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Assume unevaluated consts are equal to the other consts and add ConstEquate obligation. This delays
the need to evaluate consts eagerly and therefore gets around const eval query cycles.
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37 files changed

+369
-108
lines changed

37 files changed

+369
-108
lines changed

‎src/librustc_infer/infer/canonical/query_response.rs

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -25,7 +25,7 @@ use rustc_middle::arena::ArenaAllocatable;
2525
use rustc_middle::ty::fold::TypeFoldable;
2626
use rustc_middle::ty::relate::TypeRelation;
2727
use rustc_middle::ty::subst::{GenericArg, GenericArgKind};
28-
use rustc_middle::ty::{self, BoundVar, Ty, TyCtxt};
28+
use rustc_middle::ty::{self, BoundVar, Const, Ty, TyCtxt};
2929
use std::fmt::Debug;
3030

3131
impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
@@ -675,6 +675,10 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for QueryTypeRelatingDelegate<'_, 'tcx> {
675675
bug!("should never be invoked with eager normalization")
676676
}
677677

678+
fn const_equate(&mut self, _a: &'tcx Const<'tcx>, _b: &'tcx Const<'tcx>) {
679+
unimplemented!()
680+
}
681+
678682
fn normalization() -> NormalizationStrategy {
679683
NormalizationStrategy::Eager
680684
}

‎src/librustc_infer/infer/combine.rs

Lines changed: 15 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -164,7 +164,6 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
164164
(_, ty::ConstKind::Infer(InferConst::Var(vid))) => {
165165
return self.unify_const_variable(!a_is_expected, vid, a);
166166
}
167-
168167
_ => {}
169168
}
170169

@@ -375,6 +374,20 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
375374
debug!("generalize: success {{ {:?}, {:?} }}", ty, needs_wf);
376375
Ok(Generalization { ty, needs_wf })
377376
}
377+
378+
pub fn add_const_equate_obligation(
379+
&mut self,
380+
a_is_expected: bool,
381+
a: &'tcx ty::Const<'tcx>,
382+
b: &'tcx ty::Const<'tcx>,
383+
) {
384+
let predicate = if a_is_expected {
385+
ty::Predicate::ConstEquate(a, b)
386+
} else {
387+
ty::Predicate::ConstEquate(b, a)
388+
};
389+
self.obligations.push(Obligation::new(self.trace.cause.clone(), self.param_env, predicate));
390+
}
378391
}
379392

380393
struct Generalizer<'cx, 'tcx> {
@@ -635,6 +648,7 @@ impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
635648
}
636649
}
637650
}
651+
ty::ConstKind::Unevaluated(..) => Ok(c),
638652
_ => relate::super_relate_consts(self, c, c),
639653
}
640654
}

‎src/librustc_infer/infer/equate.rs

Lines changed: 12 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -4,7 +4,7 @@ use super::Subtype;
44
use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
55
use rustc_middle::ty::subst::SubstsRef;
66
use rustc_middle::ty::TyVar;
7-
use rustc_middle::ty::{self, Ty, TyCtxt};
7+
use rustc_middle::ty::{self, ConstKind, Ty, TyCtxt};
88

99
use rustc_hir::def_id::DefId;
1010

@@ -119,7 +119,17 @@ impl TypeRelation<'tcx> for Equate<'combine, 'infcx, 'tcx> {
119119
a: &'tcx ty::Const<'tcx>,
120120
b: &'tcx ty::Const<'tcx>,
121121
) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
122-
self.fields.infcx.super_combine_consts(self, a, b)
122+
match (a.val, b.val) {
123+
(ConstKind::Unevaluated(..), _) => {
124+
self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
125+
Ok(b)
126+
}
127+
(_, ConstKind::Unevaluated(..)) => {
128+
self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
129+
Ok(a)
130+
}
131+
_ => self.fields.infcx.super_combine_consts(self, a, b),
132+
}
123133
}
124134

125135
fn binders<T>(

‎src/librustc_infer/infer/glb.rs

Lines changed: 11 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -79,7 +79,17 @@ impl TypeRelation<'tcx> for Glb<'combine, 'infcx, 'tcx> {
7979
a: &'tcx ty::Const<'tcx>,
8080
b: &'tcx ty::Const<'tcx>,
8181
) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
82-
self.fields.infcx.super_combine_consts(self, a, b)
82+
match (a.val, b.val) {
83+
(ty::ConstKind::Unevaluated(..), _) => {
84+
self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
85+
Ok(b)
86+
}
87+
(_, ty::ConstKind::Unevaluated(..)) => {
88+
self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
89+
Ok(a)
90+
}
91+
_ => self.fields.infcx.super_combine_consts(self, a, b),
92+
}
8393
}
8494

8595
fn binders<T>(

‎src/librustc_infer/infer/lub.rs

Lines changed: 11 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -79,7 +79,17 @@ impl TypeRelation<'tcx> for Lub<'combine, 'infcx, 'tcx> {
7979
a: &'tcx ty::Const<'tcx>,
8080
b: &'tcx ty::Const<'tcx>,
8181
) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
82-
self.fields.infcx.super_combine_consts(self, a, b)
82+
match (a.val, b.val) {
83+
(ty::ConstKind::Unevaluated(..), _) => {
84+
self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
85+
Ok(b)
86+
}
87+
(_, ty::ConstKind::Unevaluated(..)) => {
88+
self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
89+
Ok(a)
90+
}
91+
_ => self.fields.infcx.super_combine_consts(self, a, b),
92+
}
8393
}
8494

8595
fn binders<T>(

‎src/librustc_infer/infer/mod.rs

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1452,6 +1452,17 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
14521452
self.report_and_explain_type_error(trace, &err)
14531453
}
14541454

1455+
pub fn report_mismatched_consts(
1456+
&self,
1457+
cause: &ObligationCause<'tcx>,
1458+
expected: &'tcx ty::Const<'tcx>,
1459+
actual: &'tcx ty::Const<'tcx>,
1460+
err: TypeError<'tcx>,
1461+
) -> DiagnosticBuilder<'tcx> {
1462+
let trace = TypeTrace::consts(cause, true, expected, actual);
1463+
self.report_and_explain_type_error(trace, &err)
1464+
}
1465+
14551466
pub fn replace_bound_vars_with_fresh_vars<T>(
14561467
&self,
14571468
span: Span,
@@ -1738,6 +1749,15 @@ impl<'tcx> TypeTrace<'tcx> {
17381749
TypeTrace { cause: cause.clone(), values: Types(ExpectedFound::new(a_is_expected, a, b)) }
17391750
}
17401751

1752+
pub fn consts(
1753+
cause: &ObligationCause<'tcx>,
1754+
a_is_expected: bool,
1755+
a: &'tcx ty::Const<'tcx>,
1756+
b: &'tcx ty::Const<'tcx>,
1757+
) -> TypeTrace<'tcx> {
1758+
TypeTrace { cause: cause.clone(), values: Consts(ExpectedFound::new(a_is_expected, a, b)) }
1759+
}
1760+
17411761
pub fn dummy(tcx: TyCtxt<'tcx>) -> TypeTrace<'tcx> {
17421762
TypeTrace {
17431763
cause: ObligationCause::dummy(),

‎src/librustc_infer/infer/nll_relate/mod.rs

Lines changed: 13 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -82,6 +82,8 @@ pub trait TypeRelatingDelegate<'tcx> {
8282
/// be related. Used for lazy normalization.
8383
fn push_domain_goal(&mut self, domain_goal: DomainGoal<'tcx>);
8484

85+
fn const_equate(&mut self, a: &'tcx ty::Const<'tcx>, b: &'tcx ty::Const<'tcx>);
86+
8587
/// Creates a new universe index. Used when instantiating placeholders.
8688
fn create_next_universe(&mut self) -> ty::UniverseIndex;
8789

@@ -603,8 +605,16 @@ where
603605
b = self.infcx.shallow_resolve(b);
604606
}
605607

606-
match b.val {
607-
ty::ConstKind::Infer(InferConst::Var(_)) if D::forbid_inference_vars() => {
608+
match (a.val, b.val) {
609+
(ty::ConstKind::Unevaluated(..), _) => {
610+
self.delegate.const_equate(a, b);
611+
Ok(b)
612+
}
613+
(_, ty::ConstKind::Unevaluated(..)) => {
614+
self.delegate.const_equate(a, b);
615+
Ok(a)
616+
}
617+
(_, ty::ConstKind::Infer(InferConst::Var(_))) if D::forbid_inference_vars() => {
608618
// Forbid inference variables in the RHS.
609619
bug!("unexpected inference var {:?}", b)
610620
}
@@ -985,6 +995,7 @@ where
985995
}
986996
}
987997
}
998+
ty::ConstKind::Unevaluated(..) => Ok(a),
988999
_ => relate::super_relate_consts(self, a, a),
9891000
}
9901001
}

‎src/librustc_infer/infer/outlives/mod.rs

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -19,7 +19,8 @@ pub fn explicit_outlives_bounds<'tcx>(
1919
| ty::Predicate::ObjectSafe(..)
2020
| ty::Predicate::ClosureKind(..)
2121
| ty::Predicate::TypeOutlives(..)
22-
| ty::Predicate::ConstEvaluatable(..) => None,
22+
| ty::Predicate::ConstEvaluatable(..)
23+
| ty::Predicate::ConstEquate(..) => None,
2324
ty::Predicate::RegionOutlives(ref data) => data
2425
.no_bound_vars()
2526
.map(|ty::OutlivesPredicate(r_a, r_b)| OutlivesBound::RegionSubRegion(r_b, r_a)),

‎src/librustc_infer/infer/sub.rs

Lines changed: 11 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -155,7 +155,17 @@ impl TypeRelation<'tcx> for Sub<'combine, 'infcx, 'tcx> {
155155
a: &'tcx ty::Const<'tcx>,
156156
b: &'tcx ty::Const<'tcx>,
157157
) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
158-
self.fields.infcx.super_combine_consts(self, a, b)
158+
match (a.val, b.val) {
159+
(ty::ConstKind::Unevaluated(..), _) => {
160+
self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
161+
Ok(b)
162+
}
163+
(_, ty::ConstKind::Unevaluated(..)) => {
164+
self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
165+
Ok(a)
166+
}
167+
_ => self.fields.infcx.super_combine_consts(self, a, b),
168+
}
159169
}
160170

161171
fn binders<T>(

‎src/librustc_infer/traits/mod.rs

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@ pub mod util;
1010

1111
use rustc_hir as hir;
1212
use rustc_middle::ty::error::{ExpectedFound, TypeError};
13-
use rustc_middle::ty::{self, Ty};
13+
use rustc_middle::ty::{self, Const, Ty};
1414
use rustc_span::Span;
1515

1616
pub use self::FulfillmentErrorCode::*;
@@ -80,6 +80,7 @@ pub enum FulfillmentErrorCode<'tcx> {
8080
CodeSelectionError(SelectionError<'tcx>),
8181
CodeProjectionError(MismatchedProjectionTypes<'tcx>),
8282
CodeSubtypeError(ExpectedFound<Ty<'tcx>>, TypeError<'tcx>), // always comes from a SubtypePredicate
83+
CodeConstEquateError(ExpectedFound<&'tcx Const<'tcx>>, TypeError<'tcx>),
8384
CodeAmbiguity,
8485
}
8586

‎src/librustc_infer/traits/structural_impls.rs

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -41,6 +41,9 @@ impl<'tcx> fmt::Debug for traits::FulfillmentErrorCode<'tcx> {
4141
super::CodeSubtypeError(ref a, ref b) => {
4242
write!(f, "CodeSubtypeError({:?}, {:?})", a, b)
4343
}
44+
super::CodeConstEquateError(ref a, ref b) => {
45+
write!(f, "CodeConstEquateError({:?}, {:?})", a, b)
46+
}
4447
super::CodeAmbiguity => write!(f, "Ambiguity"),
4548
}
4649
}

‎src/librustc_infer/traits/util.rs

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -40,6 +40,8 @@ pub fn anonymize_predicate<'tcx>(
4040
ty::Predicate::ConstEvaluatable(def_id, substs) => {
4141
ty::Predicate::ConstEvaluatable(def_id, substs)
4242
}
43+
44+
ty::Predicate::ConstEquate(c1, c2) => ty::Predicate::ConstEquate(c1, c2),
4345
}
4446
}
4547

@@ -164,6 +166,10 @@ impl Elaborator<'tcx> {
164166
// Currently, we do not elaborate const-evaluatable
165167
// predicates.
166168
}
169+
ty::Predicate::ConstEquate(..) => {
170+
// Currently, we do not elaborate const-equate
171+
// predicates.
172+
}
167173
ty::Predicate::RegionOutlives(..) => {
168174
// Nothing to elaborate from `'a: 'b`.
169175
}

‎src/librustc_lint/builtin.rs

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1220,7 +1220,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TrivialConstraints {
12201220
ObjectSafe(..) |
12211221
ClosureKind(..) |
12221222
Subtype(..) |
1223-
ConstEvaluatable(..) => continue,
1223+
ConstEvaluatable(..) |
1224+
ConstEquate(..) => continue,
12241225
};
12251226
if predicate.is_global() {
12261227
cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {

‎src/librustc_middle/ty/mod.rs

Lines changed: 10 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1203,6 +1203,9 @@ pub enum Predicate<'tcx> {
12031203

12041204
/// Constant initializer must evaluate successfully.
12051205
ConstEvaluatable(DefId, SubstsRef<'tcx>),
1206+
1207+
/// Constants must be equal. The first component is the const that is expected.
1208+
ConstEquate(&'tcx Const<'tcx>, &'tcx Const<'tcx>),
12061209
}
12071210

12081211
/// The crate outlives map is computed during typeck and contains the
@@ -1321,6 +1324,9 @@ impl<'tcx> Predicate<'tcx> {
13211324
Predicate::ConstEvaluatable(def_id, const_substs) => {
13221325
Predicate::ConstEvaluatable(def_id, const_substs.subst(tcx, substs))
13231326
}
1327+
Predicate::ConstEquate(c1, c2) => {
1328+
Predicate::ConstEquate(c1.subst(tcx, substs), c2.subst(tcx, substs))
1329+
}
13241330
}
13251331
}
13261332
}
@@ -1498,7 +1504,8 @@ impl<'tcx> Predicate<'tcx> {
14981504
| Predicate::ObjectSafe(..)
14991505
| Predicate::ClosureKind(..)
15001506
| Predicate::TypeOutlives(..)
1501-
| Predicate::ConstEvaluatable(..) => None,
1507+
| Predicate::ConstEvaluatable(..)
1508+
| Predicate::ConstEquate(..) => None,
15021509
}
15031510
}
15041511

@@ -1512,7 +1519,8 @@ impl<'tcx> Predicate<'tcx> {
15121519
| Predicate::WellFormed(..)
15131520
| Predicate::ObjectSafe(..)
15141521
| Predicate::ClosureKind(..)
1515-
| Predicate::ConstEvaluatable(..) => None,
1522+
| Predicate::ConstEvaluatable(..)
1523+
| Predicate::ConstEquate(..) => None,
15161524
}
15171525
}
15181526
}

‎src/librustc_middle/ty/outlives.rs

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -62,6 +62,11 @@ fn compute_components(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, out: &mut SmallVec<[Compo
6262
// in the `subtys` iterator (e.g., when encountering a
6363
// projection).
6464
match ty.kind {
65+
ty::Array(element, _) => {
66+
// Don't look into the len const as it doesn't affect regions
67+
compute_components(tcx, element, out);
68+
}
69+
6570
ty::Closure(_, ref substs) => {
6671
for upvar_ty in substs.as_closure().upvar_tys() {
6772
compute_components(tcx, upvar_ty, out);
@@ -139,7 +144,6 @@ fn compute_components(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, out: &mut SmallVec<[Compo
139144
ty::Opaque(..) | // OutlivesNominalType (ish)
140145
ty::Foreign(..) | // OutlivesNominalType
141146
ty::Str | // OutlivesScalar (ish)
142-
ty::Array(..) | // ...
143147
ty::Slice(..) | // ...
144148
ty::RawPtr(..) | // ...
145149
ty::Ref(..) | // OutlivesReference

‎src/librustc_middle/ty/print/pretty.rs

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2044,6 +2044,13 @@ define_print_and_forward_display! {
20442044
print_value_path(def_id, substs),
20452045
write("` can be evaluated"))
20462046
}
2047+
ty::Predicate::ConstEquate(c1, c2) => {
2048+
p!(write("the constant `"),
2049+
print(c1),
2050+
write("` equals `"),
2051+
print(c2),
2052+
write("`"))
2053+
}
20472054
}
20482055
}
20492056

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