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simplify polonius constraint generation
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@lqd
lqd committed Nov 26, 2023
1 parent f53412a commit bfd88b0
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Showing 3 changed files with 83 additions and 107 deletions.
2 changes: 1 addition & 1 deletion compiler/rustc_borrowck/src/nll.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -158,7 +158,7 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
borrow_set,
);
polonius::emit_cfg_and_loan_kills_facts(
infcx,
infcx.tcx,
&mut all_facts,
location_table,
body,
Expand Down
178 changes: 75 additions & 103 deletions compiler/rustc_borrowck/src/polonius/constraint_generation.rs
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Original file line number Diff line number Diff line change
@@ -1,61 +1,52 @@
#![deny(rustc::untranslatable_diagnostic)]
#![deny(rustc::diagnostic_outside_of_impl)]
use rustc_infer::infer::InferCtxt;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::{
Body, Local, Location, Place, PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind,
Terminator, TerminatorKind, UserTypeProjection,
};
use rustc_middle::ty::{self};
use rustc_middle::ty::{TyCtxt, Variance};

use crate::{borrow_set::BorrowSet, facts::AllFacts, location::LocationTable, places_conflict};

pub(super) fn generate_constraints<'tcx>(
infcx: &InferCtxt<'tcx>,
all_facts: &mut Option<AllFacts>,
tcx: TyCtxt<'tcx>,
all_facts: &mut AllFacts,
location_table: &LocationTable,
body: &Body<'tcx>,
borrow_set: &BorrowSet<'tcx>,
) {
let mut cg = ConstraintGeneration { borrow_set, infcx, location_table, all_facts, body };
let _prof_timer = tcx.prof.generic_activity("polonius_fact_generation");
let mut cg = ConstraintGeneration { borrow_set, tcx, location_table, all_facts, body };
for (bb, data) in body.basic_blocks.iter_enumerated() {
cg.visit_basic_block_data(bb, data);
}
}

/// 'cg = the duration of the constraint generation process itself.
struct ConstraintGeneration<'cg, 'tcx> {
infcx: &'cg InferCtxt<'tcx>,
all_facts: &'cg mut Option<AllFacts>,
tcx: TyCtxt<'tcx>,
all_facts: &'cg mut AllFacts,
location_table: &'cg LocationTable,
borrow_set: &'cg BorrowSet<'tcx>,
body: &'cg Body<'tcx>,
}

impl<'cg, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'tcx> {
fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
if let Some(all_facts) = self.all_facts {
let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
all_facts.cfg_edge.push((
self.location_table.start_index(location),
self.location_table.mid_index(location),
));

all_facts.cfg_edge.push((
self.location_table.mid_index(location),
self.location_table.start_index(location.successor_within_block()),
));

// If there are borrows on this now dead local, we need to record them as `killed`.
if let StatementKind::StorageDead(local) = statement.kind {
record_killed_borrows_for_local(
all_facts,
self.borrow_set,
self.location_table,
local,
location,
);
}
self.all_facts.cfg_edge.push((
self.location_table.start_index(location),
self.location_table.mid_index(location),
));

self.all_facts.cfg_edge.push((
self.location_table.mid_index(location),
self.location_table.start_index(location.successor_within_block()),
));

// If there are borrows on this now dead local, we need to record them as `killed`.
if let StatementKind::StorageDead(local) = statement.kind {
self.record_killed_borrows_for_local(local, location);
}

self.super_statement(statement, location);
Expand All @@ -70,21 +61,18 @@ impl<'cg, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'tcx> {
}

fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
if let Some(all_facts) = self.all_facts {
let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");
all_facts.cfg_edge.push((
self.location_table.start_index(location),
self.all_facts.cfg_edge.push((
self.location_table.start_index(location),
self.location_table.mid_index(location),
));

let successor_blocks = terminator.successors();
self.all_facts.cfg_edge.reserve(successor_blocks.size_hint().0);
for successor_block in successor_blocks {
self.all_facts.cfg_edge.push((
self.location_table.mid_index(location),
self.location_table.start_index(successor_block.start_location()),
));

let successor_blocks = terminator.successors();
all_facts.cfg_edge.reserve(successor_blocks.size_hint().0);
for successor_block in successor_blocks {
all_facts.cfg_edge.push((
self.location_table.mid_index(location),
self.location_table.start_index(successor_block.start_location()),
));
}
}

// A `Call` terminator's return value can be a local which has borrows,
Expand All @@ -99,7 +87,7 @@ impl<'cg, 'tcx> Visitor<'tcx> for ConstraintGeneration<'cg, 'tcx> {
fn visit_ascribe_user_ty(
&mut self,
_place: &Place<'tcx>,
_variance: ty::Variance,
_variance: Variance,
_user_ty: &UserTypeProjection,
_location: Location,
) {
Expand All @@ -110,75 +98,59 @@ impl<'cx, 'tcx> ConstraintGeneration<'cx, 'tcx> {
/// When recording facts for Polonius, records the borrows on the specified place
/// as `killed`. For example, when assigning to a local, or on a call's return destination.
fn record_killed_borrows_for_place(&mut self, place: Place<'tcx>, location: Location) {
if let Some(all_facts) = self.all_facts {
let _prof_timer = self.infcx.tcx.prof.generic_activity("polonius_fact_generation");

// Depending on the `Place` we're killing:
// - if it's a local, or a single deref of a local,
// we kill all the borrows on the local.
// - if it's a deeper projection, we have to filter which
// of the borrows are killed: the ones whose `borrowed_place`
// conflicts with the `place`.
match place.as_ref() {
PlaceRef { local, projection: &[] }
| PlaceRef { local, projection: &[ProjectionElem::Deref] } => {
debug!(
"Recording `killed` facts for borrows of local={:?} at location={:?}",
local, location
);

record_killed_borrows_for_local(
all_facts,
self.borrow_set,
self.location_table,
local,
location,
);
}
// Depending on the `Place` we're killing:
// - if it's a local, or a single deref of a local,
// we kill all the borrows on the local.
// - if it's a deeper projection, we have to filter which
// of the borrows are killed: the ones whose `borrowed_place`
// conflicts with the `place`.
match place.as_ref() {
PlaceRef { local, projection: &[] }
| PlaceRef { local, projection: &[ProjectionElem::Deref] } => {
debug!(
"Recording `killed` facts for borrows of local={:?} at location={:?}",
local, location
);

self.record_killed_borrows_for_local(local, location);
}

PlaceRef { local, projection: &[.., _] } => {
// Kill conflicting borrows of the innermost local.
debug!(
"Recording `killed` facts for borrows of \
PlaceRef { local, projection: &[.., _] } => {
// Kill conflicting borrows of the innermost local.
debug!(
"Recording `killed` facts for borrows of \
innermost projected local={:?} at location={:?}",
local, location
);

if let Some(borrow_indices) = self.borrow_set.local_map.get(&local) {
for &borrow_index in borrow_indices {
let places_conflict = places_conflict::places_conflict(
self.infcx.tcx,
self.body,
self.borrow_set[borrow_index].borrowed_place,
place,
places_conflict::PlaceConflictBias::NoOverlap,
);

if places_conflict {
let location_index = self.location_table.mid_index(location);
all_facts.loan_killed_at.push((borrow_index, location_index));
}
local, location
);

if let Some(borrow_indices) = self.borrow_set.local_map.get(&local) {
for &borrow_index in borrow_indices {
let places_conflict = places_conflict::places_conflict(
self.tcx,
self.body,
self.borrow_set[borrow_index].borrowed_place,
place,
places_conflict::PlaceConflictBias::NoOverlap,
);

if places_conflict {
let location_index = self.location_table.mid_index(location);
self.all_facts.loan_killed_at.push((borrow_index, location_index));
}
}
}
}
}
}
}

/// When recording facts for Polonius, records the borrows on the specified local as `killed`.
fn record_killed_borrows_for_local(
all_facts: &mut AllFacts,
borrow_set: &BorrowSet<'_>,
location_table: &LocationTable,
local: Local,
location: Location,
) {
if let Some(borrow_indices) = borrow_set.local_map.get(&local) {
all_facts.loan_killed_at.reserve(borrow_indices.len());
for &borrow_index in borrow_indices {
let location_index = location_table.mid_index(location);
all_facts.loan_killed_at.push((borrow_index, location_index));
/// When recording facts for Polonius, records the borrows on the specified local as `killed`.
fn record_killed_borrows_for_local(&mut self, local: Local, location: Location) {
if let Some(borrow_indices) = self.borrow_set.local_map.get(&local) {
let location_index = self.location_table.mid_index(location);
self.all_facts.loan_killed_at.reserve(borrow_indices.len());
for &borrow_index in borrow_indices {
self.all_facts.loan_killed_at.push((borrow_index, location_index));
}
}
}
}
10 changes: 7 additions & 3 deletions compiler/rustc_borrowck/src/polonius/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,6 @@
//! Will be removed in the future, once the in-tree `-Zpolonius=next` implementation reaches feature
//! parity.

use rustc_infer::infer::InferCtxt;
use rustc_middle::mir::{Body, LocalKind, Location, START_BLOCK};
use rustc_middle::ty::TyCtxt;
use rustc_mir_dataflow::move_paths::{InitKind, InitLocation, MoveData};
Expand Down Expand Up @@ -150,11 +149,16 @@ pub(crate) fn emit_loan_invalidations_facts<'tcx>(

/// Emit facts about CFG points and edges, as well as locations where loans are killed.
pub(crate) fn emit_cfg_and_loan_kills_facts<'tcx>(
infcx: &InferCtxt<'tcx>,
tcx: TyCtxt<'tcx>,
all_facts: &mut Option<AllFacts>,
location_table: &LocationTable,
body: &Body<'tcx>,
borrow_set: &BorrowSet<'tcx>,
) {
constraint_generation::generate_constraints(infcx, all_facts, location_table, body, borrow_set);
let Some(all_facts) = all_facts else {
// Nothing to do if we don't have any facts to fill
return;
};

constraint_generation::generate_constraints(tcx, all_facts, location_table, body, borrow_set);
}

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