172 lines
5.3 KiB
Rust
172 lines
5.3 KiB
Rust
use rustc::hir::*;
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use rustc::hir::intravisit as visit;
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use rustc::hir::map::Node::{NodeExpr, NodeStmt};
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use rustc::lint::*;
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use rustc::middle::expr_use_visitor::*;
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use rustc::middle::mem_categorization::{cmt, Categorization};
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use rustc::ty::{self, Ty};
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use rustc::util::nodemap::NodeSet;
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use syntax::ast::NodeId;
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use syntax::codemap::Span;
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use utils::{span_lint, type_size};
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pub struct Pass {
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pub too_large_for_stack: u64,
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}
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/// **What it does:** Checks for usage of `Box<T>` where an unboxed `T` would
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/// work fine.
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///
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/// **Why is this bad?** This is an unnecessary allocation, and bad for
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/// performance. It is only necessary to allocate if you wish to move the box
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/// into something.
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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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/// fn main() {
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/// let x = Box::new(1);
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/// foo(*x);
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/// println!("{}", *x);
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/// }
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/// ```
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declare_lint! {
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pub BOXED_LOCAL,
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Warn,
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"using `Box<T>` where unnecessary"
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}
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fn is_non_trait_box(ty: Ty) -> bool {
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ty.is_box() && !ty.boxed_ty().is_trait()
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}
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struct EscapeDelegate<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, 'tcx>,
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set: NodeSet,
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too_large_for_stack: u64,
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}
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(BOXED_LOCAL)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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fn check_fn(
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&mut self,
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cx: &LateContext<'a, 'tcx>,
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_: visit::FnKind<'tcx>,
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_: &'tcx FnDecl,
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body: &'tcx Body,
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_: Span,
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node_id: NodeId
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) {
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let fn_def_id = cx.tcx.hir.local_def_id(node_id);
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let mut v = EscapeDelegate {
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cx: cx,
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set: NodeSet(),
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too_large_for_stack: self.too_large_for_stack,
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};
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let region_maps = &cx.tcx.region_maps(fn_def_id);
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ExprUseVisitor::new(&mut v, cx.tcx, cx.param_env, region_maps, cx.tables).consume_body(body);
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for node in v.set {
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span_lint(cx,
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BOXED_LOCAL,
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cx.tcx.hir.span(node),
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"local variable doesn't need to be boxed here");
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}
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}
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}
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impl<'a, 'tcx> Delegate<'tcx> for EscapeDelegate<'a, 'tcx> {
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fn consume(&mut self, _: NodeId, _: Span, cmt: cmt<'tcx>, mode: ConsumeMode) {
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if let Categorization::Local(lid) = cmt.cat {
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if let Move(DirectRefMove) = mode {
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// moved out or in. clearly can't be localized
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self.set.remove(&lid);
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}
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}
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}
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fn matched_pat(&mut self, _: &Pat, _: cmt<'tcx>, _: MatchMode) {}
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fn consume_pat(&mut self, consume_pat: &Pat, cmt: cmt<'tcx>, _: ConsumeMode) {
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let map = &self.cx.tcx.hir;
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if map.is_argument(consume_pat.id) {
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// Skip closure arguments
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if let Some(NodeExpr(..)) = map.find(map.get_parent_node(consume_pat.id)) {
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return;
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}
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if is_non_trait_box(cmt.ty) && !self.is_large_box(cmt.ty) {
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self.set.insert(consume_pat.id);
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}
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return;
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}
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if let Categorization::Rvalue(..) = cmt.cat {
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if let Some(NodeStmt(st)) = map.find(map.get_parent_node(cmt.id)) {
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if let StmtDecl(ref decl, _) = st.node {
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if let DeclLocal(ref loc) = decl.node {
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if let Some(ref ex) = loc.init {
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if let ExprBox(..) = ex.node {
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if is_non_trait_box(cmt.ty) && !self.is_large_box(cmt.ty) {
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// let x = box (...)
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self.set.insert(consume_pat.id);
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}
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// TODO Box::new
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// TODO vec![]
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// TODO "foo".to_owned() and friends
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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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if let Categorization::Local(lid) = cmt.cat {
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if self.set.contains(&lid) {
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// let y = x where x is known
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// remove x, insert y
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self.set.insert(consume_pat.id);
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self.set.remove(&lid);
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}
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}
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}
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fn borrow(&mut self, _: NodeId, _: Span, cmt: cmt<'tcx>, _: ty::Region, _: ty::BorrowKind, loan_cause: LoanCause) {
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if let Categorization::Local(lid) = cmt.cat {
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match loan_cause {
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// x.foo()
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// Used without autodereffing (i.e. x.clone())
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LoanCause::AutoRef |
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// &x
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// foo(&x) where no extra autoreffing is happening
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LoanCause::AddrOf |
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// `match x` can move
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LoanCause::MatchDiscriminant => {
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self.set.remove(&lid);
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}
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// do nothing for matches, etc. These can't escape
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_ => {}
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}
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}
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}
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fn decl_without_init(&mut self, _: NodeId, _: Span) {}
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fn mutate(&mut self, _: NodeId, _: Span, _: cmt<'tcx>, _: MutateMode) {}
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}
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impl<'a, 'tcx> EscapeDelegate<'a, 'tcx> {
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fn is_large_box(&self, ty: Ty<'tcx>) -> bool {
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// Large types need to be boxed to avoid stack
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// overflows.
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if ty.is_box() {
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type_size(self.cx, ty.boxed_ty()).unwrap_or(0) > self.too_large_for_stack
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} else {
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false
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}
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}
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}
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