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Auto merge of #108121 - aliemjay:resolve-var-region, r=lcnr

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always resolve to universal regions if possible

`RegionConstraintCollector::opportunistic_resolve_var`, which is used in canonicalization and projection logic, doesn't resolve the region var to an equal universal region. So if we have equated `'static == '1 == '2`, it doesn't resolve `'1` or `'2` to `'static`. Now it does!

Addresses review comment https://github.com/rust-lang/rust/pull/107376#discussion_r1093233687.

r? `@lcnr`
This commit is contained in:
bors 2023-03-08 12:33:21 +00:00
commit 7c306f6dcd
10 changed files with 86 additions and 71 deletions
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12
compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
View file

@ -352,19 +352,17 @@ impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'cx, 'tcx> {
}
ty::ReVar(vid) => {
let resolved_vid = self
let resolved = self
.infcx
.inner
.borrow_mut()
.unwrap_region_constraints()
.opportunistic_resolve_var(vid);
.opportunistic_resolve_var(self.tcx, vid);
debug!(
"canonical: region var found with vid {:?}, \
opportunistically resolved to {:?}",
vid, resolved_vid
"canonical: region var found with vid {vid:?}, \
opportunistically resolved to {resolved:?}",
);
let r = self.tcx.mk_re_var(resolved_vid);
self.canonicalize_mode.canonicalize_free_region(self, r)
self.canonicalize_mode.canonicalize_free_region(self, resolved)
}
ty::ReStatic

45
compiler/rustc_infer/src/infer/region_constraints/mod.rs
View file

@ -420,7 +420,7 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
// `RegionConstraintData` contains the relationship here.
if *any_unifications {
*any_unifications = false;
self.unification_table().reset_unifications(|_| UnifiedRegion(None));
self.unification_table_mut().reset_unifications(|_| UnifiedRegion::new(None));
}
data
@ -447,7 +447,7 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
) -> RegionVid {
let vid = self.var_infos.push(RegionVariableInfo { origin, universe });
let u_vid = self.unification_table().new_key(UnifiedRegion(None));
let u_vid = self.unification_table_mut().new_key(UnifiedRegion::new(None));
assert_eq!(vid, u_vid.vid);
self.undo_log.push(AddVar(vid));
debug!("created new region variable {:?} in {:?} with origin {:?}", vid, universe, origin);
@ -516,13 +516,13 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
match (sub, sup) {
(Region(Interned(ReVar(sub), _)), Region(Interned(ReVar(sup), _))) => {
debug!("make_eqregion: unifying {:?} with {:?}", sub, sup);
self.unification_table().union(*sub, *sup);
self.unification_table_mut().union(*sub, *sup);
self.any_unifications = true;
}
(Region(Interned(ReVar(vid), _)), value)
| (value, Region(Interned(ReVar(vid), _))) => {
debug!("make_eqregion: unifying {:?} with {:?}", vid, value);
self.unification_table().union_value(*vid, UnifiedRegion(Some(value)));
self.unification_table_mut().union_value(*vid, UnifiedRegion::new(Some(value)));
self.any_unifications = true;
}
(_, _) => {}
@ -633,28 +633,25 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
}
}
/// Resolves the passed RegionVid to the root RegionVid in the unification table
pub(super) fn opportunistic_resolve_var(&mut self, rid: ty::RegionVid) -> ty::RegionVid {
self.unification_table().find(rid).vid
}
/// If the Region is a `ReVar`, then resolves it either to the root value in
/// the unification table, if it exists, or to the root `ReVar` in the table.
/// If the Region is not a `ReVar`, just returns the Region itself.
pub fn opportunistic_resolve_region(
/// Resolves a region var to its value in the unification table, if it exists.
/// Otherwise, it is resolved to the root `ReVar` in the table.
pub fn opportunistic_resolve_var(
&mut self,
tcx: TyCtxt<'tcx>,
region: ty::Region<'tcx>,
vid: ty::RegionVid,
) -> ty::Region<'tcx> {
match *region {
ty::ReVar(rid) => {
let unified_region = self.unification_table().probe_value(rid);
unified_region.0.unwrap_or_else(|| {
let root = self.unification_table().find(rid).vid;
tcx.mk_re_var(root)
})
}
_ => region,
let mut ut = self.unification_table_mut(); // FIXME(rust-lang/ena#42): unnecessary mut
let root_vid = ut.find(vid).vid;
let resolved = ut
.probe_value(root_vid)
.get_value_ignoring_universes()
.unwrap_or_else(|| tcx.mk_re_var(root_vid));
// Don't resolve a variable to a region that it cannot name.
if self.var_universe(vid).can_name(self.universe(resolved)) {
resolved
} else {
tcx.mk_re_var(vid)
}
}
@ -733,7 +730,7 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
}
#[inline]
fn unification_table(&mut self) -> super::UnificationTable<'_, 'tcx, RegionVidKey<'tcx>> {
fn unification_table_mut(&mut self) -> super::UnificationTable<'_, 'tcx, RegionVidKey<'tcx>> {
ut::UnificationTable::with_log(&mut self.storage.unification_table, self.undo_log)
}
}

15
compiler/rustc_infer/src/infer/resolve.rs
View file

@ -85,15 +85,12 @@ impl<'a, 'tcx> TypeFolder<TyCtxt<'tcx>> for OpportunisticRegionResolver<'a, 'tcx
fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
match *r {
ty::ReVar(rid) => {
let resolved = self
.infcx
.inner
.borrow_mut()
.unwrap_region_constraints()
.opportunistic_resolve_var(rid);
TypeFolder::interner(self).mk_re_var(resolved)
}
ty::ReVar(vid) => self
.infcx
.inner
.borrow_mut()
.unwrap_region_constraints()
.opportunistic_resolve_var(TypeFolder::interner(self), vid),
_ => r,
}
}

37
compiler/rustc_middle/src/infer/unify_key.rs
View file

@ -1,4 +1,4 @@
use crate::ty::{self, Ty, TyCtxt};
use crate::ty::{self, Region, Ty, TyCtxt};
use rustc_data_structures::unify::{NoError, UnifyKey, UnifyValue};
use rustc_span::def_id::DefId;
use rustc_span::symbol::Symbol;
@ -11,7 +11,20 @@ pub trait ToType {
}
#[derive(PartialEq, Copy, Clone, Debug)]
pub struct UnifiedRegion<'tcx>(pub Option<ty::Region<'tcx>>);
pub struct UnifiedRegion<'tcx> {
value: Option<ty::Region<'tcx>>,
}
impl<'tcx> UnifiedRegion<'tcx> {
pub fn new(value: Option<Region<'tcx>>) -> Self {
Self { value }
}
/// The caller is responsible for checking universe compatibility before using this value.
pub fn get_value_ignoring_universes(self) -> Option<Region<'tcx>> {
self.value
}
}
#[derive(PartialEq, Copy, Clone, Debug)]
pub struct RegionVidKey<'tcx> {
@ -44,11 +57,27 @@ impl<'tcx> UnifyValue for UnifiedRegion<'tcx> {
type Error = NoError;
fn unify_values(value1: &Self, value2: &Self) -> Result<Self, NoError> {
Ok(match (value1.0, value2.0) {
// We pick the value of the least universe because it is compatible with more variables.
// This is *not* neccessary for soundness, but it allows more region variables to be
// resolved to the said value.
#[cold]
fn min_universe<'tcx>(r1: Region<'tcx>, r2: Region<'tcx>) -> Region<'tcx> {
cmp::min_by_key(r1, r2, |r| match r.kind() {
ty::ReStatic
| ty::ReErased
| ty::ReFree(..)
| ty::ReEarlyBound(..)
| ty::ReError(_) => ty::UniverseIndex::ROOT,
ty::RePlaceholder(placeholder) => placeholder.universe,
ty::ReVar(..) | ty::ReLateBound(..) => bug!("not a universal region"),
})
}
Ok(match (value1.value, value2.value) {
// Here we can just pick one value, because the full constraints graph
// will be handled later. Ideally, we might want a `MultipleValues`
// variant or something. For now though, this is fine.
(Some(_), Some(_)) => *value1,
(Some(val1), Some(val2)) => Self { value: Some(min_universe(val1, val2)) },
(Some(_), _) => *value1,
(_, Some(_)) => *value2,

4
compiler/rustc_trait_selection/src/traits/project.rs
View file

@ -870,12 +870,12 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for PlaceholderReplacer<'_, 'tcx> {
fn fold_region(&mut self, r0: ty::Region<'tcx>) -> ty::Region<'tcx> {
let r1 = match *r0 {
ty::ReVar(_) => self
ty::ReVar(vid) => self
.infcx
.inner
.borrow_mut()
.unwrap_region_constraints()
.opportunistic_resolve_region(self.infcx.tcx, r0),
.opportunistic_resolve_var(self.infcx.tcx, vid),
_ => r0,
};