ast: Reduce size of ExprKind by boxing fields of ExprKind::Struct

compiler/rustc_ast/src/ast.rs

@@ -1074,7 +1074,7 @@ pub struct Expr {
 
 // `Expr` is used a lot. Make sure it doesn't unintentionally get bigger.
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
-rustc_data_structures::static_assert_size!(Expr, 120);
+rustc_data_structures::static_assert_size!(Expr, 104);
 
 impl Expr {
     /// Returns `true` if this expression would be valid somewhere that expects a value;
@@ -1244,6 +1244,13 @@ pub enum StructRest {
     None,
 }
 
+#[derive(Clone, Encodable, Decodable, Debug)]
+pub struct StructExpr {
+    pub path: Path,
+    pub fields: Vec<ExprField>,
+    pub rest: StructRest,
+}
+
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum ExprKind {
     /// A `box x` expression.
@@ -1369,7 +1376,7 @@ pub enum ExprKind {
     /// A struct literal expression.
     ///
     /// E.g., `Foo {x: 1, y: 2}`, or `Foo {x: 1, .. rest}`.
-    Struct(Path, Vec<ExprField>, StructRest),
+    Struct(P<StructExpr>),
 
     /// An array literal constructed from one repeated element.
     ///

compiler/rustc_ast/src/mut_visit.rs

@@ -1286,10 +1286,11 @@ pub fn noop_visit_expr<T: MutVisitor>(
             visit_vec(inputs, |(_c, expr)| vis.visit_expr(expr));
         }
         ExprKind::MacCall(mac) => vis.visit_mac_call(mac),
-        ExprKind::Struct(path, fields, expr) => {
+        ExprKind::Struct(se) => {
+            let StructExpr { path, fields, rest } = se.deref_mut();
             vis.visit_path(path);
             fields.flat_map_in_place(|field| vis.flat_map_expr_field(field));
-            match expr {
+            match rest {
                 StructRest::Base(expr) => vis.visit_expr(expr),
                 StructRest::Rest(_span) => {}
                 StructRest::None => {}

compiler/rustc_ast/src/visit.rs

@@ -721,10 +721,10 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
             visitor.visit_expr(element);
             visitor.visit_anon_const(count)
         }
-        ExprKind::Struct(ref path, ref fields, ref optional_base) => {
-            visitor.visit_path(path, expression.id);
-            walk_list!(visitor, visit_expr_field, fields);
-            match optional_base {
+        ExprKind::Struct(ref se) => {
+            visitor.visit_path(&se.path, expression.id);
+            walk_list!(visitor, visit_expr_field, &se.fields);
+            match &se.rest {
                 StructRest::Base(expr) => visitor.visit_expr(expr),
                 StructRest::Rest(_span) => {}
                 StructRest::None => {}