traits: Represent live alias arguments as bitsets

Cargo.lock

@@ -4858,6 +4858,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_errors",
  "rustc_hir",
+ "rustc_index",
  "rustc_infer",
  "rustc_macros",
  "rustc_middle",

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -482,8 +482,8 @@ define_tables! {
     anon_const_kind: Table<DefIndex, LazyValue<ty::AnonConstKind>>,
     const_of_item: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, ty::Const<'static>>>>,
     associated_types_for_impl_traits_in_trait_or_impl: Table<DefIndex, LazyValue<DefIdMap<Vec<DefId>>>>,
-    live_args_for_alias_from_outlives_bounds: Table<DefIndex, LazyValue<Option<ty::EarlyBinder<'static, Vec<ty::GenericArg<'static>>>>>>,
-    args_known_to_outlive_alias_params: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, Vec<(ty::Region<'static>, Vec<ty::GenericArg<'static>>)>>>>,
+    live_args_for_alias_from_outlives_bounds: Table<DefIndex, LazyValue<Option<DenseBitSet<usize>>>>,
+    args_known_to_outlive_alias_params: Table<DefIndex, LazyValue<Vec<(usize, DenseBitSet<usize>)>>>,
     mut_restriction: Table<DefIndex, LazyValue<ty::RestrictionKind>>,
 }
 

compiler/rustc_metadata/src/rmeta/parameterized.rs

@@ -106,6 +106,7 @@ trivially_parameterized_over_tcx! {
     rustc_hir::def_id::DefIndex,
     rustc_hir::definitions::DefKey,
     rustc_index::bit_set::DenseBitSet<u32>,
+    rustc_index::bit_set::DenseBitSet<usize>,
     rustc_middle::metadata::AmbigModChild,
     rustc_middle::metadata::ModChild,
     rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs,

compiler/rustc_middle/src/queries.rs

@@ -2140,9 +2140,9 @@ rustc_queries! {
         desc { "listing captured lifetimes for opaque `{}`", tcx.def_path_str(def_id) }
     }
 
-    /// For an opaque type or trait associated type, return the list of potentially live
-    /// (identity) generic args from the set of outlives bounds on that alias. Callers should
-    /// instantiate the returned args with the concrete args of the alias.
+    /// For an opaque type or trait associated type, return the indices of potentially live
+    /// generic args from the set of outlives bounds on that alias. Callers should use the
+    /// indices with the concrete args of the alias.
     /// ```ignore (illustrative)
     /// // Edition 2024: all args are captured
     /// fn foo<'a, 'b, T: 'static>(&'a &'b T) -> impl Sized + 'a {}
@@ -2155,16 +2155,16 @@ rustc_queries! {
     ///     (and so is `T`, since `T: 'static` implies `T: 'a`)
     ///   - `bar` outlives `'static`, so we know that no args are potentially live and we can return an empty set
     ///   - `baz` has no outlives bound, so return `None` and let the caller decide what to do
-    query live_args_for_alias_from_outlives_bounds(kind: ty::AliasTyKind<'tcx>) -> &'tcx Option<ty::EarlyBinder<'tcx, Vec<ty::GenericArg<'tcx>>>> {
+    query live_args_for_alias_from_outlives_bounds(kind: ty::AliasTyKind<'tcx>) -> &'tcx Option<rustc_index::bit_set::DenseBitSet<usize>> {
         arena_cache
         desc { "identifying live args for alias `{:?}`", kind }
     }
 
-    /// For each region param of an alias, the identity args that are known to
+    /// For each region param of an alias, the indices of the identity args that are known to
     /// outlive it given only the alias's declared where-clauses. Used for liveness:
     /// these are the only args whose regions the underlying type of the alias
     /// could capture while satisfying an outlives bound on that param.
-    query args_known_to_outlive_alias_params(def_id: DefId) -> &'tcx ty::EarlyBinder<'tcx, Vec<(ty::Region<'tcx>, Vec<ty::GenericArg<'tcx>>)>> {
+    query args_known_to_outlive_alias_params(def_id: DefId) -> &'tcx Vec<(usize, rustc_index::bit_set::DenseBitSet<usize>)> {
         arena_cache
         desc { "computing the args known to outlive each region param of alias `{}`", tcx.def_path_str(def_id) }
         separate_provide_extern

compiler/rustc_trait_selection/Cargo.toml

@@ -11,6 +11,7 @@ rustc_ast = { path = "../rustc_ast" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_hir = { path = "../rustc_hir" }
+rustc_index = { path = "../rustc_index" }
 rustc_infer = { path = "../rustc_infer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }