`search_graph` incorrectly overwrites existing cache entry

[lcnr]

#![feature(fn_delegation)]
#![allow(incomplete_features)]

mod opaque {
    trait Trait {}
    impl Trait for () {}

    mod to_reuse {
        use super::Trait;
        pub fn opaque_ret() -> impl Trait { () }
    }

    trait ToReuse {
        fn opaque_ret() -> impl Trait { () }
    }

    // FIXME: Inherited `impl Trait`s create query cycles when used inside trait impls.
    impl ToReuse for u8 {
        reuse to_reuse::opaque_ret; //~ ERROR cycle detected when computing type
    }
}

error[E0391]: cycle detected when computing type of `opaque::<impl at src/main.rs:18:5: 18:24>::opaque_ret::{anon_assoc#0}`
  --> src/main.rs:19:25
   |
19 |         reuse to_reuse::opaque_ret; //~ ERROR cycle detected when computing type
   |                         ^^^^^^^^^^
   |
note: ...which requires comparing an impl and trait method signature, inferring any hidden `impl Trait` types in the process...
  --> src/main.rs:19:25
   |
19 |         reuse to_reuse::opaque_ret; //~ ERROR cycle detected when computing type
   |                         ^^^^^^^^^^
   = note: ...which again requires computing type of `opaque::<impl at src/main.rs:18:5: 18:24>::opaque_ret::{anon_assoc#0}`, completing the cycle
   = note: cycle used when computing implied outlives bounds for `<u8 as opaque::ToReuse>::opaque_ret::{anon_assoc#0}` (hack disabled = false)
   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information


thread 'rustc' panicked at /home/lcnr/rust/compiler/rustc_type_ir/src/search_graph/global_cache.rs:65:17:
assertion failed: cx.evaluation_is_concurrent()