param => Ok(Some(bounds)),
                 // check whether there is any predicate that contains our `T`, like `Option<T>: Send`
                 _ => match ty.contains(expected) {
                     true => Err(()),
@@ -848,7 +848,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         let ty_param_used_in_fn_params = fn_parameters.iter().any(|param| {
                 let ty = self.astconv().ast_ty_to_ty( param);
-                matches!(ty.kind(), ty::Param(fn_param_ty_param) if expected_ty_as_param == fn_param_ty_param)
+                matches!(ty.kind(), ty::Param(fn_param_ty_param) if *expected_ty_as_param == *fn_param_ty_param)
             });
 
         if ty_param_used_in_fn_params {
@@ -1008,7 +1008,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> bool {
         let ty::Adt(adt_def, substs) = expr_ty.kind() else { return false; };
         let ty::Adt(expected_adt_def, expected_substs) = expected_ty.kind() else { return false; };
-        if adt_def != expected_adt_def {
+        if *adt_def != *expected_adt_def {
             return false;
         }
 

compiler/rustc_index/src/interval.rs

@@ -223,7 +223,7 @@ impl<I: Idx> IntervalSet<I> {
     fn check_invariants(&self) -> bool {
         let mut current: Option<u32> = None;
         for (start, end) in &self.map {
-            if start > end || current.map_or(false, |x| x + 1 >= *start) {
+            if *start > *end || current.map_or(false, |x| x + 1 >= *start) {
                 return false;
             }
             current = Some(*end);

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1144,7 +1144,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     let remainder2: Vec<_> = sub2.types().skip(common_len).collect();
                     let common_default_params =
                         iter::zip(remainder1.iter().rev(), remainder2.iter().rev())
-                            .filter(|(a, b)| a == b)
+                            .filter(|(a, b)| **a == **b)
                             .count();
                     let len = sub1.len() - common_default_params;
                     let consts_offset = len - sub1.consts().count();
@@ -2028,7 +2028,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                                                 }),
                                                 ..
                                             } = s
-                                            && init_span == &self.span {
+                                            && *init_span == self.span {
                                                 self.result = Some(*array_ty);
                                             }
                                         }

compiler/rustc_infer/src/infer/error_reporting/suggest.rs

@@ -449,7 +449,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             (expected.kind(), found.kind())
         {
             if let ty::Adt(found_def, found_substs) = *found_ty.kind() {
-                if exp_def == &found_def {
+                if *exp_def == found_def {
                     let have_as_ref = &[
                         (
                             sym::Option,
@@ -581,7 +581,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             (
                 ty::Alias(ty::Opaque, ty::AliasTy { def_id: last_def_id, .. }),
                 ty::Alias(ty::Opaque, ty::AliasTy { def_id: exp_def_id, .. }),
-            ) if last_def_id == exp_def_id => StatementAsExpression::CorrectType,
+            ) if *last_def_id == *exp_def_id => StatementAsExpression::CorrectType,
             (
                 ty::Alias(ty::Opaque, ty::AliasTy { def_id: last_def_id, substs: last_bounds, .. }),
                 ty::Alias(ty::Opaque, ty::AliasTy { def_id: exp_def_id, substs: exp_bounds, .. }),
@@ -607,14 +607,14 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                                 hir::GenericBound::Trait(tl, ml),
                                 hir::GenericBound::Trait(tr, mr),
                             ) if tl.trait_ref.trait_def_id() == tr.trait_ref.trait_def_id()
-                                && ml == mr =>
+                                && *ml == *mr =>
                             {
                                 true
                             }
                             (
                                 hir::GenericBound::LangItemTrait(langl, _, _, argsl),
                                 hir::GenericBound::LangItemTrait(langr, _, _, argsr),
-                            ) if langl == langr => {
+                            ) if *langl == *langr => {
                                 // FIXME: consider the bounds!
                                 debug!("{:?} {:?}", argsl, argsr);
                                 true

compiler/rustc_lint/locales/en-US.ftl

@@ -5,6 +5,11 @@ lint_array_into_iter =
     .use_explicit_into_iter_suggestion =
         or use `IntoIterator::into_iter(..)` instead of `.into_iter()` to explicitly iterate by value
 
+lint_ref_binop_on_copy_type =
+    binary operation on reference to `Copy` type `{$ty}`
+    .note = `{$ty}` takes `{$bytes}` bytes of memory; copying the value instead of referencing it might avoid unnecessary pointer indirections
+    .suggestion = dereferencing the expressions will allow the compiler to more consistently optimize these binary operations
+
 lint_enum_intrinsics_mem_discriminant =
     the return value of `mem::discriminant` is unspecified when called with a non-enum type
     .note = the argument to `discriminant` should be a reference to an enum, but it was passed a reference to a `{$ty_param}`, which is not an enum.

compiler/rustc_lint/src/builtin.rs

@@ -38,7 +38,8 @@ use crate::{
         BuiltinUngatedAsyncFnTrackCaller, BuiltinUnnameableTestItems, BuiltinUnpermittedTypeInit,
         BuiltinUnpermittedTypeInitSub, BuiltinUnreachablePub, BuiltinUnsafe,
         BuiltinUnstableFeatures, BuiltinUnusedDocComment, BuiltinUnusedDocCommentSub,
-        BuiltinWhileTrue, SuggestChangingAssocTypes,
+        BuiltinWhileTrue, RefBinopOnCopyTypeDiag, RefBinopOnCopyTypeSuggestion,
+        SuggestChangingAssocTypes,
     },
     types::{transparent_newtype_field, CItemKind},
     EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
@@ -2888,7 +2889,7 @@ impl ClashingExternDeclarations {
                         }
                         (Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
                             // For structural sameness, we don't need the region to be same.
-                            a_mut == b_mut
+                            *a_mut == *b_mut
                                 && structurally_same_type_impl(seen_types, cx, *a_ty, *b_ty, ckind)
                         }
                         (FnDef(..), FnDef(..)) => {
@@ -3307,6 +3308,118 @@ impl EarlyLintPass for SpecialModuleName {
     }
 }
 
+declare_lint! {
+    /// The `ref_binop_on_copy_type` lint detects borrowed `Copy` types being passed to binary
+    /// operations that have unnecessary borrows.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// # #![allow(unused)]
+    /// pub fn slice_of_ints(input: &[(usize, usize, usize, usize)]) -> usize {
+    ///     input
+    ///         .iter()
+    ///         .filter(|(a, b, c, d)| a <= c && d <= b || c <= a && b <= d)
+    ///         .count()
+    /// }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// When making comparisons (or other binary operations) between two reference values that can
+    /// be copied instead, the compiler will not always remove the references, making the execution
+    /// of the binary operation slower than it otherwise could be by making the machine code "chase
+    /// pointers" before actually finding the underlying value. If the `Copy` value is as small or
+    /// smaller than a 64 bit pointer, we suggest dereferencing the value so the compiler will have
+    /// a better chance of producing optimal instructions.
+    REF_BINOP_ON_COPY_TYPE,
+    Warn,
+    "detects binary operations on references to `Copy` types like `&42 < &50`",
+}
+
+declare_lint_pass!(RefBinopOnCopyType => [REF_BINOP_ON_COPY_TYPE]);
+
+impl<'tcx> LateLintPass<'tcx> for RefBinopOnCopyType {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
+        let hir::ExprKind::Binary(op, left, right) = expr.kind else { return; };
+        let left_ty = cx.typeck_results().expr_ty_adjusted(left);
+        let right_ty = cx.typeck_results().expr_ty_adjusted(right);
+        if let ty::Ref(_, left_ty, _) = left_ty.kind()
+            && let ty::Ref(_, left_ty, _) = left_ty.kind()
+            && let left_ty = left_ty.peel_refs()
+            && left_ty.is_copy_modulo_regions(cx.tcx, cx.param_env)
+            && let Some(size) = cx.tcx.layout_of(cx.param_env.and(left_ty)).ok().map(|layout| {
+                layout.size.bytes()
+            })
+            && let ty::Ref(_, right_ty, _) = right_ty.kind()
+            && let ty::Ref(_, right_ty, _) = right_ty.kind()
+            && let right_ty = right_ty.peel_refs()
+            && right_ty.is_copy_modulo_regions(cx.tcx, cx.param_env)
+            && let Some(size_r) = cx.tcx.layout_of(cx.param_env.and(right_ty)).ok().map(|layout| {
+                layout.size.bytes()
+            })
+            && size <= 8
+            && size_r <= 8
+        {
+            let left_start_base = left.span.shrink_to_lo();
+            let left_peeled = left.peel_borrows();
+            let left_start = left_start_base.to(left_peeled.span.shrink_to_lo());
+            let left_sugg = if left_start != left_start_base
+                && !matches!(cx.typeck_results().expr_ty_adjusted(left_peeled).kind(), ty::Ref(..))
+            {
+                ""
+            } else {
+                "*"
+            };
+            let (left_brace_start, left_brace_end, left_end) =
+                if left.precedence().order() < ast::ExprPrecedence::Unary.order() {
+                    ("(", ")", Some(left.span.shrink_to_hi()))
+                } else {
+                    ("", "", None)
+                };
+            let right_start_base = right.span.shrink_to_lo();
+            let right_peeled = right.peel_borrows();
+            let right_start = right_start_base.to(right_peeled.span.shrink_to_lo());
+            let right_sugg = if right_start != right_start_base
+                && !matches!(cx.typeck_results().expr_ty_adjusted(right_peeled).kind(), ty::Ref(..))
+            {
+                ""
+            } else {
+                "*"
+            };
+            let (right_brace_start, right_brace_end, right_end) =
+                if right.precedence().order() < ast::ExprPrecedence::Unary.order() {
+                    ("(", ")", Some(right.span.shrink_to_hi()))
+                } else {
+                    ("", "", None)
+                };
+            cx.emit_spanned_lint(
+                REF_BINOP_ON_COPY_TYPE,
+                op.span,
+                RefBinopOnCopyTypeDiag {
+                    ty: with_no_trimmed_paths!(left_ty.to_string()),
+                    bytes: size,
+                    note: Some(()),
+                    suggestion: RefBinopOnCopyTypeSuggestion {
+                        left_brace_start,
+                        left_brace_end,
+                        left_sugg,
+                        left_start,
+                        left_end,
+                        right_brace_start,
+                        right_brace_end,
+                        right_sugg,
+                        right_start,
+                        right_end,
+                    },
+                },
+            );
+        }
+    }
+}
+
 pub use rustc_session::lint::builtin::UNEXPECTED_CFGS;
 
 declare_lint_pass!(UnexpectedCfgs => [UNEXPECTED_CFGS]);

compiler/rustc_lint/src/lib.rs

@@ -204,6 +204,7 @@ late_lint_methods!(
             ImproperCTypesDefinitions: ImproperCTypesDefinitions,
             VariantSizeDifferences: VariantSizeDifferences,
             BoxPointers: BoxPointers,
+            RefBinopOnCopyType: RefBinopOnCopyType,
             PathStatements: PathStatements,
             LetUnderscore: LetUnderscore,
             // Depends on referenced function signatures in expressions