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Auto merge of #7346 - lengyijun:redundant_clone_5707, r=oli-obk

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fix 5707

changelog: ``[`redundant_clone`]``, fix #5707

# Root problem of #5707 :
```
&2:&mut HashMap = &mut _4;
&3:&str = & _5;
_1 = HashMap::insert(move _2,move _3, _);
```

generate PossibleBorrower(_2,_1) and PossibleBorrower(_3,_1).

However, it misses PossibleBorrower(_3,_2).

# My solution to #5707 :

When meet a function call, we should:
1. build PossibleBorrower between borrow parameters and return value (currently)
2. build PossibleBorrower between immutable borrow parameters and mutable borrow parameters (*add*)
3. build PossibleBorrower inside mutable borrow parameters (*add*)

For example:
```
_2: &mut _22;
_3: &mut _;
_4: & _;
_5: & _;
_1 = call(move _2, move _3, move _4, move _5);
```
we need to build
1. return value with parameter(current implementataion)
 PossibleBorrower(_2,_1)
 PossibleBorrower(_3,_1)
 PossibleBorrower(_4,_1)
 PossibleBorrower(_5,_1)

2. between mutable borrow and immutable borrow
PossibleBorrower(_4,_2)
PossibleBorrower(_5,_2)
PossibleBorrower(_4,_3)
PossibleBorrower(_5,_3)

3. between mutable borrow and mutable borrow
PossibleBorrower(_3,_2)
PossibleBorrower(_2,_3)

  But that's not enough.
 Modification to _2 actually apply to _22.
  So I write a `PossibleBorrowed` visitor, which tracks (borrower => possible borrowed) relation.
  For example (_2 => _22).
  However, a lot of problems exist here.

## Known Problems:
  1. not sure all `&mut`'s origin are collected.
  I'm not sure how to deal with `&mut` when meet a function call, so I didn't do it currently.
  Also, my implement is not flow sensitive, so it's not accurate.

```
foo(_2:&mut _, _3: &_)
```
This pr doesn't count _3 as origin of _2.

 2. introduce false negative
`foo(_2, _3)` will  emit PossibleBorrower(_3,_2) in this pr, but _3 and _2 may not have relation.
Clippy may feel that _3 is still in use because of _2, but actually, _3 is on longer needed and can be moved.

## Insight
  The key problem is determine where every `&mut` come from accurately.
  I think Polonius is an elegant solution to it. Polonius is flow sensitive and accurate.
  But I'm uncertain about whether we can import Polonius in rust-clippy currently.
  This pr actually is part of Polonius' functionality, I think.

# TODO
1. `cargo test` can't pass yet due to similar variable name
This commit is contained in:
bors 2021-07-14 10:10:14 +00:00
commit f07feca40c
4 changed files with 168 additions and 16 deletions
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108
clippy_lints/src/redundant_clone.rs
View file

@ -12,6 +12,7 @@ use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::mir::{
self, traversal,
visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor as _},
Mutability,
};
use rustc_middle::ty::{self, fold::TypeVisitor, Ty};
use rustc_mir::dataflow::{Analysis, AnalysisDomain, GenKill, GenKillAnalysis, ResultsCursor};
@ -87,13 +88,18 @@ impl<'tcx> LateLintPass<'tcx> for RedundantClone {
let mir = cx.tcx.optimized_mir(def_id.to_def_id());
let possible_origin = {
let mut vis = PossibleOriginVisitor::new(mir);
vis.visit_body(mir);
vis.into_map(cx)
};
let maybe_storage_live_result = MaybeStorageLive
.into_engine(cx.tcx, mir)
.pass_name("redundant_clone")
.iterate_to_fixpoint()
.into_results_cursor(mir);
let mut possible_borrower = {
let mut vis = PossibleBorrowerVisitor::new(cx, mir);
let mut vis = PossibleBorrowerVisitor::new(cx, mir, possible_origin);
vis.visit_body(mir);
vis.into_map(cx, maybe_storage_live_result)
};
@ -509,14 +515,20 @@ struct PossibleBorrowerVisitor<'a, 'tcx> {
possible_borrower: TransitiveRelation<mir::Local>,
body: &'a mir::Body<'tcx>,
cx: &'a LateContext<'tcx>,
possible_origin: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
}
impl<'a, 'tcx> PossibleBorrowerVisitor<'a, 'tcx> {
fn new(cx: &'a LateContext<'tcx>, body: &'a mir::Body<'tcx>) -> Self {
fn new(
cx: &'a LateContext<'tcx>,
body: &'a mir::Body<'tcx>,
possible_origin: FxHashMap<mir::Local, HybridBitSet<mir::Local>>,
) -> Self {
Self {
possible_borrower: TransitiveRelation::default(),
cx,
body,
possible_origin,
}
}
@ -585,21 +597,105 @@ impl<'a, 'tcx> mir::visit::Visitor<'tcx> for PossibleBorrowerVisitor<'a, 'tcx> {
..
} = &terminator.kind
{
// TODO add doc
// If the call returns something with lifetimes,
// let's conservatively assume the returned value contains lifetime of all the arguments.
// For example, given `let y: Foo<'a> = foo(x)`, `y` is considered to be a possible borrower of `x`.
if ContainsRegion.visit_ty(self.body.local_decls[*dest].ty).is_continue() {
return;
}
let mut immutable_borrowers = vec![];
let mut mutable_borrowers = vec![];
for op in args {
match op {
mir::Operand::Copy(p) | mir::Operand::Move(p) => {
self.possible_borrower.add(p.local, *dest);
if let ty::Ref(_, _, Mutability::Mut) = self.body.local_decls[p.local].ty.kind() {
mutable_borrowers.push(p.local);
} else {
immutable_borrowers.push(p.local);
}
},
mir::Operand::Constant(..) => (),
}
}
let mut mutable_variables: Vec<mir::Local> = mutable_borrowers
.iter()
.filter_map(|r| self.possible_origin.get(r))
.flat_map(HybridBitSet::iter)
.collect();
if ContainsRegion.visit_ty(self.body.local_decls[*dest].ty).is_break() {
mutable_variables.push(*dest);
}
for y in mutable_variables {
for x in &immutable_borrowers {
self.possible_borrower.add(*x, y);
}
for x in &mutable_borrowers {
self.possible_borrower.add(*x, y);
}
}
}
}
}
/// Collect possible borrowed for every `&mut` local.
/// For exampel, `_1 = &mut _2` generate _1: {_2,...}
/// Known Problems: not sure all borrowed are tracked
struct PossibleOriginVisitor<'a, 'tcx> {
possible_origin: TransitiveRelation<mir::Local>,
body: &'a mir::Body<'tcx>,
}
impl<'a, 'tcx> PossibleOriginVisitor<'a, 'tcx> {
fn new(body: &'a mir::Body<'tcx>) -> Self {
Self {
possible_origin: TransitiveRelation::default(),
body,
}
}
fn into_map(self, cx: &LateContext<'tcx>) -> FxHashMap<mir::Local, HybridBitSet<mir::Local>> {
let mut map = FxHashMap::default();
for row in (1..self.body.local_decls.len()).map(mir::Local::from_usize) {
if is_copy(cx, self.body.local_decls[row].ty) {
continue;
}
let borrowers = self.possible_origin.reachable_from(&row);
if !borrowers.is_empty() {
let mut bs = HybridBitSet::new_empty(self.body.local_decls.len());
for &c in borrowers {
if c != mir::Local::from_usize(0) {
bs.insert(c);
}
}
if !bs.is_empty() {
map.insert(row, bs);
}
}
}
map
}
}
impl<'a, 'tcx> mir::visit::Visitor<'tcx> for PossibleOriginVisitor<'a, 'tcx> {
fn visit_assign(&mut self, place: &mir::Place<'tcx>, rvalue: &mir::Rvalue<'_>, _location: mir::Location) {
let lhs = place.local;
match rvalue {
// Only consider `&mut`, which can modify origin place
mir::Rvalue::Ref(_, rustc_middle::mir::BorrowKind::Mut { .. }, borrowed) |
// _2: &mut _;
// _3 = move _2
mir::Rvalue::Use(mir::Operand::Move(borrowed)) |
// _3 = move _2 as &mut _;
mir::Rvalue::Cast(_, mir::Operand::Move(borrowed), _)
=> {
self.possible_origin.add(lhs, borrowed.local);
},
_ => {},
}
}
}

28
tests/ui/redundant_clone.fixed
View file

@ -55,6 +55,8 @@ fn main() {
issue_5405();
manually_drop();
clone_then_move_cloned();
hashmap_neg();
false_negative_5707();
}
#[derive(Clone)]
@ -206,3 +208,29 @@ fn clone_then_move_cloned() {
let mut x = S(String::new());
x.0.clone().chars().for_each(|_| x.m());
}
fn hashmap_neg() {
// issue 5707
use std::collections::HashMap;
use std::path::PathBuf;
let p = PathBuf::from("/");
let mut h: HashMap<&str, &str> = HashMap::new();
h.insert("orig-p", p.to_str().unwrap());
let mut q = p.clone();
q.push("foo");
println!("{:?} {}", h, q.display());
}
fn false_negative_5707() {
fn foo(_x: &Alpha, _y: &mut Alpha) {}
let x = Alpha;
let mut y = Alpha;
foo(&x, &mut y);
let _z = x.clone(); // pr 7346 can't lint on `x`
drop(y);
}

28
tests/ui/redundant_clone.rs
View file

@ -55,6 +55,8 @@ fn main() {
issue_5405();
manually_drop();
clone_then_move_cloned();
hashmap_neg();
false_negative_5707();
}
#[derive(Clone)]
@ -206,3 +208,29 @@ fn clone_then_move_cloned() {
let mut x = S(String::new());
x.0.clone().chars().for_each(|_| x.m());
}
fn hashmap_neg() {
// issue 5707
use std::collections::HashMap;
use std::path::PathBuf;
let p = PathBuf::from("/");
let mut h: HashMap<&str, &str> = HashMap::new();
h.insert("orig-p", p.to_str().unwrap());
let mut q = p.clone();
q.push("foo");
println!("{:?} {}", h, q.display());
}
fn false_negative_5707() {
fn foo(_x: &Alpha, _y: &mut Alpha) {}
let x = Alpha;
let mut y = Alpha;
foo(&x, &mut y);
let _z = x.clone(); // pr 7346 can't lint on `x`
drop(y);
}

20
tests/ui/redundant_clone.stderr
View file

@ -108,61 +108,61 @@ LL | let _t = tup.0.clone();
| ^^^^^
error: redundant clone
--> $DIR/redundant_clone.rs:63:25
--> $DIR/redundant_clone.rs:65:25
|
LL | if b { (a.clone(), a.clone()) } else { (Alpha, a) }
| ^^^^^^^^ help: remove this
|
note: this value is dropped without further use
--> $DIR/redundant_clone.rs:63:24
--> $DIR/redundant_clone.rs:65:24
|
LL | if b { (a.clone(), a.clone()) } else { (Alpha, a) }
| ^
error: redundant clone
--> $DIR/redundant_clone.rs:120:15
--> $DIR/redundant_clone.rs:122:15
|
LL | let _s = s.clone();
| ^^^^^^^^ help: remove this
|
note: this value is dropped without further use
--> $DIR/redundant_clone.rs:120:14
--> $DIR/redundant_clone.rs:122:14
|
LL | let _s = s.clone();
| ^
error: redundant clone
--> $DIR/redundant_clone.rs:121:15
--> $DIR/redundant_clone.rs:123:15
|
LL | let _t = t.clone();
| ^^^^^^^^ help: remove this
|
note: this value is dropped without further use
--> $DIR/redundant_clone.rs:121:14
--> $DIR/redundant_clone.rs:123:14
|
LL | let _t = t.clone();
| ^
error: redundant clone
--> $DIR/redundant_clone.rs:131:19
--> $DIR/redundant_clone.rs:133:19
|
LL | let _f = f.clone();
| ^^^^^^^^ help: remove this
|
note: this value is dropped without further use
--> $DIR/redundant_clone.rs:131:18
--> $DIR/redundant_clone.rs:133:18
|
LL | let _f = f.clone();
| ^
error: redundant clone
--> $DIR/redundant_clone.rs:143:14
--> $DIR/redundant_clone.rs:145:14
|
LL | let y = x.clone().join("matthias");
| ^^^^^^^^ help: remove this
|
note: cloned value is neither consumed nor mutated
--> $DIR/redundant_clone.rs:143:13
--> $DIR/redundant_clone.rs:145:13
|
LL | let y = x.clone().join("matthias");
| ^^^^^^^^^