| use clippy_utils::diagnostics::span_lint_and_then; |
| use clippy_utils::macros::root_macro_call; |
| use clippy_utils::sugg::Sugg; |
| use clippy_utils::{ |
| get_enclosing_block, is_expr_path_def_path, is_integer_literal, is_path_diagnostic_item, path_to_local, |
| path_to_local_id, paths, SpanlessEq, |
| }; |
| use rustc_errors::Applicability; |
| use rustc_hir::intravisit::{walk_block, walk_expr, walk_stmt, Visitor}; |
| use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, HirId, PatKind, Stmt, StmtKind}; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_session::declare_lint_pass; |
| use rustc_span::symbol::sym; |
| |
| declare_clippy_lint! { |
| /// ### What it does |
| /// Checks slow zero-filled vector initialization |
| /// |
| /// ### Why is this bad? |
| /// These structures are non-idiomatic and less efficient than simply using |
| /// `vec![0; len]`. |
| /// |
| /// Specifically, for `vec![0; len]`, the compiler can use a specialized type of allocation |
| /// that also zero-initializes the allocated memory in the same call |
| /// (see: [alloc_zeroed](https://doc.rust-lang.org/stable/std/alloc/trait.GlobalAlloc.html#method.alloc_zeroed)). |
| /// |
| /// Writing `Vec::new()` followed by `vec.resize(len, 0)` is suboptimal because, |
| /// while it does do the same number of allocations, |
| /// it involves two operations for allocating and initializing. |
| /// The `resize` call first allocates memory (since `Vec::new()` did not), and only *then* zero-initializes it. |
| /// |
| /// ### Example |
| /// ```no_run |
| /// # use core::iter::repeat; |
| /// # let len = 4; |
| /// let mut vec1 = Vec::new(); |
| /// vec1.resize(len, 0); |
| /// |
| /// let mut vec2 = Vec::with_capacity(len); |
| /// vec2.resize(len, 0); |
| /// |
| /// let mut vec3 = Vec::with_capacity(len); |
| /// vec3.extend(repeat(0).take(len)); |
| /// ``` |
| /// |
| /// Use instead: |
| /// ```no_run |
| /// # let len = 4; |
| /// let mut vec1 = vec![0; len]; |
| /// let mut vec2 = vec![0; len]; |
| /// let mut vec3 = vec![0; len]; |
| /// ``` |
| #[clippy::version = "1.32.0"] |
| pub SLOW_VECTOR_INITIALIZATION, |
| perf, |
| "slow vector initialization" |
| } |
| |
| declare_lint_pass!(SlowVectorInit => [SLOW_VECTOR_INITIALIZATION]); |
| |
| /// `VecAllocation` contains data regarding a vector allocated with `with_capacity` and then |
| /// assigned to a variable. For example, `let mut vec = Vec::with_capacity(0)` or |
| /// `vec = Vec::with_capacity(0)` |
| struct VecAllocation<'tcx> { |
| /// `HirId` of the variable |
| local_id: HirId, |
| |
| /// Reference to the expression which allocates the vector |
| allocation_expr: &'tcx Expr<'tcx>, |
| |
| /// Reference to the expression used as argument on `with_capacity` call. This is used |
| /// to only match slow zero-filling idioms of the same length than vector initialization. |
| size_expr: InitializedSize<'tcx>, |
| } |
| |
| /// Initializer for the creation of the vector. |
| /// |
| /// When `Vec::with_capacity(size)` is found, the `size` expression will be in |
| /// `InitializedSize::Initialized`. |
| /// |
| /// Otherwise, for `Vec::new()` calls, there is no allocation initializer yet, so |
| /// `InitializedSize::Uninitialized` is used. |
| /// Later, when a call to `.resize(size, 0)` or similar is found, it's set |
| /// to `InitializedSize::Initialized(size)`. |
| /// |
| /// Since it will be set to `InitializedSize::Initialized(size)` when a slow initialization is |
| /// found, it is always safe to "unwrap" it at lint time. |
| enum InitializedSize<'tcx> { |
| Initialized(&'tcx Expr<'tcx>), |
| Uninitialized, |
| } |
| |
| /// Type of slow initialization |
| enum InitializationType<'tcx> { |
| /// Extend is a slow initialization with the form `vec.extend(repeat(0).take(..))` |
| Extend(&'tcx Expr<'tcx>), |
| |
| /// Resize is a slow initialization with the form `vec.resize(.., 0)` |
| Resize(&'tcx Expr<'tcx>), |
| } |
| |
| impl<'tcx> LateLintPass<'tcx> for SlowVectorInit { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| // Matches initialization on reassignments. For example: `vec = Vec::with_capacity(100)` |
| if let ExprKind::Assign(left, right, _) = expr.kind |
| && let Some(local_id) = path_to_local(left) |
| && let Some(size_expr) = Self::as_vec_initializer(cx, right) |
| { |
| let vi = VecAllocation { |
| local_id, |
| allocation_expr: right, |
| size_expr, |
| }; |
| |
| Self::search_initialization(cx, vi, expr.hir_id); |
| } |
| } |
| |
| fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) { |
| // Matches statements which initializes vectors. For example: `let mut vec = Vec::with_capacity(10)` |
| // or `Vec::new()` |
| if let StmtKind::Let(local) = stmt.kind |
| && let PatKind::Binding(BindingAnnotation::MUT, local_id, _, None) = local.pat.kind |
| && let Some(init) = local.init |
| && let Some(size_expr) = Self::as_vec_initializer(cx, init) |
| { |
| let vi = VecAllocation { |
| local_id, |
| allocation_expr: init, |
| size_expr, |
| }; |
| |
| Self::search_initialization(cx, vi, stmt.hir_id); |
| } |
| } |
| } |
| |
| impl SlowVectorInit { |
| /// Looks for `Vec::with_capacity(size)` or `Vec::new()` calls and returns the initialized size, |
| /// if any. More specifically, it returns: |
| /// - `Some(InitializedSize::Initialized(size))` for `Vec::with_capacity(size)` |
| /// - `Some(InitializedSize::Uninitialized)` for `Vec::new()` |
| /// - `None` for other, unrelated kinds of expressions |
| fn as_vec_initializer<'tcx>(cx: &LateContext<'_>, expr: &'tcx Expr<'tcx>) -> Option<InitializedSize<'tcx>> { |
| // Generally don't warn if the vec initializer comes from an expansion, except for the vec! macro. |
| // This lets us still warn on `vec![]`, while ignoring other kinds of macros that may output an |
| // empty vec |
| if expr.span.from_expansion() |
| && root_macro_call(expr.span).map(|m| m.def_id) != cx.tcx.get_diagnostic_item(sym::vec_macro) |
| { |
| return None; |
| } |
| |
| if let ExprKind::Call(func, [len_expr]) = expr.kind |
| && is_expr_path_def_path(cx, func, &paths::VEC_WITH_CAPACITY) |
| { |
| Some(InitializedSize::Initialized(len_expr)) |
| } else if matches!(expr.kind, ExprKind::Call(func, _) if is_expr_path_def_path(cx, func, &paths::VEC_NEW)) { |
| Some(InitializedSize::Uninitialized) |
| } else { |
| None |
| } |
| } |
| |
| /// Search initialization for the given vector |
| fn search_initialization<'tcx>(cx: &LateContext<'tcx>, vec_alloc: VecAllocation<'tcx>, parent_node: HirId) { |
| let enclosing_body = get_enclosing_block(cx, parent_node); |
| |
| if enclosing_body.is_none() { |
| return; |
| } |
| |
| let mut v = VectorInitializationVisitor { |
| cx, |
| vec_alloc, |
| slow_expression: None, |
| initialization_found: false, |
| }; |
| |
| v.visit_block(enclosing_body.unwrap()); |
| |
| if let Some(ref allocation_expr) = v.slow_expression { |
| Self::lint_initialization(cx, allocation_expr, &v.vec_alloc); |
| } |
| } |
| |
| fn lint_initialization<'tcx>( |
| cx: &LateContext<'tcx>, |
| initialization: &InitializationType<'tcx>, |
| vec_alloc: &VecAllocation<'_>, |
| ) { |
| match initialization { |
| InitializationType::Extend(e) | InitializationType::Resize(e) => { |
| Self::emit_lint(cx, e, vec_alloc, "slow zero-filling initialization"); |
| }, |
| }; |
| } |
| |
| fn emit_lint(cx: &LateContext<'_>, slow_fill: &Expr<'_>, vec_alloc: &VecAllocation<'_>, msg: &str) { |
| let len_expr = Sugg::hir( |
| cx, |
| match vec_alloc.size_expr { |
| InitializedSize::Initialized(expr) => expr, |
| InitializedSize::Uninitialized => unreachable!("size expression must be set by this point"), |
| }, |
| "len", |
| ); |
| |
| span_lint_and_then(cx, SLOW_VECTOR_INITIALIZATION, slow_fill.span, msg, |diag| { |
| diag.span_suggestion( |
| vec_alloc.allocation_expr.span.source_callsite(), |
| "consider replacing this with", |
| format!("vec![0; {len_expr}]"), |
| Applicability::Unspecified, |
| ); |
| }); |
| } |
| } |
| |
| /// `VectorInitializationVisitor` searches for unsafe or slow vector initializations for the given |
| /// vector. |
| struct VectorInitializationVisitor<'a, 'tcx> { |
| cx: &'a LateContext<'tcx>, |
| |
| /// Contains the information. |
| vec_alloc: VecAllocation<'tcx>, |
| |
| /// Contains the slow initialization expression, if one was found. |
| slow_expression: Option<InitializationType<'tcx>>, |
| |
| /// `true` if the initialization of the vector has been found on the visited block. |
| initialization_found: bool, |
| } |
| |
| impl<'a, 'tcx> VectorInitializationVisitor<'a, 'tcx> { |
| /// Checks if the given expression is extending a vector with `repeat(0).take(..)` |
| fn search_slow_extend_filling(&mut self, expr: &'tcx Expr<'_>) { |
| if self.initialization_found |
| && let ExprKind::MethodCall(path, self_arg, [extend_arg], _) = expr.kind |
| && path_to_local_id(self_arg, self.vec_alloc.local_id) |
| && path.ident.name == sym!(extend) |
| && self.is_repeat_take(extend_arg) |
| { |
| self.slow_expression = Some(InitializationType::Extend(expr)); |
| } |
| } |
| |
| /// Checks if the given expression is resizing a vector with 0 |
| fn search_slow_resize_filling(&mut self, expr: &'tcx Expr<'tcx>) { |
| if self.initialization_found |
| && let ExprKind::MethodCall(path, self_arg, [len_arg, fill_arg], _) = expr.kind |
| && path_to_local_id(self_arg, self.vec_alloc.local_id) |
| && path.ident.name == sym!(resize) |
| // Check that is filled with 0 |
| && is_integer_literal(fill_arg, 0) |
| { |
| let is_matching_resize = if let InitializedSize::Initialized(size_expr) = self.vec_alloc.size_expr { |
| // If we have a size expression, check that it is equal to what's passed to `resize` |
| SpanlessEq::new(self.cx).eq_expr(len_arg, size_expr) |
| || matches!(len_arg.kind, ExprKind::MethodCall(path, ..) if path.ident.as_str() == "capacity") |
| } else { |
| self.vec_alloc.size_expr = InitializedSize::Initialized(len_arg); |
| true |
| }; |
| |
| if is_matching_resize { |
| self.slow_expression = Some(InitializationType::Resize(expr)); |
| } |
| } |
| } |
| |
| /// Returns `true` if give expression is `repeat(0).take(...)` |
| fn is_repeat_take(&mut self, expr: &'tcx Expr<'tcx>) -> bool { |
| if let ExprKind::MethodCall(take_path, recv, [len_arg, ..], _) = expr.kind |
| && take_path.ident.name == sym!(take) |
| // Check that take is applied to `repeat(0)` |
| && self.is_repeat_zero(recv) |
| { |
| if let InitializedSize::Initialized(size_expr) = self.vec_alloc.size_expr { |
| // Check that len expression is equals to `with_capacity` expression |
| return SpanlessEq::new(self.cx).eq_expr(len_arg, size_expr) |
| || matches!(len_arg.kind, ExprKind::MethodCall(path, ..) if path.ident.as_str() == "capacity"); |
| } |
| |
| self.vec_alloc.size_expr = InitializedSize::Initialized(len_arg); |
| return true; |
| } |
| |
| false |
| } |
| |
| /// Returns `true` if given expression is `repeat(0)` |
| fn is_repeat_zero(&self, expr: &Expr<'_>) -> bool { |
| if let ExprKind::Call(fn_expr, [repeat_arg]) = expr.kind |
| && is_path_diagnostic_item(self.cx, fn_expr, sym::iter_repeat) |
| && is_integer_literal(repeat_arg, 0) |
| { |
| true |
| } else { |
| false |
| } |
| } |
| } |
| |
| impl<'a, 'tcx> Visitor<'tcx> for VectorInitializationVisitor<'a, 'tcx> { |
| fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) { |
| if self.initialization_found { |
| match stmt.kind { |
| StmtKind::Expr(expr) | StmtKind::Semi(expr) => { |
| self.search_slow_extend_filling(expr); |
| self.search_slow_resize_filling(expr); |
| }, |
| _ => (), |
| } |
| |
| self.initialization_found = false; |
| } else { |
| walk_stmt(self, stmt); |
| } |
| } |
| |
| fn visit_block(&mut self, block: &'tcx Block<'_>) { |
| if self.initialization_found { |
| if let Some(s) = block.stmts.first() { |
| self.visit_stmt(s); |
| } |
| |
| self.initialization_found = false; |
| } else { |
| walk_block(self, block); |
| } |
| } |
| |
| fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { |
| // Skip all the expressions previous to the vector initialization |
| if self.vec_alloc.allocation_expr.hir_id == expr.hir_id { |
| self.initialization_found = true; |
| } |
| |
| walk_expr(self, expr); |
| } |
| } |