diff --git a/compiler/rustc_arena/src/lib.rs b/compiler/rustc_arena/src/lib.rs
index dfc48b0bd1cd6..43e2031db65af 100644
--- a/compiler/rustc_arena/src/lib.rs
+++ b/compiler/rustc_arena/src/lib.rs
@@ -707,6 +707,23 @@ pub macro declare_arena(
             self.dropless.alloc_str(string)
         }
 
+        #[inline]
+        pub fn alloc_os_str(&self, os_str: &::std::ffi::OsStr) -> &::std::ffi::OsStr {
+            use ::std::ffi::OsStr;
+            if os_str.is_empty() {
+                return OsStr::new("");
+            }
+            let bytes = self.dropless.alloc_slice(os_str.as_encoded_bytes());
+            // SAFETY: These bytes are an exact copy of `os_str.as_encoded_bytes()`.
+            unsafe { OsStr::from_encoded_bytes_unchecked(bytes) }
+        }
+
+        #[inline]
+        pub fn alloc_path(&self, path: &::std::path::Path) -> &::std::path::Path {
+            use ::std::path::Path;
+            Path::new(self.alloc_os_str(path.as_os_str()))
+        }
+
         #[allow(clippy::mut_from_ref)]
         pub fn alloc_from_iter<T: ArenaAllocatable<'tcx, C>, C>(
             &'tcx self,
@@ -714,6 +731,18 @@ pub macro declare_arena(
         ) -> &mut [T] {
             T::allocate_from_iter(self, iter)
         }
+
+        #[allow(clippy::mut_from_ref)]
+        pub fn alloc_index_slice_from_iter<I, T, C>(
+            &'tcx self,
+            iter: impl ::std::iter::IntoIterator<Item = T>,
+        ) -> &mut ::rustc_index::IndexSlice<I, T>
+        where
+            I: ::rustc_index::Idx,
+            T: ArenaAllocatable<'tcx, C>,
+        {
+            ::rustc_index::IndexSlice::from_raw_mut(self.alloc_from_iter(iter))
+        }
     }
 }
 
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 93a7c6cc4d305..ef6995d9c11d6 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -63,7 +63,7 @@ use rustc_hir::{
     self as hir, AngleBrackets, ConstArg, GenericArg, HirId, ItemLocalMap, LifetimeSource,
     LifetimeSyntax, MissingLifetimeKind, ParamName, Target, TraitCandidate, find_attr,
 };
-use rustc_index::{Idx, IndexVec};
+use rustc_index::{Idx, IndexSlice, IndexVec};
 use rustc_macros::extension;
 use rustc_middle::middle::resolve::{
     AstOwner, LifetimeRes, PartialRes, PerOwnerResolverData, ResolverAstLowering,
@@ -579,7 +579,7 @@ enum TryBlockScope {
 fn index_ast<'tcx>(
     tcx: TyCtxt<'tcx>,
     (): (),
-) -> IndexVec<LocalDefId, Steal<(Arc<ResolverAstLowering<'tcx>>, AstOwner)>> {
+) -> &'tcx IndexSlice<LocalDefId, Steal<(Arc<ResolverAstLowering<'tcx>>, AstOwner)>> {
     // Queries that borrow `resolver_for_lowering`.
     tcx.ensure_done().output_filenames(());
     tcx.ensure_done().early_lint_checks(());
@@ -601,8 +601,9 @@ fn index_ast<'tcx>(
 
     let index = indexer.index;
     let resolver = Arc::new(resolver);
-    let index = index.into_iter().map(|owner| Steal::new((Arc::clone(&resolver), owner))).collect();
-    return index;
+    return tcx.arena.alloc_index_slice_from_iter::<LocalDefId, _, _>(
+        index.into_iter().map(|owner| Steal::new((Arc::clone(&resolver), owner))),
+    );
 
     struct Indexer<'s, 'hir> {
         owners: &'s NodeMap<PerOwnerResolverData<'hir>>,
diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index ebdb82e2b4fe6..159295fb2b05e 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -492,14 +492,7 @@ fn early_lint_checks(tcx: TyCtxt<'_>, (): ()) {
 fn env_var_os<'tcx>(tcx: TyCtxt<'tcx>, key: &'tcx OsStr) -> Option<&'tcx OsStr> {
     let value = env::var_os(key);
 
-    let value_tcx = value.as_ref().map(|value| {
-        let encoded_bytes = tcx.arena.alloc_slice(value.as_encoded_bytes());
-        debug_assert_eq!(value.as_encoded_bytes(), encoded_bytes);
-        // SAFETY: The bytes came from `as_encoded_bytes`, and we assume that
-        // `alloc_slice` is implemented correctly, and passes the same bytes
-        // back (debug asserted above).
-        unsafe { OsStr::from_encoded_bytes_unchecked(encoded_bytes) }
-    });
+    let value_tcx = value.as_ref().map(|value| tcx.arena.alloc_os_str(value));
 
     // Also add the variable to Cargo's dependency tracking
     //
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index 08053bb2c6a60..f75da94edfe49 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -382,7 +382,7 @@ provide! { tcx, def_id, other, cdata,
     crate_name => { cdata.root.header.name }
     num_extern_def_ids => { cdata.num_def_ids() }
 
-    extra_filename => { cdata.root.extra_filename.clone() }
+    extra_filename => { tcx.arena.alloc_str(&cdata.root.extra_filename) }
 
     traits => { tcx.arena.alloc_from_iter(cdata.get_traits(tcx)) }
     trait_impls_in_crate => { tcx.arena.alloc_from_iter(cdata.get_trait_impls(tcx)) }
@@ -418,7 +418,9 @@ provide! { tcx, def_id, other, cdata,
     exported_non_generic_symbols => { cdata.exported_non_generic_symbols(tcx) }
     exported_generic_symbols => { cdata.exported_generic_symbols(tcx) }
 
-    crate_extern_paths => { cdata.source().paths().cloned().collect() }
+    crate_extern_paths => {
+        tcx.arena.alloc_from_iter(cdata.source().paths().map(|p| tcx.arena.alloc_path(p)))
+    }
     expn_that_defined => { cdata.get_expn_that_defined(tcx, def_id.index) }
     default_field => { cdata.get_default_field(tcx, def_id.index) }
     is_doc_hidden => { cdata.get_attr_flags(def_id.index).contains(AttrFlags::IS_DOC_HIDDEN) }
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index f55783e60da0c..713671c3a5b47 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -2091,7 +2091,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                     hash: self.tcx.crate_hash(cnum),
                     host_hash: self.tcx.crate_host_hash(cnum),
                     kind: self.tcx.crate_dep_kind(cnum),
-                    extra_filename: self.tcx.extra_filename(cnum).clone(),
+                    extra_filename: self.tcx.extra_filename(cnum).to_owned(),
                     is_private: self.tcx.is_private_dep(cnum),
                 };
                 (cnum, dep)
diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index 3c973d7d3a5a2..bfaef6157d02c 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -41,13 +41,10 @@ rustc_arena::declare_arena! {
             rustc_middle::middle::resolve::ResolverAstLowering<'tcx>
         >,
     index_ast:
-        rustc_index::IndexVec<
-            rustc_span::def_id::LocalDefId,
-            rustc_data_structures::steal::Steal<(
-                std::sync::Arc<rustc_middle::middle::resolve::ResolverAstLowering<'tcx>>,
-                rustc_middle::middle::resolve::AstOwner
-            )>
-        >,
+        rustc_data_structures::steal::Steal<(
+            std::sync::Arc<rustc_middle::middle::resolve::ResolverAstLowering<'tcx>>,
+            rustc_middle::middle::resolve::AstOwner
+        )>,
     crate_alone: rustc_data_structures::steal::Steal<rustc_ast::Crate>,
     crate_for_resolver: rustc_data_structures::steal::Steal<(rustc_ast::Crate, rustc_ast::AttrVec)>,
     resolutions: rustc_middle::middle::resolve::ResolverGlobalCtxt,
@@ -139,8 +136,6 @@ rustc_arena::declare_arena! {
     crate_inherent_impls: rustc_middle::ty::CrateInherentImpls,
     hir_owner_nodes: rustc_hir::OwnerNodes<'tcx>,
     token_stream: rustc_ast::tokenstream::TokenStream,
-    maybe_owner: rustc_middle::hir::ProjectedMaybeOwner<'tcx>,
-    owner_info: rustc_middle::hir::ProjectedOwnerInfo<'tcx>,
     parenting: rustc_hir::def_id::LocalDefIdMap<rustc_hir::ItemLocalId>,
     trait_candidates: rustc_hir::ItemLocalMap<&'tcx [rustc_hir::TraitCandidate<'tcx>]>,
     delayed_lints: rustc_data_structures::steal::Steal<rustc_hir::lints::DelayedLints>,
diff --git a/compiler/rustc_middle/src/queries.rs b/compiler/rustc_middle/src/queries.rs
index 85602a7d389c5..33719340f5978 100644
--- a/compiler/rustc_middle/src/queries.rs
+++ b/compiler/rustc_middle/src/queries.rs
@@ -44,7 +44,7 @@
 //! For more details, see the [rustc-dev-guide](https://rustc-dev-guide.rust-lang.org/query.html).
 
 use std::ffi::OsStr;
-use std::path::PathBuf;
+use std::path::Path;
 use std::sync::Arc;
 
 use rustc_abi as abi;
@@ -68,7 +68,7 @@ use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LocalDefIdSet, LocalModId};
 use rustc_hir::{ItemLocalId, PreciseCapturingArgKind};
-use rustc_index::IndexVec;
+use rustc_index::{IndexSlice, IndexVec};
 use rustc_lint_defs::{LintId, StableLintExpectationId};
 use rustc_macros::rustc_queries;
 use rustc_session::Limits;
@@ -204,14 +204,13 @@ rustc_queries! {
         desc { "getting the resolver for lowering" }
     }
 
-    query index_ast(_: ()) -> &'tcx IndexVec<LocalDefId, Steal<(
+    query index_ast(_: ()) -> &'tcx IndexSlice<LocalDefId, Steal<(
         // There is only a single `ResolverAstLowering` for all owners.
         // We want to drop it once the whole HIR has been lowered.
         // We rely on reference counting to know when all definitions have been stolen.
         Arc<ResolverAstLowering<'tcx>>,
         AstOwner,
     )>> {
-        arena_cache
         eval_always
         no_hash
         desc { "getting the AST for lowering" }
@@ -1313,7 +1312,6 @@ rustc_queries! {
     /// Return the set of (transitive) callees that may result in a recursive call to `key`,
     /// if we were able to walk all callees.
     query mir_callgraph_cyclic(key: LocalDefId) -> Option<&'tcx UnordSet<LocalDefId>> {
-        arena_cache
         desc {
             "computing (transitive) callees of `{}` that may recurse",
             tcx.def_path_str(key),
@@ -1442,7 +1440,6 @@ rustc_queries! {
 
     /// Generates a MIR body for the shim.
     query mir_shims(key: ty::ShimKind<'tcx>) -> &'tcx mir::Body<'tcx> {
-        arena_cache
         desc {
             "generating MIR shim for `{}`, kind={:?}",
             tcx.def_path_str(key.def_id()),
@@ -2070,16 +2067,14 @@ rustc_queries! {
 
     /// Gets the extra data to put in each output filename for a crate.
     /// For example, compiling the `foo` crate with `extra-filename=-a` creates a `libfoo-b.rlib` file.
-    query extra_filename(_: CrateNum) -> &'tcx String {
-        arena_cache
+    query extra_filename(_: CrateNum) -> &'tcx str {
         eval_always
         desc { "looking up the extra filename for a crate" }
         separate_provide_extern
     }
 
     /// Gets the paths where the crate came from in the file system.
-    query crate_extern_paths(_: CrateNum) -> &'tcx Vec<PathBuf> {
-        arena_cache
+    query crate_extern_paths(_: CrateNum) -> &'tcx [&'tcx Path] {
         eval_always
         desc { "looking up the paths for extern crates" }
         separate_provide_extern
diff --git a/compiler/rustc_middle/src/query/erase.rs b/compiler/rustc_middle/src/query/erase.rs
index 93d4c59e75c00..15a684491dcab 100644
--- a/compiler/rustc_middle/src/query/erase.rs
+++ b/compiler/rustc_middle/src/query/erase.rs
@@ -13,6 +13,7 @@ use std::mem::MaybeUninit;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::sync::{DynSend, DynSync};
+use rustc_index::{Idx, IndexSlice};
 use rustc_span::def_id::ModId;
 use rustc_span::{ErrorGuaranteed, Spanned};
 
@@ -118,6 +119,10 @@ impl<T> Erasable for &'_ [T] {
     type Storage = [u8; size_of::<&'_ [()]>()];
 }
 
+impl<I: Idx, T> Erasable for &'_ IndexSlice<I, T> {
+    type Storage = [u8; size_of::<&'_ [()]>()];
+}
+
 // Note: this impl does not overlap with the impl for `&'_ T` above because `RawList` is unsized
 // and does not satisfy the implicit `T: Sized` bound.
 //
@@ -170,6 +175,7 @@ macro_rules! impl_erasable_for_types_with_no_type_params {
 // `[u8; size_of::<Foo>()]`. ('_ lifetimes are allowed.)
 impl_erasable_for_types_with_no_type_params! {
     // tidy-alphabetical-start
+    &'_ str,
     (&'_ ty::CrateInherentImpls, Result<(), ErrorGuaranteed>),
     (),
     (traits::solve::QueryResult<'_>, &'_ traits::solve::inspect::Probe<TyCtxt<'_>>, ty::RequiredDepth),
diff --git a/compiler/rustc_mir_transform/src/inline/cycle.rs b/compiler/rustc_mir_transform/src/inline/cycle.rs
index 5b6b5203fdafa..3334c31cb1bf5 100644
--- a/compiler/rustc_mir_transform/src/inline/cycle.rs
+++ b/compiler/rustc_mir_transform/src/inline/cycle.rs
@@ -150,7 +150,7 @@ fn process<'tcx>(
 pub(crate) fn mir_callgraph_cyclic<'tcx>(
     tcx: TyCtxt<'tcx>,
     root: LocalDefId,
-) -> Option<UnordSet<LocalDefId>> {
+) -> Option<&'tcx UnordSet<LocalDefId>> {
     assert!(
         !tcx.is_constructor(root.to_def_id()),
         "you should not call `mir_callgraph_reachable` on enum/struct constructor functions"
@@ -170,7 +170,7 @@ pub(crate) fn mir_callgraph_cyclic<'tcx>(
         ty::Instance::new_raw(root.to_def_id(), ty::GenericArgs::identity_for_item(tcx, root));
     if !should_recurse(tcx, root_instance) {
         trace!("cannot walk, skipping");
-        return Some(involved.into());
+        return Some(tcx.arena.alloc(involved.into()));
     }
     match process(
         tcx,
@@ -182,7 +182,7 @@ pub(crate) fn mir_callgraph_cyclic<'tcx>(
         &mut FxHashMap::default(),
         recursion_limit,
     ) {
-        Some(_) => Some(involved.into()),
+        Some(_) => Some(tcx.arena.alloc(involved.into())),
         _ => None,
     }
 }
diff --git a/compiler/rustc_mir_transform/src/shim.rs b/compiler/rustc_mir_transform/src/shim.rs
index 426c6cd955fc6..b720e7adedb8a 100644
--- a/compiler/rustc_mir_transform/src/shim.rs
+++ b/compiler/rustc_mir_transform/src/shim.rs
@@ -28,7 +28,7 @@ use crate::{
 mod async_destructor_ctor;
 
 pub(super) fn provide(providers: &mut Providers) {
-    providers.mir_shims = make_shim;
+    providers.mir_shims = |tcx, shim| tcx.arena.alloc(make_shim(tcx, shim));
 }
 
 fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, shim: ty::ShimKind<'tcx>) -> Body<'tcx> {