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Auto merge of rust-lang#100980 - compiler-errors:normalize-opaque-w-b…
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…ound-vars, r=lcnr

Normalize opaques w/ bound vars

First, we reenable normalization of opaque types with escaping late bound regions to fix rust-lang/miri#2433. This essentially reverts rust-lang#89285.

Second, we mitigate the perf regression found in rust-lang#88862 by simplifying the way that we relate (sub and eq) GeneratorWitness types.

This relies on the fact that we construct these GeneratorWitness types somewhat particularly (with all free regions found in the witness types replaced with late bound regions) -- but those bound regions really should be treated as existential regions, not universal ones. Those two facts leads me to believe that we do not need to use the full `higher_ranked_sub` machinery to relate two generator witnesses. I'm pretty confident that this is correct, but I'm glad to discuss this further.
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bors committed Sep 22, 2022
2 parents c10f7d7 + 3fc328d commit 8ab71ab
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Showing 7 changed files with 43 additions and 24 deletions.
19 changes: 19 additions & 0 deletions compiler/rustc_infer/src/infer/equate.rs
Original file line number Diff line number Diff line change
Expand Up @@ -110,6 +110,25 @@ impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
.obligations,
);
}
// Optimization of GeneratorWitness relation since we know that all
// free regions are replaced with bound regions during construction.
// This greatly speeds up equating of GeneratorWitness.
(&ty::GeneratorWitness(a_types), &ty::GeneratorWitness(b_types)) => {
let a_types = infcx.tcx.anonymize_bound_vars(a_types);
let b_types = infcx.tcx.anonymize_bound_vars(b_types);
if a_types.bound_vars() == b_types.bound_vars() {
let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders(
a_types.map_bound(|a_types| (a_types, b_types.skip_binder())),
);
for (a, b) in std::iter::zip(a_types, b_types) {
self.relate(a, b)?;
}
} else {
return Err(ty::error::TypeError::Sorts(ty::relate::expected_found(
self, a, b,
)));
}
}

_ => {
self.fields.infcx.super_combine_tys(self, a, b)?;
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18 changes: 18 additions & 0 deletions compiler/rustc_infer/src/infer/sub.rs
Original file line number Diff line number Diff line change
Expand Up @@ -164,6 +164,24 @@ impl<'tcx> TypeRelation<'tcx> for Sub<'_, '_, 'tcx> {
);
Ok(ga)
}
// Optimization of GeneratorWitness relation since we know that all
// free regions are replaced with bound regions during construction.
// This greatly speeds up subtyping of GeneratorWitness.
(&ty::GeneratorWitness(a_types), &ty::GeneratorWitness(b_types)) => {
let a_types = infcx.tcx.anonymize_bound_vars(a_types);
let b_types = infcx.tcx.anonymize_bound_vars(b_types);
if a_types.bound_vars() == b_types.bound_vars() {
let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders(
a_types.map_bound(|a_types| (a_types, b_types.skip_binder())),
);
for (a, b) in std::iter::zip(a_types, b_types) {
self.relate(a, b)?;
}
Ok(a)
} else {
Err(ty::error::TypeError::Sorts(ty::relate::expected_found(self, a, b)))
}
}

_ => {
self.fields.infcx.super_combine_tys(self, a, b)?;
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2 changes: 1 addition & 1 deletion compiler/rustc_trait_selection/src/traits/project.rs
Original file line number Diff line number Diff line change
Expand Up @@ -499,7 +499,7 @@ impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
// This is really important. While we *can* handle this, this has
// severe performance implications for large opaque types with
// late-bound regions. See `issue-88862` benchmark.
ty::Opaque(def_id, substs) if !substs.has_escaping_bound_vars() => {
ty::Opaque(def_id, substs) => {
// Only normalize `impl Trait` outside of type inference, usually in codegen.
match self.param_env.reveal() {
Reveal::UserFacing => ty.super_fold_with(self),
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Original file line number Diff line number Diff line change
Expand Up @@ -198,7 +198,7 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
// This is really important. While we *can* handle this, this has
// severe performance implications for large opaque types with
// late-bound regions. See `issue-88862` benchmark.
ty::Opaque(def_id, substs) if !substs.has_escaping_bound_vars() => {
ty::Opaque(def_id, substs) => {
// Only normalize `impl Trait` outside of type inference, usually in codegen.
match self.param_env.reveal() {
Reveal::UserFacing => ty.try_super_fold_with(self),
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5 changes: 3 additions & 2 deletions compiler/rustc_typeck/src/check/generator_interior.rs
Original file line number Diff line number Diff line change
Expand Up @@ -218,7 +218,8 @@ pub fn resolve_interior<'a, 'tcx>(
.filter_map(|mut cause| {
// Erase regions and canonicalize late-bound regions to deduplicate as many types as we
// can.
let erased = fcx.tcx.erase_regions(cause.ty);
let ty = fcx.normalize_associated_types_in(cause.span, cause.ty);
let erased = fcx.tcx.erase_regions(ty);
if captured_tys.insert(erased) {
// Replace all regions inside the generator interior with late bound regions.
// Note that each region slot in the types gets a new fresh late bound region,
Expand Down Expand Up @@ -263,7 +264,7 @@ pub fn resolve_interior<'a, 'tcx>(
// Unify the type variable inside the generator with the new witness
match fcx.at(&fcx.misc(body.value.span), fcx.param_env).eq(interior, witness) {
Ok(ok) => fcx.register_infer_ok_obligations(ok),
_ => bug!(),
_ => bug!("failed to relate {interior} and {witness}"),
}
}

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20 changes: 1 addition & 19 deletions src/test/ui/higher-rank-trait-bounds/issue-95034.rs
Original file line number Diff line number Diff line change
@@ -1,23 +1,5 @@
// known-bug: #95034
// failure-status: 101
// check-pass
// compile-flags: --edition=2021 --crate-type=lib
// rustc-env:RUST_BACKTRACE=0

// normalize-stderr-test "thread 'rustc' panicked.*" -> "thread 'rustc' panicked"
// normalize-stderr-test "note:.*RUST_BACKTRACE=1.*\n" -> ""
// normalize-stderr-test "\nerror: internal compiler error.*\n\n" -> ""
// normalize-stderr-test "note:.*unexpectedly panicked.*\n\n" -> ""
// normalize-stderr-test "note: we would appreciate a bug report.*\n\n" -> ""
// normalize-stderr-test "note: compiler flags.*\n\n" -> ""
// normalize-stderr-test "note: rustc.*running on.*\n\n" -> ""
// normalize-stderr-test "query stack during panic:\n" -> ""
// normalize-stderr-test "we're just showing a limited slice of the query stack\n" -> ""
// normalize-stderr-test "end of query stack\n" -> ""
// normalize-stderr-test "#.*\n" -> ""

// This should not ICE.

// Refer to the issue for more minimized versions.

use std::{
future::Future,
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1 change: 0 additions & 1 deletion src/test/ui/higher-rank-trait-bounds/issue-95034.stderr

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