594 lines
20 KiB
Rust
594 lines
20 KiB
Rust
use crate::utils::{
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has_drop, is_copy, match_def_path, match_type, paths, snippet_opt, span_lint_hir, span_lint_hir_and_then,
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walk_ptrs_ty_depth,
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};
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use if_chain::if_chain;
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use matches::matches;
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use rustc::hir::intravisit::FnKind;
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use rustc::hir::{def_id, Body, FnDecl, HirId};
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::mir::{
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self, traversal,
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visit::{MutatingUseContext, PlaceContext, Visitor as _},
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};
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use rustc::ty::{self, fold::TypeVisitor, Ty};
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use rustc::{declare_lint_pass, declare_tool_lint};
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use rustc_data_structures::{
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bit_set::{BitSet, HybridBitSet},
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fx::FxHashMap,
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transitive_relation::TransitiveRelation,
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};
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use rustc_errors::Applicability;
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use rustc_mir::dataflow::{
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do_dataflow, BitDenotation, BottomValue, DataflowResults, DataflowResultsCursor, DebugFormatted, GenKillSet,
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};
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use std::convert::TryFrom;
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use syntax::source_map::{BytePos, Span};
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macro_rules! unwrap_or_continue {
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($x:expr) => {
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match $x {
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Some(x) => x,
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None => continue,
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}
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};
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}
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declare_clippy_lint! {
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/// **What it does:** Checks for a redudant `clone()` (and its relatives) which clones an owned
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/// value that is going to be dropped without further use.
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///
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/// **Why is this bad?** It is not always possible for the compiler to eliminate useless
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/// allocations and deallocations generated by redundant `clone()`s.
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///
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/// **Known problems:**
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///
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/// False-negatives: analysis performed by this lint is conservative and limited.
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///
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/// **Example:**
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/// ```rust
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/// # use std::path::Path;
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/// # #[derive(Clone)]
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/// # struct Foo;
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/// # impl Foo {
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/// # fn new() -> Self { Foo {} }
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/// # }
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/// # fn call(x: Foo) {}
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/// {
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/// let x = Foo::new();
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/// call(x.clone());
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/// call(x.clone()); // this can just pass `x`
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/// }
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///
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/// ["lorem", "ipsum"].join(" ").to_string();
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///
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/// Path::new("/a/b").join("c").to_path_buf();
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/// ```
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pub REDUNDANT_CLONE,
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perf,
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"`clone()` of an owned value that is going to be dropped immediately"
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}
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declare_lint_pass!(RedundantClone => [REDUNDANT_CLONE]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantClone {
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#[allow(clippy::too_many_lines)]
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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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_: FnKind<'tcx>,
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_: &'tcx FnDecl,
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body: &'tcx Body,
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_: Span,
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_: HirId,
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) {
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let def_id = cx.tcx.hir().body_owner_def_id(body.id());
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let mir = cx.tcx.optimized_mir(def_id);
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let dead_unwinds = BitSet::new_empty(mir.basic_blocks().len());
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let maybe_storage_live_result = do_dataflow(
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cx.tcx,
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mir,
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def_id,
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&[],
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&dead_unwinds,
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MaybeStorageLive::new(mir),
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|bd, p| DebugFormatted::new(&bd.body.local_decls[p]),
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);
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let mut possible_borrower = {
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let mut vis = PossibleBorrowerVisitor::new(cx, mir);
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vis.visit_body(mir);
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vis.into_map(cx, maybe_storage_live_result)
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};
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for (bb, bbdata) in mir.basic_blocks().iter_enumerated() {
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let terminator = bbdata.terminator();
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if terminator.source_info.span.from_expansion() {
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continue;
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}
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// Give up on loops
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if terminator.successors().any(|s| *s == bb) {
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continue;
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}
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let (fn_def_id, arg, arg_ty, _) = unwrap_or_continue!(is_call_with_ref_arg(cx, mir, &terminator.kind));
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let from_borrow = match_def_path(cx, fn_def_id, &paths::CLONE_TRAIT_METHOD)
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|| match_def_path(cx, fn_def_id, &paths::TO_OWNED_METHOD)
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|| (match_def_path(cx, fn_def_id, &paths::TO_STRING_METHOD) && match_type(cx, arg_ty, &paths::STRING));
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let from_deref = !from_borrow
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&& (match_def_path(cx, fn_def_id, &paths::PATH_TO_PATH_BUF)
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|| match_def_path(cx, fn_def_id, &paths::OS_STR_TO_OS_STRING));
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if !from_borrow && !from_deref {
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continue;
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}
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// _1 in MIR `{ _2 = &_1; clone(move _2); }` or `{ _2 = _1; to_path_buf(_2); } (from_deref)
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// In case of `from_deref`, `arg` is already a reference since it is `deref`ed in the previous
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// block.
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let (cloned, cannot_move_out) = unwrap_or_continue!(find_stmt_assigns_to(cx, mir, arg, from_borrow, bb));
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let loc = mir::Location {
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block: bb,
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statement_index: bbdata.statements.len(),
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};
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if from_borrow
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&& (cannot_move_out || possible_borrower.only_borrowers(&[arg][..], cloned, loc) != Some(true))
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{
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continue;
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}
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// _1 in MIR `{ _2 = &_1; _3 = deref(move _2); } -> { _4 = _3; to_path_buf(move _4); }`
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let referent = if from_deref {
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let ps = mir.predecessors_for(bb);
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if ps.len() != 1 {
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continue;
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}
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let pred_terminator = mir[ps[0]].terminator();
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let pred_arg = if_chain! {
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if let Some((pred_fn_def_id, pred_arg, pred_arg_ty, Some(res))) =
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is_call_with_ref_arg(cx, mir, &pred_terminator.kind);
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if res.base == mir::PlaceBase::Local(cloned);
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if match_def_path(cx, pred_fn_def_id, &paths::DEREF_TRAIT_METHOD);
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if match_type(cx, pred_arg_ty, &paths::PATH_BUF)
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|| match_type(cx, pred_arg_ty, &paths::OS_STRING);
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then {
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pred_arg
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} else {
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continue;
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}
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};
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let (local, cannot_move_out) =
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unwrap_or_continue!(find_stmt_assigns_to(cx, mir, pred_arg, true, ps[0]));
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let loc = mir::Location {
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block: bb,
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statement_index: mir.basic_blocks()[bb].statements.len(),
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};
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if cannot_move_out || possible_borrower.only_borrowers(&[arg, cloned][..], local, loc) != Some(true) {
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continue;
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}
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local
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} else {
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cloned
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};
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let used_later = traversal::ReversePostorder::new(&mir, bb).skip(1).any(|(tbb, tdata)| {
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// Give up on loops
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if tdata.terminator().successors().any(|s| *s == bb) {
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return true;
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}
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let mut vis = LocalUseVisitor {
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local: referent,
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used_other_than_drop: false,
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};
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vis.visit_basic_block_data(tbb, tdata);
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vis.used_other_than_drop
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});
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if !used_later {
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let span = terminator.source_info.span;
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let node = if let mir::ClearCrossCrate::Set(scope_local_data) = &mir.source_scope_local_data {
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scope_local_data[terminator.source_info.scope].lint_root
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} else {
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unreachable!()
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};
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if_chain! {
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if let Some(snip) = snippet_opt(cx, span);
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if let Some(dot) = snip.rfind('.');
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then {
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let sugg_span = span.with_lo(
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span.lo() + BytePos(u32::try_from(dot).unwrap())
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);
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let mut app = Applicability::MaybeIncorrect;
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let mut call_snip = &snip[dot + 1..];
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if call_snip.ends_with("()") {
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call_snip = call_snip[..call_snip.len()-2].trim();
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if call_snip.as_bytes().iter().all(|b| b.is_ascii_alphabetic() || *b == b'_') {
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app = Applicability::MachineApplicable;
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}
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}
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span_lint_hir_and_then(cx, REDUNDANT_CLONE, node, sugg_span, "redundant clone", |db| {
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db.span_suggestion(
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sugg_span,
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"remove this",
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String::new(),
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app,
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);
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db.span_note(
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span.with_hi(span.lo() + BytePos(u32::try_from(dot).unwrap())),
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"this value is dropped without further use",
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);
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});
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} else {
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span_lint_hir(cx, REDUNDANT_CLONE, node, span, "redundant clone");
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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 `kind` is `y = func(x: &T)` where `T: !Copy`, returns `(DefId of func, x, T, y)`.
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fn is_call_with_ref_arg<'tcx>(
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cx: &LateContext<'_, 'tcx>,
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mir: &'tcx mir::Body<'tcx>,
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kind: &'tcx mir::TerminatorKind<'tcx>,
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) -> Option<(def_id::DefId, mir::Local, Ty<'tcx>, Option<&'tcx mir::Place<'tcx>>)> {
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if_chain! {
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if let mir::TerminatorKind::Call { func, args, destination, .. } = kind;
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if args.len() == 1;
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if let mir::Operand::Move(mir::Place { base: mir::PlaceBase::Local(local), .. }) = &args[0];
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if let ty::FnDef(def_id, _) = func.ty(&*mir, cx.tcx).kind;
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if let (inner_ty, 1) = walk_ptrs_ty_depth(args[0].ty(&*mir, cx.tcx));
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if !is_copy(cx, inner_ty);
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then {
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Some((def_id, *local, inner_ty, destination.as_ref().map(|(dest, _)| dest)))
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} else {
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None
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}
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}
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}
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type CannotMoveOut = bool;
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/// Finds the first `to = (&)from`, and returns
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/// ``Some((from, whether `from` cannot be moved out))``.
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fn find_stmt_assigns_to<'tcx>(
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cx: &LateContext<'_, 'tcx>,
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mir: &mir::Body<'tcx>,
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to_local: mir::Local,
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by_ref: bool,
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bb: mir::BasicBlock,
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) -> Option<(mir::Local, CannotMoveOut)> {
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let rvalue = mir.basic_blocks()[bb].statements.iter().rev().find_map(|stmt| {
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if let mir::StatementKind::Assign(box (
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mir::Place {
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base: mir::PlaceBase::Local(local),
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..
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},
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v,
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)) = &stmt.kind
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{
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return if *local == to_local { Some(v) } else { None };
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}
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None
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})?;
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match (by_ref, &*rvalue) {
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(true, mir::Rvalue::Ref(_, _, place)) | (false, mir::Rvalue::Use(mir::Operand::Copy(place))) => {
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base_local_and_movability(cx, mir, place)
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},
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_ => None,
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}
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}
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/// Extracts and returns the undermost base `Local` of given `place`. Returns `place` itself
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/// if it is already a `Local`.
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///
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/// Also reports whether given `place` cannot be moved out.
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fn base_local_and_movability<'tcx>(
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cx: &LateContext<'_, 'tcx>,
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mir: &mir::Body<'tcx>,
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place: &mir::Place<'tcx>,
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) -> Option<(mir::Local, CannotMoveOut)> {
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use rustc::mir::PlaceRef;
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// Dereference. You cannot move things out from a borrowed value.
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let mut deref = false;
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// Accessing a field of an ADT that has `Drop`. Moving the field out will cause E0509.
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let mut field = false;
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let PlaceRef {
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base: place_base,
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mut projection,
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} = place.as_ref();
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if let mir::PlaceBase::Local(local) = place_base {
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while let [base @ .., elem] = projection {
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projection = base;
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deref |= matches!(elem, mir::ProjectionElem::Deref);
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field |= matches!(elem, mir::ProjectionElem::Field(..))
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&& has_drop(
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cx,
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mir::Place::ty_from(place_base, projection, &mir.local_decls, cx.tcx).ty,
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);
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}
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Some((*local, deref || field))
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} else {
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None
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}
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}
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struct LocalUseVisitor {
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local: mir::Local,
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used_other_than_drop: bool,
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}
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impl<'tcx> mir::visit::Visitor<'tcx> for LocalUseVisitor {
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fn visit_basic_block_data(&mut self, block: mir::BasicBlock, data: &mir::BasicBlockData<'tcx>) {
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let statements = &data.statements;
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for (statement_index, statement) in statements.iter().enumerate() {
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self.visit_statement(statement, mir::Location { block, statement_index });
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// Once flagged, skip remaining statements
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if self.used_other_than_drop {
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return;
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}
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}
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self.visit_terminator(
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data.terminator(),
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mir::Location {
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block,
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statement_index: statements.len(),
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},
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);
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}
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fn visit_local(&mut self, local: &mir::Local, ctx: PlaceContext, _: mir::Location) {
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match ctx {
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PlaceContext::MutatingUse(MutatingUseContext::Drop) | PlaceContext::NonUse(_) => return,
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_ => {},
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}
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if *local == self.local {
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self.used_other_than_drop = true;
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}
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}
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}
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#[derive(Copy, Clone)]
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struct MaybeStorageLive<'a, 'tcx> {
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body: &'a mir::Body<'tcx>,
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}
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impl<'a, 'tcx> MaybeStorageLive<'a, 'tcx> {
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fn new(body: &'a mir::Body<'tcx>) -> Self {
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MaybeStorageLive { body }
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}
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}
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impl<'a, 'tcx> BitDenotation<'tcx> for MaybeStorageLive<'a, 'tcx> {
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type Idx = mir::Local;
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fn name() -> &'static str {
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"maybe_storage_live"
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}
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fn bits_per_block(&self) -> usize {
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self.body.local_decls.len()
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}
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fn start_block_effect(&self, on_entry: &mut BitSet<mir::Local>) {
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for arg in self.body.args_iter() {
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on_entry.insert(arg);
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}
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}
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fn statement_effect(&self, trans: &mut GenKillSet<mir::Local>, loc: mir::Location) {
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let stmt = &self.body[loc.block].statements[loc.statement_index];
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match stmt.kind {
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mir::StatementKind::StorageLive(l) => trans.gen(l),
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mir::StatementKind::StorageDead(l) => trans.kill(l),
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_ => (),
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}
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}
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fn terminator_effect(&self, _trans: &mut GenKillSet<mir::Local>, _loc: mir::Location) {}
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fn propagate_call_return(
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&self,
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_in_out: &mut BitSet<mir::Local>,
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_call_bb: mir::BasicBlock,
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_dest_bb: mir::BasicBlock,
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_dest_place: &mir::Place<'tcx>,
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) {
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// Nothing to do when a call returns successfully
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}
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}
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impl<'a, 'tcx> BottomValue for MaybeStorageLive<'a, 'tcx> {
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/// bottom = dead
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const BOTTOM_VALUE: bool = false;
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}
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struct PossibleBorrowerVisitor<'a, 'tcx> {
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possible_borrower: TransitiveRelation<mir::Local>,
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body: &'a mir::Body<'tcx>,
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cx: &'a LateContext<'a, 'tcx>,
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}
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impl<'a, 'tcx> PossibleBorrowerVisitor<'a, 'tcx> {
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fn new(cx: &'a LateContext<'a, 'tcx>, body: &'a mir::Body<'tcx>) -> Self {
|
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Self {
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possible_borrower: TransitiveRelation::default(),
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cx,
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body,
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}
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}
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fn into_map(
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self,
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cx: &LateContext<'a, 'tcx>,
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maybe_live: DataflowResults<'tcx, MaybeStorageLive<'a, 'tcx>>,
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) -> PossibleBorrower<'a, 'tcx> {
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let mut map = FxHashMap::default();
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for row in (1..self.body.local_decls.len()).map(mir::Local::from_usize) {
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if is_copy(cx, self.body.local_decls[row].ty) {
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continue;
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}
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let borrowers = self.possible_borrower.reachable_from(&row);
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if !borrowers.is_empty() {
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let mut bs = HybridBitSet::new_empty(self.body.local_decls.len());
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for &c in borrowers {
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if c != mir::Local::from_usize(0) {
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bs.insert(c);
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}
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}
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if !bs.is_empty() {
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map.insert(row, bs);
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}
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}
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}
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let bs = BitSet::new_empty(self.body.local_decls.len());
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PossibleBorrower {
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map,
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maybe_live: DataflowResultsCursor::new(maybe_live, self.body),
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bitset: (bs.clone(), bs),
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}
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}
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}
|
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impl<'a, 'tcx> mir::visit::Visitor<'tcx> for PossibleBorrowerVisitor<'a, 'tcx> {
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fn visit_assign(&mut self, place: &mir::Place<'tcx>, rvalue: &mir::Rvalue<'_>, _location: mir::Location) {
|
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if let mir::PlaceBase::Local(lhs) = place.base {
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match rvalue {
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mir::Rvalue::Ref(_, _, borrowed) => {
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if let mir::PlaceBase::Local(borrowed_local) = borrowed.base {
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self.possible_borrower.add(borrowed_local, lhs);
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}
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},
|
|
other => {
|
|
if !ContainsRegion.visit_ty(place.ty(&self.body.local_decls, self.cx.tcx).ty) {
|
|
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:
|
|
Some((
|
|
mir::Place {
|
|
base: mir::PlaceBase::Local(dest),
|
|
..
|
|
},
|
|
_,
|
|
)),
|
|
..
|
|
} = &terminator.kind
|
|
{
|
|
// If the call returns something with some lifetime,
|
|
// let's conservatively assume the returned value contains lifetime of all the arguments.
|
|
let mut cr = ContainsRegion;
|
|
if !cr.visit_ty(&self.body.local_decls[*dest].ty) {
|
|
return;
|
|
}
|
|
|
|
for op in args {
|
|
match op {
|
|
mir::Operand::Copy(p) | mir::Operand::Move(p) => {
|
|
if let mir::PlaceBase::Local(arg) = p.base {
|
|
self.possible_borrower.add(arg, *dest);
|
|
}
|
|
},
|
|
_ => (),
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
struct ContainsRegion;
|
|
|
|
impl TypeVisitor<'_> for ContainsRegion {
|
|
fn visit_region(&mut self, _: ty::Region<'_>) -> bool {
|
|
true
|
|
}
|
|
}
|
|
|
|
fn rvalue_locals(rvalue: &mir::Rvalue<'_>, mut visit: impl FnMut(mir::Local)) {
|
|
use rustc::mir::Rvalue::*;
|
|
|
|
let mut visit_op = |op: &mir::Operand<'_>| match op {
|
|
mir::Operand::Copy(p) | mir::Operand::Move(p) => {
|
|
if let mir::PlaceBase::Local(l) = p.base {
|
|
visit(l)
|
|
}
|
|
},
|
|
_ => (),
|
|
};
|
|
|
|
match rvalue {
|
|
Use(op) | Repeat(op, _) | Cast(_, op, _) | UnaryOp(_, op) => visit_op(op),
|
|
Aggregate(_, ops) => ops.iter().for_each(visit_op),
|
|
BinaryOp(_, lhs, rhs) | CheckedBinaryOp(_, lhs, rhs) => {
|
|
visit_op(lhs);
|
|
visit_op(rhs);
|
|
},
|
|
_ => (),
|
|
}
|
|
}
|
|
|
|
struct PossibleBorrower<'a, 'tcx> {
|
|
map: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
|
|
maybe_live:
|
|
DataflowResultsCursor<'a, 'tcx, MaybeStorageLive<'a, 'tcx>, DataflowResults<'tcx, MaybeStorageLive<'a, 'tcx>>>,
|
|
bitset: (BitSet<mir::Local>, BitSet<mir::Local>),
|
|
}
|
|
|
|
impl PossibleBorrower<'_, '_> {
|
|
fn only_borrowers<'a>(
|
|
&mut self,
|
|
borrowers: impl IntoIterator<Item = &'a mir::Local>,
|
|
borrowed: mir::Local,
|
|
at: mir::Location,
|
|
) -> Option<bool> {
|
|
self.maybe_live.seek(at);
|
|
|
|
self.bitset.0.clear();
|
|
let maybe_live = &mut self.maybe_live;
|
|
for b in self.map.get(&borrowed)?.iter().filter(move |b| maybe_live.contains(*b)) {
|
|
self.bitset.0.insert(b);
|
|
}
|
|
|
|
self.bitset.1.clear();
|
|
for b in borrowers {
|
|
self.bitset.1.insert(*b);
|
|
}
|
|
|
|
Some(self.bitset.0 == self.bitset.1)
|
|
}
|
|
}
|