diff --git a/src/tools/rust-analyzer/crates/cfg/src/cfg_expr.rs b/src/tools/rust-analyzer/crates/cfg/src/cfg_expr.rs
index e4c2a28fb0607..35c0c89c70cfa 100644
--- a/src/tools/rust-analyzer/crates/cfg/src/cfg_expr.rs
+++ b/src/tools/rust-analyzer/crates/cfg/src/cfg_expr.rs
@@ -32,8 +32,8 @@ impl fmt::Display for CfgAtom {
 pub enum CfgExpr {
     Invalid,
     Atom(CfgAtom),
-    All(Vec<CfgExpr>),
-    Any(Vec<CfgExpr>),
+    All(Box<[CfgExpr]>),
+    Any(Box<[CfgExpr]>),
     Not(Box<CfgExpr>),
 }
 
@@ -90,12 +90,12 @@ fn next_cfg_expr<S>(it: &mut std::slice::Iter<'_, tt::TokenTree<S>>) -> Option<C
         Some(tt::TokenTree::Subtree(subtree)) => {
             it.next();
             let mut sub_it = subtree.token_trees.iter();
-            let mut subs = std::iter::from_fn(|| next_cfg_expr(&mut sub_it)).collect();
-            match &name {
-                s if *s == sym::all => CfgExpr::All(subs),
-                s if *s == sym::any => CfgExpr::Any(subs),
-                s if *s == sym::not => {
-                    CfgExpr::Not(Box::new(subs.pop().unwrap_or(CfgExpr::Invalid)))
+            let mut subs = std::iter::from_fn(|| next_cfg_expr(&mut sub_it));
+            match name {
+                s if s == sym::all => CfgExpr::All(subs.collect()),
+                s if s == sym::any => CfgExpr::Any(subs.collect()),
+                s if s == sym::not => {
+                    CfgExpr::Not(Box::new(subs.next().unwrap_or(CfgExpr::Invalid)))
                 }
                 _ => CfgExpr::Invalid,
             }
diff --git a/src/tools/rust-analyzer/crates/cfg/src/dnf.rs b/src/tools/rust-analyzer/crates/cfg/src/dnf.rs
index 58a250829d4f1..f3ebca0465098 100644
--- a/src/tools/rust-analyzer/crates/cfg/src/dnf.rs
+++ b/src/tools/rust-analyzer/crates/cfg/src/dnf.rs
@@ -27,7 +27,7 @@ struct Literal {
 }
 
 impl DnfExpr {
-    pub fn new(expr: CfgExpr) -> Self {
+    pub fn new(expr: &CfgExpr) -> Self {
         let builder = Builder { expr: DnfExpr { conjunctions: Vec::new() } };
 
         builder.lower(expr)
@@ -154,9 +154,9 @@ impl fmt::Display for DnfExpr {
 }
 
 impl Conjunction {
-    fn new(parts: Vec<CfgExpr>) -> Self {
+    fn new(parts: Box<[CfgExpr]>) -> Self {
         let mut literals = Vec::new();
-        for part in parts {
+        for part in parts.into_vec() {
             match part {
                 CfgExpr::Invalid | CfgExpr::Atom(_) | CfgExpr::Not(_) => {
                     literals.push(Literal::new(part));
@@ -232,27 +232,28 @@ struct Builder {
 }
 
 impl Builder {
-    fn lower(mut self, expr: CfgExpr) -> DnfExpr {
+    fn lower(mut self, expr: &CfgExpr) -> DnfExpr {
         let expr = make_nnf(expr);
         let expr = make_dnf(expr);
 
         match expr {
             CfgExpr::Invalid | CfgExpr::Atom(_) | CfgExpr::Not(_) => {
-                self.expr.conjunctions.push(Conjunction::new(vec![expr]));
+                self.expr.conjunctions.push(Conjunction::new(Box::new([expr])));
             }
             CfgExpr::All(conj) => {
                 self.expr.conjunctions.push(Conjunction::new(conj));
             }
-            CfgExpr::Any(mut disj) => {
+            CfgExpr::Any(disj) => {
+                let mut disj = disj.into_vec();
                 disj.reverse();
                 while let Some(conj) = disj.pop() {
                     match conj {
                         CfgExpr::Invalid | CfgExpr::Atom(_) | CfgExpr::All(_) | CfgExpr::Not(_) => {
-                            self.expr.conjunctions.push(Conjunction::new(vec![conj]));
+                            self.expr.conjunctions.push(Conjunction::new(Box::new([conj])));
                         }
                         CfgExpr::Any(inner_disj) => {
                             // Flatten.
-                            disj.extend(inner_disj.into_iter().rev());
+                            disj.extend(inner_disj.into_vec().into_iter().rev());
                         }
                     }
                 }
@@ -266,11 +267,11 @@ impl Builder {
 fn make_dnf(expr: CfgExpr) -> CfgExpr {
     match expr {
         CfgExpr::Invalid | CfgExpr::Atom(_) | CfgExpr::Not(_) => expr,
-        CfgExpr::Any(e) => flatten(CfgExpr::Any(e.into_iter().map(make_dnf).collect())),
+        CfgExpr::Any(e) => flatten(CfgExpr::Any(e.into_vec().into_iter().map(make_dnf).collect())),
         CfgExpr::All(e) => {
-            let e = e.into_iter().map(make_dnf).collect::<Vec<_>>();
+            let e = e.into_vec().into_iter().map(make_dnf).collect::<Vec<_>>();
 
-            flatten(CfgExpr::Any(distribute_conj(&e)))
+            flatten(CfgExpr::Any(distribute_conj(&e).into_boxed_slice()))
         }
     }
 }
@@ -281,7 +282,7 @@ fn distribute_conj(conj: &[CfgExpr]) -> Vec<CfgExpr> {
         match rest {
             [head, tail @ ..] => match head {
                 CfgExpr::Any(disj) => {
-                    for part in disj {
+                    for part in disj.iter() {
                         with.push(part.clone());
                         go(out, with, tail);
                         with.pop();
@@ -295,7 +296,7 @@ fn distribute_conj(conj: &[CfgExpr]) -> Vec<CfgExpr> {
             },
             _ => {
                 // Turn accumulated parts into a new conjunction.
-                out.push(CfgExpr::All(with.clone()));
+                out.push(CfgExpr::All(with.clone().into_boxed_slice()));
             }
         }
     }
@@ -308,25 +309,27 @@ fn distribute_conj(conj: &[CfgExpr]) -> Vec<CfgExpr> {
     out
 }
 
-fn make_nnf(expr: CfgExpr) -> CfgExpr {
+fn make_nnf(expr: &CfgExpr) -> CfgExpr {
     match expr {
-        CfgExpr::Invalid | CfgExpr::Atom(_) => expr,
-        CfgExpr::Any(expr) => CfgExpr::Any(expr.into_iter().map(make_nnf).collect()),
-        CfgExpr::All(expr) => CfgExpr::All(expr.into_iter().map(make_nnf).collect()),
-        CfgExpr::Not(operand) => match *operand {
-            CfgExpr::Invalid | CfgExpr::Atom(_) => CfgExpr::Not(operand.clone()), // Original negated expr
-            CfgExpr::Not(expr) => {
-                // Remove double negation.
-                make_nnf(*expr)
-            }
-            // Convert negated conjunction/disjunction using DeMorgan's Law.
-            CfgExpr::Any(inner) => CfgExpr::All(
-                inner.into_iter().map(|expr| make_nnf(CfgExpr::Not(Box::new(expr)))).collect(),
-            ),
-            CfgExpr::All(inner) => CfgExpr::Any(
-                inner.into_iter().map(|expr| make_nnf(CfgExpr::Not(Box::new(expr)))).collect(),
-            ),
-        },
+        CfgExpr::Invalid | CfgExpr::Atom(_) => expr.clone(),
+        CfgExpr::Any(expr) => CfgExpr::Any(expr.iter().map(make_nnf).collect()),
+        CfgExpr::All(expr) => CfgExpr::All(expr.iter().map(make_nnf).collect()),
+        CfgExpr::Not(operand) => make_nnf_neg(operand),
+    }
+}
+
+fn make_nnf_neg(operand: &CfgExpr) -> CfgExpr {
+    match operand {
+        // Original negated expr
+        CfgExpr::Invalid => CfgExpr::Not(Box::new(CfgExpr::Invalid)), // Original negated expr
+        // Original negated expr
+        CfgExpr::Atom(atom) => CfgExpr::Not(Box::new(CfgExpr::Atom(atom.clone()))),
+        // Remove double negation.
+        CfgExpr::Not(expr) => make_nnf(expr),
+        // Convert negated conjunction/disjunction using DeMorgan's Law.
+        CfgExpr::Any(inner) => CfgExpr::All(inner.iter().map(make_nnf_neg).collect()),
+        // Convert negated conjunction/disjunction using DeMorgan's Law.
+        CfgExpr::All(inner) => CfgExpr::Any(inner.iter().map(make_nnf_neg).collect()),
     }
 }
 
@@ -335,20 +338,22 @@ fn flatten(expr: CfgExpr) -> CfgExpr {
     match expr {
         CfgExpr::All(inner) => CfgExpr::All(
             inner
-                .into_iter()
+                .iter()
                 .flat_map(|e| match e {
-                    CfgExpr::All(inner) => inner,
-                    _ => vec![e],
+                    CfgExpr::All(inner) => inner.as_ref(),
+                    _ => std::slice::from_ref(e),
                 })
+                .cloned()
                 .collect(),
         ),
         CfgExpr::Any(inner) => CfgExpr::Any(
             inner
-                .into_iter()
+                .iter()
                 .flat_map(|e| match e {
-                    CfgExpr::Any(inner) => inner,
-                    _ => vec![e],
+                    CfgExpr::Any(inner) => inner.as_ref(),
+                    _ => std::slice::from_ref(e),
                 })
+                .cloned()
                 .collect(),
         ),
         _ => expr,
diff --git a/src/tools/rust-analyzer/crates/cfg/src/tests.rs b/src/tools/rust-analyzer/crates/cfg/src/tests.rs
index 278e5f61de251..597023a792bb7 100644
--- a/src/tools/rust-analyzer/crates/cfg/src/tests.rs
+++ b/src/tools/rust-analyzer/crates/cfg/src/tests.rs
@@ -29,7 +29,7 @@ fn check_dnf(input: &str, expect: Expect) {
         DocCommentDesugarMode::ProcMacro,
     );
     let cfg = CfgExpr::parse(&tt);
-    let actual = format!("#![cfg({})]", DnfExpr::new(cfg));
+    let actual = format!("#![cfg({})]", DnfExpr::new(&cfg));
     expect.assert_eq(&actual);
 }
 
@@ -43,7 +43,7 @@ fn check_why_inactive(input: &str, opts: &CfgOptions, expect: Expect) {
         DocCommentDesugarMode::ProcMacro,
     );
     let cfg = CfgExpr::parse(&tt);
-    let dnf = DnfExpr::new(cfg);
+    let dnf = DnfExpr::new(&cfg);
     let why_inactive = dnf.why_inactive(opts).unwrap().to_string();
     expect.assert_eq(&why_inactive);
 }
@@ -59,7 +59,7 @@ fn check_enable_hints(input: &str, opts: &CfgOptions, expected_hints: &[&str]) {
         DocCommentDesugarMode::ProcMacro,
     );
     let cfg = CfgExpr::parse(&tt);
-    let dnf = DnfExpr::new(cfg);
+    let dnf = DnfExpr::new(&cfg);
     let hints = dnf.compute_enable_hints(opts).map(|diff| diff.to_string()).collect::<Vec<_>>();
     assert_eq!(hints, expected_hints);
 }
@@ -82,20 +82,28 @@ fn test_cfg_expr_parser() {
 
     assert_parse_result(
         r#"#![cfg(all(foo, bar = "baz"))]"#,
-        CfgExpr::All(vec![
-            CfgAtom::Flag(Symbol::intern("foo")).into(),
-            CfgAtom::KeyValue { key: Symbol::intern("bar"), value: Symbol::intern("baz") }.into(),
-        ]),
+        CfgExpr::All(
+            vec![
+                CfgAtom::Flag(Symbol::intern("foo")).into(),
+                CfgAtom::KeyValue { key: Symbol::intern("bar"), value: Symbol::intern("baz") }
+                    .into(),
+            ]
+            .into_boxed_slice(),
+        ),
     );
 
     assert_parse_result(
         r#"#![cfg(any(not(), all(), , bar = "baz",))]"#,
-        CfgExpr::Any(vec![
-            CfgExpr::Not(Box::new(CfgExpr::Invalid)),
-            CfgExpr::All(vec![]),
-            CfgExpr::Invalid,
-            CfgAtom::KeyValue { key: Symbol::intern("bar"), value: Symbol::intern("baz") }.into(),
-        ]),
+        CfgExpr::Any(
+            vec![
+                CfgExpr::Not(Box::new(CfgExpr::Invalid)),
+                CfgExpr::All(Box::new([])),
+                CfgExpr::Invalid,
+                CfgAtom::KeyValue { key: Symbol::intern("bar"), value: Symbol::intern("baz") }
+                    .into(),
+            ]
+            .into_boxed_slice(),
+        ),
     );
 }
 
@@ -235,6 +243,6 @@ fn proptest() {
 
         let mut u = Unstructured::new(&buf);
         let cfg = CfgExpr::arbitrary(&mut u).unwrap();
-        DnfExpr::new(cfg);
+        DnfExpr::new(&cfg);
     }
 }
diff --git a/src/tools/rust-analyzer/crates/hir-expand/src/cfg_process.rs b/src/tools/rust-analyzer/crates/hir-expand/src/cfg_process.rs
index 9f927184193e9..147cf912da1ef 100644
--- a/src/tools/rust-analyzer/crates/hir-expand/src/cfg_process.rs
+++ b/src/tools/rust-analyzer/crates/hir-expand/src/cfg_process.rs
@@ -287,8 +287,8 @@ where
                 }
             }
             let group = match &name {
-                s if *s == sym::all => CfgExpr::All(preds),
-                s if *s == sym::any => CfgExpr::Any(preds),
+                s if *s == sym::all => CfgExpr::All(preds.into_boxed_slice()),
+                s if *s == sym::any => CfgExpr::Any(preds.into_boxed_slice()),
                 s if *s == sym::not => {
                     CfgExpr::Not(Box::new(preds.pop().unwrap_or(CfgExpr::Invalid)))
                 }
@@ -343,7 +343,7 @@ mod tests {
         assert_eq!(node.syntax().text_range().start(), 0.into());
 
         let cfg = parse_from_attr_meta(node.meta().unwrap()).unwrap();
-        let actual = format!("#![cfg({})]", DnfExpr::new(cfg));
+        let actual = format!("#![cfg({})]", DnfExpr::new(&cfg));
         expect.assert_eq(&actual);
     }
     #[test]
diff --git a/src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/inactive_code.rs b/src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/inactive_code.rs
index 785a42352bfab..acff811696103 100644
--- a/src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/inactive_code.rs
+++ b/src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/inactive_code.rs
@@ -15,7 +15,7 @@ pub(crate) fn inactive_code(
         return None;
     }
 
-    let inactive = DnfExpr::new(d.cfg.clone()).why_inactive(&d.opts);
+    let inactive = DnfExpr::new(&d.cfg).why_inactive(&d.opts);
     let mut message = "code is inactive due to #[cfg] directives".to_owned();
 
     if let Some(inactive) = inactive {
diff --git a/src/tools/rust-analyzer/crates/rust-analyzer/src/target_spec.rs b/src/tools/rust-analyzer/crates/rust-analyzer/src/target_spec.rs
index 162faa5619c08..67e1bad5281d0 100644
--- a/src/tools/rust-analyzer/crates/rust-analyzer/src/target_spec.rs
+++ b/src/tools/rust-analyzer/crates/rust-analyzer/src/target_spec.rs
@@ -246,7 +246,7 @@ fn required_features(cfg_expr: &CfgExpr, features: &mut Vec<String>) {
             preds.iter().for_each(|cfg| required_features(cfg, features));
         }
         CfgExpr::Any(preds) => {
-            for cfg in preds {
+            for cfg in preds.iter() {
                 let len_features = features.len();
                 required_features(cfg, features);
                 if len_features != features.len() {