Update Clippy

clippy_lints/src/casts/cast_slice_different_sizes.rs

@@ -54,7 +54,7 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>, msrv: &Msrv
 
                         diag.span_suggestion(
                             expr.span,
-                            &format!("replace with `ptr::slice_from_raw_parts{mutbl_fn_str}`"),
+                            format!("replace with `ptr::slice_from_raw_parts{mutbl_fn_str}`"),
                             sugg,
                             rustc_errors::Applicability::HasPlaceholders,
                         );

clippy_lints/src/dereference.rs

@@ -1282,10 +1282,10 @@ fn referent_used_exactly_once<'tcx>(
             possible_borrowers.push((body_owner_local_def_id, PossibleBorrowerMap::new(cx, mir)));
         }
         let possible_borrower = &mut possible_borrowers.last_mut().unwrap().1;
-        // If `only_borrowers` were used here, the `copyable_iterator::warn` test would fail. The reason is
-        // that `PossibleBorrowerVisitor::visit_terminator` considers `place.local` a possible borrower of
-        // itself. See the comment in that method for an explanation as to why.
-        possible_borrower.bounded_borrowers(&[local], &[local, place.local], place.local, location)
+        // If `place.local` were not included here, the `copyable_iterator::warn` test would fail. The
+        // reason is that `PossibleBorrowerVisitor::visit_terminator` considers `place.local` a possible
+        // borrower of itself. See the comment in that method for an explanation as to why.
+        possible_borrower.at_most_borrowers(cx, &[local, place.local], place.local, location)
             && used_exactly_once(mir, place.local).unwrap_or(false)
     } else {
         false

clippy_lints/src/format_args.rs

@@ -377,7 +377,7 @@ fn check_format_in_format_args(cx: &LateContext<'_>, call_site: Span, name: Symb
         call_site,
         &format!("`format!` in `{name}!` args"),
         |diag| {
-            diag.help(&format!(
+            diag.help(format!(
                 "combine the `format!(..)` arguments with the outer `{name}!(..)` call"
             ));
             diag.help("or consider changing `format!` to `format_args!`");

clippy_lints/src/large_enum_variant.rs

@@ -111,7 +111,7 @@ impl<'tcx> LateLintPass<'tcx> for LargeEnumVariant {
                         );
                         diag.span_label(
                             def.variants[variants_size[1].ind].span,
-                            &if variants_size[1].fields_size.is_empty() {
+                            if variants_size[1].fields_size.is_empty() {
                                 "the second-largest variant carries no data at all".to_owned()
                             } else {
                                 format!(

clippy_lints/src/len_zero.rs

@@ -361,7 +361,7 @@ fn check_for_is_empty<'tcx>(
             db.span_note(span, "`is_empty` defined here");
         }
         if let Some(self_kind) = self_kind {
-            db.note(&output.expected_sig(self_kind));
+            db.note(output.expected_sig(self_kind));
         }
     });
 }

clippy_lints/src/lib.rs

@@ -336,7 +336,7 @@ pub fn read_conf(sess: &Session, path: &io::Result<Option<PathBuf>>) -> Conf {
         Ok(Some(path)) => path,
         Ok(None) => return Conf::default(),
         Err(error) => {
-            sess.struct_err(&format!("error finding Clippy's configuration file: {error}"))
+            sess.struct_err(format!("error finding Clippy's configuration file: {error}"))
                 .emit();
             return Conf::default();
         },

clippy_lints/src/loops/explicit_counter_loop.rs

@@ -77,7 +77,7 @@ pub(super) fn check<'tcx>(
                                 applicability,
                             );
 
-                            diag.note(&format!(
+                            diag.note(format!(
                                 "`{name}` is of type `{int_name}`, making it ineligible for `Iterator::enumerate`"
                             ));
                         },

clippy_lints/src/manual_async_fn.rs

@@ -76,7 +76,7 @@ impl<'tcx> LateLintPass<'tcx> for ManualAsyncFn {
                                 let help = format!("make the function `async` and {ret_sugg}");
                                 diag.span_suggestion(
                                     header_span,
-                                    &help,
+                                    help,
                                     format!("async {}{ret_snip}", &header_snip[..ret_pos]),
                                     Applicability::MachineApplicable
                                 );

clippy_lints/src/manual_strip.rs

@@ -109,7 +109,7 @@ impl<'tcx> LateLintPass<'tcx> for ManualStrip {
 
                     let test_span = expr.span.until(then.span);
                     span_lint_and_then(cx, MANUAL_STRIP, strippings[0], &format!("stripping a {kind_word} manually"), |diag| {
-                        diag.span_note(test_span, &format!("the {kind_word} was tested here"));
+                        diag.span_note(test_span, format!("the {kind_word} was tested here"));
                         multispan_sugg(
                             diag,
                             &format!("try using the `strip_{kind_word}` method"),

clippy_lints/src/methods/inefficient_to_string.rs

@@ -36,7 +36,7 @@ pub fn check(
                 expr.span,
                 &format!("calling `to_string` on `{arg_ty}`"),
                 |diag| {
-                    diag.help(&format!(
+                    diag.help(format!(
                         "`{self_ty}` implements `ToString` through a slower blanket impl, but `{deref_self_ty}` has a fast specialization of `ToString`"
                     ));
                     let mut applicability = Applicability::MachineApplicable;

clippy_lints/src/methods/iter_skip_next.rs

@@ -29,7 +29,7 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, recv: &hir::Expr
                         application = Applicability::Unspecified;
                         diag.span_help(
                             pat.span,
-                            &format!("for this change `{}` has to be mutable", snippet(cx, pat.span, "..")),
+                            format!("for this change `{}` has to be mutable", snippet(cx, pat.span, "..")),
                         );
                     }
                 }

clippy_lints/src/methods/option_map_unwrap_or.rs

@@ -84,7 +84,7 @@ pub(super) fn check<'tcx>(
                 suggestion.push((map_arg_span.with_hi(map_arg_span.lo()), format!("{unwrap_snippet}, ")));
             }
 
-            diag.multipart_suggestion(&format!("use `{suggest}` instead"), suggestion, applicability);
+            diag.multipart_suggestion(format!("use `{suggest}` instead"), suggestion, applicability);
         });
     }
 }

clippy_lints/src/methods/str_splitn.rs

@@ -167,7 +167,7 @@ fn check_manual_split_once_indirect(
             };
             diag.span_suggestion_verbose(
                 local.span,
-                &format!("try `{r}split_once`"),
+                format!("try `{r}split_once`"),
                 format!("let ({lhs}, {rhs}) = {self_snip}.{r}split_once({pat_snip}){unwrap};"),
                 app,
             );

clippy_lints/src/methods/unnecessary_lazy_eval.rs

@@ -62,7 +62,7 @@ pub(super) fn check<'tcx>(
                     span_lint_and_then(cx, UNNECESSARY_LAZY_EVALUATIONS, expr.span, msg, |diag| {
                         diag.span_suggestion(
                             span,
-                            &format!("use `{simplify_using}(..)` instead"),
+                            format!("use `{simplify_using}(..)` instead"),
                             format!("{simplify_using}({})", snippet(cx, body_expr.span, "..")),
                             applicability,
                         );

clippy_lints/src/needless_late_init.rs

@@ -284,7 +284,7 @@ fn check<'tcx>(
 
                     diag.span_suggestion(
                         assign.lhs_span,
-                        &format!("declare `{binding_name}` here"),
+                        format!("declare `{binding_name}` here"),
                         let_snippet,
                         Applicability::MachineApplicable,
                     );
@@ -304,7 +304,7 @@ fn check<'tcx>(
 
                     diag.span_suggestion_verbose(
                         usage.stmt.span.shrink_to_lo(),
-                        &format!("declare `{binding_name}` here"),
+                        format!("declare `{binding_name}` here"),
                         format!("{let_snippet} = "),
                         applicability,
                     );
@@ -335,7 +335,7 @@ fn check<'tcx>(
 
                     diag.span_suggestion_verbose(
                         usage.stmt.span.shrink_to_lo(),
-                        &format!("declare `{binding_name}` here"),
+                        format!("declare `{binding_name}` here"),
                         format!("{let_snippet} = "),
                         applicability,
                     );

clippy_lints/src/octal_escapes.rs

@@ -125,7 +125,7 @@ fn check_lit(cx: &EarlyContext<'_>, lit: &Lit, span: Span, is_string: bool) {
             if is_string { "string" } else { "byte string" }
         ),
         |diag| {
-            diag.help(&format!(
+            diag.help(format!(
                 "octal escapes are not supported, `\\0` is always a null {}",
                 if is_string { "character" } else { "byte" }
             ));
@@ -139,7 +139,7 @@ fn check_lit(cx: &EarlyContext<'_>, lit: &Lit, span: Span, is_string: bool) {
             // suggestion 2: unambiguous null byte
             diag.span_suggestion(
                 span,
-                &format!(
+                format!(
                     "if the null {} is intended, disambiguate using",
                     if is_string { "character" } else { "byte" }
                 ),

clippy_lints/src/operators/misrefactored_assign_op.rs

@@ -50,7 +50,7 @@ fn lint_misrefactored_assign_op(
                 let long = format!("{snip_a} = {}", sugg::make_binop(op.into(), a, r));
                 diag.span_suggestion(
                     expr.span,
-                    &format!(
+                    format!(
                         "did you mean `{snip_a} = {snip_a} {} {snip_r}` or `{long}`? Consider replacing it with",
                         op.as_str()
                     ),

clippy_lints/src/redundant_clone.rs

@@ -131,7 +131,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantClone {
                 // `res = clone(arg)` can be turned into `res = move arg;`
                 // if `arg` is the only borrow of `cloned` at this point.
 
-                if cannot_move_out || !possible_borrower.only_borrowers(&[arg], cloned, loc) {
+                if cannot_move_out || !possible_borrower.at_most_borrowers(cx, &[arg], cloned, loc) {
                     continue;
                 }
 
@@ -178,7 +178,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantClone {
                 // StorageDead(pred_arg);
                 // res = to_path_buf(cloned);
                 // ```
-                if cannot_move_out || !possible_borrower.only_borrowers(&[arg, cloned], local, loc) {
+                if cannot_move_out || !possible_borrower.at_most_borrowers(cx, &[arg, cloned], local, loc) {
                     continue;
                 }
 

clippy_lints/src/same_name_method.rs

@@ -108,7 +108,7 @@ impl<'tcx> LateLintPass<'tcx> for SameNameMethod {
                                     |diag| {
                                         diag.span_note(
                                             trait_method_span,
-                                            &format!("existing `{method_name}` defined here"),
+                                            format!("existing `{method_name}` defined here"),
                                         );
                                     },
                                 );
@@ -151,7 +151,7 @@ impl<'tcx> LateLintPass<'tcx> for SameNameMethod {
                                         // iterate on trait_spans?
                                         diag.span_note(
                                             trait_spans[0],
-                                            &format!("existing `{method_name}` defined here"),
+                                            format!("existing `{method_name}` defined here"),
                                         );
                                     },
                                 );

clippy_lints/src/swap.rs

@@ -132,7 +132,7 @@ fn generate_swap_warning(cx: &LateContext<'_>, e1: &Expr<'_>, e2: &Expr<'_>, spa
                 applicability,
             );
             if !is_xor_based {
-                diag.note(&format!("or maybe you should use `{sugg}::mem::replace`?"));
+                diag.note(format!("or maybe you should use `{sugg}::mem::replace`?"));
             }
         },
     );
@@ -214,7 +214,7 @@ fn check_suspicious_swap(cx: &LateContext<'_>, block: &Block<'_>) {
                                 Applicability::MaybeIncorrect,
                             );
                             diag.note(
-                                &format!("or maybe you should use `{sugg}::mem::replace`?")
+                                format!("or maybe you should use `{sugg}::mem::replace`?")
                             );
                         }
                     });

clippy_lints/src/transmute/transmute_undefined_repr.rs

@@ -77,7 +77,7 @@ pub(super) fn check<'tcx>(
                     &format!("transmute from `{from_ty_orig}` which has an undefined layout"),
                     |diag| {
                         if from_ty_orig.peel_refs() != from_ty.peel_refs() {
-                            diag.note(&format!("the contained type `{from_ty}` has an undefined layout"));
+                            diag.note(format!("the contained type `{from_ty}` has an undefined layout"));
                         }
                     },
                 );
@@ -91,7 +91,7 @@ pub(super) fn check<'tcx>(
                     &format!("transmute to `{to_ty_orig}` which has an undefined layout"),
                     |diag| {
                         if to_ty_orig.peel_refs() != to_ty.peel_refs() {
-                            diag.note(&format!("the contained type `{to_ty}` has an undefined layout"));
+                            diag.note(format!("the contained type `{to_ty}` has an undefined layout"));
                         }
                     },
                 );
@@ -119,16 +119,16 @@ pub(super) fn check<'tcx>(
                     ),
                     |diag| {
                         if let Some(same_adt_did) = same_adt_did {
-                            diag.note(&format!(
+                            diag.note(format!(
                                 "two instances of the same generic type (`{}`) may have different layouts",
                                 cx.tcx.item_name(same_adt_did)
                             ));
                         } else {
                             if from_ty_orig.peel_refs() != from_ty {
-                                diag.note(&format!("the contained type `{from_ty}` has an undefined layout"));
+                                diag.note(format!("the contained type `{from_ty}` has an undefined layout"));
                             }
                             if to_ty_orig.peel_refs() != to_ty {
-                                diag.note(&format!("the contained type `{to_ty}` has an undefined layout"));
+                                diag.note(format!("the contained type `{to_ty}` has an undefined layout"));
                             }
                         }
                     },
@@ -146,7 +146,7 @@ pub(super) fn check<'tcx>(
                     &format!("transmute from `{from_ty_orig}` which has an undefined layout"),
                     |diag| {
                         if from_ty_orig.peel_refs() != from_ty {
-                            diag.note(&format!("the contained type `{from_ty}` has an undefined layout"));
+                            diag.note(format!("the contained type `{from_ty}` has an undefined layout"));
                         }
                     },
                 );
@@ -163,7 +163,7 @@ pub(super) fn check<'tcx>(
                     &format!("transmute into `{to_ty_orig}` which has an undefined layout"),
                     |diag| {
                         if to_ty_orig.peel_refs() != to_ty {
-                            diag.note(&format!("the contained type `{to_ty}` has an undefined layout"));
+                            diag.note(format!("the contained type `{to_ty}` has an undefined layout"));
                         }
                     },
                 );

clippy_lints/src/transmute/transmutes_expressible_as_ptr_casts.rs

@@ -24,7 +24,7 @@ pub(super) fn check<'tcx>(
             &format!("transmute from `{from_ty}` to `{to_ty}` which could be expressed as a pointer cast instead"),
             |diag| {
                 if let Some(arg) = sugg::Sugg::hir_opt(cx, arg) {
-                    let sugg = arg.as_ty(&to_ty.to_string()).to_string();
+                    let sugg = arg.as_ty(to_ty.to_string()).to_string();
                     diag.span_suggestion(e.span, "try", sugg, Applicability::MachineApplicable);
                 }
             },

clippy_lints/src/transmute/useless_transmute.rs

@@ -61,7 +61,7 @@ pub(super) fn check<'tcx>(
                 "transmute from an integer to a pointer",
                 |diag| {
                     if let Some(arg) = sugg::Sugg::hir_opt(cx, arg) {
-                        diag.span_suggestion(e.span, "try", arg.as_ty(&to_ty.to_string()), Applicability::Unspecified);
+                        diag.span_suggestion(e.span, "try", arg.as_ty(to_ty.to_string()), Applicability::Unspecified);
                     }
                 },
             );

clippy_lints/src/types/redundant_allocation.rs

@@ -31,7 +31,7 @@ pub(super) fn check(cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, qpath: &QPath<'_
             &format!("usage of `{outer_sym}<{generic_snippet}>`"),
             |diag| {
                 diag.span_suggestion(hir_ty.span, "try", format!("{generic_snippet}"), applicability);
-                diag.note(&format!(
+                diag.note(format!(
                     "`{generic_snippet}` is already a pointer, `{outer_sym}<{generic_snippet}>` allocates a pointer on the heap"
                 ));
             },
@@ -78,7 +78,7 @@ pub(super) fn check(cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, qpath: &QPath<'_
                     format!("{outer_sym}<{generic_snippet}>"),
                     applicability,
                 );
-                diag.note(&format!(
+                diag.note(format!(
                     "`{inner_sym}<{generic_snippet}>` is already on the heap, `{outer_sym}<{inner_sym}<{generic_snippet}>>` makes an extra allocation"
                 ));
             },
@@ -91,10 +91,10 @@ pub(super) fn check(cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, qpath: &QPath<'_
             hir_ty.span,
             &format!("usage of `{outer_sym}<{inner_sym}<{generic_snippet}>>`"),
             |diag| {
-                diag.note(&format!(
+                diag.note(format!(
                     "`{inner_sym}<{generic_snippet}>` is already on the heap, `{outer_sym}<{inner_sym}<{generic_snippet}>>` makes an extra allocation"
                 ));
-                diag.help(&format!(
+                diag.help(format!(
                     "consider using just `{outer_sym}<{generic_snippet}>` or `{inner_sym}<{generic_snippet}>`"
                 ));
             },

clippy_lints/src/unit_types/unit_arg.rs

@@ -129,7 +129,7 @@ fn lint_unit_args(cx: &LateContext<'_>, expr: &Expr<'_>, args_to_recover: &[&Exp
 
                 if arg_snippets_without_empty_blocks.is_empty() {
                     db.multipart_suggestion(
-                        &format!("use {singular}unit literal{plural} instead"),
+                        format!("use {singular}unit literal{plural} instead"),
                         args_to_recover
                             .iter()
                             .map(|arg| (arg.span, "()".to_string()))
@@ -142,7 +142,7 @@ fn lint_unit_args(cx: &LateContext<'_>, expr: &Expr<'_>, args_to_recover: &[&Exp
                     let it_or_them = if plural { "them" } else { "it" };
                     db.span_suggestion(
                         expr.span,
-                        &format!(
+                        format!(
                             "{or}move the expression{empty_or_s} in front of the call and replace {it_or_them} with the unit literal `()`"
                         ),
                         sugg,

clippy_lints/src/write.rs

@@ -377,7 +377,7 @@ fn check_newline(cx: &LateContext<'_>, format_args: &FormatArgsExpn<'_>, macro_c
                     // print!("\n"), write!(f, "\n")
 
                     diag.multipart_suggestion(
-                        &format!("use `{name}ln!` instead"),
+                        format!("use `{name}ln!` instead"),
                         vec![(name_span, format!("{name}ln")), (format_string_span, String::new())],
                         Applicability::MachineApplicable,
                     );
@@ -388,7 +388,7 @@ fn check_newline(cx: &LateContext<'_>, format_args: &FormatArgsExpn<'_>, macro_c
                     let newline_span = format_string_span.with_lo(hi - BytePos(3)).with_hi(hi - BytePos(1));
 
                     diag.multipart_suggestion(
-                        &format!("use `{name}ln!` instead"),
+                        format!("use `{name}ln!` instead"),
                         vec![(name_span, format!("{name}ln")), (newline_span, String::new())],
                         Applicability::MachineApplicable,
                     );

clippy_utils/src/diagnostics.rs

@@ -17,7 +17,7 @@ use std::env;
 fn docs_link(diag: &mut Diagnostic, lint: &'static Lint) {
     if env::var("CLIPPY_DISABLE_DOCS_LINKS").is_err() {
         if let Some(lint) = lint.name_lower().strip_prefix("clippy::") {
-            diag.help(&format!(
+            diag.help(format!(
                 "for further information visit https://rust-lang.github.io/rust-clippy/{}/index.html#{lint}",
                 &option_env!("RUST_RELEASE_NUM").map_or("master".to_string(), |n| {
                     // extract just major + minor version and ignore patch versions

clippy_utils/src/mir/mod.rs

@@ -5,8 +5,6 @@ use rustc_middle::mir::{
 };
 use rustc_middle::ty::TyCtxt;
 
-mod maybe_storage_live;
-
 mod possible_borrower;
 pub use possible_borrower::PossibleBorrowerMap;
 

clippy_utils/src/mir/possible_borrower.rs

@@ -1,92 +1,137 @@
-use super::{
-    maybe_storage_live::MaybeStorageLive, possible_origin::PossibleOriginVisitor,
-    transitive_relation::TransitiveRelation,
-};
+use super::possible_origin::PossibleOriginVisitor;
 use crate::ty::is_copy;
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_index::bit_set::{BitSet, HybridBitSet};
 use rustc_lint::LateContext;
-use rustc_middle::mir::{self, visit::Visitor as _, Mutability};
-use rustc_middle::ty::{self, visit::TypeVisitor};
-use rustc_mir_dataflow::{Analysis, ResultsCursor};
+use rustc_middle::mir::{
+    self, visit::Visitor as _, BasicBlock, Local, Location, Mutability, Statement, StatementKind, Terminator,
+};
+use rustc_middle::ty::{self, visit::TypeVisitor, TyCtxt};
+use rustc_mir_dataflow::{
+    fmt::DebugWithContext, impls::MaybeStorageLive, lattice::JoinSemiLattice, Analysis, AnalysisDomain,
+    CallReturnPlaces, ResultsCursor,
+};
+use std::borrow::Cow;
 use std::ops::ControlFlow;
 
 /// Collects the possible borrowers of each local.
 /// For example, `b = &a; c = &a;` will make `b` and (transitively) `c`
 /// possible borrowers of `a`.
 #[allow(clippy::module_name_repetitions)]
-struct PossibleBorrowerVisitor<'a, 'b, 'tcx> {
-    possible_borrower: TransitiveRelation,
+struct PossibleBorrowerAnalysis<'b, 'tcx> {
+    tcx: TyCtxt<'tcx>,
     body: &'b mir::Body<'tcx>,
-    cx: &'a LateContext<'tcx>,
     possible_origin: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
 }
 
-impl<'a, 'b, 'tcx> PossibleBorrowerVisitor<'a, 'b, 'tcx> {
-    fn new(
-        cx: &'a LateContext<'tcx>,
-        body: &'b mir::Body<'tcx>,
-        possible_origin: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
-    ) -> Self {
+#[derive(Clone, Debug, Eq, PartialEq)]
+struct PossibleBorrowerState {
+    map: FxIndexMap<Local, BitSet<Local>>,
+    domain_size: usize,
+}
+
+impl PossibleBorrowerState {
+    fn new(domain_size: usize) -> Self {
         Self {
-            possible_borrower: TransitiveRelation::default(),
-            cx,
-            body,
-            possible_origin,
+            map: FxIndexMap::default(),
+            domain_size,
         }
     }
 
-    fn into_map(
-        self,
-        cx: &'a LateContext<'tcx>,
-        maybe_live: ResultsCursor<'b, 'tcx, MaybeStorageLive>,
-    ) -> PossibleBorrowerMap<'b, 'tcx> {
-        let mut map = FxHashMap::default();
-        for row in (1..self.body.local_decls.len()).map(mir::Local::from_usize) {
-            if is_copy(cx, self.body.local_decls[row].ty) {
-                continue;
-            }
+    #[allow(clippy::similar_names)]
+    fn add(&mut self, borrowed: Local, borrower: Local) {
+        self.map
+            .entry(borrowed)
+            .or_insert(BitSet::new_empty(self.domain_size))
+            .insert(borrower);
+    }
+}
 
-            let mut borrowers = self.possible_borrower.reachable_from(row, self.body.local_decls.len());
-            borrowers.remove(mir::Local::from_usize(0));
+impl<C> DebugWithContext<C> for PossibleBorrowerState {
+    fn fmt_with(&self, _ctxt: &C, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        <_ as std::fmt::Debug>::fmt(self, f)
+    }
+    fn fmt_diff_with(&self, _old: &Self, _ctxt: &C, _f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        unimplemented!()
+    }
+}
+
+impl JoinSemiLattice for PossibleBorrowerState {
+    fn join(&mut self, other: &Self) -> bool {
+        let mut changed = false;
+        for (&borrowed, borrowers) in other.map.iter() {
             if !borrowers.is_empty() {
-                map.insert(row, borrowers);
+                changed |= self
+                    .map
+                    .entry(borrowed)
+                    .or_insert(BitSet::new_empty(self.domain_size))
+                    .union(borrowers);
             }
         }
+        changed
+    }
+}
 
-        let bs = BitSet::new_empty(self.body.local_decls.len());
-        PossibleBorrowerMap {
-            map,
-            maybe_live,
-            bitset: (bs.clone(), bs),
+impl<'b, 'tcx> AnalysisDomain<'tcx> for PossibleBorrowerAnalysis<'b, 'tcx> {
+    type Domain = PossibleBorrowerState;
+
+    const NAME: &'static str = "possible_borrower";
+
+    fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain {
+        PossibleBorrowerState::new(body.local_decls.len())
+    }
+
+    fn initialize_start_block(&self, _body: &mir::Body<'tcx>, _entry_set: &mut Self::Domain) {}
+}
+
+impl<'b, 'tcx> PossibleBorrowerAnalysis<'b, 'tcx> {
+    fn new(
+        tcx: TyCtxt<'tcx>,
+        body: &'b mir::Body<'tcx>,
+        possible_origin: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
+    ) -> Self {
+        Self {
+            tcx,
+            body,
+            possible_origin,
         }
     }
 }
 
-impl<'a, 'b, 'tcx> mir::visit::Visitor<'tcx> for PossibleBorrowerVisitor<'a, 'b, 'tcx> {
-    fn visit_assign(&mut self, place: &mir::Place<'tcx>, rvalue: &mir::Rvalue<'_>, _location: mir::Location) {
-        let lhs = place.local;
-        match rvalue {
-            mir::Rvalue::Ref(_, _, borrowed) => {
-                self.possible_borrower.add(borrowed.local, lhs);
-            },
-            other => {
-                if ContainsRegion
-                    .visit_ty(place.ty(&self.body.local_decls, self.cx.tcx).ty)
-                    .is_continue()
-                {
-                    return;
-                }
-                rvalue_locals(other, |rhs| {
-                    if lhs != rhs {
-                        self.possible_borrower.add(rhs, lhs);
+impl<'b, 'tcx> Analysis<'tcx> for PossibleBorrowerAnalysis<'b, 'tcx> {
+    fn apply_call_return_effect(
+        &self,
+        _state: &mut Self::Domain,
+        _block: BasicBlock,
+        _return_places: CallReturnPlaces<'_, 'tcx>,
+    ) {
+    }
+
+    fn apply_statement_effect(&self, state: &mut Self::Domain, statement: &Statement<'tcx>, _location: Location) {
+        if let StatementKind::Assign(box (place, rvalue)) = &statement.kind {
+            let lhs = place.local;
+            match rvalue {
+                mir::Rvalue::Ref(_, _, borrowed) => {
+                    state.add(borrowed.local, lhs);
+                },
+                other => {
+                    if ContainsRegion
+                        .visit_ty(place.ty(&self.body.local_decls, self.tcx).ty)
+                        .is_continue()
+                    {
+                        return;
                     }
-                });
-            },
+                    rvalue_locals(other, |rhs| {
+                        if lhs != rhs {
+                            state.add(rhs, lhs);
+                        }
+                    });
+                },
+            }
         }
     }
 
-    fn visit_terminator(&mut self, terminator: &mir::Terminator<'_>, _loc: mir::Location) {
+    fn apply_terminator_effect(&self, state: &mut Self::Domain, terminator: &Terminator<'tcx>, _location: Location) {
         if let mir::TerminatorKind::Call {
             args,
             destination: mir::Place { local: dest, .. },
@@ -126,10 +171,10 @@ impl<'a, 'b, 'tcx> mir::visit::Visitor<'tcx> for PossibleBorrowerVisitor<'a, 'b,
 
             for y in mutable_variables {
                 for x in &immutable_borrowers {
-                    self.possible_borrower.add(*x, y);
+                    state.add(*x, y);
                 }
                 for x in &mutable_borrowers {
-                    self.possible_borrower.add(*x, y);
+                    state.add(*x, y);
                 }
             }
         }
@@ -165,73 +210,98 @@ fn rvalue_locals(rvalue: &mir::Rvalue<'_>, mut visit: impl FnMut(mir::Local)) {
     }
 }
 
-/// Result of `PossibleBorrowerVisitor`.
+/// Result of `PossibleBorrowerAnalysis`.
 #[allow(clippy::module_name_repetitions)]
 pub struct PossibleBorrowerMap<'b, 'tcx> {
-    /// Mapping `Local -> its possible borrowers`
-    pub map: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
-    maybe_live: ResultsCursor<'b, 'tcx, MaybeStorageLive>,
-    // Caches to avoid allocation of `BitSet` on every query
-    pub bitset: (BitSet<mir::Local>, BitSet<mir::Local>),
+    body: &'b mir::Body<'tcx>,
+    possible_borrower: ResultsCursor<'b, 'tcx, PossibleBorrowerAnalysis<'b, 'tcx>>,
+    maybe_live: ResultsCursor<'b, 'tcx, MaybeStorageLive<'b>>,
+    pushed: BitSet<Local>,
+    stack: Vec<Local>,
 }
 
-impl<'a, 'b, 'tcx> PossibleBorrowerMap<'b, 'tcx> {
-    pub fn new(cx: &'a LateContext<'tcx>, mir: &'b mir::Body<'tcx>) -> Self {
+impl<'b, 'tcx> PossibleBorrowerMap<'b, 'tcx> {
+    pub fn new(cx: &LateContext<'tcx>, mir: &'b mir::Body<'tcx>) -> Self {
         let possible_origin = {
             let mut vis = PossibleOriginVisitor::new(mir);
             vis.visit_body(mir);
             vis.into_map(cx)
         };
-        let maybe_storage_live_result = MaybeStorageLive
+        let possible_borrower = PossibleBorrowerAnalysis::new(cx.tcx, mir, possible_origin)
             .into_engine(cx.tcx, mir)
-            .pass_name("redundant_clone")
+            .pass_name("possible_borrower")
             .iterate_to_fixpoint()
             .into_results_cursor(mir);
-        let mut vis = PossibleBorrowerVisitor::new(cx, mir, possible_origin);
-        vis.visit_body(mir);
-        vis.into_map(cx, maybe_storage_live_result)
-    }
-
-    /// Returns true if the set of borrowers of `borrowed` living at `at` matches with `borrowers`.
-    pub fn only_borrowers(&mut self, borrowers: &[mir::Local], borrowed: mir::Local, at: mir::Location) -> bool {
-        self.bounded_borrowers(borrowers, borrowers, borrowed, at)
+        let maybe_live = MaybeStorageLive::new(Cow::Owned(BitSet::new_empty(mir.local_decls.len())))
+            .into_engine(cx.tcx, mir)
+            .pass_name("possible_borrower")
+            .iterate_to_fixpoint()
+            .into_results_cursor(mir);
+        PossibleBorrowerMap {
+            body: mir,
+            possible_borrower,
+            maybe_live,
+            pushed: BitSet::new_empty(mir.local_decls.len()),
+            stack: Vec::with_capacity(mir.local_decls.len()),
+        }
     }
 
-    /// Returns true if the set of borrowers of `borrowed` living at `at` includes at least `below`
-    /// but no more than `above`.
-    pub fn bounded_borrowers(
+    /// Returns true if the set of borrowers of `borrowed` living at `at` includes no more than
+    /// `borrowers`.
+    /// Notes:
+    /// 1. It would be nice if `PossibleBorrowerMap` could store `cx` so that `at_most_borrowers`
+    /// would not require it to be passed in. But a `PossibleBorrowerMap` is stored in `LintPass`
+    /// `Dereferencing`, which outlives any `LateContext`.
+    /// 2. In all current uses of `at_most_borrowers`, `borrowers` is a slice of at most two
+    /// elements. Thus, `borrowers.contains(...)` is effectively a constant-time operation. If
+    /// `at_most_borrowers`'s uses were to expand beyond this, its implementation might have to be
+    /// adjusted.
+    pub fn at_most_borrowers(
         &mut self,
-        below: &[mir::Local],
-        above: &[mir::Local],
+        cx: &LateContext<'tcx>,
+        borrowers: &[mir::Local],
         borrowed: mir::Local,
         at: mir::Location,
     ) -> bool {
-        self.maybe_live.seek_after_primary_effect(at);
+        if is_copy(cx, self.body.local_decls[borrowed].ty) {
+            return true;
+        }
 
-        self.bitset.0.clear();
-        let maybe_live = &mut self.maybe_live;
-        if let Some(bitset) = self.map.get(&borrowed) {
-            for b in bitset.iter().filter(move |b| maybe_live.contains(*b)) {
-                self.bitset.0.insert(b);
+        self.possible_borrower.seek_before_primary_effect(at);
+        self.maybe_live.seek_before_primary_effect(at);
+
+        let possible_borrower = &self.possible_borrower.get().map;
+        let maybe_live = &self.maybe_live;
+
+        self.pushed.clear();
+        self.stack.clear();
+
+        if let Some(borrowers) = possible_borrower.get(&borrowed) {
+            for b in borrowers.iter() {
+                if self.pushed.insert(b) {
+                    self.stack.push(b);
+                }
             }
         } else {
-            return false;
+            // Nothing borrows `borrowed` at `at`.
+            return true;
         }
 
-        self.bitset.1.clear();
-        for b in below {
-            self.bitset.1.insert(*b);
-        }
-
-        if !self.bitset.0.superset(&self.bitset.1) {
-            return false;
-        }
+        while let Some(borrower) = self.stack.pop() {
+            if maybe_live.contains(borrower) && !borrowers.contains(&borrower) {
+                return false;
+            }
 
-        for b in above {
-            self.bitset.0.remove(*b);
+            if let Some(borrowers) = possible_borrower.get(&borrower) {
+                for b in borrowers.iter() {
+                    if self.pushed.insert(b) {
+                        self.stack.push(b);
+                    }
+                }
+            }
         }
 
-        self.bitset.0.is_empty()
+        true
     }
 
     pub fn local_is_alive_at(&mut self, local: mir::Local, at: mir::Location) -> bool {

tests/ui/manual_retain.fixed

@@ -1,6 +1,6 @@
 // run-rustfix
 #![warn(clippy::manual_retain)]
-#![allow(unused)]
+#![allow(unused, clippy::redundant_clone)]
 use std::collections::BTreeMap;
 use std::collections::BTreeSet;
 use std::collections::BinaryHeap;

tests/ui/manual_retain.rs

@@ -1,6 +1,6 @@
 // run-rustfix
 #![warn(clippy::manual_retain)]
-#![allow(unused)]
+#![allow(unused, clippy::redundant_clone)]
 use std::collections::BTreeMap;
 use std::collections::BTreeSet;
 use std::collections::BinaryHeap;

tests/ui/needless_borrow.fixed

@@ -1,5 +1,5 @@
 // run-rustfix
-#![feature(lint_reasons)]
+#![feature(custom_inner_attributes, lint_reasons, rustc_private)]
 #![allow(
     unused,
     clippy::uninlined_format_args,
@@ -491,3 +491,14 @@ mod issue_9782_method_variant {
         S.foo::<&[u8; 100]>(&a);
     }
 }
+
+extern crate rustc_lint;
+extern crate rustc_span;
+
+#[allow(dead_code)]
+mod span_lint {
+    use rustc_lint::{LateContext, Lint, LintContext};
+    fn foo(cx: &LateContext<'_>, lint: &'static Lint) {
+        cx.struct_span_lint(lint, rustc_span::Span::default(), "", |diag| diag.note(String::new()));
+    }
+}

tests/ui/needless_borrow.rs

@@ -1,5 +1,5 @@
 // run-rustfix
-#![feature(lint_reasons)]
+#![feature(custom_inner_attributes, lint_reasons, rustc_private)]
 #![allow(
     unused,
     clippy::uninlined_format_args,
@@ -491,3 +491,14 @@ mod issue_9782_method_variant {
         S.foo::<&[u8; 100]>(&a);
     }
 }
+
+extern crate rustc_lint;
+extern crate rustc_span;
+
+#[allow(dead_code)]
+mod span_lint {
+    use rustc_lint::{LateContext, Lint, LintContext};
+    fn foo(cx: &LateContext<'_>, lint: &'static Lint) {
+        cx.struct_span_lint(lint, rustc_span::Span::default(), "", |diag| diag.note(&String::new()));
+    }
+}

tests/ui/needless_borrow.stderr

@@ -216,5 +216,11 @@ error: the borrowed expression implements the required traits
 LL |         foo(&a);
    |             ^^ help: change this to: `a`
 
-error: aborting due to 36 previous errors
+error: the borrowed expression implements the required traits
+  --> $DIR/needless_borrow.rs:502:85
+   |
+LL |         cx.struct_span_lint(lint, rustc_span::Span::default(), "", |diag| diag.note(&String::new()));
+   |                                                                                     ^^^^^^^^^^^^^^ help: change this to: `String::new()`
+
+error: aborting due to 37 previous errors
 

tests/ui/redundant_clone.fixed

@@ -239,3 +239,9 @@ fn false_negative_5707() {
     let _z = x.clone(); // pr 7346 can't lint on `x`
     drop(y);
 }
+
+#[allow(unused, clippy::manual_retain)]
+fn possible_borrower_improvements() {
+    let mut s = String::from("foobar");
+    s = s.chars().filter(|&c| c != 'o').collect();
+}

tests/ui/redundant_clone.rs

@@ -239,3 +239,9 @@ fn false_negative_5707() {
     let _z = x.clone(); // pr 7346 can't lint on `x`
     drop(y);
 }
+
+#[allow(unused, clippy::manual_retain)]
+fn possible_borrower_improvements() {
+    let mut s = String::from("foobar");
+    s = s.chars().filter(|&c| c != 'o').to_owned().collect();
+}

tests/ui/redundant_clone.stderr

@@ -179,5 +179,17 @@ note: this value is dropped without further use
 LL |     foo(&x.clone(), move || {
    |          ^
 
-error: aborting due to 15 previous errors
+error: redundant clone
+  --> $DIR/redundant_clone.rs:246:40
+   |
+LL |     s = s.chars().filter(|&c| c != 'o').to_owned().collect();
+   |                                        ^^^^^^^^^^^ help: remove this
+   |
+note: this value is dropped without further use
+  --> $DIR/redundant_clone.rs:246:9
+   |
+LL |     s = s.chars().filter(|&c| c != 'o').to_owned().collect();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 16 previous errors