Add slow zero-filled vector initialization lint
Add lint to detect slow zero-filled vector initialization. It detects when a vector is zero-filled with extended with `repeat(0).take(len)` or `resize(len, 0)`. This zero-fillings are usually slower than simply using `vec![0; len]`.
This commit is contained in:
Guillem Nieto
Guillem Nieto
parent
69d09fbfc6
commit
e0ccc9d9af
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@ -190,6 +190,7 @@ pub mod replace_consts;
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pub mod returns;
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pub mod serde_api;
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pub mod shadow;
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pub mod slow_vector_initialization;
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pub mod strings;
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pub mod suspicious_trait_impl;
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pub mod swap;
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@ -459,6 +460,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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reg.register_late_lint_pass(box non_copy_const::NonCopyConst);
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reg.register_late_lint_pass(box ptr_offset_with_cast::Pass);
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reg.register_late_lint_pass(box redundant_clone::RedundantClone);
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reg.register_late_lint_pass(box slow_vector_initialization::Pass);
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reg.register_lint_group("clippy::restriction", Some("clippy_restriction"), vec![
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arithmetic::FLOAT_ARITHMETIC,
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@ -980,6 +982,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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methods::SINGLE_CHAR_PATTERN,
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misc::CMP_OWNED,
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mutex_atomic::MUTEX_ATOMIC,
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slow_vector_initialization::SLOW_VECTOR_INITIALIZATION,
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trivially_copy_pass_by_ref::TRIVIALLY_COPY_PASS_BY_REF,
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types::BOX_VEC,
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vec::USELESS_VEC,
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@ -0,0 +1,304 @@
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// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use crate::rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
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use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use crate::rustc::{declare_tool_lint, lint_array};
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use crate::rustc::hir::*;
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use if_chain::if_chain;
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use crate::syntax_pos::symbol::Symbol;
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use crate::syntax::ast::{LitKind, NodeId};
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use crate::syntax::source_map::Span;
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use crate::utils::{match_qpath, span_lint_and_then, SpanlessEq};
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use crate::utils::get_enclosing_block;
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use crate::rustc_errors::{Applicability};
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/// **What it does:** Checks slow zero-filled vector initialization
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///
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/// **Why is this bad?** This structures are non-idiomatic and less efficient than simply using
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/// `vec![len; 0]`.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// let mut vec1 = Vec::with_capacity(len);
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/// vec1.resize(len, 0);
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///
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/// let mut vec2 = Vec::with_capacity(len);
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/// vec2.extend(repeat(0).take(len))
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/// ```
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declare_clippy_lint! {
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pub SLOW_VECTOR_INITIALIZATION,
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perf,
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"slow or unsafe vector initialization"
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}
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#[derive(Copy, Clone, Default)]
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pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(SLOW_VECTOR_INITIALIZATION)
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}
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}
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/// VecInitialization contains data regarding a vector initialized with `with_capacity` and then
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/// assigned to a variable. For example, `let mut vec = Vec::with_capacity(0)` or
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/// `vec = Vec::with_capacity(0)`
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struct VecInitialization<'tcx> {
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/// Symbol of the local variable name
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variable_name: Symbol,
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/// Reference to the expression which initializes the vector
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initialization_expr: &'tcx Expr,
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/// Reference to the expression used as argument on `with_capacity` call. This is used
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/// to only match slow zero-filling idioms of the same length than vector initialization.
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len_expr: &'tcx Expr,
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}
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/// Type of slow initialization
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enum InitializationType<'tcx> {
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/// Extend is a slow initialization with the form `vec.extend(repeat(0).take(..))`
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Extend(&'tcx Expr),
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/// Resize is a slow initialization with the form `vec.resize(.., 0)`
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Resize(&'tcx Expr),
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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// Matches initialization on reassignements. For example: `vec = Vec::with_capacity(100)`
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if_chain! {
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if let ExprKind::Assign(ref left, ref right) = expr.node;
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// Extract variable name
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if let ExprKind::Path(QPath::Resolved(_, ref path)) = left.node;
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if let Some(variable_name) = path.segments.get(0);
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// Extract len argument
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if let Some(ref len_arg) = Pass::is_vec_with_capacity(right);
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then {
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let vi = VecInitialization {
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variable_name: variable_name.ident.name,
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initialization_expr: right,
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len_expr: len_arg,
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};
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Pass::search_slow_zero_filling(cx, vi, expr.id, expr.span);
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}
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}
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}
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fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
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// Matches statements which initializes vectors. For example: `let mut vec = Vec::with_capacity(10)`
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if_chain! {
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if let StmtKind::Decl(ref decl, _) = stmt.node;
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if let DeclKind::Local(ref local) = decl.node;
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if let PatKind::Binding(BindingAnnotation::Mutable, _, variable_name, None) = local.pat.node;
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if let Some(ref init) = local.init;
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if let Some(ref len_arg) = Pass::is_vec_with_capacity(init);
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then {
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let vi = VecInitialization {
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variable_name: variable_name.name,
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initialization_expr: init,
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len_expr: len_arg,
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};
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Pass::search_slow_zero_filling(cx, vi, stmt.node.id(), stmt.span);
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}
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}
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}
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}
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impl Pass {
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/// Checks if the given expression is `Vec::with_capacity(..)`. It will return the expression
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/// of the first argument of `with_capacity` call if it matches or `None` if it does not.
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fn is_vec_with_capacity(expr: &Expr) -> Option<&Expr> {
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if_chain! {
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if let ExprKind::Call(ref func, ref args) = expr.node;
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if let ExprKind::Path(ref path) = func.node;
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if match_qpath(path, &["Vec", "with_capacity"]);
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if args.len() == 1;
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then {
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return Some(&args[0]);
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}
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}
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None
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}
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/// Search for slow zero filling vector initialization for the given vector
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fn search_slow_zero_filling<'tcx>(
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cx: &LateContext<'_, 'tcx>,
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vec_initialization: VecInitialization<'tcx>,
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parent_node: NodeId,
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parent_span: Span
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) {
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let enclosing_body = get_enclosing_block(cx, parent_node);
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if enclosing_body.is_none() {
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return;
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}
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let mut v = SlowInitializationVisitor {
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cx,
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vec_ini: vec_initialization,
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slow_expression: None,
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initialization_found: false,
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};
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v.visit_block(enclosing_body.unwrap());
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if let Some(ref repeat_expr) = v.slow_expression {
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span_lint_and_then(
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cx,
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SLOW_VECTOR_INITIALIZATION,
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parent_span,
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"detected slow zero-filling initialization",
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|db| {
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db.span_suggestion_with_applicability(v.vec_ini.initialization_expr.span, "consider replacing with", "vec![0; ..]".to_string(), Applicability::Unspecified);
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match repeat_expr {
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InitializationType::Extend(e) => {
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db.span_note(e.span, "extended here with .. 0");
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},
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InitializationType::Resize(e) => {
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db.span_note(e.span, "resize here with .. 0");
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}
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}
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}
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);
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}
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}
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}
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/// SlowInitializationVisitor searches for slow zero filling vector initialization, for the given
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/// vector.
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struct SlowInitializationVisitor<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, 'tcx>,
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/// Contains the information
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vec_ini: VecInitialization<'tcx>,
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/// Contains, if found, the slow initialization expression
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slow_expression: Option<InitializationType<'tcx>>,
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/// true if the initialization of the vector has been found on the visited block
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initialization_found: bool,
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}
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impl<'a, 'tcx> SlowInitializationVisitor<'a, 'tcx> {
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/// Checks if the given expression is extending a vector with `repeat(0).take(..)`
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fn search_slow_extend_filling(&mut self, expr: &'tcx Expr) {
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if_chain! {
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if self.initialization_found;
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if let ExprKind::MethodCall(ref path, _, ref args) = expr.node;
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if let ExprKind::Path(ref qpath_subj) = args[0].node;
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if match_qpath(&qpath_subj, &[&self.vec_ini.variable_name.to_string()]);
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if path.ident.name == "extend";
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if let Some(ref extend_arg) = args.get(1);
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if self.is_repeat_take(extend_arg);
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then {
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self.slow_expression = Some(InitializationType::Extend(expr));
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}
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}
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}
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/// Checks if the given expression is resizing a vector with 0
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fn search_slow_resize_filling(&mut self, expr: &'tcx Expr) {
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if_chain! {
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if self.initialization_found;
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if let ExprKind::MethodCall(ref path, _, ref args) = expr.node;
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if let ExprKind::Path(ref qpath_subj) = args[0].node;
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if match_qpath(&qpath_subj, &[&self.vec_ini.variable_name.to_string()]);
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if path.ident.name == "resize";
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if let (Some(ref len_arg), Some(fill_arg)) = (args.get(1), args.get(2));
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// Check that is filled with 0
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if let ExprKind::Lit(ref lit) = fill_arg.node;
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if let LitKind::Int(0, _) = lit.node;
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// Check that len expression is equals to `with_capacity` expression
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if SpanlessEq::new(self.cx).eq_expr(len_arg, self.vec_ini.len_expr);
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then {
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self.slow_expression = Some(InitializationType::Resize(expr));
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}
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}
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}
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/// Returns `true` if give expression is `repeat(0).take(...)`
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fn is_repeat_take(&self, expr: &Expr) -> bool {
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if_chain! {
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if let ExprKind::MethodCall(ref take_path, _, ref take_args) = expr.node;
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if take_path.ident.name == "take";
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// Check that take is applied to `repeat(0)`
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if let Some(ref repeat_expr) = take_args.get(0);
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if self.is_repeat_zero(repeat_expr);
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// Check that len expression is equals to `with_capacity` expression
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if let Some(ref len_arg) = take_args.get(1);
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if SpanlessEq::new(self.cx).eq_expr(len_arg, self.vec_ini.len_expr);
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then {
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return true;
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}
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}
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false
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}
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/// Returns `true` if given expression is `repeat(0)`
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fn is_repeat_zero(&self, expr: &Expr) -> bool {
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if_chain! {
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if let ExprKind::Call(ref fn_expr, ref repeat_args) = expr.node;
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if let ExprKind::Path(ref qpath_repeat) = fn_expr.node;
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if match_qpath(&qpath_repeat, &["repeat"]);
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if let Some(ref repeat_arg) = repeat_args.get(0);
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if let ExprKind::Lit(ref lit) = repeat_arg.node;
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if let LitKind::Int(0, _) = lit.node;
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then {
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return true
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}
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}
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false
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}
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}
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impl<'a, 'tcx> Visitor<'tcx> for SlowInitializationVisitor<'a, 'tcx> {
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fn visit_expr(&mut self, expr: &'tcx Expr) {
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// Stop the search if we already found a slow zero-filling initialization
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if self.slow_expression.is_some() {
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return
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}
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// Skip all the expressions previous to the vector initialization
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if self.vec_ini.initialization_expr.id == expr.id {
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self.initialization_found = true;
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}
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self.search_slow_extend_filling(expr);
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self.search_slow_resize_filling(expr);
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walk_expr(self, expr);
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}
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fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
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NestedVisitorMap::None
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}
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}
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@ -0,0 +1,63 @@
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// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use std::iter::repeat;
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fn main() {
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resize_vector();
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extend_vector();
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mixed_extend_resize_vector();
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}
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fn extend_vector() {
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// Extend with constant expression
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let len = 300;
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let mut vec1 = Vec::with_capacity(len);
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vec1.extend(repeat(0).take(len));
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// Extend with len expression
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let mut vec2 = Vec::with_capacity(len - 10);
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vec2.extend(repeat(0).take(len - 10));
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// Extend with mismatching expression should not be warned
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let mut vec3 = Vec::with_capacity(24322);
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vec3.extend(repeat(0).take(2));
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}
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fn mixed_extend_resize_vector() {
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// Mismatching len
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let mut mismatching_len = Vec::with_capacity(30);
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// Slow initialization
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let mut resized_vec = Vec::with_capacity(30);
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let mut extend_vec = Vec::with_capacity(30);
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resized_vec.resize(30, 0);
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mismatching_len.extend(repeat(0).take(40));
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extend_vec.extend(repeat(0).take(30));
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}
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fn resize_vector() {
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// Resize with constant expression
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let len = 300;
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let mut vec1 = Vec::with_capacity(len);
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vec1.resize(len, 0);
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// Resize mismatch len
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let mut vec2 = Vec::with_capacity(200);
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vec2.resize(10, 0);
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// Resize with len expression
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let mut vec3 = Vec::with_capacity(len - 10);
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vec3.resize(len - 10, 0);
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// Reinitialization should be warned
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vec1 = Vec::with_capacity(10);
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vec1.resize(10, 0);
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}
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@ -0,0 +1,101 @@
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error: detected slow zero-filling initialization
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--> $DIR/slow_vector_initialization.rs:21:5
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21 | let mut vec1 = Vec::with_capacity(len);
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| ^^^^^^^^^^^^^^^-----------------------^
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| |
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| help: consider replacing with: `vec![0; ..]`
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|
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= note: `-D clippy::slow-vector-initialization` implied by `-D warnings`
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note: extended here with .. 0
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--> $DIR/slow_vector_initialization.rs:22:5
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22 | vec1.extend(repeat(0).take(len));
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: detected slow zero-filling initialization
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--> $DIR/slow_vector_initialization.rs:25:5
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|
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25 | let mut vec2 = Vec::with_capacity(len - 10);
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| ^^^^^^^^^^^^^^^----------------------------^
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| |
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| help: consider replacing with: `vec![0; ..]`
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|
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note: extended here with .. 0
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--> $DIR/slow_vector_initialization.rs:26:5
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26 | vec2.extend(repeat(0).take(len - 10));
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: detected slow zero-filling initialization
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--> $DIR/slow_vector_initialization.rs:38:5
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|
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38 | let mut resized_vec = Vec::with_capacity(30);
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| ^^^^^^^^^^^^^^^^^^^^^^----------------------^
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| |
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| help: consider replacing with: `vec![0; ..]`
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|
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note: resize here with .. 0
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--> $DIR/slow_vector_initialization.rs:41:5
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41 | resized_vec.resize(30, 0);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^
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error: detected slow zero-filling initialization
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--> $DIR/slow_vector_initialization.rs:39:5
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|
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39 | let mut extend_vec = Vec::with_capacity(30);
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| ^^^^^^^^^^^^^^^^^^^^^----------------------^
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| |
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| help: consider replacing with: `vec![0; ..]`
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|
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note: extended here with .. 0
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--> $DIR/slow_vector_initialization.rs:43:5
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|
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43 | extend_vec.extend(repeat(0).take(30));
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
error: detected slow zero-filling initialization
|
||||
--> $DIR/slow_vector_initialization.rs:49:5
|
||||
|
|
||||
49 | let mut vec1 = Vec::with_capacity(len);
|
||||
| ^^^^^^^^^^^^^^^-----------------------^
|
||||
| |
|
||||
| help: consider replacing with: `vec![0; ..]`
|
||||
|
|
||||
note: resize here with .. 0
|
||||
--> $DIR/slow_vector_initialization.rs:50:5
|
||||
|
|
||||
50 | vec1.resize(len, 0);
|
||||
| ^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
error: detected slow zero-filling initialization
|
||||
--> $DIR/slow_vector_initialization.rs:57:5
|
||||
|
|
||||
57 | let mut vec3 = Vec::with_capacity(len - 10);
|
||||
| ^^^^^^^^^^^^^^^----------------------------^
|
||||
| |
|
||||
| help: consider replacing with: `vec![0; ..]`
|
||||
|
|
||||
note: resize here with .. 0
|
||||
--> $DIR/slow_vector_initialization.rs:58:5
|
||||
|
|
||||
58 | vec3.resize(len - 10, 0);
|
||||
| ^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
|
||||
error: detected slow zero-filling initialization
|
||||
--> $DIR/slow_vector_initialization.rs:61:5
|
||||
|
|
||||
61 | vec1 = Vec::with_capacity(10);
|
||||
| ^^^^^^^----------------------
|
||||
| |
|
||||
| help: consider replacing with: `vec![0; ..]`
|
||||
|
|
||||
note: resize here with .. 0
|
||||
--> $DIR/slow_vector_initialization.rs:62:5
|
||||
|
|
||||
62 | vec1.resize(10, 0);
|
||||
| ^^^^^^^^^^^^^^^^^^
|
||||
|
||||
error: aborting due to 7 previous errors
|
||||
|
||||
Loading…
Reference in New Issue