327 lines
11 KiB
Rust
327 lines
11 KiB
Rust
use crate::utils::sugg::Sugg;
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use crate::utils::{get_enclosing_block, match_qpath, span_lint_and_then, SpanlessEq};
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use if_chain::if_chain;
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use rustc::hir::intravisit::{walk_block, walk_expr, walk_stmt, NestedVisitorMap, Visitor};
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use rustc::hir::*;
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use rustc::lint::{LateContext, LateLintPass, Lint, LintArray, LintPass};
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use rustc::{declare_tool_lint, lint_array};
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use rustc_errors::Applicability;
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use syntax::ast::{LitKind, NodeId};
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use syntax_pos::symbol::Symbol;
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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 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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/// `VecAllocation` contains data regarding a vector allocated 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 VecAllocation<'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 allocates the vector
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allocation_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) = Self::is_vec_with_capacity(right);
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then {
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let vi = VecAllocation {
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variable_name: variable_name.ident.name,
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allocation_expr: right,
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len_expr: len_arg,
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};
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Self::search_initialization(cx, vi, expr.id);
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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::Local(ref local) = stmt.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) = Self::is_vec_with_capacity(init);
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then {
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let vi = VecAllocation {
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variable_name: variable_name.name,
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allocation_expr: init,
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len_expr: len_arg,
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};
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Self::search_initialization(cx, vi, stmt.id);
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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 initialization for the given vector
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fn search_initialization<'tcx>(cx: &LateContext<'_, 'tcx>, vec_alloc: VecAllocation<'tcx>, parent_node: NodeId) {
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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 = VectorInitializationVisitor {
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cx,
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vec_alloc,
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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 allocation_expr) = v.slow_expression {
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Self::lint_initialization(cx, allocation_expr, &v.vec_alloc);
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}
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}
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fn lint_initialization<'tcx>(
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cx: &LateContext<'_, 'tcx>,
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initialization: &InitializationType<'tcx>,
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vec_alloc: &VecAllocation<'_>,
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) {
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match initialization {
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InitializationType::Extend(e) | InitializationType::Resize(e) => Self::emit_lint(
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cx,
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e,
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vec_alloc,
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"slow zero-filling initialization",
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SLOW_VECTOR_INITIALIZATION,
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),
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};
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}
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fn emit_lint<'tcx>(
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cx: &LateContext<'_, 'tcx>,
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slow_fill: &Expr,
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vec_alloc: &VecAllocation<'_>,
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msg: &str,
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lint: &'static Lint,
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) {
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let len_expr = Sugg::hir(cx, vec_alloc.len_expr, "len");
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span_lint_and_then(cx, lint, slow_fill.span, msg, |db| {
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db.span_suggestion_with_applicability(
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vec_alloc.allocation_expr.span,
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"consider replace allocation with",
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format!("vec![0; {}]", len_expr),
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Applicability::Unspecified,
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);
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});
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}
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}
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/// `VectorInitializationVisitor` searches for unsafe or slow vector initializations for the given
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/// vector.
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struct VectorInitializationVisitor<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, 'tcx>,
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/// Contains the information
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vec_alloc: VecAllocation<'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> VectorInitializationVisitor<'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_alloc.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_alloc.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_alloc.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_alloc.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 VectorInitializationVisitor<'a, 'tcx> {
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fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
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if self.initialization_found {
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match stmt.node {
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StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => {
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self.search_slow_extend_filling(expr);
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self.search_slow_resize_filling(expr);
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},
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_ => (),
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}
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self.initialization_found = false;
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} else {
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walk_stmt(self, stmt);
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}
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}
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fn visit_block(&mut self, block: &'tcx Block) {
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if self.initialization_found {
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if let Some(ref s) = block.stmts.get(0) {
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self.visit_stmt(s)
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}
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self.initialization_found = false;
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} else {
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walk_block(self, block);
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}
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}
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fn visit_expr(&mut self, expr: &'tcx Expr) {
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// Skip all the expressions previous to the vector initialization
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if self.vec_alloc.allocation_expr.id == expr.id {
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self.initialization_found = true;
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}
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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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