Extend redundant_clone to the case that cloned value is not consumed
This commit is contained in:
Shotaro Yamada
parent
fdce47ba7d
commit
9de642190e
6 changed files with 105 additions and 62 deletions
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@ -6,7 +6,7 @@ use if_chain::if_chain;
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use matches::matches;
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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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visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor as _},
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};
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use rustc::ty::{self, fold::TypeVisitor, Ty};
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use rustc_data_structures::{fx::FxHashMap, transitive_relation::TransitiveRelation};
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@ -110,7 +110,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantClone {
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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 (fn_def_id, arg, arg_ty, clone_ret) =
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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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@ -132,8 +133,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantClone {
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statement_index: bbdata.statements.len(),
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};
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// Cloned local
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let local = if from_borrow {
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// `Local` to be cloned, and a local of `clone` call's destination
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let (local, ret_local) = if from_borrow {
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// `res = clone(arg)` can be turned into `res = move arg;`
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// if `arg` is the only borrow of `cloned` at this point.
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@ -141,7 +142,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantClone {
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continue;
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}
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cloned
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(cloned, clone_ret)
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} else {
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// `arg` is a reference as it is `.deref()`ed in the previous block.
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// Look into the predecessor block and find out the source of deref.
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@ -153,15 +154,15 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantClone {
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let pred_terminator = mir[ps[0]].terminator();
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// receiver of the `deref()` call
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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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let (pred_arg, deref_clone_ret) = if_chain! {
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if let Some((pred_fn_def_id, pred_arg, pred_arg_ty, res)) =
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is_call_with_ref_arg(cx, mir, &pred_terminator.kind);
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if res.local == cloned;
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if res == 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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(pred_arg, res)
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} else {
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continue;
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}
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@ -188,25 +189,32 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantClone {
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continue;
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}
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local
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(local, deref_clone_ret)
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};
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// `local` cannot be moved out if it is used later
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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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// 1. `local` cannot be moved out if it is used later.
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// 2. If `ret_local` is not consumed, we can remove this `clone` call anyway.
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let (used, consumed) = traversal::ReversePostorder::new(&mir, bb).skip(1).fold(
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(false, false),
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|(used, consumed), (tbb, tdata)| {
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// Short-circuit
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if (used && consumed) ||
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// Give up on loops
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tdata.terminator().successors().any(|s| *s == bb)
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{
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return (true, true);
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}
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let mut vis = LocalUseVisitor {
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local,
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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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let mut vis = LocalUseVisitor {
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used: (local, false),
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consumed: (ret_local, false),
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};
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vis.visit_basic_block_data(tbb, tdata);
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(used || vis.used.1, consumed || vis.consumed.1)
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},
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);
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if !used_later {
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if !used || !consumed {
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let span = terminator.source_info.span;
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let scope = terminator.source_info.scope;
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let node = mir.source_scopes[scope]
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@ -240,10 +248,17 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RedundantClone {
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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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if used {
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db.span_note(
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span,
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"cloned value is not consumed",
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);
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} else {
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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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});
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} else {
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span_lint_hir(cx, REDUNDANT_CLONE, node, span, "redundant clone");
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@ -259,7 +274,7 @@ 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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) -> Option<(def_id::DefId, mir::Local, Ty<'tcx>, mir::Local)> {
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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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@ -268,7 +283,7 @@ fn is_call_with_ref_arg<'tcx>(
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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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Some((def_id, *local, inner_ty, destination.as_ref().map(|(dest, _)| dest)?.as_local()?))
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} else {
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None
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}
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@ -337,8 +352,8 @@ fn base_local_and_movability<'tcx>(
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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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used: (mir::Local, bool),
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consumed: (mir::Local, bool),
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}
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impl<'tcx> mir::visit::Visitor<'tcx> for LocalUseVisitor {
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@ -346,11 +361,6 @@ impl<'tcx> mir::visit::Visitor<'tcx> for LocalUseVisitor {
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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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@ -363,13 +373,14 @@ impl<'tcx> mir::visit::Visitor<'tcx> for LocalUseVisitor {
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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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if *local == self.used.0
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&& !matches!(ctx, PlaceContext::MutatingUse(MutatingUseContext::Drop) | PlaceContext::NonUse(_))
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{
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self.used.1 = true;
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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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if *local == self.consumed.0 && matches!(ctx, PlaceContext::NonMutatingUse(NonMutatingUseContext::Move)) {
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self.consumed.1 = true;
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}
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}
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}
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