[ICE] with min_const_generics and mir-opt-level=2

[leonardo-m]

#![feature(min_const_generics)]
#[derive(Clone)]
struct Foo<TK, TV, const LEN: usize> {
    data: [(TK, TV); LEN],
    len: usize,
}
impl<TK: PartialEq, TV, const LEN: usize> Foo<TK, TV, LEN> {
    fn insert(&mut self, k: TK, v: TV) {
        if let Some((_, v0)) = self.data[.. self.len].iter_mut().find(|(k0, _)| k == *k0) {
            *v0 = v;
        } else {
            self.data[self.len] = (k, v);
            self.len += 1;
        }
    }
}
fn main() {
    let mut z = Vec::<Foo<u32, u32, 10>>::new();
    while let Some(x) = z.pop() {
        let mut y = x.clone();
        y.insert(0, 1);
    }
}

Gives:

error: internal compiler error: /rustc/593fe977a77ad5a7aec23c6cb0f86a3470221670\compiler\rustc_middle\src\ty\consts.rs:201:32: expected usize, got Const {
    ty: usize,
    val: Param(
        LEN/#2,
    ),
}

thread 'rustc' panicked at 'Box<Any>', compiler\rustc_errors\src\lib.rs:958:9
stack backtrace:
   0: std::panicking::begin_panic
   1: rustc_errors::HandlerInner::bug
   2: rustc_errors::Handler::bug
   3: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
   4: rustc_middle::ty::context::tls::with_opt::{{closure}}
   5: rustc_middle::ty::context::tls::with_opt
   6: rustc_middle::util::bug::opt_span_bug_fmt
   7: rustc_middle::util::bug::bug_fmt
   8: rustc_middle::ty::consts::Const::eval_usize::{{closure}}
   9: rustc_mir::shim::make_shim
  10: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_shims>::compute
  11: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  12: rustc_data_structures::stack::ensure_sufficient_stack
  13: rustc_query_system::query::plumbing::get_query_impl
  14: rustc_middle::ty::<impl rustc_middle::ty::context::TyCtxt>::instance_mir
  15: rustc_mir::transform::inline::Inliner::process_blocks
  16: <rustc_mir::transform::inline::Inline as rustc_mir::transform::MirPass>::run_pass
  17: rustc_mir::transform::run_passes
  18: rustc_mir::transform::run_optimization_passes
  19: rustc_mir::transform::optimized_mir
  20: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  21: rustc_data_structures::stack::ensure_sufficient_stack
  22: rustc_query_system::query::plumbing::get_query_impl
  23: rustc_middle::ty::<impl rustc_middle::ty::context::TyCtxt>::instance_mir
  24: rustc_mir::transform::inline::Inliner::process_blocks
  25: <rustc_mir::transform::inline::Inline as rustc_mir::transform::MirPass>::run_pass
  26: rustc_mir::transform::run_passes
  27: rustc_mir::transform::run_optimization_passes
  28: rustc_mir::transform::optimized_mir
  29: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  30: rustc_data_structures::stack::ensure_sufficient_stack
  31: rustc_query_system::query::plumbing::get_query_impl
  32: rustc_middle::ty::<impl rustc_middle::ty::context::TyCtxt>::instance_mir
  33: rustc_mir::monomorphize::collector::collect_neighbours
  34: rustc_mir::monomorphize::collector::collect_items_rec
  35: rustc_session::utils::<impl rustc_session::session::Session>::time
  36: rustc_mir::monomorphize::collector::collect_crate_mono_items
  37: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  38: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::collect_and_partition_mono_items>::compute
  39: rustc_query_system::dep_graph::graph::DepGraph<K>::with_eval_always_task
  40: rustc_data_structures::stack::ensure_sufficient_stack
  41: rustc_query_system::query::plumbing::get_query_impl
  42: rustc_codegen_ssa::base::codegen_crate
  43: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  44: rustc_interface::passes::QueryContext::enter
  45: rustc_interface::queries::Queries::ongoing_codegen
  46: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  47: rustc_span::with_source_map
  48: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.50.0-nightly (593fe977a 2020-11-20) running on x86_64-pc-windows-gnu

note: compiler flags: -Z mir-opt-level=2 -C lto

query stack during panic:
#0 [mir_shims] generating MIR shim for `std::clone::Clone::clone`
#1 [optimized_mir] optimizing MIR for `<Foo<TK, TV, LEN> as std::clone::Clone>::clone`
#2 [optimized_mir] optimizing MIR for `main`
#3 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: aborting due to previous error