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Rollup merge of rust-lang#112882 - DrMeepster:new_un_derefer, r=oli-obk
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Rewrite `UnDerefer`

Currently, `UnDerefer` is used by drop elaboration to undo the effects of the `Derefer` pass. However, it just recreates the original places with derefs in the middle of the projection. Because `ProjectionElem::Deref` is intended to be removed completely in the future, this will not work forever.

This PR introduces a `deref_chain` method that returns the places behind `DerefTemp` locals in a place and rewrites the move path code to use this. In the process, `UnDerefer` was merged into `MovePathLookup`. Now that move paths use the same places as in the MIR, the other uses of `UnDerefer` no longer require it.

See rust-lang#98145
cc `@ouz-a`
r? `@oli-obk`
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@Dylan-DPC
Dylan-DPC authored Jun 30, 2023
2 parents 53aadc0 + 4fbd6d5 commit b2ce846
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Showing 8 changed files with 137 additions and 136 deletions.
2 changes: 1 addition & 1 deletion compiler/rustc_borrowck/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -222,7 +222,7 @@ fn do_mir_borrowck<'tcx>(

let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
match MoveData::gather_moves(&body, tcx, param_env) {
Ok((_, move_data)) => (move_data, Vec::new()),
Ok(move_data) => (move_data, Vec::new()),
Err((move_data, move_errors)) => (move_data, move_errors),
};
let promoted_errors = promoted
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_mir_dataflow/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,6 @@ pub mod impls;
pub mod move_paths;
pub mod rustc_peek;
pub mod storage;
pub mod un_derefer;
pub mod value_analysis;

fluent_messages! { "../messages.ftl" }
Expand Down
145 changes: 66 additions & 79 deletions compiler/rustc_mir_dataflow/src/move_paths/builder.rs
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Original file line number Diff line number Diff line change
@@ -1,11 +1,10 @@
use crate::move_paths::FxHashMap;
use crate::un_derefer::UnDerefer;
use rustc_index::IndexVec;
use rustc_middle::mir::tcx::RvalueInitializationState;
use rustc_middle::mir::*;
use rustc_middle::ty::{self, TyCtxt};
use smallvec::{smallvec, SmallVec};

use std::iter;
use std::mem;

use super::abs_domain::Lift;
Expand All @@ -21,7 +20,6 @@ struct MoveDataBuilder<'a, 'tcx> {
param_env: ty::ParamEnv<'tcx>,
data: MoveData<'tcx>,
errors: Vec<(Place<'tcx>, MoveError<'tcx>)>,
un_derefer: UnDerefer<'tcx>,
}

impl<'a, 'tcx> MoveDataBuilder<'a, 'tcx> {
Expand All @@ -35,25 +33,29 @@ impl<'a, 'tcx> MoveDataBuilder<'a, 'tcx> {
tcx,
param_env,
errors: Vec::new(),
un_derefer: UnDerefer { tcx: tcx, derefer_sidetable: Default::default() },
data: MoveData {
moves: IndexVec::new(),
loc_map: LocationMap::new(body),
rev_lookup: MovePathLookup {
locals: body
.local_decls
.indices()
.map(|i| {
Self::new_move_path(
&mut move_paths,
&mut path_map,
&mut init_path_map,
None,
Place::from(i),
.iter_enumerated()
.filter(|(_, l)| !l.is_deref_temp())
.map(|(i, _)| {
(
i,
Self::new_move_path(
&mut move_paths,
&mut path_map,
&mut init_path_map,
None,
Place::from(i),
),
)
})
.collect(),
projections: Default::default(),
derefer_sidetable: Default::default(),
},
move_paths,
path_map,
Expand Down Expand Up @@ -98,13 +100,11 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
///
/// Maybe we should have separate "borrowck" and "moveck" modes.
fn move_path_for(&mut self, place: Place<'tcx>) -> Result<MovePathIndex, MoveError<'tcx>> {
if let Some(new_place) = self.builder.un_derefer.derefer(place.as_ref(), self.builder.body)
{
return self.move_path_for(new_place);
}
let deref_chain = self.builder.data.rev_lookup.deref_chain(place.as_ref());

debug!("lookup({:?})", place);
let mut base = self.builder.data.rev_lookup.locals[place.local];
let mut base =
self.builder.data.rev_lookup.find_local(deref_chain.first().unwrap_or(&place).local);

// The move path index of the first union that we find. Once this is
// some we stop creating child move paths, since moves from unions
Expand All @@ -113,51 +113,55 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
// from `*(u.f: &_)` isn't allowed.
let mut union_path = None;

for (place_ref, elem) in place.as_ref().iter_projections() {
let body = self.builder.body;
let tcx = self.builder.tcx;
let place_ty = place_ref.ty(body, tcx).ty;

match place_ty.kind() {
ty::Ref(..) | ty::RawPtr(..) => {
return Err(MoveError::cannot_move_out_of(
self.loc,
BorrowedContent { target_place: place_ref.project_deeper(&[elem], tcx) },
));
}
ty::Adt(adt, _) if adt.has_dtor(tcx) && !adt.is_box() => {
return Err(MoveError::cannot_move_out_of(
self.loc,
InteriorOfTypeWithDestructor { container_ty: place_ty },
));
}
ty::Adt(adt, _) if adt.is_union() => {
union_path.get_or_insert(base);
}
ty::Slice(_) => {
return Err(MoveError::cannot_move_out_of(
self.loc,
InteriorOfSliceOrArray {
ty: place_ty,
is_index: matches!(elem, ProjectionElem::Index(..)),
},
));
}

ty::Array(..) => {
if let ProjectionElem::Index(..) = elem {
for place in deref_chain.into_iter().chain(iter::once(place)) {
for (place_ref, elem) in place.as_ref().iter_projections() {
let body = self.builder.body;
let tcx = self.builder.tcx;
let place_ty = place_ref.ty(body, tcx).ty;
match place_ty.kind() {
ty::Ref(..) | ty::RawPtr(..) => {
return Err(MoveError::cannot_move_out_of(
self.loc,
InteriorOfSliceOrArray { ty: place_ty, is_index: true },
BorrowedContent {
target_place: place_ref.project_deeper(&[elem], tcx),
},
));
}
ty::Adt(adt, _) if adt.has_dtor(tcx) && !adt.is_box() => {
return Err(MoveError::cannot_move_out_of(
self.loc,
InteriorOfTypeWithDestructor { container_ty: place_ty },
));
}
ty::Adt(adt, _) if adt.is_union() => {
union_path.get_or_insert(base);
}
ty::Slice(_) => {
return Err(MoveError::cannot_move_out_of(
self.loc,
InteriorOfSliceOrArray {
ty: place_ty,
is_index: matches!(elem, ProjectionElem::Index(..)),
},
));
}
}

_ => {}
};
ty::Array(..) => {
if let ProjectionElem::Index(..) = elem {
return Err(MoveError::cannot_move_out_of(
self.loc,
InteriorOfSliceOrArray { ty: place_ty, is_index: true },
));
}
}

_ => {}
};

if union_path.is_none() {
base = self.add_move_path(base, elem, |tcx| place_ref.project_deeper(&[elem], tcx));
if union_path.is_none() {
base = self
.add_move_path(base, elem, |tcx| place_ref.project_deeper(&[elem], tcx));
}
}
}

Expand Down Expand Up @@ -198,10 +202,8 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
}
}

pub type MoveDat<'tcx> = Result<
(FxHashMap<Local, Place<'tcx>>, MoveData<'tcx>),
(MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>),
>;
pub type MoveDat<'tcx> =
Result<MoveData<'tcx>, (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>)>;

impl<'a, 'tcx> MoveDataBuilder<'a, 'tcx> {
fn finalize(self) -> MoveDat<'tcx> {
Expand All @@ -217,11 +219,7 @@ impl<'a, 'tcx> MoveDataBuilder<'a, 'tcx> {
"done dumping moves"
});

if self.errors.is_empty() {
Ok((self.un_derefer.derefer_sidetable, self.data))
} else {
Err((self.data, self.errors))
}
if self.errors.is_empty() { Ok(self.data) } else { Err((self.data, self.errors)) }
}
}

Expand Down Expand Up @@ -250,7 +248,7 @@ pub(super) fn gather_moves<'tcx>(
impl<'a, 'tcx> MoveDataBuilder<'a, 'tcx> {
fn gather_args(&mut self) {
for arg in self.body.args_iter() {
let path = self.data.rev_lookup.locals[arg];
let path = self.data.rev_lookup.find_local(arg);

let init = self.data.inits.push(Init {
path,
Expand Down Expand Up @@ -286,7 +284,7 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
StatementKind::Assign(box (place, Rvalue::CopyForDeref(reffed))) => {
assert!(place.projection.is_empty());
if self.builder.body.local_decls[place.local].is_deref_temp() {
self.builder.un_derefer.derefer_sidetable.insert(place.local, *reffed);
self.builder.data.rev_lookup.derefer_sidetable.insert(place.local, *reffed);
}
}
StatementKind::Assign(box (place, rval)) => {
Expand All @@ -308,7 +306,7 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
StatementKind::StorageLive(_) => {}
StatementKind::StorageDead(local) => {
// DerefTemp locals (results of CopyForDeref) don't actually move anything.
if !self.builder.un_derefer.derefer_sidetable.contains_key(&local) {
if !self.builder.data.rev_lookup.derefer_sidetable.contains_key(&local) {
self.gather_move(Place::from(*local));
}
}
Expand Down Expand Up @@ -450,12 +448,6 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {

fn gather_move(&mut self, place: Place<'tcx>) {
debug!("gather_move({:?}, {:?})", self.loc, place);
if let Some(new_place) = self.builder.un_derefer.derefer(place.as_ref(), self.builder.body)
{
self.gather_move(new_place);
return;
}

if let [ref base @ .., ProjectionElem::Subslice { from, to, from_end: false }] =
**place.projection
{
Expand Down Expand Up @@ -512,11 +504,6 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
fn gather_init(&mut self, place: PlaceRef<'tcx>, kind: InitKind) {
debug!("gather_init({:?}, {:?})", self.loc, place);

if let Some(new_place) = self.builder.un_derefer.derefer(place, self.builder.body) {
self.gather_init(new_place.as_ref(), kind);
return;
}

let mut place = place;

// Check if we are assigning into a field of a union, if so, lookup the place
Expand Down
74 changes: 62 additions & 12 deletions compiler/rustc_mir_dataflow/src/move_paths/mod.rs
View file
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
use crate::move_paths::builder::MoveDat;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
use rustc_index::{IndexSlice, IndexVec};
use rustc_middle::mir::*;
use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
Expand Down Expand Up @@ -175,7 +175,7 @@ pub struct MoveData<'tcx> {
/// particular path being moved.)
pub loc_map: LocationMap<SmallVec<[MoveOutIndex; 4]>>,
pub path_map: IndexVec<MovePathIndex, SmallVec<[MoveOutIndex; 4]>>,
pub rev_lookup: MovePathLookup,
pub rev_lookup: MovePathLookup<'tcx>,
pub inits: IndexVec<InitIndex, Init>,
/// Each Location `l` is mapped to the Inits that are effects
/// of executing the code at `l`.
Expand Down Expand Up @@ -289,8 +289,8 @@ impl Init {

/// Tables mapping from a place to its MovePathIndex.
#[derive(Debug)]
pub struct MovePathLookup {
locals: IndexVec<Local, MovePathIndex>,
pub struct MovePathLookup<'tcx> {
locals: FxIndexMap<Local, MovePathIndex>,

/// projections are made from a base-place and a projection
/// elem. The base-place will have a unique MovePathIndex; we use
Expand All @@ -299,6 +299,9 @@ pub struct MovePathLookup {
/// base-place). For the remaining lookup, we map the projection
/// elem to the associated MovePathIndex.
projections: FxHashMap<(MovePathIndex, AbstractElem), MovePathIndex>,

/// Maps `DerefTemp` locals to the `Place`s assigned to them.
derefer_sidetable: FxHashMap<Local, Place<'tcx>>,
}

mod builder;
Expand All @@ -309,35 +312,82 @@ pub enum LookupResult {
Parent(Option<MovePathIndex>),
}

impl MovePathLookup {
impl<'tcx> MovePathLookup<'tcx> {
// Unlike the builder `fn move_path_for` below, this lookup
// alternative will *not* create a MovePath on the fly for an
// unknown place, but will rather return the nearest available
// parent.
pub fn find(&self, place: PlaceRef<'_>) -> LookupResult {
let mut result = self.locals[place.local];
let deref_chain = self.deref_chain(place);

for elem in place.projection.iter() {
if let Some(&subpath) = self.projections.get(&(result, elem.lift())) {
result = subpath;
} else {
let local = match deref_chain.first() {
Some(place) => place.local,
None => place.local,
};

let mut result = *self.locals.get(&local).unwrap_or_else(|| {
bug!("base local ({local:?}) of deref_chain should not be a deref temp")
});

// this needs to be a closure because `place` has a different lifetime than `prefix`'s places
let mut subpaths_for_place = |place: PlaceRef<'_>| {
for elem in place.projection.iter() {
if let Some(&subpath) = self.projections.get(&(result, elem.lift())) {
result = subpath;
} else {
return Some(result);
}
}
None
};

for place in deref_chain {
if let Some(result) = subpaths_for_place(place.as_ref()) {
return LookupResult::Parent(Some(result));
}
}

if let Some(result) = subpaths_for_place(place) {
return LookupResult::Parent(Some(result));
}

LookupResult::Exact(result)
}

pub fn find_local(&self, local: Local) -> MovePathIndex {
self.locals[local]
let deref_chain = self.deref_chain(Place::from(local).as_ref());

let local = match deref_chain.last() {
Some(place) => place.local,
None => local,
};

*self.locals.get(&local).unwrap_or_else(|| {
bug!("base local ({local:?}) of deref_chain should not be a deref temp")
})
}

/// An enumerated iterator of `local`s and their associated
/// `MovePathIndex`es.
pub fn iter_locals_enumerated(
&self,
) -> impl DoubleEndedIterator<Item = (Local, MovePathIndex)> + ExactSizeIterator + '_ {
self.locals.iter_enumerated().map(|(l, &idx)| (l, idx))
self.locals.iter().map(|(&l, &idx)| (l, idx))
}

/// Returns the chain of places behind `DerefTemp` locals in `place`
pub fn deref_chain(&self, place: PlaceRef<'_>) -> Vec<Place<'tcx>> {
let mut prefix = Vec::new();
let mut local = place.local;

while let Some(&reffed) = self.derefer_sidetable.get(&local) {
prefix.insert(0, reffed);
local = reffed.local;
}

debug!("deref_chain({place:?}) = {prefix:?}");

prefix
}
}

Expand Down
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