[ICE]: Compiler hangs with generic_const_exprs + over 9 trait bounds

Code

Compiler hangs with 10 or more trait bounds. Still compiles within a few seconds when 9 is used.

#![feature(generic_const_exprs)]
#![allow(incomplete_features)]
trait Cfg { const A:usize; const B:usize; const C:usize; const D:usize; const E:usize;
            const F:usize; const G:usize; const H:usize; const I:usize; const J:usize; }
struct S<C:Cfg>(std::marker::PhantomData<C>) where
    [();C::A]:,[();C::B]:,[();C::C]:,[();C::D]:,[();C::E]:,
    [();C::F]:,[();C::G]:,[();C::H]:,[();C::I]:,[();C::J]:;
trait T { fn f()->Self; }
impl<C:Cfg> T for S<C> where
    [();C::A]:,[();C::B]:,[();C::C]:,[();C::D]:,[();C::E]:,
    [();C::F]:,[();C::G]:,[();C::H]:,[();C::I]:,[();C::J]:
{ fn f()->Self { S(std::marker::PhantomData) } }
struct X;
impl Cfg for X { const A:usize=1;const B:usize=1;const C:usize=1;const D:usize=1;const E:usize=1;
                 const F:usize=1;const G:usize=1;const H:usize=1;const I:usize=1;const J:usize=1; }
#[test] fn t() { let _:S<X>=S::f(); }

Playground link

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rustc --version --verbose:

rustc 1.93.1 (01f6ddf75 2026-02-11)
binary: rustc
commit-hash: 01f6ddf7588f42ae2d7eb0a2f21d44e8e96674cf
commit-date: 2026-02-11
host: aarch64-apple-darwin
release: 1.93.1
LLVM version: 21.1.8

Error output

Based on sampling, a hang somewhere in

  compiler/rustc_trait_selection/src/traits/select/mod.rs                                                                                                 
    -> expand_abstract_consts
    → evaluate_predicate_recursively                                                                                                                      
    → evaluate_predicates_recursively 

I'll try and trace to see what exactly blows up here.

Reproduce the provided generic_const_exprs example, comparing the 9- and 10-bound cases. Start in compiler/rustc_trait_selection/src/traits/select/mod.rs and trace expand_abstract_consts through evaluate_predicate_recursively and evaluate_predicates_recursively. Done means the reproducer no longer hangs and the behavior is covered by a regression test.