diff options
author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
---|---|---|
committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
tree | 173a775858bd501c378080a10dca74132f05bc50 /src/tools/clippy/clippy_lints/src/redundant_clone.rs | |
parent | Initial commit. (diff) | |
download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/tools/clippy/clippy_lints/src/redundant_clone.rs')
-rw-r--r-- | src/tools/clippy/clippy_lints/src/redundant_clone.rs | 776 |
1 files changed, 776 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/redundant_clone.rs b/src/tools/clippy/clippy_lints/src/redundant_clone.rs new file mode 100644 index 000000000..eddca6045 --- /dev/null +++ b/src/tools/clippy/clippy_lints/src/redundant_clone.rs @@ -0,0 +1,776 @@ +use clippy_utils::diagnostics::{span_lint_hir, span_lint_hir_and_then}; +use clippy_utils::source::snippet_opt; +use clippy_utils::ty::{has_drop, is_copy, is_type_diagnostic_item, walk_ptrs_ty_depth}; +use clippy_utils::{fn_has_unsatisfiable_preds, match_def_path, paths}; +use if_chain::if_chain; +use rustc_data_structures::fx::FxHashMap; +use rustc_errors::Applicability; +use rustc_hir::intravisit::FnKind; +use rustc_hir::{def_id, Body, FnDecl, HirId}; +use rustc_index::bit_set::{BitSet, HybridBitSet}; +use rustc_lint::{LateContext, LateLintPass}; +use rustc_middle::mir::{ + self, traversal, + visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor as _}, + Mutability, +}; +use rustc_middle::ty::{self, visit::TypeVisitor, Ty}; +use rustc_mir_dataflow::{Analysis, AnalysisDomain, CallReturnPlaces, GenKill, GenKillAnalysis, ResultsCursor}; +use rustc_session::{declare_lint_pass, declare_tool_lint}; +use rustc_span::source_map::{BytePos, Span}; +use rustc_span::sym; +use std::ops::ControlFlow; + +macro_rules! unwrap_or_continue { + ($x:expr) => { + match $x { + Some(x) => x, + None => continue, + } + }; +} + +declare_clippy_lint! { + /// ### What it does + /// Checks for a redundant `clone()` (and its relatives) which clones an owned + /// value that is going to be dropped without further use. + /// + /// ### Why is this bad? + /// It is not always possible for the compiler to eliminate useless + /// allocations and deallocations generated by redundant `clone()`s. + /// + /// ### Known problems + /// False-negatives: analysis performed by this lint is conservative and limited. + /// + /// ### Example + /// ```rust + /// # use std::path::Path; + /// # #[derive(Clone)] + /// # struct Foo; + /// # impl Foo { + /// # fn new() -> Self { Foo {} } + /// # } + /// # fn call(x: Foo) {} + /// { + /// let x = Foo::new(); + /// call(x.clone()); + /// call(x.clone()); // this can just pass `x` + /// } + /// + /// ["lorem", "ipsum"].join(" ").to_string(); + /// + /// Path::new("/a/b").join("c").to_path_buf(); + /// ``` + #[clippy::version = "1.32.0"] + pub REDUNDANT_CLONE, + perf, + "`clone()` of an owned value that is going to be dropped immediately" +} + +declare_lint_pass!(RedundantClone => [REDUNDANT_CLONE]); + +impl<'tcx> LateLintPass<'tcx> for RedundantClone { + #[expect(clippy::too_many_lines)] + fn check_fn( + &mut self, + cx: &LateContext<'tcx>, + _: FnKind<'tcx>, + _: &'tcx FnDecl<'_>, + body: &'tcx Body<'_>, + _: Span, + _: HirId, + ) { + let def_id = cx.tcx.hir().body_owner_def_id(body.id()); + + // Building MIR for `fn`s with unsatisfiable preds results in ICE. + if fn_has_unsatisfiable_preds(cx, def_id.to_def_id()) { + return; + } + + let mir = cx.tcx.optimized_mir(def_id.to_def_id()); + + let possible_origin = { + let mut vis = PossibleOriginVisitor::new(mir); + vis.visit_body(mir); + vis.into_map(cx) + }; + let maybe_storage_live_result = MaybeStorageLive + .into_engine(cx.tcx, mir) + .pass_name("redundant_clone") + .iterate_to_fixpoint() + .into_results_cursor(mir); + let mut possible_borrower = { + let mut vis = PossibleBorrowerVisitor::new(cx, mir, possible_origin); + vis.visit_body(mir); + vis.into_map(cx, maybe_storage_live_result) + }; + + for (bb, bbdata) in mir.basic_blocks().iter_enumerated() { + let terminator = bbdata.terminator(); + + if terminator.source_info.span.from_expansion() { + continue; + } + + // Give up on loops + if terminator.successors().any(|s| s == bb) { + continue; + } + + let (fn_def_id, arg, arg_ty, clone_ret) = + unwrap_or_continue!(is_call_with_ref_arg(cx, mir, &terminator.kind)); + + let from_borrow = match_def_path(cx, fn_def_id, &paths::CLONE_TRAIT_METHOD) + || match_def_path(cx, fn_def_id, &paths::TO_OWNED_METHOD) + || (match_def_path(cx, fn_def_id, &paths::TO_STRING_METHOD) + && is_type_diagnostic_item(cx, arg_ty, sym::String)); + + let from_deref = !from_borrow + && (match_def_path(cx, fn_def_id, &paths::PATH_TO_PATH_BUF) + || match_def_path(cx, fn_def_id, &paths::OS_STR_TO_OS_STRING)); + + if !from_borrow && !from_deref { + continue; + } + + if let ty::Adt(def, _) = arg_ty.kind() { + if def.is_manually_drop() { + continue; + } + } + + // `{ arg = &cloned; clone(move arg); }` or `{ arg = &cloned; to_path_buf(arg); }` + let (cloned, cannot_move_out) = unwrap_or_continue!(find_stmt_assigns_to(cx, mir, arg, from_borrow, bb)); + + let loc = mir::Location { + block: bb, + statement_index: bbdata.statements.len(), + }; + + // `Local` to be cloned, and a local of `clone` call's destination + let (local, ret_local) = if from_borrow { + // `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) { + continue; + } + + (cloned, clone_ret) + } else { + // `arg` is a reference as it is `.deref()`ed in the previous block. + // Look into the predecessor block and find out the source of deref. + + let ps = &mir.basic_blocks.predecessors()[bb]; + if ps.len() != 1 { + continue; + } + let pred_terminator = mir[ps[0]].terminator(); + + // receiver of the `deref()` call + let (pred_arg, deref_clone_ret) = if_chain! { + if let Some((pred_fn_def_id, pred_arg, pred_arg_ty, res)) = + is_call_with_ref_arg(cx, mir, &pred_terminator.kind); + if res == cloned; + if cx.tcx.is_diagnostic_item(sym::deref_method, pred_fn_def_id); + if is_type_diagnostic_item(cx, pred_arg_ty, sym::PathBuf) + || is_type_diagnostic_item(cx, pred_arg_ty, sym::OsString); + then { + (pred_arg, res) + } else { + continue; + } + }; + + let (local, cannot_move_out) = + unwrap_or_continue!(find_stmt_assigns_to(cx, mir, pred_arg, true, ps[0])); + let loc = mir::Location { + block: bb, + statement_index: mir.basic_blocks()[bb].statements.len(), + }; + + // This can be turned into `res = move local` if `arg` and `cloned` are not borrowed + // at the last statement: + // + // ``` + // pred_arg = &local; + // cloned = deref(pred_arg); + // arg = &cloned; + // StorageDead(pred_arg); + // res = to_path_buf(cloned); + // ``` + if cannot_move_out || !possible_borrower.only_borrowers(&[arg, cloned], local, loc) { + continue; + } + + (local, deref_clone_ret) + }; + + let clone_usage = if local == ret_local { + CloneUsage { + cloned_used: false, + cloned_consume_or_mutate_loc: None, + clone_consumed_or_mutated: true, + } + } else { + let clone_usage = visit_clone_usage(local, ret_local, mir, bb); + if clone_usage.cloned_used && clone_usage.clone_consumed_or_mutated { + // cloned value is used, and the clone is modified or moved + continue; + } else if let Some(loc) = clone_usage.cloned_consume_or_mutate_loc { + // cloned value is mutated, and the clone is alive. + if possible_borrower.local_is_alive_at(ret_local, loc) { + continue; + } + } + clone_usage + }; + + let span = terminator.source_info.span; + let scope = terminator.source_info.scope; + let node = mir.source_scopes[scope] + .local_data + .as_ref() + .assert_crate_local() + .lint_root; + + if_chain! { + if let Some(snip) = snippet_opt(cx, span); + if let Some(dot) = snip.rfind('.'); + then { + let sugg_span = span.with_lo( + span.lo() + BytePos(u32::try_from(dot).unwrap()) + ); + let mut app = Applicability::MaybeIncorrect; + + let call_snip = &snip[dot + 1..]; + // Machine applicable when `call_snip` looks like `foobar()` + if let Some(call_snip) = call_snip.strip_suffix("()").map(str::trim) { + if call_snip.as_bytes().iter().all(|b| b.is_ascii_alphabetic() || *b == b'_') { + app = Applicability::MachineApplicable; + } + } + + span_lint_hir_and_then(cx, REDUNDANT_CLONE, node, sugg_span, "redundant clone", |diag| { + diag.span_suggestion( + sugg_span, + "remove this", + "", + app, + ); + if clone_usage.cloned_used { + diag.span_note( + span, + "cloned value is neither consumed nor mutated", + ); + } else { + diag.span_note( + span.with_hi(span.lo() + BytePos(u32::try_from(dot).unwrap())), + "this value is dropped without further use", + ); + } + }); + } else { + span_lint_hir(cx, REDUNDANT_CLONE, node, span, "redundant clone"); + } + } + } + } +} + +/// If `kind` is `y = func(x: &T)` where `T: !Copy`, returns `(DefId of func, x, T, y)`. +fn is_call_with_ref_arg<'tcx>( + cx: &LateContext<'tcx>, + mir: &'tcx mir::Body<'tcx>, + kind: &'tcx mir::TerminatorKind<'tcx>, +) -> Option<(def_id::DefId, mir::Local, Ty<'tcx>, mir::Local)> { + if_chain! { + if let mir::TerminatorKind::Call { func, args, destination, .. } = kind; + if args.len() == 1; + if let mir::Operand::Move(mir::Place { local, .. }) = &args[0]; + if let ty::FnDef(def_id, _) = *func.ty(mir, cx.tcx).kind(); + if let (inner_ty, 1) = walk_ptrs_ty_depth(args[0].ty(mir, cx.tcx)); + if !is_copy(cx, inner_ty); + then { + Some((def_id, *local, inner_ty, destination.as_local()?)) + } else { + None + } + } +} + +type CannotMoveOut = bool; + +/// Finds the first `to = (&)from`, and returns +/// ``Some((from, whether `from` cannot be moved out))``. +fn find_stmt_assigns_to<'tcx>( + cx: &LateContext<'tcx>, + mir: &mir::Body<'tcx>, + to_local: mir::Local, + by_ref: bool, + bb: mir::BasicBlock, +) -> Option<(mir::Local, CannotMoveOut)> { + let rvalue = mir.basic_blocks()[bb].statements.iter().rev().find_map(|stmt| { + if let mir::StatementKind::Assign(box (mir::Place { local, .. }, v)) = &stmt.kind { + return if *local == to_local { Some(v) } else { None }; + } + + None + })?; + + match (by_ref, rvalue) { + (true, mir::Rvalue::Ref(_, _, place)) | (false, mir::Rvalue::Use(mir::Operand::Copy(place))) => { + Some(base_local_and_movability(cx, mir, *place)) + }, + (false, mir::Rvalue::Ref(_, _, place)) => { + if let [mir::ProjectionElem::Deref] = place.as_ref().projection { + Some(base_local_and_movability(cx, mir, *place)) + } else { + None + } + }, + _ => None, + } +} + +/// Extracts and returns the undermost base `Local` of given `place`. Returns `place` itself +/// if it is already a `Local`. +/// +/// Also reports whether given `place` cannot be moved out. +fn base_local_and_movability<'tcx>( + cx: &LateContext<'tcx>, + mir: &mir::Body<'tcx>, + place: mir::Place<'tcx>, +) -> (mir::Local, CannotMoveOut) { + use rustc_middle::mir::PlaceRef; + + // Dereference. You cannot move things out from a borrowed value. + let mut deref = false; + // Accessing a field of an ADT that has `Drop`. Moving the field out will cause E0509. + let mut field = false; + // If projection is a slice index then clone can be removed only if the + // underlying type implements Copy + let mut slice = false; + + let PlaceRef { local, mut projection } = place.as_ref(); + while let [base @ .., elem] = projection { + projection = base; + deref |= matches!(elem, mir::ProjectionElem::Deref); + field |= matches!(elem, mir::ProjectionElem::Field(..)) + && has_drop(cx, mir::Place::ty_from(local, projection, &mir.local_decls, cx.tcx).ty); + slice |= matches!(elem, mir::ProjectionElem::Index(..)) + && !is_copy(cx, mir::Place::ty_from(local, projection, &mir.local_decls, cx.tcx).ty); + } + + (local, deref || field || slice) +} + +#[derive(Default)] +struct CloneUsage { + /// Whether the cloned value is used after the clone. + cloned_used: bool, + /// The first location where the cloned value is consumed or mutated, if any. + cloned_consume_or_mutate_loc: Option<mir::Location>, + /// Whether the clone value is mutated. + clone_consumed_or_mutated: bool, +} +fn visit_clone_usage(cloned: mir::Local, clone: mir::Local, mir: &mir::Body<'_>, bb: mir::BasicBlock) -> CloneUsage { + struct V { + cloned: mir::Local, + clone: mir::Local, + result: CloneUsage, + } + impl<'tcx> mir::visit::Visitor<'tcx> for V { + fn visit_basic_block_data(&mut self, block: mir::BasicBlock, data: &mir::BasicBlockData<'tcx>) { + let statements = &data.statements; + for (statement_index, statement) in statements.iter().enumerate() { + self.visit_statement(statement, mir::Location { block, statement_index }); + } + + self.visit_terminator( + data.terminator(), + mir::Location { + block, + statement_index: statements.len(), + }, + ); + } + + fn visit_place(&mut self, place: &mir::Place<'tcx>, ctx: PlaceContext, loc: mir::Location) { + let local = place.local; + + if local == self.cloned + && !matches!( + ctx, + PlaceContext::MutatingUse(MutatingUseContext::Drop) | PlaceContext::NonUse(_) + ) + { + self.result.cloned_used = true; + self.result.cloned_consume_or_mutate_loc = self.result.cloned_consume_or_mutate_loc.or_else(|| { + matches!( + ctx, + PlaceContext::NonMutatingUse(NonMutatingUseContext::Move) + | PlaceContext::MutatingUse(MutatingUseContext::Borrow) + ) + .then(|| loc) + }); + } else if local == self.clone { + match ctx { + PlaceContext::NonMutatingUse(NonMutatingUseContext::Move) + | PlaceContext::MutatingUse(MutatingUseContext::Borrow) => { + self.result.clone_consumed_or_mutated = true; + }, + _ => {}, + } + } + } + } + + let init = CloneUsage { + cloned_used: false, + cloned_consume_or_mutate_loc: None, + // Consider non-temporary clones consumed. + // TODO: Actually check for mutation of non-temporaries. + clone_consumed_or_mutated: mir.local_kind(clone) != mir::LocalKind::Temp, + }; + traversal::ReversePostorder::new(mir, bb) + .skip(1) + .fold(init, |usage, (tbb, tdata)| { + // Short-circuit + if (usage.cloned_used && usage.clone_consumed_or_mutated) || + // Give up on loops + tdata.terminator().successors().any(|s| s == bb) + { + return CloneUsage { + cloned_used: true, + clone_consumed_or_mutated: true, + ..usage + }; + } + + let mut v = V { + cloned, + clone, + result: usage, + }; + v.visit_basic_block_data(tbb, tdata); + v.result + }) +} + +/// Determines liveness of each local purely based on `StorageLive`/`Dead`. +#[derive(Copy, Clone)] +struct MaybeStorageLive; + +impl<'tcx> AnalysisDomain<'tcx> for MaybeStorageLive { + type Domain = BitSet<mir::Local>; + const NAME: &'static str = "maybe_storage_live"; + + fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain { + // bottom = dead + BitSet::new_empty(body.local_decls.len()) + } + + fn initialize_start_block(&self, body: &mir::Body<'tcx>, state: &mut Self::Domain) { + for arg in body.args_iter() { + state.insert(arg); + } + } +} + +impl<'tcx> GenKillAnalysis<'tcx> for MaybeStorageLive { + type Idx = mir::Local; + + fn statement_effect(&self, trans: &mut impl GenKill<Self::Idx>, stmt: &mir::Statement<'tcx>, _: mir::Location) { + match stmt.kind { + mir::StatementKind::StorageLive(l) => trans.gen(l), + mir::StatementKind::StorageDead(l) => trans.kill(l), + _ => (), + } + } + + fn terminator_effect( + &self, + _trans: &mut impl GenKill<Self::Idx>, + _terminator: &mir::Terminator<'tcx>, + _loc: mir::Location, + ) { + } + + fn call_return_effect( + &self, + _trans: &mut impl GenKill<Self::Idx>, + _block: mir::BasicBlock, + _return_places: CallReturnPlaces<'_, 'tcx>, + ) { + // Nothing to do when a call returns successfully + } +} + +/// Collects the possible borrowers of each local. +/// For example, `b = &a; c = &a;` will make `b` and (transitively) `c` +/// possible borrowers of `a`. +struct PossibleBorrowerVisitor<'a, 'tcx> { + possible_borrower: TransitiveRelation, + body: &'a mir::Body<'tcx>, + cx: &'a LateContext<'tcx>, + possible_origin: FxHashMap<mir::Local, HybridBitSet<mir::Local>>, +} + +impl<'a, 'tcx> PossibleBorrowerVisitor<'a, 'tcx> { + fn new( + cx: &'a LateContext<'tcx>, + body: &'a mir::Body<'tcx>, + possible_origin: FxHashMap<mir::Local, HybridBitSet<mir::Local>>, + ) -> Self { + Self { + possible_borrower: TransitiveRelation::default(), + cx, + body, + possible_origin, + } + } + + fn into_map( + self, + cx: &LateContext<'tcx>, + maybe_live: ResultsCursor<'tcx, 'tcx, MaybeStorageLive>, + ) -> PossibleBorrowerMap<'a, '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; + } + + let mut borrowers = self.possible_borrower.reachable_from(row, self.body.local_decls.len()); + borrowers.remove(mir::Local::from_usize(0)); + if !borrowers.is_empty() { + map.insert(row, borrowers); + } + } + + let bs = BitSet::new_empty(self.body.local_decls.len()); + PossibleBorrowerMap { + map, + maybe_live, + bitset: (bs.clone(), bs), + } + } +} + +impl<'a, 'tcx> mir::visit::Visitor<'tcx> for PossibleBorrowerVisitor<'a, '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); + } + }); + }, + } + } + + fn visit_terminator(&mut self, terminator: &mir::Terminator<'_>, _loc: mir::Location) { + if let mir::TerminatorKind::Call { + args, + destination: mir::Place { local: dest, .. }, + .. + } = &terminator.kind + { + // TODO add doc + // If the call returns something with lifetimes, + // let's conservatively assume the returned value contains lifetime of all the arguments. + // For example, given `let y: Foo<'a> = foo(x)`, `y` is considered to be a possible borrower of `x`. + + let mut immutable_borrowers = vec![]; + let mut mutable_borrowers = vec![]; + + for op in args { + match op { + mir::Operand::Copy(p) | mir::Operand::Move(p) => { + if let ty::Ref(_, _, Mutability::Mut) = self.body.local_decls[p.local].ty.kind() { + mutable_borrowers.push(p.local); + } else { + immutable_borrowers.push(p.local); + } + }, + mir::Operand::Constant(..) => (), + } + } + + let mut mutable_variables: Vec<mir::Local> = mutable_borrowers + .iter() + .filter_map(|r| self.possible_origin.get(r)) + .flat_map(HybridBitSet::iter) + .collect(); + + if ContainsRegion.visit_ty(self.body.local_decls[*dest].ty).is_break() { + mutable_variables.push(*dest); + } + + for y in mutable_variables { + for x in &immutable_borrowers { + self.possible_borrower.add(*x, y); + } + for x in &mutable_borrowers { + self.possible_borrower.add(*x, y); + } + } + } + } +} + +/// Collect possible borrowed for every `&mut` local. +/// For example, `_1 = &mut _2` generate _1: {_2,...} +/// Known Problems: not sure all borrowed are tracked +struct PossibleOriginVisitor<'a, 'tcx> { + possible_origin: TransitiveRelation, + body: &'a mir::Body<'tcx>, +} + +impl<'a, 'tcx> PossibleOriginVisitor<'a, 'tcx> { + fn new(body: &'a mir::Body<'tcx>) -> Self { + Self { + possible_origin: TransitiveRelation::default(), + body, + } + } + + fn into_map(self, cx: &LateContext<'tcx>) -> FxHashMap<mir::Local, HybridBitSet<mir::Local>> { + 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; + } + + let mut borrowers = self.possible_origin.reachable_from(row, self.body.local_decls.len()); + borrowers.remove(mir::Local::from_usize(0)); + if !borrowers.is_empty() { + map.insert(row, borrowers); + } + } + map + } +} + +impl<'a, 'tcx> mir::visit::Visitor<'tcx> for PossibleOriginVisitor<'a, 'tcx> { + fn visit_assign(&mut self, place: &mir::Place<'tcx>, rvalue: &mir::Rvalue<'_>, _location: mir::Location) { + let lhs = place.local; + match rvalue { + // Only consider `&mut`, which can modify origin place + mir::Rvalue::Ref(_, rustc_middle::mir::BorrowKind::Mut { .. }, borrowed) | + // _2: &mut _; + // _3 = move _2 + mir::Rvalue::Use(mir::Operand::Move(borrowed)) | + // _3 = move _2 as &mut _; + mir::Rvalue::Cast(_, mir::Operand::Move(borrowed), _) + => { + self.possible_origin.add(lhs, borrowed.local); + }, + _ => {}, + } + } +} + +struct ContainsRegion; + +impl TypeVisitor<'_> for ContainsRegion { + type BreakTy = (); + + fn visit_region(&mut self, _: ty::Region<'_>) -> ControlFlow<Self::BreakTy> { + ControlFlow::BREAK + } +} + +fn rvalue_locals(rvalue: &mir::Rvalue<'_>, mut visit: impl FnMut(mir::Local)) { + use rustc_middle::mir::Rvalue::{Aggregate, BinaryOp, Cast, CheckedBinaryOp, Repeat, UnaryOp, Use}; + + let mut visit_op = |op: &mir::Operand<'_>| match op { + mir::Operand::Copy(p) | mir::Operand::Move(p) => visit(p.local), + mir::Operand::Constant(..) => (), + }; + + match rvalue { + Use(op) | Repeat(op, _) | Cast(_, op, _) | UnaryOp(_, op) => visit_op(op), + Aggregate(_, ops) => ops.iter().for_each(visit_op), + BinaryOp(_, box (lhs, rhs)) | CheckedBinaryOp(_, box (lhs, rhs)) => { + visit_op(lhs); + visit_op(rhs); + }, + _ => (), + } +} + +/// Result of `PossibleBorrowerVisitor`. +struct PossibleBorrowerMap<'a, 'tcx> { + /// Mapping `Local -> its possible borrowers` + map: FxHashMap<mir::Local, HybridBitSet<mir::Local>>, + maybe_live: ResultsCursor<'a, 'tcx, MaybeStorageLive>, + // Caches to avoid allocation of `BitSet` on every query + bitset: (BitSet<mir::Local>, BitSet<mir::Local>), +} + +impl PossibleBorrowerMap<'_, '_> { + /// Returns true if the set of borrowers of `borrowed` living at `at` matches with `borrowers`. + fn only_borrowers(&mut self, borrowers: &[mir::Local], borrowed: mir::Local, at: mir::Location) -> bool { + self.maybe_live.seek_after_primary_effect(at); + + 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); + } + } else { + return false; + } + + self.bitset.1.clear(); + for b in borrowers { + self.bitset.1.insert(*b); + } + + self.bitset.0 == self.bitset.1 + } + + fn local_is_alive_at(&mut self, local: mir::Local, at: mir::Location) -> bool { + self.maybe_live.seek_after_primary_effect(at); + self.maybe_live.contains(local) + } +} + +#[derive(Default)] +struct TransitiveRelation { + relations: FxHashMap<mir::Local, Vec<mir::Local>>, +} +impl TransitiveRelation { + fn add(&mut self, a: mir::Local, b: mir::Local) { + self.relations.entry(a).or_default().push(b); + } + + fn reachable_from(&self, a: mir::Local, domain_size: usize) -> HybridBitSet<mir::Local> { + let mut seen = HybridBitSet::new_empty(domain_size); + let mut stack = vec![a]; + while let Some(u) = stack.pop() { + if let Some(edges) = self.relations.get(&u) { + for &v in edges { + if seen.insert(v) { + stack.push(v); + } + } + } + } + seen + } +} |