diff --git a/Cargo.lock b/Cargo.lock
index 57d43dad3f..ce71a89897 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1046,6 +1046,7 @@ checksum = "75761162ae2b0e580d7e7c390558127e5f01b4194debd6221fd8c207fc80e3f5"
 name = "mbe"
 version = "0.0.0"
 dependencies = [
+ "arrayvec",
  "cov-mark",
  "parser",
  "rustc-hash",
diff --git a/crates/hir-def/src/nameres.rs b/crates/hir-def/src/nameres.rs
index 162b6429c3..8e7ef48112 100644
--- a/crates/hir-def/src/nameres.rs
+++ b/crates/hir-def/src/nameres.rs
@@ -103,12 +103,13 @@ const PREDEFINED_TOOLS: &[SmolStr] = &[
 /// is computed by the `block_def_map` query.
 #[derive(Debug, PartialEq, Eq)]
 pub struct DefMap {
+    /// The crate this `DefMap` belongs to.
+    krate: CrateId,
     /// When this is a block def map, this will hold the block id of the block and module that
     /// contains this block.
     block: Option<BlockInfo>,
     /// The modules and their data declared in this crate.
     pub modules: Arena<ModuleData>,
-    krate: CrateId,
     /// The prelude module for this crate. This either comes from an import
     /// marked with the `prelude_import` attribute, or (in the normal case) from
     /// a dependency (`std` or `core`).
@@ -124,6 +125,7 @@ pub struct DefMap {
 
     /// Tracks which custom derives are in scope for an item, to allow resolution of derive helper
     /// attributes.
+    // FIXME: Figure out a better way for the IDE layer to resolve these?
     derive_helpers_in_scope: FxHashMap<AstId<ast::Item>, Vec<(Name, MacroId, MacroCallId)>>,
 
     /// The diagnostics that need to be emitted for this crate.
diff --git a/crates/hir-expand/src/change.rs b/crates/hir-expand/src/change.rs
index 1a3dd0e7dd..08491db372 100644
--- a/crates/hir-expand/src/change.rs
+++ b/crates/hir-expand/src/change.rs
@@ -25,7 +25,8 @@ impl ChangeWithProcMacros {
 
     pub fn apply(self, db: &mut (impl ExpandDatabase + SourceDatabaseExt)) {
         self.source_change.apply(db);
-        if let Some(proc_macros) = self.proc_macros {
+        if let Some(mut proc_macros) = self.proc_macros {
+            proc_macros.shrink_to_fit();
             db.set_proc_macros_with_durability(Arc::new(proc_macros), Durability::HIGH);
         }
         if let Some(target_data_layouts) = self.target_data_layouts {
diff --git a/crates/hir-ty/src/method_resolution.rs b/crates/hir-ty/src/method_resolution.rs
index 5ce124d6d2..ac11da789a 100644
--- a/crates/hir-ty/src/method_resolution.rs
+++ b/crates/hir-ty/src/method_resolution.rs
@@ -1322,7 +1322,7 @@ fn iterate_inherent_methods(
         callback: &mut dyn FnMut(ReceiverAdjustments, AssocItemId, bool) -> ControlFlow<()>,
     ) -> ControlFlow<()> {
         for &impl_id in impls.for_self_ty(self_ty) {
-            for &item in &table.db.impl_data(impl_id).items {
+            for &item in table.db.impl_data(impl_id).items.iter() {
                 let visible = match is_valid_impl_method_candidate(
                     table,
                     self_ty,
diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index c742cefe89..eea25ac18a 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -760,7 +760,7 @@ impl Module {
                 impl_assoc_items_scratch.clear();
             }
 
-            for &item in &db.impl_data(impl_def.id).items {
+            for &item in db.impl_data(impl_def.id).items.iter() {
                 AssocItem::from(item).diagnostics(db, acc, style_lints);
             }
         }
diff --git a/crates/hir/src/symbols.rs b/crates/hir/src/symbols.rs
index 3b88836c24..02905ca2ce 100644
--- a/crates/hir/src/symbols.rs
+++ b/crates/hir/src/symbols.rs
@@ -231,7 +231,7 @@ impl<'a> SymbolCollector<'a> {
         let impl_data = self.db.impl_data(impl_id);
         let impl_name = Some(SmolStr::new(impl_data.self_ty.display(self.db).to_string()));
         self.with_container_name(impl_name, |s| {
-            for &assoc_item_id in &impl_data.items {
+            for &assoc_item_id in impl_data.items.iter() {
                 s.push_assoc_item(assoc_item_id)
             }
         })
diff --git a/crates/mbe/Cargo.toml b/crates/mbe/Cargo.toml
index 2046fa943a..18444018e1 100644
--- a/crates/mbe/Cargo.toml
+++ b/crates/mbe/Cargo.toml
@@ -16,6 +16,7 @@ cov-mark = "2.0.0-pre.1"
 rustc-hash.workspace = true
 smallvec.workspace = true
 tracing.workspace = true
+arrayvec.workspace = true
 
 # local deps
 syntax.workspace = true
diff --git a/crates/mbe/src/benchmark.rs b/crates/mbe/src/benchmark.rs
index 19ba5c7a15..27dbc84a2b 100644
--- a/crates/mbe/src/benchmark.rs
+++ b/crates/mbe/src/benchmark.rs
@@ -170,7 +170,7 @@ fn invocation_fixtures(
             Op::Literal(it) => token_trees.push(tt::Leaf::from(it.clone()).into()),
             Op::Ident(it) => token_trees.push(tt::Leaf::from(it.clone()).into()),
             Op::Punct(puncts) => {
-                for punct in puncts {
+                for punct in puncts.as_slice() {
                     token_trees.push(tt::Leaf::from(*punct).into());
                 }
             }
@@ -187,7 +187,7 @@ fn invocation_fixtures(
                     }
                     if i + 1 != cnt {
                         if let Some(sep) = separator {
-                            match sep {
+                            match &**sep {
                                 Separator::Literal(it) => {
                                     token_trees.push(tt::Leaf::Literal(it.clone()).into())
                                 }
diff --git a/crates/mbe/src/expander/matcher.rs b/crates/mbe/src/expander/matcher.rs
index 0cec4e70da..972ad188ac 100644
--- a/crates/mbe/src/expander/matcher.rs
+++ b/crates/mbe/src/expander/matcher.rs
@@ -59,7 +59,7 @@
 //! eof: [a $( a )* a b ·]
 //! ```
 
-use std::rc::Rc;
+use std::{rc::Rc, sync::Arc};
 
 use smallvec::{smallvec, SmallVec};
 use span::{Edition, Span};
@@ -315,7 +315,7 @@ struct MatchState<'t> {
     up: Option<Box<MatchState<'t>>>,
 
     /// The separator if we are in a repetition.
-    sep: Option<Separator>,
+    sep: Option<Arc<Separator>>,
 
     /// The KleeneOp of this sequence if we are in a repetition.
     sep_kind: Option<RepeatKind>,
diff --git a/crates/mbe/src/expander/transcriber.rs b/crates/mbe/src/expander/transcriber.rs
index 0f689a2692..c09cbd1d07 100644
--- a/crates/mbe/src/expander/transcriber.rs
+++ b/crates/mbe/src/expander/transcriber.rs
@@ -195,7 +195,7 @@ fn expand_subtree(
                 .into(),
             ),
             Op::Punct(puncts) => {
-                for punct in puncts {
+                for punct in puncts.as_slice() {
                     arena.push(
                         tt::Leaf::from({
                             let mut it = *punct;
@@ -222,7 +222,7 @@ fn expand_subtree(
             }
             Op::Repeat { tokens: subtree, kind, separator } => {
                 let ExpandResult { value: fragment, err: e } =
-                    expand_repeat(ctx, subtree, *kind, separator, arena, marker);
+                    expand_repeat(ctx, subtree, *kind, separator.as_deref(), arena, marker);
                 err = err.or(e);
                 push_fragment(ctx, arena, fragment)
             }
@@ -383,7 +383,7 @@ fn expand_repeat(
     ctx: &mut ExpandCtx<'_>,
     template: &MetaTemplate,
     kind: RepeatKind,
-    separator: &Option<Separator>,
+    separator: Option<&Separator>,
     arena: &mut Vec<tt::TokenTree<Span>>,
     marker: impl Fn(&mut Span) + Copy,
 ) -> ExpandResult<Fragment> {
diff --git a/crates/mbe/src/parser.rs b/crates/mbe/src/parser.rs
index bbe00f0afc..256068a899 100644
--- a/crates/mbe/src/parser.rs
+++ b/crates/mbe/src/parser.rs
@@ -1,7 +1,9 @@
 //! Parser recognizes special macro syntax, `$var` and `$(repeat)*`, in token
 //! trees.
 
-use smallvec::{smallvec, SmallVec};
+use std::sync::Arc;
+
+use arrayvec::ArrayVec;
 use span::{Edition, Span, SyntaxContextId};
 use syntax::SmolStr;
 
@@ -86,14 +88,14 @@ pub(crate) enum Op {
     Repeat {
         tokens: MetaTemplate,
         kind: RepeatKind,
-        separator: Option<Separator>,
+        separator: Option<Arc<Separator>>,
     },
     Subtree {
         tokens: MetaTemplate,
         delimiter: tt::Delimiter<Span>,
     },
     Literal(tt::Literal<Span>),
-    Punct(SmallVec<[tt::Punct<Span>; 3]>),
+    Punct(Box<ArrayVec<tt::Punct<Span>, 3>>),
     Ident(tt::Ident<Span>),
 }
 
@@ -126,7 +128,7 @@ pub(crate) enum MetaVarKind {
 pub(crate) enum Separator {
     Literal(tt::Literal<Span>),
     Ident(tt::Ident<Span>),
-    Puncts(SmallVec<[tt::Punct<Span>; 3]>),
+    Puncts(ArrayVec<tt::Punct<Span>, 3>),
 }
 
 // Note that when we compare a Separator, we just care about its textual value.
@@ -165,7 +167,13 @@ fn next_op(
             src.next().expect("first token already peeked");
             // Note that the '$' itself is a valid token inside macro_rules.
             let second = match src.next() {
-                None => return Ok(Op::Punct(smallvec![*p])),
+                None => {
+                    return Ok(Op::Punct({
+                        let mut res = ArrayVec::new();
+                        res.push(*p);
+                        Box::new(res)
+                    }))
+                }
                 Some(it) => it,
             };
             match second {
@@ -173,7 +181,7 @@ fn next_op(
                     tt::DelimiterKind::Parenthesis => {
                         let (separator, kind) = parse_repeat(src)?;
                         let tokens = MetaTemplate::parse(edition, subtree, mode, new_meta_vars)?;
-                        Op::Repeat { tokens, separator, kind }
+                        Op::Repeat { tokens, separator: separator.map(Arc::new), kind }
                     }
                     tt::DelimiterKind::Brace => match mode {
                         Mode::Template => {
@@ -216,7 +224,11 @@ fn next_op(
                                 "`$$` is not allowed on the pattern side",
                             ))
                         }
-                        Mode::Template => Op::Punct(smallvec![*punct]),
+                        Mode::Template => Op::Punct({
+                            let mut res = ArrayVec::new();
+                            res.push(*punct);
+                            Box::new(res)
+                        }),
                     },
                     tt::Leaf::Punct(_) | tt::Leaf::Literal(_) => {
                         return Err(ParseError::expected("expected ident"))
@@ -238,7 +250,7 @@ fn next_op(
         tt::TokenTree::Leaf(tt::Leaf::Punct(_)) => {
             // There's at least one punct so this shouldn't fail.
             let puncts = src.expect_glued_punct().unwrap();
-            Op::Punct(puncts)
+            Op::Punct(Box::new(puncts))
         }
 
         tt::TokenTree::Subtree(subtree) => {
@@ -290,7 +302,7 @@ fn is_boolean_literal(lit: &tt::Literal<Span>) -> bool {
 }
 
 fn parse_repeat(src: &mut TtIter<'_, Span>) -> Result<(Option<Separator>, RepeatKind), ParseError> {
-    let mut separator = Separator::Puncts(SmallVec::new());
+    let mut separator = Separator::Puncts(ArrayVec::new());
     for tt in src {
         let tt = match tt {
             tt::TokenTree::Leaf(leaf) => leaf,
@@ -312,7 +324,7 @@ fn parse_repeat(src: &mut TtIter<'_, Span>) -> Result<(Option<Separator>, Repeat
                     '+' => RepeatKind::OneOrMore,
                     '?' => RepeatKind::ZeroOrOne,
                     _ => match &mut separator {
-                        Separator::Puncts(puncts) if puncts.len() != 3 => {
+                        Separator::Puncts(puncts) if puncts.len() < 3 => {
                             puncts.push(*punct);
                             continue;
                         }
diff --git a/crates/mbe/src/tt_iter.rs b/crates/mbe/src/tt_iter.rs
index 9c7d7af7b1..3581fbbfd8 100644
--- a/crates/mbe/src/tt_iter.rs
+++ b/crates/mbe/src/tt_iter.rs
@@ -3,7 +3,7 @@
 
 use core::fmt;
 
-use smallvec::{smallvec, SmallVec};
+use arrayvec::ArrayVec;
 use syntax::SyntaxKind;
 
 use crate::{to_parser_input::to_parser_input, ExpandError, ExpandResult};
@@ -93,13 +93,15 @@ impl<'a, S: Copy> TtIter<'a, S> {
     ///
     /// This method currently may return a single quotation, which is part of lifetime ident and
     /// conceptually not a punct in the context of mbe. Callers should handle this.
-    pub(crate) fn expect_glued_punct(&mut self) -> Result<SmallVec<[tt::Punct<S>; 3]>, ()> {
+    pub(crate) fn expect_glued_punct(&mut self) -> Result<ArrayVec<tt::Punct<S>, 3>, ()> {
         let tt::TokenTree::Leaf(tt::Leaf::Punct(first)) = self.next().ok_or(())?.clone() else {
             return Err(());
         };
 
+        let mut res = ArrayVec::new();
         if first.spacing == tt::Spacing::Alone {
-            return Ok(smallvec![first]);
+            res.push(first);
+            return Ok(res);
         }
 
         let (second, third) = match (self.peek_n(0), self.peek_n(1)) {
@@ -108,14 +110,19 @@ impl<'a, S: Copy> TtIter<'a, S> {
                 Some(tt::TokenTree::Leaf(tt::Leaf::Punct(p3))),
             ) if p2.spacing == tt::Spacing::Joint => (p2, Some(p3)),
             (Some(tt::TokenTree::Leaf(tt::Leaf::Punct(p2))), _) => (p2, None),
-            _ => return Ok(smallvec![first]),
+            _ => {
+                res.push(first);
+                return Ok(res);
+            }
         };
 
         match (first.char, second.char, third.map(|it| it.char)) {
             ('.', '.', Some('.' | '=')) | ('<', '<', Some('=')) | ('>', '>', Some('=')) => {
                 let _ = self.next().unwrap();
                 let _ = self.next().unwrap();
-                Ok(smallvec![first, *second, *third.unwrap()])
+                res.push(first);
+                res.push(*second);
+                res.push(*third.unwrap());
             }
             ('-' | '!' | '*' | '/' | '&' | '%' | '^' | '+' | '<' | '=' | '>' | '|', '=', _)
             | ('-' | '=' | '>', '>', _)
@@ -126,10 +133,12 @@ impl<'a, S: Copy> TtIter<'a, S> {
             | ('<', '<', _)
             | ('|', '|', _) => {
                 let _ = self.next().unwrap();
-                Ok(smallvec![first, *second])
+                res.push(first);
+                res.push(*second);
             }
-            _ => Ok(smallvec![first]),
+            _ => res.push(first),
         }
+        Ok(res)
     }
     pub(crate) fn peek_n(&self, n: usize) -> Option<&'a tt::TokenTree<S>> {
         self.inner.as_slice().get(n)