//! Functions dedicated to fact generation for the `-Zpolonius=legacy` datalog implementation.
//!
//! Will be removed in the future, once the in-tree `-Zpolonius=next` implementation reaches feature
//! parity.
use std::iter;
use either::Either;
use rustc_middle::mir::{Body, Local, LocalKind, Location, START_BLOCK};
use rustc_middle::ty::{GenericArg, TyCtxt};
use rustc_mir_dataflow::move_paths::{InitKind, InitLocation, MoveData};
use tracing::debug;
use crate::borrow_set::BorrowSet;
use crate::constraints::OutlivesConstraint;
use crate::type_check::MirTypeckRegionConstraints;
use crate::type_check::free_region_relations::UniversalRegionRelations;
use crate::universal_regions::UniversalRegions;
mod accesses;
mod loan_invalidations;
mod loan_kills;
mod location;
pub use self::location::*;
mod facts;
pub use self::facts::*;
/// When requested, emit most of the facts needed by polonius:
/// - moves and assignments
/// - universal regions and their relations
/// - CFG points and edges
/// - loan kills
/// - loan invalidations
/// - access facts such as variable definitions, uses, drops, and path accesses
/// - outlives constraints
///
/// The rest of the facts are emitted during typeck and liveness.
pub(crate) fn emit_facts<'tcx>(
all_facts: &mut Option<AllFacts>,
tcx: TyCtxt<'tcx>,
location_table: &LocationTable,
body: &Body<'tcx>,
borrow_set: &BorrowSet<'tcx>,
move_data: &MoveData<'tcx>,
universal_region_relations: &UniversalRegionRelations<'tcx>,
constraints: &MirTypeckRegionConstraints<'tcx>,
) {
let Some(facts) = all_facts else {
// We don't do anything if there are no facts to fill.
return;
};
let _prof_timer = tcx.prof.generic_activity("polonius_fact_generation");
emit_move_facts(facts, body, location_table, move_data);
emit_universal_region_facts(facts, borrow_set, universal_region_relations);
loan_kills::emit_loan_kills(tcx, facts, body, location_table, borrow_set);
loan_invalidations::emit_loan_invalidations(tcx, facts, body, location_table, borrow_set);
accesses::emit_access_facts(
tcx,
facts,
body,
location_table,
move_data,
&universal_region_relations.universal_regions,
);
emit_outlives_facts(facts, location_table, constraints);
}
/// Emit facts needed for move/init analysis: moves and assignments.
fn emit_move_facts(
facts: &mut AllFacts,
body: &Body<'_>,
location_table: &LocationTable,
move_data: &MoveData<'_>,
) {
facts.path_is_var.extend(move_data.rev_lookup.iter_locals_enumerated().map(|(l, r)| (r, l)));
for (child, move_path) in move_data.move_paths.iter_enumerated() {
if let Some(parent) = move_path.parent {
facts.child_path.push((child, parent));
}
}
let fn_entry_start =
location_table.start_index(Location { block: START_BLOCK, statement_index: 0 });
// initialized_at
for init in move_data.inits.iter() {
match init.location {
InitLocation::Statement(location) => {
let block_data = &body[location.block];
let is_terminator = location.statement_index == block_data.statements.len();
if is_terminator && init.kind == InitKind::NonPanicPathOnly {
// We are at the terminator of an init that has a panic path,
// and where the init should not happen on panic
for successor in block_data.terminator().successors() {
if body[successor].is_cleanup {
continue;
}
// The initialization happened in (or rather, when arriving at)
// the successors, but not in the unwind block.
let first_statement = Location { block: successor, statement_index: 0 };
facts
.path_assigned_at_base
.push((init.path, location_table.start_index(first_statement)));
}
} else {
// In all other cases, the initialization just happens at the
// midpoint, like any other effect.
facts
.path_assigned_at_base
.push((init.path, location_table.mid_index(location)));
}
}
// Arguments are initialized on function entry
InitLocation::Argument(local) => {
assert!(body.local_kind(local) == LocalKind::Arg);
facts.path_assigned_at_base.push((init.path, fn_entry_start));
}
}
}
for (local, path) in move_data.rev_lookup.iter_locals_enumerated() {
if body.local_kind(local) != LocalKind::Arg {
// Non-arguments start out deinitialised; we simulate this with an
// initial move:
facts.path_moved_at_base.push((path, fn_entry_start));
}
}
// moved_out_at
// deinitialisation is assumed to always happen!
facts
.path_moved_at_base
.extend(move_data.moves.iter().map(|mo| (mo.path, location_table.mid_index(mo.source))));
}
/// Emit universal regions facts, and their relations.
fn emit_universal_region_facts(
facts: &mut AllFacts,
borrow_set: &BorrowSet<'_>,
universal_region_relations: &UniversalRegionRelations<'_>,
) {
// 1: universal regions are modeled in Polonius as a pair:
// - the universal region vid itself.
// - a "placeholder loan" associated to this universal region. Since they don't exist in
// the `borrow_set`, their `BorrowIndex` are synthesized as the universal region index
// added to the existing number of loans, as if they succeeded them in the set.
//
let universal_regions = &universal_region_relations.universal_regions;
facts
.universal_region
.extend(universal_regions.universal_regions_iter().map(PoloniusRegionVid::from));
let borrow_count = borrow_set.len();
debug!(
"emit_universal_region_facts: polonius placeholders, num_universals={}, borrow_count={}",
universal_regions.len(),
borrow_count
);
for universal_region in universal_regions.universal_regions_iter() {
let universal_region_idx = universal_region.index();
let placeholder_loan_idx = borrow_count + universal_region_idx;
facts.placeholder.push((universal_region.into(), placeholder_loan_idx.into()));
}
// 2: the universal region relations `outlives` constraints are emitted as
// `known_placeholder_subset` facts.
for (fr1, fr2) in universal_region_relations.known_outlives() {
if fr1 != fr2 {
debug!(
"emit_universal_region_facts: emitting polonius `known_placeholder_subset` \
fr1={:?}, fr2={:?}",
fr1, fr2
);
facts.known_placeholder_subset.push((fr1.into(), fr2.into()));
}
}
}
/// For every potentially drop()-touched region `region` in `local`'s type
/// (`kind`), emit a `drop_of_var_derefs_origin(local, origin)` fact.
pub(crate) fn emit_drop_facts<'tcx>(
tcx: TyCtxt<'tcx>,
local: Local,
kind: &GenericArg<'tcx>,
universal_regions: &UniversalRegions<'tcx>,
all_facts: &mut Option<AllFacts>,
) {
debug!("emit_drop_facts(local={:?}, kind={:?}", local, kind);
let Some(facts) = all_facts.as_mut() else { return };
let _prof_timer = tcx.prof.generic_activity("polonius_fact_generation");
tcx.for_each_free_region(kind, |drop_live_region| {
let region_vid = universal_regions.to_region_vid(drop_live_region);
facts.drop_of_var_derefs_origin.push((local, region_vid.into()));
});
}
/// Emit facts about the outlives constraints: the `subset` base relation, i.e. not a transitive
/// closure.
fn emit_outlives_facts<'tcx>(
facts: &mut AllFacts,
location_table: &LocationTable,
constraints: &MirTypeckRegionConstraints<'tcx>,
) {
facts.subset_base.extend(constraints.outlives_constraints.outlives().iter().flat_map(
|constraint: &OutlivesConstraint<'_>| {
if let Some(from_location) = constraint.locations.from_location() {
Either::Left(iter::once((
constraint.sup.into(),
constraint.sub.into(),
location_table.mid_index(from_location),
)))
} else {
Either::Right(
location_table.all_points().map(move |location| {
(constraint.sup.into(), constraint.sub.into(), location)
}),
)
}
},
));
}