bjoernager/rust
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Auto merge of #116300 - cjgillot:split-move, r=petrochenkov

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Separate move path tracking between borrowck and drop elaboration.

The primary goal of this PR is to skip creating a `MovePathIndex` for path that do not need dropping in drop elaboration.

The 2 first commits are cleanups.

The next 2 commits displace `move` errors from move-path builder to borrowck. Move-path builder keeps the same logic, but does not carry error information any more.

The remaining commits allow to filter `MovePathIndex` creation according to types. This is used in drop elaboration, to avoid computing dataflow for paths that do not need dropping.
This commit is contained in:
bors 2023-10-24 00:25:32 +00:00
commit cd674d6179
19 changed files with 581 additions and 559 deletions
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186
compiler/rustc_mir_transform/src/elaborate_drops.rs
View file

@ -9,9 +9,9 @@ use rustc_mir_dataflow::elaborate_drops::{elaborate_drop, DropFlagState, Unwind}
use rustc_mir_dataflow::elaborate_drops::{DropElaborator, DropFlagMode, DropStyle};
use rustc_mir_dataflow::impls::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
use rustc_mir_dataflow::move_paths::{LookupResult, MoveData, MovePathIndex};
use rustc_mir_dataflow::on_all_children_bits;
use rustc_mir_dataflow::on_lookup_result_bits;
use rustc_mir_dataflow::MoveDataParamEnv;
use rustc_mir_dataflow::{on_all_children_bits, on_all_drop_children_bits};
use rustc_mir_dataflow::{Analysis, ResultsCursor};
use rustc_span::Span;
use rustc_target::abi::{FieldIdx, VariantIdx};
@ -54,16 +54,10 @@ impl<'tcx> MirPass<'tcx> for ElaborateDrops {
let def_id = body.source.def_id();
let param_env = tcx.param_env_reveal_all_normalized(def_id);
let move_data = match MoveData::gather_moves(body, tcx, param_env) {
Ok(move_data) => move_data,
Err((move_data, _)) => {
tcx.sess.delay_span_bug(
body.span,
"No `move_errors` should be allowed in MIR borrowck",
);
move_data
}
};
// For types that do not need dropping, the behaviour is trivial. So we only need to track
// init/uninit for types that do need dropping.
let move_data =
MoveData::gather_moves(&body, tcx, param_env, |ty| ty.needs_drop(tcx, param_env));
let elaborate_patch = {
let env = MoveDataParamEnv { move_data, param_env };
@ -178,13 +172,19 @@ impl<'a, 'tcx> DropElaborator<'a, 'tcx> for Elaborator<'a, '_, 'tcx> {
let mut some_live = false;
let mut some_dead = false;
let mut children_count = 0;
on_all_drop_children_bits(self.tcx(), self.body(), self.ctxt.env, path, |child| {
let (live, dead) = self.ctxt.init_data.maybe_live_dead(child);
debug!("elaborate_drop: state({:?}) = {:?}", child, (live, dead));
some_live |= live;
some_dead |= dead;
children_count += 1;
});
on_all_children_bits(
self.tcx(),
self.body(),
self.ctxt.move_data(),
path,
|child| {
let (live, dead) = self.ctxt.init_data.maybe_live_dead(child);
debug!("elaborate_drop: state({:?}) = {:?}", child, (live, dead));
some_live |= live;
some_dead |= dead;
children_count += 1;
},
);
((some_live, some_dead), children_count != 1)
}
};
@ -296,26 +296,36 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
fn collect_drop_flags(&mut self) {
for (bb, data) in self.body.basic_blocks.iter_enumerated() {
let terminator = data.terminator();
let place = match terminator.kind {
TerminatorKind::Drop { ref place, .. } => place,
_ => continue,
};
self.init_data.seek_before(self.body.terminator_loc(bb));
let TerminatorKind::Drop { ref place, .. } = terminator.kind else { continue };
let path = self.move_data().rev_lookup.find(place.as_ref());
debug!("collect_drop_flags: {:?}, place {:?} ({:?})", bb, place, path);
let path = match path {
LookupResult::Exact(e) => e,
LookupResult::Parent(None) => continue,
match path {
LookupResult::Exact(path) => {
self.init_data.seek_before(self.body.terminator_loc(bb));
on_all_children_bits(self.tcx, self.body, self.move_data(), path, |child| {
let (maybe_live, maybe_dead) = self.init_data.maybe_live_dead(child);
debug!(
"collect_drop_flags: collecting {:?} from {:?}@{:?} - {:?}",
child,
place,
path,
(maybe_live, maybe_dead)
);
if maybe_live && maybe_dead {
self.create_drop_flag(child, terminator.source_info.span)
}
});
}
LookupResult::Parent(None) => {}
LookupResult::Parent(Some(parent)) => {
let (_maybe_live, maybe_dead) = self.init_data.maybe_live_dead(parent);
if self.body.local_decls[place.local].is_deref_temp() {
continue;
}
self.init_data.seek_before(self.body.terminator_loc(bb));
let (_maybe_live, maybe_dead) = self.init_data.maybe_live_dead(parent);
if maybe_dead {
self.tcx.sess.delay_span_bug(
terminator.source_info.span,
@ -324,80 +334,74 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
),
);
}
continue;
}
};
on_all_drop_children_bits(self.tcx, self.body, self.env, path, |child| {
let (maybe_live, maybe_dead) = self.init_data.maybe_live_dead(child);
debug!(
"collect_drop_flags: collecting {:?} from {:?}@{:?} - {:?}",
child,
place,
path,
(maybe_live, maybe_dead)
);
if maybe_live && maybe_dead {
self.create_drop_flag(child, terminator.source_info.span)
}
});
}
}
fn elaborate_drops(&mut self) {
// This function should mirror what `collect_drop_flags` does.
for (bb, data) in self.body.basic_blocks.iter_enumerated() {
let loc = Location { block: bb, statement_index: data.statements.len() };
let terminator = data.terminator();
let TerminatorKind::Drop { place, target, unwind, replace } = terminator.kind else {
continue;
};
match terminator.kind {
TerminatorKind::Drop { place, target, unwind, replace } => {
self.init_data.seek_before(loc);
match self.move_data().rev_lookup.find(place.as_ref()) {
LookupResult::Exact(path) => {
let unwind = if data.is_cleanup {
Unwind::InCleanup
} else {
match unwind {
UnwindAction::Cleanup(cleanup) => Unwind::To(cleanup),
UnwindAction::Continue => Unwind::To(self.patch.resume_block()),
UnwindAction::Unreachable => {
Unwind::To(self.patch.unreachable_cleanup_block())
}
UnwindAction::Terminate(reason) => {
debug_assert_ne!(
reason,
UnwindTerminateReason::InCleanup,
"we are not in a cleanup block, InCleanup reason should be impossible"
);
Unwind::To(self.patch.terminate_block(reason))
}
}
};
elaborate_drop(
&mut Elaborator { ctxt: self },
terminator.source_info,
place,
path,
target,
unwind,
bb,
)
// This place does not need dropping. It does not have an associated move-path, so the
// match below will conservatively keep an unconditional drop. As that drop is useless,
// just remove it here and now.
if !place
.ty(&self.body.local_decls, self.tcx)
.ty
.needs_drop(self.tcx, self.env.param_env)
{
self.patch.patch_terminator(bb, TerminatorKind::Goto { target });
continue;
}
let path = self.move_data().rev_lookup.find(place.as_ref());
match path {
LookupResult::Exact(path) => {
let unwind = match unwind {
_ if data.is_cleanup => Unwind::InCleanup,
UnwindAction::Cleanup(cleanup) => Unwind::To(cleanup),
UnwindAction::Continue => Unwind::To(self.patch.resume_block()),
UnwindAction::Unreachable => {
Unwind::To(self.patch.unreachable_cleanup_block())
}
LookupResult::Parent(..) => {
if !replace {
self.tcx.sess.delay_span_bug(
terminator.source_info.span,
format!("drop of untracked value {bb:?}"),
);
}
// A drop and replace behind a pointer/array/whatever.
// The borrow checker requires that these locations are initialized before the assignment,
// so we just leave an unconditional drop.
assert!(!data.is_cleanup);
UnwindAction::Terminate(reason) => {
debug_assert_ne!(
reason,
UnwindTerminateReason::InCleanup,
"we are not in a cleanup block, InCleanup reason should be impossible"
);
Unwind::To(self.patch.terminate_block(reason))
}
}
};
self.init_data.seek_before(self.body.terminator_loc(bb));
elaborate_drop(
&mut Elaborator { ctxt: self },
terminator.source_info,
place,
path,
target,
unwind,
bb,
)
}
LookupResult::Parent(None) => {}
LookupResult::Parent(Some(_)) => {
if !replace {
self.tcx.sess.delay_span_bug(
terminator.source_info.span,
format!("drop of untracked value {bb:?}"),
);
}
// A drop and replace behind a pointer/array/whatever.
// The borrow checker requires that these locations are initialized before the assignment,
// so we just leave an unconditional drop.
assert!(!data.is_cleanup);
}
_ => continue,
}
}
}

7
compiler/rustc_mir_transform/src/remove_uninit_drops.rs
View file

@ -24,11 +24,8 @@ pub struct RemoveUninitDrops;
impl<'tcx> MirPass<'tcx> for RemoveUninitDrops {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let param_env = tcx.param_env(body.source.def_id());
let Ok(move_data) = MoveData::gather_moves(body, tcx, param_env) else {
// We could continue if there are move errors, but there's not much point since our
// init data isn't complete.
return;
};
let move_data =
MoveData::gather_moves(&body, tcx, param_env, |ty| ty.needs_drop(tcx, param_env));
let mdpe = MoveDataParamEnv { move_data, param_env };
let mut maybe_inits = MaybeInitializedPlaces::new(tcx, body, &mdpe)