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Auto merge of #100980 - compiler-errors:normalize-opaque-w-bound-vars, r=lcnr

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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 #89285.

Second, we mitigate the perf regression found in #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.
This commit is contained in:
bors 2022-09-22 12:47:31 +00:00
commit 8ab71ab59f
7 changed files with 43 additions and 24 deletions
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2
compiler/rustc_trait_selection/src/traits/project.rs
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@ -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),

2
compiler/rustc_trait_selection/src/traits/query/normalize.rs
View file

@ -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),